The Complexity of Plastic Pollution

You’ll often hear plastic pollution referred to as a problem. But the reality is that it’s multiple problems. Depending on the properties we need, we form plastics out of different polymers, each of which is held together by a distinct type of chemical bond. So the method we use to break down one type of polymer may be incompatible with the chemistry of another.

That problem is why, even though we’ve had success finding enzymes that break down common plastics like polyesters and PET, they’re only partial solutions to plastic waste. However, researchers aren’t sitting back and basking in the triumph of partial solutions, and they’ve now got very sophisticated protein design tools to help them out.

Breaking Down Polyurethane

That’s the story behind a completely new enzyme that researchers developed to break down polyurethane, the polymer commonly used to make foam cushioning, among other things. The new enzyme is compatible with an industrial-style recycling process that breaks the polymer down into its basic building blocks, which can be used to form fresh polyurethane.

The Challenge of Digesting Polyurethanes

The new paper that describes the development of this enzyme lays out the scale of the problem: In 2024, we made 22 million metric tons of polyurethane. The urethane bond that defines these involves a nitrogen bonded to a carbon that in turn is bonded to two oxygens, one of which links into the rest of the polymer. The rest of the polymer, linked by these bonds, can be fairly complex and often contains ringed structures related to benzene.

Digesting polyurethanes is challenging. Individual polymer chains are often extensively cross-linked, and the bulky structures can make it difficult for enzymes to get at the bonds they can digest. A chemical called diethylene glycol can partially break these molecules down, but only at elevated temperatures. And it leaves behind a complicated mess of chemicals that can’t be fed back into any useful reactions. Instead, it’s typically incinerated as hazardous waste.

Conclusion

The development of a new enzyme to break down polyurethane is a significant step forward in addressing the complex problem of plastic pollution. With the help of sophisticated protein design tools, researchers are making progress in finding solutions to the breakdown of different types of plastics. This new enzyme has the potential to make a significant impact on the recycling of polyurethane and could pave the way for further innovations in the field.

Frequently Asked Questions

Q: What is polyurethane and how is it used?

A: Polyurethane is a type of polymer that is commonly used to make foam cushioning, among other things. It is also used in a variety of other applications, including coatings, adhesives, and sealants.

Q: Why is it difficult to break down polyurethanes?

A: Polyurethanes are challenging to break down because individual polymer chains are often extensively cross-linked, and the bulky structures can make it difficult for enzymes to get at the bonds they can digest.

Q: How does the new enzyme work?

A: The new enzyme is compatible with an industrial-style recycling process that breaks the polymer down into its basic building blocks, which can be used to form fresh polyurethane.