Short answer: PHA is the family name — polyhydroxyalkanoate, a group of polyesters that microorganisms build and store as a carbon reserve. PHB is poly(3-hydroxybutyrate), the member you meet most often: a stiff, semi-crystalline homopolymer that melts near 175 °C. PHV is poly(3-hydroxyvalerate), and PHBV is the copolymer that builds hydroxyvalerate units into a PHB chain to make it more flexible. Economically, PLA is usually cheaper and needs industrial composting, while PHA grades can break down in soil, home compost or sea water at a higher cost per kilogram.
Quick Facts
- PHA = polyhydroxyalkanoate: a polymer family, not one material.
- PHB = poly(3-hydroxybutyrate), a homopolymer; semi-crystalline, melting near 175 °C.
- PHV = poly(3-hydroxyvalerate); PHBV = the copolymer P(3HB-co-3HV), softer and tougher than plain PHB.
- PLA and PHA are different families: PLA comes from lactic acid, PHA is made directly by microbial fermentation.
- Label standards: industrial compost EN 13432 / ASTM D6400; marine testing ASTM D6691; home compost is a separate certification.
Why PHA, PHB and PHV Get Mixed Up
PHA, PHB, PHV and PHBV appear on the same product pages and often in the same sentence, which makes them look like competing products. They are not. One is a family; the others are members and copolymers inside it. A resin sold simply as "PHA" is usually a PHB homopolymer or a PHBV copolymer, and every property a buyer cares about — flexibility, heat tolerance, which environment it breaks down in — follows from which member it is.
PHA: The Family Name
PHA stands for polyhydroxyalkanoate, a family of linear polyesters that microorganisms synthesize and store as an internal carbon reserve. Bacteria build PHA granules when carbon is plentiful and another nutrient runs short, then the polymer is recovered and processed into resin. Published reviews describe well over one hundred hydroxyalkanoate monomers, but only a handful are produced at scale; PHB and PHBV account for most of what a Canadian buyer will be offered.
What PHA is used for
PHA grades are chosen where a product must biodegrade beyond an industrial compost facility: films and bags, food-service ware, coated paper and board, mulch film, and some moulded parts. In healthcare supply, PHA is mostly seen in waste and collection products rather than sterile clinical items, because resin cost and heat sensitivity limit where it makes commercial sense.
How PHA breaks down
PHA biodegrades through microbial action rather than simple hydrolysis. Microorganisms that can use the polymer as a carbon source colonize the surface and release enzymes that break the chain into smaller units. That is why PHA shows measurable biodegradation in soil, compost and sea water, while PLA in the same environment may change very little.
What to ask a PHA supplier
Ask for the grade name, not just the family, and ask which standard the degradation claim was tested against. Then ask whether the certificate covers the finished article or only the raw resin, because a compostable resin combined with a non-compostable label or adhesive does not make a compostable product.
PHB: Poly(3-hydroxybutyrate)
PHB is short for poly(3-hydroxybutyrate), the first PHA discovered and the most widely studied member of the family. Its repeating unit is 3-hydroxybutyrate, and because the units are identical throughout, PHB is a homopolymer. Plain PHB is semi-crystalline and stiff, with a melting point around 175 °C and a narrow processing window, so it behaves more like a rigid polyolefin than a soft film — useful for caps and coatings, less so for a draping bag.
Where PHB appears in medical and lab supply
PHB has a long research history in resorbable implants and sutures, because the body can break it down into a natural metabolite. In everyday supply catalogues the same resin turns up in compostable bags, films and moulded items. A Canadian clinic is much more likely to meet PHB inside a waste liner than inside a sterile instrument pack.
How PHB degrades, and what to ask
PHB is attacked by a wide range of soil and marine microorganisms, has been tested under marine protocols such as ASTM D6691, and suitable grades biodegrade in home compost where aeration is adequate. That breadth is the practical difference from PLA, which is normally certified for industrial composting conditions only.
PHV and PHBV: The Copolymer Variants
PHV stands for poly(3-hydroxyvalerate). On its own it is rare in commercial supply; its real role is as a co-monomer. When the bacteria that produce PHB are fed the right precursor, they incorporate hydroxyvalerate units alongside the hydroxybutyrate units, giving the copolymer P(3HB-co-3HV), usually written PHBV. Adding HV units disrupts the crystal structure of PHB, so the result is less crystalline, melts lower, and is more flexible and tougher than the homopolymer. Two resins both labelled PHBV can still behave differently on the same line if one carries 5 mol% HV and the other 15 mol%, so ask for that figure in writing.
PLA and PHA Side by Side, for Procurement
Both PLA and PHA are bio-based polyesters that biodegrade through microbial action, and both appear in healthcare supply. They are not interchangeable in every application, and the useful comparison is about environment and economics rather than which material wins in the abstract.
| Property | PLA | PHB (homopolymer) | PHBV (copolymer) |
|---|---|---|---|
| Origin | Lactic acid from fermented plant starch | Microbial fermentation of sugars | Same route, with a co-monomer precursor |
| Feel | Stiff, rigid, crisp film | Stiff and brittle | Softer, tougher, more flexible |
| Melting behaviour | Roughly 150–180 °C by grade | Around 175 °C, narrow window | Lower than PHB, falling as HV rises |
| Industrial compost (EN 13432 / ASTM D6400) | Yes, certified grades | Yes, certified grades | Yes, certified grades |
| Home compost and marine testing | Not normally claimed | Reported for suitable grades | Reported for suitable grades |
| Typical supply uses | Liners, gowns, trays | Films, bags, moulded parts | Films and bags needing drape |
On cost, the ranking is consistent: PLA is produced at the largest scale and prices lowest, while PHA grades carry a premium. A practical rule follows from that: choose PLA where the item will reach an industrial composting stream and cost per unit matters, and choose a PHA grade where the item may end up in soil, home compost or water. In both cases the disposal route, not the resin name, decides the outcome.
Degradation Conditions and the Standards Behind the Labels
The word biodegradable on its own says very little, because biodegradation always happens in a specific environment over a specific period. The useful version of the claim names the environment and the standard used to test it.
- EN 13432 — the European standard for compostable packaging, tied to industrial composting.
- ASTM D6400 — the North American specification for plastics labelled compostable in industrial facilities.
- ASTM D6691 — a test method for aerobic biodegradation of plastic in the marine environment.
- ISO 14855 — a laboratory method for aerobic biodegradation in controlled composting.
- ISO 17088 and home compost schemes — compostable plastic specifications, plus certifications such as OK compost HOME, tested at lower temperatures.
An item certified for industrial composting is not automatically suitable for a backyard composter, and an item that biodegrades in the sea is not automatically compostable on land. Check the standard number, the environment it specifies, and whether the certificate names the finished product or only the resin.
Buying a PHA or PLA Part: Questions to Ask Before You Order
- Which member of the family is it? PHB, PHBV, or a blend, and at what HV content?
- Which standard was the claim tested to, and in which environment?
- Does the certificate cover the finished article, or only the resin?
- What is the processing window, and is a melt flow index published?
- What does my disposal stream accept? Without organics collection, a compostable liner behaves like any other.
If the application is general waste collection, a certified compostable liner such as CliniEco PLA biodegradable waste bags, 30 gallon fits sites where the bag will follow an organics route, and CliniEco PLA biodegradable isolation gowns, Level 1 covers light-duty protection where a single-use garment is required. Resin background sits in how PLA is made: from corn starch to biodegradable medical supplies. Related reads are PLA waste bags in healthcare: where biodegradable bags fit and where they don't and PLA compostability for medical supplies: industrial vs home composting. Programme context sits in the sustainability hub and the learning hub.
Related reading
Continue with how PLA is made: from corn starch to biodegradable medical supplies, PLA waste bags in healthcare: where biodegradable bags fit and where they don't and PLA compostability for medical supplies: industrial vs home composting.
Frequently Asked Questions
What is PHB in the PHA family?
PHB is poly(3-hydroxybutyrate), the most widely studied member of the PHA family. It is a homopolymer, semi-crystalline, and melts around 175 °C. It biodegrades in soil, compost and sea water.
Is PHA the same thing as PLA?
No. PLA is polylactic acid, made from lactic acid produced by fermenting plant starch. PHA is a separate family made directly by microorganisms. PLA is usually cheaper and normally certified for industrial composting, while PHA grades can be formulated for soil, home compost and marine environments at a higher cost.
What does PHV mean, and how is it different from PHBV?
PHV is poly(3-hydroxyvalerate), a monomer unit. PHBV is the copolymer combining hydroxybutyrate and hydroxyvalerate units in one chain, written P(3HB-co-3HV). Its HV content is quoted in mole percent and controls how flexible the resin is.
Does PHA degrade at home, or only in industrial composting?
It depends on the grade and the certificate. EN 13432 and ASTM D6400 cover specific industrial composting conditions, while home composting is a separate certification tested at lower temperatures.
Specify the resin, then confirm the certificate. → Start with a trial: CliniEco 24h Biological Indicator — 5-Pack Trial
CliniEco Medical is a licensed medical device establishment (MDEL #35334). This article is educational technical information about biodegradable polymer terminology and does not replace your facility's waste and infection prevention policy, product manufacturer instructions, or any provincial or municipal requirements that apply to your site.
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