Extrusion of monofilaments of thermoplastic elastomers

Thermoplastic elastomers (TPE) are widely used in extrusion of weatherseals, tubes and hoses, protective coating for optical fibres and other extruded products. However they are not a common material for fibres' extrusion. This work presents the results of a pilot study of extrusion of TPEs fibres. The extrusion process comprised of an extruder, cooling water tank, 3 stretching zones, 2 relaxation zones between them and winding machine. The process parameters were set according to the TPE manufacturer's requirements. The stretching ratio varied from 2:1 to 7:1. The monofilaments were extruded in diameters range from 2 to 5 mm. It was found that the stretching ratio significantly influenced mechanical properties of the fibres. Highly stretched fibres showed 2-3 times greater stress at break than lower stretched fibres. This is due to the orientation of polymer macromolecules in the longitudal direction. The maximum strength can be achieved when all macromolecules are highly oriented. However, there is a limit of stretching, determined by both technical and manufacturing reasons. For instance, the analysis of ruptured fibres demonstrated that the orientation of macromolecules occur mostly near the fibres surface resulting from shear deformation of polymer flow in extruder and the stretching force on the surface of rotating rollers. At the same time, there is a core of unstretched or low-stretched polymer, which prevents fibres from reaching the maximum strength. Usage of thermoplastic elastomers in monofilament and fibres production will provide manufacturers and users with a number of benefits: good processability, flexibility, softness, high chemical resistance etc. Our experience can also be useful for engineers and researchers who are looking to work with synthetic monofilaments with high content of electroconductive and magnetic fillers.