The effect of protecting waxes on staining antidegradant performance in tyre sidewall formulation

Certain materials such as wax, when incorporated into rubber formulations, bloom and form a surface barrier layer against ozone attack. The ozone resisting film results in an unpleasant appearance on the rubber surface. In tyres, sidewalls are more susceptible to ozone attack leading to degradation both in dynamic and static conditions. Also, tyre appearance is an important factor in quality control visual inspections and the acceptance of the final product in the market. In this paper, the effect of oil contents in different waxes on the physico-mechanical properties of rubber vulcanisates was investigated. It was found that in UV–Vis spectra, at different ageing times, the absorbance of extracted cured tyre sidewall compound samples at 472 nm showed the concentration of the antidegradants in the rubber vulcanisates. The migration, based on protecting function leading to degrading the antidegradants after the ageing time of 72 h. With 72 h of ageing time in the ozone chamber, the waxes with higher oil content showed a faster migration of antidegradants to the surface of the rubber vulcanisates and degraded faster than the waxes with lower oil content.