Power consumption during oscillatory mixing of pharmaceutical powders
The blending of powders is a critical step in pharmaceutical drug product manufacturing as it ensures that each dosage unit will contain the same intended fraction of active pharmaceutical ingredient (API). Under-blending thus poses a significant risk to patients where overdose or underdose can occur. Similarly, over-blending can lead to manufacturing issues such as reduced tablet tensile strengths as any included lubricants are dispersed further and further with additional blending. For these reasons, powder blending has been extensively studied in the pharmaceutical industry and a wide variety of blending processes have been implemented, including tumble bin and ‘V’ blenders with or without intensifier bars, high shear wet granulators, ribbon blenders, continuous blenders and others. A relatively new oscillatory blending process is presented by the resonant acoustic mixer (RAM), which has gained some interest in the literature.
In this work, we explore the mixing energy delivered to powders in the RAM geometry as a function of the relevant process variables such as oscillation amplitude (g-forces), sample bottle headspace, and powder mass. The mixing energy was estimated from the measured temperature rise of mixed powders. Additionally, the mixing process was modeled by both a simplified custom DEM simulation and by the derivation and solution of a second order nonhomogeneous linear differential equation, which describes a ball oscillating in a can of viscous fluid. The experimental data were evaluated in light of both models and results suggest that the derived equation (Eq. (37)) provided a better description of power delivery in oscillatory mixers than the DEM model, which does not account for the viscosity of air. The data also show that more tightly packed powders absorb less energy. This trend was also predicted by Eq. (37) and is the expected trend when confined powders begin to approximate rigid-body oscillators, which theoretically consume no power.