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PLA: The Compost Conundrum

 

You might have visited one of your favorite lunch spots recently and seen that they offer “Plant-based plastic alternatives” for your plastic cups and utensils. Plant-based plastics are becoming a popular substitute for the usual materials one might see, like PET and PP. While still a very small part of the plastics industry, plant-based plastics, or bioplastics, are being used more by manufacturers catering to the demand for oil-based plastic alternatives.

The bio-plastic seeing the most growth recently is Polylactic Acid, also known as PLA. PLA is derived from renewable resources such as corn starch or sugar cane, which makes it more eco-friendly than it’s oil-based counterparts. Currently, PLA has seen it’s rise as a substitute for PET, the material used in many products such as water bottle, clear plastic cups, and food packaging. PLA is also the primary material used in the 3D printing industry.

The increase in bio-plastics usage has, however, created a significant issue in the recycling industry. There are a number of reason why PLA and bio-plastics recycling has become problematic for recyclers and waste handlers. First, the material is still very new and the market for recycled PLA and bio-plastics is weak. The demand for recycled PLA and bio-plastics is very low because the industry is lacking infrastructure to process the waste and also that oil-based plastics still dominate the recycling industry. Second, the low recycling rate of PLA due to the misguided notion that bio-plastics like PLA are compostable and therefore thrown away with regular trash or compostable waste. The idea that bio-plastics are compostable is very misleading. 

This is not to say that PLA and bio-plastics are not more compostable and likely to break down in a landfill, just that these materials are not as compostable as the general public told. Bio-plastics can break down over time and under the right conditions whereas oil-based plastics never break down chemically nor are absorbed into their surroundings. However, the conditions necessary for proper chemical breakdown and compost for bio-plastics won’t be found in your backyard compost or even in a landfill.

The best conditions for degradation and breakdown of PLA are extreme and not normally found in nature. In order to properly break down PLA, the material must be exposed to 60 degrees Celsius (140 degrees Fahrenheit) heat for close to five continuous days. These conditions will only be found in commercial composting facilities and not in your garden compost. Also, commercial composter's are unable to capture carbon dioxide, a by-product of PLA degradation, which will eventually be released into the atmosphere.

Composting might be less of an issue if the US had a good commercial composting infrastructure, which it does not. There are only about 200 commercial composting facilities in the US and most of them do not even accept PLA as a compostable product. So between the lack of demand from the recycling industry and the true compostability of PLA, there’s little that can be done with bio-plastic waste.

While the compostability of bio-plastics is an unresolved issue, they still are a good alternative to oil-based plastics. By utilizing renewable resources while simultaneously raising awareness about the recyclability of bio-plastics, the issue of how to properly and responsibly dispose of your PLA could one day be a thing of the past.