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

Kinetics of elastic recovery in roll compaction

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 ( ER A ), characterized by a high increase of the ribbon thickness after passing the gap width, followed by a slower ER ( ER B ). Sigma minus plot analysis showed that increasing RS led to an accelerated ER A and ER B 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.

In-line temperature measurement to improve the understanding of the wetting phase in twin-screw wet granulation and its use in process development

Wetting is the initial stage of wet granulation processes during which the first contact between the powder and the liquid occurs. Wetting is a critical step to allow granule growth and consolidation, but also to ensure uniform active pharmaceutical ingredient (API) distribution over all granule size fractions. A physical understanding of the wetting stage is therefore crucial to design a robust granulation process. In twin-screw granulation, wetting is physically separated from granule consolidation, growth, breakage and attrition. The present study used this particularity to investigate the wetting step in such a way that the fundamental mechanisms governing the wetting can be linked and understood. A modified granulator barrel was used allowing the collection of granules immediately after the wetting. A low drug-loaded pharmaceutical formulation containing a poorly soluble and poorly wettable API was used for this investigation. Granules obtained after the wetting zone were analysed for granule size distribution, API distribution over the different size fractions and granule temperature. It was found that "wetting efficiency" (i.e., fraction of powder being nucleated during the wetting stage) could be predicted using an energy balance based on in-line measurement of the granule temperature. Wetting efficiency could moreover be linked to final granule quality attributes (i.e., granule size distribution) at the outlet of the granulator. It was further demonstrated that granule growth and consolidation could only be achieved when complete wetting was achieved in the wetting zone of the granulator. This study suggested a methodology based on in-line temperature measurements to quickly determine wetting efficiency. The described methodology could therefore be used as a tool to gain more fundamental understanding of the wetting stage during twin-screw granulation as well as to define suitable formulation and process ranges for further granulation process development.