Mystery mechanism heals high-tech composite

Self-healing composite materials that can fix small cracks in the structures of planes, bridges, and wind turbines could become more cost-effective thanks to a new bonding mechanism discovered by researchers in the US. Engineers have high hopes for composite materials that can repair small cracks in their structure. "When you have any damage induced by fatigue, there's usually nothing you can do except wait for catastrophic failure," says Jeffrey Moore, who led the research at the University of , Urbana, US. Self-healing composites should change that. These materials contain capsules of a liquid adhesive which leaks out and repairs tiny cracks when they appear. However, the adhesives usually require some kind of post-processing to make them set, such as curing with UV light or heating to high temperatures. What engineers would prefer, though, is a material that healed itself without any extra intervention. Rare catalyst: In 2001, Moore's group developed just such a material that relied on the mixing of two different chemicals that set like a two-part epoxy. The material contains two types of capsule: one containing a ring hydrocarbon called dicyclopentadiene and the other containing a ruthenium solvent that acts as a catalyst, causing the rings to break open and polymerise. Any crack causes the chemicals to mix and set, bonding the crack faces together. But ruthenium is rare. "An Airbus fuselage has 60,000 pounds of composites in it.

If you used the catalyst approach, a significant fraction of the world supply of ruthenium would be flying around in one plane," Moore told New Scientist. That makes it impractical for most applications, so his team set to work looking for an alternative. Seeking to improve the approach, the group changed to a nickel-based catalyst, but had to change the solvent as well. The first step was to gauge the new solvent in the absence of a catalyst.