Carboxymethylation of maize starch at mild conditions

A process for carboxymethylation of maize starch (St.) at 30 °C was adopted. Although mild reaction conditions were employed, 100% reaction efficiency and a completely cold water soluble product with a clear and transparent solution were obtained. A multifunctional catalyst was used to accelerate the carboxymethylation reaction at 30 °C. An increase in the catalyst concentration was found to increase the reaction rate, thus the reaction time was reduced from 168 to 24 h. Factors affecting the carboxymethylation reaction such as material:liquor ratio, using different solvents in the reaction medium, the ratio between solvent and water, the sequence of addition of the reactants and cooling during addition of the reactants were studied. 100% reaction efficiency was obtained using equivalent molar ratios of etherifying agents (0.2 mol/mole St.), 0.3 mol/mole St. of catalyst; isopropanol:water ratio of 90:10 and a material:liquor ratio of 1:1.5 at 30 °C for 24 h. The carboxymethylation reaction was tested for its reproducibility and suitability for other types of starch (rice and potato) while the carboxymethyl starch (CMS) prepared was further characterized for its viscosity, transparency and suitability as a sizing agent for cotton yarns. The CMS prepared was found suitable as a sizing agent. The tensile strength of the sized samples increased by 38.6% compared with the blank samples and the desizing efficiency of the sized samples was 98% at 30 °C.