How Long Does It Take for PLA to Biodegrade

Many people are curious about how long it takes for PLA to biodegrade. This article will focus on this key point and hopefully be helpful.

What is PLA ?

Polylactic acid, also known as polylactic acid or polylactide (PLA), is a plastic material.

Polylactic acid (PLA) is a renewable and sustainable emerging polymer material. Its full name is Polylactic Acid, and its Chinese name is polylactic acid. Made from plant-based raw materials, such as starch from corn and cassava, PLA has been widely used in packaging materials due to its biodegradability.

How Long Does PLA Take to Biodegrade?

PLA (polylactic acid) Under ideal industrial composting conditions (50-60°C, high humidity), degradation is typically achieved within 3-6 months (referring to EU EN 13432). Temperature, humidity, microbial activity, pH, and aerobic conditions significantly influence degradation.

How PLA Biodegradation Works

Hydrolysis (chemical degradation): When exposed to moisture, PLA's ester bonds break, reducing its molecular weight and making the material brittle.
Microbial decomposition (biodegradation): Low-molecular-weight fragments are metabolized by microorganisms (such as bacteria and fungi) into CO₂, water, and humus.

The molecular structure of polylactic acid (PLA) shows that its ester bonds are easily hydrolyzed, allowing it to be degraded in the body or in the soil by microorganisms to produce lactic acid. The final metabolic products are water and carbon dioxide, making it non-toxic and very safe to use.

In the natural environment, it first undergoes hydrolysis, breaking down unstable ester bonds in the main chain into oligomers. Microorganisms then enter the compost and decompose it into carbon dioxide and water. Under composting conditions (high temperature and high humidity), the hydrolysis reaction is readily completed and the decomposition rate is relatively fast. In environments less prone to hydrolysis, the decomposition process is more gradual.

Microorganisms are ubiquitous in nature, and PLA can be degraded by a variety of microorganisms, such as Candida albicans, Penicillium, and Humicola.

Different bacteria have different degradation profiles of PLA. Research results show that Candida albicans and Penicillium can completely absorb D,L-lactic acid, and some can also absorb soluble PLA oligomers.

Degradation Time of PLA in Different Environments

Industrial Composting Environment

PLA degrades most rapidly under industrial composting conditions (high temperatures of 55-70°C, high humidity, and microbial action), typically taking 3-6 months.

Natural environment or home composting

Under normal temperature and without specific microbial catalysis, degradation time is significantly prolonged, potentially exceeding one year.

Degradation in the human body

As an absorbable material (such as sutures and tissue engineering scaffolds), PLA undergoes complete degradation in the human body through hydrolysis and enzymatic degradation in approximately 12-24 months.

Factors affecting PLA degradation behavior:

Molecular structure factors

(1) Relative molecular weight

One of the key factors affecting PLA hydrolysis degradation. For the same mass of PLA solution, the higher the relative molecular weight, the worse the fluidity, that is, the weaker the molecular mobility, and the higher the relative molecular weight, the lower the end group concentration, the lower the probability of hydrolysis, the smaller the self-catalytic effect, resulting in slower PLA hydrolysis.

(2) Crystallinity

The degradation rate of the polymer is inversely proportional to the crystallinity, but the crystallinity will increase as the degradation proceeds.

(3) Stereotacticity

Under the condition of pH>7, the degradation rate of PLA with different stereotacticities shows an upward trend, indicating that PLA with different stereotacticities will have different degradation effects.

Environmental factors

(1) Temperature

The temperature is directly proportional to the PLA degradation reaction. During the thermal degradation of PLA, the main reaction is intramolecular ester exchange reaction, so the ester group decreases at the fastest rate. Because the increase in temperature will promote the progress of this main reaction, the ester group content will decrease rapidly. The order of decrease rate is ester group > methyl group > carbonyl group.

(2) pH value PLA can be degraded in both alkaline and acidic environments, but degradation in alkaline environments is more favorable. High concentration HO- environment is conducive to the hydrolysis of ester groups.

Process factors

(1) Heating rate

The increase in heating rate will cause obvious thermal hysteresis. The reason may be that at a higher heating rate, the system takes less time to reach the same temperature as at a lower rate.

(2) Gas atmosphere

Some researchers have pointed out that the presence of oxygen will accelerate the breakage of PLA molecular chains. The reason is that the increase in oxygen concentration reduces the activation energy of the thermal degradation reaction, the ester group breaks rapidly, and at the same time, degradation products containing terminal hydroxyl groups are generated under the action of oxygen, which further triggers the open chain depolymerization reaction of PLA, generates acetylene and volatilizes, resulting in a reduction in the hydroxyl content of PLA.

(3) Other factors

The concentration of PLA solution has a great influence on the degradation process of PLA under UV light. The lower the concentration of PLA solution, the easier it is to degrade PLA.

What Should You Do With Scrap PLA Filament?

Mechanical recycling:

The most common method involves shredding, cleaning, drying, and re-extruding waste PLA filament into new 3D printing materials or other plastic products. This method uses less energy, but the material's performance degrades after repeated recycling.

Chemical recycling:

PLA can be degraded into lactic acid or other monomers through depolymerization processes (such as methanolysis, ethanolysis, and hydrolysis). This method is suitable for PLA waste with high impurities or degraded properties, but it consumes more energy and is more suitable for high-purity recycling or specific applications.

Impact of PLA degradation on the environment and sustainable development

Advantages of PLA biodegradation:

PLA is made from agricultural crops (such as corn), resulting in lower greenhouse gas emissions during production and a significantly better carbon footprint than petrochemical plastics. It is also safe for food contact and biomedical applications.

Limitations of PLA:

Without industrial composting, PLA barely degrades in ordinary soil, oceans, and landfills, similar to traditional plastics. It may even release greenhouse gases such as methane in landfills. Furthermore, PLA cannot be mixed with traditional plastics for recycling, as this will affect the quality of the recycling system.

Advantages of PLA composting:

Only when PLA is composted in industrial composting facilities with high temperatures, high humidity, and abundant microorganisms can it achieve over 90% degradation within a few weeks to six months, making a closed-loop circular economy truly viable.

PLA vs. Traditional Plastics

Feature	PLA (Polylactic Acid)	Traditional Plastics
Raw Material	Renewable (plant-based)	Petroleum, natural gas
Greenhouse Gas Emission	Low	High
Biodegradability	Biodegradable under industrial composting conditions	Generally non-biodegradable
Performance	Easy to process; low heat resistance; moderate toughness	High heat resistance; high toughness
Recycling	Recyclable via specialized processes; affected by contamination	Well-established system; widely recycled mixed plastics
Environmental Impact	Degradable under suitable conditions; otherwise similar to conventional plastics	Persistent pollution; high microplastic risk

In normal temperature environments such as soil and ocean, PLA degradation is extremely slow and may take several years or even longer. Fragmented PLA will still pollute the environment as microplastics, posing similar risks to the ecosystem as petrochemical plastics.

The Future of PLA as a Plastic Alternative

Market Growth: The global PLA market is projected to grow at a compound annual growth rate of approximately 20% from 2021 to 2025, with rapid growth in demand in areas such as food packaging, medical devices, and textiles.

Policy Drivers: Restrictions on single-use plastics in various countries and rising consumer environmental awareness are accelerating the adoption of biodegradable materials like PLA.

Process Upgrades: Technological research and development will further optimize PLA's performance (such as heat resistance and toughness), improve degradation efficiency, reduce costs, and promote recycling and industrial upgrading.

Conclusion

Under industrial composting (high temperature and humidity), PLA can degrade by 90% within a few weeks to six months; under normal conditions, degradation is extremely slow, potentially taking years or even centuries. PLA products should be encouraged to enter specialized composting or recycling systems to prevent them from entering the natural environment or being mixed with traditional plastics, truly realizing green advantages and reducing environmental burdens.

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