Powder bed dynamics of a single-tablet-scale vibratory mixing process

Abstract

Vibratory mixing is a promising technique for the blending of pharmaceutical powders to produce solid dosage forms. In this study we evaluate the particle dynamics inside a single-tablet-scale vibratory mixing device, to gain insight on the contributions of diffusive and convective mixing on the blending performance. To investigate the influence of vibration parameters, the frequency of vibration is varied from 100 to 300 Hz keeping similar acceleration amplitudes. Particle-dynamics evaluation is realized using high-speed video recordings and PIV-analysis. The experiments showed faster onset of agitation, higher average velocity magnitudes, and higher apparent granular temperatures for lower vibration frequencies. The size of the dilute zones, predominately responsible for rapid mixing, decreased with increasing frequency. Comparison with studies on the mixing performance from literature revealed a good correlation between the observed dispersion coefficient and the mixing speed, indicating that diffusive mixing mechanisms are the major driving factor in this single-tablet-scale blending process. • Diffusion is the dominant mechanism in vibratory mixing on single-tablet-scale. • Velocity and dispersion coefficient decrease with vibration frequency. • Rapid mixing happens inside active dilute regions in the agitated powder bed. • The position and size of active dilute zones strongly impact the mixing efficacy. • The size of active dilute zones increases for decreasing frequencies.