Homogenous carboxymethylation of starch using 1-butyl-3-methylimidazolium chloride ionic liquid medium as a solvent

An ionic liquid, namely 1-butyl-3-methylimidazolium chloride (BMIMCl), was employed as a reaction medium for homogenous carboxymethylation of corn starch. The process variables affecting the carboxymethylation reaction such as amount of sodium hydroxide (NaOH) and sodium monochloroacetate (SMCA), reaction time and reaction temperature were investigated regarding the degree of substitution (DS) for the carboxymethyl starch. The highest DS of 0.76 was obtained at molar ratios of NaOH and SMCA to anhydroglucose unit (AGU) of 1.2 and 1.0, respectively, and at 90 °C for 3 h of reaction. Results from FT-IR and 13C NMR spectra indicated that the hydroxyl groups of starches were substituted by carboxymethyl groups. SEM and XRD studies showed that the morphology and crystallinity of starch was disrupted after the carboxymethylation reaction.