Flat tires: agonizing time-wasters and inducers of expletives, they are at least a good faux excuse for tardiness. But in the future, we could have to find a new fib, as scientists might have come up with a way to avoid them. By altering the rubber processing technique, researchers have managed to produce a material that exhibits self-healing properties, without sacrificing strength or elasticity.
This is a pretty big deal. Not only because of the potential to make tires significantly more resilient to puncture, but also due to the fact that it cuts out the only processing step that has been used to create car tires. Accidentally discovered back in 1839 by inventor Charles Goodyear, the technique – vulcanization – involves crisscrossing rubber molecules using heat and sulfur. Think of it like a pile of wet spaghetti: Whenever the bits of pasta cross over each other, they stick together. The end result is that the rubber becomes stronger, less gloopy but more elastic; this is ideal for tires.
But the problem is, if a cross link gets broken, for example by piercing the material, the chemical bond that held it together – a covalent bond – is permanently lost. This is why it can’t self-heal. To overcome this problem, a group of researchers in Germany decided to forgo traditional vulcanization in favor of a different technique. For their research, published in Applied Materials & Interfaces, they used the commonly used bromobutyl rubber, which as the name suggests contains bromine atoms.
But rather than using sulfur to provide the cross-linking functionality, what they did was swap atoms of bromine for chemical groups called imidazolium bromide that, instead of creating irreparable covalent bonds, form ionic bonds – those between positively and negatively charged ions. This means that if something tears the material and pulls the bonds apart, they can reform when the charged components come back in close proximity to one another. Hence, the material can “heal.”
Putting the new material to the test, the researchers found that it was able to repair a cut even at room temperature, which is a particularly useful property. It could even withstand a significant amount of stress, and heating it up made the healing process speedier. Ultimately, the dream is to be able to create a rubber tire that could fix itself while parked, although we’re not quite there yet. However, the researchers have already made suggestions that could potentially further increase the strength of the material, which is promising.