Blown film extrusion of LCP/PE blends using a counter-rotating die: Structure-property-process relationships

Polyethylene blends (LLDPE:HDPE {dollar}approx{dollar} 2:1 by wt.) used in NASA's balloon film applications can be effectively reinforced by addition of a small amount of liquid crystalline polymer (LCP). Cast and blown PE films containing {dollar}approx{dollar} 10% LCP show enhancement in tensile modulus of {dollar}approx{dollar} 400% over that of the neat PE matrix. Anisotropy of these in-situ composites is reduced by controlling LCP molecular orientation via a counter-rotating (C/R) annular die. LCP/PE blend blown films with nearly isotropic properties are obtained. While long duration balloon (LDB) modulus requirements {dollar}(approx{dollar}1000 MPa) appear to be attainable for 10% LCP/PE blends, these blends exhibit low yield stress of 20 to 30 MPa which are far below the desired LDB target value of 100 MPa. A further study has been carried out by cold drawing these films: uniaxially drawn LCP/PE films show a remarkable improvement of {dollar}approx{dollar} 600% increase in yield stress compared to that of the base PE matrix. Final film properties are; modulus {dollar}approx{dollar} 1200 MPa and yield strength {dollar}approx{dollar} 140 MPa. These property improvements appear to be the result of self-reinforcement by the LCP morphology. Microscopic results also revealed LCP fibrils with high aspect ratios of {dollar}approx{dollar} 100 or higher in the blends.