Rice University Researchers Tying Carbon Fibre in Knots
Large flakes of graphene oxide are the essential ingredient in a new recipe for robust carbon fibre created at Rice University.
The fibre spun at Rice is unique for the strength of its knots. Most fibres are most 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 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, according to the researchers.
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, a quarter the width of an average human hair. But they’re massive compared with the petroleum-based pitch used in current carbon fibre.
Like with pitch, the weak van der Waals force holds the graphene flakes together. 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. The wet-spinning process is similar to one recently used to create highly conductive fibres made of nanotubes, but in this case Xiang just used water as the solvent rather than a super acid.
Bend ability at the knot is due to the fibres bending modulus, which is a measure of its flexibility, Xiang said. “Because graphene oxide has very low bending modulus, it thinks there’s no knot there,” he said.
Tour said industrial carbon fibres — a source of steel-like strength in ultralight materials ranging from baseball bats to bicycles to bombers — haven’t improved much in decades because the chemistry involved is approaching its limits. But 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.
Heating the fibres to about 2,100 degrees Celsius, the industry standard for making carbon fibre, will likely eliminate the knotting strength, Xiang said, 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.