Kinetics of thermal degradation applied to starches from different botanical origins by non-isothermal procedures

Amylose content, crystallinity, morphology and the kinetic of thermal degradation to starches from different botanical origins are described based on XRD, SEM, DSC and TG/DTG curves. Applying the non-isothermal isoconversional Wall-Flynn-Ozawa method on the TG/DTG curves average activation energy (0.10 <= alpha <= 0.70) E = 144.1 +/- 9.8, 171.6 +/- 14.6, 158.3 +/- 7.4 and 159.4 +/- 15 kJ mol(-1) could be obtained for thermal degradation of corn, rice, potato and cassava starches, respectively. From E values and the generalized time theta, the Sestak-Berggren (SB) in which f(alpha) = alpha(m)(1 - alpha)(n) seems to be most suitable kinetic model in describing physicogeometrically the thermal degradation for the samples regardless of its botanical origins. The determination of the kinetic exponents m and n allows to obtain the pre-exponential factor (0.2 <= alpha <= 0.8) ln A = 8.8, 10.4, 9.2 and 8.9 min(-1) for corn, rice, potato and cassava starches, respectively. There were not significant differences between values of the kinetic triplet of the starches, indicating that, despite structural differences, these had little influence on the thermal degradation process of the starches. (C) 2006 Elsevier B.V. All rights reserved.