Kevlar-ceramic aerogel nanocomposite material improves thermal protection textiles for harsh environments
(Nanowerk Spotlight) Wearable thermal insulation materials for harsh environments always require a compromise during their design and manufacturing. On one hand they need to be mechanically tough to provide impact resistance. On the other hand they need to be heat resistant. In many cases this requires the use of several materials, which prevents the fabrication of robust thermal protection textiles that are still lightweight and easily wearable.
Point in case are aramid fibers, which have been widely used as a functional and structural material in protective applications – widely known as protective fibers under the Kevlar® trade name. Aramid fibers have excellent mechanical properties and are widely used as a functional and structural material in protective applications for instance for the protective clothing of firefighters and first responders. However, their thermal performance limits their applications.
However, due to their relatively high thermal conductivity and temperature-sensitive polymeric nature, aramid fibers cannot provide sufficient thermal protection across a wide range of temperatures from cryogenic to high-temperature while maintain their robust mechanical performance.
Ceramic aerogels, in contrast, have superinsulation properties due to their mesoporous structure with high specific surface and low density. However, these extremely lightweight materials suffer from mechanical brittleness and weak mechanical performance.
Combining the best of both worlds, researchers at the University at Buffalo have developed a wearable aramid/ceramic aerogel nanocomposite material with excellent mechanical and thermal properties.
A sample of the novel aramid-aerogel nanocomposite rests on a flower bud, demonstrating the lightweight nature of the material. (Reprinted with permission by Wiley-VCH Verlag)
These properties makes this novel nanocomposite a promising candidate for the low-cost manufacturing of wearable textile for applications in harsh environments, including aerospace and aviation, electronics, and personal protective clothing.
Reporting their findings in Advanced Engineering Materials ("Wearable Aramid-Ceramic Aerogel Composite for Harsh Environment"), a team led by Dr. Lu An and Prof. Shenqiang Ren, at the University at Buffalo, demonstrates a ceramic aerogel nanocomposite with low density (0.08 g cm-3), low thermal conductivity (0.034 W m-1 K-1), and high compressive mechanical strength of 1.1 MPa.
Scheme of the manufacturing process of aramid-aerogel textile with in situ cross-linking reaction of pre-aerogel precursor (HCl, CTAB micelles, urea and sodium silicate) and aramid fibers. (Reprinted with permission by Wiley-VCH Verlag) (click on image to enlarge)
"With our facile and scalable manufacturing strategy we prepared a nanocomposite through the in situ crosslinking reaction between nanoporous silica aerogel and Kevlar fibers, where the synthesized nanocomposite fibers forming 3D networks interfaced with a hollow mesoporous silica aerogel matrix.," An explains the fabrication process to Nanowerk. "The aerogel-fiber structure with interconnected porous networks and a high still air layer content provides the Kevlar fiber aerogel composite with extraordinary thermal insulation even under extreme environments ranging from-196 °C to 400 °C.
The key to this fabrication method is the in situ crosslinking that takes place between the silica pre-ceramic aerogel precursor and the Kevlar fibers. The precursor is converted to nanoporous SiO2 aerogel and deposited onto aramid fibers during an ambient pressure drying reaction.
The aramid fibers construct the percolation networks while silica aerogel would crosslink and deposit onto the fiber networks. The interfacial bonding between aramid fiber and aerogel after gelation further prevents the fibrous networks from collapsing.
A demonstration of the hydrogen flame resistance of the aramid-aerogel textile. (Image: Ren Research Group, University at Buffalo)
The researchers point out that their fabrication method is also very suitable for 3D-printing applications.
Having successfully demonstrated the excellent performance of their nanocomposite insulation material, the team is now investigating specific applications that include thermal insulation wearable system, impact resistant armor applications, and structural components in thermal sensitive applications.