WO2024049712A1 - Functionalized carbon nanofiber yarn - Google Patents

Abstract

Functionalized nanofiber yarns with increased hydrophilicity with more than doubled water absorption property are provided. Methods of treatment for producing such functionalized nanofiber yarns are also provided.

Description

FUNCTIONALIZED CARBON NANOFIBER YARN

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims priority benefit from U.S. Provisional Application No. 63/402,185, filed August 30, 2022, which is hereby incorporated by reference in its entirety.

TECHNICAL FIELD

[0002] The present disclosure generally relates to carbon nanofibers. Specifically, the present disclosure relates to carbon nanofiber yam functionalization, fabrication, and applications of such modified carbon nanofiber yarns and yarn bundles.

BACKGROUND

[0003] Carbon nanofibers, interchangeable with carbon nanotubes (CNTs), are long and thin cylinders made of carbon that are arranged in a remarkable hexagonal lattice structure. Carbon nanofibers have a broad range of electronic, thermal, and structural superior properties, making them suitable for various applications, including, but not limited to, field emitters, conductors, transistors, energy storage, and fibers and fabrics with different strengths, biomedical applications, and industrial applications. However, carbon nanofibers are generally hydrophobic in that their surface repels water making them liquid-unfriendly with a strong tendency to agglomerate for the carbon nanofibers themselves, mainly due to the Van der Waals forces. Accordingly, carbon nanofibers may not perform as well where liquid absorption properties are desired, and alternative materials may be sought for such applications. SUMMARY

[0004] According to an aspect of the present disclosure, treated nano fiber yarn bundles with higher water absorption rates with retained yam bundle structures are provided.

[0005] According to an aspect of the present disclosure, the treated nanofiber yarn bundles more than double or quadruple their water-absorption capacity than untreated or pristine nanofiber yarns or yarn bundles.

BRIEF DESCRIPTION OF THE DRAWINGS

[0006] The present disclosure is further described in the detailed description which follows, in reference to the noted plurality of drawings, by way of non-limiting examples of preferred embodiments of the present disclosure, in which like characters represent like elements throughout the several views of the drawings.

[0007] FIG. 1 is a schematic illustration of CNT synthesis by chemical vapor deposition (CVD) in accordance with an exemplary embodiment.

[0008] FIG. 2 is a schematic illustration of continuous CNT sheet production by a drawing method in accordance with an exemplary embodiment.

[0009] FIG. 3 is a schematic illustration of continuous CNT yarn production by drawing and spinning in accordance with an exemplary embodiment.

[0010] FIG. 4 is a flow chart illustrating a method of performing an acid treatment on a CNT yarn bundle in accordance with an exemplary embodiment.

[0011] FIG. 5 is a flow chart illustrating a method of performing an ozone treatment on a CNT yarn bundle in accordance with an exemplary embodiment.

[0012] FIG. 6 is a graph illustrating increases of water absorption in treated CNT yarn bundles in accordance with an exemplary embodiment. DETAILED DESCRIPTION

[0013] Through one or more of its various aspects, embodiments and/or specific features or sub-components of the present disclosure are intended to bring out one or more of the advantages as specifically described above and noted below.

OVERVIEW OF CARBON NANOFIBER

[0014] Carbon nanofibers or CNTs are long tubes with small diameters typically measured in nanometers. They have a high aspect ratio of length vs. diameter in a range of generally above 1000:1 and are made up of one or more graphene sheets rolled up into a concentric structure. Each graphene sheet is regarded as a wall; a single- wall CNT (SWCNT) is made of a single graphene sheet; a double-wall CNT is made of two graphene sheets; a multi-wall CNT (MWCNT) has multiple graphene sheets.

[0015] Many CNT synthesis methods have been developed depending on product types, precursors, heating source, reaction time, temperature, and atmosphere. The most common methods include, but are not limited to, arc discharge, electrolysis, laser ablation, chemical vapor deposition (CVD), flame synthesis, mechano-thermal, etc. The well-known CVD methods have been classified into plasma-enhanced PE-CVD, aerosol CVD (AACVD), water-assisted WA- CVD, oxygen- assisted CVD, catalytic CVD, etc.

[0016] The CVD method utilizes acetylene (C2H2), ethylene (C2H4), or other hydrocarbons as a carbon source in a reaction chamber with a catalyst and a temperature ranging from 350 to l,000°C. Depending on the actual reaction temperature, reaction time, selection of catalyst, catalyst density, and carbon sources, the resulting CNTs vary.

[0017] Within a CVD reaction chamber, a catalyst may be in a free-floating form within the reaction chamber during the synthesis (FC-CVD). The nanofibers are then collected and turned into yams involving dispersing of CNTs in a liquid with a dispersant or surfactant, followed by extrusion and continuous spinning of the dispersed mixture into a conventional solution. [0018] A variation of the above yarn spinning methods includes, but is not limited to, the use of superacid in the spinning solution and the use of polymer ethylene glycol for CNT dispersion. [0019] An alternative and commonly deployed CVD synthesis method starts with a catalyst deposition on a substrate, e.g., a silicon wafer, by electron-beam (E-beam) deposition. The substrate may also comprise stainless steel or aluminum disposed on underlying silicon (Si) wafer or other ceramic substrates. Besides E-beam deposition, other catalyst deposition methods include, but are not limited to, sputtering, electrochemical methods, atomic layer deposition, laser-assisted CVD, and plasma-enhanced CVD. Exemplary catalysts include iron on a buffer layer of silicon dioxide or aluminum oxide over a substrate.

[0020] Once the CVD process is complete, as shown on the substrate, the result is a collection of individual nanofibers aligned vertically to each other with one end of the nanofibers attached to the substrate, like a forest, frequently referred to as a CNT forest. The van der Waals force and the entanglement among adjacent nanofibers are the main attributes that these CNTs are maintained in such a vertically aligned position, considering the small diameter of these individual CNTs from 0.3 nm up to 100 nm.

[0021] A CNT forest may eventually be spun into a CNT yam, as described in WO 2007/015710 and incorporated herein.

[0022] Briefly, connect an attachment to the sidewall or near the sidewall of a CNT forest. Draw the attachment continuously in a direction away from the CNT forest with an angle in a range of about 90° to 5° between the drawing and the alignment directions of the nanofibers of the CNT forest to form a CNT sheet. Twist the CNT sheet about the axis of the draw direction to form a nanofiber yam, which is then wound around a reel.

[0023] CNT yarns may be made by other methods well known in the literature. They may be commercially available from various suppliers. CNT G/D RATIO

[0024] As described above, carbon nanofibers incorporate carbon from various carbon source materials during the synthesis steps into one of the carbon allotropes, which include, but are not limited to, diamond, graphite, fullerenes, graphene, etc. From a molecular perspective, these materials are all entirely composed of carbon-carbon (C-C) bonds, with different orientations of these bonds in a specific material, indicating a drastically different material with distinguishable properties. Ramen spectroscopy is a commonly applied non-destructive tool well suited to characterize molecular interactions and bonds of carbon material. Its measured vibrational frequency is very sensitive to the orientation of the C-C bond and weights of the atoms at either end of the bond, indicative of one or more carbon allotropes.

[0025] As essentially the rolled-up graphene sheets, the nanofibers show the graphene characteristics on a Raman spectrum, the G band at 1590 cm'¹ plus a prominent 1340 cm'¹ D- band. The latter is a defect -induced feature attributed to dislocation defects. Amorphous graphite on the surface of nanofibers may also influence this D-band in the testing sample.

[0026] The intensity ratio of both D/G bands (ID/IG) quantitively reflects the defect status of the nano fibers; it also indicates the crystallinity. A smaller ID/IG value, compared to a large one, indicates better crystallinity or fewer defects. Changes in the ID/IG value of a CNT material after a defined treatment correlate to structural or microstructural modification of CNT walls, which would appear as functional or property alterations of the CNT material.

[0027] Raman spectrometers are commercially available, from handheld to tabletop. The i- Raman Plus from B&W Tek was an exemplary spectrometer selected to scan the samples at power 100, collection time of 60,000 ms, and measure the G and D peak values at 1590 cm'¹ and 1350 cm ¹, respectively. The IG/ID ratios are calculated.

CNT WETTABILITY

[0028] Carbon nanotubes are generally hydrophobic; their surface repels water making them liquid unfriendly with a strong tendency to agglomerate for CNTs themselves, mainly due to the Van der Waals forces. Studies by atomic force microscopy and the Wilhelmy method to measure contact angles between a single CNT and various liquids found that wettability was less favorable when the liquid became more polar. Surfactants are frequently applied to disperse CNTs in solutions to make CNT suspensions.

[0029] CNT yarns appear to inherit the same hydrophobic property. Insufficient contacts and interactions between individual CNT fibers or bundles of CNT fibers (CNT yarns) and other materials or matrix materials limit the uses and applications of CNT yams.

[0030] As an exemplary instance, one hundred individual CNT yarns, about 15 pm in diameter each, made by drawing from CNT forests on supports and subsequent twisting and untwisting, were bundled together to form a single CNT bundle or a false-twisted CNT bundle, in which an individual CNT yarn within the CNT bundle is substantially parallel to a central axis of the CNT bundle. Bundles are further treated as described below to alter surface morphology and bundle functions for desired properties and applications.

[0031] Each nanofiber yarn bundle may have an equal length, e.g., 2 cm. The treated nanofiber yarn bundles are transferred into a silicone tube, which has an inner diameter of one- sixteenth inch (1/16") or an inner diameter, in general, larger than the diameter of the nanofiber yarn bundle or a collection of the nanofiber yam bundles. The initial weight was measured and recorded. One end of the nanofiber yam bundles and the silicone tube were inserted into a water container with a constant one (1) cm deep water for three (3) consecutive days in a closed chamber to avoid water evaporation. The bottom of the container was at least ten times larger than the total cross-section of the silicon tubes to ensure a sufficient amount of water supply during the water (or liquid) absorption test. Each silicon tube with the nanofiber yarn bundles was weighted and subtracted by its initial weight to calculate the water absorption. CNT TREATMENT

[0032] Untreated CNT yams and CNT yarn bundles preserve their primitive surfaces and hydrophobic characteristics and are herein referred to as pristine yarns and yam bundles.

[0033] CNT pristine yam bundles may be treated with an agent or a group of agents with a strong oxidizing potential to alter the CNT material surface and structure or microstructure to endorse new properties and functions. The agent may be substantially pure, close to 100% purity, or have a percentage between 0-100%, depending on the chemical nature of the agent. [0034] In accordance with the disclosure, an exemplary oxidizing agent may be a gas or at least two gases.

[0035] Exemplary strong oxidizing gases may include but are not limited to ozone and chlorine.

[0036] According to exemplary aspects, CNT yarn bundles may be placed in a sealed treatment chamber. Then the chamber may be filled with at least one selected oxidizing gas at a target flow rate for a predetermined period of time. Once the predetermined period is expired, the treatment chamber is purged with inert gas or gas mixture, such as argon and/or nitrogen. [0037] In accordance with the disclosure, CNT treatment may include applying strong oxidizing agents and removing such agents upon achieving desired results.

[0038] Exemplary oxidizing agents may include but are not limited to strong chemical liquids, such as one or more strong acids. Moreover, certain acids may be mixed together in a volumetric ratio, such as a two-to-one volumetric ratio. In chemistry, a strong acid is an acid which ionizes its target or substrate completely in a water solution.

[0039] Exemplary strong acids include but are not limited to nitric acid, sulfuric acid, perchloric acid, nitic acid, perchloric acid, and combinations of nitric acid and sulfuric acid, sulfuric acid and potassium dichromate, and sulfuric acid and potassium permanganate.

[0040] For liquid-based treatment, according to an exemplary embodiment, CNT yarn bundles are soaked in intended solutions for a predetermined period until reaching the desired effects before being removed. Then, the treated yarn bundles are rinsed thoroughly with deionized water (DI water) and dried in the air, in a heated oven, or in a vacuum chamber. [0041] FIG. 4 is a flow chart illustrating a method of performing an acid treatment on a CNT yarn bundle in accordance with an exemplary embodiment.

[0042] In operation S401, carbon nano tube forests were synthesized by standard chemical vapor deposition method on a silicon wafer using iron catalysts and acetylene gas as a carbon source. In operation S402, CNT forests were drawn into CNT sheets. In operation S403, the CNT sheets were twisted into CNT yarns with a predetermined diameter. The predetermined diameter may be 15 pm with standard deviation of 1 pm. In operation S404, the CNT yams are wounded into spools. In an example, a spool may have 100 loops of CNT yams. In operation S405, a spool of CNT yarns is cut open to form a CNT yarn bundle or more than one bundles, which may be referred to as a nanofiber yarn bundle or bundles.

[0043] In operation S406, the CNT yarn bundles are treated with a mixture of strong acids. According to exemplary aspects, strong acids may include, without limitation, at least nitric acid (HNO3) and sulfuric acid (H2SO4). For example, the mixture of strong acids may be formed of a 70% nitric acid mixed with a 98% sulfuric acid. Further, the nitric acid and the sulfuric acid may be mixed in a two-to-one volumetric ratio, respectively (i.e., two parts nitric acid and 1 part sulfuric acid). However, aspects of the present disclosure are not limited thereto, such that the mixture of strong acids may include, without limitation, a perchloric acid, a nitric acid, a sulfuric acid, a potassium dichromate, or a potassium permanganate. Although a mixture of acids is disclosed herein, aspects of the present disclosure are not limited thereto, such that a single acid solution may be utilized. In an example, the single acid solution may vary in its chemical concentration level.

[0044] In operation S407, the CNT yarn bundles were submerged in the mixture of strong acids for a predetermined period of time. According to exemplary aspects, the predetermined period of time may be at least 30 minutes, 300 minutes, or less than 24 hours. However, aspects of the present disclosure are not limited thereto, such that the predetermined period of time may be any amount of time that results in a target increase of hydrophilicity for as short as 10 minutes. The target hydrophilicity may be at least double or quadruple of innate hydrophilicity of untreated or pristine CNT yam bundles while maintaining the structural integrity of the CNT yarn bundles. The CNT yarn bundles may be submerged in the mixture of strong acids for the predetermined period of time with occasional stirring.

[0045] In operation S408, the treated CNT yarn bundles are removed from the acid mixture, soaked in a water bath and rinsed with distilled water thoroughly.

[0046] FIG. 5 is a flow chart illustrating a method of performing an ozone treatment on a CNT yarn bundle in accordance with an exemplary embodiment.

[0047] In operation S501, carbon nanotube forests were synthesized by standard chemical vapor deposition method on a silicon wafer using iron catalysts and acetylene gas as a carbon source. In operation S502, CNT forests were drawn into CNT sheets. In operation S503, the CNT sheets were twisted into CNT yarns with a predetermined diameter. The predetermined diameter may be 15 pm with standard deviation of 1 pm. In operation S504, the CNT yams are wounded into spools. In an example, a spool may have 100 loops of CNT yams. In operation S505, a spool of CNT yarns is cut open to form a CNT yarn bundle or more than one bundles, which may be referred to as a nanofiber yarn bundle or bundles.

[0048] In operation S506, the CNT yarn bundles are placed in a treatment chamber, and then the treatment chamber is sealed. In operation S507, the treatment chamber is filled with a selected oxidizing gas. According to exemplary aspects, oxidizing gas may be formed of 20% ozone gas plus 80% nitrogen. However, aspects of the present disclosure are not limited thereto, such that other ozone percentage makeup oxidizing gas may be utilized. In operation S508, the CNT yarn bundle may be exposed to the oxidizing gas for a predetermined period of time. In an example, the predetermined period of time may have a minimum value of 10 minutes, 30 minutes, 300 minutes, or a maximum value of 24 hours. However, aspects of the present disclosure are not limited thereto, such that the predetermined period of time may be any amount of time that results in a target increase of hydrophilicity. The target hydrophilicity may be at least double or quadruple of innate hydrophilicity of untreated or pristine CNT yarn bundles while maintaining the structural integrity of the CNT yam bundles.

[0049] In operation S509, upon expiration of the predetermined period of time (e.g., completion of ozone treatment), the treatment chamber is purged with inert gas. In an example, the inert gas may include, without limitation, nitrogen, argon and the like. In operation S510, the treatment chamber is returned to the atmospheric environment, and the treated CNT yarn bundles are promptly removed from the treatment chamber and placed in storage, preferably in a sealed storage filled with inert gas.

EFFECTS OF CNT TREATMENT

[0050] One group of CNT yam bundles is treated with a strong acid mixture for 300 minutes, as detailed in the description of FIG. 4 provided above.

[0051] The other two groups of CNT yarn bundles are treated with ozone gas for 30 minutes and 300 minutes, respectively, as detailed in the description of FIG. 5 above.

[0052] All three treated groups of CNT yarn bundles demonstrate significant changes in ID/IG ratio, as shown in Table 1, and wettability in Table 2.

[0053] In Table 1, all treated groups with three samples per group show increases in G-peak value and D-peak value. After converting these peak values into ratios, the mean IG/ID values decrease from 1.77 for the pristine CNT yarn bundles to 1.51 for the 30-min ozone-treated yam bundles, 1.39 for the 300-min ozone-treated yarn bundles, and 1.30 for the acid-treated yarn bundles. As the treatment conditions get more aggressive, the IG/ID values drop more significant, indicating more structural changes in the CNT walls. Table 1

[0054] In Table 2, all CNT yams demonstrate their water absorption before and after strong acid treatment and ozone treatment. FIG. 6 presents the same results in a bar chart. The weight gain or water absorption rate, by percentage, increases from 1.47% to 2.68%, 4.32%, and 6.68% for the pristine group, 30-min ozone-treated group (Ozone L-Treated CNT Yam Bundle), 300- min ozone-treated group (Ozone H-Treated CNT Yarn Bundle), and the acid-treated ozone group (Acid Treated CNT Yarn Bundle), respectively. The harsh treatment trend renders more water absorption into the treated nano fiber yarn bundles, leading to higher hydrophilicity. The CNT yarn water absorption capacity may be doubled or quadrupled with the most aggressive treatment, from a gain of 10 mg water per mg of CNT yarn bundles to 19 mg, 30 mg, and 47 mg for the pristine, 30-min ozone-treated, 300-min ozone-treated, acid-treated CNT yam groups, respectively.

Table 2

[0055] Increased hydrophilicity of carbon nanotubes will enable the nanostructures to retain more exogenous enzymatically active and non-active small molecules and larger molecules with a slower release property.

[0056] Exemplary molecules include, but are not limited to, biomolecules, proteins, growth hormones, recombinant proteins, small molecules, therapeutic agents, chemicals, or gas molecules.

[0057] Nanofiber yarn bundles with improved hydrophilicity sidewall may support new applications in various technical fields and industries, including but not limited to lithium intercalation, gas storage, slow-release of large active agents, new composite material, and biotechnology and medical devices (implantable and ex- vivo).

[0058] Nanofiber yarns may be treated first for improved hydrophilicity. Then a bundle of treated yarns may be twisted together to form a twisted nanofiber yarn bundle. The twisted nanofiber yarn bundle may be further untwisted to produce a false -twisted nanofiber yam bundle as detailed above.

[0059] As the hydrophilicity of the nanofiber yam's surface changes, so are the Van der Waals forces between the nanofibers. The reduced Van der Waals forces may leave with a loosely bundled twisted and false-twisted nanofiber yarn bundle, limiting such material's utilities and applications. However, the loosely bundled nanofiber yarn bundles may present opportunities and/or advantages for migration or penetration of exogenous material crossing the nanofiber yarn bundles themselves.

FURTHER CONSIDERATIONS

[0060] The foregoing description of the embodiments of the disclosure has been presented for the purpose of illustration; it is not intended to be exhaustive or to limit the claims to the precise forms disclosed. Persons skilled in the relevant art can appreciate that many modifications and variations are possible in light of the above disclosure. [0061] The language used in the specification has been principally selected for readability and instructional purposes, and it may not have been selected to delineate or circumscribe the inventive subject matter. It is therefore intended that the scope of the disclosure be limited not by this detailed description, but rather by any claims that issue on an application based hereon. Accordingly, the disclosure of the embodiments is intended to be illustrative, but not limiting, of the scope of the invention, which is set forth in the following claims.

[0062] Although the invention has been described with reference to several exemplary embodiments, it is understood that the words that have been used are words of description and illustration, rather than words of limitation. Changes may be made within the purview of the appended claims, as presently stated and as amended, without departing from the scope and spirit of the present disclosure in its aspects. Although the invention has been described with reference to particular means, materials and embodiments, the invention is not intended to be limited to the particulars disclosed; rather the invention extends to all functionally equivalent structures, methods, and uses such as are within the scope of the appended claims.

[0063] The illustrations of the embodiments described herein are intended to provide a general understanding of the various embodiments. The illustrations are not intended to serve as a complete description of all of the elements and features of apparatus and systems that utilize the structures or methods described herein. Many other embodiments may be apparent to those of skill in the art upon reviewing the disclosure. Other embodiments may be utilized and derived from the disclosure, such that structural and logical substitutions and changes may be made without departing from the scope of the disclosure. Additionally, the illustrations are merely representational and may not be drawn to scale. Certain proportions within the illustrations may be exaggerated, while other proportions may be minimized. Accordingly, the disclosure and the figures are to be regarded as illustrative rather than restrictive.

[0064] One or more embodiments of the disclosure may be referred to herein, individually and/or collectively, by the term “invention” merely for convenience and without intending to voluntarily limit the scope of this application to any particular invention or inventive concept. Moreover, although specific embodiments have been illustrated and described herein, it should be appreciated that any subsequent arrangement designed to achieve the same or similar purpose may be substituted for the specific embodiments shown. This disclosure is intended to cover any and all subsequent adaptations or variations of various embodiments. Combinations of the above embodiments, and other embodiments not specifically described herein, will be apparent to those of skill in the art upon reviewing the description.

[0065] The Abstract of the Disclosure is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. In addition, in the foregoing Detailed Description, various features may be grouped together or described in a single embodiment for the purpose of streamlining the disclosure. This disclosure is not to be interpreted as reflecting an intention that the claimed embodiments require more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive subject matter may be directed to less than all of the features of any of the disclosed embodiments. Thus, the following claims are incorporated into the Detailed Description, with each claim standing on its own as defining separately claimed subject matter.

[0066] The above disclosed subject matter is to be considered illustrative, and not restrictive, and the appended claims are intended to cover all such modifications, enhancements, and other embodiments which fall within the true spirit and scope of the present disclosure. Thus, to the maximum extent allowed by law, the scope of the present disclosure is to be determined by the broadest permissible interpretation of the following claims and their equivalents, and shall not be restricted or limited by the foregoing detailed description.

Claims

What is claimed is:

1. A nanofiber yarn bundle, comprising: at least two treated nanofiber yarns, wherein the treatment includes exposing the nanofiber yam bundle to an oxidizing agent and removing the oxidization agent.

2. The nanofiber yarn bundle of claim 1, wherein the treated nanofiber yarn bundle has an increased water absorption rate compared to an untreated nanofiber yarn bundle.

3. The nanofiber yarn bundle of claim 2, wherein the increased water absorption rate is at least 18 mg of water per 1 mg of the treated nanofiber yarn bundle.

4. The nanofiber yarn bundle of claim 3, wherein the oxidizing agent is at least one oxidizing gas or at least one strong acid.

5. The nanofiber yarn bundle of claim 4, wherein the at least one oxidizing gas includes ozone,, chlorine, or a combination thereof.

6. The nanofiber yarn bundle of claim 4, wherein the at least one strong acid includes nitric acid, sulfuric acid, perchloric acid, dichromate, permanganate acid, or a combination thereof.

7. The nanofiber yarn bundle of claim 1, wherein the nanotube yarn bundle is a carbon nanotube yarn bundle, and the at least two treated nanofiber yarns have microstructurally modified carbon nanotube walls.

8. A method of increasing hydrophilicity of a yarn bundle, the method comprising: a) preparing a nanofiber yarn bundle; b) selecting an oxidizing agent; c) exposing the nanofiber yarn bundle to the oxidizing agent; and d) removing the nanofiber yarn bundle from the exposure of the oxidizing agent and freeing the nanofiber yam bundle of the oxidizing agent.

9. The method of claim 8, wherein the oxidizing agent comprises at least one acid.

10. The method of claim 8, wherein the oxidizing agent comprises a combination of at least two acids.

11. The method of claim 10, wherein the two acids are mixed in two to one ratio.

12. The method of claim 10, wherein the two acids include at least one of a nitric acid, a sulfuric acid, and a perchloric acid.

13. The method of claim 10, wherein the combination includes a nitric acid and a sulfuric acid mixture, a sulfuric acid and a potassium dichromate mixture, or a sulfuric acid and a potassium permanganate mixture.

14. The method of claim 10, wherein the oxidizing agent includes 70% nitric acid mixed with a 98% sulfuric acid in two-to-one volumetric ratio, respectively.

15. The method of claim 8, wherein the oxidizing agent comprises at least one gas.

16. The method of claim 15, wherein the gas is ozone or chlorine.

17. The method of claim 8, wherein the nanofiber yarn bundle is exposed to the oxidizing agent for at least 300 minutes.

18. The method of claim 8, wherein the nanofiber yarn bundle is exposed to the oxidizing agent for at least 30 minutes.

19. The method of claim 8, wherein the nanofiber yarn bundle is exposed to the oxidizing agent for at least 10 minutes.