Scale Up of Powder- Blending Operations

www.pharmtech.com n the manufacture of many pharmaceutical products, dry-particle blending is a critical step that directly affects content uniformity. Tumbling blenders—a common way to mix granular constituents—are hollow containers attached to a rotating shaft; the vessel is partially loaded with materials and rotated. Their main advantages are large capacities, low-shear stresses, flexibility, containment, and easy cleaning. The blenders come in a variety of geometries and sizes (ranging from a minimum of ,16 qt to a maximum .500 ft). The convective blender is another common mixer, in which flow is created by impellers rotating within a fixed shell. The blender can impart high shear, reduce ingredient segregation, and be used for wet granulation. Although the blenders are available in several sizes, the largest capacity is often an inverse function of the maximum shear rate. Currently, no rigorous techniques can predict blending scale-up criteria for either type of blender without prior experimental work. Typically, blending studies start with a smallscale, try-it-and-see approach, during which the following questions usually arise: Scale Up of PowderBlending Operations