Quantitative characterization of surface oligomers for polyester fibers based on Soxhlet extraction with trichloroethylene enable lower-temperature extraction

Polyethylene terephthalate (PET) fibers have been widely used in various industrial fields due to their excellent chemical and physical performance. However, there is still a crucial problem of the massive precipitation of oligomers from the interior to the surface of product, which results in decreased production efficiency and harm to human health. A quantitative characterization method for surface oligomers of PET fibers based on Soxhlet extraction was developed, with lower-temperature extraction, high accuracy, excellent extraction effect and wider operability. The extraction temperature (Toe) decreased by 30°C compared to the conventional extractant of tetrachloroethylene (Te-Ex), benefiting from the trichloroethylene (Tr-Ex) extractant. The pre-wash process with trichloroethylene could ideally remove oil impurities of about 0.09% but retain the surface oligomers on the fibers, endowing the method of with promising accuracy. PET staple fibers with various contents of surface oligomers were extracted with Tr-Ex, and the achieved contents (i.e. 0.320%/0.527%/0.876%) were similar to those with Te-Ex (i.e. 0.307%/0.516%/0.828%), and the contents with Tr-Ex were all slightly higher than those with Te-Ex, indicating that the extraction efficiency of Tr-Ex improved by ∼4.10% compared with that of Te-Ex. It was confirmed that Tr-Ex method has excellent accuracy compared with as the Te-Ex method and better extraction effect than the Te-Ex method; maybe possibly dipole–dipole interaction between trichloroethylene and oligomer molecules was responsible for the better effect. This quantitative characterization method has potential application in industrial online measurement of surface oligomers on PET fibers, films and related materials.