Influence of curing systems on dynamically cured epoxidized natural rubber/thermoplastic polyurethane blends

Dynamically cured 40/60 epoxidized natural rubber (ENR)/thermoplastic polyurethane (TPU) blends with peroxide and three different types of sulfur curing system were prepared using an internal mixer. It was found that the blends with peroxide exhibited higher modulus, mixing torque, mixing temperature, hardness, and shear viscosity than the blends with the sulfur-cured systems (i.e. conventional (CV), semiefficient (semi-EV), and efficient sulfur vulcanization (EV)). This is attributed to peroxide-caused cross-linking reaction in both ENR and TPU phases. Furthermore, it was found that the dynamically CV-cured blends exhibited higher thermal resistance, relaxation behavior, cross-link density, oil resistance, and mechanical strength than those of the semi-EV and EV-cured blends. The dynamically CV-cured blends also exhibited the smallest vulcanized rubber domains dispersed in the TPU matrix. This is due to higher levels of cross-link density in ENR phase and possibly higher interfacial attraction. On the other hand, it is difficult to identify the spherical rubber particle in the peroxide-cured blend due to cross-linking reaction that occurs in the TPU matrix.