The effect of acetic acid on the structure and filtration properties of poly(vinyl alcohol) membranes

The role played by acetic acid in the formation of poly(vinyl alcohol) (PVA ) membranes was investigated. Membranes were prepared from a casting soluti on of PVA, water, and acetic acid by immersion in Na2SO4/KOH/H2O coagulatio n bath. Experimental results show that the acetic acid additive exerts an i nfluence on the structure and filtration properties of membranes. Not only the surface morphology but also the structure of cross-section could be mod ulated by adding the acetic acid in the casting solution. Obviously, the in crease of the amount of acetic acid in the casting solution decreased the t hickness of skin layer. This could be attributed to the fact that the incre ase of the amount of acetic acid in the casting solution increases H3O+ ion of the casting solution enhancing the influx rate of coagulant medium for acid-base equilibrium. A mechanism describing the affinity between the PVA solution and the coagulant medium is proposed to estimate the PVA membrane structure by adding the acid. The results presented here offer a better und erstanding of relationships between the membrane formation mechanism and th e skin structure when designing an asymmetric membrane with acetic acid as an additive. (C) 2000 Elsevier Science B.V. All rights reserved.