Modern wardrobes are expanding at an unprecedented rate, unlike any seen in previous decades. Global fiber production has now exceeded 100 million tonnes annually, with rapid production cycles and short garment lifespans driving this significant growth.

Source: Earth

Key Insights on Textile Production

• Polyester leads the surge in supply, while cotton ranks as the second-largest contributor to textile output.
• This expansive growth results in substantial mixed waste, including blended fabrics that are challenging to separate.

Long-standing disposal practices are placing stress on ecosystems, and the demand for sustainable solutions is mounting. A research team at TU Wien has investigated a novel method for fabric recycling.

Addressing Polyester Waste

A considerable portion of global waste now originates from fabrics that combine polyester and cotton fibers.

• Polyester is known for its strength and durability, while cotton provides softness and comfort.
• Blended fabrics leverage these qualities, resulting in garments with desirable performance attributes.

However, once discarded, these mixed fibers complicate recycling efforts, as the standard removal of one component can often damage the other. Mechanical methods are ineffective at separating individual fibers, and harsh solvents can harm valuable materials.

Gentle biological techniques remain viable but can break polymer chains, reducing material quality. The search for a mild yet effective solvent solution has persisted for years with limited success.

A Breakthrough in Fabric Recycling

A promising new approach has emerged using two well-known substances: menthol and benzoic acid. These compounds are solid at room temperature but become a liquid mixture when heated, classifying them as a deep eutectic solvent.

• Testing on samples from post-business sheets containing polyester and cotton showed nearly equal proportions of both fibers.
• Gentle heating of the solvent produced a clear liquid capable of dissolving polyester while preserving the integrity of cotton.

This mixture stands out due to its organic nature, low toxicity, and straightforward preparation compared to traditional chemical systems.

Swift Separation Process

The solvent reached optimal effectiveness at 216 °C, dissolving polyester within a total contact time of just five minutes across two brief treatment phases, while cotton remained intact.

Upon cooling, solid polyester reformed as precipitation occurred naturally, allowing for easy filtration and washing to eliminate residual solvent.

• Recovery rates achieved full yield for cotton and nearly full yield for polyester, with minor losses likely occurring during drying and filtration.
• Experiments across various liquid volumes demonstrated consistent performance, even with modest solvent amounts.

A solvent-to-fiber ratio of approximately one to thirty ensured complete polyester removal from the blend, while lower ratios still yielded high results.

Preservation of Material Integrity

Microscopic examination revealed clear distinctions between the original polyester and cotton fibers.

• Polyester fibers exhibited smooth cylindrical surfaces, whereas cotton fibers displayed natural twists and irregular contours.
• After treatment, only cotton fibers remained in the recovered fabric, showing no structural damage.

Thermal studies confirmed that the material properties remained undisturbed. Cotton exhibited the same decomposition pattern as untreated samples, while polyester showed no change in melting temperature before and after recovery.

The crystallinity of the recovered polyester reached 40 percent, consistent with findings in previous research.

Confirming Chemical Stability

Spectral analysis provided additional confirmation of the process's efficacy.

• Signals from polyester disappeared from the treated blend but reappeared unchanged in the recovered polyester.
• Cotton signals remained stable throughout, with no unexpected chemical peaks arising during the procedure.

A faint peak unique to mixed fabrics was present in untreated blends and solvent-treated blends before separation but vanished from the recovered polyester.

Pure cotton samples, whether treated or untreated, did not display that signal, confirming complete polyester removal from cotton without any new reactions.

Strong Preservation of Polymers

Mechanical testing evaluated the recovered cotton's suitability for new textile applications.

• While there was a slight decline in strength and elongation compared to untreated cotton, the values remained within acceptable ranges for typical cotton fibers.
• Thus, cotton is still viable for yarn production after undergoing standard tearing processes.

Polyester also met the necessary criteria for regranulation and further thermoplastic processing.

The combined results demonstrated excellent preservation of both polymers, outperforming conventional methods that often rely on harsh chemicals or significant degradation.

Advancing Large-Scale Fabric Recycling

The recovered cotton provides a clean fibrous network suitable for new yarns, nonwovens, insulation materials, and cellulose-based processes.

• The recovered polyester can serve as feedstock for packaging, filtration components, technical fibers, and apparel manufacturing.
• Quick treatment times and gentle chemical conditions support high-quality outputs.

One limitation is the high operating temperature required for full dissolution, which sharply increases energy consumption beyond 200 °C. Ongoing research aims to enhance energy efficiency and solvent reuse.

Laboratory trials show strong promise, and minor adjustments could potentially lower the required temperatures.

The Future of Fabric Recycling

A sustainable fashion landscape necessitates solutions that safeguard both natural fiber sources and synthetic polymer chains.

The menthol and benzoic acid solvent system paves a new path for the rapid separation of polyester and cotton.

Mixed fabrics that once resisted clean recycling can now undergo a process that maintains material integrity, allowing for complete cotton recovery and nearly complete polyester recovery.

This enables both components to re-enter high-value production streams, fostering a circular approach in modern textile systems. The method developed at TU Wien provides a robust foundation for this important transition.