The effect of particle fragmentation and deformation on the interparticulate bond formation process during powder compaction.

PURPOSE

The compression behaviour and the compactability of particles have been studied. In addition, an expression describing the bond strength over a tablet cross section was derived and these calculated values were compared with the experimentally determined tablet tensile strength values.

METHODS

The compression behaviour of particles of a series of size fractions of four materials were assessed by tablet surface areas (particle fragmentation propensity) and by yield pressures (particle deformability), derived from in die Heckel profiles. The porosity and the tensile strength of the tablets were also determined.

RESULTS

Sodium chloride and sodium bicarbonate possessed limited fragmentation while the converse applied for sucrose and lactose. Sodium chloride and sodium bicarbonate were the extreme materials with respect to particle deformability and compactability. Except for sodium chloride, a limited effect of original particle size on the compactability of the particles was observed.

CONCLUSIONS

The observations on the compactability of the powders was explained by postulating that fragmentation affects mainly the number of bonds in a compact cross section, while deformation affects mainly the bonding force of these bonds, through a relationship with the contact area between a pair of particles. The deviations between the predicted strength of particle-particle bonds and the determined tensile strength values was explained by a high bonding capacity of some particles, e.g. due to an unpredicted high surface deformability, or by a fracture mechanic effect during tablet strength determination.