Boeing Shows Continuous, Carbon-Nanotube-Reinforced Polymer Precursors and Carbon Fibers

The Boeing Company filed U.S. Patent Application 20100120969 which provides a continuous, carbon fiber with nanoscale features comprising carbon and carbon nanotubes, wherein the nanotubes are substantially aligned along a longitudinal axis of the fiber.  Such carbon fibers may have excellent mechanical properties suitable for manufacture of composite materials using traditional manufacturing processes such as laminating, weaving, etc. 

The Boeing method is intended to meet a need for a cost-effective method of producing a large-volume of continuous carbon-nanotube reinforced carbon fibers with nanoscale features such that their use in composites-based, primary load-bearing structures such as for aircraft is practical. It also meets a need for both melt-spinnable and solution-spinnable methods for producing continuous, carbon-nanotube-reinforced carbon fibers with nanoscale features. 

Also provided is a polyacrylonitrile (PAN) precursor including about 50% to about 99.9% by weight of a melt-spinnable PAN and about 0.01% to about 10% of carbon nanotubes. Other precursor materials such as polyphenylene sulfide, pitch and solution-spinnable PAN are also provided. The precursor can also include a fugitive polymer which is dissociable from the precursor polymer, according to inventor Thomas Karl Tsotsis.

It is well known that, as a general rule, as the diameter of carbon fibers is decreased, strength generally increases. The reasons for this are usually ascribed to improved molecular orientation (e.g., increased graphitic structure) and to a reduction in the number of flaws due to the improved quality of the cross-sectional filament structure.

 At the extreme of the continuum lie carbon nanotubes, which ideally are fully graphitic without flaws in the structure of the walls. However, the realization of the potential of the mechanical benefits of these materials is hindered by the requirement of having to transfer load along the fiber length between fibers via mechanical entanglements caused by frictional and van der Waal's interactions between the carbon nanotubes themselves and between adjacent fibers through shear coupling such as from a matrix resin. 

The carbon-nanotube-reinforced carbon fibers with nanoscale features can comprise either solid or hollow fibers. In another embodiment, a carbon fiber can include numerous internal hollow fibers bundled within a resultant filament. Such embodiments can include a honeycomb-like cross section. As such, these embodiments can comprise an overall resultant filament with nanoscale wall thicknesses between adjacent hollow-cylinder-like portions of the honeycomb cross section.

In another aspect, the invention provides a polyacrylonitrile (PAN) precursor. According to embodiments, the PAN precursor can comprise about 50% to about 99.9% by weight of a melt-spinnable PAN and about 0.01% to about 10% of carbon nanotubes. In certain embodiments, the PAN precursor includes a fugitive polymer which is dissociable from the melt-spinnable PAN. 

FIG. 1 illustrates a cross sectional view of an "islands-in-a-sea" PAN precursor having multiple islands comprising a PAN and a sea comprising a fugitive polymer;

FIG. 2 illustrates a cross-sectional view of a carbon nanofiber according to one embodiment of the present invention, wherein the fiber has a honeycomb-like cross section where the islands have been removed from an islands-in-a-sea filament to leave a continuous honeycomb-like cross section;

FIG. 3 illustrates a cross-sectional view of a carbon nanofiber according to another embodiment of the present invention, wherein the fiber has a honeycomb-like cross section where the islands have been removed from an islands-in-a-sea filament to leave a continuous honeycomb-like cross section.