Evolutions of temperature and density during roll compaction of a pharmaceutical excipient

Abstract Roll compaction is a critical unit operation in the pharmaceutical manufacture. During roll compaction, a change in the internal energy of powder due to applying of external work from the rolls can generate heat and cause an increase in the temperature of the powder, which can subsequently affect the roll compaction behaviour and the quality of ribbons. Thus, it is crucial to understand the thermal response of pharmaceutical formulations during roll compaction. This study hence aims to examine the evolution of temperature and density in powders during roll compaction. For this purpose, a systematic experimental study is performed using the peripheral quantitative computed tomography (PQCT), for the first time, and the thermographic method to investigate the thermo-mechanical behaviour of pharmaceutical powders during roll compaction. A finite element model is also developed to describe the transformation of irreversible compression work to heat as well as the energy dissipation due to the wall friction, and to predict the thermomechanical behaviour. In particular, the effect of roll speeds on the thermomechanical behaviour of powders during roll compaction is examined. It was shown that at low roll speeds, the highest temperature is reached inside of the compacted powder. As the roll speed increases, more heat is generated on the ribbon surfaces due to the powder-wall friction, while the density of ribbon deceases. It was found that the density and the temperature at the ribbon centre, were generally higher than that near to the edge, for roll compaction with fixed cheek plates.