Thermal decomposition and non-isothermal decomposition kinetics of carbamazepine

Abstract

The thermal stability and kinetics of isothermal decomposition of carbamazepine were studied under isothermal conditions by thermogravimetry (TGA) and differential scanning calorimetry (DSC) at three heating rates. Particularly, transformation of crystal forms occurs at 153.75°C. The activation energy of this thermal decomposition process was calculated from the analysis of TG curves by Flynn-Wall-Ozawa, Doyle, distributed activation energy model, Satava-Sestak and Kissinger methods. There were two different stages of thermal decomposition process. For the first stage, E and logA [s−1] were determined to be 42.51 kJ mol−1 and 3.45, respectively. In the second stage, E and logA [s−1] were 47.75 kJ mol−1 and 3.80. The mechanism of thermal decomposition was Avrami-Erofeev (the reaction order, n = 1/3), with integral form G(α) = [−ln(1 − α)]1/3 (α = ∼0.1–0.8) in the first stage and Avrami-Erofeev (the reaction order, n = 1) with integral form G(α) = −ln(1 − α) (α = ∼0.9–0.99) in the second stage. Moreover, ΔH ≠, ΔS ≠, ΔG ≠ values were 37.84 kJ mol−1, −192.41 J mol−1 K−1, 146.32 kJ mol−1 and 42.68 kJ mol−1, −186.41 J mol−1 K−1, 156.26 kJ mol−1 for the first and second stage, respectively.