Electrical properties silica reinforcement

Another important reinforcement application is in silicone rubber. Historically, fumed silicas have played the major role here, but recently precipitated silicas have been developed that possess the characteristics required for this application (6). Compared to conventional precipitated silicas, a product designed for this end use must have higher purity (to impart acceptable electrical properties, because silicone rubbers are often used as insulating materials) and lower water adsorption (to prevent bubbles from forming during extrusion and to impart resistance against moisture pickup). Good dispersibility is also important. 

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. 

The preferred reinforcing filler is high surface area silica, particularly that made by the fume process, which gives the greatest reinforcement, and, because of its high purity, yields excellent electrical insulation properties. Silicas obtained from aqueous solutions impart moderately good reinforcement but, because of the presence of water on the... 

Improved electrical properties - Resistance to hydrolysis and maintenance of a hydrophobic mineral-polymer interfaee is partieularly important to the dielectric properties of composites used in eleetrieal and electronic appHcations. Table 6 shows the ability of epojg silane to eontrol degradation of strength and electrical properties of anovaculite (silica) reinforced epoxy. 

Epoxy, polyester, phenolic and other resins are used as coatings and linings with or without reinforcement. Glass fiber, silica, carbon and many other materials can be used as filters or reinforcement to produce materials with specific properties of strength, flexibility, wear resistance and electrical conductivity. 

More recently nanoscale fillers such as clay platelets, silica, nano-calcium carbonate, titanium dioxide, and carbon nanotube nanoparticles have been used extensively to achieve reinforcement, improve barrier properties, flame retardancy and thermal stability, as well as synthesize electrically conductive composites. In contrast to micron-size fillers, the desired effects can be usually achieved through addihon of very small amounts (a few weight percent) of nanofillers [4]. For example, it has been reported that the addition of 5 wt% of nanoclays to a thermoplastic matrix provides the same degree of reinforcement as 20 wt% of talc [5]. The dispersion and/or exfoliahon of nanofillers have been identified as a critical factor in order to reach optimum performance. Techniques such as filler modification and matrix functionalization have been employed to facilitate the breakup of filler agglomerates and to improve their interactions with the polymeric matrix. 

Both the lime-alumina-borosilicate t3 pe E glass and the silica-alumina-magnesia type S glass are used for reinforcement. The less expensive E glass is preferred where electrical or thermal insulation properties take precedence over strength, whereas the more expensive S glass reinforcement is preferred where strength and modulus requirements dominate. 

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