Preparation And Characterization Of Positively Charged Membranes Via In-situ Amination

The graduate thesis introduces a novel method to prepare charged membranes using triethoamine as an aminantion agent and investigates the influence of various membrane preparation parameters on membrane properties as well as water absorption process in the NMP/BPPO/TEOA casting solution by Two-dimensional ATR-FTIR spectroscopy.Charged membrane can be used to separate charged component with much smaller size than pore size according to electrostatic repulsion. Besides,the hydrophilicity of the charged membrane is enhanced due to the introduction of the charged groups.Thus,the permeability of the membrane is increased as well.Therefore,charged membrane is attached importance to application in recycling resource and protecting environment.Driven by commercial interests,the negatively charged membrane used for antifouling in the separation of biochemical products has been deserved much attention in recent years.The development of the positively charged membrane is ignored.But to separate the species with positive charge such as the separation of biomacromolecules below the isoelectric point,and recover cathode electrophoresis lacquer,etc.,positively charged is actually indeed. However,the traditional preparation method for positively charged membrane is using chloromethyl methyl ethe and there are seldom charged membranes for industry because it is difficult and costly to prepare charged membranes.In our previous studies,a new route was initiated for preparing a positively charged asymmetric membrane using TMA by in situ amination and phase inversion. In our research,we use triethanolamine(TEOA) as the amination agent.It still avoided not only the use of chloromethyl methyl ether,which is a carcinogen and potentially harmful to human health but also the multi-steps in membrane preparations. Besides,there are three hydroxyl groups on TEOA molecule structure,which could increase the hydrophilicity and anti-fouling property of the membrane.In addition,the solvent-nonsolvent system NMP/H₂O is much cheaper and convenient than the previous chlorobenzene/ethanol.In this thesis,the influence of the membrane preparation parameter,such as polymer concentration,the proportion of the polymer to amine,charged group species, the coagulation temperature and the evaporation time and relative humidity on the membrane performance and microstructure have been investigated.In addition,the water absorption process during the membrane formation is investigated by 2D-ATR-FTIR correlation spectroscopy.This thesis includes five chapters.Chapterâ… give an overview on the research background through the introduction of the history and the classification of separation membranes,the preparation and basic characterization of the charged membrane,and the generalization of the research status of the positively charged membrane.Then the membrane preparation by phase inversion method(includes the process of the membrane forming and the influence parameters of the membrane performance),the properties of poly (2,6-dimethyl-1,4-phenylen oxide)(PPO) and its application in membrane preparation are elucidated.Finally,the research ideas and outline of the thesis are purposed.Chapterâ…¡initiates a new route for preparing positively charged asymmetric membrane by in situ amination and phase inversion in which the N-methyl-2-pyrrolidone solution of triethanolamine(TEOA) and brominated poly (2,6-dimethyl-1,4-phenylen oxide)(BPPO) are cast and immerged into distilled water gel medium.The effect of the proportion of BPPO to TEOA,different charged group species and coagulation temperature on membrane performances and morphologies are investigated.In Chapterâ…¢,the influence of evaporation time and the relative humidity on charged ultrafiltration membrane via dry-wet phase inversion is investigated.The results show that the role of evaporation time and the relative humidity on the membrane performance and morphologies for a positively charged casting system is different from the conventional rule.This is mainly due to the competition of two influence factors:evaporation of solvent and water absorption of the casting solution. The results are conformed to SEM observation and the principles of pore size distribution.Additionally,in order to compare to the dry-wet phase inversion method, a symmetric membrane was prepared by prolonging the exposure time to more than 12 hours(which is similar to vapor induced phase inversion) at different RH.Polymer nodules and pinholes on the membrane surface and a symmetrical morphology are observed by SEM.In Chapterâ…£,two-dimensional ATR-FTIR spectroscopy is used to study the water absorption process in the NMP/BPPO/TEOA casting solution.The broad OH stretching vibration of water split into four absorption bands(3635,3533,3392,and 3297 cm^-1) are identified by contrast experiments of water absorption by pure NMP and NMP/BPPO solution.Furthermore,it is proved that from 2D asynchronous spectrum,during the water absorption process,water molecules first molecularly disperse in the casting solution and then form hydrogen bonds with the hydrophilic group in the casting solution.Chapterâ…¤is the summarization of the thesis.A novel positively charged membrane is prepared using triethanolamine as aminatin agent.The effect of the proportion of BPPO to TEOA,different charged group species,coagulation temperature,evaporation time and the relative humidity on membrane performances and morphologies are investigated.Finally,the water absorption process in the NMP/BPPO/TEOA casting solution is studied by two-dimensional ATR-FTIR spectroscopy.