It should come as no surprise that we are currently facing a worldwide plastic problem, and we have been for a while. Many solutions have cropped up as ways to either fix the problem or reduce its severity: one very popular one being the usage of PLA. We here at CLP love PLA; we think it’s a great plastic that’s extremely useful for all kinds of things, be it injection molding for our disposable utensils or your awesome 3D printing projects! But the thing we most often see inscribed on PLA-made consumer objects is “Compostable”. PLA has been branded as the environmentally healthy bioplastic alternative: it’s made from corn after all! But is this really true? Or is this just very creative, very misleading marketing?
PLA as a bioplastic
One of the main factors that makes PLA such an attractive plastic alternative is that it’s not petroleum based. Because it “comes from corn” it’s made from a renewable resource, but we like to think of this fact in the context of another: ethanol is also made from corn, but we definitely would not recommend drinking ethanol. The point is that even if the source of a material is renewable and may not be as damaging to the environment as petroleum, said source had to go through many changes and processes in order to become what we know as PLA. Is it an improvement to be using bioplastics over traditional petroleum-based plastics, of course! But let’s not have the conversation end there.
Understanding the PLA lifecycle in terms of energy
So let’s take a walk through the PLA lifecycle from synthesis to composition. From the get-go it takes 27.2 MJ/kg of fossil energy to synthesize the plastic from corn and produces 1.2kg of CO2 per kg, as stated in this study by NatureWorks on their PLA production . This is a huge improvement over traditional petroleum-based plastic production, and a huge plus for PLA! Let it also be known that NatureWorks is doing a great job at trying to reduce their GHG emissions through incorporating ways to save energy in every step of the process if possible. After the PLA is used and disposed of, it’s headed, as we have come to expect, to the decomposition process.
When you think of composting what comes to mind? It’s probably a green, farm to table type of setting where everything is natural, serene, and maybe slightly smelly. The thing to keep in mind here is that though PLA is labeled as “compostable,” there’s an asterisk attached to that label that not everyone is keen to make note of. PLA is compostable in an industrial composting facility. You can’t bury a PLA cup in your backyard and hope that it breaks down. The process bioplastics undergo during composting is an energy intensive process requiring roughly 43 MJ/kg alone, as found by this study that conducts an LCA comparison among different PLA disposal methods . This is significantly higher than other forms of plastic waste disposal. It also produces an additional 1.2kg of CO2 per kg and at most only around 60% of the waste is actually successfully composted. To add insult to injury, the kind of processing capacity we need may not be something that’s accessible at least in the near future. As NatureWorks notes, these facilities are still limited.
But what if, instead of composting the PLA, we decide to mechanically recycle it? Well, in a study conducted by the University of Naples , they calculated that mechanical recycling actually produces an energy savings of 5.2 MJ per kg. Across the board mechanical recycling of plastics results in less water and crude oil consumption, less CO2, air, and water emissions, and less solid waste production compared to other forms of plastic waste disposal. The LCA study conducted by Cosate de Andrade et. al  also confirms that mechanical recycling
results in the lowest degree of environmental impact compared to other forms of disposal like chemical recycling and composting. And because mechanical recycling is a widespread practice, the capacity for recycling plastics is much higher than that of industrial composting. On top of that, because mechanical recycling upcycles the waste, the resulting material can be used again! So not only do we gain all of these reduction benefits, we also don’t have to synthesize as much plastic material either, which just adds on to the savings! On the other hand, composting downcycles the material, so we can’t use it again; it becomes compost and then we have to go and synthesize more corn to have more PLA.
So what’s the moral of the story here?
A bioplastic future is not as simple as it may seem, but that’s not to say that it won’t improve the state of things as they are today! We just need to be wise about how we handle disposal of plastics in such a way that is environmentally sound and energy efficient. There are alternative avenues for handling our plastic waste aside from composting, because a synthesis to composting cycle is still crade-to-grave no matter how you spin it. We have an opportunity here to pursue a crade-to-cradle method for handling our PLA waste and we can achieve that through mechanical recycling. So even though a “compostable” plastic sounds like a save-all, it might actually be better for us to mechanically recycle our PLA!
1.Vink, Erwin T.H. “The Eco-Profiles for Current and near-Future NatureWorks® Polylactide (PLA) Production.” Http://Cms.natureworksllc.com/, 2007, cms.natureworksllc.com/~/media/The_Ingeo_Journey/EcoProfile_LCA/EcoProfile/NTR_Eco_Profile_Industrial_Biotechnology_032007_pdf.pdf.
2.Cosate de Andrade, Marina F., et al. “Life Cycle Assessment of Poly(Lactic Acid) (PLA): Comparison Between Chemical Recycling, Mechanical Recycling and Composting.” Journal of Polymers and the Environment, Springer US, 20 July 2016, link.springer.com/article/10.1007/s10924-016-0787-2.
3. Perugini, Floriana, et al. “A Life Cycle Assessment of Mechanical and Feedstock Recycling Options for Management of Plastic Packaging Wastes.” Academia, Wiley InterScience, 11 Apr. 2005, www.academia.edu/17660265/A_life_cycle_assessment_of_mechanical_and_feedstock_recycling_options_for_management_of_plastic_packaging_wastes.