Kinetics of elastic recovery in roll compaction

Abstract

Elastic recovery (ER) has been investigated and discussed extensively in the field of tableting. However, until now only limited data is available regarding ER in roll compaction. Therefore, a previously established in-line measurement technique was rolled out to further investigate the kinetics of ER in roll compaction and the effects of specific compaction force (SCF) and roll speed (RS). In-line laser triangulation measurements at different positions within a roll rotation as well as measurement over time after the process has been stopped were utilized. Pure microcrystalline cellulose (MCC) and two placebo powder blend formulations were analysed. Successful fit of the contained ER profiles emphasized that the ER on the roll surface is build out of two exponential kinetics. Starting with a dominating fast ER (ERA), characterized by a high increase of the ribbon thickness after passing the gap width, followed by a slower ER (ERB). Sigma minus plot analysis showed that increasing RS led to an accelerated ERA and ERB which was related to the viscoelastic behaviour of MCC. The SCF only had an effect on the kinetics of ER if a brittle filler was added to the mixture. The conducted study established the first approach in literature to characterize the kinetics of ER in roll compaction. It supports the understanding and characterization of relaxation times and the effect of the RS and SCF in roll compaction.

Keywords

• Roll compaction
• Elastic recovery
• Kinetics
• Viscoelasticity