Structure and performance changes of high-modulus and low-shrinkage poly (ethylene terephthalate) industrial fibers under different heat treatment conditions

For different heat treatments, the changes in overall performance features such as tenacity, modulus, load at 5% strain and elongation at a load of 4.0 cN/dtex of high modulus low shrinkage poly (ethylene terephthalate) industrial fibers were compared. The variations in the mechanical behavior were linked to adjustments in the microstructure, as determined by Fourier transform infrared spectroscopy, wide-angle X-ray diffraction and small-angle X-ray scattering. The results confirmed that the tenacity of the fibers is less dependent on the heat treatment conditions, whereas the modulus, load at 5% strain and elongation at a load of 4.0 cN/dtex differ significantly, which could reflect the stability of the fibers in use. The intact crystal structure and the constrained conformation adjustment of molecular chains in amorphous after heat treatment are responsible for the excellent tenacity retention of high modulus low shrinkage poly (ethylene terephthalate) fibers. With a low pre-tension and a higher heating temperature, the molecular chains in the amorphous region relax and disorient, resulting in a lower modulus and load at 5% strain. Instead, in the case of high pre-tension, heat treatment prolongation or temperature increase helps to rearrange the amorphous region into an ordered structure, which can improve the initial modulus and load at 5% strain of the fibers.