The role of fumed silica in silicone rubber
Silicone rubber refers to a rubber whose main chain is composed of alternating silicon and oxygen atoms, and two organic groups are usually attached to the silicon atoms. There are many ways to classify silicone rubber. Usually, it is divided into solid silicone rubber and liquid silicone rubber according to the form before curing; it is divided into room temperature vulcanized silicone rubber and high temperature vulcanized silicone rubber according to the vulcanization temperature; according to the different monomers used, it can be divided into methyl Vinyl silicone rubber, methyl phenyl vinyl silicone rubber, fluorosilicone, nitrile silicone rubber, etc.; can be divided into general type, ultra low temperature resistant type, ultra high temperature resistant type, high strength type, and oil resistant according to different properties and uses. Type, medical type, etc.
Silicone rubber has good resistance to high and low temperature, heat insulation, insulation, moisture resistance, corrosion resistance, pollution resistance and physiological inertia. It is used in aviation, aerospace, national defense, machinery manufacturing, building decoration, Biomedicine and other fields have an irreplaceable role.
Silicone rubber was first synthesized in the United States with ferric chloride as a catalyst. In 1945, silicone rubber products came out. However, the strength of unreinforced silicone rubber generally does not exceed 0.4 MPa, which is almost unusable. To reach the level of practical application, it must be filled and modified. It was not until 1948 that silicone rubber reinforced with high specific surface area fumed silica (fumed white carbon black) was successfully developed, which enabled the performance of silicone rubber to jump to the practical stage and laid the foundation for modern silicone rubber production technology. The countries that started producing silicone rubber from the synthesis of dimethyldichlorosilane include the United States, Russia, Germany, Japan, South Korea, and China.
Compared with common inorganic powder fillers (calcium carbonate, precipitated silica, etc.), the strength of silicone rubber after adding fumed silica (fumed silica) It can be increased by up to 40 times, the yield point modulus can be increased by about 10 times, and the elongation and creep properties can also be significantly improved.
Fumed silica, also known as fumed white carbon black, molecular formula: SiO2, is an extremely fine nanometer grade obtained by the condensation of halosilane in high temperature water in a hydrogen-oxygen flame Amorphous silica. Its particle size is small, specific surface area is large, surface activity is high, and it has good reinforcement, thickening, thixotropy, anti-settling, anti-sagging, dispersion and other properties.
After research, it is found that the silanol (Si-OH) on the surface of fumed silica can form a physical or chemical bond with large silicone rubber molecules, forming silicone rubber molecular adsorption on the surface of the silica The layer constitutes a three-dimensional network structure in which silica particles and silicone rubber molecules are integrated, which effectively limits the deformation of the silicone rubber molecular chain, thereby achieving reinforcement.
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