Influence of Roll Speed during Roll Compaction and Its Effect on the Prediction of Ribbon Solid Fraction

Influence of the roll speed (RS) during roll compaction on ribbon, granule, tablet properties and its effect on the prediction of the ribbon solid fraction at-gap is often neglected or controversially discussed. The aim of this study was to investigate the effect of the RS systematically. Microcrystalline cellulose (MCC) and lactose were compressed at several maximum roll pressures (P_max) and RS combinations using a gap-controlled roll compactor. The ribbon solid fraction after elastic recovery (SF_ribbon), granule size distribution and tabletability of the granules as well as the ribbon solid fraction at-gap (SF_gap) were measured. The Midoux number (Mi), derived from the Johanson model, was used to predict the ribbon solid fraction at-gap (SF_Mi). The measured SF_gap and the predicted SF_Mi lead to a prediction accuracy (PA) of the Midoux number. The results are highly dependent on the material used and the applied P_max. Higher plasticity of the material leads to a reduction in SF_ribbon and granule size with increasing RS. However, this effect can be overcome or reduced by adjusting P_max above the yield pressure of the used material. These results allow for higher roll speeds as a potential upscaling method in roll compaction. On the other side, the PA of the Midoux number was also reduced with increased RS for MCC and had no effect for lactose. Thus, RS seems to be an important factor in the prediction of roll compaction processes and prediction models should include RS as a parameter to improve their accuracy.