Abstract. The effect of moisture content on flowability of six pharmaceutical powders (microcrystalline cellulose (MCC), hydroxypropyl methylcellulose (HPMC), carboxymethyl cellulose (CMC), polyvinylpyrrolidone (PVP), corn starch, and potato starch) was investigated. Powder flowability was measured using established static techniques and emerging dynamic avalanche behavior measurements. Static techniques did not provide enough resolution to clearly identify changes in flowability due to increasing powder moisture content. Avalanche time and its standard deviation showed that flowability of MCC, CMC, PVP, and potato starch decreased after a critical moisture content, flowability of corn starch increased and flowability did not significantly change for HPMC. The moisture decreased flowability by forming stronger interparticle liquid bridges and increased flowability by acting as a lubricant. The dynamic density of the celluloses and PVP decreased linearly with increasing moisture content as the particles swelled with water. The starches also swelled and decreased in dynamic density, but only after a moisture content corresponding to monolayer coverage of water around the particles was reached. As flowability and dynamic density change with moisture content, to ensure consistent production of high-quality tablets, the moisture content of the powders must be measured and controlled.
Pharmaceutical tablets are manufactured through a series of batch steps finishing with compression into a form using a tablet press. Lubricants are added to the powder mixture prior to the tabletting step to ensure that the tablet is ejected properly from the press. The addition of lubricants also affects tablet properties and can affect the behavior of the powder mixture. The objective of this research was to investigate the effect of lubricants on powder flowability as flowability into the tablet press is critical. Four lubricants (magnesium stearate, magnesium silicate, stearic acid, and calcium stearate) were mixed, in varying amounts, with spray-dried lactose. In addition, magnesium stearate was also mixed with placebo granules from a high-shear granulator. Measurements based on avalanche behavior indicated flowability potential and dynamic density and were more sensitive to changes in the mixture and provided a more accurate and reproducible indication of flowability than traditional static measurements. Of the tested lubricants, magnesium stearate provided the best increase in flowability even in the low amounts commonly added in formulations.
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