hmm
I'm sure you don't need me to tell you that products made out of this stuff have become
the cornerstone of our modern technological civilization. You can have any kind of plastic
nowadays can't you? It can be hard or soft, tough or flexible, airtight or air breathable, heat
resistant or heat sensitive, rigid or foldable, translucent or opaque, I mean you name it you can
have it! The vast majority of them are extremely durable, impervious to corrosion, and to all
intents and purposes pretty much indestructible in nature, which is why the flip side of this modern
technological marvel has become such a scourge in our urban, rural and ocean environments.
We've checked out several potential solutions to the plastic pollution challenge here on the
channel over the years. Everything from plastic alternatives made from corn or sugar starch,
to naturally occurring enzymes that can chomp through certain types of polymer,
like the brilliantly named Ideonella Sakaiensis, that we looked at a couple of years ago.
One of the challenges that the plastic makers of the world have accidentally set
for themselves is the very fact that the bonds of the polymer chains that create
plastics are extremely strong. If you've weakened them to enable plastics to break
down more easily then all you'd do is create a useless plastic that nobody wanted wouldn't you?
Or would you? Well, there's a team of Jolly clever scientists in a place called Constance, down here
on the border of Germany and Switzerland, who reckon they've created a polymer material that
squares that circle and solves the conundrum of a practically useful plastic material that
is genuinely compostable once it's thrown away. So we've got to check that one out haven't we?
Hello and welcome to Just Have a Think. Now, I'm not a scientist as you know, so although I think
I've made a stick model of a polymer chain here I fully expect there to be some forthright feedback
in the comments section from well-meaning materials scientists to point out that I've
incorrectly connected the balls on the model and therefore instead of creating polyester 1743-a
I have in fact created polypropylene 9384-c! Anyway the point is these stick-like bonds in a
polymer chain are really very sticky indeed, at least in the sense that they're extremely happy
where they are and are incredibly reluctant to be broken down. This new research paper from
our friends at the University of Konstanz, led by chemical material scientists Stefan Mecking,
presents us with a brand new plastic construction that appears to have all the properties of a
hard-wearing industrial material while being environmentally disposable too. All sounds
a bit too good to be true doesn't it? So what wizardry have they come up with then?
Well, to give you an idea of how I frazzle my brain researching these videos every week,
let me just read you the intro paragraph from the paper. "We report a novel polyester
material generated from readily available bio-based 118 Octodecane dicarboxylic acid
and ethylene glycol similar to high identity polyethylene which despite its crystallinity,
high melting point, and hydrophobic nature, is subject to rapid and complete hydrolytic
degradation in in-vitro assays, with isolated naturally occurring enzymes and is biodegraded
with mineralization above 95% within two months as a result of the strong impact of
the nature of the diol repeating unit, possibly related to the density of ester groups in the
amorphous phase. Depolymerization by methanolysis indicates suitability for closed loop recycling."
Now if you're a chemical material scientist you can probably switch up at this point
because I have apparently just provided you with all the information you require!
For the rest of us though, let's just have another quick look shall we.
That high density polyethylene the paper mentioned is perhaps one of the most common examples of
a polymer in which the long linear chains of hydrocarbons derived from oil pack themselves into
a tight crystalline structure held together by a phenomenon known as van Der Waals interactions
that creates an overall material that's highly water resistant and which just does not want to
come apart at all, which makes it a nightmare to get rid of when you've finished with it because
naturally occurring enzymes that might otherwise be able to dismantle this stuff find it almost
impossible to wiggle away inside the structure to chomp on the polymer links. Plastics that claim
to be biodegradable tend to be chemically manipulated to have very low crystalline
structures. That makes the polymer chains more accessible but it also removes many of the useful
structural properties of the material, which means these things are typically only ever used
for flimsy stuff like cling film. The Konstanz team had already shown that it was technically
feasible to produce a type of polyester with what they call a low density of in-chain functional
groups that could be used as breaking points in a polyethylene chain. The big advantage of this
construction was that those in-chain polyester groups didn't change the crystalline structure
of the material which meant the team were able to retain all of the useful properties
of polyethylene but with a material that could be chemically recycled at relatively low temperatures
of between 120 and 180 degrees Celsius. But nature doesn't have a fleet of Bunsen burners and glass
containers to cook all this stuff up with does it? It relies on those enzymes I mentioned earlier,
usually in the presence of water, to degrade materials over time. And that was proving to
be a bit of a wrinkle. An early version of the material, called Polyester 18-18, was found to
be sufficiently waterproof and crystalline that it displayed an ability to survive intact in an
aqueous acid solution for more than a year. In other words, no good really. This new breakthrough
material that the Konstanz team have snappily called Polyester 2-18, was created by taking
an existing material called a Dimethyl Ester and applying a very sciency sounding process called
'Dibutyltin Oxide Catalysed Polycondensation' to it to produce different diols. So how do we unpack
that lot then? Well I'm not going to explain Dibutyltin Oxide Catalysed Polycondensation
here in this video, largely because I don't have the slightest notion what it is!
Suffice to say it apparently alters the makeup of a material in meaningful ways that people
much smarter than me can measure and quantify. I can give you a bit of a steer on diols though.
They're a type of chemical compound containing two hydroxyl groups, and the most common form
of industrial diol is good old ethylene glycol, which is the stuff that makes antifreeze work.
The result of all this chemical jiggery-pokery was a material with a crystalline structure very like
commercially available high density polyethylene or HDPE and with similar tensile properties to
HDPE but which could also be readily broken down by natural enzymes in a water-based solution at
a temperature of only 37 degrees Celsius within just a few days or alternatively almost completely
biodegraded or mineralized in a couple of months at 58 degrees Celsius under industrial composting
conditions that met the stringent standards of a European Norm called ISO 14855. Now before we
get too giddy with excitement we probably need to heed the wise words of Stefan Mecking himself in a
recent interview with the online journal Sci-Tech daily. He said this "Of course we cannot transfer
the results of the composting plant one to one into any conceivable environmental condition
but they do confirm that this material is indeed biodegradable and indicate that it is much less
persistent than plastics like HDPE if it should unintentionally be released into the environment."
So when I used the phrase "breakthrough material" earlier on I perhaps should have used a phrase
like 'gently nudging material' instead. But it is arguably a step in the right direction.
Or perhaps you might be thinking that instead of encouraging our dear friends in the fossil fuel
and petrochemical industries to continue churning out billions of tons of products made from oil
we should instead be enthusiastically embracing alternatives like the bioplastics I mentioned
right at the start of the video. And that indeed is a small but rapidly growing sector.
Here's a very trendy looking example from a U.S start-up called Cove, made from PHA,
which is basically fermented sugar or corn oil. If you live in California then you'll
soon be able to buy one of these bottles from an organic grocery store there called Erewhon.
But then again if we converted all the world's plastics to corn or sugar-based materials then
our friends in the commercial world would have no choice but to start ripping up huge tracts of
land and destroying crucial ecosystems and biodiversity to create massive monoculture
plantations for the feedstock much like they already do in places like Brazil to grow sugar
cane for the bioethanol that runs the vast majority of the road vehicles in that country.
You could also argue that we should simply do away with plastics altogether and go back to a
simpler lifestyle like in the good old days before computers and TVs and telephones and life-saving
medical implants and penicillin and electricity... It's quite a moral maze isn't it? And sadly, I
can't afford Michael Burke's fee. That's a British Radio 4 reference that'll probably mean absolutely
nothing to anyone watching outside the UK so, you know, Google it. Anyway the point is there are
almost as many opinions on this topic as there are people watching this video. And given that you are
one of those people it's entirely possible that you may have one of those opinions. And if you do,
then as always the place to express it is in the comments section below this video.
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