THE ROLE OF THE DISPLACEMENT-TIME WAVE-FORM IN THE DETERMINATION OF HECKEL BEHAVIOR UNDER DYNAMIC CONDITIONS IN A COMPACTION SIMULATOR AND A FULLY-INSTRUMENTED ROTARY TABLET MACHINE

The Heckel equation has been used widely to characterize the compressi on behaviour of pharmaceutical powders, yet very little attention has been paid to the role of the displacement-time profile used to generat e this relationship. The objective of this study was to evaluate and c ompare selected standard waveforms with actual and theoretical tablet press waveforms in the Heckel analysis of representative formulations under dynamic conditions in a compaction simulator and to compare such data with that determined on the same formulation using an actual ful ly-instrumented rotary tablet press. Increased tableting rate and diff erent programmed displacement-time waveforms with the same gross punch -speed changed the Heckel behaviour of all formulations. The results o f this study suggest the pressure-volume relationship determined durin g powder-bed compression is affected by the instantaneous punch-speed profile of the displacement-time waveform for all materials studied, e ven though they deform by different mechanisms. It appears that the in stantaneous punch-speed profile of the particular displacement-time wa veform is a confounding factor of Heckel analysis. Compaction simulato rs programmed to deliver saw-toothed displacement-time traces have the advantage of constant punch-speed and may be a better choice for char acterizing a formulation by Heckel indices and the strain-rate sensiti vity index. On the other hand, they also carry the liability of not be ing a realistic representation of tableting on a rotary tablet press.