The Viscoelastic Deformation of Some Tableting Materials as Assessed by Indentation Rheology

AbstractThe time-dependent deformation of compacts prepared from four tablet compression bases has been assessed by microindentation rheology. Compacts were made from Avicel PH101, Emcompress, Emdex, and Starch 1500 at compaction pressures of 30, 60, and 90 MPa. A spherical indenter, 1.55 mm diameter, was allowed to indent into the compacts under a fixed load of 5.89 N (600 g) and the changing depth of indentation was recorded. The corresponding creep compliance versus time curve was calculated and analyzed by discrete mechanical analysis to yield Maxwell and Voigt “spring and dashpot” mechanical models. This yielded quantitative data on instantaneous elastic compliance and modulus, the time-dependent viscoelastic compliances, viscosities, and retardation times of each Voigt unit, and the Newtonian viscosity of the compacts. In general, the deformation of the compacts was in the rank order Starch 1500 > Avicel PH101 > Emdex > Emcompress. Emcompress showed negligible viscoelasticity and plasticity. For the...