Colorado State University (CSU) announced on April 11, 2023, that its chemists, led by Eugene Chen, University Distinguished Professor in the Department of Chemistry, have created a synthetic polyhydroxyalkanoate (PHA) platform. CSU states that PHAs are a class of polymers naturally created by living microorganisms or synthetically produced from biorenewable feedstocks. While they are biodegradable in the ambient environment, they are brittle and cannot easily be melt-processed and recycled. According to CSU, the synthetic PHA platform addresses each of these problems, “paving the way for a future in which PHAs can take off in the marketplace as truly sustainable plastics.”

The researchers searched for a strategy to address the intrinsic thermal instability of conventional PHAs. According to CSU, its chemists “made fundamental changes to the structures of these plastics, substituting 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.” CSU notes that the newly designed PHAs are also mechanically tough, “even outperforming the two most common commodity plastics: high-density polyethylene -- used in products like milk and shampoo bottles -- and isotactic propylene, which is used to make automotive parts and synthetic fibers.” CSU notes that the new PHA can be chemically recycled back to its building-block molecule with a simple catalyst and heat, and the recovered clean monomer can be reused to reproduce the same PHA again.

The work was supported by the U.S. Department of Energy’s (DOE) Bio-Optimized Technologies to keep Thermoplastics out of Landfills and the Environment (BOTTLE™), a DOE multi-organization consortium “focused on developing new chemical upcycling strategies for today’s plastics and redesigning tomorrow’s plastics to be recyclable-by-design.” More information is available in a Science article entitled “Chemically circular, mechanically tough, and melt-processable polyhydroxyalkanoates.”