Effect of drying rate on porosity and tabletting behaviour of cellulose pellets

The purpose of this study was to investigate the effect of drying rate during static drying on certain physical properties of pellets. Pellets were prepared from microcrystalline cellulose by granulation with different agglomeration liquids (various ethanol/water ratios) and thereafter dried without agitation at different drying rates. The dry pellets were characterised with respect to their shape, porosity, and compression shear strength and the tensile strength of tablets formed from pellets with low and high drying rates was determined. Drying of the pellets occurred at a falling rate and the reduction in liquid content with time obeyed a first order type of relationship. An increased drying rate did not affect the shape and surface texture of the dried pellets and did not cause them to fracture. However, the drying conditions did affect pellet porosity, with an increased drying rate resulting in more porous pellets. Through a relationship with pellet porosity, the drying rate also affected the deformability of the pellets (as assessed from Kawakita 1/b values) and their ability to form tablets. Owing to a strong effect of porosity on pellet compactability, marked changes in tablet tensile strength with variations in drying rate may be obtained.