Aalto researchers remove dye from cotton for recycling

Researchers at Aalto University in Finland have developed a two-step process that can remove up to 99.3% of colour from reactive-dyed cotton while keeping most of the fabric’s strength. The development could help address an important challenge in textile-to-textile recycling, removing dyes that are chemically attached to discarded cotton fibres.

The study uses two treatments in sequence to turn dark green, grey, black and navy cotton into a lighter material that can be dyed again. According to the researchers, removing colour before recycling could make recovered cotton more suitable for both chemical and mechanical recycling.

The researchers also compared their method with earlier colour-removal processes. A previously reported method achieved 97.8% colour removal but required more hydrogen peroxide and resulted in a 23.9% loss in tensile strength. In comparison, the Aalto process achieved up to 99.3% colour removal while limiting tensile-strength loss to 10.9% in the comparison.

It was examined whether the treated cotton could be dyed again. The results showed that the decolourised fabrics absorbed the new colour evenly and achieved washing and rubbing fastness similar to the reference fabric. This suggests that the process could produce a lighter feedstock that can be used for new colour applications.

The team is also exploring ways to move beyond laboratory-scale batches. According to the study, the process could potentially be adapted for continuous production using existing textile equipment, including pad-batch systems and continuous washing ranges.