(766h) A Novel Method for Grindability Assessment of Pharmaceutical Powders

In the early stages of development of a new Active Pharmaceutical Ingredient (API), insufficient material quantity is usually available for addressing process engineering issues, such as milling. Mechanical properties that are accountable for size reduction are hardness, toughness and stiffness (for semi-brittle failure), and these can be characterised using a small sample quantity by nanoindentation. However, the use of nano-indentation may not be appropriate for strain-rate sensitive solids, and hence impact testing, backed up by breakage analysis, can give better representative information on grindability. Unfortunately, there is no commercially-available single particle impact testing for fine particulate solids. In contrast, dry powder dispersers, such as the Scirocco powder disperser of Malvern Mastersizer 2000, are widely available. In this device, particles are dispersed by an air jet in a Venturi eductor configuration, impacted at a bend and presented to the laser light beam for size analysis by laser light diffraction. So this device has the potential to be used for testing the breakage propensity (grindability) of particles. However, particles of different sizes accelerate to different velocities, due to short acceleration length, and break to different extents; hence the results will be â??fuzzyâ??, unless the relation between particle size and impact velocity and nozzle pressure is established.

Three dimensional multiphase CFD simulations of the Scirocco disperser have been carried out to analyse the air flow field, following which particle trajectories and impact velocities have been calculated. These calculations are then used in the estimation of the breakage propensity parameter. The extent of breakage and change in the surface area are then related to the breakage propensity parameter, for which a good correlation is shown for a range of particle sizes of several organic particles. The obtained information shows the ease of grindability of different materials relative to each other.