TEMPERATURE EFFECT ON RHEOLOGICAL AND DEWATERING PROPERTIES FOR STARCH-BASED COATING COLORS

The effect of suspension temperature (23, 33, 43 and 53 degrees C) on different starch-based coating colors were studied by rheological and dewatering characterisations. The potato starch co-binder was modified through hypochlorite oxidation of an anionic starch and also introduc tion of cationic derivates. The molar mass at different degrees of oxi dation of the starch gave different solution viscosities, which were r educed with an increased solution temperature. There is no adsorption of the oxidized starch on clay since it is only present in the continu ous phase. A cationized starch adsorbs on to the clay particles until a maximum is reached after which only its concentration in the continu ous phase increases. At deformation forces beyond the yield stress, th e hydrodynamic properties of the suspension dominates the flow propert ies of all coating colors. This can be explained as a multi-phase syst em with its solid phase in a continuous phase of various contents of p olymers in solution. When the temperature is increased, the high shear viscosity is decreased due to a reduced continuous phase viscosity. T he water holding decreases with a temperature increase as a result of an reduced continuous phase viscosity. An increased temperature, or le ss component interaction, improved the blade runnability, with no colo r build-up on the blade.