High-efficiency carbon fiber surface treatment method and composite material thereof

Abstract

A highly efficient carbon fiber surface treatment method and its composite material belong to the field of composite material technology. Step 1: Wash the carbon fiber with acetone to completely remove sizing agent and impurities, then dry it. Step 2: Wind the carbon fiber onto a glass frame and perform plasma treatment under an O2-Ar mixed gas atmosphere. Step 3: Dissolve polyimide resin in N,N-dimethylacetamide to prepare a resin solution. Step 4: Prepare a prepreg by combining the carbon fiber and resin solution. Step 5: Stack multiple prepreg sheets, set a stepped heating program, and prepare the composite material by high-temperature hot pressing. In this invention, Ar plasma etches the carbon fiber surface, increasing the surface area and surface roughness, while O2 plasma introduces oxygen-containing functional groups into the carbon fiber surface. The synergistic effect of these two processes improves the mechanical interlocking and chemical bonding between the carbon fiber and the resin matrix, significantly enhancing the interlaminar shear strength at both room temperature and high temperature.

Description

Technical Field

[0001] This invention belongs to the field of composite material technology and relates to an efficient carbon fiber surface treatment method and its composite material. Background Technology

[0002] With the development of modern technology, people have increasingly higher requirements for material performance. Among many materials, fiber-reinforced resin matrix composites are widely used in many fields such as aerospace, weaponry, wind turbine blades, automotive, and medical equipment due to their unique properties. Among fiber-reinforced resin matrix composites, carbon fiber-reinforced resin matrix composites are the most widely used.

[0003] Carbon fiber possesses characteristics such as high modulus, high strength, and low density. Thermosetting polyimide resin, as one of the high-performance resin matrices, contains polyaromatic heterocycles with imide structures in its molecular backbone. Due to these structures, polyimide resin exhibits excellent properties such as radiation resistance, corrosion resistance, low dielectric constant, low moisture absorption, and high-temperature resistance. Theoretically, combining carbon fiber with polyimide resin can simultaneously leverage the advantages of both. However, the current challenge facing carbon fiber reinforced resin matrix composites is the relatively weak interfacial bonding between the reinforcing material and the resin matrix due to the smooth surface of carbon fibers and the lack of active groups. Therefore, improving the interfacial bonding effect between reinforcing carbon fibers and the resin matrix is ​​an urgent research topic.

[0004] This invention utilizes inductively coupled plasma (ICP) treatment technology, simultaneously introducing inert gas Ar and reactive gas O2. While increasing the surface roughness of carbon fibers through plasma etching, it also introduces oxygen-containing functional groups to improve the chemical bonding between the carbon fibers and the resin matrix, significantly enhancing the interlaminar shear strength (ILSS) of the composite material at both room temperature and 300°C. This preparation method is simple, environmentally friendly, and generates no waste. It can be extended to the surface treatment of other materials and is suitable for large-scale industrial production. Summary of the Invention

[0005] To address the problems of existing technologies, this invention provides a simple method for efficiently treating carbon fiber surfaces and preparing composite materials. Specifically, it is a high-efficiency carbon fiber surface treatment method and its composite materials. First, plasma treatment is performed under mild conditions (10 min, 40 Pa, 100 W). The gas ratio is adjusted by controlling the gas flow rate, changing the ratio of O2 to Ar. Microscopic and mechanical property tests are combined to analyze the optimal gas ratio and the synergistic mechanism of the two gases. Under mild treatment conditions, the influence of factors such as treatment time, pressure, and power is minimized, focusing solely on the performance changes caused by altering the ratio of the two gases. After obtaining the optimal gas ratio, orthogonal experiments are conducted to analyze the effects of treatment time, pressure, and power, thus determining the optimal treatment conditions and controlling the interfacial properties of the carbon fiber.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A high-efficiency carbon fiber surface treatment method, wherein the high-efficiency carbon fiber surface treatment method achieves the effects of regulating the surface roughness of carbon fibers and introducing active groups by adjusting the ratio of O2 to Ar and controlling the treatment time, treatment pressure and treatment power, thereby improving the interfacial bonding ability between carbon fibers and polyimide resin matrix and improving the room temperature and high temperature mechanical properties of composite materials, including the following steps: Step 1: Wash the carbon fiber with acetone at room temperature for 48-50 hours to completely remove the sizing agent and impurities. Then, dry the carbon fiber in an oven at 100℃-120℃ for 1-2 hours to remove the acetone. Step 2: The dried carbon fiber is wound around a square glass frame and subjected to plasma treatment under different conditions in an O2-Ar mixed gas atmosphere. After treatment, the carbon fiber is removed. Furthermore, the plasma treatment conditions are as follows: the volume ratio of O2 to Ar is 1:1, the treatment time is 15-20 minutes, the treatment pressure is 50-60 Pa, and the treatment power is 80-100 W.

[0007] Step 3: Dissolve the polyimide resin in N,N-dimethylacetamide to prepare a polyimide solution, which serves as the resin solution; wherein the mass fraction of the resin solution is 35%-37%.

[0008] Step 4: The carbon fibers treated in Step 2 are mixed with the resin solution to form sheet-like prepreg; specifically: Furthermore, the prepreg is prepared using a wet winding process. First, under traction, the carbon fibers from step 2 are passed through an impregnation tank and fully impregnated with the resin solution. Then, excess resin is scraped off the surface of the carbon fibers through a slit to maintain a stable resin content in the prepreg. Finally, the carbon fibers are unidirectionally wound on an iron frame. After winding, the prepreg is dried at 80℃-90℃ for 0.5~2 hours and then cut into sheet-like prepregs that meet the required dimensions.

[0009] Step 5: Stack multiple prepreg sheets, place them in an iron mold, set a stepped heating program, and prepare the composite material by high-temperature hot pressing.

[0010] Furthermore, in the high-temperature compression molding process, a stepped heating program is set according to the melt viscosity change of the polyimide oligomer, including six heating stages. The stepped heating process ensures that the resin gradually softens and fully impregnates the carbon fiber. Specifically, the first and second heating stages are gradually heated without covering the mold to remove the solvent. In the third and subsequent heating stages, the mold is covered, and a pressure of 2-5 MPa is applied to fill the mold with the mixture. First heating range: Maintain at 140~160℃ for 0.4~0.6 hours.

[0011] First heating range: Maintain at 180~220℃ for 0.4~0.6 hours.

[0012] The third heating range: maintain a temperature of 280~320℃ for 30-40 minutes, during which exhaust gas once every 5 minutes.

[0013] Fourth heating range: Maintain a temperature of 345~355℃ for 30-40 minutes, during which exhaust gas once every 5 minutes.

[0014] Fifth heating range: Maintain at 365~375℃ for 2 hours.

[0015] The sixth heating range: maintain at 375~385℃ for 2 hours, cool to room temperature, remove from the mold, and obtain unidirectional carbon fiber composite material.

[0016] The degassing process in this step minimizes air bubbles within the composite material, resulting in a denser and more uniform interior, thus eliminating the influence of the molding process on the composite material's strength. A unidirectional carbon fiber composite material was prepared using the above-described preparation method.

[0017] The beneficial effects of this invention are: The O2-Ar mixed gas plasma treatment used in this invention is significantly superior to single-gas plasma treatment. During the O2-Ar mixed gas plasma treatment of carbon fibers, while the Ar plasma etches the carbon fiber surface, increasing the surface area and surface roughness, the O2 plasma introduces oxygen-containing functional groups into the carbon fiber surface. The two work synergistically to improve both the mechanical interlocking and chemical bonding between the carbon fiber and the resin matrix. Interlaminar shear strength tests show that, under the optimal O2-Ar mixed gas ratio, both the room-temperature and high-temperature interlaminar shear strength of the composite material are significantly improved. Attached Figure Description

[0018] Figure 1 This is a comparison image of the carbon fiber surface obtained from the proportioning experiment in step 2 of Example 2 and the untreated carbon fiber. Figure 1 (a) is an SEM image of unprocessed carbon fibers; Figure 1 (b) is the SEM image of carbon fiber after processing with O2:Ar=3:7; Figure 1 (c) is the SEM image of carbon fiber after processing with O2:Ar=5:5; Figure 1 (d) is the SEM image of carbon fiber after processing with O2:Ar=7:3; Figure 2 This is a comparison diagram of the surface roughness Rq of carbon fiber obtained from the proportioning experiment in step 2 of Example 2 and the surface roughness Rq of untreated carbon fiber. Figure 3 This is a comparison diagram of the surface roughness Ra of carbon fiber obtained from the proportioning experiment in step 2 of Example 2 and the surface roughness Ra of untreated carbon fiber. Figure 4 The Fourier transform infrared spectra of carbon fibers before and after treatment obtained from the proportioning experiment in step 2 of Example 2; Figure 5 This is a comparison diagram of the interlaminar shear strength of composite materials made from carbon fibers treated with different gas ratios in step 2 of Example 1 and composite materials made from untreated carbon fibers. Figure 6 This is a comparison diagram of the interlaminar shear strength of composite materials made from carbon fibers treated with different experimental groups and composite materials made from untreated carbon fibers in the orthogonal experiment in step 2 of Example 1. Detailed Implementation

[0019] The present invention will be further described below with reference to specific implementation examples.

[0020] The different processing conditions used in step 2 of this invention are a gas ratio experiment and an orthogonal experiment. Specifically, in the gas ratio experiment, under the conditions of a processing time of 10 min, a processing pressure of 40 Pa, and a processing power of 100 W, the ratio of O2 to Ar was adjusted by controlling the flow rate of O2 and Ar, resulting in ratios of 1:9, 2:8, 3:7, 4:6, 5:5, 6:4, 7:3, 8:2, and 9:1, all with an O2:Ar ratio. After determining the optimal gas ratio, an orthogonal experiment was conducted. Under the optimal gas ratio of 5:5, the effects of processing time, processing pressure, and processing power were analyzed. Finally, the optimal processing conditions were determined to be a processing time of 15-20 minutes, a processing pressure of 50-60 Pa, and a processing power of 80-100 W.

[0021] Specific embodiments are given below.

[0022] Example 1 A high-efficiency carbon fiber surface treatment method includes the following steps: Step 1: Before plasma treatment, the carbon fiber needs to be washed and dried. The carbon fiber is wound on a plastic roller and placed in a Soxhlet extractor. It is repeatedly washed with acetone as a detergent for 48 hours to remove the slurry on the surface of the carbon fiber. After washing, the carbon fiber is taken out of the Soxhlet extractor and placed in an oven at 100°C for 2 hours to remove the acetone.

[0023] Step 2: The dried carbon fiber is wound onto a square glass frame and subjected to plasma treatment under different conditions in an O2-Ar mixed gas atmosphere. The carbon fiber is then removed after treatment. In this embodiment, the O2 to Ar volume ratio is 1:1, the treatment time is 20 minutes, the treatment pressure is 50 Pa, and the treatment power is 80 W. Specifically: After washing and drying, carbon fibers are wound onto a square glass frame and then placed inside the vacuum reaction chamber of the plasma instrument. The chamber is repeatedly cleaned with an O2-Ar mixed gas. After cleaning, the inlet valve is opened to simultaneously introduce O2 and Ar, and the flow rate ratio of O2 and Ar is controlled by adjusting the knob to control the amount of each gas introduced. When the pressure inside the chamber reaches the experimental requirement, the radio frequency power source is turned on for preheating. When the red indicator light illuminates, the power source switch is turned on to ensure the output power reaches the experimental requirement. The matching capacitor is then repeatedly adjusted to minimize the reflected power, not exceeding 4% of the output power, before plasma treatment begins. After the required treatment time is reached, the radio frequency power source, vacuum pump, and gas flow display are sequentially turned off, and the inlet valve is opened to slowly introduce air. Once the gas pressure inside the reaction chamber matches the external gas pressure, the plasma-treated carbon fibers are removed. The settings for each condition during plasma treatment are based on the requirements of the gas ratio experiment and orthogonal experiment.

[0024] Step 3: Dissolve the polyimide resin in N,N-dimethylacetamide to prepare a polyimide solution, which serves as the resin solution; wherein the mass fraction of the resin solution is 35%. Specifically: Weigh 90g of polyimide resin and measure 190ml of N,N-dimethylacetamide. Mix the two in a flask, turn on the oil bath heating, set the temperature to 140℃, stir slowly, and after heating for 4 hours, take out a polyimide solution with a mass fraction of 35%.

[0025] Step 4: The carbon fibers treated in Step 2 are mixed with the resin solution to form sheet-like prepreg. In this embodiment, the prepreg is prepared using a wet winding process. First, under traction, the carbon fibers from Step 2 are passed through an impregnation tank and fully impregnated with the resin solution. Then, excess resin on the surface of the carbon fibers is scraped off through a slit to maintain a stable resin content in the prepreg. Finally, the carbon fibers are unidirectionally wound on an iron frame. After winding, the prepreg is dried at 80°C for 2 hours and then cut into sheet-like prepregs with dimensions of 80mm × 40mm.

[0026] Step 5: Stack 10 prepreg sheets and place them in an iron mold to prepare the composite material through high-temperature hot pressing. The heating process is set according to the melt viscosity of the polyimide oligomer as a function of temperature. It includes six heating stages: in the first and second heating stages, the mold is gradually heated without covering the mold to remove the solvent; in the third and subsequent heating stages, the mold is covered and a pressure of 3 MPa is applied to fill the mold with the mixture; specifically: First heating range: Maintain at 150℃ for 0.5 hours.

[0027] First heating range: Maintain at 200℃ for 0.5 hours.

[0028] The third heating zone: maintain a temperature of 300℃ for 35 minutes, during which exhaust gas once every 5 minutes.

[0029] Fourth heating zone: Maintain at 350℃ for 35 minutes, with exhaust every 5 minutes.

[0030] Fifth heating zone: Maintain at 370℃ for 2 hours.

[0031] The sixth heating zone: hold at 380℃ for 2 hours, cool to room temperature, remove from the mold, and obtain unidirectional carbon fiber composite material.

[0032] Example 2 In step 1, the acetone washing time in the Soxhlet extractor is 50 hours, and the drying temperature in the oven is 120℃ for 1 hour.

[0033] In step 2, the processing time is 15 minutes, the processing pressure is 60 Pa, and the processing power is 100 W.

[0034] In step 3, the resin solution has a mass fraction of 37%.

[0035] In step 4, after the winding is completed, the prepreg is dried at 90 ℃ for 0.5 hours and then cut into sheets of 80mm×40mm.

[0036] In step 5, the temperature gradient is: First heating range: Maintain at 130℃ for 0.6 hours.

[0037] First heating range: Maintain at 180℃ for 0.6 hours.

[0038] The third heating zone: maintain a temperature of 280℃ for 40 minutes, during which exhaust gas once every 5 minutes.

[0039] Fourth heating zone: Maintain at 345℃ for 40 minutes, with exhaust every 5 minutes.

[0040] Fifth heating zone: Maintain at 365℃ for 2 hours.

[0041] The sixth heating zone: maintain at 375℃ for 2 hours, cool to room temperature, remove from the mold, and obtain unidirectional carbon fiber composite material.

[0042] Example 3 In step 1, the acetone washing time in the Soxhlet extractor is 49 hours, and the drying temperature in the oven is 110℃ for 1.5 hours.

[0043] In step 2, the processing time is 18 minutes, the processing pressure is 55 Pa, and the processing power is 90 W.

[0044] In step 3, the resin solution has a mass fraction of 36%.

[0045] In step 4, after the winding is completed, the prepreg is dried at 85 ℃ for 1 hour and then cut into sheets of 80mm×40mm.

[0046] In step 5, the temperature gradient is: First heating range: Maintain at 160℃ for 0.4 hours.

[0047] First heating range: Maintain at 220℃ for 0.4 hours.

[0048] The third heating zone: maintain a temperature of 320℃ for 30 minutes, during which exhaust gas once every 5 minutes.

[0049] Fourth heating zone: Maintain at 355℃ for 30 minutes, with exhaust every 5 minutes.

[0050] Fifth heating zone: Maintain at 375℃ for 2 hours.

[0051] The sixth heating zone: maintain at 385℃ for 2 hours, cool to room temperature, remove from the mold, and obtain unidirectional carbon fiber composite material.

[0052] Example Performance Analysis: This invention utilizes inductively coupled plasma (ICP) technology, simultaneously introducing the inert gas Ar and the reactive gas O2. While the Ar plasma etches the carbon fiber surface, increasing its surface roughness and surface area, the O2 plasma also introduces oxygen-containing functional groups onto the carbon fiber surface. O2-Ar mixed-gas plasma treatment will simultaneously improve both the mechanical interlocking and chemical bonding between the carbon fiber and the resin matrix. (SEM images attached...) Figure 1 It is possible to observe the surface of carbon fibers treated with different gas ratios, and the attached... Figure 1 (a) is an unprocessed SEM image of carbon fiber, with appended... Figure 1 (b) is a SEM image of carbon fiber after processing with O2:Ar=3:7. Figure 1 (c) is a SEM image of carbon fiber after processing with O2:Ar=5:5. Figure 1 (d) is the SEM image of carbon fiber after processing with O2:Ar=7:3; from the roughness trend map (attached) Figure 2 Appendix Figure 3 The change in carbon fiber surface roughness can also be observed in the Fourier transform infrared spectrum (see attached image). Figure 4 As can be seen from the data, the number of oxygen-containing functional groups increases after plasma treatment; from the interlayer shear data (attached) Figure 5 Appendix Figure 6 As can be seen from the data, the interlaminar shear strength at room temperature and at a high temperature of 300℃ are significantly improved after plasma treatment of carbon fibers and the composite material is made with polyimide matrix, which demonstrates the feasibility of this method.

[0053] The above embodiments are merely illustrative of the implementation methods of the present invention, but should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the protection scope of the present invention.

Claims

1. A method for efficient carbon fiber surface treatment, characterized in that, The high-efficiency carbon fiber surface treatment method achieves regulation of carbon fiber surface roughness and introduction of active groups by adjusting the ratio of O2 to Ar and controlling the treatment time, treatment pressure, and treatment power, and includes the following steps: Step 1: Wash the carbon fiber with acetone at room temperature to completely remove the sizing agent and impurities; dry the carbon fiber to remove the acetone. Step 2: The dried carbon fiber is wound around a square glass frame and subjected to plasma treatment in an O2-Ar mixed gas atmosphere. Step 3: Dissolve the polyimide resin in N,N-dimethylacetamide to prepare a polyimide solution, which serves as the resin solution; Step 4: The carbon fibers treated in Step 2 are mixed with the resin solution to form sheet-like prepreg. Step 5: Stack multiple prepreg sheets, place them in a mold, set a stepped heating program, and prepare the composite material through high-temperature hot pressing; specifically: A stepped heating program consisting of six heating stages is set based on the melt viscosity variation of polyimide oligomers.

2. The high-efficiency carbon fiber surface treatment method according to claim 1, characterized in that, In step 1, the washing time is 48-50 hours; the drying temperature is 100℃-120℃, and the time is 1-2 hours.

3. The high-efficiency carbon fiber surface treatment method according to claim 2, characterized in that, In step 2, the plasma treatment conditions are as follows: the volume ratio of O2 to Ar is 1:1, the treatment time is 15-20 minutes, the treatment pressure is 50-60 Pa, and the treatment power is 80-100 W.

4. The efficient carbon fiber surface treatment method according to claim 3, characterized in that, In step 3, the resin solution has a mass fraction of 35%-37%.

5. The efficient carbon fiber surface treatment method according to claim 4, characterized in that, In step 4, the prepreg is prepared using a wet winding process. First, under traction, the carbon fiber from step 2 is passed through an impregnation tank and fully impregnated with the resin solution. Then, excess resin on the surface of the carbon fiber is scraped off through a slit to maintain the stability of the resin content in the prepreg. Finally, the carbon fiber is unidirectionally wound on an iron frame. After winding, it is dried at 80 ℃-90 ℃ for 0.5~2 hours and then cut into sheet-like prepreg.

6. The efficient carbon fiber surface treatment method according to claim 5, characterized in that, In step 5, during the six heating processes, the first and second heating zones are gradually heated without covering the mold to remove the solvent. In the third and subsequent heating zones, the mold is covered, and a pressure of 2-5 MPa is applied to fill the mold with the mixture. Specifically: First heating range: Maintain at 140~160℃ for 0.4~0.6 hours; First heating range: Maintain at 180~220℃ for 0.4~0.6 hours; Third heating range: Maintain at 280~320℃ for 30-40 minutes, with exhaust every 5 minutes; Fourth heating range: Maintain a temperature of 345~355℃ for 30-40 minutes, during which exhaust air once every 5 minutes; Fifth heating range: Maintain at 365~375℃ for 2 hours; The sixth heating range: maintain at 375~385℃ for 2 hours, cool to room temperature, remove from the mold, and obtain unidirectional carbon fiber composite material.

7. A unidirectional carbon fiber composite material, characterized in that, It is prepared by any one of the preparation methods described in claims 1-6.

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