Retailers are beginning to switch from single-use plastic to biodegradable, compostable or recyclable alternatives, according to research by environmental think tank Green Alliance. But could these quick fixes cause further harm the environment?
We ask materials scientist Mark Miodownik, who’s leading the Big Compost Experiment, a nation-wide citizen science experiment to explore whether home-compostable plastics really do compost in your garden.
How do you make a biodegradable or compostable plastic?
Plastics are made of long-chain carbon molecules, and so polythene, for instance, is lots of little ethylene molecules linked up, and they create this sort of plastic bag material which is strong and tough and light.
It turns out that most of life also involves long-chain carbon molecules, so you can get these structures from things like corn and starch and so, you basically harvest a crop, use that as your carbon source, and create polymers based on those. These polymers work the same as the ones we derive from petrochemicals.
But you can go one stage further and you can make them sort of tasty to microorganisms, so little bacteria will eat them, and then this is where biodegradable plastics come from.
How do I dispose of biodegradable and compostable plastic?
There’s a slight problem with it at the moment. In order to get the properties that we need from plastics, i.e., for them to last six months or a year protecting your food, you want it to last a long time without it being eaten by bugs, otherwise, it would go off in your cupboard.
And you’ve got to remember, these things have got to survive humid environments, hot environments, and so, in order to get the plastics to be as good as that, you often have to do things chemically to them, and that makes them less easy for bugs to eat, and that means that their biodegradability requires certain conditions for it to happen.
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So, most of the biodegradable polymers will only really biodegrade at temperatures of 50 or 60°C, for instance, in particular conditions of what’s called an industrial composter. So, you might get something like a biodegradable wipe, and it says biodegradable on it, but unless you put that thing in an industrial composter at the right temperature and the right humidity with the right bugs, it will not biodegrade. It will still be in the environment a year later; if you put it in the sea, it will be there for years.
So, you really should put it in the general waste bin. We know when we go back to landfill sites from 30-40 years ago and dig them up, that there are still newspapers that you can read, and I mean, clearly paper and newspaper is biodegradable, but it doesn’t biodegrade under those conditions.
What’s better: biodegrading or recycling?
If you have a recyclable plastic, then you know where to put it: you put it in the recycling. We have systems in place. And the good thing here is that you’re hanging on to the carbon. But in the case of a biodegradable plastic, having got it from a crop, if you just biodegrade it in industrial composting, then potentially, you’re putting the carbon back in the atmosphere.
What we really want to do is keep carbon in the system, because we as we know, we’re trying to get rid of carbon dioxide out of the atmosphere. We want everything to be recyclable, and we want to recycle it.
Is there any value in swapping single-use plastic for ‘biodegradable’ materials that don’t biodegrade and can’t be recycled?
I think there isn’t any value at the moment, because there isn’t any such thing as a sustainable material.
Paper’s not sustainable, steel is not sustainable, glass is not sustainable. Things are not sustainable in their own right. Only a system can be sustainable. And what I mean by a system is: someone manufacturers something out of steel, you use it on like your car or your razor, you then dispose of it, it gets recycled, and then it goes back into the system. That’s a system, and that can be sustainable if you can make sure that you’re using the energy properly.
If you then try and do biodegradables, what you’re trying to do is create a system in which the CO2 plays a part, and it seems to me that we’re already problematically dealing with CO2 in the atmosphere, so this is a difficult system to become sustainable in my view.
Is it worthwhile swapping single-use plastic for a different single-use material?
There is a system for paper recycling, but if it’s contaminated with food, it won’t be recycled, and actually, paper uses more energy and water in general than plastics. So, you’re potentially making the water issues worse and climate change worse by swapping one single-use material for another. This is also true of glass.
So, the truth is that I think that people are so alarmed with plastic and disgusted about the pollution, and they’re right to be disgusted, but what we don’t want are these knee-jerk reactions which are really a greenwash.
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They’re sort of placating you, ‘Oh, we’re doing something about the problem,’ but I think the inherent way to do something about the problem is to change the system, and we need systems change, and it sounds abstract, and I think that’s part of the problem.
It’s very hard to see systems change. But we definitely don’t, I think, want to continue doing single use anything.
What’s the way forward?
We’re not going to lose plastic from our lives, because it’s very useful. It reduces food waste, it reduces waste of almost everything, and it’s very lightweight and tough for transporting goods across the planet and all of that helps reduce CO2 emissions. In our clothes, now, the average piece of clothing is 67 per cent plastic. Our shoes are mostly plastic.
Lots of stuff in our lives is all coated with plastic. It’s all vital, but we don’t have any systems for recycling those yet and I think we really, seriously fast need to redesign everything, so that there are systems for recycling everything in our lives.
We need to make sure every single plastic in a supermarket is recyclable, and it all goes into one bin and you don’t have to make any head-scratching decisions. And those plastics all get recycled back into new plastics which then get used for more packaging. That is the future.