Researchers at Aalto University in Finland have developed a process that removes up to 99.3 per cent of colour from dyed cotton textile waste.

Colour is a major challenge in textile recycling because dyes can remain attached to cotton fibres and affect the quality and appearance of recycled material. Removing them without significantly damaging the cotton is therefore important for returning textile waste to production.Colour is a major challenge in textile recycling because dyes can remain attached to cotton fibres and affect the quality and appearance of recycled material. Removing them without significantly damaging the cotton is therefore important for returning textile waste to production.

The process removes the dye in two stages. First, the fabric is treated with sodium dithionite, which breaks down the parts of the dye molecules responsible for producing colour. Hydrogen peroxide is then used to oxidise the remaining dye residues, leaving the fabric white enough to be recycled or dyed again.

During testing, the treated fabric retained an average of 87.2 per cent of its original tensile strength and experienced a maximum weight loss of 3.5 per cent. Further analysis found only limited damage to the cellulose structure.

The researchers also successfully redyed the treated fabric, which absorbed colour evenly. This indicates that the treated cotton could be reused in new textile products without the original dye affecting its colour.

For further information, please read more on NIH.