Carbon particle fiber assembly technique

<u style="single">Technical Field</u>

This invention relates to carbon particles such as carbon nanotube molecules and carbon fibrils, and more particularly, to the art of assembling carbon particles into fibers in which the carbon particles are aligned.

<u style="single">Background of the Invention</u>

Carbon particles, such as carbon nanotube molecules and carbon fibrils, have an array of properties, including electrical, mechanical, and heat conducting properties, that are highly desirable. However, the particles are relatively short, e.g., the longest ones are on the order of a few microns. Unfortunately, such lengths are generally unsuitable for applications in which the properties of the carbon particles can prove beneficial.

In concurrently filed application, United States Patent Application Serial No. 10/789,074 published as United States Patent Publication No. 2005/0188727, it is disclosed that carbon particles, such as, carbon fibrils and carbon nanotube molecules, may be assembled into aligned fibers using processes derived from the processes used to manufacture optical fiber. More particularly, the carbon particles are embedded in glass, which is then drawn to align them. By aligned it is meant that the axis along the longest dimension of each of the various particles in a local vicinity are substantially parallel.

A resulting fiber typically retains a certain amount of glass content. Such glass content may enhance the strength of the fiber. Nevertheless, it may be desirable to eliminate or substantially reduce the fiber's glass content, e.g., to achieve greater elasticity. This is often referred to in the literature as "strength" versus "toughness". Furthermore, the length of fiber that may be produced is limited by the size of the initial body from which the fiber is drawn. Additionally, it would be desirable to be able to form fibers at room temperatures using as simple a process as possible.

WO 01/12700 A1, corresponding to United States Patent No. 6,299,812, discloses a method for forming fibers/composite material having an anisotropic structure, comprising the steps of mixing an effective amount of fibers with a matrix material to form a deformable mixture containing less than about 96 weight percent of the fibers to about parts per billion of the fibers and wherein the fibers are randomly oriented in the deformable mixture. The deformable mixture can be extruded, stretched or otherwise deformed to form an extrudate. Pressure is applied about the extrudate to substantially compress the fibers in the extrudate to provide the fibers/composite material having an anisotropic structure.

<u style="single">Summary of the Invention</u>

We have recognized that, in accordance with the principles of the invention, that carbon particles, such as, carbon fibrils and carbon nanotube molecules, may be assembled into substantially pure aligned fibres by a) dispersing the carbon particles within a curable liquid, b) aligning the carbon particles by flowing the mixture of curable liquid and carbon particles down a tapering tube, and c) curing the flowing mixture of curable liquid and carbon particles in the general vicinity of the end of the tapering tube to form a fiber. In one embodiment of the invention, the curable liquid is cured, at least in part, through the use of ultraviolet light.

Depending upon the desired final properties of the fiber, various optional steps may be employed, either individually or in combination, to further process the solidified mixture. Such optional steps include d) heating the fiber so as to cause the volatile elements of the solidified curable liquid portion to substantially dissipate from the fiber, e) twisting the fiber to increase its density, f) heating the fiber to sinter the carbon particles within the fiber, and g) cladding the fiber. The order for performing any of the optional steps is dependent upon the desired properties for the fiber being made. The resulting fiber may then be spooled onto a take-up drum.

In one embodiment of the invention, the curing step may be performed, at least in part, while the mixture of carbon particles and curable liquid is still within the tapering tube. For example, if the curable liquid is cured in the presence of ultraviolet light, the tapering tube may have at least a section that passes a sufficient amount of ultraviolet light so as to cure the mixture the desired amount. In another embodiment of the invention, the curing step is performed only after the carbon particles within the curable liquid exit from the tapering tube.

In another embodiment of the invention, the carbon particles are either carbon fibrils or carbon nanotube molecules.

In yet a further embodiment of the invention, both carbon fibrils and carbon nanotube molecules are employed to make up a single fiber.

<u style="single">Brief Description of the Drawing</u>

In the drawing: <ul id="ul0001" list-style="none" compact="compact"><li>FIG. 1 shows a graphical representation of an exemplary process, in accordance with the principles of the invention, for assembling carbon particles, such as, carbon fibrils and carbon nanotube molecules, into aligned fibers.</li></ul>

<u style="single">Detailed Description</u>

Unless otherwise explicitly specified herein, the drawings are not drawn to scale.

FIG. 1 shows a graphical representation of an exemplary process, in accordance with the principles of the invention, for assembling carbon particles, such as, carbon fibrils and carbon nanotube molecules, into aligned fibers. By aligned it is meant that the axis along the longest dimension of each of the various particles in a local vicinity are substantially parallel.

Shown in FIG. 1 are a) beaker 101, b) pump 103, c) supply outlet 105, d) tapering tube 107, e) ultraviolet curing lamp 109, f) pulleys 111, g) heater 113, h) twisting platform 115, i) heater 117, j) cladding applicator 119, and k) take-up drum 121.

The carbon particles, e.g., carbon nanotube molecules, carbon fibrils, or a combination thereof, are dispersed within an ultraviolet curable liquid contained in beaker 101. In one embodiment of the invention, the curable liquid is cured, at least in part, through the use of ultraviolet light. In an exemplary embodiment of the invention, the ultraviolet curable liquid is a copolymer of methylmethacrylate (95%) with the ester (5%) of methacrylic acid and anthacenyl methanol. Such an ultraviolet curable liquid cures in the presence of ultraviolet light, e.g., 350 nm light. The polymer can be diluted with the solvent toluene to control its flow properties. In another embodiment of the invention, the ultraviolet curable liquid may be PS2067 which is commercially available from United Chemical Technologies.

Pump 103 pumps the mixture of the carbon particles dispersed within the curable liquid from beaker 101 into tapering tube 107 via supply outlet 105. By flowing through tapering tube 107 the carbon particles are caused to align. Note that tapering tube 107 need not be a single unitary piece but may be made in sections and the sections may be made of different materials. Various properties of tapering tube 107, such as its length, orifice sizes, and taper rate affect the degree of alignment of the carbon particles, and hence the final properties of the resulting fiber. In one embodiment of the invention, the flow tube is a 20cm length of quartz tubing with an inlet diameter of 5 mm and an outlet diameter of 100 microns. Similarly, the concentration of the carbon particles within the curable liquid and flow velocity, also affect the degree of alignment of the carbon particles, and hence the final properties of the resulting fiber.

In one embodiment of the invention, the flowing mixture of curable liquid is cured by shining thereon ultraviolet light from ultraviolet curing lamp 109 in the general vicinity of the end of the tapering tube, thereby forming a fiber. For example, ultraviolet curing lamp 109 may be a 500 W high-pressure ultraviolet lamp giving off 350 nm light. The curing step may be performed, at least in part, while the flowing mixture of ultraviolet curable liquid is still tapering tube 107. To this end, tapering tube 107 may have at least a section that passes a sufficient amount of ultraviolet light to permit some curing. For example, a portion of tapering tube 107 may be made of amorphous quartz which is ultraviolet transparent. In another embodiment of the invention, the curing is performed only after the flowing mixture of ultraviolet curable liquid exits from tapering tube 107. Those of ordinary skill in the art will readily recognize that liquids curable at least in part through the application of factors other than ultraviolet light may, alternatively or additionally, be employed. Means for applying such other factors may be substituted for, or supplement, ultraviolet curing lamp 109.

After exiting tapering tube 107 and being cured, resulting fiber 110 may continue to travel, e.g., from its momentum or due to the force of gravity. Additional optional processing of the fiber may be undertaken.

For example, the fiber may be routed around pulleys 111 and directed toward heater 113, which heats the fiber so as to cause the volatile elements of the solidified curable liquid portion to substantially dissipate from the fiber. At this point, the fiber is substantially made up of only carbon.

Additional pulleys 111 mounted on twisting platform may be employed to twist the fiber to increase its density.

The fiber may then be routed past optional heater 117, which heats the fiber to sinter the carbon particles within the fiber. It may be advantageous to sinter the fiber after twisting, because twisting causes the carbon particles with in the fiber to be closer together.

Cladding applicator 119 may coat the fiber with an optional cladding. For example, it may be advantageous to coat the fiber with a nonconducting cladding for use in electrical applications. On the other hand, for use in applications such as bullet-proof vests, no cladding may be desired.

Note that the when present, the order of any heating, twisting, sintering, and cladding is at the discretion of the implementor and is only dependent upon the desired properties for the fiber being made. The final fiber may then be spooled onto take-up drum 121.

Advantageously, aligned carbon particle fibers are produced which are substantially free of any noncarbon impurities.