Effect of cupric ion on thermal degradation of chitosan

The thermal degradation of chitosan and chitosan-cupric ion compounds in nitrogen was studied by thermogravimetry analysis and differential thermal analysis (DTA) in the temperature range 30-600°C. The effect of cupric ion on the thermal degradation behaviors of chitosan was discussed. Fourier transform-infrared (FTIR) and X-ray diffractogram (XRD) analysis were utilized to determine the micro-structure of chitosan-cupric ion compounds. The results show that FTIR absorbance bands of ---N---H, ---C---N---, ---C---O---C--- etc. groups of chitosan are shifted, and XRD peaks of chitosan located at 11.3, 17.8, and 22.8° are gradually absent with increasing weight fraction of cupric ion mixed in chitosan, which show that there are coordinating bonds between chitosan and cupric ion. The results of thermal analysis indicate that the thermal degradation of chitosan and chitosan-cupric ion compounds in nitrogen is a two-stage reaction. The first stage is the deacetylation of the main chain and the cleavage of glycosidic linkages of chitosan, and the second stage is the thermal destruction of pyranose ring of chitosan and the decomposition of residual carbon, in which both are exothermic. The effect of cupric ion on the thermal degradation of chitosan is significant. In the thermal degradation of chitosan-cupric ion compounds, the temperature of initial weight loss (Tst), the temperature of maximal weight loss rate (Tmax), that is, the peak temperature on the DTG curve, and the peak temperature (Tp) on the DTA curve decrease, and the reaction activation energy (Ea) varies with increasing weight fraction of cupric ion.