Assessment of the impact of process and formulation variables on the prevalence of coating and coalescence mechanism in high shear mixer (Eirich mixer)

High shear mixing of powders in the presence of liquid addition can lead to the enlargement of primary powder particles, forming larger structures referred to as granules. This particle growth can occur through distinct mechanisms, including layering, coalescence, or a combination of both, and the prevailing mechanism is influenced by a multitude of process and formulation variables. In this study, we quantified the influence of process variables such as vessel inclination, rotational direction of the vessel, impeller speed, mixing duration, and rotation speed of the vessel pan on the particle growth mechanism. We accomplished this through rigorous image analysis of granule samples produced under varying conditions. Furthermore, our investigation extended to encompass the effects of formulation variables, including the particle density of the primary powder, the quantity of binder added, and the particle size of the coating material. Our findings revealed that the coating mechanism predominantly governed particle growth when the mixing time was brief, the mixer vessel had a high inclination angle, and the vessel rotated in a direction opposite to that of the agitator. The coating material utilization factor, denoting the ratio of the mass fraction of coating material added that effectively participates in the formation of coated seeds (each with a single seed) to the fraction of coating material engaged in competing mechanisms, serves as a crucial indicator of the prevailing mechanism within specific process and formulation conditions.