Thanks to the demands of eco-conscious consumers, biodegradable and compostable plastics —no,
not those Plastics!—are cropping up everywhere.
Are these green plastics the solution to our throwaway lifestyle?
Well -- it’s complicated.
Green plastics have promise, but some potential problems as well.
Here’s what you need to know to get the most out of this new crop of eco-friendly
materials.
This plastic looks nearly the same as this kind -- but the one on the left can turn to
compost under the right conditions, and it’s hyped as a green alternative.
This is plastic made from polylactic acid, or PLA.
PLA is derived from the starches in corn or other similarly starch-endowed crops, like
sugarcane, beets, or cassava.
Those starches are fermented to produce lactic acid.
The lactic acid is further treated in a series of steps and chained together to produce a
polymer: a tough, versatile molecule that can be melted and shaped into...plastic.
PLA is made from renewable sources, and it can be returned to the ecosystem if and only
if the circumstances are just right.
Contrast that with traditional plastics like PET, and if you want to know how that gets
recycled, we have a whole video for ya.
What makes PLA different than PET is that bacteria can snack on it.
And bacterial snacking causes decomposition: the breakdown of something into component
parts that can re-enter the natural environment.
All plastics are made of carbon, and all living things use carbon as food and as the structural
material of being alive, but there are some carbon-based molecules bacteria like to eat
more than others.
There are very few bacteria that have evolved to eat the plastic in PET.
That’s why, as litter or in landfills, it lasts practically forever.
Nothing can eat it, so it just...sits there.
Like my cat on my lap on a cold day, it’s not going anywhere.
Bacteria that can eat PLA are more common.
Common enough that it can be composted, meaning munched on by bacteria in a way that turns
it into lovely soil.
But if you’re the sort of enterprising person that has a home compost bin, you should know
before you toss your PLA in that there’s a catch.
Studies show that “compostable” plastics in that backyard composter won’t break down.
What’s more, in a landfill, there’s no evidence to suggest it will break down any
faster than PET.
So this “green” plastic can still be a polluter under the wrong circumstances.
So how do you get the right circumstances?
The molecules that make up PLA plastic are really really long and form a tough crystalline
structure that makes it hard for those bacteria to find a good angle of attack.
So in order for PLA to biodegrade, you have to help the bacteria out by melting down that
tough crystal structure, so they can nom on the individual strands -- which requires heat.
Like, 65° C for 30 days type of heat – the kind of conditions that only happen in specific
industrial facilities, and not your home composter.
Some plastics even specify this important detail on their labels – see?
There aren’t a lot of these facilities around and most of them don’t collect from suburban
neighborhoods.
This is a problem if well-meaning folks try to recycle it normally.
When PLA is mixed with other plastics in recycling facilities, it can contaminate them and ruin
the whole batch.
It actually COULD be recycled like other plastics are, but recycling facilities would need to
make a few overhauls.
Until then, we shouldn’t send it their way.
PLA is lumped in with other, non-recyclable types of plastics with a number 7 in the little
arrow symbol.
If you’re about to toss it in the recycling bin, and it has a 7, don’t.
But it’s not all bad news.
A recent study in the journal Environmental Science and Technology shows that blends of
multiple types of plastics can do what PLA can’t.
For example, a blend of PLA and small amounts of another type of plastic called polycaprolactone
CAN break down in a home composter.
Polycaprolactone is made from petroleum, so it’s not renewable, but it blends well with
other plastics to improve their properties -- like making PLA more compostable.
This is a pretty new finding (as of this writing), and it would need to catch on with industrial
plastics makers.
So chemistry is trying to give us what’s best for both consumers and the planet: the
convenience of plastics with the waste-reducing powers of compost.
I for one hope they get there.
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Some of them even aren’t about plastic.