Structure–Property Relationships of Epoxidized Natural Rubber Vulcanizates

Abstract

The effects of epoxide content on the microstructure and characteristics of epoxidized natural rubber (ENR) were examined. Self-crosslinking between epoxide groups possibly occurred during the vulcanization, with C–O–C linkages in the ENR. Depending on the epoxide level, the self-crosslinking in ENR improved the maximum torque, overall crosslink density (CD) and stability at elevated temperature of the rubber. With increasing epoxide content, the moduli and tensile strengthes of the ENR also increased. The highest tensile strength was achieved at 25 mol% epoxide, exceeding that of crosslinked NR by 46%. The self-crosslinking also facilitated strain-induced crystallization (SIC), reducing the onset strain of crystallization and increasing the degree of crystallinity. Even though increased epoxide content in the NR made the crosslink network distribution less homogeneous, the CD increased so much that the thermomechanical and mechanical characteristics of ENR were improved. The C–O–C linkages from ENR self-crosslinking were also sufficient to boost the thermal stability, complementing the conventional sulfide links.