Hydrophilic Modification Of PVDF Ultrafiltration Membrane And Its Antifouling Performance

With the shortage of water occurring globally,seawater desalination and wastewater recycling have played more important roles in the world.Nowadays,membrane technology has emerged and spread rapidly in water purification due to its low cost and high efficiency.Compared with other types of membranes,polyvinylidene fluoride（PVDF）membrane is an attractive membrane material due to its excellent properties,such as high mechanical strength,outstanding thermal stability and good chemical resistance.However,the hydrophobicity of PVDF membrane makes it susceptible to fouling,which restricts its potential in water treatment.Membrane fouling is usually caused by the adsorption and deposition of colloidal particles,organic macromolecules and microorganism on the membrane surface and in the pores of the membrane,resulting in decreased flux,shorted membrane life and increased operating costs.It is generally believed that hydrophilic membrane surface can effectively reduce the adsorption and deposition of contaminants,thereby reducing the fouling of the membrane.It is very meaningful to prepare a hydrophilic and antifouling PVDF membrane by a simple and effective method.The main contents and results of this dissertation are summarized as follows:（1）The effect of exposure time in wet air on the structure of PVDF membrane has been studied.First,PVDF ultrafiltration membrane with rough network-like macroporous structure was prepared by adjusting the exposure time.Then,polydopamine was coated on the membrane surface and the hydrophilicity and antifouling properties of the membrane were studied.The results showed that the water contact angle of the membrane decreased from 83.7°to 29.5°after coating polydopamine on the surface of PVDF membrane with rough network-like macroporous structure,and the flux recovery rate increased significantly to 96%.This fully demonstrates that the modified membrane has excellent hydrophilicity and anti-pollution properties.In addition,the coarse network-like macroporous structure also has obvious help on the flux,the hydrophilicity and the anti-pollution ability of the membrane.（2）A simple method for fabrication PEGylated PVDF ultrafiltration membranes was proposed for the first time,which used the in-situ cross-linking polymerization technique.This method greatly simplifies the process of preparing PEGylated PVDF membrane.XPS and ATR-FTIR spectra verified that PPEGMA had been successfully synthesized and immobilized on the membrane surfaces.After the introduction of the PPEGMA chain,the hydrophilicity of the membrane surface was significantly enhanced and the flux recovery rate after 3 cycles still reached 90.3±2.8%,indicating that the membrane’s antifouling ability was significantly improved.（3）We successfully fabricated antifouling zwitterionic PVDF membranes based on the in situ c_ross-linking polymerization of sulfobetaine methacrylate（SBMA）in the casting solutions and the non-solvent induced phase separation（NIPS）technique.Filtration experiments showed that after the introduction of PSBMA chain,the flux recovery rate increased significantly from⁴5.1%to⁹0%,irreversible fouling(F_ir)decreased from⁵4.9%to¹0%,total flux loss（F_t）decreased from⁷7.1%to⁵0.4%and the bovine serum albumin（BSA）rejection increased from⁹.9%to⁸1.5%.It is indicated that the prepared PVDF/PSBMA membranes have excellent anti-fouling property and high separation efficiency.