Effects of Compositions and Processing Variables on Barrier and Mechanical Properties of Liquid Crystalline Polymer/Polyethylene Blend Films

摘要

Cast films of liquid crystalline polymer (LCP) and low density polyethylene (LDPE) blends have been produced and investigated. Effects of LCP content and processing parameters, i.e., processing temperature profile, screw speed, and post-die drawing, on morphology and O_2 barrier property are presented. Increasing processing temperature and LCP content tend to enhance aspect ratios (L/D) of the LCP dispersed phase and at the same time influencing LCP structure. These effects are clearly observed when LCP content is increased from 10% to 30% by wt. At high temperature profiles, LCP morphologies are presented in a more or less 'ribbon' or 'tape' like structure together with a common LCP fibrillar structure. Films of 10% and 30% LCP produced at two optimum temperature profiles show a noticeable proportion of LCP tape-like structure and interestingly high barrier properties of ～1.6 and 5.5 times that of the neat LDPE films. High barrier characteristics of such LCP/PE blend films are indicated by low oxygen transmission rate values. Apart from processing temperature effect, increases of screw speed result in films having smaller aspect ratios for both LCP fibers and ribbons; films also exhibit poorer barrier and mechanical properties. However, post-die drawing clearly demonstrates a positive effect in improving aspect ratios of LCP domains and the resulting films' moduli. Effects of post-die drawing on enhancing films' barrier properties become more pronounced at high LCP content. By comparing with the neat LDPE film (30 μm thick) having modulus of ～180 MPa and OTR of ～11000 cc/m~2.day, the developed LCP/PE films containing 30 wt% LCP show remarkably high modulus values of ～1100 MPa with low OTR of ～2000 cc/m~2.day.