Adding new polyester helped researchers restore a material property that deteriorated when sportswear scraps were recycled. The improvement came with a straightforward trade-off: the more new material they added, the less of each blend came from textile waste. Recycling (source, opens in new tab)RecyclingProperty Recovery in Thermo-Mechanically Recycled Polyester Textiles via Virgin Material Addition and PBO Chain ExtensionOpen source (opens in new tab)
The study tested recycling by melting and reshaping PET, the specific type of polyester used in these sportswear scraps. Heat and residual moisture during processing can shorten the long molecular chains that make up the plastic. Researchers tracked this through intrinsic viscosity, a measurement related to chain length. It provides an indication of changes in the material, rather than a direct test of how a garment will perform.
Two approaches were tested to raise that measurement: blending in new, or “virgin”, PET, and adding a substance intended to link or extend the polymer chains. Virgin PET produced more consistent improvements under the conditions tested. The additive, known as PBO, showed promise in laboratory trials but inconsistent results at pilot scale.
The starting material was white and coloured knitted polyester left over from cutting sportswear in garment production, all from one source. These were factory off-cuts, not worn clothes. Researchers turned them into pellets at pilot scale, then made individual filaments in laboratory trials. They did not test spun yarn or fabric, so the findings do not establish finished textile performance or commercial-scale production.
The material changed at both processing stages. Intrinsic viscosity fell by 13–16% when the off-cuts became pellets, then by a further 24–27% when those pellets became filaments. Measurements for the reported coloured sportswear off-cut pellet batches ranged from 0.51 to 0.57 dL/g, below the 0.58 dL/g threshold the paper cites for direct yarn spinning. After filament production, material from the coloured scraps was close to the cited threshold for low-grade textiles, 0.40 dL/g; material from the white scraps was just below it. These are reference points for interpreting the measurements, not evidence that a finished textile would pass a performance test.
Blends containing 30%, 50% or 70% bottle-grade virgin PET all exceeded the cited low-grade-textile threshold. Higher proportions of virgin PET produced higher intrinsic viscosity. Blending therefore offered a consistent way to improve this measurement in the trials, while moving the material further from an entirely recycled composition.
PBO offered a different approach: attempting to extend the polymer chains through an additive. At pilot scale, it did not significantly increase intrinsic viscosity in five of six treated batches. In laboratory filament trials, however, additions of 0.2% and 0.4% increased the measurement in both white and coloured samples.
The pilot and laboratory stages used different equipment and processing conditions, so the laboratory improvements cannot simply be assumed to carry over to production. The remaining question is whether an approach can deliver both dependable processing results and suitable yarn or fabric while retaining a high recycled share. This study does not establish that new PET is essential to recycling polyester textiles; it shows why recovering one material property and maximising recycled content can pull in different directions.
- Recycling · Peer-reviewed studyProperty Recovery in Thermo-Mechanically Recycled Polyester Textiles via Virgin Material Addition and PBO Chain Extensionmdpi.com · opens in new tab
