LIQUID-LIQUID SEPARATION MEMBRANE

PURPOSE:To economically obtain the title liq.-liq. separation membrane having an excellent separation factor and permeation rate from an inexpensive membrane material by applying simultaneous biaxial orientation to a hydrophilic polymer film. CONSTITUTION:For example, cellulose diacetate is dissolved in acetone to obtain a dope, and the dope is cast on a plate and dried to form a cast film. The cast film is then dipped in the swelling bath of an aq. acetone soln., and simultaneously biaxial-oriented by the swelling-wet-hot orientation which is carried out in the bath and the dry-wet orientation to obtain a liq.-liq. separation membrane. By those simultaneous biaxial orientations, the molecular structure of the film such as molecular orientation and crystallinity is reformed, and a liq.-liq. separation membrane with the improved permeation characteristics such as a separation factor and a permeation rate is obtained. The membrane is especially effective in the separation of the mixture of a water-soluble org. liq. and water by pervaporation.