MANUFACTURING OF GRANULES

Granules can be manufactured by following ways.

1. Wet Granulation

In wet granulation, a liquid binder or  an adhesive is first added to the powder mixture.  The wetted mass is then passed through a screen of the desired mesh size, and resulting granules are dried. 

The dried granules can be passed through a second screen of a smaller mesh to reduce the size of the granules even further.  Overwetting usually results in granules that are too hard for proper tableting, while underwetting usually results in the preparation of tablets that are too soft and tend to crumble. Binding agents commonly used in wet granulation are a 10–20% aqueous solution of corn starch, a 25–50% of glucose solution, molasses, various polysaccharides (e.g., acacia gum), cellulose derivatives (such as methylcellulose, carboxymethylcellulose, and microcrystalline cellulose), gelatins, and povidone (polyvinylpyrrolidone, PVP).

2. Dry Granulation

In dry granulation, granules are formed by compacting large masses of the powder mixture and subsequently crushing into pieces.  These pieces are then sized into smaller granules.  The dry-granulation method requires the drug or the diluent to have cohesive properties for the large masses to be formed.

The powder is “slugged” or compressed into large flat tablets or pellets of about 1 inch (3/4 inch or larger) in diameter.  In slugging, lubricants are required for release tablets from die.  The slugs are then broken up and pass through a desired mesh for sizing.

In roller compaction, the powder is  fed between two rollers (both are either flat or complementarily patterned) to form a  ribbon of compacted powder.  The ribbon is subsequently milled and sieved to produce a powder with better flow properties.  These methods are chosen when a drug and other materials cannot be processed by wet granulation method owing to their degradation by moisture or by

elevated temperature for drying.  Thus, it is ideal for processing moisture and heat sensitive materials.  Aspirin is commonly prepared into tablets after slugging, since it is hydrolyzed on exposure to moisture.

3.Fluidized Bed Granulation

In the fluidized bed granulation, the powder to be granulated is suspended in the heated air of a fluid bed, and a liquid binder sprayed from nozzles positioned above. An impeller is used for agitation of particles.Agglomeration or layering of particles provide granule growth which occurs in following steps:

1.     A wet particle collides with another particle and a bound is formed by a liquid bridge.

2.     Bond is solidified during the subsequent drying period.

3.     A two-fluid-nozzle can spray upwards into the fluidized bed, and wetted particles may be transported pneumatically by the nozzle air.

4.     Particles dry and fall down in the outer regions of the bed. Hence, a drying zone above the fluidized bed is formed.

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