This is an overview of particulate filler production and use.
Fillers are used in polymers for a variety of reasons: cost reduction, improved processing, density control, optical effects, thermal conductivity, control of thermal expansion, electrical properties, magnetic properties, flame retardancy and improved mechanical properties, such as hardness and tear resistance. For example, in cable applications, fillers such as metakaolinite are used to provide better electrical stability while others, such as alumina trihydrate, are used as fire retardants.
Each filler type has different properties and these in turn are influenced by the particle size, shape and surface chemistry. Filler characteristics are discussed from costs to particle morphology. Particle specific surface area and packing are important aspects. Filler loading is also critical and this is discussed. The terminology used in this field is explained and, where appropriate, illustrated.
Practical aspects of filler grading are described. For example, the use of an average particle size on data sheets can be misleading as it may not accurately reflect particle size distribution. Different measuring conditions can also give rise to variations in apparent particle size.
The principal filler types are outlined. These include carbon black, natural mineral fillers and synthetic mineral fillers. The use of clay in nanocomposites is outlined.
Carbon blacks are very important fillers, especially in the rubber industry. A brief description of their preparation and properties is included.
Filler surface modification is an important topic. Most particulate fillers are inorganic and polar, which can give rise to poor compatibility with hydrocarbon polymers and processing problems, among other effects. The main types of modifying agent and their uses are described, from fatty acids to functionalised polymers.
Fillers are also discussed in relation to different polymer types. For example, in flexible PVC, because of the plasticiser, the filler has little effect on processing. This allows relatively high filler levels to be incorporated.
This review is very clearly written by an outstanding expert in this field. Illustrations are included to explain concepts from microscopic filler structure to the effects of fillers on polymer properties.
1. Introduction
2. Filler Characteristics
2.1 Cost
2.2 Chemical Composition
2.3 Specific Gravity
2.4 Hardness
2.5 Thermal Properties
2.6 Optical Properties
2.7 Morphology (Particle Size and Shape)
3. Principal Filler Types
3.1 Mineral Fillers Produced Directly from Natural Sources
3.2 Synthetic Fillers
4. Filler Surface Modification
4.1 Principal Reasons for Using Surface Modifiers
4.2 The Main Types of Modifier
4.3 Other Approaches
4.4 Methods of Using Surface Modifiers
4.5 Treatment Levels
4.6 The Crossover Effect
5. The Use of Fillers in Polymers
5.1 Molecular Weight
5.2 Glass Transition Temperature (Tg)
5.3 Crystallinity
5.4 Second Phase Toughening
5.5 Other Changes in the Polymer Due to the Presence of Filler
5.6 Other Filler Effects
6. Use of Fillers in Different Polymer Types
6.1 Elastomers
6.2 Thermoplastics
6.3 Thermosets
7. Nanocomposites
Roger Rothon is a visiting professor at the Department of Materials Science, Manchester Metropolitan University. He has many years of experience of working with fillers, first in ICI for nearly 20 years and now as an independent consultant. Professor Rothon has worked on many patents and publications on filler production, surface modification and applications. His current projects include developing new routes to flame retardant fillers.
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