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

Abstract

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 4.4m/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 1mm distance from the spinneret. The PA6 melt subsequently behaves Newtonian until onset of neck formation by distinct elongational thinning at about 1.5MPa. Rheotens tests at 1m filament length yield stress-induced crystallization at about 2.5MPa, 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.