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Application of fumed Silica in Silicone rubber (2)

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Effect of fumed silica on processing properties of HTV silicone rubber

The effect of fumed silicon dioxide on the processing performance of HTV silicone rubber is generally expressed by the degree of structure (∆Crepe), ∆Crepe is equal to the difference between the plasticity value (P28) of the compound stored at room temperature for 28 days and the plasticity value (P0) measured immediately after mixing. The plasticity value of the compound is related to the amount of fumed silica, surface properties and structure. The structure is caused by the formation of hydrogen bonds between the surface hydroxyl group of fumed silicon dioxide and the oxygen atom in silicon rubber and the adsorption of silicon rubber molecular chain on the surface of silicon dioxide. As a result, the fluidity of the compound decreases with the extension of time, and the compound becomes hard, which affects the processing performance. So in use process need to add structure control agent or choose after surface treatment of fumed silica, the structure control agent to join and fumed surface treatment of silica, is controlled by structure machine the surface or surface treating agent and silica reaction, thus reduce the surface hydroxyl number, which resulted in the reduction and the number of silicone rubber to form hydrogen bond, The mixing time of the compound is shortened, the plasticity is increased, the structural effect is reduced, the processing performance and the storage stability are improved.

Application of fumed silica in room temperature vulcanization (RTV) silicone rubber

Room temperature vulcanized (RTV) silicone rubber is divided into one component (RTV-1) and two components (RTV-2) in product morphology. According to the curing mechanism, it can be divided into two systems: condensation type and additive type. All forms of RTV silicone rubber need to be reinforced with fillers to have the use value, at present, fumed silica is the most used and most effective RTV silicone rubber reinforcing filler. Because RTV silicone rubber is generally used as pouring, caulking, coating and other sealing materials, in order to maintain the viscosity and fluidity before vulcanization, so the amount of fumed silica is generally much less than high temperature vulcanized silicone rubber, and often used with other reinforcing and semi-reinforcing filler, in order to facilitate construction operation.

Effect of fumed silica content on tensile strength and hardness of RTV silicone rubber

Fumed silica is a very effective reinforcing filler for RTV silicone rubber, which can significantly improve its strength. On the one hand, this is due to the small size effect and large specific surface area of fumed silica particles; On the other hand, because its surface contains many silica hydroxyl groups, the particles can form a network structure through the action of hydrogen bonding and van der Waals force. Meanwhile, silica particles also have strong interaction with polysiloxane molecules, which improves the interface bonding. The smaller the particle size of fumed silica, the larger the specific surface area, the larger the contact surface of particles and rubber, the more joint points, the better the reinforcing performance of RTV silicone rubber, the tensile strength, tear strength, wear resistance and hardness of vulcanized rubber are also high, but at the same time, the dispersion becomes very difficult, the elasticity decreases, the processing performance deteriorates, therefore, RTV silicone rubber generally uses gas-phase silica with relatively low specific surface area (less than 200m2/g) as the filler [16]. The silicone rubber is brittle after vulcanization without reinforcement, and the hardness of the silicone rubber increases with the increase of the addition of silica.

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