Amidinothiourea as a secondary accelerator in a binary system for the sulphur vulcanization of natural rubber

A study of a binary accelerator system using amidinothiourea as a secondary accelerator with mercaptobenzothiazyl disulfíde (MBTS), in sulphur vulcanization of natural rubber has been undertaken. This system was found to boost MBTS accelerator activity considerably. From the results, a nucleophilic reaction mechanism was established for this system. Different compositions of the amidinothiourea were tried in different mixes using standard recipes, and reference mixes were also vulcanized. Different cure characteristics of the mixes and important physical properties of the vulcanizates were evaluated. Optimum concentrations of amidinothiourea required were derived and the experimental mixes were found to have better cure characteristics, including an advantageous reduction in the optimum cure time. Many of the physical properties of the vulcanizates studied were also found to be better compared to those of the reference mixes. Evaluation of these properties both before and after ageing showed good retention of these properties as well. An attempt was also made to correlate the variation in physical properties to chemical crosslink formation in the various vulcanizates.