Preparation Of Low Molecular Weight Chitosan

Chitosan is carbohydrate polymers which is nontoxic> biocompatible and biodegradable,are good drugs and absorbent agent. It has received much attention in many fields due to the distinct physiologic activities and potential functions. But the application of chitosan was limited duo to its low wate-solubility. The molecular weight of chitosan have great influence on chitosan. Oligochitosan are not only keep up the certain functions and properties of high poly chitosan, but also provided with physiological activities and functions, such as moisturizing effect, antitumor activity, enhance immunity, etc. Therefore, how to prepare the low molecular weight chitosan, effectively through a series of physical and chemical methods caused increasingly concerned. At present, the preparation methods of low molecular weight chitosan are mainly include chemical degradation, enzyme degradation and physical degradation, and so on. This paper studied the process of chitosan degradation with hydrogen peroxide oxidation degradation, cellulase enzymatic and papain enzymatic, respectively. Through experiment,we derive the optimum technological conditions of the three various methods.And tested the characterization of low molecular weight chitosan.(1) The process and the mechanism of chitosan degradation with hydrogen peroxide Was sutdied, and the eeffct of temperuatre, amount of hydrogen peroxide, time, Was investigated. The structure of degradated products were characterized by FT-IR, TG-DTA, XRD and water-soluble test. Results show that the optimal conditions for preparation of low molecular weight chitosan were as follows:reaction temperature 80℃, reaction time 6 h, hydrogen peroxide solution concentration is 5%, hydrogen peroxide (H2O2/sugar dosage units= 2),2% of acetic acid medium. Through the viscosity test,we know that hydrogen peroxide degradated chitosan effectively, get low weight molecular chitosan. The structure of degradated products were characterized by FT-IR, TG-DTA, XRD and water-soluble test. The results show that the structure of chitosan which is degradated have not changed, with reducing of molecular weight, water-soluble was enhanced.(2)Cellulase has obvious degradation action of chitosan. The influencing factors on the degradation reaetion, ineluding reaction time, pH temperature and cellulose amount were studied indetails. The results obtained indicated that:there relative molecular weight of degradation produet decreased markedly with the reaction time temperature and cellulose amount inereased. Different factors have different influencing degree. There was asequence as following: pH> temperature> time> cellulose amount.The best degradation condition of chitosan by cellulose that was given from the experiment results is:reaction temperature 50℃, pH value 4.5, cellulase dosage 6IU/(g chitosan), chitosan solution concentration is 1%, reaction time 8 h.(3) The depolymerization of chitosan by papain was studied. By determining the concentration of reducing sugar and viscosity in chitosan solution, the effects on the efficiency of catalytic degradation of chitosan by papain were investigated. Results show that the optimum reaction conditions is:reaction temperature 45℃, pH value 4.2, papain dosage (papain: substrate than= 1.5), chitosan solution concentration 0.5%, reaction time 20 h.