Assessment of Pharmaceutical Powder Flowability using Shear Cell-Based Methods and Application of Jenike's Methodology

Jenike's approach to hopper design for a large-scale (3150 L) conical hopper was applied to pharmaceutical powders to evaluate flow issues, such as funnel flow or cohesive arching. Seven grades of microcrystalline cellulose (MCC) and six powder blends were tested. A Schulze Ring Shear Tester measured the flow function, wall friction (using stainless steel coupons with a #2B or #8 finish) and compressibility. Hopper Index (HI, maximum hopper angle required for mass flow) and Arching Index (AI, minimum hopper outlet size to prevent cohesive arch formation) were computed using Mathcad©. For MCC, a linear relationship was observed between median particle size and the Jenike flow function coefficient. A curvilinear relationship was observed for powder blends indicating more complex flow behavior than based on median particle size alone. Powder bulk density had a minimal effect on AI for MCC grades. Overestimation of AI can occur with this method for pharmaceutical powders because the true shape of the flow function is not defined at very low consolidation pressures and linear extrapolation becomes unrepresentative. This instrumental limitation underscores the need for a precise and accurate test method to determine powder flow functions at very low levels of consolidation stress for pharmaceutical applications.