Ultrafine polyethylene fibers promise to exceed materials like Kevlar in strength and toughness. A new process, gel electrospinning, produces fibers that are a nanometer – a billionth of a meter – in diameter. Products made from these fibers, such as armor and nanocomposites, should be less expensive to manufacture than current top-of-the-line aramid fibers and gel-spun polyethylenes.
MIT professor of chemical engineering Gregory Rutledge and postdoctoral student Jay Park developed the new spinning method. Prior to their work, no fibers in the nanometer size range exhibited both the high strength and high toughness currently available in fibers used to manufacture body armor and similar products. The research evolved from Rutledge’s ongoing interest in nanoscale fibers, not a quest to create a replacement.
The process Rutledge and Park describe in their February 2018 paper for the Journal of Materials Science builds on the existing gel-spinning process by using electrical forces to spin the raw material, in this case a polymer gel. The raw materials are the same as those used in gel spinning. Despite the longer name, the new process takes one step and not multiple steps used in the older process.
The researchers’ initial goal was simply to achieve the same properties that existing super-strong and super-tough materials exhibit. When the new fibers exceeded both strength and toughness numbers for existing fibers, Rutledge and Park were surprised. Rutledge reported that “the strengths are about a factor of two better than the commercial materials and comparable to the best available academic materials. And their toughness is about an order of magnitude better.”
The nanoscale fibers offer potential advantages over their competition -- in addition to cost factors mentioned above, they are also lighter due to their lower density. The weight difference would be an important advantage in protective armor, whether the armor protects a soldier or a tank.
Why does gel electrospinning produce such strong fibers? Stay tuned -- Rutledge and Park have not yet unlocked this secret. The researchers are still investigating what accounts for this impressive performance.
“It seems to be something that we received as a gift, with the reduction in fiber size, that we were not expecting,” Rutledge said.