Carbohydrate Polymers 85 (2011) 792–797 Contents lists available at ScienceDirect Carbohydrate Polymers journal homepage: www.elsevier.com/locate/carbpol Homogenous carboxymethylation of starch using 1-butyl-3-methylimidazolium chloride ionic liquid medium as a solvent Wenlei Xie ∗ , Yanxian Zhang, Yawei Liu School of Chemistry and Chemical Engineering, Henan University of Technology, Zhengzhou 450052, PR China article info Article history: Received 17 December 2010 Received in revised form 9 February 2011 Accepted 28 March 2011 Available online 5 April 2011 Keywords: Starch Carboxymethylation Ionic liquid Homogeneous modification abstract 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 car- boxymethylation 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 13 C NMR spectra indicated that the hydroxyl groups of starches were substituted by car- boxymethyl groups. SEM and XRD studies showed that the morphology and crystallinity of starch was disrupted after the carboxymethylation reaction. Crown Copyright © 2011 Published by Elsevier Ltd. All rights reserved. 1. Introduction Starch is one of the most abundant naturally occurring biopoly- mers and is in the form of granules that exist in the plant cells. Because starch is cheaper than most other biomaterial resources, it has diverse applications in food, pharmaceuticals, textile, paper, plastics as well as in biomedical engineering industries. Unfortu- nately, the utilization of starch in its native form is often limited by some undesirable characteristics such as poor solubility, low mechanical properties, and instability at high temperature and pH during processing. The chemical modification of starch can overcome these shortcomings by derivatization reactions such as esterification and etherification, to improve significantly the functional properties of starch. In general, starch modification ∗ Corresponding author. Tel.: +86 371 67756302; fax: +86 371 67756718. E-mail address: xwenlei@163.com (W. Xie). involves the reaction of the hydroxyl groups on the anhydroglu- cose unit (AGU) with the formation of starch derivatives. Among the starch derivatives, carboxymethyl starches have attracted con- siderable attention chiefly owing to their industrial applications in many fields, for example, a sizing and printing agent in the textile industry and as an excipient in the pharmaceutical industry (Lawal, Lechner, Hartmann, & Kulicke, 2007). Carboxymethyl starch (CMS) is usually obtained by the reac- tion of starch with monochloroacetic acid or its sodium salt in the presence of an alkali. A schematic representation of the reaction of starch with sodium monochloroacetate (SMCA) is provided in Eq. (1). Apparently, the extent of variation in the physico-chemical properties of the starch derivative after modification is associated with the degree of substitution of the starch. (1) Although the reaction is usually carried out in the presence of strong bases to increase the nucleophilicity of the hydroxyl group, an undesired side reaction could also occur with sodium hydroxide, producing sodium glycolate as a by-product from SMCA according 0144-8617/$ – see front matter. Crown Copyright © 2011 Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.carbpol.2011.03.047