The development and use of a static segregation test to evaluate the robustness of various types of powder mixtures
Résumé
Particle segregation usually appears as the counterpart of any mixing operation involving particles of different physical properties. However, little attention has been paid in the literature to this problem and especially to quantifying the stability of powder mixtures to segregation during the conveying and handling operations following a mixing process. This paper gives a theoretical definition of the `robustness' of a powder mixture based on knowledge of the quality of a mixture before and after a segregation test. Specific attention is paid to the problem of homogeneity estimation through sampling. A simple static segregation device, specially developed for this study, is then used for evaluating the robustness of pharmaceutical powder mixtures. The effect of using an excipient, of the same chemical nature but different physical properties, is investigated from the point of view of size and shape of the particles. In the experiments performed here it is found that particle size has practically no influence on robustness, but it is demonstrated that particle shape has an important effect. Replacing irregular‐shaped particles in a powder mixture by spherical‐shaped particles (such as those produced by spray‐drying) can provoke a dramatic disruption of the structure of a mixture by a simple pouring. Finally, the static segregation device is used as a relative measurement of homogeneity of complex blends consisting of animal feed and aroma. The evaluation of the effect of a premix step leads to the conclusion that the process time devoted to premixing should be optimized with respect to the overall mixing.