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Can I spheronize a granulation and skip the extrusion process?

In some circumstances it is possible to omit the extrusion stage, but the results may not be what you need.

It is dependent on what you need to achieve with your result and what you want to do in the next phase of the project. Whether or not you decide to include the extrusion stage will depend on what you want to achieve with your project. 

Skipping the extrusion process

If the key objective is making pellets to obtain a batch that has slightly increased density and is approximately round in shape with a smooth surface and a large range of sizes then it is possible that the extrusion step can be avoided, saving time and cost. With this two step process, the granulation can be pelletized with some rounding and some densification, but the diameter range of the pellets will be very wide.  

If pellet size variation is not an issue, then it’s possible to simply add a granulation to a spheronizer (providing the water or other liquid binder content is within a suitable range) and pellets can readily be formed. However, the diameter range of the pellets will be very wide.  

The main issue is the wide range of sizes, resulting in inconsistent results. In some applications (some types of animal feed for example) this might be an advantage. Generally, when pellets (spheroids or microspheres) are being made from a granulation and a narrow size range is considered a requirement, then the extrusion stage is essential. 

Taking advantage of extrusion

In an extrusion and spheronization process, the most important factors determining the size range of the pellets within the batch are the liquid binder content of the granulation and the diameter of the extrudate (this is determined by the diameter of the hole in the die of the extruder).

The liquid binder content is modified at the formulation development stage, (Using The Mixer Torque Rheometer as a Tool for Pre-formulation Assessment of Excipients) but the diameter of the die in the extruder can be decided on a case-by-case basis during the processing of the product.

A typical result:

The attached photograph shows the results of a simple trial where:

  1. A small sample of lactose and microcrystalline cellulose, with water as a binder was granulated and spheronized only
  2. A seperate sample of lactose and microcrystalline cellulose was extruded after granulation and then spheronized. The results of the two different approaches are clear to see.

Can I spheronize from a granulation or do I have to extrude the material before spheronization

(Pellets on the left were not extruded, pellets on the right were extruded)

Summary

You can make pellets with only the granulation and spheronization steps. The extrusion stage is not necessary providing you do not require a narrow size range in the batch of spheres that you are making. If you require pellets with limited variation in size of the pellets then the extrusion stage is essential.

If you are working on a project involving extrusion and spheronization, or have a question about extrusion, spheronization or a topic mentioned in this article, please contact us and we will happily answer your questions.

 

By Dr Steve Robinson
5 Nov 2020 in Granulation and Mixing, Formulation Development

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