Kinetic and mechanism studies of the isothermal degradation of local chitin, chitosan and its biocomposite bentonite/chitosan

In this work, the kinetic and the mechanism of isothermal degradation of local chitin (CN), chitosan (CS) and the biocomposite Bentonite/Chitosan (5%Bt/CS) were investigated by thermogravimetric analysis in air atmosphere and in the temperatures range 285–330 °C. Fourier transform-infrared, X-ray diffractogram and differential scanning calorimetry analyses were used to determine the structure of the as prepared samples. DTG curves of the samples show that CN and CS presented one peak, while those of 5%Bt/CS presented one to three peaks as the isothermal degradation increases. This difference was linked to the strong interactions between CS and Bentonite, which improve the stability of CS in the biocomposite 5%Bt/CS. The common first DTG peak appearing in each sample was treated using the Friedman method, leading to the activation energy (Ea) of Ea(CN) = 127.18 kJ/mol > Ea(CS) = 103.90 kJ/mol > Ea(5%Bt/CS) = 80.64 kJ/mol. The auto-catalytic Sestak–Berggren model was found to be qualitatively matched the isothermal degradation process of each sample. The thermodynamic parameters show the appearance of an order in the activated complex with respect to the initial state and that the isothermal degradation process is endothermic and is not spontaneous.