Rheology and Processing of Liquid Crystal Polymers

Transcription

1 Rheology and Processing of Liquid Crystal Polymers JOIN US ON THE INTERNET VIA WWW, GOPHER, FTP OR WWW: GOPHER: gopher.thomson.com A service of loop FTP: ftp.thomson.com findit@kiosk.thomson.com

2 Polymer Liquid Crystals Series Series editors: D. Acierno, Department of Chemical Engineering, University of Salerno, Italy W.K. Brostow, Center for Materials Characterization, University of North Texas, USA AA. Collyer, formerly of the Division of Applied Physics, Sheffield Hallam University, UK The series is devoted to an increasingly important class of polymer-based materials. As discussed in some detail in Chapter 1 of Volume 1, polymer liquid crystals (PLCs) have better mechanical performances, higher thermal stabilities and better physical properties than flexible polymers. They are more easily processable than reinforced plastics and can be used in small quantities to lower dramatically the viscosities of flexible polymer melts. PLCs can be oriented easily in shearing, electric and magnetic fields. They also have interesting optical properties, making applications in optical data storage possible, such as light valves and as erasable holograms. Current applications of PLCs include automobile parts. The areas of potential applications include the electrical, electronic, chemical, aircraft, petroleum and other industries. One measure of the rapidly increasing interest in PLCs is the number of names that are used for them: in-situ composites, molecular composites, liquid crystalline polymers (LCPs), self-reinforcing plastics, etc. The very rapidly growing literature on the subject makes it more and more difficult for researchers, engineers, faculty members and students to keep up with the new developments. Newcomers to the field are typically overwhelmed by the complexity of these materials in comparison to traditional engineering plastics - as reflected in sometimes mutually conflicting conclusions in publications, phrased moreover in difficult terminology. The present book series solves these problems for people already in the field as well as for the novices. Experts in the field from allover the world have been called upon to clarify the situation in their respective areas. Thus, conflicting evidence is sorted out and general features are stressed - which becomes achievable after a uniform picture of the structures of these materials is provided. Volume 1 gives an introduction to liquid crystallinity, describes characterization of LC phases including NMR studies, discusses lyotropic (produced in solution) as well as thermotropic (produced by manipulating the temperature) PLC phases. Volume 2 deals with rheology and processing. Volume 3 deals with mechanical and thermo physical properties of PLCs and PLC-containing blends, including inorganic PLCs, formation of PLC phases - also in non-covalently bonded systems - memory effects, phase diagrams, relaxation of orientations, creep and stress relaxation, thermoreversible gels, acoustic properties and computer simulations of PLCs. Volume 4 deals with electrical, magnetic and optical properties, including a discussion of displays and also of optical storage. Overall, the book series constitutes the only truly comprehensive source of knowledge on these exciting materials. Titles in the series 1. Liquid Crystal Polymers: From structure to applications Edited by AA Collyer 2. Rheology and Processing of Liquid Crystal Polymers Edited by D. Acierno and A.A Collyer 3. Mechanical and Thermophysical Properties of Polymer Liquid Crystals Edited by W.K. Brostow (forthcoming) 4. Electrical, Magnetic and Optical Effects on Polymer Liquid Crystals Edited by W.K. Brostow and AA Collyer (forthcoming)

3 Rheology and Processing of Liquid Crystal Polymers Edited by D. Acierno Department of Chemical Engineering University of Salerno Italy and A.A. Collyer formerly of the Division of Applied Physics Sheffield Hallam University UK Innl SPRINGER-SCIENCE+BUSINESS MEDIA, BV

4 First edition Springer Science+Business Media Dordrecht Originally published by Chapman & Hall in 1996 Softcover reprint of the hardcover 1st edition 1996 Typeset in 10/12 pt Palatino by AFS Image Setters Ltd, Glasgow ISBN DOI / ISBN (ebook) Apart from any fair dealing for the purposes of research or private study, or criticism or review, as permitted under the UK Copyright Designs and Patents Act, 1988, this publication may not be reproduced, stored, or transmitted, in any form or by any means, without the prior permission in writing of the publishers, or in the case of repro graphic reproduction only in accordance with the terms of the licences issued by the Copyright Licensing Agency in the UK, or in accordance with the terms of licences issued by the appropriate Reproduction Rights Organization outside the UK. Enquiries concerning reproduction outside the terms stated here should be sent to the publishers at the London address printed on this page. The publisher makes no representation, express or implied, with regard to the accuracy of the information contained in this book and cannot accept any legal responsibility or liability for any errors or omissions that may be made. A catalogue record for this book is available from the British Library Library of Congress Catalog Card Number: e Printed on permanent acid-free text paper, manufactured in accordance with ANSIINISO Z and ANSI/NISO Z (Permanence of Paper).

5 Contents List of contributors Preface x xii 1 Introduction to liquid crystal polymers 1 A.A. Collyer 1.1 Introduction Liquid crystal mesophases Identification of mesophases Mutual miscibility of known mesogens Polarized liquid microscopy X-ray diffraction Differential scanning calorimetry (DSC) Molecular architecture in thermotropic main chain LCPs Frustrated chain packing LCPs with flexible spacers Non-linear units Lyotropic main chain LCPs Polyamides Polybenzazoles Formation of nematic mesophases Conclusion 26 Acknowledgement 26 References Theoretical aspects of the flow of liquid crystal polymers 30 G. Marrucci Introduction 30 Molecular orientation 31 Slow flows - the linear situation 34 Nonlinear behaviour - negative normal stresses 37 Defects and polydomains 39

6 vi Contents 2.6 Flow-induced orientation Acknowledgements References Hamiltonian modelling of liquid crystal polymers and blends 49 M. Grmela and B.z. Dlugogorski 3.1 Introduction Family of mutually compatible models Nonlinear Onsager-Casimir equation State variables Thermodynamic potential Kinematics Examples of the nonlinear Onsager-Casimir equation Molecular simulations Blends Concluding remarks List of symbols 81 References 83 4 Rheology and processing of liquid crystal polymer melts 86 F.N. Cogswell and K.F. Wissbrun 4.1 Introduction Structure in polymer melts Liquid crystal phenomena and the rheology of fibre filled polymers Outline characteristics of liquid crystal polymer melt rheology Thermotropic aromatic polyesters Some characteristics of thermotropic polyesters Molecular structure and mobility Molecular weight and distribution Domain structure Crystallinity Thermal and thermodynamic properties Precautions in use Rheology Small amplitude oscillatory shear Torsional flow transient behaviour and normal force measurements Steady state shear viscosity Melt elastic response Capillary viscometry Elongational flows

7 Contents vii The influence of temperature and pressure The effects of thermo-mechanical history Solid phase properties relevant to processing Processing with thermotropic melts Extrusion Free surface flows Injection moulding Processing comparisons for LCPs and fibre reinforced plastics Conclusions Key characteristics of LCP melts Similarities of LCPs and fibre reinforced melts 127 References Rheological and relaxation behaviour of filled LC-thermoplastics and their blends 135 V.G. Kulichikhin, V.F. Shumskii and A. V. Semakov 5.1 Introduction Experimental Results and discussion Rheology of the binary filled LCPs Comparison of mechanical and rheological properties of the binary filled systems Mechanical and dielectric relaxation in CB-reinforced CPE Rheology and mechanics of polymer blends filled with carbon black Conclusion References The morphology and rheology of liquid crystal polymer blends 185 A.A. Collyer 6.1 Introduction Results for capillary flows Polystyrene/LCP blends X7G/polycarbonate blends Vectra/Trogamid T blends VectraA950/polycarbonate blends Vectra B950 in polyamide 6, polybutyleneterephthalate blends and polyamide Vectra B950 in polycarbonate and polyelhersulphone SBH/polycarbonate blends 198

8 viii Contents Wholly aromatic copolyester with polycarbonate and polyamide LCP blends with polyetherimide (PEl) and polysulphone (PSF) Summary of results of capillary flows Models to explain viscosity minima Phase equilibria Droplet morphology Migration Interfacial slip Elongational flows Dynamic measurements Conclusion (capillary flows) Model to explain the viscosity minimum in capillary flows Explanation of the viscosity maximum in blends of vedra B950/PA The yield value Suitable LCPs for blending Conclusions (other flows) 213 Acknowledgements 213 References Processing of liquid crystal polymers and blends 218 J.B. Hull and A.R. Jones 7.1 Introduction Structure of LCPs Structural order Orientation and its role in processing 7.3 Processing of LCPs Injection moulding Extrusion of LCPs LCP fibre spinning 7.4 Other developments. References Time-dependent effeds in lyotropic systems P. Moldenaers 8.1 Introduction Liquid crystallinity Lyotropics versus thermotropics 8.2 Commonly investigated lyotropics Types of polymers Behaviour in steady-state flow

9 Contents ix 8.3 Time-dependent effects during shear flow Stress growth Stepwise changes in shear rate Flow reversal Intermittent shear flow Time-dependent effects upon cessation of shear flow Stress relaxation Structural relaxation Recoil Banded textures 282 References Processing and properties of rigid rod polymers and their molecular composites 288 W.-F. Hwang 9.1 Introduction Lyotropic LCPs Background Rigidity of PBZ Processing and properties of lyotropic PBZ Molecular composite systems Phase separation of rigid-rod/flexible coil blends Block/segmented rigid-rod copolymer systems Thermoplastic molecular composites as advanced matrices for continuous-filament composites Recent developments 308 References 310 Index 312

10 Contributors D.Acierno Universita di Salerno, Dipartimento Ingegnaria Chimica E Alimentare, Via Ponte Don Melillo, Fisciano (SA), Italy. F.N. Cogswell 10 Latimer Lane, Guisborough, Cleveland, TS14 8DD, UK. A.A. Collyer Flat 2, 9 Elrnhyrst Rd, Weston Super Mare, BS23 2SJ, UK; formerly of Division of Applied Physics, Sheffield Hallam University, Pond Street, Sheffield, SllWB, UK. B.Z. Dlugogorski Department of Chemical Engineering, University of Newcastle, University Drive, Callaghan, Newcastle, NSW 2308, Australia. M.Grmela Department of Chemical Engineering, Ecole Polytechnic de Montreal, 2900 Boul Eduard-Montpetit, Montreal, H3C 3A7, Canada. J.B. Hull Department of Mechanical Engineering, Nottingham Trent University, Burton Street, Nottingham NG 1 4BU, UK. W.-F.Hwang Central R&D, 1702 Building, The Dow Chemical Company, Midland, MI 48674, USA. A.R.Jones Department of Mechanical Engineering, Nottingham Trent University, Burton Street, Nottingham NG 1 4BU, UK. V.G. Kulichikhin Institute of Petrochemical Synthesis, The Russian Academy of Sciences, 29 Leninskii Park, Moscow, Russia.

11 Contributors xi G.Marrucci Dipartimento di Ingegneria Chimica, Universita di Napoli, P.le Tecchio, Naples, Italy. P. Moldenaers Chemical Engineering Department, Katholieke Universiteit Leuven, W. de Croylaan 46, B-3001 Heverlee-Leuven, Belgium. A.V. Semakov Institute of Petrochemical Synthesis, The Russian Academy of Sciences, 29 Leninskii Park, Moscow, Russia. V.F. Shumskii Institute of Macromolecular Chemistry, Ukranian Academy of Sciences, Kharkovsloye Shosse , Kiev, Ukraine. K.F. Wissbrun 1 Euclid Avenue, Appartment 4E, Summit, NJ 07901, USA.

12 Preface Liquid crystal polymers (LCPs) have many strange properties that may be utilized to advantage in the processing of products made from them and their blends with isotropic polymers. This volume (volume 2 in the series Polymer Liquid Crystals) deals with their strange flow behaviour and the models put forward to explain the phenomena that occur in such polymers and their blends. It has been known for some time that small additions of a thermotropic LCP to isotropic polymers not only gives an improvement in the strength and stiffness of the blend but improves the processability of the blend over that of the isotropic polymer. In the case of lyotropic LCPs, it is possible to create a molecular composite in which the reinforcement of an isotropic polymer is achieved at a molecular level by the addition of the LCP in a common solvent. If the phenomena can be fully understood both the reinforcement and an increase in the processability of isotropic polymers could be optimized. This book is intended to illustrate the current theories associated with the flow of LCPs and their blends in the hope that such an optimization will be achieved by future research. Chapter 1 introduces the subject of LCPs and describes the terminology used; Chapter 2 then discusses the more complex phenomena associated with these materials. In Chapter 3, the way in which these phenomena may be modelled using hamiltonians is fully covered. Chapters 4, 5 and 6 deal with the practical results associated with the flow of LCPs, filled LCPs and LCP blends with isotropic polymers. These chapters refer mainly to thermotropic LCPs; the way in which these materials are processed is described in Chapter 7. The last two chapters examine exclusively lyotropic LCPs: Chapter 8 discusses the time-dependent effects occurring in this kind of LCP; Chapter 9 describes the phenomena that occur in lyotropic LCPs and the way in which they are processed, particularly with regard to the processing of molecular composites. It is hoped that this book will be a suitable introduction to this fascinating and rapidly changing subject as well as providing a much deeper in-

13 Preface xiii sight into the flow behaviour of these materials. Apart from Chapter 3, the mathematics used is of an A level or pre-university standard. This work is of importance to all establishments in which rheological measurements are carried out on polymeric materials. Materials scientists, engineers or technologists in industry, research laboratories or academia should find this book invaluable in updating their information and understanding the processes involved in the flow of liquid crystal polymers and their blends. D. Acierno and AA Collyer 1995