Before the main extrusion process, the stored polymer feedstock is mixed with various additives, such as stabilizers, color pigments, flame retardants, fillers, lubricants, reinforcing agents, etc., to improve product quality and processability. Blending polymers with additives also help achieve target performance profile specifications.

For some resin systems, an additional drying process is often employed to prevent polymer degradation due to moisture. On the other hand, those materials that generally do not need to be dried before use may still need to be dried, especially when they are stored in a cold room and suddenly placed in a warmer environment, thereby inducing moisture on the surface of the material coagulate.

After the polymer and additives are mixed and dried, the mixture is gravity fed into a feed hopper and through the extruder throat. A common problem when handling solid materials such as polymer powders is their flowability. In some cases, material bridging may occur within the hopper. Therefore, special measures such as intermittent injection of nitrogen or any inert gas can be used to disturb any polymer build-up on the surface of the feed hopper, thus ensuring a good flow of the material.

The material flows down into the annular space between the screw and barrel. The material is also limited by the helical groove. As the screw rotates, the polymer is transported forward and the frictional force acts on it. The barrel is usually heated with a gradually increasing temperature profile. As the polymer mixture moves up from the feed zone to the metering zone, friction and barrel heating cause the material to be plasticized, uniformly mixed, and kneaded together.

Finally, as the melt approaches the end of the extruder, it first passes through the screen. The screen pack is used to filter any foreign matter in the thermoplastic melt. It also prevents the clogging of template holes. The melt is then extruded out of the die to obtain the die shape. It cools immediately and is pulled from the extruder at a constant speed.

After cooling, further processes such as flame treatment, printing, cutting, annealing, deodorization, etc. can be carried out. Extrudates are inspected and packaged and shipped if they meet all product specifications.