CHARACTERIZATION AND INFLUENCE OF ESTERIFICATION PARAMETERS ON A DEGREE OF SUBSTITUTION OF POLYSACCHARIDES EXTRACTED FROM Zea mays BY A CHLOROACETIC ACID IN 1-BUTYL-3-METHYLIMIDAZOLIUM CHLORIDE

Abstract

The use of natural resources in a development of products and materials is currently increasing. Starch is one of the investigated resources due to its bioavailability, biodegradability, safety and affordability. In this study, native maize starch was esterified with carboxylic acid. The reaction was carried out for the first time in a homogeneous manner using 1-butyl-3-methylimidazolium chloride [BMIM]Cl as a reaction medium and excellent solvent for the starch modification. Reaction conditions (temperature, time and amount of the reagent) were studied using an experimental design. Carboxymethyl starch CMS with the degree of substitution DS 0.79 were obtained when the reaction was carried out at 90 °C for 180 min with 1:1 molar ratio of chloroaceticacid:anhydroglucose unit. The determination of DS was based on nuclearmagnetic resonance 1H NMR instead of elemental analysis, which showed overestimated DS values in this study. Fourier transform infrared FTIR and nuclear magnetic resonance analyses, confirmed the esterification of the maize starch. Furthermore, the results of X-ray diffraction XRD and a scanning electron microscopy SEM revealed that the crystallinity and the morphology of the native maize starch was slightly changed during its partial gelatinisation in the ionic liquid, and was completely destroyed as a result of the formation of the esters. The thermal stability of the CMS decreased, when compared to the unmodified starch, as was indicated by a thermal gravimetric analysis TGA.