An experimental study on the carboxymethylation of granular potato starch in nonaqueous media

The optimal reaction conditions for the carboxymethylation of granular potato starch in mixtures of water and organic liquids were determined. The reaction was carried out with pellets of NaOH and sodium monochloro acetate (SMCA) powder as the carboxymethylation reagent. Different alcohols, from methyl alcohol up to the three isomers of butyl alcohol, and acetone were compared in terms of the degree of substitution, DS, and the reaction efficiency, RE. Gelatinisation of the starch granules was avoided at all times. For ethyl alcohol and isopropyl alcohol the effect of the water fraction was studied. The highest RE and the highest DS were obtained for isopropyl alcohol with 10 wt% water. For this system the effect of the temperature, the NaOH to SMCA molar ratio and the theoretical DS was studied in detail. The DS obtained in a single reaction step was limited to about 1.3, with an RE of 0.6. The modification was also carried out in three consecutive steps; resulting in granular carboxymethyl potato starch with a DS of 2.2. The results for the DS and the RE, obtained in this work, are considerably higher than the values reported in the literature.