Silicone rubber is a kind of polymer elastic material with both inorganic and organic properties. The hydrocarbon or substituted hydrocarbon organic group, this group can be methyl, unsaturated vinyl (the mole fraction generally does not exceed 01005) or other organic groups, the molecular structure of this low degree of unsaturation makes silicone rubber Has excellent heat aging resistance and weathering resistance, resistance to ultraviolet and ozone erosion. The flexibility of the molecular chain is large, and the interaction force between the molecular chains is weak. These structural features make the vulcanizate soft and elastic, but the physical properties are poor.

Silicone rubber can be divided into three categories according to its vulcanization mechanism: thermal vulcanization type, room temperature vulcanization type and addition reaction type.

characteristic

(1) High and low temperature resistance

Among all rubbers, silicone rubber has the widest operating temperature range (-100 to 350 °C). For example, properly formulated vinyl silicone rubber or low phenyl silicone rubber can still maintain elasticity after being aged at 250°C for thousands of hours or 300°C for hundreds of hours in hot air; It can still maintain elasticity after aging in hot air for hours, its glass transition temperature is -140 ℃, and its vulcanizate is still elastic at a temperature of -70 ~ 100 ℃. When silicone rubber is used as a heat-resistant coating on the inner wall of a rocket nozzle, it can withstand instantaneous high temperatures of thousands of degrees.

(2) Ozone aging resistance, oxygen aging resistance, light aging resistance and weathering aging resistance

The performance of silicone rubber vulcanizate does not change significantly after several years of outdoor exposure in free state.

(3) Electrical insulation properties

The electrical insulating properties of silicone rubber vulcanizates change little when exposed to moisture, frequency changes or temperature increases, and the silicon dioxide generated after combustion is still an insulator. In addition, there are few carbon atoms in the molecular structure of silicone rubber, and no carbon black is used as a filler, so it is not easy to scorch during arc discharge, and it is very reliable to use in high-voltage applications. Its corona resistance and arc resistance are excellent, the corona resistance life is 1000 times that of PTFE, and the arc resistance life is 20 times that of fluorine rubber.

(4) Special surface properties and physiological inertia

The surface energy of silicone rubber is smaller than that of most organic materials, and it has low hygroscopicity. The water absorption rate of long-term immersion in water is only about 1%, the physical properties do not decline, and the mildew resistance is good. effect. Silicone rubber is odorless, non-toxic, has no adverse effect on the human body, has a slight reaction with the body tissue, and has excellent physiological inertia and physiological aging.

(5) High air permeability

Compared with other polymer materials, silicone rubber has good air permeability, and the permeability of nitrogen, oxygen and air at room temperature is 30 to 40 times higher than that of NR; it has selectivity for gas permeability, such as oxygen permeability for carbon dioxide. about 5 times.

(6) Biomedical properties

The characteristics of the molecular structure of silicone rubber make it have excellent biomedical properties, which is proved by the successful application of a large number of animal and human experiments.