Evaluation of ring shear testing as a characterization method for powder flow in small-scale powder processing equipment

Analytical method development for powder characterization: Visualization of the critical drug loading affecting the processability of a formulation for direct compression

“…The microscope parameters were set to a voltage of 15 kV and 600x magnification. For determining the flowability index the sample is consolidated with a set normal stress and the force needed to overcome the internal friction of the particulate system is analysed [11]. The major principal stress and the unconfined yield strength are calculated by applying Mohr stress circles to the measurement results.…”

“…The major principal stress and the unconfined yield strength are calculated by applying Mohr stress circles to the measurement results. The flowability index is then calculated as the quotient between the unconfined yield strength and the major principle stress [11]. Thereby the flowability of a powder system can be categorized based on one single value.…”

“…However, a general chapter is under development by USP. Shear testing has the potential to be standardized method to analyse powder flow, as the results are reproducible [11]. Choosing different preshear stresses can be used to simulate the stress acting in different systems and, thereby, the test can be adapted for different needs.…”

“…These can be assessed using a ring shear tester approach [8,9]. With the knowledge of these powder properties, it is possible to predict the powder behaviour in a specific unit operation [2,10,11].…”

“…Shear testing can be performed as a fully automated process, analysing the force needed to overcome the internal cohesion of a powder system under a defined major principal stress. [10,11,16,17]. It has been shown that a ring shear tester can generate reproducible data, insensitive to operator [7,17,18].…”