The effect of crosslink structure on the tensile strength and oxygen absorption characteristics of natural rubber vulcanizates

Abstract

The chemical nature of crosslinks in natural rubber–sulfur-diphenylguanidine vulcanizates was modified by reaction with triphenylphosphine under nitrogen to determine the effect of this change on tensile strength and oxygen absorption characteristics of the vulcanizates. The vulcanizates were characterized by organically combined sulfur and polysulfidic sulfur. Polysulfidic crosslinks, i.e., crosslinks containing three or more sulfur atoms in the crosslink, were found not to be essential for the attainment of high tensile strength in these vulcanizates. Data for the samples which had lost significant amounts of polysulfidic crosslinks by reaction with triphenylphosphine fitted the tensile strength versus 300% modulus curve for the control samples. Vulcanizates which had been reacted with triphenylphosphine for 16 days at 80°C., had lost 95–99.6% of their polysulfidic sulfur. These triphenylphosphine-reacted vulcanizates exhibited significantly lower rates of oxygen absorption at 100°C. as compared to the untreated vulcanizates. This suggests that polysulfidic structures in the original vulcanizates act as oxidation initiators.