Necessary Common Knowledge of Silica Black in the Application of Silicone Rubber
Structuralization of silicone rubber is a common problem. Silica leads to the structure of silicone rubber, which is mainly based on the hydrogen bonding between silica and high molecular weight polysiloxane. The reinforcing filler for silicone rubber can be divided into reinforcing filler and non-reinforcing filler according to their reinforcing effect. The diameter of the former is 10-50 nm, the specific surface area is 70-400 m2/g, and the reinforcing effect of the latter is better; the latter is usually 300-10 000 nm, and the specific surface area is below 30 m2/g, so the reinforcing effect is poor.
The reinforcing filler used in silicone rubber mainly refers to synthetic silicon dioxide, also known as silica. Silica is divided into fumed silica and precipitated silica.
fumed silica
The size, specific surface area, surface properties and structure of fumed silica particles are related to the ratio of raw gas, combustion speed and residence time of SiO 2 nucleus in combustion chamber.
The finer the fumed silica particles are, the larger the specific surface area is, and the better the reinforcing effect is, but the worse the operation performance is. On the contrary, the particle size is thicker, the specific surface area is smaller, and the reinforcing effect is worse, but the operability is better.
Vapor silica is one of the most commonly used reinforcing agents for silicone rubber. The vulcanized rubber reinforced by it has high mechanical strength and good electrical properties. Vapor silica can also be used with other reinforcing agents or weak reinforcing agents to prepare rubber with different application requirements.
precipitated silica
Compared with the silicone rubber compound reinforced with fumed silica, the compound reinforced with precipitated silica has lower mechanical strength, lower dielectric properties, especially after moisture exposure, but better heat aging resistance and much lower cost. When the mechanical strength of products is not high, silica can be precipitated or mixed with fumed silica. The properties of precipitated silica are affected by precipitation conditions such as acidity and temperature.
Silica can be treated by appropriate compounds to produce a surface hydrophobic substance. The main treatment methods are liquid phase method and gas phase method. The conditions of liquid phase method are easy to control, the quality of products is stable and the treatment effect is good, but the process is complex and the solvent needs to be recovered. The gas phase method is simple, but the quality of products is not stable enough and the treatment effect is poor.