Research On Dissolution And Regeneration Of Silk Fibroin With Ionic Liquid As Solvent

Natural silk fibroin has attracted increasing interests of researchers for its comprehensive utilization,and it is one of the richest renewable resources. Room temperature ionic liquids(RTILs),is a class of novel environment-friendly "green solvents",which can provide a new approach for the processing of protein materials.The solubility and the dissolution rate of silk fibroin in two ionic liquids, [AMIM]Cl and[BMIM]Cl,were investigated respectively.It indicates that the solubility and dissolution rate of silk fibroin in[AMIM]Cl are higher than that in[BMIM]Cl.The dissolution rate of silk fibroin in ionic liquids increases largely with increasing the temperature and the proper temperature was 95℃～105℃.Contrarily,the dissolution rate decreases largely with increasing the concentration of silk fibroin.The molecular weight(Mw) of regenerated silk fibroin decreased with the increase of heat time and temperature from the result of viscosity.To assurance the Mw and dissolution rate,the proper condition should be at about 100℃within 5 hours.The steady and dynamic rheological behaviors were tested on HAAKE RS150L Cone-and-Plate Rheometer.The Newtonian rheological behavior was shown at low shear rate while the non-Newtonian behavior was observed at high shear rate.The critical shear-thinning rate decreased with concentration increasing or temperature decreasing,which indicates the orientation of silk fibroin macromolecules in ionic liquids at higher shear rate.The zero shear viscosity of silk fibroin/[BMIM]Cl solutions increased linearly with the concentration at low concentration while increased with concentration power function at high concentration,the power index was only 1.91,which indicated there was no high entanglement of the typical flexible polymer.The flow activation energy E_ηof silk fibroin/[BMIM]Cl solutions(9%-50.4 kJ/mol,12%-80 kJ/mol) was relative higher than that in common solvent,which indicated that the shear viscosity of concentrated silk fibroin/[BMIM]Cl solution was more sensitive to temperature. Therefore,the viscosity of the solution can be adjusted by temperature. However,the temperature must be controlled strictly to ensure the stability of solution during processing.There was no gel point was observed under experimental conditions,which is clear that solutions were quite stable.The regenerated silk films and fbers were prepared with silk fibroin as raw material,ionic liquid[BMIM]Cl as solvent,methanol and ethanol as coagulator.The spinning experiment was conducted with the silk fibroin and PAN as raw material,ionic liquid[BMIM]Cl as solvent and water as coagulator.The composite fibers were obtained by dry-wet spinning technology.The structure and properties of productions were characterized by XRD,FT-IR,TGA and SEM.It is shown that the dissolution of silk fibroin is direct without chemical reaction.The crystal structure of regenerated silk fibroin is similar with natural silk fibroin.The cross section of the fiber is circle.