(303f) Characterization of Flow Behavior of Binary Mixtures in a Rotational Shear Cell

Powder processing and handling can be encountered in virtually any manufacturing field. In pharmaceutical and catalyst industry, in particular, solid-dose products account for the majority of the market. The complex flow behavior of powders is not well understood and characterized; suitable processing conditions and formulations are determined by extensive trial-and-error procedures, and even the small changes in the said parameters can cause great variations in product performance. The properties of the materials may change dramatically during processing introducing variability into the process and affecting final product quality and characteristics. It is therefore important to meaningfully characterize and quantify the powder flow. There is a variety of methods to characterize the flow behavior of granular materials; shear test is by far the most common and accepted technique. In this work we demonstrate how the shear properties of the binary mixtures of glass, polystyrene, pharmaceutical and catalytic materials may depend on particle size and crystal density and propose a method to calculate the shear stresses for such mixtures of various concentrations.

The proposed method of shear behavior investigation takes into account the average particle size, crystal density, gravitational component and material concentration in the blend to fit the value of major principle stress to a log-linear behavior, when plotted as a function of component concentration. The method is illustrated with examples of shear behavior of the following two-component mixtures: glass spheres of various sizes, glass and polystyrene spheres of various sizes, polystyrene and nickel spheres of various sizes and catalytic blends of coarse and fine alumina boehmite and clay. The values of major principal stress for various binary mixtures of glass, polystyrene and nickel spheres, and catalytic materials were normalized by the gravitational component factor of ρ*d_p*g, where ρ is material density, d_p is a weighted mean particle diameter and g is gravity constant. The plot of normalized major principle stress against the mass fraction of one of the blend's components, resulted in a near perfect exponential fit of the form y = A*e^Bx, where A (the intercept) scales with the value of applied compression weight, B is specific to the physical properties of the materials in the mixture, and x is a mass fraction of a mixture component. The limitations of the method were also explored.