Plastics technology introduction and fundamentals 9781569907672, 9781569907689, 1569907676

Citation preview

Bonten Plastics Technology

Christian Bonten

Plastics Technology Introduction and Fundamentals

Hanser Publishers, Munich

Hanser Publications, Cincinnati

The Author: Prof. Christian Bonten, University of Stuttgart, Institut für Kunststofftechnik (IKT), Pfaffenwaldring 32, 70569 Stuttgart, Germany

Distributed in the Americas by: Hanser Publications 414 Walnut Street, Cincinnati, OH 45202 USA Phone: (800) 950-8977 www.hanserpublications.com Distributed in all other countries by: Carl Hanser Verlag Postfach 86 04 20, 81631 Munich, Germany Fax: +49 (89) 98 48 09 www.hanser-fachbuch.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 authors 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. The final determination of the suitability of any information for the use contemplated for a given application ­remains the sole responsibility of the user. Library of Congress Control Number: 2019946865 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 2019 Editor: Dr. Mark Smith Production Management: Jörg Strohbach Coverconcept: Marc Müller-Bremer, www.rebranding.de, Munich Coverdesign: Max Kostopoulos Typesetting: Kösel Media GmbH, Krugzell Printed and bound by Hubert & Co. GmbH und Co. KG BuchPartner, Göttingen Printed in Germany ISBN: 978-1-56990-767-2 E-Book ISBN: 978-1-56990-768-9

Preface

Immediately after I started working at the University of Stuttgart in late summer 2010, I revised the course “Fundamentals of Plastics Technology” with the help of my scientific staff. Since then, this important course has been held unchanged in Stuttgart for a long time. During the revision we not only updated figures and ­contents, but also gave the course a new structure, which I – inspired by didactic seminars of the German University Association  – consider more contemporary. Numerous film sequences used in the lectures enable the students to understand the contents more quickly and deeply. I am convinced that the students in my course become well equipped with a comprehensive, fundamental knowledge of plastics and plastics technology for their upcoming professional life. If students want to deepen their knowledge of the subject, they can do so in the three main areas of “Materials Engineering”, “Processing Technology”, and “Product Engineering” in other courses later on. This introductory and fundamental lecture series in Stuttgart is an elective course with four lessons per week for master students of process engineering, mechanical engineering (e. g. production engineering, automotive engineering), materials science, as well as of technology management. The course is actually aimed at technically educated students, but in the meantime non-technical students (economics, environmental issues) choose the course as well. While about 100 students had this subject examined after the 2010 winter semester, the number was growing year by year subsequently. The increasing interest of highly motivated and disciplined master’s students led me to supplement the figures with continuous text and publish them in the form of a book the first time in 2014. In winter 2012/13, students started asking me about the critical topics that are “heard in the media”. I decided to get to the bottom of the topics “environmental pollution”, “toxins in plastics”, “bioplastics”, and “life cycle analyses” right down to the original sources and to prepare this as a part of the course as well. These topics form the final chapter “plastics and the environment” of this book, and I have the impression that factual information is the best means of clarification. The reader may decide whether I have succeeded in dealing with the topics in a factual way.

VI

Preface

I was a little surprised when, just one and a half years after the start of sales of the first German edition, the publisher asked me to prepare the second one. The many reviews that were sent to the publisher were all positive, contained valuable suggestions and encouraged me to continue this book the same way. Since 2016, more than 500 students chose the course underlying this book in structure and content and also encouraged me to continue teaching in this way. In the second German edition, I concentrated on individual additions, revisions, and updates, as well as the correction of several errors. In the meantime, I am being asked by university professors from all over the world to give not only scientific presentations, but master’s courses about plastics technology there as well. Since not everyone speaks German and I usually do not speak their native language, I often hold the course in English. To help the students with the rework, I have decided to translate the second edition of this book into the ­English language and made only minor changes. I would like to thank the publisher for their trust and advice as well as for offering this book in color and hardcover. I would also like to thank my supporting staff members, who have carefully worked through and gave valuable hints on mistakes and the comprehensibility of the text of the first and second German editions. Technical staff members supported me with figures and photos from their daily work. The students Adriana Steinitz and Lisa Schleeh greatly helped me with translation of the text and the figures. I am sure that with the knowledge of the book I will give every reader/student the opportunity to quickly gain a foothold in the plastics industry and to enable her or him to decide early on in which application plastics can do great things. Stuttgart, September 2019 Univ.-Prof. Dr.-Ing. Christian Bonten

The Author: Prof. Christian Bonten

University Professor Dr.-Ing. Christian Bonten heads the Institute for Plastics Technology (Institut für Kunststofftechnik; IKT) in Stuttgart, one of the leading German research institutes in the field of plastics technology. After studying mechanical engineering in Duisburg/Germany and plastics processing at the University in Aachen/Germany, Prof. Bonten received his doctorate in the field of welding plastics under supervision of Prof. Ernst Schmachtenberg. After several years of technical responsibility and later business responsibility at the chemical company BASF and the bioplastics manufacturer FKuR, he was appointed Director and Head of the IKT by the University of Stuttgart in 2010. The institute works in all areas of plastics technology: materials engineering, processing technology, and product engineering.

How to Use This Book

The special feature of this book is the use of so-called Quick Response Codes (QR codes), which were developed more than 30 years ago in Japan. In this book they are used to connect a smartphone with the YouTube channel of the IKT and to run a film or animation matching the topic. This offers the fusion of the “frozen” printed book with the highly mobile possibilities of the new media. QR codes allow the transmission of information by scanning – very similar to the bar codes on food packaging, but with a higher information density. They are a square matrix of black and white dots, which represent the coded data in binary code. Nowadays you do not need a special scanner any more, but simply scan the code with the camera of your smartphone using suitable software (an “app”). To use the barcodes, a corresponding app (to be found e. g. under the search terms “QR code reader” or “QR code scanner”) must be installed, if the smartphone does not already have it “on board”. Of course, the smartphone must have Internet access in order to access the IKT YouTube channel. After starting the app, the QR code should be targeted in the search field: the information is usually recognized quickly and the appropriate YouTube movie runs automatically. Some of the movies have a soundtrack, so: speaker on! A video can be played here.

A video can be played here. http://www.ikt.uni-stuttgart.de/links/Videolinks/Hinweis



If teachers in schools or similar non-commercial entities want to make use of the figures used in this book, we will be happy to send them in high resolution. We kindly ask to make sure that the “Source: C. Bonten, Plastics Technology, 2019, Hanser” is always mentioned.

Contents

Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

V

The Author: Prof. Christian Bonten . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . VII How to Use This Book . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

IX 1

1.1 Plastics – Material of the Modern Age . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1.2 Applications of Plastics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 1.3 Plastics and Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 1.4 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

2

Fundamentals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

2.1 From Monomer to Polymer – Basics of Polymer Chemistry . . . . . . . . . . 13 2.1.1 Origin of Monomers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 2.1.2 Polymer Synthesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 2.1.2.1 Polymerization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 2.1.2.2 Copolymerization (Special Form of Polymerization) . . . 19 2.1.2.3 Polycondensation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 2.1.2.4 Polyaddition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 2.1.3 The Molar Mass of Polymers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 2.1.4 Binding Forces and Brownian Molecular Movement . . . . . . . . . . 27 2.1.4.1 Intermolecular Physical Bonds . . . . . . . . . . . . . . . . . . . . 29 2.1.4.2 Brownian Molecular Motion – Mobility of Polymer Chains . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 2.1.5 Mechanisms of Solidification and Subdivision of Polymers . . . . 33 2.1.6 Primary Structure of Polymers: Constitution and Configuration 36 2.1.7 Secondary and Tertiary Structures of Polymers: Conformation . 38 2.1.7.1 Amorphous Structures . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

XII

Contents

2.1.7.2 Crystalline Structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 2.1.7.3 Influence of the Primary Structure . . . . . . . . . . . . . . . . . 41 2.1.7.4 Superstructures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 2.1.8 Polymers – Raw Materials Not Only for Plastics . . . . . . . . . . . . . . 47 2.2 Fundamentals of Force Transmission . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48 2.2.1 Important Terms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48 2.2.1.1 Strength . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48 2.2.1.2 Stiffness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48 2.2.1.3 Toughness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48 2.2.1.4 Stress-Strain Diagrams . . . . . . . . . . . . . . . . . . . . . . . . . . . 49 2.2.2 State Ranges of Plastics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52 2.2.2.1 Glass Transition Temperature Tg . . . . . . . . . . . . . . . . . . . 52 2.2.2.2 Crystalline Melting Temperature Tm . . . . . . . . . . . . . . . . 53 2.2.2.3 State Ranges of Crosslinked Polymers . . . . . . . . . . . . . . 54 2.2.3 Mechanical Replacement Models . . . . . . . . . . . . . . . . . . . . . . . . . 56 2.3 Plastics and Plastics Technology – ­Definition of Terms . . . . . . . . . . . . . 60 2.4 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61

3

Plastics Materials Engineering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65

3.1 Behavior in the Melt – Flow Properties and Their Measurement . . . . . 66 3.1.1 Fluid Mechanics Basics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66 3.1.2 Influences on the Flow Behavior . . . . . . . . . . . . . . . . . . . . . . . . . . 74 3.1.3 The Concept of Representative Viscosity . . . . . . . . . . . . . . . . . . . . 79 3.1.4 Elongation of Melt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81 3.1.5 Die Swell and Shrinkage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83 3.1.6 Rheometry – the Measurement of Flow Properties . . . . . . . . . . . 85 3.1.6.1 Measurement of the Melt Flow Rate MFR . . . . . . . . . . . . 86 3.1.6.2 The High-Pressure Capillary Rheometer . . . . . . . . . . . . 87 3.1.6.3 Rotational Rheometer . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89 3.1.6.4 Extensional Rheometer . . . . . . . . . . . . . . . . . . . . . . . . . . . 94 3.2 Behavior as a Solid – Solid Properties and Their Measurement . . . . . . 95 3.2.1 Mechanical Properties of Plastics . . . . . . . . . . . . . . . . . . . . . . . . . . 96 3.2.1.1 The Tensile Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96 3.2.1.2 The High Speed Tensile Test . . . . . . . . . . . . . . . . . . . . . . 99 3.2.1.3 Influence of Time and Temperature on the Mechanical Behavior . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100 3.2.1.4 The Creep Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103 3.2.1.5 The Vibration Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105 3.2.1.6 The Bending Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107 3.2.2 Physical Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110 3.2.2.1 Electrical Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110

Contents

3.2.2.2 Magnetic Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112 3.2.2.3 Optical Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113 3.2.2.4 Acoustic Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120 3.2.3 Values for Thermal and Mass Exchange . . . . . . . . . . . . . . . . . . . . 123 3.2.3.1 Specific Enthalpy h . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123 3.2.3.2 Specific Heat Capacity cp . . . . . . . . . . . . . . . . . . . . . . . . . 124 3.2.3.3 Density ρ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127 3.2.3.4 Thermal Conductivity λ . . . . . . . . . . . . . . . . . . . . . . . . . . 128 3.2.3.5 Coefficient of Thermal Expansion α . . . . . . . . . . . . . . . . 130 3.2.3.6 Thermal Diffusivity a . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131 3.2.3.7 Heat Penetration Coefficient b . . . . . . . . . . . . . . . . . . . . . 133 3.2.3.8 Mass Transport . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133 3.3 Influence of Additives on Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137 3.3.1 Reinforcing Materials – Active Additives . . . . . . . . . . . . . . . . . . . 138 3.3.1.1 Fibers and the Principle of Reinforcement . . . . . . . . . . . 141 3.3.1.2 The Tasks of the Matrix . . . . . . . . . . . . . . . . . . . . . . . . . . 144 3.3.1.3 Force Transmission of Fiber-Reinforced Plastic Composites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145 3.3.1.4 Defects in Fiber-Reinforced Plastic Composites . . . . . . . 148 3.3.1.5 Nanoparticles as Active Additives . . . . . . . . . . . . . . . . . . 152 3.3.2 Functional Additives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 154 3.3.2.1 Viscosity-Changing Additives – Flowing Agents . . . . . . 154 3.3.2.2 Plasticizers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155 3.3.2.3 Blending of Polymers . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157 3.3.2.4 Impact Modifiers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157 3.3.2.5 Nucleating Agents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159 3.3.2.6 Coupling Agents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159 3.3.2.7 Conductive Additives . . . . . . . . . . . . . . . . . . . . . . . . . . . . 160 3.3.3 Fillers – Inactive Additives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162 3.4 From Polymer to Plastic – Introduction to Plastic Compounding . . . . . . 162 3.4.1 The Twin-Screw Extruder . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163 3.4.2 Process Technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 164 3.4.3 Characteristic Values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 168 3.4.4 Additional Units . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169 3.5 Process, Structure, Properties – Influences due to the Converting Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172 3.5.1 Residual Stresses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173 3.5.2 Orientation of Macromolecules . . . . . . . . . . . . . . . . . . . . . . . . . . . 174 3.5.3 Orientation of Fibers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 176 3.5.4 Crystallization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 177 3.5.5 Formation of a Macrostructure: Foaming of Plastics . . . . . . . . . . 178

XIII

XIV

Contents

3.6 Changes over Time – Overview into the Aging of Plastics . . . . . . . . . . . 179 3.6.1 Causes of Aging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 181 3.6.2 Aging Processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 182 3.6.2.1 Mechanical Aging Mechanisms . . . . . . . . . . . . . . . . . . . 182 3.6.2.2 Physical Aging Mechanisms . . . . . . . . . . . . . . . . . . . . . . 182 3.6.2.3 Chemical Aging Mechanisms . . . . . . . . . . . . . . . . . . . . . . 184 3.6.2.4 Mode of Action of Aging Stabilizers . . . . . . . . . . . . . . . . 186 3.6.3 Aging Phenomena . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 187 3.6.4 Characterization of the Aging Progress . . . . . . . . . . . . . . . . . . . . . 188 3.7 Brief Description of Some Important Plastics . . . . . . . . . . . . . . . . . . . . . 191 3.8 Polyethylene (PE) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 194 3.9 Polypropylene (PP) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 196 3.10 Ethylene-Propylene-(Diene) Copolymers (EPDM) . . . . . . . . . . . . . . . . . . 197 3.11 Polyvinyl Chloride (PVC) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 200 3.12 Polystyrene (PS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 202 3.13 Styrene-Butadiene-Styrene Copolymers (SBS) . . . . . . . . . . . . . . . . . . . . . 203 3.14 Styrene-Acrylonitrile Copolymers (SAN) . . . . . . . . . . . . . . . . . . . . . . . . . 204 3.15 Acrylonitrile-Butadiene-Styrene Copolymers (ABS) . . . . . . . . . . . . . . . . 207 3.16 Acrylonitrile-Styrene-Acrylate ­Copolymers (ASA) . . . . . . . . . . . . . . . . . . 208 3.17 Polyamide (PA) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 211 3.18 Polybutylene Terephthalate (PBT) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 216 3.19 Polyethylene Terephthalate (PET) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 217 3.20 Polycarbonate (PC) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 220 3.21 Polymethyl Methacrylate (PMMA) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 222 3.22 Polyoxymethylene (POM) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 224 3.23 Polytetrafluoroethylene (PTFE) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 227 3.24 Polyether Ether Ketone (PEEK) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 228 3.25 Polyethersulfone (PES) und Polysulfone (PSU) . . . . . . . . . . . . . . . . . . . . 230 3.26 Polyphenylene Sulfide (PPS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 232 3.27 Cellulose Derivatives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 234 3.28 Polyhydroxyalkanoates (PHA) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 236 3.29 Polylactide (PLA) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 237 3.30 Thermoplastic Polyurethane (TPE-U, also TPU) . . . . . . . . . . . . . . . . . . . . 239 3.31 Polyurethane (PUR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 240 3.32 Epoxy Resins (EP) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 241

Contents

3.33 Melamine Formaldehyde Resin (MF) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 242 3.34 Phenol-Formaldehyde or Phenol Resin (PF) . . . . . . . . . . . . . . . . . . . . . . . 243 3.35 Urea-Formaldehyde Resin (UF) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 244 3.36 Unsaturated Polyester Resin (UP) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 245 3.37 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 246

4

Plastics Processing Technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . 249

4.1 Extrusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 250 4.1.1 Extruder Screw and Barrel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 251 4.1.2 The Helibar® High-Performance Extruder . . . . . . . . . . . . . . . . . . . 258 4.1.3 Pipe and Profile Extrusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 260 4.1.4 Flat Film and Sheet Extrusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . 265 4.1.5 Tube and Blown Film Extrusion . . . . . . . . . . . . . . . . . . . . . . . . . . . 267 4.1.6 Extrusion Blow Molding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 268 4.1.7 Co-extrusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 270 4.2 Injection Molding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 272 4.2.1 The Injection Molding Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . 274 4.2.2 The Plasticizing Unit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 277 4.2.3 The Clamping Unit with Injection Mold . . . . . . . . . . . . . . . . . . . . 279 4.2.3.1 Rheological Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 282 4.2.3.2 Thermal Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 283 4.2.4 Influence of the Injection Molding Process on the Properties of the Component . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 286 4.2.5 Special Processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 289 4.2.5.1 Injection-Compression Molding . . . . . . . . . . . . . . . . . . . . 290 4.2.5.2 Thermoplastic Foam Injection Molding . . . . . . . . . . . . . 291 4.2.5.3 Cascade Injection Molding . . . . . . . . . . . . . . . . . . . . . . . . 291 4.2.5.4 Injection Molding Compounding . . . . . . . . . . . . . . . . . . . 292 4.2.5.5 Multi-component Processes . . . . . . . . . . . . . . . . . . . . . . . 293 4.2.5.6 Sandwich Injection Molding . . . . . . . . . . . . . . . . . . . . . . . 295 4.2.5.7 Fluid Injection Techniques . . . . . . . . . . . . . . . . . . . . . . . . 297 4.2.5.8 Back Injection Technology . . . . . . . . . . . . . . . . . . . . . . . . 298 4.2.5.9 Injection Stretch Blow Molding . . . . . . . . . . . . . . . . . . . . 299 4.2.5.10 Variothermal Mold Temperature Control . . . . . . . . . . . . 301 4.3 Processing of Crosslinking Plastics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 302 4.3.1 Compression Molding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 304 4.3.2 Transfer Molding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 305 4.3.3 Injection Molding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 306 4.3.4 Polyurethane Processing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 307

XV

XVI

Contents

4.4 Technology of Fiber-Reinforced Plastics . . . . . . . . . . . . . . . . . . . . . . . . . . 311 4.4.1 Hand Lay-up and Fiber Spraying . . . . . . . . . . . . . . . . . . . . . . . . . . 312 4.4.2 Pressing of SMC and GMT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 313 4.4.3 Pultrusion of Continuous Fibers . . . . . . . . . . . . . . . . . . . . . . . . . . 316 4.4.4 Working with Prepregs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 318 4.4.5 Resin Injection Molding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 319 4.4.6 Three-Dimensional Fiber Reinforced Plastic Structures . . . . . . . 321 4.5 Further Processing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 323 4.5.1 Thermoforming . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 323 4.5.2 Mechanical Machining of Plastics . . . . . . . . . . . . . . . . . . . . . . . . . 330 4.5.3 Welding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 333 4.5.3.1 Hot Plate Welding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 335 4.5.3.2 Hot Gas Welding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 337 4.5.3.3 Extrusion Welding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 337 4.5.3.4 Ultrasonic Welding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 339 4.5.3.5 Vibration Friction Welding . . . . . . . . . . . . . . . . . . . . . . . . 340 4.5.3.6 Laser Welding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 341 4.5.4 Adhesive Bonding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 342 4.5.5 Joining by Snap Connections, Screws, and Rivets . . . . . . . . . . . . 347 4.5.6 Coating of Plastics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 350 4.5.6.1 Coated Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 350 4.5.6.2 Coating Processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 354 4.6 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 357

5

Product Development with Plastics . . . . . . . . . . . . . . . . . . . . . . . . . 361

5.1 Plastics as Construction Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 362 5.1.1 Plastic-Specific Unique Selling Points . . . . . . . . . . . . . . . . . . . . . . 362 5.1.2 Material Preselection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 365 5.2 Geometric Subdivision of Products . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 367 5.2.1 Large-Area Products . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 368 5.2.2 Housing-Like Products . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 368 5.2.3 Container-Like Products . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 369 5.2.4 Complex Products . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 370 5.2.5 Function-Specific Products . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 370 5.2.6 Importance for the Choice of the Processing Method . . . . . . . . . 371 5.3 Designing with Plastics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 372 5.3.1 Requirements for Products and Functions . . . . . . . . . . . . . . . . . . 373 5.3.2 Benefits of Design Freedom – Integration of Functional Elements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 375 5.3.3 Use of Design Freedom – Increasing the Surface Moment of Inertia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 380

Contents

5.3.4 Material-Specific Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 383 5.3.5 Production-Oriented Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 393 5.3.6 Stress-Oriented Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 396 5.3.6.1 Dimensioning against a Permissible Stress . . . . . . . . . . 398 5.3.6.2 Dimensioning against Critical Strain . . . . . . . . . . . . . . . 400 5.3.6.3 Dimensioning against the Influence of Time – Service Life Prediction . . . . . . . . . . . . . . . . . . . . . . . . . . . 404 5.3.7 Brief Summary of Designing with Plastics . . . . . . . . . . . . . . . . . . 406 5.4 Benefits of Prototypes in ­Product ­Development . . . . . . . . . . . . . . . . . . . . 408 5.4.1 Rapid Prototyping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 408 5.4.1.1 Stereolithography (SLA) . . . . . . . . . . . . . . . . . . . . . . . . . . 409 5.4.1.2 Selective Laser Sintering (SLS) . . . . . . . . . . . . . . . . . . . . 410 5.4.1.3 Laminated Object Manufacturing (LOM) . . . . . . . . . . . . 411 5.4.1.4 3D Printing (3-D-P) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 412 5.4.1.5 Fused Deposition Modeling (FDM or FFF) . . . . . . . . . . . 413 5.4.2 Rapid Tooling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 415 5.4.2.1 Casting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 416 5.4.2.2 Laser Sintering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 419 5.4.3 Selection of a Prototype Method . . . . . . . . . . . . . . . . . . . . . . . . . . . 420 5.4.3.1 Requirements Placed on the Prototype . . . . . . . . . . . . . . 420 5.4.3.2 Prototypes for Large-Area Products and for Housing-Like Products . . . . . . . . . . . . . . . . . . . . . . . . . . . 421 5.4.3.3 Prototypes for Container-Like Products . . . . . . . . . . . . . 422 5.4.3.4 Prototypes for Complex Products . . . . . . . . . . . . . . . . . . . 423 5.5 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 425

6

Plastics and the Environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 427

6.1 Plastic Waste . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 427 6.2 Are Plastics Toxic? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 432 6.3 Biopolymers and Bioplastics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 437 6.3.1 Biodegradable Plastics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 437 6.3.2 Bio-based Plastics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 441 6.3.3 From Biopolymer to Bioplastic – Compounding of Biopolymers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 446 6.4 Conserving Resources with Plastics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 448 6.4.1 Origin of the Term “Sustainability” . . . . . . . . . . . . . . . . . . . . . . . . 448 6.4.2 The Brundtland Report and the Kyoto Protocol . . . . . . . . . . . . . . . 448 6.4.3 Conservation of Resources with Plastics . . . . . . . . . . . . . . . . . . . . 450 6.4.4 Regenerative Energy Generation with Plastics . . . . . . . . . . . . . . . 455

XVII

XVIII

Contents

6.5 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 457 6.6 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 458

A

Recommendations for Writing a Bachelor’s/Master’s Thesis at the IKT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 461

A.1 Different Demands of Bachelor’s, ­Master’s, and Doctoral Theses . . . . . 461 A.2 Scientific Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 462 A.2.1 Source-Examining Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 462 A.2.2 Theoretical Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 462 A.2.3 Empirical Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 463 A.3 Scientific Work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 463 A.4 Bachelor’s or Master’s Thesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 464 A.4.1 About the Title of the Thesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 465 A.4.2 About the Content of the Thesis . . . . . . . . . . . . . . . . . . . . . . . . . . . 465 A.4.2.1 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 465 A.4.2.2 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 466 A.4.2.3 Main Part . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 466 A.4.2.4 Concluding Remarks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 467 A.4.2.5 Appendix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 467 A.4.3 About the Scope of the Thesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . 467 A.4.4 About the Writing Style of the Thesis . . . . . . . . . . . . . . . . . . . . . . 468

Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 471

1

Introduction

“What do you think of when you hear the word ‘plastic’?” is often the first question to my master’s students at the University of Stuttgart. Interestingly, most of them think first of all about application areas (lightweight construction, automobiles, aircraft, but also packaging and thermal insulation), then about the subdivision into thermoplastics, elastomers, and thermosets, which they may have remembered from high school. Sometimes they think of processing terms such as ­injection molding or extrusion, but compared to previous years, the topics of plasticizers, recycling, and environmental pollution only emerge later and later. Plastics already seem to be such an integral part of everyday life that every student associates them with something useful and does not necessarily burden them with a “cheap” image. In this introduction, we first want to take a look at the young history of plastics and their current fields of application, before presenting the special significance of plastics for design-influenced products.

„„1.1 Plastics – Material of the Modern Age The earth is presumably 4.54 billion years old, plants (flora) originated only 540 million years ago, fungi, lichens, and the first animals (fauna) appeared about 440 million years ago. Homo sapiens sapiens, i. e. the intelligent, modern human being, has existed for about 40,000 years and in this short period of time – from a world-historical point of view – has created amazing things. The Copper Age, the last phase of the Stone Age, was followed by the Bronze Age (Figure 1.1). Bronze is an alloy consisting of at least 60% copper and also contains tin. Bronze is regarded as the first alloy specifically produced and used by humans, an achievement that already required metallurgical knowledge. Finally, the Bronze Age was gradually replaced by the early Iron Age (Hallstatt period). Iron and its alloys required even more metallurgical knowledge and higher temperatures,

2 1 Introduction

Stone Age

Bronze Age

glass known in Egypt since the fourth millennium BC

Iron Age paper invention in China approx. 105 AD

0

million years before now

Quarternary

Pliocene

Miocene

2.6

66.5 until 375 AD

Neogene

Cretaceous

Jurassic

251

until approx. until approx. 2000 BC 1000 BC

Triassic

Devonian Carbonifer. Permian

Silurian

Ordovician

Cambrian

1000

542

2000 Proterozoic

3000 Archean

4000

Hadean

4600

which finally enabled even more superior weapons and tools such as those of the ancient Romans.

until 1500

Middle Age Modern Age aluminum discovery around 1800

porcelain invention in China approx. 700 AD

plastics large scale production 1938

Figure 1.1 Chronology of development of different materials in human history

For over a millennium, actually no new material in the “known world” (from a Euro­pean perspective, i. e. Europe, Africa, Middle East) was invented. It was only at the beginning of the 18th century that J. F. Böttger and E. W. von Tschirnhaus “invented” European porcelain (which already existed in China for about 1000 years). Aluminum was first produced at the beginning of the 19th century, and in the middle of that century the early plastics were introduced (however, it took until the middle of the 20th century to implement production on a large scale). Due to the strong and increasing use of plastics, there are historians who already speak of the “plastics age”. In 1983, the worldwide consumption of plastics reached 125,000,000 m3, for the first time, exceeding that of iron [1]. In the history of plastics, a distinction is made between four eras [2]: ƒƒOrigins (until 1839), ƒƒThe era of imitation fabrics (1839 to 1914), ƒƒEra of substitutes (from approx. 1914 to approx. 1950), ƒƒThe era of materials with new properties (from around 1950). The Era of Imitation Materials At the beginning of the history of plastics there was an ecological problem, which is not strange to us even today. Due to the strong demand for ivory for balls for the

1.1 Plastics – Material of the Modern Age

billiards game popular in the USA, the elephants in Ceylon, today’s Sri Lanka, were already close to extinction in the second half of the 19th century. An American inventor, J. W. Hyatt, succeeded in 1867 in synthesizing a substitute, celluloid. But celluloid was not only attractive for billiard balls, but also for the ­inexpensive imitation of luxury products made of ivory, tortoiseshell, nacre, or horn for all kinds of everyday objects (Figure 1.2). The invention of G. Eastman, the head of the Kodak Group, who patented photographic film in 1884, has an even more epochal significance: thin strips of celluloid as a carrier for a light-sensitive layer [1].

Figure 1.2 Celluloid: replacement for expensive natural materials [Image source: Deutsches Kunststoffmuseum (German Plastics Museum)]

It was similar with the development of Bakelite®, the first fully synthetic phenolic resin-based plastic, by the Belgian Leo Hendrik Baekeland at the beginning of the 20th century. The heat distortion resistant, electrically insulating, and lightweight material was ideal for the still young electrical engineering industry for use as a housing material for radios and telephones (Figure 1.3) and for even more complex geometries of switches and lamp sockets (Figure 1.4). Electrical devices spread rapidly at that time.

 Figure  1.3  Telephone housing made of Bakelite [Image source: Deutsches Kunststoffmuseum (German Plastics Museum)]

3

4 1 Introduction

 Figure  1.4  Bell button to call for domestic servants [Image source: Deutsches Kunststoffmuseum (German Plastics Museum)]

The Era of Substitute Materials Even before World War I, the German Fritz Klatte took the first steps towards the industrial production of one of the most important mass plastics of the 20th century: polyvinyl chloride (PVC), which was invented by the Frenchman Henri Victor Regnault but could not be produced in large quantities until then. The mechanical properties and the resistance of this material to chemicals and environmental influences as well as its low-cost production made it universally applicable: from acid-resistant protective gloves to bags and suitcases made of imitation leather. The vinyl record replaced the record made of shellac, a secretion of special lice, and spun on every turntable until well into the 1980s [1]. The Era of Materials with New Properties Even before the First World War, these pioneers were often dependent only on empiricism, on ideas and experiments, in order to make new inventions in the field of plastics. This changed in 1922 when Professor Hermann Staudinger from Freiburg, Germany, explained the processes involved in the formation of polymers and plastics with his theory of macromolecules (Nobel Prize 1953). It is therefore not surprising that numerous new substances were developed in the 1930s: polymethyl methacrylate (PMMA; “Plexiglas®”) from Röhm (now Evonik), polystyrene (PS) from BASF (now INEOS), polyethylene (PE) from Imperial Che­ mical Industries (now Akzo Nobel), and the polyamide (PA) with the brandname ­Nylon® from DuPont as well as with the brandname Perlon®, at the same time invented by the University of Stuttgart chemist Paul Schlack [1]. After stagnation during the Second World War, the triumph of plastics was unstoppable. Otto Bayer had already developed polyurethane by the end of the 1930s. In the 1950s there were numerous applications for soft and rigid polyurethane (PUR) foams, mostly upholstered furniture and sporting goods. In 1949, Fritz Stastny of BASF created a very lightweight material with expanded polystyrene (EPS; Styropor®) through his process of foaming polystyrene. It was immediately used for shock-absorbing packaging of sensitive goods and for thermal insulation. In 1953, Karl Ziegler patented a safe and inexpensive process for the production of polyethylene (PE) that made this plastic truly marketable (Nobel

1.2 Applications of Plastics

Prize 1963 together with Giulio Natta). To this day, polyethylene and polypropylene (PP) are by far the most widely used materials [1]. Hermann Schnell at Bayer succeeded in synthesizing polycarbonate (PC) in 1953. It combines transparency with very good mechanical properties. The material is valued as an alternative to glass in the construction industry and for housings for electrical appliances, usually also blended with ABS. Today, shatterproof headlamp diffusers made of polycarbonate ensure greater safety and lower weight in cars. From around 1982 it was used in large quantities for the manufacture of optical data carriers. The Compact Disc (CD) almost completely replaced the proven vinyl record made of PVC, followed by DVD and Blu-ray Disc [1]. Today, however, these are increasingly being replaced by solid state disks (SSDs) that contain little plastic.

„„1.2 Applications of Plastics Plastics are increasingly being used for passenger transport because their low mass forces also reduce inertia (so-called “lightweight” construction, although inertia is not equal to weight). If inertia is reduced, sportier driving is possible for a given engine power, or alternatively the engine power and therefore the use of ­resources can be reduced. Figure 1.5 shows selected examples of vehicles and aircraft whose plastic content is constantly increasing. For example, below right, the A350 series from Airbus is shown, which now consists of more than 50% by weight carbon fiber reinforced plastics.

Figure 1.5 Application of plastics in passenger transportation [Image source: Deutsche Bahn AG, BMW AG, Honda Motor Itd., Airbus AG]

5

6 1 Introduction

The largest area of application for plastics is light food packaging, illustrated in Figure 1.6 using the example of films and plastic bottles. For many people, it is not immediately obvious which benefits are provided by packaging. On closer in­ spection, it becomes clear that plastic packaging with minimal input quantities provides a “shield” over the goods to be protected whose material or energetic ­efficiency cannot be achieved by other packaging materials. Section 6.3 deals with this more in detail.

Figure 1.6 Packaging made of plastic

Using the example of European plastics consumption, Figure 1.7 shows that packaging is a very important area of application for plastics, followed by use in the construction industry, e. g. as insulating material, for pipelines, or as heat-insulating material for window frames. This is followed by vehicles and electrical engineering applications. It is particularly noticeable that packaging is more likely a short-lived application of plastics; on the other hand, plastics in the construction sector are used for 50 years or longer. Here one already notices the d ­ ilemma under which this class of material suffers. On the one hand the product should disappear as soon as possible after usage (packaging); on the other hand it should be usable as long as possible (building industry). The term “other” is used, for example, to describe the areas of application: sports and leisure, furniture, toys, and medical technology. It becomes clear that there is actually hardly any industry in which plastics are not used! Figure 1.8 shows sports and leisure applications; most of them would be inconceivable without plastics. The images shown here have also been selected for their ­design and color variety: While technical components, which are hardly visible, are designed according to the technical requirements and usually dyed black, consumer products are often fashionably designed and dyed.

1.2 Applications of Plastics

building & construction 20.1 %

packaging 39.4 % electrical & electronics 5.4 %

automotive 8.5 %

others 26.6 % Figure 1.7 Application of plastics in Europe 2014 [3]

Figure 1.8 Application in the sports sector

7

8 1 Introduction

„„1.3 Plastics and Design Many consumer-related products use design as a unique selling point (e. g. Apple®, Samsung®, but also BRAUN® and Rimowa®). In some cases, technology and quality alone can no longer clearly differentiate a company from the competition. Plastics are the “chameleon of materials” and are therefore a material that designers like to use. The early plastics made it possible to imitate precious natural materials such as horn, tortoiseshell, nacre, and ivory (see above), and even modern plastics allow the imitation of many other high-quality materials. What also makes plastic components so attractive is not only the lower weight, but also the usually lower component costs. The low-cost primary forming process, which we will get to know in Chapter 4 “Processing Technology”, allows a wide variety of forming options and thereby freedom of design (see also Chapter 5 “Product Development”). Both are particularly attractive for engineers and industrial designers. The “cost-effective” aspect has certainly led to the fact that plastics had for a long time a “cheap” image compared to other materials. Today, plastic products are increasingly being processed into high-quality design products without losing their material identity. Plastics are less and less substitutes for other materials than a previously “non-existent innovation material” [4]. The design of a vehicle interior, the coordinated color scheme, the feel, and the sound are an experience that can hardly be associated with a “cheap” one (Figure 1.9): almost everything here is made of plastic.

Figure 1.9 High-quality vehicle interior made of various plastics [Image source: BMW AG]

Designers particularly like the fact that plastics can be colored (Figure 1.10), which is hardly possible with any other material. Lunch boxes, ballpoint pens, shower gel bottles, and many other plastic products are available in a wide range of colors and color combinations.

1.3 Plastics and Design

With the coloring, the more expensive painting step can be saved on the one hand, whereas on the other hand the component retains its color even if the surface is damaged. This is an advantage used, for example, by Japanese motorcycle manufacturers, who switch from painted sheet metal parts  – where technically possible  – to UV stabilized colored plastic components. The result is not only the above-mentioned aesthetic advantages after scratches, but also a far lower component weight at lower manufacturing costs.

Figure 1.10 Everyday objects in different colors, shapes, and surfaces

The variety of shapes has always inspired designers and artists. Figure 1.11 shows “La Chaise” by the engineer and artist couple Charles and Ray Eames from 1948, which for decades existed only as a model and was exhibited in museums. At the beginning of the 1990s, the German-Swiss furniture manufacturer Vitra dared to invest in its series production with modern materials and certainly does not regret it today.

9

10 1 Introduction

Figure 1.11 Aesthetic shape of “La Chaise” [Image source: Vitra AG]

Figure 1.12 shows the world-famous cantilever chair of the Dane Verner Panton. First he made it as a prototype from glass fiber reinforced plastic (GFRP) manually on a one-sided wooden mold and showed it to his friends. Their approval encouraged him to start series production and he found a daring company in Vitra AG, which made the chair from polyurethane with the support of Bayer AG (Section 4.3.4). It had to be sanded, primed, and painted afterwards. The chair was so well received that even larger quantities were thought of and injection molding (see Section 4.2) came into the game. Although a lot of money had to be invested in the injection mold, there was no longer any need for reworking and the color was already included in the material. BASF now supported the realization with its UV-resistant acrylic ester-styrene-­ acrylonitrile (ASA). At the end of the 1990s – as part of a retro wave – the chairs were reissued, but now injection molded from long glass fiber-reinforced poly­ propylene (PP-LGF) with a matte surface.

Figure 1.12 Different stages of the Panton chair [Image source: Vitra AG]

1.4 References

„„1.4 References [1] N. N., “http://www.deutsches-kunststoff-museum.de,” 2014. [Online]. Available: http://www.deut sches-kunststoff-museum.de/rund-um-kunststoff/zeittafel-zur-geschichte/. [Accessed April 8, 2014]. [2] F. Waentig, “Konservieren und Restaurieren von gealterten Kunststoffen,” Restaurator im Handwerk, No. 2, 2013. [3] PlasticsEurope, “Plastics – the Facts 2014 – An analysis of European latest plastics,” Brussels, 2014. [4] G. Klein, “Design for Innovative Materials,” Kunststoffe plast europe, No. 9, 2000, pp. 10–11.

11

2

Fundamentals

For the engineer working with plastics, an introduction to polymer chemistry is a necessary basis, because the properties as a material, during processing, and in the finished component depend strongly on the structure and molecular shape of the polymers. This chapter also refreshes some of the basic principles of material mechanics necessary for understanding this class of materials, aiming towards better comprehension and prediction of their special features, e. g. under the influence of time and temperature.

„„2.1 From Monomer to Polymer – Basics of Polymer Chemistry We will now get to know the origin of the monomers and the three most important polyreactions, clarify the molar mass and molar mass distribution of polymers, and gain a better understanding of the acting binding forces. Afterwards, the socalled primary, secondary, and tertiary structure of polymers will be discussed, since not only the atoms of the polymer chain, but especially also their arrangement strongly influences the later material properties.

2.1.1 Origin of Monomers Since the end of the Second World War, at the beginning of the modern era of plastics, crude oil has been used as a raw material for polymer chemistry. In a refinery, crude oil is distilled (sorted according to molecule size), cracked (split into smaller molecules), reformed (molecules partially converted), and refined (purified). Substances such as gases, gasoline (petrol), heating oil, bitumen, lubricating oil, and coke (chain length increasing) and – depending on where the oil is found – more or less sulfur is produced.

14 2 Fundamentals

Ethene and propene – two volatile gases – can be extracted from the crude petroleum called naphtha. In the past, these gases were called ethylene and propylene, names that have survived in plastics technology and polymer chemistry to this day, and were initially waste materials that were incinerated without generating useful energy. For a long time, however, naphtha has been used to produce polymers. Synthetic polymers are formed from smaller molecles, the so-called monomers (“mono”; Greek: one, alone, “mer”, Greek: part, fraction), in the form of threads. If only a few (e. g. 10) smaller molecules are strung together, so-called oligomers are formed; they are of a wax-like and partly sticky consistency. If at least 1000 atoms are linked by chemical bonds, one speaks of polymers (“poly”; Greek: a lot). These very long molecules are also called macromolecules (“macros”; Greek: large, wide, long). Figure 2.1 shows that not only ethene and propene, but also other chemicals are obtained from crude oil, which are raw materials for other polymers. With only a few raw materials (crude oil, natural gas, rock salt, sulfur, water, air), a chemical company can produce about 30 important monomers from which polymers of all kinds and with a wide range of properties can be produced. In the meantime, BASF has outsourced or sold the business of some of the polymers described to sub­ sidiaries: however, this does not mean that it does not continue to supply the raw materials for these polymers. benzene

ethylbenzene

styrene

cyclohexane

adipic acid

PBT PA

caprolactam SAN hexanediol butanediol

acetylene oil

ethylene

ethylene oxide

ethylene glycol vinyl chloride

propylene

ABS/MABS S/B-polymers PS

acrylic acid PVC acrylonitrile acrylate

C -Mix

butadiene

PE PP

Figure 2.1 Polymer production routes [Image source: BASF SE]

Since oil reserves will become scarcer and more expensive in the long term, it makes sense to try to produce more and more polymers from renewable raw mate-

2.1 From Monomer to Polymer – Basics of Polymer Chemistry

rials (Figure 2.2). Biosynthesis either takes place in nature itself (examples of ­natural polymers are proteins, cellulose, spider silk) or is deliberately induced in bioreactors: ƒƒBiopolymers from plants (e. g. rubber trees) ƒƒBiopolymers from animals (e. g. chitin, casein) ƒƒBiopolymers from microorganisms (e. g. synthesis of PHB) ƒƒBio-monomers from microorganisms (e. g. fermentation of starch to lactic acid and later synthetic polymerization to polylactic acid PLA) ƒƒBio-monomers from plants (e. g. bio-ethanol from sugar becomes bio-­polyethylene)

polymer synthesis in plants

polymer synthesis in animals / humans

polymer synthesis in microorganisms

monomer synthesis in microorganisms

monomers from plants

biobased polymers Figure 2.2 Synthesis of biobased polymers [Image source: IGVP, Univ. Stuttgart]

The example of five possible routes in Figure 2.3 shows which bio-based chemicals and polymers can be produced from glucose, a simple sugar. Glucose is mainly produced by plants using photosynthesis from sunlight, water, and carbon dioxide (CO2) and can be used by all living organisms as a source of energy and carbon. However, glucose is usually not freely available, but occurs as a disaccharide (lactose, beet sugar) or in its long-chain polymer form (such as starch, cellulose, etc.), which are both reserve substances and components of the cell structure in plants. When humans, animals, fungi, and bacteria ingest food, the long-chain saccharides are first broken down by enzymes into glucose monosaccharide before they are metabolized. In Section 6.3, we will discuss bio-based polymers and bio-based plastics more in detail.

15

16 2 Fundamentals

glucose C

ethanol CHO

lactic acid CHO

succinic acid CHO

5-HMF CHO

sorbitol CH O

ethylene

lactic acid/ acrylic acid

succinic acid butanediol

furan dicarboxylic acid

sorbitol

polyethylene

polylactic acid polyacrylic acid

polyester polyamides

polyhydroxy furanoate

polyurethanes

Figure 2.3 Polymers based on glucose [Image source: IGVP, Univ. Stuttgart]

2.1.2 Polymer Synthesis The three most important chemical reactions (polyreactions) which cause monomers to react to form polymers are polymerization, polycondensation, and poly­ addition. While polymerization is a chain growth reaction in which unsaturated monomers are combined to form polymers, polycondensation and polyaddition are step growth reactions in which different molecules react alternately to form a long molecular chain. Both step growth reactions are similar, but while polyaddition does not split off any by-products, polycondensation produces by-products such as water, hydrogen chloride, ammonia, and alcohols, which must be removed to continue the reaction. 2.1.2.1 Polymerization Polymerization is explained here using the example of a radical polymerization (Figure 2.4). In radical polymerization, a radical generator, the so-called initiator, provides radicals, i. e. molecules with free/unpaired electrons, which attack the C=C double bond in monomers such as ethene. The initiator “grabs” an electron of this double bond and forms a bond with the monomer. This step is called a chain start. By binding to the initiator, the monomer itself becomes a radical and therefore forms a bond with an adjacent monomer. This in turn becomes a radical and looks for a next partner. The molecular chain becomes longer and longer, which is called

2.1 From Monomer to Polymer – Basics of Polymer Chemistry

a chain growth reaction. The growth of the chains is often terminated by recombination, i. e. the radicals of two molecular chains form a chemical bond.

initiator

molecules (monomers with double bond) start reaction

chain growth

macromolecules (polymer)

 Figure  2.4  Schematic process of radical polymerization

QR-Code 2-1 The production of polyethylene originating from ethylene is shown, as an example of the radical polymerization. http://www.ikt.uni-stuttgart.de/links/Videolinks/Polymerization



The length of the molecular chains is determined by the concentration of the ­initiator. The higher the initiator concentration, the more chains are started at the beginning of polymerization and the less monomers are available per chain. The molecule chains therefore remain shorter with the addition of more initiator.

17

18 2 Fundamentals

A polymer with n repeating units is formed from n monomers (Figure 2.5). The monomer is usually a hydrocarbon. The simplest suitable hydrocarbon is ethene (formerly: ethylene). n vinyl chloride

n ethene H

n•

H C

H

n•

C

H

H

n styrene

H C

H

n•

C

H

Cl

H C

C

H phenyl ring

H

H

H

H

H

H

C

C

C

C

C

C

H

H

H

Cl

n polyethene with n repeating units

H

n polyvinyl chloride with n repeating units

phenyl ring

n

polystyrene with n repeating units

Figure 2.5 Structural formulas of different monomers and their corresponding polymers

A hydrogen atom is often replaced by a characteristic atom or group of atoms, the so-called substituent, which changes the chemical designation of the monomer. The replacement (substitution) of an H-atom with a Cl-atom results in the m ­ onomer chloroethene (trivial name: vinyl chloride). Substitution by a phenyl ring yields phenylethene (trivial name: styrene). From this, polyethylene (PE), polyvinyl chloride (PVC), and polystyrene (PS) are produced by radical polymerization. For some polymerization reactions there are special catalysts, so called organo­ metallic compounds which produce a polymer with a particularly regular structure. The monomer can only be coupled to the chain in a very specific way. The type of bond between catalyst and chain is called a coordinative bond and is therefore called a coordinative polymerization. Important organometallic compounds are Ziegler-Natta catalysts and metallocene catalysts. (The scientists Karl Ziegler and Giulio Natta were awarded the Nobel Prize in 1963 for their work on these catalysts.)

2.1 From Monomer to Polymer – Basics of Polymer Chemistry

2.1.2.2 Copolymerization (Special Form of Polymerization) If polymers in their chain reaction are not composed of one type of monomer but of different monomers, the reaction is called copolymerization. The macromolecules are called copolymers. The incorporation of two (rarely three) different monomers greatly influences the properties of the polymer. The sequence of monomer building blocks in the chain can be statistical, alternating, or blockwise (so-called block copolymers) (Figure 2.6). Graft copolymers are a special form of copolymers. These are polymers with a homogeneous main chain onto which shorter side chains of another type of monomer are grafted. statistically composed macromolecule

alternatingly composed macromolecule

macromolecule composed of blocks (block coploymer)

homogeneous chain with grafted side chains

monomer A monomer B

Figure 2.6 Types of copolymerization

It is not intended here to give the impression that this is a step growth reaction of two different monomers. Copolymerization is also a chain growth reaction, only with two different monomers. It should also be pointed out that the physical (not chemical!) mixture of different polymers is not the same as a copolymer. Polymer mixtures are also referred to as polymer blends, occasionally also as polymer ­alloys. These are discussed in Section 3.3.2.3. 2.1.2.3 Polycondensation Polycondensation is a step growth reaction of multifunctional molecular building blocks. In Figure 2.7, two bifunctional molecules react to form a polymer and form a by-product, which must be removed in order not to slow down the reaction. Low molar mass by-products such as water, ammonia, and hydrogen chloride are formed. If the by-products are not removed, the reaction process is interrupted.

19

20 2 Fundamentals

by-product (must be removed)

example: polyamide 6.6 O

O H

H

n•

N

C

+

N

H

C

n•

C

C

O

H

O

H

H

diamine

dicarboxylic acid

H

H N

C

N

C

C

+ (2n-1) •

C

n

O H

H

Figure 2.7 Polycondensation

In this way, polyamide 6.6 (PA66), for example, is produced from a bifunctional amine (1,6-diaminohexane) and a bifunctional carboxylic acid (e. g. adipic acid). A macromolecule with an amide group (CONH) is formed and water is removed as a by-product. As distinguished above, polycondensation is a step growth reaction since, in addition to the reaction of individual bifunctional monomers with an existing chain, two chains of any length can also react with each other to form an even longer

2.1 From Monomer to Polymer – Basics of Polymer Chemistry

chain. In comparison to radical polymerization, this does not lead to the termination of chain growth, since the chain ends still have functional groups and can therefore continue to react with bifunctional monomers, oligomers, and polymers. QR-Code 2-2 The polycondensation of heptanedioic acid and 1,6-hexanediamine is shown. http://www.ikt.uni-stuttgart.de/links/Videolinks/Polykondensation



2.1.2.4 Polyaddition In the polyaddition step growth reaction, two different multifunctional molecular building blocks (Figure 2.8, here bifunctional) also react with each other. However, no by-product is formed. The coupling of the reactive monomers results from the change of place of one or more atoms, preferably hydrogen atoms, which d ­ etach relatively easily from their respective end groups (–OH, –NH2, –COOH). An example is the polyaddition of bifunctional isocyanate with a bifunctional alcohol to polyurethane. Polyurethane is specifically discussed in more detail in Section 4.3.4 “Polyurethane Processing”.

example: polyurethane dialcohol

diisocyanate

n

O

C

N

N

C

O

+ n

C

O

H

O

O

H O

C

N

N

polyurethane

Figure 2.8 Polyaddition

O

2n

H

H

21

22 2 Fundamentals

QR-Code 2-3 The polyaddition reaction is explained using the example of an epoxy resin. http://www.ikt.uni-stuttgart.de/links/Videolinks/Example-of-Polyaddition



2.1.3 The Molar Mass of Polymers It may be known from school lessons that the molar mass, formerly called molecular weight, can be determined from the sum of the masses of the individual atoms. The molar mass of a macromolecule can now be calculated by addition of the molar masses of the individual monomer units. For this, however, it must be known how often the monomer units are contained in the polymer chain. This number is called the degree of polymerization n. Since not all polymer chains have the same length, n is always only an average value.

number of molecules ni of a fraction

Since the chain length can only be an average value, the molar mass of a polymer can only be an average value as well. In reality, there is a molar mass distribution, i. e. shorter chains, medium-long chains, and longer chains. An example of such a molar mass distribution is shown in Figure 2.9.

Mn number average

Mw weight average

molar mass Mi of a molecule fraction

Figure 2.9 Example of a molar mass distribution of a polymer

2.1 From Monomer to Polymer – Basics of Polymer Chemistry

So there are few molecules with very low molar mass (see coordinate origin) and few with very high molar mass (running to the right). In between, there is a characteristic distribution, which has its maximum at one point. Since some properties of the polymers and the plastics produced from them correlate with the molar mass, knowledge of them is very helpful. But how can such a distribution be summed up in a single number? It turns out that some properties depend on the so-called molar mass number average Mn and others on the so-called molar mass weight average Mw . The number average is simply the sum of the mathematical product of the number of single molecules present ni times the molar mass Mi, divided by the sum of the number of single molecules ni. k

Mn =

∑ ni Mi i=1 k

∑ ni

(2.1)

i=1

The weight average additionally takes into account the weight of the counted molecule lengths and is defined by the mass fraction mi of the macromolecules with the molar mass Mi. k

Mw =

∑ mi Mi i=1 k

∑ mi

(2.2)

i=1

The wider the molar mass distribution, the further apart the values of weight and number averages are. The polydispersity results from the quotient of the two mean   values. Instead,  Mw , the so called “non-uniformity” U, is also often given.  M   n U=

Mw Mn

−1 (2.3)

The difference can be clearly explained by analogy with a purse with coins (Figure 2.10). The 2 Euro (€ 2) coins correspond to particularly long chains (high molar masses) and the 1 cent (€ 0.01) coin to very short chains (low molar masses). The number average is the average value of a coin and is calculated from the total value of the coins divided by the total number of coins:

23

24 2 Fundamentals

k

i=1 k

k

=

∑ mi

∑ ni

i=1 k

∑ ni

i=1

=

5 ⋅ 0.01 + 15 ⋅ 0.02 + 27 ⋅ 0.05 + 32 ⋅ 0.1 +  50 = = 0.31 (2.4) 5 + 15 + 27 + 32 +  159

i=1

159 coins in total, value: 50 €

32

30

27

20 10 0

33

Mn = 0.31 € = 50 €/159 coins Mw = 0.87 €

27

15

15

5

0.01

stack value

40 number n i

Mn =

∑ ni Mi

5

0.02

0.05

0.1 0.2 coin value M i in €

0.5

1.0

2.0

Figure 2.10 Descriptive explanation of average value and distribution

The average value of each coin is € 0.31. The weight average can be calculated by letting the individual coin stacks participate in the formation of the total sum, not in the ratio of the effective particle numbers (number of coins), but by weighting the coin stacks. This means that the ratio of the sum of all stack values is formed by the total sum (value) of the coins. It is assumed that in the wallet there are not: Table 2.1 Determination mi Using Coins as an Example ni

Mi

mi

 5 coins at

0.01

0.05

15 coins at

0.02

0.30

27 coins at

0.05

1.35

32 coins at

0.10

3.20

etc.

but rather:

2.1 From Monomer to Polymer – Basics of Polymer Chemistry

mi · Mi

mF1

0.05 · 0.01

0.0005

0.30 · 0.02

0.0060

1.35 · 0.05

0.0675

3.20 · 0.10

0.3200

etc. mF1: stack value

The following applies to the weight average: k

k

Mw =

∑ mi Mi ∑ mF i=1 K

∑ mi i=1

=

=

i=1 k

I

=

∑ mi

0.0005 + 0.0060 + 0.0675 + 0.3200 +  50

(2.5)

i=1

43.46 = 0.87 50

Therefore, the weight average value of each coin is €0.87. Since the molar mass of the polymer is an important criterion for various properties of the later plastic, the most important methods for their determination will be briefly presented here. Measurement with the Capillary Viscometer The molar mass of the polymer can be determined using a capillary visco­meter, e. g. the Ubbelohde viscometer (Figure 2.11). The polymer must first be dissolved using a suitable solvent. Now a defined volume of this solution is allowed to flow through a capillary of the viscometer and the time required is measured.

 Figure  2.11  Ubbelohde viscometer

25

26 2 Fundamentals

With the help of physical correlations and mathematical relationships, the socalled limiting viscosity number (“Staudinger index” [η]) can ultimately be calculated. For real macromolecules, the Mark-Houwink relationship applies, with which the number-average molar mass is calculated: α

 η  = K ⋅ Mn (2.6)   K and α are characteristic parameters which are listed in the literature for a large number of polymer solvent systems at different temperatures. For linear, unbranched molecules (see “secondary structure” below), α has values between 0.5 and 1. This method is a relative method. The quality of the determination of Mn depends, among other things, on the agreement of the test conditions and the molar mass distribution (polydispersity) of the respective polymer. In addition, the polymer can also be melted instead of brought into solution and can also be pressed through a capillary. However, gravity is not sufficient to determine this so-called melt flow index (MFI) and the force of some weight plates is used to help. The results can be determined quite quickly, but do not give a value for a molar mass, but rather only an indirect statement. Further details are given in Section 3.1.6 “Rheometry – Measurement of Flow Properties”. Measurement with Size Exclusion Chromatography The measurement using size exclusion chromatography (SEC) provides an exact molar mass distribution and can also determine absolute molar masses using light scattering detectors. The polymer to be measured is applied in solution to a ­separation column with a porous structure and passes through it sequentially (Figure 2.12).

GPC separation column with porous packing

detector

detector

Figure 2.12 Size exclusion chromatography (SEC)

detector

2.1 From Monomer to Polymer – Basics of Polymer Chemistry

The principle of size exclusion chromatography: Large macromolecules only have a few pores in which they can be deposited. This is why they are detected relatively quickly by the continuous solvent stream and rinsed out of the separation column first. The smaller a macromolecule is, the more often it can settle in a pore on its way through the separation column. This means that the smaller the macromolecules, the later – i. e. with a time delay – they leave the column.

2.1.4 Binding Forces and Brownian Molecular Movement As a basis for understanding the molecular binding forces in polymers, it is necessary to provide a reminder of the different binding forces between atoms: Metallic Bonds In the metallic bond, the electrons can move freely in a metal lattice (atomic lattice) (Figure 2.13). The valence electrons (outer electrons) of the metal atoms can easily be separated from the atom because they are only bound weakly. A lattice of positively charged metal ions, the so-called atomic bodies, forms in the metal. The “electron gas”, named after the physicist Enrico Fermi, consists of free outer electrons. The high electrical conductivity, magnetism, and also the high thermal conductivity of metals are the result of this free mobility.

 Figure  2.13  Metallic bonds

Atomic Bond The atomic bond is a chemical bond and is also called the main valence bond (chemical primary valence bond). Atomic bonds are formed especially between non-metals and share at least one binding electron pair of the outer electrons (valence electrons) (Figure 2.14). The atoms in the macromolecules of polymers are linked by main valence bonds.

27

28 2 Fundamentals

 Figure  2.14  Atomic bond, using the example of a hydrogen molecule H2 (also: covalent bond, main valence bond)

Further terms for atomic bonds or main valence bonds are: covalent bonds, homopolar bonds, and electron pair bonds. An atomic bond has a certain direction of action, i. e. it is a directional bond and therefore determines the geometric structure of a compound (in contrast to an electron gas). The strength of a bond is ­described by the binding energy. The formation or breaking of an atomic bond is called a chemical reaction. Once more repeating school material, a reminder of the binding nature of these often-used elements is provided here. In general, atoms (elements) strive to take up a noble gas electron configuration when forming a chemical bond (shell model: eight outer/valence electrons; except hydrogen: two outer electrons). Electrons are always arranged in pairs. Unbound outer electrons of one atom therefore enter into a “partnership” with those of another atom – a molecule is formed. The binding energy of main valence bonds can have values from 40 to 800 kJ/mol. The number of atomic bonds an atom can form is called valency or binding capacity. It depends on the number of outer electrons. The “8-minus-n” rule applies to the binding capacity of a covalently bonded atom of the IV – VII main groups of the periodic table, with n equal to the outer electron number of the corresponding atom. For chlorine (Cl), oxygen (O), nitrogen (N), and carbon (C) with 7, 6, 5, and 4 outer electrons, respectively, a binding capacity of 1, 2, 3, and 4 is calculated. The hydrogen atom strives for the configuration of helium (noble gas) with 2 outer electrons and can thus take up 1 electron within a chemical bond. This means that hydrogen is monovalent. Since sulfur (S) stands in the main group VI of the 3rd period, this can additionally form 6 bonds. The macromolecules of a polymer are formed by such atomic bonds. The fragment of a polyethylene macromolecule shown in Figure 2.15 consists of about 70 ­ethylene monomer units. Most polyethylenes even have 100,000 repeating units. However, these cannot be shown here.

2.1 From Monomer to Polymer – Basics of Polymer Chemistry

 Figure  2.15  Fragment of a polyethylene macromolecule

Polymers are organic compounds because they are based on carbon. Besides carbon (C), important components of organic compounds are hydrogen (H), oxygen (O), and nitrogen (N). In polymers, the heteroatoms chlorine (Cl), fluorine (F), sulfur (S), and silicon (Si) are occasionally used as well. 2.1.4.1 Intermolecular Physical Bonds Physical bonds are secondary valence bonds . They describe the type and size of the attraction forces existing between the polymer chains. Further terms for secondary valence bonds are: intermolecular forces, secondary valence forces, and secondary bonds. These attractional forces are strongly distance-dependent and 2 to 2000 times weaker in relation to the main valence bonds. Dipole-Dipole Forces Dipole-dipole forces consititute a very strong secondary valence bond. They occur between molecules with permanent dipole moments. The dipole moments derive from the different electronegativities of the chemical elements. In polyvinyl chloride (PVC), for example, the chlorine atom is more electronegative than the carbon and the hydrogen atoms (Figure 2.16, left) and therefore attracts their electrons (in the orbital model, this corresponds to an asymmetric electron cloud). This creates a permanent dipole: attraction forces, the so-called dipole-dipole forces, arise between the dipoles of neighboring polymer chains. Their binding energy is 1/50 to 1/200 of a main valence bond.

29

30 2 Fundamentals

H

H

C

C

H

Cl

H

H

H

H

H

H

H

H

H

H

H

H

C

C

C

C

C

C

C

C

C

C

C

C

δ+

H

Cl

H

Cl

H

Cl

H

Cl

H

Cl

H

Cl

δ-

H

H

H

H

H

H

H

H

H

H

H

H

C

C

C

C

C

C

C

C

C

C

C

C

H

Cl

H

Cl

H

Cl

H

Cl

H

Cl

H

Cl

Figure 2.16 Dipole-dipole forces

Hydrogen Bonds Hydrogen bonds are a special form of the dipole-dipole bond and are formed by a hydrogen atom covalently bonded to a much more electronegative atom (e. g. O, N, F) whose common electrons are shifted in the direction of this atom (Figure 2.17). δ-

N H

C δ+

δ-

N H δ+

C

 Figure  2.17  Hydrogen bonds

The hydrogen atom, which is partially positively charged by the electron shift, is more strongly bound to another electronegative atom of a second macromolecule and thus acts as a “hydrogen bridge” between the two molecule chains. With ∼ 20 kJ/mol, this strongest type of intermolecular force reaches the order of weak main valence bonds. Figure 2.18 shows hydrogen bonds in polyurethane (PUR) and polyamide (PA).

2.1 From Monomer to Polymer – Basics of Polymer Chemistry

O=C HC

N H N H

O=C

CH

HC

O=C

CH CH

HC CH

HC

C=O

H N

HC

C=O

H N

CH

O=C

N H N H

CH

HC

CH

HC

HC HC

CH

H N

H N

HC

CH

O

CH

O

C=O

C=O C=O

H N

CH

HC

H N

O polyamide 6.6

CH CH

HC

CH

HC

C

C

CH C=O

O O

CH

HC

O=C

O=C

CH

polyurethane hydrogen bonds

Figure 2.18 PA66 and PUR as examples for formation of hydrogen bonds

Induction Forces Induction forces are very weak secondary valence bonds. Molecules with permanent dipoles can cause electron shifts in adjacent nonpolar molecules and thus ­induce dipole moments. The binding energy is only 1/500 to 1/2000 of a main valence bond. In summary, the following applies to the secondary valence forces already listed: a prerequisite for the occurrence of dipole-dipole forces and/or induction forces is the presence of permanent dipoles. Dispersion Forces With binding energies of 1/500 to 1/1000 of a main valence bond, dispersion forces (also Van der Waals forces, London dispersion forces) are also very weak. By random movement of the electrons and the resulting deformations of the electron cloud, momentary dipoles are formed even in non-polar molecules. These rapidly varying dipoles, which compensate each other to zero on a time average, also induce dipoles in the neighboring molecules in the rhythm of their own frequencies, but they are not permanent. To illustrate this, Figure 2.19 shows spheres strung together as atoms which are connected to each other by main valence bonds and form polymer chains. Between the polymer chains there are secondary valence forces of different kinds, depending on the atoms of the polymer chain.

31

32 2 Fundamentals

innermolecular chemical bonds (“main valence bonds”) usual notation

C C

intermolecular physical bonds (“secondary valence bonds”): • hydrogen bonds • dipole-dipole forces and induction forces • dispersion forces

Figure 2.19 Clarification of chemical and physical binding forces

2.1.4.2 Brownian Molecular Motion – Mobility of Polymer Chains QR-Code 2-4 Brownian motion is demonstrated here, viewing fat droplets in milk. http://www.ikt.uni-stuttgart.de/links/Videolinks/Brownsche_Molekularbewegung



Physical binding forces correlate with the distance between the polymer chains, and this distance between the polymer chains is temperature-dependent. The effect is based on Brownian molecular motion. Not only atoms and low-molecular molecules vibrate more strongly with each degree above absolute zero, but also macromolecules. At low temperatures the chains are close to each other and looped together, Brownian molecular motion is inhibited. Nevertheless, the average oscillation amplitude of the chains increases with increasing temperature, initially without disentanglement of the loops. The growing increase in distance during heating causes a weakening of the secondary valence forces and therefore their “adhesion” to the neighboring polymer chain. Heating initially leads to micro-Brownian motion processes. These are intramolecular movements of chain segments and side chains. Rotation and rearrangement occur, resulting in gradual conformational changes, i. e. the spatial orientation can change. As the temperature continues to rise, the polymer chains become more and more mobile. If the temperature continues to rise even more, the molecular chains can even slide away from each other, so that the molecules are even more freely mobile and derail (macro-Brownian movement). The material is now flexible and deformable. With the length of the individual polymer chains (keyword: degree of polymerization) the number of loops between the polymer chains is also increasing. The

2.1 From Monomer to Polymer – Basics of Polymer Chemistry

l­onger the polymer chains, the more Brownian movement is required for unlooping. As the temperature decreases, however, the mobility of the polymer chains decreases with each degree again, up to a (polymer-specific) temperature at which Brownian molecular movements are very small, the chains again lie very close to each other and the secondary valence forces become particularly stronger again. This temperature is referred to as the glass transition temperature Tg, since the microstructure has solidified like glass below this temperature (see also Section “State Ranges of Plastics”).

2.1.5 Mechanisms of Solidification and Subdivision of Polymers As a rule, plastics are processed into a component in a flowable state and are then supposed to solidify. According to Brockhaus [1], solidification is the “transition from the liquid to the solid state of aggregation. In the case of chemically uniform materials, this occurs when the solidification temperature falls below the pressure-­ dependent solidification temperature. The solidification of substances which are liquid under standard conditions is called freezing.” The solidification of some polymers is irreversible. Subdivision of Polymers: Thermoplastic , Thermoset, and Elastomer When substances cool down, their Brownian molecular movement is reduced, so that solidification is easy to understand with so-called thermoplastics (from Greek “thermós” = “warm” and “plasso” = “form”). In molten thermoplastics, the polymer chains come so close together during cooling that the secondary valence forces between the chains become stronger again. If a thermoplastic has a structurally favorable structure (see Section “Primary Structure of Polymers”), the macromolecules even come so close together that they form particularly ordered structures (crystals) with a high packing density (see Section “Secondary and Tertiary Structures of Polymers”). A thermoplastic is basically soluble, i. e. a suitable solvent can diffuse between the chains, widen their distance and thereby weaken the secondary valence forces. There are also polymers whose molecular chains do not form purely filamentary structures but are able to build chemical bonds with each other. This is then a main valence network and the polymers are “crosslinked”. The crosslinking reaction usually occurs during polymerization, when trifunctional monomers are used. Depending on the crosslinking density, a distinction is made between elastomers (wide-meshed network, Figure 2.20, left) and thermosets (close-meshed network, Figure 2.20, right).

33

34 2 Fundamentals

 Figure  2.20  Main valence networks of elastomers and thermosets

The network structure of elastomers is so widely meshed that it can be very extensible and still slightly absorbs (swells) “molecularly suitable” media. The strongly crosslinked structure of a thermoset is hardly stretchable and no longer meltable. It is so tightly “woven” that hardly any medium can penetrate and is therefore considered to be non-swellable. For didactic reasons, the following comparisons are used to subdivide plastics into their main groups (Figure 2.21): ƒƒA thermoplastic is like chocolate. It can be melted, brought into various shapes, and left to solidify again. If this is done too often, the quality suffers. ƒƒAn elastomer is symbolized here with jelly bears. Although the comparison is not entirely accurate, the bears are supposed to remind us of the high extensibility of elastomers. Elastomers are commonly called rubber, but be aware of that the uncrosslinked precursor is often called rubber as well. ƒƒA thermoset can be easily compared to a cookie or cake. As soon as it has been baked, i. e. chemically reacted, it can no longer be melted. plastics

thermoplastic

Figure 2.21 Different groups of plastics

elastomer

thermoset

2.1 From Monomer to Polymer – Basics of Polymer Chemistry

Crosslinking of Elastomers Crosslinking to elastomers is called vulcanization and was discovered by Charles Goodyear in 1839. A mixture consisting of (non-crosslinked) rubber, sulfur, catalysts, and fillers is heated, and the already long-chain rubber molecules are crosslinked by sulfur bridges. This transfers the material from plastic rubber to an elastic elastomer. The term vulcanization comes from the fact that crosslinking takes place with the aid of sulfur or sulfur compounds, and this odor was only known from volcanoes. The elasticity (resettability) of the elastomer depends on the number of sulfur bridges. The more sulfur bridges there are, the harder the elastomer becomes. The number of sulfur bridges again depends on the amount of sulfur added and the duration of vulcanization. As the elastomer ages, these sulfur bridges are gradually replaced by oxygen bridges and it loses its elasticity (resettability). Subsequent Crosslinking of Thermoplastics Thermoplastics are linear molecules and not crosslinked. However, they can still be crosslinked to a limited extent after synthesis. After the actual polymerization into thermoplastics, radicals can be formed on the polymer chains, for example with high-energy radiation, which combine and thus lead to crosslinking of the polymer chains. Irradiation by an electron beam usually takes place after shaping, i. e. after extrusion or injection molding (see Chapter 4). In the case of semi-crystalline thermoplastics, radiative crosslinking is only possible in the amorphous ­regions. A further variant for the subsequent crosslinking of thermoplastics is the targeted introduction of peroxides, which decompose during the manufacturing process (time-delayed process with the aid of temperature and pressure) and form radicals. The radicals attack the polymer chain, creating reactive sites that can chemically bond. In this process, crosslinking takes place in the melt. In semi-crystalline thermoplastics, the crystallites form only around these crosslinking sites. However, subsequent crosslinking of thermoplastics is considered costly and is rarely used, for example to increase heat resistance. Thermoplastic Elastomers Thermoplastic elastomers (TPE) comprise a subgroup that has only existed since the 1960s. They are very ductile (not as strong as elastomers) and can only undergo elastic recovery up to a certain elongation but can be processed thermo­ plastically. This makes them weldable and easier to recycle. A disadvantage compared to elastomers is the lower dimensional stability under heat. On the one hand, thermoplastic elastomers are made of purposefully constructed block copolymers (Figure 2.22, left) or on the other hand of mixtures (blends) of stronger, stiffer and softer, more ductile blend partners (Figure 2.22, right).

35

36 2 Fundamentals

Such block copolymers are composed of incompatible hard and soft segments. As a result of the incompatibility of these different segments, segregation occurs l­ ocally. The hard segments partially crystallize, forming a so-called domain and a physical network. The soft segments in between are particularly extensible. block copolymers

blends

domain structure

mixture of hard and soft plastics

hard soft

soft

hard

Figure 2.22 Morphology of thermoplastic elastomers

2.1.6 Primary Structure of Polymers: Constitution and Configuration Thermoplastics are used to explain the terms of the primary structure: ƒƒthe constitution and ƒƒthe configuration. The constitution describes the chemical construction principle of a molecule from atoms. For polymers, this is the type of chain atoms, their length (molar mass), and their type of sequence. This includes the type of end groups and substituents and the frequency and length of the branches (Figure 2.23). The configuration, however, describes the spatial arrangement of atoms and groups of atoms in the molecule of the same constitution. The spatial arrangement of polymer chains is described in particular by tacticity. Isotactically ordered polymer chains always arrange their substituents on the same side (i. e., all substituents have the same orientation), syndiotactic chains have their substituents alternately on both sides, and atactic chains have no order pattern (Figure 2.24) [2, 3].

2.1 From Monomer to Polymer – Basics of Polymer Chemistry

monomers form chain molecules:

H C H

H C H

n

chain molecules can be linear:

chain molecules can be branched:

Figure 2.23 Primary structure – constitution

isotactic

syndiotactic

atactic

Figure 2.24 Primary structure – configuration

37

38 2 Fundamentals

The primary structure describes the structural composition of a polymer chain and thereby influences the chemical, mechanical, and thermal properties. However, the primary structure mainly influences the formation of so-called secondary and tertiary structures, which also have a very large influence on the properties.

2.1.7 Secondary and Tertiary Structures of Polymers: Conformation The secondary structure describes the arrangement of chain sequences and the geometric shape of a single macromolecule. The secondary structure can be described by the conformation. It shows the exact spatial arrangement of molecules with defined constitution and configuration. Different conformations result from rotations around single bonds of the polymer backbone. Contrary to some pictorial representations, the chains are not linearly arranged, but the single bonds between two C atoms have a so-called valence angle of 109.5° (see Figure 2.25).

C

C

C

C

+ C

C

C

C

C

m 4n

5 0.1

φ = 109.5°

C

0.1

54

nm C

0.252 nm

Figure 2.25 Bond gaps and bond angles of polyolefins [3]

It seems proven that around the axis of a C—C single bond there is a high degree of free rotation, even better if an oxygen atom is part of the main chain. This is not possible with double or triple bonds. If double bonds are in the main polymer

2.1 From Monomer to Polymer – Basics of Polymer Chemistry

chain, it is rather stiff. Aromatic rings in the main chain are also considered stiff, but also increase temperature resistance. A polymer chain with continuous single bonds is therefore more flexible, i. e. less stiff.

Epot in kJ/Mol

In spite of the free rotatability, the example of polyethylene should show that neighboring C atoms with their substituents (in polyethylene, all the substituents are hydrogen atoms) sometimes occupy an energetically unfavorable position (Figure 2.26). In the case of polyethylene, this threshold is quite weak at 12.6 kJ/mol, so that a very free rotation can be assumed even at room temperature. However, the larger and more bulky the substituent is, the greater the hindrance (so-called steric hindrance). Examples are polystyrene with its ring substituent and poly­ propylene with CH3 as substituent (see also Figure 2.30).

12.6

| 0

| | | | | |  Figure  2.26  60 120 180 240 300 360 torsion angle in degree

Course of the potential energy for the inner rotation of a polyethylene molecule [3]

In amorphous polymers, the disordered, statistical cluster dominates (Figure 2.27), while in semi-crystalline polymers a folded chain is often present (Figure 2.28) [2, 3]. The secondary structures of polymers include: ƒƒthe stretched chain, ƒƒthe disordered ball, ƒƒthe folded chain, and ƒƒthe helix.

 Figure  2.27  Secondary structure – statistical “ball of wool”

39

40 2 Fundamentals

2.1.7.1 Amorphous Structures In the case of so called amorphous polymers, the macromolecules are present in disorder next to each other or intertwined, similar to the fibers in a cotton ball. Due to their irregular structure, amorphous polymers do not have a long-range order, but only a short-range order, i. e. an order only to the nearest neighboring atoms. Thermosets and elastomers as well as thermoplastics with “bulky” side chains or substituents, which prevent the alignment of the polymer chains, solidify amorphously. The plastic made of amorphous polymers appears transparent, as long as no refractive or colored additives are added. 2.1.7.2 Crystalline Structures In the case of semi-crystalline polymers, the macromolecules are able to “crystallize” in many places close to each other. The structure of the macromolecules must be regularly built up over a large area. It is also a requirement that there are no “bulky” substituents that prevent the molecules from aligning. Due to their regular structure, the macromolecules of a polymer capable of crystallization can be so close to each other that a dense package is formed and the secondary valence forces can act very strongly. However, not all regions can crystallize and there are also disordered amorphous regions. These polymers are therefore called semi-crystalline. In contrast to amorphous polymers, semi-crystalline polymers are opaque because the phase boundaries between amorphous and crystalline refract light. free chain ends chain folding crystallite

molecular chain

Figure 2.28 Secondary structure – folded chain

2.1 From Monomer to Polymer – Basics of Polymer Chemistry

2.1.7.3 Influence of the Primary Structure The primary structure has a large influence on the secondary and tertiary structures and thus on the properties. This shall be explained with the help of a changed configuration, the tacticity, in Figure 2.29. In isotactic polypropylene (i-PP, Figure 2.29, top), the substituents point to one side, which is why the main chains of the polypropylene can align well and close together. As a result, the i-PP has a high melting point of about 184 °C and a degree of crystallization of up to 60% (i. e., 40% remain amorphous). Crystal formation is deepened further below. The substituents of syndiotactic polypropylene (Figure 2.29, center) are arranged alternately and therefore do not align well (the packing density is lower here). This leads to a lower crystallinity compared to i-PP and to a lower melting point (Tm ∼ 160 °C). If the substituents are atactic, i. e. arranged without a rule (Figure 2.29, bottom), the main chains can hardly adhere to each other and do not crystallize. This is the case with atactic polypropylene (a-PP). It remains amorphous at room temperature, waxy and sticky, and is hardly commercially usable [4]. H

H H

C

H

H

H

C

H

H H

H

H

C

H

H

H

C

H

H H

H

H

C

H

H

H

C

H

H H

H

H

C

H

H

H

C

H

H H

H

H

C

H

H

H

C

H

H H

H

H

C

H

H

H

C

H

H

C

C

C

C

C

C

C

C

C

C

C

C

C

C

C

C

C

C

C

C

C

C

C

C

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

isotactic H H

C

H H

H

H

H

H C

C

C

C

H

H

H H

C

C

H H

H

H H

H C

C

C

C

H

H

H

H

H

H

C

C

H H

H

H

H

H C

C

C

C

H

H

H

H

H

H

C

C

H H

H

H

H

H C

C

C

C

H

H

H

H

H

H

C

C

H H

H

H H

H C

C

C

C

H

H

H

H

H

H

C

C

H

H C

C

C

H

H

H

H

C

H

H

C

H

H

syndiotactic

H H

C

H

H

H H

H H

C

C

C

H

H

H

H

H C

H

C H

C

H

H

H

C

H

H H

H

C

H

H

H H

H H

C

C

C

C

C

C

C

H

H

H

H

H

H

H

H

H C

H

C

C

H

H

C

H

H H

H

C

H

H

C

C

C

C

C

C

C

H

H

H

H

H

H

H

H

H

H H

H H

H C

H

H

C

C

H

H

C

H

H

C

C

C

C

H

H

H

H

H

H

atactic

Figure 2.29 Primary structure influences secondary and tertiary structures

Another influence of the primary structure on crystal formation, the steric hindrance, is illustrated by the example of polypropylene (PP) and polystyrene (PS) (Figure 2.30). The steric hindrance of the aromatic ring in polystyrene prevents the molecular chains from being placed close together, while the relatively small CH3 substituents of polypropylene allow a helical structure of the chains with the formation of a dense packing.

41

42 2 Fundamentals

The less “bulky” the thread molecules are and the more ordered the structure is, the larger the crystalline area is and the higher the degree of crystallization is. As  the degree of crystallization increases, properties such as density, stiffness, strength, heat resistance, and chemical resistance increase.

polypropylene

polystyrene

low steric hindrance: good crystallization

high steric hindrance due to aromatic ring: poor crystallization

Figure 2.30 Influence of the primary structure on the secondary and tertiary structure; according to [2]

Changes in the constitution are also changes in the primary structures which influence the crystallinity and thus also the properties (Figure 2.31). This will be explained in more detail below using polyethylene as an example: ƒƒAs a linear thread molecule with a few short side chains (1 to 10 C atoms long per 1000 C atoms), the polymer can crystallize very well (up to 80%) and achieve

2.1 From Monomer to Polymer – Basics of Polymer Chemistry

a high density for polyethylene (0.94–0.97 g/cm3). Therefore it is called high density polyethylene (PE-HD or HDPE). ƒƒHowever, several short side chains (15 to 30 short chains with a length of up to 6 C atoms per 1000 C atoms) interfere with crystallization (55 to max. 65%) and lead to lower density (0.92–0.94 g/cm3). This polyethylene has a very linear structure and a lower density (linear low density: PE-LLD or LLDPE). ƒƒIf many medium-length side chains (20 to 40 branches per 1000 C atoms) are allowed to grow, “bulky” branches are formed which cannot be built into the crystal. This disturbance also affects the degree of crystallization, which in this case is only between 40 and 50%. This polyethylene has an even lower density (PE-LD or LDPE) with values from 0.915–0.935 g/cm3. PE-HD (“high density”)

PE-LLD (“linear low density”)

PE-LD (“low density”)

Figure 2.31 Different constitution influences crystallinity

2.1.7.4 Superstructures If you take a closer look by means of a light microscope through a thin section at crystalline structures (Figure 2.32), you can see spherical superstructures, called spherulites. Depending on the molecular structure, additives, and cooling conditions, their size can range from 50 to 500 μm. These spherulites constitute a long-range order and are part of the tertiary structure. They show radially aligned crystal lamellae, which are only 20 to 60 nm thick. The thread molecules in the lamellae are arranged tangentially. Within the lamellae, it is assumed – and this can only be proven indirectly so far – that the molecu-

43

44 2 Fundamentals

lar chains are closely packed to each other and that high secondary valence forces prevail. Crystallization takes place at interfaces in the cooling melt (nucleation sites), since Brownian molecular motion of the polymer chains is slowed down at these – differently oscillating – interfaces. With slow cooling, macromolecules capable of crystallization have more time to arrange themselves more uniformly, i. e. to crystallize more uniformly. This also increases the degree of crystallization. In contrast, crystallization can even be suppressed at very high cooling rates (e. g. in a beverage bottle made of crystallizable polyethylene terephthalate (PET)). plastic plate / component

crystal lamella

molecular chain C C C C C C C C C C C C

C C C

C C C a

C C C C C C C Cc C C C C b

a ≈ 0.736 nm b ≈ 0.492 nm c ≈ 0.254 nm

spherulite ~50 to 500 µm

lamella thickness ~20 to 60 nm

Figure 2.32 Crystalline structures; according to [5]

In addition: the more ordered the amorphous macromolecules in the melt are (orientation), the better the macromolecules can crystallize. An ordered orientation in the melt results from a velocity distribution during processing and the resulting shear (see Section 3.1.1). Figure 2.33 shows a crystal structure with a magnification of 500 μm and an enlarged spherulite (50 μm). This is a light microscopic picture with polarization filter viewing through a polypropylene.

50 µm 500 µm

 Figure  2.33  Spherulite structure

2.1 From Monomer to Polymer – Basics of Polymer Chemistry

Thin sections of polyamide 6 (PA6) can be penetrated in the transmission electron microscope (TEM) (Figure 2.34). The black auxiliary lines are intended to identify the inner core of a spherulite. The diagram next to it shows that the crystal lamellae are not always formed by their own molecule chains which are folded back, but that molecule chains are components of different lamellae and repeatedly pass through the amorphous phase.

TEM picture of polyamide 6 (PA6)

Figure 2.34 Spherulite with lamellae and clarification of tie molecules

The illustration also shows that there are molecule chains that connect different lamellae with each other. These molecules are called “tie molecules” and are integrated in at least two lamellae. The tie molecules play an important role in deformation. While lamellae themselves transmit large forces before they deform, the load between the lamellae is carried by these tie molecules. If there are many tie molecules which tighten at the same time under a load, high forces and more energy can be carried (Figure 2.35). Many studies have shown that small spherulites must have more tie molecules than large ones. Under deformation, e. g. in the edge area of injection molded components or in welding seams, hardly any spherulites are formed during crystallization, but socalled shish-kebab structures which consist of a rod-shaped whisker and flat crystallite structures that have grown away from it laterally (Figure 2.36).

45

46 2 Fundamentals

F F

tie molecule

loose chain end

F

loose loops F

Figure 2.35 Loaded lamellae and amorphous region, according to [6]

shish-kebab

whisker

Figure 2.36 From the failure analysis facility of the IKT (left): isotactic polypropylene processed in push-pull injection molding with whisker structures; polarized transmitted light, thin section 10 µm; right: whisker and shish-kebab structures, schematically according to [6]

2.1 From Monomer to Polymer – Basics of Polymer Chemistry

47

2.1.8 Polymers – Raw Materials Not Only for Plastics At the end of these basic principles of polymer chemistry, it should be pointed out that polymers do not necessarily have to be raw materials for plastics. Polymers can be found in many forms in nature, for example. As explained above, proteins, spider silk, cotton, hair, but also the complex deoxyribonucleic acid (DNA) are polymers, as are the complex carbohydrates cellulose, starch, chitin, and wood (hemicellulose). These natural polymers are not used on an industrial scale for the production of plastics. Polymers are not only raw materials for plastics, but also for other materials (Figure 2.37). They are also raw materials for chemical fibers (polyamide, polyester ­fibers) and for natural fibers (cotton or silk fibers made from natural polymers). The chemical bases of some polymers for plastics and man-made fibers may be the same, but for fibers the molecular chains are specially aligned and arranged. Chemical fibers are a component of textile technology, not of plastics technology. In the section on fiber plastic composites (Section 3.3.1), aspects of textile technology – where necessary – in combination with plastics are discussed again specifically.

plastics

ic plast g essin proc textile processing

monomers

synthesis

polymers

plastic products

textile products

compounding coating materials

coating

textile industry

substrate surfaces

lacquer industry paper industry leather industry plastics industry textile industry

into other materials

plastics industry textile industry coatings industry

functional additives add dose

plastics industry

Figure 2.37 Polymers – raw material not solely for plastics

Polymers are used in large quantities for surface coatings. These are not always, but often, lacquers (also so-called powder lacquers); adhesives can also be regarded as very special coatings. Polymers are required as functional additives to improve the properties of coatings/lacquers, man-made fibers/textiles, plastics, cosmetics, and even food. However, they are not plastics themselves. The term “functional polymer” is sometimes used for this purpose. However, we do not speak of “functional plastics”.

48 2 Fundamentals

„„2.2 Fundamentals of Force Transmission Requirements for engineers’ products are rarely described without terms of applied force and resulting deformation. A reminder of the most important terms will be provided in this section. The behavior of polymers with increasing temperature and the resulting influence on the force transmission are also discussed. Mechanical substitute models, which can describe the behavior of polymers in melt and in solids at different t­ emperatures, are explained in order to be able to use them for predicting the material behavior.

2.2.1 Important Terms The terms strength, stiffness, and toughness are explained here in a catchy way in order to stick better in the memory. 2.2.1.1 Strength The strength of a material is its internal cohesion against an applied force and can be described in simplified terms as “resistance to cracking”. Depending on the primary, secondary, and tertiary structure of the polymer chains and the type and orientation of additives, a plastic can transfer more or less force. The higher the resistance to cracking, the “stronger” the material. (Physicists often call the internal connection “cohesion”, from the Latin cohaerere = connected.) 2.2.1.2 Stiffness The stiffness of a material describes its “resistance to deformation”. The same applies here: depending on the primary, secondary, and tertiary structure of the polymer chains and the type and orientation of additives, plastics more or less give way to an imposed load. If the resistance to deformation is high, the material is “stiff”. If the resistance is low, the material is “flexible”. 2.2.1.3 Toughness Toughness is a term used to describe the energy absorption capacity of a material. The following also applies here: depending on the primary, secondary, and tertiary structure as well as the type and orientation of additives, a material can absorb higher energy through high force absorption and/or through high ductility. The force transmission of a material is usually determined by engineers with the help of the uniaxial tensile test. A test specimen, shown in Figure 2.38 with a square cross-section A0 and length l0, is measured along its principal axis by Δl stretched.

2.2 Fundamentals of Force Transmission

A0

F

∆l stress

σ=

F A0

strain

ε=

∆l l0

E=

σ ε

l0

 Figure  2.38  Determination of the force transmission and terms of the mechanics

F

A force is induced by the forced elongation. During the measurement, this force is related to the perpendicular cross-section of the specimen. This geometry-independent force is called stress and is abbreviated as σ (“sigma”). To ensure that the change in length Δl is also geometry-independent – i. e. independent of the original length l0 – it is related to l0. The quotient Δl/l0 is called strain ε (“epsilon”). 2.2.1.4 Stress-Strain Diagrams It is possible to determine the resistance to deformation, the so-called stiffness of the material, from the tensile test as well. If the resulting stress σ is related to the given deformation ε, the quotient “modulus of elasticity” is obtained. The description of the extensibility of materials includes the terms “brittle” and “ductile”. The term “brittle” is used for materials with a low extensibility, the term “ductile” for highly extensible materials. Strangely enough, the term “ductile” is equated with “tough” in some literature. As described above, however, toughness or energy absorption increases either as a result of greater deformation (“ductility”) or as a result of higher force absorption (“strength”). Therefore, high toughness can also be achieved by high forces without large deformation (“brittle”). QR-Code 2-5 Simulation of a tensile test with the ARAMIS software. http://www.ikt.uni-stuttgart.de/links/Videolinks/Aramis



49

50 2 Fundamentals

Several stress-strain diagrams (Figure 2.39) are used to explain designations according to ISO 527-1 “Plastics – Determination of Tensile Properties – Part 1: General Principles” (Edition 2012). The strain ε is plotted on the abscissa (x-axis) to deform the specimen. The stress σ adjusted to the forced strain is applied to the ordinate (y-axis) at the same time. The characteristic values from the tensile test are described as follows according to [7]: For materials without yield strength (curve a), the maximum stress is the “tensile strength” σm and the corresponding strain is the “strain at tensile strength” σm. Here, stress at break σb and elongation at break εb are identical with these values. For materials with yield strength (curves b and c), the first maximum is called “yield strength” σy and the corresponding elongation “elongation at yield” εy. The stress at break is called “breaking stress” σb and the elongation “nominal breaking elongation” εtb. The yield strength here is also called tensile strength, regardless of whether the ultimate stress is greater (curve b) or not (curve c). In addition to materials without yield strength and with brittle behavior (curve a), there are also materials without yield strength and with ductile behavior (curve d). In this case, too, tensile strength or elongation at tensile strength and fracture stress or fracture elongation are identical by definition.

σm σb a σb σm σy

b

σm σy

c

σb σm σb E

εm εb

εm εm εy εy

εtb εtb

εm  Figure  2.39  εb Stress-strain diagram [7]

Figure 2.39 provides a reminder that the area enclosed by the diagram represents the energy absorption (toughness) (force multiplied by distance = energy). The slope at the origin (here red dotted line) is a measure for the modulus of elasticity.

2.2 Fundamentals of Force Transmission

The mechanical stress of solids and fluids can basically be described by normal stresses (tension/compression) and shear stresses (Figure 2.40). If tensile stresses occur, the body responds with “elongation”. If compressive stresses occur, the ­result is called “compression”. If shear stresses occur, the result is “shear deformation”. F

F F l0

F

l0 F

F

F l‘>l0

F tensile stress inside (response: elongation)

l‘50

>50

>50

–

>50

Stress at 50% strain

MPa

–

–

–

–

–

–

–

Breaking stress

MPa

–

–

–

–

–

40–45

–

Strain at break

%

–

–

–

–

–

3–5

–

Melting temperature

°C

105– 118

126– 135

162–168 135–155 160–168

162–168

160– 168

–

38–50

55–65

90–115

40–55

Dimen°C sional ­stability temperature HDT/ A 1.8 MPa

45–55

45–55

3.10 Ethylene-Propylene-(Diene) Copolymers (EPDM)

Property

Unit

PE-LD

PE-HD

PP-H PP-R PP-B PP-GF30 PP + homo­ random block­ glass-fiber EPDM polymer polymer copolymer reinforced

10−5/K Therm. coefficient of ­expansion, longitudinal (23– 55 °C)

23–25

14–18

12–15

12–15

12–15

6

15–18

10−5/K Therm. coefficient of ­expansion, transverse (23– 55 °C)

–

–

–

–

–

7

–

Flammability UL 94 at 1.6 mm thickness

class

HB*

HB*

HB

HB

HB

HB

HB*

Dielectric constant at 100 Hz

–

2.3

ca. 2.4

2.3

2.3

2.3

2.4–3

2.3

Dielectric loss ­factor at 100 Hz

· 10−4

2–2.4

1–2

2.5

2.5

2.5

10–15

2.5

Ω·m Spec. ­contact resistance

>1015

>1015

>1014

>1014

>1014

>1013

>1014

Ω Spec. ­surface resistance

>1013

>1013

>1013

>1013

>1013

>1013

>1013

30–40

35–40

35–40

35–40

45

35–40

Dielectric strength

kV/mm 30–40

Comparative tracking index CTI/A

600

600

600

600

600

600

600

% Water absorption at 23 °C, saturation

50

4–5

–

–

–

>50

15–30

25–80 20–45

1100– 450– 2800 1200

60–75

255

–

–

–

20– >50

5–7

–

–

–

>50

15–30

50–80 40–55

1800– 900– 3000 2000

1.04–1.13

cond.*

PA66HI impact ­modified

cond.* dry

PA6HI impact ­modified

cond.* dry

PA66GF30

cond.* dry

PA6GF30 cond.* dry

3300 1000

1.18

cond.* dry

1.06–1.09

cond.* dry

1.13–1.15

cond.* dry

g/cm

dry

MPa

3

PA6

Density

Unit

Modulus of elasticity

Property

Properties of Aliphatic, Filled, and Modified Polyamides

3.17 Polyamide (PA) 213

–

3.5– 4.2

–

· 10−4

Ω·m

Dielectric constant at 100 Hz

Dielectric loss factor at 100 Hz

Spec. ­contact ­resistance

>1013

60– 150

HB-V-2

Flammabil- class ity UL 94 at 1.6 mm thickness

10−5 /K

Therm. coefficient of expansion, ­transverse (23–55 °C)

dry

PA6

7–10

Unit

Therm. 10−5 ­coefficient /K of expansion, ­longitudinal (23–55 °C)

Property

>1010

2100– 3500

12–20

>1012

50– 150

PA610

1010

1000– 2400 >1013

70– 150

3.5

V-2

–

8 –10

cond.* dry

3.2–4 5 –11

V-2

–

7–10

cond.* dry

PA66

1010

1000– 1800

4

1013

V-2 (0.75 mm)

1.0

0.8

cond.* dry

PA46

106– 109

7–15

1013

100– 150

1011

2000– 3000

1013

140

4

HB

HB

3.8– 4.4

6–8

2–3

6–8

2–3

1011

1300– 2300

8

>1013

100– 140

3–4

HB

–

8.5 –15

>1010

500– 3000

5 –14

>1012

70– 240

1010– 1012

900– 1800

3.5–4 7– 9

HB

–

7– 8.5

cond.*

PA66HI impact ­modified

cond.* dry

PA6HI impact ­modified

cond.* dry

PA66GF30

cond.* dry

PA6GF30 cond.* dry

Properties of Aliphatic, Filled, and Modified Polyamides (continued)

214 3 Plastics Materials Engineering

9–10

2.5–3.4

%

%

Water ­absorption at 23 °C, ­saturation

Moisture ­absorption at 23 °C/ 50% hum., ­saturation

* Conditioned

600

600

2.6–3

8–9

600

25– 35 600

25–35

1.2–1.6

2.9–3.5

600

>10

>10

>10

>10 12

12

PA610 cond.* dry

10

10

PA66

cond.* dry

Comparative tracking index CTI/A

kV/ mm

Dielectric strength

>10

12

25–30

Ω

Spec. ­surface ­resistance

dry

PA6

30

Unit

Property

600

>10 10

15

3.7

600

>25

>10

cond.* dry

PA46

15–20

10 – 1014 13

13

1.4–2.0

6.0–6.7

400– 600

35– 40

>10

cond.* dry

400– 600

25–35

>10 11

1.0–1.7

5.0–5.5

400– 600

40

>10 13

400– 600

35

>10 11

1.8–2.7

6.5–9.0

600

30– 35

10 – 1012 10

600

25–30

10 – 1010 8

2.2–2.5

6.5–8.0

600

30– 35

>10 13

600

30–35

>1013

cond.*

PA66HI impact ­modified

cond.* dry

PA6HI impact ­modified

cond.* dry

PA66GF30

cond.* dry

PA6GF30

3.17 Polyamide (PA) 215

216 3 Plastics Materials Engineering

„„3.18 Polybutylene Terephthalate (PBT) Semi-crystalline engineering thermoplastic Brief Description PBT has a very similar chemical structure and similar properties to PET. It is produced by condensation of terephthalic acid and 1,4-butanediol.

Processing PBT crystallizes faster than PET and is more suitable for injection molding. It is processed by injection molding. Because of the risk of hydrolytic degradation, it must be dried before processing. PBT can be welded using a heating element, ultrasound, or hot gas. Vibration or rotational friction welding as well as bonding are also applicable. Properties during Use PBT offers a combination of good strength and stiffness, but these are slightly lower than those of PET. The impact strength does not come close to that of PA, but the sliding friction behavior is very good. PBT is a very good insulator, whose properties are only slightly influenced by temperature, humidity, or frequency. It is chemically resistant to weak acids and alkaline solutions, oils, fats, aliphatic and aromatic hydrocarbons, and carbon tetrachloride. However, it is not resistant to strong acids and alkalis and phenol, and is not suitable for long use in hot water (but better than PET). Stress cracking is not a problem. It is characterized by good weathering stability. Fields of Application (Selection) Structural components: plain bearings, roller bearings, valve parts, screws, plug strips, pump housings, gas bellows meter housings, wheels, parts for household appliances such as coffee machines, egg cookers, deep fryers, toasters, hair dryers, irons, binoculars, stove buttons, toothbrush bristles, electrical connectors and plugs, housings for electronic controls, lamp bases, sunroof frames, headlight frames. Trade Names (Selection) Arnite, Celanex, Crastin, Pibiter, Pocan, Ultradur, Valox, Vandar, Vestodur

3.19 Polyethylene Terephthalate (PET)

Good Advice PBT is a good engineering thermoplastic for housing-like parts and complex technical components. It is usually used when polyamide cannot be used due to its lower dimensional stability or due to its chemical resistance. Properties of Polybutylene Terephthalates See Table 3.12.

„„3.19 Polyethylene Terephthalate (PET) Semi-crystalline engineering thermoplastic Brief Description Polyethylene terephthalate is produced by condensation of terephthalic acid and ethylene glycol. Initially, it was only used for fibers (polyester fibers). High molar mass types allow injection molding, injection stretch blow molding, and blow molding.

Processing The main processing method is injection molding. Because of the danger of hydrolytic degradation, it must be dried before processing. A processing contraction of 1.2 to 2.5% must be taken into account. PET can be welded using heating elements, ultrasound, and hot gas. Vibration or rotational friction welding as well as bonding are also applicable. Properties during Use The mechanical properties depend strongly on the degree of crystallinity. This can be strongly influenced by parameter variation in the injection molding process. With suitable crystallization, PET offers a combination of good hardness, strength, and stiffness (but not impact strength) up to approx. 80 °C with a low creep tendency. The sliding friction properties and the electrical properties are good. It is chemically resistant to weak acids and alkaline solutions, oils, fats, aliphatic and aromatic hydrocarbons, and carbon tetrachloride. It is, however, not resistant to

217

218 3 Plastics Materials Engineering

strong acids and alkalis, phenol, nor, if applied for a long time, to hot water. Stress cracking is not a problem; it has good weathering stability. Amorphous molded parts (suppressed crystallization) are desired if, in addition to high transparency, higher toughness, low processing contraction, and high dimensional stability are required. Fields of Application (Selection) Structural components: bearings, gear wheels, shafts, guides, couplings, lock elements, door handles, motor housings, switches, relays, sensors. Other components: beverage bottles. Trade Names (Selection) Anrite, Crastin, Eastar, Selar, Tenite, Valux Good Advice PET is an underestimated material that is not only suitable for beverage bottles, but can also compete with polyamide and PBT in many respects. The main dis­ advantage is the slow crystallization. Table 3.12 Properties of Polyethylene and Polybutylene terephthalates and a blend Property

Unit

PET

PBT

PBT + ASA

amorphous PET-A

semi-­ crystalline PET-C

-GF30

unreinforced

elastomer -GF30 modified

Density

g/cm3

1.33– 1.35

1.38–1.40

1.56– 1.59

1.30– 1.32

1.2–1.28

1.52– 1.55

1.21– 1.22

Modulus of elasticity

MPa

2100– 2400

2800– 3100

9000– 11,000

2500– 2800

1100– 2000

9500– 11,000

2500

Yield stress

MPa

55

60–80

–

50–60

30–45

–

53

Yield strain

%

4

5–7

–

3.57

6–20

–

3.6

Nominal strain at break

%

>50

>50

–

20–>50

>50

–

>50

Stress at 50% strain

MPa

–

–

–

–

–

–

–

Breaking stress

MPa

–

–

160– 175

–

–

130– 150

–

Strain at break

%

–

–

2–3

–

–

2.53

–

Melting ­temperature

°C

–

250–260

250– 260

220–225

200–225

220– 225

225

3.19 Polyethylene Terephthalate (PET)

Property

Unit

PET

Dimensional stability ­temperature HDT/ A 1.8 MPa

°C

60–65

65–75

220– 230

50–65

50–60

200– 210

80

Therm. co­­ efficient of expansion, longitudinal (23–55 °C)

10−5/K

8

7

2–3

8–10

10–15

3–4.5

10

Therm. co­­ efficient of expansion, transverse (23–55 °C)

10−5/K

–

–

7–9

–

–

7–9

–

Flammability UL 94 at 1.6 mm thickness

class

HB1)

HB1)

HB1)

HB1)

HB1)

HB1)

HB1)

Dielectric constant at 100 Hz

3.4– 3.6

3.4–3.6

3.8– 4.8

3.3–4.0

3.2–4.4

3.5–4.0

3.3

Dielectric loss ·10–4 factor at 100 Hz

20

20

30–60

15–20

20–130

20–30

10

Spec. contact resistance

Ω·m

>1013

>1013

>1013

>1013

>1013

>1013

>1014

Spec. surface resistance

Ω

>1014

>1014

>1014

>1014

>1014

>1014

>1015

Dielectric strength

kV/ mm

250

30

30–35

25–30

25

30–35

30

300– 400

300–400

250– 275

600

600

350– 525

600

Comparative tracking index CTI/A

1)

PBT

PBT + ASA

Water absorption at 23 °C, saturation

%

0.6– 0.7

0.4–0.5

0.4– 0.5

0.5

0.4–0.7

0.35– 0.4

0.5

Moisture absorption at 23 °C/ 50% hum., saturation

%

0.3– 0.35

0.2–0.3

0.2

0.25

0.15–0.2

0.1– 0.15

0.2

Also available as V-0

219

220 3 Plastics Materials Engineering

„„3.20 Polycarbonate (PC) Amorphous engineering thermoplastic Brief Description Polycarbonate is produced by polycondensation of bisphenol A with phosgene.

Processing PC can be processed with all standard methods for thermoplastics. The high melt viscosity requires high processing temperatures, high injection pressures, and low flow path/wall thickness ratios. Any residual moisture in the granulate must be removed in order to avoid degradation by hydrolysis during processing. PC can be bonded and welded using ultrasound or high frequency methods. Properties during Use PC is an impact-resistant, highly transparent material with a low creep tendency that is strong over a wide temperature range. It has good electrical properties and can be stabilized against UV radiation. Application limits are set by the quite high notch sensitivity, the limited chemical resistance, and poor resistance to stress cracking as well as poor sliding friction properties. Polycarbonate with high heat distortion temperature, mixed with less heat distortion resistant ABS or ASA, leads to opaque material blends with medium heat distortion temperature, but better stress cracking resistance and higher impact strength. Fields of Application (Selection) Structural components: transparent applications such as automotive lights, instrument panels, optical lenses, signal lenses, medical applications, “white goods” enclosures, molded parts and electrical housings, large mounting plates and cable distribution cabinets, mobile phones, and other enclosures (PC/ABS blend). Other components: milk containers, microwave dishes, food containers, double-­ webbed plates for terrace roofs and greenhouses, large drinking water containers, data storage devices (CDs and DVDs). Trade Names (Selection) Calibre, Lexan, Makrolon, Novarex, Panlite, Xantar, as well as for PC/ABS or PC/ ASA e. g. Bayblend, Bayblend A, Cycoloy, Luran SC, Pulse, Ryulex, Triax

3.20 Polycarbonate (PC)

Good Advice Polycarbonate is excellently suited for large-area, container-like and housing-like components, but also for complex components. In many ways it is a leading transparent material, which also outshines some semi-crystalline thermoplastics. Properties of Polycarbonates and Their Blends Property

Unit

PC

PCGF30

Density

g/cm3

1.20

Modulus of elasticity

MPa

2300– 2400

Yield stress

MPa

Yield strain Nominal strain at break

PC/ABS

PC/ABS GF20

PC/PBT

PC/PBT GF30

1.42–1.44 1.08–1.17 1.25

1.2–1.26

1.43–1.45

5500– 5800

2000– 2600

6000

2300

7000

55–65

–

40–60

–

50–60

–

%

6–7

–

3–3.5

–

4–5

–

%

>50

–

>50

–

25–>50

–

Stress at 50% strain

MPa

–

–

–

–

–

–

Breaking stress

MPa

–

70

–

75

–

90

Strain at break

%

–

3.5

–

2

–

3

Melting ­temperature

°C

–

–

–

–

–

–

Dimensional stability ­temperature HDT/ A 1.8 MPa

°C

125–135

135–140

90–110

115

70–95

150

Therm. co­­ efficient of expansion, longitudinal (23–55 °C)

10−5/K

6.5–7

2.5–3

7–8.5

3–3.5

8–9

3

Therm. co­­ efficient of expansion, transverse (23–55 °C)

10−5/K

–

Flammability UL 94 at 1.6 mm thickness

class

V-2

V-1

HB

HB

HB

HB

Dielectric constant at 100 Hz

–

2.8–3.2

3.3

3

3.2

3.3

4

5–6

–

221

222 3 Plastics Materials Engineering

Properties of Polycarbonates and Their Blends (continued) Property

Unit

PC

PCGF30

PC/ABS

PC/ABS GF20

PC/PBT

PC/PBT GF30

Dielectric loss factor at 100 Hz

· 10−4

7–20

9–10

30–60

20–30

20–40

30–40

Spec. ­contact resistance

Ω·m

>1014

>1014

>1014

>1014

>1014

>1014

Spec. ­surface resistance

Ω

>1014

>1014

>1014

>1014

>1014

>1014

Dielectric strength

kV/mm 30–75

30–75

24

30

35

35

250–600

200–300

250–500

300–500

Comparative tracking index CTI/A

250–300

150–175

Water % absorption at 23 °C, ­saturation

0.35

0.28–0.30 0.6–0.7

0.4–0.5

0.35

0.25

% Moisture absorption at 23 °C/ 50% hum., saturation

0.2

0.11–0.15 0.2

0.15–0.2

0.15

0.1

„„3.21 Polymethyl Methacrylate (PMMA) Amorphous engineering thermoplastic Brief Description PMMA is produced by block, emulsion, or suspension polymerization of methyl methacrylate.

3.21 Polymethyl Methacrylate (PMMA)

Processing PMMA molding compounds can be injection-molded or extruded. Printing or coating is basically applicable, but due to the poor stress cracking resistance only after careful surface pre-treatment without problems. Metallization is applicable without pre-treatment. Welding is applicable with hot gas, high frequency, and ultrasound. Epoxy resin, polyurethane, and cyanoacrylate adhesives are available for bonding. Properties during Use PMMA is a low-stretch material with high strength, stiffness, heat deflection temperature, and surface hardness (scratch resistance!), and good insulation properties. It shows high optical transparency and gloss with good weathering resistance and is resistant to weak acids and alkalis, non-polar solvents, fats, oils, and water. However, the poor media resistance that causes stress cracking (e. g. with surfactants) must be taken into account. The not very high impact strength can be improved by modification, but the transparency gets lost. Fields of Application (Selection) Structural components: sanitary equipment, glasses, lenses, lighting and instrument panels, telephone keys. Other components: double-webbed panels, stadium glazing, light domes, buttons; also used in casting resins and adhesives. Trade Names (Selection) Acrylite, Altuglas, Corian, Degadur, Lucite, Modar, Oroglas, Perspex, Plexiglas, ­Silacron Good Advice Thanks to its high transparency over a wide wavelength range, PMMA offers an excellent substitute for glass. It is therefore ideally suited for flat and housing-like components, especially with optical functions, as long as neither high impact strength nor chemical resistance are required. Properties of Polymethyl Methacrylate Property

Unit

PMMA molding PMMA semi-­ PMMA-HI compounds finished p ­ roducts elastomer high mol. ­modified

Density

g/cm3

1.17–1.19

1.18–1.19

1.12–1.17

Modulus of elasticity

MPa

3100–3300

3300

600–2400

Yield stress

MPa

–

–

20–60

Yield strain

%

–

–

4.5–5

223

224 3 Plastics Materials Engineering

Properties of Polymethyl Methacrylate (continued) Property

Unit

PMMA molding PMMA semi-­ PMMA-HI compounds finished p ­ roducts elastomer high mol. ­modified

Nominal strain at break

%

–

–

20–>50

Stress at 50% strain

MPa

–

–

–

Breaking stress

MPa

60–75

70–80

–

Strain at break

%

2–6

4.5–5.5

–

Melting temperature

°C

–

–

–

Dimensional stability temperature HDT/A 1.8 MPa

°C

75–105

90–105

65–95

Therm. coefficient of expansion, longitudinal (23–55 °C)

10−5/K

7–8

7

8–11

Therm. coefficient of expansion, transverse (23–55 °C)

10−5/K

–

–

–

Flammability UL 94 at 1.6 mm thickness

class

HB

HB

HB

Dielectric constant at 100 Hz

–

3.5–3.8

3.5–3.8

3.6–4.0

Dielectric loss factor at 100 Hz

· 10

500–600

600

400–600

Spec. contact resistance

Ω·m

>1013

>1013

>1013

Spec. surface resistance

Ω

>1013

>1013

>1013

Dielectric strength

kV/mm

30

ca. 30

30

600

600

600

−4

Comparative tracking index CTI/A Water absorption at 23 °C, ­saturation

%

1.7–2.0

1.7–2.0

1.9–2.0

Moisture absorption at 23 °C/ 50% hum., saturation

%

0.6

0.6

0.5–0.6

„„3.22 Polyoxymethylene (POM) Semi-crystalline engineering thermoplastic Brief Description POM (polyoxymethylene, also polyformaldehyde, polyacetal) is produced by homo­ polymerization (POM-H) or copolymerization (POM-C) of formaldehyde.

3.22 Polyoxymethylene (POM)

Processing All common processing methods for thermoplastics are feasible. Higher molecular types can be extruded, weakly cross-linked even blow-molded. Processing temperatures of > 220 °C should be strictly avoided, as they lead to molecular degradation and the formation of gaseous formaldehyde. More degradation resistant special types are available. Due to its low internal damping, POM cannot be welded using high frequency. Properties during Use Unreinforced POM has quite high tensile strength, stiffness, and, for a semi-crystalline material, high dimensional stability. Good chemical resistance, rather low creep tendency, and late failure under alternating dynamic load are to be particularly emphasized. High surface hardness and a low coefficient of friction are reasons for good sliding and wear behavior even with the sliding partner polyamide. It is low-temperature impact resistant and can be used for short periods up to 150 °C (long term approx. 110 °C). The permeability for gases and vapors is low. No common solvent, not even fuels, can swell or dissolve POM. Homopolymer POM (POM-H) is the stronger, stiffer, low-temperature impact- and abrasion-­resistant POM. Copolymer POM (POM-C), however, dominates the market volume­wise due to its better heat and processing properties. Fields of Application (Selection) Structural components: precision parts for precision mechanics such as gear wheels, levers, bearings, ball shells; pump components carrying hot water and fuel, transport chains, fan wheels, snap locks, ski bindings, zippers, disposable lighters, parts in automotive safety systems such as belt deflectors and belt ­retractors, automotive loudspeaker covers, windscreen washer nozzles, washing armatures, door handles, valves for cisterns, spring elements in e. g. sweetener dispensers. Trade Names (Selection) Homopolymer POM: Delrin, Tenac; copolymer POM: Celcon, Duracon, Hostaform, Kepital, Tenac, Ultraform Good Advice The mixture of mechanical properties, precision, and chemical resistance makes POM very suitable for complex technical components. POM (or PA) should be selected for sliding friction partners subject to higher loads. POM feels “greasy” in the hand.

225

226 3 Plastics Materials Engineering

Properties of Polyoxymethylene Property

Unit

POM-H

POM-H-HI impact modified

POM-­ copoly­ merizate

POMCop.-HI elastomer modified

POMCop.-GF30

Density

g/cm3

1.40–1.42

1.34–1.39

1.39–1.41

1.27–1.39

1.59–1.61

Modulus of ­elasticity

MPa

3000– 3200

1400– 2500

2600–3000

1000–2200

9000–10,000

Yield stress

MPa

60–75

35–55

65–73

20–55

–

Yield strain

%

8–25

20–25

8–12

8–15

–

Nominal strain at break

%

20–>50

>50

15–40

>50

–

Stress at 50% strain

MPa

–

–

–

–

–

Breaking stress

MPa

–

–

–

–

125–130

Strain at break

%

–

–

–

–

3

Melting ­temperature

°C

175

175

164–172

164–172

164–172

Dimensional ­stability ­temperature HDT/A 1.8 MPa

°C

105–115

65–85

95–110

50–90

155–160

Therm. coefficient of expansion, longitudinal (23–55 °C)

10−5/K

11–12

12–13

10–11

13–14

2.5–4

Therm. coefficient of expansion, transverse (23–55 °C)

10−5/K

–

–

–

–

6

Flammability UL 94 at 1.6 mm thickness

class

HB

HB

HB

HB

HB

Dielectric constant at 100 Hz

–

3.5–3.8

3.8–4.7

3.6–4

3.7–4.5

4.0–4.8

Dielectric loss factor at 100 Hz

· 10−4

30–50

70–160

30–50

50–200

40–100

Spec. contact resistance

Ω·m

>1013

>1012–1013

>1013

>1011

>1013

Spec. surface resistance

Ω

>1014

>1014

>1013

>1011–1012

>1013

Dielectric strength

kV/mm 25–35

30–40

35

30–35

40

600

600

600

600

Comparative tracking index CTI/A

600

3.23 Polytetrafluoroethylene (PTFE)

Property

Unit

POM-H

POM-H-HI impact modified

POM-­ copoly­ merizate

POMCop.-HI elastomer modified

POMCop.-GF30

Water absorption at 23 °C, ­saturation

%

0.9–1.4

1.6–2.0

0.7–0.8

0.8–1.2

0.8–0.9

Moisture absorption at 23 °C/ 50% hum., ­saturation

%

0.2–0.3

0.9

0.2–0.3

0.2–0.3

0.15

„„3.23 Polytetrafluoroethylene (PTFE) Semi-crystalline high-performance thermoplastic Brief Description Polytetrafluoroethylene belongs to the fluoropolymers, i. e. the hydrogen of polyethylene is partially or completely replaced by fluorine. PTFE is basically a high-­ molecular polyethylene in which all hydrogen atoms have been replaced by fluorine atoms.

The fluorine atoms are larger and heavier and form a protective “shell” around the carbon chain. In addition, the chemical bond to the carbon is so strong that they are unable to form new compounds. These are the reasons why all fluoropolymers have a very high chemical resistance even at high temperatures (e. g. insoluble up to 300 °C). Processing The melt viscosity of PTFE is too high for injection molding. Semi-finished products and molded parts are produced using various sintering processes. RAM extrusion (powder extrusion) or paste extrusion is used to produce rods and tubes that can later be machined. PTFE can also be applied to metallic or ceramic surfaces as a sliding layer of dispersions.

227

228 3 Plastics Materials Engineering

Properties during Use PTFE is weatherproof even without stabilization, non-flammable, and impact resistant even at low temperatures. It has the highest heat resistance of all engineering plastics as well as good sliding and wear properties. Despite its high density versus other plastics (∼ 2.2 g/cm3), PTFE is neither very stiff nor very strong and can hardly be used for technical parts. The processing contraction is quite high due to the high crystallinity. Fields of Application (Selection) Structural components: seals, bellows, pistons and other machine components. Other components: crucibles, coatings (e. g. for frying pans!); in electrical engineering also substrates for printed circuits; sheets and other semi-finished products for further processing (e. g. slide rails). Trade Names (Selection) Algoflon, Dyneon, Polyflon, Teflon Good Advice In many applications, the poor mechanical properties and poor processability are not compensated by the advantages in temperature and chemical resistance. Thus, PTFE is more of a niche material for the designer who focuses on coatings or semi-finished products. Properties of Fluoropolymers See Table 3.13.

„„3.24 Polyether Ether Ketone (PEEK) Semi-crystalline high-performance thermoplastic Brief Description PEEK is a derivative of aromatic poly(aryl)ether ketones (PAEK). These are semi-­ crystalline polymers whose melt temperature depends on the proportion of ketone groups (CO groups). They are determined by the number and arrangement of the different groups, e. g. two ether groups and one ketone group form the polyether ether ketone PEEK, which, despite its high price, has gained importance for technical components.

3.24 Polyether Ether Ketone (PEEK)

Processing Despite the high melt viscosity, injection molding and extrusion are applicable at high melt temperatures (> 350 °C) and mold temperatures (> 150 °C). Rapid cooling can result in amorphous surface layers, which often crystallize after annealing. Properties during Use PEEK has high strength and stiffness in an extremely wide temperature range versus other plastics. The sliding wear properties and impact strength are also good. Even at high temperatures, it is chemically resistant to many substances (except oxidizing acids), self-extinguishing, and hot steam sterilizable, but only slightly UV-resistant. Unreinforced types are notch-sensitive. Fields of Application (Selection) Structural components: injection molded parts in the automotive, aviation, and electronics industries; chemical pumps, valves, volumetric flow meters. Trade Names (Selection) Ketaspire, Gatone, Vestakeep, Victrex Good Advice This expensive material is only produced by a few manufacturers. However, this is not a comfortable competitive situation because it constantly competes with other high-performance or engineering thermoplastics. As with all high-performance plastics, the requirement profile of the planned application must always be compared with the range of properties of PEEK. Table 3.13 Properties of Polytetrafluoroethylene and Polyether Ether Ketones Property

Unit

PTFE

PEEK

Density

g/cm3

2.13–2.23

1.32

Modulus of elasticity

MPa

400–750

3500

Yield stress

MPa

–

Yield strain

%

–

5

Nominal strain at break

%

>50

>60

Stress at 50% strain

MPa

20–40

Breaking stress

MPa

–

Strain at break

%

–

100

229

230 3 Plastics Materials Engineering

Table 3.13 Properties of Polytetrafluoroethylene and Polyether Ether Ketones (continued) Property

Unit

PTFE

PEEK

Melting temperature

°C

325–335

343

Dimensional stability temperature HDT/A 1.8 MPa

°C

50–60

155

Therm. coefficient of expansion, longitudinal (23–55 °C)

10−5/K

15–20

4.7

Therm. coefficient of expansion, transverse (23–55 °C)

10−5/K

–

Flammability UL 94 at 1.6 mm thickness

class

V-0

V-0

Dielectric constant at 100 Hz

–

2.1

3.2

Dielectric loss factor at 100 Hz

· 10−4

0.5–0.7

Spec. contact resistance

Ω·m

>1016

Spec. surface resistance

Ω

>10

Dielectric strength

kV/mm

40

Comparative tracking index CTI/A

5 · 1014

16

600

Water absorption at 23 °C, saturation

%

 120 °C, glossy molded part surfaces are produced. During injection molding, PPS can be crosslinked to form a thermoset. Heating element welding and ultrasonic welding are applicable, and high-frequency welding is less often applied. Properties during Use Polyphenylene sulfide is hard, solid, stiff, and impact resistant even at high temperatures, but has only low extensibility. It has good electrical properties combined with good chemical resistance to alkalis and non-oxidizing acids (except ­hydrochloric acid). PPS hardly absorbs water and is dimensionally stable. It is inherently flame-retardant and is usually only used glass-fiber reinforced. This results in enormous stiffness values. Fields of Application (Selection) Structural components: motor vehicle engine compartment, micro-precision injection molded parts, encapsulation of computer chips and other sensitive electronic components, lamp and headlight bases, pump housings. Trade Names (Selection) Fortron, Larton, Primef, Ryton, Supec, Tedur, Thoprene Good Advice PPS can be regarded as the “more temperature-resistant PA or PBT”, which unfortunately is also reflected in the price.

3.26 Polyphenylene Sulfide (PPS)

Table 3.14 Properties of Polyphenylene Sulfide, Polyethersulfone, Polysulfone, and Their Blends Property

Unit

PSU

PSU/ ABS

unreinforced

GF30

unreinforced

GF30

Density

g/cm3

1.60–1.67

1.36– 1.37

1.58– 1.6

1.24– 1.25

1.44– 1.45

1.13

Modulus of elasticity

MPa

13,000– 19,000

2600– 2800

9000– 11,000

2500– 2700

7500– 9500

2100

Yield stress

MPa

–

75–80

–

90

–

50

Yield strain

%

–

5–6

–

6–7

–

4

Nominal strain at break

%

–

20–50

–

20–>50

–

>50

Stress at 50% strain

MPa

–

–

–

–

–

–

Breaking stress

MPa

165–200

–

125– 150

–

110– 125

–

Strain at break

%

0.9–1.8

–

1.9–3

–

2–3

–

Melting temperature

°C

275–290

–

–

–

–

–

ca. 260

200– 205

210– 225

170– 175

185

150

2

6.5

Dimensional stability °C temperature HDT/ A 1.8 MPa Therm. coefficient of expansion, longitudinal (23–55 °C)

10−5/K

1.5–2.5

5–5.5

2–3

5.5–6

Therm. coefficient of expansion, transverse (23–55 °C)

10−5/K

3.5–5

–

4–4.5

–

–

Flammability UL 94 at 1.6 mm thickness

class

V-0

V-0

V-0

V-2/HB1) V-0/V-1

HB1)

Dielectric constant at 100 Hz

–

3.9–4.8

3.5–3.7

3.9–4.2

3.2

3.5–3.7

3.1–3.3

Dielectric loss factor at 100 Hz

· 10−4

10–20

10–20

20–30

8–10

10–20

40–50

Spec. contact ­resistance

Ω·m

>1013

>1013

>1013

>1013

>1013

>1013

Spec. surface ­resistance

Ω

>1014

>1013

>1013

>1015

>1015

>1014

Dielectric strength

kV/mm

20–30

20–30

20–30

20–30

30–35

20–30

125–150

100– 150

125– 175

125– 150

150– 175

175

Comparative tracking index CTI/A

1)

PPS-GF40 PES

Water absorption at 23 °C, saturation

%