Materials Science

Making Flame Retardant

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Science  15 Oct 2004:
Vol. 306, Issue 5695, pp. 375
DOI: 10.1126/science.306.5695.375b

Polymeric flame-retardant materials are typically made by blending traditional polymers with flame-retardant phosphorous or halogenated compounds. The most commonly used brominated additives have drawbacks due to the release of toxic and corrosive halogenated gases during combustion and because they impart a strong color to the polymer. The compounds also appear to be environmentally persistent. Siloxane-based mixed organic-inorganic polymers, such as polycarbosiloxanes, also have good flame- retardant properties but are difficult to synthesize with high molecular weight because of the physical and chemical differences of the constituent components. Using both crude and immobilized lipases—enzymes that hydrolyze lipids—Kumar et al. were able to catalyze the transesterification reaction to connect various diesters and diamides to siloxanes. Of the lipases that were tested, Novozyme-435 had high efficiency in catalyzing the reaction without inducing undesired cross reactions. The polymers were synthesized without solvent under vacuum conditions and were of much higher molecular weight and lower polydispersity than those obtained using solvent or vacuum chemical methods. The best materials showed heat resistance up to 400°C. All the materials tested had little residual char after heating to 1200°C, indicating almost complete decomposition, and produced no toxic materials. — MSL

Adv. Mat. 16, 1515 (2004).

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