Fillers silicones

Sil-Cell . [Silbrico] Glass miciocellular filler (silicon dioxide, aluminum oxide, potassium oxide) resin extender. 

TGA traces for silicone rubber and its composites with 8.1 vol.% of filler (---) silicone rubber without filler (-) silicone rubber/organo-MMT... 

Moisture-Curing Silicones. The formulation of moisture-curing sHicones includes a sHicone polymer, filler, a moisture-reactive cross-linker, and sometimes a catalyst. The most common sHicone polymer used in sealant formulations is an alternating sHicon—oxygen backbone with methyl groups attached to the sHicon such as the sHicone polymer (1). 

Silicone Heat-Cured Rubber. Sihcone elastomers are made by vulcanising high molecular weight (>5 x 10 mol wt) linear polydimethylsiloxane polymer, often called gum. Fillers are used in these formulations to increase strength through reinforcement. Extending fillers and various additives, eg, antioxidants, adhesion promoters, and pigments, can be used to obtain certain properties (59,357,364). 

Silicone foam thus formed has an open ceU stmcture and is a relatively poor insulating material. Cell size can be controlled by the selection of fillers, which serve as bubble nucleating sites. The addition of quartz as a filler gready improves the flame retardancy of the foam char yields of >65% can be achieved. Because of its excellent dammabiUty characteristics, siUcone foam is used in building and constmction fire-stop systems and as pipe insulation in power plants. Typical physical properties of siUcone foam are Hsted in Table 10. 

Greases may be made by blending the polymer with an inert filler such as a fine silica, carbon black or metallic soap. The silicone-silica greases are used primarily as electrical greases for such applications as aircraft and car ignition systems. 

Room temperature vulcanising silicone rubbers (r. t. v. rubbers) have proved of considerable value where elaborate processing equipment is not available. These rubbers are low molecular weight silicones with reactive end-groups and loaded with reinforcing fillers. The RTV silicone rubbers may be classified into two types ... 

Fumed silicas (Si02). Fumed silicas are common fillers in polychloroprene [40], natural rubber and styrene-butadiene rubber base adhesives. Fumed silicas are widely used as filler in several polymeric systems to which it confers thixotropy, sag resistance, particle suspension, reinforcement, gloss reduction and flow enhancement. Fumed silica is obtained by gas reaction between metallic silicon and dry HCl to rend silica tetrachloride (SiCU). SiC is mixed with hydrogen and air in a burner (1800°C) where fumed silica is formed ... 

Fillers can also be used to promote or enhance the thermal stability of the silicone adhesive. Normal silicone systems can withstand exposure to temperatures of 200 C for long hours without degradation. However, in some applications the silicone must withstand exposure to temperatures of 280 C. This can be achieved by adding thermal stabilizers to the adhesive formulations. These are mainly composed of metal oxides such as iron oxide and cerium oxide, copper organic complexes, or carbon black. The mechanisms by which the thermal stabilization occurs are discussed in terms of radical chemistry. 

Another advantage of the addition of inorganic filler is the significant increase in density of the silicone, which helps the dispensing process. The use of fillers also reduces the total cost of the product, as the expensive high performance silicone does not require 100% volume occupancy to fulfil its function. 

Between 250 and 450°F (121 and 232°C), plastics used include glass or mineral-filled phenolics, melamines, alkyds, silicones, nylons, polyphenylene oxides, polysulfones, polycarbonates, methylpentenes, fluorocarbons, polypropylenes, and diallyl phthalates. The addition of glass fillers to the thermoplastics can raise the useful temperature range as much as 100°F and at the same time shortens the molding cycle. 

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