PVDF blended PVDF-g-PMAA pH-responsive membrane: Effect of additives and solvents on membrane properties and performance

Poly(vinylidene fluoride) (PVDF) and its derivative copolymer PVDF-graft-poly(methacrylic acid) (PVDF-g-PMAA) were blended to prepare pH-responsive membranes. The effects of the following factors on stimuli-responsive membrane performance were systematically examined: (1) amount of PVDF-g-PMAA additives, (2) extent of purification, (3) concentration of polymer, (4) addition of poly(ethylene glycol) (PEG), and (5) type of solvent. Field-emission scanning electron microscopy (FESEM), contact angle goniometry, atomic force microscopy (AFM), attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), flux and solute rejection performance were used to characterize our fabricated membranes. We found that partially purified PVDF-g-PMAA membrane contains more surface PMAA than the purified one (purified signifies that excess unreacted species were removed). In addition, a much higher flux performance and pH-responsive coefficient were found for the partially purified PVDF-g-PMAA membranes; consequently, membranes were only partially purified throughout our work. The flux of the pH-responsive membranes is dramatically increased by decreasing the polymer concentration from 18 wt% to 15 wt% and by adding PEG and PVDF-g-PMAA. We could create a tunable broad range flux from similar to 1 to 1200 L/m(2) h by adjusting the polymer concentration, adding PEG and PVDF-g-PMAA, and using different solvents. Our tunable approach has great potential for various applications (e.g., water treatment and food processing).