BY ANTHONY KING
Upcycling is a growing trend in recycling, and now clever chemistry is being used to turn waste PET – typically from drinks bottles – into valuable products. Lou Reade reports
Waste polyethylene terephthalate (PET), generated largely by used soft drink bottles and textiles, is often seen as virtually worthless. Of the 25% of PET recycled, the ‘cleanest’ fraction is snapped up for use in new bottles; the rest is typically discarded or incinerated. With annual production of PET at around 70m t – and products like bottles having very short lives – it adds up to a very large pile of unusable plastic waste. However, chemistry is now coming to the rescue with several projects looking to create value from PET waste – converting it into everything from paint to catalysts.
Flue job
Scientists in Denmark have devised a chemical upcycling technique to convert PET waste into materials that capture carbon dioxide. The researchers, from the University of Copenhagen, have used a modified aminolysis reaction to convert PET into a bis-aminoamide called BAETA. BAETA has strong chemisorption – with high selectivity for capturing CO2 from flue gas and ambient air under humid conditions.
‘In carbon capture, the main issue is that it’s expensive,’ says Ji-Woong Lee, a professor in the department of chemistry and co-author of a paper in Science Advances (DOI: 10.1126/sciadv.adv5906).
One key factor behind the cost is that once CO2 has been captured, it must later be desorbed – and the material regenerated. ‘Regeneration needs heat energy, usually supplied by fossil fuel,’ Lee says. ‘We need better materials with a lower cost of regeneration.’
BAETA achieves this because it will absorb and desorb at the same temperature. In testing, the researchers carried out 40 absorption-desorption cycles. A gas mixture of 15% CO2 and 85% N2 was used for absorption for 30 minutes, and a 100% N2 flow was used for 20 minutes for desorption. Both processes took place at 150°C, with BAETA packed into the flue chimney in solid pellet form.
‘What we wanted was a thermally stable, long-lasting, easy to access compound – and all these criteria were met,’ Lee says.
BAETA is stable at up to 250°C, which means it can capture CO2 directly from hot flue gas. Often, the CO2 must be cooled before it can be captured by a sorbent, Lee explains. The aminolysis reaction to make BAETA differs from previous ones to produce amine-based sorbents in that it requires a minimal amount of diamine reactants.
‘Using excess diamine makes the reaction faster and more efficient, but makes final purification more difficult,’ Lee says. ‘When preparing a material for carbon capture, you want to minimise purification cost. That’s why we optimised it.’
The new method produces BAETA in 60% yield, with various oligomers comprising the other 40%. Hot filtration is used to dissolve the BAETA, while the oligomers are insoluble.
Lee says PET’s abundance – and the presence of ‘the correct functional groups’ – first led him to consider it as a starting material for a carbon-capture sorbent. His team has processed 1kg batches of waste PET in different forms. In one, shredded PET bottles produced 800g of BAETA and oligomers, in a room-temperature reaction that took two weeks. In a second, the reaction – at 60°C, over 24 hours – was applied to mixed waste, which included PET, food waste and other contaminants. Here, BAETA yield was 38%.
Lee plans to form a spin-off company later in 2026, although he admits the ‘biggest hurdle is there’s no buyer for CO2 capture’. However, he says the need to decarbonise remains – and there are many projects to convert CO2 into everything from fuel to food products.
In addition, countries like Denmark want to avoid incinerating plastic waste – so methods to depolymerise PET waste are always welcome, he says.
‘For us, plastic waste mitigation and carbon capture work well together.’
Capacitor components
Another recent upcycling project uses PET waste as a basis for supercapacitors used, for example, in automotive, electronics and consumer devices, say researchers from Michigan Technological University, US.
‘PET is used to produce over 500bn beverage bottles each year,’ says Yun Hang Hu, a professor of chemical engineering at MTU and co-author of a paper in Energy & Fuels (DOI: 10.1021/acs.energyfuels.5c03370). ‘PET-derived supercapacitors hold great potential for diverse applications.’
Supercapacitors use conductive carbon electrodes to store and release energy quickly and repeatedly. Hu and colleagues wanted to turn PET bottles into components for an electrical double-layer capacitor (EDLC), which has two porous carbon-based electrodes separated by a thin, perforated film in a liquid electrolyte. The team developed two new processes to convert PET bottles into electrodes and separator films. For the electrodes, they ground the bottles into small particles, added calcium hydroxide and heated the mixture to 700°C in a vacuum. This created a porous, electrically conductive carbon powder. They combined this powder with carbon black and a polymer binder, then dried it into thin layers. For the separator, they flattened stamp-sized plastic pieces and made holes in them using hot needles. The hole pattern optimised the passage of current through the electrolyte.
To build the supercapacitor, the researchers submerged two porous carbon electrodes in liquid potassium hydroxide and separated them with the perforated PET film. In tests, it retained 79% of its storage ability or capacitance, while a similar device with a glass fibre separator retained 78%.
Hu says the research suggests a way to transform PET waste into supercapacitor components, saying the ‘upcycled’ EDLC is less expensive to make than those that use glass fibre.
‘With further optimisation, PET-derived supercapacitors might transition from laboratory prototypes to market-ready devices in five to 10 years,’ he says.
Catalyst formation
Meanwhile, a team at Adelaide University in South Australia has developed a route to upcycle common plastics – including PET – into single-atom catalysts (SACs).
SACs contain metal atoms that are fixed within a graphene substrate. The ones made from plastic waste – a rich source of carbon – were effective at breaking down micropollutants in water and boosting technologies such as batteries and fuel cells, say the researchers.
‘What excites us is the versatility of the method, as it works across different plastics and mixtures, and produces catalysts that can be applied in water purification, batteries, and beyond,’ says Xiaoguang Duan, a professor of chemical engineering, and co-author of a paper in Nature Communications (DOI: 10.1038/s41467-025-63648-z).
One of the SACs produced in the research was used to degrade phenol in wastewater – with PET-derived and manganese-based SACs found to have the highest catalytic efficiency. In addition, the researchers used X-ray absorption spectroscopy (XAS) to determine the atomic-scale structure of the catalysts. Measurements confirmed the metals did not form nanoparticles but were dispersed as single atoms that were chemically bound within the carbon framework in a ‘favourable coordination environment’.
Surface effect
Staying in Australia, researchers have imbued PET with self-cleaning properties by modifying its microsurface. As well as resisting water and dirt, the material can also prevent ice formation. In the work, performed at the University of New South Wales (UNSW), researchers combined physical micropatterning with chemical modification to create what they call ‘superhydrophobic, self-cleaning PET sheets without relying on nanoparticles’. They said the work overcomes the intrinsic hydrophilic nature of PET, which makes it more susceptible to water and dirt accumulation, affecting long-term performance.
Taking advantage of PET’s relatively low glass transition temperature, they used thermal embossing to build textured arrays – and microscale roughness to add water repellence (hydrophobicity). Further chemical modification, using fluorinated block copolymers, introduced a nanostructure that increased the water contact angle – allowing it to slide more easily off the surface.
One goal of the research was to design ‘micro-windowpanes, which allowed water droplets to slide off at a very shallow angle: less than 8°. This also cleared insoluble materials including sand and coffee powder. One downside is that the microscale topography causes light scattering, which limits the optical transmittance of the modified PET. However, the researchers believe the modified sheet could improve the durability of PET surfaces from packaging to architectural sheet.
The work, led by associate professor Jin Zhang, was published in Advanced Materials Interfaces (DOI: 10.1002/admi.202500625).
Metal-free conversion
Meanwhile, researchers in China have devised a metal-free catalytic method to convert PET waste into valuable chemicals. By using an ionic liquid as the catalyst, researchers from Zhejiang University have seen a 99% yield for dimethyl terephthalate (DMT) and 91% for ethylene carbonate (EC) – in 2.5 hours under mild conditions. DMT is a precursor in the production of PET and a similar polymer called polybutylene terephthalate (PBT), while ethylene carbonate is a highly polar solvent used in lithium-ion batteries.
Chemical recycling via methanolysis has shown promise in the past, say the researchers, but challenges include incomplete depolymerisation and reliance on metal-based catalysts.
‘By using a metal-free ionic liquid catalyst, we improve the efficiency of PET upcycling and create a sustainable pathway for managing plastic waste,’ says Qingqing Mei, the study’s lead researcher, and co-author of a paper in Eco-Environment & Health (DOI: 10.1016/j.eehl.2025.100139).
Hydrogen bonds formed between the ionic liquid and the reactants play a key role in activating the carbonyl groups of PET and hydroxyl groups of methanol and ethylene glycol. This raises the reaction’s efficiency, leading to full conversion of PET. The researchers add that their method can be applied to various polyesters and polycarbonates, extending its potential.
Paint project
Another use for waste PET has been developed by a team from Northumbria University in the UK, which has created an ingredient for alkyd paint – a tough coating used to protect structures such as oil rigs. The project grew out of a request from Berger Paints Nigeria – via Innovate UK – to find ‘innovative solutions for recycling waste plastic into resin for paint production’.
‘We looked at what wastes were available there – and were also effectively valueless and available at large scale,’ says Justin Perry, a professor in the department of applied sciences and co-author of a paper on the technique in ACS Sustainable Chemistry & Engineering (DOI: 10.1021/acssuschemeng.3c07560).
The team has developed a chemical process in which the PET waste undergoes transesterification, breaking it down into a monomer that can replace virgin phthalic anhydride in the creation of alkyd paint. In addition, it can be co-polymerised with glycerol and tall oil fatty acid to create a partially biobased polyester resin for use in thermoset alkyd coatings.
This polyester resin – usually derived from a petrochemical source – is the binder that provides ‘rigidity’ and prevents water permeation, says Perry. The method allows the use of PET from a ‘dirty’ fraction of a recycling plant – typically including fragments of the bottle cap and paper labels – which would usually be incinerated for energy recovery.
Perry says this fraction, produced during the separation and washing steps, has a particle size of 0.5−3mm and contains 1-10% polyolefin ‘contamination’. These ‘flake and wash losses’ are estimated to remove 157,000t of PET from the closed-loop recycling process in the EU alone.
‘This grade of wPET cannot be further refined or recycled due to its degree of contamination and small particle size, and it is currently sent to landfills or incinerated for energy recovery,’ the researchers say in their paper.
However, in Northumbria’s one-pot reaction, these kinds of impurities simply float to the top because they are unreactive to transesterification.
‘It’s almost a self-purifying process,’ Perry says.
Northumbria supplied 10kg of its resin to Berger Paints in Nigeria – where there is a ready supply of PET waste. ‘PET waste in Nigeria is much cleaner than it is in the UK,’ says Perry.
Berger is currently testing the paint for potential commercialisation, which includes factors such as drying time. Ultimately, the plan would be for Berger to make the paint itself from local PET waste.
‘We don’t yet know if the paint is commercially viable, but it’s technologically viable,’ says Perry.
In parallel to this development, Thai PET producer Indorama is planning to set up a PET recycling plant in Lagos, Nigeria, producing up to 45,000t of food-grade resin/year. Startup is targeted for the first half of 2027.
PET remains one of the most used and recognised plastics – albeit one with a recycling problem.
However, clever new chemical methods promise to turn PET waste into a lucrative source of raw materials.
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