For the first time, vat dyes, spandex, and cellulose can be separated from cotton textiles by swelling, washing, and dissolving cotton without destroying the chemical structures of these components in a patent-pending technology designed by researchers at the University of Nebraska–Lincoln.
THE RESEARCH & TEAM: Yiqi Yang, a researcher, along with an interdisciplinary team, including doctorate student Yuanyi Shao, has created the first-of-its-kind technology for fibre-to-fibre or chemical recycling that effectively eliminates dyes, distinguishes between natural and synthetic blends, and produces high-quality fibres.
- The team has created an aqueous system technology that yields high-quality fibres. It not only recycles the fibres successfully, but also recycles the solvents and dyes used in the process.
- Dyes are designed to have strong affinity to fibres for excellent colourfastness, so it is difficult to remove the dyes, and what this team has done, perhaps the first in the world, is to find a way to remove the dyes, without damaging the dyes or the fibre polymers.
- Due to dyes and textile combinations, fibre-to-fibre recycling has proved difficult, if not impossible. Yang and the team has published several articles demonstrating its successful application on a variety of textiles, including cotton and cotton-polyester blends, acrylics, wools, and even carpet.
- The study applies the technology to old denim too.
- It demonstrates that the system can successfully remove vat dyes from textiles and make artificial cellulosic fibres with qualities superior to those produced by artificial fibres made from wood pulp.
- The research also demonstrated that the procedure is economically viable and scalable.
- The research team also strives to reduce environmental expenses and promote the sustainability of the textile industry, with a focus on two areas: enhancing recycling and developing novel textiles from agricultural waste, such as chicken feathers.
- The study, ‘A green technology for the close-loop recycling of vat dyed textiles’ was published in Direct Science’ Resources, Conservation and Recycling.
THE PROCESS: Specifically, the affinity of vat dyes to cotton fibres was eliminated via swelling of cotton fibres through adjusting the ratio of N-methylmorpholine N-oxide (NMMO)/H2O and then agitation and heat were used to remove all vat dyes from cotton.
- The entire separation process did not require the reduction of vat dyes.
- After the complete separation of vat dyes, cotton was dissolved in a different ratio of NMMO/H2O at a lower temperature to remove spandex fibres. The cellulose solution was then heated to the required rheology for the extrusion of quality lyocell fibres.
THE CONTEXT: Textile recycling does exist; however, it is primarily limited to breaking down textiles into fibres for use in other goods. Garment-to-garment recycling, or upcycling, is limited and cannot be done on an industrial scale. Yarn-to-yarn, or mechanical, recycling is possible, but the process is damaging and necessitates the addition of more than 50% fresh fibres to produce useable yarns.
WHAT THEY SAID:
In the last 20 years, the total fibre production has doubled. Right now, we consume more than 125 million metric tons of fibres per year. We cannot grow more natural fibres or raise more sheep. That’s not realistic, so we’re using more synthetic fibres, but the issue there is the ramification of nondegradable microparticles. If you can reuse fibres once or twice, that will be a huge reduction on the demand for new fibres and textile materials. Using our technology, you can recycle fibres from any textiles cost effectively, with excellent properties. Everything we did was having large-scale production in mind. Of course, we have to have industry interest because the industrial application requires heavy capital investment.
— Yiqi Yang
Charles Bessey Professor, Textiles, Merchandising and Fashion Design and Biological Systems Engineering
University of Nebraska–Lincoln
