POROUS BIAXIALLY DRAWN ULTRA-HIGH-MOLECULAR-WEIGHT POLYETHYLENE FILMS

The morphology and tensile properties of porous biaxially drawn ultra-high molecular weight polyethylene films were investigated as a function of draw ratio and compared to the properties obtained for non-porous reference samples. Biaxially drawn porous films possessing a porosity of over 80% for lambda greater-than-or-equal-to 3 are composed of a network of uniaxially oriented fibrils similar to biaxially drawn non-porous films. However, the fibrils in the porous films possess a fibre texture whereas in the non-porous films a mixed (100) and (110) texture can be observed. Both the Young's modulus and the tensile strength of porous biaxially drawn films are relatively poor compared to the tensile properties of non-porous films. This is due to the modulus being governed by the deformation of a loose fibrillar network, rather than by the properties of the fibrils. The tensile strength is reduced by the inhomogeneous structure and additionally by the non-uniaxial orientation of the fibrils when the film fractures.