Kinetics and mechanism of thermal decomposition of cornstarches with different amylose/amylopectin ratios

Thermal decomposition of cornstarches with different amylose/amylopectin ratios (waxy: 0/100, maize: 23/77, Gelose 50: 50/50, and Gelose 80: 80/20) under nitrogen condition was investigated by thermogravimetric analysis (TGA). Various decomposition models including Friedman, Kissinger, Flynn-Wall-Ozawa, and modified Coast-Redfern methods were used to determine the apparent activation energy of different starches. Fourier transform infrared spectrometry (FTIR) and TGA-FTIR were also used to study the mechanism of thermal decomposition process. The results show a multiple-step mechanism for the thermal decomposition of all cornstarches. The sequence of activation energy for the cornstarches is waxy>maize>G50>G80, which corresponds to amylopectin content. FTIR results confirm that the thermal decomposition of cornstarch is due to the long-chain scission. The higher activation energy for cornstarch with higher amylopectin content can be explained by its higher molecular weight and more α-1,6 bonds.