Biodegradable plastics such as polyhydroxyalkanoates (PHA), polylactic acid (PLA), and starch-based materials serve as alternatives to conventional petroleum-based plastics. Their environmental performance hinges on degradation behavior in various settings.
This analysis compares their biodegradability across environments, timelines, microplastic risks, and carbon footprints, drawing from scientific studies and standards.
Degradation Conditions & Factors
Degradation depends on conditions like temperature, humidity, and microbial activity, as well as material thickness and formulation.
Industrial Composting
Temperatures > 58°C, controlled humidity
Supports all three effectively. PHA degrades in 1–6 months, PLA in 3–12 months, and starch-based plastics in 1–6 months, often meeting standards such as ASTM D6400 or EN 13432.
Home Composting
20–30°C Ambient Temperature
Works well for PHA (3–12 months) and many starch-based variants (3–12 months), but PLA degrades slowly or incompletely due to lower temperatures.
Soil Environments
Favors PHA (3–18 months) and starch-based plastics (6–24 months). PLA takes 1–5 years due to lower microbial efficiency in cooler, uncontrolled conditions.
Marine & Freshwater
PHA breaks down in 3–24 months (OK Biodegradable Marine certified). PLA shows minimal progress (decades/centuries). Starch-based plastics perform moderately (6–36 months).
Degradation Timelines: Approximate Ranges
These timelines vary based on specific formulations and environmental conditions.
| Environment | PHA | PLA | Starch-Based |
|---|---|---|---|
| Industrial Compost | 1–6 months | 3–12 months | 1–6 months |
| Home Compost | 3–12 months | Incomplete / >1 year | 3–12 months* |
| Soil | 3–18 months | 1–5 years | 6–24 months |
| Marine | 3–24 months | > 100 years | 6–36 months |
Need a Technical Deep Dive?
For a broader overview of these materials, including mechanical properties, tensile strength, and industrial applications, refer to our comprehensive resource.
Microplastic Risks
PHA: Minimal Risk
Microbes convert it fully to CO₂, water, and biomass in most environments.
Starch-Based: Low to Moderate
Reduces risks when pure. However, commercial blends (e.g., with PBAT) may increase fragmentation if not fully degraded.
PLA: High Persistence Risk
With its slow natural breakdown, PLA often fragments into persistent particles in oceans and soils rather than mineralizing.
Carbon Footprint & Lifecycle
Lifecycle assessments show all three can lower emissions relative to traditional plastics, though production phases differ.
PHA
Moderate Footprint. Involves higher energy for microbial fermentation, but offset by reliable degradation preventing long-term pollution.
PLA
Lowest Production Emissions. Efficient at scale (20–70% lower than petroleum plastics), but benefits diminish if degradation fails in nature.
Starch-Based
Variable Footprint. Low production emissions due to simple processing, though fossil-based additives in blends can raise overall impacts.
Conclusion
PHA provides broad degradation across environments, making it suitable for diverse applications. PLA performs effectively in controlled industrial systems but less so elsewhere. Starch-based plastics balance cost and performance, with outcomes tied to composition.
Effective use requires aligning material properties with expected end-of-life conditions, supported by certifications and ongoing research.
