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Flammability of Polymer Clay Nanocomposites Consortium: Year One Annual Report.

pdf icon 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


clay; flammability; nanocomposites


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.