Feb 21, 2008
CHICAGO - ANYONE who has heard the snap of a rubber band breaking knows it's time to reach for a replacement.
But a group of French scientists have made a self-healing rubber band material that can reclaim its stretchy usefulness by simply pressing the broken edges back together for a few minutes.
The material, described on Wednesday in the journal Nature, can be broken and repaired over and over again.
It is made from simple ingredients - fatty acids like those found in vegetable oils, and urea, a waste compound in urine that can be made synthetically.
The material would be an asset to industry and might even help shed light on the physics of elasticity, wrote Philippe Cordier and colleagues at the Industrial Physics and Chemistry Higher Educational Institution in Paris.
Standard rubber bands, which can stretch up to several hundred percent then then snap back into shape, are made from long chains of cross-linked polymers.
The new material is linked by short chains of a type of molecule called ditopic, which can associate with two other molecules, and multitopic molecules, which can associate with more than two molecules.
This network of molecules is strengthened by hydrogen bonds that allow the material to stretch up to several hundred per cent, then snap back into shape.
If severed, the material mends itself when the ends are pressed together at room temperature, allowing these bonds to re-form.
'The mended samples are able to sustain large deformations and recover their shape and size when stress is released,' Mr Cordier and his colleagues wrote.
The material can 'withstand multiple fractures, needs no catalysts and is otherwise straightforward to produce,' Justin Mynar and Takuzo Aida of the University of Tokyo wrote in an accompanying article.
'A final blessing is that it can be broken down with heat and easily recycled - so it is environmentally friendly, too.' -- REUTERS