Blown Film Processing Characteristics of Metallocene and Conventional Polyethylenes

Part A ‐ A range of polyethylene films were prepared from metallocene linear low density polyethylene (mPE) and linear low density polyethylene (LLDPE). The films were manufactured using blow up ratios (BUR) of 1.3 ‐ 2.5, haul‐off rates, and screw speeds to give a uniform thickness of 50 microns. Tensile analysis of the samples showed that modulus and elongation were related to both comonomer type and polymer density. The mPE resins possessed considerable improvement in mechanical performance compared to conventional PEs. Differential Scanning Calorimetry (DSC) analysis demonstrated that the degree of crystallinity was more dependent on extrusion processing conditions and polymer density than comonomer type. Part B ‐ Films were prepared from a range of mPE resins of various comonomer types (hexene and octene). The films were manufactured at a constant blow up ratio of 1.6 by maintaining constant haul off speeds and screw speeds to give a uniform thickness of 50 microns. To effect the change in frostline height, the rate of cooling was changed. Tensile analysis of the samples showed that modulus and tensile stress were related to both comonomer type and polymer density and that frostline height variation had an effect on the final film properties. Change in the percentage crystallinity of each of the samples at the different cooling rates also demonstrated how the processing factors of the blown film line can influence film properties.