Is PLA really biodegradable?
8.6.2020
Translation: Eva Francis
PLA is the most used 3D printing material. Why? It's easy to handle and marketed as biodegradable, i.e. environmentally friendly. However, this isn't entirely true.
Ever since I started 3D printing, I've read that PLA is biodegradable. However, when a print fails, I throw it in the rubbish bin, not the compost. But is that the right thing to do? If not, where do I dispose of waste material for composting? My research revealed that PLA is only biodegradable under certain circumstances.
What is PLA?
Unlike petroleum-based plastics, PLA is made from renewable raw materials. It's almost CO₂-neutral and the material doesn't emit any toxic fumes.
PLA is a polyester produced by fermentation from a carbohydrate source such as corn starch or sugar cane. In the production process, corn is first ground wet to separate the starch. Then the starch is mixed with acid or enzymes and heated up. During this process, the starch is split into dextrose (D-glucose), corn sugar. Finally, the fermentation of glucose produces L-lactic acid, which is the basic component of PLA.
There are two methods of producing PLA from lactic acid. The first method uses L-lactide as an intermediate stage, which leads to a higher molecular weight. The second method involves direct polymerisation of lactic acid.
Biodegradable, but only under certain conditions
From an ecological point of view, it all sounds good: PLA is almost CO₂-neutral and any waste material can just be disposed of in the compost. But it's not that simple. It can take several hundred years for PLA to decompose in conventional garden composts. Studies by Williams and Tsuji and Miyauchi have revealed this. Youtuber Hobby Hoarder has turned it into a video.
The process of biodegradation and its duration are highly dependent on the environment. Oxygen, humidity, temperatures of about 60° Celsius and special microbes are necessary for the degradation of PLA. You will hardly find this combination in nature. This is where industrial composting comes into play. It creates the necessary conditions for PLA to decompose. But even with industrial composting, the material only decomposes after about six months. And not all facilities are suitable for the decomposition of PLA.
Should you recycle PLA best with other plastics? No, because the material can interfere with the recycling process of other plastics. Is incineration the best option after all? That's not the best solution either, as PLA isn't completely CO₂-neutral.
Apart from incineration and industrial composting, there another option: special PLA recycling. You can turn your waste material back into printable filament. All3dp has written an article about it, if you're interested in the details.
What's even better than recycling, incineration and composting is being thoughtful when you do 3D printing. The less waste you produce, the better for the environment.
Kevin Hofer
Senior Editor
kevin.hofer@digitecgalaxus.chFrom big data to big brother, Cyborgs to Sci-Fi. All aspects of technology and society fascinate me.
