Properties Of PVDF Membranes Research Articles

Effect of spraying polyvinyl alcohol solution on the surface of liquid film on the structure and antifouling properties of polyvinylidene membrane

Abstract Polyvinylidene fluoride (PVDF) membrane was prepared by a two-step method of surface gelation-immersion precipitation. The surface of the scraping solution film was sprayed with polyvinyl alcohol (PVA) aqueous solution to gel the film surface first, and then the liquid film was immersed in a coagulation bath for phase transformation to obtain the surface modified PVDF membrane. The effects of PVA solution with different mass fraction on the structure and properties of PVDF membrane were studied. The results showed that with the increase of spraying PVA mass fraction, the contact angle of the upper surface of PVDF membranes gradually decreased, the porosity and mean pore size of PVDF membranes gradually increased, and the crystallinity of PVDF membranes gradually decreased. The pores on upper surface of the membranes first increased and then decreased, and the finger-like macropore structure appeared inside the membranes, the water flux first increased and then decreased, and the rejection rate increased. Dynamic cycle filtration experiment of bovine serum protein (BSA) solution showed an increase in membrane flux recovery from 68.31 to 95.08% and a decrease in the irreversible fouling rate from 31.69 to 4.92%, indicating an improvement in the hydrophilicity and antifouling properties of the modified PVDF membrane.

New insights in poly(vinylidene fluoride) (PVDF) membrane hemocompatibility: Synergistic effect of PVDF-g-(acryloyl morpholine) and PVDF-g-(poly(acrylic acid)-argatroban) copolymers

Hydrophilic and hemocompatible surface design is vital for poly(vinylidene fluoride) (PVDF) membranes in biological application especially for hemodialysis. In this work, the influence and synergistic effect of PVDF-g-(acryloyl morpholine) (PVDF-g-ACMO) and PVDF-g-(poly(acrylic acid)-argatroban) (PVDF-g-(PAA-AG)) copolymers blending modification on structure and properties of PVDF membrane were investigated. The membranes were prepared through immersion phase transition method. The copolymer structure was characterized by FT-IR and 1H NMR. Modified membrane surfaces obtained were characterized by XPS. The blending modified PVDF hollow fiber membranes were confirmed to have excellent hydrophilicity, good hemocompatibility properties (protein adsorption, platelets/ red blood cells adhesion, plasma coagulation), good permeability and anti-protein fouling performance. The hydrophilic and anti-hemolytic properties were significantly improved with the weight percentage of PVDF-g-ACMO copolymer, and PVDF-g-(PAA-AG) copolymer endow the anti-coagulation of modified membranes. And when the blend ratio was up to 1:3, the blend membranes show the longest clotting time (APTT 114.15 s and PT 25.65 s). This work provides a new modification method to improve the hemocompatibility for PVDF membranes in potential biological applications.

Membrane Processing of Refined Palm Oil Wastewater Using TiO<sub>2</sub> Entrapped Nanoporous PVDF Membrane

An explosive growth of interest has been developed in creating of alternative process of crude palm oil wastewater treatment. Membrane processing offers many advantages as it can be used in almost the stage of oily wastewater treatment. Aim of this study was to investigate nanoporous membrane morphology and performance for refined palm oil wastewater treatment. The comparison of performance and morphology was carried out between neat PVDF and PVDF nanoporous membranes with nanosized TiO2particles of different compositions. Results of permeability and instrumental analysis illustrated that nanometer size obviously affected the PVDF membranes performance and structure. Smaller nanoparticles could improve the antifouling property of PVDF membrane more remarkably. Cross-section of membranes were observed with a field electronic scanning electron microscope (FESEM). The TiO2/PVDF membrane with smaller nanoparticles had smaller mean pore size on its surface and more apertures inside the membrane. X-ray diffraction (XRD) experiment was also suggested that the addition of 1.0 % TiO2nanoparticles had stronger effect on crystallization of PVDF molecules, poresize of 34.05 nm, contact angle of 53oand flux of 88.50 L/m2h of poresize. It can be concluded that nanoporous PVDF membrane with adding of TiO2has better performance for treating refined palm oil wastewater.

Structure Design and Properties of Porous PVDF Membranes Based on Ionic Liquid

Ionic liquid was used as the pore-forming additive to design the structure and properties of PVDF membranes. The crystal structure, morphology and the wettability of the membranes was investigated by Fourier transform infrared spectrometer (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM) and contact angle measurement. The results of FTIR and XRD suggested that ionic liquid could make α crystal phase in pure PVDF membrane totally transformed into β crystal phase via immersion precipitation process. SEM results also indicated that ionic liquid was a good pore-forming additive, which was in favor of the formation of the pore structure in the membranes. Contact angle results showed that the surface hydrophobic of PVDF membrane increased with the addition of ionic liquid in the casting solution. These results suggested that ionic liquid may be found its further application in the preparation of piezo-electric PVDF films with β crystal phase, and oil/water separation membranes.