(378c) DEM-PBM Modelling of the Millling Process of Pharmaceutical Ribbons

Ribbon milling is a critical process step in roll compaction, which determines the properties of produced granules, in particular, the granule size distribution. It is well recognised that fragmentation during ribbon milling is governed by two mechanisms: abrasion and impact, depending on the milling speed. Prediction of the fragmentation process during ribbon milling will enable ribbon milling to be optimised. In this study, a predictive methodology for modelling size reduction processes in ribbon milling was developed by integrating two different modelling techniques, i.e. the discrete element method (DEM) and the population balance model (PBM). DEM was used to model fragmentation at the microscopic level, giving a detailed insight into the underlying breakage mechanism. In DEM modelling, virtual ribbons were created by introducing an appropriate interfacial energy using the cohesive particle model and the fragmentation process of the virtual ribbon during abrasion and impact was analysed. The fragmentation rate and the number and size of fragments (i.e. granules) resulting from the breakage of a ribbon were determined and the effects of milling speed and interfacial energy were explored. The DEM results for single ribbon fragmentation were then incorporated into the PBM so that the ribbon milling process can be modelled at the system level, from which the granule size distribution during ribbon milling can be obtained. Comparing with the data obtained from physical experiments, it was shown that the DEM-PBM approach can predict the ribbon milling process with careful consideration of the dominant fragmentation mechanism.