New study reveals a way to process coloured polyester textile waste without chemicals

One of the main challenges in textile recycling is the handling of mixed, coloured waste. Today, chemical processes are often required to remove dyes, followed by recycling and re-dyeing in resource-intensive steps. This makes recycling challenging and limits its potential.

Now, research from the Department of textile technology led by Mohammad Neaz Morshed demonstrates that the problem can be approached in a different way. Instead of removing the dyes, supercritical carbon dioxide (CO₂) is used to allow colour to redistribute between different textiles until the material reaches a shared, uniform shade.

Dyes are reused rather than removed

In the method, polyester textiles of different colours are placed together in a high-pressure system with supercritical CO₂. In this state, where carbon dioxide exhibits properties of both a gas and a liquid, dyes can detach from the fibres, move between materials and redistribute evenly following the principle of already established colour chemistry.

Unlike conventional processes, the method requires neither water nor chemicals, and no decolourisation step is needed. Instead, the dyes already present in the material are reused.

“We have shown that a homogen colour can be achieved across all materials, while both colour fastness and the mechanical strength of the textiles are preserved. This means that mixed polyester waste can be transformed into a usable material without chemicals or water.”

“Carbon dioxide acts as a clean and recyclable carrier of colour. It moves dyes naturally between textiles instead of washing them away,” said Mohammad Neaz Morshed.

Opportunities for the textile industry

Mixed, coloured polyester waste is currently difficult to recycle because dyes interfere with both chemical and mechanical recycling processes. The method presented could therefore influence how polyester waste is handled in the future.

According to the study, the technology could reduce the need for sorting waste by colour, eliminate chemical decolourisation and simplify the recycling chain. At the same time, fibre quality is preserved, which is essential for recycling textiles into new textile products.

A step towards circular textile recycling

Globally, less than one per cent of textiles are currently recycled into new textiles. Colour contamination is one of the main reasons. By demonstrating that dyes in waste textiles can be redistributed and reused rather than removed, the study points to a possible pathway for increasing textile-to-textile recycling.

The method has so far been tested at laboratory scale, and further studies are needed, including trials with real post-consumer waste and techno-economic analyses comparing the method with existing chemical processes.

Other researchers in this work are Annah Tayebwa and Hui Deng, Master students, Swedish School of Textiles, Veronica Malm, senior Lecturer, Department of Textile Technology, Swedish School of Textiles, Molla Tadesse Abate, Postdoc, Hof University, Professor Michael Rauch, Univertsity of Applied Sciences, Hof University, and Professor Vincent Nierstrasz, Department of Textile Technology.

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The scientific study is published in the Journal of Supercritical Fluids.

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Read more about the research on textile technology

About Mohammad Neaz Morshed