PHB (Polyhydroxybutyrate)

Quick Overview

PHB is the simplest member of the PHA family, produced through bacterial fermentation. Fully biodegradable in soil, marine, and composting environments, PHB offers true biological sustainability despite processing challenges from brittleness.

What Is PHB?

Polyhydroxybutyrate (PHB) is the simplest and most studied member of the PHA family of biopolymers. Produced naturally by bacteria as an intracellular energy storage compound, PHB is a fully bio-based and fully biodegradable polyester that degrades in virtually every natural environment — soil, freshwater, and marine.

PHB’s standout property is its marine biodegradability, certified under ASTM D6691. This makes it uniquely valuable for applications where plastic leakage into aquatic environments is likely.

Properties

Advantages

• Universal biodegradability: Degrades in soil, marine, freshwater, and compost
• 100% bio-based: Produced entirely from renewable feedstocks via bacterial fermentation
• Carbon neutral: CO₂ absorbed during feedstock growth offsets production emissions
• UV resistant: Better UV stability than many other bioplastics

Challenges

• Brittleness: Low elongation at break without copolymerisation or blending
• Processing window narrow: Degrades at temperatures only slightly above its melting point (~175°C)
• Higher cost: More expensive than PLA due to lower production volumes
• Thermal stability: Difficult to process without degradation

Applications

• Marine applications: Fishing nets, aquaculture gear, marine-degradable packaging
• Agricultural: Mulch films, plant pots, seed coatings
• Personal care: Cosmetic packaging, microbeads replacement
• Rigid packaging: Containers where marine degradation is desired
• Medical: Sutures, implants (biocompatible and biodegradable in vivo)

Frequently Asked Questions

What is the difference between PHB and PHA? PHB is the simplest polymer in the PHA family. PHA is the umbrella term — PHB is one specific type (homopolymer of 3-hydroxybutyrate). PHA copolymers (like PHBV or PHBHHx) offer broader property ranges including improved flexibility.

Does PHB biodegrade in the ocean? Yes. PHB is one of the few bioplastics certified as marine biodegradable under ASTM D6691. It degrades within 6–24 months in marine conditions.

Is PHB brittle? Yes. PHB is relatively stiff and brittle compared to the PHA copolymer grades. Blending or using other PHA types improves flexibility.

Can PHB be composted at home? PHB degrades in home compost over a longer timeframe (6–12+ months) compared to industrial compost. Home compost certification is possible but not universal.

Related Terms

• PHA — The polymer family to which PHB belongs
• PLA — The most widely used bioplastic; does NOT biodegrade in marine environments
• Biodegradable — The environmental property PHB is certified for
• Compostable — PHB meets EN 13432 industrial composting standards
• Microbial Degradation — The mechanism behind PHB’s environmental breakdown