Compatibility of low-density polyethylene/poly(ethylene-co-vinyl acetate) binary blends prepared by melt mixing

The compatibility of low-density polyethylene and poly(ethylene-co-vinyl acetate) containing 18 wt % vinyl acetate units (EVA-18) was studied. For this purpose, a series of different blends containing 25, 50, or 75 wt % EVA-18 were prepared by melt mixing with a single-screw extruder. For each composition, three different sets of blends were prepared, which corresponded to the three different temperatures used in the metering section and the die of the extruder (140, 160, and 180degreesC), at a screw rotation speed of 42 rpm. Blends that contained 25 wt % EVA-18 were also prepared through mixing at 140, 160, or 180degreesC but at a screw speed of 69 rpm. A study of the blends by differential scanning calorimetry showed that all the prepared blends were heterogeneous, except that containing 75 wt % EVA-18 and prepared at 180degreesC. However, because of the high inter-facial adhesion, a fine dispersion of the minor component in the polymer matrix was observed for all the studied blends with scanning electron microscopy. The tensile strengths and elongations at break of the blends lay between the corresponding values of the two polymers. The absence of any minimum in the mechanical properties was strong evidence that the two polymers were compatible over the whole range of composition. The thermal shrinkage of the blends at various temperatures depended mainly on the temperature and EVA-18 content. (C) 2003 Wiley Periodicals, Inc.