Comparing two highly efficient methods for sulfur curing of rubber

Using chemicals to cure or vulcanize raw rubber is a common practice in the rubber industry and is an indispensable part of rubber compounding and processing. Organic chemical accelerators in combination with primary and secondary activators are integral part of sulfur cure systems in most industrial rubber formulations. This study compares two highly efficient methods developed for the sulfur vulcanization of natural rubber and ethylene-propylene-diene rubber. One method, measures the exact amount of a sulfenamide accelerator needed to react sulfur with rubbers to form chemical crosslinks and then, adds zinc oxide as an activator to improve the efficiency of the curing process. Another method treats the surface of zinc oxide with a sulfenamide accelerator in an organic solvent to provide a convenient single material component to use as additive with elemental sulfur. In both cases, no secondary accelerator and no secondary activator were used in the vulcanization process and only the optimum amount of the chemical curatives was used for the curing of the rubbers. Both methods offer substantial benefits over the more traditional sulfur cure systems by reducing the amount and the number of the chemical curatives required in the vulcanization of the rubbers. The results suggest that the sulfur cure systems currently used to vulcanize industrial rubber compounds can be improved and be made more cost-effective and safer.