Density behavior of cohesive granular materials

A new experimental methodology for the characterization of density in a powder bed utilizing X-ray micro-computerized tomography (micro-CT) was developed to quantify the density fluctuations in three common pharmaceutical powders (α-Lactose Monohydrate, Lactose 310, and Avicel 102). The method begins by filling an acrylic cylinder with powder and subsequently subjecting the system to vibrations using a mechanical shaker while monitoring the density at predetermined bed heights. Three key parameters were isolated including frequency, amplitude, and number of strokes. It was found that the three powders exhibited different packing rates and final states. It was also found that the density increased in the powder bed as a function of the number of taps, frequency, and amplitude. Additionally, a more uniform density profile was achieved by utilizing higher amplitudes. The cohesive properties of the three powders were investigated using the FT4 powder rheometer and correlated with the results found with the micro-CT scanner. It was found that changes in density were more significant in less cohesive powders, such as Avicel. As powders increase in cohesion, it was found that more mechanical energy was required to alter the agglomerated powder bed. Additionally, the density at the top of the powder bed was significantly more dense than that at the bottom for Avicel, however, the results were directly opposite for the other more cohesive powders. The results have indicated that micro-CT may be used as a more comprehensive and higher resolution technique for analyzing the density of powders and provide a unique insight to packing at different powder bed heights.