The degree of compression of spherical granular solids controls the evolution of microstructure and bond probability during compaction

The effect of degree of compression on the evolution of tablet microstructure and bond probability during compression of granular solids has been studied. Microcrystalline cellulose pellets of low (about 11%) and of high (about 32%) porosity were used. Tablets were compacted at 50, 100 and 150 MPa applied pressures and the degree of compression and the tensile strength of the tablets determined. The tablets were subjected to mercury intrusion measurements and from the pore size distributions, a void diameter and the porosities of the voids and the intra-granular pores were calculated. The pore size distributions of the tablets had peaks associated with the voids and the intra-granular pores. The void and intra-granular porosities of the tablets were dependent on the original pellet porosity while the total tablet porosity was independent. The separation distance between pellets was generally lower for tablets formed from high porosity pellets and the void size related linearly to the degree of compression. Tensile strength of tablets was higher for tablets of high porosity pellets and a scaled tablet tensile strength related linearly to the degree of compression above a percolation threshold. In conclusion, the degree of compression controlled the separation distance and the probability of forming bonds between pellets in the tablet.