Georgia Tech Professor Chuck Zhang shares his expertise on nanocomposites.
If there are renowned experts in the up-and-coming nanocomposites industry, one of them is Chuck Zhang, Ph.D., a professor at Georgia Tech’s Stewart School of Industrial & Systems Engineering in Atlanta. His research interests include scalable nanomanufacturing, development of multifunctional composites and nanocomposites materials and their manufacturing processes, and additive manufacturing (3-D printing and printed electronics). His research projects have been sponsored by many organizations and companies, ranging from the Army Research Laboratory and Office of Naval Research to General Dynamics and Lockheed Martin.
Dr. Zhang recently talked with Composites Manufacturing magazine to unravel the mysteries of nanocomposites and shine light on where the materials are headed.
Q: What exactly are nanocomposites?
A: In nanocomposites, you have one phase, primarily the reinforcement or matrix material, which is in the nanoscale. A nanoscale is defined as one dimension of the material that is less than 100 nanometers.
Q: How long have nanomaterials been used in composite products?
A: It goes back to the 1970s and the early 1980s. That was the time of the first commercial success in nanomaterials at Toyota. They developed a nanocomposite by mixing a thermoplastic matrix, like nylon, with nanoclays. It was used for auto parts close to the engine block. They replaced the metal so they could save weight.
The first report that Toyota published was in 1988. In that paper they talked about the mechanical strength; it was stronger than traditional polymer parts. Better yet, the heat distortion that they could achieve was much better than with regular plastic parts. They could actually endure more heat, and they didn’t distort.
Q: What properties do nanocomposites bring to products that other materials don’t offer?
A: Most of the nanocomposite applications are for either special properties or multifunctionalities. In auto manufacturing, when the structures – particularly plastic – are painted, the paint is like a plastic. It’s non-conductive, and there’s a static issue. So they had to put some conductive particles [made with nanomaterials] into the paint so that it would make them anti-static.
Nanocomposites can also be used in high-end products, like sporting goods. High-performance golf clubs have nanotubes that can improve the mechanical properties. The response is better, so when players swing the club they can hit the ball further. Similarly, professional tennis players use nano-enhanced rackets. The stiffness of such rackets is believed to be better, so the players can hit the ball better, at higher speed.
Q: Are most of these carbon nanocomposites?
A: Yes, most of them are either carbon nanotubes or carbon nanomaterials that are put in the matrix. Carbon is the choice for two reasons. One, carbon nanomaterials have very special multifunctional properties – including mechanical properties, electrical conductivity, thermal conductivity and barrier properties. The second reason is that carbon nanomaterial is probably one of the most commonly used nanomaterials in R&D, so there is more of it available than other types.
Q: Why are nanocomposites of interest to the composites industry?
A: In the early years of these applications, nanocomposites were used more for their mechanical properties. But later on [the automotive and aerospace industry] asked what else can you improve by using nanocomposites? They found out that if you put the nanomaterials into the composites – and if you design, arrange and manufacture them in specific ways – it can improve electric conductivity or thermal conductivity and maybe others like barrier properties, such as fire and smoke retardance.
If we put a thin layer of carbon nanomaterials close to the skin of a plastic or polymer composite structure, it significantly improves the fire retardancy. You’re talking about adding just a very thin layer, maybe 10 to 15 microns, even thinner than a piece of paper, and almost no weight. A 12 x 12-inch carbon nanotube sheet is less than one gram. So if you have an aircraft that has an accident, if the composite materials in the aircraft have this nanomaterial layer on the surfaces that will reduce the smoke and heat generation and also delay the fire. You can give passengers more time to escape.
Q: Are companies beginning to seriously look at nanocomposites?
A: We have been approached by probably more than a dozen companies in the last few years that are interested in different multifunctionalities of nanocomposites – electrical, thermal, barrier and mechanical. For example, one company was interested in putting carbon nanotubes into polymer composite structures for ships to improve their fire and smoke retardancy. Another company was looking at the possibility of replacing steel cables using lighter weight carbon nanotube-based nanocomposites for applications such as elevators.
Q: How does the industry classify nanocomposites?
A: There’s one general way for people to categorize them, by looking at their matrix materials. So you can have polymer nanocomposites, like the Toyota application. In their case the polymer or the matrix material was nylon, a thermoplastic. If you use the nanomaterial in a metal matrix, you have a metal matrix nanocomposite. There are other people working on the ceramic matrix nanocomposites; they put nanomaterials into a ceramic matrix to make ceramics with better properties.
People also categorize nanocomposites by looking at the properties, like mechanical reinforcing nanocomposites, electrical-enhancing nanocomposites or fire-retardant nanocomposites.
Q: Does the use of nanocomposites require any major changes in the composite manufacturing process?
A: For some types of material, you don’t have to change too much. With others, you do. For instance, consider carbon nanomaterials in a composite. There are two ways to use it. One is that you simply mix the nanomaterial with the matrix, like a polymer resin, and then you make a composite. For that, you actually need to change your process, because once you put a nanomaterial into the polymer, you increase the viscosity of the mixture significantly when you put a high loading of nanomaterials, and thus you need to change the manufacturing process. Once the viscosity increases to a certain level, you can no longer use typical liquid composite molding processes. Or, you have to use very high pressure, like a compression molding type of process. Most of the time, you increase the manufacturing cost.
Alternatively, you can use other types of nanomaterial format, like the thin film or membrane of carbon nanotubes that we call “buckypaper.” You can laminate multiple layers of buckypaper to make buckypaper nanocomposites just like when you handle glass fiber/carbon fiber fabrics to make conventional composites. Then you can still infuse the resin as you usually do, because this doesn’t affect the molding process. You can also put just one layer of buckypaper on top of glass/carbon fiber laminate to enhance surface properties. Once the composite is done, the layer will stay on the surface, and it can improve the electrical connectivity, thermal connectivity and the fire retardancy of that composite.
Q: Are there any pitfalls associated with using nanocomposites?
A: The first one is cost. For carbon nanotubes today, we’re talking about $200 to $300 per pound for the lower end. If you look at high-grade nanotubes for aerospace applications, we are talking about $100 to $200 per gram. It’s very, very expensive.
Another problem is the scalability of manufacturing. Currently, very few companies can mass produce nanomaterials and nanocomposites. Compared to fundamental and exploratory research for nanomaterials development, there is less R&D work and efforts in scalable manufacturing of nanomaterials and nanocomposites.
Fortunately, we have seen increasing interest in this area by funding agencies, universities and industry companies. Some research groups – and my own group is one of them – are developing scalable manufacturing techniques with sponsorship from the National Science Foundation Scalable Nanomanufacturing (SNM) Program. Our SNM project is to develop a manufacturing process and its control strategy to make high-performance carbon nanotube buckypaper in a continuous, roll-to-roll fashion, like a paper mill process. There are also some industry companies working on scalable manufacturing of nanomaterials and nanocomposites.
Another challenge is the repeatability, reliability and durability of the nanomaterial. If we want to use it, let’s say for multifunctional applications, and you want to put it in an aircraft, then you have to get the material qualified or certified by the FAA.
Q: What notable research is being done in nanocomposites today?
A: There is a lot of work being done in the area of nanocomposites. For instance, my group and colleagues at Georgia Tech are working with collaborators at Florida State University on development and scalable and repeatable manufacturing of multifunctional buckypaper, which is a very unique field of work. There are many other groups, such as those at Rice University who have done a lot of work in synthesis high-performance carbon nanotubes and their nanocomposites. Government research labs like Air Force Research Laboratories, NASA and Oak Ridge National Laboratory have also done some pioneering research in nanocomposites. There are many other groups outside of the U.S. conducting excellent R&D in this area, including the University of Cambridge, UK.
In industry, Toyota is one of the pioneers in nanocomposites, and there are other companies that create new nanomaterials. For example, Applied NanoStructured Solutions, LLC (ANS), a wholly-owned subsidiary of Lockheed Martin Corporation, has created a high-volume continuous process to mass produce carbon nanostructures that can be grown at scale on various substrates, including glass and carbon fiber, and formed into materials with superior structural and conductive properties.
Q: What can industry professionals anticipate in the future?
A: I think you’ll see unique multifunctional materials for high-end applications like space and aircraft in the near future. Auto companies would also like to use some of the nanomaterials in the future; they are thinking more about lightweight, multifunctional materials to help them meet the Corporate Average Fuel Economy (CAFE) standards. Cost has to be low and scalability needs to be good, as we are talking about a large quantity for car production.
Another area of potential applications of nanocomposites is medical and life science. Can we use nanocomposites or nanomaterials with other types of manufacturing, like 3-D printing, to make multifunctional, custom-made devices/structures for implants? We are actually working on something like that in my lab, for printing heart valves that can mimic physiological behavior of human aortic valves using 3-D printing techniques with polymer and carbon nanotubes. Right now it’s for in-vitro [outside the body] applications, but in the future it can be used for something inside the body, like an implant.
Keep an eye open. Many other things are coming!
The market for global polymer nanocomposites should show an annual growth rate of more than 24 percent through 2019, according to a recent report from Research and Markets. But high deployment costs could limit that growth, since the lack of large-scale production capabilities makes nanocomposites expensive to use.
Luxembourg-based OCSiAl says it has found a way to solve these problems for single wall carbon nanotubes. “A few years ago, the cost of single wall carbon nanotubes was $100 a gram,” says Mike Nemeth, OCSiAl’s vice president of sales and marketing. “We are now at $2 a gram.”
The price reduction is due to the company’s development of a large-volume synthesizing process. The Graphetron 1.0, its pilot facility, is currently producing one ton of nanotubes each year. With other reactors coming online, the company will be able to boost annual production to 10 tons.
“We use a continuous production method as opposed to methods used over the last decade, which were often batched. You’d have high costs of manufacturing because you’d fire up the nanotube reactors, make a couple of nanotubes and then turn them off. But we are constantly making kilograms a day of nanotubes,” he adds.
The composites industry is a good fit for nanotechnology because it is a space that values both performance and innovation, Nemeth says. Composites made with single wall carbon nanotubes can provide multifunctionality, offering strength, stiffness and conductivity.
According to OCSiAl, single wall carbon nanotubes provide high electrical conductivity with ultralow loading, which ranges from 0.01 to 0.10 percentage of the composite’s weight. Carbon nanotubes can enhance the conductivity of a variety of materials, including CFRP, SMC, BMC and other fiberglass reinforced composites. OCSiAl offers the nanotubes in whatever form the customer requires to make their adoption into the manufacturing process as seamless as possible.
Nemeth expects that the aerospace and automotive industry will become big markets for OCSiAl’s nanotube product, TUBALL™. Nanotubes could provide conductivity in auto parts while maintaining a desired color, something that carbon black additives cannot do. For aerospace, nanotube technology could enable heating applications like the de-icing of aircraft without a complex network of wires.
Although OCSiAl is now able to produce TUBALL in quantities, it will take some time for industries with long design cycles to work the carbon nanotubes into their products. “Another challenge is explaining to people that you can now consider some other opportunities that might need more than one or two grams of nanotubes, because we can give them to you not only at scale, but also at a competitive price point,” Nemeth says.