Effect of gas phase silica addition on rheological properties of RTV silicone rubber

Gas phase silica aggregate with three-dimensional branch structure, can form a interaction in decentralized system of network, the use of this feature, the gas phase silicon dioxide in the field of sealant, as thickening agent and thixotropic agent, can increase the viscosity, guarantee the freedom of the liquidity, have prevent caking, sag, subsidence, and so on. Gas phase silica thickening and thixotropic mechanism mainly through the surface of silicon hydroxyl hydrogen bonding interaction, when its polysiloxane containing different particles produced by the surface of the silicon hydroxyl hydrogen bonding interaction, forming a network of silica, make the system of liquidity is restricted, viscosity increases, have the effect of thickening; Under the action of shear force, silica network is destroyed, resulting in the decrease of system viscosity, 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 THE RTV silicone rubber compound system gradually rises, effectively preventing the hang-off phenomenon of the compound in the vulcanization process [17]. The anti-hanging characteristics of the system are closely related to the yield value and network reduction rate of the material subjected to shear during use. In practical application, the higher the yield value, the better the anti-hanging performance of the rubber. The ideal compound should have a high yield value, a high shear dilution index and a rapid reduction rate.

Effect of dispersion of gas phase silica on properties of RTV silicone rubber

When adding gas phase silica to RTV silicone rubber, attention must be paid to its dispersion in the polymer. When the dispersing process stops, the gas phase silica with the best dispersing condition will form a complete network in the system, which has high viscosity and excellent thixotropic characteristics. When the adhesive is subjected to shear force, the viscosity decreases greatly and shows a certain fluidity. After the shear force is removed, the viscosity will quickly recover. If the dispersion is insufficient or excessive, only part of the gas phase silica network will be formed, resulting in low viscosity and poor thixotropic properties. In the transparent system, the higher the transmittance, the better the dispersion of silica. Under the same dispersion conditions, gas phase silica products with larger specific surface area generally have better transparency.

In summary, gas phase silica is an essential reinforcing material for silicone rubber. Because of its unique properties, it has been widely used in other fields, such as coating, ink, medicine, cosmetics and chemical mechanical polishing (CMP), and its development prospect is very bright.