According to a new process developed by researchers at Aalto University in Finland, a two-stage chemical treatment can remove up to 99.3% of the color from reactive-dyed cotton fabrics while retaining most of the fiber strength. The study offers a solution to the problem of residual dyes in waste textile recycling, and the results were published in the journal ACS Omega.

The research team used sodium dithionite as a reducing agent, treating at 60°C for 60 minutes, followed by hydrogen peroxide under alkaline conditions at 90°C for 60 minutes. This sequential treatment breaks the chemical bonds between the dye and cellulose while avoiding severe fiber degradation. For cotton fabrics in four colors—black, dark green, navy, and gray—the color removal rates were 99.3%, 99.2%, 98.3%, and 93.1%, respectively. The treated fabrics retained 84% to 92% of their tensile strength, and although the degree of polymerization dropped from 3395 to 1404–1701, it was still sufficient for chemical recycling. In addition, fabrics re-dyed after treatment showed uniform color, with wash fastness and rub fastness comparable to the control samples.

By comparison, this method uses fewer chemicals than conventional decolorization processes and causes lower tensile strength loss (10.9% vs. 23.9%), indicating some potential for industrial application. However, the process is currently at the laboratory stage, and its economic and environmental impacts at industrial scale have not yet been verified. The research team is conducting a life cycle assessment and plans further trials at kilogram scale.

This research was funded by Business Finland and is part of the TexirC project. For the used clothing recycling industry, the ability to effectively remove color and restore the versatility of textile raw materials can significantly increase the value of recycled cotton, making it more suitable for mechanical or chemical recycling and improving the circular utilization rate of waste textiles.

Source: Aalto Researchers Tackle Cotton Recycling’s Color Problem · Originally published on 2026-08-26