Optimal conditions for obtaining polymeric membranes in binary systems: a numerical analysis

The mathematical model, describing solvent evaporation from a cast film, is used with the aim of formulating a general approach to the optimization of RO membrane production.The results were correlated in terms of a “productivity factor.” This productivity factor approaches unity when the casting film has a thin and compact layer with high asymmetric character on the evaporating surface.The model is tested for different values of the parameters contained in the concentration dependence law of the mutual diffusion coefficient in solvent-polymer binary system. Also different solvent rates at the evaporating surface (low, medium, high) are employed. The numerical results were expressed in terms of intrinsic properties of the binary system with the aid of the free volume theory.Testing the model indicates that increased productivities should be expected for solutions of low free-volume polymers in high cross-section solvents. However, in general, for a given polymer-solvent system, it is very important to adjust solvent evaporation rates by varying solvent concentration in the casting atmosphere.On the other hand it could be necessary to control the plasticizing action of the solvent on the polymer in order to influence the diffusion process.