Flowability of moist pharmaceutical powders

The effect of moisture content on four pharmaceutical powders (an active pharmaceutical ingredient (API), Aspartame, Hydroxypropyl Methylcellulose (HPMC), and Respitose ML001) has been investigated. The API and Respitose powders were found to be nonhygroscopic and were tested at their native moisture contents only. The Aspartame was tested at moisture contents of 0%, 2%, 5%, and 8% and the HPMC was also tested at moisture contents of 0%, 2%, 5%, and 10%. Powder flowability was measured using the Jenike shear index, the Hausner Ratio, the Carr Index, and the static and dynamic angles of repose. The flowability of Aspartame increased with an increase in moisture content, which is attributed to the formation of large, round agglomerates. The flowability of HPMC decreased with an increase in moisture content, attributed to the increasing strength of liquid bridges. The Jenike shear index was the only flowability indicator to capture this complex behaviour.