Deformation Profiles in Solid State Extrusion of High Density Polyethylene

Abstract

The deformation mode on solid (crystalline) state extrusions for a series of high density polyethylenes (HDPE) has been investigated as a function of extrusion draw ratio (EDR) and molecular weight (Mw). The effects of extrusion temperature, rate, die entrance angle and lubrication have also been studied. The deformation flow profiles were observed by printing a lateral line pattern on the flat surface of the initially split billet and also by inserting colored HDPE filaments into split and unsplit billets perpendicular to the extrusion direction. It was found that the mode of deformation changed from a flat or even concave form through an undulant shape to a shear parabolic shape with increasing EDR for polyethylenes with Mw<150,000. For higher-Mw, polyethylenes, the flat or concave flow pattern observed at very low EDR changed to a W-shape pattern which has not been previously reported. The extrusion variables did not alter significantly these deformation patterns.