Change in Supermolecular Structure, Dyeability and Some Physical Mechanical of Poly (ethylene terephthalate) Filament during Continuous Heat-Treatment and Fales-Twisting Process at High Wind-Up Speed

Abstract

An attempt was made to investigate change in supermolecular structure, dyeability, and some physical mechanical of poly (ethylene terephthalate) (PET) filaments during a continuous and high speed process of heat-treatment immediately followed by false-twisting. As-spun PET filaments were prepared at spinning speed of 3.5km/min and subsequently heat-treated and false-twisted with continuously at 600m/min on an apparatus, specially designed and constructed by us, with two tublar heaters and a heating roller for heat-treatment. PET filaments, which were sampled at the end of every steps in a continuous heat-treatment and false-twisting process, were characterized by X-ray diffraction, the differential scanning calorimetry (DSC), temperature dependence of the dynamic visco-elasticity, the exhaustion of disperse dye, the tensile strenth and tensile elongation. With progress of the heat-treatment, crystallinity index, crystal size, and crystal orientation increase, and the former two remain almost constant even after false-twisting and crystal orientation slightly decreases by false-twisting. Crystallinity index of the samples sampled at different stage in heat-treatment and false-twisting process were linearly proportional to thier heat of fusion _??_Hm as determined with DSC. During the heat-treatment, the amorphous region first changes to a more densely packed supermolecular structure, which shows lower dye exhaustion, but further heat-treatment relaxes the molecules in the amorphous region, resulting in an increase in the region having lower molecular packing density with higher dye exhaustion. Finally, false-twisted PET filaments dyeable under atmospheric pressure can be obtained by this continuous heat-treatment and false -twisting process.