Effect of Primary Particle Size on Granule Growth and Endpoint Determination in High Shear Granulators

ABSTRACT Three different grades of lactose monohydrate having widely differing mean particle sizes, yet similar tap densities, were granulated using a 25L instrumented Fielder mixer. The size distribution, porosity, and pore saturation of the wet granules were determined using a combination of “frozen granule” sieve analysis, mercury pycnometry, and oven drying. The granulating system was found to operate at quasi-steady-state, as granule growth ceased afler liquid addition was terminated. The resultant granule size distributions were strongly dependent on lactose grade. with coarser grades yielding larger granules for identical process conditions. In contrast. the magnitude of the power curves decreased with increasing primary particle size. Both of these observations are consistent with the fact that both the capillary and viscous interparticle fluid forces, which are believed to provide the main interparticle bonding forces in the wet mass, are inversely proportional to particle size.