Creep deformation and its correspondence to the microstructure of different polyester industrial yarns at room temperature

The room temperature creep behaviors and related microstructural changes of a high-tenacity (HT) poly(ethylene terephthalate) (PET) industrial yarn and a super-low-shrinkage (SLS) PET industrial yarn were investigated and compared by using wide-angle X-ray scattering (WAXS), small-angle X-ray scattering (SAXS), birefringence measurements and Fourier transform infrared spectroscopy (FTIR) in order to identify their respective underlying creep mechanisms. The crystal structure including crystalline orientation and crystallinity of fibers did not show obvious changes after the creep process, while the amorphous structures varied with creep stress. The HT yarn creep deformation was mainly elastic, and its creep recovery ratio was high. The amorphous orientation, amorphous layer thickness and degree of conformation change from gauche to trans conformers showed a slight increase. The mechanism of this slight change is that the coiled molecular chains are oriented under tensile loading and most of the extended chains are disoriented under offloading in the small amorphous region. By contrast, the SLS yarn underwent plastic creep deformation with a low recovery ratio. After the creep test, the amorphous orientation and lamellar thickness both increased but the crystallinity remained unchanged. The creep mechanism for the SLS yarn is that the molecular chains in the large amorphous domain are easily extended and oriented subjected to tensile loading, while conformation transition from gauche to trans conformers and the formation of irreversible mesophase take place. (c) 2018 Society of Chemical Industry