How do you make super light, super strong carbon fibers even lighter and stronger?
To lighten planes’ loads, aerospace engineers have turned to carbon-fiber composites, which match aluminum and titanium in strength, but at a fraction of the weight. These fibers can be 10 times thinner than human hair, and they’ve reduced the weight of Boeing and Airbus aircrafts by 20 percent.
Advanced composites made of carbon fibers coated with carbon nanotubes -- tiny tubes of crystalline carbon -- are even stronger and lighter.
When arranged in certain configurations, nanotubes can be hundreds of times stronger than steel, but only one-sixth the weight, making such composites attractive for use in airplanes, as well as cars, trains, spacecraft and satellites.
But growing nanotubes on fibers degrades the underlying fibers, stripping them of their strength.
Carbon fibers get stretched to near their breaking point as they’re heated to high temperatures at carbon-fiber production plants. The majority of fiber degradation in nanotube-growing labs, they discovered, came from a lack of tension when fibers are heated above a certain temperature.
So, they came up with two strategies: place coated fibers under tension and grow nanotubes at lower temps.
They covered the fiber with transparent "alumina" ceramic so the metal catalyst (necessary for nanotubes growth) would stick without damaging the fiber. Before growing a fuzzy layer of carbon nanotubes along each fiber (pictured), they covered the fiber with a polymer coating they developed called K-PSMA:
Hair conditioners have two seemingly opposite chemical features: a water-absorbent component that allows the conditioner to stick to hair, and a waterproof component that keeps hair from getting frizzy. Likewise, K-PSMA has hydrophilic and hydrophobic components, but its waterproof feature sticks to the carbon fiber, while the water-absorbent component attracts the alumina and the metal catalyst.
They’ve filed a patent for the two strategies, which could be integrated into current fiber-manufacturing processes.
The work was published in ACS Applied Materials and Interfaces.
[Via MIT News Office]
Image: Stephen Steiner