June 16, 2003
Volume 81, Number 24
CENEAR 81 24 p. 9
ISSN 0009-2347


Spinning method turns out fibers with unparalleled properties


With a little chemistry know-how, Spiderman made silk strong enough to use for swinging from building to building and tying up bad guys. But the comic book wall crawler might have been an even better match for New York's criminals had he been armed with the supertough carbon fibers prepared recently at the University of Texas, Dallas (UTD).

IN THE WEAVE Supertough carbon nanotube fibers (black) with micrometer-scale diameters can now be woven into textiles such as the few square centimeters pictured.
Researchers there have developed a procedure for spinning composite carbon nanotube fibers that are tougher than spider silk and any other natural or synthetic organic fiber reported so far [Nature,
423, 703 (2003)]. The new fibers are being used to make supercapacitors and to weave textiles.

To prepare the fibers, chemistry professor Ray H. Baughman, Alan B. Dalton, and their coworkers at UTD and at Trinity College Dublin use single-walled nanotubes synthesized from CO and a surfactant (lithium dodecyl sulfate) in a coagulation-based spinning process. The process produces nanotube-polyvinyl alcohol gel fibers that the group converts to 100-meter-long nanotube composite fibers roughly 50 µm in diameter.

On the basis of strength tests, the Texas researchers report that their nanotube product can be drawn into fibers that exhibit twice the stiffness and strength and 20 times the toughness (ability to absorb mechanical energy without breaking) of steel wire of the same weight and length. The fiber toughness is more than four times that of spider silk and 17 times greater than Kevlar fibers used in bullet-proof vests. Baughman notes that, since submitting the manuscript to Nature, the group has doubled the strength of the fibers and further increased its toughness.

Spider silk's toughness (see page 27) is attributed to relatively flexible and stretchy amorphous regions located between rigid crystalline protein blocks. By analogy, the Texas team proposes that their material's toughness may be rooted in patches of amorphous polyvinyl alcohol situated between single-walled carbon nanotubes.

Baughman and coworkers propose a number of applications for the tough fibrous materials, including safety harnesses and explosion-proof blankets for aircraft cargo areas. In addition, the combination of electronic and mechanical properties may be used to make textiles that serve as sensors, electronic interconnects, and electromagnetic shielding.

At present, Baughman's group is running the spinning process on the laboratory scale, producing hundreds of meters of fiber per run. But the process is amenable to scaling up, the team stresses. An important limitation, however, is the lack of methods for preparing single-walled carbon nanotubes inexpensively.


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