The Mechanism of Membrane Formation: Membrane Structures and Their Relation to Preparation Conditions

The application of membrane techniques for filtration, concentration, and separation purposes is continuously increasing. An outstanding example is desalinationby reverse osmosis. Nevertheless, most of the procedures developed for manufacturing membranes were formulated empirically, and the understanding of the factors governing membrane structureand its characteristics is still poor. One of the most severe problems associated with the practical application of high pressure filtration techniques is the elimination of membrane defects. The formation of voids and large cavities in cellulose acetate(CA) desalinationmembranes has been observed by many investigators[1–3] but except for empirical procedures for eliminating such defects [1,3] no study has been made of the mechanism of their formation. In this article we attempt to elucidate factors governing the formation of voids and cavities in CA membranes. We shall also show that simple and quick optical microscope experiments can serve as useful guides for outlining procedures for eliminating the formation of such defects (large finger-like cavities) in tubular desalinationmembranes.