Handbook of Plasticizers [4 ed.] 1774670224, 9781774670224

Citation preview

Handbookth of

Plasticizers, 4 Edition

George Wypych, Editor

Toronto 2023

Published by ChemTec Publishing 38 Earswick Drive, Toronto, Ontario M1E 1C6, Canada © ChemTec Publishing, 2004, 2012, 2017, 2023 ISBN 978-1-774670-22-4 (hard copy); 978-1-774670-23-1 (epub) Cover design: Anita Wypych

All rights reserved. No part of this publication may be reproduced, stored or transmitted in any form or by any means without written permission of copyright owner. No responsibility is assumed by the Author and the Publisher for any injury or/and damage to persons or properties as a matter of products liability, negligence, use, or operation of any methods, product ideas, or instructions published or suggested in this book.

Library and Archives Canada Cataloguing in Publication Title: Handbook of plasticizers / George Wypych, editor. Names: Wypych, George, editor. Description: 4th edition. | Includes bibliographical references and index. Identifiers: Canadiana (print) 20220269866 | Canadiana (ebook) 20220269874 | ISBN 9781774670224 (hardcover) | ISBN 9781774670231 (PDF) Subjects: LCSH: Plasticizers-Handbooks, manuals, etc. | LCGFT: Handbooks and manuals. Classification: LCC TP247.7 .H33 2023 | DDC 668.4/11-dc23

Printed in Australia, United Kingdom and United States of America

i

Table of Contents

TABLE OF CONTENTS 1 1.1 1.2 1.3 1.4 2 2.1 2.2 2.2.1 2.2.2 2.2.3 2.2.4 2.2.5 2.2.6 2.2.7 2.2.8 2.2.9 2.2.10 2.2.11 2.2.12 2.2.13 2.2.14 2.2.15 2.2.16 2.2.17 2.2.18 2.2.19 2.2.20 2.2.21 2.2.22 2.2.23 2.2.24 2.2.25 2.2.26 2.2.26.1 2.2.26.2 2.26.3 2.2.27

INTRODUCTION George Wypych Historical developments Expectations from plasticizers Definitions Classification PLASTICIZER TYPES George Wypych Introduction Characteristic properties of industrial plasticizers Abietates Adipates Alkyl sulfonates Amides and amines Azelates Benzoates Bioplasticizers Biodegradable plasticizers Chlorinated paraffins, Citrates Cyclohexane dicarboxylic acid, diisononyl ester Energetic plasticizers Epoxides Esters of C10-30 dicarboxylic acids Ether-ester plasticizers Glutarates Hydrocarbon oils Hydrocarbon resins Isobutyrates Maleates Oleates Pentaerythritol derivatives Phosphates Phthalate-free plasticizers Phthalates Polymeric plasticizers Esters Polybutenes Others Ricinoleates

1 1 3 5 6 9 9 13 13 14 18 20 21 23 26 28 29 32 36 39 43 46 47 50 52 54 55 57 59 61 63 66 68 76 76 79 81 82

ii

Table of Contents

2.2.28 2.2.29 2.2.30 2.2.31 2.2.32 2.3 2.4

Sebacates Succinates Sulfonamides Superplasticizers and plasticizers for concrete Tri- and pyromellitates Methods of synthesis and their effect on properties of plasticizers Reactive plasticizers and internal plasticization

84 86 87 90 93 95 102

3

TYPICAL METHODS OF QUALITY CONTROL OF PLASTICIZERS George Wypych Abbreviations, terminology, and vocabulary Acid number Aging studies Ash Brittleness temperature Brookfield viscosity Chemical resistance Color Compatibility Compression set Concrete additives Electrical properties Extractable matter Flash and fire point Fogging Fusion Gas chromatography Hardness Infrared analysis of plasticizers Kinematic viscosity Marking (classification) Melt rheology Migration Polyvinylchloride − standard specification Powder-mix time Purity Refractive index Residual contamination Sampling Saponification value Saybolt viscosity Sorption of plasticizer Specific gravity Specification Staining

105

3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9 3.10 3.11 3.12 3.13 3.14 3.15 3.16 3.17 3.18 3.19 3.20 3.21 3.22 3.23 3.24 3.25 3.26 3.27 3.28 3.29 3.30 3.31 3.32 3.33 3.34 3.35

105 106 106 106 106 107 107 108 109 109 109 110 110 110 110 111 111 111 112 112 113 113 113 115 115 115 116 116 116 117 117 117 118 118 119

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Table of Contents

3.36 3.37 3.38 3.39 3.40 3.41 3.42

Stiffness Tensile properties Thermal expansion coefficient Unsaponifiable contents Viscosity of plastisols and organosols Water concentration Weight loss

119 121 121 122 122 123 123

4

TRANSPORTATION AND STORAGE George Wypych Transportation Storage

131

4.1 4.2 5 5.1 5.1.1 5.1.2 5.1.3 5.2 5.2.1 6 6.1 6.1.1 6.1.2 6.1.3 6.1.4 6.1.5 6.1.6 6.1.7 6.1.8 6.1.9 6.1.10 6.2 6.2.1 6.2.2 6.2.3 6.3 6.3.1 6.3.1.1 6.3.1.2

MECHANISMS OF PLASTICIZERS ACTION A. Marcilla and M. Beltrán Classical theories The lubricity theory The gel theory Moorshead's empirical approach The free volume theory Mathematical models COMPATIBILITY OF PLASTICIZERS George Wypych Prediction methods of plasticizer compatibility Flory-Huggins interaction parameter Prediction of Gibbs free energy of mixing UNIFAC-FV Molar volume Polarity Hansen solubility parameters Hoy solubility parameters and other methods based on solubility parameters Hildebrand solubility parameter Molecule charge density using COSMO Mesoscale simulation using DPD Ap/Po ratio Validation methods DSC analysis Inverse gas chromatography Solid-gel transition temperature Effect of plasticizer structure and conditions of incorporation on compatibility Effect of plasticizer structure Aromaticity Branching

131 134 139 140 140 142 144 145 150 159 159 160 161 162 162 163 166 167 167 167 169 170 170 171 172 174 174 174 174

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6.3.1.3 6.3.1.4 6.3.1.5 6.3.2 6.3.2.1 6.3.2.2 6.3.2.3 6.4 6.4.1 6.4.2 6.4.3 6.4.4 6.4.5

Chain length Molecular weight Polarity Conditions of incorporation Amount (concentration) Method of processing Temperature Effect of plasticizer type on properties of plasticized material Crystallinity Exudation Permanence Thermal degradation Volatility

175 175 175 176 176 176 176 178 178 178 178 179 179

7

PLASTICIZER MOTION AND DIFFUSION George Wypych Plasticizer diffusion rate and the methods of study Plasticizer motion and distribution in the matrix Plasticizer migration Antiplasticization Effect of diffusion and mobility of plasticizers on their suitability

181

7.1 7.2 7.3 7.4 7.5 8 8.1 8.2 8.3 8.4 9 9.1 9.2 9.2.1 9.2.2 9.2.3 9.2.4 9.2.5 9.2.6 10 10.1 10.1.1

EFFECT OF PLASTICIZERS ON OTHER COMPONENTS OF FORMULATION George Wypych Plasticizer consumption by fillers Solubility of additives in plasticizers Additive molecular mobility and transport in the presence of plasticizers Effect of plasticizers on polymerization and curing reactions PLASTICIZATION STEPS A. Marcilla, J.C. García and M. Beltrán Plasticization steps Studies of plastisol's behavior during gelation and fusion Rheological characterization Studies by Scanning Electron Microscopy Study of polymer-plasticizer interactions by DSC Study of polymer-plasticizer interactions by SALS Study of polymer-plasticizer interactions by FTIR Study of polymer-plasticizer interactions by TG EFFECT OF PLASTICIZERS ON PROPERTIES OF PLASTICIZED MATERIALS George Wypych Mechanical properties Tensile strength

181 187 189 196 201 203 203 206 208 210 213 213 215 215 218 219 221 221 223 229 229 229

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10.1.2 10.1.3 10.1.4 10.1.5 10.2 10.3 10.4 10.5 10.6 10.7 10.8 10.9 10.10 10.11 10.11.1 10.11.2 10.11.3 10.11.4 10.11.5 10.12 10.13 10.14 10.15 10.16 10.17 10.18 10.19 10.20 10.21 10.22 10.23 10.24 10.25 10.26 10.27 10.28 10.29 11 11.1 11.1.1 11.1.2 11.1.3

Elongation Hardness Toughness, stiffness, ductility, modulus Other mechanical properties Optical properties Spectral properties Gloss Sound Rheological properties Magnetorheological properties Electrical properties Glass transition temperature Flammability and smoke formation in the presence of plasticizers Thermal degradation Thermal degradation of plasticizers Effect of polymer degradation products on plasticizers Effect of plasticizer degradation products on polymer degradation Loss of plasticizer from the material due to chemical decomposition reactions and evaporation Effect of plasticizers on the thermal degradation of material Effect of UV and ionizing radiation on plasticized materials Hydrolysis Biodegradation in the presence of plasticizers Crystallization, structure, and orientation of macromolecules Morphology Plasticizer effect on contact with other materials Influence of plasticizers on swelling Fogging Hydrophobic/hydrophilic properties Osmotic pressure of plasticizer in polymer Self-healing Shrinkage Soiling Free volume Dissolution Foaming Permeability Sorption

234 236 237 238 241 245 248 249 250 253 254 260 264 268 268 269 270

PLASTICIZERS USE AND SELECTION FOR SPECIFIC POLYMERS George Wypych ABS Frequently used plasticizers Practical concentrations Main functions performed by plasticizers

313

271 274 278 282 283 287 294 296 299 300 301 302 303 304 305 306 308 309 310 311

313 313 313 313

vi

11.1.4 11.1.5 11.1.6 11.2 11.2.1 11.2.2 11.2.3 11.2.4 11.2.5 11.3 11.3.1 11.3.2 11.3.3 11.3.4 11.4 11.4.1 11.4.2 11.5 11.5.1 11.5.2 11.5.3 11.5.4 11.5.5 11.6 11.6.1 11.6.2 11.6.3 11.6.4 11.7 11.7.1 11.7.2 11.7.3 11.7.4 11.7.5 11.8 11.8.1 11.8.2 11.8.3 11.8.4 11.9 11.9.1 11.9.2 11.10 11.10.1 11.10.2

Table of Contents

Mechanism of plasticizer action Effect of plasticizers on polymer and other additives Typical formulations Acrylics Frequently used plasticizers Practical concentrations Main functions performed by plasticizers Mechanism of plasticizer action Typical formulations Bromobutyl rubber Frequently used plasticizers Practical concentrations Main functions performed by plasticizers Effect of plasticizers on polymer and other additives Butyl terpolymer Frequently used plasticizers Practical concentrations Cellulose acetate Frequently used plasticizers Practical concentrations Main functions performed by plasticizers Mechanism of plasticizer action Effect of plasticizers on polymer and other additives Cellulose butyrate and propionate Frequently used plasticizers Practical concentrations Main functions performed by plasticizers Effect of plasticizers on polymer and other additives Cellulose nitrate Frequently used plasticizers Practical concentrations Main functions performed by plasticizers Effect of plasticizers on polymer and other additives Typical formulations Chitosan Frequently used plasticizers Practical concentrations Main functions performed by plasticizers Effect of plasticizers on polymer and other additives Chlorinated polyvinylchloride Frequently used plasticizers Effect of plasticizers on polymer and other additives Chlorosulfonated polyethylene Frequently used plasticizers Effect of plasticizers on polymer and other additives

314 314 315 316 316 316 317 317 318 320 320 320 320 320 321 321 321 322 322 322 323 323 325 327 327 327 327 327 329 329 329 329 330 330 332 332 332 332 332 333 333 333 336 336 336

Table of Contents

11.11 11.11.1 11.11.2 11.11.3 11.11.4 11.12 11.12.1 11.12.2 11.12.3 11.12.4 11.13 11.13.1 11.13.2 11.13.3 11.14 11.14.1 11.14.2 11.14.3 11.14.4 11.15 11.15.1 11.15.2 11.15.3 11.15.4 11.15.5 11.16 11.17 11.17.1 11.17.2 11.17.3 11.17.4 11.17.5 11.18 11.18.1 11.18.2 11.18.3 11.18.4 11.18.5 11.19 11.20 11.20.1 11.20.2 11.20.3 11.20.4 11.21

Copolymers Frequently used plasticizers Practical concentrations Main functions performed by plasticizers Mechanism of plasticizer action Cyanoacrylates Frequently used plasticizers Practical concentrations Main functions performed by plasticizers Effect of plasticizer on polymer and other additives Ethylcellulose Frequently used plasticizers Practical concentrations Effect of plasticizers on polymer and other additives Epoxy resin Frequently used plasticizers Practical concentrations Main functions performed by plasticizers Effect of plasticizers on polymer and other additives Ethylene-propylene-diene copolymer Frequently used plasticizers Practical concentrations Main functions performed by plasticizers Effect of plasticizers on polymer and other additives Typical formulations Ethylene-vinyl acetate copolymer Ionomers Frequently used plasticizers Practical concentrations Main functions performed by plasticizers Mechanism of plasticizer action Effect of plasticizers on polymer and other additives Nitrile rubber Frequently used plasticizers Practical concentrations Main functions performed by plasticizers Effect of plasticizers on polymer and other additives Typical formulations Perfluoropolymers Polyacrylonitrile Frequently used plasticizers Practical concentrations Main functions performed by plasticizers Effect of plasticizers on polymer and other additives Polyamide

vii

337 337 338 338 338 340 340 340 340 340 342 342 342 342 343 343 343 344 344 347 347 347 347 347 348 349 350 350 350 350 350 351 354 354 354 354 355 355 357 358 358 358 358 358 360

viii

11.21.1 11.21.2 11.21.3 11.21.4 11.22 11.23 11.24 11.24.1 11.24.2 11.24.3 11.25 11.25.1 11.25.2 11.25.3 11.26 11.26.1 11.26.2 11.26.3 11.27 11.27.1 11.27.2 11.27.3 11.27.4 11.28 11.28.1 11.28.2 11.28.3 11.28.4 11.28.5 11.29 11.30 11.31 11.31.1 11.31.2 11.31.3 11.31.4 11.31.5 11.32 11.32.1 11.32.2 11.32.3 11.32.4 11.33 11.33.1 11.33.2

Table of Contents

Frequently used plasticizers Practical concentrations Main functions performed by plasticizers Effect of plasticizers on polymer and other additives Polyamine Polyaniline Polybutadiene Frequently used plasticizers Practical concentrations Main functions performed by plasticizers Polybutylene Frequently used plasticizers Practical concentrations Main functions performed by plasticizers Poly(butyl methacrylate) Frequently used plasticizers Practical concentrations Main functions performed by plasticizers Polycarbonate Frequently used plasticizers Practical concentrations Main functions performed by plasticizers Effect of plasticizers on polymer and other additives Polyester Frequently used plasticizers Practical concentrations Main functions performed by plasticizers Effect of plasticizers on polymer and other additives Typical formulations Polyetherimide Polyethylacrylate Polyethylene Frequently used plasticizers Practical concentrations Main functions performed by plasticizers Mechanism of plasticizer action Typical formulations Poly(ethylene oxide) Frequently used plasticizers Practical concentrations Main functions performed by plasticizers Effect of plasticizers on polymer and other additives Poly(3-hydroxybutyrate) Frequently used plasticizers Practical concentrations

360 360 361 361 364 365 366 366 366 366 368 368 368 368 369 369 369 369 370 370 370 370 371 372 372 372 373 373 374 376 377 378 378 378 378 379 379 381 381 381 381 381 384 384 384

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11.33.3 11.34 11.35 11.35.1 11.35.2 11.35.3 11.35.4 11.36 11.36.1 11.36.2 11.36.3 11.36.4 11.37 11.37.1 11.37.2 11.37.3 11.37.4 11.38 11.38.1 11.38.2 11.38.3 11.38.4 11.38.5 11.39 11.39.1 11.39.2 11.39.3 11.39.4 11.40 11.40.1 11.40.2 11.40.3 11.40.4 11.41 11.42 11.42.1 11.42.2 11.42.3 11.42.4 11.42.5 11.43 11.43.1 11.43.2 11.43.3 11.44

Main functions performed by plasticizers Polyisobutylene Polyisoprene Frequently used plasticizers Practical concentrations Main functions performed by plasticizers Typical formulations Polyimide Frequently used plasticizers Practical concentrations Main functions performed by plasticizers Effect of plasticizers on polymer and other additives Polylactide Frequently used plasticizers Practical concentrations Main functions performed by plasticizers Effect of plasticizers on polymer and other additives Polymethylmethacrylate Frequently used plasticizers Practical concentrations Main functions performed by plasticizers Mechanism of plasticizer action Typical formulations Polypropylene Frequently used plasticizers Practical concentrations Main functions performed by plasticizers Effect of plasticizers on polymer and other additives Poly(propylene carbonate) Frequently used plasticizers Practical concentrations Main functions performed by plasticizers Effect of plasticizers on polymer and other additives Poly(N-vinylcarbazole) Poly(N-vinylpyrrolidone) Frequently used plasticizers Practical concentrations Main functions performed by plasticizers Mechanism of plasticizer action Typical formulations Poly(phenylene ether) Frequently used plasticizers Practical concentrations Main functions performed by plasticizers Poly(phenylene sulfide)

384 386 388 388 388 388 388 389 389 389 389 390 392 392 392 393 393 399 399 399 399 399 399 401 401 401 401 401 403 403 403 403 403 404 405 405 405 405 405 406 407 407 407 407 408

x

11.45 11.45.1 11.45.2 11.45.3 11.46 11.46.1 11.46.2 11.46.3 11.47 11.48 11.48.1 11.48.2 11.48.3 11.48.4 11.48.5 11.48.6 11.49 11.49.1 11.49.2 11.49.3 11.49.4 11.50 11.50.1 11.50.2 11.50.3 11.50.4 11.50.5 11.50.6 11.51 11.51.1 11.51.2 11.51.3 11.51.4 11.52 11.52.1 11.52.2 11.52.3 11.52.4 11.52.5 11.52.6 11.53 11.54 11.54.1 11.54.2 11.54.3

Table of Contents

Polystyrene Frequently used plasticizers Practical concentrations Main functions performed by plasticizers Polysulfide Frequently used plasticizers Practical concentrations Main functions performed by plasticizers Polysulfone Polyurethanes Frequently used plasticizers Practical concentrations Main functions performed by plasticizers Mechanism of plasticizers action Effect of plasticizers on polymers and other additives Typical formulations Polyvinylacetate Frequently used plasticizers Practical concentrations Main functions performed by plasticizers Effect of plasticizers on polymer and other additives Polyvinylalcohol Frequently used plasticizers Practical concentrations Main functions performed by plasticizers Mechanism of plasticizer action Effect of plasticizers on polymer and other additives Typical formulations Polyvinylbutyral Frequently used plasticizers Practical concentrations Main functions performed by plasticizers Effect of plasticizers on polymer and other additives Polyvinylchloride Frequently used plasticizers Practical concentrations Main functions performed by plasticizers Mechanism of plasticizer action Effect of plasticizers on polymer and other additives Typical formulations Polyvinylfluoride Polyvinylidenefluoride Frequently used plasticizers Practical concentrations Main functions performed by plasticizers

409 409 409 409 411 411 411 411 412 413 413 413 413 413 413 415 416 416 416 416 416 419 419 419 420 420 421 422 424 424 424 424 424 426 426 428 429 430 433 440 447 448 448 448 448

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11.54.4 11.55 11.56 11.56.1 11.56.2 11.56.3 11.56.4 11.56.5 11.57 11.57.1 11.57.2 11.57.3 11.57.4 11.57.5 11.58 11.58.1 11.58.2 11.58.3 11.58.4 11.58.5 11.59 11.59.1 11.59.2 11.59.3 11.59.4 11.60 11.60.1 11.60.2 11.60.3 11.60.4 11.61 11.61.1 11.61.2 11.61.3 11.61.4 11.61.5

Effect of plasticizers on polymer and other additives Polyvinylidenechloride Proteins Frequently used plasticizers Practical concentrations Main functions performed by plasticizers Mechanism of plasticizer action Effect of plasticizers on polymer and other additives Rubber, natural Frequently used plasticizers Practical concentrations Main functions performed by plasticizers Effect of plasticizers on polymer and other additives Typical formulations Silicone Frequently used plasticizers Practical concentrations Main functions performed by plasticizers Effect of plasticizers on polymer and other additives Typical formulations Styrene-butadiene rubber Frequently used plasticizers Practical concentrations Effect of plasticizers on polymer and other additives Typical formulations Styrene-butadiene-styrene rubber Frequently used plasticizers Practical concentrations Main functions performed by plasticizers Effect of plasticizer on polymer and other additives Starch Frequently used plasticizers Practical concentrations Main functions performed by plasticizers Effect of plasticizers on polymer and other additives Typical formulations

448 450 451 451 451 451 451 452 454 454 454 454 454 455 458 458 459 459 459 460 463 463 463 463 463 465 465 465 465 465 466 466 467 467 467 469

12

PLASTICIZERS IN POLYMER BLENDS George Wypych Plasticizer partition between component polymers Interaction of plasticizers with a blend components Effect of plasticizers on blend properties Blending to reduce or to replace plasticizers

473

12.1 12.2 12.3 12.4

473 478 480 484

xii

13 13.1 13.1.1 13.1.2 13.1.3 13.1.4 13.1.5 13.1.6 13.2 13.3 13.4 13.4.1 13.4.2 13.4.3 13.4.4 13.4.5 13.5 13.5.1 13.5.2 13.5.3 13.5.4 13.5.5 13.5.6 13.6 13.6.1 13.6.2 13.6.3 13.6.4 13.6.5 13.6.6 13.7 13.7.1 13.7.2 13.7.3 13.7.4 13.8 13.8.1 13.8.2 13.8.3 13.8.4 13.8.5 13.8.6 13.9 13.10

Table of Contents

PLASTICIZERS IN VARIOUS INDUSTRIAL PRODUCTS George Wypych Adhesives and sealants Plasticizer types Plasticizer concentration Reasons for plasticizer use Advantages and disadvantages of plasticizers use Effect of plasticizers on product properties Examples of formulations Aerospace Agriculture Automotive Plasticizer types Plasticizer concentration Reasons for plasticizer use Advantages and disadvantages of plasticizers use Effect of plasticizers on product properties Cementitious materials Plasticizer types Plasticizer concentration Reasons for plasticizer use Advantages and disadvantages of plasticizers use Effect of plasticizers on product properties Examples of formulations Coated fabrics Plasticizer types Plasticizer concentration Reasons for plasticizer use Advantages and disadvantages of plasticizers use Effect of plasticizers on product properties Examples of formulations Composites Plasticizer types Plasticizer concentrations Reasons for addition Effect of plasticizers on product properties Cosmetics Plasticizer types Plasticizer concentration Reasons for plasticizer use Advantages and disadvantages of plasticizers use Effect of plasticizers on product properties Examples of formulations Cultural heritage Dental materials

487 487 487 490 491 492 493 495 500 503 504 504 504 505 505 505 508 508 508 508 508 509 511 513 513 513 514 514 514 516 518 518 518 518 518 522 522 522 523 523 523 524 527 528

Table of Contents

13.10.1 13.10.2 13.10.3 13.10.4 13.11 13.11.1 13.11.2 13.11.3 13.11.4 13.11.5 13.12 13.12.1 13.12.2 13.12.3 13.12.4 13.13 13.13.1 13.13.2 13.13.3 13.13.4 13.13.5 13.14 13.14.1 13.14.2 13.14.3 13.14.4 13.14.5 13.15 13.15.1 13.15.2 13.15.3 13.15.4 13.15.5 13.15.6 13.16 13.16.1 13.16.2 13.16.3 13.16.4 13.16.5 13.16.6 13.17 13.17.1 13.17.2 13.17.3

Plasticizer types Plasticizer concentration Reasons for plasticizer use Advantages and disadvantages of plasticizers use Electrical and electronics Plasticizer types Plasticizer concentration Reasons for plasticizer use Advantages and disadvantages of plasticizers use Effect of plasticizers on product properties Fibers Plasticizer types Plasticizer concentration Reasons for plasticizer use Effect of plasticizers on product properties Film Plasticizer types Plasticizer concentration Reasons for plasticizer use Advantages and disadvantages of plasticizers use Effect of plasticizers on product properties Food Plasticizer types Plasticizer concentration Reasons for plasticizer use Advantages and disadvantages of plasticizers use Effect of plasticizers on product properties Flooring Plasticizer types Plasticizer concentration Reasons for plasticizer use Advantages and disadvantages of plasticizers use Effect of plasticizers on product properties Examples of formulations Foams Plasticizer types Plasticizer concentration Reasons for plasticizer use Advantages and disadvantages of plasticizers use Effect of plasticizers on product properties Examples of formulations Footwear Plasticizer types Plasticizer concentration Reasons for plasticizer use

xiii

528 529 529 529 531 531 531 532 532 533 535 535 535 535 535 539 539 540 540 541 541 544 544 544 545 545 546 550 550 550 550 550 551 551 553 553 553 554 554 554 554 557 557 557 557

xiv

13.17.4 13.17.5 13.18 13.18.1 13.18.2 13.18.3 13.19 13.19.1 13.19.2 13.19.3 13.19.4 13.19.5 13.20 13.21 13.21.1 13.21.2 13.21.3 13.21.4 13.21.5 13.21.6 13.22 13.22.1 13.22.2 13.22.3 13.22.4 13.22.5 13.22.6 13.23 13.23.1 13.23.2 13.23.3 13.23.4 13.24 13.24.1 13.24.2 13.24.3 13.25 13.25.1 13.25.2 13.25.3 13.25.4 13.25.5 13.25.6 13.26 13.26.1

Table of Contents

Advantages and disadvantages of plasticizers use Example of formulation Fuel cells Plasticizer types Plasticizer concentration Reasons for plasticizer use Gaskets Plasticizer types Plasticizer concentration Reasons for plasticizer use Advantages and disadvantages of plasticizers use Examples of formulations Household products Inks, varnishes, and lacquers Plasticizer types Plasticizer concentration Reasons for plasticizer use Advantages and disadvantages of plasticizers use Effect of plasticizers on product properties Examples of formulations Medical applications Plasticizer types Plasticizer concentration Reasons for plasticizer use Advantages and disadvantages of plasticizers use Effect of plasticizers on product properties Examples of formulations Membranes Plasticizer types Plasticizer concentration Reasons for plasticizer use Advantages and disadvantages of plasticizers use Microspheres Plasticizer types Plasticizer concentration Reasons for plasticizer use Paints and coatings Plasticizer types Plasticizer concentration Reasons for plasticizer use Advantages and disadvantages of plasticizers use Effect of plasticizers on product properties Examples of formulations Pharmaceutical products Plasticizer types

557 558 559 559 559 559 560 560 560 560 560 561 562 563 563 563 563 564 564 564 567 567 567 567 568 568 570 573 573 573 573 573 575 575 575 575 576 576 577 578 578 578 579 583 583

Table of Contents

13.26.2 13.26.3 13.26.4 13.26.5 13.26.6 13.27 13.27.1 13.27.2 13.27.3 13.27.4 13.28 13.28.1 13.28.2 13.28.3 13.28.4 13.28.5 13.28.6 13.29 13.29.1 13.29.2 13.29.3 13.29.4 13.29.5 13.29.6 13.30 13.30.1 13.30.2 13.30.3 13.30.4 13.30.5 13.30.6 13.31 13.31.1 13.31.2 13.31.3 13.31.4 13.32 13.32.1 13.32.2 13.32.3 13.32.4 13.32.5 13.32.6 13.33 13.33.1

Plasticizer concentration Reasons for plasticizer use Advantages and disadvantages of plasticizers use Effect of plasticizers on product properties Examples of formulations Photographic materials Plasticizer types Plasticizer concentration Reasons for plasticizer use Effect of plasticizers on product properties Pipes Plasticizer types Plasticizer concentration Reasons for plasticizer use Advantages and disadvantages of plasticizers use Effect of plasticizers on product properties Examples of formulations Roofing materials Plasticizer types Plasticizer concentration Reasons for plasticizer use Advantages and disadvantages of plasticizers use Effect of plasticizers on product properties Examples of formulations Tires Plasticizer types Plasticizer concentration Reasons for plasticizer use Advantages and disadvantages of plasticizers use Effect of plasticizers on product properties Examples of formulations Toys Plasticizer types Plasticizer concentration Reasons for plasticizer use Effect of plasticizers on product properties Tubing Plasticizer types Plasticizer concentration Reasons for plasticizer use Advantages and disadvantages of plasticizers use Effect of plasticizers on product properties Examples of formulations Wire and cable Plasticizer types

xv

584 584 584 585 586 590 590 590 590 590 592 592 592 592 592 592 593 595 595 595 595 596 596 596 599 599 599 599 599 599 600 602 602 602 602 602 604 604 604 604 604 604 605 607 607

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13.33.2 13.33.3 13.33.4 13.33.5 13.33.6

Plasticizer concentration Reasons for plasticizer use Advantages and disadvantages of plasticizers use Effect of plasticizers on product properties Examples of formulations

607 607 608 608 609

14

PLASTICIZERS IN VARIOUS PROCESSING METHODS George Wypych Blow molding Calendering Coil coating Compression molding Compounding (mixing) Dip coating Dry blending Extrusion Injection molding Polymer synthesis Rotational molding Rubber processing Thermoforming Web coating Wire coating

613

14.1 14.2 14.3 14.4 14.5 14.6 14.7 14.8 14.9 14.10 14.11 14.12 14.13 14.14 14.15 15 15.1 15.2 15.3 15.4 16 16.1 16.2 16.3 16.4 16.5 16.6 16.7 17 17.1

SPECIALIZED ANALYTICAL METHODS IN PLASTICIZER TESTING George Wypych Plasticizer identification Methods of determination of plasticizer concentration Determination of volatility, molecular motion, diffusion, and migration Methods of study of plasticized materials MATHEMATICAL MODELING IN APPLICATION TO PLASTICIZERS George Wypych PVC-plasticizer interaction model Gas permeation Migration Dry-blending time Gelation and fusion Thermal decomposition Potential health risk of exposure to DEHP from glove HEALTH AND SAFETY ISSUES WITH PLASTICIZERS AND PLASTICIZED MATERIALS Adjuvant effect of plasticizers Søren Thor Larsen

613 618 622 625 629 632 636 639 645 649 651 654 659 661 664 667 667 670 672 675 679 679 682 685 687 688 691 692

693 693

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17.1.1 17.1.2 17.1.3 17.1.4 17.1.4.1 17.1.4.2 17.1.5 17.2

17.2.1 17.2.2 17.2.2.1 17.2.2.2 17.2.2.3 17.2.2.4 17.2.3 17.2.3.1 17.2.3.2 17.2.4 17.2.5 17.2.5.1 17.2.6 17.3 17.3.1 17.3.2 17.3.3 17.3.4 17.3.5 17.3.6 17.4

17.4.1 17.4.2 17.4.3 17.4.3 17.4.4 17.4.5 17.4.6 17.4.7 17.4.8

Introduction Airway allergy Adjuvant effect Adjuvant effect of phthalate plasticizers Epidemiological studies In vivo (animal) studies Conclusions The rodent hepatocarcinogenic response to phthalate plasticizers : basic biology and human extrapolation Abigail L Walker and Ruth A Roberts Introduction Gene expression and cancer toxicology Gene expression Cancer biology: some basic considerations Developing areas of interest in hepatocarcinogenesis Chemical carcinogenesis Peroxisome proliferators and rodent nongenotoxic hepatocarcinogenesis The peroxisome proliferators PPARα Species differences in response to peroxisome proliferators Chemical regulation Challenges in alternative models Summary The influence of maternal nutrition on phthalate teratogenicity Janet Y. Uriu-Adams1 and Carl L. Keen Introduction Reproductive toxicity of BBP and DEHP Acute phase response-induced alterations in maternal Concluding comments Recent findings Acknowledgments Public health implications of phthalates: A review of U.S. actions to protect those most vulnerable Stephanie R. Miles-Richardson and Dhara Richardson Introduction Implications of the COVID-19 pandemic on phthalate exposure The U.S. response to phthalate exposure Some U.S. State-level actions 2008 Consumer Product Safety Improvement Act Food and Drug Administration (FDA) petition, lawsuit, and final ruling Preventing Harmful Exposure to Phthalates Act 117th Congress (2021-2022) Other U.S. Federal Agencies Conclusion

xvii

693 693 694 694 694 695 697 699 699 699 699 699 700 701 701 701 702 704 707 707 708 711 711 712 714 719 719 719 723 723 723 724 724 725 725 726 726 727

xviii

17.5 17.5.1 17.5.2 17.5.3 17.5.3.1 17.5.3.2 17.5.4 17.5.4.1 17.5.4.2 17.5.4.3 17.5.5 18 18.1 18.1.1 18.1.2 18.2 18.2.1 18.2.2 18.2.3 18.2.4 18.2.5 18.3 18.3.1 18.3.2 18.4 18.5

19 19.1 19.2. 19.3 19.4 19.5 19.6 19.7 19.8

Table of Contents

Plasticizers in the indoor environment Werner Butte Introduction Sources of indoor plasticizers Occurrence of plasticizers indoors Indoor air House dust Impact of plasticizers in the indoor environment Indoor plasticizers and health Human exposure assessment for plasticizers in the indoor environment Reference and guideline values of plasticizers to assess indoor quality Summary THE ENVIRONMENTAL FATE OF PLASTICIZERS William R. Roy Introduction Releases to the environment Levels in the environment Plasticizers in water Solubility Volatilization from water. Abiotic degradation in water Biodegradation in water Adsorption from water Soil and sediment Volatilization Biodegradation in soil Organisms Air Summary and concluding remarks REGULATIONS AND DATA George Wypych Toxic substance control Carcinogenic effect Teratogenic and mutagenic effect Workplace exposure limits Exposure from consumer products Plasticizers in drinking water Food regulatory acts Medical and other applications

729 729 730 733 733 736 741 741 743 747 748 753 753 754 755 761 761 762 765 765 766 769 769 771 773 776 777 781 781 785 787 790 793 795 797 801

Table of Contents

20 20.1 20.2 20.3 20.4 21

PERSONAL PROTECTION George Wypych Clothing Gloves Eye protection Respiratory protection

xix

803 803 805 807 808

PLASTICIZER RECOVERY & RECYCLING George Wypych

813

INDEX

819

xx

Table of Contents

1 INTRODUCTION This chapter contains brief summaries of • historical developments of plasticizers • expectations from plasticizers • definitions • classification

1.1 HISTORICAL DEVELOPMENTS Many anonymous inventors were the first in their geographic areas to use water as the first plasticizer. Pottery was most likely the first product that was produced with a plasticizer. The short history of pottery on various continents is presented in Table 1.1. Table 1.1. A short history of pottery Period

Events

28,000 BCE

statuette of a woman, named the Venus of Dolní Věstonice, from a small prehistoric settlement near Brno, Czechia

18,000 BCE

first examples of pottery appeared in Eastern Asia several thousand years later in the Xianrendong cave in China

9,000 BCE

clay-based ceramics became popular as containers for water and food, art objects, tiles, and bricks, and their use spread from Asia to the Middle East and Europe

7,500 BCE

first fired pottery produced in Japan in the Jomon period

7,000 BCE

the oldest known pottery available in the Heiseikan Building of the Tokyo National Museum

6,000 BCE

potter’s wheel introduced in Mesopotamia

5,500 BCE

houses were built in Jericho, which had a stone foundation and half meter-thick walls built from sun-dried bricks

5,000 BCE

oldest pottery in Schleswig-Holstein, Europe

5,000-3,000 BCE

Valdivia pottery in Ecuador. The so-called Venus of Valdivia resembles Venus of Jomon from Tanabatake, Japan. Each were made from local clays

3,500 BCE

pottery produced by neolithic cultures in Tigris and Euphrates river valleys, Middle East

3,150 BCE

oldest pottery in Maluku, Indonesia

3,000-2,600 BCE

bowls, plates, and platters were produced in Egypt

2,700-2,200 BCE

potters wheel was introduced in Egypt

2

Introduction

Table 1.1. A short history of pottery Period

Events

1,600-1,100 BCE

pre-Olmec pottery made in Mexico to Honduras, Central America

1,000 BCE

oldest pottery found in Colombia, South America

900-500 BCE

Etruscan pottery in North-west Italy

550 BCE

beginning of potter’s art in Greece

The above chronology of events shows that the development of technology was not evenly spread throughout the world in spite of the fact that some more developed locations were close to each other but some political barriers did not allow for technology to spread. On the other hand, technology could also travel very far, for example, as seen in Valdivia, Ecuador, which may have gotten technology from Japan. Painting is another example of the early application of plasticizers. The following chronological developments show how technology was modified until there was a need to use plasticizers (Table 1.2). Table 1.2. Technological developments in painting Period

Event

45,500 BCE

the world's oldest known cave painting has been discovered by archaeologists in Indonesia. It is a life-sized picture of a wild pig

37,000-33,500 BCE

figurative cave paintings in Grotte Chauvet-Pont d'Arc in France

17,000 BCE

imprints of hands (Lascaux Caves in France). In this early period, two methods were used: hands were dipped into fluid colorant, or the surface was coated with greasy material and pigment blown through a tube. Animal fat, urine, blood, eggs, or milk-casein were used as organic binders or dispersants of pigments

13,000-9,500

stenciled outlines of human hands in Cueva de las Manos (Cave of the Hands), Río Pinturas, Argentina, and many depictions of animals, such as guanacos

6,000 BCE

development of a secco technique which is painting on the dry wall surface with pigment and binder (neolithic period)

3,500 BCE

painted tomb at Hierakonpolis is the oldest Egyptian painting

2,500 BCE

in Egypt arriccio layer to smooth surface and intonaco layer of gypsum plaster form surface on which pigment in the binder is applied. Binder is usually gum arabic (referred to as tempera binder) plasticized with honey.

Ancient Egypt is also credited with the use of plasticizers to preserve skin. This was practiced in the mummification process in which the body was dried, which made dry skin very fragile, and thus, a mixture of cedar oil, wax, natron, and gum was rubbed to soften the skin and prevent it from cracking. Preparation of nitrocellulose by Shoenbein and Bottger in 1846 is generally considered as the beginning of the use of plasticizers, although plasticizers were not mentioned in their patent and later related discoveries.1 In 1870, camphor was used as a plasticizer for cellulose nitrate. The first US Patent, which specifically mentioned plasticizer, was

1.1 Historical developments

3

obtained by Turkington in 1924 for high boiling aldehyde used to plasticize phenol resin.2 The second US Patent, which mentioned plasticizers, was obtained in 1924 by Lindsay, who used aromatic phosphates to plasticize celluloid.3 The next patents were issued in the 1930s for the plasticization of zein, gelatin, cellulose acetate, and vinylchloride/vinylacetate copolymers. And these included many known today plasticizers, such as phthalates and phosphates. It is well documented that German scientist Friedrich Klatte was the first to receive a patent for PVC in 1913. The patent also included plasticization with many known plasticizers.4 1930s and 1940s were the golden age of plasticizers synthesis and application, whereas 2000-2010 can be credited with the elimination of many previously important plasticizers. 15-30% of Americans (45-90 million people) report that they are unusually sensitive or allergic to certain common chemicals such as detergents, perfumes, solvents, pesticides, pharmaceuticals, foods, or even a smell of dry-cleaned clothing.5 An estimated 5% (15 million people) have been diagnosed by physicians as being especially sensitive. This calls for the attention of product designers and manufacturers.5 All these examples from the past show that new technological developments were dictated by requirements of processing or the need to soften the material. There was little exchange of information during these early technological developments. 1.2 EXPECTATIONS FROM PLASTICIZERS A large number of applications of plasticizers are driven by an even larger number of expectations of improvement of original properties of polymers and products into which these polymers are formulated with the use of plasticizers. A list below shows the most important expectations of plasticizer influence on the development of desired properties: • decrease the glass transition temperature of polymer − the most typical reason for plasticizer use. This expectation is frequently related to and explained by the mechanism of plasticizer action • making the material more flexible − the influence related to the changes in polymer structure − frequently measured by a decrease in glass transition temperature • increased elongation and decreased tensile strength are typical results from glass transition temperature decrease due to the addition of plasticizers, although in some polymers or products exceptional results are also observed, especially when the plasticizer concentration in material varies • decrease in ductility of materials and improvement of their impact resistance • low-temperature properties of many materials are improved by different types and concentrations of plasticizers • viscosity control − plasticizers are low viscosity liquids, which reduce the viscosity of polymer solutions and improve the workability of complex industrial formulations. There are numerous cases reported wherein viscosity also increases due to polymer solubility in plasticizer (e.g., PVC plastisols) or interaction with other liquid components present in formulation (e.g., water in water-based products in which formation of water-in-oil emulsion causes viscosity to increase) • modification of rheological properties − most products, especially products having high polymer content, are non-Newtonian liquids. Their apparent viscosity is a function of shear rate. This, in turn, causes a complex rheological behavior

4

Introduction

•

•

•

•

•

• •

•

• • •

•

• • •

effect on chemical reactivity − lower viscosity makes molecules to move more readily and thus interact and chemically react. At the same time, the addition of plasticizer dilutes reacting components, making plasticizer influence on reactivity a composite influence of both dilution and mobility decrease of the temperature of dissolution − gelation coalescence temperatures are the most frequently affected parameters, but many other effects have been discovered in various products, such as improved smoothness of coating, decreased temperature of adhesive application, etc. effect on processability. In addition to lowering fusion and gelation temperatures, plasticizers lower melting temperatures. Addition of plasticizers frequently opens new possibilities of material processing (lower degradation rate, processing on different types of equipment, reduced pressure of extrusion, etc.). Mixing time is reduced in the presence of plasticizers modification of interaction with water by the products containing plasticizers. Hydrophobic plasticizers reduce the water sensitivity of some products, and hydrophilic plasticizers increase water absorption, which may increase the curing rate in water-reactive systems, decrease skin time, decrease or increase tackiness, cause swelling, etc. assist the dispersion of liquid and solid additives (liquid additives especially benefit if they are easily soluble in plasticizer; predispersion of fillers, pigments, and solubilization of some liquid additives improves their incorporation) effect on electric conductivity depends on the electric properties of plasticizers, which may act as additional conductors or insulators fire behavior − most plasticizers generally increase the susceptibility of the material to burn, drip during burning and produce smoke but some plasticizers (phosphates and chloroparaffins) reduce burneability of materials and smoke production resistance to biological degradation − most plasticizers increase the potential of biological attack, and some products containing plasticizers must be protected by biocides. In biodegradable materials, selected plasticizers are deliberately added to increase the biodegradation rate improvement of sound blocking and vibration damping properties improvement of optical clarity by homogenizing system components effect on volatilization of product components. Plasticizers generally reduce the amount of VOC by helping to replace some solvents, but slow diffusion and evaporation also cause the release of liquid components leading to the so-called fogging and indoor pollution effect on crystallization is generally directed towards reduction of crystallinity, but in many cases crystallizing ability can be substantially increased by increased mobility of crystallizing polymer chains or their segments increased compatibility between additives, polymer with additives, and polymers in blends improvement of photorefractive properties of some compositions migration of low molecular substances into the product and out of the product is increased. This is especially important in pharmaceutical products in which coat-

1.3 Definitions

5

ing containing a plasticizer regulates drug release rate, but it is also essential in textile dyeing and many other applications • increase in gas permeability In addition, to the above-listed expectations based on the physical-chemical properties of plasticizers and their effect on other materials, namely polymers, we also have several socio-political factors and expectations, which are the trademark of our present times. These include: • renewable resources (as a source of raw materials used in the production of plasticizers) • biodegradable (up a certain degree of biodegradability, considering that it does not harm either performance or lifetime of the final products). The global market of eco-friendly plasticizers is anticipated to grow by 13.5% during the forecast period of 2019-2027.6 • non-phthalate (even though some of the so-called “non-phthalate plasticizers” are also phthalates but tere- rather than ortho- or cyclohexane derivatives, similar in structure to ortho-phthalates) Several chapters (17-21) discuss the specificity of these issues, which are frequently based on legitimate concerns, but sometimes are based on campaigns by various consumer groups. Some of these concerns have no foundation in science but were so widely discussed that confused customers do not want to see these materials in their surroundings and frustrated manufactures follow the customer’s expectations.

1.3 DEFINITIONS Numerous definitions of plasticizers are in use, such as: • a low molecular weight material added to polymeric materials such as paints, plastics, or adhesives to improve their flexibility • plasticizer lowers Tg and makes material more flexible • plasticizer interacts with the polymer chains on the molecular level as to speed up its viscoelastic response (or increase chain mobility) • in packaging, a plasticizer is a substance added to materials to impart flexibility, workability, and elongation • the plasticizer is an ink additive that adds flexibility, softness, and adhesion • a food's texture and rheological properties are improved through the addition of a plasticizer • specialty plasticizers impart characteristic properties such as flame retarding, low-temperature flexibility, or resistance to weather conditions • external plasticizer is a plasticizer which is added to a resin or compound, as opposed to an internal plasticizer that is incorporated in a resin during the polymerization process • secondary plasticizer is a plasticizer that is less compatible with a given resin than is a primary plasticizer and exudes or causes surface tackiness if used in excess. Used in conjunction with primary plasticizers to reduce cost or to obtain improvement in electrical or low-temperature properties. Also known as an extender plasticizer

6

Introduction

•

• •

• •

•

polymeric plasticizer has a sufficiently high molecular weight (usually Mn is higher than 2,000). An increase in molecular weight contributes to its permanence due to low vapor pressure and a low diffusion rate bioplasticizer is a primary or secondary plasticizer obtained from renewable resources biodegradable plasticizer is a product of synthesis and/or processing natural products, which can be easily biodegraded. Biodegradable material has been generally defined as a material, which, under sufficient water, oxygen, and suitable nutrients and temperature, is able to decompose into carbon dioxide and water by microbes non-phthalate (or phthalate-free) plasticizer is a product of synthesis, which does not contain ortho-phthalic rest non-VOC plasticizer is a product which has long retention time usually compared with a retention time of n-hexadecane, which has retention time (by GC analysis of 10 min). Each product that has larger than n-hexadecane is considered a nonVOC or semivolatile organic product, SVOC). Semi-volatile organic products have boiling points above 260oC (VOC or volatile organic products have boiling points in the range of 60-260oC, whereas very volatile organic products, VVOC, have boiling point below 60oC) “green plasticizers” − synonymous with natural (or renewable) based products. There are tools, such as GreenScreen and CleanGredients, that help customers and manufacturers to review compliance information on materials available in the market.

1.4 CLASSIFICATION The purpose of any classification is such as to organize our knowledge that the properties of objects may be remembered and their relationships may be understood more easily for a specific objective.2 Classification helps us to deal with complexity. There are too many objects to consider individually. If we can find some common properties or behavior between them, we can make meaningful classes to help us organize our knowledge and simplify our decision-making process. Plasticizers are commonly classified based on their chemical composition because it is easier to understand the influence of structural elements (e.g., different alcohols in a homologous series of phthalates, adipates, etc.) on the properties of plasticizers and their effect on materials, which contain them. For this reason, we also group plasticizers by chemical family (or category) such as esters, phthalates, chlorinated paraffins. It is important to consider that classification should help in the extraction of an objective truth rather than to be used for crude simplifications. For example, grouping paraffins by the length of their carbon chain and concentration of chlorine helps in understanding their ecological effect and proper categorization of information and literature on the subject. Similarly, the study of the migration rate of phthalates having different alcohols or their solubilities in different solvents helps to formulate better products. On the other hand, calls for the elimination of an entire group of plasticizers without understanding the benefits or disadvantages given by the properties of individual members of the group is a crude simplification, which should have no place in science.

References

7

Section 1.2 shows that plasticizers affect different physical and chemical properties of materials. It is very likely that in many applications, a product designer intends to change the properties of the material in a certain direction that mandates the selection of a particular plasticizer. Section 1.3 shows that the definition of plasticizer is affected by its application, the reason for its use, and more recently by its effect on people and the environment. The next chapter contains a comparison of the properties of plasticizers. In order to help in studying relationships, plasticizers are classified according to their chemical families since this is the only easy way to locate individual plasticizers. The comparison of properties is made to highlight their physical properties, their influence on properties of materials in which they are used, and to find justification for their selection to achieve these properties.

REFERENCES 1 2 3 4 5 6

Ang H G, Pisharath S, Energetic Polymers, John Wiley & Sons, New York, 2012. Turkington V H, US Patent 1,503,392, Bakelite Corporation, 29 Jul 1924. Lindsay W G, US Patent 1,508,457, Celluloid Company, 16 Sep. 1924. Wypych G, PVC Degradation and Stabilization, 4td Edition. ChemTec Publishing, Toronto, 2020. Montague, P; Pellerano, M B, History of the US Environmental Movement. Reference Module in Biomedical Sciences. Elsevier, 2014, pp. 918-43. Eco-Friendly Plasticizers Market: Inclinations & Development Highlighted Status and Forecast to 2027. MarketWatch, 2021.

8

Introduction

2

PLASTICIZER TYPES 2.1 INTRODUCTION Table 2.1.1 shows world consumption of plastics additives by type. Table 2.1.1. World consumption of plastics additives by type. Additive type Plasticizers

Consumption, tons

Growth rate, % 1

10,200,000 (2020)-12,600,00 (2026)

2

3.9

Flame retardants

2,500,000 (2017)-3,100,000 (2023)

Impact modifiers

1,740,000 (2020)-2,850,000 (2030)3

8.3

Heat stabilizers

765,000 (2015)4

-

Antioxidants

103,300 (2020)5

-

4

Plasticizers are by far the most common additives. They are also less expensive than other additives used in polymers processing and applications. In spite of many changes in the use of different types of plasticizers and the elimination of some grades, the expected growth rate is reasonably high. The global plasticizers market is expected to reach $111 billion by 2023.6 Table 2.1.2 shows global consumption of plasticizers by industry in 2015.7 Table 2.1.2. Global plasticizer market by industry in 2015. Industry Flooring and walls

Consumption, % 21

Film and sheet

20.5

Wire and cable

19.2

Coated fabrics

12.8

Consumer goods

11.4

Other applications

15.1

10

Plasticizer Types

Table 2.1.3. Plasticizer end-use in 2008 in percents compared with data from 1994.8 [Data from Bisig M D, Plasticizer Update, SPI 20th Vinyl Compounding Conference, July 19-21, 2009.] 2008

1994

Film & Sheet

28

20+4=24 (technical film, tarpaulins, roofing sheet) + (packaging film)

Wire &cable

22

19+9=28-3=25 (cable sheathing, cable filling compounds, wire coating, seals, profiles, tubing) + (cable) - (tubes and profiles)

Flooring

13

19 (floor coverings, wallpapers)

Profiles

11

Coatings

13

6 (paints and printing inks)

Others

13

7+6+6=20 (lubricants, pressure rollers, laminated glass, sheet, medical) + (adhesives including glazing) + (synthetic leather)

According to the data in Table 2.1.2, the application of plasticizers in flooring dominates the market and was substantially increased in the last decade. Film & sheet use reduced consumption of plasticizers, most likely because plasticizers were found to migrate to foods and were thus replaced by non-migrating solutions. Also, the use of plasticizers in profiles increased substantially (most likely because of the larger production of profiles for window and door applications). Considering the effect of global economy on product uniformity, it should be expected that the consumption of plasticizers for the production of the same materials should be similar. This is confirmed by the following examples. For example, 63% of plasticizers are used by the cable industry, film production, flooring, profiles, and wall coverings in Russia,10 which is close to 67% of plasticizers used in Europe for similar purposes. Plasticizers’ use is driven by the cost/performance ratios of different raw materials in the production of finished goods. Asia/Pacific is the largest market for additives (68.3% by mass in 2020), followed by Europe (14.7%) and North America (10.4%), with other regions using just 6.6%.5 Table 2.1.4 shows a dramatic increase in plasticizers uses by China, which is the largest consumer of plasticizers. Table 2.1.4. World consumption of plasticizers in 202011 and 2008.12 Region

Consumption, percents 2020

2008

North America

10.4

14.4

Europe

14.7

19.6

China

52.5

33.9

Rest of Asia Pacific

15.8

21.4

Others

6.6

10.7

Total

100

100

11

Flexible polyvinylchloride accounts for 80-90% of global plasticizer consumption.11 Phthalates accounted for over 55% of world consumption of plasticizers in 2020, down from approximately 60-65% a few years ago; they are forecast to account for 50-55% of world consumption in the coming years.11 Table 2.1.5 compares shares of different phthalates in the 1990s in the European Union and global shares of different phthalates in 2008. Table 2.1.5. Shares in percents of different phthalates.10,13 Plasticizer

1990s

2008

Di-(2-ethylhexyl) phthalate

51

28.8

Didecyl phthalate

21

15.3

Dinonyl phthalate

11

24.3

Dibutyl phthalate

2

Other phthalates

15

In the past production, the largest use among phthalates belonged to di-(2-ethylhexyl) phthalate (51%), diisodecyl phthalate (21%), and diisononyl phthalate (11%). This varied from country to country. In Russia, which manufactured 300,000 tons of plasticizers (Europe manufactured over 1,300,000 tons of various plasticizers),14-16 The use of plasticizers changed because of reported findings and regulations (see Chapters 18-21). Phthalates and some chloroparaffins are the most affected groups. Production of phthalic anhydride, which is principally used for the production of phthalic esters, decreased.17 Table 2.5 shows that the use of DOP was drastically reduced. In the next sections of this chapter, plasticizers are discussed based on chemical similarity, and the discussion of two plasticizers is based on application (explosives and cementitious products) because the chemical composition of these plasticizers is very different than the plasticizers used in other markets. The discussion in the next sections is designed to find common features of plasticizers within the same chemical group and to provide information that is suitable for the comparison of properties of plasticizers from different chemical groups. This section does not contain information on specific plasticizers. Information on specific plasticizers is included in a special electronic publication on CD-ROM.18 The first edition of the CDROM database published in 2004 contained specific data on over 1272 products, including commercial plasticizers (1215) as supplied by manufacturers as well as some data on chemical compounds, which are the components of plasticizers (generic compounds − 57).18 The database in 2004 included information on products manufactured by 98 producers, who manufactured by average 12 products considered as plasticizers. The third edition (2017) of Plasticizer Database includes information on 1507 products manufactured by 89 producers worldwide. Out of 1507 plasticizers, 57 are generic, and 498 are discontinued (included to give a full background of the plasticizer market). 89 manufacturers produce by average 11 plasticizers, which is less than in 2004. It can be concluded from the above information that the number of products, manufacturers, and the average number of products per manufacturer has diminished. This is because of two reasons:

12

Plasticizer Types

•

many products are no longer in use because of environmental and health concerns • consolidation in the plasticizer manufacturing industry. Both publications − the book and the database − were designed and prepared to complement each other in providing information based on a broad collection of data available worldwide. Another publication in the form of book and ebook, Databook of Plasticizers,19 contains selection and relevant data for the most commonly used plasticizers, which can be consulted in addition to this book if data for a particular plasticizer is needed. References 1 2 3 4 5 6 7

8 9 10 11 12 13 14 15 16 17 18 19

Fernandez L, Market volume of plasticizer worldwide from 2015 to 2020, with a forecast for 2021 to 2026. Statista, 2021. McWilliams, A; Kearny, A T, Flame Retardant Chemicals: Technologies and Global Markets, bcc Reasearch, 2018 Global Impact Modifier Market Analysis: Plant capacity, Production, Operating Efficiency, Process, Technology, Demand & Supply, End Use, Grade, Type, Sales Channel, Region, Competition, Trade, Customer, and Price Intelligence Market Analysis (2015-2030), Market Publishers, 2021. Global Heat Stabilizers Market to Reach 765 Thousand Tons by 2015, Global Industry Analysts, Inc. Antioxidants Market: Triggered By Changing Diet Patterns and Significant Growth of Meat Consumption - Global Industry Analysis and Opportunity Assessment 2014 - 2020, Future Market Insights, 2014. Global Plasticizers Market Worth $111 Billion by 2023 - Granular Historic Analyses & Forecasts Through 2015-2030, Research and Markets, 2020. Plasticizers Market by Type (DINP, DIDP, DPHP, DOP, Terephthalates, Trimellitates, Epoxides, Phosphates, Sebacates, Extenders, Aliphatic Dibasic Esters, and Others) and Application (Flooring & Wall, Film & Sheet Coverings, Wires & Cables, Coated Fabrics, Consumer Goods, and Others) - Global Opportunity Analysis and Industry Forecast, 2014-2022, Allied Market Research. Menzel B, Kunststoffe, 86, 7, p. 992-996, 1996. Bisig M D, Plasticizer Update, SPI 20th Vinyl Compounding Conference, July 19-21, 2009. Kirillovich V I, Intl. Polym. Sci. Technol., 25, 4, T11-T13, 1998. Plasticizers, Chemical Economics Handbook. IHS Markit, 2021. Bisig M D, Plasticizer Update, SPI 20th Vinyl Compounding Conference, July 19-21, 2009. Peijnenburg W J G M, Phthalates in Encyclopedia of Ecology, Elsevier, 2008. Plast. Additives Compounding, October, 1999, p. 12-17. Plastics Additives in Europe, Business Communications, Co., January 2002. Markets. European plastics additives, Additives for Polymers, Elsevier, January 2002. Phthalic Anhydride. Eur. Chem. News, 6-12 Sept. 1999, p. 18. Wypych, A, Plasticizers Database, 3rd Ed., ChemTec Publishing, Toronto, 2017. Wypych, A. Databook of Plasticizers, 3rd Ed., ChemTec Publishing, Toronto, 2023.

13

2.2.1 Abietates

2.2 CHARACTERISTIC PROPERTIES OF INDUSTRIAL PLASTICIZERS 2.2.1 ABIETATES Technical abietic acid is obtained by heating rosin with or without acids. The following is the chemical formula of abietic acid esters:

H3C

O C OR

H3C

CH3 CHCH3

R = CH3 or CH2CH3 Methyl, ethyl, and benzyl esters are produced on a commercial scale. Use is rapidly declining because both rosin and esters of abietic acid are known allergens. Abietates have high boiling points (methyl abietate − 360oC). Rosin and abietates are considered to be plasticizers and tackifiers. Potentially they may be used in caulks, adhesives, and varnishes. The following table contains information on the average properties of abietic acid ester plasticizers. Property

Value

Recommended for these polymers

nitrocellulose, ethylcellulose, chlorinated rubber, natural rubber

Recommended for products

adhesives, asphalt modification, contact adhesives, hot melt adhesives, inks, lacquers, lamination, packaging, paper coatings, pressure sensitive adhesives, tapes and labels, solvent borne adhesives, water borne adhesives, wax modification

Outstanding property

excellent perfume fixative, excellent surface wetting and adhesive properties; high refractive index, low vapor pressure, high boiling point, and good thermal stability

Molecular weight, daltons o

316-393

Boiling point, C

350-360

Freezing point, oC

-45

o

Flash point, C

178-193

Density, kg/m3 at 20oC

1027-1040

Refractive index at 25oC

1.527-1.530

14

Plasticizer Types

2.2.2 ADIPATES The esters of adipic acid have the following chemical structure:

O O RO C CH2CH2CH2CH2 C OR The following table contains comparative data for this group of plasticizers. Similar to other groups, minimum and maximum values are usually selected for plasticizers having the lowest and the highest molecular weights reported in the table. The median values are usually given for the most frequently used plasticizer (in the case of this group for di(2-ethylhexyl) adipate).

Property

Value minimum

maximum

median

Main alcohols used in commercial products 2-ethylhexyl, benzyl-octyl, butyl, butoxyethyl, heptyl, isobutyl, isodecyl, isononyl, methyl, tridecyl Molecular weight, daltons NFPA health

174.19

510.85

342.52

0

1

0

NFPA flammability

1

1

1

NFPA reactivity

0

0

0

Highly recommended for these polymers

PVC, NBR, SBR, PVAc, CAB, CP, CN, VCVAc, PS

Main fields of application

film, cable & wire, coatings, masterbatches, nail care, belts, printer rollers, boots, gloves, aprons, tank liners, food wrap, adhesives, tubing, water pipe

Outstanding property

low temperature resistance, good light stability

Melting point, oC

8

o

Pour point, C

-60

Boiling point, oC

222

o

Flash point, C Refractive index Platinum-cobalt color

-70

-50

509

417

145

243

192

1.441

1.482

1.446

20

40

Specific gravity

0.905

1.057

Vapor density

12.1

12.8

Vapor pressure at 100oC, kPa pKa1 = 4.41, pKa2 = 5.28 0.02

0.1

7.31

9.64

4

26

o

Solubility in water at 25 C, wt% Hildebrand solubility parameter, (cal/cc)0.5 o

Viscosity at 20 C, mPa s

8

6.70

Moisture content, wt%

0.04

0.09

0.065

Viscosity at 23oC, mPas

15.1

3830

1920

Plasticizer’s loss (24 h at 70oC), wt%

0.06

0.11

0.075

14.5

Specific gravity at 25 C Iodine value

TLV-TWA 8 h, OSHA, mg/m3

not available

NIOSH-IDHL, mg/m3

not available

Tensile strength, 60 phr, MPa

10.8

18.2

Elongation, 60 phr, %

180

436

Shore A hardness, 50 phr

76

78

145

Esters of maleic acid have very good plasticizing properties but, similar to DOP, have strong resistance to biodegradation.9 Succinic esters of straight-chain alcohols are excellent green plasticizers.9 They have good plasticizing properties, and they are quickly

2.2.7 Bioplasticizers

27

degraded because of the favorable orientation of molecular structure (both maleic and phthalic acids have cis orientation).9 Succinic acid can be easily produced by fermentation. Biopolymers are gaining attention as potential replacements for petroleum-based polymeric materials. In their original state, they have to be modified by additive, and if additives are made out of synthetic sources, the “green” origin is lost.10,12 For this reason, the development of suitable composition, which is all based on natural products, is very important. Among additives, plasticizers are usually the most important because they are high-volume items. The most commonly used bioplasticizers include citrate, polyols, triacetin, oligomeric esteramides, and fatty acid derivatives.10,12 Biobased plasticizers improved strain at failure, mechanical and thermal properties of 3D printed poly(lactic acid) composites.13 Epoxidized soybean oil exhibited superior compatibility with poly(lactic acid) matrix.13 References 1 2 3 4 5 6 7 8 9 10 11 12 13

Fenollar O, Garcia-Sanoguera D, Sanchez-Nacher L, Lopez J, Balard R, J. Mater. Sci., 45, 4406-13, 2010. Benaniba M T, Massardier-Nageotte M, J. Appl. Polym. Sci., 118, 3499-3508, 2010. Benecke H P, Vijayendran B R, Elhard J D, US Patent 6,797,753 B2, Battelle Memorial Institute, Sep. 28, 2004. Barki A C, Aburto R A, Arenas A T, Gomez M J C, US Patent Application US2010/0010127 A1, Resinas y Materiales, Jan. 14, 2010. Flynn A, Torres L F, US Patent 7,842,761 B2, Lapol, LLC, Nov. 30, 2010. Yin B, Hakkarainen M, J. J. Appl. Polym. Sci., 119, 2400-07, 2011. Lapol. Getting Started with Lapol 108 Bioplasticizer, Lapol LLC, Rev. 100930. Stenton R, US Patent Application US 2011/0137339 A1, MedLogic Global Limited, Jun. 9, 2011. Erythropel H C, Maric M, Cooper D G, Chemosphere, 86, 759-66, 2012. Vieira M G A, da Silva M A, dos Santos L O, Beppu M M, Eur. Polym. J., 47, 254-63, 2011. Fujita Y, Sawa O, US Patent 7,166,654 B2, Daichi Chemical Industry Co., Ltd., Jan. 23, 2007. Hassan A A; Abbas A; Rasheed T; Bilal M; Iqbal H M N; Wang S, Sci. Total Environ., 682, 394-404, 2019. Bajwa D; Eichers M; Shojaeiarani J; Kallmeyer A, Ind. Crops Prod., 173, 114132, 2021.

28

Plasticizer Types

2.2.8 BIODEGRADABLE PLASTICIZERS This section is a continuation of previous section designed to stress influence of plasticizers on biodegradability of polymeric composition by showing a few examples from current patent literature.1-3 Chemical structures vary depending on the application, but polyester is the likely candidate for biodegradable plasticizer:

R1OOC(CH2)mCOOR2

Property

Value minimum

maximum

median

Main alcohols used in commercial products straight or branched alcohols containing 1 to 15 carbon atoms,1 glycerol,1 glycerol+ethylene oxide3 Other building blocks of plasticizer

hydroxyl aliphatic monocarboxylic acid and carboxylic acid amide in addition to polycarbonate diol,2 acetic anhydride3

Highly recommended for these polymers

aliphatic polyester resin, PLA

Main fields of application

film, sheet, molded articles

Outstanding property

biodegradability, flexibility, migration resistance

References 1 2 3

Fujita Y, Sawa O, US Patent 7,166,654 B2, Daichi Chemical Industry Co., Ltd., Jan. 23, 2007. Takenaka A, Tuchichashi M, US Patent 7,576,152 B2, Kao Corporation, Aug. 18, 2009. Takenaka A, Nomoto S, US Patent 7,652,085 B2, Kao Corporation, Jan. 26, 2010.

29

2.2.9 Chlorinated paraffins

2.2.9 CHLORINATED PARAFFINS The chemical formula below shows a structure of paraffin having 12 carbon atoms, which was chlorinated to contain 60% chlorine. Cl H

H

H Cl

H Cl

H

Cl

H

H

H H

H

H

Cl

H

Cl H

H H

H H

H

H

Cl

Chloroparaffins are divided into 6 groups, which include:1-6 • short chain (C10-13) • intermediate chain (C14-17) • long chain (C18-30) Each of these groups is still divided into two classes having chlorine concentration below or above 50 wt%. Each group contains a very large number of participating isomers, which differ by the number of carbon atoms (stock dependent) and chlorine atoms (process dependent).

Property Molecular weight, daltons

Value minimum

maximum

median

280

1290

560

NFPA health

0

NFPA flammability

1

NFPA reactivity

0

Highly recommended for these polymers

PVC, PU, rubber, chlorinated rubber

Main fields of application

paints, sealants, adhesives, flooring, flexible hose, cable insulation, metal-machining fluids

Outstanding property

fire retardant action, water resistance

Freezing point, oC

0

100

210

>232

Refractive index

1,486

1.532

1.5

Specific gravity

1.10

1.63

1.25

2x10-7

3x10-6

7x10-7

40

70

50

0.00005

0.0047

0.003

o

Boiling point, C Flash point, oC

Vapor pressure at 20oC, kPa Chlorine content, wt%

decomposes

Moisture content, wt% Solubility in water at 25oC, wt% Hildebrand solubility parameter, (cal/cc)0.5

2,000

Theoretical oxygen demand, g/g

maximum

median 32,000 >5,000

1.56

2.27

1.94

Partition coefficient, log Kow

0.33

8.21

3.28

Tensile strength, 50 phr, MPa

18.9

20.5

19.7

Elongation, 50 phr,%

364

400

390

Shore A hardness, 50 phr

78

87

81

Citric acid esters are discussed in the review papers, patents, and commercial literature.1-18 Citric acid-based plasticizers are one of the major contenders to replace phthalates (especially targeted to replace DOP).1 Some properties of materials plasticized with citrates can match those of DOP plasticized PVC, but the cost of their production is substantially higher. Citrates are extracted from flexible PVC at a higher rate than DOP and trimellitates.14 Eudragit, which is a choice polymer in pharmaceutical coatings, having controlled release or sustained release properties, performs its functions very well when plasticized with triethyl citrate.15 The concentration of plasticizer can be used as the parameter that regulates the release rate. A combination of triacetin and Mesamoll was patented for applications that require fast gelling time.16 This combination can be used to replace benzyl butyl phthalate, which was previously used as a fast gelling plasticizer. The biodegradable film was prepared from cellulose acetate with glycerol and triethyl citrate added as plasticizers.19 Both plasticizers can be added to polymer matrices to develop food packaging.19 Highly permeable reverse osmosis membranes are desirable to ensure water sustainability.20 The presence of green citrate plasticizers, namely tributyl citrate or acetyl tributyl citrate, led to the formation of new hydrogen bonds and inhibited the formation of the initial interchain amide-amide bonding thus markedly reducing chain rigidity as demonstrated by the decreased elasticity modulus.20 More flexible polyamide chains contributed to ultrafast water channels during filtration.20 Tributyl citrate-modified membranes exhibited more elastic polyamide layers and higher water flux than that of acetyl tributyl citratemodified membranes on account of the presence of both hydrogen bond acceptors (O−H) and hydrogen bond donors (C=O) in tributyl citrate molecules.20 Figure 2.2.10.1 illustrates the effect of citrate plasticizers on the structure of membranes.20

34

Plasticizer Types

Figure 2.2.10.1. (a) The schematic diagram of green plasticizer-assisted interfacial polymerization; (b) structural formulas of tributyl citrate, TBC, and acetyl tributyl citrate, ATBC; (c) comparison between pristine and modified membranes. [Adapted, by permission, from Qin, Y; Kang, G; Cao, Y, Sci. Total Environ., 784, 147089, 2021.]

Poly(3-hydroxybutyrate) was plasticized with variable amounts of triethyl citrate.21 The rigid amorphous fraction decreased quickly as the amount of triethyl citrate increased.21 Secondary crystallization led to a PHB/triethyl citrate phase separation. Aging resulted in embrittlement, the loss of capacity to dissipate mechanical energy, and significant changes in the relaxation spectra.21 The effects of aging on impact resistance were more pronounced when triethyl citrate concentration increased, which was due to phase separation in formulations richer in plasticizer, induced by secondary crystallization, expelling triethyl citrate from the crystalline structure.21 Manufacturers of teethers and toys have changed to other plasticizers or non-PVC plastics.22 Plasticizers identified in the 38 PVC articles included acetyltributyl citrate (20); di-(2-ethylhexyl) terephthalate (14); 1,2-cyclohexanedicarboxylic acid diisononyl ester (13); 2,2,4-trimethyl-1,3-pentanediol diisobutyrate (9); di-(2-ethyhexyl) phthalate (1); and DINP (1).22 Plasticizer concentration data were combined with migration rates and with data on mouthing duration to estimate children's exposure to plasticizers in toys and child care articles and estimated margins of exposure.22 All margins of exposure were >1,000, suggesting a low-risk potential.22 References 1 2 3 4 5 6

Jain K K; Fatma K; Saroop M, Popular Plast. Packaging, 43, No.11, Nov.1998, p.75/82. Keller M J, US Patent 6,534,577 B1, era Beschichtung GmbH & Co., Mar. 18, 2003. Castrogiovanni A, Sandewicz R W, Amato S W, US Patent 5,227,155, Revlon Consumer Products, Jul. 13, 1993. Castrogiovanni A, Sandewicz R W, Amato S W, US Patent 5,225,185, Revlon Consumer Products, Jul. 6, 1993. Castrogiovanni A, Sandewicz R W, Amato S W, US Patent 5,145,671, Revlon Consumer Products, Sep. 8, 1992. Castrogiovanni A, Sandewicz R W, Amato S W, US Patent 5,145,670, Revlon Consumer Products, Sep. 8, 1992.

2.2.10 Citrates

7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22

Castrogiovanni A, Sandewicz R W, Amato S W, US Patent 5,066,484, Revlon Consumer Products, Nov. 19, 1991. Hull E H, Frappier E P, US Patent 4,931,583, Morflex Chemical Company, Inc., Jun. 5, 1990. Hull E H, Frappier E P, US Patent 4,892,967, Morflex Chemical Company, Inc., Jan. 9, 1990. Hull E H, Frappier E P, US Patent 4,870,204, Morflex Chemical Company, Inc., Sep. 26, 1989. Hull E H, US Patent 4,824,893, Morflex Chemical Company, Inc., Apr. 25, 1989. Hull E H, Frappier E P, US Patent 4,789,700, Morflex Chemical Company, Inc., Dec. 6, 1988. Hull E H, Frappier E P, US Patent 4,711,922, Morflex Chemical Company, Inc., 1987. Adams R C, Medical Plast Biomater., 2001. Diltiazem HCl Sustained release Pellets, Degussa, Feb. 2002. Hansel J-G, Wiedemeier M, US Patent 8,026,314, B2, Lanxess Deutschland GmbH, Sep. 27, 2011. Grass M, Woelk-Faehrmann M, US Patent 7,595,421 B2, Lanxess Deutschland GmbH, Sep. 29, 2009. Wang J, Che R, Yang W, Lei J, Polym. Int., 60, 344-52, 2011. Côcco Teixeira S; Assis Silva R R; Velosode Oliveira T; Stringheta P C; Ribeiro Pinto M R M; Ferreira Soares N F, Food Biosci., 42, 101202, 2021. Qin, Y; Kang, G; Cao, Y, Sci. Total Environ., 784, 147089, 2021. Umemura R T; Felisberti M I, MaterialsToday, Commun., 25, 101439, 2020. Babich M A; Bevington C; Dreyfus M A, Regulatory Toxicology Pharmacology, 111, 104574, 2020.

35

36

Plasticizer Types

2.2.11 CYCLOHEXANE DICARBOXYLIC ACID, DIISONONYL ESTER 1,2-cyclohexanedicarboxylic acid diisononyl ester has been known as Hexamoll DINCH. Both Hexamoll and DINCH are registered trademarks of BASF. The new plasticizer is commercially manufactured since 2002 by hydrogenation of aromatic ring in diisononyl phthalate.

O

O O O

C9H19

O

H2

O

C9H19

O

C9H19 C9H19

O core-hydrogenation

1,2-cyclohexanedicarboxylic acid diisononyl ester is a non-phthalate plasticizer (see additional information in Section 2.2.24) designed specifically for human contact applications. This commercial plasticizer is also available from Evonik and several Chinese manufacturers. In comparison to other non-phthalate plasticizers, it offers a well-balanced set of properties, which justifies its use in a multitude of applications, no matter whether the method of processing is thermoplastic- or plastisol-based. Property

Value

Main alcohols used in commercial products isononyl Molecular weight, daltons

424.7

Highly recommended for these polymers

PVC and other polar polymers

Main fields of application

medical devices, toys, food contact applications, sport and leisure products

Outstanding properties

low viscosity, low volatility, good migration & extraction resistance, excellent cold flexibility and toxicology profiles

Pour point, oC

-54

Boiling point, oC

394; 240-250 (7 mbar)

Glass transition temperature, oC

-90

Flash point, oC

224

Autoignition temperature, oC

>330

Decomposition temperature, oC

>278

o

Refractive index at 20 C Platinum-cobalt color, DIN EN ISO 6271 o

Specific gravity at 20 C

1.460-1.466 40 0.944-0.954

37

2.2.11 Cyclohexane dicarboxylic acid, diisononyl ester

Property

Value

o

Vapor pressure at 20 C, kPa

1.1E-07

Surface tension at 20oC, mN/m

30.7 o

Solution temperature (at clear point) C DIN 53408 (S-PVC; K-value 71) Viscosity at 20oC, mPa s

151 44-60

Tensile strength, 67 phr, MPa

17

Elongation, 67 phr,%

360

100% modulus, 67 phr, MPa

6.4

Brittleness temperature, oC; BASF-method, similar to former DIN 53372

-43

Glass transition temperature by DMA, oC ISO 6721-7

-45

Animal testing, acute toxicity, Rat oral LD50, mg/kg

>5000

Animal testing, acute toxicity, Rat dermal LD50, mg/kg

>2000

Aquatic toxicity, Daphnia magna, 48-h LC50, mg/l

>100

Aquatic toxicity, Green algae, 72-h LC50, mg/l

>100

Partition coefficient, log Kow

10.25

DINCH has been shown to leach from PVC in amounts half of those for DEHP.1 Intravenous administration of DINCH to rats did not affect their behavior.1 DINCH caused hatching delay in zebrafish in a dose-dependent manner and altered the expression of genes involved in stress response.2 Genes associated with lipid transport, such as fatty acid synthesis and β-oxidation were significantly altered by DINCH.2 Genes involved in cholesterol biosynthesis and homeostasis were also affected by DINCH indicating possible developmental neurotoxicity.2 DINCH may induce physiological and metabolic toxicity to aquatic organisms.2 Restrictions on the use of legacy phthalate esters as plasticizer chemicals in several consumer products have led to the increased use of alternative plasticizers, such as di-(isononyl)-cyclohexane-1,2-dicarboxylate (DINCH) and di-(2-ethylhexyl) terephthalate (DEHTP).3 Metabolites of DINCH and DEHTP were detected in practically every participant, but none of the estimated daily intakes or urinary exposure levels of alternative plasticizers exceeded the available health-based guidance values.3 Close monitoring in Flanders, Belgium, showed that the exposure levels to restricted phthalate esters have decreased, while alternative plasticizers are now frequently detected in humans.3 Thirteen phthalate metabolites and two metabolites of DINCH were detected in almost all urine samples (94%) studied in Spain.4 Lower birth weight was related to higher levels of DINCH metabolites in pregnant women’s urine.4 A decrease in weight of babies

38

Plasticizer Types

at birth was significantly associated with a higher presence of OH-MINCH and oxoMINCH (both DINCH metabolites).4 Exposure to endocrine-disrupting chemicals is suggested to be responsible for the development or progression of uterine fibroids.5 However, little is known about risks related to emerging chemicals, such as organophosphate esters and alternative plasticizers.5 Cases (n = 32) and the matching controls (n = 79) were chosen based on the results of gynecologic ultrasonography among premenopausal adult women in Korea and measured for metabolites of several organophosphate esters, alternative plasticizers, and major phthalates.5 The odds ratios of uterine fibroids were significantly higher among the women with higher exposures to tris(1,3-dichloro-2-propyl) phosphate and tris(2-butoxyethyl) phosphate, di(2-ethylhexyl) terephthalate, and di-(iso-nonyl)-cyclohexane-1,2dicarboxylate.5 Significantly high odds ratios observed for OH-MEHTP and OH-MINCH could be partially supported by the estrogenic effects of DINCH and DEHTP previously reported in in vitro studies.5 DINCH showed a stimulatory effect on steroid production in vitro. DINCH metabolites activate nuclear receptors, estrogen receptors (α and β), androgen receptors, and peroxisome proliferator-activated receptors (α and γ), suggesting weak estrogenic effects related to lipid and glucose metabolisms.5 Just a few examples referenced above show how big gaps exist in understanding what is acceptable as an alternative plasticizer and how far we are from knowing what the right direction should be taken in selecting safe products for future applications is. References 1 2 3 4 5

Vanhorebeek I; Malarvannan G; Güiza F; Poma G; Derese I; Wouters P J; Joosten K; Verbruggen S; Jorens P G; Covaci A; Van den Berghe G, Environ. Int., 158, 106962, 2022. Saad N; Bereketoglu C; Pradhan A, Heliyon, 7, 9, e07951, 2021. Bastiaensen M; Gys C; Colles A; Malarvannan G; Verheyen V; Koppen G; Govarts E; Bruckers L; Morrens B; Franken C; Den Hond E; Schoeters G; Covaci A, Environ. Pollution, 276, 116724, 2021. Martínez M A; Rovira J; Sharma R P; Kumar M S V, Environ. Res., 186, 109534, 2020. Lee G; Kim S; Bastiaensen M; Malarvannan G; Poma G; Caballero Casero N; Gys C; Covaci A; Lee S; Lim J-E; Mok S; Moon H-B; Choi G; Choi K, Environ. Res., 189, 109874, 2020.

39

2.2.12 Energetic plasticizers

2.2.12 ENERGETIC PLASTICIZERS Energetic plasticizers are defined as liquid materials having positive heat of the explosion. The heat of explosion is the energy released by burning the propellant or ingredient in an inert atmosphere and then cooling to ambient temperatures in a fixed volume. Numerous plasticizers have been patented for use as energetic plasticizers in rocket propellants, pyrotechnics, explosives, and munitions.1-23 Solid propellants can be classified as being either homogeneous or composite. The former refers to the types considered true monopropellants in which each molecule contains all necessary fuel and oxygen for combustion. The composite type propellant, in contrast, consists of a physical mixture of fuel and oxidizer. The homogeneous propellants are further subclassified as being either single or double base depending on whether the composition contains a single energetic combustible or contains an additional energetic combustible or a mixture of additional energetic combustibles, which act as an energetic plasticizer for the first energetic combustible. In this specification, the first energetic combustible is referred to as the polymer, the second energetic combustible as the energetic plasticizer, and the combination of the two as the binder.9 The term plasticization is synonymous with gelatinization. It is used to describe the initial physico-chemical reaction of the polymer with the energetic plasticizer. By this reaction, the polymer and the energetic plasticizer form a soft colloidal dispersion. This dispersion is then made usable for propellant purposes by application of mild heat over a period of time to form a tough, elastic, rubbery solid. This reaction is referred to as curing the propellant composition.9 If the polymer is not plasticized by energetic plasticizers, solvents must be used in the processing to obtain the colloidal dispersion. Solvent processes always impart a varying amount of residual volatiles in the propellant, which cause the energy content to vary accordingly. Further, solvent processes require an objectionably long drying cycle and are not practical for forming most rocket propellant charges. Compounds having the following formulas are used in these applications: CH2ONO2 H HO C CH2 O C CH2OCH2 H O2NO CH2 poly(glycidyl nitrate) R2 R3 R1 R4 C O C O C R5 R6 R7 R8

O2N

NO2

O

O

O2N

NO2

2

bis(2,2-dinitropropyl) formal NO2 NO2 CH3 N (CH2)n N CH3

R1 - R8 = H, CH3, or CH3N3 multi-azido formal

N,N'-dimethyl methylenedinitramine

It is pertinent from these structures that nitro and azide groups make plasticizers have energetic properties. In addition to these plasticizers, also neutral plasticizers such as DOP and other plasticizers are used in these applications. The plasticizers or their combi-

40

Plasticizer Types

nations are selected to achieve the required effect. Inert plasticizers usually lower the energy content of polymers used in explosives (e.g., nitrocellulose).

Property Molecular weight, daltons

Value minimum

maximum

296

3,000

Highly recommended for these polymers

hydrocarbon resins, polyesters, polyurethanes

Main fields of application

solid propellants, pyrotechnics, explosives

Outstanding property

low migration, low volatility, low smoke, improved storage safety, low temperature properties, electrostatic insensitivity, low toxicity

Freezing point, oC

-60

75

Specific gravity

1.29

1.47

-18.45

-6970

0.75

0.92

31

49

Heat of combustion, kJ/kg Tensile strength, 5 phr, MPa Elongation, 5 phr, %

Plasticizers are usually incorporated into energetic compositions as processing aids to improve the workability, flexibility, and/or distensibility of the binder of the composition. These improvements are accomplished by, for example, altering mechanical properties such as glass transition temperature or formulation viscosity.3 One of the best-known energetic plasticizers is nitroglycerin. It is well known for its use with nitrocellulose in double-base and triple-base propellants and explosive powders. A significant drawback shared by nitroglycerin and other nitrate ester-containing molecules, and polyolpolynitrates, such as diethyleneglycol-dinitrate and triethyleneglycoldinitrate, is their poor thermal stability and high shock sensitivity, which make compositions containing such plasticizers dangerous to handle and extremely prone to accidental detonation.3 Energetic plasticizers tend to be somewhat viscous in nature, and this limits the amount of solids that can be included in propellant formulations while maintaining good propellant processability. Reducing the solids loading of a propellant generally results in a lowered propellant impulse.5 It is also known that some plasticizers (e.g., ferrocene and the ferrocene derivatives) have a tendency to oxidize and to migrate over time towards the surface of the propellant and sometimes even to sublimate. The plasticizer migration causes irregularities in combustion.6 Because of the tendency of plasticizer molecules to migrate or evaporate out of the propellant composition during storage, the chemical changes in the composition occur, which are harmful to the propellant and to other inert parts of the rocket motor.13 Figure 2.2.12.1 shows a plot of the percent weight loss of a poly(glycidyl nitrate) plasticizer, PGN, and of 1,2,4-butane triol trinitrate, BTTN, versus time at an average vac-

2.2.12 Energetic plasticizers

Figure 2.2.12.1. Loss of plasticizer under vacuum of 0.2 mm Hg. PGN - poly(glycidyl nitrate), BTTN 1,2,4-butane triol trinitrate. [Data from Willer R, Stern A G, Day R S, US Patent 5,380,777, 1995.]

41

Figure 2.2.12.2. Effect of ferrocene plasticizer on cure rate increase of epoxide-cured polybutadiene acrylic acid copolymer. [Data from Frankel, N B; Witucki, E F, US Patent 4,023,994, 1977.]

uum of 0.2 mm Hg. This vacuum is equivalent to an altitude greater than 61,500 m. The PGN nitrate loses very little weight (>2%) during 43 days, while the BTTN has suffered a substantial weight loss in the same time period.1 Compounds such as adiponitrile, triacetin, dibutyl phthalate are very good plasticizers but are inert and actually lower the energy content of the nitropolymer. On the other hand, compounds such as diethyleneglycoldinitrate, 1,1,1-trimethylolethanetrinitrate, nitroisobutyltrinitrate, and nitroglycerin contribute energy, but they have undesirable characteristics associated with nitrate esters, such as toxicity (headache potential), volatility, low thermal stability, and high shock sensitivity. Nitroglycerin shows these undesirable properties to the greatest extent.19 Electrostatic sensitivity is also one of the major concerns.19 In using solid propellants, a problem exists in that an undesirable amount of smoke is often produced in the exhaust gases emanating from the solid rocket motor during propulsion. Excessive amounts of smoke are extremely undesirable in the exhaust gases since this provides data, which helps to locate the sites from which the missiles or rockets are being fired.21 Plasticizers require excellent physical compatibility and greater safety at elevated temperatures during production, handling and use.6 Low temperatures also affect these materials. If plasticizer crystallizes, the solid propellant becomes brittle and has a tendency to crack, which causes irregular burning properties. Plasticizers often affect curing rate of binder, as seen in Figure 2.2.12.2.22 gem-Dinitro bis(2,2-dinitropropyl ethylene) formal (BDNPEF) was synthesized to plasticize energetic binders. BDNPEF showed good plasticization efficiency (decrease in

42

Plasticizer Types

glass transition temperature and viscosity of uncured glycidyl azide polymer blends, as well as substantial ability to plasticize the GAP-based polyurethanes).24 References 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Willer R, Stern A G, Day R S, US Patent 5,380,777, Thiokol Corporation, Jan. 10, 1995. Cho J R, Kim J S, Park B S, US Patent 6,592,692 B2, Agency for Defence Development, Jul. 15, 2003. Highsmith T K, Doll D W, Cannizzo L F, US Patent 6,425,966, 2002. Goleniewski J R, Roberts J A, US Patent 5,783,769, Hercules Inc., Jul. 21, 1998. Rindone R R, Huang D-S, Hamel E E, US Patent 5,532,390, Aerojet General Corporation, Jul. 2, 1996. Finck B, Lafurneux A, Perotto C, US Patent 5,458,706, Societe Nationale des Poudres et Explosifs, Oct. 17, 1995. Carosino L E, Hartman K O, US Patent 5,310,433, Hercules Incorporated, May 10, 1994. Rindone R R, Huang D-S, Hamel E E, US Patent 5,220,039, Aerojet General Corporation, Jun. 15, 1993. Camp A T, Haiss H S, Mosher P R, US Patent 5,205,983, Unites States of America, Apr. 27, 1993. Ampleman G, US Patent 5,124,463, Her Majestry Queen in right of Canada, Jun. 23, 1992. Adolph H G, US Patent 4,997,499, Unites States of America, Mar. 5, 1991. Gilbert E E, US Patent 4,711,679, Unites States of America, Dec. 8, 1987. Stephens W D, Jones L E, US Patent 4,482,411, Unites States of America, Nov. 13, 1984. Stephens W D, Jones L E, US Patent 4,482,410, Unites States of America, Nov. 13, 1984. Stephens W D, Jones L E, US Patent 4,482,409, Unites States of America, Nov. 13, 1984. Stephens W D, Jones L E, US Patent 4,482,408, Unites States of America, Nov. 13, 1984. Stephens W D, Rodman B K, US Patent 4,482,407, Unites States of America, Nov. 13, 1984. Stephens W D, Nieder E G, US Patent 4,482,406, Unites States of America, Nov. 13, 1984. Gill R C, Nauflett G W, US Patent 4,457,791, Unites States of America, Jul. 3, 1984. Adolph H G, US Patent 4,453,021, Unites States of America, Jun. 5, 1984. Frankel M B, Witucki E F, US Patent 4,432,817, Unites States of America, Feb. 21, 1984. Frankel M B, Witucki E F, US Patent 4,023,994, Unites States of America, Feb. 21, 1977. Varani F T, US Patent 3,933,542, Bio-Gas of Colorado, Inc., Jan. 20, 1976. Chen Y; Kwon Y; Kim J S, J. Ind. Eng. Chem., 18, 3, 1069-75, 2012.

43

2.2.13 Epoxides

2.2.13 EPOXIDES Three oils are frequently used as raw materials for the manufacture of epoxy plasticizers. The composition of fatty acids of these oils is given in Table 2.2.13.1. Table 2.2.13.1. The average composition of major fatty acid components in oils frequently used in epoxy plasticizers Soybean oil

Linseed oil

Tall oil

Average composition, wt% Palmitic

12

5.3

1.6

Stearic

5

3.5

2.2

Oleic

26

19.5

42.3 34.8

Linoleic

52

14.6

Linolenic

6

56.2

Three acids in Table 2.2.2.13.1 are unsaturated:

COOH

oleic

COOH

linoleic

COOH

linolenic

These unsaturated acids can be epoxidized with the use of hydrogen peroxide or peracetic acid, according to the following reaction scheme: CH2CH CHCH2

O CH2HC CHCH2

H2O2

Typical concentrations of oxirane oxygen are as follows: epoxidized soybean oil 5.5-7% epoxidized linseed oil 9% epoxidized tall oil 4.7% octyl epoxy stearate 3.5%

Property Main acids used in commercial products Molecular weight, daltons NFPA health

Value minimum

maximum

median

oleic, linoleic, linolenic, stearic, tallic 420

1,000

700

0

1

0

NFPA flammability

0

1

0

NFPA reactivity

0

0

0

44

Plasticizer Types

Value

Property

minimum

maximum

median

Highly recommended for these polymers

PVC, PVB, PVA emulsion, chlorinated rubber, CN, EC

Main fields of application

cables, foils, films, sheets, coated fabrics, upholstery, wallcoverings, flooring, tubes, pipes, blood bags, bottles, food wrap, medical, food

Outstanding property

improves resistance to heat and UV, low migration, low toxicity

Freezing point, oC

-22

0

-22

Boiling point, oC

260

decomposes

decomposes

Flash point, oC

215

343

260

Refractive index at 25oC

1.457

1.479

1.465

Specific gravity at 20oC

0.927

1.0454

0.96

Vapor density

25 o

Vapor pressure at 20 C, kPa Oxirane oxygen content, wt%

0.00133

0.0133

3.5

8.8-10

7

Moisture content, wt%

0.03

Solubility in water at 25oC, wt%

0.01

Hildebrand solubility parameter, (cal/cc)0.5

8.8

8.91

8.9

Viscosity at 20oC, mPa s

20

1300

580 8x1013

Volume resistivity, Ohm cm Dielectric constant o

Plasticizer’s loss (24 h at 87 C), wt%

4.17

6.57

5.49

0.3

0.9

0.6

22,500

5,000

TLV-TWA 8 h, OSHA, mg/m3

not determined

NIOSH-IDHL, mg/m3

not determined

LD50, acute - rat oral, mg/kg

2,000

Theoretical oxygen demand, g/g

2.41

2.88

2.55

Tensile strength, 50 phr, MPa

17.3

19.08

18.1

Elongation, 50 phr,%

377

405

390

Shore A hardness, 50 phr

63

78

75

o

Clash-Berg temperature, 50 phr, C

-11

A continuous search for plasticizers that may replace phthalates has created renewed interest in epoxy plasticizers because they are considered non-toxic alternatives.1-7 In the production of toys, epoxidized soybean oil alone and in combination with citrates is considered as a suitable replacement for phthalates.3 Other sources of oils, which may be epoxidized, are also studied, especially palm oil, which is readily available in Asia and Africa.4 Modification of epoxidized soybean oil is also studied to develop grades, which lower concentration of this plasticizer and retain mechanical properties obtainable with DOP.4

2.2.13 Epoxides

45

Epoxidized sunflower oil resulted in the formation of a biobased plasticizer, which increases the thermal stability of PVC and reduces plasticizer migration and extraction. This plasticizer can replace up to 25 wt% of a primary plasticizer such as DOP.1 Concentration of epoxy plasticizer can be further increased to 70 phr by tailoring its chemical structure to the required performance.2 Glycidylethylhexylphthalate was synthesized, and its performance was evaluated.7 The plasticizer was designed to act like normal phthalic plasticizers and in addition as a heat stabilizer.7 All this was accomplished, and, in addition, the resistance to bleeding was improved.7 Biodiesel was used to prepare epoxidized fatty acid isobutyl esters as biobased plasticizers.8 Transesterification of biodiesel with isobutanol catalyzed by tetrabutyl titanate was carried out in a gas-liquid tower reactor with a conversion of close to 100%.8 The epoxidation of isobutyl esters was conducted in the presence of formic acid and hydrogen peroxide.8 The thermal stability and mechanical properties of PVC films with plasticizer were significantly improved compared with DOP.8 Plasticizers based on epoxidized soybean oil were prepared through the integration of epoxidation catalyzed by α-Al2O3·H2O and ring-opening reaction with H2SO4 as a catalyst to develop an efficient biobased plasticizer in a continuous flow mode.9 Oxirane value of 6.1 was achieved.9 Less formic acid was used compared with the current general process, reducing industrial waste.9 Ether bonds in the plasticizers improved tensile strength and tensile strain.9 On the contrary, esters formed by reacting hydroxyl groups with carboxylic acids reduced tensile strength and tensile strain.9 Renewable plasticizer originating from waste cooking oil was developed.10 The ester and double bonds in waste cooking oil were converted to epoxy groups. The developed plasticizer showed better compatibility with PVC.10 The plasticizer significantly improved stability and flexibility of PVC.10 Introduction of epoxy groups to ester and carbon-carbon double bonds in fatty acid permitted the synthesis of plasticizer with higher epoxy value (6.57%).10 Glass transition temperature of PVC film decreased from 62.8 to 15.8°C with 40 phr of plasticizer.10 References 1 2 3 4 5 6 7 8 9 10

Benaniba M T, Massardier-Nageotte M, J. Appl. Polym. Sci., 118, 3499-3508, 2010. Fenollar O, Garcia-Sanoguera D, Sanchez-Nacher L, Lopez J, Balard R, J. Mater. Sci., 45, 4406-13, 2010. Moore S K, Chem. Week, 161, No.45, 1st Dec.1999, p.17. Gan L H; Ooi K S; Goh S H; Gan L M; Leong Y C, Eur. Polym. J., 31, No.8, Aug.1995, p.719-24. Vijayendran B R; Benecke H; Elhard J D; McGinniss V D; Ferris K F, Antec, Dallas, Texas, 6th-10th May, 2001, paper 604. Connelly W, Khan H I, McEwan H, US Patent 3,970,628, Canadian Industries, Ltd., Jul. 20, 1976. Kim S-W, Kim J-G, Choi J-I, Jeon I-R, Seo K-H, J. Appl. Polym. Sci., 96, 1347-56, 2005. Liang X; Wu F; Xie Q; Wu Z; Cai J; Zheng C; Fu J; Nie Y, Chinese J. Chem. Eng., in press, 2021. He W; Zhu G; Gao Y; Wu H; FAng Z; Guo K, Chem. Eng. J., 380, 122532, 2020. Cai D-L; Yue X; Hao B; Ma P-C; J. Cleaner Prod., 274, 122781, 2020.

46

Plasticizer Types

2.2.14 ESTERS OF C10-30 DICARBOXYLIC ACIDS Aliphatic diesters and unsaturated acids are low-temperature plasticizers. Some characteristic data are included in the table below.

Property

Value minimum

maximum

median

Main alcohols used in commercial products aliphatic alcohols having 1-10 carbons (preferred methyl) Dicarboxylic acids

C10-30 unsaturated acids (preferred 9-octadecenedioic acid)

Highly recommended for these polymers

PVC

Outstanding property

low temperature flexibility

Brittle point, oC

52.5

58.5

55.5

47

2.2.15 Ether-ester plasticizers

2.2.15 ETHER-ESTER PLASTICIZERS This is a very broad group containing monomeric and polymeric compounds, which may be classified as plasticizers or, in some cases, as slow evaporating solvents. The following chemical formulas describe the structures of these materials:

H(OCH2CH2)nOH polyethylene glycols H(OCH2CH2CH2)nOH

RC(OCH2CH2)nOCR O O n = 3, R = acetate, caprylate, caproate, 2-ethylhexylate

polypropylene glycols Polyethylene, polypropylene, and triethylene1 glycols are used as monomers (n=1), oligomers (diethylene, dipropylene, n=2; triethylene, tripropylene, n=3; and tetraethylene, tetrapropylene, n=4) and higher molecular weight glycols. The increased number of monomeric units increases almost linearly boiling point (see Figure 2.2.15.1), and the solvent becomes plasticizer when n becomes larger than three (boiling point increases above 250oC).

Property

Value minimum

maximum

median

Main acids used in commercial products

acetic, mixed (average C9), caprylic (octanoic), 2-ethylhexyl, capric (decanoic or decylic)

Glycols

ethylene, propylene, triethylene,1 glycerol,2 pentaerythritol,2 dipentaerythritol2

Molecular weight, daltons NFPA health

150

1,000

286

0

1

1

NFPA flammability

1

1

1

NFPA reactivity

0

0

0

Highly recommended for these polymers

PVC, PVAc, PVB, PU, NR, -NBR, SBR, CR, CTA, EPDM, EVA, acrylics, cellulose derivatives, polyesters

Main fields of application

electronic applications, cable coatings, printing inks, pharmaceuticals, cosmetics, floor tiles, paints, coatings, automotive, glues

Outstanding property

low viscosity, low temperature flexibility, low heating loss,1 excellent adhesion,1 high plasticization efficiency1

Freezing point, oC

-6

-70

-40

o

Boiling point, C

245

344

280

Flash point, oC

145

204

160

Refractive index

1.432

1.460

1.45

Specific gravity

0.941

1.129

1.11

48

Plasticizer Types

Value

Property Vapor density o

Vapor pressure at 100 C, kPa

minimum

maximum

median

2.6

5.1

3.3

1.72x10

-7

0.017

0.01

0.05

0.5

0.2

Solubility in water at 25 C, wt%

0.01

complete

Hildebrand solubility parameter, (cal/cc)0.5

8.51

9.48

12

140

Moisture content, wt% o

o

Viscosity at 20 C, mPa s

8.9 35 3x106

Volume resistivity, Ohm cm Dielectric constant Surface tension at 20oC, mN/m

6.59

37.7

33

45

Heat of combustion, kJ/kg

19,180

24,000

Cubic expansion coefficient, 10-4/oC

8.1x10-4

8.5x10-4

Specific heat at 20oC, kJ/kg K

1.2087

2.8

Thermal conductivity at 25oC, W/m K o

Plasticizer’s loss (24 h at 87 C), wt%

0.2092 7.0

36.9

11.5

3,200

20,400

12,565

TLV-TWA 8 h, OSHA, mg/m3

not determined

NIOSH-IDHL, mg/m3

not determined

LD50, acute - rat oral, mg/kg LD50, acute - rabbit dermal, mg/kg

35

2,000

>17,400

Aquatic toxicity Fathead minnow, 96-h LC50, mg/l

>10,000

73,493

>46,500

Aquatic toxicity, Daphnia magna, 48-h LC50, mg/l

>4,850

35,252

>10,000

Theoretical oxygen demand, g/g

1.29

2.4

2.0

Partition coefficient, log Kow

-2.02

6.73

-1.47

60

74

67

-57

-65

-62

Shore A hardness, 50 phr o

Clash-Berg temperature, 50 phr, C

Figure 2.2.15.2 shows that polypropylene glycol performs in a typical way by reducing the tensile strength of the material. Elongation increases when the amount of plasticizer increases.3 Poly(ethylene glycol) was used to plasticize poly(ʟ-lactic acid) to study the effect of molecular weight and content of PEG on the thermal and mechanical properties of blends.4 Big drop of elongation at break (32%) was observed at 15 wt% of PEG having a molecular weight of 5 kg/mol, while with other molecular weights, elongation was around 300%.4 PEG having a molecular weight of 5 kg/mol formed separated α′-form and α-form crystals while the other blends (molecular weight of PEG 2,000 and 8,000) formed mixed α′-form and α-form crystals.4 The competition between phase separation and PLLA crystallization determined the final structures and physical properties of PLLA/PEG blends.4

49

2.2.15 Ether-ester plasticizers

Figure 2.2.15.1. Boiling temperatures of polyethylene and polypropylene glycols having different number of monomeric units.

Figure 2.2.15.2. Tensile strength of zein films plasticized with different concentrations of polypropylene glycol. [Data from Tillekeratne M; Easteal A J, Polym. Intl., 49, No.1, Jan.2000, p.127-34.]

Glycerol/PEG combination acted as efficient plasticizer/compatibilizer for PVAl/chitosan blends.5 High concentrations of PEG caused a phase separation in PVAl/PEG blends.5 PEG was a better compatibilizer for PVAl/chitosan, but it decreased the crystallinity of the blend. References 1 2 3 4 5

Kim H, Lee K, Lee K L, Chun B, US Patent 7,326,804 B2, LG Chem. Ltd., Feb. 5, 2008. Schaefer G F, US Patent 7,498,372 B2, Ferro Corporation, Mar. 3, 2009. Tillekeratne M; Easteal A J, Polym. Intl., 49, No.1, Jan. 2000, p.127-34. Guo J; Liu X; Liu M; Han M; Liu Y; Ji S, Polymer, 223, 123720, 2021. Sofla M S K; Mortazavi S; Seyfi J, Carbohydrate Polym., 232, 115784, 2020.

50

Plasticizer Types

2.2.16 GLUTARATES Diesters of glutaric acid have the following formula:

ROCCH2CH2CH2COR O O The structure and properties of these plasticizers are similar to two groups of plasticizers: adipates and sebacates. The main advantages of these plasticizers are their lowtemperature properties. There are two reasons for lower interest in glutarates. Low molecular weight, compared with adipates, makes their volatilization and migration more likely. Synthesis of adipic acid is part of polyamide production. Adipic acid of high purity can be obtained as a product of cyclohexane oxidation. Depending on the rate of oxidation, mixtures of acids, such as adipic, glutaric, and succinic, can be obtained, which are then used as a feedstock for the synthesis of monomeric or polymeric plasticizers. Glutaric acid is more frequently used in the synthesis of polymeric (see Section 2.2.25) than monomeric plasticizers. Lower esters (methyl, ethyl) have boiling temperatures below 250oC (the limit for plasticizers). Value

Property

minimum

maximum

median

Main alcohols used in commercial products isodecyl, 2-ethylhexyl, butoxyethoxyethoxyethyl Molecular weight, daltons

384.6

412.6

NFPA health

1

NFPA flammability

1

NFPA reactivity

0

Highly recommended for these polymers

PVC, SBR, PVAc, CAB, CP, CN, VC/VAc, PS, acrylic-based elastomers, epichlorohydrin, hydrogenated rubber, natural rubber, nitrile rubber, polyacrylate

Main fields of application

adhesives, sealants, coatings, cosmetics, automotive shoes & belts, conveyor belts, fuel hose, electrical insulation, gaskets, print rolls, sealants

Outstanding property

low temperature flexibility, excellent volatility resistance in oil

Boiling point, oC

260

o

Flash point, C

280

110

193

Refractive index

1.447

1.451

Specific gravity at 25oC

0.92

1.06

Moisture content, wt%

0.2

Dielectric constant

2.43

Plasticizer’s loss (24 h at 87oC), wt% 3

4.00 28.7

TLV-TWA 8 h, OSHA, mg/m

not determined

NIOSH-IDHL, mg/m3

not determined

51

2.2.16 Glutarates

Value

Property

minimum

Shore A hardness, 50 phr

maximum

median 62

o

Clash-Berg temperature, 50 phr, C

-67

52

Plasticizer Types

2.2.17 HYDROCARBON OILS The following chemical formulas characterize the components of various types of oils: Paraffinic oils C H 3 C H 2 CH 2 CH 2 CH 2 paraffins

C H 3 C H CH 2 CH C H 2 C H 3 C H 2 CH3 CH3 isoparaffins

N aphthenic oils

derivatives of cyclohexane or decalin Arom atic oils

N H derivatives naphthalene, dibenzothiophene, carbazole, etc. S

These three groups of oils have unique properties, which depend on the source of crude and processing method. Table 2.2.17.1 shows the general composition of some crude oils. Table 2.2.17.1. Typical characteristics of some crudes. Source

Paraffins, vol%

Aromatics, vol% Naphthenes, vol%

Sulfur, wt%

Nigeria, light

37

9

54

0.2

Saudi, light

63

19

18

2

Saudi, heavy

60

15

25

2.1

Venezuela, light

52

14

34

1.5

Venezuela, heavy

35

12

53

2.3

North Sea

50

16

34

0.4

In addition to these characteristics, the molecular weight of components of different fractions vary, which affects compositions of heavier fractions, such as oils. ASTM D2226 gives the following classification oils (Table 2.2.17.2). Table 2.2.17.2. Oil classification according to ASTM D2226. Oil type Aromatic

101 102

Asphaltenes, % max

Polar compounds, % max

Saturates, %

0.75 0.5

25 12

20 (max) 20.1-35.1

Naphthenic 103

0.3

6

35.1-65

Paraffinic

0.1

1

65 (min)

104

The amount of asphaltenes determines toxicity (aromatic oils are substantially more toxic than naphthenic and paraffinic). The presence of asphaltenes determines potential

53

2.2.17 Hydrocarbon oils

use in different polymeric materials. In addition to these characteristics, the concentration of impurities such as sulfur and nitrogen are important because they affect oxidation and UV degradation. Very pure paraffinic oils are the most stable compounds. Mineral oils are always mixtures of components, but their name indicates which fractions are prevalent. Value

Property Molecular weight, daltons NFPA health

paraffinic

naphthenic

254-890

290-490

0

0

NFPA flammability

1

1

NFPA reactivity

0

0

aromatic

Highly recommended for these polymers

natural rubber, EPDM; EPM, EP, SBR, PVC

Main fields of application

sealants, coatings, degreasers, road marking paints, medical, wire & cable, rubber membranes, automotive parts, printing inks

Outstanding property

UV and color stability (paraffinic & naphthenic), low volatility, low cost

Freezing point, oC

-7 to -21

-6 to -70

10 to -38

Boiling point, oC

above 250, dec

above 200

above 250

Flash point, oC

204-310

95-248

210-245

Refractive index

1.433-1.4916

1.469-1.508

1.522-1.598

Specific gravity

0.797-0.9

0.860-0.924

1.035-1.13

>1

>1

Vapor density Vapor pressure at 100oC, kPa

0.16

Sulfur content, wt%

0.01-1

Aromatic content, wt%

5000

>5000->8000

3.4

3.4

Theoretical oxygen demand, g/g Partition coefficient, log Kow Shore A hardness, 50 phr

70,000-76,000

>6 76

78

54

Plasticizer Types

2.2.18 HYDROCARBON RESINS Hydrocarbon resins are based on low molecular weight polystyrene, having the following formula

n

The following table outlines a typical range of properties and applications of these plasticizers Value

Property

low

high

medium

300

41,800

1,360

Cloud point DACP (diacetone alcohol), C

204

190

o

Boiling point, C

395

Flash point, oC Refractive index

1.454

1.462

Specific gravity

0.862

0.928

0.88 0.3

o

Vapor pressure at 200 C, kPa

0.13

0.5

Hildebrand solubility parameter, (cal/cc)0.5

8.15

8.39

Viscosity at 20oC, mPa s

8.2

9.4

Dielectric constant

3.21

4.47

3.68

30

34

33

40,146

41,003

o

Surface tension at 20 C, mN/m Heat of combustion, kJ/kg Specific heat at 20oC, kJ/kg K

2.55

Plasticizer’s loss (24 h at 87oC), wt%

11.0

3

TLV-TWA 8 h, OSHA, mg/m

not determined

NIOSH-IDHL, mg/m3

not determined

Theoretical oxygen demand, g/g

2.79

2.98

2.84

60

Plasticizer Types

Property Partition coefficient, log Kow

Value minimum

maximum

9.21

9.49

-51

-67

Shore A hardness, 50 phr Clash-Berg temperature, 50 phr, oC

median 72

61

2.2.22 Pentaerythritol derivatives

2.2.22 PENTAERYTHRITOL DERIVATIVES The following formula characterizes the structure of pentaerythritol plasticizers: O CH2OCR O RCOCH2 C OCOR CH2OCR O

Property Main acids used in commercial products Molecular weight, daltons

Value minimum

maximum

median

benzoic,1,2 butyric, mixture of C5, C7, C9 alkanoic acids,3,4,5 valeric, fatty acids 254

818

553

NFPA health

0

0

1

NFPA flammability

0

1

1

0

0

0

NFPA reactivity Highly recommended for these polymers

PVC, PEI, rubber, alkyd resins, rosin esters, acrylic monomers for UV curing

Main fields of application

adhesives, cable & wire, thin-wall articles, plastisols, wall covering, automotive interiors

Outstanding property

true non-phthalate plasticizer, low temperature flexibility, oxidative stability, reduced smoke density

Boiling point, oC

408

o

Freezing point, C

-60

218

Flash point, oC

248

326

300

Refractive index

1.448

1.572

1.455

Specific gravity

0.97

1.38

1.02 85

Viscosity at 20oC, mPa s Volume resistivity, Ohm cm

35

110

1.0x1012

9.0x1013

1.1

2.1

Dielectric constant

5.29

Plasticizer’s loss (24 h at 87oC), wt% TLV-TWA 8 h, OSHA, mg/m3 NIOSH-IDHL, mg/m

+20

3

not determined not determined

Tensile strength, 50 phr, MPa

19.3

Elongation, 50 phr, %

310

Shore A hardness, 50 phr

72

90

74

Clash-Berg temperature, 50 phr, oC

-10

-34

-28

62

Plasticizer Types

References 1 2 3 4 5

Wideman L G, Maly N A, US Patent 6,512,036 B2, The Goodyear Tire & Rubber Company, Jan. 28, 2003. Lupinski J H, Sitnik T A, Gorczyca T B, Rice S T, Cole H S, US Patent 5,300,812, General Electric Company, Apr. 5, 1994. Schlosberg R H, Hooton J R, Krauskopf L G, Benitez F M, Gerald J D, US Patent 5,430,108, Exxon Chemical Patents Inc., Jul. 4, 1995. Walker J F, US Patent 4,605,694, Hercules, Inc., Aug. 12, 1986. Elbert D L, US Patent 4,085,080, Monsanto, Apr. 18, 1978.

63

2.2.23 Phosphates

2.2.23 PHOSPHATES

O R1O P OR2 OR3 R1, R2, R3 - the same or mixed

Property

Value minimum

maximum

median

Main alcohols used in commercial products isopropanol, butanol, butoxyethanol, 2-ethylhexyl, isodecyl, phenol, cresol, xylenol, 2-chloroethanol Molecular weight, daltons NFPA health

266

434

390

2

1

1

NFPA flammability

1

1

1

NFPA reactivity

1

0

0

Highly recommended for these polymers

PVC, PVAc, PS, PMMA, PP, PF, PA, PE, acrylics, nitrocellulose, cellulosic resins, EP, EC, NBR, SBR, natural rubber, PU, phenolic resins, CA, NC, ABS/ PC, PPO blends (with HIPS and other polymers),

Main fields of application

film, foams, paper coatings, textile coatings, latex paints, lacquers, sheet goods, wire, cable, tubing, sealants, printed circuit boards, photographic base film, synthetic leather, wall coverings, flooring, tarpaulins

Outstanding property

flame retardant, low smoke

o

Freezing point, C

8

-90

Boiling point, oC

289 dec.

420

Flash point, oC

93.5

263

Refractive index

1.441

1.564

Specific gravity at 20oC

0.98

1.30

Vapor density

12.7

14.95

0.0001

0.03066

5.3

11.7

Vapor pressure at 100oC, kPa Phosphorus content, wt% Moisture content, wt% Solubility in water at 25oC, wt% Hildebrand solubility parameter, (cal/cc)0.5 Viscosity at 20oC, mPa s Dielectric constant Surface tension at 20oC, mN/m

170 1.16

8.6

0.1

0.2

5,000

Cyclohexanedicarboxylic acid esters can also be obtained by hydrogenation of dioctyl phthalate over supported Ni catalyst.5 Nine phthalate and six non-phthalate plasticizers were detected in single-use facemasks in the US.6 Plasticizers were found at hundreds to thousands of nanograms per gram of mask.6 Dibutyl sebacate was the major plasticizer found in the facemasks.6 Inhalation exposures from wearing facemasks were in the range of 0.11-3.1 ng/kg-bw/d for phthalates and 3.5-151 ng/kg-bw/d for non-phthalate plasticizers, which were several orders of magnitude lower than those reported for dietary exposures.6 References 1 2 3 4 5 6

Weiss T, Wiedemeier M, Hansel J-G, US Patent Application US 2009/0197998 A1, Lanxess, Aug. 6, 2009. Dakka, J M, Mozeleski E J, Baugh L S, Benitez F M, Faler C A, Godwin A D, Weber J F W W, Smirnova D S, US Patent Application US 2011/0184105 A1, ExxonMobile, Jul. 28, 2011. Eastman 168. MSDS, 2011. Hexamoll DINCH, TDS, BASF, Apr. 2009. Zhao J, Xue M, Huang Y, Shen J, Catalysis Commun., 16, 30-34, 2011. Vimalkumar K; Zhu H; Kannan K, Environ. Int., 158, 106967, 2022.

68

Plasticizer Types

2.2.25 PHTHALATES There are three isomeric forms of phthalic acids and as many phthalates as shown below:

COOR COOR COOR

COOR COOR

COOR phthalates

isophthalates

terephthalates

Out of these three groups, phthalates, which are esters of ortho-phthalic acid, are popular (in fact, they constitute about 80% of all plasticizers used). Terephthalates are a popular alternative to ortho-phthalates

Property

Value minimum

maximum

median

Main alcohols used in commercial products methyl, ethyl, butyl, isobutyl, hexyl, cyclohexyl, heptyl, octyl, 2-ethylhexyl, 1-methylheptyl, butoxycarbonylmethyl, 2-propylheptyl, nonyl, isononyl, decyl, isodecyl, undecyl, tridecyl, benzyl, mixtures of alcohols (e.g., C7 to C9 or C9 to C11, etc.), 2,2,4-trimethyl1,3-pentanediol-1-isobutyrate Molecular weight, daltons NFPA health

194

530

391

0

2

1

NFPA flammability

1

1

1

NFPA reactivity

0

0

0

Highly recommended for these polymers

PVC, CA, CN, PVAc, PU, EC, EPDM, PMMA, PS, acrylics, cellophane, nitrocellulose, natural & synthetic rubber, chlorinated rubber, polysulfide

Main fields of application

automotive, cable & wire, coatings, flooring, sheeting, film, tubing, extruded profiles, sealants, adhesives, bottle caps, gloves, upholstery, nail care, sporting goods, medical, food wrappers, electronics, toys, inks, coated fabrics, carpet backing, shoes, gaskets, foam

Outstanding property

compatibility, cost effectiveness, good dielectric properties, UV & thermal stability, a broad range of properties, good balance of properties

Freezing point, oC

-67

0

Pour point, oC

-54

-42

Boiling point, oC

283

523

384

Flash point, oC

146

254

216

1.481

1.516

1.486

Refractive index

-50

69

2.2.25 Phthalates

Value

Property

minimum

maximum

10

40

Specific gravity at 20 C

0.948

1.191

Vapor density

6.69

13.5

3.0x10-8

0.12

0.02

0.2

Platinum-cobalt color o

Vapor pressure at 100oC, kPa Moisture content, wt% o

Solubility in water at 25 C, wt%

3.0x10

-7

0.5

Hildebrand solubility parameter, (MPa) o

Viscosity at 20 C, mPa s

median 0.977 1.8x10-4 0.1

-3

1.2x10

315.6

398.9

Flash point, oC

176.7

315

270

Refractive index at 25oC

1.458

1.514

1.476

1.03

1.21

Platinum-cobalt color

150

Specific gravity at 25oC Vapor density

1.11

20

25

1.3x10-7

1.3x10-1

445

540

480

2

132

20

Moisture content, wt%

0.05

0.13

Solubility in water at 25oC, wt%

8.0

Tensile strength, 50 phr, MPa

19.4

23.0

Elongation, 50 phr, %

310

360

Shore A hardness, 50 phr

72

86

-8

-25

o

Brittle temperature, 50 phr, C

1.77

80

A book chapter11 contains an extensive discussion of polymeric plasticizers.

References 1 2 3

Brink A E, Turner S R, Keep G T, US Patent 5,965,648, Eastman Chemical Company, Oct. 12, 1999. DBE Intermediates, E. I. du Pont de Nemours, 1995. Biesiada K, Fisch M, Peveler R, US Patent 6,111,004, Velsicol Chemical Corporation, Aug. 29, 2000.

78

4 5 6 7 8 9 10 11

Plasticizer Types

Widder C R, Wozniak D S, US Patent 4,504,652, Sherex Chemical Company, Inc., Mar. 12, 1985. Jacobs E F, US Patent 4,322,505, Phillips Petroleum Company, Mar. 30, 1982. Satterly K P, Livingston F E, US Patent 4,166,056, Witco Chemical Corporation, Aug. 28, 1979. Mark V, Wilson P S, US Patent 4,108,820, General Electric Company, Aug. 22, 1978. Graham P R, US Patent 4,069,517, Monsanto Company, Jan. 24, 1978. Zhou J, Ritter H, Polym. Int., 60, 1158-61, 2011. Koube S, Kiyotatsu I, Arai T, Honda T, US Patent 7,348,380 B2, Adeka Corporation, Mar.25, 2008. Langer E; Bortel K; Waskiewicz S; Lenartowicz-Klik M, Classification of Plasticizers in Plasticizers Derived from Post-Consumer PET. William Andrew, 2020, pp. 13-44.

79

2.2.26 Polymeric plasticizers

2.2.26.2 Polybutenes The following formula characterizes the chemical structure of polybutenes: CH3 CH2 H3C CH2 C CH2 CH H3C y

x

which are copolymers of y parts of isoprene and x parts of isobutylene.1-3 Maleinized polybutadiene has butadiene as a starting material with added maleic anhydride functional groups to its backbone. This type of plasticizer has improved fuel, ozone, oil, heat, creep, and chemical resistance. Its functional groups can react with epoxy, amines, and hydroxyls. The ability to react with these materials allows for the creation of unique sealants and epoxies.

Value

Property

minimum

maximum

median

Main monomers used in commercial prod- isoprene, isobutylene, n-butene, methyl vinylidene ucts Molecular weight, daltons

570

2,500

910

NFPA health

1

1

1

NFPA flammability

1

1

1

0

0

0

NFPA reactivity Highly recommended for these polymers

PE, PP, PS, ester gums, indene resins, natural rubber, SBR, polyterpene

Main fields of application

sealants, sealants for double glazed window systems, adhesives, coatings, films, cables, cosmetics

Outstanding property

low moisture vapor transmission, adhesion

o

Freezing point, C

18

-51

Flash point, oC

170

>270

-9

Refractive index 20oC

1.445

1.508

1.47

Specific gravity at 15.5oC

0.788

0.993

0.83

o

Vapor pressure at 100 C, kPa

0.4

Hildebrand solubility parameter, (cal/cc)0.5

8.05

Kinematic viscosity at 20oC, cSt

3.5

26,000

400 1x1015

Volume resistivity, Ohm cm Dielectric constant

2.16

2.19

2.18

Specific heat at 40oC, kJ/kg K

1.84

2.3

2.05

Thermal conductivity at 40 C, W/m K

0.112

0.118

0.114

Plasticizer’s loss (24 h at 87oC), wt%

0.2

2.0

o

80

Plasticizer Types

Value

Property

minimum 3

TLV-TWA 8 h, OSHA, mg/m NIOSH-IDHL, mg/m

3

maximum

median

not determined not determined

Animal testing, acute toxicity, Rat oral LD50, mg/kg

>34,600

Animal testing, acute toxicity, Rabbit dermal LD50, mg/kg

>34,000

Aquatic toxicity, Rainbow trout, 96-h LC50, mg/l

10,000

Aquatic toxicity, Daphnia magna, 48-h LC50, mg/l

1,000

Theoretical oxygen demand, g/g

3.42

References 1 2 3

Gardner J H, Addcon 99, Paper 8 pp.1-4. Wyffels D, US Patent 5,688,850, BP Chemicals Ltd., Nov. 18, 1997. EPA PF-987. Notice of Filling a Pesticide Petition to Establish a Tolerance for a Certain Pesticide Chemical in or on Food.

81

2.2.26 Polymeric plasticizers

2.26.3 Others Several polymeric plasticizers were patented. They have the following structures:1-3

OR1 CH3(CH2)n+2CH2

O CR

OR2

O

CH3(CH2)nCH2 n=0 to 20

RO3

RO3

OR2

O

n

OR1

R1, R2, R3 are C2 to C10 alkanoyls The plasticizer having structure on the left side1 was used in construction and automotive sealants, which have tack-free surfaces. The resin used was a modified silicone resin.1 The cellulose derivative (on the right-hand-side)2 was developed for plasticization of cellulose esters, poly(lactic acid), and PVC. Oligo(isosorbide adipate), oligo(isosorbide suberate), and isosorbide dihexanoate were synthesized and evaluated as renewable resource alternatives to traditional phthalate plasticizers.3 All of them show potential as PVC plasticizers.3 Polyether plasticizers, such as, for example, Plasticizer IP from Evonik, are used in silane-modified polymers. Polymerized castor oil (Vortite 110) is produced for use in cellulosics and PU foams, providing minimal extractability & volatility, as well as crosslink polymerization at the double bonds and hydroxyl groups.

References 1 2 3

Ikeda Y, Kashiwamura T, Takeuchi K, US Patent 8,017,677 B2, Idemitsu Kosan Co. Ltd., Sep. 13, 2011. Buchanan C M, Buchanan N L, Edgar K J, Lambert J L, US Patent 7,276,546 B2, Eastman Chemical Company, Oct. 2, 2007. Yin B, Hakkarainen M, J. Appl. Polym. Sci., 119, 2400-07, 2011.

82

Plasticizer Types

2.2.27 RICINOLEATES Three structures may be associated with ricinoleates:

OH O CH3(CH2)4CH2CHCH2CH CH(CH2)6CH2 C OR R = methyl, ethyl, butyl OR1 O CH3(CH2)4CH2CHCH2CH CH(CH2)6CH2 C OR R = butyl, R1 = acetyl R2OCH2CHCH2OR2 OR2 R2 = ricinoleic acid rest Glycerol tri-(acetyl ricinoleate) also belongs to this group of plasticizers. These plasticizers are seldom used because double bonds in ricinoleic acid are easily oxidized. The last formula is characteristic of castor oil, which contains 89% of ricinoleic acid. This group of plasticizers has a historical value since ricinoleates were used as early plasticizers in PVC and cellulosics. Their use has now renewed interest because they are produced from renewable resources and, as such, supported by environmental and health and safety monitoring groups.

Property

Value minimum

maximum

median

Main alcohols used in commercial products butanol, ethanol, methanol Molecular weight, daltons NFPA health

322

1060

932

0

1

1

NFPA flammability

1

1

1

NFPA reactivity

0

0

0

Recommended for polymers

PVB, PVC, CAB, NC, EC, rubber, epoxy resins, phenolic resins

Fields of potential application

textile finishing, caulks, coated fabrics, oil-based paints, varnishes, cosmetics, wire jacketing, lacquers

Outstanding property

low temperature flexibility, pigment wetting, electrical properties

Freezing point, oC

-12

-30

Flash point, oC

190

282

279

Refractive index

1.458

1.466

1.462

Specific gravity

0.925

0.967

0.945

83

2.2.27 Ricinoleates

Value

Property

minimum

maximum

o

Solubility in water at 25 C, wt%

median 150 o

Refractive index at 25 C

1.445

Viscosity at 20oC, mPa s

12

LD50, acute - rat oral, mg/kg

>2000

LD50, acute - rabbit dermal, mg/kg

>2000

Partition coefficient, log Kow

7.3

Succinate-based plasticizer mixtures have potential use as nontoxic and sustainable plasticizers and as replacements for commonly used phthalate plasticizers. Common soil bacterium Rhodococcus rhodocrous rapidly breaks down all unsubstituted succinates without the appearance of stable metabolites.2 Structure was important to the biodegradation of these compounds: larger, less water-soluble compounds were slower to disappear.2 There was some evidence that steric hindrance near the ester bonds inhibited the rate of hydrolysis.2

References 1 2

Stuart A; LeCaptain D J; Lee C Y; Mohanty D K, Eur. Polym. J., 49, 9, 2785-91, 2013. Erythropel H C; Dodd P; Leask R L; Maric M; Cooper D G, Chemosphere, 91, 3, 358-65, 2013.

87

2.2.30 Sulfonamides

2.2.30 SULFONAMIDES The following chemical structures are representative of sulfonamide plasticizers: O H3C S NH2 O p-toluenesulfonamide

O S NHCH2CH2CH2CH3 O N-butylbenzenesulfonamide

The compound on the left is solid at room temperature (melting point of 137.5-153oC). The compound on the right is liquid (melting point -30oC). This shows the main direction of the influence of chemical structure on the properties of the plasticizer.

Property Molecular weight, daltons NFPA health

Value minimum

maximum

median

171.2

256.5

213.3

1

2

1

NFPA flammability

1

1

1

NFPA reactivity

0

0

1

Highly recommended for these polymers

PVAc, PA6, PA11, PA12, PC, CA, copolyester, melamine, urea, phenolic, NC

Main fields of application

medical devices, films, fishing lines, automotive, lacquers, nail lacquers, printing inks, adhesives, marine coatings

Outstanding property

improvement of electric conductivity,2 improvement of fatigue resistance,4 reduction of melt flow with no effect on impact strength,5 non-fogging6

Freezing point, oC

-30

137.5-153

63

Boiling point, oC

196

350

340

Flash point, oC

171

216

202

Refractive index at 20oC

1.524

1.540

1.530

Specific gravity

1.146

1.35

Vapor pressure at 140oC, kPa Hildebrand solubility parameter, (cal/cc)0.5 Viscosity at 20oC, mPa s

4.66x10-2 12.68

16.22

150

180

14.39

Dielectric constant

3.51

Surface tension at 20oC, mN/m

44.5

Heat of vaporization at 25oC, J/g

461

564

Specific heat at 20oC, kJ/kg K Plasticizer’s loss (24 h at 87oC), wt%

510 1.92

6.2

33.2

88

Plasticizer Types

Value

Property

minimum 3

TLV-TWA 8 h, OSHA, mg/m NIOSH-IDHL, mg/m

3

maximum

median

not determined not determined

LD50, acute - rat oral, mg/kg

1725

2050

Theoretical oxygen demand, g/g

2.05

2.43

2.25

Partition coefficient, log Kow

0.92

3.65

2.31

86

100

Shore A hardness, 50 phr

Figure 2.2.30.1. Effect of polyaniline content in PVC/ polyaniline blend and plasticizer type on conductivity. [Data from Kulkarni V G, Wessling B, US Patent 5,217,649, 1993.]

Figure 2.2.30.2.Fatigue resistance of polyamide monofilaments vs. sulfonamide plasticizer content. [Data from Wang T-C, US Patent 6,249,928, 2001.]

Sulfonamide plasticizers have unusually high solubility parameters.1 They are not compatible with PVC. PVC plasticized with sulfonamides experiences a high loss of plasticizer (see the above table), but sulfonamides are compatible with many other polymers, which also have high values of solubility parameters, such as the polymers listed in the above table. The electrically conductive blends are made from a mixture of PVC and polyaniline.2 To increase the conductivity of such blends, a plasticizer is typically added to the formulation. Phthalates are compatible with PVC because their solubility parameters are fairly close. Polyaniline has a high solubility parameter, as do sulfonamide plasticizers. Figure 2.2.30.1 shows mixtures of polyaniline and PVC containing different proportions of both polymers.2 Conductivity increases with an increase in the amount of polyaniline, but this increase is faster in the presence of a sulfonamide plasticizer. To increase conductivity, the mobility of polyaniline, which is a conductor, must be increased by the addition of a plasticizer. This is more efficiently done by sulfonamide plasticizer because it is more polar and comparable in polarity with polyaniline.

2.2.30 Sulfonamides

89

Polyamides are another group of highly polar polymers, which are successfully plasticized with sulfonamides. Sulfonamides and polyamides have similar ranges of solubility parameters. Figure 2.2.30.2 shows the effect of the addition of N-butyl benzene sulfonamide on the fatigue resistance of monofilaments.4 Very small additions of sulfonamide plasticizer (0.25 to 2 phr) were used with polycarbonate.5 Melt flow index doubles with the addition of 0.3 to 0.5 phr depending on sulfonamide chemical composition. At the same time, this small addition does not affect impact strength. Sulfonamide plasticizers were successfully applied in the production of non-fogging automotive adhesives based on polyurethane and ethylene-vinyl acetate copolymer.6

References 1 2 3 4 5 6

Coran A Y, US Patent 4,123,411, Monsanto Company, Oct. 31, 1978. Kulkarni V G, Wessling B, US Patent 5,217,649, Americhem Inc., Jun. 8, 1993. Mallavarapu L X, US Patent 4,996,284, Feb. 26, 1991. Wang T-C, US Patent 6,249,928 B1, DuPont, Jun. 26, 2001. Mark V, Wilson P S, US Patent 4,218,357, General Electric Company, Aug. 19, 1980. Anderson L G, Chao T-C, Nakajima M, Desai C U, US Patent 6,194,498 B1, PPG Industries, Feb. 27, 2001.

90

Plasticizer Types

2.2.31 SUPERPLASTICIZERS AND PLASTICIZERS FOR CONCRETE Information on plasticizers and superplasticizers is included in Section 13.5. The following are the structures of some commercially used superplasticizers (chemical compositions of plasticizers are listed in Section 13.5):1-7 R H CH2 C CH2 O C M O n

H CH R C O O (C H 2 C H 2 O ) a C H 3

CH2

S O 3 -N a +

m

R = H or m ethyl; M = m etal acrylic acid-based polycarboxylate OCH2 NH

β-naphthalene sulfonate

NH CH2

N N

n

N NH C H 2 S O 3 -N a +

n

polym elam ine sulfonate

Superplasticizers were discovered in the 1960s. The poly-β-naphthalene sulfonates were the first to be introduced and the most widespread superplasticizers, followed by polymelamine sulfonates.2 Organic polymers having carboxylic group are the most recent additions to the product range, and they form so-called comb-type superplasticizers, which maintain the fluidity of concrete for a longer period of time without causing extensive retardation of cure. Important properties of plasticizers and superplasticizers used in concrete are very different from the requirements of other plasticizers discussed in this book. In many cases, very little information is given by manufacturers about the physical properties of their products. For these reasons, only limited information is given in the table below.

Property Molecular weight, daltons NFPA health

Value minimum

maximum

23,000

28,000

1

2

median 1

NFPA flammability

0

1

1

NFPA reactivity

0

0

0

Main fields of application

concrete industry

Outstanding property

reduction of water required, improved slump resistance

Freezing point, oC

-5

o

Boiling point, C Flash point, oC

0 105

93

91

2.2.31 Superplasticizers and plasticizers for concrete

Property Specific gravity

Value minimum

maximum

0.8

1.26

o

Vapor pressure at 25 C, kPa

median 3.2

Solubility in water at 25oC, wt%

100

Viscosity at 20oC, mPa s

128

TLV-TWA 8 h, OSHA, mg/m3

2.5

18

LD50, acute - rat oral, mg/kg

710

1260

Figure 2.2.31.1 shows that the amount of water required decreases linearly with the increase in the amount of added superplasticizer. Figure 2.2.31.2 shows that the Marsh flow time decreases with the increase in the amount of superplasticizer. The decrease in the Marsh flow time is initially very rapid, but eventually, it levels off. New high-strength superplasticizers are obtained by terpolymerization of unsaturated monomers.6 Superplasticizers give a balance of important properties to cement mixtures, such as increased initial workability in fresh and plastic periods, high mechanical strength without causing any retardation of hydration during the hardening stage, and low air-entraining effect.6 Alkanolamine is used in belite-calcium sulfoaluminate-ferrite cement to increase compressive strength.7 The effect of natural and recycled coarse aggregates in designing 3D printable concrete has been investigated.8 Reduction in superplasticizer (Masterglenium 51) dosage was required to obtain coarse aggregate mixtures with similar yield stress and buildability as in the control mixture.8 Reducing the superplasticizer dosage leads to more agglomeration of the cement particles resulting in a lower wet packing density.8

Figure 2.2.31.1. Reduction of water required as a function of the amount of W-30 superplasticizer. [Data from W-30 Superplasticizer. Specco Data, January 2000.]

Figure 2.2.31.2. Marsh flow time of concrete containing variable amount of superplasticizer.

92

Plasticizer Types

Polycarboxylate and aliphatic superplasticizers are widely used water-reducing agents in concrete.9 The addition of an aliphatic superplasticizer has been developed as a common way to alleviate bleeding and segregation of concrete plasticized by polycarboxylate superplasticizers, while the main reason for this phenomenon is not clear.9 The effect of aliphatic superplasticizer on the rheological performance of cement paste containing polycarboxylate superplasticizer was closely related to the added dosage, which was due to competitive adsorption between aliphatic superplasticizer and polycarboxylate superplasticizer.9

References 1 2 3 4 5 6 7 8 9

Sakai E, Yamada K, Ohta A, J. Advanced Concrete Technol., 1, p. 16-25, 2003. Page M, Spiratos N, The role of superplasticizers in the development of environmentally-friendly concrete, Intern. Symp. Concrete Technol. Sustainable Develop., Vancouver, BC, Canada, April 19-20, 2000. Tantawi S H, Polym.-Plast. Technol. Eng., 36, 6, p. 863-872, 1997. Ou C-C, Jeknavorian A A, Hill C L, US Patent 6,441,054 B1, W R Grace, Aug 27, 2002. Debus G, Knittel V, US Patent 4,137,088, Hoechst AK, Jan. 30, 1979. Clemente P, Ferrari G, Gamba M, Pistolesi C, Squinzi M, Surico F, Badesso L, US Patent Application US 2007/0151486 A1, Jul. 5, 2007. Gartner E, Morin V, US Patent Application US2011/0041736 A1, Lafarge, Feb. 24, 2001. Rahul A V; Mohan M K; De Schutter G; Van Tittelboom K, Cement Concrete Composites, 125, 104311, 2022. Ma B; Qi H; Tan H; Su Y; Li X; Liu X; Li C; Zhang T, Construction Build. Mater., 233, 117181, 2020.

93

2.2.32 Tri- and pyromellitates

2.2.32 TRI- AND PYROMELLITATES The following chemical structures characterize tri- and pyromellitates. The most common alcohols used in commercial products are listed in the table below.1-5

O O O C OR RO C C OR R = alcohol rest RO C C OR RO C C OR O O O O pyromellitate trimellitate

Property

Value minimum

maximum

median

Main alcohols used in commercial products 2-ethylhexyl, hexyl, 2-propenyl, C7 to C9, C8 to C10, isononyl, isodecyl Molecular weight, daltons NFPA health

330

631

546

0

1

1

NFPA flammability

0

1

1

NFPA reactivity

0

0

0

Highly recommended for these polymers

PVC, PS,CN, CA, CAB, EC, PMMA, rubber

Main fields of application

cable & wire, sheet, film, interior automotive, medical tubing, blood bags, furniture, gaskets, profiles, anti-fogging coatings, upholstery, artificial leather, adhesives, tapes

Outstanding property

low volatility and migration, heat and UV resistance, electric insulation

Freezing point, oC

-33

-56

-46

o

Boiling point, C

260

430

414

Flash point, oC

246

271

263

Refractive index

1.483

1.487

1.485

Specific gravity at 20oC

0.969

1.012

0.987

9.3x10-8

6.0x10-3

Vapor density Vapor pressure at 20oC, kPa

18.9

Moisture content, wt%

0.03

0.1

Solubility in water at 25oC, wt%

0.001

0.0001

Hildebrand solubility parameter, (cal/cc)0.5

8.75

9.00

Viscosity at 20oC, mPa s

47.5

Volume resistivity, Ohm cm Dielectric constant

5.0x10 4.4

320 9

3.4x10 6.68

252 13

94

Plasticizer Types

Value

Property o

Surface tension at 20 C, mN/m

minimum

maximum

33.7

34.9

0.3

1.1

Heat of combustion, kJ/kg

median 34,610

Plasticizer’s loss (24 h at 87oC), wt% 3

TLV-TWA 8 h, OSHA, mg/m

not determined

NIOSH-IDHL, mg/m3

not determined

LD50, acute - rat oral, mg/kg

0.5

>3,200

>5,000

1.89

2.66

Partition coefficient, log Kow

5.94

14.54

Tensile strength, 50 phr, MPa

17.12

27.0

21.45

Elongation, 50 phr, %

302

410

365

Shore A hardness, 50 phr

70

93

72

-28

-44

-32

Theoretical oxygen demand, g/g

o

Clash-Berg temperature, 50 phr, C

2.30

Tri-(2-ethylhexyl) trimellitate (TOTM or TEHTM) is a substitute for di-(2-ethylhexyl) phthalate, and it is increasingly used in PVC medical devices.6 Fast and sensitive ultra-high performance liquid chromatography-mass spectroscopy, UHPLC-MS/MS, the method enabled simultaneous quantification of six main TOTM metabolites in urine.6 The method was successfully applied to urine samples of infant patients indicating urinary levels of the TOTM metabolites examined at a very low concentration range.6

References 1 2 3 4 5 6

Adams R C; Petkus S L, Antec 2000.Conference proceedings, Orlando, Fl., 7th-11th May, 2000, paper 647. Mirci L.E.; Terescu-Boran S; Istratuca G, Mater. Plast., 35, No.4, 1998, p.239-46. Mirci L E; Boran S T; Istratuca G, Mater. Plast., 36, No.1, 1999, p.13-20. Mirci L E; Terescu S, Mater. Plast., 35, No.1, 1998, p.29-36. Mirci L E; Terescu S, Mater. Plast., 34, No.2, 1997, p.97-104. Kuhlmann L; Göen T; Eckert E, J. Chromat. B, 1171, 122618, 2021.

95

2.2.32 Tri- and pyromellitates

2.3 METHODS OF SYNTHESIS AND THEIR EFFECT ON PROPERTIES OF PLASTICIZERS The quality of raw materials used for the synthesis of plasticizers has an influence on their properties. Well-defined quality of plasticizer is especially important in applications such as food contact, medical, pharmaceutical, and electrical insulation, which frequently require special grades. Phthalates are obtained from phthalic anhydride. Phthalic anhydride is a product of catalytic oxidation of naphthalene and o-xylene: [O2]

C O [O ] H3C 2 O C O H3C

The o-xylene route is more frequently used today. Phthalic anhydride can also be recovered from waste plastics containing phthalates.1 The invention is based on finding that when the phthalate ester is heated, usually not only ester is vaporized, but it is also at least partially cracked into phthalic acid and alcohol component corresponding to the alkyl group of the ester, and also other hydrocarbons, such as a dehydrated compound from the alcohol, cracked hydrocarbon from the alcohol, and other products are formed. For example, when dioctyl phthalate is heated, octanol and octene may be formed in addition to phthalic acid. Usually, phthalic acid is immediately dehydrated so that phthalic anhydride is produced.1 The system described in the invention allows to recover of not only components of a plasticizer but also hydrogen chloride from PVC and other vital components which can be reused. This creates the possibility of conservation of natural resources by proper use of technology. Various other processes not discussed here lead to the manufacture of acids required for the production of plasticizers. As previously mentioned, the availability and price of acid may predetermine the cost of production and thus the likelihood of plasticizer’s use. Acids are used not only in their pure forms but also as mixtures. For example, DBE intermediates manufactured by DuPont are refined dimethyl esters of adipic, glutaric, and succinic acid are mixtures for plasticizer synthesis.2 There are six mixtures of different compositions that may be used for the production of polyester and diester plasticizers. Diester plasticizers are produced by transesterification according to the following equation:

O O 2ROH + CH3OC(CH2)nCOCH3

catalyst

O O ROC(CH2)nCOR + 2CH3OH

The alcohol part comes from various synthetic sources. One source described in the literature is C9 alcohol mixture that is obtained by the hydroformylation and hydrogenation of the C8 olefin mixture obtained by dimerization of the butene fraction.3-5 Two processes of purification are used by this technology. First, consistent octene fraction obtained by the butene dimerization is purified by distillation. This is followed by rectification of the reaction mixture obtained from alcohol production. After the plasticizer is produced, it is still purified by usual methods used in plasticizer synthesis.4

96

Plasticizer Types

Another invention describes the technology of production of C10 alcohol mixture, which comprises 2-propylheptanol.6,7 “Butene fraction” used as a starting material includes fractions containing butenes as the main component obtained by thermal cracking of hydrocarbon oils, including naphtha. C10 alcohol mixture can be obtained by subjecting the above-mentioned butene fraction to hydroformylation, aldol condensation, and hydrogenation. The details included in the technological process are not discussed here, but an example is given to show the potential composition of alcohols produced. The following isomers are produced in this technological process.

OH OH

OH

OH

OH

OH

The structure at the upper left corner characterizes the main product. The above technology shows that the synthesis of these products gives a mixture of several isomers. Process controls and purification methods allow keeping concentrations within the required limits. Decyl alcohols are also obtained by oligomerization of propylene in the presence of deactivated zeolites, separation of olefins containing nine carbon atoms, formylation of the mixture to aldehyde, and hydrogenation of aldehydes to corresponding alcohols.8-11 A synthesis of mixtures of C6 to C12 hydrocarbons, their separation, hydroformylation, and hydrogenation to produce alcohols having different numbers of carbon atoms is described in the invention.12 Some fractions of these alcohols are used for the production of plasticizers, with the remaining hydrocarbon stock being used as the motor fuel.12 The synthesis of the most popular alcohol used in the production of plasticizers is explained by the following chemical reactions:

CH3CH CH2

CH3CH2CH2CH2 CHCH2OH CH2CH3

catalyst +CO/H2 2H2

(90%) CH3CH2CH2CHO + CH3CHCHO CH3 -H2O CH3CH2CH2CH CCHO CH2CH3

2.2.32 Tri- and pyromellitates

97

Three stages are involved here. First, propylene undergoes hydroformylation in which n-butyraldehyde is produced with a prevailing yield, n-butyraldehyde undergoes self-condensation to produce 2-ethylhexenal, which, after hydrogenation, produces 2ehylhexyl alcohol. This is an important part of synthesis leading to products other than alcohol which are of importance in the chemical industry. Many other processes are used to produce alcohols and their mixtures, and these are described further elsewhere.13

Figure 2.3.1. Schematic diagram of technological line for purification of phthalic anhydride residue for production of phthalates. [Adapted from Jones L O, Daniels P H, Krauskopf L G, Rigopoulos K R, Schlosberg, US Patent 5,534,652, 1996.]

Figure 2.3.1 shows the stage of the production process of phthalates in which phthalic anhydride residue stream is purified for the production of plasticizers. The crude phthalic anhydride from the oxidation section is stored in the tank (246). Tank (246) is heated with steam to maintain the crude phthalic anhydride in a molten state.14 Na2CO3 can be added to the system in order to treat the crude phthalic anhydride. Na2CO3 has a beneficial effect on product quality. A solution of Na2CO3 in water can be prepared in a drum (300) and meter-pumped upstream of the decomposer (258).14 The crude phthalic anhydride from the tank (246) is heated as it passes through the preheater (260) before it enters the decomposer vessel (258). The bottoms from the decomposer vessel (258) are sent to the decomposer vessel (262) via conduit (259). Crude phthalic anhydride from decomposer vessel (262) is then pumped through a cooler (266) to light ends fractionation column (268) (i.e., first distillation tower) via pump (270).14

98

Plasticizer Types

The vapor generated from decomposer vessels (258) and (262) is piped via steamtraced conduit (272) directly to the top portion of the light ends fractionation column or first distillation tower (268).14 The fractionation segment of the finishing section consists of the first (topping or light ends) fractionation column or distillation tower (268) and second (tailing or product) fractionation column or distillation tower (274), with their respective reboilers, i.e., column (268) is connected to reboiler (276) and column (274) is connected to reboiler (280). Fully spared steam jet ejectors (not shown) are also provided on the top of fractionation columns (268) and (274) to provide a column vacuum.14 The reboilers are suppressed-vaporization pump-through types with pumps (286) and (288), respectively, which also pump out the bottom products from the associated fractionation column. Finished product from the second fractionation column (274) is pumped via pump (290) to product tankage, not shown.14 The reaction conditions under which esterification occurs can be varied considerably. The reaction proceeds very slowly at room temperature but quite rapidly at elevated temperatures. About 99% of acids or anhydrides are converted to an ester within a few hours.15 To facilitate esterification reaction, it is desirable that water, which is formed during esterification, is removed as rapidly as possible. Water has a detrimental effect on the rate of conversion. Water is removed by carrying out the reaction in a liquid medium, which forms an azeotrope having a boiling point that is lower than that of either component of the reaction.15 In the commercial production of plasticizer esters, such as phthalates, adipates, and trimellitates, conversions that are greater than 99% are desired. The unreacted portion of the acid or anhydride will react with the base in the final steps of the esterification process, and a water-soluble salt will be formed that eventually ends up in a waste treatment stream. Thus, an increased conversion from 99.0% to 99.95% reduces the waste treatment loads associated with treating unconverted acid or anhydride in plasticizer production by a factor of twenty.15 The typical process of plasticizer production includes the following steps:15 • esterification of an acid or anhydride with excess alcohols and titanium, zirconium, or tin-based catalyst at a temperature and pressure which permits boiling of the mixture in a reactor having a reactor turnover rate in the range between about 2.5 to about 20 • addition of adsorbents such as alumina, silica gel, activated carbon, clay, and/or filter aid to the reaction mixture following esterification before further treatment • addition of water and base to simultaneously neutralize the residual organic acids and hydrolyze the catalyst • removal of the water used in the hydrolysis step by heat and vacuum in a flash step • filtration of solids from the ester mixture containing the bulk of the excess alcohol used in the esterification reaction • removal of excess alcohol by steam stripping or any other distillation method and recycling of the alcohol to the reaction vessel • removing any residual solids from the stripped ester in a final filtration.

2.2.32 Tri- and pyromellitates

99

The rate of esterification reaction depends on the temperature of the reaction mixture. This temperature can be affected by the order of addition of low boiling component (alcohol). If the entire alcohol needed by reaction stoichiometry is added at once, the reaction temperature decreases, and the reaction slows down. If only 5% of the stoichiometric requirement is added, and the concentration of free alcohol is maintained throughout the process of esterification, the reaction temperature increases, as does the reaction rate. The quality of the plasticizer can be increased by the removal of dissolved oxygen from feed alcohol.16 This reduces the formation of colored products, which reduce the quality of the plasticizer or require more rigorous after-treatment. In many methods used to obtain a plasticizer having a high volume resistivity, the treatment is conducted using the adsorbent. A large amount of the adsorbent has to be used, and the method becomes uneconomical.16 A plasticizer ester having an excellent volume resistivity can easily be produced by subjecting an organic acid or its anhydride and alcohol to an esterification reaction, blowing a carbon dioxide gas into the resulting crude ester to convert the residual alkali into a carbonate, recovering excess alcohol, and then conducting fine filtration using a filter aid.16 A process for the titanate catalyzed preparation of plasticizers from polycarboxylic acids and alcohols, which minimizes wastewater and is energy efficient, has been patented.17 The reaction product is treated with aqueous caustic, and it is then filtered using an absorbent medium which removes titanium, caustic, acid salts, and water. The need for water washing is obviated, and the final plasticizer product has excellent properties. This process can be used for the production of phthalates, adipates, and trimellitates.17 The production of benzyl butyl phthalate is complicated by the need to use two different substituents. Studies show that many side reactions may take place changing the proportions of three potential phthalates (dibutyl, dibenzyl, benzyl butyl). The proportion of the three components determines the properties of the plasticizer. The secondary reactions of hydrolysis leading to the formation of unwanted components (dibutyl and dibenzyl) were found to be at a minimum when the pH of the reaction medium was slightly basic.18,19 Mono- and diesters of 2,2,4-trimethyl-1,3-pentanediol and benzoic acid are obtained with a high yield by process of transesterification in the presence of the catalytic amount of base.20 These plasticizers are useful in stain-resistant flooring. Organic titanates are used as catalysts in the synthesis of citric acid esters.21 The production steps for the citric acid esters include low-temperature esterification at 140oC or below, removal of any excess alcohol, and thereafter, alkoxylation. Conventional neutralization and finishing steps are then carried out. The alkoxylation step is carried out at a temperature less than approximately 110oC.21 Methods of synthesis of polymeric plasticizers are discussed in several patents.22-25 Endcapped polyalkylene ethers were prepared for use in polyester resins.22 Different propanediol derivatives are synthesized to form a polyester-type plasticizer.23 In the synthesis of polyester-type plasticizer, it is important to avoid the presence of unreacted acids.23 A second-stage reaction is conducted to remove the odor from the polyester plasticizer.24 First, the plasticizer is synthesized in the presence of a molar excess of alcohol, then hydroxyl groups are reacted with mono- or difunctional isocyanates.24 Polyester plasti-

100

Plasticizer Types

cizer is also produced from a waste stream of non-volatiles recovered as a by-product of oxidation of cyclohexanone. Triaryl phosphates are prepared by phosphorylation of alkyl phenols without a phosphorylation catalyst.26 This simplifies the purification of the plasticizer by eliminating the need to withdraw the purified product as a distillate.26 Mixed alkyl diaryl esters are produced in the presence of a catalytic amount of an alkali metal phenoxide. The plasticizer needs to be separated by distillation.27 Figure 2.3.2 shows the distilFigure 2.3.2. Purification process of triaryl phosphate lation process of purification of triaryl esters. [Adapted from Aal R A, Chen N H C, Chapman phosphates. A crude triaryl phosphate ester J K, US Patent 3,945,891, 1976.] reaction mixture is passed through line (2) into flash distiller (4) operated with a reboiler (3) at a temperature of about 220 to 320oC at about 2 to 10 mm Hg. Catalyst residues and other high boiling impurities are removed as an underflow through line (8) from the distiller (4). The catalyst residues are not passed to the fractional distillation column (10) to reduce catalytic decomposition reactions, which result in the formation of increased amounts of phenols. An overhead stream principally containing unreacted free phenol and the desired triaryl phosphate ester product is removed through line (6) and passed to fractional distillation column (10), entering the column midpoint or above to promote stripping. Fractional distillation of the unreacted free phenol and the desired triaryl phosphate ester product is carried out in the fractional distillation column (10). Fractional distillation is carried out at 250 to 300oC and at a pressure of 4 to 10 mm Hg at column base (12), while column top (14) is at a temperature of 60 to 200oC and at a pressure of 2 to 4 mm Hg. Precise maintenance of temperature and pressure conditions is required to produce a triaryl phosphate ester product having a free phenolic content of 100 ppm or less without the need for an after-treatment process. The product is removed from column (10) as a liquid underflow through line (16). Volatile phenolics pass through column (10) in the vapor state and are removed through the overhead line (18). Removal of the triaryl phosphate ester product as a side-stream rather than as a liquid underflow would result in a product having a substantial amount of phenolic contaminants.28 Phosphate esters are contacted with stannous fatty acid salt to decolorize esters and stabilize them against the color formation.29 Chemical recycling of PET depolymerizes it completely into monomers such as terephthalic acid, dimethyl terephthalate, BEHT, and ethylene glycol or partially depolymerizes it to oligomers or other chemical substances.30 The post-consumer PET was found to be a valuable raw material for the preparation of oligomers that can be used as plasticizers.30 Evonik Performance Materials GmbH and Leibniz-Institute for Catalysis, Rostock achieved a breakthrough in carbonylation chemistry, with the first direct carbonylation of 1,3-butadiene.31 This paves the way for the development of industrially important adipic acid derivatives that are more cost-effective and environmentally friendly.31 The key to the

2.2.32 Tri- and pyromellitates

101

breakthrough was the development of a new, highly selective, efficient, and long-lived palladium catalyst that gave 95% yields of adipic acid derivatives under industrially feasible conditions.31

References 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

Takahashi T, Fukushima T, Tanimoto Y, Muraoka A, US Patent 5,686,055, Mazda Motor Corporation, Nov. 11, 1997. DBE Intermediates, E. I. du Pont de Nemours, 1995. Miyazawa C, Orita S, Tsuboi A, US Patent 5,468,419, Mitsubishi Chemical Corporation, Nov. 21, 1995. Miyazawa C, Orita S, Tsuboi A, US Patent 5,189,105, Mitsubishi Chemical Corporation, Feb. 23, 1993. Akabayashi H, Ohyama E, Shoji S, Uemura K, Ogawa Y, US Patent 4,291,127, Nissan Chemical Miyazawa C, Tsuboi A, US Patent 4,969,953, Mitsubishi Kasei Corporation, Nov. 13, 1990. Barker G E, Forster D, US Patent 4,426,542, Monsanto Company, Jan. 17, 1984. Industries Ltd., Sep. 22, 1981. Bahrmann H, Greb W, Heymanns PP, Lappe P, Mueller T, Szameitat J, Wiebus E, US Patent 5,661,204, Hoechst AK, Aug. 26, 1997. Bahrmann H, Greb W, Heymanns PP, Lappe P, Mueller T, Szameitat J, Wiebus E, US Patent 5,463,147, Hoechst AK, Oct. 31, 1995. Bahrmann H, Greb W, Heymanns PP, Lappe P, Mueller T, Szameitat J, Wiebus E, US Patent 5,462,986, Hoechst AK, Oct. 31, 1995. Bahrmann H, Greb W, Heymanns PP, Lappe P, Mueller T, Szameitat J, Wiebus E, US Patent 5,369,162, Hoechst AK, Nov. 29, 1994. Ward D J, US Patent 4,229,586, UOP Inc., Oct. 21, 1980. Wilson A S, Plasticizers. Principles and Practice. The Institute of Materials, London, 1995. Jones L O, Daniels P H, Krauskopf L G, Konstantinos R R, Schlosberg R H, US Patent 5,534,652, Exxon Chemical Patents Inc., Jul. 9, 1996. Jones L O, Davis G W, Lyford J, Fong S-t, Hemrajani R R, US Patent 5,324,853, Exxon Chemical Patents Inc., Jun. 28, 1994. Ageishi K, Takefumi T, Numoto T, Kawabata T, Urabe E, US Patent 5,880,310, Mitsubishi Gas Chemical Company, Mar. 9, 1999. Sears J K, Darby J R, The Technology of Plasticizers, John Wiley & Sons, New York 1982. Kuznetsova E V; Golland A E, Intl. Polym. Sci. Technol., 24, No.4, 1997, p.T/51-3. Kuznetsova E V; Maksimenko E G; Kirilovich V I, Intl. Polym. Sci. Technol., 24, No.2, 1997, p.T/54-5. DiBella E P, US Patent 5,153,342, Huls America Inc., Oct. 6, 1992. Castrogiovanni A, Sandewicz R W, Amato S W, US Patent 5,066,484, Revlon Consumer Products, Nov. 19, 1991. Brink A E, Turner S R, Keep G T, US Patent 5,965,648, Eastman Chemical Company, Oct. 12, 1999. Biesiada K, Fisch M, Peveler R, US Patent 6,111,004, Velsicol Chemical Corporation, Aug. 29, 2000. Widder C R, Wozniak D S, US Patent 4,504,652, Sherex Chemical Company, Inc., Mar. 12, 1985. Satterly K P, Livingston F E, US Patent 4,166,056, Witco Chemical Corporation, Aug. 28, 1979. Giolito S L, Mirviss S B, US Patent 4,559,184, Stauffer Chemical Company, Dec. 17, 1985. Finley J H, Liao H P, US Patent 4,482,506, FMC Corporation, Nov. 13, 1984. Aal R A, Chen N H C, Chapman J K, US Patent 3,945,891, FMC Corporation, Mar. 23, 1976. Giolito S L, Worster D K, US Patent 3,931,367, Stauffer Chemical Company, Jan. 6, 1976. Langer E; Bortel K; Waskiewicz S; Lenartowicz-Klik M, Synthesis of Plasticizers From Postconsumer PET in Plasticizers Derived from Post-Consumer PET, William Andrew, 2020, pp 173-94. Addit. Polym., 2020, 2, 11, 2020.

102

Plasticizer Types

2.4 REACTIVE PLASTICIZERS AND INTERNAL PLASTICIZATION Some examples of reactive plasticizers,1-8 internal plasticization,9-12 and polymer modification13-16 are given to show other possibilities of plasticization, which are outside the scope of this monograph. Reactive plasticizers give three major advantages in formulated product applications: • addition of low molecular weight material improves processing • the reaction of plasticizer after processing eliminates problems with their migration and volatilization • polymer properties may be enhanced by chemical reactions. In polyimide used for high-temperature applications, plasticizer having very unusual structure was used:3 O C

O O

H3C

CH3

O C

O N

N O

O

O

At an elevated temperature, four-membered ring underwent scission and crosslinked polymer. Unsaturated trimethylopropane trimethylacrylate is a reactive plasticizer of PVC. Its reaction is initiated by the addition of peroxide. Because of crosslinking, PVC material has increased resistance to creep at elevated temperatures.4 4,4’-bis(3-ethynylphenoxy)diphenyl sulfone is fluid at room temperature and acts as a plasticizer during the early stages of processing thermoplastic polysulfone, and then it polymerizes to a rigid resin.5 Monohydroxy-terminated polybutadiene is a reactive or internal plasticizer for polyurethanes.6 Polysiloxanes of the different chemical structures are used as reactive plasticizers in rubber composition for tire tread.2 Photopolymerizable compounds include components, which act as process plasticizers.8 Polyester contains ethylenically unsaturated terminal groups, as does the plasticizer. Groups are reacted after performing an operation to produce a flexible polymer.1 A monomer is included in a coating composition that polymerizes after processing, which gives elastic coating without volatile components, unlike in the majority of similar coatings.9 The reactive plasticizer is dispersed within polymer-forming semi-interpenetrating network.17 After reacting, plasticizer and polymer form desired phase morphology and molecular orientation.17 Further development of this technology is used for the production of crystal clear articles, such as optical lenses.18 Comonomer having hexyl side chain was added to N-vinylpyrrolidone to improve its properties.11 It was found that the inclusion of a comonomer reduced the glass transition temperature of copolymer because it acted as an internal plasticizer. Polyimides are internally plasticized with alkyl 3,5-diaminobenzoate compounds.12 Without internal plasticization, polymer has too high a glass transition temperature that makes processing very difficult. Acrylonitrile-butadiene rubber, NBR, styrene-acrylonitrile rubber, SAN, ethylenevinyl acetate copolymer, EVA, and acrylic copolymers are helpful modifications of poly-

103

2.2.32 Tri- and pyromellitates

vinylchloride that change its processing characteristics and elastomeric properties.13 Blending with these copolymers helps to reduce the requirement for low molecular weight plasticizers. Ethylene-vinyl acetate copolymer plays the role of a high molecular weight plasticizer in the production of vinyl hose. This reduces the amount of DOP used in flexible hose applications. Ethylene copolymer was used to plasticize PVC and reduce gel.15 Phthalate plasticizers can be eliminated from water-based adhesives because of the utilization of vinyl acetate-ethylene copolymer as a high molecular plasticizer/modifier.16 Reactive monocyclic plasticizers with high ring strain energy were synthesized.19 Nonmigratory reactive monocyclic plasticizers bearing tunable click reactivity were covalently bound to energetic polyurethane binders to achieve enhanced properties.19 Dielectric film in which plasticizer does not bleed and improves low-temperature behavior has been invented.20 A dielectric film resides between a pair of electrode layers in a transducer.20 It has a reactive portion that reacts with rubber polymer crosslinking agent and a hydrophobic portion.20 The reactive portion of the reactive plasticizer is selected from the alkoxysilyl group and silanol group.20 Polymer that can be used as reactive plasticizer in a curable composition containing reactive silicon group-containing polymer, and can improve the residual tack of the curable composition under high humidity condition and curability has been invented.21 The polymer has a reactive silicon group only at one terminal.21 The reactive silicon group is either trimethoxysilyl group or (methoxymethyl) dimethoxysilyl group.21 The table below gives ranges of properties for commercial reactive plasticizers

Property

Value minimum

Main acids used in commercial products

maleic, methacrylic

Main alcohol used in commercial products

butyl, hydroquinone

maximum

NFPA health

0

NFPA flammability

0

NFPA reactivity

median

0

Highly recommended for these polymers

acrylics, vinyls, butyl rubber, CSPE, EPDM, epichlorohydrin, hydrogenated nitrile rubber, hydrogenated rubber, NBR, PAC, TPE

Main fields of application

coatings and reactive resins; automotive belts, automotive molded parts, conveyor belts, electrical jacketing, fuel hose, high-temperature applications, hose and tubing, hydraulic hose, industrial hose & tubing, and transmission seals

Outstanding property

permanence, internal plasticizer, based on raw materials recovered from natural oils, hydrophobic methacrylate monomer with low Tg

Refractive index

1.444

1.461

Specific gravity

0.92

0.99

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Plasticizer Types

References 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21

Jacobs E F, US Patent 4,322,505, Phillips Petroleum Company, Mar. 30, 1982. Ishikawa K, Yatsuyanagi F, US Patent 6,140,450, The Yokohama Rubber Co., Ltd., 2000. Cella J A, Shank G K, Serth J A, US Patent 5,688,848, General Electric Company, Nov. 18, 1997. Horng-Jer Tai, Polym. Eng. Sci., 39, No.7, July 1999, p.1320-7. Arnold F E, Loughran G A, Wereta A, US Patent 4,108,926, The United States of America, Aug. 22, 1978. Baack M, Bartkowiak J N, US Patent 4,242,468, Revertex Ltd., Dec. 30, 1980. Werber G P, US Patent 4,302,570, Eschem Inc., Nov. 24, 1981. Faust R J, Lehmann P, US Patent 4,245,030, Hoechst AK, Jan. 13, 1981. Thames S F, Panjanani K G, Fruchey O S, US Patent 6,001,913, The University of Southern Mississippi, Dec. 14, 1999. Modic M J, US Patent 5,969,034, Shell Oil Company, Oct. 19, 1999. White L A; Jonson S; Hoyle C E; Mathias L J, Polymer, 40, No.23, 1999, p.6597-605. Sasthav J R; Harris F W, Polymer, 36, No.26, 1995, p.4911-7. Pena J R; Hidalgo M; Mijangos C, J. Appl. Polym. Sci., 75, No.10, 7th March 2000, p.1303-12. Kline S A, Friedman W J, US Patent 5,939,160, SeaLand Technology Inc., Aug. 17, 1999. Hofmann G H, US Patent 5,464,903, DuPont Nov. 7, 1995. Ulyatt J, Pitture Vernici, 71, No.11, June 1995, p.29-33. Houston M R, Hino T, Soane D S, US Patent 6,746,632 B2, ZMS, LLC, Jun. 8, 2004. Soane D S, Houston M R, Hino T, US Patent 6,570,714 B2, ZMS, LLC, May 27, 2003. Ma M; Kwon Y, Eur. Polym. J., 123, 109414, 2020. Ito T; Takamatsu N; Matsuno R; Takahara A, JP2020155677A, Sumitomo Riko Co Ltd, Sep. 24, 2020. Kubota N; Sato A; JP2021055013A, Kaneka Corp., Apr. 8, 2021.

3

TYPICAL METHODS OF QUALITY CONTROL OF PLASTICIZERS GEORGE WYPYCH ChemTec Laboratories, Inc., Toronto, Canada

Many methods of plasticizer testing are included in the national and international standards. In the present move towards unification of methods of testing, the main analytical procedures can be found in documents in the domain of International Standard Organization and ASTM International. Some unique methods can also be found in documents of other standardization organizations such as Australian, British, Danish, Finish, French, German, Irish, Italian, Luxembourg, and Polish, which have been included in references. Standard methods are listed in references in alphabetical order. Methods of analysis pertinent to the application of plasticizers are summaries given in separate sections below, and these were also organized in alphabetical order.

3.1 ABBREVIATIONS, TERMINOLOGY, AND VOCABULARY Abbreviations of plasticizer names can be found in the standard terminology.34 ISO standard has a separate section for symbols used in the area of plasticizers.131 In addition to the abbreviations for individual plasticizers, Annex A contains a list of symbols for plasticizer components (alcohol part, acid part, and other elements of composition). Abbreviations of plasticizers used in rubber are given in a separate standard.172 The vocabulary of terms used in plastics is available in English and French with a list of Russian equivalents of English terms.126 Vocabulary of terms used in rubber contains terms and definitions in English, French and Russian.134 Terminology for the petroleum industry contains some references and terms descriptions for petrochemical materials used as plasticizers.146,147 Equivalent terms in English, French, German and several other languages are given for paints and varnishes.163-166 List of equivalent terms in English, French, Russian, German, Spanish, and Italian is given for conveyor belts.167 Also comparison is made between English and American terms.

106

Typical Methods of Quality Control of Plasticizers

3.2 ACID NUMBER Twenty-five grams of plasticizer is placed in a 125 ml Erlenmeyer flask, and 50 ml alcohol is added to dissolve the sample.23 If the sample is not completely soluble, 50 ml of equal amounts of alcohol and acetone are used. This sample is titrated with 0.01N NaOH or KOH in the presence of bromothymol blue used as an indicator. ISO standard135 uses a similar method of titration but phenolphthalein is used as an indicator, and 0.1 N NaOH is used as a titrating agent. The results are expressed as acidity, which is a percentage of phthalic acid.

3.3 AGING STUDIES Accelerated heat aging tests of vulcanized and thermoplastic rubber are conducted according to ISO standard.123 In respect to plasticized samples, it is important to test materials in separate ovens to prevent cross-contamination of samples, which may contain, in addition to a plasticizer, other additives that may be transferred, such as accelerators and antioxidants. Phthalate plasticizers are tested for color change after being exposed to 180oC for 2 135 h. Diallyl phthalate is excluded from this test because of the risk of explosive polymerization. After aging, the color of the plasticizer is measured and reported in Hazen units. Aging studies of fabric coated with rubber or plastics should be conducted after at least 16 h from manufacture and not later than 3 months.136 Temperature is selected according to the coating and fabric durability. Duration of test is 1, 3, 7, and 10 days. Aged samples are tested to establish changes in stiffness or determine the effect of aging on decomposition, softening, hardening, discoloration, odor, or embrittlement. Samples of cellulose acetate plasticized with dimethyl phthalate are subjected to laboratory molding at 200oC for 10 min.139 Viscosity change is measured to estimate the effect of molding on the material. Optical density can also be used to determine the effect of molding.139

3.4 ASH Approximately 50 g of plasticizer is slowly burned and then heated at 600oC in the furnace until constant weight is obtained.135 Diallyl phthalate should be used in small portions and with great caution due to the risks of its explosive polymerization.

3.5 BRITTLENESS TEMPERATURE These methods determine the temperature at which plastics and elastomers experience brittle failure under the specified impact conditions.18 Specimens are secured in a specimen holder and immersed in a cooling liquid. The specimens are struck at a specified linear speed and examined. A temperature at which 50% of specimens fail is considered as brittleness temperature. Two types of clamps and striking members are specified as well as three types of samples. When type B fixture and type III specimen are used, ASTM method18 and ISO method130 are technically equivalent. Test specimen type III for a fixture of type B is 20 mm long, 2.5 mm wide, and 1.6 mm thick. Specimens are conditioned before testing (23oC and 50% RH). Silicone oil or

3.6 Brookfield viscosity

107

methanol are used as cooling liquids (silicone oil up to -76oC and methanol up to -90oC). Specimens are impacted by a striking member having a speed of 2,000 mm/s.

3.6 BROOKFIELD VISCOSITY Shear-thinning and thixotropic properties of non-Newtonian materials at the shear rate ranging from 0.1 to 50 s-1 can be measured by the standardized method.46 The standard describes three methods of measurement. Method A is used to measure the apparent viscosity of material by measuring torque with spindle rotating at a constant speed. Apparent viscosity in centipoises (equal to mPa.s) is calculated by multiplication of scale reading of viscometer by a scale factor, which depends on spindle number and rotation speed. If the material is Newtonian, its viscosity does not depend on shear rate, and measurement at one speed is sufficient. Non-Newtonian materials require measurements at different shear rates as described in methods B and C. In method B, viscosity is measured under changing conditions. Speed of rotation is stepwise changed, and torque is recorded after ten revolutions at each speed. Speed is then decreased with the same steps and torque recorded after ten revolutions at each speed. Finally, the liquid is left to stand for an agreed period of time, and torque is measured again at the slowest speed. Viscosity is calculated for each point in the same way as in method A. Shear-thinning index can be calculated by dividing apparent viscosity at the lowest speed by the value of apparent viscosity at the highest speed (typically at 2 and 20 or 5 and 50 rpm). The resultant ratio is an index of shear thinning. All results can be used to make a plot, which is useful in understanding non-Newtonian properties of the material. Thixotropic behavior can be estimated from the ratio of viscosity at the lowest speed after and before the rest period. The higher the ratio, the higher the thixotropy. Method C involves the application of high-speed disperser (2000 rpm) to shear out the structure. This method is also used to estimate shear thinning and thixotropy.

3.7 CHEMICAL RESISTANCE Evaluation of chemical resistance may establish the potential for extraction of plasticizer incorporated in the material as well as an effect of plasticizer on the durability of the tested material.15 The standard contains information on testing chemical resistance with 50 test liquids using two methods: immersion test and test under mechanical stress. The list of test liquids includes white oil, which may be regarded as the only example of plasticizer among test liquids. Samples of known dimensions and weights are immersed in selected liquids for 168 h at room temperature. Containers are stirred every 24 h. Changes in appearance are recorded, and samples can be subjected to mechanical property testing. Tensile properties of immersed samples are most frequently compared with control samples, but another mechanical test may also be used. Special strain jigs are used for testing samples under stress. Conditions of testing of samples with and without strain are the same. At the end of the testing process, the appearance of samples is evaluated, and samples are subjected to mechanical property testing. Comparison is usually made between samples tested with and without stress. The standard method describes determination of weight loss due to extraction by chemicals.27 The method is developed to determine changes in weight of materials

108

Typical Methods of Quality Control of Plasticizers

immersed in common liquids used in households, such as water, soap solutions, cottonseed oil, mineral oil, kerosene, or any of the 50 liquids included in the previously discussed standard.15 Test specimens are squares 50 x 50 mm. Pre-weighed samples are typically immersed for 24 h at 23oC, but other times and temperatures can also be used. To account for potential absorption of liquid in samples, a correction is determined by immersion of sample for a short period of time (5 min) and determination of potential changes in its weight. The effect of immersion of plastics in various liquids can be followed by weight change, changes in physical properties, and absorption of test liquid according to ISO standard.120 A broad choice of liquids includes inorganic liquids, solvents, and a variety of other liquids − one of them being mineral oil. The following temperatures of immersion testing are recommended: 0, 20, 27, 40, 55, 85, 95, 100, 125, and 150oC. The measurement of changes in mass, dimensions, and physical properties is usually done at 23oC. Preferred duration times are 24 h, 1 week, and 16 weeks with various intermediate durations also specified. Test specimens may come directly from the manufacturing process, and as such, may have a variety of shapes or may be obtained for the purpose by molding or machining. At the end of immersion, samples are rinsed with water (e.g., in the case of acids, bases, etc.) or light naphtha (in the case of immersion in organic liquids) and dried at room temperature. The property determination follows, and results are reported. For example, the mass change is reported in either percentage change or change of mass per unit area.

3.8 COLOR Several methods are used to determine the color of plasticizers. The ASTM method of plasticizers testing23 includes an abbreviated procedure very similar to the platinum-cobalt scale method described in detail in a separate standard.25 Color of transparent liquids is also measured by the Gardener color scale.32 Saybolt chromometer originally designed for petroleum products is also used, especially in the case of mineral oils.8 The platinum-cobalt scale was originally developed by Hazen, and it is sometimes referred to as Hazen color or APHA color because it was developed by the American Public Health Association for determination of the color of the water. Both names are not correct because they do not reflect procedures used in the current method.25 Platinum cobalt reference standards are solutions of potassium chloroplatinate and cobalt chloride, which have different concentrations. They can be prepared from these chemical reagents or purchased as ready-made standards. Measurement is made in visible spectrophotometer by comparison of readings for sample and standards and selection of the closest standard. If color lies midway between standards, a darker standard is reported. ISO standard provides a procedure that is based on the original Hazen platinum-cobalt scale.149 The results of testing based on color comparison of test tubes and plasticizer are given in Hazen units. Platinum-cobalt scale is used for estimation of the color of clear liquids.170 This method gives results of measurements in units equivalent to the ASTM method.25 There are some small differences in the method of color comparison and equipment used. Gardner color scale is made of arbitrary glass standards numbered from 1 to 18.32 Similar to the platinum-cobalt scale, sample color is compared with different glass standards, and the closest glass standard is reported.

3.9 Compatibility

109

Saybolt chromometer is used for determination of the color of refined oils, petroleum waxes, and pharmaceutical white oils. The color standard is compared which the sample by changing the height of a column of a sample until the color is lighter than the standard. The recorded depth of oil is given Saybolt color number, which is reported. It was reported32 that +25 on the Saybolt scale is equivalent to 25 in the platinum-cobalt system. The exact equivalence between the two methods is not known. The tinting strength of carbon black is compared after mixing with titanium dioxide and epoxidized soybean oil used as plasticizer.168

3.9 COMPATIBILITY Plasticizer spew is determined by observation of samples bent through an arc of 180o.57 It is observed that plasticizers may become less compatible when the material is under compressive stress. Plasticizers may form spots or film on the material surface. This, in turn, may cause dirt pick up, marring, or tackiness. Plasticizers may react differently. For example, some will spew immediately, some after continuous testing for a prolonged period of time, and in some cases, plasticizer will reside on a material surface only when the material is under compression stress. The plasticizer is then immediately reabsorbed when stress is released. Testing requires a special jig and cigarette paper. Specimens are folded in the jig and stored at 23oC and 50% RH. Each sample is inspected after 4 h, 24 h, and 7 days. During inspection, a sample surface folded in the opposite direction is wiped off with cigarette paper and rated according to a 4 point scale (0 − no mark on paper or material; 1 − very faint oily mark on paper; 2 − saturated small spot but most paper surface not wetted; 3 − totally saturated paper surface). The compatibility of plasticizers is also tested under humid conditions.51 Specimens (25 cm2 of 0.75 mm thick material) are suspended over water in closed containers at either 60 or 80oC. Control for this test can be prepared using the following formulation: generalpurpose PVC − 100 parts, di-(2-ethylhexyl) phthalate − 50 parts, barium cadmium laureate − 1 part. Specimens are inspected in time intervals (60oC specimens once a week for 4 weeks; 80oC specimens after 1, 3, 7, 10, and 14 days). The eventual exudation of the plasticizer is recorded.

3.10 COMPRESSION SET The compression set is measured at room temperature and higher or lower temperatures.128 Cylindrical discs are used as specimens, and these are compressed in special devices using spacers to limit compression. Typical compression times are 24, 72, 168 h. In the case of testing at room and elevated temperature, specimens are allowed to recover at room temperature, and their thickness is measured. This differs from the testing at low temperature where specimens are allowed to recover at test temperature, and their thickness is also measured at test temperature at time intervals to obtain a plot of recovery vs. time.

3.11 CONCRETE ADDITIVES Plasticizing and plasticizing/retarding additives are evaluated in this standard on R&D and specification level.2 On the R&D level, performance requirements of additives are tested.

110

Typical Methods of Quality Control of Plasticizers

These include the time of setting, increase in a slump, compressive strength, flexural strength, shrinkage, and relative durability. Some of these parameters are also checked in time intervals. For lot uniformity and equivalence, infrared analysis is performed to confirm the presence and the type of plasticizing additives. Also, specific gravity, residues of liquid and non-liquid additives after drying are determined. Various other tests may be specified to characterize the performance and curing characteristics of concrete mix.

3.12 ELECTRICAL PROPERTIES Insulation resistance, volume resistance, the surface resistance of electrical insulating, solid materials can be determined by methods described in ASTM standard.9 Special standard was developed to determine permittivity (dielectric constant) and AC loss characteristics of solid electrical insulation.7

3.13 EXTRACTABLE MATTER Matter extractable by diethyl ether from plasticized cellulose acetate has been normalized.145 Two grams of plasticized cellulose acetate is extracted in Soxhlet apparatus for 3 h, the solvent is evaporated, and the residue determined gravimetrically. Extractable di-(2-ethylhexyl) phthalate, DOP, is determined in collapsible plastic containers for human blood and blood components.158 A sample of plastic is extracted with an ethanol-water mixture having density of 0.937 at 37oC for 60 min. The resultant solution is measured for absorbance at 272 nm, and the concentration of plasticizer is determined from the calibration curve.

3.14 FLASH AND FIRE POINT Cleveland open cup is used to determine flash and fire points of liquids with flash points above 79oC and below 400oC, typical for plasticizers.6 Standard gives the methods of determination using manual and automatic Cleveland open cup apparatus. About 70 ml of test liquid is heated first rapidly, then slowly on approaching the expected flash point. Test flame is applied to the surface to ignite vapors. Test flame is a natural or bottled gas flame (full description included in the standard). Test flame is applied first when the temperature is 28oC below expected flash point and then in 2oC intervals. The flash point is the lowest temperature at which vapors are ignited by the test flame. If temperature increase is continued, it is possible to determine the fire point. The fire point is the lowest liquid temperature at which vapors are ignited and sustain burning for a minimum of 5 s.

3.15 FOGGING The fogging characteristics of rubber or plastics coated fabrics for use in the interior of motor vehicles can be determined.171 The procedure excludes materials that produce condensates of low surface tension, which coalescence into a thin transparent film, and materials which contain very large concentrations of volatiles which, cause the droplets to

3.16 Fusion

111

coalescence and form a clear film. Flat-bottomed glass beakers closed on the top with ground glass cover are used for testing. The beaker has 90 mm diameter and 190 mm height. The test piece has a diameter of 80 mm and thickness up to 10 mm. Fogging test is done by placing the specimen in the beaker covering it with a top cover. The beaker containing sample is placed in bath adjusted to 100oC. Filter paper is placed on the top of the cover to prevent its scratching, and the cooling plate is cooled with water having a temperature of 21oC is placed on the filter paper. The test is normally conducted for 180 min after which glass cover is placed in reflectometer for measurement based on which fogging value is calculated from the following equation: R 11 R 12 R 13 R 14 100 - + -------- + -------- + -------- × --------F =  ------ R 01 R 02 R 03 R 04 4

[3.1]

where: R11 - R14 reflectometer readings for the fogged plate,% R01 - R04 reflectometer readings for the unfogged plate,%

3.16 FUSION A torque rheometer is used to determine the fusion characteristics of PVC compounds.53 Components of the formulation are first mixed in a beaker, intensive mixer, or ribbon blender. The rheometer is equipped with a roller head, and the premixed sample is added to a chamber having preselected temperature (typical temperatures used are 140 for flexible compounds, 180 for semi-rigid compounds, and 197oC for rigid compounds). The amount of sample added is selected such that it occupies 65% of the mixer bowl. Mixing is continued until the torque peak is reached. Mixing time and maximum torque are two important results of testing. In addition to fusion, the standard specifies several additional useful procedures such as thermal stability test (time from maximum torque due to fusion to the sudden torque increase caused by the thermal degradation), color-hold stability test (time to equivalent color change), and shear stability test (the data are plotted as torque vs. rpm and sensitivity is determined from the peak value as the highest rpm which does not reduce torque).53

3.17 GAS CHROMATOGRAPHY The gas chromatographic analysis is widely used for the analysis of plasticizers (see the determination of purity of plasticizers in this chapter (Section 3.26) and the first two sections in Chapter 15). A standard practice gives a method of calculation of gas chromatographic response factors.66 The response factor is a constant of proportionality used for conversion of the observed chromatographic response of a particular compound (e.g., peak area or peak height) to its mass or volume percent in composition. The standard66 shows how to obtain these response factors based on an example of the mixture of n-paraffins.

3.18 HARDNESS Eight types of durometers are described in the standard, including A, B, C, D, DO, O, OO, and M.48 The durometers are used for the determination of indention hardness of thermo-

112

Typical Methods of Quality Control of Plasticizers

plastic elastomers, vulcanized rubber, and elastomeric and cellular materials. Specific types of indentors are explained by their technical drawings. Measurements are made at 23oC. Readings below 20 and above 90 are not considered reliable and should not be recorded. Shore A (softer materials) and D (harder materials) durometers are used in the ISO method.129 The indentation hardness is inversely proportional to the penetration, and it depends on the viscoelastic properties of the material. The shape of the indenter, force applied, and duration of application influence results.

3.19 INFRARED ANALYSIS OF PLASTICIZERS PVC additives such as plasticizers, stabilizers, and fillers can be analyzed by this method.44 One gram sample of PVC is extracted in jacketed Soxhlet apparatus with ethyl ether for 6 hours. After extraction, the solvent is evaporated and dry plasticizer is determined by gravimetry. This quantitative method of analysis is not very precise because stabilizers and other additives may be extracted together with the plasticizer. To increase precision of quantitative analysis, the plasticizer sample is diluted with carbon disulfide, its infrared absorption measured, and compared with the absorptions standard of standard samples also prepared in CS2 to cover the range of concentrations from 0.5 to 3 mg/ml. For each suspected (identified) plasticizer, a series of standards have to be made and measured. It is also important to select a suitable wavelength for quantitative analysis. For dioctyl phthalate bands at 1725 and 1121 cm-1 are usually used. For tricresyl phosphate band at 1191 cm-1 is used. Similar to the gravimetric method, results are subject to various interferences when a mixture of plasticizers or a mixture of plasticizers with other additives is used. Identification of plasticizer is based on a comparison of the full spectrum of the sample in the range from 4000 to 650 cm-1 with a set of standard spectra or computerized database. This is also the subject of interferences by mixture components. A sample used for identification is usually used for quantitative analysis as discussed above, or a special sample is extracted for the purpose of direct quantitative analysis.

3.20 KINEMATIC VISCOSITY The viscosity of Newtonian liquids can be measured by calibrated glass capillary viscometer. Kinematic (the resistance to the flow of a fluid under gravity) and dynamic (the ratio between the applied shear stress and the rate of shear of a liquid) viscosities can be calculated from the measured time of flow using the following equations: ν = Ct η = νρ10 where:

ν C t η r

[3.2] –3

kinematic viscosity, mm2 s-1 calibration constant of viscometer supplied with instrument, (mm2 s-1) s-1 measured flow time, s dynamic viscosity, mPa.s density, kg m-3

[3.3]

3.21 Marking (classification)

113

A variety of manual and automatic instruments exists. Also, a number of calibration liquids can be used. The standard suggests a large selection of both viscometers and calibration liquids. Measurement is simple since it requires measuring the time of flow of standard volume of liquid. The largest source of error is due to the dirty viscometer or temperature changes during testing.

3.21 MARKING (CLASSIFICATION) A standardized marking system has been developed to mark the composition of plastics according to ASTM standard.41 The marking system allows indicating the amounts of additives present in the composition. No special symbol was allocated to plasticizers in ASTM standard.41 Plasticizer concentration can be specified in styrenic thermoplastic elastomers, but, also, no special symbol was allocated.65 In highly crosslinked thermoplastic vulcanizate “other” category was reserved to be used for any additional category, and this can be used to give a concentration of plasticizer if needed.71 Standard classification62 allows introducing comprehensive marking system which includes composition and various properties of the product. This includes also volatile loss given numerical value after symbol “R.” The standard for polyamides143 makes a provision for inclusion of plasticizer in the designation. This is done by adding the letter P after the symbol is separated from it by a hyphen (e.g., Pa 610-P). Marking of plastics shall include information on plasticizers.182 Symbol P for plasticizer should follow the abbreviated polymer name and hyphen. This can be followed by the name of plasticizer in parentheses (e.g., >PVC-P(DBP)3× transport reductions of oxygen and carbon dioxide as compared with PET film, which does not Antiplasticization contain caffeine.56 affects diffusion more significantly than penetrant sorption.56 Antiplasticization occurs via hole filling and chain motion restriction mechanisms.56 Figure 7.4.6 Figure 7.4.6. Effect of caffeine on oxygen diffusion in shows a schematic diagram of the proposed PET. [Adapted, by permission, from Burgess, S K; Lee, mechanism.56 This study only investigates J S; Mubarak, C R; Kriegel, R M; Koros, W J, Polymer, the effect of caffeine antiplasticization in 65, 34-44, 2015.] amorphous PET.56 The presence of both crystallinity and orientation may help mitigate the Tg reductions observed in this work.56 In transdermal patches, unpredictable alteration of the mechanical behavior of the pressure-sensitive adhesive can occur if a drug (ibuprofen) is added.57 The shear adhesion of the PSA was decreased at all investigated ibuprofen concentrations.57 The main reason for the decrease in shear adhesion was a shift of the Tg to lower temperatures, while antiplasticization had only a marginal effect.57

7.4 Antiplasticization

199

Cassava starch was plasticized with water in all cassava starch-complexing fatty acid blends.58 At low moisture content (below 11 wt%), complexing fatty acids provoked the antiplasticization of transformed cassava starch.58 Amylose-lipid complex formation explained the antiplasticizing effect of complexing fatty acids.58 The Tg of the neat chitosan film was observed at 125°C, which was consistent with that reported by other researchers.61 For xylitol or maltitol plasticized films, they displayed a similar Tg of about 127 °C, whereas glycerol plasticized chitosan film showed a higher Tg of about 165°C.61 The higher Tg may have resulted from the antiplasticization effect of glycerol.61 The above data imply that antiplasticization is manifested by slowing down the motion of plasticizers below some critical amount (here 6 vol%). In a separate study,1 it was measured that there were two different mobilities of plasticizer: one (slower) for plasticizer molecules surrounded by polymeric chains and the other (faster) for plasticizer molecules surrounded by other molecules of the same kind (see more in Section 7.2).

References 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32

Bergquist P; Zhu Y; Jones A A; Inglefield P T, Macromolecules, 32, No.23, 16th Nov. 1999, p.7925-31. Guohua Chen; Kangde Yao; Jingtai Zhao, J. Appl. Polym. Sci., 73, No.3, 18th July 1999, p.425-30. Kazarian S G; Brantley N H; Eckert C A, Antec '98. Volume II. Conf. proc., SPE, Atlanta, Ga., 26th-30th April 1998, p.1415-7. Rizos A K; Johnsen R M; Brown W; Ngai K L, Macromolecules, 28, No.16, 31st July 1995, p.5450-7. Gibbons W S; Kusy R P, Polymer, 39, No.14, 1998, p.3167-78. Gibbons W S; Kusy R P, Polymer, 39, No.26, 1998, p.6755-65. Kovalenko V I; Kuzmin A A; Mazitova V A; Maklakova L N, Polym. Sci. Ser. B, 37, Nos.5-6, May-June 1995, p.207-10. Gramann P J; del Pilar Noriega; Rios A C; Osswald T A, Antec 97. Volume III. Conf. proc., SPE, Toronto, 27th April-2nd May 1997, p.3713-7. US Patent 5,527,847. Dean P R, Rubber World, 213, No.5, Feb.1996, p.30-3. Morgan H; Foot P J S; Brooks N W, J. Mater. Sci., 36, No.22, 15th Nov. 2001, p.5369-77. Prut E V; Yerina N A, Antec 2000.Conference proceedings, Orlando, Fl., 7th-11th May, 2000, paper 643. Seung-Hwan Lee; Shiraishi N, J. Appl. Polym. Sci., 81, No.1, 5th July 2001, p.243-50. Landry C J T; Lum K K; O'Reilly J M, Polymer, 42, No.13, 2001, p.5781-92. Audic J-L; Poncin-Epaillard F; Reyx D; Brosse J-C, J. Appl. Polym. Sci., 79, No.8, 22nd Feb.2001, p.1384-93. Ruckert D; Cazaux F; Coqueret X, J. Appl. Polym. Sci., 73, No.3, 18th July 1999, p.409-17. Parmentier J, Pitture Vernici, 74, No.18, Nov.1998, p.24/31. Papaspyrides C D; Tingas S G, Food Additives Contaminants, 15, No.6, 1st Aug.1998, p.681-9. Zaikov G E; Gumargalieva K Z; Semenov S A; Zhdanova O A, Intl. Polym. Sci. Technol., 25, No.2, 1998, p.T/72-4. Messadi D; Djilani S E, Eur. Polym. J., 34, Nos.5/6, May/June 1998, p.815-8. Hammarling L; Gustavson H; Svensson K; Karlsson S; Oskarsson A, Food Additives Contaminants, 15, No.2, 1998, p.203-8. Lakshmi S; Jayakrishnan A, Polymer, 39, No.1, 1998, p.151-7. Vladkova T G; Goelander C G; Christoskova S C; Joensson E S, Polym. Adv. Technol., 8, No.6, June 1997, p.347-50. Lambert C; Larroque M; Lebrun J C; Gerard J F, Food Additives Contaminants, 14, No.2, 1st Feb.1997, p.199-208. Giroud J P, Geosynthetics Intl., 2, No.6, 1995, p.1099-113. Hamdani M; Feigenbaum A, Food Additives Contaminants, 13, No.6, Aug/Sept.1996, p.717-30. Sreenivasan K, J. Appl. Polym. Sci., 59, No.13, 28th March 1996, p.2089-93. US Patent 5,428,087. Kwan K S; Ward T C, Pitture Vernici, 71, No.13, Aug.1995, p.26-7. Jayakrishnan A; Sunny M C; Rajan M N, J. Appl. Polym. Sci., 56, No.10, 6th June 1995, p.1187-95. Papakonstantinou V; Papaspyrides C D, J. Vinyl Technol., 16, No.4, Dec.1994, p.192-6. US Patent 6,011,108.

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Plasticizer Motion and Diffusion

Papaspyrides C D; Tingas S G, J. Appl. Polym. Sci., 79, No.10, 7th March 2001, p.1780-6. Thomas N L; Harvey R J, Prog. Rubber Plast. Technol., 17, No.1, 2001, p.1-12. Gamage P K, Farid A S, J. Appl. Polym. Sci., 121, 823-38, 2011. Csefalvayova L, Strlic M, Karjalainen H, Anal. Chem., 83, 5101-6, 2011. Guart A, Bon-Blay F, Borrell A, Lacorte S, Food Addit. Contaminants, 28, 5, 676-85, 2011. Li X, Xiao Y, Wang B, Lu Y, Tang Y, Wang C, Adv. Mater. Res., 160-162, 401-6, 2011. Amber-Mueller J P, Hauri U, Schlegel U, Hohl C, Brueschweiler B J, J. Verbe. Lebensm., 5, 429-42, 2010. Navarro R, Perrino M P, Tardajos M G, Reinecke H, Macromolecules, 43, 2377-81, 2010. Yang B, Bai Y, Cao Y, J. Appl. Polym. Sci., 115, 2178-82, 2010. Narayana Reddy N, Mohan Y M, Varaprasad K, Ravindra S, Vimala K, Raju K M, J. Appl. Polym. Sci., 115, 1589-97, 2010. Atek D, Belhaneche-Bensemra N, Turki M, Int. J. Polym. Mater., 59, 342-52, 2010. Gourlay T, Shedden L, Horne D, Stefanou D M, Perfusion, 25, 1, 31-9, 2010. Hoeglund A, Hakkarainen M, Albertsson A-C, Biomacromolecules, 11, 277-83, 2010. Lindstroem A, Hakkarainen M, J. Appl. Polym. Sci., 104, 2458-67, 2007. Wang Q, Storm B K, Macromol. Symp., 225, 191-203, 2005. Marcilla A, Garcia S, Garcia-Quesada J C, Polym. Testing, 27, 211-33, 2008. Goulas A E, Zygoura P, Karatapanis A, Georgantelis D, Kontominas M G, Food Chem. Toxicol., 45, 585-91, 2007. Marcilla A, Garcia S, Garcia-Quesada J C, J. Anal. Appl. Pyrolysis, 71, 457-63, 2004. Thinius K, Chemie, Physik und Technologie der Weichmacher. Leipzig, 1963. Lykov A V, Transfer effects in capillary-porous bodies, Moscow, Gostechizdat, 1954. Malkin A Ya, Chalych A E, Diffusion and viscosity of polymers. Evaluation methods. Moscow, Khimiya, 1979. Anderson S L; Grulke E A; DeLassus P T; Smith P B; Kocher C W; Landes B G, Macromolecules, 28, No.8, 10th April 1995, p.2944-54. Challa S R; Wang S Q; Koenig J L, Appl. Spectroscopy, 49, No.3, March 1995, p.267-72. Burgess, S K; Lee, J S; Mubarak, C R; Kriegel, R M; Koros, W J, Polymer, 65, 34-44, 2015. Michaelis, M; Brummer, R; Leopold, C S, Eur. J. Pharm. Biopharm., 86, 2, 234-43, 2014. Luk, E; Sandoval, A J; Cova, A; Mueller, A J, Carbohydrate Polym., 98, 1, 659-64, 2013. Langer E; Bortel K; Waskiewicz S; Lenartowicz-Klik M, Essential Quality Parameters of Plasticizers in Plasticizers Derived from Post-Consumer PET, William Andrew, 2020, pp. 45-100. Ubbink J, Current Opinion in Food Sci., 21, 72-8, 2018. Ma X; Qiao C; Wang X; Yao J; Xu J, Int J. Biol. Macromol., 135, 240-5, 2019.

7.5 Effect of diffusion and mobility of plasticizers on their suitability

201

7.5 EFFECT OF DIFFUSION AND MOBILITY OF PLASTICIZERS ON THEIR SUITABILITY This is a short summary of the implications of theoretical findings in the area of diffusion and mobility of plasticizers on their performance in plasticized materials. The complex nature of requirements does not give a simple answer, which may determine plasticizer selection but rather a list of opportunities and warnings as well as the underlining need for making compromises. The fundamental reason behind plasticizer properties can simply be summarized by classical data from Hansen’s publication.1 Figure 7.5.1 shows that plasticizing efficiency decreases with molecular volume (or weight) of plasticizer increasing. The plasticizing efficiency plotted here is for liquids of various volatility (solvents and plasticizers). If the plasticizing efficiency had been plotted against the boiling temperature of these liquids, it would have been discovered that the most efficient in plasticization are solvents because of their low molecular weight. Increasing molar volume to above 200 cm3 mol-1, boiling Figure 7.5.1. Plasticizing efficiency (Tg/volume fractemperatures increase above 250oC, which tion) vs. molar volume. Data from Hansen C H, Off. is regarded as the borderline between plastiDig. J. Paint Technol. Eng., 37, 57-77, 1965.] cizers and solvents. This example shows the most important compromise, which must always be made, is between plasticizing efficiency and plasticizer volatility. Below are several general rules related to plasticizer diffusion and mobility: • plasticizer uptake rate increases with plasticizer molecular weight decrease • glass transition of the plasticized composition decreases when the molecular weight of plasticizer increases • the diffusion rate of elongated molecules of plasticizers is faster than that of compact molecules • diffusion rate increases with temperature increase • polymer-plasticizer interaction affects both diffusion and migration rates • there is a difference in the behavior of “bound” and “free” plasticizer (e.g., mobility or effect on properties) • plasticizer concentration at the surface is usually lower than in bulk • the difference between plasticizer concentration in bulk and at the surface decreases with temperature increase • an increase in the total plasticizer concentration in material causes an increase in its migration and diffusion rates.

References 1

Hansen C H, Off. Dig. J. Paint Technol. Eng., 37, 57-77, 1965.

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Plasticizer Motion and Diffusion

8

EFFECT OF PLASTICIZERS ON OTHER COMPONENTS OF FORMULATION George Wypych ChemTec Laboratories, Inc., Toronto, Canada

8.1 PLASTICIZER CONSUMPTION BY FILLERS Several factors influence the consumption of plasticizers by fillers.1-3 These include: • particle size distribution − a combination of small and large particle sizes leaves less free space between filler particles, and thus, less plasticizer is required to fill this space • particle shape − the closer the shape of particle to the spherical shape the better packing, and less free space between particles to fill. The particle shape of fillers can be conveniently measured by the aspect ratio, which for the majority of fillers is within the range of 1 to 3, but may be much larger for flaky fillers (10 to 100) and largest for fibers (above 100) • particle size distribution and particle shape both contribute to the packing volume of filler which is a fraction of the total volume occupied by fillers. This may vary widely depending on filler design. For ordinary mineral fillers, the maximum packing volume is usually within the range of 0.3 to 0.5. It is usually much lower for flakes and fumed silica (below 0.1) but can be above 0.5 for glass beads and other fillers produced with well-controlled geometry • surface roughness and pore volume and size contribute to plasticizer uptake by filler. Small pores (e.g., molecular sieves) do not permit plasticizer to enter them because plasticizer molecule is too bulky to fit small diameters of pores. On the other end of the spectrum, diatomaceous earth is made of pores and voids, which occupy 85% of its volume • many physical and chemical interactions reduce or increase plasticizer uptake. These include interactions between filler particles, formation of agglomerates and aggregates, flocculation, zeta potential, acid/base interactions, surface energy, chemical interactions between filler and plasticizer. The above aspects of fillers performance are discussed in detail in the specialized monograph on fillers.1 The most common method of estimation of plasticizer uptake by a filler is by measurement of oil absorption.4

204

Effect of Plasticizers on Other Components of Formulation

Barium and strontium sulfates have the lowest oil absorption (below 10 g per 100 filler). Many common fillers and pigments have oil absorptions between 10 and 20 g per 100 g filler. Some highly absorbing fillers may take up to 10 times the weight of various liquids, including plasticizers. In addition to the amount of plasticizer consumed by filler, it is important to analyze the potential for interaction between filler and polymer. Simple consumption of plasticizer by filler affects only rheological properties of the material, but chemical interaction may affect numerous other properties relevant for plasticizer application in a specific formulation. Figure 8.1.1 shows that plasticizer plays an essential role in the exfoliation of clay particles.5 TEM and AFM analysis of the nanocomposites indicate that there is an optimum concentration of DOP for the process.5 If plasticizer is used at high concentrations, the ability to transfer forces to the clay particles through the polymer matrix decreases due to a substantial decrease in viscosity.5

Figure 8.1.1. Model system showing dispersion of fillers in plasticized PVC matrix during melt compounding. [Adapted, by permission, from Yalcin B, Cakmak M, Polymer, 45, 6623-38, 2004.]

In studies of exfoliation in the starch-clay system, it was found that plasticizer amount and type both influence the process.6 When the glycerol content decreased from 20% to 5%, the degree of clay exfoliation increased.6 Formamide plasticized starch gave even better results at 15 wt% concentration of plasticizer than glycerol at 5 wt%.6 Some plasticizers (e.g., sorbitol) were not suitable for montmorillonite exfoliation.7 Phase separation was observed in their presence.7 In PVC coating plastisols, fillers should not absorb plasticizers nor interfere with the pseudoplastic behavior of the paste that is determined by the resin properties and by choice of plasticizers.1

205

The manufacturers of some fillers offer a wetted grade of antimony oxide to reduce dust.1 This is made by the addition of 3-4% plasticizer (DIDP, DOP, DINP, or ethylene glycol).1 Concentrates are produced by manufacturers and specialized companies.1

References 1 2 3 4 5 6 7

Wypych G, Handbook of Fillers, 5th Edition, ChemTec Publishing, Toronto, Canada, 2021. Montgomery T T, Antec 2001.Conference proceedings, Dallas, Texas, 6th-10th May, 2001, paper 655. Chazeau L; Paillet; Cavaille J Y, J. Polym. Sci.: Polym. Phys. Ed., 37, No.16, 15th Aug.1999, p.2151-64. ISO 787. General methods of test for pigments and extenders. Yalcin B, Cakmak M, Polymer, 45, 6623-38, 2004. Tang X, Alavi S, Herald T J, Carbohydrate Polym., 74, 552-58, 2008. Chivrac F, Pollet E, Dole P, Averous L, Carbohydrate Polym., 79, 941-47, 2010.

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Effect of Plasticizers on Other Components of Formulation

8.2 SOLUBILITY OF ADDITIVES IN PLASTICIZERS There are many reasons to be concerned about the solubility of additives in plasticizers, including:1-4 • some additives have to be present on the material surface or at interphase with another material to act. Several groups of additives, including adhesion promoters, antistatics, biocides, curatives, lubricants, UV stabilizers, act when delivered to the material surface • some additives need to be quickly replenished to act efficiently. These include antioxidants and thermal stabilizers. They are used in a chemical reaction, and their concentration must be quickly equilibrated to protect the material from further damage • plasticizers are used to prepare concentrates of additives. These concentrates should contain high concentrations of additives, frequently dissolved for better incorporation. Concentrates are prepared to reduce the toxicity of additives (e.g., commonly used biocide contains arsenic in its structure (10,10’-oxybisphenoxyarsine) and is sold as 2-3% solution in various plasticizers (e.g., di-(heptyl, nonyl, undecyl) phthalate).2 Here, solubility assists in obtaining highly concentrated solutions, but also plasticizer type must be compatible with the system in which concentrate is used • type of plasticizer may also help in achieving certain application goals. For example, toxic biocide is dissolved in polymeric plasticizer, which is solid at room temperature, and solution is micronized to obtain product easy to disperse but this method reduces toxic effect • application of additives in the plasticized system must also include negative aspects of mutual diffusion, which causes their faster migration to the surface (and potential loss) than without plasticizers. These aspects were discussed in Chapter 7, and some additional aspects are discussed in Section 8.3. The above list shows that mutual solubility of additives and plasticizers is important for good performance of additives but there is very little support in literature. This is partially due to the fact that solubility has to be studied for a particular pair of materials and there are too many combinations in use. The effect of additive solubility is well illustrated by the antioxidation of polyvinylbutyral in safety glass application. The adhesive layer contains substantial concenFigure 8.2.1. Solubility of ethylene glycol of 3,5-di-tert- trations of antioxidant, which do not disbutyl-4-hydroxyphenyl propionic acid in dihexyl adisolve in polymer and forms separate phase pate at 60oC. [Data from Mar'in A P; Tatarenko L A; causing turbidity, which in this application Shlyapnikov Y A, Polym. Deg. Stab., 62, No.3, 1998, is unacceptable. Figure 8.2.1 shows that the p.507-11.]

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addition of dihexyl adipate plasticizer increases the solubility of antioxidants.1 By studying solubility at various temperatures, it is possible to predict the suitable concentrations of antioxidants and plasticizers in the formulation, which permits to use the product in the expected temperature range of product performance.

References 1 2 3 4

Mar'in A P; Tatarenko L A; Shlyapnikov Y A, Polym. Deg. Stab., 62, No.3, 1998, p.507-11. Plast. World, 53, No.5, May 1995, p.85. van Hoboken N J, van de Worp R, Verploegh M C, US Patent 5,358,979, Akzo Nobel, Oct. 24, 1994. Wypych G, Handbook of Material Weathering, 6th Ed., ChemTec Publishing, Toronto, Canada, 2018.

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Effect of Plasticizers on Other Components of Formulation

8.3 ADDITIVE MOLECULAR MOBILITY AND TRANSPORT IN THE PRESENCE OF PLASTICIZERS Section 7.3 discussed the migration of plasticizers with some references to the simultaneous migration of several components. The principles of additives migration are the same. Specific research on additive migration is reported here based on scarce available data.1-7 The migration of additives of different types was studied in polyolefins. Figure 8.3.1 shows that the minimum hole size required for the displacement of additives, Bd, correlates well with a specific volume of additives, v0,AO, extrapolated from measured values at 0K. Figure 8.3.2 shows that diffusion coefficient, D, increases with the reciprocal fraction of free volume of the non-crystalline phase of polymer, 1/fa, increase. The linear relationship was obtained from studies on several polymers (EVA, LDPE, LLDPE), which indicates that additive mobility is independent of the type of ethylene polymer. These two graphs and some other data included in the original publication strongly suggest that the mobility of additives above the glass transition temperature of the polymer is well explained by the free volume theory (see Chapter 5) and depends on the specific volume of additive (or molecular size).7 Similar to the migration of plasticizers (see Section 7.3), the shape of the molecule plays a role (linear molecules migrate faster than spherical molecules). Fungicide loss from plasticized PVC depends on plasticizer concentration (Figure 8.3.3). It is surprising that the maximum migration rate was found. It is easy to explain why the migration of fungicide increases with the concentration of plasticizer increase because chain mobility and additive mobility increase with the plasticizer concentration increase. Silanes are added to some formulations to increase adhesion to substrates in contact. Silane can only act when it is available close to the interface with the substrate. This

Figure 8.3.1. The minimum hole size required for additive displacement vs. specific volume of additive. 1 - 1,1,3-tris(2’-methyl-4’hydroxy-5’tert-butylphenyl)-butane, 2 - Irganox 1010, 3 - BHT, 4 - Irganox 1076. [Adapted, by permission, from Foldes E, Polym. Bull., 34, No.1, Jan.1995, p.93-9.]

Figure 8.3.2. Diffusion coefficient of Topanol CA vs. reciprocal fraction of free volume. [Data from Foldes E, Polym. Bull., 34, No.1, Jan.1995, p.93-9.]

8.3 Additive molecular mobility and transport in the presence of plasticizers

Figure 8.3.3. Loss of N-dichlorofluoromethylthiophthalimide from PVC film surface vs. DOP concentration. [Adapted, by permission, from Mura C; Yarwood J; Swart R; Hodge D, Polymer, 41, No.24, 2000, p.8659-71.]

209

Figure 8.3.4. Diffusion coefficient of silane A1891 in plasticized PVC by dihexyl adipate vs. plasticizer concentration. [Data from Eaton P; Holmes P; Yarwood J, Appl. Spectroscopy, 54, No.4, April 2000, p.508-16.]

means that fast silane migration to interphase is very important. Figure 8.3.4 shows that the diffusion coefficient of silane increases parallel to the increase in the concentration of plasticizer. It is interesting to note that silane diffusion is only efficient above the glass transition temperature. Either the addition of a plasticizer is used to bring glass transition down to be within room temperature, or unplasticized PVC must be heated to about 70oC (glass transition temperature of unplasticized PVC) to increase diffusion rate. The results are quite similar.2 PVC foams are a quite an interesting examples of migration-controlled processes.5 Several components control the foaming process. These include blowing agents, kickers, and inhibitors. Depending on plasticizer concentration, they may reside in different phases and thus have different influences on the process of foaming.5

References 1 2 3 4 5 6 7

Mura C; Yarwood J; Swart R; Hodge D, Polymer, 41, No.24, 2000, p.8659-71. Eaton P; Holmes P; Yarwood J, Appl. Spectroscopy, 54, No.4, April 2000, p.508-16. Baes M; Galina C; Vanlandschoot K, J. Cellular Plast., 35, No.5, Sept./Oct.1999, p.438-57. Lambert C; Larroque M; Lebrun J C; Gerard J F, Food Additives Contaminants, 14, No.2, 1st Feb.1997, p.199-208. Anghel C; Bucevschi M D; Balau M T, Kunststoffe Plast Europe, 84, No.6, June 1994, p.19-20. Adhesives Age, 38, No.5, May 1995, p.10. Foldes E, Polym. Bull., 34, No.1, Jan.1995, p.93-9.

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Effect of Plasticizers on Other Components of Formulation

8.4 EFFECT OF PLASTICIZERS ON POLYMERIZATION AND CURING REACTIONS Numerous books and papers have been published on various effects of solvents on chemical reactions and reactivity.1-2 Also, many scales were developed to rank the solvent effect of reactivity by cation or anion solvation.2 There are many properties of solvents that affect chemical reactivity. These can be divided into physical and chemical effects. Physical effects of solvents may be generalized as follows: • solubility of reagents (reactions between reagents residing in different phases require diffusion of one reagent through interphase, which dramatically slows down reaction) • solubility of reaction product(s) (insoluble reaction product may increase conversion and the reaction rate) • plasticizing effect of the solvent decreases glass transition temperature and thus reduces temperature. It may also facilitate diffusion of monomer or initiator into polymer phase • the viscosity of solvent and solution (lowering viscosity increases Brownian motion and reaction probability • morphology and crystalline structure of products of synthesis depends on the solvent Chemical effects of solvents may be generalized as follows: • alteration of charge distribution, polarizability, dipole density (these effects may slow down or increase rates of chemical reactions) • effect on configuration and conformation of molecules which influence steric hindrance • formation of complexes that are capable of reducing or increasing the activation energy of reaction, increasing the stability of radicals, etc. • influence on relative rates of simultaneously occurring reactions, which change reaction mechanism and product characteristics The above points characterize only the most obvious influences and are not a complete list of solvent effects. These effects are very well studied for solvents and can be predicted by a variety of methods and scales for several hundred solvents. In comparison to understanding in the case of solvents, studies on the effects of plasticizers on chemical reactivity are still Figure 8.4.1. Conversion in sunlight cured MMA-acry- at the stage of infancy. Only sporadic conlate copolymers in the presence of variable concentratributions were published.3-11 Plasticizers tions of DOP. [Data from Decker C; Bendaikha T, J. are used today in about 60 polymers and Appl. Polym. Sci., 70, No.11, 12th Dec.1998, p.2269more than 30 groups of products, for many 82.]

8.4 Effect of plasticizers on polymerization and curing reactions

Figure 8.4.2. Conversion after 600 min of reaction of diglycidyl ether of resorcinol-diaminopyridine system in the presence of variable amounts of di-butyl phthalate. [Data from Smirnov Yu N; Dzhavadyan E A; Golodkova F M, Polym. Sci. Ser. B, 40, Nos.5-6, MayJune 1998, p.190-3.

211

Figure 8.4.3. Effect of di-octyl sebacate concentration in PVC composition on the average molecular weight between crosslinks. [Data from Wang Y; Simonsen J; Neto C P; Rocha J; Rials T G; Hart E, J. Appl. Polym. Sci., 62, No.3, 17th Oct.1996, p.501-8.

of which reactivity is an important issue. The question is, how well the effect of plasticizer is understood without the benefit of fundamental knowledge of what happens during processing? Figure 8.4.1 shows that the conversion of monomers in photopolymerization of PMMA-acrylate increases with the amount of plasticizer. Polymerization rate and conversion are affected by plasticizers. Figure 8.4.2 shows more complex behavior attributed to the cure of epoxy oligomers. With very small additions of plasticizer (up to 1%) cure rate increases. This may be explained by the decrease in the activation energy due to the formation of complexes. Further increase in plasticizer concentration reduces rate because of dilution effect and complexing with proton donors, which inhibit the reaction. Comparison of results shows that the addition of plasticizer is more complex, as commonly thought, than a simple reduction in viscosity by the addition of inert liquid. Figure 8.4.3 shows that the presence of di-octyl sebacate, DOS, increases the effectiveness of crosslinker. Here, it is believed that the increase in DOS increases the compatibility of the components, and reaction proceeds with higher efficiency. Polymer plasticization and overcoming compatibility problems help in the synthesis of many polymers in the presence of supercritical carbon dioxide.2 Carbon dioxide has been found inert towards free radicals and cations but dramatically decreases glass transition temperature of the polymer due to plasticization (e.g., polystyrene Tg is reduced by about 50oC).2 Plasticization is especially useful in the melt phase polycondensation processes. The effects of small molecule plasticizer of liquid acrylonitrile-butadiene rubber on coordination crosslinking reaction between acrylonitrile-butadiene rubber and copper sul-

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fate were investigated.12 The results showed that addition of plasticizer to NBR/CuSO4 system could accelerate coordination crosslinking reaction between NBR and CuSO4.12 The polyester-urethane network was polymerized in the presence of triacetin.13 The presence of triacetin during polymerization induced the formation of elastically inactive chains such as dangling chains and loops.13 The hydrolysis of these chains did not change the elastic properties of the network.13 The 1,3-dipolar cycloaddition reaction in triazole-crosslinked polymers was slightly inhibited at the early stages in the presence of plasticizer.14 But, even at high amounts of plasticizer, sufficient initial curing reactivity, and good conversion were observed.14 At the same time, the high levels of plasticization considerably delayed the increase of viscosity.14 The above information shows that there is a high potential in material modification by an educated selection of plasticizers, but substantially more fundamental studies are needed before this happens.

REFERENCES 1 2 3 4 5 6 7 8 9 10 11 12 13 14

Reichardt C; Welton, T; Solvents and Solvent Effects in Organic Chemistry, VCH Weinheim, 2010. Linert, W, in Handbook of Solvents, Vol. 1, 3rd Ed., Wypych G, Ed., ChemTec Publishing, Toronto, Canada, 2019. White L A; Jonson S; Hoyle C E; Mathias L J, Polymer, 40, No.23, 1999, p.6597-605. Decker C; Bendaikha T, J. Appl. Polym. Sci., 70, No.11, 12th Dec.1998, p.2269-82. Eck H, Fleischmann G, Wierer K, US Patent 5,750,617, Wacker-Chemie GmbH, May 12, 1998. Smirnov Yu N; Dzhavadyan E A; Golodkova F M, Polym. Sci. Ser. B, 40, Nos.5-6, May-June 1998, p.190-3. Shmakova N A; Slovokhotova N A; Sukhov F F, Intl. Polym. Sci. Technol., 24, No.7, 1997, p.T/25-8. Wang Y; Simonsen J; Neto C P; Rocha J; Rials T G; Hart E, J. Appl. Polym. Sci., 62, No.3, 17th Oct.1996, p.501-8. Williams G; Smith I K; Aldridge G A; Holmes P A; Varma S, Macromolecules, 34, No.20, 25th Sept.2001, p.7197-209. Yong-Zhong Bao; Zhi-Xue Weng; Zhi-Ming Huang; Zu-Ren Pan, J. Appl. Polym. Sci., 76, No.6, 9th May 2000, p.868-74. Cooper A I, J. Mater. Chem., 10, No.2, Feb.2000, p.207-34. Yuan X, Shen F, Wu G, Wu C, Polym. Compos., 29, 302-6, 2008. Richaud, E; Derue, I; Gilormini, P; Verdu, J; Vaulot, C; Coquillat, M; Desgardin, N; Vandenbrouke, A, Eur. Polym. J., 69, 232-46, 2015. Lee, D-H; Kim, K T; Jung, H; Kim, S H; Jeon, H B; Paik, H-j; Min, B S; Kim, W, J. Taiwan Inst. Chem. Eng., 45, 6, 3110-6, 2014.

9

PLASTICIZATION STEPS A. Marcilla, J.C. García and M. Beltrán Chemical Engineering Department, Alicante University, Spain

9.1 PLASTICIZATION STEPS Most applications of plasticized materials involve their transformation from a solid, paste, or liquid into rubbery material due to the effect of temperature. The case of plasticization of PVC is by far the most studied, and so this chapter deals with steps observed during PVC plasticization. Plasticized PVC compounds can be obtained either from plastisol (a liquid suspension of emulsion PVC in a plasticizer) or from a dry mixture of suspension PVC with plasticizers, obtained by dry blending. In both cases, the behavior of these materials is quite similar and as is the number of steps that have been described in the literature. The interactions that occur between PVC and plasticizer, as well as the changes in these materials caused by the effect of temperature, are responsible for the observed behavior. Titow1 described two stages during plasticization of PVC: • Gelation, the process where the adsorption of plasticizer by PVC particles takes place as a consequence of an increase in temperature and/or drastic aging. After the gelation process, a weak gel is obtained, in which the mechanical properties are still to be developed. • Fusion, the process, where, as a consequence of a further heating (usually at temperatures well above 150ºC), PVC particles and the plasticizer melt together to form a homogeneous material. After cooling, the material develops a maximum of its mechanical properties. During gelation and fusion, some intermediate steps have been described.2-4 The number of steps and temperatures at which they occur vary slightly from one author to another depending on the type of experiment carried out. From the work of many researchers, Sears and Darby2 identified six steps which are described below. During the first step, at the beginning of the gelation process, plasticizer molecules penetrate the porous structure of PVC in an irreversible way. Adsorption of plasticizer takes place. Subsequently, there is an induction period where the plasticizer slowly solvates the resin surface. During the third step, the absorption of the plasticizer takes place. During this step, PVC particles swell, and the total volume of the material decreases. A diffusion process takes place with low activation energy. In the fourth step, drastic changes take place that transcur with high activation energy. The plasticizer forms clusters

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among the polymer segments and penetrates into the molecular segments of polymer, solvating hydrogen bonding and polar groups available. During this step, the PVC particles lose their identity, and the mixture can be seen as a melted homogeneous material. If heating progresses (step 5), the material behaves as a fluid melt. The clusters of polymer or plasticizer molecules disappear, and a homogeneous material is formed. The sixth step takes place during cooling. The polymer hardens due to crystallization and the creation of weak van der Waals forces and hydrogen bonding between plasticizer molecules and the polymer segments. Steps one and two can take place at ambient temperatures after the plasticizer and PVC are mixed (aging). The third step can also take place at ambient temperatures, but the actual temperature depends on the solvent power of the plasticizer. For the fourth step to occur, which is the step with high activation energy, it is necessary to heat the sample. The crystallization of small PVC crystals and the formation of weak bonds happens during cooling. This step may take hours or days.

References 1 2 3 4

Titow W V, PVC Plastics, Elsevier Science Publishers, London, 1990. Sears J K, Darby J R, The Technology of Plasticizers, John Wiley & Sons, New York, 1982. Nakajina N, Harrell E R, Adv. Polym. Technol., 6, 409 (1986). Marcilla A, García J C, Eur. Polym. J., 34, 1341 (1998).

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9.2 STUDIES OF PLASTISOL'S BEHAVIOR DURING GELATION AND FUSION During plasticization, the morphology and properties of plastisols are strongly modified. The above plasticization steps change viscoelastic, mechanical, optical, and dielectric properties, glass transition temperature, refractive index, etc., since polymer structure and superstructure disappear to yield plasticized material. Different techniques have been successfully applied to study and characterize the behavior of PVC plastisols during gelation, fusion, and the intermediate steps. Obviously, depending on the measured property, experimental conditions, or formulation, some or all the steps described can be observed. In this chapter, more works on the studies of interactions during plasticization are discussed. Probably the more relevant works and those providing more information, are those carried out by determining viscoelastic properties and using scanning electron microscopy (García and Marcilla4-7 and Nakajima et al.).8-11 Another technique employed to study gelation and fusion of plastisols, such as differential scanning calorimetry, infrared spectroscopy, thermogravimetric analysis, are also commented.

9.2.1 RHEOLOGICAL CHARACTERIZATION The plasticization steps can be monitored to some extent by rheological analysis, using instrumented mixers or blenders, or alternatively cone-plate and parallel plates rheometers. The use of cone-plate and plate-plate rheometers became more frequent because measurements are easy and employ oscillatory tests,3-15 which impose very low deformations and hence minor disturbance in plasticizer uptake. Nakajima et al.8-11 were the first to measure the modification of viscoelastic properties of plastisols during gelation and fusion. The earlier works of these authors attempted to establish experimental conditions under which the sample is not disturbed during testing.8,16 It is also desirable to measure the behavior of plastisol under low oscillatory frequencies since in industrial processing, these materials are rarely subjected to large forces.12 Slow oscillation frequencies need low heating rates because temperature should be kept constant during cyclic measurements. But, in the industry, high heating rates are common. Nakajima proposed to employ oscillatory frequencies of 1 Hz.11 García5 showed that for low amplitudes, around 0.005, the gelation and fusion processes are not modified by oscillation frequencies in the range 0.2 to 20 Hz. As stated in Section 10.4, elastic and Figure 9.2.1. Simplified behavior of modulus of PVC viscous modulus and complex viscosity are plastisols with temperature. the magnitudes determined commonly by temperature scans in oscillatory tests. In general terms, when a PVC-plasticizer mixture is heated, these magnitudes undergo at least 3 steps in the “rheograms”, as shown in Figure 9.2.1 in a simplified way.

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Step 1: The first consequence of an increase in temperature is a decrease in both modulus and viscosity due to the reduction of the plasticizer viscosity. Step 2: A temperature is reached (70-90ºC), at which interactions between PVC particles and plasticizer begin, producing an increase in modulus and viscosity due to plasticizer adsorption by PVC particles and the subsequent PVC dissolution. This step, known as gelation, can be observed as more than one process. This depends on concentrations of plasticizer and PVC resin and their types. Different particle sizes or molecular weight distributions of PVC can be responsible for different interactions or dissolution rates of plasticizers. Step 3: The increase in modulus and viscosity is observed until all plasticizer and PVC have interacted, reaching the maximum at temperatures between 130 and 170ºC, which are temperatures at which gelation has been concluded, and thermal expansion and fusion of PVC microcrystallites began, provoking a pronounced decrease in modulus and viscosity. The extent of changes and temperature at which these steps occur is strongly influenced by the type and the concentration of plasticizer, as well as by the type of resin and additives present in the formulation. The effect of plasticizer type has been studied by different authors resulting in different behaviors observed for plasticizers of different solvent power.13,14,18,19 The gelation takes place at lower temperatures for a more compatible plasticizer. Nakajima13 stated that depending on the plasticizer type and its concentration, some deviations in behavior can be observed. Nakajima et al.11,13 and Marcilla and García4 studied the effect of the resin type (molecular weight and particle size) on plastisol behavior during gelation and fusion by rheometry. The resins, having lower molecular weights, gel faster than the resins having higher molecular weight. The viscosity of molten plastisol is higher for the resin having a higher molecular weight. Particle size and particle size distribution strongly affect the initial viscosity of plastisol13 but less likely the gelation rate. The viscosity of plastisol between 90 and 160ºC is also influenced by these variables. In this range of temperatures, plastisols containing PVC of smaller particle sizes develop higher viscosities. The higher the number of fine particles, the higher the surface of contact points of interaction between PVC and plasticizer, and the higher the resultant viscosity.6,10 With respect to the effect of the plasticizer concentration, the results vary from one author to another. As stated by Titow,1 the behavior during gelation and fusion depends on the type of plasticizer and resin and on their interactions, but it is not influenced by their relative concentrations. According to Daniels et al.15 and Guoquan et al.,12 the gelation rate, gelation temperature, and fusion temperature, as measured by rheometry, are do not depend on the plasticizer concentration. With higher plasticizer concentrations, the viscosity and the modulus take higher values, but the temperature at which different processes take place does not change. Gilbert and Ramos,17 working with a Brabender rheometer and dry mixtures of PVC and plasticizer, found that the fusion temperature diminishes when plasticizer concentration is increased because of increased mobility of polymer chains. Although this generalized behavior happens in most cases, as shown in Figure 9.2.1, the actual behavior of elastic and viscous moduli is more complex. Marcilla and García4

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suggested a qualitative model that may explain behavior observed for both moduli, and it is applicable to formulations containing different concentrations of plasticizer, plasticizers with different solvent power, and different types of PVC resins. The model4 distinguishes four different steps for both moduli, in addition to the initial decrease due to the effect of temperature on plasticizer viscosity (Figure 9.2.2).

Figure 9.2.2. Schematic behavior of elastic modulus and viscous modulus for plastisols with different concentration of plasticizer: C1 < C2 < C3. [Adapted by permission, from Marcilla A, García J C, Eur. Polym. J., 34, 1341, 1998].

•

•

•

Step 1: The interactions between plasticizer and PVC resin begin, provoking a pronounced increase in both moduli, due to the dissolution of easier dissolving resin (i.e., the outer layers of big particles and the small particles) and swelling of gel particles, which may begin to contact each other. Step 2: Once interaction between PVC and plasticizer have started, PVC glass transition may occur, and this can be reflected in different ways by both moduli (if cohesive forces between plasticizer and swollen PVC particles are sufficiently strong). The result is a net increase in viscous modulus and a decrease or almost inappreciable change in elastic modulus. Logically, the magnitude in which PVC glass transition can be reflected in both moduli also depends on the amount of unaltered PVC resin at the temperature at which it occurs. Thus, systems having high plasticizer concentration or plasticizers of good solvent power do not show the effect of the glass transition temperature since at this temperature, low amounts of remaining PVC resin are still present. Plasticizers, having poor solvent power that hardly dissolve resin (because of large particle sizes or high molecular weight), permit observation of PVC glass transition. Step 3: Following the previous step, or simultaneously, the plasticizer interacts with the rest of the resin, producing an increase in both moduli. When this step occurs at the same time as the second step, the moduli observed are the combinations of the contributions of both steps.

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•

Step 4: Once the previous step has been concluded, all PVC resin has been dissolved in a plasticizer, and a marked decrease is observed in both moduli due to thermal expansion and the fusion process of the gel obtained.

9.2.2 STUDIES BY SCANNING ELECTRON MICROSCOPY The use of Scanning Electron Microscopy, SEM, permits the observation of morphological changes in PVC particles during gelation and fusion. The evolution of the initial structure, the aspect ratio of PVC particles, and the progressive disappearance until the homogeneous material is formed may offer valuable qualitative information, which cannot be obtained by another technique. It has already been shown that SEM is a reliable technique to monitor PVC plasticization,3,7,9,10 although Figure 9.2.3. Behavior of the elastic and viscous moduli it cannot distinguish all steps described in of a commercial PVC plastisol containing DIDP. the previous sections. [Adapted by permission, from García J C, Marcilla A, To obtain samples suitable for obserPolymer, 39, 3507, 1998]. vation by SEM, the mixture PVC-plasticizer is heated to the desired temperature and then rapidly cooled in liquid nitrogen. The specimen is fractured at low temperature to obtain surfaces ready to be observed. The behavior of a PVC plastisol of a commercial resin and diisodecyl phthalate, DIDP, is given in Figure 9.2.3, which shows elastic and viscous moduli curves. The same plastisol was analyzed by SEM.7 The results are given in Figure 9.2.4. At the first stages of the gelation process (90ºC), most of the finest particles present in the PVC resin have already disappeared, and a small fraction of a continuous phase, i.e., a gel phase, covers the PVC particles holding them joined together. As the temperature is increased, the size of PVC particles decreases progressively (see Figures 9.2.4c and 9.2.4d), coinciding with the gelation process as monitored by the rheometer. At a temperature close to the maximum in moduli (Figure 9.2.3), the amount of remaining PVC particles is low (Figure 9.2.4d), and most of the observed area by SEM is composed of the continuous phase. At higher temperatures, once the maximum in both moduli has occurred, there is no further evidence of PVC particles, and only one homogeneous phase can be observed (Figure 9.2.4f). Nakajima13 compared the results obtained by SEM and by rheology. With more compatible plasticizers, the structure of PVC particles disappears at lower temperatures than in the case of less compatible plasticizers. There are some good solvents at lower temperatures that become bad plasticizers as influenced by concentration and temperature. For example, in dibutyl sebacate, DBS, it is possible to observe high rates of PVC particles swelling at low temperatures, but at higher temperatures, at which fusion should already be completed, there are still PVC particles present that have not been affected by the treatment.

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Figure 9.2.4. Aspect of samples of PVC: a) pure resin, b to f) mixed with DIDP and heated at: b) 90ºC, c) 100ºC, d) 110ºC, e) 140ºC, f) 160ºC, [Adapted by permission, J.C. García A. and Marcilla, Polymer, 39, 3507, 1998].

9.2.3 STUDY OF POLYMER-PLASTICIZER INTERACTIONS BY DSC The differential scanning calorimetry, DSC, is usually employed to measure glass transition temperature, Tg, of polymers. For PVC, the glass transition temperature is in the range of 80 to 90 ºC, while for most plasticizers, it is around −100 to −60ºC. In plastisol, which has not been previously heated, it is possible to observe the glass transition temperature of both plasticizer and polymer. When the mixture is heated, different transitions are observed. Glass transition temperatures depend on the final temperature reached, which corresponds to the evolution of the gelation and fusion processes,20 as observed in Figure 9.2.5. By increasing the highest temperature of the mixture, the transition temperatures tend to become equal, and their intensities diminish. When the highest temperature reached by the mixture is sufficiently high, one transition temperature appears, which corresponds to the glass transition temperature of the plasticized polymer. For PVC-plasticizer mixtures, Nakajima20 attributed these intermediate transitions to the existence of at least three phases: 1. constituted by pure plasticizer or plasticizer with a small quantity of dissolved PVC 2. PVC particles swelled by plasticizer 3. PVC that has not interacted with a plasticizer.

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Plasticization Steps

Figure 9.2.5. DSC scans of PVC plastisols with Geon 121 and DOP. The bottom curve is the first scan which was carried to 85ºC, and the one above is the second scan. All other curves are the second scans for which the curves of the first scan are not shown. The highest temperature of the first scan is identified by the temperature in parentheses. [Adapted by permission, from Nakajima N, Yavornitzky C M, Roche E J, Harrell E R, J. Appl. Polym. Sci., 32, 3749, 1986].

Along with the progress of gelation and fusion processes, the relative proportion of phases Figure 9.2.6. Schematic representation of the (1) and (3) diminishes while phase (2) increases. possible DSC thermographs: (A) virgin PVC, When the material is completely gelled and fused, (B) PVC-plasticizer mixture, (C) PVC plasticizer mixture processed a temperatures below only phase (2) exists, and so just one single glass the gelation temperature, and (D) plasticized transition temperature can be observed. PVC processed above the gelation temperature. Experiments carried out by Gomez-Ribelles [Adapted by permission, from Potente H, Schultheis S M, Kunstst. German Plast. 77, 4, et al.21 with low proportions of plasticizer 1987] revealed that the Tg of pure PVC can be split into two different transition temperatures very close to each other. These authors concluded that in pure PVC, there are two different phases with the same Tg, but only one of them is able to interact with the plasticizer. When plasticizer is added to PVC, the glass transition temperature of the phase, which is able to adsorb plasticizer, diminishes, while the Tg of the other phase remains the same. The extent to which plasticizer decreases glass transition temperature of the polymer (measured by DSC or DMA) has been used by different authors22-24 as a function of the type and/or the concentration of plasticizer. According to the free volume theory, the addition of plasticizer to the polymer creates a large free volume in the polymer (Chapter 5), and so diminishing the glass transition temperature of the plasticized polymer. Compatible plasticizers are more effective in decreasing Tg and in a narrower range of temperatures.25,26 DSC has also been employed to establish the degree of fusion attained in plasticized PVC. Potente and Schultheis27 give schematic diagrams of the evolution of DSC thermographs of samples that reached different degrees of fusion (Figure 9.2.6). The different endotherms were attributed to the progress of the gelation process (area b in Figures 9.2.6B and 9.2.6C) and to the heat needed to destroy structures formed in completely pro-

9.2 Studies of plastisol's behavior during gelation and fusion

221

cessed samples (area a in Figures 9.2.6C and 9.2.6D). From areas a and b in Figure 9.2.6, the degree of gelation of plasticized samples could be determined. Other authors attributed these large endotherm areas in processed PVC to the fusion of small crystallites, which were formed during cooling.28 A decrease in the glass transition temperature of the polymer is one of the reasons for the addition of plasticizers. Figure 9.2.7 shows the effect of polymeric plasticizer concentration on the glass transition temperature of polymer films.29 Glass transition temperature of PVC monotonically Figure 9.2.7. Glass transition of PVC film vs. copolyesdecreased with plasticizer content ter plasticizer content. [Data from Zhou J, Ritter H, Polym. Int., 60, 1158-61, 2011.] increased.49 The same observations come from studies of the plasticizing effect of triethyl citrate and polysorbate in Eudragit RS membranes.30 In addition to the study on the effect of plasticizer concentration on Tg determined by DSC, the actual reading of Tg was used to predict plasticizer leaching.50

9.2.4 STUDY OF POLYMER-PLASTICIZER INTERACTIONS BY SALS Using Small Angle Light Scattering (SALS), it is possible to study the swelling of PVC particles during gelation.31 If the difference between refractive indices of PVC and plasticizer is high enough, the method follows the changes in particle sizes of PVC during their solvation by plasticizer. From the swelling rate, it is possible to determine the solvent power of the plasticizer. Nakajima32 applied SALS to plasticizers of different compatibility with PVC. For more compatible plasticizers, the size of PVC particles increased faster and at lower temperatures than in the case of less compatible plasticizers. The beginning of swelling takes place around the glass transition temperature of PVC. At this temperature, the PVC chains have enough mobility to allow plasticizer penetration. Hwee-Khim and Shaw33 employed this technique to establish the compatibility of a series of plasticizers in PVC gels (concentrations around 1-15%). Under these conditions, the authors found a clear relation between the gelation temperature and the plasticizer concentration. 9.2.5 STUDY OF POLYMER-PLASTICIZER INTERACTIONS BY FTIR Marcilla and Beltrán studied changes of PVC-plasticizer mixtures by FTIR during heating.34,35 When the plasticizer spectrum was subtracted from the plastisol spectrum, the resultant spectral difference was nearly the same as the spectrum of pure PVC (some modifications observed depended on plasticizer type). Figure 9.2.8 shows results for DBP, DOP, and DIDP. The more compatible plasticizer (DBP > DOP > DIDP) caused greater modifications in the PVC spectrum (DIDP difference spectrum nearly matches that of pure resin). Moreover, it was observed that the relative intensity of the crystalline bands of PVC (1427 and 637 cm-1) decreases as compared to the amorphous bands (at 1435 and

222

Figure 9.2.8. Difference spectra of plastisols formulated with 65 phr of DBP, DOP, and DIDP as compared to the spectrum of PVC (a) between 3100 and 2700 cm-1; (b) between 1600 and 580 cm-1. [Adapted by permission, from Beltrán M, García J C, Marcilla A, Eur. Polym. J., 33, 453, 1997].

Plasticization Steps

Figure 9.2.9. Difference spectra of the plastisols formulated with 65 phr of DBP, DOP, and DIDP at 30, 45, 69, 95, 123 and 143 ºC; (a) between 1500 and 1350 cm-1; (b) between 900 and 550 cm-1. [Adapted by permission, from Beltrán M, García J C, Marcilla A, Eur. Polym. J., 33, 453, 1997].

616 cm-1, respectively) with increasing compatibility between resin and plasticizer, showing that the crystallinity changes more extensively with compatible plasticizers (stronger interactions). When plastisols are heated to moderate temperatures (around 150ºC), a gradual decrease in A1427/A1435 and A637/A616 ratios are observed (Figure 9.2.9). The initial intensity of these bands was recovered after cooling, showing the reversibility of the process. The same behavior was also observed in PVC without plasticizer and attributed to a decrease in PVC crystalline content with heating, and thus, the plasticizer type did not have influence. In the region of 1800 to 1650 cm-1, the carbonyl group of plasticizer is observed. A shift in this band to higher wavenumbers was observed during heating. The shift was of irreversible nature since in subsequent cooling and heating processes, the original intensity of the band position was not recovered. Consequently, the modification of the carbonyl band was related to the process of plastisol gelation. The temperature at which the shift in this band took place for different plasticizers was compared with gelation temperature obtained from the loss tangent by rheometry with a good agreement. Interaction between PVC and plasticizer is believed to take place between chlorine atoms and electrophilic plasticizer groups.36 For this reason, resin syndiotacticity, and plasticizer polarity are two fundamental variables, which define compatibility between

9.2 Studies of plastisol's behavior during gelation and fusion

223

polymer and plasticizer.36 The interaction increases with plasticizer polarity increasing, and it is inversely proportional to the syndiotacticity of PVC.36 In a study of a series of plasticizers by FTIR compatibility order of PVC/plasticizer has been found to be as follows: Bisoflex 911 < TOM < DnOP < DOS < DOA < DOA/DOP < DIDP < DOP < DBP.37 Dynamic behavior of polyester film in the presence of triphenyl phosphate was analyzed by using ATR-based dynamic compression modulation step-scan Fourier transform infrared spectroscopy and 2D correlation analysis.38 It was assumed that the presence or absence of plasticizers might affect polymer’s microscopic structure, changing the nature of molecular interactions between polymers and plasticizers.38 However, relatively few detailed studies concerning the dynamic molecular interactions between polymers and plasticizers have been reported so far.38 In the PES without TPP, the dynamic response of the side-chain (C=O) group was faster than that of the backbone (C–C–O stretching).38 With 15% TPP, however, this situation was reversed. The responses of the backbone (C– C–O stretching) bands became faster than the side-chain (C–O stretching) bands.38

9.2.6 STUDY OF POLYMER-PLASTICIZER INTERACTIONS BY TG Thermogravimetric analysis has been widely employed to characterize polymers by their decomposition behavior. Marcilla and Beltrán presented a series of papers39-42 in which the behavior during the decomposition of PVC, plasticizers, and plastisols was compared to each other, showing a clear dependence on the concentration and the type of plasticizer used. Figure 9.2.10 shows the experimental and theoretical curves (obtained by adding the thermographs of the components) for plastisols containing 65 phr of DBP, DOP, and DIDP. The evolution of plasticizer when it is in the plastisol initially takes place at the same temperatures as when it is alone. After a certain period of time, plasticizer suffers a delay as compared with pure plasticizer; the presence of resin in addition to the gelation and fusion processes hinders its evolution.

Table 9.2.1. Temperature to 50% weight loss for plasticizers alone (from ref. 40) and in plastisols (approx. 20% weight loss of the total plastisol). [Adapted by permission, from Marcilla A, Beltrán M, Polym. Deg. Stab., 53, 261, 1996]. o

o

Table 9.2.2. Temperatures to 50% weight loss corresponding to the first stage of the decomposition of resin in plastisol (approx. 58% weight loss of plastisol). [Adapted by permission, from Marcilla A, Beltrán M, Polym. Deg. Stab., 53, 261, 1996]. Plastisol

T, oC

pure: T, C

in plastisol: T, C

PVC

313

DIBP

178

192

PVC + DIBP

285

DBP

188

197

PVC + DBP

288

DHP

234

240

PVC + DHP

293

DOP

237

241

PVC + DOP

294

DINP

252

255

PVC + DINP

297

DIDP

260

262

PVC + DIDP

305

DOA

218

226

PVC + DOA

290

DNA

242

246

PVC + DNA

292

224

Plasticization Steps

Figure 9.2.11. Thermographs of plastisols formulated with 65 phr of DBP, DIBP, DHP, DOP, DINP, DIDP, DOA, and DNA, at 5ºC/min. [Adapted by permission, from Marcilla A, Beltrán M, Polym. Deg. Stab., 53, 261, 1996].

Figure 9.2.12. DTG curves for plastisols with resin E450 and 65 phr of DIBP, DOP, DIDP and DNA, at 5ºC/min. [Adapted by permission, from Marcilla A, Beltrán M, Polym. Deg. Stab., 53, 261, 1996].

The decomposition of PVC occurs at lower temperatures when it is in plastisol than when tested alone. When tested alone, PVC is in powder form, and the particle size may play an important role in its decomposition.43 When they are in plastisol, the PVC particles disappear during gelation and fusion processes, and, thus, decomposition occurs in the film. In this case, the heat transfer is expected to be better than for PVC powder, and a higher autocatalytic effect of HCl is expected.43,44 Figure 9.2.10. TG and DTG curves. Experimental (dotFigure 9.2.11 shows the thermographs ted line) and theoretical curves (full lines) for plastisols obtained for plastisols formulated with containing 65 phr of DBP (a), DOP (b) and DIDP (c), at 5ºC/min. [Adapted by permission, from Marcilla A, eight different plasticizers. Figures 9.2.12 Beltrán M, Polym. Deg. Stab., 53, 261, 1996]. and 9.2.13 show the corresponding deriva-

9.2 Studies of plastisol's behavior during gelation and fusion

225

tive curves. For more volatile plasticizers, two different steps can be observed in Figure 9.2.11, while in the case of less volatile plasticizers, these processes overlap. Table 9.2.1 shows the temperature corresponding to 50% weight loss of plasticizer in plastisols (approximately 20% of the total weight loss), compared to the same temperature for pure plasticizer. In all cases, a delay in plasticizer evolution is observed in comparison with a pure plasticizer. The more comFigure 9.2.13. DTG curves for the plastisols with the patible the plasticizer, the higher the delay. resin E450 and 65 phr of DHP, DINP, DOA and DBP, at 5ºC/min. [Adapted by permission, from Marcilla A, Table 9.2.2 shows the temperature for 50% Beltrán M, Polym. Deg. Stab., 53, 261, 1996]. weight loss (corresponding to a 58% weight loss in plastisol) compared with unplasticized PVC. More volatile plasticizers are also more compatible, and, consequently, they should have disappeared when the resin begins to decompose. Such plasticizers affect PVC decomposition more extensively. According to Naqvi,46 addition of polar substances to PVC induces an unstabilizing effect, which increases as plasticizer polarity increases. Minsker47 observed that plasticizers induced degrading effects as a consequence of solvatation of the PVC chains, which was more pronounced when increasing the compatibility of plasticizers. According to Wypych,48 plasticizers of rapid gelation (i.e., those more compatible) yield more viscous melts, hindering the diffusion of HCl and other products formed, which catalyze the dehydrochlorination process. Another remarkable aspect observed in Figures 9.2.12 and 9.2.13 is a splitting of the peak corresponding to PVC decomposition. Phase splitting during gelation and fusion of plastisols has been observed by other authors, as has been pointed out in other parts of this chapter. Part of PVC, due to its characteristics such as lower molecular weight12,49 and lower crystalline content,48,50 can be more easily solvated by the plasticizer. Other parts of resin presented higher resistance to plasticizer action. These fractions, which undergo the decomposition process at lower temperatures, are probably those more altered by plasticizer. Marcilla and Beltrán studied the phase splitting during decomposition of plasticized PVC with different plasticizer concentrations and processed at different heating rates,41,42 and applied the mathematical model correlating simultaneously the curves obtained in the different experiments. The splitting in the peak corresponding to resin is more pronounced when the concentration of plasticizer decreases. Larger amounts of almost unaltered resin remain, decomposing at temperatures very close to the temperatures when the resin is studied alone. The heating rate has a pronounced effect on the decomposition of plasticized materials. At high heating rates, the solvating process seems to be less complete, and the phase

226

Plasticization Steps

splitting is less pronounced. The mathematical model proposed three different steps during the decomposition of plasticized PVC: PL PVC1 PVC2

G1 k2 k3

g2G2 + r1R1 g 3 G 3 + r2 R 2

The first reaction corresponds to the plasticizer fraction, which has not interacted with resin (PL0); the second one corresponds to the strongly plasticized PVC fraction (PVC10), and PVC20 is the remaining PVC fraction unaltered by the plasticizer. The model includes the usual kinetic parameters as well as two fitting parameters corresponding to the proportion of PL0, PVC10, and PVC20. The thermographs obtained at four different heating rates and for plastisols with three different concentrations of plasticizer were simultaneously correlated, obtaining a very satisfactory reproduction of the experimental Figure 9.2.14. Evolution of the parameters PL0, PVC1, data. The evolution of the fitting parameand PVC2 obtained with the model with the concentra- ters corresponding to the proportion of tion of plasticizer. [Adapted by permission, from Mareach phase is shown in Figure 9.2.14, cilla A, Beltrán M, Polym. Deg. Stab., 60, 1, 1998]. where it can be observed how PL0 increases and PVC20 decreases as the plasticizer concentration increases, while PVC10 slightly increases, corroborating the behavior mentioned above.

References 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21

Titow W V, PVC Plastics, Elsevier Science Publishers, London, 1990. Sears J K, Darby J R, The Technology of Plasticizers, John Wiley & Sons, New York, 1982. Nakajina N, Harrell E R, Adv. Polym. Technol., 6, 409 (1986). Marcilla A, García J C, Eur. Polym. J., 34, 1341 (1998). Marcilla A, García J C, Eur. Polym. J., 33, 349 (1997). García J C, Marcilla A, Polymer, 39, 431 (1998). García J C, Marcilla A, Polymer, 39, 3507 (1998). Nakajima N, Ward D W, Collins E A, J. Appl. Polym. Sci., 20, 1187 (1976). Nakajima N, Isner J D, Harrell E R, J. Macromol. Sci.-Phys., B20, (2), 349 (1981). Nakajima N, Isner J D, Harrell E R, Daniels C A, Polym. J., 13, 955 (1981). Nakajima N, Ward D W, Rubb. Chem. Technol., 1096 (1981). Guoquan W, Yiaotin C, Polym. Testing, 10, 315 (1991). Nakajima N, Sadeghi M R, Intern. Polym. Process. IV, 1, 16-(1989). Nakajima N, Kwak S Y, J. Vinyl Technol., 13, 212 (1991). Daniels P H, Brofman C M, Harvey G D, J. Vinyl Technol., 8, (4), 160 (1986). Nakajima N, Ward D W, Collins E A, Polym. Eng. Sci., 19, (3), 210 (1979). Gilbert M, Ramos de Valle R, Plast. Rub. Proces. Appl., 13, (3), 157 (1990). Gilbert M, Ramos de Valle L, J. Vinyl Tech., 12, (4), 222 (1990). Gonzalez-Roa C, Ramos de Valle L F, Sánchez Adame M, ANTEC'91 (1991). Nakajima N, Yavornitzky C M, Roche E J, Harrell E R, J. Appl. Polym. Sci., 32, 3749 (1986). Gómez-Ribelles J L, Diaz-Calleja R, Ferguson R, Cowie J M, Polymer, 28, 2262 (1987).

9.2 Studies of plastisol's behavior during gelation and fusion

22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

Ceccorulli G, Pizzoli M, Scandola M, Polymer, 28, 2077 (1987). Hwee-Khim Boo, Shaw M T, J. Vinyl Technol., 9, (4), 168 (1987). Nijenhuis K T, Winter H H, Macromolecules, 22, 411 (1989). Patel S V, Gilbert M, Plast. Rub. Proces. Appl., 6, 321 (1986). Patel S V, Gilbert M, Plast. Rub. Proces. Appl., 8, 215 (1987). Potente H, Schultheis S M, Kunstst. German Plast., 77, 4 (1987). Patel S V, Gilbert M, Plast. Rub. Process. Appl., 5, (1), 85 (1985). Zhou J, Ritter H, Polym. Int., 60, 1158 (2011). Gruetzmann R, Wagner K G, Eur. J. Pharmaceutics Biopharmaceutics, 60, 159 (2005). Seung-Yeop Kwak, Polym. Eng. Sci., 35, (13), 1106 (1995). Nakajima N, Sadeghi M R, Kyu T, J. Appl. Polym. Sci., 41, 889 (1990). Hwee-Khim Boo, Shaw M T, J. Vinyl Technol., 11, (4), 176 (1989). Marcilla A, Beltrán M, García J C, Mang D, J. Vinyl Add. Technol., 1, (1), 10 (1995). Beltrán M, García J C, Marcilla A, Eur. Polym. J., 33, (4), 453 (1997). Gonzalez N, Fernandez-Berridi M J, J. Appl. Polym. Sci., 107, 1294 (2008). Gonzalez N, Fernandez-Berridi M J, J. Appl. Polym. Sci., 101, 1731 (2006). Nishikawa Y, Nakano T, Noda I, Vibrational Spectroscopy, 49, 219 (2009). Marcilla A, M. Beltrán M, J. Vinyl Add. Technol., 1, 15 (1995). Marcilla A, M. Beltrán M, Polym. Deg. Stab., 53, 261 (1996). Marcilla A, Beltrán M, Polym. Deg. Stab., 57, 101 (1997). Marcilla A, Beltrán M, Polym. Deg. Stab., 60, 1 (1998). Patel K, Velázquez A, Calderón H S, Brown G R, J. Appl. Polym. Sci., 46, 179 (1992). Minsker K S, Lisitski W W, Kolesov S V, Zaikov G E, J. Macromol. Sci.-Rev. Macromol. Chem., C20, (2), 243 (1981). Marcilla A, Beltrán M, Polym. Deg. Stab., 53, 251 (1996). Naqvi T T, Kalen T, Turcsanyi B, Tudos F, Polym. Bull., 2, 749 (1980). Minsker K S, Kolesov S V, Zaikov G E, Degradation and Stabilization of Vinyl Chloride Based Polymers, Pergamon Press, Oxford, 1988. Wypych J, Polyvinyl Chloride Degradation, Elsevier Science Publishers, Amsterdam, 1985. Nakajima N, Ward D W, J. Appl. Polym. Sci., 28, 807 (1983). Tabb D L, Koenig, J L, Macromolecules, 8, (6), 929 (1975).

227

228

Plasticization Steps

10

EFFECT OF PLASTICIZERS ON PROPERTIES OF PLASTICIZED MATERIALS George Wypych ChemTec Laboratories, Inc., Toronto, Canada

10.1 MECHANICAL PROPERTIES Commercial literature usually contains some data on the mechanical properties of test formulations. This information is frequently not very useful because it refers to a simple formulation (very different from real industrial formulations). The commercial data are determined for formulations freely selected by manufacturers, therefore, cannot be compared between different manufacturers. Finally, these results are not presented in fundamental form, which may guide the user in the selection of plasticizers for his needs. Open literature usually offers information134 aiming at analysis of reasons for the observed behavior of materials, but the number of published studies is limited by interest and resources.

Figure 10.1.1. Tensile properties of PVC plasticized materials containing variable amounts of plasticizers. (711P is Palatinol 711P). [Data from Palatinol 711P. Technical Data Sheet. BASF 1996.]

10.1.1 TENSILE STRENGTH Tensile strength is the most frequently used indicator of changes caused by plasticization.3-4,7-8,10,14-16,18-19,22,27,28-30,32 Since plasticizers must plasticize polymer; the typical expectation is that the tensile strength of plasticized material decreases with increased amounts of plasticizers. Figure 10.1.1 shows the effect of concentration increase of several plasticizers on the tensile strength of plasticized material. Good linear relationships are recorded for all

230

Effect of Plasticizers on Properties of Plasticized Materials

plasticizers on tensile strength. The regression equations show very little differences between various plasticizers (constants a and b of these equations are very similar), but their chemical structures are also very similar. Figure 10.1.2 shows that the molecular weight of alcohol used in plasticizers affects tensile strength. In this study, the influence of the plasticizer was normalized by using the PHR ratio given by the equation: PHR exp PHR ratio = -----------------PHR min mass of plasticizer PHR exp = -------------------------------------------- × 100 mass of PVC molecular weight of plasticizer PHR min = -------------------------------------------------------------------------- × 100 875

[10.1.1]

The set of equations is self-explanatory with the exception of coefficient (875), which is a molecular weight of one helical unit of PVC. This method of data presentation normalizes results for plasticizers and eliminates the effect of molecular weight. Figure 10.1.2 shows tensile strength for two PHR ratios. If ratio equals one, it means that there is one molecule of plasticizer present to separate two chains in each helical unit (isolating all polar groups in PVC by a monolayer of plasticizer).10 If the ratio equals three, there is a substantial amount of free plasticizer in the system. Figure 10.1.2 shows that for both ratios, tensile strength decreases with the number of carbon atoms increasing. In the interpretation of these results, we need to consider that the largest alcohol (octyl) forms a plasticizer, which has the same length as PVC helical unit (note that this statement is correct for phthalic acid); therefore all other plasticizers are shorter than the helical unit. This may

Figure 10.1.2. Tensile strength of PVC plasticized materials containing diesters of sebacic acid of different alcohols (methyl, ethyl, butyl, and octyl). [Data from Gibbons W S; Kusy R P, Polymer, 39, No.26, 1998, p.6755-65.]

Figure 10.1.3. Tensile strength of PVC plasticized materials containing dioctyl esters of different acids (adipic, azelaic, and sebacic). [Data from Gibbons W S; Kusy R P, Polymer, 39, No.26, 1998, p.6755-65.]

10.1 Mechanical properties

231

suggest that shorter plasticizers do not completely separate chains, and some polar interactions may still occur, which increases structure and thus tensile strength. Figure 10.1.3 shows the effect of the number of methylene groups in the acid of the diester. Here, also, the bulkier the acid, the lower the tensile strength. Similar to Figure 10.1.2, the results in Figure 10.1.3 are normalized; therefore the effect of molecular weight of plasticizer is eliminated, which means that morphological features (dimensions of plasticizer molecules and helical segments of PVC) must play an essential role in the plasticization of polyvinylchloride. In addition to the molecular weight and molecular dimensions, plasticizers may differ in their polarity. It will be interesting to understand how polarity affects the mechanical properties of polymers. Unfortunately, only very scarce information is available. More studies may help to improve many products. Figure 10.1.4 compares two plasticizers of sulfonated polystyrene ionomer − nonpolar DOP and polar glycerol. Tensile strength on lower additions of polar plasticizer (up to 20%) only slightly decreases, but addition also improves elongation. Both combined together improve fracture toughness, as will be shown below. The addition of a nonpolar plasticizer decreases the tensile strength of the ionomer and has no effect on elongation. No data were found on the effect of hydrogen bonding or other chemical interactions between the plasticizer and matrix polymer on the mechanical properties of Figure 10.1.4. Tensile strength and elongation of Nasulfonated polystyrene ionomer without and with 10% plasticized material. Intuitively, it can be plasticizer (either DOP or glycerol). [Data from Ma X; Sauer J A; Hara M, J. Polym. Sci.: Polym. Phys. Ed., 35, anticipated that interaction of plasticizer with polymer should increase tensile No.8, June 1997, p.1291-4.] strength, but this should be verified by future experiments. It is expected from the nature of plasticization that the tensile strength of materials decreases with an increase in plasticizer concentration. This is a generally correct assumption, but many physical and experimental exceptions can be found. In Section 7.4, antiplasticization is discussed, which is an example of tensile strength increase on the addition of small amounts of plasticizer to some polymers. Antiplasticization can be postulated when a simultaneous increase in elongation also occurs. This phenomenon may also be treated as one example of the chemical interaction of polymer and plasticizer discussed in the previous paragraph. Figure 10.1.5 shows the effect of compatibility on polymer plasticization.31 Polylactide plasticized with DINCH shows clear phase separation.31 Plasticizer resides in spherical voids, unlike in the case of tributyl citrate, which is evenly distributed in the polymer matrix.31 In both cases, the tensile strength of the material was reduced, but the reduction

232

Effect of Plasticizers on Properties of Plasticized Materials

Figure 10.1.6. Tensile strength as a function of the glass transition temperature for films based on blends of gelatin and five types of PVAl and with 0, 25 and 45 g of glycerol/100 g of macromolecules. [Adapted, by permission, from Maria T M C, de Carvalho R A, Sobral P J A, Habitante A M B Q, Solorza-Feria J, J. Food Eng., 87, 191-9, 2008.]

Figure 10.1.5. FESEM micrographs of cryogenically fractured surface of polylactide/DINCH (100/20) (a) and PLA/tributyl citrate (100/20) (b). [Adapted, by permission, from Wang R, Wan C, Wang S, Zhang Y, Polym. Eng. Sci., 49, 2414-20, 2009.]

was substantially larger in the case of Figure 10.1.7. The effect of triethyl citrate concentration on tensile strength of internally plasticized cellulose DINCH.31 diacetate. [Data from Seung-Hwan Lee; Shiraishi N, J. The plasticizer is added, among other Appl. Polym. Sci., 81, No.1, 5th July 2001, p.243-50.] reasons, to decrease the glass transition temperature of plasticized material. Figure 10.1.6 shows that there is a correlation between glass transition temperature and tensile strength.33 The lower the glass transition temperature, the higher the content of the plasticizer and the lower the tensile strength of the material.33 Figure 10.1.7 shows that the tensile strength of internally plasticized cellulose diacetate increases with an increased amount of external plasticizer, triethyl citrate. Internal plasticization by reaction with maleic anhydride increases stiffness and brittleness of diethyl acetate. The addition of an external plasticizer helps to obtain more flexible material.3

10.1 Mechanical properties

Figure 10.1.8. Effect of processing method of internally plasticized diethyl cellulose on tensile strength. 1 − one-step kneading for 20 min., 2 − one-step kneading for 60 min., 3 − two-step kneading process. [Data from Seung-Hwan Lee; Shiraishi N, J. Appl. Polym. Sci., 81, No.1, 5th July 2001, p.243-50.]

233

Figure 10.1.9. Tensile strength of PVC plasticized with 60 phr of Adilene 150 vs. temperature of processing. [Adapted, by permission, from Jimenez A; Lopez J; Iannoni A; Kenny J M, J. Appl. Polym. Sci., 81, No.8, 1881-90, 2001.]

Figure 10.1.8 comes from the same study, and it shows that improved mixing increases the tensile strength of the material. This observation should be considered in experiment design and interpretation of data from different sources. It may help in understanding that some unusual results may be obtained due to different regimes of mixing.3 Figure 10.1.9 gives an example of how processing conditions influence mechanical properties. Tensile strength of material rapidly increases with tempera4 Figure 10.1.10. Tensile strength of PVC plasticized with ture until it reaches a plateau. Similar results are available for the duration of the variable amounts and proportions of plasticizer mixtures (Uniplex FRP-45 and 546-A). [Data from Uniplex gelation process.4 In experimental studies FRP-45. Flame retardant plasticizer. Unitex Chemical comparing different compositions, this Corporation.] phenomenon is difficult to interpret. Changes in the amount of plasticizer influence gelation temperature (time-temperature regime); therefore comparison of different samples prepared under the same conditions may produce error either due to insufficient gelation or early thermal degradation. Figure 10.1.10 shows still another reason for the tensile strength increase.27 Here, a mixture of two plasticizers is used. Uniplex FRP-45 is a flame-retardant plasticizer, and its percentage in the mixture increases (0, 30, 54, 74, 100 percent of plasticizers mixture).

234

Effect of Plasticizers on Properties of Plasticized Materials

Along with the graph’s total plasticizer content, also amount of Uniplex FRP-45 increases, and because Uniplex FRP-45 gives stronger material, the overall tensile strength of PVC increases. This shows that the combinations of plasticizers may be effectively used to change the mechanical properties of materials. Mechanical performance of material can also be influenced by the effect of plasticizers on polymer crystallization. This was reported for the plasticization of polylactide with fatty acid ester.7 This process requires not only the right combination of materials but also specific thermal conditions (in the reported study,7 crystallization was observed after exposing the material to 100oC for 24 h). Tensile properties of PVC plasticized by several plasticizers decreased with a molecular weight of alcohol increasing, similar to the relationship in Figure 10.1.2.10 The relationship between plasticizer concentration and tensile strength was complex. Until the addition of 17.5 wt% of each plasticizer, tensile strength increased, followed by a steep decrease to 30 wt%. There is no explanation for this behavior. Perhaps, this unusual behavior was caused by the method of sample preparation, which involved solvent casting on the surface of mercury. Two plasticizers (di-(2-ethylhexyl) phthalate and epoxidized soybean oil) were used in the range of concentrations from 0 to 50 phr. Tensile strengths of both samples were very similar and almost linearly decreased with the increase in plasticizer concentration. Urethane polymers with variable urethane contents were plasticized with 10% dibutyl phthalate. Tensile strength of both plasticized and unplasticized polyurethanes increased with urethane content. Addition of plasticizer always reduces tensile strength, but the reduction is substantially larger for higher concentrations of urethanes (e.g., 25, 34, and 45%, tensile strength reduction for 46, 50, 53% urethane content, respectively).14

10.1.2 ELONGATION Based on the definition of plasticization, the elongation should increase with the increase in plasticizer concentration (Figure 10.1.11). On the other hand, plasticizers are frequently capable of dissolving crystalline structures of polymers or separate elements of physical crosslinking. Figure 10.1.11. Elongation of PVC plasticized materials Therefore an excess plasticizer may affect containing variable amounts of Adilene 150. [Data from the network and cause a decrease in elonJimenez A; Lopez J; Iannoni A; Kenny J M, J. Appl. gation. Figure 10.1.11 shows that gains in Polym. Sci., 81, No.8, 22nd August 2001, p.1881-90] elongation may be substantial.4 Plasticization of polylactide with a plasticizer (semi-solid at room temperature) shows that incompatibility and formation of domains by plasticizer may also lead to elongation decrease.7

10.1 Mechanical properties

Figure 10.1.12. Elongation of PVC plasticized with 60 phr of Adilene 150 vs. versus time at 150oC. [Adapted, by permission, from Jimenez A; Lopez J; Iannoni A; Kenny J M, J. Appl. Polym. Sci., 81, No.8, 22nd August 2001, p.1881-90.]

235

Figure 10.1.13. Elongation of PVC plasticized with 60 phr of Adilene 150 vs. temperature of processing. [Adapted, by permission, from Jimenez A; Lopez J; Iannoni A; Kenny J M, J. Appl. Polym. Sci., 81, No.8, 22nd August 2001, p.1881-90.]

The increase in elongation depended on the molecular weight of alcohol used in the plasticizer. The higher the molecular weight of alcohol, the higher the elongation of plasticized material.8 Both time and temperature of fusion affected elongation of PVC plasticized materials, as Figures 10.1.12 and 10.1.13 illustrate. Both curves are similar. They show ranges of gradual increase, which are followed by plateau corresponding to the conditions of processing.

Figure 10.1.14. Dually plasticized cellulose. [Adapted, by permission, from Lee W, Chung J W, Kwak S-Y, Eur. Polym. J., 162, 110882, 2022.]

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Effect of Plasticizers on Properties of Plasticized Materials

Figure 10.1.5 shows the morphology of PLA with two different plasticizers.31 In the case of Hexamoll DINCH, plasticizer resides in the separate domains, but it still influences elongation.31 Elongation at the break for pure PLA is 4%, whereas it is 130 and 200% with 10 and 20 wt% DINCH, respectively.31 It may be related to DINCH domains acting as stress concentrators, which are capable of absorbing energy. 31 The internally- and externally-plasticized (i.e., dually-plasticized) cellulosic material bearing alkyl-branched polydecalactone-grafted cellulose and a hyperbranched polycaprolactone provided enhanced plasticization with highly improved stretchability (Figure 10.1.14).35 Eudragit® E films, used for drug-in-adhesive patches, plasticized with hydrophobic plasticizers (triacetin, dibutyl sebacate, and triethyl citrate) increased elongation at break with increasing plasticizer concentration.36 By contrast, hydrophilic plasticizers (poly(ethylene glycol) 300 and propylene glycol) demonstrated only a slight increase in elongation at break, even at the higher concentrations.36 It has been suggested that such significant differences in mechanical characteristics of fabricated films could be attributed to the miscibility of polymer with plasticizers.36 The elongation of plasticized materials is more predictable and consistent with the mechanism of plasticization than the tensile strength.

10.1.3 HARDNESS The hardness decreases with the amount of plasticizer increase (Figure 10.1.15).2,4,25,28 Excellent linear relationships exist. The regression equations show little difference between plasticizers (constants a and b of these equations are very similar), but their chemical structures are also very similar. The overall tendency suggests that hardFigure 10.1.15. Hardness of PVC plasticized materials ness increases with the molecular weight of containing variable amounts of plasticizers. (711P is Palatinol 711P). [Data from Palatinol 711P. Technical the plasticizer increasing. This is in line Data Sheet. BASF 1996.] with plasticizer efficiency, which depends on molar concentration. Similar results were obtained for cellulose acetate, for which Rockwell hardness had a linear correlation with the percentage of plasticizer in the formulation.2 Shore A hardness of PVC/acrylate copolymer blends decreased with the amounts of plasticizers increasing but also with incompatible liquids such as silicone oil.25 Hardness is easy to determine but does not give precise results, as studies of time and temperature regimes show.34 General trend of results agrees with tensile and elongation studies reported above − hardness increases with time and temperature of thermal treatment. This may be caused either because of degradative processes or plasticizer loss.34 Comparison of DOA and acetyl tributyl citrate in PVC shows that even though citrate has

10.1 Mechanical properties

237

a more branched structure and as such, it should be a less volatile plasticizer, but it is lost more readily because its loss is also affected by hydrolysis.34 Maltodextrin addition improved the structure and quality of extruded buckwheat noodles.37 Hydrogen bonds formed between maltodextrin and buckwheat starch molecules.37 The plasticization effects of maltodextrin enhanced the maximum elongation of noodles.37 All PVC samples plasticized with furan-based plasticizer exhibited lower hardness than pure PVC.38 With the increasing amount of plasticizer, the hardness of PVC plastic decreased.38 Compared to diethylhexyl phthalate, the hardness of samples containing furan-based plasticizers was lower, indicating that the plasticizing efficiency of diethylhexyl phthalate was inferior to that of furan-based plasticizers.38 Hardness measurements are frequently used to determine the stability of a variety of materials on environmental exposures.

10.1.4 TOUGHNESS, STIFFNESS, DUCTILITY, MODULUS Toughness, stiffness, ductility, and modulus are all related to the tensile strength and the elongation measurements, and they follow the trends discussed above. Figure 10.1.16 shows an example of the effect of plasticizer content on the toughness of sheets made out of plasticized polyester. Accumulation of errors from stress and deformation determination results in larger cumulative error than is typical for tensile strength and elongation determinations.12 Considering that tensile strength decreases and elongation increases with the molecular weight of plasticizer increasing, it is not surprising that toughness, which is a surface area under the strain-stress curve, remains constant for both different alcohols and acids in diester plasticizers (Figures 10.1.17 and 10.1.18).10 Stiffness decreases, and ductility

Figure 10.1.16. Fracture toughness of polyester plasticized with variable concentration of plasticizer. [Adapted, by permission, from Parameswaran V; Shukla A, J. Mater.Sci., 33, No.13, 1st July 1998, p. 3303-11.]

Figure 10.1.17. Toughness of PVC plasticized materials containing diesters of sebacic acid of different alcohols (methyl, ethyl, butyl, and octyl). [Data from Gibbons W S; Kusy R P, Polymer, 39, No.26, 1998, p. 6755-65.]

238

Effect of Plasticizers on Properties of Plasticized Materials

Figure 10.1.18. Toughness of PVC plasticized materials containing dioctyl esters of different acids (adipic, azelaic, and sebacic). [Data from Gibbons W S; Kusy R P, Polymer, 39, No. 26, 1998, p. 6755-65.]

Figure 10.1.19. Toughness of Na-sulfonated polystyrene ionomer vs. concentration of plasticizer. [Adapted, by permission, from Ma X; Sauer J A; Hara M, J. Polym. Sci.: Polym. Phys. Ed., 35, No.8, June 1997, p. 1291-4.]

increases with a molecular weight of plasticizer increase (either because of increase in molecular weight of alcohol or acid). Along with plasticizer concentration increase, the stiffness and the toughness decrease, and ductility of material increases.10 Figure 10.1.19 shows the effect of polar plasticizer on Na-sulfonated polystyrene ionomer. The toughness of plasticized ionomer increases up to 20% concentration of polar plasticizer to decrease with further increase in

Figure 10.1.20. Izod impact strength of PVC plasticized with a variable amount of DOP. [Data from Matuana L M; Park C B; Balatinecz J J, J. Vinyl Additive Technol., 3, No.4, Dec.1997, p.265-73.]

Figure 10.1.21. Low temperature properties of PVC plasticized materials containing variable amounts of plasticizers. (711P is Palatinol 711P). [Data from Palatinol 711P. Technical Data Sheet. BASF 1996.]

10.1 Mechanical properties

239

plasticizer concentration. With nonpolar plasticizer (DOP), toughness decreases with plasticizer concentration increasing.

10.1.5 OTHER MECHANICAL PROPERTIES Figure 10.1.20 shows that the impact strength of plasticized PVC increases with an increase in the amount of plasticizer. The impact improvement is not gradual but requires a certain critical concentration of plasticizer. This critical concentration of plasticizer depends on the properties of the pair polymer/plasticizer. For example, in plasticization of polyamide-11, the ductile-brittle transition occurred at 4-6% of one plasticizer and in the vicinity of 15% of another plasticizer. Tensile yield strength decreases with an increase in plasticizer concentration.16 At higher values of stress intensity, fatigue occurs by shear yielding, and this is more likely to occur as a function of increased concentration of plasticizer.26 The creep resistance of PVC was increased by a reactive plasticizer.6 Flexural moduli of PC and PPE were increased by an increase in the concentration of plasticizers, such as aromatic phosphates and phthalates.17 Figure 10.1.21 shows that low-temperature properties of plasticized PVC are always improved by the increased amount of plasticizer, but they also depend on the properties of the plasticizer.28 The regression equations show that there is a linear relationship between low-temperature properties and the amount of plasticizer, but the relationships for each plasticizer differ.28 References 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26

Bohnert T; Stanhope B; Gruszecki K; Pitman S; Elsworth V, Antec 2000. Conference proceedings, Orlando, Fl., 7th-11th May, 2000, paper 648. Garner D P; DiSano M T, Polym. Mater. Sci. Eng., 75, 301-2, 1996. Seung-Hwan Lee; Shiraishi N, J. Appl. Polym. Sci., 81, No.1, 5th July 2001, p.243-50. Jimenez A; Lopez J; Iannoni A; Kenny J M, J. Appl. Polym. Sci., 81, No.8, 22nd August 2001, p.1881-90. Li Q F; Tian M; Kim D G; Wu D Z; Jin R G, J. Appl. Polym. Sci., 83, No.7, 14th Feb. 2002, p.1600-7. Horng-Jer Tai, Polym. Eng. Sci., 39, No.7, July 1999, p.1320-7. Jacobsen S; Fritz H G, Polym. Eng. Sci., 39, No.7, July 1999, p.1303-10. Donempudi S; Yaseen M, Polym. Eng. Sci., 39, No.3, March 1999, p.399-405. Colletti T A; Renshaw J T; Schaefer R E, J. Vinyl Additive Technol., 4, No.4, Dec.1998, p.233-9. Gibbons W S; Kusy R P, Polymer, 39, No.26, 1998, p.6755-65. Nakajima N; Varkey J P, J. Appl. Polym. Sci., 69, No.9, 29th Aug.1998, p.1727-36. Parameswaran V; Shukla A, J. Mater.Sci., 33, No.13, 1st July 1998, p.3303-11. Saad A L G; Hussien L I; Ahmed M G M; Hassan A M, J. Appl. Polym. Sci., 69, No.4, 25th July 1998, p.685-93. Baoyan Zhang; Huimin Tan, Eur. Polym. J., 34, Nos.3-4, March/April 1998, p.571-5. Ishiaku U S; Shaharum A; Ismail H; Mohd.Ishak Z A, Polym. Intl., 45, No.1, Jan.1998, p.83-91. Matuana L M; Park C B; Balatinecz J J, J. Vinyl Additive Technol., 3, No.4, Dec.1997, p.265-73. Nanasawa A; Takayama S; Takeda K, J. Appl. Polym. Sci., 66, No.1, 3rd Oct.1997, p.19-28. Ma X; Sauer J A; Hara M, J. Polym. Sci.: Polym. Phys. Ed., 35, No.8, June 1997, p.1291-4. Matuana L M; Balatinecz J J; Park C B, Antec 97. Volume III. Conf. proc., SPE, Toronto, 27th April-2nd May 1997, p.3580-5. Spathis G; Maggana C, Polymer, 38, No.10, 1997, p.2371-7. Pron A; Nicolau Y; Genoud F; Nechtschein M, J. Appl. Polym. Sci., 63, No.8, 22nd Feb.1997, p.971-7. Gul' V E; Sdobnikova O A; Khanchich O A; Peshekhonova A L; Samoilova L G, Intl. Polym. Sci. Technol., 23, No.9, 1996, p.T/85-7. Winsor D L; Scheinbeim J I; Newman B A, J. Polym. Sci.: Polym. Phys. Ed., 34, No.17, Dec.1996, p.2967-77. Shmakova N A; Slovokhotova N A; Shukhov F F, Intl. Polym. Sci. Technol., 22, No.6, 1995, p.T/50-3. Greenlee W S, Vyvoda J C, Wypart R W, US Patent 5,380,786, Geon Company, Jan. 10, 1995. Moskala E J; Pecorini T J, Polym. Eng. Sci., 34, No.18, Sept.1994, p.1387-92.

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27 28 29 30 31 32 33 34 35 36 37 38

Effect of Plasticizers on Properties of Plasticized Materials

Uniplex FRP-45. Flame retardant plasticizer. Unitex Chemical Corporation. Palatinol 711P. Technical Data Sheet. BASF 1996. Cerquiera M A, Souza B W S, Teixeira, J A, Vicente A A, Food Hydrocolloids, 27, 175-84, 2012. Fenollar O, Garcia-Sanoguera D, Sanchez-Nacher L, Lopez J, Balart R, J. Mater. Sci., 45, 4406-13, 2010. Wang R, Wan C, Wang S, Zhang Y, Polym. Eng. Sci., 49, 2414-20, 2009. Kim H T, Kim M H, Kim B, Koo C M, Koo K K Hong S M, Mol. Cryst. Liq. Cryst., 512, 188-98, 2009. Maria T M C, de Carvalho R A, Sobral P J A, Habitante A M B Q, Solorza-Feria J, J. Food Eng., 87, 191-9, 2008. Persico P, Ambrogi V, Acierno D, Carfagna C, J. Vinyl Addit. Technol., 15, 139-46, 2009. Lee W, Chung J W, Kwak S-Y, Eur. Polym. J., 162, 110882, 2022. Kim S, Fouladian P, Afinjuomo F, Song Y, Youssef S H, Vaidya S, Garg S, Int. J. Pharm., 611, 121316, 2020. Xu X, Gao C, Xu J, Meng L, Wang Z, Yang Y, Shen X, Tang X, Food Chem., in press, 131613, 2021. He Z, Lu Y, Lin C, Jia H, Wu H, Cao F, Ouyang P, Polym. Testing, 91, 106793, 2020.

10.2 Optical properties

241

10.2 OPTICAL PROPERTIES The photo-refractive materials combine photoconductivity and electro-optical properties. They constitute one example of plasticizer application helpful in achieving certain optical properties.1-13 The photooptical effects result from the separation of electrical charges, generated by a spatially modulated light intensity, to produce an electric field within the material.2 The electric field changes the refractive index. The refractive index modulation is measured by internal diffraction efficiency given by the following equation: I diff η = ---------I total where:

[10.2.1]

η internal diffraction efficiency Idiff intensity of light diffracted by photorefractive material Itotal total light intensity (diffracted and transmitted)

High-performance hybrid photo-refractive materials have been developed by a combination of photoconductors, photosensitizers, plasticizers, and nonlinear optical components.14 Plasticizer is commonly added into photo-refractive composites to decrease the glass transition temperature and to enhance chromophore reorientation in the electric field for higher electro-optical effects.14 A suitable Tg should be around operating temperature, namely room temperature.14 N-ethyl-carbazole, a common plasticizer, was found suitable in this application.14 Hyperbranched polymer with enhanced photo-refractive effect at low and zero applied electric field keeps a high loading of the nonlinear optical component chromophore, which is expected for better photo-refractive performance.14 Several methods have been proposed to control birefringence in polymeric materials, such as polymer blending and copolymerization techniques.9 Material must possess simultaneously photoconductivity and electro-optical effect to have photo-refractive properties. Typical candidate materials have low glass transition temperature reduced by the plasticizer. Diffraction efficiency is improved by the addition of plasticizer because chromophore groups have higher rotational mobility and increase their contribution of birefringence to the total refractive index modulation.1

Figure 10.2.1. Effect of plasticizers on birefringence. [Adapted, by permission, from Manaf M E A, Tsuji M, Shiroyama Y, Yamaguchi M, Macromolecules, 44, 3942-49, 2011.]

Figure 10.2.1 shows the mechanism of participation of plasticizers in orientation birefringence.9 The addition of tricresyl phosphate, TCP, increased the orientation bire-

242

Effect of Plasticizers on Properties of Plasticized Materials

fringence of cellulose triacetate, CTA, and cellulose acetate propionate, CAP. In the case of CTA, which has negative birefringence with ordinary wavelength dispersion, the addition of TCP changed the sign of the birefringence to become positive.9 After the removal of TCP from the stretched CTA/TCP film by methanol, the film reverted to negative birefringence.9 This suggests that TCP molecules have positive birefringence associated with polarizability anisotropy parallel to the long axis and are aligned to the stretching direction accompanying the chain orientation of CTA and CAP.9 Because TCP is a liquid Figure 10.2.2. Orientation birefringence Δno plotted against draw ratio for CAP46 (thin dotted line) and CAP compound with low molecular weight, the with various plasticizers: TCP (closed circles); DEP orientation relaxation occurs during a short (closed diamonds); DIDP (open diamonds); and DOA (open circles). Stretching was performed at the tempera- timescale after stretching, leading to negature at which the tensile storage modulus was 10 MPa at tive orientation birefringence with ordinary 10 Hz. [Adapted, by permission, from Yamaguchi M, dispersion if not properly quenched.9 Iwasaki T, Okada K, Okamoto K, Acta Materialia, 57, Figure 10.2.2 shows that plasticizers 823-29, 2009.] having good miscibility enhance orientation birefringence (e.g., TCP, 20.9 MPa1/2).11 On the contrary, plasticizers such as DIDP (18.0 MPa1/2) and DOA (17.6 MPa1/2) having lower solubility parameters show a lower level of orientation birefringence than that exhibited by pure CAP.11 Photo-refractive properties are only relevant to some specialized materials, but some observations are important to the general application of plasticizers. The addition of plasticizers decreases the glass transition temperature of the polymer in photo-refractive material and increases diffraction efficiency. With the smaller addition of plasticizer (up to 10%), photoconductivity increases, but then it decreases when more plasticizer is added. This is explained by the dilution of charge transporting groups.1 This means that the addition of a larger amount of plasticizer affects order within the material (e.g., crystalline), which is compatible with observations in other fields. It is even more important to note that photorefractive properties may be improved either by the addition of a plasticizer or by increased temperature. Temperature also affects birefringence and photoconductivity. This is again observed in the practice of plasticization that the effect of temperature increase is similar to the effect of glass transition decrease by plasticization. Molar refraction values of polyethylene glycols, having molecular weights in the range of 300 to 6,000, increase with molecular weight increase because higher molecular weight species are more likely to form molecular associations.12 Plasticization also affects photoimaginable compositions.4 These are photoimaging resists required to tent through-holes in circuit boards improving contact with copper due to better adhesion. Suitable acid-labile plasticizers are used in specularly non-reflective compositions for diffusion patterning.7 Matt PVC compositions are obtained by plasticization.7

10.2 Optical properties

243

The direct effect of plasticizer on the clarity and color of the resultant material is rarely related to the quality of the plasticizer. They are usually transparent and colorless liquids with clearly indicated optical properties by their manufacturers.10 Haze of medical devices was not affected by the presence of DOP before and after irradiation.10 Clarity may be affected by incompatibility with resin and the effect of moisture absorption. Incompatibility is sometimes encountered with polymeric plasticizers. Some plasticized and unplasticized materials become cloudy and white on moisture absorption. This is a temporary state that can be reversed by drying. Before stabilizers are considered, the effect of moisture on other components of the formulation should be established.6 If plasticizer contributes to cloudiness, the polarity of plasticizer should be evaluated. Polar plasticizers are more likely to contribute to water absorption, which causes reversible cloudiness. Random poly(butylene succinate-co-lactic acid) (3-5 phr) was used as a multi-functional additive for enhancing miscibility, toughness, and clarity of PLA/PBS blends (80/20 wt%).15 A significant decrease in Tg (from 52 to 43°C) and a noteworthy increase in elongation at break (four-fold) confirmed the role of plasticizer.15 A decrease in Tc (from 10 to 85°C), together with an increase in the degree of crystallinity and spherulite growth rate with homogeneously dispersed spherulite, suggested effective and rapid nucleation.15 The film clarity was improved by better compatibility of PLA/PBS (80/20) blend, as well as the decrease in the size of spherulite diameter (~15 μm). Figure 10.2.3 illustrates the chemistry and changes.15

Figure 10.2.3. Effect of poly(butylene succinate-co-lactic acid) on clarity of PLA/PBS blends. [Adapted, by permission, from Supthanyakul R, Kaabbuathong N, Chirachanchai S, Polymer, 105, 1-6, 2016.]

Refractive indices of plasticizer and polymer are behind brilliance. The closer the indices to each other, the better the brilliance. Usually, this is achieved by the selection of

244

Effect of Plasticizers on Properties of Plasticized Materials

plasticizers of high refractive index. It should be noted that the refractive index is not the only determinant. An incompatibility or tendency of plasticizer to crystallize offsets gains due to the refractive index match. A hologram recording material was developed based on a combination of polyvinylacetate, diethyl sebacate, and some other components.13 Composition has excellent transparency and diffraction efficiency, which are characteristics required for holograms.13 Transferable holographic film was developed using water-based polyurethane plasticized with acetyl tributyl citrate (Figure 10.2.4).16

Figure 10.2.4. Image of transferable PET/WPU-ATBC/hologram/Al composite films consisting of 1) 18-μmthick PET film substrate (described as a top green layer here) without release agent/2) 1-μm-thick WPU-ATBC film protective layer (a middle sky-blue layer here)/3) color holographic layer (an orange layer here)/4) deposited Al nanofilm layer (a bottom silver-gray layer here). [Adapted, by permission, from Li X-G, Xie Y-B, Huang M-R, Umeyama T, Imahori H, J. Cleaner Prod., 279, 123496, 2021.]

References 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Van Steenwinckel D; Hendrickx E; Samyn C; Engels C; Persoons A, J. Mater. Chem., 10, No.12, Dec.2000, p.2692-7 Zhang L, Zhang G, Carlisle G O, Crowder G A, J. Mater. Sci., Mater. Electronics, 11, 229-234, 2000. Nagayama N; Yoyoyama M, Molecular Crystals Liquid Crystals, 327, 1999, p.19-22. Lundy D E, Barr R, US Patent 5,939,239, Nichigo-Morton Co., Ltd., Aug 17, 1999. Diaz-Garcia M A; Wright D; Casperson J D; Smith B; Glazer E; Moerner W E; Sukhomlinova L I; Twieg R J, Chem. Mater., 11, No.7, July 1999, p.1784-91. Agarwal N; Farris R J, J. Appl. Polym. Sci., 72, No.11, 13th June 1999, p.1407-19. Felten J J, Hertler W R, Ma S-H, US Patent 5,654,354, DuPont, Aug. 5, 1997. Koga T, Shigemitsu M, Matsumoto O, Suzuki M, US Patent 5,614,593, Shin-Etsu Chemical, Mar. 25, 1997. Manaf M E A, Tsuji M, Shiroyama Y, Yamaguchi M, Macromolecules, 44, 3942-49, 2011. Ahmed S, Mehmood M, Igbal R, Radiat. Phys. Chem., 79, 339-42, 2010. Yamaguchi M, Iwasaki T, Okada K, Okamoto K, Acta Materialia, 57, 823-29, 2009. Dredan J, Zelko R, David A Z, Antal I, Int. J. Pharmaceutics, 310, 25-30, 2006. Tanigawa H, Matoba Y, Saika T, Matsuo T, Yokoyama K, US Patent 7,361,432 B2, National Institute of Advanced Industrial Science and Technology, Apr. 22, 2008. Zhang K, Yang H, Li M, Li J, Wu W, Xu S, Liu Y, Cao S, Dyes Pigments, 180, 108473, 2020. Supthanyakul R, Kaabbuathong N, Chirachanchai S, Polymer, 105, 1-6, 2016. Li X-G, Xie Y-B, Huang M-R, Umeyama T, Imahori H, J. Cleaner Prod., 279, 123496, 2021.

10.3 Spectral properties

245

10.3 SPECTRAL PROPERTIES Spectral properties of plasticizers are useful in various studies. They especially help to understand various aspects of the mechanism of plasticizer action.1-4 Table 10.3.1 shows some typical IR absorption peaks of major representative groups of plasticizers. Table 10.3.1 Main peaks of IR absorption of main representative groups of plasticizers Group

Plasticizer

Main absorption peaks

Adipate

di-(2-ethylhexyl) di-n-decyl diisodecyl

1739, 1457, 1387, 1247, 1176, 1125, 739 1739, 1467, 1355, 1240, 1174, 1077, 720 1736, 1461, 1381, 1237, 1173, 1077, 729

Azelate

di-(2-ethylhexyl) diisodecyl

1739, 1464, 1381, 1240, 1173, 1093, 726 1739, 1464, 1381, 1247, 1170, 1093, 726

Chloroparaffin 50% Cl

1441, 1378, 1263, 915, 653

Citrate

acetyl triethyl triethyl triisooctyl

1739, 1467, 1445, 1371, 1301, 1192, 1116, 1026, 860 1739, 1467, 1445, 1371, 1301, 1192, 1116, 1026, 860 1739, 1467, 1381, 1342, 1186, 1061, 988

Epoxidized

soybean oil

1742, 1464, 1378, 1237, 1160, 1100, 720

Isophthalate

di-(2-ethylhexyl)

1726, 1461, 1381, 1301, 1237, 1132, 1093, 1068, 729

Oleate

butyl 1739, 1464, 1243, 1174, 720 tetrahydrofurfuryl 1739, 1464, 1240, 1170, 1087, 1026, 723

Palmitate

isooctyl

1739, 1467, 1243, 1173, 716

Phthalate

benzyl butyl di-(2-ethylhexyl) diamyl di-n-octyl

1729, 1601, 1579, 1457, 1374, 1285, 1122, 1068, 1036, 739 1729, 1598, 1582, 1464, 1381, 1272, 1122, 1068, 1039, 742 1729, 1601, 1582, 1467, 1381, 1286, 1122, 1074, 1039, 742 1729, 1601, 1579, 1497, 1381, 1285, 1122, 1074, 1039, 740

Phosphate

tri-(2-ethylhexyl) tributyl tricresyl

1461, 1378, 1282, 1026, 879, 767 1464, 1381, 1279, 1026, 908, 764 1585, 1493, 1301, 1189, 1141, 1112, 1007, 966, 774

Polyester

Mw = 6000

1739, 1457, 1419, 1378, 1237, 1176, 1081, 755

Sebacate

di-(2-ethylhexyl) diisooctyl

1736, 1461, 1384, 1234, 1170, 1096, 1026, 723 1739, 1461, 1378, 1240, 1173, 1100, 723

Stearate

2-butoxyethyl butyl

1739, 1464, 1250, 1173, 1125, 720 1739, 1464, 1240, 1170, 716

Sulfonamide

n-ethyl-p-toluene

1598, 1496, 1422, 1323, 1160, 1094, 943, 812

Tartrate

dibutyl

1745, 1464, 1384, 1272, 1128, 1087, 1072, 943, 739

Trimellitate

triisodecyl tri-n-octyl

1729, 1611, 1572, 1464, 1381, 1279, 1234, 1116, 1068, 978 1729, 1611, 1576, 1464, 1282, 1237, 1116, 1068, 953, 752

Plasticizers, with few exceptions, have characteristic, strong carbonyl absorption at ~1739 cm-1. It is shifted to lower wavenumber for phthalates and to higher wavenumber for tartrates, but otherwise, it stays fairly constant. Chloroparaffins, phosphates, and sulfonamides do not have this absorption. There are similar absorption patterns within the group, but it is usually easy to recognize plasticizer type from some characteristic absorptions (for example, phthalates can be recognized by having two small peaks around 1601 and 1579 cm-1). Characteristic absorption wavelengths provide for a convenient method of

246

Effect of Plasticizers on Properties of Plasticized Materials

study of changes during fusion and gelation of PVC.2 Carbonyl band was very convenient in this study since it does not have any interference from PVC absorption. It is also possible to use IR spectra for qualitative analysis of plasticizers’ mixtures.4 Plasticizers identified in small micro-plastics (300 decomp

60-110

225-280

-118 to -133

125-135

-49 to -61

220-260

143-158

334-350

60-85

245-265

190-385

340-408

Polyisoprene

-70 to -75

370-384

Polypropylene

-3 to -51

120-176

Polystyrene

85-102

275

Polyurethane

-19 to -60

141-157

82-87

103-230

Polyvinylchloride

Table 10.9.2 shows that many polymers require some modification to improve their toughness, low-temperature properties, glass transition temperature. Unfortunately, many of these polymers cannot be modified by plasticizers. Many modeling methods were adapted to predict the glass transition temperature of the polymer/plasticizer mixture. Fox model is given by the following equation:9 f polymer f plasticizer 1 --------------- = ----------------------- + --------------------------T g, polymer T g, plasticizer T g, mix

[10.9.1]

where: f

mass fraction

Kelley-Bueche and Gordon-Taylor expanded the Fox equation with factor k, which represents the free volume ratio of the two components:9

262

Effect of Plasticizers on Properties of Plasticized Materials

( f polymer T g, polymer + kf plasticizer T g, plasticizer ) T g, mix = -----------------------------------------------------------------------------------------------------------f polymer + kf plasticizer

[10.9.2]

The constant k can be estimated from the density ratio of polymer to plasticizer and corresponding slopes of the expansion coefficients of polymer and plasticizer near their glass transition temperatures.9 These models, and many other models, such as the Couchman-Karasz model based on the entropy continuity of the mixture at Tg, are difficult to operate because of the lack of data limits of their applicability.9 The three discussed models did not correctly predict the experimental values of Tg of cellulose acetate plasticized with glycerol triacetate and triethyl citrate within the studied concentration range (1540 wt%).9 A model has been developed to estimate the glass transition temperature of polymer-plasticizer mixtures (up to 30 wt% plasticizer).10 The model was based on the Sanchez-Lacombe equation of state Figure 10.9.1. Glass transition temperature of PVC as a and the Gibbs-DiMarzio criterion, which function of plasticizer (di(2-ethylhexyl)phthalate). Data: states that the entropy of a mixture is zero (♦). Curve is model prediction. [Adapted, by permission, at the glass transition.10 The polymers studfrom Martin TM, Young DM, Polymer, 44, 16, 4747-54, ied included polystyrene and polyvinyl2003.] chloride.10 The model qualitatively accounted for the effect of different plasticizers on glass transition temperature of composition.10 Above 30 wt% plasticizer model predicted substantially lower values of Tg than measured (Figure 10.9.1).10 The model predicted that the plasticizer efficiency parameter is a parabolic function of molecular weight for phthalate esters in PVC.10 Considering that determination of glass transition temperature is readily available and simple, mathematical modeling has less importance.

References 1 2

3 4 5 6

7

Sicar AK, Chartoff RP, STP15377S. Measurement of the Glass Transition Temperature of Elastomer Systems Paroli RM, Penn J, STP15380S. Measuring the Glass Transition Temperature of EPDM Roofing Materials: Comparison of DMA, TMA, and DSC Techniques Wiedermann HG, Widman G, Bayer G, STP15373S. Glass Transition in Polymers: Comparison of Results from DSC, TMA, and TOA Measurements Bair HE, STP15365S. Glass Transition Measurements by DSC Rodriquez EL, STP15379S. The Glass Transition Temperature of Glassy Polymers Using Dynamic Mechanical Analysis Foreman J, Kelsey M, Widman G, STP14351S. Factors Affecting the Accuracy of TMA Measurements. ISO 11357-2:2020. Plastics — Differential scanning calorimetry (DSC) — Part 2: Determination of glass transition temperature and step height ISO 22768:2020. Raw rubber and rubber latex — Determination of the glass transition temperature by differential scanning calorimetry (DSC) ISO 6721-11:2019. Plastics — Determination of dynamic mechanical properties — Part 11:

10.9 glass Transition temperature

8 9 10

263

Glass transition temperature ISO 4664-3:2021. Rubber, vulcanized or thermoplastic — Determination of dynamic properties — Part 3: Glass transition temperature (Tg) ISO 11359-2:2021. Plastics — Thermomechanical analysis (TMA) — Part 2: Determination of coefficient of linear thermal expansion and glass transition temperature Erdmann R, Kabasci S, Heim H-P, Polymers, 2021, 13, 1356, 1-14, 2021. Martin TM, Young DM, Polymer, 44, 16, 4747-54, 2003.

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Effect of Plasticizers on Properties of Plasticized Materials

10.10 FLAMMABILITY AND SMOKE FORMATION IN THE PRESENCE OF PLASTICIZERS Several methods are available, which improve the flame resistance of materials. These methods include:1-16 • use of halogen-containing compounds • use of suitable fillers and/or inorganic additives • use of phosphate plasticizers • use of flame retardants. Polyvinylchloride is very popular in flame-resistant applications because of its intrinsic protection due to its high content of chlorine (57%). At the same time, PVC is a rigid material and requires plasticizers to produce flexible articles. The addition of plasticizers reduces chlorine content and, thus, some form of enhancement of flame retardancy is required by plasticized formulation. Chloroparaffins were commonly used as the secondary plasticizers due to their very high chlorine content (up to 70%), but they are now on the lists of restricted substances in the majority of industrial countries due to environmental issues. Their use is gradually phased out. The method of flame retardancy improvement by the increase in halogen concentration uses bromine-containing flame retardants added to the formulation for these purposes. There are several fillers and inorganic/organic additives used in flame retarded materials. These include: antimony oxide, aluminum trihydrate, zinc borate, ammonium octamolybdate, and zinc stannate. The details related to the composition required and performance characteristics of inorganic additives can be found in the specialized monograph.17 Below, some of these compounds are discussed in relation to their effects on enhancements of phosphate plasticizers. Plasticization of PVC for improved flame retarding properties usually relies on a combination of phosphate plasticizers with other plasticizers or inorganic additives listed in the previous paragraph. The selection of combination depends on the level of protection required. Several methods are used to evaluate the effect and efficiency of these additives, such as • limiting oxygen index, LOI, is the lowest concentration of oxygen in the mixture with inert gas, which does not support flame under test conditions • cone calorimeter determines the peak heat of release rate, PHRR, which is maximum heat released by sample, and the flame time, which is a time from self-ignition to no heat energy produced • NBS smoke chamber is used for determination of smoke density by measurement of optical density of smoke • char residue and properties. Figures 10.10.1 and 10.10.2 show smoke density and oxygen index for PVC plasticized with three different plasticizers. Comparison of results in these two figures shows that smoke density does not correlate with oxygen index (diphenyl 2-ethylhexyl phosphate is the best choice for smoke density improvement, but the worst for flame retarding properties as determined by limiting oxygen index).18 This shows that formulations must be optimized to improve both properties. According to Figures 10.10.3 and 10.10.4, flame retardant properties increase with the increase in the amount of flame retarding plasticizer.

10.10 Flammability and smoke formation in the presence of plasticizers

265

Figure 10.10.1. Smoke density of PVC compounds containing different plasticizers. Formulation: PVC 65 wt%, plasticizer 35 wt%. Disflamoll DPO - diphenyl 2-ethylhexyl phosphate, TKP - tricresyl phosphate, DPK - diphenyl cresyl phosphate. [Data from Polymer Additives. Plasticizers, Bayer SP-PMA 8013 E, 2000.]

Figure 10.10.2. Limiting oxygen index of PVC compounds containing different plasticizers. Formulation: PVC 65 wt%, plasticizer 35 wt%. Disflamoll DPO diphenyl 2-ethylhexyl phosphate, TKP - tricresyl phosphate, DPK - diphenyl cresyl phosphate. [Data from Polymer Additives. Plasticizers, Bayer SP-PMA 8013 E, 2000.

Figure 10.10.3. Oxygen index of PVC containing variable amounts of Uniplex FRP-45. Formulation: PVC 100, Uniplex 546-A decreasing from 60 to 0, lead stabilizer 5, Sb2O3 15. [Data from Uniplex FRP-45. Flame retardant plasticizer. Unitex Chemical Corporation.]

Figure 10.10.4. Smoldering of PVC compound containing variable amounts of Uniplex FRP-45. Formulation: PVC 100, Uniplex 546-A decreasing from 60 to 0, lead stabilizer 5, Sb2O3 15. [Data from Uniplex FRP-45. Flame retardant plasticizer. Unitex Chemical Corporation.]

Note that with the maximum amount of plasticizer, LOI is still below the level of pure PVC (49.8%).11 Figure 10.10.5 shows that the majority of plasticizers reduce limiting oxygen index. Phosphate plasticizers reduce LOI to a much lesser extent than DOP and

266

Effect of Plasticizers on Properties of Plasticized Materials

DOS. Substitution of bromine in the molecule of plasticizer helps in maintaining (or slight improvement) of the original properties of PVC.13 Burning time and limiting oxygen index depend on plasticizer type and its amount. They are not greatly affected by the addition of antimony oxide, aluminum trihydrate, or zinc borate. 5,7,9 On the other hand, the addition of antimony oxide, aluminum trihydrate, or zinc borate in combination with phosphate plasticizers reduces the peak heat release rate. The addition of aluminum trihydrate is the best choice in Figure 10.10.5. Limiting oxygen index of PVC compo- this respect, which is consistent with its sition containing 50 phr of the following plasticizers: mechanism of action (water released TD − trisdibromopropyl phosphate, TC − trichloroethyl phosphate, DOP − dioctyl phthalate, DOS − dioctyl seb- quenches fire). Inorganic additives also acate. [Data from Golovnenko N I; Kitaigora E A; increase the amounts of char produced.5,7,9 Sereda E A; Mozzhukhin V G; Nikolaev V G; Soboleva Limiting oxygen index was not affected by N S, Intl. Polym. Sci. Technol., 22, No.9, 1995, p.T/31additions of zinc borate, ammonium octa2.] molybdate, and zinc stannate to PVC compositions containing DOP or its mixtures with phosphate plasticizers.10 Ammonium octamolybdate was found to catalyze the oxidation of organic residues by which it reduced the amount of char. Reduction in char amount does not seem to depend on the amount of ammonium octamolybdate, which supports the suggested catalytic effect. Also, char is softer in the presence of ammonium octamolybdate. The effect of inorganic additives on smoke formation depends on the composition of plasticizers used. In DOP plasticized material, ammonium octamolybdate helped to reduce smoke but to a much lesser extent in composition with phosphate plasticizers. The effect of polymer blending on flammability was studied in a combination of ABS (one of the most flammable polymers) and PVC (intrinsically flame retardant polymer). The 30 wt% PVC in the blend was not sufficient to make substantial changes in ABS behavior.11 Only the addition of iron peroxide helped to increase LOI and reduce smoke by 45%. Flexibilizers based on ethylene copolymer resin can be used to replace liquid plasticizers in flame retardant compounds. These flexibilizers substantially reduce smoke and help in retaining the mechanical performance of PVC.1 A plasticizer was developed for flame retarded polyurethanes.4 It is based on benzoate esters, which are popular in PU applications, but the plasticizer contains at least one (and up to four) bromine atoms in the benzene ring. A flame retarding plasticizer is based on polyethylene stibnite phosphate esters. It contains all essential elements present in compounds having flame retarding properties, such as Sb, P, and halogens. The plasticizer has an advantage in uniform distribution of antimony oxide, which is formed in situ, but it is not sufficiently stable at elevated tem-

10.10 Flammability and smoke formation in the presence of plasticizers

267

peratures and hydrolysis.6 Low smoke generation was obtained with plasticizer based on pentaerythritol.14 Polymeric solar absorbers are cost-effective solar energy harvesters that can significantly reduce the energy cost for individual households.19 One of the concerns related to polymers is their flammability.19 To mitigate the flammability risk, solar absorber paints with flame retardant properties were developed.19 Bridged 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) derivatives in concentration range of 10-15 wt% were used in polyurethane-based matrix.19 Several references are useful in the selection and assessment of compounds useful in the reduction of flammability by plasticized materials.20-23 Two books contain comprehensive information on flame retardants.24-25

References 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25

Griffin E R, Antec 2000.Conference proceedings, Orlando, Fl., 7th-11th May, 2000, paper 650. Tomy G T; Westmore J B; Stern G A; Muir D C G; Fisk A T, Analytical Chem., 71, No.2, 15th Jan.1999, p.446-51. Fielding W R, Vinyltec '98. Retec proceedings, SPE, Vinyl Div., East Brunswick, N.J., 13th-14th Oct.1998, p.55-64. US Patent 5,728,760. Moy P Y, J. Vinyl Additive Technol., 4, No.1, March 1998, p.22-5. Kannan P; Kishore K, Eur. Polym. J., 33, Nos.10-12, Oct.-Dec.1997, p.1799-803. Moy P Y, Plast. Eng., 53, No.11, Nov. 1997, p.61-3. Plast. World, 55, No.7, July 1997, p.26-8. Moy P Y, Antec 97. Volume III. Conf. proc., SPE, Toronto, 27th April-2nd May 1997, p.3506-10. Ferm D J; Shen K K, J. Vinyl Additive Technol., 3, No.1, March 1997, p.33-40. Carty P; White S, Polym. Deg. Stab., 54, Nos 2-3, 1996, p.379-81. Balayan S R; Alimukhamedov M G; Magruppov F A, Intl. Polym. Sci. Technol., 22, No.10, 1995, p.T/81-3. Golovnenko N I; Kitaigora E A; Sereda E A; Mozzhukhin V G; Nikolaev V G; Soboleva N S, Intl. Polym. Sci. Technol., 22, No.9, 1995, p.T/31-2. US Patent 5,430,108. Molesky F; Schultz R; Midgett S; Green D, Property Enhancement with Modifiers and Additives. Retec proceedings, SPE,Palisades Section; SPE, Polym. Modifiers & Additives Div., New Brunswick, N.J., 18th-19th Oct.1994, p.49-54. Carty P; White S, Eng. Plast., 8, No.4, 1995, p.287-96. Wypych G, Handbook of Fillers, 5th Ed., ChemTec Publishing, Toronto, 2021. Polymer Additives. Plasticizers, Bayer SP-PMA 8013 E, 2000. Štirn Z, Čolović M, Vasiljević J, Šobak M, Žitko G, Čelan Korošin N, Simončič B, Jermana I, Solar Energy, 231, 104-14, 2022. Gad, S C, Phosphate Ester Flame Retardants. Reference Module in Biomedical Sciences from Encyclopedia of Toxicology, 3rd Ed., Elsevier, 2014, pp. 909-12. Weil, E; Levchik, S V, Comments on Flammability Development and Smoke Tests Useful in Development. Flame Retardants. 2nd Ed. Elsevier, 2016, pp. 303-21. Wypych, G, PVC Degradation and Stabilization, 4th. Ed., ChemTec Publishing, Toronto, 2020. Wypych, G, PVC Formulary, 3rd Ed., ChemTec Publishing, Toronto, 2020. Wypych G, Handbook of Flame Retardants, ChemTec Publishing, Toronto, 2021. Wypych A, Wypych G, Databook of Flame Retardants, ChemTec Publishing, Toronto, 2021.

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Effect of Plasticizers on Properties of Plasticized Materials

10.11 THERMAL DEGRADATION Thermal degradation of the plasticized system may involve:1-36 • thermal degradation of plasticizer • effect of polymer degradation products on plasticizer degradation • effect of plasticizer degradation products on polymer degradation • loss of plasticizer from the material due to the chemical decomposition reactions and evaporation • effect of plasticizers on the thermal degradation of materials. The importance of these processes for the quality of plasticized products leads one to expect that a large body of information is available on the subject. It is shown below that there are substantial gaps in our present knowledge.

10.11.1 THERMAL DEGRADATION OF PLASTICIZERS Thermal degradation of carboxylic ester plasticizers occurs according to the following mechanism:5 O

O

C

O

R

C

O

R

C

Δ

OH + ROH and mixture of alcohol degradation products

C

O

OR

O Δ O C O

+ ROH

C O

In this reaction, acid is a more thermally stable product. Phthalic acid decomposes at 230oC to phthalic anhydride, which has a boiling temperature of 295oC. Alcohols used in plasticizers have boiling points dependent on their molecular weights and branching. Figure 10.11.1 shows the boiling temperatures of some normal alcohols. It is pertinent that alcohols may require a lower temperature to undergo conversion, which usually includes the formation of water and unsaturated hydrocarbon rest: CH2CH3 Δ -H O 2 CH (CH ) C CH2 CH3(CH2)3CHCH2OH 3 2 3 CH2CH3

Pyrolysis of 1 mol of DOP yielded 0.97 mol of 2-ethylhexene-1 and 0.78 mol of 2ethylhexanol. Pyrolysis of 1 mol of DOS yielded two mols of 2-ethylhexene-1.5 This seems to suggest that alcohol is produced as a side effect of anhydride formation because no alcohol was formed from DOS, which does not form anhydride. Triaryl phosphates

10.11 Thermal degradation

269

have high boiling temperatures and are thermally stable, but aryl alkyl phosphates are not. The 2-ethylhexyl diphenyl phosphate undergoes decomposition at 170oC:36 C8H17 O

OH

P

P

O

O

+ C8H16

The exact kinetics of degradation of different plasticizers are not available. It would be convenient to know in the future the compositions of degradation products of plasticizers at different temperatures.

10.11.2 EFFECT OF POLYMER DEGRADATION PRODUCTS ON PLASTICIZERS Polyvinylchloride is the prime example of polymer, which produces gaseous degradation product, such as HCl, which is potentially dangerous to the stability of plasticizers. Since plasticizers are esters, they may undergo hydrolysis assisted by acids. Figure 10.11.2 shows the acid number of plasticizers in simple PVC formulation heated at 170oC for 90 min. The rate of hydrolysis depends on plasticizer type (both acid and alcohol seem important). In recent studies, polyvinylbutyral was subjected to thermal degradation in temperatures ranging from 50 to 200oC without and with phthalate plasticizer. A free carboxylic acid was produced from the degradation of the polymer. It was postulated that plasticizer is degraded by the radical formation in the ester group. Changes in plasticized materials began to occur above 150oC.2 Future studies need to find out the exact mechanism of plasticizers degradation in the presence of degradation products with special attention to acid formed during degradation.

Figure 10.11.1. Boiling temperatures of normal alcohols.

Figure 10.11.2. Acid number of PVC dry blends heated at 170oC for 90 min. Formulation PVC 100, plasticizer 40, barium stearate 1.5, calcium stearate 1.5. PG polyester based on thriethylene glycol. [Data from Barshtein R S, Plastmassy, 12, 13-15, 1968.]

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Effect of Plasticizers on Properties of Plasticized Materials

10.11.3 EFFECT OF PLASTICIZER DEGRADATION PRODUCTS ON POLYMER DEGRADATION It was pointed out in the previous two sections that three types of products are produced during plasticizer degradation: unsaturated hydrocarbons, alcohols, and acids. Hydrocarbons are not discussed here because they are, in most cases, too volatile to conduct the proper tests and unlikely to affect polymer degradation. Figure 10.11.3 shows the effect of the addition of various acids to plasticized PVC on its thermal stability. The details of the determination of thermostability number A are fully disclosed elsewhere.39-40 The higher the thermostability number, the more stable the film and the lower the influence of acid. Figure 10.11.3. Thermostability number A of PVC film vs. pK1 of acid added to formulation. Formulation: PVC Phosphoric and phthalic acids are much 100 phr, DOP 60 phr, acid 2 phr. Acids: 1 - phosphoric, stronger than all other acids (low pK1) 2 - phthalic, 3 - glutaric, 4 - adipic, 5 - heptanedioic, 6 included in the studies, and these two acids sebacic, 7 - stearic. [Adapted, by permission, from substantially decrease PVC stability.38 Wypych G, Selected Properties of PVC Plastisols, Wroclaw University Press, Wroclaw, 1977.] When pK1 of acids approaches 4.3 (glutaric acid), acids become much weaker, and their influence on PVC degradation rapidly decreases to the extent that different relationship is formed. Note that most of these acids (all except stearic) are polyprotic acids, and thus, they have two constants characterizing their dissociation. The second constant, pK2, is very similar for dicarboxylic acids (adipic acid − 5.41, glutaric acid − Table 10.11.1. Thermal stability of PVC compo- 5.42, phthalic acid − 5.43, heptanedisitions containing various alcohols. [Data from oic acid − 5.58, and sebacic acid − Wypych G, Selected Properties of PVC Plasti- 5.59). The elimination of the second sols, Wroclaw University Press, Wroclaw, 1977.] alcohol rest has an unlikely similar influence as the liberation of the first Alcohol/rest Thermostability number A,% carboxylic group. In the case of phosXylene 50.8 phoric acid, there are three constants Isobutanol 50.1 involved: pK1 − 2.16, pK2 − 7.12, and pK3 − 12.32. Two groups have basic Octanol 55.9 character and may contribute to strong 2-ethylhexanol 56.4 influence on PVC degradation if it is C7-C9 alcohols 56.7 proven that degradation of plasticizer C9-C11 alcohols 57.1 may be so advanced (so far, there is no Decanol 57.1 information on the nature of products Isononanol 57.4 formed from the degradation of phosphate plasticizers). Control 60.7

10.11 Thermal degradation

271

It is well established in organic chemistry that acids increase rates of halogen elimination. There is still no agreement on the mechanism of thermal dehydrochlorination of PVC, but ionic mechanisms prevail in disputes. More detailed description is available in monographic sources,1,2 which suggest polarization of H−C and C−Cl bonds to form carbanion or carbonium ion. If such a course of the reaction is accepted, then the participation of acids is well explained by the mechanism of thermal degradation. Table 10.11.1 shows the influence of alcohol part of plasticizer degradation on plasticized PVC dehydrochlorination rate. Here thermal stability of films (PVC 100 phr, DOP 60 phr, and alcohol 2 phr) was also measured using kinetic determination of HCl evolution and expressed by thermostability number A.39-40 It is evident that alcohols of higher molecular weight (above six carbon atoms) have very little influence on PVC thermal degradation rate. Only volatile xylene and isobutanol increase degradation in comparable levels to some weakest acids.

10.11.4 LOSS OF PLASTICIZER FROM THE MATERIAL DUE TO CHEMICAL DECOMPOSITION REACTIONS AND EVAPORATION Numerous studies were conducted by thermogravimetry.6,11,13,17,20,21 Several aspects important for understanding thermal stability of PVC were addressed in these studies, including: • effect of plasticizer type and concentration • effect of heating rate • effect of polymer-plasticizer interaction • sequence of events in PVC thermal degradation The thermogravimetric analysis provides information on the loss of mass, which may be a result of degradation with volatilization of plasticizer component, plasticizer evaporation, or degradation and volatilization of any other component of the tested mixture (most likely polymer and stabilizer because test formulations are usually kept simple). Because of these different reasons for the mass loss, the results are difficult to interpret. In some studies reported here, evaporation loss of plasticizer was distinguished from the loss of degradation products by running two separate tests: one for pure plasticizer and the other for the entire composition. This may help to better understand the reasons for the mass loss, but it changes conditions because plasticizer degradation products affect the degradation rate of polymer, and polymer degradation products affect the degradation of plasticizers, as discussed in the previous sections of this chapter. There is not much one can do to improve results other than to apply a strict regime of testing. Thus, the results and conclusions should be viewed with these experimental restrictions in mind. Figure 10.11.4 shows that the temperatures to 50% loss of plasticizer tested alone and mixed with polymer are related to the boiling temperature of plasticizer.27 The temperature of 50% plasticizer loss from pure plasticizer is always slightly lower (e.g., 9oC for DBP and 2oC for DIDP) than temperature to 50% weight loss of plastisol. It is difficult to understand the reasons for the differences between various plasticizers, but it is quite possible that the presence of polymer (PVC) delays the mass loss. Considering that plastisols were prepared by mixing plasticizer and resin with no addition of a stabilizer, part of this mass loss must also come from the degradation of the polymer. Thus, delay in the loss of plasticizer is, in reality, even longer. Note that the reported studies were conducted

272

Effect of Plasticizers on Properties of Plasticized Materials

Figure 10.11.4. Temperature to 50% of weight loss during thermogravimetric experiment conducted for pure plasticizer and plasticizer mixed with PVC (plasticizer - 65 phr) vs. boiling temperature of plasticizer. [Data from Marcilla A; Beltran M, Polym. Deg. Stab., 53, No.2, 1996, p.261-8.

Figure 10.11.5. Rate of plasticizer loss from PVC formulation containing 50 phr plasticizer vs. molecular weight of plasticizer. [Data from Dedov A V, Bablyuk E B, Nazarov V G, Polym. Sci., Ser. B, 42, Nos.5-6, May-June 2000, p.138-9.]

under nitrogen. Therefore thermal oxidation is unlikely. The question is open for discussion why such a delay in plasticizer loss is observed? There are two possible answers: 1. plasticizer interaction with resin requires some additional energy to separate both before plasticizer can be evaporated 2. evaporation of any liquid is always slower when liquid is mixed with any solid material (interacting or not interacting) due to the dilution and tortuosity of pathways of escape. Considering that the differences between plasticizer loss and plastisol loss are very small compared with data variability (compare points at around 200oC departed from both lines by about 30oC and a relatively small distance between both lines (2-9oC)), the above question cannot be answered without bias. Studies of variable concentrations of plasticizer in the initial mixture and variable heating rates show that the times to 50% mass loss are fairly constant for different concentrations of plasticizer. The proportional increase in temperature to 50% loss is observed along with an increase in the heating rate.17 Figure 10.11.5 shows that the rate of stabilizer loss corresponds to the molecular weight of the plasticizer.11 Lower molecular weight plasticizers seem to have a steeper relationship than the less volatile plasticizers. Several theoretical models were used to determine the best method of data interpretation and prediction of the loss rate. It was found that the following relationship is useful for the analysis of data on the plasticizer loss: M -------τ = kτ d M0

[10.11.1]

10.11 Thermal degradation

where: Mτ M0 k τ d

273

plasticizer lost during time τ initial plasticizer content k rate of loss time constant (under experimental conditions d = 0.5).

The relationship between coefficient k and the molecular mass as given in Figure 10.11.5 is described by the following formula:11 log k = 1 − 0.0062M

[10.11.2]

where: M

molecular weight of plasticizer.

It has to be pointed out that the plasticizer loss occurs at any temperature, and it is substantial at temperatures well below the boiling point of plasticizer or conditions typically used in the thermogravimetric analysis. The processes leading to the loss of plasticizer can be accelerated by contact with other materials, which increases plasticizer diffusion to the surface. When plasticizer loss occurs, it seems to affect properties of plasticized material beyond predicted values of properties relative to the actual concentration of plasticizer.

Figure 10.11.6. Effect of plasticizer type and content on thermostability of PVC plasticized material containing: PVC 100 g, plasticizer − 0.03 to 0.06 moles. DOAz − dioctyl azelate, DOA − dioctyl adipate, DOP − dioctyl phthalate. [Adapted, by permission, from Wypych G, Selected Properties of PVC Plastisols, Wroclaw University Press, Wroclaw, 1977.]

Figure 10.11.7. Effect of plasticizer type and content on thermostability of PVC plasticized material containing: PVC 100 g, plasticizer - 0.03 to 0.06 moles. DBB − benzyl butyl phthalate, DBP − dibutyl phthalate, DPOP − diphenyl octyl phosphate, TCP − tricresyl phosphate. [Adapted, by permission, from Wypych G, Selected Properties of PVC Plastisols, Wroclaw University Press, Wroclaw, 1977.]

274

Effect of Plasticizers on Properties of Plasticized Materials

Figure 10.11.8. Thermostability number A from Figures 10.45 and 10.46 for 0.06 M plasticizer vs. dielectric constants of plasticizers.

Figure 10.11.9. Thermostability number A from Figures 10.45 and 10.46 for 0.06 M plasticizer vs. cohesion energy solubility parameter of Hansen’s scale of plasticizers.

10.11.5 EFFECT OF PLASTICIZERS ON THE THERMAL DEGRADATION OF MATERIAL Figures 10.11.6 and 10.11.7 show that the effect of plasticizer concentration increase cannot be described by a simple relationship. Some plasticizers (e.g., dioctyl azelate, dioctyl adipate, and dioctyl phthalate) increase the stability of PVC composition when their concentrations increase, and other plasticizers (e.g., benzyl butyl phthalate, dibutyl phthalate, diphenyl octyl phosphate, and tricresyl phosphate) decrease the stability of plasticized material when their concentrations increase. Both groups display linear relationships with good correlation coefficients. Comparing the two groups of plasticizers, one may postulate that the group, which Figure 10.11.10. Thermostability number A from Figincreases the stability of PVC contains less ures 10.45 and 10.46 for 0.06 M plasticizer vs. dissoluaggressive plasticizers than the group, tion temperature determined according to DIN 53408. [Data from Polymer Additives. Plasticizers, Bayer SPwhich decreases PVC stability. PMA 8013 E, 2000.] To better understand these data, the results of thermostability testing are compared with dielectric constant, ε, polar cohesion energy solubility parameter of Hansen’s

10.11 Thermal degradation

275

scale, δP, and solution temperature determined according to DIN 53408. The resultant plots are given in Figures 10.11.8, 10.11.9, and 10.11.10, respectively. In all three plots, good correlation was obtained. Figure 10.11.8 shows that the plastisol thermostability decreases with an increase in the dielectric constant of the plasticizer. Figure 10.11.9 confirms that the dielectric constant is a measure of solvent polarity. The increased polarity of plasticizer affects ionic polarization and increases the probability of dehydrochlorination. Figure 10.11.10 shows that plasticizers, which have better gelation abilities, also cause more degradation. The existence of two types of relationships (Figures 10.11.6 and 10.11.7) is thus a result of two competing influences: 1. diluting effect of plasticizer, which decreases the probability of dehydrochlorination 2. ionic polarization increasing the probability of HCl splitting off. Thermogravimetric analyses sometimes divert attention from the main problems. It was concluded in one study14 that “one of two reactions involved in the mechanism (of PVC degradation) is the evaporation of plasticizer, which influences the kinetics of other reaction, i.e., dehydrochlorination of PVC molecules”. It is true that from the point of view of stages of thermogravimetric analysis, this sequence may be correct, but in real situations, only a very small fraction of plasticizer is lost during processing, but material undergoes sufficient thermal degradation to postulate that processing history influences performance of the material in real applications. It is not necessarily a high rate of evaporation of plasticizer that makes a difference in material degradation but the loss of plasticizer is accelerated by temperatures encountered by materials outdoors on sunny days or in the car interior. These temperatures (70 to 110oC) cause acceleration of plasticizer loss7 and subsequent deterioration of material properties − some of them caused by differences in elastic behavior of surface and bulk. This difference in the performance of different layers of material may cause surface cracking, which makes the material even more vulnerable to degradative processes. Spectral analysis of volatile products shows that pure plasticizer evaporates before the thermal degradation of PVC is recorded.20 Kinetic models of PVC thermal decomposition for interpretation of thermogravimetric data were proposed and verified by experimental data.26,32 The stability of PVC plastisols used in protective coatings was evaluated by theoretical calculation of energies of attraction and repulsion in the region of solvation-adsorption layers.34 Poly(vinyl butyral) without plasticizer has begun to degrade at 100oC in contrast to plasticized PVB, which required a temperature of 200oC to produce similar progress of degradation.33 Chain scission reaction was a prevailing mode of thermal degradation reactions. Polyaniline thermal stability was increased by plasticization with oligoesters of phosphoric acid.15 Plasticization of polyimide decreased thermal stability of materials with dimethyl phthalate decreasing initial degradation temperature substantially more than diethylene glycol dibenzoate.16 Plasticizer-induced stabilization of polyvinylchloride was postulated.10,13,29 This is based on the observation that the rate of PVC dehydrochlorination in 2% solution can be correlated to the basicity of solvents or plasticizers. When the concentration of PVC is increased above 2%, solvents/plasticizers interact with PVC preventing HCl formation. In review publication, it is suggested that studies of degradation in solution may be useful to

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Effect of Plasticizers on Properties of Plasticized Materials

understand degradative processes on a molecular level.12 The activation energy of plasticized material degradation decreased with an increase in plasticizer polarity, which is in agreement with the above-reported findings. Di(isononyl) cyclohexane-1,2-dicarboxylate (DINCH) was used as a plasticizer for poly(lactic acid), and the effects of DINCH and tributyl citrate ester, TBC, on the morphology, mechanical and thermal properties, and durability of PLA were compared.41 PLA/DINCH mixtures had constant glass transition temperature, whereas TCB was able to effectively reduce glass transition temperature.40 Sterilization resistance of PVC plasticized materials containing citrate plasticizers and DINCH was comparable to phthalates.44 Glycidylethylhexyl phthalate improved the heat resistance of PVC films because the epoxy groups could react with HCl, which was generated during the thermal decomposition of PVC, similar to epoxidized soybean oil.42 Epoxidized soybean oil was preventing PVC discoloration unless thermal stabilizers were added, which interfered with color retention.43 Epoxidized plasticizers produced from several oils, such as sunflower, linseed, Jatropha curcas, and soybean oil, were found to contribute to the increased thermal stability of PVC.45 The thermal stability of cellulose esters was improved when plasticizers having boiling temperatures above 370oC were used.46 These high boiling plasticizers are phthalates and trimellitates of high boiling alcohols.46 Cellulose acetate films plasticized with glycerol showed low plasticizer exudation with an approximate value of 2.3% for films plasticized with 7.2 mol.47 Films plasticized with glycerol and triethyl citrate were stable at high temperatures.47 Therefore, both plasticizers can be added to polymer matrices to develop food packaging.47

References 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23

Wypych G, Polyvinylchloride Degradation, Elsevier, Amsterdam, 1985. Wypych G, Polyvinylchloride Stabilization, Elsevier, Amsterdam, 1986. Weng D, Andries J, Suanders K, Macaluso J, Brookman R, Antec 2000.Conference proceedings, Orlando, Fl., 7th-11th May, 2000, 3352-3356. Morgan H, Foot P J S, Brooks N W, J. Mater. Sci., 36, No.22, 15th Nov. 2001, p.5369-77. Schoonover J R, Zhang S L, Bridgewater J S, Havrilla G J, Fletcher M A, Lightfoot J M, Appl. Spectroscopy, 55, No.7, July 2001, p.927-34. Farahat M S, Macromol. Mater. Eng., 286, No.2, 28th Feb.2001, p.88-93. Monney L, Jamois-Tasserie M, Dubois C, Villa F, Lallet P, Renaud C, Polym. Deg. Stab., 72, No.3, 2001, p.459-68. Jimenez A, Torre L, Kenny J M, Polym. Deg. Stab., 73, No.3, 2001, p.447-53. Djidjelli, Sadoun T, Benachour D, J. Appl. Polym. Sci., 78, No.3, 17th Oct.2000 p.685-91. Kulish E I, Kolesov S V, Minsker K S, Polym. Sci., Ser. B, 42, Nos.5-6, May-June 2000, p.124-6. Dedov A V, Bablyuk E B, Nazarov V G, Polym. Sci., Ser. B, 42, Nos.5-6, May-June 2000, p.138-9. Zaikov G E, Gumargalieva K Z, Pokholok T V, Moiseev Y V, Zaikov V G, Polym. Plast. Technol. Eng., 39, No.3, 2000, p.567-650. Ishiaku U S; Lim F S; Ishak Z A; Senake Perera M C, Polym. Plast. Technol. Eng., 38, No.5, 1999, p.939-45. Jimenez A; Lopez J; Torre L; Kenny J M, J. Appl. Polym. Sci., 73, No.6, 8th Aug.1999, p.1069-79. Pielichowski J; Pielichowski K, J. Thermal Analysis Calorimetry, 53, No.2, 1998, p.633-8. Totu E; Segal E; Covington A K, J. Thermal Analysis Calorimetry, 52, No.2, 1998, p.383-91. Marcilla A; Beltran M, Polym. Deg. Stab., 60, No.1, 1998, p.1-10. Baoyan Zhang; Huimin Tan, Eur. Polym. J., 34, Nos.3-4, March/April 1998, p.571-5. Ishiaku U S; Shaharum A; Ismail H; Mohd.Ishak Z A, Polym. Intl., 45, No.1, Jan.1998, p.83-91. Beltran M; Marcilla A, Eur. Polym. J., 33, No.8, Aug.1997, p.1271-80. Marcilla A; Beltran M, Polym. Deg. Stab., 57, No.1, 1997, p.101-7. Marcilla A; Garcia J C; Beltran M, Eur. Polym. J., 33, No.5, May 1997, p.753-9. Han W H; McKenna G B, Antec 97. Volume II. Conf. proc., SPE, Toronto, 27th April-2nd May 1997,

10.11 Thermal degradation

24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47

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p.1539-45. Ishiaku U S; Shaharum A; Ishak A Z M; Ismail H, Kautchuk Gummi Kunststoffe, 50, No.4, April 1997, p.292-8. van Soest J J G; Knooren N, J. Appl. Polym. Sci., 64, No.7, 16th May 1997, p.1411-22. Beltran M; Marcilla A, Polym. Deg. Stab., 55, No.1, 1997, p.73-87. Marcilla A; Beltran M, Polym. Deg. Stab., 53, No.2, 1996, p.261-8. Jimenez A; Berenguer V; Lopez J; Vilaplana J, J. Appl. Polym. Sci., 60, No.12, 20th June 1996, p.2041-8. Minsker K S, Intl. J. Polym. Mater., 33, Nos.3-4, 1996, p.189-97. Voskanyan P S; Sarkisyan M B; Mkhitaryan M A; Badalyan V E, Intl. Polym. Sci. Technol., 22, No.10, 1995, p.T/1-3. Xi Xu; Shaoyun Guo, Polym. Plast. Technol. Eng., 34, No.5, 1995, p.679-88. Marcilla A; Beltran M, J. Vinyl Additive Technol., 1, No.1, March 1995, p.15-20. El-Din N M S; Sabaa M W, Polym. Deg. Stab., 47, No.2, 1995, p.283-8. Makarewicz E, Intl. Polym. Sci. Technol., 21, No.8, 1994, p.T/89-94. Wilson A S, Plasticizers − Selection, Application, and Implications, Rapra, Shawbury, 1997. Sears J K, Darby J R, The Technology of Plasticizers, John Wiley & Sons, New York, 1982. Barshtein R S, Plastmassy, 12, 13-15, 1968. Wypych G, Selected Properties of PVC Plastisols, Wroclaw University Press, Wroclaw, 1977. Wypych G, Analusis, 3, 443, 1975. Prochaska K, Wypych G, Analusis, 3, 448, 1975. Wang R, Wan C, Wang S, Zhang Y, Polym. Eng. Sci., 49, 2414-20, 2009. Kim S-W, Kim J-G, Choi J-I, Jeon I-R, Seo K-H, J. Appl. Polym. Sci., 96, 1347-56, 2005. Karmalm P, Hjertberg T, Jansson A, Dahl, Polym. Deg. Stab., 94, 2275-81, 2009. Burgos N, Jimenez A, Polym. Deg. Stab., 94, 1473-78, 2009. Barki A C, Ramirez de Arellano Aburto N, Torres Arenas A, Javier Cruz Gomez M, US Patent Application Publication US 2010/0010127, Resinas y Materiales, Jan. 14, 2010. Godfrey D A, US Patent 8,007,918, Eastman, Aug. 30, 2011. Côcco Teixeira S, Resende Assis Silva R, Velosode Oliveira T, Stringheta PC, Moacir Ribeiro Pinto MR, de Fátima Ferreira Soares N, Food Bioscience, 42, 101202, 2021.

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10.12 EFFECT OF UV AND IONIZING RADIATION ON PLASTICIZED MATERIALS Environmental exposures add to the temperature effect of additional strains, such as high energy radiation, moisture, and catalytic quantities of acids. This combination is certainly more degrading than the short-term use of thermal energy during processing. It is also more difficult to study because of the numerous potential influences.1-22 The thermal degradation studies have shown that the temperatures available at the environmental conditions (~100oC) accelerate plasticizer diffusion. Thus, plasticizer loss may be one of the most essential results of materials weathering. Figure 10.12.1 shows that film surfaces have a deficiency of plasticizer after outdoor exposure. Similar plasticizer distribution was determined for samples, which were immersed in hot water. This prompted authors to suggest that plasticizer removal outdoors was caused by condensation and rain.8 Studies of PVC electrical cable recycling showed that only 2 wt% plasticizer was lost during 18 years of service.5 Polymer was suitable for recycling. An only a small fraction of exhausted thermal stabilizer required replacement. PVC cables and sheating were used indoors for up to 34 years.6 Tensile strength and elongation showed very little change. Simulation studies were performed indicating that changes, which occur during four weeks in an 80oC oven, are equivalent to cable performance for 44 years.6 FTIR studies of 6 to 14 years old PVC roofing materials show some increase in absorption of the C− Cl band, which was interpreted as being caused by the plasticizer loss.9 During 30 years of use, aircraft wires have lost 58% DOP. Outdoor exposures of PVC films containing DOS in Yakutsk and Batumi, Russia, led to a 57% loss of plasticizer after two years of exposure.10

Figure 10.12.1. Depth profile of dioctyl phthalate in PVC film exposed for two years outdoors. Adapted, by permission, from A. Murase, M. Sugiura, T. Araga, Polym. Deg. Stab., 43, 415 (1994).]

Figure 10.12.2. Elongation of PVC plasticized with two different contents of DOS vs. exposure time in Yakutsk, Russia. [Data from Gumargalieva K Z; Ivanov V B; Zaikov G E; Moiseev J V; Pokholok T V, Polym. Deg. Stab., 52, No.1, 1996, p.73-9.]

10.12 Effect of UV and ionizing radiation on plasticized materials

279

PVC objects of art or commercial products exposed in museums are known to suffer from plasticizer loss.21,23 This is demonstrated by the surface cracking of automotive seat covers made from artificial leather or the formation of white deposits on the surface of PVC objects or an increase in the surface tack. The white deposits were found to be formed from phthalic acid − a product of plasticizer degradation.23 Plasticized PVC containing 50 wt% dioctyl phthalate showed severe loss of tensile strength and elongation.7 Degradation rate depended on stabilization system, which in this case used dibutyltin dilaurate − stabilizer of relatively low reactivity. Figure 10.12.2 shows changes in elongation of plastic films exposed in Yakutsk.20 Elongation deteriorated rapidly, most likely due to the type of plasticizer used. Tensile strength initially decreased to increase after one-year of exposure, which suggested that crosslinking reactions were favored. Plasticizers and their different concentrations do not perform in the same manner. More volatile plasticizers yield films with a shorter outdoor life expectancy. Clear films, including UV absorber, plasticized at 50 phr were exposed in Florida. Four general-purpose plasticizers were studied: diisodecyl phthalate, DIDP, diisononyl phthalate, DINP, di(2-ethylhexyl) phthalate, DOP, and heptyl nonyl undecyl phthalate, HNUP. Less branched and linear phthalate plasticizers (DOP and HNUP) performed very well for 36 months, whereas samples with two highly branched plasticizers (DIDP and DINP) were brown after 24 months of exposure. Figure 10.12.3 shows that the addition of plasticizer decreased the dehydrochlorination rate of PVC. Crosslinking rate was reduced by the presence of plasticizers. Also, carbonyl group formation was slower in the presence of plasticizer.17 Comparison of data presented by the same authors for the effect of radiation above17 and below22 290 nm

Figure 10.12.3. Cl index of neat and plasticized PVC with diisodecyl phthalate vs. exposure time to filtered mercury lamp radiation above 290 nm. [Data from Balabanovich A I; Denizligil S; Schnabel W, J. Vinyl Additive Technol., 3, No.1, March 1997, p.42-52.]

Figure 10.12.4. Dehydrochlorination rate of PVC in dioctyl phthalate solution at 212oC vs. PVC concentration. [Adapted, by permission, from G E Zaikov, K Z Gumargalieva, T V Pokholok, Y V Moiseev, V G Zaikov, Polym. Plast. Technol. Eng., 39, No.3, 2000, 567-650.]

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Effect of Plasticizers on Properties of Plasticized Materials

stresses the importance of wavelength selection that affects results obtained. When studies were conducted with an unfiltered mercury lamp, the presence of phthalates increased carbonyl group formation. Figure 10.12.4 shows that the rate of PVC dehydrochlorination increases with PVC concentration increasing.4 Similar should be the effect of plasticizer (interacting or non-interacting) added in excess to reduce viscosity, lower mechanical strength, increase elongation, etc. Figure 10.12.5 shows that similar is the effect of plasticizer concentration on γ-irradiation − Figure 10.12.5. Change in yellowness index of PVC increase in plasticizer concentration plasticized with variable amount of plasticizer exposed 19 to 5 Mrads of γ-radiation. [Data from Luther D W; Lin- decreases sample yellowing. Leaching of sky L A, J. Vinyl Additive Technol., 2, No.3, Sept.1996, products of γ-irradiation is controlled by p.190-2.] Fickean diffusion.25 Subsequent crosslinking and grafting reactions diminish diffusion coefficient.25 The main organic leaching products are phthalic ions formed by hydrolysis of phthalic esters in the alkaline leaching solution.25 Migration of DOP decreased with a dose of radiation increased.28 Studies of the effect of plasticizers on the PVC film stability were conducted using samples cast from tetrahydrofuran, THF.18 Samples, which contained THF, degraded more rapidly, which is well known in the weathering studies.24 THF exposed to UV radiation forms radicals, which accelerate thermal degradation of PVC. Based on this example, it should also be noted that plasticizer performance in any other aspect than weathering is not likely affected by admixtures, but admixtures may be very critical for the outdoor performance of many products. It is thus important to check the source and quality of the plasticizer. The sulfonic acid ester plasticizer is broken down to produce sulfonic acid and sulfuric acid fragments, which are sufficiently acidic to catalyze TiO2 when plasticizer loadings are >50%.26 The carboxylic acid fragments from phthalates seem incapable of catalysis even at the highest levels used in the present work (70%).26 Di-(2-propylheptyl) phthalate had much better retention than diisodecyl phthalate when exposed to outdoor or artificial weathering conditions.27 Oleochemical plasticizers derived from natural oils protect PVC compounds from the effect of UV radiation.29 Cellulose acetate has been plasticized using eco-friendly plasticizers such as triacetin, tripropionin, triethyl citrate, tributyl citrate, tributyl 2-acetyl citrate, and poly(ethylene glycol) of low molecular weight.30 The plasticization of cellulose acetate triggered an increase of the weight loss between 50 and 90%.30 The low molecular weight plasticizers were shown to be more degrading.30

10.12 Effect of UV and ionizing radiation on plasticized materials

281

Co-ZnS quantum dots were synthesized by the water phase co-precipitation method.31 The inequivalent lattice-doping of Co for Zn led to the generation of surface sulfur vacancies, and thus surface modulation of the material to form an electronic nonequilibrium surface.31 Plasticizer micropollutants were completely degraded within only tens of seconds in the Co-ZnS quantum dots/peroxymonosulfate system due to this type of surface modulation.31 The interfacial reaction mechanism revealed that pollutants tend to be adsorbed on the cobalt metal sites as electron donors, where the internal electrons of pollutants are captured by the metal species and transferred to the surface of sulfur vacancies.31 Peroxymonosulfate adsorbed on the surface sulfur vacancies was reduced to radicals by capturing electrons, achieving effective electron recovery.31 Dissolved oxygen molecules were also easily attracted to catalyst defects and were reduced to O2•−, further promoting the degradation of pollutants.31

References 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

Bowley H J, Gerrard D L, Williams K J P, Biggin I S, J. Vinyl Technol., 8, 176, 1986. Thominette F, Metzger G, Dalle B, and Verdu J, Eur. Polym. J., 27, 55, 1991. US Patent 6,120,869. Zaikov G E, Gumargalieva K Z, Pokholok T V, Moiseev Y V, Zaikov V G, Polym. Plast. Technol. Eng., 39, No.3, 2000, 567-650. Brebu M, Vasile C, Antonie S R, Chiriac M, Precup M, Yang J, Roy C, Polym. Deg. Stab., 67, No.2, Feb.2000, 209-21. Jakubowicz I, Yarahmadi N, Gevert T, Polym. Deg. Stab., 66, No.3, 1999, 415-21. Guillermo Martinez J, Oliverio S R F, Santiago S L, Eduardo R V, Allen NS, Polym. Deg. Stab., 54, No.1, 1996, 49-55. Murase A, Sugiura M, Araga T, Polym. Deg. Stab., 43, 415 (1994). Paroli R M; Delgado A H, Polym. Mater. Sci. Eng., 75, p.69-70, 1997. Margolin A L, Shlyapintokh V Ya, Intern. J. Polym. Mater., 47, 443-456, 2000. Yagoubi N; Baillet A; Legendre B; Rabaron A; Ferrier D, J. Appl. Polym. Sci., 54, No.8, 21st Nov.1994, p.1043-8. Caspar J V; Khudyakov I V; Turro N J; Weed G C, Macromolecules, 28, No.2, 16th Jan.1995, p.636-41. Sastry P K; Satyanarayana D; Rao D V M, J. Appl. Polym. Sci., 70, No.11, 12th Dec.1998, p.2251-7. Bohnert T; Izadi R; Pitman S; Stanhope B, Antec '98. Volume III. Conf. proc., SPE, Atlanta, Ga., 26th-30th April 1998, p.3284-90. Zuchowska D; Steller R; Meissner W, Polym. Deg. Stab., 60, Nos 2-3, 1998, p.471-80. Funke U; Bergthaller W; Lindhauer M G, Polym. Deg. Stab., 59, Nos 1-3, 1998, p.293-6. Balabanovich A I; Denizligil S; Schnabel W, J. Vinyl Additive Technol., 3, No.1, March 1997, p.42-52. Hollande S; Laurent J L, Polym. Deg. Stab., 55, No.2, Feb.1997, p.141-5. Luther D W; Linsky L A, J. Vinyl Additive Technol., 2, No.3, Sept.1996, p.190-2. Gumargalieva K Z; Ivanov V B; Zaikov G E; Moiseev J V; Pokholok T V, Polym. Deg. Stab., 52, No.1, 1996, p.73-9. Katz S, Mater. World, 3, No.8, Aug. 1995, p.377-8. Denizligil S; Schnabel W, Angew. Makromol. Chem., 229, July 1995, p.73-92. Shashoua Y R, Inhibiting the Deterioration of Plasticized Poly(vinyl chloride) - Museum Perspective, PhD Thesis, Technical University of Denmark, 2001. Wypych G, Handbook of Materials Weathering, 6th Edition, ChemTec Publishing, Toronto, 2018. Colombani J, Herbette G, Rossi C, Joussot-Dubien C, Labed V, Gilardi T, J. Appl. Polym. Sci., 112, 1372-77, 2009. Martin G, Robinson A J, Worsley D, Mater. Sci. Technol., 24, 4, 427-34, 2008. Kozlowski R R, Storzum U, J. Vinyl Addit. Technol., 11, 155-59, 2005. Ito R, Miura N, Ushiro M, Kawaguchi M, Nakamura H, Iguchi H, Ogino J-i, Oishi M, Wakui N, Iwasaki Y, Saito K, Nakazawa H, Int. J. Pharm., 376, 213-18, 2009. Barki A C, Ramires de Arellano Aburto N, Torres Arenas A, Javier Cruz Gomez M, US Patent Application Publication US 2010/0010127, Resinas y Materiales, Jun. 14, 2010. Quintana, R; Persenaire, O; Lemmouchi, Y; Sampson, J; Martin, S; Bobbaud, L; Dubois, P, Polym. Deg. Stab., 98, 9, 1556-62, 2013. Gu Y, Gao T, Zhang F, Lu C, Cao W, Fu Z, Hu C, Lyu L, Chinese Chem. Lett., in press, 2021.

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Effect of Plasticizers on Properties of Plasticized Materials

10.13 HYDROLYSIS Plasticizer architecture can be used to adjust polylactide hydrolysis.1 The effect is based on the hydrophilic/hydrophobic properties of plasticizers.1 Hydrophilic plasticizers increase water uptake and thus increase hydrolysis rate.1 For example, hydrophobic acetyl tributyl citrate decreases the hydrolysis rate of polylactide.2 Poly(ε-caprolactone), used as a plasticizer in polylactide, accelerated its hydrolytic degradation.3 The increase in the degree of crystallinity during hydrolysis suggests that degradation of polylactide occurs preferably in the amorphous phase.3 Potato peel was hydrolyzed in a mild acid medium, gelatinized in different amounts of one of two plasticizers, glycerol or polyglycerol, and films were obtained by casting followed by compression molding.4 The results indicate that polyglycerol-plasticized films presented higher thermal resistance and reduced water vapor permeability than the glycerol-plasticized potato peel films.4

References 1 2 3 4

Andersson S R, Hakkarainen M, Albertsson A-C, Biomolecules, 11, 3617-23, 2010. Hoeglund A, Hakkarainen M, Albertsson A-C, Biomolecules 11, 277-83, 2010. Olewnik-Kruszkowska, E; Kasperska, P; Koter, I, Reactive Functional Polymers, in press, 2016. Merino D, Paul UC, Athanassiou A, Food Packaging Shelf Life, 29, 100707, 2021.

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283

10.14 BIODEGRADATION IN THE PRESENCE OF PLASTICIZERS Plasticizers affect several important properties related to the biodegradation rate of synthetic polymers:1-14 • composition − C, H, P, O supply nutrients necessary for the growth of many microorganisms • structural similarity − functional groups found in plasticizers, such as ester, epoxy, etc., are more likely to be degraded by the existing microorganisms • molecular weight − increasing molecular weight decreases biodegradation rate. In most cases, microorganisms do not degrade synthetic materials, which have a molecular weight higher than 20,000 daltons • mobility of structural elements − increases the probability of biodegradation by facilitating the formation of complexes of enzyme-substrate, which require a certain configuration. Plasticizers increase the probability of such changes by providing increased mobility to the structural elements of polymer chains • functional groups − hydrophilic groups increase the probability of enzymatic reactions because they either increase polymer solubility or at least attract water (water is needed in most biodegradation reactions) • crystallinity − amorphous regions are preferentially degraded. Crystalline material can only be degraded at a lamellar surface. Enzymes cannot easily penetrate the interior of densely packed crystallites. Plasticizers reduce the crystallinity of polymers • structure porosity − increased surface area increases the probability of contact and concentration of enzyme-substrate complexes, which are rate-controlling. Plasticizer loss increases the porosity of materials • contact type − the best conditions exist when the material is in a liquid state • concentration of substrate and product − enzymes work best in dilute solutions. Table 10.14.1. Biological resistance of selected unplasticized polymers. [Data from Zyska B, Microbiologiczna Korozja Materialow, WNT, Warsaw, 1977.] Polymer

Comments

Resistance

Epoxide resin

affected by Aspergillus and Pseudomonas

Phenolic resin

affected by Aspergillus and Penicillium

1.04 0.33

Polyacrylonitrile

affected by Aspergillus

Polyamide

affected by Aspergillus, Chaetomium, Nigrospora, Penicillium

Polycarbonate

affected by Alternaria, Aspergillus, Chaetomium, Penicillium, and Trichoderma

1.39

Polyester

affected by Penicillium

0.20

Polyethylene

affected by Deauteromycotina, Penicillium, and Aspergillus

0.34

Polymethylmethacrylate affected by Alternaria, Aspergillus, Dactylium, Peacilomyces, Penicillium, and Trichoderma

1.44

Polystyrene

0.54

resistant

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Effect of Plasticizers on Properties of Plasticized Materials

Table 10.14.1. Biological resistance of selected unplasticized polymers. [Data from Zyska B, Microbiologiczna Korozja Materialow, WNT, Warsaw, 1977.] Polymer

Comments

Polyurethane

affected by Aspergillus, Stemphylium, Pseudomonas, Cladosporium, Haligena, and Zalerion

Polyvinylchloride

polymer resistant but some polymerization additives are not

Resistance

0.51

Only main groups of microorganisms are listed in comments based on the documented findings. Resistance scale: 0-0.99 − resistant material, 1-1.99 − material affected by microorganism growth, above 2 − non-resistant material (the resistance rating is based on averages from the available data)

The data in the table show that polymers in their pure forms are mostly affected by biological growth. This becomes even more complicated when materials are processed in their full formulations containing additives supporting biological life. Epoxidized soybean oil and low-temperature plasticizers (adipates, azelates, and sebacates) are mostly affected by various microorganisms. Phthalates are more resistant than low-temperature plasticizers, but they also support the growth of microorganisms and provide nutrients for their growth. The most resistant are aryl phosphates.1 The following are the most likely groups of microorganisms, which make use of plasticizers: Aspergillus, Chaetomium, Cladosporium, Penicillium, Pullularia, and Trichoderma. In addition to the loss of properties such as weight, mechanical performance, biological growth causes discoloration of material forming spots of different colors (e.g., Aspergillus versicolor − red, Cheatomium alba-arenulium − gray to black, Dactylium fusarioides − pink to red, Epicoccum nigrum − pink to orange, various strains of Penicillium − yellow, pink, green, and red).1 Plasticized PVC was subjected to elevated temperature and humidity (29oC and 100% RH) with and without growth of Aspergillus niger for 12 months. The original concentration of dialkyl phthalate was 27.2%, and it was reduced to 25.8% by the effect of temperature and humidity and to 20.4% by additional action of fungus. The data analysis shows that quantitative loss of plasticizer by any of the two processes depends on the diffusion coefficient of plasticizer. The role of microorganism is similar to extracting medium, which increases the process of diffusion by changing the concentration of plasticizer on the material surface.7,9 A plasticizer was developed that is resistant to microbial growth and, as such suitable for application in water-based acrylic caulks.11 The plasticizer is based on a combination of monobenzoate and dibenzoate plasticizers, which have better fungal resistance. Diethyl phthalate used as a plasticizer in cellulose acetate films was found to be completely degraded in 4 weeks of composting degradation.12 Citrate esters used as a plasticizer in cellulose acetate improved properties and processing characteristics but also dramatically increased its biodegradability.14 These two examples show that plasticizers can also be effectively used in biodegradable materials. Polylactide can be internally plasticized by copolymerization with lactic acid and ethylene oxide.2 Low molecular weight additives increase enzymatic degradation of poly(3-hydroxybutyrate), which is by itself also biodegradable.3 Addition of oils to polyethylene-starch blends increases their biodegradation rates.8 Addition of plasticizer to

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285

highly crystalline polymer reduced its crystallinity and subsequently increased its biodegradation rate.13 Activated vermiculite was found to be a suitable solid matrix for conducting biodegradability testing.5 Vermiculite by itself does not affect biological growth but can be activated to perform tasks typically associated with mature compost, which is a very complex, difficult to standardize biological mixture. Diisononyl phthalate was efficiently degraded by Sphinogobium chungbukense.15 Products of degradation included monoisononyl phthalate and phthalic acid before plasticizer degraded further.15 Pseudomonas putida, Staphylococcus epidermis, and Micrococcus sp. were efficient in the degradation of polyvinylalcohol films.16 Their mixture degraded film within 250 h of exposure.16 The removal of DOP in the slurry-phase reactor achieved the percentage of 99% in 49 days, with biodegradation following the first-order kinetic model with a biodegradation coefficient of 0.127 day-1. In simulation experiments of colonization in space applications, bacterial biofilms formed readily on the surfaces of materials at a wide range of temperatures and relative humidities. The biofilm population was dominated by Pseudomonas aeruginosa, Ochrobactrum anthropi, Alcaligenes denitrificans, Xanthomonas maltophila, and Vibrio harveyi. Subsequently, degradation of polymeric materials was mostly a result of both fungal and bacterial colonization in sequence, and fungi may have advantages in the early phase of surface colonization over bacteria, especially on relatively resistant polymeric materials. The hydrophobicity of the cell surface was shown to be a factor in plasticizer degradation. The primary carbon source could be either water-soluble or hydrophobic, and a hydrophobic substrate led to cell surface that attracted plasticizer and facilitated degradation. The most hydrophobic plasticizer, DOP, was particularly sensitive to this effect. The plasticizers di-2-ethylhexyl phthalate and di-2-ethylhexyl adipate are ubiquitous in the environment and undergo partial biodegradation in the presence of soil microorganisms such as Rhodococcus rhodochrous with 2-ethylhexanal in gas phase emissions. Two strains of the genus Rhodococcus were found able to utilize Mesamoll as the sole source of carbon and energy. Growth experiments along with enzymatic measurements indicated that both strains utilized phenol that was released from alkylsulfonic acid phenyl ester − probably by enzymatic hydrolysis catalyzed by esterases − via the ortho-pathway. Mycobacterium sp. readily degraded DOP to two major products, determined by gas chromatography/mass spectrometry, such as 2-ethylhexanol and 1,2-benzenedicarboxylic acid. Biodegradable plasticizers, such as succinates and maleates with linear side chains of four to eight carbons performed as well or better, in several of the mechanical tests, as commercial plasticizers such as DEHP and Hexamoll® DINCH.23 Poly(lactic acid) was plasticized with dibutyl esters of maleic or fumaric acids.24 The choice of plasticizer was motivated by the biodegradability of maleic and fumaric esters and their efficiency as green plasticizers.24 Dibutyl fumarate (trans) more efficiently plasticizes PLA than dibutyl maleate (cis).24 Better plasticization of dibutyl fumarate was attributed to the end-to-end distance of plasticizer molecules.24 The intramolecular interactions induced twisted conformation for the cis-isomer, while, on the trans-isomer, the

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Effect of Plasticizers on Properties of Plasticized Materials

weak intramolecular hydrogen bonds contributed to the planar conformation of the central fragment of the molecule.24 As a result, the end-to-end distance for the dibutyl fumarate molecule was 15.8 Å, while that of the dibutyl maleate molecule was 9.7 Å.24 This suggests that dibutyl fumarate can more efficiently inhibit polymer-polymer interactions as a consequence of the extensiveness of hindrance provided by butyl side groups.24 Monographic source contains comprehensive information on biodegradation, biodeterioration, and biostabilization of polymers and manufactured products.25

References 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25

Zyska B, Microbiologiczna Korozja Materialow, WNT, Warsaw, 1977. Bechtold K; Hillmyer M A; Tolman W B, Macromolecules, 34, No.25, 4th Dec.2001, p.8641-8. Yoshie N, Nakasato K, Fujiwara M, Kasuya K, Abe H, Doi Y, Inoue Y, Polymer, 41, 3227-3234, 2000. Mura C; Yarwood J; Swart R; Hodge D, Polymer, 41, No.24, 2000, p.8659-71. Bellia G; Tosin M; Floridi G; Degli-Innocenti F, Polym. Deg. Stab., 66, No.1, 1999, p.65-79. Gumargilieva K Z; Zaikov G E; Semenov S A; Zhdanova O A, Polym. Sci. Ser. A, 40, No.10, Oct.1998, p.948-9. Gumargalieva K Z; Zaikov G E; Semenov S A; Zhdanova O A, Polym. Deg. Stab., 63, No.1, 1999, p.111-2. Sastry P K; Satyanarayana D; Rao D V M, J. Appl. Polym. Sci., 70, No.11, 12th Dec.1998, p.2251-7. Zaikov G E; Gumargalieva K Z; Semenov S A; Zhdanova O A, Intl. Polym. Sci. Technol., 25, No.2, 1998, p.T/72-4. Funke U; Bergthaller W; Lindhauer M G, Polym. Deg. Stab., 59, Nos 1-3, 1998, p.293-6. US Patent 5,676,742. Jiang L; Hinrichsen G, Angew. Makromol. Chem., 253, Dec.1997, p.193-200. US Patent 5,516,825. Ghiya V P; Dave V; Gross R A; McCarthy S P, J. Macromol. Sci. A, A33, No.5, 627-38, 1996. Park J-M, Jeon M, Lim E-S, Um H-j, Kim Y-C, Min J, Kim Y-H, Curr. Microbiol., 57, 515-18, 2008. Sedlarik V, Saha N, Kuritka I, Saha P, Int. J. Polym. Anal. Charact., 11, 253-70, 2006. de Moura Carrara S M C, Morita D M, Boscov M E G, J. Harardous Mater., 197, 40-48, 2011. Gu J-D, Int. Biodet. Biodeg., 59, 170-79, 2007. Nalli S, Cooper D G, Nicell J A, Chemosphere 65, 1510-17, 2006. Nalli S, Cooper D G, Nicell J A, Sci. Total. Environ., 366, 286-94, 2006. Hintner J-P, Fortnagel P, Franke S, Francke W, Schmidt S, Res. Microbiol., 156, 656-62, 2005. Nakamiya K, Hashimoto S, Ito H, Edmonds J S, Yasuhara A, Morita M, J. Biosci. Bioeng., 99, 2, 115-19, 2005. Erythropel, H C; Shipley, S; Bormann, A; Nicell, J A; Maric, M; Leask, R L, Polymer, 89, 18-27, 2016. Llanes LC, Clasen SH, Pires ATN, Gross IP, Eur. Polym. J., 142, 110112, 2021. Falkiewicz-Dulik, M; Janda, K; Wypych, G, Handbook of Biodegradation, Biodeterioration, and Biostabilization, 2nd Ed., ChemTec Publishing, Toronto, 2015.

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10.15 CRYSTALLIZATION, STRUCTURE, AND ORIENTATION OF MACROMOLECULES Several important properties, which determine the structure of plasticized materials, are involved in this discussion including:1-25 • effect of plasticizers on chain mobility and free volume • place of residence of plasticizers • effect of plasticizers on crystallinity • effect of conditions (time-temperature) on crystallization • structural elements of polymer involved in the interaction • microstructure and elements of crystalline phase Two processes may potentially take place in the presence of plasticizers: increased mobility may induce crystallization, or solvating power of plasticizer may affect crystalline phase or interfere with crystallization. Before these two potential results are discussed, the effect of plasticizers on chain mobility is reviewed. Figure 10.15.1 shows that the glass transition temperature of plasticized PVC is a linear function of plasticizer concentration. Figure 10.15.2 shows that introduction of a plasticizer increases a free volume. Figure 10.15.3 shows that the free volume linearly increases in plasticized polyethylene oxide.4 These three graphs are characteristic of the main functions of plasticizers, which are to make polymers more elastic and increase their tolerance to lowering the temperature. In fact, the addition of plasticizer and temperature increase have a very similar effects on the resultant flexibility and mobility of the chain (plasticization and plastification, respectively). The linear-PLLA rich blends, small amounts of cyclic-PLLA (i.e., 5 or 10 wt%) increase nucleation density, nucleation rate, spherulitic growth rate, and overall crystalli-

Figure 10.15.1. Effect of tricresyl phosphate concentration on glass transition temperature of PVC. [Data from Borek J; Osoba W, J. Polym. Sci.: Polym. Phys. Ed., 36, No.11, Aug.1998, p.1839-45.]

Figure 10.15.2. Effect of tricresyl phosphate concentration on free volume in PVC. [Data from Borek J; Osoba W, J. Polym. Sci.: Polym. Phys. Ed., 36, No.11, Aug.1998, p.1839-45.]

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Effect of Plasticizers on Properties of Plasticized Materials

zation rate, when compared with neat linear-PLLA, due to a synergistic effect (i.e., nucleation plus plasticization).26 In contrast, the opposite effect was found in the cyclic-PLLA rich blends (Figure 10.15.4).26 The addition of small amounts of linear-PLLA to a matrix of cyclic-PLLA chains caused a decrease in the nucleation density due to threading effects between cyclic and linear chains.26 The linear-PLLA only acts as a plasticizer for the PLA matrix, whereas cyclic-PLLA has a synergistic effect in accelerating the crystallization of PLA that goes beyond simple plasticization.26 The addition of small Figure 10.15.3. Free volume in plasticized polyethylene oxide vs. DOP concentration. [Data from Queiroz S M; amounts of cyclic-PLLA affects not only Machado J C; Porto A O; Silva G G, Polymer, 42, No.7, PLA crystal growth but also its nucleation 2001, p.3095-101.] due to the unique cyclic chains topology.26

Figure 10.15.4. Illustration of plasticization effect induced by (a) linear chains in PLA/l-PLLA 95/5, and (b) cyclic chains in PLA/c-PLLA 95/5 blends. [Adapted, by permission, from Betegón Ruiz M, Pérez-Camargo RA, López JV, Penott-Chang E, Múgica A, Coulembier O, Müller AJ, Int. J. Biol. Macromol., 186, 255-67, 2021.]

The exact location of the plasticizer is frequently evaluated to better understand the structure of plasticized polymers. In poly[(vinylidene fluoride)-co-hexafluoropropene], VDF/HFP, plasticized with dibutyl phthalate, SAXS measurements indicated that DBP resided in the amorphous zone outside the lamellar stacks. If crystallization is slow, the inclusion of DBP inside the lamellar stacks is also possible.2 In another contribution for

10.15 Crystallization, structure, and orientation of macromolecules

Figure 10.15.5. Degree of crystallinity of plasticized PVC vs. tricresyl phosphate concentration. [Data from Borek J; Osoba W, J. Polym. Sci.: Polym. Phys. Ed., 36, No.11, Aug.1998, p.1839-45.]

289

Figure 10.15.6. Crystallinity of plasticized poly[(vinylidene fluoride)-co-hexafluoropropene] vs. concentration of dibutyl phthalate plasticizer. [Data from Marigo A; Marega C; Bassi M; Fumagalli M; Sanguineti A, Polym. Intl., 50, No.4, April 2001, p.449-55.]

the same copolymer, plasticizer was also found in the amorphous phase close to the interface with crystalline structures, which was evidenced by almost constant spacing in the presence of tricresyl phosphate studied.14 In plasticized PVC, plasticizer molecules were found in the amorphous area but were also present in interlamellar, interfibrillar, interspherulitic regions, and in amorphous fold surfaces.19 The crystallinity of poly(ethylene oxide) plasticized with DOP in the concentration range from 0 to 25% was fairly constant.4 Dibutyl phthalate did not affect the amount of VDF/HFP, which was able to crystallize in the presence of up to 50% plasticizer. Reduced crystallinity in polybutadiene urethane was found when DOS concentration was increased from 17 to 34%, but this was compensated by the annealing process at 100oC.6 Concentration of plasticizer up to 50% in plasticized PVC did not affect its crystalline order.12 Very little difference in crystallinity was observed between unplasticized PVC and PVC containing 33% tricresyl phosphate (78 and 73%, respectively).19 Figure 10.15.5 is characteristic of the results discussed so far. The crystallinity of plasticized PVC remains constant, with plasticizer concentration changing from 0 to 35%.17 There is some increase in crystallinity due to annealing, but this may still be within an experimental error. Solvents/plasticizers were introduced to conducting polymers to increase chain mobility and cause reorganization.8 It was possible to regulate the degree of crystallinity and related mechanical and electrical properties of conductive polymers. The list of potential candidates to tailor the properties of materials includes many popular plasticizers.8 In quenched films of VDF/HFP containing variable amounts of tricresyl phosphate (0-10%), crystallinity was fairly constant. It rapidly increased in slow-cooled films and was dependent on plasticizer content.14 Crystals present in plasticized films were found more perfect and larger than in

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Effect of Plasticizers on Properties of Plasticized Materials

the unplasticized film. This had led to speculations that perhaps smaller crystals are not stable in the presence of plasticizer.14 Figure 10.15.5 indicates that temperature is an essential factor in the creation of crystalline structure. Figure 10.15.6 shows the importance of crystallization time on the structure of plasticized material.2 Three major parameters are involved here: concentration of plasticizer, temperature, and time. On the one hand, these parameters influence material’s structure, and on the other, the time-temperature regime is one of the factors complicating the determination of the degree of crystallinity. In spite of many methods used for crystallinity determination (IR, WAXS, DSC) or perhaps because of many methods and variability in conditions of sample preparation and treatment, only rough estimates of crystallinity may be obtained for semicrystalline materials.12 DOP does not inhibit the secondary crystallite of PVC and almost has no effect on the primary crystallite of PVC.22 The coexistence of the microcrystalline structure of PVC and plasticizer (DOP) resulted in high elastic networks in the PVC/DOP systems.22 Plasticizer participation in structure formation is still a matter of discussion. This began with Staudinger’s experiment in which he has obtained and identified the PVC degradation product of reaction with nitric acid. Since this experiment, the helical unit having a molecular weight of 875 and 28 carbon atoms is considered to be a basic structural unit of PVC. This structural element, after folding, has a length of 16.5 D, precisely the same as is the length of di-n-octyl phthalate. This has ignited speculation that DOP is the most efficient plasticizer. It also has a bearing on the “stoichiometric” amount of plasticizer needed to interact with all polar groups. For DOP, this is 45 phr (391/875). Studies on the structure of plasticized materials suggest the presence of various forms. PVC is believed to be composed of “pseudo-crystals” differing widely in perfection and size, which produces a wide melting range.12 Very small crystals are ordered perpendicular to the polymer backbone. The size, tacticity, and thickness of layers are not known. Two phases are present based on NMR studies: one rigid (crystalline) and another mobile (amorphous) with plasticizer acting in the second phase.12 Two glass transition temperatures are detected in plasticized PVC.13 Studies of plasticized PVC at elevated temperature (below 165oC) show that there are domains (about 15% of total PVC) in which PVC is not plasticized. These domains form the third phase. Only after the temperature is increased above the melting of these domains, the material is fully fused.13 Plasticizers may slow down the formation of crystalline structures because they interfere with spherulites growth since they are present in fold surfaces of crystalline lamellae.19 Spherulites grown in the presence of tricresyl phosphate are coarser and less birefringent. In ionomers, plasticizer helps to form aggregates (multiplets) and clusters in which polymer chains have restricted mobility.10 It was verified by wide-angle X-ray diffraction that neat poly(lactic acid) and its blends with triphenyl phosphate crystallized isothermally in the temperature range of 113128oC and formed α-form crystal after sufficient annealing time.23 The PLA chain mobility was increased by adding up to 10 wt% acetyl triethyl citrate and polyethylene glycol as plasticizers.17 The non-isothermal data showed that the combination of nucleant and plasticizer is necessary to develop significant crystallinity at high cooling rates.24 Several plasticizers used decreased glass transition temperature and increased the ability of PLA to cold crystallization.25 While an amorphous plasticized PLA could be deformed to about

10.15 Crystallization, structure, and orientation of macromolecules

291

550%, a semicrystalline PLA with the same total plasticizer content exhibited nonuniform plasticization of the amorphous phase and less ability to plastic deformation.25

Figure 10.15.7. Scanning electron micrographs of chemically etched specimens isothermally crystallized at 130°C: A) Neat PLA, B) 5 wt% PEG, C) 0.05 wt% CNF-5 wt% PEG, D) 0.05 wt% CNC-5 wt% PEG, E) 0.55 wt% CNC-5 wt% PEG, and F) 0.05 wt% Talc-5 wt% PEG. [Adapted, by permission, from Clarkson CM, El Awad Azrak SM, Schueneman GT, Snyder JF, Youngblood JP, Polymer, 187, 122101, 2020.]

Polylactide materials manufactured by fused filament fabrication technique are usually in amorphous form and thereby exhibit poor mechanical properties and thermal resistance.27 Overcoming this issue requires a good knowledge of the crystallization behavior of PLA materials during the fused filament fabrication process.27 Polyethylene glycol was used as a plasticizer and tetramethylene-dicarboxylic dibenzoyl-hydrazide as a nucleating agent.27 At a temperature of 60°C, polyethylene glycol played a stronger effect on crystal-

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Effect of Plasticizers on Properties of Plasticized Materials

lization behavior than the nucleating agent and even than the combination of nucleating agent and polyethylene glycol.27 This resulted in an increase of crystallinity from 8% for both neat PLA and PLA/nucleating agent samples to 18% for the samples containing polyethylene glycol.27 With the increase of temperature to 90°C, nucleating agent and polyethylene glycol separately or synergistically had prominent effects on enhancing the crystallization ability of PLA during the fused filament fabrication process, leading to the highly crystalline PLA parts with the crystallinities in the range of 30-40%.27 Isothermal crystallization of plasticized poly(lactic acid), nucleated with nanocellulose and talc, was studied.28 Cellulose nanocrystals and cellulose nanofibrils improved crystallization rates, even at very small loadings.28 Polyethylene glycol and nanocellulose exhibited a synergistic effect on the crystallization kinetics of poly(lactic acid).28 Nanocomposites exhibited morphology differences compared to neat or plasticized poly(lactic acid) (Figure 10.15.7).28 The addition of polyethylene glycol alone changed the crystal morphology of PLA.28 PLA spherulites were denser and fuller (very fine lamella), with distinct interfaces between neighboring spherulites.28 The addition of polyethylene glycol produced large, coarse spherulites where small gaps between neighboring crystals could be observed; this space may be caused by the ejection or exclusion of polyethylene glycol to the interface during crystallization.28 Additionally, larger pores or pockets of free space were observed in the samples after etching (Figure 10.15.7 C and D).28 The addition of nucleation agents (CNC, CNF, or talc) resulted in additional changes to the crystal microstructure of PLA.28

References 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26

Horng-Jer Tai, Polym. Eng. Sci., 41, No.6, June 2001, p.998-1006. Marigo A; Marega C; Bassi M; Fumagalli M; Sanguineti A, Polym. Intl., 50, No.4, April 2001, p.449-55. Prut E V; Yerina N A, Antec 2000.Conference proceedings, Orlando, Fl., 7th-11th May, 2000, paper 643. Queiroz S M; Machado J C; Porto A O; Silva G G, Polymer, 42, No.7, 2001, p.3095-101. Lodge T P; Pudil B J; Alahapperuma V; Hanley K J, Polym. Preprints, 40, 2, 998, 1999. Tereshatov S V; Klyachkin Y S; Tereshatova E N, Intl. Polym. Sci. Technol., 26, No.12, 1999, p.T/27-T/30. Smits A L M; Hulleman S H D; Van Soest J J G; Feil H; Vliegenthart J F G, Polym. Adv. Technol., 10, No.10, Oct.1999, p.570-3. US Patent 5,969,024. Uzomah T C; Ugbolue S C O, J. Mater. Sci., 34, No.16, 15th Aug.1999, p.4057-64. Joon-Seop Kim; Eisenberg A, Polym. J. (Japan), 31, No.3, 1999, p.303-5. Orler E B; Gummaraju R V; Calhoun B H; Moore R B, Macromolecules, 32, No.4, 23rd Feb.1999, p.1180-8. Barendswaard W; Litvinov V M; Souren F; Scherrenberg R L; Gondard C; Colemonts C, Macromolecules, 32, No.1, 12th Jan.1999, p.167-80. Marossy K, Polym. Bull., 41, No.6, Dec.1998, p.729-36. Winsor D L; Scheinbeim J I; Newman B A, J. Polym. Sci.: Polym. Phys. Ed., 37, No.1, 1st Jan.1999, p.19-28. Fras I; Boudeulle M; Cassagnau P; Michel A, Polymer, 39, No.20, 1998, p.4773-83. Morales E; Acosta J L, J. Appl. Polym. Sci., 69, No.12, 19th Sept.1998, p.2435-40. Borek J; Osoba W, J. Polym. Sci.: Polym. Phys. Ed., 36, No.11, Aug.1998, p.1839-45. Nojima S; Tanaka H; Rohadi A; Sasaki S, Polymer, 39, Nos.8-9, 1998, p.1727-34. Marentette J M; Brown G R, Polymer, 39, Nos.6-7, 1998, p.1415-27. Nanasawa A; Takayama S; Takeda K, J. Appl. Polym. Sci., 66, No.1, 3rd Oct.1997, p.19-28. Angelopoulos M; Saraf R; MacDiarmid A G; Zheng W; Feng J; Epstein A J, Antec 97. Volume II. Conf. proc., SPE, Toronto, 27th April-2nd May 1997, p.1352-8. Zou J, Su L, You F, Chen G, Guo S, J. Appl. Polym. Sci., 121, 1725-33, 2011. Xioa H W, Li P, Ren X, Jiang T, Yeh J-T, J. Appl. Polym. Sci., 118, 3558-69, 2010. Li H, Huneault M A, Li H, Polymer, 48, 6855-66, 2007. Kulinski Z, Piotrkowska E, Polymer, 46, 10290-300, 2005. Betegón Ruiz M, Pérez-Camargo RA, López JV, Penott-Chang E, Múgica A, Coulembier O, Müller AJ,

10.15 Crystallization, structure, and orientation of macromolecules

27 28

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Int. J. Biol. Macromol., 186, 255-67, 2021. Gao X, Qi S, Yang B, Su Y, Li J, Wang D, Polymer, 215, 123426, 2021. Clarkson CM, El Awad Azrak SM, Schueneman GT, Snyder JF, Youngblood JP, Polymer, 187, 122101, 2020.

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10.16 MORPHOLOGY Fixed phase morphology is obtained by a process called “morphology-trapping”.1 In this process, polymer, reactive plasticizer, and initiator are mixed together.1 Further processing is used to achieve desired phase morphology, molecular orientation, and desired shape of the polymerizable composition.1 This phase is controlled by supplying sufficient energy without mixing.1 This technology is applied in the production of optical lenses.2 According to morphological studies, the antiplasticization of PVC originates from the occurrence of strong and specific interactions between structures associated with long isotactic sequences and plasticizer, thereby hindering motions at the latter structures.3 The skin is formed on the surface of PVC grains due to the presence of the suspending agent.3 The composition of the skin (whether it is PVC, VC-VAc copolymer, or PVAc) is not known.3 It is more likely that it is composed of one of the last two since skin affects fusion and plasticizer penetration.3 In the case of bulk polymerized resins; there is no barrier to the diffusion of plasticizer and other liquids because there is no skin similar to the suspension PVC, and there is no melted surface as in the case of other resins since they are subjected to heat during drying.3 The blending resins used in PVC processing are porous, and they are capable of absorbing plasticizers.3 They are used to regFigure 10.16.1. TEM images of PVC nanocomposite systems with ulate flow properties of plastisols 10-wt% clay and 30 (top) and 50 (bottom) phr DOP loading (samand the concentration of the plasples cut along the thickness plane). [Adapted, by permission, from ticizer.3 Yalcin B, Cakmak M, Polymer, 45, 19, 6623-38, 2004.] The above-mentioned morphological features of PVC have a strong influence on its degradation because of the catalytic effect of dehydrochlorination since HCl can be trapped inside these morphological features.3 More information on the subject of morphology illustrated by micrographs can be found in the monographic source on PVC degradation and stabilization.3 Figure 10.16.1 compares morphological features of PVC containing 10 wt% montmorillonite clay and two concentrations of plasticizer.4 In the top image, PVC contains 30 phr DOP, and the measured thickness of tactoid structures ranges from 10 to 70 and sometimes even up to 250 nm.4 When the DOP content was increased (bottom image), the dispersion was improved, and individual layers with reduced thicknesses (less stacking) were visible.4

10.16 Morphology

References 1 2 3 4

Houston M R, Hino T, Soane D S, US Patent 6,746,632, ZMS LLC, Jun. 8, 2004. Soane D S, Houston M R, Hino T, US Patent 6,570,714, ZMS LLC, May 27, 2003. Wypych, G, PVC Degradation and Stabilization, 4th Ed., ChemTec Publishing, Toronto, 2020, pp. 47-78. Yalcin B, Cakmak M, Polymer, 45, 19, 6623-38, 2004.

295

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Effect of Plasticizers on Properties of Plasticized Materials

10.17 PLASTICIZER EFFECT ON CONTACT WITH OTHER MATERIALS Some applications require a combination of rigid and flexible plasticized material (e.g., PVC windows and weather strips). Plasticizer migration from one material to another causes problems with their performance.1,4 Figure 10.17.1 shows that plasticizer migration increases with the increase in the plasticizer concentration in PVC. The migration process follows Fickian diffusion and can be approximated using the following equation: Q 4 Dt 1 ⁄ 2 ------t- = ---  ------ Q∞ l π

[10.17.1]

where: Qt Q∞ l D t

amount of plasticizer migrated after time t amount plasticizer migrated after infinite time thickness diffusion coefficient time.

There was no evidence of plasticizer accumulation at the interface between the two types of PVC, and the amount of migrating plasticizer was approaching equilibrium. The exchange between the contents of the package and the packaging material may occur because of one of the three possible processes: permeation, scalping, or migration.2 Each of these processes will change the properties of the packaged products. The rate of this change determines the suitability of the packaging material. Permeation is a process by which volatile liquid (solvent, water, flavor, etc.) from the product is transported to the outside environment. This can be assisted by plasticizer due to the process of mutual diffusion or cooperative diffusion (see Chapter 7). Scalping is the removal of product component by the packaging material (e.g., absorption of aroma by adhesive between packaging

Figure 10.17.1. DOP loss from plasticized PVC on contact with unplasticized PVC during 120 days. [Data from Papaspyrides C D; Papakonstantinou V, J. Polym. Eng., 15, Nos.1-2, 1995/96, p.153-9.]

Figure 10.17.2. Staining of flooring based on plasticized PVC vs. Small’s solubility parameter of plasticizer (PVC solubility parameter is 9.65). [Data from Colletti T A; Renshaw J T; Schaefer R E, J. Vinyl Additive Technol., 4, No.4, Dec.1998, p.233-9.]

10.17 Plasticizer effect on contact with other materials

297

layers). This can be assisted by the mutual diffusion of plasticizers. Migration is the diffusion of material from packaging into the product. The occurrence of any of the above processes may change the properties of the product. In this case, amounts of substances, which change location, are less important, but their influence on the overall sensoric properties of the product are very important and have to be determined to establish a permissible limit of such exchange.2 The migration of phthalates from cardboards to 50% EtOH showed the following trend: bis(2-ethylhexyl)phthalate < benzyl butyl phthalate ≤ dicyclohexyl phthalate < monobutyl phthalate, which could be related to the water solubility of the target compounds.7 Material staining is a complicated process caused by either migration of staining agent or extraction of stain by materials in contact. Resilient flooring application was stained by the migration of dyes into plasticized material. Figure 10.17.2 shows that when Small's parameter of plasticizer approaches the Small's constant for PVC (9.65), marginal staining occurs. When solubility parameters of plasticizer and polymer are close to each other, plasticizer becomes more compatible with the polymer and less likely to participate in the diffusion of stain. Figure 10.17.3 shows that staining Figure 10.17.3. Staining of flooring based on plasticized correlates with the resistance of plasticizer to kerosene extraction. It is a similar princiPVC vs. plasticizer loss during extraction for 96 h by kerosene. [Data from Colletti T A; Renshaw J T; Schae- ple to the effect of the solubility parameter. fer R E, J. Vinyl Additive Technol., 4, No.4, Dec.1998, Extraction of plasticizer is easier when it is p.233-9.] less compatible with the polymer, and more compatible plasticizer does not increase dye diffusion. There are many similar problems related to plasticizer compatibility. Plasticizer migrated from rubber into polyurethane when crosslink density of polyurethane was lower. Polyurethane had a sufficiently penetrable structure by molecules having sizes of penetrating plasticizer. Coated fabrics lost plasticizer due to its migration into polyurethane foam used in seats. Plasticizer was absorbed by the contacting fabrics, and many other similar cases of two materials in contact with each other, which were able to exchange their components, were reported. Plasticizer leaching from tubes and bags made out of plasticized PVC to blood is well known. This can be prevented by placing a surface layer of polyurethane which prevents plasticizer diffusion.5 Plasticization of poly(lactic acid) with acetyl tributyl citrate decreased barrier properties of resulting composition.6

References 1 2 3

Papaspyrides C D; Papakonstantinou V, J. Polym. Eng., 15, Nos.1-2, 1995/96, p.153-9. Risch S J, 1998 Polym. Laminations Coat. Conference. Book 2. Conf. proc., TAPPI, San Francisco, Ca., 30th Aug.-3rd Sept.1998, p.1157-9. Montgomery T T, Antec 2001.Conference proceedings, Dallas, Texas, 6th-10th May, 2001, paper 655.

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Papakonstantinou V; Papaspyrides C D, J. Vinyl Technol., 16, No.4, Dec.1994, p.192-6. Jayabalan M; Lizymol P P, J. Mater. Sci. Lett., 14, No.8, 15th April 1995, p.589-91. Courgneau C, Domenec S, Guinault A, Averous L, Ducruet V, J. Polym. Environ., 19, 362-71, 2011. Blanco-Zubiaguirre L, Zabaleta I, Prieto A, Olivares M, Zuloaga O, Elizalde MP, Food Chem., 344, 128597, 2021.

10.18 Influence of plasticizers on swelling

299

10.18 INFLUENCE OF PLASTICIZERS ON SWELLING Migration and swelling kinetics of poly(lactic acid) and polypropylene were studied.1 Swelling strongly affected plastic additive migration from food contact materials.1 The effect of molecular weight on additive migration can be overruled by plasticizers.1 The kinetic curves of both migration and swelling concentrations were evaluated using variography to determine objectively starting points of long-lasting plateaus as well as short halts in the increase.1 A strong correlation between migration and swelling was observed.1 The kinetic curves showed that migration always followed swelling.1 Regardless of the shape of the kinetic curves, for all additives, the greater the swelling, the higher migration concentrations observed.1

References 1

Kirchkeszner C, Petrovics N, Tábi T, Magyar N, Kovács J, Szabó BS, Nyiri Z, Eke Z, Food Control, 132, 108354, 2022.

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10.19 FOGGING The fogging test is a special case of test chamber examination of compounds generally known as semivolatile organic compounds such as plasticizers and flame retardants, which are precipitated inside the chamber on a cooled surface.1 This method had initially been developed for examining automotive parts in order to determine the portion of “fogging-active” substances.1 The fogging data can be used for assessing possible dermal and oral intake in an indoor environment.1 For calculation purposes, a model room with a volume of 17 m3 and a surface of 24 m2 as described in DIN EN 13419-1 has been used as a basis.1 The maximum values for di-n-butyl-phthalate and di(2-ethylhexyl)-phthalate after 14 days correspond to 30 μg/day for di-n-butyl-phthalate and 1449 μg/day for di(2-ethylhexyl)-phthalate.1 The results of passenger car studies show that under the extreme climatic conditions present during the test stand studies (65°C; heavily restricted air exchange rate), measurable concentrations of phthalates can be detected inside the car.1 In the context of automobile interiors, fogging is defined as the deposition of volatile components on windows arising from materials inside the cabin under the influence of high temperatures, which can lead to decreased visibility for the driver.2 The use of specific plasticizers for car interior components can help decrease the incidence of fogging in order to meet specific fogging standards (e.g., DIN 75201, ISO 6452, SAE J1756).2 In general, longer chain, linear phthalates have better fogging performance and cold crack resistance than shorter chain phthalates.2 An exposure assessment of diundecyl phthalate, a high molecular weight phthalate plasticizer present in automobile upholstery, was conducted.2 Oral exposures from hand-to-mouth contact were estimated to represent 99% of all exposures.2 The estimated daily absorbed doses were far lower than the reported noobserved-adverse-effect-level, NOAEL, and derived no-effect level, DNEL values.2 The maximum oral intake dose was 0.01% of the human oral NOAEL dose for diundecyl phthalate.2 Application areas for Oxsoft L9TM (linear trinonyltrimellitate) include non-fogging automotive interiors, special sheets, profiles and gaskets, and base stock for lubricating oils.3

References 1 2 3

Wensing E, Uhde T, Salthammer T, Sci. Total Environ., 339, 1-3, 19-40, 2005. Perez AL, Liong M, Plotkin K, Rickabaugh KP, Paustenbach DJ, Chemosphere, 167, 541-50, 2017. Addit. Polym., 2015, 7, 2, 2015.

10.20 Hydrophobic/hydrophilic properties

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10.20 HYDROPHOBIC/HYDROPHILIC PROPERTIES Biodegradable and natural polymers are intrinsically hydrophilic because they are composed of polar moieties.1 This hydrophilic character can often lead to water absorption that is responsible for the deterioration of mechanical properties and dimensional instability, which are highly undesirable for packaging materials.1 Film production usually requires the use of a plasticizer to increase flexibility.1 Many plasticizers (sorbitol, glycerol, polyethylene glycol) have hydrophilic character.1 So, both water permeability and matrix susceptibility to the moisture increase.1 The inclusion of hydrophobic components, such as diethyl phthalate, triacetin, tributyl citrate, or triethyl citrate, is an alternative to reduce this effect.1 Gelatin-based films presented surfaces with hydrophobic character.2 Films were modified by plasticization with glycerol and acetyl tributyl citrate.2 All films had hydrophobic characters.2 Gelatin film with acetyl tributyl citrate showed the lowest surface hydrophobicity.2 Hydrophilic and hydrophobic plasticizing agents were incorporated into aqueous dispersions of Eudragit® L 30 D-55 and coated onto hydrophilic and hydrophobic tablet compacts.3 Plasticizer concentration and plasticizer type were found to influence the adhesive properties of the acrylic polymer.3 Films containing water-soluble plasticizers were found to adhere more strongly to the tablet compacts than the water-insoluble agents due to more effective disruption of the intermolecular attractions between the polymer chains.3 Adhesion of the polymer to tablet compacts was found to be significantly influenced by the hydrophobicity of the tablet surface when the water-soluble plasticizers were incorporated into the film coating, whereas no significant differences in the adhesive properties were found when the polymer was plasticized with water-insoluble agents.3 Plasticizers are critical components of drug-in-adhesive patches as they can significantly affect mechanical, adhesive, and drug release characteristics of the patches.4 Eudragit® E is a methacrylate-based cationic copolymer capable of producing flexible and adhesive films for topical application.4 Pressure-sensitive adhesives were prepared with hydrophilic (PEG 300 and PG) or hydrophobic (triacetin, DBS and TEC) plasticizers. Films without plasticizer were brittle and non-adhesive.4 Films containing hydrophobic plasticizers were highly elastic and adhesive, and films plasticized with PEG 300 displayed moderate flexibility without adhesion.4

References 1 2 3 4

Corsaro C, Mallamace D, Neri G, Fazio, E, Physica A: Statistical Mech. Appl., 580, 126189, 2021. Pulla-Huillca PV, Gomes A, Quinta Barbosa Bittante AM, Vinícius Lourenço R, do Amaral Sobral PJ, J. Food. Eng., 297, 110480, 2021. Felton LA, McGinity JW, Int. J. Pharm., 154, 2, 167-78, 1997. Kim S, Fouladian P, Afinjuomo F, Song Y, Youssef SH, Vaidy S, Garg S, Int. J. Pharm., 611, 121316, 2022.

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10.21 OSMOTIC PRESSURE OF PLASTICIZER IN POLYMER In pharmaceutical formulations, the pharmacokinetic behavior of the active pharmaceutical ingredients is significantly affected by their dissolution profiles.1 Cellulose acetate was employed to create an external shell of an osmotically active core containing Diltiazem as a model drug, and mannitol was used as both plasticizer and osmotic agent, whereas NaCl was added to enhance the osmotic properties of the formulation.1 By removing parts of the shell (upper surface, linear lateral segments), dosage forms were created that modified their shape at specific time frames under the effect of the gradually induced osmotic pressure.1 Membrane coating of the immediate release dosage form is an effective means of producing an extended drug delivery system.2 Polymers, when coated alone, have limited ability to form the rate-controlling membrane with good mechanical properties.2 Addition of plasticizer is vital to the formation of a robust rate-controlling membrane.2 Plasticizers have the ability to interact with polymer chains and provide desired flexibility, shock resistance, and smoothness to the resultant system.2 In addition to the plasticizing effect, they also play an important role in modulating drug release profiles.2 Increasing the concentration of hydrophilic plasticizer in the semi-permeable membrane increased drug release, while the drug release decreased while increasing hydrophobic plasticizer concentration.2

References 1 2

Gioumouxouzis CI, Tzimtzimis E, Katsamenis OL, Dourou A, Markopoulou C, Bouropoulos N, Tzetzis D, Fatouros DG, Eur. J. Pharm. Sci., 143, 105176, 2020. Khatri P, Desai D, Shelke N, Minko T, J. Drug Delivery Sci. Technol., 44, 231-43, 2018.

10.22 Self-healing

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10.22 SELF-HEALING A self-healing approach for optically transparent thermoplastic polymers, based on plasticizer-induced solvent welding, was reported.1 System was based on filled urea-formaldehyde capsules containing dibutyl phthalate, which were dispersed in polymethylmethacrylate.1 Upon a damage event, DBP was released into the crack, and the plasticizer swelled polymer, enabling it to remend.1 Smaller capsules were particularly important for thin polymer films, which were not thick enough to hold the larger capsules.1 Polymer films with smaller capsules had very good transmission properties due to the minimization of light scattering by the small size of the capsules.1 Large capsules enabled healing of larger damage events and resulted in some light scattering.1 This system had some limitations. First of all, the size of the scratch (which could not be predicted) determined the amount of plasticizer (or size of capsule) needed to heal the damage.2 Also, if scratch occurred more than once in the same place, there was no plasticizer to provide local mobility to the matrix.2 The self-healing behavior was achieved by the introduction of a small amount of suitable plasticizer, such as benzyl alcohol. Diels-Alder reaction, which is thermally reversible, was used for designing thermosetting self-healing polymers.3 The chemical linkages disconnected on heating and then reconnected upon cooling.3 The scratch was removed in this process.3 The tensile testing revealed 48% restoration of its pristine mechanical strength.3 Self-healable waterborne polyurethane coatings having high strength used polyamine whose molecular structure containing primary amine and secondary amine formed ionic bonds and hydrogen bonds with carboxyl-type waterborne polyurethanes.4 Polymine played the role of crosslinker and plasticizer, endowing the material with good self-repairing performance.4 After self-healing at 30°C for 24 h, the tensile strength, and elongation at the break of waterborne polyurethanes reached 3.26 MPa and 451%, respectively.4 Concrete is susceptible to cracking typically under tensile stresses, which reduces the mechanical resistance and endangers the overall durability of the structure.5 Superabsorbent polymers were used with varying superplasticizer content to evaluate the efficiency of self-healing concrete.5 Crack width up to 234 µm was healed with the addition of 2.2 wt% superplasticizer.5

References 1 2 3 4 5

Jackson A C, Bartelt J A, Braun P V, Adv. Funct. Mater., 21, 4705-11, 2011. Lutz, A; Mol, J M C; DGraeve, I; Terryn, H, Smart Composite Coatings and Membranes. Transport, Structural, Environmental and Energy Applications. Woodhead Publishing, 2016, pp. 157-81. Postiglione, G; Turri, S; Levi, M, Prog. Org. Coat., 78, 526-31, 2015. Lei Y, Wu B, Yuan A, Fu X, Jiang L, Lei J, Prog. Org. Coat., 159, 106433, 2021. Sidiq A, Gravina R, Setunge S, Giustozzi F, Construction Building Mater., 253, 119175, 2020.

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Effect of Plasticizers on Properties of Plasticized Materials

10.23 SHRINKAGE Plasticizer has the most significant effect on the shrinkability of PVC sheets among the seven variables studied.1 The shrinkability of PVC films decreases with increasing plasticizer content.1 Plasticizers reduce the polymeric chain entanglements, leading to less shrinkage.1 Another factor can be presumed to be the reduction in resin content by increasing additives content.1 The plasticizer migration from starch ester film to milk system was accelerated during microwave heating.2 The crystalline structure of the film was changed.2 The milk permeation into the amorphous region of the film impeded the shrinkage and aggregation of amorphous starch ester chains, but the ordered microaggregations were shrunk.2 These structural changes, including the expanded amorphous region and shrunk ordered microregions, could be the reason for the greater plasticizer migration during the microwave treatment.2 Four types of superplasticizers were used in conjunction with three types of silica fume to prepare cement concrete slab specimens that were utilized to measure plastic shrinkage strain and time to attain maximum strain.3 The type of superplasticizer was found to affect the plastic shrinkage strain.3 The use of superplasticizer in silica fume cement concrete improved its ability to resist plastic shrinkage cracking.3

References 1 2 3

Hadi P, Babaluo A A, J. Appl. Polym. Sci., 106, 3967-74, 2007. Huang, C; Zhu, J; Chen, L; Li, L; Li, X, Food Control, 36, 1, 55-62, 2014. Baghabra Al-Amoudi OS, Abiola TO, Maslehuddin M, Construction Building Mater., 20, 9, 642-7, 2006.

10.24 Soiling

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10.24 SOILING The effects of three plasticizers (Benzoflex 2088, DOP, and Hexamoll DINCH) and two plasticizer concentrations (20 and 30 wt%) on the topography and soiling of polyvinylchloride were studied.1 Plasticized PVC was hydrophobic and oleophilic.1 The topography of the surface, as measured by atomic force microscopy, was not greatly influenced by plasticizer type or its concentration.1 Both the type and concentration of the plasticizer influenced the structure of oily soil on plasticized PVC.1 The cleanability of plastic materials was affected by the presence of plasticizers.2 According to the radiochemical studies, hydrophobic properties and surface structure of plasticized materials affected cleanability.2 The materials containing 20% plasticizer were cleaned more efficiently than those containing 30% plasticizer.2,3 Smooth (unstructured) surface materials were cleaned easier than the structured materials.2

References 1 2 3

Koponen H-K, Suvanto M, Pakkanen T A, J. Appl. Polym. Sci., 105, 3047-53, 2007. Maatta J, Kuisma R, Kymalainen H-R, Constr. Build. Mater., 25, 2860-66, 2011. Maatta J, Koponen H-K, Kuisma R, Kymalainen H-R, Pesonen-Leinonen E, Uusi-Rauva A, Hurme K-R, Sjoberg A-M, Suvanto M, Pakkanen T A, Appl. Surf. Sci., 253, 5003-10, 2007.

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Effect of Plasticizers on Properties of Plasticized Materials

10.25 FREE VOLUME It was demonstrated that there exists a threshold plasticizer concentration – above which the matrix crystallinity and moisture content can be significantly altered in sorbitol plasticized starch.1 The free volume changes due to amylose-MMT interactions, which were affected by the concentration of the sorbitol plasticizer.1 The free volume analysis revealed that when the concentration of sorbitol was low (5 wt%), the bionanocomposite showed a bimodal distribution for free volume pore-size.1 As the sorbitol concentration increased, these free volume pores coalesced.1 Positron annihilation lifetime spectroscopy was used to assess free volume developed in starch-containing filler and plasticizers (glycerol and sorbitol).2 Some plasticizers occupied the void spaces, and therefore decreased the total free volume in the matrix.2 The small-angle X-ray scattering analysis revealed that free volume change is a result of the interplay between the plasticizer-plasticizer interactions and the polymer-plasticizer interactions. In the case of glycerol, the pore radii changed from 0.27 to 0.26 nm, whereas they increased with sorbitol from 0.23 to 0.28 nm.2 Various aspects of void formation are further analyzed in monographic source on the subject.3 Molecular dynamics calculations, focusing on short- and long-range structure correlations with ionic transport near the glass transition, were done for lithium-ion polyacrylonitrile-based electrolytes using DMSO as a plasticizer.4 The decrease in activation energy above the glass transition was associated with the increase in the free volume and also with the increase of lithium-ion coordination to DMSO plasticizer molecules creating different mobile species.4 The role of the DMSO plasticizer was crucial as it participated directly in the solvation of lithium ions occupying empty spaces between polymer chains, particularly above Tg, yielding to a decrease in the ionic pairing with perchlorate anions with a consequent decrease in the activation energy.4 The free volume increased with an increase in MWCNT content up to 1% CNT but exceptionally decreased at higher loadings.5 The increase in free volume resulted due to intercalation of carbon nanotubes with plasticized polymer chains, which introduced slight disorder to nanocomposites.5 The decrease in the free volume was caused by the bridging of polymer chains by carbon nanotubes, resulting in the decrease in free volume at the vicinity of carbon nanotubes.5 With 35% plasticizer loading, the free volume radius of plasticized PVC was 0.31 nm, which was in the range of thickness calculated from HRTEM studies.5 Liquid polymers used in elastomeric compounds to modify their processing and final characteristics are considered polymeric plasticizers and are used to substitute or supplement conventional plasticizers, such as paraffinic or aromatic oils or hydrocarbon resins.6 Their plasticizing effect and contribution to the crosslinking in sulfur-cured styrene-butadiene copolymer mixtures are studied.6 The free volume – measured by positron annihilation lifetime spectroscopy – increased with the amount of liquid polymer's incorporation in the main polymer.6 Various amounts of n-alkylbenzenes were doped into polymethylmethacrylate films, and the emission and thermal properties of each film were measured together with their solid-state 13C NMR spectra.7 The aim of the work was to estimate the size distribution of free volume in amorphous regions of polymer solids heavily doped with plasticizers.7 The

10.25 Free volume

307

amount by which plasticization increased the free volume of PMMA was limited by the size of the dopant and the inherent free volume of the polymer matrix.7

References 1 2 3 4 5 6 7

Liu H, Chaudhary D, Roberts J, Weed R, Sullivan J, Buckman S, Carbohydrate Polym., in press, 2012. Liu, H; Chaudhary, D; Campbell, C; Roberts, J; Buckman, S; Sullivan, J, Mater. Chem. Phys., 148, 1-2, 349-55, 2014. Gladysz, G M, Intrinsic Voids in Polymers. Voids in Materials. Elsevier, 2015, pp. 37-48. Pignanelli F, Romero M, Faccio R, Mombrú AW, J. Non-crystalline Solids, 561, 120744, 2021. Francis E, Zhai L, Kim HC, Ramanchandran R, Amaredra G, Balerao GM, Kalarikkal N, Varughese KT, Kim J, Thomas S, Polymer, 141, 232, 43, 2018. Gruendken M, Koda D, Dryzek J, Blume A, Polym. Testing, 100, 107239, 2021. Itagaki H, Ochiai A, Nakamori T, Eur. Polym. J., 42, 8, 1939-52, 2006.

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Effect of Plasticizers on Properties of Plasticized Materials

10.26 DISSOLUTION Polymer films are promising platforms for the delivery of poorly water-soluble drug particles.1 The study focused on the impact of plasticizers and their concentrations on the properties and dissolution rate of polymer films loaded with poorly water-soluble drug nanoparticles.1 Glycerin, triacetin, and polyethylene glycol were selected as film plasticizers. Griseofulvin was used as a model biopharmaceutics classification system class II drug, and hydroxypropyl methylcellulose was used as a film-forming polymer.1 A decrease in glass transition temperature was observed with increasing plasticizer concentration, along with a decrease in film tensile strength and an increase in film elongation, as is typical of plasticizers performance.1 The type of plasticizer or its concentration had an insignificant effect on dissolution; they can be therefore selected to achieve films of required mechanical performance.1 Poly(methacrylic acid-methyl methacrylate, 1:2) (Eudragit S) is a commonly used pH-responsive polymer that can facilitate delivery to the ileo-colonic region of the gastrointestinal tract.2 Different plasticizers have been used to reduce the brittleness of Eudragit S films in the coating solid dosage forms.2 Dissolution of the films was influenced by the solubility and structure of the plasticizers.2 The low temperature thermally stimulated depolarization currents spectra showed a relationship of the total secondary relaxation area and relaxation of the carboxylic acid functional group with dissolution time.2 Drug dissolution and leaching of plasticizer were studied in theophylline pellets coated with 30 wt% Eudragit® S100:L100 (1:1) plasticized with different levels of triethyl citrate.3 Theophylline was completely dissolved from pellets coated with Eudragit® S100:L100 (1:1) plasticized with 50% triethyl citrate at pH 6.0 after 2 h.3 Both the dissolution of theophylline and the leaching of triethyl citrate decreased during storage due to further coalescence of the acrylic polymers.3

References 1 2 3

Krull SM, Patel HV, Li M, Bilgili E, Davé RN, Eur. J. Pharm. Sci., 92, 146-55, 2016. Fadda HM, Hernández MC, Margetson DN, McAllister SM, Basit AW, Brocchini S, Suárez N, J. Pharm. Sci., 97, 9, 3957-71, 2008. Bando H, McGinity JW, Int. J. Pharm., 323, 1-2, 11-17, 2006.

10.27 Foaming

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10.27 FOAMING Thermoplastic starch foams were prepared by a melt extrusion process, and the effects of polyvinylalcohol and glycerol/water plasticizer contents on the physical and cellular properties of these foams were investigated.1 The density of thermoplastic starch foam decreased by 70%, and cell density increased up to 60-fold by adding 20% PVAl.1 In addition to the positive effect of the PVAl on improving processability and cellular uniformity, it also acted as a polymeric plasticizer.1 Its addition permitted to decrease another low molecular weight plasticizer content in thermoplastic starch/PVAl blends.1 Foaming of polycaprolactone with dispersed hydroxyapatite particles by supercritical CO2 and either ethyl lactate or ethyl acetate as plasticizer has been studied.2 Both plasticizers enhanced low-temperature foaming.2 The method of incorporation of plasticizer was critical for enhancing composite foaming.2 The best results were achieved when ethyl acetate was pre-mixed with polymeric powder before foaming.2

References 1 2

Kahvand F, Fasihi M, Macromolecules, 157, 359-67, 2020. Salerno A, Fanovich MA, Pascual CD, J. Supercritical Fluids, 95, 394-406, 2014.

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Effect of Plasticizers on Properties of Plasticized Materials

10.28 PERMEABILITY Gas permeability depends on chain mobility and intermolecular distances (free volume). Both properties can be modified by plasticizers. Figure 10.28.1 shows that by the increasing the amount of plasticizer or increasing temperature, water permeability is increased. This is a simple illustration of the influence of the free volume on permeability. Replacement of the low molecular weight plasticizer (DOP) by polyolefin flexibilizer decreased oxygen permeability by a factor 2.5.1 In membrane-based CO2 separation, glassy polymeric materials suffer from the plasticization phenomenon.2 To suppress plasticization, crosslinking is a possible Figure 10.28.1. Permeability coefficient, P of plasticized remedy, which, however, significantly PVC vs. temperature and plasticizer content. [Data from alters separation performance.2 The Lelchuk S L, Sedlis V I, J. Appl. Chem. USSR, 30, 1106increased glass transition temperature of 1113, 1957. polymers with crosslinking density enhanced rigidity due to crosslinking, which reduced packing efficiency of polymer chains and led to higher fractional free volume, hence increasing CO2 diffusivity.2 Analyses of CO2-accessible free volume evolution as a function of pressure showed increased plasticization resistance with crosslinking.2 A thermodynamic model describes penetrant permeability in the glassy polymer.3 Diffusivity is described as a product of kinetic mobility and thermodynamic factor.3 The plasticization factor was associated with the swelling coefficient of the polymer matrix.3

References 1 2 3

Weng D, Andries J, Saunders K, Macaluso J, Brookman R, Antec, Orlando, Fl., 7th-11th May, 2000, p.3352-3356. Balçık M, Velioğlu S, Tantekin-Ersolmaz SB, Ahunbay MG, Polymer, 205, 122789, 2020. Minelli M, Sarti GC, J. Membrane Sci., 444, 429-39, 2013.

10.29 Sorption

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10.29 SORPTION Sulfur dioxide is an electron acceptor; therefore materials, which are either electron donors or have basic groups, will interact with sulfur dioxide.1 Figure 10.29.1 shows that molar sorption of sulfur dioxide by various polymers depends on their Gutman’s donor numbers.1 Infrared and NMR studies confirm the formation of hydrogen bonds between water and polar groups of resins.2 Permeability of oxygen through plasticized ethylcellulose increased with an increase in polarity of the polymer-plasticizer mixture.3

Figure 10.29.1. Sulfur dioxide molar sorption by polymeric membranes vs. their Gutman’s donor number. [Data from Semenova S I; Smirnov S I, J. Membrane Sci., 168, Nos.1-2, 13th March 2000, p.167-73.]

References 1 2 3

Semenova S I; Smirnov S I, J. Membrane Sci., 168, Nos.1-2, 13th March 2000, p.167-73. Maggana C; Pissis P, J. Polym. Sci.: Polym. Phys. Ed., 37, No.11, 1st June 1999, p.1165-82. Beck M I; Tomka I, J. Polym. Sci.: Polym. Phys. Ed., 35, No.4, March 1997, p.639-53.

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Effect of Plasticizers on Properties of Plasticized Materials

11

PLASTICIZERS USE AND SELECTION FOR SPECIFIC POLYMERS George Wypych ChemTec Laboratories, Inc., Toronto, Canada The goals of this chapter are to provide the information according to the following breakdown: • types of plasticizers used • concentration range in practical applications • reasons for their selection • specific mechanisms of plasticizers action • potential effects on other additives used and on the polymer properties • typical generic formulations This scheme is followed as much as the information from available literature permits.

11.1 ABS 11.1.1 FREQUENTLY USED PLASTICIZERS Several types of plasticizers are used in ABS. These include: hydrocarbon processing oil,1 phosphate esters (e.g., triphenyl phosphate,1,9 resorcinol bis(diphenyl phosphate),2 or oligomeric phosphate),1 long-chain fatty acid esters,3,4 and aromatic sulfonamide.5 11.1.2 PRACTICAL CONCENTRATIONS • hydrocarbon processing oils: 1-3 phr • phosphate esters: 2 phr (flow improvement) 10-15 wt% for flame retardation9 • long-chain fatty acid esters: 0.2-0.5 wt% • aromatic sulfonamide: 2-10 phr 11.1.3 MAIN FUNCTIONS PERFORMED BY PLASTICIZERS Plasticizers play secondary roles in ABS, such as: • reduction of melt viscosity and processing temperature • improved mold release • flame retardation and smoke reduction In addition, aromatic sulfonamide plasticizer is designed to produce non-fogging parts for the automotive industry from ABS, its blends, and other polymers.

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Plasticizers Use and Selection for Specific Polymers

11.1.4 MECHANISM OF PLASTICIZER ACTION No studies are available so far which are broad enough to be used to propose a mechanism of action of plasticizers in any function listed in Section 11.1.3. 11.1.5 EFFECT OF PLASTICIZERS ON POLYMER AND OTHER ADDITIVES Even small additions (1-2 wt%), such as required to increase flowability, affect the mechanical properties of ABS. This influence is complex. For example, the addition of process oil reduces both tensile strength and elongation, whereas phosphate plasticizers have an only small effect on its tensile strength but increase elongation. On the other hand, mineral oil substantially (by ~50%) increased impact strength. Phosphate plasticizers reduce impact strength when their concentration increases.1 Flexural strength and modulus are not affected by additions of small amounts of plasticizers (up to 4 wt%). The melt flow rate depends on the type and the concentration of the plasticizer selected. Resorcinol bis(diphenyl phosphate) at a concentration of 4 wt% almost doubled melt flow rate, and it was substantially more effective than triphenyl phosphate. Mineral oil did not affect the melt flow when added at 2 wt% but reduced it when concentration was doubled. This, and the effects on mechanical properties, indicates that phosphate compounds interact with polymer chains as typical of plasticizers, whereas mineral oil acts as an external lubricating oil incompatible with polymer. Even small amounts of phosphate plasticizers improve flame retarding properties, but at least 8 phr are needed to meet typical flammability requirements. The concentration depends on the formulation, which may include other flame retarding components. When ABS is contacted with other materials, which contain plasticizers (e.g., PVC), stress cracking may occur. Time to break and force required were drastically reduced when ABS was contacted with nineteen samples of PVC, each containing different plasticizers.6 This shows that ABS performance may depend on the presence of other materials. In the study of the compatibility of different plasticized polymers, the phthalate plasticizers included in the study, such as DINCH, DEHP, and DINP, were found to be acceptable with ABS.11 Nine organophosphorus flame retardants/plasticizers were detected in house and car dust in the Netherlands, with the exception of tris(butyl) phosphate and tris(isobutyl) phosphate in car dust. Tris(2-butoxyethyl) phosphate (median 22 µg g-1) was dominant in house dust collected around and on electronics followed by tris(2-chloroisopropyl) phosphate (median 1.3 µg g-1), tris(2-chloroethyl) phosphate (median 1.3 µg g-1) and tris(phenyl) phosphate (median 0.8 µg g-1).10 Car dust was dominated by tris(1,3dichloroisopropyl) phosphate with the highest levels found in the dust collected from the car seats (1100 µg g-1). A polymer electrolyte was composed of a blend of ABS and polymethylmethacrylate as a host polymer, a mixture of ethylene carbonate and propylene carbonate as plasticizers, and LiClO4 as a salt.11 Because of different miscibilities of ABS and PMMA with plasticizers, phase separation occurred, as revealed by SEM studies.11 The ionic conductivity of the electrolytes decreased with increasing ABS/PMMA ratio and increased with the increasing plasticizer content at LiClO4 content of 15%, which was explained by morphology and thermal characteristics of electrolytes.11 The SEM observations and DSC analysis showed that a dual-phase structure was created in which the plasticizer-rich phase provided a path for ion transportation and the ABS-rich phase acted as a mechanically sup-

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portive matrix.11 The mechanical properties of electrolytes were significantly improved over pure PMMA, plasticizer, and lithium salt.11

11.1.6 TYPICAL FORMULATIONS Flame retarding formulation:12 PC/ABS (5:1) 91.9 wt% Fyrolflex RDP 8.0 wt% PTFE 0.1 wt% UL94 1.6/3.2 mm V0/V0 Flow modification:12 ABS 98 wt% Fyrolflex RDP 2 wt% 42% increase in melt flow index over control (no plasticizer). ABS containing starch was plasticized using a combination of glycerol and water for use in 3D printing applications.8 References 1 2 3 4 5 6 7 8 9 10 11 12

Moy P Y, J. Vinyl Additive Technol., 4, No.4, Dec.1998, p.216-21. Fyroflex Flame Retardant Plasticizer, Akzo Nobel, November 1998. Loxil EP-PTS, Cognis, 2001. Loxiol P 861/3.5, Cognis, 2001. US Patent 6,194,498. Ezrin M, Plastics Failure Guide. Cause and Prevention. Hanser, Munich, 2013. Addit. Polym., 2013, 11, 4-5, 2013. Kuo, C-C; Liu, L-C; Teng, W-F; Chang, H-Y; Chien, F-M; Liao, S-J; Kuo, W-F; Chen, C-M, Composites Part B: Eng., 86, 36-9, 2016. Wei, P; Tian, G; Yu, H; Qian, Y, Polym. Deg. Stab., 98, 5, 1022-9, 2013. Brandsma, S H; de Boer, J; van Velzen, M J M; Leonards, P E G, Chemosphere, 116, 3-9, 2014. Hou X; Siow KS, Polymer, 41, 24, 8689-96, 2000. Taylor J W; Klots T D, 29th Annual Waterborne Symposium, New Orleans, February 5-6, 2002.

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11.2 ACRYLICS 11.2.1 FREQUENTLY USED PLASTICIZERS Acrylic copolymers may be internally plasticized by the selection of the appropriate composition of monomers, which give copolymer required glass transition temperature. This process, although known and possible, may not be useful for the production of commercial materials because of several important reasons. The following examples may explain the reasons for the use of plasticizers in certain products containing acrylic polymers. Acrylic binders in water-based paints must have film-forming properties at temperatures of paint drying. If paint would contain polymer, which has such a low glass transition temperature, Tg, as to form a film at room temperature, then the film will have low hardness and would not perform its protective functions. Different properties of polymer during curing and normal service are thus required (low Tg during cure and higher Tg during its lifetime). Different methods can be used to achieve this − the use of coalescing solvents is the most popular method. Coalescing solvents plasticize acrylic copolymer, which lowers Tg below the ambient temperature and helps in film formation. The mechanism of action of coalescing solvents is discussed in Section 11.2.4.1 Typical coalescing solvents include ethylene and propylene glycols and their esters, butyl cellosolve, butyl carbitol, and many others. More information on types of coalescing solvents can be found elsewhere.2 Controlled drug release properties are obtained by the application of surface coating. Surface coating is applied in the microencapsulation process, which frequently uses plasticized acrylic copolymer.3 The type and concentration of plasticizer determine the rate of drug release. Triethyl citrate is a typical plasticizer used in microencapsulation. Topical patches containing 5-fluorouracil are a feasible alternative to overcome the shortcomings of commercial cream for the treatment of non-melanoma skin cancer.12 Plasticizers are critical components of drug-in-adhesive patches as they can significantly affect mechanical, adhesive, and drug release characteristics of the patches.12 Eudragit® E is a methacrylate-based cationic copolymer capable of producing flexible and adhesive films for topical application.12 Eudragit® E plasticized with 40% triacetin, 30% dibutyl sebacate, or 40 wt% triethyl citrate produced elastic and adhesive films most suitable for topical application.12 Acrylic sealants, adhesives, and coatings use the following permanent coalescent/ plasticizers: m,p-cresol propoxylate (Macol 85), and alkyl benzyl phthalate (Santicizer 160). Acrylic-based floor polishes use alkyl benzyl phthalate (Santicizer 160) and dialkyl adipate (Santicizer 141). These plasticizers are also permanent coalescing agents. Many other applications of plasticizers are reported in literature, such as dioctyl phthalate in ink for jet printers,4 dibutyl phthalate or phosphate in dentures,5 various types in pressure sensitive adhesives,6 diesters of phthalic and benzoic acids in surface coatings for polymers,7 and plasticizers and coalescing agents in nail varnishes.8 11.2.2 PRACTICAL CONCENTRATIONS • water-based coatings: 0-15% (coalescing solvents) • polymer surface coating: 1-25% (plasticizers/coalescents) • controlled-release drugs: up to 15% • concrete sealer: 1-3% (coalescent)

11.2 Acrylics

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sealants: 2-10% (plasticizer/coalescent) ink for jet printer: 1.5%4 nail varnish: 6.6% (plasticizers 4.8%, coalescing solvents 1.8%)8 drug-in-adhesive patches contain 30-40% plasticizer12

11.2.3 MAIN FUNCTIONS PERFORMED BY PLASTICIZERS The following functions are performed by plasticizers and coalescing agents in acrylic resins: • coalescing (film-forming properties, mechanical properties improvement) • decrease of glass transition temperature (improved elongation, elasticity, lowtemperature curing) • control of migration rate of drug (controlled-release properties) • adhesion promotion (softening surface of polymer-coated by surface layers) 11.2.4 MECHANISM OF PLASTICIZER ACTION Figure 11.2.1 shows macroscopic stages of film formation. Four stages are illustrated here, including:2 • application of wet film (I) • initial evaporation of water (II) • close packing of latex particles on further evaporation of liquid phase (III) • formation of a film.

Figure 11.2.1. Macroscopic stages of film formation from water-bourne coating. [Adapted, by permission from Randall D in Handbook of Solvents, Wypych G, Ed., 2nd Ed., ChemTec Publishing, Toronto, 2013.]

In order to understand this mechanism further, we have to consider thermodynamic and chemical mechanisms of film formation, specifically: • kinetics of evaporation of water and solvent/plasticizer • trace solvent

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• effect of the micellar structure of latex (surfactants) • coalescence of particles. Without understanding these fundamental principles, the mechanism cannot be described. After coating was applied on the surface of the substrate, water began to evaporate, which was accompanied by the loss of coalescing solvent (usually less volatile than water). Latex particles come closer to each other when liquids evaporate, but they are kept apart by repulsion forces of surface coating by surfactants used in polymerization. It is not well established when and why these repulsion forces are finally overcome and what is the role of solvent concentration and dissolving characteristics. Current understanding1 implies that solvent promotes the diffusion of polymer chains from one particle to another. As they cross boundaries, they help in the formation of the uniformly built film. Temperature also plays a role here, as does the polymer structure. The mobility of polymer chains is rapidly increased above the glass transition temperature. It is, therefore, a combination of ambient temperature, the glass transition temperature of the polymer, and effective reduction of glass transition temperature by coalescing solvent, which determines the rates of diffusion of polymer chains. The selection of solvent must consider its loss rate. If the rate is too rapid, the film properties will not be fully developed; if it is too slow curing rate will suffer. In addition, slow evaporating solvents increase concentration and time of removal of trace solvents and thus increase dangers of indoor pollution. The presence of slowly evaporating coalescent solvent or permanent coalescent affects also the hardness of the coating, its dirt pick-up properties, and increases the costs of maintenance. A pressure-sensitive adhesive includes a wax chosen from ethylene-acrylic acid copolymer and ethylene-vinyl acetate, which helps to minimize and/or resist plasticizer migration.10

11.2.5 TYPICAL FORMULATIONS Drug release coating:3 Acrylic resin (Eudragit RS30D) 12 Triethyl citrate 1.5 Magnesium stearate (antitackiness agent) 1.0 Water 60.0 This composition processed at 38oC (film-forming temperature) was suitable for the controlled release of salbutamol. Concrete sealer: Acrylic copolymer 100 Water 150 Butyl cellosolve 8 This composition, after spraying and drying at ambient temperature, substantially reduces water uptake by concrete. Fingernail lacquer11 Nitrocellulose 20.00 Acrylic copolymer 10.00 Ethyl alcohol 37.99 Acetyl tributyl citrate 3.00

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Butyl acetate 28.98 Ethyl-2-cyano-3,3-diphenylacrylate 0.03 Acrylic plastisol ink9 Plastisol ink composition contains acid-functionalized acrylic core-shell resin, non-phthalate plasticizer (selected from the group consisting of benzoate esters, citrates, alkylsulfonic acid phenyl esters, and esters of 1,2-cyclohexane dicarboxylic acid), pigment, thixotropic agent, and optionally, filler and additional additives.9 Adhesive composition13 Acrylic triblock copolymer 100 Tackifying resin (Floral 85) 35 Plasticizer DOP or ATBC) 30

References 1 2 3 4 5 6 7 8 9 10 11 12 13

Taylor J W; Klots T D, 29th Annual Waterborne Symposium, New Orleans, February 5-6, 2002. Randall D in Handbook of Solvents, Vol. 1. 3rd Ed., Wypych G, Ed., ChemTec Publishing, Toronto, 2019. Govender T; Dangor C M, J. Microencapsulation, 14, No.4, July-Aug.1997, p.445-55. US Patent 6,458,294. US Patent 6,441,354. US Patent 6,379,791. US Patent 6,361,826. US Patent 6,267,950. Hurley, J M, WO2014209963, PolyOne Corporation, Dec. 31, 2014. Chen, Y; Li, X, WO20141233670, Honeywell International Inc., Aug. 14, 2014. Homma, M M; Homma, V M, US9050272, Jun. 9, 2015. Kim S; Fouladian P; Afinjuomo F; Song Y; Youssef SH; Vaidy S; Garg S, Int. J. Pharm., 611, 121316, 2022. Ono T, Takasaki T, Nakada K, JP2019085587A, Kuraray Co. Ltd., Jun. 6, 2019.

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11.3 BROMOBUTYL RUBBER 11.3.1 FREQUENTLY USED PLASTICIZERS Poly(ethylene vinyl alcohol) and cellulose acetate are used in the tire innerliner,1 and high molecular weight, polyisobutylene plasticizer (molecular weight 2300 daltons) is used in pressure-sensitive tape for roofing applications.2 Petroleum-based oils are used as a plasticizers.4 Paraffinic oil is used as plasticizer in windshield wipers.6 Oligomers of butene are preferred plasticizers for medical rubber products because of their good compatibility with bromobutyl rubber.7 11.3.2 PRACTICAL CONCENTRATIONS • tire innerliner:1 amount adequate to lower the softening point of starch plasticizer mixture is in the range 110-170oC (without plasticizer, it is over 200oC) • pressure-sensitive adhesive2 35-55% • 0.3-1.5 of stearic acid used as a plasticizer in a gas seal5 11.3.3 MAIN FUNCTIONS PERFORMED BY PLASTICIZERS Bromobutyl rubber is relatively impermeable to air and moisture, and it is often used as a major portion of the tire innerliner composition. The addition of dispersion of starch/plasticizer composite reduces the already low air permeability of the butyl rubber-based composition. Too high a softening point of starch makes it difficult to incorporate it into rubber composition.1 In pressure-sensitive roofing tape, plasticizer gives a resiliency and permanent tack.2 It is essential to select suitable concentration of plasticizer that depends on the type and concentration of tackifying resin. 11.3.4 EFFECT OF PLASTICIZERS ON POLYMER AND OTHER ADDITIVES From the studies performed on the roofing tape,2 it is known that lowering molecular weight of plasticizer to 1290 daltons results in extensive bleeding at elevated temperatures (116oC). Tekni-plex3 developed technology using dry reinforcing ingredients, which allow producing plasticizer-free products from several resins, including bromobutyl rubber. References 1 2 3 4 5 6 7

US Patent 6,390,164. US Patent 6,120,869. www.tekni-plex.com/news/031300.html. Wypych, G, Handbook of Polymers, 3rd Ed., ChemTec Publishing, Toronto, 2022. Jurgens, W, US20150203669, Enrichment Technology Company, Jul. 23, 2015. Pieters, E; Lay, R; Gotzen, N; Duval, V, DE102013202109, Robert Bosch GmbH, Aug. 14, 2014. Hochi, K; Minagawa, Y, EP2597047, Sumitomo Rubber Industries, Ltd., Jul. 1, 2015.

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11.4 BUTYL TERPOLYMER 11.4.1 FREQUENTLY USED PLASTICIZERS Polybutene1 and polyisobutylene2,3 are the most frequently used plasticizers. Paraffinic, naphthenic, and aromatic process oils are also used.2,3 Esters of fatty acids and phosphates are less common plasticizers.3 11.4.2 PRACTICAL CONCENTRATIONS • polyisobutylene:2,3 5-9% • polybutene, having molecular weight of 800-2000/mol, was used as plasticizer of roofing underlayment in concentration from 17.5-40 wt%4 • process oil:3 26-28% References 1 2 3 4

Product information. Polysar Butyl XL 21306. Bayer. Coatings and Colorants Division. US Patent 6,297,324. US Patent 5,663,230. Keuler DP, Bausch CC, Alper MD, WO2021041418A1, Bostik, Inc., Mar. 4, 2021.

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11.5 CELLULOSE ACETATE 11.5.1 FREQUENTLY USED PLASTICIZERS Large body of information is available on plasticization of cellulose acetate because of early attempts of its plasticization and wide spread application of plasticized materials from cellulose acetate.1-41 The following plasticizers and plasticizing compounds are frequently used: • 1-butyl-3-methylimidazolium chloride (ionic liquid)39 • acetyl triethyl citrate (biodegradable film,12 cigarette filter24) • tributyl citrate (osmotic membrane26) • triethyl citrate (biodegradable film,12 food wraps,18 cigarette filters,19,24 osmotic membrane,26 eco-composite32) • tri-(2-ethylhexyl) phosphate (flame retarding plasticizer) • triphenyl phosphate (photographic film base,8,31 flame retardant in sheeting, moldings and coatings,2 magnetic tape produced between 1935 and 1960, conductive composite22) • tricresyl phosphate (orientational birefringence30) • dimethyl phthalate ((film, varnishes, rocket propellants, lacquers, safety glass)14 conductive composite22) • diethyl phthalate (eye-wear frames,1 biodegradable film,10 fast-fusing plasticizer,16 scotch tape, mulch film,20 conductive composite,22 film,27 archival films,37 biodegradable, compostable plastics29) • di-(2-ethylhexyl) phthalate (coatings)15 • dimethyl sebacate • dioctyl sebacate (membranes6) • polyalkylene glycol (biodegradable foam23) • polyethylene glycol (fibers,7 osmotic membrane26) • polypropylene glycol (film13) • sulfolane (2,3,4,5-tetrahydrothiophene-1,1-dioxane)17 • toluenesulfonamide derivatives (paper laminate25) • triacetin − glyceryl triacetate (cigarette filter,24,28,40 microspheres,21 paper laminate25) • internal plasticization (reaction with maleic anhydride, glycerol, and citrate esters during melt processing2) • liquids and vapor in contact (water,1 methanol4) • carbohydrate and polyol esters (polymer compositions34) • sugar ester (liquid crystalline displays35). 11.5.2 PRACTICAL CONCENTRATIONS The following are the most typical ranges of plasticizer concentrations in different products: • acetyl triethyl citrate (biodegradable film12 − 20-50%, cigarette filter24 − 1-40 wt%) • tributyl citrate (osmotic membrane26 − 21-23 wt%) • triethyl citrate (biodegradable film12 − 20-50%, osmotic membrane26 − 5-8 wt%, eco-composite32 − 20 wt%)

11.5 Cellulose acetate

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323

triphenyl phosphate (photographic film base2 − 13-17 phr,8 flame retardant in sheeting2 − 15 phr, moldings2 − 20 phr, conductive composite22 − 30-60 phr) tricresyl phosphate (orientation birefringence30 − 5 wt%) dimethyl phthalate (conductive composite22 − 30-60 phr) diethyl phthalate (biodegradable film10 − 10%, mulch film20 − 17 wt%, conductive composite22 − 30-60 phr, biodegradable, compostable plastic9 − 25 wt%); partial miscibility (characterized by differential scanning calorimetry) is observed above 25 wt% of DEP content38 dioctyl sebacate (membranes6 − 34 wt%) polyalkylene glycol (biodegradable foam23 − 20-40 phr) polyethylene glycol (fibers7 − 10-40 wt%) polypropylene glycol (film13 − 19 wt%) triacetin (cigarette filter28,40 − 6-9 wt%, microspheres21 − 6-10 wt%, paper laminate25) sugar ester35 − 5-15 wt%

11.5.3 MAIN FUNCTIONS PERFORMED BY PLASTICIZERS The following functions are performed by plasticizers: • reducing material hardness and other mechanical properties such as tensile strength, tensile modulus, flexural strength, flexural modulus1,31 • reducing glass transition temperature12,31 • influencing diffusion coefficient of liquids and gases permeating through membranes4,6 • phosphates impart flame retarding properties2,30-31 • orientation birefringence30 • environmentally friendly32 • low haze35 • improvement of LCP properties35 • permanent coalescing agent and solvent • fiber-to-fiber bonding agent • shortening the drying process in solvent-containing processes by reducing the amount of solvent required In the archival films, the higher the plasticizer content, the greater the ability to strain hardening, and therefore the least vulnerable to mechanical damage from archival handling.37 The critical plasticizer content and the working properties of cellulose acetate film provide a means of assessing stability and highlights artifacts at risk from physical damage.37 11.5.4 MECHANISM OF PLASTICIZER ACTION In many instances, polymers are contacted with liquids that penetrate their structure. This process is usually enhanced when the liquid has a plasticizing effect on polymer. Permeation of solvent through pervaporation membrane is a special case of such a situation. Figure 11.5.1 shows a schematic transport model of a mixture of methanol, MeOH, and methyl tert-butyl ether, MTBE, through cellulose triacetate pervaporation membrane.4 In this composition of solvents, MeOH has a much greater plasticizing effect than MTBE. Experimental data show that when methanol concentration in feed is low, the per-

324

Figure 11.5.1. Schematic transport model of MeOH and MTBE. A. Low MeOH concentration. B. High MeOH concentration. X - hydrophilic groups. [Adapted, by permission, from Shuguang Cao, Yanqiao Shi, Guanwen Chen, Polym. Intl., 49, No.2, Feb.2000, p.209-15.]

Plasticizers Use and Selection for Specific Polymers

Figure 11.5.2. Glass transition temperatures of cellulose acetate samples plasticized with variable quantities of of triethyl citrate, TCE, and acetyl triethyl citrate, ATEC. [Data from Ghiya V P; Dave V; Gross R A; McCarthy S P, J. Macromol. Sci. A, A33, No.5, 1996, p.627-38.]

Figure 11.5.3. Rockwell hardness of cellulose acetate samples plasticized with variable quantities of diethyl phthalate. [Data from Garner D P; DiSano M T, Polym. Mater. Sci. Eng., 75, 2, 301-2, 1996.]

Figure 11.5.4. Rockwell hardness of cellulose acetate samples plasticized with 24.9 wt% of diethyl phthalate at different moisture levels. [Data from Garner D P; DiSano M T, Polym. Mater. Sci. Eng., 75, 2, 301-2, 1996.]

meation of MTBE is very low, and it drastically increases above 15 wt% of MeOH in feed. Permeation of MeOH is quite independent of its concentration in the feed. At a low concentration of MeOH in feed, a large number of both MeOH and MTBE molecules are dissolved in the membrane, and only smaller molecules of methanol permeate (Figure 11.5.1.A). With the extend of plasticization increased (with MeOH concentra-

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325

tion increased), more hydrophilic groups are blocked by MeOH, and MTBE passes through the membrane unabsorbed. This causes an increase in MTBE pervaporation flux (Figure 11.5.1.B).

11.5.5 EFFECT OF PLASTICIZERS ON POLYMER AND OTHER ADDITIVES Figure 11.5.2 shows that the addition of citrate plasticizer decreases the glass transition temperature of the polymer as expected from plasticizing effect. There is very little difference between the plasticizers − most likely because plasticizers studied had very similar chemical structures.12 Figure 11.5.3 shows that increased concentration of plasticizer reduces the hardness of cellulose acetate parts. Figure 11.5.4 shows that the potential moisture absorption must be accounted for to predict real properties of products in their normal performance conditions.1 Water acts as a co-plasticizer and changes properties of the product depending on the amount of equilibrium moisture absorbed. Because of its origin, cellulose acetate is considered an environmentally-friendly polymer. It is therefore important that additives used for its processing do not change its toxicity or decrease its biodegradability. Figure 11.5.5 shows that the addition of triethyl citrate increases the degradation rate of the polymer. The higher the concentration of the plasticizer, the faster the decomposition of the polymer during composting.12 Glycerol and triethyl citrate plasticizers affected molecular, thermal, mechanical, and barrier properties of cellulose acetate films.41 Cellulose acetate plasticized by 10 wt% of diethyl phthalate had the same biodegradation rate, measured by conversion Figure 11.5.5. Loss of triethyl citrate, TEC, and total composition (cellulose acetate + TEC) during compost- of carbon to CO , as an unplasticized poly2 ing for 30 days. [Data from Ghiya V P; Dave V; Gross R 10 At the same time, plasticizers A; McCarthy S P, J. Macromol. Sci. A, A33, No.5, 1996, mer. decomposed very rapidly to harmless degp.627-38.] radation products. After 10 weeks, more than 80% plasticizer was converted compared to about 20% polymer conversion. Cellulose acetate undergoes degradation, producing acetic acid. This process is of considerable importance in the preservation of magnetic tapes and laminated documents. Magnetic recording tape backing was manufactured from cellulose acetate from its invention in 1935 in Germany until 1960. Polymer deterioration led to the loss of plasticizer (triphenyl phosphate), causing rapid deterioration of the tape. Similar problems existed in films where plasticized cellulose acetate was used until 1985. The degradation process was increased by increased temperature and humidity. In the middle of XXth century, some museum-quality documents were preserved for display by laminating between the sheets of cellulose acetate. Declaration of Indepen-

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dence, written by Thomas Jefferson in 1776, is one such document. In 1947, this document was laminated between two sheets of cellulose acetate. It is feared that this treatment may ultimately lead to the complete deterioration of the document.36

References 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41

Garner D P; DiSano M T, Polym. Mater. Sci. Eng., 75, 2, 301-2, 1996. Seung-Hwan Lee; Shiraishi N, J. Appl. Polym. Sci., 81, No.1, 5th July 2001, p.243-50. Landry C J T; Lum K K; O'Reilly J M, Polymer, 42, No.13, 2001, p.5781-92. Shuguang Cao, Yanqiao Shi, Guanwen Chen, Polym. Intl., 49, No.2, Feb.2000, p.209-15. Mikheev Y A; Guseva L N; Zaikov G E, Polym. Sci. Ser. A, 41, No.2, Feb.1999, p.236-45. Mowery K A; Meyerhoff M E, Polymer, 40, No.22, 1999, p. 6203-7. US Patent 5,707,737. US Patent 5,686,036. Mikheev Y A; Guseva L A; Zaikov G E, J. Appl. Polym. Sci., 67, No.10, 7th March 1998, p.1693-700. Jiang L; Hinrichsen G, Angew. Makromol. Chem., 253, Dec.1997, p.193-200. Gul' V E; Sdobnikova O A; Khanchich O A; Peshekhonova A L; Samoilova L G, Intl. Polym. Sci. Technol., 23, No.9, 1996, p.T/85-7. Ghiya V P; Dave V; Gross R A; McCarthy S P, J. Macromol. Sci. A, A33, No.5, 1996, p.627-38. Mayer J M; Elion G R; Buchanan C M; Sullivan B K; Pratt S D; Kaplan D L, J. Macromol. Sci. A, A32, No.4, 1995, p.775-85. Dimethyl phthalate. Chemical Fact Sheet. Spectrum. Palatinol AH. Technical Leaflet M 2189. BASF 2000. Palatinol A. Technical Leaflet M 1552. BASF 2000. Sulfonate. Kemicon. Citroflex 2 Citrofol AI. US Patent 6,462,120. US Patent 6,251,432. US Patent 6,235,220. US Patent 6,221,924. US Patent 5,947,126. US Patent 5,928,777. US Patent 5,783,213. US Patent 5,705,632. US Patent 5,568,819. US Patent 5,505,830. Abd Manaf M E, Tsuji M, Shiroyama Y, Yamaguchi M, Macromolecules, 44, 3942-49, 2011. Kim H T, Kim M H, Kim B, Koo C M, Koo K K, Hong S M, Mol. Cryst. Liq. Cryst., 512, 188-98, 2009. Park H-M, Misra M, Drzal L T, Mohanty A K, Biomacromolecules, 5, 2281-88, 2004. Godfrey D A, US Patent 8,007,918 B2, Eastman Chemical Co., Aug. 30, 2011. Buchanan C M, Buchanan N L, Edgar K J, Lambert J L, US Patent 7,276,546 B2, Eastman Chemical Co., Oct. 2, 2007. Hisakado Y, Takeda J, Fujiwara I, Nagura M, Fukagawa N, US Patent Application US 2011/0255037 A1, Fuji Film, Oct. 20, 2011. Conley J, Today’s Chemists at Work, 7, 2, 42-44, 46, 1998. Richardson, E; Giachet, M T; Schilling, M; Learner, T, Polym. Deg. Stab., 107, 231-6, 2014. Bao, C Y; Long, D R; Vgelati, C, Carbohydrate Polym., 116, 95-102, 2015. Bendaoud, A; Chalamet, Y, Carhydrate Polym., 108, 75-82, 2014. Lemmouchi, Y; Quintana, R; Persenaire, O; Bonnaud, L; Dubois, P, WO2013011301, British American Tobacco, Jan. 24, 2013. CôccoTeixeira S, Assis Silva R, Velosode Oliveira T, Stringheta PC, Moacir Ribeiro Pinto MR, de Fátima Ferreira Soares N, Food Sci., 42, 101202, 2021.

11.6 Cellulose butyrate and propionate

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11.6 CELLULOSE BUTYRATE AND PROPIONATE 11.6.1 FREQUENTLY USED PLASTICIZERS The use of the following plasticizers was documented:1,5-12 • cellulose butyrate: octyl adipate,12 diethylene glycol dibenzoate,14 2-ethylhexyl)1,4-benzenedicarboxylate,14 o-phenylphenol ethylene oxide adduct,13 N-toluene sulfonamide13 • cellulose propionate: poly(1,3-butylene glycol adipate) (Drapex 429),1 polyester sebacate (Paraplex G-25),1 tricresyl phosphate,2 diethylene glycol dibenzoate,14 carboxydrate esters of polyol,4 octyl adipate12 11.6.2 PRACTICAL CONCENTRATIONS Dioctyl adipate was used in the concentration range from 6 to 14 wt%.12 Polyester sebacate was used in a concentration of 7.7 wt%, tricresyl phosphate was used in a concentration of 5 wt%,2 and polyglycol adipate at a concentration of 11.9 wt%.1 11.6.3 MAIN FUNCTIONS PERFORMED BY PLASTICIZERS Plasticizers were used to lower the glass transition temperature of polymer1,12 and to improve its moldability.12 Tricresyl phosphate was used to affect orientation birefringence in cellulose propionate.2 Plasticizer of invention had a boiling point greater than 370oC.3 11.6.4 EFFECT OF PLASTICIZERS ON POLYMER AND OTHER ADDITIVES Figures 11.6.1 and 11.6.2 show that both yield strength and elastic modulus of cellulose acetate propionate linearly decrease when concentration of plasticizer increases. A plasticizer containing a photoactive agent was added to cellulose ester fibers to obtain plasticized cellulose ester fibers useful for the production of degradable filters.15 The plasticizer was triacetin, and the photoactive agent included different types of tita-

Figure 11.6.1. Yield strength of cellulose acetate propionate vs. octyl adipate concentration. [Data from Moskala E J; Pecorini T J, Polym. Eng. Sci., 34, No.18, Sept.1994, p.1387-92.]

Figure 11.6.2. Elastic modulus of cellulose acetate propionate vs. octyl adipate concentration. [Data from Moskala E J; Pecorini T J, Polym. Eng. Sci., 34, No.18, Sept.1994, p.1387-92.]

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nium dioxide, for example, mixed-phase titanium dioxide particles.15 The filters were useful for preparing cigarette filters.15

References 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Landry C J T; Lum K K; O'Reilly J M, Polymer, 42, No.13, 2001, p.5781-92. Abd Manaf M E, Tsuji M, Shiroyama Y, Yamaguchi M, Macromolecules, 44, 3942-49, 2011. Godfrey D A, US Patent 8,007,918 B2, Eastman Chemical Co., Aug. 30, 2011. Buchanan C M, Buchanan N L, Edgar K J, Lambert J L, US Patent 7,276,546 B2, Eastman Chemical Co., Oct. 2, 2007. US Patent 6,036,913. US Patent 5,985,951. US Patent 5,720,803. US Patent 5,711,793. US Patent 5,609,677. Beck M I; Tomka I, J. Polym. Sci.: Polym. Phys. Ed., 35, No.4, March 1997, p.639-53. Braun D; Bahlig K H, Angew. Makromol. Chem., 224, Jan.1995, p.61-71. Moskala E J; Pecorini T J, Polym. Eng. Sci., 34, No.18, Sept.1994, p.1387-92. Allison R W, Archive of Watermarks and Papers in Greek Manuscripts. About Dylux Paper, 1996. Basu, S K; Helmer, B J; Shelby, M D; Wood, M; Dagenhart, C S; De, W J S; Testa, C A, WO2013086079, Eastman Chemical Company, Jun. 13, 2013. Wilson, S A; Steach, J K; Fauver, J S, CA2835662, Eastman Chemical Company, Dec. 27, 2012.

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11.7 CELLULOSE NITRATE 11.7.1 FREQUENTLY USED PLASTICIZERS The following plasticizers are/were used in plasticization of cellulose nitrate:1-15 • 2-ethylhexyl diphenyl phosphate16 • acetyl tributyl citrate4,16 • acrylic resin (Acronal 700 L)5 in UV resistant lacquers and coatings on paper, plastic film, and aluminium foil • aliphatic polyurethane as polymeric plasticizer in paints12 • butyl benzyl phthalate in nail enamel3 and jet ink composition13 • camphor in nail enamel,1 celluloid11 (two parts of cellulose nitrate and one part of camphor), horn-like material (credited as the first application of plastics beginning in 1870),11 cinematographic film from 191517 • castor oil (the first use of plasticizer which begun in 1860)11 • dibutyl phthalate4,11 in nail enamel,1 films,11 and preparation stimulating nail growth15 • dimethyl phthalate7 − auxiliary plasticizer for surface coatings • diisooctyl phthalate in lacquers11 • epoxidized soybean oil4 • 2-ethylhexyl diphenyl phosphate • glyceryl triacetate4 • glyceryl tribenzoate in nail enamel3 • N-ethyl (o,p)-toluenesulfonamide14 as plasticizer in alcohol-resistant jet ink • octyl diphenyl phosphate8 in flame retarding, low smoke formulations • sucrose acetate isobutyrate4 in nail enamel3 • tricresyl phosphate6 for flame retarded products and coatings and in films11 • triethylene glycol10 • urea resin (Plastigen G)9 in flexible coatings having reduced yellowing, high gloss retention, and resistance to aging 11.7.2 PRACTICAL CONCENTRATIONS • nail enamel: camphor − 5 phr + dibutyl phthalate 27.7 phr,1 combination of three plasticizers − 10 wt%3 • lacquer: cellulose nitrate/urea resin = 1/1.59 • film:11 camphor − 33 wt% or phthalate plasticizer − 20 wt% • jet ink composition: butyl benzyl phthalate − 25 phr13 or N-ethyl (o,p)-toluenesulfonamide − 20 phr14 • nail growth stimulating formulation: dibutyl phthalate − 20 phr15 11.7.3 MAIN FUNCTIONS PERFORMED BY PLASTICIZERS The following are the main functions played by plasticizers in cellulose nitrate: • softening and imparting flexibility to polymeric film (e.g., nail enamel1 or jet ink13) • promoting heat-sealability and adhesion of coating3 • flame retarding properties (phosphate plasticizers) • improvement of outdoor performance9

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• •

improvement of processability11 improvement of solvent resistance14

11.7.4 EFFECT OF PLASTICIZERS ON POLYMER AND OTHER ADDITIVES Measurement of the saturated vapor pressure of plasticizers over plasticized cellulose nitrate was used for calculation of chemical potentials of plasticizers and partial enthalpies and entropies of mixing.2 Phthalate plasticizers were stable in cellulose nitrate films, which, tested after 41 years of storage, retained all initial amounts of 20 wt% of plasticizers.11 Camphor is known to be slowly lost from celluloid. After 30-40 years, it reaches a concentration of 15 wt% (initial concentration 33 wt%), and then concentration remains quite stable.11 The process of plasticizer loss may be accelerated by the decomposition of resin, which produces nitrous oxides combining with water to form nitrous and nitric acids. Acids affect the stability of plasticizers and their interaction with polymer. 11.7.5 TYPICAL FORMULATIONS Fast-drying, non-bubbling pigmented nail enamel:1 Ethyl acetate Butyl acetate Isopropyl alcohol Nitrocellulose Polyester film-forming resin Camphor Dibutyl phthalate Benzophenone-1 Vinyl silicone fast-drying copolymer VS-80 Stearalkonium hectorite Pigments Dow Corning 200/350 antifoam agent Jet ink composition:13 Acetone Ethanol, anhydrous Cellulose nitrate (35%, isopropanol 15%, acetone 50%) Super ester A-75 (Arakawa) Benzyl butyl phthalate Primary amyl acetate Orasol Black RLI (Ciba) Silwet L-7622 (Crompton)

30.5 wt% 25.0 5.0 18.0 9.0 1.0 5.0 0.5 0.8 2.0 3.0 0.2

50.0 wt% 20.0 18 3.0 1.5 3.0 4.0 0.5

References 1 2 3 4 5 6 7

US Patent 5,972,095. Pleshakov D V; Lotmentsev Yu M; ZiQiang S; Kondakova N N; Lukashev A V, Polym. Sci. Ser. A, 41, No.3, March 1999, p.364-70. US Patent 5,662,891. Swain M, Polym. Paint Colour J., 186, No.4384, Sept.1996, p.26-7. Acronal 700 L. Technical information T/ED-N 338, BASF, 1999. Phosflex Lindol XP Plus. Akzo Nobel, 1998. Palatinol M. Technical Leaflet M 803 e, BASF, 2001.

11.7 Cellulose nitrate

8 9 10 11 12 13 14 15 16 17

331

Santicizer 141. Ferro Corporation, 2002. Plastigen G. BASF. Triethylene glycol. Technical Data Sheet. Slovnaft. Selwitz C, Cellulose Nitrate in Conservation, J. Paul Getty Trust, 1988. Cerqueira M A, Souza B W S, Teixeira J A, Vincente A A, Food Hydrocolloids, 27, 175-84, 2012. US Patent 5,969,045. US Patent 6,414,071. US Patent 5,539,188. Wypych, G, Handbook of Polymers, 3rd Ed., ChemTec Publishing, Toronto, 2022. Ciliberto, E; Gemmellaro, P; Iannuso, V; La Delfa, S; Urso, R G; Viscuso, E, Procedia Chem., 8, 175-84, 2013.

332

Plasticizers Use and Selection for Specific Polymers

11.8 CHITOSAN 11.8.1 FREQUENTLY USED PLASTICIZERS • glycerol1,3,5,7 • corn oil1 • ethylene glycol3 • sorbitol3 • imidazolium-based ionic liquids in biomimetic composites4 • poly(ethylene glycol)5 (increases biodegradability in composting) 11.8.2 PRACTICAL CONCENTRATIONS • addition of 2 wt% of glycerol decreased glass transition temperature of the film by 140oC • addition of 0.75 wt% corn oil increased glass transition temperature by 30oC.1 11.8.3 MAIN FUNCTIONS PERFORMED BY PLASTICIZERS • improve ductility • increase elongation • increase biodegradability 11.8.4 EFFECT OF PLASTICIZERS ON POLYMER AND OTHER ADDITIVES Films plasticized with increasing amounts of glycerol had lower tensile strength and higher elongation, but films containing corn oil as a plasticizer had both lower tensile and elongation.1 Water sensitivity of glycerol films has increased, and these films gave good water-barrier properties.1 Glycerol was more effective as a plasticizer than oleic acid, resulting in as high as 70% strain, compared to 26% strain obtained with 30 wt% oleic acid.2 Biofilms were degraded in compost.5 The addition of poly(ethylene glycol) to chitosan increased its biodegradability to a value of BOD5 of 2.33 O2/mg CO.5 Chitosan films were prepared with the addition of antioxidant poly(β-pinene) oligomer.6 The morphology of the blends was significantly altered due to poly(β-pinene) load.6 Poly(β-pinene) promoted plasticizing effect on chitosan macromolecular chains.6 References 1 2 3 4 5 6 7

Cerqueira M A, Souza B W S, Teixeira J A, Vincente A A, Food Hydrocolloids, 27, 175-84, 2012. Vlacha, M; Giannakas, A; Katapodis, P; Stamalis, H; Ladavos, A; Barkoula, N-M, Food Hydrocolloids, 57, 10-9, 2016. Figueiredo, L; Moura, C; Pinto, L F V; Ferreira, F C; Rodrigues, A, Procedia Eng., 110, 175-82, 2015. Boesel, L F, Carbohydrate Polym., 115, 356-63, 2015. Kammoun, M; Haddar, M; Kallel, T K; Dammak, M; Sayarin A, Int. J. Biol. Macromol., 62, 433-8, 2013. Ribeiro Rodrigues P, Marangoni Junior L, Cândidode Souza WF, Harumi Sato H, Vercelino Alves RM, Pioli Vieira R, Int. J. Biol. Macromol., 193A, 425-32, 2021. Zhang X, Felts J, WO2020237205A1, Cruz Foam, Inc., Nov. 26, 2020.

11.9 Chlorinated polyvinylchloride

333

11.9 CHLORINATED POLYVINYLCHLORIDE 11.9.1 FREQUENTLY USED PLASTICIZERS • 1,4-cyclohexane dimethanol dibenzoate • chloroparaffin6 • diisodecyl phthalate7 in extrusion molding compound 11.9.2 EFFECT OF PLASTICIZERS ON POLYMER AND OTHER ADDITIVES Chlorination of polyvinylchloride increases tensile, compression, and flexural strengths by about 30%. Impact strength is more than doubled, and even elongation is doubled. Considering this, plasticization most likely acts in the opposite direction and reverses these positive changes for some applications.2,3 In addition, plasticization lowers heat distortion temperature, which in many applications of chlorinated polyvinylchloride, CPVC, is a critical performance characteristic.2 In one application,4 plasticizer was used to improve processability and to take advantage of antiplasticization to improve some final properties of the material. CPVC was plasticized with 1,4-cyclohexane dimethanol dibenzoate (Benzoflex R 352). When plasticizer was used at 7 phr, the viscosity was reduced because of replacing polymer-polymer hydrogen bonding with polymer-plasticizer hydrogen bonding.1 Lowering plasticizer level to 4 phr resulted not only in lowering viscosity and increasing thermal stability, but also tensile strength, flexural strength, and modulus were increased. At the same time, oven sag resistance and impact strength were decreased. These changes were explained by the effect of antiplasticization.4 In the cable industry, plasticization of CPVC by phthalates and phosphates improves the flexibility and processability of CPVC. At the same time, the addition of plasticizers lowers the limiting oxygen index and increases smoke production. The schematic diagram below illustrates the mechanism of degradation in the absence (A) and presence of smokesuppressing compound − basic iron oxide, FeOOH (B).5

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Plasticizers Use and Selection for Specific Polymers

A)

COOR COOR

COOH

Δ HCl

+ 2RCl

COOH Δ

SMOKE

+ 2CO2

combustion

B)

COOR COOR

FeOOH + HCl

COOH COOH

COOH

Δ HCl

COOH

+ 2RCl

FeOCl + H2O

+ FeOCl

COCl

Δ

COOH

+ FeOOH

Δ

HCl +

CO O CO

FeOOH FeOCl + H2O

CPVC produces substantial quantities of HCl, which is a volatile product of degradation. Without the presence of FeOOH (A), first, phthalic acid is produced, which is then decarboxylated to benzene. Under high-temperature conditions, benzene is further degraded and produces smoke. Only traces of phthalic anhydride are detected under these conditions. When small amounts of FeOOH (0.25 phr) are present, smoke production is suppressed by 40%. This is attributed to the formation of phthalic anhydride, as shown by the reactions in the scheme (B). Only small quantities of FeOOH are needed because it is used in a cyclical process, which keeps both required forms in equilibrium. Phthalic acid produces four times more smoke than phthalic anhydride, which sublimes out of the system. A plasticizer may be added to the chlorinated vinylchloride resin composition for the purpose of improving processability during molding, but a large amount may lower the thermal stability of the molded product.8 The plasticizer type is not particularly limited,

11.9 Chlorinated polyvinylchloride

335

and examples include dibutyl phthalate, di-2-ethylhexyl phthalate, and di-2-ethylhexyl adipate.8

References 1 2 3 4 5 6 7 8

Santicizer 141. Ferro Corporation, 2002. US Patent 5,969,045. US Patent 6,414,071. US Patent 5,539,188. Carthy P; White S; Price D; Lu L, Polym. Deg. Stab., 63, No.3, 1999, p.465-8. Hahma, A; Licha, J; Phamshoenwetter, O, WO201400896, Diehl Btg Defence GmbH, Jan. 16, 2014. Yamasugi, R; Nakazato, K; Yano, H; Otsuka, K; Tono, M, CA2854590, Sekui Chemical Company, Jun., 6, 2013. JPWO2021039993A1, Nov. 2, 2021.

336

Plasticizers Use and Selection for Specific Polymers

11.10 CHLOROSULFONATED POLYETHYLENE 11.10.1 FREQUENTLY USED PLASTICIZERS • plasticizers used infrequently and in small quantities, mainly as process oils1 • poly(ethylene glycol)7 • dioctyl sebacate • dioctyl adipate 11.10.2 EFFECT OF PLASTICIZERS ON POLYMER AND OTHER ADDITIVES Chlorosulfonated polyethylene, CSP, was developed by Dupont to be used in vulcanized and non-vulcanized products. It is a very flexible material without the use of plasticizers, and as such, it found many applications competing with plasticized PVC. For this reason, most products do not use plasticizers, but some exceptions can be found. Antitack rubber suitable for manufacturing pneumatic tires is produced from a combination of CSP and natural rubber.2 This composition used 3 wt% of undisclosed plasticizer (process oil). Paper transport belt made from a composition of CSP and EPDM rubber used 3 phr of polyethylene glycol and 25 phr of dioctyl sebacate.3 A membrane obtained from blending CSP and chlorinated polyethylene contained 6 phr of tri(2-ethylhexyl) phosphate.5 All these cases seem to suggest that plasticizer may function here as a compatibilizer of the polymer blend. In one case,5 it was mentioned that phosphate type plasticizer was selected because it reduced mildew growth in conjunction with common fungicide (Busan 11). Process oil, which is either dioctyl adipate or dioctyl sebacate, is used for the production of the transmission belt.4 It is also expected that it will act as a “softener”. In application of fluoro-plastic additives, Dupont’s research gave a formulation of vulcanized CSP, which contained 20 phr of dioctyl sebacate.6 It can be thus concluded that some quantities of plasticizers can also be found in CSP, even more likely in vulcanized products. REFERENCES 1 2 3 4 5 6 7

Wypych, G, Handbook of Polymers, 3rd Ed., ChemTec Publishing, Toronto, 2020. US Patent 6,363,989. US Patent 6,206,364. US Patent 5,711,734. US Patent 5,523,357. Morgan R A; Stewart C W; Thomas E W; Stahl W M, Reinforcement with Fluoroplastic Additive. Dupont. WO2021004099A1, Jan. 14, 2021.

11.11 Copolymers

337

11.11 COPOLYMERS Unlike for other polymers, the information given here for copolymers is much less material-specific because the group has a wide variety of chemical compositions and structures.1-14 The information is intended to show the importance of plasticizers in the plasticization of copolymers. Examples that are given also include some polymeric plasticizers made out of copolymers.

11.11.1 FREQUENTLY USED PLASTICIZERS The following plasticizers were used for the plasticization of various copolymers: • citrate esters were used to prepare plastic compositions for medical containers for storage of red blood cells. Polyolefin based copolymer was used as a matrix.5 • naphthenic oil and dioctyl phthalate were used for plasticization of styrene-ethylene-butylene-styrene, SEBS, copolymer (Kraton G type). The plasticized copolymer was used to modify asphalt in roofing, sealing, paving, and waterproofing applications.6 • high levels of plasticizer (white oil) were used to produce crystal gels from linear SEBS copolymers8 • non-fugitive polyoxyethylene aryl ether plasticizer was found to improve filmforming properties of coating based on urethane acrylic copolymer7 • poly(ethylene glycol)18 • hydroxyl group-containing monomer is used in copolymerization with vinyl chloride alone or in the mixture with other monomers. The presence of hydroxyl groups in the polymer increases plasticizer (dioctyl or dihexyl phthalate) uptake in water-based system10 • lauric, sebacic, and citric acids esters were used as plasticizers added in large concentrations to form biodegradable copolymer products in aqueous dispersions11 • polystyrene oligomer and dioctyl phthalate selectively plasticized styrene blocks in ε-caprolactone-styrene diblock copolymers13 • a variety of plasticizers, including most common groups, were proposed for use in interpolymers of α-olefin/vinylidene aromatic copolymer for applications in films, adhesives, sealants, and molded parts12 • photopolymerizable unsaturated liquid plasticizer based on bisphenol-diacrylate or ethoxylated trimethylenol propane triacylate was used in the preparation of photoresists and solder mask2 • copolymer of ethylene and carbon monoxide with grafted benzotriazole UV absorber was developed for use in PVC formulations1 • large quantities of water are absorbed by acrylic-based latex, but an only small part of this water plasticizes copolymer with the remaining part being separated from polymer9 • sorbitol was used as water-soluble plasticizer for ion-sensitive polymeric materials4 • 1,5-diazido-3-nitrazapentane, DIANP, was used as an energetic plasticizer in copolymer of 3,3’-bis(azidomethyl) oxetane19

338

Plasticizers Use and Selection for Specific Polymers

• • •

•

ethylene-vinyl acetate copolymer is used as a plasticizer in polyvinylchloride and polylactate15 PVC graft copolymers do not require plasticizer16 glycerol tribenzoate and 1,4-cyclohexane dimethanol dibenzoate are used as solid plasticizers in hotmelt adhesive from the mixture of copolymers (ethyleneoctene copolymer and styrene-ethylene-butylene-styrene copolymer)17 glycerol was used as a plasticizer to increase the flow of poly(acrylonitrile)-costyrene copolymer during spinning20

11.11.2 PRACTICAL CONCENTRATIONS Concentrations of plasticizers used in various applications vary in a wide range: • 2 phr polyoxyethylene aryl ether plasticizer improved film-forming properties of coating based on urethane acrylic copolymer7 • 11 wt% of copolymeric plasticizer with grafted UV absorber was used in PVC formulation1 • 5-20 wt% of citrate plasticizer was used in the formation of red blood cells container made from polyolefin-based copolymer5 • 25 to 40 wt% of naphthenic oil alone or in the mixture with dioctyl phthalate was used to plasticize SEBS for asphalt modification6 • 40 phr dihexyl phthalate and 5 phr of epoxidized soybean oil were incorporated into water-based coating obtained from hydroxyl group-containing copolymer10 • 10-50 phr of plasticizer was incorporated in biodegradable copolymer product11 • 250 phr of white mineral oil was used to form crystal gels from linear SEBS copolymers8 11.11.3 MAIN FUNCTIONS PERFORMED BY PLASTICIZERS The following functions were performed by plasticizers in copolymers: • providing reactive sites for grafting UV absorber1 • facilitating processing with ingredient, which is photopolymerizable2 • lowering viscosity without affecting adhesive strength3 • suppressing hemolysis (premature breakdown) of red blood cells5 • non-fugitive coalescing agent, which assists in film formation and contributes to the flexibility of coating7 • improving crack propagation, tear, and fatigue resistance8 • increasing plasticizer take-up by interacting with hydroxyl groups of binder in water-based system10 • helping in biological degradation of material11 • lowering glass transition temperature by affecting a selected block13 11.11.4 MECHANISM OF PLASTICIZER ACTION Diblock copolymer was synthesized, which contains ε-caprolactone, PCL, and polystyrene, PS, blocks.13 This copolymer did not crystallize at any temperature when quenched. PCL is the crystallizing block, and it has a melting temperature of 50oC. PS block has a glass transition temperature of 95oC. Because PS block solidifies before PCL may begin crystallization, the crystallization of copolymer does not occur. To remediate the situation, it is necessary to increase the mobility of PS block by selective plasticization. Two plasticizers were used for this purpose: oligomeric polystyrene and dioctyl phthalate, DOP.

11.11 Copolymers

339

Both plasticizers were expected to plasticize PS blocks without affecting PCL blocks. Figure 11.11.1 shows that the assumption is correct. Regardless of the concentration of plasticizer, the melting point of PCL blocks remained unchanged at about 50oC. The higher the plasticizer concentration (the lower the φPS), the lower the glass transition temperature. This means that DOP plasticizes PS blocks without affecting PCL blocks. It is also noticeable that the plasticizer is fully miscible with PS blocks. Crystallinity studies13 show that there is a dramatic change in PCL crystallinity when the concentration of plasticizer is sufficient to reduce glass transition temperaFigure 11.11.1. Glass transition temperatures of polystyture of PS block to about 40oC, which is at rene block, Tg,PS, and melting temperatures of ε-caprolactone block, Tm,PCL, for ε-caprolactone-styrene φPS ~ 0.4. Thus, intuitively suggested readiblock copolymer plasticized with variable amounts of son for lack of crystallization is now conDOP (φPS = (weight of PS)/(total weight of PS and firmed by results. DOP). [Data from Nojima S; Tanaka H; Rohadi A; Sasaki S, Polymer, 39, Nos.8-9, 1998, p.1727-34.] The above results illustrate important practical principles, which may help in developing systems having suitable properties for certain applications by simply choosing the right concentration of the right plasticizer in block copolymers or perhaps polymer blends as well.

References 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

US Patent 6,147,170. US Patent 6,083,660. US Patent 6,008,148. US Patent 5,986,004. US Patent 5,952,423. US Patent 5,929,144. US Patent 5,783,303. US Patent 5,884,639. Agarwal N; Farris R J, J. Appl. Polym. Sci., 72, No.11, 13th June 1999, p.1407-19. US Patent 5,756,617. US Patent 5,750,617. US Patent 5,739,200. Nojima S; Tanaka H; Rohadi A; Sasaki S, Polymer, 39, Nos.8-9, 1998, p.1727-34. Volkova N N; Erofeev L N; Smirnov L P; Tarasov, Polym. Sci. Ser. A, 38, No.4, April 1996, p.353-9. Wypych, G, Handbook of Polymers, 3rd Ed., ChemTec Publishing, Toronto, 2022. Brizzolara, D; Fischer, I; Gehrke, J-S; Polte, D; Stieneker, A; Sturm, H, US20160075870, Vestolit GmbH, Mar. 17, 2016. Vitrano, M D; Stafeil, K; Hailemichael, T, EP2694609, Bostik, Inc., Feb. 12, 2014. Wurm, D; Grissom, C; Vicari, R, WO2014093509, Seisui Specialty Chemicals America, Llc, Jun. 19, 2014. P j-f; Wu Z-k; Hu Y-w; Fu X-l; Wang J-n; Song X-d; Sun Z-g; Wang M-x, in press, 2021. Fleming R, Candido TO, Granado NP, Pardini LC, Polym. Deg. Stab., 192, 109702, 2021.

340

Plasticizers Use and Selection for Specific Polymers

11.12 CYANOACRYLATES Most commercial glues, such as the popular Crazy Glue, do not use plasticizers. These glues are based on ethyl and butyl derivatives of cyanoacrylate. Applications as adhesive in medicine and veterinary of octyl-2-cyanoacrylate usually require plasticizers.

11.12.1 FREQUENTLY USED PLASTICIZERS For medical purposes, acetyl tributyl citrate is most likely used.1,7 Older inventions also suggested dioctyl phthalate as a useful plasticizer for contact with human skin.11-12 In veterinary applications, dioctyl phthalate2-6,9 and acetyl tributyl citrate2 are likely to be used. It should be underlined that this difference between medical and veterinary applications is more of precautionary nature than formulation based on previous results of studies or regulations, which may limit dioctyl phthalate use for these applications. Acetyl-tri-n-butyl citrate is used to modify the intra-cyanoacrylate alkyl group.13 It is used in storage-stable medical-grade glues.14 Polydimethylsiloxane, hexadimethylsilazane, and polymethylmethacrylate are also added with the aim of increasing the flexibility and elasticity of the polymer.8 Finally, adhesive can be made plasticizer-free by using the composition of polymers in which alkyl is a mixture C1 to C8.10 Use of suitable proportions of different monomers results in required properties. 11.12.2 PRACTICAL CONCENTRATIONS acetyl tributyl citrate was used in concentration ranges as below: 5-7 wt%1 10-30 wt%4 18-25 wt%5,7 dioctyl phthalate was used in concentration ranges as below: 20 wt%2,3 10-30 wt%4 18-25 wt%5,7,11,12 10-15 wt%6 The above shows that concentrations of plasticizers are fairly consistent. 11.12.3 MAIN FUNCTIONS PERFORMED BY PLASTICIZERS In most inventions, the reasons for the use of plasticizers are to increase flexibility. A more extensive study was conducted for dioctyl phthalate, DOP, where appearance, curing time, film formation, flexibility, and durability were compared for n-butyl cyanoacrylates containing from 15 to 50 wt% plasticizer. When DOP was 35 wt% or above, no film was formed. On the contrary, with plasticizer at 15 wt% flexibility and durability suffered. This shows why 20-25 wt% is the most common choice. The plasticizer is also used for viscosity adjustment of hotmelt adhesive comprising cyanoacrylate as a curing compound.15 11.12.4 EFFECT OF PLASTICIZER ON POLYMER AND OTHER ADDITIVES The photocurable composition includes cyanoacrylate component (ethyl cyanoacrylate), metallocene component (ferrocene), photoinitiator (2,4,6-trimethylbenzoydiphenyl phosphine oxide), and plasticizer component (short-chain alkylene compound having a plurality of alkyl esters and/or reverse alkyl esters, such as dimethyl adipate, acetyl triethyl

11.12 Cyanoacrylates

341

citrate, dibutyl sebacate, tributyl trimellitate, or Hexamoll DINCH).16 The best compromise of results was obtained with acetyl triethyl citrate at concentrations between 15 and 25 wt%.16

References 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

US Patent 6,433,096. US Patent 6,342,213. US Patent 6,328,910. US Patent 6,248,800. US Patent 6,214,332. US Patent 6,207,193. US Patent 6,191,202. US Patent 6,183,593. US Patent 6,086,906. US Patent 5,998,472. US Patent 5,665,817. US Patent 5,480,935. Lim, J I; Lee, W-K, Colloids Surf. B: Biointerfaces, 122, 669-73, 2014. Kerber, C W; Adams, C; Friedman, P, US20130089505, Valor Medical, Inc., Apr. 11, 2013. Heemann, M; Paul, C W; Xenidou, M; Schroeder, M; Kostyra, S; Phelan, M, EP2961807, Henkel, Jan. 6, 2016. Li L, Wei X, Attarwala ST, WO2020206405A1, Henkel IP & Holding GmbH, Oct. 8, 2020.

342

Plasticizers Use and Selection for Specific Polymers

11.13 ETHYLCELLULOSE 11.13.1 FREQUENTLY USED PLASTICIZERS • triethyl citrate1-2,4 • dibutyl sebacate3 in controlled-release of drugs 11.13.2 PRACTICAL CONCENTRATIONS • 1-5 wt% triethyl citrate in films2 • 27-33 wt% dibutyl sebacate3 • 10 wt% triethyl citrate5 11.13.3 EFFECT OF PLASTICIZERS ON POLYMER AND OTHER ADDITIVES Ethylcellulose-based microsphere formulations were prepared without and with triethyl citrate content of 10% and 30% by water-in-oil emulsion-solvent evaporation technique.1 Plasticizer was used as a pore-forming agent, and it helped to release the drug from microspheres.1 One of the common strategies to improve the printability of pharmaceutical polymers is by the addition of plasticizers.5 Plasticizers can reduce glass transition temperature of the polymer and decrease operating temperature during hotmelt extrusion and FDM printing.5 Addition of inert filler (i.e., talc), a drug with high melting points (i.e., diclofenac sodium), and polymer with high strength (i.e., plasticized ethylcellulose) effectively improved printability of plasticized Eudragit® EPO.5 Typical plasticizers include triethyl citrate and polyethylene glycol.5 References 1 2 3 4 5

Sengel-Turk C T, Hascicek C, Gonul N, AAPS PharSciTech, 12, 4, 1127-35, 2011. Hegyesi, D; Sovany, T; Berkesi, O; Intye-Hodi, K; Regdon, G, Microchem. J., 110, 36-9, 2013. Vynckler, A-K; Dierickx, L; Saerens, L; Voorspeols, J; Gonnissen, Y; De Beer, T; Vervaet, C; Remon, J P, Int. J. Pharm., 464, 1-2, 65-74, 2014. Wright, C; Oshlack, B; Breder, C, US9060976, Purdue Pahrma, Jun. 23, 2015. Yang Y, Wang H, Xu X, Yang G, Int. J. Pharm., 599, 120410, 2021.

11.14 Epoxy resin

343

11.14 EPOXY RESIN 11.14.1 FREQUENTLY USED PLASTICIZERS Many conventional plasticizers such as phosphates and phthalates are not compatible with the majority of epoxy resins, especially at higher concentrations. They are easily lost from the system, and if retained, they do not affect flexibility.1 Several groups of flexibilizers are used in epoxy resins to modify their mechanical properties. These include: • monofunctional epoxy compounds (e.g., epoxidized oils), which influence the molecular weight of cured resin3 • low molecular weight polyamide resins (e.g., condensation products of trimerized or dimerized vegetable oils and polyamines). These are curing agents, which added at certain proportions to other curatives in the system, may help to modify properties • mercaptan-terminated materials (e.g., polysulfides)4 • polypropylene glycols (300-510 Daltons)20 • reactive diluents (e.g., derivatives of glycidyl ether). These are added to the resin side to reduce its viscosity but are reactive with curative. Similar to monofunctional epoxy compounds, they affect the molecular weight of the polymer and thus its mechanical properties.5 • alkyl- and aryl-substituted phosphonic acid esters are compatible with epoxy resins, also known plasticizers23 For the above reasons, plasticizers are not major components of formulations used for modification of mechanical properties of the final product but are still quite useful, especially in modification of processing characteristics (viscosity) of epoxy resins. The following compounds are found in various formulations: • dibutyl phthalate7,8,15 • low molecular weight (~2000 daltons), condensation product of adipic acid and ethylene and diethylene glycols1 • isodecyl pelargonate (high migration in epoxy systems)12 • poly(propylene glycol alkylphenyl ether) (Plastilit 3060) a hydrophobic plasticizer13 • a variety14 of phthalates,18 phosphates, adipates, and sebacates • cyclohexyl pyrrolidone16 • di-n-decyl phthalate19 • polyoxypropylene diols and triols and hydroxyl-terminated polybutadiene20 11.14.2 PRACTICAL CONCENTRATIONS The following concentrations of plasticizers were used: • dibutyl phthalate − 0-30 wt%,7 0-40 phr,10 30 wt%15 • dioctyl phthalate − 2 wt%11 • di-n-decyl phthalate − 0.2-2 wt%19 • cyclohexyl pyrrolidone − 1 wt%16 • poly(propylene glycol alkylphenyl ether) − 4.3 wt%13 • polysulfide (Thiocol LP3) − 0-60 phr4 • copolymer of adipic acid and ethylene and diethylene glycols − 5 wt%8

344

Plasticizers Use and Selection for Specific Polymers

11.14.3 MAIN FUNCTIONS PERFORMED BY PLASTICIZERS The short-list of functions of plasticizers in epoxy resins includes: • viscosity reduction3,14,16,18,20 • decrease of apparent activation energy of curing reaction4 • reduction of hardness15 It is apparent that plasticizers are mostly used in epoxy resins to reduce viscosity. At the same time, they increase the mobility of reacting components and help in the dissipation of thermal energy formed from exothermic curing reactions. Minor amounts of higher molecular weight, relatively non-volatile monoalcohols, polyols, and other epoxy- or isocyanato-reactive diluents may be used, if desired, to serve as plasticizers in the epoxy compositions.22 11.14.4 EFFECT OF PLASTICIZERS ON POLYMER AND OTHER ADDITIVES Figure 11.14.1 shows that the initial curing rate of epoxy resin decreases when the concentration of dibutyl phthalate increases. Plasticizer acts as an inhibitor because its molecules form complexes with proton donors. Even a small amount of dibutyl phthalate may substantially decrease concentrations of free ~NH and HO~ groups involved in epoxide ring-opening because the ester group of plasticizer is a much stronger donor than the ether group of oxirane ring. Epoxy thermosets suffer from high flammability, which limits their applica9,10-Dihydro-9-oxa-10-phosptions.24 Figure 11.14.1. Reduced initial curing rate of epoxy haphenanthrene-10-oxide, DOPO, can react resin vs. concentration of dibutyl phthalate. [Data from Smirnov Yu N; Dzhavadyan E A; Golodkova F M, with both nucleophiles and electrophiles Polym. Sci. Ser. B, 40, Nos.5-6, May-June 1998, into derivatives that contain desired funcp.190-3.] tional groups to extinguish polymers in gaseous and condensed phases.24 But, most flame retardant additives of this composition have poor dispersibility, and its plasticization effect often leads to the reduction of glass transition temperature and mechanical performance.24 Imide-DOPO derivative with bulky aromatic structure benefits from space hindering and intermolecular interaction (π-π stacking).24 It does not lead to the loss of glass transition temperature and causes only minor damage of tensile and impact strengths.24 With only 0.78 wt% loading of phosphorus (10 wt% imide-DOPO), the epoxy composite achieves UL-94 V-0 and a high LOI value of 35%.24 Figure 11.14.2 illustrates the chemistry and benefits of the addition of imide-DOPE (BMP).24

11.14 Epoxy resin

345

Figure 11.14.2. Effect of addition of imide-DOPO and its chemical structure. [Adapted, by permission, from He L, Chen T, Zhang Y, Hu L, Wang T, Han R, He J-L, Luo W, Liu Z-G, Deng J-N, Chen M-J, Compos. Part B: Eng., 230, 109553, 2022.]

Hyperbranched benzoxazine was synthesized from the reaction of Jeffamine D230, 1,1,1-tris(4-hydroxyphenyl)ethane, and paraformaldehyde through a simple one-step Mannich condensation reaction.25 It had a plasticization effect on epoxy resin and reduced its brittleness.25 The flexural strength of copolymer was also enhanced, and impact strength of modified thermoset with the incorporation of 12 wt% hyperbranched benzoxazine was improved by 247.4%, which constitutes a great improvement of the toughness of epoxy resin.25 The fatty acid methyl ester was converted to epoxy plasticizer by in situ auto-catalyzed formation of performic acid in a biphase reaction system.26

References 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17

Lee H; Neville K, Epoxy Resins. Their Applications and Technology. McGraw-Hill, New York, 1957. Bailey J A; Dyer R B; Graff D K; Schoonover J R, Appl. Spectroscopy, 54, No.2, Feb.2000, p.159-63. US Patent 5,789,039. Maggana C; Pissis P, J. Polym. Sci.: Polym. Phys. Ed., 37, No.11, 1st June 1999, p.1165-82. Monte S J, Plast. Additives. An A-Z reference, London, Kluwer, 1998, p.211-6. Jensen R E; O'Brien E; Wang J; Bryant J; Ward T C; James L T; Lewis D A, J. Polym. Sci.: Polym. Phys. Ed., 36, No.15, 15th Nov.1998, p.2781-92. Smirnov Yu N; Dzhavadyan E A; Golodkova F M, Polym. Sci. Ser. B, 40, Nos.5-6, May-June 1998, p.190-3. Mustata F; Bicu I, Polym. Plast. Technol. Eng., 37, No.2, 1998, p.127-40. Han W H; McKenna G B, Antec 97. Volume II. Conf. proc., SPE, Toronto, 27th April-2nd May 1997, p.1539-45. Spathis G; Maggana C, Polymer, 38, No.10, 1997, p.2371-7. Lambert C; Larroque M; Lebrun J C; Gerard J F, Food Additives and Contaminants, 14, No.2, 1st Feb.1997, p.199-208. Kwan K S; Ward T C, Pitture Vernici, 71, No.13, Aug.1995, p.26-7. US Patent 6,413,642. US Patent 6,407,146. US Patent 6,290,756. US Patent 6,248,204. US Patent 6,180,317.

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US Patent 6,153,709. US Patent 5,935,372. US Patent 5,575,956. Schaal S, Ghoul C, Gonzalez P, US Patent Application Publication US2011/0184092 A1, ABB Research Ltd., Jul. 28, 2011. Jacob, G C; Srivastava, Y N; Verghese, N E; Theofanous, T; Valette, L; Pham, H Q, WO2013070478, DOW Global Technologies, May 16, 2013. Timberlake, L D; Hanson, M V; Bel, K, WO2012158353, Chemtura Corporation, No. 22, 2012. He L, Chen T, Zhang Y, Hu L, Wang T, Han R, He J-L, Luo W, Liu Z-G, Deng J-N, Chen M-J, Compos. Part B: Eng., 230, 109553, 2022. Cai W, Yuan Z, Wang Z, Guo Z, Zhang L, Wang J, Liu W, Tang T, Reactive Functional Polym., 164, 104920, 2021. Bai Y, Wang J, Liu D, Zhao X, J. Cleaner Prod., 259, 120791, 2020.

11.15 Ethylene-propylene-diene copolymer, EPDM

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11.15 ETHYLENE-PROPYLENE-DIENE COPOLYMER, EPDM 11.15.1 FREQUENTLY USED PLASTICIZERS EPDM is an elastic polymer, which is processed in most applications without plasticizers, and it usually competes in plasticizer-free applications, but there are some specific applications, which use the following plasticizers: • polyisobutylene was the most frequently used as a non-migrating plasticizer of EPDM compositions.1,7,8-13 • paraffin oil2,5,10,14 • dibutyl phthalate2 • dioctyl phthalate6 • vulcanized vegetable oil12 • soy polyol14 11.15.2 PRACTICAL CONCENTRATIONS The following concentrations of plasticizers in different products were used • pressure sensitive tapes used to join rubber membranes 40-50 wt% of polyisobutylene1,12 5-9 wt% polyisobutylene7 60 phr8 • hose formulation − 16.8 wt% dioctyl phthalate6 • cold shrinkable cable joint protection − 20 wt% paraffinic oil10 • weatherstripping composition − 15 wt% of vulcanized vegetable oil11 • 5-15 wt% paraffinic petroleum oil in low cost timing belt16 11.15.3 MAIN FUNCTIONS PERFORMED BY PLASTICIZERS In pressure-sensitive tapes, the most frequent function of plasticizers is their participation in the formation of surface tack. This function can be broadened by adding that previous pressure-sensitive tapes suffered from poor heat resistance, creep failure, reduced tack at lower temperatures, poor resistance to UV, and extensive bleeding. All these drawbacks can be corrected by a proper selection of plasticizers. Hydrocarbon plasticizers are necessary for rubber formulations for improving the processing of the rubber by lowering the compound's viscosity and also for modification of low-temperature flexibility of the formulated rubber.14 11.15.4 EFFECT OF PLASTICIZERS ON POLYMER AND OTHER ADDITIVES Surface tack was solved by the use of a combination of matrix materials, tackifier, and plasticizers. This combination affects the concentration of plasticizers, which is variable as seen in Section 11.15.2. An intermediate layer of a multilayer pipe conveying a fluid to be heated or cooled is composed of an EPDM containing a paraffinic plasticizer.15 The formulation is given in the next section.15

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11.15.5 TYPICAL FORMULATIONS Multilayer pipe15 Vistalon 7500 (EPDM) Buna EP G 5567 (EPDM) PX 82 (phase change material; paraffin grafted on silica) Paraffin oil Carbon black Peroxide crosslinking system References 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

80 35 200 10 50 12.7

US Patent 6,120,869. Bashir H; Linares A; Acosta J L, J. Polym. Sci.: Polym. Phys. Ed., 39, No.10, 15th May 2001, p.1017-26. Kurian T; Khastigir D; De P P; Tripathy D K; De S K; Peiffer D G, Polymer, 37, No. 21, Oct. 1996, p.4865-8. Kurian T; De P P; Tripathy D K; De S K; Peiffer D G, J. Appl. Polym. Sci., 62, No.10, 5th Dec.1996, p.1729-34. Kurian T; De P P; Tripathy D K; De S K, Kautchuk Gummi Kunststoffe, 49, No.11, Nov.1996, p.755-9. US Patent 6,440,512. US Patent RE37,683. US Patent 6,291,571. US Patent 6,235,805. US Patent 6,111,200. US Patent 5,801,209. US Patent 5,686,179. Wypych, G; Handbook of Polymers, 3rd Ed., ChemTec Publishing, Toronto, 2022. Kim, W; Argento, A; Flanigan, C; Mielewski, D F, Polymer Testing, 46, 33-40, 2015. Van Eibergen, A; Swoboda, B; Le Rossignol, B; Dominiak, C, US8895124, Hutchinson, Nov. 25, 2014. Burrowes, T; Gregg, M J W, US20140332144, Veyance Technologies, Inc., Nov. 13, 2014.

11.16 Ethylene-vinyl acetate copolymer, EVA

349

11.16 ETHYLENE-VINYL ACETATE COPOLYMER, EVA EVA is an internally plasticized copolymer used to plasticize or reduce the amount of plasticizer in polyvinylchloride. A graft copolymer of EVA and PVC is produced (Vinnolit VK 801) containing equal amounts of both polymers.1 The graft copolymer is either used alone for the production of unplasticized articles or as a PVC additive. The addition of EVA to PVC may be considered either as modification by solid plasticizer or polymer blending. The elimination of plasticizers from certain articles (e.g., medical and toys) frequently uses this technology. Membranes are formulated by using a combination of PVC and EVA in order to limit the amount of low molecular weight plasticizers such as dioctyl phthalate or sebacate.4 Low odor hose was formulated from a combination of PVC, EVA, and low molecular weight plasticizer, such as DOP. The formulation shows that only a small amount of DOP was added, most likely to accommodate pigments and fillers:2 PVC resin 46.35 wt% BaZn stabilizer 1.16 Calcium carbonate 11.59 EVA polymer 32.45 DOP plasticizer 6.95 Stearic acid lubricant 0.12 Titanium dioxide 1.38 Pigment Sometimes plasticizer is deliberately added to the product to make it less sensitive to external plasticizer. This laminating adhesive is used in conjunction with PVC:3 Polyurethane dispersion 17.5 wt% EVA dispersions 69.0 Acrylate dispersions 7.5 Plasticizer 5.0 Stabilizers, coloring 1.0 To perform as an adhesive, the formulation does not require a plasticizer, but it is known from art that migration of plasticizer from PVC affects adhesive. Properties can be selected if plasticizer is added during compounding, and this addition will limit its migration from PVC. EVA was also used in combination with poly(lactic acid) to formulate biodegradable shrink film.4 Here, di-(2-ethyl-hexyl) azelate was used as a plasticizer.

References 1 2 3 4 5

Thermoplastic Processing Products - Specialty Products. Vinnolit VK 801. Vinnolit GmbH & Co. KG, 2001. US Patent 6,216,284. US Patent 5,821,297. US Patent 5,738,774. US Patent 5,726,220.

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11.17 IONOMERS 11.17.1 FREQUENTLY USED PLASTICIZERS Two groups of plasticizers are reported for ionomers − regular and ionic plasticizers: • dioctyl phthalate in plasticization of polymethylmethacrylate ionomer,2,5,8 polyphenylene oxide ionomer,3 sulfonated polystyrene ionomer,6 and sodium and zinc neutralized ethylene-methacrylic acid copolymer based ionomers9 • 4-decylaniline in plasticization of polymethylmethacrylate ionomer2,8 • glycerol in plasticization of polymethylmethacrylate ionomer2,5,8 and sulfonated polystyrene ionomer6 • salts of 2-ethylhexyl-p-dimethylaminobenzoate in plasticization of poly(styreneb-isobutylene-b-styrene)1 • sodium salts of benzenesulfonic and dodecylbenzenesulfonic acids in plasticization of sulfonated syndiotactic polystyrene ionomers4 • zinc stearate in plasticization of poly(styrene-b-isobutylene-b-styrene)1 • fatty acid ester such as dipropylene glycol dibenzoate11 in polyamide/ionomer golf balls 11.17.2 PRACTICAL CONCENTRATIONS The following concentrations of plasticizers were used in ionomers: • dioctyl phthalate − 13 and 26 wt%,2 4 to 31 wt%,3 22.4 and 40.2 wt%,5 and 10 wt%6,9 glycerol − 13 and 27 wt%,2 9.2 and 19.4 wt%,5 and 10 wt%6 • 4-decylaniline − 14 and 26 wt%2 • sodium salts of benzenesulfonic and dodecylbenzenesulfonic acids − molar ratios of plasticizer to sodium sulfonate groups: 0.5, 1, and 24 • salts of 2-ethylhexyl-p-dimethylaminobenzoate − 4.8-8.5 wt%1 11.17.3 MAIN FUNCTIONS PERFORMED BY PLASTICIZERS • modification of nature and strength of electrostatic interactions7 • lowering processing temperature1 • modification of morphological properties2,5 • modification of viscoelastic properties5,6 • influencing cluster formation3,8 • influencing crystallization4 11.17.4 MECHANISM OF PLASTICIZER ACTION In addition to the regular plasticizers also ionic plasticizers are used here. This is a specific case of plasticization, which acts on different segments of ionomers. Ionomers are composed of polymeric chains, which have a certain number of ionic groups. Ionic groups separate from nonpolar polymer chain forming aggregates known as multiplets. The multiplets are ionic crosslinks surrounded by a matrix of polymer chains. At certain ionic content, the restricted mobility of ionic crosslinks becomes obvious since they began to exhibit their own glass transition temperature. The above structure suggests that two different kinds of plasticizers may be needed to plasticize ionomers:

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•

regular plasticizers, which plasticize polymeric chains but also may affect ionic crosslinks • ionic (polar) plasticizers preferentially act on ionic crosslinks. From the above description, it is pertinent that ionomers may be selectively modified by choice of plasticizer type and concentration.

11.17.5 EFFECT OF PLASTICIZERS ON POLYMER AND OTHER ADDITIVES There is a strong electrostatic interaction between ionic groups of sulfonated syndiotactic polystyrene ionomer. This strong interaction creates a barrier to crystallization from the melt. The addition of ionic plasticizer, such as sodium salt of dodecylbenzenesulfonic, dramatically increases the crystallizabity of the ionomer. Figure 11.17.1 shows that the heat of fusion of isothermally crystallized ionomer increases with the addition of plasticizer. This behavior is attributable to the separation of ionic domains, which enhances the molecular mobility of crystallizable chains and also crystallization rate as the amount of plasticizer increases.4 Plasticization of poly(styrene-b-isobutylene-b-styrene) ionomer by 2-ethylhexyl-pdimethylaminobenzoate causes decrease in glass transition temperature, Tg, as the amount of plasticizer increases (Figure 11.17.2). Lowering Tg indicates that there is a slight plasticization of nonionic polystyrene phase. The much larger shift is observed at the temperature at which tanδ = 3. This indicates preferential plasticization of the ionic clusters.1 Figure 11.17.3 illustrates the effect of dioctyl phthalate on clusters and matrix of polyphenylene oxide ionomer. As stated in Section 11.14.4, dioctyl phthalate, DOP, influ-

Figure 11.17.1. Heat of fusion of isothermally crystallized Na+ sulfonated syndiotactic polystyrene ionomer vs. molar ratio of sodium salt of dodecylbenzenesulfonic acid. [Data from Orler E B; Gummaraju R V; Calhoun B H; Moore R B, Macromolecules, 32, No.4, 23rd Feb.1999, p.1180-8.]

Figure 11.17.2. Effect of fraction of stoichiometric concentration of 2-ethylhexyl-p-dimethylaminobenzoate used for ionic plasticization of poly(styrene-bisobutylene-b-styrene), having 4.7% sulfonated phenyl units, on glass transition temperature, Tg, and temperature at which tanδ=3. [Data from Storey R F; Baugh D W, Polym. Eng. Sci., 39, No.7, July 1999, p.1328-34.]

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Figure 11.17.3. Glass transition temperatures of matrix and clusters of polyphenylene oxide ionomer plasticized with variable quantities of dioctyl phthalate. [Adapted, by permission, from Hee-Seok Kim; JoonSeop Kim; Jin-Wook Shin; Young-Kwan Lee, Polym. J. (Japan), 31, No.3, 1999, p.306-8.]

Figure 11.17.4. Effect of plasticizer type and content used for plasticization of PMMA ionomer on glassy modulus. [Adapted, by permission, from Ma X; Sauer J A; Hara M, Polymer, 38, No.17, 1997, p.4425-31.]

Figure 11.17.5. Molding temperature of polyphenylene oxide ionomer plasticized with variable quantities of dioctyl phthalate. [Data from Hee-Seok Kim; JoonSeop Kim; Jin-Wook Shin; Young-Kwan Lee, Polym. J. (Japan), 31, No.3, 1999, p.306-8.]

Figure 11.17.6. Tensile strength of sulfonated polystyrene ionomer plasticized with variable amounts of glycerol. [Adapted, by permission, from Ma X; Sauer J A; Hara M, J. Polym. Sci.: Polym. Phys. Ed., 35, No.8, June 1997, p.1291-4.]

ences both matrix polymer and ionic clusters. But the intensity of these effects is different. Up to about 10 wt% DOP, the matrix Tg rapidly decreases (DOP preferentially plasticizes polymer chains). Above 10 wt%, the Tg of both matrix and clusters decreases with similar rates.3 Comparing results in Figures 11.17.2 and 11.17.3, it is possible to conclude that regular plasticizers have a preferential effect on polymer matrix whereas ionic plasticizers on

11.17 Ionomers

353

ionic clusters. This is the reason for a clear distinction between the mechanisms of their action, as indicated in Section 11.17.4. Figure 11.17.4 compares the effect of polar glycerol and nonpolar DOP on PMMA ionomers. Polar plasticizer decreases modulus at a three times greater rate than nonpolar DOP. Glycerol acts as a dual plasticizer of clusters and matrix polymer, whereas DOP preferentially plasticizes matrix polymer.5 Controlling plasticizer type and its concentration, it is possible to improve the processability of ionomers. Figure 11.17.5 shows that the molding temperature of polyphenylene oxide ionomer decreases quite rapidly with the increased addition of dioctyl phthalate.3 Two rates of tensile strength decrease are seen in Figure 11.17.6. Slighter decrease is most likely in the range of gradual plasticization, and a sudden decrease occurs when some critical concentration of plasticizer is attained. Above the critical amount, plasticizer clusters are sufficiently separated to destroy ionic structures, which reinforce ionomer. The presence of plasticizers in polyamides makes them more susceptible to salt stress cracking.10 The addition of ionomer makes polyamide-6 flexible without a negative effect on stress cracking.10 Toughening brittle polylactide without losing its attractive transparency remains a great challenge for polylactide-based blends because of the indispensable phase-separated structure.12 Imidazolium-functionalized polyether-based ionomers obtained by facile quaternization reaction from renewable epichlorohydrin elastomer and various comprehensive imidazoles were combined with polyethylene glycol to produce toughening agents for polylactide.12 Supertough (impact strength of 82.2 kJ/m2) and highly transparent (≥80%) blends were obtained owing to a refractive index matching mechanism.12 The importance of rigidity of shell region surrounding the ionic core in controlling tensile mechanical properties of sodium-neutralized poly(ethylene-co-methacrylic acid) ionomers blended with several fatty acids with different alkyl tail lengths was emphasized.13 Fatty acids with short alkyl tails effectively plasticize the restricted shell region. The rigidness of the shell region affects stretchability and toughness of EMAA ionomers.13

References 1 2 3 4 5 6 7 8 9 10 11 12 13

Storey R F; Baugh D W, Polym. Eng. Sci., 39, No.7, July 1999, p.1328-34. Joon-Seop Kim; Eisenberg A, Polym. J. (Japan), 31, No.3, 1999, p.303-5. Hee-Seok Kim; Joon-Seop Kim; Jin-Wook Shin; Young-Kwan Lee, Polym. J. (Japan), 31, No.3, 1999, p.306-8. Orler E B; Gummaraju R V; Calhoun B H; Moore R B, Macromolecules, 32, No.4, 23rd Feb.1999, p.1180-8. Ma X; Sauer J A; Hara M, Polymer, 38, No.17, 1997, p.4425-31. Ma X; Sauer J A; Hara M, J. Polym. Sci.: Polym. Phys. Ed., 35, No.8, June 1997, p.1291-4. Plante M; Bazuin C G; Jerome R, Macromolecules, 28, No.5, 27th Feb.1995, p.1567-74. Kim J-S; Kim H-S; Eisenberg A, Bull. Korean Chem. Soc., 19, 6, p.625-628, 1998. US Patent 6,371,869. Chou, R T; Beridler, H V, WO2013101891, DuPont, Jul. 4, 2013. Bulpett, D A; Sullivan, M J; Btte, M L; Blink, R; Comeau, B, US20150190680, Acushnet Company, Jul. 9, 2015. Wang H, Chen X, Ding Y, Huang D, Ma Y, Pan L, Zhang K, Wang H, Polymer, 229, 123964, 2021. Miwa Y, Koike M, Kohbara Y, Kutsumizu S, Polymer, 197, 122495, 2020.

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11.18 NITRILE RUBBER 11.18.1 FREQUENTLY USED PLASTICIZERS Aromatic mineral oil plasticizers are highly compatible with nitrile rubber, NBR, naphthenic oils are only partially compatible, and paraffinic mineral oil plasticizers are incompatible with nitrile rubber.1 Dibenzyl ether, phthalates, and polyglycol ether are the most frequently used plasticizers in NBR.1 Also, synthetic or fatty acid esters,2 vulcanized vegetable oils (factice),3 chloroparaffins,4 and phosphate plasticizers5 are in frequent use. The following plasticizers were used in formulations of various products: • dioctyl phthalate in production of materials for automotive applications with low permanent compression set,6 artificial leather,7 plastisol containing a mixture of PVC and NBR,8 seal,9,15 rubber laminate,11 slush molding compositions12,14 • fatty acid ester (Struktol WB 222) in production of sealing strip10 molded article13 • imidazolium-based ionic liquids,18 in addition to plasticization some increased conductivity from 10-11 to 10-5 S/cm at 30 phr concentration • di(butoxyethoxyethyl) adipate in PVC/NBR blend19 • di-2-ethylhexanoate in polyamine-cure, highly saturated nitrile rubber composition for fuel oil applications20 The above examples show that, although numerous plasticizers can be used in nitrile rubber applications, DOP is the most frequent choice. 11.18.2 PRACTICAL CONCENTRATIONS • 2 phr fatty acid ester in NBR sealing strip10 • 5 phr DOP in NBR sealing member9,15 • 5-20 phr DOP in NBR compound for automotive parts having low compression set16 • 15 phr DOP in NBR laminate11 • 25-45 wt% DOP in artificial leather strip based on PVC/NBR blend7 • 30 phr fatty acid ester in article molded from NBR/PVC=80/2013 • 50 wt% of DOP in plastisol based on PVC/NBR blend8 • 45-85 phr in slush molding compound based on PVC/NBR plastisol12 • 70-100 phr in slush molding compound based on PVC/NBR plastisol14 The above data show that low to moderate concentrations are used in articles composed of NBR or having high NBR content, unlike in blends with PVC, which utilize high concentrations of plasticizers. 11.18.3 MAIN FUNCTIONS PERFORMED BY PLASTICIZERS • viscosity reduction in plastisols8 • dispersion aid of solid additives10 • modification of rheological properties to make plastisols useful in slush molding process12,14 • lowering sliding resistance13 • modification of viscoelastic properties (“cheesecutter” effect)7

11.18 Nitrile rubber

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11.18.4 EFFECT OF PLASTICIZERS ON POLYMER AND OTHER ADDITIVES The thermal aging of NBR is a process of loss of additives and oxidation/crosslinking of the matrix.17 Volatiles in NBR produced by different time/temperature regimes were detected. They were the decomposition or volatilization products of curing agents, accelerants, plasticizers, and antioxidants.17 Products of degradation of the following plasticizers were detected: 1,2-benzene dicarboxylic di-n-butyl ester, plasticizer di-n-butyl sebacate, and 1,2-benzene di-carboxylic acid di(2-ethylhexyl) ester. Considering that plasticizers increase the mobility of rubber chains by which they contribute to the elasticity of NBR, their loss hardens the rubber and affects its mechanical properties.17 The eco-friendly monomer fatty acid-derived polyethylene glycol methyl ether esters (MA-n) exhibited excellent tensile, low-temperature, and oil resistance properties due to the contribution of oxyethyl units in both improving the compatibility between MA-n and NBR and in promoting the dispersion of carbon black in the NBR matrix.21 Particularly, the overall performances of NBR samples plasticized by MA-3 or MA-4 are comparable or better than the properties of NBR compound blended with DOP, suggesting that MA-n (n = 3 or 4) can be used as alternatives to totally replace the toxic DOP. Figure 11.18.1 illustrates the synthesis of plasticizer.21

Figure 11.18.1. Synthetic route of MA-n. [Adapted, by permission, from Tan J, Fu Q, Qu Y, Wang F, Wang W, Wang F, Cao Y, Zhu X, J. Cleaner Prod., 289, 125821, 2021.]

11.18.5 TYPICAL FORMULATIONS Typical formulation for processing nitrile rubbers: Nitrile rubber 100 parts Carbon black 65 DOP 15 Zinc oxide 5 Stearic acid 1 Trimethyldihydroquinoline 1 Dicumyl peroxide 5 Coagent 0-20 References 1 2 3 4

Kleemann W; Weber K, Elastomer Processing. Formulas and Tables. Hanser Verlag, Munich, 1998. Struktol Plasticizers. Application of factice in rubber compound. Paroil® Liquid Chlorinated Paraffins, Dover Chemical Corporation.

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Plasticizers Use and Selection for Specific Polymers

Santicizer 148, Plasticizer Product Profile, Ferro. US Patent 5,362,787. US Patent 6,348,255. US Patent 6,054,524. US Patent 6,003,876. US Patent 5,876,566. US Patent 5,855,976. US Patent 5,840,236. US Patent 5,744,211. US Patent 5,739,203. US Patent 5,695,198. US Patent 5,552,468. Liu, X; Zhao, J; Liu, Yang, R, J. Anal. Appl. Pyrolysis, 113, 193-201, 2015. Marzec, A; Laskowska, A; Boiteux, G; Zaborski, M; Gain, O; Serghei, A, Eur. Polym. J., 53, 139-46, 2014. Tsukada, A; Shibuya, T; Takeyama, Y; Nakamura, T, EP2824140, Zeon Corporation, Jan. 14, 2015. Aoyagi, A; Uchida, K, EP2857448, NOK Corporation, Apr. 8, 2015. Tan J, Fu Q, Qu Y, Wang F, Wang W, Wang F, Cao Y, Zhu X, J. Cleaner Prod., 289, 125821, 2021.

11.19 Perfluoropolymers

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11.19 PERFLUOROPOLYMERS Four fluorocompounds were used to plasticize amorphous perfluoropolymers.1 Plasticizers of low molecular weight were less compatible.1 Oligoether was the most powerful plasticizer.1 To improve flexibility of poly(perfluoro-2-methylene-4-methyl-1,3-dioxolane), perfluoropolyether was added as a plasticizer to the dioxolane polymer.2 Film flexibility and elongation were significantly improved by the addition of the perfluoropolyether.2

References 1 2

Lugert E C, Lodge T P, Buehlmann P, J. Polym. Sci., Part B: Polym. Phys., 46, 516–25, 2008. Chaing H-C, Fang M, Okamoto Y, J. Fluorine Chem., 236, 109572, 2020.

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11.20 POLYACRYLONITRILE 11.20.1 FREQUENTLY USED PLASTICIZERS • dibutyl phthalate1,2 • glycerin5 • polyethylene glycol5 • polypropylene glycol5 • tributyl phosphate6 • poly(ethylene glycol) borate ester in lithium batteries14 • supercritical fluids (carbon dioxide, methanol, ethanol, and propylene) in production of hollow carbon fibers15 11.20.2 PRACTICAL CONCENTRATIONS • 20 wt% dibutyl phthalate1,2 11.20.3 MAIN FUNCTIONS PERFORMED BY PLASTICIZERS • pore-forming after extraction1,2 • electrolyte formation3-4,7,9 • absorption of infrared6 • melt viscosity reduction10-13 • reduction of intermolecular interaction to improve the solubility of PAN polymer and the processability of PAN precursor fibers16 11.20.4 EFFECT OF PLASTICIZERS ON POLYMER AND OTHER ADDITIVES Plasticizers are very important for the development of new technologies based on polyacrylonitrile, PAN, but plasticizer definition, types, and reason for its use are frequently very different from plasticizers used in other polymers. In plastic Li-ion batteries, 20 wt% of dibutyl phthalate is added to the composition to be later extracted with diethyl ether. This results in a microporous electrode suitable for the purpose.1,2 PAN-based lithium-salt electrolytes are obtained by plasticizing with propylene carbonate, ethylene carbonate, dimethylformamide, dimethylsulfoxide, etc. These compounds are considered solvents in applications with other polymers, but in electrolytes, they are used to lower glass transition temperature, dissolve the salt, and make polymer amorphous. Some of these functions are typical of plasticizers.3,4,7 Improved version of electrolyte is based on ternary mixtures of plasticizers consisting of ethylene, propylene, and butylene carbonates.9 Use of this mixture improves low-temperature conductivity. Many plasticizers can be used in absorbent hydrogel particles for wound dressing.5 These include glycerin, polyethylene glycol, polypropylene glycol, and vegetable and mineral oils. Tributyl phosphate is a plasticizer employed in polyacrylonitrile-based material for barcode printing. This system, because of the properties of the polymer, absorbs infrared, which is radiated or reflected from a pattern.6 Polyacrylonitrile has decomposition temperature below the melting point.10 Its melt processing requires the use of fugitive plasticizers (or, in other words, solvents, which have plasticizing action) for processing. Ethylene carbonate is used as a fugitive plasti-

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cizer in a process by which films, fibers, or shaped products can be extruded from pellets.7,11-12

References 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Du Pasquier A; Disma F; Bowmer T; Gozdz A S; Amatucci G; Tarascan J-M, J. Electrochem. Soc., 145, 2, 472, 1998. Gozdz A S; Plitz I; Du Pasquier A; Zheng T, 198th Meeting of the Electrochemical Society, Phoenix, AZ, October 2000. Wang Z; Huang B; Xue R; Huang X; Chen L, Spectroscopic investigation of interactions among components and ion transport mechanism in polyacrylonitrile based electrolytes. US Patent 6,290,878. US Patent 5,977,428. US Patent 5,971,276. US Patent 5,861,442. US Patent 5,766,796. Peramuge D; Pasquariello D M; Abraham K M, Rechargeable Lithium Battery with Solid Electrolyte, Report. Gupta A K; Paliwal D K; Bajaj P, J. Appl. Polym. Sci., 70, No.13, 26th Dec.1998, p.2703-9. US Patent 5,589,520. US Patent 5,434,205. Batchelor, B L; Mahmood, S F; Jung, M; Shin, H; Kulikov, O V; Voit, W; Novak, B M; Yang, D J, Carbon, 98, 681-8, 2016. Kaynak, M; Yusuf, A; Aydin, H; Taskiran, M U; Bozkurt, A, Electrochim. Acta, 164, 108-13, 2015. Choi, Y-H; Han, D S; Choi, C-H, US8501146, Hyundai Motors Company, Aug. 6, 2013. Dyke, C A, EP2744859, Nanoridge Materials, Inc., Jun, 25, 2014.

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11.21 POLYAMIDE 11.21.1 FREQUENTLY USED PLASTICIZERS The following plasticizers were useful in modification of properties of polyamides: • N-butylbenzenesulfonamide, BBSA,1,3,8,12-15,17,19,20,22,27 • N-ethylbenzenesulfonamide, EBSA,3,15,16 • N-propylbenzenesulfonamide, PBSA,15 • N-butyl-N-dodecylbenzenesulfonamide, BDBSA,3 • N,N-dimethylbenzenesulfonamide, DMBSA,3 • p-methylbenzenesulfonamide2 • o,p-toluene-sulfonamide8 • p-toluene-sulfonamide8 • carboxylic acid amide13 • 2-ethylhexyl-4-hydroxybenzoate1,12,13,17 • hexadecyl-4-hydroxybenzoate7 • 1-butyl-4-hydroxybenzoate2 • dioctyl phthalate16,17 • diisodecyl phthalate17 • di-(2-ethylhexyl) adipate17 • tri-(2-ethylhexyl) phosphate17 • tributyl citrate29 • acetyl tributyl citrate29 • low molecular weight polyamide (3,000-17,000)24 • Leona by Asahi Kasei25 • glycol ether having molecular weight of 10,00026 • ethyl oleate or propylene carbonate28 From the above long list of different compounds used in the plasticization of polyamide, a great majority is used for either experimental or specific purposes. N-butylbenzenesulfonamide and 2-ethylhexyl-4-hydroxybenzoate are two main plasticizers of various polyamides in commercial applications. Due to the nature of polymers, plasticizers that are most likely used are polar compounds. 11.21.2 PRACTICAL CONCENTRATIONS • N-butylbenzenesulfonamide − from zero up to stoichiometric equivalent of amide units,3 1 to 5 wt% in adhesive composition,8 3 to 8 wt% in polyamide thermoplastic composition,12 15 wt% in molded articles,13 3 to 13.7 wt% in monofilaments,14,15 and 10 to 25 wt% of combination of this plasticizer and one phthalate, adipate or phosphate • N-ethylbenzenesulfonamide − from zero up to stoichiometric equivalent of amide units3 and 20 wt% in hotmelt adhesive16 • 2-ethylhexyl-4-hydroxybenzoate − 3 to 8 wt% in polyamide thermoplastic composition12 and 15 wt% in molded articles13 • dioctyl phthalate − 5 wt% in hotmelt adhesive16 • carboxylic acid amide − 20 wt%23 • low molecular weight polyamide − 2-5 wt%24 • glycol ether − 10-80 wt%26

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11.21.3 MAIN FUNCTIONS PERFORMED BY PLASTICIZERS • improvement of impact strength,2 especially at low temperatures13,17 • improvement of toughness6 • increase of fatigue life14 • decrease of glass transition temperature3,28 • improvement of open time of hotmelt adhesives8,16 • increase in chain mobility27 • formation of hydrogen bonds29 11.21.4 EFFECT OF PLASTICIZERS ON POLYMER AND OTHER ADDITIVES Figure 11.21.1 shows the effect of two plasticizers on the Izod impact strength of polyamide 11. p-methylbenzene sulfonamide has a dramatic effect on impact strength.2 Even several percent of plasticizer rapidly improves impact strength. When using p-butyl hydroxybenzoate, larger additions are required to obtain similar effects. Figure 11.21.2 shows that both plasticizers have none or minor influence on the tensile strength of polyamide 11. Both graphs illustrate that substantial improvements can be made by the application of plasticizers. Figure 11.21.3 shows that even small additions of plasticizer substantially increase the fatigue life of monofilaments obtained from plasticized polyamide-6,6. Considering that the minimum fatigue life required by a commercial product is 50 minutes, at least 3 wt% plasticizer is needed to make a product useful in practical applications.14 The enhanced chain mobility relative to the concentration of plasticizer (N-butylbenzenesulfonamide) can impact interfacial compatibilization and phase coalescence.27 The

Figure 11.21.1. Izod impact strength of polyamide 11 plasticized with variable quantities of p-methylbenzene sulfonamide, A, and p-butyl hydroxybenzoate, B. [Data from Li Q F; Tian M; Kim D G; Wu D Z; Jin R G, J. Appl. Polym. Sci., 83, No.7, 14th Feb. 2002, p.1600-7.]

Figure 11.21.2. Tensile strength of polyamide 11 plasticized with variable quantities of p-methylbenzene sulfonamide, A, and p-butyl hydroxybenzoate, B. [Data from Li Q F; Tian M; Kim D G; Wu D Z; Jin R G, J. Appl. Polym. Sci., 83, No.7, 14th Feb. 2002, p.1600-7.]

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threshold level of 5-10 wt% plasticizer provides an optimum level of chain mobility.27 The presence of green citrate plasticizers, namely tributyl citrate or acetyl tributyl citrate, led to hydrogen bonding, which inhibited the formation of interchain amide-amide bonds, markedly reducing chain rigidity as demonstrated by the decreased elasticity modulus.29 More flexible polyamide chains resulted in the creation of ultrafast water channels during filtration.29 By blending a polyamide resin with a plasticizer such as N-butylbenzenesulfonamide, the polyamide resin is plasticized, Figure 11.21.3. Effect of N-methylbenzene sulfonamide and its flexibility and processability are on fatigue life of polyamide-6,6. [Data from US Patent improved, but this plasticizer does not have 6,249,928.] sufficient heat resistance, and it is thermally decomposed and/or volatilized during processing.30 This problem can be solved by the use of a plasticizer made of aliphatic dibasic acid having 4 to 14 carbon atoms (adipic, sebacic, and succinic acids used in examples) and glycol having 3 to 6 carbon atoms (2methyl-1,3-propanediol, 1,3-propanediol, 1,6-hexanediol, and 3-methyl-1,5-pentanediol use in examples).30

References 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26

Kohan M I, Nylon Plastics Handbook, Hanser Verlag, Munich, 1995. Li Q F; Tian M; Kim D G; Wu D Z; Jin R G, J. Appl. Polym. Sci., 83, No.7, 14th Feb. 2002, p.1600-7. Groote Ph D; Devaux J; Godard P, Polym. Intl., 51, No.1, Jan. 2002, p.40-9. US Patent 5,981,058. Sheng-Huei Hsiao; Chin-Ping Yang; Ming-Hung Chuang; Shene-Jen Lin, J. Polym. Sci.: Polym. Chem. Ed., 37, No.24, 15th Dec.1999, p.4510-20. Loo L S; Cohen R E; Gleason K K, Macromolecules, 32, No.13, 29th June 1999, p.4359-64. Modern Plast. Intl., 28, No.10, Oct.1998, p.233. US Patent 5,672,677. Germain Y, Polym. Eng. Sci., 38, No.4, April 1998, p.657-61. US Patent 5,548,027. Angelopoulos M; Saraf R; MacDiarmid A G; Zheng W; Feng J; Epstein A J, Antec 97. Volume II. Conf. proc., SPE, Toronto, 27th April-2nd May 1997, p.1352-8. US Patent 6,376,037. US Patent 6,348,563. US Patent 6,249,928. US Patent 6,190,769. US Patent 5,827,393. US Patent 5,789,529. US Patent 5,620,762. Huppert N; Wuertele M; Hahn H H, Fresenius’ J Anal. Chem., 362, 6, p.529-536, 1998. Butylbenzensulphoneamide, Proviron, 2002. Tohmide #558. Sanho Chemical Co., Ltd. Private info. Schmid E, Rexin O, US Patent 7,312,263 B2, EMS-Chemie AG, Dec. 25, 2007. Tsou A H, Soeda Y, Hara Y, Neasmer B, US Patent 8,021,730 B2, ExxonMobil, Sep. 20, 2011. Nishino R, Uejou H, Piolax Inc., US Patent 6,769,453 B2, Piolax Inc., Aug. 3, 2004. Tanigawa H, Matoba Y, Salka T, Matsuo T, Yokohama K, US Patent 7,361,432 B2, National Institute of

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27 28 29 30

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Advanced Idustrial Science and Technology, Apr. 22, 2008. Bhadane, P A; Tsou, A H; Cheng, J; Ellul, M D; Favis, B D, Polymer, 55, 16, 3905-14, 2014. Sullivan, M J; Bulpett, D A; Blink, R; Binette, M L; Comeau, B, US20140323243, Acushnet Company, Oct. 30, 2014. Qin Y, Kang G, Cao Y, Sci. Total Environ., 784, 147089, 2021. Kasai C, Kamimura S, JP2021054879A, Adeka Corp., Apr. 8, 2021.

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11.22 POLYAMINE Polyamines are mainly used as curing agents for polyurethane or epoxy systems.1-3 These are two-component systems used as adhesives, coatings, or electrocoatings. The role of plasticizers in these coatings is to make both parts have similar weights, to reduce the rate of cure (increase pot life), and improve rheological properties such as flowability and selfleveling. The type of plasticizer used here is less critical, although it should have very good compatibility with polyamine and cured polymer. Good compatibility with polyamine reduces the amount of plasticizer required, and good compatibility with cured material reduces physical losses of plasticizer from the product. Suitable plasticizers include phthalates, phosphates, partially hydrogenated terpenes, adipates, chloroparaffins, castor oil, etc. It is usually needed that the plasticizer does not contain water since it will otherwise interfere with the cure of polyurethanes. The amounts used are limited by properties required and properties of the final product. For example, in the case of cold curable two-component polyurethane used in waterproofing,1 addition of plasticizer lower than 20 wt% did not extent potlife as per requirements. Additions larger than 130 wt% caused plasticizer bleedout. This gives a very broad range of concentrations to adjust the properties of the product.

References 1 2 3

US Patent 5,688,892. US Patent 5,672,652. US Patent 5,559,174.

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11.23 POLYANILINE The process of making polyaniline, PANI, conductive is called doping. This involves protonation, partial oxidation, or partial reduction. Doped polyanilines have low solubilities in solvents, which complicates their processing.1 Two processing methods are generally used: melt processing (e.g., extrusion or injection molding) or solution processing (e.g., casting or spraying). To conduct these processes, PANI or deprotonated PANI (emeraldine base) are processed, followed by a post-doping process. In addition to the processes, which activate conductive properties of PANI, it has to be incorporated in carrier polymer (e.g., polymethylmethacrylate, cellulose acetate, etc.). This process requires a certain temperature regime related to the properties of both the polyaniline derivative and the matrix polymer. This causes further complication since PANI derivatives, which are normally quite thermally stable, may not withstand processing temperature. The above explanations show two potential reasons for the use of plasticizers: decrease in processing temperature of either matrix polymer or PANI or its derivative. Simple substances such as hydroquinone, resorcinol, tert-butyl hydroquinone, 4-hexyl resorcinol, and bisphenol-A were used as plasticizers in conjunction with polymethylmethacrylate as the matrix polymer.1 In addition to improved processability, plasticizers were helpful in an organization (hydrogen bonding and phenyl stacking), which resulted in better charge transfer between PANI chains.1 Diesters of phosphoric acid are the best protonating agents for PANI, and they are also good plasticizers.2 Oligoester of phosphoric acid was synthesized and applied as plasticizer/doping agent for PANI. It improved the thermostability of the plasticized polymer.2 Derivatives of phosphonic acids (phenyl phosphonic acid) and aliphatic diesters of phosphoric acid (diphenyl, dioctyl, and dibutyl) were used as plasticizers.7 Three groups of plasticizing/protonating agents were used in the preparation of conductive composite from PANI and cellulose acetate: sulfonic acids, phosphonic acids (phenyl phosphonic acid), and aliphatic diesters of phosphoric acid (diphenyl, dioctyl and dibutyl).3,4 Plasticizers influenced the flexibility of the film but also significantly lowered the percolation threshold. The addition of plasticizer improved the dispersion of PANI in cellulose acetate.4 In this and other inventions5 based on the polymer composite, it was important that plasticizer not only helped to dissolve or soften PANI but also plasticized the matrix polymer. In some inventions,6 a combination of plasticizers was used. For example, dodecylbenzenesulfonic acid acted as a doping agent and plasticizer of PANI and many other compounds, including alcohols, ethers, phenols, and amines were used to plasticize matrix polymer.6 A plasticizer was added to the polyaniline composite to improve its mechanical properties, such as tensile strength and bending strength.8 Specific examples of plasticizers included phthalic esters or phosphoric esters.8

References 1 2 3 4 5 6 7 8

Morgan H; Foot P J S; Brooks N W, J. Mater. Sci., 36, No.22, 15th Nov. 2001, p.5369-77. Pielichowski J; Pielichowski K, J. Thermal Analysis Calorimetry, 53, No.2, 1998, p.633-8. Pron A; Nicolau Y; Genoud F; Nechtschein M, J. Appl. Polym. Sci., 63, No.8, 22nd Feb.1997, p.971-7. US Patent 6,235,220. US Patent 5,866,043. US Patent 5,585,040. Wypych, G, Handbook of Polymers, 3rd Ed., ChemTec Publishing, Toronto, 2022. Jibiki, Y; Bando, T; Oda, S; US20140008582, Idemitsu Kosan Co., Ltd., Jan. 9; 2014.

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11.24 POLYBUTADIENE 11.24.1 FREQUENTLY USED PLASTICIZERS Plasticizers used in polybutadiene include: • dioctyl sebacate in power transmission belt1 • chlorinated paraffins in power transmission belt1 • dibutyl phthalate in adhesive composition2 • dioctyl phthalate in compatibilization of polystyrene/polybutadiene immiscible blends8 • alkyl benzyl phthalate9,10 • paraffinic, aromatic, or naphthenic mineral oils in pressure-sensitive adhesives3 and tire tread4,5 • 1,2-dinitratodecane and 2-ethylhexyl nitrate in solid propellant binder6 • nitroglycerin and 1, 2, 4-butanetriol trinitrate in propellants15 • polyisobutylene7,13 11.24.2 PRACTICAL CONCENTRATIONS • 1-100 phr in power transmission belt1 • 10-30 phr in pressure-sensitive adhesive3 • 10-40 phr in tire compounds5 • 30 wt% in adhesive2 • 40-75 wt% in propellant binder6 • 12.65 wt%11,12 11.24.3 MAIN FUNCTIONS PERFORMED BY PLASTICIZERS The following functions are played by plasticizers in polybutadiene compounds: • enhancing tackifying action2,3 • increasing elasticity of product4,5 • lowering temperature of processing6 • supplying energy from burning and fuel oxidizing6 • compatibilization of blend components8 • polybutadiene is used as a plasticizer in clear, photo-curable adhesive14 References 1 2 3 4 5 6 7 8 9 10 11 12 13 14

US Patent 6,464,607. US Patent 6,433,091. US Patent 6,162,868. US Patent 6,119,743. US Patent 5,851,321. US Patent 5,578,789. Polyisobutylene. Texas Petrochemicals LP. Structure of Immiscible Blends. Rheometric Scientific, Inc., Application Brief AB022. Reyes A M, Cosman M A, Quinto A R, US Patent Application Publication US2010/0159238 A1, PPG Industries, Jun 24, 2010. Reyes A M, Short J R, Randazzo US Patent Application Publication US2006/0278338 A1, PPG Industries, Dec. 14, 2006. Odrobina E; Jianrong Feng; Winnik M A, J. Polym. Sci.: Polym. Chem. Ed., 38, No.21, 1st Nov.2000, p.3933-43. Rizos A K; Petihakis L; Ngai K L; Wu J; Yee A F, Macromolecules, 32, No.23, 16th Nov. 1999, p.7921-4. Wypych, G, Handbook of Polymers, 3rd Ed., ChemTec Publishing, Toronto, 2022. Lu, D; Kanari, M; Sawanobori, J, WO2013173976, Henkel (China), Nov. 23, 2013.

11.24 Polybutadiene

15

367

Singh H, Pande SM, Kumar A, Mishra S, Khanna PK, More PVC, MaterialsToday, Chem., 16, 100244, 2020.

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11.25 POLYBUTYLENE 11.25.1 FREQUENTLY USED PLASTICIZERS Low molecular polybutylene is a plasticizer of some polymers (e.g., polyethylene and polystyrene). It is approved by EPA for use in the manufacture of articles for food contact applications.1 Its composition with aliphatic lactate ester is proposed as a plasticizer for many resins.6 It is also plasticized by: • mineral oil in hotmelt adhesive2-4 • polybutene in hotmelt adhesive2-4 • dioctyl adipate, phthalate, maleate, dibutyl phthalate, isodecyl pelargonate, and oleyl nitrile in propellants5 11.25.2 PRACTICAL CONCENTRATIONS • 5-15 wt% in hotmelt adhesive2-4 11.25.3 MAIN FUNCTIONS PERFORMED BY PLASTICIZERS • providing viscosity control2-4 • improving propellant processing5 • improving brushability of plasticized resin compound6 References 1 2 3 4 5 6

Environmental Protection Agency. FRL-6760-6. US Patent 6,218,457. US Patent 6,114,261. US Patent 6,008,148. US Patent 5,942,720. US Patent 5,688,850.

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11.26 POLY(BUTYL METHACRYLATE) 11.26.1 FREQUENTLY USED PLASTICIZERS • Texanol was used in poly(butyl methacrylate) latex to demonstrate the effect of plasticization on interparticle chain diffusion of polymer in waterborne system1 • phthalates, adipates, citrates, epoxy and polymeric plasticizers in rubber eraser composition2 • ionic oligomer in coatings3 • triethyl citrate4 in delayed-release film coating 11.26.2 PRACTICAL CONCENTRATIONS • 3-9 wt% in coating3 • 30-50 wt% in rubber composition2 11.26.3 MAIN FUNCTIONS PERFORMED BY PLASTICIZERS • affecting polymer diffusion rate in waterborne systems3 • increasing film formation rate3 • improving film properties3 references 1 2 3 4

Winnik M A, Wang Y, Haley F J, J. Coat. Technol., 811, 64, 1992, p.51 US Patent 5,521,239. Odrobina E; Jianrong Feng; Winnik M A, J. Polym. Sci.: Polym. Chem. Ed., 38, No.21, 1st Nov.2000, p.3933-43. Reyes, G; Cunningham, C R; Farrell, T P; Young, C, EP2961387, BPSI Holdings, LLC, Jan. 6, 2016.

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11.27 POLYCARBONATE 11.27.1 FREQUENTLY USED PLASTICIZERS The following plasticizers were used: • tritolyl phosphate, pentaerythritol tetraborate, and trimellitic acid tridecyloctyl ester to increase crystallization rate17 • tetraethylene glycol dimethyl ether to increase crystallization rate7 • tri-(2-ethylhexyl) phosphate1,2 • dicyclohexyl phthalate in the thermal transfer of image4 • dibutyl phthalate in electrolyte for lithium batteries6 • dioctyl phthalate in photoconductive element10 • phthalate plasticizers in impact-resistant laminate8 • mineral oil in cover tapes9 • resorcinol diphenyl phosphate in flame retarded blends with polyphenylene oxide12 • epoxy reactive plasticizer13 • diallyl o-phthalate14 and p-phthalate and its various derivatives16 • bioplasticizer based on a mixture of C3 to C7 carboxylic acids and polyhydroalcohols15 11.27.2 PRACTICAL CONCENTRATIONS • 300 ppm to 1 phr to improve crystallization7 • 1-2 phr to improve melt flow12 • 10-15 to provide flame retarding12 • up to 5 wt% in molding composition5 • 10 wt% trimellitic acid tridecyloctyl ester to increase the crystallization rate • 10-30 wt% of epoxy reactive plasticizer13 • 10-40 wt% of reactive diallyl o-phthalate14 • up to 100 phr in the electrolyte to obtain porous membrane6 Polycarbonate is an example of a polymer in which small additions of plasticizers cause substantial changes in properties. 11.27.3 MAIN FUNCTIONS PERFORMED BY PLASTICIZERS The use of plasticizers in polycarbonate causes many typical and unusual changes such as: • increased rate of crystallization7 • lowering glass transition temperature1 • affecting γ-relaxation (spacial arrangement of phenyl rings)1 • causing antiplasticization1 • plasticizer interacting with another molecule of plasticizer has increased mobility in the system as compared with a single molecule of plasticizer surrounded by polymer molecules2 • reaction engineering13,14,16 • plasticizer increases transfer rate of dye4 • extraction of plasticizer allows the formation of porous membrane6 • increased flexibility and toughness9,11 • increased resistance to stress corrosion10

11.27 Polycarbonate

• •

371

lowered viscosity and improved melt flow12 flame retarding properties12

11.27.4 EFFECT OF PLASTICIZERS ON POLYMER AND OTHER ADDITIVES The solubility of supercritical carbon dioxide was independent of the molecular weight of polycarbonate.18 Supercritical carbon dioxide acted as a plasticizer.18 Crystallinity and crystallization rate decreased with increasing molecular weight.18 Benzyl butyl phthalate was detected well below the specific migration limit in polycarbonate used for the production of water bottles.19 A flexible imaging member having an anti-curl back coating was based on plasticized polycarbonate.20 The plasticizer was diethyl phthalate.20 Polycarbonate resin composition has improved impact strength, flow index, and light transmittance.21 By selecting phosphazene-based compound as a plasticizer, the flow index of the polycarbonate composition was improved, thereby improving moldability and injection properties.21 5 wt% plasticizer was added for improved performance.21 Hexaphenoxycyclotriphosphazene was used as plasticizer.21 Plasticizers used in polycarbonate include phthalic acid esters such as dioctyl-4,5epoxy-hexahydrophthalate, tris-(octoxycarbonylethyl)isocyanurate, tristearin, epoxidized soybean oil.22 Plasticizers are used in amounts from 0.5 to 3.0 wt%.22 References 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22

Rizos A K; Petihakis L; Ngai K L; Wu J; Yee A F, Macromolecules, 32, No.23, 16th Nov. 1999, p.7921-4. Bergquist P; Zhu Y; Jones A A; Inglefield P T, Macromolecules, 32, No.23, 16th Nov. 1999, p.7925-31. Nanasawa A; Takayama S; Takeda K, J. Appl. Polym. Sci., 66, No.1, 3rd Oct.1997, p.19-28. US Patent 6,420,310. US Patent 6,350,798. US Patent 6,300,016. US Patent 6,255,435. US Patent 5,773,139. US Patent 5,670,254. US Patent 5,665,501. US Patent 5,556,908. Fyrolflex RDP-B. Akzo Nobel Chemicals Inc., 1998. Liang G G, Cook W D, Tcharkhtchi A, Sautereau H, Eur. Polym. J., 47, 1578-88, 2011. Liang G G, Cook W D, Sautereau H J, Tcharkhtchi, Eur. Polym. J., 44, 366-75, 20008. Yu R C U, Tong Y, US Patent Application Publication US2010/0297544, Xerox, Nov. 25, 2010. Flynn A, Torres L F, US Patent 7,842,761 B1, Lapol LLC, Nov. 30, 2010. Wypych, G, Handbook of Polymers, 3rd Ed., ChemTec Publishing, Toronto, 2022. Sun, Y; Matsumoto, M; Haruki, M; Khara, S-i; Takashima, S, J. Supercritical Fluids, 113, 144-9, 2016. Guart, A; Wagner, M; Mezquida, A; Lacorte, S; Oehlmann, J; Borrell, A, Food Chem., 141, 1, 373-80, 2013. Yu, R C U; Grabowski, E F, US20130202995, Xerox Corporation, Aug. 8, 2013. KR20210087638A, Jul. 13, 2021. Jenkins LL, Williams III E, Spangler G, EP3795636A1, SABIC Global Technologies BV SHPP Global Technologies BV, Mar. 24, 2021.

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11.28 POLYESTER 11.28.1 FREQUENTLY USED PLASTICIZERS Various low molecular weight polyesters are polymeric plasticizers. These are likely to be compatible with polyester resins.9 Other groups of plasticizers are also used in the plasticization of aliphatic and aromatic polyesters and copolyesters, as follows: • polyalkylene ethers (e.g., polyethylene glycol, polytetramethylene glycol, polypropylene glycol, or their mixtures), having a molecular weight in the range from 400 to 1500 daltons1,5 • glyceryl monostearate in shrink film applications3 • octyl epoxy soyate, epoxidized soybean oil, epoxy tallate, epoxidized linseed oil in shrink film applications6,7 • polyhydroxyalkanoate in biodegradable compositions8,18 • glycols (e.g., ethylene glycol, pentamethylene glycol, hexamethylene glycol, etc.) in biodegradable fiber11 • anionic and cationic plasticizers (e.g., dioctyl sulfosuccinate, alkane sulfonate, or sulfonated fatty acid) in sulfonated polyesters in hotmelt applications12 • phthalate and trimellitate plasticizers in hotmelt traffic marking composition13 • polyethylene glycol di-(2-ethylhexoate) in flame-resistant compositions (additional brominated flame retardant used)14 • di-(2-ethylhexyl) phthalate16 • tricresyl phosphate16 • acetyl tributyl citrate in hyperbranched polyester20 • dimethylisosorbide, propylene carbonate, methylbenzyl alcohol, glycerol carbonate acetate, and glycerol carbonate ethyl ether can be used in degradable polyester filter tow21 • polyester plasticizer in shrink film22 • succinate ester (bis(butyldiglycol)succinate) in biodegradable polyester23 11.28.2 PRACTICAL CONCENTRATIONS • 1-4 wt% of glyceryl monostearate • 1-5 wt% of phthalate or trimellitate13 • 3-4 wt% of polyethylene glycol di-(2-ethylhexoate)14 • 1-10 wt% of octyl epoxy soyate6,7 • 10 phr of polyester sebacate9 • up to 15 wt% of glycol11 • DOP − 5-15 wt%16 • 0.5-25 wt% of polyalkylene ethers1,5 • up to 30 wt% of ionic plasticizer12 • TCP − 5-30 wt%16 Low to moderate concentrations of plasticizers are used in polyester. Most products from polyesters are produced without plasticizers. Mylar film is a well-known example of material, which does not contain plasticizer, as well as numerous formulations of plastic bottles.

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373

11.28.3 MAIN FUNCTIONS PERFORMED BY PLASTICIZERS • melt viscosity adjustment1 and gel viscosity reduction10,18 • lowering glass transition temperature1,3,16 • lowering softening point10 • regulation of shrink rate3 • lowering the on-set temperature of shrinking3 • increase in fracture toughness4 • reduction of crystallinity8 11.28.4 EFFECT OF PLASTICIZERS ON POLYMER AND OTHER ADDITIVES Figure 11.28.1 shows that glass transition temperature decreases linearly with a very similar slope for two different plasticizers. Figure 11.28.2 shows that the effect of plasticizer concentration on film shrinkage is a complex phenomenon. The influence of glass transition temperature on the process of shrinking is clearly visible from shrinkage at 60oC. The more plasticizer is present in the formulation, the higher the shrinkage of the film. At higher shrinking temperatures, both glass transition temperature and the shrinking process temperature work together to produce results. For a shrinking process, it is important that material is able to change the structure, but the material should also retain its shape memory to adjust to changing shape of wrap. At higher temperatures and higher concentrations of plasticizers, this shape memory is not retained, and the material does not shrink as expected. One of the reasons for changes in mechanical properties is related to changes in crystallinity. It was reported8 that the addition of 10 wt% of polyhydroxyalkanoate reduced crystallinity from 50-90% to 30%.

Figure 11.28.1. Glass transition temperature of polyester shrink film containing variable amounts of plasticizers. A - octyl epoxy soyate, B - glyceryl monostearate. [Data from US Patents 5,824,398, and 5,589,126.]

Figure 11.28.2. Shrinkage of polyester film plasticized with variable amounts of octyl epoxy soyate at different shrinking temperatures. [Data from US Patent 5,589,126.]

374

Figure 11.28.3. Break stress of polyester film plasticized with variable amounts of octyl epoxy soyate. MD − machine direction, TD − transverse direction. [Data from US Patent 5,589,126.]

Plasticizers Use and Selection for Specific Polymers

Figure 11.28.4. Break strain of polyester film plasticized with variable amounts of octyl epoxy soyate. MD − machine direction, TD − transverse direction.[Data from US Patent 5,589,126.]

Figure 11.28.3 shows that two different rates of break stress are recorded for oriented (MD) and unoriented (TD) directions in film. Break stress changes more rapidly in an oriented direction because plasticizer affects crystallinity and orientation. In Figure 11.28.4, break strain and its changes are very different in both directions. The addition of plasticizer affects the integrity of the amorphous phase, which causes that strain to decrease in an unoriented direction. Plasticization of the crystalline phase causes an increase in strain in an oriented direction.6 Polyesters synthesized from the liquefied wood and depolymerized poly(ethylene terephthalate) were used as renewable raw materials and evaluated as plasticizers for poly(vinyl acetate) dispersion adhesives for flooring applications.19 Plasticizers improved thermal stability of adhesive and had a great influence on tensile strength and elongation.19 End-capped saturated polyesters with high biobased content were developed.24 Endcapping with alkyl moieties improved plasticizing effect.24 End-capped plasticizers had a very low migration tendency in PVC formulations.24 Polyester resin composition contained plasticizer that was an acetylated monoglyceride, propylene glycol fatty acid ester, a fatty acid triglyceride, having melting points of 190-210°C.25 Plasticizer enhanced molecular mobility, particularly at low temperatures, and promoted supercooling, that is, crystallization in a solid phase state.25 Therefore, it was possible to crystallize at a lower temperature and obtain a finer crystal system.25 Biobased bis(ethoxy-cardanolyl) sebacate was used to plasticize biobased polyester resin.26

11.28.5 TYPICAL FORMULATIONS Shrink film:7 Polyester Octyl epoxy soyate

96 wt% 4

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Shrink film:3 Polyester Glyceryl monostearate

97 wt% 3

Flame resistant composition:14 PET PET/PEO copolymer Bromine flame retardant Polyethylene glycol di(2-ethylhexoate) Nucleating agent

21 parts 18 16 4 4

References 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26

US Patent 5,965,648. Zhikai Zhong; Sixun Zheng; Yongli Mi, Polymer, 40, No.13, 1999, p.3829-34. US Patent 5,824,398. Parameswaran V; Shukla A, J. Mater.Sci., 33, No.13, 1st July 1998, p.3303-11. US Patent 5,624,987. US Patent 5,589,126. US Patent 5,534,570. US Patent 5,516,825. US Patent 6,405,775. US Patent 6,403,685. US Patent 6,045,908. US Patent 6,001,910. US Patent 5,973,028. US Patent 5,700,857. US Patent 6,037,100. Bakar M, Djaider F, J. Thermoplastic Compos. Mater., 20, 53-64, 2007. Takenaka A, Tuchihashi M, US Patent 7,576,152 B2, Kao Corp., Aug. 18, 2009. Schaefer G F, US Patent 7,498,372 B2, Ferro Corp., Mar. 3, 2009. Jasiukaityte-Grojzdek, E; Kunaver, M; Kukanja, D; Moderc, D, Int. J. Adhesion Adhesives, 46, 56-61, 2013. Yang, T-C; Cheng, K-C; Huang, C-C; Lee, B-S, Dental Mater., 31, 6, 695-701, 2015. Don Sebastian, A; Sears, S B; Jackson, T J; Dooly, G L, EP2736359, R J Reynolds Tobacco Company, Jun. 4, 2014. Shih, W K; Carico, K C; Kinkade, N E, WO2014093041, Eastman Chemical Company, Jun. 19, 2014. Vanheule, J; Declerck, J; Stankovic, S, WO2015090619, Proviron Holding NV, Jun. 25, 2015. Pereira VB, Fonseca AC, Costa CSMF, Ramalho A, Coelho JFJ, Serra AC, Polym. Testing, 85, 106406, 2020. WO2021241145A1, Dec. 2, 2021. Robinson JJ, Vicol RL, Moebus JH, Calayan T, Sacripante GG, US11072694B1, Evoco Ltd., Jul. 27, 2021.

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11.29 POLYETHERIMIDE Pentaerythritotetrabenzoate ester (Benzoflex S-552) was used for the plasticization of poly(arylene ether)/polyetherimide blends.1 Microporous membrane was manufactured from plasticized polyetherimide. The plasticizer was then removed by leaching into a suitable solvent.2 Triallyl isocyanurate is miscible with polyetherimide and can be used as a reactive plasticizer.3 Pentaerythritol tetrabenzoate and resorcinol bis(diphenyl phosphate) are suitable plasticizers for polyetherimides.4 Contact surface hardness of the short-carbon-fiber-reinforced polyetherimide composite was reduced after a sliding test in water due to plasticization phenomenon, especially seawater accelerated diffusion of water molecules into the matrix, making the specific wear rate in seawater ten times of that in tap water for highly-loaded conditions.5

References 1 2 3 4 5

US Patent 6,166,137. US Patent 5,888,434. Rusli, A; Raffi, N S M; Imail, H, Procedia Chem., 19, 776-81, 2016. Richards, W D; Smigielski, P M; Pickett, J E, WO2014164010, Sabic Innovative Plastics, Oct. 9, 2014. Zhang Y-Y, Chen Q, Mo X-L, Huang P, Li Y-Q, Zhu C-C, Hu N, Fu S-Y, Compos. Sci. Technol., 216, 109044, 2021.

11.30 Polyethylacrylate

377

11.30 POLYETHYLACRYLATE Dipropylene glycol dibenzoate, isodecyl diphenyl phosphate, dibutyl phthalate, and 2,2,4trimethyl-1,3-pentanediol monoisobutyrate were used in stripable film coating composition.1 Dibutyl, dihexyl, and dioctyl phthalates were studied regarding their effect on the rubbery modulus of polyethylacrylate.2 It was found that the rubbery modulus was independent of the plasticizer type at all concentrations studied.

References 1 2

US Patent 5,604,282. Nakajima N; Varkey J P, J. Appl. Polym. Sci., 69, No.9, 29th Aug.1998, p.1727-36.

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Plasticizers Use and Selection for Specific Polymers

11.31 POLYETHYLENE It may come as a surprise but many polyethylene technologies use plasticizers for various purposes as discussed below.

11.31.1 FREQUENTLY USED PLASTICIZERS • dioctyl phthalate, DOP, in low-density polyethylene,1 in the formation of the microporous film,6 in composite based on chlorinated polyethylene,9,13 and hotmelt adhesive for pavement marking15 • glyceryl tribenzoate in adhesives12,18 • polyethylene glycol, having a molecular weight of 8,000 daltons, in polyethylene foam2 and in biodegradable plastics composition10 • sunflower oil in biodegradable formulations containing starch3 • paraffin wax, having a molecular weight from 400 to 1,000 daltons, in preparation of surface-modified film4,11 and porous film13 • paraffin oil in the formation of microporous film6 • mineral oil in fusion process of fishing line5 • glycerin in binder formulation for metal and ceramic powder injection molding7 and in biodegradable plastic composition10 • EPDM as high molecular weight plasticizer in extruded polyethylene pipe6 • EVA as high molecular weight plasticizer in extruded polyethylene pipe8 • non-functionalized hydrocarbon16 • polyethylene glycol and sunflower oil17 • 1,4-cyclohexane dimethanol dibenzoate18 11.31.2 PRACTICAL CONCENTRATIONS • 0.1 wt% of sunflower oil as biodegradable plasticizer3 • 0.1-3 wt% of polyethylene glycol in compatibilizing foam components2 • 1.5 wt% of glycerin in sintering process7 • 1-3 wt% of dioctyl phthalate, DOP, in hotmelt adhesive15 • 3-10 wt% of EDPM to plasticize pipe8 • 5 wt% of glyceryl tribenzoate in adhesive12 • 30 phr of DOP in plasticized low-density polyethylene1 • 20-75 phr of DOP to plasticize chlorinated polyethylene9 • 60-80 parts of paraffin wax to prepare surface modified film by plasticizer extraction4,11 • 50-70 wt% of DOP in production of microporous film6,13 • immersion in mineral oil fusion of fishing line5 11.31.3 MAIN FUNCTIONS PERFORMED BY PLASTICIZERS There are many reasons to add plasticizers to polyethylene formulations. Smaller additions are added for conventional reasons, such as to make the material more flexible. This includes applications in hotmelt adhesives12,15 and plasticization of pipe material.8 It was shown that up to 30 phr of plasticizer could be added to polyethylene.1 Small amount of plasticizer were also needed to compatibilize different polymers7 or formulation components,2 as well as to initiate biodegradation.3

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379

Chlorinated polyethylene requires larger additions of plasticizers. The amounts of plasticizers and types used in chlorinated polyethylene are very similar to plasticizers used in polyvinylchloride. Very large concentrations of plasticizers are used to produce permeable films and films with surface modification. In these cases,4,6,11,13 plasticizer may consist of up to 70% of the initial composition. This mixture is then extruded, the plasticizer is removed by extraction, and the film is stretched to improve mechanical properties of microporous or surface-modified film. The density and crystallinity of polymer were controlled by the diffusion of biodiesel.19 Biodiesel had higher plasticization efficiency than toluene.19 Biodiesel and toluene have different modes of plasticization of polyethylene.19 Absorbed biodiesel lubricated the inter-crystalline chains, promoting crystal slippage during plastic deformation with no increase in internal stress.19 HDPE-chitosan composites, prepared using maleic anhydride as a compatibilizer and palm oil as a plasticizer, have been subjected to dielectric characterization and thermal studies.20 The addition of palm oil to the optimized blend showed improved segmental mobility due to the interaction of polar amine group in chitosan with HDPE.20 The incorporation of 5 wt% of palm oil has improved stability with an increase in activation energy to 348.2 kJ/mol.20

11.31.4 MECHANISM OF PLASTICIZER ACTION It is suggested that plasticization of low-density polyethylene, LDPE, occurs inside the spherulitic crystallite in the interlamellar and interfibrillar regions. DOP-plasticized LDPE melts at lower temperatures as a result of plasticization.1 11.31.5 TYPICAL FORMULATIONS Composition for metal sintering process:7 Stainless steel powder Polyvinyl alcohol Glycerin Water Release aid High-density polyethylene Extruded polyethylene pipe:8 High-density polyethylene Additives EPDM molecular weight 6,500 Pavement marking compound:15 Hydrocarbon resin Polyethylene DOP Glass beads Titanium dioxide Calcium carbonate

91.35 wt% 5.25 1.46 0.366 0.551 1.023 92.40 wt% 2.60 5.00 12 parts 5 3 20 8 52

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Plasticizers Use and Selection for Specific Polymers

References 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Shieh Y-T; Liu C-M, Polym. Preprints, 41, 2, 2000, p.1112-3. US Patent 5,905,098. Sastry P K; Satyanarayana D; Rao D V M, J. Appl. Polym. Sci., 70, No.11, 12th Dec.1998, p.2251-7. US Patent 5,624,627. US Patent 6,148,597. US Patent 6,127,438. US Patent 6,008,281. US Patent 5,958,530. US Patent 5,914,195. US Patent 5,861,461. US Patent 5,840,235. US Patent 5,766,731. US Patent 5,759,678. US Patent 5,728,772. Miller R A, Polyethylene and Amorphous Polyolefins in Adhesives and Sealants, Eastman Chemical Company, 2000. Li W, Lin C-Y, Chapman B R, Kelly M B, US Patent 7,985,801 B2, ExxonMobil, Jul. 26, 2011 Wypych, G, Handbook of Polymers, 3rd Ed., ChemTec Publishing, Toronto, 2022. Vitrano, M D; Stafeil, K; Hailemichael, T, WO2012139120, Bostik, Inc., Oct. 11, 2012. Saad AK, Gomes FPC, Thompson MR, Fuel, 252, 246-53, 2019. Shelly M, Mathew M, Pradyumnan PP, Francis T, MaterialsToday, Proc., 46, 7, 2742-6, 2021.

11.32 Poly(ethylene oxide)

381

11.32 POLY(ETHYLENE OXIDE) 11.32.1 FREQUENTLY USED PLASTICIZERS • dioctyl phthalate2 • ethylene carbonate2,6 • propylene carbonate3 • polyethylene and polypropylene glycols in pressure sensitive adhesives4,5 • tetraethylene glycol and tetraglyme in polymer electrolytes6 • polyoxyethylene-sorbitane monolaureate (Tween 20) in polymer-modifier compositions1 • polyethylene glycol and glycerin in transdermal drug delivery systems11 • broad range of plasticizers in denture stabilizing composition10 • tetraethylene glycol and tetraglyme12 • ethylene carbonate, propylene carbonate, and diethyl carbonate are used in solid electrolyte for batteries14 11.32.2 PRACTICAL CONCENTRATIONS • 22 wt% of polyoxyethylene-sorbitane monolaureate (Tween 20)8 • up to 25 wt% DOP in polymer gel2 • up to 30 wt% of plasticizer in denture stabilizing composition10 • 32.3 wt% of polyethylene glycol and 32.3 wt% of glycerin in transdermal drug delivery system9 • up to 70 wt% of ethylene or propylene glycol in pressure sensitive adhesive4,5 • 50 wt% ethylene carbonate13 11.32.3 MAIN FUNCTIONS PERFORMED BY PLASTICIZERS • improvement of processability2 • increased flexibility2 • weakening of interchain interaction2 • increasing space between molecules2 • increasing free volume2,6 • decreasing of glass transition temperature2,6 • increasing ionic conductivity in Li-based batteries6,7 • creating ionically-conducting pathways in amorphous phase6 • increase of conductivity (addition of 50 wt% ethylene carbonate and TiO2 increases conductivity to 1.6x10-4 S/cm)13 11.32.4 EFFECT OF PLASTICIZERS ON POLYMER AND OTHER ADDITIVES Figure 11.32.1 shows that rapid changes in glass transition temperature occur only for lower concentrations of plasticizer (up to 10 wt%). It is known that the compatibility limit of dioctyl phthalate with poly(ethylene oxide) is 15 wt%.2 Free volume increases linearly with the amount of plasticizer increasing (Figure 11.32.2), but crystallinity of polymer changes only a little. This shows that the plasticizer modifies mostly the amorphous phase. Membranes based on aromatic copolymers contained 2,6-substituted pyridine groups and PEO pendant sequences.15 The incorporation of the pendant, hydrophilic PEO groups onto a rigid aromatic backbone, had a dual functionality, enabling both water and CO2 permeability. PEO groups plasticized the polymer backbone, resulting in increased chain

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Plasticizers Use and Selection for Specific Polymers

Figure 11.32.1. Glass transition temperature of plasticized poly(ethylene oxide) vs. concentration of dioctyl phthalate. [Data from Queiroz S M; Machado J C; Porto A O; Silva G G, Polymer, 42, No.7, 2001, p.3095-101.]

Figure 11.32.2. Mean free volume of plasticized poly(ethylene oxide) vs. concentration of dioctyl phthalate. [Data from Queiroz S M; Machado J C; Porto A O; Silva G G, Polymer, 42, No.7, 2001, p.3095-101.]

mobility and flexibility, which in turn led to increased gas/vapor diffusion and contributed to CO2 solubility.15 All gases (CO2, N2, and CH4) exhibit increased permeability under humid conditions due to plasticization induced by water vapor, which leads to increased permeability.15 Ion conduction in poly(ethylene oxide)-based electrolytes was explained by ion movement coupled with polymer segmental motions (free volume).16 Positron annihilation spectroscopy was used to investigate the free volume structure of PEO-LiTFSI solidstate electrolyte with varying electrolyte concentrations.16 Addition of LiTFSI had plasticization effect, increasing free volume size in the polymer matrix.16 Li based salts act as a plasticizer for PEO leading to a decrease of its crystallinity.16 The introduction of liquid plasticizers, such as propylene carbonate, ethylene carbonate, or ionic liquids to PEO-based solid polymer electrolytes is known as an effective method.17 It facilitates solubility and dissociation, thereby increasing the ionic conductivity, but mechanical properties of solid polymer electrolytes deteriorate, and lithium dendrite growth occurs with ongoing cycling.17 Organic ionic plastic crystals (triethylmethylammonium bis(fluorosulfonyl)imide and lithium bis(fluorosulfonyl) imide), having low volatility, non-flammability, and excellent thermal stability, were used as solid plasticizers.17 In addition to decreased crystallinity of the polymer and dissociable Li salt in the composite systems due to plasticizing effect, good mechanical properties were also obtained.17

References 1 2 3 4 5

US Patent 5,888,434. Queiroz S M; Machado J C; Porto A O; Silva G G, Polymer, 42, No.7, 2001, p.3095-101. Morales E; Acosta J L, J. Appl. Polym. Sci., 69, No.12, 19th Sept.1998, p.2435-40. US Patent 5,660,178. US Patent 5,489,624.

11.32 Poly(ethylene oxide)

6 7 8 9 10 11 12 13 14 15 16 17

383

Chintapalli S; Frech R, Macromolecules, 29, No.10, 6th May 1996, p.3499-506. Bookeun Oh, Won Il Jung, Dong-Won Kim, Hee Woo Rhee, Bull. Korean Chem. Soc., 23, 5, 2002, p.653. US Patent 6,403,706. US Patent 6,072,100. US Patent 5,658,586. Hogan T E, Corsaut W J, US Patent Application Publication US2010/0063178 A1, Bridgestone Americas, Mar. 11, 2010. Wypych, G, Handbook of Polymers, 3rd Ed., ChemTec Publishing, Toronto, 2022. Vignarooban, K; Disnayake, M A K L; Albinsson, I; Mellander, B-E, Solid State Ionics, 266, 25-8, 2014. Zhou, M; Zhong, L; Wang, Y, US20150037655, Ocean’s King Lightning Science & Technology, Feb. 5, 2015. Ioannidi A, Anastasopoulos C, Vroulias D, Kallitsis J, Ioannides T, Deimede V, Separation Purification Technol., 280, 119790, 2022. Utpalla P, Sharma SK, Sudarshan K, Sahu M, Pujari PK, Solid State Ionics, 339, 114990, 2019. Wang W, Fang Z, Zhao M, Peng Y, Zhang J, Guan S, Chem. Phys. Lett., 747, 137335, 2020.

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Plasticizers Use and Selection for Specific Polymers

11.33 POLY(3-HYDROXYBUTYRATE) 11.33.1 FREQUENTLY USED PLASTICIZERS • dioctyl phthalate1 • dioctyl sebacate1 • acetyl tributyl citrate1,3,5 • polyethylene glycol2 • soybean oil4 • epoxidized soybean oil4 • triethyl citrate4 • tributyrin8 11.33.2 PRACTICAL CONCENTRATIONS • 25-40 wt% dioctyl sebacate1 • 10-30 wt% acetyl tributyl citrate1 • 15 wt% tributyrin in packaging films8 11.33.3 MAIN FUNCTIONS PERFORMED BY PLASTICIZERS • DOP and DOS decrease and ATC increases glass transition temperature of plasticized material1 • ATC affects mechanical performance1 • rapid thermal degradation above 190oC in the presence of ATC3 • triethyl citrate performed much better than soybean oils4 Incorporation of 10 wt% PHB-rubber composite reduced crystallization half-times of polylactide by 32-fold and lowered kinetic parameter and folding surface energy, indicating rapid polymer chain folding and the super-nucleating capability due to simultaneous instigated nucleation and plasticization.6 Poly(3-hydroxybutyrate) undergoes physical aging and becomes brittle.7 The plasticization of PHB is considered as a strategy for overcoming this problem.7 The plasticized formulations were less brittle than PHB, but they suffered to a greater extent from the deleterious effects of physical aging on impact resistance and strain at break.7 The effects of aging on impact resistance were more pronounced when triethyl citrate concentration increased.7 The dynamic mechanical behavior suggested phase separation in formulations richer in plasticizer, induced by secondary crystallization, which expelled triethyl citrate from the crystalline structure.7 Polylactide was mixed with PHB and plasticized with tributyrin to enhance its properties.8 PHB and tributyrin addition changed PLA fracture behavior from brittle to ductile.8 PLA/PHB/tributyrin blends formed flexible and tough films suitable for packaging.8 Incorporation of tributyrin reduced glass transition temperature and a melting point of PLA matrix and increased its crystalline degree due to an increase in molecular mobility.8 The plasticizing effect of tributyrin changed the quasi-static fracture behavior of PHB from brittle to semi-brittle and that of PLA from semi-brittle to the ductile to brittle transition regime.8 References 1 2 3

Wang L, Zhu W, Wang X, Chen X, Chen G-Q, Xu K, J. Appl. Polym. Sci., 107, 166-73, 2008. Parra D F, Fusaro J, Gaboardi F, Rosa D S, Polym Deg. Stab., 91, 1954-59, 2006. Erceg M, Kovacic T, Klaric I, Polym. Deg. Stab., 90, 313-18, 2005.

11.33 Poly(3-hydroxybutyrate)

4 5 6 7 8

Choi J S, Park W H, Polym. Test., 23, 455-60, 2004. Krishnaswamy R K, WO2012142100, Metabolix Inc., Oct.18, 2012. Yeo JCC, Lin TT, Koh JJ, Low LW, Tan BH, Li Z, He C, Compos. Commun., 27, 100894, 2021. Umemura RT, Felisberti MI, MaterialsToday, Commun., 25, 101439, 2020. Iglesias Montes ML, Cyras VP, Manfredi LB, Pettarín V, Fasce LA, Polym. Testing, 84, 106375, 2020.

385

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Plasticizers Use and Selection for Specific Polymers

11.34 POLYISOBUTYLENE Depending on molecular weight, polyisobutylene, PIB, can be liquid or solid. Liquid grades of PIB are frequently used as plasticizers. Solid grades are chemically inert elastomers, which have resistance to oxidative and thermal degradation and low gas permeability. Because of these properties, they find many applications. Some of these applications require plasticizers. Low molecular weight PIB is used in many adhesive compositions, where it plays the role of plasticizer and/or tackifier. Adhesive composition based on EPDM rubber, useful for providing water-tight joints in roofing membranes, contains 5-9 wt% PIB.1,2 Pressure sensitive roofing tape is also based on PIB plasticized EPDM.3 In sporting goods, PIB plasticized EPDM is used for grips of golf clubs, tennis rackets, bicycles, and also tools. Such grips provide good non-slipping properties.4 PIB plays the role of tackifier in adhesive compositions used as a wound dressing.5 EPDM and brominated butyl rubber-based formulations use PIB as a plasticizer for water-tight joints in rubber membranes.6 In these systems, peroxide curing causes some degradation of brominated butyl rubber that tackifies products. Antioxidant was chemically attached to a low molecular weight PIB and used in natural rubber.8 Improved aging and ozone resistance was determined because of better retention of antioxidant. Solid PIBs are used in plasticized formulations. In the drug-containing adhesive of a transdermal patch, 10-40 wt% plasticizer (mineral oil, silicone oil, octyl palmitate, etc.) is added to plasticize material and impart hydrophobic properties.7 Petrolatum or mineral oil was used in the adhesive skin barrier, which is a pressure-sensitive adhesive based on PIB.12 Self-fusing tape is based on a composition containing halogenated PIB and medium molecular weight PIB.9 A composition also contains 2 to 18 wt% of polybutene, which is a non-extractable plasticizer.9 Mineral oil, silicone oil, and octyl palmitate are used as plasticizers of polyisobutylene.13 Interphase transfer of di-2-ethylhexyl adipate between ethylene-propylene copolymer and polyisobutylene in the laminated sheets was studied.14 The amount of DOA in each phase was determined by the ambient temperature.14 DOA moved to EPR from PIB at a temperature of −20°C. The reverse trend was observed at 40°C.14 DOA content before lamination was 10 phr.14 This behavior was attributed to the change of interaction parameters between DOA and each rubber as a function of temperature.14 Water-stop composition works based on its expansion and controlled swelling on immersion in water. The following is the composition:10 Crosslinked butyl rubber 10-12 wt% Polyisobutylene 6-8 Non-swelling clay (ball clay) 14-19 Talc 1-2 Carbon black 1-2 Cellulose fiber 3-4 Plasticizer (process oil − Kendex 0842) 26-28 Tall oil fatty acid 5-2

11.34 Polyisobutylene

Water swellable sodium and calcium bentonites

387

13-16.5 each

References 1 2 3 4 5 6 7 8 9 10 11 12 13 14

US Patent RE37,683. US Patent 6,297,324. US Patent 6,120,869. US Patent 5,981,649. US Patent 5,622,711. US Patent 5,733,621. US Patent 5,948,433. Sulekha P B; Joseph R; George K E, Polym. Deg. Stab., 63, No.2, Feb.1999, p.225-30. US Patent 5,914,371. US Patent 5,663,230. US Patent 5,492,943. Jacobsen S; Fritz H G, Polym. Eng. Sci., 39, No.7, July 1999, p.1303-10. Wypych, G, Handbook of Polymers, 3rd Ed., ChemTec Publishing, Toronto, 2022. Kuhakongkiat, N; Wachteng, V; Nobukawa, S; Yamaguchi, M, Polymer, 78, 208-11, 2015.

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11.35 POLYISOPRENE 11.35.1 FREQUENTLY USED PLASTICIZERS • broad range of esters of phthalic acid and other dicarboxylic acids, aliphatic, aromatic and naphthenic oils, low molecular weight polybutenes in sealants and adhesives1 • polybutene is used as a non-extractable plasticizer in self-fusing tape2 • aromatic or paraffinic oil, esters of phthalic, adipic, and sebacic acids in rubber composition for tires and belts3 • esters of cyclohexane polycarboxylic acids4 11.35.2 PRACTICAL CONCENTRATIONS • 5 wt% of naphthenic oil and 15 wt% of polyisobutylene1 • 2-18 wt% of polybutene2 • 5 wt% of aromatic oil3 11.35.3 MAIN FUNCTIONS PERFORMED BY PLASTICIZERS • change of rheological properties of uncured mixture1 • affects vibration damping1 • affects elastic properties of cured rubber3 11.35.4 TYPICAL FORMULATIONS Sealant with damping properties:1 3,4-polyisoprene Chalk Precipitated calcium carbonate Terpene phenolic resin Naphthenic oil Polyisobutylene Antioxidant Calcium oxide Zinc oxide References 1 2 3 4

10 wt% 32 25 10 5 15 1 1 1

US Patent 6,204,321. US Patent 5,914,371. US Patent 5,679,744. Hogan T E, Corsaut W J, US Patent Application Publication US2010/0063178 A1, Bridgestone Americas, Mar. 11, 2010.

11.36 Polyimide

389

11.36 POLYIMIDE 11.36.1 FREQUENTLY USED PLASTICIZERS • diethylene glycol dibenzoate and dimethyl phthalate in membranes1 • reactive plasticizer having two four-membered rings2 • triallyl phosphate2 • diethynyldiphenyl methane and phenylethynyldiphenyl methane as reactive plasticizers in resin-transfer molding • 4-hydroxybenzophenone3 11.36.2 PRACTICAL CONCENTRATIONS • 10-60 wt% diethylene glycol dibenzoate and dimethyl phthalate1 • 12-17 wt% of reactive plasticizer2 • 0.25-5 wt% triallyl phosphate2 • 10 wt% 4-hydroxybenzophenone3 11.36.3 MAIN FUNCTIONS PERFORMED BY PLASTICIZERS • lowering glass transition temperature1,2 • increasing membrane flexibility1 • affecting optical properties of the membrane (transparent with diethylene glycol dibenzoate and opaque with dimethyl phthalate)1 • enhancing processability2 • increasing dimensional and thermooxidative stability2 • facilitating crystallinity and increasing crystallization window by 50oC3 • lowering viscosity

Figure 11.36.1. Initial decomposition temperature of polyimide membrane of different types and amounts of plasticizers. DGD − diethylene glycol dibenzoate, DMP − dimethyl phthalate. [Data from Totu E; Segal E; Covington A K, J. Thermal Analysis Calorimetry, 52, No.2, 1998, p.383-91.]

Figure 11.36.2. Glass transition temperature of polyimide membrane for different types and amounts of plasticizers. DGD − diethylene glycol dibenzoate, DMP − dimethyl phthalate. [Adapted, by permission, from Totu E; Segal E; Covington A K, J. Thermal Analysis Calorimetry, 52, No.2, 1998, p.383-91.]

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Plasticizers Use and Selection for Specific Polymers

11.36.4 EFFECT OF PLASTICIZERS ON POLYMER AND OTHER ADDITIVES Figures 11.36.1 and 11.36.2 show initial decomposition and glass transition temperatures for two plasticizers. Plasticizer, which rapidly decreases glass transition temperature, forms less thermally stable material. It was proven within the course of this research that a combination of both plasticizers permits optimizing properties.1 A combination of reactive and non-reactive plasticizers was found to offer advantages. Reactive plasticizer reduces the amount of potential volatiles in the final product and helps in reduction of viscosity, and thus improves processability. On the other hand, reactive plasticizer crosslinks material, which thus needs non-reactive plasticizer to increase its flexibility.2 Crystallization rate and the range of temperatures, at which crystallization may occur, depend on glass transition temperature. It was found that the small addition of plasticizer (10 wt%) enhanced crystallizing abilities of polyimide.3 Hydrogen sulfide and carbon dioxide are acid gases that must be removed from natural gas prior to transmission and use.4 H2S/CH4 and CO2/CH4 separation performance of two polyimide membranes was assessed.4 The so-called plasticization effects of polyimides are generally viewed as negative features when using such membranes, but when H2S is present in the feed, the polyimide membrane plasticization is actually a tool for performance optimization.4 Polyimide plasticization can provide large performance benefits for H2S/CH4 separation by offering higher H2S permeability and attractive H2S/CH4 selectivity.4 Figure 11.36.3 shows the effect of plasticization on membrane separation quality.4 Plasticization of polyimides is a benefit for H2S/CH4 separation by promoting sorption separation factor, whereas it is a drawback for CO2/CH4 separation due to partial loss of the molecular sieving effect.4

Figure 11.36.3. Fundamental analysis of plasticization effect on H2S/CH4 and CO2/CH4 separation by polymer membranes. [Adapted, by permission, from Liu Y, Liu Z, Liu G, Qiu W, Bhuwania N, Chinn D, Koros WJ, J. Membrane Sci., 593, 117430, 2020.]

Crown-ether ring size and rigidity influence gas separation performance of CO2/N2 and plasticization behavior of crown-ether-containing polyimide membranes.5 The crownethers provide membrane material with good affinity to CO2 due to the polar ether segments.5 Both solubility and permeability of CO2 and N2 are decreased in these crownether-containing membranes over the whole pressure range.5 When the molecular size of the crown-ether decreases, the permeability increases.5 The incorporation of more rigid

11.36 Polyimide

391

crown-ethers causes rigidification of polymer matrix, contributing to lower permeability of membranes.5 No plasticization was observed for the crown-ether-containing membranes in the mixed gas conditions as a result of lower solubility of the crown-ether-containing membranes and competition effects of CO2 and N2.5

References 1 2 3 4 5

Totu E; Segal E; Covington A K, J. Thermal Analysis Calorimetry, 52, No.2, 1998, p.383-91. US Patent 5,688,848. Koning C E; Teuwen L; De Plaen A; Mercier J P, Polymer, 37, No.25, 1996, p.5619-25. Liu Y, Liu Z, Liu G, Qiu W, Bhuwania N, Chinn D, Koros WJ, J. Membrane Sci., 593, 117430, 2020. Koros W, Liu Y, Liu Z, Bhuwania N, Chinn D, WO2020251937A1, Chevron U.S.A. Inc., Georgia Tech Research Corporation, Dec. 17, 2020. Houben M, Borneman Z, Nijmeijer K, Separation Purification Technol., 255, 117307, 2021.

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Plasticizers Use and Selection for Specific Polymers

11.37 POLYLACTIDE 11.37.1 FREQUENTLY USED PLASTICIZERS Polylactide is a very popular environmentally friendly polymer, which needs plasticizers for its various applications. The following plasticizers were used: • polypropylene glycol and epoxy-functionalized polypropylene glycol (molecular weights 720 and 640, respectively) were studied as biodegradable plasticizers1,29 • polyethylene glycol having a molecular weight in the range from 600 to 8,000 in film applications,2 injection-molded parts,3 in polymer scaffolds,11 in biodegradable compositions,19 in nanocomposites,20 and in fibers34 • partial fatty acid ester (Loxiol GMS 95) and glucose monoester (Dehydrat VPA 1726) in injection molded parts3 • a range of biologically-degradable plasticizers including citrate or adipate esters, epoxidized soybean oil, acetylated coconut oil, and linseed oil in impact modified product5,6,18 • acetyl tributyl citrate,33 glycerol triacetate, and glycerol tripropionate in molded product and film,7 and acetyl tributyl citrate in surface coating12 • citrate ester grafting • di-(2-ethylhexyl) azelate or di-(2-ethylhexyl) adipate25 in biodegradable shrink films8 • citrate plasticizers18 (triethyl citrate, tributyl citrate, acetyl triethyl citrate, and acetyl tributyl citrate) in films,9 coated paper,16 films, or moldings13 • lactide monomer, oligomeric lactic acid,10 or lactic acid345 • epoxidized soybean oil or epoxidized linseed oil15 • Hexamoll DINCH24 • ionic liquids22 • oligomeric malonate esteramides27 • poly(ε-caprolactone)30 • sunflower-oil biodiesel-oligoesters32 The above list shows that a wide range of plasticizers can be used. One common expectation from plasticizer is that it will be biologically degradable, and it will increase the biodegradation rate of the composition. 11.37.2 PRACTICAL CONCENTRATIONS • polyethylene glycol: 2.5-10 wt%,3 10-20 wt%,2 20 wt%,20 and up to 25 wt%19 • 10-40 wt% of polypropylene glycols1,29 • partial fatty acid ester: 2.5-10 wt%3 • glucose monoester: 2.5-10 wt%3 • adipate esters: 8-15 wt%, 5-20 wt%,6 and 5-20 phr8 • azelate ester: 5-20 phr8 • citrate esters: 1-10 wt%,16 6-12 wt%,12 8-15 wt%,5 9-15 wt%,7 5-20 wt%,6 10-30 wt%,9 and 20-30 wt%13 • epoxidized soybean oil: 5-20 wt%6 • acetylated coconut oil: 5-20 wt%6 • lactide: 15-25 wt%10 • oligomeric lactic acid: 30-60 wt%10

11.37 Polylactide

•

393

Hexamoll DINCH: 10-20 phr24

11.37.3 MAIN FUNCTIONS PERFORMED BY PLASTICIZERS • increasing ductility of this normally quite brittle polymer1,3 • increasing very low elongation of unplasticized polymer (typically 3-5%)1 • increasing elastic properties without affecting anti-blocking properties7 • improvement of impact strength8 • improvement of tear resistance13 • decreasing glass transition temperature9,15,18 • reducing melt viscosity12 • reducing die pressure • mobility restriction by surface grafting28 • retaining or increasing biodegradation rate5,6,13-16 • improvement of coating quality18 • reducing tendency of coating to crack18 11.37.4 EFFECT OF PLASTICIZERS ON POLYMER AND OTHER ADDITIVES Figure 11.37.1 shows that polypropylene glycol acts as a plasticizer since it decreases glass transition temperature. The epoxy group was grafted on plasticizer in order to prevent its loss from the product. Crystallization temperature decreases parallel to the glass transition temperature. In fact, the difference between crystallization, Tc, and glass transition, Tg, temperatures is constant in the whole range of plasticizer concentration.1 Lowering the glass transition temperature increases chain mobility and this, in turn, increases crystallization rate. In another study,20 the same conclusion comes from the determination

Figure 11.37.1. Glass transition temperature, Tg, and crystallization temperature, Tc, of polylactide plasticized with variable amounts of epoxidized polypropylene glycol having molecular weight of 640 daltons. [Data from McCarthy S; Song X, Antec 2001.Conference proceedings, Dallas, Texas, 6th-10th May, 2001, paper 363.]

Figure 11.37.2. Crystallization enthalpy of polylactide plasticized with variable amounts of polypropylene glycol having molecular weight of 1000. [Data from Paul M-A; Alexandre M; Degee P; Pluta M; Gleski A; Dubois P, New Nanocomposite Materials Based on Plasticized Poly(l-lactide) and Organo-modified Montmorillonites, Belgian Polymer Group Meeting 2002, Mons, Belgium.]

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Plasticizers Use and Selection for Specific Polymers

Figure 11.37.3. Tensile strength of polylactide plasticized with variable amounts of epoxidized polypropylene glycol having molecular weight of 640 daltons. [Data from McCarthy S; Song X, Antec 2001.Conference proceedings, Dallas, Texas, 6th-10th May, 2001, paper 363.]

Figure 11.37.4. Elongation of polylactide plasticized with variable amounts of epoxidized polypropylene glycol having molecular weight of 640 daltons. [Data from McCarthy S; Song X, Antec 2001.Conference proceedings, Dallas, Texas, 6th-10th May, 2001, paper 363.]

Figure 11.37.5. Tensile strength of lactide plasticized polylactide. [Adapted, by permission, from Sinclair R G, J. Macromol. Sci. A, A33, No.5, 1996, p.585-97.]

Figure 11.37.6. Tensile strength of oligomeric lactic acid plasticized polylactide. [Adapted, by permission, from Sinclair R G, J. Macromol. Sci. A, A33, No.5, 1996, p.585-97.]

of crystallization enthalpy, which increases when plasticizer concentration increases (Figure 11.37.2). Figure 11.37.3 shows that the tensile strength of polylactide plasticized with epoxymodified polypropylene glycol decreases monotonically with the increased addition of plasticizer. Figure 11.37.4 shows that polylactide unplasticized and plasticized with a small amount of polypropylene glycol has very little elongation, which then rapidly

11.37 Polylactide

Figure 11.37.7. Weight loss of polylactide subjected to 28 days of hydrolytic degradation vs. concentration and type of plasticizer (ATEC − acetyl triethyl citrate, TEC − triethyl citrate). [Data from Labrecque L V; Kumar R A; Dave V; Gross R A; McCarthy S P, J. Appl. Polym. Sci., 66, No.8, 21st Nov.1997, p.150713.]

395

Figure 11.37.8. Tensile strength of polylactide unplasticized and plasticized with 10 wt% of oligomeric lactic acid vs. exposure time to seawater. [Data from Sinclair R G, J. Macromol. Sci. A, A33, No.5, 1996, p.585-97.]

increases and remains almost constant. This is due to the fact that brittle behavior is replaced by ductile behavior when more plasticizer is present.1 Comparison of Figures 11.37.5 and 11.37.6 with Figure 11.37.3 shows that each plasticizer has different behavior. Polylactide can be plasticized with its own monomer (Figure 11.37.5), but the results are not very good because polymer loses tensile strength rapidly. This is improved by the use of lactic acid oligomer (Figure 11.37.6), but tensile strength change is still substantially more rapid than with polypropylene glycol (Figure 11.37.3). This shows that the selection of type and concentration of plasticizer is essential for building properties of products designed with polylactide. It should be added that lactide migrates to the surface and changes its properties. It may also cause premature degradation of polylactide.5 Figure 11.37.7 shows that the plasticizer structure and the amount determine the biodegradation rate of plasticized polylactide. Figure 11.37.8 shows that plasticizer increases the degradation rate on exposure to seawater. This is important for products in packaging applications intended to reduce the threat to marine life.10 It is estimated that about 100,000 marine animals and about 1-2 million sea birds are killed yearly by toxic residues of plastic litter. PLA crystallized in the presence of triphenyl phosphate at a broad range of conditions, always producing α-form crystals with and without plasticizer.21 Crystallization temperature varied in the range of 113 to 128oC.21 The hydrolysis rate of PLA can be tuned using a plasticizer by regulating water uptake of plasticized material using plasticizer architecture and hydrophilicity.22

396

Plasticizers Use and Selection for Specific Polymers

PLA plasticized with commercial polyadipates had lower Tg and did not show any physical changes on long storage.26 The addition of poly(ε-caprolactone) as a plasticizer increased the hydrolysis rate of polylactide.30 Attenuated total reflectance-mid infrared spectroscopy coupled with independent components analysis is a fast method to determine plasticizers in polylactide.31 The addition of 14% grafted acryl-poly(ethylene glycol), acryl-PEG, to polylactide induced an increment in the apparent activation energy and temperature of the β-relaxation due to the different nature of the acryl-pendant group in plasticized PLA.35 The crystallization rate of plasticized PLA was much faster compared to that of neat PLA, which hindered movements of the acryl-pendant group, thus requiring more energy to orient the dipoles.35 The plasticizing effect of acryl-PEG effectively aided the large-scale motions associated with glass transition that are the origin of α-relaxation.35 The plasticizer increases the capacity of the amorphous zone to reorganize and increase this relaxation.35 Plasticization of amorphous polylactide with acetyl tributyl citrate shifts glass transition and extends its temperature range of crystallization to lower temperatures.36 Plasticizer accumulates in the amorphous phase because it is excluded from the growing crystal.36 The formation of the rigid amorphous fraction is favored by the low crystallization temperature. It reaches values up to 50% in plasticized polylactide.36 Positron annihilation lifetime spectroscopy was used to determine free volume in neat and plasticized polylactide (Figure 11.37.9) as a function of temperature.36 In the glassy state, free volume was nearly constant and increased from 1.6 for neat PLA to 1.8% for PLA containing 10 wt% plasticizer.36 An increase in free volume was characterFigure 11.37.9. Free volume as a function of temperature in initially amorphous neat and plasticized PLA istic of the glass transition, which was assessed from positron annihilation lifetime spectroslikely caused by an increase in the intercopy data. Solid lines indicate the slopes of the free volchain space as the segments easily moved ume vs. temperature variations in the glass, the glass transition, and the cold crystallization temperature away from each other in the liquid.36 When domains. These domains are delimited by dashed lines cold crystallization begins, another increase for clarity. [Adapted, by permission, from Varol N, Delpouve N, Araujo S, Domenek S, Guinault A, Golovchak of free volume is recorded, being signifiR, Ingram A, Delbreilh L, Dargent E, Polymer, 194, cantly steeper than during the glass transi122373, 2020.] tion.36 Two isomeric molecules, 1,2-cyclohexanediol and isohexide (isosorbide and isomannide) demonstrated potential as rigid building blocks in PLA plasticizer design with tunable material performances.37 Based on the calculated Hansen solubility parameters, all the synthesized plasticizer candidates were expected to be miscible with PLA, which was experimentally proven by a significant decrease of glass transition temperature and an increase in strain at break.37 For instance, PLA plasticized with 20 wt% cyclohexanediol levulinate (cis- and trans- mixture) had the lowest Tg of 25°C and the highest strain at

11.37 Polylactide

397

break of 265%, which equaled to 44 times of the initial strain at break of neat PLA.37 Isohexide-based plasticizers with larger rigid cores, isosorbide levulinate, and isomannide levulinate enabled superior thermal stability, higher Young’s modulus and stress at the break in PLA blends compared with cyclohexanediol-based plasticizers, while retaining high strain at break.37 Stronger influence of stereo-isomerism on plasticization was also observed in PLA blends with isohexide-based plasticizers compared with cyclohexanediol-based plasticizers.37 Poly(ethylene glycol) was used to plasticize PLLA and systematically study the effect of its molecular weight and content of PEG on the thermal and mechanical properties of PLLA/PEG blends.38 The competition between phase separation and crystallization determined the final structures and physical properties of the blends.38 Low MW PEG, e.g., Mn ≤ 2 kg/mol, was miscible with PLLA while high MW PEG e.g., Mn ≥ 8 kg/mol, could entangle with PLLA to suppress phase separation and crystallization of PEG.38 When an intermediate MW PEG, e.g., 5 kg/mol, was used, phase separation and crystallization of PEG occurred simultaneously, resulting in poor plasticization.38

References 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33

McCarthy S; Song X, Antec 2001.Conference proceedings, Dallas, Texas, 6th-10th May, 2001, paper 363. US Patent 6,117,928. Jacobsen S; Fritz H G, Polym. Eng. Sci., 39, No.7, July 1999, p.1303-10. Jacobsen S; Degee Ph; Fritz H G; Dubois Ph; Jerome R, Polym. Eng. Sci., 39, No.7, July 1999, p.1311-9. US Patent 5,908,918. US Patent 5,756,651. US Patent 5,763,513. US Patent 5,726,220. Labrecque L V; Kumar R A; Dave V; Gross R A; McCarthy S P, J. Appl. Polym. Sci., 66, No.8, 21st Nov.1997, p.1507-13. Sinclair R G, J. Macromol. Sci. A, A33, No.5, 1996, p.585-97. US Patent 6,472,210. US Patent 6,458,064. US Patent 6,353,086. US Patent 6,312,823. US Patent 6,291,597. US Patent 6,183,814. US Patent 6,143,863. US Patent 5,998,552. US Patent 5,939,467. Paul M-A; Alexandre M; Degee P; Pluta M; Gleski A; Dubois P, New Nanocomposite Materials Based on Plasticized Poly(l-lactide) and Organo-modified Montmorillonites, Belgian Polymer Group Meeting 2002, Mons, Belgium. Xioa H W, Li P, Ren X, Jiang T, Yeh J-T, J, Appl. Polym. Sci., 118, 3558-69, 2010. Andersson S R, Hakkarainen M, Albertsson, A-C, Biomacromolecules 11, 3617-23, 2010. Park K, Ha J U, Xanthos M, Polym. Eng. Sci., 50, 1105-10, 2010. Wang R, Wan C, Wang S, Zhang Y, Polym. Eng. Sci., 49, 2414-20, 2009. Martino V P, Jimenez A, Ruseckaite R A, J. Appl. Polym. Sci., 112, 2010-18, 2009. Martino V P, Rusenckaite R A, Jimenez A, Polym. Int., 58, 437-44, 2009. Ljungberg N, Colombini D, Wesslen B, J. Appl. Polym. Sci., 96, 992-1002, 2005. Hassouna F, Raquez J-M, Addiego F, Toniazzo V, Dubois P, Ruch D, Eur Polym. J., 48, 404-15, 2012. Piotrkowska E, Kulinski Z, Galeski A, Masirek R, Polymer, 47, 7178-88, 2006. Olewnik-Kruszkowska, E; Kasperska, P; Koter, I, Reactive Functional Polym., 103, 99-107, 2016. Kassoul, A; Ruellan, A; Bouveresse, D J-R; Rutledge, D N; Domenek, S; Mealoudy, J; Chebib, H; Ducruet, V, Talanta, 147, 569-80, 2016. Santos, E F; Oliveira, R V B; Reiznautt, Q B; Samios, D; Nachtigall, S M B, Polym. Testing, 39, 23-9, 2014. Monnier, X; Delpouve, N; Basson, N; Guinault, A; Domenek, S; Saiter, A; Mallon, P E; Dargent, E, Polymer, 73, 68-78, 2015.

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34 35 36 37 38

Plasticizers Use and Selection for Specific Polymers

McEneany, RM J; Topolkaraev, V A; He, A, US8461262, Kimberly-Clark Worlwide, Inc., Jun. 112, 2013. Pascual-Jose B, Badia JD, Múgica A, Addiego F, Müller AJ, Ribes-Greus A, Polymer, 223, 123701, 2021. Varol N, Delpouve N, Araujo S, Domenek S, Guinault A, Golovchak R, Ingram A, Delbreilh L, Dargent E, Polymer, 194, 122373, 2020. Xuan W, Odelius K, Hakkarainen M, Eur. Polym. J., 157, 110649, 2021. Guo J, Liu X, Liu M, Han M, Liu Y, Ji S, Polymer, 223, 123720, 2021.

11.38 Polymethylmethacrylate

399

11.38 POLYMETHYLMETHACRYLATE 11.38.1 FREQUENTLY USED PLASTICIZERS • di-(2-ethylhexyl) phthalate in eraser9 • 2-hydroxyethyl methacrylate in bone cement2 • 4-cyanophenyl 4-heptylbenzoate in photorefractive materials1 • fatty acid amines11 • plasticizers used in PMMA ionomers are discussed in Section 11.17 Plasticizers are used in polymethylmethacrylate in very specific cases only. PMMA ionomers are the most likely users of ionic plasticizers. 11.38.2 PRACTICAL CONCENTRATIONS • 37 wt% of di-(2-ethylhexyl) phthalate9 • 10 and 20 wt% of 4-cyanophenyl 4-heptylbenzoate1 11.38.3 MAIN FUNCTIONS PERFORMED BY PLASTICIZERS • reduction of glass transition temperature1 • improvement of diffraction efficiency of photorefractive materials1 • increased rotational mobility1 • improvement of ability to absorb water by hydrophilic additive2 • improvement of impact resistance2 • improvement of crack growth inhibition2 • improvement of elongation2 • improvement of elastic modulus by DOP in nanocomposite • improvement of scratch resistance1 11.38.4 MECHANISM OF PLASTICIZER ACTION In bone connective prosthesis, it is important to modify polymethylmethacrylate to improve elongation, adhesion to the bone, inhibition of crack growth in connecting cement, and impact resistance. All these requirements can be addressed by plasticization, which usually improves all these parameters. Considering the type of application, it is also essential that plasticization has permanent nature because of difficulties in replacement and potential hazards from migrating chemicals. The method selected was to add a hydrophilic monomer, which cannot migrate because it is attached to the copolymer backbone, but its presence can help in the absorption and retention of a certain amount of moisture. Water is a known plasticizer of many polymers, including polymethylmethacrylate. A constant presence of water modifies the polymer to requirements.2 11.38.5 TYPICAL FORMULATIONS Rubber eraser9 Polymethylmethacrylate Di-(2-ethylhexyl) phthalate Calcium carbonate

25 wt% 37 38

400

Plasticizers Use and Selection for Specific Polymers

Transdermal delivery system for anti-hypersensitive drug patch12 PMMA 90 mg Ethyl cellulose 10 mg Drug (Losartan) 20 mg PEG-400 (plasticizer) 20 vol% DMSO (penetration enhancer) 10 vol% Chloroform (solvent) 10 ml

REFERENCES 1 2 3 4 5 6 7 8 9 10 11 12

Van Steenwinckel D; Hendrickx E; Samyn C; Engels C; Persoons A, J. Mater. Chem., 10, No.12, Dec.2000, p.2692-7. US Patent 6,136,038 Guohua Chen; Kangde Yao; Jingtai Zhao, J. Appl. Polym. Sci., 73, No.3, 18th July 1999, p.425-30. Joon-Seop Kim; Eisenberg A, Polym. J. (Japan), 31, No.3, 1999, p.303-5. Mikheev Y A; Guseva L N; Zaikov G E, Polym. Sci. Ser. A, 41, No.2, Feb.1999, p.236-45. Mills A; Lepre A; Wild L, Analytica Chimica Acta, 362, Nos 2-3, 1998, p.193-202. Mikheev Y A; Guseva L A; Zaikov G E, J. Appl. Polym. Sci., 67, No.10, 7th March 1998, p.1693-700. Ma X; Sauer J A; Hara M, Polymer, 38, No.17, 1997, p.4425-31. US Patent 5,521,239. Torres, J H, Stafford, C M, Vogt, B D, ACSNano, 4, 9, 5357-65, 2010. Mansha, M, Gauthier, C, Ferard, P, Schirrer, R, Wear, 271, 671-79, 2011. Pisipati, A; Satya, S C V, J. Pharm. Res., 6, 5, 551-4, 2013.

11.39 Polypropylene

401

11.39 POLYPROPYLENE 11.39.1 FREQUENTLY USED PLASTICIZERS Atactic (amorphous) polypropylene is a popular plasticizer in many applications, such as modified bitumen roofing, paper lamination, adhesives and sealants, asphalt pavement modification, wire and cable, carpet tiles, films, and automotive. In some applications, plasticizers are used in polypropylene processing: • polybutenes in flexible film applications, such as shelf-liners, tablecloth, shower curtains, and wallpapers1 • dioctyl sebacate4 • paraffinic oil4 • non-functional hydrocarbon11,12 • isooctyl tallate4 • plasticizing oil (Drakeol 34)5 • paraffinic, naphthenic, and aromatic processing oils in automotive weatherseals6 • glycerin in ceramic and metal powder injection molding7 • polyol as a compatibilizer of mixtures of several polymers8 • mineral oil and/or polybutene in hotmelt adhesive based on low melting point polypropylene13 11.39.2 PRACTICAL CONCENTRATIONS • 5-10 wt% of polybutene (5 wt% polybutene reduces modulus by 40%)1 • 15-40 wt% mineral oil and/or polybutene in hot melt adhesive13 • 3.7-23.7 wt% of dioctyl sebacate4 • 4.5-36 phr of isooctyl tallate4 • 4.5-72 phr of paraffinic oil4 • 1.3-1.6 wt% of glycerin7 11.39.3 MAIN FUNCTIONS PERFORMED BY PLASTICIZERS • improvement of film flexibility1 • reduction of secant modulus1 • improvement of clarity and gloss1 • increase in tear strength1 • improvement of Izod impact strength4 • depression of glass transition temperature4 • facilitation of molding7 • compatibilization of polymers8 11.39.4 EFFECT OF PLASTICIZERS ON POLYMER AND OTHER ADDITIVES Figure 11.39.1 shows that the glass transition depression is a linear function of plasticizer concentration. Two ester plasticizers depress the glass transition temperature more extensively than paraffinic oil.6 Dioctyl sebacate decreased flexural modulus more rapidly at smaller concentrations of plasticizer (up to 10 wt%), then the flexural modulus leveled off. In the case of paraffinic oil and isooctyl tallate, flexural modulus decreased linearly with plasticizer concentration increasing (Figure 11.39.2).6

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Plasticizers Use and Selection for Specific Polymers

Figure 11.39.1. Glass transition temperature of polypropylene plasticized with variable quantities of different plasticizers. A − dioctyl sebacate, B − isooctyl tallate, C − paraffinic oil. [Data from Ellul M D, Rubber Chem. Technol., 71, No.2, May/June 1998, p.24476.]

Figure 11.39.2. Flexural modulus of polypropylene plasticized with variable quantities of different plasticizers. A − dioctyl sebacate, B − isooctyl tallate, C − paraffinic oil. [Data from Ellul M D, Rubber Chem. Technol., 71, No.2, May/June 1998, p.244-76.]

References 1 2 3 4 5 6 7 8 9 10 11 12 13

Kalkar A K; Parkhi P S, J. Appl. Polym. Sci., 57, No.2, 11th July 1995, p.233-43. Caspar J V; Khudyakov I V; Turro N J; Weed G C, Macromolecules, 28, No.2, 16th Jan.1995, p.636-41. Gardner J H, Polybutenes. A Versatile Modifier for Plastics, Addcon World '99. Conf. proc., RAPRA Technol. Ltd., Prague, 27th-19th Oct.1999, paper 8, pp.4. Margolin A L; Shlyapintokh V Ya, Polym. Deg. Stab., 66, No.2, 1999, p.279-84. Uzomah T C; Ugbolue S C O, J. Mater. Sci., 34, No.16, 15th Aug.1999, p.4057-64. Ellul M D, Rubber Chem. Technol., 71, No.2, May/June 1998, p.244-76. Tollefson N M; Roy S; Shepard T A; Long W J, Polym. Eng. Sci., 36, No.1, Mid-Jan.1996, p.117-25. US Patent 6,368,700. US Patent 6,008,281. US Patent 5,696,186. Yang H W-H, Lundmark B R, Lin C-Y, Cheng C Y, Chapman B R, Eiselt P, Ourieva G, Nair-Varma M, Coffy J N, Schregenberger S D, Lohse D J, Yang N, Zudock J T, Wittenbrink R J, US Patent 7,619,026, ExxonMobil, Nov 17, 2009. Lundmark B R, Chapman B R, Schregenberger S D, Lohse D J, US Patent 7,619,027 B2, ExxonMobil, Nov. 17, 2009. Hamann, R; Rachow, L, US20140350155, Bostik, Inc., Nov. 27, 2014.

11.40 Poly(propylene carbonate)

403

11.40 POLY(PROPYLENE CARBONATE) 11.40.1 FREQUENTLY USED PLASTICIZERS • poly(diethylene glycol adipate) in biodegradable compound2 11.40.2 PRACTICAL CONCENTRATIONS • 5-20 wt%2 11.40.3 MAIN FUNCTIONS PERFORMED BY PLASTICIZERS • eco-friendly product2 • biodegradability2 • viscosity decrease2 • glass transition decrease2 • improved elongation2 11.40.4 EFFECT OF PLASTICIZERS ON POLYMER AND OTHER ADDITIVES This biodegradable plastic can be reinforced and toughened using low molecular weight polyurethanes. Hydrogen-bonding interaction is responsible for the mechanism of reinforcement and can be used to regulate process.1 The cyclic propylene carbonate acts as a plasticizer in the final polymer and, therefore, significantly decreases its Tg.3 The cyclic propylene carbonate is a side product of the synthesis of poly(propylene carbonate).3 The stiffness of the poly(propylene carbonate) increased by 75% when plasticizing side products were removed by the solid-liquid extraction.3 References 1 2 3

Chen L, Quin L, Wang X, Zhao X, Wan F, Polymer, 52, 4873-80, 2011. Hao, Y; Yang, H; Zhang, H; Zhang, G; Bai, Y; Gao, G; Deng, L, Polym. Deg. Stab., 128, 286-93, 2016. Barreto, C; Hansen, E; Fredriksen, S, Polym. Deg. Stab., 97, 6, 893-904, 2012.

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Plasticizers Use and Selection for Specific Polymers

11.41 POLY(N-VINYLCARBAZOLE) Poly(N-vinylcarbazole), PVK, is a glassy polymer, which easily fails by cracking fracture. Plasticizers are needed to improve mechanical properties, reduce viscosity, and lower processing temperature.1 PVK is employed in photorefractive systems, and as such, it must possess photoconductivity and electro-optic effects. These are related to crystallization and glass transition temperature.2 Numerous photoconductive plasticizers are used to lower glass transition temperature to below 20oC and act as hole transportable plasticizers.2 These include N-methylcarbazole, N-ethylcarbazole, N-butylcarbazole, N-hexylcarbazole, N-phenylcarbazole, 1,3biscarbazolylpropane, o-nitroanisole, m-nitroanisole, p-nitroanisole, and triphenylamine.2,4 Individual plasticizers may be used, but a frequently good balance of properties is achieved by using plasticizers’ mixtures.2 A combination of 1,3-biscarbazolylpropane and N-ethylcarbazole gave required low glass transition temperature (-6.3oC) and high stability.2 Plasticizers are added in concentrations needed to achieve the required properties. Practical concentrations are in the range of 6 to 50 wt%, most frequently about 30%.2,4 Tri(6-acryloyloxyhexyl)1,3,5-benzenetricarboxylate is crosslinkable plasticizer for processing poly(N-vinylcarbazole) in electronics applications.5

References 1 2 3 4 5

Pearson J M; Stolka M, Poly(n-vinylcarbazole). Gordon and Breach, New York, 1981. Nagayama N; Yoyoyama M, Molecular Crystals Liquid Crystals, 327, 1999, p.19-22. Diaz-Garcia M A; Wright D; Casperson J D; Smith B; Glazer E; Moerner W E; Sukhomlinova L I; Twieg R J, Chem. Mater., 11, No.7, July 1999, p.1784-91. US Patent 5,744,267. Molaire, M F, WO2015095859, Molaire Consulting LLC, Jun. 25, 2015.

11.42 Poly(N-vinylpyrrolidone)

405

11.42 POLY(N-VINYLPYRROLIDONE) 11.42.1 FREQUENTLY USED PLASTICIZERS • glycerin1,2,4 • polyethylene glycol having a molecular weight in the range from 200 to 600 daltons1 in solid dispersions of drugs6 • dioctyl adipate3 • triethyl citrate, acetyl triethyl citrate, or tributyl citrate4 • dipropylene glycol dibenzoate5 • ionic liquid7,8 11.42.2 PRACTICAL CONCENTRATIONS • glycerin in biomedical electrodes from 50 to 75 wt% and 5 to 35 wt% in pressuresensitive adhesive4 • 15 wt% of dioctyl adipate in thermoplastic composition compatibilized by poly(N-vinyl pyrrolidone), PVP3 • from 2 to 10 wt% of dipropylene glycol dibenzoate in photosensitive polymer composition for flexographic printing plates5 11.42.3 MAIN FUNCTIONS PERFORMED BY PLASTICIZERS • improvement of processing characteristics2 • reduction of swelling in hot oil3 • improvement of flexibility3 11.42.4 MECHANISM OF PLASTICIZER ACTION The glass transition temperature, Tg, relates directly to cohesive polymer energy and its packing density. Tg depression can be used to predict the influence of plasticizer on the Tg of a system.1 Fox equation was used for estimation of the effect of water and plasticizer, as follows: w PVP w H2 O w p 1 ----- + ------------- + ------= -----------Tg Tg Tg Tg PVP

H2 O

[11.42.1]

p

where: Tg Tgi wi

glass transition temperature of system glass transition temperatures of mixture components (poly(N-vinyl pyrrolidone), water, and plasticizer, respectively) weight fractions of mixture components (poly(N-vinyl pyrrolidone), water, and plasticizer, respectively)

Equation 11.42.1 adequately describes the influence of plasticizers, which have one hydroxyl group per molecule. When more hydroxyl groups are present in plasticizer (e.g., glycerin or polyethylene glycol, PEG), a negative deviation results, which may be corrected by adjusting parameter, which is a weight fraction of plasticizer that interacts by two or more hydroxyl groups with polymer.1 Figure 11.42.1 shows that plasticizers substantially decrease Tg. At the same time, experimental values are below the values predicted by equation 11.42.1, which means that more than one hydroxyl group in the plasticizer interacts with polymer to form hydrogen bonds.1

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Plasticizers Use and Selection for Specific Polymers

Figure 11.42.1. Glass transition temperature of poly(N- vinyl pyrrolidone) plasticized with different amounts of PEG having molecular weight of 400 daltons and glycerin. [Data from Feldstein M M; Shandryuk G A; Plate N A, Polymer, 42, No.3, 2001, p. 971-9.]

Figure 11.42.2. Density of hydrogen bond network formed between poly(N-vinyl pyrrolidone) plasticized with different amounts of PEG having molecular weight of 400 daltons. [Data from Feldstein M M; Shandryuk G A; Plate N A, Polymer, 42, No.3, 2001, p. 971-9.]

Figure 11.42.2 shows that the hydrogen bond network density passes through a maximum when [PEG]/[PVP] is around 0.15 or [OH]/[PVP] = 0.3.1 Further increase in plasticizer concentration causes network swelling, which results in a decrease in network density. At the same time, hydrogen bonds remain unaffected even at large excess of plasticizer.

11.42.5 TYPICAL FORMULATIONS Thermoplastic composition compatibilized by PVC and plasticizer:3 Poly(vinylidene fluoride) 40 parts Nitrile rubber 60 Poly(N-vinyl pyrrolidone) 3.2 Dioctyl adipate 15 Phenolic curative 4.8 References 1 2 3 4 5 6 7 8

Feldstein M M; Shandryuk G A; Plate N A, Polymer, 42, No.3, 2001, p.971-9. US Patent 5,520,180. US Patent 6,066,697. US Patent 5,700,478. US Patent 5,698,371. Papadimitriou, S A; Barmpalexis, P; Karavas, E; Bikiaris, D N, Eur. J. Pharm. Biopharm., 82, 1, 175-86, 2012. Saroj, A L; Singh, R K; Chandra, S, Mater. Sci. Eng.: B, 178, 4, 231-8, 2013. Bahadur, I; Momin, M I K; Koorbanally, N A; Sattari, M; Ebenso, E; Katata-Seru, L M; Singh, S; Ramjugernath, D, J. Mol. Liquids, 213, 13-6, 2016.

11.43 Poly(phenylene ether)

407

11.43 POLY(PHENYLENE ETHER) 11.43.1 FREQUENTLY USED PLASTICIZERS • diphenyl phthalate, triphenyl trimellitate, or pentaerythritol tetrabenzoate in flame retarded composition containing boron compound1,4 • triphenyl phosphates and diphenyl phthalates in blends with polycarbonate and in a secondary battery container5 • triphenyl and other aromatic phosphates in flame retarded compositions3,9 • polyethylene glycol, polyamide oligomers, ethylene-bis-stearamide, and polyethylene oligomers in blends with polystyrene6,7 • triphenyl phosphate or phthalic acid ester in thermoplastic resin composition10 • polybutene in formulations with improved environmental stress cracking resistance11 • triaryl phosphate in the flexible, wrinkle-resistant cable jacketing12 11.43.2 PRACTICAL CONCENTRATIONS • phosphates: 15-35 wt% in blends with PC,8 40 phr in flame retarded compositions,9 15 wt% in flame retarded composition containing boron compound,4 11 to 17 wt% in flamed retarded blends with polystyrene,5 and 65 to 100 phr in flame retarded composition9 • phthalates: 15-35 wt%2 The above examples show that it is still unclear what is the minimum concentration of phosphate plasticizer required to obtain flame-retarded composition. 11.43.3 MAIN FUNCTIONS PERFORMED BY PLASTICIZERS • to impart flame retarding properties1,3,4,9 • to increase flexural modulus of blend with PC2 • to increase the flexibility of molded part3 • to improve environmental stress cracking resistance11 References 1 2 3 4 5 6 7 8 9 10 11 12

US Patent 5,648,415. Nanasawa A; Takayama S; Takeda K, J. Appl. Polym. Sci., 66, No.1, 3rd Oct.1997, p.19-28. US Patent 5,594,054. US Patent 5,466,733. US Patent 6,040,084. US Patent 6,031,049. US Patent 5,952,431. US Patent 5,717,014. US Patent 5,594,054. US Patent 5,539,050. Indopol Polybutenes, BP. Shan, W, WO2014075291, Sabic Innovative Plastics, May 22, 2014.

408

Plasticizers Use and Selection for Specific Polymers

11.44 POLY(PHENYLENE SULFIDE) The microporous membrane was made from poly(phenylene sulfide) containing plasticizer.1 The membrane was produced from a mixture of components, which were extruded or cast to form a membrane, followed by controlled cooling (quenching) or coagulation. The membrane was then passed through a section where plasticizer (and optionally second polymer) were leached out of the system into a solvent, which did not affect poly(phenylene sulfide). Before, during, or after the leaching operation, the membrane was stretched. There is a criterion set for plasticizer, which should be capable of dissolving at least 10 wt% of poly(phenylene sulfide) at extrusion or casting temperatures. Some plasticizers are capable of dissolving even more than 50% poly(phenylene sulfide). These include diphenyl methyl phosphate, triphenyl phosphate, diphenyl phthalate, tetraethylene glycol dimethyl ester, hydrogenated terphenyl, etc. Diphenyl phthalate and hydrogenated terphenyl were selected for manufacturing samples of membranes according to the invention.1 Concentrations of plasticizers were in the range of 40 to 47 wt%, and methylene chloride was the leaching solvent. Concentration and type of plasticizer and conditions of stretching and leaching determined the pore sizes and density of pores.1 γ-Isocyanatepropyltriethoxysilane was used as a plasticizer compatible with poly(phenylene sulfide) in the production of films used in an acoustic instrument vibrating plate and in speakers.2

References 1 2

US Patent 5,888,434. Machida, T; Imanishi, Y; Okhura, M; Higashioji, T, US8742061, Toray Industries, Inc., Jun. 3, 2014.

11.45 Polystyrene

409

11.45 POLYSTYRENE 11.45.1 FREQUENTLY USED PLASTICIZERS • polybutenes1 • liquid paraffin and zinc stearate as internal plasticizers added during styrene polymerization1 • dimethyl, diethyl, dipropyl, dibutyl, diheptyl, dioctyl, and diisodecyl phthalates in optical sensing films4 and in decoy flare compositions11 • di- and tri-isopropylbiphenyls6,15 • dioctyl phthalate7,9,17 • benzyl butyl phthalate11 • tricresyl phosphate in plastisols7 • dioctyl sebacate9 • mineral oil10 • paraffinic mineral oil16 • Fischer-Tropsch derived white oil18 • polyisoalkylene19 • adipates and glutarates in expanded polystyrene13 • polyol as compatibilizer14 • D-limonene in expanded PS20 • triglyceride oil in blends with polylactide21 11.45.2 PRACTICAL CONCENTRATIONS • liquid paraffin − up to 7 wt% and zinc stearate − 0.1 wt% (addition during polymerization)1 • dimethyl phthalate − 7 wt% in decoy flare composition11 • dibutyl phthalate − 25 to 100 phr in sensing film4 • dioctyl phthalate − 5 to 25 wt% or 3 wt%17 • dioctyl sebacate − 5 to 25 wt%9 • tricresyl phosphate − 18 wt% in plastisol8 • mineral oil − up to 10 wt% and 5 to 10 wt% in oriented polystyrene compositions16 11.45.3 MAIN FUNCTIONS PERFORMED BY PLASTICIZERS • improvement of processability1 • improvement of impact resistance1 • improvement of heat resistance (polybutenes)1 • improvement of environmental stress cracking (polybutenes)1 • increase in sensitivity of optical sensing films (phthalates)4 • formation of chlorine-free plastisols8 • antiplasticization10 • lowering melting point11 • compatibilization of different polymers14 • improvement of product clarity (small amounts)16 • improvement of impact strength16 • enlargement of orientation and thermoforming window16

410

Plasticizers Use and Selection for Specific Polymers

• •

addition of D-limonene permits reduction of pentane20 addition of triglyceride oil increases biodegradability of PS/PLA blend21

References 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21

Gardner J H, Polybutenes. A Versatile Modifier for Plastics, Addcon World '99. Conf. proc., RAPRA Technol. Ltd., Prague, 27th-19th Oct.1999, paper 8, pp.4. Orler E B; Gummaraju R V; Calhoun B H; Moore R B, Macromolecules, 32, No.4, 23rd Feb.1999, p.1180-8. Rodriguez F; Wannamaker E J; Birch D D, Polym. Mater. Sci. Eng., 78, 1998, p.34-5. Mills A; Lepre A; Wild L, Analytica Chimica Acta, 362, Nos 2-3, 1998, p.193-202. Ma X; Sauer J A; Hara M, J. Polym. Sci.: Polym. Phys. Ed., 35, No.8, June 1997, p.1291-4. US Patent 5,489,646. Nicolai T; Brown W, Macromolecules, 29, No.5, 26th Feb.1996, p.1698-704. US Patent 5,418,279. Schausberger A; Ahrer I V, Macromol. Chem. Phys., 196, No.7, July 1995, p.2161-72. Anderson S L; Grulke E A; DeLassus P T; Smith P B; Kocher C W; Landes B G, Macromolecules, 28, No.8, 10th April 1995, p.2944-54. US Patent 6,432,231. US Patent 6,403,707. US Patent 6,403,661. US Patent 5,696,186. US Patent 5,696,184. US Patent 5,565,163. Etchenique R; Weisz A D, J. Appl. Phys., 86, 4, 1999, p.1994. Null V K, US Patent Application Publication US2009/0171009, Shell Oil Company, Jul. 2, 2009. Harris T G, Tippet J, US Patent Application Publication US2009/0281235 A1, Fina Technology Inc., Nov 12, 2009. Gibeault, J-P, US8772362, Nexkemia Petrochinie Inc., Jul. 8, 2014. Wang, W; Knoeppel, D W; Li, F; Sosa, J M, US20150218358, Fina Technology, Inc., Aug. 6, 2015.

11.46 Polysulfide

411

11.46 POLYSULFIDE 11.46.1 FREQUENTLY USED PLASTICIZERS • isooctyl benzyl phthalate (Santicizer 261) in caulks, sealants,1,2 and bridge joint construction6 • benzyl butyl phthalate in the recycling of hardened adhesives and sealants3 • C4 to C8 terephthalate8 • chlorinated paraffins in sealants2,7 • alkyl sulfonic acid esters of phenol and/or cresol in the recycling of hardened adhesives and sealants3 • hydrogenated perphenyl (HB-40) in corrosion-inhibiting sealants4,7 • 2,2,4-trimethyl-1,3-pentanediol and 1-isobutyrate benzyl phthalate (Texanol benzyl phthalate or Santicizer 278) in fuel resistant cables5 • halogen-terminated sulfur-containing polymer11 11.46.2 PRACTICAL CONCENTRATIONS • isooctyl benzyl phthalate − 15-30 wt%,2 5-45 wt%6 • chlorinated paraffins − 15-30 wt%2 • benzyl butyl phthalate − 40-60 wt% (solution recycling of sealants)3 • texanol benzyl phthalate − 23.5 wt%5 11.46.3 MAIN FUNCTIONS PERFORMED BY PLASTICIZERS • viscosity control1 • increased filler loading1 • improved mixing of two-component sealants4 • carrier liquid for depolymerization reaction3 • carrier liquid for curative4 • masterbatch liquid improving dispersion of minor components5,7 • increased modulus of sealant4 • sealant composition8 • VersaBond plasticizer for polysulfide glazing sealant applications was introduced by Eastman Chemical as a replacement for phthalate plasticizers10 References 1 Santicizer 261. Plasticizer Product Profile, Ferro, 1999.

2 3 4 5 6 7 8

9 10 11

US Patent 6,383,324. US Patent 6,117,971. US Patent 6,027,767. US Patent 5,795,652. US Patent 5,664,906. US Patent 5,663,219. Kettner M R, Stimpson M J, Holt M S, Whitson R L, Pont J D, US Patent Publication, US 2008/0057317 A1, Eastman Chemical Company, Mar 6., 2008. US Patent 6,420,514. Addit. Polym., 2014, 11, 3-4, 2014. Hamada, Y; Suga, Y; Echigoya, K; Matsumoto, K; Oba, T, CA2843367, Toray Fine Chemicals, Jan. 19, 2016.

412

Plasticizers Use and Selection for Specific Polymers

11.47 POLYSULFONE In the production of transparent articles from polysulfone, a plasticizer was added to specially purified polysulfone to remove certain reaction impurities.1 Plasticizer was added to improve film flexibility. Plasticizers having high compatibility with polysulfone include diethyl phthalate, benzyl butyl phthalate, tricresyl phosphate, and methyl phthalyl ethyl glycolate. Up to 30 wt% of plasticizer can be used, but usually, 10 wt% of plasticizer is added.1 Compressed CO2 and N2O plasticize polysulfone. N2O is more polar than CO2, and is slightly more effective in the plasticization of polysulfone.2 Polyvinylalcohol has plasticizing effect in polysulfone membranes.3 Highly permeable composite membranes of polysulfone/1-ethyl-3-methylimidazolium tetrafluoroborate ionic liquid were fabricated and tested for CO2/CH4 separation.4 Adding ionic liquid led to the high porosity of membranes due to its plasticizing effects.4 The addition of plasticizer reduced viscosity and formed more porous and irregular structures.4 The size and distribution of pores depended on the type and concentration of incorporated ionic liquid into the polysulfone matrix.4 The pure polysulfone membrane is transparent, while the membranes containing ionic liquids show different degrees of opaqueness.4

References 1 2 3 4

US Patent 5,611,985. Kishimoto Y; Ishii R, Polym. Bull., 43, Nos.2-3, Sept./Oct.1999, p.255-60. Filimon, A; Albu, R M; Stoica, I; Avram, E, Composites Part B: Eng, 93, 1-11, 2016. Farrokhara M, Dorosti F, Chinese J. Chem. Eng., 28, 9, 2301-11, 2020.

11.48 Polyurethanes

413

11.48 POLYURETHANES 11.48.1 FREQUENTLY USED PLASTICIZERS • bis(2,2-dinitropropyl)-acetal/formal1 • dioctyl adipate2 • dipropylene glycol dibenzoate3 • glycerol triacetate1 • N-butyl-N-(2-nitroxyethyl)nitramine1 • polyamine4 • tributyl citrate5 11.48.2 PRACTICAL CONCENTRATIONS • 10-20 wt% PEI in self-healing compositions4 • 20-30 wt% in icephobic surfaces6 • 20-30 wt% in adhesive system3 • 100% energetic plasticizers1 11.48.3 MAIN FUNCTIONS PERFORMED BY PLASTICIZERS • faster recovery2 • self-healing4 • making material soft, flexible, elastic, and pliable3 11.48.4 MECHANISM OF PLASTICIZERS ACTION Influence mechanisms of energetic and inert plasticizers on the decomposition of hydroxyl-terminated polyether-based PU are different.1 NO· free radical generated by pyrolysis of N-butyl-N-(2-nitroxyethyl)nitramine and bis(2,2-dinitropropyl)-acetal/formal is the major incentive of chain scission, resulting in depolymerization of hydroxyl-terminated polyether based PU, and chain scission temperatures are shifted forward with increasing concentration of NO· as the N-butyl-N-(2-nitroxyethyl)nitramine-PU is more vulnerable.1 Carbanion and electrophilic intermediate, resembling CO2 generated by the decarboxylation reaction of carboxylic acid, are the major reactive products in glycerol triacetate.1 Microdefects caused by migration of glycerol triacetate accelerate the degradation of hydroxyl-terminated polyether-based PU under acidic conditions.1 11.48.5 EFFECT OF PLASTICIZERS ON POLYMERS AND OTHER ADDITIVES Self-healable waterborne polyurethane coatings were developed using carboxyl-type waterborne polyurethanes and polyamine, whose molecular structure containing primary amine and secondary amine formed ionic bonds and hydrogen bonds with carboxyl-type waterborne polyurethanes.4 PEI plays the role of both crosslinker and plasticizer, endowing the material with good self-repairing performance.4 PEI can absorb moisture from the air, acting as a plasticizer.4 When its amount exceeds a certain value, the plasticizing effect of PEI becomes greater than the crosslinking effect, which makes polymer molecular chains easier to slip and the motion ability enhances.4 Van der Waals forces between molecular chains are weakened, and the mobility of the molecular chains is enhanced.4 Therefore, the chains can move at lower temperatures, leading to the decrease of the glass transition temperature.4

414

Plasticizers Use and Selection for Specific Polymers

The tube actuator was fabricated from shape memory polyurethane and dibutyl adipate plasticizer, which produced softness and glass transition temperature switching close to human body temperature.2 With plasticizer addition, shape memory polyurethane had a quicker recovery rate during tube compression and expansion.2 The shape recovery ratio was increased by 83%, and its shape recovery ratio during tensile deformation was up to 99%.2 Figure 11.48.1 shows potential applications of tube actuators.2

Figure 11.48.1. Potential applications of gel tube actuators for (a) drug delivery and (b) artificial blood vessels. [Adapted, by permission, from Pringpromsuk S, Xia H, Ni Q-Q, Sensors Actuators A: Phys., 332, 2, 113164, 2021.]

Thermal decomposition behavior of hydroxyl-terminated polyether-based polyurethanes containing glycerol triacetate, bis(2,2-dinitropropyl)-acetal/formal, and N-butyl-N(2-nitroxyethyl)nitramine, respectively, as plasticizers, were investigated.1 Electrophilic O=C=O intermediate was the major reactive product of glycerol triacetate decarboxylation reaction.1 The modulus of polyurethane subjected to high pressure of CO2 decreased as the gas pressure was increased, indicating that polyurethane was plasticized by carbon dioxide.7 The plasticization effect became less dominant at pressures above 12 MPa.7 Infra-red spectroscopic measurements of the CO2-polyurethane system indicated that hydrogen bonding between polymer chains was disrupted by the imbibed gas.7 Surfaces having low ice adhesion are designed to include imparting hydrophobicity, lubrication, crosslink density reduction, or induction of interfacial slippage.6 For icephobic surfaces to find widespread use, it is imperative that they are durable.6 Suitable plasticizer was used to modify the crosslink density and stiffness of polyurethane elastomeric coating.6 The plasticizer used was a medium-chain triglyceride.6 The surface of the coat-

11.48 Polyurethanes

415

ing contained some fraction of oil, and the presence of plasticizer introduced interfacial slippage.6 The interfacial slippage helped in reducing the ice adhesion, and the change in crosslink density altered the bulk properties of the elastomer.6 A polyurethane elastomer composition of (a) organic diisocyanate, (b) polyester resin; (c) chain extender comprised of polyhydric alcohol, (d) crosslinker, (e) plasticizer, (f) surfactant, (g) blowing or foaming agent, and (h) optional dye was developed for a broad range of applications.5 Tributyl citrate was used as plasticizer.5 Aqueous dispersion adhesives, based on aqueous polyurethane or polyurethane-urea dispersions, were developed for bonding foam substrates by spray coagulation process.3 Biobased bis(cardanol) succinate, bis(ethoxy-cardanolyl) succinate, bis(cardanol) sebacate, bis(ethoxy-cardanolyl) sebacate were developed as plasticizers for polyurethane elastomers.8 A one-component solvent-free anti-sagging polyurethane waterproof coating has composition given in the next section.9

11.48.6 TYPICAL FORMULATIONS Anti-sagging polyurethane waterproof coating9 25-50 parts of a polyurethane prepolymer (prepolymer is made by reacting 19-72 parts of a composite resin diol, 1-10 parts of a polyether triol, 0-32 parts of a composite isocyanate, and 0.1-0.5 parts of an aliphatic amine chain extender), 10-20 parts of a heavy filler, 10-20 parts of a nano-filler, 0.05-0.2 parts of a composite catalyst, 0.1-0.3 parts of a physical defoamer, 0.1-0.3 parts of a chemical defoamer, 5-20 parts of a plasticizer (diisononyl phthalate, diisodecyl phthalate, chlorinated paraffin, a vegetable oil, dioctyl adipate, glycol benzoate, trioctyl phosphate, or phenyl alkylsulfonate), 0.1-0.3 parts of a dispersant, 0.05-0.2 parts of a dehydrating agent, and 2-5 parts of a reactive diluent (oxazolidine reactive diluent). References 1 2 3 4 5 6 7 8 9

Ou Y, Sun Y, Guo X, Jiao Q, J. Anal. Appl. Pyrolysis, 132, 94-101, 2018. Pringpromsuk S, Xia H, Ni Q-Q, Sensors Actuators A: Phys., 332, 2, 113164, 2021. EP3789448A1, Covestro Deutschland AG, Mar. 10, 2021. Lei Y, Wu B, Yuan A, Fu X, Jiang L, Lei J, Prog. Org. Coat., 106433, 2021. Robinson JJ, Sacripante GG, Vicol RL, Abu Ghalia M, Wang Y, Mullick S, US10934384B1, Evoco Ltd, Mar. 2, 2021. Sivakumar G, Jackson J, Ceylan H, Sundararajan S, Wear, 426-427A, 212-8, 2019. Briscoe BJ, Kelly CT, Polymer, 36, 16, 3099-3102, 1995. Jason James Robinson JJ, Vicol RL, Moebus JH, Calayan T, Sacripante GG, US11072694B1, Evoco Ltd, Jul. 27, 2021. Shen Y, Hermanns F-H, Wamprecht C, Reichert P, WO2021023750A1, Covestro Intellectual Property GmbH & Co. Kg, Feb. 11, 2021.

416

Plasticizers Use and Selection for Specific Polymers

11.49 POLYVINYLACETATE 11.49.1 FREQUENTLY USED PLASTICIZERS Polyvinylacetate in partially saponified form functions as a plasticizer,4 but, in other applications and structures, it is plasticized by the following plasticizers: • dibutyl phthalate1 • benzyl butyl phthalate in paper adhesive10 • dipropylene glycol dibenzoate (Benzoflex 9-88)6 in textile inks7 • castor oil in cosmetics3 • glycerin, ethylene, and propylene6 glycols and their derivatives, and polyols in biodegradable compositions5 • polar compounds having high solubility parameters (glycerin, triethanolamine, ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, etc.) in fragrance-containing products11 • propylene glycol and glycerin in edible food coatings8 • ethylene glycol in paper adhesive10 • triacetin, triethyl citrate, acetyl triethyl citrate, tributyl citrate, and epoxidized soybean oil in surface stabilization of sand and soil9 • diacetic tartaric acid12 • glycerol triacetate12 11.49.2 PRACTICAL CONCENTRATIONS • dibutyl phthalate − 5 to 25 wt%1 • benzyl butyl phthalate (5.53 wt%) in addition to ethylene glycol (1.86 wt%)10 • dipropylene glycol dibenzoate (1 wt%) in addition to polypropylene glycol (1.2 wt%)6 • polar plasticizer − 2 to 13 wt%11 • dipropylene glycol dibenzoate − 10 to 15 phr7 • propylene glycol − 3 to 5 wt%8 • triacetin, triethyl citrate, acetyl triethyl citrate, tributyl citrate, or epoxidized soybean oil − either at 5 wt% is suitable for sand/soil stabilization9 • triethyl citrate - 10 wt% improves the flexibility of the films and allows compaction of the pellets13 Typical of this polymer are small additions of plasticizers. Plasticizers, in most instances, must be compatible with water-based systems and environmentally friendly. 11.49.3 MAIN FUNCTIONS PERFORMED BY PLASTICIZERS • lowering glass transition temperature1,12 • increasing viscosity of water-based system1 • imparting flexibility3,4,7,12 • increasing water vapor permeability8 • increasing cohesion in particulate material9 11.49.4 EFFECT OF PLASTICIZERS ON POLYMER AND OTHER ADDITIVES Figure 11.49.1 shows a gradual decrease of the glass transition temperature of polyvinylacetate composition when the amount of plasticizer increases.1

11.49 Polyvinylacetate

Figure 11.49.1. Glass transition temperature of polyvinylacetate plasticized with dibutyl phthalate vs. plasticizer concentration. [Data from Averco-Antonovich I U; Gotlib D M; Chakirov R R; Sokolova Y A, Macromol. Symp., 176, Nov. 2001, p.181-7.]

417

Figure 11.49.2. Surface stress of water dispersion of polyvinylacetate in presence of variable amounts of dibutyl phthalate, DBP, and mixture of dioxane derivatives, DD. [Adapted, by permission, from AvercoAntonovich I U; Gotlib D M; Chakirov R R; Sokolova Y A, Macromol. Symp., 176, Nov. 2001, p.181-7.]

The effect of two plasticizers (DBP − dibutyl phthalate and DD − a mixture of dioxane derivatives) on surface stress was compared (Figure 11.49.2). The surface stress is a useful parameter to follow in the evaluation of the effect of plasticizer on the critical concentration of micelle formation and potential stability of water dispersion of stabilizer. The critical concentration of micelle formation, GT, is a limiting value of absorption, Gm, calculated from the equation: 1 dσ G m =  – -------- --------------- RT d ( ln c )

[11.49.1]

where: R T σ c

gas constant absolute temperature surface stress critical concentration of micelle formation.

Knowledge of the critical concentration of micelle formation is useful in calculating the surface area occupied by one plasticizer molecule: 1 S o = --------------G∞ NA

[11.49.2]

where: NA

Avogadro’s number

Figure 11.49.2 shows two different behaviors of plasticizers. Plasticizer based on a mixture of dioxane derivatives, DD, decreases surface stress, which means it has a surface activity similar to non-ionogenic surfactants and the ability of micelle formation. Dibutyl

418

Plasticizers Use and Selection for Specific Polymers

phthalate, DBP, does not have this surface activity, which may cause problems with the stability of its water dispersion.1 A decrease in the amount of plasticizer (diethyl phthalate) was observed after aging polyvinylacetate paints used in artworks.14 The change in the mechanical properties of PVAc paints has been related to the slow migration and evaporation of plasticizer, resulting in embrittlement and damage of the paint film.14 In polymeric membranes, the effect of plasticization on pure PVAc is clearly evident from approx. 3 times increase in the CO2 permeability along with 33% reduction in actual selectivity.15 High CO2 sorption in pure PVAc increases chain mobility, and thus plasticization occurs.15 Incorporation of Mg-metal-organic framework crystals improves the selectivity of mixed matrix membranes at both pressures investigated, compared to pure PVAc matrix.15

References 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Averco-Antonovich I U; Gotlib D M; Chakirov R R; Sokolova Y A, Macromol. Symp., 176, Nov. 2001, p.181-7. Li Y; Mlynar J; Sarkanen S, J. Polym. Sci.: Polym. Phys. Ed., 35, No.12, 15th Sept.1997, p.1899-910. US Patent 6,395,263. US Patent 6,294,265. US Patent 6,277,899. US Patent 6,268,413. US Patent 6,231,951. US Patent 6,162,475. US Patent 5,846,601. US Patent 5,804,618. US Patent 5,543,439. Bridger L A, Kerr A S D, Dufour J-P G, Siloock P J, Vincent S T, US Patent Application US 2006/ 0083818 A1, Knobbe Martens Olson & Bear LLP, Apr. 20, 2006. Kolter, K; Dashevsky, A; Irfari, M; Bodmeier, R, Int. J. Pharm., 457, 2, 470-9, 2013. Wei, S; Pintus, V; Schreiner, M, J. Anal. Appl. Pyrolysis, 97, 158-63, 2012. Majumdar S, Tokay B, Martin-Gil V, Campbell J, Castro-Muñoz R, Ahmad MZ, Fila V, Separation Purification Technol., 238, 116411, 2020.

11.50 Polyvinylalcohol

419

11.50 POLYVINYLALCOHOL 11.50.1 FREQUENTLY USED PLASTICIZERS • polyethylene glycol in blend with methylcellulose,1 in the pharmaceutical tablets coating composition,10 in production of sintered products from ferrite,12 in moldable and the extrudable composition,16,31 in light-sensitive material,18 in hydrogels,19 in the coating of enzyme-containing granules,21 and in hydrogel used in wound-dressing23 • ethylene glycols in removable coatings,2 in masking automotive coating,6 in adhesive gel,9 in tire sidewalls coating,11 in hydrogels,19 in blends with polyamide,20 in the coating of enzyme-containing granules,21 and in extruded fragrance34 • propylene glycol in adhesive gel,9 in the coating of enzyme-containing granules,21 in controlled-release bleach activator,26 and in extruded fragrance34 • polypropylene glycol in light-sensitive material,18 in hydrogels,19 in the coating of enzyme-containing granules,21 in hydrogel used in wound-dressing23 • polyol ester37 • glycerin (1,2,3-propanetriol) in masking automotive coating used to prevent paint overspray,6 in high-performance compound,3 in blends with pectin,7,8 in adhesive gel, in the pharmaceutical tablets coating composition,10 tire sidewalls coating,11 in water-soluble film,13 in preventive coating for fresh produce,14 in moldable and extrudable composition,16,28,31 in topsoil for gardens and lawns,17 in lightsensitive material,18 in hydrogels,19 in the coating of enzyme-containing granules,21 in hydrogel used in wound-dressing,23 in the moldable polymeric compound,24 in controlled-release bleach activator,26 in biodegradable composite articles,27 in the mop head,30 in orthopedic casting gloves,32 membranes,35 material for hot spinning,36 and in extruded fragrance34 • diglycerin in packaging film45 • monostearyl citrate in preventive coating for fresh produce • triacetin in soil erosion prevention15 • soy lecithin acts as a plasticizer by attracting moisture without compromising barrier properties of coating22 • benzyl butyl phthalate in adhesive for bonding paper to particle board25 • dipropylene glycol dibenzoate in strippable coating33 • lactone-modified polyvinylalcohol, PVOH, is used as a plasticizer29 • multihydroxyl polyhedral oligomeric silsesquioxane38 Water-soluble plasticizers are used in most cases unless improved water protection is required then water insoluble plasticizers are used. In many applications, biodegradable plasticizers are used. It is recognized that plasticizers in PVOH coatings increase tackiness and reduce barrier properties of such coatings. This is typical of polyethylene glycol.10 Glycerin is known to migrate to surface, which makes product sticky. Also glycerol facilitates crystallization of PVOH which may cause product inhomogeneity and deformation.24 11.50.2 PRACTICAL CONCENTRATIONS • polyethylene glycol: 10 to 25 wt%,10 5 to 50 wt%,12 and 1 to 10 wt%16 • ethylene glycol: 2 wt%,6 0.5 to 3 wt%,9 1 to 3 wt%,11 and 10 wt%20

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Plasticizers Use and Selection for Specific Polymers

propylene glycol: 0.5 to 3 wt% and 5 wt%26 glycerin: 1 wt%,6 0.5 to 3 wt%,9,35 1 to 3 wt%,11 20 wt%,13 0.1 to 5 wt%,14 0.5 to 5 wt%, 17 5 wt%,26 12 to 19 wt%,28 20 to 40 wt%,36 and 5 to 9 wt%32 • soy lecithin: 0.3 to 0.5 wt%22 • benzyl butyl phthalate: 8.6 wt%25 • dipropylene glycol dibenzoate: 0.7 to 4 wt%33 • multihydroxyl polyhedral oligomeric silsesquioxane: 0.0001-30 wt%38 In the majority of applications, plasticizers are added in modest quantities, most likely because larger additions affect surface properties of products and cause problems related to the hydrophilic nature of plasticizers used. Larger quantities of plasticizers were added to products such as controlled-release of pharmaceutical tablets, sintered materials produced from ferrites, and water-soluble films. • •

11.50.3 MAIN FUNCTIONS PERFORMED BY PLASTICIZERS • improvement of thermooxidative stability3 • reduction of processing temperature3 • improvement of oil and chemical resistance3 • improvement of film flexibility7, 11,14,23-25,32 • increased molecular mobility,14 which allows for attaining better packing efficiency through molecular rearrangement8 • reduction of glass transition temperature10,21,28 • improvement of gas permeability14 • improvement of biodegradability15 • improvement of adhesion and agglomeration in particulate materials17 • improvement of processing of highly viscous materials20,25 11.50.4 MECHANISM OF PLASTICIZER ACTION TG-IR analysis showed that −NH2 reacted with CO2 to form −HNCOO− at normal temperature and pressure, which contributed to the diffusion of CO2 and improved uniformity of cell size.40 With increasing formamide content, the cell density increased from 3.22×109 cm-3 to 1.79×1010 cm-3.40 Figure 11.50.1 illustrates the outcome.40 If a weak alkaline compound, which acts as a plasticizer, is pre-plasticized, CO2 may react reversibly with such basic compound (e.g., amine compounds) to form carbamate groups.40 The

11.50 Polyvinylalcohol

421

amine compound promotes dissolution of CO2 and provides a nucleation site, improving nucleation efficiency.40

Figure 11.50.1. Illustration of preparation and effect of amines on foaming properties of PVAl microcellular foams. [Adapted, by permission, from Xiang A, Yin D, He Y, Li Y, Tian H, J, Supercritical Fluids, 170, 105156, 2021.]

11.50.5 EFFECT OF PLASTICIZERS ON POLYMER AND OTHER ADDITIVES The observed order of glass transition temperature depression of polyvinylalcohol containing 15 wt% plasticizer was 1,4-butanediol > 1,2,6-hexanetriol > pentaerythritol > xylitol > mannitol, which was similar to the sequence of the thermal stability changes of the materials.39 Citric acid has been used as crosslinking agent and/or plasticizer.41 Addition of a small amount of plasticizer made films more elastic.41 The main limitation of supercritical-CO2 used in the microcellular foaming industry is its solubility.40 Formamide and polyhedral oligomeric silsesquioxane plasticized PVAl and helped in supercritical-CO2 diffusion.40 The content of formamide has a great influence on the foaming behavior of PVAl.40 Processability of polyvinylalcohol, a water-soluble polymer, into melt-extruded filaments and then into 3D printed tablets was studied by fused deposition modeling.42 Sorbitol was selected to enhance melt extrudability of PVAl.42 Carvedilol and haloperidol, two basic compounds with pH-dependent solubility, were used as model drugs.42 Miscibility of drugs with PVAl, with and without sorbitol, was also tested to determine whether any amorphous solid dispersion was formed that would facilitate rapid and pH-independent dissolution.42 Due to the high melting point and high melt viscosity of PVAl, filaments containing 10% and 20% drug required 180-190°C for extrusion, which was reduced to ~150°C by adding 10% sorbitol.42 Triacetin caused a reduction of glass transition temperature and melt temperature in both PVAl (hydrolysis degree of 88% and 99%) with the larger reduction in 88% hydrolyzed PVAl.43 Both Tg and Tm were reduced with increasing triacetin up to 15% and then plateaued with 20% triacetin.43

422

Plasticizers Use and Selection for Specific Polymers

Polyvinylalcohol-based resin film contained plasticizer and one or more types selected from sodium polyoxyethylene alkyl ether acetate, disodium polyoxyethylene alkyl sulfosuccinate salt, N-alkyl-N-methyl-β-alanine sodium salt, and sodium alkane-1,2diol acetate salt.44 Polyvinylalcohol-based resin was developed to be used in a water sealing process and/or to lower the adhesion force of the film to metal seal bar, etc., during heat sealing.44 Glycerin and/or sorbitol were selected as plasticizer(s).44 Polyvinylalcohol film produced a polarizing film that sufficiently suppressed reduction in light transmittance of a polarizing plate in high-temperature durability tests.46 Polyhydric alcohol is preferably used as a plasticizer, and specific examples include ethylene glycol, glycerin, propylene glycol, diethylene glycol, diglycerin, triethylene glycol, tetraethylene glycol, and trimethylolpropane.46 Of these, glycerin was selected because of the improved stretchability of PVAl film.46

11.50.6 TYPICAL FORMULATIONS Film coating of tablets (pharmaceutical, nutritional supplements, food, etc.):10 Polyvinylalcohol 38 to 46 wt% Polyethylene glycol 10 to 25 Talc 9 to 20 Pigment/opacifier 20 to 30 Lecithin 0 to 4 Topdressing soil for gardens and lawns:17 Sand 50-70 wt% Polyvinylalcohol 0.4-5 Glycerol 0.5-5 Water 5-20 Clay (hydrated aluminum silicate) 10-40 Coloring pigment 1-5 Urea 1-2 Peat moss 5-20 Moisture barrier coating:22 Polyvinylalcohol Flow aid Colorant Soy lecithin Suspending agent Water

7 to 12 wt% 3 to 5 4.8 to 8 0.3 to 0.5 0.07 to 0.12 75 to 85

References 1 2 3 4 5 6 7 8 9

Jun-Seo Park; Jang-Woo Park; Ruckenstein E, J. Appl. Polym. Sci., 80, No.10, 31st May 2001, p.1825-34. Zhuravleva I I; Laktionov V M, Intl. Polym. Sci. Technol., 26, No.7, 1999, p.T/50-3. Modern Plast. Intl., 29, No.8, Aug.1999, p.126. Hodge R M; Bastow T J; Hill A J, Polym. Mater. Sci. Eng., 76, 1, 1997, p.532-3. US Patent 5,885,720. US Patent 5,750,190. US Patent 5,646,206. Coffin D R; Fishman M L; Ly T V, J. Appl. Polym. Sci., 61, No.1, 5th July 1996, p.71-9. US Patent 5,322,880.

11.50 Polyvinylalcohol

10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46

US Patent 6,448,323. US Patent 6,443,202. US Patent 6,416,681. US Patent 6,166,117. US Patent 6,165,529. US Patent 6,122,860. US Patent 6,103,823. US Patent 6,048,377. US Patent 6,013,408. US Patent 5,972,375. US Patent 5,939,158. US Patent 5,879,920. US Patent 5,885,617. US Patent 5,846,214. US Patent 5,804,653. US Patent 5,804,618. US Patent 5,800,755. US Patent 5,798,152. US Patent 5,792,809. US Patent 5,712,334. US Patent 5,707,731. US Patent 5,661,217. US Patent 5,649,428. US Patent 5,604,282. US Patent 5,543,439. Mohsin M, Hossin A, Haik Y, J. Appl. Polym. Sci., 122, 3102-9, 2011. Lin C-A, Ku T-H, J. Mater. Process Technol., 200, 331-38, 2008. Urian D C, Morken P A, Visioli D L, US Patent Application Publication US 2008/0182937, DuPont, Jul 31, 2008. Lin H-M, Wang W-C, Pen H-C, US Patent Application Publication US 2010/0270518, PAI, Oct. 28, 2010. Aydin, A A; Ilberg, V, Carbohydrate Polym., 136, 441-8, 2016. Xiang A, Yin D, He Y, Li Y, Tian H, J, Supercritical Fluids, 170, 105156, 2021. Wen L, Liang Y, Lin Z, Xie D, Zhen Z, Xu C, Lin B, Polymer, 230, 124048, 2021. Wei C, Solanki NG, Vasoya JM, Shah AV, Serajuddin ATM, J. Pharm. Sci., 109, 4, 1558-72, 2020. Zuber SANA, Rusli A, Ismail H, MaterialsToday, Proc., 17, 3, 560-7, 2019. Shigemasa M, Kuchina Y, Ohsawa H, EP3919559A1, Aicello Corp, Dec. 8, 2021. JP2021143295A, Sep. 25, 2021. WO2020184587A1, Sep. 17, 2020.

423

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Plasticizers Use and Selection for Specific Polymers

11.51 POLYVINYLBUTYRAL 11.51.1 FREQUENTLY USED PLASTICIZERS • tetraethylene glycol di-n-heptanoate in laminated glass application1,10 • triethylene glycol di-(2-ethylhexanoate) in laminated glass applications12 • triethylene glycol diheptanoate in laminated glass13 • triethylene glycol-bis-2-ethyl hexanoate for UV protection contains UV absorber26 • dihexyl adipate in laminated glass2-4,6,12-13,15-17,19,21,24 • hexyl cyclohexyl adipate in laminated glass13 • dibutyl sebacate in laminated glass2 • polyethylene glycol in cathodes for fuel cells14 • biphenyl or its derivatives in electrographic photoconductor18 • diglycidyl ether of bisphenol A as resins plasticizer in aqueous emulsions23 • dibenzoate of alkylene and polyalkylene glycols25 11.51.2 PRACTICAL CONCENTRATIONS • tetraethylene glycol di-n-heptanoate: 37.4 phr,1 and 35 to 45 phr10 • triethylene glycol di-(2-ethylhexanoate): 25 to 45 phr12 • triethylene glycol diheptanoate: 25 to 45 phr13 • dihexyl adipate: 33 phr3,6-17,19 and 25 to 45 phr12-13,15-16,21,24 • hexyl cyclohexyl adipate: 25 to 45 phr13 11.51.3 MAIN FUNCTIONS PERFORMED BY PLASTICIZERS • affect solubility, migration, and diffusivity of other additives2 • reduce stiffness of polymer12 • increase absorption of impact forces by laminated glass12 • control adhesion to glass13 • reduce residual stress in photoconductive layer18 • affect maximum processing temperature above which undesirable bubbles are formed22 • improve film-forming properties23 11.51.4 EFFECT OF PLASTICIZERS ON POLYMER AND OTHER ADDITIVES In high extrusion throughput processes involving polyvinylbutyral, PVB, the resin is partially melted before plasticizer addition. The location of the plasticizer injection port is important. If plasticizer is injected too far downstream, high yellowness and discharge melt temperature surging occur.1 If plasticizer is injected too close, the plasticizer can back up into the primary feed barrel inlet and cause plugging.1 In addition to plasticizer and resin, other additives are included in the composition, such as, for example, antioxidants2 or UV stabilizers.16 Figure 11.51.1 shows that with small additions of plasticizer, an antioxidant dissolves better than predicted by a sum of its solubilities in polymer and plasticizer. Larger addition of plasticizer causes strong polymer-plasticizer interaction, which decreases antioxidant dissolution.2 Figure 11.51.2 shows that the solubility of antioxidant in dihexyl adipate and triethylene glycol is lower than its solubility in dibutyl sebacate, but the type of plasticizer made only a little difference in plasticized resin.2

11.51 Polyvinylbutyral

Figure 11.51.1. Effect of dihexyl adipate on solubility of 4-[3,5-bis(tert-butyl)-4-hydroxyphenyl]butane-2,2diol in plasticized PVB vs. concentration of plasticizer. [Adapted, by permission, from Mar'in A P; Tatarenko L A; Shlyapnikov Y A, Polym. Deg. Stab., 62, No.3, 1998, p.507-11.]

425

Figure 11.51.2. Solubility of 4-[3,5-bis(tert-butyl)-4hydroxyphenyl]butane-2,2-diol in plasticizer and resin containing 26 wt% plasticizer. DET − triethylene glycol, DBS − dibutyl sebacate, DET − dihexyl adipate. [Data from Mar'in A P; Tatarenko L A; Shlyapnikov Y A, Polym. Deg. Stab., 62, No.3, 1998, p.507-11.]

References 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26

US Patent 5,886,075. Mar'in A P; Tatarenko L A; Shlyapnikov Y A, Polym. Deg. Stab., 62, No.3, 1998, p.507-11. US Patent 5,656,365. US Patent 5,573,842. US Patent 5,585,056. US Patent 5,434,207. Voskanyan P S; Sarkisyan M B; Mkhitaryan M A; Badalyan V E, Intl. Polym. Sci. Technol., 22, No.10, 1995, p.T/1-3. El-Din N M S; Sabaa M W, Polym. Deg. Stab., 47, No.2, 1995, p.283-8. US Patent 5,322,875. US Patent 6,451,435. US Patent 6,132,882. US Patent 6,093,471. US Patent 5,728,472. US Patent 5,688,292. US Patent 5,631,315. US Patent 5,618,863. US Patent 5,595,818. US Patent 5,561,016. US Patent 5,547,736. US Patent 5,536,347. US Patent 5,529,849. US Patent 5,529,654. US Patent 5,525,669. US Patent 5,482,767. Papenfuhs B, Steuer M, US Patent 6,984,679, Kurray Specialities Europe GmbH, Jan 10, 2006. Lellig, P; Keller, U, US9206299, Kuraray Europe GmbH, Dec. 8, 2015.

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Plasticizers Use and Selection for Specific Polymers

11.52 POLYVINYLCHLORIDE 11.52.1 FREQUENTLY USED PLASTICIZERS The majority of plasticizer types discussed in Chapter 2 were either designed for or used for polyvinylchloride, PVC. But, the list of most common plasticizers changes due to various circumstances, such as cost of their production, environmental and safety concerns,8,20 development of a new group of materials, etc. For example, di-(2-ethylhexyl) phthalate dominated plasticizer use for many decades until findings, which questioned its health safety and its readiness to leach out of medical products. The problems related to the use of such prominent representative of a group suddenly changed the structure of supply and demand. The list below characterizes current preferences: Phthalates • di-n-hexyl phthalate25,29 • diisohexyl phthalate25,29 • diisoheptyl phthalate25,29 in sheet flooring34 • di-(2-propylheptyl) phthalate116 • di-(2-ethylhexyl) phthalate25,89 in PVC reinforced with cellulose whiskers,9 in flexible hose for toilet systems,13 in the studies of interaction with blood,18 as a co-plasticizer in flame retarded composition,22 in sheet flooring,34,92 in plastisol composition containing nitrile rubber,39,91,100 in studies on use of newsprint as a filler,45 in studies of gelation and fusion properties,48-50,68 in photolytic studies,52 in glass transition temperature studies,55 in compatibilized blend,78 in recycling carpet waste,83 and in acoustical control earpieces86 • diisononyl phthalate1 in creep resistant plastisol23 and in antimicrobial gloves manufacture95 • diisodecyl phthalate in electrical insulation,33 in compression set studies,42 and in photolytic studies52 • diisoundecyl phthalate in photolytic studies52 • diundecyl phthalate in light stable retroreflective highways signs,75 in oil resistant applications,84 in flame retardant composition,97 and in medical container104 • benzyl butyl phthalate in sheet flooring34 and in masonry bondable membrane98 • glycidylhexylphthalate in materials having improved thermal resistance118 • di-(2-ethylhexyl) tetrabromophthalate in flame retarding applications,36,77,81,87,96 • di-(2-ethylhexyl) tetrachlorophthalate in synergistic flame retarding system81,87 Low temperature and other general plasticizers: • a mixture (1:1) of diethylene glycol dibenzoate and dipropylene glycol dibenzoate,35 blends with triethylene glycol dibenzoate and di-(2-ethylhexyl) adipate,38 blends of dibenzoate and phthalate plasticizers117 • dihexyl adipate in interlayer of laminated glass85 and in glazing compound93 • di-(2-ethylhexyl) adipate,2 in food contact and medical applications,82 in interlayer of laminated glass,85 in acoustical control earpieces,86 in glazing compound,93 and in biocompatible material94 • diisodecyl adipate in glass transition temperature studies55 • dihexyl azelate in interlayer of laminated glass85 and in glazing compound93

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427

di-(2-ethylhexyl) sebacate in ion-selective membranes12 and in NO diffusion studies • n-butyryl tri-n-hexyl citrate in composition for medical containers76 • di-(2-ethylhexyl) trimellitate81 as medically acceptable plasticizer in flexible medical products14 and in the studies of interaction with blood18,132 • tri-(2-ethylhexyl) trimellitate in composition for medical containers,76 in flame retarded composition for wire and cable,87 and in biocompatible materials94 • pyromellitates in studies on potential candidates for plasticizers26,27 • alkylsulfonates as fast gelling plasticizers123 • triacetin-based fast gelling plasticizers124 • 1,2-phenylene oxo-diester plasticizers • triglyceride plasticizers • cyclohexane dicarboxylate diesters as highly solvating plasticizers • tetracarboxylic ester plasticizers • palm oil-based plasticizers131 • medium-chain-length poly(3-hydroxy alkanoate) natural-based eco-friendly plasticizer134 Flame retardant plasticizers: • isopropylphenyl diphenyl phosphate in flame retarded applications41,43,47 • 2-ethylhexyl diphenyl phosphate in the glass transition temperature studies55 and in semiconducting floor covering79 • alkyl aryl phosphate (Santicizer 2148) in smoke suppression53 and in flame retarded composition96 • chloroparaffin in flame retarded composition22 • diallyl orthophthlate as reactive plasticizer120 Other monomeric plasticizers: • epoxidized soybean oil1-2,22-23,53,82,92-93,97 • 2-nitrophenyl octyl ether in ion-selective membranes12 and in NO diffusion studies21 • triallyl cyanurate as a reactive plasticizer which promotes high temperature creep resistance1 • pentaerythritol ester plasticizer in flame retarded composition96 • lower alkyl biphenyls99 • polyol in plasticizing/compatibilizing blend with starch106 • ionic liquids121 Polymeric plasticizers and blends: • ethylene interpolymers (Evaloy) low smoke flexibilizers3-4 and as an aid in melt compounding46 • polyester-type, propanediol-based polymeric plasticizers5 • polyester adipate in paintable PVC sheet103 • poly(butylene adipate) in the migration resistant goods115 • polyester glutarate (Plasthall P-550) in the light stable retroreflective highways signs75 • polymeric plasticizer which withstands fats (e.g., Plaxter P20 or P80) in multilayer hose for transporting hot fluids80 •

428

Plasticizers Use and Selection for Specific Polymers

•

polymer blending with various polymers, such as acrylonitrile butadiene rubber,10 ethylene vinyl acetate10 (in flexible hose for toilet systems13), ethylene acrylic copolymer,10,102 and nitrile rubber39,86,91,100 • natural rubber, nitrile rubber, and carboxylated nitrile rubber119 • carbohydrate esters and polyol esters122 • polycaprolactone135 In addition to the chemical structure of the plasticizer, special requirements are common, such as food-grade, electrical grade, etc. Electrical grade plasticizers are commonly available. They differ from general grades by tight control of ionic impurities.33 The above analysis of the most recent applications of plasticizers shows that phthalates and di-(2-ethylhexyl) phthalate are still the main PVC plasticizers. It is interesting to note that diundecyl phthalate receives interest in applications where leaching, evaporation, and migration are serious drawbacks. Other types of plasticizers are used according to requirements related to properties (low temperature, flame retarding, etc.). Epoxidized soybean oil continues to be an important plasticizer of many formulations because it plays the dual role of a secondary plasticizer and a secondary stabilizer. Trimellitates seem to gain more applications due to their biocompatibility and environmentally friendly composition. It appears that polymeric plasticizers are not gaining many new applications, but instead, blending with other polymers is used for low fogging/low odor formulations.

11.52.2 PRACTICAL CONCENTRATIONS • di-(2-ethylhexyl) phthalate: 85 to 100 phr in slush molding composition containing up to 30 phr of highly crosslinked nitrile rubber,39 50 phr when used as a single plasticizer in smoke suppressed formulation using inorganic additives,53 80 phr in polymer blend,78 80 phr in a compatibilized blend containing PVC, polyolefin and/or styrenic polymer,89 5 to 35 phr in calendered flooring sheet,92 and 85 phr in slush molding composition100 • diisononyl phthalate: 48 wt% (100 phr) in cold dip molding of antimicrobial gloves95 • diisodecyl phthalate: 55 phr in wire and cable applications33 • diundecyl phthalate: 137.29 phr per 100 phr of PVC and 107.14 phr of crosslinked nitrile rubber84 and 50 phr in composition flame retarded by Sb2O397 • benzyl butyl phthalate: 100 phr in masonry bondable membrane98 • di-(2-ethylhexyl) adipate: 16 phr in addition to 10 phr of epoxidized soybean oil in food contact/medical grade PVC,18 50 phr in laminating layer for safety glass,85 65 wt% in earplug formulation,86 and 31 wt% (48 phr) in medical application94 • di-(2-ethylhexyl) azelate: 55 phr in laminated glazing unit93 • tri-(2-ethylhexyl) trimellitate: 120 phr (53% wt) in plasticization of ultra-high molecular weight PVC having high absorption limit of plasticizer (57 wt% as compared with 41 wt% for general PVC resins),14 37 to 40.5 weight percent in medical tubing,18 and ~50% of total plasticizers (n-butyryl tri-n-hexyl citrate − 20% and epoxidized soybean oil − 30%) in medical containers which have 30 wt% total plasticizer76

11.52 Polyvinylchloride

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•

isopropylphenyl diphenyl phosphate: up to 50 phr when used as a single plasticizer in flame retarded composition41 • 2-ethylhexyl diphenyl phosphate: minimum 30 phr with addition to general plasticizer in the range of 0 to 50 phr depending on the amount of filler and polymer type79 • di-(2-ethylhexyl) tetrabromophthalate: 10 phr (in addition to 20 phr of DOP) in flame retardant composition77 and 40 phr with the addition of 10 phr of di-(2-ethylhexyl) tetrachlorophthalate and 34.3 phr of tri-(2-ethylhexyl) trimellitate in flame resistant, low smoke wire and cable81,87 • pentaerythritol ester plasticizer: 33 phr in addition to 10 phr di-(2-ethylhexyl) tetrabromophthalate and 5 phr of isodecyl diphenyl phosphate in flame retarding composition96 • epoxidized soybean oil: 3 to 10 phr53,78 • polymeric plasticizer: 70 phr (propanediol derivative polyester),5 25 to 45% of polyester glutarate of total plasticizer composition for fluorescent highway retroreflective signs (total plasticizer is 30 to 35 phr),75 and 40-60 phr in cable and wire system88 • ethylene-vinyl acetate copolymer: 30-40 wt% (in addition to up to 30 wt% low molecular weight plasticizer)13 As expected from the requirements of numerous processing technologies used in PVC, the concentrations of plasticizers vary in a broad range. Other polymers discussed in this chapter are usually processed by one or two different methods of processing, and thus, plasticizer concentration reflects more precisely the requirements of a particular polymer. Plasticizer concentration in PVC must be reviewed in the context of the processing method and rigidity of articles produced.

11.52.3 MAIN FUNCTIONS PERFORMED BY PLASTICIZERS • make products more flexible5 • lower glass transition temperature51,55 • affect packing density and free volume54,62 • affect chain mobility and crystallization54 • improve compatibility with other polymers51,78,90,106 • lower processing viscosity5 • determine rheological characteristics of plastisols and melts30,45,69,91 • determine viscoelastic properties of materials36,54 • determine impact resistance of material46,110 and impact dispersing properties81 • determine scratch, wear, and slip resistance of material92 • lower processing temperature5 • determine fusion temperature30,48-50,68 • determine gelation temperature30,48-50,68,107 • affect discoloration of PVC56,77,118 • absorb radiation between 300 and 340 nm in laminated glass93 • affect thermal degradation of PVC58,61-64,85,118 • affect outdoor performance of products65,72,73,75,94 • affect biodegradation rate129,133 • affect plasticizer take up rate (or dry-blending time)24

430

Plasticizers Use and Selection for Specific Polymers

make products of varying rigidity10 creep resistance at elevated temperatures can be promoted by reactive plasticizers23 or blending111 • determine flammability of product36,77,81,87,96,97 • determine limiting oxygen index36 • determine heat release rate43 • reduction of smoke (high molecular weight flexibilizers) • increase of low temperature flexibility3,4 • affect foaming rate and microcellular structure59,107 • increase chemical and oil resistance (high molecular weight flexibilizers)3,4,80 • increase filler loading22,45 • affect water uptake12,103 • improve water-based coating receptivity103 • determine permeability to different gasses21 • reduction of odor by limiting carbon disulfide solubility13 • determine fogging32,102 • affect shrinkage of product due to plasticizer loss60 • determine surface tack of product or improve sliding resistance105 • affect acoustical properties of materials86,108,109 • determine biological stability of a product and antimicrobial properties950 • affect the concentration of ionic impurities33,88 • lower plasticizer migration115 • affect stain resistance of material34 • affect retroreflective properties of materials75 • affect blood compatibility18,76,104 • affect environmental compatibility of product19 • determine health hazards, especially in medical and food applications19,82,104,132 • affect performance of other additives53 • determine cost of product30 • help in material recycling83 The above list created on the basis of experimental findings and product development shows the importance of plasticizers for the properties of materials manufactured from PVC. These effects are discussed in many parts of this book, and their importance for some groups of products are discussed in Chapter 13. The above list may be frequently consulted to evaluate potential changes in material caused by plasticizer addition (also in other polymers). • •

11.52.4 MECHANISM OF PLASTICIZER ACTION The incorporation of plasticizer in PVC system is expected to lead to increased free volume. Experimental determination of free volume is very difficult as it requires decreasing the temperature to absolute zero. Early developments searched for the reasons of free volume change and the relationship between free volume and changes in chain mobility, which parallel free volume changes. These findings suggest that free volume can be increased by: • increase in temperature

11.52 Polyvinylchloride

431

•

decrease in molecular weight (either low molecular polymer or additives (e.g., plasticizers)) • increase in chain mobility (more end groups, lower interaction between chains (e.g., low polarity, decreased hydrogen bonding) • increase in hydrodynamic volume (e.g., numerous, long side chains) Combinations of these properties affect free volume. The space occupied by the plasticizer depends on its molecular shape. The size of the plasticizer molecule affects free volume but also affects plasticizing efficiency, processing, and permanence characteristics of materials through diffusion. Free volume increase brought about by plasticization is quantified in terms of the glass transition temperature, Tg, of polymer/plasticizer blend according to the following equation: V f = V [ 0.025 + α f ( T – T g ) ]

[11.52.1]

where: Vf V αf T Tg

average free volume in the polymer total volume of sample thermal expansion coefficient sample temperature glass transition temperature.

Glass transition temperature can be predicted from the equation: [11.52.2]

T g = T g2 – kw 1 where: Tg Tg2 k w1

glass transition temperature of polymer-plasticizer(s) mixture glass transition temperature of the unplasticized polymer plasticizer efficiency parameter weight fraction of plasticizer.

Figure 11.52.1. Projections of di-n-octyl phthalate molecule on different planes as labelled. Minimum energy conformation was calculated. [Adapted, by permission, from Coughlin C S, Mauritz K A, Storey R F, Macromolecules, 23, 3187-31-92, 1990.]

Figure 11.52.2. Mean radii of spherical wells for PVC plasticized with dioctyl phthalate vs. plasticizer concentration. [Data from Borek J; Osoba W, J. Polym. Sci.: Polym. Phys. Ed., 34, No.11, Aug.1996, p. 1903-6.]

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Plasticizers Use and Selection for Specific Polymers

Figure 11.52.3. Orthopositronium lifetime for PVC plasticized with dioctyl phthalate vs. plasticizer concentration. [Data from Borek J; Osoba W, J. Polym. Sci.: Polym. Phys. Ed., 34, No.11, Aug.1996, p. 19036.]

Figure 11.52.4. Glass transition temperature of PVCdi-(2-ethylhexyl) phthalate vs. weight fraction of PVC. [Data from Vilics T; Schneider H A; Manoviciu V; Manoviciu I, Polymer, 38, No.8, 1997, p.1865-70.]

Free volume depends on the size and conformation of the plasticizer molecule. This can be analyzed by assuming a regular geometry and using a radius of the sphere occupied by a molecule of plasticizer, but this leads to substantial errors, as can be seen from Figure 11.52.1.112 Real molecules are far from having a regular shape (each projection gives a different total and free volumes). Increased concentration of plasticizer increases free volume, as seen from Figure 11.52.2. The mean radius of spherical well correlates with free volume, which has a linear correlation with plasticizer concentration.113 Positron annihilation spectroscopy was employed to study the effect of plasticizer addition on free volume. The positronium atoms may form in amorphous regions of polymer. In these regions, free volume exists if orthopositronium may live for several nanoseconds.113 The lifetime of the longest-lived component, τ3, is attributed to the pick-off annihilation of orthopositronium. Figure 11.52.3 shows that the lifetime of the longestlived component, τ3, increases when the concentration of plasticizer increases. The lifetime also approached several nanoseconds; thus, free volume is increased.113 Glass transition temperature, Tg, is another fundamental quantity related to plasticization. Equation 11.52.1 shows that Tg and free volume are related. Equation 11.52.2 assumes that there is a simple linear relationship between properties of plasticizer, described by its efficiency parameter, k, and Tg. In reality, these functions are complex and non-linear. Any equation based on additivity fails to correctly predict Tg of plasticizer-polymer mixtures because it neglects specific PVC-plasticizer interactions. Figure 11.52.4 shows that Tg versus plasticizer concentration curve appears discontinuous as if composed of two different curves: below and above certain critical composition. The point of discontinuity is called “cusp”. Cusp was theoretically predicted114 by assuming that below the glass

11.52 Polyvinylchloride

Figure 11.52.5. tanδ of PVC-di-(2-ethylhexyl) phthalate vs. weight fraction of plasticizer. [Data from Vilics T; Schneider H A; Manoviciu V; Manoviciu I, Polymer, 38, No.8, 1997, p.1865-70.]

433

Figure 11.52.6. Spin-spin relaxation times of di-(2ethylhexyl) phthalate in mixture with PVC, T2, and pure state, T2o, vs. plasticizer concentration. [Adapted, by permission from Garnaik B; Sivaram S, Macromolecules, 29, No.1, 1st Jan.1996, p.185-90.]

transition temperature of the critical blend, the plasticizer does not further contribute to free volume changes of the mixture.55 Dynamic mechanical analysis also confirms the critical concentration of the plasticizer. On approaching the critical concentration, tanδ curve peaks begin to flatten and broaden with increasing plasticizer content to sharpen again on further concentration increase. Figure 11.52.5 shows that the tanδ peak has a minimum value at cusp (30 wt% for di-(2-ethylhexyl) phthalate). It is suggested that concentration at cusp point corresponds to maximum homogeneity of PVC-plasticizer blend. NMR studies still bring another contribution to understanding of the plasticization mechanism of polyvinylchloride. The spin-spin relaxation time, T2, is sensitive to low-frequency motions. It is useful in monitoring interactions between hydrogens in the PVC chain and carbonyl groups of plasticizers. Figure 11.52.6 shows the relationship between dimensionless values of T2/T2o and plasticizer weight fraction.66 T2 is the spin-spin relaxation time of plasticizer in PVC/di-(2-ethylhexyl) phthalate (the same plasticizer as used in studies reported in Figures 11.52.4 and 11.52.5) mixture, and T2o is the spin-spin relaxation time for pure plasticizer. Smaller additions of plasticizers do not cause any change in ratio. Apparently, plasticizer is utilized for interaction with PVC, and thus, the mobility of plasticizer is reduced. Once the certain critical point is passed, plasticizer mobility (and value of ratio) suddenly increases and ultimately attains constant value again, after which further addition of plasticizer may lead to inhomogeneous mixture of PVC and plasticizer. These data seem to point in the same direction as the data discussed above.

11.52.5 EFFECT OF PLASTICIZERS ON POLYMER AND OTHER ADDITIVES Chapter 9 contains a broad discussion of steps of plasticization with special attention to PVC. For this reason, we only show a few examples of plasticizer influence. Figure 11.52.7 shows that increased concentration of plasticizer reduces viscosity during the gelation process.

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Plasticizers Use and Selection for Specific Polymers

Figure 11.52.7. Complex viscosity of PVC plastisol at 140oC vs. concentration of di-(2-ethylhexyl) phthalate. [Data from Marcilla A; Garcia J C, Eur. Polym. J., 33, No.3, March 1997, p.357-63.]

Figure 11.52.8. Peak temperatures of loss and storage moduli for various concentrations of di-(2-ethylhexyl) phthalate. [Data from Marcilla A; Garcia J C, Eur. Polym. J., 33, No.3, March 1997, p.357-63.]

Figure 11.52.9. Final gelation temperatures of plastisols containing phthalates of alcohols having different lengths of hydrocarbon chains. [Data from Krauskopf L G; Godwin A D, J. Vinyl Additive Technol., 5, No.2, June 1999, p.107-12.]

Figure 11.52.10. Relative dry-blending time for plastisols containing phthalates of alcohols having different lengths of hydrocarbon chains. [Data from Krauskopf L G; Godwin A D, J. Vinyl Additive Technol., 5, No.2, June 1999, p.107-12.]

Figure 11.52.8 shows that there is a considerable difference in peak temperatures of storage and loss moduli at different plasticizer concentrations.49 Both curves show that there is an increase in the temperature of gelation when plasticizer concentration increases. This is because more plasticizer needs to be absorbed. The temperature peak of loss modulus is mainly affected by the fusion of PVC crystallites, whereas storage modulus is affected by both fusion and gelation processes, and thus, temperature maxima are most likely to be different.49

11.52 Polyvinylchloride

Figure 11.52.11. Compression set of PVC plasticized with variable amounts of didodecyl phthalate. [Data from Rehm T, J. Vinyl Additive Technol., 3, No.4, Dec.1997, p.286-91.]

435

Figure 11.52.12. Shore A of PVC plasticized with variable amounts of didodecyl phthalate. [Data from Rehm T, J. Vinyl Additive Technol., 3, No.4, Dec.1997, p.28691.]

Figure 11.52.9 shows that the higher the alcohol in the plasticizer, the higher the temperature of gelation. It is not only the temperature increase but also dry-blending time (Figure 11.52.10), which are important components of processing time and cost.24 During cooling, plasticized PVC regains its microcrystalline structure, which is responsible for its high degree of elasticity.42 Figure 11.52.11 shows that plasticizer concentration has little effect on the compression set of plasticized PVC. The higher melting fractions of the microcrystalline structure are responsible for Figure 11.52.13. Creep rate of PVC plasticized with triallyl cyanurate vs. crosslink density. [Data from Horng- excellent retention of shape by plasticized PVC.42 Mechanical properties change with Jer Tai, Polym. Eng. Sci., 41, No.6, June 2001, p.9981006.] concentration of plasticizer. Figure 11.52.12 shows that shore A linearly decreases with plasticizer concentration increasing.42 Similar is the effect of plasticizer on tensile strength. At the same time, the material becomes more elastic, and elongation adequately increases with increased concentration of plasticizer. Microcrystalline properties of plasticized PVC depend on PVC type, plasticizer type, and conditions of processing (heating and cooling temperatures and rates). These compositions and conditions may be varied to obtain required properties, but there is a limit of how far creep and high-temperature properties can be adjusted by formulation and pro-

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Plasticizers Use and Selection for Specific Polymers

Figure 11.52.14. Distance in Hansen space for plasticizers containing phthalates having alcohols of different lengths of hydrocarbon chains. [Data from Krauskopf L G; Godwin A D, J. Vinyl Additive Technol., 5, No.2, June 1999, p.107-12.]

Figure 11.52.15. Absorbance of coal tar staining component versus concentration of di-(2-ethylhexyl) phthalate. [Data from Colletti T A; Renshaw J T; Schaefer R E, J. Vinyl Additive Technol., 4, No.4, Dec.1998, p.233-9.]

cessing characteristics. If lesser creep or stability of shape at elevated temperatures are required, then polymer must be modified by the use of reactive plasticization. Figure 11.52.13 shows creep rate decreases with increased crosslink density because of the use of reactive plasticizer (triallyl cyanurate). Crosslinking increases gel content and decreases the swell ratio.101 Similar results were obtained when trimethylopropane trimethacrylate was used as a reactive plasticizer. Due to the formation of the crosslinked network, material also withstands higher temperatures (lower creep at elevated temperatures).23 The introduction of plasticizer causes separation of PVC chains relative to the concentration of plasticizer (see Section 11.52.4 on the discussion of the effect of plasticizer on free volume). Also, plasticizer type plays a role in this process. Figure 11.52.14 shows that the interaction radius of different plasticizers, expressed here by distance in Hansen space, increases with the size of the plasticizer molecule.24 Plasticizer concentration has a similar effect on the separation of chains and mobility of different molecules within the system. This modification of structure has implications on some properties discussed below. Figure 11.52.15 shows that plasticized PVC is stained more readily when the concentration of plasticizer increases. It is interesting to note that only the amount of plasticizer actually present in formulation affects staining. More volatile plasticizers escape more readily from plasticized material, and thus the real concentration of plasticizer in the formulation is lower than if less volatile plasticizer was used in spite of the fact that the same concentration of plasticizer was initially added. Figure 11.52.16 shows the absorbance of oil-soluble dye for plasticizers having different volatility. The more volatile the plasticizer, the higher its loss from the product during processing and the lower the staining.34

11.52 Polyvinylchloride

Figure 11.52.16. Absorbance of yellow dye stainant versus volatility of different plasticizers (diisononyl, di-(2-ethylhexyl), and diisoheptyl phthalates). [Data from Colletti T A; Renshaw J T; Schaefer R E, J. Vinyl Additive Technol., 4, No.4, Dec.1998, p.233-9.]

437

Figure 11.52.17. Temperature to 50% weight loss of pure and plastisol plasticizers having different number of atoms in alcohol part. [Data from Marcilla A; Beltran M, Polym. Deg. Stab., 53, No.2, 1996, p.261-8.]

The volatility of pure plasticizers and the volatility of plasticizers in plasticized PVC differ (Figure 11.52.17).61 Temperature of loss of pure plasticizer is consistently lower than the temperature of plasticizer loss from plastisol. This is due to the interaction between plasticizer and PVC chain. To remove plasticizer from plastisol, additional energy is required to overcome hydrogen bonding. Compatibility between plasticizer and polymer also plays a role since small differences are recorded for higher molecular weight (less compatible) plasticizers.61 Figure 11.52.18 shows the principles of diffusivity of plasticizers. The diffusion coefficient, k, comes from the following equation: M -------τ = kτ d M0 where:

[11.52.3]

Mτ amount of plasticizer which outdiffused from material in time τ, M0 initial concentration of plasticizer k, d coefficients (in data in Figure 11.61 d=0.5)

Several mathematical models were proposed to quantify diffusion. The following simple equation relates diffusion coefficient, k, to the molecular weight of plasticizer, M: log k = 1 − 0.0062 M

[11.52.4]

The equation is only approximate, but it shows, together with data in Figure 11.52.18, that diffusion of plasticizer decreases with its molecular weight increase. Plasticizer migration creates numerous problems in the use of PVC articles. Plasticizers are known to migrate to food, blood, and pharmaceuticals.2,70 Production of multilayer materials from PVC having different compositions of layers also creates problems

438

Figure 11.52.18. Diffusion coefficient for phthalates having different number of carbon atoms in alcohol part. [Data from Dedov A V; Bablyuk E B; Nazarov V G, Polym. Sci. Ser. B, 42, Nos.5-6, May-June 2000, p.138-9.]

Plasticizers Use and Selection for Specific Polymers

Figure 11.52.19. Plasticizer loss from PVC plasticized with 10 phr of epoxidized soybean oil and 40 phr of di(2-ethylhexyl) phthalate and 40 phr of poly(ethyleneco-vinyl acetate-co-carbon monoxide). [Data from Audic J-L; Poncin-Epaillard F; Reyx D; Brosse J-C, J. Appl. Polym. Sci., 79, No.8, 22nd Feb.2001, p.138493.]

because of plasticizer migration. It was found that 27 to 30% of initial contents of plasticizers in formulations containing 48 to 100 phr migrates into rigid PVC.70 This precludes feasibility of design based on required performance (e.g., surface layers of floor covering benefit from low concentration of plasticizers, which will reduce staining and mechanical wear, whereas core layers benefit from larger concentrations of plasticizers, which improve flexibility and damping characteristics). High-performance liquid chromatographic-UV detection method was developed for fast quantification of PVC Figure 11.52.20. The effect of treatment time on surface plasticizers used in the tubing.130 The free energy of PVC plasticized with 10 phr of epoximethod is useful in the selection of replacedized soybean oil and 40 phr of di-(2-ethylhexyl) 130 phthalate and 40 phr of poly(ethylene-co-vinyl acetate- ment plasticizers. co-carbon monoxide). [Data from Audic J-L; PoncinPlasma treatment is exploited as a Epaillard F; Reyx D; Brosse J-C, J. Appl. Polym. Sci., potential solution to the migration problem. 79, No.8, 22nd Feb.2001, p.1384-93.] The action of plasma changes surface functional groups, surface wettability and causes the formation of crosslinks in surface layers. Several cold plasma treatments were applied to PVC plasticized by di-(2-ethylhexyl)

11.52 Polyvinylchloride

439

phthalate.2 The best results were obtained with argon plasma treatment. Figure 11.52.19 shows that the plasticizer does not migrate when treatment is sufficiently long. The effect observed was explained by changes in wettability (Figure 11.52.20) and the effect of elastomeric copolymer − both suppressing plasticizer migration. Surface free energy, γs, and its non-dispersed term, γnds, increase along with the duration of treatment, whereas disperse energy, γds, remains practically constant. It may not be frequently noticed that loss of plasticizer either by migration or evaporation leads to shrinkage. The approximate shrinkage (or change of dimensions can be calculated from equations):60

where:

ΔL GM p L --------------- ≈ ----L GMo 7

[11.52.5]

C Po – C p p L = ---------------------------C Po ( 1 – C p )

[11.52.6]

ΔLGM LGMo pL CPo Cp

change in dimension [m] dimension before plasticizer loss [m] plasticizer loss ratio [dimensionless] plasticizer fraction before shrinkage [dimensionless] plasticizer fraction after shrinkage [dimensionless]

Equation [11.52.5] shows that shrinkage depends on the initial plasticizer content and its loss. The relationship is based on some simplifications such as uniform distribution of plasticizer during its loss (in reality, there is a gradient of plasticizer concentration; less plasticizer on the surface) and isotropy of material (in reality, materials have different properties along with their length and thickness, such as orientation, crystallinity, and many related properties). On the other hand, these simplifications do not change the general character of the relationship between plasticizer loss and shrinkage. Basicity of plasticizer impacts thermal dehydrochlorination rate of PVC degradation (Figure 11.52.21). Studies on PVC Figure 11.52.21. PVC dehydrochlorination rate vs. plas- cables from laboratory samples and materiticizer basicity. [Data from Minsker K S, Intl. J. Polym. als collected from field applications after 34 Mater., 33, Nos.3-4, 1996, p.189-97.] years of service show that there is very little change in properties and plasticizer concentration. Cables plasticized with chloroparaffin and DOP lost only 4% of the initial plasticizer after 4 weeks of aging at 100oC.15 This

440

Plasticizers Use and Selection for Specific Polymers

shows that thermal degradation of PVC is likely to affect product performance during the production stage but not during its use. Plasticizers may protect PVC from UV degradation. Figure 11.52.22 shows that the addition of diisoundecyl phthalate protects the C−Cl bond from dissociation.52 Also, carbonyl group formation is reduced in the presence of plasticizers. The activation energies derived from dehydrochlorination and plasticizer migration were 120 and 89 kJ/mol, respectively.136 In studies on migration and evaporation of plasticizer in PVC cables by liquid chromatography, the activation enerFigure 11.52.22. Cl index of neat PVC and PVC plasti- gies for diffusion (89 kJ/mol) and evaporacized with diisoundecyl phthalate vs. time of exposure to 290 nm in the presence of air. [Data from Balabanovich tion (99 kJ/mol) of DEHP in PVC cables A I; Denizligil S; Schnabel W, J. Vinyl Additive Technol., were reported based on the Arrhenius 3, No.1, March 1997, p.42-52.] method.136 The dehydrochlorination is dominant at temperatures above 200°C, while plasticizer migration is dominant at low temperatures.136 Since PVC cables are usually used at room temperature, then the migration of plasticizer has a dominant effect on the embrittlement of the cable.136 An extensive review of studies on PVC degradation and stabilization is published in special monograph.137

11.52.6 TYPICAL FORMULATIONS Electrical grade PVC:33 PVC 100 parts Diisodecyl phthalate 55 Stearic acid 0.5 Calcium carbonate 20 Clay (Glomax LL) 10 Barium stearate 3 Zinc stearate 0.5 BTH antioxidant 1 Diphenyl isodecyl phosphite 1 Titanium dioxide 2 Barium oxide 0.5 All raw materials must be of electrical grade quality (low ionic content) Low odor permeability hose:13 PVC BaZn stabilizer Calcium carbonate EVA polymer DOP

100 parts 2.5 25 70 15

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441

Stearic acid 0.25 Titanium dioxide 3 The formulation has low solubility of carbon disulfide. Composition for medical containers:76 PVC 59 wt% Vitamin E 12 n-Butyryl tri-n-hexyl citrate 6 Tri-(2-ethylhexyl) trimellitate 13.8 Epoxol 9-5 9 Calcium zinc stabilizer (CZ-11) 0.1 Acrawax 0.1 The presence of vitamin E and selected plasticizers suppresses hemolysis of red blood cells Food contact and medical applications:82 PVC 100 parts Di-(2-ethylhexyl adipate) 16 Epoxidized soybean oil 10 Ethoxylated nonylphenol (antifogging agent)4 Wax E 0.2 Dilauryl 3,3’-thiodipropionate 0.7 Zn stearate 0.2 BHT 0.1 Biocompatible material for blood lines with irradiation resistance:94 PVC 65 wt% Dioctyl adipate 31 Epoxidized soybean oil 2.9 CaZn stabilizer 1 Lubricant 0.1 Product can be subjected to radiation sterilization Flame retardant composition:77 PVC DOP Di-2-ethylhexyl tetrabromophthalate Sb2O3 Tin stabilizer The formulation has LOI=33.5

100 parts 20 10 5 3

Flame retarded composition of high performance:81 PVC 100 parts 15 Sb2O3 Trioctyl trimellitate 34.3

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Plasticizers Use and Selection for Specific Polymers

Lead stabilizer 5 Dioctyl tetrabromophthalate 30 Dioctyl tetrachlorophthalate 10 The formulation for cable and wire has LOI=37, low smoke (276) and good low temperature properties A compatibilized blend of polymers of high thermal stability:78 PVC 100 parts DOP 80 BaZn heat stabilizer 5.91 Epoxidized soybean oil 9.84 Stearic acid 0.39 Zinc stearate 0.39 Antioxidant 0.28 Chlorinated polyethylene 55.96 Ethylene 1-octene copolymer 28.12 Composition containing nitrile rubber:84 PVC 100 parts Diundecyl phthalate 137.29 Crosslinked nitrile rubber 107.14 Heat stabilizer 7.91 Antioxidant (Irganox 1010) 0.56 Co-stabilizer (Irgafos 168) 0.56 Stearic acid 0.28 Processing aid (K-175) 3.39 The formulation has oil resistance, good low temperature, smoke suppressing and char forming properties The formulation for lamination of safety glass:85 PVC 100 parts Dioctyl adipate 50 Epoxidized soybean oil 5 BaZn stabilizer (UZB 793) 3 Perchlorate stabilizer (CPL 46) 0.2 Antioxidant (Irganox 1010) 1 UV absorber (Tinuvin 328) 0.2 Formulation provides impact energy dissipation properties, and long-term service use stability Laminated glazing unit interlayer:93 PVC Dihexyl azelate Perchlorate stabilizer (#5377) UV absorber (Tinuvin 328)

100 parts 55 0.1 0.5

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BaZn stabilizer (L-1960) 1.5 BaZn stabilizer (KP-11) 0.5 The formulation is capable of eliminating UV radiation between 300 and 340 nm Sound attenuation composite:109 PVC (Geon 178) PVC (Formolon 40) Barium sulfate Microspheres (K-1) Hydrated alumina (ATH 204) Mineral spirits Plasticizer (H-150) Heat stabilizer (Thermchek 1776) Heat stabilizer (Thermchek 904) Pigment paste Flammability additive (Thermoguard CPA) Flame retardant (Frysol CEF) Surfactant (Triton 114) Compatibilizer (Desical) Froth stabilizer (Silicone DC 1250)

12.19 wt% 2.44 61.57 1.27 1.47 2.68 9.6 0.47 0.15 0.99 0.73 1.49 1.07 0.44 3.47

Impact-resistant coating:110 PVC VC-VA copolymer Calcium carbonate Hollow plastic spheres Phthalic ester of C9 or higher alcohol

20-30 wt% 10-20 15-20 0.3-0.4 30-40

The entire book contains a selection of formulations for all important aspects of PVC processing.138

References 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17

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67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125

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Sanderson R D; Schneider D F; Schreuder I, J. Appl. Polym. Sci., 57, No.6, 8th Aug.1995, p.727-38. Marcilla A; Beltran M; Garcia J C; Mang D, J. Vinyl Additive Technol., 1, No.1, March 1995, p.10-14. Chee K K, Eur. Polym. J., 31, No.2, Feb.1995, p.155-9. Papakonstantinou V; Papaspyrides C D, J. Vinyl Technol., 16, No.4, Dec.1994, p.192-6. Makarewicz E, Intl. Polym. Sci. Technol., 21, No.8, 1994, p.T/89-94. Wypych J, Polyvinylchloride Degradation, Elsevier, Amsterdam, 1985. Wypych J, Polyvinylchloride Stabilization, Elsevier, Amsterdam, 1986. Krauskopf L G; Godwin A D, Antec '99. Volume III. Conf. proc., SPE, New York City, 2nd-6th May 1999, p.3526-36. US Patent 6,472,050. US Patent 6,468,258. US Patent 6,448,310. US Patent 6,417,260. US Patent 6,406,768. US Patent 6,397,894. US Patent 6,369,264. US Patent 6,362,264. US Patent 6,306,318. US Patent 6,271,301. US Patent 6,180,246. US Patent 6,129,175. US Patent 6,114,425. US Patent 6,087,428. US Patent 6,063,846. US Patent 6,054,538. US Patent 6,054,524. US Patent 6,022,606. US Patent 6,001,462. US Patent 5,955,519. US Patent 5,906,823. US Patent 5,886,072. US Patent 5,863,967. US Patent 5,860,255. US Patent 5,847,040. US Patent 5,840,236. US Patent 5,834,543. US Patent 5,811,474. US Patent 5,777,014. US Patent 5,772,960. US Patent 5,744,211. US Patent 5,696,186. US Patent 5,695,696. US Patent 5,681,408. US Patent 5,622,662. US Patent 5,563,188. US Patent 5,502,111. Coughlin C S, Mauritz K A, Storey R F, Macromolecules, 23, 3187-31-92, 1990. Borek J; Osoba W, J. Polym. Sci.: Polym. Phys. Ed., 34, No.11, Aug.1996, p. 1903-6. Braun G, Kovacs A, Physics of Non-Crystalline Solids, North-Holland, Amsterdam, 1965. Lindstoem A, Hakkarainen M, J. Appl. Polym. Sci., 104, 2458-67, 2007. Kozlowski R R, Storzum U, J. Vinyl Addit. Technol., 11, 155-159, 2005. Arendt W D, Strepka A M, Petrovich D C, Joshi M, J. Vinyl Addit. Technol., 11, 150-54, 2005. Kim S-W, Kim J-G, Choi J-I, Jeon I-R, Seo K-H, J. Appl. Polym. Sci., 96, 1347-56, 2005. Sunny M C, Ramesh P, George K E, 20-29. Cook W D, Laing G G, Lu M, Simon G P, Yeo E, Polymer, 48, 7291-300, 2007. Rahman M, Brazel C S, Polym. Deg. Stab., 91, 3371-82, 2006. Buchanan C M, Buchanan N I, Edgar K J, Lambert J L, US Patent 7,276,546 B2, Eastman, Oct. 2, 2007. Weiss T, Wiedemeier M, US Patent Application Publication US 2009/0197998, Lanxess, Aug. 6, 2009. Hansel J-G, Wiedemeier M, US Patent 8,026,314 B2, Lanxess, Sep. 27, 2011. Dakka J M, Mozeleski E J, Baugh L S, Benitez F M, Faler C A, Weber J F W, Smirnova D S, US Patent

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Application Publication US 2011/0184105 A1, ExxonMobil, Jul. 28, 2011. 126 Dakka J M, Mozeleski E J, US Patent Application Publication, US 2011/0151162 A1, ExxonMobil, Jun. 23, 2011. 127 Kinkade N E, Chanberlin K S, Olsen D J, Holt M S, Stimpson M J, Kelly, C E, US Patent 7,973,194 B1, Eastman, Jul 5, 2011. 128 Baugh L S, Berluche E, Colle K S, Varma-Nair M, Saleh R Y, Stanat J E R, Zushma S, DeFlorio V, US Patent Application Publication US 2011/0257317, ExxonMobil, Oct. 20, 2011. 129 Fava, F; Raddadi, N; Giacomucci, L; Lotti, N, New Biotech., 31, S141-2, 2014. 130 Radaniel, T; Genay, S; Simon, N; Feutry, F; Quagliozzi, F; Barthelemy, C; Lecoeur, M; Sautou, V; Decaudin, B; Odou, P, J. Chromat. B, 965, 158-63, 2014. 131 Waskitoaji, W; Triwulandari, E; Haryono, A, Procedia Chem., 4, 6313-21, 2012. 132 Eckert, E; Mueller, J; Goen, T, J. Chromat. A, 1410, 173-80, 2015. 133 Kositchaiyong, A; Rosarpitak, V; Hamada, H; Sombatsompop, N, Int. Biodet. Biodeg., 91, 128-37, 2014. 134 Tan, I K P; Gan, S N; Annuar, M B M; Sin, M C, WO20142014337, University of Malaya, Jan. 23, 2014. 135 Shoemaker, C L; Lee, S H; Grant, J L; Bertino, J G; Barcon, A, WO2014070355, Polyone Corporation, May 8, 2014. 136 Koga Y, Arao Y, Kubouchi M, Polym. Deg. Stab., 171, 109013, 2020. 137 Wypych G, PVC Degradation and Stabilization, 4th Ed., ChemTec Publishing, Toronto, 2020. 138 Wypych G, PVC Formulary, 3rd Ed., ChemTec Publishing, Toronto, 2020.

11.53 Polyvinylfluoride

447

11.53 POLYVINYLFLUORIDE Because of the severe susceptibility of PVF to thermal degradation, its processing resembles plastisol technology in which polyvinylchloride is mixed with a plasticizer before molding and processing.1 The difference between PVF and PVC processes is that the solvent is removed from the PVF product, while the plasticizer is retained in the PVC article.1 Development of processing technology for PVF allowed the manufacturing of biaxially orientable films from this polymer.1 Dimethyl, butyl, and dioctyl phthalates trioctyl trimellitate, and dioctyl sebacate were used with polyvinylfluoride.2 Dimethyl phthalate has the highest solubility parameter and was found to be the most compatible plasticizer, giving plasticized products the lowest melting temperatures.2

References 1 2

Ebnesajjad S, Polyvinyl Fluoride: The First Durable Replacement for Paint in Introduction to Fluoropolymers, 2nd Ed., William Andrew, 2021, pp. 331-8. Wang J, Lu Y, Yuan H, Polym.-Plast. Technol. Eng., 46, 461-68, 2007.

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11.54 POLYVINYLIDENEFLUORIDE 11.54.1 FREQUENTLY USED PLASTICIZERS • dibutyl sebacate in inner sheath of flexible oil pipe1 • adipic polyester in porous membrane2 • glyceryl tributylate3 • glyceryl triacetate and dioctyl adipate (sacrificial plasticizer in membrane)12 • tricresyl phosphate4 • dibutyl phthalate6,7,8 • ionic liquid9 • polyester10 • absorbed moisture on catheter surface11 11.54.2 PRACTICAL CONCENTRATIONS • 5 to 10 wt% of tricresyl phosphate4 • 10 wt% dibutyl sebacate1 • 15 phr of dibutyl phthalate7 • up to 46 wt% of dibutyl phthalate6 • 50 to 117 phr of adipic polyester2 11.54.3 MAIN FUNCTIONS PERFORMED BY PLASTICIZERS • creation of porous structure by extraction of plasticizer from membrane2,12 • formation of gels3,6 • enhancing piezoelectric activity4 • helping in crystal perfection4 • assisting in obtaining the most polar polymorph4,6 • improvement in ferroelectric switching4 • formation of polymer electrolytes7 • improved thermal stability10 11.54.4 EFFECT OF PLASTICIZERS ON POLYMER AND OTHER ADDITIVES Sea-island nanostructured polyvinylidenefluoride/zeolitic imidazolate framework polyelectrolyte with superior mechanical and ionic properties for boosting energy storage performances of the supercapacitors has been developed.13 Nanoparticles uniformly distributed in PVDF substrate displayed plasticization effect, and thus, improved the mechanical properties of the membrane.13 Microcellular PVDF/multiwalled carbon nanotube nanocomposite foamed part was fabricated by supercritical carbon dioxide using bead foaming technology.14 During the bead foaming process, the induced crystallization effect of MWCNT as well as the plasticizing and squeezing effect of supercritical-CO2 on PVDF matrix contributed to the increase of the β-phase crystal in PVDF matrix, thus endowing the composite foaming part with good piezoelectric properties.14 CO2 adsorption in polymer matrix plasticized polymer molecular chains, having a significant impact on foaming.14 References 1 2

Glennon D; Cox P A; Nevell R T; Nevell T G; Smith J R; Tsibouklis J; Ewen R J, J. Mater. Sci., 33, No.14, 15th July 1998, p.3511-7. US Patent 5,626,805.

11.54 Polyvinylidenefluoride

3 4 5 6 7 8 9 10 11 12 13 14

449

Mal S; Nandi A K, Macromol. Symp., 114, Feb.1997, p.251-6. Winsor D L; Scheinbeim J I; Newman B A, J. Polym. Sci.: Polym. Phys. Ed., 34, No.17, Dec.1996, p.2967-77. US Patent 5,380,786. Marigo A; Marega C; Bassi M; Fumagalli M; Sanguineti A, Polym. Internl., 50, No.4, April 2001, p.449-55. Croce F, Appetecchi G B, Slane S, Salomon M, Tavarez M, Report, AD-A304868, 1996. Du C-H, Xu Y-Y, Zhu B-K, J. Appl. Polym. Sci., 114, 3645-51, 2009. Guo L, Liu Y, Zhang C, Chen J, J. Membrane Sci., 372, 314-21, 2011. Ohira S, Munakata K, Mizuno, T, Masumura M, US Patent 6,512,032, Kureha Chemical Industry, Jan. 28, 2003. Guo, X; Johnson, D P, US20140276643, St. Jude Medical, Cardiology Division, Inc., Sep. 18, 2014. Schuster, O; Huanf, Q; Duong, N-P; Bauer, K; Ansorge, W, US20160089638, 3M Innovative Company, Mar. 31, 2016. Lu C, Chen X, J. Powder Source, 448, 227587, 2020. Xu D, Zhang H, Pu L, Li L, Compos. Sci. Technol., 192, 108108, 2020.

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11.55 POLYVINYLIDENECHLORIDE Packaging films with the controlled transmission of CO2 and O2 are produced from plasticized polyvinylidenechloride, PVCD. This film is suitable for the packaging gassing cheese.1 The film contains 8 to 10 wt% plasticizer selected from the following group: polymeric condensation product of azelaic acid and 1,3-butanediol, polymeric plasticizer of adipic acid and propylene glycol, epoxidized soybean oil, or acetyl tri-n-butyl citrate. The film formulations are so designed that CO2 permeability increases and O2 permeability possibly remains the same.1,4 Packaging film from plasticized PVCD has improved thermal stability and reduced stickiness to metal surfaces when only 2 wt% of epoxidized soybean oil is added as a plasticizer. In addition, metal soaps of ricinoleic acid are added, which also act as plasticizers.2 The addition of 1 to 4 wt% tetraethylene glycol di-(2-ethylhexoate) is expected to reduce oxygen transmission rates and improve extrudability of film.3 A mixture of the epoxidized unsaturated fatty acid ester and pentaerythritoltetravalerate was used in a highly stable plasticized polyvinylidenechloride composition.10

References 1 2 3 4 5 6 7 8 9 10

US Patent 5,538,770. US Patent 5,914,194. US Patent 5,759,702. US Patent 5,726,229. Jeczalik J, Polimery, 42, 487 (1997). Balayan S R; Alimukhamedov M G; Magruppov F A, Plasticheskie massy, No 1, 21 (1995). French Patent Application 2,782,723. US Patent 5,444,128. Von Hassel A., Plast.Technol., 29, 21 (1983). Paulsson, C, WO2016043639, Perstorp AB, Mar. 24, 2016.

11.56 Proteins

451

11.56 PROTEINS 11.56.1 FREQUENTLY USED PLASTICIZERS • glycerin in foamed packaging container,1 in soy plastics,2,4 in chewable pet toys,5 in medical purpose sealants,7-8 in thermoplastic articles,9,16,20 in protein coated medical substrates for local delivery of genes,11 in solubilized protein,13 in biodegradable articles,14 in edible barrier coatings,14 films,22-23 and drug delivery systems24 • propylene glycol in foamed packaging container,1 gelatin films,20 and in soy plastics5 • triethylene and ethylene glycols in foamed packaging containers1 and in soy plastics5 • polyethylene glycol (molecular weight of 200 and 400) in soy plastics,5 in sustained-release of bioactive proteins,10 and in edible barrier coatings5 • polyethylene glycol having molecular weight of 300 to 20,00019-20 • sorbitol in medical purpose sealants7,8 and in edible barrier coatings5 • triacetin in sustained-release of bioactive proteins1 • acetyltributyl citrate and tributyl citrate • water16,22-23 • 2-mercaptoethanol16 • hydrogen-bonded liquids17 • ethanol-, diethanol-, and triethanol-amines19 • sorbitol in drug delivery systems24 11.56.2 PRACTICAL CONCENTRATIONS • glycerin: 8 phr,6 5-20 wt%,13 10-25 phr,4 17-25 phr14 • propylene glycol: 10-25 phr1 • polyethylene glycol: 360 phr (liquid suspension)10 • triacetin: 360 phr (liquid suspension)10 Water acts as a plasticizer affecting the practical concentration of organic plasticizer added to achieve the required effect. 11.56.3 MAIN FUNCTIONS PERFORMED BY PLASTICIZERS • improvement of processability1,4,6 • improvement of material flexibility1,4,6,11,15 • modification of fracture behavior2 11.56.4 MECHANISM OF PLASTICIZER ACTION In polar biopolymers, such as polysaccharides and proteins, plasticization depends to a large extent on the hydrogen bond network.26 Glycerol-plasticized protein systems based on wheat gluten were investigated, in combination with the effects of water.26 In a dry system, the main effect of glycerol was to break protein-protein hydrogen bonds.26 In the moist system, glycerol was partly out-competed by water in forming hydrogen bonds with the protein, making the glycerol plasticizer less effective than in dry conditions.26 Molecular dynamics simulations successfully predicted plasticizer concentrations at which the onset of efficient plasticization occurred.26 The onset of efficient plasticization in the starch-glycerol system occurred in the range of 20-30 wt% of glycerol.26 The glass transi-

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tion temperature with increasing glycerol content was almost identical to that observed in the experimental data for the dry system, with the most significant decrease between 24 and 26 wt% glycerol.26

11.56.5 EFFECT OF PLASTICIZERS ON POLYMER AND OTHER ADDITIVES The addition of water to process the mixture reduces processing viscosity but does not affect glass transition temperature, which is the same as for dry soy protein (150oC). The addition of 25 wt% of glycerin drastically decreases glass transition temperature to −50oC. Normally brittle polymer loses mechanical strength but gains flexibility. Figures 11.56.1 and 11.56.2 show the effect of propylene glycol on tensile strength and elongation of plasticized soy protein. The calculated thermodynamic parameters suggested that hydrophobic interactions dominated the interaction process between protein and phthalate plasticizers.21 The interaction of phthalate plasticizers with human serum albumin caused a conformational change of the protein, with the loss of α-helix stability.21 The effect of plasticizer and zein subunit on the viscoelasticity of the zein network was studied.25 In this study, total zein (comprising α-, β- and γ-subunits) or α-zein (comprising mainly α-subunit) were used to prepare a network with two plasticizers, ethanol or acetic acid.25 The glass transition temperature of total zein was higher than that of α-zein due to β- and γ-zein.25 The zein network with acetic acid could maintain its viscoelasticity consistently, while the zein network with ethanol hardened gradually.25 The more plasticized zein, the more uniform and ordered zein network.25 Plant protein-based materials possess attractive thermomechanical properties, which make them prospective sources for use in 3D printing.27 Plasticizers are required to reduce the brittleness and increase thermoplasticity, but excess plasticizer may severely decrease mechanical properties, resulting in material not being useful for 3D printing.27 Protein sources and plasticizers, as well as treatments and modifications that can be used to custom tailor material properties for 3D applications, are discussed in a broad review.27

Figure 11.56.1. Tensile strength of soy protein plasticized with variable amounts of propylene glycol. [Data from Jane Jaay-lin and Su She Zhang, US Patent 5,710,190.]

Figure 11.56.2. Elongation of soy protein plasticized with variable amounts of propylene glycol. [Data from Jane Jaay-lin and Su She Zhang, US Patent 5,710,190.]

11.56 Proteins

453

Biodegradable gelatin-silk fibroin electrolytes with smart humidity sensitivity were fabricated.28 The degradable aqueous zinc-ion battery can be completely degraded within 45 days.28 The battery exhibited a high specific capacity (311.7 mAh g-1) and excellent cycle stability.28 Recombinant spider silk composition was formed from a silk-based extrudate to a stable film that adsorbs to the skin.29 Silk is a structural protein that has many qualities that make it desirable for use in applications such as skincare and cosmetics.29 Plasticizer was used to interact with a polypeptide sequence to prevent the polypeptide sequence from forming tertiary structures and bonds and to increase the mobility of the polypeptide sequence.29 Glycerin was the plasticizer.29

References 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29

US Patent 5,710,190 Sue H J; Wang S; Jane J L, Polymer, 38, No.20, 1997, p.5035-40. Cuq B; Gontard N; Guilbert S, Polymer, 38, No.16, 1997, p.4071-8. US Patent 5,523,293. Wang S; Sue H J; Jane J, J. Macromol. Sci. A, A33, No.5, 1996, p.557-69. US Patent 6,379,725. US Patent 6,299,639. US Patent 6,177,609. US Patent 6,034,198. US Patent 6,011,011. US Patent 6,004,943. US Patent 5,801,141. US Patent 5,763,583. US Patent 5,665,152. US Patent 5,543,164. Gillgren T, Barker S A, Belton P S, Georget D M R, Standing M, Biomolecules, 10, 1135-39, 2009. Coppola M, Djabourov M, Ferrand, Polymer, 2012 in press. Andreuccetti C, Carvalho R A, Grosso C R F, Food Res. Int., 42, 1113-21, 2009. Cao N, Yang X, Fu Y, Food Hydrocolloids, 23, 729-35, 2009. Vanin F M, Sobral P J A, Menegalli F C, Carvalho R A, Habitante A M Q B, Food Hydrocolloids, 19, 899-907, 2005. Yue, Y; Liu, J; Liu, R; Sun, Y; Li, X; Fan, J, Food Chem. Toxicology, 71, 244-, 2014. Zubeldia, F; Ansorena, M R, Marcovich, N E, Polym. Testing, 43, 68-77, 2015. Yun, H; Kim, M K; Kwak, H W; Lee, J Y; Kim, M H; Lee, K H, Int. J. Biol. Macromol., 82, 946-51, 2016. Zilberman, M; Peles, Z; WO2012120516, Ramot, Sep. 13, 2012. Zhang X, Gao M, Zhang Y, Dong C, Xu M, Hu Y, Luan G, Food Hydrocolloids, 123, 107140, 2022. Özeren HD, Wei X-F; Nilsson W, Olsson RT, Hedenqvist MS, Polymer, 232, 124149, 2021. Rowat SJA, Legge RL, Moresoli C, J. Food Eng., 308, 110623, 2021. Zhou J, Li Y, Xie L, Xu R, Zhang R, Gao M, Tian W, Li D, Qiao L, Wang T, Ciao J, Wang D, Hou Y, Fu W, Yang B, Zeng J, Chen P, Liang K, Kong B, MaterialsToday, Energy, 21, 100712, 2021. Wray L, El-Difrawy NE, Guerette PA, Boulet-Audet M, Rice GW, Kittleson JT, WO2021011431A1, Bolt Threads, Inc., Jan. 21, 2021.

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11.57 RUBBER, NATURAL 11.57.1 FREQUENTLY USED PLASTICIZERS Natural rubber is compatible with paraffinic, naphthenic, and aromatic oil plasticizers. Only butyl rubber has similar compatibility with all other synthetic rubbers compatible with a limited spectrum of mineral oils. These are some significant applications: • aromatic mineral oil in tires having high abrasion resistance,1 in tire treads having low rolling resistance and improved ABS braking,9 and in rail support1 • paraffin oil in antimicrobial articles5 and in-vehicle vibration-damping device12 • processing oil in anti-tack bladder6 and in tire sidewall composition13 • mineral oil (paraffinic, aromatic or naphthenic) in sealing composition, which swells on contact with water,7 in rubber part suitable for dampening vibration,8 in engine mount,10 and in the grips of articles14 • ester plasticizers (adipates, sebacates, phthalates, or phosphates) in sealing composition, which swells on contact with water7 • polyethylene glycol in antimicrobial articles5 • triethyl citrate in gentamicin sulfate-containing natural rubber films for wound dressing17 • dibutyl phthalate in nicotine transdermal patches18 • epoxidized fatty acid alkyl ester plasticizer from natural oil soap stock19 11.57.2 PRACTICAL CONCENTRATIONS • aromatic mineral oil: 8 wt%,5 20-25 phr,9 37.5 phr1 • paraffinic oil: 1.5 phr,12 or 10-12 phr13 20 phr (in addition to 5 phr of polyethylene glycol)5 • naphthenic oil: 10-20 phr14 • processing oil: 3 phr6 • mineral oil: 1-10 wt%8,10 • epoxidized low molecular weight natural rubber: 15 wt%20 11.57.3 MAIN FUNCTIONS PERFORMED BY PLASTICIZERS • increasing softness of rubber (mineral oils are frequently called softeners)4,12 • improvement of dispersion of minor components and fillers1 • dissolving other rubber components1 • aid in the breakdown of elastomer5,12 • unsaturated fatty acids act as a plasticizer and accelerate crystallization rate16 • lowering expenditure of energy necessary to mix rubber mixtures22 11.57.4 EFFECT OF PLASTICIZERS ON POLYMER AND OTHER ADDITIVES Epoxidized low molecular weight natural rubber has the potential to improve both processing and vulcanizate properties due to its plasticizing effect and epoxide-silica interactions.20 Epoxidized low-molecular-weight natural rubber is a highly viscous rubber of relatively low molecular weight that is generally used as a plasticizer or processing aid.20 It also has a random distribution of epoxide groups along the polymer backbone.20 Low molecular weight rubber molecules act as internal plasticizers in rubber compounds, improving the mobility of rubber chains.20

11.57 Rubber, natural

455

Maleic anhydride was chemically attached to depolymerized natural rubber by a photochemical reaction and used as a reactive polymeric plasticizer for chloroprene.21 This polymeric plasticizer reduced heat buildup, improved rebound resilience, compression set and aging, and oil resistance of chloroprene vulcanizates.21 A rubber composite comprised natural and synthetic rubber polymer and a plasticizer comprising a liquid natural rubber.22 The liquid natural rubber was liquid guayule natural rubber.22 Guayule is a woody plant.22 Guayule natural rubber can be extracted according to known methods, which include cultivating guayule, harvesting it, milling or grinding the harvested guayule, extracting the rubber by solvent, removing impurities, and removing the solvent.22 Social and environmental concerns regarding the use of crumb rubber from end-oflife car tires in the construction of different sport and recreational facilities have been increasing due to the presence of hazardous compounds.23 Worldwide research attempted assessment of 42 organic chemicals, including polycyclic aromatic hydrocarbons, phthalates, adipates, antioxidants, and vulcanization agents in a large number of samples (91) from synthetic turf football pitches of diverse characteristics and geographical origin.23 Samples were taken worldwide, in 17 countries on 4 continents, to show the global dimension of this problem.23 Plasticizers were detected in all crumb rubber samples. Plasticizers included DIBP, DBP, BBP, and DEHP.23

11.57.5 TYPICAL FORMULATIONS Antimicrobial articles:5 Natural rubber Processing aid (pentaerythritol tetrastearate) Polyethylene glycol Silica Calcium oxide (desiccant) Titanium dioxide Zinc oxide Calcium carbonate Paraffinic oil Ethylene glycol dimethacrylate Di-(tert-butyl-peroxy-isopropyl)benzene Di-(tert-butyl-peroxy-trimethyl)-cyclohexane Antimicrobial Anti-tack bladder:6 Natural rubber Chlorosulfonated polyethylene Carbon black (N660) Calcium carbonate Processing oil Zinc oxide Stearic acid n-phenyl-p-phenylenediamine Wax

100 parts 2 5 40 10 5 3 20 20 2.5 1 1 quantum satis

43 parts 57 5 32.2 3 5 1 1 3

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Plasticizers Use and Selection for Specific Polymers

Titanium dioxide Magnesium oxide Sulfur Benzothiazyl disulfide

5 13.3 0.96 1

Rail support rubber mixture:11 Natural rubber Styrene-butadiene rubber Soot N 550 Aromatic plasticizer Stearic acid Dihydroquinoline derivative p-phenylene-diamine derivative Sulfonamide accelerator Zinc oxide Sulfur

40.0 wt% 20.0 25.0 8.0 1.6 0.3 0.5 0.7 2.4 1.5

Vehicle vibration-damping devices:12 Natural rubber SMR20 Paraffinic oil (Flexon 815) Carbon black N550 Process aid (Struktol WB 212) Zinc oxide Antioxidant (Flectol H) Stearic acid Antioxidant ZMTI Coagent (Sartomer 350) Sulfur Peroxide (Vulkup 40

100 parts 1.5 27 3 5 0.4 1 0.6 3 1 6

References 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

US Patent 6,093,756. Shershnev V A; Goncharova L T, Intl. Polym. Sci. Technol., 22, No.5, 1995, p.T/32-3. Barlow F W, Rubber Compounding. Principles, Materials, and Techniques, Second Edition, Marcel Dekker, New York, 1993. Brydson J A, Rubbery Materials and Their Compounds, Elsevier Applied Science, London, 1988. US Patent 6,448,306. US Patent 6,363,989. US Patent 6,358,580. US Patent 6,197,885. US Patent 6,063,853. US Patent 5,904,220. US Patent 5,735,457. US Patent 5,571,883. US Patent 5,532,312. US Patent 5,482,993. US Patent 6,140,450. Krishen, A; Schafer, MA, Reference Module in Chemistry, Elsevier, 2013, pp. 250-7. Phaechamud, T; Issarayungyuen, P; Pichayakom, W, Int. J. Biol. Macromol., 85, 634-44, 2016. Pichayakorn, W; Suksaeree, J; Boonme, P; Amnuaikit, T; Taweepreda, W; Ritthidej, G C, J. Membrane Sci., 411-412, 81-90, 2012.

11.57 Rubber, natural

19 20

21 22 23

457

Dastidar, A G; Mundra, M; Mauer, B R; Zhang, X, WO2014149723, Dow Global Technologies LLC, Sep. 25, 2014. Kaewsakul W, Noordermeer JWM, Sahakaro K, Sengloyluan K, Saramolee P, Dierkes WK, Blume A, Natural rubber and epoxidized natural rubber in combination with silica fillers for low rolling resistance tires in Chemistry, Manufacture, and Application of Natural Rubber, 2nd Ed., Woodhead Publishing in Materials, 2021, pp. 247-316. Avirah SA, Dileep U, MaterialsToday, Proc., 25, 2, 169-72, 2020. Tardiff JL, Barrera-Martinez CS, Cornish K, Ren X, US20200308375A1, Ford Motor Co, Oct. 1, 2020. Armada D, Llompart M, Celeiro M, Garcia-Castro P, Ratola N, Dagnac T, de Boer J, Sci. Total Environ., 812, 152542, 2022.

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Plasticizers Use and Selection for Specific Polymers

11.58 SILICONE 11.58.1 FREQUENTLY USED PLASTICIZERS • hydroxyl end-blocked polysiloxane4 in silicone rubber sponge,12,15 in silicone sealant, at room temperature vulcanizing composition,19 and in pressure-sensitive adhesive38 • dimethylsiloxane oligomer end-blocked with silanol in silicone composition,17 in RTV silicone,18 in provisional dental reconstructive materials,21 in sealant compositions,22 in alkoxy-crosslinking RTV silicone rubber,25 in continuously manufactured silicone rubber compositions,26,30 in silicone sealants,27,29 in heatcurable compositions,31 in liquid compositions,32 and in compositions for injection molding34 • hydroxy-terminated polydimethylsiloxane in fire-resistant silicone vulcanizates6 and in filler containing compositions13 • silicone oil of molecular weight lower than 7000 daltons,9 in slip control films,10 and in compatibilized blends with polyamide (polyamide is further plasticized with either phthalates or trimellitates)11 • phthalates (alkyl or alkyl-aromatic) in room temperature vulcanizing compositions19 • polyisobutylene in room temperature vulcanizing compositions19 • low viscosity silicone oil in cosmetics33 • tripropylene glycol monoethyl ether in cosmetic compositions7 • ethylene or propylene glycol in hair styling compositions20,23 • glycerin in hair styling compositions20,23 • glycerin in the form of droplets mixed-in37 • dioctyl sebacate1 • di-(2-ethylhexyl) phthalate3 • di-(2-ethylhexyl) adipate3 in hair styling compositions16 and in custom-fitting articles35 • tricresyl phosphate3 • diethylene glycol dibenzoate3 • acetyl triethyl citrate in hair styling compositions16 • trialkyl citrates in hair styling compositions7,24 • epoxidized soybean oil in custom-fitting articles35 • 9-methylenenanodecane, 2-decyl-2-octyloxirane in construction and automotive sealants36 Products, which eventually cure to form silicone rubber, use low molecular weight polysiloxanes as plasticizers. These may have different names, such as, for example, the first four materials on the above list, which are non-reactive low viscosity liquids. The viscosity of some silicone plasticizers is as low as 10-30 cps (or mPas). In cosmetics, ester-type plasticizers are used or plasticizers, which have hydrophilic properties thus additionally acting as the so-called humectants, which bring moisture to the formulation. Many common organic plasticizers can also be used in rubber formulation as listed above.

11.58 Silicone

459

11.58.2 PRACTICAL CONCENTRATIONS • hydroxyl endblocked polysiloxane: 2.6 phr4 and 10 phr17 • hydroxyl-terminated polydimethylsiloxane: 5 wt%6 • silanol endblocked polysiloxane: 5-50 parts per 100 parts of silica filler,11 up to 15 wt%,14 3-30 wt%,19 15-30 wt,21 up to 25 wt%,22 up to 20 wt%,24 up to 25 wt%,25 up to 40 wt% per 100 parts of reinforcing silica,26 10 wt%,27 7 wt% (silica filler was silane treated),29 10 wt%,30 3 phr,31 and 30 phr32 • silicone oil: up to 25 wt% in adhesive composition38 • dioctyl sebacate: 8 wt%1 • di(2-ethylhexyl) adipate: 4-6 phr3 • di-(2-ethylhexyl) phthalate: up to 50 phr3 and 15 phr35 • tricresyl phosphate: 30 phr3 • diethylene glycol dibenzoate: 30 phr3 • tripropylene glycol monomethyl ether: 10 phr7 • acetyl triethyl citrate: 0.05-1 wt%16 The amount of polysiloxane-based plasticizer depends on the combination of factors, including designed modulus of rubber, amount of silica filler, type of silica filler (treated or untreated with silane). 11.58.3 MAIN FUNCTIONS PERFORMED BY PLASTICIZERS • reduction of viscosity8,18,20 • improvement of flow properties9,19,24 • reduction of creep hardening26 • increase level of dispersion27 • reduction of modulus4 • reduction of rubber hardness19 • dilution and expansion of rubber network21 • densification of filler9 • improvement of silica filler compatibility12,15 • make material heat meltable28 • improvement of storage stability of sealants24 • reduction of cost21 • hair style retention and restyling capability20 • water affinity37 of glycerin droplet-containing elastomer 11.58.4 EFFECT OF PLASTICIZERS ON POLYMER AND OTHER ADDITIVES Figure 11.58.1 shows that silicone rubber responds to plasticization in a similar manner as other polymers. Modulus and elongation increase with the amount of plasticizer increase, and tensile strength is decreased with increased addition of plasticizer. Plasticizer type plays some role, but all tested plasticizers have similar compatibility with polymer (Figure 11.58.2). The addition of ester-type plasticizers to silicone formulation increased UV absorption and UV degradation rate of rubber.3 To improve elastic properties of silicone elastomer, a silicone plasticizer was selected, such as trimethylsiloxy-terminated polydimethylsiloxanes having a viscosity from 35 to 1000 mPa·s at 23°C.39

460

Plasticizers Use and Selection for Specific Polymers

Figure 11.58.1. Effect of the amount of di-(2-ethylhexyl) phthalate on modulus of plasticized silicone rubber. [Data from Hayashida A, Mori S, Tabei E, US Patent 5,804,257.]

Figure 11.58.2. Effect of plasticizer type on modulus of plasticized silicone rubber. TCP − tricresyl phosphate, DEGDB − diethylene glycol dibenzoate, DOP − di-(2-ethylhexyl) phthalate. [Data from Hayashida A, Mori S, Tabei E, US Patent 5,804,257.]

An antistatic adhesive comprising a base polymer, crosslinker, filler, adhesion promoter, catalyst, and plasticizer.40 The base polymer includes vinyl-terminated silicone oil composites.40 The filler includes white carbon black, quartz powder, calcium carbonate, aluminum oxide, zinc oxide, titanium dioxide, aluminum hydroxide, magnesium hydroxide, carbon black, and/or iron black.40 The crosslinker includes siloxane compounds.40 The adhesion promoter includes silanes.40 The catalyst includes titanate chelate.40 The plasticizer includes hydrogenated silicone oils.40

11.58.5 TYPICAL FORMULATIONS Skin cleaning agent:8 Myristic acid Palmitic acid Stearic acid Beeswax Polyethylene glycol 6000 Ethylene glycol distearate Coconut oil fatty acid diethanolamide Glycerin Potassium hydroxide Purified water Sodium N-lauroylsarcosine Tabular powder of organic silicone resin Face powder (the so-called Pan-Cake):8 Titanium oxide Kaolin Talc

15 wt% 5 3 3 2 2 3 15 5 35 10 2

5 wt% 5 52

11.58 Silicone

461

Zinc myristate Iron oxide red Iron oxide yellow Iron oxide black Tabular powder of organic silicone resin Porous globular silica Squalane Glyceryl trioctanoate Antiseptic Perfume

5 0.7 2.1 0.2 15 10 3 2 proper proper

Hair spray:16 Non-silicone polymer Silicone grafted polymer Isododecane Triethyl citrate Propylene glycol Potassium hydroxide Perfume Water Ethanol Propellant (isobutane) Propellant (hydrofluorocarbon 152)

1 wt% 2.5 2 0.21 0.02 0.32 0.10 8 62.85 7.02 15.98

Silicone sealant with increased work time:27 Base polymer 58 parts 15 CaCO3 10 SiO2 Crosslinker (ethyltriacetoxysilane 4.80 Catalyst 0.0257 Plasticizer 10.00 Adhesion promoter 1.17 Pigment 1.00 Tooling time − 180 s Silicone sealant with improved high temperature adhesion:29 Polydimethylsiloxane having a viscosity of 50,000 cps 55 parts Calcium carbonate treated with stearic acid 15 Fumed silica reinforcing filler treated with cyclic polydimethylsiloxane15 Ethyltriacetoxysilane crosslinking component 5.2 Dibutyl tin dilaureate tin condensation cure catalyst 0.033 Iron carboxylate salt 0.5 Polydimethylsiloxane linear plasticizing fluid 7 Di-t-butoxydiacetoxysilane adhesion promoter 1.27 Carbon black pigment 1

462

Plasticizers Use and Selection for Specific Polymers

References 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40

Mowery K A; Meyerhoff M E, Polymer, 40, No.22, 1999, p.6203-7. Zuevy S, Intl. Polym. Sci. Technol., 26, No.1, 1999, p.t/13-9. US Patent 5,804,257. US Patent 5,844,038. US Patent 5,776,614. US Patent 6,443,049. US Patent 6,432,418. US Patent 6,399,081. US Patent 6,391,234. US Patent 6,376,067. US Patent 6,362,288. US Patent 6,346,556. US Patent 6,323,262. US Patent 6,319,982. US Patent 6,300,384. US Patent 6,248,316. US Patent 6,239,205. US Patent 6,235,832. US Patent 6,172,150. US Patent 6,149,898. US Patent 6,121,362. US Patent 6,114,438. US Patent 6,113,883. US Patent 6,111,003. US Patent 6,020,449. US Patent 6,017,996. US Patent 5,948,853. US Patent 5,939,477. US Patent 5,932,650. US Patent 5,912,287. US Patent 5,883,171. US Patent 5,880,199. US Patent 5,725,882. US Patent 5,607,992. US Patent 5,555,584. Ikeda Y, Kashiwamura T, Takeuchi K, US Patent 8,017,677 B2, Idemitsu Kosan, Sep. 13, 2011. Mazurek, P; Hvilsted, S; Skov, A L, Polymer, 87, 1-7, 2016. Wibaux, A M; Van, V, EP2750723, Avery Dennison Corporation, Jul. 9, 2014. Hechtl W, US20210277238A1, Sep. 9, 2021. WO2020206797A1, Oct. 15, 2020.

11.59 Styrene-butadiene rubber

463

11.59 STYRENE-BUTADIENE RUBBER 11.59.1 FREQUENTLY USED PLASTICIZERS Styrene-butadiene rubber, SBR, is compatible with all mineral oils but has limited compatibility with paraffinic oils. • elastomer plasticizers, such as rosin esters in chewing gum1,4,5 • terpene resins derived from α-pinene, β-pinene, or d-limonene in chewing gum1,4,7 • aromatic mineral oil (Renopal 450) in vulcanizable rubber compounds2 and in rubber mixture for rail support6 • paraffinic mineral oil (Flexon 395) in rubber composition containing waste polymers7 • process oil (PW380 manufactured by Idemitsu Kosan Ltd.) in outsoles3 • modified soybean oil8 in environment-friendly compound 11.59.2 PRACTICAL CONCENTRATIONS • 10 to 30 phr in chewing gum1,4,5 • mineral oils: aromatic − 8 phr2,6; paraffinic − 2-10 phr7 11.59.3 EFFECT OF PLASTICIZERS ON POLYMER AND OTHER ADDITIVES Silanized plasticizer was chemically derived and synthesized from soybean oil co-vulcanized with bis-(3-(triethoxysilyl)-propyl) tetrasulfide by using the sulfur-accelerated curing system and used in styrene-butadiene rubber/silica composites.9 Silanized plasticizer promoted plasticizing and reinforcing effects in SBR composites.9 11.59.4 TYPICAL FORMULATIONS Outsoles of shoes:3 SBR Filler Silane coupling agent (Si69) Plasticizer (process oil) Zinc oxide Stearic acid Stabilizer (Nocrac 200) Sulfur Accelerator (Nocceler NS) Rubber compound for rail support:6 Natural rubber SBR Soot N 550 Aromatic plasticizer Stearic acid Dihydroquinoline derivative p-phenylene-diamine derivative

100 parts 50 5 5 3 1 2 2 1

40 wt% 20 25 8 1.6 0.3 0.5

464

Plasticizers Use and Selection for Specific Polymers

Sulfonamide accelerator Zinc oxide Sulfur

0.7 2.4 1.5

References 1 2 3 4 5 6 7 8 9

US Patent 6,399,721. US Patent 6,359,045. US Patent 6,335,392. US Patent 6,242,553. US Patent 6,235,319. US Patent 5,735,457. US Patent 5,510,419. Li, J; Isayev, A I; Ren, X; Soucek, M D, Polymer, 60, 144-56, 2015. Hassan AA, Formela K, Wang S, Compos. Sci. Technol., 197, 108271, 2020.

11.60 Styrene-butadiene-styrene rubber

465

11.60 STYRENE-BUTADIENE-STYRENE RUBBER 11.60.1 FREQUENTLY USED PLASTICIZERS • white mineral oil in hot melt adhesive1,3 • aromatic-free oils in sealants4 • asphalt in low-cost sealant and paving applications4 • dibutyl or dioctyl phthalate in shrink film2 • mineral oil in hot melt, positioning adhesive5 11.60.2 PRACTICAL CONCENTRATIONS A simple swelling test can be used to check the amount of oil, which plasticizes formulation, but would not likely bleed out. Resin samples are allowed to swell to equilibrium, and half of the amount of absorbed oil is used in the application.4 • white mineral oil: 18-20 wt%2,3 and 20 phr4 • phthalates: 8 wt%2 11.60.3 MAIN FUNCTIONS PERFORMED BY PLASTICIZERS • increasing tack together with tackifying resin1,3 • effect on temperature at which films begins to shrink2 • decrease hardness and modulus4 • reduce melt and solution viscosity4 • improve compounding4 • decrease cohesive strength or increase plasticity4 11.60.4 EFFECT OF PLASTICIZER ON POLYMER AND OTHER ADDITIVES The high-grade asphalt concrete composition comprises 0.01-5 parts by weight of a styrene-butadiene-styrene block copolymer; 10-20 parts by weight of a styrene-isoprene-styrene block copolymer; 0.01-5 parts by weight of an acrylonitrile-butadiene-styrene resin; 10-40 parts by weight of aged rubber powder obtained by mixing waste rubber powder of which a surface is activated with a plasticizer at a weight ratio of 1:1 and aging the mixture at a temperature of 150-175°C for 50-70 minutes.6 The plasticizer is diisononyl isophthalate and citric acid ester in the ratio of 1 to 1.6 References 1 2 3 4 5 6

US Patent 6,486,229. US Patent 6,255,388. US Patent 5,750,623. Kraton polymers for adhesives and sealants, Shell Chemical Company, SC:198-97. Stafeil, K; Gerschke, K; Gerarden, K, WO2015109160, Bostik, Inc., Jul. 23, 2015. KR102011916B1, Oct. 22, 2019.

466

Plasticizers Use and Selection for Specific Polymers

11.61 STARCH Starch is used today in a large number of products with very diverse properties. The roles played by starch include load-bearing polymeric material, a component of biodegradable blends, a filler of biodegradable materials, and even a role of plasticizer. Its popularity stems from low price, being a renewable source, being a familiar component of the natural environment, and as such easily convertible by natural means, chemically reactive, and compatible with many materials.

11.61.1 FREQUENTLY USED PLASTICIZERS • glycerin4,13 in polymer blend with polyurethane,1 in a blend with polyvinyl alcohol,6 in blends with polyethylene or polypropylene,8 in extruded film,9,55,63-64,67 in plastic sheets,11,52 in pet chew,18 in gel capsules,20,23,26 in the thermoplastic composition,22 in biodegradable plastics,24,36 in biodegradable fibers,24 in wood fiber reinforced starch,27-28 in protective coating for fresh produce,39 in biodegradable cigarette filter,32 in biodegradable non-woven fabric,33 in food and beverage containers,35,39 in cellular plastics for containers,37 in foamed starch,42 in shortening substitute,45 in materials which stimulate plant growth,46 and in starch products57 • glycerol ester in biodegradable material20 • xylitol in extruded goods50-52 and film55 • sunflower oil in a blend with polyethylene7 • vegetable oil in film-forming composition which promotes seed germination44 • soybean oil in pharmaceutically active agent19 • sorbitol in extruded film,9 in biodegradable material,20 in gel capsules,21,23 in biodegradable fibers,25 and in food and beverage containers35,39 • sorbitol acetate in biodegradable plastics24,36 • poly(ethylene glycol)2 in food and beverage containers35,39 • propylene glycol16 in film-forming composition which promotes seed germination44 • tributyl acetyl citrate in biodegradable hunting and shooting cartridges30 • triacetin in materials having cellular matrix for beverage containers41 • diethylene glycol dibenzoate and dipropylene glycol dibenzoate 50/50 weight blend (Benzoflex 50) in adhesive for non-woven fabrics47 • succinate polyester in moisture barrier coatings3 • polyester of polyethylene glycol and adipic or succinic acid in moisture barrier coatings31 and in release coatings34 • polyol in compatibilization of starch with various polymers43 • polyvinylalcohol in starch foams for absorbent articles49 • starch as a plasticizer in the manufacture of building panels48 • hydroxyalkylformamides53 • formamide55 • N-(2-hydroxypropyl) formamide and N-(2-hydroxyethyl) formamide • ethanolamine, diethanolamine, and ethyl formate54 • 1-ethyl-3-methylimidazolium acetate58 • isosorbide59,62 renewable-resource, solid plasticizer

11.61 Starch

467

• imidazole-based deep eutectic plasticizers/solvents60 • urea61 in fertilizer production Plasticizer selection depends on material application, with special attention given to its water resistance. In biodegradable and other similar materials, water must be permitted to penetrate the material structure and thus help in the biological digestion of material. In these applications, glycerin and other similar compounds capable of attracting moisture are used. This provides products with the benefit of water acting as co-plasticizer, effectively reducing the amount of organic plasticizer. If water barrier or water resistance properties are required, hydrophobic materials are needed as those placed towards the end of the list. Still, care is taken that plasticizers are environmentally friendly to make the entire product compatible with the environment.

11.61.2 PRACTICAL CONCENTRATIONS • glycerin: 0.1-5 wt%,29 0.5 wt%,45 2 wt%,33 3-7 wt%,22 10-40 wt%,26 16.9 wt%,18 15-30 wt%,46 33 wt%,9 or 25-75 wt%21 • vegetable oils: 0.1 wt%,7 0.5%,19 or 6.25 wt%44 • sorbitol: 35 wt%42 • tributyl acetyl citrate: 3 wt%30 • triacetin: 5-25 wt%40 • diethylene glycol dibenzoate and dipropylene glycol dibenzoate 50/50 weight blend: 2-30 wt%46 • poly(ethylene glycol): 30-40 wt%2 • polyester plasticizer: 5-25 wt%,3,31,34 33 phr,3 or 57 phr1 11.61.3 MAIN FUNCTIONS PERFORMED BY PLASTICIZERS • decrease in glass transition temperature of starch10 • increase in flexibility and decrease in brittleness on plasticized material27 • influence on moisture absorption rate and equilibrium1 • at smaller concentration may cause antiplasticization (glycerin)13 • influence on thermal degradation properties (effect of both type and concentration).15 In some controlled processes the thermal degradation of starch in the presence of plasticizer is called as thermomechanical digestion46 • strong interaction with starch (glycerol molecules are immobilized as determined by NMR)4 • increase in biodegradation rate caused by environmental exposure (e.g., vegetable oil, tributyl acetyl citrate, etc.)7,16,30,32-33 • some plasticizers (e.g., glycerin) play role of humectant28,41 • some plasticizers help to form moisture barrier (e.g., polyethylene glycol, polyester plasticizers, etc.)31 or prevent re-dispersibility of water in adhesive47 • starch acts as plasticizer in cement-containing formulations. It retards reaction of setting by removing majority of moisture. Starch also helps to create small air bubbles which increase insulation value of building panels48 11.61.4 EFFECT OF PLASTICIZERS ON POLYMER AND OTHER ADDITIVES Figure 11.61.1 shows that the glass transition temperature of starch films plasticized with glycerin is a linear function of plasticizer concentration. Glass transition temperature is around room temperature at a plasticizer concentration of about 15 wt%. Figure 11.61.2

468

Figure 11.61.1. Glass transition temperature of starch films plasticized with variable amounts of glycerin. [Data from Lourdin D; Bizot H; Colonna P, J. Appl. Polym. Sci., 63, No.8, 22nd Feb.1997, p.1047-53.]

Plasticizers Use and Selection for Specific Polymers

Figure 11.61.2. Water content in starch plasticized by glycerin at different relative humidities and concentrations of plasticizer. [Data from Lourdin D; Coignard L; Bizot H; Colonna P, Polymer, 38, No.21, 1997, p.5401-6.]

shows the relationship between elongation of starch films plasticized with glycerin versus concentration of plasticizer. Figure 11.61.2 indicates antiplasticization-like behavior. At lower concentrations of plasticizer, the elongation decreases up to 12 to 17 wt% of glycerin to increase rapidly. A combination of data from Figures 11.61.1 and 11.61.2 seems to offer an explanation.13 At room temperature, material is in a brittle state if the concentration of plasticizer is below ~15%. A small decrease in elongation noted up to 12 wt% of plasticizer is most likely due to gradually increased crystallization facilitated by increased chain mobility and interactions in the presence of plasticizer. After passing through the minimum, elongation rapidly Figure 11.61.3. Elongation of starch films plasticized with variable amounts of glycerin. [Data from Lourdin increases because polymer (starch) changes D; Bizot H; Colonna P, J. Appl. Polym. Sci., 63, No.8, behavior from brittle to ductile. 22nd Feb.1997, p.1047-53.] The addition of increased amounts of glycerin increases moisture absorption (Figure 11.61.3). The equilibrium moisture depends on both plasticizer concentration and relative humidity of the surrounding atmosphere.13 It is also noticeable that starch without plasticizer behaves differently (lower rate of moisture increase at different relative humidities). This indicates that glycerin controls

11.61 Starch

469

moisture absorption in plasticized samples. The presence of glycerin seems more important than its concentration. Traditional screw extruders based on shear deformation cannot disperse plasticizer evenly and plasticize the starch well, which affects the comprehensive mechanical properties.65 The elongational rheology produced during processing in biaxial eccentric rotor extruder promoted the dispersion of glycerol in starch and improved the melt-plasticizing effect of thermoplastic starch, and the comprehensive mechanical properties of the thermoplastic starch prepared by biaxial eccentric rotor extruder were excellent with elongation at break of 226.1%.65 Plasticized starch-based film was loaded with chitosan nanoparticles as a reinforcing and antibacterial agent.66 Numerous plasticizers, including sorbitol, glycerol, and water, are used to obtain thermoplastic starch and glycerol and water were used in this development.66

11.61.5 TYPICAL FORMULATIONS Edible pet chew:18 Soy protein Wheat gluten Gelatin Corn starch Garlic powder Onion powder Lecithin Turkey powder Chicken powder CaCO3 Tricalcium phosphate Water Glycerol

15.55 parts 15.55 8.5 25.4 1.1 1.1 0.6 2.8 2.8 0.6 0.6 8.47 16.9

Film-forming composition for soft capsules:23 Iota-carrageenan 6-12 wt% in wet film Modified starch 12-30 Plasticizer 5-30 Buffer 0.5-2 Preservative 0-0.2 Biodegradable polymeric composition:24 Starch with 12 wt% water 40.5 Poly(ethylene vinyl alcohol) 30.4 Poly(ethylene acrylic acid) 4.3 Erucamide 0.25 Plasticizer* 21.5 Fluidizer** 3.1 *sorbitol acetate 65.5 wt% + water 14 wt% + glycerine 0.5 wt% **sorbitol ethoxylate trioctadecanoate

470

Plasticizers Use and Selection for Specific Polymers

Biodegradable fiber:25 Starch Sorbitol Glycerol Thermoplastic starch Water Polyamide

38.2 weight parts 12.8 8.5 54.5 400 plastic-related and >3500 dishwasher-related compounds has been tested in extensive studies.19 One of the plasticizers detected in all plastic bottles was laurolactam, the monomer of polyamide-12.19 Polyamide-12 is used for films in packing material in the food industry.19 When added to polyethylene films, it improves water vapor permeability and aroma impermeability.19 The peak intensity was higher in the used bottles compared with the new bottles.19 Tris-(2-butoxyethyl) phosphate was detected in the used bottles, with 50% higher peaks after dishwasher than after flushing.19 TBEP is a flame retardant but also primarily plasticizer for most resins and elastomers.19 It is a light-stable plasticizer intended for contact with food or drink.19 Isopropylmyristate is also a plasticizer, detected in all four used plastic bottles after additional flushing, but only in one of the red bottles directly after the dishwasher.19 The plasticizer tributyl phosphate was detected only in the red bottles, with 50% peak intensity decrease after additional flushing.19

References 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Guisto-Norkus R; Gounili G; Wisniecki P; Huball J A; Ruven Smith S; Stuart J D, J. Chem. Education, 73, 12, 1996, p.1176-78. Kumar R, Amer. Lab., Nov. 1999, p.32-35. Das V T; Manura J J; Hartman T G, Volatile organic compounds from electron beam cured and partially electron beam cured packaging using automated short path thermal desorption, PittaCon99 Meeting, Orlando, FL, March 1999. Stringer R; Labunska I; Santillo D; Johnston P; Siddorn J; Stephenson A, Environ. Sci., Pollut. Res., 7, 2000, p.1-10. Ehara Y; Sakamoto K, Anal. Sci., 16, March 2000, p.283-86. EPA. Method 525.1 Determination of Organic Compounds in Drinking Water by Liquid-Solid Extraction and Capillary Column Gas Chromatography/Mass Spectrometry, May 1991. EPA. Method 625 - Base/Neutrals and Acids. Office of the Federal register, National Archives and Administration, Beman, Lanham, MD, 40 CFR Chapter 1, 1995, p.821-48. Gimeno, P; Thomas, S; Bousquet, C; Maggio, A-F; Civade, C; Brenier, C; Bonnet, P-A, J. Chromat. B, 949-950, 99-108, 2014. Germinario, G; van der Werf, I D; Sabbatini, L, Microchem. J., 124, 929-39, 2016. Kozlowski R R; Gallagher T K, J. Vinyl Additive Technol., 3, September 1997, p.249-55. ASTM D2124-99. Standard Test Method for Analysis of Components in Poly(vinyl chloride) Compounds Using Infrared Spectrophotometric Technique. Saviello, D; Toniolo, L; Goidanich, S; Casadio, F, Microchem. J., 124, 868+77, 2016. Kumar A; Camenzind M J; Chargin C J, Identifying organic contaminants in ultrapure water at sub-parts-per-billion levels,18th Annual Semiconductor Pure Water and Chemicals Conference, Santa Clara, CA, March 1999. Park H-M; Kim Y-M; Cheong C S; Ryu J-C; Lee D W; Lee K-B, Anal. Sci., 18, April 2002, p.477-79. Lever T J; Price D M; Warrinton S B, Evolved gas collection from a thermogravimetric analyzer and identification by gas chromatography-mass spectrometry, Proc. 28th Conf. North amer. Thermal Analysis Soc., October 4-6, 2000, Savannah, GE. Rothenbacher T, Schwack W, Rapid Commun. Mass Spect., 23, 2829-35, 2009. Self R L, Wu W-H, Food Control, 25, 13-16, 2012. Kuki A, Nagy L, Zsuga M, Keki S, Int. J. Mass Spect., 303, 225-28, 2011. Tisler S, Christensen JH, J. Hazardous Mater., in press, 128331, 2022. Akoueson F, Chbi C, Monchy S, Paul-Pont, I, Doyen P, Dehaut A, Duflos G, Sci. Total Environ., 773, 145073, 2021.

670

Specialized Analytical Methods in Plasticizer Testing

15.2 METHODS OF DETERMINATION OF PLASTICIZER CONCENTRATION Plasticizers are not chemically bound in most cases thus they can be separated by either extraction or evaporation. Then selection of solvents for extraction includes the following factors:2 • safety • the high solubility of plasticizers • minimum solubility of the matrix polymer. In earlier studies, chlorinated solvents (methylene chloride or carbon tetrachloride) and ethyl ether were used due to their excellent abilities to partition a large spectrum of plasticizers. Today, hexane1 or its 1:1 mixture with methanol2 is likely to be used for extraction. It is also important to increase the surface area of the sample and its contact with a solvent. This is best achieved by cryogenic grinding and sonication.1 With this technology of plasticizer extraction, 79.6 to 99.5% of plasticizers were recovered from the blank matrix and 55 to 94% from spiked samples. Plasticizer recovery was also carefully evaluated in water samples containing 0.2 ppb.3 43 to 97% of the original quantity of plasticizer was determined by TD-GC-MS.3 This decreased with duration before analysis and increased with alkane chain length increased.3 The precision of determination depends on the entire procedure used. Twenty laboratories in 13 countries tested their abilities to determine di-(2-ethylhexyl) phthalate and diisononyl phthalate.4 They used methods typical of a particular laboratory. Most laboratories used GC/MS, but liquid chromatography and gravimetric analysis were also used. Plasticizers were mostly extracted in Soxhlet apparatus using different solvents such as diethyl ether, dichloromethane, chloroform, carbon tetrachloride, or their mixtures with methanol. In a few cases, samples were dissolved in tetrahydrofuran and precipitated with acetonitrile or dissolved in dimethylacetamide and precipitated with methanol. For sample containing 17% of di-(2-ethylhexyl) phthalate, the mean value was 16.79, and most results (14) oscillated between 15 and 17.5%; the remaining six results were outside this range, and there was no detectable pattern explaining why results differed. For diisononyl phthalate, 44% of laboratories had very large errors of determination. This shows that large discrepancies are possible between results, and this cannot be explained by differences in methods since most methods followed requirements of ASTM D 3421, and thus procedures were not so different.4 Depth profiling studies were conducted using Raman mapping. Microscope attachment was capable of analyzing sample with a spatial resolution of 2 μm3.5 PVC/DOP ratio was determined by scanning surface under C−Cl peaks between 590 and 750 cm-1 for PVC and under C=O peak at 1726 cm-1 for plasticizer.5 Thermogravimetric, TGA, studies conducted under vacuum show that it is possible to determine plasticizer with reasonable precision in polyamide and PVC.6 Gravimetric determination of plasticizer by Soxlet extraction from polyamide gave 13.86% plasticizer compared to 12.40, 13.41, and 13.77% obtained by TGA analysis performed under different conditions. High-resolution GC-MS was used to determine adipates, sebacates, and phthalates in olive oil.7 LC-MS/MS was used to determine phosphate plasticizers in urine,8 and FT-

15.2 Methods of determination of plasticizer concentration

671

Raman in determining adipates in PVC samples.9 Attenuated total reflectance-mid infrared spectroscopy coupled with independent components analysis was used as a fast method to determine plasticizers in polylactide.10 The application of plastic mulching film greatly improved dryland productivity, but the release of phthalate esters from the plastic film has generated concern.11 The effects of mulched plastic film and residual plastic film on the phthalate esters concentrations in the soil-crop system were studied.11 Soil and plant samples were freeze-dried.11 The dried soil and plant samples were ground and passed through a 0.15 mm stainless steel sieve.11 Dried soil samples (5 g), dried maize roots (3.0 g), dried maize stems and leaves (4.0 g), dried maize grains (4.5 g), and dried potato tubers (5.5 g) were used for the phthalate esters determination.11 15 phthalate esters present in samples were analyzed by gas chromatography-mass spectrometry.11 The limitation of detections and limit of quantification were 0.07-1.84 μg/L and 0.22-6.17 μg/L, respectively, and the recovery rates of target phthalate esters were 81.1%-108.7% in soil, 77.0%-103.3% in maize roots, 76.1%103.4% in maize shoots, 79.5%-101.4% in maize grains, and 75.7%-90.2% in potato tubers.11

References 1 2 3 4 5 6 7 8 9 10 11

Stringer R; Labunska I; Santillo D; Johnston P; Siddorn J; Stephenson A, Environ. Sci., Pollut. Res., 7, 2000, p.1-10. Kozlowski R R; Gallagher T K, J. Vinyl Additive Technol., 3, September 1997, p.249-55. Kumar A; Camenzind M J; Chargin C J, Identifying organic contaminants in ultrapure water at sub-parts-per-billion levels,18th Annual Semiconductor Pure Water and Chemicals Conference, Santa Clara, CA, March 1999. Starink R J; Visser R G; Audier M, Results of Proficiency Test. Phthalates in PVC. Institute for Interlaboratory Studies, Dordrecht, the Netherlands, April 2002. Mura C; Yarwood J; Swart R; Hodge D, Polymer, 41, No.24, 2000, p.8659-71. Affolter S; Schmid M; Wampfler St.Gallen B, Kautchuk Gummi Kunststoffe, 52, Nos.7-8, July/Aug.1999, p.519-28. Dugo G, Fotia V, Lo Turco V, Maisano R, Potorti A G, Salvo A, Di Bella F, Food Control, 22, 982-88, 2011. Reemtsma T, Lingott J, Roegler S, Sci. Total Environ., 409, 1990-93, 2011. Berg R W, Otero A D, Vibrational Spec., 42, 222-5, 2006. Kassouf, A; Ruellan, A; Jouan-Rimbaud Bouveresse, D; Rutledge, D N; Domenek, S; Maalouly, J; Chebib, H; Ducruet, V, Talanta, 147, 569-80, 2016. Wang D, Xi Y, Shi X-Y, Zhong Y-J, Guo C-L, Han Y-N, Li F-M, Environ. Pollution, 286, 117546, 2021.

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Specialized Analytical Methods in Plasticizer Testing

15.3 DETERMINATION OF VOLATILITY, MOLECULAR MOTION, DIFFUSION, AND MIGRATION Sublimation and evaporation are zero-order processes. Under isothermal conditions, the rate of mass loss is expected to be constant if the free surface area does not change.1 Langmuir equation for free evaporation relates the rate of mass loss to the vapor pressure: dm M – -------- = pα -------------dt 2πRT

[15.3.1]

where: m t p α M R T

mass time vapor pressure vaporization coefficient molecular mass gas constant absolute temperature

Knowledge of vapor pressure helps in the estimation of the volatility of plasticizers. It is therefore important to find a method of determination that is precise, easy to handle and uses commonly available equipment, such as, for example, thermobalance. A quick and simple method was developed to determine vapor pressure at different temperatures using thermobalance.1 Figure 15.3.1 shows the data measured by the method and data from other studies. It is evident that data are obtained with high precision. Details of the method and the use of modulated temperature programs are described.1 Concentrated polymer systems containing plasticizers show the existence of slow and fast relaxations, which are temperature-dependent. Slow motions are characteristic of polymer. Fast reorientations are characteristic of relatively small molecules of plasticizers.2 The dynamics of molecules and their rates of motion can be Figure 15.3.1. Vapor pressure of di-(2-ethylhexyl) phthalate at different temperatures, measured by therestimated based on the results of polarized mogravimetric method (as indicated) or found in litera- and depolarized light scattering and dielecture. [Data from Price D M, J. Thermal Analysis tric spectroscopy.2 Calorimetry, 64, No.1, 2001, p. 315-22.] Diffusion of plasticizer and effect of plasticizer on the diffusion of other components of formulation can be studied by various methods.3 The crudest method involves immersion of a slab of polymeric material in a plasticizer and determination of weight gains in time intervals. Depth profiling gives the concentration of plasticizer or additive at varying depth from the material surface. These studies can be conducted using stacked films, thin slices, or diagonal slices.4 These specimens were measured by FTIR with ATR or microscopic attachments. Sometimes it is convenient to use Raman microscopic depth profiling.3

15.3 Determination of volatility, molecular motion, diffusion, and migration

673

Migration measurements are complicated by the presence of additional media into which plasticizer migrates. These media have complex and variable compositions because they are either food products or various body fluids (saliva, blood, etc.). It is usually not very practical to study real materials, but simulants must be developed to resemble a group of products. Food products differ in composition, with special attention given to fats, solvents (e.g., alcohol), and acids because these components of food may increase absorption or extraction of plasticizers. In the evaluation of plasticizers for medical applications, interaction of plasticizer with body fluids and their components is important since it may affect biocompatibility (see more on this aspect in Section 13.18), but the actual extracting ability of body fluid is also important because it affects the quantity of migrated substance (see more on this aspect in Section 13.26). First attempts in the 1960s in the development of food simulants resulted in suggesting 10% water solution of ethanol and 3% of acetic acid. It was soon discovered that oils and fats are the most important in food simulants because migrating plasticizers must be replaced by compatible components of food simulants. Then heptane, diethyl ether, paraffin oil were used but gave substantially different results than real foods. Isooctane, ethanol, hexane, olive, and sunflower oils are in frequent use now to simulate fatty foods.5-8 In addition to better control of composition, simulants also make the analytical treatment of samples more precise. In some instances, the migration of plasticizers is tested on real foods. This is especially common in the case of packaging materials for solid foods.9 Testing of migration of plasticizer into body fluids may become complicated by numerous variables. This can be illustrated based on estimation of migration of di-(2-ethylhexyl) phthalate, DOP, into child saliva from chewable toys (additional information in Section 13.26).10 The saliva simulant having the following composition: sodium chloride 4.5 g potassium chloride 0.3 g sodium sulfate 0.3 g ammonium chloride 0.4 g urea 0.2 g lactic acid 3.0 g in 1000 ml of distilled water adjusted to pH=4.5 to 5 with 5M NaOH can be found in British Standard.11 In addition to the composition of saliva, temperature and time of exposure are selected (usually temperature of 37oC and time of 6 hours).10 Also, mechanical action is applied. This can be as simple as mixing of liquid surrounding the sample with the sample moving around the base of the beaker. It can be as complicated as a simulation of chewing action using glass dentures pressed to the tested film with the weight of 85 g and a frequency of 140 per minute. Shaking with a glass ball (small or large) and with plates was also used. Also, the proportion between saliva and sample and the shape and thickness of the sample are essential parameters. The results differed widely from 41 mg of DOP extracted per 1 g of film in static, six-hours test to 1006 mg of DOP extracted per 1 g of film in test with shaking plates. The repeatability of results within a single procedure was also not good. The influence of branching on the plasticizer migration behavior of heptyl succinate plasticizers blended with polyvinylchloride was evaluated.12 An increase in branching led

674

Specialized Analytical Methods in Plasticizer Testing

to a decrease in the migration of plasticizers into both hexanes and vegetable oil media.12 Quantitative 1H NMR method was used to identify plasticizer concentration in the leachates and compared to a gravimetric standard test method.12 The concentrated leachate was dissolved with 2 ml of an internal standard solution of 1,3,5-trimethoxylbenzene (10 mg/ ml) in deuterated chloroform (CDCl3), which was subsequently analyzed using 1H NMR.12 The quantitative 1H NMR proved to be a more direct method to assess leaching.12 In comparison to commercial plasticizer di-(2-ethylhexyl) phthalate, all branched species displayed superior migration resistance into hexanes (two to ten-fold).12 Samples 3×3 mm were put into three food simulants (water, ethanol, and heptane).13 The migration temperatures were set at 278 K, 288 K, and 298 K, respectively.13 The supernatants were used for analysis migration of DEHP plasticizer by the GC-MS.13 Combined experimental and molecular dynamic simulation was performed to understand the migration kinetics of DEHP.13 Plasticizer migration from childrens’ toys was measured by a variation of the European Commission's Joint Research Centre method.14 A punch press was used to cut three test disks from each sample.14 Typically, the surface areas of the test disks were between 10 and 13 cm2.14 Many disks featured irregular surfaces; in these cases, the surface areas were approximated. Samples were extracted with simulated saliva consisting of:14 0.82 mM magnesium chloride, MgCl2 1.0 mM calcium chloride, CaCl2 3.3 mM dipotassium hydrogen phosphate, K2HPO4 3.8 mM potassium carbonate, K2CO3 5.6 mM sodium chloride, NaCl 10 mM potassium chloride, KCl in deionized water and adjusted to pH 6.8 using dilute hydrochloric acid.14 Three disks from each sample were extracted two times each in 50 ml of simulated saliva in a 250 ml Schott Duran bottle for 30 min.14 Samples were analyzed using a modified GC-MS. Plasticizers identified by in the 38 PVC articles included acetyltributyl citrate; di (2-ethylhexyl) terephthalate; 1,2-cyclohexanedicarboxylic acid diisononyl ester; 2,2,4-trimethyl1,3-pentanediol diisobutyrate; di-(2-ethyhexyl) phthalate; and DINP.14 Half of the tested articles contained multiple plasticizers.14

References 1 2 3 4 5 6 7 8 9 10 11 12 13 14

Price D M, J. Thermal Analysis Calorimetry, 64, No.1, 2001, p.315-22. Rizos A K; Johnsen R M; Brown W; Ngai K L, Macromolecules, 28, No.16, 31st July 1995, p.5450-7. Eaton P; Holmes P; Yarwood J, Appl. Spectroscopy, 54, No.4, April 2000, p.508-16. Wypych G, Handbook of Material Weathering, 6th Edition, ChemTec Publishing, Toronto, 2018. Simoneau C; Hannaert P, Food Additives Contaminants, 16, No.25, 1st May 1999, p.197-206. Papaspyrides C D; Tingas S G, Food Additives Contaminants, 15, No.6, 1st Aug.1998, p.681-9. Messadi D; Djilani S E, Eur. Polym. J., 34, Nos.5/6, May/June 1998, p.815-8. Hamdani M; Feigenbaum A, Food Additives Contaminants, 13, No.6, Aug/Sept.1996, p.717-30. Boccacci Mariani M; Chiacchierini E; Gesumundo C, Food Additives Contaminants, 19, 5, 1999, p.207-213. Steiner I; Scharf L; Fiala F; Washuettl J, Food Additives Contaminants, 15, No.7, 1st Oct.1998, p.812-7. BS 6684:1989 Specification for safety harnesses (including detachable walking reins) for restraining children when in perambulators (baby carriages), pushchairs and high chairs and when walking. Withdrawn Halloran MW, Nicell JA, Leask RL, Marić M, Materials Today Commun., 29, 102874, 2021. Wang X, Song M, Liu S, Wu S, Thu AM, Food Chem., 317, 126465, 2020. Babich MA, Bevington C, Dreyfus MA, Regulatory Toxicol. Pharmacol., 111, 104574, 2020.

15.4 Methods of study of plasticized materials

675

15.4 METHODS OF STUDY OF PLASTICIZED MATERIALS A large number of analytical methods can be used to study plasticized materials. Most methods, such as tensile strength, elongation, impact strength, and other methods characterizing changes in the mechanical behavior of material having different concentrations of plasticizers, are frequently used, and these studies are performed according to standards (see Chapter 3). Addition of plasticizer should change glass transition temperature as defined by equation: T g = w 1 T g1 + w 2 T g2

[15.4.1]

where: Tg Tg1, Tg2 w1, w2

glass transition temperature of mixture of plasticizer and polymer glass transition temperature of polymer and plasticizer, respectively weight fractions of polymer and plasticizer respectively.

Glass transition temperature studies are very common due to the wide-spread use of DSC (see more on this subject in Section 11.44). One application is to determine glass transition temperature for various concentrations of plasticizers (Figure 15.4.1). It can be seen that the relationship is not completely linear because of the presence of a cusp (see Section 10.9 for further explanations). The glass transition temperature difference for various compositions (or rate of its change) can be used to predict efficiency of plasticizer. Glass transition temperature can also be used to determine plasticizer loss using master curve, but the simplest method of determination of plasticizer loss is by gravimetric methods (Figure 15.4.2). Gravimetric method2 was also used for evaluation of fogging behavior of materials containing liquid additives but there are available standard methods specially developed for this purpose (see Chapter 3).

Figure 15.4.1. Glass transition temperature of PVC plasticized with different concentrations of diisodecyl phthalate. [Data from Turi E A, Thermal Characterization Polymeric Materials. Volume 2. Second edition, London, 1997, Academic Press Ltd.]

Figure 15.4.2. Plasticizer loss from PVC plasticized with 30 phr of diisodecyl phthalate. [Data from Turi E A, Thermal Characterization Polymeric Materials. Volume 2. Second edition, London, 1997, Academic Press Ltd.]

676

Specialized Analytical Methods in Plasticizer Testing

Figure 15.4.3. Apparent activation rate of curing epoxy oligomer with aromatic amine vs. concentration of dibutyl phthalate. [Data from Smirnov Yu N; Dzhavadyan E A; Golodkova F M, Polym. Sci. Ser. B, 40, Nos.5-6, May-June 1998, p.190-3.]

Figure 15.4.4. Free volume in PVC plasticized with different concentrations of tricresyl phosphate. [Data from Borek J; Osoba W, J. Polym. Sci.: Polym. Phys. Ed., 36, No.11, Aug.1998, p.1839-45.]

Fourier transform infrared, FTIR, is used in plasticizer-containing systems. A special cell was constructed to follow the degradation of plasticized PVC. FTIR was used here to follow the concentration of various plasticizers during thermogravimetric, TGA, studies of plasticized PVC. It was concluded that the evaporation of plasticizers is the first step of thermal degradation under conditions of TGA studies.1 Nuclear magnetic resonance, NMR, was used to study microstructure,3 polymer dynamics,4 and polymer-plasticizer interaction5 in plasticized systems. A combination of 13 C solution and solid-state NMR was used to reveal the crystallinity of PVC-DOP samples containing PVC of different tacticities.3 Plasticizer acted as a solvent for the amorphous phase but did not have an influence on the crystallized part. 13C NMR spin-lattice relaxation times, T1, were used to investigate the effect of plasticizers on polymer dynamics. The addition of plasticizers increased polymer mobility and T1 time. If plasticizer had a strong interaction with polymer segments then it reduced both polymer mobility and T1 time.4 Hydrogen bonding between plasticizer and polymer caused a downward change in chemical shift.5 Calorimetric measurements were used to study the effect of plasticizers on the curing rate of epoxy oligomers. It was found that plasticizer inhibits curing reaction because it forms complexes with proton donors. Plasticizer also decreases the apparent activation energy of reaction (Figure 15.4.3) because it changes the reaction mechanism.2 Gelation of plasticized polymers can be conveniently observed by dynamic mechanical analysis and microscopy (see more on this subject in Chapter 9). Aggregation and formation of clusters in the solution can be followed by dynamic light scattering experiments.6 Positron annihilation spectroscopy was used to determine free volume in plasticized PVC.7-8 Figure 15.4.4 shows that free volume increases linearly with an increase in plasticizer concentration.

15.4 Methods of study of plasticized materials

677

An experimental and theoretical study using molecular dynamics calculations focused on short- and long-range structure correlations with ionic transport near the glass transition for lithium-ion polyacrylonitrile-based electrolytes using dimethyl sulfoxide as a plasticizer.11 The presence of subtle modifications of the polymeric structural features near the glass transition temperature was relevant for studies of free volume in polymerbased electrolytes.11 The in situ small-angle X-ray scattering analysis at different temperatures evidenced an increment of free volume, and partial loss of long-range coherence between polyacrylonitrile neighbor chains just above the glass transition temperature in strong correlation with an Arrhenius behavior crossover observed for the ionic transport in these polyacrylonitrile-based electrolytes.11

References 1 2 3 4 5 6 7 8 9 10 11

Beltran M; Marcilla A, Eur. Polym. J., 33, No.8, Aug.1997, p.1271-80. Smirnov Yu N; Dzhavadyan E A; Golodkova F M, Polym. Sci. Ser. B, 40, Nos.5-6, May-June 1998, p.190-3. Barendswaard W; Litvinov V M; Souren F; Scherrenberg R L; Gondard C; Colemonts C, Macromolecules, 32, No.1, 12th Jan.1999, p.167-80. Forsyth M; Meakin P; MacFarlane D R, J. Mater.Chem., 7, No.2, Feb.1997, p.193-201. Garnaik B; Sivaram S, Macromolecules, 29, No.1, 1st Jan.1996, p.185-90. Reinecke H; Mijangos C, Colloid Polym. Sci., 276, No.6, June 1998, p.544-8. Liu, H; Chaudhary, D; Campbell, C; Roberts, J; Buckman, S; Sullivan, J, Mater. Chem. Phys., 148, 1-2, 349-55, 2014. Hughes, D; Tedeschi, C; Leuenberger, B; Roussenova, M; Coveney, A; Richardson, R; Badolato Bönisch, G; Alam, M A; Ubbink, J, Food Hydrocolloids, 58, 316-23, 2016. Turi E A, Thermal Characterization Polymeric Materials. Volume 2. Second edition, London, 1997, Academic Press Ltd Borek J; Osoba W, J. Polym. Sci.: Polym. Phys. Ed., 36, No.11, Aug.1998, p.1839-45. Pignanelli F, Romero M, Faccio R, Mombrú AW, J. Non-Crystalline Solids, 561, 120744, 2021.

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Specialized Analytical Methods in Plasticizer Testing

16

MATHEMATICAL MODELING IN APPLICATION TO PLASTICIZERS Mathematical models are very valuable because they permit using empirical data for the calculation of other useful quantities and predicting complex variables. Mathematical models usually explain the reasons for particular behavior by relationships and data, leading to their further development and validation. Accumulation of knowledge and data is a usual prerequisite to the development of the mathematical model. In this sense, the existence of a mathematical model usually indicates that sufficient work has been done to interpret data in a fundamental way. Below, some of the existing relationships, which help in using data on plasticizers, are discussed.

16.1 PVC-PLASTICIZER INTERACTION MODEL The glass transition temperature is a very useful parameter that helps in the verification of the plasticizing quality of various additives. It is assumed that energetic effects are created by binary heterocontacts, which cause conformation redistribution in the neighborhood of these contacts.1 This assumption results in the following equation:1 T g – T g1 2 3 ---------------------= ( 1 + K 1 )w 2c – ( K 1 + K 2 )w 2c + K 2 w 2c T g2 – T g1

[16.1.1]

where: Tg Tgi K1 K2 w2c

glass transition temperature of the mixture of polymer and plasticizer glass transition temperatures of components parameter of the power equation, which depends on the difference between the interaction energies of the binary hetero- and homo-contacts parameter of power equation, which depends on additional energetic contributions due to conformational entropy changes during binary contact formation weight fraction of the component with higher Tg2, corrected for the different volume expansivity of the blend components:

K GT w 2 w 2c = ------------------------------w 1 + K GT w 2c

[16.1.2]

where: KGT Gordon-Taylor parameters defined as:

ρ Δα K GT =  ----1-  ---------2-  ρ 2  Δα 1

[16.1.3]

680

where:

Mathematical Modeling in Application to Plasticizers

densities of plasticizer and polymer ρi Δαi the increments of expansion coefficients of plasticizer and polymer at glass transition temperature.

According to Simha-Boyer rule ΔαTg = constant, and thus the Gordon-Taylor parameter can be expressed as: ρ 1 T g1 K GT =  -----  --------  ρ 2  T g2

[16.1.4]

If we assume that there are no interactions (K1 = K2 = 0), Gordon-Taylor equation becomes: w 1 T g1 + K GT w 2 T g2 T g = ----------------------------------------------w 1 + K GT w 2

[16.1.5]

Further simplification by assuming that there is no contribution of different densities turns the Gordon-Taylor equation to the Fox equation: w w 1 ----- = -------1- + -------2T g1 T g2 Tg

[16.1.6]

In Sections 11.44 and 15.4, there is experimental evidence showing that interactions change the character of this relationship and that linear relationships, such as the Fox equation ([16.1.6]), are not precise. Two coefficients characterizing interactions are given by the following equations [16.1.7] and [16.1.8]: [ ( E 12 – 1 + E 12 – 2 ) – ( E 11 – 1 + E 22 – 2 ) ] – [ ( e 12 – 2 – e 12 – 1 ) + ( e 11 – 1 – e 11 – 2 ) ] K 1 = -----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------T g2 – T g1 ( 2e 12 – 1 – e 11 – 1 – e 22 – 1 ) – ( 2e 12 – 2 – e 11 – 2 – e 22 – 2 ) K 2 = -----------------------------------------------------------------------------------------------------------------------------------T g2 – T g1 where: Eij-k ij k eij-k

stored interaction energy, which has to be overcome at Tg binary contact neighborhood the energetic contributions to the contact energies due to induced conformational redistributions by binary heterocontact formation.

Below w2c (or below cusp), heterogenic interactions are formed, and K1 is always small and positive, and K2 is either positive or slightly negative. At higher plasticizer content (above cusp), values of both parameters are large and negative, suggesting that plasticizer-plasticizer contacts prevail, which increases the entropic effect. Plasticizer performance was predicted by molecular simulation based on three metrics, namely compatibility between plasticizer and PVC, plasticization efficiency, and plasticizer mobility.2 Small quantities of plasticizers lead to a change in the Tg of two-component system, which is usually a linear function with respect to the solvent mass fraction:3

16.1 PVC-plasticizer interaction model

T g = T g, p – λ 0 ϕ s

681

[16.1.9]

where: Tg,p λ0 ϕs

glass transition temperature of the polymer softener efficiency parameter solvent's mass fraction.

This linear relationship was linked with diffusion theory and used to define the modification model of plasticized PVC with dialkyl phthalates.3

References 1 2 3

Vilics T; Schneider H A; Manoviciu V; Manoviciu I, Polymer, 38, No.8, 1997, p.1865-70. Li D, Panchal K, Vasudevan NK, Mafi R, Xi L, Chem. Eng. Sci., 249, 117334, 2022. Langer E, Bortel K, Waskiewicz S, Lenartowicz-Klik M, Essential Quality Parameters of Plasticizers in Plasticizers Derived from Post-Consumer PET, William Andrew, 2020, pp. 45-100.

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Mathematical Modeling in Application to Plasticizers

16.2 GAS PERMEATION Diffusion of gases occurs as a result of redistribution of free volume within the matrix. Gas transport is enabled by microvoids present in the matrix. Gas permeate must have a critical volume smaller than the size of microvoids.1 The equations that are given below help to solve this problem. The average size of hole is given by the following equation:1 ∞

 υ h exp ( – ( υ h E coh ) ⁄ ( RT ) ) dυ h  υ h =

0 -------------------------------------------------------------------------∞

[16.2.1]

 exp ( – ( υ h E coh ) ⁄ ( RT ) ) dυ h 0

where:

υh Ecoh R T

average hole size microvoid volume cohesive energy density gas constant absolute temperature.

From Simha-Somcynsky equation of state, one obtains the following relationship: υ∗ N L E coh N L E coh - exp  – -----------------------D = k ( 1 – y ) ----------------= kC ( υ h ≥ υ∗ )  RT RT 

[16.2.2]

where: D k 1−y NL υ* C(υh8υ∗)

diffusion coefficient proportionality factor fraction of unoccupied lattice cells Loschmidt number (the number of molecules in a gram-molecule) critical volume concentration of holes satisfying the minimum hole volume condition.

This equation shows that diffusion can only occur when microvoids are larger than the critical volume of gas. Critical volumes of gases differ; for example, critical volumes are 48, 81, 93, and 107 in D3 for hydrogen, oxygen, nitrogen, and carbon dioxide, respectively. Figure 16.2.1 shows that unoccupied volume increases with an increase in plasticizer fraction. Figure 16.2.2 shows that the diffusion coefficient of oxygen also increases with the plasticizer fraction. The following equation is convenient in the calculation of the size of penetrant:1 RT ∂ ln ( D ⁄ E coh ) υ∗ =  --------  ------------------------------ NL    ∂E coh

[16.2.3]

Pyrene-labeled and pyrene-doped flexible polyvinylchloride were plasticized with ultrasmall branched star poly(ε-caprolactone), and fluorescence intensities were observed with temperature changes to ascertain the actual glass transition behavior of polymer chains.2 The labeled pyrene moieties along PVC chains exhibited limited movement due to the cooperative reptation motion of polymer chains, even when the space for the poly-

16.2 Gas permeation

Figure 16.2.1. Unoccupied volume fraction in ethylcellulose films plasticized with variable concentrations of tributyl citrate. [Data from Beck M I; Tomka I, J. Polym. Sci.: Polym. Phys. Ed., 35, No.4, March 1997, p.639-53.]

683

Figure 16.2.2. Oxygen diffusion coefficient in ethylcellulose films plasticized with variable concentrations of tributyl citrate. [Data from Beck M I; Tomka I, J. Polym. Sci.: Polym. Phys. Ed., 35, No.4, March 1997, p.639-53.]

mer chain to move sufficiently was created by an increase in the free volume.2 In contrast to the pyrene-doped polymeric system, the pyrene-labeled polymeric system exhibited that the polymeric chains were constrained, despite the increase in free volume above the glass transition temperature, Tg.2 In membrane-based CO2 separation, glassy polymeric materials suffer from the plasticization phenomenon.3 To suppress plasticization, crosslinking is a possible remedy, which, however, significantly alters the separation performance of a membrane.3 The increased glass transition temperature of polymers with crosslink density is due to enhanced rigidity caused by crosslinking, which reduces the packing efficiency of polymer chains and leads to higher fractional free volume, hence increasing the CO2 diffusivity.3 Analyses of CO2-accessible free volume evolution as a function of pressure show increased plasticization resistance with crosslinking.3 However, radial distribution function analyses indicate that crosslinking reduces the number of preferential sorption sites for CO2 molecules and prevents the expansion of free volume elements around these sites.3 Consequently, CO2 solubility of the polymers decreases while diffusivity increases with increasing crosslinking density.3 This study reveals that the resultant effect of thermal crosslinking on 2,2′-bis-(3,4-dicarboxyphenyl) hexafluoropropane dianhydride-bis-[4-(4aminophenoxy) phenyl] sulfone/3,5-diaminobenzoic acid copolyimide is an increase in both CO2 permeability and plasticization resistance.3 The suppression of CO2-induced plasticization in polyimide membranes at supercritical conditions up to 120 bar has been investigated.4 Three approaches (polymer blending, thermal treatment, and chemical crosslinking) known from relatively low-pressure applications were applied, and their effectiveness to suppress membrane plasticization at high CO2 pressures and under supercritical conditions was systematically evaluated. CO2 sorption measurements revealed that Henry sorption promoted plasticization and that the corresponding Henry sorption parameter (kD) correlated with d-spacing and Tg of

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Mathematical Modeling in Application to Plasticizers

membranes.4 A lower d-spacing and higher Tg resulted in the reduced kD parameter and thus a higher resistance to plasticization.4 A high interchain rigidity was required to suppress plasticization at the highly plasticizing liquid-like CO2 densities.4 Chemical and thermo-oxidative crosslinking resulted in the largest decrease in interchain mobility and therefore showed the highest resistance to plasticization, but also a significantly lower permeability.4 Thermal treatment of membranes in N2 helped in retaining a high permeability while still displaying significant plasticization resistance.4 Polymer blending increased plasticization resistance but strongly reduced permeability.4 Plasticization of amorphous polylactide shifts the glass transition and extends its temperature range of crystallization to lower temperatures.5 Plasticizer accumulates in the amorphous phase because it is excluded from the growing crystal.5 The formation of the rigid amorphous fraction is favored by the low crystallization temperature.5 It reaches values up to 50% in plasticized polylactide.5 The increase in the content of rigid amorphous fraction coincides with both the increase of free volume quantified by positron annihilation lifetime spectroscopy and the decrease in the cooperativity length obtained from the temperature fluctuation approach.5

References 1 2 3 4 5

Beck M I; Tomka I, J. Polym. Sci.: Polym. Phys. Ed., 35, No.4, March 1997, p.639-53. Choi W, Lee W, Yu YJ, Priestley RD, Chung JW, Kwak S-Y, Polymer, 234, 124240, 2021. Balçık M, Velioğlu S, Tantekin-Ersolmaz SB, Ahunbay MG, Polymer, 205, 122789, 2020. Houben M, Kloos J, van Essen M, Nijmeijer K, Borneman Z, J. Membrane Sci., in press, 120292, 2022. Varol N, Delpouve N, Araujo S, Domenek S, Guinault A, Golovchak R, Ingram A, Delbreilh L, Dargent E, Polymer, 194, 122373, 2020.

16.3 Migration

685

16.3 MIGRATION Several mathematical equations are used to process data obtained from migration studies usually conducted by gravimetric methods. Typically plasticized film is sandwiched between two layers of unplasticized film and kept for variable amounts of time in the oven. Weight change of plasticized film is measured in time intervals. These data can be processed using several equations given below:1 M -------τ = kτ d M0 where: Mτ M0 k τ d

[16.3.1]

mass of migrated plasticizer in time τ initial mass of plasticizer coefficient proportional to the mass of migrated plasticizer time interval coefficient.

The above is the basic equation that can be used to predict the kinetics of migration. In two-sided migration experiments, the integral form of the second Fick’s law is frequently used:  4π 2 Dτ 2 - M τ = M 0 1 – ( 8 ⁄ π ) exp  – --------------2  L 

[16.3.2]

where: D L

diffusion coefficient of plasticizer thickness of test film.

Equation [16.3.2] is useful in the determination of diffusion coefficient. The following equation is also frequently used: 2

L D = 0.049 -------τ 0.5

[16.3.3]

In this case, a time interval is measured in which half of the plasticizer has migrated (Mτ/M0 = τ0.5). Experimental data show that the coefficient k from the equation [16.3.1] decreases with the molecular mass of the plasticizer increasing (Figure 16.3.1). It is possible to predict the coefficient k included in equation [16.3.1] by using the following relationship:1 logk = 1 − 0.0062M

[16.3.4]

Figure 16.3.2 shows that the diffusion coefficient decreases with the molecular weight of the plasticizer increasing. Figure 16.3.2 also shows that both equations ([16.3.2] and [16.3.3]) give similar results. Analysis of migration of plasticizers from PVC-based medical devices resulted in the development of an infusion model.2 The structures of starch and starch-based materials determine additives migration from the material matrix.3 Propionylated starch derived from waxy, normal, Gelose 50 and

686

Mathematical Modeling in Application to Plasticizers

Figure 16.3.1. Coefficient k of equation [16.3.1] vs. molecular weight of phthalate plasticizer used in PVC. [Data from Dedov A V; Bablyuk E B; Nazarov V G, Polym. Sci. Ser. B, 42, Nos.5-6, May-June 2000, p.138-9.]

Figure 16.3.2. Diffusion coefficients estimated from the same data using equations [16.3.1 red] and [16.3.2 blue] vs. molecular weight of phthalate plasticizer used in PVC. [Data from Dedov A V; Bablyuk E B; Nazarov V G, Polym. Sci. Ser. B, 42, Nos.5-6, MayJune 2000, p.138-9.]

Gelose 80 starch were selected as the matrix.3 The amylose effect on plasticizer (triacetin) migration as well as structural changes in hydrophobic starch-based films were studied.3 The constant (k1) of first-order rate and initial release rate (V0) of triacetin migration were consistent with the increment of amylose content.3 Diffusion model disclosed that Fick's second law was useful for characterizing the short-term migration of triacetin, and larger diffusion coefficient (D) values of short- and long-term migration were also found in films with higher amylose content, indicating that amylose-formed structures were in favor of triacetin migration.3 Van der Waals' interactions between propionylated amylose and triacetin were easier to weaken with the migration of triacetin, which promoted the decrease of wavenumber of C−O−C and enlarged the inter-planner spacing of crystalline structures, promoting the formation of amorphous structures and wrinkles and embossments in films with higher amylose content.3 Phospholipid coating enhanced the migration of plasticizers and their primary degradation products from PVC tubing into streaming blood.4 The enhancement effect was found to be slightly greater in the case of tri-(2-ethylhexyl) trimellitate, but since tri-(2ethylhexyl) trimellitate migrates at significantly lower levels than di-(2-ethylhexyl) phthalate, tri-(2-ethylhexyl) trimellitate was recommended as an alternative plasticizer to di-(2-ethylhexyl) phthalate in medical devices.4

References 1 2 3 4

Dedov A V; Bablyuk E B; Nazarov V G, Polym. Sci. Ser. B, 42, Nos.5-6, May-June 2000, p.138-9. Bernard, L; Cueff, R; Chagnon, M C; Abdoulouhab, F; Décaudin, B; Breysse, C; Kauffmann, S; Cosserant, B; Souweine, B; Sautou, V, Int. J. Pharm., 494, 1, 136-45, 2015. Zhu J, Zhang S, Liu Y, Chen S, Li L, Int. J. Biol. Macromol., 195, 41-8, 2022. Münch F, Höllerer C, Klapproth A, Eckert E, Rüffer A, Cesnjevar R, Göen T, Chemosphere, 202, 742-9, 2018.

16.4 Dry-blending time

687

16.4 DRY-BLENDING TIME Figure 16.4.1 shows that plasticizer viscosity is an influential parameter determining the duration of the dry-blending process. The data included in this study are for eleven phthalates, four trimellitates, and three adipates. Regression analysis of data showed that the specific gravity of the plasticizer is the second most important factor. Including these two variables, one may predict dry-blending time using the following equation:

Figure 16.4.1. Dryblending time determined according to ASTM D 2396 for PVC plastificates containing different plasticizers vs. plasticizer viscosity. [Data from Krauskopf L G; Godwin A D, J. Vinyl Additive Technol., 5, No.2, June 1999, p.107-12.]

Dry-blending time = 10.05 + 0.218η − 10.08d where:

η d

[16.4.1]

viscosity of plasticizer specific gravity of plasticizer.

The molecular weight of the plasticizer also influenced the processing of modified material.2 This is because material usually becomes more difficult to process when the molecular weight of the plasticizer increases.2 A high molecular weight of polymeric plasticizer required to be heated up before dry blending and needed a higher process temperature.2

References 1 2

Krauskopf L G; Godwin A D, J. Vinyl Additive Technol., 5, No.2, June 1999, p.107-12. Langer E, Bortel K, Waskiewicz S, Lenartowicz-Klik M, Classification of Plasticizers in Plasticizers Derived from Post-Consumer PET, William Andrew, 2020, pp. 13-44.

688

Mathematical Modeling in Application to Plasticizers

16.5 GELATION AND FUSION Figure 11.52.3 shows that the final gelation temperature of phthalates increases with the number of carbon atoms in alcohol increasing. Gelation depends on the solubility parameters of plasticizers and can be conveniently compared with the radius of the interaction sphere in Hansen’s space. Figure 16.5.1 shows that phthalates and trimellitates form almost the same relationship, but the data for adipates have a separate relationship. Figure 16.5.2 shows stages of processes leading to fusion as selected for process modeling (see more in Chapter 9).2 The following equations characterize kinetic rates of processes occurring at each stage: Figure 16.5.1. Final gelation temperature vs. radius of interaction sphere in Hansen space between polymer and plasticizers from groups as labeled. [Data from Krauskopf L G; Godwin A D, J. Vinyl Additive Technol., 5, No.2, June 1999, p.107-12.] T

a b

W1 =

t

bc

W 2 =  ke

( – E a ⁄ RT )

0 T

cd

W3 =

t

2

–( 1 ⁄ 2 ) [ ( T – T0 ) ⁄ σ ] ( – E a ⁄ RT ) n 1 dT –  ke W 1 dt  -------------- e 2πσ 0 0

1 2πσ f

 ---------------- e 0

T

n W 1 dt

2

–( 1 ⁄ 2 ) [ ( T – Tf ) ⁄ σf ] 1 –  ---------------- e dT 2πσ f 0

–( 1 ⁄ 2 ) [ ( T – Tf ) ⁄ σf ]

[16.5.2]

2

dT

where: W1 W2 W3 T T0 Tf t σ σf k Ea R n

[16.5.1]

fraction of resin at the stage b (absorption of plasticizer) fraction of resin at a stage c (partial gelation) fraction of resin at a stage d (fusion) temperature temperature at which the rate of the first step (a to b) is at maximum temperature at which the rate of the fusion step (c to d) is at maximum time standard deviation of distribution around T0 standard deviation of distribution around Tf kinetic constant of the second stage of gelation step (b to c) activation energy of the second stage of gelation step (b to c) gas constant reaction order of the second stage of gelation step (b to c).

[16.5.3]

16.5 Gelation and fusion

689

Figure 16.5.2. Stages of gelation and fusion processes. a. mixture of PVC and plasticizer − plastisol; b. particles that absorbed plasticizer have been swollen, and viscosity has been increased; c. partial gelation accompanied with further viscosity increase, swelling and dissolving − borders of individual particles are still visible; d. fused state. [Adapted, by permission, from Marcilla A; Garcia J C, Eur. Polym. J., 33, No.3, March 1997, p.357-63.]

The above set of equations was used to model viscosity throughout the processes leading through fusion. Viscosity was calculated using the following equation: η calc = W p V p + W 1 V 1 + W 2 V 2 + W 3 V 3 ≅ W 1 V 1 + W 2 V 2 + W 3 V 3 where:

ηcalc Wp Vp V1 V2 V3

[16.5.4]

calculated viscosity fraction of resin at stage a (plastisol) viscosity at stage a (plastisol) viscosity at stage b (swelling) viscosity at stage c (partial gelation) viscosity at stage d (fusion).

Viscosity calculated from the model equations was in full agreement with viscosity determined by the dynamic viscoelastic measurements.2

690

Mathematical Modeling in Application to Plasticizers

References 1 2

Krauskopf L G; Godwin A D, J. Vinyl Additive Technol., 5, No.2, June 1999, p.107-12. Marcilla A; Garcia J C, Eur. Polym. J., 33, No.3, March 1997, p.357-63.

16.6 Thermal decomposition

691

16.6 THERMAL DECOMPOSITION Thermal decomposition of PVC is believed to be linked to the loss of plasticizers.1-2 Activation energy of thermal degradation is given by equation: E a = E ev + E∗

[16.6.1]

where: Ea activation energy of PVC thermal degradation Eev activation energy of plasticizer evaporation E* activation energy of PVC degradation.

Plasticizer evaporation during thermogravimetric analysis is given by equation:2 m pl E ev = E pl -------mt

[16.6.2]

where: Epl energy needed to evaporate plasticizer mpl plasticizer mass mt total mass of material containing plasticizer.

The amount of plasticizer in the sample did not affect the temperature of plasticizer removal, but the maximum temperature of plasticizer removal increased when the rate of temperature increase during thermogravimetric studies was lower.1 The thermal stability and activation energy of HDPE-chitosan composites prepared using maleic anhydride as a compatibilizer and palm oil as a plasticizer were computed using the Coats-Redfern model.3 With the addition of chitosan, the thermal stability of the HDPE/chitosan composites increased.3 The addition of palm oil increased plasticization, and it did not affect the thermal stability of the composites as observed from the activation energies computed using the Coats-Redfern model. In fact, the incorporation of 5 wt% of palm oil to HDPE/chitosan has further improved stability with an increase in activation energy to 348.2 kJ mol-1.3

References 1 2 3

Marcilla A; Beltran M, Polym. Deg. Stab., 60, No.1, 1998, p.1-10. Jimenez A; Berenguer V; Lopez J; Vilaplana J, J. Appl. Polym. Sci., 60, No.12, 20th June 1996, p.2041-8. Shelly M, Mathew M, Pradyumnan PP, Francis T, Materials Today, Proc., 46, 7, 2742-6, 2021.

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Mathematical Modeling in Application to Plasticizers

16.7 POTENTIAL HEALTH RISK OF EXPOSURE TO DEHP FROM GLOVE Dermal exposure to DEHP may occur when DEHP leaches from the glove.1 Dermal dose can be calculated from the following equation:1 Jd × As × Et × Ef × Ed DD = --------------------------------------------------Bw × At

[16.7.1]

where: DD Jd As Et Ef Ed Bw At

dermal dose dermal penetration rate of DEHP through human skin surface area of exposed skin daily exposure time exposure frequency exposure duration body weight averaging lifetime

The study concluded that the dermal absorption of DEHP released from the gloves might pose a potential health risk to the workers.1 Frequent use of gloves is a source of dermal exposure to plasticizers because it favors the occlusion of the skin barrier.2 It can contribute to their transcutaneous migration since plasticizers are not covalently bound.2 Thus, they may affect dermal microvascular endothelial cells.2 The GC-MS analysis of the vinyl gloves revealed the presence of three main plasticizers, namely di-(2-ethylhexyl) phthalate, di-(2-ethylhexyl) terephthalate, and di-isononyl phthalate. Amounts reported were up to 44.44 wt%.2 Following single exposure, results showed higher cell viability after 24 hours of exposure to DEHP, DINP, and their mixture.2

References 1 2

Chao, K-P; Huang, C-S; Wei, C-Y, J. Hazardous Mater., 283, 53-9, 2015. Poitou, K, Corbière, C, Monteil, C, Rogez T, P20-25. Abstracts/Toxicology Letters, 350S, 2021.

17

HEALTH AND SAFETY ISSUES WITH PLASTICIZERS AND PLASTICIZED MATERIALS 17.1 ADJUVANT EFFECT OF PLASTICIZERS Søren Thor Larsen National Research Centre for the Working Environment, Copenhagen, Denmark

17.1.1 INTRODUCTION Several studies have proposed that exposure to chemical with so-called adjuvant effect may contribute to the increase in prevalence of allergic diseases, such as rhinitis and asthma. Chemicals with adjuvants effect usually do not induce allergy per se, but they may increase the potency of allergens. Among the numerous chemicals with adjuvant effect are members of the group of phthalate plasticizers, including di-(2-ethylhexyl) phthalate, DEHP. The effect of phthalates on the immune system and their ability to promote allergy has been studied in both epidemiological studies, in laboratory animal studies and using in vitro (cellular) models. The present chapter discusses the possible role for phthalates in the development of allergic airway diseases. 17.1.2 AIRWAY ALLERGY The two main functions of the immune system are to distinguish “self” from “non-self” material and to distinguish harmful from harmless. A failure to distinguish self from nonself is seen in autoimmune diseases such as diabetes and arthritis, where the immune system attacks tissue belonging to its own host. Failure to distinguish harmful from harmless may lead to an overreaction to innocuous substances such as allergens which may lead to development of allergy1. Allergens belong to a diverse group of substances such as proteins from pollen, furred pets, house dust mites as well as other chemicals which may act as skin sensitizers. Allergic reactions can be categorized into four types (Type I-IV reactions) 1, but most cases of airway allergy belong to the Type I allergy. Briefly, Type I allergic reactions are mediated via production of allergen-specific IgE antibodies, which upon stimulation with the appropriate allergen, cause mast cell degranulation, that is release of inflammatory mediators including histamine, prostaglandins and leukotrienes.1 These

694

Health and Safety Issues with Plasticizers and Plasticized Materials

mediator substances are key factors in the allergic inflammation reaction and are to a large extent responsible for the observed clinical symptoms. For allergic asthma, symptoms include difficulties in breathing due to bronchoconstriction and for rhinitis. The typical symptoms include sneezing, runny nose and increased tear flow.1 Apart from being hypersensitive to specific allergens, subjects with airway allergy are often also hypersensitive to non-specific exposures, including airway irritants, organic solvent vapor, tobacco smoke and dry or cold air.2 Since some of these exposures may occur at work places, subjects with allergic airway diseases may be considered as susceptible population in the working environment. The prevalence of allergic airway diseases has been increasing in Western Europe and the US since the Second World War.3-4 Although inheritable predisposition to allergy is the main risk factor, increasing evidence point toward environmental factors and conditions may play important roles. These changes in environmental factor include changes in diet, changes in the microbial environment or exposure to substances with impact on the immune system, including the so-called environmental adjuvants. Environmental chemicals with well-known adjuvant effect include tobacco smoke, ozone and diesel exhaust particles.5-7

17.1.3 ADJUVANT EFFECT An immunological adjuvant (from Latin adjuvare, which means to assist or help) may be defined as any substance that, when given in combination with an immunogen (e.g., a vaccine antigen) acts generally to direct, accelerate, prolong or enhance the quantity of the immune response.8 Adjuvants do not necessarily by themselves elicit any antigenic response; their effect is rather to increase the potency of e.g., immunogenic substances such as vaccine antigens. The group of immunological adjuvants is very diverse and includes aluminium salts (“alum”), oil-based formulations (including Freund's incomplete adjuvant and Freund's complete adjuvant) and cholera toxin.9-10 The mechanisms through which adjuvants exert their influence on immune responses are complex, but it is believed that enhanced antigen presentation or generation of “danger” signals that increase the alertness of the immune system may be involved.11 Some adjuvants seem to specifically promote the so-called T-helper cell type 2 (Th2) response12-13 which is closely linked to IgE-mediated allergies such as rhinitis and allergic asthma. 17.1.4 ADJUVANT EFFECT OF PHTHALATE PLASTICIZERS? Several studies have addressed the question whether phthalate plasticizers may possess adjuvant effect and, if so, whether this adjuvant effect increases the risk for IgE-mediated allergies. Studies include both epidemiological investigations, in vivo (laboratory animal) and in vitro (cell culture) studies. Some of the most important epidemiological and in vivo studies are presented and discussed in the following sections. In vitro studies are not included due to their limited interpretability in relation to human risk assessment. 17.1.4.1 Epidemiological studies The first study describing a possible association between exposure to phthalate and respiratory symptoms was published in 1997 by Øie and co-workers.14 Two years later, a study demonstrating an association between exposure to phthalates and the exacerbation of respiratory symptoms, such as bronchial obstruction or wheeze in children was published15. A later study on this topic found a correlation between presence of plastic wall

17.1 Adjuvant effect of plasticizers

695

coverings at work and an increased risk of asthma.16 Another study investigated the association between DEHP in indoor dust and wheezing among preschool children.17 In general, the epidemiological studies reported an increased risk of developing various respiratory symptoms in the presence of the plastic materials in the indoor environment. Although valuable, these studies also have some limitations: Firstly, the studies demonstrate an association rather than a causal link between exposure to phthalates and development of respiratory symptoms. Secondly, most of the studies provide imprecise information on exposure levels since the exposure assessment was done after onset of symptoms, i.e. the true exposure conditions during the period where symptoms developed are not known. Thirdly, in most of the published studies, levels of allergen in the indoor environment were not measured. Since phthalate is adsorbed by the dust grain over time, it could be speculated that a high phthalate concentration in the dust is a marker of low cleaning frequency, which is likely also associated with a higher allergen concentration, which is a known risk factor for the development of respiratory allergy.18

17.1.4.2 In vivo (animal) studies Several in vivo studies have been performed to assess an adjuvant effect of the phthalates. Adjuvant effect was in most cases based on increase in the production of antibodies against a co-administered antigen. Most studies are based on mouse models where a protein antigen in combination with a phthalate plasticizer is administered through subcutaneous injection, intraperitoneal injection, dermal application19-26 or, using the human relevant exposure routes, namely oral administration or inhalation of phthalate and antigen particles.27-28 Adjuvant effect can be assessed by several immune parameters, but with respect to allergic airway diseases, the measurement of allergen-specific IgE or total IgE antibodies as well as eosinophilic airway inflammation are the most relevant and interpretable parameters. In the mouse, the production of IgE antibodies is often closely linked to the formation of IgG1 antibodies, wherefore also this antibody may be useful for risk assessment. 29 However, it is important for the interpretation of data derived from mouse models to mention that IgG1 is much less effective at stimulating mast cell degranulation (i.e., release of inflammatory mediators) than is IgE.30 Furthermore, the productions of IgG1 and IgE antibodies do not always follow the same trend,31 wherefore IgE production is the most clinical relevant and most interpretable parameter in relation of risk assessment. A structure-activity study24 of a series of phthalate plasticizers and related substances (Figure 17.1.1) has been performed in order to rule out structural and physicochemical parameters of importance for the adjuvant effect. The substances were injected intraperitoneally in combination with the model allergen OVA in BALB/c mice and the potency of the phthalates were assessed based on their ability to increase the level of OVA-specific IgG1 (Table 17.1.1). It was concluded that the most potent phthalate plasticizers had two vicinal (neighbor) alkyl chains with a sum of 16 carbon atoms, which is the case for e.g., DEHP. Another study21 investigated adjuvant effect and development of allergic lung inflammation upon inhalation of DEHP and OVA aerosols. Since DEHP and allergen are both associated with dust particles, this study mimics human exposure and is consequently useful for risk assessment. The study was a 14-week repeated dose inhalation study using different concentrations (0.022, 0.094, 1.7 or 13 mg/m3) of DEHP in combination with

696

Health and Safety Issues with Plasticizers and Plasticized Materials

Figure 17.1.1. Structures and names of substances studied in ref. 24.

0.14 mg/m3 OVA. The study showed that DEHP upon inhalation had adjuvant effect similar to that seen after intraperitoneal or subcutaneous injection, that increased anti-OVA IgG1 antibody levels, whereas no effect was seen on the OVA-specific IgE antibody production. Eosinophilic and lymphocytic lung inflammation, indicators of allergic airway inflammation, was seen at the highest DEHP exposure level. The “margin-of-safety”, which is the distance from the highest DEHP exposure level not giving rise to an effect in mice to the actual human exposure levels, was calculated to be in the range 50-100.28 Consequently it was concluded that “realistic” DEHP exposure levels likely to be encountered in the indoor environment would not be expected to cause adjuvant effects in humans, or to result in allergic inflammation of the lung Since the majority of phthalate intake is through the diet32 it is relevant also to study the effect of orally administered phthalate on the immunological effects in mice. This was recently done by Guo et al.27 who administered DEHP (30, 300 or 300 μg/kg) daily for 52 days and immunized mice by the i.p. route (day 25, 39 and 47) followed by OVA aerosol

697

17.1 Adjuvant effect of plasticizers

challenge. The authors found an association between combined DEHP/OVA exposures and serum total IgE whereas no effect was seen on OVA-specific IgE. The highest dose of DEHP furthermore increased the number of eosinophils in the lungs. Also, the highest dose of DEHP increased the bronchial hyperactivity, an indicator of asthma-like conditions, in the animals. Table 17.1.1. Adjuvant effect of test compounds based on the IgG1 levels. Compound

Adjuvant factor* (dose of test compound)

1: Di-n-butyl phthalate

24 (10 μg)

2: Benzyl butyl phthalate

1

3: Di-(2-ethylhexyl) phthalate (DEHP)

13 (10 μg) 61 (100 μg)

4: Butyl dodecyl phthalate (BDP)

20 (10 μg) 68 (100 μg)

5: Di-n-octyl phthalate

61 (100 μg)

6: Bis-(2-ethylhexyl) terephthalate (DOTP)

4 (100 μg)

7: Diisononyl phthalate

42 (both 10 and 100 μg)

8: Diisodecyl phthalate

1

9: Trioctyl trimellitate (TOTM)

1

10: Methyl palmitate (MP)

1

* Adjuvant factor = ratio between the IgG1 level in the test group and the OVA only control group.

17.1.5 CONCLUSIONS Results from epidemiological studies suggest an association between exposure to phthalates and development of respiratory symptoms related to asthma. However, it remains unclear whether the phthalate exposure has actively contributed to the development of respiratory diseases or whether the phthalate exposure may exacerbate an already existing respiratory allergy. Also, it could be speculated that the phthalate exposure could act as a surrogate marker of other exposure. Finally, although thorough phthalate exposure assessments have been made in some of the epidemiological studies, measurements are often made after onset of symptoms and it is therefore not possible to obtain exposure data for the period wherein a possible sensitization has occurred. Regarding the animal studies, there are several studies demonstrating an adjuvant effect of some of the phthalates when these are injected, ingested or inhaled. The main adjuvant effect in mice was an increase in the IgG1 response, which is less interpretable than IgE in relation to human allergic sensitization. Furthermore, the only long-term inhalation study performed showed that adjuvant effect of DEHP occurred only at very high exposure concentrations, giving a margin-of-exposure of 50-100, suggesting that realistic DEHP exposure levels, i.e., those that can be found in private homes and offices, are not likely to cause allergic sensitization and promote allergic lung inflammation. A single animal study demonstrated adjuvant effect of orally administered phthalate at dose levels not far from human exposure levels.27 The role of orally administered

698

Health and Safety Issues with Plasticizers and Plasticized Materials

phthalate on the risk of sensitization needs further investigation, including elucidation of mechanisms to assess the human relevance of these observations. Bearing in mind that most of the inhaled phthalate is bound to dust particles, one effective method to reduce the amount of inhaled phthalate is to keep the indoor environment clean. Since removal of dust furthermore reduces the allergen level, cleaning seems to be an effective prevention for both phthalate and allergen exposures and it further reduces any possible “cocktail effect” between the two exposures as also proposed by Nielsen et al.33

REFERENCES 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33

Mygind N, Dahl R, Pedersen S, Thestrup-Pedersen K, Essential Allergy, Blackwell Science Ltd., Oxford, 1996. Peden, D, Reed, C E, J. Allergy Clin. Immunol., 125, S150-60, 2010. Anderson H R, Ruggles R, Strachan D P, Austin B R, Burr M, Jeffs D, Standring P, Steriu A, Goulding R, Br. Med. J., 328, 1052–1053, 2004. Latvala J, von Hertzen L, Lindholm H, Haahtela T, Br. Med. J., 330, 1186–1187, 2005. Peterson B, Saxon A, Ann. Allergy Asthma Immunol., 77, 263-270, 1996. Platts-Mills T A, Erwin E, Heymann P, Woodfolk J, Allergy, 60, 25-31, 2005. von Mutius E, Immunobiology, 212 433-439, 2007. Vogel F R, Dev. Biol. Stand., 92, 241-248 (1998) Schijns V E, Curr. Opin. Immunol., 12, 456-463, 2000. Lindblad E B, Vaccine, 22, 3658-68, 2004. Gallucci S, Lolkema M, Matzinger P, Nat. Med., 5, 1249-1255, 1999. De Gregorio E, Tritto E, Rappuoli R, Eur. J. Immunol., 38, 2068-2071, 2008. Freytag L C, Clements J D, Vaccine, 23, 1804-1813, 2005. Øie L, Hersoug L-G, Madsen J Ø, Environ Health Perspect, 105, 972-978, 1997. Jaakkola J J K, Øie L, Nafstad P, Botten G, Samuelsen S O, Magnus P. Am J Publ Health, 89, 188-192, 1999. Jaakkola J J K, Ieromnimon A, Jaakkola M S, Am. J. Epidemiol., 164, 742-749, 2006. Kolarik B, Naydenov K, Larrson M, Bornehag C-G, Sundell J, Environ. Health Perspect., 116, 98-103, 2008. Nielsen G D, Hansen J S, Lund R M, Bergqvist M, Larsen S T, Clausen S K, Thygesen P, Poulsen O M., Pharmacol. Toxicol., 90, 231-242, 2002. Larsen S T, Lund R M, Nielsen G D, Thygesen P, Poulsen O M, Toxicol. Lett., 125, 11-18, 2001. Larsen S T, Lund R M, Nielsen G D, Thygesen P, Poulsen O M, Pharmacol. Toxicol., 91, 264-272, 2002. Larsen S T, Lund R M, Thygesen P, Poulsen O M, Nielsen G D, Food Chem. Toxicol., 41, 439-446, 2003. Lee M H, Park J, Chung S W, Kang B Y, Kim S H, Kim T S, Int. Arch. Allergy Immunol., 134, 213-222, 2004. Larsen S T, Nielsen G D, Toxicol. Lett., 170, 223-228, 2007. Larsen S T, Nielsen G D, BMC Immunol., 9, 61-69, 2008. Dearman R J, Betts C J, Beresford L, Bailey L, Caddick H T, Kimber I, J. Appl. Toxicol., 29, 118-125, 2009. Dearman R J, Beresford L, Bailey L, Caddick H T, Betts C J, Kimber I, Toxicology, 244, 231-241, 2008. Guo J, Han B, Qin L, Li B, You H, Yang J, Liu D, Wei C, Nanberg E, Bornehag C-G, Yang X, PLoS one, 7, 2012. Larsen S T, Hansen J S, Hansen E W, Clausen P A, Nielsen G D, Toxicology, 235, 119-129, 2007. Snapper C M, Finkelman F D, Paul W E, Immunol. Rev., 102, 51-75, 1988. Ovary Z, Int. Arch. Allergy Appl. Immunol., 69, 385-392, 1982. Sarlo K, Dearman R J, Kimber I. Guinea pig, mouse and rat models for safety assessment of protein allergenicity. In: Tryphonas H, Fournier M, Blakley B R, Smits J E G, Brousseau P (Eds.), Investigative Immunotoxicology, CRC Press LLC, Taylor and Francis, Boca Raton, 2005. Wormuth M, Scheringer M, Vollenweider M, Hungerbuhler K, Risk Anal., 26, 803-824, 2006. Nielsen G D, Larsen S T, Olsen O, Lovik M, Poulsen S K, Glue C, Wolkoff P. Indoor Air, 17, 236-255, 2007.

17.2 The rodent hepatocarcinogenic response to phthalate plasticizers: basic biology and human

17.2 THE RODENT HEPATOCARCINOGENIC RESPONSE TO PHTHALATE PLASTICIZERS: BASIC BIOLOGY AND HUMAN EXTRAPOLATION

1

Abigail L Walker1 and Ruth A Roberts2,3~ ~ Corresponding Author

Walker Clarity, Wilmslow, SK9 1DG, UK ApconiX, Alderley Park, Macclesfield, SK10 4TG, UK 3 School of Biosciences, University of Birmingham, Edgbaston, B12 2TT, UK 2

17.2.1 INTRODUCTION Certain phthalate plasticizers such as di-(2-ethylhexyl) phthalate, DEHP, belong to the peroxisome proliferator, PP, family of rodent liver carcinogens.1-5 Here, the evidence for peroxisome proliferator-mediated rodent carcinogenesis in response to PPs will be considered together with an evaluation of the molecular basis for rodent-human species differences in response. Specifically, this chapter will focus on the role and mechanisms of peroxisome proliferator-induced rodent peroxisomal gene expression and the evidence for lack of relevance of the mechanism to humans.

17.2.2 GENE EXPRESSION AND CANCER TOXICOLOGY 17.2.2.1 GENE EXPRESSION Within an organism such as a human or a rodent, there are many different types of cells with diverse appearances and functions. However, since they are all derived from a single fertilized egg, it is generally accepted that they all share the same genetic information. Thus, diversity of function and appearance between, for example, a muscle and a skin cell is derived from the expression of different parts of the genetic information in different tissues. In addition to diverse gene expression between cell and tissue types, certain genes are only expressed at certain times and in response to particular stimuli. For example, the hormone oestrogen peaks at certain times in the female reproductive cycle, temporarily switching on certain genes in certain tissues. Each gene consists of two principal parts; the coding sequence and the promoter that acts as an on/off switch for that particular gene (Figure 17.2.1). In turn, certain genes encode regulatory proteins that control expression of the structural genes. These regulatory proteins control gene expression by operating the switch found in the gene promoter region. 17.2.2.2 CANCER BIOLOGY: SOME BASIC CONSIDERATIONS Functioning of the normal human body requires exquisite control of cell survival and proliferation; unwanted cells die whereas others proliferate just enough to maintain health or to repair injury. Cancer occurs when this regulation breaks down causing inappropriate cell proliferation, sometimes in just one cell of the billions of cells in the body. Thus, one shouldn't ask “Why does cancer occur?” but rather “Why doesn't cancer occur more frequently?” The answer to this lies in the multiple checks and balances that operate in the human body to maintain healthy function against the wealth of internal and external challenges from natural and man-made sources.

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Health and Safety Issues with Plasticizers and Plasticized Materials

Figure 17.2.1. DNA, genes and proteins. Each gene consists of a coding sequence and a promoter sequence. The coding sequence contains the information or “blueprint” for new proteins and the promoter contains a regulatory sequence or “switch”. This switch can be turned on or off by regulatory proteins, controlling gene expression.

The field of cancer research has evolved to incorporate an appreciation of the role played by epigenetics in early molecular events that precede mutational changes during tumorigenesis. Pathways, not individual genes, seem to govern the course of cancer and these pathway alterations can be driven by inherited, spontaneous, or environmentally induced epigenetic alterations. Therefore, it appears that cancer arises in three steps: an epigenetic disruption of progenitor cells, an initiating mutation, then genetic and epigenetic plasticity.6

17.2.2.3 DEVELOPING AREAS OF INTEREST IN HEPATOCARCINOGENESIS Areas of developing interest in hepatocarcinogenesis research include the role of functionally diverse proteins including telomerase, p38 MAPK gamma, and tight junction proteins all of which indirectly contribute to liver cancers. Telomerase is an enzyme that prevents telomere shortening during cell division and its inactivity in most adult liver cells underlies hepatocyte senescence. When telomerase becomes reactivated it enables the uncontrolled cell proliferation that precedes hepatocellular carcinoma. Telomerase reverse transcriptase (TERT) encodes part of the telomerase complex and genetic changes to TERT, including amplification, translocation, and promoter mutations, have been implicated in telomerase reactivation.7 Another enzyme of interest in hepatocellular carcinoma (HCC) research is p38 MAPK gamma (p38γ) which acts similarly to, and cooperates with, conserved cyclindependent kinase (CDK), a cyclin protein complex that regulates cell cycle initiation.8

17.2 The rodent hepatocarcinogenic response to phthalate plasticizers

701

Tomás-Loba et al.9 showed that p38γ induced proliferation in mouse hepatocytes while treatment with a p38γ inhibitor protected against chemically induced liver tumor formation and impaired liver regeneration following a partial hepatectomy. The same group then confirmed the significance of p38γ in human hepatocellular carcinoma by analysis of HCC patient tissue biopsies which also showed elevated expression of p38γ. A recent review10 has drawn attention to tight junction (TJ) proteins and their involvement in the pathogenesis of liver disease. TJ proteins are integral to the formation of tight junctions which act as barriers throughout the gastrointestinal tract and liver. When expressed outside of structural tight junctions, TJ proteins also support trafficking, recruitment of signaling proteins, and regulation of gene expression.11 TJ proteins are increasingly being scrutinized for their role in liver cancer as they also serve as cell entry receptors for the hepatitis C virus, a known cause of HCC. Although more data are needed to clarify the role of TJ proteins in hepatocarcinogenesis, they are currently being explored as a potential target for novel therapies for treating liver disease.

17.2.2.4 CHEMICAL CARCINOGENESIS Chemicals can cause cancer in one of two main ways: they can damage DNA or they can interfere with the normal regulation of cell proliferation and cell disposal. Chemicals that damage DNA are called genotoxic (toxic to the genome) and they cause cancer by altering or mutating the genetic code. Chemicals that do not mutate DNA yet cause cancer are called nongenotoxic carcinogens. These chemicals interfere with normal cell regulation, resulting in a proliferation of unwanted cells or in the persistence of "anarchic" cells that should have been eliminated. Genotoxic chemical carcinogens can be detected easily using a range of laboratory tests that detect the genetic mutations correlated with cancer. However, for nongenotoxic chemicals, there are no such assays and detection depends principally upon tests in laboratory animals such as rats and mice given the chemicals throughout their lifetime. Occasionally, cancer does occur in mice alone or sometimes in rats and mice, particularly in the liver. On the strength of the occurrence or not of cancer in one or two rodent species, some chemicals are classed as likely or unlikely human carcinogens. This seems a reasonable "default" approach if there is no evidence to the contrary. However, experimental and epidemiological evidence shows marked species differences in response to some chemicals between rodents and humans with humans failing to show the adverse response noted in rats and mice. The more we understand about how nongenotoxic carcinogens cause cancer in rodents, the more sophisticated this experimental system can be and the more sophisticated the extrapolation to humans. Recent progress means that today we are able to explain many of these changes at the level of the DNA sequence itself via the modulation of gene expression.

17.2.3 PEROXISOME PROLIFERATORS AND RODENT NONGENOTOXIC HEPATOCARCINOGENESIS 17.2.3.1 THE PEROXISOME PROLIFERATORS Peroxisome proliferators, PPs, constitute a large and chemically diverse family of nongenotoxic rodent hepatocarcinogens.12-16 This family includes fibrate hypolipidaemic

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Health and Safety Issues with Plasticizers and Plasticized Materials

drugs such as bezafibrate and gemfibrozil17-19 given to patients at risk of heart disease to lower blood cholesterol and restore lipid balance. Also, the PP class includes chemicals of environmental and industrial significance such as the plasticizer DEHP.1,4,20-21 In the rodent, the evidence for liver tumors in response to PPs is clear and unequivocal. In addition to this hepatocarcinogenesis, PPs induce peroxisomes that are responsible for metabolism of fatty acids.13 One of the key enzymes in this pathway is acyl CoA oxidase, ACO.22-24 Levels of ACO are increased dramatically in the livers of rodents treated with PPs but there is no increase in this enzyme in humans. Because of the close association between peroxisome proliferation and ACO, this enzyme is used as a marker or indicator of the rodent response to PPs. The link between peroxisome proliferation and hepatocarcinogenesis remains to be elucidated. However, evidence suggests a commonality and there is consensus that peroxisome proliferation is necessary but not sufficient per se for the observed onset of rodent liver cancer after prolonged exposure to PPs.25-28

17.2.3.2 PPAR α The liver is a major site of biotransformation and is critical in modulating chemical and metabolically induced toxicity. Peroxisome proliferator-activated receptor (PPAR) subfamily of nuclear receptors, (PPAR)α, β (also known as δ), and γ, identified in the early 1990s, function as sensors for fatty acids and fatty acid derivatives and control important metabolic pathways involved in the maintenance of energy balance. PPARs also regulate other diverse biological processes such as development, differentiation, inflammation, and neoplasia. Specifically, PPARα and PPARβ participate in energy burning, whereas PPARγ is critical in regulating adipocyte differentiation, energy storage by adipocytes and in the immune system. PPARs exhibit differential expression patterns in the liver and there is evidence to suggest that PPARs may modulate hepatotoxicity. PPARα and PPARβ exhibit a protective function in liver toxicity and studies suggest that PPARβ/δ may enhance chemically induced liver toxicity.29-34 PPARs exhibit distinct and noninterchangeable functional roles in mammalian energy metabolism but display high levels of homologies at the protein level. The PPAR subfamily consists of three members namely PPARα (NR1C1), PPARβ/δ (NR1C2), and PPARγ (NR1C3) has two isoforms with a high degree of sequence conservation across the species. All three PPARs in the human and mouse are encoded by separate genes that are on different chromosomes.29,30 PPARα is expressed in tissues with high fatty acid oxidation activities, which include predominantly liver, but also in kidney, small intestine, heart, and skeletal muscle, which is consistent with its predominant functional role in regulating lipid catabolism. In the liver, PPARα is the master regulator of mitochondrial, peroxisomal, and microsomal fatty acid oxidation systems where it is activated by synthetic peroxisome proliferators and in addition senses the influx of fatty acids during fasting to upregulate the fatty acid burning capacity. Also in the liver, PPARβ can be activated by plasma free fatty acids which influx during fasting conditions.30-33.36-37 Generally, a given nuclear receptor regulates the expression of a prescribed set of target genes, co-activators are likely to influence the functioning of many regulators and thus affect the transcription of many genes at different times and during different cellular processes.

17.2 The rodent hepatocarcinogenic response to phthalate plasticizers

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As depicted in Figure 17.2.1, these regulatory proteins can bind to DNA and switch on gene expression. PPARα is such a regulatory protein. It switches on genes by recognizing and binding to the gene promoter region via a specific DNA sequence known as a peroxisome proliferator response element, PPREs. These areas of DNA that can be recognized by PPARα are found in the promoter regions located upstream of PP-responsive genes such as Figure 17.2.2. PPARα mediates the rodent response to that for the peroxisomal enzyme of β-oxiPPs. Binding sites for PPARα have been found in the dation, acyl-CoA oxidase (ACO) (Figure promoters of genes associated with peroxisome prolifer17.2.2.). In the nucleus, PPARs exist as ation such as acyl CoA oxidase, providing proof that PPARα can operate the “switch” and turn on expression heterodimers with retinoid X receptor-α of rodent genes known to be responsive. The binding site bound to DNA with co-repressor molewithin the gene promoter is called a peroxisome prolifercules. Upon binding of a ligand, PPARs ator response element (PPREs) and is defined by the DNA sequence TGACCT repeated once with a one letter undergo shape changes that aid the “spacer” to give TGACCT n TGACCT. removal of co-repressor molecules and invoke a space fitting recruitment of transcription co-factors including coactivators such as PPAR-binding protein (PBP/PPARBP), thyroid hormone receptor-associated protein 220 (TRAP220), mediator complex subunit 1 (MED1) and co-activator-associated proteins. These associations may exert a broader influence on the functions of several nuclear receptors and their target genes. Functional significance for the existence of over 200 nuclear receptor cofactors is not readily evident, but emerging gene knockout mouse models show that some of the coactivators are essential for embryonic growth and survival and for controlling receptor specific target gene expression in cell specific need based demands.

Figure 17.2.3. The response to PPs is lost in a transgenic mouse that has had its DNA altered so that it no longer has the regulatory protein, PPARα. In the PPARα null mouse, there is no peroxisome proliferation, cell proliferation, liver enlargement nor tumors in response to PPs.

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PPARα activation is responsible for the pleiotropic effects of PPs seen in rodents such as enzyme induction, peroxisome proliferation, liver enlargement, and tumors.38-41 Evidence for this is strong and is derived from studies of mice that have had their DNA altered so that they no longer possess PPARα (Figure 17.2.3). These mice are referred to as PPARα null transgenic mice. The PPARα null mouse is refractory to the effects of PPs such as peroxisome proliferation, cell proliferation, liver enlargement, and tumorigenesis, indicating that activation of PPARα is required to mediate these effects.42-43 Transgenic mice have also been developed which exhibit hepatocyte-specific constitutively active PPARα.44-45 Even without PP treatment, these mice spontaneously developed traits similar to those seen in wild-type mice treated with PPs such as decreased serum fatty acid levels and numerous liver effects including increased cell proliferation, hepatomegaly, peroxisome proliferation, and hepatocyte hypertrophy but no carcinogenesis. Thus, data support the position that the pleiotropic effects of PPs in the rodent are mediated by PPARα. The validity of this conclusion has been tested rigorously in the PPARα null mouse using doses of DEHP sufficient to cause significant body weight loss and 100% mortality in wild-type mice by 16 weeks. In this study, PPARα null mice fed DEHP beyond the time at which the wild-type mice had died showed no liver effects.40,46,47 In summary, PPARα mediates the hepatocarcinogenic effects of PPs in the rodent; there are no data to support such effects independent of PPARα.48 Researchers must rely largely on animal models of PPARα activation because human studies on the role of non-therapeutic PPARα agonists and liver cancer cannot be conducted and instead rely on incidental exposure to environmental contaminants. Trichloroethylene is metabolized in humans and rodents alike into molecules acting as PPARα ligands. Exposure to trichloroethylene is a known cause of liver toxicity and cancer in rodents but similar effects are difficult to prove in humans following exposure.49-50 Typically, cohorts are small, confidence intervals are wide, and there are difficulties in establishing a link between potential exposure to environmental chemicals and a particular health outcome. Critics of PPARα null and humanized genetic models have argued that the genetic knockout itself can have consequences independent of treatment with PPs including elevated liver weights in untreated PPARα-humanized mice, reduced lifespans in PPARαnull mice, and altered hepatocellular structure.6 The discovery that DEHP also acts as a potent agonist to CAR2, a human-specific ligand-activated novel constitutive androstane receptor, has also raised questions as to the use of animal models in assessing the impact of PPs on human carcinogenesis.51 However, the validity of such criticisms has been extensively refuted52 on the basis of poor study design, overemphasis of findings, and incomplete statistical analyses in the original papers.

17.2.4 SPECIES DIFFERENCES IN RESPONSE TO PEROXISOME PROLIFERATORS It is well established that there are species difference in response to PPARα activation and peroxisome proliferation.13,52-59 Peroxisome proliferator chemicals are classic nongenotoxic carcinogens. These agents cause liver cancer when chronically administered to rats and mice (not hamster). Available data (both in vitro and in vivo) suggest the rat as the most sensitive and man as the non responsive species to this effect. Furthermore, studies

17.2 The rodent hepatocarcinogenic response to phthalate plasticizers

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with cultured human hepatocytes show that there is no peroxisome proliferation or induction of S-phase in response to PPs. The cascade of molecular events leading to liver cancer in rodents involves hepatocyte proliferation, oxidative stress, increase in proinflammatory cytokines, and inhibition of apoptosis.60 The direct target genes involved in the hepatocarcinogenic effect are not known but certainly there is induction of genes involved in lipid metabolism but not in hepatocellular proliferation.7,47,61-66 It has been shown67 that the mechanism of hepatocellular proliferation involves downregulation of the microRNA let-7c gene by PPARα. Let-7c controls levels of proliferative c-myc by destabilizing its mRNA. Thus, upon suppression of let-7c, c-myc mRNA and protein are elevated, resulting in enhanced hepatocellular proliferation. This effect has been widely reported in studies measuring c-myc expression in both rats and mice following treatment with different PPARα activators.52 In contrast, PPARα humanized mice are resistant to peroxisome proliferator-induced cell proliferation and do not exhibit downregulation of let-7c gene expression and are therefore resistant to hepatocellular carcinogenesis. Furthermore, in a study in cyno monkeys after given a high dose (1g/kg/day) orally of DEHP for 28 days53 a subtle increase in the numbers of peroxisomes (in the same magnitude as the control group given corn oil) with slight enlargements of the mitochondria was demonstrated. The activity of the mitochondrial enzyme CPT increased significantly in males (also in the same magnitude as the corn oil control). This non-compound related response to peroxisome proliferators in monkeys after a very high dose of DEHP was considered to be closer to the response in humans than that seen in rodents. From these data it could be concluded that DEHP induced hepatic peroxisome proliferation in cynomolgus monkeys. However, the degree of increase was very low, hepatomegaly or hepatic proliferation was not observed, and the exposure level was extremely high. Despite the huge number of investigations performed, the underlying mechanism behind PPARα agonist-induced hepatocarcinogenesis is not yet fully understood but is believed to involve increased hepatocyte DNA synthesis and cell proliferation.52 In contrast to genotoxic carcinogens that are activated to electrophilic derivatives that can bind DNA and directly mutate genes, peroxisome proliferators are not metabolically activated. We can assume that hepatic peroxisome proliferation in humans resulting from DEHP is subtle, just as in the case of cynomolgus monkeys.68 There have been no reports showing that peroxisome proliferators induce mitochondrial changes in humans. The issue for peroxisome proliferators is the risk of hepatocarcinogenesis, not peroxisome proliferation itself. Hoivik et al.69 suggested that the primate may be refractory to PPAR-induced hepatocarcinogenesis because cynomolgus monkeys responded to fibrates in a manner that is different from the rodent; that is to say, there was no indication of cell proliferation, and there was no remarkable increase in the mRNA levels for most proteins known to respond to oxidative stress. In addition, the human liver does contain a functional PPARα70 although the expression of PPARα in humans is around 10-fold lower when compared with responsive species such as rat and mouse with non-human primates also exhibiting less PPARα mRNA expression than rodents.58,71-73 Indeed, long-term studies of large human cohorts have found no elevated risk of mortality from liver cancer or other adverse liver effects associated with use of hypolipidaemic drugs.74-75 In total, these data support a "quantitative" hypothesis whereby PPARα expression in humans is sufficient to mediate

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Health and Safety Issues with Plasticizers and Plasticized Materials

the beneficial effects of hypolipidaemic drugs via regulation of genes for enzymes and lipid transporters. Expression levels are too low, however, for modulation of the full battery of genes that are activated in rats and mice such as those involved in peroxisome proliferation and perturbation of hepatocyte growth control. The second hypothesis to explain lack of human response is based on quality of the PPARα-mediated response. Thus, even in the presence of sufficient human PPARα, genes associated with rodent peroxisome proliferation and cancer would not be switched on. Evidence in support of this hypothesis arises from work that shows species difference in the sequence of the ACO gene promoter,76 a marker for rodent Figure 17.2.4. A. Rat, B. Human. Species differences in peroxisome proliferation (Figure 17.2.4). ACO gene promoter sequence and activity. The rat ACO The rat ACO gene promoter contains bindgene is switched on when PPs activate their receptor ing sites for PPARα known as PPREs and, PPARα since PPARα can bind to a specific DNA sequence (TCACCT T TGTCCT) found in the rat gene as expected, rodent ACO levels are promoter. This results in rat ACO gene expression. In increased in the presence of PPs.60 In concontrast, the DNA that makes up the human gene promoter has a different sequence that cannot be switched trast, the human gene sequence differs from on and the human ACO gene is not expressed in the rat gene sequence resulting in an inacresponse to PPs. tive “switch” and no ACO increase in human hepatocytes. Thus, lack of human response to PPs may be attributed to a non-functional “switch” in the genes associated with rodent peroxisome proliferation. The mode of action (MOA)77 for PPARα agonist induced liver cancer is relatively well established despite some early criticisms. An influential paper questioning the acceptance of the PPARα MOA78 has since been refuted as it was found to place too much emphasis on a study with several methodological and statistical limitations (reviewed in Corton et al., 2018).52 There is good evidence showing a profound species difference in the response to PPARα agonism in liver, with rodent models consistently showing enhanced sensitivity as compared to non-human primate and human models, which typically show a diminished response believed to arise from biological and toxicodynamic differences.47,79 These data have been taken to conclude that the MOA for PPARα activation in rodents is either irrelevant, or unlikely to be relevant, to humans. In total, there is good reason to suggest that humans are refractory to PPARα agonist-induced liver cancer, but there are clearly some data gaps that should be filled to specifically delineate the mechanisms underlying the species differences. In summary, to date there have been no reports showing that peroxisome proliferators cause hepatocarcinogenesis in non-human primates or humans.

17.2.5 Chemical regulation

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17.2.5 CHEMICAL REGULATION Since 2007 all chemicals are assessed under the EU chemical legislation REACH (Registration, Evaluation, Authorization and Restriction of Chemicals). The aim of this legislative activity is to ensure a high level of protection for workers, consumers, and the environment against dangerous chemicals.80 The category the chemical is placed in is represented on the label and can have significant economic consequences, restriction of use, and progressive substitution of the most dangerous chemicals when suitable alternatives have been identified. The risk assessment, and therefore the categorization, is based on hazard identification through in vivo studies and exposure calculations. DEHP is a good example of how scientific evidence contributes to the risk assessment and can affect the categorization. Prior to the REACH legislation a 2000 report by the International Agency for Research on Cancer (IARC)81 concluded that PPARα receptor activation was the sole mode of action for DEHP to induce carcinogenicity. Although DEHP causes liver tumors in rats after prolonged exposure, the mechanistic understanding and in vivo evidence of peroxisome proliferator-mediated rodent carcinogenesis explains why these are not considered to be relevant to humans, therefore at the time DEHP was classified as a Group 3 agent (not classifiable as relates to carcinogenicity to humans). In the years since, critics6,78 have questioned the the dismissal of PPARα agonists as a health risk to humans. Subsequently a 2011 IARC appraisal82 looked at new mechanistic data from studies that used PPARα-null mice, studies with several different transgenic mouse lines, in vitro testing, and studies of human DEHP environmental exposure. Collectively, these data indicated that rather than arising from a singular molecular event (PPARα activation), cancer development in rodents arises from several different molecular signals and pathways in a multitude of different cells in the liver. As the IARC could not rule out the human relevance of the molecular events leading to DEHP-induced cancer in rat and mice target tissues the classification of DEHP was changed from a Group 3 agent to a Group 2B-agent (possibly carcinogenic to humans).

17.2.5.1 CHALLENGES IN ALTERNATIVE MODELS In 2007 the National Research Council83 called for a new safety testing paradigm with a focus on short term models of toxicity pathways with the aim of increasing the efficiency and predictive capabilities of chemical evaluation. These alternative models incorporate early biomarkers of effect and higher throughput data streams into risk assessment and have changed how toxicological science approaches human hazard characterization.84-86 This new information now needs to be translated into practical models to guide risk assessment decisions.87 To successfully integrate molecular data into established chemical safety frameworks certain challenges must be overcome including linking molecular changes to functional cellular and pathological effects, differentiating between adverse changes and adaptive or non-adverse changes, and translating data from acute exposure assays to chronic outcomes.88 All toxicity pathways are linked to an adverse health outcome but often the level of change in the toxicity pathway within a model, for example PPARα, is insufficient to produce an adverse health consequence. Lake et al.89 demonstrated highly variable effect

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thresholds for early key events in the MOA for mouse liver tumors mediated by PPARα activation with phthalates including DEHP. These thresholds were then used to anchor early molecular responses with later phenotypic outcomes, demonstrating the importance of well-defined effect thresholds to link observed effects to adverse health outcomes.

17.2.6 SUMMARY In summary, the adverse response of rodents to PPs is mediated by PPARα. The scientific evidence demonstrates that humans are less sensitive to peroxisome proliferation and nonresponsive to tumours induced by PPs such as DEHP. These species differences may be attributed to both differences in the quantity of PPARα and to DNA sequence differences in the promoter regions of genes found to be responsive to PPs in the rodent. At least for one gene that is a marker of rodent peroxisome proliferation, these sequence differences result in a non-functional switch that cannot be activated. These data suggest that PPs, such as the phthalate DEHP, pose no significant risk of cancer to humans.

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17.3 The influence of maternal nutrition on phthalate teratogenicity

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17.3 THE INFLUENCE OF MATERNAL NUTRITION ON PHTHALATE TERATOGENICITY 1

2

Janet Y. Uriu-Adams1 and Carl L. Keen1,2

Departments of Nutrition and Internal Medicine, University of California at Davis, One Shields Avenue, Davis, California, 95616-8669, USA

17.3.1 INTRODUCTION It has been estimated that 2-3% of the world's annual 140 million births will have a major congenital malformation. Despite improvements in the infant mortality rate, birth defects remain the leading cause of infant death in the United States followed by prematurity/low birth weight.1 The World Health Organization, WHO, defines low birth weight as a birth weight