Simulation of melt spinning including flow-induced crystallization - Part II. Quantitative comparisons with industrial spinline data

The mathematical model for melt spinning of Doufas et al. [A.K. Doufas, A.J. McHugh, C. Miller, J. Non-Newtonian Fluid Mechanics, 1999] coupling fiber microstructure (molecular orientation and crystallinity) with the macroscopic velocity/stress and temperature fields, is tested extensively against industrial spinline data for several nylon melts. Model fits and predictions are shown to be in very good quantitative agreement with spinline data for the fiber velocity and temperature fields at both low and high-speed conditions, and, with birefringence data available for high speeds. The effects of processing parameters: quench air velocity, capillary diameter and mass throughput, as well as material characteristics: molecular weight (RV) and polymer type (i.e., homopolymers with or without additives, and copolymers), on the spinline dynamics are accurately predicted. Under high-speed conditions, strain softening occurs and the tensile stress at the freeze point is predicted to be essentially independent of the processing parameters investigated, in agreement with experimental observations. Birefringence data and model predictions show that crystallization occurs mostly after the freeze point, under the locked-in tensile stress. Under low-speed conditions, the velocity and crystallization profiles (experimental and predicted) are shown to evolve smoothly towards a plateau value and strain hardening behavior is predicted throughout the spinline. The ability to quantitatively describe spinline data over a wide range of conditions and material characteristics, renders the model a useful tool for optimization of melt spinning processes as well as a framework for simulation of other polymer processes involving flow-induced crystallization. (C) 2000 Elsevier Science B.V. All rights reserved.