Solute diffusion in swollen membranes : Part VIII. Characterization of and diffusion in asymmetric membranes

Abstract

Novel asymmetric poly (vinyl alcohol) membranes were prepared by a new drying/precipitation/crosslinking procedure. A 10 wt% aqueous solution of PVA with M̄ n = 52,800 was cast to a thickness of 0.5 mm and dried at 40°C for 60-90 minutes. A precipitation solution consisting of (NH 4) 2SO 4, ZnCl 2 and Na 2SO 4·10H 20 was poured over the membrane and left for 15-120 minutes. This phase inversion process was followed by crosslinking with glutaraldehyde at 40°C for four hours. The membranes produced were washed and swollen in water at 37°C. Scanning electron micrographs showed an asymmetric structure of approximately 6-10% dense skin supported by a highly porous substructure containing 50% pores and 50% swollen polymer. Equilibrium swelling data showed polymer volume fractions ranging from 19.8% to 30.4% depending on the conditions of preparation. The stress-strain behavior of equilibrium swollen membranes under a constant rate of extension at 37°C was determined, and the initial tensile modulus, ultimate tensile strength, and elongation at break were calculated. Solute diffusion studies were performed with theophylline and vitamin B 12. Solute diffusion and permeability coefficients were determined. The diffusion coefficients ranged from 1.8 to 11.1% of that in water for theophylline and from 6.8 to 13.1% of that in water for vitamin B 12.