Effect of deaeration on processability of poorly flowing powders by roller compaction

Roller compaction (RC) is a common granulation process for manufacturing solid dosage forms. However, its applicability to the growing number of powders with very low bulk densities and high cohesiveness can be limited due to poor powder feeding. Although deaeration with a vacuum in the feeding line is an effective approach to enhance the powder feeding performance, a systematic assessment of its effects on RC process is lacking. In this work, we have examined the effect of vacuum on the processability of RC using an extremely poorly flowing powder, colloidal silica, and two grades of microcrystalline cellulose (MCC). A processable range is defined by roll speed and screw speed that attain stable feeding under the roller-gap controlled mode. A 0.35 barg vacuum level was sufficient to make the colloidal silica processable and a higher vacuum level solved the subfeeding issue and significantly expanded the RC operation range. In contrast, deaeration slightly narrowed the processable range for MCC PH105 and PH101, while only minimally affects the relationship between roll speed and screw speed. The effects of vacuum on the processability of these materials qualitatively correlated with the sensitivity of their bulk densities to pressure. A better understood effects of material properties (bulk density), process parameters (roller gap), and deaeration (vacuum level) on RC processability of powders help to determine an appropriate use of a vacuum line to improve the RC process.