The effect of dry granulation on flow behaviour of pharmaceutical powders during die filling

Flowability that quantifies the flow behaviour of powders is an important material attribute for such applications as packing, hopper flow and powder transport. It is also one of the critical material attributes of pharmaceutical formulations for solid dosage forms. It is anticipated that size enlargement via dry/wet granulation will improve the flowability of feed powders, but it is still unclear how significant the flowability can be enhanced. Therefore, in this study, an experimental investigation was performed to explore how dry granulation affects the flowability of pharmaceutical powders, such as microcrystalline cellulose (MCC5), mannitol and lactose. Both as-received powders and binary mixtures were considered. Granules of various sizes were produced using roll compaction followed by ribbon milling, and the flowability of as-received powders and produced granules was characterised using two methods: 1) the critical filling speed measured using a model die filling system and 2) the flow index measured using a Flodex tester. It was shown that the flowability increases as the size of the granules increases for all materials considered. Furthermore, it was found that there is a strong correlation between the critical filling speed and the flow index: the critical filling speed is proportional to the flow index to a power of - 5/2. (C) 2017 Elsevier B.V. All rights reserved.