Melt die-swell behavior of polyoxymethylene blended with ethylene-vinyl acetate copolymer and high-density polyethylene

The influence of extrusion conditions (temperature ranging from 170 to 220 degrees C, loads varying from 1.2 to 12.5 kg) and high-density polyethylene (HDPE) content on swelling behavior of polyoxymethylene (POM)/ethylene-vinyl acetate copolymer (EVA)/HDPE blend melts was examined. It was found the melt die-swell ratio of the blends decreased approximately linearly with rise in temperature, while it increased as a quadratic function with increasing shear rate or shear stress. The melt die-swell ratio increased with increasing HDPE weight fraction under constant test temperature, and the effect of temperature on the sensitivity of the melt die swell ratio to the HDPE weight fraction was insignificant, while the effect of load on the melt die-swell ratio was significant. The correlation between the melt die-swell ratio of the blends and the HDPE weight fraction followed a quadratic relation. The melt extrudate swell behavior mechanisms of the blends during the die extrusion flow are discussed.