Silicone rubber products have the following characteristics:
1, oil resistance, chemical resistance
General silicone rubber products have medium oil resistance and solvent resistance, which mainly depends on the type of silicone rubber, the type and amount of fillers, the type of additives and crosslinking density. Silicone rubber products into polar organic solvents, the volume will increase by 10% to 15%, in ASTM 1 oil and 3 oil at 150 ° C for 70H, can expand 10% and 45%, respectively, while in non-polar solvents and fuel will expand 150% to 200%, but the solvent can be restored after volatilization, and has little impact on its physical properties. The oil resistance of silicone rubber products at room temperature is not as good as natural rubber and neoprene rubber; However, when it is above 100℃, it is significantly better than the latter. Silicone rubber products show better durability for animal and plant oils that can dissolve organic rubber. Silicone rubber products have the ability to resist dilute acid and dilute alkali water solution, but can cause depolymerization and decomposition under strong acid and alkali conditions. The oil and solvent resistance of silicone rubber products can be greatly improved by the introduction of CF3CH2CH2- base. However, the expansion degree in polar solvents such as acetone is still large.
2, water vapor resistance
Silicone rubber products durable low-pressure water vapor (below 130 ° C) performance is quite good, it is soaked in warm water and boiling water for a long time, the volume increase is less than 1%, and rarely affects its mechanical properties and electrical characteristics. However, water vapor exceeding 140 ° C is easy to cause Si-O-Si main chain to break, so that the physical and mechanical properties of silicone rubber products are rapidly reduced. The water vapor resistance of silicone rubber products is related to the type and amount of filler used, the cross-linking density and the type of vulcanizing agent.
3, thermal expansion, thermal conductivity, specific heat capacity and flame retardant
The thermal expansion coefficient of silicone rubber products is larger than that of general organic rubber, and mainly depends on the amount of filler, that is, the greater the relative density of silicone rubber products, the smaller the expansion rate. The shrinkage rate of silicone rubber products generally varies between (2 to 4) 10-4/K, which is equivalent to 2.0 to 2.5 times of organic rubber, or 20 times of steel. The thermal conductivity of silicone rubber products is 0.20 ~ 0.30W/(m.K), which is equivalent to 2 times that of organic rubber, and special grades can exceed 1.2W/m.K. Because the thermal conductivity of silicone rubber products is large, the internal temperature of rubber is fast during vulcanization, which can speed up the vulcanization rate or reduce the vulcanization time. When silicone rubber products are added to thermal conductivity fillers such as AI2O3, BN, MgO, Ag, etc., the thermal conductivity can be increased to 2.0 ~ 14W/(m.K).The combustion temperature of silicone rubber products is about 430 ° C, and the flame temperature can reach 750 ° C. During combustion, SiO2 is generated and non-corrosive gas is released. The special grade added with flame retardants has a limiting oxygen index (LOI) of 27% to 55%, and the flame retardant rate can reach UL94V-1 or even UL94V-0.