Introduction to silicone rubber
Silicone rubber refers to the main chain consists of silicon and oxygen atoms alternately, silicon atoms are usually connected with two organic groups of rubber. Silicone rubber has good low temperature resistance and can still work at -55℃. With the introduction of phenyl group, the temperature can reach -73℃. Silicone rubber heat resistance is also very prominent, at 180℃ can work for a long time, slightly higher than 200℃ can also withstand a few weeks or longer time is still elastic, instantaneous resistance to high temperature above 300℃. Silicone rubber has good air permeability and the oxygen transmittance is the highest among the synthetic polymers. As one of the most important forms of organosilicate, silicone rubber can remain elastic in a certain temperature range for a long time, and has excellent electrical properties and chemical stability, and can play a role in water resistance, ozone resistance and aging resistance, plays an extremely important role in industry and civil use.
Silicone rubber classification
Silicone rubber can be divided into hot vulcanized type (high temperature vulcanized silica gel HTV) and room temperature vulcanized type (RTV) according to its vulcanization mechanism.
Silicone rubber properties
(1) high and low temperature resistance
Of all rubbers, silicone rubber has the widest operating temperature range (-100 ~ 350℃). For example, after the appropriate match of vinyl silicone rubber or low phenyl silicone rubber, after 250℃ for thousands of hours or 300℃ for hundreds of hours of hot air aging can still maintain elasticity; Low phenyl silicone rubber vulcanized rubber after 350℃ tens of hours of hot air aging can still maintain elasticity, its glass temperature is -140℃, the vulcanized rubber in -70 ~ 100℃ temperature is still elastic. Silicone rubber can withstand instantaneous high temperature of thousands of degrees when used as thermal protective coating on the inner wall of rocket nozzle.
(2) ozone aging resistance, oxygen aging resistance, light aging resistance and weather aging performance
The properties of silicone rubber vulcanizates have not changed significantly after being exposed to the sun for several years in a free state.
(3) electrical insulation performance
The electrical insulation performance of silicone rubber vulcanized rubber changes little when it is affected with moisture, frequency change or temperature rise, and the silicon dioxide generated after combustion is still an insulator. In addition, silicone rubber molecular structure of carbon atoms less, and do not need carbon black as filler, so in the arc discharge is not easy to burn, use in high pressure occasions is very reliable. Its corona resistance and arc resistance is very good, 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 inertia
The surface energy of silicone rubber is smaller than most organic materials, with low hygroscopicity, 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 occur adhesion, can play an isolation role. Silicone rubber is tasteless, non-toxic, has no adverse effects on the human body, and the body tissue reaction is slight, with excellent physiological inertia and physiological aging.
(5) high air permeability
Compared with other polymer materials, silicone rubber has good air permeability. The permeability of nitrogen, oxygen and air is 30 ~ 40 times higher than that of NR at room temperature. It is selective to gas penetration, such as the permeability of carbon dioxide is about 5 times that of oxygen.
(6) Biomedical performance
Silicone rubber has excellent biomedicine properties due to its molecular structure, which has been proved by a large number of successful applications in animal and human experiments.
