Silica as Antiblocking Filler

Silicas, which are in competition with carbon blacks as functional fillers for plastics and rubbers, have one significant advantage their white color [62]. The most important role of silicas is as elastomer reinforcements, inducing an increase in the mechanical properties. Other functions, in addition to their use as antiblocks for PE, PP, and other films, are (a) to promote adhesion of rubber to brass-coated wires and textiles, (b) to enhance the thermal and electrical properties of plastics, (c) in accumulator separators, and (d) as rubber chemical carriers. 

As fumed silica enhances several different properties in formulation, such as thickening liquids or improving flowability of powders, it is used in a variety of applications [63], including plastics, rubbers, coatings, cosmetics, adhesives, sealants, inks, and toners. 

The term silica is used for the compound silicon dioxide, Si02, which has several crystalline forms as well as amorphous forms, and may be hydrated or hydroxylated [64]. It is the chemical inertness and durability of silica that has made it very popular in many applications [34]. 

Silica can he precipitated from a sodium sihcate solution by acidifying (by sulfuric or hydrochloric acid) to a pH less than 10 or 11, usually using a lower concentration than in the silica gel preparation descrihed hdow. Typical reactions are 

The product is separated by filtration, washed, dried, and milled. The final product properties, such as porosity, specific surface area, size and shape of particles and 

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