Fabrication Of Anti-fouling Poly (vinylidene Fluoride) Microfiltration Membrane And Study On The Performance

In this dissertation,we chose poly(Vinylidene fluoride) (PVDF) as membranematerial and used different methods for fabricating anti-fouling microporousmembrane. Due to its exceptional chemical resistance,well-controlled porosity,andgood thermal and mechanical properties,poly(Vinylidene fluoride) is widely used forthe preparation of microporous membranes. However, the fabrication methods havegreat effect on the mechanical properties,and there is serious membrane fouling dueto its strong hydrophobic property．So it is important to fabricate anti fouling PVDFmembranes with high mechanical strength by developing a new-method.Blend method can change the properties of the membrane materials by thecomplementarity and synergistic effect between different polymers,and adjust themembrane structure and performance. In order to improve the performance of PVDFmicroporous membranes,cellulose acetate (CA) was used as an additive formembrane preparation by non-solvent induced phase separation. Scanning electronmicroscopy (SEM) revealed that the fabricated PVDF membranes have the typicalasymmetric structure. When CA content was increased from 0 to 10 wt％,the watercontact angles of the PVDF membranes were decreased from 98±2 to 72.6±3,thewater contents of the membranes were increased from 63％to 79％, and the amountsof adsorbed protein were dramatically decreased from 35.2μg/cm to 0,Whichindicated the hydrophily and the ability of resisting protein adsorption improvedgreatly. X-ray photoelectron spectroscopy (XPS) analysis confirmed the enrichmentof CA segments on the PVDF membrane surfaces due to surface segregation forlowering of interface free energy. The shift of Fls binding energy from 687.8 to 687.0eV due to the addition of CA indicated that there are interactions between PVDF andthe added CA. All prepared PVDF microfiltration membranes have a higher fluxrecovery ratio than 90％in protein separation and purification.In the present work,we fabricated PVDF microporous membranes with highwater fluxes and excellent mechanical properties by a simple freeze method towardthe poor mechanical properties by non-solvent induced phase separation.Dimethylsulfoxide (DMSO) Was selected as a solvent,the solidification of castingsolutions was achieved at a temperature of-10℃with a refrigeratory．It was observedthat the formation of the spherulites throughout the PVDF membranes by scanning electron microscopy(SEM). Increasing PVDF concentration in DMSO castingsolutions to 30,40 wt％,the PVDF spherulites piled up denser. the porosity decreasedfrom 70.7％to 40.5％, the water flux was from 1110 to 176 L/m~2h under anoperation pressure of 50 kPa, and the Youngs modulus was dramatically enhanced to120 MPa. The fabricated PVDF microporous membranes have potential applicationsin microfiltration,lithium batteries,cell culture,etc.Choosing CA as additive,the PVDF microporous membranes with differentfreeze time were fabricated by freeze-phase inversion composition method. XPSanalysis confirmed that the degree of CA surface coverage of the PVDF membrane forfreezing 10 min reached 43.4％, which indicated the strong hydrophily. And themicrofiltration experiment indicated that the flux recovery ratio maintained 100％The mechanical properties test proved the Youngs modulus reached 85 MPa whichwas kept on a high level. And due to the study of membrane stability,after immersingthe membrane of freezing 10 min in sodium hypochlorite solution (active chlorineconcentration 500 mg/L) for nine days,the flux recovery ratio reached 97％,whichindicated the macromolecular additive CA could keep stable during chemicalcleaning.