Graded Hydrophilic Membranes Based On Cellulose Acetate and Their Solute Permeability

Graded hydrophilic membranes were prepared by hydrolysis of cellulose diacetate membrane in a NH₃ and NaOH aqueous solution under various conditions. The reaction progress of deacetylation from the outside into the inside of film depended on the alkaline hydrolysis conditions. The hydrolysis behavior of cellulose acetate film in a NH₃ aqueous solution was different in a NaOH solution. The water content of the membrane partially hydrolyzed in a NH3 aqueous solutions was higher than that of the membrane completely hydrolyzed for 16 h at 90 ˚C (like cellulose membrane). This tendency was pronounced at the shorter hydrolysis time and higher temperature of hydrolysis. The solute permeability of KCl and CaCl₂ through the prepared membranes was affected by the chemically graded structure on the acetylation degree as well as the water content. In the case of the completely hydrolyzed membranes, the water content and KCl flux of the membranes hydrolyzed in a 1.34 M NH3 solution were 129% and 1350 mmol h^-1 cm^-2 while those of the membranes hydrolyzed in a 0.03 M NaOH solution were 67% and 850  mmol h^-1 cm^-2. Moreover, for the membrane hydrolyzed in a 1.34 M NH3 solution for 0.5 at 80 ˚C, the permeation of CaCl₂ was not observed although the permeation of KCl was observed. In this case, the flux of KCl was 3 mmol h^-1 cm^-2. It suggests that the thin layer which separates salts was formed in the center of the membrane. The swelling behavior and solute permselectivity were controlled by the hydrolysis conditions of cellulose acetate membrane.