| Chitin is the most abundant natural polymer except cellulose in the earth. Treated with chitin in alkali solution, the acetamide group in its molecule structure will hydrolyze to get rid of acetyl group and leave dissociated amine group and become chitosan. Chitosan, deacetylated product of chitin, is a kind of natural polysaccharide source, which has important value in various areas. However, most of the research work on chitin and chitosan is concerned on application, instead of mechanism of preparation of Chitosan.In this thesis, three factors are emphasized and the optimum condition of preparation of chitosan has been obtained by cross-test design. Two series of chitosan were easily prepared by this method in lab, one had the same degree of deacetylation but different molecular weight, and the other had the same molecular weight but different degree of deacetylation. The effect of preparing method and material shapes on deacetylation were investigated.Deacetylation of chitin was studied under different conditions, such as different temperature, time and concentration of alkaline. The temperature was chosen at 80℃ 90℃ ,100℃ , 110℃ , 120℃ respectively, and the concentration of alkaline was 40% and 50% (mass percentage) differently, and the chitin samples were taken out at different reaction time for determining the degree of deacetylation. OH- group participated two processes in the deacetylation; one was diffusion in chitin solid and the other was mucleophilic substitution reaction. Three models were deduced: the first one was the chemical reaction controlled model; second was diffusion-chemical reaction controlled model; last was diffusion controlled model. According to the experiment result and computer fitting effect, the last model, diffusion controlled model, was approximatelysuited to describe the deacetylation of chitin. Especially at the beginning stage of deacetylation, when D.D reached to 70%, the diffusion model could forecast the experiment result well. Therefore, conclusion can be drawn that the mechanism of deacetylation was controlled by OH" group diffusion in chitin solid.Chitosan was used for treatment of cotton fabrics to impart antibacterial activity. The effect of concentration, molecular weight and degree of deacetylation of chitosan on antibacterial activity to Escherichia coli and Hay bacillus was investigated in detailed. Evaluation the bacteria reduction was measured by the method of Modified Quinn method. The Escherichia coli was effectively inhibited at 0.3g/l of chitosan solution and the Hay bacillus at 0.5g/1. To bond chitosan to fabric chemically, the glutaric dialdehyde was chosen as the crosslinking agent. The cotton fabrics treated with glutaric dialdehyde and chitosan showed a good ability to inhibit the bacteria reproduction. The IR spectra of cotton fabrics reflected on the surface and the SEM picture of fiber were measured.Application of chitosan on cotton fabrics dyeing to cotton fabric is also studied in this thesis, the influence of concentration of chitosan solution, the condition of dyeing and effect of two parameters (D.D and M.W) of chitosan. Different reactive dyestuffs were studied by testing K/S value as well. Experiment result showed chitosan could increase the uptaking of reactive dyes and economize the dosage of salt.
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