A rationale for the preparation of Loeb‐Sourirajan‐type cellulose acetate membranes

Abstract An attempt has been made to rationalize the variables in the preparation procedure of Loeb‐Sourirajan‐type reverse‐osmosis membranes. The quaternary phase diagram of the system cellulose acetate–acetone–formamide–water was determined and has proved a useful tool in the discussion of membrane structures and properties. A mechanism based on differences in the precipitation rate of the polymer during the membrane formation process has been suggested to explain the observed asymmetry in the membrane structure. The porosity of the membrane has been ascribed to the relative rates of water entering and solvent leaving the cast film. The effects of the casting solution composition, the evaporation time, the wash bath temperature, and the annealing procedure have been studied. X‐Ray diffraction and electron microscopy were used to supplement flux and retention data of membranes made from a cellulose acetate–formamide–acetone casting solution.