Preparation of microporous films from immiscible blends via melt processing

Microporous films from immiscible blends were produced via melt processing and post-step treatments. Polystyrene (PS)/polypropylene (PP) and poly(ethylene terephthalate) (PET)/polypropylene blend systems with different viscosity ratios were studied. The blends were first compounded in a co-rotating twin-screw extruder and subsequently extruded through a sheet die to obtain the precursor films. These were uniaxially or biaxially drawn (100-400%) with respect to the original dimension to induce microporous structure and post treated at elevated temperature to maintain the porous structure which consisted of uniform microcracks in the order of a few hundred nanometers. The fabrication process here is shown to be a promising technique for producing microporous films that can be used for liquid and gas separations.