New structures 'tougher than Kevlar'

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Researchers have created new structures that exploit the electromechanical properties of nanofibres to stretch to up to seven times their length, while remaining tougher than Kevlar.

Developed by researchers at the University of Texas at Dallas, these structures are said to absorb up to 98 joules per gram whilst Kevlar, a common material in bulletproof vests, can absorb up to 80 joules per gram. The University claims also that the material can reinforce itself at points of high stress and could potentially be used in military aircraft or other defence applications.

In a study published by ACS Applied Materials and Interfaces, researchers twisted nanofibre into yarns and coils. The electricity generated by stretching the twisted nanofibre formed an attraction 10 times stronger than a hydrogen bond, which is considered one of the strongest forces formed between molecules.

Researchers sought to mimic their earlier work on the piezoelectric action of collagen fibres found inside bone in hopes of creating high-performance materials that can reinforce itself, said Dr Majid Minary, an assistant professor of mechanical engineering in UT Dallas’ Erik Jonsson School of Engineering and Computer Science and senior author of the study.

“We reproduced this process in nanofibres by manipulating the creation of electric charges to result in a lightweight, flexible, yet strong material,” Minary said in a statement. “Our country needs such materials on a large scale for industrial and defence applications.”

For their experiment, researchers first spun nanofibres out polyvinylidene fluoride (PVDF) and its co-polymer, polyvinvylidene fluoride trifluoroethylene (PVDF-TrFE).

Researchers then twisted the fibres into yarns, and then continued to twist the material into coils.

“It’s literally twisting, the same basic process used in making conventional cable,” Minary said.

Researchers then measured mechanical properties of the yarn and coils such as how far it can stretch and how much energy it can absorb before failure.

“Our experiment is proof of the concept that our structures can absorb more energy before failure than the materials conventionally used in bulletproof armours,” Minary said. “We believe, modelled after the human bone, that this flexibility and strength comes from the electricity that occurs when these nanofibres are twisted.”

The next step in the research is to make larger structures out of the yarns and coils, Minary said.

The USA’s Air Force Office of Scientific Research Young Investigator Research Program and National Science Foundation funded the work.