| Low-molecular-weight chitosan(LMWT) has received great attention due to its excellent biological, chemical and physical properties. However, the methods for preparing LMWT have the main disadvantages of environmental pollution, expensive cost and so on. Therefore, it is necessary to investigate an efficient way for degrading chitosan, which improves the applications of chitosan in biomedical field. The research has important practical significance to protecting human health and improving our quality of life. The non-thermal plasma technology has been extensively used due to its excellent performance, such as high degradation efficiency, normal temperature, low power consumption, complete degradation, no secondary pollution. In this thesis, the plasma apparatus was constructed. Degradation of chitosan by plasma and plasma in the presence of H2O2(PH) were investigated. The degradation kinetic of chitosan was explored. The simulation of degradation of chitosan has been performed. The correlation between the yield of·OH radical and the degradation ratio was researched. Structural characteristics and bioactivities of the degraded chitosan were analyzed.The plasma apparatus was constructed. The effects of needle-plate electrode, plate-plate electrode, line-line electrode and its packed-bed on the degradation of chitosan were evaluated. The results show that the optimal electrode is needle-plate electrode.·OH radical can be effectively produced in the reaction system.The effects of the distance between the electrodes, H2O2concentration, chitosan concentration, acetic acid concentration, sodium acetate concentration and treatment time on the degradation of chitosan were evaluated. The results show that chitosan can be degraded by plasma. Under the optimization conditions of plasma, the degradation ratio was72.63%and the molecular weight was311.5kDa. H2O2effectively enhanced the degradation of chitosan. Under the optimization conditions of PH, the degradation ratio was97.97%and the molecular weight was23.1kDa. The degradation ratio of PH was32.61%higher than that of plasma.Based on the degradation process, the degradation kinetic and the numerical simulation of plasma were investigated. The results show that the degradation rate of PH was as25times higher as compared to plasma. The degradation reaction by plasma and PH was a first-order reaction. Then, based on the degradation kinetic of chitosan, this work presents a numerical model of the degradation of chitosan under different the distance between the electrodes, H2O2concentration, treatment time and chitosan concentration. The results show that the numerical simulation was able to predict the results. The correlation between the yield of·OH radical and the degradation ratio was researched. The results show that·OH radicals play a major role under plasma,. However,·OH radicals and·O radicals may play a major role for PH. The components of the degraded chitosan were analyzed through MALDI-TOF. The results show that the degraded chitosan was mainly composed of (GlcN)x. The GLcN-GLcN linkage was mainly cleaved by plasma. The degraded chitosan was mainly composed of (GlcN)x-(GlcNAc) and (GlcN)x-(GlcNAc)2. The GLcN-GLcNAc and GLcNAc-GLcN linkages were mainly cleaved by PH.Under the optimization conditions, the degraded chitosan were obtained under treatment time of60,120and180min. Structures of the degraded chitosan were characterized by UV, FTIR, NMR, XRD, SEM, TG. The water solubility of the degraded chitosan was evaluated. The results show that the main chain structure of chitosan still existed in the degraded chitosan. The crystalline structure was destroyed. The thermal stability was declined. The water solubility was improved. Antioxidant activity was investigated by scavenging DPPH, scavenging ABTS, reducing power, lipid peroxidation. The inhibition ability of the degraded chitosan against E.coli, S.aureus and B.subtilis were evaluated. The antioxidant activity and antibacterial activity of the degraded chitosan were enhanced. PH possessed higher improving effect on bioactivity of chitosan compared with plasma. |
