Kevlar and Twaron are famously tough materials, but there’s a bit of a trade-off to be made between strength, heat resistance and weight. Now, researchers have created a new nanofiber version of the material that’s just as strong, but much more insulating against heat.
Kevlar and Twaron get their protective properties from their molecular structure, and changing this changes what they’re effective against. For mechanical blows, such as in bullet-proof vests, the material takes on a highly-ordered structure, which allows it to redistribute the force. Insulating materials have a much more porous structure, which minimizes the amount of heat that can pass through.
Normally it’s one or the other, so if a wearer wants both thermal and ballistic protection, they’d have to put on multiple layers, which gets bulky. And bulk is not what you need in the kinds of situations where you require this much protection. So, the researchers on the new study set out to combine both types into one.
“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,” says Grant Gonzalez, first author of the study.
To do so, the researchers needed to combine the two types of molecular structures – highly-ordered yet porous – into one material. It was made using a process called immersion Rotary Jet-Spinning (iRJS). Basically, a device spins and forces a liquid polymer solution out through a tiny hole, forming long polymer strands. It hits a liquid bath pinned against the wall of the centrifuge and solidifies. The solid threads then collect around the base.
The researchers are able to tweak the viscosity of the starting polymer liquid to give the final threads the desired properties. In the end, they were able to produce sheets of long, aligned nanofibers with plenty of pores between them.
Next, they had to test that the nanofiber sheets really were protective against both ballistics and heat. In tests firing BB-like pellets at stacks of the sheets, the team found that the new material held up about as well as regular woven Twaron.
In thermal tests, the new material was found to be about 20 times better at insulating against heat than commercial Twaron and Kevlar. All together, the material would save people from having to layer up.
Using the current setup, the team could spin sheets measuring about 10 by 30 cm (3.9 by 11.8 in) in around 10 minutes, but this could probably be improved if scaled up for production.
“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,” says Gonzalez.
The research was published in the journal Matter.
Source: Harvard