Preparations and properties of sodium alginate formed-in-place membranes

Abstract

Sodium alginate formed-in-place membranes were formed on a macroporous titanium dioxide membrane substrate at pH 3.3, 6.5, and 10.5. To investigate the rate and the mechanism of the membrane formation, the dependence of the pressure-to-flux ratio, P/J, on time, t, during the formation was evaluated using diagnostic graphs ; (P/J) 2 , (P/J) 1/2 and -ln(P/J) vs. t. The microfiltration properties of the membranes were investigated by determining the permeability, J/P, and the rejection of a protein, bovine serum albumin (BSA), in 1 g/L solutions as a function of the concentration of added KCl. The stability of the membranes was evaluated by comparing the ratio of the resistances of the membranes at the end of the formation, R, after crossflow rinsing, R m , and after crossflow rinsing following the BSA microfiltration experiment, R α . The linearity of the graphs of (P/J) 2 vs. t of the membranes formed in neutral or basic conditions indicated that the membranes were formed by deposition of a layer, or cake, of the polyelectrolyte on the substrate, while the membrane formed at lower pH was initially deposited as a layer followed by a more complex mechanism. Only the membranes formed pH 3.3 were stable to the crossflow water rinse and retained high BSA rejection at high ionic strength. Their permeabilities were about 50% lower than the permeabilities obtained with the membranes formed at higher pH. The BSA rejection results imply that a continuous sodium alginate membrane is present for the membranes formed at pH 3.3 and that membranes retaining a macroporous structure are present for the membranes formed at pH 6.5 and 10.5.