Electrophysical phenomena in the tribology of polymers

195 Pages·1999·4.75 MB·English

by  A I Sviridewok, A F Kilmovich, V N Kestelman

Electrophysical Phenomena
in the Tribology
of Polymers
A. I. Sviridenok
Research Center on Resources Savings
National Academy of Sciences
Grodno, Belarus
A. F. Klimovich
Institute of Mechanics of Metal Polymer Systems
National Academy of Sciences
Gomel, Belarus
and
V. N. Kestelman
KVN International
King of Prussia, Pennsylvania
USA
Gordon and Breach Science Publishers
Australia • Canada • China • France • Germany • India •
Japan • Luxembourg • Malaysia • The Netherlands •
Russia • Singapore • Switzerland
Copyright © 1999 OPA
Copyright © 1999 OPA (Overseas Publishers Association) N.V. Published by license
under the Gordon and Breach Science Publishers imprint.
All rights reserved.
No part of this book may be reproduced or utilized in any form or by any means,
electronic or mechanical, including photocopying and recording, or by any
information storage or retrieval system, without permission in writing from the
publisher. Printed in Malaysia.
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British Library Cataloguing in Publication Data
Sviridenok, A. I.
Electrophysical phenomena in the tribology of polymers. –
(Polymer science & engineering monographs ; v. 5 – ISSN 1023-7720)
1. Tribology 2. Polymers – Surfaces 3. Polymers – Electric
properties
I. Title II. Klimovich, A. F. III. Kestelman, V. N. 547.7´045´7
ISBN 90-5699-577-4
Copyright © 1999 OPA
CONTENTS
Introduction to the Series ix
Preface xi
Abreviation List 1
1 Principles of Friction Electrophysics in Polymers 3
1.1 Atomic and Molecular Electrophysical Concepts of the Nature of Friction in
Polymers 5
1.2 Surface States. The Electron Theory of Disordered Systems 15
1.3 Static Triboelectrification and Electret Efect in Polymers 22
References 32
2 Experimental Techniques of Investigating Electrical
Phenomena in the Friction of Polymers 36
2.1 Current Measuring and Probing Techniques
of Investigating Triboelectrification 36
2.2 Thermal Analysis of Electrets 41
2.3 Analysis of Emision Proceses 47
2.4 Triboelectrical Measurements in Various Media 49
2.5 Decoration Technique 53
References 56
3 Triboelectrification of Polymer Powders 59
3.1 Static Electrification of Liquid-Circulated
and Fre-Sprayed Polymers 59
3.2 Variations in Structures and Behavior of Polymers 76
3.3 Mechanism of Triboelectrification of Polymer Powders 83
References 85
4 Triboelectrification of Block and Molten Polymer Materials 87
4.1 General Characteristics of Triboelectrification 87
Copyright © 1999 OPA
vi CONTENTS
4.2 Charge Sign Reversal 97
4.3 Triboelectrification of Polymer Melts 100
4.4 Triboelectrification of Polymer Composites 101
4.5 Efect of Electrification on Friction 106
References 109
5 Triboelectret State of Polymers 111
5.1 Generation of Triboelectrets and Their Effect on Friction and Wear 111
5.2 The Combined Effect of Electretization and Triboelectrification 122
5.3 The Role of Electret State in Polymer Composites 125
5.4 Frictional Behavior of Radioelectret Polymer Coatings 137
5.5 Mechanism of Producing the Electret State in Friction of Polymers 141
References 142
6 Environmental Effects on Electrophysical Processes in Friction 144
6.1 Efect of Atmospheric Humidity 144
6.2 Friction in Fluids 152
6.3 Friction in Vacum 156
References 160
7 Applications of the Triboelectrification and Electret Effects in Polymers 162
7.1 Friction Asemblies 162
7.2 Diamond Cuting 168
7.3 Polymer Coatings 174
7.4 Electret Filters 178
7.5 Polymer Composites 181
7.6 Prospective Applications of Triboelectic Phenomena 183
Copyright © 1999 OPA
CONTENTS vii
Conclusion 185
References 186
Copyright © 1999 OPA
INTRODUCTION TO THE SERIES
This series will provide, in the form of single-topic tutorial volumes, state-of-the-art
information in specific research areas of basic applied polymer science. Volumes may
incorporate a brief history of the subject, its theoretical foundations, a thorough review
of current practice and results, the relationship to allied areas, and a bibliography.
Books in the series will act as authoritative references for the specialist, acquaint the
non-specialist with the state of science in an allied area and the opportunity for
application to his own work, and offer the student a convenient, accessible review that
brings together diffuse information on a subject.
Copyright © 1999 OPA
PREFACE
Polymer materials come into contact with solids in the course of fabrication,
processing and operation. Gradually, contacting surfaces disintegrate due to wear
induced by friction.
The nature of physical and chemical processes governing and accompanying the
tribodeformation and tribodisintegration of polymers is highly intricate and far from
being well understood. Electrophysical phenomena in polymer materials, such as
contact electrification and emergence of the electret state, are even less understood.
This area of polymer science has not yet reached the state of coherence.
Numerous practical problems connected to triboelectric phenomena remain unsolved,
both in fabrication and behavior of polymer threads and fabrics in a variety of
industrial articles. In many respects, this is due to lack of knowledge on how contact
electrification and electret effect cause friction and wear. In this book the authors
strive to fill in gaps in the science of tribology, using results of unique studies.
The first experiments on electrification confirmed the presence of
triboelectrification in all types of friction, for any combinations of contacting solid,
liquid or gaseous bodies.
Modern ideas about surface states have allowed development of a physical model
of electrification in solids and accumulation of more knowledge about the mechanism
of triboelectrification in polymers. Studies of general properties of electrophysical,
physical and mechanical processes and structural transformations of dispersed
polymers under various mechanical influences are the most informative in this respect.
Intensive dynamic contacts between dispersions are accompanied by deformations and
structural transformations of polymers that raise local microcontact temperatures up to
3
10 K. A very strong electrification of dispersed polymers is observed. The electrical
potential can reach 250 kV when confined to a closed cycle. A persistent electret state
has been identified in mechanically activated polymers.
Natural and induced electret states in block polymers and composites
strongly affect the parameters of friction and wear due to the structural
transformations and superposition of electret state and triboelectrif ication. The
Copyright © 1999 OPA
xii PREFACE
current inversion, observed during friction between polar and non-polar dispersed
block and composite polymer materials, is a general phenomenon in the process of
triboelectrification.
Explanation of the mechanisms of such electrification and appearance of the
electret state in friction of polymers uses basic postulates of the electrical theory of
adhesion, some results of the electron theory of disordered systems and surface states.
It has allowed us to identify links between processes of electrification and appearance
of electrets at frictional contacts between polymer materials, and to outline available
knowledge in the area of friction triboelectrophysics.
It should be emphasized that during our 30-year professional careers in studying
the tribology of polymers, we have closely cooperated with many leading tribologists:
K. C. Ludema, L. H. Lee and S. Jahanmir from the USA; D. Tabor, P. Jost, B. Briscoe
and C. Taylor from the UK; R. Kurtel, D. Maugis and D. Barkens from France; K.
Tanaka from Japan and others. Notwithstanding good personal and professional
relations, there have always been some “specific” terminological barriers. These have
been successfully removed through translations of publications and joint publications,
notably: Tribology in the USA and the Former Soviet Union; Studies and Applications,
eds. V. A. Belyi, K. C. Ludema and N. K. Myshkin (Allerton, 1994).
The major objectives of the present work are to inform English-speaking readers
about achievements in the area of triboelectrical phenomena in polymers made by
scientists from CIS countries and to standardize English and Russian terms, their
compatibility and clarity.
This book is intended for researchers and industrial engineers; it can also be
useful to graduate students and post-doctoral associates.
Copyright © 1999 OPA
ELECTROPHYSICAL PHENOMENA IN THE TRIBOLOGY OF
POLYMERS
A.I. Sviridenok, A.F. Klimovich, and V.N Kestelman
ABBREVIATION LIST
AE auxiliary platinum electrode
DTA differential thermal analysis
EEE exoelectron emission
EIB electron-ion bombardment
EIT electron-ion technology
EMF electromotive force
ES electret state
ESCD effective surface charge density
HDPE high density polyethylene
HEE high energy electrons
MCDP momentary charge discharge pulses
Me metal
PA polyamide
PC polycarbonate
PCA polycaproamide
PE polyethylene penton poly [3,3-bis-(chormetyl) oxetan]
PETP polyethylene terephtalate (lavsan)
PFR phenol formaldehyderesin
PMMA polymetylmethacrylate
PP polypropylene
PS polystryrene
PTFCE polyfluorine chlorine ethylene
PTFE polytetrafluorethylene
PVB polyvinylbutyral
PVC polyvinylchloride
RCA real contact area
RE reference electrode
SC semiconductor
SCC short circuit current
SCD space charge domain
SE studied electrode
SS surface
TGA thermogravimetric analysis
TSC thermally stimulated current
TSD thermostimulated depolyarization
VS volume states
WPC wood-polymer composite
Copyright © 1999 OPA
CHAPTER 1
PRINCIPLES OF FRICTION ELECTROPHYSICS
IN POLYMERS
Accumulation and systematization of scientific information about the fundamental
properties of friction have allowed formulation of the most important part of tribology -
triboanalysis and its most essential branches, tribomechanics, tribochemistry, and
tribophysics [1–3].
Tribomechanics deals with the surface contact problems, microscopic and
submicroscopic processes in solids induced by tribomechanical effects and
accompanying structural transformations. Tribochemistry analyzes the chemophysical
and chemical changes created in solids by tribomechanical energy. Tribophysics deals
with relations between factional and physical effects at the interface between two solids
or between a solid and its environment.
The tribomechanical energy alters the morphology, the electronic structure and the
chemical composition of solids. Tribophysics identifies the leading atomic, microscopic
and macroscopic physical processes evolving when solids are exposed to mechanical
effects [4]: emission of photons; emission of electrons; static electrification; electrostatic
discharges; emergence of the electret state; variations of the electrical conductivity;
emission of lattice components; excitation of phonons; emergence and migration of
lattice and electron defects; local heating in the solid phase; appearance of juvenile
surfaces; surface expansion; cracking; abrasion; mass transfer between solids;
amorphization; penetration of impurities; plastic deformation. They are all accompanied
by complex dissipation processes due to different life-times of excited states and
duration of relaxation (Table 1.1) [4].
Friction contact due to its discrete pattern is characterized by non-
equilibrium processes and disintegration of a multitude of contacts with the
parameters continuously varying in time and space. It is accompanied
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