New binary accelerator systems for sulphur vulcanisation of styrene butadiene rubber

Abstract

It is suggested that binary systems of rubber vulcanisation containing thiourea proceed by a nucleophilic reaction mechanism. The exact mechanism of the chemical reactions involved when binary accelerator systems are used in rubber vulcanisation is not fully understood even now. It differs with the systems and the nature of the elastomer used. In the present work, a derivative of thiourea, N-amidino N'-phenyl thiourea (APT), was studied as a secondary accelerator along with tetramethyl thiuram disulphide (TMTD)/mercaptobenzothiazyl disulphide (MBTS) in the sulphur vulcanisation of styrene butadiene rubber. Thiourea binary systems were used as controls. The binary systems containing APT are very effective in reducing the optimum vulcanisation time. APT being more nucleophilic than thiourea, is more reactive here (as observed by the reduction in cure time). A nucleophilic reaction mechanism is indicated in the vulcanisation reaction under review. Different concentrations of APT were tried in various mixes using standard recipes, and reference mixes were also evaluated. The optimum dosage of APT required has been derived based on the cure characteristics of the mixes and the physical properties of the vulcanisates.