Preparation Of Bioinspired Superhydrophilic EVOH Ultrafiltration And The Study Of Anti-Fouling Performance

Ultrafiltration process is a membrane filtration process between micro filtration process and nanofiltration process.It uses the transmembrane pressure on both sides of the membrane as the driving force to achieve the interception of macromolecules larger than pore structure through the pore structure of the membrane surface.Compared with other membrane filtration processes,UF process has advantages such as energy saving,high processing efficiency,and no secondary pollution.Inspired by the mussel effect,the ultrafiltration membrane with superhydrophilic property was prepared by the combining coating hydrophilic substance with constructing rough structure on the membrane surface.In this paper,a method of combining micro-molding with immersion precipitation was adopted,in which the casting solution was casted on the mold surface.Then the liquid membrane and the mold were put into a coagulation bath at a certain temperature to complete the phase separation process and solidify into a membrane.The nascent membrane was peeled from the mold to obtain the membrane surface with micro-nano hierarchical structures.Compared with the membrane obtained by the smooth mold,the membrane surface obtained by sandpaper had many duplicated micro-structures,which gave the membrane surface better hydrophilicity.The structure and performances of membranes obtained by different molds was studied in this experiment,and the optimal mold was selected.Since the molding process occurred at the membrane bottom,the finger-like structures crossed the body structure of the membrane,and the finger-like structures was connected to the membrane micro-structures,which was very easy to collapse and caused irreversible damage to the membrane.Therefore,the method of regulating the composition and temperature of coagulation bath was adopted to regulate the structure of the membrane,determined the final coagulation bath temperature and composition.For microporous membrane,it is not suitable for UF process.Therefore,in order to achieve UF process,it is necessary to coat microporous membrane.The coating method was selected to spraying to ensure the uniformity of coating on the membrane surface.The coating solution was sodium alginate aqueous solution(SA)and polyvinyl alcohol aqueous solution(PVA).The final coating concentration was determined respectively: SA solution:6wt%,PVA solution: 8wt%,and then the membrane was crossed link.The ultrafiltration membrane obtained under this condition with excellent hydrophilicity and retention rate of99%.In order to verify the anti-fouling performance of the obtained ultrafiltration membrane,a certain concentration of humic acid aqueous solution was used as a natural water solution for 4 consecutive cycles.Anti-fouling performance was analyzed from the flux decay rate of the membrane and flux recovery of the membrane: In each cycle,the SA composite membrane with the strongest hydrophilicity had the lowest flux decline rate and the smooth membrane had the largest flux decline rate.In the cleaning process,the membrane with microstructures on the membrane surface possessed the best recovery performance,which indicated that the existence of microstructures is of great significance to the recovery of membrane performance.Escherichia coli solution was used to explore the anti-biofouling performance of the obtained membrane: The membrane with microstructures had the best anti-biofouling performance and the best cleaning effect.