Simultaneous Effects of Phenyl-β-Naphthylamine, Sulfur, and Vulcanization Accelerators on the Oxidation of Rubber

Abstract

Abstract Most rubber mixtures contain, besides antioxidants, sulfur and vulcanization accelerators, and these latter have a substantial influence on the oxidation process. Consequently a study of the action of these substances when present simultaneously with antioxidants is important, particularly since there have been no reports concerning this question in the scientific literature. In an earlier article we showed that sulfur, when dissolved in purified sodium-butadiene rubber, is a negative catalyst of oxidation. Above 70° C, the inhibitory effect of sulfur is only slight, and is manifest in a retardation of the autocatalytic process. This retarding effect is much more characteristic of sulfur than of ordinary rubber antioxidants. For example, when added to purified rubber, phenyl-β-naphthylamine prolongs the induction period, but has little influence on the rate of the final auto-accelerated reaction. This behavior of phenyl-β-naphthylamine can be explained by its great inhibitory activity. It acts as a true inhibitor, even in the smallest concentrations'. Consequently, the autocatalytic reaction commences only when almost no phenyl-β-naphthylamine is present, whereas the period of partial retardation of this reaction in the case of an ordinary inhibitor is negligible.