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By Lynn L. Bergeson and Carla N. Hutton
 
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.”


 

By Lynn L. Bergeson and Carla N. Hutton
 
To celebrate its 125th anniversary, ASTM International invited case study submissions from committee members to highlight standards that have made a significant impact in society. One of the winning entries is on a set of standards for biodegradable plastic from Committee D20 on Plastics. According to ASTM International’s article, standard test methods for determining the biobased content of solid, liquid, and gaseous samples using radiocarbon analysis (D6866) allows industry, regulators, and government to determine experimentally the percent biobased carbon present in a product or fuel. The article notes that the U.S. Department of Agriculture’s (USDA) BioPreferred® program, mandated by Congress in the 2018 Farm Bill, authorizes the procurement of biobased products by the federal government. The article states that this standard is required to be used to report the percent biobased content of product for federal procurement, as well as for labeling a product with the BioPreferred logo showing biobased content.
 
The article states that there are two companion specification standards for compostable plastics and paper coatings, “redesigning plastic polymers for biodegradability in industrial composting for an environmentally responsible, managed end-of-life”:

  • Standard specification for labeling of plastics designed to be aerobically composted in municipal or industrial facilities (D6400); and
  • Standard specification for labeling of end items that incorporate plastics and polymers as coatings or additives with paper and other substrates designed to be aerobically composted in municipal or industrial facilities (D6868).

The standard specifications, which are “grounded in strong science and driven by consensus, provided much-needed clarity and credibility for acceptance in the marketplace and by regulatory bodies in states like California, Washington, Minnesota, Rhode Island, and Connecticut.” The article states that the BioPreferred program mandates D6866 as the only accepted standard for determining and reporting biobased content of products, and that the U.S. Environmental Protection Agency (EPA) requires the standard for reporting on biobased content in fuels. According to the article, industry uses D6400 and D6868 exclusively for making claims of biodegradability under industrial composting conditions. These standards are also the basis of certifications issued by U.S. and European organizations. The article notes that many stakeholders require that compostable products meet D6400 for plastics and D6868 for coatings on paper, and that industrial composters also require certification that the compostable products are certified to these standards.