Cure characteristics and physico-mechanical properties of a conventional sulphur-cured natural rubber with a novel anti-reversion agent

Vulcanization of natural rubber (NR) with conventional accelerated sulphur (CV) system leads to vulcanizate with polysulfidic linkages in the network. These polysulfidic linkages are less stable at elevated temperature due to reversion, which reduces the mechanical properties and increases the compression set. Moreover, the high temperature vulcanization of NR is limited due to reversion. To solve these problems, 4, 4′-bis (maleimido) diphenylmethane (BMDM) was used as an anti-reversion agent. The cure behaviour of NR-CV system with 5 phr of BMDM exhibited excellent reversion stability even at high temperature without adversely affecting the scorch safety as well as the rate of vulcanization. The crosslink densities of NR-CV were greatly increased with the content of BMDM. This enabled us to reduce the compression set values of NR-CV from 38 to 18 % at 70 °C and from 68 to 38 % at 100 °C with the use of 5 phr of BMDM. The glass transition temperature of the NR-CV system was slightly increased while the damping factor (tan δ) was decreased with the use of BMDM.