Penetration of water-soluble solutes into cellulose films



Nonsolvent water determined in very dilute solutions of polymetaphosphate can be used as a measure of the true swelling of cellulose films. From these values and determinations of nonsolvent water under conditions permitting a penetration of the solute into the film, the average molality of trimetaphosphate, polymetaphosphate, and polyglycols inside the film has been determined under equilibrium conditions. With the electrolytes, the molality ratio (film: external solution) is strongly dependent upon the external concentration, which can at least partly be ascribed to the effect of the charged carboxyl groups inside the film. With polyglycols the molality ratio increases with decreasing molecular weight. With dense films there is no detectable penetration of high molecular weight polyglycols. A comparison between various films is made. It is shown that these contain areas of varying packing densities. The dialysis of trimetaphosphate and polymetaphosphate across the cellulose films has also been studied. In dialysis against water there is, within a wide range of concentration, a linear relationship between the rate of dialysis (flux) and the average internal concentration determined in equilibrium experiments. It is interesting to note that this simple relation holds true although the films are inhomogeneous.