Thermal shrinkage stress in high-speed-spun, high molecular weight poly(ethylene terephthalate) filaments

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.