If humanity is ever going to curb our waste problem, we’ll need to get creative with recycling and reusing materials. In a new study, researchers at Rice University and Ford’s Research and Innovation Center have demonstrated how waste plastic from old cars could be used to make graphene foam that can then be used in new cars.
The study advances a technique called flash joule heating, which the Rice team first demonstrated in 2020 to make graphene out of waste materials like food scraps, plastic and old tires. The waste materials are ground into a powder, then zapped with a high voltage to heat them to between 2,027 °C and 2,727 °C (3,680 °F and 4,940 °F). That rapidly converts the carbon in the material to graphene flakes, while other elements are vaporized into gases that can be collected and used in other industrial processes.
Not only is this a much cheaper way to make graphene, but it requires far less energy and gets rid of materials that otherwise usually go to landfill or an incinerator. And in the new study, the Rice scientists demonstrated a new way the cycle could work in the real world.
After seeing the original paper, researchers at Ford reached out to the James Tour's lab at Rice University to test whether the technique could be used to recycle mixed plastic waste from end-of-life vehicles. So the motor company sent over 4.5 kg (10 lb) of shredded plastic from bumpers, gaskets, carpets, mats, seating and door casings from old F-150 pickup trucks. Importantly, the plastics don’t even need to be sorted first.
The Rice team first ground up the material into a fine powder, then flashed it in two steps. First, it was heated with a low current for 10 to 16 seconds, which creates a highly carbonized plastic material. Only 30 percent of the original bulk remains as a solid, with the majority of it outgassing or forming waxes and oils rich in hydrocarbons, which the team says could also be useful industrial materials.
Next, the carbonized plastic is flashed with a high current, which converts 85 percent of it into graphene. The remainder, again, is outgassed as hydrogen, oxygen, chlorine, silicon and trace metals.
The resulting graphene can be used in the many applications we’ve come to expect from this wonder material. In this case, the Rice team sent it back to the Ford team who used it to reinforce their polyurethane foam, which is used to insulate their vehicles against noise and vibrations. With just 0.1 percent graphene by weight, the new foam had a 34 percent higher tensile strength and was 25 percent better at absorbing low-frequency sounds.
To really demonstrate the circular recycling potential, samples of this foam were then sent back to Rice, where the researchers showed that it could also be flashed into new graphene. This shows that the method could really be useful in real world situations, giving new life to waste materials.
The research was published in the journal Nature Communications Engineering.
Source: Rice University
