An Isothermal Model for High-Speed Spinning of Liquid Crystalline Polymer Fibers Coupling

Experiments show high-speed spinning of many synthetic bers is accompanied by the partial crys-tallization of the initially amorphous melt. This crystallization is induced by some combination of the extensional ow, molecular orientation and extension, and temperature dependence. The crystallization of the material couples back to aaect the ber rheology, through a process of stress-hardening. Recently Forest, Wang and Bechtel have derived isothermal 1-D equations from macroscopic approximations of Doi-type liquid crystalline polymer (LCP) kinetic equations; their equations model the coupling between the extensional ow and the molecular orientation. Here we extend that model to include a fully three-way coupling of ow, orientation and crystallization mechanics, adopting an Avrami crystallization law with an orientation-dependent rate constant as proposed by Ziabicki, and the Kikutani stress-hardening law. We show that there is a signiicant diierence in the ber diameter proole, orientation and crys-tallinity with the inclusion of the stress-hardening to the extensional ow. Of interest here also is the role of crystallization in localizing the drawdown into a so-called neckk region. We illustrate important qualitative and quantitative eeects due to the development of crystallization: a pronounced drop in the ber radius, an increased rapid uid acceleration, and enhanced molecular alignment with the ber cen-terline axis. These three features all occur over the short orientation-induced crystallization lengthscale, and are isolated in the rst 20% of the crystallizing region along the spinline for draw ratios typical of high-speed spinning.