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Graphene oxide flakes strengthen carbon fibre knots

09 July 2013

Large flakes of graphene oxide are the essential ingredient in a new recipe for a robust type of carbon fibre created at Rice University in the US.

The fibre spun at Rice is notable for the strength of its knots. Most fibres are likely to snap under tension at the knot, but Rice's fibre demonstrates what the researchers refer to as "100 percent knot efficiency," where the fibre is as likely to break anywhere along its length as at the knot.

The researchers believe the material could be used to increase the strength of many products that use carbon fibre, like composites for strong, light aircraft or fabrics for bulletproof apparel.

Credit goes to the unique properties of graphene oxide flakes created in an environmentally friendly process patented by Rice a few years ago. The flakes that are chemically extracted from graphite seem small. They have an average diameter of 22 microns but they're massive compared with the petroleum-based pitch used in current carbon fibre, which is two nanometres in size.

As with the pitch, the weak van der Waals force holds the graphene flakes together. But unlike pitch, the atom-thick flakes have an enormous surface area and cling to each other (like the scales on a fish) when pulled into a fibre. Bendability at the knot is due to the fibre's bending modulus. As graphene oxide has very low bending modulus, it is as if there is no knot present.

The new carbon fibres spun at room temperature at Rice already show impressive tensile strength and modulus and have the potential to be even stronger when annealed at higher temperatures.

The researchers believe that heating the fibres to about 2,100 deg C - the industry standard for making carbon fibre - will likely eliminate the knotting strength, but should greatly improve the material's tensile strength, which will be good for making novel composite materials.

The Rice researchers also created a second type of fibre using smaller 9-micron flakes of graphene oxide. The small-flake fibres, unlike the large, were pulled from the wet-spinning process under tension, which brought the flakes into even better alignment and resulted in fibres with strength approaching that of commercial products, even at room temperature.

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