Compostable plastics are designed to break down into natural substances such as carbon dioxide, water, and biomass under specific environmental conditions. This process is known as compostable plastic degradation.
Unlike traditional plastics, which can persist in the environment for hundreds of years, compostable plastics are engineered to decompose through biological processes when exposed to heat, moisture, oxygen, and microorganisms.
Understanding how compostable plastics degrade is essential for using compostable products correctly and ensuring they deliver their intended environmental benefits.
In this guide, we will explain:
- how compostable plastic degradation works
- the biological and chemical processes involved
- the conditions required for decomposition
- how long compostable plastics take to degrade
- why industrial composting is often required
If you are new to compostable materials, start with our introduction to what are compostable materials.
What Is Compostable Plastic Degradation?
Compostable plastic degradation is the process in which compostable polymers are broken down by microorganisms into natural substances.
The final products of compostable plastic degradation typically include:
- carbon dioxide (CO₂)
- water
- biomass
- organic matter
These substances are safely returned to the natural environment without leaving harmful microplastics.
Many compostable plastics are made from plant-based polymers such as PLA (polylactic acid) and PBAT. These materials are part of the broader category of bioplastics.
The Stages of Compostable Plastic Degradation
Compostable plastics do not disappear instantly. Instead, they break down through several stages.
1. Hydrolysis
The first step is hydrolysis, a chemical reaction where water molecules break down the polymer chains.
During this stage:
- long polymer chains begin to break into smaller fragments
- the plastic becomes brittle
- molecular weight decreases
Hydrolysis is particularly important for materials such as PLA.
2. Microbial Decomposition
After the polymer chains are broken into smaller molecules, microorganisms begin to consume them.
Bacteria and fungi convert these molecules into:
- carbon dioxide
- water
- microbial biomass
This stage is known as biodegradation.
3. Mineralization
The final stage is mineralization, where organic compounds are completely converted into natural substances.
At this stage:
- no visible plastic fragments remain
- the material becomes part of the compost
- nutrients return to the soil
This complete cycle differentiates compostable plastics from conventional plastics, which often fragment into microplastics rather than fully degrading.
Conditions Required for Compostable Plastic Degradation
Compostable plastic degradation only occurs efficiently when several environmental conditions are present.
Temperature
Most compostable plastics degrade best at temperatures between:
50°C – 70°C (122°F – 158°F)
These temperatures are commonly achieved in industrial composting systems.
Learn more in our guide to industrial composting.
Moisture
Water is necessary for hydrolysis and microbial activity.
Without adequate moisture, compostable plastics may remain intact for long periods.
Oxygen
Composting is an aerobic process, meaning it requires oxygen.
Oxygen allows microorganisms to metabolize organic materials efficiently.
Microorganisms
Microbial activity is essential for the biodegradation phase.
Common microorganisms involved include:
- bacteria
- fungi
- actinomycetes
These microorganisms convert degraded polymers into organic matter.
How Long Do Compostable Plastics Take to Degrade?
The degradation time of compostable plastics depends heavily on environmental conditions.
Typical timelines include:
| Environment | Degradation Time |
|---|---|
| Industrial composting | 90–180 days |
| Home composting | Several months to over a year |
| Landfill | Extremely slow degradation |
Because of these differences, many compostable products are designed specifically for industrial composting systems.
If compostable plastics are sent to landfill, they may not break down properly. Learn more in our article on do compostable bags break down in landfills.
Why Industrial Composting Is Often Necessary
Industrial composting facilities provide the optimal environment for compostable plastic degradation.
These facilities maintain:
- high temperatures
- controlled moisture levels
- continuous oxygen supply
- active microbial populations
As a result, compostable plastics can degrade much faster and more completely.
In contrast, home compost systems often operate at lower temperatures and may not provide consistent conditions.
To understand the differences, read our comparison of home composting vs industrial composting.
Certification Standards for Compostable Plastics
To ensure compostable plastics degrade properly, many products must meet certification standards.
Common compostable plastic standards include:
- ASTM D6400
- EN 13432
- BPI certification
These standards test whether a material can:
- biodegrade within a defined time
- disintegrate during composting
- leave no toxic residues
You can learn more in our article on ASTM D6400 certification.
Factors That Affect Degradation Speed
Several factors influence how quickly compostable plastics degrade.
Material composition
Different materials degrade at different rates.
Examples include:
- PLA
- PBAT
- starch-based polymers
Thickness
Thicker films take longer to degrade.
Compost conditions
Temperature, oxygen, and moisture levels all influence degradation speed.
Microbial activity
The diversity and activity of microorganisms affect the biodegradation process.
The Importance of Proper Disposal
Even though compostable plastics are designed to degrade, they must be disposed of correctly.
Improper disposal can prevent degradation and reduce environmental benefits.
For example:
- compostable bags placed in recycling streams contaminate plastic recycling
- compostable plastics sent to landfill may not degrade properly
For guidance on correct disposal methods, see how to dispose of compostable bags.
Conclusion
Compostable plastic degradation is a biological and chemical process that converts compostable polymers into natural substances such as carbon dioxide, water, and organic matter.
This process requires specific environmental conditions including heat, moisture, oxygen, and microbial activity.
When compostable plastics are sent to appropriate composting systems, they can break down efficiently and contribute to nutrient-rich compost. However, improper disposal—such as sending compostable plastics to landfill—can prevent the degradation process from occurring.
Understanding how compostable plastic degradation works helps ensure compostable materials are used and disposed of responsibly.
FAQ
What is compostable plastic degradation?
Compostable plastic degradation is the process in which compostable polymers are broken down by microorganisms into natural substances such as carbon dioxide, water, and biomass.
Do compostable plastics break down naturally?
Compostable plastics degrade effectively only under composting conditions that include heat, moisture, oxygen, and microbial activity.
How long does compostable plastic take to degrade?
In industrial composting systems, compostable plastics typically degrade within 90 to 180 days.
Can compostable plastics degrade in landfills?
Most compostable plastics do not degrade efficiently in landfills because landfill environments lack the oxygen and microbial activity required for composting.
If you are sourcing certified compostable packaging products, explore our compostable bag manufacturing solutions Compostable Bags Manufacturer
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