Enzymatic Recycling of Polyurethane Foams 

Royce’s Industrial Collaboration Programme (ICP) awarded £174,612 to this project which evaluated the efficacy of a wide panel of PET degrading enzymes. 

Enzymatic approaches to plastic recycling have received considerable attention, however, to date efforts have largely focussed on PET deconstruction. Here we show that through automated laboratory evolution, we can quickly reengineer PETases so that they deconstruct more recalcitrant polyurethane plastics into their component monomers for subsequent re-use, thus supporting bio-based recycling strategies. 

There is a pressing need to develop new methods of recycling end-of-life polymers to tackle the global challenge of plastics pollution. Thus far, limited progress has been made in the development of sustainable solutions for recycling plastics that have been engineered for a long-lifespan. This project has delivered an enzyme-based technology for the low-energy breakdown of challenging polymers into their building blocks for subsequent reuse, thus supporting industrial materials design and bio-based recycling in a future circular economy.  

This study focused on polyurethane (PU), a heterogenous group of polymers typically constructed from alternating aromatic diisocyanate (e.g. MDI) and polyol building blocks. PU represents almost 8% of plastics produced globally, with nearly 20 M metric tons produced per annum, with the majority of PU in the form of flexible of rigid foams, used in e.g. upholstery, bedding and insulation materials. Currently, glycolysis is the most promising method of recycling but it is hindered by the presence of feedstock impurities. Enzymatic recycling technologies that are efficient and rapid at scale have huge potential to present a step-change in end-of-life management of PU. Given the chemical heterogeneity of PU polymers (which vary in both the diisocyanate and polyol building blocks). Our labs have recently reported the development of an automated, high-throughput directed evolution platform for engineering polymer degrading enzymes (Nature Catalysis, 2022, 5, 673), taking advantage of the Royce infrastructure housed in MIB. This state-of-the-art infrastructure implemented by Royce funding has enabled has streamlined directed evolution platform that has produced new enzymes for plastics deconstruction. 

Armed with this enzyme engineering platform, we have now discovered and engineered a new family of polyurethanase enzymes that can cleave both ester and urethane bonds (unpublished data) to generate aromatic diamine products (i.e. MDA), which can be readily converted to aromatic diisocyanate monomers (MDI) using established chemical methods. The workflow outlined in this project has delivered several enzymes for plastic deconstruction and has established an in-house evolution platform which in the future, can be used to engineer other plastic degrading enzymes towards more complex challenges. On the back of this work, a report has been produced discussing the challenges and utilities of polyurethane-deconstructing enzymes in industry. 

“Biocatalytic strategies for recycling plastics have received considerable attention, however to date efforts have largely focussed on PET deconstruction. In this project, we have now expanded the repertoire of plastic recycling enzymes to include polyurethanases, a family of polymers that accounts for ca. 8% of plastics produced globally and poses significant challenges for end-of-life recycling.”

Anthony P. Green
Professor in Organic Chemistry, The University of Manchester 

FURTHER INFORMATION

• £174, 612 (all awarded to Royce Partner)
• Engagement with Johnson Matthey as potential end-users of PU degrading enzymes