Effects of sulfur vulcanization system on cure characteristics, physical properties and thermal aging of epoxidized natural rubber

The epoxidized natural rubber (ENR) with 40 mol% epoxidation (ENR-40) was initially prepared via ‘ in situ ’ epoxidation of concentrated natural rubber latex with formic acid (1M to isoprene unit) and hydrogen peroxide (0.75 M to isoprene unit) at 50oC for 8 h. The as-prepared ENR-40 was then cured with three different sulfur vulcanization/curing systems, including conventional (CV), semi-efficiency (semi-EV) and efficiency (EV) systems using tetrabenzylthiuram disulphide (TBzTD) as a non-carcinogenic accelerator on a compression molding machine. The effects of sulfur to accelerator ratio on the cure characteristics, tensile properties (tensile strength, modulus at 300% strain (M300) and elongation at break), thermal aging, thermal stability and oil resistance were investigated. The results revealed that the EV system exhibited the longest scorch time ( t s2 ) and cure time ( t 90 ) and the highest elongation at break (both before and after thermal aging), but the lowest crosslink density. The CV system had the highest crosslink density, tensile strength and M300 (both before and after thermal aging) and oil resistance, but the lowest thermal stability. Moreover, the semi-EV system exhibited the highest cure rate and thermal stability, but the lowest t s2 , t 90 and elongation at break (both before and after thermal aging).