The basic properties of the silicone rubber

Low temperature performance
Rubber has high elasticity, due to the thermal motion of rubber molecules weakened in low temperature environment, macromolecules and molecular chain segments are frozen, which will gradually lose elasticity. Two important factors affecting the low-temperature properties of the rubber are the glass transition temperature and the crystallization temperature. For all current rubber products, silicone rubber has the lowest glass transition temperature. Russian scientists made non-crystalline silicone rubber at -60 ℃, -90 ℃, -100 ℃ and -120 ℃ low temperature and rubber products can work long-term in the air, inert gas and vacuum environment. Some people improve the low-temperature performance of silicone rubber by copolymerization modification in the polydimethylsiloxane molecular chain on the introduction of other large volume groups. The principle is to destroy the regularity of molecular chains by using the large volume of structural units. This modification can make the glass transition temperature of silicone rubber increase slightly, but it can reduce the crystallization rate of silicone rubber, inhibit its crystallization, thereby improving the low temperature silicone rubber properties. With the study of silicone rubber properties, Ethyl silicone rubbers with the lowest operating temperatures of -120 ℃ to -90℃ were present. The minimum operating temperatures for various silicone rubbers are dimethyl silicone rubber (MQ) -60℃, methyl vinyl silicone rubber (MVQ) -70℃ to -60℃, phenyl silicone rubber-70C, methylphenyl Vinyl silicone rubber -100℃ to -70℃, methyl ethyl silicone rubber -100℃, ethyl silicone rubber -120℃ to -90℃, fluorosilicone rubber (FMVQ) -60℃.

High temperature performance
There are two main processes for the thermal aging of silicone rubber: Firstly, the side chain of the main chain of oxidative decomposition, resulting in excessive crosslinking, the silicone rubber becomes brittle, hard. Secondly, the main chain scission, generates low molecular weight cyclic and linear polysiloxane oligomers, silicone rubber soft, sticky, which is mainly related to its main chain, side chain groups, terminal structure and the type of additives are closely related. Therefore, many scholars have made a lot of research in this field. It is proposed to improve the thermal aging resistance of silicone rubber by changing the main chain and side chain structure of polysiloxane, using new curing system, adding additives, adding silicon nitrogen compounds to improve the thermal aging properties of silicone rubber. At present, RTV silicone rubber has been able to work continuously at 150 ℃ for a long time, and can work continuously for 10 000 h in the environment of 200 ℃, even some silicone rubber products can work at 350 ℃ for a short time. Although silicone rubber products are superior to other rubbers in heat resistance, they need to be able to work continuously at higher temperatures for a longer period of time, so the future development of the normal work at 300 ℃ silicone rubber as the focus of the study.

Weather resistance
Silicone rubber has excellent weather resistance, and it is not sensitive for ozone aging , even if a long time in the wind and rain, ultraviolet radiation and other conditions exposed to its physical properties will not be substantial damage. The silicone rubber nitrile rubber and styrene-butadiene rubber together placed in natural light, the first time to observe the rubber surface crack the time required, the results showed that nitrile rubber only six months to a year, while the styrene-butadiene rubber takes two years to two and a half of the time and the silicone rubber will take about 10 years. Another test is to expose the above three kinds of rubber under natural light to calculate the elongation to reduce the original half of the time required, the results show that nitrile rubber takes about 7 years, styrene-butadiene rubber takes about 4 years, while the silicone rubber It takes more than 10 years. These data indicate that silicone rubber has better Weather resistance than other rubbers.

Water resistance
Excellent water repellent properties of silicone rubber, which was soaked in water for a long time, can only absorb about 1% moisture, and will not cause damage to its mechanical properties and electrical properties. The water vapor test of silicone rubber found that under normal pressure, the water vapor will not cause damage to silicone rubber, but with the pressure increases, the impact of silicone rubber will become increasingly evident. The data show that: 150 ℃ under high pressure conditions, polysiloxane molecular chain fracture, the performance of silicone rubber decreased, this situation can be selected by adjusting the appropriate intermediate material to improve the structure of silicone rubber, there are many modified silicone rubber products can withstand high temperature steam.

Corrosion resistance
Silicone rubber has a good resistance to oil, even at high temperatures, can also be a good resistance to oil erosion. In some common organic rubber, nitrile rubber and chloroprene rubber at 100 ℃ below also has excellent resistance to oil, but at a higher temperature silicone rubber can show than their excellent oil resistance. In addition, silicone rubber also has excellent resistance to organic solvents and chemical reagents, it is basically free from polar organic solvents, in non-polar organic solvents, silicone rubber will be swelling phenomenon, but unlike other Organic rubber degrades, and when the silicone leaves the solvent, it returns to its original state. Silicone rubber is poor on the strong acid resistance, thus should make attention when using it .

Other properties
In addition to the above-mentioned characteristics of organic silicone rubber there are other important properties. Silicone rubber is a good insulating material, the resistivity can reach 1~100 TΩ•m, and the insulation in a large temperature range can remain stable so it is ideal for some electronic components insulating material. Silicone rubber thermal conductivity rate is about 0.2W / mΩ•K, slightly higher than other rubber, is conducive to the production of friction surface with its equipment, such as textile machinery on the rubber roller. When the silicone rubber close to the flame is not easy to ignite, but once ignited will continue to burn down. By adding fire protection ingredients can make it self-extinguishing, and some silicone rubber products have passed the United States UL94 combustion performance standards. In the use of rubber gasket, due to high temperature, gasket deformation recovery ability is particularly important, silicone rubber compression deformation recovery ability to be stable at -60 ℃~250 ℃. Vibration in some mechanical products, rubber vibration absorption capacity of the gasket is also very important that the actual performance of silicone rubber gasket absorption vibration is also very good. In addition, silicone rubber also has good sealing, can be applied to the air bag airbags.

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pdfApplication of Silicone Rubber in Textiles.pdf

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