Since the discovery of graphene by Russian scientists working at the University of Manchester, graphene has had a significant impact in 15 years. Six years after it was discovered, Andrei Geim and Konstantin Novoselov won the Nobel Prize in Physics for their work, and the word "graphene" has entered public awareness.
Graphene, like diamond, graphite, fullerene, and carbon nanotubes, is an allotrope of carbon. In graphene, carbon atoms are arranged in a two-dimensional single-layer hexagonal lattice. They have a planar structure similar to a barbed wire. It is 200 times stronger than steel and has excellent sound insulation.
The list of potential applications is huge, from paints and inks to touch screens and even shoes. Scientists at Ford Emerging Materials want to know if the automotive industry can take advantage of its unusual properties.
The company has been trying to add graphene to rigid plastics for years to make it stronger and harder. The goal is to replace some metal parts in the car. However, according to Debbie Mielewski, senior technology lead for the company's emerging materials, none of these attempts have been successful. "We can't even put it in the extruder," she said.
Chance
Almost out of frustration, they tried it in a polyurethane foam formulation and quickly succeeded. Adding graphene is fairly straightforward because it is included in the polyol component of the formula.
"It's fun to struggle so hard on one thing, and then almost out of frustration, trying and succeeding on polyurethane foam," she said.
Ford works closely with tier one supplier Eagle Industries and graphene expert XG Sciences to optimize the performance of the foam. "We need to modify graphene and make sure it is cost-effective," Mielewski said.
"We did most of the foam experiments here because we have a partnership with Michigan State University. Dr. Larry Drzal has been researching other nanomaterials for many years, and XG is one of his subsidiaries. There are not many research facilities It's possible to make polyurethane formulations, and no equipment to make hard plastics. It's the frustrations of hard plastics that let us try on foam. "
Right grade
According to Xamide's chief business officer Bamidele Ali, the company has created about 16 or 17 different grades of graphene nanosheets. "These can give polyurethane systems a variety of mechanical, electrical, and thermal properties," he said. "Ford used one of our graphene nanosheets, which is very good for mechanical strength and thermal conductivity. We helped them formulate new polyurethane foam for the under-hood parts."
"It provides better sound insulation and the engine can withstand higher temperatures and maintain better structure."
XG has two different processes for making graphene particles, one is chemical based and the other is mechanical. "The graphene we use with Ford is machined," Bamidele Ali said. "It is a high surface area graphene nanoparticle that disperses well in polyols at low polyol content. Generally, our mechanical systems produce 150-800m2 / g of graphene nanoparticles."
Although graphene is incorporated into the polyol component of the foam before pouring, it is not just as simple as stirring graphene particles into the polyol.
"You can't just take graphene, put it into the system, and expect it to work," he said. "The quality and composition of graphene, including its morphology and surface energy, are important. We choose which kind of graphene combines best with a particular polyol."
He added that it is important to properly mix graphene into polyols. "The ability to disperse graphene well and ensure that the system retains its capacity over time depends on the energy that graphene disperses," he said. "No dispersion, no performance."
Dispersion and distribution
Although the method used to disperse into the Ford foam is proprietary, Bamidele Ali says the company has six to seven methods for dispersing graphene into different systems.
"It depends on energy and composition," he said. "It's a somewhat complicated algorithm that includes the starting ingredients, the composition of the graphene, the temperature, and the environment. Sometimes-rarely-we just mix or stir, but we also have to use complex mechanical systems and sometimes quite complex additional Chemical reaction to achieve it. "
expensive
Graphene is very expensive. If it contains too high a content, it will make the formula uneconomical.
"We started to reduce the graphene content in the foam and found that even with a very small amount of graphene in polyurethane foam, its performance can be greatly improved," Mielewski said. "Contents below 0.5% reduce noise transmission by 17%, improve mechanical properties by 20%, and increase heat resistance by 30%. All of these are ideal for applications under the hood, we have noisy pumps and engines, and high calories."
After filing a patent, it was found that this low content of graphene resulted in a significant improvement in these properties. This bubble is now entering production mode.
Initially, it was used in the Ford F150 pickup truck (the Ford F-Series model has been the best-selling model in the United States for 30 years) and Mustang. Mielewski said other plans will end by the end of 2018.
She said the fact that it works well at such low loads is crucial. "We've been working with other nanomaterials in hard plastics for years and realized that if you don't make a big impact with very small amounts, you can't afford the cost of performance improvements," she said.
"We added 1.5% to the foam and think we'd better see what improvements we have achieved with smaller amounts, as this is allowed by the business case."
Asymptotically non-linear
The higher the graphene content, the more obvious the improvement effect, but the increase is not linear. "At this level, you really get the most returns, less than 0.5%," Mielewski said. But they also found that graphene nucleates the foam, making the structure in the polyurethane foam more consistent and the bubbles smaller. This also helps to improve mechanical properties.
She says graphene-reinforced foam has other benefits. Due to the nucleation, the foam weighs less, so we only need a small amount of polyurethane. This helps balance the cost of graphene. It's a win-win for everyone: consumers get a quieter car that has higher heat resistance under the hood foam, and in Ford's research we found a A way to create and implement new technologies.
Bamidele Ali said that the performance of the foam under the shell product is only a small part of what graphene brings to such a system.
"Graphene can affect the weight and impact strength of products," he said. (It can increase) 20-30% compressive strength and provide better wear performance in the system. "
He added that while it is a bit difficult in polyurethane systems, graphene can impart some barrier properties in harder foam structures. It also prevents UV rays and increases sound absorption. In addition, cycle times may decrease due to greater thermal conductivity.
"Characteristics of graphene at very low load levels make processing faster, heating and cooling faster because it is a good thermal conductor," he said.
"The processing efficiency and energy savings our customers see in multiple systems are not issues we often discuss, but often it speeds up the manufacturing process, which has a wide range of uses in polyurethane."
Under the hood
"We first applied it to the fuel rail cover and the hood. Then there were about 10 components under the hood of the vehicle." Mielewski said.
She believes it also has potential elsewhere in the vehicle. "The improvement in compression set may be useful for folding seats in the third row," she said. "These have been folded for a long time, but the foam still needs to bounce. Graphene foam can be used in this application and it really benefits customers."
And there has been a lot of interest elsewhere. Someone called Mielewski to ask if it would help make the cabin quieter.
"Some companies called and mentioned the foam in the roof lining of the car. It does reduce the noise in the car very well. So I think we will also start focusing on other applications. As long as we can reduce costs, the door Open. "
Reduce noise
There is also a complete migration plan that can be ported to other models. "Once we get to a self-driving car, people don't have to drive anymore, they want a quiet environment inside the car to take a nap or work," she said. This will be a real advantage in the future. "
Other parts of the car that benefit from graphene foam are the headrests-used to reduce noise, and other areas where thermal management is important.
"We will look for where it's too hot and where it needs to be shielded," Mielewski said. "Graphene is a great solution."