Drying is the most important step of tablet manufacturing in pharmaceutical industries.
Purpose Of Drying
Why we use drying process or what is the purpose of drying step in tablet manufacturing?It is one of the most important question and the answer of this question is,
We are familiar that tablet manufacturing by wet granulation method involves addition of solvent or binder solution, meaning we add solvent in the mixed blend of powders to convert powders into granules and a wet mass is formed.
The purpose of drying is to remove or evaporate the extra amount of the solvent from the wet mass and to dry the granules to maintain the required level of moisture content or LOD.
Equipment Used For Drying
Two types of equipment are used in pharmaceutical industries to dry the granules
- Tray Dryer
- Fluid Bed Dryer
Try Dryer
Tray dryer is the conventional type of the dryer which is used in pharmaceutical industries for the drying of wet mass.
In tray dryers our product is spread in different trays and these trays are arranged inside the dryer.
Air circulation with heating is turned on and due to the circulation of the hot air our product is dried.
There are two types of the tray dryers one is with plain bottom trays known as a plain bottom trays tray dryer and other is with perforated trays known as the perforated bottom trays tray dryer.
Fluid Bed Dryer
FBD or fluid bed dryer is the advanced type of the dryers used in pharmaceutical industries for the drying purpose.In fluid bed dryer we load our product into a product trolley and is fluidised by the hot air pressure.
Hot air removes the extra moisture from the granules and dried granules are collected into product trolley.
Fluid bed dryers are of two type,
- Vertical fluid bed dryer
- Horizontal fluid bed dryer
Vertical FBDs are the most commonly used fluid bed dryers in pharma.
Critical Process Parameter Of Drying (CPPs)
The CPPs or critical process parameters of drying are those parameters which must be critically observed and maintained during the process of drying.
For drying following are critical process parameters,
- Inlet air temperature
- Outlet air temperature
- Product temperature
- Air flow volume
- LOD
Defects During Drying
If the process of drying is not performed carefully it may result in the following defect.
- Over Drying
- Under drying
- Mottling
- Excessive Fine
Over Drying
Overdriving is the defect where LOD or moisture content is very low as compared to the recommended ranges means we have less amount of moisture content in our product.
Over drying of granules have an impact on the compression process where tablet capping and lamination defects are observed due to low moisture content.
Under Drying
Underdrawing is the defect where our product is not properly dried and it contains more moisture content as compared to the recommended values.
For easy understanding, higher moisture content in granules after the drying is known as under drying.
Under drying also results in various defects during the tablet compression process and the most common defects are tablet sticking,picking and rat holing.
Rat hole defect results in flow issues which also results in weight variation.
Mottling
Mottling is a defect which is usually observed during the drying process when we use the traye dryers.In this defect the color migrates with solvent evaporation when we apply the heat.
The best solution is to use moderate heat initially at the drying stage and use the excipients which retain moisture like microcrystalline cellulose.
Excessive Fine
Production of more fine during the drying process is observed when we dry our product in a fluid bed dryer at higher fluidisation.
Due to the higher fluidisation the fragile granules are broken down into fine powder and more fine is observed.
Presence of more fine in the final blend results in various tablet compression defects like weight variation,tablet sticking and capping.
Conclusion
To conclude we can say that drying is one of the most important steps of the tablet manufacturing process and it must be carried out under strict supervision to avoid various defects related to the drying process.