Preparation of Ultra-High Molecular Weight Polyethylene Microporous Membranes via Thermally Induced Phase Separation

Abstract

Ultra-high molecular weight polyethylene (UHMWPE) microporous membranes were fabricated via thermally induced phase separation (TIPS). Thermogravimetric analyzer was used to obtain the true concentration of films. To characterize the permeation property, the testing of water flux was carried out and it was found that with the increase of thickness, concentration and molecular weight, a decrease in water flux occurred. However, the water flux changed slightly when the thickness turned into 150μm and the molecular weight reached 4,000,000. Moreover, the pore structure investigated by Field emission scanning electron microscopy (FESEM) was consistent with the above phenomena. It is known that the pore size is affected by two factors: crystallization rate and the diffusion rate of diluent. The curves of the relative crystallinity (Xt) with time for the various films under the cooling rate of 10°C/min showed that the difference between crystallization rate of various membranes was small. So it was considered that the viscosity of system did greater influence on diffusion rate of diluent. In addition, the disparity between cloud points (Tcd) and crystallization temperature (T0) was not obvious, indicating that only solid-liquid phase separation could be observed in the range of cooling rates during the non-isothermal process.