A team of researchers at Massachusetts Institute of Technology (MIT) has published a paper detailing a new method for producing super strong fibers that measure just a few hundred nanometers in diameter.
The research findings could benefit nanocomposite material manufacturing, which can be used in applications such as armoured vests and also lightweight structures.
The new process, which is referred to as gel electrospinning, is the brainchild of Gregory Rutledge, MIT professor of chemical engineering, and postdoctoral researcher Jay Park, who are both authors of the paper.
The new process is similar to the more traditional gel spinning process used to make high performance fibers, except that with electrospinning, an electrical force is used to draw out the polymer gel feedstock, rather than the mechanical forces used in traditional gel spinning. With gel electrospinning, the charged fibers induce a “whipping” instability process that produces their ultrafine dimensions. And those narrow dimensions, it turns out, lead to the unique properties of the fibers.
These unique properties are produced as a result of the trade-offs that are eliminated when this new method is used. In material science, compromises are made when aiming for optimal parameters. When material scientists try to enhance one material characteristic, they tend to see the reduction of another characteristic. It seems that with gel electrospinning, scientists have found a method that allows them to have their cake and eat it too, at least in terms of mechanical parameters.
“Strength and toughness are a pair like that. Usually when you get high strength, you lose something in the toughness,” explained Rutledge. “The material becomes more brittle and therefore doesn’t have the mechanism for absorbing energy, and it tends to break. It’s a big deal when you get a material that has very high strength and high toughness.
“There hasn’t been a whole lot new happening in that field in many years, because they have very top-performing fibers in that mechanical space,” continued Rutledge. “What really sets those apart is what we call specific modulus and specific strength, which means that on a per-weight basis, they outperform just about everything.”
Compared to carbon fibers and ceramic fibers, which are widely used in composite materials, the new gel-electrospun polyethylene fibers have comparable degrees of strength but are much tougher and have lower density. This means that, pound for pound, they outperform standard materials by a wide margin.
In other words, the materials are lightweight and strong, which is perfect for applications such as those used in aerospace as well as protective body armor. The high strength-to-weight ratio means that stronger, less bulky armor can be developed to protect military and law enforcement personnel.
It’s no surprise, then, that the research was supported by the U.S. Army through the Natick Soldier Research, Development and Engineering Center, and the Institute for Soldier Nanotechnologies, and by the National Science Foundation’s Center for Materials Science and Engineering. The military always gets the best toys!
The paper will be published in the February edition of the Journal of Materials Science.
You can also see details of the patented process at this link.