Much of the technical difficulty in recycling worn-out clothes back into new clothing comes down to their composition. The majority of clothes in our wardrobes are made from a blend of textiles, with polyester the most widely produced fibre, accounting for a 54% share of total global fibre production, according to the global non-profit Textile Exchange. Cotton is second, with a market share of approximately 22%. The reason for polyester‘s prevalence is the low cost of fossil-based synthetic fibres, making them a popular choice for fast fashion brands, which prioritise price above all else – polyester costs half as much per kg as cotton. While the plastics industry has been able to break down pure polyester (PET) for decades, the blended nature of textiles has made it challenging to recycle one fibre, without degrading the other. (Read more about why clothes are so hard to recycle.)
By using 100% textile waste – mainly old T-shirts and jeans – as its feedstock, the Renewcell mill makes a biodegradable cellulose pulp they call Circulose. The textiles are first shredded and have buttons, zips and colouring removed. They then undergo both mechanical and chemical processing that helps to gently separate the tightly tangled cotton fibres from each other. What remains is pure cellulose.
After drying, the pulp sheet feels like thick paper. This can then be dissolved by viscose manufacturers and spun into new viscose fabric. Renewcell says it powers its process using 100% renewable energy, generated using hydropower from the nearby Indalsälven river.
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As the most common manmade cellulosic fibre (MMCF), viscose is popular because of its lightweight, silk-like quality. MMCFs have a market share of about 6% of the total fibre production. Dissolving pulp cellulose is used by the textiles industry to make around 7.2 million tonnes of cellulosic fabrics each year, according to Textile Exchange. But the majority comes from wood pulp, with more than 200 million trees logged every year, according to Canopy, a US non-profit whose mission is to protect forests from being cut down to make packaging and textiles, like viscose and rayon. Not only does Renewcell’s technology help keep forests intact, it also produces a higher pulp yield. “A tree is made up of different parts, including cellulose, but about 60% of it is non-cellulose content that you can’t do much with,” says Renewcell strategy director Harald Cavalli-Björkman. “Aside from a small loss, all of the waste cotton we use is turned into pulp.”
The mill has a contract with Chinese viscose manufacturer Tangshan Sanyou Chemical Industries for 40,000 tonnes per year, and is in talks with other large viscose manufacturers, such as Birla in India and Kelheim Fibres in Germany. Swedish fashion brand H&M, which produces three billion garments per year and is an early investor in Renewcell, has signed a five-year, 10,000 tonne deal with the pulp mill – the equivalent of 50 million T-shirts. Zara also partnered with Renewcell on a capsule collection in 2022.
“We want to build more mills,” says Cavalli-Björkman, adding that Renewcell hopes to be able to recycle 600 million T-shirts within a year – the equivalent of 120,000 tonnes of textile waste and a doubling of its current capacity. “But that is still very little compared to the global market for textile fibres. By 2030, we’re aiming for a capacity of 360,000 tonnes.”
But Renewcell’s technology has limitations: it can only recycle clothes that are made of cotton, with an allowance of up to just 5% non-cotton content. “Partly, it’s because it’s difficult to separate polyester, too much of which affects product quality, but also, we want to make sure we have a decent yield coming out the other end,” says Cavalli-Björkman. “With the exception of things that require exceptional durability like workwear or specific properties like waterproof clothing, the only reason for using polyester is because it’s cheap – yet with a huge cost to the environment. We’d like to turn back that tide, to get clean materials and fewer blends into circularity.”