Research-based dye makes polyester greener

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Scientists have unlocked a way to dye polyester using 90% fewer chemicals and 40% less water. 

Fizzy water was the key to making polyester dye less harmful to the environment in the creation of a new method developed by an interdisciplinary team at the University of Leeds spin-out company, SwitchDye. 

Polyester makes up more than half of all global fibre output, with production increasing each year – but it takes centuries to decompose and it can be difficult to recycle from garment-to-garment. Textile production is estimated to be responsible for about 20% of global clean water pollution, largely due to chemicals released in the wastewater from dyeing. 

The startup aims to tackle these challenges at the dyeing stage by reducing harmful chemicals, water waste and costs. This could also make it easier and safer to recycle polyester garments, according to researchers and co-founders Dr Nathaniel Crompton, Dr Harrison Oates, Professor Richard Blackburn and Professor Chris Rayner. 

The concept was invented by Professors Blackburn and Rayner, and Dr Crompton developed the SwitchDye technique as his PhD project in the Schools of Chemistry and Design. Now the Chief Executive Officer of the startup, Dr Crompton said: “SwitchDye could transform the textile industry by reducing its huge water use footprint and its pollution problem.  

“Not many people know that even more toxic chemicals are used to turn brightly coloured wastewater into transparent liquid. When released into freshwater, this is a secret killer that harms people, animals and the environment.  

“We can't solve this problem without the backing of industry, investors and policymakers, so we’re excited to share SwitchDye publicly as we aim to scale up.” 

Born from an ongoing collaboration between the Schools of Design and Chemistry at Leeds, SwitchDye makes it easier to insert and remove dyes from the fibre by injecting a small amount of carbonated water into the dye bath. This triggers the dyes’ unique switching behaviour within the polyester fibres. 

SwitchDye, which is based at the University’s innovation community, Nexus, also works on other synthetic fibres, such as nylon and elastane, and is just as effective as widely used dye, without compromising on colour. Importantly, it uses all the same equipment that manufacturers already have.  

Dr Oates, SwitchDye’s Chief Technology Officer, who carried out his PhD as part of the Priestley Centre for Climate Futures, said: “Polyester is highly durable, and straightforward to recycle, however the main issue is the colour in the fabric.  

“SwitchDye can be more easily removed from the fibre, making the clothes much more recyclable. Ultimately, SwitchDye helps to make the textile industry more circular and sustainable, in both the dyeing and recycling stages." 

Dr Crompton and Dr Oates met while carrying out PhDs in the Wolfson CO2 Chemistry lab, a unique facility for developing novel carbon dioxide-based processes in the School of Chemistry, where they quickly became friends and then business partners.  

The world-class facilities at the University’s School of Design and the Leeds Institute of Textiles and Colour (LITAC) have enabled the researchers to rigorously test the dyes over many years, making sure they meet or exceed industry standards for colour fastness. 

Chris Rayner, Professor of Organic Chemistry in the School of Chemistry, said: “Richard and I have collaborated together for nearly 25 years on sustainability and green chemistry for coloration and textiles, combining our individual expertise. We are proud of how our multidisciplinary approach continues to pioneer innovative solutions to solve real-world problems.” 

Richard Blackburn, Professor of Sustainable Materials in the School of Design, added: “It’s been really exciting to see how the technology has developed, and we are especially grateful to The Clothworkers’ Foundation for funding our initial concept that was the subject of Nat's PhD, and to The Clothworkers’ Company for continuing to support the commercialisation of the technology through LITAC.”  

To date, the project has received funding from organisations including The Clothworkers’ Foundation, The Dyers' Company, LITAC, The John Lewis Partnership Circular Future Fund in collaboration with Hubbub, the Northern Triangle Talent Project (led by the University of Sheffield), and the UKRI Engineering and Physical Sciences Research Council (EPSRC). 

Jane Nicholson, Executive Director of Research at EPSRC said: “Sustainable approaches to polyester dyeing are paving the way to a cleaner, more circular textile industry. This startup company is an excellent example of how EPSRC investment in training, specifically in sustainable chemistry, is not only developing leaders of tomorrow but leading to new discoveries that fuel innovation.” 

Over the next six months, the team aims to close its first investment round, scale up dye synthesis and begin trials of its dyeing process on commercial scale machines.