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Self-healing materials may soon be part of every day life

University of Illinois researchers have developed a new catalyst-free, self-healing material system that offers a far less expensive and far more practical way to repair composite materials used in structural applications, ranging from airplane fuselages to wind-farm propeller blades.

Washington, November 28 : University of Illinois researchers have developed a new catalyst-free, self-healing material system that offers a far less expensive and far more practical way to repair composite materials used in structural applications, ranging from airplane fuselages to wind-farm propeller blades.

Jeffrey Moore, the Murchison-Mallory Professor of Chemistry at Illinois, has revealed that the new self-healing system incorporates chlorobenzene microcapsules, as small as 150 microns in diameter, as an active solvent.

The researcher said that the expensive, ruthenium-based Grubbs' catalyst that was needed in their first approach was not longer required.

"By removing the catalyst from our material system, we now have a simpler and more economical alternative for strength recovery after crack damage has occurred. Self-healing of epoxy materials with encapsulated solvents can prevent further crack propagation, while recovering most of the material's mechanical integrity," said Jeffrey Moore.

The new chemistry has been described in a report posted on Macromolecules journal's Web site.

The report says that during normal use, epoxy-based materials experience stresses that can cause cracking, which can lead to mechanical failure.

It further states that autonomous self-healing, a process in which the damage itself triggers the repair mechanism, can retain structural integrity and extend the lifetime of the material.

"Although we demonstrated the self-healing concept with a ruthenium-based catalyst, the cost of the catalyst made our original approach too expensive and impractical. Our new self-healing system is simple, very economical and potentially robust," said Moore, who also is affiliated with the university's Frederick Seitz Materials Research Laboratory and with the Beckman Institute.

In the researchers' original approach, self-healing materials consisted of a microencapsulated healing agent (dicyclopentadiene) and Grubbs' catalyst embedded in an epoxy matrix.

As the material cracked, microcapsules would rupture and release the healing agent, which would then react with the catalyst to repair the damage.

However, in the new approach, microcapsules containing chlorobenzene break when a crack forms in the epoxy material.

The solvent disperses into the matrix, where it finds pockets of unreacted epoxy monomers. The solvent then carries the latent epoxy monomers into the crack, where polymerisation takes place, restoring structural integrity.

Moore revealed that in fracture tests, self-healing composites with catalyst-free chemistry recovered as much as 82 per cent of their original fracture toughness.

According to the researcher, the new catalyst-free chemistry has taken down the barriers to cost and level of difficulty.

"From an economics and simplicity standpoint, self-healing materials could become part of everyday life," Moore said.

ANI