Synthesis Of Water-soluble Chitosan And Application In Antibacterial Paper

Chitosan is used as antibacterial agent because of its unique antibacterial activity. However, chitosan with poor water solubility is only soluble in some dilute acid solution. In this paper, water-soluble chitosan was synthesized by degradation and modification and was then applied in bamboo tissue to prepare antibacterial paper.Low molecular weight chitosan was prepared by H2O2 and NaCIO degradation respectively. The optimal conditions of H2O2 degradation were that:the ratio of chitosan to liquor was 1:40, H2O2 content was 5%, reaction temperature was 60℃ and reaction time was 6h. The best technology parameters of NaClO degradation were as follows:the ratio of chitosan to liquor was 1:40, NaClO content was 20%, reaction temperature was 70℃ and reaction time was 6h. The optimum conditions for chitosan’s NaCIO degradation were estimated to be 1:41.6 of chitosan to liquor ratio,20.55% of NaClO content, a temperature of-71.65℃, and a time of 5.28 h through the response surface optimization method. It was found that synthesis under these optimized conditions achieved the lowest molecular weight (13780.00). The effect of H2O2 degradation was better than NaCIO degradation by comparing the analysis. The results of low molecular weight chitosan from structural characterization showed that the degree of crystallinity dropped, water solubility improved and thermal stability declined with the decreasing of molecular weight. Besides, surface porosity increased, amino content didn’t decrease, and the molecular structure was not destroyed after degradation.Chitosan quaternary ammonium salt was synthesized by chitosan and glycidyl trimethyl ammonium chloride (GTAMC) through quaternary ammonium chemical modification. The optimum reaction conditions were shown below:mole ratio of chitosan and GTAMC was 1:4, reaction temperature was 85℃, and the reaction time was 8h. The degree of substitution (DS) under these conditions was in the range of 0.6765-0.8594. Quaternary ammonium salt group was successfully grafted in chitosan molecule using FTIR,1H NMR and XPS detection. And the water solubility improved obviously after chemical modification. But thermal stability declined and surface porosity decreased.Low molecular weight chitosan and chitosan quaternary ammonium salt which were synthesized by the above methods as antibacterial agents were added into bamboo tissue to prepare antibacterial paper. Antibacterial agents were filled in the fiber pores in the form of granular without influencing the surface roughness by SEM and AFM detection. The water absorption and softness were not affected though adding antibacterial agents. The antibacterial activity increased with the decreasing of molecular weight and with the increasing of antibacterial agent content by antimicrobial properties test. Besides, the antibacterial activity to staphylococcus aureus was the strongest and to Candida albicans was the weakest under the same conditions. What’s more, low molecular weight chitosan is more suited for preparing antibacterial paper in comparison with chitosan quaternary ammonium salt.