Chemical upcycling of polyethylene terephthalate (PET) plastic waste into materials to capture carbon dioxide could address two key problems at once – plastic rubbish and cutting emissions – a new study has concluded.

PET is among the most widely produced plastics, but recycling is limited due to inadequate collection infrastructure and the complexity of sorting. It is estimated that between 85–90% of PET is either incinerated or sent to landfill.

Looking for a solution to the problem, chemists based in Denmark developed a simple process whereby PET was broken down by way of aminolysis using low-cost 1,2-ethylenediamine to form a bis-aminoamide (BAETA) and oligomers.

‘The reaction is very simple, because we don’t use any solvents or catalysts, and we also optimise the reaction to use the least needed amount of ethylenediamine, so just two molecules,’ explains Margarita Poderyte, a PhD fellow in the chemistry department at the University of Copenhagen and one of the researchers involved in the study. ‘Then it’s just 60°C, 24 hours and we have the material.’

In contrast to many carbon capture systems on the market, which are based on liquids, the BAETA material is a thermally stable solid at up to 220°C and able to capture carbon dioxide effectively under flue gas conditions, as well as directly from the air, for multiple cycles.

‘It has dual application for carbon capture at high temperatures for flue gas, but also room temperature, high humidity levels [and] direct air capture – that’s why it’s very interesting, because it’s quite versatile,’ Poderyte says.

The researchers tested their aminolysis procedure with various sources of PET waste, including bottles, food packaging and textiles, all of which were smoothly converted into BAETA. They also assessed the scalability of the approach with one, and then two, kilograms of untreated PET consumer waste at room temperature and plan to now test it on a much larger scale.

‘We are trying to solve a problem of carbon capture without creating another problem,’ Poderyte says.