Crosslinked PVDF membranes for aqueous and extreme pH nanofiltration

Loose poly(vinylidene difluoride) nanofiltration membranes were crosslinked using a one-pot reaction with para-xylenediamine in alkaline conditions. The crosslinking reaction was characterized using ATR-FTIR and EDXbased elemental analysis as function of reaction time. Upon crosslinking, the retention of the membranes improved dramatically for rose Bengal (RB) (from 90% to 100%) and MO (from 49% to 91%) without significant loss of permeability. The physico-chemical changes of the membrane during the crosslinking reaction were further characterized through XRD, TGA, DSC and DMA. Crosslinking resulted in a strong decrease in crystallinity of the semi-crystalline PVDF and tensile strength and thermal stability. The 24 h crosslinked PVDF membranes were tested for NF application in extreme pH conditions. The membranes were found to be suitable in both extreme acidic and alkaline conditions (5M HCl or NaOH). The RB retention was not affected at all by the extreme conditions. Although a small decrease in permeance was observed for the acid treated membrane, the permeance of the alkaline treated membrane was not affected. This proves that crosslinking is a suitable strategy to improve the stability of PVDF, especially in alkaline conditions where pristine PVDF is not applicable at all, and furthermore is a tool to decrease the MWCO.