Thermal and Flammability Properties of Polypropylene/Carbon Nanotube Nanocomposites.
Thermal and Flammability Properties of
Polypropylene/Carbon Nanotube Nanocomposites.
(3679 K)
Kashiwagi, T.; Grulke, E.; Hilding, J.; Groth, K. M.;
Harris, R. H., Jr.; Butler, K. M.; Shields, J. R.;
Kharchenko, S.; Douglas, J. F.
Polymer, Vol. 45, No. 12, 4227-4239, May 2004.
Keywords:
nanocomposites; thermal properties; flammability
properties; polypropylene; thermal conductivity
Abstract:
The thermal and flammability properties of
polypropylene/multi-walled carbon nanotube, (PP/MWNT)
nanocomposites were measured with the MWNT content
varied from 0.5 to 4% by mass. Dispersion of MWNTs in
these nanocomposites was characterized by SEM and
optical microscopy. Flammability properties were
measured with a cone calorimeter in air and a
gasification device in a nitrogen atmosphere. A
significant reduction in the peak heat release rate was
observed; the greatest reduction was obtained with a
MWNT content of 1% by mass. Since the addition of carbon
black powder to PP did not reduce the heat release rate
as much as with the PP/MWNT nanocomposites, the size and
shape of carbon particles appear to be important for
effectively reducing the flammability of PP. The
radiative ignition delay time of a nanocomposite having
less than 2% by mass of MWNT was shorter than that of PP
due to an increase in the radiation in-depth absorption
coefficient by the addition of carbon nanotubes. The
effects of residual iron particles and of defects in the
MWNTs on the heat release rate of the nanocomposite were
not significant. The flame retardant performance was
achieved through the formation of a relatively uniform
network-structured floccule layer covering the entire
sample surface without any cracks or gaps. This layer
re-emitted much of the incident radiation back into the
gas phase from its hot surface and thus reduced the
transmitted flux to the receding PP layers below it,
slowing the PP pyrolysis rate. To gain insight into this
phenomena, thermal conductivities of the nanocomposites
were measured as a function of temperature while the
thermal conductivity of the nanocomposite increases with
an increase in MWNT content, the effect being
particularly large above 160 DGC, this increase is not as
dramatic as the increase in electrical conductivity,
however.
Building and Fire Research Laboratory
National Institute of Standards and Technology
Gaithersburg, MD 20899