Study On The Filtration Of Electrospun PVDF Nanofiber And Its Modified Membrane To Oily Wastewater

Today, water pollution, air pollution and noise pollution are known as three major pollutionsin the world. And oily wastewater, one of the water pollution, does great harm to human healthand the ecological environment. Electrospinning technique is the simplest and easy method ofpreparing nanofibers, which are widely used in the field of filter materials, biomedical, tissueengineering and composite materials. Electrospun nanofiber membranes had a wide use andconcern in the treatment of oily wastewater. Therefore, the nanofiber of PVDF, which is oftenused in the water treatment, was prepared in this paper. Three methods of modification wereapplied to PVDF membranes, and then the filtration properties of oily wastewater were tested andcompared to the common commercial PVDF membrane. Thus it shows that the electrospunnanofiber membrane has an excellent advantage in filtration applications, and which also hasleading importance to study and application of the filtering materials.Firstly, the orthogonal experiment method was used in this paper to design the PVDFsolution concentration, applied voltage and receiving distance, which are the main three impactfactors to the electrospun PVDF nanofiber diameter dispersion coefficient. The morphology ofdifferent experimental PVDF nanofiber was observed under a scanning electron microscope(SEM). The fiber diameter histogram mapped, the visual analysis and variance analysis oforthogonal test were used to determine that the PVDF solution concentration was the significantparameter affecting the nanofiber dispersion coefficient. Then the PVDF nanofibers of smallerdiameter and uniform distribution were prepared under optimal process parameters.Secondly, the PVDF/PAN blend solutions under different blend ratios were prepared. Thenthe viscosity and conductivity of the different solutions were measured, and the results indicatedthat the viscosity decreased with the PAN proportion increasing and the conductivity presented asubstantially positive correlation relationship with the PAN ratio. The electrospun PVDF/PAN nanofiber membranes under different blend ratios were prepared. Scanning electron microscopywas used to characterize the morphology of elctrospun PVDF/PAN nanofiber membrane.Additionally, the tensile strength and elongation, the pore size and surface hydrophilicity ofelectrospun membrane were tested. And most importantly, the filtration properties of electrospunPVDF/PAN membranes under different blend ratio on self-emulsified oily wastewater wereexplored. The experiment results showed that the fiber diameter decreased with PAN increasing;the fracture strength and elongation also decreased with the PAN ratio increasing; the watercontact angle decreased as the proportion of PAN increased, and the drop rate was30°, whichindicated that the hydrophilicity of membrane was improved by adding PAN. Moreover, theaverage pore size of all the blend membranes ranged from0.784μm to2.070μm. Finally, thefiltration experiments revealed that the pure water flux of blend membrane was4019～5340L/（m2·h）, which was about30times of the PVDF commercial ultra-filtration membrane; and thehighest emulsion rejection rate reached95.31%, which was just a little smaller than that of PVDFcommercial ultrafiltration membrane（97%）.Thirdly, the PVDF/TiO2polymer solutions under different TiO2mass fraction were prepared.And the viscosity and conductivity were also tested, which indicated that the viscosity showed anincreasing trend with the TiO2mass fraction increasing, and the conductivity increased obviouslytoo. The PVDF/TiO2nanofibers were prepared and the SEM indicated that the fiber increased withthe TiO2mass fraction increasing. The tensile properties were also measured. The test resultsrevealed that both the fracture strength and elongation firstly increased and then decreased withthe adding of TiO2; the water contact and the pure water flux test indicated that the contact anglesdecreased from140.98°to106.67°, which was very significant, the pure water flux suggest theopposite change, it increased, up to4550L/（m2h）, which was25times of commercial PVDFmembrane; the anti-fouling properties was measured and the flux attenuation decreased, whichstood the improvement of anti-fouling ability of the PVDF/TiO2membrane.Finally, the glutaraldehyde (GA) and the polyvinyl alcohol (PVA) were crosslinked on thePVDF nanofiber membrane, and the hydroxyl group was introduced during this reaction, whichaimed to improve the hydrophilicity of the PVDF membrane. Firstly, the crosslinking condition-PVA solution mass fraction, the crosslinking temperature and the crosslinking time were designed.And finally the optimal crosslinking condition was obtained that the PVA mass fraction was1%,crosslinking temperature was50℃and the crosslinking time was4.5h. The modified membrane’spure water flux reached4280L/（m2h）and the emulsion rejection rate was91.5%under theoptimal crosslinking condition. The pure water flux was improved and the retention effect wasensured on some degree compared to the non-crosslined PVDF membrane.