Powder functionality test: a methodology for rheological and mechanical characterization

In most pharmaceutical formulations, the part of the excipients, in quantity and number, is larger than that of active principles, justifying particular attention to their characteristics to ensure quality, efficacy, and reproducibility of final forms. Whereas chemical specifications are described in Pharmacopeias, physical characteristics, up to now, have not been sufficiently considered. Nevertheless, there is a need for tests to objectively compare technological performances of products and justify composition of medicinal products. The powder functionality test described in this article is based on the analysis of the global behavior of materials under pressure. The powder compression is performed using an instrumented uniaxial press, Lloyd 6000R, and a compression cell of 1 cm3 in volume, allowing a complete and early characterization with a few grams of material. Indices characterizing packing, densification energies, energetic yields, and deformation mode of the particles are proposed from the analysis of compression cycles. Cohesion and energy of rupture are deduced from the diametral rupture cycles of the compacts. Application of this methodology to supplied celluloses has shown better flow properties of microcrystalline celluloses due to their higher bulk density and particle size. The energy fraction lost as frictions is very important and independent of the type of celluloses, whereas elastic energy is higher for powdered celluloses P100 and G250. Finally the efficacy to convert compaction energy into cohesion is higher for products with a small degree of polymerization, i.e., microcrystalline celluloses, except A301 and A302, which also are distinguished by their low porosity.