Thermal stability of biodegradable films based on soy protein and corn starch

In this paper, films were prepared from soy protein and corn starch in different proportions and thermal stability and kinetic parameters were determined through degradation reactions in an inert atmosphere. Solid residues and decomposition products were identified by infrared spectroscopy. Films from corn starch were less thermally stable than soy protein films. The films containing both components had lower thermal stabilities when compared to those of the pure biopolymers. The mechanism of starch thermal degradation seems to occur in a single step, which can be confirmed by the constant E-values during the thermal degradation reaction. For the pure protein and its mixtures an increase in the activation energy was observed during the reaction. Solid residues for protein at different temperatures showed mainly bands related to C=O stretching, angular deformation of N-H and C-H groups. For starch, absorptions related to free and bound O-H, C=O stretching of COD CO and carbonyl compounds were observed. For the 50/50 mixture bands related to soy protein and corn starch were observed. The gaseous products for soy protein showed absorptions related to CO2, CO, C=O, NH3 and C-H stretching. For pure starch absorptions related to O-H stretching from alcohol, C=O from CO2, CO and carbonyl compounds. The 50/50 mixture had the same characteristics as pure soy protein and corn starch.