Biodegradable

Term

Quick Overview

Biodegradable materials can be broken down by microorganisms into natural substances like water, carbon dioxide, and biomass. Biodegradation rates and conditions vary significantly by material and environment, making standardized testing essential.

Related terms: Compostable PLA PHA Microbial Degradation

Definition

Biodegradable refers to the material property of being capable of decomposition into natural, environmentally benign substances (water, carbon dioxide, and biomass) through the action of microorganisms such as bacteria, fungi, and other living organisms. The process occurs through enzymatic hydrolysis and microbial metabolism, ultimately leading to complete mineralization of the polymer material.

The term “biodegradable” is fundamentally different from “biodegradable within a specific timeframe and under specific conditions.” A material may be theoretically biodegradable but take decades to degrade under ambient conditions, whereas the same material might fully biodegrade within 90 days in an industrial composting facility. This distinction is critical for understanding realistic end-of-life environmental impacts.

Biodegradation Mechanisms

Enzymatic Hydrolysis: The primary mechanism of polymer biodegradation involves enzymatic breakdown of chemical bonds:

Microorganisms produce specialized enzymes (lipases, esterases, depolymerases) capable of cleaving polymer backbone bonds
These enzymes break polymer chains into smaller oligomers and monomers
Smaller fragments are more readily metabolized by microbial populations

Microbial Metabolism: Once enzymatic hydrolysis creates accessible fragments, microbes utilize these compounds for:

Energy production (ATP generation through respiration)
Synthesis of new cellular material (biomass growth)
Production of metabolic byproducts

Environmental Factors Affecting Biodegradation: Multiple conditions influence biodegradation rates:

Temperature: Higher temperatures accelerate enzymatic activity; industrial composting typically requires 55-60°C for optimal biodegradation
Moisture: Microorganisms require adequate water; wet conditions favor biodegradation
Oxygen availability: Different microbes thrive in aerobic (oxygen-rich) or anaerobic (oxygen-free) conditions
Microbial population: Presence of adapted microorganisms with appropriate enzymes is essential
pH: Optimal pH varies by microorganism; neutral to slightly alkaline conditions generally favor activity
Nutrient availability: Microbes require nitrogen, phosphorus, and other nutrients for growth

Types of Biodegradability

Aerobic Biodegradation: Occurs in oxygen-rich environments:

Industrial composting systems (controlled aerobic conditions)
Soil environments (especially near surface)
Freshwater systems with adequate aeration
End products: CO2, H2O, and biomass

Anaerobic Biodegradation: Occurs in oxygen-depleted environments:

Landfills and anaerobic digesters
Marine sediments and deep soils
End products: CO2, CH4 (methane), H2O, and biomass
Typically slower than aerobic degradation

Marine Biodegradation: Degradation in salt water environments:

Requires specialized marine microorganisms
Generally slower than composting
Marine certification (e.g., ASTM D6691) requires degradation evidence
Particularly important for preventing ocean plastic pollution

Home Composting: Degradation in household compost conditions:

Lower temperatures (typically 40-50°C) than industrial facilities
Variable microbial populations
Less controlled conditions
Some materials (like PLA) do NOT reliably degrade in home compost

Soil Biodegradation: Degradation in terrestrial soil:

Variable depending on soil composition, temperature, and moisture
Beneficial for agricultural mulch films and plant pots
Generally slower than industrial composting
Requires certified biodegradability standards

Critical Distinctions

Biodegradable ≠ Compostable:

A material can be biodegradable but NOT compostable if it doesn’t meet strict industrial standards
Compostable materials must biodegrade completely within a specific timeframe (typically 180 days) at defined temperatures
Example: A material might eventually biodegrade in a landfill but still not qualify as “compostable”

Biodegradable ≠ Naturally Sourced:

Origin of material (bio-based vs. petroleum-based) doesn’t determine biodegradability
A petroleum-based polyester (like PBAT) can be biodegradable
A plant-derived bioplastic (like some PLA formulations) may not biodegrade in ambient conditions

Biodegradable ≠ Environmental Solution Alone:

Biodegradation requires proper end-of-life management
Materials ending up in landfills biodegrade very slowly without oxygen and appropriate microbial conditions
Ocean-accumulated plastics, even biodegradable ones, persist for years
Ultimate environmental benefit depends on composting infrastructure availability

Biodegradation Timeframes by Material Type and Environment

Industrial Composting (55-60°C, controlled conditions):

PHA: 60-90 days
PHB: 60-90 days
Starch-based: 45-90 days
PLA (with additives): 90-180 days
PBAT: 90-180 days
PBS: 90-180 days
PCL: 6-12 months

Soil Conditions:

PHA: 6-12 months
PHB: 6-12 months
Starch-based: 2-6 months
PLA: 2-4 years (very slow in ambient soil)
PCL: 1-2 years
PBS: 6-24 months

Marine Environments:

PHA: 6-24 months (certified marine biodegradable)
PHB: 6-24 months (certified marine biodegradable)
PLA: Does NOT biodegrade readily (persists for years)
PBAT: Does NOT biodegrade readily
PBS: Variable degradation over extended periods

Ambient/Room Temperature:

Most bioplastics degrade very slowly at room temperature (years to decades)
Requires presence of adapted microorganisms
Moisture is critical factor

Testing and Certification Standards

EN 13432 (European Standard): The most stringent and widely recognized composting standard:

Requires 90% biodegradation within 180 days at industrial composting conditions (58°C)
Requires disintegration (fragmentation) to less than 2mm
Requires ecotoxicity testing to ensure no harmful residues
Used for certification of compostable packaging and products

ASTM D6400 (North American Standard): USA and Canada standard for compostable plastics:

Similar requirements to EN 13432
Allows both industrial and home composting certification
Increasingly aligned with EN 13432 for international trade

ASTM D6691 (Marine Biodegradation): Specifically for marine environments:

Requires evidence of degradation in marine settings
Less stringent timeframe than composting (allows 1-3 years)
Important for fishing gear, ocean applications

OK Compost Certification: European certification program:

TÜV Austria certification body
Validates both EN 13432 compliance and practical composting capability
Widely recognized on consumer products

ISO 14855 Series: International standards for testing methods:

ISO 14855-1: Aerobic biodegradation measurement methods
ISO 14855-2: Anaerobic biodegradation measurement methods
Establishes protocols for determining biodegradation percentages

Environmental and Practical Considerations

Infrastructure Dependency: Biodegradable material benefits depend entirely on appropriate composting infrastructure:

Material in landfill without oxygen degrades extremely slowly
Material in marine environment persists despite theoretical biodegradability
Effectiveness requires separate collection systems from conventional recycling

Consumer Confusion: The term “biodegradable” without context creates misunderstandings:

Consumers may assume biodegradable materials are environmental solutions when carelessly discarded
Clear communication about required conditions (industrial composting, soil, marine) is essential
Labeling should specify timeframe and conditions

Cost-Benefit Analysis: Biodegradable materials add cost:

Processing and material costs typically 30-200% higher than conventional plastics
Benefits only realized if proper composting infrastructure exists
In regions without composting, biodegradable materials offer no advantage over conventional options

Complementary Solutions: Biodegradability works best as part of comprehensive approach:

Product design to minimize unnecessary use (lightweight packaging)
Consumer education on proper disposal
Development of composting infrastructure
Regulatory incentives for compostable materials
Integration with existing waste management systems

Biodegradable Materials Overview

Most Readily Biodegradable:

PHA (all environments): 6-24 months
PHB (all environments): 6-24 months
Starch-based (industrial/soil): 2-6 months

Readily Biodegradable (Industrial Composting):

PLA (requires composting): 90-180 days
PBAT (requires composting): 90-180 days
PBS (requires composting): 90-180 days
Starch/PBAT blends: 90-180 days

Slowly Biodegradable:

PCL (all environments): 6-24 months
PLA (soil, marine): Years to decades

Non-Biodegradable Despite “Bio” Origin:

Bio-PE (from sugarcane): Persists like conventional PE
Bio-PP: Persists like conventional PP
Bio-PET: Persists like conventional PET

Future Perspectives

As understanding of biodegradation mechanisms improves, next-generation bioplastics will likely feature:

Engineered degradation pathways triggered by specific environmental signals
Customizable biodegradation timeframes matching intended application lifespans
Materials designed for specific end-of-life scenarios (composting, marine, soil)
Reduced dependence on specific infrastructure conditions

The ultimate goal is creating materials that provide necessary functionality during their service life while genuinely degrading appropriately in their final environmental destination—whether that’s a composting facility, agricultural soil, or marine environment.