A modified model and algorithm for flow‐enhanced crystallization—Application to fiber spinning

Abstract

AbstractA modified version of the two‐phase flow‐induced crystallization model of Doufas et al. (J Non‐Newtonian Fluid Mech 2000, 92, 27) for melt spinning of polymeric fibers is presented to address three issues: (1) discontinuities generated due to the imposition of continuation conditions at the crystallization onset at Tmo; (2) excessive strength of the flow enhancement component coupling the total extra stress tensor invariant to the crystallization kinetics; and (3) Avrami isotherms used. The modified model provides seamless, two‐phase predictions for all‐state variables in the fiber‐spinning process and significantly reduces discontinuities. Moreover, a new component for the flow‐induced crystallization rate and Avrami crystallization rate isotherms increase the predictive capability of the model. Quantitative prediction of the velocity, stress, temperature, density (or crystallinity), and birefringence profiles are demonstrated for Nylon 66 and PET melts for a variety of process conditions, including predictions of quenched‐sample density profiles and the take‐up speed dependence of as‐spun fiber density. The new algorithm, assisted by the coupling model, provides a more efficient and robust convergence of steady‐state calculations and has been tested to predict spinning phenomena up to spin speeds of 9000 m/min. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3240–3254, 2006