DICARBOXY-STARCH BY SODIUM-HYPOCHLORITE BROMIDE OXIDATION AND ITS CALCIUM-BINDING PROPERTIES

Various aspects of the glycolic oxidation of the glucose units of starch with stoichiometric amounts of sodium hypochlorite applying sodium bromide as the catalyst have been investigated. The main objective of the study was to optimize the reaction conditions for the preparation of dicarboxy-starch and to establish the calcium sequestering capacity of the material. The products, polycarboxylates, are obtained in high yields (90-95%) and they have a sequestering capacity up to 1.4 mmole Ca/g, which is somewhat higher than that of the materials obtained in a non-catalyzed oxidation. This result is attributed to the facts that the reaction with sodium bromide may be carried out at higher pH (> 9) than the non-catalyzed reaction and that a relatively low concentration of hypochlorite throughout the process could be maintained. In this way the decomposition of hypochlorous acid/hypochlorite, especially occurring at high concentration of hypochlorous acid at lower pH (6-8) is prevented. Other advantages of this procedure are the colourless appearance of the materials and the higher reaction rate. The feasibility for large-scale preparation follows from the results of a few exploratory experiments, including an electrochemical preparation.