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Definition

The characteristics of particulate-filled thermoplastics are determined by four factors: component properties, composition, structure, and interfacial interactions. The most important filler characteristics are particle size, size distribution, specific surface area, and particle shape, while the main matrix property is stiffness. Segregation, aggregation, and the orientation of anisotropic particles determine the structure. Interfacial interactions lead to the formation of a stiff interphase considerably influencing properties. Interactions are changed by surface modification, which must be always system specific and selected according to its goal. Under the effect of external load, inhomogeneous stress distribution develops around heterogeneities, which initiate local micromechanical deformation processes determining the macroscopic properties of the composites.

Introduction

Particulate-filled polymers are used in very large quantities in all kinds of applications. The total consumption of fillers in Europe alone is currently estimated as 4.8 million tons (Table 1) (Rothon 2007). In spite of the overwhelming interest in nanocomposites, biomaterials, and natural fiber-reinforced composites, considerable research and development is done on particulate-filled polymers even today. The reason for the continuing interest in traditional composites lays, among others, in the changed role of particulate fillers. In the early days, fillers were added to the polymer to decrease price. However, the ever increasing technical and aesthetical requirements as well as soaring material and compounding costs require the utilization of all possible advantages of fillers. Fillers increase stiffness and heat deflection

Table 1 Consumption of particulate fillers in Europe in 2007 (Rothon 2007)

Filler

Amount (ton)

Carbon black

2,000,000

Natural calcium carbonate and dolomite

1,500,000

Aluminum hydroxide

250,000

Precipitated silica

225,000

Talc

200,000

Kaolin and clay

200,000

Fumed silica

100,000

Cristobalite, quartz

100,000

Precipitated calcium carbonate

75,000

Calcined clay

50,000

Magnesium hydroxide

20,000

Wollastonite

20,000

Wood flour and fiber

20,000

temperature, decrease shrinkage, and improve the appearance of the composites (Katz and Milevski 1978; Pukanszky 1995). Productivity can be also increased in most thermoplastic processing technologies due to their decreased specific heat and increased heat conductivity (Wong and Bollampally 1999; Weidenfeller et al. 2005). Fillers are very often introduced into the polymer to create new functional properties not possessed by the matrix polymer at all, like flame retardancy or conductivity (Bertelli et al. 1989; Almeras et al. 2003). Another reason for the considerable research activity is that new fillers and reinforcements emerge continuously among other layered silicates (Alexandre and Dubois 2000; Pinnavaia and Beall 2001; Ray and Okamoto 2003), wood flour (Bledzki and Gassan 1999; Bledzki et al. 2002), sepiolite (Bokobza et al. 2004; Bilotti et al. 2008), etc.

The properties of all heterogeneous polymer systems are determined by the same four factors: component properties, composition, structure, and interfacial interactions (Pukanszky 1995, 2000). Although certain fillers and reinforcements including layered silicates, other nanofillers, or natural fibers possess special characteristics, the effect of these four factors is universal and valid for all particulate-filled materials. As a consequence, in this entry we focus our attention on them and discuss the most important theoretical and practical aspects of composite preparation and use accordingly. The general rules of heterogeneous materials apply also for nano- and wood-reinforced composites.

 
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