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• Since its invention, Kevlar has saved thousands of lives thanks to the synthetic polymer being both incredibly lightweight and incredibly strong.
  
• However, Kevlar is far from the last word on ballistic protection, and a new study reports a material woven with carbon nanotubes that’s both three times stronger than Kevlar and only 1.8 millimeters thick.
  
• Scientists created this material by combing carbon nanotubes with aramid polymers (which are also used in Kevlar) and aligning them in just the right way to protect against slippage under immense impact.
  

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Since the invention of Kevlar in the 1960s, this extra-strong synthetic fiber woven into rugged body armor has saved the lives of at least 3,000 police officers, according to the National Institute of Justice. In many regards, it’s a wonder of materials science, and while Kevlar’s performance and manufacture has improved over time, scientists have developed a handful of candidates that could be Kevlar’s next-generation replacement—molecular “chainmail,” another polymer-based material called Dyneema, even spider silk.
Now, scientists may have developed another challenger to the Kevlar crown—a lightweight material that’s three times stronger than Kevlar, only 1.8 millimeters thick, and laced with carbon nanotubes (CNTs).

Quote:Progress and potential
Ultra-high dynamic strength and toughness are crucial for fibrous materials in impact-protective applications. However, the trade-off between strength and toughness is a persistent challenge in materials science. Achieving simultaneous breakthroughs in both properties demands innovative fabrication strategies. Polymer chains tend to slip during loading, which undermines the effective utilization of their high intrinsic mechanical properties, thereby limiting the strength and toughness of polymer fibers. To address this issue, we developed an effective strategy that regulates the orientation of carbon nanotubes within fibers to inhibit chain slippage. Carbon nanotubes and aramid chains were molecularly engineered to achieve compatibility, while multi-stage drafting was designed for the alignment of both carbon nanotubes and aramid chains to optimize the hierarchical structures of fibers. Such optimization of hierarchical structures improves the interfacial interactions and enhances load transfer efficiency, inducing inhibited slippage and thus remarkable breakage of aramid chains under high-speed impacts. Based on this strategy, we fabricated aramid fibers with a dynamic strength up to 10 GPa and dynamic toughness up to 700 MJ m−3. Fabrics woven from these fibers also exhibit superior anti-ballistic impact performance, shedding light on practical applications of these fibers. These findings provide fresh insights into the design of high-performance fibrous materials.
Highlights
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High-strength and high-toughness aramid fibers were fabricated
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The orientation of carbon nanotubes was regulated by introducing a flexible monomer
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The excellent performance is attributed to the remarkable breakage of aramid chains
Summary
Ultra-high dynamic strength and toughness are crucial for fibrous materials in impact-protective applications. However, the trade-off between strength and toughness is a persistent challenge in materials science. Herein, by regulating the orientation of long carbon nanotubes within fibers, we fabricated carbon nanotube/heterocyclic aramid composite fibers with a dynamic strength of 10.3 GPa and a dynamic toughness of 706.1 MJ m−3. The ultra-high dynamic performance is attributed to the inhibited slippage and thus remarkable breakage of polymer chains during the high-strain-rate loading process; these behaviors are due to the improved alignment of polymer chains, reduced porosity, and thus enhanced interfacial interactions and load transfer efficiency therein induced by aligned long carbon nanotubes and multi-stage drafting. This work provides a fresh understanding and a feasible route for utilizing the intrinsic mechanical performance of polymer chains at the macroscale.