Abstract

One polypropylene melt was extruded through capillary rheometer with several die diameters for testing its shear viscosity at different shear rates and temperatures when the extrudate distortion was observed. Under certain conditions, the melt exhibits shear thinning in viscosity with shear rate. The die with greater aspect ratio of length-to-diameter allows the melt to relax more being embodied by decrease shear viscosity. In capillary flow, the applied shear orients, uncoils or disentangles molecular chains to store energy for elasticity. At 180 °C, the extrudate swells and distorts spirally until random fracture. The distortion and the swelling can be weakened by using the die with larger aspect ratio or by increasing temperature due to chain relaxation.

Keywords: Instable melt extrusion; Capillary rheometer; Polypropylene melt; Distortion; Swell; Viscosity