Compositions containing carbon nanotubes for low hysteresis elastomers

Abstract

This application relates to novel discrete carbon nanotubes with surface modifications that disperse well in elastomers and crosslink the elastomer at or near the surface of the discrete carbon nanotubes. Significant improvements in the performance of elastomer compounds having surface modifications and a plurality of discrete carbon nanotubes with silica and / or carbon black result, for example, in improved wear resistance while simultaneously reducing hysteresis effects during cyclic deformation. These improved properties are highly desirable for fuel-efficient and extended wear life tire compounds.

Description

[Technical Field]

[0001] government support Portions of this material may be based on work supported by the U.S. Department of Energy, Office of Science SC-1 under Grant DE-SC0021823.

[0002] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to U.S. Provisional Application No. 63 / 328,429, filed April 7, 2022, which is incorporated herein by reference.

[0003] FIELD OF THE INVENTION This application relates to novel discrete carbon nanotubes with surface modifications that disperse well in elastomers and crosslink the elastomer at or near the surface of the discrete carbon nanotubes. The unexpected improvement in performance of elastomer compounds having a plurality of discrete carbon nanotubes with surface modifications and silica and / or carbon black results in a combination of improved wear resistance while simultaneously providing reduced hysteresis effects during cyclic deformation. The combined properties of improved wear resistance with reduced hysteresis effects are highly desirable features for fuel-efficient, long-life tire tread compounds. [Background technology]

[0004] Tire rolling resistance is the energy lost when a vehicle's tires move across a road surface at a constant speed. A major contributor to tire rolling resistance is a process known as hysteresis. Hysteresis is essentially the energy loss that occurs during cyclical movements, such as deformation events, as the tire compresses and expands during rotation under vehicle load. This energy loss must be overcome by the vehicle's engine or battery, resulting in higher energy consumption. Tire tread compounds with improved lifespan and better energy efficiency are desirable for any vehicle, provided other properties, such as tensile strength and grip, are maintained under various atmospheric conditions. These improved properties are particularly beneficial for electric vehicles (EVs), because EVs generally weigh more and have a greater torque profile than similarly sized conventional internal combustion engine (ICE) vehicles, and the combination of increased weight and torque causes tires to wear more quickly. EVs also benefit more from improved tires with better energy efficiency than ICE vehicles because EVs have more efficient drivetrains and therefore lose proportionally more energy to tire rolling resistance. The improvement in tire wear resistance also reduces tire tread wear particle contamination. Currently, many passenger car tire tread compounds use solution-synthesized styrene-butadiene polymers (SSBR) and polybutadiene elastomer blends (BR or PBR), with reinforcing silica bonded via organosilane and a small amount of carbon black for coloring and static dissipation. Silica-based tires have good wet grip and rolling resistance, but are less durable than carbon black-based tires.

[0005] Carbon nanotubes (CNTs) can be classified by the number of walls: single-walled, double-walled, and multi-walled. Each wall of a CNT can be further classified as chiral or non-chiral. Some of the carbon atoms in a CNT may be replaced with nitrogen atoms. Some of the walls may contain Stones-Wales defects, defined as a seven-membered ring-five-membered ring pair. CNTs are currently produced in large quantities using chemical vapor deposition reactors, producing aggregated bundles or ropes of carbon nanotubes. However, their commercial applications are very limited due to their poor performance as reinforcing fillers in the aggregated state. The use of CNTs as reinforcing or conductive fillers in polymer composites is an area where CNTs are predicted to have significant utility if they can be prepared as discrete carbon nanotubes and uniformly dispersed within an elastomer matrix.

[0006] U.S. Patent No. 9,212,273 teaches a composition comprising a cured elastomer containing discrete carbon nanotubes, wherein the discrete carbon nanotubes have an aspect ratio of 10 or greater, are double-walled or multi-walled, are present in an amount ranging from 0.1 to 30 weight percent based on the total weight, and are functionalized. An article prepared from this composition can be a tire tread or tire casing. More specifically, a carbon nanotube surface modifier or surfactant is chemically or physically (or both) bonded to the elastomer and / or isolated fibers or fillers in the compound. One example is provided: oleylamine (1-amino-9-octadecene) can be reacted with carbon nanotubes containing carboxylic acid groups to produce an amide. Adding the amide-modified carbon nanotubes to a vinyl-containing polymeric material, such as styrene-butadiene, followed by the addition of a crosslinking agent, such as peroxide or sulfur, can covalently bond the vinyl-containing polymer to the amide functional groups on the carbon nanotubes. Although much improved properties of the filled elastomeric composition were obtained, such as tear energy, the increase in rolling resistance was modest at about 2-3%, as measured by tan delta at 30°C in a dynamic mechanical analyzer as seen in Example 8 of U.S. Pat. No. 9,212,273. There remains a need for even more significant improvements in rolling resistance. Hysteresis in filled elastomers has been attributed to polymer-polymer friction, polymer-filler, and filler-filler interactions. Hysteresis in elastomeric compounds increases with filler content, but the complex nature of these interactions can often result in lower or higher hysteresis with varying degrees of filler coupling. For example, Manna et al. (J. Appl. Polym. Sci. 84: 2171-2177, 2002) demonstrated that high-temperature (180°C) molding of epoxidized natural rubber (ENR) filled with precipitated silica results in chemical bond formation between the epoxy groups of the ENR and the silanol groups of the silica. The extent of chemical bond formation is further enhanced in the presence of a silane coupling agent. Chemical bond formation between the filler and polymer should decrease polymer-filler friction, and hysteresis is expected to decrease. However, hysteresis loss was found to increase with increasing coupling agent loading and strain-dependent dynamic mechanical properties, demonstrating that the filler structure can be destroyed, which increases with increasing coupling agent loading. Sulfur-cured systems exhibit higher filler structure destruction, resulting in higher hysteresis compared to non-sulfur systems. Balancing filler structure destruction and silane coupling for hysteresis benefits is a complex endeavor that depends on the filler structure, the coupling agent that provides the crosslinking, and the ratio of these compositional elements to each other.

[0007] Essentially, tire manufacturers and their raw material suppliers seek lower rolling resistance as a way to improve fuel economy, but are constrained by a simplistic principle known as the "magic triangle of tire technology," which posits that improvements in rolling resistance must come at the expense of wet grip and durability. Compositions that can provide lower, i.e., improved, rolling resistance without sacrificing wet grip and durability are highly desirable. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] U.S. Patent No. 9,212,273 [Non-patent literature]

[0009] [Non-Patent Document 1] Manna et al., J. Appl. Polym. Sci. 84: 2171-2177, 2002 Summary of the Invention

[0010] The present invention relates to a composition comprising a plurality of discrete carbon nanotubes having selected surface functionalization that are initially well dispersed with unsaturated molecules selected from the group consisting of unsaturated monomers, unsaturated oligomers, unsaturated polymers, and any mixture thereof, wherein the surface modification, e.g., under heat treatment, in this case, causes crosslinking of the unsaturated molecules at or near the surface of the discrete carbon nanotubes. The degree of crosslinking can be controlled to some extent by the type of surface functional group, the concentration of surface functional groups on the discrete carbon nanotube surface, the heat treatment, and the type of unsaturated molecule. An additional amount or type of crosslinking agent is optionally added to further crosslink the unsaturated molecules present.

[0011] The type of unsaturated polymer may include, but is not limited to, natural or synthetic elastomers selected from the group consisting of natural rubber, polybutadiene rubber, solution-polymerized styrene-butadiene rubber, bromobutadiene rubber, styrene-butadiene rubber, acetonitrile butadiene rubber, polyisoprene rubber, styrene-isoprene rubber, ethylene propylene diene rubber, and nitrile rubber. Additional elastomer types may be blended with unsaturated polymers, such as, but not limited to, polyisobutylene, hydrogenated butadiene, and styrene-hydrogenated butadiene. Unsaturated polymers with glass transition temperatures below about 25°C are preferred.

[0012] A plurality is defined herein to mean a majority based on the number of total carbon nanotubes. The discrete carbon nanotubes are selected from the group consisting of single-walled carbon nanotubes, double-walled carbon nanotubes, multi-walled carbon nanotubes, and any mixture thereof. The carbon nanotubes may also contain other elements, such as nitrogen or boron, within the walls of the layers.

[0013] Furthermore, a majority of the discrete carbon nanotubes have a length greater than about 0.2 micrometers. In some cases, the length distribution of the discrete carbon nanotubes can be unimodal, bimodal, or multimodal.

[0014] The amount of the plurality of discrete single-walled carbon nanotubes having surface functionalization present in the unsaturated molecule ranges from about 0.1 to about 3 wt %, preferably from about 0.2 to about 2 wt %, and most preferably from about 0.2 to about 1.5 wt %, of the total weight of the carbon nanotubes and the unsaturated molecule.

[0015] The amount of the plurality of discrete double-walled carbon nanotubes having surface functionalization present in the unsaturated molecule ranges from about 0.2 to about 6 wt %, preferably from about 0.4 to about 4 wt %, and most preferably from about 0.4 to about 3 wt %, of the total weight of the carbon nanotubes and the unsaturated molecule.

[0016] The amount of the plurality of discrete multi-walled carbon nanotubes having surface functionalization present in the unsaturated molecule ranges from about 1 to about 30 wt %, preferably from about 2 to about 20 wt %, and most preferably from about 2 to about 15 wt %, of the total weight of the carbon nanotubes and the unsaturated molecule.

[0017] The surface functional groups are selected from the group of molecules capable of cross-linking unsaturated molecules, such as, but not limited to, molecules containing sulfur, or azide, or peroxide, and mixtures thereof. Preferred molecules capable of cross-linking molecules are those containing di- or tetra-sulfur moieties.

[0018] At least a portion of the surface functional groups are bonded to the discrete carbon nanotubes by hydrogen, ionic, or covalent bonds, or a mixture thereof, with covalent bonds being preferred.

[0019] The surface functional groups are present in a concentration of at least 0.05 millimoles of surface functional groups per gram of discrete carbon nanotubes, where mole is taken to mean the molecular weight of the surface functional group in grams.

[0020] The composition comprising a plurality of discrete carbon nanotubes, wherein the discrete carbon nanotubes comprise surface functionalization, can further comprise a filler selected from the group consisting of silica, carbon black, oxidized carbon black, graphene, turbostratic graphene, carbon fiber, glass fiber, halloysite, clay, and any mixture thereof. Silica is preferred.

[0021] The silica filler may be present in the range of about 20 to about 55 weight percent of the total composition. The silica is preferably treated with a silane coupling agent to improve bonding to the elastomeric medium.

[0022] The modulus of the at least partially crosslinked composition having a plurality of discrete carbon nanotubes and a filler can be controlled by varying the ratio of the plurality of discrete carbon nanotubes to the filler, for example, the modulus can be maintained by gradually removing the amount of silica present as the amount of the plurality of discrete carbon nanotubes increases.

[0023] A plurality of discrete carbon nanotubes having surface functional groups can be prepared by first functionalizing a bundle of carbon nanotubes and then using high-energy mixing conditions to create a plurality of discrete carbon nanotubes. Alternatively, discrete carbon nanotubes can be created first and then their surfaces functionalized. In yet another method, discrete carbon nanotubes can be surface functionalized in the presence of unsaturated molecules, as long as the temperature of mixing does not cause the unsaturated molecules to crosslink upon surface functionalization.

[0024] A convenient method for adding surface functionalization to carbon nanotubes is to oxidize the carbon nanotube surface and then attach a surface functionalization capable of cross-linking unsaturated molecules. A preferred method is to oxidize a plurality of discrete carbon nanotubes and then use silane chemistry to react with the hydroxyl groups present on the oxidized carbon nanotube surface. Silanes containing disulfide or tetrasulfide moieties are most preferred.

[0025] The composition comprising a plurality of discrete carbon nanotubes, wherein the discrete carbon nanotubes comprise surface functionalization, can further comprise an additive selected from the group consisting of a crosslinker, a plasticizer, a processing oil, an epoxide, an antiozonant, an antioxidant, and mixtures thereof.

[0026] The unexpected improvement in the performance of elastomer compounds having a plurality of discrete carbon nanotubes, silica, and / or carbon black with selected surface modifications results in a highly desirable combination of improved wear resistance while simultaneously providing reduced hysteresis effects. The combined properties of improved wear resistance and reduced hysteresis effects are highly desirable features for fuel-efficient, longer wear life tire compounds and other applications, such as, but not limited to, conveyor belts in mining operations. [Brief explanation of the drawings]

[0027] [Figure 1] FIG. 1 shows a stylized depiction of each coupling step in Example 1. [Figure 2] Figure 1 shows plots of tan δ at 60 °C from DMA curves of the samples tested, demonstrating a decrease in tan δ values ​​at all strains when silane-functionalized CNTs are coupled with polymer compared to the control (w / and w / o Si69) and oxidized but not crosslinked CNTs. [Figure 3]FIG. 1 shows summarized material properties of Example 3 elastomer composite for EV tire tread. [Figure 4] FIG. 1 shows the analytical levels of submicron particle generation during cut and tip abrasion. [Figure 5] FIG. 1 shows the analytical levels of submicron particle generation during cut and tip abrasion. DETAILED DESCRIPTION OF THE INVENTION

[0028] In the following description, specific details such as specific quantities, sizes, etc. are set forth to provide a thorough understanding of the present embodiments disclosed herein. However, it will be apparent to those skilled in the art that the present disclosure may be practiced without such specific details. In many cases, details regarding such considerations and the like are omitted because they are not necessary for a complete understanding of the present disclosure and are within the skill of those skilled in the relevant art.

[0029] While most of the terms used herein are recognizable to those skilled in the art, it should be understood that, unless explicitly defined, terms should be interpreted as having the meaning currently accepted by those skilled in the art. Where a term's construction renders it meaningless or essentially meaningless, the definition should be taken from Webster's Dictionary, 3rd Edition, 2009. Definitions and / or interpretations should not be incorporated from other patent applications, patents, or publications, whether related or not. As those skilled in the nanotube art will appreciate, since at least 2010, "plurality" has been used in the art to mean more than one. That is, a plurality of discrete carbon nanotubes means that there are more discrete nanotubes than would be present, for example, in a representative sample, aggregated as bundles or ropes. A plurality of discrete oxidized carbon nanotubes can be those in which the amount of oxidized discrete carbon nanotubes is greater than about 50% based on the total number of all carbon nanotubes present.

[0030] The surface-functionalized carbon nanotubes of the present invention generally refer to chemical modification of the surface of carbon nanotubes. Such modifications may include the nanotube ends, the interior and / or exterior sidewalls, or both. Chemical modifications may include, but are not limited to, covalent bonding, ionic bonding, chemisorption, intercalation, surfactant interactions, polymer wrapping, scission, solvation, and combinations thereof. In some embodiments, carbon nanotubes may be functionalized before, during, or after being singulated or exfoliated. The surface functionalization of the present invention is selected to enable crosslinking of unsaturated molecules. Unsaturated molecules are considered to be molecules containing carbon-carbon double bonds, carbon-carbon triple bonds, and carbon-nitrogen triple bonds.

[0031] Any of the embodiments disclosed herein using discrete carbon nanotubes can also be modified within the spirit and scope of the present disclosure to replace other layered nanostructures, including, for example, inorganic or mineral nanotubes. Inorganic or mineral nanotubes include, for example, silicon nanotubes, boron nitride nanotubes, and carbon nanotubes with heteroatom substitution within the nanotube structure. The nanotubes can contain or be associated with, for example, organic or inorganic elements such as carbon, silicon, boron, and nitrogen. Association can occur inside or outside the inorganic or mineral nanotube via van der Waals, ionic, or covalent bonding to the nanotube surface.

[0032] As produced, carbon nanotubes can be obtained in the form of bundles or entangled aggregates from different sources, e.g., CNano Technology, Nanocyl, Arkema, OcSiAl, and Kumho Petrochemical. Acid solutions, preferably nitric acid solutions with concentrations greater than about 60% by weight, more preferably greater than 65% by weight, can be used to reduce undesirable catalyst residues, typically containing elements such as, but not limited to, iron, aluminum, or cobalt, as well as to oxidize the surface of the carbon nanotubes. Acids or mixed acid systems (e.g., nitric acid and sulfuric acid), such as those disclosed in U.S. Pat. No. 9,212,273, the disclosure of which is incorporated herein by reference, can also be used to produce discrete, oxidized carbon nanotubes from as-produced bundled, or entangled, or rope-like carbon nanotubes.

[0033] As-produced carbon nanotubes using metal catalysts, such as iron, aluminum, or cobalt, can retain significant amounts of catalyst associated or entrapped within the carbon nanotubes, up to about 15 wt. % or more. These residual metals can be detrimental in applications such as electronic devices due to enhanced corrosion or can interfere with the vulcanization process when curing elastomer composites. Furthermore, these divalent or polyvalent metal ions can associate with carboxylic acid groups present on the oxidized carbon nanotubes, potentially preventing their subsequent dispersion. Catalyst residues in as-produced carbon nanotubes can be reduced using acid or thermal means. In other embodiments, the carbon nanotubes contain residual metal concentrations of less than about 25,000 ppm, preferably less than about 5,000 ppm. Metal composition and concentration can be conveniently determined using energy-dispersive X-ray spectroscopy or thermogravimetric analysis.

[0034] Carbon nanotubes (CNTs) can be classified by the number of walls within the tube: single-walled, double-walled, and multi-walled. Each wall of a CNT can be further classified as chiral or non-chiral. Some of the carbon atoms in a CNT may be substituted with nitrogen or boron atoms. Some of the walls may contain Stones-Wales defects, defined as a seven-membered ring-five-membered ring pair. CNTs are currently produced in large quantities using chemical vapor deposition reactors, producing aggregated bundles or ropes of carbon nanotubes. However, their commercial applications are very limited due to their poor performance as reinforcing fillers in the aggregated state. The use of CNTs as reinforcing or fillers in polymer composites or as thermally or electrically conductive fillers is an area where CNTs are predicted to have significant utility if they could be prepared as discrete carbon nanotubes. However, the utilization of CNTs in these applications has been hindered by the general inability to reliably produce discrete or individualized CNTs and uniformly disperse them in a medium.

[0035] In elastomer compositions containing carbon nanotubes and optionally additional fillers, a range of desired performance enhancements, such as abrasion resistance and lower hysteresis, require a variety of materials and complex structures. Without being bound by theory, it is believed desirable to have several structural parameters: a plurality of discrete carbon nanotubes exceeding a specific aspect ratio (length-to-diameter ratio) of at least about 30; a plurality of discrete carbon nanotubes dispersed within the elastomer medium without being bundled or modified into aggregates; a plurality of discrete carbon nanotubes not bonded to fillers such as silica or carbon black; a plurality of discrete carbon nanotubes strongly bonded to the elastomer; and a layer of elastomer adjacent to the surface of the discrete carbon nanotubes that is sufficiently crosslinked.

[0036] In the present invention, we have discovered that the desired structural parameters for much improved properties in elastomer compositions can be achieved by selecting carbon nanotube surface functional groups that can enable dispersion of discrete carbon nanotubes among uncrosslinked unsaturated molecules without crosslinking the unsaturated molecules, and then using the surface functional groups to promote crosslinking of the unsaturated molecules after dispersion of the discrete carbon nanotubes. Furthermore, by employing discrete carbon nanotubes that are crosslinked into the elastomeric medium and have a fully crosslinked layer of the medium adjacent to the surface of the discrete carbon nanotubes, the modulus of the elastomeric medium can be much increased, resulting in less filler being required to maintain the modulus values ​​of the elastomer and filler without the discrete carbon nanotubes. This reduction in filler content further reduces the hysteresis of the composite due to a lower overall amount of polymer-filler and filler-filler interactions in the elastomer.

[0037] Another additional feature of the present invention, although not limited to this feature, is that the plurality of discrete carbon nanotubes having surface functional groups, when activated and crosslinked, provide an interconnected structure on a scale much larger than the crosslinked mesh size of the crosslinked elastomer or polymer. The average mesh size of the interconnected structure is related to the average length of the plurality of discrete carbon nanotubes and is inversely proportional to the amount of the plurality of discrete carbon nanotubes present in the elastomer composition. Further modifications to the properties of the interconnected structure can be made, for example, but not limited to, by selecting the plurality of discrete carbon nanotubes with different lengths, aspect ratios, carbon nanotube types, amount of surface functionalization, type of surface functionalization, and mixtures thereof. The interconnected structure on a scale larger than the crosslinked mesh size of the elastomer allows the composite to better limit crack propagation under mechanical strain, resulting in improved durability of the elastomer composite.

[0038] To provide the performance advantages of obtaining dispersed, discrete carbon nanotubes and being able to crosslink with unsaturated molecules, bis(3-triethoxysilylpropyl)tetrasulfide (Si69 Evonic), bis(3-triethoxysilylpropyl)disulfide (Si75 Evonic), and 3-thiocyanatopropyltriethoxysilane (Si264, Evonic) are preferred for coupling with the hydroxyl and carboxylic acid groups of oxidized carbon nanotubes. Alternatively, γ-tert-butylperoxypropyltrimethoxysilane or azidosulfonylsilane can be employed.

[0039] EV tire treads wear at a much faster rate (30%+) than their ICE counterparts. This is primarily due to heavier vehicle weights, near-instantaneous torque, and urban driving. The present invention addresses this market need and improves tire tread life. Passenger tires are typically manufactured with tread compounds that utilize a blend of solution-polymerized styrene-butadiene rubber (SSBR) and polybutadiene rubber (BR) with silica bonded by silane. Small amounts of carbon black are usually added to impart a black color and static dissipative properties. This tread polymer composite is preferred for improved fuel economy and wet grip and is typically referred to as a "green" compound, referring to the superior fuel economy and lower carbon black content than typical tires. A typical "green" tire tread compound can be found in Roben et al.'s (2017) published paper, while Evonik provides several graphs on its website illustrating the differences between a conventional carbon black-filled tire tread and a "green" tire tread with a high silica loading. The formulations provided by Roben et al. (2017) are used as a basis by the inventors in the following examples to demonstrate existing technology and advantages over prior art.

[0040] An embodiment of the present invention.

[0041] Embodiment 1 is a composition comprising a plurality of discrete carbon nanotubes, at least a portion of the plurality of discrete carbon nanotubes comprising surface functionalization crosslinking molecules selected from the group of unsaturated monomers, unsaturated oligomers, unsaturated polymers, and any mixture thereof.

[0042] Embodiment 2. The composition of embodiment 1, wherein the composition further comprises an unsaturated natural or synthetic elastomer.

[0043] Embodiment 3. The composition of embodiment 2, wherein the natural or synthetic elastomer is selected from the group consisting of natural rubber, polybutadiene, solution polymerized styrene-butadiene rubber, bromobutadiene, styrene butadiene rubber, acetonitrile butadiene, polyisoprene, styrene-isoprene rubber, ethylene propylene diene rubber, nitrile rubber, and any mixture thereof.

[0044] Embodiment 4. The composition of embodiment 3, wherein the composition further comprises an additional elastomer selected from the group consisting of polyisobutylene, ethylene propylene, hydrogenated butadiene, styrene-hydrogenated butadiene, and any mixture thereof.

[0045] Embodiment 5. The composition of embodiment 1, wherein the carbon nanotubes in the plurality of discrete carbon nanotubes are selected from the group consisting of single-walled carbon nanotubes, double-walled carbon nanotubes, multi-walled carbon nanotubes, and any mixture thereof.

[0046] Embodiment 6. The composition of embodiment 1, wherein a majority of the plurality of discrete carbon nanotubes have a length greater than about 0.2 micrometers.

[0047] Embodiment 7. The composition of embodiment 1, wherein the plurality of discrete carbon nanotubes comprises at least bimodality in length of the plurality of discrete carbon nanotubes.

[0048] Embodiment 8. The composition of embodiment 1, wherein at least a portion of the surface functionalization is covalently attached to at least a portion of the plurality of discrete carbon nanotubes.

[0049] Embodiment 9. The composition of embodiment 1, wherein the surface functionalization is selected from the group of molecules that crosslink unsaturated molecules containing sulfur, disulfide, tetrasulfide, azide, peroxide moieties, or any mixture thereof.

[0050] Embodiment 10. The composition of embodiment 1, wherein the surface functionalization is present in a concentration of at least 0.05 millimoles of surface functionalization per gram of discrete carbon nanotubes in the composition.

[0051] Embodiment 11. The composition of embodiment 1, wherein the unsaturated polymer is selected from the group of unsaturated polymers having a glass transition temperature of less than about 25° C.

[0052] Embodiment 12. The composition of embodiment 1, wherein the composition further comprises a filler.

[0053] Embodiment 13. The composition of embodiment 12, wherein the filler is selected from the group consisting of silica, carbon black, oxidized carbon black, graphene, turbostratic graphene, carbon fiber, glass fiber, halloysite, clay, and any mixture thereof.

[0054] Embodiment 14. The composition of embodiment 1, wherein the surface functionalization is selected such that the discrete carbon nanotubes are substantially dispersible in an unsaturated monomer, an unsaturated oligomer, an unsaturated polymer, or a mixture thereof.

[0055] Embodiment 15. The composition of embodiment 1, wherein at least a portion of the plurality of discrete carbon nanotubes and the unsaturated molecule are at least partially crosslinked.

[0056] Embodiment 16. The composition of embodiment 1, wherein at least a portion of the plurality of discrete carbon nanotubes are at least partially crosslinked to other discrete carbon nanotubes.

[0057] Embodiment 17. The composition of embodiment 2, wherein at least a portion of the amount of discrete single-walled carbon nanotubes present in the unsaturated polymer is at least about 0.1 to about 3 weight percent of the total weight of the unsaturated polymer and the discrete single-walled carbon nanotubes.

[0058] Embodiment 18. The composition of embodiment 2, wherein the amount of discrete multi-walled carbon nanotubes present in the unsaturated polymer is at least about 1 to about 30 weight percent of the total weight of the unsaturated polymer and the discrete multi-walled carbon nanotubes.

[0059] Embodiment 19. The composition of embodiment 2, further comprising silica, wherein the silica comprises from about 3 to about 20 times the total amount of discrete multi-walled carbon nanotubes in the composition by weight.

[0060] Embodiment 20. The composition of embodiment 19, wherein the composition has a hysteresis value that is less than about 95% of the hysteresis value of a comparable composition lacking surface functionalization.

[0061] Embodiment 21. The composition of embodiment 19, wherein the composition has a particle weight loss value in a DIN abrasion test that is less than about 95% of that of a comparable composition lacking surface functionalization.

[0062] Embodiment 22. The composition of embodiment 19, wherein the composition has an average size of lost particles in a DIN abrasion test that is more than about 1.05 times the average size of lost particles of an equivalent composition lacking surface functionalization.

[0063] Embodiment 23. The composition of embodiment 2, further comprising an additive selected from the group consisting of plasticizers, processing oils, epoxides, antiozonants, antioxidants, and any mixture thereof.

[0064] Embodiment 24. The composition of embodiment 8, wherein at least a portion of the surface functionalization is covalently bonded to at least a portion of the plurality of discrete carbon nanotubes using a silane.

[0065] Embodiment 25. A method for preparing the composition of embodiment 24, comprising: a) first oxidizing a plurality of discrete carbon nanotubes using an oxidizing reagent; b) washing the plurality of discrete carbon nanotubes to remove excess oxidizing reagent; c) drying the oxidized plurality of discrete carbon nanotubes; d) redispersing the plurality of discrete carbon nanotubes in an aprotic solvent that dissolves functional silane molecules attached to the surface of the plurality of discrete carbon nanotubes; e) reacting the functional silane molecules with the oxidized carbon nanotubes; and f) removing the aprotic solvent.

[0066] Embodiment 26. A method for preparing the composition of embodiment 24 in the presence of unsaturated molecules, comprising: a) first oxidizing a plurality of discrete carbon nanotubes using an oxidizing reagent; b) washing the plurality of discrete carbon nanotubes to remove excess oxidizing reagent; c) drying the oxidized plurality of discrete carbon nanotubes; d) adding the dried plurality of oxidized discrete carbon nanotubes to unsaturated molecules; e) adding functional silane molecules to attach to the surfaces of the plurality of discrete oxidized carbon nanotubes; and f) selecting mixing and temperature conditions to obtain a dispersion of a plurality of discrete oxidized carbon nanotubes having surface functional groups attached in the presence of the unsaturated molecules without crosslinking the unsaturated molecules.

[0067] Embodiment 27. The composition of embodiment 1 in the form of a molded or fabricated article.

[0068] Embodiment 28. The composition of embodiment 27, wherein the article is a tire, a hose, a belt, a seal, or a truck.

[0069] The following examples are intended to illustrate certain embodiments of the present application and are not intended to be limiting in any way.

[0070] Acid oxidation of carbon nanotubes has been previously described in U.S. Patent Nos. 8,475,961, 8,993,161, and 9,065,132, the disclosures of each of which are incorporated herein by reference. Oxidation of carbon nanotubes (CNTs) can be carried out by suspending the CNTs in acid at a concentration of 2-4 wt. % CNTs in acid at a temperature of approximately 80-90°C. After oxidation, the acid is removed by solid / fluid separation, e.g., filtration. The amount of acid removed by weight from the acid / CNT mixture ranges from 60%-70% by vacuum pump-assisted filtration and 80-90% by centrifugation. The oxidized CNTs are then washed with an aqueous medium, e.g., water, preferably deionized water, to a pH of approximately 3-4 to remove residual acid.

[0071] In an alternative process, the concentration of carbon nanotubes in the reaction process is increased. For example, the use of a high CNT concentration (65% concentration) mixture of nitric acid in the range of 20-50% by weight of CNTs in nitric acid results in an unexpectedly flowable powder consistency. Once the oxidation process is complete, the acid is not removed, but is diluted with water and then filtered during the washing process. This eliminates the acid filtration step to recover the acid. The amount of acid wasted in the washing process is significantly less than processes utilizing a much lower concentration of CNTs in the reaction.

[0072] The oxidized carbon nanotubes are then suspended in water at a concentration of 0.5% to 4% by weight, preferably 1.5% by weight. The solution has a viscosity of 10 to 10 Joules / m 3The oxidized carbon nanotubes are subjected to the intense disruptive forces generated by shear (turbulence) and / or cavitation using process equipment capable of generating high energy densities. Apparatuses contemplated herein include, but are not limited to, ultrasonic devices, cavitators, mechanical homogenizers, pressure homogenizers, and microfluidizers. After shear and / or cavitation treatment, the oxidized carbon nanotubes become oxidized discrete carbon nanotubes. Typically, based on a given starting amount of as-received and as-produced entangled carbon nanotubes, a plurality of discrete oxidized carbon nanotubes emerges from this process, preferably at least about 60%, more preferably at least about 75%, most preferably at least about 95%, and as high as 100%, with a minority of the layers, usually the majority of the layers, remaining entangled or not fully individualized.

[0073] In various embodiments, a plurality of carbon nanotubes are disclosed, including single-walled, double-walled, or multi-walled carbon nanotube fibers having an aspect ratio of about 10 to about 5000, preferably about 40 to about 2000, and an overall oxidation level of about 0.1% to about 15% by weight, preferably about 0.2% to about 10% by weight, more preferably about 0.5% to about 5% by weight, and more preferably about 1% to about 3% by weight. The oxidation level is defined as the amount of oxygenated species covalently attached to the carbon nanotube divided by the mass of the total weight of the oxygenated nanotubes. A thermogravimetric method for determining the weight percent of oxygenated species on the carbon nanotube involves taking about 7 to 15 mg of dried, oxidized carbon nanotubes and heating them in a dry nitrogen atmosphere from 100°C to 700°C at 5°C / min. The percent weight loss from 200°C to 600°C is considered the percent weight loss of the oxygenated species. Oxygenated species can be identified by Fourier transform infrared spectroscopy, FTIR, particularly at 1730-1680 cm -1 It can also be used in the wavelength range of The carbon nanotubes can have oxidation species, including carboxylic acid or derivative carbonyl-containing species, and are essentially discrete, individual nanotubes, not entangled in clumps. Typically, the amount of discrete carbon nanotubes after completing the oxidation and shearing process is a majority (i.e., multiple), possibly as much as 70, 80, 90, or even 99% of the discrete carbon nanotubes, with the remaining layers still partially entangled in some form. Complete conversion (i.e., 100%) of the nanotubes to discrete, individualized layers is most preferred. The derivative carbonyl species can include phenols, ketones, quaternary amines, amides, esters, acyl halides, carboxylic acid groups, hydroxyl groups, monovalent metal salts, and the like, and can vary between the inner and outer layers. For example, an acid can be used to oxidize the outer surface of the layer, followed by water washing and induced shearing, thereby disrupting and separating the layers. If desired, the resulting discrete layers can be substantially free of oxidation of the inner wall, preferably less than about 1 / 2%, more preferably zero. The carbon nanotubes can be further oxidized with a different oxidizing agent, or with the same oxidizing agent used on the outer wall surface of the layer at different concentrations, resulting in different amounts and / or types of interior and surface oxidation.

[0074] In some embodiments, the discrete carbon nanotubes can have carboxylic acid groups (COOH) of about 0.01 moles / g to about 0.4 mmoles / g of layer. The concentration of hydroxyl groups (OH) can be about 0.01 mmoles / g to about 0.4 mmoles / g, and the concentration of lactones can be about 0.05 mmoles / g to about 0.3 mmoles / g. The total surface area can be about 150 m for discrete multi-walled carbon nanotubes. 2 / g to approximately 2000m for discrete single-walled carbon nanotubes. 2 The density of the discrete layers can be from about 1.5 to about 1.9 g / cm 2 It could be.

[0075] One common method for attaching surface functional groups to carbon nanotubes is to dry a plurality of discrete oxidized carbon nanotubes at 110°C, then disperse them in 1 wt% dry toluene, followed by the addition of a silane containing a reactive cross-linking moiety. The mixture is then heated to 90°C with stirring for one hour, after which the carbon nanotubes are filtered and washed with toluene to remove unreacted silane containing a reactive cross-linking moiety. A catalytic amount of glacial acetic acid can be added to promote the reaction. The plurality of discrete carbon nanotubes with surface functional groups are then dried in a vacuum at 60°C.

[0076] Another common method is to add a plurality of discrete oxidized carbon nanotubes to a mixture of unsaturated molecules, preferably a mixture of styrene-butadiene and polybutadiene, and mix in a mixer, such as a Banbury mixer, to obtain a dispersion of a plurality of discrete oxidized carbon nanotubes, while maintaining the temperature of the mixture below the temperature required for the functional groups to crosslink the unsaturated molecules. By this method, a masterbatch can be prepared, which can then be diluted or undiluted as desired.

[0077] The composition may further comprise a plasticizer selected from the group consisting of dicarboxylic / tricarboxylic acid esters, trimellitates, adipates, sebacates, maleates, glycols and polyethers, polymeric plasticizers, bio-based plasticizers, and mixtures thereof. The term "plasticizer" includes both synthetic and natural waxes, as well as mixtures thereof. An example of a natural wax is carnauba wax. An example of a synthetic wax (sometimes called a decomposed wax) is a very low molecular weight polyethylene polymer, trademarked ENGAGE™, prepared by The Dow Chemical Company. Ultra-low molecular weight polyethylene waxes have a molecular weight of 300 to 10,000, preferably 2,000 to 4,000. The compositions disclosed herein may comprise at least one of these waxes. The composition may comprise a plasticizer comprising a process oil selected from the group consisting of naphthenic oil, paraffin oil, paraben oil, aromatic oil, vegetable oil, seed oil, and mixtures thereof.

[0078] The composition may also include antioxidants and antiozonants.

[0079] All test plaques with dimensions of 150 mm x 150 mm x 2 mm are pressed using a PHI hydraulic compression press at 150°C and 45 tons of pressure for t90+2 minutes.

[0080] Tensile testing is performed according to ASTM D412-16 using an Instron 3360. The die used to prepare the tensile specimens is DIN-53504-S2. Five specimens are prepared from each formulation to be tested. When applicable, tear testing is performed using the Die C test according to ASTM D 624.

[0081] Dynamic properties of the cured slab strips are measured using a TA Instruments DMA Q800. Strain sweep tests are performed in tension mode (0.01 N preload and 1 Hz frequency) at three different temperatures: 0°C, 60°C, and 100°C, from 0.1% to 30% strain. The ratio of loss modulus to storage modulus, or tan δ, is measured at 10% strain for each of these temperatures. tan δ at 0°C relates to wet grip (WG), at 60°C to rolling resistance (RR), and at 100°C to heat buildup (HBU) of the elastomeric compound. For an improved tread compound compared to the control, the tan δ value at 0°C should be higher, and the values ​​at 60°C and 100°C should be lower. Higher tan δ values ​​at 0°C correlate to improved rubber sliding properties at speeds across micrometer-roughened road surfaces, while lower tan δ values ​​at 60°C and 100°C correlate to lower dynamic hysteresis, i.e., less energy loss during movement, resulting in improved rolling resistance and heat buildup characteristics, respectively.

[0082] The cut and chip resistance of cured compounds is measured using a Montech CC3000. The compounds are cured into wheels measuring 51 mm diameter x 13 mm thick with a 13 mm diameter center hole, using a time of t90 + 5 minutes for each sample. The specimens are rolled at 1080 RPM, and the impact blade frequency is set at 30 Hz. The test time is 5 minutes. Mass loss and diameter loss measurements are taken after the test time. Cut and chip resistance is calculated as the reciprocal of the volume loss calculated from the theoretical density and the resulting mass loss. The cut and chip test is used as the preferred method for testing wear-resistant tire tread compounds for off-road tires and truck and bus tires.

[0083] The abrasion resistance of cured compounds is determined using a typical DIN abrasion tester according to DIN 53516 Method B. Compounds are cured onto wheels measuring 51 mm diameter x 13 mm thick with a 13 mm diameter central hole, using a time of t90 + 5 minutes for each sample. DIN abrasion test specimens measuring 16 mm diameter x 13 mm thick are then cut from the wheels using a rotating sharp die. The samples are tested according to DIN 53516 Method B, and the reference specimens of ISO 4649 B.2 are used to determine the abrasion resistance of the sheets and the associated DIN resistance index reference values. All values ​​are calculated according to DIN 53516 Method B.

[0084] Transmission electron microscopy (TEM) images are taken using a JEOL STEM. Samples are prepared using a Leica cryomicrotome, with the samples taken below the glass transition temperature to facilitate sectioning to a thickness of approximately 40 nm.

[0085] The description provided herein is for the purpose of teaching those skilled in the art how to carry out the present application and is not intended to describe in detail all obvious modifications and variations thereof that would become apparent to those skilled in the art upon reading the description. However, all such obvious modifications and variations are intended to be included within the scope of the present application as defined by the appended claims. The claims are intended to cover the claimed elements and steps in any order effective to fulfill the purposes intended therein, unless the context specifically indicates to the contrary.

[0086] Example 1 Oxidized discrete multiwalled carbon nanotubes, such as those disclosed in the examples of U.S. Pat. No. 10,414,656 (Swogger et al.), are further functionalized with an organosilane manufactured by Evonik under the trade name Si69®, which has tetrasulfide end groups and is covalently bonded to the discrete MWCNTs. The covalent bonding of the organosilane to the -OH and -COOH groups of the oxidized CNTs occurs at temperatures above 100°C, most effectively above 110°C in the presence of moisture. This bonding can occur in air, under an inert gas blanket, in a solvent, or in a polymer solution, wet or dry. Once bonded, the sulfur-functionalized discrete MWCNTs are then bonded to the sulfur end groups (S x The rubber is crosslinked to the polymer matrix, in this example SSBR, via a crosslinking agent (shown as 'C'). This crosslinking occurs at temperatures above 100°C, most effectively above 120°C, and can occur during the mixing or "cure" of the rubber composite. For ease of understanding, the methodology of the covalent bonds and resulting chemical structures for each simplified step is stylized in Figure 1.

[0087] Example 2 Example 2 illustrates the novelty and improvement of the present invention. Discrete multi-walled carbon nanotubes sulfur-bonded via organosilane moieties, as described in Example 1 above, are utilized in a simplified tire tread formulation, and the resulting material properties are compared to a formulation without carbon nanotubes or organosilane, a formulation without nanotubes but with organosilane, and a formulation with prior art nanotubes but without organosilane (oxidized but not covalently bonded to anything). The discrete carbon nanotubes have the trade name Molecular Rebar (MR), which is frequently referenced throughout the following examples. A masterbatch (MB) of 10 wt% sulfur silane-functionalized MR and SSBR was prepared using a HAAKE Rheomix in a batch size of approximately 55 g before thorough mixing. The MB was then reduced to a simplified "green" tire tread formulation (without other fillers to avoid excessive variability) to approximately 4.7 wt% and 7.2 wt% MR, respectively, in the final formulation. A pure organosilane (Si69®) was also added to the base polymer formulation to identify and prove that the effect of MR + sulfur through Si69 is truly a combined effect, rather than the individual, specific effects of -OH / -COOH (oxidized) MR or Si69. The oxidized MR, in this case discrete multiwalled carbon nanotubes, is an example of prior art, as disclosed in U.S. Pat. No. 10,414,656 (Swogger et al.), and does not have covalently bonded sulfur groups capable of crosslinking to the surrounding rubber matrix. The two different loadings of CNTs in this example, with and without crosslinkable functionalization, show reproducible results. This example provides evidence that sulfur-linked and cross-linked discrete CNTs (Silane-MR, MR w / Si69, or sulfur-Silane-MR) are substantially different from and offer significant advantages over the prior art of oxidized, non-cross-linked discrete MWCNTs. The formulations are shown in Table 1 and the results are presented in Figure 2, with component amounts shown as parts per hundred parts PHR or resin.

[0088] [Table 1]

[0089] Akrochem's antioxidant DQ is a polymerized 2,4-trimethyl-1,2-dihydroquinoline antioxidant, TMQ is trimethylquinolium hydroxide, an antioxidant, 6PPD N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine is an antioxidant, DPG is 1,3-diphenylguanidine, an accelerator, and TBBS is Nt-butyl-2-benzothiazole sulfenamide, an accelerator.

[0090] The samples were tensile tested. It was observed that the addition of Si69 did not significantly change the tensile properties of the baseline polymer alone. The use of oxidized MR alone (without silane functionalization) increased both tensile strength and modulus, demonstrating much improved reinforcement. When silane was attached to the MR and the resulting sulfur groups were subsequently covalently bonded to the polymer during crosslinking, the tensile strength and modulus were further improved from the same loading of CNTs without Si69. The combined effect of MR attached with sulfur groups via Si69 was superior to the effect of oxidized MR by itself and the (negligible) effect of Si69 on the baseline polymer system (without CNTs) in both tested formulations in Example 2.

[0091] The value of tan δ at 60 °C, a common laboratory measurement performed for DMA, which is the ratio of loss modulus to storage modulus to correlate the rolling resistance of tire elastomer composites, is reduced (improved) when organosilanes are covalently bonded to the surface of multiple discrete carbon nanotubes. The hysteresis curves in Figure 2 demonstrate the improvement in both filler-filler interaction (low strain) and filler-polymer interaction (high strain), indicating superior covalent bonding of the filler (CNT / MR) to the polymer matrix (SSBR).

[0092] The summarized results of Example 2 are shown in Table 2, which demonstrates that a plurality of discrete carbon nanotubes covalently bonded to a rubber matrix via organosilane-sulfur groups improves both the modulus and rolling resistance index of the composite over compositions containing no carbon nanotubes or separate, oxidized, but not covalently bonded, carbon nanotubes.

[0093] [Table 2]

[0094] Example 3 A masterbatch of organosilane-linked Molecular Rebar (discrete multi-walled carbon nanotubes) is produced as in Example 2 above, on a larger scale of several kilograms. The masterbatch is then mixed in a typical three-pass mix system using a 1.6 L Banbury with other typical "green" tire tread compound ingredients, as shown in the formulations in Table 3. The control compound is a current state-of-the-art EV tire tread compound, and the use of covalently linked CNTs in an optimal loading mode is demonstrated in two different formulations.

[0095] [Table 3]

[0096] Reducing the amount of oil and silica and using Molecular Rebar (discrete CNTs) covalently bonded via organosilane resulted in significant property improvements. The compositional properties demonstrated below have optimal properties for two different use cases in the tire industry. 20% oil, 5% MR, and 60% silica were a good combination of approximately 26% improved DIN abrasion resistance and approximately 20% improved rolling resistance, but at the expense of some wet grip properties. On the other hand, the 15.5% oil, 13% MR, and 45% silica compound had significantly improved DIN abrasion resistance (+37%), far superior to that produced using MR without crosslinkable functionalization, with no change in rolling resistance or heat buildup. Summary results for the use of the novel crosslinkable MR are shown in Figure 3.

[0097] When used in place of silica with some oil concentration adjustment, functionalized MR (with silane linkages) provides the necessary property enhancements, such as improved DIN abrasion resistance and reduced rolling resistance, for "green" tread compounds for electric vehicles. These improvements were made and measured using commercially available techniques, demonstrating the commercial potential of this functionalized Molecular Rebar product. The use of dispersed, covalently bonded MR with significantly reduced amounts of silica can simultaneously improve the life and rolling resistance of tire tread rubber composites.

[0098] Example 4 (reduced submicron particle generation): Two similar rubber compounds are manufactured using standard industry techniques—primarily a 1.6 L tangential mixer (Banbury BR Lab Mixer) with standard three-pass mixing, followed by sheeting on an 18-inch, two-roll mill (Farrel) per the formulation in Table 1. The compounds are mixed in an identical manner. In the first pass, the elastomer, the corresponding sample Silane-MR masterbatch, is added first, followed by carbon black (if present), silica, silane, and finally the remaining ingredients—oil, stearic acid, 6PPD, wax, and DQ / TMQ. The material is mixed under ram pressure for approximately 4 minutes to reach 140°C before being transferred to a roll mill. The material is added again to the tangential mixer for a second pass, where it is mixed above 120°C for at least 2 minutes to "condition" the material or complete silane coupling with the silica. The material is then transferred to a roll mill. The material is then returned to the tangential mixer, and the curatives (S, DPG, ZnO, TBBS) are added after the rubber reaches a malleable temperature. The compound is mixed until 105°C or the mixing time reaches approximately 2 minutes. The material is then transferred to a two-roll mill and sheeted to a uniform thickness. All ingredients are listed as parts per hundred parts of compound (phr). The compound was selected based on its relationship to current state-of-the-art tires for electric vehicles, and the MR concentration is the same as that previously disclosed in Example 3.

[0099] [Table 4]

[0100] A Monsanto R100 single frequency oscillating die rheometer (ODR) is used to determine the rheology and cure kinetics of the samples. A precision mold: 51 mm diameter x 13 mm thick pucks with a 13 mm diameter center hole is used to prepare the pucks for cut and chip testing. The pucks are cured in a hydraulic hot press at 150 °C for 90 hours + 5 minutes using a compression mold to achieve full crosslink density without reversal. The packs are tested using a MonTech CC3000 Cut & Chip Tester, operating at 1080 RPM and 30 Hz for a 10-minute test time. A DustTrak II Aerosol Monitor 8530 is used to characterize particle production during testing. The nozzle for the DustTrak is positioned above the test sample, and a cloth filter with a measured pore size of approximately 0.6 mm is installed to reduce entrapment of larger particles and reduce the risk of failure of the 1 μm impactor filter's efficiency.

[0101] Five background samples are tested throughout the day, interspersed throughout the sample test cycle, to obtain an average background concentration of submicron particles that increases slightly over time. This results in an average background concentration of 0.0325 mg / m 3 , with a standard deviation of 0.0049 mg / m 3 The control formulation (sans Silane-MR) is tested eight times per day, with tests of the control pack interspersed with tests of two to three experimental samples. The Silane-MR samples are tested six times. This testing regimen results in an average standard deviation of approximately 15% for the control samples and less than 10% for the Silane-MR samples. The results of these tests are analyzed by averaging the concentrations at each measurement point over the 10-minute test period. The standard deviation is also calculated for each point. The overall results are shown in Figure 4.

[0102] As each sample progresses through the 10-minute test cycle, the concentration of submicron particles in the ambient environment increases, as all three averaged curves exhibit an upward linear trajectory. This observation is consistent with the hypothesis that the test chamber is not fully evacuated each time the abrasive blade contacts the test pack. Furthermore, submicron particles have some airborne residence time that is longer than the time it takes for the chamber to fully evacuate. As these events accumulate, the concentration level of submicron particles in the chamber increases. The fitted linear slope and corresponding coefficient of determination are shown in Table 5. The increase in submicron particles is also found to be linear with respect to the time tested. Because samples are tested sequentially and each sample starts with approximately the same initial concentration of submicron particles, it is assumed that the particles either 1) remain airborne for a short period of time or 2) are expelled from the test chamber during sample exchange.

[0103] [Table 5]

[0104] The control samples have significantly higher submicron particle generation than the Silane-MR samples, averaging over 33%. The reduction in overall submicron particle generation likely translates into less particle generation due to tread wear per mile driven, reducing tire-related pollution.

[0105] Example 5 (Submicron Particle Size Increase): The same method and procedure as outlined in Example 4 above, except that the formulation used with Silane-MR was different as shown in Table 6 below.

[0106] [Table 6]

[0107] The overall results for these formulations are shown in FIG.

[0108] Example 5 differs from the previous examples. The formulations of the previous examples demonstrated a reduction in overall rubber composite mass / volume loss during abrasion testing by approximately 25% while simultaneously reducing the generation of submicron particle sizes compared to the control compound without Silane-MR. The formulations of this example do not significantly reduce the overall rubber composite mass / volume loss during abrasion testing. The formulations of this example utilizing Silane-MR have approximately the same mass / volume loss during abrasion, but still generate significantly less submicron particles during the abrasion event compared to the control compound. While the same total mass / volume loss from the compound is comparable, the overall particle size distribution is skewed toward the larger end, resulting in fewer submicron particle generation and more micron-sized and larger particles. This reduces potentially harmful submicron environmental contaminants from tire tread wear, even though the total number of contaminants is the same by mass or volume.

Claims

1. A composition comprising a plurality of discrete carbon nanotubes, wherein at least a portion of the plurality of discrete carbon nanotubes is surface-functionalized to crosslink molecules selected from the group consisting of unsaturated monomers, unsaturated oligomers, unsaturated polymers, and any mixture thereof.

2. The composition according to claim 1, further comprising an unsaturated natural or synthetic elastomer.

3. The aforementioned natural or synthetic elastomer is selected from the group consisting of natural rubber, polybutadiene, solution-polymerized styrene-butadiene rubber, bromobutadiene, styrene-butadiene rubber, acetonitrile butadiene, polyisoprene, styrene-isoprene rubber, ethylene propylene diene rubber, nitrile rubber, and any mixture thereof. Preferably, the composition according to claim 2 further comprises an additional elastomer selected from the group consisting of polyisobutylene, ethylene propylene, hydrogenated butadiene, styrene-hydrogenated butadiene, and any mixture thereof.

4. The carbon nanotubes in the plurality of discrete carbon nanotubes are selected from the group consisting of single-walled carbon nanotubes, double-walled carbon nanotubes, multi-walled carbon nanotubes, and any mixture thereof, and / or Most of the plurality of discrete carbon nanotubes have a length greater than approximately 0.2 micrometers, and / or The plurality of discrete carbon nanotubes include at least bimodal length characteristics of the plurality of discrete carbon nanotubes. The composition according to claim 1.

5. The composition according to claim 1, wherein at least a portion of the surface functionalization is covalently bonded to at least a portion of the plurality of discrete carbon nanotubes.

6. The aforementioned surface functionalization, - Selected from the group of molecules that crosslink unsaturated molecules, including sulfur, disulfide, tetrasulfide, azide, peroxide moiety, or any mixture thereof, and / or - The composition contains a surface functionalization concentration of at least 0.05 mmol per gram of discrete carbon nanotubes, and / or - The discrete carbon nanotubes are selected such that they are substantially dispersible in unsaturated monomers, unsaturated oligomers, unsaturated polymers, or mixtures thereof. The composition according to claim 1.

7. The composition according to claim 1, wherein the unsaturated polymer is selected from the group of unsaturated polymers having a glass transition temperature of less than about 25°C.

8. The composition according to claim 1, wherein the composition further comprises a filler, preferably selected from the group consisting of silica, carbon black, carbon oxide black, graphene, randomly layered graphene, carbon fiber, glass fiber, halloysite, clay, and any mixture thereof.

9. - At least a portion of the plurality of discrete carbon nanotubes and the unsaturated molecules are at least partially crosslinked, and / or - The composition according to claim 1, wherein at least a portion of the plurality of discrete carbon nanotubes are at least partially crosslinked with other discrete carbon nanotubes.

10. - At least a portion of the amount of discrete single-walled carbon nanotubes present in the unsaturated polymer is at least about 0.1 to about 3% by weight of the total weight of the unsaturated polymer and discrete single-walled carbon nanotubes, and / or - The amount of discrete multilayer carbon nanotubes present in the unsaturated polymer is at least about 1 to about 30% by weight of the total weight of the unsaturated polymer and the discrete multilayer carbon nanotubes. The composition according to claim 2.

11. The composition is - Further comprising additives selected from the group consisting of plasticizers, processing oils, epoxides, ozone degradation inhibitors, antioxidants, and any mixture thereof, - Further containing silica, wherein the silica in the composition is approximately 3 to approximately 50 times the total amount of discrete multilayer carbon nanotubes by weight. The composition is - Having a hysteresis value less than approximately 95% of the hysteresis value of an equivalent composition lacking the aforementioned surface functionalization, and / or - Having a particle weight loss value in the DIN abrasion test that is less than approximately 95% of that of equivalent compositions lacking the aforementioned surface functionalization, and / or - In the DIN abrasion test, the average size of lost particles is more than approximately 1.05 times that of the equivalent composition lacking the surface functionalization, The composition according to claim 2.

12. The composition according to claim 5, wherein at least a portion of the surface functionalization is covalently bonded to at least a portion of the plurality of discrete carbon nanotubes using silane.

13. A method for preparing the composition described in Claim 12, wherein the method is: a) First, a step of oxidizing multiple discrete carbon nanotubes using an oxidizing reagent, b) A step of washing the plurality of discrete carbon nanotubes to remove excess oxidizing reagent, c) A step of drying the plurality of oxidized discrete carbon nanotubes, d) A step of redispersing the plurality of discrete carbon nanotubes in an aprotic solvent that dissolves functional silane molecules attached to the surface of the plurality of discrete carbon nanotubes, e) A step of reacting the functionalized silane molecule with the oxidized carbon nanotube, f) A method comprising the step of removing the aprotic solvent.

14. A method for preparing the composition according to claim 12 in the presence of an unsaturated molecule, a) First, a step of oxidizing multiple discrete carbon nanotubes using an oxidizing reagent, b) A step of washing the plurality of discrete carbon nanotubes to remove excess oxidizing reagent, c) A step of drying the plurality of oxidized discrete carbon nanotubes, d) A step of adding the dried plurality of oxidized discrete carbon nanotubes to an unsaturated molecule, e) A step of adding functional silane molecules to be attached to the surface of the plurality of discrete carbon oxide nanotubes, f) A method comprising the step of selecting mixing and temperature conditions to obtain a dispersion of a plurality of discrete carbon oxide nanotubes with surface functional groups attached, in the presence of unsaturated molecules without crosslinking the unsaturated molecules.

15. A composition according to claim 1 in the form of a molded or processed article, wherein the article is preferably a tire, hose, belt, seal, or truck.

Images