Compression analysis for assessment of pellet plasticity: Identification of reactant pores and comparison between Heckel, Kawakita, and Adams equations

• Published in: Chemical engineering research & design Vol. 110; pp. 183 - 191
• Main Authors: Persson, Ann-Sofie, Nordström, Josefina, Frenning, Göran, Alderborn, Göran
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.06.2016
• Subjects: Adams equation; Compression; Effective porosity; Heckel equation; Kawakita equation; Plasticity; Heckel equation; Compression; Effective porosity; Adams equation; Kawakita equation; Plasticity
• ISSN: 0263-8762; 1744-3563
• DOI: 10.1016/j.cherd.2016.01.028

•Granular plasticity was assessed from compression analysis.•The granule plasticity could not be differentiated with global Heckel numbers.•The voidage Heckel profiles captured the plastic differences to a higher extent.•The voidage was thus considered as a better descriptor of the reactant pore system.•Plastic differentiation was enabled using Kawakita and Adams parameters. The issue of accurate derivation of a granule yield stress by the traditional procedure using the Heckel equation in addition to the Kawakita and Adams equations has been addressed. The accuracy of the derived parameters was assessed from comparison of single-particle yield pressures from uniaxial compressions. The single-particle yield pressure was nearly four-fold higher for microcrystalline pellets of low (LP) compared to of high (HP) porosity. Heckel profiles were derived using in situ (in-die) and ex situ (out-of-die) global porosities and ex situ voidage porosities derived from mercury porosimetry of pellets and retrieved pellets from tablets. The voidage Heckel profiles enabled a clear distinction between the LP and HP pellets in contrast to the global Heckel profiles. Thus, the voidage was concluded as a better descriptor of the effective porosity of the reactant pore system than the global porosity for calculations of the Heckel numbers. Due to the challenging and tedious work of deriving precise voidage data, derivation of Kawakita b−1 and Adams parameters remains an interesting approach for assessing granule plasticity. These clearly differentiated between the HP and LP plasticity, thus suggesting that both parameters can be used as a descriptor of pellet plasticity in analytical powder compression analysis.