Investigations of single microcrystalline cellulose-based granules subjected to confined triaxial compression

• Single pharmaceutical granules were compressed triaxially under confined conditions.
• Triaxial results were compared to unconfined uniaxial and confined bulk compression.
• Granule porosity was shown to control the onset of plastic incompressibility.
• Granules compressed triaxially cracked but tended to keep their integrity.
• Confined single granule compression reflected bulk compression experiments.

Confined triaxial compression of single granules was performed in order to assess the contact force development and modes of granule deformation under these conditions. In the study, four microcrystalline cellulose-based granule types of different characteristics were investigated. Results from triaxial single-granule compression experiments were evaluated using an analytical model as well as by comparison to unconfined single-granule compression and to confined bulk compression experiments. It was observed that single granules deform and densify, but tend to keep their integrity during confined triaxial compression, as evident from both compression data and from morphological analysis. Results from confined single granule compression were well represented by the analytical model. These results also largely reflected those from bulk compression experiments, including features of the force–displacement curves as well as rank order between the granule types in terms of contact stiffness. Furthermore, it was shown that intragranular porosity to a high extent governs the onset of plastic incompressibility.

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