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article imageSelf-healing rubber invented and triggers business interest

By Tim Sandle     Aug 17, 2017 in Science
Imagine a tire on a freight vehicle that could heal after being punctured, without the need to call out a breakdown service? This is the technology that has been developed by researchers from the Harvard John A. Paulson School in the U.S.
The scientists have produced a developed a new type of rubber that is as tough as natural rubber but can also self-heal. This process will be of great interest to the freight and transport industry once it becomes commercialized and, as it spins out, all types of car manufactures will be evaluating the technology for all types of vehicles. The use of the self-healing rubber does not stop there. How about rubber bands that can reform once they have been snapped?
To data self-healing materials, like the progress made with hydrogels, have relied on water being an essential part of the material. This is because water is needed within the reversible bonds that promote healing. Progress with dry materials, like rubber, has been limited so far. This is down to the chemistry of rubber, where the covalent bonds that give the material its strength are unable to reconnect once the bonds have been broken.
The manipulation of the bonds was therefore essential to changing the state of the material. This involved making the bonds connecting the polymers reversible. This enabled the bonds to be altered so they could break and reform. This was achieved by creating a hybrid rubber with both covalent and reversible bonds.
The basis of the technology was a type of molecular rope to tie two types of bonds together (termed randomly branched polymers). The process allowed for two previously unmixable bonds to be mixed together homogeneously on a molecular scale. The output was a transparent, tough, self-healing rubber.
What is special about the rubber is that, when pulled and stretched, the hybrid rubber develops what are called ‘crazes’ throughout the material. These are like cracks but they are connected by fibrous strands. The crazes function to redistribute the stress; this means there is no localized point of stress that could cause a catastrophic failure. As stress is released, the material is able to snaps back and turns back into its original form. One of the first trials with the material will be to develop a tire that is capable of self-healing when a puncture occurs. Although this will take time to develop, this type of technology will appeal to the transport and logistics sectors.
As lead researcher Dr. Li-Heng Cai told Controlled Environments: “If you have a cut through the tire, this tire wouldn't have to be replaced right away. Instead, it would self-heal while driving enough to give you leeway to avoid dramatic damage.”
The findings to date are published in the journal Advanced Materials, with the paper titled “Tough Self-Healing Elastomers by Molecular Enforced Integration of Covalent and Reversible Networks.”
More about Rubber, selfhealing, materials science, Physics
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