Ozone Resistance of Rubber Products
November 18, 2020
Rubber products are prone to ageing because the atmosphere contains ozone, and because ozone is more active than oxygen, its attack on rubber, especially unsaturated rubber, is much more severe than oxygen.
Unsaturated rubber is easily oxidized with ozone, and the appearance characteristics after ozonation are different from thermal oxidative aging. Ozonation is carried out on the surface of rubber products. It is a process from the surface to the inside, and the rubber reacts with ozone. It will produce a silver-white hard film (about 10nm thick).
Under static conditions, this film can prevent deep contact between ozone and rubber. To better protect rubber products from reacting with ozone, it is necessary to understand some of their reaction mechanisms.
The activation energy of the reaction between ozone and unsaturated rubber is very low, and the reaction is very easy to proceed until the double bond of the rubber is consumed. At this time, a silvery white film that loses elasticity is formed on the surface of the rubber. Crack, the rubber will no longer continue to ozonize.
If the ozonized rubber is stretched or dynamically deformed, the resulting ozonized film will crack, and the exposed rubber surface will react with ozone, which makes the cracks continue to grow.
According to the experimental data, the mechanism of crack generation and growth is proposed.
The occurrence of cracks is the result of broken molecular chains generated by the decomposition of ozonide under stress, and the tendency to separate from each other is greater than the tendency to recombine.
The growth of cracks is related to the concentration of ozone and the mobility of rubber molecular chains. When the concentration of ozone is constant, the greater the mobility of the molecular chains, the faster the crack growth.