Changing processing has made far stronger carbon nanotube based reinforced polymer fiber

Mar­ilyn Minus, an assis­tant pro­fessor of engi­neering at North­eastern, has devel­oped a type of carbon nanotube based polymer fiber that is stronger than the first kevlar, spectra and—even in its first generation—closely approaches the strength of the fourth (Zylon). It’s the crys­tal­liza­tion process that drives the remark­able prop­er­ties recently reported. In their research, Minus and her col­leagues showed that they could easily turn these prop­er­ties on or off. By changing nothing but the pat­tern of heating and cooling the mate­rial, they were able to increase the strength and tough­ness of fibers made with the very same ingre­di­ents. In the cur­rent research, Minus and her col­leagues worked out the recipe and process for one par­tic­ular polymer: polyvinyl alcohol. “But we can do this with other poly­mers and we are doing it,” she said.

From carbon black powder to metallic par­ti­cles, a variety of mate­rials can guide the for­ma­tion of spe­cific crystal types in a process called nucle­ation. But before carbon nan­otubes, Minus said, “we’ve never had a nucle­ating mate­rial so sim­ilar to poly­mers.” This sim­i­larity allows the nan­otubes to act likes skates along which the long polymer chains can slide, per­fectly aligning them­selves with one another.

Macromolecular Materials and Engineering – Forming Crystalline Polymer-Nano Interphase Structures for High-Modulus and High-Tensile/Strength Composite Fibers

Minus will now work out (with DARPA funding) the method for a polymer called poly­acry­loni­trle, or PAN. This is the dom­i­nant mate­rial used to form carbon fibers, which are of par­tic­ular interest in light­weight com­posite mate­rials such as those used in the Boeing 787 air­liner. With the more orga­nized struc­ture afforded by Minus’ method, this mate­rial could see a vast increase in its already great performance.

ABSTRACT – PVA/single-walled nanotube (SWNT) composite fibers are fabricated using a steady shear-flow gel-spinning method. The resultant fibers show excellent tensile strength, modulus, and toughness of 4.9 GPa, 128 GPa, and 202 J · g−1, respectively. Templated interfacial crystallization of PVA in the vicinity of SWNT is controlled by tailoring the degree of undercooling of PVA during the composite solution preparation. WAXD shows that the templated crystallization behavior of the PVA at the SWNT interfacial region is new. PVA/SWNT fibers that exhibit interfacial structure show a predominant crystallization plane of (001) as compared to the (101) plane seen in PVA/SWNT fibers without a distinct interfacial structure. This demonstrates that the PVA interfacial region around SWNT has denser crystalline chain-packing.

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