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 duri ng static drying on certain physical properties of pellets. Pellets were pr epared from micro crystalline cellulose by granulation with different agglo meration liquids (various ethanol/water ratios) and thereafter dried withou t agitation at different drying rates. The dry pellets were characterised w ith respect to their shape, porosity, and compression shear strength and th e 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 rela tionship. An increased drying rate did not affect the shape and surface tex ture 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 poros ity, the drying rate also affected the deformability of the pellets (as ass essed from Kawakita 1/b values) and their ability to form tablets. Owing to a strong effect of porosity on pellet compactability, marked changes in ta blet tensile strength with variations in drying rate may be obtained. (C) 2 001 Elsevier Science BN. All rights reserved.