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Tablet Granulation
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Introduction Granulation is the process in which primary
powder particles are made to adhere to
form larger, multi particle entities called
granules.
Pharmaceutical granules typically have a
size range between 0.2 and 4.0 mm.
Granules are used in the production of
tablets or capsules.
Granules in such cases are made as an
intermediate product and have a typical size
range between 0.2 and 0.5 mm.
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Reasons for Granulation
To prevent segregation of the constituents of the
powder mix.
Segregation (or demixing) is due primarily to differences inthe size or density of the components of the mix.
The smaller and/or denser particles concentrating at the base
of a container
The larger and/or less dense ones above them.
An ideal granulation will contain all the constituents of the mix
in the correct proportion in each granule and segregation of
the ingredients will not occur
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Granulation prevent segregation
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Reasons for Granulation
To improve the flow properties of the mix Many powders, because of their small size,
irregular shape or surface characteristics, arecohesive and donot flow well.
Poor flow will often result in a wide weight
variation within the final product owing to variable
fill of tablet dies etc.
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Reasons for Granulation
To improve the compaction characteristics of themix Some powders are difficult to compact even if a readily
compactable adhesive is included in the mix and some arecompacted easily. This is associated with the distribution of the adhesive within the
granule and is a function of the method employed to producethe granule.
Solute migration occurring during the postgranulation dryingstage results in a binder-rich outer layer to the granules. This in turn leads to direct binder–binder bonding, which assists
the consolidation of weakly bonding materials.
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Other Reasons
The granulation of toxic materials will reduce thehazard associated with the generation of toxic dustthat may arise when handling powders.
Materials which are slightly hygroscopic mayadhere and form a cake if stored as a powder.Granulation may reduce this hazard, as thegranules will be able to absorb some moisture andretain their flow ability because of their size.
Granules, being denser than the parent powder mix, occupy less volume per unit weight. They aretherefore more convenient for storage or shipment.
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Methods of Preparation
Wet Granulation Method
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Wet Granulation
Wet granulation is widely employed method for theproduction of compressed tablets.
The steps required for the wet granulation can be
divided into following stages: Weighing and blending the ingredients. Preparing the wet granulation. Screening the dam mass in to pellets or granules.
Drying the granules. Dry screening. Lubricating and blending. Tablet by compression.
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WEIGHING AND BLENDING
The active ingredients and any diluents and
disintegrating agent required in the tablet
formulation are weighed in the amount required
for the number of the tablet to be produced.
This mixture is mixed thoroughly .
The diluents used for this purpose are Lactose,
kaolin, mannitol.
Disintegrating agent used include corn and
potato starch, cellulose derivatives.
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PREPARING THE WET GRANULATION
Granulation is accomplished by adding liquid binder or adhesive to the powder.
The wet mass is then passed through the screen of desiredmesh size.
The granules so obtained are dried. Then again they are passed though a second screen of
smaller mesh size to further reduce the size of the granules. The binding agent used are
10-20% aqueous preparations of corn starch. 25-50% solution of glucose. Natural gums (acacia) Cellulose derivatives ( methylcellulose, carboxy methylcellulsoe)
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SCREEING THE DAMP MASS
INTO PELLETS OR GANULES The wet granulation is pressed through a
No. 6 or 8 mesh size.
This may be done with hand or specialmachines.
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DRYING THE GRANULATION
The granules are dried in spl drying
cabinets the have circulating air systems
and are thermostatically controlled. Among the newer methods employed for
the drying is fluidization conducted in
fluid bed drier.
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DRY SCREEING
The degree to which the granules are reduced
depends upon the size of the punch and tablet to
be produced.
The smaller tablet size, smaller the granules
used.
Sizing of the granules is important so that die
cavity of die is fully filled with granules.
The voids are air spaces could result in tablet of
varying evenness.
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LUBRICATION
After dry screening, dry lubricant Is
generally added.
The more commonly used lubricants aretalc, magnesium stearate and calcium
stearate.
Range at which it is added is from as low
as 0.1% to 5%.
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UTILITY OF LUBRICANTS
The improve the flow property of thegranules from hopper to the die.
Prevent the adhesion of the tabletformulation to the punches and dieduring compression.
They reduce the friction between the die
and the punch. They provide a sheen to the finished
product.
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FLOW CHART FOR THE WET
GRANULATION