December 03, 2010

Carbon nanotube polymer stronger than Kevlar

Researchers at Northwestern University have nanoengineered a new kind of fiber that could be tougher than Kevlar.

The group have created a high performance fiber from carbon nanotubes and a polymer that is remarkably tough, strong, and resistant to failure. Using state-of-the-art in-situ electron microscopy testing methods, the group was able to test and examine the fibers at many different scales — from the nano scale up to the macro scale — which helped them understand just exactly how tiny interactions affect the material’s performance. Their results were recently published in the journal ACS Nano.

“We want to create new-generation fibers that exhibit both superior strength and toughness,” said Espinosa said. “A big issue in engineering fibers is that they are either strong or ductile — we want a fiber that is both. The fibers we fabricated show very high ductility and a very high toughness. They can absorb and dissipate large amounts of energy before failure. We also observed that the strength of the material stays very, very high, which has not been shown before. These fibers can be used for a wide variety of defense and aerospace applications.”

Previous work by Espinosa in 2008 was to use irradiation to strengthen carbon nanotubes and to precisely measure the strength of fibers



To create the new fiber, researchers began with carbon nanotubes —cylindrical-shaped carbon molecules, which individually have one of the highest strengths of any material in nature. When you bundle nanotubes together, however, they lose their strength — the tubes start to laterally slip between each other.

Working with the MER Corporation and using the corporation’s CVD reactor, the team added a polymer to the nanotubes to bind them together, and then spun the resulting material into yarns. Then they tested the strength and failure rates of the material using in-situ SEM testing, which uses a powerful microscope to observe the deformation of materials under a scanning electron beam. This technology, which has only been available in the past few years, allows researchers to have extremely high resolution images of materials as they deform and fail and allows researchers to study materials on several different scales. They can examine individual bundles of nanotubes and the fiber as a whole.

“We learned on multiple scales how this material functions,” said Tobin Filleter, a postdoctoral researcher in Espinosa’s group. “We’re going to need to understand how molecules function at these nanometer scales to engineer stronger and tougher fibers in the future.”

“Carbon nanotubes, the nanoscale building blocks of the developed yarns, are still 50 times stronger than the material we created,” said Mohammad Naraghi, a postdoctoral researcher in Espinosa’s group. “If we can better engineer the interactions between bundles, we can make the material stronger.”

The group is currently looking at techniques — like covalently crosslinking tubes within bundles using high-energy electron radiation – to help better engineer those interactions.

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