Fractal Aspects of Static and Dynamic Flow Properties of Pharmaceutical Excipients

Abstract

Purpose Characterisation of powder flow is important for pharmaceutical processing and manufacturing. This work aims at a better understanding of how fractal particle and bulk properties affect the static and dynamic flow of excipients. Methods Traditional methods of flowability testing, e.g. the angle of repose or the flow through an orifice, were complemented by avalanching in a rotational drum. Dynamic image analysis provided a fractal contour line dimension of the powder bulk in the drum (bD F ). This was compared to the contour line fractal dimension of particles (pD F ) as obtained from the box-counting method. Avalanche testing was able to measure also cohesive materials that were otherwise difficult or not measurable at all using the classical methods. Results The values of the avalanche energy were in good agreement with the different flow properties of the samples. These flow properties showed good correlations with bD F in that poor flow properties were associated with a more rugged contour line of the bulk and hence higher bD F . Conclusions Interestingly, there was no correlation observed between pD F and bD F , which may suggest that a distinct bulk structure typically emerges from the particles under dynamic flow. Future research should further clarify how fractal powder aspects affect pharmaceutical manufacturing processes.