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.