Novel Polyurethane/Polyvinyl chloride-co-vinyl acetate crosslinked membrane for reverse osmosis (RO)

Novel Polyurethane/Polyvinyl chloride-co-vinyl acetate (PU/PVCA) blend RO membranes were synthesized in four different ratios 90/10, 80/20, 70/30, 60/40. On the basis of appreciable salt rejection, PU/PVCA-4 (60/40) was selected for chemical crosslinking with 1 to 4 wt% of Epichlorohydrin (ECH). The confirmation of physical and chemical crosslinking between PU and PVCA was validated by Fourier transform infrared spectroscopy (FTIR). The SEM micrographs confirmed the dense film structure for all crosslinked and un-crosslinked membranes. Tensile testing, thermogravimetric analysis (TGA) and dynamic mechanical analysis (DMA) evaluated the performance of ECH crosslinked membranes. In addition, DMA revealed the existence of single glass transition temperature (Tg) in case of crosslinked membranes advocating the compatibility of PU and PVCA. In terms of flux and salt rejection, PU/PVCA-4 membrane crosslinked with 3 wt% ECH demonstrated the optimum results. The permeation data was collected at two different temperatures i.e. 25 °C and 70 °C for crosslinked membranes and the results indicated ~ 67.6% higher flux at 70 °C over the flux obtained at 25 °C. This amelioration in flux shows the thermo-sensitive behavior of crosslinked membranes. These results demonstrate that ECH crosslinked PU/PVCA membranes can outstand the conventional PU membranes in terms of mechanical, thermal and permeation properties.