Flash Joule heating can be used to make carbon nanotubes and carbon nanofibers from mixed waste plastics, a method that is 90% more efficient than existing production processes. The nanotube diameter can be controlled by changing the power or catalyst used. (Image courtesy of Tour lab/Rice University)
Scientists at Rice University developed a way to turn recycled waste plastic into a hybrid carbon nanomaterial for a multitude of uses.
Researchers expect plastic production to triple by 2050, while plastic waste globally doubled over the past 20 years. Most waste ends up in landfills, incinerated or otherwise mismanaged, they said, citing the Organization for Economic Cooperation and Development.
According to a news release, some estimates suggest that only 5% of the waste is recycled.
Rice graduate student and lead author of a study, Kevin Wyss, and a team found a new way to make the most of this waste. The study, published in Advanced Materials, demonstrated how Wyss and colleagues — in chemist James Tour’s lab —used flash Joule heating to turn plastic into valuable carbon nanotubes and hybrid nanomaterials.
“We were able to make a hybrid carbon nanomaterial that outperformed both graphene and commercially available carbon nanotubes,” Wyss said.
Such nanomaterials offer strength and chemical robustness with low density and lots of surface area. Combined with conductivity and broadband electromagnetic absorption abilities, they offer uses in medical, industrial and electronics applications.
“What was really interesting about our results this time is that we were able to make these carbon nanotubes with bits of graphene attached on the ends,” Wyss said. “You can think of the structure of this new hybrid nanomaterial as similar to bean sprouts or lollipops. These are normally really hard to make, and the fact that we were able to make them out of waste plastic is really special.”
How the nanomaterial works
According to the researchers, the structure of this nanomaterial enhances its performance.
Wyss compared to to pulling a string of yarn out of a sweater. If you pull a “straight and smooth” string, it can come out quite easily and ruin the weave. With these carbon nanotubes, having masses of graphene attached at the ends makes them harder to remove, strengthening the composite.
“You can also think of it this way: If you get a splinter, it’s easy to take out. But if you get pricked with something that has a curve on the end, like a fishing hook, it’s a lot harder to take out,” Wyss explained.
The researchers “flash” the plastic at temperatures over 3,100 kelvins (about 5,120 degrees Fahrenheit). They grind the material into small pieces, add iron and mix in a different carbon — charcoal, for example — for conductivity.
According to the researchers, flash Joule heating offers “considerably” more energy-efficient benefits compared to existing processes. They say it provides more environmentally friendly benefits compared to existing nanotube production methods, too.
“Recycling plastic costs more than just producing new plastic,” he added. “There’s very little economic incentive to recycle plastic. That’s why we turned to upcycling, or turning low-value waste materials into something with a higher monetary or use value. If we can turn waste plastic into something more valuable, then people can make money off of being responsible in how they deal with discarded plastics.”
“Compared to commercial methods for carbon nanotube production that are being used right now, ours uses about 90% less energy and generates 90%-94% less carbon dioxide,” Wyss said.