Old t-shirts left over? UvA scientists recycle them into sugar and plastic
Worldwide, millions of tonnes of clothing are thrown away every year. UvA chemists came up with a solution. Using super-concentrated hydrochloric acid, they recycle clothes into sugar and plastic.
An average European discards about 11 kilos of textiles every year. Less than 1 per cent of that is recycled into new clothes, because the technology to do so has hardly been developed yet.
Now a new technique has been added. UvA researchers, in collaboration with chemical company Avantium, succeeded in recycling polyester and cotton clothing with highly concentrated hydrochloric acid. The results were published in the journal Nature Communications. According to Gert-Jan Gruter, associate professor at the UvA and chief technology officer at Avantium, it is “the first truly effective method to recycle both cotton and polyester with high efficiency”.
One hundred years old
The idea is simple. Clothes are brought together with hydrochloric acid, a highly corrosive acid that breaks down cotton into glucose, or sugar. The polyester is a plastic and does not break down due to the hydrochloric acid and can be easily fished out of the solution afterwards.
Polyester can then be recycled into new plastic, such as PET bottles or clothing. Glucose can be used in industry as a raw material for plastics, resins and solvents. Avantium can make good use of the glucose to make renewable plastics.
With the technique, Avantium is preparing for a world in which plastics are no longer made from petroleum but from plants. Currently, maize and corn are used to produce bioplastics, but in the future this may compete with the food supply, reasons Avantium.
“The technique is already a hundred years old,” explains Nienke Leenders, UvA PhD student and first author of the study. “Originally, it was designed to obtain sugars from wood. Avantium is working on that in a pilot plant in Delfzijl. And so the plan arose to try it out on clothing as well. And then specifically cotton and polyester, because that is the most common combination in the clothing industry.”
Horse remedy
And it worked. Leenders conducted the experiments in the UvA’s lab and an Avantium pilot plant. She put clothes in a reactor vessel saw the cotton dissolve into sugar. “It’s so incredibly simple. Within 24 hours, all the cotton has broken down.”
This does require super high concentrations of hydrochloric acid, 43 per cent to be precise. This is not without danger, as hydrochloric acid in such high concentrations can easily burn through many materials and cause serious burns. “You have to work with it carefully and make sure, for example, that there are no metal zips and buttons in the textiles, because these too rust away. But it can be done. Avantium has already shown that process with 230-litre reactors is safe.”
Such a high concentration of hydrochloric acid was needed for complete recycling. Leenders: “The cotton in clothing is very recalcitrant. At 37 per cent hydrochloric acid, we saw that only 20 per cent of sugars were recovered from cotton. At 43 per cent hydrochloric acid, it is almost 75 per cent. At a lower concentration, we cannot completely separate the cotton from the polyester, and it is precisely this complete separation that allows us to recycle both substances.”
And is it really sustainable to use hydrochloric acid – quite a horse remedy after all – for textile recycling? “In any chemical process, you need chemicals,” Leenders ponders. “Textiles are currently burnt or buried. I think the most important thing about sustainability is that you can reuse all your materials again.”
And that is possible, the hydrochloric acid can be reused, although the aqueous solution of hydrochloric acid and glucose is still proving difficult to separate on a commercial scale. “We are working on that, though. For now, we circumvent that step by first converting glucose into an intermediate, which we can later use again for Avantium’s products. We can separate that substance from hydrochloric acid.”
Textile mountain
According to Avantium’s cost-benefit analysis, the production process is feasible on an industrial scale. Leenders: “Since this year, the textile industry has also been obliged to contribute to the processing and recycling of textile waste. Of course, that also helps a lot.”
So in the future, does it mean you can now throw your clothes in the garment bin with peace of mind? “That’s already better than in the bin,” says Leenders. “I see this technology more as a cure for a problem. Eventually, we will also just have to buy less clothes.”
