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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 to the environment? We talk to
Mark Miodownik, a materials scientist who’s leading
the Big Compost Experiment. This nationwide citizen
science experiment will explore whether home-
compostable plastics really do compost in your garden.HOW DO YOU MAKE BIODEGRADABLE PLASTICS?
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, 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 SHOULD WE DISPOSE OF BIODEGRADABLE AND
COMPOSTABLE PL ASTIC?
There’s a slight problem with it at the moment. In order
to get the properties that we need from plastics, 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, food would go off in your cupboard.
And you’ve got to remember, these plastics need to
survive humid and 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. That makes them less
easy for bugs to eat, and that means that their
biodegradability requires certain conditions.
So, most biodegradable polymers will only biodegrade
at temperatures of 50°C or 60°C, for instance, in the
particular conditions of an industrial composter. You
might get something like a biodegradable wipe, and it“Most biodegradable polymers will onlybiodegrade at temperatures of 50°C or 60°C, in theparticular conditions of an industrial composter”ABOVEThis
recycled
plastic in a
factory can
have a new
lease of life
over and over
again. Mark
Miodownik
says that
more effort
should be
made to
ensure all
plastics are
recyclable,
rather than
creating
compostable
versionssaysbiodegradable 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.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 an industrial
composter 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 THESE ‘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 2Visitthe BBC’sReality Checkwebsite at
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