Study On Modified Polysulfone UF Membranes With Copolymers Containing Capsaicin Derivative Structure

Polysulfone(PSF) is a kind of polymer membrane materials with excellentmechanical strength, chemical properties and heat resistance. But PSF membranes areeasily to suffer membrane fouling due to the hydrophobicity of the PSF material,which often shortens the membrane service lifie. At present, in order to improve themembrane anti-fouling property, a number of research on the hydrophilic modificationof membrane surface has been carried out. When the membarens are used into a realwater treatment, such as seawater desalination, not only hydrophilicity andanti-organic-fouling of the membarne are required, also the ability to bear thepollution of microbial and algae. For this, a kind of new antibacterial ultrafilration(UF) membranes with good hydrophilicity and excellent bacteriostasis were prepared.First, the antibacterial dipolymer P(H-co-M) was synthesized through a freeradical initiated pomerization from capsaicin derivative structure HMBA and methylmethacrylate (MMA). In order to enhance the hydrophilicity of the polymer, acid(AAc) was added as one nomoner, and, terpolymer P(H-M-A) was synthesized as thesame method above. Stuctures of these polymers were confirmed using the infraredabsorption spectrum (FT-IR) and thermo gravimetric analysis.A given amount of dipolymer P(H-co-M) was added into the PSF castingsolution, and a kind of new antibacterial PSF/P(H-co-M) UF membrane namedmodified dipolymer UF membrane was prepared through the immersion precipitationphase inversion. The effects of P(H-co-M) contentbath temperature and heatingtreatment on the membrane structure, separation performanece and antibacterialproperty were investigated. The results showed that, the hydrophilicity of membranesurface were improved; When the content of P(H-co-M) was0.5wt%and the gel bathtemperature was20℃, the separation performance of the modified membrane wasimproved with the the steady flux of122.2L/m~2.h and rejection of84.4%for5mg/L humic acid (HA) solution, which increased by19.2%and9.2%compared to theunmodified PSF UF membrane, respectively. When the content of P(H-co-M) was1.0wt%, the modified membrane had an excellent antibacterial property and theantibacterial rate was up to80.7%. Heat treatment played little influence in flux andrejection of the modified dipolymer UF membrane.As the same method above, A given amount of P(H-M-A) was added into thecasting solution, and PSF/P(H-M-A) UF membrane named modifief terpolymer UFmembrane was prepared. The effects of P(H-M-A) content and bath type (differentconcentration of ethanol and acetic acid) on the membrane structure, separationperformanece and antibacterial property were evaluated. The results were as follows.When P(H-M-A) was added, the membrane surface hydrophilicity was dramaticallyimproved, when the content of P(H-M-A) was0.5wt%, the contact angle reduced by30.0%and15.1%compared to the unmodified membrane and modified dipolymer UFmembrane, respectively. When the content of P(H-M-A) was0.5wt%and A25%ethanol solution was used as gel bath, the membrane separation performance wasenhanced with the steady flux of55.9L/m~2.h and rejection of80.3%for5mg/L HAsolution. Moreover, the modified terpolymer UF membrane had an excellentantibacterial property and the antibacterial rate was up to89.2%, which is better thanthe modified dipolymer UF membrane.In order to investigate the anti-organic-fouling propertis of these two UFmembranes, filtration experiments for a relatively long operating period (8h) werecariied out. The flux recovery rate was used as a parameter for evaluating theanti-organic-fouling property.5mg/L HA solution and raw seawater were used as thefeed, respectively. The sepeartion perfomamnces and anti-organic-fouling propertiesof various membarens, including PSF/P(H-M-A) membrane, PSF/P(H-co-M)membrane and PSF membrane, were systematically investigated. The results showthat, after filtering8hours with5mg/L HA solution, the steady fluxes of the modifieddipolymer and terpolymer UF membrane were86.4L/m~2.h and95.9L/m~2.h, and therejections were84.3%and80.8%, respectively, which were all higher than theunmodified UF membrane (67.0L/m~2.h and76.1%). After cleaning with NaOH solution, the flux recovery rates of the modified dipolymer and terpolymer UFmembrane were96.7%and98.4%, respectively. After filtering8hours with rawseawater, the steady fluxes of the two kinds modified UF membranes were142.3L/m~2.h and145.7L/m~2.h, which were higher than the unmodified PSF membrane;rejections were41.6%and36.6%, which increased by40.4%and32.2%compared tothe unmodified membrane, respectively. After cleaning with NaOH solution, the fluxrecovery rates of the modified dipolymer and terpolymer UF membrane were53.9%and59.0%, respectively. Therefore, the modified terpolymer UF membrane was thebest in antifouling property among all other testing membranes.