Carbon nanotube fibers from mixed-composition carbon nanotube materials

Abstract

Recyclable carbon nanotube fibers and other structures, and more particularly to fully recyclable carbon nanotube structures from mixed-composition carbon nanotube materials. Solution-spun CNT structures can be fully and easily recycled. Continuous structures made out of different CNT composition materials can be mixed together in solution and reprocessed into a recycled fiber with the same morphology, structure, alignment, and properties of the virgin fiber obtained by mixing the raw CNTs.

Description

CARBON NANOTUBE FIBERS FROM MIXED-COMPOSITION CARBON NANOTUBE MATERIALS CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

[0001] The application claims priority to U.S. Patent Appl. Serial No. 63 / 642,547, filed May 3, 2024, entitled “Fully Recyclable Carbon Nanotube Fibers From Mixed-Composition Carbon Nanotube Materials,” which patent application is commonly owned by the owner of the present invention and is incorporated herein in its entirety.TECHNICAL FIELD

[0002] The present invention relates to carbon nanotube fibers, and more particularly to carbon nanotube fibers from mixed-composition carbon nanotube materials, including fully recyclable carbon nanotube fibers from mixed-composition carbon nanotube materials. The present invention further relates to other carbon nanotubes structures in addition to carbon nanotubes fibers, such as CNT filaments, CNT yarns, CNT cables, CNT films, CNT tapes, CNT mats, CNT sheets, CNT aerogels, CNT foams, CNT ribbons, CNT three-dimensional structures, and other related CNT structuresGOVERNMENT INTEREST

[0003] This invention was made with government support under Grant No. DE-AR0001015, awarded by the Department of Energy, Advanced Research Projects Agency-Energy, and Grant No. FA9550-18-1-0014, awarded by the Air Force Office of Scientific Research. The government has certain rights in the invention.BACKGROUND

[0004] Recycling is critical to lowering the energy consumption, carbon dioxide (CO2) emissions, and waste generation associated with making materials, fostering sustainable development and realizing the Global Goals set by the United Nations. [United Nations 2015 United Nations 2015], As environmental policies become increasingly stringent, it is crucial to establish a circular economy paradigm where all available resources — feedstock, energy, andwaste — are more efficiently used, recovered, and reused. [Ghisellini 2 16; Geissdoerfer 2017}. Incumbent industrial materials such as metals, polymers, and carbon fibers represent one of the largest opportunities for improvement in the transition ahead, since they are very energy- and CCh-intensive to produce, very difficult to recycle, or both. [Ashby 2013; International Energy 2007 Gielen 2008; Gielen 2016\. Additionally, some materials such as carbon fibers do not currently have a path to recycle where the virgin material properties can be recovered and imparted in the recycled product, reducing marketability and commercial fitness for use.

[0005] Mining and converting metal ores into usable refined metals such as aluminum, copper, and steel consumes 70-80 EJ / year (-12% of the world's primary energy) and generates 4.5-5 GT CCh / year (-60% of the industrial emissions). [Ashby 2013; International Energy 2007}. In principle, metals can be indefinitely recycled without detriment to their properties; in practice, however, recycling metals is challenging and often inefficient because, aside from socio-techno-economic factors, the thermodynamics of their mixtures and alloys hinders the separation and purification of elemental forms. [Ayers 1997; Graedel 2011; Reck 2012}. Thermoplastic polymers (e.g., polyethylene, polypropylene, polyethylene terephthalate) can be synthesized and processed at relatively low energy and emissions costs [Ashby 2013; International Energy 2007 but cannot be recycled without some degree of property degradation [Ignatyev 2014; Singh 2017; Ragaert 2017; Maris 2018; Schyns 2021}. Thermoset plastics (e.g., epoxies) are essentially unrecyclable. [Morici 2022; Nicholls 2024}. Finally, carbon fibers, which have been increasingly used in high-end structural applications, are even more energy- and CCh-intensive to produce than metals [Ashby 2013; International Energy 2007}, as their manufacturing involves multiple solution processes in organic solvents and high-temperature reactions [Das 2015; Newcomb 2016; Khayyam 2020}, and even more difficult to recycle than polymers, experiencing severe property degradation [Oliveux 2015; Verma 2018; Giorgini 2020; Zhang 2020; Pakdel 2021}.

[0006] Thermoplastic polymers and carbon fibers lose properties after recycling because their intrinsic molecular architecture and constitution are fundamentally altered upon reclaiming and reprocessing. [Ignatyev 2 14: Singh 2 17: Ragaert 2017: Maris 2018: Schyns 2021: Oliveux 2015 Verma 2018,' Giorgini 2020,' Zhang 2020,' Pakdel 2021}. Thermoset plastics harden by forming irreversible covalent bonds when heated (set) and cannot be reshaped by melting or dissolution in solvents [Morici 2022,' Nicholls 2024 . Likewise, carbon fibers form irreversible covalent bonds across the entire fiber during the processes of carbonization and graphitization.[Das 2015,' Newcomb 2016,' Khayyam 2020}. Thermoplastic polymers can be remelted or redissolved, yet suffer thermal-mechanical degradation, which lowers their molecular weight, and face compatibility and miscibility constraints that hamper their stability. [Ignatyev 2014,' Singh 2017,' Ragaert 2017,' Maris 2018,' Schyns 2021}. Carbon fibers must be reduced to powder or small fragments, which destroys the structural integrity of their original continuous form, and undergo thermal and chemical treatments that damage their surface. [Oliveux 2015,' Verma 2018,' Giorgini 2020,' Zhang 2020,' Pakdel 2021}. Furthermore, current recycling routes for most metals, polymers, and carbon fibers at industrially relevant scales are generally laborious, hazardous, and costly in terms of energy and emissions, creating low added value to their recyclates [Ayers 1997,' Graedel 2011: Reck 2012,' Ignatyev 2014,' Singh 2017,' Ragaert 2017,' Maris 2018,' Schyns 2021, Oliveux 2015,' Verma 2018,' Giorgini 2020,' Zhang 2020,' Pakdel 2021},' particularly for polymers and carbon fibers, recycled materials are mainly designated to low-end products and less demanding applications than their virgin counterparts [Ignatyev 2014,' Singh 2017,' Ragaert 2017,' Maris 2018,' Schyns 2021, Oliveux 2015,' Verma 2018,' Giorgini 2020,' Zhang 2020,' Pakdel 2021}.

[0007] Carbon nanotubes (CNTs) have emerged as promising building blocks for multifunctional materials with a unique set of mechanical, electrical, and thermal properties.[Li 2017,' Rao 2018,' Meunier 2022}. Today, high-performance CNT fibers can bemanufactured at small scales with only one chemical reaction (gas-phase catalytic decomposition of hydrocarbons) and one room-temperature solution process (wet spinning of CNT solutions or wet densification of direct-spun CNT fibers), competing with metals in electrical and thermal conductivity as well as with polymers and carbon fibers in mechanical strength. [Behabtu 2008; Behabtu 2013; Taylor 2021; Smail 2019; Pasquali 2021}. Additionally, fiber-grade CNTs can be scalably synthesized with the co-production of clean hydrogen. [Pasquali 2021; Sun 2023; Kim 2024; Huntsman 2023}. As a result, cost reduction and process efficiency in CNT synthesis and CNT fiber manufacturing have been progressing to the point that CNT fibers can attain parity with incumbent industrial materials within the next decade [Taylor 2021; Smail 2019; Pasquali 2021; Sun 2023; Kim 2024; Huntsman 2023}, providing a route to decarbonizing industrial sectors via material substitution [Pasquali 2021}. Previous studies have already demonstrated the recyclability of solution-spun CNT fibers made from single-composition CNT materials [Davis 2009} (also known as “single-source” CNT materials) and, more recently, the reusability of direct-spun CNT sheets recycled from thermoset composites [Mikhalchan 2024}. Yet, establishing effective end-of-life recycling pathways of macroscopic CNT materials such as fibers made from different CNT composition materials is a key step prior to their adoption into relevant applications at industrial scales.

[0008] This invention was funded in part by the Welch Foundation under Welch Grant No. C-1668.SUMMARY OF THE INVENTION

[0009] The present invention relates to carbon nanotube fibers, and more particularly to carbon nanotube fibers from mixed-composition carbon nanotube materials, including fully recyclable carbon nanotube fibers from mixed-composition carbon nanotube materials. The present invention further relates to other carbon nanotubes structures in addition to carbon nanotubes fibers, such as CNT filaments, CNT yarns, CNT cables, CNT films, CNT tapes, CNT mats,CNT sheets, CNT aerogels, CNT foams, CNT ribbons, CNT three-dimensional structures, and other related CNT structures

[0010] In general embodiments, the present invention is directed to a mixed-composition carbon nanotube fiber that includes a mixed-composition carbon nanotube material. The mixed-composition carbon nanotube material includes a mixture of (a) a plurality of a first type of carbon nanotubes and (b) a plurality of a second type of carbon nanotubes. The first type of carbon nanotubes is measurably distinct from the second type of carbon nanotubes.

[0011] Implementations of the invention can include one or more of the following features:

[0012] The plurality of the first type of carbon nanotubes can be a plurality of a first virgin type of carbon nanotubes of a first grade. The plurality of the second type of carbon nanotubes can be a plurality of a second virgin type of carbon nanotubes of a first grade.

[0013] The plurality of the first type of carbon nanotubes can be a plurality of a first virgin type of carbon nanotubes of a first grade. The plurality of the second type of carbon nanotubes can be from second carbon nanotube fibers of a second grade.

[0014] The plurality of the first type of carbon nanotubes can be from first carbon nanotube fibers. The plurality of the second type of carbon nanotubes can be from second carbon nanotube fibers.

[0015] The properties of the mixed-composition carbon nanotube fiber can be the same as a combination of properties of the first carbon nanotube fibers and the second carbon nanotube fibers.

[0016] The first carbon nanotube fibers and the second carbon nanotube fibers can be each recycled carbon nanotubes fibers.

[0017] The carbon nanotube fiber can be a fully recyclable carbon nanotube fiber formed from the mixed-composition carbon nanotube material.

[0018] In further general embodiments, the present invention is directed to a method offorming a mixed-composition carbon nanotube fiber. The method includes selecting a plurality of first type of carbon nanotubes. The method further includes selecting a plurality of a second type of carbon nanotube fibers. The first type of carbon nanotubes is different from the second type of carbon nanotubes. The method further includes mixing the plurality of the first type of carbon nanotubes and the plurality of the second type of carbon nanotubes to form a mixed-composition carbon nanotube material. The method further includes forming the mixed-composition carbon nanotube fiber from the mixed-composition carbon nanotube material.

[0019] Implementations of the invention can include one or more of the following features:

[0020] The plurality of the first type of carbon nanotubes can be a plurality of a first virgin type of carbon nanotubes of a first grade. The plurality of the second type of carbon nanotubes can be a plurality of a second virgin type of carbon nanotubes of a first grade.

[0021] The plurality of the first type of carbon nanotubes and the plurality of the second type of carbon nanotubes can be from different composition.

[0022] The plurality of the first type of carbon nanotubes and the plurality of the second type of carbon nanotubes can be made by different processes.

[0023] The plurality of the first type of carbon nanotubes can be a plurality of a first virgin type of carbon nanotubes of a first grade. The plurality of the second type of carbon nanotubes are from second carbon nanotube fibers of a second grade.

[0024] The plurality of the first type of carbon nanotubes can be from first carbon nanotube fibers. The plurality of the second type of carbon nanotubes can be from second carbon nanotube fibers.

[0025] The first carbon nanotube fibers and the second carbon nanotube fibers can be from different compositions.

[0026] The properties of the mixed-composition carbon nanotube fiber can be the same as a combination of properties of the first carbon nanotube fibers and the second carbon nanotubefibers.

[0027] There can be no property degradation of the mixed-composition carbon nanotube fiber as compared to combined properties of the first carbon nanotube fibers and the second carbon nanotube fibers.

[0028] The first carbon nanotube fibers and the second carbon nanotube fibers can be each recycled carbon nanotubes fibers.

[0029] The carbon nanotube fiber can be a fully recyclable carbon nanotube fiber formed from the mixed-composition carbon nanotube material.

[0030] In further general embodiments, the present invention features a mixed-composition carbon nanotube structure that includes a mixed-composition carbon nanotube material. The mixed-composition carbon nanotube material include a mixture of (a) a plurality of a first type of carbon nanotubes and (b) a plurality of a second type of carbon nanotubes. The first type of carbon nanotubes is measurably distinct from the second type of carbon nanotubes.

[0031] Implementations of the invention can include one or more of the following features: The mixed-composition carbon nanotube structure can be a solution-spun mixed-composition carbon nanotube fiber.

[0032] The first type of carbon nanotubes is measurably distinct from the second type of carbon nanotubes based upon at least one characteristic selected from the group consisting of length distribution, diameter distribution, number of walls distribution, aspect ratio, and combinations thereof.

[0033] The mixed-composition carbon nanotube structure can be identified as a mixed-composition carbon nanotube structure based upon a characteristic selected from the group consisting of length distribution, diameter distribution, number of walls distribution, aspect ratio, and combinations thereof.

[0034] The mixed-composition carbon nanotube structure can have a structure selected has astructure selected from the group consisting of fibers, filaments, yarns, cables, films, tapes, mats, sheets, aerogels, foams, ribbons, and three-dimensional structures.

[0035] The mixed-composition carbon nanotube structure can be a mixed-composition carbon fiber.

[0036] The plurality of the first type of carbon nanotubes can be a plurality of a first virgin type of carbon nanotubes of a first grade. The plurality of the second type of carbon nanotubes can be a plurality of a second virgin type of carbon nanotubes of a first grade.

[0037] The plurality of the first type of carbon nanotubes can be a plurality of a first virgin type of carbon nanotubes of a first grade. The plurality of the second type of carbon nanotubes can be from second carbon nanotube structures of a second grade.

[0038] The plurality of the first type of carbon nanotubes can be from first carbon nanotube structures. The plurality of the second type of carbon nanotubes can be from second carbon nanotube structures.

[0039] The properties of the mixed-composition carbon nanotube structure can be the same as a combination of properties of the first carbon nanotube structures and the second carbon nanotube structures.

[0040] The first carbon nanotube structures and the second carbon nanotube structures can be each recycled carbon nanotubes structures.

[0041] The carbon nanotube structure can be a fully recyclable carbon nanotube structure formed from the mixed-composition carbon nanotube material.

[0042] Each of the first carbon nanotube structures, the second carbon nanotube structures, and the recycled carbon nanotubes structures can have has a structure selected has a structure selected from the group consisting of fibers, filaments, yams, cables, films, tapes, mats, sheets, aerogels, foams, ribbons, and three-dimensional structures.

[0043] The structure can be a fiber.

[0044] In further general embodiments, the present invention features a carbon nanotube product that includes CNT materials. The CNT materials are selected to form a mixed-composition CNT product.

[0045] In further general embodiments, the present invention features a composition of matter that includes CNT materials. The CNT materials are selected from two or more measurably distinct CNT compositions.

[0046] In further general embodiments, the present invention features a method of forming a mixed-composition carbon nanotube structure. The method includes selecting a plurality of first type of carbon nanotubes. The method further includes selecting a plurality of a second type of carbon nanotube structures. The first type of carbon nanotubes is measurably distinct from the second type of carbon nanotubes. The method further includes mixing the plurality of the first type of carbon nanotubes and the plurality of the second type of carbon nanotubes to form a mixed-composition carbon nanotube material. The method further includes forming the mixed-composition carbon nanotube structure from the mixed-composition carbon nanotube material.

[0047] Implementations of the invention can include one or more of the following features:

[0048] The step of forming the mixed-composition carbon nanotube structure from the mixed-composition carbon nanotube material can include solution spinning a solution including the mixed-composition carbon nanotube material.

[0049] The solvent of the solution can be CSA.

[0050] The first type of carbon nanotubes can be different from the second type of carbon nanotubes based upon a characteristic selected from the group consisting of length distribution, diameter distribution, number of walls distribution, aspect ratio, and combinations thereof.

[0051] The plurality of the first type of carbon nanotubes can be a plurality of a first virgin type of carbon nanotubes of a first grade. The plurality of the second type of carbon nanotubescan be a plurality of a second virgin type of carbon nanotubes of a first grade.

[0052] The plurality of the first type of carbon nanotubes and the plurality of the second type of carbon nanotubes can be from different compositions.

[0053] The plurality of the first type of carbon nanotubes and the plurality of the second type of carbon nanotubes can be made by different processes.

[0054] The plurality of the first type of carbon nanotubes can be a plurality of a first virgin type of carbon nanotubes of a first grade. The plurality of the second type of carbon nanotubes can be from second carbon nanotube structures of a second grade.

[0055] The plurality of the first type of carbon nanotubes can be from first carbon nanotube structures. The plurality of the second type of carbon nanotubes can be from second carbon nanotube structures.

[0056] The first carbon nanotube structures and the second carbon nanotube structures can have measureable distinct CNT compositions.

[0057] The properties of the mixed-composition carbon nanotube structure can be a blend of properties of the first carbon nanotube structures and the second carbon nanotube structures.

[0058] There can be no property degradation of the mixed-composition carbon nanotube structure as compared to combined properties of the first carbon nanotube structures and the second carbon nanotube structures.

[0059] The first carbon nanotube structures and the second carbon nanotube structures can each be recycled carbon nanotubes structures.

[0060] The carbon nanotube structure can be a fully recyclable carbon nanotube structure formed from the mixed-composition carbon nanotube material.

[0061] The mixed-composition carbon nanotube structure can have a structure selected has a structure selected from the group consisting of fibers, filaments, yarns, cables, films, tapes, mats, sheets, aerogels, foams, ribbons, and three-dimensional structures.

[0062] Each of the first carbon nanotube structures, the second carbon nanotube structures, and the recycled carbon nanotubes structures can have a structure selected has a structure selected from the group consisting of fibers, filaments, yams, cables, films, tapes, mats, sheets, aerogels, foams, ribbons, and three-dimensional structures.

[0063] In further general embodiments, the present invention features a method to produce a desired characteristic CNT product. The method includes selecting a first CNT material having a first composition having a first characteristic property. The method further includes selecting a second CNT material having a second composition having a second characteristic property. The first characteristic property is measurably distinct from second characteristic property.

[0064] Implementations of the invention can include one or more of the following features:

[0065] The desired characteristic CNT product can have a desired characteristic property that is the result of the mixture of the first characteristic property and the second characteristic property.

[0066] The desired characteristic CNT product can be a CNT structure with desired and tailored characteristics.

[0067] The CNT structure can have a structure selected has a structure selected from the group consisting of fibers, filaments, yarns, cables, films, tapes, mats, sheets, aerogels, foams, ribbons, and three-dimensional structures.

[0068] The CNT structure can be a CNT fiber.

[0069] The desired characteristic property can operably improve commercial viability of the CNT product, as compared to CNT products made only from the first CNT material or the second CNT material.

[0070] The desired characteristic property can be selected from the group consisting of cost, mechanical, thermal, electrical, processability, and combinations thereof.

[0071] In further general embodiments, the present invention features an article that includesa desired characteristic CNT product produced from one of the above-described methods.BRIEF DESCRIPTION OF THE DRAWINGS

[0072] FIGS. 1A-1D show CNT diameter and number of walls. Histograms of the diameter and number of walls distributions of Tuball CNTs (SWCNTs) (FIGS. 1A-1B) and Meijo CNTs (DWCNTs) (FIGS. 1C-1D).

[0073] FIGS. 2A-2D show Raman spectroscopy. FIGS. 2A-2C show Raman spectra of SWCNTs and DWCNTs at, respectively, 532, 633, and 785 nm excitation wavelengths; for proper visualization, the spectra of SWCNTs were shifted by 1 a.u. FIG. SD shows Raman IG / ID relative intensity ratio of SWCNTs and DWCNTs at the three excitation wavelengths tested; the horizontal axis is not to scale.

[0074] FIGS. 3A-3B show thermogravi metric analysis. FIGS. 3A-3B show, respectively, normalized mass and normalized differential mass of SWCNTs and DWCNTs.

[0075] FIGS. 4A-4B show scanning electron microscopy. FIGS. 4A-4B show SEM images of, respectively, SWCNTs and DWCNTs.

[0076] FIGS. 5A-5B show transmission electron microscopy. FIGS. 5A-5B show TEM images of, respectively, SWCNTs and DWCNTs.

[0077] FIGS. 6A-6C show capillary thinning extensional rheology of single-composition CNT-CSA solutions. FIG. 6A shows representative profiles of the mid-filament diameter temporal decay of single-composition CNT-CSA solutions of raw SWCNTs at 365 ppmw and raw DWCNTs at 44 ppmw. FIGS. 6B-6C show snapshots of the liquid filament near the breakup.

[0078] FIGS. 7A-7C show workflows outlining the recycling of solution-spun CNT fibers.FIG. 7 A shows raw SWCNTs and raw DWCNTs are independently mixed in two CSA solutions and separately processed into two virgin, single-composition CNT fibers. FIG. 7B shows equal masses of SWCNT fiber and DWCNT fiber are recovered, mixed together in asingle CSA solution, and reprocessed into a recycled, mixed-composition CNT fiber (also referred to as a “mixed-source” CNT fiber). FIG.7C shows equal masses of raw SWCNTs and raw DWCNTs are mixed together in a single CSA solution and processed into a virgin, mixed-composition CNT fiber.

[0079] FIGS. 8A-8H show CNT solubility and phase behavior. Unpolarized and polarized optical light images of CNT-CSA solutions of raw SWCNTs (FIGS. 8A-8B), raw DWCNTs (FIGS. 8C-8D), recovered mixture of SWCNTs and DWCNTs (FIGS. 8E-8F), and virgin mixture of raw SWCNTs and raw DWCNTs (FIGS. 8G-8H). For proper visualization, all samples were diluted from the respective spin dopes and imaged at 0.1 wt.%. The crossed arrows at the top right corner of the polarized light images indicate the polarizer / analyzer relative orientation.

[0080] FIGS.9A-9I show CNT fiber morphology, structure, and alignment. Scanning electron images of the outer surface and cross section of the virgin, single-composition SWCNT fiber (FIGS. 9A-9B), virgin, single-composition DWCNT fiber (FIGS. 9C-9D), recycled, mixed-composition CNT fiber (FIGS.9E-9F), and virgin, mixed-composition CNT fiber (FIGS.9G-9H) FIG. 91 shows orientational order parameter of fiber alignment for the four fibers (5 = 0.75-0.82); representative polarized Raman spectra are shown in FIGS. 10A-10D.

[0081] FIGS. 10A-10D show polarized Raman spectroscopy. FIGS. 10A-10D show polarized Raman spectra of the virgin, single-composition SWCNT fiber (FIG. 10A), virgin, singlecomposition DWCNT fiber (FIG. 10B), recycled, mixed-composition CNT fiber (FIG. 10C), and virgin, mixed-composition CNT fiber (FIG. 10D) at 532 nm excitation wavelength with three different incident and scattering configurations (VV, VH, and HHy, for proper visualization, the W and VH spectra were shifted by 0.5 and 0.25 a.u., respectively.

[0082] FIGS. 11A-11C show CNT fiber properties. FIGS. 11A-11B shows, tensile strength and electrical conductivity, respectively of solution-spun CNT fibers as a function of CNT AR.FIG. 11C shows ratio of properties of the recycled, mixed-composition CNT fiber to properties of the virgin, mixed-composition CNT fiber.

[0083] FIGS. 12A-12B show CNT fiber specific properties. Same as in FIGS. 11A-11B but for specific properties.

[0084] FIGS. 13A-13C show capillary thinning extensional rheology of mixed-composition CNT-CSA solutions. Same as in FIGS. 13A-13C, but for mixed-composition CNT-CSA solutions of recovered SWCNTs and DWCNTs at 104 ppmw and virgin SWCNTs and DWCNTs at 98 ppmw.

[0085] FIGS. 14A-14H show CNT solubility and phase behavior of different-diameter CNTs. Same as in FIGS. 8A-8H, but for CNT-CSA solutions of raw HiPCO 177.7 CNTs (FIGS.14A-14B), raw Meijo 1.5P CNTs (FIGS. 14C-14D), recovered mixture of HiPCO CNTs and Meijo CNTs (FIGS. 14E-14F), and virgin mixture of raw HiPCO CNTs and raw Meijo CNTs (FIGS. 14G-14H) For proper visualization, all samples were imaged at 0.3 wt.%.

[0086] FIG. 15 shows Raman radial breathing mode of CNT fibers. Radial breathing mode (50-350 cm'1) from Raman spectra of the virgin, single-composition SWCNT fiber, virgin, single-composition DWCNT fiber, recycled, mixed-composition CNT fiber, and virgin, mixed-composition CNT fiber (magenta) at 532 nm excitation wavelength.DETAILED DESCRIPTION

[0087] The present invention relates to carbon nanotube fibers, and more particularly to carbon nanotube fibers from mixed-composition carbon nanotube materials, including fully recyclable carbon nanotube fibers from mixed-composition carbon nanotube materials. The present invention further relates to other carbon nanotubes structures in addition to carbon nanotubes fibers, such as CNT filaments, CNT yarns, CNT cables, CNT films, CNT tapes, CNT mats, CNT sheets, CNT aerogels, CNT foams, CNT ribbons, CNT three-dimensional structures, and other related CNT structures. While the below detailed description discussed CNT fibers,fibers are representative of other structures, such as fibers, filaments, yarns, cables, films, tapes, mats, sheets, aerogels, foams, ribbons, three-dimensional structure, and other related structures.

[0088] In the present invention, it has been discovered that solution-spun CNT fibers can be fully and easily recycled without loss of properties (property degradation) and irrespective of their constituent composition materials (their constituent CNTs). In embodiments of the present invention, continuous segments of virgin, single-composition CNT fibers made from different CNTs have been mixed together in solution and reprocessed into a recycled, mixed-composition CNT fiber with the same morphology, structure, alignment, and properties as would be conferred when producing a virgin, mixed-composition CNT fiber made by directly mixing the raw CNTs.Different CNT Types / Characterization

[0089] As used herein, “different CNTs” or “different CNT types” or “distinct CNT types” means that the CNTs have one or more measurable characteristics that are measurable unique (or “measurably distinct”) from one another, such as, length distribution , diameter distribution, number of walls distribution, length to diameter aspect ratio, chemical structure, phase and polymorphy, crystallinity, molecular interactions, etc. Such difference in CNT types can be a result of different reaction methods, carbon feedstock, catalyst precursors, etc. It is important to clarify that any CNT composition will have an inherent distribution of properties / characteristics due to variability in the manufacturing processes, but the present invention deliberately selects CNT compositions based on measurably distinct CNT properties / characteristics which is of high import for the CNT product to be produced from the distinct composition CNT constituent materials thereby producing a mixed-composition CNT product such as a CNT fiber.

[0090] As representative of different CNT types during analysis of the present invention, CNTswere deliberately chosen from two commercial suppliers that employ different production methods, carbon feedstock, and catalyst precursors: (i) plasma based floating catalyst chemical vapor deposition (FCCVD) Tuball CNTs from OCSiAl and (b) enhanced direct injection pyrolytic synthesis (eDIPS) Meijo CNTs from Meijo Nano Carbon. Tuball CNTs were oxidized in a box furnace (Thermo Scientific Thermolyne FB1415M) at 450 °C for 20 hours to remove carbonaceous impurities, washed in hydrochloric acid (37%, Sigma- Aldrich) at room temperature for 3 hours to remove catalyst impurities, washed in boiling water until neutral, and dried in an oven (Thermo Scientific Lindberg / Blue M) at 115 °C overnight, as described in Taylor 2024. Meijo CNTs were purified by the manufacturer and used as received.

[0091] CNTs were imaged with scanning electron microscopy (SEM) and transmission electron microscopy (TEM). CNT diameter and number of walls were measured from TEM images using the ImageJ software, as in Tsentalovich 2016. FIGS. 1A-1D show the histograms of the diameter and number of walls distributions of the two CNT composition materials, as determined from ~30 individualized CNTs from each composition. It was found that Tuball CNTs have a mean diameter of 1.9 ± 0.6 nm and 1.2 ± 0.4 walls (z.e., mainly SWCNTs), while Meijo CNTs have a mean diameter of 1.9 ± 0.5 nm and 1.9 ± 0.6 walls (z.e., mainly DWCNTs). For simplicity, Tuball CNTs and Meijo CNTs are referred herein as SWCNTs and DWCNTs, respectively.

[0092] CNT crystallinity and level of defects were studied with Raman spectroscopy at 532, 633, and 785 nm excitation wavelengths (Renishaw inVia). FIGS.2A-2D show representative Raman spectra as well as the relative intensity ratio IG / ID of the G-peak to the Z>-peak of the two CNTs at the three excitation wavelengths tested. It was found that IG / ID ~ 80, 45, and 10 for SWCNTs and IG / ID ~ 50, 50, and 45 for DWCNTs with increasing excitation wavelength. The high IG / ID indicates that both composition materials have high-quality CNTs with high graphitic crystallinity and low defect density, as in Tsentalovich 2017.

[0093] CNT purity and content were analyzed with thermogravi metric analysis (TGA) at a temperature ramp of 10 °C / min and airflow of 100 mL / min (Mettler Toledo TGA / DSC 3+).FIG. 3A-3B show representative TGA results for the normalized mass and normalized differential mass of the two CNTs. (FIG. 3A has plots 301-302 for SWCNTs and DWCNTs, respectively; FIG. 3B has plots 311-312 for SWCNTs and DWCNTs, respectively). It was found that, after purification, both composition materials present negligible amounts of residual carbonaceous (e.g., amorphous carbon) and catalyst (e.g., iron nanoparticles) impurities; from the residual mass after oxidation, it was determined that their purity was higher than ~96 wt.% (z.e., the amount of non-CNT material was less than ~4%), as in Tsentalovich 2017. The high quality and high purity of the two CNT composition materials were qualitatively confirmed by SEM and TEM images, as shown in FIGS. 4A-4B and FIGS. 5A-5B, respectively. White arrows 501-502 in FIGS. 5A-5B, respectively, point to individualized CNTs. The high purity of the CNTs is very important for certain applications and makes it possible to be commercially viable.

[0094] Mixed-composition CNT-CSA solutions at different concentrations were prepared (here and elsewhere as later discussed) by adding the appropriate CNT mass, either from the raw CNT composition materials (in the case of virgin solutions) or from continuous segments of as-produced CNT fibers (in the case of recovered solutions) to the target CSA volume. The samples were prepared in glass vials reinforced with Teflon-lined silicone caps to prevent degradation and mixed in a speed mixer (FlackTek DAC 600) until complete homogenization (few minutes to a couple of hours, depending on the solution concentration), as in previous studies \Behabtu 2008,' Taylor 2021~. Pure (99.9%, Sigma-Aldrich) chlorosulfonic acid (CSA) was used as received. Due to its widespread utility, CSA is extensively used in industry; it is shipped in 90 ton tank cars and has a total production and application volumes well above 1 MT / year [Cremlyn 2002,' Fact. MR 2023].

[0095] CNT solubility and phase behavior were studied with transmitted light optical microscopy (Zeiss Axioplan 2). To avoid contact with moisture in the air, the samples were examined in flame-sealed rectangular glass capillaries (VitroCom) with an inner width (z.e., path length) of 100 pm, as in Tsentalovich 2016. CNT viscosity-averaged aspect ratio (AR) was extracted from the uniaxial extensional viscosity of semidilute CNT-CSA solutions, as determined from the rate of decay of the mid-filament diameter (Dmid) vs. time ( / ) profile of capillary thinning extensional rheology experiments (Cambridge Trimaster), as also detailed in Tsentalovich 2016.

[0096] FIGS. 6A-6C show representative capillary thinning extensional rheology results for the two CNT composition materials. Plots 601-602 of FIG. 6A are for, respectively, virgin solution of raw SWCNTs and virgin solution of raw DWCNTs. The filled symbols in FIG.6A are the data used to fit a straight line whose slope yields the solution uniaxial extensional viscosity. FIGS. 6B-6C show snapshots and of the liquid filament near the breakup for virgin solution of raw SWCNTs and virgin solution of raw DWCNTs, respectively. These are the frames used to measure the solution uniaxial extensional viscosity in FIG. 6A.

[0097] It was found that AR = 1000 for SWCNTs and AR = 5600 for DWCNTs, which correspond to CNT viscosity-averaged lengths of 2 and 11 pm, respectively. The recycling method is predicated on CNT dissolution in CSA. The AR and length of the two CNTs used here are comparable to those of previous high-quality, high-purity CNTs used in manufacturing high-performance CNT fibers via wet spinning of CNT-CSA solutions [Behabtu 2 13: Taylor 2027; Tsentalovich 2 17: Headrick 2018}, it is presently not known whether the dissolution and fiber spinning of CNTs in CSA has an intrinsic CNT length limitation that would prevent the fabrication of fibers with the “ultimate strength” (~40 GPa, as demonstrated by Bai 2018).CNT Fiber Spinning / Characterization

[0098] For large-scale manufacturing of solution-spun CNT fibers, CNT fiber spinning fromCNT-CSA solutions has already been scaled to above 1 ton fiber / year. [CERAWeek 2025], Continuous CNT fibers were solution-spun from CNT-CSA spin dopes at a concentration of 2 wt.% according to the CNT fiber spinning method introduced by Behabtu 2013 and later detailed in Tsentalovich 2107.

[0099] It is noteworthy that, while solutions of CNTs of the same type have been solution-spun into CNT fibers, as discussed in more detail below, the behavior of solutions of two (or more) different types of CNTs was surprising and the ability to solution-spin a CNT fiber from a mixture of different types of CNTs was unexpected and remarkable. It is believed that the present invention is the first instance in which CNT fibers have been reported to have been solution-spun from different types of CNTs.

[0100] The dopes were first filtered to remove impurities and undissolved particles and then extruded at 1 to 2 m / min through a 150 pm diameter spinneret into an acetone bath (99.5%, Fisher Chemical) to remove the acid; the forming fiber filament was continuously collected onto a winding drum at draw ratios (z.e., ratio of extrusion velocity to collection speed) of 1.2 to 1.5 to improve packing and alignment (extrusion velocity and draw ratio were optimized for each spinning experiment).

[0101] Fiber diameter was measured with SEM and cross sections were imaged after focused ion beam (FIB) milling, linear density was measured by weighing 4 m long samples in a microbalance (Citizen CM 21 X) and volumetric density was calculated as the ratio of linear density to cross sectional area, breaking force was measured by stretching 20 mm long samples at 0.1 mm / s in a strain-controlled rheometer (TA Instruments ARES G2), electrical resistance was measured with a customized 7 cm long four-point probe connected to a digital multimeter (Siglent SDM 3055), thermal conductivity was measured on samples suspended in vacuum with resistance thermometry techniques such as three-omega and steady-state self-Joule heating methods, and Young’s modulus was calculated from the slope of the stress vs. straincurves below 0.2% elongation. Fiber alignment was quantified by a scalar orientational order parameter calculated as S = (37iv + 3IVH - IHH)I( IW + 127 + IHH), where Ivv, IVH, and IHH are the G-peak intensities of polarized Raman spectra obtained with 532 nm excitation wavelength and three different incident and scattering configurations, namely, W (both aligned with the fiber axis), VH (the former aligned with the fiber axis and the latter aligned perpendicularly to the fiber axis), and HH (both aligned perpendicularly to the fiber axis). Properties were measured on multiple segments of as-produced fibers and are summarized in TABLE I. Most of the fiber characterization experiments are the same as in previous studies \Behabtu 2013 Taylor 2021; Tsentalovich 2017; Headrick 2018],TABLE I CNT Fiber PropertiesSummary of the main properties of the four CNr’ fibers hereinVirgin, Virgin,Recycled, Virgin, singlesinglemixed- mixed- Property composition compositioncomposition composition SWCNT DWCNT CNT fiber CNT fiber fiber fiberCNT aspect ratio (AR) 960 ± 40 5610 ± 140 3260 ± 80 3310 ± 60 Order parameter (5) 0.79 ± 0.02 0.77 ± 0.09 0.75 ± 0.02 0.82 ± 0.04 Tensile strength (GPa) 0.34 ± 0.11 2.36 ± 0.43 1.37 ± 0.13 1.39 ± 0.18 Specific strength (N / tex) 0.28 ± 0.05 1.46 ± 0.04 0.92 ± 0.04 0.88 ± 0.05 Electrical cond. (MS / m) 3.9 ± 1.2 8.6 ± 0.7 5.9 ± 0.9 6.1 ± 0.6 Specific elect, cond.3065 ± 140 5180 ± 80 3790 ± 85 3785 ± 70 (Sm2 / kg)Young’s modulus (GPa) 50 ± 10 180 ± 15 110 ± 15 105 ± 15 Thermal cond. (W / m K) 150 ± 30 350 ± 50 220 ± 20 230 ± 25 Elongation at break (%) 1.5 ± 0.3 4.0 ± 0.4 3.6 ± 0.2 3.3 ± 0.4 Diameter (pm) 23.0 ± 3.1 18.2 ± 1.2 21.4 ± 1.6 22.9 ± 1.3 Density (g / cm3) 1.26 1.65 1.23 1.61Linear density (dtex) 5.25 4.31 5.62 6.62 Recyclability

[0102] In the present invention, it has been demonstrated that full recyclability of a CNT product can be achieved where the inherent properties of the CNT constituent materials are not degraded. CNT products are selected from any product which uses constituent CNT materials whether the product is 100% comprised of CNT materials or less than 10% comprised of CNTmaterials. The constituent CNTs can be extracted from a CNT product and used to produce any CNT product using these recycled CNT materials. This cycling process of CNT constituent materials can continue infinitely enabling a circular process. To demonstrate a CNT product successfully being produced with recycled constituent CNT materials, the present invention demonstrates CNT fiber formation from recycled CNT constituent materials. Additionally, the CNT constituent materials can consist of mixed-composition CNT materials, virgin and / or recycled.

[0103] The recyclability of solution-spun CNT fibers is demonstrated in three steps, as shown in the workflows in FIGS. 7A-7C.Virgin, Single-Composition CNT Fibers

[0104] First, as shown in FIG. 7A, the two CNT composition materials were independently mixed in respective CSA solutions and separately processed into two virgin, singlecomposition CNT fibers. FIGS. 8A-8D show that the two CNTs fully dissolve into homogeneous systems and self-assemble into polydomain nematic liquid crystals that display strong birefringence and texture under crossed polarizers. The solubility and phase behavior of the two CNTs confirm that their quality and purity are appropriate for CNT fiber spinning, as previously reported. [Behabtu 2013; Taylor 2027; Tsentalovich 2017; Headrick 2018 .

[0105] FIGS. 9A-9D show that the two fibers have a uniform outer surface, with CNTs highly aligned in the axial direction, and a dense inner structure, with CNTs tightly packed in a nearly circular cross section. FIG. 91 presents the results for the orientational order parameter of fiber alignment, where S = 0.79 for the SWCNT fiber and S = 0.77 for the DWCNT fiber (with representative polarized Raman spectra for virgin, single-composition SWCNT fiber and virgin, single-composition DWCNT fiber shown, respectively, in FIGS. 10A-10B). The degree of alignment of the two fibers is higher than that of shear-aligned CNT films (5 = 0.45-0.66) and comparable to that of earlier solution-spun CNT fibers (5 = 0.64-0.76), both fromHeadrick 2018. The overall morphology, structure, and alignment of the two fibers indicate effective drawing and proper coagulation during spinning, as in previous studies. [Behabtu 2013; Taylor 2021; Tsentalovich 2017; Headrick 2018}.

[0106] Previous work showed that the mechanical and electrical properties of solution-spun CNT fibers made of high-quality, high-purity CNTs improve with CNT AR. [Tsentalovich 2017; Headrick 2018}. Therefore, the SWCNTs and DWCNTs selected here are expected to produce fibers at opposite ends of the CNT fiber property spectrum. In fact, FIGS. 11A-11B and FIGS. 12A-12B show that the tensile strength and electrical conductivity, both volumetric and specific, of the two fibers agree well with the structure-property relationships constructed by Tsentalovich 2017 for optimized fibers spun from CNT-CSA dopes at the same 2 wt.% concentration. See TABLES I-II. The Young’s modulus, elongation at break, and thermal conductivity of the two fibers also improve with CNT AR (see TABLE I) and are consistent with previous data for fibers spun from CNT-CSA dopes of CNTs with AR = 1000-7000.[Behabtu 2013; Taylor 2021; Tsentalovich 2017; Headrick 2018}.

[0107] In FIGS. 11A-11B, the data are for the virgin, single-composition SWCNT fiber (circles 1101), virgin, single-composition DWCNT fiber (circles 1102), recycled, mixed-composition CNT fiber (diamonds 1111), and virgin, mixed-composition CNT fiber (circles 1112) herein and the ten optimized CNT fibers from Tsentalovich 2017 (squares 1103). The solid lines are power fits to the literature data; the triangles at the bottom right corner of each panel indicate the slope of the fitted curves. Similar plots for specific properties are shown in FIGS. 12A-12B (virgin, single-composition SWCNT fiber (circles 1201), virgin, singlecomposition DWCNT fiber (circles 1202), recycled, mixed-composition CNT fiber (diamonds 1211), virgin, mixed-composition CNT fiber (circles 1212), and ten optimized CNT fibers from Tsentalovich 2017 (squares 1203)). Fiber properties are summarized in TABLE I and the data from Tsentalovich 2017 are presented in TABLE II.TABLE IICNT Fiber Properties From Tsentalovich 2017SpecificTensile strength Electrical Specific electrical CNT AR strength(GPa) cond. (MS / m) cond. (S m2 / kg) (N / tex)435 ± 40 0.15 ± 0.03 0.8 ± 0.1 0.14 ± 0.03 725 ± 90 1260 ± 90 0.65 ± 0.07 2.9 ± 0.1 0.47 ± 0.05 2030 ± 100 2310 ± 70 0.88 ± 0.12 4.3 ± 0.1 0.58 ± 0.08 2555 ± 80 2600 ± 90 0.77 ± 0.10 4.2 ± 0.1 0.56 ± 0.08 3340 ± 70 2800 ± 60 1.00 ± 0.20 5.0 ± 0.3 0.77 ± 0.15 2200 ± 230 2800 ± 90 1.13 ± 0.04 2.4 ± 0.1 0.80 ± 0.03 1665 ± 30 4010 ± 80 1.25 ± 0.02 6.3 ± 0.1 0.86 ± 0.02 3645 ± 80 4350 ± 200 1.64 ± 0.18 6.7 ± 0.2 1.09 ± 0.12 4445 ± 130 4400 ± 80 2.43 ± 0.10 8.3 ± 0.3 1.54 ± 0.09 4940 ± 1905150 ± 130 1.11 ± 0.10 3.3 ± 0.1 0.91 ± 0.12 2690 ± 80Recycled, Mixed-Composition CNT Fibers

[0108] To test recyclability, equal masses of each virgin, single-composition CNT fiber were recovered, mixed together in a single CSA solution, and reprocessed into a recycled, mixed- composition CNT fiber. See FIG. 7B. The recovered solution is completely homogeneous and unexpectedly presents no signs of demixing and phase separation, as shown in FIG. 8E-8F.Also, the recycled fiber is equivalent to the two original virgin fibers, both in terms of morphology and structure, as shown in FIG. 9E-9F, and alignment, as presented in FIG. 91, where S = 0.75 (with representative polarized Raman spectra for recycled, mixed-composition CNT fiber shown in FIG. 10C).

[0109] Because the viscosity of CNT solutions is determined by the length distribution of the dissolved CNTs [Tsentalovich 2016}, the AR of the recovered mixture of SWCNTs and DWCNTs is expected to fall in between the AR of the raw SWCNTs and raw DWCNTs. It was found that AR ~ 3300, which is approximately the average of the AR of the two constituent CNTs (FIG. 13A). It was also found that the properties of the recycled fiber similarly fall in between the properties of the two original virgin fibers, fitting in the same structure-property relationships from Tsentalovich 2917, as shown in FIG. 11A-11B and FIG. 12A-12B (see TABLES I -II)Virgin, Mixed-Composition CNT Fibers

[0110] Finally, equal masses of each CNT composition material were mixed together in a single CSA solution and processed into a virgin, mixed-composition CNT fiber (see FIG. 7C) with the same CNT content of the recovered solution and recycled fiber (z.e., equal masses of SWCNTs and DWCNTs). It was found that the two mixed-composition CNT solutions (virgin and recovered) have qualitatively the same solubility and phase behavior, as shown in FIG.8G-8H. It was also found that the two mixed-composition fibers (virgin and recycled) have equivalent morphology and structure, as shown in FIG. 9G-9H, and alignment, as presented in FIG. 91, where S = 0.82.

[0111] Of import, it was found that AR ~ 3300 for the virgin mixture of raw SWCNTs and raw DWCNTs, which is the same AR of the recovered mixture of SWCNTs and DWCNTs (FIG.13A)

[0112] Plots 1301-1302 of FIG. 13A are for, respectively, virgin and recovered solutions of mixed SWCNTs and DWCNTs. The filled symbols in FIG. 13A are the data used to fit a straight line whose slope yields the solution uniaxial extensional viscosity. FIGS. 13B-13C show snapshots and of the liquid filament near the breakup for virgin and recovered solutions of mixed SWCNTs and DWCNTs, respectively. These are the frames used to measure the solution uniaxial extensional viscosity in FIG. 13A.

[0113] Equally of import, it was found that the properties of the virgin, mixed-composition fiber obtained by directly mixing equal masses of raw SWCNTs and raw DWCNTs also match the properties of the recycled, mixed-composition fiber obtained by mixing equal masses of SWCNT fiber and DWCNT fiber, as shown in FIG. 11C (see TABLE I). The overlap between the AR of the virgin and recovered mixed-composition solutions (within 2%) and between the properties of the virgin and recycled mixed-composition fibers (within 5%) indicate that processing, reclaiming, and reprocessing CNTs into new CNT fibers via solution spinning hadno detrimental effect to the CNTs’ length distribution and intrinsic molecular properties. Therefore, unlike conventional polymers and carbon fibers, the present invention surprisingly demonstrates that solution-spun CNT fibers can be fully recycled even when recovered from different CNT composition materials.CNT Behavior

[0114] The surprising recyclability of solution-spun CNT fibers from multiple composition materials is a direct consequence of the (equally surprising) behavior of the virgin solutions of mixed SWCNTs and DWCNTs shown in FIG. 8G-8H. The miscibility of CNTs sharply contrasts the behavior of polymers, most of which form thermodynamically immiscible blends due to unfavorable enthalpic and entropic contributions to their free energies of mixing [Bates 1997; Manias 2014}, as predicted early on by the Flory-Huggins theory [Flory 1942: Huggins 1942} and extensions thereof [Bates 1994: Fredrickson 1994}.

[0115] Polymers with different chemical and structural characteristics are immiscible due to differences in the potential energy of their intermolecular interactions; for most nonpolar polymers, such as polyethylene, polystyrene, and polyisoprene, intermolecular interactions are primarily due to van der Waals’ forces [Bates 1991,' Manias 2014}, similar as for CNTs. Nevertheless, even isotopic mixtures of otherwise identical protonated and deuterated versions of the same polymer may not be perfectly miscible due to subtle monomer concentration fluctuations. [Bates I 1988,' Bates II 1988}. CNTs may not be affected by similar mixing shortcomings, likely because their high bending stiffness [Fakhri 2009,' Green 2009} minimizes the architectural and conformational asymmetries that hinder the miscibility of flexible polymers [Bates 1994,' Fredrickson 1994,' Bates 11988,' Bates II 1988}. Thus, their behavior may be expected to be closer to that of stiff rods.

[0116] However, stiff rods are also expected to phase separate when their dimensions are significantly different. Vroege and Lekkerkerker [Vroege 1993} showed that nematic-nematicdemixing in bidisperse rod-like particle systems occurs due to competing entropic effects — namely, orientation and mixing entropy — when rod length ratios exceed a critical threshold (-3.2:1). Such demixing minimizes the free energy by forming two nematic phases with distinct compositions. Although the rod length ratio in our mixed-composition CNT solutions (-5.8:1) exceeds this critical threshold (and the diameters are comparable), nematic-nematic phase separation was not observed. In fact, good mixing was found at all length scales, even though CNTs had been arranged into -20 pm diameter fiber pieces before redissolution and could have remained phase-separated at these length scales.

[0117] This suggests that while demixing may be thermodynamically favored, as in the case of most polymer blends and mixtures of different-sized rods, this may only happen on time scales much longer (days or longer) than the typical time scales of dope preparation and fiber spinning (minutes to hours) due to the low diffusivity of highly concentrated stiff rods with high aspect ratio. [Davis 2009,' Green 2009], As a result, CNTs from different composition materials spontaneously dissolve and mix in CSA, forming homogeneous liquid crystalline systems of athermal rigid rods with high aspect ratio polydispersity. In fact, the similarity between the liquid crystalline texture of the virgin and recovered solutions of mixed SWCNTs and DWCNTs shown in FIG. 8F and FIG. 8H and the virgin solution of the longer DWCNTs alone shown FIG. 8D indicates that the phase behavior of the two mixed-composition CNT-CSA solutions is determined by the longest CNTs in the system, as predicted by extensions of Onsager’s theory to idealized poly disperse rigid rods. [Davis 2009, Green 2009],

[0118] While the SWCNTs and DWCNTs used here differ by the number of walls and aspect ratio but coincidently have approximately the same mean diameter, it was confirmed that other mixed-composition CNT-CSA solutions made of CNTs with different diameters, number of walls, and aspect ratios (e.g., single-walled HiPCO 177.7 CNTs with a mean diameter of 1 nm and AR = 550 and double-walled Meijo 1.5P CNTs with a mean diameter of 1.8 nm diameterand AR = 4800) also form homogeneous liquid crystalline systems with the phase behavior determined by the longest length of the two constituent CNTs (see FIGS. 14A-14H). Although this demonstrated the mixed-composition recyclability of fiber-grade CNTs only in CSA solutions, similar behavior is anticipated and believed in alternative acid solvent systems. These include less hazardous and more versatile mixtures of oleum with either methanesulfonic acid (MSA) or / ?-Toluenesulfonic acid ( ToS), which offer greater compatibility with substrates. [Headrick 2022],

[0119] Following the absence of any observed processing challenge, the uniform outer surface, dense inner structure, and high degree of alignment of the two mixed-composition fibers reported in FIGS. 9E-9I confirm that the two mixed-composition solutions depicted in FIGS.8E-8H were indeed homogeneous and free of undissolved particles. Undissolved particles are deleterious to CNT fiber production and known to have a negative impact on CNT fiber spinning by causing spinneret clogging, pumping oscillations, and line breaks. [Tsentalovich 2017], In particular, the lack of heterogeneity in the recycled fiber further confirms that CNTs from each of the two virgin fibers dissolved into constituent CNTs and intimately mixed with each other in solution prior to reprocessing. By analyzing the radial breathing modes from Raman spectra of the four fibers, it was seen that the two mixed-composition fibers not only display approximately the same spectra but also appear easily distinguishable from their two single-composition fiber counterparts. FIG. 15 (with plots 1501-1504 for, respectively, virgin, single-composition SWCNT fiber; virgin, single-composition DWCNT fiber; recycled, mixed-composition CNT fiber; and virgin, mixed-composition CNT fiber).

[0120] Indeed, by measuring / analyzing one or more characteristics, such as size distribution, diameter distribution, number of walls distribution, length to diameter aspect ratio, chemical structure, phase and polymorphy, crystallinity, molecular interactions of the CNT fiber, it is possible to determine whether the CNT fiber is a mixed-composition CNT fiber. For instance,as shown in FIG. 15, plots 1503-1504 for mixed-composition CNT fibers (recycled and virgin) exhibit similar Raman spectra to one another, which being distinct from plots 1501-1502 for virgin single-composition CNT fibers (SWNT and DWCNT). Indeed, plots 1503-1504 exhibit multiple peaks that coincide with distinct peaks from each of plots 1501-1502, which indicates these CNT fibers are mixed-composition. Further, it is possible to use a technique such as gel permeation chromatography and / or suitable methods to measure the length distribution to analyze the length distributions present in the mixed-composition CNT fiber once it has been dissolved in CSA. Use of such method allows for mixed-composition CNT fibers to be measurably identified through use of deliberately selected length distributions to produce tailored CNT fibers.Advantages / Utility

[0121] The preservation of CNT intrinsic molecular properties and CNT fiber properties after recycling represents a striking advantage compared to incumbent industrial materials, particularly thermoplastic polymers and carbon fibers. Although polymer manufacturing scrap can be recycled within the same plant, which is also known for solution-spun CNT fibers [Davis 2009], polymers tend to be thermally and mechanically degraded upon reclaiming and reprocessing due to the high temperatures and high shear stresses inherent to melting and extrusion, which lowers their molecular weight through chain scission, chain branching, and crosslinking.

[0122] Recycling of plastic solid waste is further complicated by demixing and phase separation issues induced by chemical and structural differences between mixed streams of polymers recovered from different plants [Ignatyev 2 14,' Singh 2 17,' Ragaert 2 17,' Maris 2018,' Schyns 2021], Continuous carbon fibers state of the art cannot be recycled and must be reduced to staple fibers via shredding or milling, sometimes combined with thermal and chemical reactions such as pyrolysis and solvolysis, which destroys their structural integrityand damages their surface morphology and adhesiveness \Oliveux 2 15; Verma 2018; Giorgini 2020 Zhang 2020; Pakdel 2021] . In both cases, recy elates have inferior performance and lower economic viability than their virgin counterparts.

[0123] Conversely, continuous solution-spun CNT fibers can be fully recycled without detriment to their morphology, structure, alignment, and properties because recovering CNTs by redissolving CNT fibers in CSA and reprocessing recovered CNT-CSA solutions into new CNT fibers does not change the CNTs’ fundamental architecture and constitution at the molecular level. Of import, the simple yet effective recycling strategy described herein requires no steps other than those already used in the preparation of virgin solutions and processing of virgin fibers, adding no extra labor or hazard and minimal cost to the manufacturing of recyclates with equivalent performance. A similar approach is also likely to work with CNT fibers spun from surfactant-stabilized CNT solutions in water [Vigolo 2000; Vigolo 2002], although sonication may reduce the properties of the recycled fibers by shortening their constituent CNTs during the recovery and resuspension processes [Lucas 2009; Pagani 2012],

[0124] Further, conversely, other types of CNT fibers, such as those formed by direct spinning from floating-catalyst chemical vapor deposition (FCCVD) reactors [Smail 2019; Li 2004], are unlikely to be recyclable, at least via analogous mixed-stream methods, but could still be reused in their extant form, as recently demonstrated for non-woven CNT sheets. [Mikhalchan 2024],

[0125] Moreover, unlike base metals such as aluminum and copper, which are often used in multicomponent alloys but need to be separated into their pure elemental forms prior to recycling [Ayers 1997; Graedel 2011; Reck 2012], CNT fibers from multiple compositions can be recycled together without sorting the recovered CNTs into individual single-composition samples, yielding mixed-composition CNT fibers with properties dictated by the AR of the recovered CNT mixture.

[0126] The recyclability of solution-spun CNT fibers has been demonstrated after a singlerecycling cycle and with no exposure to use. Polymeric materials exposed to chemicals, light, and heat can be damaged and lose properties and recyclability during their use phase [Ignatyev 2014,' Singh 2017,' Ragaert 2017,' Maris 2018,' Schyns 2021},' yet, because of CNTs’ higher stability to chemical attack, radiation, and temperature compared to polymers [Rao 2 1 ,' Tasis 2006}, CNT degradation is likely to happen in a limited range of CNT fiber extreme working conditions, allowing for their full recyclability in most use cases. Because dissolution in acids and spinning into fibers do not damage CNTs measurably [Davis 2009,' Green 2009}, the recycling route should remain effective throughout several cycles, allowing a high utilization rate. As for most materials, CNT synthesis is the most resource-intensive step in the manufacturing of solution-spun CNT fibers; therefore, the energy and emissions costs inherent to their recovery and reprocessing steps (including redissolution in acids) are unlikely to affect the overall sustainability benefits of their recycling at scale.

[0127] CNT fibers are already competitive in terms of properties and are becoming increasingly economically viable as sustainable alternatives to hard-to-decarbonize incumbent industrial materials such as metals, polymers, and carbon fibers. [Taylor 2027; Pasquali 2021}. Per the present invention, solution-spun CNT fibers can be straightforwardly recycled without property degradation and irrespective of their constituent composition materials, which can be a critical attribute for their adoption into relevant applications at industrial scales. For instance, because of their superior mechanical flexibility, CNT fibers may be better suited than conventional carbon fibers to form composites with thermoplastic polymers, which could lead to the full recyclability of high-end composite panels used in aircraft, motor vehicles, and civil infrastructures. Even though the large-scale (MT / year) adoption of CNT materials is still predicated on significant advances in synthesis and manufacturing, the early establishment of effective end-of-life recycling pathways can mitigate some of the sustainability problems that have plagued synthetic polymers and carbon fibers upon technology maturation andwidespread deployment, further positioning CNT materials such as fibers as one of the most appealing candidates for the next materials transition necessary to realize a greener future with a circular economy.

[0128] Key advantages of the present invention are notable when achieving desired characteristic of CNT products using deliberately selected CNT compositions. When deliberately selecting CNT compositions it will be possible to (A) reduce costs (B) tailor properties such as electrical, mechanical, thermal, processability (C) and combinations of (A) and (B) of the CNT products.

[0129] While embodiments of the invention have been shown and described, modifications thereof can be made by one skilled in the art without departing from the spirit and teachings of the invention. The embodiments described and the examples provided herein are exemplary only, and are not intended to be limiting. Many variations and modifications of the invention disclosed herein are possible and are within the scope of the invention. The scope of protection is not limited by the description set out above, but is only limited by the claims which follow, that scope including all equivalents of the subject matter of the claims.

[0130] The disclosures of all patents, patent applications, and publications cited herein are hereby incorporated herein by reference in their entirety, to the extent that they provide exemplary, procedural, or other details supplementary to those set forth herein.

[0131] Amounts and other numerical data may be presented herein in a range format. It is to be understood that such range format is used merely for convenience and brevity and should be interpreted flexibly to include not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly recited. For example, a numerical range of approximately 1 to approximately 4.5 should be interpreted to include not only the explicitly recited limits of 1 to approximately 4.5, but also to include individualnumerals such as 2, 3, 4, and sub-ranges such as 1 to 3, 2 to 4, etc. The same principle applies to ranges reciting only one numerical value, such as “less than approximately 4.5,” which should be interpreted to include all of the above-recited values and ranges. Further, such an interpretation should apply regardless of the breadth of the range or the characteristic being described.

[0132] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood to one of ordinary skill in the art to which the presently disclosed subject matter belongs. Although any methods, devices, and materials similar or equivalent to those described herein can be used in the practice or testing of the presently disclosed subject matter, representative methods, devices, and materials are now described.

[0133] Following long-standing patent law convention, the terms “a” and “an” mean “one or more” when used in this application, including the claims.

[0134] Unless otherwise indicated, all numbers expressing quantities of ingredients, reaction conditions, and so forth used in the specification and claims are to be understood as being modified in all instances by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth in this specification and attached claims are approximations that can vary depending upon the desired properties sought to be obtained by the presently disclosed subject matter.

[0135] As used herein, the term “about” and “substantially” when referring to a value or to an amount of mass, weight, time, volume, concentration or percentage is meant to encompass variations of in some embodiments ±20%, in some embodiments ±10%, in some embodiments ±5%, in some embodiments ±1%, in some embodiments ±0.5%, and in some embodiments ±0.1% from the specified amount, as such variations are appropriate to perform the disclosed method.

[0136] As used herein, the term “substantially perpendicular” and “substantially parallel” ismeant to encompass variations of in some embodiments within ±10° of the perpendicular and parallel directions, respectively, in some embodiments within ±5° of the perpendicular and parallel directions, respectively, in some embodiments within ±1° of the perpendicular and parallel directions, respectively, and in some embodiments within ±0.5° of the perpendicular and parallel directions, respectively.

[0137] As used herein, the term “and / or” when used in the context of a listing of entities, refers to the entities being present singly or in combination. Thus, for example, the phrase “A, B, C, and / or D” includes A, B, C, and D individually, but also includes any and all combinations and subcombinations of A, B, C, and D.REFERENCES

[0138] Ashby, M. F., Materials and the Environment: Eco-Informed Material Choice (Butterworth-Heinemann, 2013) ("Ashby 2013'"').

[0139] Ayres, R. U., “Metals recycling: Economic and environmental implications. Resources," Conservation and Recycling, 1997, 21, 145-173 ('Ayres 1997').

[0140] Bai, Y., et al., “Carbon nanotube bundles with tensile strength over 80 GPa,” Nature Nanotechnology, 2018, 13, 589-595 (fBai 2018").

[0141] Bates, F. S., et al., “Conformational asymmetry and polymer— polymer thermodynamics,” Macromolecules, 1994, 27, 1065-1067 (" ales 1994").

[0142] Bates, F. S., “Polymer-polymer phase behavior,” Science, 1991, 251, 898-905 (" ales 1991").

[0143] Bates, F. S., et al., “Thermodynamics of isotopic polymer mixtures: Poly(vinylethylene) and poly(ethylethylene) ,” Macromolecules, 1988, 21, 1086-1094 (" ates 11988").

[0144] Bates, F. S., et al., “Thermodynamics of isotopic polymer mixtures: Significance of local structural asymmetry,” The Journal of Chemical Physics, 1988, 89, 535-544 (f Bates I1988").

[0145] Behabtu, N., et al., “Strong, light, multifunctional fibers of carbon nanotubes with ultrahigh conductivity. Science, 2013, 339, 182-186 ^Behabtu 2013").

[0146] Behabtu, N., et al., “Carbon nanotube-based neat fibers,” Nano Today 3, 24-34 ^Behabtu 2008").

[0147] CERAWeek 2025 by S&P Global, “Moving Ahead: Energy strategies for a complex world, 2025 (“CERAWeek 2025").

[0148] Cremlyn, R. J., “Chlorosulfonic Acid: A Versatile Reagent,” The Royal Society of Chemistry, 1stedition, 2002 (“Cremlyn 2002").

[0149] Das, S., et al., “Global Carbon Fiber Composites Supply Chain Competitiveness Analysis,” (Tech. Rep. ORNL / SR-2016 / 100 | NREL / TP-6A50-66071, Clean Energy Manufacturing Analysis Center, Joint Institute for Strategic Energy Analysis for the U.S. Department of Energy’s Clean Energy Manufacturing Initiative), 2016 (“Das 2016").

[0150] Davis, V. A., et al., “True solutions of single-walled carbon nanotubes for assembly into macroscopic materials,” Nature Nanotechnology, 2009, 4, 830-834 (“ avis 2009").

[0151] Fact.MR, “Chlorosulphonic Acid Market Oulook (2023 to 2033), 2023 (“Fact. MR 2023").

[0152] Fakhri, N., et al., “Diameter-dependent bending dynamics of single-walled carbon nanotubes in liquids,” Proceedings of the National Academy of Sciences, 2009, 106, 14219— 14223 (f Fakhri 2009").

[0153] Flory, P. J., “Thermodynamics of high polymer solutions,” The Journal of Chemical Physics, 1942, 10, 51-61 (f Flory 1942").

[0154] Fredrickson, G. H., etal., “Entropic corrections to the Flory -Huggins theory of polymer blends: Architectural and conformational effects,” Macromolecules, 1994, 27, 2503-2511 (“ Fredrickson 1994").

[0155] Geissdoerfer, M., et aL, “The circular economy - A new sustainability paradigm?” Journal Cleaner Production, 2017, 143, 757-768 ("Geissdoerfer 2017”).

[0156] Ghisellini, P., et al., “A review on circular economy: The expected transition to a balanced interplay of environmental and economic systems,” Journal Cleaner Production, 2016, 114, 11-32 (f Ghisellini 2016”).

[0157] Gielen, D., et al., “Climate and energy challenges for materials science,” Nature Materials, 2016, 15, 117-120 (f Gielen 2016”).

[0158] Gielen, D. et al., “Recycling industrial energy use and CO2 emissions: The role of materials science” MRS Bulletin, 2008, 33, 471-477 (f Gielen 2008”).

[0159] Giorgini, L., etal., “Recycling of carbon fiber reinforced composite waste to close their life cycle in a cradle-to-cradle approach,” Current Opinion in Green and Sustainable Chemistry, 2020, 26, 100368 (f Giorgini 2020”).

[0160] Graedel, T. E., et al., “What do we know about metal recycling rates?” Journal of Industrial Ecology, 2011, 15, 355-366 ("Graedel 2011”).

[0161] Green, M. J., et al., “Nanotubes as polymers,” Polymer, 2009, 50, 4979-4997 f Green 2009”).

[0162] Headrick, R. I, etal., “Versatile acid solvents for pristine carbon nanotube assembly,” Science Advances, 2022, 8, eabm3285 (“ Headrick 2022”).

[0163] Headrick, R. I, et al., “Structure-property relations in carbon nanotube fibers by downscaling solution processing,” Advanced Materials, 2018, 30, 1704482 f Headrick 2018”).

[0164] Huggins, M. L., “Some properties of solutions of long-chain compounds,” The Journal of Physical Chemistry, 1942, 46, 151-158 (f Huggins 1942”).

[0165] Huntsman Corporation, Investor Presentation, Fourth Quarter, 2023 (f Huntsman 2023”).

[0166] Ignatyev, I. A., et al., “Recycling of polymers: A review,” ChemSusChem, 2014, 7,1579-1593 ‘Ignatyev 2014”).

[0167] International Energy Agency, “Tracking Industrial Energy Efficiency and CO2 Emissions,” 2007) (‘International Energy 2007").

[0168] Khayyam, H., etal., “PAN precursor fabrication, applications and thermal stabilization process in carbon fiber production: Experimental and mathematical modelling,” Progress in Materials Science, 2020, 107, 100575 (‘Khayyam 2020”).

[0169] Kim, M., et al., “Human and environmental safety or carbon nanotubes across their life cycle,” Nature Review s Materials, 2024, 9, 63-81 (‘Kim 2024”).

[0170] Li, Y., “The quarter-century anniversary of carbon nanotube research. ACS Nano, 2017, 11, 1-2 (‘Li 2017”).

[0171] Li, Y.-L., et al., “Direct spinning of carbon nanotube fibers from chemical vapor deposition synthesis,” Science, 2004, 304, 276-278 (‘Li 2004”).

[0172] Lucas, A., etal., “Kinetics of nanotube and microfiber scission under sonication,” The Journal of Physical Chemistry C, 2009, 113, 20599-20605 (‘Lucas 2009”).

[0173] Manias, E., etal., “Thermodynamics of Polymer Blends” in Polymer Blends Handbook, L. A. Utracki, C. A. Wilkie, Eds. (Springer), 2014, 171-289 (‘Manias 2014”).

[0174] Maris, J., et al., “Mechanical recycling: Compatibilization of mixed thermoplastic wastes,” Polymer Degradation and Stability, 2018, 147, 245-266 (‘Maris 2018”).

[0175] Meunier, V., et al., “Carbon science perspective in 2022: Current research and future challenges,” Carbon, 2022, 195, 272-291 (“Meunier 2022”).

[0176] Mikhalchan, A., et al., “Network structure enabling re-use and near full property retention in CNT sheets recycled from thermoset composites,” Carbon, 2024, 220, 118851 (‘Mikhalchan 2024”).

[0177] Morici, E., et al., “Recycling of thermoset materials and thermoset-based composites: Challenge and opportunity,” Polymers, 2022, 14, 4153 (‘Morici 2022”).

[0178] Newcomb, B. A., “Processing, structure, and properties of carbon fibers,” Composites Part A: Applied Science and Manufacturing, 2016, 91, 262-282 f Newcomb 2016").

[0179] Nicholls, B. T., etal., “Closing the loop on thermoset plastic recycling,” Science, 2024, 384, 156-157 (f Nicholls 2024").

[0180] Oliveux, G., etal., “Current status of recycling of fibre reinforced polymers: Review of technologies, reuse and resulting properties,” Progress in Materials Science, 2015, 72, 61-99 (fOliveux 2015").

[0181] Pagani, G. J., et al., “Competing mechanisms and scaling laws for carbon nanotube scission by ultrasonication,” Proceedings of the National Academy of Sciences, 2012, 109, 11599-11604 (fPagani 2072”).

[0182] Pakdel, E., et al., “Recent progress in recycling carbon fibre reinforced composites and dry carbon fibre wastes,” Resources, Conservation & Recycling, 2021, 166, 105340 (fPakdel 2021'').

[0183] Pasquali, M., et al., “We can use carbon to decarbonize — and get hydrogen for free,” Proceedings of the National Academy of Sciences, 2021, 118, e2112089118 (“Pasquali 2027”).

[0184] Ragaert, K., et al. , “Mechanical and chemical recycling of solid plastic waste. Waste Management., 2017, 69, 24-58 ("Ragaert 2077”).

[0185] Rao, R., et al., “Carbon nanotubes and related nanomaterials: Critical advances and challenges for synthesis toward mainstream commercial applications,” ACS Nano, 2018, 72, 11756-11784 (fRao 2018").

[0186] Reck, B. K., et al., “Challenges in metal recycling,” Science, 2012, 337, 690-695 (fReck 2072”).

[0187] Schyns, Z. O. G., et al., “Mechanical recycling of packaging plastics: A review,” Macromolecular Rapid Communications, 2021, 42, 2000415 (“Schyns 2027”).

[0188] Singh, N., et al., “Recycling of plastic solid waste: A state of art review and futureapplications,” Composites Part B: Engineering, 2017, 115, 409-422 (“ Singh 2017").

[0189] United Nations General Assembly, “Transforming our world: The 2030 Agenda for Sustainable Development,” 2015 {‘United Nations 2015"").

[0190] Smail, F., et al., “Direct spinning of CNT fibres: Past, present and future scale up,” Carbon, 2019, 152, 218-232 (“ Smail 2019"").

[0191] Sun, E., et al., “A semi-continuous process for co-production of CCh-free hydrogen and carbon nanotubes via methane pyrolysis,” Cell Reports Physical Science, 2023, 4, 101338 {‘Sun 2023"").

[0192] Tasis, D., etal., “Chemistry of Carbon Nanotubes,” Chemical Reviews, 20, 106, 11 OS-1136 {‘Tasis 2006").

[0193] Taylor, L. W ., etal., “Purification of carbon nanotubes for dissolution in chlorosulfonic acid,” Carbon, 2024, 228, 119317 {‘Taylor 2024"").

[0194] Taylor, L. W ., etal., “Improved properties, increased production, and the path to broad adoption of carbon nanotube fibers,” Carbon, 2021, 171, 689-694 {‘Taylor 2021"").

[0195] Tsentalovich, D. E., et al., “Influence of carbon nanotube characteristics on macroscopic fiber properties,” ACS Applied Materials & Interfaces, 2017, 9, 36189-36198 {‘Tsentalovich 2017").

[0196] Tsentalovich, D. E., et al., “Relationship of extensional viscosity and liquid crystalline transition to length distribution in carbon nanotube solutions,” Macromolecules, 2016, 49, 681-689 {‘Tsentalovich 2016’").

[0197] United Nations Intergovernmental Panel on Climate Change, “Global warming of 1.5°C,” 2018 {‘United Nations 2018"").

[0198] Verma, S., et al., “Recycling, reclamation and re-manufacturing of carbon fibres. Current Opinion in Green and Sustainable Chemistry, 2018, 13, 86-90 {‘Verma 2018"").

[0199] Vigolo, B., et al. , “Improved structure and properties of single-wall carbon nanotubespun fibers,” Applied Physics Letters, 2002, 81, 1210-1212 (“Vigo lo 2002").

[0200] Vigolo, B., et al. , “Macroscopic fibers and ribbons of oriented carbon nanotubes,” Science, 2000, 290, 1331-1334 (“Vigolo 2000").

[0201] Vroege, G. J., et al., “Theory of the isotropic-nematic-nematic phase separation for a solution of bidisperse rodlike particles,” The Journal of Physical Chemistry, 1993, 97, 3601- 3605 (fVroege 1993").

[0202] Zhang, J., etal., “Current status of carbon fibre and carbon fibre composites recycling,” Composites Part B: Engineering, 2020, 193, 108053 ("Zhang 2020").

Claims

WHAT IS CLAIMED IS:

1. A mixed-composition carbon nanotube structure comprising a mixed-composition carbon nanotube material, wherein the mixed-composition carbon nanotube material comprises a mixture of (a) a plurality of a first type of carbon nanotubes and (b) a plurality of a second type of carbon nanotubes, wherein the first type of carbon nanotubes is measurably distinct from the second type of carbon nanotubes.

2. The mixed-composition carbon nanotube structureof Claim 1, wherein the mixed-composition carbon nanotube fiber is a solution-spun mixed-composition carbon nanotube structure.

3. The mixed-composition carbon nanotube structure of any of Claims 1-2, wherein the first type of carbon nanotubes is measureably distinct from the second type of carbon nanotubes based upon at least one characteristic selected from the group consisting of length distribution, diameter distribution, number of walls distribution, aspect ratio, and combinations thereof.

4. The mixed-composition carbon nanotube structure of any of Claims 1-3, wherein the mixed-composition carbon nanotube structure can be identified as a mixed-composition carbon nanotube structure based upon a characteristic selected from the group consisting of length distribution, diameter distribution, number of walls distribution, aspect ratio, and combinations thereof.

5. The mixed-composition carbon nanotube structure of any of Claims 1-4, wherein the mixed-composition carbon nanotube structure has a structure selected has a structure selectedfrom the group consisting of fibers, filaments, yams, cables, films, tapes, mats, sheets, aerogels, foams, ribbons, and three-dimensional structures.

6. The mixed-composition carbon nanotube structure of any of Claims 1-4, wherein the mixed-composition carbon nanotube structure is a mixed-composition carbon fiber.

7. A carbon nanotube product comprising CNT materials, wherein the CNT materials are selected to form a mixed-composition CNT product.

8. A composition of matter comprising CNT materials, wherein the CNT materials are selected from two or more measurably distinct CNT compositions.

9. A method of forming a mixed-composition carbon nanotube structure, wherein the method comprises:(a) selecting a plurality of first type of carbon nanotubes;(b) selecting a plurality of a second type of carbon nanotube structure, wherein the first type of carbon nanotubes is measurably distinct from the second type of carbon nanotubes;(c) mixing the plurality of the first type of carbon nanotubes and the plurality of the second type of carbon nanotubes to form a mixed-composition carbon nanotube material; and(d) forming the mixed-composition carbon nanotube structure from the mixed- composition carbon nanotube material.

10. The method of Claim 9, wherein the step of forming the mixed-composition carbon nanotube structure from the mixed-composition carbon nanotube material comprising solution spinning a solution comprising the mixed-composition carbon nanotube material.

11. The method of any of Claims 9-10, wherein the first type of carbon nanotubes is different from the second type of carbon nanotubes based upon a characteristic selected from the group consisting of length distribution, diameter distribution, number of walls distribution, aspect ratio, and combinations thereof.

12. The method of Claim 11, wherein the plurality of the first type of carbon nanotubes and the plurality of the second type of carbon nanotubes are made by different processes.

13. The method of any of Claims 9-12, wherein(a) the plurality of the first type of carbon nanotubes are from first carbon nanotube structures; and(b) the plurality of the second type of carbon nanotubes are from second carbon nanotube structures.

14. The method of Claim 13, wherein the first carbon nanotube structures and the second carbon nanotube structures have measureable distinct CNT compositions.

15. The method of any fo Claims 13-14, wherein the first carbon nanotube structures and the second carbon nanotube structures are each recycled carbon nanotubes structures.

16. The method of any of Claims 9-15, wherein the mixed-composition carbon nanotube structure has a structure selected has a structure selected from the group consisting of fibers, filaments, yams, cables, films, tapes, mats, sheets, aerogels, foams, ribbons, and three-dimensional structures.

17. The method of any Claims 13-16, wherein each the first carbon nanotube structures, the second carbon nanotube structures, and the recycled carbon nanotubes structures has a structure selected has a structure selected from the group consisting of fibers, filaments, yarns, cables, films, tapes, mats, sheets, aerogels, foams, ribbons, and three-dimensional structures.

18. A method to produce a desired characteristic CNT product, the method comprising:(a) selecting a first CNT material having a first composition having a first characteristic property;(b) selecting a second CNT material having a second composition having a second characteristic property, wherein the first characteristic property is measurably distinct from second characteristic property.

19. The method of Claim 19, wherein the desired characteristic CNT product has a desired characteristic property that is the result of the mixture of the first characteristic property and the second characteristic property.

20. An article comprising a desired characteristic CNT product produced from the method of any of Claims 18-19.

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