High-Efficient Preparation of Carboxymethyl Starch via Ball Milling With Limited Solvent Content

Carboxymethyl starch (CMS) is successfully prepared via ball milling in the presence of limited amounts of solvent, monochloro acetate, or dichloroacetic acid. In the process, several factors affecting carboxymethylation reaction such as solvent, NaOH/ClCH2COONa ratio, ClCH2COONa/anhydroglucose unit (AGU) ratio, reaction time, and amount of dichloroacetic acid are investigated in terms of the degree of substitution (DS) for the CMS and the optimum conditions are established. Under this condition, the substitution degree of the prepared CMS is 0.65 and the reaction efficiency can reach up to 80%. Additionally, crosslinked carboxymethyl starch is prepared by using dichloroacetic acid as crosslinking agent in the same condition in order to increase the viscosity of CMS. The crystallinity of CMS is measured by X-ray diffraction. And the results shows that the crystallinity of the product is decreased with the increasing milling time and substitution degree. FTIR and (HNMR)-H-1 spectra indicates that the hydroxyl groups of starches are substituted by carboxymethyl groups. Our work provides a simple method for high-efficient preparation of CMS via ball milling in the presence of monochloro acetate and dichloroacetic acid and has great potential for broadening the application of starch.