(243d) Wet Granule Breakage in High Shear Mixer Granulation

Granulation product attributes are controlled by the balance of granulation rate processes during the grnaulation process, namely (1) nucleation and wetting, (2) growth and consolidation, and (3) breakage. Wet granule breakage is relatively poorly understood with some basic questions still open eg. do granules break by shear or impact? What mechanical proerties dictate the probability of breakage?

In this paper, wet granule breakage is studied in a breakage only granulator. The granulator is laboratory scale, vertical shaft high shear mixer. The powder bed consists of a cohesive powder formed from coarse sand coated with silicone oil. The flow pattern of the cohesive sand is well characterised. A small number of granules are placed in the granulator and the proportion that break is measured. Twenty formulations are used with combinations of different powders and binders giving a wide range of mechanical behaviours.

The effect of granule mechanical properties, impeller speed and impeller type on breakage probability are reported. Hypotheses on the mode of granule breakage are compared critically with breakage data and implications for the development of a wet granule regime map are discussed.