The effect of shape and porosity on the compression behaviour and tablet forming ability of granular materials formed from microcrystalline cellulose.

The compression behaviour of two types of granules prepared from microcrystalline cellulose was evaluated. Three sets (low, intermediate and high intragranular porosity) of irregular granules and three sets of nearly spherical granules (called pellets) were prepared from microcrystalline cellulose by wet agglomeration or wet agglomeration followed by extrusion/spheronisation. The granules and pellets were similar in size. The range of intragranular porosity, although wide, was also similar for both types. The compression behaviour was evaluated in terms of the degree of compression, the appearance of the tablets and the size distribution of retrieved aggregates (after deaggregation). The compactability of the granules and pellets was also studied. Both types of granules kept their integrity during compression. The dominant mechanism during compression appeared to be permanent deformation. However, during compression of high porosity granules, fragmentation or attrition seemed to occur alongside deformation. Tablets formed from granules had a closer pore structure than those formed from pellets of equal intragranular porosity and the granules seemed to deform to a higher degree during compression. The total tablet porosity was almost independent of the intragranular porosity and the shape of the granules before compression. It is suggested that the degree of granule deformation was controlled by the intragranular porosity and voidage of each bed of granules before compression. The tensile strength of the tablets was also dependent on the porosity and the shape of the granules; tablets formed from irregular granules were stronger than those formed from pellets of an equal intragranular porosity.