| In the 21st century,marine resources have received more and more attention,in pursuing sustainable development.As an abundant natural polymer with the reserve only less than cellulose,chitin is renewable,degradable,highly biocompatible,non-toxic and non-polluting.In addition,chitin also contains a large number of derivatizable functional groups such as hydroxyl and acetamide,which can be used to construct functional materials.Chitin has so many attractive advantages that it is very potential in the fields of biomedicine,packaging,separation and adsorption and photoelectric functional materials.However,the strong inter/intra molecular interactions of chitin makes it difficult to be dissolved and melt,resulting in that the processing and applications of chitin are greatly restricted.In this thesis,chitin was dissolved,and was regenerated in electrolyte sodium propionate aqueous solution for the first time.In this way,the chitin-based functional material with good performance is constructed.Characterization methods are involved to analyze the structure and properties of materials,such as elemental analysis（EA）,wide-angle X-ray diffraction（XRD）,thermogravimetric analysis（TGA）,ultraviolet-visible spectroscopy（UV）,Fourier transform infrared spectroscopy（FT-IR）,nuclear magnetic resonance carbon spectroscopy(13C NMR),polarized light microscope（XY-P）,scanning electron microscope（SEM）,and other characterization methods,as well as mechanical and electrical tests.Therefore,we have provided new methods for the research and application of chitin in this thesis.The innovations of this paper including the following points:（1）For the first time,The sodium propionate aqueous solution was used as the poor solvent of chitin to regenerate the chitin solution after dissolving chitin in NaOH/urea aqueous solution,and the nanofiber woven structure of regenerated chitin was constructed.Then,based on the interaction between protein and chitin,gelatin was coated on the surface of the chitin nanofibers to form a bionic composite structure in which the chitin nanofibers were embedded in the protein matrix.Gelatin greatly contributed to improving the mechanical properties of the chitin film.（2）The sodium propionate aqueous solution was used to regenerate the chemically cross-linked chitin,and the sodium propionate solution further played part of the ion conductive medium to prepare the ionic conductive chitin hydrogel.With high transparency,good mechanical properties and electrical conductivity,the ionic conductive chitin hydrogel performed excellently both as strain and pressure sensors,which showed that it was a promising flexible electronic device.This thesis mainly carried on the research and the discussion from the following several parts:In the first place,the NaOH/urea aqueous solution was used as solvent of chitin,and a transparent and viscous chitin solution was obtained after freeze-thaw cycles.For the first time,we used the electrolyte sodium propionate aqueous solution as the poor solvent of chitin to regenerate the chitin solution.The results showed that chitin regeneration in sodium propionate led to chitin film with nanofibrous structure.Then we coated the chitin nanofibers with gelatin to prepare a bionic structure in which the chitin nanofibers were embedded in the protein matrix to obtain a chitin/gelatin composite material.The experimental results displayed that the chitin film has a loose three-dimensional nanofiber structure,and gelatin was combined with chitin through physical and chemical effects.After coating gelatin,the nanofiber structure of chitin was denser,and more homogenous.What’s more,the reduce of defects enhanced significantly the mechanical properties of the composite functional material.Meanwhile,the results revealed that mechanical properties of the composite film were almost dependent on the concentration of gelatin:when the concentration of the gelatin solution increased from 0 to 4.0 wt%,the mechanical properties of the composite film improved with the increase of the concentration.The highest tensile strength is 98 MPa,which is raised by 78%compared with chitin film.Our method is simple and green,as well as effective to improve the aggregated structure of regenerated chitin and expand the application range of chitin materials.We also constructed a chitin-based ionic conducting hydrogel.In order to obtain high transparency,stretchability,high recovery,and conductivity,the following experimental steps were carried out.After dissolved in NaOH/urea species,the chitin solution was chemically cross-linked in epichlorohydrin（ECH）.Then,the cross-linked chitin is regenerated with sodium propionate aqueous solution as a poor solvent,and the sodium propionate solution is directly used as the ionic conductive medium of the hydrogel.When used as a strain sensor,the resistance change rate of the chitin hydrogel showed good sensing performance within the tested strain range,including the advantages of fast response,low hysteresis and good cycle stability.When used as a pressure sensor,chitin hydrogel had good sensitivity,responsiveness and resilience.In addition,when used as strain and pressure sensors,the chitin hydrogel maintained good transparency which simultaneously met the needs of optical devices for light transmission.In a word,this work provided a convenient method for the preparation of chitin ionic conducting hydrogel and expanded the application potential of biomass resources in the fields of sensing and flexible electronic devices.In this thesis,for the first time,electrolyte sodium propionate was used as a poor solvent for chitin to regenerate the chitin solution in NaOH/urea.Both the chitin/gelatin composite material and the chitin ionic conductive hydrogel possessed distinguished performances and great application potentials.This paper opened up a new way of utilize chitin,which is conducive to promoting the development and utilization of renewable resources such as chitin,and the experimental method is simple and green,which is in line with the sustainable development strategy. |
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