NR-EPDM covulcanization: A novel approach

Bis(diisopropyl)thiophosphoryl disulfide (DIPDIS) was used successfully as a novel coupling agent cum accelerator to co-vulcanize the elastomer blend comprising highly unsaturated natural rubber (NR) and ethylene propylene diene rubber (EPDM) of low unsaturation content. The blend vulcanizates produced exhibit improved physical properties that can be further enhanced by implementing a two-stage vulcanization technique, as well as by judicious selection of the NR-to-EPDM ratio. The results indicate coherency and homogeneity in the blend composition of two-stage vulcanizates. The cure-rate mismatch problem could thus be solved through the formation of rubber-bound intermediates with a multifunctional rubber additive (i.e., DIPDIS), thereby restricting the curative migration from lower to highly unsaturated rubber. The blend morphology as revealed by SEM studies accounts for significant improvement in physical properties, particularly in two-stage vulcanizates. (C) 2001 John Wiley & Sons, Inc.