poly3hydroxybutyrate

Poly(3-hydroxybutyrate), commonly abbreviated PHB, is a biobased, biodegradable thermoplastic polyester. It belongs to the polyhydroxyalkanoates (PHAs), a family of intracellular storage polyesters produced by many bacteria to store carbon and energy.

PHB is formed from the monomer 3-hydroxybutyrate and polymerizes into a semicrystalline polymer with a relatively high melting point. The repeating unit has the formula C4H6O2. PHB is known for high crystallinity, which confers stiffness and a sharp melting transition, but also contributes to brittleness at room temperature. The material can be processed by conventional plastic techniques, but its processing window is narrow and thermal stability is limited.

Production of PHB occurs in bacterial fermentation, where carbon-rich substrates and nutrient limitation trigger PHB accumulation. The best-known producer is Cupriavidus necator (formerly Ralstonia eutropha). After fermentation, PHB is recovered from cells by solvent extraction or digestion of the biomass, followed by purification.

In terms of applications and challenges, PHB is used in packaging, disposable items, and certain medical devices. Its widespread use is limited by relatively high cost and brittleness. Copolymers such as poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) improve flexibility and toughness, and blends with other polymers or additives are common to tailor properties.

Environmental aspects point to PHB as biodegradable and potentially industrially compostable, with degradation occurring in soil and marine environments under appropriate microbial activity. Degradation rates depend on temperature, microbial communities, crystallinity, and the specific PHB formulation. Ongoing research seeks to optimize production, processing, and cost to broaden commercial adoption.