The Studies Of Preparation And Performance Of Poly(Vinylidene Fluoride) Charged Ultrafiltration Membranes

The water purification is one of the hottest topics in21st century. As a green and energy-efficient separation technology, ultrafiltration exhibits great application value in field of water treatment. However, at present membrane fouling caused by the biological macromolecules in polluted water still constitutes a bottleneck of its development. Hence, improving the anti-fouling performance of ultrafiltration membranes is particularly urgent. It has been shown that electrostatic interaction has direct effect on the membrane fouling. Therefore, membrane charge modification can be an effective way to reduce the membrane fouling with the combination effect of membrane pore size.In this paper, a favorable method of applying high voltage external electric field (2kV) was used to prepare a series of PVDF ultrafiltration membranes when PEG was used as additive via the immersion precipitation phase inversion process. The effects of the external electric field on the structure, surface functional groups, membrane potential, and surface hydrophilicity of the membranes were investigated. In addition, anti-fouling property and separation performances of the membranes were also researched. The results showed that the protein adsorption amount on the electric treated membranes was distinctly reduced when comparing with the un-treated membranes. Meantime, the contact angle of the PVDF membrane was decreased under the influence of the external electric field. Especially for the PVDF membrane added with PEG600, the protein adsorption amount decreased43%, reaching132.54μg·cm-2and the value of contact angle was64.8°. While there was no detectable effect of the external electric field on the other membrane performance, such as pure water flux and rejection.Effect of PVP K30content on PVDF ultrafiltration membrane performances was also researched in this work. With the increase of PVP K30content, the separation performance of PVDF membranes increased. The electric treated membrane was also superior to that of the un-treated membrane. Meantime, the surface hydrophilicity of the electric treated PVDF membrane was greater than the un-treated membrane. The protein adsorption amount on the electric treated membranes was also distinctly reduced. Especially for the electric treated PVDF membrane, when the mass fraction of PVP K30was9%, the value of water contact angle reached65.4°and the protein adsorption amount decreased46%, reaching26.40μg·cm-2. When increasing the PVP K30content, the membrane potential increased. Furthermore, all the membrane potential of the electric treated membranes was negative. The negative membrane potential meant that negative charges existed at the top surface of the electric treated membranes. Based on the above results, the PVDF ultrafiltration membranes with different molecular weight of polyvinyl pyrrolidone (PVP) were successfully prepared. The effects of porogen molecular weight and the external electric field on membrane properties were investigated. The experiment found that when increasing the PVP molecular weight, the membrane potential decreased. The separation performance of the external electric field treated membrane was also superior to that of the un-treated membrane. Meantime, the BS A protein adsorption experiment results showed that the anti-fouling ability of the external electric field treated membranes was distinctly enhanced when comparing with the un-treated membranes due to more negative charges were fixed on the surface of the treated membranes by the external electric field. For the external voltage treated membranes, the BSA adsorption amount decreased by65-78%. All the experimental results indicated that the research in this work will has efficient value for preparing a new kind of ultrafiltration membrane with high anti-fouling properties via phase inversion technique.