Japanese researchers simplify dye method for polyester recycling

Researchers at the University of Fukui in Japan have developed a method that could simplify the recycling of coloured polyester textiles by redistributing existing dyes rather than removing them. The approach aims to reduce reliance on the chemicals, water and energy often required to remove dyes during conventional recycling processes.

The researchers demonstrated the method at 120°C using polyester fabrics coloured with blue BG, yellow G and red 4G dyes. During treatment, dye molecules migrated from areas of higher concentration to lower concentration, allowing the existing colours to redistribute across the fibres. By adjusting the proportions and combinations of differently coloured fabrics, the team produced uniform blended shades.

To predict the resulting colour strength, the researchers used Kubelka–Munk values and developed a colour-matching model incorporating pairwise interaction coefficients calculated using a trust-region reflective algorithm. According to the team, the model accurately predicted colour strength following treatment.

The findings suggest a potential route towards more resource-efficient polyester recycling without first stripping dyes from the material. However, the technology has yet to be tested with real textile waste and more complex dye combinations, which will be necessary to assess its practical applicability. If validated at a larger scale, the approach could help address the challenge of recycling coloured textiles and support progress towards textile-to-textile circularity.