The part of an old car that is turned into graphene could become a better part for a new car.
Rice University chemists working with Ford Motor Company researchers are transforming plastic parts from “end-of-life” vehicles into graphene via the university’s Joule flash heating process.
The average SUV contains up to 350 kilograms (771 pounds) of plastic that could sit in a landfill for centuries, but for the recycling process reported in the first issue of a new Nature journal, Communications Engineering.
The goal of the project led by chemist Rice James Tour and graduate student and lead author Kevin Wyss was to reuse this graphene to make improved polyurethane foam for new vehicles. Tests showed that the graphene-infused foam had a 34% increase in tensile strength and a 25% increase in low-frequency noise absorption. It is with only 0.1% by weight or less of graphene.
And when that new car is old, the foam can be turned into graphene again.
“Ford sent us 10 pounds of mixed plastic waste from a vehicle shredding facility,” Tour said. “It was muddy and wet. We flashed it, sent the graphene back to Ford, they put it in new foam composites and it did everything it was supposed to do.
“Then they sent us the new composites and we flashed them and turned them into graphene,” he said. “It’s a great example of circular recycling.”
The researchers cited a study that estimates the amount of plastic used in vehicles has increased by 75% in the past six years alone as a way to reduce weight and increase fuel economy.
Separating mixed end-of-life plastics by type for recycling is a long-term issue for the auto industry, Tour said, and it’s becoming increasingly critical due to potential environmental regulations for end-of-life vehicles. life. “In Europe, cars go to the manufacturer, who are only allowed to landfill 5% of a vehicle,” he said. “That means they have to recycle 95%, and that’s just overwhelming for them.”
Much of the mixed plastic ends up being incinerated, according to co-author Deborah Mielewski, technical sustainability officer at Ford, who noted that the United States destroys 10 to 15 million vehicles each year, including more than 27 million worldwide.
“We have hundreds of different combinations of plastic resin, filler and reinforcements on vehicles that make the materials impossible to separate,” she said. “Each application has a specific loading/mixing that most economically meets the requirements.”
“They’re not recyclable materials like plastic bottles, so they can’t melt them down and reshape them,” Tour said. “So when Ford researchers spotted our paper on Joule flash heating graphene plastic, they reached out.”
The Flash Joule heater for making graphene, introduced by the Tour lab in 2020, packs mixed ground plastic and a coke additive (for conductivity) between electrodes in a tube and detonates it at high voltage. The sudden, intense heat – up to nearly 5,000 degrees Fahrenheit – vaporizes other elements and leaves behind easy-to-solubilize turbostratic graphene.
Flash heating offers significant environmental benefits, as the process does not require solvents and uses minimal energy to produce graphene.
To test whether end-of-life mixed plastic could be reprocessed, the Rice lab ground up shredder “lint” consisting of plastic bumpers, gaskets, mats, mats, seats and bezels. door from end-of-life F-150 pickup trucks. into fine powder without washing or pre-sorting the components.
The lab flashed the powder in two stages, first at low current and then at high current in a custom-designed Wyss heater for the experiment.
The powder heated between 10 and 16 seconds at low current produced a highly carbonized plastic representing approximately 30% of the initial volume. The remaining 70% was degassed or recovered as hydrocarbon-rich waxes and oils which Wyss says could also be recycled.
The charred plastic was then subjected to high-intensity flashing, converting 85% of it to graphene while outgassing hydrogen, oxygen, chlorine, silicon and trace metal impurities.
The possibility of integrating life cycle analysis (LCA) into a rice research project also attracted Wyss. “I’m driven by sustainability, and that’s where I want to focus in my career,” he said.
The LCA involved comparing graphene from flashed auto parts to that produced by other methods and evaluating recycling efficiency. Their results showed that Joule flash heating produced graphene with a substantial reduction in energy, greenhouse gas emissions, and water consumption compared to other methods, including even energy. needed to reduce plastic shredder lint to powder.
Ford uses up to 60 pounds of polyurethane foam in its vehicles, of which about 2 pounds are graphene-enhanced since 2018, according to co-author Alper Kiziltas, a technical expert at Ford Research who focuses on sustainability and emerging materials. . “When we got the graphene from Rice, we incorporated it into our foam in very small amounts and saw a significant improvement,” he said. “It exceeded our expectations by providing both excellent mechanical and physical properties for our applications.”
Graphene clearly has a future at Ford. The company first introduced it in a variety of other under-hood components and in 2020 added a graphene-reinforced engine cover. Kiziltas said the company plans to use it to reinforce hard plastics as well.
“Our collaborative discovery with Rice will become even more relevant as Ford transitions to electric vehicles,” Mielewski said. “When you remove the noise generated by the internal combustion engine, you can hear everything else inside and outside the vehicle much more clearly.”
“It’s much more essential to be able to attenuate the noise,” she said. “So we desperately need foam materials that better absorb noise and vibration. This is exactly where graphene can provide incredible noise attenuation using extremely low levels.”
The other co-authors of the article are Robert DeKleine and Rachel Couvreur of Ford. Tour is the TT and WF Chao Chair in Chemistry and Professor of Materials Science and Nanoengineering.
The Air Force Office of Scientific Research (FA9550-19-1-0296), Department of Energy National Energy Technology Laboratory (DE-FE0031794), and a National Science Foundation Senior Fellowship supported the research.