Membranes formation of a hydrosoluble biopolymer (PVA) using a supercritical CO2-expanded liquid

Supercritical CO2 (SC-CO2) assisted phase inversion has been recently proposed to produce polymeric membranes. The major drawback of this technique is the very limited affinity between CO2 and water at the ordinary process conditions; as a consequence, this process cannot be used to produce membranes of water-soluble polymers (i.e., the majority of biopolymers). To remove these limitations, in this work the phase inversion of water-soluble polymers is proposed using liquids expanded by SC-CO2. This process is applied to the production of poly(vinyl alcohol) (PVA) membranes using expanded ethanol. Using this process, it is possible to take advantage of the capability of the organic solvents to solubilize large quantities of water and of the presence of SC-CO2 to confer to the solution near-critical properties at very low temperatures. We tested the feasibility of this process and analyzed the effect of process parameters on PVA membranes formation and morphology. Several ethanol:CO2 ratios (from 20:80 to 80:20, w/w), PVA concentrations (from 10% to 30%, w/w), temperatures (from 35 to 65 °C) and pressures (from 150 to 250 bar) were tested. PVA membranes characterized by open cellular structures with cell size ranging between 0.5 and 4 μm and with a dense or porous skin were obtained at different process conditions.