Study On The Preparation And Application Of Antibacterial Biomass Material Based On Chitosan

Chitin, the second most abundant natural polymer on earth, could be isolated from an enormous number of living organisms such as crab, shrimp, tortoise, and insects. As reported, at least 10 gigatons of chitin is synthesized and degraded each year in the biosphere, thus the corresponding utilization would have great potentialities. But chitin was for a long time considered as an untreatable polymer because of its inherent insoluble nature(in almost all common solvents) and intractable molecular structure. Chitosan, as the most important deacetylate derivative, due to a number of interesting properties including nontoxicity, biocompatibility, biodegradability, easy-processing and so on, has been widely applied in chemical industry, biomedical, biotechnology, food industry, agriculture and environmental protection. Due to the unique amino functional group, chitosan has the broad-spectrum antibacterial property and received considerable attention in recent years. But some problems are still existed, for example, the antimicrobial activity of chitosan is still lower than the antimicrobial agents currently used. And the antimicrobial activity of chitosan is limited to in acidic conditions due to its poor solubility in neutral environment. In this paper, we try to introduce different functional groups onto molecular structure of chitosan via chemical reaction to improve the water-solubility and antimicrobial activity of chitosan derivatives. The main content and the results of this paper are as following:Microwave-assisted hydrogen peroxide/ultraviolet radiation process was used to prepare the chito-oligosaccharides. The experiment results showed that the oxidative degradation reaction of chitosan was accelerated by microwave and UV irradiation under the condition of low temperature and low concentration of H2O2. Compared with H2O2/microwave and H2O2/UV oxidative degradation, the oxidative degradation reaction rate of microwave-assisted H2O2/UV could increase by 2 times and 4 times, respectively. The prepared chito-oligosaccharides have good water-solubility and the basic sugar ring structure and functional groups has not changed. XRD analysis showed that the oxidative degradation destroyed the crystalline structure of the chitosan molecule and improved its water- solubility. TG tests show the thermal stability of the chito-oligosacchride deteriorates with molecular weight decreased. Antibacterial tests showed chitosan and chito-oligosaccharide both have a certain inhibitory effect, but there is no correspondence between the antibacterial activity and molecular weight of chitosan.Due to chitosan possesses highly reactive primary amine groups and hydroxyl groups, it could be chemical modified by introducing different functional groups onto the molecular skeleton to obtain different chitosan derivatives. The C2-NH2 of CS was first protected by benzaldehyde. Then the C6-OH of CS introduced cationic quaternary ammonium group. This intermediate was reacted with chloride acetyl thiourea followed by the deprotection of C2-NH2 with acid to furnish the thiosemicarbazide of OQCS and get the object product OQCATUCS. Another bearing double antibacterial functional groups of chitosan derivative, OFTMCS, was prepared by the selectively chemical modification. When submitted to intensive methylation, CS generates a trimethylated derivative characterized by having permanent positive charges in the chains as a consequence of the quaternization of the amino groups in the C2 position in the chitosan backbone. Then MeSO3 H was applied as catalyst and solvent agent, O-monomethyl fumarate-N,N,N- trimethyl chitosan was synthesized by esterification between TMCS and chlorocarbonylacrylic acid. The prepared chitosan derivatives were endowed with good water solubility. The structures and properties of synthesized products were characterized by FT-IR, NMR, XRD and TG analysis, respectively. The degree of substitution functional groups were evaluated by XPS analysis. The antibacterial activity tests indicated that all the chitosan derivatives displayed certain antibacterial activities. Compared with unmodified CS, the prepared CS derivative had significantly improved antibacterial activity toward Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, Aspergillus niger and Bacillus subtilis. The antibacterial activities of quaternary ammonium chitosan derivative was depends on the positive charge density. High degree of substitution of quaternary ammonium resulted in the high charge density electropositive and better antibacterial activity. It is also indicated that the antibacterial activities of chitosan derivatives bearing double antibacterial functional groups were stronger than that bearing single antibacterial functional group. The mode of action of chitosan derivatives activities solution against Staphylococcus aureus and Escherichia coli was further examined in this study. Antibacterial activity of chitosan derivatives in this study was found mainly due to the damage of cell membrane, which was evidenced by both the cell lysis observed by transmission electron microscopy, and the increased release of cell materials based on the measurement of cell membrane integrity.Water-soluble chitosan derivatives such as carboxymethyl chitosan(CMC), N-trimethyl quaternary ammonium chitosan(TMCS) and N-phenyl methoxy methyl quaternary ammonium chitosan(VQCS) were prepared. The chitosan derivatives rapidly intercalated with α-zirconium phosphate under microwave irradiation in the aqueous solution. The FT-IR characteristic absorption peaks and XRD results indicated that the chitosan derivatives were already intercalated into the organic activated modified OZr P. Its interlayer spacing, average particle size and Zeta potential was changed with chitosan derivatives. TG results indicated that the intercalation of α-ZrP improved the high-temperature performance of chitosan derivatives, enhanced its thermal stability. Antibacterial experiment showed the prepared nanocomposites have good antimicrobial properties.Immobilized silver nano-particles possess excellent antimicrobial property due to their unique surface characteristics. In this paper, immobilized silver nanoparticles(Ag NPs) were synthesized in the presence of chitin nano-crystals(CNC) based on the Tollens mechanism(reduction of silver ion by aldehydes in the chitosan oligosaccharides(COS)) under the microwave-assisted condition. The prepared Ag NPs-loaded CNC nano-composites were then applied onto the paper surface via coating for the preparation of antibacterial paper. The spectra results of Fourier transform infrared(FT-IR) and X-ray diffraction(XRD) confirmed that the Ag NPs were immobilized onto the CNC. The transmission electron microscope(TEM) photos, atomic force microscopy(AFM) and field emission scanning electron microscopy(FE-SEM) results further revealed that the spherical Ag NPs(8- 15 nm) were well dispersed on the surface of CNC. The coated paper made from the Ag NPs-loaded CNC nano-composites exhibited high effectiveness of the antibacterial activity against E. coli or S. aureus.