Recycling polyester to improve textile sustainability

A team from the University of Copenhagen have developed an environmentally friendly and straightforward approach to recycling polyester that involves just heat, a non-toxic solvent, and a basic household ingredient. The new technique could reduce environmental pollution as well as offering new opportunities for upcycling and creating high-quality materials.

Polyester, a blend of plastic and cotton fibers, is difficult to separate and therefore recycle. Only about 15% is currently recycled, with the rest ending up in landfills or being incinerated, creating further carbon emission. As around 60 million tons of the fabric is produced annually, this is a major environmental problem. In addition, recycling approaches tend to prioritize preserving the plastic component, leading to the loss of the cotton fibers, and are expensive, complex, and produce metal waste from the use of metal catalysts.

However, as reported in ACS Sustainable Chemistry & Engineering [Yang et al. ACS Sustain. Chem. Eng. (2023) DOI: 10.1021/acssuschemeng.3c03114], this new traceless catalytic technique, based on a synergistic combination of chemistry and materials science, depolymerizes polyester into its monomers while at the same time recovering cotton at a scale of hundreds of grams.

It was tested by cutting polyester fabric into small pieces, adding some mild solvent and then ammonium bicarbonate (known as hartshorn salt), a common leavening agent in baked goods. Heating the mixture to 160⁰C and leaving it for 24 hours left a liquid in which the plastic and cotton fibers had settled into distinct layers. The hartshorn salt is broken down into ammonia, CO₂ and water, with the first two acting as a catalyst, initiating a selective depolymerization reaction that breaks down the polyester while preserving the cotton fibers.

Before finding it also worked on polyester fabric, the technique was initially effective on polyethylene terephthalate(PET), the most common type of plastic in the world, a third of which is used to produce polyester and other synthetic textiles. Such polyester recycling and cotton recovery could lead to a more sustainable, closed-loop production of both plastics and textiles for a more circular economy. For instance, textile manufacturers could now produce eco-friendly fabrics by integrating recycled cotton.

As researcher Jiwoong Lee told Materials Today, “we've gained a deeper understanding of how traceless catalysts can be harnessed for selective depolymerization. Our work showcases the potential of using basic chemical principles to solve complex recycling challenges, contributing valuable insights to the broader domain of sustainable materials processing.”

The team now hope to further optimize and refine the process to improve its viability at larger scales for practical applications, and commercialize the technology through collaboration with industry partners.

“We've gained a deeper understanding of how traceless catalysts can be harnessed for selective depolymerization. Our work showcases the potential of using basic chemical principles to solve complex recycling challenges, contributing valuable insights to the broader domain of sustainable materials processing.”Jiwoong Lee