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Kevlar has met its match. For decades, it has been the gold standard for impact protection, from bulletproof vests to armored vehicles, and is still widely used. But scientists have now developed a new composite material that is stronger, tougher and better at stopping bullets than Kevlar even though it is much thinner. Their study is in the journal Matter.

To stop high-speed impacts, like a bullet, a material needs to resist breaking under force (high strength) and be able to absorb a lot of energy without shattering or failing (high toughness). However, there is a problem with current solutions, such as Kevlar, which is made from aramid fibers. When scientists try to make these fibers stronger, they often become more brittle, making it difficult to achieve both simultaneously. This is a common trade-off in materials science when you try to improve a material's overall performance.

Steps toward a super-fiber

But after six years of working on this problem, Jin Zhang from Peking University, China, and his colleagues have come up with a solution. They created a new type of fiber by combining two materials: a heterocyclic aramid, a high-performance fiber similar to Kevlar, and treated long carbon nanotubes (tl-SWNTs). These super-strong carbon tubes are incredibly stiff and lightweight, and much thinner than a human hair.

The key to creating the new super-fiber wasn't just in combining them, but in the way the researchers lined them up. They forced the aramid chains and carbon nanotubes to be straight and parallel with each other. They achieved this by making the base aramid fiber more flexible and then used a multi-step stretching process to align the polymer chains and nanotubes perfectly. This alignment is fundamental because it locks the components together so tightly that when it is hit, the chains can't slip past each other. Therefore, the material can absorb more energy without failing.

Better than Kevlar

The scientists subjected their new material to high-speed tests, including ballistic tests similar to those used for body armor. It achieved a dynamic strength significantly higher than existing fibers, and its ability to absorb energy more than doubled the previous record, reaching 706.1 megajoules per cubic meter. When woven into a fabric, this new super-fiber showed superior anti-ballistic performance compared to current protective fabrics.

"Our study not only presents an effective strategy for the fabrication of aramid fibers with ultra-high dynamic strength as well as the highest recorded dynamic toughness, but also provides fresh mechanism insights," wrote the team in their paper.

Ultimately, if this fiber is put to use, it can make future protective gear dramatically lighter, thinner and safer.

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