Is PLA Biodegradable and Compostable? Testing, Standards & Facts
What Is PLA?
Polylactic acid (PLA) is a thermoplastic aliphatic polyester derived from renewable feedstocks—primarily corn starch, sugarcane, or cassava. It was one of the first commercially viable bio-based polymers and has become widely used in 3D printing, packaging, disposable foodservice items, agricultural films, and biomedical applications.
PLA is frequently marketed as “biodegradable” and “compostable,” making it an attractive alternative to fossil fuel-derived plastics in sustainability-focused applications across the packaging, consumer goods, and agricultural industries. However, the conditions required for PLA to biodegrade are far more specific than many consumers realise.
Is PLA Biodegradable?
The short answer is: yes, but only under specific conditions.
PLA is biodegradable by hydrolysis—water molecules attack the ester bonds in the polymer backbone, breaking the polymer chains into smaller oligomers and ultimately into lactic acid, which is then metabolised by microorganisms to produce carbon dioxide and water. However, this hydrolysis process occurs at meaningful rates only at elevated temperatures.
Why PLA Does Not Biodegrade Easily at Ambient Conditions
At ambient temperature (20–25°C) and typical environmental humidity, PLA hydrolysis is extremely slow. Studies show that PLA films placed in soil or seawater may persist for years with minimal degradation. This means PLA does not behave like biologically degradable materials such as paper or food waste under real-world conditions.
Is PLA Compostable?
PLA is compostable, but only under industrial composting conditions as defined by ASTM D6400 and EN 13432. Industrial (or commercial) compostable means:
- Temperature: ≥58°C (136°F) sustained for the required period
- Humidity: A high moisture environment is maintained by the composting process management
- Time: Disintegration within 12 weeks; complete biodegradation within 6 months under these conditions
Under home composting conditions (15–35°C), PLA degrades very slowly and may not achieve complete biodegradation within a reasonable timeframe. PLA is generally not considered suitable for home compost programs.
Certifications for Compostable PLA
Products claiming compostability should carry third-party certification:
- BPI (Biodegradable Products Institute) Certified Compostable — US standard
- OK Compost INDUSTRIAL (TÜV Austria) — European certification
- DIN CERTCO — German certification for EN 13432
Certification verifies that the material meets the disintegration, biodegradation, ecotoxicity, and heavy metal limits of ASTM D6400 or EN 13432.
PLA vs. Conventional Plastics: Environmental Comparison
Property | PLA | PET | HDPE |
Bio-based feedstock | Yes | No | No |
Industrial compostable | Yes (ASTM D6400) | No | No |
Home compostable | Generally no | No | No |
Recyclable | Limited (separate stream) | Yes | Yes |
Marine biodegradable | No | No | No |
Challenges in PLA Waste Management
PLA in conventional recycling streams contaminates PET recycling because PLA and PET appear similar visually but have incompatible melt temperatures. PLA must be composted in industrial facilities—a relatively limited infrastructure in most regions—or sent to landfill, where it degrades very slowly in the absence of oxygen.
Conclusion
PLA is a bio-based thermoplastic that offers a more sustainable alternative to conventional plastics, particularly in applications like packaging and 3D printing. While it is technically biodegradable and compostable, this only occurs efficiently under controlled industrial composting conditions—not in typical natural environments or home compost systems.
Understanding these limitations is essential for responsible use and disposal. When properly managed through certified composting systems, PLA can contribute to reduced environmental impact, but without the right infrastructure, its sustainability benefits may not be fully realised.
Why Choose Infinita Lab for PLA and Bioplastic Testing?
Infinita Lab offers compostability and biodegradability testing per ASTM D6400, ASTM D5338, and EN 13432 standards for PLA and other bioplastics. Our accredited laboratory network also provides mechanical, thermal (DSC, TGA), and chemical characterisation for bioplastic material development and certification support.
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Frequently Asked Questions (FAQs)
What temperature does PLA need to compost? PLA requires sustained temperatures of at least 58°C (136°F) in the presence of moisture and active microbial communities to achieve meaningful composting rates. Industrial composting facilities maintain these conditions; backyard compost piles typically do not.
Will PLA degrade in the ocean? No. PLA is not marine biodegradable. In cold seawater conditions, PLA degrades extremely slowly—potentially over years or decades—and should not be considered a solution to marine plastic pollution.
Can PLA be recycled with other plastics? PLA has a dedicated recycling stream (resin code 7 – "Other") that is separate from PET (code 1) and HDPE (code 2). Mixing PLA with PET in recycling causes contamination. Separate PLA collection and composting or specialized recycling streams are required.
What are the mechanical properties of PLA compared to conventional plastics? PLA has tensile strength similar to PET (~50–70 MPa) and higher stiffness than many polyolefins, but lower impact toughness and heat resistance (HDT ~55–65°C). These limitations restrict PLA use in applications requiring ductility or elevated temperature performance.
What does ASTM D6400 require for a plastic to be labelled "compostable"? ASTM D6400 requires: ≥90% disintegration to pieces <2 mm within 12 weeks at 58°C; ≥90% biodegradation (conversion to CO₂) within 180 days at 58°C; no ecotoxicity to plants (germination and biomass tests); and heavy metal content below defined thresholds.
