A MODEL FOR THE NECKING PHENOMENON IN HIGH-SPEED FIBER SPINNING BASEDON FLOW-INDUCED CRYSTALLIZATION

In this work we investigate the use of an inhomogeneous structural mod el which explicitly takes into account flow-induced crystallization fo r representing the necking phenomenon in high-speed fiber spinning. Fo r simplicity, we have considered a one-dimensional (cross-section aver aged) approximation for an isothermal system with no surface tension a nd air drag, viith or without inertia. Flory's approach [J. Chem. Phys . 15, 397-408, (1947)] is used to predict the onset of crystallization in the spinline. After the onset of crystallization, the fiber is mod eled as an inhomogeneous medium with two separate (meso) phases-one se mi-crystalline and the other amorphous. The amorphous phase, before an d after the onset of crystallization, is modeled as a viscoelastic flu id, represented here by the extended White-Metzner model. The semi-cry stalline phase is modeled as an anelastic solid. We demonstrate neck f ormation for a variety of processing conditions and material property values consistent with those encountered in practice. In particular, t he addition of inertial effects, which can also be important in high-s peed fiber spinning, shifts jut does not eliminate the window in param eter space over which the inertialess model predicts neck formation. B ased on these results, we propose as a mechanism for the neck formatio n the structural changes within the material induced by the crystalliz ation and the ability of the semi-crystalline phase to rapidly take up high stresses. (C) 1998 The Society of Rheology.