Flow of polymer melts through a well-lubricated,conical die

The concept of gross melt fracture of polymer melts as a tensile failure in the die entry region was supported in this work by the observation of a dramatic increase in the melt fracture of poly-ethylene extrudates upon lubricating thoroughly a conical, converging extrusion die. This flow, according to an analysis using a Fromm viscoelastic model, was found capable of producing axial tensile stresses in the extrudate in excess of 10⁶ dynes/cm² at the very moderate exit shear rate (no lubricant) of 100 sec^?1. A calculated stress level of about 5 × 10⁶ dynes/cm² caused sharp, deep transverse cuts to appear in the extrudate. The ability of tensile stresses of this magnitude to fracture melts was demonstrated by separate experiments run in simple tension on molten rods, using similar rates and total deformations. A large qualitative difference between high and low-density polyethylene in both these experiments was noted.