Studies And Application Of Functional Biomaterials Based On Hemicellulose-Chitosan

Lignocelluloses consisted of cellulose, lignin and hemicelluloses are the most abundant biomass in nature. As a class of heteropolysacharides, hemicelluloses play an important role of connecting lignin and cellulose fibers. However, the systematic theoretical work on hemicelluloses is extremely lacking due to their high heterogeneity, source-dependent diversity, high branching and amorphous molecular structure, which lead to a consequence that the potential application of hemicelluloses has not yet been exploited on an industrial scale. On the other hand, chitosan is the only natural alkali polysaccharide derived from chitin by deacetylation, which is the second abundant polysaccharide in nature. Owing to its antibacterial, antitumor, immune enhancing effects, and non-toxic, biocompatibility, biodegradability, chitosan is widely used in the field of medicine, food industry, functional materials, cosmetic, agriculture, environment protect and textile manufacturing. Therefore, hemicelluloses modified by chitosan would open new channels for their exploitation and utilization. Based on the Maillard reaction between the recuction of carbonyl at the end of hemicellulose chains and the amino groups on chitosan, the novel functional biomaterials and biochemical products were prepared by the regulation of reaction process. To this end, our study will broaden the scope of the research and application of hemicellulose.In this study, a series of novel functional biomaterials based on hemicellulose and chitosan or its derivatives were constructed by the regulation of Maillard reaction process. Meanwhile, the relationship between structure and property of the novel biomaterials was studied in detail. The main innovation points in this study are listed as following:(1) The structure of hemicellulose extracted from corncob was confirmed for the first time. The lowest degree of branching and lower molecular weight of hemicellulose from corncob lead to low steric hindrance comparing with hemicelluloses derived from the cunninghamia, aspen and bamboo, which were beneficial to Mailard reaction proceeded on this kind of hemicelluloses.(2) Maillard reaction based on hemicellulose and chitosan or its derivatives was successfully achieved, and xylan-chitooligomer-zinc complex (XCGZC) with excellent antioxidant and antimicrobial activity was firstly prepared by optimizing experimental configurations.(3) Hemicellulose/chitosan or carboxymethyl chitosan/nanoTiO2hybrids with high-efficiency hemostatic and broad-spectrum antimicrobial properties were constructed based on the Schiff base and micellization by solid/liquid interface self-assembly;(4) The hemicellulose/chitosan/nanoTiO2was constructed based on the high porous structure and affinity of nanoTiO2, which exhibited highly efficiency sorption capabilities for the combined pollution of various heavy metals especially on Cr+and Hg+The main contents and conclusions of this work can be divided into four parts.The isolation and structure characterization of hemicellloses derived from different biomass. Hemicelluloses were extracted from corncob, bamboo, cunninghamia lanceolata and aspen wood by alkali aqueous solution, and17hemicelllose fractions were separated by15%-90%(v/v) ethanol precipitation method. The chemical component, molecular weight, molecular structure and thermostability of hemicellulosic fractions were characterized by high performance anion-exchange chromatography (HPAEC), gel permeation chromatography (GPC), static light scattering (SLS), fourier transform infrared spectroscopy (FT-IR), nuclear magnetic resonance (’H,13C NMR) and thermogravimetric analysis (TGA). The results showed that the main molecular chains of hemicelluloses from four sources were all D-xylopyranosyl, while the side chain and branched degree had significant differences. Among them, the side group of the hemicellulose from corncob was mainly composed of arabino-4-O-metylglucuronic acid. The type of the side group of the hemicellulosic subfraction extracted from bamboo was arabinoxylans. The side group of the hemicellulose from cunninghamia lanceolata was mainly composed of L-arabino-4-O-methyl-glucuronic acid, and the side group of the hemicellulose derived from aspen wood was O-acetyl-4-O-methyl glucuronic acid. In several of the separated hemicellulose, hemicelluloses from corncob had the lowest degree of branching, the highest degree of linear main chain and lower molecular weight, which showed a small steric hindrance so as to perform the Maillard reaction. Therefore, we selected the linear hemicellulose of corncob as a reactant. In addition, it was found that the thermostability of hemicellulose from wood was higher than that from gramineous plants, which could be enhanced with the increasing of the molecular weight of hemicellulose.The studies of antioxidant and antibacterial activity of Maillard reaction products (MRPs). Maillard reaction between xylan from corncob and chitosan or its derivatives was successfully achieved for the first time, by which xylan-chitosan, xylan-chitooligomer, xylan-glucosamine hydrochloride, xylan-taurine and xylan-chitooligomer-zinc complex were prepared. The reaction kinetics, structures and properties of MRPs were characterized by ultraviolet absorption spectroscopy (UV), browning intensity, fluorescence change, FT-IR, X-ray diffraction (XRD), antioxidant activity and antimicrobial assessment. Meanwhile, the effects of different molecular weight of reactants on the Maillard reaction and MRPs performance were investigated. The results showed that the lower molecular weight of the reactants was, and the more easily Maillard reaction happened. The antioxidant ability of MRPs increased with the higher molecular weight of reactants. Especially, the antimicrobial activity of MRPs was decreasing with the decrease of amino content. Xylan-chitooligomer-zinc complex (XCGZC) with superior antioxidant and antimicrobial activity was obtained by optimizing the reaction conditions. The results showed that antioxidant capacity and antibacterial activity of XCGZC was2.5times and5times higher than that of chitooligomer, respectively. XCGZC displayed excellent antibacterial activity for Escherichia coli, Staphylococcus aureus, Bacillus subtilis, Salmonella and Bacillus megaterium, and its IC50(concentrationin micrograms per millilitre required to inhibit DPPH radical formation by50%) was5.37mg/mL. Thus, this work opened a new avenue for the research and exploitation of hemicelluloses.The construction of hemicellulose/chitosan composites and their hemostasis and antibacterial functions. The novel biomaterials was constructed via Schiff base reaction between the amino group of the chitosan or carboxymethyl chitosan molecular chain and the reductive carbonyl group of the hemicellulose molecular chain end by incorporating TiO2nanoparticles modified with sodium dodecyl sulfate into the network structure. The novel biomaterials exhibited excellent antibacterial activity and hemostasis properties. Among them, the hemostasis time of hemicellulose/chitosan/nanoTiO2as a hemostatic material for rabbit ear artery trauma was1min, and the amount of bleeding was0.08g, which was significantly superior to the commercially absorbable gelatin sponge and hemostatic sponge. The synergy effects between polymer matrices and TiO2nanoparticles had greatly enhanced anticoagulation and antibacterial function of hybrid. The cell toxicity test indicated that the hybrids were nontoxic and had a good biocompatibility for human embryonic lung fibroblast (2BS). Besides, the hybrid had excellent antibacterial activity against bacillus megaterium, S.aureus, E.coli, salmonella typhimurium, bacillus subtilis, pneumococcus and proteusbacillus vulgaris, The antibacterial rate of the chitosan-xylan-TiO2treated with pneumococcus for2h reached100%. The antibacterial rate of chitosan-xylan-TiO2treated with bacillus megaterium and proteusbacillus vulgaris for2-4h was84.93-86.76%and84.23-88.46%. This study greatly broadened the application scope of hemicellulose in the biomedicine fields.The construction of porous materials based on hemicellulose for high-efficency heavy metal adsorption. Xylan-chitosan-nanoTiO2hybrid with multiple structure and abundant adsorption sites were successfully prepared by the reaction between amino group of chitosan molecular chain and reductive carbonyl group of xylan molecular chain end. Meanwhile, the three dimensional space structure and adsorption surface area of the hybrid could be improved by changing the content of TiO2nanoparticles to build up efficient adsorption materials. Meanwhile, the structures and performances of xylan-chitosan-nanoTiO2hybrid were characterized by FT-IR, TGA, Brunauer-Emmett-Teller surface area measurement (BET), scanning electron microscope (SEM) and transmission electron microscope (TEM). Especially, the swelling properties and adsorption function of the hybrid for Cu+, Cr6+, Ni2+, Cd2+, and Hg2+were studied in detail, and the effects of pH, temperature, contact time and initial concentration of metal ions on these heavy metal ions (HMI) adsorption were also discussed. Finally, the mechanism of adsorption was explained by Langmuir and Freundlich isotherm adsorption model. The results showed that the xylan-chitosan-nanoTiO2hybrid exhibit highly porous structure, large specific surface area, salt-and pH-sensitivity and high adsorption capacity. Meanwhile, Langmuir model illustrated that the HMI adsorption on the surface of the hybrid was monolayer biosorption and Freundlich parameter n indicated that the adsorption of HMI onto the hybrid was favorable at high concentrations. Thermodynamic parameters indicated that the process was spontaneous and endothermic in nature. The pseudo-second-order kinetic model suggested that the chemical adsorption was the rate-limiting step in ion diffusion. The hybrid exhibited highly efficiency sorption capabilities for the combined pollution of various heavy metals such as Cu+, Cr6+, Ni2+, Cd2+and Hg2+, and their maximum adsorption capacities (Qm) were158.7,97.1,96.2,78.1and76.3mg g-1, respectively. The HMI adsorption capacities of the recycled hybrid can still maintained at80%level at the fourth adsorption-desorption cycles. Xylan-chitosan-nanoTiO2hybrid would be an outstanding candidate as a kind of recyclable, effective, and selective bioadsorbent for the removal of HMI from wastewater, which is expected to be applied in the field of wastewater treatment and heavy metal contaminated soil repair.In this dissertation, combining with the advantages and disadvantages of the molecular structural characteristics of hemicellulose and chitosan, a series of functional materials based on hemicellulose-chitosan were successfully constructed by Maillard reaction. Meanwhile, the correlations between structure and properties were figured out. These basic researches would provide new methods and scientific basis for the effective utilization of hemicelluloses to produce polymeric materials, biochemical product and other high value-added products, which significantly broadens hemicellulose in various application fields such as food, biomedical and water treatment. Therefore, this work exhibits obvious creativity, important academic value and application prospect.