A carbon fiber / epoxy electromagnetic shielding composite material with strong interfacial bonding and its preparation method

Abstract

The application relates to the technical field of composite materials, and particularly discloses a carbon fiber / epoxy electromagnetic shielding composite material with strong interface bonding and a preparation method thereof, which comprises the following steps: hydrothermal reaction of oxidized carbon fibers O-CF, an organic ligand and an iron source in a solvent, washing and drying of the fibers to obtain MIL-loaded carbon fibers, carbonization treatment to obtain iron-based oxide-loaded carbon fibers dF@CF, vacuum-assisted introduction of epoxy resin into the multilayer carbon fibers dF@CF, and curing to obtain the carbon fiber / epoxy electromagnetic shielding composite material. The organic ligand and trivalent iron ions are used to synthesize a large number of rhombic MILs on the active sites on the surface of the carbon fibers, the MILs are reduced into iron-based oxide nanoparticles after carbonization, the iron-based oxide nanoparticles are closely loaded on the surface of the carbon fibers, the interface bonding performance is improved, the electromagnetic shielding efficiency is increased, and the carbon fiber / epoxy composite material with both the interface and the electromagnetic shielding efficiency is realized.

Description

Technical Field

[0001] This invention relates to the field of composite material technology, specifically to a carbon fiber / epoxy electromagnetic shielding composite material with strong interfacial bonding and its preparation method. Background Technology

[0002] Carbon fiber reinforced resin matrix composites possess lightweight, high specific strength, and high specific modulus, making them widely used in aerospace, transportation, and electronics industries. However, the poor interfacial properties between carbon fiber and the resin matrix remain a key challenge for these composites. Furthermore, the electromagnetic shielding provided by carbon fiber / epoxy composites relies primarily on reflection loss, which can cause secondary environmental pollution. Therefore, improving the interfacial bonding strength between carbon fiber and the resin matrix through surface modification, while simultaneously increasing absorption loss for electromagnetic shielding, is crucial for expanding their application areas.

[0003] Currently, traditional carbon fiber / epoxy composite materials still suffer from poor electromagnetic shielding and interfacial properties, and further research is needed on modifications that balance both properties.

[0004] For example, CN115710824A discloses a method for preparing a water-soluble epoxy resin emulsion for carbon fiber surface treatment. The carbon fiber is sized with a water-soluble epoxy resin emulsion prepared from polyethylene glycol, epoxy resin and catalyst as raw materials, which increases the roughness and wettability of the carbon fiber surface and can improve the interfacial properties between the carbon fiber and the thermosetting matrix.

[0005] For example, CN117698176A discloses a method for preparing graphene-carbon fiber / epoxy composite material. A self-made graphene oxide dispersion is coated on carbon fiber fabric, hydrogen is introduced into a vacuum chamber, annealing is performed, and then the temperature is raised and carbon source and hydrogen are introduced. Finally, a prepreg is obtained by resin impregnation, and an electromagnetic shielding composite material is obtained by hot pressing.

[0006] The above inventions only studied the single interface or electromagnetic shielding properties of carbon fiber / epoxy composites. Therefore, carbon fiber / epoxy resin composites that combine both interface and electromagnetic shielding properties still need further research.

[0007] In-situ growth is one of the methods for modifying carbon fiber surfaces to improve the interface and electromagnetic shielding performance of carbon fiber / epoxy composites. Researchers have also focused on growing conductive nanoparticles on the surface of carbon fibers to enhance the interface and electromagnetic shielding effectiveness of epoxy composites. However, conductive particles increase the proportion of reflection loss in electromagnetic shielding of carbon fiber / epoxy composites, causing secondary electromagnetic pollution. Research on improving the interface performance and electromagnetic shielding of carbon fiber / epoxy composites by in-situ growth of magnetic particles on the surface of carbon fibers to form electromagnetic synergy with the carbon fibers, while simultaneously increasing the proportion of absorption loss, is still rare. Summary of the Invention

[0008] This invention addresses the shortcomings of existing epoxy resin-based carbon fiber composites, such as poor interfacial bonding performance and inadequate electromagnetic shielding effectiveness. It provides a carbon fiber / epoxy electromagnetic shielding composite material with strong interfacial bonding. By modifying the surface of the carbon fiber, its interfacial bonding performance is improved while its electromagnetic shielding effectiveness is increased, thus achieving a carbon fiber / epoxy composite material that combines both interfacial bonding and electromagnetic shielding effectiveness.

[0009] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0010] A method for preparing a carbon fiber / epoxy electromagnetic shielding composite material with strong interfacial bonding, comprising the following steps:

[0011] Step 1: Oxidize the desized carbon fiber with nitric acid to obtain oxidized carbon fiber O-CF;

[0012] Step 2: O-CF, organic ligand and iron source are subjected to hydrothermal reaction in solvent. After washing and drying, the fiber is obtained as MIL-loaded carbon fiber.

[0013] Step 3: Carbonize the MIL-loaded carbon fiber in an inert gas environment to obtain iron-based oxide-loaded carbon fiber dF@CF;

[0014] Step 4: Epoxy resin is introduced into multilayer carbon fiber dF@CF using a vacuum-assisted method, and then cured to obtain the carbon fiber / epoxy electromagnetic shielding composite material.

[0015] This invention utilizes micron-scale carbon fibers. Under specific conditions, organic ligands and ferric ions are used to synthesize a large number of rhombic microcrystalline ligands (MILs) at active sites on the carbon fiber surface. The MIL-modified carbon fibers are then subjected to high-temperature carbonization under an inert gas atmosphere. The MILs are reduced to iron-based oxide nanoparticles that are tightly loaded onto the carbon fiber surface. An epoxy resin-based composite material is then prepared under vacuum assistance, resulting in a MIL-derived iron-based oxide-modified carbon fiber / epoxy electromagnetic shielding composite material. The MIL-derived iron-based oxides loaded on the carbon fiber surface increase the surface roughness, enhance the mechanical interlocking of the epoxy resin, and improve its interfacial adhesion. Simultaneously, the iron-based oxides and carbon fibers form an electromagnetic synergistic effect, increasing electromagnetic shielding effectiveness and improving the proportion of absorption loss, thus achieving a carbon fiber / epoxy composite material that combines both interfacial and electromagnetic shielding performance.

[0016] The organic ligand includes at least one of terephthalic acid, fumaric acid, and trimesic acid; the iron source includes at least one of ferric nitrate nonahydrate, ferric chloride hexahydrate, and ferric nitrate nonahydrate.

[0017] The molar ratio of the organic ligand to the iron source is 1:0.1 to 1:5; preferably 1:1.

[0018] In step 2, the total molar concentration of the organic ligand and iron source in the solvent is 20% to 30%.

[0019] In the hydrothermal reaction of step 2, the mass-volume ratio of O-CF carbon fiber to solvent is 40g~70g:300~500ml.

[0020] In step 1, desizing is performed using an organic solvent extraction method. The extraction temperature is 60℃~100℃ and the time is 50~100h. The organic solvent includes at least one of methanol, ethanol, and acetone.

[0021] The desizing was performed using an organic solvent extraction method, with a mass-to-volume ratio of carbon fiber to solvent of 40g-70g:500ml-700ml.

[0022] In step 1, the oxidation treatment temperature is 20–120℃, the reaction time is 1–48 h, and the concentration of nitric acid is 90–98%.

[0023] The solvent in step 2 includes one or more of the following: water, ethanol, diethyl ether, acetone, acetonitrile, tetrahydrofuran, and N,N-dimethylformamide.

[0024] The hydrothermal reaction is carried out at a temperature of 60–100°C for 2–10 hours.

[0025] In step 3, the carbonization temperature is 300-600℃, and the processing time is 1-10 hours. Preferably, the carbonization temperature is 300-500℃, more preferably 350-450℃, and even more preferably 400℃.

[0026] The curing agent used in step 4 includes one or more combinations of diethylenetriamine, triethylenetetramine, m-phenylenediamine, and polyamide; the mass ratio of epoxy resin to curing agent is 1:0.05 to 1:0.25.

[0027] The curing process in step 4 is 0.5-2 hours at 70-90℃, 1-3 hours at 100-130℃, and 1-3 hours at 140-160℃.

[0028] The present invention also provides a carbon fiber / epoxy electromagnetic shielding composite material with strong interfacial bonding obtained according to the preparation method described above.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] In this invention, rhombic micro-layers (MILs) are loaded onto the surface of carbon fibers. After carbonization, the rhombic MILs on the surface undergo structural decomposition at high temperatures and are reduced to iron-based oxides. This increases the surface roughness of the carbon fibers, serving as mechanical anchors for bonding with the resin and increasing the interfacial adhesion strength between the carbon fibers and the resin. The iron-based oxides introduced onto the surface of the carbon fibers in the carbon fiber / epoxy composite material increase magnetic loss, multiple reflection loss, and interfacial polarization loss, thereby effectively improving electromagnetic shielding performance. Attached Figure Description

[0031] Figure 1 This is a scanning electron microscope image of the rhombic MIL grown in situ on the carbon fiber surface in Example 1.

[0032] Figure 2 This is a scanning electron microscope image of the iron-based oxide derived from rhombic MIL grown in situ on the carbon fiber surface in Example 1.

[0033] Figure 3 This is a scanning electron microscope image of the iron-based oxide derived from rhombic MIL grown in situ on the carbon fiber surface in Example 2.

[0034] Figure 4 This is a scanning electron microscope image of the iron-based oxide derived from rhombic MIL grown in situ on the carbon fiber surface in Example 3. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Modifications or equivalent substitutions made by those skilled in the art based on their understanding of the technical solutions of this invention, without departing from the spirit and scope of the invention, should be covered within the protection scope of this invention.

[0036] The raw materials used in the following specific embodiments were all purchased from the market. The carbon fiber plain weave fabric was provided by Toray Industries, Inc. of Japan, model 12k-T700.

[0037] The interfacial performance evaluation device evaluated the interfacial shear strength between carbon fiber and epoxy resin through a microdroplet debonding test. First, a single carbon fiber was fixed onto a concave metal frame (26mm × 58mm) using high-temperature resistant adhesive. Second, epoxy resin (E-51) and curing agent (TETA) were thoroughly mixed at a mass ratio of 100:12, degassed under vacuum, and finally micro-coated onto the carbon fiber surface using a steel needle. Due to the surface tension effect, the liquid resin on the fiber surface spontaneously shrinks into an ellipsoid. Then, it was cured at 120℃ for 6 hours. The IFSS value can be calculated using equation (1):

[0038]

[0039] In the formula, Fmax is the maximum recorded load, d is the average diameter of the CF, and l is the embedding length of the epoxy droplet. The IFSS data for each sample is the average of at least 30 valid data points.

[0040] The interlaminar shear strength (ILSS) of the composite material was tested using an Instron 5985 universal testing machine, and the test standard was ASTM D2344.

[0041] The electromagnetic interference shielding efficiency (EMI SE) of the composite material was tested using an E506A vector network analyzer. The test frequency was 8.2-12.4 GHz (X-band). The length × width × thickness of the test rectangular strip was 10.16 mm × 22.86 mm × 2 mm.

[0042] Comparative Example 1

[0043] Carbon fibers were placed in a Soxhlet extractor and desized with acetone at 80°C for 72 hours. After desizing, the fibers were rinsed three times with deionized water and dried in an oven at 80°C for 12 hours to obtain desized carbon fibers, denoted as d-CF. Epoxy resin and triethylenetetramine were mixed at a mass ratio of 1:0.12, degassed at room temperature, and the resin was injected into 5 layers of d-CF of equal size using a vacuum-assisted injection molding process. The mixture was then kept at 80°C for 2 hours and allowed to cool naturally before being removed to obtain the desized carbon fiber / epoxy composite material. The test results are shown in Table 1.

[0044] Comparative Example 2

[0045] The d-CF prepared in Comparative Example 1 was acidified with concentrated nitric acid at 100℃ for 2 hours, introducing a large number of hydroxyl and carboxyl active groups onto the carbon fiber surface. After washing until neutral, it was kept in an oven at 80℃ for 12 hours to obtain oxidized carbon fiber, denoted as O-CF. Five-layer oxidized carbon fiber / epoxy composite materials were prepared using the same preparation method and curing process as Comparative Example 1, and the test results are shown in Table 1.

[0046] Example 1

[0047] 10.82 g of ferric chloride and 4.64 g of fumaric acid were added sequentially to 300 ml of N,N-dimethylformamide and dissolved by magnetic stirring. The reaction solution was poured into a hydrothermal reactor, and 60 g of O-CF prepared in Comparative Example 2 was added. The reactor was then tightened and placed in an oven at 100 °C for 4 h. After natural cooling, the reactor was removed, washed, and dried in a vacuum oven at 60 °C for 12 h to obtain carbon fibers with rhombic micrometers loaded on the surface. The microstructure of the carbon fibers is as follows. Figure 1 As shown.

[0048] The in-situ grown carbon fibers were placed in a high-temperature tube furnace and maintained at 400℃ for 4 hours under a nitrogen atmosphere with a heating rate of 5℃ / min. After natural cooling, carbon fibers loaded with iron oxide nanoparticles were obtained, denoted as dF-400@CF, and their microstructure is shown in the figure. Figure 2 As shown, the rhombic MILs are oxidized to form iron oxides that adhere to the fiber surface. A five-layer modified carbon fiber / epoxy composite material, denoted as dF-400@CF / EP composite material, was prepared using the same preparation method and curing process as Comparative Example 1. The test results are shown in Table 1.

[0049] Example 2

[0050] The carbon fibers loaded with rhombic MILE from Example 1 were placed in a high-temperature tube furnace and kept at 300°C for 4 hours under a nitrogen atmosphere with a heating rate of 5°C / min. After natural cooling, carbon fibers loaded with iron oxide nanoparticles were obtained, denoted as dF-300@CF, and their microstructure is as follows. Figure 3As shown in Table 1, a five-layer modified carbon fiber / epoxy composite material, denoted as dF-300@CF / EP composite material, was prepared using the same preparation method and curing process as Comparative Example 1. The test results are shown in Table 1.

[0051] Example 3

[0052] The carbon fibers loaded with rhombic MILE from Example 1 were placed in a high-temperature tube furnace and heated to 500°C for 4 hours under a nitrogen atmosphere at a heating rate of 5°C / min. After natural cooling, carbon fibers loaded with iron oxide nanoparticles were obtained, denoted as dF-500@CF, and their microstructure is as follows. Figure 4 As shown in Table 1, a five-layer modified carbon fiber / epoxy composite material, denoted as dF-500@CF / EP composite material, was prepared using the same preparation method and curing process as Comparative Example 1. The test results are shown in Table 1.

[0053] Comparative Example 3

[0054] Using the same preparation method and curing process as Comparative Example 1, a 5-layer carbon fiber cloth / epoxy composite material was prepared using Toray T700 12k plain weave carbon fiber from Japan. The test results are shown in Table 1.

[0055] Table 1. Properties of carbon fiber / epoxy composites prepared in the examples and comparative examples.

[0056]

[0057] In Example 1, the abundant iron-based oxides on the carbon fiber surface provide more mechanical anchor points, enhancing mechanical interlocking with the resin and resulting in higher interfacial performance. Furthermore, the increased iron-based oxides in Example 1 improve the magnetic loss, multiple reflection loss, and interfacial polarization loss of the carbon fiber / epoxy composite, effectively increasing electromagnetic shielding effectiveness and the proportion of absorption loss. The loaded iron-based oxides generated after MIL pyrolysis at 400℃ in Example 1 are more uniform and denser than those in Examples 2 and 3, resulting in a epoxy composite with stronger interfacial bonding and electromagnetic shielding effectiveness. In Example 2, the carbonization temperature of 300℃ is too low, preventing the complete conversion of the MIL loaded on the carbon fiber surface into iron-based oxides, leading to a composite with lower electromagnetic shielding effectiveness than the composite in Example 1. In Example 3, the carbonization temperature of 500℃ is too high, causing the MIL loaded on the carbon fiber surface to pyrolyze and detach, resulting in a composite with lower interfacial performance and electromagnetic shielding effectiveness than the composite in Example 1, but overall performance is superior compared to the control group.

Claims

1. A method for preparing a carbon fiber / epoxy electromagnetic shielding composite material with strong interfacial bonding, characterized in that, The method comprises the steps of: Step 1, oxidizing the desized carbon fiber by using nitric acid with a concentration of 90-98%, the temperature of the oxidation treatment is 20-120℃, and the reaction time is 1-48h, to obtain oxidized carbon fiber O-CF; Step 2, hydrothermal reaction of O-CF, organic ligand and iron source in a solvent, and the fiber is washed and dried to obtain MIL-loaded carbon fiber; the organic ligand comprises at least one of terephthalic acid, fumaric acid and trimesic acid; Step 3, carbonization of the MIL-loaded carbon fiber in an inert gas environment, carbonization treatment at 300-500℃ for 1-10h, to obtain iron-based oxide-loaded carbon fiber dF@CF; Step 4, introducing epoxy resin into the multi-layer carbon fiber dF@CF by a vacuum-assisted method, and curing to obtain the carbon fiber electromagnetic shielding epoxy composite material.

2. The method of producing a carbon fiber / epoxy electromagnetic shielding composite material with strong interfacial bonding according to claim 1, characterized by, The iron source comprises at least one of ferric nitrate nonahydrate and ferric chloride hexahydrate.

3. The method of producing a carbon fiber / epoxy electromagnetic shielding composite material with strong interfacial bonding according to claim 1, characterized by, The molar ratio of the organic ligand to the iron source is 1:0.1-1:

5. In step 2, the total molar concentration of the organic ligand and the iron source in the solvent is 20%-30%.

4. The method of making a strongly interfacially bonded carbon fiber / epoxy electromagnetic shielding composite of claim 1, wherein, In step 1, the desizing is carried out by using an organic solvent extraction method, the extraction temperature is 60-100℃, and the time is 50-100h; the organic solvent comprises at least one of methanol, ethanol and acetone.

5. The method of manufacturing a strong interfacial bonded carbon fiber / epoxy electromagnetic shielding composite of claim 1, wherein, The solvent in step 2 comprises one or a combination of water, ethanol, diethyl ether, acetone, acetonitrile, tetrahydrofuran and N,N-dimethylformamide; The temperature of the hydrothermal reaction is 60-100℃, and the reaction time is 2-10h.

6. The method of making a strongly interfacially bonded carbon fiber / epoxy electromagnetic shielding composite of claim 1, wherein, In step 4, the curing agent used for curing comprises one or a combination of diethylenetriamine, triethylenetetramine, m-phenylenediamine and polyamide; the mass ratio of the epoxy resin to the curing agent is 1:0.05-1:0.

25.

7. The method of making a strongly interfacially bonded carbon fiber / epoxy electromagnetic shielding composite of claim 1, wherein, In step 4, the curing process is 0.5-2h at 70-90℃, 1-3h at 100-130℃ and 1-3h at 140-160℃.

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