Technology & Science

Plant-based? Compostable? What you need to know about bioplastics

Plastics made from fossil fuels generate a lot of greenhouse gas emissions and waste. 'Bioplastics,' especially compostable plastics made from plants, have been touted as a greener alternative. But what are they really? And are they really more environmentally friendly? Here’s a closer look.

What they are, how they're greener than traditional plastics and why they’re not a perfect solution

This cup is made from PLA, a compostable, plant-based bioplastic. But not all bioplastics are biobased and not all of them are biodegradable. (David Donnelly/CBC)

Plastics are an integral part of our lives, but they also pose some big environmental problems.

They generate a lot of waste, most of which isn't recycled. A recent study from Environment and Climate Change Canada found that even in our country, only nine per cent of plastics are recycled — the rest is either incinerated, landfilled or ends up in the environment, where it can harm wildlife such as whales, turtles or seabirds. Those are some of the reasons the federal government plans to ban many single-use plastics by 2021

But the plastic problem is global. As of 2015, humankind had produced 8.3 billion tonnes of plastic, one study estimated, of which 70 per cent had already become waste. 

Plastic production and its disposal by incineration also generates greenhouse gas emissions linked to climate change. A 2019 study from the Center for International Environmental Law estimates that if plastics production grows at its current rate, emissions from plastics could reach 1.2 gigatonnes per year by 2030, equivalent to the emissions of 295 new 500-megawatt coal-fired power plants.

"Bioplastics" aim to curb both those environmental impacts. 

They're one of the solutions touted by Canadian supermarkets who say they've taken steps to reduce the massive amounts of plastic waste they generate, after a CBC Marketplace report found they've been slow to act. Marketplace will share their update on plastic waste in supermarkets Friday.

In the meantime, here's what you need to know about bioplastics.

'Bioplastic' can mean 3 different things.

Plastics are moldable materials that are typically made from long chains of smaller molecules joined together, which is why their names often start with the prefix "poly" — for example polystyrene or polyethylene.

Traditionally, they've been made from fossil fuels and take a very long time to break down in the environment — sometimes hundreds of years.

Bioplastics are plastics that can be:

  • Biobased; that is, derived from biological sources such as corn, potatoes, wood, food waste or lobster shells.

  • Biodegradable, meaning they can be broken down by microbes into natural substances such as water, carbon dioxide and compost under certain conditions. 

  • Both biobased and biodegradable (some examples in the first bullet point fall into this category).

Toronto-based Genecis uses bacteria to convert food waste into pellets of a compostable bioplastic called PHA. Bio-based bioplastics can be made from a variety of other biological materials, including wood, sugar cane and lobster shells. (Craig Chivers/CBC)

Many bioplastics aren't biodegradable. And some are chemically identical to regular plastics.

The only difference between biopolyethylene or bio-PET (used in Coke's "PlantBottle") and regular polyethylene or PET is they use a raw ingredient from plants (ethanol) instead of fossil fuels to make the same material.  

Those kinds of plastics are known as "drop-in" plastics because they can be dropped in as direct replacements for traditional plastics and mixed with them in any quantity (the PlantBottle originally included 30 per cent plant-based ingredients and 70 per cent regular PET that still represents 7 per cent of the company's bottles sold around the world. Coca-Cola has since also made a 100 per cent bio-PET version).

Because they're identical, they take just as long as traditional plastics to break down. 

Plastics made mostly or entirely from fossil fuels can be called 'biobased' and 'bioplastics', respectively.

To be labelled a "biobased" product in the U.S. under Department of Agriculture rules (Canada has no equivalent rules), it only need contain a minimum of 25 per cent carbon from biological as opposed to fossil sources — that is, up to 75 per cent of the carbon can come from fossil fuel sources.

In fact, a plastic that is made 100 per cent from fossil fuels can still be considered a bioplastic if it's biodegradable.

For example, a plastic called PBAT (polybutylene adipate terephthalate), sold by chemical company BASF under the name "ecoflex," is a completely fossil fuel-derived plastic that's certified compostable and biodegradable — and is therefore considered a bioplastic.

Coca-Cola's original PlantBottle, unveiled for the 2010 Vancouver Olympics, contained 30 per cent bio-PET. The company has since made a version that is 100 per cent bio-PET. It's chemically identical to regular plastic bottles. (The Coca-Cola Company)

Bioplastics can help reduce carbon emissions. But not always a lot.

Bio-based bioplastics typically generate fewer carbon emissions over their life cycle compared to traditional plastics. That's because growing plants suck in and store carbon, which is released later if the bioplastics are burned or decomposed.

"You're not adding extra carbon dioxide to the atmosphere," said Amar Mohanty, distinguished research chair in sustainable biomaterials at the University of Guelph, who has been developing and researching bioplastic and biobased materials for more than 30 years.

In practice, things are more complicated than that because energy is used to grow crops and for transportation, manufacturing, processing and distribution — and that may generate emissions.

How big the difference in emissions is between the two can vary a lot depending on the types of biobased ingredients used, how they were grown, how locally the bioplastic was manufactured, what happened to it at the end of its useful life and exactly what plastics are being compared. 

For example, one study found the bioplastic PHA, made from corn leaves, stalks and husks, generates 80 per cent fewer emissions per kilogram over its lifetime, compared to fossil-derived PET or polystyrene.

Farmer Tom Brus, left, and Russell Mier from New Ventures Ag Tech Initiative, kneel in Brus's recently harvested corn field near Walcott, Iowa, with a hand full of corn stover. Stover can be used to make ethanol, which can be turned into bioplastic. ( John Schultz/Quad-City Times/Associated Press)

But a 2018 study by the European Commission's Joint Research Centre found that in Europe there would be no real difference in lifetime emissions between traditional PET bottles and those made from bioplastics. That's largely because regular PET is manufactured in Europe, while bio-PET is mostly manufactured in the U.S. and lots of emissions would be generated during transport.

As mentioned, some bio-based plastics are not biodegradable and can remain for hundreds of years. Some researchers have argued burying such plastics at their end of life is one way to store carbon captured by plants and keep it from getting into the atmosphere.

Compostable plastics often end their life in places where they don't break down.

A benefit of degradable or compostable plastics is that they can theoretically reduce harm to wildlife and ecosystems caused by traditional plastics and reduce the need for landfill space, which is a problem in some countries. That's because they can be broken down completely into carbon dioxide, water and compost under certain conditions without leaving behind microplastics. Mohanty describes it as "natural recycling."

That said, even popular compostable plastics such as PLA (polylactic acid), which is used to make drinking cups, clamshell containers and plastic cutlery, are not accepted by most municipal composting programs in Canada, and some commercial ones. That means they're often sent to landfill, where one study estimated they would take more than a century to break down and another found they would release the potent greenhouse gas methane during decomposition

Nor do they necessarily break down in a timely fashion in places like the ocean (where they pose the biggest threat to wildlife) or the soil. Ecoflex, PLA, and two other kinds of biodegradable plastics all survived a year in either seawater or freshwater without breaking down, a 2017 University of Bayreuth study showed. A 2019 University of Plymouth study found that "compostable" bags buried in soil were still there after 27 months, and "biodegradable" bags could still hold groceries after three months in the ocean.

This cutlery is made from the compostable and recyclable plastic PLA. However, most municipal organics programs will not accept compostable plastics and most recycling programs won't accept them either, so they typically end up in the landfill. (David Donnelly/CBC)

Bioplastics are often recyclable, but often aren't recycled.

As might be expected, bio-based versions of recyclable plastics such as bio-PET are recyclable with the regular, fossil-fuel based versions of the same plastic.

PLA is also theoretically recyclable. It's not currently accepted by most recycling programs, but that may change in the future.

Bioplastics could potentially have environmental drawbacks.

A number of studies have calculated that huge net emissions are generated if rainforests, peatlands, savannahs or grasslands are converted to agriculture in order to grow crops to produce bioplastics. 

But bioplastics are only a tiny fraction of plastic in the world today.

In 2019, land used to grow crops for bioplastics represented just 0.016 per cent of farmland, according to an estimate by European Bioplastics, which represents the bioplastics industry in Europe.

They're just one per cent of the 359 million tonnes of plastic produced around the world each year, estimates European Bioplastics.

(CBC)

Add some “good” to your morning and evening.

A variety of newsletters you'll love, delivered straight to you.

Sign up now

Comments

To encourage thoughtful and respectful conversations, first and last names will appear with each submission to CBC/Radio-Canada's online communities (except in children and youth-oriented communities). Pseudonyms will no longer be permitted.

By submitting a comment, you accept that CBC has the right to reproduce and publish that comment in whole or in part, in any manner CBC chooses. Please note that CBC does not endorse the opinions expressed in comments. Comments on this story are moderated according to our Submission Guidelines. Comments are welcome while open. We reserve the right to close comments at any time.