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Suit up with nanofiber for protection against explosions and high temperatures

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Where explosions are concerned you might expect to see some army research and you would be right. A June 29, 2020 news item on ScienceDaily breaks the news,

Since World War I, the vast majority of American combat casualties has come not from gunshot wounds but from explosions. Today, most soldiers wear a heavy, bullet-proof vest to protect their torso but much of their body remains exposed to the indiscriminate aim of explosive fragments and shrapnel.

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

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

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A June 29, 2020 Harvard University news release (also on EurekAlert) by Leah Burrows, which originated the news item, expands on the theme,

“When I was in combat in Afghanistan, I saw firsthand how body armor could save lives,” said senior author Kit Parker, the Tarr Family Professor of Bioengineering and Applied Physics at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) and a lieutenant colonel in the United States Army Reserve. “I also saw how heavy body armor could limit mobility. As soldiers on the battlefield, the three primary tasks are to move, shoot, and communicate. If you limit one of those, you decrease survivability and you endanger mission success.”

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

In order to achieve this practical goal, the researchers needed to explore the tradeoff between mechanical protection and thermal insulation, properties rooted in a material’s molecular structure and orientation.

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

Kevlar and Twaron are commercial products used extensively in protective equipment and can provide either ballistic or thermal protection, depending on how they are manufactured. Woven Kevlar, for example, has a highly aligned crystalline structure and is used in protective bulletproof 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 woven, ordered structure of fibers with the porosity of aerogels to make long, continuous fibers with porous spacing in between,” said Gonzalez. “In this system, the long fibers could resist a mechanical impact while the pores would limit heat diffusion.”

The research team used immersion Rotary Jet-Spinning (iRJS), a technique developed by Parker’s Disease Biophysics Group, to manufacture the fibers. In this technique, a liquid polymer solution is loaded into a reservoir and pushed out through a tiny opening by centrifugal force as the device spins. When the polymer solution shoots out of the reservoir, it first passes through an area of open air, where the polymers elongate and the chains align. Then the solution hits 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 spinner — the nanofibers follow the stream of the vortex and wrap around a rotating collector at the base of the device.

By tuning 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 disorder to protect against heat. In about 10 minutes, the team could spin sheets about 10 by 30 centimeters in size.

To test the sheets, the Harvard team turned to their collaborators to perform ballistic tests. Researchers at CCDC SC in Natick, Massachusetts simulated shrapnel impact by shooting large, BB-like projectiles at the sample. The team performed 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 protective equipment for warfighters, specifically,” said Gonzalez.

“Academic collaborations, especially those with distinguished local universities such as Harvard, provide CCDC SC the opportunity to leverage cutting-edge expertise and facilities to augment our own R&D capabilities,” said Kathleen Swana, a researcher at CCDC SC and one of the paper’s authors. “CCDC SC, in return, provides valuable scientific and soldier-centric expertise and testing capabilities to help drive the research forward.”

In testing for thermal protection, the researchers found that the nanofibers provided 20 times the heat insulation capability of commercial Twaron and Kevlar.

“While there are improvements that could be made, we have pushed the boundaries of what’s possible and started moving the field towards this kind of multifunctional material,” said Gonzalez.

“We’ve shown that you can develop highly protective textiles for people that work in harm’s way,” said Parker. “Our challenge now is to evolve the scientific advances to innovative products for my brothers and sisters in arms.”

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

Here’s a link to and a citation for the paper,

para-Aramid Fiber Sheets for Simultaneous Mechanical and Thermal Protection in Extreme Environments by Grant M. Gonzalez, Janet Ward, John Song, Kathleen Swana, Stephen A. Fossey, Jesse L. Palmer, Felita W. Zhang, Veronica M. Lucian, Luca Cera, John F. Zimmerman, F. John Burpo, Kevin Kit Parker. Matter DOI: https://doi.org/10.1016/j.matt.2020.06.001 Published:June 29, 2020

This paper is behind a paywall.

While this is the first time I’ve featured clothing/armour that’s protective against explosions I have on at least two occasions featured bulletproof clothing in a Canadian context. A November 4, 2013 posting had a story about a Toronto-based tailoring establishment, Garrison Bespoke, that was going to publicly test a bulletproof business suit. Should you be interested, it is possible to order the suit here. There’s also a February 11, 2020 posting announcing research into “Comfortable, bulletproof clothing for Canada’s Department of National Defence.”

Prima donna of nanomaterials (carbon nanotubes) tamed by scientists at Rice University (Texas, US), Teijin Armid (Dutch/Japanese company), and Technion Institute (based in Israel)

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The big news is that a multinational team has managed to spin carbon nanotubes (after 10 years of work) into threads that look like black cotton and display both the properties of metal wires and of carbon fibers. Here’s more from the Jan. 10, 2013 news item on ScienceDaily,

“We finally have a nanotube fiber with properties that don’t exist in any other material,” said lead researcher Matteo Pasquali, professor of chemical and biomolecular engineering and chemistry at Rice. “It looks like black cotton thread but behaves like both metal wires and strong carbon fibers.”

The research team includes academic, government and industrial scientists from Rice; Teijin Aramid’s headquarters in Arnhem, the Netherlands; the Technion-Israel Institute of Technology in Haifa, Israel; and the Air Force Research Laboratory (AFRL) in Dayton, Ohio.

The Jan. 10, 2013 Rice University news release on EurekAlert, which originated the news item, describes some of the problems presented when trying to produce carbon nanotube fiber at an industrial scale,

The phenomenal properties of carbon nanotubes have enthralled scientists from the moment of their discovery in 1991. The hollow tubes of pure carbon, which are nearly as wide as a strand of DNA, are about 100 times stronger than steel at one-sixth the weight. Nanotubes’ conductive properties — for both electricity and heat — rival the best metal conductors. They also can serve as light-activated semiconductors, drug-delivery devices and even sponges to soak up oil.

Unfortunately, carbon nanotubes are also the prima donna of nanomaterials [emphasis mine]; they are difficult to work with, despite their exquisite potential. For starters, finding the means to produce bulk quantities of nanotubes took almost a decade. Scientists also learned early on that there were several dozen types of nanotubes — each with unique material and electrical properties; and engineers have yet to find a way to produce just one type. Instead, all production methods yield a hodgepodge of types, often in hairball-like clumps.

Creating large-scale objects from these clumps of nanotubes has been a challenge. A threadlike fiber that is less than one-quarter the thickness of a human hair will contain tens of millions of nanotubes packed side by side. Ideally, these nanotubes will be perfectly aligned — like pencils in a box — and tightly packed. Some labs have explored means of growing such fibers whole, but the production rates for these “solid-state” fibers have proven quite slow compared with fiber-production methods that rely on a chemical process called “wet spinning.” In this process, clumps of raw nanotubes are dissolved in a liquid and squirted through tiny holes to form long strands.

Thank you to the writer of the Rice University news release for giving me the phrase “prima donna of nanomaterials.”

The news release goes on to describe the years of work and collaboration needed to arrive at this point,

Shortly after arriving at Rice in 2000, Pasquali began studying CNT wet-spinning methods with the late Richard Smalley, a nanotechnology pioneer and the namesake of Rice’s Smalley Institute for Nanoscale Science and Technology. In 2003, two years before his untimely death, Smalley worked with Pasquali and colleagues to create the first pure nanotube fibers. The work established an industrially relevant wet-spinning process for nanotubes that was analogous to the methods used to create high-performance aramid fibers — like Teijin’s Twaron — which are used in bulletproof vests and other products. But the process needed to be refined. The fibers weren’t very strong or conductive, due partly to gaps and misalignment of the millions of nanotubes inside them.

“Achieving very high packing and alignment of the carbon nanotubes in the fibers is critical,” said study co-author Yeshayahu Talmon, director of Technion’s Russell Berrie Nanotechnology Institute, who began collaborating with Pasquali about five years ago.

The next big breakthrough came in 2009, when Talmon, Pasquali and colleagues discovered the first true solvent for nanotubes — chlorosulfonic acid. For the first time, scientists had a way to create highly concentrated solutions of nanotubes, a development that led to improved alignment and packing.

“Until that time, no one thought that spinning out of chlorosulfonic acid was possible because it reacts with water,” Pasquali said. “A graduate student in my lab, Natnael Bahabtu, found simple ways to show that CNT fibers could be spun from chlorosulfonic acid solutions. That was critical for this new process.”

Pasquali said other labs had found that the strength and conductivity of spun fibers could also be improved if the starting material — the clumps of raw nanotubes — contained long nanotubes with few atomic defects. In 2010, Pasquali and Talmon began experimenting with nanotubes from different suppliers and working with AFRL scientists to measure the precise electrical and thermal properties of the improved fibers.

During the same period, Otto [Marcin Otto, Business Development Manager at Teijin Aramid] was evaluating methods that different research centers had proposed for making CNT fibers. He envisaged combining Pasquali’s discoveries, Teijin Aramid’s know-how and the use of long CNTs to further the development of high performance CNT fibers. In 2010, Teijin Aramid set up and funded a project with Rice, and the company’s fiber-spinning experts have collaborated with Rice scientists throughout the project.

“The Teijin scientific and technical help led to immediate improvements in strength and conductivity,” Pasquali said.

Study co-author Junichiro Kono, a Rice professor of electrical and computer engineering, said, “The research showed that the electrical conductivity of the fibers could be tuned and optimized with techniques that were applied after initial production. This led to the highest conductivity ever reported for a macroscopic CNT fiber.”

The fibers reported in Science have about 10 times the tensile strength and electrical and thermal conductivity of the best previously reported wet-spun CNT fibers, Pasquali said. The specific electrical conductivity of the new fibers is on par with copper, gold and aluminum wires, but the new material has advantages over metal wires.

Here’s an explanatory video the researchers have provided,

A more commercial perspective is covered in the Teijin Armid Jan. 11, 2013 news release (Note: A link has been removed),

“Our carbon nanotube fibers combine high thermal and electrical conductivity, like that seen in metals, with the flexibility, robust handling and strength of textile fibers”, explained Marcin Otto, Business Development Manager at Teijin Aramid. “With that novel combination of properties it is possible to use CNT fibers in many applications in the aerospace, automotive, medical and (smart) clothing industries.”

Teijin’s cooperation and involvement was crucial to the project. Twaron technology enabled improved performance, and an industrially scalable production method. That makes it possible to find applications for CNT fibers in a range of commercial or industrial products. “This research and ongoing tests offer us a glimpse into the potential future possibilities of this new fiber. For example, we have been very excited by the interest of innovative medical doctors and scientists exploring the possibilities to use CNT fiber in surgical operations and other applications in the medical field”, says Marcin Otto. Teijin Aramid expects to replace the copper in data cables and light power cables used in the aerospace and automotive industries, to make aircraft and high end cars lighter and more robust at the same time. Other applications could include integrating light weight electronic components, such as antennas, into composites, or replacing cooling systems in electronics where the high thermal conductivity of carbon nanotube fiber can help to dissipate heat.

Teijin Aramid is currently trialing samples of CNT fiber on a small scale with the most active prospective customers. Building up a robust supply chain is high on the project team’s list of priorities. As well as their carbon fiber, aramid fiber and polyethylene tape, this new carbon nanotube fiber is expected to allow Teijin to offer customers an even broader portfolio of high performance materials.

Teijin Group (which is headquartered in Japan) has been mentioned here before notably in a July 19, 2010 posting about a textile inspired by a butterfly’s wing (Morphotex) which, sadly, is no longer being produced as noted in a more recent April 12, 2012 posting about Teijin’s then new fiber ‘Nanofront™’ for use in sports socks.