Bio-based plastics: a mixed bag. Just because they come from plants, does that mean they break down easily? Research from the University of California San Diego into biologically sourced microplastics sheds light on this topic and prompts some thinking.
The National Geographic Society says it might take ages literally hundreds to thousands of years for plastics to fully break down. Meanwhile, they just keep breaking into smaller pieces, like microplastics and nanoplastics. This isn’t just from tossing plastic stuff away carelessly or the usual recycling and dumping routines. It’s also about things like treating sewage, losing stuff into the ocean during shipping, tires wearing down, and washing certain fabrics. All this ends up spreading tiny plastic bits everywhere, causing widespread contamination in terrestrial and marine ecosystems, with significant negative impacts on human, animal, and plant organisms [source: “A Global Perspective on Microplastics” – Journal of Geophysical Research: Oceans, 2020].
A deep dive by Seoul National University [“Effects of microplastics on the terrestrial environment: A critical review” – Environmental Research, 2022] focuses on the dangers posed by the numerous interactions of microplastics with the soil. «They’re getting into all sorts of nasty stuff, like pesticides, pollutants, heavy metals, and antibiotics, and spreading them around. They even make their way up the food chain, which could be bad news for everyone’s health».
The game plan? To come up with new types of plastics that are not only kinder to the planet but also vanish quickly after we’re done with them. But it’s not as simple as it sounds. The whole idea of “biodegradability” and what it really means according to EU rules and the chemical makeup of the alternative materials is where things get tricky.
If these factors are not considered, it is difficult to understand why many types of biologically based plastics (also known as “bio-based” or “bioplastics”) currently in circulation, despite reducing the carbon footprint compared to those obtained from petroleum, are not at all biodegradable. This brings us back to square one.
TAKEAWAYS
What makes plastic “biodegradable”?
Let’s start by noting that, in chemistry, a compound undergoes biodegradation through enzymatic processescarried out by microorganisms present in the environment (such as bacteria or fungi), which transform it into natural substances (water, carbon dioxide, or mineral salts) and thus integrate it into nature’s cycles.
Key guidelines for calling a plastic material “biodegradable” include the UNI EN ISO 14855-1:2013. This one’s about the European standards for figuring out if plastic materials can fully break down “aerobically under controlled composting conditions” – basically, 90% of it needs to decompose in six months or less, as proven by solid biodegradability tests.
There are also other standards, like EN 13432:2000 for compostable plastics in packaging and UNI EN 14995:2007 for all other plastic goodies. Part of what they look for is whether the material can pass biodegradability (again, 90% in six months) and disintegration tests, which means the material needs to break down into tiny pieces smaller than 2mm within three months.
Biodegradability: a matter of chemical structure rather than material origin
When it comes to how quickly compostable plastics can break down and fall apart, a study that caught everyone’s eye last year was a joint effort from the University of California San Diego and Northwest University. They published a piece in PLOS One on 24 May 2023, named “Not so biodegradable: Polylactic acid and cellulose/plastic blend textiles lack fast biodegradation in marine waters”, that took a hard look at some compostable materials out there «that are labeled as “biodegradable”. Yet, these materials need very specific conditions to break down quickly, conditions that you’d only find in industrial setups with high heat, not out in nature».
The focus was on the well-known compostable bioplastic made from polylactic acid (PLA), which is made from the sugars in corn and beetroot.
The team checked how well it breaks down in the ocean by testing textiles made with this bioplastic, and they didn’t stop there. They also looked at textiles made from cellulose-based plastic and oil-based, non-biodegradable plastics, finding out this:
«The findings show that polylactic acid doesn’t break down in marine environments for more than 428 days. This was true for oil-based polypropylene and polyethylene terephthalate too, even when mixed into cellulose/plastic textiles. On the flip side, natural and regenerated cellulose fibers fully biodegrade in about 35 days»
In a fresher piece of research by the same San Diego crew, titled “Rapid biodegradation of microplastics generated from bio-based thermoplastic polyurethane” and released in Scientific Report on 12 March 2024, the study group pointed out that for biodegradation to kick in, the plastic’s chemical structure needs to have chemical bonds that enzymes, which microorganisms use, can get to.
This sheds light on why «even though loads of bio-based plastics come from renewable sources like bio-polyethylene and bio-polyethylene terephthalate (bioPET), both from sugarcane, they might still stick around in the environment. That’s because the chemical tweaks that make them durable also lock them away from being broken down biologically».
It might sound odd, but – as the researchers underline – you can actually create biodegradable plastics from petroleum or other fossil materials. This is because whether something can biodegrade or not is down to its chemical structure, not so much where it originally comes from.
Biodegradable plastic: a glimpse on bio-based thermoplastic polyurethane
On the hunt for plastics that don’t hang around too long, creating microplastics that last just a few months at most, the team from the University of California San Diego took a close look at polyurethanes. These are the kind of polymers you find in all sorts of stuff like glues, paints, and those squishy foam cushions.
They zeroed in on thermoplastic polyurethane (TPU for short), which is kind of like a hybrid between rubber and plastic. It’s tough but also has that give and flexibility we often need.
The researchers started off thinking that because of the way polyurethane is put together – with ester and urethane links – «it might break down quickly and completely if we let the right enzymes get to work on it».
To put this theory to the test, they ran a couple of experiments on a material made from thermoplastic polyurethane that comes from algae biomass, a green resource.
The experiments aimed to see if they could turn this bio-based plastic material into microplastics through bio-based thermoplastic polyurethane, and then check how quickly it breaks down and disappears, possibly turning into something useful like plant fertilizer, in your garden compost.
Test results: how fast microplastics broke down (in soil and water)
«The team counted up the microplastic particles and found that the ones from bio-based thermoplastic polyurethane vanished completely in 200 days when buried in soil. On the flip side, particles from a non-biodegradable polymer, ethylene-vinyl acetate, didn’t budge in number over the same period», the researchers noted.
They also measured how much carbon dioxide got pumped out (a sign that biodegradation is happening thanks to enzyme action) when turning the bio-based thermoplastic polyurethane back into natural stuff. They used a tool called a “respirometer” – typically used to check how much oxygen plants are using – and confirmed that, under the same composting conditions, the algae-based thermoplastic polyurethane particles broke down and went back to nature.
Regarding biodegradability in water, the team found that «after 90 and 200 days, they got pretty much all of the oil-based microplastics back because they hadn’t broken down at all».
But it was a different story with the algae-based microplastics. After 90 days, they only found 32% of them, showing that a big chunk had already broken down. And by 200 days, a mere 3% were left, meaning a whopping 97% had completely disappeared.
Glimpses of Futures
The work described demonstrates that adopting plant-based plastics, which have a zero environmental impact and biodegrade quickly when released into the soil or water, is an achievable goal. However, this is contingent on researchers and manufacturers considering two indispensable factors: the chemical properties of the chosen material and the environmental conditions to which it is exposed for biodegradation.
On this latter point, it’s vital to look beyond the high temperatures of industrial facilities typically used for biodegradation tests. We’ve seen this with bioplastics made from polylactic acid, «prone to hydrolysis in industrial composting facilities, but not in marine environments».
Conversely, the microplastics generated from algae-based thermoplastic polyurethane, according to initial tests in home composting conditions, promise to degrade rapidly (and in large proportion) in the environment, thereby not posing a pollution source for ecosystems.
Using the STEPS matrix, let’s try to anticipate future scenarios by evaluating the potential impacts that the evolution of the described methodology for researching and developing environmentally harmless plastics – because they are bio-based – and, at the same time, rapidly and completely biodegradable, could have from a social, technological, economic, political, and sustainability perspective.
S – SOCIAL: could we see a world without microplastics invading our soils and seas, thereby polluting the entire food chain, within the next thirty years? The study sheds light on more than just hope, heralding a future scenario where fossil resources like gas, oil, and derivatives are completely replaced in plastic production by plant organisms which – crucially – will be genuinely biodegradable. Not just in industrial ovens but by transforming into water, carbon dioxide, mineral salts, or other entirely natural substances through the action of bacteria and fungi present in the environment and within the times set by EU reference regulations.
T – TECHNOLOGICAL: from a methodological and technical standpoint, combining a specific material like thermoplastic polyurethane – durable, flexible, and biodegradable through direct enzymatic action without resorting to the high temperatures of industrial facilities – with algae biomass has allowed the research team to achieve a balance between the bio-based element of the obtained plastic and its complete and rapid disintegration in the environment. Future tests, however, must examine composting conditions in contexts beyond the domestic to broaden the research scope and experiment with natural settings where the biodegradation of algae-based thermoplastic polyurethane could have different impacts in terms of timing and methods.
E – ECONOMIC: in the long term, the introduction of “truly” biodegradable bioplastics into global markets, which degrade quickly on soil and in water, would completely change the economic perspective of the reference markets, also in view of possible future regulations on certification systems established by public authorities. Currently, 2023 data on global bioplastics production, made available by the European Bioplastics Association, show a very positive situation, set to evolve further, moving from about 2.18 million tonnes produced in 2023 to about 7.43 million tonnes in 2028. But the question that arises, in light of the most recent studies, is whether these figures only include bioplastics that adhere to biodegradability standards tested in natural and not just industrial environments, or if they refer to a catch-all category that also includes the frequently mentioned polylactic acid, which is only seemingly biodegradable.
P – POLITICAL: from a political standpoint, the impact of the advent of bioplastics, with biodegradability tested and anticipated within the timelines established by EU regulations, is already being felt. On January 17, 2024, the European Parliament, with the Directive against greenwashing and misleading consumer information – coming into effect on March 26, 2024, and becoming operational on September 27, 2026 – made a significant, almost epoch-making decision against vague claims by companies, unsupported by tangible evidence, regarding their products’ environmental and sustainability features. This includes the use of the term “biodegradable,” as well as phrases like “zero climate impact,” “environmentally friendly,” and other similar expressions. To put an end to the practice of disseminating misleading information and, instead, to support the selection of accurate and truthful information for product packaging, the future will see the regulation of so-called “sustainability labels,” which will be based on certifications obtained only after a comprehensive process of testing, evidence, and verification.
S – SUSTAINABILITY: the recent study from the University of California San Diego described here, along with last year’s study by the same institution on plastics of dubious biodegradability, highlights the need in Europe for sustainability that is not just flaunted and advertised but certified, proven, and tested by businesses operating in the environmental, ecological, energy, and green sectors. Remember, 2030, the deadline set by the UN Agenda for achieving the 17 Sustainable Development Goals, including Goal 14, on the conservation of oceans, seas, and marine resources as fundamental elements for the health and preservation of the entire planet, and Goal 15, on the protection and promotion of sustainable use of terrestrial ecosystems, is not far off.
