Compaction mechanics of plastically deformable dry granules

• Drucker Prager Cap (DPC) model was calibrated to improve compaction understanding.
• Microcrystalline cellulose (MCC) powder and MCC monodisperse dry granules were used.
• Granule solid fraction (SF) impacts the shear failure surface of the DPC model.
• Cohesion and tablet tensile strength decrease as the granule SF increases.
• All other DPC parameters and the yield cap surface are insensitive to granule SF.

To improve the understanding of how dry granulation and in particular, granule solid fraction (SF) impact the compaction behavior of plastically deformable microcrystalline cellulose (MCC), in this study, the Drucker Prager Cap (DPC) model parameters were calibrated using monodisperse MCC dry granules as model granules. Dry granules were produced as directly compressed small cylindrical compacts of MCC with SF in the range of 0.40 to 0.70 which were monodisperse in both size and SF. Virgin MCC powder and granules were compressed into tablets with SF in the range of 0.70 to 0.90. The DPC parameters (cohesion, internal friction angle, cap eccentricity, and hydrostatic yield stress), Young's modulus and Poisson's ratio were experimentally determined from diametrical and uniaxial compression, and in-die compaction tests. Results showed that calibration of the shear failure surface only may be adequate for MCC granules when the DPC model is completely calibrated for virgin MCC. Increasing granule SF significantly decreased the cohesion only. All other parameters were impacted by the tablet SF only. In the 2D yield surface, only the shear failure surface expanded as the granule SF increased. MCC of any granulation status requires the same in-die compaction stress state for densification to a given tablet solid fraction.

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