Carboxymethylation of Maize Starch

Abstract

Abstract Maize starch was reacted with monochloroacetic acid in presence of sodium hydroxide. The reaction involved is known as carboxymethylation. The latter was carried out under a variety of conditions. For every set of conditions carboxymethylation was studied with respect to the extent expressed as degree of substitution (DS) and reaction efficiency (RE). Results indicated that starch:water ratio of 1:2.5 constitutes the optimal material to liquor ratio. Increasing sodium hydroxide concentration up to 8N causes significant enhancement in DS and R. E. while higher concentrations bring about sharp decrement. DS increases as the monochloroacetic acid concentration increases; opposite trend was observed with respect to RE. Increasing duration (0.5–3 h) and temperature (60–70°C) acts in favour of both DS and RE. DS is also governed by the reaction medium. Water and organic solvents were used independently as well as in admixture of solvent/water. It was found that the highest DS is achieved with isopropyl alcohol and the least with water. The DS follows the order: isopropanol > cyclohexane > dimethyl formamide > methanol > acetone > water. Isopropanol: water mixture (80:20) constitutes the most favourable medium for the carboxymethylation reaction under the conditions used.