Preparation Of EVOH Nanofiber/Quaternary Ammonium Polymer Composite Anion Exchange Material And Study On Its Separation Performance For BSA

Bovine serum albumin（BSA）is widely used in the biochemical field and is a very important biological product.It is often used as a stabilizer for enzymes and plays a protective role in enzymes.However,due to the limitations of traditional biological macromolecule separation and purification technologies,BSA molecular products still face problems such as low yield and low purity.Ethylene vinyl alcohol copolymer（EVOH）is a thermoplastic polymer with good hydrophilicity and biocompatibility.After being prepared into nanofibers by melt extrusion phase separation,it has high porosity,large specific surface area,and is easy to functionalize.In this paper,EVOH nanofibers were combined with quaternary ammonium ion groups（NH₄⁺Cl^-）to prepare strong anion exchange chromatography materials.A strong anion chromatography membrane material with high saturation adsorption capacity and high throughput was obtained,which is of great significance for achieving efficient and rapid separation and purification of BSA.The main research contents are as follows:Ion exchange nanofiber chromatographic membranes with high pore structure and surface quaternization were successfully prepared using melt extrusion phase separation,dispersion in situ crosslinking,wet film formation,and surface chemical modification methods.The effects of the content of crosslinking agent（glutaraldehyde aqueous solution）and modifier（polyethyleneimine）on the pore morphology and surface chemical properties of the membrane were studied,and the adsorption of biological macromolecule BSA on the membrane was studied.It has been found that the pore structure formed by irregular stacking of nanofibers plays an extremely important role in the functional modification of nanofibers,and the integrity of the pore structure is crucial for improving the saturated adsorption capacity.The results showed that when the content of polyethyleneimine was 2.5wt%,the comprehensive performance of the film was optimal.At this time,the pore structure of the film remained relatively complete,its static water contact angle was 0°,the tensile strength was increased from unmodified 17.1 MPa to 31.7 MPa,and the surface zeta potential was51.39 m V.In addition,due to the high pore structure formed by the stacking of nanofibers,their BSA saturated adsorption capacity can reach 177 mg/g,which is 4.8 times higher than the adsorption capacity of non quaternized membranes.In order to solve the problems of incomplete retention of pore structure,cumbersome preparation process,and low saturated adsorption capacity,we successfully prepared an anion exchange membrane（EVOH/CSQAS）with complete pore structure,high flux,and high saturated adsorption capacity by selecting suitable quaternary ammonium salts and using in situ co mixing and cross-linking method to cross-link quaternary ammonium salts with high degree of substitution on the surface of EVOH nanofibers,greatly simplifying the preparation process。The effects of the content of chitosan quaternary ammonium salt（CSQAS）on the pore structure,specific surface area,pore size distribution,and BSA adsorption performance of the membrane were studied.The results showed that when the content of chitosan quaternary ammonium salt（concentration:10 g/L）was 25%,its comprehensive performance was the best,exhibiting excellent hydrophilicity（static water contact angle 0°）,high pore structure,and high specific surface area.The BSA adsorption test results show that EVOH/CSQAS exhibits a high static saturated adsorption capacity（724.9 mg/g）and a high pure water flux（8890 L/hm2）,which is the result of the joint action of the pore structure formed by the nanofiber stack and the chitosan quaternary ammonium salt.Compared with flat plate membrane materials,aerogel materials have the advantages of high porosity,low density and good compression resilience.In order to solve the limitations of membrane materials in practical application and further improve the adsorption performance,a three-dimensional aerogel anion exchange material was constructed with EVOH nanofiber as the aerogel skeleton,chitosan quaternary ammonium salt as the modifier,and glutaraldehyde as the crosslinking agent.The results showed that when the concentration of chitosan quaternary ammonium salt was 10 g/L and the content was 25 vt%,the morphology,pore structure and adsorption performance of the aerogel were optimal.At this time,the aerogel has a random porous channel structure,the adsorption capacity is 1121 mg/g,and the compression stress in air is 23.21 MPa.