The Effect of Orientation on Extrusion Cast Metallocene Polyethylenes and the Role of Processing Conditions in the Die Swell of Metallocene and Conventional Polyethylenes

Cast films were prepared from a range of metallocene polyethylenes (mPEs) of varied co-monomer types (hexene, octene) using a Killion single screw extruder, using different haul off speeds (8-4m/min) and die gaps (700-250µm). Samples with greater orientation in one direction had increased tensile strength and shrinkage in that direction. DSC analysis showed crystallinity to decrease with decreasing haul off speed. Extrusion of mPEs and conventional linear low density polyethylenes (LLDPEs) by single capillary rheology showed that die swell increased with increasing extrusion rate and decreasing melt temperature. Increased die swell was found for the broader molecular weight distribution (M.W.D.) LLDPEs and in the higher molecular weight resins. Furthermore, long chain branching was found to increase die swell.