Nanomaterial researchers have employed carbon nanotubes and impact-responsive polymers to form a composite which senses the force of a bullet or knife stab and stiffens accordingly. If applied to bullet-proof and anti-stab vests, the novel nanotechnology could save countless lives.

Current body armour technology is frequently based on the trade-marked material Kevlar. But Kevlar has its problems.

As a ballistic material it is relatively flexible, but that elasticity means that even when it stops a bullet, the energy is still conveyed directly to the user at the point of impact. While the projectile might not pierce the skin, the force created means that the wearer is still punched with the power of the speeding bullet. That energy continues into the wearer’s body and may be enough to cause serious and sometimes fatal internal injuries.  

To minimise this effect, especially in military situations where multiple impacts are possible or where high-velocity rounds are in use, Kevlar is sometimes coupled with thick steel or ceramic plates. This added protection is bulky and heavy, but does help to disperse the impact across a broader area.

Carbon nanotube technology has solved this problem.

The breakthrough was made by Wanquan Jiang and co-workers from the University of Science and Technology of China and was based on their earlier research in creating a number of shear-thickening polymers which stiffen when strain is applied. Using this know-how, the team then focused on developing a Kevlar composite which would remain flexible when worn but would strengthen and become more rigid at the moment of impact.

“We have introduced a shear stiffening polymer into Kevlar fabric to give a novel flexible body armour material with enhanced mechanical performance,” says Jiang. “We included carbon nanotubes in the composite which gives the material excellent force sensing capability.”

The team have now experimented with varying combinations of shear-stiffening polymer and Kevlar. With loads varying from 4.8 weight% polymer to 84 weight% polymer, tests have shown the clear advantages of adding nanomaterials to conventional raw materials used in body armour.

Specifically, the study (now published in the journal Soft Matter), states that, “Stab resistance performance tests under quasi-static and dynamic conditions show that the maximum resistance force and penetration impact energy for the S-ST/Multi-walled Carbon Nanotube/Kevlar-based wearable electronic textile (WET) are 18 N and 11.76 J, which represent a 90% and 50% increment with respect to the neat Kevlar, respectively.” Adding that, “Dynamic impact resistance tests show that the WET absorbs all the impact energy. The maximum resistance force of the WET is 1052 N, which represents an improvement of about 190% with respect to neat Kevlar. With the incorporation of multi-walled carbon nanotubes (MWCNTs), the WET can achieve a stable electrical conductivity of ∼10−2 S m−1, and the conductivity is highly sensitive to external mechanic forces.”

“The carbon nanotubes form a conductive network within the composite, enabling the fabric to detect impacts, similar to how a touch screen works,” explains the Royal Chemical Society’s Will Bergius in a report for Chemistry World. “The result is a smart fabric that offers 90% more ballistic protection and 50% more stab resistance than Kevlar alone, with the capability to detect the force and location of impacts, even if it has been pierced.”

The U.S. military and numerous police forces are now looking to apply this technology into its hardware, while others are exploring how it could be applied to civilian activities, such as sporting equipment.

Ballistic experts are now predicting that the inclusion of nanomaterials into body armour may become an industry standard, offering a golden opportunity for saving lives. As Jaroslaw Drelich a member of Michigan Technological University’s Surface Innovations research group simply states, “Adding conductive carbon nanotubes is a very clever solution and should attract the attention of many R&D centres around the world.”

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