ADDITION OF ALUMINA TO CELLULOSE-ACETATE MEMBRANES

Asymmetric ceramic-polymer membranes were prepared by dry and wet phas e inversion processes using dispersions containing cellulose acetate, acetone, water and colloidal alumina particles. When the alumina conte nt is low, the microstructure contains macrovoids (pore diameter simil ar to 15 mu m) below a dense polymer rich skin. The addition of greate r amounts of alumina results in a microstructural transition from macr ovoids to a uniform small pore network (pore diameter similar to 2 mu m). However, the alumina particles have a negligible effect on the por osity of the dense skin that forms at the air/membrane or water immers ion bath/membrane interface. In all membranes, the alumina particles a re unagglomerated and uniformly dispersed throughout the cellulose ace tate network. Changes in the microstructure are attributed to delayed phase separation of cellulose acetate in the presence of ceramic parti cles.