High-speed melt spinning of bicomponent fibers: Mechanism of fiber structure development in poly(ethylene terephthalate)/polypropylene system

High-speed bicomponent spinning of poly(ethylene terephthalate) (PET) (core) and polypropylene (PP) (sheath) was carried out and the structure development in the individual components, PET and PP,was investigated. The orientation and crystallinity development in the PET component was enhanced as compared to that of the single-component spinning while the PP component remained in a low orientation state and had a pseudo-hexagonal crystal structure even at high take-up speeds. To clarify the mutual interaction between the two components in bicomponent spinning, a semiquantitative numerical simulation was performed. The simulation results obtained using the Newtonian fluid model showed that the solidification stress in the PET component was enhanced while that of the PP component was decreased in comparison with the corresponding single-component spinning. This is due to the difference in the temperature dependence of their elongational viscosity. Simulation with an upper-convected Maxwell model as the constitutive equation suggested that significant stress relaxation of the PP component can occur in the spinline if the PET component solidifies earlier than does PP. Based on the structural characterization results and the simulation results, it was concluded that the difference in the activation energy of the elongational viscosity and solidification temperature between the two polymers are the main factors influencing the mutual interaction in the bicomponent spinning process. (C) 1996 John Wiley & Sons, Inc.