Effects of powder flowability on die-fill properties in rotary compression

The flow behavior of a powder during high-speed tableting with a rotary press has been investigated using a mixed powder of microcrystalline cellulose (MCC) and spray-dried lactose as a model. Characteristics of the powder such as angle of repose, compressibility, dynamic flowability, expansion displacement and the morphology of particles were measured and are discussed in relation to the die-fill properties in a rotary press. This study revealed that the die-fill properties correlated with the static flowability properties such as the angle of repose and compressibility in the case of gravity feeding in a rotary press, but the dynamic flowability measured by a powder rheometer was the most important factor in the case of force feeding using a die feeder. The flowability of mixed powders containing 20-40% long, narrow MCC particles was statically low but dynamically high, and these powders had excellent die-fill properties. It is suggested that the use of long, narrow MCC particles is suitable for high-speed tableting, because they become entangled with other particles and hold air uniformly in a powder bed when agitated in a die feeder.