The skyrocketing quantity of textile waste fast fashion is considered one of the biggest technological problems in the circular economy. This is also because the technical problems in recycling are still unresolved. A research group from Vienna has shown how fibre-to-fibre recycling might work in the future.

There is steadily mounting pressure to find a solution. About two years ago, the EU passed Directive 2018/851, set to enter into force in 2025. From then on, a separate collection of used textiles will be mandatory. Although the concrete recycling rate is still being negotiated, one thing is already clear: without new technical solutions, the goal of feeding used textiles back into the circular economy cannot be achieved.

On the one hand, the quantities of used textiles are growing at an ever-faster rate; on the other, the previous recycling channels are collapsing. Fast fashion produces more and more clothes in less and less time. A decade ago, three or four collections a year sufficed. Today, they already appear at monthly, even almost weekly, intervals.

The challenge of used textile

In 2009, the garment industry recorded about EUR 178 million in sales. In 2019, sales had already risen to EUR 221 million despite generally falling clothing prices. The use of raw materials demonstrates the fast pace of the industry even more clearly. From 2000 to 2018, the output of the most important source materials for the garment industry, namely synthetic polymer fibres, cellulose chemical fibres, and cotton, nearly doubled worldwide from 56 million tonnes to more than 100 million tonnes.

Simultaneously, the previous recycling mechanisms, which were already questionable anyway in terms of their social and ecological compatibility, had completely imploded. The overwhelming majority of used textiles collected in Europe has been exported to Africa in recent decades. For charitable organizations, the sale of used textiles to wholesalers, who then resold them locally, was a good source of income for a long time. A less pleasant result has been that these mass exports have ruined local African textile production. Kenya, therefore, imposed a ban on used clothing imports in 2020. However, it had to do so under the pretext that COVID-19 posed a risk of infection, probably to avoid alienating the many mini-merchants dependent on the used textile business.

But the main reason why the export-based recycling of used textiles has ground to a near halt in the meantime has to do with the decline in prices. In 2019, exporters could count on a price of EUR 500 to EUR 600 per tonne; then the price plummeted to EUR 200. Today, traders are increasingly stuck with their containers. Industry observers say that two phenomena are responsible for this trend: increasing exports from the United States and COVID-19. For lack of other possible distractions during the lockdown, countless people began doing something they had kept postponing before, namely, cleaning out their wardrobes and homes.

Research on the future from Vienna

Andreas Bartl is keenly aware of all these developments. For years, this process engineer at the Technical University of Vienna and his team have been researching possible treatments for used textiles that would allow them to become a secondary raw material. “The current solutions are unsatisfactory across the board: landfill or incineration is contrary to the idea of the circular economy. Exports to the Third World are socially incompatible and besides, the clothes are worn again by others eventually end up in the trash anyway.”

The task that Bartl has taken on is by no means an easy one. After all, textiles are rarely made of a single material. And even if they are, recycling them is anything but simple. But there are processes in the meantime that help to produce high-quality lyocell fibres from used textiles made solely of cotton.

Generally speaking, however, clothing is made of fabrics containing at least two components. They are very often cotton on the one hand and PET on the other. When it comes to recycling these fabrics, the first challenge is to separate these components from each other. The process used by Bartl’s research group relies on enzymes.

In nature, there are enzymes that break down cellulose, the natural polymer in cotton, into glucose. If cotton-PET blends are treated with a dispersion comprising water and these enzymes, the cotton turns into glucose (sugar) and the PET components of the fabric are left behind. For this enzymatic hydrolysis process to work effectively, however, the used textiles must be pulverised beforehand.

Successful pilot project

Glucose produced during enzymatic hydrolysis can be put to subsequent use for energy metabolism or for the synthesis of new chemical compounds. The remaining plastic fractions undergo further processing: PET is fusible, so it can be granulated into rPET flakes, from which new fibres can then be spun. Non-fusible materials, i.e. aramids such as Kevlar, for instance, are found mostly in protective clothing and do not allow this intermediate step to be taken. Cotton-aramid blends are therefore broken down to a lesser extent prior to hydrolysis, so a certain fibre length can still be maintained for reprocessing.

In a pilot project, the research team from the Technical University of Vienna has now successfully shown how fibre-to-fibre recycling of used textiles might function in the future. First, the group used enzymatic hydrolysis to isolate the PET fibres from PET-cotton blended fabric. The resulting granulate was spun into fibres, with recycled granulate being mixed with primary granulate. At the end of the tests, the portion of recycled granulate was able to be increased to 50%. Consequently, the PET yarn and cotton yarn were processed together in the same way as in the production of textiles made of new PET material.

The success of the project is evident from the subsequent weaving of the fabric, which was trouble-free, and also from the end product itself: a towel. “Its quality is hardly distinguishable from a towel made of primary material,” says project manager Bartl.

However, he is also well-aware that his project is just a small puzzle piece, albeit an important one, in the effort to solve the used textile problem: “Many garments consist of more than just two components and the more components there are, the more difficult it becomes to separate them from each other in such a way that they can be processed afterwards.”

For this reason, Bartl feels it is essential to take measures in advance. “It is important to use only materials that can be recycled relatively easily. We may even develop new materials that fit the bill. Above all, however, we must limit the volume of new textiles we produce and do so despite all the technology that we have and that naturally excites me as a process engineer.”


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