FRICTIONAL WORK IN DOUBLE-SIDED TABLET COMPRESSION

The aim of this study was to evaluate the friction during double-sided tablet compression. Dicalcium phosphate dihydrate and lactose were ta bletted with a compaction simulator with symmetrical and asymmetrical double-sided sawtooth punch displacement profiles. The estimation of f orce transmission in a powder column was based on an exponential equat ion, including the material parameter consisting of both the friction coefficient and Poisson's ratio. This parameter was predetermined from a single-sided compression. A novel equation was derived from a previ ously presented equation for friction work in single-sided tablet comp ression. The basic assumption was drawn from the linearly decreasing m ovement of infinitely thin particle layers, which are produced as the compressing punch surface approaches the other punch. This calculation was also based on the assumption that the equilibrium point, where th e particles do not move, is halfway between the punches in the symmetr ical profile and at a distance proportional to the amplitudes of the a symmetrical upper and lower sawtooth profiles. The tensile strength of tablets compressed with single-double-sided profiles was identical, a nd thus the behavior of the materials studied under compression was in dependent of the compression profiles. The friction work values that w ere calculated with the proposed expression for double-sided profiles were close to the theoretical values, as estimated by calculations bas ed on compressions with single-sided profiles. in conclusion, the nove l mathematical expression opens new possibilities for the evaluation o f friction in double-sided compression; for example, in rotary press t abletting.