Heat-resistant silicone rubber

Heat resistance is one of the remarkable properties of silicone rubber. Its high temperature resistance depends on the molecular skeleton of silicone rubber rubber is composed of high bond energy si-O-Si bond (bond energy 451 kJ/mol), and the Si-C bond (bond energy 214 kJ/mol) on the side group of the Si atom is also very strong. Therefore, silicone rubber has high stability at high and low temperature, and some silicone rubber is used for a long time in the environment of -100 ~ 300℃. However, silicone rubber can not meet the requirements of higher temperature, at high temperature environment, silicone rubber rubber molecules because of side organic group oxidation and thermal rearrangement of the main chain degradation and loss of physical and mechanical properties.

The methods to improve the heat resistance of silicone rubber are as follows:

(1) Introducing special groups (such as phenyl) into the side chain of silicone rubber molecules to prevent oxidative degradation of side groups and thermal rearrangement degradation of the main chain;

(2) To improve the thermal stability of the crosslinking bond of the vulcanized rubber, a large volume of chain segments (such as phenyl, cyclodisilazane, carbdecboronyl) were introduced into the main chain of the silicone rubber molecule;

(3) Heat-resistant additives (such as SnO2, Fe2O3, etc.) were introduced into the compound formula system to prevent main chain cyclization and degradation and side chain oxidation and crosslinking, etc. It is the most common and effective method to introduce heat-resistant additives into the compound formulation system.

Flame retardant silicone rubber

The flash point of silicone rubber is as high as 750℃, the flash point is 450℃, and its oxygen index is higher than other rubber with carbon as the main chain. When burning, the heat release rate is low, flame propagation is slow, no dropping, combustion products are almost non-toxic, non-corrosive, on the surface of the formation is still flame retardant ceramic carbon silicon layer. Despite its excellent flame retardancy, silicone rubber still has defects, especially its susceptibility to smouldering and potential combustion hazards. In some high temperature, heat, high voltage special occasions (such as aerospace, electrical and electronic transmission lines, etc.), the flame retardant requirements of silicone rubber are extremely high.

Improving the flame retardant of silicone rubber is generally considered from the following aspects:

(1) promote the formation of the barrier effect of ceramic carbon silicon layer;

(2) Promote the crosslinking of silicone rubber at high temperature to form a stable structure;

(3) the inorganic filler is added to act as a flame retardant to reduce the surface temperature of combustion, improve thermal conductivity or form an air barrier layer to play a flame retardant role;

(4) Capture the free radicals generated during combustion, inhibit and slow down combustion;

(5) to prevent unbuckling degradation and reduce the release of combustible small molecules.

Commonly used flame retardants are generally divided into additive flame retardants and reactive flame retardants. The former is only physically dispersed in the matrix without chemical reaction. The latter, as a monomer or auxiliary reagent, participates in the legal reaction and becomes a part of the silicone rubber structure.