PHA is a family of polyesters (PHB (polyhydroxybutyrate), PHBH, PHBV, P3HB-4HB and others) that bacteria accumulate inside their cells when fed sugars or oils. Unlike PLA (polylactic acid, a plant-based plastic), PHA biodegrades in soil, fresh water and seawater as well as in composting, which makes it the most interesting bioplastic for items likely to escape collection.
It replaces plastic straws, cutlery, coffee pods, flexible films, paper extrusion coatings, rigid containers, artificial-turf infill, fibres and 3D-printing filament. Kaneka (Japan) makes Green Planet PHBH and expanded capacity to 20,000 tonnes a year at Takasago. CJ Biomaterials (Korea and US) sells PHACT amorphous PHA, commercial since 2022, and in 2025 launched an all-PHA extrusion-coating platform for repulpable, home-compostable paper. Danimer Scientific (US), which built the first commercial-scale PHA plant at 25,000 tonnes a year in Kentucky, filed for bankruptcy protection (US Chapter 11) in March 2025 after a key fast-food customer cut volumes and was sold to Teknor Apex for US$19 million in June 2025, so supply is fragile.
Peer-reviewed marine evidence is good but conditional: PHB and PHBV samples lost 61 to 97 percent of mass in 28 days in Thai seawater (Polymers, 2022); the degradation rate roughly triples between 20 and 30 degrees C (Journal of Hazardous Materials, 2023); and field studies report lifetimes in estuarine and marine settings (Marine Pollution Bulletin, 2024). Compostability certifications (EN 13432, ASTM D6400, TÜV HOME) exist for many grades; marine claims require the TÜV OK biodegradable MARINE mark and should never be made without it.
Drawbacks: resin costs US$4 to 7 a kg in Western markets, or about US$3.4 a kg from China, against US$1.2 to 1.6 for PE, a two to four times premium; the simplest type, PHB, is brittle. The biggest greenwashing risk is that marine-degradable messaging encourages littering: present it as a safety net, never as a disposal route.