Submicron Freestanding Ultrahigh-Molecular-Weight Polyethylene Membranes: Application in Membrane Distillation

This paper reports the preparation and characterization of freestanding submicrometer ultrahigh-molecular-weight polyethylene (UHMWPE) membranes aimed at the application of membrane distillation (MD). The membranes' high porosity and mechanical robustness were achieved by inducing orientation and crystallization through biaxial stretching. Then, the MD performance of these membranes was rigorously investigated, where the thinnest UHMWPE membrane tested was only 350 nm, almost 1-10th of the mean free path of the water vapor molecule. Based on the previous prediction, this freestanding submicrometer thick and submicrometer porous material can hardly be employed in conventional membrane-based unit operations. Nevertheless, the submicron UHMWPE turned out to be a kind of eligible MD membrane with a high flux of 85.50 kg center dot m(-2)center dot h(-1) and a rejection rate of 99.99% at 60 degrees C. This may prove that the MD membrane seldom contributes to the selectivity but primarily functions as a physical barrier to hold the liquid-vapor interface. To sum up, this work provides insights into the promising role of ultrathin polyolefin membranes as effective separators for MD and other similar membrane separations based on phase transition.