Tài liệu Handbook of fillers, fourth edition

Handbook of Fillers 4th Edition George Wypych Toronto 2016 Published by ChemTec Publishing 38 Earswick Drive, Toronto, Ontario M1E 1C6, Canada © ChemTec Publishing, 1993, 2000, 2010, 2016 ISBN 978-1-895198-91-1 (bound) ISBN 978-1-927885-10-9 (epub) Cover design: Anita Wypych All rights reserved. No part of this publication may be reproduced, stored or transmitted in any form or by any means without written permission of copyright owner. No responsibility is assumed by the Author and the Publisher for any injury or/and damage to persons or properties as a matter of products liability, negligence, use, or operation of any methods, product ideas, or instructions published or suggested in this book. Library and Archives Canada Cataloguing in Publication Wypych, George, author Handbook of fillers / George Wypych. -- Fourth edition. Includes bibliographical references and index. Issued in print and electronic formats ISBN 978-1-895198-91-1 (bound).--ISBN 978-1-927885-10-9 (epub) 1. Fillers (Materials). Fillers (Materials)--Handbooks, manuals, etc. I. Title. TP1142.W96 2016 668.4'11 C2015-907779-6 C2015-907780-X Printed in Australia, United Kingdom and United States of America Table of Contents iii Table of Contents 1 Introduction 1.1 Expectations from fillers 1.2 Typical filler properties 1.3 Definitions 1.4 Classification 1.5 Markets and trends References 2 2.1 2.1.1 2.1.2 2.1.3 2.1.4 2.1.5 2.1.6 2.1.7 2.1.8 2.1.9 2.1.10 2.1.11 2.1.12 2.1.13 2.1.14 2.1.15 2.1.16 2.1.17 2.1.18 2.1.19 2.1.20 2.1.21 2.1.22 2.1.23 2.1.24 2.1.25 2.1.26 2.1.27 Fillers - Origin, Chemical Composition, Properties, and Morphology Particulate fillers Aluminum flakes and powders Aluminum borate whiskers Aluminum nitride Aluminum oxide Aluminum trihydroxide Anthracite Antimonate of sodium Antimony pentoxide Antimony trioxide Ammonium octamolybdate Apatite Ash, fly Attapulgite Barium metaborate Barium sulfate Barium & strontium sulfates Barium titanate Bentonite Beryllium oxide Boron nitride Calcium carbonate Calcium fluoride Calcium hydroxide Calcium phosphate Calcium silicate Calcium sulfate Carbon black 1 1 5 6 9 10 11 13 13 13 18 19 20 23 27 29 30 32 34 36 37 39 42 43 48 49 51 54 55 58 71 72 73 75 76 78 iv 2.1.28 2.1.29 2.1.30 2.1.31 2.1.32 2.1.33 2.1.34 2.1.35 2.1.36 2.1.37 2.1.38 2.1.39 2.1.40 2.1.41 2.1.42 2.1.43 2.1.44 2.1.45 2.1.46 2.1.47 2.1.48 2.1.49 2.1.50 2.1.51 2.1.52 2.1.53 2.1.54 2.1.55 2.1.56 2.1.57 2.1.58 2.1.59 2.1.60 2.1.61 2.1.62 2.1.63 2.1.64 2.1.65 2.1.66 2.1.67 2.1.68 2.1.69 2.1.70 Table of Contents Carbonyl iron powder Cellulose particles Ceramic beads Chitosan Clamshell powder Clay Cobalt powder Copper Corn cob powder Cristobalite Diatomaceous earth Dolomite Eggshell filler Ferrites Feldspar Gadolinium oxide Glass beads Gold Graphene Graphene oxide Graphite Ground tire powder Halloysite Huntite Hydrous calcium silicate Illite Iron Iron oxide Kaolin Lead oxide Lithopone Magnesium oxide Magnesium hydroxide Magnetite Metal-containing conductive materials Mica Molybdenum Molybdenum disulfide Molybdenum oxide Nanofillers Nickel Nickel oxide Nickel zinc ferrite 94 96 97 99 100 101 103 104 106 107 109 113 114 115 117 119 120 126 127 129 131 136 137 139 140 142 143 144 146 151 152 153 154 157 159 163 167 168 169 170 179 182 183 Table of Contents v 2.1.71 Nutshell powder 2.1.72 Perlite 2.1.73 Polymeric fillers 2.1.74 Potassium hexatitanate whisker 2.1.75 Pumice 2.1.76 Pyrophyllite 2.1.77 Rubber particles 2.1.78 Sepiolite 2.1.79 Silica 2.1.79.1 Fumed silica 2.1.79.2 Fused silica 2.1.79.3 Precipitated silica 2.1.79.4 Quartz (Tripoli) 2.1.79.5 Sand 2.1.79.6 Silica gel 2.1.80 Silicon carbide 2.1.81 Silicon nitride 2.1.82 Silver powder and flakes 2.1.83 Slate flour 2.1.84 Talc 2.1.85 Titanium dioxide 2.1.86 Tungsten 2.1.87 Vermiculite 2.1.88 Wollastonite 2.1.89 Wood flour and similar materials 2.1.90 Zeolites 2.1.91 Zinc borate 2.1.92 Zinc oxide 2.1.93 Zinc stannate 2.1.94 Zinc sulfide 2.2 Fibers 2.2.1 Aramid fibers 2.2.2 Carbon fibers 2.2.3 Carbon nanotubes 2.2.4 Cellulose fibers 2.2.5 Cellulose nanofibrils 2.2.6 Glass fibers 2.2.5 Other fibers 184 185 186 191 192 193 194 196 198 199 204 205 207 209 210 213 214 215 217 218 223 232 233 234 238 240 242 244 247 248 250 250 252 256 260 263 264 266 3 3.1 3.2 3.3 267 267 269 271 Fillers Transportation, Storage, and Processing Filler packaging External transportation Filler receiving vi Table of Contents 3.4 3.5 3.6 3.7 3.8 3.9 3.10 3.11 Storage In-plant conveying Semi-bulk unloading systems Bag handling equipment Blending Feeding Drying Dispersion References 272 274 278 279 280 281 283 285 291 4 4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 4.9 4.10 4.11 4.12 4.13 4.14 4.15 4.16 4.17 4.18 4.19 4.20 4.21 4.22 4.23 4.24 4.25 4.26 4.27 4.28 4.29 4.30 4.31 4.32 Quality Control of Fillers Absorption coefficient Acidity or alkalinity of water extract Ash content Brightness Coarse particles Color CTAB surface area Density Electrical properties Extractables Fines content Heating loss Heat stability Hegman fineness Hiding power Iodine absorption number Lightening power of white pigments Loss on ignition Mechanical and related properties Oil absorption Particle size Pellet strength pH Resistance to light Resistivity of aqueous extract Sieve residue Soluble matter Specific surface area Sulfur content Tamped volume Tinting strength Volatile matter 293 293 293 293 294 294 294 294 295 295 295 295 296 296 296 296 296 296 297 297 297 298 298 298 298 298 298 299 299 299 299 299 300 Table of Contents vii 4.33 4.34 Water content Water-soluble sulfates, chlorides & nitrates References 300 300 300 5 5.1 5.2 5.3 5.4 5.5 5.6 5.7 5.8 5.9 5.10 5.11 5.12 5.13 5.14 5.15 5.16 5.17 5.18 5.19 5.20 5.21 5.22 5.23 5.24 5.25 5.26 5.27 5.28 5.29 5.30 5.31 5.32 5.33 5.34 5.35 5.36 5.37 Physical Properties of Fillers and Filled Materials Density Particle size Particle size distribution Particle shape Particle surface morphology and roughness Specific surface area Porosity Particle-particle interaction and spacing Agglomerates Aggregates and structure Flocculation and sedimentation Aspect ratio Packing volume pH Zeta-potential Surface energy Moisture Absorption of liquids and swelling Permeability and barrier properties Oil absorption Hydrophilic/hydrophobic properties Optical properties Refractive index Friction properties Hardness Intumescent properties Thermal conductivity Thermal expansion coefficient Thermal degradation Melting temperature Glass transition temperature Electrical properties Relative permittivity Electrical percolation EMI shielding Magnetic properties Shape memory References 303 303 306 309 313 314 316 317 318 320 322 324 327 328 332 332 334 338 340 342 343 344 345 347 348 349 351 352 353 354 354 355 355 359 359 360 361 362 363 viii Table of Contents 6 6.1 6.2 6.3 6.4 6.5 6.6 6.7 6.8 6.9 6.10 6.11 Chemical Properties of Fillers & Filled Materials Reactivity Chemical groups on the filler surface Filler surface modification Filler modification and material properties Resistance to various chemicals Cure in fillers presence Polymerization in fillers presence Grafting Crosslink density Reaction kinetics Molecular mobility References 373 373 376 379 392 396 398 402 403 404 406 407 409 7 7.1 7.2 7.3 7.4 7.5 7.6 7.7 7.8 7.9 7.10 7.11 7.12 7.13 7.14 7.15 7.15 Organization of Interface and Matrix Containing Fillers Particle distribution in matrix Orientation of filler particles in a matrix Distance between particles Voids Matrix-filler interaction Chemical interactions Other interactions Interphase organization Interfacial adhesion Interphase thickness Filler-chain links Chain dynamics Bound rubber Debonding Mechanisms of reinforcement Benefits of organization on molecular level References 415 415 420 426 427 428 429 432 436 439 441 443 444 445 451 454 459 461 8 The Effect of Fillers on the Mechanical Properties of Filled Materials Tensile strength and elongation Tensile yield stress Mullins’ effect Elastic modulus Flexural strength and modulus Impact resistance Hardness Tear strength 467 467 474 479 479 482 484 488 490 8.1 8.2 8.3 8.4 8.5 8.6 8.7 8.8 Table of Contents ix 8.9 8.10 8.11 8.12 8.13 8.14 8.15 8.16 8.17 8.18 8.19 8.20 8.21 8.22 8.23 8.24 Compressive strength Fracture resistance Wear Friction Abrasion Scratch resistance Fatigue Failure Adhesion Thermal deformation Shrinkage Warpage Compression set Load transfer Residual stress Creep References 491 492 499 501 503 504 506 510 512 514 515 517 518 519 521 522 523 9 9.1 9.2 9.3 9.4 9.5 9.6 9.7 9.8 9.9 9.10 9.11 The Effect of Fillers on Rheological Properties of Filled Materials Viscosity Flow Flow induced filler particle orientation Torque Viscoelasticity Dynamic mechanical behavior Complex viscosity Shear viscosity Elongational viscosity Melt rheology Yield value References 533 533 535 537 539 540 542 543 545 547 548 548 549 10 10.1 10.2 10.3 10.4 10.5 10.6 10.7 Morphology of Filled Systems Crystallinity Crystallization behavior Nucleation Crystal size Spherulites Transcrystallinity Orientation References 553 553 555 558 560 561 565 566 567 x Table of Contents 11 11.1 11.2 11.3 11.4 11.5 11.6 Effect of Fillers on Exposure to Different Environments Irradiation UV radiation Temperature Liquids and vapors Stabilization Degradable materials References 571 571 573 579 581 583 584 585 12 12.1 12.2 12.3 12.4 12.5 12.6 12.7 12.8 12.9 Flammability of Filled Materials Definitions Limiting oxygen index Ignition and flame spread rate Heat transmission rate Decomposition and combustion Emission of gaseous components Smoke Char Recycling References 589 589 590 591 593 595 597 597 599 599 602 13 Influence of Fillers on Performance of Other Additives and Vice Versa Adhesion promoters Antistatics Blowing agents Catalysts Compatibilizers Coupling agents Dispersing agents and surface active agents Flame retardants Impact modifiers UV stabilizers Other additives References 605 605 607 608 609 610 613 615 617 618 619 622 623 Testing Methods in Filled Systems Physical methods Atomic force microscopy Autoignition test Bound rubber Char formation Cone calorimetry 627 627 627 628 629 629 630 13.1 13.2 13.3 13.4 13.5 13.6 13.7 13.8 13.9 13.10 13.11 14 14.1 14.1.1 14.1.2 14.1.3 14.1.4 14.1.5 Table of Contents xi 14.1.6 14.1.7 14.1.8 14.1.9 14.1.10 14.1.11 14.1.12 14.1.13 14.1.14 14.1.15 14.1.16 14.1.17 14.1.18 14.1.19 14.1.20 14.1.21 14.1.22 14.1.23 14.1.24 14.1.25 14.1.26 14.1.27 14.2 14.2.1 14.2.2 14.2.3 14.2.4 14.2.5 14.2.6 14.2.7 14.2.8 14.2.9 Contact angle Dispersing agent requirement Dispersion tests Dripping test Dynamic mechanical analysis Electric constants determination Electron microscopy Fiber orientation Flame propagation test Glow wire test Image analysis Limiting oxygen index Magnetic properties Optical microscopy Particle size analysis Radiant panel test Rate of combustion Scanning acoustic microscopy Smoke chamber Sonic methods Specific surface area Thermal analysis Chemical and instrumental analysis Electron spin resonance Electron spectroscopy for chemical analysis Inverse gas chromatography Gas chromatography Gel content Infrared and Raman spectroscopy Nuclear magnetic resonance UV and visible spectroscopy X-ray analysis References 631 633 633 634 634 635 637 638 638 640 640 642 642 643 644 645 645 645 646 646 648 648 649 649 650 651 653 654 654 656 658 658 659 15 15.1 15.2 15.3 15.4 15.5 15.6 15.7 15.8 Fillers in Commercial Polymers Acrylics Acrylonitrile-butadiene-styrene copolymer Acrylonitrile-styrene-acrylate Aliphatic polyketone Alkyd resins Bismaleimide Cellulose acetate Chitosan 665 665 668 669 670 671 671 672 672 xii 15.9 15.10 15.11 15.12 15.13 15.14 15.15 15.16 15.17 15.18 15.19 15.20 15.21 15.22 15.23 15.24 15.25 15.26 15.27 15.28 15.29 15.30 15.31 15.32 15.33 15.34 15.35 15.36 15.37 15.38 15.39 15.40 15.41 15.42 15.43 15.44 15.45 15.46 15.47 15.48 15.49 15.50 15.51 Table of Contents Elastomers, TPO Epoxy resins Ethylene vinyl acetate copolymer, EVA Ethylene vinyl alcohol copolymer, EVOH Ethylene ethyl acetate copolymer, EEA Ethylene propylene copolymers, EPR & EPDM Ionomers Liquid crystalline polymers, LCP Perfluoroalkoxy resin, PFA Phenolic resins Poly(acrylic acid), PAA Polyacylonitrile, PAN Polyamides, PA Polyamideimide, PAI Polyamines Polyaniline, PANI Polyaryletherketone, PAEK Poly(butylene succinate), PBS Poly(butylene terephthalate), PBT Polycaprolactone, PCL Polycarbonate, PC Polydicyclopentadiene Polyetheretherketone, PEEK Polyetherimide, PEI Polyethersulfone, PES Polyethylene, PE Polyethylene, chlorinated, CPE Polyethylene, chlorosulfonated, CSM Poly(ethylene oxide), PEO & PEG Poly(ethylene terephthalate), PET Polyimide, PI Poly(lactic acid) Polymethylmethacrylate, PMMA Polyoxymethylene, POM Poly(phenylene ether), PPO Poly(phenylene sulfide), PPS Polypropylene, PP Polypyrrole Polystyrene & high impact, PS & HIPS Polysulfide Polysulfone, PSO Polytetrafluoroethylene, PTFE Polyurethanes, PU & TPU 673 674 677 678 678 679 681 681 682 682 684 684 685 688 689 689 690 691 691 693 693 695 696 697 697 698 702 703 703 705 706 708 709 710 711 711 712 717 718 719 719 720 721 Table of Contents xiii 15.52 15.53 15.54 15.55 15.56 15.56.1 15.56.2 15.56.3 15.56.4 15.56.5 15.56.6 15.56.7 15.56.8 15.57 15.58 15.59 15.60 15.61 Poly(vinyl acetate), PVA Poly(vinyl alcohol), PVA Poly(vinyl butyral), PVB Poly(vinyl chloride), PVC Rubbers Natural rubber, NR Nitrile rubber, NBR Polybutadiene rubber, BR Butyl rubber, HR Polychloroprene Polyisobutylene, PIB Polyisoprene, IR Styrene-butadiene rubber, SBR Silicones, SI Styrene-acrylonitrile copolymer, SAN Tetrafluoroethylene-perfluoropropylene Unsaturated polyesters Vinylidene-fluoride terpolymer, PVDF References 723 724 724 725 727 728 730 732 732 733 734 735 735 737 739 739 740 741 742 16 16.1 16.2 16.3 16.4 Fillers in Materials Combinations Blends, alloys and interpenetrating networks Composites Nanocomposites Laminates References 763 763 772 776 781 783 17 Formulation with Fillers References 787 792 18 18.1 18.2 18.3 18.4 18.5 18.6 18.7 18.8 18.9 18.10 18.11 18.12 Fillers in Different Processing Methods Blow molding Calendering and hot-melt coating Compression molding Dip coating Dispersion Extrusion Foaming Injection molding Knife coating Mixing Pultrusion Reaction injection molding 793 793 794 795 797 798 800 803 804 807 808 811 811 xiv Table of Contents 18.13 18.14 18.15 18.16 18.17 18.18 Resin transfer molding Rotational molding Sheet molding Spinning Thermoforming Welding and machining References 812 813 814 815 816 816 817 19 19.1 19.2 19.3 19.4 19.5 19.6 19.7 19.8 19.9 19.10 19.11 19.12 19.13 19.14 19.15 19.16 19.17 19.18 19.19 19.20 19.21 19.22 19.23 19.24 19.25 19.26 19.27 19.28 19.29 19.30 19.31 19.32 19.33 19.34 Fillers in Different Products Adhesives Agriculture Aerospace Appliances Automotive materials Bottles and containers Building components Business machines Cable and wire Coated fabrics Coatings and paints Cosmetics and pharmaceutical products Dental restorative composites Electrical and electronic materials Electromagnetic interference shielding Fibers Film Foam Food and feed Friction materials Geosynthetics Hoses and pipes Magnetic devices Medical applications Membranes Noise dampening Optical devices Paper Radiation shields Railway transportation Roofing Telecommunication Tires Sealants 823 823 826 827 827 828 830 830 831 831 832 833 837 839 841 842 844 845 847 847 848 848 849 849 850 853 853 854 855 858 858 859 859 860 862 Table of Contents xv 19.35 19.36 19.37 19.38 Siding Sports equipment Waterproofing Windows References 864 865 865 866 866 20 Hazards in Filler Use References 873 880 Index 881 1 Introduction This introduction: • Lists the properties of materials which are influenced by fillers • Lists typical properties of fillers • Provides definition of the term “filler” • Defines how fillers function in various applications • Suggests how fillers may be classified • Discusses the markets for fillers and the emerging trends in filler use The introduction will define the scope of the book and provide a brief overview of each chapter. It is our intention to show how an understanding of the diverse functions of fillers in materials can lead to a well designed material formulation. 1.1 EXPECTATIONS FROM FILLERS What caused fillers to be added to materials in the first place was probably the quest for lower costs. Fillers were inexpensive, thus using them would make the material cheaper. We do not know who the inventor of the idea was but it was probably not one, but many people in many different places. However, as the following discussion shows, cost reduction is no longer the only, or even the most important, consideration for using fillers in formulating composite materials. These examples which follow list attributes of materials to the formulators various objectives. Table 1.1. Attributes of fillers Cost reduction Cost reduction depends on the relative cost of the polymer and the filler. Polymer prices in May 2015 were approximately:1 US$/kg US$/l ABS 2.02 2.10 HDPE 1.51 1.43 PET 2.00 2.76 PP 1.43 1.35 LLDPE 1.54 1.49 PVC 2.55 3.31 2 Introduction Table 1.1. Attributes of fillers Cost reduction Filler prices depend greatly on the particle size but also on surface preparation, shape, particle size distribution, purity, and many other factors. Here are approximate prices of selected fillers (August, 2006):2 US$/kg US$/l calcium carbonate (ground) 0.06 0.17 calcium carbonate (precipitated) 0.26-0.95 0.73-2.66 carbon black 1.10 1.98 carbon nanotubes 250-75,000 450-135,000 kaolin 0.28 0.73 magnesium hydroxide 1.00 2.40 silver powder 892-1225 9,366-12,863 titanium dioxide 2.61 11.06 zinc borate 2.64-4.84 7.39-13.55 If we consider only cost, it is the cost per unit volume that must be compared. The table shows that only the use of large particle size calcium carbonate ground (very crude products) can potentially contribute to savings in the manufactured cost of materials made from commodity polymers. At the same time, these fillers decrease many mechanical properties of the material so the cost reduction is achieved at the expense of performance. Medium particle sized fillers are less attractive economically because costs of processing, inventory and transportation are higher. This shows that there must be other motives to compound polymers with fillers. These follow. Material density3 Fillers can be used either to increase or to decrease the density of a product. Because the density of a filler can be as high as 19.35 g/cm3 or as low as 0.03 g/cm3, there may be a large difference between the density of the filler and the polymer. Thus a broad range of product densities can be obtained. There are high density products (above 3 g/ cm3) required in materials used in appliances or casings for electronic devices. More common are densities below 2 g/cm3, glass fiber filled composites being a typical example. The effective density of the polymer can be decreased by filling a foam with hollow polymer spheres. In this example, the density of a material can be lower than 0.1 g/cm3. Optical properties4-7 Optical properties of compounded materials depend on the physical characteristics of the filler and the other major ingredients including the polymer. Most important is the relative refractive index of the two ingredients. Depending on how they match, one can obtain clear or opaque materials. Light absorption by the non-polymer ingredients is essential in preventing UV degradation. Some fillers (e.g., TiO2, ZnO or talc) effectively absorb light but small particle size fillers (especially nanofillers) do not absorb effectively in visible region. Aluminum trihydroxide in UV curable polyurethanes is noteworthy in that it accelerates the curing process because it is transparent to UV light. Calcinated clay as a filler in greenhouse film at a 10% level drastically reduces infrared absorption during the day and heat loss during the night. This application of physical principles has been an important factor in increasing the productivity of greenhouses. Specially designed fillers, added in small quantities, can be used as product markers because of their peculiarities in absorption of radiation. Leafy fillers can be used to reflect radiation which decreases temperature behind a membrane (e.g., roofing) or creates special effects (e.g., automotive paints) 1.1 Expectations from fillers 3 Table 1.1. Attributes of fillers Color Fillers frequently cause problems in color matching and must be accounted for in product color design. Many fillers have a distinctive color which is useful in material coloring. Some fillers (e.g., barium sulfate, zinc oxide, or lithopone) help to reduce white pigment level due to their lightening abilities. Recently metal powders have been used in combination with pigments to make the composite appear metal like. Surface properties8-12 For hundreds of years sticky surfaces have been dusted with powder (e.g., talc) to keep them separated. Talc is broadly used in cable and profile extrusion to obtain a smooth surface. Similarly, in injection molding, the application of aluminum trihydroxide gives a better surface finish. Talc, CaCO3, and diatomite provide anti-blocking properties. Graphite and other fillers decrease the coefficient of friction of materials. PTFE, graphite and MoS2 permit production of self-lubricating parts. Here, PTFE, a polymer in a powder form, acts as a filler in other polymers. Matte surfaced paint is obtained by the addition of silica fillers. Also surface properties of fillers determine many properties of materials such as interfacial adhesion, reinforcement, crystallinity, and compatibility but also thermal stability of some elastomers. Product shape7,13,14 Fillers reduce shrinkage of polymer foams. Mica and glass fiber reduce warpage and increase the heat distortion temperature. Intumescent fillers increase in volume rapidly as they degrade thermally expanding the material and blocking fire spread. Thermal properties15 Fillers may decrease thermal conductivity. The best insulation properties of composites are obtained with hollow spherical particles as a filler. Conversely, metal powders and other thermally conductive materials substantially increase the dissipation of thermal energy. Electrical properties16 Volume resistivity, static dissipation and other electrical properties can be influenced by the choice of filler. Conductive fillers in powder or fiber form, metal coated plastics and metal coated ceramics will increase the conductivity. Many fillers increase the electric resistivity. These are used in electric cable insulations. Ionic conductivity can be modified by silica fillers. Magnetic properties17 Ferrites induce ferromagnetic properties and are used to make plastic magnets. Permeability8 Gas and liquid permeability are influenced by the choice of filler. The platelet structure of mica or talc as a filler in paints and plastics decreases the transmission of gases and liquids. Mechanical properties18,19 All mechanical properties are affected by fillers. Filler combinations may be selected to optimize a variety of mechanical properties. Fillers reinforce and provide abrasion resistance. Chemical reactivity12,19 Many fillers can be used to influence chemical reactions occurring in their presence. The reaction rate can be decreased or increased. Fillers such as ZnO will react with UV degradation products in PE to limit damage. The pot-life of curing mixtures can be increased. Cure rates can be slowed, exothermic effects can be controlled, incompatible polymers can be blended and molecular mobility reduced. Burning properties of materials can be modified by fillers and some toxic gases normally emitted can be absorbed and reacted. 4 Introduction Table 1.1. Attributes of fillers Rheology8,11 The rheology of many industrial products depends on the filler addition. Examples include sealants, toothpastes, cosmetics, hotmelts, papers, paints, etc. Normally, additions of fillers increase the viscosity and contribute to non-Newtonian flow characteristics, but there are also combinations such as filler mixtures and specially designed glass beads which either reduce the viscosity or do not affect it. Morphology13,21 Polymer crystallization and structure are affected by fillers. They may increase or decrease the nucleation rate (and thus the crystallization rate). An increase in the nucleation rate is observed in PET in the presence of mica or polypropylene in the presence of talc. Fillers, especially fibers, may also decrease the mechanical properties of filled materials because of their effect on transcrystallinity. The polymer structure at the interface with fillers is different than in the bulk. Material durability4,7,14,20,22-24 Fillers which screen radiation and react with degrading molecules contribute to material durability. The opposite effects may also occur if fillers participate in photochemical reactions which decrease photostability. Some fillers are used for their absorption of highly penetrating radiation such as nuclear radiation or filler is used in neutron shielding. Thermal degradation can be either decreased and increased by the presence of fillers. Fillers such as borates and montmorillonite also protect materials from biodegradation. The addition of starch generates numerous mechanisms which increase biodegradability by supplying nutrients and also participate in initiation of thermal and UV degradation which reduces chain length and permits biological conversions. Environmental impact25-28 Fillers contribute to fire retardancy by suppressing fire, increasing autoignition temperature, decreasing smoke formation, increasing char formation, reducing heat transmission rate, preventing dripping, etc. Fillers are used in combinations to balance properties. For example, antimony trioxide increases smoke whereas Al(OH)3 and Mg(OH)2 reduce it. It is possible to make paper fire retardant through the proper selection of fillers. Plastics recycling can be improved by incorporating fillers which reduce thermodegradation (stabilize some polymers). Complex mixtures of polymer waste are more easily blended if compounded with fillers. Performance of other additives Fillers are instrumental in improving the performance of other additives. Antistatics, blowing agents, catalysts, compatibilizers, coupling agents, organic flame retardants, impact modifiers, rheology modifiers, thermal and UV stabilizers are all influenced by a fillers presence. Health & safety Fillers are probably the least hazardous components among additives. The major exception here is asbestos which is seldom, if ever, used now. Other fillers which may be hazardous are being carefully investigated although disputes still occur when data is incomplete or questionable. Fillers produced today are manufactured by sophisticated processes. There are numerous examples of surface modification which changes a fillers properties. Numerous nanofillers are now synthesized as well as fillers having specific morphology as demanded by properties of materials into which they are incorporated. Preparation of materials for specific medical applications can be carried out using template polymerization.29 This has become a well established discipline which has contributed to the understanding of poly- 1.2 Typical filler properties 5 mer structure. Here, the polymer is produced on organic and inorganic (e.g., fillers) templates. By choosing the template structure, polymer properties can be tailored to requirements. Natural biological materials are formed in this manner and synthetic materials can be formed in a similar manner. Filler properties can also be tailored by synthesizing fillers in the presence of other materials. This is used in medical applications where the filler becomes compatible with its surroundings as it forms in body fluids. Artificial bone materials can thus be formed with surface characteristics acceptable to (compatible with) the body’s environment. These techniques are at the most advanced levels of engineering and design in filler synthesis. In summary, • Fillers usually do not reduce the cost of material manufacturing • Fillers are not inert materials added to fill space (if they are used in this way, they likely degrade properties of the material) • Fillers can be modified and tailored to any application • Fillers modify practically all properties of the material and influence the design, manufacture, and use • Plastics performance and the performance of other materials are highly influenced by fillers • The plastics applications base has expanded greatly as the use of fillers has increased 1.2 TYPICAL FILLER PROPERTIES We have outlined the product performance characteristics of fillers. This leads us to an identification of filler properties which permit comparison and evaluation of different fillers. When we go on to develop a definition of fillers in Section 1.3, this list will help to make the definition inclusive yet precise. It will also assist in the classification of fillers discussed in Section 1.4. Table 1.2. Range of fillers properties Physical state All materials discussed are solids but they might be available in a predispersed state (water slurries) Chemical composition May be inorganic or organic and of an established chemical composition. May also be a single element, natural products, mixtures of different materials in unknown proportions (waste and recycled materials), or materials of a proprietary composition Particle shape30 Spherical, cubical, irregular, dendritic, block, plate, flake, fiber, mixtures of different shapes Particle size Range from a few nanometers to tens of millimeters (nanofillers to fibers) Aspect ratio30 1 (spherical or cubical) to 1,600 (fibers) Particle size distribution Mono disperse, designed mixture of sizes, Gaussian distribution, irregular distribution