Defense Tech Briefs - Continuous Carbon Nanofibers for Structural Composites

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Continuous Carbon Nanofibers for Structural Composites

Air Force Research Laboratory, Wright-Patterson Air Force Base, Ohio

Dec 01 2007

Page 1 of 2

Continuous carbon nanofibers offer advantages over carbon nanotubes.

A program of research has addressed key issues in the production of continuous carbon nanofibers and the utilization of carbon nanofibers as the reinforcing components in matrix/fiber composite materials. The goal of this research is to contribute to the development of advanced lightweight structural composites in which the exceptionally high strengths of carbon nanofibers are exploited to obtain mechanical strengths, delamination toughnesses, and fatigue lives greater than would otherwise be possible.

These Stress-vs.-Strain Plots from an edge-delamination tension test show that a specimen reinforced with continuous carbon nanofibers failed at higher stress and strain than did an otherwise equivalent specimen that was not so reinforced.

Continuous carbon nanofibers are related to, but not the same as, carbon nanotubes, which can also be considered superstrong nanofibers in their own right but are discontinuous (in other words, too short) and cannot be produced and aligned easily or economically in the quantity and quality needed for use as reinforcements in advanced structural composites. In this program, continuous carbon nanofibers were made in a process that began with electrospinning of nanofibers from commercial polyacrlyonitrile (PAN) precursors. The as-spun PAN nanofibers were stabilized by crosslinking of their molecules, then carbonized by heating to various high temperatures. Nanofibers at the as- spun, stabilized, and carbonized stages of manufacture were studied by scanning electron microscopy and x-ray diffraction. It was found that the nanofibers were uniform in diameter and that unlike in the production of carbon nanotubes, extensive purification was not necessary. Higher carbonization temperatures were found to result in better nanostructure.

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