image: Recycling cotton-polyester clothes is closer to reality with a new method that can (1) dissolve the blended materials, (2) separate the cellulose and (3) spin new lyocell-like fibers. view more
Credit: Simone Haslinger/Herbert Sixta, Ph.D.
SAN FRANCISCO, April 2, 2017 -- Pollution created by making and dyeing clothes has pitted the fashion industry and environmentalists against each other. Now, the advent of "fast fashion" -- trendy clothing affordable enough to be disposable -- has strained that relationship even more. But what if we could recycle clothes like we recycle paper, or even upcycle them? Scientists report today new progress toward that goal.
The team will present the work at the 253rd National Meeting & Exposition of the American Chemical Society (ACS). ACS, the world's largest scientific society, is holding the meeting here through Thursday. It features more than 14,000 presentations on a wide range of science topics.
"People don't want to spend much money on textiles anymore, but poor-quality garments don't last," Simone Haslinger explains. "A small amount might be recycled as cleaning rags, but the rest ends up in landfills, where it degrades and releases carbon dioxide, a major greenhouse gas. Also, there isn't much arable land anymore for cotton fields, as we also have to produce food for a growing population."
All these reasons amount to a big incentive to recycle clothing, and some efforts are already underway, such as take-back programs. But even industry representatives admit in news reports that only a small percentage gets recycled. Other initiatives shred used clothing and incorporate the fibers into carpets or other products. But Haslinger, a doctoral candidate at Aalto University in Finland, notes that this approach isn't ideal since the carpets will ultimately end up in landfills, too.
A better strategy, says Herbert Sixta, Ph.D., who heads the biorefineries research group at Aalto University, is to upcycle worn-out garments: "We want to not only recycle garments, but we want to really produce the best possible textiles, so that recycled fibers are even better than native fibers." But achieving this goal isn't simple. Cotton and other fibers are often blended with polyester in fabrics such as "cotton-polyester blends," which complicates processing.
Previous research showed that many ionic liquids can dissolve cellulose. But the resulting material couldn't then be re-used to make new fibers. Then about five years ago, Sixta's team found an ionic liquid -- 1,5-diazabicyclo[4.3.0]non-5-ene acetate -- that could dissolve cellulose from wood pulp, producing a material that could be spun into fibers. Later testing showed that these fibers are stronger than commercially available viscose and feel similar to lyocell. Lyocell is also known by the brand name Tencel, which is a fiber favored by eco-conscious designers because it's made of wood pulp.
Building on this process, the researchers wanted to see if they could apply the same ionic liquid to cotton-polyester blends. In this case, the different properties of polyester and cellulose worked in their favor, Haslinger says. They were able to dissolve the cotton into a cellulose solution without affecting the polyester.
"I could filter the polyester out after the cotton had dissolved," Haslinger says. "Then it was possible without any more processing steps to spin fibers out of the cellulose solution, which could then be used to make clothes."
To move their method closer to commercialization, Sixta's team is testing whether the recovered polyester can also be spun back into usable fibers. In addition, the researchers are working to scale up the whole process and are investigating how to reuse dyes from discarded clothing.
But, Sixta notes, after a certain point, commercializing the process doesn't just require chemical know-how. "We can handle the science, but we might not know what dye was used, for example, because it's not labeled," he says. "You can't just feed all the material into the same process. Industry and policymakers have to work on the logistics. With all the rubbish piling up, it is in everyone's best interest to find a solution."
A press conference on this topic will be held Monday, April 3, at 9:30 a.m. Pacific time in the Moscone Center. Reporters may check-in at the press center, South Building, Foyer, or watch live on YouTube http://bit.ly/ACSLive_SanFrancisco. To ask questions online, sign in with a Google account.
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The researchers received funding support from the European Union's Trash-2-Cash project and the Finnish government.
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Title
Novel recycling process for cotton polyester blended waste textiles
Abstract
In less than ten years, the global population will exceed 8 billion people. The spread of urban areas and consequences of global warming simultaneously decrease the area of arable land.1 Cotton industry will consequently compete for acreage with food and biofuels.2 The creation of a circular economy therefore seems indispensable. Currently, the lack of adequate recycling strategies prevents the usage of worn out textiles as a source of raw material for new value added products.3 Textiles on the market represent almost exclusively multi-component garments with cotton polyester blends being the most prominent mixture, which poses severe challenges onto their recycling due to their inherent heterogeneity.4 Recently developed recycling strategies propose the dissolution of the cellulosic component in N-methylmorpholine N-oxide5,6 or imidazolium derived ionic liquids.7,8 Although these approaches suggest subsequent fiber spinning, they fail to demonstrate the feasibility of the concept. The process presented herein aims to overcome these weaknesses in state-of-the-art methodologies. A superbase-derived ionic liquid dissolves the cotton component selectively without any significant degradation of the residual polyester. After filtration, the cellulose solution is subjected to dry-jet wet spinning to obtain Lyocell-type fibers, while the recovered polyester can be fed back to conventional industrial processes such as melt spinning. The ionic liquid is regained by thin film evaporation.
1 Hämmerle, F. M. Lenzinger Berichte 2011, 89, 12-21.
2 The Fiber Year 2015.
3 Briga-sà, A.; D. Nascimento; N. Teixeira; J. Pinto; F. Caldeira; H. Varum; and A. Paiva. Constr. Build. Mater. 2013, 38, 155-160.
4 Muthu, S.S., Li, Y., Hu, J.Y. et al. Fibers Polym. 2012, 13, 1065-70.
5 Negulescu, I. I.; H. Kwon; B. J. Collier; J. R. Collier; A. Pendse. Text. Chem. Color 1998, 30 (6), 31-35.
6 Brinks, G. J.; G. H. Bouwhuis; P. B. Agrawal; H. Gooiljer. W.O. Patent 2014/081291 A1. May 30, 2014.
7 Lv, F.; C. Wang; P. Zhu; C. Zhang. Carbohyd. Polym. 2015, 123, 424-31.
8 De Silva, R., X. Wang, N. Byrne. RSC Adv 2014., 4, 29094-98.