Graphene may unlock carbon fiber potential
A trace can double strength, half the cost of graphite fibers Metal Tech News Weekly Edition – May 27, 2020
Last updated 6/27/2020 at 6:11am
A bit of graphene could double the strength of carbon fiber while reducing the cost of this material prized for its strength-to-weight ratio.
About half the weight of aluminum but much stronger and rigid, carbon fiber is an ideal material for aircraft, sporting and safety equipment. At more than $10 a pound, however, this material has yet to compete with aluminum, which sells for less than $1/lb, for most commercial applications.
The aerospace sector, where carbon fiber's superior strength-to-weight ratio outweighs the price tag, consumes about a third of the material produced today. High-end sporting equipment – bicycles, golf clubs, tennis rackets, hockey sticks and protective helmets – are other products where carbon fiber's performance enhancements is worth the price. This lightweight and strong material is also used in a wide array of military gear, from equipment worn and carried by soldiers to aircraft and missiles.
Though carbon fiber is multiples stronger and lighter than both aluminum and steel, the auto industry has yet to widely adopt this material also known as graphite fiber for vehicles due to the high cost.
"Even though carbon fibers have really nice features, they would make a car far more expensive" with the way carbon fibers are manufactured now," said Adri van Duin, professor of mechanical and chemical engineering, Penn State. "If you can get these properties easier to manufacture then you can make cars significantly lighter, lower the cost of them and make them safer."
Van Duin, along with colleagues at Penn State Materials Research Institute, University of Virginia, and Oak Ridge National Laboratory, have identified a new way of creating carbon fibers that has the potential to more than double the strength and half the costs of producing this lightweight material that could make cars and aircraft safer and more efficient.
"Currently most carbon fibers are produced from a polymer known as polyacrylonitrile, or PAN, and it is pretty costly," said Małgorzata Kowalik, researcher at Penn State Department of Mechanical Engineering. "The price of PAN makes up about 50% of the production cost of carbon fibers."
This is because turning PAN into carbon fibers requires an enormous amount of energy.
First, PAN fibers must be heated to 200 to 300 degrees Celsius (390 to 570 Fahrenheit) to oxidize them. Next, they must be heated to 1,200 to 1,600 degrees Celsius (2,190 to 2,900 degrees Fahrenheit) to transform the atoms into carbon. Finally, this carbon must be heated to 2,100 degrees Celsius (3,810 degrees Fahrenheit) so that the molecules are aligned properly. Without this series of steps, the resulting material would lack its needed strength and stiffness.
Simulations run on a supercomputer at Penn State, along with lab testing, show that adding only 0.075% graphene to the first stages of this process creates a carbon fiber that is 225% stronger and 184% stiffer than the conventionally made PAN-based carbon fibers.
The team was not only able to demonstrate that this process works but were able to glean why adding a trace of graphene makes stronger carbon fiber with less energy; knowledge that will allow them to test ways to further optimize the process.
One of the things they found is the 2D structure of graphene, a single layer of very tightly bonded carbon atoms organized into a hexagonal lattice, helps align PAN molecules consistently throughout the fiber, which is needed in the production process.
Graphene edges also have a natural catalytic property at high temperatures, so that "the rest of PAN condenses around these edges," said van Duin.
With the goal of getting the cost of producing carbon fiber down to $5/lb, considered a key price point for widespread adoption of this lightweight and strong material by the automotive and other industries, the team is exploring ways to further incorporate graphene in the process using cheaper precursors and cutting out some of the energy intensive steps.
While $5/lb remains much more expensive than steel or aluminum, carbon fiber's light weight means you need less pounds to build an automobile that is lighter and stronger – more energy efficient and safer – than its metallic counterpart. It may only take a bit of carbon fiber's 2D cousin, graphene, to shift this exotic material reserved for aerospace, high-end gear and supercars to an everyday material that is used in buildings, wind turbines and family SUVs.