Nanoporous Membranes Prepared from Homogeneous Lamellar Structure Developed via Biaxial Melt-Drawing of Ultra-High Molecular Weight Polyethylene/Normal Molecular Weight Polyethylene Blend Films

Biaxial melt-drawing of blend films composed of ultra-high molecular weight polyethylene and normal molecular weight polyethylene produced a unique network structure consisting of 30-nm thick homogeneous folded chain crystals. Subsequent biaxial solid-drawing produced a nanoporous structure covering a large area of the membrane surface (120 mm x 120 mm). Effects of preparation parameters, including annealing and subsequent solid-drawing, on resultant nanoporous morphology are also testified to achieve the desirable membrane. The higher gas permeability coefficients of the nanoporous membranes indicate that these nanopores are interconnected along the thickness direction. Despite such excellent porosity, the tensile strength reached 30 MPa, which is similar to that for the initial non-porous film. Consistence of membrane porousness and robustness is highly desirable for various separation applications, including filtration, water purification, dialysis, and lithium-ion batteries.