Study of synthesis parameters and active layer morphology of interfacially polymerized polyamide-polysulfone membranes

Thin film composite (TFC) polyamide membranes were prepared on a polysulfone support membrane and the effect of various synthesis conditions on the active layer morphology, the physicochemical properties and the membrane performance was investigated. The support membrane porosity factor had a significant effect on the TFC membrane performance. A polyamide top layer was formed within 15 s of reaction. Prolonging the reaction time, although resulting in a thicker active layer, only had a minor influence on the membrane performance. This highlights the importance of the incipient layer of the polyamide structure on its performance. The addition of both a surfactant and a base to the amine solution resulted in a change of the active layer morphology and an improved performance. The effect of additives was attributed to changes in the polymerization mechanism. In addition, it was demonstrated that curing at 50 °C resulted in an improved membrane performance, due to more cross-linking of the active layer. Curing at higher temperatures deteriorated the structure of the support membrane. This research shows that the TFC membrane performance is well correlated with the changes in the active layer morphology, measured using SEM, AFM and TEM; whereas only minor changes in the physicochemical characteristics of the membranes were detected by zeta potential and ATR-FTIR spectroscopy when the same synthesis parameters were varied.