Tensile and Shear Testing of Some Pharmaceutical Powders

Design and validation of an annular shear cell for pharmaceutical powder testing

An annular shear cell was constructed for powder flow testing, the influence of design and process parameters was characterized, and the results were compared with other flow methods. The shear cell was designed with interchangeable parts to mimic other shear cells. The texture of the powder-metal interface and the gap distance between the lid and side wall of the trough were varied, and the effects of shear rate, powder bed thickness, and consolidation times were tested. Shear parameters, such as cohesion, angles of friction, and flow factors, were measured for microcrystalline cellulose, anhydrous lactose, spray-dried lactose, mannitol, dibasic calcium phosphate dihydrate, anhydrous theophylline, and theophylline monohydrate powder. The results were then compared with the Carr index, mass flow rate, and flowability index. Design parameters such as surface texture and the gap distance significantly affected the shear call results, whereas for the process parameters studied, the shear rate, consolidation time, and powder bed height had a minimal effect on the shear cell results. Of the shear parameters obtained, the angles of friction best represented the known flow properties of powders and were in general agreement with those from other flow tests.

Studies of powder flow using a recording powder flowmeter and measurement of the dynamic angle of repose

This paper describes the utility of the dynamic measurement of the angle of repose for pharmaceutical systems, using a variable rotating cylinder to quantify powder flow. The dynamic angle of repose of sodium chloride powder sieve fractions was evaluated using a variable rotating cylinder. The relationship between the static and the dynamic angle of repose is discussed. The dynamic angle of repose of six lots of a multivitamin preparation were compared for inter- and intralot variation. In both cases, no significant differences (p greater than 0.05) were observed. In the multivitamin formulation, lubricants at lower concentration levels did not show a significant effect (p greater than 0.05) on the dynamic angle of repose when compared with flow rates. The effect of different hopper sizes and geometry has been evaluated using the recording powder flowmeter. The results indicate that although different hoppers affect the quantitative nature of the results, the same general trends are apparent. Thus, it appears possible to use a recording powder flowmeter with small quantities of material to predict the effect of formulation and processing variables on the flow of production scale quantities. This paper does not describe a comprehensive evaluation of the pharmaceutical utility of measuring the dynamic angle of repose. However, the results discussed are not encouraging and suggest that the recording powder flowmeter is more sensitive to the effects of formulation and production variables on powder flow.