Ultrahigh-strength medium-modulus carbon fiber surface treatment method, surface modified carbon fiber and composite material

Abstract

The invention discloses an ultrahigh-strength medium-modulus carbon fiber surface treatment method, a surface modified carbon fiber and a composite material, the surface treatment method comprises the following steps: (1) carrying out first-stage anodic oxidation treatment on ultrahigh-strength medium-modulus carbon fibers by adopting a nitric acid solution so as to generate carboxyl active functional groups on the surfaces of the ultrahigh-strength medium-modulus carbon fibers; (2) washing and drying the carbon fibers obtained in the step (1); and (3) carrying out second-stage anodic oxidation and electrochemical grafting treatment on the carbon fibers obtained in the step (2) by adopting a mixed electrolyte containing ammonium bicarbonate and diethylenetriamine so as to form nitrogen-containing active groups on the surfaces of the carbon fibers. By means of the method, surface treatment of the ultrahigh-strength medium-modulus carbon fibers can be achieved, the tensile strength and the tensile modulus of the treated carbon fibers are not reduced, and meanwhile the problem that the requirement for the strength of the ultrahigh-strength medium-modulus carbon fiber composite short beam is high is solved.

Description

Technical Field

[0001] This invention belongs to the field of carbon fiber, specifically relating to a surface treatment method for ultra-high strength intermediate modulus carbon fiber, surface-modified carbon fiber, and composite materials. Background Technology

[0002] Carbon fiber is an advanced material with high specific strength and high specific modulus. Over the past few decades, carbon fiber production technology has continuously improved. Currently, carbon fiber grades can be broadly classified into three categories: high-strength standard modulus, high-strength medium modulus, and high-strength high modulus. Among them, high-strength medium modulus carbon fiber (T800 and T1000 grades) has always represented the highest strength carbon fiber. With the continuous advancement of carbon fiber manufacturing technology, domestic and international manufacturers have begun developing even higher-strength ultra-high-strength medium modulus carbon fibers. In 2014, the US and Japan successively launched T1100 grade ultra-high-strength medium modulus carbon fiber with a strength of approximately 7 GPa and a modulus of approximately 320 GPa. In 2023, Toray Industries of Japan launched T1200 grade ultra-high-strength medium modulus carbon fiber with a strength of 8 GPa and a modulus of 315 GPa. Other domestic and international manufacturers have also followed suit, continuously achieving ultra-high strength (6... Technological breakthroughs in medium modulus (315-350 GPa) carbon fibers (600-8000 MPa) have led to the current situation where ultra-high strength carbon fibers fall under the category of medium modulus carbon fibers. However, their modulus is 10-20% higher than that of commonly used high-strength medium modulus (T800, T1000) carbon fibers (modulus 294 GPa). As a result, the surface is more inert and the interfacial properties deteriorate. However, since the elongation at break of ultra-high strength medium modulus carbon fibers increases with the increase of strength, in order to be suitable for large deformation of composite materials, the requirements for the interfacial properties of composite materials (evaluated by short beam strength) are higher. Therefore, it is necessary to develop new surface treatment technologies to meet the application requirements of ultra-high strength medium modulus carbon fibers. Summary of the Invention

[0003] This invention provides a surface treatment method for ultra-high strength intermediate modulus carbon fiber. This method can achieve surface treatment of ultra-high strength intermediate modulus carbon fiber without reducing the tensile strength and tensile modulus of the treated carbon fiber. At the same time, it solves the problem of high strength requirements for short beams in ultra-high strength intermediate modulus carbon fiber composite materials.

[0004] In one aspect of the present invention, a surface treatment method for ultra-high strength intermediate modulus carbon fibers is proposed. The method includes: (1) performing a first-stage anodic oxidation treatment on the ultra-high strength intermediate modulus carbon fibers using a nitric acid solution to generate carboxyl active functional groups on the surface of the ultra-high strength intermediate modulus carbon fibers; (2) washing and drying the carbon fibers obtained in step (1); and (3) performing a second-stage anodic oxidation and electrochemical grafting treatment on the carbon fibers obtained in step (2) using a mixed electrolyte comprising ammonium bicarbonate and diethylenetriamine to form nitrogen-containing active groups on the surface of the carbon fibers.

[0005] Furthermore, the nitrogen-containing active groups on the surface of the carbon fiber include CN- and / or CONH-.

[0006] Furthermore, the nitrogen atom content on the surface of the carbon fiber is 3%-8%.

[0007] Further, in step (1), the strength of the ultra-high strength intermediate modulus carbon fiber is 7500GPa-8300GPa and the modulus is 315GPa-350GPa.

[0008] Furthermore, the mass concentration of the nitric acid solution is 0.5%-2%.

[0009] Furthermore, the temperature of the nitric acid solution is 20-40°C.

[0010] Furthermore, the current density of the first stage of anodizing treatment is 5A / m²-15A / m², and the time is 30s-90s.

[0011] Further, in step (3), the mass concentration of ammonium bicarbonate in the mixed electrolyte is 3wt%-7wt%.

[0012] Furthermore, the mass concentration of diethylenetriamine in the mixed electrolyte is 1%-3%.

[0013] Furthermore, the temperature of the alkaline electrolyte is 20-40°C.

[0014] Furthermore, the current density of the second stage of anodic oxidation and electrochemical grafting treatment is 5A / m²-10A / m², and the time is 60s-180s.

[0015] Furthermore, the above method also includes: (4) washing, drying, sizing the carbon fiber obtained in step (3) and then winding it up.

[0016] In a second aspect, the present invention provides a surface-modified carbon fiber, which is prepared by the method described above.

[0017] In a third aspect, the present invention provides a composite material prepared using the aforementioned surface-modified carbon fibers.

[0018] This invention involves anodizing ultra-high strength intermediate modulus carbon fibers in a nitric acid solution to generate carboxyl functional groups on the carbon fiber surface, which is beneficial for subsequent grafting with diethylenetriamine. Simultaneously, the oxidative etching process removes surface impurities from the carbon fibers, reducing the sharpness of weak layer grooves, micropores, and microcracks, thus mitigating stress concentration under load. This results in no decrease or a slight increase in the tensile strength and tensile modulus of the carbon fibers. After nitric acid treatment, the fibers are washed and dried to remove surface nitric acid and prevent reaction with the subsequent alkaline electrolyte. Then, anodizing and electrochemical grafting are carried out in a mixed electrolyte containing ammonium bicarbonate and diethylenetriamine. The process can significantly increase the number of nitrogen-containing functional groups on the carbon fiber surface. The carboxyl functional groups generated by the first stage of anodic oxidation can themselves undergo a grafting reaction with diethylenetriamine. Ammonium bicarbonate in the mixed electrolyte provides an alkaline environment that can improve the stability of diethylenetriamine. In addition, ammonium bicarbonate improves the conductivity of the mixed electrolyte and increases the electric field strength. The nitrogen atoms in diethylenetriamine have lone pairs of electrons, which easily migrate to the carbon fiber anode under the action of an electric field, thus effectively improving the electrochemical grafting efficiency. At the same time, although the oxidation effect of ammonium bicarbonate as an electrolyte is weaker than that of nitric acid, it can still further enhance the electrochemical oxidation effect to a certain extent. The unreacted amino groups and the tertiary amine groups generated by the reaction in the diethylenetriamine grafted onto the carbon fiber can both react with the epoxy resin matrix, thus effectively improving the interfacial properties and increasing the short beam strength of ultra-high strength medium modulus carbon fiber composites. Detailed Implementation

[0019] The present invention will be further described in detail below with reference to the embodiments. The following embodiments are merely descriptive and not limiting, and should not be used to limit the scope of protection of the present invention.

[0020] In one aspect of the present invention, a surface treatment method for ultra-high strength intermediate modulus carbon fiber is provided. According to an embodiment of the present invention, the method includes: S1: The first stage of anodizing treatment of ultra-high strength intermediate modulus carbon fiber is carried out using nitric acid solution. In this step, ultra-high strength intermediate modulus carbon fibers (strength 7500MPa-8300MPa, modulus 315GPa-350GPa) undergo a first-stage anodizing treatment in a nitric acid solution, generating carboxyl functional groups on the surface of the ultra-high strength intermediate modulus carbon fibers. Specifically, the mass concentration of the nitric acid solution is 0.5wt%-2wt% (prepared using ultrapure water), preferably 1wt%, the temperature of the nitric acid solution is 20-40℃, preferably 30℃, the current density of the first-stage anodizing treatment is 5-15A / m², and the time is 30s-90s. The inventors have found that by anodizing ultra-high strength intermediate modulus carbon fibers under the above conditions, the activation efficiency of the carbon fibers can be significantly improved, thereby increasing the carboxyl content on the surface of the ultra-high strength intermediate modulus carbon fibers, which is beneficial for subsequent grafting of diethylenetriamine. At the same time, the oxidative etching removes impurities from the carbon fiber surface, reduces the sharpness of weak layer grooves, micropores, microcracks, etc., weakens stress concentration under load, and ensures that the tensile strength and tensile modulus of the carbon fibers do not decrease or slightly increase.

[0021] S2: The carbon fiber obtained in step S1 is washed and dried. In this step, the carbon fiber obtained in step S1 is washed with water to remove the residual nitric acid solution on the carbon fiber. Ultrapure water is used in the washing process; the drying temperature is set to 120-140℃.

[0022] S3: The carbon fibers obtained in step S2 are subjected to a second stage of anodic oxidation and electrochemical grafting treatment using a mixed electrolyte comprising ammonium bicarbonate and diethylenetriamine. In this step, a mixed electrolyte comprising ammonium bicarbonate and diethylenetriamine is used to perform a second-stage anodic oxidation and electrochemical grafting treatment on the carbon fibers obtained in step S2. This significantly increases the nitrogen content on the carbon fiber surface. The carboxyl functional groups generated during the first-stage anodic oxidation can themselves undergo a grafting reaction with diethylenetriamine. The ammonium bicarbonate in the mixed electrolyte provides an alkaline environment that enhances the stability of diethylenetriamine. Furthermore, ammonium bicarbonate improves the conductivity of the mixed electrolyte and increases the electric field strength. The nitrogen atoms in diethylenetriamine have lone pairs of electrons, which easily migrate to the anode of the carbon fiber under the influence of the electric field, thus effectively improving the electrochemical grafting efficiency. At the same time, although the oxidation effect of ammonium bicarbonate as an electrolyte is weaker than that of nitric acid, it can still further enhance the electrochemical oxidation effect to some extent. The unreacted amino groups and the tertiary amine groups generated by the reaction in the diethylenetriamine grafted onto the carbon fibers can both react with the epoxy resin matrix, thus effectively improving the interfacial properties and increasing the short beam strength of the ultra-high strength medium-modulus carbon fiber composite material. Specifically, the mass concentration of ammonium bicarbonate in the mixed electrolyte is 3-7 wt%, the concentration of diethylenetriamine is 1-3 wt%, the temperature of the mixed electrolyte is 20-40℃, the current density of the second stage of anodizing and electrochemical grafting treatment is 5-10 A / m², and the time is 60-180 s. The inventors discovered that by continuing anodizing and surface grafting treatment on carbon fibers under the above conditions, the activation efficiency of carbon fibers can be significantly improved, thereby increasing the active functional groups on the carbon fiber surface and thus improving the interfacial bonding force between the carbon fibers and resins such as epoxy resins. Simultaneously, surface grafting can effectively alleviate the performance degradation of carbon fibers. After this anodizing and grafting treatment, the tensile strength and tensile modulus of the carbon fiber body remain essentially unchanged.

[0023] Furthermore, the nitrogen-containing active groups on the surface of the carbon fiber include CN- and / or CONH-. Furthermore, the nitrogen atom content on the surface of the carbon fiber is 3%-8%, thereby allowing this amount of nitrogen to undergo extensive chemical reactions with the matrix resin, improving interfacial properties.

[0024] S4: The carbon fiber obtained in step S3 is washed, dried, sized, and wound to obtain carbon fiber. In this step, the carbon fiber obtained in step S3 is washed with ultrapure water; the drying temperature is set to 120-140℃; and the sizing agent is a conventional epoxy emulsion type sizing agent in the prior art.

[0025] Therefore, this method can achieve surface treatment of ultra-high strength intermediate modulus carbon fibers without reducing the tensile strength and tensile modulus of the treated carbon fibers, and at the same time solves the problem of high strength requirements for short beams of ultra-high strength intermediate modulus carbon fiber composites.

[0026] In a second aspect, the present invention provides a surface-modified carbon fiber. According to an embodiment of the present invention, the surface-modified carbon fiber is prepared by the method described above. As a result, the carbon fiber surface has a high number of active groups, which simultaneously enhances the hydrophilicity of the carbon fiber and significantly increases the surface energy. Furthermore, the short beam strength of the resulting surface-modified carbon fiber composite with epoxy resin reaches over 120 MPa.

[0027] In a third aspect, the present invention provides a composite material. According to an embodiment of the invention, the composite material is prepared using the aforementioned surface-modified carbon fiber. Specifically, taking the composite of the aforementioned surface-modified carbon fiber and epoxy resin matrix as an example, the short beam strength of the resulting surface-modified carbon fiber and epoxy resin matrix composite material is significantly improved.

[0028] The present invention will now be described with reference to specific embodiments. It should be noted that these embodiments are merely descriptive and should not be construed as limiting the present invention in any way.

[0029] Example 1 (a) Prepare a 1% nitric acid solution with ultrapure water and pour it into the first electrolytic cell. Set the electrolysis temperature to 30°C and the current density to 5A / m². Pass ultrapure water into the first water washing tank after the first electrolytic cell. Set the temperature of the first drying furnace to 130°C.

[0030] (ii) Prepare a mixed alkaline solution with ammonium bicarbonate mass concentration of 5% and diethylenetriamine mass concentration of 2% using ultrapure water and pour it into the second electrolytic cell. The electrolysis temperature is 30℃ and the current density is 5A / m². Ultrapure water is introduced into the second water washing tank after the second electrolytic cell. The temperature of the second drying furnace is set to 130℃.

[0031] (III) The carbon fiber (tensile strength of 7901MPa, tensile modulus of 339GPa) was sequentially passed through the first electrolytic cell (residence time of 60s, first water washing tank, first drying furnace), the second electrolytic cell (residence time of 120s, second water washing tank, second drying furnace, sizing tank (2.5% solid content epoxy emulsion sizing agent) and the sizing drying furnace (temperature of 140℃), and 100 meters of carbon fiber were collected for mechanical property testing.

[0032] Example 2 (a) Prepare a nitric acid solution with a mass concentration of 0.5% using ultrapure water and pour it into the first electrolytic cell. Set the electrolysis temperature to 40℃ and the current density to 15A / m². Pass ultrapure water into the first water washing tank after the first electrolytic cell. Set the temperature of the first drying furnace to 130℃.

[0033] (ii) Prepare a mixed electrolyte solution with an ammonium bicarbonate mass concentration of 3% and a diethylenetriamine mass concentration of 3% using ultrapure water and pour it into the second electrolytic cell. The electrolysis temperature is 40℃ and the current density is 10A / m². Ultrapure water is introduced into the second water washing tank after the second electrolytic cell. The temperature of the second drying furnace is set to 130℃.

[0034] (iii) The same batch of carbon fibers as in Example 1 were sequentially passed through the first electrolytic cell (residence time of 90s, first water washing tank, first drying furnace, second electrolytic cell (residence time of 180s), second drying furnace, sizing tank (epoxy emulsion sizing agent with 2.5% solid content) and sizing drying furnace (temperature of 140℃). After drying, 100 meters of carbon fibers were collected for mechanical property testing.

[0035] Example 3 (a) Prepare a 2% nitric acid solution with ultrapure water and pour it into the first electrolytic cell. Set the electrolysis temperature to 20°C and the current density to 10A / m². Pass ultrapure water into the first water washing tank after the first electrolytic cell. Set the temperature of the first drying furnace to 130°C.

[0036] (ii) Prepare a mixed alkaline solution with an ammonium bicarbonate mass concentration of 7% and a diethylenetriamine mass concentration of 1% using ultrapure water and pour it into the second electrolytic cell. The electrolysis temperature is 20℃ and the current density is 8A / m². Ultrapure water is introduced into the second water washing tank after the second electrolytic cell. The temperature of the second drying furnace is set to 130℃.

[0037] (III) The carbon fiber (tensile strength of 7598MPa, tensile modulus of 318GPa) was sequentially passed through the first electrolytic cell (residence time of 30s, first water washing tank, first drying furnace), the second electrolytic cell (residence time of 60s, second water washing tank, second drying furnace, sizing tank (2.5% solid content epoxy emulsion sizing agent) and the sizing drying furnace (temperature of 140℃), and 100 meters of carbon fiber were collected for mechanical property testing.

[0038] Comparative Example 1 (a) Prepare a 9% ammonium bicarbonate solution with ultrapure water and pour it into the first electrolytic cell; set the electrolysis temperature to 30°C and the current density to 15A / m²; introduce ultrapure water into the first water washing tank after the first electrolytic cell; and set the temperature of the first drying furnace to 130°C.

[0039] (ii) The second electrolytic cell, the second washing tank, and the second drying furnace are left unused.

[0040] (iii) The same batch of carbon fiber as in Example 1 was sequentially passed through the first electrolytic cell (residence time of 60s), the first water washing tank, the second drying furnace, the sizing tank (epoxy emulsion sizing agent with 2.5% solid content) and the sizing drying furnace (temperature of 140℃), and 100 meters of carbon fiber were collected for mechanical property testing.

[0041] Comparative Example 2 (a) Prepare a nitric acid solution with a mass concentration of 0.3% using ultrapure water and pour it into the first electrolytic cell. Set the electrolysis temperature to 50°C and the current density to 3A / m². Pass ultrapure water into the first water washing tank after the first electrolytic cell. Set the temperature of the drying furnace to 130°C.

[0042] (ii) The second electrolytic cell, the second washing tank, and the second drying furnace are left unused.

[0043] (iii) The same batch of carbon fiber as in Example 1 was sequentially passed through the first electrolytic cell (residence time of 120s), the first water washing tank, the first drying furnace, the sizing tank (epoxy emulsion sizing agent with 2.5% solid content) and the sizing drying furnace (temperature of 140℃), and 100 meters of carbon fiber were collected for mechanical property testing.

[0044] The mechanical properties of the surface-modified carbon fibers and the short beam strength of the composite materials obtained in Examples 1-3 and Comparative Examples 1-2 were tested, and the test results are shown in Table 1.

[0045] XPS tests were performed on the surface-modified carbon fibers obtained in Examples 1-3 and Comparative Examples 1-2. The test results showed that the surface of the surface-modified carbon fibers in Examples 1-3 and Comparative Examples 1-2 contained CN- and CONH- groups.

[0046] The strength of the composite short beam was tested according to standard JC / T 773-2010. The composite material was a unidirectional composite material, prepared by compression molding, with a fiber volume fraction of 60%. The short beam strength specimen size was 20mm*10mm*2mm (length, width, thickness). The resin system used for preparation was AG80 / DDS, and the curing regime was 140℃ / 2.5h + 160℃ / 3h + 180℃ / 2h + 200℃ / 15min.

[0047] Table 1

[0048] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A surface treatment method for ultra-high strength intermediate modulus carbon fiber, wherein, include: (1) The ultra-high strength intermediate modulus carbon fiber is subjected to a first stage of anodic oxidation treatment using nitric acid solution in order to generate carboxyl active functional groups on the surface of the ultra-high strength intermediate modulus carbon fiber; (2) The carbon fiber obtained in step (1) is washed with water and dried; (3) The carbon fibers obtained in step (2) are subjected to a second stage of anodic oxidation and electrochemical grafting treatment using a mixed electrolyte including ammonium bicarbonate and diethylenetriamine, so as to form nitrogen-containing active groups on the surface of the carbon fibers.

2. The method as described in claim 1, wherein, The nitrogen-containing active groups on the surface of the carbon fiber include CN- and / or CONH-.

3. The method as described in claim 1 or 2, wherein, The nitrogen atom content on the surface of the carbon fiber is 3%-8%.

4. The method of claim 1, wherein, In step (1), the ultra-high strength intermediate modulus carbon fiber has a tensile strength of 7500MPa-8300MPa and a tensile modulus of 315GPa-350GPa; and / or The nitric acid solution has a mass concentration of 0.5%-2%; and / or The temperature of the nitric acid solution is 20-40℃.

5. The method of claim 1, wherein, The current density of the first stage of anodizing treatment is 5A / m²-15A / m², and the time is 30s-90s.

6. The method of claim 1, wherein, In step (3), the mass concentration of ammonium bicarbonate in the mixed electrolyte is 3wt%-7wt%; and / or The mass concentration of diethylenetriamine in the mixed electrolyte is 1%-3%.

7. The method of claim 1, wherein, The temperature of the mixed electrolyte is 20-40℃; and / or The current density for the second stage of anodic oxidation and electrochemical grafting treatment is 5A / m²-10A / m², and the time is 60s-180s.

8. The method of claim 1, wherein, Further includes: (4) The carbon fiber obtained in step (3) is washed, dried, sized and then wound up.

9. A surface-modified carbon fiber, wherein, The surface-modified carbon fiber is prepared by any one of claims 1-8.

10. A composite material, wherein, The composite material is prepared using the surface-modified carbon fiber described in claim 9.

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