Fluoropolymer Applications in the Chemical Processing Industries 9780815515029, 0815515022

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Fluoropolymers Applications in Chemical Processing Industries The Definitive User’s Guide and Databook

Sina Ebnesajjad, Ph.D. DuPont Fluoroproducts Wilmington, Delaware

Pradip R. Khaladkar DuPont Engineering Technology Wilmington, Delaware

Copyright © 2005 by William Andrew, Inc. No part of this book may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying, recording, or by any information storage and retrieval system, without permission in writing from the Publisher. Plastics Design Library and its logo are owned by William Andrew, Inc. ISBN: 0-8155-1502-2 Library of Congress Cataloging-in-Publication Data Ebnesajjad, Sina. Fluoropolymers applications in chemical processing industries : the definitive user’s guide and databook / Sina Ebnesajjad and Pradip R. Khaladkar. p. cm. Includes bibliographical references and index. ISBN 0-8155-1502-2 (alk. paper) 1. Fluoropolymers--Industrial applications. I. Khaladkar, Pradip R. II. Title. TP1180.F6E34 2005 668.4'238--dc22 2004016616

Printed in the United States of America. This book is printed on acid-free paper. 10 9 8 7 6 5 4 3 2 1 Published in the United States by William Andrew, Inc. 13 Eaton Avenue Norwich, NY 13815 1-800-932-7045 www.williamandrew.com

NOTICE To the best of our knowledge the information in this publication is accurate; however the Publisher does not assume any responsibility or liability for the accuracy or completeness of, or consequences arising from, such information. This book is intended for informational purposes only. Mention of trade names or commercial products does not constitute endorsement or recommendation for use by the Publisher. Final determination of the suitability of any information or product for any use, and the manner of that use, is the sole responsibility of the user. Anyone intending to rely upon any recommendation of materials or procedures mentioned in this publication should be independently satisfied as to such suitability, and must meet all applicable safety and health standards.

William Andrew, Inc., 13 Eaton Avenue, Norwich, NY 13815 Tel: 607/337/5080 Fax: 607/337/5090

Dedicated to Ghazale and Shaila

Series Editor’s Preface This is the latest book in the PDL (Plastics Design Library) Fluorocarbon Series. The original idea for the Fluorocarbon Series was conceived in the mid1990s. Two important rationales precipitated the development of the collection. First, there were no definitive sources for the study of fluorinated polymers that included the commercial products. A researcher seeking the properties and characteristics of fluorinated plastics did not have a book that could serve as a single-source reference. Information put out by commercial manufacturers of polymers has long been the source of choice. Second, the post-war generation (a.k.a., baby boomers) were beginning to retire, thus reducing the available knowledge in the industry and academia. The selection of the topics for the books has been made based on the importance of the practical applications of fluorinated polymers. Inevitably, a number of fluorinated macromolecule classes that are important in their own right had to be left out of the Sina Ebnesajjad

series. In each class, the size of its audience was simply too small to meet the economic requirements of publishing. The first two books of the series cover commercial fluoropolymers (ethylinic); the third book focuses on their applications in the chemical processing industries. The fourth book deals with fluoroelastomers, the fifth with fluorinated coatings and finishes, and the sixth book is about fluorinated ionomers such as Nafion®. The authors of these handbooks are leaders in their fields who have devoted their professional careers to acquiring substantial expertise. Each book is a product of decades of the author’s experience and several years of research into the available body of knowledge. Our hope is that these books will meet the needs of the people who work with fluorinated polymers for any reason. Future revisions are planned to keep this series abreast of progress in these fields. July 2004

Authors’ Preface The first two books in this series dealt with fluoropolymers manufacturing, properties, and fabrication technologies. The aim of the present book is to build upon the information in the first two books to address the use of fluoropolymers in the chemical processing industry (CPI) and other allied industries. They include food, pharmaceutical, semiconductor, and pulp and paper industries. This book is both a reference and a source for learning the basics for those involved in the entire product value chains related to the chemical industries, from fluoropolymer producers all the way to the end-users. The reader will be able to read about how the unique characteristics of fluoroplastics are utilized in the design and construction of equipment exposed to harsh chemical environments. This book offers information helpful to engineers, maintenance personnel, students, material managers, and all others involved in the chemical processing industries. This book emphasizes the practical over the theoretical. There are numerous sources for in-depth study of topics including polymerization and the polymer science of fluoropolymers. Some of these references have been listed at the end of pertinent chapters, serving as both bibliography and additional reading sources. Review papers are particularly helpful as a starting point for finding additional sources for concentrated reading in a selected area. The chapters of this book have been written to allow sequential and independent reference to them. Chapters 1 and 2 introduce the reader to fluoropolymers, fluoroelastomers, and the other materials of construction used to manufacture parts Sina Ebnesajjad Pradip R. Khaladkar

that come in contact with chemicals in factories. Chapters 3 and 4 elaborate on the properties of fluoropolymers and their selection for various parts. Chapters 5 and 6 describe processes to convert fluoropolymers into shapes and parts. Chapter 7 covers the fabrication techniques used to finish the fluoropolymer shapes/parts. Chapter 8 reviews design and construction of the basic process components of a chemical handling plant. Chapter 9 describes the operation and maintenance of vessels and tanks. Chapter 10 provides an approach and material on laboratory techniques that can be applied to determine the cause of failure of parts. Chapter 11 offers a modeling methodology to predict and analyze failure of fluoropolymer parts, thus allowing design improvement. Chapters 12–14 are devoted to the cost analysis, safety considerations, and future trends of fluoropolymers. The “Glossary,” “Appendixes,” “Trademarks,” and “Index” sections provide additional information and tools to facilitate finding information in the book. We have tried to present the data in SI units in most of the book. A large number of parts are, however, still specified in English units. In such cases, conversion factors have been listed in footnotes to allow the reader to convert to metric units. None of the views or information presented in this book reflects the opinions of any of the companies or individuals that have contributed to the book. If there are errors, they are oversights on the part of the authors. A note to the publisher indicating the specific error, for the purpose of correcting future editions, would be much appreciated. July 2004

Acknowledgments We owe the majority of our learning and experience in the field of fluoropolymers to our employment at the DuPont Company. DuPont Fluoroproducts and DuPont Engineering Technology have generously contributed to this volume by providing a great deal of the data and research material, and by supporting literature searches, securing reference material, and the preparation of the manuscript. We thank the companies that have provided us with information, photographs, and illustrations; they have been cited usually in the captions, and in some cases in the bibliography section at the end of the chapter. A number of companies have furnished the authors with information, which has been cited in the bibliography section at the end of each chapter. The following corporations have provided the authors with the data in their commercial information bulletins: DuPont, Solexis, Daikin, Dyneon, Asahi Glass America, Atofina, Crane Resistoflex, Edlon, Dualam, RMB Co., Xomox, RL Industries, Electrochemical Engineering and Manufacturing Company, and Wisconsin Protective Coatings Co. We sincerely appreciate the contribution that the data supplied by each company have made to this book. Special thanks go to our friend Dr. Lawrence McKeen, DuPont Fluoropolymer Solutions, for contributing the powder coating technology section included in Chapter 8. We would like to sincerely thank Dr. Jörgen Bergström and Dr. Stewart Brown

from Exponent, Inc., for their generosity in contributing Chapter 11 to this book. This is a better book because of the contribution of these colleagues who are at the forefront of the science and technology. We have made a great deal of use of data developed and organized by our colleagues and friends in the DuPont Company, S. A., in Geneva, Switzerland. We would like to specially acknowledge Dr. Theodore Schroots for data, figures, and tables that he has developed over the last three decades. Mr. Tom Johns from DuPont Information and Computing Technology conducted the literature search for this book; we thank Tom and his colleagues for the reference material, including articles, books, and patents. Our sincere thanks go to Mrs. Jeanne Roussel and the Write One staff for converting the raw manuscript into a real book with care and patience. Editorial suggestions and support by Ms. Millicent Treloar, William Andrew Publishing, have greatly upgraded the organization and the text. It would have been impossible for us to complete this project without the many helpful suggestions and moral support of William Woishnis, CEO of Plastics Design Library, at William Andrew Publishing. Finally, there are not enough words for the authors to thank their life partners, Ghazale Dastghaib and Shaila Khaladkar, who have provided unlimited encouragement throughout this project.

Table of Contents 1 Introduction to Fluoropolymers .................................................................................................. 1 1.1 1.2 1.3 1.4 1.5

Introduction ............................................................................................................................. 1 What are Fluoropolymers? ............................................................................................................ 1 Fundamental Properties of Fluoropolymers ................................................................................. 2 Developmental History of Fluoropolymers .................................................................................. 3 Examples of Uses of Fluoropolymers ........................................................................................... 5

References ................................................................................................................................................ 6

2 Materials of Construction ............................................................................................................ 7 2.1 2.2 2.3 2.4

Introduction ............................................................................................................................. 7 Historical Background .................................................................................................................. 7 Definition of Polymer-based Materials ........................................................................................ 8 Comparison Between Polymer-based Materials and Metals ........................................................ 8 2.4.1 Position of Fluoropolymers in the Materials Spectrum .................................................. 10 2.5 Applications of Polymer-based Materials for Corrosion Control .............................................. 10 2.5.1 Applications of Fluoropolymers for Corrosion Control ................................................. 10

References .............................................................................................................................................. 14

3 Properties of Neat (Unfilled) and Filled Fluoropolymers ....................................................... 15 3.1 Introduction ........................................................................................................................... 15 3.2 Influence of Processing on Fluoroplastics .................................................................................. 15 3.3 Chemical Compatibility of Fluoropolymers ............................................................................... 15 3.3.1 Chemical Compatibility of Perfluoropolymers ............................................................... 15 3.3.1.1 Effect of Ozone on Fluoropolymers .................................................................. 16 3.3.1.2 Oxygen Compatibility of PTFE ......................................................................... 17 3.3.2 Chemical Compatibility of Partially Fluorinated Fluoropolymers ................................. 17 3.3.3 Chemical Compatibility of Polychlorotrifluoroethylene ................................................ 18 3.4 Permeation Fundamentals ........................................................................................................... 18 3.4.1 Permeation Measurement and Data ................................................................................. 20 3.5 Environmental Stress Cracking ................................................................................................... 21 3.6 Properties and Characteristics of PTFE ...................................................................................... 23 3.6.1 Introduction to Filled PTFE Compounds ........................................................................ 23 3.6.1.1 Granular-based Compounds .............................................................................. 23 3.6.1.2 Fine Powder-based Compounds ........................................................................ 25 3.6.1.3 Compounding with Engineering Polymers ........................................................ 25 3.6.1.4 Reinforced Gasketing Material.......................................................................... 26 3.6.1.5 Co-Coagulated Compounds ............................................................................... 26 3.6.1.6 Fabrication of Parts from Compounds .............................................................. 26 3.6.1.7 Typical Properties of Filled Fluoropolymers .................................................... 27 3.6.2 Mechanical Properties of PTFE ...................................................................................... 28 3.6.2.1 Deformation Under Load (Creep) and Cold Flow ............................................ 35 3.6.2.2 Fatigue Properties .............................................................................................. 36 3.6.2.3 Impact Strength .................................................................................................. 36 3.6.2.4 Hardness ............................................................................................................ 36 3.6.2.5 Friction ............................................................................................................... 36

xii

CONTENTS 3.6.2.6 PV Limit ............................................................................................................ 47 3.6.2.7 Abrasion and Wear ............................................................................................ 47 3.6.3 Electrical Properties of PTFE .......................................................................................... 47 3.6.4 Thermal Behavior of PTFE ............................................................................................. 47 3.6.4.1 Thermal Stability ............................................................................................... 47 3.6.4.2 Thermal Expansion ............................................................................................ 51 3.6.4.3 Thermal Conductivity and Heat Capacity ......................................................... 51 3.6.4.4 Heat Deflection Temperature ............................................................................ 51 3.6.5 Irradiation Resistance of PTFE ....................................................................................... 51 3.6.6 Standard Measurement Methods for PTFE ..................................................................... 52 3.7 Properties and Characteristics of Melt-processible Fluoroplastics ............................................ 55 3.7.1 Mechanical and Dynamic Properties ............................................................................... 55 3.7.1.1 Tensile Properties .............................................................................................. 55 3.7.1.2 Moduli ................................................................................................................ 55 3.7.1.3 Deformation Under Load (Creep) ..................................................................... 69 3.7.1.4 Poisson’s Ratio .................................................................................................. 69 3.7.1.5 Flex Fatigue Properties ...................................................................................... 69 3.7.1.6 Impact Strength .................................................................................................. 70 3.7.1.7 Hardness ............................................................................................................ 82 3.7.1.8 Friction, Wear, and Abrasion ............................................................................. 82 3.7.2 Thermal Properties of Melt-processible Fluoropolymers ............................................... 86 3.7.2.1 Thermal Stability ............................................................................................... 86 3.7.2.2 Temperature-related Properties ......................................................................... 89 3.7.2.3 Thermal Aging ................................................................................................... 89 3.7.3 Weatherability of Melt-processible Fluoroplastics ......................................................... 94 3.7.4 Electrical Properties of Melt-processible Fluoroplastics ................................................ 96 3.7.4.1 Perfluoroalkoxy Polymers ................................................................................. 96 3.7.4.2 FEP ..................................................................................................................... 98 3.7.4.3 PVDF ................................................................................................................. 98 3.7.4.4 ETFE ................................................................................................................ 100 3.7.4.5 ECTFE ............................................................................................................. 100 3.7.5 Optical and Spectral Properties of Melt-processible Fluoroplastics ............................ 100 3.7.6 Radiation Effect on Melt-processible Fluoroplastics .................................................... 100 3.7.7 Flammability of Melt-processible Fluoroplastics ......................................................... 110 3.7.8 Biofilm Formation of Melt-processible Fluoroplastics ................................................. 110 References ............................................................................................................................................ 112

4 Selecting Fluoropolymers for Corrosion Control .................................................................. 117 4.1 Introduction ......................................................................................................................... 117 4.1.1 Corrosion of Metals ....................................................................................................... 117 4.1.2 Corrosion of Polymer Materials .................................................................................... 117 4.1.3 Approaches to Selection ................................................................................................ 117 4.2 Economics of Selecting Fluoropolymers .................................................................................. 118 4.3 Preparing to Determine Compatibility ...................................................................................... 118 4.4 Current Technology for Determining Compatibility ................................................................ 118 4.4.1 Experience ..................................................................................................................... 118 4.4.2 Manufacturers’ Literature ............................................................................................. 119 4.4.3 Testing ......................................................................................................................... 149 4.4.3.1 Coupon Testing ................................................................................................ 149

CONTENTS

xiii 4.4.3.2 Simulated Testing ............................................................................................ 150 4.4.3.3 Special Testing ................................................................................................. 154 4.4.4 Fabrication Considerations in Materials Selection ....................................................... 154 4.4.5 Inspection and Maintenance Aspects of Materials Selection ....................................... 157

References ............................................................................................................................................ 157

5 Manufacturing of Parts from Polytetrafluoroethylene Polymers ........................................ 161 5.1 Granular Resin Processing ........................................................................................................ 161 5.1.1 Resin Selection .............................................................................................................. 161 5.1.2 Compression Molding ................................................................................................... 162 5.1.2.1 Equipment ........................................................................................................ 162 5.1.2.2 Densification and Sintering Mechanism ......................................................... 163 5.1.2.3 Billet Molding .................................................................................................. 164 5.1.3 Automatic Molding ........................................................................................................ 167 5.1.4 Isostatic Molding ........................................................................................................... 168 5.1.4.1 Introduction to Isostatic Molding .................................................................... 168 5.1.4.2 Comparison of Isostatic with Other Fabrication Techniques .......................... 169 5.1.4.3 Wet- and Dry-Bag Isostatic Molding ............................................................... 170 5.1.5 Ram Extrusion ............................................................................................................... 170 5.1.5.1 Introduction to Ram Extrusion ........................................................................ 170 5.1.5.2 Ram Extrusion: Basic Technology .................................................................. 170 5.2 Fine Powder Resin Processing .................................................................................................. 174 5.2.1 Resin Handling and Storage .......................................................................................... 174 5.2.2 Paste Extrusion Fundamentals ....................................................................................... 175 5.2.3 Extrusion Aid or Lubricant ............................................................................................ 176 5.2.4 Wire Coating .................................................................................................................. 176 5.2.4.1 Blending the Resin with Lubricant .................................................................. 176 5.2.4.2 Preforming ....................................................................................................... 176 5.2.4.3 Extrusion Equipment and Process ................................................................... 177 5.2.5 Extrusion of Tubing ....................................................................................................... 178 5.2.5.1 Spaghetti Tubing .............................................................................................. 178 5.2.6 Pressure Hoses ............................................................................................................... 178 5.2.6.1 Blending Lubricant and Pigment and Preforming ........................................... 183 5.2.6.2 Extrusion Process for Pressure Hoses ............................................................. 183 5.2.6.3 Quality Control of Pressure Hoses .................................................................. 183 5.2.7 Unsintered Tape ............................................................................................................. 185 5.3 Fluoropolymer Dispersion Processing ...................................................................................... 185 5.3.1 Dispersion Applications ................................................................................................ 186 5.3.2 Storage and Handling of Dispersions ............................................................................ 186 5.3.3 Dispersion Formulation and Characteristics ................................................................. 187 5.3.3.1 Formulation ...................................................................................................... 188 5.3.4 Glass Cloth Coating by Dispersion ............................................................................... 188 5.3.4.1 Equipment ........................................................................................................ 189 5.3.4.2 Processing ........................................................................................................ 189 5.3.5 Dispersion Impregnation of Flax and Polyaramide ....................................................... 191 5.3.5.1 Processing ........................................................................................................ 191 5.3.6 Coating Metal and Hard Surfaces with Dispersion ....................................................... 191 References ............................................................................................................................................ 192

xiv

CONTENTS

6 Manufacturing Parts from Melt-processible Fluoropolymers ............................................. 193 6.1 Introduction ......................................................................................................................... 193 6.2 Materials of Construction ......................................................................................................... 193 6.3 Rheology of Fluoropolymer Melts............................................................................................ 193 6.3.1 Characterization of Rheology of Fluoropolymers ......................................................... 194 6.4 Thermal Stability of Fluoropolymers ....................................................................................... 198 6.5 Melt Extrusion ......................................................................................................................... 199 6.5.1 The Extruder .................................................................................................................. 199 6.5.2 Film Extrusion ............................................................................................................... 202 6.5.3 Sheet Extrusion .............................................................................................................. 202 6.5.3.1 Production ........................................................................................................ 202 6.5.4 Pipe and Tube Extrusion ............................................................................................... 202 6.5.4.1 Production ........................................................................................................ 203 6.5.5 Coextrusion .................................................................................................................... 203 6.5.6 Drawdown Ratio (DDR) ................................................................................................ 205 6.6 Fluoropolymer Tube Extrusion ................................................................................................. 206 6.6.1 Sizing of Tubes .............................................................................................................. 206 6.6.1.1 Small Diameter Tubes ..................................................................................... 207 6.6.1.2 Medium Diameter Tubes ................................................................................. 207 6.6.1.3 Large Diameter Tubes ..................................................................................... 208 6.6.2 Heat Shrink Tubes ......................................................................................................... 208 6.7 Fluoropolymer Film Extrusion ................................................................................................. 209 6.7.1 PVDF Films ................................................................................................................... 210 6.7.2 ETFE and ECTFE Films ............................................................................................... 214 6.7.3 Perfluoropolymer Films ................................................................................................. 217 6.8 Injection Molding ...................................................................................................................... 219 6.8.1 Injection Molding of Fluoropolymers ........................................................................... 219 6.8.1.1 Injection Molding Equipment .......................................................................... 219 6.8.1.2 Process Conditions and Operations ................................................................. 222 6.8.1.3 Dimensional Stability of Parts ......................................................................... 225 6.9 Rotational Molding ................................................................................................................... 226 6.9.1 Basic Process Technology ............................................................................................. 229 6.9.2 Rotomolding and Rotolining Processing Conditions .................................................... 229 6.9.2.1 ECTFE ............................................................................................................. 231 6.9.2.2 ETFE ................................................................................................................ 232 6.9.2.3 PFA .................................................................................................................. 232 6.9.3 Conclusion ..................................................................................................................... 233 6.10 Other Part Manufacturing Techniques ...................................................................................... 235 6.10.1 Compression Molding of Fluoropolymers .................................................................... 235 6.10.2 Transfer Molding of Fluoropolymers ............................................................................ 237 6.10.2.1 Mold Design .................................................................................................... 237 6.10.2.2 Operation of the Mold ..................................................................................... 239 6.10.2.3 Transfer Molding Process Variables................................................................ 239 6.10.3 Examples of Transfer Molded Parts .............................................................................. 241 6.10.4 Blow Molding Fluoropolymers ..................................................................................... 244 6.11 Vacuum Bagging ....................................................................................................................... 248 References ............................................................................................................................................ 250

CONTENTS

xv

7 Fabrication Techniques for Fluoropolymers .......................................................................... 253 7.1 Introduction ......................................................................................................................... 253 7.2 Machining ......................................................................................................................... 253 7.2.1 Sawing and Shearing ..................................................................................................... 254 7.2.2 Drilling (Tapping and Threading) ................................................................................. 254 7.2.3 Skiving ......................................................................................................................... 254 7.3 Adhesive Bonding Methods ...................................................................................................... 255 7.3.1 Contact Adhesives ......................................................................................................... 255 7.3.2 Bonding Adhesives ........................................................................................................ 255 7.3.3 Sodium Etching ............................................................................................................. 256 7.3.4 Plasma Treatment .......................................................................................................... 258 7.3.5 Flame Treatment ............................................................................................................ 261 7.3.6 Corona Discharge (Hybrid Plasma) Treatment ............................................................. 262 7.4 Welding and Joining.................................................................................................................. 265 7.4.1 Welding Techniques ...................................................................................................... 266 7.4.2 Welding PTFE ............................................................................................................... 267 7.4.3 Welding FEP .................................................................................................................. 269 7.4.4 Welding PFA .................................................................................................................. 269 7.4.5 Welding PVDF ............................................................................................................... 271 7.4.6 Welding ETFE ............................................................................................................... 273 7.5 Heat Bonding ......................................................................................................................... 273 7.5.1 Sheet Liners ................................................................................................................... 274 7.6 Thermoforming ......................................................................................................................... 274 7.7 Other Processes ......................................................................................................................... 274 References ............................................................................................................................................ 276

8 Design and Construction of Linings and Vessels ................................................................... 279 8.1 Introduction ......................................................................................................................... 279 8.2 Lining of Vessels ....................................................................................................................... 279 8.2.1 Adhesively Bonded Linings for Vessels ........................................................................ 280 8.2.2 Rotolining ...................................................................................................................... 281 8.2.3 Spray and Baked Coatings ............................................................................................. 286 8.2.3.1 Powder Coating Processes ............................................................................... 287 8.2.3.2 Liquid Dispersion Coatings ............................................................................. 295 8.2.4 Loose Lining .................................................................................................................. 295 8.2.5 Dual Laminate ............................................................................................................... 296 8.3 Lining of Pipes and Fittings ...................................................................................................... 299 8.4 Lined Valves ......................................................................................................................... 299 8.4.1 Plug Valves .................................................................................................................... 301 8.4.2 Ball Valves ..................................................................................................................... 301 8.4.3 Butterfly Valves ............................................................................................................. 301 8.4.4 Diaphragm Valves .......................................................................................................... 301 8.4.5 Clamp Valves ................................................................................................................. 301 8.5 Lined Hoses ......................................................................................................................... 301 8.6 Lined Expansion Joints ............................................................................................................. 304 8.7 Lining or Coating of Internals................................................................................................... 304 8.8 Design and Fabrication of Vessels for Lining .......................................................................... 304 8.9 Shop Versus Field Fabrication .................................................................................................. 304

xvi

CONTENTS References ............................................................................................................................................ 309

9 Operations and Maintenance .................................................................................................. 311 9.1 Operations ......................................................................................................................... 311 9.2 Maintenance ......................................................................................................................... 311 9.2.1 Visual Examination ....................................................................................................... 311 9.2.1.1 Visual Inspections of Vessels .......................................................................... 311 9.2.1.2 Visual Inspection of Piping and Fittings ......................................................... 312 9.2.1.3 Visual Inspection of Valves ............................................................................. 312 9.2.1.4 Visual Inspection of Hoses .............................................................................. 312 9.2.1.5 Visual Inspection of Expansion Joints ............................................................ 312 9.2.2 Nondestructive and Destructive Examination ............................................................... 312 9.2.3 Non-Intrusive Examination ........................................................................................... 313 9.2.4 Risk-based Inspection Strategy (RBI) ........................................................................... 313 9.3 Repairs ......................................................................................................................... 314

10 Failure Analysis ........................................................................................................................ 315 10.1 10.2 10.3 10.4

Introduction ......................................................................................................................... 315 Part Failure ......................................................................................................................... 315 Defect Analysis ......................................................................................................................... 316 Application of Failure Analysis Methodology ......................................................................... 322 10.4.1 Infrared Spectroscopy .................................................................................................... 324 10.4.2 Electron Microscopy Techniques .................................................................................. 328 10.4.2.1 Scanning Electron Microscopy (SEM) ............................................................ 328 10.4.2.2 Transmission Electron Microscopy (TEM) ..................................................... 328 10.4.2.3 Energy Dispersive X-Ray (EDX) Spectroscopy ............................................. 328 10.4.3 Mass Spectroscopy (MS) ............................................................................................... 328 10.4.4 Gas Chromatography (GC) ............................................................................................ 331 10.4.5 Nuclear Magnetic Resonance (NMR) ........................................................................... 331 10.4.6 Differential Scanning Calorimetry (DSC) ..................................................................... 331 10.4.7 Differential Thermal Analysis (DTA) ........................................................................... 332 10.4.8 Dynamic Mechanical Analysis (DMA) ......................................................................... 339 10.4.9 Thermogravimetric Analysis (TGA) ............................................................................. 342 10.5 Surface Analysis ....................................................................................................................... 342 10.5.1 Electron Spectroscopy for Chemical Analysis (ESCA) ................................................ 342 10.5.2 Secondary Ion Mass Spectroscopy (SIMS) ................................................................... 345 10.6 Examples of Failure Analysis ................................................................................................... 345 10.6.1 Case 1: Failed Lined Pipe .............................................................................................. 345 10.6.2 Case 2: Failed Check Valves ......................................................................................... 345 10.6.3 Case 3: Black Spots on FEP Coating ............................................................................ 348 10.6.4 Case 4: Braided Hose Failure ........................................................................................ 348 10.7 Physical Defects Due to Part Fabrication ................................................................................. 350 10.7.1 Polytetrafluoroethylene (PTFE) .................................................................................... 350 10.7.2 Melt-processible Fluoropolymers .................................................................................. 352 10.7.2.1 Injection Molding ............................................................................................ 352 10.7.2.2 Rotational and Transfer Molding .................................................................... 352 10.7.3 Measurement of Flaws .................................................................................................. 352 References ............................................................................................................................................ 356

CONTENTS

xvii

11 Modeling and Mechanical Analysis of Fluoropolymer Components ................................... 359 J. S. Bergström and S. Brown, EXPONENT Engineering, Inc. 11.1 Introduction ......................................................................................................................... 359 11.2 Review of Modeling Techniques ..............................................................................................359 11.3 Currently Available Material Models ....................................................................................... 360 11.3.1 Linear Elasticity ............................................................................................................. 362 11.3.2 Hyperelasticity ............................................................................................................... 362 11.3.3 Linear Viscoelasticity .................................................................................................... 363 11.3.4 Dual Network Fluoropolymer (DNF) Model ................................................................ 364 11.4 Failure and Deformation Predictions ........................................................................................368 11.4.1 Failure under Monotonic Loading ................................................................................. 369 11.4.2 Failure under Cyclic Loading ........................................................................................ 370 11.5 Examples ......................................................................................................................... 371 11.5.1 Corrugated PTFE Hose .................................................................................................. 371 11.5.2 Threaded Connection Gasket ........................................................................................ 372 11.6 Summary ......................................................................................................................... 378 References ............................................................................................................................................ 380

12 Cost Analysis ............................................................................................................................. 381 12.1 Introduction 12.2 Cost Analysis

......................................................................................................................... 381 ......................................................................................................................... 381

References ............................................................................................................................................ 384

13 Safety, Disposal, and Recycling of Fluoropolymers ............................................................... 385 13.1 13.2 13.3 13.4 13.5

Introduction ......................................................................................................................... 385 Toxicology of Fluoropolymers ................................................................................................. 385 Thermal Properties of Fluoropolymers ..................................................................................... 385 Emission During Processing ..................................................................................................... 386 Safety Measures ........................................................................................................................ 386 13.5.1 Ventilation ...................................................................................................................... 386 13.5.2 Processing and Fabrication ............................................................................................ 389 13.5.2.1 Sintering ........................................................................................................... 389 13.5.2.2 Paste Extrusion ................................................................................................ 389 13.5.2.3 Dispersion Coating .......................................................................................... 389 13.5.2.4 Melt Processing ............................................................................................... 389 13.5.2.5 Machining ........................................................................................................ 390 13.5.2.6 Soldering and Melt Stripping .......................................................................... 390 13.5.2.7 Welding Fluoropolymer ................................................................................... 390 13.5.2.8 Welding and Flame-Cutting Fluoropolymer-Lined Metals ............................. 390 13.5.3 Spillage Cleanup ............................................................................................................ 390 13.5.4 Equipment Cleaning and Maintenance.......................................................................... 390 13.5.5 Protective Clothing ........................................................................................................ 390 13.5.6 Personal Hygiene ........................................................................................................... 390 13.5.7 Fire Hazard .................................................................................................................... 390 13.5.8 Material Incompatibility ................................................................................................ 391 13.6 Food Contact and Medical Applications .................................................................................. 391 13.7 Fluoropolymer Scrap and Recycling ........................................................................................ 391

xviii

CONTENTS 13.8 Environmental Protection and Disposal Methods .................................................................... 391 References ............................................................................................................................................ 392

14 Future Trends ............................................................................................................................ 393 14.1 14.2 14.3 14.4 14.5

Introduction ......................................................................................................................... 393 Fluoropolymer Applications ...................................................................................................... 393 Fluoropolymer Resin Manufacturing ........................................................................................ 393 Growth of Fluoropolymer Industries ......................................................................................... 393 Technological Needs of Chemical Processing Industry ............................................................. 394 14.5.1 Non-destructive and Non-intrusive Condition Assessment ............................................ 394 14.5.2 Accelerated Testing for Compatibility ........................................................................... 394

References ............................................................................................................................................ 394

Appendix I: Permeation Properties of Perfluoroplastics ............................................................. 395 I.1 Perfluoroalkoxy Resin ............................................................................................................... 395 I.1.1 Permeability to Gases..................................................................................................... 395 References ............................................................................................................................................ 400

Appendix II: Permeation Properties of Partially Fluorinated Fluoroplastics ........................... 401 II.1 Polyvinylidene Fluoride ............................................................................................................. 401 II.1.1 Permeability ................................................................................................................... 401 II.1.2 Permeability To Gases ................................................................................................... 401 II.1.3 Permeability To Liquids ................................................................................................. 401 II.2 Ethylene Tetrafluoroethylene Copolymer .................................................................................. 410 II.3 Ethylene Chlorotrifluoroethylene Copolymer ............................................................................ 412 II.3.1 Permeability to Gases and Water Vapor......................................................................... 412 II.4 Polyvinyl Fluoride ..................................................................................................................... 417 II.5 Fluorinated Polyethylene ........................................................................................................... 417 II.5.1 Permeability to Oxygen .................................................................................................. 417 References ............................................................................................................................................ 420

Appendix III: Permeation of Automotive Fuels Through Fluoroplastics .................................. 421 III.1 Test Method ......................................................................................................................... 421 III.1.1 Fuel Types ...................................................................................................................... 421 References ............................................................................................................................................ 422

Appendix IV: Permeation of Organic and Inorganic Chemicals Through Fluoroplastic Films ......................................................................................................................... 423 References ............................................................................................................................................ 426

Appendix V: Chemical Resistance of Thermoplastics ................................................................. 427 V.1 Chemical Resistance of Fluoropolymers ..................................................................................427 V.2 PDL Resistance Rating ..............................................................................................................427

Chemical Resistance Tables......................................................................................................................429 Glossary ........................................................................................................................................... 521 Trademarks...................................................................................................................................... 549 Index ................................................................................................................................................ 551

1 Introduction to Fluoropolymers 1.1

Introduction

This book is about the use of fluoropolymers in chemical processing industries. These industries include those that handle chemicals, usually corrosive, during the manufacturing of diverse products. Examples of important industries include chemical manufacturing, plastics manufacturing and processing, semiconductor manufacturing, pharmaceutical and biopharmaceutical industries, and food processing. Fluoropolymers often replace exotic alloys in processes involving corrosive chemistry. This plastic family has successfully met the requirement of purity which is essential in semiconductor, food, and biopharmaceutical production. The nonstick surface and extreme temperature characteristics of fluoropolymers have reserved a special place for them in the world of construction materials. This chapter offers a brief history of the discovery and the evolution of fluoropolymers, their applications, and the introduction of various types of this plastic family. The era of fluoropolymers began with a small mishap which did not go unnoticed by the ingenious and observant Dr. Roy Plunkett of DuPont Company.[1] In 1938, he had been at DuPont for two years, concentrating mostly on the development of fluorinated refrigerants. He was experimenting with tetrafluoroethylene (TFE) for synthesis of a useful refrigerant (CClF2–CHF2).[2] The effort was spurred by the desire to create safe, nonflammable, nontoxic, colorless, and odorless refrigerants. On the morning of April 6, 1938, when Plunkett checked the pressure on a full cylinder of TFE, he found none. However, the cylinder had not lost weight. Careful removal of the valve and shaking the cylinder upside down yielded a few grams of a waxy looking white powder—the first polymer of tetrafluoroethylene.[2] Plunkett analyzed the white powder, which was conclusively proven to be polytetrafluoroethylene (PTFE). The slippery PTFE could not be dissolved in any solvent, acid, or base, and upon melting formed a stiff clear gel without flow.[3] Later, research led to the discovery of processing techniques similar to those used with metal powders. At the time, the Man-

hattan Project was seeking new corrosion-resistant materials for gaskets, packings, and liners for UF6 handling. PTFE provided the answer and was used in production. The US government maintained a veil of secrecy over the PTFE project until well after the end of World War II. Large-scale monomer synthesis and controlled polymerization were technical impediments to be resolved. Intensive studies solved these problems and small-scale production of Teflon® (trademark, 1944) began in 1947. In 1950, DuPont scaled up the commercial production of Teflon® in the USA with the construction of a new plant in Parkersburg, West Virginia. In 1947, Imperial Chemical Industries built the first PTFE plant outside the US, in Western Europe. Since then, many more plants have been built around the globe. Over the last six decades, many forms of PTFE and copolymers of other monomers and TFE have been developed and commercialized. The words of Plunkett himself best summarize the discovery of PTFE. He recounted the story of Teflon® in a speech to the American Chemical Society at its April 1986 meeting in New York. “The discovery of polytetrafluoroethylene (PTFE) has been variously described as (i) an example of serendipity, (ii) a lucky accident, and (iii) a flash of genius. Perhaps all three were involved. There is complete agreement, however, on the results of that discovery. It revolutionized the plastics industry and led to vigorous applications not otherwise possible.”[2]

1.2

What are Fluoropolymers?

Traditionally, a fluoropolymer or fluoroplastic is defined as a polymer consisting of carbon (C) and fluorine (F). Sometimes these are referred to as perfluoropolymers to distinguish them from partially fluorinated polymers, fluoroelastomers, and other polymers that contain fluorine in their chemical structure. For example, fluorosilicone and fluoroacrylate polymers are not referred to as fluoropolymers. An example of a linear fluoropolymer is tetrafluoroethylene polymer (PTFE):

2

FLUOROPOLYMERS APPLICATIONS IN CHEMICAL PROCESSING INDUSTRIES

F

F

F

F

C

C

C

C

F

F

F

F

A simplistic analogy would be to the chemical composition of polyethylene [(–CH2–CH2–)n] where all the hydrogen atoms have been replaced by fluorine atoms. Of course, in practice, PTFE and polyethylene are prepared in totally different ways. There are branched fluoropolymers such as fluorinated ethylene propylene polymer (FEP): F

F

F

F

F

F

C

C

C

C

C

C

F

F

F F

F F

F

C

ety of polymer properties such as lower crystallinity, clarity, and resistance to water vapor. There is a second class of fluoropolymers called “partially fluorinated” in contrast to “perfluorinated” polymers. These molecules include hydrogen (H) in addition to fluorine and carbon. Examples include polyvinyl fluoride, polyvinylidene fluoride, ethylene tetrafluoroethylene copolymer, and ethylene chlorotrifluoroethylene copolymer. H

H

H

H

C

C

C

C

H

F

H

F

Polyvinyl fluoride

F

Oxygen (O) and chlorine (Cl) are present in the chemical structure of some commercial fluoropolymers. Examples include perfluoroalkoxy polymer and polychlorotrifluoroethylene:

H

F

H

F

C

C

C

C

H

F

H

F

Polyvinylidene fluoride (PVDF) F

F

H

H

F

F

F

F

F

F

F

F

C

C

C

C

C

C

C

C

C

C

C

C

F

F

H

H

F

F

F

F

F

O

F

F

Rf

Perfluoroalkoxy polymer (PFA)

F

F

F

F

C

C

C

C

F

Cl

F

Cl

Polychlorotrifluoroethylene (PCTFE) Rf is usually a perfluorinated group consisting of carbon and fluorine. Introduction of nonlinearity, oxygen and side chains, or chlorine invokes a vari-

Ethylene tetrafluoroethylene copolymer (ETFE) Partially fluorinated fluoropolymers are significantly different from the perfluoropolymers with respect to properties and processing characteristics. For example, perfluoropolymers are more thermally stable but physically less hard than partially fluorinated polymers. Both classes of fluoropolymers are discussed in Ch. 3.

1.3

Fundamental Properties of Fluoropolymers

The basic properties of fluoropolymers arise from the atomic structure of fluorine, carbon, and their co-

INTRODUCTION TO FLUOROPOLYMERS valent bonding in specific chemical structures. These properties are weakened as the chemical structure becomes less “perfluorinated,” as in polyvinylidene fluoride. Because PTFE has a linear structure, it is a good subject for discussion of extreme properties. The backbone is formed of carbon-carbon bonds and carbon-fluorine bonds. Both are extremely strong bonds (C–C = 607 kJ/mole and C–F = 552 kJ/ mole.)[4][5] The basic properties of PTFE stem from these two very strong chemical bonds. The PTFE molecule resembles a carbon rod completely blanketed with a sheath of fluorine atoms.[6] The size of the fluorine atom allows the formation of a uniform and continuous sheath around the carbon-carbon bonds and protects them from attack, thus imparting chemical resistance and stability to the molecule. The fluorine sheath is also responsible for the low surface energy (18 dynes/cm)[7] and low coefficient of friction (0.05–0.08, static)[6] of PTFE. Another attribute of the uniform fluorine sheath is the electrical inertness (or non-polarity) of the PTFE molecule. Electrical fields impart only slight polarization to this molecule, so volume and surface resistivity are high. Table 1.1 summarizes the fundamental properties of PTFE, which represents the ultimate polymer among all fluoroplastics. The basic properties of perfluoropolymers provide beneficial attributes with high commercial value (Table 1.2).

Table 1.1. Fundamental Properties of PTFE

• High melting point, 342°C • High thermal stability • Useful mechanical properties at extremely low and high temperatures • Insolubility • Chemical inertness • Low coefficient of friction • Low dielectric constant/dissipation factor • Low water absorptivity/adsorptivity • Excellent weatherability • Flame resistance • Purity

3 Table 1.2. Useful Attributes of Perfluoropolymers

• Stability – high continuous-use temperature – excellent weatherability – excellent chemical resistance – excellent fire properties • Low Surface Energy – good release properties – biological inertness – low friction • Cryogenic Properties – retains flexibility • Electrical Properties – low dielectric constant – low dissipation factor

1.4

Developmental History of Fluoropolymers

The development of fluoropolymers began with the invention of PTFE in 1938, continued to 1992 when a soluble perfluoropolymer (Teflon® AF) was introduced, and to 2002 when fluoroplastics polymerized in supercritical carbon dioxide were introduced. Table 1.3 summarizes the timeline for the development of fluoropolymers that have brought about major changes in properties and/or fabrication processes. The discovery of PTFE was a major leap forward in material science. Yet the new polymer could not be fabricated by melt-processing. The next two forms of PTFE, fine powder and dispersion, were also not melt-processible. The pursuit of a more easily processible polymer led to FEP, which could be melted in an extruder. Compared with PTFE, the major disadvantage of FEP is its reduced thermal stability and lower maximum continuous-use temperature (200°C) (Table 1.3). PFA, which was introduced in 1973, offers both melt-processing and the same upper continuous-use temperature as PTFE (260°C).

4

FLUOROPOLYMERS APPLICATIONS IN CHEMICAL PROCESSING INDUSTRIES

Table 1.3. Commercialization Timeline of Major Fluoropolymers vs Key Processing/Application Trade-Offs

Fluoropolymer

Year Commercialized

Monomers

Trade-off +

Trade-off -

PTFE

1947

TFE

Continuous-use temperature: 260°C

Non melt-processible

PCTFE

1953

CTFE

Melt-processible/Non meltprocessible

Maximum continuous-use temperature: 180°C

FEP

1960

TFE, HFP3

Melt-processible

Maximum continuous-use temperature: 200°C

PVF

1961

VF1

Thin film/weatherable

Maximum continuous-use temperature: 107°C

PVDF

1961

VDF2

Melt-processible

Maximum continuous-use temperature: 150°C

ECTFE

1970

CTFE, E4

Hardness/toughness

Maximum continuous-use temperature: 150°C

PFA

1972

TFE, PAVE5

Continuous-use temperature: 260°C

ETFE

1973

TFE, E

Hardness/toughness

Maximum continuous-use temperature: 150°C

TeflonAF

1992

TFE, PDD6

Soluble in special halogenated solvents

High cost

Melt-processible

1

Low molecular weight

4

Vinyl fluoride (CH2=CHF)

Ethylene (CH2=CH2)

2

5

Vinylidene fluoride (CH2=CF2)

Perfluoroalkylvinylether (CF2=CF–O–Rf)

3

6

Hexafluoropropylene (CF2=CF–CF3)

2,2-Bistrifluoromethyl-4,5-difluoro-1,3-dioxole: FC

O CF3

ETFE addresses the need for a mechanically stronger polymer, albeit at a loss of fluoropolymer properties because of the presence of hydrogen in its molecule: F

F

H

H

F

F

C

C

C

C

C

C

F

F

H

H

F

F

Compared to PTFE, ETFE has a lower continuoususe temperature (150°C), less chemical resistance, and a higher coefficient of friction. Mechanical properties including tensile strength, elongation at break, and tensile modulus are increased, leading to cutthrough resistance.

CF C

O CF3

Teflon® AF is an amorphous polymer which is soluble in select halogenated solvents. It can be applied as a solution followed by the removal of the solvent. The remaining coating will be as resistant to almost as many chemicals as PTFE. The thickness of the coating can range upward from less than a micrometer. There are a number of other polymers in this family including polychlorotrifluoroethylene (PCTFE), polyvinyl fluoride (PVF), polyvinylidene fluoride, ethylene chlorotrifluoroethylene (ECTFE), tetrafluoroethylene/hexafluoropropylene/vinylidene fluoride terpolymers, and chlorotrifluoroethylene/vinyl ether copolymers.

INTRODUCTION TO FLUOROPOLYMERS

1.5

5

Examples of Uses of Fluoropolymers

The consumption of fluoropolymers has increased over the years as technological advancement has required the properties of these plastics. The applications of fluoropolymers, in general, span all facets of human life from household uses to the aerospace and electronic industries. Useful properties (Table 1.2) of fluoropolymers in various applications include: chemical resistance, thermal stability, cryogenic properties, low coefficient of friction, low surface energy, low dielectric constant, high volume and surface resistivity, and flame resistance. Applications for fluoropolymers always exploit one or more of the properties (Table 1.4) that set them apart from other plastics.

In the chemical processing industry, for example, fluoropolymers are selected for their resistance to chemical attack. They serve as linings for carbon steel vessels, and for piping and other fluid handling components. They provide durable, low maintenance, and economical alternatives to exotic metal alloys. In these applications, fluoropolymers also offer thermal stability for use at high temperatures. And because they do not react with process streams, they help prevent contamination of products. Electrical properties of fluoropolymers are highly valuable in electronic and electrical applications. In data communications, for example, FEP is used to insulate cables installed in air-handling spaces (plenums) in office buildings. FEP provides the excellent dielectric properties these cables require to perform well at high data-transmission rates as well as

Table 1.4. Major Applications and Some Uses of Fluoropolymers Industry/Application Area

Key Properties

Typical Uses

Chemical Processing

Chemical resistance Good mechanical properties Thermal stability Cryogenic properties

Gaskets, vessel liners, valve and pipe liners, tubing, coatings

Electrical & Communications

Low dielectric constant High volume/surface resistivity High dielectric breakdown voltage Flame resistance, thermal stability

Wire and cable insulation, connectors

Automotive & Office Equipment

Low coefficient of friction Good mechanical properties Cryogenic properties Chemical resistance

Seals and rings in automotive power steering, transmission, and airconditioning. Copier roller and food processing equipment covering.

Houseware

Thermal stability Low surface energy Chemical Resistance

Cookware coatings

Medical

Low surface energy Stability Excellent mechanical properties Chemical resistance

Cardiovascular grafts, heart patches, and ligament replacement

Architectural Fabric

Excellent weatherability Flame resistance Low surface energy

Coated fiberglass fabric for stadium and airport roofs

Semiconductor Fabrication

Chemical resistance Purity Non-shedding Thermal stability

Process surfaces Wafer carrier basket Tubing, valves, pumps, and fittings

6

FLUOROPOLYMERS APPLICATIONS IN CHEMICAL PROCESSING INDUSTRIES

long-term stability so performance will not change over the life of the cabling system. Most importantly, FEP helps these cables meet strict building code requirements for low flame spread and low smoke generation. Fluoropolymers are used to insulate wire for critical aerospace and industrial applications where chemical and thermal resistance is essential. They are also materials of construction for connectors for high-frequency cables and for thermocouple wiring that must resist high temperatures. In the automotive, office equipment, and other industries, the mechanical properties of fluoropolymers are beneficial in low-friction bearings and seals that resist attack by hydrocarbons and other fluids. In food processing, the Food and Drug Administration (FDA) has approved fluoropolymer grades as fabrication material for equipment due to their resistance to oil and cleaning materials, and their anti-stick and low friction properties.

In houseware, fluoropolymers are applied as nonstick coatings for cookware and appliance surfaces. These applications depend on thermal and chemical resistance as well as anti-stick performance. PTFE and ETFE are chosen to insulate appliance wiring that must withstand high temperatures. Medical articles such as surgical patches and cardiovascular grafts rely on the long-term stability of fluoropolymers as well as their low surface energy and chemical resistance. For airports, stadiums, and other structures, fiberglass fabric coated with PTFE is fabricated into roofing and enclosures. This architectural fabric is supported by cables or air pressure to form a range of innovative structures. PTFE provides excellent resistance to weathering, including exposure to the ultraviolet rays in sunlight, flame resistance for safety, and low surface energy for soil resistance and easy cleaning.

References 1. Plunkett, R. J., US Patent 2,230,654, assigned to DuPont Co. (Feb. 4, 1941) 2. Plunkett, R. J., The History of Polytetrafluoroethylene: Discovery and Development, in: High Performance Polymers: Their Origin and Development, Proc. Symp. Hist. High Perf. Polymers: at the ACS Meeting in New York, April 1986, (R. B. Seymour and G. S. Kirshenbaum, eds.), Elsevier, New York (1987) 3. Gangal, S. V., Polytetrafluoroethylene, Homopolymers of Tetrafluoroethylene, in: Encyclopedia of Polymer Science and Engineering, 2nd ed., 16:577–600, John Wiley & Sons, New York (1989) 4. Cottrell, T. L., The Strength of Chemical Bonds, 2nd ed., Butterworths, Washington, DC (1958) 5. Sheppard, W. A., and Sharts, C. M., Organic Fluorine Chemistry, W. A. Benjamin, Inc., New York (1969) 6. Gangal, S. V., Polytetrafluoroethylene, in: Kirk-Othmer Encyclopedia of Chemical Technology, 4th ed., 11:621–644, John Wiley & Sons, New York (1994) 7. Zisman, W. A., Surface Properties of Plastics, Record of Chemical Progress, 26:1 (1965)

2 Materials of Construction 2.1 Introduction An engineer has a wide choice of materials of construction for corrosion control. There are three broad categories of materials, used either individually or in combination with each other: metals, polymers, and ceramics. This chapter describes the differences between them and explains the phenomenology of applications of polymer-based materials. It also places fluoropolymer materials in their appropriate contexts. Polymer-based materials are also known as polymerics, polymeric materials, or simply plastics, which is often not accurate and can lead to confusion.

2.2

Historical Background

Lead, wood, and rubber are probably the earliest known materials of construction for the chemical processing industry. Interestingly, it took a little more than a century for rubber to be established as a lining material after Charles Goodyear accidentally discovered vulcanized rubber in 1839. Wood is the first composite material to be used in the chemical processing industry. Until the onset of World War II, these naturally occurring materials continued to play a major role in chemical handling applications. Although stainless steels were discovered at the turn of the century and copper silicon alloys started to emerge at about the same time, the real explosion of materials research and development began at around the beginning of World War II. Polymer science and technology were no exception. Nylon was already developed at the DuPont Company. Alloy 20 was developed by DuPont in the late thirties. At about the same time, polytetrafluoroethylene (PTFE) (Teflon®) was discovered which led to further development of fluoropolymers and ushered in an era of high-performance polymer materials for corrosion control. The 1950s were known for the explosive development and growth in elastomers. DuPont Company developed a whole range of synthetic elastomers such as neoprene (polychloroprene), Hypalon® (chloro-

sulfonated polyethylene), and Nordel® (terpolymer of ethylene propylene-diene monomer). These were followed later by fluoroelastomers such as Viton® and Kalrez®. The 1960s and 1970s saw further refinement of these fluorine-containing elastomers with several new grades developed for specific needs in the chemical processing industry. Rigid thermosetting materials have always attracted the interest of engineers in the chemical processing industry since Bakelite® (phenol formaldehyde) was put to use for commercial applications. Various fiber and particulate additives were developed to make useful structures out of these materials. The 1940s saw major initiatives in the development of polyester resins. Bisphenol A fumarate resins with unsaturation sites for crosslinking were developed for processing vessels and piping. These resins, in their reinforced forms, were the early man-made composites for the chemical processing industry. Development of vinyl esters, chlorendic anhydride, and furans added greatly to the versatility of fiberglass reinforced polyester (FRP). These became the workhorses in the chloralkali industry for handling chlorine and chlorine-containing chemicals. While the US was pursuing the FRP route, Europeans were busy taking the lead in developing technologies using thermoplastic materials such as polyethylene, polyvinyl chlorides, and polypropylenes. The result was an increased use of these materials as self-supporting structures as well as linings. They achieved this through an effective partnership of governments, industry, and academia, which ultimately produced several autonomous testing and training centers. A major outcome was the use of low-end thermoplastics (PE, PVC, and PP) for “dual laminate” structures where the structural component is FRP and the lining is a thermoplastic material. This technology was subsequently exported to Canada and then to the US. Manufacturing technologies (injection molding, transfer molding, contact molding, compression molding, isostatic molding, ram extrusion) and design procedures were concurrently developed to promote the use of these materials. The resin con-

8

FLUOROPOLYMERS APPLICATIONS IN CHEMICAL PROCESSING INDUSTRIES

verters played a bigger role in these activities than the resin manufacturers. The creation of a multitude of materials in a relatively short time led to high expectations and less-than-careful application of some of these materials. Failures, some catastrophic, inevitably occurred. Notable among these were ruptures of FRP storage tanks and vessels resulting in total discharge of corrosive and hazardous contents. Less notable but equally damaging failures also occurred in linings of various types. The underlying causes were improper material selection, design, quality of fabrication, exceeding operating parameters, inability to adequately inspect, or some combination of these.

2.3

Definition of Polymer-based Materials

Polymers are long chain molecules made from organic chemicals. These materials are defined by three distinct characteristics. • Organic chemistry basis • Mechanical strength basis • Thermal processing basis Polymers can be distinguished from each other by their generic organic chemistry description such as polyolefins, fluorocarbons, styrenics, epoxies, etc. They can also be classified by their mechanical strength: rigid (elastic modulus > 690 MPa), semirigid (modulus between 69 and 690 MPa), and nonrigid (modulus < 69 MPa). Additionally, polymeric materials are classified by the way they are thermally processed: thermoplastics and thermosets. Thermoplastics are those which can be remelted and reprocessed repeatedly. Thermosets cannot be remelted for reprocessing since they are crosslinked (also known as vulcanized in the world of elastomers). Any attempt to remelt thermosets will result in degradation and, ultimately, charring. Fluoropolymers are thermoplastic and nonrigid materials while fluoroelastomers have elastomeric properties. See Tables 2.1 and 2.2 for a comparison of physical and mechanical properties of select plastics and elastomers including fluorinated materials.

Elastomers are a special class of nonrigid materials distinguished by high elongation and high recovery. A complete description of a polymer system must necessarily include references to all three categories. Some examples below illustrate the point. 1. A fiberglass tank is made of vinyl ester resin, which is a thermoset and is semirigid in its composite form 2. A rubber (elastomeric) gasket can be made of polychloroprene, which is a thermoset and is nonrigid. 3. A fluoropolymer lining for a vessel is thermoplastic and nonrigid.

2.4

Comparison Between Polymerbased Materials and Metals

There are some obvious and subtle differences between polymer-based materials and metals. The obvious differences are in strength (high for metals), elongation (high for polymers), and maximumuse temperature (much higher for metals). Not so obvious are anisotropy (polymers), homogeneity (metals), changing properties in service (plastics), responsiveness to nondestructive testing (high for metals), ability to predict remaining life (low for polymers), ability to carry out accelerated testing for corrosion rates (high for metals), and sensitivity to workmanship (high for polymers). All these factors make using plastics as effective as metals and with the same degree of confidence a challenge for the end user. Phenomenology of corrosion for metals and polymer materials is not the same. For example, the terms such as corrosion rate, pitting, end grain attack, and intergranular attack used to describe metals’ behaviors are not applicable to plastics. Not only are the terms for plastics different (blistering, discoloration, cracking, etc.) but they are based on a nakedeye observation and not at a microscopic level as for metals.

MATERIALS OF CONSTRUCTION

9

Table 2.1. Physical and Mechanical Properties of Plastics[1][2]

Specific Gravity

Mold Shrinkage, %

Tensile Strength, MPa

Break Elongation, %

Tensile Modulus, MPa

Flexural Strength, MPa

Flexural Modulus, Mpa 23°C

Impact Notched Izod J/m (23°C)

Compressive Strength, MPa

D792

D955

D638

D638

D638

D790

D790

D256

D695

Polystyrene

1.06

0.5

46

2.2

3,172

96

3,103

10.8

96.6

ABS

1.05

0.6

48

8.0

2,069

72

2,621

242

69

SAN

1.08

0.4

72

3.0

3,862

103

3,793

27

103

Test Method ASTM

Polypropylene

0.90

1.5

32

15.0

1,310

41

2,069

27

34.5

Polyethylene

0.96

2.0

30

9.0

1,034

38

1,517

70

27.6

Polyacetal

1.41

1.8

61

60.0

2,827

90

2,552

70

36

Polyester

1.30

2.0

55

200.0

2,758

88

2,345

10.8

90

Polyamide, nylon 6

1.13

1.3

81

200.0

2,758

103

2,759

53.8

90

Polyamide, nylon 6,6

1.14

1.8

79

300.0

1,310

103

1,310

53.8

34

Polycarbonate

1.20

0.6

62

110.0

2,379

93

2,345

161

86

Polysulfone

1.24

0.7

70

75.0

2,482

106

2,690

32

96.6

Test Method ASTM

D792

Measured on parts

D4894-5 D1708 D638

D4894-5 D1708 D638

D638

D790

D790

D256

PTFE

2.14– 2.22

2–10

20–35

300–550

550

No break

340–620

188

PFA

2.15

3.5–6.0

20–26

300

276

551

No break

FEP

2.15

3.5–6.0

20–28

300

345

No break

655

No break

15.2

ETFE

1.71

1–7

45

150–300

827

38

1,034–1,171

No break

17.2

PVDF

1.78

0.2–3

31–52

50–250

1,040– 2,070

45–74

1,140–2,240

107–427

55–110

34.5

Table 2.2. Physical and Mechanical Properties of Elastomers[3] Trade Name Viton®

Aflas®

Fluorosilicone

Kalrez®

Adiprene®

Neoprene

Hypalon®

Nordel®

Chemical Name TetrafluoroFluorinated ethylene/ Fluorosilicone ydrocarbon propylene copolymer

Property Continuous-use temperature, °C

Min

-29 to -57

-29

Max 227 204 to 230 Tensile strength, 3.4–20.7 13.8–22.1 Mpa*1 Tensile modulus at 100% elongation, 1.4–14 6.2–17.2 Mpa*1 Hardness (durometer) 50A–95A 60A–100A Compression set @ 9–16, 70h 25, 70h temperature, °C @24 @93 Elongation, % 100–500 50–400 *1 To convert from MPa to psi, multiply by 145.

Perfluoroelastomer

Polyurethane

Polychloroprene

Chlorosulfonated polyethylene

Ethylene/ propylene copolymer

-80 to -68

-38

-54

-62

-54

-59

232

290 to 315

121

149

135

163

3.4–9.6

3.4–10.3

2.1–24.1

3.4–27.6

–

2.1–24.1

6.2

6.2–13.1

0.7–20.7

0.7–20.7

3.1–3.4

0.7–20.7

35A–80A 17–25, 22h @149 100–480

65A–95A 20–40, 70h @21 60–170

30A–90A 20–60, 70h @100 100–700

15A–95A 20–60h @100 100–800

40A–100A 38–80, 22h @100 100–700

30A–90A 20–60, 70h @100 100–700

10

FLUOROPOLYMERS APPLICATIONS IN CHEMICAL PROCESSING INDUSTRIES

2.4.1

Position of Fluoropolymers in the Materials Spectrum

Fluoropolymers are fluorine-containing polymers. They are thermoplastic in nature and are semirigid, and are classified in two ways:

2.5

Applications for corrosion control are classified as follows: • Barrier (linings)

• Homopolymers or copolymers (preferred by chemists)

• Self-supporting structures • Others (seals, gaskets, column internals, etc.)

• Fully fluorinated or partially fluorinated (preferred by engineers) These materials have the highest chemical resistance (Tables 2.3 and 2.4) among the polymer materials, as well as maximum-use temperature. Corrosion resistance is a function of the level of fluorine, hence the fully fluorinated ones are usually preferred for tough applications. 1. Fully Fluorinated • PTFE (polytetrafluoroethylene) • FEP (fluorinated ethylene propylene) copolymer • PFA (perfluoroalkoxy) (perfluoropropyl vinyl ether) • MFA (perfluoroalkoxy) (perfluoromethyl vinyl ether) 2. Partially Fluorinated • ETFE (ethylene tetrafluoroethylene polymer) • ECTFE (ethylene chlorotrifluoroethylene polymer) • PVDF (polyvinylidene fluoride) Table 2.5 presents a summary of structure-rheology-fabrication process relationship for commercial fluoropolymers.

Applications of Polymer-based Materials for Corrosion Control

Table 2.6 shows the applications and the materials typically used. It is clear from the table that fluoropolymers are used principally for barriers (linings) and other applications such as column internals, seals and gaskets. In rare situations they are used to construct self-supporting structures. 2.5.1

Applications of Fluoropolymers for Corrosion Control

Fluoropolymers are principally used as barriers, i.e., linings for storage vessels, reactors, columns, piping, valves, pumps, expansion joints, and hoses. In a few cases, they are also used as self-supporting structures such as piping and tubing. Linings are achieved by various manufacturing techniques such as thermoforming, welding, isostatic molding, ram extrusion, and injection molding. Sizes range from large fielderected storage tanks to packings for column internals in complex shapes. Various techniques are used to manufacture parts; these are covered in Chs. 6 and 7. Issues related to the successful use of fluoropolymers are covered in Ch. 9. Supply chains are typically long and complex; these are covered in Ch. 8. Choosing fluoropolymers implies evaluation of all candidate materials including metals and other polymers. The selection methodology is covered in Ch. 4. This book covers the use of fluoropolymers for corrosion control in chemical processing industries (CPI).

MATERIALS OF CONSTRUCTION

11

Table 2.3. Water Absorption and the Effect* of Inorganic Chemicals on Polymers[1][2]

Material

Weak Bases and Salts

Strong Bases

Strong Acids

Strong Oxidants

24-hour Water Absorption

25°C

93°C

25°C

93°C

25°C

93°C

25°C

93°C

Weight Change, %

Polyacetal

1–3

2–5

1–5

2–5

5

5

5

5

0.23

ABS

1

2–4

1

2–4

1–4

5

1–5

5

0.1–0.4

Nylons

1

2

2

3

5

5

5

5

0.2–1.9

Polyester

1

3–4

2

5

3

4–5

2

3–5

0.06–0.09

Polyethylene

1

1

1

1

1

1

1

1

66 12t 151 23 23 23 23 118 149 149 149 23 149

Cane Sugar

can sugar liquors

Caprylic Acid Carbon Dioxide

dry wet

11

11 11

Load

PDL Rating 8 2 3 8 8 8 8 5 8 8 8 8 8

23

8

23 121

8 8

23

8

23 149 23 121 23 66 23 149 23 149 23 149 23 149 23 149 23 149 23 149 23 149

8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8

Calcium Oxide Calcium Sulfate

Time

23 149 23 66 23 66 23 23

Weight

% Retained Tensile Modulus Strength

Elongation

Resistance Note

Material Note

recommended for use

Ausimont Halar

not recommended for use 10.5

90

T35

[Borax I Boric Acia

>90

Atochem Kynar i.!Bmp.fsmax.fecom. na visual change

Atochem Foraflon Atochem Kynar

chlorinated acid Atochem Foration

acid basic 'aqueous solution

Chemical Resistance

. polyvinylidene Fluoride

511

bent specimen

ro o CO

512

Chemical Resistance - Polyvinylidene Fluoride

Reagent

Reagent Note

Cone.

Temp.

Time

Load

POL Rating

% Change

% Retained

Weight

Tensile Strength

(tfay*) Bromine

Resistance Note

Material Note

bromine liquid

66

8

exp, temp, is max. recom.

Atochem Kynar

dry gas

66

8

u

«

bromine water

100

3

u

«

dry

100

7

no visual change

Atochem Foraflon

moist

100

7

7

90

7

90

8

66

Bromobenzene

u Atochem Foraflon

8

exp, temp, ES max. recom.

Atochem Kynar

8

«

«

not recommended for use

Atochem Foraflon Atochem Foraflon

100 121

Butane

121 135

8

aqueous solution or liquid

7

7

Butanone

» Atochem Kynar

«

6$

Butadiene

7

« exp. temp, te max, recom.

no visuaf change

8

Bromoform

Butanediol

o

90

«

2

Butene

130

7

7

90

no visual change

Butyl Acetate

25

7

7

90

«

«

exp. temp, ts max. recom.

Atochem Kynar

no visual change

Atochem Foraflon

8

27 25

Butyl Acrylate

7

7

Butyl Alcohol

n-butanol

75

7

7

107 75

Butyl Alcohol (sec-) aqueous solution or liquid

aqueous solution or liquid

Butyl Chloride Butyl Ether

90

90

90

8 7

7 8

7

7

90

exp. temp, ts max. recom.

Atochem Kynar

no visual change

Atochem Foraflon

exp, temp, is max. recom.

Atochem Kynar

no visual change:

Atochem Foraflon

exp. temp, ts max. recc-m.

Atochem Kynar

no visual change

«

exp. temp, ts max. recom.

Atochem Kynar

m visual change

Atochem Foraflon

141

8

exp, temp, ts max. recom.

Atochem Kynar

141

8

M

«

33

8

to

100

Butyl-2-Hydroxybenzene-

7

93 100

Butyl Bromide

>90

8 7

93 75

Butyl Alcohol (tert-)

90 >90

exp. temp, is max. recom.

7

7

>yyyyy:y'yy^yyyy>-90 >90

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Atochem Kynar Atochem Foraflon «