Stability of particle suspensions after fine grinding

Abstract

Abstract The objective of this work was to investigate the physical stability of sub-micron particle suspensions of organic crystalline food compounds after grinding. A Dynomill ball mill was used in combination with zirconium oxide grinding medium beads. The organic product was a poor water soluble product. During grinding the average particle diameter of the particulate product was reduced to a minimum value in the sub-micron range. Forward light scattering was used to analyze the particle size distribution. Dynamic light scattering measurements, on the other hand, showed that there were aggregates present after grinding. The difference in the obtained particle size distributions using both techniques was related to the shear in the measurement device, i.e. in the laser diffraction measurement the shear was higher than in the dynamic light scattering device. Thus in the laser diffraction measurement the aggregates were broken up by shear, while this was not the case in the dynamic light scattering measurements. The difference in the measurements showed that the particles formed aggregates at low to zero shear. The aggregation behaviour of the particles was studied by measuring the sedimentation behaviour of the particles suspension at various pH values. The impact of the pH on the aggregation rate was explained by the zeta potential of the particles. The suspensions were less stable near the iso-electric point of the particles.