Wet granulation is a method of making granules by adding a liquid to powders while mixing. The liquid helps the powder particles stick together and form wet granules.
How it works:
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A liquid (like water, ethanol, or isopropanol) is sprayed or poured onto the powder.
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Mixing is done using equipment such as:
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High-shear granulator (impeller)
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Twin-screw granulator (screws)
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Fluidized bed granulator (air)
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The liquid wets the powder, making particles stick and form granules.
Liquids used:
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Must be safe, non-toxic, and able to evaporate after drying.
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Water is common (safe and cheap), but sometimes not strong enough to hold particles together.
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In such cases, a binder (like PVP – polyvinyl pyrrolidone) is added with the liquid to make stronger bonds.
Process steps:
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Add liquid (with or without binder) to the powder.
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Powders stick together to form wet granules.
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Granules are dried (solvent or water evaporates).
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Dried granules are milled to the desired size.
Key points:
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Traditional method: Wet mass → pass through sieve → dry → mill.
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Usually done in batches, but the industry is moving towards continuous wet granulation (e.g., using a twin-screw extruder).
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Continuous methods are faster, more efficient, and recommended by the FDA.