Hydrophilic Modification Of Polyethersulfone (PES) Nanofiltration Membranes And Study On Antifouling Property

Nanofiltration is a kind of novel and effective membrane separation technology,which has been widely applied in many industries. Membrane fouling is a bottleneck for application of nanofiltration, while developing antifouling membrane is fundamental way to solve this problem. In order to improve membrane separation property and reduce membrane fouling, antifouling nanofiltration membranes were investigated.A charged polyethersulfone (PES)/sulfonated PES(S-PES) blends nanofiltration membranes were prepared by phase inversion in a wet process. The result of FTIR and XPS analysis provided that enrichment of sulfonic acid group on the membranes. The result of contact angle and water uptake showed that membranes became more hydrophilic as S-PES content increased. The water flux of S-PES nanofiltration membranes increased as S-PES content increased. The result of nanofiltration for inorganic salts showed that the rejection for S-PES nanofiltration membranes became higher with the increasing percentage of S-PES, rejection for salts in the order of RNa2SO4 >RNaCl, this phenomenon could be explained by electrostatic interactions between charged ions and membranes surface. The nanofiltration of dyes were carried out to characterize membrane separation property, the results showed that a near 100% rejection to high molecular weight dye, higher rejection for low molecular weight dyes compared to pristine PES membrane. This is mainly because membranes blending with S-PES are more hydrophilic, have more pores and a smaller pore radius.A polyethersulfone-polymethacrylate (PMAA) copolymer was synthesized by water-phase precipitation copolymerization, using benzoyl peroxide as an initiator. A series of PES/PMAA blends nanofiltration membranes were prepared by phase inversion method. FTIR revealed that O=S=O adsorption peak at 1149cm" attributed to PES exiting. The result of contact angle and water uptake indicated that membranes became more hydrophilic as PES-PMAA content increased. The water flux of PES-PMAA nanofiltration membranes increased as PES-PMAA content increased. The experiment of nanofiltration for inorganic salt showed that the salt rejection for PES-PMAA nanofiltration membranes first increased then decreased, this phenomenon is because electrostatic interactions between charged ions and membranes surface was weakened by hydraulic power. The results of nanofiltration of dyes showed that the rejection of high molecular weight dye became higher with the increasing percentage of PES-PMAA, rejection for methylene blue first increased then decreased, which results from the bigger pore radius of membranes. In addition, water flux of PES-PMAA nanofiltration membranes is turnable due to the switch of the stretched and collapsed states of the polymer chains for PMAA at different pH value in the solution.As modifiers pluronic F127 and aminoethanol were used to fabricate antifouling S-PES and PES-PMAA membranes respectively. The surface chemical composition and cross-sectional morphology of modified membranes were characterized by XPS and SEM respectively. The antifouling property of modified nanofiltration membranes was investigated using three model foulants, bovine serum albumin (BSA), sodium alginate (SA), humic acid (HA) representative of proteins, polysaccharides and natural organic matter. The antifouling experiments revealed that the fouling of modified membrane with F127 was remarkably reduced for three foulants and the antifouling property of PES-PMAA membrane for BSA was remarkably improved by aminoethanol modification.