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Recycling breakthrough for cotton-polyester blend material

United States – ‘Millions of tons’ of cotton-polyester blend material currently dumped in landfills could now be recycled thanks to a patented process capable of removing dyes from textiles while separating cotton from fabric blends and depolymerising polyesters, claims the US-headquartered BCD Group Inc.

Involving only non-toxic chemicals, the ‘easy-to-operate’ process employs low-cost, reusable reagents in a way that retains the strength of the cotton fibres. Fabric blends of cotton and polyethylene terephthalate (PET) are first shredded and then the material is treated in a common stirred-tank reactor, with base and a proprietary phase-transfer catalyst (PTC) which cleaves the dyes, polyesters and other chemicals bonded to cotton.

The solid cotton fibre is removed from the reactor after processing for up to 20 minutes at temperatures of around 90-120°C before final depolymerisation of PET. The process ultimately yields terephthalic acid, which is recovered by filtration for reuse. Researchers argue that conventional depolymerisation methods cannot be used for separating cotton-polyester blends because the high temperatures and long process times ‘destroy’ cotton fibres.

This innovation could be extended to the recycling of other materials too. ‘The nucleophilic reactions catalysed by the PTC can be controlled,’ explains Charles Rogers, a process engineer with BCD.

The new method can also effectively recover monomers from composites and other polymers, and can recover silver metal from polymeric X-ray films.

The company is now looking for partners to help commercialise the technology.

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