A Study of the Deactivating Effect

Abstract

Abstract It has already been shown by Le Bras that certain substances protect vulcanized rubber from deterioration by oxygen without retarding to any significant extent its rate of oxidation. In this case the phenomenon is different from a true antioxygenic effect, where protection is evident by a notable retardation of the rate of oxidation. The phenomenon was first manifest in a systematic comparison of a series of antioxygenic agents of different chemical types with respect to their influence on the oxidizability of a vulcanizate and the protection which they impart in the artificial accelerated aging of the vulcanizate. It was proved that, in conformity with the mechanism of the antioxygenic effect, there was in general a retardation of the rate of oxidation and protection against deterioration by oxygen at the same time. Only a vulcanizate containing mercaptobenzimidazole (a substance classed among antioxygenic agents, since it is known to increase resistance to accelerated aging) showed an anomalous behavior with respect to the rate of oxidation. Although this particular vulcanizate showed good resistance to artificial aging, its oxidizability was of the same order as that of the control vulcanizate containing no protective agent, which deteriorated very rapidly. In this case, consequently, the protection against deterioration by oxygen involved a mechanism quite different from that characteristic of the classic antioxygenic effect.