Reinforcing effect of precipitated silica on silicone rubber
Compared with the silicone rubber compound reinforced with fumed silica, the compound reinforced with precipitated silica for silicone rubber China Manufactuerer has slightly lower mechanical strength, poor dielectric properties, especially after wetting, but better heat aging resistance, and much lower cost of compound. When the mechanical strength of the products is not high, precipitated silica or fumed silica can be used together. The performance of precipitated silica is affected by precipitation conditions such as acidity and temperature.
White carbon black for silicone rubber can be treated by suitable compounds to produce a surface hydrophobic substance. The treatment methods mainly include liquid phase method and gas phase method. The conditions of liquid phase method are easy to control, the product quality is stable, and the treatment effect is good, but the process is complex, and the solvent needs to be recycled; The gas phase treatment process is simple, but the quality of the product is not stable enough and the treatment effect is poor.
Surface treatment agent is the material principle used as surface treatment agent There are the following types that can interact with the hydroxyl groups on the surface of silica:
1) alcohols 2) chlorosilane 3) alkoxysilane 4) hexamethyldisilane 5) silazane.
The reinforcing mechanism of silica on silicone rubber is considered to have the following two kinds.
a. The rubber is adsorbed by the filler particles, which adsorb the polymer, so that the rubber molecular chain segments are directly fixed near the filler particles or oriented along the filler surface or retained by the filler aggregate.
b. The combination of rubber and filler particles the combination of filler particles and polymer segments produces effective cross-linking and polymer entanglement of filler particles
Based on the above two functions, silica can reinforce silicone rubber.
Due to different production methods, the acidity and alkalinity of white carbon black are different. Fumed silica is acidic, while precipitated silica is alkaline. The pH value of the purest HCI free fumed silica is 6, which is caused by the dissociation of hydroxyl groups on the surface of silica in water to produce h+. When the pH value is lower than 4.6, it is due to the HCI bow left by high-temperature hydrolysis.