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Compaction of pharmaceutical powders on a high-speed rotary press Zhao, Jinying


BACKGROUND: The compression behavior of pharmaceutical powders has been previously shown to significantly influence the quality and commercial viability of a tablet formulation. The compression conditions have also been reported to affect the behavior of a tablet formulation. Formulations developed on small-scale analytical tableting machines may not work on high-speed rotary presses that are the most commonly used commercial presses. OBJECTIVE: The overall objective of this research was to model the in-process compression behavior of pharmaceutical powders during high-speed compression based on viscoelastic theory and porosity-pressure relationships, which might provide an effective tool in characterization and prediction of the compression behavior of pharmaceutical powders. METHODS: Five pharmaceutical materials with well-established compression properties were compressed using an instrumented Manesty Betapress under representative manufacturing conditions. Two methods were used to model the compression data. Firstly, the time dependent behavior of the materials was investigated based on viscoelastic models describing a continuous body. Secondly, the compression data were evaluated based on two mathematical equations describing powder densification process, namely the Heckel equation (a well-known equation in the field) and the Gurnham equation (a new model proposed for pharmaceutical powder compaction in this work). RESULTS AND DISCUSSION: Modeling of the compression process using viscoelastic theory was not very successful. The measured stress-strain responses suggested that powder densification behavior instead of viscoelastic behavior dominates most of the compression phase. Nonetheless, the behavior of two ductile materials under relatively low pressures displayed viscoelastic characteristics during their peak offset phase. However, the modeling results using powder densification equations seemed promising. Using results at peak pressure, linear relationships between pressure and porosity following the Gurnham equation were observed and the slopes of these linear plots were related to the compressibility of materials. Compared to the well-known Heckel equation, the Gurnham equation provided reasonable predictions for pure brittle materials and processed compounds, which has always been a limitation of the Heckel equation. CONCLUSIONS: The results of this work seem to suggest that the powder densification approach is more appropriate in describing the compression process under current experimental setting than the viscoelastic approach. Moreover, the powder densification equation proposed in this work, the Gurnham equation, shows potential in modeling the behavior of pharmaceutical powders during high-speed compression.

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