Dissolution Of Chitin At Low Temperature And New Materials Based On It

Chitin is an abundant biomacromolecule existing in exoskeletons of crab andshrimp, and it has been first identified in1884. It is a linear polysaccharide ofN-acetyl-D-glucosamine （GlcNAc） connecting through α β（1�'4） glycosidic linkage.Due to the advantages of being biocompatible, biodegradable, antibacterium andalmost non-toxic, chitin has attracted more and more attention. Chitin has beenextensively investigated as adsorbents for the removal of metal ions from wastewater,and its efficient adsorption potential can be attributed to high hydrophilicity and highchemical reactivity due to large number of functional groups. This biopolymer showsan attractive alternation for many materials because of its physico-chemicalcharacteristics, chemical stability, high reactivity, excellent chelation behavior andhigh selectivity toward pollutants. However, chitin is very difficult to dissolve incommon solvents, resulting in serious limitations in the research and development ofchitin as sorbents. Some new solvents, such as LiCl/Dimethylacetamide （DMAc）mixtures and ionic liquids have been developed to dissolve the chitin and to preparematerials. However, the costs of using these solvents are too high for practical use. Inour laboratory, a novel solvent, aqueous NaOH/urea, and a new method, which candissolve chitin to obtain a homogeneous solution have been developed. The structure,properties, and structure-activity relationship of hydrogels were characterized bydifferential scanningcalorimetry （DSC）, Fourier transform infrared spectroscopy（FTIR）, X-ray diffraction （XRD）, transmission electron microscopy （TEM）, scanningelectron microscope （SEM）, thermogravimetric analysis （TGA）, dynamicmechanicalanalysis （DMA）, UV-visspectroscopy （UV） and mechanical testing. The correlation ofstructure to properties was researched, and biobased functional materials wereconstructed to evaluate their potential applications.The innovation of this work was as follows:chitin were successfully dissolved in NaOH/urea aqueous solution via thefreezing/thawing method to obtain a transparent chitin solution, and biobasedfunctional materials were constructed, such as chitin/cellulose blend membrane, chitinhydrogel, Fe₃O₄magnetic chitin beads, Ag₂Mo₂O₇/chitin gel-membrane， andinvestigated its application in agriculture, environment, medical and other.The primary content and conclusion of this work was as follows:Chitin/cellulose blend membranes were successfully prepared in7wt% NaOH/12wt%urea aqueous solution via a freezing/thawing method to dissolve chitin,and then by coagulating with5wt%Na2SO4to regenerate. The experimental resultsrevealed that the composite membranes exhibited efficient removing of heavy metalions （mercury, copper and lead） from aqueous solution, as a result of theirmicroporous structure, large surface area and affinity on metal ions. Moreover, thechitin/cellulose membranes could be easily regenerated. This work provided a “green”pathway for removing of the hazardous materials in wastewater.A chitin hydrogel with concentration3wt%（CG3） was successfully preparedfrom chitin solution dissolved in8wt%NaOH/4wt%urea aqueous system at lowtemperature by crosslinking with5wt%epichlorohydrin. The experimental resultsrevealed that CG3exhibited high efficiency to remove dye （malachite green） fromaqueous solution, as a result of their microporous structure, large surface area andaffinity on the dye. This work provided an attractive adsorbent for removing of theorganic dye ls from wastewater.Novel chitin magnetic beads （CM beads） were successfully prepared by in situsynthesis of Fe₃O₄nanoparticles in regenerated chitin beads to be used to packfixed-bed columns. The interpenetrated porous structure in the regenerated chitinbeads at the swollen state could serve as templates for the preparation of inorganicnanoparticles. The adsorption experiment results revealed that the CM beads exhibitedefficient adsorption of Cd²⁺ions from the aqueous solution, as a result of theirmicroporous structure, large surface area and affinity for metal ions. The CM beadsshould have potential applications in the fields of chromatography packing andadsorbent both at the laboratory and industrial scales.Novel Ag₂Mo₂O₇/chitin gel-membranes were successfully prepared by in situsynthesis of Ag₂Mo₂O₇nanoparticles in regenerated chitin gel-membrane to be usedto pack fixed-bed columns. The interpenetrated porous structure in the chitingel-membrane at the swollen state could serve as templates for the preparation ofinorganic nanoparticles. The experiment results revealed that the Ag₂Mo₂O₇/chitin gelmembranes have a strong antibacterial capacity, in a short period of time to kill E. coliand Staphylococcus aureus.In the chitin hydrogels prepared in NaOH/urea aqueous solution via afreezing/thawing method, and then crosslinking with epichlorohydrin have beensuccessfully applied to the soilless cultivation of seeds. The large surface area,excellent hydrophilicity of chitin chains and the homogeneous microporous structure of the chitin hydrogels led to a good water uptake ability, compared with agar and soil.This work provided a new pathway for the application of the chitin hydrogels asculture mediums in seed germination and growth.This work developed a series of chitin based materials by using our “green”solvent system, and clarified the relationships between their structure and properties.These basic researches provided valuable information for construction, anddevelopment of biobased materials with different properties from renewable resource,and there were great scientific significance and prospects of applications. Therefore,this thesis is highly valuable for academic study and great important for a sustainabledevelopment.