Ultrasound-Assisted Removal of Unfixed Dyes on Polyurethane Fibers as an Efficient Strategy for Improving the Washing Fastness of Polyester/Spandex Elastic Fabric

To improve the fastness properties of disperse dyes on polyester/spandex blend fabric, ultrasound was applied during the post-clearing process to assist in the removal of unfixed dyes on polyurethane fibers. The blend fabrics were pre-dyed with C.I. Disperse Brown 1, which was found to be able to severely stain spandex component in previous studies. The dyed blends were treated via an ultrasound-assisted clearing process, with varied frequency, temperature, and time, to optimize the clearing conditions. Three methods were compared in terms of the removal degree of unfixed dyes on polyurethane materials, which include the normal reduction clearing by mechanical oscillation and ultrasonic reduction clearing with or without the addition of auxiliaries. Scanning electron microscopy was used to observe the degree of dye aggregation on the surface of treated or untreated polyurethane fibers. The staining degree on polyurethane fibers decreased significantly with increasing ultrasonic frequency, temperature, and time. The addition of polyoxyethylene-type nonionic surfactants to the ultrasound-assisted reduction clearing could enhance the removal of dyes on polyurethane fibers. Polyester/spandex fabric samples were dyed with high-energy disperse dyes (in the three primary colors), and the optimized ultrasound-assisted reduction clearing process was applied to evaluate the washing fastness properties.