The Compression Behavior of Respirable Powders at Different Relative Humidity Measured by a Compressed Bulk Density Tester for Small Sample Masses

Compressed bulk density provides the bulk density of a powder under different levels of applied load and is an established method of describing density and compressibility of pharmaceutical powders (1). The powder bulk density depends on several factors such as powder handling history, sample preparation conditions, testing environment, and the state of powder compaction (1, 2). An often overlooked factor is the moisture content of the powder, in spite of the fact that it has been shown to play an important role in consolidation and densification behavior of pharmaceutical ingredients (3, 4). In this study, we present a novel technique for measuring compressed bulk density of small powder samples and investigate the effects of relative humidity on the compression behavior. Traditional density measurement techniques are very material consuming, which is a disadvantage for the characterization of expensive powders in pharmaceutical industry (2, 5-8). In this study, we applied an alternative method (5) that requires only milligram quantities rather than the several grams (2, 8), needed for conventional techniques or tapped density measurements.