Advantages of the Twin-Screw Extruder in Hot-Melt Extrusion

The proprietary hot-melt extrusion process is carried out with the use of an extruder. An extruder is a barrel with a platform supporting either one or two rotating screws that are used to push substances down the barrel. Extruders are of two types, namely, the single screw extruders and the twin-screw extruders.

Continue reading this blog to learn more about the twin-screw extruders and their advantages in hot-melt extrusion.  

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Twin-Screw Extruders

Twin-screw extruders are more advanced devices that contain twin-screw systems, having counter-rotating or co-rotating screws. These extruders are used to melt polymers and mix them with other substances such as pigments and APIs. They can also be used to remove volatile materials.

This type of screw usually consists of length-to-diameter ratio. And this is generally around twenty to forty ration one. The extruders generally used in pre-commercial plants are between eighteen to thirty millimeters in diameter. While those used for its production have a much higher diameter that typically exceeds fifty millimeters.

1. It Has Lower Tendency to Overheat

Increasing the speed of the screws in the single-screw extruder produces heat. And this can degrade drugs that are delicate to an elevated temperature. Heat is controlled with twin-screw extruders. This is achieved by external sources and produced independently of screw speed. The tendency to overheat is much lower, which represents an essential advantage for heat-sensitive drugs and for decreasing residence time.

2. Increased Versatility

Twin-screw extruder enables varying conditions and different configurations in the different extruder zones. Different varieties of twin-screw extruders are, thus, available with various operating mechanisms that can be used for diverse applications.

3. Increased Flexibility

Process consideration can continuously and easily be controlled. This depends on the mixing function and extrusion. The die plates are also quickly changed if a dissimilar extrudate diameter is preferred, which means a wide range of formulations can be processed using a single device.

4. It is Self-Cleaning

In this type of extruder with intermeshing co-rotating screws, one of the screws’ flights wipes the base of the parallel screw. And this ensures the total emptying of the device. It also reduces the quantity of wasted product at the end of each batch.

5. Decreased Residence Time

The durability of time a substance stays in the extruder is reduced, basically because of the relatively quick-melting time when compared to the length of time required in a single-screw extruder. Extrusion process typically lasts between 5-10 minutes.

6. Improved Mixing

Better mixing is achieved with twin-screw extruders because of the intermeshing co-rotating screws. Either dispersive mixing or distributive mixing can be achieved. Distributive mixing enables limited degradation and the even blending of substances, which is advantageous for processing APIs that are sensitive to shearing or heat.

On the other hand, in dispersive mixing processes, the solid domain is fragmented into a tinier state, which facilitates the compounding of two or more APIs.