Ford finds graphene helps PU rise to challenges

Graphene has made a remarkable impact in the 15 years since it was discovered by Russian scientists working at the University of Manchester. Just six years after its discovery, Andrei Geim and Konstantin Novoselov had won the Nobel prize for physics for their work, and the word "graphene" had worked its way into the public consciousness.

Graphene is—like diamond, graphite, fullerenes and carbon nanotubes—an allotrope of carbon. In graphene, carbon atoms are arranged in two-dimensional single layers of hexagonal lattices. They have a planar structure resembling chicken wire.

Its remarkable properties include the ability to conduct both electricity and heat very efficiently. It is also incredibly strong—200 times stronger than steel—and has excellent sound insulating properties.

The list of potential applications is enormous, ranging from paints and inks to touch screens and even footwear. And scientists in Ford's emerging materials group wondered whether the automotive industry could take advantage of its unusual properties.

The company had been trying for years to incorporate graphene into hard plastics to make them stronger and stiffer. The goal was to replace some metal components in cars. But, according to Debbie Mielewski, the company's senior technical leader for emerging materials, these attempts were unsuccessful. "We can't even get it into an extruder," she said.

Almost out of frustration, they tried it in polyurethane foam formulations, and success was rapid. Adding the graphene was fairly straightforward, as it is included in the polyol component of the formulation.

"It was kind of funny to struggle so hard at one thing, and then almost out of frustration try it in foam and succeed," she said.

Ford worked very closely with Tier 1 supplier Eagle Industries and graphene specialist XG Sciences to optimize the foam. "We needed to modify the graphene, and make sure that it was cost-effective," Mielewski said.

"We did the majority of foam experiments here, because we have had a relationship with Michigan State University. Larry Drzal there has for many years worked on other nanomaterials. XG is one of his spin-off companies. There are not many research facilities that do urethane formulation, and have the equipment to do hard plastics as well. It was the frustration with hard plastic that led us to try foam."

According to XG's chief commercial officer Bamidele Ali, the company created about 16 or 17 different grades of graphene nanoplatelets. "These are able to impart multiple mechanical properties, electrical properties and thermal properties into systems," he said. "Ford took one of our graphene nanoplatelets that is really good for mechanical strength and thermal conductivity. We helped them formulate the new polyurethane foam for under-the-hood parts.

"It gives a better sound barrier, and the engine can run hotter as it withstands higher temperatures, holding its structure much better."

XG has two different processes for making its graphene particles, one chemical-based and the other mechanical. "The graphene that we use with Ford is mechanically processed," Ali said. "It is a high surface area graphene nanoparticle that will disperse well at low loading levels in the polyol. Typically, our mechanical systems produce graphene nanoplatelets at 150-800m2/g."

Although the graphene is incorporated into the polyol component of the foam before it is poured, Ali says it's not as simple as merely taking graphene particles and stirring them into the polyol.

"You can't just take graphene, drop it into a system, and expect it to work," he said. "The quality and composition of the graphene, including its morphology and surface energy, are important. We choose which graphene bonds best with that particular polyol."

Mixing graphene into the polyol correctly is very important, he added. "The ability to disperse graphene very well, and make sure that the system holds over time depends on the energy that you put in with the graphene to get it to disperse," he said. "No dispersion, no performance."

Although the method used for the dispersion that goes into Ford's foam is proprietary, Ali says that the company has six or seven methods that it uses to disperse graphene into different systems.

"It depends on the energy and the composition," he said. "It's a somewhat complex algorithm, including the starting composition, the composition of the graphene, the temperature and the environment. Sometimes—very rarely—we get to just mix or stir things in, but we also have to use sophisticated mechanical systems, and sometimes pretty sophisticated additional chemistry, to make it happen."

Graphene is very expensive. If the level it is included at is too high, it makes the formulation uneconomic.

"We started to reduce the amount of graphene in the foam, and found that even with a very tiny amount of graphene in a urethane foam, its properties could be improved greatly," Mielewski said. "Less than 0.5 percent caused a 17 percent reduction in noise transmission, 20 percent improvement in mechanical properties, and 30 percent improvement in heat endurance properties. All those things are great for under-hood applications, where we have noisy pumps and engines, and high heat as well."

A patent was submitted for the discovery that such low amounts of graphene led to these large improvements in performance. And the foam is now going into production models.

At first, it is being used in the Ford F150 pick-up truck (Ford F-series models have been the U.S.'s largest-selling vehicles in any class for more than 30 years), and the Mustang. Other programs will follow at the end of 2018, Mielewski said.

The fact that it works so well at such low loadings is crucial, she said. "We have worked with other nanomaterials in hard plastics over many years, and realized that if you didn't get a big effect with a very tiny amount, then you were never going to be able to afford the property improvement," she said.

"We started at 1.5 percent in the foams, and thought we had better see what improvements we got with smaller amounts because that is all the business case would allow."

Higher levels of graphene do give greater improvements, but the increases are not linear. "You really get the most bang for your buck at this level, less than 0.5 percent," Mielewski said. But they also found that the graphene nucleates the foam, giving a more consistent structure in the urethane foam, with smaller bubbles. This also contributes to the improvement with mechanical properties.

There are other knock-on benefits of the graphene-enhanced foam, she said. "Because of nucleation, the foam weighs a little less, so we pay for a little bit less polyurethane. This helps to balance the cost of the graphene," she said. "It is a win–win for everybody: the customer gets a quieter car with a more heat-durable under-hood foam, and here at Ford research we get to find a way to be creative and implement new technologies."

Ali said the properties that the foam exhibits in under-the-hood products is just a small proportion of what the graphene brings to a system like this.

"Graphene can impact the lightweighting of products and impact strength," he said. "(It can improve) compression strength by 20–30 percent, and impart better wear properties in systems."

He added that, although it is a little more difficult in a polyurethane system, in more rigid foam structures graphene can impart some barrier properties. It can also protect against UV and increase sound absorption. Additionally, cycle times can fall because of greater thermal conductivity.

"The properties that graphene imparts at very low loading levels allows faster processing, with faster heating and cooling because it is a good thermal conductor," he said.

"The processing efficiency and energy savings that our customers see in multiple systems is not something we get to talk about very often, but typically it speeds up the manufacturing process, which has uses in polyurethane."

However, fuel rail covers and engine covers are among the first components to use the foam. "We are starting with about 10 parts under the hood of most vehicles," Mielewski said.

She believes it has potential elsewhere in the vehicle, too. "The compression set improvement could be useful in folding seats in the third row," she said. "These are folded for a long time, but the foam still needs to rebound. Graphene foam could be used in that application, and really provide a benefit for the customer."

And there has been great interest from elsewhere, as well. People called Mielewski asking if it could help make the cabin quieter, too.

"A number of our Tier 1 companies called. What about the headliner inside of the vehicle—that very thin piece of foam above your head?" she said. "That could do a very good job of lowering the noise inside the vehicle. So yes, I think we are going to start looking at other applications as well. The door is open, as long as we can keep the costs down."

There is a whole migration plan for it going into other models, too. "Once we get to autonomous vehicles, where people are relieved of the task of driving, they are going to want a quiet environment inside to take a nap or do some work," she said. "That will be a real advantage for the future."

Other parts of the car that might benefit from the graphene foam are headrests — to reduce noise, and other areas where heat management is important.

"We will be looking for where it is too hot and where we need to shield for heat—graphene is a good solution to look at," Mielewski said. "There are so many different emerging materials, and I am really hopeful that technology is going to help us in the future to be a little bit better to the planet."