A word on compostable and degradable plastics

At the end of Plastic Free July, bojblaz wrote an interesting comment about technological solutions for improving packaging, particularly whether there are more sustainable ways of producing and using plastic. I wrote a quick answer at the time, but I want to delve further into the available alternatives to traditional petrochemical plastics.

Just Degrading

One of the big problems with traditional plastic is that it takes hundreds of years to break down. “Degradable” plastics are often touted as the green alternative to regular plastics, and many plastic bags these days come with the statement “This bag is degradable” proudly stamped across their base. However, degradable plastics are not all they’re cracked up to be.

Some degradable plastics are compostable, which means they can be broken down into water, carbon dioxide and other nontoxic molecules in a composting system. Sounds great, right? Unfortunately, most compostable plastics will only biodegrade in the high temperatures of commercial composting facilities, not in a home compost heap, and they typically don’t finish composting within the time-frame of a commercial composting cycle. All of which means compostable plastics that don’t get fully broken down in a commercial composting plant can end up being just as polluting as regular plastic.

Some plastics are biodegradable; this means they can’t be composted, but they can be broken down by bacteria or other microorganisms. PLA (polylactic acid) is one of the most common biodegradable plastics and seems to be a popular choice for companies seeking more sustainable packaging options.

And some plastics are simply degradable. These are awful. Most stores these days seem to use bags made of degradable plastic. I have plastic bags from clothing purchases over a decade ago that are still going strong, but any “degradable” bags I’ve inadvertently acquired in the last few years begin to fall apart within a matter of months and can’t be reused. This doesn’t mean they’re biodegrading — far from it. Instead they’re breaking into smaller and smaller pieces that are harder to contain and more likely to end up as plankton-food in the ocean. Just what we’re trying to avoid! Unfortunately, somewhere along the line the term “degradable plastic” got wrapped up in greenwash and is now seen as the greatest thing since “plastic that lasts forever”. It still lasts forever, it just lasts forever in tiny little pieces.

Petrol or Plants

Plastics are traditionally made from fossil fuels like petroleum and natural gas. About 4% of petroleum is used to make plastic; the rest is used as fuel. It doesn’t concern me that plastics are made out of a non-renewable resource, because we can’t afford burn even a fifth of the fossil fuels we already have in reserve. However, fossil-fuel-derived plastics are problematic in that they tend to contain and leach harmful chemicals like endocrine (hormone) disruptors.

A variety of plant-based plastics are now available. In fact, one of the earliest bioplastics is cellophane, which was invented in the early 20th century. Cellophane is derived from plant cellulose fibres and is biodegradable, apparently even breaking down under home composting conditions.

Some more recently developed bioplastics — like PLA — are also biodegradable. Others, like the sugarcane-derived plastics now used in ecostore bottles, are chemically identical to petrochemical plastics and can be recycled together. However, as ecostore acknowledge, using plant-based plastics can help to reduce carbon emissions only if the plastic is recycled over and over, and not burnt in a waste-to-energy system. In addition, non-biodegradable plastics ultimately still contribute to the growing problem of too much plastic in the environment.

A New Hope

So far, things are looking pretty grim. We have compostable and biodegradable plastics that need very specific conditions to break down, and plant-based plastics that don’t actually reduce the amount of plastic waste accumulating.

But technology is continuously evolving, and it turns out a local kiwi company has developed a plastic film that will actually break down in a home composting system. I stumbled across this innovation thanks to Trade Aid’s new chocolate bar wrappers, (it’s also used by Kokako for their drinking chocolate) and I was super impressed to learn that the packaging will even break down in a worm bin!

Of course, bringing it back to the original question, technological breakthroughs are only part of the solution for improving packaging and reducing waste. Not everyone has a compost heap or worm bin at home, and I don’t know how this new compostable plastic fares if it gets chucked in the rubbish or winds up in the sea. So we also need better systems for collecting and separating our waste to ensure it all goes to its best possible use (e.g., making sure all organic waste gets composted). And we need better policies and incentives to reduce unnecessary packaging wherever possible.

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2 thoughts on “A word on compostable and degradable plastics

    • Thanks! Part of me feels like it’s too good to be true, but I’ve got a half-eaten pack of the new Trade Aid chocolate at home so I’m looking forward to seeing how it goes in my own worm bin!

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