Flame Retardant Mechanism of Silica Gel/Silica.
Flame Retardant Mechanism of Silica Gel/Silica.
(2311 K)
Kashiwagi, T.; Gilman, J. W.; Butler, K. M.; Harris, R.
H., Jr.; Shields, J. R.; Asano, A.
Recent Advances in Flame Retardancy of Polymeric
Materials: Materials, Applications, Research and
Industry Developments, Markets. Volume 11. Business
Communications Co., Inc. (BCC). May 22-24, 2000,
Stamford, CT, Business Communications Co., Inc.,
Norwalk, CT, Lewin, M., Editor(s), 58-83 pp, 2000.
Fire and Materials, Vol. 24, No. 6, 277-289,
November/December 2000.
Keywords:
silica; polypropylene; flame retardants; polyethylene
oxide
Abstract:
Various types of silica, silica gel, fumed silicas and
fused silica were added to polypropylene and
polyethylene oxide to determine their flame retardant
effectiveness and mechanisms. Polypropylene was chosen
as a non-char-forming thermoplastic and polyethylene
oxide was chosen as a polar char-forming (slight)
thermoplastic. Flammability properties were measured in
the cone calorimeter and the mass loss rate was measured
in our radiative gasification device in nitrogen to
exclude any gas phase oxidation reactions. The addition
off low density, large surface area silicas, such as
fumed silicas and silica gel to polypropylene and
polyethylene oxide significantly reduced the beat
release rate and mass loss rate. However, the addition
of fused silica did not reduce the flammability
properties as much as other silicas. The mechanism of
reduction in flammability properties is based on the
physical processes in the condensed phase instead of
chemical reactions. The balance between the density and
the surface area of the additive and polymer melt
viscosity determines whether the additive accumulates
near the sample surface or sinks through the polymer
melt layer. Fumed silicas and silica gel used in this
study accumulated near the surface to act as a thermal
insulation layer and also to reduce the polymer
concentration near the surface. However, fused silica
used in this study mainly sank through the polymer melt
layer and did not accumulate near the surface. The heat
release and the mass loss rate of polypropylene
decreased nearly proportionally with an increase in mass
loading level of silicca gel up to 20% mass fraction.
Polyethylene oxide samples with fumed silicas and silica
gel formed physically strong char/silica surface layers.
This layer acted not only as thermal insulation to
protect virgin polymer but also acted as a barrier
against the migration of the thermal degradation
products to the surface.
Building and Fire Research Laboratory
National Institute of Standards and Technology
Gaithersburg, MD 20899