| Poly (vinylidene fluoride)(PVDF) was widely used in the field of wastewatertreatment and purification due to its high intensity, acid and alkali resistance, goodmechanical properties and the stable chemical properties. However, its strong hydro-phobic remains a major limitation for the wide application of PVDF. Recently, eth-ylene/vinyl alcohol copolymer (EVOH) with good hydrophilicity has caused more andmore attention as membrane material. In this paper, the hydrophilicity of PVDF mem-brane was improved by blending EVOH in the membrane. Polyethylene terephthalate(PET)/EVOH composite membrane was also prepared by phase inversion method forovercoming the weak intensity of EVOH. Several conclusions can be drawn:(1) PVDF/EVOH blend membrane was prepared by phase inversion method. Theeffect of polymer blend ratio, blending time and coagulation bath temperature onmembrane performance were systematically investigated. Results show that the bestPVDF/EVOH blend ratio and mixing time were9/1and24h, respectively. Comparedwith PVDF membrane, the hydrophilic of was improved significantly. The hydrophilicand tensile strength of PVDF/EVOH blend membrane increased when the coagulationbath temperature increases, while its pure water flux decreased with the increase ofcoagulation bath temperature, this may due to the formation of dense membrane sur-face layer under high coagulation bath temperature. Moreover, the surface topographyof PVDF/EVOH blend membrane was more level off, smooth than that for PVDFmembrane. There were irregular finger holes and a lot of spongiform pores with vari-ous sizes in the cross section of PVDF/EVOH blend membrane, while the sectionstructure of PVDF membrane was only some slender finger holes.(2) PET/EVOH composite flat ultrafiltration membrane was also prepared by phase inversion method, and the best conditions for the preparation of membrane wereobtained. The effect of swelling agent content of acetone, coagulation bath temperature,blending time, EVOH content of polymer and the evaporation time on membraneproperties (such as pure water flux, reject rate, membrane surface roughness) werediscussed. The results indicate that there is a close relationship between acetone andthe stability, flux of composite membrane. The permeation flux composite membranewas mainly controlled by the coagulation bath temperature, and there was a positivecorrelation between the coagulation bath temperature and the microstructure (surfaceroughness, cross-section structure) of composite membrane. Furthermore, it was evi-dent that many asymmetrical pores and finger hole were formed on surface andcross-section of composite membrane under stirring time8h, while the surface andcross-section structure of composite membrane was more uniform under stirring time16h and24h.(3) To further unravel the antifouling property of PET/EVOH and PVDF/EVOHmembranes, the adhesion forces of membrane-hydrophilic/hydrophobic organic mat-ters (membrane foulants) were investigated by atomic force microscopy (AFM) inconjunction with self-made colloidal probes. Corresponding fouling experiments werecarried out. The results indicate that the adhesion force and membrane fouling rate ofmodified membranes (PET/EVOH or PVDF/EVOH) were weaker than that of PVDFmembrane, suggests that the antifouling property of ultrafiltration membrane was im-proved by adding EVOH. In addition, the adhesion force between modified membraneand hydrophobic foulant was stronger than the adhesion force of modified mem-brane-hydrophilic foulant, it was evident that the modified membranes were moresuitable to treat the wastewater which contained more hydrophilic foulants.(4) Compared with PVDF/EVOH blend membrane, the strength, hydrophilic,membrane flux and rejection rate of PET/EVOH composite membrane were superior,and its microstructure was more stable. Moreover, the flux recovery rate of HA-fouledPET/EVOH membrane was lower than that for PVDF/EVOH blend membrane, whilethe flux recovery rate of SA-fouled PET/EVOH and PVDF/EVOH membranes wereequivalent. |
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