Glycolysis method breaks down mixed textiles for recycling

A new chemical recycling strategy breaks down polyester and spandex into useful monomers, while keeping cotton and nylon intact and ready for reuse. The method could offer a way to increase the amount of textile waste that is recycled, while minimising the need for sorting and separation processes.

Around 100 billion items of clothing are sold each year. Since the turn of the century ‘fast fashion’ trends have seen a surge in textile production. But the manufacture and short lifespan of low-cost clothing items has a serious impact on the environment.

‘Fast fashion increases waste because clothes are discarded more quickly, contributing to an estimated 92 million tons of textile waste globally annually,’ says Erha Andini from the University of Delaware, US.

Currently, less than 1% of this waste is recycled, with most ending up in landfills or being incinerated. This is because although mechanical and chemical recycling technologies exist, most clothing items contain complex mixtures of fibres and additives that are very hard to separate and sort. ‘Separating different fabrics requires unpicking stitching which was designed to be permanent,’ says Alice Payne, an expert in fashion and textiles from RMIT University in Australia. ‘These challenges require considerable labour and logistics to resolve, for a relatively low gain,’ she adds.

Now, Andini and her US-based colleagues have shown how a simple and fast chemical recycling method can be applied to the most common components in mixed textiles. The technique uses microwave-assisted glycolysis with a zinc oxide catalyst to separate polyester, cotton, nylon, and spandex in mixed waste streams.

The team first applied the catalytic conditions to pure samples of polyester and cotton, as these are the biggest-selling fibres on the market. The researchers found that polyester degraded into monomers, with 90% of that being bis(2-hydroxyethyl) terephthalate (BHET), a useful ingredient for yarns, resins, and filaments. Cotton experienced a mass loss of around 8% but otherwise remained intact. The team then performed the same technique on T-shirts made of a 50:50 blend of polyester and cotton at various temperatures and times. Higher temperatures sped up the breakdown of polyester, with complete depolymerisation achieved at 210°C in less than 15 minutes.

As real textile waste is diverse and contains many additives and impurities, the team then tested the process on textiles containing various dyes and finishes. This reduced the yield of BHET, suggesting that additives can hinder the zinc oxide catalyst’s activity.

Finally, the team looked at blends containing other common textile fibres. When the researchers treated a 90% nylon/10% spandex blend, the nylon remained unchanged in structure. However, the spandex broke down into monomers, including 4,4′-methylenedianiline, a key component in polyurethane foam and fiberglass plastics.

When applying the process to mixtures containing polyester, cotton, spandex and nylon, the team was able to depolymerise both polyester and spandex while separating intact cotton and nylon.

‘We need more studies like this that recognise the inherent complexity of modern textiles and develop valorisation processes to get use back from them,’ says James Clark, an expert in green chemistry from the University of York, UK. ‘Putting together known methods in a way that is not currently used is vital, as this approach should be more attractive to industry than creating new methods,’ he adds.

‘The scalability of the depolymerisation process for mixed textiles using microwave-assisted glycolysis is promising, but there are challenges,’ says Andini. ‘These include managing the impact of dyes and finishes, ensuring economic viability and optimising reaction conditions for various textile compositions,’ she adds.

The team suggests that a refined version of their process could enable the recycling of up to 88% of global textiles. But Clark thinks the real obstacle will be the widespread adoption of such methods. ‘Once these methods are proven, more will follow and we can aim for a scenario where valorisation of waste textiles at material and molecular levels is built into the textiles market,’ he says.