Method for fabricating composite matrices via incorporation of carbon nanotubes

Abstract

A method for fabricating a composite matrix through the incorporation of CNTs is disclosed. The method includes a first step of mixing components comprising CNTs and one or more inorganic surfactants at a low shear rate to form a treated mixture, a second step of mixing the treated mixture with one or more polymers to form a polymer-based mixture, and curing the polymer-based mixture to obtain a composite matrix. The effects of the individual components and additives in the first and second mixing steps are discussed for various rubber compounds.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of U.S. Provisional Patent Application No. 63 / 065,087, filed August 13, 2020. The entire disclosure of the provisional patent application is incorporated herein by reference. do. [Background technology]

[0002] background Carbon nanotubes (CNTs) resemble rolled-up graphene sheets, but are not made from them, and exhibit unique physical and chemical properties that emerge as a direct result of their structure. Consequently, this structure is due to the chiral vector that nanotubes would form if constructed from actual two-dimensional graphene sheets. The bonding arrangement of graphene, a conjugated plane of hexagonal carbon atoms, restricts nanotubes to three possible types, termed "zigzag," "armchair," or "chiral," each of which exhibits unique electrical properties. For example, armchair nanotubes are highly conductive, while zigzag and chiral nanotubes are semiconductive.

[0003] Both single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs) can be produced, the latter containing at least one, but often many, concentric SWCNTs. Synthesis conditions vary, resulting in different tube length and diameter distributions, along with the presence of carbonaceous by-products or transition metal catalyst impurities. Regardless of these variations, however, due in part to the inherent chemical properties of CNTs, scaled-up production methods yield bundles of hundreds to thousands of entangled, rather than discrete, CNTs. The inter-tube attractive forces that result in these bundles are believed to be the most significant hurdle to fully exploiting the desirable properties of CNTs when incorporating them into polymers.

[0004] As isolated entities, CNTs have primarily been the focus of academic research, but they also find utility in functional applications when incorporated into polymers to form composites. Upon incorporation, as-produced CNTs can impart some of their properties to the encapsulation matrix. This imbuement (1) disrupts the strong van der Waals forces that bind the tubes together, resulting in the CNTs being uniformly dispersed throughout the matrix; (2) Great improvements can be achieved if the attractive interactions at the CNT / matrix interface are maximized. Two important strategies have emerged to achieve these goals: covalent functionalization of the CNT surface and non-covalent functionalization of the CNT surface.

[0005] Covalent functionalization typically involves severing the conjugated system of CNTs and then adding functional groups (carboxyl, amino, or other). This functionalization can create stronger attractive interactions in composites (as well as other resident fillers), but it is expensive. Covalent functionalization is primarily sp 2 From the hybridized system, sp 3 This requires conversion to a system containing hybridized localizations, the concentration of which increases proportionally with the degree of functionalization. Furthermore, it has been reported that the harsh chemical treatments required to attach these moieties often significantly reduce the aspect ratio of the nanotubes, severely limiting their practical use as fillers in matrices. To date, few, if any, methods have been devised to carry out covalent functionalization methods on a production scale.

[0006] Noncovalent functionalization offers an alternative approach to exfoliating and incorporating CNTs into polymer matrices without sacrificing their structure or electron transport capabilities. Noncovalent approaches involve solvents, preferably surfactants, that can penetrate the gaps between bundled CNTs and ensure their solubilized colloidal stability. This mechanism of physical adsorption, rather than chemical reaction, preserves the conjugated structure of the nanotubes, facilitating a range of interactions, including but not limited to van der Waals, π-π, and CH-π.

[0007] Several noncovalent functionalization methods have been reported. Favorable interactions, mediated by the appropriate selection of solvents and surfactants, have been shown to promote the exfoliation and stability of debundled nanotubes. The effectiveness of this technique is further enhanced when the process is accompanied by a high-shear-rate mixing step; however, excessively intense shear rates (e.g., high-power jet mixing, sonication, etc.) not only reduce the nanotube aspect ratio but also introduce undesirable impurities along the nanotube sidewalls and end caps, partially negating the benefits of this method. Summary of the Invention [Means for solving the problem]

[0008] Considering the above-mentioned difficulties associated with incorporating CNTs for use in practical applications, this paper describes a new method for fabricating composite matrices, such as rubber compounds, on a production scale based on the efficient non-covalent functionalization of CNTs using various processing techniques. The method described herein provides conductive materials that retain elastomeric properties. Composite Matrix This is particularly useful for inexpensively producing [Brief explanation of the drawings]

[0009] BRIEF DESCRIPTION OF THE DRAWINGS [Figure 1] 1 is a flowchart outlining the entire fabrication process. [Figure 2]1 is a flowchart detailing a process 100 for producing a treated mixture. [Figure 3A] 1 is a list of examples of inorganic surfactants, where Me (methyl group) = CH3 and Ph (phenyl group) = C6H5. [Figure 3B] 1 is a list of examples of inorganic surfactants, where Me (methyl group) = CH3 and Ph (phenyl group) = C6H5. [Figure 3C] 1 is a list of examples of inorganic surfactants, where Me (methyl group) = CH3 and Ph (phenyl group) = C6H5. [Figure 3D] 1 is a list of examples of inorganic surfactants, where Me (methyl group) = CH3 and Ph (phenyl group) = C6H5. [Figure 3E] FIG. 1 is a general molecular diagram of a linear polysiloxane. [Figure 3F] FIG. 1 is a general molecular diagram of a branched polysiloxane. [Figure 3G] FIG. 1 is a general molecular diagram of a cyclic polysiloxane. [Figure 4] 3 is a flow chart detailing a process 300 for obtaining raw and cured composite matrices. [Figure 5] Photograph of a scanning electron microscope image showing an example of a silicone-based composite matrix containing well-dispersed individual SWCNTs. [Figure 6A] 1 is a photograph showing an example of raw, untreated CNTs. [Figure 6B] 1 is a photograph showing an example of a treated mixture after pressing. [Figure 7A] FIG. 1 is a general molecular diagram of a hydrosilylation reaction precursor having a linear organohydrogenpolysiloxane. [Figure 7B] FIG. 1 is a general molecular illustration of a hydrosilylation reaction precursor based on an inhibitor such as an acetylenic alcohol. [Figure 8] 1 is a table listing the ingredients used to produce Processed Mixture 1. [Figure 9] 1 is a table listing the ingredients used to create Processed Mixture 2. [Figure 10] 1 is a table listing ingredients used in a second mix other than the treated mix to produce the base silicone rubber. [Figure 11] 1 is a table listing ingredients used in a second mix other than the treated mix to produce the base fluorosilicone rubber. [Figure 12] 1 is a table listing ingredients used in a second mix other than the treated mix to produce the base EPDM rubber. [Figure 13] 1 is a table listing ingredients used in a second mix other than the treated mix to produce the base nitrile rubber. [Figure 14] 1 is a table listing experimental results on the electrical, physical, and rheological properties of various base rubbers and composite matrices (treated with Mix 1 or 2). [Figure 15] 1 is a table listing experimental results on the electrical, physical, and rheological properties of various base rubbers and composite matrices (treated with Mix 1 or 2). [Figure 16] 1 is a table listing experimental results on the electrical, physical, and rheological properties of various base rubbers and composite matrices (treated with Mix 1 or 2). [Figure 17] 1 is a table listing experimental results on the electrical, physical, and rheological properties of various base rubbers and composite matrices (treated with Mix 1 or 2). [Figure 18] 1 is a table listing experimental results on the electrical, physical, and rheological properties of various base rubbers and composite matrices (treated with Mix 1 or 2). [Figure 19] 1 is a table listing experimental results on the electrical, physical, and rheological properties of various base rubbers and composite matrices (treated with Mix 1 or 2). [Figure 20]1 is a table listing experimental results on the electrical, physical, and rheological properties of various base rubbers and composite matrices (treated with Mix 1 or 2). [Figure 21] 21 is a chart showing the main characteristics and trends of the characteristics based on the data compiled in FIGS. 14 to 20. [Figure 22] 21 is a chart showing the main characteristics and trends of the characteristics based on the data compiled in FIGS. 14 to 20. [Figure 23] 21 is a chart showing the main characteristics and trends of the characteristics based on the data compiled in FIGS. 14 to 20. [Figure 24] 21 is a chart showing the main characteristics and trends of the characteristics based on the data compiled in FIGS. 14 to 20. [Figure 25] 21 is a chart showing the main characteristics and trends of the characteristics based on the data compiled in FIGS. 14 to 20. [Figure 26] 21 is a chart showing the main characteristics and trends of the characteristics based on the data compiled in FIGS. 14 to 20. DETAILED DESCRIPTION OF THE INVENTION

[0010] Detailed Description This study explores the non-covalent processing of carbon nanotubes (CNTs) to produce a mixture thereof. The resulting processed mixture is then blended with a polymer to produce a composite matrix. This composite matrix can be further processed to create a finished product. The process steps are designed to achieve production-scale manufacturing of polymer-based products, such as high-performance rubber compounds. Initial processing conditions the CNT bundles to exfoliate and debundle them into mostly individual tubes. Other additives can be included in the processed mixture to create a finished product with improved electrical, thermal, mechanical, and other properties. Some examples of this implementation and application are described below. While specific values ​​are cited herein to describe various steps, experiments, and results, it should be understood that these are exemplary values, approximations, and / or values ​​within the tolerances or resolution of the equipment, as can be understood by those skilled in the art.

[0011] Figure 1 is a flowchart outlining the overall fabrication process. First, in step 100, a processed mixture is produced by dispersing CNTs in one or more inorganic surfactants, with or without additives, through non-covalent functionalization. Details of how the processed mixture is obtained in step 100 are described later with reference to Figure 2. The resulting processed mixture can then be used as is or in a pressed form. Pressing includes compaction, pelletization, and other operations to increase bulk density. A pressed form is often required for efficient transportation or shipping. Therefore, in step 200, pressing of the processed mixture can be performed if necessary. Details of the pressing operation and its effects are described later with reference to Figures 6A and 6B. In step 300, a composite matrix is ​​obtained by blending the processed mixture with components, including one or more polymers, with or without additives. Details of how the composite matrix is ​​produced in step 300 are described later with reference to Figure 4. After the composite matrix is ​​obtained, fabrication procedures for the composite matrix are often required depending on the type of finished product. Examples of fabrication procedures include molding, calendaring, and extrusion. In step 400, the preparation of a composite matrix is ​​carried out by using one or more of the preparation procedures described above. In step 500, a finished product having the required properties is thus obtained from the composite matrix. It should be noted that according to this method of preparing a composite matrix through the incorporation of CNTs, the various steps in the process shown in the flowchart do not have to be in the order shown, but can be interchanged, in a different order, or performed in parallel depending on the convenience of the operation efficiency, application, or any other scenario.

[0012] FIG. 2 is a flowchart detailing step 100 for producing a processed mixture. Steps 104-112 provide the necessary components. Step 104 provides CNTs. Typically, CNTs include single-walled carbon nanotubes (SWCNTs), double-walled carbon nanotubes (DWCNTs), multi-walled carbon nanotubes (MWCNTs), and impurities. To obtain a high-quality finished product, a batch of high-purity SWCNTs is used in this process. For example, the CNTs may comprise at least 99% single-walled carbon nanotubes (SWCNTs) in powder form. Examples include, but are not limited to, SWCNT powder, ZEONANO (registered trademark) SG101, manufactured by Zeon Nano Technology Co., Ltd., which has a carbon purity of 99% or more, an impurity concentration of less than 1%, and a high aspect ratio (average diameter of 3-5 nm and length of 100-600 μm).

[0013] Commercially available batches of pristine CNTs typically contain bundled CNTs. Therefore, the procedure used to disperse CNTs in solution has a significant impact on the final suspension properties, which in turn can lead to high performance. Composite Matrix The electrical and thermal conductivity of the CNTs are affected. As previously mentioned, several technological approaches, including covalent and noncovalent functionalization of CNTs, can be employed to prepare stable, uniform dispersions of CNTs. The noncovalent approach is employed in this process because it leaves the surface structure and electrical conductivity of the CNTs substantially intact. Specifically, through noncovalent functionalization, it is possible to exfoliate and debundle bundled CNTs without substantially sacrificing the intrinsic structure and electron transport capabilities of the individual CNTs. This is because the noncovalent approach utilizes a solvent or surfactant that can penetrate into the gaps between the bundled CNTs through a physical adsorption mechanism rather than a chemical reaction, thereby substantially preserving the intrinsic structure and electrical properties of the individual CNTs.

[0014] In step 108, one or more inorganic surfactants are applied to effect non-covalent functionalization of the CNTs. Specifically, a combination of two or more fluid polymers or a single fluid polymer can be selected to optimally promote attraction to and adsorption along the surface of the CNTs. Each of these fluid polymers can contain a linear, branched, or cyclic polysiloxane backbone and pendant or terminal substituents. These substituents can be selected to complement each other in their interaction with the CNTs. It has been reported that certain moieties interact strongly with the π-electron-rich surface of CNTs, allowing less bulky moieties to penetrate the interstices of the CNT bundles, thereby facilitating their exfoliation and debundling. Here, "moieties" refer to branches in organic or inorganic molecules extending from a carbon or siloxane backbone, including methyl groups (CH), hydroxyl groups (COH), silanol groups (SiOH), aryl groups (such as phenyl and naphthyl groups), or combinations thereof. 3A-3D provide a list of examples of inorganic surfactants where Me (methyl group) = CH3 and Ph (phenyl group) = C6H5.

[0015] As described above, this study demonstrates that one or more inorganic surfactants, such as vinyl-terminated polydimethylsiloxane, vinyl-terminated diphenylsiloxane dimethylsiloxane, silanol-terminated polydimethylsiloxane, hydride-terminated polyphenyl-(dimethylhydrosiloxy)siloxane, hydride-terminated polyphenylmethylsiloxane, hydride-terminated polyphenyl-(dimethylsiloxy)siloxane, or combinations thereof, can efficiently penetrate bundled CNTs and adsorb along the surfaces of individual CNTs. These polysiloxane-based fluid polymers exhibit viscosities measured at 25 °C ranging from 0.01 to 10 Pa-s, with the actual viscosity corresponding to the molecular weight of the polymer. In some cases, combining a low-viscosity fluid polymer (e.g., silanol-terminated) with a high-viscosity fluid polymer (e.g., phenylated) is expected to adsorb to individual CNTs more efficiently than using only low-viscosity or only high-viscosity fluid polymers. As will be discussed later, this study demonstrated that optimal results can be achieved by using a silanol-terminated fluid polymer, such as silanol-terminated polydimethylsiloxane, as a single inorganic surfactant, rather than using two or more different inorganic surfactants in combination. Because CNTs remain expensive in today's market, a low weight percent of CNTs in a mixture of CNTs and one or more inorganic surfactants is preferred. In one example, 23 weight percent CNTs and 77 weight percent silanol-terminated polydimethylsiloxane are used.

[0016] Figures 3E, 3F, and 3G show general molecular diagrams of the above surfactants, i.e., linear polysiloxane, branched polysiloxane, and cyclic polysiloxane, respectively, where a is an integer between 0 and 3, and b has a value sufficient to satisfy the above viscosity. In any of the above examples, R can generally include substituted or unsubstituted hydrocarbon groups having 1 to 12 carbon atoms, preferably 1 to 5 carbon atoms, such as alkyl groups such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, hexyl, cyclohexyl, octyl, and dodecyl, aryl groups such as phenyl and tolyl, and halogen-substituted hydrocarbon groups such as 3,3,3-trifluoropropyl. Examples of R' include alkyl, alkenyl, phenyl, hydride, and hydroxyl groups, selected to maximize the desired noncovalent interactions with the CNTs.

[0017] Depending on the properties desired for the finished product, one or more additives can be provided as components of the processed mixture in step 112 to enhance certain properties. Thus, a first mixing in step 116 can be performed to combine the CNTs with one or more inorganic surfactants, with or without one or more additives, referred to herein as first additives. Each of several possible first additives is described below.

[0018] To produce a treated mixture, one or more cure modifiers can be added as a first additive. It has been reported that untreated CNTs can interfere with common (platinum-, peroxide-, or sulfur-based) rubber cure systems. Here, "rubber cure system" refers to the chemical components included in a rubber formulation that enable the formation of a thermoset after a curing procedure, e.g., the application of heat and / or pressure. This interference is not only seen in the finished product, but also in the cure profile. This is particularly evident in certain cured silicone rubbers that undergo hydrosilylation curing reactions, such as platinum-cured silicone rubbers with silicon hydride crosslinkers. Further details regarding optimizing the hydrosilylation cure reaction of silicone rubbers are discussed later in this document, in this case improving CNT encapsulation within the composite matrix.

[0019] The addition of one or more cure modifiers will depend on the type of finished product and the desired properties. Furthermore, they can be added later in the process, for example, just before the curing process, if desired. However, it should be noted that incorporating the required cure modifiers in the processed mixture from the beginning consolidates the preparation steps, which not only improves CNT encapsulation in the composite matrix, but also makes the overall process more efficient.

[0020] Carbon black can be added as the first additive to produce the processed mixture. Carbon black is a material produced by the incomplete combustion of petroleum products and has a form of paracrystalline carbon. It has traditionally been used as a reinforcing filler in tires and other rubber products. Examples of high-purity conductive grade carbon black include the acetylene-based Tokai Black #5500 (from Tokai, headquartered in Japan) and Denka Black Li-400 (from Denka, headquartered in Japan). Generally, when conductive black fillers such as CNTs or carbon black are dispersed in insulating polymers, the electrical percolation threshold is characterized by a sharp drop in electrical resistance by several orders of magnitude. The electrical percolation threshold is related to the formation of an interconnected conductive network of fillers within the host medium. Compared to media filled with carbon black alone, media containing only CNTs, which exhibit a much higher aspect ratio, can achieve the electrical percolation threshold at a much lower filler percentage. However, the incorporation of both CNTs and carbon black into the host medium has been reported to produce a synergistic effect resulting from their respective contributions to the formation of an interconnected conductive network. As shown in the examples below, carbon black added to the processed mixture acts synergistically with the CNTs to bridge the electron transport pathways and strengthen the conductive network in the composite matrix more than if CNTs were included alone.

[0021] A partitioning agent can be added as a first additive to generate the processed mixture. Examples of nanoscale or microscale partitioning agents include glass beads, glass bubbles, and conductive metal powders. Examples of such partitioning agents include 3M™ Glass Bubbles iM30K and Glass Bubbles iM16K (available from 3M, headquartered in the United States). The addition of these ingredients is expected to facilitate debundling of CNTs during the subsequent first mixing stage 116 due to a ball-bearing grinding effect. In addition, the incorporation of glass beads (GBs) into a silicone-MWCNT combination has been reported to significantly improve the dispersion of MWCNTs in silicone. Specifically, the electrical conductivity of a silicone / MWCNT / GB composite was approximately twice that of a composite without GBs due to improved uniformity of MWCNT dispersion in silicone. Furthermore, the presence of GBs is expected to improve the mechanical properties of the composite, such as tensile strength and elongation at break, in addition to electrical conductivity. As shown in the examples below, a distribution agent, e.g., glass bubbles, added to the processed mixture improves the uniformity of the dispersion of CNTs, e.g., SWCNTs, thereby improving the electrical conductivity and mechanical properties of the composite matrix.

[0022] A thickening agent or blowing agent can be added as a first additive to produce the processed mixture. Examples of thickening agents or blowing agents include foam formers, expandable cell composites, and other void modifiers, which function to increase void space in the composite matrix, strengthen the interconnecting conductive network, and improve electrical conductivity. An example of thermally expandable thermoplastic microspheres includes a polymer shell made from ethylenically unsaturated monomers encapsulating a propellant, commonly known under the brand name Expancel® Microsphere Products (from Nouryon, headquartered in the Netherlands). Considering the overall process flow, expanding spheres are added to produce the processed mixture in first mixing 116, and then the processed mixture is mixed with one or more polymers in second mixing 316. During the process, the spheres first expand upon heating, and then the expanded cells are permanently fixed by curing 320 of the composite matrix. Foaming agents, such as those based on azodicarbonamide and p-p'-oxybis(benzenesulfonylhydrazide), accelerated with treated urea, have been shown to provide fine foaming and cellular structure in cured fabricated products. These agents can be added as the initial additive to produce processed mixtures in a manner similar to that used for expandable cellular composites. With silicones in particular, foam-forming agents can be used to create voids upon heating and harden during the process. These agents include combinations of water, silicon hydride crosslinkers, and phenylsilicones. Phenylsilicone fluids are selected from those consisting of linear polysiloxane chains with methyl-phenyl or diphenyl pendant groups substituted with dimethyl along the polysiloxane backbone, and viscosities measured at 23°C ranging from 0.01 to 10 Pa-s. When added to produce processed mixtures and then incorporated into polymer matrices, these agents efficiently foam the composite matrix through the creation of numerous nucleation sites, which result in the creation of fine foam cells that grow to maintain a surface skin upon cure.

[0023] After all the necessary ingredients are prepared in steps 104-112 above, the ingredients are placed in a first mixer and mixed in the first mixing step 116 of Figure 2. The first mixer can be a cone mixer or a pin mixer with a simple mixing mechanism. In this experiment, a speed in the range of 100-100,000 1 / sec was used. low With shear rate Tami It has been found that using a mixer for a period ranging from 5 minutes to 1 hour results in gentle debundling of the CNTs, resulting in a high quality dispersion with minimal damage to their conjugated structure. , with well-dispersed and substantially undamaged CNTs; A treated mixture is obtained.

[0024] Generally, conventional mixing methods for non-covalent functionalization involve jet mixers, ultrasonicators, or is high High shear rate , i.e., shear rates greater than 100,000 1 / sec These include the use of other costly and powerful machinery involving shear rates exceeding 100,000 1 / sec. For example, typical shear rates produced by jet mixers exceed 100,000 1 / sec, which often damages the CNTs. Ultrasonic treatment with ultrasonicators also shortens the CNTs, thereby reducing their aspect ratio and significantly reducing their usefulness as conductive fillers. Furthermore, ultrasonic treatment naturally generates heat, necessitating cooling during the procedure. In contrast, as explained with reference to the first mixing step 116 above, In the range of 100-100,000 1 / sec With low shear rate Sea A mixer is used in the present process to mix the CNTs with other ingredients to obtain a processed mixture containing substantially debundled CNTs with minimal breakage and high quality dispersion properties.

[0025] FIG. 4 is a flowchart showing details of step 300. Raw and curedProcessing steps are performed to produce a composite matrix. In steps 304 and 308, the necessary components are provided. In step 304, one or more polymers are provided. In this process, a combination of two or more polymers can be used to form the base polymer matrix to modify specific properties, for example, to increase strength after curing. Examples of polymers that can be used in this process include polysiloxanes (with methyl, trifluoropropyl, or phenyl substituents), ethylene-propylene copolymers, ethylene-propylene-diene terpolymers, acrylonitrile-butadiene copolymers, styrene-butadiene copolymers, isoprene polymers, isobutylene-isoprene copolymers, chloroprene polymers, butadiene polymers, chlorinated polyethylene polymers, epichlorohydrin polymers, ethylene-acrylic copolymers, polyacrylate copolymers, ethylene-vinyl acetate copolymers, polypropylene oxide copolymers, fluorocarbon elastomeric copolymers, tetrafluoroethylene copolymers, perfluoro-elastomeric copolymers, polyether-urethane polymers, polyester-urethane polymers, Silicone rubber base, fluorosilicone rubber base, vinyl terminated polydimethylsiloxane, ethylene propylene diene polymer, butadiene-acrylonitrile copolymer (39% ACN), Other commercially available polymers or copolymers, and any combination thereof.

[0026] Step 308 provides the processed mixture in either the as-produced form obtained in step 100 or the pressed form obtained in step 200. In step 312, other ingredients can be added to enhance specific properties, depending on the desired properties of the finished product. Thus, a second mixing step 316 can be performed to combine the processed mixture obtained according to the previous step with one or more polymers, as shown in FIG. 2, with or without one or more additives, referred to herein as second additives. Examples of such second additives include fillers, plasticizers, stabilizers, cure initiators, cure modifiers, cure accelerators, catalysts, curing agents, and any combination thereof. Examples of fillers include silica, fumed silica, nanosilica, functionalized or non-functionalized silicone resins, natural and synthetic fibers, polysaccharides, cork, graphite and carbon black, graphene, clay, boron nitride, finely divided metals and metal oxides, and any combination thereof.

[0027] After preparing all the necessary ingredients in steps 304-312 above, the ingredients are placed in and mixed in a second mixer in a second mixing step 316 of Figure 4. The second mixer can be a conventional rubber processing mill or mixer with a low shear rate of less than 100 1 / sec to obtain a polymeric mixture, i.e., an as-processed, raw composite matrix before curing, with substantially debundled CNTs and other ingredients.

[0028] In step 320, the polymer-based mixture produced by the above mixing is , i.e., the raw composite matrixThe resulting composite matrix is ​​then subjected to a curing process, during which it irreversibly hardens to produce a thermoset. Typically, curing is induced by heat or suitable irradiation and can be accelerated by high pressure or mixing with a catalyst. A catalyst can be added in the second mixing step 316. A transition metal-based catalyst synthesized from chloroplatinic acid and chloroplatinic acid can be used for this curing. The curing is based on a chemical reaction that causes extensive cross-linking between polymer chains to produce a substantially injectable and insoluble polymer network. Thus, a composite matrix with the intended properties is stabilized and obtained in step 324. Figure 5 shows a scanning electron microscope image of an example of a silicone-based composite matrix containing well-dispersed individual SWCNTs. The composite matrix can then be subjected to fabrication procedures such as molding, calendering, and extrusion, as required, in step 400 of Figure 1, ultimately resulting in a finished product in step 500 of Figure 1.

[0029] Referring back to the pressing procedure of step 200 in FIG. 1 , pressing can include compression, pelletizing, and other bulk density-increasing operations. An example of a pelletizing procedure involves the use of a pelletizer to cylindrically form the processed mixture into pellets. A binder, such as a cyclic polysiloxane, can be added to the pelletizer. The resulting pellets are heated to remove the binder at a temperature below the activation temperature of the other additives in the processed mixture, i.e., the first additive. After cooling, the pellets can be packaged for shipping. However, it should be noted that surfactants often function sufficiently to function as binders. Therefore, the addition of a specific binder, such as a cyclic polysiloxane, may not be necessary, and therefore, in this case, the subsequent heating and cooling processes are not necessary. Instead of pelletizing, light pressing or tamping can be performed to increase bulk density. Generally, shipping and handling of commercially available raw CNTs, e.g., SWCNT powder, is inefficient due to their extremely low bulk density, resulting in lightweight raw CNTs occupying large cargo space.

[0030] FIG. 6A is a photograph showing an example of raw, unprocessed CNTs, with a mass of 7.122 g and an occupied volume of approximately 270 cm. 3 Therefore, the bulk density is about 26 kg / m 3 FIG. 6B is a photograph showing an example of the treated CNTs, i.e., the treated mixture after pressing in step 200, which in this case has a mass of 19.339 g and occupies a volume of approximately 91 cm. 3 Therefore, the bulk density is about 213 kg / m 3 The pressing operation herein involves tamping or pressing using manual or mechanical pressure without the use of an additional binder to achieve a compression ratio of greater than 8 times, e.g., about 8.2.

[0031] Referring back to step 112 of Figure 2, as previously described, one or more cure modifiers can be added when preparing the treated mixture. In this study, the hydrosilylation cure reaction in silicone rubber is optimized by maintaining a stoichiometric balance of Si-H to vinyl. An imbalanced hydrosilylation cure system can result in either an under-cure condition, resulting in poor elastomeric properties, or an over-cure condition, resulting in undesirable adhesion to mold surfaces and other substrates. As noted, hydride-functional polysiloxanes form non-covalent interactions with CNTs; in addition, they are also hydrosilylation reaction precursors (described as crosslinkers). As a result, a competition occurs between the cure reaction and the affinity of CNTs for the crosslinker. This competition can disrupt the stoichiometric balance over time due to different reaction rates.

[0032] An additional problem arises when processing composite matrices containing CNTs. As mentioned, the composite matrix is ​​optimized when carbon nanotubes are exfoliated from the CNT bundles into separate individual tubes. These individual tubes must also be fully encapsulated within the composite matrix. Any exposed CNTs, or uncured composite matrices containing CNTs, can result in the undesirable surface effect of the exposed tubes being removed by abrasion or scraping, leaving black marks on the surface they come into contact with. This is sometimes referred to as sloughing, because the CNTs produce a black, oily residue along the surface of the composite matrix.

[0033] To remedy the adverse effects of CNTs on the composite matrix, this study involves using a cure modifier consisting of a hydrosilylation reaction precursor containing a hydrosilylation crosslinker and a reaction inhibitor, which is added to the mixture processed in the first mixing step (step 116). The addition of the crosslinker compensates for absorption through the CNTs and balances the Si-H to vinyl stoichiometry in the hydrosilylation reaction. The addition of the inhibitor allows the composite matrix to be cured at higher temperatures without the undesirable problem of scorch (defined as premature curing). These higher process temperatures allow for more extensive and complete crosslinking, resulting in more complete encapsulation of individual CNTs by the polymer link. The surface of the composite matrix is ​​clean and contains fully encapsulated CNTs. Hydrosilylation inhibitors have been reported to inhibit the activation of transition metal catalysts synthesized from platinum chloride and chloroplatinic acid. These platinum divinyltetramethyldisiloxane complexes, known as Karstedt catalyst complexes, are typically: platinum(0)-1,3-divinyl,1,1,3,3-tetramethyldisiloxane), platinum(0)-2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane complex, bis(acetylacetonato)platinum, (m-cyclopentadienyl)trialkylplatinum complexes, platinum triazenide complexes, platinum, iron, palladium and rhodium complexes, or any combination thereof.

[0034] The following formulations illustrate how the addition of a crosslinker and inhibitor as a cure modifier can be performed, specifically using a hydrosilylation reaction precursor consisting of a hydrosilylation crosslinker and a reaction inhibitor. Note that phr in the tables below is defined as parts per hundred rubber; values ​​in the formulations can be converted to percent by dividing the amount of the component by the total amount and multiplying by 100.

[0035] Table 1 lists the phr values ​​used in Formulation Example 1, which is a less than optimal formulation that results in a composite matrix characterized by high adhesion to molds and other substrates and poor CNT encapsulation (degradation).

[0036] [Table 1]

[0037] Table 2 lists the phr values ​​used for Formulation Example 2, a more optimal formulation, which results in a composite matrix characterized by low adhesion to molds and other substrates and good CNT encapsulation.

[0038] [Table 2]

[0039] In Tables 1 and 2 above, the "First Mix" column refers to step 116 of mixing CNTs and inorganic surfactant with or without one or more first additives to produce a treated mixture, the "Second Mix" column refers to step 316 of mixing the treated mixture with a polymer with or without one or more second additives to create a composite matrix, and the "Combination of First Mix and Second Mix" column lists the combined total of all components in both the first mix and the second mix.

[0040] In the "First Mix and Second Mix Combination" column of Table 2, the crosslinker level was reduced from 3.55 phr to 0.73 phr and added only in the first mix, while the inhibitor level was increased from 0.28 phr to 0.56 phr, with half of that amount added to each of the first and second mixes. This experiment demonstrates that cure modifiers added in this order, first in the first mix as part of the processed mix, better maintain the Si-H to vinyl stoichiometric balance, allowing for improved CNT encapsulation in the resulting composite matrix.

[0041] To further illustrate the effect of the cure modifier on the hydrosilylation reaction precursor, the following table shows how the addition of a cure modifier in the first mix affects the cure start time (TS2) and cure completion time (TC90). These cure rates are directly related to cure efficiency. Generally, the inclusion of CNTs in the mix tends to decrease cure efficiency. One solution to this problem is to add the cure modifier in the second mix, as in the example formulation in Table 1 above, but this often results in a composite matrix with high adhesion to molds and other substrates and poor CNT encapsulation (degradation). A preferred method is to add the cure modifier in the first mix, as in Table 2. Table 3 below shows that adding a cure modifier in this way improves cure efficiency, with cure rates approaching those for the "no treated CNT mix" case, e.g., TS2 = 30 seconds and TC90 = 66 seconds (177°C). Specifically, the levels of crosslinker and inhibitor of the cure modifier in the first mix can be adjusted to restore cure efficiency and provide high throughput, thereby achieving an economically produced composite matrix.

[0042] [Table 3]

[0043] The cure modifier composition can include a hydrosilylation reaction precursor having a linear organohydrogenpolysiloxane, a general molecular illustration of which is shown in FIG. 7A, where y is an integer from 1 to 98, z is an integer from 2 to 50, and y+z is 9 to 100; R2 is independently an optionally substituted monovalent hydrocarbon group containing 1 to 10 carbon atoms; and R3 is R2 or a hydrogen atom.

[0044] FIG. 7B is a general molecular illustration of another hydrosilylation reaction precursor based on an inhibitor such as an acetylenic alcohol, in which the same or different substituents R1 and R2 independently represent a linear or branched monovalent alkyl, cycloalkyl, (cycloalkyl)alkyl, aromatic, or arylalkyl group, which can be joined in pairs to form a 5-, 6-, 7-, or 8-membered aliphatic ring optionally substituted with one or more substituents.

[0045] In this study, we used the above-mentioned method based on the incorporation of CNTs. Composite Matrix Various experiments were conducted to produce the CNTs, and their properties and characteristics were analyzed to understand the effects of CNTs and various additives. The results and special technical features are described below with reference to Figures 8 to 26.

[0046] As previously described with reference to FIG. 2, two processed mixtures, Processed Mixture 1 and Processed Mixture 2, are produced based on the first mixture. FIGS. 8 and 9 are tables listing the components used to produce Processed Mixture 1 and Processed Mixture 2, respectively. The weight percent (wt%) of each component in the processed mixture is shown in the rightmost column of each table. SWCNT powder with a carbon purity of 99% or higher is used as the CNT, and the terms CNT and SWCNT are used interchangeably in the tables and charts of FIGS. 8 through 26. Carbon black and glass bubbles are used as the first additive to produce both Processed Mixtures 1 and 2. Processed Mixture 1 contains 30 wt% of one inorganic surfactant. Processed Mixture 2 contains 10 wt% each of three inorganic surfactants.

[0047] The processed mixture produced based on the first blend is then mixed with one or more polymers and a second additive based on the second blend to produce a polymer-based mixture. , i.e., composite matrix (as processed / raw material) This is cured as described above with reference to Figure 4. profit hand, In this experiment Composite Matrix Su Fabrication procedures such as molding, calendering, and extrusion are then performed as needed to process the composite matrix and produce the final product, in this case a rubber product. Figures 10-13 are tables listing the ingredients used in the second mix, other than the processed mix, to produce the base silicone rubber, base fluorosilicone rubber, base EPDM rubber, and base nitrile rubber, respectively. That is, each of Figures 10-13 shows: Composite Matrix 1A-1C are tables showing base rubber formulations containing one or more polymers and a second additive that are mixed with the processed mixture in a second mix to produce a base rubber composition comprising one or more polymers and a second additive. The weight percent of each component in the base rubber is shown in the right-most column of each table.

[0048] Figures 14 to 20 show various base rubbers and Composite Matrix1 is a table listing experimental results for the electrical, physical, and rheological properties of (including processed mixtures 1 or 2). The rheological properties are presented in terms of ML (minimum torque), MH (maximum torque), TS2 (time to start setting), and TC90 (time to complete setting).

[0049] FIG. 14 shows the results of the base silicone rubber and the silicone rubber obtained by mixing the base silicone rubber formulation with treated mixture 1 at effective SWCNT weight percentages of 1 wt%, 2 wt%, and 3 wt%, respectively. Composite Matrix Figure 15 shows the details of the formulation of the base silicone rubber and the silicone rubber obtained by mixing the base silicone rubber formulation with treated mixture 2 at 1 wt%, 2 wt%, and 3 wt% effective SWCNT weight percentages, respectively. Composite Matrix The effective weight percent of each ingredient is Composite Matrix The weight percentage of the component is based on the total weight of all components.

[0050] FIG. 16 shows the base silicone rubber and the silicone rubber obtained by mixing the base silicone rubber formulation with pristine SWCNTs without any treatment (i.e., without first mixing with one or more inorganic surfactants) at effective SWCNT weight percentages of 1 wt %, 2 wt %, and 3 wt %, respectively. Composite Matrix Includes details of the formulation.

[0051] Figure 17 shows the silicone rubber obtained by blending the base silicone rubber formulation with the raw SWCNTs and raw carbon black without treatment (i.e., without first blending with one or more inorganic surfactants) with 1 wt% raw SWCNTs and 3.1 wt% raw carbon black, and with 2 wt% raw SWCNTs and 7.1 wt% raw carbon black (CB), respectively. Composite Matrix Includes details of the formulation.

[0052] FIG. 18 shows the results of the base fluorosilicone rubber and the fluorosilicone obtained by blending the base fluorosilicone rubber formulation with treated mixture 1 at effective SWCNT weight percentages of 1 wt%, 2 wt%, and 3 wt%, respectively. Composite Matrix Includes details of the formulation.

[0053] FIG. 19 shows the results of the base EPDM rubber and the EPDM rubber obtained by mixing the base EPDM rubber compound with treated Mix 1 at effective SWCNT weight percentages of 0.9 wt%, 1.7 wt%, and 3 wt%, respectively. Composite Matrix Includes details of the formulation.

[0054] FIG. 20 shows the results of the base nitrile rubber and the nitrile rubber obtained by mixing the base nitrile rubber formulation with treated mixture 1 at effective SWCNT weight percentages of 0.9 wt%, 2 wt%, and 3 wt%, respectively. Composite Matrix Includes details of the formulation.

[0055] Figures 21-26 are charts showing key features and trends in properties based on the data summarized in Figures 14-20. Note that the weight percent of CNTs in these charts corresponds to the effective weight percent of SWCNTs in the tables of Figures 14-20.

[0056] FIG. 21 shows the results of the treated mixture 1, treated mixture 2, pristine CNT, and silicone containing pristine CNT plus pristine carbon black (CB), respectively. Composite Matrix 1 is a chart showing the volume resistivity as a function of the weight percent CNT in the base silicone rubber based on the base silicone rubber formulation. The weight percent CNT and CB are equal for silicone rubbers containing treated mixture 1 and treated mixture 2. Composite Matrix Both are silicones containing raw CNTs. Composite Matrix and silicone containing raw CNT + raw CB Composite Matrix The silicone containing treated mixture 1 and treated mixture 2 exhibits a low volume resistivity compared to either of the silicone containing treated mixture 1 and treated mixture 2. Composite MatrixThe electrical percolation thresholds for both silicone and pristine CNTs are Composite Matrix and silicone containing raw CNT + raw CB Composite Matrix It is shown that the treated mixture is filled with a lower weight percent of CNTs than either of the treated mixtures. It is also shown that the carbon black added to the treated mixture functions synergistically with the CNTs to bridge the electron transport pathways and strengthen the conductive network in the composite matrix, compared to when only CNTs are included. Furthermore, the addition of a distribution agent, such as glass bubbles, to the treated mixture improves the uniformity of the CNT dispersion, thereby enhancing the uniformity of the rubber compound. A composite matrix such as The conductivity in the film can be improved.

[0057] FIG. 22 shows the results of the processed mixture 1, processed mixture 2, pristine CNT, and silicone containing pristine CNT plus pristine carbon black (CB), respectively. Composite Matrix 21 and 22 are charts showing durometer as a function of the weight percent CNT in the base silicone rubber based on the base silicone rubber formulation. Typical rubber applications fall within the durometer range of 40 to 70 Shore A. Referring to FIGS. 21 and 22, both silicone rubber compounds containing Treated Mix 1 and Treated Mix 2 exhibit durometers within this desirable range, while the silicone rubber containing raw CNTs exhibits a durometer within this desirable range. Composite Matrix The electrical percolation threshold is met at a lower wt% of CNT compared to either the silicone rubber compound containing pristine CNTs and pristine CB.

[0058] FIG. 23 shows the results of the treated mixture 1, treated mixture 2, pristine CNT, and silicone containing pristine CNT plus pristine carbon black (CB), respectively. Composite Matrix 21 and 23 are charts showing the tensile strength as a function of the weight percent CNT in the base silicone rubber based on the base silicone rubber formulation. Composite Matrix Both are silicones containing raw CNTs. Composite Matrix and silicone containing raw CNT + raw CB Composite Matrix The electrical percolation threshold is met at a lower weight percent of CNTs than either of the above, while maintaining appreciable tensile strength. Typically, many rubber applications calling for electrically conductive materials do not prioritize tensile strength as a required feature, and for such applications, a tensile strength of 400 psi is often considered sufficient.

[0059] FIG. 24 shows the results of the silicone containing treated mixture 1, treated mixture 2, pristine CNT, and pristine CNT plus pristine carbon black (CB), respectively. Composite Matrix 1 is a chart showing the elongation at break as a function of the weight percent CNT in the base silicone rubber based on the base silicone rubber formulation. Composite Matrix 21 and 24, the silicone containing processed mixture 1 at 2 wt% CNTs exhibits improved elastomeric properties compared to the other cases. Composite Matrix The silicone containing processed mixture 1 exhibits the lowest volume resistivity (highest conductivity) and the highest elongation at break. In addition, in the range of 0 wt% CNT to 3 wt% CNT, including 1 wt% CNT and 2 wt% CNT, the silicone containing processed mixture 1 exhibits the lowest volume resistivity (highest conductivity) and the highest elongation at break. Composite Matrix The distribution agent, e.g., glass bubbles, added to the processed mixture improves the uniformity of the CNT dispersion, thereby Composite Matrix It can be seen that this improves the mechanical properties of the material.

[0060] FIG. 25 shows the results of the silicone containing treated mixture 1, treated mixture 2, pristine CNT, and pristine CNT plus pristine carbon black (CB), respectively. Composite Matrix 1 is a chart showing the tear strength as a function of the weight percent CNT in the base silicone rubber based on the base silicone rubber formulation, as well as the silicone containing treated mixture 1. Composite Matrixshows tear strengths comparable to the base silicone rubber at 1 and 2 wt% CNT. Referring to Figures 1 and 25, this tear strength is not significantly compromised at the CNT wt% required to meet the electrical percolation threshold.

[0061] Figure 26 shows the silicone containing the treated mixture 1, respectively. Composite Matrix , fluorosilicone containing treated mixture 1 Composite Matrix , EPDM containing treated mixture 1 Composite Matrix , and the treated mixture 1 containing nitrile Composite Matrix 1 is a chart showing the volume resistivity as a function of CNT weight percent in silicone when processed mixture 1 was used using the method described herein. Composite Matrix , fluorosilicone Composite Matrix , and nitrile Composite Matrix All of the materials passed the electrical percolation threshold at 0-2 wt% CNTs, while EPDM Composite Matrix passed the electrical percolation threshold at 2–3 wt % CNTs.

[0062] While this document contains many specific details, these should not be construed as limitations on the scope of the invention or what may be claimed, but rather as descriptions of features specific to particular embodiments of the invention. Certain features that are described herein in the context of separate embodiments can also be implemented in combination in a single embodiment. Conversely, various features that are described in the context of a single embodiment can also be implemented in multiple embodiments separately or in any suitable subcombination. Furthermore, while features may be described above as acting in a particular combination, and may even initially be claimed as such, one or more features from a claimed combination can, in some cases, be exercised in combination, and the claimed combination can be directed to a subcombination or variations of the subcombination.

Claims

1. 1. A method of making a composite matrix, comprising: a first mixture comprising components including carbon nanotubes (CNTs) and one or more inorganic surfactants to form a treated mixture, the first mixture configured to have a shear rate ranging from 100 to 100,000 1 / sec, the one or more inorganic surfactants comprising moieties characterized by an ability to interact with the surfaces of the CNTs and penetrate interstices of the bundled CNTs, thereby facilitating exfoliation and debundling of the bundled CNTs; a second mixing step of mixing the treated mixture with a component comprising one or more polymers to form a composite matrix; Including, the one or more inorganic surfactants comprise at least one inorganic surfactant selected from the group consisting of vinyl-terminated polydimethylsiloxanes, vinyl-terminated diphenylsiloxanedimethylsiloxanes, silanol-terminated polydimethylsiloxanes, hydride-terminated polyphenyl-(dimethylhydrosiloxy)siloxanes, hydride-terminated polyphenylmethylsiloxanes, hydride-terminated polyphenyl-(dimethylsiloxy)siloxanes, and combinations thereof; The method, wherein said one or more polymers do not include said one or more inorganic surfactants.

2. 10. The method of claim 1, wherein the first mixing uses a cone mixer or a pin mixer.

3. 10. The method of claim 1, wherein the second mixing uses a rubber mixing mill or mixer.

4. 10. The method of claim 1, wherein the moiety comprises at least one moiety selected from the group consisting of a methyl group, a hydroxyl group, a silanol group, an aryl group, and combinations thereof.

5. The method of claim 1 , wherein the one or more inorganic surfactants comprise a silanol-terminated polydimethylsiloxane.

6. the first mixing includes mixing ingredients further comprising one or more first additives to produce the treated mixture; 10. The method of claim 1, wherein the one or more first additives comprise at least one first additive selected from the group consisting of cure modifiers, carbon black, partitioning agents, thickening agents, blowing agents, and combinations thereof.

7. the second mixing includes mixing components further comprising one or more second additives to produce the composite matrix; 10. The method of claim 1, wherein the one or more secondary additives comprise at least one secondary additive selected from the group consisting of fillers, plasticizers, stabilizers, cure initiators, cure modifiers, cure accelerators, catalysts, curing agents, and combinations thereof.

8. 8. The method of claim 7, wherein the filler comprises at least one filler selected from the group consisting of silica, fumed silica, nanosilica, silicone resin, natural and synthetic fibers, polysaccharides, cork, graphite, carbon black, graphene, clay, boron nitride, metal powders, metal oxide powders, and combinations thereof.

9. the one or more second additives include one or more cure modifiers; 8. The method of claim 7, wherein the first mixing combines ingredients further comprising one or more first additives to produce the treated mixture, the one or more first additives comprising the one or more cure modifiers.

10. 10. The method of claim 1, wherein the one or more polymers comprise at least one polymer selected from the group consisting of polysiloxanes having substituents comprising any of methyl, trifluoropropyl, phenyl, or combinations thereof; ethylene-propylene copolymers; ethylene-propylene-diene terpolymers; ethylene-propylene-diene polymers; acrylonitrile-butadiene copolymers; styrene-butadiene copolymers; isoprene polymers; isobutylene-isoprene copolymers; chloroprene polymers; butadiene polymers; chlorinated polyethylene polymers; epichlorohydrin polymers; ethylene-acrylic copolymers; polyacrylate copolymers; ethylene-vinyl acetate copolymers; polypropylene oxide copolymers; fluorocarbon elastomeric copolymers; tetrafluoroethylene copolymers; perfluoroelastomeric copolymers; polyether-urethane polymers; polyester-urethane polymers; silicone rubber-based; fluorosilicone rubber-based; vinyl-terminated polydimethylsiloxanes; ethylene propylene diene polymers; butadiene-acrylonitrile copolymers with 39% acetonitrile; and combinations thereof.

11. The method of claim 1 further comprising pressing the treated mixture after the first mixing.

12. 12. The method of claim 11, wherein the pressing comprises tamping to increase the bulk density of the treated mixture by more than 8 times compared to the bulk density of the untreated CNTs.

13. The method of claim 1 further comprising curing the composite matrix.

14. 2. The method of claim 1, wherein the CNTs comprise at least one type of CNT selected from the group consisting of single-walled carbon nanotubes (SWCNTs), double-walled carbon nanotubes (DWCNTs), and multi-walled carbon nanotubes (MWCNTs).

15. The method of claim 1 further comprising curing the composite matrix to obtain a conductive material.

16. The method of claim 6 , wherein the carbon black comprises an acetylenic carbon black.

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