There are significant differences in performance and price between various imported and domestic brands of silica. In terms of performance, there are significant differences in specific surface area, particle size, impurity content and moisture content. Therefore, after the compound is made, the appearance color, whiteness, impurity points, transparency of the rubber sheet, physical and mechanical properties, yellowing during secondary vulcanization and the mixing speed of the compound are all quite different. At the same time, the prices of different varieties also vary by several times. Therefore, how to select the type of silica is an important part of designing the compound formula.
The reinforcing mechanism of silica on silicone rubber has never been fully understood,one of the important reasons might be that the chemical structures of the main chains of silica and silicone rubber molecules are relatively similar, which leads to a strong interaction force between them. Because the polysilicon oxygen chain is relatively easy to adsorb on the surface of silica particles and make some chain links orderly arranged, this not only makes silica a physical crosslinking point, but also can produce a crystallization effect. The smaller the particle size of silica, the larger its specific surface area, and the better its reinforcing effect on silicone rubber.
In addition, some semi-reinforcing fillers and weight-increasing fillers, such as diatomite, calcium carbonate quartz powder, titanium dioxide, aluminum hydroxide, magnesium oxide, etc., are often added to silicone rubber to further enhance the hardness of the vulcanized rubber.