Investigation on the melt flow properties of polyethylene and polypropylene blends

Abstract

A blown-film extrusion grade polypropylene (PP) was melt-blended with an injection grade high density polyethylene (HDPE) and a blown-film extrusion grade low density polyethylene (LDPE) using a screw extruder, respectively, and the capillary flow properties such as flow curve, end effect, temperature and shear dependence of the shear viscosity for the blend melts were studied. With addition of the weight percentage content of PP (φ pp), the end pressure losses increased for PP/HDPE blends and decreased for PP/LDPE blends. The shear flow did not strictly obey the power law. The apparent shear viscosity (η a) was increased with addition of φ pp for both PP/HDPE and PP/LDPE blend melts. The flow properties of PP melt was obviously improved when it was melt-blended with a little HDPE or LDPE. The dependence of the shear viscosity (η w) for the blend melts on temperature accorded with the Arrhenius equation approximately. At a fixed wall shear stress, η w was increased with increasing φ pp, but a local maximum value occurred at φ pp = 50% for PP/LDPE blends and a local minimum value of η w appeared at φ pp = 20% for PP/HDPE blends.