The role of intra-granular porosity in powder compaction

A common property of direct-compression (DC) tabletting vehicles used in the pharmaceutical industry is high intra-granular porosity. This high porosity leads to increased interparticulate friction on compaction and subsequently an increased extent of bonding compared with the compaction of the parent crystals. Granules formed by the irreversible agglomeration of ground particles in a rotary ball mill exhibit considerably higher porosity and friability leading to stronger compact strength than DC vehicles of the same compound that do not contain a binder. This effect is limited, as increased surface area leads to increased elastic deformation and bond breakage during subsequent elastic recovery. Consequently, optimum energy of compaction utilization in the production of strong tablets is obtained when materials possessing high intra-granular porosity are combined with an efficient binder.