The Effect And Application Of Rapid Freezing Combined With Alkali/Urea System Pretreatment On The Silk Fibroin Irradiation

Silk fibroin fiber is a kind of natural polymer material,which not only has excellent mechanical properties,biodegradability and biocompatibility,but also has unique physical and chemical properties.It has a wide range of applications in the fields of biomedicine,flexible conduction and so on.The downside is that silk fibroin has several disadvantages compared to other synthetic fibers,such as wrinkling,deformation,microbial degradation,light-induced aging and yellowing.Therefore,Silk fibroin is usually modified by various methods to meet different environmental needs.Besides,the radiation-induced radical modification is a significant method among many modification methods,which has the characteristics of uniform modification,green environmental protection,simple operation,and wide application.During the modification of silk fibroin,the free radicals largely determines the final modification results.It is possible to change the molecular structure of silk fibroin through pretreatment of silk fibroin to improve the performance of free radicals induced by irradiation.It is possible to change the molecular structure of silk fibroin through pretreatment of silk fibroin to improve the performance of free radicals induced by irradiation,thereby improving the irradiation process of silk fibroin and improving the modification efficiency.In this paper,a simple silk fiber pretreatment method was proposed.The effect of this pretreatment method on the molecular structure of silk fibroin fibers is studied,and the transformation mechanism of silk fibroin after pretreatment was discussed.The attribution and performance of free radicals after pretreatment are discussed.Silk-based gel electrolyte was prepared using this method to verify the feasibility.This research will provide theoretical and experimental basis on modifying silk fibroin fibers via irradiation technology.The main research and results are showing as bellow:(1)The pretreatment of silk fibroin was carried out by the rapid pretreatment method combined with the alkali/urea system.Scanning electron microscopy(SEM),thermogravimetric analysis(TGA),Fourier infrared spectroscopy(FTIR),X-ray diffraction(XRD),and synchrotron radiation small angle scattering(SR-SAXS)were used to study the effects of morphology,microstructure,and thermal stability after pretreatment of silk fibroin fibers.The results show that the radius of gyration of the silk fibroin becomes smaller and the spatial structure becomes tighter,after pretreated with rapid freezing and alkali/urea system In addition,the crystal structure of the silk fibroin fragment were changed,some Silk I structures were changed to Silk.II.Furthermore,the pretreated silk fibroin fragments generated a new crystal structure.This transition may be beneficial to silk-based materials with better stability and better mechanical properties.One of the possible reasons for the crystal structure transition may come from the molecular chain folding,and the hydrogen bonding within the molecular chain may be the main reason for the molecular chain folding.In addition,the thermal stability of silk fibroin fragments was improved after pretreatment,which may be related to the hydrogen bonding in the molecular chain.(2)The pretreated and untreated silk fibroin fragments were irradiated in the air atmosphere and using electron spin-resonance spectroscopy(ESR)to explored the types,yield,stability and evolution behavior of free radical.The results show that the types of free radicals,including carbon-centered free radicals and aromatic residue free radicals(Trp^·Tyr^·).the concentration and stability of the free radicals produced by the pretreatment of silk fibroin fragments are greater increased.When the absorbed dose is25k Gy,the concentration of free radicals generated by the sample after pretreatment is increased by ten times.When the absorbed dose is 50 k Gy,the free radical concentration is 8.04*10¹⁹spins/g,which is equivalent to the saturated free radical concentration when the untreated silk fibroin fragments are above 200 k Gy,and the half-life of free radicals generated at the same absorbed dose was extended by nearly 10 times.Combined with synchrotron radiation wide-angle scattering SR-WAXS,and terahertz time-domain spectrum(THz-TDS)to explore the structure change of silk fibroin before and after irradiation.The result show that the crystal structure of the sample after irradiation did not change significantly before irradiation.(3)The silk-based gel polymer electrolyte(SB-GPE)was prepared by cross-linking silk fibroin and polyacrylonitrile(PAN)successfully by irradiation.Using differential scanning calorimeter(DSC),Fourier infrared spectroscopy(FTIR),X-ray diffraction(XRD)and other means to study the molecular structure conductivity,swelling,anti-freezing and other properties of SB-GPE.The results show that after PAN and pretreated silk fibroin form a new chemical bond,its crystal structure has also changed.The prepared SB-GPE has a swelling ratio of up to 44 and a conductivity of 2.1×10^-3S/cm.In addition,the phase transition temperature is around-95?,which expands the application of super capacitors(EDLC)under extreme conditions...