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 b asis of the stress-deformation curve; This curve distinguishes between small, elastic deformation and large, viscous deformation. Small defo rmations can be quantified by the dynamic Young's modulus. The results demonstrated an effect of both rate of strain and initial particle si ze on the Young's modulus. The yield strength of compacts is a quantif ication of large deformations. There appeared to be an effect of strai n rate on yield strength, but no clear relation between initial partic le size and yield strength. The study relates elastic deformation with storage of elastic energy. The amount of stored energy was found to i ncrease with compaction speed, and is postulated to be the driving for ce 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 relat ion to compaction speed. It is therefore concluded that the effect of compaction speed on tablet properties is purely an effect of the amoun t of stored energy, The reciprocal value of expansion capacity demonst rated a direct relation with the constant that fits the relation betwe en tablet strength and porosity. The expansion capacity is hence a qua ntification of bonding.