The Role of Particle Surface Area and Adhesion Force in the Sticking Behavior of Pharmaceutical Powders

The effect of particle surface area and adhesion force on sticking behavior for a model pharmaceutical blend was studied. Various lots of an active pharmaceutical ingredient (API) differing in particle size distribution and surface area were blended with commercial grades of microcrystalline cellulose ranging in size from 20 to 110 μm. A dry-coating technique was also used to modify the surface of microcrystalline cellulose to reduce its adhesion force. This allowed study of sticking behavior due to effects associated with particle adhesion force independently from effects associated with surface area. Using a removable-tip experiment to quantify the mass of adhered material to a tablet punch, this study concludes that both particle surface area and adhesion force significantly affect sticking behavior. Tablets with higher tensile strength comprised of API with lower surface area relative to the excipient surface area resulted in less sticking. This study found that the difference between the tablet tensile strength of the blend and that of the API normalized by the surface area fraction of API in the blend correlates well with the rate of mass adhered to the punch. This quantity, referred to as the sticking index, can be used to assess sticking propensity for a pharmaceutical blend.