Thermal characterization and detailed kinetic analysis of Cassava starch thermo-oxidative degradation

• Cassava starch.
• Competitive reactions.
• High value of reaction order (n = 3.49).
• Nonlinear least squares analysis.
• Free radical mechanism.

Detailed kinetic analysis of Cassava starch thermo-oxidative degradation was performed, using thermogravimetric analysis (TGA) and derivative thermogravimetry (DTG) at four different heating rates. It was found that degradation process is very complex, as identified through continuous change of apparent activation energy with degree of degradation. It was established that process proceeds through three main degradation stages with one additional sub-stage attached to the second degradation stage, which was detected by appearance of “shoulder” on DTG curves. It was found that most important degradation stage can be described by “lumped” model, which implies that free radicals simultaneously attack both linear and branched molecular forms of the starch. This is characterized by an unusually high value of obtained reaction order (n = 3.49). Application of nonlinear least squares method was confirmed the reliability of evaluated kinetic parameters and function of reaction mechanism, which were derived on the basis of other kinetic methods.

It can be observed a very similar shape of distributions for Step I and Sub-step I, representing one reaction unit. The probability of process realization increases for Step I and Sub-step I, going to singularity. In contrast, the probability of process realization continuously decreases in case of Step II.Figure optionsDownload as PowerPoint slide