The structuring of silicone rubber is a common issue. The reinforcing filler used in silicone rubber mainly refers to synthetic silica, also known as white carbon black.
White carbon black leads to the structuring of silicone rubber, mainly based on the hydrogen bonding between white carbon black and high molecular weight polydimethylsiloxane. Silicone rubber reinforcement fillers can be divided into reinforcing fillers and non reinforcing fillers according to their different reinforcement effects. The former has a diameter of 10-50nm and a specific surface area of 70-400m2/g, with better reinforcement effect; The latter is usually between 300-10000nm, with a specific surface area below 30m2/g, and has poor reinforcement effect.
White carbon black is divided into gas-phase white carbon black and precipitated white carbon black.

fumed silica 
The size, specific surface area, surface properties, and structure of gas-phase white carbon black particles are related to factors such as the proportion of raw gas, combustion rate, and residence time of SiO2 nuclei in the combustion chamber.
The finer the gas-phase white carbon black particles, the larger their specific surface area, and the better the reinforcement effect, but the poorer their workability. On the contrary, if its particles are coarser and have a smaller specific surface area, the reinforcement effect will be poorer, but the operability will be better.
Gas phase white carbon black is one of the most commonly used reinforcing agents for silicone rubber. The rubber material reinforced by it has high mechanical strength and good electrical performance after vulcanization. Gas phase white carbon black can be used in combination with other reinforcing agents or weak reinforcing agents to produce rubber materials with different usage requirements.

precipitated silica 
Compared with silicone rubber compounds reinforced with gas-phase white carbon black, those reinforced with precipitated white carbon black have slightly lower mechanical strength, poorer dielectric properties, especially after moisture, but better heat aging resistance, and much lower cost of rubber mixing. When the mechanical strength requirements for the product are not high, precipitated white carbon black can be used or combined with gas-phase white carbon black. The performance of precipitated white carbon black is affected by precipitation conditions such as acidity, temperature, etc.

White carbon black can be treated with appropriate compounds to create a surface hydrophobic substance. There are two main methods for processing: 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 recovered; The gas-phase treatment process is simple, but the product quality is not stable enough and the treatment effect is poor.

To be continued.

Methyl silicone Gum, plz check MY 101