The study, published in The Journal of Supercritical Fluids, suggests using supercritical CO2 may enable the creation of new, uniform fabric shades without the need for conventional dye removal methods that often require significant water, energy or chemicals.
A team from the University of Fukui treated differently coloured polyester fabrics with scCO₂, observing that existing dyes moved between the fibres until the resultant colours became uniform.
"The textile industry currently faces a major challenge: large quantities of used textiles are discarded, while recycling coloured fibres can require dye removal, along with huge quantities of chemicals and water. Our research explores a way to change the colour of polyester fibres directly by redistributing the dyes already in them using scCO₂," senior assistant professor Jianhua Ren explained.
The researchers subjected polyester samples dyed in blue, yellow and red to scCO₂ under controlled temperature (120°C) and pressure (25 MPa) conditions.
By combining fabrics in specific proportions, they demonstrated that after 90 minutes of treatment, the different shades achieved almost identical new colours. Microscopic analysis indicated even dye distribution, while the fibre structure remained unchanged. The team measured colour strength before and after treatment, using the Kubelka–Munk function (K/S).
The results prompted the development of a predictive model that accounted for interactions between dye types. The model significantly improved prediction accuracy for colour strength at multiple wavelengths.
The findings address a significant barrier in the textile recycling chain: colour removal from polyester, which typically involves energy-intensive or chemical-heavy processes.
Globally, more than 92 million tonnes of textile waste are generated each year, yet less than 1% of coloured textiles undergo closed-loop recycling, according to data cited by the researchers.
Professor Kazumasa Hirogaki of the University of Fukui noted the work demonstrates a possible path to modify colours in polyester without needing to remove existing dyes.
"The next step is to determine how the approach performs with real textile waste and more complex dye combinations," he added.
However, the study involved only fabrics with known dye types, not mixed post-consumer waste. The research team acknowledged that further investigation is required to validate the method with real-world textile blends and on industrial scales.
The study highlights an alternative strategy to current fibre-to-fibre recycling approaches, combining laboratory evidence of direct dye redistribution with a predictive framework for producing new shades.
While further work is needed to trial the process with actual textile waste and at greater volumes, the approach lays groundwork for potentially more sustainable recycling of coloured polyester fibres.
