Devulcanization of waste rubber poses a challenging environmental, economical, and disposal problem in the world because of their cross-linked three-dimensional network structure. Devulcanization of gum natural rubber vulcanizate containing three different sulfur/accelerator ratios was carried out in 90 degrees C for 10 min with the help of open two-roll cracker cum mixing mill in presence and absence of thiol acid as a devulcanizing agent. The vulcanizate properties markedly depended on devulcanizing agent and also devulcanization techniques. Revulcanized rubber obtained by devulcanizing with thiol acid offered better mechanical properties. Decrease in scorch time and increase in rheometric torque were observed for revulcanized rubber containing devulcanizing agent. The onset degradation temperature largely depended on presence of thiol acid. IR spectroscopic results revealed that the main polymeric chain did not oxidize at the time of milling above the room temperature. Increase in storage modulus and decrease in loss modulus were observed for revulcanized rubber from DMA study. The SEM was considered to study the failure mechanism and homogeneity of the vulcanizate. By adopting this devulcanization technique, more than 85% mechanical property of vulcanized natural rubber was retained. (c) 2005 Wiley Periodicals, Inc.