Carbon Nanotubes Target Fuel Systems, Bumpers

Auto makers soon may expand the use of carbon nanotube-filled plastics from today's use in fuel lines to other fuel system parts, predicts Hyperion Catalysis International Inc., a Cambridge, MA-based advanced materials supplier.

Patrick Collins, Hyperion marketing director, says auto makers are moving fuel system components from steel to plastics reinforced with carbon nanotubes to improve performance and design flexibility.

Carbon nanotubes currently are used in some resin fuel lines because the high-tech material reduces the risk of a fuel line rupture in a low-temperature accident, and it's a conductive additive for plastics.

Conductive components can be grounded to control static electricity discharges — an important trait for fuel lines handling flammable gasoline. “Static around fuel is not a good thing,” Collins says.

With the auto industry pressing for conductive fuel systems, Collins claims, carbon nanotubes have the opportunity to win several new product applications. “We're talking about the fuel pump, lines, filter, possibly even the fuel rail,” he says. “All of a sudden, the market that we could potentially service has gone from fuel lines to the whole fuel system — everything between the tank and the engine block. So we're pretty excited. There's 20 million lbs. (9 million kg) of resin in those applications.”

Not so fast, Hyperion. General Motors Corp. and the Chrysler Group acknowledge interest in carbon nanotube technology, but neither indicates a major switch from steel is under way or on the horizon for fuel systems applications. “We're always interested in new technologies,” says a Chrysler spokesman. “But at this point, there's not a lot to talk about.”

So we'll talk about it for them. In 1983, Hyperion was the first company to create multi-walled nanotubes, a very pure form of graphitic carbon. They are made through a gas-phase continuous reaction of low molecular weight hydrocarbons combined with a Hyperion proprietary catalyst. Nanotubes are 10 to 12 nanometers in diameter and 10 or more microns long. A common virus has a larger diameter.

Carbon nanotubes are longer and smaller in diameter than other particulate additives, such as carbon black or carbon fiber. So when they are used to make a plastic component, they are better distributed throughout the part — providing universal conductivity, better surface quality and more ductility. The levels of shear commonly found in injection molding, a process used to make plastic, frequently affect larger additives. This can cause additives to be irregularly dispersed throughout a component, especially one with corners, openings or other 3-dimensional details. As a result, conductivity levels throughout the part are uneven.

Carbon nanotubes clearly have impressive properties, and their potential goes beyond fuel systems.

Collins says carbon nanotubes are finding success in Europe, where the industry is trending toward thermoplastic fenders for reduced weight, recycling requirements and increased styling freedom.

In order to eliminate primer steps, reduce emissions and wrap paint around corners, bumpers are electrostatically painted. The process works well for metal components, but plastic parts provide a challenge because they are not conductive. “So you put a conductive filler, like carbon nanontubes, in the plastic,” says Collins.

Long-term, Collins foresees an opportunity for the advanced material in fuel cells.

Billed as the potential future for automotive powerplants, fuel cells require thin bi-polar plates with high levels of conductivity that generally are unattainable for powdered graphite, carbon fiber or other macro-conductive fillers.

Carbon nanotubes' conductivity and toughness provide an edge, Collins argues. “We're excited about our opportunity in the auto industry.”