Comparative study of vulcanization system on strain-induced crystallization of epoxidized natural rubber

Vulcanization systems and epoxidation degree play an important role for the microstructure and macro-property of epoxidized natural rubber (ENR). Effect of sulfur (S), dicumyl peroxide (DCP) and itaconic acid (IA) vulcanization systems on the strain-induced crystallization (SIC), molecular chain orientation and microstructure evolution of ENRs were compared by WAXD, polarized FTIR spectroscopy and AFM modulus images. Results demonstrated that ENR-10 with 10% epoxidation degree showed the best mechanical properties, and its tensile strength and elongation of break increased by 137%, 167%, and 19%, 20% compared with the ENR-10-DCP and ENR-10-IA, respectively. ENR-10-DCP and ENR-10-IA had a similar higher molecular chain orientation than ENR-10-S which resulted in the stress larger than ENR-10-S at strain lower than 1. While at high strain, the heterogeneous microstructure, rapid growth of molecular chain orientation and earliest SIC led to the mechanical properties of ENR-10-S being significantly higher than ENR-10-DCP and ENR-10-IA. In addition, compared with NR-S, the introduction of epoxy groups could promote the molecular chain orientation and SIC, thus ENR-10-S showed better mechanical strength than NR-S.