Thermal Characteristics, Kinetics and Thermodynamics of Thermal Degradation Reaction, and Hydrophobicity of Corn Starch Affected by Chemical and Physical Modifications

In this work, glacial-acetic (A) and citric (C) acids from organic acids "family with one and three functional groups, respectively", oleic acid (O) from the fatty acids family and sodium acetate (S) are used for esterification of corn starch in solution in the absence and the presence of 15%wt glycerin as a physical modifier. Discoloration test using CIELAB and as well as thermal gravimetric analysis shows that the glacial-acetic acid leads to lower reduction in thermal characteristics of the modified starch. The variations of thermal properties start from T > 112 degrees C, T>136 degrees C, T>100 degrees C, and T> 124 degrees C for the modified starches with C, A, O, and S reagents, respectively, and the changes are constant beyond the amount of 4%wt reagent. The evaluations of kinetics and thermodynamics of thermal degradation reaction for the modified starches via a Coats-Redfern (CR) model prove that the acetic acid causes more activation energy for degradation compared to other reagents. Also, acetic acid-modified starch demonstrates the highest hydrophobicity among other modified starches - even native starch - in the moisture sorption examination at 75% relative humidity (RH). The results illustrate that glycerin has the worst effect on the thermal and hydrophobicity properties of the modified starches.