CN113322678B - Surface modified carbon fiber and modification method thereof - Google Patents

Surface modified carbon fiber and modification method thereof Download PDF

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CN113322678B
CN113322678B CN202110506529.0A CN202110506529A CN113322678B CN 113322678 B CN113322678 B CN 113322678B CN 202110506529 A CN202110506529 A CN 202110506529A CN 113322678 B CN113322678 B CN 113322678B
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carbon fiber
imidazole
ionic liquid
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mixed solution
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CN113322678A (en
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曹维宇
李鸿鑫
徐樑华
童元建
高爱君
李常清
王宇
赵振文
王梦梵
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Beijing University of Chemical Technology
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Abstract

The invention discloses a surface modified carbon fiber and a modification method thereof, wherein the method for modifying the carbon fiber comprises the following steps: (1) removing glue on the surface of the carbon fiber; (2) contacting the carbon fiber subjected to degumming obtained in the step (1) with an oxidant for oxidation reaction so as to obtain oxidized carbon fiber; (3) and performing electrochemical reaction by taking the oxidized carbon fiber as a cathode, graphite as an anode and a mixed solution containing imidazole ionic liquid, an organic solvent, a condensing agent and a conductive agent as an electrolyte so as to graft imidazole ions on the surface of the carbon fiber in a covalent manner. The interface shear strength of the carbon fiber with the imidazole ions grafted on the surface obtained by the method is greatly improved compared with that of the unmodified carbon fiber, so that the application of the carbon fiber in the field of composite materials is expanded.

Description

Surface modified carbon fiber and modification method thereof
Technical Field
The invention belongs to the field of carbon fibers, and particularly relates to a surface modified carbon fiber and a modification method thereof.
Background
As one of the most advanced composite materials in the modern, the carbon fiber composite material not only has the characteristics of light weight, high specific strength, high specific modulus and the like, but also has the advantages of high temperature resistance, creep resistance, fatigue resistance and the like, so that the carbon fiber composite material is widely applied to the fields of life production, rail transit, renewable energy, aerospace, military and national defense and the like. However, when the composite material is formed, because the surface of the carbon fiber is of a graphite microcrystal structure and is chemically inert, a substrate with chemical activity is lacked, so that the wettability between the carbon fiber and the substrate is poor, and the carbon fiber and the substrate can not be connected through more effective chemical bonds, so that the excellent performance of the carbon fiber resin composite material can not be fully exerted, and the improvement of the performance of the composite material and the expansion of the application are limited to a certain extent.
In recent years, the research on the surface modification of carbon fibers has been more fully developed, and at present, there are ways of chemical grafting, plasma treatment, chemical oxidation, etc. which can improve the interface performance of carbon fiber composite materials to different degrees, but often have complex processes and relatively low efficiency or require special conditions, thus further limiting the application of the carbon fiber composite materials in continuous production.
Therefore, the modification of the existing carbon fiber is urgently needed.
Disclosure of Invention
The technical problem to be solved by the invention is to provide a surface modified carbon fiber and a modification method thereof, and the interface shear strength of the carbon fiber with imidazole ions grafted on the surface obtained by the method is greatly improved compared with that of the unmodified carbon fiber, so that the application of the carbon fiber in the field of composite materials is expanded.
In one aspect of the invention, a method of modifying carbon fibers is provided. According to an embodiment of the invention, the method comprises: (1) removing glue on the surface of the carbon fiber; (2) contacting the carbon fiber subjected to degumming obtained in the step (1) with an oxidant for oxidation reaction so as to obtain oxidized carbon fiber; (3) and performing electrochemical reaction by taking the oxidized carbon fiber as a cathode, graphite as an anode and a mixed solution containing imidazole ionic liquid, an organic solvent, a condensing agent and a conductive agent as an electrolyte so as to graft imidazole ions on the surface of the carbon fiber in a covalent manner.
Preferably, step (1) is carried out using the following steps: and heating the carbon fiber by a continuous heating furnace in an inert atmosphere, wherein the heating temperature is 300-600 ℃, and the time is 2-10 min.
Preferably, in step (2), the oxidizing agent includes at least one of concentrated nitric acid, concentrated sulfuric acid, and hydrogen peroxide.
Preferably, in the step (2), the temperature of the oxidation reaction is 65-85 ℃, and the reaction time is 3-6 h.
Preferably, in step (3), the anion of the imidazole-based ionic liquid comprises at least one of chloride ion, bromide ion, tetrafluoroborate ion and hexafluorophosphate ion.
Preferably, in the step (3), the organic solvent includes at least one of dimethylformamide, tetrahydrofuran, and carbon tetrachloride.
Preferably, in step (3), the condensing agent comprises at least one of HATU, DCC/DMAP.
Preferably, in the step (3), the conductive agent includes at least one of potassium chloride, sodium chloride, and potassium sulfate.
Preferably, in the step (3), the mass ratio of the oxidized carbon fibers to the imidazole-based ionic liquid is (0.3 g-0.5 g): (0.5 g-15 g).
Preferably, in the step (3), the volume ratio of the mass of the imidazole ionic liquid to the organic solvent is (0.5 g-15 g): (45 mL-80 mL).
Preferably, in the step (3), the mass ratio of the imidazole-based ionic liquid to the condensing agent is (0.5g to 15 g): (3 mg-10 mg).
Preferably, in the step (3), a ratio of the mass of the conductive agent to the volume of the organic solvent is (8mg to 15 mg): (45 mL-80 mL).
Preferably, in the step (3), the temperature of the electrochemical reaction is 20-30 ℃, and the reaction time is 1-3 h.
Preferably, in step (3), the current density of the electrochemical reaction is 5A m-2～30A*m-2。
In a second aspect of the invention, a surface modified carbon fiber is provided. According to the embodiment of the invention, the surface modified carbon fiber is prepared by the method.
Compared with the prior art, the method has the advantages that the oxidized carbon fiber is used as a cathode, the mixed solution containing the imidazole ionic liquid, the organic solvent, the condensing agent and the conductive agent is used as the electrolyte to carry out electrochemical reaction, imidazole ions are covalently grafted on the surface of the carbon fiber under the action of the condensing agent, and the carbon fiber with the imidazole ionic liquid grafted on the surface is prepared.
Drawings
FIG. 1 is a schematic flow diagram of a method of modifying carbon fibers according to one embodiment of the present invention;
FIG. 2 is a plot of the peak separation fit of C1s in XPS for imidazole-ion covalently grafted carbon fibers obtained in example 1;
FIG. 3 is a peak fitting graph of C1s in XPS of carbon fiber after degumming obtained from comparative example;
FIG. 4 is an SEM image of imidazole ion covalently grafted carbon fibers obtained in example 1;
fig. 5 is an SEM image of the carbon fiber after degumming obtained in the comparative example.
Detailed Description
The present invention will be further described with reference to the following examples and fig. 1 thereof, which are illustrative and not limiting, and the scope of the present invention is not limited thereby.
In one aspect of the invention, a method of modifying carbon fibers is provided. According to an embodiment of the invention, with reference to fig. 1, the method comprises:
s1: removing glue on the surface of the carbon fiber
In the step, the carbon fiber is heated by a continuous heating furnace in an inert atmosphere to remove the sizing agent on the surface of the carbon fiber, so that carbon on the surface of the carbon fiber is exposed and is favorable for subsequent covalent bonding with imidazole ions, wherein the heating temperature is 300-600 ℃, and the time is 2-10 min.
S2: the carbon fiber after the degumming obtained in the step S1 is contacted with an oxidant for oxidation reaction
In the step, the carbon fiber after the degumming obtained in the step S1 is contacted with an oxidant for oxidation reaction, so that oxygen-containing functional groups are formed on the surface of the carbon fiber, and the oxidized carbon fiber is obtained, namely, active functional groups such as carboxyl, hydroxyl, carbonyl and the like are introduced on the surface of the carbon fiber, thereby facilitating the subsequent grafting reaction. It should be noted that the type of the above-mentioned oxidizing agent is not particularly limited as long as the above-mentioned effects can be achieved, and for example, the oxidizing agent may include at least one of concentrated nitric acid, concentrated sulfuric acid, and hydrogen peroxide; the temperature of the oxidation reaction is 65-85 ℃, and the reaction time is 3-6 h.
S3: taking oxidized carbon fiber as a cathode, graphite as an anode and a mixed solution containing imidazole ionic liquid, organic solvent, condensing agent and conductive agent as electrolyte to carry out electrochemical reaction
In this step, the oxidized carbon fiber obtained in the step S2 is used as a cathode, graphite is used as an anode, a mixed solution containing an imidazole-based ionic liquid, an organic solvent, a condensing agent and a conductive agent is used as an electrolyte to perform an electrochemical reaction, in the process, carboxyl on the surface of the carbon fiber reacts with amino in the imidazole ionic liquid structure under the action of the condensing agent, so as to generate amido bonds to connect the two, then imidazole ions connected to the surface of the carbon fiber are subjected to free radical polymerization reaction (the imidazole ions are cracked into alkyl free radicals and imidazole ring free radicals at a cathode) to generate polyion liquid, so as to graft imidazole ions on the surface of the carbon fiber in a covalent way (the introduction of the imidazole ions can improve the surface wettability of the carbon fiber and can participate in the curing process of a resin matrix to obtain a good interface effect), and then the obtained carbon fiber is washed and dried.
Specifically, the electrochemical reaction mechanism is as follows: when the reaction starts, imidazole ions carry positive charges and can quickly cover the surface of the carbon fiber under the driving of an electric field; when the method is used, a part of imidazole ions can be adsorbed on the surface of the carbon fiber to accept electrons to form a free radical and a carbene structure, and some imidazole ions can be grafted to the surface of the carbon fiber through the reaction of self amino and carboxyl on the surface of the carbon fiber; and then the imidazole ions grafted to the surface of the carbon fiber form carbene under the action of electrons, and the carbene and free radicals generated at the non-grafted part of the fiber are subjected to polymerization reaction, so that the imidazole ions are covalently grafted on the surface of the carbon fiber.
Figure BDA0003058608400000041
Further, the anion of the imidazole ionic liquid includes at least one of chloride ion, bromide ion, tetrafluoroborate ion and hexafluorophosphate ion. Meanwhile, the organic solvent comprises at least one of dimethylformamide, tetrahydrofuran and carbon tetrachloride; the condensing agent comprises at least one of HATU, DCC and DMAP; the conductive agent comprises at least one of potassium chloride, sodium chloride and potassium sulfate.
Further, the mass ratio of the oxidized carbon fiber to the imidazole ionic liquid is (0.3 g-0.5 g): (0.5 g-15 g), and the volume ratio of the mass of the imidazole ionic liquid to the organic solvent is (0.5 g-15 g): (45 mL-80 mL); the mass ratio of the imidazole ionic liquid to the condensing agent is (0.5 g-15 g): (3 mg-10 mg); the ratio of the mass of the conductive agent to the volume of the organic solvent is (8 mg-15 mg): (45 mL-80 mL). The inventor finds that the imidazole ionic liquid with too high concentration can generate a cage effect on free radicals generated on the surface of the carbon fiber, influence the free radical polymerization reaction and reduce the content of the polymer on the surface; when the concentration of the condensing agent is too high or too low, the amide reaction of the amino group on the surface of the ionic liquid and the carboxyl group on the surface of the carbon fiber is influenced; in addition, in a certain range, the increase of the conductive agent is beneficial to the conduction of electrons, and when the conductive agent is excessive, the conductive agent exists at the bottom of the mixed liquid in the form of crystal grains and cannot be dissolved.
Furthermore, the temperature of the electrochemical reaction process is 20-30 ℃, and the reaction time is 1-3 h. The inventors have found that an excessively high temperature affects the activity of the condensing agent, and an excessively long reaction time causes the polymer chains to be broken, thereby reducing the amount of the graft.
Further, the current density of the electrochemical reaction is 5A m-2～30A*m-2. The inventors have found that if the current density is too high, it may cause local over-concentration of imidazole ionic liquid radicals, resulting in termination of coupling and reduction of surface grafts.
According to the method for modifying the carbon fiber, provided by the embodiment of the invention, the surface of the carbon fiber is subjected to oxidation after removing the glue, so that oxygen-containing functional groups are formed on the surface of the carbon fiber, then the oxidized carbon fiber is used as a cathode, a mixed solution containing imidazole ionic liquid, an organic solvent, a condensing agent and a conductive agent is used as an electrolyte to perform an electrochemical reaction, and imidazole ions are covalently grafted on the surface of the carbon fiber under the action of the condensing agent, so that the carbon fiber with the imidazole ionic liquid grafted on the surface is prepared, and the interfacial shear strength of the carbon fiber with the imidazole ions covalently grafted on the surface is greatly improved compared with that of the carbon fiber which is not grafted, so that the interfacial property of a carbon fiber composite material can be effectively improved.
In a second aspect of the invention, a surface modified carbon fiber is provided. According to the embodiment of the invention, the surface modified carbon fiber is prepared by the method. It should be noted that the features and advantages described above for the method of modifying carbon fibers are equally applicable to the surface modified carbon fibers and will not be described in further detail here.
The invention will now be described with reference to specific examples, which are intended to be illustrative only and not to be limiting in any way.
Example 1
The method for preparing the modified carbon fiber comprises the following steps:
(1) the carbon fiber is put into a continuous heating furnace with inert gas to react for 4min at the temperature of 400 ℃ to obtain the carbon fiber after degumming;
(2) the carbon fiber after the glue removal is reacted with concentrated nitric acid, the reaction temperature is 80 ℃, and the reaction time is 4 hours, so that oxidized carbon fiber is obtained;
(3) 0.3g of carbon oxide fiber is taken as a cathode, graphite is taken as an anode, and the carbon oxide fiber is placed in a mixed solution containing 4g of imidazole tetrafluoroborate ionic liquid, 70mL of dimethylformamide, 5mg of HATU and 10mg of KCl at the temperature of 25 ℃ and the current density of 25A m-2Electrifying for 2h under the condition, washing for multiple times by using dimethylformamide and deionized water, drying in a vacuum oven to obtain imidazole ion covalent grafting carbon fibers (a peak-splitting fitting graph of C1s in XPS is shown in figure 2, and an SEM graph is shown in figure 4), mixing E51 epoxy resin, a methyl tetrahydrophthalic anhydride curing agent and an aminoethylpiperazine accelerator according to a certain proportion to obtain a resin mixed solution, coating the resin mixed solution on the surface of the modified carbon fibers to prepare the composite material in a compounding manner, wherein the interfacial shear strength of the obtained composite material is 95.52 MPa.
Example 2
The method for preparing the modified carbon fiber comprises the following steps:
(1) enabling the carbon fiber to pass through a continuous heating furnace with inert gas, and reacting for 4min at the temperature of 400 ℃ to obtain the carbon fiber after degumming;
(2) the carbon fiber after the glue removal is reacted with concentrated nitric acid, the reaction temperature is 80 ℃, and the reaction time is 4 hours, so that oxidized carbon fiber is obtained;
(3) 0.3g of carbon oxide fiber is taken as a cathode, graphite is taken as an anode, and the carbon oxide fiber is placed in a mixed solution containing 5g of imidazole chloride ionic liquid, 73mL of dimethylformamide, 6mg of HATU and 8mg of KCl at the temperature of 25 ℃ and the current density of 25A × m-2Electrifying for 2h under the condition, washing for multiple times by using dimethylformamide and deionized water, drying in a vacuum oven to obtain imidazole ion covalent grafted carbon fibers, mixing E51 epoxy resin, a methyl tetrahydrophthalic anhydride curing agent and an aminoethyl piperazine accelerator according to a certain proportion to obtain a resin mixed solution, coating the resin mixed solution on the surface of the modified carbon fibers to prepare the composite material in a composite mode, and enabling the interface shear strength of the obtained composite material to be 93.88 MPa.
Example 3
The method for preparing the modified carbon fiber comprises the following steps:
(1) the carbon fiber is put into a continuous heating furnace with inert gas to react for 4min at the temperature of 400 ℃ to obtain the carbon fiber after degumming;
(2) The carbon fiber after the glue removal is reacted with concentrated nitric acid, the reaction temperature is 80 ℃, and the reaction time is 4 hours, so that oxidized carbon fiber is obtained;
(3) taking 0.3g of carbon oxide fiber as a cathode, taking graphite as an anode, and placing the carbon oxide fiber in a mixed solution containing 5g of imidazole hexafluorophosphate ionic liquid, 53mL of dimethylformamide, 5mg of HATU and 10mg of KCl at the temperature of 25 ℃ and the current density of 25A × m-2Electrifying to react for 2 hours under the condition, washing with dimethylformamide and deionized water for multiple times, drying in a vacuum oven to obtain imidazole ion covalent grafted carbon fibers, mixing E51 epoxy resin, a methyl tetrahydrophthalic anhydride curing agent and an aminoethyl piperazine accelerator according to a certain proportion to obtain a resin mixed solution, coating the resin mixed solution on the surface of the modified carbon fibers to prepare a composite material in a composite manner, wherein the interface shear strength of the obtained composite material is 94.21 MPa.
Example 4
The method for preparing the modified carbon fiber comprises the following steps:
(1) the carbon fiber is put through a continuous heating furnace with inert gas, and the reaction time is 6min under the condition that the temperature is 450 ℃, so that the carbon fiber after degumming is obtained;
(2) the carbon fiber after the glue removal is reacted with concentrated nitric acid, the reaction temperature is 80 ℃, and the reaction time is 4 hours, so that oxidized carbon fiber is obtained;
(3) Taking 0.3g of carbon oxide fiber as a cathode, taking graphite as an anode, and placing the carbon oxide fiber in a mixed solution containing 5g of imidazole bromide ionic liquid, 53mL of dimethylformamide, 5mg of DCC/DMAP and 10mg of KCl at the temperature of 25 ℃ and the current density of 5A x m-2Carrying out electrifying reaction for 2h under the condition, washing the carbon fiber with dimethylformamide and deionized water for multiple times, drying the carbon fiber in a vacuum oven to obtain imidazole ion covalent grafting carbon fiber, and promoting E51 epoxy resin, methyl tetrahydrophthalic anhydride curing agent and aminoethyl piperazineThe additives are mixed according to a certain proportion to obtain a resin mixed solution, the resin mixed solution is coated on the surface of the modified carbon fiber to prepare the composite material in a composite mode, and the interface shear strength of the obtained composite material is 92.91 MPa.
Example 5
The method for preparing the modified carbon fiber comprises the following steps:
(1) the carbon fiber is put into a continuous heating furnace with inert gas to react for 4min at the temperature of 400 ℃ to obtain the carbon fiber after degumming;
(2) the carbon fiber after the glue removal is reacted with concentrated nitric acid, the reaction temperature is 80 ℃, and the reaction time is 4 hours, so that oxidized carbon fiber is obtained;
(3) 0.3g of carbon oxide fiber is taken as a cathode, graphite is taken as an anode, and the carbon oxide fiber is placed in a mixed solution containing 5g of imidazole chloride ionic liquid, 68mL of dimethylformamide, 6mg of HATU and 9mg of KCl at the temperature of 25 ℃ and the current density of 10A m -2Electrifying for 2h under the condition, washing for multiple times by using dimethylformamide and deionized water, drying in a vacuum oven to obtain imidazole ion covalent grafted carbon fibers, mixing E51 epoxy resin, a methyl tetrahydrophthalic anhydride curing agent and an aminoethyl piperazine accelerator according to a certain proportion to obtain a resin mixed solution, coating the resin mixed solution on the surface of the modified carbon fibers to prepare the composite material in a composite mode, and enabling the interface shear strength of the obtained composite material to be 92.65 MPa.
Example 6
The method for preparing the modified carbon fiber comprises the following steps:
(1) allowing the carbon fiber to pass through a continuous heating furnace with inert gas, and reacting at 300 ℃ for 8min to obtain the carbon fiber after degumming;
(2) the carbon fiber after the glue removal is reacted with concentrated nitric acid, the reaction temperature is 80 ℃, and the reaction time is 4 hours, so that oxidized carbon fiber is obtained;
(3) 0.3g of oxidized carbon fiber was used as a cathode, graphite was used as an anode, and the resulting mixture was placed in a mixed solution containing 10.4g of an imidazole tetrafluoroborate ionic liquid, 65mL of dimethylformamide, 8mg of HATU, and 10mg of KCl at a temperature of 25 ℃ under a current of 10mgDensity of 25A m-2Electrifying for 3h under the condition, washing for many times by using dimethylformamide and deionized water, drying in a vacuum oven to obtain imidazole ion covalent grafting carbon fibers, mixing E51 epoxy resin, a methyl tetrahydrophthalic anhydride curing agent and an aminoethyl piperazine accelerator according to a certain proportion to obtain a resin mixed solution, coating the resin mixed solution on the surface of the modified carbon fibers to prepare the composite material in a composite mode, and enabling the interface shear strength of the obtained composite material to be 94.35 MPa.
Example 7
The method for preparing the modified carbon fiber comprises the following steps:
(1) the carbon fiber is put into a continuous heating furnace with inert gas to react for 10min at the temperature of 300 ℃ to obtain the carbon fiber after the glue is removed;
(2) the carbon fiber after the glue removal is reacted with concentrated nitric acid, the reaction temperature is 80 ℃, and the reaction time is 4 hours, so that oxidized carbon fiber is obtained;
(3) 0.4g of carbon oxide fiber was used as a cathode, graphite was used as an anode, and the carbon oxide fiber was placed in a mixed solution containing 3.5g of an imidazole tetrafluoroborate ionic liquid, 53mL of tetrahydrofuran, 3mg of HATU, and 8mg of NaCl at a temperature of 25 ℃ and a current density of 20A × m-2Electrifying for 1h under the condition, washing for multiple times by using dimethylformamide and deionized water, drying in a vacuum oven to obtain imidazole ion covalent grafting carbon fibers, mixing E51 epoxy resin, a methyl tetrahydrophthalic anhydride curing agent and an aminoethyl piperazine accelerator according to a certain proportion to obtain a resin mixed solution, coating the resin mixed solution on the surface of the modified carbon fibers to prepare the composite material in a composite mode, and enabling the interface shear strength of the obtained composite material to be 97.88 MPa.
Example 8
The method for preparing the modified carbon fiber comprises the following steps:
(1) The carbon fiber is put into a continuous heating furnace with inert gas to react for 4min at the temperature of 400 ℃ to obtain the carbon fiber after degumming;
(2) the carbon fiber after the glue removal is reacted with concentrated nitric acid, the reaction temperature is 80 ℃, and the reaction time is 4 hours, so that oxidized carbon fiber is obtained;
(3) 0.5g of carbon oxide fiber is taken as a cathode, graphite is taken as an anode, and the carbon oxide fiber is placed in a mixed solution containing 7g of imidazole tetrafluoroborate ionic liquid, 63mL of carbon tetrachloride, 5mg of HATU and 8mg of KCl at the temperature of 25 ℃ and the current density of 20A m-2Electrifying to react for 1.5h under the condition, washing with dimethylformamide and deionized water for multiple times, drying in a vacuum oven to obtain imidazole ion covalently grafted carbon fibers, mixing E51 epoxy resin, a methyl tetrahydrophthalic anhydride curing agent and an aminoethyl piperazine accelerator according to a certain proportion to obtain a resin mixed solution, coating the resin mixed solution on the surface of the modified carbon fibers to prepare the composite material in a composite mode, and the interface shear strength of the obtained composite material is 96.13 MPa.
Example 9
The method for preparing the modified carbon fiber comprises the following steps:
(1) the carbon fiber is put into a continuous heating furnace with inert gas to react for 4min at the temperature of 400 ℃ to obtain the carbon fiber after degumming;
(2) The carbon fiber after the glue removal is reacted with concentrated nitric acid, the reaction temperature is 80 ℃, and the reaction time is 4 hours, so that oxidized carbon fiber is obtained;
(3) 0.4g of oxidized carbon fiber is taken as a cathode, graphite is taken as an anode, and the carbon fiber is placed in a mixture containing 12g of imidazole tetrafluoroborate ionic liquid, 73mL of dimethylformamide, 7mg of HATU and 14mg of K2SO4At a temperature of 25 ℃ and a current density of 30A m-2Electrifying to react for 3 hours under the condition, washing with dimethylformamide and deionized water for multiple times, drying in a vacuum oven to obtain imidazole ion covalent grafted carbon fibers, mixing E51 epoxy resin, a methyl tetrahydrophthalic anhydride curing agent and an aminoethyl piperazine accelerator according to a certain proportion to obtain a resin mixed solution, coating the resin mixed solution on the surface of the modified carbon fibers to prepare a composite material in a composite manner, wherein the interface shear strength of the obtained composite material is 95.66 MPa.
Example 10
The method for preparing the modified carbon fiber comprises the following steps:
(1) enabling the carbon fiber to pass through a continuous heating furnace with inert gas, and reacting for 4min at the temperature of 400 ℃ to obtain the carbon fiber after degumming;
(2) the carbon fiber after the glue removal is reacted with concentrated sulfuric acid, the reaction temperature is 70 ℃, and the reaction time is 4 hours, so that oxidized carbon fiber is obtained;
(3) 0.3g of carbon oxide fiber is taken as a cathode, graphite is taken as an anode, and the carbon oxide fiber is placed in a mixed solution containing 3.5g of imidazole tetrafluoroborate ionic liquid, 75mL of dimethylformamide, 6mg of HATU and 13mg of KCl, the temperature is 30 ℃, and the current density is 20A × m-2Electrifying for 2h under the condition, washing for multiple times by using dimethylformamide and deionized water, drying in a vacuum oven to obtain imidazole ion covalent grafted carbon fibers, mixing E51 epoxy resin, a methyl tetrahydrophthalic anhydride curing agent and an aminoethyl piperazine accelerator according to a certain proportion to obtain a resin mixed solution, coating the resin mixed solution on the surface of the modified carbon fibers to prepare the composite material in a composite mode, and the interface shear strength of the obtained composite material is 97.26 MPa.
Example 11
The method for preparing the modified carbon fiber comprises the following steps:
(1) the carbon fiber is put into a continuous heating furnace with inert gas to react for 5min at the temperature of 500 ℃ to obtain the carbon fiber after degumming;
(2) the carbon fiber after the glue removal is reacted with hydrogen peroxide at the reaction temperature of 75 ℃ for 4 hours to obtain oxidized carbon fiber;
(3) 0.3g of carbon oxide fiber as a cathode and graphite as an anode were put in a mixed solution containing 3.5g of an imidazole tetrafluoroborate ionic liquid, 75mL of dimethylformamide, 10mg of HATU and 13mg of KCl at a temperature of 30 ℃ and a current density of 30A m -2Electrifying to react for 2 hours under the condition, washing with dimethylformamide and deionized water for multiple times, drying in a vacuum oven to obtain imidazole ion covalent grafted carbon fibers, and then adding E51 epoxy resin, methyl tetrahydrophthalic anhydride curing agent and aminoethylThe piperazine accelerant is mixed according to a certain proportion to obtain a resin mixed solution, the resin mixed solution is coated on the surface of the modified carbon fiber to prepare the composite material in a composite mode, and the interface shear strength of the obtained composite material is 93.54 MPa.
Example 12
The method for preparing the modified carbon fiber comprises the following steps:
(1) the carbon fiber is put into a continuous heating furnace with inert gas to react for 2min at the temperature of 600 ℃ to obtain the carbon fiber after degumming;
(2) the carbon fiber after the glue removal is reacted with concentrated nitric acid, the reaction temperature is 70 ℃, and the reaction time is 4 hours, so that oxidized carbon fiber is obtained;
(3) 0.3g of carbon oxide fiber is taken as a cathode, graphite is taken as an anode, and the carbon oxide fiber is placed in a mixed solution containing 15g of imidazole tetrafluoroborate ionic liquid, 80mL of dimethylformamide, 10mg of HATU and 15mg of KCl at the temperature of 30 ℃ and the current density of 30A m-2Electrifying for 3h under the condition, washing for many times by using dimethylformamide and deionized water, drying in a vacuum oven to obtain imidazole ion covalent grafted carbon fibers, mixing E51 epoxy resin, a methyl tetrahydrophthalic anhydride curing agent and an aminoethyl piperazine accelerator according to a certain proportion to obtain a resin mixed solution, coating the resin mixed solution on the surface of the modified carbon fibers to prepare the composite material in a composite mode, and enabling the interface shear strength of the obtained composite material to be 98.01 MPa.
Comparative example
The method for preparing the modified carbon fiber comprises the following steps:
(1) the carbon fiber is put through a continuous heating furnace with inert gas and reacts for 4min at the temperature of 400 ℃, and the carbon fiber after degumming is obtained (the peak fitting diagram of C1s in XPS is shown in figure 3, and the SEM diagram is shown in figure 5);
(2) and then mixing the E51 epoxy resin, the methyl tetrahydrophthalic anhydride curing agent and the aminoethyl piperazine accelerator according to a certain proportion to obtain a resin mixed solution, coating the resin mixed solution on the surface of the carbon fiber after the glue removal to prepare a composite material in a composite mode, and obtaining the carbon fiber composite material by using the carbon fiber after the glue removal, wherein the interface shear strength of the carbon fiber composite material is 42.27 MPa.
XPS analysis of the carbon fibers obtained by covalent grafting of imidazole ions according to examples 1 to 12 and the carbon fibers obtained by comparative example after degumming showed the relative content of the surface functional groups, and the analysis results are shown in Table 1.
TABLE 1
Figure BDA0003058608400000101
Figure BDA0003058608400000111
Comparing fig. 2 and 3, and combining table 1, it can be obtained that the relative C-N content of the imidazole ion covalently grafted carbon fiber obtained in example 1 is significantly increased, which indicates that the imidazole ion is successfully grafted on the surface of the carbon fiber, and a new-CONH-peak appears at 288.2eV, which indicates that the carbon fiber is connected with the imidazole ion through an amide bond; and the carbon fibers covalently grafted with imidazole ions obtained in examples 2 to 12 have a significantly increased C ═ N compared with the comparative examples, which indicates that the carbon fibers covalently grafted with imidazole ions obtained in examples 2 to 12 have a-CONH-peak and that the carbon fibers are linked with the imidazole ions through amide bonds.
Comparing fig. 4 and fig. 5, it can be seen that the non-grafted carbon fiber of the comparative example has a smooth surface and a large number of fine grooves, while the imidazole-based ion covalently grafted carbon fiber obtained in example 1 has a large number of grafts on the surface and a significantly increased surface roughness.
The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the technical principle of the present invention, and these modifications and decorations should not be regarded as the protection scope of the invention.

Claims (11)

1. A method of modifying carbon fibers, comprising:
(1) removing glue on the surface of the carbon fiber;
(2) contacting the carbon fiber subjected to degumming obtained in the step (1) with an oxidant for oxidation reaction so as to obtain oxidized carbon fiber;
(3) taking the oxidized carbon fiber as a cathode, graphite as an anode, and a mixed solution containing imidazole ionic liquid, an organic solvent, a condensing agent and a conductive agent as an electrolyte to carry out electrochemical reaction so as to covalently graft imidazole ions on the surface of the carbon fiber,
wherein, the step (1) is carried out by adopting the following steps: heating the carbon fiber by a continuous heating furnace in inert atmosphere at the temperature of 300-600 ℃ for 2-10 min,
In the step (3), the mass ratio of the oxidized carbon fibers to the imidazole ionic liquid is (0.3 g-0.5 g): (0.5 g-15 g); the volume ratio of the mass of the imidazole ionic liquid to the organic solvent is (0.5 g-15 g): (45 mL-80 mL); the mass ratio of the imidazole ionic liquid to the condensing agent is (0.5 g-15 g): (3 mg-10 mg).
2. The method of claim 1, wherein in step (2), the oxidizing agent comprises at least one of concentrated nitric acid, concentrated sulfuric acid, and hydrogen peroxide.
3. The method according to claim 1 or 2, wherein in the step (2), the temperature of the oxidation reaction is 65-85 ℃ and the reaction time is 3-6 h.
4. The method according to claim 1, wherein in step (3), the anion of the imidazole-based ionic liquid comprises at least one of chloride, bromide, tetrafluoroborate and hexafluorophosphate ions.
5. The method according to claim 1, wherein in step (3), the organic solvent comprises at least one of dimethylformamide, tetrahydrofuran, and carbon tetrachloride.
6. The method of claim 1, wherein in step (3), the condensing agent comprises at least one of HATU, DCC/DMAP.
7. The method according to claim 1, wherein in step (3), the conductive agent comprises at least one of potassium chloride, sodium sulfate, and potassium nitrate.
8. The method according to claim 1, wherein in step (3), the ratio of the mass of the conductive agent to the volume of the organic solvent is (8mg to 15 mg): (45 mL-80 mL).
9. The method according to claim 1, wherein in the step (3), the temperature of the electrochemical reaction is 20 ℃ to 30 ℃ and the reaction time is 1h to 3 h.
10. The method according to claim 1 or 9, wherein in step (3), the current density of the electrochemical reaction is 5A m-2～30A*m-2。
11. A surface-modified carbon fiber, characterized in that it is produced by the process according to any one of claims 1 to 10.
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US4844781A (en) * 1986-12-02 1989-07-04 Office National D'etudes Et De Recherches Aerospatiales Electrochemical method of surface treating carbon; carbon, in particular carbon fibers, treated by the method, and composite material including such fibers

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