Carbon fiber with surface uniformly coated with carbon nanotubes, and preparation method and application thereof

Abstract

The invention discloses a carbon fiber with the surface evenly coated with carbon nanotubes and a preparation method and application thereof, and belongs to the technical field of surface functionalization of carbon fibers.The preparation method comprises the following steps that carbon nanotube water-based slurry is prepared, dispersed and then subjected to ultrasonic treatment, carbon nanotube dispersion liquid is obtained, carbon nanotube dipping slurry is obtained after dilution, and the carbon nanotube dipping slurry is subjected to surface functionalization; and mixing the pretreated carbon fibers and the carbon nanotube dipping slurry according to a mass ratio of 1: (50-500), performing vacuum filtration and ultrasonic treatment at the same time to obtain a carbon nanotube coated carbon fiber sample, and performing low-temperature drying to obtain the composite coating with the carbon nanotube uniformly coated on the surface of the carbon fibers. The method is used for solving the technical problems that a coating prepared by a current coating preparation process is not uniform, and the dispersion force and the seepage force of carbon nanotubes in carbon fiber bundles are not strong.

Description

Technical Field

[0001] This invention belongs to the field of surface functionalization technology of carbon fiber, specifically relating to a carbon fiber with uniformly coated carbon nanotubes on its surface, its preparation method, and its application. Background Technology

[0002] Carbon fiber reinforced resin matrix composites (CFRPs) possess excellent specific strength and specific modulus, good fatigue performance, corrosion resistance, and designability, making them widely used in aerospace, automotive, and sporting goods industries. However, despite these advantages, the macroscopic mechanical properties of carbon fiber composites, particularly interlaminar shear strength, fracture toughness, and impact resistance, are often far lower than theoretical values. This is mainly due to the weak interfacial bonding between the carbon fibers and the polymer matrix.

[0003] To overcome these challenges, researchers have proposed various strategies to enhance the interfacial properties between carbon fibers and the matrix and to endow composite materials with multifunctionality. Among these, introducing nanomaterials, particularly carbon nanotubes (CNTs), onto the surface of carbon fibers is considered a highly promising approach. CNTs possess ultra-high strength and modulus, excellent electrical and thermal conductivity, and a large specific surface area. Constructing a uniform and robust CNT coating on the carbon fiber surface can, on the one hand, increase the surface roughness and surface energy of the fibers, forming mechanical interlocking and enhancing chemical bonding sites, significantly improving the interfacial bond strength between the fibers and the matrix, thereby increasing the interlaminar shear strength and fracture toughness of the composite material; on the other hand, the conductive / thermal network formed by CNTs can effectively reduce the contact resistance and thermal resistance between fibers, endowing the composite material with excellent electrical and thermal properties, and even achieving structural / functional integration.

[0004] However, uniformly and firmly coating CNTs onto the surface of carbon fibers, especially within complex fiber bundles or fabric structures, remains a significant technical challenge. Current main techniques include: dip-coating, spraying, ultrasonic impregnation, electrophoretic deposition, and chemical vapor deposition. While dip-coating, spraying, and ultrasonic impregnation are simple and easy to implement, CNTs are prone to agglomeration and have poor permeability within fiber bundles, making uniform coating difficult. Electrophoretic deposition and chemical vapor deposition are complex processes, require sophisticated equipment, and are costly. Chinese patent CN120625340A discloses a "mesh + mosaic" structure coated modified carbon fiber and its preparation method and application. This preparation method involves stepwise vacuum filtration: first, a CNT dispersion is filtered, then an epoxy resin dispersion is filtered, proceeding in two steps. The sample must be manually rotated to achieve double-sided deposition, making the process complex and failing to effectively promote CNT penetration into the fiber bundle and achieve uniform coating. In summary, current technologies have limitations in various aspects, including the uniformity of CNT dispersion, permeability within carbon fiber bundles, process simplicity, cost, and environmental friendliness. In particular, when it is necessary to uniformly coat carbon fiber bundles or fabrics, effectively permeating the CNT dispersion is a critical issue. Summary of the Invention

[0005] In order to overcome the shortcomings of the prior art, the present invention aims to provide a carbon fiber with uniformly coated carbon nanotubes, its preparation method and application, so as to solve the technical problems of uneven coating and weak dispersion and penetration of carbon nanotubes in the carbon fiber bundle in the current coating preparation process.

[0006] To achieve the above objectives, the present invention employs the following technical solution: This invention employs an ultrasonic-assisted vacuum filtration process. By immersing carbon fibers in a CNTs-based water slurry, the slurry is driven through the carbon fiber layer using vacuum suction, while ultrasonic vibration is applied. This method can effectively penetrate CNTs into the interior of the carbon fiber fabric and uniformly deposit them onto the carbon fibers, resulting in carbon fibers with a uniform surface coating of carbon nanotubes.

[0007] To achieve the above-mentioned objectives, the preparation method provided by this invention includes the following steps: S1: Remove the sizing agent from the carbon fiber surface by immersion in a chemical solvent; S2: Prepare water-based CNT slurry by using high-shear mixing to disperse CNTs and break up large agglomerates, followed by ultrasonic treatment to obtain a CNT dispersion, and finally dilute it into a CNT impregnation slurry. S3: Place the product obtained in S1 on the porous support layer in the vacuum filtration device, pour in CNTs water-based slurry, the mass ratio of the product obtained in S1 to the CNTs water-based slurry is 1:(50-500), and then perform vacuum filtration and ultrasonic treatment simultaneously to obtain a CNTs-coated carbon fiber sample; wherein, a vacuum filtration device is used for vacuum filtration, and the filtration rate is controlled by applying vacuum pressure to the vacuum filtration device and adjusting the vacuum degree. S4: Take out the carbon fiber sample coated with CNTs from the vacuum filtration device and dry it in a vacuum drying oven at low temperature to obtain carbon fiber with carbon nanotubes uniformly coated on the surface.

[0008] Preferably, the carbon fiber in step S1 is a long filament bundle or fabric; the chemical solvent immersion method includes: immersing the carbon fiber in a mixed solution of dimethyl ester and anhydrous ethanol at a mass ratio of 1:1 for 30-240 minutes.

[0009] Further preferably, ultrasonic treatment is used during soaking to promote the removal of the sizing agent, with the ultrasonic frequency controlled at 20-60kHz.

[0010] Preferably, in step S2, the CNTs water-based slurry is composed of CNTs and deionized water, and the concentration of the CNTs water-based slurry is 0.5wt%-5wt%; the concentration of the diluted slurry is 0.20wt%-0.35wt%.

[0011] More preferably, in step S2, the high-shear dispersion process includes homogenization or mechanical stirring.

[0012] Preferably, the homogenization conditions include: rotation speed controlled at 1000-4500 rpm and time controlled at 1-20 min.

[0013] Preferably, in step S2, the ultrasonic treatment conditions include: a frequency of 20-60 kHz and a time of 10-60 min; Preferably, in step S3, the vacuum degree is controlled at 10-50 kPa, but more preferably 20-30 kPa, during the simultaneous vacuum filtration and ultrasonic treatment; the ultrasonic frequency is controlled at 20-80 kHz, but more preferably 40-60 kHz.

[0014] Preferably, in step S4, the low-temperature drying conditions include: a drying temperature of 60-80℃ and a drying time of 2-48h.

[0015] The present invention also provides an apparatus used in the above preparation method, including a filtration device, a vacuum pump installed on the filtration device, an ultrasonic transducer connected to one side of the filtration device, an ultrasonic generator connected to one end of the ultrasonic transducer, and carbon fibers and CNTs solution placed sequentially on the porous support layer of the filtration device.

[0016] The present invention also provides carbon fibers with uniformly coated carbon nanotubes on their surface obtained by the above preparation method.

[0017] The present invention also provides the application of the above-mentioned carbon fibers with uniformly coated carbon nanotubes on their surface in the field of carbon fiber reinforced resin matrix composites.

[0018] Compared with the prior art, the present invention has the following beneficial effects: This invention proposes a method for preparing carbon fibers with uniformly coated carbon nanotubes (CNTs). A novel ultrasound-assisted vacuum filtration process is employed, which enables the uniform coating of CNTs onto the carbon fiber surface, significantly improving the uniform dispersion and deep penetration of CNTs within the carbon fiber bundle. This method is environmentally friendly, economical, and scalable, providing a new solution for the surface functionalization of carbon fibers and the application of CNTs in composite materials. The ultrasound-assisted vacuum filtration process provides the driving force for directional flow, prompting CNTs to migrate and deposit on the fiber surface with the liquid. Simultaneous ultrasonic treatment continues during the filtration process, helping to maintain the dispersion of CNTs, preventing premature clogging in the fiber interstices, and promoting more uniform distribution and penetration of CNTs into the fiber bundle, thus achieving a high-quality CNT coating layer. Compared with existing technologies, this method is more environmentally friendly and economical, with a relatively simple process and good controllability and scalability.

[0019] Furthermore, by controlling the vacuum degree of the filtration process within a relatively low range of 10-50 kPa and coordinating it with ultrasound of a specific frequency, this invention avoids the problem of uneven bridging and clogging of CNTs on the fiber surface caused by excessively rapid filtration, thus providing a time window for the rearrangement of CNTs. At the same time, through the ultrasonic cavitation effect and microfluidic action, CNTs penetrate into the fiber bundle and disperse between the monofilaments, achieving a perfect synergy between vacuum directional driving and ultrasonic three-dimensional penetration.

[0020] Furthermore, the present invention, through the combination of chemical soaking and ultrasonic treatment, can effectively dissolve and remove sizing agents and organic pollutants on the surface of carbon fibers without damaging the fiber itself.

[0021] Furthermore, the present invention prepares the impregnation slurry through a two-step dilution-based method. First, a high-concentration water-based slurry of 0.5wt%-5wt% is prepared, which is beneficial to obtain sufficient energy input during high shear dispersion. Then, it is precisely diluted to the optimal impregnation concentration of 0.20wt%-0.35wt%. This method is a key prerequisite for achieving high dispersion of CNTs in the slurry and uniform adhesion on the fiber surface.

[0022] Furthermore, by using high-speed shear dispersion, with the rotation speed controlled at 1000-4500 rpm and the time controlled at 1-20 min, the macroscopic aggregates of CNTs can be effectively torn into smaller bundles or near-single strands.

[0023] Furthermore, ultrasonic treatment with an energy of 20 kHz - 60 kHz for 10-60 min can further dissociate the micro-aggregates of CNTs and make the CNTs more uniformly distributed in the liquid.

[0024] Furthermore, the present invention employs a low-temperature drying process of 60-80℃, which helps CNTs to achieve a tighter and stronger bond with the carbon fiber surface through van der Waals forces, forming a composite coating with complete structure and stable performance.

[0025] This invention proposes an ultrasonic-assisted vacuum filtration process device. The device effectively integrates the ultrasonic device and the vacuum filtration device in terms of physical structure. Through the synergistic effect of the ultrasonic field excited by one end of the ultrasonic transducer and the ultrasonic generator and the vacuum field excited by the vacuum pump and the filtration device, ultrasonic treatment and vacuum filtration are realized in situ and synchronously, so that CNTs are more uniformly and efficiently impregnated inside the fiber bundle.

[0026] The present invention also provides carbon fibers with uniformly coated carbon nanotubes on their surface obtained by the above preparation method.

[0027] This invention also provides the application of the aforementioned carbon fibers with uniformly coated carbon nanotubes in the field of carbon fiber reinforced resin matrix composites. This invention is universally applicable. It can be widely applied to various forms of carbon fibers (such as fiber bundles, fabrics, and felts), is compatible with different types of carbon nanotubes (such as single-walled and multi-walled CNTs), and has the potential to be extended to coating other nanomaterials (such as graphene, metal, or ceramic nanoparticles). Therefore, it provides a general and flexible technical strategy for preparing various functionalized fibers to meet the needs of different application fields (such as advanced composite materials, sensors, and electrodes). Attached Figure Description

[0028] Figure 1This is a structural diagram of the ultrasonic-assisted vacuum filtration device of the present invention; wherein, 1-ultrasonic generator; 2-ultrasonic transducer; 3-filtration device; 4-vacuum pump; 5-porous support layer; 6-carbon fiber; 7-CNTs solution; Figure 2 This is a scanning electron microscope image of carbon fibers with uniformly coated carbon nanotubes prepared in Example 1 of the present invention; Figure 3 This is a scanning electron microscope image of carbon fibers with uniformly coated carbon nanotubes prepared in Example 2 of the present invention; Figure 4 This is a scanning electron microscope image of carbon fibers with uniformly coated carbon nanotubes prepared in Example 3 of the present invention; Figure 5 This is a scanning electron microscope image of carbon fibers with uniformly coated carbon nanotubes prepared in Example 4 of the present invention; Figure 6 This is a scanning electron microscope image of carbon fiber obtained in Comparative Example 1 of the present invention. Detailed Implementation

[0029] To enable those skilled in the art to understand the features and effects of the present invention, the following descriptions and definitions are only general descriptions of the terms and expressions mentioned in the specification and claims. Unless otherwise specified, all technical and scientific terms used herein have the ordinary meaning understood by those skilled in the art regarding the present invention, and in the event of any conflict, the definitions in this specification shall prevail.

[0030] The theories or mechanisms described and disclosed herein, whether right or wrong, should not in any way limit the scope of the invention, that is, the contents of the invention can be implemented without being limited by any particular theory or mechanism.

[0031] In this document, all features defined by numerical ranges or percentage ranges, such as numerical values, quantities, contents, and concentrations, are for the sake of brevity and convenience only. Accordingly, descriptions of numerical ranges or percentage ranges should be considered as covering and specifically disclosing all possible sub-ranges and individual numerical values ​​(including integers and fractions) within those ranges.

[0032] In this article, unless otherwise specified, “contains,” “includes,” “containing,” “has,” or similar terms cover the meanings of “composed of” and “mainly composed of,” for example, “A contains a” covers the meanings of “A contains a and others” and “A contains only a.”

[0033] For the sake of brevity, not all possible combinations of the technical features in each implementation scheme or embodiment are described herein. Therefore, as long as there is no contradiction in the combination of these technical features, the technical features in each implementation scheme or embodiment can be combined arbitrarily, and all possible combinations should be considered within the scope of this specification.

[0034] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0035] The following examples use instruments and equipment conventional in the art. Experimental methods in the following examples, unless otherwise specified, are generally performed under conventional conditions or as recommended by the manufacturer. All raw materials used in the following examples are conventional commercially available products with specifications conventional in the art. In this specification and the following examples, unless otherwise specified, "%" represents weight percentage, "parts" represents parts by weight, and "ratio" represents weight proportion.

[0036] Example 1 This embodiment 1 provides a method for preparing carbon fibers with uniformly coated carbon nanotubes, comprising the following steps: S1: Immerse the carbon fiber sample in a mixed solution of dimethyl ester and anhydrous ethanol at a mass ratio of 1:1 for 90 minutes, then place it in an ultrasonic cleaning tank and apply ultrasonic energy at a frequency of 40 kHz to promote the removal of sizing agent and impurities. S2: Prepare a 2wt% CNTs water-based slurry, disperse the CNTs in the slurry using a homogenizer to break up large agglomerates, then perform ultrasonic treatment to obtain a CNTs dispersion, and finally dilute it to a 0.20wt% CNTs impregnation slurry; the homogenization process is performed at a speed of 2000 rpm for 5 min; the ultrasonic treatment is performed at a frequency of 60 kHz for 60 min; S3: Place the product obtained in S1 on the porous support layer in the vacuum filtration device, pour in the CNTs impregnation slurry, the mass ratio of the product obtained in S1 to the CNTs impregnation slurry is 1:200, apply vacuum pressure to the vacuum filtration device, control the filtration rate by adjusting the vacuum degree to 30kPa, and simultaneously apply ultrasonic energy with an ultrasonic frequency of 60kHz during the filtration process to obtain a carbon fiber sample coated with CNTs. S4: Take out the carbon fiber sample coated with CNTs from the vacuum filtration device and dry it in a vacuum drying oven at 60°C for 24 hours to obtain carbon fiber with carbon nanotubes uniformly coated on the surface.

[0037] like Figure 1 As shown, the apparatus used in the above steps of this embodiment 1 includes a filtration device 3, a vacuum pump 4 is installed on the filtration device 3, an ultrasonic transducer 2 is connected to one side of the filtration device 3, an ultrasonic generator 1 is connected to one end of the ultrasonic transducer 2, and carbon fiber 6 and CNT solution 7 are placed sequentially on the porous support layer 5 of the filtration device 3.

[0038] The carbon fibers with uniformly coated carbon nanotubes prepared in Example 1 are as follows: Figure 2 As shown. From low magnification Figure 2 (a) It can be observed that the surface of the carbon fiber is basically covered by a layer of CNTs; from high magnification Figure 2 (b) It can be observed more clearly that CNTs are uniformly attached to the carbon fiber surface in a network structure, forming a relatively thin but continuous and complete coating layer, effectively covering the fiber body with no obvious exposed areas.

[0039] Example 2 A method for preparing carbon fibers with uniformly coated CNTs is provided, the steps of which are basically the same as in Example 1, except that the concentration of the diluted impregnation slurry in S2 is 0.25 wt%, and the resulting carbon fibers with uniformly coated CNTs are as follows: Figure 3 As shown, with Figure 2 In comparison, low magnification Figure 3 (a) shows that the thickness of the CNT coating layer on its surface has increased, at high magnification. Figure 3 (b) shows that CNTs remain highly uniformly distributed on the fiber surface, without significant aggregation, thus constructing a denser three-dimensional network structure.

[0040] Example 3 A method for preparing carbon fibers with uniformly coated CNTs is provided, the steps of which are basically the same as in Example 1, except that the concentration of the diluted impregnation slurry in S2 is 0.30 wt%, and the prepared carbon fibers with uniformly coated CNTs are as follows: Figure 4 As shown, it can be observed that at low magnification... Figure 4 (a) Shows further thickening of the CNT coating on the carbon fiber surface. At high magnification... Figure 4 In (b), the network structure formed by the interwoven CNTs is more compact, completely covering the fiber matrix and forming a significant and uniform modified layer.

[0041] Example 4 A method for preparing carbon fibers with uniformly coated CNTs is provided, the steps of which are basically the same as in Example 1, except that the concentration of the diluted impregnation slurry in S2 is 0.35 wt%, and the resulting carbon fibers with uniformly coated CNTs are as follows: Figure 5 As shown, low magnification Figure 5 (a) This shows that the thickest CNT encapsulation layer within the scope of this invention has formed on the carbon fiber surface at this point. High magnification Figure 5 (b) shows that the CNTs are densely interwoven to form a relatively thick and still uniform surface structure, which fully demonstrates that the method of the present invention can still achieve stable and controllable loading of CNTs even at high slurry concentrations.

[0042] Comparative Example 1 The comparative example implementation steps are basically the same as those in Example 1, except that the concentration of the diluted impregnation slurry in S2 is 0.10 wt%, and the resulting carbon fibers with uniformly coated CNTs are as follows: Figure 6 As shown, CNTs are sparsely and unevenly distributed on the fiber surface, with numerous exposed areas, failing to form a continuous and complete coating layer. At low concentrations, the insufficient number of CNTs in the slurry, along with slight agglomeration tendencies or Brownian motion, can lead to fluctuations in CNT concentration in localized areas, resulting in irregular deposition points on the carbon fiber surface. Furthermore, during filtration, the low viscosity of the slurry and the sparse distribution of CNTs reduce their capillary penetration and directional deposition efficiency within the fiber bundle. Liquid may pass through rapidly without effective CNT adhesion, thus failing to form a continuous and uniform coating across the entire fiber surface, especially within the complex fiber bundle. This result demonstrates that the specific process method of this invention can only achieve uniform and controllable CNT coating within an appropriate concentration range; excessively low concentrations or improper processes will not achieve the technical effects of this invention.

[0043] Example 5 A method for preparing carbon fibers uniformly coated with CNTs is basically the same as that in Example 1, except that: in S1, the carbon fiber soaking time is 240 min and the ultrasonic treatment frequency is 60 kHz; in S2, the mass fraction of the carbon nanotube water-based slurry is 0.5 wt%, the high shear dispersion speed is 1000 rpm, the high shear dispersion time is 20 min, and the ultrasonic treatment time is 10 min; in S3, the mass ratio of carbon fiber to CNTs impregnation slurry is 1:50 (1 g of carbon fiber and 50 g of impregnation slurry), the vacuum degree of air filtration is 50 kPa, and the ultrasonic treatment frequency is 20 kHz; in S4, the low-temperature drying temperature is 80℃ and the low-temperature drying time is 2 h.

[0044] Example 6 A method for preparing carbon fibers uniformly coated with CNTs is provided, with steps essentially the same as in Example 1, except that: in S1, the carbon fiber soaking time is 30 min, and the ultrasonic treatment frequency is 20 kHz; in S2, the mass fraction of the carbon nanotube water-based slurry is 5 wt%, the high-shear dispersion rotation speed is 4500 rpm, and the high-shear dispersion time is 1 min; in S3, the mass ratio of carbon fiber to CNTs impregnation slurry is 1:500 (1 g of carbon fiber and 500 g of impregnation slurry); in S3, the vacuum degree of vacuum filtration is 10 kPa, and the ultrasonic treatment frequency is 80 kHz; and in S4, the low-temperature drying time is 48 h. The above description is merely illustrative of the technical concept of this invention and should not be construed as limiting the scope of protection of this invention. Any modifications made to the technical solution based on the technical concept proposed in this invention fall within the scope of protection of the claims of this invention.

Claims

1. A method for preparing carbon fibers with uniformly coated carbon nanotubes, characterized in that, Includes the following steps: A water-based carbon nanotube slurry was prepared, dispersed, and then ultrasonically treated to obtain a carbon nanotube dispersion. After dilution, a carbon nanotube impregnation slurry was obtained. The pretreated carbon fibers and the carbon nanotube impregnation slurry were mixed at a mass ratio of 1:(50-500) and then vacuum filtered and ultrasonically treated simultaneously to obtain a carbon nanotube-coated carbon fiber sample. After low-temperature drying, a composite coating of carbon nanotubes uniformly coated on the surface of the carbon fibers was obtained.

2. The method for preparing carbon fibers with uniformly coated carbon nanotubes according to claim 1, characterized in that, During the simultaneous vacuum filtration and ultrasonic treatment process, the vacuum level is 10 kPa - 50 kPa and the ultrasonic frequency is 20 kHz - 80 kHz.

3. The method for preparing carbon fibers with uniformly coated carbon nanotubes according to claim 1, characterized in that, Carbon fiber is either a long filament bundle or a fabric. The pretreatment process of carbon fiber includes: immersing the carbon fiber in a mixed solution of dimethyl ester and anhydrous ethanol at a mass ratio of 1:1 for 30-240 minutes, while simultaneously performing ultrasonic treatment at a frequency of 20 kHz-60 kHz.

4. The method for preparing carbon fibers with uniformly coated carbon nanotubes according to claim 1, characterized in that, The carbon nanotube water-based slurry is composed of carbon nanotubes and deionized water, with a concentration of 0.5wt%-5wt%. The concentration of the carbon nanotube impregnation slurry is diluted to 0.20wt%-0.35wt%.

5. The method for preparing carbon fibers with uniformly coated carbon nanotubes according to claim 1, characterized in that, A high-shear dispersion process was used to disperse water-based carbon nanotube slurry. The dispersion conditions included a rotation speed of 1000-4500 rpm and a dispersion time of 1-20 min.

6. The method for preparing carbon fibers with uniformly coated carbon nanotubes according to claim 1, characterized in that, The ultrasonic treatment conditions after dispersing carbon nanotubes included a frequency of 20 kHz - 60 kHz and a time of 10-60 min.

7. The method for preparing carbon fibers with uniformly coated carbon nanotubes according to claim 1, characterized in that, The conditions for low-temperature drying include: a temperature of 60-80℃ and a time of 2-48h.

8. An apparatus used in a method for preparing carbon fibers with uniformly coated carbon nanotubes as described in any one of claims 1-7, characterized in that, The device includes a filtration device (3), on which a vacuum pump (4) is installed. An ultrasonic transducer (2) is connected to one side of the filtration device (3), and an ultrasonic generator (1) is connected to one end of the ultrasonic transducer (2). Carbon fiber (6) and CNT solution (7) are placed sequentially on the porous support layer (5) of the filtration device (3).

9. A carbon fiber with a uniformly coated carbon nanotube surface obtained by the preparation method of carbon fiber with a uniformly coated carbon nanotube surface according to any one of claims 1-7.

10. The application of the carbon fiber with uniformly coated carbon nanotubes as described in claim 9 in the field of carbon fiber reinforced resin matrix composites.

Images