Thermal degradation kinetics study of curcumin with nonlinear methods

The results of TG/DTG when curcumin was used as the food colouring agent indicated that the processing temperature of the food should not exceed 190 degrees C. The decomposition process of curcumin involved two stages. The results of E-alpha, values, determined by an advanced isoconversional method, showed that the two stages were both single-step processes. The most probable mechanisms of the two stages were estimated by using comparative and nonlinear model-fitting methods. The mechanisms obtained from the two methods are the same, which are the assumed random nucleation and its subsequent growth for stage I and one-dimensional diffusion for stage II, respectively. The values of pre-exponential factor A for both stages were obtained on the basis of E-a and g(alpha). Besides, some thermodynamic functions (Delta S-not equal, Delta H-not equal and Delta G(not equal)) of the transition state complexes for the two stages were also calculated. (C) 2014 Elsevier Ltd. All rights reserved.