Two-dimensional simulation of melt spinning with a microstructural model for flow-induced crystallization

The constitutive model for flow-induced crystallization (FIC) developed by the present authors [Doufas et al. (1999, 2000a, 2000b), Doufas and McHugh (2001)], coupling polymer microstructure (chain extension, molecular orient ation, and crystallinity) with the macroscopic transport equations (mass, m omentum and energy), is applied to a two-dimensional simulation of melt spi nning. The model predicts the radial variation of tensile stress and micros tructure driven by the radial variation of the temperature, which is caused by low polymer thermal conductivity. In the limit of infinite thermal cond uctivity, radially uniform profiles for the temperature and the microstruct ure are consistently predicted. The formation of a skin-core structure obse rved experimentally is also predicted, where the molecular orientation, cry stallinity, and tensile stress are highest at the surface of the fiber and lowest at the centerline. The microstructure is predicted to lock in below the freeze point preserving its radial variation despite the collapse of th e temperature radial variation at large distances below the spinneret. Unde r the conditions investigated, for both nylon and polyethylene teraphythala te systems, the cross-sectionally averaged variables do not deviate signifi cantly from the respective uniform quantities of the one-dimensional formul ation at the freeze point. We suggest that the model can be used as an opti mization tool for melt spinning processes predicting the final fiber proper ties through the radial variation of the microstructural variables. (C) 200 1 The Society of Rheology.