Polyethylene Biaxial Shrink Films - Stretchability and Morphology Study

摘要

Three Ziegler-Natta catalyzed polyethylene resins representing different co-monomer distributions have been converted into biaxially oriented films using a biaxial stretcher. The physical performance, shrinkage behavior and morphological structure of the oriented films were examined. The orientation temperature window of a resin can be predicted quite accurately using the temperature at which 95% of the resin melts and its VICAT temperature. Four techniques have been employed to study the morphologies of the biaxially oriented films and the blown films -wide-angle X-ray diffraction, Fourier transform infrared spectroscopy, differential scanning calorimetry and atomic force microscopy. The biaxially oriented films of the resins showed different morphological structures and different physical properties from those films made by single-bubble film blowing process. A model has been proposed to account for the observed morphological changes during biaxial orientation: re-orientation of crystallites, disintegration of the original crystallites into smaller crystallites, and formation of new crystallites.