Synthetic rubber repairs itself

8 August 2014

A new synthetic rubber developed by EU-funded researchers repairs itself. That means longer-lasting components, plus reduced maintenance costs and waste. The rubber will initially be used for reducing rail and traffic noise, with many more applications to follow.

Known to most folk as synthetic rubber, a certain class of stretchy plastic is to chemists an "elastomer" (elastic polymer). While very useful in industry, for instance as seals, it wears out and must be replaced. That means maintenance costs.

When the worn components are inside machines, this may add extra layers of maintenance difficulty, especially if the machines are remote or inaccessible. The more durable a rubber seal, the lower the maintenance requirements, although even the toughest rubber will still wear out eventually.

The ultimate solution would be an elastomer that "heals" itself. It would last longer, and require less maintenance. Worn parts would need replacing less frequently. It sounds like science fiction, but that kind of self-healing elastomer is exactly what the EU-funded SHINE project aims to develop.

SHINE's new material will repair itself repeatedly, at room temperatures, and without human intervention. Micro-cracks in the material will zip themselves back together, within seconds. This stops a larger crack developing and so prevents the breakdown of the material.

"The project started just one year ago (in February 2014), but already we have some quite remarkable breakthroughs," says SHINE coordinator Ronald Korstanje of the Dutch Polymer Institute. "Our elastomers have some pretty extreme self-healing characteristics."

The process relies on the interplay between strong chemical bonds (covalent) and weak ones (hydrogen or sulphur) in the polymer. In simple terms, weak bonds may readily break down; the strong bonds continue to hold the material together while the weak bonds automatically re-establish themselves.


Breakthroughs already

SHINE has manufactured the elastomers at lab scale, and also at pilot industrial scales. Under tests, SHINE's elastomers have demonstrated interesting self-healing characteristics, though the researchers do not yet know how long these will ultimately last. The repaired substance also retains at least 97% of its initial strength.

"For a first-year result, that's more than I would have expected," says Korstanje.

The new materials would be used for a variety of applications, including bearing seals for wind-turbines and other machines - such as vehicles, vibration and noise reduction systems for roads and bridges, and new kinds of asphalt.

In each case, self-healing elastomers would mean less maintenance and lower overall costs. In terms of road maintenance, any reduction would mean fewer traffic jams, fewer delays and less road congestion.

Korstanje says pads of self-healing elastomers can be used on train tracks and bridges to muffle vibration, as any suitable rubber would. However, SHINE's new elastomers would reduce maintenance costs due to their auto-repairing properties.

These applications only scratch the surface of the possibilities, he adds. During SHINE's remaining years, the team will investigate other uses of the materials and also performance improvements.

The current partial rigidity of the repaired material is a concern, and the project will be working to determine which combinations solve this problem. Solutions may require different processing techniques, which is why SHINE will be developing new methods for mixing and analysing both the materials and eventual final products. These methods will also help to fully industrialise the elastomers.

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