“That creates some very unique features,” says Ferland. “We have a true, solid nanowire. It’s straight, not curved or crooked or difficult to untangle like carbon nanotubes, and it’s not spherical like nanosilica. So, it has a very high aspect ratio and a very high surface area. Being aluminum oxide, it has very high strength intrinsically; it’s one of the hardest substances next to diamonds.” Dispersing the aluminum oxide nanofibers into resin systems improves the systems’ mechanical properties.
Ferland says that composites produced using Nafen have demonstrated increases in interlaminar shear strength, flexural toughness and impact toughness. “A lot of companies are putting macro fibers into their resins trying to use them as a reinforcement. What that does is create more filler in the resin system but the resin itself still isn’t improved … .With nanomaterials you’re actually changing the chemical structure of the resin and making the resin tougher. So, if you hit something and it starts to crack, the crack propagation is stopped much faster because on a molecular scale this energy is being absorbed by this crisscross mesh. It’s like a 3-D mesh of nanofibers mixed through the system.”
The Alchemie Group uses Nafen nanofibers in epoxy resins that are combined with its AuTx™ yarns/textiles to produce armor composites. According to CEO Haslen Back, the company was able to reduce the weight of a vest fragmentation pack of an improved outer tactical vest for the U.S. Department of Defense by 27 percent using AuTx textiles. The company is now working on reducing military helmet weight with AuTx composites.
Purdue University testing “confirmed that AuTx has twice the toughness (dynamic strength) of para-aramid fibers like Kevlar KM2+ and Twaron 50f1000,” says Back. Armor composite samples with Nafen particles showed a 20 to 40 percent improvement in performance over para-aramid armor composites using velocity-50 percent (V50) ballistics testing. (In V50 test, bullets are fired at higher and higher velocities until they start penetrating. The V50 rating comes from the point at which 50 percent of the bullets penetrate and 50 percent do not.)
Back admits that AuTx is more expensive than a HMWPE like Dyneema and that HMWPE laminates are better at stopping some types of bullets at certain temperatures. But AuTx performs well under a wider range of operating temperatures (-40 to 248 F) and has a very high modulus while retaining toughness. It’s also possible to vary the resin content of its epoxy system, so the front of an armor ceramic-faced composite can receive more resin reinforcement than the back. That variation in resin is not possible with HMWPEs, according to Back.