Tech Brief: Preparing Wet Granulations In A Planetary Mixer

Granulation requires the addition of binding fluid/adhesive to a blend of powders. The liquid is added at a pre-determined rate to the batch while it is being mixed. The resulting wet mass is dried and sometimes passed through a mill to produce granules of a chosen size. The product is tested to determine particle size and other physical attributes that indicate suitability for downstream processing, i.e. pressing the granules into tablets or filling them into capsules.

Double planetary mixers have been proven to satisfy the requirement of product uniformity and particle size enlargement (granule formation) in the wet massing phase of wet granulations. They move material by rotating two identical blades on their own axes as they orbit on a common axis. The blades continuously advance along the periphery of the mix vessel, removing material from the walls and transporting it towards the interior.

Mixer speed and liquid addition level both influence the size of the granules. A vacuum-capable double planetary mixer with jacketed vessel can be used to dry the granulation under vacuum after the liquid binder/adhesive solution has been added and thoroughly coated on the powders. The mixer layout and design allow for a virtually complete discharge, ensuring high-yield and very minimal product loss.