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A New High-Strength Nanofiber Material: Bulletproof and Insulating, May Be the Next Generation of Spacesuit Material

Innovation of Kevlar — Nanoscale Kevlar

The materials used in spacesuits have been the focus of research by scientists at home and abroad, and the design of protective equipment in extreme environments needs to take into account a variety of potential external threats. Kevlar and Nomex, for example, were used in Apollo-era spacesuits to deal with space debris and solar radiation. Among them, the strong mechanical toughness of Kelvar results from its rigid para-aromatic polyamide skeleton, which is spontaneously arranged and crystallized by ordered liquid crystal solution under the stress of fiber spinning. Nomex's thermal insulation is derived from the interposition direction polyamide skeleton. The kinked polymer backbone inhibits the accumulation of polymer, so that heat is transferred slowly over the disordered polymer chain. It is well known that multilayer structures are often used in the design of multifunctional materials, but in practice, it is difficult to construct bulletproof and flame-retardant materials through multilayer structures due to the competition between adiabatic and mechanical energy dissipation processes. However, nanoscale Kevlar can change the structure-function relationship of the aramid material and disperse ordered microcrystals in a randomly arranged ordered film to construct multifunctional materials.
Kevin Kit Parker research group of Harvard University developed a new bullet-proof thermal insulation material. Its design concept is to combine porous network structure and directional fiber to obtain both thermal insulation and bulletproof performance, overcoming the limitation that traditional protective material design cannot meet various requirements. This design can be applied to military, aerospace and other fields, and has important application value. The work is published in Matter as "Para-Aramid Fiber Sheets for Simultaneous Mechanical and Thermal Protection in Extreme Environments."

Manufacturing Technique

A contrapuntal arylon fiber board was synthesized by immersive rotary air jet spinning platform (iRJS). It arranges the counterpoint aramid fibers along the direction of mechanical load of aerogel. Directional contrapuntal aramide fibers can effectively cope with mechanical stress, while porous network structures can achieve lower limit heat diffusion without damaging structural functions. The fragmentation tests show that the bulletproof performance of the textile pAFS is comparable to that of commercial bulletproof textiles. In addition, pAFS has a very low thermal conductivity and provides a 20-fold improvement in thermal insulation compared to commercially available contralateral aromatic polyamides.
Immersive rotary air jet spinning platform (iRJS) relies on the centrifugal force of spinning spinnerets rotating at high speed (> 1,000 rpm) to synthesize nanofibers. The solution of poly (p-benzoyl p-phenyldicarbonamide – sulfuric acid (PPTA-H2SO4c was continuously flowing into the spinnast. Polymer jet in hit the rotating collects solid fiber board, plating solution along the vortex line pull the fiber to the collector and interconnected to form a network, after freeze drying for a quick continuous contrapuntal aramid fiber sheets, by adjusting the PPTA – – H2SO4 concentration, viscosity, shear rate, temperature and other parameters, in order to regulate the viscoelasticity of PPTA – – H2SO4 in order to obtain the best performance of fiber.

Functional Test

In order to study the bulletproof properties of materials, the scientists, in collaboration with the Soldier Center of the U.S. Army's Combat Capability Development Command, used simulated bullets to evaluate the bulletproof properties by observing whether bullets penetrated the material. Subsequently, the experimenters overlapping the fiber nanosheets into 0°, 90°, placed between multiple layers of fabric, visual inspection can find its good bulletproof effect. Then they tested that increasing the number of layers of pAFS can effectively improve its bulletproof performance. It is found that the two-layer bulletproof capability V50 is 525ft S, the five-layer bulletproof V50 is 657 ft S. To determine the adiabatic coefficient of the material, the team conducted another experiment. In order to simulate the thermal insulation capability in extreme environments, the experimenters exposed the astronaut simulation dummy without coating protection, Twaron protection and pAFS protection to a 350 °C heat source to compare their thermal insulation properties. The astronaut man melted in five minutes without any protection. The doll protected by Twaron melted within 17 minutes. Under the protection of pAFS material, it did not melt after 30 minutes under high temperature, which further verified its thermal insulation capability.
These two features of the nanoscale Kevlar make it a natural fit for a space suit.In the future, and it will play an important role in many fields, including aviation.

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