(605a) Development of a Novel PAT for in-Line Measurement of Powder Dynamic Density inside Feed Frame of Rotary Tablet Presses

Consistent filling of the tablet press die with a uniform weight of powder has always been an empirical approach with little understanding of the powder flow pattern within the feed frame, especially at the last moment before powder is fed into the die and tablet potency is set.  Compression is a complex unit operation comprising different regimes of powder flow (depending on the shear rate and packing fraction) which need to be fundamentally understood in order for this to be a predictable process. 

In this work we studied powder flow (with application to die filling) in the feed frame of various rotary tablet presses by developing a novel in-line process analytical technology (PAT), the dielectric probe. This tool enabled us to capture powder dynamic density regime maps in different sections of a feed frame. The basic measurement principle of the probe is to estimate the physical properties of bulk solids (e.g. solid fraction or density) by standard correlation with the measured electrical properties (e.g. dielectric permittivity) through proper calibration for each formulation.

We investigated effects of press speed, feed frame speed, paddle design, and formulation properties on the die filling process by looking at dynamic density of powder and its fluctuations inside the feed frame. We discuss how these measurements can be used for faster and more effective set-up of the tablet press and to find and maintain the optimum operating condition throughout the entire compression. Furthermore, we show how these data are helpful in scale-up of the tablet press, especially for formulations that are sensitive to over-lubrication where it is important to maintain similar level of shear energy among different scales.