Multiwall carbon nanotubes are rapidly emerging as an interesting alternate to carbon black for electrostatic discharge applications.
"There will be three important applications for multiwall carbon nanotubes," says Page McAndrew, senior research scientist at Arkema, one of the leading developers of the new reinforcement technology. "One is imparting electrical conductivity, primarily for ESD applications. Two is for improving mechanical performance, and three is for flame retardancy."
Any automotive components that come in contact with fuel must have electrostatic discharge properties. The Society of Automotive Engineers (SAE) recommends a maximum specific volume resistance of 106 ohm/cm for materials used for parts with fuel contact.
Carbon black is typically used as a conductive filler so plastics can meet the requirement. However, loadings of 10 to 20 percent may be required, a level that could compromise some of the critical physical properties of the plastic, either permeability or impact resistance.
"You can preserve those properties if you use carbon nanotubes instead because you can get the same ESD performance at loadings of just 1-2 percent," says McAndrew.
Costs of multiwall carbon nanotubes; however, may be an issue, at least short-term. According to industry sources, prices now are in the $50 to $70 per lb range, while conductive grades of carbon black are sold in the range of $2 to $10 per lb. The loading differential tilts the economics toward carbon nanotubes by a factor of 10.
If carbon black works for a given application, there is little incentive to convert to carbon nanotubes. Applications that benefit from the performance enhancement are expected to convert to multiwall carbon nanotubes, particularly as prices drop.
Production for multiwall carbon nanotubes is still in the pilot stage and global capacity today is estimated by trade sources at less than 500 metric tons. Capacity could grow tenfold or more based on announced increases in capacity.
Arkema, for instance, inaugurated a 20-ton-per-year pilot plant in Lacq, France in 2006 and is planning an increase to 550 metric tons based on announcements.