Interfacial polymerization on hydrophobic PVDF UF membranes surface: Membrane wetting through pressurization

Abstract

PVDF is widely used in water treatment membranes because of it high chemical resistance and thermal stability levels, and desirable mechanical properties. On the other hand, it is seldom used as support membrane for RO membranes, as it is difficult to undertake interfacial polymerization by traditional methods due to characteristic of hydrophobic surface. However, if the MPD solution is applied at pressures which exceed the pressure at which the PVDF membrane pushes water away, then it can be wetted within the membrane and PA/PVDF composite membrane can be prepared through the reaction of the wetted MPD and TMC. The theoretical penetration pressure needed to wet MPD solution in PVDF with pore size of 10nm, calculated using Jurin's Law, is 8.8bar. In this study, PVDF membrane was immersed in MPD solution for 4h at pressures higher than theoretical penetration pressure using N2 gas at 25°C. Interfacial polymerization with TMC was undertaken with surface of the PVDF membrane wetted in MPD solution in this manner to form a thin but consistent PA layer, which was verified through FT-IR and SEM. Salt rejection and permeation flux measurements for NaCl 5000ppm was conducted for the PA/PVDF membranes prepared in this manner at 25°C, 30bar using cross-flow water permeation system. PA/PVDF composite membrane wetted with MPD solution and interfacial polymerization undertaken at 10, 16 and 20bar with N2 gas displayed salt rejection ratio of 37.94, 41.79 and 51.03%, and permeation flux of 7.38, 5.26 and 7.94LMH, respectively. The salt rejection ratio for membrane wetted with MPD at 16bar with CO2 gas displayed salt rejection ratio of 78.26% and permeation flux of 4.91LMH. The results confirmed the possibility of using PVDF UF membrane of superior properties as support membrane for NF and RO.