| Abstract: | High‐speed spinning of poly(ethylene terephthalate) with an intrinsic viscosity of 0.98 dL/g was performed at a take‐up velocity of 2.5–5.5 km/min, and the effects of the fiber structure on the isothermal and nonisothermal shrinkage‐stress evolution in as‐spun filaments were investigated. In isothermal measurements, the peak shrinkage stress was consistent with the degree of amorphous orientation, whereas the so‐called frozen stress relaxation was rather constant with respect to the take‐up velocity. The maximum shrinkage stress in nonisothermal testing was also consistent with an amorphous orientation. A spontaneous elongation phenomenon took place for filaments spun at 2.5 and 3 km/min that resulted in the lowering of shrinkage stresses in both experiments. A simple calculation showed that the inertial force in the spin line was about half of the resultant shrinkage force. Filaments spun at 5.5 km/min had markedly lower shrinkage stresses and shrinkage with respect to the degree of amorphous orientation. This was attributed to the fiber structure, which gave a much lower loss‐tangent maximum for these filaments. In addition, a hypothetical model is proposed suggesting the possibility that filaments spun at 5.5 km/min may have narrow tie‐chain‐length distributions that provide relatively longer shortest tie molecules. © 2001 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 964–972, 2001 |
