To be used as an alternative adhesive for sand cores in a foundry, a solid water-soluble modified starch [carboxymethyl starch (CMS)] was synthesized by a new dry reaction process. With this process, a series of CMS products was obtained with degrees of substitution (DSs) ranging from 0.25 to 0.78 at a high reaction efficiency and characterized with regard to their molecular structure and aqueous solution viscosity. On the basis of the dry synthesis of CMS, the properties of CMS-bonded shell core sand were investigated, and practical production experiments were carried out. The results show that there was a new sharp peak in the infrared spectrum that represented the carboxymethyl groups and formation of CMS. The viscosity of the CMS aqueous solution increased with increasing DS and amount of CMS. When DS was in the range 0.3-0.5 and the mass fraction was 5-7%, the CMS aqueous solution had a suitable viscosity, which was helpful for the improvement of the properties, such as flowability, permeability, and strength, of the CMS core sand. In addition, a CMS shell core with an appropriate wall thickness (10-20 mm) for the purpose of obtaining both sufficient strength and permeability could be made with the CMS-bonded core sand and a hot-core-box process. The final pouring results prove that high-quality iron castings with smooth inner cavities could be produced with the CMS-bonded shell core and that it (namely the CMS-bonded shell-core) could be used as a replacement for the furan resin-bonded sand core. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 116: 2893-2900, 2010