Mechanical properties and superstructure of poly(ethylene terephthalate) fibers zone‐drawn and zone‐annealed by CO₂ laser heating

A laser‐heating zone‐drawing and zone‐annealing method using a continuous‐wave carbon dioxide laser was applied to poly(ethylene terephthalate) (PET) fiber to improve its mechanical properties. The as‐spun fiber was zone‐drawn under a applied tension (σ a ) of 4.44 MPa at a laser power density (PD) of 6.08 W cm −2 , and then the laser‐heated zone‐drawn fiber was zone‐annealed. The laser‐heating zone‐annealing was carried out in three steps: the first annealing was carried out under σ a = 139 MPa at 4.83 W cm −2 ; the second annealing was carried out under σ a = 283 MPa at 4.83 W cm −2 , and the third annealing was carried out under σ a = 432 MPa at 3.45 W cm −2 . The surface temperature distribution of the fiber irradiated with the CO 2 laser was measured by using an infrared thermographic camera equipped with a magnifying lens. The relation between the laser power and the surface temperature of the fiber became clear in the laser‐heating zone‐drawing and the laser‐heating zone‐annealing. The fiber obtained finally had a birefringence of 0.239, a degree of crystallinity of 55%, a tensile modulus of 19.8 GPa, and a storage modulus of 25.7 GPa at 25°C. In FTIR measurements, a trans conformation increased with the processing, but a gauche one decreased. The laser‐heating zone‐drawing and zone‐annealing method was found to be effective in producing the PET fiber with high modulus and high strength.