Powder blending

 

Powder blending

The successful mixing of powder is acknowledged to be more difficult unit operation because, unlike the situation with liquid, perfect homogeneity is practically unattainable. In practice, problems also arise because of the inherent cohesiveness and resistance to movement between the individual particles. The process is further complicated in many system, by the presence of substantial segregation influencing the powder mix. They arise because of difference in size, shape, and density of the component particles. The powder/granules blending are involved at stage of pre granulation and/or post granulation stage of tablet manufacturing. Each process of mixing has optimum mixing time and so prolonged mixing may result in an undesired product. So, the optimum mixing time and mixing speed are to be evaluated. Blending step prior to compression is normally achieved in a simple tumble blender. The Blender may be a fixed blender into which the powders are charged, blended and discharged. It is now common to use a bin blender which blends.

In special cases of mixing a lubricant, over mixing should be particularly monitored. The various blenders used include “V” blender, Oblicone blender, Container blender, Tumbling blender, Agitated powder blender, etc. But now a day to optimize the manufacturing process particularly in wet granulation the various improved equipment’s which combines several of processing steps (mixing, granulation and/or drying) are used. They are “Mixer granulator” or “High shear mixing machine”.

 

Granulation

Following particle size reduction and blending, the formulation may be granulated, which provides homogeneity of drug distribution in blend.

Drying

Drying is a most important step in the formulation and development of pharmaceutical product. It is important to keep the residual moisture low enough to prevent product deterioration and ensure free flowing properties. The commonly used dryer includes Fluidized–bed dryer, Vacuum-tray dryer, Microwave-dryer, Spray-dryer, Freeze-dryer, Turbo–tray dryer, Pan-dryer, etc.