The Study Hydrophilic Modification Of PVDF/PVA UF Membranes And Their Anti-fouling Properties

Nowadays the PVDF untrafiltration has been widely used in the water treatmentfield. However, it has not been popularized due to the membrane fouling caused by itsstrong hydrophobic. Many researchers modified PVDF membrane for hydrophilizationby blending, grafting, surface coating and other technologies.But researchers usuallyassess the pollution resistance properties about modified ultrafiltration membranes byhydrophilcity, the flux decline rates，pollution adsorption, and the fundamental reasonand theoretical basis of modified membrane pollution resistance characteristics were notmentioned. At present, Stanford, Hokkaido and other universities have demonstratedthat atomic force microscopy (AFM) in conjunction with colloidal probe is a powerfulmethod for predicting the organic fouling of membranes. In the present studyhydrophilic polymer polyvinyl alcohol (PVA) was coating on the PVDF membranesurface via dip-coating method to make the hydrophilic modification. The contactangles, flux decline rates and other properties of hydrophilic homemade PVDF/PVAmodified membranes which are preperating in different conditions were examined todetermin the optimal preparation conditions.The membrane-filtration experiments andcleaning experiments of PVDF/PVA membranes and PVDF membranes by simulatedwastewater (humic acid, sodium alginate solution), the actual wastewater(hydrophilic, hydrophobic, tiny hydrophobic solution separated from secondaryeffluent of municipal sewage by resin) were carried out.Membrane flux decline rates,membrane-foulant adhesion forces, flux recovery rates were examined by atomic forcemicroscopy in conjunction with colloidal probes and other technologies. The mainconclusions are presented as follows:（1）The properties of PVDF/PVAmodified membranes will be impacted by PVA concentration, pressing time, crosslinking reaction time and heat treatment time.Theoptimal conditions for the preparation of modified membranes: PVA concentration is1.0wt%, the pressing time is5min, the crosslinking reaction time is5min, the heattreatment time is60S. The flux of the modified membrane is550L/（m2·h），the BSAretention rate is99.4%，the contact angle is55°.（2）Compared withthe PVDF membranes, the roughnesss of PVDF/PVAmembrane preperated in the optimal conditions increases, the surface hydrophilicityincreases, the water flux decreases, BSA retention rates increases.（3）It was found that the hydrophilic composition affected membrane foulingseverely by PVDF membrane and PVDF/PVA modified membrane foulingexperiments. the interaction forces between membrane and foulant were investigated byAFM，in conjunction with colloidal probes.Results showed that the adhesion force isgreater, the more serious membrane fouling..The decrease of membrane-foulantinteraction force is an effective strategy to improve the anti-fouling property of PVDFmembranes.(4) The physical cleaning experients of PVDF and PVDF/PVA memranes showedthat the membrane fouling caused by the hydrophilic composition in secondary effluentof municipal sewage was seriously and the flux recovery rate was low.