Study of heat shrinkability of crosslinked low-density polyethylene/poly(ethylene vinyl acetate) blends

In this study, the heat-shrinkage property in polymer was induced by first compounding low-density polyethylene/poly(ethylene vinyl acetate) (LDPE/EVA) blends with various amounts of peroxide in a twin-screw extruder at about 130degreesC. The resulting granules were molded to shape and chemically crosslinked by compression molding. A process of heating-stretching-cooling was then performed on the samples while on a tensile machine. Shrinkability and effective parameters were also investigated using thermal mechanical analysis. The results showed that the gel fraction was higher for the sample of higher EVA content with the same amount of dicumyl peroxide (DCP). A decrease in the melting point and heat of fusion (DeltaH(f)), as determined from DSC, was observed with an increase in the DCP content. Studies on the heat shrinkability of the samples showed that samples stretched above the melting point had a higher shrinkage temperature than those stretched around the crystal transition temperature. The results showed that by increasing the peroxide content, the shrinkage temperature was decreased. These could be attributed to the formation of new spherulites as well as changes in the amount and the size of crystals. Furthermore, in samples elongated at 120degreesC (above the melting point), the rate of stretching had no effect on the shrinkage temperature. The results showed that the extent of strain had no effect on the temperature of shrinkage, but rather on the ultimate shrinkage value. (C) 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1389-1395, 2004.