Effect of curing systems on vulcanization, mechanical properties, and stress softening of hydrogenated nitrile butadiene rubber vulcanizates

Hydrogenated nitrile butadiene rubber (HNBR) is cured by sulfur (S), dicumyl peroxide (DCP), and S donor, respectively. Effect of curing systems on vulcanization, mechanical properties, and cyclic compression of HNBR vulcanizates was investigated. The dependence of storage modulus ( G′) on strain was evaluated by Rubber Processing Analysis (RPA) analysis. The Mullins effect and degree of stress softening were also investigated by cyclic compression test. The energy dissipation of cyclic compression was calculated. The presumed mechanism of stress softening of HNBR was presented. The results show that the curing speed, torque, and G′ are higher for S curing system compared with DCP and S donor. The elongation of break and hardness for S system are higher than that of DCP and S donor. The maximum compressive stress, stress softening, and dissipated energy decreased with the increasing number of cycles. The degree of stress softening for S is lower due to the bigger cross-link density and stronger filler–rubber interaction in S-cured HNBR.