Development of an Improved Fluidization Segregation Tester for Use with Pharmaceutical Powders

Understanding the segregation potential of pharmaceutical dry powders and granules is an important aspect of solid oral-dosage form development. Powder segregation demixes a homogenous powder blend. Further processing of this heterogeneous mixture can result in final-product quality deficiencies such as variable dosage-form potency, variable tablet or capsule fill weight, variable tablet hardness, and nonuniform appearance. Segregation also can affect manufacturing process robustness through erratic or unstable powder flow, under- or overcompression, variation in tablet-core tensile strength, and unacceptable blend uniformity (1).
Figure 1Fluidization segregation is a common segregation mechanism for pharmaceutical dry-powder and granule systems (1). It can occur during unit operations such as blender-to-bin transfers, bin discharge, pneumatic conveyance, bin-to-tablet press transfer, and fluidization in a fluid bed. The fluidization segregation mechanism is illustrated in Figure 1 using the example of a bin discharge unit operation. Before discharge, the particles in the bin are arranged homogeneously (see Figure 1a). During discharge, the particles are entrained in a counterflow air stream (see Figure 1b). Smaller particles and less-dense particles will be carried higher in the air stream. They also have a lower terminal velocity and will settle at a slower rate compared with larger particles. These particles also can be deflected easily by air turbulence, further increasing settling time. This results in a layer of small particles on top of a bed of larger particles or a particle-size gradient in the settled pile (see Figure 1c).

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