Modified carbon fiber as well as preparation method and application thereof

Abstract

The invention discloses a modified carbon fiber and a preparation method and application thereof, the modified carbon fiber comprises a carbon fiber matrix, at least part of the surface of the carbon fiber matrix is coated with a coupling agent, and the coupling agent is grafted with polyhydroxy acid. The preparation method of the modified carbon fiber comprises the following steps: performing electrochemical oxidation treatment on the carbon fiber to activate the surface of the carbon fiber; carrying out silane coupling agent grafting on the carbon fiber, and introducing an active functional group; polyhydroxy acid reacts with the carbon fiber grafted with the silane coupling agent, and a firm amido bond is formed through amidation reaction, so that modification of the carbon fiber is realized. Carboxyl of the polyhydroxy acid reacts with amino on the surface of the carbon fiber to form a stable amido bond, and hydroxyl at the other end can chemically react with a resin matrix, so that the interface bonding force is effectively improved. In addition, the flexible chain segment of the cinnamic acid molecule can absorb and disperse stress, thereby possibly generating a positive effect on improving the toughness of the interface.

Description

Technical Field

[0001] This invention relates to the field of modified carbon fiber technology, specifically to a modified carbon fiber, its preparation method, and its uses. Background Technology

[0002] Carbon fiber is widely used in aerospace, automotive, and sporting goods due to its excellent properties such as high specific strength, high specific modulus, and corrosion resistance. However, the high chemical inertness of carbon fiber surface results in weak interfacial bonding with the resin matrix, making the composite material prone to interfacial delamination under stress, thus affecting the overall mechanical properties.

[0003] To improve the interfacial properties between carbon fibers and resins, surface treatments are typically applied to carbon fibers. Existing technologies include oxidation treatment, plasma treatment, and sizing agent coating. However, each single method has its limitations. While improving fiber surface activity, it can also cause varying degrees of damage to the fiber matrix. Moreover, the effects of single-method modification are limited, and they have not yet been widely used in industrial production. Summary of the Invention

[0004] The purpose of this invention is to overcome the problems existing in the prior art and to provide a modified carbon fiber, its preparation method, and its uses.

[0005] The technical problem solved by this invention is achieved by the following technical solution.

[0006] The present invention provides a modified carbon fiber, comprising: a carbon fiber matrix, wherein at least a portion of the surface of the carbon fiber matrix is ​​coated with a coupling agent, and a polyhydroxy acid is grafted onto the coupling agent.

[0007] The present invention provides a method for preparing the above-mentioned modified carbon fiber, comprising the following steps: after surface activation of carbon fiber, grafting a coupling agent, and then reacting the carbon fiber grafted with the coupling agent with a polyhydroxy acid to obtain modified carbon fiber.

[0008] This invention provides a use of the above-mentioned modified carbon fiber as a reinforcing fiber in a polymer matrix.

[0009] The present invention has the following beneficial effects: By electrochemical oxidation, coupling agent grafting, and polyhydroxy acid modification, active functional groups are introduced onto the carbon fiber surface, and amide bonds are constructed. The hydroxyl groups at the acid terminus of the polyhydroxy acids can form strong hydrogen bonds or chemical bonds with the resin matrix, enhancing the interfacial adhesion between the carbon fibers and the resin, achieving efficient stress transfer, and improving the interfacial shear strength of the composite material. Furthermore, the polyhydroxy acid molecular chains possess a certain length and flexibility, enabling the formation of flexible buffer regions in the interfacial layer. When the composite is subjected to external impact, these flexible chain segments can deform and absorb energy, preventing crack propagation, thereby improving the toughness and impact resistance of the composite. Detailed Implementation

[0010] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0011] The following is a detailed description of a modified carbon fiber, its preparation method, and its uses provided by embodiments of the present invention.

[0012] In a first aspect, the present invention provides a modified carbon fiber, comprising: a carbon fiber matrix, wherein at least a portion of the surface of the carbon fiber matrix is ​​coated with a coupling agent, and a polyhydroxy acid is grafted onto the coupling agent.

[0013] The modified carbon fiber provided by this invention has a coupling agent coated on at least a portion of the carbon fiber matrix surface. This coupling agent can introduce active groups such as amino groups onto the carbon fiber matrix. The amino groups introduced onto the carbon fiber matrix can further undergo an amidation reaction with the carboxyl groups of polyhydroxy acids to form amide bonds, thus achieving surface modification of the carbon fiber. When the modified carbon fiber is used to composite with a resin matrix, the coupling agent coated on at least a portion of the carbon fiber matrix surface, and the organic functional groups introduced onto the carbon fiber matrix surface, can enhance the chemical bonding with the resin. Simultaneously, the hydroxyl active groups contained in the polyhydroxy acids grafted onto the modified carbon fiber surface can also chemically react with the epoxy resin and other matrices. Furthermore, its flexible segments can absorb stress, further improving the interfacial toughness and bonding strength of the composite material, enabling the resulting composite material to be better applied in aerospace, automotive, and sporting goods fields.

[0014] In some alternative embodiments, the polyhydroxy acid is selected from 3,4-dihydroxycinnamic acid, and the amount of 3,4-dihydroxycinnamic acid used is 1.0-3.0% of the amount of carbon fiber matrix. For example, the amount of 3,4-dihydroxycinnamic acid used can be any other value between 1.0%, 1.5%, 2.0%, 2.5%, 3.0% or 1.0-3.0% of the amount of carbon fiber matrix.

[0015] In some alternative embodiments, the coupling agent comprises an aminosilane coupling agent, preferably γ-aminopropyltriethoxysilane, and the amount of the coupling agent is 0.8-1.0% of the amount of the carbon fiber matrix. Exemplarily, the amount of the coupling agent can be any other value between 0.80%, 0.85%, 0.90%, 0.95%, 1.00%, or 0.8-1.0% of the amount of the carbon fiber matrix.

[0016] Secondly, the present invention provides a carbon fiber surface treatment method, comprising the following steps: S1: Electrochemical oxidation treatment of carbon fibers to activate the carbon fiber surface; S2: Grafting of carbon fibers after electrochemical oxidation treatment with silane coupling agent; S3: Reaction of carbon fibers grafted with polyhydroxy acids and silane coupling agents yields modified carbon fibers.

[0017] This invention provides a carbon fiber surface treatment method. Electrochemical oxidation treatment can effectively introduce oxygen-containing functional groups (such as carboxyl and hydroxyl groups) to improve surface activity. Coupling agent grafting can introduce organic functional groups (such as amino groups) on the carbon fiber surface to enhance chemical bonding with resin. Finally, the carboxyl group of polyhydroxy acid reacts with the amino group on the carbon fiber surface to form a strong amide bond, thereby achieving modification of carbon fiber.

[0018] In some optional embodiments, in step S1, the electrochemical oxidation treatment is carried out using an electrolyte, which includes at least one of sulfuric acid, nitric acid, and phosphoric acid, with an electrolyte charge of 10-60 C / g and a treatment time of 15-30 s. Controlling these parameters within a suitable range is beneficial for efficiently activating the carbon fiber surface and avoiding excessive corrosion. For example, the electrolyte charge for the electrochemical oxidation treatment can be 10 C / g, 20 C / g, 30 C / g, 40 C / g, 50 C / g, 60 C / g, or any other value between 10-60 C / g, and the treatment time can be 15 s, 20 s, 25 s, 30 s, or any other value between 15 s and 30 s.

[0019] In some optional embodiments, in step S2, the silane coupling agent includes an aminosilane coupling agent, preferably γ-aminopropyltriethoxysilane. The silane coupling agent grafting reaction temperature is 50°C-80°C, and the reaction time is 1h-4h. Grafting with a silane coupling agent introduces amino groups onto the carbon fiber surface, providing active sites for subsequent reactions with 3,4-dihydroxycinnamic acid. Exemplarily, the silane coupling agent grafting reaction temperature can be any other value between 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, or 50°C-80°C, and the reaction time can be any other value between 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, or 1h-4h.

[0020] It is worth noting that in step S2, the amount of silane coupling agent is 0.8-1.0% of the amount of carbon fiber matrix. If the amount is too low, a complete and dense coupling agent molecular layer cannot be formed on the carbon fiber surface, and the modification effect is not significant; if the amount is too high, the excess coupling agent is prone to self-crosslinking and aggregation, forming a loose and unstable thick film on the fiber surface. This thick film will become a weak point at the interface, leading to a decrease in the performance of the composite material.

[0021] In some optional embodiments, in step S3, the reaction of the polyhydroxy acid with the silane coupling agent-grafted carbon fibers is carried out in a solvent, including at least one of N,N-dimethylformamide, dimethyl sulfoxide, or ethanol. The reaction temperature is 60°C-90°C, and the reaction time is 2h-6h. Furthermore, a condensing agent, such as N,N'-dicyclohexylcarbodiimide or 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride, may be added to promote the amidation reaction. Exemplarily, the reaction of the polyhydroxy acid with the silane coupling agent-grafted carbon fibers in the solvent can be carried out at a temperature of 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, or any other value between 60°C and 90°C, and the reaction time can be 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, 5.5h, 6h, or any other value between 2h and 6h.

[0022] It is worth noting that in step S3, the amount of polyhydroxy acid used is 1.0-3.0% of the amount of carbon fiber matrix. If the amount of polyhydroxy acid is too low, it cannot effectively cover and modify the carbon fiber surface, resulting in fewer active functional groups; if the amount is too high, it may form a loose layer of multi-layered physical adsorption, which may lead to a decrease in interfacial performance.

[0023] Thirdly, the present invention provides the use of the above-mentioned modified carbon fiber as a reinforcing fiber in a polymer matrix.

[0024] In some alternative embodiments, the polymer matrix is ​​a resin matrix.

[0025] This invention provides a modified carbon fiber, comprising: a carbon fiber matrix, wherein at least a portion of the surface of the carbon fiber matrix is ​​coated with a coupling agent, and a polyhydroxy acid is grafted onto the coupling agent. In some embodiments, the polyhydroxy acid is selected from 3,4-dihydroxycinnamic acid. The 3,4-dihydroxycinnamic acid grafted onto the surface of the carbon fiber matrix undergoes an amidation reaction between the carboxyl groups on the 3,4-dihydroxycinnamic acid and the amino groups on the carbon fiber surface, forming a strong amide bond. Simultaneously, the hydroxyl groups in the 3,4-dihydroxycinnamic acid molecule can form hydrogen bonds or chemical bonds with a resin matrix (such as epoxy resin), effectively improving interfacial bonding strength. Furthermore, the flexible segments of the 3,4-dihydroxycinnamic acid can absorb stress, further improving interfacial toughness and bonding strength. In addition, 3,4-dihydroxycinnamic acid can be directly extracted from natural cinnamon plants and then modified, providing a more environmentally friendly route for the preparation of carbon fiber composites and reducing dependence on petroleum-based chemical products.

[0026] The present invention will be further described below with reference to embodiments.

[0027] Example 1 This embodiment provides a modified carbon fiber, the preparation method of which includes the following steps: (1) Electrochemical oxidation treatment: The carbon fiber bundle is used as the anode and the graphite plate is used as the cathode. The mixture is placed in sulfuric acid electrolyte and treated for 20s at 30C / g charge. After removal, it is washed with deionized water and dried.

[0028] (2) Silane coupling agent grafting: The carbon fibers after electrochemical oxidation treatment were immersed in an ethanol solution containing 2wt% γ-aminopropyltriethoxysilane. The amount of γ-aminopropyltriethoxysilane was 0.85% of the amount of carbon fiber matrix. The reaction was carried out at 70℃ for 2h. After removal, the carbon fibers were washed with ethanol and dried.

[0029] (3) 3,4-Dihydroxycinnamic acid reaction: The carbon fibers grafted with silane coupling agent were immersed in a solution of N,N-dimethylformamide containing 0.1 mol / L 3,4-dihydroxycinnamic acid and 0.12 mol / L N,N'-dicyclohexylcarbodiimide. The amount of 3,4-dihydroxycinnamic acid was 1.5% of the amount of carbon fiber matrix. The reaction was carried out at 80°C for 4 h. After removal, the carbon fibers were washed with solvent and dried to obtain modified carbon fibers.

[0030] Example 2 This embodiment provides a modified carbon fiber, the preparation method of which differs from that of Example 1 in that: in step (1), the charge is 10C / g and the processing time is 25s.

[0031] Example 3 This embodiment provides a modified carbon fiber, the preparation method of which differs from that of Example 1 in that: in step (2), the amount of γ-aminopropyltriethoxysilane used is 0.7% of the amount of carbon fiber matrix.

[0032] Example 4 This embodiment provides a modified carbon fiber, the preparation method of which differs from that of Example 1 in that: in step (2), the amount of 3,4-dihydroxycinnamic acid is 0.5% of the amount of carbon fiber matrix.

[0033] Example 5 This embodiment provides a modified carbon fiber, the preparation method of which differs from that of Example 1 in that: in step (2), the amount of 3,4-dihydroxycinnamic acid used is 3.5% of the amount of carbon fiber matrix used.

[0034] Comparative Example 1 This comparative example provides a carbon fiber whose preparation method differs from that of Example 1 in that: Steps (2) and (3) are omitted, and only electrochemical oxidation treatment is performed.

[0035] Comparative Example 2 This comparative example provides a carbon fiber whose preparation method differs from that of Example 1 in that: in step (3), 3,4-dihydroxycinnamic acid is not used, but acetic acid is used instead.

[0036] Test case Composite materials were prepared by combining the carbon fibers provided in Examples 1-5 and Comparative Examples 1-2 with epoxy resin, and the interfacial shear strength (IFSS) was tested. The results are shown in Table 1. The specific test methods are as follows: Interfacial shear strength (IFSS): Resin, curing agent, and acetone are mixed in a specific ratio, thoroughly stirred, and allowed to stand until no more air bubbles remain. A small amount of resin droplet is slowly and evenly applied onto a carbon fiber monofilament fixed to a sample holder. Air bubbles in the resin droplet are removed under vacuum at room temperature. The sample coated with resin droplets is then placed in a vacuum oven for curing, creating an interfacial shear strength test sample. The test is performed using a droplet debonding apparatus, with the fixture moving horizontally away from the cured resin. The interfacial shear strength (IFSS) is calculated using the following formula: IFSS=F max / πdL Among them, F max denoted as the peak shear force during the debonding process of the resin microdroplets, d is the diameter of the carbon fiber, and L is the effective length of the carbon fiber embedded in the resin.

[0037] Table 1. Performance test results of carbon fiber in the examples and comparative examples.

[0038] As shown in Table 1, the modified carbon fibers prepared in Examples 1 and 2 of this invention exhibit significantly higher interfacial shear strengths in their composite materials compared to Comparative Examples 1 and 2. This indicates that the surface treatment method of this invention effectively enhances the interfacial bonding force between the carbon fibers and the resin.

[0039] A comparison of the results of Examples 1 and 4 and 5 shows that when the amount of 3,4-dihydroxycinnamic acid is in the range of 1.0%-3.0%, an effective modified layer can be formed, and the interfacial shear strength between the fiber and the resin is high.

[0040] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A modified carbon fiber, characterized by, The application relates to a modified carbon fiber and a preparation method thereof. The carbon fiber substrate is coated with a coupling agent on at least part of the surface, and the coupling agent is grafted with a polyhydroxy acid.

2. The modified carbon fiber according to claim 1, characterized by, The polyhydroxy acid is selected from 3,4-dihydroxycinnamic acid, and the coupling agent comprises at least one of amino silane coupling agents, preferably gamma-aminopropyl triethoxysilane, N-(beta-aminoethyl)-gamma-aminopropyl trimethoxysilane and gamma-aminopropyl trimethoxysilane.

3. The modified carbon fiber according to claim 1, wherein The amount of the coupling agent is 0.8-1.0% of the amount of the carbon fiber substrate.

4. The modified carbon fiber according to claim 1, wherein The amount of the polyhydroxy acid is 1.0-3.0% of the amount of the carbon fiber substrate.

5. A method for producing the modified carbon fiber according to any one of claims 1 to 4, characterized by, The application further relates to a preparation method of the modified carbon fiber. The method for activating the surface of the carbon fiber comprises the following steps: taking a carbon fiber bundle as an anode, taking a graphite plate as a cathode, and placing the carbon fiber bundle and the graphite plate in an electrolyte for electrochemical oxidation treatment.

6. The production method according to claim 5, wherein Preferably, the electrolyte for the electrochemical oxidation treatment comprises at least one of sulfuric acid, nitric acid and phosphoric acid, the electric quantity for the electrochemical oxidation treatment is 10-60 C / g, and the time is 15-30 s. The method for grafting the coupling agent after the surface of the carbon fiber is activated comprises the following steps: after the electrochemically oxidized carbon fiber is washed and dried, the carbon fiber is immersed in an ethanol solution containing 2 wt% of gamma-aminopropyl triethoxysilane for reaction.

7. The production method according to claim 6, wherein Preferably, the coupling agent comprises at least one of amino silane coupling agents, preferably gamma-aminopropyl triethoxysilane; the reaction temperature is 50-80 DEG C, and the reaction time is 1-4 h. The method for reacting the carbon fiber grafted with the coupling agent with the polyhydroxy acid comprises the following steps: after the carbon fiber grafted with the coupling agent is washed and dried, the carbon fiber is placed in a solvent containing a condensing agent and 1.0-3.0% of the polyhydroxy acid for reaction.

8. The method of claim 7, wherein, Preferably, the solvent comprises at least one of N,N-dimethylformamide, dimethyl sulfoxide and ethanol; the condensing agent comprises at least one of N,N'-dicyclohexyl carbodiimide and 1-ethyl-(3-dimethylaminopropyl) carbodiimide hydrochloride, the reaction temperature is 60-90 DEG C, and the reaction time is 2-6 h.

9. The modified carbon fiber according to any one of claims 1-4 is used as a reinforcing fiber of a polymer matrix. The polymer matrix is a resin matrix.

10. Use according to claim 9, characterized in that, ​

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