Oxidation of Vulcanized Natural Rubber

Abstract

Abstract The chemistry of oxidative main chain scission in NR and its vulcanizates has been investigated using radiolabelled 2,4-dinitrophenyl hydrazine and dimedone. In this way the number of scission events has been measured and the initial products of oxidation identified and estimated. Product studies have also been carried out with 2-methylpent-2-ene, 2-methyloct-2-ene, and 2,6-dimethylocta-2,6-diene. From these results a more simple and rational mechanism has been suggested for scission in natural rubber. Studies have also been made using radiochemical techniques, of the effect of sulfur compounds structurally related to the crosslinks in vulcanized NR and of conventional antioxidants, on the efficiency of scission. In general both types of compounds increase scission. The effect of mixtures of conventional antioxidants and sulfur compounds on the rate of oxidation of polyisoprenes has been followed. Usually the sulfur compounds reduce the potency of the other antioxidants and reasons are given for this antagonistic action.