Zwitterionic Modification Of Nanofiltration Membranes To Improve Anti-fouling Property

Nano-filtration membrane has been widely used in the separation process,because of its low operating pressure and good separation ability.However,it easily polluted by protein,the flux and rejection rate are decreased obviously and the life of membrane are shortened.This greatly limits the application of nano-filtration membrane,thus it's very important to solve the problem of nano-filtration membrane fouling.As zwitterion polymers can form effective water layer through hydrogen bonding and coulomb Ian force to prevent protein adsorption effectively,it become effective modified material to prepare low fouling membrane surface.This work mainly studied a anti-fouling membrane by grafting tertiary ammonium group and sulfonic acid group on the membrane surface.Focused on the property of zwitterion nano-filtration membrane and its influencing factors.Poly(meth acrylic acid)N,N-two methyl ethyl ester(DMAEMA)was firstly grafted onto the polypiperazine amide nano-filtration membrane by the activation of AIBN then carboxylic zwitterion emerged on the membrane surface by the quaternization of 1,3-propanesulfonate.The modified membranes were characterized by FTIR?XPS?AFM and SEM to analysis the chemical components of the membrane surface.The results show that the amphoteric ion has been successfully grafted onto the membrane surface.The AFM analysis shows that the roughness of membrane is increased,and then the contact area between the membrane surface and water is increased,thus the flux will be increased.At the same time,the water contact angel(WCA)analysis shows that the hydrophilicity of the modified membrane is higher than the one of original membrane.It's obvious by SEM that the surface and cross-section structure of the membrane did not change obviously.These results show that the structure of the membrane is not destroyed by modification reaction.Moreover,bovine serum albumin(BSA)is used as a model protein to analyze the filtration performance of the modified membrane by protein static adsorption and dynamic filtration experiments.The results show the nano-filtration membranes with different grafting density have different protein adsorption.As the increase of zwitterion graft density,the protein adsorption of the modified membrane decrease from 120 ?g/cm2 to 1.86 ?g/cm2,which indicates that the anti-fouling properties of modified membrane has been greatly improved.Dynamic membrane filtration experiments show that the flux recovery rate of modified nano-filtration membrane has increased significantly.When the grafting density was 311 g/cm2,the membrane water flux was increased from 68.3L/m2·h to 88 L/m2·h.At the same time,the protein pollution flux reduction rate was 37.2%,while the original membrane flux reduction rate was 57.6%.The flux recovery rate of modified membrane can reach 92%,and the flux recovery rate of original membrane was only 67.20%,which indicating the anti-fouling properties of membrane has greatly improved.At last,the resistance and its distribution of the modified nano-filtration membranein the process of protein separation were analyzed by the resistance superposition model.The result shows that the resistance of modified nano-filtration membrane mainly comes from membrane resistance(Rm),which accounts for about 75.38% of the total resistance,but concentration polarization resistance and boundary layer resistance are only 15.08%,9.53%.These results show that the anti-fouling performance of modified membrane is increased significantly compared with the original membrane,it has a good application prospect in the field of protein separation and biomedicine.