Fluoroelastomers Handbook: The Definitive User's Guide

Fluoroelastomers Handbook THE DEFINITIVE USER’S GUIDE AND DATABOOK

Albert L. Moore, Sc.D. Wilmington, Delaware

Copyright © 2006 by William Andrew, Inc. No part of this book may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying, recording, or by any information storage and retrieval system, without permission in writing from the Publisher.

Plastics Design Library and its logo are owned by William Andrew, Inc.

Library or Congress Catalog Card Number: 2005023558 Library of Congress Cataloging-in-Publication Data Moore, Albert L. Fluoroelastomers handbook : the definitive user’s guide and databook / Albert L. Moore. p. cm. Includes bibliographical references and index. ISBN 0-8155-1517-0 (acid-free paper) 1. Elastomers—Handbooks, manuals, etc. 2. Fluorocarbons—Handbooks, manuals, etc. I. Title. TA455.E4M66 2005 620.1’94—dc22 2005023558

Printed in the United States of America This book is printed on acid-free paper. 10 9 8 7 6 5 4 3 2 1

Published by: William Andrew Publishing 13 Eaton Avenue Norwich, NY 13815 1-800-932-7045 www.williamandrew.com

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

Contents

Series Editor’s Preface .......................................................................................................

ix

Preface ...............................................................................................................................

xi

Acknowledgments .............................................................................................................. xiii Part I. 1.

2.

Fundamentals .........................................................................................................................

3

1.1

Introduction .................................................................................................................

3

1.2

Scope: Fluorocarbon Elastomers ................................................................................

4

1.3

Nature of Fluoroelastomers .........................................................................................

5

1.4

Fundamental Properties .............................................................................................. 1.4.1 VDF Copolymers ............................................................................................ 1.4.2 TFE/Olefin Copolymers .................................................................................. 1.4.3 Perfluoroelastomers ....................................................................................... 1.4.4 Other Compositions .......................................................................................

6 6 6 6 6

1.5

Developmental History: Compositions, Cure Technology ...........................................

7

1.6

Major Uses of Fluoroelastomers .................................................................................

9

1.7

Producers of Fluoroelastomers ...................................................................................

11

References ..............................................................................................................................

12

Fluoroelastomer Composition and Properties .........................................................................

13

2.1

Major Families of Fluorocarbon Elastomers ................................................................

13

2.2

VDF/HFP/(TFE) Elastomers ........................................................................................

15

2.3

VDF/PMVE/TFE Elastomers .......................................................................................

17

2.4

TFE/PMVE Perfluoroelastomers .................................................................................

17

2.5

TFE/P Elastomers .......................................................................................................

19

2.6

E/TFE/PMVE Elastomers ............................................................................................

20

References ..............................................................................................................................

22

Part II. 3.

Fluoroelastomers Overview

Fluoroelastomers Technology

Fluoroelastomer Monomers ....................................................................................................

25

3.1

Introduction .................................................................................................................

25

3.2

Vinylidene Fluoride (VDF) ........................................................................................... 3.2.1 VDF Properties .............................................................................................. 3.2.2 VDF Synthesis ...............................................................................................

25 25 26

iii

iv

4.

Contents 3.3

Tetrafluoroethylene (TFE) ........................................................................................... 3.3.1 TFE Properties ............................................................................................... 3.3.2 TFE Synthesis ................................................................................................

26 27 27

3.4

Hexafluoropropylene (HFP) ........................................................................................ 3.4.1 HFP Properties .............................................................................................. 3.4.2 HFP Synthesis ...............................................................................................

29 29 29

3.5

Perfluoro(Methyl Vinyl Ether) (PMVE) ......................................................................... 3.5.1 PMVE Properties ........................................................................................... 3.5.2 PMVE Synthesis ............................................................................................

31 31 31

3.6

Olefins: Ethylene and Propylene .................................................................................

32

3.7

Cure-site Monomers .................................................................................................... 3.7.1 Types of Cure-site Monomers ........................................................................ 3.7.2 Halogenated Vinyl Monomers ........................................................................ 3.7.3 Functional Vinyl Ethers ..................................................................................

32 32 32 33

3.8

Safety Aspects of Monomer Handling ......................................................................... 3.8.1 Toxicity Considerations .................................................................................. 3.8.2 Flammability ................................................................................................... 3.8.3 Explosivity ......................................................................................................

33 33 34 34

References ..............................................................................................................................

35

Production of Fluoroelastomers ..............................................................................................

37

4.1

Introduction .................................................................................................................

37

4.2

General Process Description ......................................................................................

37

4.3

Free Radical Copolymerization ................................................................................... 4.3.1 General Reaction Scheme ............................................................................. 4.3.2 Copolymer Composition Relationships .......................................................... 4.3.3 Monomer Reactivity Ratios ............................................................................

38 38 39 40

4.4

Emulsion Polymerization ............................................................................................. 4.4.1 Emulsion Polymerization Kinetics .................................................................. 4.4.2 Continuous Emulsion Polymerization ............................................................ 4.4.3 Semibatch Emulsion Polymerization ..............................................................

41 42 49 53

4.5

Suspension Polymerization ......................................................................................... 4.5.1 Polymer Compositions ................................................................................... 4.5.2 Polymerization Mechanism and Kinetics ....................................................... 4.5.3 Reactor Design and Operation ...................................................................... 4.5.4 Polymerization Control ...................................................................................

59 61 61 63 63

4.6

Process Conditions and Polymer Characteristics ....................................................... 4.6.1 Molecular Weight Distribution ........................................................................ 4.6.2 End Groups .................................................................................................... 4.6.3 Composition and Monomer Sequence Distributions ......................................

65 65 68 68

4.7

Monomer Recovery .....................................................................................................

71

4.8

Isolation .......................................................................................................................

71

5.

Contents

v

4.9

Process Safety ............................................................................................................

73

4.10

Commercial Process Descriptions ..............................................................................

74

References ..............................................................................................................................

75

Cure Systems for Fluoroelastomers .......................................................................................

77

5.1

Introduction .................................................................................................................

77

5.2

VDF/HFP/(TFE) Copolymers: Diamine, Bisphenol, Peroxide ..................................... 5.2.1 Diamine Cure ................................................................................................. 5.2.2 Bisphenol Cure .............................................................................................. 5.2.3 Peroxide Cure ................................................................................................

77 77 78 83

5.3

VDF/PMVE/TFE Elastomers: Peroxide (Bisphenol) ....................................................

89

5.4

Perfluoroelastomers – Various Systems .....................................................................

93

5.5

TFE/Propylene Elastomers: Peroxide, Bisphenol .......................................................

95

5.6

Ethylene/TFE/PMVE Elastomers: Peroxide, Bisphenol ..............................................

99

References .............................................................................................................................. 101 6.

Processing of Fluoroelastomers ............................................................................................. 103 6.1

Introduction ................................................................................................................. 103

6.2

Mixing 6.2.1 6.2.2 6.2.3

6.3

Extrusion ..................................................................................................................... 106

6.4

Molding ........................................................................................................................ 6.4.1 General Considerations ................................................................................. 6.4.2 Compression Molding .................................................................................... 6.4.3 Transfer Molding ............................................................................................ 6.4.4 Injection Molding ............................................................................................

6.5

Calendering ................................................................................................................. 117

6.6

Other Processing Methods .......................................................................................... 119 6.6.1 Latex .............................................................................................................. 119 6.6.2 Thermoplastic Elastomers ............................................................................. 119

.......................................................................................................................... Compounding Ingredients .............................................................................. Mill Mixing ...................................................................................................... Internal Mixers ...............................................................................................

103 103 103 105 110 110 111 112 113

References .............................................................................................................................. 122

Part III. Environmental Resistance and Applications of Fluoroelastomers 7.

Fluid Resistance of VDF-containing Fluoroelastomers ........................................................... 125 7.1

Introduction ................................................................................................................. 125

7.2

Fluid Resistance Data ................................................................................................. 125

7.3

Discussion of Results .................................................................................................. 125

7.4

Fluid Service Recommendations ................................................................................ 126 Table 7.1 Chemical Resistance - FKM, VDF/CTFE, FKM/TFE Fluoroelastomers ..................................................................................... 127 Acetaldehyde to Butyl Cellosolve ............................................................. 127

vi

Contents

Table 7.2

Butyl Ether to Ethylene Trichloride ........................................................... Ethylenediamine to Lime Sulfur ............................................................... Lindol to Ramjet Fuel ............................................................................... Rapeseed Oil to Zinc Sulfate ................................................................... Fluid Resistance of Fluoroelastomer Families .........................................

138 150 165 178 192

References .............................................................................................................................. 193 8.

Fluid and Heat Resistance of Perfluoroelastomers ................................................................. 195 8.1

Introduction ................................................................................................................. 195

8.2

Fluid Resistance Data ................................................................................................. 195

8.3

Heat Resistance Data ................................................................................................. 195

8.4

Resistance to Special Environments ........................................................................... 196

8.5

Major Applications ....................................................................................................... Table 8.1 Chemical Resistance: FFKM Fluoroelastomer ......................................... Abietic Acid to Lithium Hypochlorite ......................................................... Lithium Nitrate to Zirconium Nitrate .......................................................... Table 8.2 Chemical Resistance ............................................................................... Table 8.3 Upper Continuous Service Temperatures for Perfluoroelastomer Compounds .............................................................................................. Table 8.4 Tecnoflon PFR: Heat Aging ..................................................................... Table 8.5 Perfluoroelastomer Black Compounds for Chemical Processing Industry .................................................................................................... Table 8.6 Perfluoroelastomer Compounds for Semiconductor Applications ............

196 198 198 212 223 223 224 224 225

References .............................................................................................................................. 226 9.

Fluid Resistance of TFE-olefin Fluoroelastomers ................................................................... 227 9.1

Introduction ................................................................................................................. 227

9.2

Fluid Resistance of TFE/Propylene Elastomers .......................................................... 9.2.1 TFE/P Dipolymer ............................................................................................ 9.2.2 TFE/P/VDF Terpolymers ................................................................................ 9.2.3 TFE/P/TFP Terpolymers ................................................................................ 9.2.4 Service Recommendations ............................................................................

227 227 233 234 236

9.3

Fluid Resistance of Ethylene/TFE/PMVE Elastomer .................................................. 9.3.1 Fluid Resistance Data .................................................................................... 9.3.2 Resistance to Oil Field Environments ............................................................ 9.3.3 Cure System Effects ...................................................................................... 9.3.4 Service Recommendations ............................................................................

236 237 237 237 237

References .............................................................................................................................. 239 10.

Fluoroelastomer Applications .................................................................................................. 241 10.1

Introduction ................................................................................................................. 241

10.2

Major End Uses ........................................................................................................... 241

10.3

Fabrication Methods .................................................................................................... 241

Contents 11.

vii

Compounds for O-rings and Molded Goods ........................................................................... 243 11.1

O-rings 11.1.1 11.1.2 11.1.3

........................................................................................................................ Specifications ................................................................................................. Compression Set Measurement .................................................................... VDF/HFP Dipolymer Compounds ..................................................................

243 243 243 245

11.2

VDF/HFP/TFE Compounds ......................................................................................... 253

11.3

VDF/PMVE/TFE Compounds ...................................................................................... 259

11.4

Seal Design Considerations ........................................................................................ 260

11.5

Additional Fluoroelastomer Molding Compounds ....................................................... 260

References .............................................................................................................................. 277 12.

Compounds for Auto Fuel Systems ........................................................................................ 279 12.1

Introduction ................................................................................................................. 279

12.2

Fuel Line Veneer ......................................................................................................... 280

12.3

Fuel Tank Components ............................................................................................... 287

12.4

Fuel Injector Seals ...................................................................................................... 288

12.5

Development Trends ................................................................................................... 289

References .............................................................................................................................. 290 13.

Compounds for Auto Power Train Service .............................................................................. 291 13.1

Introduction ................................................................................................................. 291

13.2

Oil Seal Requirements ................................................................................................ 291

13.3

Compounds for Oil Seals ............................................................................................ 294 13.3.1 FKM Elastomers ............................................................................................ 294 13.3.2 FEPM Elastomers .......................................................................................... 295

13.4

Compounds for Transmission Seals ........................................................................... 296

References .............................................................................................................................. 298 14.

Compounds for Power Plant Service ...................................................................................... 299 14.1

Introduction ................................................................................................................. 299

14.2

Flue Duct Expansion Joints ......................................................................................... 299

14.3

High-fluorine Terpolymers ........................................................................................... 299

References .............................................................................................................................. 302 15.

Other Fluoroelastomer Applications and Processing .............................................................. 303 15.1

Introduction ................................................................................................................. 303

15.2

Latex and Coatings ..................................................................................................... 303

15.3

Thermoplastic Processing ........................................................................................... 303

15.4

Fluoroelastomer Caulks .............................................................................................. 304

15.5

Processing Aids for Hydrocarbon Plastics .................................................................. 304

References .............................................................................................................................. 305 16.

Fluoroelastomer Safety and Disposal ..................................................................................... 307 16.1

Introduction ................................................................................................................. 307

16.2

Safety in Production .................................................................................................... 307

viii

Contents 16.3

Safety in Applications .................................................................................................. 308

16.4

Disposal ...................................................................................................................... 308

References .............................................................................................................................. 309

Appendix: PDL Ratings .................................................................................................... 311 Glossary ............................................................................................................................ 313 Trademarks ....................................................................................................................... 347 Index .................................................................................................................................. 349

Series Editor’s Preface The original idea for the Fluorocarbon Series was conceived in the mid 1990s. Two important rationales required the development of the collection. First, there were no definitive sources for the study of fluorinated polymers including the commercial products. A researcher seeking the properties and characteristics of fluorinated plastics did not have a single source to use as a reference. Information put out by commercial manufacturers of polymers have long been the sources of choice. Second, the post war generation (a.k.a., Baby Boomers) were beginning to retire, thus reducing the available knowledge in the industry and academia. Selection of the topics of the books has been based on the importance of the practical applications of the fluorinated polymers. Inevitably, a number of fluorinated macromolecule classes, that are important in their own rights, were left out of the series. In each case, the size of its audience was

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

September 2005

Sina Ebnesajjad, Editor Plastics Design Library Dr. Sina Ebnesajjad is a senior technical consultant at the DuPont Company, where he has been in a variety of technical assignments since 1982. Dr. Ebnesajjad is the author of several handbooks on the science, technology, and applications of fluoroplastics published by William Andrew, Inc.

He is the Series Editor for the Fluorocarbon Handbook Series, which includes handbooks on fluoroplastics, fluoroelastomers, fluorinated coatings, and fluoroionomers. He has been the Editor of the Plastics Design Library since September, 2004.

Preface Fluoroelastomers based on copolymers of vinylidene fluoride and hexafluoropropylene and terpolymers containing tetrafluoroethylene, introduced commercially in the late 1950s and early 1960s, greatly extended the utility of elastomers. The heat and fluid resistance of fluoroelastomers is superior to that of other elastomers. Fluoroelastomer seals and other components have contributed to reliability, safety, and environmental protection in many areas including the aeronautical, automotive, oil, and chemical industries. Subsequent development of improved cure systems in the 1970s has led to better processing characteristics and enhanced properties of fluoroelastomers. New compositions, including specialty polymers based on perfluoro(methyl vinyl ether) and perfluoroelastomers based on copolymers of tetrafluoroethylene and perfluoro(alkyl vinyl ethers) with new cure systems imparting outstanding thermal and fluid resistance, have further extended service limits of elastomers. Various fluoroelastomer families are useful in long-term service in contact with a wide range of fluids up to 200°C to 300°C. New products with enhanced performance continue to be developed after more than forty-five years. As in the first two volumes on fluoroplastics in this handbook series, the aim of this volume is to compile a working knowledge of the chemistry and physics of fluoroelastomers, with descriptions of polymerization and production of polymers, processing and curing into fabricated products, and important applications. Emphasis is on technology currently used

commercially, along with some developments likely to become important in the future. The book focuses on providing a reference and a source for learning the basics for those involved in fluoroelastomer production and part fabrication, as well as for end users of fluoroelastomer parts and for students. The first part of this book is an overview of fluorocarbon elastomers, including descriptions of the nature of fluoroelastomers, properties of various compositions, developmental history, and major uses. Part II provides more details of fluoroelastomer technology, including monomer properties and synthesis, polymerization and production processes, cure systems, and processing methods. The last part covers fluid resistance of various fluoroelastomer families and major applications of fluoroelastomers. Since the main expertise of the author is in the area of fluoroelastomers’ synthesis, sections on polymerization include considerable theoretical detail. However, the main emphasis is on practical rather than theoretical technology. References at the end of each chapter serve as bibliography and additional reading resources. These references are not intended to be exhaustive; additional references in selected areas are available in a number of review articles. None of the views or information presented in this book reflects the opinions of any of the companies or individuals that have contributed to this book. Any errors are oversight on the part of the author. Albert L. Moore

August 2005

Acknowledgments Most of my knowledge and experience in the field of fluoroelastomers was acquired during a nearly forty-year career in elastomers research and development at DuPont and DuPont Dow Elastomers. I spent about twenty-five years in fluoroelastomers polymer development. Much of the technical information in this book is drawn from technical papers and product literature published by DuPont and DuPont Dow. I have drawn on knowledge obtained during discussions and collaboration with many of my former colleagues. As far as possible, I have tried to attribute credit for their contributions to individuals in the presentation of various topics in this book, but undoubtedly have missed some, for which I apologize. I have been fortunate in my career to have participated in the development of fluoroelastomers to take advantage of the bisphenol curing technology introduced in the early 1970s; in later development of specialty polymers for peroxide curing, and of bisphenol-curable polymers with improved processing characteristics; and still later with base-resistant fluoroelastomer compositions. All of this required close collaboration with colleagues in research, market technical groups, polymer production, and sales, along with advice from helpful customers. Many of these developments were worldwide efforts, involving research and development in the U.S., production in the U.S. and Europe, and technical service in the U.S., Europe, and Japan. It is impossible to list all those who contributed, but I will mention a number of colleagues with whom I worked closely. Walter W. Schmiegel has taught me much about curing elastomers over the years, allowing more rational design of polymers with good curing characteristics. S. David Weaver, Albertus van Cleeff, Lori D. Weddell, and Paul E. M. Wijnands have contributed much to my understanding of polymerization and production technology. Phan L. Tang, Donald F. Lyons, and Michael C. Coughlin, in addition to helpful discussions on fluoroelastomer polymerization, have provided much background material, including patents and publications, used in this book. John R. Richards and John P. Congalidis of DuPont have been helpful in clarifying many details of polymerization kinetics. Many colleagues in marketing technical groups have

been helpful to me in a number of developments over the years, including Albert L. Moran, David L. Tabb, John G. Bauerle, Ronald D. Stevens, and Stephen Bowers. In addition to collaboration, Eric W. Thomas and Theresa M. Dobel have provided me with a number of useful technical papers and reports. Fluoroelastomers’ suppliers have engaged in healthy competition over the years, from which we have all benefited by being pushed to develop improved products and processes for making them. DuPont and DuPont Dow have used continuous polymerization processes to make a wide range of polymer compositions and have developed cure systems for specialty fluoroelastomers. Dyneon (3M) has developed many bisphenol-curable products with excellent processing characteristics and properties. Daikin has contributed a “living radical” polymerization process to make peroxide-curable fluoroelastomers with excellent processing characteristics. Solvay Solexis and its predecessor companies Ausimont and Montefluos have developed efficient semibatch polymerization systems to make fluoroelastomers with carefully tailored architecture. Asahi Glass persisted in developing viable polymerization and curing systems for tetrafluoroethylene/propylene copolymers. In many cases, technical people have provided continuity in developments through significant changes in corporate structure. Much data in this book is excerpted from papers and product literature provided by these companies. I have tried to give adequate recognition of the accomplishments of the technical people involved. I have been supported in my career, and have been given considerable freedom in choosing directions for polymer and process development, by a number of managers in DuPont and DuPont Dow. Herman E. Schroeder was my research director for many years, including my first five-year assignment in fluoroelastomers, during which he supported a difficult development project involving considerable plant test work. Of several managers of fluoroelastomers research, Patrick S. Ireland, Subhash Gangal, and Dennis L. Filger have been particularly supportive. Fluoroelastomers Global Technical Director James D. MacLachlan and Technology Vice President Ashby L. Rice of DuPont Dow have supported

XIV

my work on this book, allowing me to start before retirement and to continue helpful contacts with colleagues after retiring. Sina Ebnesajjad, editor of the PDL Fluorocarbon Series, has provided invaluable help in guiding me through the writing of this volume. He provided much of the material in chapters on Fluoroelastomers Monomers and Processing of Fluoroelastomers, and led me to incorporate data from other books in the PDL Handbook Series in the Fluoroelastomers

FLUOROELASTOMERS HANDBOOK Applications section. I also wish to thank Millicent Treloar, Senior Acquisitions Editor of Plastics Design Library at William Andrew Publishing, for her support and suggestions. Many thanks are due to Jeanne M. Roussel and her staff at Write One for carefully handling the myriad details involved in converting my rough manuscript into a finished book. Finally, I am grateful for the continuing patience and support of my wife, Betty, during my career and during the writing of this book in the last few years.

Part I Fluoroelastomers Overview

1 Fundamentals 1.1

Introduction

Components fabricated from fluoroelastomers enhance reliability, safety, and environmental friendliness in such areas as automotive and air transportation, chemical processing industries, and power generation. Worldwide production of fluorocarbon elastomers was about 15,000 metric tons in 1999, but this modest volume of products is growing in importance for meeting more stringent performance requirements in these industries. Fluoroelastomers have outstanding resistance to most fluids at elevated temperatures, and are replacing other elastomers in applications where improved sealing performance is necessary. Automotive applications, mainly seals, hoses, and other small components in fuel and power train systems, account for over half of fluoroelastomers’ use. A wide range of fluoroelastomer products have been developed to meet performance requirements in many hostile environments, and to attain fabrication characteristics comparable to other elastomers. Examples of typical parts made from fluoroelastomers are shown in Fig. 1.1. O-ring seals account for about one third of fluoroelastomers’ usage. Shaft seals (about one quarter of usage) are of great im-

portance, especially for automotive power train applications. Other molded parts and extruded shapes (e.g., fuel hose) make up most of the rest of fluoroelastomers’ uses. The outstanding heat and oil resistance of fluoroelastomers compared to other elastomers is shown in Fig. 1.2, a chart developed by the American Society for Testing Materials (ASTM). Typical bisphenol-cured fluoroelastomers are given the ASTM classification HK. This means that for typical fluoroelastomer compounds aged 70 hours at 250°C, tensile strength changes no more than 30%, elongation-atbreak decreases less than 50%, and hardness changes no more than 15 points from original properties. Also after exposure to oil for 70 hours at 150°C, volume swell is no more than 10%. No other family of elastomers is close to this combination of heat and fluid resistance. This level of heat resistance translates to long useful service life of fluoroelastomers components, as shown in Fig. 1.3, with service life greater than 1000 hours at temperatures below 260°C, and short-term resistance to higher temperature excursions. Compared to other elastomers, fluoroelastomers exhibit much longer effective performance in seal applications at elevated temperatures, as illustrated in Fig. 1.4.

Figure 1.1 Typical fluoroelastomers parts. (DuPont Dow Elastomers.)

4

FLUOROELASTOMERS HANDBOOK

Figure 1.2 Heat and oil resistance of elastomers. (ASTM.)

Figure 1.3 Fluoroelastomer heat resistance. (DuPont Dow Elastomers.)

Figure 1.4 Retained o-ring sealing force. (DuPont Dow Elastomers.)

1.2

Only current commercial products are treated in detail. Some products previously sold, but now discontinued, are mentioned in this introductory chapter, but not in the more detailed sections that follow. Major topics covered include: compositions and characteristics of various fluoroelastomer families; major monomers, their synthesis and handling; polymerization and production technology; cure systems, cure-site monomers, and curative components; com-

Scope: Fluorocarbon Elastomers

This book emphasizes the technology and applications of fluorocarbon elastomers based on fluorinated organic polymers with carbon-carbon linkages in the backbone of the molecules. Fluoroelastomers with inorganic backbones, such as fluorosilicones and fluorinated polyphosphazenes, are described briefly.

1 FUNDAMENTALS

5

pounding and processing; and design for specific applications. Trends in product development, emerging uses, and methods of fabrication are discussed.

1.3

Nature of Fluoroelastomers

To exhibit elastomeric behavior, a polymer must be flexible and recover from substantial deformation at temperatures above about 0°C. This requires the polymer to be substantially amorphous, and above its glass transition temperature, so that chain segments have adequate mobility to allow the material to return to its original state after stress is removed.[1] Ordinarily the polymer is cross linked to form a threedimensional network with tie points between chains to minimize irreversible flow under stress. The driving force for recovery is the tendency of chain segments to return to the more disordered state with higher entropy when the stress causing a deformation is removed. Generally, fluorocarbon chains are relatively stiff compared to hydrocarbons, so fluoroelastomers exhibit rather slow relaxation and recovery from strain (i.e., leathery rather than highly

resilient behavior). Thus, most fluoroelastomers are used in static, rather than dynamic, applications. Fluorocarbon elastomers are copolymers made up of two or more major monomer units. One or more monomers give straight chain segments, which would tend to crystallize if long enough. A monomer with a bulky side group is incorporated at intervals to break up the crystallization tendency and produce a substantially amorphous elastomer. Commercial fluorocarbon elastomers are made by free radical polymerization of vinyl monomers. Monomers used in straight chain segments include: vinylidene fluoride (VDF), CH2=CF2; tetrafluoroethylene (TFE), CF2=CF2; and ethylene (E), CH2=CH2. Monomers that provide bulky side groups include hexafluoropropylene (HFP), CF2=CF–CF3, perfluoro(methyl vinyl ether) (PMVE), CF2=CF–O–CF3, and propylene (P), CH2=CH–CH3. The combinations of monomers used must produce substantially amorphous copolymers with glass transition temperatures low enough for elastomeric behavior at temperatures encountered in practical use. Monomer combinations used in several commercial product families are shown in Table 1.1. Major characteristics of these fluoroelastomer families are described in the following section.

Table 1.1 Major Monomers in Commercial Fluoroelastomers

Monomers with Bulky Side Groups

HFP

Monomers in Straight Chain Segments VDF

TFE

Example

E

Viton A Viton B

Viton GLT PMVE

Viton ETP Kalrez Perfluoroelastomer

P

Aflas 100 Aflas 200

6

1.4 1.4.1

FLUOROELASTOMERS HANDBOOK

Fundamental Properties VDF Copolymers

Copolymers of VDF with HFP in about 80/20 mole ratio comprise the highest volume fluoroelastomer family. These are readily cured with bisphenols to give excellent properties over a useful temperature range of –18°C to 250°C. These dipolymers are particularly useful for o-ring seals with good compression set resistance. TFE may be used to replace part of the VDF in terpolymers to get better fluid resistance with some sacrifice in low-temperature flexibility. Up to about 30% TFE may be incorporated without imparting excessive crystallinity in terpolymers. Elastomers with high fluorine content (low VDF levels) may contain cure-site monomers to allow peroxide-initiated free-radical curing. Specialty polymers with major monomers VDF, PMVE, and TFE have better low-temperature flexibility than the HFP family described above. Cure-site monomers must be incorporated to allow effective cross linking of these polymers, usually by free-radical cure systems. Products based on these compositions are becoming more important in automotive fuel system sealing applications, since good sealing performance is possible down to about –40°C. VDF-based fluoroelastomers are resistant to a wide range of fluids. However, because of the polar nature of VDF units, the polymers are soluble in low molecular weight esters and ketones, and vulcanizates are highly swollen by such polar solvents. Bisphenol-cured compounds contain relatively high levels of inorganic metal oxide and hydroxide, so these are susceptible to swelling and attack by hot aqueous fluids. Peroxide-cured compounds are more resistant to such aqueous environments. Strong inorganic base and organic amines at high temperatures also attack VDF-based polymers. In spite of these limitations, VDF-containing fluoroelastomers have performed well in severe environments, including automotive seals in contact with hot oils that contain considerable amine moieties.

1.4.2

nonpolar elastomers based on TFE and olefins have been developed. The major product here is a dipolymer with alternating TFE and propylene units. While difficult to process and cure, this polymer is used in wire and cable, oil field, and some automotive seal applications. TFE/P dipolymers have glass transition temperatures near 0°C, thus rather poor flexibility at low temperature. Also, their swell in hydrocarbons is high because of their low fluorine content. Terpolymers containing VDF have higher fluorine content and somewhat better low-temperature flexibility. These have better processing characteristics, but sacrifice some base resistance. A terpolymer of ethylene, TFE, and PMVE with cure sites allowing peroxide curing has excellent base resistance and fair low-temperature characteristics.[2] This specialty material is finding use in fluid environments where other fluoroelastomers have deficiencies. Ethylene has also been incorporated to partially replace VDF in a tetrapolymer with major monomers E/VDF/HFP/TFE and cure sites for peroxide curing.[3] The polymer, designed for enhanced resistance to base and amines, has been offered for use in oil seals for automotive power trains.

1.4.3

Perfluoroelastomers

To attain the fluid and thermal resistance of perfluorinated TFE-based plastics, two families of perfluoroelastomers have been developed. One is based on copolymers of TFE and PMVE, with various cure sites allowing a range of applications. The second family is based on a copolymer of TFE with a perfluoro(alkoxy alkyl vinyl ether) with a halogen cure site for peroxide curing. This polymer has better low temperature characteristics, but its upper service temperature is limited. Generally, parts made from perfluoroelastomers are used in extremely severe fluid service applications, where other elastomers are unsatisfactory. Main uses for perfluoroelastomer parts are in seals for chemical process and transportation industries, oil field service, aeronautical and aerospace, and semiconductor fabrication lines.

TFE/Olefin Copolymers

Because of the susceptibility of VDF/HFP-based fluoroelastomers to attack by polar fluids and bases,

1.4.4

Other Compositions

Fluoroelastomers based on copolymerization of VDF with chlorotrifluoroethylene (CTFE),

1 FUNDAMENTALS CF2=CFCl, have been offered commercially. In these copolymers, potential crystallinity from VDF sequences is avoided by incorporation of CTFE with its bulky chlorine side group. Two elastomeric copolymers, Kel-F® 5500 and 3700, containing 50 and 70 mole % VDF, were developed. These elastomers have good resistance to oxidizing acids. However, resistance to heat, fluids, and compression set is inferior to that of HFP-based fluoroelastomers.[4] The CTFE-based elastomeric products have been discontinued, but CTFE-based plastics, some with small amounts of VDF incorporated to reduce brittleness, are produced.[5] Two families of fluoroelastomers based on inorganic backbones have been offered commercially. Fluorosilicone and fluoroalkoxyphosphazene polymers have better low-temperature characteristics than fluorocarbon elastomers, but have lower resistance to high temperature. The flexible main chains of these polymers, allowing service at temperatures as low as –65°C, consist of alternating silicon and oxygen or phosphorus and nitrogen atoms. Fluorosilicone elastomers are similar to silicone elastomers, polydimethylsiloxane polymers, in which one methyl substituent on each silicone atom is replaced with a 3,3,3-trifluoropropyl group:[6] CH3 | –(Si–O)n– | CH2–CH2–CF3 Fluorosilicone processing and parts fabrication technology is basically the same as that of silicone elastomers, quite different from that of fluorocarbon elastomers. Fluoroalkoxyphosphazene elastomers have been withdrawn from the market. These elastomers were made from dichlorophosphazene polymers by displacing chlorine with fluorocarbon alkoxides:[7] O–CH2–CF3 | –(P=N)n– | O–CH2–CF2–CF2–CF3

7

1.5

Developmental History: Compositions, Cure Technology

Elastomeric copolymers of vinylidene fluoride and chlorotrifluoroethylene, made by M. W. Kellogg Co. under contract from the U.S. Army Quartermaster Corps, were described in 1955.[8] These fluoroelastomers had better heat and fluid resistance than elastomers available at the time. At DuPont, fluoroelastomer development work led by H. E. Schroeder centered on copolymerizing monomers that did not contain chlorine,[9] in order to obtain still better heat stability. A copolymer of VDF with hexafluoropropylene was described in 1956; details of its curing and properties were published soon afterward.[10] Polymer preparation was covered in a patent[11] issued later, after overcoming an interference proceeding brought by M. W. Kellogg. DuPont commercialized the VDF/HFP dipolymer in 1958 as Viton® A. A terpolymer with TFE, Viton B, was introduced in 1960; this has better heat and fluid resistance than the dipolymer.[12] The 3M Co., which had acquired Kellogg’s fluoropolymer assets, introduced a similar dipolymer under the trade name Fluorel®, under license from DuPont. With initial impetus provided by military applications, VDF/HFP fluoroelastomers quickly achieved commercial success, especially in molded seals. Faced with DuPont patents on VDF/HFP/(TFE) polymers, Montecatini-Edison S.p.A. in Europe developed Tecnoflon® dipolymers[13] and terpolymers[14] based on use of 1-hydropentafluoropropylene, CHF=CF–CF3, in place of hexafluoropropylene. With their lower fluorine content, these polymers had lower stability than HFP-based fluoroelastomers, so they were replaced with HFP polymers when the patents expired. In Japan, Daikin Kogyo started offering Dai-el® VDF/HFP/(TFE) fluoroelastomers in 1970 under license from DuPont. A Russian VDF/ HFP dipolymer, SKF-26,[15] has been consumed internally, with little offered on the world market. Polymer production processes differ among the suppliers. DuPont patents describe a continuous emulsion polymerization process with a continuous isolation process using centrifuges.[16] This allows high production rates for a given product to be sustained without interruption. Other suppliers use a semibatch polymerization process, in which water,

8

FLUOROELASTOMERS HANDBOOK

dispersing aids, initiator, and an initial monomer mixture are charged to the reactor. Then monomers are fed at the rate and composition corresponding to the polymer production. When the desired emulsion solids level is attained, monomer feed is stopped and the dispersion is discharged for polymer isolation. The high reactivity of the monomer mixture usually leads to the main limitation on rate being control of the heat of polymerization to maintain reactor temperature constant. During the 1960s, VDF-based fluoroelastomers were cured with diamines. The main curing agent used was hexamethylenediamine carbamate, +H N–(CH ) –NH–CO –. This blocked diamine 2 2 6 2 dehydrofluorinates HFP-VDF sequences to form double bonds and then the amine moieties add to the double bonds to form cross links. The HF formed is neutralized with magnesium oxide, forming water that is later removed in an oven postcure. This cure system is characterized by scorch—premature reaction at processing and forming temperatures—and relatively slow cure in the mold. With this cure system, mold sticking and fouling problems cause high scrap rates undesirable with such expensive materials. By 1970, DuPont and 3M developed better cure systems based on bisphenols, along with improved polymers designed to give better processing and performance with the new curatives. The bisphenol cure system has allowed development of products for fabrication of high-performance seals with much enhanced compression set resistance.[17] The preferred cross linking agent is Bisphenol AF, 2,2-bis(4-hydroxyphenyl)hexafluoropropane [I], with an accelerator such as benzyltriphenylphosphonium chloride [II].[18]

[I]

[II]

For optimum curing and compression set resistance, the polymers must have low ionic end-group levels.[19] A number of fluoroelastomers have been designed for excellent processing and curing with this system, and polymerization processes have been

developed to make such polymers efficiently.[20] Because of crosslicensing between DuPont and 3M of the preferred phosphonium accelerators, other producers were forced to use alternatives such as quaternary ammonium salts. Fluoroelastomer suppliers have developed a large number of bisphenolcurable products tailored for specific applications and customer processes, including precompounds of fluoroelastomers with bisphenols, accelerators, and processing aids. During the late 1970s, DuPont introduced peroxide-curable polymers to make vulcanizates less susceptible to degradation by steam and acid.[21] Bromine-containing monomers are incorporated to make sites reactive with free radicals at curing temperatures; the resulting radical sites on the chains then react with multifunctional radical traps to form a cross linked network.[22] This cure system has been particularly useful in high-fluorine polymers difficult to cure with bisphenols. Also, this curing technology was applied to VDF/PMVE/TFE polymers to allow development of specialty products with much improved low-temperature performance. Daikin introduced peroxide-curable fluoroelastomers with iodine on nearly all chain ends of polymers with very narrow molecular weight distribution made with a novel “living radical” semibatch polymerization process.[23] Compared to bromine-containing polymers, these iodine-containing polymers cured faster to give vulcanizates with better compression set resistance. DuPont later developed fluoroelastomers made in a continuous process to incorporate bromine cure sites along chains and iodine end groups.[24] These gave vulcanizates with better heat resistance than those from polymers containing iodine end groups as the only cure sites. To attain fluid and thermal resistance comparable to that of polytetrafluoroethylene plastics, DuPont scientists developed elastomeric copolymers of TFE with PMVE during the 1960s.[25] The perfluorinated polymer backbone imparts great resistance to heat and most fluids, but its inertness leads to difficulty in curing the elastomer. Considerable effort was put into development of suitable curesite monomers and cure systems that retain the desired properties of the perfluoroelastomer backbone. Of several cure systems studied by DuPont, those based on cure sites from perfluoroalkoxyvinyl ethers with functional groups gave outstanding high-temperature stability. Starting in 1972, DuPont offered

1 FUNDAMENTALS Kalrez® Perfluoroelastomer Parts for service in severe environments. Perfluoroelastomers with perfluorophenyl sites cured with bisphenols,[26] and those with perfluorocarbon nitrile sites cured with tetraphenyltin to get triazine cross links,[27] retain good properties for long periods at 288°C. Halogen cure sites from bromine-containing monomers or iodine end groups can be used with peroxide cure systems. Peroxide-cured vulcanizates have excellent fluid resistance, but no better thermal resistance than obtained with other fluoroelastomers. However, the bulk of perfluoroelastomer applications require excellent fluid resistance at temperatures below 200°C, within the capability of peroxide-cured components. In the early 1960s, workers at DuPont[28] and Asahi Glass[29] studied elastomeric copolymers of tetrafluoroethylene and propylene. These monomers have a strongly alternating tendency to free radical polymerization, so the copolymers contain about 50 mole % of each monomer. With glass transition temperature near 0°C, the copolymers have mediocre low-temperature flexibility. With their high propylene level and relatively low fluorine content, vulcanizates exhibit high swell in hydrocarbon fluids. However, these nonpolar elastomers are resistant to polar solvents and to organic and inorganic base. DuPont did not commercialize this elastomer family because of difficulty in polymerization and curing, combined with lack of interest by U.S. customers. Asahi Glass worked out semibatch polymerization conditions to get adequate molecular weight, and developed a heat treatment to get sites active enough to allow curing with peroxide and radical traps. Asahi Glass offers TFE/P elastomers as Aflas®. The largest market in Japan is for wire and cable applications; TFE/P

9 elastomers have better electrical resistivity than the more polar VDF-based fluoroelastomers. Terpolymers of TFE and propylene with VDF have also been developed. These may be cured with diamines[30] or bisphenols[31] to obtain better low-temperature characteristics and hydrocarbon resistance, but somewhat lower base resistance than TFE/P dipolymer products. To get a combination of properties better than those of TFE/P polymers, DuPont workers developed elastomeric terpolymers of TFE and PMVE with ethylene.[32] These products are resistant to base and most fluids, and have better low-temperature characteristics than TFE/P copolymers.

1.6

Major Uses of Fluoroelastomers

Fluoroelastomers are used mainly in seals and barrier layers subjected to environments too severe for other elastomers. Fluoroelastomer components have long service life at temperatures above 150°C, and some specialty perfluoroelastomer parts can withstand sustained temperatures above 300°C. Fluoroelastomers are resistant to a wide range of fluids, so long as proper polymer compositions and cure systems are chosen for particular environments. The low permeability and service reliability of fluoroelastomers have resulted in their increasing use to reduce emissions and releases in the chemical processing and transportation industries. Automobile applications comprise the largest fluoroelastomers market, with components used in drive train and fuel handling systems (see Fig. 1.5).

Figure 1.5 Fluoroelastomer components in auto fuel systems. (DuPont Dow Elastomers.)

10

FLUOROELASTOMERS HANDBOOK

Glass transition temperatures of fluoroelastomers are in the range 0°C to –30°C, generally higher than those of hydrocarbon elastomers. At moderate temperatures, fluoroelastomers recover relatively slowly from imposed strain, and are not suitable for many dynamic applications. Most fluoroelastomers are used as static seals or barriers in applications where rapid recovery from strain is not necessary, (e.g., in o-rings, gaskets, and hoses). Even in shaft seals, the designs are such that fluoroelastomers’ compositions do not need to exhibit rapid recovery, and thus can function well. O-ring seals comprise the largest volume product form of fluoroelastomers. One of the initial uses of fluoroelastomers was in aircraft and aerospace seals, especially in engines and fuel handling systems. In automobiles, fluoroelastomer o-rings are particularly important as fuel injector seals. A variety of fluoroelastomer polymer compositions are used for o-ring seals in the chemical processing and chemical transportation industries. The bulk of o-ring seals are made from bisphenol-cured VDF/HFP dipolymers, formulated for the best long-term resistance to compression set. However, some environments require better long-term resistance to aggressive fluids under severe conditions, so o-ring seals made of more resistant fluoroelastomer compositions are becoming more important. These include high-fluorine terpolymers of VDF/HFP/TFE and VDF/ PMVE/TFE, perfluoroelastomers, TFE/propylene elastomers, and ethylene/TFE/PMVE elastomers. Fluoroelastomer shaft seals have found increasing use, especially in automotive drive train systems, where temperatures are increasing and lubricants have been formulated for better performance. Seal lifetime requirements have become more stringent—automobile shaft seals are expected to last for more than 100,000 miles without significant leakage. Fluoroelastomer suppliers have been particularly challenged to develop materials for low-cost shaft seals resistant to modern lubricants at temperatures exceeding 160°C. Dispersants, antioxidants, and other additives in these lubricants generate amines which attack VDF-containing fluoroelastomers at high temperature and cause failure by embrittlement or network breakdown. Various low-VDF or no-VDF fluoroelas-

tomers are being evaluated for the most severe uses. The intricate shapes of shaft seals (see Fig. 1.6), along the requirement for good adhesion of rubber to metal insert, necessitate design of the base polymers and compounds for excellent processing characteristics (e.g., excellent mold flow, rapid cure, and clean demolding). Gaskets and packing make up a significant market for fluoroelastomers for sealing against fluids at high temperatures for extended periods. Lower-performance elastomers are being replaced, especially in automotive and chemical process seals, to attain the better reliability and service lifetimes required for protection of the environment. As part of efforts to reduce automotive fuel emissions, fluoroelastomer hose components have become important. One of the first fuel-system uses for fluoroelastomers was in composite fuel-line hose, in which a thin veneer of extruded fluoroelastomer serves as an inner barrier layer. Originally VDF/HFP dipolymer was used, but lower emission standards have necessitated use of high-fluorine terpolymers or thicker veneers. Because of the resulting higher cost of such fluoroelastomer hose, some of this application has been taken over by thermoplastics. However, molded hose and other components, especially in the fuel tank, are being fabricated of fluoroelastomers. To reduce pollution in the electrical generation industry, fluoroelastomer-coated fabric is used in expansion joints for exhaust ducts that handle hot, acidic flue gas from desulfurization systems. Special fluoroelastomer compounds are used in oil and gas production, especially in deep wells where elastomer

Figure 1.6 Shaft seal cross section. (CR Industries.)

1 FUNDAMENTALS

11

components must withstand corrosive fluids at high temperature.

1.7

Producers of Fluoroelastomers

Major producers of fluoroelastomers are listed in Table 1.2, in order of their worldwide market share. Also listed are trade names and locations of corporate headquarters and polymer manufacturing facilities. All of these companies produce a wide range of fluoroelastomer and perfluoroelastomer compositions, except for Asahi Glass, which makes TFE/ propylene polymers only (also marketed by Dyneon and DuPont Dow). DuPont Dow Elastomers LLC, a joint venture of DuPont and Dow Chemical formed in 1996, took over the former Viton® Fluoroelastomers and Kalrez® Perfluoroelastomer Parts businesses of DuPont. With the breakup of the joint venture in mid-2005, the fluoroelastomers business became part of DuPont Performance Elastomers, a wholly owned DuPont subsidiary. Dyneon is a wholly owned

subsidiary of 3M Company; the trade name for its fluoroelastomers products was changed from Fluorel to Dyneon® in 1999. Solvay Solexis was formed in 2003 after the Solvay Group acquired Ausimont and joined these assets with Solvay fluoropolymer activities. Ausimont was formerly Montefluos, a part of the Montedison group. All the fluoroelastomers producers are part of, or allied with, fluoroplastics and fluoromonomers businesses. Other fluoroelastomer producers sell little or no product on the open international market. Nippon Mektron Ltd. makes fluoroelastomers and perfluoroelastomers for the Freudenberg-NOK Group (FNGP), major worldwide manufacturers of seals. Suppliers of materials used mainly in their own countries, with little export sales, include 3F Company, Shanghai, China, and KCCE, Kirovo-Chepetsk, Russia. The S. V. Lebedev Synthetic Rubber Institute (VNIISK) in St. Petersburg has developed most of the fluoroelastomers made in Russia under the trade name Fluorelast. A large number of companies make seals, molded and extruded parts, and other fabricated components from fluoroelastomers.

Table 1.2 Fluoroelastomers Producers and Trade Names

Company and Headquarters

Trade Names

Production Locations

DuPont Performance Elastomers LLC Wilmington, DE

Viton, Kalrez

Deepwater, NJ Dordrecht, Netherlands

Dyneon LLC Oakdale, MN

Dyneon

Decatur, AL Zwijndrecht (Antwerp), Belgium

Solvay Solexis SpA Bollate, Italy

Tecnoflon

Spinetta-Marengo (Milan), Italy Thorofare, NJ

Daikin Industries Ltd. Osaka, Japan

Dai-el

Settsu (Osaka), Japan

Asahi Glass Co. Ltd. Tokyo, Japan

Aflas

Ichihara (Chiba), Japan

12

FLUOROELASTOMERS HANDBOOK

REFERENCES 1. W. W. Schmiegel, Organic Fluoropolymers, in: Chemistry of Organic Fluorine Compounds II, ACS Monograph 187:1111 (1995) 2. A. L. Moore, U.S. Patent 4,694,045, Base Resistant Fluoroelastomers, assigned to DuPont (September 15, 1987) 3. M. Albano et al., U.S. Patent 5,354,824 (May 22, 1992) 4. R. G. Arnold, A. L. Barney, and D. C. Thompson, Fluoroelastomers, in: Rubber Chemistry and Technology, 46:625 (1973) 5. D. P. Carlson and W. W. Schmiegel, Organic Fluoropolymers, in: Ullman’s Encyclopedia of Industrial Chemistry, A11:411 (1988) 6. Ibid., 418 7. H. R. Allcock et al., Inorganic Chemistry, 5:1709 (1966) 8. M. E. Conroy et al., Rubber Age, 76:543 (1955) 9. H. E. Schroeder, Facets of Innovation (Goodyear Medal address), in: Rubber Chemistry and Technology, 57:G94 (1984) 10. S. Dixon, D. Rexford, and J. S. Rugg, Industrial and Engineering Chemistry, 49:1687 (1957) 11. D. R. Rexford, U.S. Patent 3,051,677, assigned to DuPont (1962) 12. J. R. Pailthorp and H. E. Schroeder, U.S. Patent 2,968,649, assigned to DuPont (1961) 13. D. Sianesi, C. Bernardi, and A. Regio, U.S. Patent 3,331,823 (1967) 14. D. Sianesi, C. Bernardi, and G. Diotalleri, U.S. Patent 3,335,106 (1967) 15. S. V. Sokolov, Fluororubbers, in: Synthetic Rubber, I. V. Garmonova, ed., Leningrad (1983) 16. F. V. Bailor and J. R. Cooper, U.S. Patent 3,536,683, assigned to DuPont (October 27, 1970) 17. R. G. Arnold et al., op. cit., 631. 18. A. L. Moran and D. B. Pattison, Rubber World, 103:37 (1971) 19. E. K. Gladding and J. L. Nyce, U.S. Patent 3,707,529, assigned to DuPont (December 26, 1972) 20. A. L. Moore, U.S. Patent 3,839,305, assigned to DuPont (October 1, 1974) 21. H. E. Schroeder, op. cit., G96 22. D. Apotheker and P. J. Krusic, U.S. Patent 4,214,060, assigned to DuPont (1980) 23. M. Tatemoto, T. Suzuki, M. Tomoda, Y. Furukawa, and Y. Ueta, U.S. Patent 4,243,770 (1980) 24. A. L. Moore, U.S. Patents 4,948,852 (1990), 4,973,633 (1990), 5,032,655 (1991), and 5,077,359 (1991) 25. G. A. Gallagher, U.S. Patent 3,069,401, assigned to DuPont (1962) 26. G. H. Kalb, A. A. Khan, R. W. Quarles, and A. L. Barney, ACS Advances in Chemistry Series, No. 129, pp. 13–26 (1973) 27. A. F. Breazeale, U.S. Patent 4,281,092, assigned to DuPont (July 28, 1981) 28. W. R. Brasen and C. S. Cleaver, U.S. Patent 3,467,635, assigned to DuPont (1969) 29. Y. Tabata, K. Ishigure, and H. Sobue, Journal of Polymer Science, Part A-2, 2235 (1964) 30. J. R. Harrell and W. W. Schmiegel, U.S. Patent 3,859,259, assigned to DuPont (1975) 31. G. Kojima and H. Wachi, International Rubber Conference, p. 242, Kyoto, Japan (1985) 32. A. L. Moore, Elastomerics, 118(No. 9):14–17 (1986)

2 Fluoroelastomer Composition and Properties 2.1

Major Families of Fluorocarbon Elastomers

fluoride, tetrafluoroethylene, and ethylene) would contribute to crystallinity if incorporated in sufficiently long sequences. The other three monomers [hexafluoropropylene, perfluoro(methyl vinyl ether), and propylene] have bulky side groups that hinder crystallization and allow synthesis of amorphous elastomers. VDF and PMVE contribute to low glasstransition temperature (Tg) and thus to good lowtemperature flexibility. All the fluoromonomers impart good resistance to hydrocarbons. VDF is a polar moiety, especially when incorporated adjacent to perfluorinated monomer units, so it contributes to swelling in contact with low molecular weight polar solvents and is susceptible to attack by base. Ethylene and propylene units contribute to swelling in contact with hydrocarbons, but are resistant to polar solvents and base. Several families of commercial fluoroelastomers have been designed with various combinations of these major monomers to get characteristics necessary for successful performance in wide ranges of applications and environments. Dipolymers of vinylidene fluoride (VDF) and hexafluoropropylene (HFP) make up the largest volume of fluoroelastomers sales. Only one composition (VDF/HFP about 60/40 weight percent or 78/22 mole %, 66% fluorine) is of commercial importance, but it is offered in a wide range of viscosities and in numerous formulations tailored for

Fluorocarbon elastomers are copolymers of various combinations of monomers. Composition can be chosen to get a desired combination of properties. The main characteristics affected by composition are fluid resistance, stability at high temperatures, and flexibility at low temperatures. Ease of processing and curing also vary with composition. The situation with fluoroelastomers is analogous to that of several hydrocarbon-based elastomers in which composition determines the trade-off between oil resistance and low-temperature characteristics. For example, in the nitrile rubber family (NBR, copolymers of butadiene and acrylonitrile), higher acrylonitrile content enhances oil resistance, but gives poorer lowtemperature flexibility. The same trade-off exists for acrylate content of elastomers based on copolymers of ethylene and ethyl acrylate. Chlorine content exerts similar effects in chlorinated polyethylene elastomers. The range of property variation that can be attained by varying composition is much greater for fluoroelastomers than for the hydrocarbon-based elastomer families. Effects of various major monomers on important fluoroelastomer characteristics are indicated in Table 2.1. Three of the monomers (vinylidene

Table 2.1 Fluoroelastomer Characteristics Imparted by Major Monomers

Contribution Monomer

Formula

Resistance to: Tg

Crystallinity

Hydrocarbons

Polar Solvents

Base

VDF

CH2= CF2

↓

↑

↓

↓

↓

HFP

CF2= CF–CF3

↑

↓

↑

↑

−

TFE

CF2= CF2

↑

↑

↑

↑

−

PMVE

CF2= CF–O–CF3

↓

↓

↑

↑

−

E

CH2= CH2

↑

↑

↓

↑

↑

P

CH2= CH–CH3

↑

↓

↓

↑

↑

14 specific applications. Other dipolymer compositions can be made, but higher VDF content leads to significant crystallinity, while lower VDF levels give much higher glass-transition temperatures, both detrimental to low-temperature flexibility. Terpolymers of VDF and HFP with tetrafluoroethylene (TFE) afford a better way to get enhanced fluid resistance without such severe effects on low-temperature characteristics. Useful terpolymers can be made with VDF content as low as about 30% to get fluoroelastomers with higher fluorine content (up to about 71%) and better fluid resistance. Most curing of these elastomers is based on the versatile bisphenol cure system, but some TFE-containing polymers are designed for free radical (peroxide) curing. A family of fluoroelastomers growing in importance because of better low-temperature characteristics is based on use of perfluoro(methyl vinyl ether) [PMVE] in place of HFP in copolymers with VDF and TFE. Incorporation of a small amount of cure site is necessary to facilitate curing with peroxide systems. These PMVE-containing elastomers are useful at temperatures 10°C to 20°C lower than possible with HFP-containing polymers with comparable VDF content. Figure 2.1 shows trends in fluid resistance and low-temperature flexibility for vulcanizates of VDF/HFP/TFE and VDF/PMVE/

FLUOROELASTOMERS HANDBOOK TFE elastomers with varying fluorine (VDF) content. All these elastomers are resistant to a wide range of fluids. However, for this comparison, a fuel mixture (M15 Fuel) containing 15% methanol and 85% standard hydrocarbon Fuel C was chosen to show the relatively large increase in volume swell with higher VDF content (lower fluorine content). The measure of low-temperature characteristics shown, TR-10, is a test carried out on cured strips of elastomer. The specimen is stretched, locked in the elongated condition, and cooled to very low temperature; then the specimen is released, and allowed to retract freely while raising the temperature at a uniform rate. TR-10 is the temperature at which the specimen has retracted 10%. For a vulcanizate of medium hardness, TR-10 is close to the glass transition temperature of the base polymer. TR-10 decreases with increasing VDF content, and is much lower for PMVE-based fluoroelastomers. Perfluoroelastomers, copolymers of TFE with PMVE or a perfluoro(alkoxyalkyl vinyl ether), have excellent resistance to most fluids. With properly designed cure systems, TFE/PMVE elastomer vulcanizates have long service life at temperatures up to 300°C. Perfluoroelastomer parts can be designed for use in extreme environments that would destroy other elastomers.

Figure 2.1 Fluid resistance and low-temperature flexibility of VDF-based fluoroelastomers.[6]

2 FLUOROELASTOMER COMPOSITION AND PROPERTIES Two families of fluoroelastomers are based on copolymerization of fluoromonomers with ethylene or propylene. Copolymers of TFE and propylene are resistant to polar fluids and base, but susceptible to high swell in hydrocarbons. Incorporation of VDF improves oil resistance at the expense of some base resistance. Ethylene may be used in place of VDF in copolymers with TFE and PMVE to get excellent resistance to most solvents and polar fluids, including base and amines. Determination of fluoroelastomer composition is rather difficult. VDF/HFP dipolymer composition and monomer sequencing were determined by 19 F nuclear magnetic resonance (NMR).[1] A typical spectrum is shown in Fig. 2.2. In studies related to curing, W. W. Schmiegel has interpreted the more complicated VDF/HFP/TFE and VDF/PMVE/TFE terpolymer spectra.[2] For quantitative analysis of terpolymers, VDF may be determined by 1H NMR; then TFE and HFP or PMVE can be calculated from 19F NMR on the same polymer. In practice, NMR analysis is not sufficiently rapid or precise for routine use in polymerization plant control. Elemental analyses for C, H, and F are of limited utility, with fluorine determination being particularly susceptible to bias errors because of interaction of fluorine with laboratory glassware used in the analysis. (Values of fluorine content of fluoroelastomers reported by suppliers are based on calculations from overall monomer composition, rather than direct analysis.) Usually a number of well characterized copolymers of varying composition are used as standards for

Figure 2.2 19F NMR spectrum, VDF/HFP dipolymer.[2]

15 calibration of suitable Fourier Transform Infrared (FTIR) methods for the various fluoroelastomer families. Careful monomer mass balances around wellcontrolled laboratory polymerization reactors allow preparation of precise composition standards. Even so, some inconsistencies probably exist in reported values of fluorine content by different fluoroelastomer suppliers.

2.2

VDF/HFP/(TFE) Elastomers

A ternary plot[3] of all the possible polymer compositions from VDF, HFP, and TFE monomers is shown as Fig. 2.3, based on polymer synthesis and thermal characterization studies by the author. A number of VDF/HFP and VDF/TFE dipolymers and VDF/HFP/TFE terpolymers were made by emulsion polymerization in a continuous reactor, with compositions determined by monomer mass balances. Glass transition temperatures, melting points, and heats of fusion were determined by differential scanning calorimetry (DSC). Polymers were designated as elastomers if they had glass transition temperatures less than 20°C, crystalline melting points below 60°C, and heats of fusion below 5 joules per gram. The Tg limit set the high-HFP, low-VDF boundary, and the limits on crystallinity set the lowHFP, high-VDF or high-TFE boundary of the elastomeric range. The large region of high-VDF or highTFE plastics was characterized by high crystallinity (heats of fusion above 10 J/g) with melting points

16

FLUOROELASTOMERS HANDBOOK be obtained with peroxide-cured, high-fluorine types. These elastomers are not recommended for contact with low molecular weight ketones and esters (e.g., acetone or ethyl acetate) because of excessive swell. They are attacked by strong bases and concentrated amines at high temperature.

Table 2.2 VDF Fluoroelastomers - Composition, Tg

Type

% VDF

%F

Tg, °C

60

66

-18

AL

60

66

-21

BL

50

68

-18

B

45

69

-13

F

36

70

-8

VDF/HFP A VDF/HFP/TFE Figure 2.3 A ternary plot of all the possible polymer compositions from VDF, HFP, and TFE monomers.

above 120°C. These plastics have been described in the first two volumes of this handbook series.[4] The intermediate region labeled “elastoplastics” comprises polymers with considerable crystallinity melting at 60°C–120°C. These are rather stiff polymers with higher modulus than elastomers. They do not generally have adequate mechanical properties for commercial usefulness. The unlabeled region of highHFP compositions would have high Tg and low crystallinity; these are impractical to make because of poor polymerizability of high-HFP mixtures. Approximate compositions of commercial elastomeric products are shown on the ternary diagram, with letters denoting the various composition families using the Viton® type nomenclature developed by DuPont Dow Elastomers, as listed in Table 2.2. HFP levels in these commercial polymers were chosen to be high enough to avoid significant crystallinity, but were kept as low as possible to get reasonable low-temperature flexibility and processing characteristics. All these polymers can be cured with the versatile bisphenol cure system, which gives good processing characteristics and excellent vulcanizate properties. These fluoroelastomers are recommended for use in contact with aromatic hydrocarbons, chlorinated solvents, gasoline, motor oils, and hydraulic fluids. Products with high fluorine content are useful in contact with alcohol-containing fuels. Good resistance to hot water, steam, and acids can

VDF/PMVE/TFE GLT

54

64

-29

GFLT

36

67

-23

Figure 2.4 Ternary diagram showing all the possible polymer compositions based on VDF, PMVE, and TFE monomers.

2 FLUOROELASTOMER COMPOSITION AND PROPERTIES

2.3

VDF/PMVE/TFE Elastomers

The ternary diagram, Fig. 2.4, shows all the possible polymer compositions based on VDF, PMVE, and TFE monomers. The elastomeric range is much more extensive for this system, since amorphous polymers with low Tg can be obtained with low, or no, VDF content. Two VDF-containing commercial products, Viton GLT and GFLT, are indicated on the ternary plot and listed in Table 2.2. The terpolymers cannot be cured satisfactorily with bisphenols; instead, small amounts of bromine or iodine cure sites are incorporated to allow peroxide curing. Recently, a new class of VDF/PMVE/TFE products has been developed, with incorporation of a reactive cure-site monomer to allow bisphenol curing in special formulations.[5] Processing of the bisphenol-curable products is significantly improved over that of peroxide-cured versions, especially in facilitating efficient molding with extremely low mold fouling and parts rejection rates. Fluid resistance depends on VDF content, similar to that of HFP-containing elastomers. However, the PMVE-based fluoroelastomers have much better low-temperature characteristics than those of HFP-based polymers, as shown in Figs. 2.1, and 2.5, a plot of Tg versus VDF content.

Figure 2.5 VDF-based fluoroelastomers: Tg vs % VDF.

17 Low-temperature characteristics of fluoroelastomers are often assessed by relatively simple tests, such as Tg of raw polymer, TR-10 of cured strips, or brittle point (temperature at which a sample cracks on bending). Such tests provide only a rough indication of usefulness of the materials in actual applications. While difficult and time-consuming to measure precisely, o-ring seal performance at low temperature has been evaluated for a number of fluoroelastomers.[6] Using a specially designed o-ring seal rig, the temperature at which nitrogen under pressure started to leak appreciably was recorded. Seal test results are shown in Fig. 2.6, in comparison to screening tests on fluoroelastomers of various compositions. Minimum temperatures for effective sealing are significantly lower than Tg or TR-10 values, and generally somewhat higher than brittle points.

2.4

TFE/PMVE Perfluoroelastomers

Copolymers of TFE with 25–40 mole % perfluoroalkyl vinyl ether are elastomeric. With properly chosen cure systems, they may have oxidative, chemical, and thermal resistance approaching that of polytetrafluoroethylene plastics. Copolymers of

18

FLUOROELASTOMERS HANDBOOK

Figure 2.6 Low-temperature properties of VDF-based fluoroelastomers.[6]

TFE and PMVE containing about 45% PMVE are amorphous and have glass transition temperatures of about –4°C, as shown as Kalrez in Fig. 2.4 and FFKM in Fig. 2.5. Cure systems developed by DuPont[7] use perfluorinated cure-site monomers to get vulcanizates stable for extended service at 300°C and resistant to most aggressive fluids. The most successful of these cure sites are formed by copolymerizing about 1 mole % of functional vinyl ether of general structure: CF2=CF–O–RFX, with RF denoting perfluoroalkylene and X a functional group, OC6F5 or O(CF2)nCN. Copolymers with perfluorophenyl cure sites are crosslinked with a specially designed bisphenol system. Those with pendant cyano groups are cured using tetraphenyltin as catalyst to form highly stable triazine crosslinks.[8] Relatively long press cures followed by long postcures in an oven under nitrogen are necessary to attain the final stable crosslink structures of the finished parts. These copolymers are made by emulsion polymerization using an inert perfluorinated soap. Reaction temperatures must be kept low to get intact

incorporation of the functional vinyl ether cure-site monomers. The persulfate-sulfite redox initiation system used by DuPont for the first perfluoroelastomer products gave predominantly sulfonate end groups which form ionic associations stable at temperatures normally used for mixing, extruding, and forming molded shapes. Thus they could not be processed readily like other fluoroelastomers. Because of this, DuPont developed specialized handling methods for making parts (mainly o-ring seals) sold as Kalrez Perfluoroelastomer Parts®. Later products developed by DuPont Dow and other producers are made with other initiator systems to get more tractable elastomers processible by conventional means. Iodine or bromine cure sites have been incorporated in perfluoroelastomers by use of suitable comonomers or transfer agents. These polymers can be cured with conventional peroxide systems using multifunctional crosslinking agents such as triallylisocyanurate. The resulting vulcanizates retain most of the fluid resistance of the perfluoroelastomer parts

2 FLUOROELASTOMER COMPOSITION AND PROPERTIES previously described, but peroxide-cured products have lower thermal resistance (maximum long term service temperature about 230°C) and are susceptible to attack by strong oxidizing agents. To get better low-temperature flexibility (Tg about –20°C), Daikin[9] developed peroxide-curable perfluoroelastomers based on TFE copolymerization with complex vinyl ethers of structure CF2=CF[OCF 2– CF(CF3)]nOCF2–CF2–CF3 with n = 1–4. These products are sold as raw polymer for conventional processing by parts fabricators. In spite of high cost, perfluoroelastomers are used in many applications where other materials are unsatisfactory. In the chemical processing industries, perfluoroelastomers provide reliable seals against most fluids over a wide range of conditions. Such high performance results in lower costs for seal replacement and in avoiding emission of hazardous materials. Perfluoroelastomers are finding increased use as seals in semiconductor fabrication lines, since these materials withstand exposure to plasmas and other aggressive fluids at high temperatures without contamination of the semiconductor parts. One of the first uses of perfluoroelastomers was in parts to protect electrical components used in oil field exploration and production. These parts withstand the high temperatures and pressures involved in deep wells, as well as aggressive sour gas and corrosive fluids. Perfluoroelastomer seals are used in aerospace and in military and commercial aircraft. Because of their inertness and cleanliness, perfluoroelastomers are approved for seals in the food and pharmaceutical industries. To assure adequate performance of perfluoroelastomers seals at temperatures up to 300°C above ambient, special design considerations must be taken into account. Perfluoroelastomers have high coefficients of thermal expansion, and their compounds contain relatively low levels of filler, so seal groove geometry has to allow adequate space for the elastomer to expand at high temperatures. If the grooves are too small, seal failure may occur by extrusion of the elastomer out of the groove, or by cracking due to local strains exceeding the elongation-at-break of the elastomer. DuPont Dow Elastomers offers finite element analysis to fabricators as an aid to designing proper shapes of the perfluoroelastomer parts and the seal apparatus for specific applications.

19

2.5

TFE/P Elastomers

Because of the strong alternating tendency of TFE and propylene monomers in free radical polymerization, the dipolymers vary little in composition. Commercial TFE/P elastomers are made slightly rich in TFE (about 53 mole %) to avoid contiguous propylene units that would tend to give lower thermal stability. The regular alternating chain structure, –[CF2–CF2–CH2–CH(CH3)]n–, is elastomeric because the random orientation of methyl groups from nonstereospecific incorporation of propylene prevents crystallization. However, glass transition temperature is relatively high, near 0°C, so the elastomer has mediocre low-temperature flexibility. The low fluorine content (about 55%) leads to poor resistance to hydrocarbons, especially aromatic solvents. Since the hydrogen-bearing carbon atoms are adjacent to only one fluorine-bearing carbon (rather than two as in VDF-containing polymers), TFE/P copolymers are nonpolar. Thus the elastomer is highly resistant to polar solvents and to dehydrofluorination by base or amines. With its good electrical resistivity, the nonpolar dipolymer has found considerable application in wire and cable insulation. Asahi Glass developed a thermal treatment process to obtain enough active sites for curing with peroxide and radical trap crosslinking systems.[10] Processing characteristics of TFE/P compounds are inferior to those of VDFcontaining fluoroelastomers, so the elastomer is used only in situations where resistance to base or polar fluids is required. Incorporation of small amounts of potential cure-site monomers (e.g., monomers containing bromine or iodine) in TFE/P elastomers has not led to practical cures. Various terpolymers of TFE and propylene with 10%–40% VDF have been developed to get better processing and curing characteristics, as well as high fluorine content for better hydrocarbon resistance. Terpolymers with TFE/P mole ratio about 1.5 contain about 59% fluorine and are curable with bisphenol if VDF content is above 10%.[11] Such terpolymers are more polar in nature, so base resistance is significantly reduced compared to the dipolymer. However, resistance to automotive lubricants containing amine moieties at high temperature is greater than that of VDF/HFP/TFE fluoroelastomers. TFE/P/VDF terpolymers containing 30% or more VDF have better low-temperature flexibility (Tg about –15°C) than dipolymers.

20

FLUOROELASTOMERS HANDBOOK

Recently, copolymers of TFE and propylene with relatively low levels (3%–5%) of trifluoropropylene, CH2=CH–CF3, have been developed.[12] These can be cured with bisphenol systems, and have fluid and base resistance similar to that of TFE/P dipolymer.

2.6

E/TFE/PMVE Elastomers

To get better resistance to polar fluids and bases than that of VDF/HFP/TFE and VDF/PMVE/TFE elastomers, and better low-temperature flexibility and resistance to hydrocarbons than that of TFE/P polymers, elastomeric copolymers (ETP) of ethylene with TFE and PMVE were developed.[13] The useful elastomeric range for this monomer combination is approximately 10–40 mole % ethylene units, 20–40 mole % PMVE units, and 32–60 mole % TFE units. Higher ethylene or lower PMVE contents lead to increased Tg and crystallinity. Glass transition temperatures are higher, about –5°C to –15°C, for the range of E/TFE/PMVE compositions noted than for VDF/TFE/PMVE elastomers of similar fluorine content. Because of the strong alternating tendency of olefins with perfluorinated monomers in free radical polymerization, ethylene is incorporated as isolated units flanked by TFE or PMVE units. Typical monomer sequences are shown in Fig. 2.7 for ETP and GFLT, a VDF/TFE/PMVE elastomer. The polymers have 67% fluorine content and es-

sentially the same elemental content. The change from sequences of contiguous VDF units to E-TFE dyads leads to higher Tg by about 10°C, and to much enhanced resistance to polar solvents and to chemical attack by base or amines. Various cure-site monomers have been studied for ETP curing. Commercial products are based on bromine cure sites that allow conventional peroxide curing with crosslinking agents such as triallyl isocyanurate or trimethallyl isocyanurate. Mechanical properties and thermal stability of such ETP vulcanizates are similar to those of similarly cured VDF-containing fluoroelastomers. Vulcanizate properties and environmental resistance of ETP are compared with other fluoroelastomers in Table 2.3, in tests chosen to show the different characteristics of the elastomers. ETP is compared with a bisphenolcured VDF/HFP dipolymer (A), a peroxide-cured high-fluorine VDF/HFP/TFE polymer (GF), and a peroxide-cured TFE/P dipolymer. Compared to VDF-containing elastomers, ETP has resistance to aliphatic and aromatic fluids similar to that of GF, but greatly superior resistance to polar fluids (e.g., ketones), base, and oil additives. Compared to TFE/ P, ETP has better low-temperature flexibility, similar resistance to base and amine-containing fluids, better resistance to aliphatic and aromatic fluids, and somewhat better resistance to polar fluids. All these fluoroelastomers swell more in fluids than perfluoroelastomers.

ETP: E/TFE/PMVE, 67% F –CF2–CF–CF2–CF2–CH2–CH2–CF2–CF2– | O–CF3 GFLT: VDF/TFE/PMVE, 67% F –CF2–CF–CH2–CF2–CH2–CF2–CF2–CF2– | O–CF3 Figure 2.7 Typical monomer sequences of ETP and GFLT.

2 FLUOROELASTOMER COMPOSITION AND PROPERTIES

21

Table 2.3 Properties of ETP vs Other Fluoroelastomers[14]

A VDF/HFP 66 2 Bisphenol

Polymer GF TFE-P VDF/HFP/TFE TFE/P 70 55 1 4 Peroxide Peroxide

Monomers %F %H Cure Original properties M-100, MPa 1.0 1.2 a T-B, MPa 16.3 19.8 b E-B, % 190 215 Hardness, Shore A 77 79 TR-10, ºC -17 -7 Brittle Point, ºC -20 -48 Heat Aged 70 h at 250ºC T-Ba change, % -4 4 b E-B change, % -3 0 Hardness change, points 1 1 Aged 168 h at 150ºC in EP Gear Lube T-Ba change, % -36 -53 b E-B change, % -58 -56 Hardness change, points 7 2 Volume increase, % 1 3 Aged 168 h at 40ºC in toluene T-Ba change, % -41 -27 b E-B change, % -21 -2 Hardness change, points -10 -10 Volume increase, % 23 11 Aged 168 h at 23ºC in methyl ethyl ketone T-Ba change, % -92 -86 b E-B change, % -79 -77 Hardness change, points -42 -38 Volume increase, % 222 183 Aged 168 h at 100ºC in 30% potassium hydroxide T-Ba change, % -94 -93 b E-B change, % 58 -44 Hardness change, points -47 -49 Volume increase, % 132* 12*

*Samples breaking up. a

T-B = Tensile strength-at-break. b E-B = Elongation-at-break.

ETP E/TFE/PMVE 67 1 Peroxide

0.7 17.1 255 73 2 -58

1.4 15.4 205 82 -11 -34

-16 10 -1

0 17 0

-8 10 -5 6

-6 15 -1 3

-66 -43 -35 64

-21 7 -8 9

-66 -47 -34 77

-34 5 -17 19

12 10 -1 1

-8 29 -3 6

22

FLUOROELASTOMERS HANDBOOK

REFERENCES 1. Ferguson, R. C., J. Amer. Chem. Soc., 86:2003 (1964) 2. Schmiegel, W. W., Die Angewandte Makromolekulare Chemie, 76/77:39–65 (1979) 3. England, D. C., Uschold, R. E., Starkweather, H., and Pariser, R., “Fluoropolymers: Perspectives of Research,” Proc. The Robert A. Welch Conferences on Chemical Research XXVI: Synthetic Polymers, Houston, Texas (1982) 4. Ebnesajjad, S., Fluoroplastics – Volume 1: Non-Melt Processible Fluoroplastics (2000), and Volume 2: Melt Processible Fluoroplastics (2002), Plastics Design Library, William Andrew Inc., Norwich, N.Y. 5. Bowers, S., and Thomas, E. W., “Improved Processing Low Temperature Fluorohydrocarbon Elastomers,” ACS Rubber Division meeting (Oct 17–20, 2000) 6. Stevens, R. D., Thomas, E. W., Brown, J. H., and Revolta, W. N. K., “Low Temperature Sealing Capabilities of Fluoroelastomers,” SAE International Congress and Exposition, Detroit, Michigan (Feb 26 – March 2, 1990) 7. Logothetis, A. L., “Fluoroelastomers,” in; Organofluorine Chemistry: Principles and Commercial Applications, p. 389, (R. E. Banks, et al., eds.), Plenum Press, New York (1994) 8. Breazeale, A. F., U.S. Patent 4,281,092, assigned to DuPont Co. (Jul 28, 1981) 9. Amano, T., and Tatemoto, M., U.S. Patent 4,487,903 (1984) 10. Morozumi, M., Kojima, G., and Abe, T., U.S. Patent 4,148,982, assigned to Asahi Glass Co. Ltd. (Apr 10, 1979) 11. Grootaert, W. M. A., and Kolb, R. E., U.S. Patent 4,882,390, assigned to Minnesota Mining and Manufacturing Co. (Nov 21, 1989) 12. Bauerle, J. G., and Schmiegel, W. W., U.S. Patent Application Publication No. U.S. 2003/0065132 (Apr 3, 2003) 13. Moore, A. L., U.S. Patent 4,694,045, assigned to DuPont Co. (Sep 15, 1987) 14. Stevens, R. D., and Moore, A. L., “A New, Unique Viton® Fluoroelastomer With Expanded Fluids Resistance,” ACS Rubber Division, Cleveland, Ohio (Oct 21-24, 1997)

Part II Fluoroelastomers Technology

3 Fluoroelastomer Monomers 3.1

Introduction

range of monomer mixtures is a major consideration for fluoroelastomers producers.

The major fluorinated monomers for fluoroelastomers are the same as those used for fluoroplastics. Production volumes of fluoroplastics, and thus of their monomers, are much higher than the volumes of fluoroelastomers. This allows the supply of modest amounts of monomers for fluoroelastomers at reasonable cost. Most producers of fluoroelastomers are also producers of fluoroplastics, or allied with these suppliers. Vinylidene fluoride (VDF) accounts for about half the volume of monomers used for fluoroelastomers. Tetrafluoroethylene (TFE) and hexafluoropropylene (HFP) are the other main fluorinated monomers in fluoroelastomers. Perfluoro(methyl vinyl ether) (PMVE), used in specialty fluoroelastomers, is not used in fluoroplastics, but can be made in facilities used for manufacturing the perfluoro(alkyl vinyl ethers) (PEVE and PPVE), monomers used in fluoroplastics. A number of curesite monomers and fluorinated chain-transfer agents are also made in low volumes for specialty fluoroelastomers. Safe handling of these monomers and a wide

3.2

Vinylidene Fluoride (VDF)

Vinylidene fluoride is incorporated at levels of 50 to 80 mole % (30 to 65 weight percent) in the major family of copolymers with hexafluoropropylene and tetrafluoroethylene, and at similar levels in the specialty family of copolymers with perfluoro(methyl vinyl ether) and tetrafluoroethylene. In both families, VDF contributes to low glass transition temperatures to allow good elastomeric behavior. Long sequences of VDF units would lead to undesired crystallinity.

3.2.1

VDF Properties

Vinylidene fluoride (VDF), CH2=CF2, is flammable and is a gas at room temperature. Physical properties of vinylidene fluoride are presented in Table 3.1. It is colorless and almost odorless and

Table 3.1 Properties of Vinylidene Fluoride[1]

Property

Value

Molecular weight

64.038

Boiling point, °C

-84

Freezing point, °C

-144

Vapor pressure at 21°C, kPa

3,683

Critical pressure, MPa

4.434

Critical temperature, °C

30.1

Critical density, kg/m3

417

Heat of formation at 25°C, kJ/mole

-345.2

Heat of polymerization at 25°C, kJ/mole

-474.2

Explosive limits, vol % in air

5.8-20.3

Solubility in water, cm3/100 g at 25°C at 10 kPa

6.3

Activation energy of polymerization, Eo, kJ/mole

161

26

FLUOROELASTOMERS HANDBOOK

boils at –84°C. Vinylidene fluoride can form explosive mixtures with air. Polymerization of this gas is highly exothermic and takes place above its critical temperature and pressure. Propagation rates of VDF with itself and other fluorinated monomers are high, facilitating high production rates of VDF-containing fluoroelastomers.

3.2.2

VDF Synthesis

There are numerous ways to prepare vinylidene fluoride (VDF) which is the main monomer for polyvinylidene fluoride homopolymers and copolymers. A number of these methods are based on dehydrohalogenation of halohydrocarbons. Examples include dehydrobromination of 1-bromo-1,1-difluoroethane[2] or dehydrofluorination of 1,1,1-trifluoroethane.[3][4] Two methods, including the popular commercial technique for VDF production, are described here. Conversion of 1,1,1-trifluoroethane[3] begins by passing this gas through a platinum-lined Inconel tube, which is heated to 1,200°C. Contact time is about 0.01 seconds. The exit gases are passed through a sodium fluoride bed to remove the hydrofluoric acid and are then collected in a liquid nitrogen trap. Vinylidene fluoride (boiling point –84°C) is separated by low temperature distillation. Unreacted trifluoroethane is removed at –47.5°C and is recycled. The effect of temperature and contact time is illustrated in Table 3.2, clearly favoring the high temperature process.

Table 3.2 Effects of Contact Time and Temperature on Vinylidene Fluoride Yield from Dehydrofluorination of 1,1,1-Trifluoroethane[3]

Variable

Case 1

Case 2

Temperature, °C

1,200

800

Contact time, s

0.01

4.4

Space velocity, 1/h

9,700

200

Total conversion, mole %

75.4

76

Conversion to vinylidene fluoride, mole %

74

66

Vinylidene fluoride yield, %

98.1

86.5

By-products yield, %

1.9

13.5

CH3–CF3 → CH2=CF2 + HF The commercial method begins with hydrofluorination of acetylene followed by chlorination,[5] by hydrofluorination of trichloroethane,[6] or by hydrofluorination of vinylidene chloride.[7] In each case the final product, 1-chloro-1,1-difluoroethane, is stripped of a molecule of hydrochloric acid to yield VDF. The following one-step reaction scheme is shown for vinylidene chloride as the starting ingredient: CH2=CCl2 + 2HF → CH3–CClF2 + HCl CH3–CClF2 → CH2=CF2 + HCl A mixture of vinylidene chloride (VC2) and hydrofluoric acid is passed through a heated catalyst bed. The catalyst is prepared by heating CrCl3·6H2O under vacuum to 300°C until it changes color from dark green to a solid violet throughout the porous mass. In this operation, crystallization water is removed (35% weight loss). The cooled mass is comminuted and screened into particles of 2–5 mm diameter that are loaded into a cylindrical reactor and heated to the reaction temperature (250°C–350°C). The resulting gases are condensed and vinylidene fluoride (boiling point –84°C) is separated by low temperature distillation. Table 3.3 provides yield information for a few different reaction conditions. It appears that nearly a 100% yield can be achieved in Case 3. In another one-step process,[8] a mixture of vinylidene chloride and hydrofluoric acid is heated to 400°C–700°C in the presence of oxygen and a catalyst. Aluminum fluoride, alone or in combination with a transition metal such as cobalt, chromium, nickel, zinc or their combinations, is the catalyst for the reaction.

3.3

Tetrafluoroethylene (TFE)

Tetrafluoroethylene is incorporated at up to 30 mole % in VDF-containing fluoroelastomers. Partial replacement of VDF with TFE in these copolymers results in higher fluorine content and thus greater fluid resistance. In perfluoroelastomers and in fluoroelastomers containing olefins, TFE is incorporated at higher levels, some 40 to 70 mole %.

3 FLUOROELASTOMER MONOMERS

27

Table 3.3 Effect of Contact Time and Temperature on Vinylidene Fluoride Yield from Hydrofluorination of Vinyl Chloride[7]

Variable

Case 1

Case 2

Case 3

Case 4

Temperature, °C

345

330

290

250

Space velocity, 1/hr

300

155

200

200

Mole ratio VC2:HF

1:4.7

1:2.7

1:5.3

1:4.7

Vinylidene fluoride yield, %

97.0

96.5

99.8

95.0

3.3.1

TFE Properties

Table 3.4 lists the properties of tetrafluoroethylene. It is a colorless, odorless, tasteless, nontoxic gas that boils at –76.3°C and freezes at –142.5°C. Critical temperature and pressure of tetrafluoroethylene are 33.3°C and 3.92 MPa. TFE is stored as a liquid; vapor pressure at –20°C is 1 MPa. Its heat of formation is reported to be –151.9 kcal/mole. Polymerization of tetrafluoroethylene is highly exothermic and generates –41.12 kcal/mole heat. The extent of the exothermic nature of TFE polymerization can be seen when it is compared with the polymerization of vinyl chloride and styrene, which have heats of polymerization of 23–26 and 16.7 kcal/mole, respectively. A complete description of explosive hazards of tetrafluoroethylene can be found in Ref.10. Safe storage of TFE requires its oxygen content to be less than 20 ppm. A great deal of research has been devoted to safe handling of tetrafluoroethylene. [11] Temperature and pressure should be controlled during its storage. Increasing temperature, particularly at high pressures, can initiate deflagration in the absence of air. In the presence of air or oxygen, TFE forms explosive mixtures. Detonation of a mixture of tetrafluoroethylene and oxygen can increase the maximum pressure to 100 times the initial pressure.[12] Tetrafluoroethylene undergoes free radical addition reactions typical of other olefins. It readily adds Br2, Cl2, and I2, halogen halides IBr and ICl, and nitrosyl halides such as NOCl and NOBr.[13][14] Addition reactions of chlorofluoromethanes and chloromethanes in presence of catalysts like aluminum chloride have been reported.[15] A variety of

other compounds such as alcohols, primary amines, and ammonia can be reacted with tetrafluoroethylene to prepare tetrafluoroethers (HCF2CF 2OR), difluoroacetamides (HCF2CONHR), and substituted triazines.[16] Oxygen can be added to TFE to produce polymeric peroxide[17] or tetrafluoroethylene epoxide.[18] In the absence of hydrogen, sodium salts of alcohols will react with TFE to yield trifluorovinylethers (ROCF=CF2) which can be homo- and copolymerized.

3.3.2

TFE Synthesis

It is difficult to establish exactly the first successful synthesis of tetrafluoroethylene. Publications in the 1890s report a variety of attempts to synthesize TFE by direct reaction of fluorine with carbon, fluorine with chloromethanes, and tetrachloroethylene with silver fluoride.[19]–[22] The data presented are insufficient to determine that these efforts actually lead to TFE. Humiston[23] reported the first documented preparation of TFE in 1919 which has been disputed because of erroneous property data. The first reliable and complete description of synthesis was published in 1933 by Ruff and Bretschneider,[24] who prepared TFE from decomposition of tetrafluoromethane in an electric arc. Separation of TFE from the pyrolysis products was accomplished by bromination followed by dehalogenation with zinc. Numerous other papers have reported synthesis of tetrafluoroethylene. The works that report commercially significant techniques for TFE preparation list fluorspar (CaF2 ), hydrofluoric acid, and chloroform as the starting ingredients.[25]–[32] The reaction scheme is shown below:

28

FLUOROELASTOMERS HANDBOOK

Table 3.4 Properties of Tetrafluoroethylene[9]

Property

Value

Molecular weight

100.02

Boiling point at 101.3 kPa, °C

- 76.3

Freezing point, °C

- 142.5

Liquid density vs. temperature (°C), g/mL - 100 < t 10, Y is ~ 1.1, indicating r1 ~ 0.01 for TFE. The monomer pair VDF and TFE appears to approximate the case r1r2 = 1. Substitution of 1/r1 for r2 in the copolymer composition equation (Eq. 4.10) leads to Y = r1 X, indicating that the monomer ratio in the polymer is directly proportional to the ratio of unreacted monomer, so-called random copolymerization. VDF/TFE copolymers are crystalline plastics with melting points varying with composition. Terpolymers with relatively high TFE content (45%–65%) and low HFP content (15%–20%) are sold by Dyneon as flexible thermoplastics with melting points 120°C–180°C. In elastomeric terpolymers of VDF and TFE with HFP or PMVE, the reactivity ratios of HFP or PMVE with respect to either VDF or TFE can be considered as near zero. Thus units of HFP or PMVE are usually isolated between mixed sequences of VDF and TFE units.

4.4

Emulsion Polymerization

Essentially all fluorocarbon elastomers are produced commercially by emulsion polymerization, depicted schematically in Fig. 4.2. As previously described, polymerization occurs in monomer-swollen polymer particles some 100 to 1000 nanometers (nm) in diameter, not in a liquid-liquid emulsion as implied by the name. Particles are stabilized by surfactant,

Table 4.2 Mass Balance on TFE/PMVE Monomer with a Small Amount of BTFE Cure-site Monomer

Monomer Monomer: TFE (1)

Feed g/h 260

Unreacted g/h mol/h 14 0.14

g/h 246 183

1.10

41.8

30.4

2.0

1.6

0.71

Polymer mol/h wt % 2.46 56.2

Monomer: PMVE (2)

300

117

Monomer: BTFE

10

1

9

0.06

Total

570

132

438

3.62

mol % 68.0

42

FLUOROELASTOMERS HANDBOOK Eq. (4.15)–O3SO– OSO3– → 2 •OSO3– The rate of decomposition is determined mainly by temperature, but is also somewhat dependent on pH. Fluoroelastomer polymerization is usually carried out at relatively low pH (~ 3–6), and the first order thermal decomposition rate coefficient kd (min-1) is given in the Arrhenius form as[10]

Eq. (4.16) Figure 4.2 Emulsion polymerization.

either added or made in situ by polymerization in the aqueous phase. A water-soluble initiator system generates free radicals, some of which grow and form or enter particles. In most fluoroelastomer polymerization systems, there is no sizeable reservoir of liquid monomer present. Much of the monomer is dissolved in the polymer particles, and is replenished by a continuous feed during the polymerization. Even in semibatch polymerization, the amount of monomer in the reactor vapor space is relatively small. The segregation of growing radicals in small particles under conditions of limited termination by incoming radicals allows attainment of the high molecular weights desired for good elastomeric properties. Especially for VDF-based fluoroelastomers, emulsion systems allow very high productivity in reactors of modest size.

E  k d = A exp a   RT   − 17070  = 5.62 × 1018 exp   T 

In this equation, the factor A is in units min-1, activation energy Ea is in cal/mole, gas constant R = 1.987 cal/mole K, and absolute temperature T is in kelvin. With the high activation energy Ea = –33,900 cal/ mol, the rate of decomposition of persulfate is quite sensitive to temperature (Table 4.3). At temperatures below about 80°C, persulfate decomposition is slow, so relatively high initiator concentrations would be necessary to get reasonable radical generation rates. Instead various redox initiator systems may be used. Sulfite is a typical reducing agent that reacts rapidly with persulfate to generate two types of radicals: Eq. (4.17)

–O

3SO–OSO3

–

+ SO32–

→ SO42– + •SO3– + •OSO3–

4.4.1

Emulsion Polymerization Kinetics

Recent work by R. G. Gilbert[9] and coworkers at Sydney University and DuPont has greatly clarified the various complicated steps involved in emulsion polymerization, allowing development of improved kinetics models and setting of conditions to get polymer structures desired for commercial applications. Polymerization mechanism. In emulsion polymerization, a water-soluble initiator system forms free radicals in the aqueous phase. Typically, thermal decomposition of persulfate is used to generate radicals by symmetrical scission of the O– O bond of the anion:

Table 4.3 Thermal Decomposition of Persulfate[10]

Temperature, °C

103 kd, min-1

Half life, min

50

0.063

11,000 (184 h)

60

0.307

2,260 (38 h)

70

1.37

507 (8.4 h)

80

5.60

124 (2.0 h)

90

21.2

33

100

4.9

9

110

247

3

120

769

1

4 PRODUCTION OF FLUOROELASTOMERS At temperatures below 60°C, a small amount of a catalyst such as a copper salt may be added to increase the redox rate. In continuous polymerization, the components of the redox initiator system are fed to the reactor in separate streams. In semibatch polymerization at low temperature, persulfate is usually charged initially, and the reducing agent is added at a controlled rate to get the desired radical flux, twice the molar addition rate of sulfite times an efficiency factor. A considerable fraction of primary radicals may be lost by recombination with each other before monomer addition occurs to complete the initiation process. For VDF/TFE/HFP or PMVE elastomers, VDF and TFE are the most likely monomers to add to primary initiator radicals. For initiation with sulfate ion radicals, the following reactions would be typical: Eq. (4.18)

CH2=CF2 + •OSO3– → •CF2– CH2– OSO3–

Eq. (4.19)

CF2=CF2 + •OSO3– → •CF2– CF2–OSO3–

Perfluorinated sulfate end groups are likely to hydrolyze to carboxylate ends at polymerization conditions: Eq. (4.20)

•~CF2– CF2– OSO3– + 2 H2O → •~CF2– COO– + H2SO4 + 2 HF

The generation of sulfuric and hydrofluoric acids by hydrolysis reactions usually necessitates addition of a base or buffer to keep the pH above 3. Initiation with •SO3– leads to formation of sulfonate end groups, e.g.: Eq. (4.21)

CF2=CF2 + •SO3– → •CF2– CF2– SO3–

Unlike perfluorinated sulfate end groups, perfluorinated sulfonate ends are resistant to hydrolysis. These small radicals propagate further in the aqueous phase, reacting with the small amount of dissolved monomer present. Because polymer particles are stabilized by adsorbed anionic surfactant

43 and also carry surface charge from ionic end groups of polymer, growing radicals in the aqueous phase must add several monomer units (say, 3 to 5) to become surface active and hydrophobic enough to overcome the electrostatic surface barriers and enter particles. With this delay in entry, small radicals may undergo other reactions (e.g., termination reactions) such as: Eq. (4.22) •CF2– CH2– CF2– CH2– OSO3– + •CF2– CH2– CF2–CH2–CF2–CH2–OSO3– → –O3SO– (CH2– CF2)2– (CF2CH2)3– OSO3– The resulting combination products may serve as effective surfactants to stabilize particles. Depending on initiator level, little or no added surfactant may be necessary for adequate stabilization of dispersions of VDF copolymers. Note that if, instead of VDF or TFE, other less reactive monomer units such as HFP or PMVE add to these short radicals, termination becomes more likely than further propagation. Transfer to an active water-soluble species may result in a nonionic radical (e.g., transfer with isopropyl alcohol): Eq. (4.23) •CF2– CH2– OSO3– + (CH3)2CHOH → HCF2– CH2– OSO3– + (CH3)2C •OH Presumably, such a polar, uncharged radical would need to add only one or two monomer units to become hydrophobic enough to enter a particle. With all these possible aqueous-phase reactions, the fraction of primary radicals generated that grow and enter particles to continue growth to high polymer may be rather low (0.2–0.6), especially at high initiator levels. Once a radical enters a particle, it propagates rapidly by addition of monomer dissolved in the particle at much higher concentration than present in the aqueous phase. In some systems (e.g., TFE/ PMVE), high added soap levels give a large number of small particles (say, 200 nm in diameter) highly swollen with 20%–30% monomer. It is likely that the ideal emulsion 0,1 polymerization case prevails

44 here. That is, each particle contains only one or no growing radical at any time. No more than one radical at a time propagates in such a small particle; entry of a second radical leads to rapid termination, with no radical activity until another radical enters to restart polymerization. At the other extreme are most VDF copolymer systems. Here, very low added soap levels give a small population of large particles (500–1000 nm diameter) with relatively low concentration of dissolved monomer (about 10%). In these highly viscous particles, the mobility of long-chain radicals is so low that termination rates are drastically reduced. Only very small radicals entering from the aqueous phase or formed by transfer reactions are effective in terminating long chains. A large number of growing radicals (10 or more) may coexist in such large particles. Radical lifetimes may be quite high in such systems, so polymerization rates and molecular weights may be high. Typically, transfer agents are used to control molecular weights. Soaps used in the emulsion polymerization of fluoroelastomers are usually fully or partially fluorinated anionic surfactants. Efficacy at low concentrations and high water solubility are desirable to get low residual soap levels in isolated polymer. Soaps should be unreactive to radicals at polymerization conditions, to avoid excessive transfer and attachment of ionic soap moieties to polymer chain ends. Perfluoroalkyl carboxylates or sulfonates with 8- or 9-carbon alkyl chain lengths are inert and effective dispersion stabilizing agents. Ammonium perfluorooctanoate has been preferred for many fluoroelastomer emulsion systems. However, this stable soap is persistent in the environment and is not readily eliminated from the body after exposure. A major supplier (3M Co.) has stopped its production, and its use in fluoropolymer production is being phased out or reduced. A number of partially fluorinated soaps are effective, especially for VDF copolymers. These are usually of the structure F– (CF2– CF2)n–CH2– CH2– X–M+, with n = 2–8 (mostly 3–4); – X– may be sulfate, phosphate, or sulfonate, and M+ is H+, NH4+, or an alkali metal ion. The sulfate and phosphate forms are highly effective,[11] but may participate in unwanted transfer reactions. Recently, a particular partially fluorinated alkyl sulfonate form, F–(CF2– CF2)3– CH2– CH2– SO3–Na+, has been found to be a good replacement for ammonium perfluorooctanoate in many fluoroelastomer emulsion polymerization systems, both semibatch and con-

FLUOROELASTOMERS HANDBOOK tinuous.[12] This soap is effective as a dispersion stabilizer, inert to radical attack by transfer, and readily removed during polymer isolation. Polymerization rate Rp in an emulsion system can be represented as:

Eq. (4.24)

Rp =

k p [M ]N p nr M o NA

In this relationship, kp is the overall propagation rate coefficient in the particles; [M] is the molar monomer concentration in a particle; Np is the total number of particles; nr is the average number of radicals per particle; Mo is the average monomer molecular weight; and NA is Avogadro’s number (6.022 × 1023). Note that kp[M ]Mo may be applied to a copolymer using average values for a particular composition. For most systems of interest, available data are insufficient to evaluate key parameters in the rate expression. The number of particles and the average number of radicals per particle are particularly difficult to determine. Factors that affect the number of particles are considered in the next section on particle nucleation. Particle formation mechanisms. Most studies of emulsion polymerization are based on batch polymerization of a liquid monomer, so particle formation and growth are treated as occurring in three distinct intervals:[13] I. Particle nucleation period: characterized by presence of monomer droplets and soap micelles, with formation of particles that grow in number and size. Polymerization rate Rp increases. II. Particle growth period: monomer droplets are present, but no micelles; particle number is constant, particle size grows. Rp is steady or increases. III. Final stage: monomer is consumed, so Rp decreases with decreasing monomer concentration in particles. This is not an adequate picture of the fluoroelastomer emulsion polymerization processes. These are semibatch or continuous polymerizations in which monomer composition and concentration in particles are kept essentially constant by continuous feed of monomer to the reactor. No large reservoir of reactive monomer is present. Thus, only modified forms of

4 PRODUCTION OF FLUOROELASTOMERS intervals I and II exist in semibatch polymerization, and nucleation and growth stages coexist in continuous polymerization. For most fluoroelastomer systems, polymerization ceases when fresh monomer feed is stopped. The composition of unreacted monomers in the reactor, while necessary to set the copolymer composition, is not usually reactive enough toward propagation to support appreciable polymerization rates. In his analysis of particle formation, Gilbert[14] notes that a short radical formed from initiator with monomer addition must meet one of three fates: aqueous-phase termination, entry into a particle, or forming a new particle. Entry into a particle can occur when a sufficient degree of polymerization (number of monomer units added to an initiator fragment) denoted as z is reached so that the radical becomes surface active. Particle formation can occur when such a z-mer enters a micelle or when the radical grows to a sufficient longer degree of polymerization, jcrit , to homogeneously precipitate and nucleate to a precursor particle. Particle formation ceases when the number and size of particles reach levels such that all z-mer radicals are captured. Thus, two mechanisms of particle formation may occur: homogeneous nucleation in systems with soap levels below the critical micelle concentration (cmc), and micellar entry in systems above the cmc. Both particle formation mechanisms must be considered in fluoroelastomer polymerization systems. For VDF copolymers, the polymerizations are

45 characterized by low surfactant levels and high propagation rates at low monomer concentrations. In these systems, particle formation is by homogeneous nucleation. For most TFE copolymers containing no VDF (e.g., TFE/PMVE, TFE/P), soap levels are very high and propagation rates are low. Micellar entry may prevail as the major mode particle formation in these systems. Particle formation by homogeneous nucleation. Figure 4.3 illustrates steps in particle formation by homogeneous nucleation and coagulation as described by Gilbert.[15] After initiation by addition of a monomer unit to a primary ionic radical, the small radical may propagate in the aqueous phase. With ionic head groups such as sulfate, sulfonate, or carboxylate, these radicals are soluble in water when only a few monomer units (say, 1–3) have been added. Many are lost by mutual termination, becoming dead chains with one or two ionic head groups. Depending on their size, these may serve as surfactants to stabilize particles. When a sufficient number of units, z, have been added, a growing z-mer becomes surface active so that it can overcome the electrostatic surface barrier and enter a particle. A radical that propagates further to a critical length, jcrit , becomes insoluble in water, so it may coil and precipitate to form a precursor particle. Monomers enter such precursor particles, so the radicals may continue to grow. Precursor particles grow both by propagation and by co-

Figure 4.3 Particle formation by homogeneous-coagulative nucleation.[15]

46 agulation with other precursor particles, eventually becoming mature particles. Particles are stabilized by ionic end groups on their surfaces. These are from a combination of added surfactant, oligomeric surfactant formed in situ by aqueous phase termination of short radicals, and polymeric chains anchored in the particles. Ordinarily, the total of such ionic end groups is relatively low, since little or no soap is added and initiator levels may be low. Such dispersions usually have low particle number and large particle size. The first quantitative model of homogeneous nucleation was developed by Fitch and Tsai[16] and augmented by Hansen and Ugelstad[17] as HUFT theory. Coagulation of small particles was taken into account by Richards, Congalidis, and Gilbert,[18] using an extension of the standard DLVO model of colloid science.[19] This describes the coagulation of small particles stabilized by surface charge. Later versions of the model take better account of the variation of the number of particles with ionic strength.[20] Richards and Congalidis have developed proprietary models applicable to various DuPont products, including fluoroelastomers. Gilbert gives the general approach to formulation of such complicated models.[21] Particle formation by micellar entry. Figure 4.4 illustrates the micellar entry mechanism for particle formation, as described by Gilbert.[22] This mechanism is likely to prevail in systems with levels of added surfactant significantly higher than the critical micelle concentration. The initial steps are simi-

Figure 4.4 Particle formation by micellar entry.[22]

FLUOROELASTOMERS HANDBOOK lar to those for homogeneous nucleation, with formation of small radicals from initiator and monomer addition in the aqueous phase. When radicals reach the z-mer stage, they are readily incorporated into micelles. Even though a micelle is a dynamic moiety, with individual surfactant molecules residing in the micelle for only a short time, the micelle protects a growing radical from rapid termination with radicals in the aqueous phase. Also, the micelles solubilize monomers to facilitate rapid chain growth. Few radicals in the aqueous phase grow much longer than z-mer length before capture when micelles are present. Thus, homogeneous nucleation is unlikely when soap concentrations are well above the cmc. Micelles grow into mature polymer particles by radical propagation and coagulation with other particles. As the particle population and size grow, the surface area may become large enough to adsorb enough surfactant that the aqueous concentration falls below the cmc and micelles disappear. No new particles then can form by micellar entry, but homogeneous nucleation could occur when surfactant concentration falls to or below the cmc in the aqueous phase. Models that allow for both homogeneous nucleation and micellar entry generally predict a low particle number for soap concentrations below the cmc, then a large increase in the particle number as soap concentration is raised to and just above the cmc. However, most experimental data indicate a more gradual change in particle as the soap concentration is increased through the cmc. This suggests that,

4 PRODUCTION OF FLUOROELASTOMERS with homogeneous nucleation below the cmc, particles are more effectively stabilized against coagulation as surfactant concentration increases. Thus the particle number becomes relatively high as soap concentration is raised, well before the cmc is reached. Secondary nucleation. So-called secondary nucleation involves the formation of new particles in the presence of an established population of seed or previously formed particles. Gilbert[23] gives criteria for this situation. The number and size (thus the surface area) of established particles must be low enough that aqueous-phase radicals have sufficient probability of growing beyond the z-mer stage to jcrit size for nucleation. This case is important in continuous emulsion polymerization systems, which require continuing formation of new particles in the presence of a large number of particles present in the dispersion. Kinetics relationships. Complex models, such as those described by Richards, Congalidis, and Gilbert in Reference 20, can represent emulsion polymerization systems well, allowing extrapolation to conditions outside the range of available experimental data and providing insight into the effects of changing reaction variables. However, such models require considerable physical and kinetic data (e.g., solubilities of monomers in copolymers of varying composition over a range of temperatures and pressures, individual propagation rate coefficients and values of z and jcrit for oligomer entry and coagulation into particles). Such information has been obtained for only a few copolymers. Some parameter adjustment is usually necessary to fit experimental data. A particular difficulty seems to be prediction of both number-average molecular weight and particle number in a given system. It should be noted that both of these parameters are difficult to measure accurately so experimental error contributes considerably to differences from model predictions. In spite of the limited scope of the models developed so far, the models have helped workers understand the behavior of more complex terpolymer and tetrapolymer systems. Bonardelli, Moggi, and Russo[24] studied particle formation in the soapless emulsion polymerization of vinylidene fluoride (VDF) and hexafluoropropylene (HFP). Semibatch polymerizations were carried out in a five-liter reactor charged with 3.5 liters of water, using ammonium persulfate as initiator at

47 85°C with no added soap. Copolymer composition was held constant at a molar ratio VDF/HFP = 79/ 21, the same as most commercial dipolymers, by feeding this monomer mixture during polymerization. Reaction was stopped at 400 grams of polymer per liter of water (29% solids). Monomer concentration and initiator levels were varied in the study. Dispersion samples were taken during the polymerization for measurement of particle size by laser light scattering; the number of particles was calculated from average particle volume and total polymer formed. Experimental results were interpreted using Eq. (4.24), treating the constant copolymer composition as if it were a homopolymer. Monomer concentration [M] was expressed in terms of the product of average monomer fugacity fM and Henry’s Law constant H, so the rate equation becomes

Eq. (4.25)

Rp =

k p Hf M M o N p nr NA

It should be noted that the concentration of monomer in the aqueous phase as well as that in the polymer particles varies with monomer fugacity (or total monomer pressure). Thus, the aqueous oligomeric radical growth and polymerization rate in the particles are both affected by varying monomer fugacity. For this copolymerization system, Bonardelli and coworkers[24] observed very long nucleation periods, with the number of particles Np increasing up to about 200 grams polymer/liter (17% solids). The polymerization rate also increased during this period, corresponding to interval I. Nucleation periods were longer in experiments with lower monomer fugacity or higher initiator level. Even during interval II, when Np and Rp are essentially constant, further particle formation may occur if balanced by particle agglomeration. The polymerization rate Rp and final particle number Np in interval II varied about as expected with initiator concentration [I], with Rp ∝ [I]0.6 and Np ∝ [I]0.4. Variation with monomer fugacity was somewhat more difficult to explain, with Rp approximately second order in fugacity and final Np varying inversely with monomer fugacity. Bonardelli and coworkers account for this by noting that monomer concentration affects particle size and the number of radicals per particle nr. They rearrange Eq. (4.25) into the form

48

Eq. (4.26)

FLUOROELASTOMERS HANDBOOK

Rp N A Np fM

= k p HM o nr

This states that the polymerization rate per mole of particles divided by monomer fugacity is proportional to the number of radicals per particle. A plot of the left-hand side of Eq. (4.26) versus particle size indicates that nr is low and nearly constant at small particle size, but increases greatly with size at particle diameters above about 260 nm. At small sizes, particles would be expected to have either one or no radicals present because of rapid termination by incoming radicals, giving a 0,1 system with nr = 0.5. The more usual case for commercial VDF/HFP copolymerization with no soap (or low soap) is to have relative large particle sizes in the range 400 to 900 nm, and thus many radicals per particle. Consequently, we would expect a strong dependence of polymerization rate on monomer concentration in such systems. Also, initiation levels play a considerable role in determining rate and particle number. The hindered termination in large particles leads to significant broadening of molecular weight distribution in the absence of transfer agents. For production of commercial fluoroelastomers, empirical relationships are usually applied to estimate polymerization rates and to set and control polymer viscosities since most parameters in fundamental kinetics models are not known for most compositions. Polymerization rates may be correlated by equations of the form Eq. (4.27)

Rp = kp fMq ρ r(1 + S s)

Such equations may be applicable to VDF copolymerization with soap added at low concentration S. Monomer concentration may be represented by partial pressure or fugacity fM. An overall radical generation rate at 100% efficiency ρ is used, and an overall polymerization rate coefficient kp for the particular copolymer composition and reaction temperature. The usual ranges for the exponents are: q ~ 1–2, r ~ 0.5–0.7, and s ~ 0.4. It may also be necessary to incorporate additional factors to account for the effects of polymer concentration in the dispersion, or alternatively, for reaction time in a semibatch reactor or residence time in a continuous reactor. Ordinarily, Rp is known from experience and a commercial reactor is run at the same rate and

other conditions for a given product. Operating rates are often not set by kinetics, but are limited at lower levels because of other plant design constraints considered in Secs. 4.4.2 and 4.4.3. Relationships showing the dependence of polymer molecular weight or viscosity on reaction variables are of more use in setting and controlling fluoroelastomer properties. Number-average molecular weight Mn can be expressed as the ratio of polymerization rate (Rp g/h) to rate of chain formation (mol/h). For most fluoroelastomer emulsion systems, long chains are started and stopped by radical entry into particles (rate ρe), or by reactions with an added transfer agent (rate rtr). Ordinarily, transfer reactions with monomer, polymer, initiator, or adventitious impurities are negligible.

Eq. (4.28)

Mn =

Rp  ρe   + rtr   2 

A more convenient measure of molecular weight than Mn is desirable for routine monitoring of product. In most situations, molecular weight distribution is reasonably constant, and thus Mv/Mn can be assumed constant. For a given polymer composition and solvent, the limiting viscosity number or intrinsic viscosity [η] is related to viscosity-average molecular weight Mv by the Mark-Houwink equation:[25] Eq. (4.29)

[η] = K´ Mvα

For commercial VDF copolymers in a good solvent such as methyl ethyl ketone, the exponent α is in the range 0.55–0.75. A good approximation to [η] is the inherent viscosity or logarithmic viscosity number: Eq. (4.30)

ηinh = (ln ηr)/c

The relative viscosity ηr is measured as the ratio of solvent to solution efflux times in a capillary viscometer, with solution concentration c = 0.1 g/dL. The overall radical generation rate at 100% efficiency ρ is used instead of radical entry rate, so an empirical relationship for inherent viscosity then becomes

Eq. (4.31)

ηinh

Rp   =   K (ρ + 2rtr )

a

4 PRODUCTION OF FLUOROELASTOMERS

49

The parameters K and a can be determined for a given polymer composition by making a number of experimental polymerization runs at varying initiator levels without any transfer agents present. Equation (4.31) simplifies to

Eq. (4.32)

ηinh

 Rp   =   Kρ 

a

For analysis of experimental data, this can be put in the form

Eq. (4.33)

 Rp  log ηinh = a log  − a log K  ρ 

A plot of log ηinh versus log (Rp/ρ) has slope a, and K can be calculated from the intercept. With these parameters evaluated for a given copolymer composition, Eq. (4.32) can be used over a wide range of polymerization conditions with no transfer agent present. For the usual case of initiation by thermal decomposition of persulfate, ρ can be calculated from values of kd estimated from Eq. 4.16. To extend the correlation to include effects of transfer reactions, one must decide on an appropriate form to express the transfer rate rtr. The usual preference is for highly reactive transfer agents, so that transfer rate is proportional to feed rate of transfer agent Ftr. For VDF copolymers, transfer agents with active hydrogen are often used (e.g., low molecular weight alcohols, esters, or ketones). For such agents used at moderate levels at relatively high reaction temperatures (>100°C), Eq. (4.31) may be modified to the form

Eq. (4.34)

Rp   ηinh =    K (ρ + 2 K tr Ftr )

a

With K and a already evaluated as above for a system, experiments may be run with varying transfer agent feed rates to determine the transfer coefficient ktr. For evaluation of ktr from experimental data, Eq. 4.24 may be put in the form:

Eq. (4.35)

ηinh

−1 a

−

F Kρ = 2 Kk tr tr Rp Rp

The left-hand side of Eq. (4.35) is plotted versus Ftr /Rp to get a straight line (if the assumptions above hold), and ktr can be calculated from the slope. Polymerization conditions for which a given value of ktr applies are quite restricted. Transfer rates are not highly sensitive to temperature, so ktr may be approximately constant over a range of 10°C–20°C. However, transfer agents such as those listed above for VDF copolymers are soluble in both polymer particles and the aqueous phase. Thus, these agents distribute between phases, and the fraction in the polymer particles increases with increasing solids. Thus, Eq. (4.34) may apply to only a narrow range of dispersion solids. Alternatively, ktr will appear to vary with reaction time in a semibatch reactor or with residence time in a continuous reactor. For less reactive transfer agents that might be used in a semibatch reactor at low temperature, a correlation in the classical form[26] based on the ratio of transfer agent to monomer in polymer particles may be used to obtain transfer coefficients:

Eq. (4.36)

ηinh

−1 a

−

[T ] Kρ = C tr [M ] Rp

The applicability of these relationships for controlling product characteristics varies with the type of reactor system employed. Design, operation, and control of continuous and semibatch emulsion polymerization systems are considered in Secs. 4.4.2 and 4.4.3.

4.4.2

Continuous Emulsion Polymerization

DuPont pioneered VDF/HFP/(TFE) polymerization in continuous stirred tank reactors (CSTRs) in the late 1950s. An early version of a continuous fluoroelastomer production process, including isolation, is described by Bailor and Cooper.[27] Recent versions of the continuous emulsion polymerization process, as run by DuPont Dow Elastomers, feature more feed components, monomer recovery with continuous recycle of unreacted monomers, and considerably more monitoring and control systems. A schematic diagram of such a continuous polymerization system, including monomer recovery and recycle, is shown in Fig. 4.5. Details of monomer recovery are discussed in Sec. 4.7.

50 Continuous polymerization has the advantage of allowing sustained production at steady state. High rates are attained at moderately high dispersion solids (15%–30%). Most or all of the heat of polymerization is removed by the temperature rise of chilled feed water, so polymerization rates are not limited by relatively low rates of heat removal through a reactor cooling jacket. Continuous polymerization is particularly advantageous for production of a few high-volume types, especially if individual product campaigns are two days or more in length. After initial adjustments are made, uniform polymer can be produced at the same conditions for a considerable period. Continuous polymerization is less attractive for a product line comprising many types, requiring short campaigns with frequent reactor startups and shutdowns. Modern control systems allow rapid attainment of goal polymer characteristics and thus good quality even in this situation. However, semibatch systems are better suited to making product lines with many low-volume specialty types. The range of products suitable for a continuous emulsion polymerization process is somewhat restricted. Monomer compositions must allow aqueous-phase oligomerization rates high enough so that continuous generation of new particles occurs, and thus steady polymerization rates can be attained.

Figure 4.5 Continuous emulsion polymerization system.

FLUOROELASTOMERS HANDBOOK Reasonably high radical generation rates are required, with dispersion stabilization by ionic oligomers and added soap. Suitable compositions include most vinylidene fluoride copolymers, especially the commercially important VDF/HFP/(TFE) and VDF/ PMVE/TFE products. For continuous emulsion polymerization of these VDF copolymers, P. L. Tang has found that low levels of highly water-soluble short-chain hydrocarbon alkyl sulfonates (e.g., sodium octyl sulfonate) are effective in place of fluorinated soaps.[28] TFE/PMVE perfluoroelastomers and ethylene/TFE/PMVE base-resistant elastomers can also be made in continuous reactors, though at much lower rates. Sustained particle nucleation is difficult to attain for TFE/propylene compositions; these do not appear suitable for production in a continuous polymerization. Certain polymer designs that require initial formation of particles with little or no further initiation must be made in semibatch reactors. An example is the Daikin family of polymers with almost all chain ends capped with iodine, made in a living radical polymerization. Continuous reactor design and operation. Continuous stirred tank reactors used for emulsion polymerization of fluoroelastomers are run essentially liquid-full at pressures high enough to keep unreacted monomers dissolved in polymer particles.[29] Operating pressures are in the range 2–7

4 PRODUCTION OF FLUOROELASTOMERS MPa at temperatures 60°C–130°C. Most VDF copolymers are made at 5–7 MPa and 100°C–120°C with residence times of 10–60 minutes. Slower polymerizing specialties (e.g., TFE/PMVE and E/TFE/ PMVE copolymers) are made at low pressures and temperatures, with longer residence time (2–4 hours). Potential corrosion from dispersions with pH’s in the range 2–6 at elevated temperatures is avoided by stainless steel reactor construction. To facilitate rapid dissolution of feed monomers and good mixing of the dispersion, fairly intense agitation is necessary, usually with baffled turbine impellers. A number of inlets must be provided for various components. Gaseous monomers are usually introduced into regions of high shear near impeller tips. Especially for operation at short residence times, it is necessary for agitation systems to be designed with high impeller flow, so that liquid turnover times are much shorter than residence times. VDF copolymer dispersions are usually not highly stable, since it is desirable to minimize added soap which must be readily removed during isolation. Thus, the maximum shear rate or impeller tip speed must be limited to avoid shear coagulation. Dispersion exits the reactor through a back-pressure control valve. Stability of the dispersion must be high enough to withstand the high shear involved in the letdown to much lower pressure in the degasser. Removal of heat of polymerization is a major consideration in reactor design for fluoroelastomers. For specialty types such as perfluoroelastomers made at low rates and low temperatures in relatively small reactors, heat removal through a cooling jacket is feasible. VDF copolymers are generally made at much higher rates per unit volume and high overall rates that require larger reactors. Cooling jackets are inadequate in this situation, so such reactors are usually operated adiabatically, with the heat of polymerization taken up by the temperature rise of water fed to the reactor. Heat of polymerization calculated from bond energies is in the range 300–350 kcal/kg for commercial VDF copolymer compositions. For adiabatic operation, dispersion solids must be limited so that the ratio of water fed to polymer made is high enough to allow a reasonable temperature rise from a practical water feed temperature to the reaction temperature. For example, a practical VDF/HFP/TFE polymerization may be run at about 20% solids, with 4 kg water per kg polymer in the reactor dispersion. In this case, if the heat of poly-

51 merization is 320 kcal/kg, a water temperature rise of 80 degrees is necessary, so a reaction temperature of 110°C requires a water feed temperature of 30°C. Similar conditions are described in DuPont patent examples:[30] VDF/HFP (60/40 wt%) copolymer made at 107°C, 10–12 minutes residence time, 18% solids, with polymerization rate 1.1 to 1.3 kg/h·L. Operation of a continuous reactor is quite different from semibatch polymerization. CSTR startup procedures are crucial to proper operation. Aqueous feeds are first established to fill the reactor at the desired operating pressure and temperature. These feeds include the main water flow, initiator components, soap, and buffering agents. Other liquid feeds—cure-site monomer, chain-transfer agent—that may retard polymerization are usually withheld until reaction has been established. Polymerization is started by commencing monomer feed at full rate and calculated overall composition suitable for the copolymer being made. When the reaction starts, a considerable exotherm (“heat kick”) occurs, tending to increase the reactor temperature. Water feed temperature is reduced and jacket cooling may be applied to bring the reactor temperature back to goal. Polymer particles are formed quickly, but some oscillation of particle number occurs in the first few reactor turnovers. High monomer conversion (80%–95%) is attained within 1–2 turnovers when feeds and other operating conditions are properly set up. Steady-state operation at full dispersion solids concentration is established after about six reactor turnovers. Unreacted monomer recovered from degassing vessels is recycled back to the feed compressor and fresh feeds are adjusted to maintain the desired polymer composition and production rate. Monomer feeds to a CSTR are illustrated in Table 4.4 taken from Ex. 4 of Ref. 30 describing VDF/HFP copolymer production in a 10-gallon (38liter) reactor at 89% conversion. At steady state, with recycle set equal to unreacted offgas rate, the fresh feed rate and composition equals polymer rate and composition. The total monomer feed to the reactor remains constant throughout the operation. At startup, before any recycle is established, fresh feed must equal total feed. CSTR shutdown is accomplished by shutting off the monomer feeds. This immediately stops the polymerization, since the unreacted monomer mixture

52

FLUOROELASTOMERS HANDBOOK

Table 4.4 CSTR Monomer Mass Balance (from Ref. 30)

Monomer

Fresh feed (polymer)

Recycle (offgas)

Total feed

kg/h

%

kg/h

%

kg/h

%

VDF

24

60

1.25

25

25.25

56

HFP

16

40

3.75

75

19.75

44

Total

40

held up in the reactor is quite unreactive toward propagation. Initiator and chain-transfer agent flows are then stopped. The main water feed, including soap, is maintained long enough to displace remaining polymer dispersion from the reactor to the degasser and blend tank. Continuous emulsion polymerization control. Control of a continuous emulsion polymerization reactor involves a number of aspects including temperature, conversion stability, radical generation rate, polymerization rate, polymer composition, and polymer viscosity. These control issues are discussed below. Temperature control systems must be sufficiently robust to overcome the inherent instability of this type of CSTR. Polymerization rate Rp and monomer conversion are sustained by radical generation rate, which must be adequate to form new particles continuously, thus maintaining the particle population. Radical generation rate ρ, especially if based on persulfate thermal decomposition, is sensitive to temperature. Thus, a decrease in temperature decreases ρ, which in turn decreases Rp and heat generation, tending to further decrease temperature. The control system must be able to respond fast enough to overcome this sequence of events that could lead to loss of reaction. For an adiabatic reactor, the heat exchanger on the main water feed must be able to switch quickly from heating the feed to goal reactor temperature at startup to cooling the feed well below the reactor temperature to take up the heat of polymerization. Partially bypassing the exchanger may be a means to make such a rapid transition. The system must also respond rapidly to prevent decreases in reactor temperature. CSTR polymerization systems have two possible steady states—the desired high conversion state and a very low conversion state, with an unstable inter-

5.00

45.00

mediate region. Upsets such as loss of initiator or excessive feed of a retarder may cause a flip from high to very low conversion. The low conversion situation means unreacted monomer builds up in the reactor, causing poor agitation and excessive monomer flow to the degasser, leading to potential safety hazards. Recovery from such a low conversion state is accomplished by stopping monomer feeds, continuing aqueous feeds to displace unreacted monomer and refill the reactor, followed by correcting the problem that caused loss of reaction, and restarting the polymerization. As noted above, radical generation rate sustains the polymerization rate in a CSTR, supplying radicals to existing polymer particles, and renewing the particle population by supporting aqueous oligomerization for particle nucleation and stabilization. The ratio ρ/Rp determines the ionic end-group level in the polymer and is a major factor in setting polymer molecular weight. For the usual case of persulfate thermal decomposition, the overall radical generation rate ρ can be calculated for a CSTR with water volume Vr and total water volumetric feed rate Fw with initiator concentration [I]o by making a mass balance on initiator to get its concentration [I] in the reactor. Eq. (4.37)

Fw[I]o = Fw[I] + Vrkd[I] or

[I] = [I]o (1 + kd θ) The first order decomposition rate coefficient kd for persulfate can be estimated from Eq. (4.16) or Table 4.3. Reactor residence time θ is the ratio Vr /Fw of water volume in the reactor to water flow.

4 PRODUCTION OF FLUOROELASTOMERS The water volume Vr is less than the total reactor volume because of the presence of polymer and unreacted monomer. The total radical generation rate at 100% efficiency is then

Eq. (4.38)

ρ = 2kdVr [I] = =

2kdVr [I]o (1 + kd θ)

2k d θFI (1 + kd θ)

The molar feed rate of initiator FI is equal to Fw[I]o and kdθ/(1 + kdθ) is the fraction of initiator decomposed in a CSTR with residence time θ, operating at a temperature giving an initiator decomposition rate coefficient kd. The radical entry rate ρe is lower than ρ by an efficiency factor f:

Eq. (4.39)

ρe =

2 f kd θFI (1 + kd θ)

Radical entry efficiency is usually low in these systems, about 0.2 to 0.6, but is ordinarily not known, so overall ρ is used for practical correlations applied to reactor control. Polymerization rate and in turn monomer feed rate goals are set by estimates from kinetics models (see “Kinetics Relationships” in Sec. 4.4.1), empirical correlations (e.g., Eq. 4.27), or plant experience. Monomer feed adjustments may be necessary to get goal Rp and polymer composition. Reactor effluent samples may be analyzed to determine composition and dispersion solids. Several estimates of Rp can be made from CSTR monitoring the following: • Calculation from water feed rate and dispersion solids • Monomer mass balance from flow meters and GC analysis of fresh feed, recycle, total feed, and offgas monomer streams

53 Control actions are facilitated if Rp is set below the maximum possible for the goal polymer composition and molecular weight at the prevailing reactor temperature and pressure. Then the monomer conversion is high enough that the monomer concentration in the particles is below the solubility limit. In this situation, changing a variable in a direction that tends to reduce Rp and conversion results in an increase in monomer concentration that tends to offset the change in Rp. Then most individual control actions can be accomplished without significant changes in Rp or conversion. Polymer viscosity control is facilitated by the use of relationships such as Eq. (4.34), which can be used to set ρ and transfer agent feed rate Ftr in ratio to Rp to get the desired ηinh. The ratio ρ/Rp sets the ionic end-group level in the polymer; this in turn affects bulk viscosity and bisphenol curing characteristics. Usually, ηinh is monitored from analyses of effluent samples. Then Ftr can be adjusted from correlations like Eq. (4.34) to get the desired polymer viscosity. Reactor dynamics must be taken into account in managing such control actions, since a change in a reactor input variable takes about six turnovers (6θ) to be fully reflected in dispersion effluent analyses. Dispersion stability is affected by soap feed rate, ρ, and pH. Base or buffer feed is set as a ratio to ρ, with adjustments made in response to pH measurements on effluent dispersion. With proper setup of polymerization conditions, control actions taken after startup should be only small adjustments. Redundant measurements of reactor variables (e.g., monomer flow and composition) are desirable to allow checking for instrument errors. Besides the measurements taken around the reactor used for direct polymerization control, monitoring of many other systems—monomer feed and recycle compressors, degassers, agitators, impurities in feeds, and leaks—is necessary for safe, smooth operation.

• Heat balance on an adiabatic reactor Monomer mass balances also provide estimates of polymer composition. The total monomer feed composition may be adjusted to obtain goal polymer composition. Cure-site monomer feed is usually set in ratio to Rp or total gaseous monomer feed, and cure-site level is monitored by analysis of effluent polymer.

4.4.3

Semibatch Emulsion Polymerization

All fluoroelastomer producers use semibatch emulsion polymerization systems. Detailed descriptions of commercial fluoroelastomer semibatch systems are not available in the open literature, but

54 smaller scale reactors are described in a number of patents. Figure 4.6 is a schematic representation of a fluoroelastomer semibatch reactor with associated charging and feed systems, and monomer recovery system. Shown are components usually charged initially, and those that may be fed during the course of the polymerization. Semibatch polymerization is suitable for a wide range of compositions, including those having very slow polymerization rates. Semibatch reactors are more versatile than continuous reactors for making specially designed polymers. Feeds of initiator, transfer agents, and cure-site monomers can be varied during the course of a batch to make polymers with different molecular weights and molecular weight distributions, end groups, and curesite distribution along chains. This allows control of rheology, processing, and curing behavior to an extent not attainable in CSTRs. Polymer composition and polymerization rate are readily controlled by setting monomer feeds during the reaction. Commercial semibatch reactors are capable of making a considerable number of low volume specialty products. However, the necessity of keeping different products separate in downstream handling equipment limits the versatility of the reactor system.

Figure 4.6 Semibatch emulsion polymerization system.

FLUOROELASTOMERS HANDBOOK Semibatch reactors have limitations compared to continuous reactors in the production of high-volume, fast-polymerizing types. Heat of polymerization must be removed by means of a cooling jacket. With this limited cooling capability, polymerization rates must be limited well below those possible in adiabatic CSTRs for many important high-volume products (e.g., VDF copolymers containing 60-80 mole % VDF). In campaigns of high-volume types, many batches with attendant shutdowns and startups are required, and batch-to-batch variability may be significant. For many types, reaction times may be too short to allow monitoring of product characteristics, feedback, and adjustments within each batch. Adjustments can be made on subsequent batches, but large blend tanks may be required to reduce final product variability. Holdup of gaseous monomer mixtures in semibatch reactors and feed systems is greater than that in CSTR systems. Considerable volumes of monomer mixtures under pressure in semibatch reactor vapor spaces and in accumulators after compressors may present potential explosion hazards. The lower operating pressures of semibatch reactors somewhat offsets this hazard, compared to

4 PRODUCTION OF FLUOROELASTOMERS CSTRs. However, barricades around semibatch reactors and feed facilities may be necessary to protect personnel. Semibatch reactor design and operation. Semibatch reactors are generally run at lower temperature and pressure than CSTRs. Usual ranges for semibatch operation are 60°C–100°C and 1–3 MPa (150–450 psi). Reaction times required to get dispersion solids of 25%–35% are quite variable, depending on composition and other variables related to polymer design, and may range from 2 hours to as much as 40 hours. Usually, the volume of aqueous dispersion is 60%–85% of total reactor volume. Dispersion volume increases significantly during the course of polymerization because of the increasing volume of polymer swollen with monomer. The general procedure for operation of a semibatch reactor is as follows: The reactor is charged with water and soap solution, and with monomers of the composition necessary to be in equilibrium with the desired polymer composition. Usually the unreacted monomer mixture from a previous batch makes up the bulk of the monomer charge. Ordinarily, this initial feed would bypass the accumulator after the compressor. The reactor is brought to the desired operating temperature and pressure. Reaction is started by adding persulfate initiator and chain-transfer agent. During polymerization, monomers are fed at the desired polymer composition to maintain reactor pressure. Additional initiator, transfer agent, cure-site monomer, and buffer may be fed during the polymerization as necessary to make the desired polymer. In semibatch emulsion polymerization of fluoroelastomers, particle formation occurs during the early part of the polymerization, but may be prolonged to rather high solids concentrations. With the increase in number of particles and growing radicals, the polymerization rate may also increase over a considerable fraction of the reaction time. To handle the large differences in monomer feed rate necessary to match the varying polymerization rate, an accumulator may be used between the feed compressor and reactor. The accumulator is maintained in a pressure range above the reactor pressure. A monomer mixture of the desired polymer composition is fed from the accumulator to maintain constant reactor pressure. Monomers may be fed periodically through the compressor to keep the accumulator in a set pressure range. This arrangement

55 allows metering of the monomers at convenient rates for accuracy in setting composition. The use of an accumulator does add a significant volume of highpressure monomer mixture to the feed system. This may be a potential explosion hazard for some monomer mixtures. Careful investigation is necessary to determine the extent of such hazards and provide means of avoiding damage or injury from possible deflagration of monomer mixtures. When the desired amount of polymer has been made, as estimated from the cumulative amount of monomer fed during the polymerization, shutdown is accomplished by stopping the feeds of monomer, initiator, and other minor components. Monomer may be removed by venting directly from the reactor. However, with the limited head space in this vessel, foaming and dispersion carryover into vapor lines can be a severe problem. It is more feasible to transfer the dispersion from the reactor to a larger degassing and blend tank. If the same composition is to be made in the next batch, it is convenient to leave a heel of dispersion in the reactor, along with the remaining unreacted monomer in the vapor space. This facilitates recharging and startup of the next batch. Commercial semibatch reactors used for manufacture of fluoroelastomers are generally 1,000 to 12,000 liters in size, larger than the CSTRs described in the previous section. Relatively small sizes are used for fast-polymerizing high-volume VDF copolymers, while larger reactors may be used for specialty types with lower polymerization rates. For copolymers of 60–80 mole % VDF with HFP and TFE or PMVE and TFE, rates may be limited by heat transfer capability. This situation can be analyzed by reference to Fig. 4.7, which shows a jacketed cylindrical reactor with diameter D, total height HT, and dispersion depth HL to get dispersion volume VL and heat exchange area A:

Eq. (4.40)

VL = ðD 2 H L 4

Eq. (4.41)

A = π DHL

Consider the case of a reactor with total heightto-diameter ratio HT/D = 1.85, 83% full of dispersion, and thus with liquid height HL = 1.5D. Then, from Eq. 4.40, the liquid volume is given by VL =

56

FLUOROELASTOMERS HANDBOOK

Figure 4.7 Semibatch reactor: heat exchange area and liquid volume.

1.5πD 3/4, and the diameter can be expressed in terms of the liquid volume by D = (4VL/1.5π )1/3. The heat exchange area, from Eq. 4.41, can be expressed as A = 1.5πD 2, or related to liquid volume as A = 1.5π(4VL/1.5π)2/3 = 4.23VL2/3. For the situation with the maximum rate of polymerization limited by heat transfer capability, the following relationships apply:

Eq. (4.42)

Rp max =

=

UA∆t ∆hp

4.23U∆t VL ∆hp

2/ 3

In Eq. 4.42, Rp max is the maximum polymerization rate for a polymer with heat of polymerization ∆hp in a reactor with heat exchange area A, overall heat transfer coefficient U, maximum average temperature difference between dispersion and jacket coolant ∆t, and dispersion volume VL. The maximum rate is proportional to the heat exchange area, thus to the two-thirds power of dispersion volume (or reactor volume). These relationships can be used to approximate the scale-up situation for semibatch reactors making polymer compositions for which rates are limited by heat exchange capabilities. A reasonable base case is that of a 1,500-liter reactor, charged with 1,000 liters of water, with capability of making 400

kg of VDF copolymer (28.6% solids in the dispersion after degassing) in two hours reaction time, thus Rp max = 200 kg/h. Assuming the monomer-swollen polymer has density 1.6 kg/liter, polymer volume is 250 liters and total dispersion volume, VL, is 1,250 liters or 1.25 m3, corresponding to 83% full. With HL/D = 1.5, D = 1.02 m from Eq. (4.40) and A = 4.89 m2 from Eq. 4.41, ∆hp = 320 kcal/kg or 1.34 MJ/kg and maximum ∆t = 50 K, which corresponds to a reaction temperature of 80°C and average coolant temperature of 30°C. The overall heat transfer coefficient U is 260 kcal/m2·h·K or 1.1 MJ/ m2·h·K, a reasonable value. Now consider scaling up this polymerization to a reactor eight times the size (12,000 liters) to make 3,200 kg polymer per batch. For the large reactor, VL = 10 m3, D = 2.04 m, and A = 19.6 m2, even with the optimistic assumption that U will be the same for the large reactor, the fourfold increase in heat exchange area limits the maximum rate to 800 kg/h, so that the reaction time increases twofold to four hours. This is probably a good tradeoff for scaling up, since total batch cycle time for the large reactor to make 3,200 kg would be much less than the total time required for eight batches in the small reactor. Offsetting the advantage of the larger reactor would be the cost of scaling up feed equipment, downstream blending, and isolation capacity. The larger monomer volumes under pressure may also introduce severe explosion hazards for the larger reactor. Design considerations for semibatch reactors differ significantly from those for continuous reactors. Since polymerization rates per unit volume are lower in semibatch reactors, these are usually much larger than continuous reactors. Pressures and temperatures are usually lower in semibatch reactors. Intensity of agitation is ordinarily lower, since high shear regions are not necessary to disperse monomers and other feeds to a semibatch reactor. Agitation systems should be designed for reasonable liquid turnover, with minimal baffling to avoid elastomer agglomeration and fouling. The presence of a sizeable volume of monomers under pressure in the head space of the reactor creates the potential for explosion hazards. Care must be taken to preclude possible sources of ignition, such as rubbing of moving metal parts, presence of air or other initiators, and electrical arcs or sparks. Proper relief area must be provided, which is capable of relieving the overpressure from a deflagration in the vapor space. For some

4 PRODUCTION OF FLUOROELASTOMERS monomer mixtures, this consideration may limit the reactor pressure or size. Feed systems for semibatch operation involve a combination of initial charging of some components and of feeding components at variable rates during polymerization. These requirements will be discussed in the next section. Semibatch emulsion polymerization control. Basic control of semibatch systems for making older VDF-based copolymer and terpolymer products is somewhat simpler than control of continuous reactor systems. However, new products require complex schemes for operation of the semibatch polymerization reactor to get the desired processing and curing characteristics. Major requirements of a semibatch reactor control system include: accurate initial charging of ingredients, good control of feeds of major monomers and minor components during polymerization, and maintaining the reactor at goal temperature and pressure. Before charging, it is necessary to clear air from the reactor system by flushing with inert gas, evacuation, or displacement of vapor with water. The proper amount of water (usually 50%–70% of total reactor volume) is charged along with dispersant (usually soap and buffer), and the reactor contents are heated to the desired polymerization temperature. Monomer is then charged with the appropriate composition to be in equilibrium with the desired polymer composition, and in an amount to bring the reactor to a chosen pressure at goal temperature. Major monomer composition is checked by gas chromatography. Polymerization is started by adding initiator. Then a monomer mixture with a composition essentially the same as the desired polymer composition is fed at a rate to maintain goal reactor pressure. Jacket coolant temperature is adjusted to keep the reactor at goal temperature as polymerization proceeds. Additional initiator is usually fed to hold the radical generation rate in a range that will maintain the polymerization rate and attain the desired polymer molecular weight and ionic end-group level. A transfer agent may be added to control the polymer’s molecular weight and molecular weight distribution. A cure-site monomer may be fed in ratio to the main monomer feed. Depending on reactor size and the polymerization rate, feeds of minor components may require special metering equipment to deliver low flows or small incremental shots accurately. Both instantaneous rates and cumulative amounts of ma-

57 jor monomers and minor components need to be monitored. The polymerization rate and total polymer formed are estimated from major monomer feeds. Note that the polymerization rate and the monomer feed rate may vary considerably over the course of a semibatch polymerization. An accumulator between the feed compressor and reactor may be necessary to facilitate delivery of a controlled monomer composition, especially during the early stages of the reaction when rates may be low. Polymerization is stopped by shutting off the monomer feeds when a desired dispersion-solids level is reached or a desired polymer viscosity is attained, both estimated from cumulative monomer feed. Reactor sampling may be feasible for relatively slow polymerizations with long enough reaction time to allow adjustments of feeds. The vapor space may be monitored by gas chromatography. Dispersion sampling may be difficult, especially in the usual situation of a barricaded reactor system precluding operating entry. Often the polymer characteristics must be inferred from monitoring of feed components during the polymerization. A number of strategies may be used for addition of initiator, transfer agent, and cure-site monomer components during a semibatch emulsion polymerization. The simplest initiator feed method is to add all of it at the start of polymerization. In this case, the total moles of persulfate initiator, I, in the reactor decrease with time, t, according to first order thermal decomposition kinetics: Eq. (4.43)

dI/dt = -kdI

Eq. (4.44)

It = I0 exp(-kdt)

Total radical generation rate, ρ t, at time, t, is given by Eq. (4.45)

ρ t = 2kdIt = 2kd I0 exp(-kdt)

In a semibatch emulsion polymerization, radical entry efficiency varies considerably as the particle population builds up. Since the efficiency is not readily estimated, it is easier to use total generation rate for correlation and monitoring purposes. The cumulative number of moles of radicals generated from time 0 to time t is Eq. (4.46)

Σρt = 2I0 [1- exp(-kdt)]

58

FLUOROELASTOMERS HANDBOOK

This method of adding initiator all at once may be usable for some semibatch polymerizations carried out at relatively low temperatures, say 80°C or below, with a persulfate initiator half life of two hours or more. The relatively high radical generation rate at the start facilitates particle formation, and the slowly decreasing radical generation rate may adequately sustain polymerization in later stages. However, this method is not versatile enough to control the polymerization rate, molecular weight, and end groups for most products of interest. A second method, often used for small reactors, is to add incremental shots of initiator to keep the initiator level between chosen levels, I0 and It, at intervals of time, t. The increment size, ∆I = I0 – It, is readily calculated from Eq. 4.44. Corresponding radical generation rates and cumulative radicals are estimated from Eqs. 4.45 and 4.46. For larger reactors, initiator may be fed continuously to get a desired profile of radical generation rate versus time, thus optimizing polymer viscosity and ionic end-group level, taking into account changes in polymerization rate over the course of the reaction. Initiator feed, FI, can be chosen to obtain constant, increasing, or decreasing ρ. For constant initiation rate, FI, is set equal to the initiator decomposition rate so that It = I0; then FI = kd I0 and ρ = 2kd I0. For the more general case, the following relationships apply:

Eq. (4.47)

Eq.(4.48)

dI = FI − kd I dt

I t = I 0 exp(− k d t ) + FI

[1 − exp(− kdt )] kd

Eq. (4.49) ρ t = 2k d I t

= 2kd I 0 exp(− kd t ) + 2 FI [1 − exp(− k d t )]

Eq. (4.50)

 F  Σρt = 2 I 0 − I [1 − exp(− k d t )] + 2 FIt kd  

Note that Eq. 4.50 can be applied to a number of intervals with varying initiator feed rates to get an overall summation of radicals generated over the course of the reaction. Chain-transfer agents are often used to control the molecular weight of fluoroelastomers. However, chain-transfer correlations and predictions are less readily obtained for semibatch systems than for continuous polymerization systems. Basic relationships like Eq. 4.31 are difficult to apply to semibatch systems. For transfer agents with low reactivity at the relatively low temperatures normally used in semibatch polymerization, Eq. 4.37 may be usable. This relationship is based on the ratio of transfer agent to monomer in particles. The transfer agent level in particles may not be readily estimated for agents that have substantial solubility in water because they are distributed between the aqueous and polymer phases. For some fluoroelastomer compositions, hydrocarbons may be used as transfer agents. These may be volatile enough to monitor by gas chromatography analysis of the vapor phase in the reactor. Such transfer agents are not usually used for VDF-containing polymers, because the hydrocarbon radicals formed by transfer are much less reactive toward propagation than the fluorocarbon radicals, thus retarding polymerization. Highly reactive transfer agents (e.g., lower alcohols or esters) may be fed continuously in set ratio to the monomer feed or the radical generation rate to get the desired polymer viscosity. However, while most of the chaintransfer agent reacts immediately in continuous systems operating at higher temperatures, that assumption can not be made for semibatch systems. Thus, considerable small scale polymerization work is often necessary to establish how to charge and/or feed transfer agents to obtain the desired polymer viscosity and molecular weight distribution for each composition. In a special case of transfer in semibatch emulsion polymerization, perfluorocarbon diiodides are used to make fluoroelastomers that have narrow molecular weight distribution and iodine at most chain ends for curing. As originally developed by Daikin workers,[31] a “living radical” polymerization is set up with very low levels of initiation and termination, so that propagation and transfer predominate. Soap levels are set high enough to obtain a large population of small particles containing no more than one growing radical each. Ordinarily, all of the diiodide

4 PRODUCTION OF FLUOROELASTOMERS transfer agent is added soon after polymerization starts, so that very few chains form without iodine end groups. Iodide ends, whether on polymer chains or the original perfluorocarbon iodide, continue to undergo transfer. Individual chains grow until they undergo transfer; the resulting iodide may transfer subsequently to allow further propagation and an increase in molecular weight. Since most chains start near the beginning of the polymerization, and very little radical-radical termination occurs, the chains have equal opportunity to grow. The result is a polymer with a very narrow molecular weight distribution and with iodine on most chain ends. Molecular weight continues to increase as polymerization proceeds; it can be estimated from the ratio of cumulative monomer feed to moles of iodide charged. Polymerization is stopped by shutting off the monomer feed when the estimated molecular weight goal is attained. In these polymerizations, adventitious impurities that may transfer to form unreactive radicals must be minimized. Even so, small amounts of initiator must be added from time to time to sustain the radical population and desired polymerization rate. It is crucial that a known amount of iodine is charged initially to allow an adequate estimation of molecular weight. Since these polymerizations are slow, it may be possible to take dispersion samples for measurement of the polymer’s inherent viscosity. A plot of inherent viscosity versus cumulative monomer feed may then be used to estimate the cumulative monomer level that will give the desired final viscosity. Most cure-site monomers are incorporated into the polymer at low levels. For many of these monomers, conversion is high, so they are not charged initially, but are fed in controlled ratio to the major monomers fed during the reaction. In a few cases, cure-site monomers may also be charged along with the initial monomer charge. Cure-site monomers, with active groups such as iodine or bromine, used for free radical curing present special problems in semibatch polymerization. Unlike the situation in continuous systems with continuous removal of polymer from the reactor, all chains formed in semibatch systems stay in the reactor until shutdown. This means that incorporated monomer units with reactive cure sites are exposed to radicals for considerable periods of time. The resulting chain transferto-polymer reactions may lead to excessive branching and gel formation, which may be detrimental to

59 processing characteristics. This situation has been circumvented in recent developments (e.g., by Ausimont workers)[32] by using small amounts of iodine-containing olefin monomer in conjunction with perfluorocarbon diiodide transfer agent. This allows production of fluoroelastomers with iodine units incorporated along the chains as well as at chain ends. Chain branching can then be controlled to allow reasonable polymer rheology and compound processing characteristics. A preferred Ausimont process variant for attaining reasonably high polymerization rates is a microemulsion process. A stable emulsion of perfluoropolyoxyalkalene solvent stabilized with a perfluoropolyoxyalkalene carboxylate surfactant is charged initially with monomers to obtain a large number of small particles and a subsequently high polymerization rate.

4.5

Suspension Polymerization

Suspension polymerization is used to make a number of thermoplastic polymers. In suspension polymerization, all reactions are carried out in relatively large droplets or in polymer particles stabilized by a small amount of water-soluble gum. Organic peroxide initiators are used to generate radicals within the droplets. A solvent may be used to dissolve a monomer at relatively high concentration. The main advantages of suspension polymerization over emulsion systems are that no surfactants, which are difficult to remove from the product, are used, and no ionic end groups are present which may be unstable during processing at high temperatures. What follows is a general introduction of suspension polymerization; S. Ebnesajjad[33] has presented an extensive review of suspension polymerization of vinylidene fluoride. In one semibatch suspension process for making VDF homopolymer,[34] the reactor is charged with water containing a cellulose gum (about 0.03%) as the suspending agent, an initiator solution, and a VDF monomer. The initiator of choice is diisopropyl peroxydicarbonate, which has a half life of about two hours at 50°C. The jacketed reactor is heated with agitation to a temperature in the range 40°C to 60°C, with a pressure in the range 6.5 to 7.0 MPa maintained by adding additional water or monomer

60 during the polymerization period of about 3.5 hours. Chain-transfer agents may also be fed. Average particle diameter is typically about 0.1 mm for the dispersion obtained in suspension polymerization. At the end of polymerization, the reactor is cooled, the dispersion is degassed by letting off pressure from the reactor, the polymer is separated by filtering or centrifuging the dispersion, and washed to remove residual dispersion stabilizer. Major features of this process were adapted by workers at Asahi Chemical Industry Co., Ltd. to make VDF/HFP/(TFE) fluoroelastomers. In the initial version of the Asahi Chem suspension polymerization process,[35] a relatively large amount of an inert solvent, trichlorotrifluoroethane (CFC-113, CCl2F–CClF2), is dispersed in water containing 0.01%–0.1% methyl cellulose suspending agent. The mixture is heated under agitation to the desired polymerization temperature (usually 50°C) and the proper composition of VDF/HFP/(TFE) monomer mixture to make the desired copolymer is charged in the amount necessary to get the goal concentration in the monomer-solvent droplets. With the solvent used, the pressure is usually relatively low, about 1.2–1.6 MPa. Reaction is started by adding diisopropylperoxydicarbonate initiator solution and a monomer mixture, with composition essentially that of the polymer being made, is fed to maintain the reactor pressure constant. Polymerization starts in the monomer-solvent droplets, with initial formation of a low molecular weight fraction. As polymerization proceeds, viscosity of the particles increases, long-lived radicals form, and both polymerization rate and molecular weight increase with reaction time. The resulting polymer has a bimodal molecular weight distribution, with the minor low molecular weight fraction acting as a plasticizer for the bulk high molecular weight polymer. Normally no chain-transfer agents are used for polymers cured with bisphenol. Polymer viscosity is set from the ratio of total polymer formed to initiator charged. Since reaction times are fairly long (six hours or more) to attain high dispersion solids (30%–40%), dispersion samples can be taken from the reactor during polymerization to monitor inherent viscosity and predict when to stop polymerization for goal viscosity. After polymerization is stopped by turning off the monomer feed, monomers are removed by venting the reactor. Considerable care is necessary during this operation to reduce pressure in stages so

FLUOROELASTOMERS HANDBOOK that rapid release of monomer from particles does not occur, and carryover of particles into vapor lines is avoided. Particle sizes after degassing are 0.1 to 1 mm in diameter, and are readily separated by filtering or centrifuging the dispersion. Fluoroelastomers made by the suspension process have no ionic end groups and contain a significantly low molecular weight fraction. These copolymers can be made with high inherent viscosities for enhanced vulcanizate properties, while they still retain good processibility because their compounds have relatively low viscosity at processing temperatures. Compared to emulsion products of similar composition, bisphenol-curable suspension products exhibit better compression set resistance, faster cure, and better mold release characteristics. Asahi Chem also developed peroxide-curable VDF/HFP/TFE fluoroelastomers by charging methylene iodide along with the initiator to the suspension polymerization reactor. The resulting chaintransfer reactions allow incorporation of iodine on more than half the chain ends. Final polymer molecular weight is determined mainly by the ratio of total monomer fed during the polymerization to iodine incorporated. The suspension process has been adapted to make bimodal VDF/HFP/TFE polymers for extrusion applications, such as automobile fuel hoses, to get smooth extrudates with minimal die swell at high shear rates.[36] These polymers contain 50%–70% very high molecular weight fractions (ηinh about 2.5 dL/g, Mn about 106 daltons) and 30%– 50% very low molecular weight fraction (ηinh about 0.15 dL/g, Mn about 17,000 daltons), with polymer bulk viscosity determined by the relative amounts of the two fractions. The low viscosity fraction has a molecular weight below the critical chain length for entanglement (Me about 20,000 to 25,000), so it acts as a plasticizer to facilitate extrusion with low die swell. Similar bimodal polymers with low viscosity fractions having molecular weights greater than Me would exhibit very high die swells. Synthesis of these polymers is carried out in two stages of suspension polymerization. A very small amount of initiator is used in the first stage to make the high molecular weight fraction. Then additional initiator and a relatively large amount of methylene iodide are charged to make the low viscosity fraction. The relative amounts of each fraction are estimated from the cumulative monomer feed in each stage. The amount of methylene iodide charged is that required to in-

4 PRODUCTION OF FLUOROELASTOMERS corporate 1.5%–2% iodine in the low viscosity fraction. Polymerization rate in the second stage is very low, so the total reaction time required for the bimodal polymer synthesis is some 40–45 hours. These bimodal polymers are ordinarily cured with bisphenol, but the iodine ends on the low viscosity fraction allow a mixed cure system with both bisphenol and radical components. The radical system links very short chains into longer moieties that can be incorporated into the bisphenol crosslinked network. Similar bimodal polymers made by emulsion polymerization with conventional chain-transfer agents are cured only with bisphenol. The resulting vulcanizates contain sizeable fractions of short chains that are not incorporated into the network and are thus susceptible to extraction when exposed to solvents. The suspension process described above was used by Asahi Chem for commercial production of Miraflon fluoroelastomers during the early 1990s. However, it was recognized that the use of large amounts of the ozone-depleting solvent CFC-113 would need to be phased out. A second version of the suspension process uses a small amount of a hydrogen-containing solvent such as HCFC-141b, CH3-CFCl2. Since only enough solvent is used to dissolve the initiator, the reactor operating pressure must be increased to 1.5–3.0 MPa so that a fraction (10–30%) of the initial monomer charge condenses to form an adequate volume of droplets to serve as the polymerization medium. In a further improvement, the hydrochlorofluorocarbon solvent is replaced with a small amount of a water-soluble hydrocarbon ester, preferably methyl acetate or t-butyl acetate.[37] These polar hydrocarbon solvents are used mainly to feed the initiator to the reactor. The methyl or tbutyl groups are relatively inactive toward transfer, and these solvents are so soluble in water that little is in the polymer phase. After the Asahi Chem suspension polymerization technology was acquired by DuPont in 1994, additional development was carried out to extend the technology to VDF/PMVE/ TFE fluoroelastomers with cure-site monomers incorporated along the chains.[38] Cure-site monomers can be incorporated evenly along chains by careful feed in controlled ratio to polymerization rate of major monomers. In this way, bromine- or iodine-containing monomers can be incorporated, in addition to iodine on chain ends from methylene iodide transfer agent, to get polymers with improved characteristics in free radical cures. It should be noted that simi-

61 lar polymers can be made more readily by continuous emulsion polymerization.[39] Of more interest are bisphenol-curable VDF/PMVE/TFE compositions with 2H-pentafluoropropylene, CF2=CH–CF3, as cure-site monomer. Bisphenol-cured parts from such polymers have better thermal stability than products made by radical curing.

4.5.1

Polymer Compositions

The suspension polymerization process works well for VDF/HFP/TFE and VDF/PMVE/TFE compositions. These monomer mixtures exhibit high propagation rates at relatively low temperatures (45%–60°C) and low monomer concentrations (less than 15% in monomer/polymer particles). Reasonably high polymerization rates are possible at temperatures below 60°C, so elastomer particle agglomeration is minimized. The amorphous polymers are insoluble in the monomer/solvent mixtures and also the monomer and solvent have low solubility in the polymer-rich phases. The high viscosity of the polymer-rich phase gives hindered termination, so that long-lived radicals can grow to high molecular weights. The initial monomer mixtures charged to the reactor can be partially condensed at about 50°C and moderate pressure to form droplets as the initial locus of polymerization, without the need for charging large amounts of solvent or for charging polymer seed particles. Slower propagating compositions like TFE/ PMVE give a lower molecular weight and a less useful polymer when made by suspension polymerization than polymer that can be obtained by emulsion polymerization. For these perfluoroelastomers, monomer solubility in the polymer is high, so particle viscosity remains too low for hindered termination and the formation of long-lived radicals. Considerable initiator must be fed during the polymerization to sustain reasonable reaction rates. Several other TFE copolymer compositions give similar results.

4.5.2

Polymerization Mechanism and Kinetics

In all versions of the suspension-polymerization process, an initial dispersion of low-viscosity droplets is present, either from solvent containing dissolved monomer or from liquid monomer partially

62

FLUOROELASTOMERS HANDBOOK

condensed from the initial monomer charge. With the low viscosity of the monomer-solvent phase and the relatively high initial radical flux, both initiation and radical-radical termination rates are high, so the polymer formed in the early stages of the reaction is low in molecular weight. Solution kinetics apply in this early stage. The general reaction scheme outlined in Sec. 4.3.1, describing initiation, propagation, and termination reactions (Eqs. 4.1, 4.2, and 4.4) can be used in this situation. In the mobile droplets, rates of radical generation and termination are equal: Eq. (4.51)

2f kd[I] = 2kt[R·]2

Radical concentration in the droplets can be expressed as

Eq. (4.52)

  [R ·] =  f k d [I ]  kt 

12

The polymerization rate, Rp, and the numberaverage molecular weight Mn (assuming termination by radical combination) are then given by:

Eq. (4.53)

 f k [I ] Rp = k p [M ][R ·] = k p [M ] d   kt 

Eq. (4.54)

Mn =

12

k p [M ]

( f kd k t [I])1 2

The high termination rate coefficient, kt, leads to a low rate and molecular weight in this initial stage of suspension polymerization. As the reaction proceeds, the insoluble polymer formed builds up as a second high-viscosity phase in the droplets. Radical mobility is limited in this viscous polymer-rich phase, so termination rate decreases and both molecular weight and polymerization rate increase with time. In the later stages of polymerization, kt approaches zero. Long-lived radicals persist in the dominant viscous polymer phase, so that growth of these chains continues even though most of the initiator has decomposed and the new radical formation rate is low. Ordinarily, the initial low molecular weight polymer is a small fraction of the total polymer formed.

When methylene iodide is used to form iodine end groups for radical curing, initiator levels are minimized so that transfer reactions predominate. Depending on iodide level, polymerization rates may be quite low, even in the later stages of the reaction. Ordinarily, all the methylene iodide is charged with the initiator. Since the iodide is somewhat soluble in water, its level in the droplets is initially low enough so the polymerization can be started at a reasonable rate. As the reaction proceeds, all the iodide enters the droplets and undergoes transfer. As in the semibatch emulsion case with perfluorinated iodide as the transfer agent, chains undergo alternating periods of propagation interrupted with iodide transfer from other chain ends. Usually the suspension polymers made with methylene iodide contain no more than about 1.5 iodine ends per chain and have somewhat broader molecular weight distribution than semibatch emulsion polymers made with perfluorinated iodides and very low initiation levels. The suspending agent, usually a water-soluble gum such as methyl cellulose with moderate molecular weight, prevents agglomeration of droplets and monomer-swollen polymer particles by forming a water-swollen coating on them. These gums are effective at low concentrations, typically less than 0.1% concentration in the water charged. Also polymerization temperature must be less than about 70°C so the swollen elastomer particles are not too sticky. Cellulose derivatives contain structures that normally would participate in chain-transfer reactions. However, these materials are so water-soluble that essentially none is in the droplets or polymer particles, thus do not reduce polymer molecular weight. The initiator of choice for fluoroelastomer suspension polymerization is diisopropyl peroxydicarbonate (or isopropyl percarbonate, IPP), R–O– C(:O)–O–O–C(:O)–O–R, where R is isopropyl. Under polymerization conditions, the IPP added to the reactor is dissolved in the fluorinated monomer/ polymer droplets, and its half-life is about 2.5 hours (kd = 0.27/h) at 50°C. IPP decomposition by thermal homolysis gives isopropyl carbonate radicals, R– O–C(:O)–O·, which react readily with fluorinated monomers to initiate polymerization. In the absence of a reactive monomer, the isopropyl carbonate radicals may undergo further decomposition to isopropoxy radicals, R–O·, and carbon dioxide. Isopropoxy radicals may react with IPP to induce

4 PRODUCTION OF FLUOROELASTOMERS further decomposition. The IPP decomposition rate varies with the medium, and increases significantly in polar solvents. Thus solutions must be kept cold and used soon after makeup. IPP is supplied as a solid (m.p. 8°C–10°C) which must be stored in a dedicated freezer at temperatures below –20°C. Above –10°C, IPP decomposes slowly, but generates heat internally so that the temperature may increase rapidly and the decomposition autoaccelerates. Decomposition products include flammable vapors which may be ignited. Proper storage and handling procedures are necessary to avoid these problems.

4.5.3

Reactor Design and Operation

A reactor used for the suspension polymerization of fluoroelastomers must be designed to minimize agglomeration of swollen particles and fouling of vessel surfaces. Agitation must be sufficient to disperse the initial condensed monomer-solvent phase into small droplets and to keep polymer particles from settling. Standard turbine agitators may be used with minimal baffling that is sufficient to avoid vortex formation without producing regions of high turbulence. Reactor fouling must be monitored and removed periodically. This maintains heat removal capacity through the cooling jacket and allows adequate temperature control. Removal of polymer deposits is facilitated by ports for water jets. As with emulsion semibatch reactors, vessel size must accommodate a considerable increase in volume of the liquid phase as reaction proceeds to high solids. Typically, the initial aqueous solution charge occupies about 60% of the vessel volume. The final dispersion, containing up to about 40% polymer, may occupy some 80%–85% of total volume. If degassing is carried out by letting down reactor pressure after completion of a batch, enough vapor space must be allowed to minimize entrainment of particles in the vapor stream vented from the reactor. This ordinarily requires a ratio of length-to-diameter of about two for the vessel. Adequate relief area should be provided for the vapor space to avoid damage from potential monomer deflagration. As with semibatch emulsion polymerization, monomer feed rates for a suspension reactor may vary over a wide range during the course of each batch operation. An accumulator may be necessary between the feed compressor and reactor to facili-

63 tate metering, as discussed in semibatch reactor design and operation. Careful measurement of initiator, modifier, and cure-site monomer feeds is also necessary. Special design considerations apply to storage and handling of peroxydicarbonate initiator, as noted in Sec. 4.5.2.

4.5.4

Polymerization Control

Similar polymerization control considerations apply to semibatch suspension systems as those described in semibatch emulsion polymerization control. Reference 38 describes suspension polymerization system operating and control procedures for making two fluoroelastomers of different compositions: one is a VDF/HFP/TFE polymer with a bromine-containing cure-site monomer and iodine end groups for peroxide curing, and the other is a VDF/ PMVE/TFE polymer with a cure-site monomer for bisphenol curing. In both cases, a 40-liter reactor was configured for carrying out semibatch polymerizations. The gaseous monomer feed system consisted of a source line for each gaseous monomer, a compressor, an accumulator, and a pressure controller between the accumulator and reactor vessel. At the beginning of the polymerization, monomers were consumed in the reactor at a low rate. The monomer supply rate to the compressor was considerably higher to maintain an accurate monomer composition. The difference in the amount of monomer fed to the compressor and the amount consumed in the reactor was stored in the accumulator. The storage in the accumulator was controlled by a pressure controller, which was cascaded to several flow controllers metering the monomer mixture to the compressor. As monomers flowed into the accumulator, the pressure increased to a high preset limit. When the high limit was reached, the flow controllers closed the gaseous monomer feed valves. As monomers flowed into the reactor, the accumulator pressure dropped to a low limit. At the low limit, the monomer supply valves opened and compressed gases were fed to the accumulator until pressure reached the high set limit, which shut off the monomer feed. This cycle continued until the polymerization was terminated. An exponential digital filter was used to calculate the average flow rate of gaseous monomers during each period that the supply valves were in the open position. The calculated average gaseous monomer flow rates were used to adjust

64

FLUOROELASTOMERS HANDBOOK

the flow rate of the metering pump delivering the liquid cure-site monomer to the reactor during the same time periods. For the peroxide-curable VDF/HFP/TFE elastomer, the 40-liter reactor was charged with 20 liters of water containing 14 g (0.07%) methyl cellulose (Mn about 17,000 daltons) and was heated to 50°C. Gaseous monomers were charged as listed to bring the reactor pressure to 2.56 MPa: Monomer

Amount, g

Wt %

TFE

183

6.3

VDF

872

29.8

HFP

1,870

63.9

Total

2,925

Part of the monomer charged condensed under these conditions to form liquid droplets. The polymerization was initiated by adding a solution of 20 g diisopropyl peroxydicarbonate (IPP) in 80 g methyl acetate. A solution of 36 g methylene iodide in 44 g methyl acetate was also charged to the reactor; about a third was added at the start and the rest during the feed of the first 1,800 g of incremental monomer. A gaseous incremental major monomer mixture was fed to maintain constant reactor pressure at the controlled temperature of 50°C. The liquid cure-site monomer, 4-bromo-3,3,4,4-tetrafluorobutene-1 (BTFB), was fed in a controlled ratio into the incremental gaseous monomer feed. BTFB was initially fed at a ratio of 0.35% to the digitally filtered value of monomer flow. The ratio was gradually increased to 0.75% to attain an overall average of 0.60% BTFB, based on the total incremental monomer fed. The polymerization rate was approximately equal to the incremental monomer feed rate, and increased from approximately 100 g/h initially to 1,000 g/h after 10 hours. A total of 14,278 g incremental monomer was fed over a 20-hour period in the amounts shown:

ery was 15.4 kg, corresponding to 43% solids in the dispersion. Major monomer composition in the polymer was determined by FTIR, and bromine and iodine cure-site levels by x-ray fluorescence. Polymer composition was 22.1% TFE, 51.4% VDF, 25.7% HFP, 0.54% BTFB, and 0.20% I, close to the goal composition set by incremental monomer feeds. Polymer inherent viscosity was 0.73 dL/g, Mooney viscosity ML-10 (121°C) was 42, and glasstransition temperature, Tg, was -19°C. The addition of the cure-site monomer BTFB in a closely controlled ratio to the incremental monomer feed allowed the polymerization to proceed at a satisfactory rate to form a high molecular weight polymer having a homogeneous distribution of cure sites for good curing characteristics. For the bisphenol-curable VDF/PMVE/TFE elastomer, the 40-liter reactor was charged with 20 liters of water containing 14 g methyl cellulose and heated to 50°C. Gaseous monomers, including the cure-site monomer 2H-pentafluoropropylene (2HPFP), were charged in the amounts listed to bring the reactor pressure to 1.55 MPa: Monomer

Amount, g

Wt %

TFE

45

3.0

VDF

405

27.0

PMVE

600

40.0

2H-PFP

455

30.0

Total

1,505

The polymerization was started by adding an initiator solution of 40 g IPP in 160 g methyl acetate. A gaseous incremental monomer mixture was fed to maintain constant pressure at 50°C. The gaseous cure-site monomer, 2H-PFP, was fed along with the major monomers. The incremental feed rate, approximately equal to the polymerization rate, increased from about 176 g/h initially to about 1,956 g/h at the termination of the polymerization period of 10.7 hours. A total of 12,000 g incremental monomer was fed:

Monomer

Amount, g

Wt %

TFE

2,736

19.2

VDF

7,056

49.4

Monomer

HFP

4,486

31.4

TFE

480

4.0

Total

14,278

VDF

6,960

58.0

PMVE

4,320

36.0

240

2.0

The polymerization was terminated after 20 hours by discontinuing the incremental monomer feed. After degassing, the resulting polymer slurry was filtered and washed. Total dry polymer recov-

2H-PFP Total

Amount, g Wt %

12,000

4 PRODUCTION OF FLUOROELASTOMERS

65

After termination of the polymerization by discontinuing the incremental monomer feed, the polymer slurry was degassed, filtered, and washed. Total polymer recovery was 12.0 kg, corresponding to 37% solids in the dispersion. Polymer composition and properties are listed, with the ratio of 2H-PFP to PMVE determined by 19F nmr: Inherent viscosity, dL/g Mooney viscosity, ML-10 (121°C)

0.81

4.6.1

Molecular Weight Distribution

43

Composition, wt % TFE

3

VDF

59

PMVE

36

2H-PFP

2

Glass transition temperature, Tg, °C –31 Curing characteristics and physical properties of cured compounds were determined for the medium-viscosity bisphenol-curable polymer above and a high-viscosity peroxide-curable commercial polymer made by continuous emulsion polymerization. The commercial polymer, Viton GLT®, has a composition 10% TFE, 54% VDF, 35% PMVE, and 1.2% BTFB, and has inherent viscosity about 1.3 dL/g, and a Mooney viscosity ML-10 (121°C) about 90. As shown in Table 4.5, cure rates and physical properties are similar, but the bisphenol-cured compound gives much better mold release and better retention of properties after heat aging at 250°C. Peroxide Luperox 101XL is 2,5-dimethyl-2,5di(t-butyl peroxy)hexane, 45% on an inert filler. Tremin EST is an epoxysilane-treated wollastonite mineral filler. This formulation, with the special filler molecular sieve zeolite, and metal oxides (but no calcium hydroxide), is advantageous for bisphenol curing of VDF/PMVE/TFE elastomers containing the reactive 2H-PFP cure-site monomer.

4.6

ably by choice of polymerization process and operating conditions. The nature of chain end groups, determined by initiation and transfer reactions, may affect both processing and curing behavior. Polymer composition and monomer sequence distributions affect suitability for various end uses.

Process Conditions and Polymer Characteristics

Processing behavior, curing characteristics, and vulcanizate physical properties of fluoroelastomers are largely set by polymerization process conditions. Molecular weight distribution is important for most polymer compositions, and can be varied consider-

Little information on molecular weight distribution of commercial fluoroelastomers has been published. The usual method of size exclusion liquid chromatography (SELC; also known as gel permeation chromatography, GPC) is not easy to apply. SELC measures macromolecule size in solution, which varies with polymer composition as well as molecular weight. Reliable calibrations exist for only a few VDF copolymer compositions. Several TFE copolymers are so resistant to fluids that solvents suitable for SELC measurements are not available. However, some generalizations can be made, especially for VDF/HFP/TFE and VDF/PMVE/TFE fluoroelastomers, on the variation of molecular weight distribution with polymerization process condition. For these polymer families, average monomer unit weight is about 100 daltons, and polymers with low to medium-high bulk viscosities have a number-average molecular weight, Mn, in the range 60,000 to 120,000 daltons corresponding to 600 to 1,200 monomer units per chain. Bulk characteristics such as viscosity are related to weight-average molecular weight, Mw, which varies from 1.2 to 8 or more times Mn, depending on the distribution set by the polymerization process and operating conditions. Older products, such as Viton® A and B, made by the original DuPont continuous emulsion polymerization process with no added soap or transfer agents have relatively broad molecular weight distribution, with Mw/Mn about 4 to 8. The large particles (about 1 µm in diameter) contain many growing radicals. Termination is hindered, but may involve a combination of long-chain radicals as well as a combination of long-chain radicals with entering oligomeric radicals, leading to broad distribution. A similar semibatch operation, with low soap and use of an initiator level to set overall polymer viscosity, also results in broad molecular weight distribution. Such polymers and their compounds have high green strength and modulus, but poor extrusion characteristics.

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FLUOROELASTOMERS HANDBOOK

Table 4.5 Comparison of Curing Characteristics and Physical Properties[38]

Formulation, phr Polymer Tremin 283600 EST filler

GLT

Suspension Polymer

100

100

45

45

MT Black, Thermax FF N990

2.5

2.5

Calcium oxide VG

–

6.0

MgO, Elastomag 170

–

1.0

Molecular sieve 13X

–

3.0

Bisphenol AF

–

2.0

Tetrabutyl ammonium hydrogen sulfate

–

0.5

Ca(OH)2, Rhenofit CF

5

–

Peroxide, Luperox 101XL 45

2

–

Triallyl isocyanurate, Diak 7

4

–

GLT

Suspension Polymer

Process aid, octadecyl amine, Armeen 18

0.5

–

Process aid, rice bran wax, VPA 2

1.0

1.0

ML, dN·m

3.9

2.2

MH, dN·m

22.9

23.8

Formulation, phr

Cure Characteristics (MDR, 180°C)

ts2, minutes

0.52

0.29

t´50, minutes

0.93

0.42

t´90, minutes

2.74

2.70

Tensile Properties M100, MPa

14.3

8.2

TB, MPa

18.5

12.0

EB, %

153

176

Hardness, Shore A

75

74

Compression set (disks), % (70 h @ 200°C)

32

37

4 PRODUCTION OF FLUOROELASTOMERS Newer types made by either continuous or semibatch emulsion polymerization use added soap to get smaller particle size and chain-transfer agents to control polymer viscosity. These have narrow molecular weight distribution, with Mw/Mn about 2–3. Such polymers and their compounds exhibit relatively low green strength and modulus, but have good flow and extrusion characteristics. Perfluorocarbon diiodide modifiers in semibatch emulsion systems with very low initiator levels may attain “living radical” polymerizations, resulting in fluoroelastomers with very narrow molecular weight distributions, Mw/Mn about 1.2–1.5.[40] Other iodidemodified polymers made with higher initiator levels and optional cure-site monomers in continuous or semibatch emulsion systems have somewhat broader molecular weight distributions, with Mw/Mn about 1.8–2.5.[41] When bromine- or iodine-containing curesite monomers are incorporated in fluoroelastomers made by continuous emulsion polymerization with little or no added chain-transfer agents, these reactive sites may undergo transfer and branching reactions. The long chain branches give considerable high molecular weight fractions, and broad distributions,

67 with Mw/Mn about 4–8. Extensive branching and gel formation may occur in semibatch polymerization, since all polymer made stays in the reactor until polymerization is stopped. Such highly branched, broad distribution polymers give marginal to poor processing characteristics. Figure 4.8 illustrates characteristic molecular weight distributions produced by the three process variations described for polymers made with iodide transfer and/or bromine-containing curesite monomers. Operating conditions in continuous emulsion polymerization or semibatch emulsion or suspension systems can be manipulated to get tailored bimodal molecular weight distributions. To obtain a bisphenol-curable VDF copolymer with good processing characteristics, a blend of a major modified low-viscosity (LV) component with a high-viscosity (HV) component is made by cyclic operation of a single continuous emulsion polymerization reactor.[42] HV component is made with a low persulfate initiator level for a period of at least six reactor turnovers; then a chain-transfer agent is fed for a longer period of time to make the LV component. HV and LV periods alternate in a series of cycles of several hours

Figure 4.8 Fluroelastomer molecular-weight distributution.

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FLUOROELASTOMERS HANDBOOK

each, with conditions otherwise set to maintain a nearly constant polymerization rate and polymer composition. Effluent dispersion from the reactor is blended in tanks downstream before isolation of the bimodal polymer. Operation of a semibatch reactor is readily adapted to making bimodal polymers (see Sec. 4.5 for an example involving suspension polymerization). The reactor is started up with a low initiator level to make the HV component; then a transfer agent is fed to make the LV fraction desired.

4.6.2

End Groups

Three kinds of end groups are important for fluoroelastomers: ionic, nonionic, and reactive ends. The types of chain ends may largely determine the product processing and curing characteristics. The process variations discussed in the previous section give varying molecular weight distributions and also result in different end groups. Ionic end groups form from the inorganic initiators used in emulsion polymerizations. Transfer reactions with anionic soaps may also contribute to ionic end groups. Persulfate initiation results in a mixture of sulfate and carboxylate end groups in VDF copolymers, or in carboxylate end groups in TFE/ PMVE perfluoroelastomers. Redox systems, such as persulfate-sulfite, give sulfonate end groups. These ionic end groups increase the bulk viscosity of polymers and compounds by forming ionic clusters that act as chain extenders or temporary crosslinks. The effects are larger for polymers with higher fluorine content. Perfluoroelastomers made with full redox initiation and no chain-transfer agents contain sulfonate ends, which form clusters that are stable at the usual processing temperatures. The compounds are very difficult to mix and form into parts. VDF copolymers made with high persulfate initiator levels may have enough ionic end groups to interfere with bisphenol curing. The ionic ends tend to tie up variable fractions of the quaternary ammonium or phosphonium accelerators used, leading to variable cure rates. Residual soap and oligomers with ionic ends may also affect bisphenol curing. Ionic ends have little effect on radical curing, but these acidic ends may cause some premature decomposition of the organic peroxides used for curing. Ionic end groups contribute to compression set of o-ring seals. Ionic ends may be labile enough to form clusters when the seal is under strain

at high temperature. When the seal is cooled, the secondary network of ionic clusters prevents full recovery of seal shape and sealing force. Nonionic end groups form from the use of organic chain-transfer agents in emulsion polymerization, or from organic peroxide initiators used in suspension polymerization. Fluoroelastomers with mostly nonionic end groups have lower bulk viscosity, lower green strength of uncured compounds, and lower modulus and tensile strength of vulcanizates compared to similar composition with predominately ionic end groups. The polymers with nonionic end groups exhibit better compound flow and bisphenol cure characteristics. Compression set resistance is improved, since the nonionic ends do not impede shape recovery on relief of strain. Reactive ends are mainly formed from use of iodide transfer agents. When enough iodide end groups are present, the chains can be linked by attachment of multifunctional crosslinking agent to chain ends. The resulting networks can attain very good compression set resistance in seals.

4.6.3

Composition and Monomer Sequence Distributions

In the usual operation of a continuous or semibatch reactor, the monomer feed composition is essentially constant, and the reactor contains a constant composition of unreacted monomer. Under these conditions, copolymer composition is constant, with a very narrow overall composition distribution. However, the same copolymerization kinetics (reactivity ratios) that determine overall polymer composition as described in Secs. 4.3.2 and 4.3.3 also allow for the presence of monomer sequences that may differ considerably from the overall average composition. The fraction and length of certain monomer sequences may affect polymer characteristics such as the tendency to crystallize. Reactor operation may also be manipulated to produce blends of different compositions or block copolymers containing segments of different compositions within the same chain. Both of these situations are discussed in this section. W. Ring[43] calculated monomer sequencing in dipolymers by considering the relative probabilities of each monomer adding to a given radical end. The probability P11 of Monomer 1 adding to a radical ending in a Monomer 1 unit is given by:

4 PRODUCTION OF FLUOROELASTOMERS

69

k11 [M 1 ] P11 = k11 [M 1 ] + k12 [M 2 ]

tially amorphous and where they have significant crystallinity. For VDF/HFP copolymers, Sec. 4.3.3 notes that, to a good approximation, the HFP monomer does not add to a radical ending in an HFP unit, so r2 = 0 and the copolymer composition relationship reduces to Y = r1X + 1. The monomer addition probabilities P11 and P12 given by Eqs. 4.55 and 4.56 can then be expressed in terms of polymer composition Y, the ratio of VDF to HFP units in the copolymer:

Eq. (4.55)

=

r1 X r1 X + 1

Similarly, the probability P12 of Monomer 2 adding to a Monomer 1 radical end is:

Eq. (4.56)

P12 = =

k12 [M 2 ] k11 [M 1 ] + k12 [M 2 ]

Eq. (4.59)

P11 =

Y −1 Y

Eq. (4.60)

P12 =

1 Y

1 = 1 − P11 r1 X + 1

The probability P1(n) of a sequence containing n Monomer 1 units is then: Eq. (4.57)

The bulky –CF3 of HFP is attached directly to the polymer chain, crowding adjacent groups to produce severe steric hindrance, and thus stiffens the chain to reduce segment mobility for 1–2 VDF units on either side of an HFP unit. Thus, a long sequence of some 12 VDF units seems to be the minimum length required for crystallization with other similar sequences. Using α = 12 in Eq. 4.58, crystallizable fractions for VDF/HFP copolymers of various compositions can be estimated, as shown in Table 4.6. The average VDF sequence length for each composition is Y. The last column gives an estimate of the maximum crystallizable fraction in each co-

P1(n) = P11n-1P12

The fraction Q1 of Monomer 1 units in sequences α or longer in length is: Eq. (4.58)

Q1 = αP11α-1 – (α – 1)P11α

The weight fraction of copolymer in the form of Monomer 1 sequences α or longer is w1Q1, where w1 is the total weight fraction of Monomer 1 in the copolymer. These relationships can be applied to fluoroelastomer families of interest to determine composition ranges where the copolymers are essen-

Table 4.6 Crystallizable Fractions of VDF/HFP Copolymers (α = 12)

Mol % VDF

100 w1, Wt % VDF

Y, VDF/HFP

P11

Q1

100 w1Q1, % cryst’n

70.1

50

2.34

0.573

0.013

0.6

74.1

55

2.86

0.651

0.043

2.4

77.9

60

3.52

0.716

0.104

6.2

71.3

65

4.35

0.770

0.200

13.0

84.5

70

5.47

0.817

0.327

22.9

87.5

75

7.03

0.858

0.474

35.6

90.4

80

9.38

0.893

0.628

50.3

93.0

85

13.28

0.925

0.773

65.7

70

FLUOROELASTOMERS HANDBOOK

polymer. Actual crystallinity would be less, and would depend on thermal history of the copolymer (e.g., rate of cooling from the melt, annealing time, and temperature). These calculations are in general accord with observations for various VDF/HFP copolymer compositions. Copolymers containing 60% or less VDF have little or no crystallinity, and are amorphous elastomers. Copolymers containing 65%– 70% VDF have significant crystallinity, with relatively low melting ranges (40°C to 80°C). At higher VDF contents, the copolymers behave as crystalline thermoplastics, with melting ranges increasing with VDF level (100°C to 140°C). Crystalline copolymers with high VDF contents have poor lowtemperature flexibility, even though the glass transition temperature of amorphous regions decreases with increasing VDF content. From Sec. 4.3.3 on reactivity ratios, composition relationships for TFE/PMVE perfluoroelastomers are approximated reasonably well by assuming r1r2 = 0.5. From Eq. 4.14, the following relationship for r1X can be substituted into Eq. 4.55 for estimating P11 values from polymer composition Y:

Eq. (4.61)

r1 X =

(

Y −1 + 1+ Y 2 2

to a partially crystalline polymer that gives vulcanizates with a high modulus, but poor low-temperature flexibility. Special reactor operating conditions may be set up to obtain blends or block copolymers with amorphous elastomer and crystalline thermoplastic components. An elastomer in powder form has been made in a two-stage continuous emulsion polymerization system.[44] In one example, an elastomeric VDF/HFP copolymer (58% VDF) was made in the first reactor at high conversion to minimize the amount of unreacted HFP. The total effluent dispersion, including the unreacted monomer, was fed to a second reactor along with the VDF monomer and additional aqueous feed containing initiator. A thermoplastic VDF/HFP component (about 91% VDF) was made in an amount about 29% of the total blend. The dispersion from the second reactor was flocculated and spray-dried to a fine powder. Since the monomer in the second reactor was soluble in the elastomeric particles, the thermoplastic component formed as a separate phase within the elastomer matrix. The composite product, containing about 68% VDF, exhibited a glass-transition temperature of -20°C, characteristic of the elastomeric component and a crystalline melting point of about 140°C, characteristic of the thermoplastic component. The blend was cured with bisphenol to obtain a vulcanizate with a higher modulus and tensile strength than that of the first-stage elastomer alone; elongation-at-break and compression set were comparable. Compared to a physical blend of VDF/HFP elastomer with commercial poly-VDF, the cascade blend gave vulcanizates with a lower modulus, higher elongation, and better compression set resistance. In the cascade reactor operation, relatively few active radicals of the elastomeric component enter the second stage to add thermoplastic chain segments in the same macromolecule. The blend consists mostly of separate chains of the two components.

)

12

The –O–CF3 group of PMVE does not hinder chain segment mobility greatly, with the flexible –O– linkage separating the bulky –CF3 group from the chain. Thus, relatively short TFE sequences are able to crystallize, and a value of α = 8 appears reasonable for the lower limit of crystallizable segment lengths. Estimates of crystallizable fractions for a few TFE/PMVE compositions are shown in Table 4.7. The first two compositions, with TFE content up to about 55%, are nearly amorphous, with little crystallinity likely. The third composition corresponds

Table 4.7 Crystallizable Fractions of TFE/PMVE Copolymers (α = 8)

Mol % TFE

100 w1, Wt % TFE

Y, TFE/PMVE

P11

Q1

100 w1Q1, % cryst’n

62.4

50

1.66

0.565

0.074

3.7

67.0

55

2.03

0.622

0.131

7.2

73.9

63

2.83

0.707

0.269

17.0

4 PRODUCTION OF FLUOROELASTOMERS The Daikin “living radical” semibatch emulsion polymerization process can be used to make block copolymers with segments of different composition.[45] An iodine-terminated VDF/HFP/TFE elastomeric component is made with perfluorocarbon diiodide and a small amount of initiator in a first stage of operation. Unreacted monomer is removed, the dispersion is recharged to the reactor, and polymerization is continued with VDF or TFE/E added to make thermoplastic chain segments attached to central elastomeric segments of block copolymer macromolecules. The copolymer can be compounded and cured by the usual elastomer processing techniques. However, it can also be molded as a thermoplastic at a relatively low temperature, then can be removed from the mold and optionally cured by raising the temperature of the part.[46] Adapting a similar diiodo transfer process, Carlson developed A-B-A segmented thermoplastic elastomers with compositions more resistant to strong base and solvents.[47] In one embodiment, the central elastomeric B blocks have the base-resistant composition E/TFE/PMVE, and the outer thermoplastic blocks are E/TFE. Uncompounded molded parts have good properties without curing, but may be cured by ionizing radiation for enhanced properties.

4.7

Monomer Recovery

In the continuous emulsion polymerization process, as shown in Fig. 4.5, pressure is let down at the reactor exit so that the unreacted monomer flashes in the line leading to a degassing vessel. A small amount of defoamer may be added to avoid entrainment and carryover of polymer dispersion from the degasser. Effluent from the degasser goes to a second vessel at a lower pressure to remove most of the rest of the monomer by diffusion from the small particles. The vaporized monomers may be recycled directly back to the suction of the reactor feed compressor. However, it is usually more convenient to take the unreacted monomers through a recycle compressor to a monomer recovery tank. The monomer can then be fed at a controlled rate from the recovery tank to the reactor feed compressor. Less volatile components in reactor efflu-

71 ent dispersion are usually not recovered in this process; they are removed in polymer drying. In semibatch polymerization processes, as shown in Fig. 4.6, the monomer is recovered after completion of the polymerization batch. It is possible to vent unreacted monomer directly from the reactor to a monomer recovery compressor and hold tank. However, control of foaming and carryover is difficult with the limited head space in the reactor. Usually, the dispersion is let down at a controlled rate to a degassing vessel maintained at a low pressure. If a polymer of a similar composition is to be made in the next reactor batch, a heel of dispersion plus a considerable fraction of the unreacted monomer may be left in the reactor. Monomer vaporized from the degasser goes through a compressor to a recovery tank. The degassing vessel may be heated to allow final monomer removal by unsteady state diffusion at low pressure. The recovered monomer is fed to the reactor feed compressor to provide a proper composition for starting the next polymerization batch.

4.8

Isolation

In fluoroelastomer emulsion polymerization processes, dispersions are stabilized by anionic soaps, oligomers, and end groups. Salts of aluminum, calcium, or magnesium are usually used to cause coagulation into particles of convenient size (about 1 mm diameter) for washing and separation by filtering or centrifuging. The coagulant metal ion is chosen for its effectiveness at low concentration and also to keep the soap in solution to facilitate its removal. Coagulation conditions (temperature, holdup, concentration) are controlled to get reliable crumb size for washing, separation, and drying. In the original DuPont continuous emulsion polymerization process for VDF/HFP/(TFE) elastomers, described in Ref. 27 and shown in Fig. 4.9, isolation is also a continuous operation. Potassium aluminum sulfate solution is added to the dispersion in an agitated tank to produce a slurry of crumb that is fed to a continuous centrifuge for removal of most soap and salts. Crumb from the centrifuge is suspended in fresh water in a second wash tank. The slurry is again centrifuged and the wet crumb is fed to a continuous-belt conveyer air oven dryer. Dry crumb is

72

FLUOROELASTOMERS HANDBOOK

Figure 4.9 Isolation by crumb washing and drying.

taken to a crumb blender, then fed to an extruder to produce the final form of pellets or sheet for packaging. Isolation of a polymer from a semibatch emulsion process is similar. Batch coagulation may be carried out by adding coagulant to the dispersion in a stirred tank. Polymer crumb may be separated by filtration or centrifuging, and washed to remove residual soap and salts before drying in an air oven or extruder. In a different version of a continuous isolation process,[48] polymer dispersion is pumped through a coagulation section to a dewatering extruder, as shown in Fig. 4.10. Coagulant is added in-line, and conditions are set to produce large polymer agglomerates. The extruder is set up in a vertical configuration with the inlet in the top section with a large diameter screw. Water containing residual soap and salts is removed from the top. The system is maintained under enough pressure to collapse vapor bubbles that could otherwise cause some polymer crumb to rise to the top water exit. The screw picks

up the polymer and compresses it in a metering section with a smaller diameter to force almost all of the water out of the top of the machine. Polymer with less than 5% water content exits the bottom outlet of the extruder. Final drying is carried out in a vented drying extruder. Since the dewatering extruder removes some 99% of the water in the original dispersion, most water-soluble soap and salts are also removed. Such a system is adequate for continuous emulsion polymerization systems using modest soap levels for dispersion stabilization. Extrusion isolation systems can also be used in semibatch emulsion polymerization processes. However, the higher soap levels used may necessitate a separate coagulation and crumb-washing step before extrusion. A major fraction of the bisphenol-curable VDF/ HFP/TFE fluoroelastomers produced is sold as a precompound, rather than a gum polymer. The isolated gum polymer from a process described above is sent to a compounding facility for incorporation of bisphenol crosslinking agent, accelerator, and optional

4 PRODUCTION OF FLUOROELASTOMERS

73

Figure 4.10 Extruder isolation system.

processing aids. The precompound compositions are usually proprietary, and are designed for specific end uses and fabrication methods. The advantage of precompounds to customers is that the supplier assures good dispersion of curatives and reproducible processing characteristics. Conventional rubber compounding equipment is used, usually an internal mixer and a sheet extruder.

4.9

Process Safety

The major hazards in fluoroelastomer production processes involve handling of toxic or potentially explosive monomer mixtures. Hazards relating to individual monomers are discussed in Ch. 3. In some cases, mixtures may be less hazardous than one or more of the monomers present. For example, the explosive potential of TFE or VDF is reduced in mixtures containing HFP or PMVE. In other cases, mixtures may be more energetic than the individual monomers (e.g., TFE with olefins such as propylene or ethylene). Explosivity testing is necessary to establish the explosion potential of various mixtures at conditions encountered in production facilities. Such testing can be used to establish ratios of required pressure relief areas to volumes of monomer under pressure. Tests can also establish ranges of

monomer composition, pressure, and temperature that can be allowed in plant operation. Systems designed for VDF/HFP copolymerization may not be suitable for TFE/propylene polymerization, for example. In addition to proper design of relief systems, it may be necessary to provide additional protection to personnel by barricading some systems to avoid consequences of possible compromising of relief devices by polymer plugs. Volumes of monomers under pressure should be minimized in monomer feed and polymerization reactor systems. This may be difficult for semibatch systems, as discussed in semibatch reactor design and operation Sec. 4.4.3. Propagation of deflagration pressure pulses from one vessel to another should be prevented by proper placement of relief devices and by minimizing line sizes. Potential ignition sources for monomer deflagration should be minimized by proper design of the system and by proper operating procedures. Electrical systems should not produce arcs or sparks, and surface temperatures should be limited. Electrical energy in instruments should be lower than levels necessary for ignition of monomer mixtures. Metal parts of moving equipment such as agitators should be designed to avoid metal-to-metal contact that could produce sparks or hot surfaces. Trace oxygen levels in monomers should be monitored, and operating steps should be taken to remove oxygen

74 and air from the systems. Trace oxygen can lead to initiation of polymerization through formation and decomposition of monomer peroxides. Polymerization in high-pressure monomer feed systems can give plastic compositions that can cause plugging or local hot spots that might initiate deflagration. Monomer piping should be as direct as possible, avoiding sharp elbows and tees to closed pipe sections, with dead volumes that cannot be readily flushed. In addition to having operating procedures set up to avoid monomer hazards during normal production operation, adequate procedures for equipment maintenance and modification are needed. A large fraction of mishaps causing injury or equipment damage have occurred during mechanical maintenance rather than production operation. Special attention must be paid to assuring adequate flushing and clearing of equipment before mechanical work is started. Similar attention is necessary when putting equipment back into service, especially in careful removal of air before introducing monomers. A number of toxic materials are present in a fluoroelastomer production facility. Very low exposure limits have been established for several major fluoromonomers. Monitoring of work areas is necessary to detect leakage of gaseous monomers, so that steps can be taken to limit exposure of operators to potentially toxic levels. Handling of minor liquid components, such as bromine- or iodine-containing cure-site monomers and transfer agents, may require special procedures and personal protective equipment. For some materials, toxicity information may be limited; these should be handled by procedures adequate to protect personnel from exposure. Peroxide initiators should be handled by procedures recommended by their suppliers to avoid potential hazards caused by decomposition in storage or contact with readily oxidized materials. Considerations for storage and handling of peroxydicarbonates are discussed in Sec. 4.5.2. Monomer compressors should be carefully monitored and controlled to avoid condensation between stages because of the potential for equipment damage or release of excessive amounts of monomers from relief devices. Maximum temperatures should be kept well below those at which monomer decomposition can occur. Trace oxygen levels should be monitored and controlled to avoid possible polymerization in compressor systems which have the potential to plug or initiate monomer deflagration.

FLUOROELASTOMERS HANDBOOK In continuous emulsion polymerization at normally high conversion, loss of reaction (e.g., by interruption of initiator feed or by introduction of a retarder) may lead to the rapid buildup of monomer mixtures with an increased explosivity hazard and with volume flows above the handling capacity of the downstream degassing equipment. Quick action is required to shut off the monomer feeds and to clear the monomers from the reactor by continuing the water feed. The reason for the loss of reaction should be established and corrected before restarting with the normal operating procedure. Proper design and operating procedures are necessary to assure the safe operation of other equipment normally present in chemical process plants, including pumps, agitated vessels, conveyors, extruders, and the like. These will not be covered here.

4.10 Commercial Process Descriptions Commercial continuous fluoroelastomer production facilities used by DuPont Dow Elastomers have the general configuration depicted in Fig. 4.5 for continuous polymerization and monomer recovery, with isolation carried out either by crumb handling as shown in Fig. 4.9 or by extruder dewatering and drying as shown in Fig. 4.10. With the wide range of VDF/HFP/TFE and VDF/PMVE/TFE compositions made, polymerization rates per unit volume vary over a wide range. To keep the overall production rate in a reasonably narrow range for good operation and control, it is convenient to have more than one reactor size available in each facility. Then, a relatively small reactor can be used for products with high polymerization rates per unit volume, and a larger reactor is available for slower polymerizing types. This arrangement also allows for optimizing reaction conditions to get the desired polymer characteristics. Other considerations for design, operation, and control of continuous emulsion polymerization systems are discussed in Sec. 4.4.2 under the headings “Continuous reactor design and operation” and “Continuous emulsion polymerization control.” Monomer recovery and isolation systems are described in Secs. 4.7 and 4.8.

4 PRODUCTION OF FLUOROELASTOMERS Less information is available on the various semibatch process facilities operated by the other fluoroelastomer suppliers. Generally, polymerization system configurations are as shown in Fig. 4.6 and as described in Secs. 4.4.3, and 4.7 and 4.8. As in the continuous process, it may often be convenient to have reactors of different sizes available to accommodate the very wide ranges of polymerization rates per unit volume exhibited by different products. Previous discussion of major monomer handling has assumed that these monomers would be

75 fed as gases at temperatures well above critical temperatures for individual components or mixtures. It is also possible to keep the feed monomers in the liquid phase, as in some processes for making plastic TFE copolymers. Feed system pressures need to be high and temperatures low to keep monomers in liquid form. Such a system may be particularly useful for a product like the Daikin perfluoroelastomer, since the perfluoroalkyl vinyl ether used as the major comonomer is a liquid with a high critical temperature.

REFERENCES 1. Dostal, H., Monatsh. 69:424 (1936) 2. Alfrey,.T., Jr., and Goldfinger,G., J. Chem. Phys. 12:205 (1944) 3. Mayo, F. R., and Lewis, F. M., J. Am. Chem. Soc. 66:1594 (1944) 4. Simha, R., and Branson, H., J. Chem. Phys. 12, 253 (1944) 5. F. T. Wall, J. Am. Chem. Soc. 66:2050 (1944) 6. Walling, C., and Briggs, E. R., J. Am. Chem. Soc. 67:1774 (1945) 7. Moore, A. L., and Tang, W. K., U.S. Patent 3,929,934, DuPont Co., (Dec. 30, 1975) 8. Apotheker, D., and Krusic, P. J., U.S. Patent 4,035,565, DuPont Co., (Jul. 12, 1977) 9. Gilbert, R. G., Emulsion Polymerization – A Mechanistic Approach, Academic Press (1995) 10. Bovey, F. A., Kolthoff, I. M., Medalia, A. I., and Meehan, E. J., “Emulsion Polymerization” (1955) 11. Khan, A. A., U.S. Patent 4,524,197, DuPont Co., (Jun. 18, 1985) 12. Lyons, D. F., Moore, A. L., and Tang, P. L., U.S. Patent 6,774,164, DuPont Dow Elastomers LLC, (Aug. 10, 2004) 13. Gilbert, R. G., op .cit., pp. 51–53. 14. Gilbert, R. G., Particle Formation, op. cit., Ch. 7, pp. 292–342. 15. Gilbert, R. G., op. cit., p. 299. 16. Fitch, R. M., and Tsai, C. H., Polymer Colloids, (R. M. Fitch, ed.), Plenum, New York (1971) 17. Ugelstad, J., and Hansen, F. K., Rubber Chem. Tech. 49:536 (1976) 18. Richards, J. R., Congalidis, J. P. and Gilbert, R. G., J. Appl. Polym. Sci. 37: 2727 (1989) 19. Overbeek, J. T. G., Colloid Science, (H. R. Kruyt, ed.), Elsevier, Amsterdam (1960) 20. Richards, J. R., Congalidis, J. P., and Gilbert, R. G., ACS Symp. Series (Computer Applications in Applied Polymer Science), (T. Provder, ed.), Am. Chem. Soc., Washington, DC 404:360 (1992) 21. Gilbert, R. G., op. cit., 314–320 22. Gilbert, R. G., op. cit., 326 23. Gilbert, R. G., op. cit., 310–313 24. Bonardelli, P., Moggi, G., and Russo, S. Makromolekulare Chemie, Suppl. 10/11 11–23 (1985) 25. Billmeyer, F. W., Jr., Textbook of Polymer Science, 79–83, Interscience Publishers, New York (1965) 26. Billmeyer, F. W., Jr., op. cit., pp. 277–279.

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FLUOROELASTOMERS HANDBOOK

27. Bailor, F. V., and Cooper, J. R., U.S. Patent 3,536,683, DuPont Co., (Oct. 27, 1970) 28. Tang, P. L., U.S. Patent 6,512,063, DuPont Dow Elastomers LLC, (Jan. 28, 2003) 29. Rexford, D. R., U.S. Patent 3,051,677, DuPont Co., (Aug. 28, 1962) 30. Moore, A. L., U.S. Patent 3,839,305, DuPont Co., (Oct. 1, 1974) 31. Tatemoto, M., Suzuki, T., Tomada, M. , Furukawa, Y., and Ueta, Y., U.S. Patent 4,243,770, Daikin Kogyo Co., (1980) 32. Arcella, V., Brinati, G., Albano, M., and Tortelli, V., U.S. Patent 5,674,959, Ausimont S.p.a. (Oct. 7, 1997) 33. Ebnesajjad, S., Fluoroplastics, Melt Processible Fluoropolymers, Vol. 2, 84-88, William Andrew Inc., Norwich, NY, (2003) 34. Dumoulin, J., U.S. Patent 4,524,194, Solvay & Cie, (Jun. 18, 1985) 35. Hayashi, K., and Matsuoka, Y., U.S. Patent 4,985,520, Asahi Chemical Industry Co., Ltd. (Jan. 15, 1991) 36. Hayashi, K., Saito, H., and Toda, K., U.S. Patent 5,218,026, Asahi Chemical Industry Co., Ltd., (Jun. 8, 1993) 37. Hayashi, K., Hashimura, K., Kasahara, M., and Ikeda, Y., U.S. Patent 5,824,755, DuPont Co. (Oct. 20, 1998) 38. Duvalsaint, F., and Moore, A. L., U.S. Patent 6,348,552 B2, DuPont Dow Elastomers, L.L.C. (Feb. 19, 2002) 39. Moore, A. L., U.S. Patent 5,032,655, DuPont Co., (Jul. 16, 1991) 40. Tatemoto, M., and Morita, S., U.S. Patent 4,361,678, Daikin Kogyo Co., (Nov. 30, 1982) 41. Moore, A. L., U.S. Patent 5,077,359, DuPont Co., (Dec. 31, 1991) 42. Moore, A. L., U.S. Patent 3,839,305, DuPont Co., (Oct. 1, 1974) 43. Ring, W., J. Polymer Science, Part B, Polymer Letters 1, 323 (1963) 44. Moore, A. L., and Tang, W. K., U.S. Patent 3,929,934, DuPont Co., (Dec. 30, 1975) 45. Tatemoto, M., Suzuki, T., Tomoda, M., Furukawa, Y., and Ueta, Y., U.S. Patent 4,243,770, Daikin Kogyo Co. (Jan. 6, 1981) 46. Tatemoto, M., U.S. Patent 5,198,502, Daikin Kogyo Co. (Mar. 30, 1993) 47. Carlson, D. P., U.S. Patent 5,284,920, DuPont Co. (Feb. 8, 1994) 48. Covington, R. A., and Ekiner, O. M., U.S. Patent 4,132,845, DuPont Co., (Jan. 2, 1979); U.S. Patent 4,408,038, DuPont Co. (Oct. 4, 1983)

5 Cure Systems for Fluoroelastomers 5.1

Introduction

Elastomer cure systems are designed to give stable networks for good mechanical properties and environmental resistance comparable to that of the base polymers. In addition, cure kinetics must be controlled to get adequate processing safety (i.e., negligible crosslinking at temperatures of 100°C to 140°C). This allows for mixing of compounds on tworoll mills or in internal mixers, and for extrusion of rod or sheet preforms. At molding temperatures of 160°C to 200°C, an adequate delay is necessary for mold flow before onset of rapid crosslinking to a high state of cure. Compounds should be designed to facilitate good mixing, smooth extrusion, and clean demolding of cured parts. These cure system characteristics are also desirable for fluoroelastomers, but the nature of the polymers makes it difficult to attain all the desirable features noted above. Fluoroelastomers are designed for outstanding resistance to high temperature and aggressive fluids, so development of crosslinking systems with comparable environmental stability is a major challenge. In a fluorinated matrix, most cure system components have limited solubility and reactivities are often quite different from those in hydrocarbon elastomers. Polymer and cure system development for the various fluoroelastomer compositions should be carried out together to obtain compounds suitable for economical commercial production of parts. In most cases, the cure system used initially for each polymer family has been replaced or modified substantially to attain better processing and curing behavior and enhanced final product properties. This chapter discusses the major cure systems developed for four fluoroelastomer families: VDF/HFP/(TFE), VDF/PMVE/TFE, perfluoroelastomers, and TFE/olefin elastomers.

5.2

VDF/HFP/(TFE) Copolymers: Diamine, Bisphenol, Peroxide

Three major systems have been used commercially for curing of VDF/HFP dipolymers and VDF/ HFP/TFE terpolymers. Two systems are based on

dehydrofluorination of reactive HFP-VDF sequences to form double bonds in the polymer chains, followed by reaction of nucleophilic diamine or bisphenol to form crosslinks. For VDF/HFP/TFE elastomers with high fluorine content, peroxide or radical cure systems have been developed utilizing bromine or iodine cure sites.

5.2.1

Diamine Cure

The first practical cure system for VDF/HFP fluoroelastomers was based on diamine derivatives with magnesium oxide. The diamine served as both dehydrofluorinating agent and crosslinker, and the magnesium oxide took up the HF formed. Diamines such as hexamethylene diamine are too reactive at low temperature, so derivatives were devised to moderate the activity and allow acceptable processing safety. The most widely used derivative was the carbamate salt of hexamethylene diamine, +H3N– (CH2)6–NH–COO–, sold by DuPont as Diak No. 1 curative. A dicinnamylidene derivative (Diak No. 3) has also been used, ΦCH=CH–CH=N–(CH2 )6 – N=CH–CH=CHΦ, where Φ represents a phenyl group. The usual acid acceptor in the compound was MgO with relatively large particle size. Compounds were relatively simple, containing polymer, diamine, MgO, inert filler, and an optional processing aid. A typical dipolymer formulation is listed below: VDF/HFP Dipolymer

100

MT black (N990)

30

MgO (Maglite Y)

15

Diak No. 1

1.5

Processing Aid

1

MT black is often used as a non-reinforcing filler in fluoroelastomers. This carbon black is produced by a thermal process, and has relatively large particles with few reactive groups on surfaces. A typical processing aid is a wax such as carnauba wax that is somewhat incompatible with the fluoroelastomer at elevated temperature so that it migrates to interfaces and acts as a flow lubricant or mold release aid. The mechanism proposed for the diamine cure[1] involves reaction of the amine base with polymer chains to eliminate HF and form double bonds, followed by reaction of the nucleophilic diamine with

78

FLUOROELASTOMERS HANDBOOK

the double bonds to form crosslinks with imine structure. The exact nature of active sites in the chains or of the resulting crosslinks was not determined. Water formed from the neutralization of HF by MgO had to be removed by postcuring in an air oven. With water present in vulcanizates at high temperature, hydrolysis of crosslinks could occur, forming carbonyl structures on the polymer chains with regeneration of the amine crosslinking agent. Except for some use of Diak No. 3 in latex compounding, the diamine cure system is little used now. The system has considerable processing deficiencies, giving premature crosslinking (scorch) at 100°C to 140°C and relatively slow cures at molding temperatures (160°C to 180°C). Vulcanizate properties are good, but high-temperature compression set resistance is mediocre, and retention of physical properties on long exposure to temperatures above 200°C is relatively poor. The chemistry of the diamine cure gives some insight into the problem of embrittlement of seals made of VDF/HFP/TFE fluoroelastomers in longterm exposure at high temperatures to automotive lubricants. Engine oils and transmission lubricants contain large amounts of metal corrosion inhibitors and dispersants that break down to form multifunctional amines. These can react to form enough additional crosslinks to lead to excessive hardness and eventual seal failure. However, actual performance of VDF/HFP/TFE elastomers in automotive oil seals has been excellent, with rare failures under extreme service conditions. The high fluorine content of the terpolymers greatly reduces swelling by oil and incursion of amines, thus minimizing additional crosslinking and giving long service lifetime of the seals.

5.2.2

Bisphenol Cure

Starting in 1970, the bisphenol cure system displaced the diamine system for curing VDF/HFP and VDF/ HFP/TFE fluoroelastomers. This system has the advantages of excellent processing safety, fast cures to high states, excellent final properties, and especially high-temperature compression set resistance in seals. While a number of aromatic dihydroxy compounds can be used as crosslinking agents, including the simplest bisphenol (hydroquinone), the preferred crosslinker is Bisphenol AF, 2,2-bis-(4-hydroxyphenyl)hexafluoropropane, HOΦ–C(CF3)2–ΦOH.[2] An

accelerator such as benzyltriphenylphosphonium chloride,[3] Φ3P+CH2ΦCl– (BTPPC), is necessary, along with inorganic bases, usually calcium hydroxide and magnesium oxide with small particle sizes. A number of other quaternary phosphonium or ammonium salts may also be used as accelerators. A typical VDF/HFP dipolymer compound used for oring seals is as follows: VDF/HFP Dipolymer MT black

100 30

MgO (Maglite D)

3

Ca(OH)2

6

Bisphenol AF

2

BTPPC

0.55

The dipolymer has to be designed to have low ionic end groups[4] to avoid interference with the accelerator, and polymer molecular weight distribution may be adjusted to get the desired rheology for processing.[5] The cure response of this compound is shown in Fig. 5.1,[6] as measured by oscillating disk rheometry (ODR). The torque sensed by the oscillating disk is a measure of the modulus of the compound at the curing temperature of 177°C. For this system, no cure occurs for more than 30 minutes at a processing temperature of 121°C, and a delay of some 2.5 minutes, sufficient to allow mold flow, is observed at the cure temperature of 177°C. Rapid crosslinking then occurs, so that a high cure state is reached within about 5 minutes. Bisphenol and accelerator levels can be adjusted to vary cure rates and states for various applications and processing methods, while retaining the general shape of the cure curve. Crosslink density is proportional to Bisphenol AF level in the range 0.5 to 4 phr (parts per hundred parts of polymer).[7] Curing and properties are shown in Table 5.1 for a VDF/HFP copolymer product[8] offered for compression or injection molding of o-rings, extruded shapes, and calendared sheet. This material is typical of available commercial products, mostly precompounds containing bisphenol and accelerator, offered by the major fluoroelastomer suppliers. The polymer has viscosity, molecular weight distribution, and end groups adjusted for excellent rheology in mold flow and extrusion with low die swell. The polymer is precompounded with curatives to assure the good dispersion necessary for reproducible cure response. Curative levels are not disclosed,

5 CURE SYSTEMS FOR FLUOROELASTOMERS but the precompound probably contains about 2 phr Bisphenol AF crosslinker and 0.5 phr BTPP+ accelerator (as a salt with the bisphenol, no chloride present) to get the high state of cure and moderately high cure rate required for this application. The precompound, VITON® A-401C, has medium viscosity, ML-10 (121°C) = 42. The compound shown meets major specifications for fluoroelastomer o-rings, including original stress-strain properties, retention of properties after aging at 275°C, low swell in fuel and lubricating fluid, and resistance to compression set at 200°C. The heat aging data are consistent with very long service life of bisphenol-cured fluoroelastomers, >3,000 hours at 232°C (450°F) and >1000 hours at 260°C (500°F). The modest decrease in tensile strength and increase in elongation at break indicate some network breakdown at 275°C. The mechanism of bisphenol curing has been elucidated by W. W. Schmiegel in a series of studies of the reactions of various VDF copolymers with a hydroxylic base, amines, and phenols in a solution, using 19F nuclear magnetic resonance (NMR) measurements to determine structural changes in the polymers.[9][10] Figure 5.2[10] shows NMR spectra of a VDF/HFP copolymer before and after treatment with a hydroxylic base in dimethylacetamide, CH3–C(:O)–N–(CH3)2,

79 (DMAC) solution. Schmiegel[10] interpreted these changes as involving the highly selective dehydrofluorination of isolated VDF units, in the chain sequence -HFP-VDF-HFP-, with eventual formation of a diene structure, as shown in Fig. 5.3. The concentration of isolated VDF units can be estimated using the monomer sequencing relationships in Sec. 4.5.3. For a VDF/HFP dipolymer containing 60 wt% VDF, the mole ratio VDF/ HFP is Y = 3.52 and the probability of VDF addition to a VDF radical end is P11 = (Y – 1)/Y = 0.716. From Eq. (4.58), the fraction Q1 of VDF sequences two or more units in length (a = 2) is 2P11 – P112 = 0.92, so the fraction of VDF in isolated units is 1 – Q1 = 0.08, equivalent to about 0.75 moles VDF in -HFP-VDF-HFP- sequences per kg polymer. In the reaction scheme shown in Fig. 5.3, attack by hydroxide results in a double bond formed by abstraction of the tertiary fluorine of HFP and the adjacent acidic hydrogen of VDF. Fluoride ion initiates rearrangement of the double bond, and the resulting allylic hydrogen is abstracted by fluoride, a relatively strong base in the dipolar aprotic DMAC solvent. The reaction sequence results in formation of bifluoride and a conjugated diene structure in the chain.

Figure 5.1 ODR – Bisphenol cure.[6] Cure response by oscillating disk rheometry (ODR) at 177°C of a compound optimized for use in o-rings. The maximum cure rate is the initial slope of the curve: ts2, the time to initiation (increase of the torque by two points from the minimum); tc90 is the time for 90% completion of the cure; and ML, the degree of the state of the cure. The recipe consists of 100 parts polymer, 30 parts MT Black, 6 parts calcium hydroxide, 3 parts magnesium oxide, 0.55 parts of benzyltriphenylphosphonium chloride (BTPPC), and 2 parts of Bisphenol AF.

80

FLUOROELASTOMERS HANDBOOK

Table 5.1 Performance of Bisphenol-Cured VDF/HFP Dipolymer[8]

Compound, phr VITON® A-401C precompound

100

Magnesium oxide (Maglite D)

3

Calcium hydroxide

6

MT Black (N990)

0

Cure, ODR at 177ºC, Microdie, 3º arc ML, in-lb

15

MH, in-lb

122

ts2, minutes

1.7

tc90, minutes

3.2

Vulcanizate Properties, Stress/Strain at 23ºC Press cured 10 minutes at 177ºC M100, MPa

4.6

TB, MPa

9.9

EB, %

57

Hardness, Durometer A

74 After heat aging 70 hours in air at:

Post cured 24 hours at 232ºC

Original

M100, MPa TB, MPa EB, % Hardness, Durometer A

200ºC

232ºC

6.4

6.9

7.2

13.4

14.0

14.0

275ºC

10.3

199

198

177

240

75

78

80

75

Compression set, %, Method B, 25×3.5-mm o-rings 70 hours at 200ºC

15

336 hours at 200ºC

29

70 hours at 232ºC

37

5 CURE SYSTEMS FOR FLUOROELASTOMERS

81

Figure 5.2 NMR of dipolymer before and after base treatment.[10] NMR spectra (94.1 MHz 19F) of VF2 /HFP polymer before (top) and after (bottom) treatment with hydroxylic base in DMAC solution at 20°C (2,5dichlorobenzotrifluoride internal standard). Arrows indicate changes in peak intensities.

Figure 5.3 Reaction of dipolymer and base.[10]

82 Schmiegel made further NMR measurements on VDF/HFP dipolymer treated with a cyclic amidine base and Bisphenol AF or its monofunctional analog to demonstrate the formation of the diene sequence shown in Fig. 5.3, and subsequent nucleophilic substitution of the phenol. NMR measurements were also made on a solvent-swollen pseudovulcanizate of a low molecular weight fluid dipolymer compounded with Bisphenol AF, BTPPC, MgO, and Ca(OH)2. From these studies, Schmiegel concluded that, in practical curing situations, a bisphenol-derived phenolate attacks the diene structure in the polymer, leading to dienic phenyl ether crosslinks, as shown in Fig. 5.4. When a phosphonium salt such as BTPPC is used as accelerator, the phosphonium ion is believed to undergo several cycles of conversion from fluoride (or bifluoride), to hydroxide, to phenoxide, to fluoride, before exhaustion of the phenol. Ultimately, the benzyltriphenylphosphonium ion is converted to triphenylphosphine oxide, which is probably removed during the oven post cure. For the oring compound described previously, the Bisphenol

Figure 5.4 Bisphenol crosslinking scheme.[10]

FLUOROELASTOMERS HANDBOOK AF crosslinker level of 2 phr corresponds to about 60 mmol/kg polymer and the BTPPC accelerator level of 0.55 phr is considerably lower at about 14 mmol/kg polymer. Thus, a number of accelerator reaction cycles are necessary to utilize the bisphenol functionality. This level of bisphenol gives about 120 mmol linkages per kg polymer, corresponding to an average segment molecular weight between links of about 8300 Daltons, or 100 mer units. For low to medium viscosity polymers with number average molecular weights in the range 80,000 to 100,000 Daltons, this relatively high crosslink density corresponds to about 10 to 12 links per chain. It should be noted that the total concentration of reactive -HFP-VDF-HFP- sequences in commercial dipolymer is far higher than that needed for curing. Schmiegel[10] found that, in the absence of free bisphenol, hydroxide attack on the diene structure could form a dienone, as shown in Fig. 5.5. This structure would be susceptible to further hydrolysis and chain cleavage. Commercial bisphenol vulcanizates contain excess calcium hydroxide, so exposure to hot water or steam can lead to eventual network breakdown. VDF/HFP/TFE fluoroelastomers with high fluorine content and greater fluid resistance than the VDF/HFP copolymers discussed above generally give slower cures. Schmiegel[10] studied reactivities in solution of such terpolymers and of several VDF/TFE thermoplastic compositions made by the author. He found that all sequences of single VDF units isolated between perfluorinated monomer units could be dehydrofluorinated readily, but ease of nucleophilic attack on the resulting unsaturated structures varied considerably. Unsaturated structures from sequences -TFE-VDF-TFE- and -TFE-VDF-HFPhad low reactivity toward nucleophiles, and thus, gave little crosslinking by bisphenols. Diene structures from -HFP-VDF-HFP- and -HFP-VDF-TFE- were readily attacked by nucleophiles and crosslinked by bisphenols. Rates of gelation by Bisphenol AF and a cyclic amidine base in DMAC solution were higher for VDF/HFP/TFE (61/17/22 mole %) terpolymer than for VDF/HFP (78/22 mole %) dipolymer. Thus, the slower terpolymer cures in practical bulk systems appear to be caused by the more highly fluorinated medium. The

5 CURE SYSTEMS FOR FLUOROELASTOMERS

Figure 5.5 Hydroxide attack on diene.[10]

terpolymer is less polar, so it is less able to support the ionic intermediates formed during curing. Also the solubility and mobility of curatives are lower in high-fluorine terpolymers. A number of accelerators have been developed for bisphenol curing as alternatives to phosphonium salts such as BTPPC. Patent cross-licensing between DuPont and 3M initially excluded Daikin and Montedison from using the preferred phosphonium accelerators. Daikin developed various bases containing nitrogen heterocyclic structures, including cyclic amidines such as 8-benzyl-1,8-diazabicyclo[5,4,0]-7-undecenium chloride. Montedison developed accelerators based on amino phosphinic derivatives[11] and bis(triarylphosphin)iminium salts.[12] Most of these accelerators were included with bisphenol as ingredients in proprietary fluoroelastomer precompounds offered commercially; exact compositions are generally not disclosed by suppliers. As noted for the DuPont compound described in Table 5.1, a useful variant of a phosphonium accelerator is its bisphenolate salt, thus eliminating the halide anion that could cause demolding problems. Quaternary ammonium salts are also effective accelerators for bisphenol cures. In particular, Schmiegel and Carlson[13] found that tetrabutylammonium hydrogen sulfate (TBAHS) gives fast cures of high-fluorine VDF/HFP/TFE terpolymers to high states with good scorch resistance. A major advantage is that compounds with TBAHS accelerator give much less mold fouling than compounds

83 with accelerators containing chloride, bromide, or iodide anions. In addition to hydrogen sulfate, other anions associated with tetrabutylammonium ion give little or no mold fouling, including fluoride, dihydrogen phosphate, acetate, methane sulfonate, toluene sulfonate, periodate, and bisphenolate. TBAHS was also shown in patent examples to work well with bisphenols other than Bisphenol AF. TBAHS and BTPPC are compared in terpolymer compounds in patent examples from Ref. 13, summarized in Table 5.2. The terpolymers have composition VDF/HFP/ TFE = 45/30/25 wt % (68.5% F) and 35/35/30 wt % (70% F), and were compounded with 30 phr MT black, 4.5 phr calcium hydroxide, and 3 phr high activity magnesium oxide, and curatives as listed in Table 5.2. Compared to BTPPC in these high-fluorine terpolymers, TBAHS gives lower compound viscosity, faster cures to higher states, better compression set resistance, and much less fouling in compression molding tests carried out for fifty molding cycles.

5.2.3

Peroxide Cure

Fluoroelastomers cured with peroxides, or free radicals, exhibit improved resistance to steam, hot water, and aqueous acids over those cured with bisphenols. Peroxide-cured compounds generally do not contain much unsaturation and inorganic bases, so they are less susceptible to attack by aqueous fluids. On the other hand, the crosslinking agents (“radical traps”) used give lower thermal stability than bisphenols. For peroxide curing, fluoroelastomers must contain sites reactive toward free radicals, usually bromine or iodine introduced within chains by incorporation of cure-site monomers or at chain ends by chain-transfer agents. In the late 1970s, DuPont offered the first commercial peroxide-curable fluoroelastomers, containing about 0.5%–0.9% bromine in cure-site monomers such as 4-bromo3,3,4,4-tetrafluorobutene (BTFB).[14] Conditions in the continuous emulsion polymerization process used can be adjusted to minimize unwanted transfer to incorporated bromine-containing units, thus avoiding excessive long-chain branching. Such transfer and branching reactions are more difficult to minimize in semibatch processes, since all the polymer formed remains in the reactor exposed to free radical activity until the end of the batch polymerization. Daikin later developed the semibatch “living radical” iodine

84

FLUOROELASTOMERS HANDBOOK

Table 5.2 Comparison of Accelerators in Bisphenol Cures of VDF/HFP/TFE Terpolymer Compounds[13]

Elastomer

Terpolymer, 68.5% F

Patent Example

Terpolymer, 70% F

4

3

Comparative 2

5

Comparative 3

Bisphenol AF

1.90

1.90

1.9

2.00

2.3

TBAHS

0.67

1.00

Curatives, phr

BTPPC

0.86 1.00

1.03

Mooney Scorch, 121°C Minimum torque

54

49

72

48

62

Minutes to 1-point rise

15

>30

>30

>30

8

Oscillating disk rhometer, ASTM D-2084, 177°C MH-ML, N·m

5.3

4.7

4.6

3.9

3.8

ts0.2, minutes

2.9

2.8

2.5

4.5

4.2

tc90, minutes

4.3

3.8

4.2

6.7

8.9

Stress/Strain, 23°C After press cure (10 min/177°C) M100, MPa

5.1

4.7

4.0

4.2

4.4

TB, MPa

12.1

11.3

10.2

11.3

10.0

EB, %

225

230

280

280

320

M100, MPa

7.0

6.7

6.1

5.4

5.7

TB, MPa

15.2

14.7

13.3

14.4

14.8

EB, %

170

180

187

210

255

After post cre (24 h/232°C)

After heat aging (70 h/275°C) M100, MPa

3.7

4.0

3.7

3.0

3.5

TB, MPa

11.2

10.4

10.4

8.9

7.2

EB, %

245

240

280

345

430

23

30

28

38

50

None

None

Heavy

None

Heavy

Compression Set, ASTM D-395-61, Method B, %, 70 h/200ºC Deposits in mold after 50 cycles

5 CURE SYSTEMS FOR FLUOROELASTOMERS

85 cyanurate (TMAIC), and triallyl cyanurate (TAC) are shown in Fig. 5.6. With its hindered allyl groups, the alternative trap TMAIC does not homopolymerize like TAIC, thus it gives slower cures. TAC gives good cure rates and states, but lower thermal stability than vulcanizates crosslinked with TAIC or TMAIC. Small amounts of metal oxides are useful for absorbing traces of hydrogen fluoride that may be generated during curing. For curing a fluoroelastomer containing about 0.7% bromine incorporated through a cure-site monomer such BTFB, a typical recipe might be:

transfer process to make peroxide-curable polymers with very narrow molecular weight distribution and iodine incorporated on most chain ends.[15] Using multifunctional radical traps to link chain ends results in uniform networks that give low compression set. Thermal resistance of such chain end-linked networks is limited, since loss of relatively few linkages results in formation of many loose long chain segments that do not contribute to elastic recovery, so that physical properties deteriorate considerably. More recently, fluoroelastomers have been made with iodine end groups and bromine- or iodine-containing cure-site monomers to get higher functionality per chain.[16] In a study of peroxide curing of bromine-containing fluoroelastomers,[17] DuPont workers obtained satisfactory cures with aliphatic peroxides 2,5dimethyl-2,5-di-t-butylperoxyhexane, and 2,5-dimethyl-2,5-di-t-butylperoxyhex-3-yne, available from Atochem as Luperco 101XL and 130XL (45% active ingredient on inert support). These peroxides have a half life of 0.8 and 3.4 minutes at 177°C, respectively. Lower molecular weight aliphatic peroxides such as di-t-butylperoxide were found to be active, but too volatile, being partially lost during compound mixing. Peroxides with aromatic substituents (e.g., dicumyl peroxide), gave variable results, probably because of excessive acid-catalyzed decomposition in the fluoroelastomer matrix. Of the radical traps tested, the most effective crosslinker is triallylisocyanurate (TAIC), as judged by cure state and compression set of vulcanizates. Other effective crosslinkers contain unhindered allyl or vinyl groups attached to N, O, or Si; all are electron-rich groups. Electron-poor traps effective in hydrocarbon elastomers, such as m-phenylene-bis-maleimide, are ineffective in fluoroelastomers. Structures of the effective radical traps TAIC, trimethallyl iso-

Fluoroelastomer

100

MT black (N990)

30

ZnO

3

Peroxide (101XL)

3

TAIC

3

This recipe would give time to 90% cure, for about 3 minutes at a temperature of 177°C. Ordinarily, an oven post cure, say 24 h/232°C, is used to develop optimum properties. The cure state of compounds based on bromine-containing fluoroelastomers increases significantly during post curing. Fluoroelastomers with iodine cure sites cure faster to higher cure states during molding, and do not require long post cures at high temperatures. In the DuPont peroxide curing study[17] cited, cure rate and state as measured by ODR modulus increase were directly proportional to the level of bromine-containing cure-site monomer in the polymer. Compression set of vulcanizates improved with cure-site content, with the effect leveling off above about 20 mmol cure-site/kg polymer. At constant cure-site monomer concentration, cure rate increases with increasing levels of both peroxide and radical trap. Cure rate also increases strongly with N

N

CH2

CR

O

C

C

O

CH 2

N

N

CH2

CH 2

CH 2

CH

CH 2

O

C

C

N CH2

CR

CR

CH 2

C

N

O

R=H R =CH 3

Figure 5.6. Radical traps for peroxide curing of fluoroelastomers.

CH2

C

O

T AlC T M AlC

O

TAC

CH2

CH

CH 2

CH

CH 2

86

FLUOROELASTOMERS HANDBOOK

increasing temperature in the range of 160°C to 204°C, with ODR cure times correlated with peroxide half life (approximately the same relationship for peroxides 101XL and 130XL). The state of cure depends mostly on the radical trap level. The cure state increases with peroxide 101XL only up to about 3 phr. Measurements of volatile materials generated during curing at 190°C give further insight into the various reactions occurring in peroxide curing of fluoroelastomers. The polymer used in the study contained about 56 mmol Br/kg polymer (about 0.45% Br). The recipe used was: Fluoroelastomer

100

MT black (N990)

30

Calcium hydroxide

4

Peroxide (101XL)

4

TAIC

4

The peroxide level corresponds to about 60 mmol/kg polymer. The measured levels of volatile products are listed in Table 5.3. No volatiles were formed from the large 2,5-dimethyl-2,5-oxyhexane radical fragment of the peroxide, but the amount of acetone formed was about 80% of the maximum possible for fragmentation of the primary t-butoxy radicals into acetone and methyl radicals. The sum of the amounts of t-butanol (formed by hydrogen transfer to t-butoxy radicals) and isobutene (formed from dehydration of t-butanol) was about eightfold lower than the amount of acetone evolved. The

Table 5.3 Volatiles Generated in Peroxide Curing[17]

Compound

Amount generated, mmoles/kg polymer

Acetone

94.5

t-Butanol

7.8

Isobutene

3.9

Methyl bromide

1.8

Methane

26.8

Ethane

2.6

Propane + propylene

4.1

Water

166

amounts of methyl bromide and volatile hydrocarbons formed from methyl radicals were low relative to the acetone level. This suggests that most of the methyl radicals react with the allyl groups of the TAIC radical trap to form radical adducts that may propagate with other allyl groups, undergo transfer reactions with bromine groups on polymer chains, or add to polymeric radicals. The TAIC level of 4 phr in the compound tested corresponds to about 480 mmoles of allyl functionality per kg polymer, far in excess of that needed for crosslink formation. The amount of water evolved amounts to about 0.3% on polymer, consistent with levels expected in isolated polymer and calcium hydroxide. Consistent with these results, Fig. 5.7 shows the probable reactions resulting from initiator decomposition in a typical compound. Most of the primary tbutoxy radicals undergo ß-scission to acetone and methyl radicals. A major fraction of the methyl radicals add to allyl functionality of the TAIC coagent to form radical adducts. Only a minor fraction of methyl radicals are involved in transfer reactions with fluoroalkyl bromide sites on polymer chains to form methyl bromide and polymeric radicals. If the radical trap concentration is reduced considerably, the amount of methyl bromide increases by up to a factor of two, still relatively low versus the total amount of methyl radicals produced. Proposed crosslinking reactions are shown in Fig. 5.8. Coagent adduct radicals react with bromine cure sites on polymer chains to form polymer radicals. Allyl groups add to these radicals to form crosslinks. The idealized structure shown for crosslinks in Fig. 5.8 is not likely for TAIC radical trap at usual levels >1 phr in compounds. The main reaction for TAIC is polymerization to form oligomers; attachment to polymer chains is a side reaction. However, TMAIC does not homopolymerize, so the structure shown is more likely for this trap. Stock and vulcanizate properties are shown in Table 5.4 for peroxide curing of VDF/HFP/TFE Viton® types containing bromine cure sites from incorporated monomer.[18] Viton® GBL-900 and GBL200 contain about 68% fluorine; GBL-200 also has iodine end groups. GF contains about 70% fluorine for enhanced fluid resistance. All compounds contain 100 Polymer, 30 MT black (N990), 3 Zinc oxide, 1 Carnauba wax, 0.75 VPA#3 processing aid, 2 TMAIC, and 4 Peroxide (Luperco 101XL). Slabs were press cured 10 min/177°C and post cured 24 h/232°C.

5 CURE SYSTEMS FOR FLUOROELASTOMERS

87

Figure 5.7 Probable reactions from peroxide decomposition.[17]

Figure 5.8 Proposed crosslinking mechanism.[17]

These bromine-containing polymers have fairly good thermal resistance, showing good retention of properties after short-term service at 232°C. Based on approximate bromine and iodine levels, and number average molecular weights, the average chain contains some 4–10 cure sites. Thus, most chains are linked into the network at several points, so degradation of linkages must be extensive to cause significant loss of mechanical properties. Mold sticking and fouling are often encountered in peroxide curing of bromine-containing fluoroelastomers. Processing and release aids are usually included in their compounds to minimize molding problems. Typical peroxide cure properties of a VDF/HFP/ TFE (70% fluorine) terpolymer with iodine end groups are shown in Table 5.5.[19] The polymer is Daikin Dai-el® G-902, which contains an average of about 1.8 iodine ends per chain. Thus chains are tied to the network at no more than two points. Generally, cured products are satisfactory for long-term service up to 200°C. At higher temperatures, thermal breakdown of a relatively small fraction of linkages results in severe loss of mechanical properties. Since the iodine sites are very reactive toward radicals, cures are very fast. Usually TAIC is used for crosslinking, since the allyl groups add readily to fluorinated radicals at chain ends. TMAIC is not satis-

factory for curing these iodine-containing polymers. The hindered methallyl groups add much more slowly to chain radicals, so that other reactions may occur and limit the efficiency of crosslinking. Good mold release is obtained when TAIC is used with iodinecontaining polymers. Good properties are obtained with little or no post cure. Only a press cure of 15– 20 minutes at 170°C was used for the compound shown in Table 5.5, with the recipe: 100 polymer (Dai-el® G-902), 20 MT black, 3 magnesium oxide (low activity grade), 3 peroxide (equivalent to 101XL), and 3 TAIC. Premature curing during processing (scorch) of peroxide compounds can be minimized, if necessary, by addition of small amounts of phenolic or amine free radical inhibitors such as 2,6-di-t-butyl-4methylphenol.[17] Long-chain aliphatic amines may also serve as processing aids. A number of peroxide-curable fluoroelastomers have been developed recently that have iodine on most chain ends and additional iodine in cure-site monomer units incorporated along chains.[20] Such polymers give fast cures to high state, excellent demolding characteristics, excellent compression set resistance, and thermal resistance comparable to that of bromine-containing polymers such as those in Table 5.4.

88

FLUOROELASTOMERS HANDBOOK

Table 5.4 Peroxide Curing of VDF/HFP/TFE Fluoroelastomers Containing Bromine Cure Sites[18]

Polymer: Viton®

GBL 900

GBL 200

GF

86

37

87

44 >30

19 >30

46 >30

21 79 2.2 7.4

10 77 1.6 6.8

18 70 2.3 7.4

5.9 20.0 220 75

4.3 19.1 315 79

7.0 20.6 261 80

5.7 21.1 227 76

4.7 19.2 267 78

7.1 21.2 228 81

8.7 20.7 178 76

8.8 15.9 146 78

8.6 21.1 201 81

17 51 66

18 68 81

18 63 72

5 65 4 3 9

5 65 6 2 9

3 4 6 2 8

–46 –15

–46 –16

30

28

ML, in-lb

24

17

MH, in-lb

89

101

ts2, minutes

1.1

0.9

tc90, minutes

5.2

4.4

M100, MPa

7.5

7.0

TB, MPa

18.7

17.9

EB, %

180

180

Hardness, durometer A

72

72

M100, MPa

7.2

5.3

TB, MPa

17.9

16.7

EB, %

200

253

33

33

Fuel C, 168 hours at 23ºC

5

4

Methanol, 168 hours at 23ºC

8

6

Glass transition temperature, ºC

-23

-25

Stock Properties Mooney Scorch, MS at 121ºC

ODR at 177ºC, Microdie, 3º arc

Vulcanizate Properties Stress/strain at 23ºC – original

Stress/strain at 23ºC – Aged 70 h/250ºC

Compression set, method B, O-rings, % 70 hours at 200ºC Fluid resistance, volume swell, %

92

FLUOROELASTOMERS HANDBOOK

Table 5.7 Curing of VDF/PMVE/TFE Elastomers with Bisphenol or Peroxide[22]

Polymer Example 1B Control Composition, wt % VDF 54.1 55 PMVE 33.9 34.8 TFE 10.0 10 2H-PFP 2.0 -BTFB -1.2 Viscosity Inherent viscosity (MEK, 30ºC) 1.10 1.3 ML-10 (121ºC) 89 90 Glass transition temperature, ºC -29 -30 Formulation Example 1B Control Polymer 100 100 MT Black (N990) 30 30 Calcium oxide 6 -Calcium hydroxide -5 Molecular sieve 13X 3 -Peroxide 101XL -4 TMAIC -2 TBAHS 0.5 -Bisphenol AF 2.5 -Cure Characteristics Example 1B Control ODR at 180ºC ML, dN·m 7.1 10.3 MH, dN·m 43.9 56.8 ts2, minutes 3.2 1.8 tc50, minutes 7.3 3.7 tc90, minutes 18.0 7.2 Vulcanizate Properties (press cure 15 minutes at180ºC, post cure 24 hours at 232ºC) Stress/strain at 23ºC M100, MPa 5.0 6.1 TB, MPa 15.1 20.1 EB, % 244 212 Hardness (shore A) 71 69 TR-10, ºC -26 -28 Compression set, pellets, % 70 hours at 200ºC 32 26

5 CURE SYSTEMS FOR FLUOROELASTOMERS

5.4

Perfluoroelastomers— Various Systems

DuPont workers developed perfluoroelastomers based on TFE/PMVE copolymers. These polymers are almost as resistant to fluids as polytetrafluoroethylene thermoplastics, and are usable at temperatures up to 315°C (600°F). A major problem in early product development was to find practical cure systems with thermal stability of crosslinks comparable to that of the polymer. The system used for the first commercial products is based on bisphenol curing of perfluoroelastomers containing the cure-site monomer perfluoro(2-phenoxypropyl vinyl ether).[23] The preferred curing system uses the dipotassium salt of Bisphenol AF (K2AF) with a crown ether such as dicyclohexyl-18-crown-6, which coordinates with potassium ion and facilitates transport of ionic species to cure sites.[24] The crosslink formation reaction presumably involves removal of a fluorine from a pendent perfluorophenoxy group and addition of bisphenolate ion at this site to form an ether linkage. To avoid excessive degradative transfer during incorporation of the perfluorovinyl ether cure-site monomer units, polymerization temperatures must be low, typically 65°C to 85°C. Persulfate-sulfite redox initiation systems are used for these polymers, resulting in mostly sulfonate end groups. Ionic clusters of these end groups are stable at temperatures over 200°C, so polymer viscosity is extremely high at processing and molding temperatures. Mixing with fillers (e.g., 10 phr SRF black) and curatives is difficult, as is fabrication of preforms for molding of parts. Little cure occurs in a press at 190°C, so the mold must be cooled before removal of parts to prevent sponging. Curing is completed in a long post cure, some two days at temperatures up to 288°C (550°F) under nitrogen. Because of the great difficulties encountered in processing and curing, DuPont decided to make and sell perfluoroelastomer fabricated parts rather than polymer.[25] Compared to parts from hydrofluoroelastomers, the resulting Kalrez® K1000 series perfluoroelastomer parts have much higher thermal stability: after 20 days at 288°C in air, 100% modulus decreases by 50

100

5

$

6

121

5

8

8

9

3

F 60

149

28

9

0.1

F 61

149

28

9

0.7

23 Ferric Chloride aqueous

23 14

Ferric Nitrate 23

aqueous Ferric Sulfate

23

aqueous

92

95

Fish Oil

DuPont Viton B (FKM/TFE); 20 phr MT black, 15 phr magnesia or litharge, curing agent

AO exc. resist., little or no effect

8

recommended for use

a

little/no effecVsevere eond. may cause change

8

recommended for use

$

349

4

20

(FKM) 3M Fiuorel (FKM)

recommended for use (rttla/no effect-severe cond. may cause change

8

recommended for use

8

Ifflte/no effect-severe cond. may cause change

8

recommended for use

23

8

20

6

itttte/no effect-severe cond. may cause change 113

120

liquid 23

Fluorobenzene 23 Fluorolube Fluorosilicone

minor to moder. effect

6

may cause si. visible swell/loss of prop,

8

recommended for use

8

tittle/no effect-severe cond, may cause change

6

minor to moder. effect may cause si. visible swell/loss of prop,

€

Occidental Chemical

23 70

7

9

0.6

A-4

70

7

9

1

A-4

FS-1281, Dow Corning

Fluothane

6

FS-1280, Dow Corning

8

2$

Fluosilicic Acid 2-bromo, 2-chloro 1,1,1trifluoroethane

1

2

75

24

1

2

75

not recommended, substantial effect

20

7

8

not suitable for service 0.7

110

116

4 Formic Acid

23

(FKM) (FKM) (FKM)

(FKM)

3M Fiuorel (FKM)

unsatisfactory lor use

1

23 37

(FKM)

DuPont Viton A (FKM); 20 phr MT black, 15 phr magnesia or litharge, curing agent

2 Formaldehyde

(FKM)

DuPont Viton; 20 phr MT black, 15 phr magnesia or litharge, curing agent little/no effect-severe cond. may cause change

20

(FKM)

DuPont Viton; 20 phr MT black, 15 phr magnesia or litharge, curing agent

6.9 Fluorine

(FKM)

not recommended, substantial effect

8

Fluoboric Acid

3M Fiuorel (FKM)

littte/no effect-severe cond. may cause change

8

Fish Oils

(FKM)

unsatisfactory lor use

7

Fatty Acids

Material Note

DuPont Viton B (FKM/TFE); 20 phr MT black, 15 phr magnesia or litharge, curing agent

2 205

lubricant, Dow, high temperature

Resistance Note

2 23

50

Tensile i Modulus Elongation Hardness Strength Change

(FKM) DuPont Viton A (FKM); 20 phr MT black, 15 phr magnesia or litharge, curing agent

A-2

moder. to severe effect

4

modef./savere swell and/or loss of prop,

(FKM)

not recommended, substantial effect

3M Fiuorel (FKM)

70

7

2

70

7

2

20

21

5

22

70

84

DuPont Viton B (FKM/TFE); 20 phr MT black, 15 phr magnesia or litharge, curing agent

20

21

4

18

61

73

DuPont Viton A (FKM); 20 phr MT black, 15 phr magnesia or litharge, curing agent

20

28

4

34

61

77

83

DuPont Viton B (FKM/TFE); 20 phr MT black, 15 phr magnesia or litharge, curing agent recommended for use

8

Freon 11

A-18

(Cont'd.)

Table 7.1 (Cont'd.) % Retained

% Change Reagent

Reagent Note

Cone. Temp. Time Idavst

Freon 11 with Suniso 3G

50

with 50% Sunsiso 3G

50

23 24 149 150

7

28

8 8 6 5

7

23

Freon 113 20

20

7

6 6 e 6 6 4

20

7

5

20

7

6 6 7

23 24

7

20

28

23 25

27

Freon 114 23

Freon 114B2 Dupont

23

Freon 115 chloropentafluoroethane

Freon 12 23 24 149 160 with 50% ASTM oil no. 2

50

with ASTM Oil No. 2

50

with Suniso 4G

50

with 50% Sunsiso 4G

50

93 93 149 150

28 7 7

28

8 6 8 5

23

Freon 13B1 bromotrifluoromethane

20 23 24

28

20

7

24

7

Freon 14 tetrafluoromethane

Freon 142B Freon 152 A Freon 152B

Dupont

23

Dupont

23

€ 6 6 4

7

7 7

Freon 13 Dupont

6 6 6 5

6 6 6 4

7

Volume

Tensile

Modulus Elongation

6 6 8

18

Resistance Note

Material Note

may cause si. visible swell/loss of prop,

(FKM)

good-exc. resist., moder. effect

3M Fluorel (FKM)

16 DuPont Viton A (FKM); 20 phr MT black, 15 phr magnesia or litharge, curing agent

16 recommended for use little/no affect-severe cond. may cause change

(FKM)

minor to moder. effect 18

38

75

DuPont Viton A (FKM); 20 phr MT black, 15 phr magnesia or litharge, curing agent

A-6

15

may cause si. visible swell/loss of prop,

(FKM)

good-exc. resist., moder. effect

3M Fluorel (FKM)

minor to moder. effect may cause si. visible swell/loss of prop,

(FKM)

minor to moder. effect 11

46

50

A-3

DuPont Viton A (FKM); 20 phr MT black, 15 phr magnesia or litharge, curing agent

11

75

62

A-5

DuPont Viton B (FKM/TFE); 20 phr MT black, 15 phr magnesia or litharge, curing agent may cause si. visible swell/loss of prop,

(FKM)

minor to moder. effect DuPont Viton; 20 phr MT black, 15 phr magnesia or litharge, curing agent

16

16

may cause si, visible swell/loss of prop,

(FKM)

good-exc. resist., moder. effect

3M Fluorel (FKM)

minor to moder, effect 21

46

75

DuPont Viton A (FKM); 20 phr MT black, 15 phr magnesia or litharge, curing agent

A-6

21

may cause si. visible swell/loss of prop,

(FKM)

good-exc. resist., moder. effect

3M Fluorel (FKM)

20 20

36

75

DuPont Viton A (FKM); 20 phr MT black, 15 phr magnesia or litharge, curing agent

A-11

25 good-exc. resist, moder. effect

25

3M Fluorel (FKM)

17 17

30

75

DuPont Viton; 20 phr MT black, 15 phr magnesia or litharge, curing agent

A-12 recommended for use may cause sJ. visible swell/loss of prop,

(FKM)

recommended: for use 19

46

75

DuPont Viton A (FKM); 20 phr MT black, 15 phr magnesia or litharge, curing agent

A-6

19

may cause si. visible swell/loss of prop.

(FKM)

goQQ^exc, resist., moder, effect

3M Fluorel (FKM)

recommended f of use 0.6

9 2 1 2 1

Hardness Phanf№

Qafinn 6 € 6 7

28

Freon112 Dupont

PDl

0.6

95

98

A2

DuPont Viton A (FKM); 20 phr MT black, 15 phr magnesia or litharge, curing agent exc. resist, little or no effect unsatisfactory for use

3M Fluorel (FKM)

not suitable for service unsatisfactory for use

(FKM)

not suitable for service (FKM)

(Cont'd.)

Table 7.1 (Cont'd.)

Reagent

Reagent Note

Cone. Temp. Time P D l (days) Rating ( 0 C) (%)

Hardness Change

Resistance Note

Material Note

14

20

14

2

80

DuPont Viton GF (Perox. Cur.); 20 phr MT black, 15 phr magnesia or litharge, curing agent

20

20

2

90

DuPont Viton A (FKM); 20 phr MT black, 15 phr magnesia or litharge, curing agent

20

21

20

21

2 2

77 84

Freon 218 23

Freon 22

23 24 liquid

93

Frigen 22; vapor

180 1SO

20 7 14 14

unsatisfactory Io r use not suitable for service

(FKM)

recommended foruse little/no effect-severe cond. may cause change

(FKM)

unsatisfactory for use

80

DuPont Viton B (FKM/TFE); 20 phr MT black 15 phr magnesia or litharge, curing agent

31 37

54 54

A-15 A-19

DuPont Viton B (FKM/TFE); 20 phr MT black, 15 phr magnesia or litharge, curing agent

1 2 5

90 32

4

50

DuPont Viton B (FKM/TFE); 20 phr MT black, 15 phr magnesia or litharge, curing agent

3

60

DuPont Viton GF (Perox. Cur.); 20 phr MT black, 15 phr magnesia or litharge, curing agent

32

50

not suitable for service

(FKM)

not recommended, substantial effect

3M Fluorel (FKM) DuPont Viton A (FKM); 20 phr MT black, 15 phr magnesia or litharge, curing agent

Dupont

23

Dupont

23

liquid

20

14

5 2 1 2 1 6 2

20

14

4

Dupont

23

vapor

180

14

6 €

28

DuPont Viton B (FKM/TFE); 20 phr MT black, 15 phr magnesia or litharge, curing agent

180

14

S

36

DuPont Viton GF (Perox. Cur.); 20 phr MT black, 15 phr magnesia or litharge, curing agent

7

8 8 8 3 7

with ASTM Oil No. 2

50

93

7

Freon 31 Freon 32 Freon 502

Freon BF Freon C316 Freon C318

Tensile Modulus Elongation Strength

20

23

liquid

% Retained

Volume

2 1 8 8 2 2

Freon 21

Dupont

% Change

tetrachlorodifluoroethane

23

Dupont

23

Dupont

20 23

Freon MF Dupont

23

Dupont

23

Dupont

23

Freon TA Freon TC

6 6 e 4 4 8 8

good-exc. resist., moder. effect unsatisfactory for use

3M Fluorel (FKM)

not suitable for service unsatisfactory for use

(FKM)

not suitable for service mtoof to moder, effect

66

(FKM) DuPont Viton GF (Perox. Cur.); 20 phr MT black, 15 phr magnesia or litharge, curing agent DuPont Viton B (FKM/TFE); 20 phr MT black, 15 phr magnesia or litharge, curing agent

may cause si. visible swell/loss of prop,

(FKM)

recommended for use tittle/no effect-severe cond. may cause change

(FKM)

recommended for use

16

DuPont Viton; 20 phr MT black, 15 phr magnesia or litharge, curing agent may cause si. visible swell/loss of prop, minor to moder. effect

(FKM)

may cause si. visible swell/loss of prop, moder. to severe effect

(FKM)

moder./severe swell and/or loss of prop, recommended for use

(FKM)

IttSe/no effect-severe cond, may cause change (FKM)

(Cont'd.)

Table 7.1 (Cont'd.)

Reagent

Reagent Note

Cone. Temp. Time f°CH

PDL Ways) Rating

Hardness Change

Resistance Note

Material Note

150

40

HEF-2, high energy, trialkyl pentaborane

135

3

3

HTF1 experimental high temperature

288

3

3

28

8 8 2 1 1

86

21

53

A-38

121

28 28

4 1

86 120

20

43

A-38

20

2

2 9

0.6

DuPont Viton; 20 phr MT black, 15 phr magnesia or litharge, curing agent

20

10

1

DuPont Viton B (FKM/TFE); 20 phr MT black, 15 phr magnesia or litharge, curing agent

£0

56

70

10

Freon TMC Dupont

Freon TP35 Dupont

23 23

Freon TWD602 Dupont

23

20

Shell #6

149

acidic 23

Fumaric Acid 2$

Furfural furfuraldehyde

23 70 70

Furfuraldehyde Furfuryl Alcohol

Fyrquel Fyrquel 150

Tensile Modulus Elongation Strength

Bunker C, 6000 second fluid oil

£3

Fuels

% Retained

Volume

6 6 8 8 8 8 8 8 8 8 8 8 8 a

Freon TF

FR Fluid Fuel Oils

% Change

Stauffer Chemical

MIL-G-23652, type Il

(FKM)

recommended for use tittle/no effecteBvere cond, may cause change

(FKM)

recommended for use little/no effect-sevBre cond. may cause change

(FKM)

recommended for use

5

little/no effect-severe pond, may cause change

(FKM)

exc. resist., little or no effect

3M Fluorel (FKM)

recommended for use M

little/no effect-severe cond, may cause change 87

96

A-3

11

65

9

A24

17

31

310

A-9

(FKM) DuPont Viton A (FKM); 20 phr MT black, 15 phr magnesia or litharge, curing agent

a

recommended 1cr use littte/no effect-severe cond, may cause change

(FKM)

unsatisfactory to* use not suitable for service

(FKM) DuPont Viton A (FKM); 20 phr MT black, 15 phr magnesia or litharge, curing agent

good-exc. resist,, moder, etteet

3M Fluorel (FKM) DuPont Viton A (FKM); 20 phr MT black, 15 phr magnesia or litharge, curing agent

unsatisfactory 1or use

3

DuPont Viton; 20 phr MT black, 15 phr magnesia or litharge, curing agent

58

DuPont Viton B (FKM/TFE); 20 phr MT black, 15 phr magnesia or litharge, curing agent

100

7

8 8 8

13

94

106

A-3

DuPont Viton A (FKM); 20 phr MT black, 15 phr magnesia or litharge, curing agent

100

7

8

5

96

118

A-1

DuPont Viton B (FKM/TFE); 20 phr MT black, 15 phr magnesia or litharge, curing agent

100

7

8

3

88

86

A-3

DuPont Viton GF (Perox. Cur.); 20 phr MT black, 15 phr magnesia or litharge, curing agent

1OO

3

8 8

4

89

105

A-4

1QO

3

8

10

89

94

A-6

100

3 3

7 8

7 4

95

128

86

89

A-1 A-1

23

Fyrquel 220 MIL-G-23652, type I

9

minor to moder. effect may cause si. visible swell/loss of prop,

100

little/no effect-severe cond. may causa change

(FKM)

recommended to* use

recommended tor use DuPont Viton B (FKM/TFE); 20 phr MT black, 15 phr magnesia or litharge, curing agent DuPont Viton A (FKM); 20 phr MT black, 15 phr magnesia or litharge, curing agent DuPont Viton B (FKM/TFE); 20 phr MT black, 15 phr magnesia or litharge, curing agent

(Cont'd.)

Table 7.1 (Cont'd.)

Reagent

Reagent Note

Fyrquel GT

Cone. Temp. Time PDt (0C) Ways) Ratino (%)

Hardness Chanoe

Resistance Note

Material Note

7

6

14

good-exc. resist., motfer. effect

3M Fluorel (FKM)

7

S

3

exc. resist., little or no effect

3M Fluorel FLS 2330 (FKM)

30

9

good-exc resist matter, effect

3M Fluorel (FKM)

100

Esso Golden

Tensile Modulus Elongation Strength

100

30

Gasoline

% Retained

Volume

100 too

Gallic Acid

% Change

23

O 19

8

recommended for use

S

little/no effect-severe cond. may cause change

8

recommended for use

(FKM)

$

super Shell

8 M 15 fuel

20

3

7

7

80

100

A-10

DuPont Viton GF (Perox. Cur.); 20 phr MT black, 15 phr magnesia or litharge, curing agent

antioxidant no. 22

20

7

9

1

96

95

AO

DuPont Viton A (FKM); 20 phr MT black, 15 phr magnesia or litharge, curing agent

automotive fuel 2B

20

28

7

automotive fuel 60

20

28

7

13

automotive fuel 6OB

20

28

30

automotive fuel RF2

20

28

6 9

Esso golden

20

28

a

4

A-6

Shell super

20

28

2

A-5

automotive fuel 2B

20

50

9 7 7 $ 8

automotive fuel 60

20

50

automotive fuel 6OB

£0

50

automotive fuel RF2

20

50

liquefied, LPG

23

a

producer

23

8

23

Gasoline

unleaded

23

7

24

7

24

7

a

16

5

17 15 30 9 !ittte/nG etfset-severe cond.rosycause change a 5

W

44

98.75

73

A-1

3M KeI-F 3700 (VDF/CTFE); Shore A65; 100:10:10:1:6 - KeI-F: ZnO2: Dyphos: Luperco 101XL: TAIC

60

100

72

A-1

3M KeI-F 3700 (VDF/CTFE); Shore A55; 100:10:10:3 phr - KeI-F: ZnO2: Dyphos: benzoylperox.

42

70

80

A2

3M KeI-F 3700 (VDF/CTFE); Shore A53; 100:10:10:3 phr - KeI-F: ZnO2: Dyphos: Diak #1

$ & unleaded

24

7 5

automotive fuel 6OB

24

28

30

good-exc. resist., motor, effect

Esso golden

24

28

&

4

exc. resist.. little or no effect

Shell super

24

28

a

2.3

automotive fuel 6OB

24

30

30

automotive fuel 2B

25

28

automotive fuel 60

2$

28

automotive fuel RF2

25

28

automotive fuel 2B

25

50

automotive fuel 60

25

50

6 6 7 8 6 7

automotive fuel RF2

25

50

a

9

premium 51% arom.,0 .1 wt% antiox. no.22

43

3

8

premium w/26% arom. content, 2.47 g/gal regular

43

3

43

3

premium 51% arom.,0 .1 wt% antiox. no.22

43

7

9 7

(FKM)

3M Fluorel (FKM)

good*8xc resist., moder. effect

16

U

13

me. resist., little or no effect

5 17

good+exc resist* moder. effect

15

exc. resist., little or no effect

5

94

100

A-8

2

99

100

A-7

2

101

100

A-6

8

88

90

A-11

DuPont Viton A (FKM); 20 phr MT black, 15 phr magnesia or litharge, curing agent

(Cont'd.)

Table 7.1 (Cont'd.)

Cone. Temp. Time PDt Ways) Rating (0C) (%)

% Change

% Retained

Volume

Tensile Modulus Elongation Strength

Hardness Change

Reagent

Reagent Note

Gasoline

premium w/26% arom. content, 2.47 g/gal

43

7

9

4

98

98

A-8

regular

43

7

3

98

95

A-11

Gasoline Additive Gear Lubricants

Gear Oils

lead, 2.03 mg/l antioxidant no. 22

43

14

8 6

6

101

100

A-10

premium 51% arom.,0 .1 wt% antiox. no.22

43

14

8

12

101

100

A-13

9 5

5

101

100

A-7

14

57

76

A-8

8 4

23

55

81

A-25

regular

43

14

M 15 fuel

54

7

Texaco Premium

60

2

M 15 fuel

65

3

gasoline antioxidant #22

24

7

GL-4A

149

3

GL-4B

149

3

lead soap-active sulfur

149

3

MIL-L-2105

149

3

SCL, sulfur-chlorine-lead

149

3

GL-4A

150

3

GL-4B

15Q

3

lead soap-active

150

3

sulfur MIL-L-2105, 15% additive meeting

150

3

SCL, sulfur-chlorine-lead

150

3

HD 90

175

7

GE 81406

177

7

HD 90

177

7

149

7

149

21

150

7

Texaco 3450

Texaco 3450, rear axle oil

150 21

Gelatin Gelatins Girling Crimson Glaubers Salt

£3 70 14 23

Glucose 23

Glues 23

Glycerin

glycerol glycerin

glycerol

20

2

20

28

20 23

56

7

Resistance Note

DuPont Viton A (FKM); 20 phr MT black, 15 phr magnesia or litharge, curing agent DuPont Viton A (FKM); 20 phr MT black, 15 phr magnesia or litharge, curing agent

DuPont Viton GF (Perox. Cur.); 20 phr MT black, 15 phr magnesia or litharge, curing agent exc. resist., little or no effect

3M Fluorel (FKM) DuPont Viton GF (Perox. Cur.); 20 phr MT black, 15 phr magnesia or litharge, curing agent

exc. resists little or no effect

3M Fluorel (FKM)

9 9 9 9 9 9 9

1.3

2

96

99

AO

9 9 9

1

96

98

A1

1

99

100

AO

1

93

97

AO

9 5

2

91

99

A-1

4

60

60

A-6

9 7 6 8 7 9

O

exc. resist., iittle or no effect

3.7

good-exc. resist,, moder, ettect

9.1

exc, resist, iittle or no effect

6 8 8 2 6 8 8 8 8 8 8 9 9 9 8

Material Note

2 1 1 1 1.6 DuPont Viton A (FKM); 20 phr MT black, 15 phr magnesia or litharge, curing agent

DuPont Viton; 20 phr MT black, 15 phr magnesia or litharge, curing agent 3M Fluorel (FKM)

recommended for use 3M Fluorel (FKM)

26 9

26

56

95

100

A2

78

86

A-7

DuPont Viton A (FKM); 20 phr MT black, 15 phr magnesia or litharge, curing agent recommended for use little/no effect-severe eond. may cause change

(FKM)

not recommended, substantial effect

3M Fluorel (FKM)

minor to moder, effect ttttle/no effect-severe cond. may cause change

(FKM)

recommended for use littte/no effect-severe cond. may cause change

(FKM)

recommended for use Itttte/no effect-severe cond. may cause change

(FKM)

recommended fot use -0.4

DuPont Viton; 20 phr MT black, 15 phr magnesia or litharge, curing agent

0 -0.5 Ifttte/ho efleci-severe cond. may cause change

(FKM)

(Cont'd.)

Table 7.1 (Cont'd.) % Retained

% Change Cone. Temp. Time PDt /0Ct O&*in ft

Volume

Reagent

Reagent Note

Glycerin

glycerin

70

2

9

-0.6

U

70

28

9

-0.4

70

56

9

-0.1

121

5

9

1

Glycols 23 Greases

recommended lor use

light grease

8

Shell Alvania #2

8 100

21

9

A-2

magnet

100

21

9

2

A-2

100

21

9

2

A-2

Shell Air GG-1034 WTR

175

3

6

13

85

133

A-6

Supermil ASU-06752, American Oil Co.

175

3

6

19

66

87

A-5

Shell Air GG-1034 WTR

175

7

7

17

90

80

A-1

Supermil ASU-06752, American Oil Co.

175

7

4

32

39

40

A2

Halowax Oil

lubricant; Ucon 50HB280X, Union Carbide

DuPont Viton; 20 phr MT black, 15 phr magnesia or litharge, curing agent

DuPont Viton B (FKM/TFE); 20 phr MT black, 15 phr magnesia or litharge, curing agent

8

recommended for use

8

(Mla/no affect-severe cond. may cause change

8

recommended for use

8

U

(FKM)

(FKM)

8

23 175

7

7

8

205

14

9

3

76

105

DuPont Viton A (FKM); 20 phr MT black, 15 phr magnesia or litharge, curing agent

A-4 A2

tittle/no effect-severe cond. may cause change

DuPont Viton B (FKM/TFE); 20 phr MT black, 15 phr magnesia or litharge, curing agent

8

Helium

8

N-Heptane vinyl plasticizer, Hercules

150

14

4

13

66

133

A-11

150

14

6

17

76

100

A-14

recommended for use

N-Hexaldehyde n-Hexaldehyde

Hexane

1

swallow

Hanover MIL-H-83282

(FKM)

8

machine oil no. 120

Halothane

Hexaldehyde

B

Ifttle/no effect-severe cond. may cause change

23

Hercoflex 600

DuPont Viton B (FKM/TFE); 20 phr MT black, 15 phr magnesia or litharge, curing agent recommended for use

8

Koppers

Material Note

DuPont Viton; 20 phr MT black, 15 phr magnesia or litharge, curing agent

8

Green Sulfate Liquor

Heptane

Resistance Note

Keystone #87HX

Sunoco; all purpose

Heat Transfer Fluids

Tensile Modulus Elongation Hardness Strength PHjinnA

23

N-Hexane-1

DuPont Viton B (FKM/TFE); 20 phr MT black, 15 phr magnesia or litharge, curing agent DuPont Viton A (FKM); 20 phr MT black, 15 phr magnesia or litharge, curing agent

2

unsatisfactory for use

1

no! suitable for service

8

recommended for use

(FKM)

8 n-Hexane

20

21

Hexene Hexyl Acetate

8

1

23

7

9

1

n-Hexane

25

21

9

1

n-Hexene-1

23 5

20

10

1 1

little/no effect-sever© cond. may cause change

(FKM)

exc. resist., little or no effect

3M Fluorel (FKM)

little/no effect-severe cond. may cause change

a

20

DuPont Viton A (FKM); 20 phr MT black, 15 phr magnesia or litharge, curing agent

A-10

8

23

290

A-30

308

A-26

(FKM) DuPont Viton B (FKM/TFE); 20 phr MT black, 15 phr magnesia or litharge, curing agent

(Cont'd.)

Table 7.1 (Cont'd.)

Reagent

Reagent Note

Cone. Temp. Time PDt Ways) Rating ( 0 C) (%)

Hexyl Alcohol 23 1-hexanol

HEF 2

70

7

135

3

high energy fuel

Houghto Safe 271

water & glycol base

Houghto Safe 620 HS 1010 HS 1055 HS 1120

water & glycol base

70

HS 5040 HS 620 HTF

experimental high temperature fuel

HyTran17 Hydraulic Fluids

14

70

7

1OO

14

8 4 6 6 6 6 6 7 6 9 7 3

% Retained

Volume

Tensile M&dultIS Elongation Strength

Hardness Change

recommended for use 11

not recommended, substantial eifecf

14

good-exc. resist^ moder. effect

3M Fluorel (FKM)

minor to moder. effect good-exc- resist^ mader. effect

13

3M Fluorel (FKM)

20

14 14

70

14

70

14

288

3

288

3

70

7

6 8

2 5

9.1 20 1.7

exc. resists little or no effect

7.9

good-exc. resist., moder, effect

17

31

310

DuPont Viton A (FKM); 20 phr MT black, 15 phr magnesia or litharge, curing agent

A-9

17

good-exCv resist., moder. effect

3M Fluorel (FKM) DuPont Viton B (FKM/TFE); 20 phr MT black, 15 phr magnesia or litharge, curing agent

8

38

1095

Shell Iris 902, water-inoil emulsion

66

28

9

Bray Oil 762

70

7

7

Cellulube, triaryl phosphate ester

70

7

9

2

CHX-604

70

7

8

3

FR fluid 20

70 70

7 7

8 7

13

Houghto-Safe 1120, phosphate ester base

70

14

8

9

A-5

Houghto-Safe 62, EF Houghton

70

14

7

8

A-9 A-1

recommended for use 64

86

A-7

DuPont Viton A (FKM); 20 phr MT black, 15 phr magnesia or litharge, curing agent

A-2 84

107

78

94

80

106

A-3

DuPont Viton B (FKM/TFE); 20 phr MT black, 15 phr magnesia or litharge, curing agent

A-1

DuPont Viton A (FKM); 20 phr MT black, 15 phr magnesia or litharge, curing agent

A-2

DuPont Viton; 20 phr MT black, 15 phr magnesia or litharge, curing agent

AO

2

DuPont Viton A (FKM); 20 phr MT black, 15 phr magnesia or litharge, curing agent

Shell Tellus 33, petroleum base

70

28

9

0.6

Univis J-43, petroleum base, Exxon Mine Fluid 3XF, Shell, fire resistant

70

28

9

2

90

21

8

0.7

105

105

1QO

3

8

7

100

112

A-3

100

3

8

3

92

95

A-3

100

3

9

2

92

100

A-5

100

3

6

14

82

94

A-18

100

3

6

16

76

121

A-6

Houghto-Safe 520, water glycol base

3M Fluorel (FKM)

minor to moder. effect

Oronite 8200, disiloxane, high temp.

Houghto-Safe 1120, phosphate ester base

(FKM) DuPont Viton B (FKM/TFE); 20 phr MT black, 15 phr magnesia or litharge, curing agent

6

8 8 6

Houghto-Safe 1010, phosphate ester base

Material Note

recommended for use

70

Sunsafe; fire resistant

Resistance Note

little/no effect-severe cond. may cause change

100

Univis 40

Hydraulic Fluids

8 8 8

% Change

AO A-9

DuPont Viton B (FKM/TFE); 20 phr MT black, 15 phr magnesia or litharge, curing agent DuPont Viton GF (Perox. Cur.); 20 phr MT black, 15 phr magnesia or litharge, curing agent

DuPont Viton B (FKM/TFE); 20 phr MT black, 15 phr magnesia or litharge, curing agent

{Cont'd.)

Table 7.1 (Cont'd.)

Reagent Hydraulic Fluids

Reagent Note

% Change

% Retained

volume

Tensile Modulus Elongation Strength

Hardness Change

Resistance Note

Material Note

Houghto-Safe 520, water glycol base

100

3

7

9

89

129

A-2

Houghto-Safe 1120, phosphate ester base

1OO

7

8

8

97

118

A-1

100

7

B

4

94

116

A-3

DuPont Viton B (FKM/TFE); 20 phr MT black, 15 phr magnesia or litharge, curing agent

100

7

9

2

94

106

A-5

DuPont Viton GF (Perox. Cur.); 20 phr MT black, 15 phr magnesia or litharge, curing agent

100

7

5

21

57

89

A-10

100

7

5

33

50

95

A-8

DuPont Viton B (FKM/TFE); 20 phr MT black, 15 phr magnesia or litharge, curing agent

100

7

6

22

63

118

A-4

DuPont Viton A (FKM); 20 phr MT black, 15 phr magnesia or litharge, curing agent

Houghto-Safe 1055,phosphate ester base

100

14

7

20

A-5

Houghto-Safe 1120, phosphate ester base

1QO

14

6

20

A-12

Hydro-Drive MIH-50, high viscosity

100

14

9

0.3

DP 47, ICI, silicone base, fire resist.

100

40

9

O

121

180

&

15

66

105

135 149 150

7

9 8 9

3

89

100

A-1

93

100

AO

264

7

22

A-54

177

14

41

A-56

Houghto-Safe 520, water glycol base

Univis J-43, petroleum base, Exxon BP Aero no. 1

Hydraulic Fluids

Cone. Temp. Time PDl CC) Ways) Rating 121

€

Phenol 23 carbolic acid

minor to moder. effect recommended for use

8

little/no effect-severe cond. may cause change

(FKM)

exc. mi$l> JiUIe or no effect

3M Fluorel (FKM)

3

9

70

28

7

7

85

100

A-11

10

89

140

A-14

0

DuPont Viton A (FKM); 20 phr MT black, 15 phr magnesia or litharge, curing agent

100

28

5

100

28

8

10

exc. resist* little or no effect

149

28

6

24

good-exc, resist,, motfer, effect

150

28

2

24

70

8

with 15% H2O

85

8

technical

65

biphenyl/diphenyl

57

210

A-19

U

DuPont Viton B (FKM/TFE); 20 phr MT black, 15 phr magnesia or litharge, curing agent

A2

8

recommended for use

a

little/no effect-sevgre cond may cause change

(FKM)

dissolved

DuPont Viton A (FKM); 20 phr MT black, 15 phr magnesia or litharge, curing agent

8 O 131

Phenylethyl Ether

unsatisfactory for use 2 1

phenetole

3M Fluorel (FKM) DuPont Viton; 20 phr MT black, 15 phr magnesia or litharge, curing agent

recommended for use 2

7

as

PDA

3M Fluorel (FKM)

8

with 30% H2O

Phenyl Benzene

recommended tor use

a$

66

(FKM)

exc. resist.t little or no effect

8 may cause change

7 8

4

89

110

A-8

4.2

23 205

little/no effect-severe cond. may cause change

8 1

A

98

85

87

A19

1

5

42

75

113

A9

Pickling Solutions 23

(FKM) (FKM)

3M Fluorel (FKM); compounds w/ lead based metal oxides recommended

recommended for use (FKM) DuPont Viton A (FKM); 20 phr MT black, 15 phr magnesia or litharge, curing agent DuPont Viton B (FKM/TFE); 20 phr MT black, 15 phr magnesia or litharge, curing agent

205 6

minor to moder. effect

6

may cause si. visible swell/loss of prop,

8

recommended for use

(FKM)

8

molten 23 Pine Oil

(FKM)

DuPont Viton A (FKM); 20 phr MT black, 15 phr magnesia or litharge, curing agent exc, resist,, little or no effect

8

Phosphorous Trichloride

H2O solution

(FKM)

8

20

Picric Acid

Material Note

8

concentrated

Phthalic Anhydride

Resistance Note

white

8

little/no effect-severe cond. may cause change

8

recommended for use

(FKM)

8 white

23

8

23

8 8

Pinene 70

7

Piperidine 23 Hercoflex 600, Hercules Plasticizers

(FKM)

recommended for use

8

23 Pinene flJ-)

Plating Solutions

little/no effect-severe cond. may cause change

tittle/no effectsevere cond. may cause change

8

A6

2

unsatisfactory for use

1

not suitable For service

(FKM) DuPont Viton B (FKM/TFE); 20 phr MT black, 15 phr magnesia or litharge, curing agent (FKM)

150

14

6

17

76

100

A-14

DuPont Viton A (FKM); 20 phr MT black, 15 phr magnesia or litharge, curing agent

150

14

4

13

66

133

A-11

DuPont Viton B (FKM/TFE); 20 phr MT black, 15 phr magnesia or litharge, curing agent

chrome

8

others

8

chrome

23

8

others

23

8

recommended for use little/no effect-severe cond, may cause change

Pneumatic Service

8

recommended for use

Potassium Acetate

2

unsatisfactory for use

23 Potassium Chloride 23 Potassium Cuprocyanide 23 Potassium Cyanide 23

1

not suitable for service

8

recommended for use

8

tittle/no effecf-severe cond. may cause change

8

recommended for use

8

tittle/no effect-severe cond. may cause change

8

recommended for use

8

little/no effect-severe cond. may cause change

(FKM)

(FKM) (FKM) (FKM) (FKM)

(Cont'd.)

Table 7.1 (Cont'd.)

% Change Reagent

Reagent Note

Cone. Temp. Time PDl Ways) Rating {%)

Potassium Dichromate 23 Potassium Hydroxide 23 Potassium Nitrate 70

% Retained Tensile Modulus Elongation Hardness Strength Change

5

Resistance Note

8

recommended tor use

8

little/no effect-SBvere cond. may causa change

6

minor to rooder. effect

1

not suitable for service

8

recommended fof use

a

23 30

Potassium Permanganate

Volume

6

Potassium Salts

8

Potassium Sulfate

$

fitt1$/no eftect^evere cond. may cause change 28

A-11

littte/no effect-severe cond. may cause change

8

recommended lor use

Producer Gas

8

(FKM)

(FKM)

8

Propane 125 psi

3

160 psi

3 23

Propane Propionitrile

6

2

exc, resist., little or no effect

11

good-exc. resist, moder. effect

8

little/no effect-severe cond. may cause change

8

recommended for use

2

Propyl Acetate n-propyl acetate

20

8

methyl butyl ketone

1

23

not suitable for service

2

unsatisfactory for use

1

not suitable For service recommended fof use

20

8

9

0.6

20

21

8

2

23

n-propyl alcohol

25

21

8

2

70

4

8

6

20

7

2 1

140

n-propyl Nitrate

25

Propylene 23 Propylene Oxide 23 Pydraul 1OE 23 Pydraul 115E hydraulic fluid; Monsanto

23

A10

1

DuPont Viton A (FKM); 20 phr MT black, 15 phr magnesia or litharge, curing agent Kftla/no attect-severa cond, may cause change

(FKM)

good-exc. resist., moder. affect

3M Fluorel (FKM) DuPont Viton B (FKM/TFE); 20 phr MT black, 15 phr magnesia or litharge, curing agent

140

A-38

DuPont Viton A (FKM); 20 phr MT black, 15 phr magnesia or litharge, curing agent not suitable for service

(FKM)

not recommended, substantial effect

3M Fluorei (FKM)

8

recommended iat use

8

tittte/no effect-severe cond. may cause change

2

unsatisfactoryioruse

1

not suitable for service

8

recommended lor use

8

littte/no effect-severe cond. may causa change

8

recommended for use

8

little/no effect-severe cond. may causa change

8

recommended tor use

23

8

litUa/no a*fect-$evera cond may causa change

23

8

little/no effect-severe cond. may causa change

8

recommended for use

Pydraul 230E U

7

(FKM)

unsatisfactory for use

1

23

(FKM)

DuPont Viton B (FKM/TFE); 20 phr MT black, 15 phr magnesia or litharge, curing agent

8

1-propanol

Propyl Nitrate

(FKM)

DuPont Viton B (FKM/TFE); 20 phr MT black, 15 phr magnesia or litharge, curing agent

8

Propyl Alcohol

3M Fluorel (FKM)

unsatisfactory for use 200

1

23 Propyl Acetate (N-)

Pydraul 29 ELT

(FKM)

recommended for use

8

Propyl Acetone

(FKM)

DuPont Viton A (FKM); 20 phr MT black, 15 phr magnesia or litharge, curing agent

Potassium Sulfite

23

Material Note

(FKM) (FKM) (FKM) (FKM) (FKM)

(Cont'd.)

Table 7.1 (Cont'd.)

Reagent Pydraul 3OE

Reagent Note

Cone. Temp. Time PDl Ways) Rating ( 0 C) (%)

hydraulic fluid; Monsanto

23 70

Pydraul312

U

7

Pydraul 65E

118

A5

72

120

A-10

4

110

130

AO

3

104

110

AO

DuPont Viton GF (Perox. Cur.); 20 phr MT black, 15 phr magnesia or litharge, curing agent

121

14

recommended for use Kttte/no effect-severe cond. may cause change

14.6

9

5

95

105

AO

DuPont Viton B (FKM/TFE); 20 phr MT black, 15 phr magnesia or litharge, curing agent

14.6

8

6

85

103

A3

DuPont Viton A (FKM); 20 phr MT black, 15 phr magnesia or litharge, curing agent

121 121

83

6

78

103

A-2

83

a 7

6

90

121

A-2

1

8 8 8 8 8 8 3

23 66

14 7 7

8 8 8 a 8 8 9

fittle/no effect-severe cond. may cause change fcWe/no effect-severe cond. may cause change

recommended lor use little/no effect-severe cond. may cause change

2.7

RJ 1

little/no effect-severe cond. may cause change

(FKM)

exc, resist, r little or no effect

3M Fluorel (FKM)

3 DuPont Viton A (FKM); 20 phr MT black, 15 phr magnesia or litharge, curing agent

A-1

2

recommended for use

149

7

8

5

little/no effect-severe cond. may cause change

(FKM) DuPont Viton B (FKM/TFE); 20 phr MT black, 15 phr magnesia or litharge, curing agent

exc. resist., little or no effect

3M Fluorel (FKM)

unsatisfactory (or use

2

20

3

3

120

20 23 25

7

1

119

DuPont Viton A (FKM); 20 phr MT black, 15 phr magnesia or litharge, curing agent

A-15 21

67

A-25

1

Pyrrole

(FKM)

recommended for use

4

23

(FKM) DuPont Viton; 20 phr MT black, 15 phr magnesia or litharge, curing agent

60

8

Pyroligneous Acid

(FKM)

recommended for use

9

1

(FKM)

recommended 1or use

4

3

DuPont Viton B (FKM/TFE); 20 phr MT black, 15 phr magnesia or litharge, curing agent little/no effect-severe cond, may cause change

23 100

oil

RJ1;MIL-F-25558B

DuPont Viton B (FKM/TFE); 20 phr MT black, 15 phr magnesia or litharge, curing agent

121

a

RJ-1, petroleum base

(FKM) DuPont Viton A (FKM); 20 phr MT black, 15 phr magnesia or litharge, curing agent

A6

121

23 82 100 70

GE hydraulic fluid

Ramjet Fuel

89

7 9

Pyranol

Pyridine

5 10

14

Pydraul 9OE

Transformer Oil, GE

Material Note

7 6

121

23

Pydraul F9

Resistance Note

118

7

hydraulic fluid; Monsanto

Pydraul A200

Hardness Change

91

28

23

Monsanto, industrial hydraulic fluid

Tensile Modulus Elongation Strength

2

1QO

Pydraul 540C Pydraul 60

% Retained

Volume

8 8 8

100

23

Pydraul 312C Pydraul 312E Pydraul 5OE

% Change

120

not suitable for service

(FKM)

not recommended, substantial effect

3M Fluorel (FKM)

2

unsatisfactory for use

1

not suitable for service

2

unsatisfactory for use

23 20

28

9

1

23 24

28

6 9

1

not suitable for service

1 A-2

little/no effect-severe cond. may cause change exc. resist., littfe or no effect

(FKM) (FKM) DuPont Viton A (FKM); 20 phr MT black, 15 phr magnesia or litharge, curing agent (FKM) 3M Fluorel (FKM)

(Cont'd.)

Table 7.1 (Cont'd.)

Reagent

Reagent Note

Cone. Temp. Time PDl Ways) Rating (%)

Rapeseed Oil 23 RD 6195

Red Oil

Monsanto, hydraulic fluid

Tensile Modulus Elongation Strength |

recommended tor use (FKM)

exc. resist., little or no effect

3M Fluorel (FKM)

2.7

150

40

5

3

199

40

6

20

200

40

4

20

DuPont Viton A (FKM); 20 phr MT black, 15 phr magnesia or litharge, curing agent good-exc, resist., mader. effect

39

36

A-6

8

recommended for use

9

1

7

9

0

MIL-L-23699

205

3

a

12

6 8

A-4

130

A-6

66

96

A-14

19

(FKM) DuPont Viton A (FKM); 20 phr MT black, 15 phr magnesia or litharge, curing agent

exc. resist., little or no effect 78

3M Fluorel (FKM) DuPont Viton A (FKM); 20 phr MT black, 15 phr magnesia or litharge, curing agent

recommended for use

28

MIL-H-25576 C

A-5

little/no effect-severe cond. may cause change

20

3

132

8

200

205

57

8

Shell

MIL-R-25576

Material Note

little/no effect-severe pond, may cause change

RP-1, petroleum base

RP 1

Resistance Note

8 8

MIL-F-25558

Hardness Change

8 40

MIL-H-5606

Rotella Oil Royco 899

3M Fluorel (FKM) DuPont Viton A (FKM); 20 phr MT black, 15 phr magnesia or litharge, curing agent

recommended for use

23

8

KttleAio effect-severe cond- may cause change

(FKM)

24

9

exc, resist, little or no effect

3M Fluorel (FKM)

28

Sal Ammoniac 23

Salicylic Acid 23

Salt Brine Santosafe 300

% Retained

Volume

149

23

RJ 1 Rocket Fuel

% Change

chlorinated

8

0.9

recommended for use

8

fit tie/no effect-severe cond. may cause change

8

recommended for use

8

little/no effect-severe cond. may cause change

8

recommended for use

(FKM) (FKM)

8 70

7

8

1

91

118

A3

100

7

7

3

83

110

A5

8

23

Sea Water

little/no effect-severe cond. may cause change

25

30

9

1.5

100

30

8

4.5

200

3

5

24

59

100

A-14

200

3

6

16

75

90

A-11

20

6.9

7

106

120

exc, resist, little or no effect

Shinol TWS-R

Silicone Greases

DuPont Viton A (FKM); 20 phr MT black, 15 phr magnesia or litharge, curing agent DuPont Viton B (FKM/TFE); 20 phr MT black, 15 phr magnesia or litharge, curing agent DuPont Viton; 20 phr MT black, 15 phr magnesia or litharge, curing agent

8

rBcommendBd for use

23

8

tittle/no effect-severe cond, may cause change

23

a

Silicate Esters

(FKM) 3M Fluorel (FKM) 3M Fluorel (FKM); compounds w/ lead based metal oxides recommended

recommended for use

8

Sewage Shell Turbine No. 307

DuPont Viton A (FKM); 20 phr MT black, 15 phr magnesia or litharge, curing agent

(FKM)

recommended for use

8

a

Silicone Oils

littie/no effect-severe cond, may cause change

8

23 F 60, low viscosity

1$O

28

9

0.1

A-5

F 61, high viscosity

150

28

9

0.7

A-1

DC 200, Dow Corning

175

28

9

-2

A2

Silver Nitrate 23

(FKM) DuPont Viton A (FKM); 20 phr MT black, 15 phr magnesia or litharge, curing agent

8

recommended for use

8

little/no effect-severe cond, may cause cfiange

(FKM)

{Cont'd.)

Table 7.1 (Cont'd.)

Reagent Skelly Solvent

Reagent Note

Cone. Temp. Time P D l (days) Rating ( 0 C) (%)

Skydrol 500B

fire resist, hydraulic fluid

aircraft hydraulic fluid

Monsanto; hydraulic fluid

Soap

7

1

174

12

45

A-54

DuPont Viton B (FKM/TFE); 20 phr MT black, 15 phr magnesia or litharge, curing agent

100

7

1

171

27

61

A-22

DuPont Viton A (FKM); 20 phr MT black, 15 phr magnesia or litharge, curing agent

121

7

2

151

23

90

A-44

DuPont Viton B (FKM/TFE); 20 phr MT black, 15 phr magnesia or litharge, curing agent

121

7

3

45

50

81

A-20

DuPont Viton GF (Perox. Cur.); 20 phr MT black, 15 phr magnesia or litharge, curing agent

121 121

14

4 1

31

62

90

A-22

92

35

60

A-27

150 150

7

139

16

61

A-56

236

13

35

A-54

14

(FKM)

good-exc. resist., moder. effect

3M Fluorel FLS 2330 (FKM)

266

11.4

22

A-52

DuPont Viton A (FKM); 20 phr MT black, 15 phr magnesia or litharge, curing agent

DuPont Viton B (FKM/TFE); 20 phr MT black, 15 phr magnesia or litharge, curing agent

2OQ

3

15

36

33

A-4

DuPont Viton A (FKM); 20 phr MT black, 15 phr magnesia or litharge, curing agent

200

3

4

12

34

61

A-5

DuPont Viton B (FKM/TFE); 20 phr MT black, 15 phr magnesia or litharge, curing agent

200

14

17

13

30

A-1

200

14

4 4

24

14

19

A-4

1

8 8 8 8 8

88

93

AO

8 7

78

112

A-4

102

97

A-1

23

121 121

1

175

.1.

175

7

177

1

177

7

23

Sodium Bicarbonate 23 baking soda 23

Sodium Borate 23

soda ash

45

6 6 4

Sodium Acetate

Sodium Carbonate

unsatisfactory for use not suitable for service

1 1

23

Sodium Bisulfite

recommended for use

7

23

vapor, N2 atmosphere liquid vapor, nitrogen atmosphere

Material Note

150

solutions

liquid

Resistance Note

7

Soda Ash Sodium

Hardness Change

7

Skydrol 7000 Skylube 450

Tensile Modulus Elongation Strength

23 149 150

solvent E

Skydrol 500 Skydrol 500A

% Retained

Volume

8 a 8 2 1. 5 1

solvent B solvent C

Monsanto; hydraulic fluid

% Change

9 8 8

DuPont Viton A (FKM); 20 phr MT black, 15 phr magnesia or litharge, curing agent minor to moder. effect may cause si. visible swell/loss of prop.

(FKM)

DuPont Viton A (FKM); 20 phr MT black, 15 phr magnesia or litharge, curing agent recommended lor use little/no effect-severe cond. may cause change

(FKM)

recommended tor use little/no effect-severe cond. may cause change

(FKM) DuPont Viton A (FKM); 20 phr MT black, 15 phr magnesia or litharge, curing agent

exc. resist., little or no effect

3M Fluorel (FKM) DuPont Viton; 20 phr MT black, 15 phr magnesia or litharge, curing agent

exc. resist., little or no effect

2 1 8 8

little/no effect-severe cond. may cause change

a

recommended for use

8 8 8 8

littte/no effect-severe cond. may cause change

3M Fluorel (FKM)

unsatisfactory for use not suitable for service

(FKM)

recommended for use (FKM) (FKM)

recommended for use littfe/no effect-severe cond, may cause change

(FKM)

recommended for use

(Cont'd.)

Table 7.1 (Cont'd.)

% Retained

% Change Reagent

Reagent Note

Cone. Temp. Time tfays) ( 0 C) (%)

Sodium Chloride 23 Sodium Cyanide 23 Sodium Hydroxide

Volume

Tensile Modulus Elongation Hardness Strength Change

Resistance Note

8

recommended tor use

8

little/no effect-severe cpnd. may cause change

8

recommended for use

8

little/no effect-severe cond. may cause change

6

mfrtor to moder. effect may cause si. visible swell/loss of prop.

6

23

Material Note

(FKM) (FKM) (FKM)

30

70

14

5

34

53

114

46.5

20 38

7

8

2

75

100

A1

46.5

180

6

73

86

A-5

46.5

38

365

5

54

81

A-6

46.5

38

730

3

32

67

A-9

46.5

38

1095

2

17

62

A-17

50

24

7

9

2.1

exc. resist., little or no effect

50

38

180

7

-9.5

good+exc. resist., mqder. effect

50

70

7

8

0.5

50

70

14

6

-7

69

115

A3

DuPont Viton B (FKM/TFE); 20 phr MT black, 15 phr magnesia or litharge, curing agent

50

70

14

6

-8

47

120

A-2

DuPont Viton GF (Perox. Cur.); 20 phr MT black, 15 phr magnesia or litharge, curing agent

Sodium Hypochlorite 23

recommended for use

9

0.8

5

24

28

9

0.8

5

70

28

7

24

20

70

28

7

24

23 Sodium Peroxide 23 dibasic

DuPont Viton; 20 phr MT black, 15 phr magnesia or litharge, curing agent

{fttJa/no effect-severe cond. may cause change

28

23

DuPont Viton B (FKM/TFE); 20 phr MT black, 15 phr magnesia or litharge, curing agent

8

20

Sodium Perborate

DuPont Viton A (FKM); 20 phr MT black, 15 phr magnesia or litharge, curing agent

A-10

8 5

Sodium Metaphosphate

Sodium Phosphate

PDt Rating

exc. resist, little or no effect 89

110

exc. resist,, little or no effect

8

little/no effect-severe cond, may cause change

8

recommended: for use

8

littte/no effect-severe cond, may cause change

8

recommended for use

8

little/no effect-severe cond. may cause change

8

recommended for use

8 8

a

{(ttte/no effect-sevBre cond. may cause change

Sodium Salts

8

recommended 1of use

Sodium Silicate

8

23

Sodium Sulfate 23 Sodium Sulfide Sodium Sulfite

3M Fluorel (FKM); compounds w/ lead based metal oxides recommended DuPont Viton A (FKM); 20 phr MT black, 15 phr magnesia or litharge, curing agent

A-6

recommendedforuse

mono

(FKM) DuPont Viton A (FKM); 20 phr MT black, 15 phr magnesia or litharge, curing agent

8

tribasic

3M Fluorel (FKM)

8

recommended fof use

8

[fttfe/no effect-severacond. may cause change

8

recommended lor use

3M Fluorel (FKM); compounds w/ lead based metal oxides recommended (FKM) (FKM) (FKM)

(FKM)

(FKM)

8

Sodium Thiosulfate

8 23

Irttte/no effect-severe cond, may cause change

(FKM)

(Cont'd.)

Table 7.1 (Cont'd.)

Reagent

Reagent Note

Cone. Temp. Time PDl {days) Rating ( 0 C) (*)

9

0.5

8 4 a 8 9

9

exe. resist., little or no effect

24

not recommended, substantial effect

Sour Gas

3

Soybean Oil 23 121

7

24

7

fuel fuel 7

and water

recommended for use 0.8

exc. resist., little or no effect

3M Fluorel (FKM)

recommended for use exc. resist., little or no effect

2.3

1

8 7

1

100 100 100 121 121

3M Fluorel (FKM) (FKM)

recommended for use

little/no effect-severe cond. may cause change

(FKM)

109

120

2

89

176

A2

DuPont Viton A (FKM); 20 phr MT black, 15 phr magnesia or litharge, curing agent

4

3

42

230

A-7

DuPont Viton B (FKM/TFE); 20 phr MT black, 15 phr magnesia or litharge, curing agent

3

9

1.3

14

1.4

7

9 9 6 9

125

50

5

14£

21

8

21

1 1 5

70

81

A-7

DuPont Viton; 20 phr MT black, 15 phr magnesia or litharge, curing agent

162

7

7

6

73

95

AO

DuPont Viton A (FKM); 20 phr MT black, 15 phr magnesia or litharge, curing agent

162

7

9

1

94

105

A4

45

91

A-13

DuPont Viton GF (Perox. Cur.); 20 phr MT black, 15 phr magnesia or litharge, curing agent DuPont Viton B (FKM/TFE); 20 phr MT black, 15 phr magnesia or litharge, curing agent

4

34

140

A-11

-2

82

106

A7

13

49

70

A-5

2

87

105

A2

149 150

Steam

(FKM) DuPont Viton B (FKM/TFE); 20 phr MT black, 15 phr magnesia or litharge, curing agent

6.9

1.4MPa, 200 psig

and water

0.4

little/no effect-severe cond. may cause change

23 20

3M Fluorel (FKM)

recommended for use ItKIeA)O effect-severe cond, may cause change

8 8 8 8 7

23

Stannous Chloride

Stauffer 7700 Steam

DuPont Viton B (FKM/TFE); 20 phr MT black, 15 phr magnesia or litharge, curing agent

recommended for use

50 aqueous

8 9 a &

Material Note DuPont Viton A (FKM); 20 phr MT black, 15 phr magnesia or litharge, curing agent

a

Stannic Chloride

Stannous Fluoroborate

Resistance Note

7

50 24 70

aqueous

Hardness Change

7

7

24

Tensile Modulus Elongation Strength

1

50

SR 6

% Retained

Volume

9

Sodium Thiosulfate

SR 10

% Change

42 7

162

9

4

162 162

14.6

4 8

162 162

14.6 21 21

5 9

DuPont Viton; 20 phr MT black, 15 phr magnesia or litharge, curing agent recommended for use

exc. resist., little or no effect

3M Fluorel (FKM); compounds w/ lead based metal oxides recommended

1.8 10.8

good-exc, resist,, moder, effect

3M Fluorel (FKM)

1.5

exc. resist., Iittte or no effect

3M Fluorel (FKM); compounds w/ lead based metal oxides recommended

64

75

A-9

6

DuPont Viton; 20 phr MT black, 15 phr magnesia or litharge, curing agent exc. resist., little or no effect

3M Fluorel (FKM); compounds w/ lead based metal oxides recommended

not suitable for service

(FKM)

DuPont Viton A (FKM); 20 phr MT black, 15 phr magnesia or litharge, curing agent DuPont Viton GF (Perox. Cur.); 20 phr MT black, 15 phr magnesia or litharge, curing agent

(Cont'd.)

Table 7.1 (Cont'd.)

Reagent

Reagent Note

Steam

Steam

and water

Cone. Temp* Time PDl Ways) Rating ( 0 C) (%)

Styrene

styrene monomer

Sucrose

SBR polymerization modifier, Phillips

Sulfur

liquors

9

A-3

DuPont Viton A (FKM); 20 phr MT black, 15 phr magnesia or litharge, curing agent

46

87

A-3

DuPont Viton; 20 phr MT black, 15 phr magnesia or litharge, curing agent

175 177 197

50

15

49

A-13

7

2 2 2 2

200 204 204

0.3 3 3

9 8 7

204

7

8

204

14

20

7

7 8 8 $ 6 8

20

28

4

7 7

6 6 5

23

23 25 50

ZZ 23 20

7

23 Sulfur Chloride

Sulfur Dioxide

23 20

wet liquid moist

2

8 8 8 8 9 8 8 8 8 8 8 9 8 2

dry liquidified; under pressure dry

Material Note

5

molten

Sulfur Oichloride

Resistance Note

4

Sulfite Liquors Sulfole

Hardness Change

6

solutions solution

Tensile Modulus Elongation Strength

170

monomer styrene monomer

% Retained

Volume

175

Stoddard Solvents white spirits

% Change

23 23 23

Sulfur Hexafluoride 23 Sulfur Trioxide 23

8 8 8 8 4 6 8 8

0.7

unsatisfactory tor use 29

49

1 O 3 1 2

A16

DuPont Viton A (FKM); 20 phr MT black, 15 phr magnesia or litharge, curing agent

A-1 good-exc. resist, moder. effect

3M Fluorel (FKM) 3M Fluorel FLS 2330 (FKM); compounds w/ lead based metal oxides recommended

82

110

A-1

68

114

A-5

DuPont Viton GF (Perox. Cur.); 20 phr MT black, 15 phr magnesia or litharge, curing agent recommended for use ffttfe/no effect-severe cond. may causa change

(FKM)

minor to modsr effect

6 11

DuPont Viton B (FKM/TFE); 20 phr MT black, 15 phr magnesia or litharge, curing agent -16

DuPont Viton A (FKM); 20 phr MT black, 15 phr magnesia or litharge, curing agent may cause si. visible swell/loss c-J prop,

11 31

good-exc, resist., moder, effect

(FKM) 3M Fluorel (FKM) DuPont Viton A (FKM); 20 phr MT black, 15 phr magnesia or litharge, curing agent

recommended for use littte/no effect-severe cond. may cause change

(FKM)

recommended for use little/no effect-severe cond. may cause change

(FKM) DuPont Viton B (FKM/TFE); 20 phr MT black, 15 phr magnesia or litharge, curing agent

-0.1 recommended for use

(ittle/no effect-severe cond. may cause change

(FKM)

recommended for use little/no effect-severe cond. may cause change

(FKM) DuPont Viton B (FKM/TFE); 20 phr MT black, 15 phr magnesia or litharge, curing agent

3 recommended for use unsatisfactory lor use recommended for use littte/no effect-severe send, may cause change

(FKM)

moder. to severe effect may cause si. visible swell/loss sf prop,

(FKM)

recommended (or use littte/no effect-severe cond. may cause change

(FKM)

(Cont'd.)

Table 7.1 (Cont'd.)

Reagent

Reagent Note

Cone. Temp. Time CC)

Sulfuric Acid

Ways)

3 molar concentrated dilute fuming; 20/25% oleum fuming, 20% oleum

Rating

Hardness Change

recommended iat use

a

3

A-5

DuPont Viton A (FKM); 20 phr MT black, 15 phr magnesia or litharge, curing agent

20

9

4

A-2

DuPont Viton B (FKM/TFE); 20 phr MT black, 15 phr magnesia or litharge, curing agent

20

36

6

28

A8

20

24

20

fuming, 20% oleum

8 8 8 7 7

28 12

littfe/no effect-severe cond. may cause change

DuPont Viton A (FKM); 20 phr MT black, 15 phr magnesia or litharge, curing agent (FKM)

exc. resist., little or no effect

3M Fluorel (FKM)

a

92.5

102.5

123

A-1

3M KeI-F 3700 (VDF/CTFE); Shore A65; 100:10:10:1:6 - KeI-F: ZnO2: Dyphos: Luperco 101XL: TAIC

7

6

82

123

66

AO

3M KeI-F 3700 (VDF/CTFE); Shore A53; 100:10:10:3 phr - KeI-F: ZnO2: Dyphos: Diak #1

24

7

7

95

127

90

A-1

3M KeI-F 3700 (VDF/CTFE); Shore A55; 100:10:10:3 phr - KeI-F: ZnO2: Dyphos: benzoylperox.

20

100

3

9

-2

106

A2

40

115

28

6

27

DuPont Viton GF (Perox. Cur.); 20 phr MT black, 15 phr magnesia or litharge, curing agent DuPont Viton; 20 phr MT black, 15 phr magnesia or litharge, curing agent

51

38

17

8

8

60

70

7

9

0.5

60

70

28

8

0.5

90

90

A-11

60 90

121 38

28 180

8 8

10

90 119

100 95

A-5

90 90 90 95 95

38 38 38 20 20

365 730

14 14

1 0.2 0.5

103 101 102 99 104

100 98 86 95 100

A2

1095

9 9 9 $ 9

95 98

70 20

28 7

8 9

5 7

88 101

90 108

102

DuPont Viton B (FKM/TFE); 20 phr MT black, 15 phr magnesia or litharge, curing agent 6KC, resist. t little or no effect

Sulfuric Acid

Material Note

7

20

dilute 25% Oleum

Resistance Note

7

36 7 7

concentrated

with 28% nitric, 4% HNOSO4,17% water

Tensile Modulus Elongation Strength

20

23 23 23 24 25 24

20% oleum

Sulfuric Acid

% Retained

Volume

8 8 8. 8 8

20% oleum

fuming

% Change

3M Fluorel (FKM); compounds w/ lead based metal oxides recommended DuPont Viton A (FKM); 20 phr MT black, 15 phr magnesia or litharge, curing agent

A2

DuPont Viton B (FKM/TFE); 20 phr MT black, 15 phr magnesia or litharge, curing agent

A3 A3 AO A6

DuPont Viton A (FKM); 20 phr MT black, 15 phr magnesia or litharge, curing agent

A1 A-2

DuPont Viton GF (Perox. Cur.); 20 phr MT black, 15 phr magnesia or litharge, curing agent

98

20

30

8

10

A6

DuPont Viton A (FKM); 20 phr MT black, 15 phr magnesia or litharge, curing agent

98

20

30

8

7

A-5

DuPont Viton B (FKM/TFE); 20 phr MT black, 15 phr magnesia or litharge, curing agent

98

100

14

6

21 good-exc. resist., moder. effect

3M Fluorel (FKM); compounds w/ lead based metal oxides recommended

(Cont'd.)

Table 7.1 (Cont'd.) % Change Reagent

Reagent Note

Cone. Temp. Time PDl tfays) Rating (0C) (%)

Sulfurous Acid 20

5% sulfur dioxide

7

23 SX 90

Mobil Oil

90

tannin

23

21

Tannic Acid 10 Tar Tartaric Acid

Tellus 33

Resistance Note

severely cracked and swelled

8

little/no effect-severe cond. may cause change

(FKM)

exc. resist., iittle or no effect

3M Fluorel (FKM)

g

recommended lor use

0.7

8

recommended Io r use

8

little/no effect-severe cond. may cause change

8

recommended lor use

8

little/no effect-severe cond, may cause change

8

recommended for use

23

8

little/no effect-severe cond. may cause change

23

1

not suitable for service

Shell

70

Tetrabromoethane

28

9

0.6

exc. resist., little or no effect

8

recommended for use little/no effeci-sevefe cond. may cause change

23

8

23

8 8

recommended for use

23

8

little/no effect-severe cond. may cause change

8

recommended lor use

Tetrabromomethane Tetrabutyl Titanate

8

23 Tetrachloroethane

Material Note

8 1

toluene diisocyanate

Terpineol

little/no effect-severe cond, may cause change

20

21

7

3

25

21

8

3

8

Tetrachloroethylene 20

14

23 Tetraethyllead

% Retained Tensile Modulus Elongation Hardness Strength Change

DuPont Viton A (FKM); 20 phr MT black, 15 phr magnesia or litharge, curing agent

(FKM)

8

bituminous 23

TDI

Volume

blend

9

A10

(FKM) (FKM) 3M Fluorel (FKM) (FKM)

(FKM) (FKM) DuPont Viton A (FKM); 20 phr MT black, 15 phr magnesia or litharge, curing agent

exc. resist., little or no effect

3M Fluorel (FKM)

recommended for use 2

8

little/no effect-severe cond. may cause change

8

recommended for use

DuPont Viton B (FKM/TFE); 20 phr MT black, 15 phr magnesia or litharge, curing agent (FKM)

8 23 Tetrahydrofuran 20

6

7

Tetralin tetrahydronaphthalene, Dupont

23

unsatisfactory lor use

1

281

1

not suitable for service recommended for use

8

little/no effect-severe cond, may cause change

7

177

7

9

177

7

9

8

recommended for use 3.1

exc, resist, little or no effect

1.4

exc. resist., little or no effect

1.9

exc. resist,, little or no effect

recommended for use

8

Texamatic Fluid 3401

recommended for use

8

Texamatic Fluid 3525

recommended io r use

8

Texamatic Fluid 3528 Kearsley thinners

DuPont Viton B (FKM/TFE); 20 phr MT black, 15 phr magnesia or litharge, curing agent

8

177

(FKM)

200

8

Texamatic Fluid 1581

Thinners

little/no effect-severe cond. may cause change

1

23 23

8 2

177

7

9

2.1

24

40

8

3.5

(FKM)

(FKM)

3M Fluorel (FKM) 3M Fluorel (FKM) 3M Fluorel (FKM)

exc. resist,, little or no effect 3M Fluorel (FKM)

(Cont'd.)

Table 7.1 (Cont'd.)

Reagent

Reagent Note

Cone. Temp. Time PDt CC) {days) Rating (%)

Thionyl Chloride 20

28

23

with 20% toluene -2,6 diisocyanate

Chlorextol, AINsChalmers

3 4 3 4

52

75

22

67

70

7

5

13

70

7

8

95

93 70

4 14

6 6

95

70

80

20

7

7 7

8 8 8 8 8 8 8 7

automatic type A type A; Esso Texamatic «A» type A Esso,type A

23 100 100

DuPont Viton A (FKM); 20 phr MT black, 15 phr magnesia or litharge, curing agent (FKM)

recommended for use

7.8 7.5 20 29

(FKM)

exc, resist.> little or no effect

3M Fluore! (FKM)

good-exc. resist, mader. effect

may cause si. visible sweff/loss of prop,

(FKM)

recommended for use

8 4.8 17

little/no effect-severe cond, may cause change

(FKM)

exc, resist., little or no effect

3M Fluorel FLS 2330 (FKM)

good-exc, resistM moder. effect

3M Fluorel (FKM)

54

72

A-12

54

72

64

86 83

A-14 A-23 A-19 A-17

59

80

A-10

DuPont Viton B (FKM/TFE); 20 phr MT black, 15 phr magnesia or litharge, curing agent

4

73

100

A-3

DuPont Viton GF (Perox. Cur.); 20 phr MT black, 15 phr magnesia or litharge, curing agent

15 17

73

100

A-14

DuPont Viton GF (Perox. Cur.); 20 phr MT black, 15 phr magnesia or litharge, curing agent

61

100

A-18

DuPont Viton B (FKM/TFE); 20 phr MT black, 15 phr magnesia or litharge, curing agent

DuPont Viton A (FKM); 20 phr MT black, 15 phr magnesia or litharge, curing agent

DuPont Viton; 20 phr MT black, 15 phr magnesia or litharge, curing agent

good-exc. resist., moder. effect

not suitable for service

3M Fluorel FLS 2330 (FKM)

(FKM)

unsatisfactory for use DuPont Viton; 20 phr MT black, 15 phr magnesia or litharge, curing agent

1 8 8 6 8

Material Note

may cause si. visible swetl/ioss of prop,

26

8

23 100

A-20

1 2 9

23

Resistance Note

may cause si. visible swell/loss of prop,

5

Mobilgas WA200; Type A

Transmission Fluids

83

365 730 1095 2

Pyranol

Transformer Oils

46

38 38 38 50

TDI

Hardness Change

recommended lor use

22

7 7 14 180

trinitrotoluene

1095 7 28 20

14 Toluene Diisocyanate Toluene Diisocyanide Toluene-2,4-diisocyanate

Tensile Modulus Elongation Strength

23 23 25 25 38

23 38 177 204 250 23

TJ 15

with 5% pyridine

% Retained

Volume

6 8 6 8 7 6 6 6 S 8 8 S 6 4

Titanium Tetrachloride

TJ 35 TNT Toluene

8 4

% Change

recommended for use tittle/no effect-severe cond. may cause change

6

(FKM) DuPont Viton B (FKM/TFE); 20 phr MT black, 15 phr magnesia or litharge, curing agent

recommended tor use a recommended lor use

3 2

77

79

A-1

little/no effect-severe cond. may cause change

(FKM)

exc, resist,, little or no effect

3M Fluorel (FKM) DuPont Viton A (FKM); 20 phr MT black, 15 phr magnesia or litharge, curing agent

(Cont'd.)

Table 7.1 (Cont'cn

Reagent Transmission Fluids

Reagent Note super 284 OS19381 Satfa EC-3686 Esso,type A

Transmission Fluids

% Change

% Retained

Volume

Tensile Modulus Elongation Strength

Hardness Chance

135

3

7

3

85

73

A3

135 149 149 150

3 3 40 40

8 9 8

4

89

80

A1

petroleum base, Ford

175

3

Texamatic Fluid 1581, Texaco

175

7

Texamatic Fluid 3401, Texaco

175

7

Texamatic Fluid 3525, Texaco

175

7

Texamatic Fluid 3528, Texaco

175

7

Sunoco Sunomatic 136 ATF

121

14

Texaco TL-8262B ATF

121 121

14.6

Sunoco Sunomatic 136 ATF

14

7

1 4

74

105

A-11

1

80

100

AO

DuPont Viton B (FKM/TFE); 20 phr MT black, 15 phr magnesia or litharge, curing agent

90

95

A2

DuPont Viton A (FKM); 20 phr MT black, 15 phr magnesia or litharge, curing agent

1

80

88

A-2

2

95

95

AO

2

80

82

A2

0.6

96

104

A2

9 9

1

88 95

100

A-1

100

A-4

1

100

A-4

2

92

A3

2

95 73 100

100

AO

9 8 9 8 9

1

3 3

150

3

6

2

72

65

A3

150

3

7

2

82

73

AO

Sunoco Sunomatic 136 ATF

150

14

9

1

94

109

AO

Texaco TL-8262B ATF

150 150 150

14

9 6 8

2

90 67 94

96

A-2

69

A4

3

Dexron ATF

Chevron PD-4645 ATF Sunoco Sunamatic 141 ATF WSX-8762B, Exxon factory fill type

Sunoco Sunamatic 141 ATF WSX-8762B, Exxon Chevron PD-4645 ATF ATF 1, viscosity index 134, sap. no.53

14.6 14.6

3M Fluorel FLS 2330 (FKM) 3M Fluorel (FKM) DuPont Viton A (FKM); 20 phr MT black, 15 phr magnesia or litharge, curing agent

3

9

9 7 9

Sunoco Sunamatic 141 ATF

Material Note DuPont Viton B (FKM/TFE); 20 phr MT black, 15 phr magnesia or litharge, curing agent

exc. resist, little or no effect

14.6

Dexron ATF

Resistance Note

4.2

121 150 150

Texaco TL-8262B ATF

Transmission Fluids

Cone. Temp, Time PDl ( 0 C) {days) Ratincf (%)

2 2

76

A1

98 63

86

A-1

43

A8

71

A1

68

A1

150 150

41.7 41.7

9 5

163 163

3 3

7 7

2 1

74 79

103 163

3 7

7 3

1

80

71

A2

2.8

57.9

47

A-1

163 163 163

7 7 7

4 4 3

2.5

137.9

53

AO

2.9

64.4

53

A-1

2.6

34.2

25

A4

163 163 163

7 7 7

3 3 6

1.9

35.6

38

A3.5

2.1

45.9

48

A4

2

69

59

AO

163 163 175

7 14 3

6 6 7

2

74 62 76

64

A1

3

2 3

DuPont Viton B (FKM/TFE); 20 phr MT black, 15 phr magnesia or litharge, curing agent

DuPont Viton A (FKM); 20 phr MT black, 15 phr magnesia or litharge, curing agent

DuPont Viton B (FKM/TFE); 20 phr MT black, 15 phr magnesia or litharge, curing agent

DuPont Viton A (FKM); 20 phr MT black, 15 phr magnesia or litharge, curing agent DuPont Viton B (FKM/TFE); 20 phr MT black, 15 phr magnesia or litharge, curing agent

showed cracking/crazing

3M Fluorel (FKM); 66 wgt.% fluorine; Shore

W

61

A2

84

A-1

3M (FKM/TFE); high fluoride (70 wgt.%) peroxide cured; Shore A76

DuPont Viton B (FKM/TFE); 20 phr MT black, 15 phr magnesia or litharge, curing agent

M

DuPont Viton A (FKM); 20 phr MT black,. 15 phr magnesia or litharge, curing agent

(Cont'd.)

Table 7.1 (Cont'd.)

Reagent Transmission Fluids

Reagent Note

Cone. Temp. Time PDt (%) CC) {days) Rating

% Retained

Volume

Tensile Modulus Elongation Strength

175

3

7

2

77

82

A-1

ATF 3, viscosity index 136, sap. no. 2.0

175

3

7

2

75

78

A-1

ATF 4, viscosity index 140, sap. no. 6.0

175

3

7

2

76

80

AO

ATF 5, viscosity index 147, sap. no. 3.3

175

3

6

2

53

61

A-1

Chevron PD-4645 ATF

175

3

7

2

84

73

AO

Sunoco Sunamatic 141 ATF

175

3

7

2

76

64

AO

WSX-8762B, Exxon

175 177 177 177 177 177 20

3 3 3 3 3 3 30

6 S 9 9 9

2

67

62

A2

2.1

a

1.5

20

30

25

7

8

100

7 7

2 1 8 8 8 8 8 8 2 1 1 1

150

7

AFT 2 AFT 3 AFT 4 AFT 5 trifluralin-preemergent herbicide-Elanco

with water + 5% surfactant

50

Triacetin 23

Triaryl Phosphate 23

Tributoxyethyl Phosphate 23

Tributyl Mercaptan 23

Tributyl Phosphate 23 1OO

7 7

20

7

1 4 4 8 7

20

21

7

21 28 28

8 7 5 2

7

8 8

Trichloroacetic Acid 23

Trichloroethane

23 25 1OO 100

Trichloroethylene 20

Resistance Note

Hardness Change

ATF 2, viscosity index 140, sap. no. 2.0

AFT1

Treflan

% Change

Material Note DuPont Viton A (FKM); 20 phr MT black, 15 phr magnesia or litharge, curing agent

DuPont Viton B (FKM/TFE); 20 phr MT black, 15 phr magnesia or litharge, curing agent

2.6

exc, resist* little or no effect

3M Fluorel (FKM)

2.3 2.5 3 2

83

118

AO

DuPont Viton B (FKM/TFE); 20 phr MT black, 15 phr magnesia or litharge, curing agent

91

144

AO

DuPont Viton GF (Perox. Cur.); 20 phr MT black, 15 phr magnesia or litharge, curing agent exc. resist., little or no effect

3.5

3M Fluorel (FKM)

unsatisfactory for use not suitable for service ;

(FKM)

recommended for use

little/no effect-severe cond. may cause change

(FKM)

recommended for use tittle/no effect-severe cond. may cause change

(FKM)

recommended for use little/no effect-severe cond. may cause change

(FKM)

unsatisfactory for use not suitable for service 380

not recommended, substantial effect

380 400

3

(FKM) 3M Fluorel (FKM) DuPont Viton A (FKM); 20 phr MT black, 15 phr magnesia or litharge, curing agent

moder. to severe effect moder./severe swell and/or loss of prop,

(FKM)

recommended for use 11

DuPont Viton; 20 phr MT black, 15 phr magnesia or litharge, curing agent A10

3

DuPont Viton A (FKM); 20 phr MT black, 15 phr magnesia or litharge, curing agent little/no effect-severe cond, may cause change

(FKM)

good-exc. resist., moder. effect

3M Fluorel (FKM)

46 46

31

60

A28

DuPont Viton A (FKM); 20 phr MT black, 15 phr magnesia or litharge, curing agent recommended f or use

10

DuPont Viton A (FKM); 20 phr MT black, 15 phr magnesia or litharge, curing agent

(Cont'd.)

Table 7.1 (Cont'd.)

Reagent

Reagent Note

Trichloroethylene

tetrachloroethylene

Cone. Temp. Time PDL CC) tfays) Rating (%)

175

A-18

DuPont Viton B (FKM/TFE); 20 phr MT black, 15 phr magnesia or litharge, curing agent

20

7

€

7

65

86

A-5

20

14

9

4

DuPont Viton GF (Perox. Cur.); 20 phr MT black, 15 phr magnesia or litharge, curing agent DuPont Viton B (FKM/TFE); 20 phr MT black, 15 phr magnesia or litharge, curing agent

20 23 25 25 70 70

14

8 8 8 8 6 6

6

7 7 28 28

3 180 365 730 1095 14 14

6 8 7 9 8 8 6 6 7

6

little/no effect-severe cand. may cause change

(FKM)

exc, resist,, little or no effect

3M Fluorel (FKM)

7

3M Fluorel FLS 2330 (FKM)

15 15

good-exc, resist,, moder. effect 61

95

A-12

3M Fluorel (FKM) DuPont Viton A (FKM); 20 phr MT black, 15 phr magnesia or litharge, curing agent

minor to moder. effect 13 98

100

AO

90

90

A-3 A-12

92

98

13

72

85

A-9

21

76

106

A-13

5

83

118

A-4

tittle/no eflecf-severe cond, may cause change

(FKM)

exc. resist., little or no effect

3M Fluorel (FKM) DuPont Viton A (FKM); 20 phr MT black, 15 phr magnesia or litharge, curing agent

DuPont Viton B (FKM/TFE); 20 phr MT black, 15 phr magnesia or litharge, curing agent

7

7 7

21

84

104

A-7

DuPont Viton A (FKM); 20 phr MT black, 15 phr magnesia or litharge, curing agent

150

7

8

7

93

110

A-3

DuPont Viton B (FKM/TFE); 20 phr MT black, 15 phr magnesia or litharge, curing agent

150 150

14

6 7

7

81

125

A-6

20

74

86

A-2

18

62

70

A-13

7

71

83

A-3

140 150

7

14 21 21

23 71

6

30

8 8 9

7

8 € € 6 6

7

8 8 8

Trifluoroethane Trinitrotoluene Trioctyi Phosphate 23 70 china wood oil

23 149

3M Fluorel (FKM)

DuPont Viton A (FKM); 20 phr MT black, 15 phr magnesia or litharge, curing agent DuPont Viton B (FKM/TFE); 20 phr MT black, 15 phr magnesia or litharge, curing agent unsatisfactory for use not suitable for service

(FKM)

minor to moder. effect may cause si, visible swell/loss of prop.

30

Triethylborane 23 71

4 6

exc. resist, little or no effect

17

2 1 6

23

Triethylaluminum

Sunamatic 137

Material Note

62

Triethanolamine

Turbine Engine Lubricant

Resistance Note

9

150 150

Tung Oil

Hardness Change

4

38 38 38 100 100

Trioxane

Tensile I Modulus Elongation Strength

7

23 38 38

TEA

% Retained

Volume

20

Tricresyl Phosphate

Tricresyl Phosphate

% Change

(FKM) DuPont Viton A (FKM); 20 phr MT black, 15 phr magnesia or litharge, curing agent

30 recommended for use little/no effect-severe cond. may cause change 5

(FKM) DuPont Viton A (FKM); 20 phr MT black, 15 phr magnesia or litharge, curing agent

recommended for use minor to moder. effect may cause sJ. visible swell/loss of prop, 23

(FKM) DuPont Viton B (FKM/TFE); 20 phr MT black, 15 phr magnesia or litharge, curing agent

recommended for use 3

little/no effect-sever* cond. may cause change

(FKM)

exc, resist., little or no effect

3M Fluorel (FKM)

(Cont'd.)

Table 7.1 (Cont'd.) % Change Cone. Temp. Time PDl ttays) Rating CC) (W

Reagent

Reagent Note

Turbine Oil

#15; MIL-L-7808A

8

#35

8

Volume

% Retained Tensile Modulus Elongation Hardness Strength Change

Resistance Note

Material Note

recommended tor use

8 8

Turpentine

8

23

Ucon50HB100

70

28

8

9

70

28

7

8.6

Ucon 50HB55

38

205

14

9

lubricant

8

8

Ucon LB300

8

recommended 1o r use 44

8

oil

8

Ucon LB400X

8

lubricant

8

Ucon LB65 unsymmetrical dimethyl hydrazine

1

23 70

Univis J43

135

28

9

1.8

7

8

2.6

2

unsymmetrical (UDMH) 24

4

8

10

24

7

8

2.6

Varnish

23 23

not suitable for service

(FKM)

exc. resist., little or no effect

3M Fluorel (FKM)

unsatisfactory lor use

Valclene

Vegetable Oils

DuPont Viton B (FKM/TFE); 20 phr MT black, 15 phr magnesia or litharge, curing agent

8

Ucon LB285

Unsymmetrical Dimethylhydrazine

A2

3

8

lubricant

Ucon LB135

UDMH

recommended l o i use

8 8

Ucon LB625

DuPont Viton A (FKM); 20 phr MT black, 15 phr magnesia or litharge, curing agent

8

Ucon Hydrolube J4

Ucon LB385

A-7

8

Ucon 50HB660 Ucon LB1145

3M Fluorel (FKM)

8 oil; polyacrylonitrile glycol derivative heat transfer lubricant

Ucon50HB5100

105

(FKM)

exc. resist > little or no effect

8

lubricant

Ucon 50HB260 Ucon 50HB280X

84

little/no effect-severe cond. may cause change

exc. resist., iittte or no effect

8

recommended for use

8

little/no effect-severe cond. may cause change

8

recommended for use little/no effect-severe cond. may cause change

8

(FKM) (FKM)

20

30

5

12

69

118

A-10

DuPont Viton B (FKM/TFE); 20 phr MT black, 15 phr magnesia or litharge, curing agent

20

30

6

2

88

133

A-7

DuPont Viton GF (Perox. Cur.); 20 phr MT black, 15 phr magnesia or litharge, curing agent

Vernam

Versilube Versilube F50

3M Fluorel (FKM)

23 177

28

260

3

Vinegar 23

8

recommended for use

8

little/no effect-severe cond. may cause change

(FKM)

good-exc. resist, moder. effect

3M Fluorel (FKM)

7

3

7

-3

8

recommended fo ruse

8

little/no effect-severe cond. may cause change

(FKM)

(Cont'd.)

Table 7.1 (Cont'd.)

Reagent Vinyl Acetylene

Reagent Note

Cone. Temp. Time PDl (0C) tfays) Rating (%)

% Retained

Volume

Tensile Modulus Elongation Strength

Hardness Change

-20

7

23 20

7

7

A-2 littJe/no effect-severe cond, may cause change

8

recommended for use

7

7

6

drinking

8

salt water

8

Material Note

DuPont Viton A (FKM); 20 phr MT black, 15 phr magnesia or litharge, curing agent

8 12

(FKM) DuPont Viton A (FKM); 20 phr MT black, 15 phr magnesia or litharge, curing agent

8

23 25

$

Resistance Note unsatisfactory lor use

2

monovinyl acetylene

Vinyl Chloride Vinyl Fluoride

% Change

12

tittle/no effect-severe cond. may cause change

(FKM)

good-exc. resist., moder. effect

3M Fluorel (FKM)

recommended for use

8 distilled

Water

Water

20

30

9

0.6

A5

DuPont Viton A (FKM); 20 phr MT black, 15 phr magnesia or litharge, curing agent

20

30

9

0.8

A-5

DuPont Viton B (FKM/TFE); 20 phr MT black, 15 phr magnesia or litharge, curing agent

180

8

3

cold

23

distilled

70

8

iittle/no effect-severe cond. may cause change 69

100

AO

80

130

A6

(FKM) DuPont Viton A (FKM); 20 phr MT black, 15 phr magnesia or litharge, curing agent

70

365

7

11

70

730

6

5

plus 1% soluble oil

90

4.2

9

5

and steam

100

3

9

1.3

100

7

6

59.5

90

86

A-2

3M KeI-F 3700 (VDF/CTFE); Shore A65; 100:10:10:1:6 - KeI-F: ZnO2: Dyphos: Luperco 101XL: TAIC

100

7

8

80

105

90

A-4

3M KeI-F 3700 (VDF/CTFE); Shore A55; 100:10:10:3 phr - KeI-F: ZnO2: Dyphos: benzoyl perox.

100

7

3

33

140

43

A-7

3M KeI-F 3700 (VDF/CTFE); Shore A53; 100:10:10:3 phr - KeI-F: ZnO2: Dyphos: Diak #1

distilled

100

10

9

104

111

A-1

DuPont Viton A (FKM); 20 phr MT black, 15 phr magnesia or litharge, curing agent

and steam

100

14

9

1.4

distilled

100

28

9

0.3

99

117

A2

100

28

6

0.7

83

125

A-18

DuPont Viton B (FKM/TFE); 20 phr MT black, 15 phr magnesia or litharge, curing agent

2

and steam

1

exc. resist., little or no effect

3M Fluorel (FKM); compounds w/ lead based metal oxides recommended

3M Fluorel (FKM); compounds w/ lead based metal oxides recommended exc. resist., little or no effect

DuPont Viton A (FKM); 20 phr MT black, 15 phr magnesia or litharge, curing agent

100

30

8

117

AO

DuPont Viton A (FKM); 20 phr MT black, 15 phr magnesia or litharge, curing agent

100

30

6

50.5

68.75

95

A-2

3M KeI-F 3700 (VDF/CTFE); Shore A65; 100:10:10:1:6 - KeI-F: ZnO2: Dyphos: Luperco 101XL: TAIC

100

30

6

65

91

103

A-10

3M KeI-F 3700 (VDF/CTFE); Shore A55; 100:10:10:3 phr - KeI-F: ZnO2: Dyphos: benzoylperox.

100

30

5

31.25

97

63

A-6

3M KeI-F 3700 (VDF/CTFE); Shore A53; 100:10:10:3 phr - KeI-F: ZnO2: Dyphos: Diak #1

100

42

9

104

1.8

3M Fluorel (FKM); compounds w/ lead based metal oxides recommended exc. resist., little or no effect

(Cont'd.)

Table 7.1 (Cont'd.)

Reagent Water

Reagent Note

Cone. Temp. Time PDt (0C) ttays) Rating (%)

and steam

distilled

Water

and steam

with glysantin 1:1

Whiskey White Oil

50

Hardness Change

Resistance Note

Material Note 3M Fluorel (FKM) 3M Fluorel (FKM); compounds w/ lead based metal oxides recommended

6 9

10.8

good-exc. resist., moder. effect

1.5

8KC. resist., little or no effect

149 162

21 7

8 8

6 9

86

95

A6

162

7

8

5

86

105

A-7

162 162

21 21

S 7

5 11

94 84

121 110

A-3 A4

170 170 175 204 204

4 8 6 3 3

9 9 5 8 7

2

90

4.2

9

2

23 25 25 70 70

7 14 28 28

8 8 8 8 8 8 8 8 8 9 7 6 5

20

10

9

23

23 Xenon Xylene

mixed aromatic amines di-methyl aniline

Tensile Modulus Elongation Strength

7 7

Wolmar Salt Wood Oil

Xylidine

% Retained

Volume

121 121

& wines

Xylene (m-)

% Change

23

Zeolites 23

DuPont Viton A (FKM); 20 phr MT black, 15 phr magnesia or litharge, curing agent DuPont Viton GF (Perox. Cur.); 20 phr MT black, 15 phr magnesia or litharge, curing agent DuPont Viton A (FKM); 20 phr MT black, 15 phr magnesia or litharge, curing agent

A-3 A4

4 O

good-exc. resist., moder. effect

3

3M Fluorel (FKM) 3M Fluorel FLS 2330 (FKM); compounds w/ lead based metal oxides recommended DuPont Viton A (FKM); 20 phr MT black, 15 phr magnesia or litharge, curing agent

recommended for use tittle/no effect-severe cond. may cause change

(FKM)

recommended tor use

50

tittle/no effect-severe cond. may cause change

126

(FKM)

recommended lor use

2

little/no effect-severe cond. may cause change

(FKM)

exc. resist., littte or no effect

3M Fluorel FLS 2330 (FKM)

12

3M Fluorel (FKM)

18

good-exc, resist., moder. effect

A-16

18

DuPont Viton A (FKM); 20 phr MT black, 15 phr magnesia or litharge, curing agent

5

DuPont Viton B (FKM/TFE); 20 phr MT black, 15 phr magnesia or litharge, curing agent

2 1 8 8

unsatisfactory for use not suitable For service

(FKM)

recommended for use little/no effect-severe cond. may cause change

(FKM)

unsatisfactory for use

Zinc Acetate 23 Zinc Chloride 23 Zinc Salts Zinc Sulfate 23

1 8 8 8 8 8

not suitable for service

(FKM)

recommended for use

66

85

little/no effect-severe cond. may cause change

(FKM)

recommended for use little/no effect-severe cond. may cause change

(FKM)

192

FLUOROELASTOMERS HANDBOOK

Table 7.2 Fluid Resistance of Fluoroelastomer Families[4]

Fluoroelastomer Type Composition % Fluorine

A

B

VDF/HFP 66

Cure System

F

GB

GF

VDF/HFP/TFE 68

70

67

GLT

GFLT

VDF/PMVE/TFE 70

Bisphenol

64

67

Peroxide

Typical % Volume Change, 75-durometer vulcanizate Fuel C, 7 days / 23ºC

4

3

2

5

2

Methanol, 7 days / 23ºC

90

40

5

90

5

>200

>200

>200

>200

>200

Methyl ethyl ketone, 7 days / 23ºC Potassium hydroxide, 7 days / 70ºC

Samples highly swollen and degraded

Service Rating Hydrocarbon Auto, Aviation Fuels Oxygenated Auto Fuels

E

E

E

E

E

E

E

NR

VG

E

VG

E

NR

E

Motor Oils SE-SF Grades

VG

E

E

E

E

E

E

SG-SH Grades

G

VG

VG

E

E

E

E

Aliphatic

E

E

E

E

E

E

E

Aromatic

VG

VG

E

E

E

VG

E

G

VG

VG

E

E

E

E

Amines; high pH aqueous base

NR

NR

NR

NR

NR

NR

NR

Low mol wt ketones and esters

NR

NR

NR

NR

NR

NR

NR

Hydrocarbon Process Fluids

Aqueous Fluids: Hot water, Steam, Mineral Acids

Service Ratings: E - Best choice for service; minimal volume increase or change in physical properties. VG - Good serviceability; small volume increase and/or changes in physical properties. G - Suitable for service; acceptable volume increase and/or changes in physical properties. NR - Not recommended; excessive volume increase or change in physical properties.

7 FLUID RESISTANCE OF VDF-CONTAINING FLUOROELASTOMERS

193

REFERENCES 1. Chemical Resistance Volume 2: Elastomers, Thermosets and Rubbers, PDL Handbook Series, Chemical Resistance - FKM, VDF/CTFE, FKM/TFE Fluoroelastomers, Second Edition, pp. 190–254, William Andrew Inc., Norwich, NY (1994) 2. Chemical Resistance Guide, DuPont Performance Elastomers, Viton ® Technical Information, www.dupontelastomers.com (2005) 3. Dyneon® Fluoroelastomer Chemical Resistance, Product Information Bulletin 98-0504-1316-4 www.Dyneon.com (2000) 4. Viton® Fluoroelastomer Selection Guide, Technical Information Bulletin 301794A (1998)

8 Fluid and Heat Resistance of Perfluoroelastomers 8.1

Introduction

Perfluoroelastomers are copolymers of TFE and PMVE or a perfluoro(alkoxyalkyl vinyl ether) with various cure sites incorporated, as described in Sec. 2.4. The chemical resistance of perfluoroelastomer vulcanizates approaches that of polytetrafluoroethylene (PTFE) thermoplastics. The heat resistance of perfluoroelastomer vulcanizates depends mainly on the cure system used, as discussed in Sec. 5.3. Peroxide-curable perfluoroelastomers are sold to selected fabricators by Daikin and Solvay Solexis. DuPont Performance Elastomers sells fabricated perfluoroelastomer parts, based on proprietary compounds of various polymers and cure systems. Information available from perfluoroelastomer parts suppliers does not always allow identification of the polymer composition, cure system, and compound ingredients for a given product. The original Kalrez ® perfluoroelastomer parts were based on a bisphenol cure system that gives excellent fluid and heat resistance. Later perfluoroelastomer products (e.g., Daikin Perfluor) based on peroxide cure systems have excellent fluid resistance, especially to hot aqueous media, but much lower heat resistance. Fabricated parts from Kalrez® 4079 make up a large fraction of DuPont perfluoroelastomer production. Curing is effected by catalyzed reaction of –RfCN groups to form highly stable triazine cross links. Solvay Solexis has recently developed peroxide-curable perfluoroelastomers with excellent heat resistance.

8.2

lar results. For long-term exposure to hot aqueous environments, perfluoroelastomers cured with peroxide or bisphenol are more stable than those with triazine cross links. More detailed fluid resistance information, including product recommendations for service at various temperatures, is available in the interactive Chemical Resistance Guide for Kalrez® on the DuPont Performance Elastomers website.[2] A summary of chemical resistance for perfluoroelastomers cured with various systems is shown in Table 8.2.[3] For the Kalrez compounds listed, 1050LF is cured with bisphenol, 2035 is cured with peroxide and radical trap using a bromine-containing cure site, 4079 has triazine cross links, and 6375 has a proprietary cure system probably based on –RfCN cure sites. Some differences in fluid resistance are noted in Table 8.2 that are not apparent in the Table 8.1 listing which does not contain information on compounds with different cure systems. Iodine-containing Daikin Perfluor and Solvay Solexis Tecnoflon PFR polymers cured with peroxide would have broad fluid resistance similar to that for the Kalrez 2035 compound. This includes the major fluid seal compound, Chemraz® 505, offered by Greene, Tweed & Co., apparently based on peroxide-cured Perfluor.[4] The information in these tables should be used only for initial guidance. When exposure conditions are known for a given application, suppliers of perfluoroelastomers or fabricated parts can give better recommendations for specific compounds that will give satisfactory service. In many cases, decisions should be based on performance requirements other than fluid resistance.

Fluid Resistance Data

Table 8.1 contains a tabulation of chemical resistance for perfluoroelastomer vulcanizates, taken from a previous volume in the PDL Handbook Series.[1] The standard ASTM designation FFKM for perfluoroelastomers is used in the table. All the data are for DuPont Kalrez® perfluoroelastomer vulcanizates exposed to fluids at temperatures up to 100°C. Under these conditions, the perfluoroelastomers are resistant to most of the test fluids, so PDL ratings are high (usually 8), indicating suitability for service. (See Appendix for a more complete description of the PDL Ratings.) Other perfluoroelastomers would give simi-

8.3

Heat Resistance Data

Some heat resistance data for perfluoroelastomers cured with various crosslinking systems were shown in Table 5.8, recording changes in tensile strength after ten days of exposure at several temperatures. Data such as these were used to recommend upper temperatures for continuous service of various Kalrez compounds, as listed in Table 8.3.[5] The heat resistance of TFE/PMVE perfluoroelastomers with –RfCN cure sites that form triazine cross links is outstanding, with long-term service over

196 300°C possible. Bisphenol-cured perfluoroelastomers also have excellent thermal stability. Such compounds require long press cures, followed by very long (40 hours or more) oven postcuring under nitrogen at high temperature. Most fabricators of fluoroelastomer parts do not have capability for such curing operations, so DuPont Performance Elastomers makes and sells perfluoroelastomer fabricated parts, largely through a distributor network. The upper service temperature limit for peroxide cures of perfluoroelastomers with iodine or bromine cure sites using triallylisocyanurate (TAIC) as radical trap (crosslinking agent) is the same as that for VDF-containing fluoroelastomers. Some improvement is obtained when perfluoroelastomers with –RfCN cure sites are cured with peroxide and TMAIC.[6] As noted in Sec. 5.3, Solvay Solexis has developed peroxide-curable perfluoroelastomers with enhanced heat resistance. [7] These polymers are made in a microemulsion “living radical” semibatch process, with I(CF2)6I transfer agent charged initially to get chains with iodine end groups and with CH2=CH–(CF2)6– CH=CH2 fed during the course of the polymerization to get significant branching and some pendant vinyl groups. The branched polymer chains contain more than two iodine groups per chain. Heat-aging data for two peroxide-cured Tecnoflon PFR perfluoroelastomer compounds are shown in Table 8.4. PFR 94 is cured with peroxide and TAIC trap to give vulcanizates with stability similar to that usually obtained with other fluoroelastomers containing iodine end groups.[8] PFR 95, a similar branched polymer which may contain considerable pendant vinyl groups and probably additional CH2=CH–(CF2)6–CH=CH2, is cured with peroxide only (no TAIC) to give a vulcanizate stable up to 290°C.[9] Evidently, cross links based on divinylperfluoroalkane are more stable than those from triallylisocyanurate. Recently, Greene, Tweed & Co. developed Chemraz 615 seals for high-temperature service[10] up to 324°C. O-ring compression set resistance is claimed to be better than that of compounds like Kalrez 4079. The polymer and cure systems were not disclosed. The heat resistance information in this section is for exposure to hot air and should be used for general guidance only. For exposure to other environments at high temperature, recommendations should be obtained from perfluoroelastomer parts’ suppliers.

FLUOROELASTOMERS HANDBOOK

8.4

Resistance to Special Environments

High-cost perfluoroelastomers are mainly used for seals in environments to which hydrofluorocarbon elastomers are not sufficiently resistant to give adequate service life. Perfluoroelastomers have low swell in polar fluids that excessively swell VDF-containing fluoroelastomers, and are resistant to strong organic and inorganic bases and acids that may degrade VDFcontaining fluoroelastomers. Perfluoroelastomers are also resistant to strong oxidizing agents which attack fluoroelastomers containing either VDF or olefin monomer units. Several perfluoroelastomer compounds have excellent heat stability, allowing longterm service at 275°C–320°C, well above service limits for hydrofluorocarbon elastomers. Perfluoroelastomers have mediocre low-temperature flexibility. TFE/PMVE copolymers have glass temperatures of about -5°C, while Daikin copolymers of TFE with a perfluoro(alkoxyalkyl vinyl ether) have somewhat lower Tg, about -15°C. In common with other fluoroelastomers with high TFE content, perfluoroelastomers have low brittle points, near -40°C, so static seals may function at temperatures down to about -20°C, considerably below their Tg. Thermal expansion of perfluoroelastomer compounds must be taken into account, especially for seals for high-temperature service. For compounds with medium hardness, the coefficient of linear expansion is about 3.2 × 10-4/°C.[11] For a temperature rise of 200°C above ambient, linear dimensions of a perfluoroelastomer seal would increase by 64%. Thus, an o-ring groove must be sized to allow for such a large dimensional increase so that the seal does not overfill the groove and extrude at high temperatures. Part of the reason for such high thermal expansion is that perfluoroelastomer compounds generally contain low filler levels, typically 10–15 phr of black. Hardness increases greatly at higher black levels.

8.5

Major Applications

Most perfluoroelastomers are used in high-performance seals in several application areas: chemical processing industry, oil fields, aeronautical, pharmaceutical, and semiconductor fabrication. Lower-cost fluoroelastomers are also used in many of these areas, but perfluoroelastomers have greater

8 FLUID AND HEAT RESISTANCE OF PERFLUOROELASTOMERS resistance to the more severe environments often encountered, and provide assurance of long-term performance. Perfluoroelastomers are often economical when the costs of seal failure are high, involving high downtime and replacement costs, environmental emissions or spills, safety of people, or contamination of products. In the chemical processing industry, perfluoroelastomer seals provide long-term service in most fluids and mixtures. Typical parts include o-rings, valve stem packing, gaskets, and diaphragms. With more stringent requirements for avoiding emissions and chemical spills, perfluoroelastomer use has been increasing. Service temperatures are usually below 200°C in most chemical processes, so peroxide-cured fluoroelastomer compounds, such as Greene, Tweed Chemraz® 505, are generally satisfactory. DuPont has offered several compounds with different cure systems to meet chemical processing industry requirements over a wider range of temperatures (e.g., Kalrez® 4079, 1050LF, and 2035). Recently, compounds with a wide range of fluid resistance and with very high temperature resistance have been developed, including Kalrez® SpectrumTM 6375[3] and 7075 and Chemraz® 615.[10] Characteristics of these compounds are listed in Table 8.5. Of these compounds, Kalrez® 4079 is not recommended for service in hot water, steam, or amines. Oil field applications require seals with good resistance to base-containing organic and aqueous mixtures. At depths below about 18,000 feet (5500 m), high temperatures result in significant concentrations of hydrogen sulfide and carbon dioxide. Perfluoroelastomer compounds have been developed that are resistant to the environments encountered in deep wells. Special compounds with high black loading are designed to minimize damage from explosive decompression. This phenomenon occurs when pressure is reduced on a compound which contains a high concentration of carbon dioxide (CO2 is quite soluble in perfluoroelastomers). In aeronautical applications, perfluoroelastomers may be necessary for seals against jet aircraft engine lubricants where temperatures may exceed 200°C for extended periods.[12] At such high temperatures, conventional VDF-containing fluoroelastomers and TFE/P elastomers may swell excessively in heat-resistant lube oils so that o-ring seals may overfill standard grooves, extrude, and break up. Perfluoroelastomer compounds such as Kalrez® 4079 undergo little swell in such fluids, and are resistant to temperatures up to 316°C.

197

For the pharmaceutical industry, a number of perfluoroelastomer compounds have been designed to minimize contamination from filler particles, and to withstand sterilization in steam. Usually, these are white-filled peroxide-cured compounds such as Kalrez® 2037 or Chemraz® SD585. The semiconductor fabrication industry is a major application area for perfluoroelastomer seals, and many compounds have been, and continue to be, developed for various semiconductor fabrication processes. Each new generation of semiconductor fabrication lines requires better seal performance, especially for service life in aggressive environments and for cleanliness. Perfluoroelastomer parts’ suppliers offer special compounds finished and packaged under clean room conditions. Semiconductor fabrication involves plasma and gas deposition, thermal, and wet processing operations, each with different temperature ranges and environments. [13] Plasma processes include etching and ashing in fluorine or oxygen plasmas at temperatures up to 250°C. Gas deposition processes are carried out in a number of plasmas or reactive gas mixtures at temperatures up to 250°C, often under high vacuum. Seals must exhibit very low weight loss, particle generation, and outgassing under severe conditions. Thermal processes are carried out at 150°C to 300°C, and include oxidation diffusion furnaces, rapid thermal processing, and infrared lamp annealing. Seals must have excellent thermal stability with resistance to acidic or basic gases, along with low outgassing and particle generation. Wet processing includes wafer preparation, cleaning, and rinsing; etching; photolithography developing and rinsing; stripping; and copper plating operations. Maximum temperatures for these operations are in the range of 100°C to 180°C. Seals must be resistant to a variety of aggressive fluids including organic and inorganic acids, aqueous bases, and amines. Perfluoroelastomer compound recommendations are listed in Table 8.6 for these processes based on bulletins from DuPont Dow[13] for Kalrez® and from Greene, Tweed for Chemraz® 513,[14] 550,[15] 571,[16] 639,[17] and 655.[18] The preferred compounds listed generally meet the most stringent requirements for service in the process indicated, while alternative choices may give adequate service in situations with less severe environmental resistance or cleanliness requirements. The listing is not comprehensive; many other compounds are used, and new offerings are expected for this highly competitive industry.

Table 8.1 Chemical Resistance: FFKM Fluoroelastomer[1]

Reagent

Reagent Note

Cone, Temp. Time PDL % Volume Ways) Rating Change (0C) (%)

Abietic Acid

100

6