Effect of Mechanical Activation on Starch Oxidation with Sodium Hypochlorite in a Rotor-stator Device

In this work, in order to intensify the oxidation of starch with sodium hypochlorite, mechanical activation of starch suspension in a rotor-stator device (RSD) was used for the first time. Activation of starch suspension (concentrations of 10, 20, 30 and 40%) before oxidation was carried out for 10, 20, and 30 s in two ways: either before the introduction of the oxidizing agent (A-OS) or after its introduction (AOS). The activation of starch in RSD for 10-30 s increased the rate of oxidant consumption during subsequent oxidation. The oxidized starches were analyzed by scanning electron microscopy (SEM), X-ray diffraction, and FTIR spectroscopy. Mechanical activation caused erosion of starch granules, increased porosity and specific surface areas.The mechanical activation of the starch increased the content of carbonyl groups in the range 46-61% and that of carboxyl groups in the range 60-100%, compared with the oxidation without activation (OS). In the case of (AOS), a higher yield of carbonyl and carboxyl groups was achieved compared to (A-OS). It was found that the effective viscosity and consistency coefficient of the starch hydrogels monotonically decrease as the duration of preactivation of the starch suspensions increased. Mechanical activation in RSD can be used to improve the oxidizing degree of oxidized starch or to reduce process time on a large scale.