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The molecular structure of polyesters enables a wide spectrum of recycling approaches, both mechanical and chemical. Somewhere in the middle ground between solvent-based extraction approaches and advanced recycling technologies that break down molecules all the way back to the monomer level, sits a company called .

Macrocycle, founded by CEO Stwart Peña Feliz and CTO Jan-Georg Rosenboom, is developing a process based on the phenomenon of ring opening polymerization.

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The process uses specialized solvents, catalyst systems and thermodynamics to convert polymer molecules into macrocyclic oligomers, selectively extract them and then upgrade them to a linear PET structure.

Macrocycle is looking at both packaging waste and textile waste as feedstock materials, and is processing both at its pilot facility. While mechanical recycling is well established and effective at processing clear bottle flake, other feed streams are more challenging. “We’re not going after those clear flakes, we’re going after the bad stuff, stuff the mechanical recyclers don’t want. And we are going after the emerging supply of textile waste,” Rosenboom says.

CTO Jan-Georg Rosenboom and CEO Stwart Peña Feliz compare their upgraded PET to postconsumer waste samples. Source: Macrocycle.

Textile waste is not widely recycled, mostly ending up in a landfill or incinerator in the United States, so the polyester textile waste that is widely available is postindustrial. But that could change. In 2022, which makes it illegal to dispose of textiles in trash. 

“I think collection of textiles will emerge, and there are folks looking at that waste stream coming online and becoming viable, but they need to figure out how to upgrade the polymer quality and how to remove the impurities that are present,” Rosenboom says. Macrocycle is working with its partner a waste collector that brings in textile waste from various brands. Macrocycle analyzes the waste for contaminants before and after recycling to confirm its process removes them.

Macrocycle’s processing system with engineer Dr. Andres Granados Focil. Source: Macrocycle

According to Rosenboom, the process is inherently purifying, such that even if a feedstock contains unwanted or nonintentionally added substances (NIAS), these are removed by the Macrocycle recycling process itself. Testing conducted thus far has found the resulting rPET product to be free of BPA and to have only low levels of acetaldehyde.

Rosenboom’s work in ring opening polymerization began as part of his Ph.D. research at ETH Zurich. At that time, the focus was on finding processes for polyethylene furaonate (PEF), a bio-based polyester. Later, this technology formed the foundation for Macrocycle, which Rosenboom formed with Feliz at MIT. “Soon enough I realized this fascinating ring opening-ring closing chain equilibrium chemistry is applicable not only to bioplastic waste but also to existing plastic waste which is already out there,” Rosenboom says. Instead of PEF, Macrocycle focuses on recycling processes for PET, going after a polyester already ubiquitous in the market.

In discussions with potential customers, Macrocycle has found that requirements such as viscosity can vary, especially between textile and packaging applications. Macrocycle can produce materials of different chain lengths to meet these needs. “We can tune our process very well, and are excited to offer our tailored solutions to industries,” Rosenboom says.

Based on technical and economic analysis, the company expects to see both environmental and economic benefits from skipping the repolymerization steps necessary in competitive technologies which go completely back to monomer. According to Rosenboom, much of the energy demand lies in heating and cooling the solvent systems, whereas depolymerization methods incur significant costs in the purification of monomers. “We believe we can be competitive with fossil-grade PET,” Rosenboom says, “so, the breakthrough is: lower energy demand and lower cost.” Even customers that are not otherwise incentivized to use recycled materials may take notice at the prospect of cheap resin.

Macrocycle recently raised $6.5 million in funding to commercialize its PET recycling technology, which the company will use to expand operations and scale up pilot capacity. With the completion of this round, Macrocycle will be producing larger quantities of material so it can work with customers to develop products such as packaging and textiles. Currently, the company has more requests to test material than it can supply. Before moving to industrial scale, another fundraising round will need to be completed, currently targeted for 2026 or 2027.

Dr. Eduardo Terreni, research engineer at Macrocycle, displays polyester resin (right) made from colored polyester textile waste (left). Source: Macrocycle.