Study of the thermoplastic wheat starch cationisation reaction under molten condition

Abstract

This paper deals with the functionalization of thermoplastic wheat starch with cationic groups under the action of thermo-mechanical energy. Two reagents, leading to the same reactive species, are used: 3-chloro-2-hydroxypropyltrimethylammonium chloride and 2-epoxypropyltrimethylammonium chloride. An experimental study and a theoretical approach for reactive extrusion operations were carried out in a bench-top twin-screw microcompounder. The theoretical model developed is in satisfactory agreement with the experimental results obtained in the molten state, with low water content. Reaction kinetic studies, performed at different temperatures between 100 and 140°C, show that starch cationisation follows a second order reaction, with rate constants following the Arrhenius law. The obtained results allow calculation of the values of activation energy. The analysis of the thermoplastic unmodified and modified cationic starches by size exclusion chromatography (SEC) shows a decrease of the excluded fraction, which is attributed to the effect of the thermo-mechanical melting process. The X-ray diffraction spectra typical of molten starches were obtained.