Ionic polyurethane IPN membranes for the pervaporation of water-ethanol mixture

Abstract

Interpenetrating polymer network(IPN) membranes of hydrophilic polyurethane (PU) and hydrophobic polystyrene(PS), and cationic PU and anionic acrylic copolymer were prepared using the simultaneous polymerization method, and the pervaporation characteristics of ethanol-water mixture were analyzed. The PU networks were prepared by reacting the PU prepolymer based on hexamethylene diisocyanate and a polyol mixture of poly(tetramethylene ether)glycol and N-methyl diethanol amine with triethanol amine (or trimethylol propane) as the crosslinking agent. Cationic charges were introduced in the PU network by quaternizing the tertiary amine in the PU backbone with benzylchloride. PS networks were prepared by crosslinking styrene monomer with divinylbenzene. The acrylic networks were prepared by crosslinking monomer mixture of methyl methacrylate and acrylic acid with ethyleneglycol dimethacrylate as the crosslinking agent. Neutralization was done by treating with aqueous NaOH solution to form the anionic network. Preferential pervaporation of water and high permeation rate were observed in the IPN membranes. In the hydrophilic PU/hydrophobic PS membranes, as the content of PS was increased, the permeation rate decreased while the separation factor increased, indicating that the PS domains suppressed the swelling of the PU phase and reduced the plasticizing effect. The average diffusion coefficient, computed from the permeation rate and solubility, was found to be highly dependent on the viscosity and concentration of the permeant in the membrane. The pervaporation behavior of cationic/anionic IPN membrane was explored with varying IPN composition and ion concentration in the membrane. The permeation rate of the membrane increased with increasing the cationic PU content when the water concentration in the feed was low, while it decreased when the water concentration was high. The separation factor increased as the content of the anionic component in the membrane increase...