A new type of plastic can repair itself underwater, even when conditions are harsh here. The plastic retains its strength during this process and can therefore possibly be used during emergency situations on or in the sea.

The new type of plastic is called RUSSE, which stands for Rapid Underwater Self-healing Stiff Elastomer. This material repairs itself underwater. This is exceptional, as most self-healing polymers do not work well below the surface of the water. ‘Self-repairing polymers that work at room temperature are often not stable underwater. They are also difficult to repair themselves and the process takes a long time,’ says research leader Lili Chen, molecular engineer at Tsinghua University in China.

Extensively tested

RUSSE is made from a type of soft polymer that is also found in some paints. Small pieces of polymer are linked together by minute chains of a harder type of polymer. These chains are no more than a few nanometers long. The research team tested the properties of the material by stretching it, cutting it and even hitting it with a hammer.

The properties of the new type of plastic were extensively tested by the researchers. Image: Chen et al. (2021).

attraction

The material withstood all tests. It could be stretched as much as 1400 percent without breaking. Also, it could bear 1000 times its own weight without changing its shape. When the researchers cut the material in half and then pressed the ends back together, it rejoined in ten seconds.

The molecules that make up the polymers have a positive and a negatively charged end. These two ends pull together and intertwine again. In those ten seconds, more and more molecules reconnected, causing the material to slowly regain its strength. Less than five minutes later, the material was almost completely back to its original state.

In case of emergency

The research team also tested the effectiveness of RUSSE in salt water. These conditions almost did not affect the elasticity and self-healing function of the material. The plastic was also cut in two underwater; within five minutes the material was back at 80 percent of its original hardness. These results were the same when the self-healing plastic was immersed in acidic and basic solutions. Even when the material was left in salt water for a month, it kept its properties.

Even underwater, the plastic was able to repair itself.

These results indicate that the material could be used for underwater repairs in an emergency, Chen said. She gives an example of a diver: when the air tank tubes break unexpectedly and the gas flow is interrupted, the diver can die within seconds. ‘Self-healing materials like RUSSE can play a crucial role in such dangerous and urgent situations.’ The plastic can even be used as a coating in underwater pipelines to make them faster and easier to repair, Chen said.

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