Tailoring viscoelastic and mechanical properties of the foamed blends of EVA and various ethylene‐styrene interpolymers

Foamed materials (EVA/ESI) have been prepared from blends of ethylene‐vinyl acetate copolymer (EVA) and ethylene‐styrene interpolymers (ESI) in the presence of various amounts of dicumyl peroxide (DCP). Four ESIs of different compositions were employed in this study; their styrene contents ranged from 30 to 73 wt% and their T_g ranged from −2 to 33°C. It has been found that microcellular morphology, degree of crosslinking and expansion ratio were strongly affected by the DCP concentration and the type of ESI employed. A minimum degree of crosslinking was required for making good foams and the same degree of crosslinking could be achieved by employing a smaller amount of DCP for an EVA/ESI blend having a higher styrene content. In contrast to other EVA blends, such as EVA/LDPE, these EVA/ESI blends exhibited no existence of any optimum DCP concentration, and the α glass transition temperatures of the foams varied with the ESI type, covering a wide span from 0°C to 37°C. Therefore, it was possible to tailor the T_g of an EVA/ESI blend by choosing an appropriate type of ESI. Furthermore, by correctly tailoring the T_g, the EVA/ESI foam could be made into a rubbery material with a custom‐designed damping factor. Tensile strength and modulus of the EVA/ESI foams increased generally with an increase in the styrene content, with the exception that ESIs with very low styrene content will confer on the blend a high modulus at small strain and a large elongation at break.