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. © 2018 Society of Chemical Industry

No abstract

No abstract

In order to solve the problem that it is difficult to balance the high strength and flame retardancy of polyester industrial yarn, the possibility of controlling the uniform dispersion of flame retardant without affecting the crystallization of polyester was discussed in this paper. The long-chain branched flame retardant with good thermal stability in the range of processing temperature was chosen to blend with high viscosity polyester. The addition of flame retardant reduced the melt viscosity and the crystallization ability of polyester, so the melt spinning and drawing process of the flame retardant polyester industrial yarn were optimized for the sufficient crystallization of polyester based on the rheological and crystallization properties of flame retardant polyester. Due to the steric effect of flame retardant, it was eliminated from the crystal region and only existed in the amorphous region of polyester. As a result, the microstructure with high crystallinity and orientation and the morphology with a uniform dispersion of flame retardant were obtained. The flame retardant high strength polyester industrial yarn was successfully prepared with a limiting oxygen index of 32.0% and a breaking strength of 8.0 cN/dtex, which meets the UL-94 V-0 standard and shows good durability of flame retardant after washing and rubbing treatment, achieving the goal of flame retardancy and high strength for the polyester industrial yarn.