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Posted: August 17, 2006
New flame retardant with nanoparticles provides effective shield
(Nanowerk News) t’s all a question of the right recipe – in chemistry as in breadbaking: the finished result should be crusty, but not burnt. In the next generation of chemical flame retardants, nanoparticles incorporated in paint will ensure that a crust forms to protect the underlying surface.
When fire breaks out, every second is precious. Within a very short time, the density of smoke, heat and flames can rise to life-threatening proportions. To prevent fires, or at least slow down their propagation, many wood-based products, plastics and textiles are treated with a flame retardant. This cuts off the supply of oxygen to the fire, promotes carbonization, produces an impermeable or insulating surface layer, or captures chemical radicals. But many standard flame-retardant substances are a hazard to human health or the environment.
Above a certain concentration, they can also impair the mechanical, electrical or chemical properties of the material in which they are incorporated. “If, for instance, a manufacturer wishes to avoid the use of ecologically questionable halogens such as chlorine or bromine, and instead mixes esters of phosphor into a flame-retardant paint, the paint will not harden sufficiently”, explains Dr. Andreas Hartwig of the Fraunhofer Institute for Manufacturing Engineering and Applied Materials Research (IFAM) in Bremen.
But there is nevertheless a substitute for at least a certain proportion of the flame-retardant chemicals employed at present, involving the use of nanoparticles. A mixture containing a five-percent additive of microscopic particles of silicon dioxide or alum clay is sufficient to significantly reduce the quantity of the more toxic substances used in the past. The nanoparticles fuse to form a protective “crust” around the burning material, slowing down the release of toxic vapor from the flame-retardant chemicals.
A new flame-retardant paint developed by the IFAM demonstrates how well this formula works. The epoxy resin obtains its fire-resistant properties from a combination of organically modified nanoparticles and an organic-phosphor flame retardant. The phosphor compound withdraws oxygen from the fire and fuses with the nanoparticles to form a solid crust that prevents the treated object from igniting. The paint has already passed its first fire-exposure tests. “The same principle can be applied to all common plastics such as polyurethane or acrylic resins”, says Dr. Hartwig, “but the formulation has to be readapted for each new material.”