Numerical simulation of rheological effects in fiber spinning

The fiber‐spinning process is an important industrial operation to manufacture synthetic fibers. The process occurs under free‐surface conditions, and the final properties of the fiber are characterized by the extensional properties of the polymer. Specifically, the non‐isothermal response of the polymer in uniaxial extension dominates the process. The fiber‐spinning process is analyzed by means of a unidirectional approach because the thickness of the fiber is very small with respect to its lateral dimension. The analysis accounts for the prehistory of the material inside the die, based on purely extensional strains. For viscoelastic polymer melts, the constitutive equation must be able to describe adequately the rheological behavior of the polymer in extensional flow. A good candidate for such modeling is the K‐BKZ integral constitutive equation, with a spectrum of relaxation times, which captures well the nonlinear viscoelastic response of polymer melts. The non‐isothermal response is taken into account with a temperature shift factor utilizing the Morland‐Lee hypothesis. The present work includes effects due to gravity, inertia, and air drag, where applicable. Simulation results are compared with experiments on polypropylene (PP), poly(ethylene terephthalate) (PET), and low‐density polyethylene (LDPE) melts at low and high speeds. Results are also compared with previous simulations. It is shown that in some cases the extrudate swell at the spinneret exit must be taken into account to accurately predict the drawing forces, which makes a fully two‐dimensional analysis a necessity for such operations. © 2000 John Wiley & Sons, Inc. Adv Polym Techn 19: 155–172, 2000