||This thesis is concerned with the development of a novel and environmentally friendly process which leads to high performance porous UHMWPE membrane structures. We have successfully shown that: firstly, the addition of a non-toxic solvent mineral oil to UHMWPE leads to enhanced chain mobility, particle inter-facial cohesion by the solvation effect, Secondly, we have developed a two-stage compression process which enables the formation of biaxially oriented porous films that are both stiff and ductile. In the first stage of the compression mineral oil acts as a solvent to dissolve chains at the particle boundaries at low temperature. A higher processing temperature was employed in the second stage compression which then results in samples with much higher toughness and retained ductility. Mechanical property measurements carried out on the two-stage compression prepared samples show that an optimum second stage preparation temperature was around 150°C and first stage was 140°C. All samples were drawable up to 9 times which were more than twice of the natural draw ratio for UHMWPE. The drawn film shows a high Young's modulus of 8 to 9GPa, tensile strength of 350MPa and ductility of 10.5%. Thermal and morphological analysis show that high chain orientation was achieved and a porous structure of lμm by 1μm was apparent. Such structures may find uses for environmental applications in membranes and absorbents. Finally, attempts were also made to extract the mineral oil using the supercritical fluid extraction (SFE) technique. It was found by combining SFE and rinsing in volatile acetone, more than 98% of the mineral oil added may be removed. As the extraction was carried out on the final product which may contain less mineral oil than initially added, the removal can be considered 100% effective.