What if the answer to our massive plastic waste problem was a new material that could
take any shape, any color, be used in any way and instead of having to throw it away
at the end of its lifetime, we could just recycle it forever?
Well... that material just might be here in the form of a brand new kind of plastic.
Recycling plastic is actually trickier than it sounds.
First of all, plastic is super diverse, so you can’t use the same recycling process
on all the different plastic things we make.
Looking at these horrific displays of plastics polluting the environment, whether that was
in our oceans or on land and in landfills.
And it was pretty clear that plastics needed a redo in terms of how we design them, specifically
addressing the eventuality that their end of life needed to be revisited a little bit.
The “end life” is why plastic products have to be separated into different streams
to be recycled in different ways.
The polymers will respond different to heat during the recycling process.
Hence the various numbers you see on the bottom of the containers—and even then, not all
plastics with the same number can be recycled together.
Most commercial plastics contain lots of extras, or additives, like dyes and ingredients to
make them stronger or more heat-resistant.
These additives are very difficult to remove from the plastic, making it hard to recycle
just the plastic.
Or the monomer building blocks, and the presence of the additives can also make the resulting
recycled plastic product unreliable and unpredictable.
So, all of those additives end up becoming associated with the plastic.
That heterogeneity essentially makes it very, very, very difficult to think about what to
do with the plastic outside of grinding it up into little pieces and trying to pelletize
it with a bunch of other different plastics that all have their own additives.
But luckily, new innovations are leading to plastics that could be infinitely recycled.
The team at Lawrence Berkeley National Lab has turned to a new kind of plastic called
poly(diketoenamine) or PDK for short.
PDKs are an interesting type of plastic that differ from conventional plastics in that
we completely replaced the static covalent bonds
that typically comprise... that make up the polymer backbone and we replaced them with
dynamic covalent bonds that allow you to do a number of new things.
Picture the bonds of a polymer in a traditional plastic like a metal chain.
To break down the plastic, you have to break the links of the chain and then spend time
and energy trying to re-form them, with the addition of a lot of glue and maybe even some
new metal.
With a material like PDK, the links between atoms in the polymer chain are actually reversible.
Because they use dynamic bonds between monomers called diketoenamines, which is a triketone
and amine stuck together.
You can just open ‘em up by dunking them in an acid bath and separate them from their
additives, ready to use the plastic again.
And the end result is the fluffy powder that’s actually the exact same plastic from the beginning
of the process, it didn’t lose any of its integrity in the recycling process!
And the acid isn’t far from what researchers already use in the lab.
Honestly anything below a pH 1 could work, but the final call was sulfuric acid and for
a couple different reasons.
Sulfuric acid as a result, because it’s a byproduct of petroleum refining, is very,
very inexpensive.
So, acid is used to depolymerize PDKs and in the course of depolymerizing PDKs and once
you go through the full cycle of recycling both the triketones and the amine monomers,
you generate salty water.
And this salty water can be recovered and purified by reverse osmosis facilities.
These types of facilities would be able to also recover the water and recover the commodity
value of the chemicals embodied by the salt in the water as well.
And so, I think that that sets up a landscape for being able to do efficient resource recovery
even while you're doing PDK plastic, chemical circularity.
The hope is that PDK could pave the way for plastic products that are infinitely recyclable
in the same way that glass and metal are.
While this material is still in its early stages, the researchers are looking at how
we could incorporate PDK into existing manufacturing processes, experimenting with how it could
be used in textiles, shoes, and food packaging.
And I think what we need to do is figure out of the sustainability challenges that we have
in specific markets, where are those best solved by this particular plastic?
And in solving that, do we also identify what might be needed to advance the next design
that is also circular.
Which is essential, because in 2015, the U.S. actually only recycled 9% of its generated
plastics.
The rest goes to landfills, is incinerated, or apparently makes its way to the ocean.
Over 13 million metric tonnes of plastic end up in the ocean each year, so unless we want
to lose our oceans and be buried under mountains of trash à la Wall-E, something’s gotta
give.
This new material holds great promise for modernizing our recycling world and making
it more efficient, hopefully pushing toward a world where plastic products are not only
much more recyclable, but don’t end up in a landfill or our oceans at all.
If you’re interested in how plastics are probably getting into your body through the
food you’re eating, check this other video here.
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and thanks for watching.