Breakthrough solvent unlocks true recycling for blended fabrics

Modern wardrobes grow at a pace unseen in earlier decades. Global fiber output now surpasses 100 million tonnes each year, with strong growth fueled by rapid production cycles and short garment lifespans.

Polyester supply rises fastest, while cotton remains the second-largest contributor to textile flow.

Expansion on such a scale produces an immense amount of mixed waste. Part of that waste contains blended fabrics that do not separate easily.

Long-standing disposal habits strain ecosystems, and pressure for sustainable solutions continues to intensify. A research group at TU Wien explored a new separation route for fabric recycling.

Polyester waste and the need for recycling

A large portion of global waste now comes from fabrics containing intertwined polyester and cotton fibers.

Polyester offers strength and durability, while cotton offers softness and comfort. Blended fabrics combine those qualities and create garments with desirable performance.

However, once discarded, mixed fibers hinder recycling progress because conventional removal of one component often harms the other. Mechanical force cannot free individual fibers, and harsh solvents damage useful material.

Gentle biological methods remain possible but break polymer chains and reduce material quality. A search for a mild yet effective solvent solution continued for many years without strong progress.

A new concept for fabric recycling

A promising route emerged from two familiar substances. Menthol and benzoic acid remain solid under normal conditions yet form a liquid mixture once heated. That mixture belongs to the deep eutectic solvent class.

“What may be surprising at first: both menthol and benzoic acid are solid at room temperature. But together they form a liquid a so called deep eutectic solvent. This novel liquid is a powerful, non-toxic and easy to produce solvent with a wide range of possible applications,” noted study co-author Andreas Bartl.

A sample made from post-business sheets containing polyester and cotton underwent careful testing. Material analysis revealed near-equal shares of both fibers. Gentle heating of the solvent created a clear liquid able to dissolve polyester while leaving cotton untouched.

Organic origin, low toxicity, and simple preparation set this mixture apart from traditional chemical systems.

Separation in minutes

The solvent reached full effectiveness once heated to 216 °C. Polyester dissolved within a total contact time of five minutes across two short treatment stages. Cotton remained as intact fabric.

Cooling produced solid polyester again as precipitation occurred naturally. Filtration and washing removed residual solvent.

Recovery reached full yield for cotton and nearly full yield for polyester. Handling during drying and filtration likely produced minor polyester loss.

Experiments across a wide range of liquid volumes revealed stable performance even with modest solvent amounts.

A ratio near one to thirty ensured complete removal of polyester from the blend. Lower ratios still produced high yields and demonstrated robust solvent action.

Material integrity was preserved

Microscopy revealed clear differences between original polyester fibers and original cotton fibers. Polyester exhibited smooth cylindrical surfaces, while cotton displayed natural twists and irregular contours.

After treatment, only cotton fibers remained in the recovered fabric. No structural harm appeared on fiber surfaces.

Thermal studies confirmed undisturbed material properties. Cotton displayed the same decomposition pattern observed in untreated cotton. Polyester displayed an identical melting temperature before and after recovery.

Crystallinity of recovered polyester reached 40 percent, which aligns with standard polyester reported in earlier research.

A slight increase in crystallinity likely emerged from polymer chain rearrangement during dissolution and precipitation.

Chemical stability revealed

Spectral analysis offered further confirmation. Polyester signals vanished from the treated blend and returned unchanged within recovered polyester.

Cotton signals remained stable in all samples. No unexpected chemical peaks formed during the procedure.

A faint peak unique to mixed fabric appeared in untreated blends and in solvent-treated blends before separation but disappeared from recovered polyester.

Pure cotton samples, untreated or treated, did not contain that signal. Overall spectral clarity confirmed full removal of polyester from cotton without new reactions.

Strong preservation of polymers

Mechanical tests evaluated the suitability of recovered cotton for new textile applications. Strength and elongation declined slightly compared to untreated cotton.

However, measured values remained within accepted ranges for normal cotton fibers. Cotton therefore remained suitable for yarn production after passing through a standard tearing line.

Polyester also met the conditions required for regranulation and further thermoplastic processing.

The combined results demonstrated strong preservation of both polymers. No method in common use reached such efficiency without harsh chemicals or heavy degradation.

Large-scale fabric recycling

Recovered cotton offered a clean fibrous network for new yarns, nonwovens, insulation materials, and cellulose-based processes.

Recovered polyester provided feedstock for packaging, filtration components, technical fibers, and apparel manufacturing. Short treatment times and mild chemical conditions supported high-quality outputs.

One limitation involved the high operating temperature required for full dissolution. Energy use rises sharply once temperatures exceed two hundred degrees Celsius. Current work explores methods to improve energy efficiency and solvent reuse.

Laboratory trials already show strong promise, and minor adjustments may lower required temperatures.

Solvent systems based on deep eutectic mixtures carry good biodegradability, low toxicity, and affordable preparation. These qualities strengthen industrial potential further.

The future of fabric recycling

A sustainable fashion landscape demands solutions that protect both natural fibre sources and synthetic polymer chains.

A solvent system containing menthol and benzoic acid opens a new route for rapid separation of polyester and cotton.

Mixed fabrics that once resisted clean recycling now enter a process that preserves material integrity.

Complete cotton recovery and near-complete polyester recovery allow re-entry of both components into high-value production streams.

Modern textile systems rely on constant renewal. A circular approach can grow only when blended fabrics stop becoming permanent waste. The method introduced at TU Wien offers a powerful foundation for that transition.

The study is published in the journal Waste Management.

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