Migration and Chemical Characterization of Cyclic Oligomers from Polyester Fiber in Waterless Dyeing System

Polyester yarn is successfully dyed with disperse dye in a low-pressure non-aqueous medium dyeing system. However, oligomers with different low molecular mass are formed during manufacture of polyesters, which can diffuse into the dyeing bath or be adsorbed on the dyeing machine during dyeing process. In this investigation, oligomers of different polyester yarns were extracted with tetrachloroethane solution, and analyzed using Fourier transform infrared spectroscopy (FTIR), proton nuclear magnetic resonance (NMR), thermogravimetric analysis (TGA), high performance liquid chromatography (HPLC), and liquid chromatography-mass spectrometry (LCMS). The amount of oligomer that was isolated by reprecipitation method ranged from 1.83 % to 4.07 % (on the weight of yarn) in the respective yarn, and more than 80 % of the components are cyclic oligomers. The thermal profile of oligomer showed it had a faster weight loss at 183 °C and 470 °C which was compared with polyester (473 °C). HPLC and LC-MS analysis results further indicated that 99 % of the oligomers were cyclic trimers during dyeing. Moreover, the dyeing color depth of dyed yarn and the uptake of dye would be greatly improved after the oligomer of polyester yarn was removed. Otherwise, the oligomer may affect the color fastness and levelness of the dyed polyester samples.