Multifunctional nanofiber protects against explosions

Since World War I, the vast majority of American combat victims have come not from gunshot wounds but from explosions. Today, most soldiers wear a heavy bulletproof vest to protect their torso, but much of their body remains exposed to the indiscriminate target of explosive fragments and shrapnel.

Designing equipment to protect limbs from extreme temperatures and the deadly projectiles that accompany an explosion has been difficult due to a fundamental property of materials. Materials that are strong enough to protect against ballistic threats cannot protect against extreme temperatures and vice versa. As a result, much of today’s protective gear is made up of multiple layers of different materials, leading to heavy and bulky gear that, if worn on the arms and legs, would severely limit a soldier’s mobility.

Now, researchers at Harvard University, in collaboration with the U.S. Army Combat Capability Development Command Soldier Center (CCDC SC) and West Point, have developed a lightweight, multifunctional nanofiber material It can protect users from extreme temperatures and ballistic threats.

The research is published in the journal. to import.

“When I was in combat in Afghanistan, I saw firsthand how body armor could save lives,” said lead author Kit Parker, a professor of bioengineering and applied physics for the Tarr family at the John A. Paulson School of Engineering and Applied Sciences Harvard (SEAS) and a lieutenant colonel in the United States Army Reserve. “I also saw how heavy armor could limit mobility. As soldiers on the battlefield, the three main tasks are moving, shooting, and communicating. If you limit one of them, you decrease survival and jeopardize the success of the mission.” .

“Our goal was to design a multi-functional material that could protect someone working in an extreme environment, such as an astronaut, firefighter, or soldier, from the different threats they face,” said Grant M. González, a postdoctoral fellow at SEAS and first author. from the article.

To achieve this practical goal, researchers needed to explore the trade-off between mechanical protection and thermal insulation, properties rooted in the structure and molecular orientation of a material.

Materials with strong mechanical protection, such as metals and ceramics, have a highly ordered and aligned molecular structure. This structure allows them to resist and distribute the energy of a direct blow. Insulating materials, on the other hand, have a much less ordered structure, which prevents heat transmission through the material.

Kevlar and Twaron are commercial products widely used in protective equipment and can provide ballistic or thermal protection, depending on how they are manufactured. Woven Kevlar, for example, has a highly aligned crystalline structure and is used in bulletproof protective vests. Porous Kevlar aerogels, on the other hand, have been shown to have high thermal insulation.

“Our idea was to use this Kevlar polymer to combine the neat and woven structure of the fibers with the porosity of the aerogels to make long, continuous fibers with a pore space in between,” said Gonzalez. “In this system, long fibers could withstand mechanical impact, while pores would limit heat diffusion.”

The research team used rotary immersion rotation (iRJS), a technique developed by the Parker Disease Biophysics Group, to make the fibers. In this technique, a liquid polymer solution is loaded into a reservoir and pushed through a small opening by centrifugal force as the device rotates. When the polymer solution shoots out of the reservoir, it first passes through an open air area, where the polymers elongate and the chains align. Then, the solution reaches a liquid bath that removes the solvent and precipitates the polymers to form solid fibers. Since the bath is also spinning, like water in a salad bowl, the nanofibers follow the vortex stream and wrap a rotating manifold at the base of the device.

By adjusting the viscosity of the liquid polymer solution, the researchers were able to spin long, aligned nanofibers into porous sheets, providing enough order to protect against projectiles but enough mess to protect against heat. In about 10 minutes, the team could rotate the sheets about 10 by 30 centimeters in size.

To test the blades, the Harvard team turned to their collaborators for ballistic testing. CCDC SC researchers in Natick, Massachusetts simulated the impact of shrapnel by firing large BB-like projectiles at the sample. The team conducted tests by sandwiching the nanofiber sheets between sheets of woven Twaron. They observed little difference in protection between a stack of all woven Twaron sheets and a combined stack of woven Twaron and spun nanofibers.

“The capabilities of the CCDC SC allow us to quantify the successes of our fibers from the perspective of the protection team for combatants, specifically,” said González.

“Academic collaborations, especially those with distinguished local universities like Harvard, provide CCDC SC the opportunity to take advantage of cutting-edge expertise and facilities to augment our own R&D capabilities,” said Kathleen Swana, a CCDC SC researcher and one of the authors of the article. . “CCDC SC, in return, provides valuable scientific and soldier-centered experience and testing capabilities to help drive research.”

By testing thermal protection, the researchers found that nanofibers provided 20 times the thermal insulation capacity of commercial Twaron and Kevlar.

“While improvements can be made, we have pushed the limits of what is possible and have begun to move the field toward this type of multifunctional material,” said Gonzalez.

“We have shown that you can develop highly protective textiles for people who work in a harmful way,” said Parker. “Our challenge now is to evolve scientific advancements into innovative products for my brothers and sisters in arms.”

The Harvard Office of Technology Development has filed a patent application for the technology and is actively seeking commercialization opportunities.