RELATIONSHIP BETWEEN MASS-RATIO OF NONSOLVENT-ADDITIVE TO SOLVENT IN MEMBRANE CASTING SOLUTION AND ITS COAGULATION VALUE

A simple equation has been developed to determine the relationship bet ween the mass ratio of nonsolvent-additive to solvent (R(a/s)) in a me mbrane casting solution and its coagulation value (G(v)) in preparing asymmetric membranes by the wet or the dry/wet please inversion proces s. The equation is based on the precipitation values of the nonsolvent -additive (PVa) and the coagulant (PVc) in the binary polymer/solvent system. The validity of this equation was examined with observed exper imental results for PESf/NMP/alcohol, PESf/NMP/H2O, PSf/DMAC/alcohol a nd PSf/DMAC/H2O polymer casting solutions using water or ethanol as th e coagulant; and also with the experimental data reported in the liter ature for the PSf/NMP/PA system using water as the coagulant. The resu lts show that the developed equation describes the observed experiment al data very well. This equation may be used to indicate variation of phase separation behavior of the membrane casting solution with a coag ulant by the introduction of a nonsolvent-additive in the solution. It can be applied readily for the formulation of composition of the memb rane casting solution to make flat sheet or hollow fiber membranes. Th e equation may be useful in the study and control of membrane morpholo gy.