Thin-Film Composite Membranes and Formation Mechanism of Thin-Film Layers on Hydrophilic Cellulose Acetate Propionate Substrates for Forward Osmosis Processes

Abstract

For the first time, the potential of using hydrophilic cellulose acetate propionate (CAP) as microporous substrates for the fabrication of thin-film composite (TFC) forward osmosis (FO) membranes has been explored. Two types of TFC flat sheet membranes with well-designed substrate structures were prepared. The CAP-TFC membranes show very low Js/Jw ratios (i.e., the ratio of reverse draw solute flux to water flux) of about 0.05 g/L with reasonably high water fluxes under the pressure-retarded osmosis (PRO) mode using 2 M NaCl as the draw solution and deionized water as the feed. When using model seawater as the feed, the water flux is about 12.3 LMH which is comparable to the best in the literature. These results, combined with positron annihilation spectroscopy (PAS) data, confirm the hypothesis that a finger-like morphology in the substrate is not crucial to the performance of TFC FO membranes. Moreover, the surface and skin morphology of the substrate may play essential roles in the formation of the pol...