Key Takeaways
- Polyester recycling via depolymerization recovers dimethyl terephthalate (DMT) monomer with 99%+ purity enabling indefinite repolymerization cycles
- Nylon hydrolysis recovers caprolactam from nylon-6 and hexamethylenediamine from nylon-6,6 with sufficient purity for virgin fiber regeneration
- Elastane (spandex) presents distinct challenge comprises 5-10% of synthetic textile waste but decomposes in polyester recycling processes unless pre-separated
- Mixed polyester-nylon blends now processable through selective depolymerization where polyester converts to monomers while nylon remains fibrous, enabling downstream separation
- Dye removal from synthetic fibers achieved through supercritical CO2 extraction or chemical oxidation, producing color-neutral fibers for any shade application
- Commercial facilities processing 20,000-50,000 tons annually of synthetic fiber waste increasingly achieve cost parity with virgin fiber production
The Unique Challenge of Synthetic Polymer Recycling
Synthetic fibers—polyester, nylon, acrylic, polypropylene—comprise approximately 65-70% of global fiber production and dominate contemporary apparel composition. Yet synthetic fiber recycling presents distinct challenges differing fundamentally from cellulose fiber (cotton, linen) processing. Understanding these challenges and emerging solutions is essential for developing effective recycling strategies for textile waste dominated by synthetics.
Polyester Recycling: The Primary Challenge and Solution
Polyester represents approximately 50% of global synthetic fiber production and dominates apparel composition. Polyester recycling has therefore become central to textile recycling advancement. The fundamental polyester recycling challenge: mechanical approaches degrade polymer chains and shorten fibers, limiting output to lower-value applications. Chemical approaches must break polymer bonds while recovering monomers of sufficient purity for repolymerization.
Polyester (polyethylene terephthalate, PET) comprises long chains of repeating ethylene terephthalate units. Depolymerization processes selectively break the ester bonds linking these units, recovering dimethyl terephthalate (DMT) or terephthalic acid (TPA) plus ethylene glycol (EG)—the monomer building blocks.
Glycolysis employs ethylene glycol or diethylene glycol with zinc oxide (ZnO) catalyst at moderate temperature (200-250°C). The glycol attacks ester bonds, progressively converting polyester chains to smaller fragments and eventually to monomers. Reaction times of 30-60 minutes achieve near-complete conversion.
Hydrolysis employs water with alkali or acid catalysts—typically sodium hydroxide or phosphoric acid—at elevated temperature (150-180°C) and pressure. Water molecules attack ester bonds, progressively hydrolyzing polymer chains. Hydrolytic approach requires careful process control but achieves high monomer yield.
Methanolysis employs methanol with zinc acetate or other catalysts. Methanol reacts with ester bonds, directly producing dimethyl terephthalate (DMT) and ethylene glycol simultaneously. Loop Industries’ proprietary methanolysis achieves commercial scale processing 20,000+ tons polyester waste annually.
All three approaches achieve monomer recovery with purity exceeding 99%, sufficient for direct repolymerization into virgin polyester fiber. This achievement represents critical breakthrough: polyester can now recycle indefinitely without property degradation.
Nylon Recycling: A Different Chemistry
Nylon—polyamide—comprises approximately 4-5% of global fiber production but is increasingly used in high-performance apparel and technical textiles. Nylon recycling presents distinct chemistry. Rather than ester bonds, nylon comprises amide bonds—different chemical linkage requiring different depolymerization approach.
Nylon-6 hydrolysis via hot water and catalysts achieves depolymerization yielding caprolactam monomer—the building block for nylon-6 fiber. Caprolactam purity of 95%+ is achievable, enabling repolymerization.
Nylon-6,6 hydrolysis is technically more challenging. Nylon-6,6 comprises two distinct monomers—hexamethylenediamine and adipic acid—that must be separated during recovery. Recent advances in selective hydrolysis achieve recovery of both monomers with sufficient purity for virgin polyamide production.
The challenge in nylon recycling: lower historical demand has driven less development than polyester chemistry. Fewer commercial-scale facilities exist. Industrial infrastructure less mature. However, nylon recycling is progressively advancing as demand increases.
Elastane (Spandex): The Contaminant Challenge
Elastane (synthetic rubber, polyurethane-based fiber)—trade-named Spandex in North America, Lycra globally—comprises 5-10% of synthetic textile waste and presents exceptional recycling challenge. Elastane provides stretch and recovery properties enabling fitted apparel. Yet elastane decomposes in standard polyester recycling chemistry, releasing volatile organic compounds and potentially damaging processing equipment.
Pre-separation of elastane from polyester-elastane blends is historically required before polyester recycling. However, pre-separation is expensive and reduces recovered polyester purity. Recent innovations enable elastane tolerance in selective depolymerization processes. Aquafil’s regeneration technology achieves elastane separation without destructive decomposition, recovering both polyester and elastane separately.
This advancement is critical: polyester-elastane blends represent majority of contemporary apparel. Processing capability for these blends dramatically expands recyclable waste streams.
Dye Removal and Color Challenges
Synthetic fibers retain dyes from original garments. Polyester dyes are typically azo dyes or anthraquinone dyes—large complex molecules physically bound to fiber surface and potentially embedded within polymer structure.
Supercritical CO2 extraction employs supercritical carbon dioxide at high pressure and temperature to selectively dissolve and remove dyes while leaving polymer intact. The recovered fiber is color-neutral, suitable for redyeing any color. This approach maintains polyester structure throughout dye removal.
Chemical oxidation employs hydrogen peroxide or other oxidants to chemically break down dye molecules, rendering them soluble and removable through aqueous washing. Oxidative bleaching is aggressive and requires careful control to avoid fiber damage, but achieves effective dye removal.
Supercritical water processing represents emerging approach employing heated pressurized water at supercritical conditions to dissolve and remove dyes. Process is environmentally friendly (water is solvent) and reportedly maintains fiber properties.
Effective dye removal is enabling recycled polyester production in any color—previously limited to dyed colors matching original textiles.
Mixed Synthetic Fiber Challenges: Polyester-Nylon Blends
Polyester-nylon blends represent substantial portion of contemporary synthetic textiles—approximately 15-20% of synthetic fiber production. These blends offer performance characteristics impossible with single fibers. Yet polyester-nylon recycling is more complex than single-fiber processing.
Recent breakthroughs enable selective depolymerization where polyester converts to monomers via glycolysis or hydrolysis while nylon remains structurally intact. Subsequent solvent-based separation isolates recovered polyester monomers from nylon fibers. This approach handles real textile waste composition without requiring expensive pre-separation.
This capability is transformative: polyester-nylon blends now enter recycling streams previously requiring pre-sorting, dramatically expanding recyclable waste volumes.
Contamination Challenges and Solution
Synthetic fiber waste often includes contaminants: heavy metals from dyes, persistent organic pollutants from finishes, microbiological contamination from wear, and physical contaminants from collection processes.
Heavy metals—particularly chromium, copper, nickel—can accumulate in recycled material if not removed. Advanced pre-treatment processes employing chelation chemistry, precipitation, or selective extraction remove heavy metals prior to depolymerization. These pre-treatment steps add cost but ensure recovered monomer and regenerated fiber purity.
Persistent organic pollutants including brominated flame retardants, per- and polyfluorinated compounds (PFOA/PFOS), and others similarly require removal. These substances can interfere with repolymerization or persist in regenerated fiber, creating product quality and regulatory compliance issues.
Commercial Viability and Cost Trajectory
Synthetic fiber recycling profitability depends on recovered monomer value and processing cost. Contemporary polyester monomer (DMT) pricing is approximately USD 0.60-0.80 per kilogram. Recycling cost (collection, sorting, depolymerization) approximates USD 0.40-0.70 per kilogram, yielding modest margin of USD 0.10-0.40 per kilogram.
This margin is improving as technology matures and scale increases. Large-scale commercial facilities are achieving cost reduction of 15-20% annually through efficiency improvement. Some analysts project cost parity between virgin and recycled polyester within 2-3 years—threshold transforming economics.
Nylon recycling is less economically mature, with higher processing cost relative to monomer value. However, nylon’s premium market position and stronger demand for virgin nylon (compared to commodity polyester) suggests higher-value market positioning for recycled nylon.
Future Trajectory: Scale and Integration
Commercial polyester recycling facilities are scaling substantially. Aquafil’s capacity continues expansion toward 50,000+ tons annually. Loop Industries’ capacity is expanding. Emerging competitors are establishing commercial facilities. By 2030, commercial-scale synthetic fiber recycling capacity should approach 2-3 million tons annually globally.
This scaling depends on continued technology maturation, cost reduction, and integration with apparel brand supply chains. As technology proves commercial viability, investment capital will increasingly flow toward capacity expansion.
