The effect of die flow on the dynamics of isothermal melt spinning

The effect of die flow variables on the stability of isothermal melt spinning has been studied, both theoretically and experimentally. A die flow analysis provides the boundary conditions for a differential treatment of the spinline, both as a steady flow problem and as a linear stability problem. From the latter, one can predict the onset of draw resonance as a function of draw ratio, certain rheological parameters, and the stresses in the die. The experimental materials were two commercial polypropylenes and the apparatus consisted of a short (1.5–6 cm) isothermal spinning chamber; the agreement with theory was quite satisfactory. In most cases, high shear rates in the die (and subsequent high die swells) decrease the spinline stability but the magnitude of this interaction depends on many variables. In general, there is a high propensity for draw resonance (or ductile breakage) when the spinline is operating under conditions of severe thinning in a rheological sense.