Effect of Rubber Content on Mechanical Properties and Heat Shrinkage of Ethylene Vinyl Acetate Copolymer Blended with Epoxidized Natural Rubber

Ethylene vinyl acetate (EVA, 18 mol %. vinyl acetate) and epoxidized natural rubber (ENR, 50 mol % epoxidation) were blended in an internal mixer and compared to EVA. Dicumyl peroxide (DCP) was used as a curing agent. The blends consisted of 10-50 wt % of ENR and were compared with crosslinked EVA in terms of heat shrinkage, mechanical properties, and degree of crystallinity. It is found that the blends showed a decrease in mechanical properties with increasing ENR content because DCP was not a good vulcanizing agent of ENR. The addition of ENR did not affect heat shrinkability of EVA. The maximum heat shrinkage obtained was 80% for EVA and the blends. ENR did not affect thermal properties of EVA investigated by the differential scanning calorimetry. The X-ray diffractometry showed discrepancy in degree of crystallinity before and after specimen stretching and after heat shrinking. It is believed that ENR particles decreased molecular orientation of EVA resulting in a decrease in degree of crystallinity but the remained orientation was sufficient for heat shrinking. The blend showed better extrudability than EVA after increasing take-up speed. Therefore, the extruded tube prepared from the blend provided higher heat shrinkage than EVA tube. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 112: 1817-1825, 2009