The Misleading Biodegradability of PLA

PLA is a polymer made from high levels of polylactic acid molecules. For PLA to biodegrade, you must break up the polymer by adding water to it (a process is known as hydrolyzing). Heat and moisture are required for hydrolyzing to occur.

The vast majority of FDM (fused deposition modeling) 3D printers primarily consume ABS or PLA filament. ABS, a petroleum-based thermoplastic, is a little tougher and a bit more flexible than PLA, but also a little more finicky to print with. ABS generally requires a heated bed to reduce warpage and also emits a potentially troublesome scent as it is extruded. PLA on the other hand, or polylactic acid, is derived from starchy sources – most often sugarcane or corn starch and has a far more palatable (some note a breakfast waffle-like) scent when extruded.

Marketers love to tout the biodegradability of the material, and it’s true, that at some point it will biodegrade, like what Pura Vida Bioplastics already produces!

The reality, however, is most are using PLA and that process will take several hundred years in a typical landfill. To biodegrade, PLA requires a laundry list of conditions to effectively break down. Specifically – oxygen, a temperature of 140+ degrees, and a 2/3 cocktail of an organic substrate. Collectively, these are absent in any scenario outside of industrial composting facilities. This means that PLA plastic will sit in that landfill right alongside ABS and other plastics for a very long time.

When considering the environmental friendliness of a particular product, it is essential to consider the amount of energy used to create that product. For all plastics, the energy required is particularly significant. This dictates that the ultimate waste of that energy is to literally discard it. For this reason, keeping the material in its intended physical form is far more responsible. 

 

Is PLA Sustainable?

Bioplastic refers to plastic made from plant / biological material instead of oil. Polylactic acid/polylactide (PLA) is an example of a bioplastic.
However, bioplastics – such as PLA – compete for land with food crops. According to the Guardian, bioplastics need several million acres of farmland, which reduces the space available for food crops growth. However, this problem may be over-stated as according to an estimation by European Bioplastics, “… the land area used to grow biomass for the production of bioplastics in 2017 corresponded to 0.016 percent of the global agricultural area, 97 percent of which are used to grow food and feed. Even with the predicted high growth-rates… the land-use share would only slightly increase to up to 0.021 percent of the agricultural area by 2022.”

Is PLA Biodegradable?

 

Biodegradability refers to the ability of a material to decompose after interactions with biological elements. Whilst PLA is biodegradable, it does so very slowly. Analysts estimate that a PLA bottle could take up to 1000 years to decompose in a landfill. Even NatureWorks, the world’s largest producer of PLA, has openly accepted that its products would not fully break down on landfill sites.

Further research by nova-Institut GmbH illustrates PLA is only biodegradable under industrial/anaerobic composting conditions. No evidence exists to prove biodegradability in soil, home compost nor landfill.

Is PLA Compostable?


Composting Process

While biodegradable materials are designed to break down within landfills, compostable materials require special composting conditions.

According to Elizabeth Royte, writing in Smithsonian, ‘PLA is said to decompose into carbon dioxide and water in a controlled composting environment in fewer than 90 days. However, ‘controlled composting environment’ refers to industrial composting facility heated to 140 degrees Fahrenheit and fed a steady diet of digestive microbes.

Whilst this proves PLA is biodegradable/compostable, again it’s feasibility versus practicality argument. The Guardian found that only a handful of anaerobic digesters exist in Britain, and even then without a centralized collection infrastructure the average consumer is unable to access such facilities.

Is PLA Recyclable?

As concluded in a 2016 academic paper, “…mechanical recycling presented the lowest environmental impact…”. The (mechanical) recycling process of PLA includes the following steps: separation, grinding, washing, drying, extrusion, cooling, granulation, and sieving of recycled PLA.  Whilst recycling PLA is certainly feasible it is not necessarily practical. Because PLA of different origin than regular plastic, it must be kept separate when recycled, otherwise it can contaminate the recycling stream – thus making such streams unsaleable. As the BBC stated in February 2019, the technology for plant-based compostables has come so far that it is hard to tell which is plastic and which is bio-plastic (PLA).

Conclusion

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PRODUCTION GREENHOUSE GAS EMISSIONS INCLUDING BIOGENIC CARBON UPTAKE (Natureworks.com)

Whilst there are elements of greenwashing when it comes to the marketing of PLA, the evidence still suggests it is a step in the right direction in our attempts to reduce the consumption of non-renewable petroleum. Not only is PLA plant-based, but [according to Natureworks] it also emits a fraction of the greenhouse gases compared to other plastics, as well as much less energy-intensive.

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