Orthogonal carbon nanotube-based nanoforests for high-performance hierarchical multifunctional nanocomposites

Abstract

A reinforcement and manufacturing method for improving the strength, toughness, and other properties of composites in both the transverse and in-plane directions. The reinforcement has a layer of a nanoforest of vertical nanotubes or nanowires and a layer of horizontal nanotubes or nanowires. The reinforcement can be made by rolling a vertical nanoforest to create a crushed layer of horizontal nanotubes or nanowires, and then growing a vertical nanoforest on the crushed layer. The reinforcement can be grown directly on the fibers used to reinforce the composite, or it can be interleaved with layers of those fibers before curing the composite part. The reinforcement and manufacturing method are compatible with nearly all composites in any shape, including epoxy, polymer, or ceramic matrix composites, or any manufacturing method, including prepreg, wet layup, and matrix film lamination. The invention reduces scrap, rework, and repair time for composite manufacturing.

Description

[Technical Field]

[0001] [Cross-Reference to Related Applications] This application claims the priority and benefit of U.S. Provisional Patent Application No. 62 / 966,958, filed on January 28, 2020, entitled "Orthogonal Carbon-Nanotube-Based Nanoforest For High-Performance Hierarchical Multifunctional Nanocomposites", the entire content of which is incorporated herein by reference.

[0002] [Statement of Federally Sponsored Research and Development] This invention was made with government support under Contract No. N68335-20-C-0493 awarded by the Office of Naval Research. The government has certain rights in this invention. [Background Art]

[0003] The present invention relates to nanoreinforcements for multifunctional structural and non-structural nanocomposites.

[0004] It is to be noted that the following description may refer to a number of publications and references. Discussion of such publications herein is given for a more complete background of the scientific principles and should not be construed as an admission that such publications are prior art for the purpose of patentability determination.

[0005] The field of nanocomposites includes the study of multiphase materials in which at least one of the constituent phases has dimensions less than 100 nm. This is a region where phenomena related to atomic and molecular interactions strongly influence the macroscopic properties of materials. Because the components of nanocomposites are nanoscale and nanomaterials have enormous surface areas, numerous interfaces exist between the mixed phases. The special properties of nanocomposites arise from the interactions of their phases at the interfaces and / or interphase regions. In contrast, in conventional composites utilizing micrometer-sized fillers such as carbon fibers, the surface-to-volume ratio of the interfaces between the filler and matrix components is much smaller than in bulk materials, and therefore, the degree to which they influence the properties of the host structure is much smaller. The potential of nanocomposites lies in their multifunctionality, that is, the possibility of realizing unique combinations of various properties that cannot be achieved with conventional materials. Motivated by the strong interest in nanotechnology in recent years, the development of nanocomposites has become one of the rapidly developing fields of composite research.

[0006] Scientists and engineers working with fiber-reinforced composites have practiced this “bottom-up” approach to processing and manufacturing at the micron level for decades. When designing composites, material properties are tuned to the desired performance across various length scales (e.g., from micro to macro). From the selection and processing of matrix and fiber materials and structures, to the layup of thin layers in laminated composites, and ultimately to the formation of the network structure of macroscopic composite components, the comprehensive approach used in composite processing is a notable example of the successful use of a “bottom-up” approach (albeit at the micron level) even before the development of nanocomposites.

[0007] Future composites will likely represent greater advancements than today's. Recent developments in the manufacturing and characterization of various nanoparticles have created numerous new opportunities for developing nanocomposites for diverse applications. The development of carbon nanotube (CNT) reinforced nanocomposites is promising for a wide range of applications, including polymer nanocomposites with high mechanical damping, strength, fracture strain, fracture toughness, and electrical and thermal conductivity, while also reducing their coefficient of thermal expansion. However, the use of CNTs as structural reinforcements depends on their ability to transfer load from the matrix to the nanotubes.

[0008] Significant improvements in the in-plane mechanical properties of CNT-reinforced composites have been reported compared to unreinforced counterparts. For example, the compressive modulus of multi-walled carbon nanotube (MWCNT) / epoxy nanocomposites is higher than the tensile modulus, indicating much higher load transfer to the nanotubes in the composite during compression. Nanomaterials have been used with epoxy and polyester to improve the strength, fracture strain, and fracture toughness of developed nanocomposites. Given their importance and usefulness in the fields of space, aerospace (both commercial and military), automotive, communications, sporting goods, and renewable energy, carbon fiber reinforced polymers (CFRP) and glass fiber reinforced polymers (GFRP) are now widely studied and used. This is because these types of materials possess excellent properties, low weight, high fracture toughness, and relatively high strength.

[0009] Patent Document 1, incorporated herein by reference, discloses the growth of a nanoforest of carbon nanotubes on the surface of a woven fabric in order to develop a high-performance composite material with improved strength, stiffness, toughness, damping properties, conductivity, and thermal conductivity, and reduced CTE (coefficient of thermal expansion) properties. The nanotape technology can be arranged alternately between composite layers by either wet layup or prepreg.

[0010] The effects of incorporating nanoscale materials into adhesives for bonding two dissimilar materials have not been fully investigated. This may be due to large variability in functionality, complexity of geometric shapes, material incompatibility, and operating conditions. Structurally bonded joints can fail at various locations and in various failure modes. When bonding composite materials using adhesives, failure may occur or begin in the adhesive or adherends depending on the geometric configuration, the materials of the adherends, the adhesive, and the manufacturing process.

[0011] To join composite materials using mechanical fasteners, notches (such as circular holes) are typically introduced into the structure. The presence of such holes increases stress concentration by three times in isotropic materials such as metals, alloys, ceramics, and polymers, and by less than three times in anisotropic materials such as composites. [Overview of the project]

[0012] One embodiment of the present invention is a nanoforest-based reinforcing material comprising: a first layer comprising a nanoforest comprising substantially vertically oriented nanotubes or nanowires; and a second layer comprising substantially horizontally oriented nanotubes or nanowires. The first layer preferably has a height of about 10 to about 20 microns. The second layer preferably has a height of about 5 to about 10 microns. The nanoforest-based reinforcing material preferably has a total height of less than about 50 microns. The nanotubes or nanowires optionally include carbon, BN, Si, CuO, or ZnO. Any of the aforementioned elements or features can be combined in any combination with one or more of the other aforementioned elements or features.

[0013] Another embodiment of the present invention is a composite component comprising multiple layers of the aforementioned nanoforest-based reinforcement material arranged alternately with multiple fiber-reinforced layers. The nanoforest-based reinforcement material is optionally grown directly on the fiber-reinforced layers. The composite component preferably comprises a matrix comprising a curing material selected from the group consisting of epoxy, thermosetting polymer resin, thermoplastic polymer resin, polyimide resin, bismaleimide resin, and preceramic polymer. The fiber-reinforced layers optionally comprise carbon, glass, Kevlar, Spectra, silicon carbide, silicon nitride, alumina, or a combination thereof. Each fiber-reinforced layer optionally comprises fabric. The composite component optionally comprises a flat, curved, curved, or multi-curvature geometric shape. Any of the aforementioned elements or features can be combined in any combination with one or more of the other aforementioned elements or features.

[0014] Another embodiment of the present invention is a method for producing a nanoforest-based reinforcement, comprising the steps of: growing a first nanoforest containing nanotubes or nanowires on a substrate, wherein the nanotubes or nanowires are oriented substantially perpendicular to the surface of the substrate; rolling the nanoforest to form a crushed layer containing nanotubes or nanowires oriented substantially parallel to the surface of the substrate; and growing a second nanoforest containing nanotubes or nanowires on the crushed layer, wherein the nanotubes or nanowires are oriented substantially perpendicular to the surface of the substrate. The method optionally includes the step of removing the first nanoforest from the substrate before the rolling step. The nanoforest optionally includes the step of placing the nanoforest between two polytetrafluoroethylene sheets before the rolling step. The nanoforest may be placed between two metal sheets before the rolling step, with or without the polytetrafluoroethylene sheets. Each metal sheet contains aluminum, steel, copper, or zinc and has a thickness of about 1 mm. This method optionally includes the step of depositing a catalyst layer on a substrate before the step of growing the first nanoforest. Any of the aforementioned steps, elements, or features can be combined in any combination with one or more of the other aforementioned steps, elements, or features.

[0015] Another embodiment of the present invention is a method for manufacturing a composite component, comprising the steps of: manufacturing a nanoforest-based reinforcing material manufactured according to the method described above; arranging a plurality of layers containing the nanoforest-based reinforcing material alternately with a plurality of fiber-reinforced material layers; and curing the composite component. The substrate material is optionally selected from the group consisting of silicon, silicon oxide, steel, stainless steel, silicon carbide, silicon oxide, boron carbide, boron nitride, silicon nitride, alumina, quartz, glass, quartz glass, and copper. The substrate is preferably removed from the nanoforest-based reinforcing material before the alternating arrangement step. The fiber-reinforced material layers optionally include a prepreg layer. Alternatively, the method optionally includes the step of wetting the alternately arranged nanoforest-based reinforcing material layers and fiber-reinforced material layers with a liquid matrix material before the curing step. The liquid matrix material is preferably selected from the group consisting of epoxy, thermosetting polymer resins, thermoplastic polymer resins, polyimide resins, bismaleimide resins, and preceramic polymers. Alternatively, this method optionally includes a step of laminating alternating nanoforest-based reinforcing layers and fiber-reinforced layers with a plurality of matrix film layers prior to the curing step. Any of the aforementioned steps, elements, or features can be combined in any combination with one or more of the other aforementioned steps, elements, or features.

[0016] Another embodiment of the present invention is a method for manufacturing a composite component, comprising the steps of: manufacturing a nanoforest-based reinforcement manufactured according to the method described above, wherein the substrate comprises a fiber-reinforced cloth; laminating a plurality of layers of the fiber-reinforced cloth; and curing the composite component. The method optionally includes wetting the laminated layers with a liquid polymer matrix material prior to the curing step, or optionally laminating these layers with a plurality of matrix film layers prior to the curing step. Any of the steps, elements, or features described above can be combined in any combination with one or more of the other steps, elements, or features described above.

[0017] Another embodiment of the present invention is a method for manufacturing a composite component, comprising the steps of: manufacturing a nanoforest-based reinforcement manufactured according to the method of claim 12; and incorporating the nanoforest-based reinforcement into a composite component using a manufacturing method selected from the group consisting of wet layup, prepreg grayup, automatic or manual wet layup or prepreg roll wrapping, tape lamination for thermosetting composites or thermoplastic composites, room temperature curing, autoclave curing, internal autoclave treatment, external autoclave treatment, resin transfer molding (RTM), open or closed vacuum-assisted resin transfer molding (VARTM), reaction injection molding (RIM), structural reaction injection molding (SRIM), elastic reservoir molding (ERM), sheet molding compound (SMC), compression molding, co-curing sandwich structure manufacturing, pultrusion, diaphragm molding / forming, hydroforming, thermoforming, and matched die molding.

[0018] The object, advantages and novel features of the present invention, as well as its further scope, are partially described in the following detailed description in conjunction with the accompanying drawings, and in part will become apparent to those skilled in the art by examining the following, or can be acquired through the practice of the present invention. The object and advantages of the present invention can be realized and achieved by means and combinations particularly indicated in the accompanying claims. [Brief explanation of the drawing]

[0019] The accompanying drawings incorporated herein and forming part of this specification illustrate embodiments of the invention and, together with the description, help to illustrate the principles of the invention. The drawings are for illustrative purposes only and should not be construed as limiting the invention. [Figure 1] This is a schematic diagram of a simple chemical vapor deposition system for growing carbon nanotubes. [Figure 2] This is a schematic diagram of a chemical vapor deposition system for growing multi-walled carbon nanotubes. [Figure 3]It is a photograph of a chemical vapor deposition system for growing multi-walled carbon nanotubes. [Figure 4] It is a typical photograph of vertically aligned high-density arrays of multi-walled carbon nanotubes (MWCNTs) grown on silicon and silicon oxide wafers using chemical vapor deposition (CVD). [Figure 5] It is a scanning electron microscope (SEM) image of vertically aligned high-density arrays of MWCNTs grown on silicon and silicon oxide wafers using CVD. [Figure 6] It is a schematic diagram showing an example of using a tough flexible metal sheet in the rolling process of Figures 8 to 9. [Figure 7] It shows a typical tough flexible metal sheet for the rolling process of Figures 8 to 9. [Figure 8] It is a schematic diagram showing a single press rolling technique for producing horizontally aligned carbon nanotube nanoforests (HA-CNT-NF) from vertically aligned carbon nanotube nanoforests (VA-CNT-NF). [Figure 9] It is a schematic diagram showing a double press rolling technique for producing HA-CNT-NF from VA-CNT-NF. [Figure 10] It is a schematic diagram of a typical orthogonal nanoforest technology of the present invention, wherein VA-CNT-NF is grown on or arranged on HA-CNT-NF. [Figure 11] It is a schematic diagram of HA-CNT-NF embedded in a composite material. [Figure 12] It shows the interlayer distance between two plies of a CNT-free composite material, and the inset shows a nanocomposite material whose interlayer distance is filled with HA-CNT-NF. [Figure 13] It shows the dimensions of a single carbon fiber compared with horizontally aligned carbon nanotubes in HA-CNT-NF. [Figure 14] It shows a CVD furnace used for producing the orthogonal nanoforest of the present invention. [Figure 15] It is an SEM micrograph showing a top view of the orthogonal nanoforest of the present invention, showing the VA-CNT-NF layer. [Figure 16] This is a SEM micrograph showing a top view of the edge of a sample orthogonal nanoforest (NF). [Figure 17] This is a SEM micrograph showing a side view of the edge of the sample orthogonal NF. [Figure 18] This figure shows the successful transfer of orthogonal NF from the substrate to the prepreg fabric. [Figure 19] This is an SEM micrograph showing that orthogonal NF completely covers the surface of the prepreg after transfer from the substrate. [Figure 20] These are schematic diagrams and photographs of prepreg panels that are vacuum-sealed for autoclave processing. [Figure 21] The image shows the initial state of the carbon / epoxy prepreg panel (right) and the carbon / epoxy prepreg panel containing orthogonal NF (left) after curing in an autoclave. [Figure 22] The specimen is shown cut from the initial panel on the right side of Figure 21 before the double cantilever (DCB) test. [Figure 23] The specimen cut from the orthogonal NF panel on the left side of Figure 21 before the DCB test is shown. [Figure 24] Figure 22 shows the fracture surface of the specimen in its initial state after the DCB test. [Figure 25] Figure 23 shows the fracture surface of the orthogonal NF specimen after DCB testing. [Figure 26] This graph shows the load-versus-extension data for the initial state of the sample obtained by the DCB test. The hinge of sample 1 was fractured during the experiment and is therefore omitted from this graph. [Figure 27] This graph shows the load-versus-extension data of orthogonal NF samples obtained by DCB testing. [Figure 28] This demonstrates the successful transfer of orthogonal NF onto carbon / polyimide prepregs. [Figure 29] The orthogonal NF carbon / polyimide prepreg panel after autoclave curing is shown. [Figure 30]Typical initial carbon / polyimide test samples before DCB testing (top) and orthogonal NF (bottom) are shown. [Figure 31] Typical fracture surfaces of carbon / polyimide test samples in their initial state after DCB testing (top) and orthogonal NF (bottom) are shown. [Figure 32] This graph shows the load-to-stretch data for the initial state carbon / polyimide sample obtained by DCB testing. [Figure 33] This graph shows the load-to-stretch data for orthogonal NF carbon / polyimide samples obtained by DCB testing. Detailed description of the invention

[0020] Embodiments of the present invention are novel types of nanoreinforcements ("orthogonal carbon nanotube-based nanoforests") that can be used to develop multifunctional structural and non-structural nanocomposites. In some embodiments, the "orthogonal" nanoforests (NFs) of the present invention include carbon nanotubes (CNTs) in both in-plane and out-of-plane directions. Although carbon nanotubes are often specified throughout this description, the present invention can use nanotubes or nanowires containing any material, including but not limited to carbon, ZnO, BN, Si, CuO, and ZnO.

[0021] The present invention can be used with any type of polymer resin, such as thermosetting polymers, thermoplastic polymers, or preceramic polymers, to produce nanocomposites having higher performance than the resin. The present invention can also be used in composite systems to produce high-performance, hierarchical (as the present invention is a bottom-up approach from nanoforests to microfibers and further to macrocomposites) and multifunctional (as many different properties are improved) nanocomposites by alternating any type of fibrous material, such as carbon, glass, Kevlar, Spectra, silicon carbide, alumina, or hybrids / combinations thereof, and any type of fibrous structure, such as unidirectional, 2D weave, 3D triaxial / braided, or any combination thereof, within a regular and continuous fibrous composite of wet layup or prepreg-based polymers. The present invention can also be used in adhesives for joining two adherends to improve strength and toughness by locally reinforcing the bonding area and stress concentration areas. The present invention is also used to locally reinforce joint areas and stress concentration areas in mechanical joint areas and notches (such as holes) and / or around them where mechanical fasteners for composite materials are required. The structure around the hole area is locally reinforced in the area where the hole is cut out (after composite panel manufacturing) by locally inserting orthogonal nanoforests between layers (preferably during composite manufacturing), thereby effectively reducing the stress concentration factor, resulting in a localized increase in the strength, fracture strain, and toughness of the material around the hole and mechanical fastener (if required), and thus substantially improving the overall performance of the structure.

[0022] The present invention is applicable to most polymer composite manufacturing technologies, including room temperature curing, autoclave (in-autoclave and out-autoclave) curing, compression molding, resin transfer molding (RTM), open or closed vacuum-assisted resin transfer molding (VARTM), reaction injection molding (RIM), structural reaction injection molding (SRIM), elastic reservoir molding (ERM), sheet molding compound (SMC), manual or automatic wet layup or prepreg roll wrapping, co-cured sandwich structures, pultrusion, manual or automatic wet layup or prepreg tape lamination, in-situ (online compaction) thermoplastic composite tape lamination, filament winding by in-situ (online compaction) thermoplastic composite tape lamination, diaphragm formation, matched die formation, hydroforming, and thermoforming.

[0023] The present invention is useful for any shape, such as flat, curved, curved, and multi-curvature, and can be applied locally (i.e., around specific areas where properties need to be locally improved) or globally (i.e., for an entire structure where properties need to be improved globally and at all points within the structure). Structures containing orthogonal nanoforests of the present invention have improved physical properties, chemical properties, mechanical properties (both static properties such as strength, stiffness / modulus, strain, and toughness, and dynamic properties such as fatigue, shock, vibration, and damping), conductivity, thermal conductivity, thermoelastic properties, thermomechanical properties, electromagnetic interference, electromagnetic pulse, flame retardancy, and improved properties such as reduced coefficient of thermal expansion (CTE) and reduced moisture absorption coefficient. These improvements are preferably orthogonal anisotropic improvements using orthogonal nanoforests. Furthermore, the alternating arrangement of orthogonal nanoforests within a layered structure may be continuous between all layers, alternating with a predetermined number of layers, or arranged only within some layers. In addition, depending on the application, if specific material properties are required, some of the orthogonal nanoforests can be replaced with some thin layer of metal (e.g., aluminum foil) or polymer (thermoplastic film).

[0024] In one or more embodiments of the present invention, orthogonal multilayer carbon nanotubes (MWCNTs) having a diameter of less than 100 nm form orthogonal nanoforests for use as reinforcing materials to improve the overall performance of resins, adhesives, and composites, either overall (when grown directly on fibers or when alternately arranged within a composite to cover the entire surface of a component) or locally (when used to locally reinforce locations such as joints, notches, or holes where stress concentrations exist). One embodiment of a method for manufacturing orthogonal nanoforests is as follows: A suitable substrate (either fibers for direct growth of CNTs or a substrate for fabricating a CNT nanoforest) is preferably made using any thin catalyst layer (iron, nickel, cobalt, etc.) with a thickness of about 10 to 20 microns, which is suitable for carbon nanotube growth. Any substrate suitable for nanotube or nanowire growth can be used, including but not limited to silicon, silicon oxide, steel, stainless steel, ceramics (silicon carbide, silicon oxide, boron carbide, boron nitride, silicon nitride, alumina, etc.), quartz, glass, or copper. Nanotubes or nanowires can be grown directly onto fibers or fabrics, including but not limited to carbon, glass, Kevlar, Spectra, or ceramic fibers. As used herein and throughout the claims, the term “substrate” includes substrates, fibers, and fabrics.

[0025] The fibers or substrate are placed in a CVD furnace, and a suitable mixture of a carbon source fluid (such as xylene) and a suitable catalyst material such as ferrocene (if the substrate does not yet have a catalyst layer) is supplied to the CVD furnace at about 750°C, preferably in a ratio of 2 g of ferrocene to 100 g of xylene, preferably under suitable flow conditions, to grow vertically aligned carbon nanotube nanoforests (VA-CNT-NF) having a height of preferably about 10 to 20 microns on the substrate. The material is then cooled, preferably to room temperature, preferably under an inert gas such as argon, and removed from the CVD furnace. As will be described in more detail below, one or more Teflon films (or equivalents) having a thickness of preferably about 25 microns are placed on the nanoforest, and then rolled under pressure to crush and horizontally orient the CNTs, preferably forming horizontally aligned carbon nanotube nanoforests (HA-CNT-NF) with a height of about 5 to 10 microns after crushing. By removing one or more Teflon films, placing HA-CNT-NF (on fibers or a substrate) in a CVD furnace, and repeating the CNT growth process for VA-CNT-NF, a VA-CNT-NF with a height of approximately 10-20 microns is grown on the HA-CNT-NF, thereby obtaining an orthogonal nanoforest suitable for alternating placement between composite layers, containing CNTs in both the horizontal (i.e., in-plane) and vertical (i.e., out-of-plane) directions, and preferably having a total height of approximately 20-30 microns. The heights of the HA-CNT-CNT, VA-CNT-NF, and orthogonal NF are not limited to the heights described herein and can be any desired height, shorter or higher.

[0026] There are several techniques for growing VA-CNT-NF, including CVD, arc discharge, and laser ablation. In the CVD method, it is preferable to use a substrate. The substrate may optionally contain one or more fibers. To grow VA-CNT-NF by CVD, a catalyst layer is required on the substrate so that carbon atoms can form carbon nanotubes. There are two possible methods for depositing the catalyst layer on the substrate. In the first method, direct sputtering is performed on an iron, nickel, or cobalt substrate, preferably including a thin coating of several microns, as shown in Figure 1. The catalyst-coated substrate is then placed in a CVD furnace, and a carbon source is supplied to the CVD furnace to grow carbon nanotubes. In the second method, as shown in Figures 2-3, the substrate is placed in a CVD furnace, and then a source of a mixture of a carbon source (e.g., 100 g xylene) and a catalyst material (e.g., 2 g ferrocene) is supplied to the CVD furnace, and carbon nanotubes are grown using appropriate temperature and flow conditions. In this method, catalyst particles heavier than carbon atoms in the xylene-ferrocene mixture first precipitate on the substrate, and then carbon atoms deposit on top of the catalyst particles to form carbon nanotubes. In either case, after the VA-CNT-NF has grown to the desired length, the furnace can be turned off, an inert gas (e.g., argon) can be flowed through the furnace to cool it to near room temperature, and then the VA-CNT-NF on the fiber or substrate can be removed from the furnace. CVD allows the CNTs to grow perpendicular to the surface of the fiber or substrate, as shown in Figures 4-5. The growth of carbon nanotubes on the fiber surface is limited by the chemical composition of the surface, the area on which carbon nanotubes can grow in CVD, and the fiber's resistance to high-temperature processing in CVD. If necessary, a thin coating of a material such as a polymer with a glass or ceramic backbone can be applied to the fiber, which is then heated to a conversion temperature, and on which CNTs can be easily grown. The techniques described above have been successfully used in applications where CNT reinforcement of composites is mainly required in the thickness direction, and in applications to improve the interlayer properties of composites.

[0027] The process of crushing VA-CNT-NF (or the CNTs within it) into HA-CNT-NF without completely or partially crushing them can be carried out using rollers or a rolling mill. VA-CNT-NF10 is optionally removed from the substrate, fiber, or cloth 60 and placed between the upper Teflon film 15 and the lower Teflon film 20. This sandwich is then optionally placed between the upper metal sheet 30 and the lower metal sheet 40, as shown in the schematic diagram of Figure 6 (not to scale). An example of a preferably tough, flexible, and pliable flexible metal sheet containing aluminum about 1 mm thick is shown in Figure 7. Figures 8 and 9 are schematic diagrams showing mechanisms for crushing VA-CNT-NF10 into HA-CNT-NF50 by single-sided rolling and double-sided rolling, respectively. The upper metal sheet is not used in Figure 8 but can be used in other embodiments. Similarly, the substrate is not shown in Figures 8 and 9. In other embodiments, VA-CNT-NF can be rolled while still on a substrate or fiber. Finally, NanoForest can be placed directly between metal sheets without the use of Teflon®.

[0028] By observing the color change of the NF layer, it is possible to visually determine whether the vertical NF has been flattened to a horizontal orientation by the roller. Vertically oriented CNTs absorb almost all of the incident light directed towards them, so they appear as a darker shade of black compared to horizontally oriented CNTs, which appear gray.

[0029] Alternatively, instead of first creating HA-CNT-NF (as described above) and then growing VA-CNT-NF directly on top of it (on the fiber / fabric or substrate), the VA-CNT-NF is grown on a separate substrate, then removed, and placed on top of the HA-CNT-NF (on the fiber or fabric or substrate).

[0030] Figure 10 shows a schematic diagram of the orthogonal nanoforest of the present invention, including VA-CNT-NF grown on HA-CNT-NF. Alternatively, instead of having HA-CNT-NF at the bottom and VA-CNT-NF at the top, a configuration opposite to "orthogonality" can be created, namely a configuration with VA-CNT-NF at the bottom and HA-CNT-NF at the top. The orientation of the HA-CNT-NF and VA-CNT-NF carbon nanotubes in the orthogonal nanoforest may deviate from a perfectly horizontal and / or perfectly vertical alignment, i.e., they may form some angle other than vertical relative to each other, which may be desirable in some particular application. The nanoforest shown in Figure 10 as [HA-CNT-NF, VA-CNT-NF]n has n=1, but this n can be 1, 2, 3, etc. Alternatively, it can be [VA-CNT-NF, HA-CNT-NF]n, where n=1, but this n can be 1, 2, 3, etc., as described above.

[0031] Key characteristics of good nanoforest growth are the height, orientation, and density of the nanoforests on the fibers or substrate. The total height of the orthogonal nanoforests preferably has a height of 20 to 40 micrometers to fill the gaps between each ply in the cured composite laminate. NF systems higher than about 50 micrometers may result in a thicker laminate than expected. Since the amount of resin on the prepreg is limited and preferably no additional resin is added to the nanoforests during layup, if the NF is much thicker than 50 micrometers, it can lead to a resin deficiency in the laminate derived from the prepreg system, resulting in reduced material properties of the resulting nanocomposite.

[0032] Figures 11-13 show typical HA-CNT-NF filling the approximately 50-micron gap between carbon fiber layers in a composite material. The orthogonal NF of the present invention, removed from the substrate, can be used in a similar manner. To fabricate the nanocomposite of the present invention, the orthogonal NF can be transferred to layers of composite fibers or fabric for subsequent wet layup and arranged alternately, transferred and placed on another layer of film (film lamination), and / or combined with a prepreg.

[0033] Alternatively, to form a composite material, orthogonal nanoforests may be manufactured directly on fibers or fabric, then wetted with a liquid polymer matrix or matrix film, laminated or superimposed, and cured in an autoclave or in a hot-pressed / compression-molded vacuum bag.

[0034] Example 1: Carbon / Epoxy Prepreg System A stainless steel substrate was placed inside a quartz tube in a CVD (chemical vapor deposition) furnace. Sanding and cleaning the substrate with alcohol before placing it in the furnace enabled more uniform NF growth. The CVD end cap was bolted on, and a syringe was filled with xylene and ferrocene precursors in a ratio of 100g to 2g and placed on the syringe pump. The quartz tube was then purged with argon. To enable more uniform NF growth, the argon gas was passed through a flask filled with water before entering the furnace and preheater. Once the tube was purged, the preheater and furnace were turned on and set to heat to approximately 200°C and 750°C, respectively. After the furnace and preheater reached the desired temperatures, the syringe pump and hydrogen gas were turned on to start the growth cycle. The precursors were pressurized through the line to the preheater, where they evaporated upon entering the furnace. When the syringe was empty, the growth process stopped, and the syringe pump, furnace, preheater, and hydrogen gas flow were stopped. The argon valve was turned to prevent argon from passing through the water any further. After the furnace cooled to below 200°C, the argon was turned off, the substrate was removed, and the furnace was allowed to cool to room temperature.

[0035] A layer of vertically oriented carbon nanotubes (CNTs) was rolled using a rolling mill until the CNTs were oriented flat (i.e., horizontally). The substrate was then returned to the furnace for a second round of NF growth, where vertically oriented CNTs were grown on top of the horizontal CNTs from the first cycle to produce orthogonal NF. After the second cycle of CNT growth was completed (and after the pumping / injection of the xylene / ferrocene mixture flow was stopped), the orthogonal NF was chemically separated from the substrate as follows: The furnace, preheater, and hydrogen gas remained in place, and argon continued to flow into the furnace through water. After about 30 minutes, the furnace, preheater, and hydrogen were turned off, and the argon valve was switched to prevent the gas from passing through the water flask. At this point, the furnace began to cool under argon flow. When the furnace reached about 200°C, the argon was turned off, the substrate (with the orthogonal NF) was removed, and it was cooled to room temperature.

[0036] Figure 14 shows the CVD furnace used in this example. Figures 15 and 16 are SEM top views of the orthogonal NF showing VA-CNT-NF as the top layer. Figure 17 is an SEM side view of the orthogonal NF. Figures 16 and 17 were photographed at the edge of the sample showing the horizontally aligned CNTs of the lower layer at the edge where the vertically aligned CNTs overlap.

[0037] Next, the orthogonal NF was removed from the substrate and transferred onto the carbon / epoxy prepreg ply. This removal and transfer should be achieved with minimal damage to the orientation and coating. The prepreg was placed on top of the orthogonal NF, and then some gentle heat and pressure were applied to the assembly. At this point, epoxy adheres to the prepreg, causing the substrate, the orthogonal NF, and the prepreg to bond. Using a razor, the orthogonal NF was mechanically scraped off the substrate, preferably in the direction in which the orthogonal NF was rolled to planarize the first layer. (In other examples, the orthogonal NF was first removed from the substrate using a mechanical razor blade and then placed on the prepreg with some gentle heat and pressure.) A photograph of the successful transfer of the orthogonal NF to the prepreg is shown in Figure 18.

[0038] Complete coating of orthogonal NF on the prepreg reduces or eliminates the possibility of voids or thickness variations in the final laminate. The SEM micrograph in Figure 19 shows a top view of the orthogonal NF coating on the prepreg after transfer from the substrate, showing HA-CNT-NF applied on top of VA-CNT-NF in contact with the entire surface of the prepreg. Thus, the order of the orthogonal NF layers is reversed from the order on the substrate due to the transfer process.

[0039] To determine the effect of orthogonal NF on the material properties of the composite, two panels were fabricated. The first panel (i.e., the initial state panel) was used as the baseline material and consisted of 16 plies of prepreg plain weave carbon cloth / epoxy without the addition of orthogonal NF layers. The second panel contained 16 layers of prepreg plain weave carbon cloth / epoxy, with orthogonal NF layers added between each prepreg layer. Both panels were placed in vacuum bags as shown in Figure 20 and cured in an autoclave using the manufacturer's recommended curing cycle. Figure 21 shows the initial state (right) and the panel with orthogonal NF after autoclaving (left).

[0040] Each panel was cut into five test specimens of approximately 160 mm × 25 mm × 4 mm using a water jet, in accordance with ASTM D5528-01 standard (2019). The interlaminar fracture toughness of Mode I G was determined from the test specimens using the double cantilever beam (DCB) test, ASTM test method standard D5528-01 (2019). Ic To determine the effect of orthogonal NF on the material, tests were conducted using an Instron testing machine. According to the ASTM Manual, the test specimens should have a length of at least 125 mm, a width of 20–25 mm, and a thickness of 3–5 mm. Since each woven ply is 0.010 inches thick, using 16 layers produces a laminate with a thickness of approximately 0.16 inches (approximately 4 mm). Figures 22 and 23 show the initial state (indicated by "P") and orthogonal NF (indicated by "NF") test specimens before testing, respectively, and Figures 24 and 25 show the initial state and orthogonal NF test specimens after DCB testing, respectively.

[0041] Figures 26 and 27 show the load-versus-extension (i.e., Instron jaw displacement) data for the initial specimen and the orthogonal NF specimen, respectively. 342.62 J / m 2 Orthogonal NF samples with measured mean fracture toughness have interlaminar fracture toughness G Ic It showed a 62.3% improvement, reaching 211.08 J / m³. 2 It was able to withstand higher maximum loads and higher elongation values ​​while maintaining higher loads than the initial sample with measured average fracture toughness.

[0042] Example 2: Carbon / Polyimide Prepreg System Orthogonal NF was fabricated on the substrate in the same manner as described in Example 1. In this experiment's carbon / RM-1100 high-temperature polyimide prepreg system, the resin in the polyimide prepreg was tacky at room temperature, allowing the transfer process to be carried out with minimal pressure and without the use of additional heat. As in Example 1, the orthogonal NF was mechanically scraped off the substrate using a razor. The successful transfer of orthogonal NF to the prepreg is shown in Figure 28. Two sets of panels were fabricated to determine the effect of orthogonal NF on the material properties of the composite in this example. The first "initial state" panel was used as the baseline material and contained an 8-ply 8-harness woven (i.e., carbon fiber reinforced polyimide) carbon / polyimide prepreg cloth without the addition of orthogonal NF. The second panel contained an 8-layer 8-harness woven carbon / polyimide prepreg cloth with orthogonal NF between each layer. The untreated 8-harness woven carbon / polyimide prepreg layer was thicker than the plain weave carbon / epoxy prepreg layer in Example 1. Next, both panels were placed in vacuum bags and cured in an autoclave using the manufacturer's recommended curing cycle. Figure 29 shows the carbon / polyimide panels with orthogonal NF after curing in the autoclave.

[0043] The test specimen was subjected to a Mode I interlaminar fracture toughness test (G) based on ASTM Test Method Standard D5528-01, Double Cantilever Beam (DCB) Test (2019). IcTo determine the effect of orthogonal NF on the material, the test was performed using an Instron tester. According to the ASTM Manual, the test specimen should have a length of at least 125 mm, a width of 20-25 mm, and a thickness of 3-5 mm for DCB testing. In the 8-harness woven carbon / polyimide prepreg system used here, 8 layers of prepreg produce a laminate with a thickness of approximately 3 mm. Therefore, the panel was waterjet cut to dimensions of approximately 160 mm × 25 mm × 3 mm. Figure 30 shows a typical initial state (top, labeled "P") and orthogonal NF (bottom, labeled "NF") sample of the carbon / polyimide prepreg system used in this example. Figure 31 shows typical fracture surfaces of the initial state (top) and orthogonal NF (bottom) carbon / polyimide test samples after DCB testing.

[0044] Figures 32 and 33 show the load-to-tensile (instron jaw displacement) values ​​for the initial state of the NF specimen and the orthogonal NF specimen, respectively. 900.07 J / m 2 Orthogonal NF samples with measured mean fracture toughness have interlaminar fracture toughness G Ic This shows a 27.1% improvement, reaching 707.96 J / m³. 2 It was able to withstand higher maximum loads and higher elongation values ​​while maintaining higher loads than the initial sample with measured average fracture toughness.

[0045] In the specification and claims, “about” or “approximately” means within 20 percent (20%) of the cited figures. Where used herein, the singular forms “a,” “an,” and “the foregoing” include multiple references unless the context clearly indicates otherwise. Thus, for example, a reference to “functional group” refers to one or more functional groups, and a reference to “method” includes references to equivalent steps and methods that would be understood and recognized by those skilled in the art.

[0046] The present invention has been described in detail with particular reference to the disclosed embodiments, but other embodiments can achieve the same results. Variations and modifications of the present invention will be obvious to those skilled in the art, and it is intended to cover all such modifications and equivalents. The entire disclosures of all patents and publications cited above are incorporated herein by reference. [Prior art documents] [Patent Documents]

[0047] [Patent Document 1] U.S. Patent Application Publication No. 2013 / 0216811

Claims

1. A NanoForest-based reinforcing material, A first layer comprising a nanoforest containing substantially vertically oriented nanotubes or nanowires grown on a second layer, wherein the second layer comprises substantially horizontally oriented nanotubes or nanowires, The nanotube or nanowire comprises carbon, BN, Si, CuO, or ZnO. The first layer substantially covers the entire surface of the second layer, or the second layer substantially covers the entire surface of the first layer. NanoForest-based reinforcing material.

2. The nanoforest-based reinforcing material according to claim 1, wherein the first layer has a height of 10 to 20 microns.

3. The nanoforest-based reinforcing material according to claim 1, wherein the second layer has a height of 5 microns to 10 microns.

4. A nanoforest-based reinforcing material according to claim 1, having an overall height of less than 50 microns.

5. A composite component comprising multiple layers of nanoforest-based reinforcing material according to claim 1, arranged alternately with multiple fiber-reinforced material layers.

6. The composite component according to claim 5, wherein the nanoforest-based reinforcing material is grown directly on the fiber-reinforced material layer.

7. The composite component according to claim 5, comprising a matrix containing a material selected from the group consisting of cured epoxy, cured thermosetting polymer resin, cured thermoplastic polymer resin, cured polyimide resin, cured bismaleimide resin, and ceramicized preceramic polymer.

8. The composite component according to claim 5, wherein the fiber-reinforced layer includes carbon, glass, para-aramid synthetic fibers, polyethylene fibers, silicon carbide, silicon nitride, alumina, or a combination thereof.

9. The composite component according to claim 5, wherein each fiber-reinforced layer includes fabric.

10. The composite component according to claim 5, including a flat, curved, curved, or multi-curvature geometric shape.

11. A method for manufacturing a nanoforest-based reinforcing material, A step of growing a first nanoforest comprising nanotubes or nanowires on a substrate, wherein the nanotubes or nanowires are oriented substantially perpendicular to the surface of the substrate; A nanoforest rolling step, in which the nanoforest is rolled to form a crushed layer containing nanotubes or nanowires oriented substantially parallel to the surface of the substrate, A method comprising the step of growing a second nanoforest comprising nanotubes or nanowires on the crushed layer, wherein the nanotubes or nanowires are oriented substantially perpendicular to the surface of the substrate, the nanotubes or nanowires comprise carbon, BN, Si, CuO, or ZnO, and the first layer substantially covers the entire surface of the second layer, or the second layer substantially covers the entire surface of the first layer.

12. The method according to claim 11, further comprising the step of removing the first nanoforest from the substrate before the rolling step of the nanoforest.

13. The method according to claim 11, further comprising the step of placing the nanoforest between two polytetrafluoroethylene sheets prior to the rolling step of the nanoforest.

14. The method according to claim 11, further comprising the step of placing the nanoforest between two metal sheets prior to the rolling step of the nanoforest.

15. The method according to claim 14, wherein each metal sheet comprises aluminum, steel, copper, or zinc and has a thickness of 1 mm.

16. The method according to claim 11, further comprising the step of placing the nanoforest between two polytetrafluoroethylene sheets prior to the rolling step of the nanoforest, and then placing the nanoforest and the two polytetrafluoroethylene sheets between two metal sheets.

17. The method according to claim 16, wherein each metal sheet comprises aluminum, steel, copper, or zinc and has a thickness of 1 mm.

18. The method according to claim 11, comprising the step of depositing a catalyst layer on the substrate prior to the step of growing a first nanoforest.

19. A method for manufacturing composite parts, A step of manufacturing a nanoforest-based reinforcing material manufactured according to the method of claim 11, The steps include arranging multiple layers containing the NanoForest-based reinforcing material alternately with multiple fiber-reinforced material layers, A method comprising the step of curing the composite component.

20. The method according to claim 19, wherein the material of the substrate is selected from the group consisting of silicon, silicon oxide, steel, stainless steel, silicon carbide, silicon oxide, boron carbide, boron nitride, silicon nitride, alumina, quartz, glass, quartz glass, and copper.

21. The method according to claim 19, further comprising the step of removing the nanoforest-based reinforcing material from the substrate before the step of alternating arrangement.

22. The method according to claim 19, wherein the fiber-reinforced material layer includes a prepreg layer.

23. The method according to claim 19, further comprising the step of wetting the alternatingly arranged nanoforest-based reinforcing layers and fiber-reinforcing layers with a liquid matrix material prior to the step of curing the composite component.

24. The method according to claim 23, wherein the liquid matrix material is selected from the group consisting of epoxy, thermosetting polymer resin, thermoplastic polymer resin, polyimide resin, bismaleimide resin, and preceramic polymer.

25. The method according to claim 19, further comprising the step of laminating the alternatingly arranged nanoforest-based reinforcing layers and fiber-reinforcing layers with a plurality of matrix film layers prior to the step of curing the composite component.

26. A method for manufacturing composite parts, A step of producing a nanoforest-based reinforcing material manufactured according to the method of claim 11, wherein the substrate includes a fiber-reinforced material cloth, The steps include laminating multiple layers of the aforementioned fiber-reinforced fabric, A method comprising the step of curing the composite component.

27. The method according to claim 26, comprising the step of wetting the laminated layers with a liquid polymer matrix material before the step of curing the composite component.

28. The method according to claim 26, further comprising the step of laminating the layer with a plurality of matrix film layers prior to the step of curing the composite component.

29. A method for manufacturing composite parts, A step of manufacturing a nanoforest-based reinforcing material manufactured according to the method of claim 11, A method comprising the step of incorporating the nanoforest-based reinforcing material into the composite component using a manufacturing method selected from the group consisting of wet layup, prepreg grayup, automatic or manual wet layup or prepreg roll wrapping, tape lamination for thermosetting composites or thermoplastic composites, room temperature curing, autoclave curing, internal autoclave treatment, external autoclave treatment, resin transfer molding (RTM), open or closed vacuum-assisted resin transfer molding (VARTM), reaction injection molding (RIM), structural reaction injection molding (SRIM), elastic reservoir molding (ERM), sheet molding compound (SMC), compression molding, co-curing sandwich structure manufacturing, pultrusion, diaphragm molding / forming, hydroforming, thermoforming, and matched die molding.

30. The composite component according to claim 5, characterized in that each of the plurality of layers of the nanoforest-based reinforcing material satisfies between 40% and 80% of the distance between consecutive fiber-reinforced material layers.

31. The method according to 19, characterized in that, after the step of alternating arrangement, each of the plurality of layers of the nanoforest-based reinforcing material satisfies between 40% and 80% of the distance between the consecutive fiber-reinforced material layers.

32. The composite component according to claim 30, characterized in that each of the multiple layers of the nanoforest-based reinforcing material has a height of 20 to 40 micrometers to fill a 50-micrometer gap between consecutive fiber-reinforced material layers.

33. The method according to 31, characterized in that, after the step of alternating arrangement, each of the multiple layers of the nanoforest-based reinforcing material has a height of 20 to 40 micrometers to fill the 50-micrometer gap between the consecutive fiber-reinforced material layers.

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