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Rubber Goes Self-healing

Rubber Goes Self-healing

It looks like the run-flat tyre concept is running flat into a new conceptual challenge – self-healing rubber. When the rubber in the tyre itself can heal on its own when punctured, then the run-flat technology can as well be forgotten, says researcher Amt Das. He is the leader of the German research team that is developing a new technique that drops vulcanisation from the rubber production process

The recent research finding by a German team can do wonders when it is fine-tuned to suit the commercial needs of tyre-making. It is a technology that self-heals rubber facilitating punctured tyre to heal itself.
The team has been working on converting commercially available and widely used bromobutyl rubber (BIIR) into a highly elastic material with extraordinary self-healing properties without using conventional cross-linking or vulcanising agents.
The researchers included of Amit Das, Aladdin Sallat, Frank Böhme, Marcus Suckow, Debdipta Basu, Sven Wießner, Klaus Werner Stöckelhuber, Brigitte Voit, and Gert Heinrich from Leibniz-Institut für Polymerforschung Dresden, Tampere University of Technology, Finland, and Technische Universität Dresden.
“Normally, a tyre gets its durability through sulfer vulcanisation while retaining elasticity. It strengthens the rubber,” says Das. “However, when the tyre gets punctured, it breaks the chemical bonds and makes the tyre unusable.”
According to Das, vulcanising produces a material held together by strong chemical links in a kind of network. “Unfortunately, once these links are broken, they can’t be reassembled.”
“The scientists at Dresden’s Technical University and its Leibniz Institute for Polymer Research, instead used a process of ionic association or ionic clustering ionisation to hold together the rubber, binding it into a solid with a network of electrostatic bonds,” he said in an interview.
A tyre in running condition feels always a stressed and the healing nature of the modified rubber might not be realised in full extent during vehicle operation. Although, in tear fatigue analysis the researchers observed that the crack propagation rate is much slower than standard sulfur vulcanised rubber. However, during parking the healing efficiency would be much faster as there would be less stress on the tyre components, Das said.
The team found that instead of sulfer vulcanisation, the use of a carbon/nitrogen compound offers extraordinary self-healing properties, without compromising the much needed durability and elasticity.
Das says that the self-healing system works on the principle of self-association of ionic segments of macromolecular strands which repair the defects that might be created within the material while in service.
The development of ionic character to the polymer leads to an ionic association of the groups, which ultimately leads to a network structure formation of the rubber chains. The ionic modification of the rubber is very simple and shows unusual self-healing properties.

New concept

The new product, although tested under laboratory conditions, proved that it heals at room temperature. Later it was found that the self-healed rubber stood up to pressures of over 750psi, which is almost 20 times higher than what a normal passenger car tyre handles.
Das said that this is a very new concept of rubber chemistry. “The concept of rubber curing by addition of different sulfur curatives could be totally transformed by withdrawing the different chemicals used in rubber compounding.
In present case, the curing process could be realised by the association of the ionic parts of the elastomeric stands which is the intrinsic property of the new rubber. The ionic parts of the modified rubber form the network structure which is very crucial to get elastic properties of rubbers. “This finding may revolutionise the common understanding of rubber technology,” Dr Das said.
“This simple and easy approach to preparing a commercial rubber with self-healing properties offers unique development opportunities in the field of highly engineered materials, such as tyres, for which safety, performance, and longer fatigue life are crucial factors,” the report, published in the American Chemical Society’s Applied Materials & Interfaces journal, said.
According to Das, the developed material is very close to the real application when compared with other self-healing works in the literature. Most of the reported self-healing rubbers are known to be remained in the laboratory scale, he said.
“But in our work we utilise a common commercial rubber. We just have it modified it by a very simple chemical process. So this material is very close to the reality and be easily produced. But a lot of care and further detailed research are very necessary to realise in practical application,” he said.

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