Shear and Flow Properties of Binary Powder Mixtures

Majority of pharmaceutical products today are solid dosage forms, such as tablets, capsules, and powders for inhalation, thus making powder technology critical for the manufacturing process. The complex behavior of pharmaceutical powders is not well understood and characterized; suitable processing conditions and formulations are determined by extensive trial-and-error procedures, and even the small changes in the said parameters can cause great variations in powder. The properties of the materials may change dramatically during processing introducing variability into the process and affecting final product quality and characteristics. It is therefore important to meaningfully characterize and quantify the powder flow.

In this study the flow behavior of nine well-mixed two-component blends with varying concentrations of fine and coarse catalytic powders was characterized by a gravitational displacement rheometer (GDR) and a rotational shear cell. Principal stresses, cohesion and flow functions were obtained via shear cell techniques; flow and dilation index were determined with the GDR and compared with the mixture compressibility. At lower consolidations the mixtures displayed non-linear shear stress behavior; however, when normalized, the major principal stresses were found to be proportional to the mixture composition and particle density and size. Values of cohesion and flow factors obtained from the shear cell showed dependence on material compressibility and correlated discernibly with the flow and dilation indices obtained from the GDR.