Polyvinyl alcohol as the barrier layer in thin film composite nanofiltration membranes: preparation, characterization, and performance evaluation.

The present paper describes the preparation, characterization, and performance evaluation of thin film composite (TFC) nanofiltration (NF) membranes having porous polysulfone as base support and polyvinyl alcohol (PVA, degree of hydrolysis 86-87% and molecular weight 125,000) as the final barrier layer. Maleic acid (MA) was used as the cross-linker of PVA. The membranes were characterized by their molecular weight cutoff, FTIR, SEM, and contact angle. The effects of variation of different parameters like concentration of polysulfone, polyvinyl alcohol, maleic acid, and cure time on the membrane performance (flux and rejection of inorganic salts) were studied and the optimum membrane composition was evaluated. From the analysis of flux and rejection data it may be concluded that membranes prepared from 17%PSF, 1%PVA, with MA solution concentration of 0.2% (w/w) cured at a temperature of 125+/-2 degrees C for 30 min give the optimum balance of flux and rejection (R). Such membranes show differential rejection among the sulfate and chloride salts. For membranes prepared under optimum conditions the average rejections of NaCl and MgSO4 are 22.8% and 83.8%, respectively; i.e., on an average 60% difference exists between the rejection of MgSO4 and NaCl. The overall trend of rejection by such membranes is R(Na2SO4) > R(MgSO4) > R(NaCl) > R(CaCl2) approximately = R(MgCl2) (R = rejection). The average MWCO of these membranes varies between 250 and 350 Da.