The researchers had been searching for a strategy to address the intrinsic thermal instability of conventional PHAs; their lack of heat resistance also makes it difficult to melt-process them into end products. The CSU 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.
What's more, these newly designed PHAs are 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. 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.
"We are adding three key desired features to the biological PHAs, including closed-loop chemical recycling, which is essential for achieving a circular PHA economy," Chen said. The work was supported by the Department of Energy's BOTTLE Consortium.