Improved Spinnability of Metallocene Polyethylenes by Using Processing Aids

Abstract Melt spinning is a polymer processing technique that is strongly influenced by the extensional flow behaviour of polymer melts. Therefore only a few polymeric materials are usable for this kind of processing with sufficient take-up speeds. When approaching critical conditions of deformation most polymers show either fibre break in the molten state either by a brittle cohesive rupture or a ductile failure. During the melt spinning of pure and modified metallocene poylethylenes additional flow instabilities occur within the spinning die. Namely, wall slip, ‘sharkskin’ and pressure oscillations (gross fracture) may be obtained dependending on the volume flow rate. Pressure oscillations lead to diameter oscillations of the melt extrudate, which create local increase of tensile stress in the spin line. This effect immediately causes fiber break in the spinline. Therefore, melt spinning of polyethylenes was only possible up to a critical molecular weight or its relating melt viscosity. The limitation o...