Effects of composition and processing variables on barrier property of liquid crystalline polymer/polyethylene blend films

Abstract

Cast films of liquid crystalline polymer I polyethylene were investigated. Effects of compatibilizer and LCP content as well as processing parameters i.e., processing temperature profile, use of mixing elements, screw speed, and post-die drawing on morphology , barrier performance and tensile properties were presented. Increasing processing temperature and LCP content tended to enhance aspect ratio (L/D) and continuity of LCP dispersed phase. LDPE films containing 10 wt% of LCP produced at all six temperature profiles generally possess effective LCP fibers with high aspect ratio of 100 or higher. Interestingly, at high temperature profiles, LCP morphologies presented in a more or less "ribbon-like" structure together with a common LCP fibrillar structure. Mixing elements performed a good potential in increasing degree of mixing, initial LCP size and dispersion, when low processing temperature profiles were used. Screw speed of 12 RPM and 0.5 wt% of compatibilizer were found to be optimal values in this LCP/LDPE blend system. Improvements of modulus of approximately 800% and barrier property of 40 % were obtained in the LCP/LDPE films, as compared to LDPE film alone having similar thickness of60 µm. Increasing of LCP content in blend films tended to decrease OTR linearly. Post-die drawing clearly improved aspect ratios of the LCP domains and the resulting films' moduli. Effects of post-die drawing on enhancing films' barrier properties became more pronounced at high LCP content. LDPE films containing 30 wt%LCP showed increases of modulus and barrier property of 35 and 4 folds, respectively over LDPE films of similar thicknesses of 30 µm. LLDPE/LDPE (30:70) blends were prepared in order to improve toughness of blend films instead of using LDPE matrix alone. Toughness enhancement of  80% was obtained when films were produced under appropriate conditions.