Contents. Preface. 1 What are plastics? 1. 2 Mechanical properties of polymeric materials 21

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1 Contents Preface.XV 1 What are plastics? Introduction A brief history of the development of plastics What are plastics, polymers and macromolecules? A simple analogy for a polymer chain What factors influence the physical properties of thermoplastic materials? How are polymers made? Polyethylene: the simplest linear polymer chain Step growth polymerisation Ring opening polymerisation Effect of chemical structure on physical properties of polymers Ability of polymer molecules to pack together Copolymers Polymer design for application Polymer Classification Molar mass and molar mass distribution Molar mass averages How does the method of synthesis influence the molar mass distribution? 19 Brief summary of chapter 20 References and additional reading 20 2 Mechanical properties of polymeric materials Introduction Assessment of mechanical properties Stress-strain measurements Volume change and shear The process of simple shear Principal elastic moduli Energy Stretching of a wire Bending a thin beam Cantilever Beam loaded in the middle Poisson's ratio Dynamic modulus Methods of measurement of mechanical properties Tensile testing Clamping of samples Problems with sample clamping Extensometers and measurement of strain Properties measured 33 v Pethrick, R. A. Polymer science and technology for scientists and engineers 2010 digitalisiert durch: IDS Basel Bern

2 vi Contents Strain Ultimate tensile strength Flexural modulus Shear modulus Pendulum impact tests Drop tests Instrumented methods Ductile vs brittle fracture Creep properties How to determine stress relaxation? Fatigue testing Compression testing Modes of deformation in compression testing Other mechanical property measurements in polymer Systems Dynamic mechanical thermal analysis Thermal expansion coefficient measurements Molar mass dependence of glass transition point Influence of chemical structure on the glass transition point Plasticisation Examples of T calculations Other molecular mass effects What is happening at the critical molecular mass? EfFects of chain entanglement on the mechanical properties of thermoplastics polymers Viscoelastic behaviour Maxwell model Kelvin Voigt model More complex modeis Standard linear solid: Zener solid Use of the time-dependent modulus approach What does the experimental data look like for a real polymer system? Other mechanical properties of polymer Systems EfFects of water Environmental stress crazing 62 Brief summary of chapter 63 References and further reading 63 3 Crystallinity and polymer morphology Introduction Crystallography and crystallisation Single crystal growth Habit of polymer crystals Crystal lamella and other morphological features " Melt crystallised lamellae Polymer spherulites Differential scanning calorimetry Polytetrafluororethylene Other types of morphology in semicrystalline polymer Systems 77

3 Contents vii 3.10 Copolymers and phase Separation What are the implications of phase Separation? Alternating, random copolymers and blends of two polymers Block copolymers of incompatible monomers Varying the styrene butadiene ratio in triblock copolymers Why do we need to be able to change the modulus of Polymerie materials? Polyurethanes High-temperature polymers 86 Brief summary of chapter 88 Additional reading 88 Chemistry of polymer processing Introduction Processing thermoplastic materials Thermosets: elastomers Rubbers and vulcanisation Siloxanes Rubber elasticity Thermoset polymers: rigid materials Cure of thermoset resins and time temperature transformation diagrams How do we effectively eure resins? Thermoset eure resins Mechanical properties of the cured resin System Commercial thermoplastic polymers Antioxidants Fillers Carbon black Quartz, silica and clay fillers What is the strueture of a clay? Plasticisers 102 Brief summary of chapter 102 Additional reading 102 Polymer processing: thermoplasticsand thermosets Introduction Processing thermoplastics Rotational moulding Moulding process Theory of the rotational moulding process Powder deposition Powder melting in contact with the heated surface Bubble removal Behaviour of the polymer melt Degradation effects on the melt SoÜdification Moulding cycle 110

4 viii I Contents 5.4 Injection moulding Extruder Feed or mixing zone Compression zone Metering zone Analysis of flow in extruder Drag flow Pressure flow Leakageflow Free-flow condition Flow into a mould or die Extruder volume efficiency Power requirements Location of melt front Twin-screw extruders Use of vented barrel Simplest use of extruder Fabrication of simple, continuous profile materials Polymer-coated products Blow moulding Moulding ofbottles Tensar process Compression moulding Vacuum and compression forming Pressure forming process Injection moulding Plunger-type injection moulding machine Extruders used for injection moulding Selection of plastics for extruder applications Plastisol processes Thermoset processing Hand lay-up process Spray lay-up method Vacuum bagging Resin transfer moulding Resin infusion processes Composite fabrication Autoclave prepreg moulding Filament winding Pultrusion Cure monitoring Repair of composite parts Basic repair process Types of repair Damage assessrnent General physical characteristics of composites 145 Brief summary of chapter 146 References and additional reading 146

5 Contents ix 6 Composites Introduction Classification of composites Why do we need composite materials? Particle-reinforced composites Fibre-reinforced fillers Structures Sandwich structures Prediction of characteristics of filled composite materials Volume fractions Fibre-reinforced composites Fibre Performance Influence of fibre length Influence of fibre orientation and concentration Fibre phase Fabrication Failure Factors influencing the Performance of composites Adhesive properties Mechanical properties Microcracking Fatigue resistance Water ingress Osmosis Adhesive properties of the resin System Uses of plastic composites Elastic behaviour of composite materials Different types of anisotropic materials Monoclinic materials Orthotropic material Unidirectional material Isotropie materials Moduli of elasticity Uniaxial tension or compression Shear modulus Spherical compression or tension Elastic behaviour of composite materials Transverse Youngs modulus Longitudinal Poisson ratio Longitudinal shear modulus Halpin-Tsai equations Orthotropic composites Elasticity relations for an off-axis orientation OfF-axis tensile testing Fracture mechanisms induced in composite materials Unidirectional composite subjeeted to longitudinal tension Fracture mechanisms induced in composite materials Practical composite structures 179

6 x Contents Fracture in laminate structures Failure criteria Maximum stress criterion OfF-axis failure criterion Interactive criteria Hill's criterion 183 Brief summary of chapter 184 References and additional reading 184 Appendix Case studies Introduction Environmental stress Cracking: some case studies Failure in 'sight glasses' High density Polyethylene blow moulded Containers Cracks in communication wiring Failure of polycarbonate electronic housing Environmental stress cracking in Polyethylene Model for environmental stress cracking failure How is resistance to environmental stress cracking assessed? Energy absorption and Vibration damping Which materials are useful for energy damping? Rubber balls and tyres Tyre technology Effect of cross-linking on rubber characteristics Adhesion and adhesives Polymers as adhesives Adhesion mechanisms Examples of specific interactions which can occur in surfaces How does surface tension help to achieve a good bond? Issues which arise during the bonding process Adhesive bond design Stresses in adhesive joints Axially loaded butt joints: tensile measurements Single lap joints Fracture mechanics Service life of an adhesive Joint Toughingof adhesives Polymers in corrosion protection Gas difrusion through polymer matrices Selection of polymeric materials for particular applications 222 Brief summary of chapter 224 References and additional reading Polymer chemistry and synthesis Introduction Condensation polymerisation Degree of polymerisation and molar mass 227

7 Contents xi Molar mass distribution Molar mass control Vinyl polymerisation Initiation Kinetics of vinyl or addition polymerisation Kinetics of free radical polymerisation Experimental measurement of polymerisation kinetics Molecular weight and DP n Inhibition and retardation Determination of absolute rate constants Free radical copolymerisation Kinetic of copolymerisation Mean sequence length Methods of polymerisation Specialist chemical reactions Heterogeneous catalysis Homogeneous catalysis Homogeneous metallocene catalysts Atom transfer radical polymerisation Group transfer polymerisation Cobalt-catalysed polymerisation Polymer degradation Analysis of polymer degradation: thermogravimetric analysis Kinetics of polymer degradation: the random scission model Degradation of Polyethylene General mechanism of radical depolymerisation Depolymerisation versus transfer Degradation of Polyvinylchloride Polyvinyl acetate Polymethylmethacrylate Degradation routes for alkylmethacrylate polymers Degradation of polyethyleneterephthalate Polystyrene Hydrolysis Importance of /Jhydrogen in degradation Polymers and fire Cone calorimeter Experimentally measurable parameters Improved fire retardancy of polymers Flame chemistry Effect of various fillers on limiting oxygen index Stabilisers Final comments on fire issues Use of nanofillers to form nanocomposites Polymer identification Tests to identify an unknown polymer Burning tests 276 Brief summary of chapter 276 References and additional reading 276

8 xii I Contents 9 Polymer physics: modeis of polymer behaviour Introduction Simple Statistical modeis of isolated polymer molecules in Solution Freely jointed random coil model Valence constrained random coil model Rotational isomeric states model Long-range interactions: excluded volume Comparison of the theoretical modeis Dynamic response of polymer Solutions Theories of polymer dynamics Rouse model Zimm model Dynamics of polymer molecules in oscillatory shear Rouse model: mode theory Zimm model: theory Dynamic rheological behaviour of polymers with molar mass above M Relaxation times Stress relaxation and viscosity Rubber elasticity Separation of energetic and entropic terms Unentangled rubber elasticity: affine network model Polymer crystal growth Thermodynamic of polymer molecule in the melt Nucleation Minimum energy conditions and simple theory of growth Nature of chain folding Crystals grown from the melt and lamellae Stacks Location of chain ends Crystallisation kinetics Equilibrium melting temperature General Avrami equation Comparison of experiment with theory Determination of molar mass and size Absolute method of determination Number average molar mass Scattering methods for molar mass determination Light scattering by small particles (size compared to the wavelength oflight) Light scattering from molecules larger than A/ Viscosity measurements Relative methods of molar mass determination: gel permeation chromatography and size exclusion chromatography 318 Brief summary of chapter 321 Additional reading Polymers for the electronics industry Introduction Lithographie materials 325

9 Contents xiii Semiconductor processing Front-end processing Metallayers Photolithography Wafer processing Chemistry of photoresists Applications of lithography Intrinsically conducting polymers Organic light-emitting polymers 340 Brief summary of chapter 342 Additional reading Medical applications of polymers Applications in medical devices Polymers used in devices and therapy Silicone breast implants Hipjoints Heart valve replacement Contact lenses Polymers used in devices and therapy 347 Brief summary of chapter 347 Additional reading Recycling of plastics and environmental issues Introduction Recycling plastics Issues of plastic identification Why do we need to recycle plastics? Methods for recycling plastics Degradation and bioplastics Bioplastics Polyhydroxyalkonates Polylactides and polyglycolides Issues with recycling Feedstock recycling Conclusions 354 Brief summary of chapter 354 Additional reading 354 Index 355

An Introduction to Polymer Physics

An Introduction to Polymer Physics David I. Bower Formerly at the University of Leeds (CAMBRIDGE UNIVERSITY PRESS Preface Acknowledgements xii xv 1 Introduction 1 1.1 Polymers and the scope of the book