2025 Volume 73 Issue 10 Pages 951-961
The flowability of powders in pharmaceutical formulations is critical for manufacturing robustness and content uniformity. Shear cell measurements aid in assessing flowability under consolidation and provide useful parameters for predicting powder behavior in real manufacturing. However, some of the parameters vary with void fraction (indentation load), thereby necessitating specification of the consolidation conditions under which the value was obtained; moreover, the given single value still cannot be used to predict flowability under different conditions. If flowability could be expressed using a parameter that reflects an intrinsic property of the powder, it would be useful for quality control of raw materials and for efficient formulation design. Therefore, we investigated the relationship between various parameters obtained from constant-volume shear cell measurements and consolidation conditions using pharmaceutical powders with different particle sizes and shapes. We found that, when the substance of the sample is the same, the preshear points align on a single straight line passing through the origin, regardless of differences in indentation load, particle size, or shape. In other words, the slope of the critical state line (ϕCSL) connecting the preshear points was relatively insensitive to particle size and shape, indicating high robustness. These findings reveal that ϕCSL could serve as an intrinsic flowability parameter of the powder. The ϕCSL values of several fine powders with particle sizes <10 µm deviated from this trend, suggesting that interparticle cohesive forces may have influenced their flowability.
