Researchers from the Leibniz Institute for Polymer Research Dresden have developed a new kind of rubber imbued with the ability to heal itself, possibly finding a permanent solution to flat tires.

In a study published in the journal ACS Applied Materials & Interfaces, the researchers detailed how they were able to come up with tire-grade rubber that didn't incorporate vulcanization, a processing step essential to inflatable tires since they were invented. Vulcanization makes rubber more durable without affecting its elasticity by adding sulfur or another curative. However, once rubber is cut or pierced, it can no longer be patched up for long-term use.

Other researchers have begun developing self-healing rubber earlier than the study but many of the prototypes produced were not able to achieve long-term stability. This is what Amit Das and colleagues were interested in addressing with their research.

The researchers turned to a simple approach that converted widely used, commercially available bromobutyl rubber into a highly elastic material imbued with self-healing properties. The approach, however, didn't include vulcanizing or cross-linking agents conventionally used. The result? Bromobutyl rubber's bromine functionalities were transformed into ionic imidazolium bromide groups that formed reversible ionic associates that promotes self-healing in the material, particularly when stress or heat is applied. The researchers also found that the self-healing rubber they developed were superior in terms of ductility, tensile strength and elastic modulus compared to the conventional rubber tire. Strength can be further improved though by including reinforcing agents like carbon black or silica to the material.

To test the rubber, the researchers cut the material and observed that it was able to heal at room temperature, a convenient feature that means it will be possible for a tire to repair itself while the vehicle is parked. However, heating the material to 212 degrees Fahrenheit within the first 10 minutes of being cut allowed the repair process to speed up. After 8 days since self-healing, the rubber was shown to be capable of withstanding stress equivalent to 754 pounds per square inch.

Other authors for the study include: Gert Heinrich, Brigitte Voit, Klaus Werner Stöckelhuber, Sven Wießner, Debdipta Basu, Marcus Suckow, Frank Böhme and Aladdin Sallat. Some of the researchers were also affiliated with the Tampere University of Technology and the Dresden University of Technology.

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