What are biodegradable fossil-based polymers?
Biodegradable fossil-based polymers are synthetic plastics made from petroleum or natural gas that microorganisms can still break down into water, carbon dioxide and biomass under the right conditions. They prove a point that runs through all of polymer science: biodegradability comes from chemical structure, not from where the raw material was dug up.
People meeting the bioplastics classification for the first time usually assume “bio” means it rots and “fossil” means it lasts forever. PBAT, PCL and PBS are the counterexamples. They are not bio-based, and their biodegradation performance matches or beats some biodegradable bioplastics.
Why these polymers biodegrade
Biodegradation needs chemical bonds that microbial enzymes can recognize and cut. Most conventional fossil-based polymers such as polyethylene and polypropylene have carbon-carbon backbones too stable for enzymes to touch. These polymers instead carry ester bonds (–COO–) in the main chain, and ester linkages hydrolyze and yield to the lipases, esterases and cutinases that soil and compost microorganisms produce.
How fast and how completely that happens depends on four things:
- Polymer crystallinity — Amorphous (disordered) regions degrade faster than crystalline (ordered) regions, as enzymes access the chains more easily.
- Molecular weight — Lower molecular weight polymers generally biodegrade faster.
- Environmental conditions — Temperature, moisture, pH, and the presence of active microbial communities all influence degradation kinetics.
- Material thickness — Thinner films and smaller particles present more surface area to microorganisms, accelerating the process.
The three main polymers
PBAT, PCL and PBS dominate the category commercially. Each has its own territory across packaging, agriculture and biomedical use, and each is frequently blended with bio-based biodegradable polymers to balance cost against performance.
PBAT (polybutylene adipate terephthalate)
PBAT is an aliphatic-aromatic copolyester made from 1,4-butanediol, adipic acid and terephthalic acid, all currently petrochemical. The two kinds of segment do different jobs: the aliphatic parts give it biodegradability, the aromatic terephthalate units give it strength and flexibility.
It is the most produced biodegradable fossil-based polymer in the world. BASF’s ecoflex is the best-known commercial grade, with capacity in the hundreds of thousands of tonnes a year. PBAT is certified compostable under EN 13432 and ASTM D6400, so it biodegrades fully in industrial composting within the required time.
Commercially its main job is as a blending partner for brittle bio-based polymers. Mixed with PLA or thermoplastic starch it produces flexible film: compostable shopping bags, food packaging film, agricultural mulch. Novamont’s Mater-Bi line combines starch with PBAT precisely to get the flexibility and tear resistance a carrier bag needs to pass EN 13432.
Work is under way on partially or fully bio-based PBAT, through bio-based 1,4-butanediol from succinic acid fermentation and bio-based adipic acid. That would move PBAT out of the fossil-based column entirely, though commercial-scale bio-based PBAT is still limited as of 2026.
PCL (polycaprolactone)
Polycaprolactone (PCL) is a semi-crystalline aliphatic polyester made by ring-opening polymerization of ε-caprolactone, itself derived from the petrochemical intermediate cyclohexanone. It melts at about 60 °C, unusually low, and stays flexible at room temperature.
PCL biodegrades by enzymatic hydrolysis in soil, compost and water, at rates that can be tuned through molecular weight and crystallinity. In active compost it disappears within 6 to 12 months.
Its established home is the biomedical sector: absorbable sutures, drug delivery systems, tissue engineering scaffolds and orthopedic fixation devices, where biocompatibility and a predictable in-vivo degradation rate are what surgeons need. Outside medicine it works as a blending agent, improving the flexibility and processability of PLA and starch-based materials.
Production volumes are modest next to PBAT, and the price keeps it out of commodity packaging. That low melting point, though, makes shape-memory applications and hot-melt adhesives possible, and nothing else does the same job.
PBS (polybutylene succinate)
Polybutylene succinate (PBS) is an aliphatic polyester made by polycondensation of succinic acid and 1,4-butanediol. Its properties sit close to polypropylene: good mechanical strength, moderate heat resistance with a melting point around 114 °C, and easy processing.
PBS biodegrades in industrial composting, and more slowly in soil. It is certified compostable under EN 13432. Commercial grades come from Mitsubishi Chemical as BioPBS, partly bio-based through bio-succinic acid, from Showa Denko, and from PTT MCC Biochem, a joint venture making bio-based PBS in Thailand from cassava-derived succinic acid.
PBS sits on the boundary of this whole category, because succinic acid can be made petrochemically from maleic anhydride or by fermenting sugars. As bio-based succinic acid scales, PBS keeps shifting toward renewable carbon, and some grades already reach 50% bio-based content or more. The copolymer PBSA (polybutylene succinate-co-adipate) biodegrades faster and bends further, which suits mulch film and compostable bags.
Properties compared
| Property | PBAT | PCL | PBS |
|---|---|---|---|
| Chemical type | Aliphatic-aromatic copolyester | Aliphatic polyester | Aliphatic polyester |
| Primary feedstock | Petrochemical | Petrochemical | Petrochemical (transitioning to bio-based) |
| Melting point (°C) | 110 – 120 | ~60 | ~114 |
| Tensile strength (MPa) | 15 – 25 | 10 – 25 | 30 – 40 |
| Elongation at break (%) | 500 – 800 | 300 – 800 | 200 – 400 |
| Biodegradation environment | Industrial compost, soil | Compost, soil, aquatic | Industrial compost, soil (slower) |
| EN 13432 certified | Yes | Yes | Yes |
| Primary role | Flexible film, blending with PLA/starch | Biomedical, blending agent | Packaging, mulch film, injection molding |
| Major producers | BASF (ecoflex), Novamont, Kingfa | Ingevity, Daicel | Mitsubishi Chemical, PTT MCC Biochem |
Where they are used
The list of applications is short and commercially solid.
Compostable packaging film
PBAT, alone or blended with PLA and starch, is the main material for compostable bags and flexible packaging film: supermarket produce bags, bin liners for organic waste collection, wrap for fresh food. The European market grew sharply after Italy required compostable carrier bags from 2011.
Agricultural mulch film
Conventional PE mulch film has to be lifted and disposed of after harvest, and soil contamination makes recycling it impractical. Biodegradable film based on PBAT, PBS and their blends can be tilled straight into the soil, where it breaks down over the following months. That removes the collection cost and stops plastic accumulating in agricultural soil. EN 17033 is the standard written for exactly this use.
Biomedical devices
PCL’s biocompatibility and controlled degradation put it in absorbable sutures, tissue scaffolds and drug-eluting implants, where it holds the mechanical load while healing happens and then gives way as the body’s own tissue takes over. PBS is being investigated for bone fixation devices.
Blending and modification
This may be the category’s most important role. PLA is cheap and available and also brittle. Blending it with PBAT or PCL produces materials that are tougher, stretch further and process more easily, with compostability intact. Most compostable products on the market today depend on that blend.
Standards and certification
The same standards and certifications apply here as to biodegradable bioplastics:
- EN 13432 (Europe) — Requires industrial compostable packaging to achieve at least 90 % disintegration within 12 weeks and 90 % biodegradation (CO₂ evolution) within 6 months at 58 °C.
- ASTM D6400 (North America) — Comparable to EN 13432, with similar biodegradation thresholds for composting environments.
- EN 17033 (Europe) — Specific to biodegradable mulch films for use in agriculture, requiring soil biodegradation rather than composting.
- ISO 17088 (International) — Specifications for compostable plastics, harmonized with regional standards.
TUV Austria issues the OK compost, OK soil and OK biodegradable MARINE marks, and DIN CERTCO issues its own, which is how waste managers tell certified material from claims. “Biodegradable” is a general property; “compostable” is a certification against defined test conditions. Only certified compostable products belong in a composting waste stream.
Environmental trade-off
These materials deliver real end-of-life benefits: they make composting and soil biodegradation possible, keeping waste out of landfill and returning carbon to soil as humus. They also come from non-renewable petroleum, so their production carries the same upstream burden as any conventional plastic, including fossil resource depletion, refinery emissions and the supply chain risk that goes with oil.
That is why the industry keeps pushing them toward bio-based feedstock. PBS moving to bio-based succinic acid and the research into bio-based PBAT monomers both aim at the same result: biodegradability and renewable origin in one material, which would move these polymers into the bio-based quadrant.
Market position
Market data puts PBAT second only to PLA in global biodegradable polymer capacity. Demand concentrates in Europe and Asia, where composting infrastructure and regulation give it somewhere to go. China has become a major PBAT production hub, with several large plants commissioned since 2020 in response to domestic single-use plastic restrictions.
Two trends will decide what happens next:
- Feedstock transition — As bio-based monomer production scales up, the distinction between “fossil-based biodegradable” and “bio-based biodegradable” will increasingly blur. PBS is already well along this path.
- Infrastructure expansion — The value of compostable polymers depends on the availability of composting facilities. As organic waste collection and industrial composting expand — driven by the EU’s revised Waste Framework Directive and similar legislation worldwide — the addressable market for all compostable plastics, including PBAT, PCL, and PBS, will grow accordingly.
Where they sit in the classification
In the four-quadrant system used across this knowledge zone, these polymers occupy the bottom-left: fossil feedstock, biodegradable end-of-life. They share the feedstock axis with non-biodegradable fossil-based polymers such as PE, PP and PET, and part company entirely on biodegradability.
Their existence is the proof that the two axes are independent. A plastic can be bio-based and never biodegrade, like bio-PE, or fossil-based and biodegrade completely, like PBAT.
Questions or corrections are welcome through our contact page. The knowledge zone overview covers the other three quadrants.