Effect of Structurizing Agents on the Plasticization and Vulcanization of Butadiene-Styrene Rubber

Abstract

Abstract Compounds of the type of p-anisidine and N,N′-diphenyl-p-phenylenediamine cause structural changes in SKS-30A rubber and its solutions, particularly during heating. Vulcanization accelerators, in particular, mercaptobenzothiazole, greatly accelerate these structural changes in rubber in the presence of p-anisidine or N,N′-diphenyl-p-phenylenediamine during both heat oxidative plasticization and vulcanization. The degree and nature of the structural changes in rubber vary according to the type of accelerator. The structurizing action of p-anisidine and of N,N′-diphenyl-p-phenylenediamine during vulcanization is manifested in the increase of the tensile strength, equilibrium modulus, and rebound resilience of vulcanizates, and the retention of high relative elongations. The agents cited accelerate somewhat the process of combination of sulfur with the rubber in the initial stage of vulcanization, without increase of combined sulfur content at the point of optimum vulcanization. The hypothesis is advanced that the influence of p-anisidine and N,N′-diphenyl-p-phenylenediamine on the observed structural changes in SKS-30A rubber during its heat plasticization and vulcanization is related directly to the character of the oxidation processes, and may be caused by the reaction of the oxidized segments of the rubber (peroxide radicals, stable peroxides, functional oxygen groups, etc.) In unvulcanized rubber, this leads to a loss of plasticity and solubility, and, by vulcanization, to the formation of additional cross-links, to an increase of tensile strength, and with retention of high elongation at rupture. Vulcanization accelerators, such as mercaptobenzothiazole, which activate the oxidation processes in the rubber, increase considerably the rate and extent of these structural changes.