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

Abstract

Abstract 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.