PREPARATIONS AND PROPERTIES OF SODIUM ALGINATE FORMED-IN-PLACE MEMBRANES

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 inve stigate the rate and the mechanism of the membrane formation, the depe ndence of the pressure-to-flux ratio, P/J, on time, t, during the form ation 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 i nvestigated by determining the permeability, J/P, and the rejection of a protein, bovine serum albumin (BSA), in 1 g/L solutions as a functi on of the concentration of added KCl. The stability of the membranes w as evaluated by comparing the ratio of the resistances of the membrane s at the end of the formation, R, after crossflow rinsing, R(m), and a fter crossflow rinsing following the BSA microfiltration experiment, R (a). The linearity of the graphs of (P/J)2 vs. t of the membranes form ed in neutral or basic conditions indicated that the membranes were fo rmed by deposition of a layer, or cake, of the polyelectrolyte on the substrate, while the membrane formed at lower pH was initially deposit ed 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 h igh BSA rejection at high ionic strength. Their permeabilities were ab out 50% lower than the permeabilities obtained with the membranes form ed at higher pH. The BSA rejection results imply that a continuous sod ium alginate membrane is present for the membranes formed at pH 3.3 an d that membranes retaining a macroporous structure are present for the membranes formed at pH 6.5 and 10.5. (C) 1996 John Wiley & Sons, Inc.