The role of fumed silica in silicone rubber

Silicone rubber refers to a rubber in which the main chain consists 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. Generally, 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 curing 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.; according to different properties and uses, it can be divided into general type, ultra low temperature resistant, ultra high temperature resistant, high strength type, and oil resistant 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 has an irreplaceable role in aviation, aerospace, national defense, machinery manufacturing, building decoration, biomedicine and other fields.

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 made the performance of silicone rubber jump to the practical stage and laid the foundation for modern silicone rubber production technology. The United States, Russia, Germany, Japan, South Korea and China have started to produce silicone rubber from the synthesis of dimethyldichlorosilane.

Compared with common inorganic powder fillers (calcium carbonate, precipitated silica, etc.), silicone rubber added with fumed silica (fumed silica) can increase its strength by up to 40 times, and its yield point modulus can be increased by up to 40 times. Increased by about 10 times, 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 nano-scale amorphous silica obtained by condensation of halosilane in high temperature water in a hydrogen-oxygen flame. Its particle size is small, specific surface area is large, surface activity is high, it has good reinforcement, thickening, thixotropy, anti-settling, anti-sagging, dispersion and other properties.

After research, it is found that the silanol group (Si-OH) on the surface of fumed silica can form a physical or chemical bond with large silicone rubber molecules to form a silicon rubber molecular adsorption layer on the surface of the silica to form silica particles and silicone rubber molecules The integrated three-dimensional network structure effectively limits the deformation of the molecular chain of silicone rubber, thereby achieving reinforcement.