A lightweight but strong plastic almost twice as fire retardant as similar materials has been made by researchers in China and South Korea. The key to the material’s ability to keep flames at bay are small amounts of graphene combined with an element best known for its role in making, rather than stopping, fire: phosphorus.
The most widely used flame retardants are brominated compounds. However, they have been suspected to be toxic, particularly for children. As many countries move towards banning them altogether, scientists have been searching for alternatives. But in addition to being fire-retardant, materials need to be light and strong, as well as cheap and easy to produce on a large scale.
Jianxing Geng from the Chinese Academy of Sciences and colleagues have developed a non-burning polyimide foam that is strong enough to support a beaker of liquid weighing 6kg, but light enough to balance on a rose. Its flame-retardant properties come from 2% of red phosphorus-hybridised graphene – a combination of graphite and red phosphorus produced by ball milling.
The tiny phosphorus particles oxidise quickly when heated and promote char formation. Combined with graphene platelets, which are chemically stable even at high temperatures, the material forms an oxygen-proof layer on the surface. This stops the underlying material from burning.
Because polyimide foams are already made on industrial scale, Geng’s team thinks that scaling up the phosphorus graphene foam synthesis should also be feasible.