Materials Science

Nanotube Firefighters

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Science  16 Dec 2005:
Vol. 310, Issue 5755, pp. 1743
DOI: 10.1126/science.310.5755.1743a

When polymers are heated and reach the temperature at which they begin to decompose, bubbles often form beneath the surface because the boiling points of the degradation products are usually lower than the decomposition temperature of the parent polymer. The evolution of these bubbles prevents the formation of a solid layer of char, which would insulate the rest of the polymer from further heating. With the advent of restrictions on halogenated flame-retardant additives, nanoscale reinforcing materials, such as clay particles, have been investigated as alternatives.

Kashiwagi et al. have found that carbon nanotubes and nanoparticles can also act both as reinforcing materials and as flame retardants, and in some cases can surpass the performance of nanoclay materials. Coaxing the asymmetric fibers into a continuous network structure is the key to reducing bubbling. At fixed loads under radiant heat, the best results were obtained using single-walled carbon nanotubes (SWNTs), which left a residue with an undulating surface but no deep cracks. In contrast, multiwalled carbon nanotubes (MWNTs) yielded only islands of protection, and neither carbon nanofibers (CNF) nor carbon black particles helped very much. Flame retardancy was found to correlate with rheology, because the best materials showed a gel-like response, which matches their ability to form networks. — MSL

Nat. Mater. 4, 928 (2005).

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