High-modulus carbon fiber surface modification method for improving interface performance through anodic oxidation

Abstract

The invention discloses a carbon fiber surface modification method for improving interface performance through anodic oxidation. According to the method, on the basis of the anodic oxidation principle, an auxiliary reagent perchloric acid is added into electrolyte diammonium hydrogen phosphate to react on the surface of the carbon fiber, the surface oxidation treatment degree of the carbon fiber is increased, and on the basis of original anodic oxidation, the surface damage of the carbon fiber is reduced by reducing the current density, shortening the electrolysis time and other experimental parameters; the interlaminar shear strength is improved, the binding force between the carbon fibers and the resin is enhanced, and the performance of the high-modulus carbon fiber composite material is improved.

Description

Technical Field

[0001] The invention belongs to the field of carbon fiber surface treatment and relates to a surface modification method of high-modulus carbon fiber. Background Art

[0002] Polyacrylonitrile (PAN)-based carbon fibers can be divided into standard modulus carbon fibers (modulus 230-240GPa), medium modulus carbon fibers (modulus 290-330GPa) and high modulus carbon fibers (modulus 340-590GPa) according to their modulus. Among them, high modulus carbon fibers have excellent stiffness and strength properties due to their highly ordered crystal structure and regular arrangement of carbon atoms. However, high modulus carbon fibers have a high degree of graphitization on the surface, showing significant chemical inertness, and have low surface roughness and shallow grooves, resulting in poor interfacial bonding with the resin matrix, which seriously restricts the mechanical properties of the composite material.

[0003] High modulus carbon fibers are usually combined with a resin matrix to form composites to provide excellent mechanical properties and chemical resistance. The performance of carbon fiber-resin composites depends largely on the interfacial bonding between the fiber and the resin. The interface layer is connected through mechanical meshing and chemical bonding mechanisms. The former relies on the microgrooves on the surface of the resin-filled fiber to form an anchoring effect; the latter relies on the chemical reaction between the active oxygen-containing groups on the fiber surface and the epoxy groups or curing agents in the resin. However, due to the high inertness and low roughness of the high modulus carbon fiber surface, the effects of these two bonding mechanisms are insufficient, resulting in low interlaminar shear strength (ILSS) of the composite.

[0004] In order to improve the interface properties of high modulus carbon fiber composites, surface treatment technologies such as surface coating, surface grafting, plasma treatment and surface oxidation are often used. In particular, electrochemical surface oxidation has become one of the main research directions due to its strong process controllability, high efficiency and ease of industrial application. However, while existing electrochemical treatment methods improve the interfacial bonding strength, they often lead to a significant decrease in the tensile strength of carbon fibers, restricting the overall performance of the material. How to minimize fiber damage while improving interfacial strength is a key technical problem that needs to be solved urgently. Summary of the invention

[0005] 1. The purpose of the present invention is to provide a surface modification method for high modulus carbon fiber. The technical problem to be solved is to improve the surface activity of carbon fiber by anodizing, so that the interlaminar shear strength (ILSS) of carbon fiber composite materials is improved while the degree of damage to the carbon fiber surface is reduced, thereby giving the high modulus carbon fiber composite materials better mechanical properties.

[0006] 2. The surface treatment method of high modulus carbon fiber, the specific steps are as follows:

[0007] 3. Step (1), electrolyzing high modulus carbon fiber with a modulus of 400-560 GPa in an electrolytic cell, wherein the electrolyte is diammonium hydrogen phosphate with perchloric acid added, and the electrolyte temperature is 20-40° C.;

[0008] 4. Step (2), the electrolyzed carbon fiber tow passes through a water washing tank containing deionized water;

[0009] 5. Step (3), the washed carbon fiber tow passes through a drying tank.

[0010] 6. Optionally, in step (1), the solid content of diammonium hydrogen phosphate in the electrolyte is 1.5-5%.

[0011] 7. Optionally, in step (1), the solid content of the electrolyte is 0.05-0.3%.

[0012] 8. Optionally, in step (1), the current density of the electrochemical surface treatment is 0.1-0.5 A / m 2 .

[0013] 9. Optionally, in step (1), the electrolysis time is 60-130s.

[0014] 10. Optionally, in step (2), the temperature of the deionized water is 20-50°C.

[0015] 11. Optionally, in step (3), the drying temperature is 100-140°C.

[0016] 12. The present invention performs an anodic oxidation treatment on the high modulus carbon fiber by placing it in an electrolyte with auxiliary reagents added. The auxiliary reagents can increase the degree of surface oxidation, shorten the electrolysis time, and produce more active groups on the surface of the carbon fiber, thereby ultimately increasing the interlaminar shear strength while reducing the damage to the carbon fiber surface, thereby improving the mechanical properties of the high modulus carbon fiber composite material. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 Schematic diagram of the structure of a high modulus carbon fiber surface treatment device according to an embodiment of the present invention. DETAILED DESCRIPTION

[0018] The present invention will be described in detail below in conjunction with the accompanying drawings, but this should not limit the protection scope of the present invention.

[0019] Example 1

[0020] The high modulus carbon fiber with a modulus of 450 GPa was placed in an electrolytic cell. The electrolyte was a solution containing 2.0% diammonium hydrogen phosphate and 0.05% perchloric acid. The electrolyte temperature was 35°C. The current density was set to 0.4 A / m 2, the electrolysis time is 60 seconds. After electrolysis, the carbon fiber is placed in deionized water at 30°C for washing and then dried at 120°C. The treated carbon fiber is sized with a 2% E44 / acetone solution, then dried and wound. The tensile strength of the obtained carbon fiber is 4.03GPa and the interlaminar shear strength (ILSS) is 64.97MPa.

[0021] Example 2

[0022] The high modulus carbon fiber with a modulus of 460 GPa was placed in an electrolytic cell. The electrolyte was a solution containing 2.5% diammonium hydrogen phosphate and 0.02% perchloric acid. The electrolyte temperature was 35°C. The current density was set to 0.2 A / m 2 , the electrolysis time is 100 seconds. After electrolysis, the carbon fiber is washed in deionized water at 30°C and then dried at 120°C. The treated carbon fiber is also sized and dried and wound. The tensile strength of the obtained carbon fiber is 4.13GPa and the I LSS is 58.76MPa.

[0023] Example 3

[0024] The high modulus carbon fiber with a modulus of 470 GPa was placed in an electrolytic cell. The electrolyte was a solution containing 2.5% diammonium hydrogen phosphate and 0.05% perchloric acid. The electrolyte temperature was 35°C. The current density was set to 0.3 A / m 2 , the electrolysis time is 120 seconds. After electrolysis, the carbon fiber is washed in deionized water at 30°C and dried at 120°C. Then sizing, drying and winding are performed. The tensile strength of the obtained carbon fiber is 4.09GPa and the I LSS is 61.42MPa.

[0025] Example 4

[0026] The high modulus carbon fiber with a modulus of 480 GPa was placed in an electrolytic cell. The electrolyte was a solution containing 2.5% diammonium hydrogen phosphate and 0.05% perchloric acid. The electrolyte temperature was 35°C. The current density was set to 0.25 A / m 2 , the electrolysis time is 140 seconds. After electrolysis, it is washed in deionized water at 30°C and dried at 120°C. The treated carbon fiber is sized, dried and wound. The tensile strength of the obtained carbon fiber is 4.15GPa and the I LSS is 62.53MPa.

[0027] Comparative Example

[0028] Comparative Example 1

[0029] The high modulus carbon fiber was directly sized (the sizing agent was 2% E44 / acetone solution), dried and wound without any surface treatment. The tensile strength of the obtained carbon fiber was 4.13 GPa and the I LSS was 25.72 MPa.

[0030] Comparative Example 2

[0031] The high modulus carbon fiber was placed in an electrolytic cell, the electrolyte was 1.5% diammonium hydrogen phosphate solution (without perchloric acid), the electrolyte temperature was 30°C, and the current density was 0.35A / m 2 , the electrolysis time is 60 seconds. After electrolysis, it is washed with 30℃ deionized water, dried at 120℃, and then sizing and winding are performed. The tensile strength of the obtained carbon fiber is 3.86GPa, and the I LSS is 44.33MPa.

[0032] Comparative Example 3

[0033] The high modulus carbon fiber was placed in an electrolytic cell, the electrolyte was 2.0% diammonium hydrogen phosphate solution, the electrolyte temperature was 30°C, and the current density was 0.3A / m 2 The electrolysis time is 70 seconds. After electrolysis, it is washed with deionized water at 30°C, dried at 120°C, and then sized and wound. The tensile strength of the obtained carbon fiber is 3.89GPa, and the I LSS is 45.25MPa.

[0034] Table 1 Tensile strength and interlaminar shear strength of high modulus carbon fiber under different process parameters

[0035]

[0036]

[0037] Comparative Example 1 is compared with other examples, indicating that the interlaminar shear strength of the high modulus carbon fiber is increased and the tensile strength is reduced after the electrochemical surface treatment. Comparative Examples 1-3 show that different current densities, electrolysis times, electrolyte concentrations and electrolyte temperatures can lead to large differences in the tensile strength and interlaminar shear strength of the carbon fiber.

[0038] It can be seen from the results of Examples 1-4 that the high modulus carbon fiber after electrochemical surface treatment of the present invention has a higher interface strength with the resin because this method improves the surface activity of the carbon fiber, reduces the surface damage of the carbon fiber, shortens the electrolysis time, and makes the carbon fiber and the resin more tightly bonded, thereby improving the interlayer shear strength.

Claims

1. A method for surface modification of carbon fiber by improving interface performance through anodization, characterized in that: The following steps are involved: (1) Placing high modulus carbon fibers with a modulus of 400-560 GPa in an electrolytic cell for electrochemical surface treatment, wherein the electrolyte is a diammonium hydrogen phosphate solution containing perchloric acid, the electrolyte temperature is 20-40°C, and the current density is 0.1-0.5 A / m 2 , processing time is 60-130 seconds; (2) washing the electrochemically treated carbon fiber with deionized water at a water temperature of 20-50° C.; (3) Drying the washed carbon fiber at 100-140°C.

2. The surface modification method according to claim 1, characterized in that: In step (1), the solid content of diammonium hydrogen phosphate in the electrolyte is 1.5-5%.

3. The surface modification method according to claim 1, characterized in that: In step (1), the solid content of perchloric acid in the electrolyte is 0.05-0.3%.

4. The surface modification method according to claim 1, characterized in that: In step (1), the current density of the electrochemical surface treatment is 0.2-0.4A / m 2 .

5. The surface modification method according to claim 1, characterized in that: In step (1), the electrolysis time is 70-120 seconds.

6. The surface modification method according to claim 1, characterized in that: In step (2), the temperature of the deionized water is 25-45°C.

7. The surface modification method according to claim 1, characterized in that: In step (3), the drying temperature is 110-130°C.

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