Extrusion swell unit

Optional as an option for capillary rheometer

(1) Extrusion swell is a typical phenomenon of elasticity of polymer liquid. From the point of view of elastic deformation, the melt is subjected to strong tensile action at the entrance area before entering the die, resulting in elastic deformation. Although this deformation is partially relaxed when flowing inside the die, the relaxation time of polymer materials is generally long, and some of them are still retained until the die outlet. Therefore, after the extrusion die loses its constraint, the elasticity recovers, causing the extrudate to swell.

(2) From the point of view of entropy elasticity, the random thread like macromolecular chain is strongly stretched at the entrance of the die, the conformation changes and the conformational entropy decreases. Similarly, this conformational change was relaxed in the inner part of the die, but some of it did not recover until the die was extruded. The extruded molecular chain reverts to a new random coil conformation, which makes the entropy increase and swell.

(3) The experimental results show that all the factors affecting the elasticity of polymer melt have an effect on the extrusion swell behavior. If the extrusion temperature increases, or the extrusion speed decreases, or the elastic deformation of polymer melt decreases due to the addition of fillers in the system, the extrusion swell phenomenon will be significantly reduced.