Nonedible Starch Based Green Thermoset Resin Obtained via Esterification Using a Green Catalyst

In this study, a biobased thermoset resin was developed from a nonedible starch source obtained from mango processing industrial waste. Mango seed starch (MSS) was extracted from defatted mango seed kernels and cross-linked using a green cross-linker/catalyst system, 1,2,3,4-butane tetracarboxylic acid (BTCA)/sodium propionate (NaP), to obtain the thermoset resin. The tensile properties of the cross-linked MSS were found to be adequate to replace edible starch based thermoset resins, e.g., potato or corn or proteins such as soy. The cross-linking or the esterification reaction proceeds faster and at lower temperature in the presence of a suitable catalyst. Sodium hypophosphite (SHP), a widely used catalyst for esterification using poly(carboxylic acid)s and hydroxyl groups of starch or cellulose, contains phosphorus and the effluents containing SHP, i.e., phosphorus, are toxic to humans and can adversely affect the fauna in water. Also, SHP decomposes to toxic phosphine gas when heated. The results of the present study indicate that sodium propionate (NaP), used as a nonphosphorus green catalyst, is as effective and efficient as SHP. The cross-linking of starch was confirmed directly using ATR-FTIR spectra and the degree of substitution (DS) values obtained by chemical titrations as well as indirectly through an increase in the tensile properties. Higher modulus and strength and lower degree of swelling in water of films cross-linked using NaP confirmed that NaP acts as a better catalyst than the conventional SHP.