Rheotens tests and viscoelastic simulations related to high-speed spinning of Polyamide 6

This work addresses high-speed fibre spinning of PA6 in two ways: First, we provide isothermal viscoelastic simulations of the spinline up to the point of inflection (onset of neck formation) making use of a K-BKZ-type integral constitutive equation and Polyflow. We focus on a (as far as possible) reliable set of the material parameters and study the role of melt elasticity and non-Newtonian elongational viscosity on the shape of the filament. Second, we present non-isothermal Rheotens experiments at draw down speeds up to 4.4 m/s, to demonstrate the change of filament morphology from amorphous (due to rapid quench), to stress-induced semi-crystalline, using wide angle X-ray scattering (WAXS). As a result of the two approaches, we are able to identify tensile stress levels both for the onset of distinct elongational thinning as well as for the occurrence of stress-induced crystallization. Extrudate swell is complete at about 1 mm distance from the spinneret. The PA6 melt subsequently behaves Newtonian until onset of neck formation by distinct elongational thinning at about 1.5 MPa. Rheotens tests at 1 m filament length yield stress-induced crystallization at about 2.5 MPa, WAXS showing meridian reflexes from α-crystals. The ratio of the said tensile stress levels corresponds to the cross sectional change within the neck in PA6 high-speed spinning.