phas

PHAs, or polyhydroxyalkanoates, are a diverse family of biopolymers produced by many microorganisms as intracellular carbon and energy storage granules. They accumulate as inclusions within the cytoplasm and can be mobilized when needed.

Chemically, PHAs are polyesters built from hydroxyalkanoate monomers. The most common material is polyhydroxybutyrate (PHB), but many bacteria produce copolymers such as polyhydroxybutyrate-co-hydroxyvalerate (PHBV) or other compositions. They are thermoplastics that are generally biodegradable and biocompatible; properties vary with monomer composition and molecular weight.

Biosynthesis occurs under nutrient limitation with excess carbon. Microorganisms channel precursors like acetyl-CoA into PHA production. Core enzymes include PhaA (β-ketothiolase), PhaB (acetoacetyl-CoA reductase), and PhaC (PHA synthase), which polymerizes hydroxyacyl-CoA into PHA. Proteins such as PhaP associate with granules and influence their size and stability.

Industrial production uses microbial fermentation with strains such as Cupriavidus necator. Feedstocks span sugars, glycerol, and plant oils derived from renewable resources. After cultivation, cells are harvested and polymers are extracted and purified; recovery costs are a key consideration. Monomer composition or blending can tune material properties.

Applications and environmental impact: PHAs are renewable, biodegradable alternatives to conventional plastics, usable in packaging, agricultural films, and medical devices. They can be processed by standard plastics methods and degrade via microbial depolymerases in soil and aquatic environments, with compostability occurring under appropriate conditions.

Standards and regulation: Compostability standards exist, including EN 13432 and ASTM D6400. Lifecycle assessments address sustainability of feedstocks and end-of-life implications, influencing commercial adoption.