The Effect of E/P Ratio and VA Content on the Structure, Properties, and Failure Mechanism of EPDM and EVA Blends

Abstract

The effect of EPDM, with different ethylene/propylene (E/P) ratios and vinyl acetate (VA) contents of EVA, on the cure characteristics, structures, and physical, chemical, and thermal properties have been studied. These properties, together with phase morphology and fracture mechanisms of melt mixed blends of EPDM rubber and EVA copolymer have been studied over the entire range of composition in the presence of dicu myl peroxide as the curing agent. The viscosity of the virgin EPDMs decreases as their E/P ratio decreases. However, for high-VA-content EVA, the medium-E/P-ratio EPDM is characterized by more of a decrease in viscosity followed by low- and high-E/P-ratio EPDM. A high rate of cure accompanied by a high state of cure is observed for the EPDM with high E/P ratio. The modulus is very much dependent on the crystallinity. The ther mogram suggests early degradation of the medium-E/P-ratio EPDM. This observation is also in line with high-temperature isothermal aging. A possible curing mechanism has been suggested involving both EPDM and EVA in the presence of dicumyl peroxide. SEM suggests different modes of failure depending on the E/P ratio and VA content of EPDM and EVA, respectively.