Protection Mechanism of Rubbers from Ozone Attack

Ozone is a pollutant at the ground level derived from the anthropogenic activities such as combustion and volatile organic compounds release in the environment. The ozone concentration at the ground level passed from <10 ppb in pre-industrial era to 50 ppb of the present time. Ozone concentration at ground level is growing at a rate of 1% per year. Rubber articles and tires are degraded by the ozone attack. The increasing ozone concentration in air requires adequate protection of rubber goods to avoid premature aging and failure. At present, the best antiozonant molecules used in the industrial practice are N,N’-substituted p-phenylenediamines (PPDs). In this review, the reaction of ozone with diene rubber double bonds is examined together with the macroscopic effects produced by ozone in the rubber articles. Since the protection of rubber from ozone is ensured by the addition of PPDs; in this review, the early stages of ozone reaction with PPDs are discussed in detail using both theoretical and experimental results. The stoichiometry O3/PPD was determined experimentally. It was found that each single PPD molecule is able to scavenge at least four ozone molecules.