Wednesday, February 20, 2008

Damaged rubber can heal itself

French chemists on Wednesday announced they had created rubber that heals itself after it has been cut, a breakthrough that could lead to clothes that self-mend if torn and toys that repair themselves if damaged by a tot.

The molecular concoction -- described by other scientists as having "a touch of magic about it" -- can self-heal at room temperature in around 15 minutes by simply pressing the damaged pieces together, they report in the British weekly science journal Nature.

Conventional rubber typically comprises long, cross-linked chains of polymers that can stretch and then recover to their original size and shape.

The new formula made by a team at France's National Centre for Scientific Research (CNRS) and a private firm, Arkema, achieves the same elasticity by using a mixture of two different kinds of smaller molecules.

Some are ditopic, which means they can hook up with two other molecules, and others are tritopic, meaning they can associate with three molecules.

The network is meshed together by weaker hydrogen bonds, which get broken when the rubber is cut but also provide an atomic "glue," recombining into chains to bridge severed parts.

The ingredients comprise fatty acids made from ordinary vegetable oils, combined in a stepped process with diethyline triamine and urea, both cheap and common chemicals.

The result is a substance that at eight degrees Celsius (46 degrees Fahrenheit) becomes a translucent glassy plastic that, like soft rubber, can be strained five times its length before breaking.

Unlike rubber, though, the pieces can be mended at room temperature (20 C, 68 F) without the need for them to be heated or even pressed together strongly. And the substance can be easily reprocessed.

"If you drill into a rubber sealing in a wall, the hole will repair by itself," said lead researcher Ludwik Leibler, of the CNRS' Soft Matter and Chemistry Laboratory.

"Anything involved with compression, such as joints and rubberised coatings, can be fixed. The fracture and healing process can be repeated many times."

Arkema and CNRS have already worked on other "self-healing" materials, including paint that smooths itself out if scratched, Arkema researcher Manuel Hidalgo said.

The first products from that research should be on the market "in a year or two," he told AFP.

In a commentary also published by Nature, synthetic materials scientists Justin Mynar and Takuzo Aida noted that when the Spanish conquistadores first witnessed the Aztecs playing a game with a bouncing rubber ball, they thought such balls must be possessed by evil spirits.

"Imagine their reaction if, on cutting the ball in half, it was made as good as new simply by pressing the two halves together," they write.

"Even today, such a feat would have a touch of magic about it. But this is what (has been) achieved."


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