The Effect of Extrusion Processing Conditions on the Properties of Blown and Cast Polyolefin Packaging Films

Abstract

Abstract Thin mono‐layer films of metallocene catalysed polyethylene, linear low density and conventional low density polyethylene, as well as polypropylene, were produced from a 38mm extruder through a 75mm diameter blown film die and a 600mm cast film die. By using the same die gap on each die to achieve equal draw‐down ratios, the influence of orientation from the two processes on the mechanical properties of each firm was investigated. Tensile strength at break, Young's Modulus, percentage elongation at break, tear propagation resistance, in both machine and transverse direction all gave significant differences in properties with cast film when compared to different blow‐up ratios for blown film. Differential Scanning Calorimetry was used to measure the percentage of crystallinity in each film. Differences were found to show that the cooling process as the melt exits the die has a significant effect on the percentage of crystallinity.