Why blended fibres resist recycling

Walk into any UK textile recycling facility and you will see the problem stacked in bales: cotton-polyester workwear, polycotton bed linen, sportswear with elastane, and countless T-shirts with printed logos. These blends are engineered for comfort, durability, and cost. But that same intimacy of mixing makes them a nightmare to separate. Cotton and polyester have different densities, chemical resistances, and melting points. Once spun together into a yarn, they cling to each other at the fibre level. Mechanical pulling tears both fibres; chemical dissolution often damages one while recovering the other. Add dyes, softeners, and elastane, and the recycling yield drops further. Yet the opportunity is huge: the UK throws away over a million tonnes of textiles each year, and a large share is blended. The good news is that both mechanical and chemical routes are improving, with yields that would have seemed impossible a decade ago.

Mechanical routes: sorting, shredding, and spinning again

Mechanical recycling is the workhorse. It starts with sorting. Near-infrared (NIR) scanners can now identify fibre composition on conveyor belts, separating pure cotton from polycotton from polyester-rich streams. Colour sorting follows: optical sensors blow coloured items into different bins, because dye removal is difficult and costly. Then comes shredding, tearing, and carding. The goal is to open the fabric back into individual fibres without turning them into dust.

In practice, mechanical recycling of blends yields two main products: a short-fibre fraction that can be re-spun into coarser yarns, and a waste stream of fines, dust, and entangled pills. For a typical polycotton, a well-tuned line might recover 50–60% of the input as usable fibre. The rest is lost. Rotor spinning and wrap spinning can handle these shorter fibres, producing yarns for denim, workwear, and blankets. But the yarns are weaker and more irregular than virgin equivalents, so they are often blended with virgin cotton or polyester to reach acceptable strength. Mechanical recycling is cheap, scalable, and already commercial. Its limitation is that it cannot separate the fibres; it can only re-mix them.

Chemical separation: dissolving one fibre to save the other

Chemical routes aim to dissolve one fibre while leaving the other intact. For cotton-polyester blends, the usual approach is to dissolve the cotton. Cotton is cellulose, and cellulose can be dissolved in ionic liquids, NMMO (as used in lyocell production), or certain switchable solvents. The polyester remains as a solid that can be filtered, washed, and re-melted. Alternatively, you can dissolve the polyester using solvents such as dichlorobenzene or more benign alternatives, leaving cotton fibre behind. The choice depends on the blend ratio and the desired output.

Enzymatic separation is emerging as a gentler option. Cellulase enzymes can digest cotton into glucose, which can be fermented or used as a chemical feedstock, while polyester survives. This works best on clean, undyed waste. For elastane-contaminated blends, selective solvents can remove the elastane first. Chemical plants are now achieving over 90% purity for recovered polyester, and regenerated cellulose fibres from waste cotton are entering the market. The obstacles are cost, solvent recovery, and energy use. But for high-value blends, the numbers are starting to work.

From reclaimed fibre to new yarns and nonwovens

Once you have separated fibres, the next challenge is turning them back into products. Recovered cotton is often too short for ring spinning. It works well in open-end rotor spinning, air-jet spinning, or as a blend component. Recovered polyester can be re-melted and spun into filament or staple fibre, though its molecular weight may have dropped. For nonwovens, the story is simpler. Shredded blend waste can be needlepunched, hydroentangled, or thermally bonded into products where strength is less critical: insulation batts, geotextiles, automotive trim, acoustic panels, and cleaning cloths. These markets are large and growing, and they tolerate colour variation.

• Yarns: rotor-spun recycled cotton/polyester blends for denim, socks, and workwear.
• Nonwovens: needlepunched insulation, automotive carpets, and horticultural mats.
• Regenerated fibres: dissolved cotton reformed into lyocell-type filaments; dissolved polyester into new staple.
• Composites: blended waste bonded with bio-resins for low-load panels and furniture.

Making the economics and quality stack up

Recycling blended fibres is not just a technical problem; it is an economic one. Virgin polyester costs around £1 per kilogram, and virgin cotton fluctuates but is often cheaper than the cost of chemical separation. Recycled fibres must compete on price, performance, and consistency. Brands and retailers are driving demand through voluntary commitments and, increasingly, UK extended producer responsibility (EPR) fees that penalise non-recyclable blends. That policy pressure is beginning to tip the balance.

Quality control is critical. Recycled fibres vary in length, fineness, and colour. Blending them with virgin fibres is standard practice, but the recycled content still reduces carbon footprint and waste. For nonwovens, the specification is more forgiving. For yarns, spinners must adjust machine settings, accept lower tenacity, and design fabrics that hide irregularities. The most successful recyclers combine mechanical pre-sorting with chemical finishing, using each route where it adds most value.

Designing for the next loop

The long-term fix is better design. Mono-material garments, easily removable trims, and fewer elastane blends make recycling far easier. But we cannot wait for perfect future textiles. Today, the practical route is a tiered approach: mechanical recycling for nonwovens and coarse yarns, chemical separation for high-value cotton-polyester streams, and policy support to level the playing field with virgin fibres. For textile engineers, the opportunities are clear: improve sorting speed, reduce solvent losses, increase fibre length retention, and build supply chains that keep blended waste in the UK rather than shipping it abroad. Every percentage point of yield matters. And with each improvement, the mountain of blended waste looks less like a problem and more like a resource.