3. Structure control agent
The silicone rubber rubber reinforced with gas phase white hair black will harden during storage and reduce plasticity, thus gradually losing the processing performance. This phenomenon is called "structural" effect. Experiments have shown that the degree of hardening of the compound is related to the specific surface area of the silica and the isolated hydroxyl groups on the surface of the silica.
The reason is that the white carbon black particles have a large specific surface area and a large amount of Si-OH groups on the surface (the cohesive force between the particles is quite strong, and it is easy to agglomerate to make it difficult to disperse in the silicone rubber raw rubber, which is not conducive to reinforcement), and the activity is The Si-OH group and its adsorbed water are condensed with the silanol group and the residual alkoxy group at the end of the raw rubber molecule at room temperature, and some of the active hydroxyl groups can form a hydrogen bond type chemical adsorption with the silicone rubber molecular chain to form a stereoscopic shape. Network structure.
      
A compounding agent added to prevent and attenuate this "structural" tendency is referred to as a "structural control agent." The structure control agent prevents or retards the structuring because the reactive groups of these materials condense with the active hydroxyl groups on the surface of the silica, thereby preventing the interaction between the silica and the green rubber.
Two methods of treating reinforcing filler silica and adding a structuring agent during mixing can be generally employed. However, the cost of treating white carbon black is too high, and most of the methods of treating silica in situ by adding a structured control agent during mixing are now used. The addition of a suitable structured control agent not only solves the processability and storage stability of the silicone rubber compound, but also significantly improves the overall performance of the rubber compound such as tear resistance, elongation, rheology, and the like. In the case of performance, the amount of filler is increased to reduce the cost.
The structure control agent is usually a low molecular organosilicon compound containing Si-OH, Si-NH-Si or a boron-containing atom. Can be summarized into the following four categories:
 (1) Hydroxy-containing silanes The higher the hydroxyl content, the greater the activity and the better the anti-structuring effect;
 (2) alkoxysilanes including various alkoxysilanes and low molecular polysiloxanes;