Effects of acidity, number of hydroxyl group, and carbon chain length of carboxylic acids on starch cross-linking

Corn starch film samples cross-linked using malic, malonic, and succinic acids, and thermoplastic starch were characterized and tested for their water absorption, surface morphology, structural change, and thermomechanical properties. The acids vary in acidity, number of hydroxyl groups, and carbon chain length. The presence of an additional hydroxyl group has helped malic acid form more hydrogen bonding between starch molecules. The relatively higher acidity in malic acid compared to succinic acid is found to be another factor for its better cross-linking potential. The additional carbon chain in succinic acid, which reduces its solubility and acidity; has negatively affected its cross-linking potential. Among the three variables studied, number of hydroxyl group has highly influenced the cross-linking potential, followed by acidity and carbon chain length, respectively. Consequently, the elongation at break and water absorption resistance of thermoplastic starch were improved from 108.63 ​MPa to 175.72 ​MPa and from 140% to 80%, respectively, cross-linking corn starch with malic acid.