Polyester recycling has an elastane problem.

A research team led by Donghua University says it has developed a chemical recycling process capable of breaking down polyester in blended textiles while leaving more than 96 percent of accompanying cotton and spandex intact, potentially addressing one of the more stubborn obstacles to recycling stretch apparel.

The solvent-based process completely depolymerized polyethylene terephthalate, or PET, at 80 degrees Celsius in 80 minutes and recovered its primary building block, terephthalic acid (TPA), at roughly 99 percent purity and 99 percent monomer recovery, according to a study published in the Aug. 1 issue of the Journal of Hazardous Materials.

More consequentially for textile recycling, the researchers demonstrated the process on both PET/cotton and PET/spandex fabrics without similarly breaking down the companion fibers.

The distinction matters because blended fabrics remain difficult feedstocks for textile-to-textile recycling. Polyester and cotton are already challenging to separate efficiently, but even relatively small amounts of elastane can further complicate recycling because chemical treatments designed to attack PET may damage or destroy the polyurethane-based stretch fiber at the same time.

Previous research cited by the Donghua team, for example, achieved high polyester monomer recovery from PET/spandex through guaiacol-assisted methanol alcoholysis but completely depolymerized the spandex. That process, conducted at 120 degrees Celsius, yielded 94 percent dimethyl terephthalate and 98 percent ethylene glycol, according to the Donghua researchers.

The new approach instead attempts to exploit the different chemical susceptibilities of the polymers.

Researchers combined ethylene glycol and potassium hydroxide with sulfolane, a polar aprotic solvent commonly used in industrial chemical processes. They found that sulfolane altered the hydrogen-bonding environment around ethylene glycol while swelling the PET matrix, making it easier for reactive species to penetrate and attack polyester’s ester bonds.

The team investigated the mechanism using in-situ Fourier-transform infrared spectroscopy and density functional theory calculations. It also compared sulfolane with several other solvents, including dichloromethane, tetrahydrofuran, 2-methyltetrahydrofuran and dimethyl sulfoxide.

Under optimized conditions, PET was completely depolymerized at 80 degrees Celsius within 80 minutes. The researchers reported recovering more than 96 percent of the accompanying cotton and spandex while preserving the fibers’ structural integrity.

That selectivity could be more important than the polyester yield itself.

Chemical recycling technologies can already produce high-quality PET monomers under controlled conditions. Mixed textile waste presents another problem: recovering one polymer is of limited circular value if doing so destroys everything attached to it.

The study describes the recovered cotton and spandex as structurally intact, but that does not by itself establish whether the fibers retain the mechanical performance necessary for textile-to-textile reuse.

The researchers tested more than pristine polymer. Materials included waste PET fabric, PET/cotton fabric and PET/spandex fabric supplied by textile manufacturer Yuyue Home Textile, as well as PET foam and bottles. The process was also evaluated against other polyester-family materials, including polylactic acid, polybutylene adipate terephthalate and polybutylene terephthalate.

The system also removed dyes during PET depolymerization, another potentially useful characteristic for textile waste.

Colorants, finishes and other additives can complicate chemical recycling and affect the quality of recovered materials. The Donghua researchers reported that their process enabled simultaneous polymer separation and decolorization, with dyes moving into the solvent phase rather than remaining with the recovered fibers.

The comparatively mild operating conditions are another point of distinction. The study contrasts its 80 degrees Celsius treatment with PET hydrolysis and glycolysis processes cited in the literature that require temperatures above 120 degrees Celsius, including examples operating at 210 degrees Celsius for four hours and 250 degrees Celsius for 2.5 hours.

Lower temperature, however, does not by itself establish that the process would consume less energy, cost less or carry a smaller environmental footprint at commercial scale.

Sulfolane in particular deserves scrutiny.

The researchers describe the solvent system as green and recyclable, citing sulfolane’s low volatility, thermal stability and ability to be reused. But the solvent’s environmental and health profile is more complicated. Sulfolane has received less favorable assessments under more recent solvent-selection guidance, including concerns around reproductive toxicity.

For an industrial textile-recycling process, the environmental case would therefore depend in part on how efficiently the solvent could be recovered and recirculated while limiting worker and environmental exposure.

The researchers reported that the system maintained its performance through repeated solvent-use cycles. The laboratory results, however, do not establish the recovery efficiencies, containment systems or economics that would be required at commercial scale.

The work builds on earlier research from Donghua professor Ye Chen’s group examining selective polyester recycling.

In another study published this year, researchers used a DMPU/ethylene glycol-potassium hydroxide system to completely convert PET in polyester/cotton blends at 70 degrees Celsius in 30 minutes, recovering TPA while preserving the cotton component.

The sulfolane work broadens that problem from separating polyester and cellulose toward handling a wider assortment of mixed polyester waste, including stretch textiles.

Whether it can make the same leap outside the laboratory remains unanswered.

The study does not include a commercial-scale demonstration or establish the economics of processing mixed textile waste. Nor does recovering a fiber with its structure intact necessarily establish that it retains sufficient mechanical performance to return to clothing.

The published materials included waste PET fabric and manufacturer-supplied PET/cotton and PET/spandex fabrics, but the study does not establish that the blended samples were post-consumer garments.

Real post-consumer garments could create still more complications. Apparel can combine PET and elastane with nylon, acrylics, coatings, printing inks, water-repellent finishes, adhesives, metal components and contaminants accumulated during use.

Still, the experiment tackles a problem that becomes more significant as textile recyclers move beyond relatively clean, single-fiber feedstocks.

A process that recovers polyester monomers while merely relocating the recycling problem to damaged cotton or elastane would offer limited progress toward textile-to-textile circularity. The Donghua work suggests selective chemistry may offer another route: dismantling the polymer a recycler wants without dismantling everything else along with it.

Whether those surviving fibers are good enough to become clothing again may now be the more important test.