A method for surface modification of fibers

Abstract

The present invention discloses a method for fiber surface modification, comprising the following steps: preparing an aqueous solution of catechol and an aqueous solution of metal ions; fiber pretreatment: placing the fiber cleaned with an organic solvent in a container, adding deionized water and submerging the fiber; fiber modification treatment: sequentially adding the aqueous solution of catechol-based organic compounds and the aqueous solution of metal ions into the container containing the fiber and deionized water, stirring evenly, adding a buffer solution to adjust the pH of the solution in the container to be greater than 3, continuing to submerge the fiber in the container for chelation for 1 to 5 minutes, and then taking out the fiber; fiber post-treatment: washing the catechol-based organic compounds and metal ions that did not participate in chelation on the fiber surface with deionized water, and then drying the fiber to obtain the modified fiber. According to the present invention, it can effectively improve the interfacial properties between the fiber and the matrix.

Description

Technical Field

[0001] The present invention relates to the field of surface modification, and particularly to a method for surface modification of fibers. Background Art

[0002] High-performance fibers have excellent mechanical properties, good thermal stability and corrosion resistance. Fiber reinforced composites made with them as reinforcing materials have advantages such as light weight and high strength. However, due to the inherent chemical inertness of the fiber surface, the interfacial bonding performance between it and the resin matrix is weak, which limits the application of fiber reinforced composites in fields such as aerospace.

[0003] In order to improve the interfacial properties between the fiber and the matrix, researchers have proposed to perform modification treatment on the fiber surface. Traditional methods are mainly divided into chemical modification and physical modification. Among them, chemical methods mainly include oxidation treatment, mixed acid treatment, etc. The mechanism is to introduce active groups such as carboxyl groups and hydroxyl groups on the fiber surface through chemical reactions, increase the surface polarity of the fiber, and then improve the interfacial properties between the fiber and the matrix. However, the treatment process causes great damage to the fiber itself, resulting in a significant decline in the mechanical properties of the fiber. In addition, a large amount of toxic and harmful waste liquid will be generated during the modification, bringing serious environmental problems. Physical modification mainly includes gas phase deposition method, dip coating method, etc. The purpose is to deposit nanomaterials such as carbon nanotubes and silica particles on the fiber surface, thereby increasing the surface roughness of the fiber and enhancing the mechanical interlocking effect between the fiber and the matrix to achieve the improvement of interfacial properties. However, due to the high cost and equipment requirements of physical modification methods, it is difficult to achieve industrial production. Summary of the Invention

[0004] In order to overcome the problems existing in the above fiber surface modification methods, the technical problem to be solved by the present invention is to provide a method for fiber surface modification, depositing a chelate produced by the chelation of catechol groups and metal ions on the fiber surface, and the formed three-dimensional microstructure can increase the surface roughness of the fiber and effectively improve the interfacial properties between the fiber and the matrix.

[0005] The method for fiber surface modification of the present invention to solve the above technical problems includes the following steps:

[0006] Prepare an aqueous solution of catechol and an aqueous solution of metal ions;

[0007] Fiber pretreatment: Place the fiber cleaned with an organic solvent in a container, add deionized water and submerge the fiber;

[0008] Fiber modification treatment: Sequentially add the aqueous solution of catechol organic compound and the aqueous solution of metal ions into the container containing the fiber and deionized water and stir evenly. After adding a buffer solution, adjust the pH of the solution in the container to be greater than 3, continue to submerge the fiber in the container for chelation for 1 - 5 minutes, and then take out the fiber;

[0009] Fiber post-treatment: Wash the catechol-based organic compounds and metal ions that did not participate in chelation on the fiber surface with deionized water, and then dry the fiber to obtain modified fiber.

[0010] In addition to one or more of the features disclosed above, or as an alternative, in the preparation of the catechol aqueous solution and the metal ion aqueous solution, the molar ratio of catechol to metal ion is 3:1 - 0.1:1.

[0011] In addition to one or more of the features disclosed above, or as an alternative, the fiber is at least one of carbon fiber, glass fiber, basalt fiber and aramid fiber.

[0012] In addition to one or more of the features disclosed above, or as an alternative, based on mass percentage, the raw materials for preparing the catechol aqueous solution include:

[0013] Deionized water 90 - 99wt%;

[0014] Catechol-based organic compound 1 - 10wt%.

[0015] In addition to one or more of the features disclosed above, or as an alternative, the catechol-based organic compound is: an organic compound having a catechol group.

[0016] In addition to one or more of the features disclosed above, or as an alternative, the catechol-based organic compound is at least one of tannic acid, gallic acid, dopamine and caffeic acid.

[0017] In addition to one or more of the features disclosed above, or as an alternative, the raw materials for preparing the metal ion aqueous solution include:

[0018] Deionized water 95 - 99.9wt%;

[0019] Metal ion hydrate 0.1 - 5wt%.

[0020] In addition to one or more of the features disclosed above, or as an alternative, the metal ion is: at least one of silver ion, iron ion, ferrous ion, copper ion, nickel ion.

[0021] In addition to one or more of the features disclosed above, or as an alternative, the chelate after chelation of the catechol group and the metal ion is: at least one of iron ion - tannic acid tridentate chelate, iron ion - tannic acid bidentate chelate, silver ion - tannic acid monodentate chelate and copper ion - gallic acid monodentate chelate.

[0022] In addition to one or more of the features disclosed above, or as an alternative, the organic solvent in the fiber pretreatment is at least one of acetone, methyl ethyl ketone, and N,N-dimethylformamide.

[0023] One of the technical solutions in the above technical solutions has the following advantages or beneficial effects: Since the method of depositing the chelate produced by the chelation of catechol groups and metal ions on the fiber surface is used to modify the fiber surface, this process is simple in operation, low in cost, short in time, does not damage the fiber, and greatly improves the interfacial bonding performance between the fiber and the matrix.

[0024] Another technical solution in the above technical solutions has the following advantages or beneficial effects: Since the formed chelate relies on the excellent adhesion of the catechol structure, it can modify the surface of any fiber.

[0025] Another technical solution in the above technical solutions has the following advantages or beneficial effects: Since the three-dimensional microstructure formed by the chelate on the fiber surface increases the fiber surface roughness, and improves the interfacial bonding strength between the fiber and the matrix by enhancing the mechanical interlocking effect between the fiber and the matrix, the modification method of the present invention can improve the interfacial performance between the fiber and any matrix. Description of the Drawings

[0026] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings of the embodiments will be briefly introduced below. Obviously, the drawings described below only relate to some embodiments of the present invention and do not limit the present invention, where:

[0027] Figure 1 It is a flowchart of fiber surface modification provided according to an embodiment of the present invention;

[0028] Figure 2 It is an X-ray photoelectron spectroscopy (XPS) diagram of carbon fiber in Embodiment 1 of the present invention, where: Figure 2 a is a wide-spectrum diagram, Figure 2 b and Figure 2 c are respectively the high-resolution spectra of Fe 2p and O1s of the carbon fiber before modification, Figure 2 d and Figure 2 e are respectively the high-resolution spectra of Fe 2p and O1s of the carbon fiber after modification;

[0029] Figure 3 It is a scanning electron microscope (SEM) diagram of the surface of carbon fiber in Embodiment 1 of the present invention, where a is the carbon fiber after being cleaned with acetone, and b is the carbon fiber with a chelate formed by the coordination of tannic acid and iron ions deposited on the surface;

[0030] Figure 4AFM images of the carbon fiber surface in Example 1, where a is the carbon fiber after acetone cleaning and b is the carbon fiber with a chelate formed by depositing tannic acid-iron ions on the surface. Detailed implementation mode

[0031] Aiming at the deficiencies of the prior art, the purpose of the present invention is to provide a method for fiber surface modification, depositing a chelate produced by the chelation of catechol groups and metal ions on the fiber surface, and the three-dimensional microstructure formed can increase the fiber surface roughness and effectively improve the interfacial performance between the fiber and the matrix.

[0032] To achieve the above technical effects, the present invention is realized through the following technical solutions:

[0033] A method for fiber surface modification, comprising the following steps:

[0034] Prepare an aqueous solution of catechol and an aqueous solution of metal ions;

[0035] Fiber pretreatment: Place the fiber cleaned with an organic solvent in a container, add deionized water and immerse the fiber;

[0036] Fiber modification treatment: Sequentially add the aqueous solution of catechol organic compound and the aqueous solution of metal ions into the container containing the fiber and deionized water, stir evenly, add a buffer solution to adjust the pH of the solution in the container to be greater than 3, continue to immerse the fiber in the container for chelation for 1-5 minutes, and then take out the fiber;

[0037] Fiber post-treatment: Wash the catechol organic compound and metal ions that did not participate in chelation on the fiber surface with deionized water, and then dry the fiber to obtain the modified fiber.

[0038] Preferably, in the preparation of the aqueous solution of catechol and the aqueous solution of metal ions, the molar ratio of catechol to metal ions is 3:1 - 0.1:1.

[0039] Preferably, the fiber is at least one of carbon fiber, glass fiber, basalt fiber and aramid fiber.

[0040] Preferably, calculated by mass percentage, the raw materials for preparing the aqueous solution of catechol include:

[0041] Deionized water 90 - 99wt%;

[0042] Catechol organic compound 1 - 10wt%.

[0043] Preferably, the catechol organic compound is an organic compound with a catechol group.

[0044] Preferably, the catechol-based organic compound is at least one of tannic acid, gallic acid, dopamine, and caffeic acid.

[0045] Preferably, based on mass percentage, the raw materials for preparing the metal ion aqueous solution include:

[0046] Deionized water 95 - 99.9 wt%;

[0047] Metal ion hydrate 0.1 - 5 wt%.

[0048] Preferably, the metal ion is at least one of silver ion, iron ion, ferrous ion, copper ion, and nickel ion.

[0049] Preferably, the chelate formed after chelation of the catechol group and the metal ion is at least one of iron ion - tannic acid tridentate chelate, iron ion - tannic acid bidentate chelate, silver ion - tannic acid monodentate chelate, and copper ion - gallic acid monodentate chelate.

[0050] Preferably, the organic solvent in the fiber pretreatment is at least one of acetone, butanone, and N, N - dimethylformamide.

[0051] The beneficial effects of the present invention are:

[0052] 1. A method of modifying the fiber surface by depositing a chelate produced by the chelation of a catechol group and a metal ion on the fiber surface. This process is simple to operate, low in cost, short in time, does not damage the fiber, and greatly improves the interfacial bonding performance between the fiber and the matrix.

[0053] 2. Since the formed chelate relies on the excellent adhesion of the catechol structure, it can modify the surface of any fiber.

[0054] 3. Since the three - dimensional microstructure formed by the chelate on the fiber surface increases the fiber surface roughness and improves the interfacial bonding strength between the fiber and the matrix by enhancing the mechanical interlocking effect between the fiber and the matrix, the modification method of the present invention can improve the interfacial performance between the fiber and any matrix.

[0055] The following combines specific embodiments to further elaborate the present invention. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of this application.

[0056] Example 1

[0057] This example provides a method for modifying the fiber surface, including the following steps:

[0058] Step S101: Prepare an aqueous catechol solution and an aqueous metal ion solution. In this embodiment, the aqueous catechol solution is an aqueous tannic acid solution, and the aqueous metal ion solution is an aqueous ferric chloride hexahydrate solution. Among them, the concentration of tannic acid is 5.87 mM / L, and the concentration of the ferric chloride hexahydrate solution is 23.48 mM / L.

[0059] Step S102: Fiber pretreatment: Place the fiber cleaned with an organic solvent in a container, add deionized water and submerge the fiber. In this embodiment, place the carbon fiber cleaned with acetone in a beaker, add a certain amount of deionized water to completely submerge the carbon fiber in the deionized water. It should be noted that the amount of deionized water can be adjusted according to the amount of carbon fiber and the capacity of the beaker, as long as the carbon fiber can be completely submerged in the deionized water; it can be understood that the order of steps S101 and S102 can be changed, that is, it can first execute step S101 and then step S102, or first execute step S102 and then step S101, or even steps S101 and S102 can be executed synchronously. The specific execution order can be set according to the actual situation and is not limited here.

[0060] Step S103: Fiber modification treatment: Sequentially add the aqueous catechol organic compound solution and the aqueous metal ion solution into the container containing the fiber and deionized water, stir evenly, add a buffer solution and adjust the pH of the solution in the container to be greater than 3, continue to submerge the fiber in the container for chelation for 1 - 5 minutes, and then take out the fiber; in this embodiment, pour the same amount of aqueous tannic acid solution and aqueous ferric chloride hexahydrate solution into the beaker at the same time, stir at a speed of 800 revolutions per minute for 1 minute, then add a 5wt% Tris solution to adjust the solution pH to 8, keep stirring for 3 minutes, and then take out the carbon fiber.

[0061] Step S104: Fiber post-treatment: Wash the catechol organic compounds and metal ions that did not participate in chelation on the fiber surface with deionized water, and then dry the fiber to obtain the modified fiber; specifically, in this embodiment, wash the carbon fiber surface with deionized water 2 - 3 times to remove the residual tannic acid monomers and iron ions on the carbon fiber surface, and then put the washed carbon fiber into an oven to evaporate the moisture on the carbon fiber surface. The oven temperature can be set to 60°C, take it out after drying for 30 minutes, and the carbon fiber with chelates (tannic acid - iron ions) deposited on the surface can be obtained.

[0062] Furthermore, the method for modifying the fiber surface further includes:

[0063] Step S105, preparing a carbon fiber / epoxy microdroplet specimen: Take 20 parts by mass of epoxy resin, add 1 part by mass of curing agent, and stir evenly in a container. Subsequently, paste the two ends of the modified carbon fiber monofilament on two gaskets of the same height, dip a small amount of epoxy resin and drop it on the surface of the modified carbon fiber filament to form an epoxy resin microsphere, and place it in an oven to cure the epoxy resin. The oven temperature can be 60 °C and the curing time is 1 hour.

[0064] In this embodiment, in the preparation of the catechol aqueous solution and the metal ion aqueous solution, the molar ratio of catechol to metal ions is 1:4.

[0065] In this embodiment, by mass percentage, the raw materials for preparing the catechol aqueous solution include:

[0066] Deionized water 99 wt%;

[0067] Catechol organic compound 1 wt%.

[0068] In this embodiment, by mass percentage, the raw materials for preparing the metal ion aqueous solution include:

[0069] Deionized water 99.37 wt%;

[0070] Metal ion hydrate 0.63 wt%.

[0071] Preferably, the chelate after chelation of the catechol group and the metal ion is: iron ion-tannic acid tridentate chelate or iron ion-tannic acid bidentate chelate.

[0072] Example 2

[0073] This embodiment provides a method for fiber surface modification, including the following steps:

[0074] Step S201, preparing a catechol aqueous solution and a metal ion aqueous solution. In this embodiment, the catechol aqueous solution is a gallic acid aqueous solution, and the metal ion aqueous solution is a copper dichloride dihydrate aqueous solution. Among them, the concentration of gallic acid is 2.94 mM / L, and the concentration of the copper dichloride dihydrate solution is 2.94 mM / L.

[0075] Step S202, Fiber Pretreatment: Place the fibers cleaned with an organic solvent in a container, add deionized water to submerge the fibers. In this embodiment, place the glass fibers cleaned with methyl ethyl ketone in a beaker, add a certain amount of deionized water to completely submerge the glass fibers in the deionized water. It should be noted that the amount of deionized water can be adjusted according to the amount of glass fibers and the capacity of the beaker, as long as the glass fibers can be completely submerged in the deionized water; it can be understood that the order of Step S201 and Step S202 can be changed, that is, it can first execute Step S201 and then execute Step S202, or first execute Step S202 and then execute Step S201, or even Step S201 and Step S202 can be executed synchronously. The specific execution order can be set according to the actual situation and will not be limited here.

[0076] Step S203, Fiber Modification Treatment: Sequentially add an aqueous solution of a catechol-based organic compound and an aqueous solution of metal ions into a container containing fibers and deionized water and stir evenly. After adding a buffer solution, adjust the pH of the solution in the container to be greater than 3, continue to submerge the fibers in the container for chelation for 1 - 5 minutes, and then take out the fibers; in this embodiment, pour an equal amount of an aqueous solution of gallic acid and an aqueous solution of copper chloride dihydrate into the beaker at the same time, stir at a speed of 1000 revolutions per minute for 1 minute, then add a 5wt% NaOH solution to adjust the solution pH to 8, keep stirring for 3 minutes, and then take out the glass fibers.

[0077] Step S204, Fiber Post-treatment: Wash the catechol-based organic compounds and metal ions that did not participate in chelation on the fiber surface with deionized water, and then dry the fibers to obtain modified fibers; specifically, in this embodiment, wash the surface of the glass fibers with deionized water 2 - 3 times to remove the residual gallic acid monomers and copper ions on the surface of the glass fibers, and then put the washed glass fibers into an oven to evaporate the moisture on the surface of the glass fibers. The oven temperature can be set to 60°C, and after drying for 30 minutes, take them out to obtain glass fibers with chelates (gallic acid - copper ions) deposited on the surface.

[0078] Furthermore, the method for modifying the fiber surface further includes:

[0079] Step S205, Preparation of Glass Fiber / Epoxy Resin Microdrop Specimen: Take 20 parts by mass of epoxy resin, add 1 part by mass of a curing agent, and stir evenly in a container. Then paste the two ends of the modified glass fiber monofilament on two gaskets of the same height, dip a small amount of epoxy resin and drop it on the surface of the modified glass fiber filament to form an epoxy resin microsphere, and put it into an oven to cure the epoxy resin. The oven temperature can be 60°C, and the curing time is 1 hour.

[0080] In this embodiment, in the preparation of the catechol aqueous solution and the metal ion aqueous solution, the molar ratio of catechol to metal ions is 1:1.

[0081] In this embodiment, based on mass percentage, the raw materials for preparing the catechol aqueous solution include:

[0082] Deionized water 92 wt%;

[0083] Catechol organic compound 8 wt%.

[0084] In this embodiment, based on mass percentage, the raw materials for preparing the metal ion aqueous solution include:

[0085] Deionized water 98.5 wt%;

[0086] Metal ion hydrate 1.5 wt%.

[0087] Preferably, the chelate after chelation of the catechol group and the metal ion is: copper ion-gallic acid monodentate chelate.

[0088] Example 3

[0089] This embodiment provides a method for fiber surface modification, including the following steps:

[0090] Step S301, prepare a catechol aqueous solution and a metal ion aqueous solution. In this embodiment, the catechol aqueous solution is a caffeic acid aqueous solution, and the metal ion aqueous solution is a nickel chloride hexahydrate aqueous solution. Among them, the concentration of tannic acid is 1.28 mM / L, and the concentration of ferric chloride hexahydrate solution is 2.56 mM / L.

[0091] Step S302, fiber pretreatment: Place the fiber cleaned with an organic solvent in a container, add deionized water and submerge the fiber. In this embodiment, place the basalt fiber cleaned with N,N-dimethylformamide in a beaker, add a certain amount of deionized water to completely submerge the basalt fiber in the deionized water. It should be noted that the amount of deionized water can be adjusted according to the amount of basalt fiber and the capacity of the beaker, as long as the basalt fiber can be completely submerged in the deionized water; it can be understood that the order of step S301 and step S302 can be changed, that is, it can first execute step S301 and then step S302, or first execute step S302 and then step S301, or even step S301 and step S302 can be executed synchronously. The specific execution order can be set according to the actual situation and is not limited here.

[0092] Step S303. Fiber modification treatment: Sequentially add an aqueous solution of a catechol-based organic compound and an aqueous solution of metal ions into a container containing fibers and deionized water, and stir evenly. After adding a buffer solution, adjust the pH of the solution in the container to be greater than 3. Immerse the fibers in the container for chelation for 1 - 5 minutes and then take out the fibers. In this embodiment, pour an equal amount of aqueous caffeic acid solution and aqueous nickel chloride hexahydrate solution into a beaker simultaneously, stir for 1 minute at a speed of 900 revolutions per minute, then add 10 wt% Tris solution to adjust the pH of the solution to 8, and keep stirring for 3 minutes and then take out the basalt fibers.

[0093] Step S304. Fiber post-treatment: Wash the catechol-based organic compounds and metal ions that did not participate in chelation on the fiber surface with deionized water, and then dry the fibers to obtain modified fibers. Specifically, in this embodiment, wash the surface of the basalt fibers with deionized water 2 - 3 times to remove the residual caffeic acid monomer and nickel ions on the surface of the basalt fibers. Then put the washed basalt fibers into an oven to evaporate the water on the surface of the basalt fibers. The oven temperature can be set at 60°C. After drying for 30 minutes, take them out to obtain basalt fibers with chelates (caffeic acid - nickel ions) deposited on the surface.

[0094] Furthermore, the method for fiber surface modification further includes:

[0095] Step S305. Preparation of basalt fiber / epoxy resin microdroplet specimens: Take 20 parts by mass of epoxy resin, add 1 part by mass of curing agent and stir evenly in a container. Then paste the two ends of the modified basalt fiber monofilament on two gaskets of the same height, dip a small amount of epoxy resin and drop it on the surface of the modified basalt fiber filament to form epoxy resin microspheres, and put them into an oven to cure the epoxy resin. The oven temperature can be 60°C and the curing time is 1 hour.

[0096] In this embodiment, in the preparation of the aqueous catechol solution and the aqueous metal ion solution, the molar ratio of catechol to metal ions is 1:2.

[0097] In this embodiment, calculated by mass percentage, the raw materials for preparing the aqueous catechol solution include:

[0098] Deionized water 95 wt%;

[0099] Catechol-based organic compounds 5 wt%.

[0100] In this embodiment, calculated by mass percentage, the raw materials for preparing the aqueous metal ion solution include:

[0101] Deionized water 99 wt%;

[0102] Metal ion hydrate 1 wt%.

[0103] Preferably, the chelate formed by the chelation of the catechol group and the metal ion is: nickel ion-caffeic acid bidentate chelate or nickel ion-caffeic acid monodentate chelate.

[0104] Example 4

[0105] This example provides a method for fiber surface modification, including the following steps:

[0106] Step S401: Prepare an aqueous solution of catechol and an aqueous solution of metal ions. In this example, the aqueous solution of catechol is an aqueous solution of catechin, and the aqueous solution of metal ions is an aqueous solution of ferrous chloride tetrahydrate. Among them, the concentration of tannic acid is 0.5 mM / L, and the concentration of ferric chloride hexahydrate solution is 1.5 mM / L.

[0107] Step S402: Fiber pretreatment: Place the fiber cleaned with an organic solvent in a container, add deionized water and submerge the fiber. In this example, place the aramid fiber cleaned with acetone in a beaker, add a certain amount of deionized water to completely submerge the aramid fiber in the deionized water. It should be noted that the amount of deionized water can be adjusted according to the amount of aramid fiber and the capacity of the beaker, as long as the aramid fiber can be completely submerged in the deionized water; it can be understood that the order of steps S401 and S402 can be changed, that is, it can first execute step S401 and then step S402, or it can first execute step S402 and then step S401, or even steps S401 and S402 can be executed synchronously. The specific execution order can be set according to the actual situation and will not be limited here.

[0108] Step S403: Fiber modification treatment: Add the aqueous solution of catechol-based organic compound and the aqueous solution of metal ions to the container containing the fiber and deionized water in sequence and stir evenly. After adding the buffer solution, adjust the pH of the solution in the container to be greater than 3, continue to submerge the fiber in the container for chelation for 1-5 minutes, and then take out the fiber; in this example, pour an equal amount of aqueous solution of catechol and aqueous solution of ferrous chloride tetrahydrate into the beaker at the same time, stir at a speed of 800 revolutions per minute for 1 minute, then add 10 wt% NaOH solution to adjust the solution pH to 8, and take out the aramid fiber after maintaining the stirring state for 3 minutes.

[0109] Step S404. Fiber post-treatment: Wash the catechol-based organic compounds and metal ions that did not participate in chelation on the fiber surface with deionized water, and then dry the fiber to obtain modified fibers. Specifically, in this embodiment, wash the surface of the aramid fiber with deionized water 2-3 times to remove the residual catechol monomer and ferrous ions on the surface of the aramid fiber. Then put the washed aramid fiber into an oven to evaporate the moisture on the surface of the aramid fiber. The oven temperature can be set at 60 °C. Take it out after drying for 30 minutes, and the aramid fiber with chelates (catechol-ferrous ions) deposited on the surface can be obtained.

[0110] Furthermore, the method for modifying the fiber surface further includes:

[0111] Step S405. Prepare an aramid fiber / epoxy resin microdroplet specimen: Take 20 parts by mass of epoxy resin and add 1 part by mass of curing agent, and stir evenly in a container. Then paste the two ends of the modified aramid fiber monofilament on two gaskets of the same height, dip a small amount of epoxy resin and drop it on the surface of the modified aramid fiber filament to form an epoxy resin microsphere, and put it into an oven to cure the epoxy resin. The oven temperature can be 60 °C, and the curing time is 1 hour.

[0112] In this embodiment, in the preparation of the catechol aqueous solution and the metal ion aqueous solution, the molar ratio of catechol to metal ion is 1:3.

[0113] In this embodiment, by mass percentage, the raw materials for preparing the catechol aqueous solution include:

[0114] Deionized water 90 wt%;

[0115] Catechol-based organic compound 10 wt%.

[0116] In this embodiment, by mass percentage, the raw materials for preparing the metal ion aqueous solution include:

[0117] Deionized water 99.5 wt%;

[0118] Metal ion hydrate 0.5 wt%.

[0119] Preferably, the chelate after chelation of the catechol group and the metal ion is: ferrous ion-catechol monodentate chelate.

[0120] Comparative example

[0121] Directly prepare a microdroplet specimen with the carbon fiber filament washed with acetone and epoxy resin. The process is the same as step S104 in Example 1.

[0122] Fiber interface shear strength test description: The interface shear strength test between carbon fiber and epoxy resin was conducted on a universal material testing machine produced by Shenzhen WanCheng Testing Equipment Co., Ltd. The test speed was 0.5 mm / min, and the maximum load when the fiber was pulled out of the epoxy resin droplet was recorded. No less than 10 samples were tested, and the average of at least 10 valid data points was recorded. The interface shear strength between the fiber and epoxy resin was then calculated according to formula (1).

[0123]

[0124] Among them, F p is the maximum pull-out load, d is the fiber diameter, and l is the bonding length between the resin and the fiber.

[0125] Fiber tensile strength test description: Carbon fiber tensile strength tests were conducted on a universal material testing machine manufactured by Shenzhen WanCheng Testing Equipment Co., Ltd. The test speed was 1 mm / min, and the maximum load during the test was recorded. No fewer than 10 samples were tested, and the average of at least 10 valid data points was recorded. The tensile strength of the fiber was then calculated according to formula (2).

[0126]

[0127] Among them, F T is the maximum load recorded and d is the fiber diameter.

[0128] Experimental results

[0129] Figure 2 The XPS spectra of carbon fiber surface before and after modification. Figure 2 a It can be seen that the oxygen content of the modified carbon fiber surface increased from 20.41% to 29.48%, indicating that tannic acid has successfully adhered to the carbon fiber surface. Figure 2 In d, we can see that Fe 2p splits into Fe 2p1 / 2 peak and Fe 2p3 / 2 peak and the interval between the two peaks is 14eV, indicating the presence of iron ions on the carbon fiber surface. Figure 2 In e, it can be seen that the O1s spectrum can be fitted and separated into two peaks, corresponding to Fe-OH and Fe-O respectively. Fe-O indicates that a coordination bond has been formed between the iron ion and tannic acid, proving that the two have been successfully chelated on the carbon fiber surface.

[0130] from Figure 3As can be seen in a, obvious grooves appear on the surface of the carbon fiber after being cleaned with acetone, indicating that the sizing agent on the carbon fiber surface has been cleaned. This groove structure is conducive to forming mechanical interlocking between the fiber and the resin, enhancing the interfacial strength between the fiber and the resin. However, due to the inherent inertness of the carbon fiber surface, the bonding performance between it and the resin is poor. After modification, a chelate formed by the coordination of tannic acid and iron ions is deposited on the carbon fiber surface, such as Figure 3 b. The chelate forms a uniform and dense granular three-dimensional microstructure network on the fiber surface and completely covers the grooves on the carbon fiber surface. Due to the large number of hydroxyl groups contained in the tannic acid molecule, the chelate has good hydrophilicity, further promoting the penetration of the resin into the chelate network and finally forming a more reliable mechanical interlock.

[0131] Figure 4 The AFM three-dimensional topography shown further reflects the surface structure of the carbon fiber before and after modification. Before modification, obvious axial groove topography exists on the carbon fiber surface, consistent with SEM Figure 1 results. After modification, the grooves on the carbon fiber surface are completely covered by the chelate formed by the coordination of tannic acid and iron ions and form a rougher three-dimensional granular structure. The average surface roughness Ra increases from 50.2 nm before modification to 91.6 nm after modification. The increase in Ra further promotes the penetration of the resin into the chelate network, ultimately significantly enhancing the mechanical interlocking effect between the fiber and the resin.

[0132] Table 1: Comparison of Interfacial Shear Strength and Tensile Strength of Examples and Comparative Examples of the Present Invention

[0133]

[0134] As shown in Table 1, compared with the comparative examples, the interfacial shear strengths of Examples 1-4 with epoxy resin are increased by 69.57%, 81.15%, 77.33% and 78.28% respectively. In addition, the fiber tensile strengths of the comparative example and Examples 1-4 are 3.77 MPa, 3.75 MPa, 3.81 MPa, 3.84 MPa and 3.71 MPa respectively. It shows that this modification method can effectively improve the interfacial adhesion strength between the fiber and epoxy resin, while the process is simple, the cost is low, and the fiber is not damaged during the modification process.

Claims

1. A method for modifying the surface of a fiber, characterized in that: The following steps are involved: preparing a catechol aqueous solution and a metal ion aqueous solution; Fiber pretreatment: Place the fiber cleaned with an organic solvent in a container and add deionized water to immerse the fiber; Fiber modification treatment: Add catechol organic compound aqueous solution and metal ion aqueous solution to a container containing fiber and deionized water in sequence and stir evenly. After adding buffer solution, adjust the pH of the solution in the container to greater than 3. Continue to immerse the fiber in the container for chelation for 1 to 5 minutes and then remove the fiber. Fiber post-treatment: using deionized water to clean the catechol organic compounds and metal ions that are not involved in the chelation on the fiber surface, and then drying the fiber to obtain modified fiber; Wherein, the raw materials for preparing the metal ion aqueous solution include, by mass percentage: Deionized water 95~99.9wt%; Metal ion hydrate 0.1~5wt%; Wherein, the metal ion is at least one of silver ion, iron ion, ferrous ion, copper ion and nickel ion.

2. The method according to claim 1, wherein In the preparation of the catechol aqueous solution and the metal ion aqueous solution, the molar ratio of catechol to metal ions is 3:1-0.1:

1.

3. The method according to claim 1, wherein The fiber is at least one of carbon fiber, glass fiber, basalt fiber and aramid fiber.

4. The method according to claim 1, wherein The raw materials for preparing the catechol aqueous solution include, by mass percentage: Deionized water 90~99wt%; Catechol organic compounds 1~10wt%.

5. The method according to claim 4, wherein The catechol organic compound is an organic compound having a catechol group.

6. The method according to claim 4 or 5, characterized in that The catechol organic compound is at least one of tannic acid, gallic acid, dopamine and caffeic acid.

7. The method according to claim 1, wherein The chelate formed by the chelation of the catechol group and the metal ion is at least one of: an iron ion-tannic acid tridentate chelate, an iron ion-tannic acid bidentate chelate, a silver ion-tannic acid monodentate chelate and a copper ion-gallic acid monodentate chelate.

8. The method according to claim 1, wherein The organic solvent in the fiber pretreatment is at least one of acetone, butanone and N,N-dimethylformamide.

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