The world is drowning in plastic waste.
Our bodies are full of microplastics and no environment is safe. Plastics are strewn atop the most remote mountains, the deepest parts of the sea, and the Great Pacific Garbage Patch is so prominent that it has become a proper noun and its own ecosystem.
Polyethylene, the world’s most-produced plastic, provides us with bags, food packaging, and household goods containers. It’s also especially polluting because it’s designed to be sturdy and long-lasting.
Yet the future holds promise, because chemical engineers at the University of Surrey in the United Kingdom have created a unique new plastic with the qualities needed to support a more cyclical materials economy.
As they report in the journal Macromolecules, this proof-of-concept polymer readily breaks down into a gas when heated. And then, like the mythical Phoenix, rises from the ‘ashes’ to reassemble itself.
“Most plastics are designed to be stable, which is exactly what makes them difficult to remove or recycle,” explains Peter Roth, chemical engineer at the University of Surrey.
“We’ve shown that it’s possible to create a material that behaves very differently – one that can transform into vapor at relatively low temperatures before naturally rebuilding itself into the same polymer.”
This novel polymer is called poly(1,2-dithiolane), meaning that it’s a chain made of individual links, or monomers, of 1,2-dithiolane, a ring-like molecule made of carbon, hydrogen, and two linked sulfur atoms.
The reversible nature of this sulfur link makes the polymer readily and repeatedly degradable.
“This isn’t a replacement for conventional plastics, and it’s certainly not a solution to the global plastic waste problem. But it does introduce a new concept that could inspire an entirely new generation of circular materials,” Roth adds.
As such, it addresses multiple issues that complicate the effective recycling of plastics.
First, it more easily undergoes depolymerization – the breaking down of a complex polymer into its simpler, constituent monomers, like disassembling a LEGO set into its pieces. Goodbye pirate ship, hello Medieval castle!
But LEGO sets don’t rebuild themselves (not yet, anyway). Plus, conventional plastics may need to be heated to around 200 degrees Celsius (nearly 400 degrees Fahrenheit) before they start to break down.
And whatever emerges may require additional processing, potentially generating polluting, hazardous byproducts.
Uniquely, the researchers’ new polymer breaks down at only around 90 degrees Celsius, sublimating from a solid to a gas while skipping the liquid phase and “constituting a first example of a polymer showing this behavior,” the researchers say.
To demonstrate its practical applications, they dipped a rolled-up filter paper into it, showing that the polymer vapor ‘hugged’ the paper with a waterproof coating.
Afterward, they removed the coating just as simply by heating it. And though discolored, the paper regained its initial water-absorbing qualities.
The plastic, meanwhile, can readily rebuild itself as it cools back into a solid, ready to be reused.
This experiment may eventually be replicated in industrial settings, the researchers suggest, with untold potential.
Polymer coatings are ubiquitous. They improve insulation, lubrication, and resistance against corrosion, moisture, and wear and tear.
They protect the inner workings of the manufacturing machines that crank out grocery goodies, and keep our household appliances in working order.
Coatings also protect our houses themselves by staving off icky, ichorous mold or repelling rainwater so we don’t have to catch dripping drops in pots and pans – which are also protectively coated.
Finally, the researchers highlighted the potential of using polymer sublimation to improve plastic recycling efficiency, by “contaminating” their polymer with Nile red dye.
Normally, removing such additives from plastic waste requires additional, cost- and resource-intensive chemical processing. Not so here, as the researchers removed the dye from their polymer in a single step by heating it.
Overall, it’s unlikely we’ll be buying Pokémon figurines made from poly(1,2-dithiolane), or getting our to-go orders in boxes that reassemble themselves, minus the grease.
But, who knows, even biomedical applications may result from similar biodegradable polymers, including surgical adhesives, hydrogels that yield breathable contact lenses, and nanoparticles that deliver drugs at the site of illness, the researchers imagine.
Related: Plastic Waste Has Been Turned Directly Into Hydrogen Fuel – No Sorting Required
“The exciting part is that we’ve demonstrated a principle that wasn’t previously available,” says Touseef Kazmi, chemical engineer at the University of Surrey and the study’s lead author.
“If we can learn how to tailor this chemistry, it could eventually lead to new materials that are easier to apply, remove and recycle than many of today’s plastics.”
This research was published in Macromolecules.
This article was fact-checked by Michael Irving and edited by Michael Irving. While we pride ourselves on our process, we are only human. If you spot a mistake, please let us know.
