Researchers at Japan’s University of Fukui have demonstrated a method for changing the colour of polyester fabrics without first removing their existing dyes, potentially simplifying textile-to-textile recycling.

The process uses supercritical carbon dioxide (scCO₂) to redistribute dye molecules between differently coloured polyester fibres, producing a uniform new shade. By adjusting the proportions of the original fabrics, researchers can control the resulting colour.

📈 In one experiment, blue and yellow polyester fabrics were treated together at 120°C and 25 MPa. After 90 minutes, both achieved an identical green shade.

The team also developed a mathematical model to predict colour strength following treatment. Microscopic analysis showed that dye distribution became more uniform while the fibre microstructure remained unchanged.

The approach could reduce the need for conventional dye-removal and re-dyeing processes. However, further testing is needed with mixed textile waste, more complex dye combinations and larger-scale processing.
The findings offer a potential new route for recovering value from coloured polyester that is difficult to recycle through conventional processes.