Abstract
An efficient reaction of carboxymethylation using reactive extrusion (REX) on plasticized starch was studied. The reaction products were characterized by Nuclear Magnetic Resonance (NMR) spectroscopy and high-performance liquid chromatography (HPLC). Several parameters affecting the reaction were investigated including the amount of plasticizer, reagent stoichiometry and reaction time. Reaction efficiency (RE) up to 65% was achieved in one step after 5 min of reaction, showing that the reaction kinetics is hundred times faster than the same reaction described in solution. The degree of substitution (DS) of 2.1 was obtained in 3 steps. The regioselectivity of the reaction on the anhydroglucose monomers units (AGU) was respectively C-2 > C-6 > C-3. A significant deviation from the Spurlin statistical model was observed. Multisubstituted AGU were analyzed by chromatography. Different multi-substitution patterns were obtained by using different starch sources. Tetra-carboxymethyl glucose corresponding to the complete modification of the terminal non-reducing glucoses from branched amylopectin chains was analysed.
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