polyhydroxyalcanoates

Polyhydroxyalkanoates (PHAs), sometimes spelled polyhydroxyalcanoates, are a family of natural polyesters produced by many bacteria as intracellular carbon and energy storage compounds. They consist of hydroxyalkanoate monomers, and the most common is 3-hydroxybutyrate (3HB). Copolymers such as poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) combine different monomers to tailor properties; polyhydroxybutyrate (PHB) is the simplest PHA.

PHAs are biodegradable and biocompatible thermoplastics. They are typically semicrystalline, and their melting temperature and mechanical properties depend on monomer composition; PHB is relatively stiff and brittle, while PHBV and other copolymers can be more ductile. They can be processed by standard plastic fabrication methods such as extrusion and injection molding. Biodegradation rates vary with environment and polymer composition.

Production involves cultivating microorganisms under nutrient limitation with excess carbon, causing accumulation of PHAs as granules. After fermentation, PHAs are recovered and purified for use. In addition to renewable carbon sources, waste streams are explored to improve sustainability.

Applications include biodegradable packaging, agricultural films, medical devices, sutures, and tissue engineering scaffolds. End-of-life options typically include industrial composting, with marine degradation depending on conditions. Cost and processing challenges, including brittleness of some PHAs and relatively high production costs, limit wide replacement of conventional plastics, though advances in feedstocks, fermentation, and downstream processing aim to improve competitiveness.