Fumed silica powder is a very effective reinforcing filler for room temperature vulcanized silicone rubber, which can significantly improve its strength.
On the one hand, it is due to the small size effect and large specific surface area of particles of fumed silica powder; On the other hand, because its surface contains a lot of silicon hydroxyl groups, the particles can form a network structure through the action of hydrogen bond and van der Waals force. At the same time, silica particles also have a strong interaction with polysiloxane molecules, which improves the interfacial adhesion.
The smaller the particle size of fumed silica powder, the larger the specific surface area, the larger the contact surface between particles and rubber, and the more bonding points, the better the reinforcement performance of RTV silicone rubber. The tensile strength, tear strength, wear resistance and hardness of vulcanizate are also high, but at the same time, dispersion becomes very difficult, elasticity decreases and processing performance deteriorates.
Therefore, fumed silica powder with relatively low specific surface area (less than 200m2/ g) is generally used as filler for RTV rubber silicone. The unreinforced silicone rubber is brittle after vulcanization. After adding fumed silica powder for reinforcement, the hardness of silicone rubber increases with the increase of addition.
The fumed silica powder aggregate has a three-dimensional branch structure, which can form an interactive network in the dispersion system. Using this characteristic, the fumed silica powder, as a thickener and thixotropic agent in the field of sealant, can increase the viscosity, ensure the free fluidity of the rubber, and prevent caking, sagging and collapse.
The thickening and thixotropy mechanism of fumed silica for sale is mainly realized through the interaction of hydrogen bonds of surface silicon hydroxyl groups. When it is dispersed in polysiloxane, hydrogen bonds are generated between different particles through the silicon hydroxyl groups on its surface to form a silica network, which limits the fluidity of the system, increases the viscosity and plays the role of thickening.
Under the action of shear force, the silica network is damaged, resulting in the decrease of system viscosity and thixotropic effect, which is conducive to construction. Once the shear force disappears, the hydrogen bond is re formed, the silica network is restored, and the viscosity of RTV silicone rubber compound system also gradually rises, which can effectively prevent the sagging phenomenon of the compound in the vulcanization process.
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