Structural Adhesives: Chemistry and Technology

512 Pages·1986·7.98 MB·English

by  S. R. Hartshorn (auth.)

Structural Adhesives
Chemistry and Technology
TOPICS IN APPLIED CHEMISTRY
Series Editors: Alan R. Katritzky, FRS
Kenan Professor of Chemistry
University of Florida, Gainesville, Florida
Gebran J. Sabongi
Technical Manager, Graphic Research Laboratory
3M, St. Paul, Minnesota
STRUCTURAL ADHESIVES
Edited by S. R. Hartshorn
A Continuation Order Plan is available for this series. A continuation order will bring delivery of
each new volume immediately upon publication. Volumes are billed only upon actual shipment. For
further information please contact the publisher.
Structural Adhesives
Chemistry and Technology
Edited by
S. R. Hartshorn
3M
St. Paul, Minnesota
Plenum Press • New York and London
Library of Congress Cataloging in Publication Data
Structural adhesives.
(Topics in applied chemistry)
Includes bibliographies and index.
1. Adhesives. l. Hartshorn, S. R. II. Series.
TP968.S83 1986 624.1'899 86-4871
ISBN 978-1-4684-7783-2 ISBN 978-1-4684-7781-8 (eBook)
DOl 10.1 007/978-1-4684-7781-8
© 1986 Plenum Press, New York
Softcover reprint of the hardcover 18t edition 1986
A Division of Plenum Publishing Corporation
233 Spring Street, New York, N. Y. 10013
All rights reserved
No part of this book may be reproduced, stored in a retrieval system, or transmitted
in any form or by any means, electronic, mechanical, photocopying, microfilming,
recording, or otherwise, without written permission from the Publisher
Contributors
Charles W. Boeder, Adhesives, Coatings and Sealers Division, 3M, St. Paul,
Minnesota 55144
B. H. Edwards, Adhesives, Coatings and Sealers Division, 3M, St. Paul,
Minnesota 55144
S. R. Hartshorn, Adhesives, Coatings and Sealers Division, 3M, St. Paul,
Minnesota 55144
G. H. Millet, Industrial and Consumer Sector Research Laboratory, 3M,
St. Paul, Minnesota 55144
John M. Muggee, Adhesives, Coatings and Sealers Division, 3M, St. Paul,
Minnesota 55144
Alphonsus V. Pocius, Adhesives, Coatings and Sealers Division, 3M, St. Paul,
Minnesota 55144
Gene B. Portelli, Industrial and Consumer Sector Research Laboratory, 3M,
St. Paul, Minnesota 55144
Janis Robins, Adhesives, Coatings and Sealers Division, 3M, St. Paul,
Minnesota 55144
K. P. Subrahmanian, Adhesives, Coatings and Sealers Division, 3M, St. Paul,
Minnesota 55144
Philip H. Thompson, Formerly with 3M. 2445 Londin Lane #206, St. Paul,
Minnesota 55119
Charles D. Wright, Adhesives, Coatings and Sealers Division, 3M, St. Paul,
Minnesota 55144
v
Preface
Adhesives in general and structural adhesives in particular are the subjects
of much academic interest as well as commercial importance. Structural
bonding, as a method of joining, offers a number of advantages over
mechanical fastening. However, in order to achieve satisfactory results, the
proper adhesive must be selected and the appropriate bonding procedures
followed.
The purpose of Structural Adhesives: Chemistry and Technology is to
review the major classes of structural adhesives and the principles of
adhesion and bonding as these relate to structural joints. Each chapter
provides an overview of the topic under discussion with a list of references
to the relevant literature. In addition to describing the chemistry involved,
other aspects of structural adhesive technology are covered, such as formula
tion, testing, and end uses.
Some structural adhesives, especially epoxies and phenolics, have a
long history of successful use and are now widely employed. Others, such
as the structural acrylics and cyanoacrylates, are beginning to gain industrial
acceptance. Urethanes and anaerobics have limited but important uses,
while high-temperature adhesives are still largely in the research and
development stage.
A number of chapters in this book are devoted to topics that are of
more general interest. Thus one chapter covers the fundamentals of adhesion
and discusses the principles that provide a necessary background for an
understanding of adhesive bonding. Another deals with the important
subject of environmental resistance and the factors affecting the durability
of structural adhesive joints. The design, analysis, and testing of adhesive
joints also play essential roles in the successful use of structural adhesives.
Finally, some consideration is given to methods of application, to indicate
how structural adhesives are handled in typical industrial situations and to
mention some of the factors that need to be considered when choosing a
method of application.
vii
viii Preface
It is not the intention to provide a thorough coverage of the subject;
that would not be possible in a single volume of this size. Rather, it is hoped
that this book will serve as an introduction to structural adhesives and
structural adhesive bonding and that it will be a useful source reference to
the subject.
S. R. Hartshorn
St. Paul, Minnesota
Contents
Introduction
S. R. Hartshorn
I. Definitions . . . . . .
A. Structural Adhesives 1
B. Classification 3
C. Organization of Book 4
D. Units and Conversion Factors 5
II. Background ..... 5
A. Structural Bonding 6
1. Joining Methods 6
2. Advantages of Structural Adhesives 9
3. Limitations of Structural Adhesives 10
B. Principles of Structural Bonding . . . 11
1. Surface and Interfacial Phenomena 11
2. Phase Change 11
3. Bond Failure . . . . 12
C. Design of Adhesive Joints 12
D. Testing ....... . 13
E. Adhesive Selection 14
III. Markets for Structural Adhesives 14
A. Adhesive Markets ..... 14
B. Markets for Structural Adhesives 17
1. Transportation 17
2. Construction 18
3. Other Rigid Bonding 18
4. Consumer Products 18
IV. Applications 19
References 19
1. Fundamentals of Structural Adhesive Bonding
Alphonsus V. Pocius
l. Introduction 23
ix
x Contents
II. Physical Properties of Polymers and Adhesives 24
A. Stress-Strain Properties ..... 24
B. Dynamic Mechanical Properties 30
III. Surface Energy and Aspects of Cohesion 33
A. Thermodynamics ....... . 33
B. Cohesive Strength . . . . . . . . 36
C. Fracture Mechanics for Linear Elastic Solids 40
IV. Theories of Adhesion . . . . . 46
A. Introduction . . . . . 46
B. Wettability/ Adsorption Theory 47
C. Contact Angles and Wettability 47
D. Components of Surface and Interfacial Tension 51
E. van der Waals Forces 55
F. Kinetics of Wetting 56
G. Mechanical Interlocking 58
H. Chemical Bonding at Interfaces 60
I. Acid-Base Interactions . . . . 62
J. The Diffusion Theory of Adhesion 63
V. Criteria for Optimum Bond Strength 65
References ............. . 65
2. Phenolic Resins
Janis Robins
I. Introduction . . . . . . . . . . . . . . . . . . . 69
II. Mechanism of Phenol-Formaldehyde Reactions 72
A. Reactions under Strongly Acidic Conditions (pH 1-4) 72
B. Reactions under Weakly Acidic Conditions (pH 4-7) 74
1. High ortho-ortho N ovolacs 74
2. Superacidity ..... . 77
3. High ortho-ortho Resoles . 78
4. Dibenzylic Ether Linkages 80
5. Cyclic Polynuclear Species 82
C. Reactions under Basic Conditions (pH 7-11) 82
1. Resoles .......... .... . 82
2. Self-condensation 83
D. Resorcinol and m-Aminophenol Modified Phenolic Resins 85
E. Modified Phenolic Resins ..... . 86
1. Etherified Resoles . . . . . . . . . 86
2. Modification at the Phenolic Hydroxyl 87
III. Curing Reactions . . . 88
A. Curing of Resoles 88
B. Curing of Novolacs 90
C. Thermal Degradation 91
IV. Structural Phenolic Adhesives 92
A. Introduction ..... 92
B. Phenolic Resins for Wood Bonding 92
I. Phenolic Resins . . . . . . . 92
2. Resorcinol Modified Novolacs 93
3. m-Aminophenol Modified Novolacs 94
Contents xi
C. Polymer Blends for Metal Bonding 94
I. Phenolic-Epoxy Blends 95
2. Phenolic-Polyvinyl Blends 97
3. Phenolic-Nitrile Blends 99
4. Polyamide Phenolics 101
5. Nylon Phenolics 101
6. Acrylic Phenolics 101
7. Neoprene Phenolics 102
8. Urethane Phenolics 102
D. Cure Conditions and Properties 102
E. Commercially Available Materials 106
References 106
3. Epoxy Structural Adhesives
Charles D. Wright and John M. Muggee
I. Introduction 113
II. Compounding Epoxy Structural Adhesives 116
A. Overview of Adhesives and Epoxy Raw Materials 116
B. Two-Part Room Temperature Curing Epoxy Adhesives 117
1. Nitrogen-containing Curatives 117
2. Sulfur-containing Curatives 127
3. Carboxyl-containing Curatives 128
4. Lewis Acid Catalysts 128
5. Encapsulation 128
C. One-Part Heat Curing Paste Adhesives 129
1. Catalysts 129
2. Toughening Agents 130
3. Fillers, Filler Treatments, and Surfactants 130
4. Thixotropic Additives 131
5. Adhesion Promoters 131
D. Epoxy Film Adhesives 132
III. Recent Developments in Epoxy Structural Adhesives 134
A. Epoxy Resins 134
B. Room Temperature Amine Curing Agents 137
C. Room Temperature Sulfur Curing Agents 142
D. Room Temperature Acid Catalysts 142
E. Heat Cure Amine Curatives and Catalysts 144
1. Primary Amine Curatives 144
2. Secondary Amine Curatives 146
3. Tertiary Amine Catalysts 149
4. Dicyandiamide and Derivatives 152
5. Imidazole Derivatives 154
F. Heat Cure Carboxylic Acid Curatives 157
G. Heat Cure Anhydride Curatives 159
H. Heat Cure Cationic Catalysts 162
I. FJexibilizing and Toughening Agents 164
1. Flexibilizing Agents 165
2. Toughening Agents 166