Characterization and removal of surface oligomers on polyester yarns dyed in decamethylcyclopentasiloxane waterless dyeing system

During the dyeing process, some oligomers present in the undyed polyester fibers migrate from the interior portions of the polyester fibers to their surfaces, resulting in stains and dyeing defects on the dyed products. In traditional aqueous dyeing processes, these oligomers can be effectively removed using an additional aqueous reduction cleaning method, which generates more wastewater. Although waterless dyeing of polyester is a revolutionary innovation with significant environmental and economic benefits, the currently used aqueous reduction cleaning method cannot be utilized in a waterless dyeing system. It has been found that over 95 % of the oligomers on the surface of polyester fiber were cyclic trimers. A comparison and analysis were conducted on the surface oligomer content of polyester after dyeing in decamethylcyclopentasiloxane, water and liquid paraffin . The removal methods for surface oligomers were explored, and recyclable organic solvents such as perchloroethylene , dimethyl sulfoxide , 1, 4-dioxane, n-butyl acetate and dimethylformamide were investigated as potential cleaning media, achieving oligomer removal rates ranging from 60 % to 95 %. The solubility of the cyclic trimer in solvent media was determined. Furthermore, the analysis of surface electrostatic potential revealed that the solubility of cyclic trimers in solvents is significantly influenced by electrostatic bonding and the molecular polarity index (MPI). Specifically, a stronger electrostatic bonding effect between the solvent and the cyclic trimer, or a smaller disparity in their MPI, results in higher solubility of the cyclic trimer in the solvent. This research enriches the theoretical understanding of oligomers in the waterless dyeing system. • The oligomers of filament yarns are more than those of spun yarns. • Solvents with higher solubility to the oligomers can reduce their adsorption on the polyester. • Washing dyed polyester yarns with any of the selected solvents can remove 60 %-95 % of the surface oligomers. • Solvent cleaning can replace reduction cleaning process.