A method for controllable assembly of a decreasing gradient transition layer to enhance the interface performance of carbon fiber composites and applications

Abstract

The application relates to a method and application for enhancing the interface performance of a controllable assembly decreasing gradient transition layer of carbon fiber composite material, and relates to a method and application for enhancing the interface of carbon fiber composite material. The application aims to improve the interface bonding strength of carbon fiber / epoxy resin composite material. The method comprises the following steps: one, extraction treatment of carbon fiber; two, oxidation treatment of carbon nanotube; and three, sizing treatment of the carbon fiber. The application introduces a decreasing gradient modulus transition layer on the surface of the carbon fiber. The structure of the decreasing gradient modulus transition layer can promote the formation of a wider and thicker interface transition layer between the carbon fiber and the resin, the modulus of the interface transition layer changes in a multi-stage gradient, the modulus of the fiber and the resin can be balanced, so that the two can achieve the best matching effect; meanwhile, the cracks can be effectively absorbed and uniformly dispersed; the application opens up a new way for preparing high-performance carbon fiber composite material and establishing a simple and effective composite interface. The functionalized carbon fiber prepared by the application is used for reinforcing epoxy resin.

Description

Technical Field

[0001] This invention relates to a method and application for reinforcing the interface of carbon fiber composite materials. Background Technology

[0002] Carbon fiber reinforced epoxy resin matrix composites possess the advantages of being lightweight and high-strength, making them ideal structural materials for aerospace, automotive, and defense industries. Generally, the overall performance of carbon fiber / resin matrix composites is determined by the interfacial phase structure. An excellent interfacial phase can transfer loads from the resin to the fiber, reducing stress concentration and enhancing the interfacial properties of the composite. However, due to the non-polar and chemically inert surface of carbon fibers, the interfacial strength of the composite is relatively weak, and there is a modulus mismatch between the carbon fibers and the resin. Furthermore, the complexity of the interfacial modification process has become a bottleneck in improving the performance of the composite. Therefore, it is urgent to explore a simple and efficient composite modification method to obtain an excellent interfacial phase, thereby improving the interfacial properties of the composite. Summary of the Invention

[0003] The purpose of this invention is to address the problem of improving the interfacial bonding strength of carbon fiber / epoxy resin composites, and to provide a method for controlling the assembly of a decreasing gradient transition layer to enhance the interfacial properties of carbon fiber composites.

[0004] A method for controllably assembling a decreasing gradient transition layer to enhance the interfacial properties of carbon fiber composites is accomplished by the following steps:

[0005] I. Extraction Processing of Carbon Fiber:

[0006] The carbon fiber bundle was placed in a Soxhlet extractor, and acetone was used as a solvent. The acetone was continuously evaporated and condensed in the Soxhlet extractor at a temperature above the boiling point of acetone. The extraction was carried out for 48 to 72 hours to remove the coating and impurities on the surface of the carbon fiber. Finally, the carbon fiber was taken out and dried in an oven to obtain the extracted carbon fiber.

[0007] II. Oxidation treatment of carbon nanotubes:

[0008] ① Prepare a mixed solution of sulfuric acid and nitric acid at room temperature, wherein the volume ratio of sulfuric acid to nitric acid is 3:1;

[0009] ② Immerse carbon nanotubes in a mixed solution of sulfuric acid and nitric acid, heat to 80℃~100℃, and then keep at 80℃~100℃ to obtain the treated carbon nanotubes.

[0010] ③ Soak the treated carbon nanotubes in distilled water, then centrifuge to remove the supernatant;

[0011] ④ Repeat step 2. ③ until the pH of the supernatant is 7, then filter it, and finally freeze-dry it in a freeze dryer to obtain carbon oxide nanotubes.

[0012] III. Sizing treatment of carbon fiber:

[0013] ① Preparation of CNT sizing agents with different mass fractions;

[0014] Four parts of epoxy resin were dissolved in four parts of acetone, and then four parts of carbon nanotubes of different masses were added. The mixture was ultrasonically treated to obtain CNTs sizing agents with different mass fractions.

[0015] The mass fractions of carbon nanotubes in the CNTs sizing agent mentioned in step 3① are 7%, 5%, 3%, and 1%, respectively.

[0016] ② The extracted carbon fiber is immersed in a 7% CNTs sizing agent, stirred, removed and placed in a vacuum drying oven for vacuum drying to obtain carbon fiber coated once.

[0017] ③ Immerse the carbon fiber coated once into a 5% CNTs sizing agent, stir, remove and place in a vacuum drying oven to dry under vacuum, to obtain carbon fiber coated twice.

[0018] ④ Immerse the carbon fiber coated once into a 3% CNTs sizing agent, stir, remove and place in a vacuum drying oven to dry under vacuum, to obtain carbon fiber coated three times.

[0019] ⑤ The carbon fiber coated once is immersed in a 1% CNTs sizing agent, stirred, removed and placed in a vacuum drying oven for vacuum drying to obtain carbon fiber coated four times, which is functionalized carbon fiber. This completes a method for controllable assembly of a decreasing gradient transition layer to enhance the interfacial properties of carbon fiber composites.

[0020] The principle of this invention:

[0021] This invention introduces a decreasing gradient modulus transition layer on the surface of carbon fibers; carbon oxide nanotubes weaken the ability of initial crack propagation, trigger more small cracks, making the crack propagation process more diverse, effectively absorbing and uniformly dispersing crack energy; the "stepped modulus" structure can improve mechanical interlocking and wettability, achieve modulus matching between fibers and resin, thereby significantly improving the interfacial properties of composite materials.

[0022] Advantages of this invention:

[0023] I. This invention introduces a decreasing gradient modulus transition layer on the surface of carbon fiber. The decreasing gradient modulus transition layer structure can promote the formation of a thicker interface transition layer with a multi-level gradient change in modulus between carbon fiber and resin, which can balance the modulus of fiber and resin, thereby achieving the best matching effect between the two; at the same time, it effectively absorbs and uniformly disperses crack energy.

[0024] Second, this invention introduces carbon nanotubes onto the surface of carbon fibers through a simple and efficient physical coating method to construct a gradient-decreasing transition interface layer structure, which will open up a new way for preparing high-performance carbon fiber composite materials and establishing simple and effective composite interfaces.

[0025] Third, the interlaminar shear strength between the functionalized carbon fiber and epoxy resin prepared by this invention can reach 90.7 MPa, which is 65.7% higher than the interlaminar shear strength between carbon fiber and epoxy resin.

[0026] IV. The tensile strength between the functionalized carbon fiber and epoxy resin prepared by this invention can reach 33.6 MPa, which is 107.4% higher than the tensile strength between carbon fiber and epoxy resin. Attached Figure Description

[0027] Figure 1 The images show SEM images of carbon fibers before and after modification. In the images, (a) is untreated CF, (b) is C1-CNTs-CF, (c) is C2-CNTs-CF, (d) is C3-CNTs-CF, and (e) is C4-CNTs-CF.

[0028] Figure 2 The figure shows the C1s peak fitting curve of carbon fiber. In the figure, (a) is the untreated CF, (b) is C1-CNTs-CF, (c) is C2-CNTs-CF, (d) is C3-CNTs-CF, (e) is C4-CNTs-CF, and (f) is a bar chart of carboxyl content.

[0029] Figure 3 A bar chart showing the average interface thickness;

[0030] Figure 4 A bar chart showing tensile strength;

[0031] Figure 5 This is a bar chart of interlaminar shear strength. Detailed Implementation

[0032] Specific Implementation Method 1: This implementation method provides a method for controllably assembling a decreasing gradient transition layer to enhance the interfacial properties of carbon fiber composite materials, which is completed according to the following steps:

[0033] I. Extraction Processing of Carbon Fiber:

[0034] The carbon fiber bundle was placed in a Soxhlet extractor, and acetone was used as a solvent. The acetone was continuously evaporated and condensed in the Soxhlet extractor at a temperature above the boiling point of acetone. The extraction was carried out for 48 to 72 hours to remove the coating and impurities on the surface of the carbon fiber. Finally, the carbon fiber was taken out and dried in an oven to obtain the extracted carbon fiber.

[0035] II. Oxidation treatment of carbon nanotubes:

[0036] ① Prepare a mixed solution of sulfuric acid and nitric acid at room temperature, wherein the volume ratio of sulfuric acid to nitric acid is 3:1;

[0037] ② Immerse carbon nanotubes in a mixed solution of sulfuric acid and nitric acid, heat to 80℃~100℃, and then keep at 80℃~100℃ to obtain the treated carbon nanotubes.

[0038] ③ Soak the treated carbon nanotubes in distilled water, then centrifuge to remove the supernatant;

[0039] ④ Repeat step 2. ③ until the pH of the supernatant is 7, then filter it, and finally freeze-dry it in a freeze dryer to obtain carbon oxide nanotubes.

[0040] III. Sizing treatment of carbon fiber:

[0041] ① Preparation of CNT sizing agents with different mass fractions;

[0042] Four parts of epoxy resin were dissolved in four parts of acetone, and then four parts of carbon nanotubes of different masses were added. The mixture was ultrasonically treated to obtain CNTs sizing agents with different mass fractions.

[0043] The mass fractions of carbon nanotubes in the CNTs sizing agent mentioned in step 3① are 7%, 5%, 3%, and 1%, respectively.

[0044] ② The extracted carbon fiber is immersed in a 7% CNTs sizing agent, stirred, removed and placed in a vacuum drying oven for vacuum drying to obtain carbon fiber coated once.

[0045] ③ Immerse the carbon fiber coated once into a 5% CNTs sizing agent, stir, remove and place in a vacuum drying oven to dry under vacuum, to obtain carbon fiber coated twice.

[0046] ④ Immerse the carbon fiber coated once into a 3% CNTs sizing agent, stir, remove and place in a vacuum drying oven to dry under vacuum, to obtain carbon fiber coated three times.

[0047] ⑤ The carbon fiber coated once is immersed in a 1% CNTs sizing agent, stirred, removed and placed in a vacuum drying oven for vacuum drying to obtain carbon fiber coated four times, which is functionalized carbon fiber. This completes a method for controllable assembly of a decreasing gradient transition layer to enhance the interfacial properties of carbon fiber composites.

[0048] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that: the drying temperature in step one is 75℃~85℃, and the drying time is 8h~12h; the extraction temperature in step one is 75℃~85℃. Other steps are the same as in Specific Implementation Method One.

[0049] Specific Implementation Method Three: This implementation method differs from Specific Implementation Method One or Two in that: in step two ①, the mass fraction of sulfuric acid in the mixed solution of sulfuric acid and nitric acid is 98%, and the mass fraction of nitric acid is 65%. The other steps are the same as in Specific Implementation Method One or Two.

[0050] Specific Implementation Method Four: This implementation method differs from Specific Implementation Methods One to Three in that: in step two ②, the constant temperature time at 80℃~100℃ is 6h~8h; the mass ratio of the carbon nanotubes to the volume ratio of the mixed solution of sulfuric acid and nitric acid in step two ② is (2.0g~4.0g):(500mL~1000mL). Other steps are the same as in Specific Implementation Methods One to Three.

[0051] Specific Implementation Method Five: The difference between this implementation method and Specific Implementation Methods One to Four is that the mass ratio of the treated carbon nanotubes to the volume of distilled water in step two, ③, is (2.0g~4.0g):(400mL~600mL). The other steps are the same as in Specific Implementation Methods One to Four.

[0052] Specific Implementation Method Six: This implementation method differs from Specific Implementation Methods One to Five in that the freeze-drying temperature in step two, fourth, is -41℃ to -39℃, and the freeze-drying time is 12h to 24h. The other steps are the same as in Specific Implementation Methods One to Five.

[0053] Specific Implementation Method Seven: The difference between this implementation method and Specific Implementation Methods One to Six is ​​that the mass ratio of epoxy resin to acetone in step three① is (1.0g~2.0g):(50mL~100mL). The other steps are the same as in Specific Implementation Methods One to Six.

[0054] Specific Implementation Method Eight: This implementation method differs from Specific Implementation Methods One to Seven in that: the ultrasonic treatment time in step three ① is 1 to 2 hours; the stirring time in steps three ②, three ③, three ④, and three ⑤ is the same, ranging from 1 to 5 minutes. Other steps are the same as in Specific Implementation Methods One to Seven.

[0055] Specific Implementation Method Nine: This implementation method differs from Specific Implementation Methods One to Eight in that the vacuum drying temperature and time in steps three ②, three ③, three ④, and three ⑤ are the same. The vacuum drying temperature is 80℃~90℃, and the vacuum drying time is 20min~30min. The other steps are the same as in Specific Implementation Methods One to Eight.

[0056] Specific Implementation Method 10: This implementation method uses functionalized carbon fiber to reinforce epoxy resin.

[0057] The beneficial effects of the present invention are verified using the following embodiments:

[0058] Example 1: A method for enhancing the interfacial properties of carbon fiber composites, comprising the following steps:

[0059] I. Extraction Processing of Carbon Fiber:

[0060] 1.5g of carbon fiber bundle was placed in a Soxhlet extractor. Acetone was used as the solvent. The acetone was continuously evaporated and condensed in the Soxhlet extractor at a temperature above the boiling point of acetone (82℃). The extraction was carried out for 72 hours to remove the coating and impurities on the surface of the carbon fiber. Finally, the carbon fiber was taken out and dried in an oven at 75℃ for 10 hours to obtain the extracted carbon fiber.

[0061] II. Oxidation treatment of carbon nanotubes:

[0062] ① Prepare a mixed solution of sulfuric acid and nitric acid at room temperature, wherein the volume ratio of sulfuric acid to nitric acid is 3:1;

[0063] In step 2①, the mixed solution of sulfuric acid and nitric acid has a mass fraction of 98% sulfuric acid and a mass fraction of 65% nitric acid.

[0064] ② Immerse carbon nanotubes in a mixed solution of sulfuric acid and nitric acid, heat to 90°C, and then keep at 90°C for 7 hours to obtain the treated carbon nanotubes.

[0065] The mass ratio of the carbon nanotubes mentioned in step 2② to the volume ratio of the mixed solution of sulfuric acid and nitric acid is 3.0 g: 800 mL;

[0066] ③ Soak the treated carbon nanotubes in distilled water, then centrifuge to remove the supernatant;

[0067] The mass ratio of the treated carbon nanotubes to the volume of distilled water in step 2③ is 3.0 g: 500 mL.

[0068] ④ Repeat step 2. ④ until the pH of the supernatant is 7, then filter it, and finally freeze-dry it in a freeze dryer to obtain carbon oxide nanotubes.

[0069] The freeze-drying temperature described in step 2④ is -41℃, and the freeze-drying time is 24 hours;

[0070] III. Sizing treatment of carbon fiber:

[0071] ① Preparation of CNT sizing agents with different mass fractions;

[0072] Dissolve 2g of epoxy resin in 100mL of acetone, then add carbon nanotubes, and sonicate for 2h to obtain CNTs sizing agent.

[0073] The mass fraction of carbon nanotubes in the CNTs sizing agent mentioned in step 3① is 7%;

[0074] ② The extracted carbon fiber is immersed in a 7% CNTs sizing agent and stirred for 1 minute. After stirring, it is taken out and placed in a vacuum drying oven for vacuum drying at a temperature of 90°C for 30 minutes to obtain carbon fiber coated once (C1-CNTs-CF); which is functionalized carbon fiber.

[0075] Example 2: A method for enhancing the interfacial properties of carbon fiber composites, comprising the following steps:

[0076] I. Extraction Processing of Carbon Fiber:

[0077] 1.5g of carbon fiber bundle was placed in a Soxhlet extractor. Acetone was used as the solvent. The acetone was continuously evaporated and condensed in the Soxhlet extractor at a temperature above the boiling point of acetone (82℃). The extraction was carried out for 72 hours to remove the coating and impurities on the surface of the carbon fiber. Finally, the carbon fiber was taken out and dried in an oven at 75℃ for 10 hours to obtain the extracted carbon fiber.

[0078] II. Oxidation treatment of carbon nanotubes:

[0079] ① Prepare a mixed solution of sulfuric acid and nitric acid at room temperature, wherein the volume ratio of sulfuric acid to nitric acid is 3:1;

[0080] In step 2①, the mixed solution of sulfuric acid and nitric acid has a mass fraction of 98% sulfuric acid and a mass fraction of 65% nitric acid.

[0081] ② Immerse carbon nanotubes in a mixed solution of sulfuric acid and nitric acid, heat to 90°C, and then keep at 90°C for 7 hours to obtain the treated carbon nanotubes.

[0082] The mass ratio of the carbon nanotubes mentioned in step 2② to the volume ratio of the mixed solution of sulfuric acid and nitric acid is 3.0 g: 800 mL;

[0083] ③ Soak the treated carbon nanotubes in distilled water, then centrifuge to remove the supernatant;

[0084] The mass ratio of the treated carbon nanotubes to the volume of distilled water in step 2③ is 3.0 g: 500 mL.

[0085] ④ Repeat step 2. ④ until the pH of the supernatant is 7, then filter it, and finally freeze-dry it in a freeze dryer to obtain carbon oxide nanotubes.

[0086] The freeze-drying temperature described in step 2④ is -41℃, and the freeze-drying time is 24 hours;

[0087] III. Sizing treatment of carbon fiber:

[0088] ① Preparation of CNT sizing agents with different mass fractions;

[0089] Two 2g portions of epoxy resin were dissolved in two 100mL portions of acetone, and then two portions of carbon nanotubes of different masses were added. The mixture was ultrasonically treated to obtain CNTs sizing agents with different mass fractions.

[0090] The mass fractions of carbon nanotubes in the CNTs sizing agent mentioned in step 3① are 7% and 5%, respectively.

[0091] ② The extracted carbon fiber is immersed in a 7% CNTs sizing agent, stirred, removed and placed in a vacuum drying oven for vacuum drying to obtain carbon fiber coated once.

[0092] ③ The carbon fiber coated once is immersed in a 5% CNTs sizing agent, stirred, taken out and placed in a vacuum drying oven for vacuum drying to obtain carbon fiber coated twice (C2-CNTs-CF), which is functionalized carbon fiber.

[0093] The ultrasonic treatment time in step 3① is 2 hours; the stirring time in steps 3② and 3③ is the same, 1 minute.

[0094] The vacuum drying temperature and time are the same for both steps 3② and 3③. The vacuum drying temperature is 90℃ and the vacuum drying time is 30min.

[0095] Example 3: A method for enhancing the interfacial properties of carbon fiber composites, comprising the following steps:

[0096] I. Extraction Processing of Carbon Fiber:

[0097] 1.5g of carbon fiber bundle was placed in a Soxhlet extractor. Acetone was used as the solvent. The acetone was continuously evaporated and condensed in the Soxhlet extractor at a temperature above the boiling point of acetone (82℃). The extraction was carried out for 72 hours to remove the coating and impurities on the surface of the carbon fiber. Finally, the carbon fiber was taken out and dried in an oven at 75℃ for 10 hours to obtain the extracted carbon fiber.

[0098] II. Oxidation treatment of carbon nanotubes:

[0099] ① Prepare a mixed solution of sulfuric acid and nitric acid at room temperature, wherein the volume ratio of sulfuric acid to nitric acid is 3:1;

[0100] In step 2①, the mixed solution of sulfuric acid and nitric acid has a mass fraction of 98% sulfuric acid and a mass fraction of 65% nitric acid.

[0101] ② Immerse carbon nanotubes in a mixed solution of sulfuric acid and nitric acid, heat to 90°C, and then keep at 90°C for 7 hours to obtain the treated carbon nanotubes.

[0102] The mass ratio of the carbon nanotubes mentioned in step 2② to the volume ratio of the mixed solution of sulfuric acid and nitric acid is 3.0 g: 800 mL;

[0103] ③ Soak the treated carbon nanotubes in distilled water, then centrifuge to remove the supernatant;

[0104] The mass ratio of the treated carbon nanotubes to the volume of distilled water in step 2③ is 3.0 g: 500 mL.

[0105] ④ Repeat step 2. ④ until the pH of the supernatant is 7, then filter it, and finally freeze-dry it in a freeze dryer to obtain carbon oxide nanotubes.

[0106] The freeze-drying temperature described in step 2④ is -41℃, and the freeze-drying time is 24 hours;

[0107] III. Sizing treatment of carbon fiber:

[0108] ① Preparation of CNT sizing agents with different mass fractions;

[0109] Three 2g epoxy resins were dissolved in three 100mL acetones, and then three different masses of carbon nanotubes were added. The mixtures were then ultrasonically treated to obtain CNTs sizing agents with different mass fractions.

[0110] The mass fractions of carbon nanotubes in the CNTs sizing agent mentioned in step 3① are 7%, 5%, and 3%, respectively.

[0111] ② The extracted carbon fiber is immersed in a 7% CNTs sizing agent, stirred, removed and placed in a vacuum drying oven for vacuum drying to obtain carbon fiber coated once.

[0112] ③ Immerse the carbon fiber coated once into a 5% CNTs sizing agent, stir, remove and place in a vacuum drying oven to dry under vacuum, to obtain carbon fiber coated twice.

[0113] ④ Immerse the carbon fiber coated once into a 3% CNTs sizing agent, stir, remove and place in a vacuum drying oven to dry under vacuum, to obtain carbon fiber coated three times (C3-CNTs-CF), which is functionalized carbon fiber.

[0114] The ultrasonic treatment time in step 3① is 2 hours; the stirring time in steps 3②, ​​3③, and 3④ is the same, which is 1 minute.

[0115] The vacuum drying temperature and time are the same for steps 3②, ​​3③, and 3④. The vacuum drying temperature is 90℃ and the vacuum drying time is 30min.

[0116] Example 4: A method for controllably assembling a decreasing gradient transition layer to enhance the interfacial properties of carbon fiber composites, comprising the following steps:

[0117] I. Extraction Processing of Carbon Fiber:

[0118] 1.5g of carbon fiber bundle was placed in a Soxhlet extractor. Acetone was used as the solvent. The acetone was continuously evaporated and condensed in the Soxhlet extractor at a temperature above the boiling point of acetone (82℃). The extraction was carried out for 72 hours to remove the coating and impurities on the surface of the carbon fiber. Finally, the carbon fiber was taken out and dried in an oven at 75℃ for 10 hours to obtain the extracted carbon fiber.

[0119] II. Oxidation treatment of carbon nanotubes:

[0120] ① Prepare a mixed solution of sulfuric acid and nitric acid at room temperature, wherein the volume ratio of sulfuric acid to nitric acid is 3:1;

[0121] In step 2①, the mixed solution of sulfuric acid and nitric acid has a mass fraction of 98% sulfuric acid and a mass fraction of 65% nitric acid.

[0122] ② Immerse carbon nanotubes in a mixed solution of sulfuric acid and nitric acid, heat to 90°C, and then keep at 90°C for 7 hours to obtain the treated carbon nanotubes.

[0123] The mass ratio of the carbon nanotubes mentioned in step 2② to the volume ratio of the mixed solution of sulfuric acid and nitric acid is 3.0 g: 800 mL;

[0124] ③ Soak the treated carbon nanotubes in distilled water, then centrifuge to remove the supernatant;

[0125] The mass ratio of the treated carbon nanotubes to the volume of distilled water in step 2③ is 3.0 g: 500 mL.

[0126] ④ Repeat step 2. ④ until the pH of the supernatant is 7, then filter it, and finally freeze-dry it in a freeze dryer to obtain carbon oxide nanotubes.

[0127] The freeze-drying temperature described in step 2④ is -41℃, and the freeze-drying time is 24 hours;

[0128] III. Sizing treatment of carbon fiber:

[0129] ① Preparation of CNT sizing agents with different mass fractions;

[0130] Four 2g portions of epoxy resin were dissolved in four 100mL portions of acetone, and then four portions of carbon nanotubes of different masses were added. The mixtures were then ultrasonically treated to obtain CNTs sizing agents with different mass fractions.

[0131] The mass fractions of carbon nanotubes in the CNTs sizing agent mentioned in step 3① are 7%, 5%, 3%, and 1%, respectively.

[0132] ② The extracted carbon fiber is immersed in a 7% CNTs sizing agent, stirred, removed and placed in a vacuum drying oven for vacuum drying to obtain carbon fiber coated once.

[0133] ③ Immerse the carbon fiber coated once into a 5% CNTs sizing agent, stir, remove and place in a vacuum drying oven to dry under vacuum, to obtain carbon fiber coated twice.

[0134] ④ Immerse the carbon fiber coated once into a 3% CNTs sizing agent, stir, remove and place in a vacuum drying oven to dry under vacuum, to obtain carbon fiber coated three times.

[0135] ⑤ The carbon fiber coated once is immersed in a 1% CNTs sizing agent, stirred, taken out and placed in a vacuum drying oven for vacuum drying to obtain carbon fiber coated four times (C4-CNTs-CF), which is functionalized carbon fiber. This completes a method for controllable assembly of a decreasing gradient transition layer to enhance the interfacial properties of carbon fiber composites.

[0136] The ultrasonic treatment time in step 3① is 2 hours; the stirring time in steps 3②, ​​3③, 3④ and 3⑤ is the same, which is 1 minute.

[0137] The vacuum drying temperature and time are the same for steps 3②, ​​3③, 3④ and 3⑤. The vacuum drying temperature is 90℃ and the vacuum drying time is 30min.

[0138] Figure 1The images show SEM images of carbon fibers before and after modification. In the images, (a) is untreated CF, (b) is C1-CNTs-CF, (c) is C2-CNTs-CF, (d) is C3-CNTs-CF, and (e) is C4-CNTs-CF.

[0139] Figure 1 As can be seen, untreated carbon fibers (CFs) have a smooth surface, thus lacking the mechanical interlocking effect caused by grooves; coated CFs are well adhered to by carbon nanotubes (CNTs), significantly increasing the surface roughness and specific surface area of ​​CFs, resulting in good mechanical interlocking properties between the fiber and matrix; with increasing coating times, the number of CNTs on the CF surface first increases and then decreases, indicating the successful construction of the gradient modulus layer. The gradient modulus layer increases the surface roughness, specific surface area, and wettability of CFs, reduces the modulus difference between the CFs and resin, and better facilitates mechanical interlocking and compatibility with the resin matrix.

[0140] Figure 2 The figure shows the C1s peak fitting curve of carbon fiber. In the figure, (a) is the untreated CF, (b) is C1-CNTs-CF, (c) is C2-CNTs-CF, (d) is C3-CNTs-CF, (e) is C4-CNTs-CF, and (f) is a bar chart of carboxyl content.

[0141] Figure 2 The changes in elemental content and functional groups of functionalized carbon fibers (Cn-CNTs-CF) obtained by coating CF with modified fibers n times are shown in Figure ae. It can be observed from Figure ae that the surface composition of CF changed significantly after CNT coating. CF has three peaks, representing sp... 3 - Hybridized CC (284.4 eV), CO (285.6 eV), and C=O (286.3 eV). After CNT coating treatment, a new peak appeared at 288.4 eV, which was caused by the COO of the CNTs coated on the CF surface. In addition, with the increase of coating times, the COO content increased from 14.5% to 15.8% and 16.4% respectively. After further coating, since the CNT content in the coating agent is much lower than that in the resin, the carboxyl content decreased to 15.6%, which further proves the successful construction of the decreasing gradient modulus layer.

[0142] Figure 3 The interfacial thickness variation of functionalized carbon fibers (Cn-CNTs-CF) obtained by coating modified fibers with CF and n times is shown in [reference needed]. Figure 3 As shown;

[0143] Depend on Figure 3It can be seen that the average interface thickness gradually increases from 0.24 μm to 0.72 μm, 0.79 μm, 0.97 μm, and 1.12 μm. This indicates that a decreasing gradient modulus interface layer is established in the interphase region of the composite material. This helps to uniformly transfer the applied load from the matrix to the CFs surface, thereby improving the interfacial properties of the composite material.

[0144] According to ASTM D638, on GT-7000-A2X (Taiwan, China), the accuracy is 1 mm·min. -1 The tensile speed was used for transverse fiber bundle (TFB) testing. For TFB samples, the carbon fibers (CFs) were fixed in the grooves of a custom dumbbell-shaped mold under tension at both ends. Then, a uniformly mixed curing agent (H-256) and resin (epoxy resin E-51) were poured into the mold, and the matrix resin was allowed to fully impregnate the carbon fibers. The mass ratio of curing agent to resin was 32:100. Vacuum was applied until the epoxy resin was free of bubbles. Finally, the mold was placed in an oven preheated to 80°C and held for 2 hours, then heated to 100°C and held for 2 hours, and then cured at 120°C for 2 hours. Finally, the TFB samples were cooled to room temperature and removed. The carbon fibers were CF, C1-CNTs-CF, C2-CNTs-CF, C3-CNTs-CF, and C4-CNTs-CF. The TFB strength can be obtained by the following formula:

[0145]

[0146] In the formula, F is the maximum load, and b and h are the fiber bundle width and thickness, respectively.

[0147] The CF, C1-CNTs-CF, C2-CNTs-CF, C3-CNTs-CF, and C4-CNTs-CF prepared in Examples 1-4 were tested according to the above testing standards. (See attached text.) Figure 4 As shown;

[0148] Figure 4 A bar chart showing tensile strength;

[0149] Figure 4 TFBT performance tests were conducted on functionalized carbon fibers (Cn-CNTs-CF) obtained by coating modified fibers with CF and N layers to investigate the effect of decreasing gradient modulus layer structure on mechanical properties. The tensile strength of CF / EP was 16.2 MPa. The functionalized Cn-CNTs-COOH-CF / EP exhibited higher tensile strengths, increasing sequentially to 20.3 MPa, 26.6 MPa, 29.9 MPa, and 33.6 MPa. Compared with CF / EP, Cn-CNTs-COOH-CF / EP showed significantly higher tensile strengths, increasing by 25.3%, 64.2%, 84.6%, and 107.4%, respectively.

[0150] Interlaminar shear strength test:

[0151] This experiment used the three-point bending method to test the ILSS of carbon fiber composites on a GT-7000-A2X electronic universal testing machine (Taiwan, China). First, 20 turns of carbon fiber were wound around a 20cm long frame. Then, epoxy resin E-51 and curing agent H-256 (mass ratio 100:32) were weighed and mixed evenly. The carbon fiber was then fully impregnated with the matrix resin. Next, the mixture was placed in a mold, which was then placed in a vacuum drying oven for degassing. Finally, the mold was placed on a hot press and cured according to the following process: constant temperature treatment at 90℃, 120℃, and 150℃ for 2h, 2h, and 3h, respectively, to obtain the carbon fiber / epoxy resin composite material. During the test, the sample size was 20mm × 6mm × 2mm, the span-to-thickness ratio was 5, and the load application rate was 1mm·min. -1 The test was conducted at room temperature. Fifty valid data points were measured for each sample and their average value was calculated. The carbon fibers were CF, C1-CNTs-CF, C2-CNTs-CF, C3-CNTs-CF, and C4-CNTs-CF. The interlaminar shear strength (ILSS) can be obtained according to formula (2):

[0152]

[0153] In the formula, F represents the maximum load (N) at the fault location.

[0154] b—width of the sample cross-section (mm);

[0155] h — Thickness of the sample cross-section (mm).

[0156] The CF, C1-CNTs-CF, C2-CNTs-CF, C3-CNTs-CF, and C4-CNTs-CF prepared in Examples 1-4 were tested according to the above testing standards. (See attached text.) Figure 5 As shown;

[0157] Figure 5 A bar chart of interlaminar shear strength;

[0158] Figure 5The interlaminar shear strength (ILSS) of functionalized carbon fibers (Cn-CNTs-CF) obtained by coating modified fibers with CF and N layers was tested to investigate the effect of the decreasing modulus layer structure on mechanical properties. The interlaminar shear strength of the composite material showed the same trend as that of the transverse tensile strength. The ILSS value of CF / EP was 54.8 MPa. With the construction of the gradient modulus layer, the ILSS of Cn-CNTs-CF / EP gradually increased to 70.1 MPa, 83.1 MPa, 89.1 MPa, and 90.7 MPa, respectively, representing increases of 27.9%, 51.6%, 62.6%, and 65.7% compared to CF. The high mechanical strength of Cn-CNTs-CF / EP is mainly due to three factors: First, the introduction of numerous oxygen-containing functional groups by CNTs enhances wettability with epoxy resin. Second, CNTs increase the surface roughness of the fiber, further increasing the specific surface area of ​​the CFs and improving the mechanical interlocking between the fiber and resin. Third, the decreasing modulus layer allows for better modulus matching between the fiber and resin, enabling cracks to propagate from the resin to the CFs surface, reducing stress concentration. The improved tensile strength demonstrates that this interface modification method effectively improves the interfacial bonding between carbon fibers and resin.

[0159] Example 5: A method for controllably assembling a decreasing gradient transition layer to enhance the interfacial properties of carbon fiber composites, comprising the following steps:

[0160] I. Extraction Processing of Carbon Fiber:

[0161] 1.5g of carbon fiber bundle was placed in a Soxhlet extractor. Acetone was used as the solvent. The acetone was continuously evaporated and condensed in the Soxhlet extractor at a temperature above the boiling point of acetone (85℃). The extraction was carried out for 72 hours to remove the coating and impurities on the surface of the carbon fiber. Finally, the carbon fiber was taken out and dried in an oven at 80℃ for 10 hours to obtain the extracted carbon fiber.

[0162] II. Oxidation treatment of carbon nanotubes:

[0163] ① Prepare a mixed solution of sulfuric acid and nitric acid at room temperature, wherein the volume ratio of sulfuric acid to nitric acid is 3:1;

[0164] In step 2①, the mixed solution of sulfuric acid and nitric acid has a mass fraction of 98% sulfuric acid and a mass fraction of 65% nitric acid.

[0165] ② Immerse 2.0g of carbon nanotubes in a 500mL mixed solution of sulfuric acid and nitric acid, heat to 100℃, and then keep at 100℃ for 8 hours to obtain the treated carbon nanotubes.

[0166] The mass ratio of the carbon nanotubes mentioned in step 2② to the volume ratio of the mixed solution of sulfuric acid and nitric acid is 3.0 g: 800 mL;

[0167] ③ Soak the treated carbon nanotubes in distilled water, then centrifuge to remove the supernatant;

[0168] The mass ratio of the treated carbon nanotubes to the volume of distilled water in step 2③ is 2.0 g: 400 mL;

[0169] ④ Repeat step 2. ④ until the pH of the supernatant is 7, then filter it, and finally freeze-dry it in a freeze dryer to obtain carbon oxide nanotubes.

[0170] The freeze-drying temperature described in step 2④ is -41℃, and the freeze-drying time is 24 hours;

[0171] III. Sizing treatment of carbon fiber:

[0172] ① Preparation of CNT sizing agents with different mass fractions;

[0173] 2g of epoxy resin was dissolved in 100mL of acetone, then carbon nanotubes were added, and the mixture was ultrasonically treated for 1h to obtain a CNTs sizing agent.

[0174] The mass fraction of carbon nanotubes in the CNTs sizing agent mentioned in step 3① is 5%;

[0175] ② The extracted carbon fibers are immersed in a 5% CNTs sizing agent, stirred for 5 minutes, removed and placed in a vacuum drying oven for vacuum drying, which is the functionalized carbon fiber.

[0176] The vacuum drying temperature in step 3② is 90℃, and the vacuum drying time is 30 minutes.

[0177] The experimental results of Example 5 are as follows:

[0178] Changes in microstructure of carbon fiber before and after modification: The gradient decreasing modulus layer in Example 5 was not successfully constructed.

[0179] Carbon fiber interfacial shear strength analysis: ILSS increased from 54.8 MPa in the precursor fiber to 80.3 MPa, an increase of 46.5%.

[0180] Transverse fiber bundle tensile test analysis of carbon fiber: TFB strength increased from 16.2 MPa to 24.4 MPa, an increase of 50.6%.

[0181] Analysis shows that Example 4 is more effective.

Claims

1. A method for controllably assembling a decreasing gradient transition layer to enhance the interfacial properties of carbon fiber composites, characterized in that... This method is completed in the following steps: I. Extraction Processing of Carbon Fiber: The carbon fiber bundle was placed in a Soxhlet extractor, and acetone was used as a solvent. The acetone was continuously evaporated and condensed in the Soxhlet extractor at a temperature above the boiling point of acetone. The extraction was carried out for 48-72 hours to remove the coating and impurities on the surface of the carbon fiber. Finally, the carbon fiber was taken out and dried in an oven to obtain the extracted carbon fiber. II. Oxidation treatment of carbon nanotubes: ① Prepare a mixed solution of sulfuric acid and nitric acid at room temperature, wherein the volume ratio of sulfuric acid to nitric acid is 3:1; ② Immerse carbon nanotubes in a mixed solution of sulfuric acid and nitric acid, heat to 80℃~100℃, and then keep the temperature constant at 80℃~100℃ to obtain the treated carbon nanotubes. ③ Soak the treated carbon nanotubes in distilled water, then centrifuge to remove the supernatant; ④ Repeat step 2. ③ until the pH of the supernatant is 7, then filter it, and finally freeze-dry it in a freeze dryer to obtain carbon oxide nanotubes. III. Sizing treatment of carbon fiber: ① Preparation of CNT sizing agents with different mass fractions; Four parts of epoxy resin were dissolved in four parts of acetone, and then four parts of carbon nanotubes of different masses were added. The mixture was ultrasonically treated to obtain CNTs sizing agents with different mass fractions. The mass fractions of carbon nanotubes in the CNTs sizing agent mentioned in step 3① are 7%, 5%, 3%, and 1%, respectively. ② The extracted carbon fiber is immersed in a 7% CNTs sizing agent, stirred, removed and placed in a vacuum drying oven for vacuum drying to obtain carbon fiber coated once. ③ Immerse the carbon fiber coated once into a 5% CNTs sizing agent, stir, remove and place in a vacuum drying oven to dry, thus obtaining carbon fiber coated twice. ④ Immerse the carbon fiber coated twice into a 3% CNTs sizing agent, stir, remove and place in a vacuum drying oven to dry, thus obtaining carbon fiber coated three times. ⑤ The carbon fiber coated three times is immersed in a 1% CNTs sizing agent, stirred, removed and placed in a vacuum drying oven for vacuum drying to obtain carbon fiber coated four times, which is functionalized carbon fiber. This completes a method for controllable assembly of a decreasing gradient transition layer to enhance the interfacial properties of carbon fiber composites.

2. The method for controllably assembling a decreasing gradient transition layer to enhance the interfacial properties of carbon fiber composites according to claim 1, characterized in that... The drying temperature in step one is 75℃~85℃, and the drying time is 8h~12h; the extraction temperature in step one is 75℃~85℃.

3. The method for controllably assembling a decreasing gradient transition layer to enhance the interfacial properties of carbon fiber composites according to claim 1, characterized in that... In step 2①, the sulfuric acid has a mass fraction of 98% and the nitric acid has a mass fraction of 65%.

4. The method for controllably assembling a decreasing gradient transition layer to enhance the interfacial properties of carbon fiber composites according to claim 1, characterized in that... In step 2, the temperature is maintained at 80℃~100℃ for 6h~8h; the mass ratio of the carbon nanotubes to the volume ratio of the mixed solution of sulfuric acid and nitric acid in step 2 is (2.0g~4.0g):(500mL~1000mL).

5. The method for controllably assembling a decreasing gradient transition layer to enhance the interfacial properties of carbon fiber composites according to claim 1, characterized in that... The mass ratio of the treated carbon nanotubes to the volume of distilled water in step 2③ is (2.0g~4.0g):(400mL~600mL).

6. The method for controllably assembling a decreasing gradient transition layer to enhance the interfacial properties of carbon fiber composites according to claim 1, characterized in that... The freeze-drying temperature in step 2④ is -41℃ to -39℃, and the freeze-drying time is 12h to 24h.

7. The method for controllably assembling a decreasing gradient transition layer to enhance the interfacial properties of carbon fiber composites according to claim 1, characterized in that... The mass ratio of epoxy resin to acetone in step 3① is (1.0g~2.0g):(50mL~100mL).

8. The method for controllably assembling a decreasing gradient transition layer to enhance the interfacial properties of carbon fiber composites according to claim 1, characterized in that... The ultrasonic treatment time in step 3① is 1h~2h; the stirring time in steps 3②, ​​3③, 3④ and 3⑤ is the same, which is 1min~5min.

9. The method for controllably assembling a decreasing gradient transition layer to enhance the interfacial properties of carbon fiber composites according to claim 1, characterized in that... The vacuum drying temperature and time are the same for steps 3②, ​​3③, 3④ and 3⑤. The vacuum drying temperature is 80℃~90℃ and the vacuum drying time is 20min~30min.

10. The application of the functionalized carbon fiber prepared by the method of claim 1, characterized in that... Functionalized carbon fibers are used to reinforce epoxy resins.

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