Analysis of factors affecting rubber aging video
The good aging properties of rubber compounds are essential for providing the required service life of rubber products. The type of elastomer used is the principal factor in considering aging properties. In general, the more saturated the backbone of the elastomer, the better is the aging properties.
Unsaturated polymers are susceptible to oxidation thermally or by reaction with ozone; thus antioxidants and antiozonants are needed to extend the useful service lives of products made with these elastomers.
The factors affecting the aging of general‐purpose rubber having conventional sulfur and accelerator systems are as follows：
1.Oxygen
The addition of only 1 to 2% of oxygen is sufficient to cause deterioration of properties for most general‐purpose elastomers. Oxidation proceeds by free‐radical mechanisms and leads to chain scission and cross‐linking. In the chain scission reaction, free radicals attack the unsaturated polymer backbone causing chain breaking, which results in softening and weakening.
2.Heat
As expected, heat accelerates oxidation. Because oxidation is a chemical reaction, a temperature increase of 10°C almost doubles the rate of oxidation.
3.Flexing
Flex cracking is a common mode of fatigue failure in rubber compounds. The higher the rate of flexing, the greater is the heat generation, and the worse is the fatigue life of the compound or product.
4.Ozone
Effective antiozonants protect rubber surfaces initially by a sacrificial reaction with ozone, and then by the formation of a protective surface layer on the rubber surface by the reaction products called ozonides which are formed in reaction with ozone, but which can also further react to protect the rubber. Certain polymers also provide good ozone protection.
5.Light
Ultraviolet (UV) light promotes free‐radical oxidation at the rubber surface causing discoloration and formation of a brittle film of oxidized rubber.
6.Sulfur
Low sulfur compounds and efficient vulcanized (EV) sulfur‐accelerated systems have better aging resistance. Normally, the oxidation rate increases with the amount of sulfur used in the cure.
7.Metals
Transition‐metal ions, such as iron, copper, manganese, and cobalt, when present even in small amounts, catalyze rubber oxidative reactions by affecting the breakdown of peroxides in such a way as to accelerate further attack by oxygen. Natural rubber vulcanizates are especially affected. Therefore, these metals and their soluble salts, such as oleates and stearates, should be avoided.