Vulcanization Accelerators

Abstract

Vulcanization is a cross linking process in which individual molecules of rubber (polymer) are converted into a three dimensional network of interconnected (polymer) chains through chemical cross links(of sulfur). The vulcanization process was discovered in 1839 and the individuals responsible for this discovery were Charles Goodyear in USA and Thomas Hancock in England. Both discovered the use of Sulfur and White Lead as a vulcanization system for Natural Rubber. This discovery was a major technological breakthrough for the advancement of the world economy. Vulcanization of rubbers by sulfur alone is an extremely slow and inefficient process. The chemical reaction between sulfur and the Rubber Hydrocarbon occurs mainly at the C = C (double bonds) and each crosslink requires 40 to 55 sulphur atoms (in the absence of accelerator). The process takes around 6 hours at 140°C for completion, which is uneconomical by any production standards. The vulcanizates thus produced are extremely prone to oxidative degradation and do not possess adequate mechanical properties for practical rubber applications. These limitations were overcome through inventions of accelerators which subsequently became a part of rubber compounding formulations as well as subjects of further R&D. Following is the summary of events which led to the progress of 'Accelerated Sulfur Vulcanization'.