Swelling behavior and pervaporation properties of new composite membrane systems: Porous polyethylene film-poly(acrylic acid) hydrogel

摘要

A new type of composite membrane for pervaporation has been developed. These membranes were prepared by free-radical copolymerization of acrylic acid with a macromolecular polyfunctional crosslinker (allylhydroxyethylcellulose) inside the porous polyethylene (PE) film. It was shown that the porous structure of the PE matrix is filled with poly(acrylic acid) (PAA), and a layer of acid is formed on the film surface. To investigate the effect of the porous matrix on the composite membrane properties, a hydrogel membrane of crosslinked PAA was also prepared without the matrix using the same procedure. PAA in both membranes was in the neutralized form (K+). Swelling behavior of the membranes and their separation characteristics for pervaporation were investigated in water-ethanol solutions depending on the ethanol concentration. All membranes exhibited a high degree of equilibrium swelling (Q = 20-50 g/g) in dilute ethanol solutions (0-30 vol%), and Q sharply dropped to 1.5-2 g/g at a EtOH concentration of 30 - 40 vol% due to collapse of the gel. All membranes under study were highly permeable and selective to water over a wide range of ethanol concentrations in the feed (50-96 vol%), but composite membranes had a higher separation factor due to the restriction effect of the matrix porous structure on swelling of PAA(K+) inside the pores. However, composite membranes were characterized by a lower permeation rate, compared to the crosslinked PAA membranes without a matrix, because of their lower effective surface for diffusion. (C) 2004 Wiley Periodicals, Inc.