A modified carbon fiber and its preparation method and application in enhancing the mechanical properties of composite materials

Abstract

The present invention discloses a modified carbon fiber, a preparation method thereof, and an application in enhancing the mechanical properties of composite materials, belonging to the technical field of carbon fiber surface treatment and composite material preparation. The present invention constructs two layers of tannic acid / octaamino cage-like polysilsesquioxane and a layer of amino carbon nanotubes on the surface of carbon fiber by chemical bond interaction, and designs a three-layer sandwich structure on the surface of the carbon fiber. The present invention combines the sandwich structure carbon fiber with epoxy resin to prepare a sandwich structure carbon fiber epoxy resin composite material with high toughness and high strength. Compared with the untreated carbon fiber epoxy resin composite material, the three-layer sandwich structure carbon fiber epoxy resin composite material prepared by the present invention can simultaneously have high strength and high toughness.

Description

Technical Field

[0001] The invention relates to a modified carbon fiber and a preparation method thereof and application in enhancing the mechanical properties of composite materials, belonging to the technical field of carbon fiber surface treatment and composite material preparation. Background Art

[0002] Carbon fiber combines excellent mechanical properties with outstanding electrical and optical properties, boasting a range of exceptional properties, including high strength, high modulus, low thermal expansion coefficient, high temperature resistance, chemical resistance, and good electrical conductivity. It combines the inherent properties of carbon materials with the flexible processability of textile fibers. Research is ongoing to improve the performance of carbon fiber itself, resulting in numerous technological breakthroughs. For example, sizing, grafting, chemical vapor deposition, plasma treatment, and high-energy radiation are methods used to modify the inert surface of carbon fibers, introducing additional chemical reaction sites and adhesion surface area, thereby promoting bonding with the resin matrix. However, these treatments can compromise the inherent properties of the carbon fibers. Strong, tough, and lightweight composite materials are promising engineering materials for future applications in aerospace, automotive, and medical devices. However, the realization of synthetic structural materials that achieve excellent mechanical properties and microcrack propagation, transitioning from the macroscale to the nanoscale, remains a major challenge. Summary of the Invention

[0003] In order to simultaneously improve the interlaminar shear strength and bending strength of a carbon fiber epoxy resin composite material, the present invention provides a modified carbon fiber and a preparation method thereof and an application thereof in enhancing the mechanical properties of the composite material.

[0004] The technical solution of the present invention:

[0005] One of the purposes of the present invention is to provide a modified carbon fiber, specifically a tannic acid / octaamino caged polysilsesquioxane layer, an amino carbon nanotube layer and a tannic acid / octaamino caged polysilsesquioxane layer are sequentially grown on the surface of the carbon fiber.

[0006] A second object of the present invention is to provide a method for preparing the modified carbon fiber, which comprises the following steps:

[0007] Step 1: desizing of carbon fiber;

[0008] Step 2: oxidizing the desizing carbon fiber and drying it to obtain oxidized carbon fiber;

[0009] Step 3: Immersing the oxidized carbon fiber in a soaking solution containing tannic acid and octaamino caged polysilsesquioxane, and drying the solution to obtain a carbon fiber having a tannic acid / octaamino caged polysilsesquioxane layer grown on the surface;

[0010] Step 4: soaking the carbon fiber treated in step 3 in an amino carbon nanotube solution, drying, and continuing to grow an amino carbon nanotube layer on the tannic acid / octaamino caged polysilsesquioxane layer of the carbon fiber;

[0011] Step 5: Immerse the carbon fiber treated in step 4 in a solution containing tannic acid and octaamino caged polysilsesquioxane, dry it, and continue to grow a tannic acid / octaamino caged polysilsesquioxane layer on the amino carbon nanotube layer of the carbon fiber to obtain a modified carbon fiber.

[0012] It is further defined that step one is to place the carbon fiber in acetone for heat treatment to remove the sizing agent on the surface of the carbon fiber, then wash away excess acetone with deionized water and then vacuum dry.

[0013] It is further defined that the heating treatment temperature is 70-90°C and the time is 48-72h.

[0014] It is further defined that the drying temperature is 60-80°C and the drying time is 10-12 hours.

[0015] It is further defined that step 2 is to immerse the desizing carbon fiber in a H2O2 solution for polar oxidation treatment.

[0016] It is further defined that the concentration of the H2O2 solution is 30 wt%, the immersion temperature is 80°C, and the immersion time is 2 h.

[0017] It is further defined that the drying treatment in step 2 is a vacuum drying treatment at a temperature of 60-80° C. for 6 hours.

[0018] It is further defined that the concentration of tannic acid in the soaking solution used in step 3 is 4 g / L, and the concentration of octaamino caged polysilsesquioxane is 250 mg / L; and the soaking time is 6-8 hours.

[0019] It is further defined that the pH of the soaking solution in step three is 8.5.

[0020] It is further defined that the drying treatment in step 3 is a vacuum drying treatment at a temperature of 50-60° C. and a time of 12-14 hours.

[0021] It is further defined that the concentration of the amino-treated carbon nanotube solution used in step 4 is 1 g / L; and the soaking time is 2-4 hours.

[0022] It is further defined that the soaking temperature in step 4 is 20-30°C.

[0023] It is further defined that the drying treatment in step 4 is a vacuum drying treatment at a temperature of 60-80° C. and a time of 2-3 hours.

[0024] It is further defined that the concentration of tannic acid in the soaking solution used in step five is 4 g / L, and the concentration of octaamino caged polysilsesquioxane is 250 mg / L; and the soaking time is 6-8 hours.

[0025] It is further defined that the pH of the soaking solution in step 53 is 8.5.

[0026] It is further defined that the drying treatment in step five is a vacuum drying treatment at a temperature of 50-60° C. for 12-14 hours.

[0027] A third object of the present invention is to provide a composite material prepared using the modified carbon fiber. The raw materials for preparing the composite material include epoxy resin, curing agent and modified carbon fiber.

[0028] It is further defined that the curing agent is diethylenetriamine.

[0029] It is further defined that the mass ratio of epoxy resin to curing agent is 100:(10.8-14.8).

[0030] A fourth object of the present invention is to provide a method for preparing a composite material using the modified carbon fiber. Specifically, a sandwich structure carbon fiber, a curing agent and an epoxy resin are mixed, and a vacuum-assisted resin infusion molding method or a mechanical hot pressing molding method is used to obtain a composite material.

[0031] It is further defined that the modified carbon fiber is cut and placed in a mold, and a mixed system of epoxy resin matrix and curing agent is added, and the mold is cured to obtain a sandwich structure carbon fiber / epoxy resin composite material.

[0032] It is further defined that the curing temperature is 100-120°C and the curing time is 1-6 hours.

[0033] The present invention uses a chemical reaction method to construct two layers of tannic acid and octaamino caged polysilsesquioxane and a layer of amino-modified carbon nanotubes on the carbon fiber surface, creating a new interface phase on the carbon fiber surface. This improves the adhesion between the fiber and the resin matrix, effectively transfers loads, and avoids stress concentration. Compared with the existing technology, the present invention has the following advantages:

[0034] (1) Tannic acid is widely distributed in nature, abundant in content, and has a very rich source. It is widely found in various tree barks. It is clean and non-toxic, has excellent film-forming and adhesion properties, and is rich in hydroxyl groups. Carbon nanotubes can increase the surface roughness and enhance the mechanical interlocking of the interface. Octaamino caged polysilsesquioxane has abundant amino groups and can react with epoxy resin.

[0035] (2) The present invention utilizes the excellent mechanical properties of carbon nanotubes, and the tannic acid and octaamino caged polysilsesquioxane layers have rich polar groups and a certain elastic deformation ability, so that hydrogen bonds, ester bonds and π-π bonds interact at the interfaces of the carbon fiber surface layers. Compared with the untreated carbon fiber epoxy resin composite material, the modified carbon fiber composite material has stronger interlaminar shear strength and bending strength.

[0036] (3) The preparation method of the modified carbon fiber provided by the present invention is simple to operate, and the composition and structure are easy to control. It will not cause damage to the carbon fiber itself, and the strength and toughness of the carbon fiber itself are retained to the greatest extent. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 A schematic diagram of the structural changes during the preparation process of the modified carbon fiber provided by the present invention;

[0038] Figure 2 Graph showing the interlaminar shear strength test results of the composite materials obtained in Comparative Examples 1-2 and Examples 1-3;

[0039] Figure 3 Graph showing the test results of flexural strength and flexural modulus of the composite materials obtained in Comparative Examples 1-2 and Examples 1-3;

[0040] Figure 4 FT-IR curve comparison spectra of the products at each stage of the modified carbon fiber preparation process provided in Example 3;

[0041] Figure 5 This is a scanning electron microscope image of CFO-TA / NH2-POSS-CNT-TA / NH2-POSS prepared in Example 3;

[0042] Figure 6 This is a scanning electron microscope photograph of CFO-TA / NH2-POSS-CNT-TA / NH2-POSS prepared in Example 4. DETAILED DESCRIPTION

[0043] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0044] The experimental methods used in the following examples are conventional methods unless otherwise specified. The materials, reagents, methods, and instruments used are conventional in the art and can be obtained commercially by those skilled in the art unless otherwise specified.

[0045] All raw materials used in the following examples are commercially available. Epoxy resin model E51 was purchased from Nantong Xingchen Synthetic Materials Co., Ltd.

[0046] Example 1

[0047] The specific operation process of preparing the modified carbon fiber composite material in this embodiment is as follows:

[0048] (1) The carbon fiber cloth was cut into small pieces of 80×80 mm in size, placed in acetone and heated at 80°C for 48 h, and then washed with deionized water to remove excess acetone and dried at 60°C in a vacuum for 10 h to obtain desized carbon fiber cloth.

[0049] (2) Immersing the Desized Carbon Fiber Cloth The desized carbon fiber cloth was immersed in a 30 wt% hydrogen peroxide solution at 80° C. for 2 h, and then vacuum dried at 80° C. for 6 h to obtain an oxidized carbon fiber cloth.

[0050] (3) The oxidized carbon fiber cloth was immersed in a mixed solution of 4 g / L tannic acid and 250 mg / L octaamino caged polysilsesquioxane, and after immersion for 6 h, vacuum dried at 60° C. for 12 h to obtain a carbon fiber cloth with tannic acid and octaamino caged polysilsesquioxane layers grown on the surface.

[0051] (4) Take 8 layers of carbon fiber cloth with tannic acid and octaamino caged polysilsesquioxane layers grown on the surface, lay them out and put them into a mold, and then inject epoxy resin and curing agent diethylenetriamine (mass ratio of 100:10.8) into the mold under vacuum after removing bubbles, and cure them at 100°C for 2h and 120°C for 2h to obtain a carbon fiber composite material.

[0052] The carbon fiber composite material obtained in this embodiment was subjected to mechanical property testing, and the interlaminar shear strength of the composite material was measured to be 62.3 MPa, and the flexural strength and flexural modulus were 752.66 MPa and 57.86 GPa, respectively. Figure 2 and 3 shown.

[0053] Example 2

[0054] The specific operation process of preparing the modified carbon fiber composite material in this embodiment is as follows:

[0055] (1) The carbon fiber cloth was cut into small pieces of 80×80 mm in size, placed in acetone and heated at 80°C for 48 h, and then washed with deionized water to remove excess acetone and dried at 60°C in a vacuum for 10 h to obtain desized carbon fiber cloth.

[0056] (2) Immersing the Desized Carbon Fiber Cloth The desized carbon fiber cloth was immersed in a 30 wt% hydrogen peroxide solution at 80° C. for 2 h, and then vacuum dried at 80° C. for 6 h to obtain an oxidized carbon fiber cloth.

[0057] (3) The oxidized carbon fiber cloth was immersed in a mixed solution of 4 g / L tannic acid and 250 mg / L octaamino caged polysilsesquioxane, and after immersion for 6 h, vacuum dried at 60° C. for 12 h to obtain a carbon fiber cloth with tannic acid and octaamino caged polysilsesquioxane layers grown on the surface.

[0058] (4) The carbon fiber cloth with tannic acid and octaamino caged polysilsesquioxane layers grown on the surface was immersed in a 1 g / L dispersion of amino-treated carbon nanotubes. After soaking for 2 h, the cloth was vacuum-dried at 80° C. for 6 h to obtain a carbon fiber cloth with amino-treated carbon nanotubes grown on the surface.

[0059] (5) Take 8 layers of carbon fiber cloth with amino-modified carbon nanotubes grown on the surface, lay them out and put them into a mold, remove the bubbles and inject epoxy resin and curing agent diethylenetriamine (mass ratio of 100:10.8) into the mold under vacuum, cure at 100°C for 2h and 120°C for 2h to obtain a carbon fiber composite material.

[0060] The mechanical properties of the carbon fiber composite material obtained in this embodiment were tested, and the interlaminar shear strength of the composite material was measured to be 74.23 MPa. The flexural strength and flexural modulus were 848 MPa and 71.36 GPa respectively. Figure 2 and 3 shown.

[0061] Example 3

[0062] like Figure 1 As shown, the specific operation process of preparing the modified carbon fiber composite material in this embodiment is as follows:

[0063] (1) The carbon fiber cloth was cut into small pieces of 80 × 80 mm in size, placed in acetone and heated at 80 °C for 48 h, and then washed with deionized water to remove excess acetone and dried at 60 °C in a vacuum for 10 h to obtain desized carbon fiber cloth, referred to as CF.

[0064] (2) Immersing the desized carbon fiber cloth in a 30 wt% hydrogen peroxide solution at 80° C. for 2 h, followed by vacuum drying at 80° C. for 6 h to obtain an oxidized carbon fiber cloth, referred to as CFO.

[0065] (3) The oxidized carbon fiber cloth was immersed in a mixed solution of 4 g / L tannic acid and 250 mg / L octaamino caged polysilsesquioxane. After immersion for 6 h, the mixture was vacuum-dried at 60 °C for 12 h to obtain a carbon fiber cloth with tannic acid and octaamino caged polysilsesquioxane layers grown on the surface, which was referred to as CFO-TA / NH2-POSS.

[0066] (4) The carbon fiber cloth with tannic acid and octaamino caged polysilsesquioxane layers grown on the surface was immersed in a 1 g / L dispersion of amino-treated carbon nanotubes. After soaking for 2 h, the cloth was vacuum-dried at 80 °C for 6 h to obtain a carbon fiber cloth with carbon nanotubes grown on the surface, which was referred to as CFO-TA / NH2-POSS-CNT.

[0067] (5) The oxidized carbon fiber cloth was immersed in a mixed solution of 4 g / L tannic acid and 250 mg / L octaamino caged polysilsesquioxane. After immersion for 6 h, the mixture was vacuum-dried at 60 °C for 12 h to obtain a carbon fiber cloth with tannic acid and octaamino caged polysilsesquioxane layers grown on the surface, which was abbreviated as CFO-TA / NH2-POSS-CNT-TA / NH2-POSS.

[0068] (6) Take 8 layers of carbon fiber cloth with a three-layer sandwich structure grown on the surface and lay them out in a mold. After removing bubbles, epoxy resin and curing agent diethylenetriamine (mass ratio of 100:10.8) are vacuum injected into the mold and cured at 100°C for 2h and 120°C for 2h to obtain a carbon fiber composite material.

[0069] The carbon fiber composite material obtained in Example 3 was tested, and the interlaminar shear strength of the composite material was measured to be 79.83 MPa, and the flexural strength and flexural modulus were 1044.33 MPa and 89.83 GPa, respectively. Figure 2 and 3 shown.

[0070] The scanning electron microscope photo of CFO-TA / NH2-POSS-CNT-TA / NH2-POSS obtained in this example is as follows Figure 5 shown.

[0071] Example 4

[0072] The difference between this embodiment and embodiment 3 is that the soaking time in steps (3) and (5) is 8 hours, and the soaking time in step (4) is 4 hours. The remaining process steps and parameter settings are the same as those in embodiment 3.

[0073] The scanning electron microscope photo of CFO-TA / NH2-POSS-CNT-TA / NH2-POSS obtained in this example is as follows Figure 6 shown.

[0074] contrast Figure 5 and Figure 6 It can be seen that if the reaction time is too long, there will be too many carbon nanotubes and tannic acid / octaamino caged polysilsesquioxane polymers assembled on the carbon fiber surface, which is not conducive to the interfacial bonding between the fiber and the resin matrix. Therefore, it is crucial to control the reaction time.

[0075] Comparative Example 1

[0076] The specific operation process of preparing the carbon fiber composite material in this comparative example is as follows:

[0077] (1) The carbon fiber cloth was cut into small pieces of 80×80 mm in size, placed in acetone and heated at 80°C for 48 h, and then washed with deionized water to remove excess acetone and dried at 60°C in a vacuum for 10 h to obtain desized carbon fiber cloth.

[0078] (2) Take 8 layers of desizing carbon fiber cloth and lay them in a mold. After removing bubbles, epoxy resin and curing agent diethylenetriamine (mass ratio of 100:10.8) are vacuum injected into the mold and cured at 100°C for 2h and 120°C for 2h to obtain a carbon fiber composite material.

[0079] The carbon fiber composite material obtained in Comparative Example 1 was subjected to mechanical testing, and the interlaminar shear strength of the composite material was measured to be 50.43 MPa, and the flexural strength and flexural modulus were 618.7 MPa and 42.93 GPa, respectively. Figure 2 and 3 shown.

[0080] Comparative Example 2

[0081] The specific operation process of preparing the oxidized carbon fiber composite material in this comparative example is:

[0082] (1) The carbon fiber cloth was cut into small pieces of 80×80 mm in size, placed in acetone and heated at 80°C for 48 h, and then washed with deionized water to remove excess acetone and dried at 60°C in a vacuum for 10 h to obtain desized carbon fiber cloth.

[0083] (2) The desized carbon fiber cloth was immersed in a 30 wt% hydrogen peroxide solution for 2 h, and then vacuum dried at 80° C. for 6 h to obtain an oxidized carbon fiber cloth.

[0084] (3) Take 8 layers of oxidized carbon fiber cloth and lay them into the mold. After removing bubbles, epoxy resin and curing agent diethylenetriamine (mass ratio of 100:10.8) are vacuum injected into the mold, and cured at 100°C for 2h and 120°C for 2h to obtain a carbon fiber composite material.

[0085] The carbon fiber composite material obtained in Comparative Example 2 was tested, and the interlaminar shear strength of the composite material was measured to be 55.8 MPa, and the flexural strength and flexural modulus were 658.7 MPa and 51.73 GPa, respectively. Figure 2 and 3 shown.

[0086] Effect Examples

[0087] from Figure 2 and Figure 3It can be seen that the carbon fiber sandwich three-layer sandwich structure provided in Example 3 significantly improves the interfacial adhesion with the matrix, but the reaction time is too long, and there are too many carbon nanotubes, tannic acid and octaamino cage polysilsesquioxane polymers assembled on the surface of the carbon fiber, which is not conducive to the interfacial bonding between the fiber and the resin matrix. Therefore, it is crucial to control the reaction time.

[0088] Figure 4 The FT-IR curve comparison spectra of CF, CFO, CFO-TA / NH2-POSS, CFO-TA / NH2-POSS-CNT and CFO-TA / NH2-POSS-CNT-TA / NH2-POSS prepared in Example 3 are shown in FIG. Figure 4 It can be seen that the reaction process of tannic acid and octaamino caged polysilsesquioxane is as follows:

[0089]

[0090] In summary, the hydroxyl groups and adhesion of the polymer obtained by the reaction of tannic acid and octaamino caged polysilsesquioxane, as well as the excellent mechanical properties of carbon nanotubes, promote the effective combination of carbon fiber and epoxy resin, giving it good interfacial properties, thereby simultaneously improving the interlaminar shear strength and flexural strength of the composite material.

[0091] Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Anyone familiar with this technology can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be based on the definition of the claims.

Claims

1. A method for preparing modified carbon fiber, characterized in that: A tannic acid / octaamino caged polysilsesquioxane layer, an amino carbon nanotube layer, and a tannic acid / octaamino caged polysilsesquioxane layer are sequentially grown on the surface of the carbon fiber; The preparation method comprises: Step 1: desizing of carbon fiber; Step 2: oxidizing the desizing carbon fiber and drying it to obtain oxidized carbon fiber; Step 3: Immersing the oxidized carbon fiber in a soaking solution containing tannic acid and octaamino caged polysilsesquioxane, and drying the solution to obtain a carbon fiber having a tannic acid / octaamino caged polysilsesquioxane layer grown on the surface; Step 4: soaking the carbon fiber treated in step 3 in an amino carbon nanotube solution, drying, and continuing to grow an amino carbon nanotube layer on the tannic acid / octaamino caged polysilsesquioxane layer of the carbon fiber; Step 5: Immerse the carbon fiber treated in step 4 in a solution containing tannic acid and octaamino caged polysilsesquioxane, dry it, and continue to grow a tannic acid / octaamino caged polysilsesquioxane layer on the amino carbon nanotube layer of the carbon fiber to obtain a modified carbon fiber.

2. The method for preparing modified carbon fiber according to claim 1, wherein The second step is to immerse the desizing carbon fiber in a H2O2 solution for polar oxidation treatment.

3. The method for preparing modified carbon fiber according to claim 2, wherein: The concentration of H2O2 solution was 30wt%, the immersion temperature was 80℃, and the immersion time was 2h.

4. The method for preparing modified carbon fiber according to claim 1, wherein: In the soaking solution used in step 3, the concentration of tannic acid is 4 g / L, and the concentration of octaamino caged polysilsesquioxane is 250 mg / L; the soaking time is 6-8 hours.

5. The method for preparing modified carbon fiber according to claim 1, wherein: The concentration of the amino-treated carbon nanotube solution used in step 4 is 1 g / L; the soaking time is 2-4 hours.

6. The method for preparing modified carbon fiber according to claim 1, characterized in that: In the soaking solution used in step 5, the concentration of tannic acid is 4 g / L, and the concentration of octaamino caged polysilsesquioxane is 250 mg / L; the soaking time is 6-8 hours.

7. A composite material prepared by using the modified carbon fiber prepared by the method according to claim 1, characterized in that: It is made of epoxy resin, curing agent and modified carbon fiber.

8. The composite material prepared from the modified carbon fiber according to claim 7, characterized in that: The curing agent is diethylenetriamine.

9. A method for forming a composite material according to claim 8, characterized in that: It is vacuum assisted resin infusion molding or mechanical hot pressing molding.

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