Renewable and recyclable PDK plastics found better than petrochemicals

Scientists have engineered microbes to make ingredients for recyclable plastics -- replacing finite, polluting petrochemicals with sustainable alternatives.

The new approach, published in ‘Nature Sustainability’, shows that renewable and recyclable plastics are not only possible, but also outperform those from petrochemicals.

Plastic waste is a problem. Most plastics can’t be recycled, and many use finite, polluting petrochemicals as basic ingredients.

In the study, researchers from Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) successfully engineered microbes to make biological alternatives for starting ingredients in an infinitely recyclable plastic known as poly(diketoenamine) or PDK.

"This is the first time that bio-products have been integrated to make a PDK that is predominantly bio-based," said Brett Helms, staff scientist at the Molecular Foundry, who led the project.

"And it is for the first time that you see a bio-advantage over using petrochemicals, both with respect to the material’s properties and the cost of producing it at scale," Helms said.

Unlike traditional plastics, PDK can be repeatedly deconstructed into pristine building blocks and formed into new products with no loss in quality. PDKs initially used building blocks derived from petrochemicals, but those ingredients can be redesigned and produced with microbes instead.

The team manipulated E. coli to turn sugars from plants into some of the starting materials -- a molecule known as triacetic acid lactone, or bioTAL -- and produced a PDK with roughly 80 per cent bio-content.

"We’ve demonstrated that the pathway to 100 per cent bio-content in recyclable plastics is feasible," said Jeremy Demarteau, a project scientist on the team, contributing to biopolymer development.

"You’ll see that from us in the future."

PDKs can be used for a variety of products, including adhesives, flexible items like computer cables or watch bands, building materials, and "tough thermosets", rigid plastics made through a curing process.

Researchers were surprised to find that incorporating the bioTAL into the material expanded its working temperature range by up to 60 degrees Celsius compared to the petrochemical version.

This opens the doors for using PDKs in items that need specific working temperatures, including sports gear and automotive parts like bumpers and dashboards, they said.