(13c) Carboxymethylation of Starch Using Reactive Extrusion

Corn starch was carboxylated using a Brabender TSE-20 co-rotating twin screw extruder. Extrusion presents a novel solvent-less procedure for carboxymethyl etherification of starch. The effect of moisture content, sodium hydroxide content and temperature on the degree of substitution (DS) of carboxymethyl starch was studied. Also, the effects of adding small amounts of citiric acid and sodium tri poly phosphate (STPP), as cross linking agents, to the reaction mixture prior to the extrusion, were determined. Two methods of using sodium hydroxide, adding prills and spraying an aqueous solution were used and their comparative effects on DS of carboxymethyl starch were studied.