Biobased polyols for industrial polymers 9781119620167, 1119620163

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Biobased Polyols for Industrial Polymers

Scrivener Publishing 100 Cummings Center, Suite 541J Beverly, MA 01915-6106 Publishers at Scrivener Martin Scrivener ([email protected]) Phillip Carmical ([email protected]) Editor-at-Large Sina Ebnesajjad

Biobased Polyols for Industrial Polymers

Deny Kyriacos

This edition first published 2020 by John Wiley & Sons, Inc., 111 River Street, Hoboken, NJ 07030, USA and Scrivener Publishing LLC, 100 Cummings Center, Suite 541J, Beverly, MA 01915, USA © 2020 Scrivener Publishing LLC For more information about Scrivener publications please visit www.scrivenerpublishing.com. All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, except as permitted by law. Advice on how to obtain permission to reuse material from this title is available at http://www.wiley.com/go/permissions. Wiley Global Headquarters 111 River Street, Hoboken, NJ 07030, USA For details of our global editorial offices, customer services, and more information about Wiley products visit us at www.wiley.com. Limit of Liability/Disclaimer of Warranty While the publisher and authors have used their best efforts in preparing this work, they make no rep­ resentations or warranties with respect to the accuracy or completeness of the contents of this work and specifically disclaim all warranties, including without limitation any implied warranties of merchant-­ ability or fitness for a particular purpose. No warranty may be created or extended by sales representa­ tives, written sales materials, or promotional statements for this work. The fact that an organization, website, or product is referred to in this work as a citation and/or potential source of further informa­ tion does not mean that the publisher and authors endorse the information or services the organiza­ tion, website, or product may provide or recommendations it may make. This work is sold with the understanding that the publisher is not engaged in rendering professional services. The advice and strategies contained herein may not be suitable for your situation. You should consult with a specialist where appropriate. Neither the publisher nor authors shall be liable for any loss of profit or any other commercial damages, including but not limited to special, incidental, consequential, or other damages. Further, readers should be aware that websites listed in this work may have changed or disappeared between when this work was written and when it is read. Library of Congress Cataloging-in-Publication Data ISBN 978-1-119-62016-7 Cover image: W  atercolor "Water Lilies in September" by Deny Kyriacos. Copyright reserved by the artist Cover design by Russell Richardson Set in size of 11pt and Minion Pro by Manila Typesetting Company, Makati, Philippines Printed in the USA 10 9 8 7 6 5 4 3 2 1

Contents Preface xi 1 Vegetable Oils, Animal Fats, Carbohydrates and Polyols 1.1 Introduction 1.2 Sustainability 1.3 Polyols from Vegetable Oils 1.3.1 Polyols from Triglycerides 1.3.2 Polyols from Glycerol 1.4 Polyols from Carbohydrates 1.4.1 Ligno-Cellulosics 1.4.2 Cellulose 1.4.2.1 Hydrolysis 1.4.2.2 Oxidative Degradation 1.4.2.3 Thermal Degradation 1.4.3 Hemicellulose 1.4.4 Lignin 1.4.5 Sucrose 1.4.6 Starch 1.4.6.1 Glucose 1.4.6.2 Sorbitol References

1 1 3 5 5 10 12 12 12 13 13 14 14 15 16 19 19 20 22

2 Polyurethanes, Polyesters and Epoxies 2.1 Introduction 2.2 Polyurethanes 2.2.1 Rigid Foams 2.2.1.1 Isocyanates 2.2.1.2 Polyols 2.2.2 Flexible Foams 2.2.2.1 Isocyanates 2.2.2.2 Polyols

25 25 25 25 26 26 27 28 28 v

vi  Contents 2.2.3 Microcellular Elastomers 2.2.3.1 Footwear 2.2.3.2 Integral Skin 2.2.4 Thermoplastic Polyurethane (TPU) Elastomers 2.2.4.1 Isocyanates 2.2.4.2 Polyols/Diols (Chain Extenders) 2.2.5 Casting Systems 2.2.5.1 Isocyanates 2.2.5.2 Polyols 2.2.5.3 Crosslinkers 2.2.5.4 Examples 2.2.6 Coatings 2.2.6.1 Urethane Oils/Uralkyds 2.2.6.2 Moisture Curable Coatings 2.2.6.3 Blocked Isocyanates 2.2.6.4 Two-Component Coatings 2.3 Polyesters 2.3.1 Unsaturated Polyesters 2.3.1.1 Alkyds 2.3.1.2 Drying Oils 2.3.2 Thermoplastic Polyesters 2.3.3 Polyester Polyols 2.4 Epoxies References 3 Vegetable Oils and Fats 3.1 Introduction 3.2 Sources, Components and Extraction of Vegetable Oils 3.2.1 Soybean Oil 3.2.1.1 Source 3.2.1.2 Components of Soya Bean 3.2.1.3 Triglyceride (Oil) Extraction 3.2.2 Palm Oil 3.2.2.1 Source 3.2.2.2 Components 3.2.2.3 Extraction 3.2.3 Corn Oil 3.2.3.1 Source 3.2.3.2 Corn Kernel Components 3.2.3.3 Processing of Corn Kernels 3.2.3.4 Corn Oil Extraction and Refining

28 29 31 32 33 34 34 36 36 36 36 37 37 38 39 39 40 40 40 42 43 45 46 48 51 51 52 52 52 54 67 73 74 76 79 85 85 87 88 92

Contents  vii 3.2.4 Linseed Oil 3.2.4.1 Source 3.2.4.2 Components of Flaxseed 3.2.5 Castor Oil 3.2.5.1 Source 3.2.5.2 Oil Extraction 3.2.5.3 Castor Oil Components 3.2.6 Rapeseed Oil 3.2.6.1 Source 3.2.6.2 Oil Extraction 3.2.6.3 Components of Canola Seeds, Rapeseeds and Canola Oil 3.2.7 Sunflower Oil 3.2.7.1 Source 3.2.7.2 Processing 3.2.7.3 Components of Sunflower Oil 3.2.7.4 Producers of Sunflower Oil 3.2.8 Vernonia Oil 3.2.9 Cashew Nut and Nutshell Oil 3.3 Comparative Data 3.3.1 Typical Oil Extraction from 100 kg of Oil Seeds 3.3.2 Fatty Acid Components of Vegetable Oil Triglycerides 3.3.3 Global Production 3.4 Fats 3.4.1 Fish Oil 3.4.2 Animal Fat 3.4.2.1 Lard 3.4.2.2 Beef Tallow 3.4.3 Comparative Data References 4 Chemistry of Triglycerides and Fatty Acids 4.1 Introduction 4.2 Reactions of Double Bonds 4.2.1 Epoxidation 4.2.1.1 Chemical Epoxidation 4.2.1.2 Enzymatic Epoxidation 4.2.2 C=C Bond Cleavage 4.2.2.1 Ozonolysis 4.2.2.2 Metal Catalysis 4.2.2.3 Microbial Oxidation 4.2.2.4 Acid-Catalyzed Oxidation

93 93 94 94 94 94 100 100 100 101 105 107 107 109 110 110 110 113 117 117 118 118 120 120 123 123 124 124 126 133 133 133 133 134 139 140 140 142 144 144

viii  Contents 4.2.3 C=C Bond Metathesis 4.2.4 Polymerization Reactions of Vegetable Oils 4.2.4.1 Homopolymerization 4.2.4.2 Copolymerization 4.2.4.3 Oxypolymerization 4.2.5 Hydrogenation 4.2.6 Dihydroxylation 4.2.6.1 Anti-Dihydroxylation 4.2.6.2 Syn Dihydroxylation 4.2.7 Addition 4.2.7.1 Hydroxybromination 4.2.7.2 Addition of Acetone/Malonic Acid 4.3 Reactions of Ester Groups 4.3.1 Hydrolysis of Ester Groups 4.3.1.1 Chemical Hydrolysis 4.3.1.2 Enzymatic Hydrolysis 4.3.2 Alcoholysis/Glycerolysis 4.3.3 Transesterification 4.3.4 Aminolysis 4.4 Reactions of Hydroxyl Groups 4.4.1 Dehydration 4.4.2 Esterification References 5 Polyols from Triglycerides 5.1 Introduction 5.2 Reactions of Epoxides 5.2.1 Hydrolysis of Oxirane Rings 5.2.1.1 With Inorganic Acids 5.2.1.2 With Organic Acids 5.2.2 Alcoholysis of Oxirane Rings 5.2.2.1 Clay Catalyzed 5.2.2.2 HBF4 Catalyzed 5.2.3 Esterification of Oxirane Rings 5.2.3.1 With Carboxylic Acids 5.2.3.2 Acid Anhydrides 5.2.3.3 Hydroxy Carboxylic Acids 5.2.4 Aminolysis 5.3 Reactions of Ozonides 5.3.1 Ozonolysis Followed by Hydrogenation

145 148 149 149 153 155 158 158 159 160 160 161 162 162 162 163 164 167 168 170 170 170 171 177 177 178 179 179 180 182 182 184 185 185 188 188 189 191 191

Contents  ix 5.3.2 Polyols from the Transesterification of Ozonolysis Intermediates 193 5.3.2.1 Amidification of Esters 194 5.3.2.2 Interesterification with Glycerol 194 5.4 Hydroformylation 196 5.5 Examples of Synthetic Methods 199 5.5.1 Glycerol Propoxylates 199 5.5.2 Castor Oil Alkoxylates 199 5.5.3 Mixed Alkoxylates 200 5.5.4 Oxidation in the Presence of Organometallic Complexes 200 5.5.5 Use of Double-Metal Cyanide (DMC) Complex Catalysts 201 5.5.6 Polyols from Palm Oil 203 5.5.7 Polyols from Oleic Acid (or Canola Oil) 206 5.5.8 Polyols from Soybean Oil and Chicken Fat 207 5.5.9 Autocatalytic Polyols 208 5.5.9.1 From Diethanolamine and Epoxidized Soybean Oil 208 5.5.9.2 Mannich Polyols from Cardanol 210 References 213 6 Carbohydrate-Based Polyols 6.1 Introduction 6.2 Bio Ethylene Oxide 6.3 Bio Propylene Glycol 6.3.1 1,3-Propanediol 6.3.1.1 Fermentation 6.3.1.2 Hydrogenation 6.3.2 1,2-Propanediol 6.3.2.1 Hydrocracking 6.3.2.2 Fermentation 6.4 Bio-Butanediol 6.5 Sucrose 6.5.1 Introduction 6.5.1.1 Sucrose from Cane Sugar 6.5.1.2 Sucrose from Beets 6.5.2 Propoxylated Sucrose Initiated Polyols 6.5.3 Propoxylated/Ethoxylated Polyols with Mixed Initiators 6.5.3.1 Sucrose/Ethylene Diamine Initiators 6.5.3.2 Sucrose/Glycerol Initiators

219 219 219 223 223 224 225 225 225 226 226 228 228 229 230 231 232 233 233

x  Contents 6.5.4 Propoxylation of Glucose Obtained from Starch 6.6 Sorbitol 6.6.1 Synthesis 6.6.2 Synthesis of Polyols from the Alkoxylation of Sorbitol 6.6.3 Sorbitol Derivatives 6.7 Carbohydrates from Corn Fibers 6.7.1 Chemical Treatment 6.7.2 Biochemical Treatment References 7 Biobased Polyols and Their Applications 7.1 Commercial Vegetable Oil Polyols 7.1.1 Producers 7.1.2 PU Applications 7.1.2.1 Rigid Foams 7.1.2.2 Flexible Foams 7.1.2.3 Viscoelastic Foams 7.1.2.4 Castings/Sealants 7.1.2.5 Carpet Backing 7.1.2.6 Elastomers and Coatings 7.1.3 Epoxies 7.1.4 Polyesters 7.1.4.1 Alkyd Resins 7.1.4.2 Thermoplastic Polyesters 7.1.5 Acrylate Coatings 7.1.5.1 Introduction 7.1.5.2 Examples 7.2 Commercial Carbohydrate-Derived Polyols 7.2.1 Producers 7.2.2 General Technical Considerations References

234 235 235 236 237 239 239 240 242 247 247 247 247 247 269 275 284 289 295 302 306 306 309 311 311 311 313 313 314 315

Appendix 319 Index 327

Preface The use of naturally occurring molecules in the production of industrial polymers and polymeric intermediates attracts more and more the attention of manufacturing companies. From a scientific point of view, the laboratory preparation of commodity polymers based on natural products was already examined many decades ago. However, the recent advent of issues related to terms such as biobased, biodegradable, sustainability and cyclic economy, all of which concern the protection of the environment from the deleterious effects of some petrochemicals as well as from the irreversible accumulation of thermoplastics and thermosets in nature, has prompted governments and industries alike to examine the marketing of polymers that consist at least partly of naturally sourced components in their macromolecular structure. This book is addressed to readers interested in learning the basics of the chemistry of biobased polyols in the manufacture of commercial polymers. The latter include, among others, polyurethanes, epoxides and polyesters, both saturated and unsaturated. The introductory chapter of this book gives an account of the various biobased polyols and their initiators, as well as the prices of vegetable oils compared to crude oil. The ubiquitous word, sustainability, is also subject to the author’s comments. The second chapter briefly describes most applications in which the polyols may be commercially valuable. This is followed by a thorough investigation of the chemical structures as well as the extraction processes of fatty acids, which are the major constituents of naturally occurring fats and oils. The fourth chapter is dedicated to an understanding of the basic chemistry of the groups present in triglyceride molecules. Several examples of routes to the synthesis of biobased polyols from fatty acids, as well as from vegetable oils, are given in the fifth chapter. Carbohydrate initiated polyols are not new in the industrial world. They cannot be considered as fully biobased unless they are ethoxylated or propoxylated with epoxides originating from natural products. The synthesis of those epoxides from natural sources is described in the sixth chapter xi

xii  Preface and several practical examples are included. The last chapter addresses the technology of products made from biobased polyols. Accompanying the text of each chapter of this book are many graphs and photographs. The author wishes to thank all the scientists, engineers, technicians and marketers whose work is mentioned in this book, often in great detail. Thanks are also extended to the originators of the photographs included herein. Finally, the initiatives of all manufacturing companies, the management of which operate their businesses with a commitment to solving environmental problems, are also acknowledged. Dr. Deny Kyriacos Brussels, Belgium January 2020

1 Vegetable Oils, Animal Fats, Carbohydrates and Polyols 1.1 Introduction This chapter describes polyols in detail, including diols, the chemical components of which are obtained from sources other than crude oil. The polyols are used in the manufacture of commercial polymers and polyurethanes, for example. Among the major natural chemicals from which polyols can be derived are: • • • •

Vegetable oils Fish oils Animal fats Carbohydrates

For industrial purposes vegetable oils and carbohydrates are the most approachable sources of chemicals. Work on polyols derived from animal fats can be found in the patent literature [1]. Those products are, quite rightly, described as green products because they originate from natural sources, the production of which humans can control almost at will. They are renewable because, in contrast to crude oil, they originate from non-depletable sources. Their availability is not the monopoly of some countries which possess vast amounts of oil reserves. Agricultural products require the right weather conditions to grow as well as an area large enough for them to be cultivated on. The first detailed studies on the use of vegetable oils and animal fats in polyurethane technology date back to the late fifties and early sixties.

Deny Kyriacos. Biobased Polyols for Industrial Polymers, (1–24) © 2020 Scrivener Publishing LLC

1

2  Biobased Polyols for Industrial Polymers Among the reasons given for utilizing polyols from natural sources were: • Since a favorable price differential exists for castor oil over most polyesters, information concerning the properties of various castor urethane foams should be useful to manufacturers and consumers of expanded foams [2]. • Dimer acids are commercially available and are produced by the polymerization of polyunsaturated fatty acids derived from soybean, cottonseed, and linseed oils. Less expensive polyols should result from the condensation of ethylene oxide with dimer acid [3, 4]. • The properties of the castor oil-based foams (PU) are comparable to those of foams obtained from more costly polyols [5]. • A large potential market exists for polyols from natural sources in the rapidly expanding urethane foam industry [6]. In general, the price of oil (Figure 1.1) used to produce the components of polyether and polyester polyols is determined by speculation largely founded on the production policies of the OPEC cartel. Unfortunately, the pricing of basic carbohydrates or bean oils generally is not much different from that of crude oil. Soybean oil futures are traded at the Chicago Futures Market, where the price of soybean oil is still lower than that of petroleum (Figure 1.2). This means that, triglycerides, even if considered renewable sources of chemicals, are subject to speculative pricing the same way crude oil is. However, the difference is that their production is not restricted to only a

Crude oil price, USD/barrel, Brent Texas-Dubai

70 68 66 64 62 60 58 56 54 52 50 Sep-18

Oct-18

Dec-18

Feb-19

Mar-19

May-19

Jul-19

Figure 1.1  Crude oil (petroleum) price chart (1barrel of crude ~ 140 kg) [7].

Vegetable Oils, Animal Fats, Carbohydrates and Polyols  3 800

Price, USD/Ton

750 700 650

Soybean oil

600 550 500 450 400

Crude brent

350 300 Sep-18

Oct-18

Dec-18

Feb-19

Mar-19

May-19

Jul-19

Figure 1.2  Soybean oil price variation compared to that of crude oil in USD/ton [7].

few countries. Bean oil, or carbohydrate cartels, will be difficult to establish and organize on a global scale. This trading approach does not exclude speculative price hikes similar to those of crude oil. Polyols based on renewable raw materials, such as fatty acid triglycerides, sugar, sorbitol, glycerol and dimer fatty alcohols, are already used in diverse ways as raw materials in the preparation of polymer chemicals. It is claimed that soybean-oil-based polyols cost less than the petroleum polyols they replace, because they require considerably less energy to produce; can be used in a broad range of polyurethane applications; and produce polyurethane products with equivalent or better physical characteristics [8]. In any event, polyols manufactured from petrochemical sources constitute the majority of the polyols, polyesters as well as polyethers used in industry. Another source of polyols has emerged from the co-polymerization of CO2 and epoxides [9].

1.2 Sustainability During the last few years, the term sustainability has been mentioned repeatedly in published articles, speeches, presentations as well as in company reports, to say the least. This was not the case when fluorocarbons, for example, were widely used as blowing agents in the polyurethanes industry. Many decades have elapsed since their deleterious effect on the ozone layer was discovered.

4  Biobased Polyols for Industrial Polymers The negative effect of CO2 on the atmosphere and the migration of bisphenol A from polycarbonate utilized in feeding bottles are additional examples which indicate that the consequences of chemicals are spotted only after a type of specific damage has already been inflicated on the environment, the economy, human health, etc. According to the Cambridge Dictionary, the verb “to sustain” has the following meanings: • To allow something to continue for a period of time; (The economy looks set to sustain its growth into next year.) • To keep alive; (Many planets are unable to sustain human or plant life.) • To experience; (The company has sustained heavy losses this year.) • To support emotionally. A succinct but detailed definition of the name derived from the verb “to sustain,” i.e., sustainability is given in Wikipedia. Accordingly, “Sustainability is the process of maintaining change in a balanced fashion, in which the exploitation of resources, the direction of investments, the orientation of technological development and institutional change are all in harmony and enhance both current and future potential to meet human needs and aspirations.” Not long ago, the course of the polyurethanes industry was sluggish. Sustainablility studies carried out by some multinationals pointed to the closure of old isocyanate plants. A few months later, the state of the economy changed. The polyurethanes market picked up and the same plants, instead of being shut, were upgraded. Ironically, a short time later, the same companies showed poor earnings because the market did not follow the predicted growth trend. But this is not the exception. The biobased chemicals market has recently seen the collapse of bio-­ succinic acid producer BioAmber, despite the numerous reorganizations aimed at reviving the sales of the company. A year before the company was shut, BioAmber was planning a seven-fold increase of its production capacity. According to their management, the business plan the company put forward to its creditors was sustainable. Succinic acid is a dicarboxylic acid widely used in the manufacture of polyester polyols. The manufacturing process from natural sources proves to be expensive, even if the science involved is brilliant. Therefore, the profit margins generated to sustain its production must be high. BioAmber’s capacity was 30 Ktpa, but the returns did not justify the operation of the company.

Vegetable Oils, Animal Fats, Carbohydrates and Polyols  5 Whereas the applications of succinic acid in the polymers industry are well known, the production of polyols from natural sources has only recently gained momentum. Their successful inclusion in current technologies will show whether their use is sustainable. There is no need to use a polyol produced from palm or rapeseed oil in a polyurethane formulation if its contribution to the properties of the end product does not offer any economic or qualitative appeal to the consumer. There is no doubt that the final outlet of all industrial and agricultural products are aimed at the direct or indirect consumption by humans. The higher the production rates, the more energy will be required by the production processes. A simple mathematical model will certainly prove that sustainabilty as well as cyclic economy will be convincigly achieved and implemented, at least, when the growth of the world population will be controllable. But this is a very difficult target to attain.

1.3 Polyols from Vegetable Oils Vegetable oils have been known to mankind since prehistoric times. Humans have used fats and oils for food, healing and other ends. Over the years, the extraction of oils from agricultural products has been elaborated. Nowadays, for some polymerization purposes, many vegetable oil molecules must be chemically transformed in order to include hydroxyl groups in their structure. For instance, soybean oil does not contain any hydroxyl groups but has an average of 4.6 double bonds per triglyceride molecule. The unsaturation of the vegetable oil molecule can accommodate hydroxyl groups. However, many reactions for preparing polyols from vegetable oils are not very selective. By-products are created during the transformation. Furthermore, many conventional methods of preparing polyols from vegetable oils do not produce polyols having a significant content of hydroxyl groups, and the available methods do not produce products having a desirable viscosity. Greases or waxes often result as a consequence of such chemical transformations.

1.3.1 Polyols from Triglycerides Chemically, vegetable oils are defined as triglycerides (also called glyceryl trialkanoates) because they are esters of glycerol and fatty acids (Figure 1.3). The structures in Figure 1.4 put the glyceride definition in a broader context.

6  Biobased Polyols for Industrial Polymers CH2-O-CO-R1

CH2-OH

R1-COOH

CH-O-CO-R2 Hydrolysis CH-OH + R2-COOH CH2-O-CO-R3

CH2-OH

R3-COOH

Triglyceride

Glycerol

Fatty acids

(R1,R2 & R3 are saturated of unsaturated unbranched chains of 4 to 28 C atoms)

Figure 1.3  Products resulting from the hydrolysis of triglycerides. CH3(CH2)7CH=CH(CH2)7C(O)O-CH2 CH3(CH2)7CH=CH(CH2)7C(O)O-CH2

HO-CH2

CH3(CH2)7CH=CH(CH2)7C(O)O-CH

HO-CH

HO-CH

CH3(CH2)14C(O)O-CH2 Triglyceride

CH3(CH2)14C(O)O-CH2 CH3(CH2)14C(O)O-CH2 Diglyceride

Monoglyceride

Figure 1.4  The definition of glycerides reflects the number of esterified hydroxyl groups of glycerol.

In practice, the carboxylic acid moieties are not all the same, but mixtures of several ones, as shown in Figures 1.3 and 1.4. They are also present in different triglyceride molecules in variable ratios. The acids are called fatty because their structure is similar to the acidic constituents of triglycerides found in fats. Fats are solid triglycerides whereas oils are liquids. The carboxylic acids are monobasic with a long hydrocarbon tail chain. Fatty acids, as shown in Figure 1.5, can be fully saturated but they can also contain unsaturated sites as well as hydroxyl groups (ricinoleic acid for example). Further down in the text, it will be shown how unsaturated triglycerides are hydroxylated. The hydroxylated compounds can be made useful, for example, in the formation of urethanes, by reacting the hydroxyl groups with isocyanates. Coatings, adhesives, elastomers, foams and composites can be made from elastomers using such hydroxy functional compounds. For example, in a first step an excess of a diisocyanate, such as MDI or TDI, the structures of which are shown in Figure 1.6, is reacted with a hydroxyl-containing triglyceride, such as castor oil, so as to form a prepolymer containing an excess of isocyanate groups [10, 11]. O

O

OH

OH Palmitic acid

OH

Ricinoleic acid

Figure 1.5  Structures of some saturated and unsaturated fatty acids.

Vegetable Oils, Animal Fats, Carbohydrates and Polyols  7 CH3 3

OCN

2

4

2' 1

5

CH2

6

3' 4'

1'

6'

CH3

1 6

NCO

1

OCN

2

2

5

4

3 4

NCO

Methylene diphenyl 4,4'-diisocyanate (MDI)

NCO

6

3

5

5'

NCO

Toluene 2,4 diisocyanate

Toluene 2,6 diisocyanate

Figure 1.6  Chemical structures of some commercial aromatic diisocyanates.

Those free NCO groups originate either from free isocyanates or from the reaction products of castor oil with TDI (or MDI), as shown in the reaction scheme in Figure 1.7. By reacting the isocyanate mixture with water in the presence of an amine catalyst a foamed product is obtained, because of the evolution of CO2. The reaction is shown in Figure 1.8. O CH2-O-C-(CH2)7-CH=CH-CH2-CH-OH (CH2)5-CH3

CH3 N

O

C

CH-O-C-(CH2)7-CH=CH-CH2-CH-OH O

(CH2)5-CH3

+

CH2-O-C-(CH2)7-CH=CH-CH2-CH-OH

O

C

O

N

(CH2)5-CH3 Castor oil (OH value 161.5) The ricinoleic acid moiety is the major component

2,4 Toluene diisocyanate (TDI) (excess)

CH3 N=C=O O CH2-O-C-(CH2)7-CH=CH-CH2-CH-O C

CH3 N

NH

O (CH2)5-CH3 O O CH-O-C-(CH2)7-CH=CH-CH2-CH-O C NH

(CH2)5-CH3 O O CH2-O-C-(CH2)7-CH=CH-CH2-CH-O C NH (CH2)5-CH3 Castor oil/TDI prepolymer (NCO terminated)

CH3

+

N=C=O O

C

C

O

N

CH3 N=C=O 2,4- Toluene diisocyanate (unreacted)

Figure 1.7  Reaction products of castor oil with an excess of 2,4-toluene diisocyanate (TDI).

8  Biobased Polyols for Industrial Polymers R-NCO+ H2O → R-NH-COOH → R-NH2 + CO2↑

Figure 1.8  Reaction of isocyanate with water.

Polyols obtained from triglycerides are very often propoxylated and/or ethoxylated with propylene oxide or ethylene oxide respectively in order to increase their molecular weight and subsequently their chain flexibility. The structure of each alkylene oxide is shown in Figure 1.9. An example of such a polyol synthesis is described below [12]: First, 267.2 g castor oil and 5.73 g KOH are flushed with nitrogen in an autoclave at 110°C with stirring. Then, 747.3 g of propylene oxide are added. After a reaction time of 4 h, 186.8 g ethylene oxide is metered under pressure. After 1 h, the contents of the reactor are cooled to 40°C and neutralized by the addition of 132 g distilled water and 32.4 g, 11.85% sulfuric acid. After addition of 0.65 g Irganox 1076 (antioxidant), dehydration is carried out in vacuo and the mixture is heated thoroughly for 3 h at 110°C and then filtered. The OH number of the product is 51.7 mg KOH/g, and the viscosity at 25°C is 500 mPas.

The reaction sequences of the above-described experiment are shown in Figure 1.10. It should be noted that propoxylation leads to alcohols with secondary hydroxyl end groups for steric reasons. Ethoxylation, in turn, introduces primary OH groups, which are more reactive towards carboxylic acids and isocyanates. Therefore, in order to synthesize a completely biobased polyol, chemicals such as propylene oxide and ethylene oxide must also emerge from natural sources. This text will examine if such a process is feasible. Nevertheless, the final polyurethane cannot be defined as fully biobased as long as the isocyanate component is aromatic. The source of aromatics being, until now, petrochemical. The same argument is valid for other technologies where polyols originating from natural sources are constituents of thermosets, such as unsaturated polyesters, for example. O H H

C

C

H H

Ethylene oxide

H

H H

H

C C O

C

H

H Propylene oxide

Figure 1.9  Chemical structures of ethylene and propylene oxide.

Vegetable Oils, Animal Fats, Carbohydrates and Polyols  9 O CH2-O-C-(CH2)7-CH=CH-CH2-CH-OH

H H

H

(CH2)5-CH3 H C C

C

O CH-O-C-(CH2)7-CH=CH-CH2-CH-OH

(CH2)5-CH3 O CH2-O-C-(CH2)7-CH=CH-CH2-CH-OH (CH2)5-CH3

O

H

O CH3 CH=CH-CH2-CH-O-CH2-CH−OH H CH2-O-C-(CH2)7z (CH2)5-CH3 O CH3 CH-O-C-(CH2)7-CH=CH2-CH-O-CH2-CH−OH

Propoxylation

y

(CH2)5-CH3 O CH3 CH2-O-C-(CH2)7-CH=CH-CH2-CH-O-CH2-CH−OH (CH2)5-CH3

Castor oil

y

O

Ethoxylation

H C H

C

H H

O CH3 CH2-O-C-(CH2)7-CH=CH-CH2-CH-O-CH2CH−O−CH2-CH2−OH z

p

(CH2)5-CH3 O CH3 CH-O-C-(CH2)7-CH=CH-CH2-CH-O-CH2CH−O−CH2-CH2−OH y

n

(CH2)5-CH3 O CH3 CH2-O-C-(CH2)7-CH=CH-CH2-CH-O-CH2CH−O−CH2-CH2−OH (CH2)5-CH3

x

m

Figure 1.10  Propoxylation followed by ethoxylation of castor oil.

The U.S. Federal Procurement Process has provisions which may favor products which are biobased over those that are petroleum-based. For example, for wall construction, the U.S. Department of Agriculture (USDA) has proposed a minimum biobased content of 8% to be classified as a biobased product for federal procurement purposes. Furthermore, in the United States, again, the Code of Federal Regulations (CFR Title 7 Part 2902) details guidelines for designating biobased products for federal procurement. In this guideline, the preferred procurement product must have a biobased content of at least 7%, based on the amount of qualifying biobased carbon in the product as a percent of the weight (mass) of the total organic carbon in the finished product. The guideline is specifically for spray-in-place plastic foam products designed to provide a sealed thermal barrier for residential or commercial construction applications [13]. The biobased content is determined according to ASTM D6866. ASTM D6866-08 includes Standard Test Methods for Determining the Biobased Content of Solid, Liquid, and Gaseous Samples Using Radiocarbon Analysis.

10  Biobased Polyols for Industrial Polymers

1.3.2 Polyols from Glycerol Synthetic glycerol is manufactured on an industrial scale mainly from the hydrolysis of epichlorohydrin, as shown in Figure 1.11 [14]. Since glycerol forms the backbone of triglycerides, it is produced upon their saponification or transesterification. This method is a preferred green method, epichlorohydrin being an unsafe product. Glycerol has been used as such in rigid foam formulations, even if its efficiency as well as its role are very often doubtful. The reactivity of the secondary OH group is low compared to the reactivity of the primary OH groups. The use of glycerol in spray foam formulations contributes to the volume/equivalent weight requirements of the polyol and the isocyanate components. Glycerol is also used in the manufacture of triols through propoxylation and ethoxylation. Those triols have applications in rigid as well as in flexible polyurethane foams. For example, Voranol 9815 is a glycerol initiated polyoxypropylene polyoxyethylene (propoxylated and then ethoxylated to introduce primary OH groups) polyol having an average hydroxyl number of 28, which is available from the Dow Chemical Company. Voranol CP 4702 is a glycerol initiated polyoxypropylene polyoxyethylene polyol having an average hydroxyl number of 32. Voranol CP 3001 is a glycerol initiated polyoxypropylene polyoxyethylene polyol having an average hydroxyl number of 56. These polyols are used in flexible foam formulations because of their low OH value or high molecular weight. On the other hand, Daltolac R 570 is a rigid foam, glycerol initiated polyoxypropylene polyoxyethylene triol produced by Huntsman. Its OH value is 570 mg KOH/g.

HOC1 C1-CH2-CHC1-CH2(OH) HC1 C12 + + CH3-CH=CH2 C1-CH2-CH(OH)-CH2C1 500ºC C1-CH2-CH=CH2 Propylene 13-dichlorohydrin Allyl chloride Ca(HO)2 H2C C1

CH2

HC O

Epichlorohydrin

Figure 1.11  Reactions involved in the synthesis of epichlorohydrin.

Vegetable Oils, Animal Fats, Carbohydrates and Polyols  11 Glycerol has become the source of diols, such as 1,3-propane diol, through a fermentation process (Figure 1.12) first developed in the 19th century [15]. DuPont and Genencor have developed an Escherichia coli (E. coli) strain capable of producing 1,3-propanediol (PDO) from glucose. However, glucose is not the only component of corn. DuPont and Tate & Lyle have developed a fermentation system that converts corn sugar into propanediol (“BioPDO”). Such a bioprocess is more energy efficient than conventional petrochemical processes (conversion of propylene into propanediol). The bioprocess has smaller environmental impact, lower operating costs, smaller capital investment, and greater sustainability due to the use of renewable corn feedstock [16]. 1,3-Propanediol is also a monomer employed in the industrial production of polyester fibers [17] and diols for polyurethanes. It has been used as a chain extender in thermoplastic polyurethanes [18]. 1,3-Propane diol can also be condensed with biobased succinic acid to produce polyester diols [19], as shown in Figure 1.13. The diols can be reacted with a chain extender like butane diol to give a thermoplastic polyurethane. Biobased 1,3-propane diol is used by DuPont to manufacture the more resilient and comfortable Sorona polyester. This polypropylene terepthalate has applications in apparel, upholstery, home fashions, and carpets. 

CH2-OH CH-OH CH2-OH Glycerol

Fermentation

CH2-OH

Chlostridium diolis Clostridium pasteurianium Kelbsiella pneumoniae

OH

Fermentation

CH2

HO HO

O OH

Corn

OH

CH2-OH 1,3 propane diol

D-Glucose

Figure 1.12  Propane diol obtained from the fermentation of glucose and glycerol.

HO-[(CH2)3-OOC-(CH2)2-COO-]n(CH2)3-OH HO-(CH2)3-OH Condensation Low molecular weight polyester diol 1,3 propane diol OCN-R-NCO + di-isocyanate OCN-R-NH-CO[O(CH2)3-OOC-(CH2)2-CO]nO(CH2)3-OCO-NH-R-NCO HOOC-(CH2)2-COOH Succinic acid HO-(CH2)3-OH -{[O(CH2)3-OOC-(CH2)2-CO]n[O(CH2)3-OOC-NH-R-NHCO]m}xPolyester polyurethane

Figure 1.13  Synthesis of a thermoplastic polyurethane.

12  Biobased Polyols for Industrial Polymers

1.4 Polyols from Carbohydrates Carbohydrates are renewable, which makes them an attractive source of chemicals. The main sources of carbohydrates are: • Ligno-Cellulosics (Lignin, Cellulose, Hemicellulose) • Sucrose • Starch Carbohydrates bear hydroxyl groups and can therefore be regarded as a viable source of polyols.

1.4.1 Ligno-Cellulosics Lignocellulose refers to plant biomass that is composed of cellulose, hemicellulose, and lignin. The percentage of each constituent of lignocellulose is shown in Figure 1.14. Cellulosic biomass can be pretreated with dilute sulfuric acid to recover high yields of sugars directly from hemicellulose and, subsequently, by enzymatic hydrolysis of the residual cellulose.

1.4.2 Cellulose Cellulose is the most common organic compound on Earth. Its structure is shown in Figure 1.15. About 33% of all plants is cellulose (the cellulose content of cotton is 90% and that of wood is 50%).

Cellulose 38-50%

Cellulose Hemicellulose Lignin

Lignin 15-25% Hemicellulose 23-32%

macromolecule consisting of glucose units branched macromolecule from pentoses Three-dimensional macromolecule from methoxyphenyl-propane units

Figure 1.14  Lignocellulose composition.

Vegetable Oils, Animal Fats, Carbohydrates and Polyols  13

HO HO

OH O OH

O HO

OH O

HO O

OH

OH O

OH O OH

O HO

OH

Cellobiose unit H O

O HO H O O HO H O O HO H O O HO

HO O OH O H

O

HO O OH O H HO O O OH O H HO O O OH O H O

H O O O HO H OH O O O HO H OH O O O HO H OH O O O HO OH

HO O

n

HO O OH O H

OH

HO O O OH O H HO O O OH O H

OH

O

HO O OH O H

O

OH O OH

O HO

OH O

OH

OH

O

O OH O OH O

Figure 1.15  Cellulose structure (macromolecules build up from glucose units).

For industrial use, cellulose is mainly obtained from wood pulp and cotton. It is mainly used to produce cardboard and paper. To a lesser extent, it is converted into derivative products such as cellophane and rayon. Cellulose is composed of linear chains of covalently linked glucose residues. Chemically, it is very stable. It is extremely insoluble. Cellulose chains form crystalline structures called microfibrils. A microfibril with a diameter of 20–30 nm contains about 2000 glucose molecules. Cellulose undergoes the following basic reactions.

1.4.2.1 Hydrolysis Acids attack the acetal linkages, cleaving the 1-4-glycosidic bonds. Since acetals are quite stable toward alkali, hydrolysis at high pH requires very vigorous conditions. Cellulose is also degraded by cellulase enzymes. Termites and fungi digest cellulose, but the synthetic process of obtaining ethanol from cellulose remains slow. The drawback is the sluggish rate at which the cellulose enzyme complex breaks down tightly bound cellulose into sugars, which are then fermented into ethanol.

1.4.2.2 Oxidative Degradation In general, oxidation of cellulosic hydroxyls forms aldehydes, ketones, and carboxyl groups. Strong oxidizing agents and/or vigorous reaction conditions convert cellulose into CO2 and H2O.

14  Biobased Polyols for Industrial Polymers

1.4.2.3 Thermal Degradation The applied temperature determines the nature of the degradation products. At low temperatures the degradation products are water, CO, CO2 and a carbonaceous char. At high temperatures, depolymerization of the cellulose chain takes place. Anhydroglucose derivatives, volatile organic materials and tars are formed. At still higher temperatures, more-or-less random bond cleavage of cellulose and intermediate decomposition products results in formation of a variety of low molecular weight compounds. The conversion of cellulose to glucose is described in several patents [20–23]. For example, a mixture of coniferous wood chips is heated at 200°C in the presence of water, CaCl2 and HCl. The conversion of cellulose to glucose is 80.5%. Other products formed include 5-hydroxymethylfurfural, xylose and furfural. Their structures are shown in Figure 1.16.

1.4.3 Hemicellulose Hemicellulose consists of shorter chains of 500–3000 sugar units as opposed to 7000–15000 glucose molecules per polymer chain present in cellulose. Its main constituent carbohydrate molecules are shown in Figure 1.17. O

OH HO HO

O

O OH Glucose

O

OH

HO

H

Furfural

O

H

HO

OH

O

5(hydroxy methyl) furfural

OH OH

Xylose

Figure 1.16  Products resulting from the hydrolysis of coniferous chips. H-C=O H-C-OH HO-C-H H-C-OH H-C-OH CH2-OH

CH2-OH O

D-glucose

H-C=O H-C-OH HO-C-H H-C-OH H-C-OH COOH

H-C=O HO-C-H H-C-OH H-C-OH CH2-OH

D-arabinose

COOH O

D-glucuronic acid

H-C=O HO-C-H HO-C-H

CH2-OH O

H-C-OH H-C-OH CH2-OH

D-mannose

H-C=O H-C-OH HO-C-H H-C-OH CH2-OH

D-xylose

Figure 1.17  Some monomers of hemicellulose. Xylose is always the sugar present in the largest amount.

Vegetable Oils, Animal Fats, Carbohydrates and Polyols  15 In contrast to cellulose that is crystalline and resistant to hydrolysis, hemicellulose has a random, amorphous structure with little strength. It is easily hydrolyzed by dilute acids or bases as well as by hemicellulase enzymes.

1.4.4 Lignin Lignin is found in the cell walls of plants. Lignin constitutes approximately 30–35 wt% of the dry weight of softwoods, about 20–25% of hardwoods and 15–20% of non-woods. Lignin is a branched phenolic natural biopolymer primarily composed of three phenylpropanoid building units (Figure 1.18). It is obtained industrially in large quantities especially from kraft pulping processes in the form of “black liquor.” Because of the abundance of OH groups in their structure, certain lignins can function as polyol components in polyurethane systems. They are mainly used in combination with other polyols [24, 25]. Example [26]: In this procedure, 300 parts of a lignin produced from a solvent pulping process and 700 parts of a polyether polyol are mixed. This mixture is heated to 93°C to improve the rate of dissolution. The mixing is continued until a dark solution results. Its viscosity is 1532 centistokes at 38°C.

In addition, depolymerization of lignin is a viable route for the preparation of low molecular weight products such as polyols, for the preparation of polyurethanes, phenol formaldehyde resins and epoxy biomaterials [27–30]. Sinapyl alcohol moiety

Coniferyl alcohol derivatives O

OH

HO

O HO

OH

OH OH

CH3O

O

OCH3

OCH3 OH

HO

OH

OCH3

CH3O

ol oh alc yl ve ar ti m iva Cu der

p-

OH O HO

O

OCH3

O OCH3 HO HO

O

OCH3

OH O

OH

O OH CH3

H3C

O

O OH CH3

OCH3

OH O HO

O

HO

O CH3O

OH

OCH3

HO O

OH

O

OH

HO

OH

OH

OH OH OCH3

OCH3

Lignin structure and components

Figure 1.18  Lignin and its components.

Cumaryl alcohol

Coniferyl alcohol

Sinapyl alcohol

16  Biobased Polyols for Industrial Polymers

1.4.5 Sucrose Sucrose (table sugar or saccharose) is a disaccharide of glucose and fructose. The chemical structures of the latter are shown in Figure 1.19. Sucrose, the chemical structure of which is shown in Figure 1.20, is extracted from sugar cane or sugar beet and then purified and crystallized. Polyols with a sucrose initiator have eight hydroxyl groups. They are obtained from the propoxylation/ethoxylation of sucrose. Because of their high functionality they are used in rigid polyurethane foam applications. The preparation of the first alkoxylated sucrose polyols is disclosed in several references [31–33]. A general reaction scheme is shown in Figure 1.21. In an early patent, the propoxylation of sucrose was carried out as follows: About 4.76 kg of sucrose is dissolved in 1 liter of water. About 120 g of KOH is added and the mixture is heated close to boiling. Then 4.85 kg of propylene oxide is added under pressure over a period of 3 h. This is followed by the addition of another 4.85 kg of propylene oxide over

Haworth projection

H OH 6 4

6CH2OH 4

5 O OH OH 1

OH 3

2

Fischer projection

Cyclohexane projection

HO HO

OH

H

2

2

HO

5 H O

3 H H

OH 1 H

CH2OH

CHO1

OH

3

H H

4

O

OH

HO

H

H

CH2OH OH O H OH HO H OH CH2OH OH CH2OH

OH

OH 5 CH2OH 6

(β-D-Fructofuranose) Fischer projection Fructose

α-D-Glucose

Figure 1.19  Chemical components of sucrose.

OH

CH2OH H O H OH OH H

OH

CH2OH H O H HO O CH2OH OH H

Figure 1.20  Chemical structure of sucrose.

HO HO

O OH O

OH

O OH

OH OH

Vegetable Oils, Animal Fats, Carbohydrates and Polyols  17

CH2OH CH2OH H H O H O OH H H HO O CH2OH OH H OH OH H

H

H

H

H

C

C

C

O

H

H

→

Propoxylation

CH3 HO-CH-CH2-O x CH2

CH3 O-CH2-CH-OH q CH2 O H CH3 CH3 O H HO-CH-CH 2-O H O-CH2-CH-OH y w O CH2-O-CH2-CH-OH HO-CH-CH2-O z CH3 CH3 n H O O H HO-CH-CH2 CH2-CH-OH p CH 3 CH3 m

Sucrose

Propoxylated surcrose

Figure 1.21  Propoxylation of sucrose.

a period of 1 h and 45 min. The resulting polyol has a hydroxyl value of 455.1 mg KOH/g and a viscosity of 140 000 cP.

Daltolac R 585 (Huntsman) is a sucrose amine-initiated polyol for rigid polyurethane foam. Its OH value is 585 mg KOH/g and its viscosity is 3500 mPa.s at 25°C. The arguments which have already been mentioned above concerning polyols derived from triglycerides, also hold for sucrose-based polyols. • First, sugar futures are traded in commodity exchanges. Therefore, the price of sucrose is subject to speculation. Price variations of sugar as well as rapeseed oil, which is also a source of biobased polyol, over a six-month period are shown in Figure 1.22 and Figure 1.23. • Second, the polyols, which are derived from sucrose, involve ethoxylation and propoxylation. Therefore, unless ethylene oxide (EO) or/and propylene oxide (PO) originate from green sources, the polyol itself can hardly be defined as entirely biobased. 295

Price, USD/Ton

290 285 280 275 270 265 Sep-18

Oct-18

Dec-18

Feb-19

Figure 1.22  Sugar monthly price variations [7].

Mar-19

May-19

Jul-19

18  Biobased Polyols for Industrial Polymers 870

Price, USD/Ton

860 850 840 830 820 810 800 Sep-18

Oct-18

Dec-18

Feb-19

Mar-19 May-19

Jul-19

Figure 1.23  Rapeseed oil monthly price [7].

Initiators, such as sucrose, are not the only chemical component and, consequently, the sole components influencing the price of polyols. Propylene oxide as well as ethylene oxide and eventually their precursors propylene and ethylene respectively contribute to the final price of the polyol. Ethylene oxide (oxirane) is prepared industrially by the direct oxidation of ethylene, as represented in Figure 1.24. On the other hand, propylene oxide is traditionally produced via the conversion of propylene to chloropropanols as shown in Figure 1.25. The reaction produces a mixture of 1-chloro-2-propanol and 2-chloro-1-propanol, which is then dehydrochlorinated. The reaction is shown in Figure 1.26. The other general route (PO-SM or Propylene Oxide-Styrene Monomer) to propylene oxide involves the co-oxidation of propylene and ethyl benzene. In the presence of catalyst, air oxidation occurs as follows (Figure 1.27). In April 2003, Sumitomo Chemical commercialized the first PO-only plant in Japan, which produces propylene oxide from the oxidation of 7 CH2=CH2 + 6 O2 → 6 (CH2CH2)O + 2 CO2 + 2 H2O

Figure 1.24  Synthesis of ethylene oxide. 2 H3C-CH=CH2 + C12 + H2O

→

H3C-CH(C1)-CH2OH + H3C-CH(OH)-CH2C1

Figure 1.25  Synthesis of chloropropanols. H3C-CH(OH)-CH2C1 +OH- →

Figure 1.26  Synthesis of propylene oxide.

O H3C

+Cl-

+H2O

Vegetable Oils, Animal Fats, Carbohydrates and Polyols  19 CH3CH=CH2 + Ph-CH2CH3 + O2 → CH3[(CHCH2)O] + Ph-CH=CH2 + H2O

Figure 1.27  PO-SM route to propylene oxide.

H3C Φ-H

+ CH3CH=CH2

Benzene

Propylene

→

Φ-CH(CH3)2 Cumene + H2O

OOH CH3

O2 → Cumene hydroperoxide ↓CH3-CH=CH2 CH3[(CHCH2)O] + OH H3C CH3

H2 Dimethylbenzyl alcohol

Figure 1.28  Sumitomo Chemical route to the synthesis of propylene oxide. CH3CH=CH2 + H2O2 → CH3[(CHCH2)O] + H2O

Figure 1.29  HPPO route to propylene oxide.

cumene without significant production of other products. The reaction scheme is shown in Figure 1.28. In March 2009, BASF and Dow started their new HPPO (Hydrogen Peroxide-PO) plant in Antwerp, Belgium. In this process, propylene is oxidized to propylene oxide. The reaction is shown in Figure 1.29.

1.4.6 Starch Many crops, such as maize, rice, wheat, potato, etc., are a source of starch. Starch is made of glucose molecules attached by α-(1,4) bonds, with some branching by means of α-(1,6) bonds, as shown in Figure 1.30. The degree of branching depends on the source of the starch.

1.4.6.1 Glucose Glucose (dextrose) is produced commercially via the enzymatic hydrolysis of starch. Its propoxylation leads to a pentol. The whole set of reactions is shown in Figure 1.31 and Figure 1.32.

20  Biobased Polyols for Industrial Polymers CH2OH O

O HO

CH2OH O

O HO

HO

OH

α–1,6-glycosidic linkage

O CH2 O

O HO

HO

α–1,4-glycosidic linkage

CH2OH O

O HO

OH O

Starch

Starch structure

Figure 1.30  Structure and photograph of starch. CH2OH O OH

O

CH2OH O OH O O O OH HO6 CH2 CH2OH CH2OH 5 O O O 1 4 OH OH OH O O 2 O 3 OH OH OH

105ºC

→

CH2OH O OH

Amylospectin

α-amylase (enzyme)

Partially hydrolysed starch

60ºC ph= 4-4.5

OH HO HO

→

O OH

OH

Glucose

Glucoamylase

Amylose

O

OH

Starch slurry

Figure 1.31  Synthesis of glucose from the enzymatic hydrolysis of starch. OH HO HO

H H

O OH

H

OH

Glucose

C

C O

H C

H

H

Propoxylation

CH3 CH2-CH-OH

O CH3 O HO-CH-CH2 O e HO-CH-CH2 O O d CH3 HO-CH-CH2 CH3 c

a

O

CH3 CH2-CH-OH b

Figure 1.32  Synthesis of glucose-initiated pentol from the propoxylation of glucose.

Glucose can be propoxylated in the presence of cationic catalysts (BF3, HBF4). On the other hand, the α methyl glucoside is propoxylated in the presence of KOH or tertiary amines to yield the corresponding tetrol, as shown in Figure 1.33. Finally, as shown in Figure 1.34, the steam cracking of glucose leads to several low molecular weight diols which are useful in the manufacture of thermoplastics as well as thermosets.

1.4.6.2 Sorbitol The structure of sorbitol and its stereoisomer mannitol are shown in Figure 1.35. It is obvious that the presence of hydroxyl groups makes them eligible as initiators for the synthesis of polyols.

Vegetable Oils, Animal Fats, Carbohydrates and Polyols  21 OH

MeOH

O

HO HO

OH

OH

OH HO HO

O OH

O CH3

H H H H C C C H O H

CH3 HO-CH-CH2O e

Propoxylation

Me α-Dglucopyranose

α-D-glucopyranose (Glucose)

O

CH3 CH2-CH-OH a

O

HO-CH-CH2 O O d CH3 HO-CH-CH2 CH3 c

O

CH3

Figure 1.33  Synthesis of a tetrol from the propoxylation of methylated glucose.

Glucose Steam H2

Hydrogenation Sorbitol intermediate

Steam H2

Hydrocracking Glycols & Alcohols

Steam

Separations Products Propylene glycol Ethylene glycol Glycerol Butane doils Alcohols

Figure 1.34  Flow sheet for glucose cracking [34].

Sorbitol is produced through the catalytic hydrogenation of dextrose (α-D-glucose, α-D-glucopyranose), as exemplified in Figure 1.36. Polyols for rigid polyurethane foams are obtained from the propoxylation/ethoxylation of sorbitol. For example, Daltolac R 475 (Huntsman) is OH

OH

OH OH

OH

HO OH

OH Sorbital

OH

HO OH

OH

Mannitol is a sorbitol stereoisomer

Figure 1.35  Chemical structures of sorbitol and mannitol.

22  Biobased Polyols for Industrial Polymers CHO H HO

CH2OH

OH H

H

OH

H

OH CH2OH

OH

H + H2

Ni

HO

H

H

OH

H

OH CH2OH

Figure 1.36  Reduction of D-glucose (dextrose) to sorbitol.

a sorbitol-initiated polyol. It has an OH value of 475 mg KOH/g. Its viscosity is very high (15000 mPa.s at 25°C). The average functionality of sorbitol-based polyols can be reduced by using a mixture of sorbitol and glycerol as initiators of the propoxylation reaction. Daltolac R 440 (Huntsman) is a sorbitol/glycerol-initiated polyol. It has an OH value of 437 mg KOH/g. Its viscosity is 1650 mPa.s (25°C).

References 1. A. Sorrell, T. Newbold, J. Qian, S. Yalamanchili, N. Noldelman. United States Patent US2013217798 assigned to Biobased Technologies LLC, August 2013. 2. Yeadon, D.A., McSherry, W.F., Goldblatt, L.A., Preparations and properties of castor oil urethane foams. J. Am. Oil Chem. Soc., 36, 16–20, 1959. 3. Cowan, J.C., Dimer Acids. J. Am. Oil Chem. Soc., 39, 534, 1962. https://doi. org/10.1007/BF02672546. 4. Lyon, C.K., Garrett, V.H., Frankel, E.N., Rigid urethane foams from hydroxymethylated castor oil, safflower oil, oleic safflower oil, and polyol esters of castor acids. J. Am. Oil Chem. Soc., 51, 8, 331–334, 1974. 5. Lyon, C.K., Garrett, V.H., Goldblatt, L.A., Solvent-blown, rigid urethane foams from low cost castor oil-polyol mixtures. J. Am. Oil Chem. Soc., 39, 1, 69–71, 1961. 6. Scholnick, F., Saggesse, E.G., Wrigley, A.N., Ault, W.C., Monroe, H.A., Zubillaga, M., Urethane foams from animal fats. IV. Rigid foams from epoxidized glycerides. Presented at the AOCS Meeting, New Orleans, 1967, ­https://­doi.org/10.1007/BF02890710. 7. Index Mundi (www.indexmundi.com). 8. Urethane Soy Systems Company, subsidiary of South Dakota Soybean Processors LLC. 9. W. Hinz, E.M. Dexheimer, E. Bohres, G.H. Grosch, Process for the copolymerization of alkylene oxides and carbon dioxide using suspensions

Vegetable Oils, Animal Fats, Carbohydrates and Polyols  23 of multi-metal cyanide compounds, United States Patent US2003149232 assigned to BASF Corp., August 2003. 10. S.R. Detrick and E. Barthel, Cellular plastic materials which are condensation products of hydroxy containing fatty acid glycerides and arylene diisocyanates, United States Patent US2787601 assigned to DuPont, April 1957. 11. S.R. Detrick and E. Barthel, Arylene diisocyanate-fatty acid ­triglyceride-polyol cellular materials and process of producing same, United States Patent US2833730 assigned to DuPont, May 1958. 12. K. Lorenz, R. Albers, F. Otto, U. Leyrer, D.S. Wardius, K.J. Headley, Process for the preparation of polyether-ester polyols, European Patent EP1923417 assigned to Bayer Material Science AG, May 2008. 13. C.A. McAdams, E. Gnedin, L.J. Garcia, Board stock foam having biobased content, United States Patent US2010298453 assigned to Invista North America, November 2010. 14. Bijsterbosch, J.W., Das, A., Kerkhof, F.P.J.M., Clean technology in the production of epichlorohydrin. J. Clean. Prod., 2, 3–4, 181–184, 1984. 15. Freund, A., Über die Bildung und Darstellung von Trimethylenalkohol aus Glycerin. Monatsh. Chem., 2, 636, 1881. https://doi.org/10.1007/BF01516545. 16. Muska, C.F. and Alles, C., Paper presented on behalf of DuPont. BioPerspectives. BREW Symposium, May 11, 2005, 2005, https://pdfslide. net/documents/biobased-13-propanediol-a-new-platform-chemical-forthe-21st-century-carl.html. 17. J.V. Kurian and Y. Liang, Processes for making elastomeric polyester esters from post-consumer polyester, United States Patent US20090131625, May 2009. 18. W.H. Boon and T.C. Froschner, TPU’s prepared from trimethylene carbonate soft segment, European Patent EP1268599 assigned to Shell Research, January 2003. 19. Albertsson, A.C. (Ed.), Advances in Polymer Science, Vol 157, Degradable Aliphatic Polyesters, Springer, New York, 2002. 20. D.F. Day and W.E. Workman, Process for the conversion of cellulose to glucose, United States Patent US4487831 assigned to Research Corp., December 1984. 21. B.A. Rugg and W. Brenner, Process for the chemical conversion of cellulose waste to glucose, United States Patent US4316747 assigned to Univ. New York, March 1980. 22. R.T. Nagle, Process for converting cellulose to glucose and other saccharides, United States Patent US4699124 assigned to Power Alcohol Inc., October 1987. 23. D.E. Eveleigh, C.R. Waldron, T. Bartley, A method for the conversion of a cellulosic substrate to glucose using microbispora bispora strain Rutgers P&W, WIPO Patent WO8501065 assigned to Parsons & Whitmore Inc., March 1985. 24. H. Hatakeyama and S. Hirose, Lignin-based polyurethane and process for producing the same, United States Patent US2005014919 assigned to National Institute of Advanced Industrial Science and Technology, January 2005.

24  Biobased Polyols for Industrial Polymers 25. H.J. Reese, F. Heimpel, H. Forster, Pressurized, blowing agent-containing isocyanate semiprepolymer mixtures based on lignin-polyether polyols and their use for producing polyurethane foams, United States Patent US5834529 assigned to Elastogran GmbH, November 1998. 26. K.R. Kurple, Lignin based polyols, European Patent EP0812326 assigned to K.R. Kurple, December 1997. 27. Nguyen, T.D.H., Maschietti, M., Belkheiri, T., Amand, L.E., Theliander, H., Vamling, L., Olausson, L., Andersson, S.I., Catalytic depolymerisation and conversion of Kraft lignin into liquid products using near critical water. J. Supercrit. Fluids, 86, 67–75, 2014. https://www.slideshare.net/ ThiDieuHuyenNguyen/2014nguyen-et-al​the-journal-of-supercritical-fluids. 28. Mahmood, N., Yuan, Z., Schmidt, J., Xu, C., Production of polyols via direct hydrolysis of kraft lignin: Effect of process parameters. Bioresour. Technol., 139, 13–20, 2013, doi: 10.1016/j.biortech.2013.03.199. 29. Yuan, Z., Cheng, S., Leitch, M., Xu, C., Hydrolytic degradation of alkaline lignin in hot-compressed water and ethanol. Bioresour. Technol., 101, 23, 9308–9313, 2010. https://doi.org/10.1016/j.biortech.2010.06.140. 30. C. Xu, N. Mahmood, Z. Yuan, F. Ferdosian, B. Li, M. Paleologou, Depolymerisation of lignin for the production of biobased polyols and phenols and lignin based PF/PU/Epoxy resins/foams, WIPO Patent WO2018205020 assigned to FPInnovations, November 2018. 31. LeMaistre, J.W. and Seymour, R.B., The reaction of sucrose with ethylene oxide. J. Org. Chem., 13, 5, 782–785, 1948. https://doi.org/10.1021/ jo01163a026. 32. M. Wismer and J.F. Foote, Method of preparing polyethers of mono and disaccharides, United States Patent US3085085 assigned to Pittsburgh Plate Glass Co., April 1963. 33. M. Wismer, L.R. Lebras, J.F. Foote, Polymers of organic polyisocyanates and polyether polyols derived from sucrose and methods for the preparation thereof, United States Patent US3153002 assigned to Pittsburgh Plate Glass Co., October 1964. 34. International Polyols Chemicals Inc., http://polyolchem.com.

2 Polyurethanes, Polyesters and Epoxies 2.1 Introduction This chapter includes a short account on the chemistries of the main polymers where biobased polyols have a fit. Those polymers are: • Polyurethanes which are the reaction products mainly of polyols with isocyanates. In such reactions, the polyols derived from petrochemical sources can be substituted by biobased polyols, the main sources of which are natural oils and fats. • Polyesters are the condensation product of a short-chain diol, such as ethylene glycol, with a dibasic acid. Polyethylene terephthalate is the most well-known aromatic polymer. On the other hand, aliphatic dicarboxylic adipic acid-based polyester macro-diols, like the short-chain ethylene glycol, are obtained from natural sources. • Epoxies in which epoxide groups are introduced in the double bonds available in the fatty acid molecules of triglycerides.

2.2 Polyurethanes [1–3] When a reaction is carried out in the presence of a blowing agent and a surfactant, foams are produced. The blowing agent may also be CO2, which results from the reaction between an isocyanate and water. This section aims to succinctly explain the structural differences which exist between the various types of polyurethanes. Those structural differences determine the properties of the foams and thus their applications.

2.2.1 Rigid Foams Rigid polyurethane foams result from the reaction between a polyol and a polyisocyanate in the presence of a blowing agent and a surfactant. Both Deny Kyriacos. Biobased Polyols for Industrial Polymers, (25–50) © 2020 Scrivener Publishing LLC

25

26  Biobased Polyols for Industrial Polymers reactants have a functionality which is higher than 2. This leads to a crosslinked structure which imparts rigidity to the final cellular product. The basic technological requirement for rigid polyurethane foams is thermal insulation. The component with the major contribution to thermal insulation is the blowing agent. The formulator can adjust the reaction variables as well as the nature of the components in order to adapt it to the technical requirements of a specific application such as spray, lamination, bun, refrigeration, etc.

2.2.1.1 Isocyanates The isocyanates used in the manufacture of rigid PU foams are aromatic polymeric isocyanates. They have the general structure shown in Figure 2.1. Aromatic polyisocyanates come in various viscosities and functionalities. Those parameters are used to fine tune the processability of the polyurethane system.

2.2.1.2 Polyols The polyol component of a polyurethane system for rigid foam may contain mixtures of several polyols. The formulator may combine the polyols in order to obtain the required physical properties of the foam, the homogeneity of the polyol component, as well as the necessary processing characteristics of the system. The main polyol in a rigid foam system has a high functionality and a relatively low molecular weight. For example, it can consist of a propoxylated/ethoxylated sorbitol, the functionality of which is 6. The polyol component may also contain diols, which would reduce the overall functionality of the system and, as a result, its crosslink density. The structure of some initiators is shown in Figure 2.2. The hydroxyl value (details in the appendix) of rigid foam polyols lies, in general, in the range of 350–500 mg KOH/g. For example, a glycerol-initiated polyol with an OH value of 460 mg KOH/g, would have an equivalent weight of 56100/460 = 122 and its molecular weight would be 3 × 122 = 366. NCO

OCN CH2

H n

Figure 2.1  Poly methylene di(phenyl isocyanate) n>1.

Polyurethanes, Polyesters and Epoxies  27 CH2OH CH2OH H O H O OH H H HO O CH2OH OH H OH OH H

CH2-OH OH

H

Sucrose (functionality = 8)

OH OH

HO OH

OH

Sorbitol (functionality = 6)

CH-OH CH2-OH Glycerol (functionality = 3)

Figure 2.2  Examples of polyol initiators.

To put those values in perspective, a glycerol-initiated polyol used in the formulation of flexible foams has a OH value of 56.1 mg KOH/g or an equivalent weight of 1000.

2.2.2 Flexible Foams A flexible foam results from chemical constituents which impart flexibility to the molecular structure. Whereas the formation of rigid PU foams is mostly dependent on the reaction between an isocyanate and a polyol, the formation of PU flexible foams also involves the reaction of water with the isocyanate. As a consequence, subsequent isocyanate reactions are expected, as shown below. • Reaction of the isocyanate with water, which results in an amine and carbon dioxide R-NCO + H2O → [R-NH-COOH] → R-NH2 + CO2↑ • Reaction of a free isocyanate with the generated amine, which results in urea R-NCO + R-NH2 → R-NH-CO-NH-R • Reaction of a free isocyanate with the generated urea to give a biuret R-NCO + R-NH-CO-NH-R → R-NH-CO-NR-CO-NH-R • Reaction of a free isocyanate with an already formed urethane group to form an allophanate R-NCO + R-NH-COOR’ → R-NH-CO-NR-COOR’ Two different types of production methods distinguish PU flexible foams: • The continuous slabstock process. Most of the foams are produced continuously, from the super soft to the high load bearing.

28  Biobased Polyols for Industrial Polymers • The discontinuous molding process, where articles of a desired shape are obtained by foaming in a mold. Cushions for car seats are produced in this way.

2.2.2.1 Isocyanates The workhorse in PU flexible production is toluene diisocyanate (TDI) and more specifically an 80 to 20 mixture of 2,4 TDI and 2,6 TDI. Both structures are shown in Figure 2.3. Flexible foams for cars seats can also be molded from specially formulated systems based on polymeric isocyanates.

2.2.2.2 Polyols The PU flexible foams can be classified as ester or ether foams, depending on the choice of the polyol component. They can also be distinguished as standard or high resilient foams. Typical properties of polyols used in the manufacture of TDI-based foams are given in Table 2.1 below.

2.2.3 Microcellular Elastomers Polyurethane shoe soles are the reaction products of an isocyanate prepolymer and a polyol system. Their hardness is imparted by the precipitation of hard segments in the polymer matrix and their density is the result of the evolution of CO2 generated from the reaction of the isocyanate and water, as well as because of the presence of small amounts of a blowing agent in the mix, as is the case of polyether systems.

CH3

CH3

1

1

OCN 6

2

5

NCO

3

NCO

6

2

3

5

4

4

NCO Toluene 2, 6 diisocyanate

Toluene 2, 4 diisocyanate

Figure 2.3  TDI isomers used in flexible foam production.

Polyurethanes, Polyesters and Epoxies  29 Table 2.1  Basic properties of polyols used in the manufacture of PU flexible foams. Type

Polyether

Polyether

Structure

Propoxylated Ester of adipic Propoxylated Ethoxylated glycerol acid with propoxylated propylene diethylene trimethylolpropane glycol glycol and a small amount of trimethylol propane

Average molecular weight

2000 + 100

4800 + 300

3000 + 200

2400

OH value

56 + 3

35 + 2

56 + 3

57 – 63

3

2

>2

Functionality 2

Polyether

Polyester

2.2.3.1 Footwear The polyurethane used systems fall into two categories: • Polyether systems [4] They result in soles with excellent surface finish. They are used in street shoes and are very resistant to hydrolysis. A very useful prepolymer is based on MDI and a mixture of di- and tri-propylene glycols, the structure of which is shown in Figure 2.4. The average equivalent weight of the prepolymer is 171.7. A typical formulation is the one shown in Table 2.2.

OH O OH

O OH

Dipropylene glycol (DPG), M.W.: 134.18; m.p.:–40°C

O OH Tripropylene glycol (TPG), M.W.: 192; m.p.:–49°C

Figure 2.4  Polyols used in the synthesis of MDI prepolymers.

30  Biobased Polyols for Industrial Polymers Table 2.2  Typical formulation of expanded PU elastomers used in polyether shoe sole manufacture. Components of the polyol blend

Equivalent weight

Parts

Ethoxylated, propoxylated diol

2000

70.5

Ethylene oxide tipped polyoxypropylene triol

2000

17.63

1,4 Butane diol

45

9.34

Ethylene glycol (MEG)

31

0.53

Amine catalyst

60

1.76

Metal salt catalyst

0.013

Silicone surfactant

0.087

Water

9

0.14

The polyol component has a hydroxyl value of ~167 mg KOH/g and a viscosity of ca.1000 cP at 20°C. Expanded polyether polyurethane shoe soles are shown in Figure 2.5. • Polyester Systems They result in low density soles with excellent resistance to abrasion. They are used as interlayers as well as soles of sport shoes, especially tennis shoes. Polyester shoe sole systems expand only under the influence of carbon dioxide. The formulations do not contain unreactive blowing agents. The two major components of polyester footwear systems are the isocyanate prepolymer and the polyol blend. The isocyanate prepolymer is the reaction product of pure MDI (methylene diphenyl isocyanate) with a linear polyester polyol.

Outer skin

Polyether PU soles

Figure 2.5  Photographs of polyether shoe soles.

Foam core

Cross section of a polyether PU sole

Polyurethanes, Polyesters and Epoxies  31 Elastomers with excellent properties are obtained when the polyester is the condensate of ethylene glycol [HO-(CH2)2-OH] and 1,4 butane diol [HO-(CH2)4-OH] with a small amount of adipic acid [HOOC-(CH2)4-COOH]. The condensate should have a molecular weight of 2000 (OH value 56 mg KOH/g), an acid value below 1% and a viscosity of 2000 cPs at 50°C. One disadvantage of using a completely linear diol (functionality = 2) is that the demold time of the final product will be extremely long. To improve the processability of the final formulation, it is preferable to increase the functionality of the diol to 2.01–2.1 by adding a small quantity of a triol during the esterification step. Whereas polyether formulations include polyols of different functionalities and molecular weights in the polyol blend, polyester formulations, on the other hand, are generally based on the same polyester polyol. Usually a small quantity of a diethylene glycol adipate is added to the formulation in order to reduce the rate of solidification of the blend. The preferred chain extender in polyester formulations is butane diol.

2.2.3.2 Integral Skin Typical applications of PU integral skin foams are car steering wheels, head rests, arm rests, bike seats, etc., photographs of which are shown in Figure 2.7. Polyether shoe sole systems as the ones explained above can be regarded as high density integral skin foams because the inner foam core is surrounded by a dense, homogeneous, skin, formed from the collapse of the

Sport shoe sole

Dual density sport shoe sole

Soles of safety boots

Figure 2.6  Photographs of shoes with expanded polyester polyurethane soles. The twolayer sole in the center has a non-expanded bottom layer.

32  Biobased Polyols for Industrial Polymers

Steering wheels

Headrest

Armrests

Figure 2.7  Photographs of PU integral skin applications.

Figure 2.8  Cross section of an integral skin PU foam headrest [5].

cells in contact with the mold. The cellular structure is shown under a magnifying lens in Figure 2.8.

2.2.4 Thermoplastic Polyurethane (TPU) Elastomers Thermoplastic polyurethane elastomers [6] result from the reaction of a macrodiol with a diisocyanate, most often MDI, and a short-chain diol, usually butanediol. One -NCO equivalent adds to one –OH equivalent. When equivalent amounts of NCO groups and OH groups are present in the mixture, the isocyanate index is 100. The reaction is represented in Figure 2.9. HO -------------- OH + 2 OCN-φ-CH2-φ-NCO + HO[CH2]4OH High molecular Diisocyanate butanediol weight diol (MDI)

Figure 2.9  Chemical components of thermoplastic polyurethanes.

Polyurethanes, Polyesters and Epoxies  33 The resulting chains consist of short, hard segments made of carbamate (urethane) bonds linking the low molecular weight diol with the isocyanate, as well as long flexible (soft) segments made of urethane bonds linking the isocyanate with the high molecular weight diol (macroglycol), as shown in Figure 2.10. The MDI/Butane diol segments aggregate through the effect of hydrogen bonds and precipitate in the amorphous matrix formed by the MDI and the high molecular weight diol chains. The matrix structure is represented diagramatically in Figure 2.11.

2.2.4.1 Isocyanates The workhorse in the synthesis of TPUs is 4,4’-diphenylmethane diisocyanate. Other aromatic isocyanates which may be used in TPU applications are shown in Figure 2.12. Aliphatic diisocyanates are used in applications where extreme resistance to UV radiation is required. Their chemical structure is shown in Figure 2.13. < ------------Soft segment-----------> ---OOCNH-φ-CH2-φ-NHCO O[CH2]4OOCHN-φ-CH2-φ-NHCO----------OOCHN-φ-CH2-φNHCOO--

Figure 2.10  Chain structure of a TPU.

Hydrogen bond

Soft segment

Hard segment

Figure 2.11  TPU matrix sketch showing the formation of crystallites of hard segments.

OCN

NCO

CH3

NCO OCN

CH3 NCO

OCN

NCO

NCO

CH3

NCO p-PDI (para-phenylene diisocyanate

CH3

TDI

3,3’ -Dimethyl-4,4’biphenyl diisocyanate (TODI)

Figure 2.12  Aromatic isocyanates used in the synthesis of TPU.

NCO 1,5 naphthalene diisocyanate (NDI)

34  Biobased Polyols for Industrial Polymers NCO OCN

CH2 H12-MDI

NCO

H3C H3C

NCO CH2 NCO CH3

IPDI, isophorone diisocyanate

OCN-(CH2)6-NCO OCN Hexamethylene diisocyanate

Cyclohexane 1,4 diisocyanate

Figure 2.13  Aliphatic isocyanates used in the synthesis of TPU.

2.2.4.2 Polyols/Diols (Chain Extenders) TPUs are made from long-chain diols (macroglycols) with an an average molecular weight of 600 to 4000. The usual molecular weight is 2000. The most common diols are the polyester diols, the diols resulting from caprolactone and the polyether diols. Other diols, such as polycarbonate diols, are also used in particular applications. Depending on the nature of the macrodiol, TPUs are defined as polyester TPUs and polyether TPUs, each of which has specific properties. Polyester TPUs have a good resistance to abrasion whereas their polyether counterparts have an excellent resistance to hydrolysis. Other properties characteristic of TPUs are puncture resistance as well as resistance to low temperatures. Some applications where advantage is taken of these properties are shown in Figure 2.14.

2.2.5 Casting Systems The reactive components of PU casting systems include a high molecular weight polyol, either a polyester or a polyether, a crosslinker or chain extender, such as butane diol, and an isocyanate. A catalyst as well as fillers are usually added to the system. Casting systems fall into two categories: • One-shot systems, whereby all ingredients are mixed and then cast in a mold. • Prepolymer systems, where the isocyanate component consists of an NCO-terminated prepolymer produced from the reaction of the isocyanate with a high molecular weight polyester of polyether. The free isocyanate in the prepolymer is of the order of 3–10%. A final cast product is obtained when the prepolymer is reacted with an equivalent amount of a crosslinker.

Polyurethanes, Polyesters and Epoxies  35 The polyester diols most frequently used in TPU manufacture are: Polybutanediol adipate H-{O-CH2-(CH2)2-CH2-O-CO-CH2-(CH2)2-CH2-CO-}nO-CH2-(CH2)2-CH2-OH Polycaprolactones are made from ε-caprolactone and a bifunctional initiator such as hexane diol. There are two classes of polyethers of technical importance. The poly(oxypropylene) glycols and the poly(oxytetramethylene)glycols (PTMEG) PTMEGs are linear chain polyols with reactive primary hydroxyls and functionality of 2.0. PTMEGs have molecular weights of the order of 650, 1000 and 2000. Finally, the most important chain extenders for TPU are glycols such as - Ethylene glycol [HO-CH2-CH2-OH], - 1,4 butane diol [HO-CH2-(CH2)2-CH2-OH], - 1,6 hexane diol [HO-CH2(CH2)4-CH2-OH], - Hydroquinone bis(2-hydroxyethyl)ether, [HO-CH2-CH2-O-C6H4-O-CH2-CH2-OH] 1,4 butane diol is the most used chain extender.

Cable jacketing

Ski boots

Gear stick handles

Film

Cattle tags

Hose lining

Figure 2.14  Photographs of TPU applications.

Casting systems are further subdivided into: • Hot cure systems. In such systems the components are heated before being mixed. • Cold cure systems, where the components are mixed at room temperature.

36  Biobased Polyols for Industrial Polymers

2.2.5.1 Isocyanates Most prepolymers are based on MDI or TDI. The oldest high property, hot cure casting system is based on 1,5-napthalene diisocyanate (NDI). Isocyanates, such as 1,6-diisocyanatohexane (HDI), isophorone diisocyanate (IPDI) and TODI, are used in very specialized applications.

2.2.5.2 Polyols Polyesters and polyethers are used in hot cure systems. The polyesters are linear, 1000 to 3000 molecular weight adipates or polycaprolactones. On the other hand, poly tetrahydrofurans are used whenever a good resistance to hydrolysis is required. Poly(oxypropylene glycol) and poly(oxyethylene-oxypropylene glycol) polyethers with molecular weights between 600 and 5000 are used in cold cure systems. Natural products such as castor oil are also used in cold cure systems.

2.2.5.3 Crosslinkers They preferably include short-chain glycols such as butanediol, though diamines can also be used.

2.2.5.4 Examples • Hot cure system A prepolymer is prepared from 1740 g NDI and 5800 g polyethylene adipate (OH no. 56 mg KOH/g). The prepolymer is heated to 125°C and 405 g butanediol is added with rapid stirring. The homogeneous mixture is then cast in a rotating centrifugal drum, coated with release agent and heated to 110°C. A film is formed which can be demolded in 50 minutes. • Cold cure system A typical prepolymer would consist of 73 pbw of polyoxypropylene glycol (OH no. 56 mg KOH/g) reacted with 27 pbw TDI. The polymerization is carried out at 60°C. This yields a prepolymer with 10% free NCO. The polyol system consists of the chemical components shown in Table 2.3. Applications of cold cure systems are shown in Figure 2.15.

Polyurethanes, Polyesters and Epoxies  37 Table 2.3  Typical formulation of a polyol cold cure system. Component

Parts by weight (pbw)

Polyether diol (molecular weight 4000)

60

Butane diol

4

Fillers and pigments

35

Catalyst

1

Cast gear

Roller

Timing belt

Figure 2.15  Applications of PU cold cure cast systems.

2.2.6 Coatings 2.2.6.1 Urethane Oils/Uralkyds Urethane oils/uralkyds are also defined as isocyanate modified drying oils. They consist of solutions of polyurethanes whereby the polyol component contains unsaturation sites. The oil solidifies when the unsaturation sites react as a result of a freeradical polymerization process initiated by catalysts such as cobalt naphthenate. The polyol component may consist of a polyester polyol resulting from the condensation of oleic acid with pentaerythritol. Other polyols result from the transesterification of soybean or linseed oils with glycerine and a 1100 molecular weight polyether triol. The resulting polyester polyol is reacted with TDI to give a urethane oil containing unsaturation sites, as shown in Figure 2.16. This uralkyd is dissolved in a solvent, usually xylene, and cured with a free-radical polymerization catalyst.

38  Biobased Polyols for Industrial Polymers

Oleate segment

Pentaerythritol Urethane segment

Figure 2.16  Structure of a uralkyd.

A castor oil-based uralkyd may consist of a prepolymer produced by reacting TDI and castor oil under nitrogen at 50–60°C. The prepolymer is dissolved in xylene. A simple formulation is shown in Table 2.4.

2.2.6.2 Moisture Curable Coatings Moisture curable coatings consist of solutions of NCO-terminated polyurethanes. Curing results from the reaction between the isocyanate groups and atmospheric moisture. The polyurethane prepolymer may be an ether or an ester. A typical formulation is shown in Table 2.5. The major structural factor which influences the film properties is the crosslink density. High crosslink levels increase chemical resistance but reduce flexibility. Table 2.4  Typical formulation of a polyol cold cure system. Chemical component

Parts by weight (pbw)

TDI

570

Castor oil

Castor oil

Xylene

Xylene

Polyurethanes, Polyesters and Epoxies  39 Table 2.5  Formulation of a polyether-based moisture curable coating. Prepolymer component

Concentration

Polypropylene glycol (1000 molecular weight)

1 mole

1,3 Butane diol

1 mole

Trimethylol propane

2 moles

Toluene diisocyanate (80/20)

8 moles

Antioxidant

0.25%

Flow control agent

21%

Xylene (solvent)

21%

2.2.6.3 Blocked Isocyanates Blocked isocyanates consist of isocyanate-terminated prepolymers. The free NCO group is reacted with a blocking agent such as phenols, oximes or lactams. Upon heating, the blocking agent is released and the freed isocyanate group reacts with a polyol which is present in the reaction mixture. The set of reactions is shown in Figure 2.17.

2.2.6.4 Two-Component Coatings In two-component PU coatings a solution of a polyol in a non-reactive solvent is mixed with an equivalent amount of a solution of a prepolymer in the same solvent. The polyol component may be a 40% xylene or toluene or MEK, etc., solution of a linear or branched polyether with a molecular weight in the range of 1000 to 2000. Polyester polyols, including vegetable oil modified ones, with molecular weights in the range of 500 to 5000 can also be used. The isocyanate component is again a 40% solution of an NCOterminated prepolymer. The isocyanates which may be used are TDI, MDI, Isophorone diisocyanate, HDI, etc. Examples of applications of polyurethane-based coatings are shown in Figure 2.18. R-NH-CO-OAr + Heat (150ºC) → RNCO + ArOH RNCO + HO-R’-OH → R-NH-CO-O-R’-O-CO-NH-R

Figure 2.17  Polyurethane formation from a blocked isocyanate.

40  Biobased Polyols for Industrial Polymers

Coatings based on Coatings based on trimerized HDI trimerized HDI/Polyols are used on high-speed trains

Blocked isocyanates are applied as baking finishes for coils and wires

Figure 2.18  Applications of polyurethane-based coatings [7].

2.3 Polyesters [8] 2.3.1 Unsaturated Polyesters [9] 2.3.1.1 Alkyds [10, 11] Among the oldest polymers produced from triglyceride oils are alkyd resins resulting from the esterification of polyhydroxy alcohols with polybasic acids and fatty acids. As early as 1914, fatty acids have been used in the preparation of polyester resins. The resulting alkyd resins exhibited good film properties. The general synthetic method involves the alcoholysis of the oil by a polyol. Then, the free hydroxyls of the alcoholysis product are esterified by a polycarboxylic acid or its anhydride, as shown in Figure 2.19. Conventional alkyd resins are prepared from the condensation of a short-chain diol, such as propylene glycol, with a dicarboxylic acid like terephthalic acid or an anhydride such as phthalic anhydride. Unsaturation

CH2-OH CH-O-CO-R + CH2-OH

O O

O O C

O C O CH2 CH CH2 O

O

O C =O R

Monoglyceride (R contains unsaturation sites)

Phthalic anhydride

Figure 2.19  Synthesis of a monoglyceride-based alkyd resin.

Alkyd

n

Polyurethanes, Polyesters and Epoxies  41 is introduced in the chain through maleic anhydride. The reaction scheme is shown in Figure 2.20. Such alkyds are produced either by reacting all the components simultaneously or by first producing a hydroxyl-terminated polyester prepolymer from propylene glycol and terephthalic acid. In a second stage, the prepolymer is reacted with maleic anhydride. During this reaction, most of the maleate structure is converted into the trans-fumarate structure. All the reaction steps are represented in Figure 2.21. The alkyds are dissolved in a monomer. The most common monomer is styrene (Ph-CH=CH2). The crosslinking mechanism is a free-radical copolymerization between styrene and the unsaturation sites of the polyester chain. It is initiated by a free-radical initiator. The resulting structure is shown in Figure 2.22. The above-described alkyds are related to the subject of this book, because low molecular weight diols, such as propylene glycol, can be obtained from renewable sources. The relevant chemistry is dealt with in another chapter. Figure 2.23 shows examples of the applications of unsaturated polyester resins. O

O

H

O

+

O Phthalic anhydride (1 mole)

O

H

+

200°C HO-CH(CH3)-CH2-OH

O Maleic anhydride (1 mole)

Propylene glycol (2.2 moles)

Alkyd (Unsaturated polyester)

Figure 2.20  Synthesis of an alkyd. O HO

OH O

Pressure CH3 → O O-CH2-CH-OH Heat (–H2O) HO-CH-CH -O O 2 n CH3 Prepolymer

+ HO-CH-(CH3)-CH2OH

Propylene glycol (2.2 moles)

Terephthalic acid (1 mole)

O HO-CH-CH2-O CH3

CH3 O-CH2-CH-OH O

Prepolymer

n

+

H H

O O

O Maleic anhydride (1 mole)

200°C → (–H2O)

Figure 2.21  Two-stage synthetic route of an alkyd resin.

Alkyd (Unsaturated polyester)

42  Biobased Polyols for Industrial Polymers T=Teraphthalate P=-CH2-CH(CH3)HO-[PTP]a-OOC

COO-[PTP]b-OOC CH=CH CH=CH x

COO-[PTP]c-OOC

COO-[PTP]d-O-H CH=CH y

Styrene CH2=CH-C6H5

a, b, c, d ~ 1 to 3 x, y ~ 1 to 3

COO-[PTP]d-O-H COO-[PTP]b-OOC CH−CH CH−CH CH−CH COO-[PTP]c-OOC HO-[PTP]a-OOC CH2-CH-C6C5 CH2-CH-C6C5 C C -CH-CH C6C5-CH-CH2 6 5 2 C6C5-CH-CH2 COO-[PTP]c-OOC HO-[PTP]a-OOC CH−CH CH−CH CH−CH COO-[PTP]b-OOC COO-[PTP]d-O-H

Figure 2.22  Chain network in a cured, commercial unsaturated polyester.

Glass reinforced polyester (GRP) tank

Boat hull in GRP

GRP sinks

Figure 2.23  Applications of unsaturated polyester resins.

2.3.1.2 Drying Oils [12] A drying oil is defined as an oil which hardens to a tough, solid film with absorption of oxygen either from the environment (autoxidation) or with the addition of oxygen through chemical reactions, i.e., with peracids. The term “drying” does not refer to the evaporation of water or other solvents, but to a series of chemical reactions wherein the fatty acid side chains of the triglyceride are polymerized and crosslinked. Drying oils are a key component of oil paint and many varnishes, as shown in Figure 2.24. Some commonly used drying oils include linseed oil and tung oil. The “drying,” hardening, or curing of linseed oil is the result of an exothermic reaction as the oil polymerizes to form long, chain-like molecules. The oil polymers crosslink to form a network which results in a solid film. Over time, ionic bonds also form between

Polyurethanes, Polyesters and Epoxies  43

Drying oils for paints

Pigments suspended in drying oil

Figure 2.24  Applications of drying oils.

functional groups and metal ions of the pigment (for example, in paints). The excellent drying property of linseed oil arises from the ability to form crosslinks by modifications of the non-conjugated double bonds in the fatty acid chain. Crosslinking occurs by several methods, primarily when the activated methylene groups in the unsaturated fatty acids or oils of the alkyd are oxidized to give hydroperoxides, which subsequently decompose to generate free radicals, leading to oxidative crosslinking, as shown in Figure 2.25. This oxidative crosslinking process is commonly accelerated by adding driers such as various salts of cobalt, zirconium, calcium, and manganese. Carbon to carbon crosslinking can also occur. Crosslinking may be induced using chemicals, i.e., peroxides, sulfur vulcanization, driers or by epoxidation or by physical means, i.e., light, heat, air, atmospheric oxygen, UV radiation. High alpha linolenic acid flax (linseed) oil contains a high concentration of unsaturated fatty acid and thus yields more material available for crosslinking and/or polymerization per unit weight. As a result, materials based on a crosslinked linseed oil result in a tougher, stronger final product. Alkyd resins can also be classified in terms of their oil length, that is, the amount of oil they contain. This is shown in Table 2.6.

2.3.2 Thermoplastic Polyesters [13] The most important members of this class of thermoplastics are: • Polybutylene terephthalate (PBT) • Polyethylene terephthalate (PET)

44  Biobased Polyols for Industrial Polymers COOH O2 Equimolar a, b, c & d

a–

b–

c–

d–

13

COOH

OO• 12

COOH

OO• 10

COOH

OO• 9

COOH OO•

Crosslinking 2

COOH OO•

O O

COOH COOH

+ O2

Figure 2.25  Oxidative crosslinking of fatty acids.

Table 2.6  Classification of alkyd resins. Terminology

Oil content

Short oil

less than 50% oil content

Medium oil

50%–70% oil content

Long oil

more than 70% oil content

Butane diol as well as ethylene glycol can be manufactured from non-petrochemical sources [14–16]. One method of manufacturing PET is shown in Figure 2.26. Its applications are shown in Figure 2.27.

Polyurethanes, Polyesters and Epoxies  45 O HO

OH O

Terephthalic acid

+

HO-CH2-CH2OH

220– O 260°C → (–H2O) HO-CH2-CH2-O

Ethylene glycol

O-CH2-CH2-OH O

Polyethylene terephthalate

n

Figure 2.26  Synthetic route to polyethylene terephthalate.

PET fibers

PET bottles

PET film

Figure 2.27  Main polyethylene terephthalate applications.

To the above-mentioned list of commercial terephthalates can be added PBAT (polybutylene adipate terephthalate), which is a biodegradable random copolyester of adipic acid, 1,4-butanediol and terephthalic acid (from dimethyl terephthalate). When composted, PBAT is fully biodegradable due to the presence of butylene adipate groups. It is mainly used in packaging applications.

2.3.3 Polyester Polyols [17] Adipic acid is most commonly employed as the acidic component of polyester polyol intermediates used in the polyurethane industry. In the esterification process, typical polyol components, such as ethylene glycol, propane diol [18] and butane diol, are also produced from renewable sources. Adipic acid is produced, industrially, from the oxidation of benzene, as shown in Figure 2.28. Adipic acid can also be produced from renewable sources [19]. Among the intermediates in the process is hexane diol (Figure 2.29). However, the conversion of glucose to the intermediates shown below is far from quantitative. Dimeric acids, which are produced by the dimerization of unsaturated fatty acids, are used in the manufacture of polyester polyols from entirely renewable sources.

46  Biobased Polyols for Industrial Polymers Hydrogenation Cyclohexane

Benzene

Oxidation

HOOC-(CH2)4-COOH Adipic acid

Figure 2.28  Adipic acid manufactured from petrochemical sources.

5-Hydroxymethyl furfural

Biomass

Glucose Acid hydrolysis

HO-CH2

O

Raney Ni

H2

Copper chromite

1,6 hexane diol

HO-CH2

O

CH2-OH

CHO

H2

Hydrogenation

1,6 adipic acid

Gluconobacter oxydans

Figure 2.29  Synthesis of adipic acid from renewable sources.

2.4 Epoxies [20] Most commercial epoxy resins are prepared by condensing epichlorohydrin with chemicals possessing at least two reactive hydrogen atoms. Those chemicals include bisphenol A, as shown in Figure 2.30.

O

+ CI

Epichlorohydrin

NaOH

CH3 OH

HO CH3

Bisphenol A

→

CH3

O CH3

Repeat unit

Figure 2.30  Polymerization of epichlorohydrin and bisphenol A.

OH O-CH2-CH-CH2 n

+ NaCl + H2O

Polyurethanes, Polyesters and Epoxies  47 The largest quantity of the epoxy resins used worldwide is derived from the diglycidyl ether of bisphenol A, shown in Figure 2.31, which is the glycidyl-terminated repeat unit of Figure 2.32. Crosslinking results from the reaction of the epoxy groups with a diamine (Figure 2.34). The totally crosslinked structure of an epoxy resin is shown in Figure 2.33. The double bonds of the unsaturated fatty acid moieties of triglycerides can be epoxidized. The different methods of epoxidizing double bonds are exposed separately in another chapter. Ring-opening polymerization of epoxidized triglycerides [21] is initiated by triethylenetetramine, p-phenylenediamine, phenylbiguanidine, etc. The resulting semi-fluid epoxy resins are used as surface coatings. Examples of epoxy applications are shown in Figure 2.34.

O

CH3

OH

O

O

CH3

O-CH2-CH-CH2 -O CH3

O CH3

n

Figure 2.31  Major constituent of epoxy resins based on diglycidyl ether of bisphenol A (n = 2 – 12).

O CH CH2

O H2 C H

N

CH

H

R H CH O

CH2

N

H H2C CH O OH

OH CH CH2

N

CH2 CH

R CH CH2

N

CH2 CH

OH

Figure 2.32  Crosslinking of epoxy resins initiated by an amine catalyst.

OH

48  Biobased Polyols for Industrial Polymers OH

OH CH CH2

N

CH2 CH

R OH CH CH2

N

OH CH2 CH

CH CH2 OH

N

CH2 CH OH

OH CH CH2

R CH CH2 OH

N

N

OH CH2 CH

R CH2 CH OH

OH CH CH2

N

OH CH2 CH

CH CH2 OH

N

CH2 CH OH

R OH CH CH2

CH CH2 OH

N

CH2

OH CH

CH CH2 OH

N

CH2 CH OH

OH CH CH2

N

R

R

N

N

CH2 CH

CH CH2 OH

OH

OH CH2 CH

CH2 CH OH

Figure 2.33  Structure of a crosslinked epoxy.

Epoxy flooring

Two-component epoxy glue

Epoxy potting

Figure 2.34  Examples of applications of epoxy resins.

References 1. Oertel, G. (Ed.), Polyurethane Handbook. Hanser publishers, Germany, 1985. 2. Woods, G. (Ed.), 2nd edition, John Wiley and Sons, USA, 1990. 3. Saunders, J.H. and Frisch, K.C. (Eds.), Polyurethanes Chemistry and Technology II. Technology Part II (High Polymers Vol. XVI). Interscience publishers, USA, 1964. 4. Kyriacos, D. (Ed.), Formulate your own polyether PU shoe sole systems. http:// www.gem-chem.net/soleform.html, GEM-Chem, Belgium, 2019. 5. Covestro, A.G. https://solutions.covestro.com/en/materials/foams, Covestro AG website, 2019.

Polyurethanes, Polyesters and Epoxies  49 6. Kyriacos, D., Thermoplastic Polyurethanes. From Chemistry to Marketing. http://www.gem-chem.net/bookputpu.html, GEM-Chem, 2019. 7. Tosoh Inc., Nippon Polyurethane Industry. https://www.tosoh.com. Tosoh website, 2019. 8. Scheirs, J. and Long, T.E., Modern Polyesters: Chemistry and Technology of Polyesters and Copolyesters. J. Wiley & Sons publishers, ISBN: 9780471498568, USA, 2000. 9. Unsaturated Polyester Resins: Fundamentals, Design, Fabrication, and Applications. 1st edition, Elsevier Science Publishing Co. Inc, ISBN: 9780128161296, UK, 2019. 10. Panda, H., Alkyd Resins Technology Handbook. Asia Pacific Business Press, ISBN: 9788178331348, India, 2010. 11. Hlaing, N.N. and Oo, M.M., Manufacture of alkyd resin from castor oil, in: World Academy of Science, Engineering and Technology, vol. 48, 2008, http://citeseerx.ist.psu.edu/viewdoc/download?doi = 10.1.1.193.5314&rep = rep1&type = pdf. 12. Lukey, C.A., Thermoset coatings. Encyclopedia of Materials: Science and Technology, 2nd Ed. 9209–9215, 2001. https://doi.org/10.1016/ B0-08-043152-6/01659-4. 13. Fakirov, S. (Ed.), Handbook of Thermoplastic Polyesters: Homopolymers, Copolymers, Blends, and Composites, Wiley-VCH Verlag GmbH & Co. KGaA, ISBN: 9783527301133, Wiley-VCH; 1st edition (July 9, 2002), 2002. 14. Haldor-Topsoe catalysis. https://www.topsoe.com/, Haldor Topsoe website, 2019. 15. Braskem. https://www.braskem.com.br/news-detail/braskem-signs-partnershipwith-haldor-topsoe-to-develop-biobased-meg, Braskem website, 2017. 16. https://www.novamont.com/eng/read-press-release/mater-biotech/, Novamont Press Release Thursday 29th September 2016. 17. Songwon. https://www.songwon.com, Songwon website, 2019. 18. https://www.engineering-airliquide.com/bio-propylene-glycol. 19. M. Faber, Process for producing adipic acid from biomass. United States Patent US4400468, assigned to Hydrocarbon Research Inc, August 1983. 20. Ellis, B. (Ed.), Chemistry and Technology of Epoxy Resins, Springer, Netherlands, 1993 21. T.W. Findlay, Prepolymers from a polyamino compound and an epoxidized fatty acid ester. United States Patent US3291764 assigned to Swift & Co, December 1966.

3 Vegetable Oils and Fats 3.1 Introduction Vegetable oils are oils obtained from plants that are fatty, dense and non-volatile, such as olive and soybean. This is in contrast to essential oils, which are volatile in nature. Some of the most common oils are soybean oil, castor oil, palm oil, etc. Vegetable oils are derived mainly from seeds. Essential oils are derived from flowers, fruits and leaves. The major oilseeds are soybeans, rapeseed, cottonseed, sunflower seed, palm, canola, linseed and maize. A general scheme on the extraction of triglycerides from seeds is shown in Figure 3.1 [1, 2]. Vegetable oils can be oxidized. Oxidized oils are also known as blown oils. They of triglyceride molecules joined together with oxygen linkages to form oxidized polymers. They are manufactured under thermally controlled conditions in the presence of air to give products with increased viscosities, specific gravities and reactivities [3]. Oleochemical oils, chemically designated as triglycerides, are produced from the fats and oils, for example, of beef tallow, palm oil, lard, castor oil, peanut oil, rapeseed oil, cottonseed oil, soybean oil, sunflower oil, and linseed oil. As mentioned earlier, fats are solid triglycerides whereas oils are liquids. Animal fats include fish oils, which can also be liquid, depending on the structure of the constituent fatty acids.

Deny Kyriacos. Biobased Polyols for Industrial Polymers, (51–132) © 2020 Scrivener Publishing LLC

51

52  Biobased Polyols for Industrial Polymers Seeds Press Oil

Meal + Oil Solvent extraction of oil

Degumming (Phospholipids removal) Consists of agitating the oil with 2 to 3% water, at 50°C and removing the hydrated phospholipids by means of setting or centrifugation. Degumming is also performed with phosphoric acid Neutralisation Caustic soda is used to remove free fatty acids. The process also produces a reduction in phospholipid and colouring matter content Bleaching Heating the oil to 85°C and treating it with adsorbents (Fuller’s earth, acid activated montmorillonite clays or activated carbon) permits an almost complete elimination of all colouring materials. Dewaxing Solid matter responsible for haze is removed by cooling and filtration Deodorisation Steam or nitrogen stream distillation under reduced pressure is used to remove volatile compounds with undesirable flavours, most of which originate from oxidation of the oil

Figure 3.1  Processes for extracting triglycerides from seeds.

3.2 Sources, Components and Extraction of Vegetable Oils 3.2.1 Soybean Oil 3.2.1.1 Source The soybean or soya bean, photographs of which are shown in Figure 3.2, is a species of legume native to East Asia. As shown in Figure 3.3, the beans are harvested mechanically.

Vegetable Oils and Fats  53

Soya bean plant fields The plant is annual. It may grow from 20 cm up to 2 meters in height.

Soya stems, pods seeds, fresh and mature, ready for harvest

Soya bean seeds

Figure 3.2  Photographs of soya bean plants, stems, pods and seeds [4].

Figure 3.3  Soya bean harvester [5].

Figure 3.4 shows that the major soya bean producing countries are located mainly in Asia and the Americas. On the other hand, the major soybean oil producers are represented by the histograms in Figure 3.5. With each ton of crude soybean oil, approximately 4.5 tons of soybean oil meal with a protein content of about 44% are produced [10]. The major soybean oil manufacturers are: • Cargill Inc. • Archer Daniels Midland Co. • Bunge Limited

54  Biobased Polyols for Industrial Polymers

100 10 1

Figure 3.4  Soya bean producers [6, 7]. 16000 14000 12000 Ktpa

10000 8000 6000 4000 2000

pt Eg y

Ru ss ia Pa ra gu ay

ico

a

M ex

In di

Eu ro pe

Br az il

U SA Ar ge nt in a

Ch

in a

0

Figure 3.5  Major soybean oil producers (2018 estimates) [8, 9].

• DuPont • Wilmar International • Unilever

3.2.1.2 Components of Soya Bean The bean or seed structure consists of the seed coat (hull or testa) and two cotyledons, plus two additional structures of lesser weight: the hypocotyl and plumule. See Figure 3.6 for more details. The hull or seed coat or testa, accounts for roughly 8% of the seed weight. It holds the two cotyledons together and provides an effective protective layer.

Vegetable Oils and Fats  55 Follage leaves

Plumule

Cotyledon

Hypocotyl Cotyledons Cotyledon

Root

Axis

Testa The Plumule represents the “bud” or shoot tip of the embryo. The Epicotyl includes the Plumule and any other stem tissue above the Hypocotyl.

Testa

During germination the root is the Cross section of a bean seed. first organ to emerge. The Hypocotyl elongates and drags the swollen Cotyledons above the ground.

Figure 3.6  Soya bean seed structure [11].

The major constituents of hulls on a dry weight basis are shown in Table 3.1 [12]. The cotyledon represents 90% of the seed weight and contains practically all the oil and protein in cells. Microscopic examination of these cells reveals the presence of protein bodies and lipid bodies which constitute storage bodies for proteins and oil, respectively. A visual representation is found in Figure 3.7 [13]. Protein bodies measure, on average, 10 microns, while the lipid bodies are, typically, 0.2 to 0.5 microns in diameter. The soya bean main components, including the hull, are shown in Table 3.2. • Soybean Proteins Soybean proteins consist of sequences of essential and non-essential amino acids, as shown in Tables 3.3 and 3.4, respectively. Nonessential amino acids are those which are produced by humans. Essential ones cannot be produced by the human organism [14]. Isoflavones are the major flavonoids found in legumes, particularly soybeans. Isoflavones are compounds with estrogenic activity. In other words, they contribute to the development of plants. The two primary isoflavones in soybeans are daidzein and genistein and their respective glucosides, genistin and daidzin. Their chemical structures are shown in Figures 3.8 and 3.9 respectively. On a dry weight basis, raw soybeans contain between two and four milligrams of isoflavones/ gram [15].

56  Biobased Polyols for Industrial Polymers Table 3.1  Composition of soya bean hulls. Component

Content (g/100 g of hull)

Cellulose 

14–25

Structure OH

OH

HO

O

O

O

O

OH

HO

OH

Cellulose contains only anhydrous glucose Hemicellulose 

14–20

Pectin

10–12

Besides glucose, sugar monomers in hemicellulose can include xylose, mannose, galactose, rhamnose, and arabinose. Xylose is always the sugar monomer present in the largest amount, but mannuronic acid and galacturonic acid also tend to be present. OH O O

O

OH

OH O OH

OH

O

O O

O O OH O

OH

OH O OH

OH O O

O O O

Protein

9–12

Uronic acid

7–11

O

OH O

Details further down in the text O H HO H

OH H OH

H

OH

O

OH

Glucuronic acid Ash (metals)

4–5 (Continued)

Vegetable Oils and Fats  57 Table 3.1  Composition of soya bean hulls. (Continued) Component

Content (g/100 g of hull)

Lignin

3–4

Structure H2COH CH2

H2COH

H2COH

CH2

OCH3

CH3

HOC

OH

H2COH

OCH3

HC

O HC

O

HC OCH3 HC

O

HC HOCH2 HOCH HC

O

O

CH

O CH3O

HOC

CH

CH

CH3O

HOCH2

CH2OH HC

CH2

HCOH

CHO CH CH

H2COH HC

CH

O CH3O

CH3O

CH O

OCH3 O

HOCH

OH HC

O

O

HOCH2

HC

O

CH

HO

H2COH

HCOH

H2CO

HC

O

HCOH

CHO

H2COH CO

HC

HC H2COH

CH3O

OCH3 O

OCH3 O

CH

H2COH

CH

O

HOCH2 CH3O CO

HC

H2COH O

HOCH

CH

H2COH

CH

H2COH O

CH

HCO

CH2O

O

OH

CH3O

CH

CH3O

H2C

CH

HO

(Carbohydrate) OCH3 H2COH CH3O

C 2H CH

CHH2C OCH3

CH

O

HC

CH3O

CH

CH3O

CH

CH3O

HCOH CH CH2OH O HC

O CH3O

H2COH

CH2

CH2

OH

HC

CH2 HC

O

OCH3 O

OCH3

HCOH

CH3O O

OCH3 OH

Lipid bodies

Protein bodies

Protein bodies

Lipid bodies

Cell wall

5µ

Cell wall

Figure 3.7  Transmission electron microscopy of soybean cotyledon cells.

• Soybean Lipids Soybean lipids fall into two major categories. One category comprises the saponifiable or hydrolyzable lipids such as the triglycerides and the phospholipids. The unsaponifiable lipids consist of phytosterols. Lipids are stabilized against oxidation by the presence of tocopherols.

58  Biobased Polyols for Industrial Polymers Table 3.2  Constituents of soya beans. Component

%

Comments

Proteins

38

All eight essential amino acids are found in soya bean protein. Soya bean meal is generally classified into high protein soya bean meal (49% protein) and low protein soya bean meal (44% protein). Soy proteins contain isoflavones.

Lipids

18

The lipids of soybeans consist typically of 96% triglycerides, 2% phospholipids, 1.6% unsaponifiables, 0.5% free fatty acids and minute amounts of carotenoid pigments. The unsaponifiables contain mainly tocopherols and phytosterols.

Soluble carbohydrates

11

The principal soluble carbohydrates, saccharides, of mature soya beans are the disaccharide sucrose (2.5–8.2%), the trisaccharide raffinose (0.1–1.0%) composed of one sucrose molecule connected to one molecule of galactose, and the tetrasaccharide stachyose (1.4 to 4.1%) composed of one sucrose connected to two molecules of galactose.

Insoluble carbohydrates (Hull)

11

They consist of the polysaccharides’ cellulose, hemicellulose, and pectin. The soybean pulp hemicellulosic hydrolysates consist of 7 sugar components, in which the major components are galactose (56.1%), arabinose (21.1%), glucose (12.1%), mannose (6.6%) and xylose (3.6%), while the minor components are fructose and rhamnose.

Minerals

5

The mineral content of soybeans is determined to be ash. When soybeans are processed, most of the mineral constituents go with the meal and a few with the oil. The major mineral constituents are potassium, calcium and magnesium. The minor constituents comprise trace elements of nutritional importance, such as iron, zinc, copper, etc.

Moisture

Vegetable Oils and Fats  59 Table 3.3  Essential amino acids present in the protein structure of soybean cells. Essential g/Kg dry amino acid matter Arginine

Structural formula

28.6

O

NH

H N

H2N Histidine

N H

NH2

10.5

O N

H3C

C O

C O H N

OH

C C O H N

C

O H N C C

H N

CH3 O

18.7

N

N C

NH2

R C

H

H

OH

HN Isoleucine

OH

C

C

H

R

N C C

O

Primary protein structure Chain of amino acids

H N

O H H C N C N O C H C N C O C

H

C

O

C H N C O

C

H

C

O O O O H H H H C CN C C N C CN C C N CC CC N CC N CC N H H O O O H O

C N

H

C

H H H O H O O O C C C C C N CN C N CN C N CN C N CN C H O C H O C H O H O C

Secondary structure (β pleated sheet) O (R groups not shown) Chains of amino acids linked Secondary structure (α helix) by hydrogen bonds

NH2 Leucine

30.8 H

OH

H2N

Tertiary protein structure α helices, β pleated sheets and random coils

O Lysine

NH2

26.1 H

OH

H2N Methionine

O

6.1

O S

H3C Phenylalanine

OH NH2

20.2 H H2N

Threonine

O OH O

15.2

OH

H3C Tryptophan

OH

NH2 NH2

4.8

COOH N H Valine

20.1

H H2N

OH O

Quaternary protein structure Several tertiary structures

60  Biobased Polyols for Industrial Polymers Table 3.4  Nonessential amino acids present in the protein structure of soybean cells. Nonessential amino acid

g/Kg dry matter

Alanine

17

Structural formula O H3C

OH NH2

Aspartate

44.8

O O

OH OH

Cystine

NH2

6.5

OH NH2

O

H

S S

H

O

H2N

OH

Glutamate

67.1

O

O

HO

OH NH2

Glycine

16.6

O OH NH2

Proline

20.6

H OH

N H

Serine

16.9

O OH

H

O

H2N OH

Tyrosine

OH

14.8 H OH

H2N O

Vegetable Oils and Fats  61 OH

O

HO

O

OH

HO HO

O

O O

OH

O

OH HO OH

Genistein

Genistin-Glucoside of genistein (Genistein-7-O-glucoside)

Figure 3.8  Structure of genistein and its glucoside. HO

HO

O

O O

O

OH

O

OH O

OH

HO

Daidzein

OH

Daidzin-Glucoside of daidzein (Daidzein-7-O-glucoside)

Figure 3.9  Structure of daidzein and its glucoside.

Triglycerides It has already been mentioned earlier in the text that triglycerides are esters of glycerol which result in fatty acids upon hydrolysis. The reaction scheme is again shown below in Figure 3.10. The fatty acids resulting from the hydrolysis of soybean triglycerides are shown in Table 3.5. Linolenic acid exists in two isomers, namely α and γ. There is no β form. α-Linolenic acid, the structure of which is shown in Figure 3.11, is found in many common vegetable oils. γ-Linolenic acid, Figure 3.12, (sometimes called gamolenic acid) is found primarily in vegetable oils originating from evening primrose, blackcurrant seed, borage and hemp seed. CH2-O-CO-R1 | CH-O-CO-R2 ---Hydrolysis---> | CH2-O-CO-R3 Vegetable oil Triglyceride

CH2-OH | CH-OH | CH2-OH Glycerol

R1-COOH +

R2-COOH R3-COOH Fatty acids

Figure 3.10  Products resulting from the hydrolysis of triglycerides.

62  Biobased Polyols for Industrial Polymers Table 3.5  Fatty acid content of soybean triglycerides [16].

12:0