Preparation, Characterization And Anti-fouling Performance Of PEO-b-PMMA/PVDF Ultrafiltration Membrane

In this dissertation, amphiphilic block copolymer was introduced into the polymeric casting solution for preparation of blend ultrafiltration membrane and anti-fouling performance of resultant membrane was investigated. From the point of structure design, a series of amphiphilic block copolymers (PEO-b-PMMA) with different length of hydrophobic chain were synthesized. Base on the obtained amphiphilic block copolymers, a series of PEO-b-PMMA/PVDF blend ultrafiltration membranes were prepared. The effects of the composition and the content of the block copolymer on the structure and properties of ultrafiltration membrane were investigated. The main research contents of this thesis are as follows:1. A series of amphiphilic block copolymers (PEO-b-PMMA) with different length of hydrophobic chain were synthesized via atom transfer radical polymerization (ATRP) approach. The structure and molecular distribution of the resultant PEO-b-PMMA block copolymers were characterized using Nuclear Magnetic Resonance (NMR), Fourier Transform Infrared Spectrometer (FTIR), Gel Permeation Chromatography (GPC). The characterization results confirmed that the molecular weight of the series amphiphilic block copolymer is 6500,13000,20000 g/mol and the corresponding polydispersity index (PDI) is 1.07,1.23,1.31, respectively. Transmission electron microscope images and dynamic light scattering results confirm the size of PEO-b-PMMA micelle increases with the increasing of molecular weight.2. The obtained series of amphiphilic block copolymers PEO-b-PMMA were introduced into the casting solution of PVDF membrane system. A series of PEO-b-PMMA/PVDF blend ultrafiltration membranes were prepared via nonsolvent induce phase separation process. The pure water flux, retention and contact angles of the resultant membranes were evaluated and the amount of amphiphilic block copolymers in membrane casting solution was optimized. The results show that when the content of block copolymer is 3%, the pure water flux of blend ultrafiltration membrane isl30.4 L/m2 h, and time dependence of contact angle compared to pure PVDF membrane is reduced by about 6°.Surface structure and roughness of PEO-b-PMMA/PVDF membrane characterized by Atomic Force Microscope (AFM), with the increase of content of the amphiphilic block copolymer PEO-b-PMMA, the surface roughness of PVDF membrane increased. In addition, the effects of hydrophobic segment length in block copolymers on the structure and properties of the blend ultrafiltration membrane were investigated. The results show that with the block copolymer molecular weight increases, the hydrophilic properties of the blend ultrafiltration membrane are significantly improved. When the PEO-b-PMMA molecular weight is 20000g/mol, the water flux is 403.4 L/m2h, while the corresponding rejection rate is 93.6%, and time dependence of contact angle compared to pure PVDF membrane is reduced by about 9°3. By using bovine serum albumin and humic acid as the representative of protein contaminants and natural organic pollutants, the anti-fouling performance of PEO-b-PMMA/PVDF blend ultrafiltration membrane was studied. The results show that the introduction of amphiphilic block copolymer of PEO-b-PMMA can dramatically improve the anti-fouling performance of PVDF membrane. The water flux recovery rate after bovine serum albumin and humic acid contamination can increase from 58.6 to 87.8%,58.6to 86.8%, respectively. In addition, the experiment of the protein with static adsorption show that when amphiphilic block copolymers PEO-b-PMMA was added, it improves the hydrophilic and the anti-fouling performance.4. To explore the reasons on improvement of anti-fouling performance of the blend ultrafiltration membrane, the visual information on the composition distribution around membrane pores was obtained by mapping technique of Raman spectra. The results indicate the distribution of PEO chain segment around membrane pores is much higher than that in membrane matrix. The obtained membrane is of typical surface segregation. The improvement of hydrophilicity and antifouling performance of PEO-b-PMMA/PVDF blend ultrafiltration membranes is describe to the higher PEO chain segment distribution around the membrane pores than that of in membrane matrix. Based on the analysis, the membrane formation and anti-fouling mechanism of blend membranes was proposed.