Colorado State University polymer chemists, led by Eugene Chen, University Distinguished Professor in the Department of Chemistry, have created a synthetic platform that could pave the way to truly sustainable plastics.

Polyhydroxyalkanoates, or PHAs, are already the basis of a fledgling industry. They’re a class of polymers naturally created by living microorganisms or synthetically produced from biorenewable feedstocks. They’re biodegradable in the ambient environment, including oceans and soil.

But crystalline PHAs are not as durable and convenient as conventional plastics. They cannot easily be melt-processed into end products and recycled, making them expensive to produce.

At the molecular level

Chen’s team had been searching for a strategy to address this intrinsic drawback of conventional PHAs at the molecular level. They substituted reactive hydrogen atoms responsible for thermal degradation with more robust methyl groups. This structural modification drastically enhances the PHAs’ thermal stability, resulting in plastics that can be melt-processed without decomposition.

What’s more, these newly designed PHAs are mechanically tough, even outperforming the two most common commodity plastics: high-density polyethylene used in products such as milk and shampoo bottles, and isotactic propylene used to make automotive parts and synthetic fibers. 

The best part is that the new PHA can be chemically recycled back to its building-block molecule, called a monomer, with a simple catalyst and heat, and the recovered clean monomer can be reused to reproduce the same PHA again – in principle, infinitely.

Chen and colleagues reported this new class of redesigned PHAs, readily accessible via chemical catalysis, in the journal  Science.