28 April 2021

New Process to Recycle Waste Polyurethanes Using Enzymatic Degradation

This circular loop which combines biotechnology and chemistry could be repeated a very large number of times

A research team from University of Strasbourg has developed a new process combining biotechnology and chemistry by putting the polyurethane at the end of its life in contact with enzymes. The team is called BioTeam and is led by Professor Luc Averous at the Institute of Chemistry and Processes for Energy, the Environment and Health (ICPEES, unit CNRS and University of Strasbourg).

Controlled Enzymatic Degradation Process

This controlled enzymatic degradation process makes it possible to obtain reusable “bricks”, and thus produce a second generation of polyurethane to manufacture new objects, without using toxic isocyanates, using a circular and sustainable “Chem-Biotech” process.

Within the ICPEES BioTeam research team, researchers have focused on controlled enzymatic degradation, which allows enzymes to meet plastics at the end of their life to produce molecules or building blocks. From these building blocks researchers could chemically obtain a second generation of polymers.

Bio-recycling of Difficult to Process Polymers

The researchers thus tackled the bio-recycling of a family of polymers which is very difficult to process: polyurethanes. It is the fifth family of plastics. They have exceptional properties, but they currently pose enormous problems, particularly at the end of use. They are found, for example, in large quantities in microplastics, in the oceans. Indeed, resistant and often very low density, they disperse easily in nature after use.

Concretely, polyurethanes are foams at more than 60%. They are found in mattresses, in car seats, they are present in closed cell foams, in the thermal insulation of buildings. These foams have a so-called crosslinked 3D structure. This means that, if you heat them, they do not soften before breaking down. It is therefore impossible to recycle material by melting as is commonly done for thermoplastics, such as PET in water bottles.

Beyond the urethane groups which are known to be particularly strong, polyurethanes also have ether and ester groups and it is the latter which have been broken using enzymes, keeping the urethane functions intact.

Esterases Enzymes at Work

There is a large family of enzymes called esterases which have the function of hydrolyzing these ester groups. Once the network has been deconstructed by these enzymes, bricks are obtained which carry active chemical groups which can be used to manufacture a second generation of polyurethanes, and this without using toxic isocyanates. This circular loop which combines biotechnology and chemistry could be repeated a very large number of times.

In addition to recycling foams at the end of their use, a new life is possible for used foams, to prevent them from ending up in fine particles in the environment. This would give new life to old mattresses by transforming them into sports shoes, for example, in a sustainable and circular approach.

Source: bioplastics MAGAZINE, 2021-04-15.

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