1.1 Classification According to different vulcanization mechanism, silicone rubber can be divided into three categories: hot vulcanization type, room temperature vulcanization type and addition reaction type.
1.2 Characteristics
(1) High and low temperature resistance In all rubber, silicone rubber has the broadest operating temperature range (-100 ~ 350℃). For example, properly matched vinyl silicone rubber or low phenyl silicone rubber can remain elastic after hot air aging at 250 ° C for thousands of hours or 300 ° C for hundreds of hours; Low phenyl silicone rubber vulcanized rubber can remain elastic after tens of hours of hot air aging at 350 ° C, its glass transition temperature is -140 ° C, and its vulcanized rubber is still elastic at a temperature of -70 ~ 100 ° C. When the silicone rubber is used as the thermal protection coating on the inner wall of the rocket nozzle, it can withstand the instantaneous high temperature of thousands of degrees.
(2) Ozone aging resistance, oxygen aging resistance, light aging resistance and weather aging resistance silicone rubber vulcanizate in the free state after outdoor exposure for several years, the performance has no significant change.
(3) Electrical insulation properties The electrical insulation properties of silicone rubber vulcanizates change little when exposed to moisture, frequency changes or temperature increases, and the silica generated after combustion is still an insulator. In addition, there are fewer carbon atoms in the molecular structure of silicone rubber, and carbon black is not used as a filler, so it is not easy to char during arc discharge, and it is very reliable to use in high-pressure situations. Its corona resistance and arc resistance is excellent, corona resistance life is 1000 times that of PTFE, arc resistance life is 20 times that of fluorine rubber.
(4) Special surface properties and physiological inert silicone rubber surface energy is smaller than most organic materials, with low moisture absorption, long-term immersion in water water absorption rate is only about 1%, physical properties do not decline, good mildew resistance, and many materials do not bond, can play an isolating role. Silicone rubber is odorless, non-toxic, has no adverse effects on the human body, reacts slightly with body tissues, and has excellent physiological inertia and physiological aging.
(5) Compared with other polymer materials, high permeability silicone rubber has good permeability, and the permeability of nitrogen, oxygen and air at room temperature is 30 to 40 times higher than that of NR; It is selective to gas penetration, such as carbon dioxide permeability is about 5 times that of oxygen.
(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 tests.