The Influence of Activators on the Vulcanization Process. II. The Influence of Zinc Oxide on the Structure of Vulcanizates

Abstract

Abstract The influence of zinc oxide and stearic acid on the structures of vulcanizates was traced in stocks with mercaptobenzothiazole by means of the kinetics of swelling. It was found that zinc oxide in the presence of stearic acid has a marked influence on the rate and degree of crosslinked network formation in vulcanizates. In the formation of crosslinks (sulfur bridges) a number of reactions participate: the direct combination of rubber molecules with biradicals of sulfur, during which polysulfide bonds are mainly formed; the oxidation of rubber mercaptans (-SH groups), which is followed by the formation of mono-sulfide, disulfide and polysulfide links; and the decomposition of polysulfide links, which is followed by the formation of new crosslinks with a smaller number of sulfur atoms per crosslink. Zinc oxide has a varying influence on the individual reactions : the first two are activated by it, and the last one is retarded by it, because it does not react with the polysulfide sulfur to form zinc sulfide.