Improved heat shrinkage and mechanical performances of polyethylene trilayer blown film prepared via novel multilayer coextrusion method

Abstract

In this work, polyethylene (PE) trilayer blown film was prepared using a self‐made rotating coextrusion blown film die (RCBD) with the aim to manufacture trilayer film with excellent comprehensive heat shrinkage and mechanical performances. Polymer resins in this unique blown film die are subjected to a complicated flow field combining both shear circulation and pressure flow. As a result, the melt shows a helix movement in our novel die. The effect of additional parameter (mandrel rotation speed) on the heat shrinkability and mechanical properties of trilayer film was investigated and compared with that of various blow‐up ratios (BURs). The shrinkage rate and shrinkage force along transverse direction (TD) were significantly improved by the mandrel rotation, rather than BUR. Similar trends were observed in tensile strength along TD. However, no considerable changes in heat shrinkability and mechanical properties of PE films along machine direction (MD) were observed. In summary, samples prepared at mandrel rotation speed of 4 rpm were obtained excellent comprehensive performances. Moreover, the morphological investigations confirmed that the formation of high ordered lamellae could be induced by mandrel rotation, and the row structure of oriented lamellae tended to incline to TD under higher rotation speed of mandrel. Besides, the crystal dimension and percent crystallinity were increased because of the mandrel rotation.