On the physical interpretation of the initial bending of a Shapiro–Konopicky–Heckel compression profile

The relationship between the natural logarithm of the tablet porosity and the applied pressure is used to describe the compression behavior of a powder. Such a relationship, here referred to as a Shapiro–Konopicky–Heckel (SKH) profile, is usually divided into three regions, of which the first often is non-linear. The objective of this work was to address the question of the mechanisms controlling the compression and the bending of the first region of a SKH profile for dense particles. In this paper, the first region was described by the Shapiro General Compression Equation, from which a compression parameter was derived as a measure of the bending. The results indicate that for powders undergoing significant particle rearrangement at low applied pressures, the particle rearrangement is the major cause for the initial bending of the SKH profile. For powders showing limited particle rearrangement, the initial bending is mainly caused by the change in particle diameter due to particle fragmentation. It is concluded that the evaluation of the first region of a SKH profile in terms of bending may be used to assess particle fragmentation. The SKH profile could hence be a useful tool to describe powder compression behavior in terms of particle fragmentation and particle deformation from one single compression analysis.