New models to explain the compaction and relaxation behaviour of some pharmaceutical excipients submitted to low strain

Seven commercially available pharmaceutical excipients used for direct tabl eting were studied. Flowability, true and tap density, loss on drying, part icle size, specific surface area and scanning electron micrographs were use d to characterize these powders with low compaction pressures (lower than 1 0 MPa). The relaxation mode was analysed to describe the behaviour of each product under strain. Three new models are proposed to aid understanding th e physical phenomena involved in the compaction phase, and the Peleg model was applied to the relaxation phase. The models were related with the physi cal properties measured, and illustrate the sliding friction, the viscoelas tic behaviour and the aptitude of particles to fragment during compaction, as well as the elastic behaviour during the stress relaxation of powders. ( C) 2000 Kluwer Academic Publishers.