Formation kinetics of a polyphthalazine ether sulfone ketone membrane via phase inversion

Formation kinetics of polyphthalazine ether sulfone ketone (PPESK) membrane via wet phase inversion process has been studied experimentally and theoretically. The membrane morphology has been observed using an online optical microscope-CCD camera experimental system and the precipitation front move X, has been measured. Three different linear correlations between the value of X² and gelation time, t, have been identified. This result is different from a commonly accepted conclusion that a single linear correlation between X² and t exists for the whole gelation process. Compared to the morphology evolution of the membrane, it is realized that these three correlations correspond to three consecutive gelation steps: Formation of the skin layer, formation of the transition layer and formation of the finger layer. Rheological property and its effect on formation kinetics have also been studied. A plot of the natural logarithm value of the viscosity of the PPESK-NMP solution, ln(η) against the PPESK concentration, C, gives a straight line. The variation of the apparent viscosity with the temperature can be described by the Arrhenius equation and the viscous flow activation energy, Eη has been calculated at different PPESK concentrations. The result shows that the value of ln(Eη) monotonously increases with the increase of the PPESK concentration, and that the gelation rate decreased with the increase of the viscous flow activation energy of PPESK. These results may be used to guide the membrane manufacturing processes.