How to Compost PLA?

Industrial Composting Process, Chemical Stages and Recommendations to Consumers:

PLA (Polylactic Acid) is a biobased thermoplastic derived from renewable resources, such as corn starch and sugarcane. PLA, which is used in various applications such as packaging, disposable products, and 3D printing, is environmentally friendly; however, it is necessary to closely examine the composting process to understand its environmental impact fully.

In this article, we provide a comprehensive overview of the industrial composting process for PLA, including the chemicals involved, its environmental impact, EU standards, and specific recommendations for consumers.

Is PLA Really Compostable?

In short: Yes, but only under controlled industrial conditions.

Because PLA does not degrade in the compost bin at home or when left in nature:

Its crystal structure is organised; it requires high temperature, humidity and oxygen; it takes time to break down into chains of molecules that microorganisms can break down in the natural environment.

Industrial Composting Process: How PLA Degrades

Industrial composting plants are controlled systems that provide the high temperature and humidity required for the breakdown of PLA.

Parameter	Value
Temperature	58 ± 2 °C
Nem	%50-60
Oxygen level	≥ %18
Duration	60-90 days
pH	6.0-7.5 (neutral)

Composting Stages:

Phase	Duration	Process	Conclusion
Hydrolysis	0-10 days	PLA molecular chains are broken down by heat and moisture.	Small molecules such as lactic acid and lactide are formed.
Biodegradation	10-40 days	Microorganisms metabolise lactic acid.	CO₂, H₂O and biomass are formed.
Stabilisation and maturation	40-90 days	The compost transforms into a soil-like structure.	Odour and acidity are stabilised, and safe organic matter is obtained.

Chemicals arising in the process:

Chemical	Source	Effect / Usage
Lactic Acid (C₃H₆O₃)	Hydrolysis of PLA	Carbon source for microorganisms
CO₂	Breakdown of lactic acid	Released during composting
Water (H₂O)	Metabolism by-product	Provides moisture balance
Microbial biomass	Proliferation of microorganisms	Structural component of the final compost

No toxic substances are formed in this process. PLA does not contain BPA, phthalates or heavy metals.

European Union Compostability Standard: EN 13432

In Europe, a product must meet the EN 13432 standard to be considered compostable. This standard includes the following requirements:

Criteria	Necessity
Biodegradability	90+% conversion to CO₂ within 180 days
Degradability	At 12 weeks, more than 90% should be fragmented ≤2 mm
Toxicity testing	Compost must not inhibit plant growth
Heavy metal limit	Metals such as lead, cadmium below certain limits

A PLA product without EN 13432 certification is not considered "compostable".

Recommendations for Consumers
When using products containing PLA, the following points should be noted:

Check the certificate:
Do not compost products that are not labelled EN 13432, OK compost INDUSTRIAL or TÜV Austria HOME. All PLA products offered by UTTIL are produced with raw materials labelled "TÜV Austria, OK compost INDUSTRIAL".

Do not recycle, PLA products should be disposed of in the organic waste bin:
If PLA is mixed with plastics such as PET, it disrupts the recycling system. PLA products should be disposed of in the organic waste bin, not recycled.

Do not dispose of in home compost (usually):
Standard PLA does not degrade in home compost. If you wish to compost it at home, the product must be labelled "home compostable".

Is it Possible to Compost PLA at Home?
It is not easy,, but technically possible. Here are some tips for successful home PLA composting:

Application	Description
High temperature	Target ≥50 °C per day (hot composting technique)
Shredding	The PLA pieces should be cut into small pieces or ground into chips.
Pre-treatment	PLA can be kept in boiling water for 1-2 hours to initiate hydrolysis.
Humidity control	Maintain humidity between 50-60 per cent.
Compost additive	The microbial diversity can be increased by adding manure, vermicompost, or mushrooms.
Time	PLA can take 6-12 months to dissolve in home compost completely.

However, this method is not completely reliable for commercial PLA products. Products labelled "home compostable" have a high probability of success.

Conclusion

PLA is a more sustainable option than traditional plastics.

However, being compostable does not mean that it will degrade in any environment.

The actual dissolution only takes place under industrial composting conditions.

Certificates such as EN 13432 are vital indicators to check that this process is working properly.

Making conscious choices as a consumer makes a significant difference in reducing the impact of not only PLA but also all bioplastics on the environment.

Sources:

European Bioplastics Association - https://www.european-bioplastics.org

EN 13432:2000 - Packaging: Requirements for Packaging Recoverable Through Composting and Biodegradation

ISO 17088 - Specifications for Compostable Plastics

ASTM D6400 - Specification for Labelling of Plastics Designed to be Aerobically Composted

NatureWorks LLC - PLA Industrial Composting Data Sheet