Pocius Adhesion and Adhesives Technology Alphonsus V. Pocius Adhesion and Adhesives Technology An Introduction 3rd Edition Hanser Publishers, Munich Hanser Publications, Cincinnati The Author: Dr. Alphonsus V. Pocius, 445 Highpoint Curve South, Maplewood, MN 55119-6754, USA Distributed in North and South America by: Hanser Publications 6915 Valley Avenue, Cincinnati, Ohio 45244-3029, USA Fax: (513) 527-8801 Phone: (513) 527-8977 www.hanserpublications.com Distributed in all other countries by Carl Hanser Verlag Postfach 86 04 20, 81631 München, Germany Fax: +49 (89) 98 48 09 www.hanser.de The use of general descriptive names, trademarks, etc., in this publication, even if the former are not especially identified, is not to be taken as a sign that such names, as understood by the Trade Marks and Merchandise Marks Act, may accordingly be used freely by anyone. While the advice and information in this book are believed to be true and accurate at the date of going to press, neither the author nor the editors nor the publisher can accept any legal responsibility for any errors or omissions that may be made. The publisher makes no warranty, express or implied, with respect to the material contained herein. Library of Congress Cataloging-in-Publication Data Pocius, Alphonsus V. Adhesion and adhesives technology : an introduction / Alphonsus V. Pocius. -- 3rd ed. p. cm. Includes bibliographical references and index. ISBN 978-1-56990-511-1 (hardcover) -- ISBN 978-3-446-43177-5 (e-book) 1. Adhesion. 2. Adhesives. 3. Chemistry, Physical and theoretical. I. Title. QC183.P72 2012 668’.3--dc23 2012007729 Bibliografische Information Der Deutschen Bibliothek Die Deutsche Bibliothek verzeichnet diese Publikation in der Deutschen Nationalbibliografie; detaillierte bibliografische Daten sind im Internet über <http://dnb.d-nb.de> abrufbar. ISBN 978-1-56990-511-1 E-Book ISBN 978-3-446-43177-5 All rights reserved. No part of this book may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying or by any information storage and retrieval system, without permission in writing from the publisher. © Carl Hanser Verlag, Munich 2012 Production Management: Steffen Jörg Coverconcept: Marc Müller-Bremer, www.rebranding.de, München Coverdesign: Stephan Rönigk Typesetted by Manuela Treindl, Fürth Printed and bound by CPI buch bücher.de gmbh Printed in Germany This book is dedicated to my wife, Janice, to whom I owe everything, including my life which she helped save. The book is also dedicated to our children: our son Nick, his wife Eliza, our daughter Amanda, and our grandson, Vincent James Preface Adhesion science is a multidisciplinary field, which encompasses aspects of engineering as well as physical and organic chemistry. The breadth of the field is possibly the reason that there have been so few books on the subject written by a single author. The books in this area have tended to be handbooks, treatises, or other compilations by multiple authors. I have attempted to provide a broad view of the field, but with a consistent style, that leads the reader from one step to another in the understanding of the science. This book also includes problems for the student to work in order to help build on the information presented in the text. The text assumes that the reader has little or no knowledge of the science of adhe- sion. The bulk of the book is written with the supposition that the reader has had a course in college level calculus as well as college level organic and physical chem- istry. The book has also been written in such a fashion that even a person that has a meager knowledge of these subjects can learn something about adhesion science from reading this book. That is, the emphasis is on understanding the science rather than a complete and detailed exposition on any part of it. An attempt has been made to describe as much as possible in words and examples rather than in detailed math- ematical derivations. That mathematics has been included in those sections where more detail seemed necessary. Each section or chapter starts with a simple view of the subject area, starting at the same point an entry-level textbook would begin. Each section or chapter then builds to a point at which more detail is available for the reader who is or wants to be a practitioner of the art and science of adhesion. Many sections also includes helpful practical suggestions about how measurements can be made, how surfaces can be modified, or how adhesives can be formulated to lead to a useful result. The third edition of this book includes a number of new topics such as the durability of structural adhesive bonds and adhesion in biological systems. The wish of the author is to produce a well-rounded introductory view of each of the fields, which form adhesion science no matter what the technical back- ground of the reader may be. As science progresses, our understanding of natural phenomena changes. This book also includes news aspects of the understanding of adhesion science, in particular the connection between fundamental adhesion and the practical adhesive bond strengths of adhesive bonds is expanded upon. VIII Preface I would like to acknowledge some of the people at 3M who have assisted me either by reviewing this manuscript or by providing support to pursue my study of the science of adhesion. These people include Sam Smith, Bill Schultz, Dave Wangsness, Ted Valentine, Brian Smillie, Dick Hartshorn, Don Theissen, George Allen, Tom Savereide, Morgan Tamsky, Larry Clemens, Rich Newell, Mike Engel, Ilya Gorod- isher, Chris Campbell, Zhong Chen and Terry Smith. Without their friendship and support, it is doubtful that I would have had the opportunity to build the base of expertise necessary to prepare a book this book. I would also like to acknowledge the late Prof. Bob Kooser at Knox College who inspired me to pursue a career in physical chemistry. Al Pocius Contents Preface .................................................................. VII 1 Introduction ............................................................ 1 1.1 Introduction and Chapter Objectives ................................. 1 1.2 Basic Definitions .................................................... 2 1.3 Advantages and Disadvantages of Adhesive Bonding .................. 2 1.4 Uses of Adhesive Bonding in Modern Industry........................ 6 1.5 Economics of Adhesive Technology ................................. 12 1.6 Literature and Other Sources of Information ......................... 12 1.7 Summary ......................................................... 14 References ............................................................ 15 2 The Mechanical Properties of Materials as They Relate to Adhesion ...... 17 2.1 Introduction ....................................................... 17 2.2 Definition of Mechanical Stresses for Materials Testing .............. 17 2.3 Stress-Strain Plots and the Definition of Materials Property Parameters ........................................................ 19 2.3.1 Tensile Forces ............................................. 19 2.3.2 Shear Forces .............................................. 22 2.3.3 Strain Energy Density ..................................... 23 2.4 Introduction to Linear Elastic Fracture Mechanics ................... 24 2.5 Introduction to Rheology of Liquids ................................. 27 2.6 Introduction to Linear Viscoelasticity ............................... 29 2.7 An Application of Materials Properties and Mechanics: The Bending of Beams ............................................. 35 2.8 Summary ......................................................... 43 Bibliography ........................................................... 43 Problems and Review Questions ........................................ 44 X Preface 3 Mechanical Tests of Adhesive Bond Performance ........................ 47 3.1 Introduction ....................................................... 47 3.2 Failure Modes and the Definition of Practical Adhesion .............. 48 3.3 Tensile Testing of Adhesive Bonds .................................. 49 3.4 Shear Loading of Adhesive Bonds ................................... 52 3.4.1 The Standard Lap Shear Specimen ......................... 54 3.4.2 Variations on the Lap Shear Specimen ...................... 57 3.4.3 Specimen for Determining the True Shear Properties of an Adhesive ............................................ 60 3.4.4 The Goland-Reissner Analysis of the Lap Shear Specimen .... 61 3.5 Cleavage Loading of Adhesive Bonds ................................ 68 3.5.1 Cleavage or Fracture Specimens ............................ 69 3.5.1.1 Double Cantilever Beam Specimens ........................ 70 3.5.1.2 Linear Elastic Fracture Mechanics Applied to the Double Cantilever Beam Specimen ......................... 71 3.5.2 Blister Test ................................................ 73 3.5.3 Compact Tension Test ..................................... 74 3.5.4 Wedge Test ............................................... 74 3.6 Peel Tests ......................................................... 75 3.6.1 Stress Analysis in a Peel Specimen ......................... 78 3.7 Summary ......................................................... 82 Bibliography ........................................................... 82 References ............................................................ 82 Problems and Review Questions ........................................ 83 4 The Basics of Intermolecular Forces and Surface Science ................ 85 4.1 Introduction ....................................................... 85 4.2 Fundamental Forces ............................................... 86 4.2.1 Electrostatic Forces ........................................ 87 4.2.2 van der Waals Interactions ................................. 88 4.2.2.1 Dipole–Dipole Interactions ................................. 89 4.2.2.2 Dipole-Induced Dipole ..................................... 90 4.2.2.3 Dispersion Forces ......................................... 91 4.2.3 Interactions through Electron Pair Sharing ................. 93 4.2.4 Repulsive Forces .......................................... 93 4.3 Surface Forces and Surface Energy ................................. 94 4.4 Work of Cohesion and Adhesion .................................... 99 4.5 Methods of Measurement of Surface Energy and Related Parameters ....................................................... 101 4.5.1 Surface Tension .......................................... 101 4.5.1.1 Drop Weight/Volume Method ............................. 102 Preface XI 4.5.1.2 Du Nuoy Tensiometer ..................................... 102 4.5.2 Surface Energy of Solids .................................. 102 4.5.2.1 Contact Angle Methods ................................... 103 4.5.2.2 Contact Mechanics and Direct Measurement of Solid Surface Energy ........................................... 105 4.6 Surface Thermodynamics and Predictions of Surface and Interfacial Tensions ......................................................... 112 4.6.1 The Good-Girifalco Relationship ........................... 114 4.6.2 The Fowkes Hypothesis and Fractional Polarity ............ 115 4.6.3 The Zisman Plot .......................................... 117 4.6.4 Modern Application of Contact Angle Measurements ....... 118 4.7 Modern Methods of Surface Analysis .............................. 120 4.7.1 Modern Methods for Analysis of the Chemistry of Surfaces ................................................. 120 4.7.2 Topological Methods of Surface Analysis ................... 122 4.8 Summary ........................................................ 123 Bibliography .......................................................... 124 References ........................................................... 124 Problems and Review Questions ....................................... 126 5 Basic Physico/Chemical Properties of Polymers ........................ 129 5.1 Introduction ...................................................... 129 5.2 Basic Terminology ................................................ 130 5.2.1 Monomers versus Polymers ............................... 130 5.2.2 Basic Types of Polymeric Materials ........................ 130 5.2.3 Molecular Weight ........................................ 132 5.3 Thermal Transitions of Polymers .................................. 134 5.3.1 Measurement of T ....................................... 135 g 5.4 Dynamic Mechanical Measurements and Viscoelasticity ............ 136 5.4.1 Methods of Measurement of Dynamic Mechanical Properties ............................................... 136 5.4.2 Examples of Dynamic Mechanical Data for Polymers ....... 138 5.5 Time-Temperature Superposition .................................. 142 5.6 Summary ........................................................ 144 Bibliography .......................................................... 144 References ........................................................... 144 6 The Relationship of Surface Science and Adhesion Science ............. 145 6.1 Introduction ...................................................... 145 6.2 Rationalizations of Adhesion Phenomena ........................... 145 6.3 Electrostatic Theory of Adhesion ................................... 146 XII Preface 6.4 Diffusion Theory of Adhesion ...................................... 149 6.4.1 Diffusive Adhesive Bonding and Block Copolymers at Interfaces ............................................. 152 6.5 Mechanical Interlocking and Adhesion ............................. 155 6.5.1 Kinetics of Pore Penetration ............................... 158 6.6 Wettability and Adhesion .......................................... 160 6.7 Acid-Base Interactions at Interfaces ................................ 163 6.8 Covalent Bonding at Interfaces .................................... 166 6.8.1 Coupling Agents ......................................... 168 6.9 The Relationship of Fundamental Forces of Adhesion and Practical Adhesion ......................................................... 170 6.10 The Weak Boundary Layer ......................................... 175 6.11 Summary ........................................................ 176 Bibliography .......................................................... 176 References ........................................................... 177 Problems and Review Questions ....................................... 178 7 The Surface Preparation of Adherends for Adhesive Bonding ............ 181 7.1 Introduction ...................................................... 181 7.2 Plastic Surface Preparation ........................................ 183 7.2.1 Corona Discharge Treatment .............................. 184 7.2.1.1 Corona Discharge Treatment of Polyethylene ............... 185 7.2.1.2 Corona Discharge Treatment of Polypropylene ............. 188 7.2.1.3 Corona Discharge Treatment of Poly(ethylene terephthalate) .............................. 189 7.2.1.4 Corona Discharge Treatment of Other Materials ............ 190 7.2.2 Flame Treatment ......................................... 191 7.2.3 Plasma Treatment ........................................ 193 7.2.3.1 Plasma Treatment of PE .................................. 194 7.2.3.2 Plasma Treatment of Other Substrates ..................... 195 7.2.4 Other Physical Treatment Methods of Polymer Surfaces .... 197 7.2.4.1 Treatments Using Ultraviolet Radiation .................... 197 7.2.4.2 Other Vacuum Methods of Surface Preparation ............. 197 7.2.5 Wet Chemical Methods of Treatment of Polymer Surfaces ... 198 7.2.5.1 Single Surface Chemical Functionalization and Chromic Acid Treatment of PE ............................ 198 7.2.5.2 Wet Chemical Surface Treatment of Poly(tetrafluoroethylene) ................................. 200 7.2.6 Priming of Polymer Surfaces .............................. 201 7.2.6.1 Priming of Polyolefins for Cyanoacrylates .................. 201 7.2.6.2 Chlorinated Polyolefins ................................... 201