Thermo-oxidative aging and fatigue behavior of dynamically vulcanized PVC/ENR thermoplastic elastomers

Abstract

Dynamically vulcanized poly(vinyl chloride)/epoxidized natural rubber (PVC/ENR) thermoplastic elastomers (TPEs) were prepared following a semi-efficient vulcanization system (semi-EV) with the incorporation of di-ethylhexyl phthalate (DOP) as a plasticizer. The PVC/ENR TPEs were melt mixed at 150°C and 50 rpm using a Brabender Plasticorder. The effect of dynamic curing on the fatigue behavior of the PVC/ENR TPEs was investigated. The properties investigated include fatigue life, stress - strain behavior, strain energy, morphology, and the effect of hysteresis. The unaged samples showed that as the sulfur concentration increases the fatigue life increases which could be related to the increase in cross-link density as indicated from the swelling index data. The increase in cross-link density increases the resistance of these materials against external dynamic stress. Hysteresis study revealed that samples with higher sulfur concentration are less sensitive towards changes in strain energy. As a result they exhibited lower heat build-up and consequently higher fatigue life. The effect of thermo-oxidative aging (TOA) on the fatigue behavior was investigated by exposing the PVC/ENR TPEs in an air oven at 80°C for 168 hours. It was found that all the properties studied decreased after thermo-oxidative aging process. This suggests that some micro-structural changes such as the formation of new cross-links due to post curing has taken place. This accounts for the reduced fatigue life and resilience while hysteresis, modulus, and hardness increased.