Regulation of Supermolecular Structure of Poly (ethyleneterephthalate) Fiber Spun at High Wind-Up Speed by Means of High Temperature-Short Period Heat Treatment

Abstract

An attempt was made to investigate the effect of annealing on supermolecular struture of poly (ethyleneterephthalate) (PET) fibers spun at various wind-up speeds and to show a technological possibility of controlling the supermoleular structure of PET fiber by choosing adequate conditions of melt spinning and subsequent annealing. PET fiber was spun at wind-up speed ranging 2-9 km/min and then annealed at a temperature Tαbetween 190-270°C for a given period of time tα (0.5-10s). In this case, the feed ratio Fr was varied in the range-5∼+5%. Supermolecular structure of annealed PET fiber was characterized by the temperature dependence of the dynamic viscoelasticity, X-ray diffraction, and infra-red spectroscopy.The difference in supermolecular structure between perperial and central parts of a fiber generated in the high speed melt spinning process has a tendency to become more significant by annealing. In the range Tα<Tc, (Tc is a characteristic temperature, depending on the spinning speed), as Tα is increased the peak value of tanδ, (tan δ) max increases and the peak temperature Tmax shifts to lower temperature. In the range Tα>Tcthe region having lower molecular packing density increases with Ta and this trend is noticeable for larger tαand Fr. By annealing, the crystallinity index and crystalline size increase remarkably and the crystallineorientation increases slightly. This tendency is more significant for PET fiber spun at lower speed. The fraction of trans conformation of ethylene glycol unit increases by heat treatment and in PET fiber annealed at Ta>Tc, ethylene glycol unit tends to orientate perpendicular to the fiber axis.