Flammability of Polymer Clay Nanocomposites Consortium: Year One Annual Report.
Flammability of Polymer Clay Nanocomposites Consortium:
Year One Annual Report.
(1330 K)
Gilman, J. W.; Kashiwagi, T.; Morgan, A. B.; Harris, R.
H., Jr.; Brassell, L. D.; VanLandingham, M. R.; Jackson,
C. L.
NISTIR 6531; 55 p. July 2000.
Order number: PB2000-106701
Keywords:
clay; flammability; nanocomposites
Abstract:
We recently found that polymer layered-silicate (clay)
nanocomposites have the unique combination of reduced
flammability and improved physical properties. However,
the details of the fire retardant mechanism were not
well understood. In October of 1998 a NIST-industrial
consortium was formed to study the flammability of these
unique materials. During the first year our goals were
to compare the flammability properties of: 1)
intercalated versus delaminated nanocomposites, 2)
tethered versus non-tethered nanocomposites, 3)
nanocomposites with different layered silicates (clays),
4) nanocomposites crosslinked to different degrees, 5)
nanocomposites with different melt viscosities, 6)
nanocomposites with different silicate loading levels,
and 7) nanocomposites incorporating a charring-resin,
polyphenyleneoxide (PPO), into a blend. The most
important result from our first year's work is the
discovery that a clay-reinforced carbonaceous char forms
during combustion of nanocomposites. This is
particularly significant for systems whose base resin
normally produces little or no char when burned alone
(PS, PPgMA, PA-6 and EVA). It appears from the
gasification data (videos and mass loss data) that this
clay-reinforced carbonaceous char is responsible for the
reduced mass loss rates, and hence the lower
flammability. Furthermore, we conclude that intercalated
nanocomposites perform as well as delaminated
nanocomposites. We were not able to determine if there
is an effect of tethering, due to the weak effect
observed for the epoxy nanocomposites. We did not
explore nanocomposites with different layered silicates
(clays). We believe that a small but significant effect
on flammability may be due to the greater melt viscosity
of the nanocomposites, but rheological measurements
still need to be made to confirm this hypothesis. In
terms of the effect of loading level, the effectiveness
of the nanocomposite approach to reducing flammability,
in most cases, levels off at a mass fraction of 5%
silicate loading. And finally, the use of a
char-enhancer (PPO) did not decrease the flammability of
the PA-6 nanocomposites, but other char-enhancing
co-additives should be explored.
Building and Fire Research Laboratory
National Institute of Standards and Technology
Gaithersburg, MD 20899