A method for surface modification of high modulus carbon fibers to improve interfacial properties through anodic oxidation

Abstract

The present invention discloses a method for modifying the surface of carbon fibers by anodic oxidation to improve interfacial properties. Based on the principle of anodic oxidation, the method adds an auxiliary reagent, perchloric acid, to the electrolyte, diammonium hydrogen phosphate, to react on the carbon fiber surface, increasing the degree of surface oxidation. By reducing experimental parameters such as current density and electrolysis time, compared to conventional anodic oxidation, the method reduces surface damage to the carbon fibers while increasing interlaminar shear strength, strengthening the bonding between the carbon fibers and the resin, and improving the performance of high-modulus carbon fiber composites.

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. High modulus carbon fibers, due to their highly ordered crystal structure and regular arrangement of carbon atoms, possess excellent stiffness and strength properties. However, high modulus carbon fibers have a high degree of surface graphitization, exhibiting significant chemical inertness, and have low surface roughness and shallow grooves, resulting in poor interfacial bonding with the resin matrix, which severely restricts the mechanical properties of the composite material.

[0003] High-modulus carbon fibers are typically combined with a resin matrix to form composites, providing 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 both mechanical meshing and chemical bonding mechanisms. The former relies on the resin filling the microgrooves on the fiber surface 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 effectiveness of both bonding mechanisms is insufficient, resulting in low interlaminar shear strength (ILSS) of the composite.

[0004] In order to improve the interfacial 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 the carbon fiber, which restricts the overall performance of the material. How to minimize fiber damage while improving the 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 anodic oxidation, thereby improving the interlaminar shear strength (ILSS) of carbon fiber composite materials while reducing the degree of damage to the carbon fiber surface, thereby giving 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 fibers 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 anodizing treatment on high modulus carbon fibers by placing them in an electrolyte to which auxiliary reagents are added. The auxiliary reagents can increase the degree of surface oxidation, shorten the electrolysis time, and generate more active groups on the carbon fiber surface, thereby ultimately increasing the interlaminar shear strength while reducing damage to the carbon fiber surface, thereby improving the mechanical properties of high modulus carbon fiber composite materials. 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 with reference to the accompanying drawings, but this should not limit the scope of protection 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 2The electrolysis time was 60 seconds. After electrolysis, the carbon fibers were washed in deionized water at 30°C and then dried at 120°C. The treated carbon fibers were sized with a 2% E44 / acetone solution, dried, and wound. The resulting carbon fibers exhibited a tensile strength of 4.03 GPa and an interlaminar shear strength (ILSS) of 64.97 MPa.

[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 was 100 seconds. After electrolysis, the carbon fibers were washed in deionized water at 30°C and then dried at 120°C. The treated carbon fibers were similarly sized, dried, and wound. The resulting carbon fibers had a tensile strength of 4.13 GPa and an I LSS of 58.76 MPa.

[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 was 120 seconds. After electrolysis, the carbon fibers were washed in deionized water at 30°C and dried at 120°C. Sizing, drying, and winding were then performed. The resulting carbon fibers had a tensile strength of 4.09 GPa and an I LSS of 61.42 MPa.

[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 was 140 seconds. After electrolysis, the carbon fibers were washed in deionized water at 30°C and dried at 120°C. The treated carbon fibers were sized, dried, and wound. The resulting carbon fibers had a tensile strength of 4.15 GPa and an I LSS of 62.53 MPa.

[0027] Comparative Example

[0028] Comparative Example 1

[0029] The high modulus carbon fibers were directly sized (the sizing agent was 2% E44 / acetone solution), dried, and wound without any surface treatment. The resulting carbon fibers had a tensile strength of 4.13 GPa and an ILSS of 25.72 MPa.

[0030] Comparative Example 2

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

[0032] Comparative Example 3

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

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

[0035]

[0036]

[0037] Comparative Example 1, compared to the other examples, demonstrates that electrochemical surface treatment of the high modulus carbon fiber increases interlaminar shear strength while decreasing tensile strength. Comparative Examples 1-3 demonstrate that varying current density, electrolysis time, electrolyte concentration, and electrolyte temperature can significantly influence the tensile and interlaminar shear strengths 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. This is 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 bond more tightly, thereby improving the interlayer shear strength.

Claims

1. A method for surface modification of carbon fiber by improving interfacial properties through anodic oxidation, characterized in that: The following steps are involved: (1) High modulus carbon fibers with a modulus of 400-560 GPa are placed in an electrolytic cell for electrochemical surface treatment. 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 temperature of 20-50°C; (3) Dry 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, wherein In step (1), the current density of the electrochemical surface treatment is 0.2-0.4A / m 2 .

4. The surface modification method according to claim 1, wherein In step (1), the electrolysis time is 70-120 seconds.

5. The surface modification method according to claim 1, wherein In step (2), the temperature of the deionized water is 25-45°C.

6. 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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