NOVEL MEMBRANES MADE FROM A SEMIINTERPENETRATING POLYMER NETWORK FOR ETHANOL-ETBE SEPARATION BY PERVAPORATION

The design of high-performance pervaporation membranes for the selecti ve removal of ethanol from ethyl t-butyl ether (ETBE) was performed by using semi-interpenetrating polymer network (s-IPN) materials. The ch osen linear polymer in the s-IPN was a cellulose ester, and the networ k was formed by photopolymerization of a dimethacrylate, or a dimethac rylate and one or two co-monomers. Membranes with good mechanical prop erties and moderate to good selectivity were obtained. Large permeabil ity increases without loss in selectivity were observed with s-IPN fil ms formed by cellulose propionate or cellulose butyrate interpenetrate d by a network of poly(ethyleneglycol dimethacrylate). The use of dime thacrylate with longer spacers of the poly(ethoxy) type in these mater ials further increased the permeability. The permeation flux of cellul ose acetate-based membranes is improved only when a methacrylate with poly(ethoxy) side chains is incorporated in the network by copolymeriz ation with the poly(ethoxy)-type dimethacrylate. When the poly(ethylen eglycol dimethacrylate) in cellulose butyrate-based s-IPN films increa ses, the selectivity remains constant, while the film permeability goe s through a maximum. The results are interpreted on the basis of a ''p lasticization'' effect exerted on the linear polymer by interpenetrate d networks composed of methacrylates with poly(ethoxy) chains. The res ulting improved segment mobility favors the permeability at low networ k contents. The stability of s-IPN membranes in hot liquid mixtures wa s explained by extended entanglements of the linear polymer with the b ranches of the network meshes. (C) 1997 by John Wiley & Sons, Ltd.