Porosity expansion of tablets as a result of bonding and deformation of particulate solids

This paper describes the tabletting process of gamma-sorbitol on the basis of the stress-deformation curve; This curve distinguishes between small, elastic deformation and large, viscous deformation. Small deformations can be quantified by the dynamic Young's modulus. The results demonstrated an effect of both rate of strain and initial particle size on the Young's modulus. The yield strength of compacts is a quantification of large deformations. There appeared to be an effect of strain rate on yield strength, but no clear relation between initial particle size and yield strength. The study relates elastic deformation with storage of elastic energy. The amount of stored energy was found to increase with compaction speed, and is postulated to be the driving force for changes of tablet porosities after compression. The attraction between particles causes resistance against porosity expansion, and is defined as expansion capacity. The expansion capacity showed no relation to compaction speed. It is therefore concluded that the effect of compaction speed on tablet properties is purely an effect of the amount of stored energy, The reciprocal value of expansion capacity demonstrated a direct relation with the constant that fits the relation between tablet strength and porosity. The expansion capacity is hence a quantification of bonding.