DIFFUSION-INDUCED PHASE-SEPARATION WITH CRYSTALLIZABLE NYLONS .1. MASS-TRANSFER PROCESSES FOR NYLON-4,6

Mass transfer during membrane formation by means of phase inversion fo r a polymeric system with both a solid-liquid and a liquid-liquid equi librium was studied on the basis of the theory developed by Reuvers an d Smolders. During the first moments of immersion in the coagulation b ath, the concentrations at the interface between bath and film are gov erned by the virtual liquid-liquid equilibrium. This equilibrium no lo nger exists at a larger time scale. The interfacial concentrations as a result of the local liquid-liquid equilibrium during mass transfer a re located deeply in the crystallization region or solid-liquid demixi ng area and after an induction time the solid-liquid phase separation (crystallization) takes place when membranes are formed with an initia l polymer concentration of 20% or larger. The calculated initial conce ntration profiles show a shallow pattern in polymer content for the fi lms with initial concentration of 20 and 25%. From the calculated init ial concentration profiles an isotropic morphology in the final membra ne can be expected. A steep increase of the polymer concentration at t he interface was observed for the more concentrated films correlated w ith a skinned morphology in the final membrane.