Kneading is a technical term used in pharmaceutical industries for a specific step of wet granulation.In this article we will learn what is kneading & factors affecting the kneading process.
Kneading Technique
The process of mixing the fine powders with solvent/binder solution,slurry or paste in a high shear or low shear mixer is known as kneading.The kneading process is commonly known as wetting step in pharmaceutical industries & many professionals are not aware that the technical name of this step is kneading.
Importance Of Kneading In Wet Granulation
The kneading step is the mother of wet granulation because all the properties of granules manufactured by wet granulation method are dependent on the process of kneading.There may be over wetting or under wetting
if the process of kneading is not monitored critically by exactly following the critical process parameters of the kneading.
Factors Affecting The Kneading Process
Following are the main factors which have a great impact on the kneading process.
- Amount Of Solvent
- Rate Of Binder Addition
- Impeller Speed
- Chopper Speed
Amount Of Solvent
The granules quality produced by wet granulation is dependent on the amount of solvent used for the kneading step.
If we use a high quantity of solvent it will result in over wet damp mass which will be difficult to wet sieve.
If the quantity of solvent used is very low the proper granulation end point is not achieved & more fine will be produced after drying.
Always use the optimum quantity of solvent for wet granulation to ensure the production of uniform size granules.
Rate Of Binder Addition
If we are using optimum quantities of solvent but the rate of binder solution/solvent addition is not controlled it will also result in granulation defects.
If the binder addition rate is too fast it will result in localized over wetting & later on results in case hardening.
If the binder solution addition is too slow it will take extra time than the recommended time during which granulation is achieved.
Impeller Speed
Impeller blades are mounted in the bottom of the mixing bowl of a high shear granulator & the speed of these impeller blades is one of the most important factors which may affect the kneading process.
It is generally observed that if the speed of impeller blades is very high the end point of wet granulation can be achieved earlier with less solvent quantity as compared to the situation where the speed of impeller blades is slow.
Chopper Speed
Chopper is mounted on the side wall of the mixing bowl of the high shear granulator & its purpose is to break down the lumps formed during the process of kneading to ensure uniform wetting & distribution of binder solution.
In simple words it’s aim is to perform cutting action during the kneading stage.
If the speed of chopper blades is very low the lumps will not be properly cut down & very large lumps will be formed in the mixing bowl.
If speed is very high it may result in breakdown of properly sized granules as well & production of more fine during drying due to weak or fragile granules.
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