Factors affecting the thermal aging of rubber grommets

In the case of carbon chain rubber, saturated carbon chain rubber is more resistant to oxidation than unsaturated carbon chain rubber. In the saturated carbon chain rubber molecular chain, although the tertiary hydrogen atom has a large activity due to the electron inducing effect and the superconjugation effect, the oxidation initiation reaction tends to occur at this position, but the CH bond is cleaved to generate active radicals, and Compared with the aH bond cleavage on the unsaturated carbon chain rubber molecule, the fracture activation energy is much more entangled, so it is not easily oxidized.

The a hydrogen atom in the macromolecular structural unit of the unsaturated carbon chain rubber has a relatively low reactivity, and an oxidative dehydrogenation reaction can be generated at a lower temperature, and a stable macromolecular radical R is formed, followed by oxidation. In the chain reaction, the oxidation reaction has obvious autocatalytic characteristics. The saturated carbon chain rubber has no obvious autocatalytic characteristics in the oxidation process. This is because the oxidation of the saturated carbon chain rubber must be carried out at a relatively high temperature. At this time, the generated hydrogen peroxide ROOH is quickly decomposed and it is difficult to fully Play an automatic catalysis.

A hetero-chain rubber such as silicone rubber is composed of inorganic silicon atoms and oxygen atoms in the main chain, and it has no tendency to decompose by free radicals. The initiation reaction of oxidation can only start from the side alkyl group, and the oxidation reaction temperature is higher than that of the above rubber crucible. Much, the low molecular volatiles are produced at temperatures above 280 °C, and the autocatalytic characteristics of the reaction are not obvious. This shows that silicone rubber grommets are more resistant to oxidation than ordinary carbon chain rubber.