Design and structure-property relationship of heterophasic ethylene-propylene copolymers

Transcription

1 Design and structure-property relationship of heterophasic ethylene-propylene copolymers DISSERTATION Zur Erlangung des akademischen Grades Doktor-Ingeneur (Dr.-Ing.) vorgelegt der Mathematisch-Naturwissenschaftlich-Technischen Fakultät - Fachbereich Ingenieurwissenschaften - Martin-Luther Universität Halle-Wittenberg von Herrn Dipl.-Ing. Petar Doshev geboren am 25. Oktober 1978 in Sofia, Bulgarien Dekan der Fakultät: Gutachter: Prof. Dr.-Ing. habil. H. Altenbach Prof. Dr.-Ing. habil. H.-J. Radusch Prof. Dr.-Ing. habil. J. Karger-Kocsis Merseburg (Saale), den

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3 Berichte aus der Kunststofftechnik Petar Doshev Design and Structure-Property Relationship of Heterophasic Ethylene-Propylene Copolymers Shaker Verlag Aachen 2006

4 Bibliographic information published by the Deutsche Nationalbibliothek The Deutsche Nationalbibliothek lists this publication in the Deutsche Nationalbibliografie; detailed bibliographic data are available in the Internet at Zugl.: Halle, Univ., Diss., 2005 Copyright Shaker Verlag 2006 All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, without the prior permission of the publishers. Printed in Germany. ISBN-10: ISBN-13: ISSN Shaker Verlag GmbH P.O. BOX D Aachen Phone: 0049/2407/ Telefax: 0049/2407/ Internet: info@shaker.de

5 Design and structure-property relationship of heterophasic ethylene-propylene copolymers Abstract Heterophasic ethylene-propylene copolymers represent the most commercially relevant group of impact modified polypropylene. These polypropylene resins serve typically in engineering and automotive applications where high impact strength is required within relative broad temperature range. The heterophasic ethylene-propylene copolymers comprise a polypropylene (PP) matrix and an ethylene propylene copolymer (EPC) dispersed phase. In contrast to the mechanical PP/EPC blends, they are synthesized in a sequential copolymerization process in a reactor or reactor cascade. Utilization of such an in situ blending technique enables materials design to be performed readily on molecular level, thus giving a far wider possibility for structure and accordingly property tailoring. This work encompasses comprehensive structural and mechanical characterization of heterophasic ethylene-propylene copolymers as affected by variation of different system parameters. All the employed materials were produced in a batch reactor under industrially relevant conditions. The main focus was on exploiting the opportunities given by a proper process control in the polymerization stage for producing reactor blends of targeted molecular structure and interrelating it to their macroscopic mechanical performance. The main variables utilized were EPC composition (ethylene/propylene ratio) as well as molecular weight of EPC and PP phases. Besides the conventional heterophasic ethylene-propylene copolymers, this work embraces the development and characterization of reactor blends containing two different ethylenepropylene copolymers forming the dispersed phase. The two EPC phases distinguish in their composition and molecular weight. The design concept of such blends is to combine the elastomer phases in a synergistic manner and represents a further approach for property optimization, which has only scarcely being reported. Generally, the results of this study perform a contribution to clarification of the complex structure-property relationship existing in elastomer modified semi-crystalline materials under the specific consideration of reactor blending. On the basis of material science fundamentals, correlations between rheological behavior, phase structure, morphology evolution and the mechanical performance have been derived serving the purpose of tailored, applicationoriented materials development.

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7 Acknowledgement Acknowledgement At this point, I would like to take the opportunity to thank the many people who helped me and supported me in the course of this work. I would like to express my deep gratitude to my university tutor Prof. Dr. H.-J. Radusch (Chair of Polymer Engineering) for providing me the opportunity and facility to accomplish this thesis, for his incessant guidance, encouragement and always valuable advises. My thanks are due to A. Heuvelsland for the chance to complete this work in close cooperation with the Polypropylene R&D at DOW Olefinverbund GmbH (Schkopau, Germany), for his interest and pragmatic monitoring of the work, as well as for the responsiveness and financial support. Sincere thanks go to Dr. G. Lohse, my tutor at DOW Olefinverbund GmbH (Schkopau, Germany) for his constant engagement to the work, always contributing with new ideas and worthwhile remarks, for the long and fruitful discussions and for the brainstorming questions keeping me on track. The generous help and assistance of all associates of the Institute of Materials Science and especially of the Chair of Polymer Engineering at Martin Luther University Halle-Wittenberg are gratefully acknowledged. - Dr. R. Androsch (Chair of Polymer Engineering) for the helpful discussions and suggestions concerning the crystallization experiments, for accomplishment of the WAXD measurements as well as for the proof reading of parts of this work. - Dr. I. Kolesov (Chair of Polymer Engineering) for the extensive consulting regarding dynamic mechanical analysis and for performing some of the DSC investigations. - My roommate Dr. A. Wutzler (Chair of Polymer Engineering) for introducing me the optical microscopy and FTIR techniques, for the numerous valuable suggestions and general remarks in the course of the work, for the proof reading of plenty of German texts, for the nice time in the office and the inspiring discussions. - Dr. S. Ilisch (Chair of Polymer Engineering) for carrying out the AFM investigations and being always friendly and responsive. - Dr. R. Lach (Chair of Materials Diagnostics and Testing) for the help and support concerning the fracture mechanics investigations and their interpretation.

8 Design and structure-property relationship of heterophasic ethylene-propylene copolmyers - Dipl.-Phys. S. Henning (Chair of General Materials Science) for the beautiful SEM micrographs and the appendant discussions. - Dr. M. Krumova and Dipl.-Phys. V. Seydewitz (Chair of General Materials Science) for performing the TEM and HVEM observations. Special thanks go to Dr. S. Frangov, Dr. D. Scharnowski, Dr. H. Le Hong (Chair of Polymer Engineering) and Dr. D. Nikolova (Chair of Surface Technology) for creating an inspiring social and working environment and giving me a lot of useful advises. Thanks are due to the laboratory staff of the Chair of Polymer Engineering: Mrs. Busch, Mrs. Kittel, Mrs. Schwarz and of the Chair of Materials Diagnostics and Testing: Mrs. Schreier and Mrs. Sachse for their kindness and support by accomplishment of the experiments. I would like to thank Dr. D. Wulff, W. Bohnenberger, M. Hohlbein and M. Schönrock at DOW Olefinverbund GmbH (Schkopau, Germany) for the preparation of part of the materials, rheological investigations and injection molding of the test specimens, respectively. I would like to express my deepest gratitude to my family and especially to my parents for their constant encouragement and moral support and to my girlfriend for the endurance to be always by my side. The financial support of the State Government of Sachsen-Anhalt and DOW Olefinverbund GmbH (Schkopau, Germany) is gratefully acknowledged. Merseburg, August 2005 Petar Doshev

9 Table of Contents Table of Contents List of symbols IV List of abbreviations VIII 1 Introduction 1 2 Objective 2 3 Heterophasic Ethylene-Propylene Copolymers Catalyst and polymerization aspects Structure and morphology of heterophasic 5 ethylene-propylene copolymers 3.3 Manufacturing process Process control 7 4 Toughening concept Brittle-to-tough transition 8 5 Structure-property relationships of heterophasic ethylene-propylene copolymers Relationship between structure and toughness of 11 polypropylene/elastomer blends Effect of the intrinsic properties of the blend components Polypropylene Chain stereoregularity Molecular parameters Ethylene-propylene copolymer Chemical composition Molecular parameters Effect of blend morphology Morphology control Effect of elastomer weight fraction Effect of matrix/dispersed phase adhesion Effect of the elastomer inclusions on the stiffness of 22 polypropylene elastomer blends 5.3 Polypropylene based ternary blends 25 6 Experimental Materials Analytical characterization of the synthesized products Determination of the elastomer content 28 I

10 Design and structure-property relationship of heterophasic ethylene-propylene copolymers Determination of the ethylene content Molecular characterization Processing and sample preparation Overview of the investigated heterophasic ethylene-propylene 32 Copolymers 6.5 Experimental Techniques Rheological investigation Differential scanning calorimetry (DSC) Dynamic mechanical analysis (DMA) Wide angle X-ray scattering (WAXS) Morphological characterization Optical microscopy Scanning electron microscopy (SEM) Transmission electron microscopy (TEM) Atomic force microscopy (AFM) Morphology quantification Analyses of microdeformation processes Mechanical performance Tensile testing Conventional impact testing Fracture mechanics testing Instrumented falling weight impact test (IFWI) 44 7 Results and Discussion Rheological properties Effect of EPC composition Effect of EPC and PP molecular parameters Thermal Properties Effect of EPC composition Effect of EPC and PP molecular parameters Phase Behavior and Mechanical Relaxation Profile Effect of EPC composition Effect of EPC and PP molecular parameters Morphological Analysis Effect of EPC composition Effect of EPC and PP molecular parameters 67 II

11 Table of Contents 7.5 Mechanical properties Tensile properties Effect of EPC composition Effect of EPC and PP molecular parameters Fracture behavior Effect of EPC composition Effect of EPC and PP molecular parameters Brittle-to-tough transition Effect of EPC composition Effect of EPC and PP molecular parameters Deformation mechanisms during fracture Development of heterophasic copolymers containing two 88 ethylene-propylene copolymer phases EPC1 EPC2 Effect of composition ratio ( Et. / Et. ) EPC1 EPC2 Effect of weight content ratio ( / ) 97 8 Heterophasic ethylene-propylene copolymers 105 morphology, properties and applications 9 Summary Zusammenfassung 115 References 122 Appendix III