‘Dream’ biodegradable plastics redesigned by chemists

May 02, 2023 | Biology

Also known as dream plastics, polyhydroxyalkanoates (PHAs) are a class of natural polymers produced by living organisms. Thus, they are sustainable and environmentally-benign. They can also be produced synthetically from biorenewable feedstocks. However, PHAs haven’t taken off as a better alternative to traditional plastics due to crystalline PHAs’ thermal instability and lack of heat resistance. This in turn affects its durability and subsequent convenience of use.

To address these problems, chemists from Colorado State University created a synthetic PHA platform that would allow sustainable PHAs to replace traditional plastics in the marketplace. The team produced a new class of redesigned PHAs which are readily made available by chemical catalysis.

Making fundamental changes to the structure of PHAs, they switched the reactive hydrogen atoms, which are responsible for thermal degradation, with more robust methyl groups. This structural modification enhances PHAs’ thermal stability and allows these plastics to be melt-processed without decomposition. Moreover, these redesigned PHAs are mechanically tough compared to the other two most common commodity plastics: high-density polyethylene and isotactic propylene.

On top of that, the new PHA can be chemically recycled back to its monomer with simple heat and then can be reused again to reproduce the same PHA again - a closed-loop chemical recycling process that can proceed infinitely in principle.

The team was able to add three key desired features to the PHAs, which are all considered essential for achieving a circular PHA economy.