Physical Properties and Dyeability of Heat-Treated Poly (ethyleneterephthalate) Fiber Spun at High Wind-Up Speed

Abstract

An attempt was made (1) to prepare poly (ethyleneterephthalate) (PET) fiber having thermally stable amorphous region by heat treatment at higher temperature for short period of time for the sample of as-spun fibers obtained at high wind-up speed, (2) to establish the relations between the supermolecular structure and dyeability and (3) to clarify physical and thermal properties of the fibers prepared thus (in (1)). For this purpose, PET fibers were obtained at wind-up speed of 3-9 km/min under the same conditions except the spinning speed. The fibers were heat-treated at temperature Ta between 190 and 270°C for the time ta ranging 0.510 sec and for feed ratio Fr ranging -55% . The heat-treated fibers were characterized by the dynamic viscoelasticity vs. temperature curve, dye exhaustion of disperse dyes at 100°C, the stress-strain curve, and differential scanning calorimetry. The supermolecular structure of PET fiber, annealed at Ta 240°C for ta= 1 sec does not change during dyeing at 100°C . Therefore, it became evident that the thermally stable amorphous region is produced by heat treatment at higher temperature. When as-spun fiber is heat-treated above Tc, which is characteristic temperature mainly depeding on the spinning speed, the dye exhaustion in creases significantly by the heat treatment. For Ta≥Tc, the amount of dye exhaustion increases by the heat treatment if the treatment is made for higher Ta, linger ta and larger Fr. There is a close correlation between the distribution function of the molecular packing density in amorphous region F' (n) and the dye exhaustion : the fiber having larger amount of the region with lower packing density shows larger dye exhaus tion. PET fibers spun at higher than 5.5 km/min have almost constant tensile strength, before and after the heat treatment at Ta≥Tc with Fr= 0%, while their tensile elongation decreases. By choosing the adequate conditions of melt spinning and heat treatment, it is possible to obtain PET fibers dyeable under atmospheric pressure and also having physical properties of practical uses.