Preparation And Performance Of CA/PEI Affinity Microfiltration Membrane And Its Applications

Affinity membrane has received significant attention in recent decades because itcan provide reliable and efficient method for the purification of biomolecules, byintegrating membrane technology and affinity chromatography. Usually,affinitymembranes are prepared by modifying commercial membranes which can result insome undesired changes in membrane structure. By other methods, as in situcopolymerization of two functional monomers, affinity membrane discs can beprepared, but there are some difficult problems in scale-up.In this dissertation, we developed a simple method to directly prepare affinitymembrane. Cellulose acetate (CA), as a matrix polymer, was blend with PEI, afunctional ligand to prepare CA/PEI microfiltration membranes which combine theproperties of CA in membrane formation, such as high consistency of the pore sizedistribution and mechanical rigidity, and the properties of PEI such as chemicalreactivity and capability of selectively adsorbing biological macromolecules. Themethod can simplify procedures of preparing affinity membranes and the aminegroups of PEI blended in membranes make further modification easier under mildconditions. Thus, we can overcome shortcomings such as change of pore size andloss of rigidity coming from multiple steps under harsh conditions during themodification of commercial polymer membranes. By use of multi-function of PEI,CA/PEI membranes were applied to several separation processes such as purificationof proteins, removal of heavy metal ions, endotoxin and bilirubin and so on.Based on developing a method to prepare CA microfiltration membrane, CA/PEImembranes were prepared. The effects of the composition of casting,blend ratio,amount of crosslinking agent and condition of membrane preparation etc. onmembrane performance were investigated and optimized. With moderatecrosslinking, the stability of membrane performance was enhanced and the effects ofblended PEI on membrane formation and membrane structure can be eliminated.Comprehensive results of the investigations show that the optimal composition ofcasting solution is: the mass ratio of CA, solvent and glycerol of 1:10: 3.3, blendratio of 50% PEI solution and CA of 0.15, mass ratio of amount of crosslinkingagent and PEI of 0.5; the optimal condition of membrane formation is: the castedmembranes were kept at the surroundings of 50~55℃and RH>95% for 2 minutes toinduce phase inversion by absorbing water vapor and evaporating acetone, thenimmersed into 20℃water to remove the solvent and additive and solidify themembrane structure. Application studies show that CA/PEI membranes can achieve efficient adsorptionof goal solutes with high capacity because the binding kinetics dominates theadsorption process with the convective flow of solution through the pores. SoCA/PEI membranes can meet the demands in the applications as wastewatertreatment, purification of proteins, removal of endotoxin, blood purification.