They are now working on dividing up the ideas. Some make most sense for Covestro to run with, while others would be more appropriate for MRC; there are also some that might be best shared with the wider value chain for further consideration.
While the ideas are still being narrowed down, but there are a number of obvious potential uses for rebonded foam, he said, such as cushioning for comfort, acoustics, and vibration dampening. ‘With some technology development, can opportunities be created for these materials?’ Skorpenske said. ‘Mechanical recycling is typically low energy, which is also a good thing.’
Covestro is also looking at opportunities in states where MRC does not look after the mattress recycling programme. ‘One of the biggest challenges we have for the remainder of the country is the collection and sorting aspect,’ he said. ‘There are many voluntary schemes, and some retailers have programmes to take back mattresses, either free or with a fee. We need to engage with contacts in the value chain to talk about ways collection and sorting might be enhanced.’
The problems will be greater in more sparsely populated areas – if material has to be transported a long way, the environmental benefits of recycling reduce very quickly. ‘We have to figure out how to do things on a local scale,’ he said.
Of course, mattresses are far from the only source of end-of-life PU foam, with a significant proportion also coming from upholstered furniture. There is a further issue to consider here: while US legislative changes in recent years have greatly reduced the amounts of flame retardants present in new foam used in furniture in the country, this is not the case for many older items now reaching the end of their life. In order to pass the old fire standards, large amounts of flame retardants were incorporated into the foam; the advent of the smoulder test to replace open flame tests has led to a dramatic reduction in their use. But FR-heavy foam is now being discarded.
‘We need to be conscientious about legacy materials when looking at circular economy solutions,’ Skorpenske said. ‘Materials like pBDEs have now been legislated out, and the smoulder test has led to a reduction in FRs in flexible foam. Going forward, we should be in very good shape with regard to end-of-life foam, but some applications we may have to be more conscientious about. It’s not what’s is being made now, it’s what’s been in the market for multiple years.’
Chemistry in action
Even with additional markets being identified for rebonded foam, there is unlikely to be sufficient demand to use up all the discarded PU foam as it reaches end of life. While it could be burnt and the energy captured, the other obvious way to keep it out of landfill is to chemically recycle it – take the polymer molecules apart and then reuse the fragments to make more polyurethane, or other materials.
The idea of chemolysis to recycle polyurethane into monomers is not new: Huntsman and Recticel, for example, have both developed processes to recover polyols from polyurethane. But polyols are not the only constituent parts of PU – there’s also the isocyanates. And Covestro has managed to develop a way of getting both parts back for reuse.
‘Chemolysis has been well-known since the 1980s,’ said Karin Clauberg, the company’s venture manager for flexible foam chemolysis. ‘Our process is a split-phase chemolysis, followed by steps to improve the quality.’ As well as the polyol, the Covestro process produces a diamine, which can be phosgenated to give an isocyanate. Importantly, she said, lab tests show that the substances are almost identical to virgin materials.
Key to the ability to regenerate the isocyanate is a phase separation step of the type familiar to chemistry students carrying out organic synthesis experiments, albeit on a much larger scale. The top phase contains the polyol; after a hydrolysis step, toluene diamine comes out of the bottom layer.