Heat-resistant silicone rubber
Heat resistance is one of the remarkable characteristics of silicone rubber. Its high temperature resistance depends on the molecular skeleton of the raw silicone rubber is composed of Si-O-Si bonds with high bond energy (bond energy of 451 kJ/mol), and Si-C bonds connected to the side groups of Si atoms ( The bond energy is 214 kJ/mol) is also very strong. Therefore, silicone rubber has high stability under high and low temperature conditions, and some silicone rubbers are used for a long time in an environment of -100 to 300°C. However, silicone rubber cannot meet the higher temperature requirements. Under high temperature environments, silicone rubber raw rubber molecules lose their physical and mechanical properties due to oxidation of side organic groups and thermal rearrangement degradation of the main chain.

There are mainly the following methods to improve the heat resistance of silicone rubber:
(1) Introduce special groups (such as phenyl) in the side chain of silicone rubber molecules to prevent the oxidative degradation of the side groups and the thermal rearrangement degradation of the main chain;
(2) Introduce larger segments (such as phenylene, cyclodisilazane, carbodecaboryl) into the main chain of the silicone rubber molecule to improve the thermal stability of the cross-linked bond of the vulcanizate;
(3) Introduce heat-resistant additives (such as SnO2, Fe2O3, etc.) into the rubber formula system to prevent the main chain cyclization degradation and side chain oxidative cross-linking. Among them, the introduction of heat-resistant additives into the rubber formulation system is currently the most commonly used and effective method.

Flame retardant silicone rubber
Silicone rubber has a flash point of up to 750°C and an ignition point of 450°C, and its oxygen index is higher than other carbon-based rubbers. When burning, the heat release rate is low, the flame spreads slowly, and there is no dripping. The combustion products are almost non-toxic and non-corrosive, and a ceramic carbon silicon layer that is still flame-retardant is formed on the surface. In spite of its excellent flame retardancy, silicone rubber still has drawbacks. In particular, it is easy to smolder and has a potential burning hazard. In some special occasions with high temperature, heat generation and high voltage (such as aerospace, electronic and electrical and power transmission lines, etc.), the flame retardancy of silicone rubber is extremely high.

Increasing the flame retardancy of silicone rubber is generally considered from the following aspects:
(1) Promote the formation of a ceramicized carbon silicon layer that has a barrier effect;
(2) Promote cross-linking of silicone rubber at high temperature to form a stable structure;
(3) Inorganic fillers are added to act as flame retardants to reduce the surface temperature during combustion, improve thermal conductivity, or form an air barrier layer to play a flame retardant effect;
(4) Capture free radicals generated during combustion to inhibit and slow down combustion;
(5) Prevent tripping degradation and reduce the release of flammable small molecules.

Commonly used flame retardants are generally divided into additive flame retardant materials and reactive flame retardants. The former is only physically dispersed in the matrix and does not undergo chemical reactions; the latter acts as a monomer or auxiliary reagent to participate in legal reactions and become part of the silicone rubber structure.

The oxygen index of MMT/silicone rubber composites prepared by melt blending method increases first and then slowly with the increase of the amount of MMT added. The mixed flame retardant system of magnesium hydroxide/zinc borate can also improve the flame retardancy of silicone rubber and enhance the ceramic layer formed after combustion.