Flame-Retardant Mechanism of Silica: Effects of Resin Molecular Weight.
Flame-Retardant Mechanism of Silica: Effects of Resin
Kashiwagi, T.; Shields, J. R.; Harris, R. H., Jr.;
Davis, R. D.
Journal of Applied Polymer Science, Vol. 87, No. 9,
1541-1553, February 28, 2003.
silica; flame retardants; molecular weight
The effects of resin molecular weight on the
flame-retardant mechanism of silica were studied with
two different molecular weights of poly(methyl
methacrylate) (PMMA), 122,000 and 996,000 g/mol, and two
silicas, fused silica with a small surface area and
silica gel with a large surface area. A total of six
different samples were studied, with a mass fraction of
10% silica. The mass loss rate of the six samples in
nitrogen and the heat release rate from burning in air
were measured at an external radiant flux of 40 kW/m2.
The addition of silica gel to the low-molecular weight
PMMA significantly reduced the mass loss rate and heat
release rate; addition to the high-molecular-weight PMMA
provided the largest reductions of these quantities in
this study. For fused silica, some reduction in mass
loss rate and heat release rate was observed when it was
added to the high-molecular-weight PMMA; addition to the
low-molecular-weight PMMA did not reduce either loss
rate. Chemical analysis of the collected residues and
observation of the sample surface during gasification
reveal the accumulation of silica near the surface; the
larger its coverage over the sample surface was, less
the mass loss rate and heat release rate were. Both the
level of accumulation and its surface coverage depended
strongly not only on the silica characteristics but also
on the melt viscosity of the PMMA.