Effect of different coagulation baths on the structure and performance of regenerated cellulose ultrafiltration membranes
The application of various ultrafiltration membranes in biopharmaceutical production presents promising opportunities,offering effective separation of target substances with low energy consumption and minimal chemical additives.These membranes achieve effective separation of target substances from solutions while requiring minimal supplementary chemical additives.Materials such as poly ethersulfone(PES),poly vinylidene difluoride(PVDF),and cellulose are commonly used for membrane fabrication.Among them,regenerated cellulose(RC)ultrafiltration membranes demonstrate unique advantages in practical filtration.Due to their excellent hydrophilicity of cellulose,they significantly reduce protein adsorption during filtration,thus prolonging membrane lifespan.Additionally,cellulose,being abundant and renewable,aligns with sustainability goals by mitigating environmental impact.The use of cellulose products can reduce the environmental impact of synthetic products,aligning with sustainability goals.However,the abundant hydrogen bonds and high crystallinity of cellulose make it nearly insoluble in common solvents,posing challenges for direct processing.Currently,most cellulose ultrafiltration membranes on the market are either cellulose acetate membranes or are obtained through hydrolyzing cellulose acetate membranes.Although chemical modification can enhance the processability of cellulose,the industrial production of cellulose derivatives still relies on heterogeneous reaction methods,which are typically limited to the surface of cellulose and difficult to control,leading to issues such as adverse reactions and waste.Developing efficient cellulose dissolution systems is necessary for directly dissolving and preparing RC products from cotton pulp.To meet the requirements of sustainable development,a series of low-cost and recyclable room-temperature cellulose solvents have been developed,enabling the clean preparation of green RC ultrafiltration membranes.To achieve the direct preparation of RC ultrafiltration membranes from cotton linters at room temperature,this study selected ZnCl2/AlCl3 as the cellulose dissolution system and used water,ethanol,ethylene glycol,and acetone as coagulation baths.RC ultrafiltration membranes were prepared using the NIPS method.The influence of different coagulants on the structure of RC ultrafiltration membranes was studied,and based on this,the effect of ethanol proportion in water/ethanol mixed coagulation baths on the structure of RC ultrafiltration membranes was investigated.Finally,the impact of these structural changes on the separation performance of ultrafiltration membranes was analyzed and evaluated through water flux,MWCO,and membrane retention capacity for blue dextran(BD)and human immunoglobulin G(IgG).The results show that RC ultrafiltration membranes prepared in different coagulation baths have different structures.RC membranes obtained in specific organic solvent(such as ethanol and ethylene glycol)coagulation baths exhibit typical ultrafiltration structures,including a dense surface layer and a support layer with large pores.In contrast,ultrafiltration membranes with large sponge-like pores can only be obtained in water.With the increase of ethanol concentration in water/ethanol mixed coagulation baths,the thickness of the RC ultrafiltration membrane's skin layer gradually increases,the pore size of the skin layer decreases,and finger-like pores begin to appear inside the membrane when the ethanol concentration reaches 70％.Such structural changes significantly enhance the water flux and retention performance of RC ultrafiltration membranes.The water flux of RC-ET(regenerated from pure ethanol)can reach 628.57 LMH/bar,with a MWCO value of 314.5 kDa,effectively separating virus markers BD and IgG.This new method for preparing RC ultrafiltration membranes is simple,economical,and requires no additional energy consumption,thus holding broad prospects for application in pharmaceutical production.
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