Two Nature publications present methods for giving hard-to-recycle polymers a second life. ’It is an excellent scientific study showing that it is possible to break down classical epoxy resins into starting compounds such as BPA.’

Danish researchers have developed a way to break down wind turbine blades into their original building blocks. Wind turbine blades are made of epoxy composites reinforced with carbon fibres. Epoxy resins are reactive polymers containing epoxy groups. This type of material is also used in the automotive and aerospace industries. These composites structures are usually buried at the end of their life because there is no suitable recycling strategy. They published their findings in Nature.

Filip Duprez6135

Filip Du Prez

Beeld: Bart Cloet

Polymer professor at the Centre for Macromolecular Chemistry of Ghent University.

Alexander Ahrens and his team have developed a ruthenium-catalysed protocol which targets a specific C-O bond for the recovery of bisphenol A (BPA) and intact carbon fibres from epoxy composites. Bisphenol A is a widely used chemical building block. ’In 2012, global production of bisphenol A was 3.8 million tonnes,’ says Filip Du Prez, professor of polymers at the Centre for Macromolecular Chemistry at Ghent University. ’It will now exceed 5 million tonnes. In terms of the circular economy, there may be an interest in recovery, but only if it is economically viable.’ Carbon fibres are expensive, and recovering them may be something that composites companies can do something about.

Du Prez points out that this does not solve the problem of old wind turbine blades. ’The Danish study is a proof of concept. The researchers are using a high proportion of toxic and expensive ruthenium. In this kind of high-volume application, it is economically and practically unfeasible. But it is an excellent scientific study showing that it is possible to break down classical epoxy resins into starting compounds such as BPA.’ To generate industrial interest, we would need to find non-toxic, low-cost catalysts that can do the same with much smaller amounts of catalyst. ’We are looking at completely different approaches to recycling wind turbine blades, for example using dynamic bonds in epoxy resins.’


Epoxy group

A second publication by US and Indian researchers focuses on recycling mixed plastics. Mixed plastic waste is a challenge within the plastics problem because mixed plastics, such as blends of polar and non-polar polymers, are usually incompatible with each other and break down into phases, leaving inferior materials. Instead of deconstructing and reconstructing polymers, the researchers developed a method to unify polymer blends with specially designed dynamic crosslinkers.

It is a relatively simple and universal chemical way of upcycling mixed plastic waste,’ explains Du Prez. You add specific crosslinkers, or crosslinkers that contain exchangeable bonds. With these specific dynamic crosslinkers, they combine polyolefins and polyesters into multi-block copolymers. Du Prez is concerned that this multi-step synthesis is not scalable. They have done it on a gram scale with commercial substances, but the step to the scale needed for the millions of tonnes of plastic waste seems very far away. Hopefully they will find companies willing to invest in it. Nevertheless, he is enthusiastic about the publication. This paper will initiate or strengthen many new lines of research into solutions for mixed plastic waste.

Ahrens et al. (2023) Nature (Open Access) 
Clarke et al. (2023) Nature