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.
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