Polyester and polyethylene terephthalate (PET) are two different names for the same polymer. PET plastics have been recycled into ‘new’ plastics or fibres for decades now, using thermomechanical processes. This technique can also be used to recycle polyester textiles, and may offer a much-needed, short-term, circular solution for synthetics.

Thermomechanical recycling is one of three main methods used to recycle textiles into textiles. It sits in an intermediate category between mechanical and chemical processes. The mechanical shredding and ‘refibrising’ of textiles, works well for wool and cotton, but not so much for synthetics; it leads to shorter fibre length. A 2024 report by EU-funded research project CISUTAC found that mechanically recycled synthetic fibres “tend to lose 75% of their value and can generally not be used to remanufacture new clothes, unless they are mixed with virgin fibres”.

Chemical recycling processes draw high levels of media attention and generous funding. But these so-called ‘advanced’ techniques have yet to scale in some cases, and to reach technical maturity in countless others. It could be another decade or so before these methods become mainstream. Furthermore, processes that depoly- merise synthetics require a great amount of energy, both to break down the polymer chains and to build them back up. 

Thermomechanical recycling, the method commonly used for PET plastics, are fully operational, but need specific elements to handle textile waste. Scraps of fabric, for one thing, do not ‘flow’ like plastics, and for another, the heating phase of the process degrades the polymer to some extent. However, it requires less energy than chemical recycling, and with the development of machines made for fibrous waste, it could be the unsung hero of a circular solution for synthetic textiles.

The switch from plastics to textiles 

Thermomechanical recycling is also known as melt recycling or pelletising, as it generally produces polymer chips or granules. While beverage bottles are chopped into flakes, fabrics are cut into small pieces, which requires special feeders capable of handling the low bulk density of textiles. The difference between PET plastics and polyester fibres is that PET is “a high-quality polyester with a high molecular weight, almost 10 times that of a polyester fibre,” says Gloria Yao, project development director at the Hong Kong Research Institute of Textiles and Apparel (HKRITA). “Thermomechanical recycling is an ecological and an economic process,” she says, “but it does not yield as high a quality as the rPET made from bottle flakes. Companies will need to blend bottle chips with polyester chips to achieve fibre requirements, and this is not considered a true closed loop.”  

Once melted and filtered, plastic flakes are condensed to achieve a certain viscosity. This, says Josse Kunst, sales manager for Dutch company CuRe, is a critical point. “Textiles may, to use an analogy, have the viscosity of peanut butter, making it difficult to filter out contaminants. The fibres in a textile can have different melting points and various finishes. Even spin sizing can alter their viscosity once melted, rendering thermomechanical recycling of textiles limited to very pure textile sources only.” CuRe has developed a method that breaks down polyester into its oligomers, which he says are polymers with shorter molecular chains. “Instead of peanut butter, our technology results in a substance with the viscosity of olive oil, which is easier to filter and purify.” Chemical recycling down to monomers, he concedes, yields the purest form of recycled polymers, but it also has the highest carbon footprint. “CuRe seeks to strike a balance between the two,” he says. 

Thermomechanical processes require ‘high- quality’ feedstock, like mechanical and chemical ones, notes Ashley Holding, sustainability expert at Circuvate, a sustainability and circular economy consultancy. He says that the presence of elastane or even cotton in the feedstock can be a problem, as well as unmelted components. He believes this method is mostly used to recycle production waste, and notes that there is often little transparency in the source of feedstock. 

Adapting machinery 

Machinery makers, too, have been working on adapting PET recycling lines to textiles. A solution developed by German company Gneuss skips the granulation stage. Erema, another German engineering company, has also simplified the process by removing some operations. “With our PureLoop technology, a client can place the textiles or garments directly on the conveyor, without cutting them into small pieces,” Merlijn van Essen, sales manager, tells us. Once melted, filtered and pelletised, the chips can be used to make filaments or plastics. Blended waste materials will not necessarily be suitable for reuse as fibres. “They will have different viscosities that would cause too many problems in filament production,” he says. For monofibre waste, such as pure polyester, “after filtration, the melt is fed in a liquid-state into a polycondensation (LSP) reactor. This reactor increases the intrinsic viscosity (IV) levels to 0.7 or 0.8 so that the pellets can be made into 100% recycled fibres of up to 2 dtex. The advantage of this process is that the polymer is brought back to an almost virgin state”. 

The company is working on adapting the PureLoop system to certain types of fibre blends, such as polyester with low amounts of elastane, and has achieved positive results, according to van Essen “We are currently seeking to optimise filtration which might make it possible to process post-consumer materials.” Erema founded PureLoop in 2014, and has since sold just over 200 custom-made machines in several sectors, including textiles. 

A specially designed PureLoop line has been in operation for a year now at Project Re:Claim, in the UK, a venture initiated by the Salvation Army Trading Company (SATCoL) and Project Plan B, a company founded by Tim Cross. A garment designer and manufacturer specialising in workwear and uniforms, Mr Cross is intent on phasing out virgin polyester and replacing bottle-flake polyester with textile rPET. In addition to the need for specially designed equipment, “we also learned the clothing needed to be designed so that it can be easily recycled,” he tells us. 

The need for monomaterial design 

For Mr Cross, monomaterial design is simple: “Take a polo shirt, choose polyester buttons instead of nylon ones and sew it with polyester threads. When a large supermarket makes this switch, we are talking of millions of garments. If it were applied worldwide, it would have an incredible impact.” To encourage the transition to monomaterial garment design, he founded the Circular Textile Foundation that assists brands in developing single-fibre products and delivers a special label and certification mark.  “Every single recycler needs products that are designed to be recycled. Until now, there has been no traceability on a product before it reaches a recycling plant. We need to change that.” 

Re:Claim’s facility in Kettering, on a Salvation Army garment collecting site, has a capacity to recycle 20 tonnes a day, and although the company operates at half of that, all of its pellet production is sold out, says Mr Cross. But its recycled textile granules are typically mixed with 25% to 50% plastic-flake pellets. “In time we’ll be able to produce high-quality yarns from 100% textile pellets,” he expects. The relatively low cost of thermomechanical recycling lines, he says, could make it an easily replicable solution worldwide. Mr Cross sees potential in installing units where cutting waste is produced, in Bangladesh or the Far East. “We could install smaller thermomechanical units where there is feedstock. The machines cost €2-€3 million and can be rapidly up and running and profitable. Unlike chemical recycling, we don’t need expensive chemists to run the machines.”

Earth Protex, a company based in Canada, with divisions in China, Portugal and the US, uses thermomechanical methods to make its Tex2Tex recycled polyester staple fibres and filaments. The company optimises polymer quality with its ThermoMechanical Reactor, which “removes contamination, and homogenises and the extends polymer chains,” says Samuel Goldstein, chief operating officer.

Textile waste (mostly post-production) is sorted into light and dark shades. “For coloured fibres, we add dope-dye masterbatch (pigment) to homogenise colour and offer a low-impact fibre,” he says. “This solution yields a more uniform colour than mechanically recycled fibres.”

Earth Protex maintains 60,000 tonnes per year of Tex2Tex rPET production capacity in China, and is preparing to install an additional 30,000 tonnes per year facility outside of China. The new facility will focus on post-consumer garment recycling and will pilot next generation Tex2Tex bolt-on technologies, including mixed polymer separation and dye removal and recovery.

Unifi, a major supplier of virgin and recycled PET plastic polyester, announced last summer that it was scaling up its capacity to recycle textile waste in its Repreve platform. Its Textile Takeback programme allows it to take in post-industrial and post-consumer textile waste that is sorted by light and dark colours. Unifi now offers white-dyeable or dope-dyed black recycled polyester fibres. The company says that at least half of the composition of the 100% recycled yarns comes from textile waste and is mixed with rPET from plastic.

Repreve Takeback yarns are the result of an “advanced thermomechanical process, augmented with a material-grading and purification system, in addition to strengthening, colour and traceability technologies,” says Meredith Boyd, product development manager for Unifi. “We are working with global brands to take back their waste and keep materials in circulation longer.”

“Thermomechanical recycling is efficient, scalable, and does not require breaking polymers down into molecular chains,” she says. “This makes it faster and less energy-intensive than other technologies. Before moving to chemical recycling, LCA data suggests first considering if a material can be thermomechanically recycled.”  

Re&Up, a new venture created by Turkey-based conglomerate Sanko, has ambitious plans to scale up textile-to-textile recycling using mechanical, thermomechanical and hydrothermal technologies, all developed in-house. “What sets us apart is our ability to separate different fibre types from blends, including elastane, and remove dyes. Our decolourisation capability is a real game-changer,” says Andreas Dorner, who heads the new division, which is based in the Netherlands. “We use thermomechanical methods because they allow us to remove colours from fabrics and fibres, which is key to achieving high-quality recycled materials.” For blended post-consumer garments, Re&Up sorts and separates the fibres, “turning them into spinnable recycled cotton and polyester chips specifically for textile-to-textile use.” Currently, Re&Up has a capacity to recycle some 80,000 tonnes annually, but its plan moving forward is to reach 1 million tonnes annually by 2030. 

Newcomers to textile-to-textile recycling, such as Re:Claim and Re&Up seek to phase out PET plastics from the recycled polyester stream, but it is not clear what proportion of recycled plastics the rPET yarns sold on the market today contain. 

Until volumes of sorted monomaterial feedstocks are available, this recycling method will probably mostly be used to process production waste. But, North America and Europe generate more end-of-life clothing than manufacturing waste. As Jeanne Meillier, a project manager at French eco-research hub Euromaterials, says: “Post-consumer waste is a European problem, we need solutions to recycle it locally. It is not worth exporting it to Asia.” She adds that “chemical recyclers need large volumes to make their systems viable, in the order of 20,000 tonnes.” 

For Tim Cross at Project Re:Claim, thermo- mechanical recycling works, but would benefit from garment redesigns. “I address the issue from the point of view of a garment designer, and with the aim of setting up a system that works now, not in 15 years.”
“Thermomechanical methods are more energy efficient and should be the first step in a recycling process,” agrees Karla Magruder, founder of Accelerating Circularity. But, she says, these materials will eventually need to be chemically recycled, as “over time thermomechanical recycling degrades the polymers.” 

Proponents of thermomechanical recycling point out that the technology is operational, the machinery compact and less costly than chemical depolymerising equipment. Units could be installed where waste is generated, creating recycled chips to produce new fibres or for use in injection moulding. This unsung hero of recycling is potentially a more versatile and agile solution. 

PureLoop’s thermomechanical recycling machinery is said to be flexible and low-energy. Developed for pure synthetic fibres, the company has successfully tested blends of polyester with low amounts of elastane.
Credit: PureLoop by Erema

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