Thermal and kinetics of the degradation of chitosan with different deacetylation degrees under oxidizing atmosphere

Highlights: • The least deacetylated chitosan presented the highest thermal stability. • The isoconversional methods showed a strong dependence with the conversion. • The 3-R Gaussian DAEM model was more accurate that the isoconversional methods. The degradation process of chitosan with degrees of deacetylation (DD) varying from 54 to 84% was investigated by thermogravimetric analysis at different heating rates under air atmosphere. The chitosan with DD of 54% presented the highest thermal stability and slower changes in its structure as the temperature was increased, according to the infrared spectroscopy analyses. The activation energies (E_a) of the degradation process were estimated by the Flynn-Wall-Ozawa and the Vyazovkin isoconversional methods, obtaining values between 90 and 319 kJ/mol. The 3R-Gaussian distributed activation energy (3R-Gaussian DAEM) model was applied and adjusted successfully to the experimental data. In addition, DAEM model allowed to determine the E_a associated to each degradation reaction stage of chitosan (between 163–346.3 kJ/mol), in contrast to isoconversional methods. Consequently, the 3R-Gaussian DAEM model is a suitable option to describe the kinetics of chitosan degradation process.