Novel negatively-charged amphiphilic copolymers of PVDF-g-PAMPS and PVDF-g-PAA to improve permeability and fouling resistance of PVDF UF membrane

Novel negatively charged polyvinylidene fluoride (PVDF) membranes containing amphiphilic copolymer additives: PVDF-g-2-acrylamido-2-methylpropane sulfonic acid (PVDF-g-PAMPS) and PVDF-g-acrylic acid (PVDF-gPAA) were synthesized via the phase inversion method. The formation of functional groups and chemical composition of the synthesized amphiphilic copolymers ((PVDF-g-PAMPS) and (PVDF-g-PAA)) were investigated by Fourier transform infrared (FTIR) spectroscopy and 1H nuclear magnetic resonance (1H NMR) spectroscopy. The characterization of the copolymerized blended membranes ((PVDF-g-PAMPS/PVDF) and (PVDF-g-PAA/ PVDF)) were investigated by using ATR-FTIR, SEM, AFM, porosity, mean pore radius, water contact angle, zeta potential, and mechanical stability techniques. The membrane hydrophilicity and antifouling performance of the copolymerized membranes were evaluated using the filtration performance. It was found that the negatively charged modified membranes with 10 wt% PVDF-g-PAMPS and 10 wt% PVDF-g-PAA presented a significant pure water flux (181.6 and 336.7 L/m2h, respectively at 0.2 MPa) and an outstanding flux recovery ratio (FRR) (up to 100%) in comparison with the original PVDF (97.5 L/m2h and 74%). Besides, the surface zeta potential of the copolymerized membranes confirmed noteworthy negatively charged in the copolymer surface, which showed better performance of BSA protein and Direct Red 23 dye rejection capability of 100% and more than 99%, respectively. The strong synergetic impacts of hydrogen bonding and the electrostatic repulsion of negatively charged grafted sulfonic and carboxylic groups against protein foulants were ascribed to the increased performance of the copolymerized blended membranes.

Automated summary

This study synthesized novel PVDF membranes with negatively charged amphiphilic copolymer additives and investigated their properties. The modified membranes showed improved pure water flux, flux recovery ratio, and antifouling performance compared to the original PVDF membranes. The synergistic effects of hydrogen bonding and the electrostatic repulsion of negatively charged groups were attributed to the enhanced performance of the copolymerized blended membranes.