As discussed in a previous story, oil majors are hoping to shift to petrochemicals as the world attempts to replace fossil fuels with renewable energy.
Due to the historic role these conglomerates have played in our ongoing ecological collapse as well as the basic need to move away from fossil fuels altogether, industrial society might instead aim to supplant petro-based polymers with polymers derived from other natural sources.
In this series, we’ll discuss biopolymers that could become prominent feedstock in additive manufacturing (AM), as well as some that are already being used in 3D printing.
One of them is so important, however, that it’s worth spending an entire article on the topic. Naturally, we have start to with polylactic acid (PLA).
Where Does PLA Come from?
PLA is the most popular material for desktop 3D printers, largely due to the fact that it is easy to process and has decent durability. Many 3D printer operators also believe PLA to be safe since it is derived from natural materials.
PLA is made from natural sugars, which can be derived from corn starch, sugarcane, as well as cassava roots, chips or starch.
In part due to the massive corn subsidies in the U.S., the most widely available brand of PLA is the corn-based Ingeo from NatureWorks, jointly owned by Cargill, the largest privately owned company in the U.S., and the Thai state-owned oil and gas business PTT Public Company Limited.
The second-largest PLA manufacturer is Corbion, which manufactures Luminy brand PLA from sugarcane.
Ingeo comes from a specific breed of corn known as grade #2 yellow dent corn (or “field corn”), grown for industrial purposes such as livestock feed, sweetener, ethanol, starch for adhesives and other materials, and Ingeo.
PLA is made only from the kernels of the corn, which are milled before the starch is extracted and converted from glucose to dextrose.
Microorganisms ferment the dextrose into lactic acid, which is then converted into lactide and formed into long polymer chains using ring-opening polymerization to create PLA.
How Sustainable is PLA?
Instinct might tell us that PLA is more sustainable than petro-based plastics because they are not derived from petroleum or natural gas, but from biomass.
Therefore, supplanting petroplastics with PLA could reduce the 1 percent of U.S. greenhouse gas (GHG) emissions associated with plastic production.
In fact, a 2017 study determined that doing so would reduce GHG emissions by 25 percent and that, by powering plastic production facilities (PLA or not) with renewable energy, emissions could be cut by 50 to 75 percent.
However, there are other factors to consider related to PLA that should be taken into account, many of which are associated with the crops used to make PLA.
PLA releases fewer GHGs from outgassing as it degrades in the environment when compared to petro-plastics; however, the fertilizers and pesticides used to grow the plants that make up PLA in the first place could release more pollutants.
This could be reduced by switching to organic, non-genetically modified crops. In the meantime, NatureWorks gives its customers the option of purchasing non-GMO Ingeo, but the default product uses GMO plants, which are correlated with higher pesticide usage.
Moreover, fertilizers used to grow PLA feedstock are responsible for a large amount of GHG emissions. Nitrous oxide, a byproduct of low-cost, nitrogen-based fertilizers, is 310-times more potent than carbon dioxide.
A competing bioplastic manufacturer calculated that, “if Natureworks was at full capacity in production it would create 56 [terra grams] of carbon dioxide equivalent more than all of the landfills combined in the United States…”
PLA is also considered compostable and recyclable, but it such a categorization is misleading due to the fact that it can only be composted in an industrial compositing facility.
Only one-quarter of the 113 total such facilities in the U.S. accept residential waste. In other words, not only is PLA not compostable in one’s backyard, but it is even difficult to compost via municipal waste collection in the U.S.
As a result, PLA in the U.S. tends to end up in landfills, with researchers unable to determine the exact natural decomposition rate but estimating between 100 and 1,000 years. As it decomposes, it releases methane, a gas 23 times more potent than carbon dioxide.
We should also note the amount of water required to make PLA, which is about 2.5-times less than is needed to produce Styrofoam but 38 percent more than polypropylene and 10 percent more than PET. If we look at total water usage throughout production, some estimates state that around 50 Kg of water is needed for one kilogram of PLA.
This is probably higher than you imagined but is still significantly lower than the 700 Kg needed for one kilogram of Polyamide 66. If we look at the water footprint of bioplastics one researcher found that PLA compares well to almost all bioplastics in that regard.
We might consider the amount of land that PLA feedstock requires.
The Plastic Pollution Coalition projected that, to meet global demand for bioplastics by 2019, 3.4 million acres of land (bigger than Belgium, the Netherlands and Denmark combined), would be required.
In a climate-disrupted world with a rising population, where agricultural yields are shrinking as a result of volatile weather, increased drought, and more pests, land for bioplastics will be competing with land used for food production.
This is then linked to how land by PLA manufacturing agro-businesses is used. Putting aside its issues that aren’t directly tied to the climate crisis—such as its human rights abuses, child trafficking and land grabs—Cargill has been heavily involved in deforestation to make room for the production of its crops, such as soy, palm oil and cocoa.
For all of these reasons, we will have to thoughtfully consider the role that we want plastics, petro-based or otherwise, to play in a society constrained by climate disruption.
In the next section of this series, we will consider more of these bioplastics with the hope of overcoming some of the issues associated with desktop 3D printing’s favorite plastic, PLA.
Published on 3dprint.com
- Polylactic Acid Polyols in Urethane Coatings
- Plantbased? Compostable? What You Need to Know About Bioplastics
- Quality and Performance of Recycled Polymers in Europe
- Biodegradable Polymers in Various Environments