Towards an Accurate Shear Testing Method for Characterizing Pharmaceutical Particulate Systems

When using shear testing to determine wall friction of pharmaceutical particulate systems, it is crucial to measure at the correct wall normal stress. By comparing data obtained at a wall normal stress of 1000 to 200 Pa, the effect of the applied stress on the accuracy and precision of the method was assessed. INTRODUCTION When powder flows under gravity from a hopper, it follows one of two patterns, mass flow or funnel flow, Fig 1. Funnel flow is a persistent challenge when processing pharmaceutical bulk solids. Segregation and stagnant zones with uneven density and composition at the hopper outlet during production are common problems associated with funnel flow. Figure 1. Mass flow (on the left) and funnel flow (on the right) . Shear testing is a well-established method for determining mechanical properties of bulk solids. Applying shear testing for determining the mechanical properties of pharmaceutical systems can help to predict in-process flow patterns. Especially, the powder-wall adhesion of the bulk solid, i.e. wall friction, affects the flow pattern of the powder system. This property can be determined by shearing a bulk solid against a wall material sample which is representative of the hopper wall. The wall friction angle at a given wall normal stress is a measure used to quantify the wall friction. By applying Jenike’s method, the flow pattern from a hopper with a given wall inclination can be assessed based on the properties of the powder examined, Fig 2. Figure 2. Mass flow diagram for a conical hopper, based on Jenike’s method . Towards an Accurate Shear Testing Method for Characterizing Pharmaceutical Particulate Systems Troels Pedersen, Søren Søgaard, Jukka Rantanen and Morten Allesø Department of Pharmacy, University of Copenhagen, Universitetsparken 2, DK-2100 Copenhagen, Denmark. Biologics and Pharmaceutical Science, H. Lundbeck A/S, Ottiliavej 9, DK-2500 Valby, Denmark.*corresponding authors: [email protected], [email protected]