Sub‐micrometre coatings as an infrared mirror: A new route to flame retardancy

SUMMARY Most of the polymeric materials used are easy to ignite and show extensive flame spread along their surfaces. Apart from extensive heat release rates, their short time to ignition ( t ig ), in particular, is a key fire hazard. Preventing ignition eliminates fire hazards completely. Protection layers that shift t ig by more than an order of magnitude are powerful flame retardancy approaches presenting an alternative to the usual flame retardancy concepts. Coatings are proposed that consist of a three‐layer system to ensure adhesion to the substrate, acting as an infrared (IR) mirror and protecting against oxidation. The IR‐mirror layer stack is realised by physical vapour deposition in the sub‐micrometre (<1 µm) range, reducing heat absorption by up to an order of magnitude. Not only is the ease of ignition diminished ( t ig is increased by several minutes), the flame spread and fire growth indices are also remarkably reduced to as little as 1/10 of the values of the uncoated polymers open for further optimization. Sub‐micrometre thin IR‐mirror coatings yielding surface absorptivity <0.1 are proposed as a novel and innovative flame retardancy approach.