Modified epoxy resin sizing agent containing amide structure as well as preparation method and application of modified epoxy resin sizing agent

Abstract

The invention relates to the technical field of sizing agents for fibers, in particular to a modified epoxy resin sizing agent containing an amide structure and a preparation method and application of the modified epoxy resin sizing agent. The sizing agent comprises modified epoxy resin and water, the modified epoxy resin is a polymer obtained by introducing an anhydride functional group into a bisphenol A type epoxy resin chain segment and grafting an amide group through an amidation reaction, and on the basis of the total weight of the sizing agent, the content of the modified epoxy resin is 0.1-50 wt%, and the content of the water is 0.1-50 wt%. And the content of water is 50-99.9 wt%. According to the modified epoxy resin sizing agent containing the amide structure, the heat resistance is further improved on the basis of good stability, good carbon fiber surface film-forming property and the like; the characteristic can meet the processing and forming process requirements of the carbon fiber and the high-temperature-resistant epoxy resin.

Description

Technical Field

[0001] The invention relates to the technical field of sizing agents for fibers, and in particular to a modified epoxy resin sizing agent containing an amide structure, and a preparation method and application thereof. Background Art

[0002] In the process of carbon fiber manufacturing, sizing has become one of the key links. The sizing layer helps to avoid damage to the brittle material of carbon fiber, such as hair and broken fibers, improves the inherent shortcomings of the carbon fiber surface, such as non-polarity and few active groups, enhances the interface performance between carbon fiber and matrix resin, and improves the overall mechanical properties of the composite material.

[0003] Epoxy resin has a unique position among thermosetting resins due to its superior performance and low price, and is widely used in composite materials with carbon fiber as reinforcement. Theory and practice have proved that the more the main components of the sizing agent and the matrix resin match, the better the overall performance of the carbon fiber composite material. The research on epoxy sizing agents with epoxy resin as the main component has been very mature, especially as people pay more and more attention to environmental protection, water has replaced organic solvents as the dispersion medium of epoxy sizing agents and has been more widely used.

[0004] Recently, emulsion-type sizing agents are mostly used for sizing carbon fibers. However, there are problems such as poor heat resistance, cumbersome preparation process, inability to regulate the functional groups contained in the sizing agent, low interface strength between carbon fibers and resin matrix, and poor overall mechanical properties of carbon fiber composites. For example, an epoxy sizing agent prepared in patent CN201910124499.X has good stability and an emulsion particle size of less than 200nm, but the interface performance with the resin matrix needs to be improved, and the interlaminar shear performance is around 70MPa. This also limits the application of this sizing agent in the field of high-performance composite materials.

[0005] Therefore, it is of great significance to research and develop an epoxy sizing agent for carbon fiber with good heat resistance and excellent interface bonding ability of carbon fiber composite materials. Summary of the invention

[0006] The purpose of the present invention is to overcome the problems of poor heat resistance and poor interface bonding performance of the existing epoxy sizing agent in the prior art, and to provide a modified epoxy resin sizing agent containing an amide structure and a preparation method and application thereof. The sizing agent has excellent heat resistance and effectively improves the interface bonding performance of the composite material.

[0007] In order to achieve the above-mentioned object, the first aspect of the present invention provides a modified epoxy resin sizing agent containing an amide structure, wherein the sizing agent comprises a modified epoxy resin and water, wherein the modified epoxy resin is a polymer obtained by introducing anhydride functional groups into bisphenol A epoxy resin segments and then grafting amide groups through an amidation reaction, and based on the total weight of the sizing agent, the content of the modified epoxy resin is 0.1-50% by weight, and the content of water is 50-99.9% by weight.

[0008] A second aspect of the present invention provides a method for preparing a modified epoxy resin sizing agent containing an amide structure, the method comprising:

[0009] (1) in the presence of an initiator, bringing the bisphenol A epoxy resin represented by formula (1′) into first contact with a modified monomer;

[0010]

[0011] Wherein, R3 is methyl, ethyl or hydrogen, and n is 3-6;

[0012] The modified monomer is selected from pyromellitic anhydride and / or 3,3',4,4'-benzophenone tetracarboxylic dianhydride;

[0013] (2) In the presence of a solvent, the product obtained in step (1) is contacted with 4,4'-diaminodiphenyl ether for a second time.

[0014] The third aspect of the present invention provides a modified epoxy resin sizing agent containing an amide structure prepared by the aforementioned preparation method.

[0015] A fourth aspect of the present invention provides a use of the aforementioned modified epoxy resin sizing agent containing an amide structure in surface modification of fibers.

[0016] Through the above technical scheme, the modified epoxy resin sizing agent containing an amide structure of the present invention, the amide structure in the modified epoxy resin has excellent heat resistance, the amide component in the sizing agent can form abundant hydrogen bonds and chemical bonds with the surface of the carbon fiber, and the amide component in the sizing film formed by drying on the surface of the carbon fiber has excellent heat resistance similar to that of polyimide. In addition, the modified epoxy resin of the present invention retains the main chain structure of the epoxy resin as much as possible, can achieve "similar compatibility" with the epoxy resin matrix to the greatest extent possible, establish a strong interactive connection, and effectively improve the interface bonding of the composite material.

[0017] Compared with the prior art, the modified epoxy resin sizing agent containing an amide structure described in the present invention has further improved heat resistance on the basis of good stability and good film-forming property on the carbon fiber surface. This feature will meet the processing and molding requirements of carbon fiber and high-temperature resistant epoxy resin, and expand the application field of carbon fiber / epoxy resin composite materials. DETAILED DESCRIPTION

[0018] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0019] The first aspect of the present invention provides a modified epoxy resin sizing agent containing an amide structure, the sizing agent comprising a modified epoxy resin and water, wherein the modified epoxy resin is a polymer obtained by introducing anhydride functional groups into bisphenol A epoxy resin segments and then grafting amide groups through an amidation reaction, and based on the total weight of the sizing agent, the content of the modified epoxy resin is 0.1-50% by weight, and the content of water is 50-99.9% by weight.

[0020] The modified epoxy resin sizing agent containing an amide structure of the present invention has excellent heat resistance in the amide structure of the modified epoxy resin, and the amide component in the sizing agent can form abundant hydrogen bonds and chemical bonds with the surface of the carbon fiber, and the amide component in the sizing film formed by drying on the surface of the carbon fiber has excellent heat resistance similar to that of polyimide. In addition, the modified epoxy resin of the present invention retains the main chain structure of the epoxy resin as much as possible, can achieve "similar compatibility" with the epoxy resin matrix to the greatest extent possible, establish a strong interactive connection, and effectively improve the interface bonding of the composite material.

[0021] According to a preferred embodiment of the present invention, the modified epoxy resin is selected from at least one of the polymers having a structure as shown in formula (1);

[0022]

[0023] Wherein, in formula (1), R1 is selected from -CH(COOH)CH(COOH)CH3 or -CH(COOH)CH2COOH;

[0024] n is 3-6;

[0025] R is shown in formula (2):

[0026]

[0027] In formula (2), R2 is selected from one of the structures shown in formula (3), formula (4), formula (5), formula (6), formula (7), and formula (8);

[0028]

[0029]

[0030] * represents the connection site between R2 and the carbonyl carbon in formula (1), and # represents the connection site between R2 and the carbonyl carbon in formula (2).

[0031] According to a preferred embodiment of the present invention, in formula (1), n ​​is 3-6.

[0032] According to a preferred embodiment of the present invention, in formula (1), R1 is -CH(COOH)CH2COOH.

[0033] According to a preferred embodiment of the present invention, in formula (2), R2 is selected from one of the structures shown in formula (2) and formula (6).

[0034] A second aspect of the present invention provides a method for preparing a modified epoxy resin sizing agent containing an amide structure, the method comprising:

[0035] (1) in the presence of an initiator, bringing the bisphenol A epoxy resin represented by formula (1′) into first contact with a modified monomer;

[0036]

[0037] Wherein, R3 is methyl, ethyl or hydrogen, and n is 3-6;

[0038] The modified monomer is selected from at least one of pyromellitic anhydride and / or 3,3',4,4'-benzophenone tetracarboxylic dianhydride;

[0039] (2) In the presence of a solvent, the product obtained in step (1) is contacted with 4,4'-diaminodiphenyl ether for a second time.

[0040] In the preparation method of the modified epoxy resin sizing agent containing amide structure of the present invention, the epoxy resin segment is introduced into the anhydride functional group by free radical polymerization under the action of initiator, and further, the anhydride functional group and the amino group react to form an amide bond structure in the emulsion by polycondensation reaction. This amide structure can improve the heat resistance of epoxy resin. The epoxy resin segment is modified by modified monomers of different molecular structures, and the introduced functional group structure and content are flexibly adjusted to expand the application range of the prepared sizing agent, and enhance the effect of the sizing agent on the surface treatment of carbon fiber.

[0041] In the present invention, the bisphenol A epoxy resin represented by formula (1') can be softened by heating before first contacting with the modified monomer, preferably, the resin is softened by heating at 80-90°C.

[0042] According to a preferred embodiment of the present invention, the bisphenol A epoxy resin and the modified monomer shown in formula (1') are both raw materials for removing water, for example, the water-containing components therein are removed by benzoyl peroxide.

[0043] According to a preferred embodiment of the present invention, the initiator is an organic peroxide, preferably benzoyl peroxide.

[0044] According to a preferred embodiment of the present invention, the first contact conditions include: a temperature of 100-110° C. and a contact time of 8-10 h.

[0045] According to a preferred embodiment of the present invention, the second contact condition includes: temperature of 2-30°C and contact time of 5-7h.

[0046] According to a preferred embodiment of the present invention, the solvent is selected from one or more of N,N'-dimethylformamide, N,N'-dimethylacetamide and dioxane.

[0047] According to a preferred embodiment of the present invention, in step (1), the amount of the initiator used is 1.8-2.7 wt % of the mass of the bisphenol A epoxy resin represented by formula (1').

[0048] According to a preferred embodiment of the present invention, in step (1), the mass ratio of the bisphenol A epoxy resin represented by formula (1') to the modified monomer is 25:6-9.

[0049] According to a preferred embodiment of the present invention, in step (2), the molar ratio of 4,4'-diaminodiphenyl ether to the modified monomer is 1:1-1.2.

[0050] According to a preferred embodiment of the present invention, in step (2), the amount of the solvent used is 60-80 wt % of the mass of the modified monomer.

[0051] According to a preferred embodiment of the present invention, the method for preparing a modified epoxy resin sizing agent containing an amide structure further comprises: adding water to the reactant obtained in step (2), preferably, the amount of water used is such that the content of the modified epoxy resin in the sizing agent is 0.1-50 wt %.

[0052] The third aspect of the present invention provides a modified epoxy resin sizing agent containing an amide structure prepared by the aforementioned preparation method.

[0053] Compared with the prior art, the modified epoxy resin sizing agent containing an amide structure described in the present invention has further improved heat resistance on the basis of good stability and good film-forming property on the carbon fiber surface. This feature will meet the processing and molding requirements of carbon fiber and high-temperature resistant epoxy resin, and expand the application field of carbon fiber / epoxy resin composite materials.

[0054] A fourth aspect of the present invention provides a use of the aforementioned modified epoxy resin sizing agent containing an amide structure in surface modification of fibers.

[0055] According to a preferred embodiment of the present invention, the fiber includes carbon fiber and / or graphite fiber, preferably carbon fiber. Preferably, the carbon fiber includes but is not limited to one or more of SCF-35S-12K, SCF-35S-24K, SCF-35S-48K carbon fiber.

[0056] According to a preferred embodiment of the present invention, the amount of the fiber used is 2500-4000 g relative to 100 mL of the sizing agent.

[0057] According to a preferred embodiment of the present invention, the method for surface modification of carbon fiber using a modified epoxy resin sizing agent containing an amide structure comprises:

[0058] Put a modified epoxy resin sizing agent containing an amide structure into a sizing tank, immerse unsized carbon fibers in the sizing agent and pass through the sizing tank at a speed of 4m / min-8m / min, with a sizing time of 0.05-0.1min, squeeze out excess sizing agent from the carbon fibers exiting the tank, and then dry the sized carbon fibers at 120°C-180°C, preferably, dry them at a three-stage temperature gradient of 140°C-160°C-180°C.

[0059] The sizing carbon fiber can be used to prepare composite materials at high temperature, which improves the compatibility of the carbon fiber / resin matrix interface and improves the interlaminar shear strength of the composite material.

[0060] The present invention will be described in detail below through examples.

[0061] In the following embodiments, heat resistance: the sizing agent after drying is tested for thermal weight loss by a thermogravimetric analyzer (Pyris I TGA) to analyze its heat resistance; wherein, the 5% decomposition temperature refers to the temperature corresponding to the decomposition of 5% by mass of the sizing agent after drying, which represents the maximum processing temperature during the processing and molding of the sizing carbon fiber composite material.

[0062] In the following examples and comparative examples, the preparation of sized carbon fibers comprises the following steps:

[0063] Put the modified epoxy resin sizing agent containing amide structure into the sizing tank, immerse the unsized carbon fiber in the sizing agent and pass through the sizing tank at 4m / min-8m / min, the sizing time is 0.05-0.1min, squeeze out the excess sizing agent of the carbon fiber out of the tank, and then dry the sized carbon fiber in three stages of temperature gradient drying at 140℃-160℃-180℃.

[0064] The preparation of sized carbon fiber / epoxy resin unidirectional composite specimens and the testing of the interlaminar shear strength of the specimens include the following steps:

[0065] (1) mixing epoxy resin (E51) and curing agent (methyl nadic anhydride) in a mass ratio of 1:1 to prepare an epoxy resin matrix;

[0066] (2) Evenly apply the resin on the unidirectionally sized carbon fiber tow, lay it flat in the mold with a size of 200*10*2mm, and fix it firmly with a clip to allow the resin to fully infiltrate the carbon fiber and remove the bubbles in the mold;

[0067] (3) Place the sample in an oven and cure it at 100°C for 1 h and at 130°C for 2 h;

[0068] (4) demoulding after cooling to room temperature to obtain a composite material specimen;

[0069] (5) The interlaminar shear strength of composite material specimens was measured on a wire tensile tester (5566A) using the standard ISO 14130:1991 short beam method.

[0070] Example 1

[0071] 1) 100 g of E44 bisphenol A epoxy resin (in formula (1'), n is 3 and R3 is hydrogen) was added to a three-necked flask and heated at 90° C. for 1 h to soften the epoxy resin;

[0072] 2) Raise the temperature to 100°C, add 24g of pyromellitic anhydride and 1.8g of benzoyl peroxide, and react with mechanical stirring for 9h;

[0073] 3) After cooling to room temperature, add 20 g of 4,4'-diaminodiphenyl ether and 20 mL of N,N'-dimethylformamide, and react with mechanical stirring for 5 h;

[0074] 4) After the reaction is completed, add 500 mL of water, stir at high speed to make it dispersed evenly, and dilute with water to a solid content of 1 wt%.

[0075] 5) On the side line of the carbon fiber production line, sizing the SCF-35S-12K carbon fiber and winding it to obtain the sizing carbon fiber;

[0076] The interlaminar shear strength test results of the composite material specimens prepared by the sized carbon fiber and epoxy resin and the heat resistance test results of the sizing agent are shown in Table 1.

[0077] Example 2

[0078] 1) 100 g of E51 bisphenol A epoxy resin (in formula (1'), n is 4 and R3 is hydrogen) was added to a three-necked flask and heated at 80° C. for 1 h to soften the epoxy resin;

[0079] 2) Raise the temperature to 100°C, add 24g of pyromellitic anhydride and 1.8g of benzoyl peroxide, and react with mechanical stirring for 8h;

[0080] 3) After cooling to room temperature, add 20 g of 4,4'-diaminodiphenyl ether and 20 mL of N,N'-dimethylformamide, and react with mechanical stirring for 5-6 hours;

[0081] 4) After the reaction is completed, add 500 mL of water, stir at high speed to make it evenly dispersed, and dilute with water to a solid content of 1 wt%;

[0082] 5) On the side line of the carbon fiber production line, sizing the SCF-35S-12K carbon fiber and winding it to obtain the sizing carbon fiber;

[0083] The interlaminar shear strength test results of the composite material specimens prepared by the sized carbon fiber and epoxy resin and the heat resistance test results of the sizing agent are shown in Table 1.

[0084] Example 3

[0085] 1) 100 g of E20 bisphenol A epoxy resin (in formula (1'), n is 6 and R3 is hydrogen) was added to a three-necked flask and heated at 85° C. for 1 h to soften the epoxy resin;

[0086] 2) Raise the temperature to 100°C, add 24g of pyromellitic anhydride and 1.8g of benzoyl peroxide, and react with mechanical stirring for 8h;

[0087] 3) After cooling to room temperature, add 20 g of 4,4'-diaminodiphenyl ether and 20 mL of N,N'-dimethylformamide, and react with mechanical stirring for 5-6 hours;

[0088] 4) After the reaction is completed, add 500 mL of water, stir at high speed to make it evenly dispersed, and dilute with water to a solid content of 1 wt%;

[0089] 5) On the side line of the carbon fiber production line, sizing the SCF-35S-12K carbon fiber and winding it to obtain the sizing carbon fiber;

[0090] The interlaminar shear strength test results of the composite material specimens prepared by the sized carbon fiber and epoxy resin and the heat resistance test results of the sizing agent are shown in Table 1.

[0091] Example 4

[0092] 1) 100 g of E44 bisphenol A epoxy resin was added into a three-necked flask and heated at 90° C. for 1 h to soften the epoxy resin;

[0093] 2) Raise the temperature to 100° C., add 24 g of modified monomer (pyromellitic anhydride and 3,3',4,4'-benzophenone tetracarboxylic dianhydride in a molar ratio of 1:1) and 1.8 g of benzoyl peroxide, and react with mechanical stirring for 9 h;

[0094] 3) After cooling to room temperature, add 20 g of 4,4'-diaminodiphenyl ether and 20 mL of N,N'-dimethylformamide, and react with mechanical stirring for 5 h;

[0095] 4) After the reaction is completed, add 500 mL of water, stir at high speed to make it dispersed evenly, and dilute with water to a solid content of 1 wt%.

[0096] 5) On the side line of the carbon fiber production line, sizing the SCF-35S-12K carbon fiber and winding it to obtain the sizing carbon fiber;

[0097] The interlaminar shear strength test results of the composite material specimens prepared by the sized carbon fiber and epoxy resin and the heat resistance test results of the sizing agent are shown in Table 1.

[0098] Example 5

[0099] 1) Take 100 g of E51 bisphenol A epoxy resin and add it into a three-necked flask, and heat it at 80°C for 1 hour to soften the epoxy resin;

[0100] 2) Raise the temperature to 100° C., add 24 g of modified monomer (pyromellitic anhydride and 3,3',4,4'-benzophenone tetracarboxylic dianhydride in a molar ratio of 1:1) and 1.8 g of benzoyl peroxide, and react with mechanical stirring for 8 h;

[0101] 3) After cooling to room temperature, add 20 g of 4,4'-diaminodiphenyl ether and 20 mL of N,N'-dimethylformamide, and react with mechanical stirring for 5-6 hours;

[0102] 4) After the reaction is completed, add 500 mL of water, stir at high speed to make it evenly dispersed, and dilute with water to a solid content of 1 wt%;

[0103] 5) On the side line of the carbon fiber production line, sizing the SCF-35S-12K carbon fiber and winding it to obtain the sizing carbon fiber;

[0104] The interlaminar shear strength test results of the composite material specimens prepared by the sized carbon fiber and epoxy resin and the heat resistance test results of the sizing agent are shown in Table 1.

[0105] Comparative Example 1

[0106] The method of Example 2 is different in that after the E51 bisphenol A epoxy resin is grafted with anhydride, it does not react with 4,4'-diaminodiphenyl ether, specifically:

[0107] 1) Take 100 g of E51 bisphenol A epoxy resin and add it into a three-necked flask, and heat it at 80°C for 1 hour to soften the epoxy resin;

[0108] 2) Raise the temperature to 100°C, add 24g of pyromellitic anhydride and 1.8g of benzoyl peroxide, and react with mechanical stirring for 8h;

[0109] 3) After the reaction is completed, add 500 mL of water, stir at high speed to make it evenly dispersed, and dilute with water to a solid content of 1 wt%;

[0110] 4) On the side line of the carbon fiber production line, sizing the SCF-35S-12K carbon fiber and winding it to obtain the sizing carbon fiber;

[0111] The interlaminar shear strength test results of the composite material specimens prepared by the sized carbon fiber and epoxy resin and the heat resistance test results of the sizing agent are shown in Table 1.

[0112] Comparative Example 2

[0113] The composite material prepared by unsized SCF-35S-12K carbon fiber and epoxy resin, the interlaminar shear strength test results of the composite material specimens are shown in Table 1.

[0114] Table 1

[0115] serial number 5% decomposition temperature (℃) Interlaminar shear strength (MPa) Example 1 276.98 91.92 Example 2 284.86 94.62 Example 3 280.29 92.74 Example 4 292.08 94.43 Example 5 262.45 95.04 Comparative Example 1 227.1 84.18 Comparative Example 2 174.3 70.47

[0116] As shown in Table 1, the heat-resistant epoxy sizing agent can effectively improve the heat resistance of carbon fiber and the interfacial bonding performance of sized carbon fiber / epoxy resin composite materials. This is because the main polymer chain segment in the heat-resistant epoxy sizing agent contains an amide structure, which can show a high decomposition temperature similar to that of polyimide, and can effectively improve the heat resistance of epoxy resin. The components contained in the sizing agent can form abundant hydrogen bonds and chemical bonds with the surface of carbon fiber, and can also form strong interactions with the epoxy resin matrix, thereby improving the interlaminar shear strength of the sized carbon fiber / epoxy resin composite material.

[0117] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A modified epoxy resin sizing agent containing an amide structure, characterized in that: The sizing agent comprises a modified epoxy resin and water, wherein the modified epoxy resin is a polymer obtained by introducing anhydride functional groups into bisphenol A epoxy resin segments and then grafting amide groups through an amidation reaction. Based on the total weight of the sizing agent, the content of the modified epoxy resin is 0.1-50% by weight, and the content of water is 50-99.9% by weight.

2. The sizing agent according to claim 1, wherein The modified epoxy resin is selected from at least one of the polymers having a structure as shown in formula (1); Wherein, in formula (1), R1 is selected from -CH(COOH)CH(COOH)CH3 or -CH(COOH)CH2COOH; n is 3-6; R is shown in formula (2): In formula (2), R2 is selected from one of the structures shown in formula (3), formula (4), formula (5), formula (6), formula (7), and formula (8); * represents the connection site between R2 and the carbonyl carbon in formula (1), and # represents the connection site between R2 and the carbonyl carbon in formula (2).

3. The modified epoxy resin according to claim 2, wherein In formula (1), n ​​is 3-6; and / or In formula (1), R1 is -CH(COOH)CH2COOH; and / or In formula (2), R2 is selected from one of the structures shown in formula (2) and formula (6).

4. A method for preparing a modified epoxy resin sizing agent containing an amide structure, characterized in that: The method includes: (1) in the presence of an initiator, bringing the bisphenol A epoxy resin represented by formula (1′) into first contact with a modified monomer; Wherein, R3 is methyl, ethyl or hydrogen; n is 3-6; The modified monomer is selected from at least one of pyromellitic anhydride and / or 3,3',4,4'-benzophenone tetracarboxylic dianhydride; (2) In the presence of a solvent, the product obtained in step (1) is contacted with 4,4'-diaminodiphenyl ether for a second time.

5. The preparation method according to claim 4, wherein The initiator is an organic peroxide, preferably benzoyl peroxide; The first contact conditions include: a temperature of 100-110°C and a contact time of 8-10h; The second contact conditions include: temperature of 2-30°C, contact time of 5-7h; The solvent is selected from one or more of N,N'-dimethylformamide, N,N'-dimethylacetamide and dioxane.

6. The preparation method according to claim 4 or 5, wherein In step (1), the amount of the initiator used is 1.8-2.7 wt % of the mass of the bisphenol A epoxy resin represented by formula (1'); In step (1), the mass ratio of the bisphenol A epoxy resin represented by formula (1') to the modified monomer is 25:6-9; In step (2), the molar ratio of 4,4'-diaminodiphenyl ether to the modified monomer is 1:1-1.2; In step (2), the amount of the solvent used is 60-80 wt % of the mass of the modified monomer.

7. The preparation method according to claim 4, wherein The method for preparing the modified epoxy resin sizing agent containing an amide structure further comprises: adding water to the reactant obtained in step (2), preferably, the amount of water used is such that the content of the modified epoxy resin in the sizing agent is 0.1-50% by weight.

8. A modified epoxy resin sizing agent containing an amide structure prepared by the preparation method according to any one of claims 4 to 7.

9. Use of the modified epoxy resin sizing agent containing an amide structure according to any one of claims 1 to 3 or claim 8 in surface modification of fibers.

10. The use according to claim 9, wherein: The fibers include carbon fibers and / or graphite fibers, preferably carbon fibers; and / or Relative to 100 mL of the sizing agent, the amount of the fiber used is 2500-4000 g.

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