Fumed silica is an important inorganic functional material with a wide range of applications. It is mainly used as a reinforcing agent in silicone rubber and special rubber, and its reinforcing effect even exceeds carbon black. Adding fumed silica to the silicone rubber can increase the tensile strength of the rubber by about 20 times, the tear strength by 40 times, and the transparency. The gas phase white carbon black is used in the rubber of the butadiene rubber, the hydroxybutadiene rubber, the neoprene rubber, the EPDM rubber, and the performance of the rubber parts for the oil field is compared with the rubber compound using precipitated silica or carbon black. It has higher hardness, tensile strength, and better wear resistance and lower water swelling.

The reinforcing properties of fumed silica for rubber mainly depend on the size, structure and surface chemistry of the silica particles.

In general, the size of the particles is represented by an average particle diameter or a specific surface area, and the measurement method is electron microscopy or BET adsorption. The gas phase white carbon black was observed under TEM electron microscope. The white carbon black particles were spherical particles. They were not present as individual particles. Many white carbon black particles were aggregated together, and these aggregates were agglomerated together to form a belt. The structure of the void forms a three-dimensional network structure after being dispersed and stationary in the base material. The three-dimensional network structure is a dynamic and temporary structure, which will be deformed under the action of external force, and the shape and size of the void will also be It changes with it and it is very "sexual". It can also be observed under TEM electron microscopy that the surface of the silica particles is covered with a lot of micropores which extend from the surface of the particles to the inside, but the micropores are small and the rubber molecules are difficult to enter.

Infrared testing of fumed silica, it can be found that the surface of the particles has a large number of silanol groups (SiOH), there are two hydroxyl groups, one is the isolated free hydroxyl group, "coupling" on the surface of the particles at a certain spacing; The second is the associated hydroxyl group that forms a hydrogen bond, and the inside of the particle is bound by Si-O-Si. Due to the hydrogen bonding of the surface, the agglomerates formed are both developed and firm.

The three-dimensional network structure formed by the fumed silica in the binder acts as a skeleton, thereby reinforcing the silicone rubber and the special rubber, the size of the reinforcing effect and the shape of the mesh structure. There is a direct relationship to the degree of firmness. The smaller the particle size of white carbon black, the larger the specific surface area, the stronger the rigidity of the formed agglomerates, the larger the contact surface between the particles and the rubber compound, the more the bonding points, the better the reinforcing property to the rubber, and the stretching of the vulcanized rubber. The strength, the tear strength, and the abrasion resistance are also high, but the elasticity is lowered, so the kneading viscosity is increased, and the workability is deteriorated. In addition, studies have shown that when there are too many micropores on the surface of the particles, the surface roughness is large, which has a certain influence on the reinforcing property of the rubber compound, especially the wear resistance is lowered.
The amount of hydroxyl groups on the surface of silica also has a large effect on the performance of silica. The amount of hydroxyl groups is too small, the agglomerates formed are less rigid, and the reinforcing effect on rubber is lowered. On the contrary, the amount of hydroxyl groups is too high, resulting in an increase in the viscosity of the rubber compound, and even a structuring phenomenon, which is not conducive to processing. In general, the amount of hydroxyl groups on the surface of silica is rich. The surface modification of the fumed silica is to select a suitable surface treatment agent to react with the hydroxyl groups on the surface of the silica through a certain process to reduce and adjust the amount of surface silicon hydroxyl groups to achieve the best use effect.

The surface of the unmodified fumed silica is acidic, and the vulcanization system has a strong adsorption effect in the rubber compound, and the vulcanization system is delayed. It is often necessary to add an active agent to the rubber compound to adjust the vulcanization rate. In addition, the content of impurities in the fumed silica also affects the use of the effect, such as high iron content, will accelerate the aging of the vulcanizate.

The fumed silica has an excellent reinforcing effect on rubber, but it is only used for silicone rubber and special rubber in the rubber industry due to its high price, which limits its use to some extent. With the rise of the domestic fumed silica industry, the continuous expansion of production capacity and the increasingly reasonable price of products, it is possible to broaden its application fields. Guangzhou Ji Bi Shi Technology Industrial Co., Ltd. has developed a process for the production of fumed silica by using organosilicon by-products, which greatly reduces the production cost. The products have partially replaced imports and achieved good economic and social benefits. The development of the silicon industry and related industries has played a huge role in promoting.

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