Evaluation of Crosslinking Coagents in Ethylene-Propylene Rubber

Abstract Ethylene-propylene rubber (EPR), a saturated elastomer, is usually vulcanized by a peroxide-sulfur curing system. However, several disadvantages associated with this system—undesirable odor for some applications, narrow curing range, and poor strength obtained with mineral fillers—emphasize the need for other reactive chemicals as crosslinking coagents for EPR. Certain polyfunctional monomers such as ethylene dimethacrylate, and polyfunctional polymers such as 1,2-polybutadiene were promising crosslinking coagents for EPR. When used in place of sulfur, they decrease peroxide requirements of moderately filled EPR compounds. They also impart higher states of cure, improve the cure cycle, and decrease odor. The coagents are much superior to sulfur in mineral-filled EPR compounds where, in addition to increasing the crosslinking efficiency, they also improve the wetting of the filler particles by the rubber. However, in highly loaded (carbon black and oil) EPR formulations, the superiority of the peroxide-coagent system is mainly due to the ability to replace sulfur and, consequently, to improve odor.