Plastic fantastic
With 250 million tonnes of waste plastic polluting our oceans,
scientists are working to create new-age polymers that can disintegrate once
they outlive their usefulness
Young, energetic and clean shaven, Scott Phillips looks the very
antithesis of Santa Claus. Just as well: he makes toys disappear.
The Western world's festive consumer frenzy contributes to a
global crisis that has left the planet up to its neck in long-lasting plastic
tat, and its oceans, according to a recent estimate, awash with some 250
million tonnes of the stuff. What we wouldn't give for plastics that could
transform into something else, fall apart or even vanish altogether. In his lab
at Penn State University, Phillips is on the case. “We make plastic objects
disappear all the time,“ he says. Perhaps it won't be too long before the
season's must-have toy comes equipped with a self-destruct button.
But today's plastics are not just for Christmas. Indeed, their
durability and low cost mean that many everyday objects are destined to hang
around for decades. We can only guess at how long some plastics survive in
landfill, but in many cases it extends beyond the 50 years or so we've been
producing and discarding them on a grand scale. If we recycle plastic instead,
melting it down takes a lot of energy and can release toxic components.And even
then, the resulting mix of hard plastics that usually enters a recycling stream
creates a polymer soup peppered with various dyes and solvents, so we end up
with a hunk of junk plastic fit only for a single, final use, like a park
bench.
It was that end-of-life problem, rather than any Scrooge-like
tendencies, that prompted Phillips to try to design self-destructing toys.
“It's a nice place to start minimising the accumulation of plastic waste,“ he
says.
The first step is some basic chemistry. Research in the past few
years has produced new sorts of polymers, the long, chain-like molecules that
make up plastics. These polymers are just as durable as conventional ones in
normal use, but contain chemical units at points within them, or at their ends,
that prompt the material to break up at room temperature when it meets a
particular stimulus. Phillips's lab has been developing plastics that break
down in ultraviolet light not ideal for toys, but good for components not ex
posed to sunlight, for example on the inside of electronic devices.
Destruction
trigger
One challenge is ensuring that the self-destruct signal spreads
from a plastic's surface right through the material. Here, Phillips and his
colleagues were inspired by plants such as the Venus flytrap, where a fleeting
touch to a leaf causes a change in the whole plant. “We are building
selfpropagating reactions into our materials,“ says Phillips. In a proof-ofconcept
design, one molecular component of a water-repelling polymer film reacts to a
specific wavelength of light, starting a chemical reaction that spreads through
the whole polymer and turns it hydrophilic.
Phillips has also been building plastic objects from layers that
react to different triggers, so that applying a sequence of them makes the
objects change shape. These morphing materials might not quite make a real-life
Transformer toy, but Phillips thinks they could be useful for creating adaptive
tools: think bolts and washers that shrink to fit a range of screws or that
change from rigid to rubbery. Other plastics can be engineered to give out a
chemical or light signal as they break down, with potential applications in
medicine. Phillips is not alone in trying to make plastics vanish. At the
University of the West of England in Bristol, UK, researchers want to avoid
rigid plastics and toxic power supplies for the robots they are
developing.Instead, they plan to build them from soft, biodegradable polymers
such as latex or collagen, with microbial fuel cells that extract energy from
waste liquids such as urine. The team hopes to develop tricks to change the
expiry date of such plastics, perhaps by embedding substances that will ooze
out or self-destruct in response to a signal if the robot gets lost.
Meanwhile, James Hedrick from IBM Research, and his team were
looking for new materials to use in computer hardware when they developed a
gentler chemical process to break down both PET plastics, commonly used in
drink bottles, and the hard plastics used in smartphones and CDs that usually
end up in landfill. “Now when I look at a bottle I don't see garbage, I see a
feedstock for all types of new materials,“ he says.
With Phillips's plastics, mass production is a long way off:
they are slightly toxic and too expensive. But he thinks his materials could be
put to immediate use as self-destructing adhesives. Small amounts can double as
glue on glass, metal and plastic, and they are just as strong as conventional
adhesive. “What's neat is that ours can also be reversed,“ says Phillips.“By
applying a signal, the object you've glued together will fall apart.“
Phillips imagines a further, perhaps unexpected boon from his
plastics. While his ultimate goal is to create a vanishing plastic that emits
nothing but inert gases when it decays, many of those developed so far
decompose in liquids meaning the toilet might be an ideal garbage disposal
unit. Imagine plastics that respond to a signal from sewer-dwelling bacteria,
or even components in urine, so parents can take unusual vengeance on an
annoying toy by peeing on it. Not that Phillips wants to make a splash with
that particular idea. “It often creeps people out when I mention it,“ he says.
Sandrine Ceurstemont 2016, Tribune Content Agency
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