The C-C bond energy, which is the main axis of organic synthetic rubber, is 83 kcal/mol, while the Si-O bond energy is 108 kcal/mol. This difference in bond energy results in excellent heat resistance of the silicone rubber. The serviceable temperature of silicone rubber is usually 150-250℃, and if used intermittently for a short period of time, it can be up to 350℃.
Low temperature flexibility
The cold resistance of silicone rubber is the best of all kinds of rubber. The saturation point of general organic rubber is -20℃ to -40℃, whereas silicone rubber is -60℃ to -70℃, so it maintains elasticity almost unchanged even at low temperatures when general organic rubber is shock-destroyed, and silicone rubber (PVMQ) containing phenyl groups in the side chain can be used at such ultra low temperature up to -100℃.
Unlike other organic rubbers, silicone rubber does not have double bonds that react with oxygen, ozone, and ultraviolet rays in the atmosphere in its molecular structure to cause cracks, so it has excellent weather resistance and little change in physical properties even when left outdoors for a long time.
The compression set of organic rubber increases significantly with temperature changes, while silicone rubber maintains elasticity and resilience in a wide temperature range from -100℃ to 250℃, which is excellent even when compressive deformation is required under extreme conditions.
Silicon rubber has excellent oil resistance at high temperature, where ordinary organic rubber other than organic fluoro-elastomer cannot be used.
Chemical resistance and steam resistance
Silicon rubber has excellent chemical resistance and is rarely infringed by polar organic compounds such as acids and alkalis. But concentrated acids and alkalis may infringe the properties of silicone rubber. Silicone rubber is stable after being immersed in water for a long time and in contact with steam. It may be decomposed by superheated steam, but can be improved by selecting an appropriate curing agent or curing condition, etc.
Silicone rubber is widely used as an insulating material because it is resistant to arc or corona discharge under high voltage. The insulating properties come from a unique chemical structure of low carbon ratio in molecules and no carbon black as a reinforcing. On the other hand, there is also conductive silicone rubber that has a volume resistivity of 5Ω-cm or less by mixing conductive fillers such as conductive carbon black.
Silicone rubber does not burn easily because it contains less hydrocarbons than organic rubber due to its molecular structure, and it does not generate toxic gases during combustion.
Other features of silicone rubber
The gas permeability of silicone rubber is 30 to 40 times higher than that of organic rubber, so it is also used for special applications such as air purifiers and water separation devices. Silicone rubber is durable against radiation, especially PVMQ based material shows excellent performance. It is transparent and easily pigment-able. It is chemically inert, does not corrode other materials. and has excellent self-lubricating properties. Silicone rubber has lower green strength than organic rubber, so it gives excellent workability.