Properties And Structural Characterization Of MXene/Regenerated Silk Protein Composite Fibers

Regenerated silk fibroin fiber（SF）has been widely used and researched as a sustainable biomaterial,but its cumbersome preparation process and poor mechanical properties limit its large-scale production and application fields.This paper adopts a wet spinning process,and uses ammonium sulfate sodium sulfate coagulation bath and 75%ethanol stretching bath to avoid the process of dialysis and concentration of regenerated silk fibroin solution.MXene,which has excellent mechanical properties and is rich in oxygen-containing groups on the surface,is used as a reinforcing agent for regenerated silk fibers,and Ca²⁺is used as an ion to induce the formation of silk fibroinβ-sheets.So as to achieve the purpose of micron-scale MXene and nano-scaleβ-sheet synergistically strengthening the regenerated silk fibroin from the micro-and nano-scale.First,the effects of Ca²⁺and MXene on the thermal and mechanical properties of regenerated silk fibers prepared by wet spinning were studied,and the morphology characteristics of MXene,the spinnability of spinning solution,and the influence of Ca²⁺and MXene on fiberwere morphologytized;Secondly,using wet spinning as a model,explore the strengthening process and mechanism of Ca²⁺and MXene on regenerated silk fiber,mainly study the molecular chain orientation of regenerated silk fiber and the transformation process of fiber secondary structure in form,observes Changes in the spinning morphology at different stages of the process.Finally,the effect of MXene on the self-assembly of silk fibroin was explored by using the compound protein prepared from tannic acid precipitation protein as a model.Mainly by characterizing the effect of MXene-inducedβ-sheet phase transformation and its combined crystal size,the thermal and mechanical properties of the complex protein were explored under different MXene contents.The specific research results are as follows:（1）The results of the study on the strengthening mechanism of Ca²⁺and MXene to regenerated silk fibroin fiber show that:The fiber is not fully formed at the beginning of the spinning stretch ratio,and the higher the draw ratio,the better the internal density of the fiber.And with the increase of the draw ratio,the molecular chain orientation degree of the regenerated silk fiber is higher,so that its mechanical properties are improved.When the fiber is stretched twice,the mechanical properties are optimal.Compared with the non-stretched fiber,the elongation at break increases by 186%,the breaking strength increases by 56.9%,the tensile modulus increases by 389%,and the yield strength increases 22.3%.At the same time,when the Ca²⁺concentration is between 0 and 10 mg/m L,it is beneficial to improve the orientation degree of the fiber,but when the concentration is high,the orientation degree will be reduced.And Ca²⁺and MXene can induce the relative content ofβsheet in regenerated silk fibroin fiber to increase,and the relative content ofβsheet increases with the increase of Ca²⁺and MXene content.（2）The interaction form between MXene and silk fibroin molecular chains and the mechanism of induced transformation ofβ-sheets were mainly explored through characterization techniques of Fourier transform infrared spectroscopy and X-ray diffraction.In solution,Ca²⁺has electrostatic interaction with silk fibroin molecular chains,MXene and silk fibroin molecular chains interact with each other through hydrogen bonds,and MXene will preferentially combine with Ca²⁺,which weakens the combination of Ca²⁺and silk fibroin molecular chains;In the composite protein,the hydrogen bond between TA and silk fibroin molecular chain and the ionic bond between Ca²⁺and silk fibroin can increase the content ofβsheets andβturns in composite silk fibroin;MXene can also increase the content ofβsheets,and the crystallinity of the composite protein containing 10%MXene increases by 10.46%;and the crystal size of the composite silk fibroin increases by 0.13 and 0.20nm on the 200and 210 crystal planes,respectively,indicating that MXene The reason for increasing its crystallinity is to increase its crystal size in addition to increasing the number of crystals.（3）The effects of Ca²⁺and MXene on the thermal and mechanical properties of regenerated silk fiber prepared by wet spinning showed that:The Ca²⁺in the regenerated silk fiber helps to improve the mechanical properties of the fiber,and the comprehensive performance is the best when the Ca²⁺concentration is 5 mg/m L.Its elongation at break increased by 395%,breaking strength increased by 367%,tensile modulus increased by 89%,and yield strength increased by 149%.The enhancement effect of MXene on the mechanical properties of fibers is obvious.The breaking strength,tensile modulus and yield strength increase with the increase of MXene content,but the breaking elongation will decrease;When the MXene content is 5wt‰of the mass of silk fibroin and the Ca²⁺concentration is 5 mg/m L,concentration relative to Ca²⁺is 5 mg/m L,Its breaking strength increased by 102%,tensile modulus increased by 320%,and yield strength increased by 234%,but the elongation at break decreased by 45%.Ca²⁺improved the thermal stability and glass transition temperature of regenerated silk fibroin.When its concentration was 20 mg/m L,its residual amount,the degradation temperature corresponding to the maximum degradation rate and the glass transition temperature increased by 3.1%,19℃and 7.6℃;When the MXene content was between 0 and 10wt‰,the thermal stability of the regenerated silk fiber decreased.When the MXene content was 10wt‰,the temperature corresponding to the maximum degradation rate（MAXT）decreased by 19℃,and the glass transition temperature increased 8.8℃.Overall,This article provides a simple method for preparing regenerated silk fibroin fibers.The electrostatic interaction and hydrogen bonding between Ca²⁺and MXene with silk fibroin molecular chains,as well as the template effect of MXene,have enabled the regeneration of silk fibroin fibersβThe increase in folding content significantly improves the mechanical properties of regenerated silk fibroin fibers;Among them,Ca²⁺can effectively improve the thermal stability of regenerated silk fibroin fibers,but MXene causes a decrease in its thermal stability.