Carbon fiber surface treatment method based on solvation layer regulation and control and carbon fiber

Abstract

The invention belongs to the technical field of carbon fiber surface treatment, and provides a carbon fiber surface treatment method based on solvation layer regulation and control and a carbon fiber. The method comprises the following steps: placing carbon fibers in an electrolyte for electrochemical treatment to obtain pretreated carbon fibers; carrying out post-treatment on the pretreated carbon fiber; the solute of the electrolyte comprises ammonium bicarbonate and / or ammonium bisulfate; the electrolyte contains a solvation structure regulating agent, and the solvation structure regulating agent contains one or more of ethylene glycol, glycerol, urea and propylene glycol. According to the surface treatment method, the content of oxygen-containing functional groups on the surfaces of the carbon fibers is increased by 40% or above, the tensile strength of carbon fiber monofilaments is reduced by not more than 10%, and the interface bonding performance of a composite material prepared from the treated carbon fibers and vinyl resin is improved by 30% or above.

Description

Technical Field

[0001] This invention relates to the field of carbon fiber surface treatment technology, and in particular to a carbon fiber surface treatment method based on solvation layer control and carbon fiber. Background Technology

[0002] Carbon fiber, due to its superior properties such as high specific strength, high specific modulus, and good corrosion resistance, is widely used in aerospace, wind turbine blades, high-end equipment manufacturing, and advanced composite materials. However, during the preparation of carbon fiber, the degree of surface graphitization continuously increases, and the carbon fiber surface gradually becomes inert, with a low content of polar functional groups and insufficient surface energy. This results in limited wettability and interfacial bonding strength between the carbon fiber and the resin matrix, restricting further improvement of the overall performance of carbon fiber reinforced composites.

[0003] To improve the interfacial properties between carbon fibers and the resin matrix, research on carbon fiber surface modification technology is crucial. Introducing oxygen-containing functional groups such as hydroxyl, carboxyl, and carbonyl groups, or polar functional groups such as nitrogen groups, onto the carbon fiber surface can increase the surface energy and simultaneously enhance the interfacial interaction between the carbon fiber and the resin matrix. Currently, commonly used industrial methods for carbon fiber surface modification mainly include chemical oxidation, electrochemical anodizing, and plasma treatment. Among these, electrochemical anodizing, with its mature process, controllable parameters, and ease of continuous wire feeding, has become one of the most widely used surface modification technologies in the industrial production of carbon fibers.

[0004] Currently, several patents have proposed electrochemical or anodizing treatment methods for carbon fiber surfaces. For example, Chinese patent CN105063994A discloses a carbon fiber surface treatment method that wets the carbon fiber bundle with deionized water before electrochemical anodizing to improve the wettability of the electrolyte on the fiber, thereby improving the uniformity of the anodizing treatment and enhancing the interfacial bonding performance between the carbon fiber and the resin matrix. Chinese patent CN104562631A discloses a carbon fiber anodizing surface treatment method that improves the surface morphology and oxygen-containing functional group content of carbon fibers through pretreatment, anodizing, and cleaning and drying processes, thereby enhancing the mechanical properties of carbon fibers and their interfacial bonding performance in composite materials. In addition, US patent US4839006A also discloses a multi-step electrochemical treatment process that introduces oxygen-containing functional groups into the carbon fiber surface by using carbon fibers as the anode and treating them under different electrolysis conditions, thereby improving the surface properties and interfacial bonding ability of the carbon fibers. The aforementioned existing technologies, through optimization of macroscopic process parameters such as electrolyte system, process flow, and current conditions, have improved the surface activity of carbon fibers and the interfacial properties of their composites to a certain extent, providing an important technical foundation for the industrial surface modification of carbon fibers. However, the following shortcomings still exist: ① The electrochemical anodizing reaction mainly relies on macroscopic conditions such as current density, processing time, or electrolyte oxidizing properties for regulation, which can easily lead to non-selective oxidation reactions on the carbon fiber surface, causing continuous surface etching, easily damaging the microcrystalline structure of carbon fibers, and resulting in a decrease in the mechanical properties of single filaments; ② Under continuous fiber feeding and large fiber bundle processing conditions, there are differences in mass transfer and reaction environments between the inner and outer layers of the carbon fiber bundle, and existing technologies cannot effectively control the uniformity of processing from the intrinsic level of the interface; ③ Some processes rely on complex potential programs or external field coupling methods, requiring high levels of equipment and process control, which is not conducive to stable and continuous industrial production.

[0005] From the perspective of electrochemical reaction mechanism, the solvation layer at the anolyte interface, composed of water molecules and dissolved ions, is a key interfacial region for oxidizing species to approach the carbon fiber surface. The structure and thickness of the solvation layer directly affect the location, depth, and mode of oxidation reaction. However, existing electrochemical surface treatment technologies generally focus on improving macroscopic parameters such as current, potential, and electrolyte composition. There has been little research or attention paid to the structure of the solvation layer at the anolyte interface and its influence on oxidation reaction behavior. Therefore, an effective technical solution for finely controlling carbon fiber surface oxidation by adjusting the intrinsic properties of the solvation layer has not yet been developed.

[0006] Therefore, it is necessary to propose a new electrochemical surface treatment method for carbon fibers. Without relying on strong corrosion conditions or complex potential programs, this method can effectively control the depth and uniformity of oxidation reaction on carbon fiber surfaces by adjusting the structure and thickness of the solvation layer at the anodic interface, thereby changing the way oxidizing species approach the carbon fiber surface and the oxidation reaction behavior. Summary of the Invention

[0007] The purpose of this invention is to provide a carbon fiber surface treatment method and carbon fiber based on solvation layer regulation, addressing the shortcomings of existing technologies.

[0008] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a carbon fiber surface treatment method based on solvation layer regulation, comprising the following steps: 1) Carbon fibers are placed in an electrolyte and subjected to electrochemical treatment to obtain pretreated carbon fibers; 2) Post-process the pretreated carbon fibers; The solute in the electrolyte contains ammonium bicarbonate and / or ammonium bisulfate; The electrolyte contains a solvation structure modifier, which includes one or more of ethylene glycol, glycerol, urea, and propylene glycol.

[0009] Preferably, the mass of the solvation structure modifier is 0.1-3% of the mass of the electrolyte.

[0010] Preferably, the mass fraction of the solute in the electrolyte is 0.1-5%.

[0011] Preferably, the current density of the electrochemical treatment is 0.5~25A / m², and the electrochemical treatment time is 0.3~5min.

[0012] Preferably, the post-processing includes sequential ultrasonic cleaning and drying.

[0013] Preferably, the ultrasonic cleaning power is 300~400W and the ultrasonic cleaning time is 10~30min.

[0014] Preferably, the drying temperature is 70~90℃ and the drying time is 30~60min.

[0015] The present invention also provides carbon fibers obtained by using the carbon fiber surface treatment method based on solvation layer regulation.

[0016] The beneficial effects of this invention are: 1) This invention uses ammonium bicarbonate and / or ammonium bisulfate as the electrolyte and introduces specific types of solvation structure modifiers into the electrolyte. By adjusting the hydrogen bond network structure of water molecules, the structure and thickness of the solvation layer at the anode interface are controlled. During the continuous wire-flying anodizing of carbon fibers, by matching the thickness of the solvation layer with the residence time of the carbon fibers in the electrolyte, the ability of oxidizing species to approach the carbon fiber surface and the oxidation reaction mode are controlled. This allows the oxidation reaction to preferentially occur in the defective carbon or edge carbon structure regions on the carbon fiber surface, effectively suppressing non-selective continuous etching, reducing damage to the carbon fiber microcrystalline structure, and achieving precise control over the oxidation reaction depth, oxidation reaction mode, and uniformity on the carbon fiber surface. This achieves the regulation of the anodizing reaction from the intrinsic interface level. It can effectively reduce damage to the carbon fiber microcrystalline structure and mechanical properties while increasing the functional group content on the carbon fiber surface without the need for strong corrosion conditions or complex potential programs. It is suitable for industrial continuous processing and is beneficial for improving the interfacial properties of carbon fiber reinforced composites.

[0017] 2) The surface treatment method of the present invention increases the content of oxygen-containing functional groups on the carbon fiber surface by more than 40%, reduces the tensile strength of carbon fiber monofilament by no more than 10%, and improves the interfacial bonding performance of the composite material prepared by carbon fiber and vinyl resin by more than 30%. Attached Figure Description

[0018] Figure 1 The images are scanning electron microscope (SEM) images of carbon fibers treated in Examples 1-8 and Comparative Examples 1-3, where (a) is Comparative Example 1, (b) is Comparative Example 2, (c) is Comparative Example 3, (d) is Example 1, (e) is Example 2, (f) is Example 3, (g) is Example 4, (h) is Example 5, (i) is Example 6, (j) is Example 7, and (k) is Example 8. Detailed Implementation

[0019] This invention provides a carbon fiber surface treatment method based on solvation layer regulation, comprising the following steps: 1) Carbon fibers are placed in an electrolyte and subjected to electrochemical treatment to obtain pretreated carbon fibers; 2) Post-process the pretreated carbon fibers; The solute in the electrolyte contains ammonium bicarbonate and / or ammonium bisulfate; The electrolyte contains a solvation structure modifier, which includes one or more of ethylene glycol, glycerol, urea, and propylene glycol.

[0020] In this invention, the mass of the solvation structure regulator is preferably 0.1-3% of the electrolyte mass, more preferably 0.5-2.5%, and even more preferably 1-2%. Under the combined influence of the electric field and the solvation structure regulator, water molecules and dissolved ions at the anode interface form a solvation layer of a specific thickness. The solvation layer regulates the ability of oxidizing species to approach the carbon fiber surface through its hydrated shell structure and hydrogen bond network. When the thickness of the solvation layer increases, the oxidation reaction tends to be milder; when the thickness of the solvation layer decreases, oxidizing species are closer to the carbon fiber surface, which is conducive to the formation of surface functional groups. By adjusting the type and amount of the solvation structure regulator, and in conjunction with the current density and electrochemical treatment time, the thickness of the solvation layer can be controlled, so that the oxidation reaction preferentially acts on the defect carbon or edge carbon structure on the carbon fiber surface, thereby achieving precise control over the oxidation reaction depth and oxidation reaction mode on the carbon fiber surface.

[0021] In this invention, the mass fraction of the solute in the electrolyte is preferably 0.1-5%, more preferably 0.5-4%, and even more preferably 1-3%.

[0022] In this invention, the current density of the electrochemical treatment is preferably 0.5~25A / m², more preferably 2.5~20A / m², and even more preferably 5~15A / m²; the electrochemical treatment time is preferably 0.3~5min, more preferably 0.5~3min, and even more preferably 1~2min.

[0023] In this invention, the post-processing preferably includes sequential ultrasonic cleaning and drying.

[0024] In this invention, the power of the ultrasonic cleaning is preferably 300-400W, more preferably 320-380W, and even more preferably 350W; the ultrasonic cleaning time is preferably 10-30 minutes, more preferably 15-25 minutes, and even more preferably 20 minutes. Ultrasonic cleaning removes residual electrolyte and solvated structure modifiers.

[0025] In this invention, the drying temperature is preferably 70~90℃, more preferably 75~85℃, and even more preferably 80℃; the drying time is preferably 30~60min, more preferably 40~50min, and even more preferably 45min.

[0026] In this invention, the carbon fiber is preferably placed in an electrolytic cell in a continuous feeding manner and used as an anode for electrochemical treatment.

[0027] In this invention, the cathode of the electrochemical treatment is preferably a graphite electrode, which is preferably placed parallel to the carbon fiber along the fiber feeding direction to ensure the stability of the electric field distribution and the continuity of the treatment process.

[0028] The present invention also provides carbon fibers obtained by using the carbon fiber surface treatment method based on solvation layer regulation.

[0029] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0030] In the embodiments and comparative examples of the present invention, the electrochemical treatment is carried out in an electrochemical treatment device, which includes an electrolytic cell, a DC regulated power supply, a guide roller assembly, and a tension control device. The carbon fiber enters the electrolytic cell through the guide roller assembly in a continuous feeding manner and serves as the anode, being completely immersed in the electrolyte. A graphite cathode is provided in the electrolytic cell, which is arranged parallel to the carbon fiber along the feeding direction. The tension control device ensures that the carbon fiber passes continuously through the electrolytic cell.

[0031] The materials used in the examples and comparative examples are shown in Table 1.

[0032] Table 1 Material Information Sheet

[0033] Example 1

[0034] Add 60g of ammonium bicarbonate to 4000g of deionized water and stir magnetically until fully dissolved to obtain a 1.5% ammonium bicarbonate solution. Add 41.0g of ethylene glycol to the ammonium bicarbonate solution and stir magnetically until fully dissolved to obtain the electrolyte (ethylene glycol accounts for 1% of the electrolyte mass). Place the electrolyte in the electrolytic cell of the electrochemical treatment device and apply a current density of 10A / m. 2 The carbon fiber was electrochemically treated for 2 minutes to obtain pretreated carbon fiber. The pretreated carbon fiber was placed in deionized water and ultrasonically cleaned with 350W power for 20 minutes, and then dried at 80℃ for 50 minutes to obtain surface-treated carbon fiber.

[0035] Example 2

[0036] In Example 1, ethylene glycol was replaced with glycerol, and everything else was the same as in Example 1.

[0037] Example 3

[0038] Replace ethylene glycol in Example 1 with urea, otherwise remain the same as in Example 1.

[0039] Example 4

[0040] Add 60g of ammonium bisulfate to 4000g of deionized water and stir magnetically until fully dissolved to obtain a 1.5% ammonium bisulfate solution. Add 41.0g of ethylene glycol to the ammonium bisulfate solution and stir magnetically until fully dissolved to obtain the electrolyte (ethylene glycol accounts for 1% of the electrolyte mass). Place the electrolyte in the electrolytic cell of the electrochemical treatment device and apply a current density of 10A / m. 2 The carbon fiber was electrochemically treated for 2 minutes to obtain pretreated carbon fiber. The pretreated carbon fiber was placed in deionized water and ultrasonically cleaned with 350W power for 20 minutes, and then dried at 80℃ for 50 minutes to obtain surface-treated carbon fiber.

[0041] Example 5

[0042] In Example 4, ethylene glycol was replaced with glycerol, and everything else was the same as in Example 4.

[0043] Example 6

[0044] In Example 4, ethylene glycol was replaced with urea, and everything else was the same as in Example 4.

[0045] Example 7

[0046] Add 60g of ammonium bisulfate to 4000g of deionized water and stir magnetically until fully dissolved to obtain a 1.5% ammonium bisulfate solution. Add 85g of ethylene glycol to the ammonium bisulfate solution and stir magnetically until fully dissolved to obtain the electrolyte (ethylene glycol accounts for 2% of the electrolyte mass). Place the electrolyte in the electrolytic cell of the electrochemical treatment device and apply a current density of 10A / m³. 2 The carbon fiber was electrochemically treated for 2 minutes to obtain pretreated carbon fiber. The pretreated carbon fiber was placed in deionized water and ultrasonically cleaned with 350W power for 20 minutes, and then dried at 80℃ for 50 minutes to obtain surface-treated carbon fiber.

[0047] Example 8

[0048] 60g of ammonium bisulfate was added to 4000g of deionized water and magnetically stirred until fully dissolved, yielding a 1.5% ammonium bisulfate solution. 126g of ethylene glycol was added to the ammonium bisulfate solution and magnetically stirred until fully dissolved, yielding the electrolyte (ethylene glycol constitutes 3% of the electrolyte mass). The electrolyte was placed in the electrolytic cell of the electrochemical treatment device and subjected to a current density of 10A / m³. 2 The carbon fiber was electrochemically treated for 2 minutes to obtain pretreated carbon fiber. The pretreated carbon fiber was placed in deionized water and ultrasonically cleaned with 350W power for 20 minutes, and then dried at 80℃ for 50 minutes to obtain surface-treated carbon fiber.

[0049] Comparative Example 1

[0050] The carbon fiber was placed in deionized water and ultrasonically cleaned at 350W for 20 minutes, and then dried at 80℃ for 50 minutes.

[0051] Comparative Example 2

[0052] The ethylene glycol in Example 1 is omitted, and everything else is the same as in Example 1.

[0053] Comparative Example 3

[0054] The ethylene glycol in Example 1 was replaced with anhydrous ethanol, and everything else was the same as in Example 1.

[0055] Comparative Example 4

[0056] In Example 1, ethylene glycol was replaced with acetone, and everything else was the same as in Example 1.

[0057] Comparative Example 5

[0058] The ethylene glycol in Example 4 is omitted, and everything else is the same as in Example 4.

[0059] Comparative Example 6

[0060] In Example 4, ethylene glycol was replaced with anhydrous ethanol, and everything else was the same as in Example 4.

[0061] Comparative Example 7

[0062] In Example 4, ethylene glycol was replaced with acetone, and everything else was the same as in Example 4.

[0063] The carbon fibers treated in Examples 1-8 and Comparative Examples 1-7 were subjected to monofilament tensile strength and interfacial shear properties tests, respectively. The content of oxygen-containing functional groups on the carbon fiber surface was also tested. The test results are shown in Table 2.

[0064] The tensile strength of a single filament was tested using an LLY-06E electron micro-tense tensile tester at a tensile speed of 5 mm / min. The tensile strength was calculated as: maximum load at break of the single filament / cross-sectional area of ​​the single filament. Twenty single filaments were tested, and the average value was taken.

[0065] The interfacial shear strength (IFSS) test method is as follows: Bisphenol A type vinyl resin and methyl ethyl ketone peroxide (LPT) are mixed evenly at a mass ratio of 100:2 to obtain a resin solution. The resin solution is applied to the surface of carbon fiber monofilaments using an acupuncture needle, and then cured at 140℃ for 2 hours to obtain a composite material. Composite material samples with a resin coverage length of 50~80µm are selected, and the maximum external force (denoted as Fm) during the microdroplet debonding process is tested using a composite material evaluation device HM410 (TOEI KASEI, Japan). The cross-sectional shear strength is calculated according to the formula IFSS=Fm / πdL, where d is the diameter of the carbon fiber monofilament and L is the sampling length. Six monofilaments are tested, and the average value is taken.

[0066] The surface chemical composition of carbon fibers was characterized by X-ray photoelectron spectroscopy to calculate the content of oxygen-containing functional groups. Monochromatic Al Kα X-rays (hν=1486.6eV) were used as the excitation source, and the full-spectrum scan pass energy was set to 100 eV.

[0067] Table 2 Results of tensile strength and interfacial shear properties of monofilaments

[0068] As shown in Table 1, the oxygen-containing functional group content on the carbon fiber surface of Examples 1-8 is significantly higher than that of the untreated Comparative Example 1 and the Comparative Examples 2 and 5 treated with traditional electrochemical methods. Compared with Comparative Examples 3, 4, 6, and 7, which used anhydrous ethanol and acetone as solvation modifiers, the oxygen-containing functional group content increases by more than 40%, indicating a significant improvement in carbon fiber activity. Correspondingly, the interfacial shear strength of Examples 1-8 is improved to varying degrees, reaching more than 30%. On this basis, the tensile strength of the single filament of the carbon fiber in Examples 1-8 is reduced by no more than 10% compared with the untreated Comparative Example 1. The above results indicate that by adding ethylene glycol, glycerol, urea, or propylene glycol as solvation structure modifiers to participate in the electrochemical treatment of carbon fibers in this invention, the content of oxygen-containing functional groups on the carbon fiber surface and the corresponding interfacial shear strength can be significantly improved without significantly reducing the tensile strength of the single filament.

[0069] Figure 1 Scanning electron microscope (SEM) images of carbon fibers treated in Examples 1-8 and Comparative Examples 1-7, wherein (a) is Comparative Example 1, (b) is Comparative Example 2, (c) is Comparative Example 3, (d) is Comparative Example 4, (e) is Comparative Example 5, (f) is Comparative Example 6, (g) is Comparative Example 7, (h) is Example 1, (i) is Example 2, (j) is Example 3, (k) is Example 4, (l) is Example 5, (m) is Example 6, (n) is Example 7, and (o) is Example 8. Figure 1 As can be seen, the carbon fibers treated in Examples 1-8 exhibited uniform surface morphology, with no obvious etching, cracks, or other defects. This indicates that the processing method of the present invention is uniform and controllable, does not cause significant damage to the carbon fiber matrix, and is beneficial for maintaining mechanical properties. It also helps to enhance the interfacial interaction between the carbon fiber and the resin matrix, thereby improving the interfacial shear strength between the carbon fiber and the resin matrix.

[0070] As can be seen from the above embodiments, the present invention provides a carbon fiber surface treatment method based on solvation layer regulation. By adding a solvation structure regulator to the electrolyte, the structure and thickness of the solvation layer at the anode interface are directionally regulated. By controlling the type and amount of the solvation structure regulator, the oxidation reaction is limited to the defective carbon or edge carbon structure regions on the carbon fiber surface, effectively suppressing non-selective continuous etching. This achieves fine control over the oxidation reaction depth, oxidation reaction mode, and uniformity on the carbon fiber surface, thereby regulating the anodic oxidation reaction at the intrinsic interface level. This increases the oxygen-containing functional group content on the carbon fiber surface by more than 10%, reduces the tensile strength of carbon fiber monofilaments by no more than 10%, and improves the interfacial bonding performance of composite materials made from treated carbon fiber and vinyl resin by more than 30%.

[0071] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A carbon fiber surface treatment method based on solvation layer regulation, characterized in that, It includes the following steps: 1) Carbon fibers are placed in an electrolyte and subjected to electrochemical treatment to obtain pretreated carbon fibers; 2) Post-process the pretreated carbon fibers; The solute in the electrolyte contains ammonium bicarbonate and / or ammonium bisulfate; The electrolyte contains a solvation structure modifier, which includes one or more of ethylene glycol, glycerol, urea, and propylene glycol.

2. The carbon fiber surface treatment method based on solvation layer regulation according to claim 1, characterized in that, The mass of the solvation structure modifier is 0.1-3% of the mass of the electrolyte.

3. The carbon fiber surface treatment method based on solvation layer regulation according to claim 1 or 2, characterized in that, The mass fraction of the solute in the electrolyte is 0.1-5%.

4. The carbon fiber surface treatment method based on solvation layer regulation according to claim 3, characterized in that, The current density of the electrochemical treatment is 0.5~25A / m², and the electrochemical treatment time is 0.3~5min.

5. The carbon fiber surface treatment method based on solvation layer regulation according to claim 4, characterized in that, The post-processing includes sequential ultrasonic cleaning and drying.

6. The carbon fiber surface treatment method based on solvation layer regulation according to claim 5, characterized in that, The ultrasonic cleaning power is 300~400W, and the ultrasonic cleaning time is 10~30min.

7. The carbon fiber surface treatment method based on solvation layer regulation according to claim 5 or 6, characterized in that, The drying temperature is 70~90℃, and the drying time is 30~60min.

8. Carbon fibers obtained by the carbon fiber surface treatment method based on solvation layer control as described in any one of claims 1 to 7.

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