The Preparation Of Water-Soluble Chitosan In Heterogeneous System

Chitosan, which is a natural macromolecule compound, is obtained by deacetylation of chitin. The chitosan exhibited some particular physiological activities and medicinal value. However, the application of chitosan is limited because of its high molecular weight and low water-solubility. Low molecular weight chitosan is not only keep up the cetain functions and properties of high poly chitosan, but also provid with physiological functions and activities, such as inhibiting bacteria activity, antitumor activity, hygroscopicity. Therefore, how to prepare the low molecular weight chitosan, effectively through a serises of chemical and physical methods cause increasingly concerned. At present, the main preparation methods of low molecular weight chitosan are physical degradation, chemical degradation and biological degradation. This paper studied the process of which chitosan degrdation in heterogeneous system, supported by catalysts and unsupported by catalysts were catalysed hydrogen peroxide oxidation degradation of chitosan and prepared water-soluble chitosan.The optimum technological conditions of two kinds of catalysts was found. The results showed that:(1) the deacetylated degree material of chitosano was 83.7%through acid-base titration method. By the viscosity method, the viscosity-average molecular weight of raw material was 100,000 Da.The raw material of chitosan, chitin and starch of hygroscopicity and moisture were lower than the glycerin, raw material of chitosan which was almost insoluble in water and dilute-sulphuric acid, soluble in dilute-hydrochloric acid and acetic acid by contrast experimentation. (2) In heterogeneous system, through the single factor experiment and response surface analysis, the results showed that optimal conditions for preparation of water-soluble chitosan were as follows:reaction temperature was 70℃, reaction time was 4h, the value R(H2O2/sugar dosage units) was 2, catalyst dosage was 0.02. The number average molecular weight of water-soluble chitosan was around 1500Da, degree of deacetylation was 74.13%, and the color of product was white or light yellow. (3) The supported phosphotungstic acid catalyst was prepared by reflux adsorption method. The loading of catalyst were 8.99%、20.90%、28.34%、 36.17%、41.51% respectively, and the pore diameter were mainly distributed about 90 μm. The supported or unsupported catalyst was contrasted,the results shows that supported phosphotungstic acid efficiency of catalyst was better than that of unsupported efficiency of catalyst. The different loading catalytic efficiency was contrasted under the same catalyst dosage, as catalyst dosage had increased, the number-average molecular weight of production had increased and the yield had decreased. Supported phosphotungstic acid catalyst reused 3 times still maintained a high catalytic activity in the repeated catalyst experiment.