Sizing agent for carbon fibers, preparation method of sizing agent and method for sizing carbon fibers

Abstract

The invention provides a sizing agent for carbon fibers, a preparation method of the sizing agent and a method for sizing the carbon fibers, the sizing agent for the carbon fibers comprises 20-60 parts by weight of modified epoxy resin, 1-20 parts by weight of an emulsifier and 50-300 parts by weight of deionized water, the modified epoxy resin is prepared by reacting first epoxy resin with a curing agent and a first catalyst, the emulsifier is prepared by grafting epoxy resin with a hydrophilic chain segment PEG (Polyethylene Glycol). By adopting the sizing agent for the carbon fibers, the shear strength of a material interface can be improved.

Description

Technical Field

[0001] This invention belongs to the field of fibers. Specifically, this invention relates to a sizing agent for carbon fibers, its preparation method, and a method for sizing carbon fibers. Background Technology

[0002] Carbon fiber is a brittle material with excellent mechanical properties such as high specific strength and high specific modulus. It is generally used as a reinforcement in composite materials with resin matrices to leverage its mechanical advantages. However, the inert surface of carbon fiber results in relatively weak bonding with the resin matrix, leading to interfacial debonding and fiber pull-out in carbon fiber reinforced composites during use. This causes the composite material's strength to fall short of expectations. The most common solution is sizing. Sizing can fill some defects on the fiber surface, increase the fiber's bundle structure and wear resistance, and enhance the surface activity of the carbon fiber, thereby strengthening the compatibility and interfacial forces between the carbon fiber and the resin matrix.

[0003] Sizing agents can be classified into solvent-based sizing agents, water-soluble sizing agents, and emulsion-based sizing agents. Solvent-based sizing agents are generally made by dissolving resin in organic solvents, which has drawbacks such as solvent pollution and resin residue on guide rollers after solvent evaporation, contaminating the equipment. Water-soluble sizing agents incorporate hydrophilic segments into lipophilic resins, giving the resin both hydrophilic and lipophilic segments. Water-soluble sizing agents have higher stability, but excessive introduction of hydrophilic segments can lead to excessive water absorption. Emulsion-based sizing agents consist of a main resin, an emulsifier, and water. The emulsifier has both hydrophilic and lipophilic properties. During the gradual addition of water, the system undergoes an inversion process from "oil" encapsulating "water" to "water" encapsulating "oil." Compared to the previous two types, emulsion-based sizing agents have the advantages of being pollution-free and less absorbent, while also exhibiting good preparation stability and low production costs.

[0004] Composite materials often contain two or more components with varying compositions. These components form a composite interface, which plays a decisive role in the overall performance of the composite material. Therefore, with the increasing importance of composite materials in recent years, improving the interfacial properties of materials has gradually become a key focus for researchers in order to further enhance their performance. Summary of the Invention

[0005] To address the aforementioned issues, this invention provides a sizing agent for carbon fibers, its preparation method, and a method for sizing carbon fibers. The sizing agent for carbon fibers prepared according to this invention can improve the interfacial shear strength of the material.

[0006] The first aspect of the present invention provides a sizing agent for carbon fiber, comprising 20-60 parts by weight of modified epoxy resin, 1-20 parts by weight of emulsifier and 50-300 parts by weight of deionized water, wherein the modified epoxy resin is prepared by reacting a first epoxy resin with a curing agent and a first catalyst, and the emulsifier is prepared by grafting hydrophilic PEG epoxy resin.

[0007] Furthermore, the modified epoxy resin is prepared by using a mass ratio of the first epoxy resin to the curing agent and the first catalyst of (20-60):(1-10):(0-5).

[0008] Further, the first epoxy resin includes one or more of E51, E44, E20, TDE-85, AG-80, AFG-90, ethylene glycol diglycidyl ether, and glycerol triglycidyl ether.

[0009] Furthermore, the curing agent includes one or more of diethylenetriamine, DDM, DDS, m-phenylenediamine, phthalic anhydride, and tetrahydrophthalic anhydride.

[0010] Furthermore, the first catalyst comprises one of ammonium persulfate, potassium persulfate, tetrabutylammonium bromide, triphenylphosphine bromide, and boron trifluoride diethyl ether.

[0011] Furthermore, the method for preparing the modified epoxy resin using the first epoxy resin, curing agent, and first catalyst includes: adding the first epoxy resin, curing agent, and first catalyst into a three-necked flask equipped with a reflux condenser and stirring; placing the three-necked flask in an oil bath and heating it at an oil bath temperature of 120℃-170℃ for a reaction time of 3-4 hours.

[0012] Furthermore, the method for preparing emulsifiers using hydrophilic PEG grafted epoxy resin includes: adding hydrophilic PEG, a second epoxy resin and a second catalyst into a three-necked flask equipped with a reflux condenser and stirring; placing the three-necked flask in an oil bath and heating it at a temperature of 100-140℃ for a reaction time of 1-4 hours.

[0013] Further, the mass ratio of the hydrophilic PEG segment, the second epoxy resin, and the second catalyst is (50-100):(5-10):(0.5-1).

[0014] Furthermore, the hydrophilic PEG segment includes one or more of PEG-2000, PEG-4000, and PEG-6000.

[0015] Further, the second epoxy resin includes one or more of E51, E44, E20, TDE-85, AG-80, AFG-90, ethylene glycol diglycidyl ether, and glycerol triglycidyl ether.

[0016] Furthermore, the second catalyst comprises one or more of ammonium persulfate, potassium persulfate, tetrabutylammonium bromide, triphenylphosphine bromide, and boron trifluoride diethyl ether.

[0017] A second aspect of the present invention provides a method for preparing the above-mentioned sizing agent for carbon fibers, comprising:

[0018] The modified epoxy resin was mixed with an emulsifier to obtain a mixture.

[0019] The mixture was emulsified using a high-speed shear emulsifier, and deionized water was added to the high-speed shear emulsifier to obtain a sizing agent for carbon fibers.

[0020] Furthermore, the stirring rate of the mixture during the emulsification process using a high-speed shear emulsifier is 1500-2500 rpm.

[0021] Furthermore, deionized water is added to the high-speed shear emulsifier using a peristaltic pump at a rate of 5-10 g / min.

[0022] A third aspect of the present invention provides a method for sizing carbon fibers, comprising:

[0023] Carbon fibers are sized with a carbon fiber sizing agent, and the sized carbon fibers are then dried. The carbon fiber sizing agent includes the carbon fiber sizing agent described above or a carbon fiber sizing agent obtained by the above method.

[0024] Furthermore, the sizing time is 15-60 seconds.

[0025] Furthermore, the sizing temperature is 20-50℃.

[0026] Furthermore, the drying time is 3-10 minutes.

[0027] Furthermore, the amount of the sizing agent used for carbon fiber is 0.5-1.5 wt%.

[0028] Furthermore, the carbon fiber includes high-modulus carbon fiber M40J.

[0029] Compared with the prior art, the present invention has at least the following beneficial effects: the carbon fiber sizing agent composed of the present invention can improve the interfacial shear strength of the material.

[0030] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. The following examples are merely descriptive and not limiting, and should not be used to limit the scope of protection of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0032] The first aspect of the present invention discloses a sizing agent for carbon fiber, the sizing agent comprising 20-60 parts by weight of modified epoxy resin, 1-20 parts by weight of emulsifier and 50-300 parts by weight of deionized water, wherein the modified epoxy resin is prepared by reacting a first epoxy resin with a curing agent and a first catalyst, and the emulsifier is prepared by grafting hydrophilic PEG epoxy resin.

[0033] In this invention, the sizing agent for carbon fiber is prepared by using modified epoxy resin, emulsifier, and deionized water in the above proportions. The modified epoxy resin is prepared by reacting a first epoxy resin with a curing agent and a first catalyst, that is, by introducing an appropriate amount of curing agent into the epoxy resin molecular chain to extend the epoxy resin chain. The resulting modified epoxy resin has a higher modulus than epoxy resin without curing agent. The interface is the hub connecting the fiber and the resin. When force is transmitted through the interface layer, the rapid change in modulus at the interface can easily cause stress concentration at the interface, leading to problems such as interface debonding failure. The sizing agent prepared with this modified epoxy resin can effectively improve the modulus of the sizing agent interface layer and form a transition layer with a modulus gradient between the high-modulus fiber and the low-modulus resin. This overcomes the problem of stress concentration on the carbon fiber surface caused by excessive modulus change between the carbon fiber surface and the reinforcing resin. Furthermore, the emulsifier is prepared by grafting hydrophilic PEG segments onto epoxy resin. PEG has excellent hydrophilic properties, enabling the introduction of sufficient hydrophilic segments onto the epoxy resin. Since PEG is solid at room temperature, the prepared emulsifier remains solid at room temperature, facilitating transportation and storage. Therefore, the sizing agent for carbon fibers prepared according to this invention can improve the interfacial shear strength of composite materials.

[0034] In some embodiments of the present invention, the modified epoxy resin is prepared by using a mass ratio of the first epoxy resin to the curing agent and the first catalyst of (20-60):(1-10):(0-5).

[0035] The first epoxy resin includes one or more of E51, E44, E20, TDE-85, AG-80, AFG-90, ethylene glycol diglycidyl ether, and glycerol triglycidyl ether; the curing agent includes one or more of diethylenetriamine, DDM, DDS, m-phenylenediamine, phthalic anhydride, and tetrahydrophthalic anhydride; and the first catalyst includes one of ammonium persulfate, potassium persulfate, tetrabutylammonium bromide, triphenylphosphine bromide, and boron trifluoride ethyl ether.

[0036] In some embodiments of the present invention, the method for preparing the modified epoxy resin using a first epoxy resin, a curing agent, and a first catalyst includes: adding the first epoxy resin, the curing agent, and the first catalyst into a three-necked flask equipped with a reflux condenser and stirring; placing the three-necked flask in an oil bath and heating it at a temperature of 120°C-170°C for a reaction time of 3-4 hours.

[0037] In some embodiments of the present invention, the method for preparing an emulsifier using hydrophilic PEG grafted epoxy resin includes: adding hydrophilic PEG, a second epoxy resin and a second catalyst into a three-necked flask equipped with a reflux condenser and stirring; placing the three-necked flask in an oil bath and heating it at a temperature of 100-140°C for a reaction time of 1-4 hours.

[0038] In some embodiments of the present invention, the mass ratio of the hydrophilic PEG segment, the second epoxy resin, and the second catalyst is (50-100):(5-10):(0.5-1), wherein the second epoxy resin serves as the matrix for grafting the hydrophilic PEG segment, providing the emulsifier with certain lipophilic properties and ensuring certain compatibility with the main component modified epoxy resin; the hydrophilic PEG segment includes one or more of PEG-2000, PEG-4000, and PEG-6000; the second epoxy resin includes one or more of E51, E44, E20, TDE-85, AG-80, AFG-90, ethylene glycol diglycidyl ether, and glycerol triglycidyl ether; the second catalyst includes one or more of ammonium persulfate, potassium persulfate, tetrabutylammonium bromide, triphenylphosphine bromide, and boron trifluoride ethyl ether.

[0039] A second aspect of the present invention provides a method for preparing the above-mentioned sizing agent for carbon fibers, comprising:

[0040] The modified epoxy resin was mixed with an emulsifier to obtain a mixture.

[0041] The mixture is emulsified using a high-speed shear emulsifier, and deionized water is added to the high-speed shear emulsifier to obtain a sizing agent for carbon fibers.

[0042] In some embodiments of the present invention, the stirring rate of the mixture emulsification process using a high-speed shear emulsifier is 1500-2500 rpm.

[0043] In some embodiments of the present invention, a peristaltic pump is used to add deionized water to the high-speed shear emulsifier at a rate of 5-10 g / min.

[0044] A third aspect of the present invention provides a method for sizing carbon fibers, comprising:

[0045] Carbon fibers are sized with a carbon fiber sizing agent, and the sized carbon fibers are dried. The carbon fiber sizing agent includes the carbon fiber sizing agent described in the first aspect above or the carbon fiber sizing agent obtained by the method described in the second aspect above.

[0046] In some embodiments of the present invention, the sizing time is 15-60 seconds, the sizing temperature is 20-50°C, the drying time is 3-10 minutes, and the sizing amount of the carbon fiber sizing agent is 0.5-1.5 wt%.

[0047] In some embodiments of the present invention, the carbon fiber includes high-modulus carbon fiber M40J.

[0048] The embodiments described below are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in the art or in accordance with the product manual.

[0049] Example 1

[0050] In this embodiment, the sizing agent for carbon fiber includes 60g of modified epoxy resin, 3g of emulsifier, and 189g of deionized water.

[0051] (A) The modified epoxy resin is prepared by the following steps:

[0052] (1) Prepare the raw materials according to the following components: 100g epoxy resin E51, 3g curing agent DDM;

[0053] (2) Add the epoxy resin and curing agent from step 1) into a three-necked flask equipped with a reflux condenser and stir. Place the three-necked flask in an oil bath and heat it at 130°C for 3 hours to obtain the modified epoxy resin.

[0054] (B) The emulsifier is prepared by the following steps:

[0055] (1) Prepare the raw materials according to the following components: 7g epoxy resin E44, 90g PEG4000, 1g catalyst tetrabutylammonium bromide;

[0056] (2) Add the epoxy resin, PEG and catalyst from step 1) into a three-necked flask equipped with a reflux condenser and stir. Place the three-necked flask in an oil bath and heat it at 130°C for 3 hours to obtain the emulsifier.

[0057] The method for preparing sizing agents for carbon fibers comprises the following steps:

[0058] The modified epoxy resin prepared above was mixed evenly with the emulsifier and then added to a high-speed shear emulsifier for emulsification. The stirring rate was 2000 rpm / min. During the stirring process, deionized water was added to the emulsifier at a rate of 5 g / min using a peristaltic pump. Finally, the solid content of the emulsion was adjusted to 25% to obtain a sizing agent for carbon fiber.

[0059] Sizing treatment of high-modulus carbon fiber M40J:

[0060] The carbon fiber was diluted with water to a solid content of 2.5%. The diluted emulsion was poured into the sizing tank. The unsized high-modulus carbon fiber M40J was sized through the sizing tank. The sized carbon fiber was then dried in a drying oven.

[0061] The sizing time was 30 seconds; the sizing temperature was 25°C; the drying time was 5 minutes; and the sizing amount of the carbon fiber was 0.9 wt%.

[0062] Example 2

[0063] The sizing agent used for carbon fiber in this embodiment is basically the same as that in Example 1, except that the curing agent DDM used to prepare the modified epoxy resin is 6g.

[0064] Example 3

[0065] The sizing agent for carbon fiber in this embodiment is basically the same as that in Example 1, except that the curing agent DDM used to prepare the modified epoxy resin is 9g.

[0066] Example 4

[0067] The sizing agent used for carbon fiber in this embodiment is basically the same as that in Example 1, except that the curing agent DDM used to prepare the modified epoxy resin is 12g.

[0068] Example 5

[0069] The sizing agent for carbon fiber in this embodiment is basically the same as that in Example 1, except that the curing agent used to prepare the modified epoxy resin in this example is 3g DDS.

[0070] Example 6

[0071] The sizing agent for carbon fiber in this embodiment is basically the same as that in Example 1, except that the epoxy resin used to prepare the modified epoxy resin in this example is 80g E51 and 20g E20.

[0072] Example 7

[0073] The sizing agent for carbon fiber in this embodiment is basically the same as that in Example 1, except that the epoxy resin used to prepare the modified epoxy resin in this example is 70g E51 and 30g E20.

[0074] Example 8

[0075] The sizing agent for carbon fiber in this embodiment is basically the same as that in Example 6, except that the epoxy resin used to prepare the modified epoxy resin in this example is 60g E51 and 40g E20.

[0076] Example 9

[0077] The sizing agent used for carbon fiber in this embodiment is basically the same as that in Example 1, except that the epoxy resin used to prepare the modified epoxy resin in this example is 80g TDE-85 and 20g E20.

[0078] Example 10

[0079] The sizing agent used for carbon fiber in this embodiment is basically the same as that in Example 1, except that the epoxy resin used to prepare the modified epoxy resin in this example is 80g AFG-90 and 20g E20.

[0080] Example 11

[0081] The carbon fiber sizing agent in this embodiment is basically the same as that in Example 1, except that the emulsifier used to prepare the carbon fiber sizing agent in this example is 6g.

[0082] Example 12

[0083] The carbon fiber sizing agent in this embodiment is basically the same as that in Example 11, except that the emulsifier used to prepare the carbon fiber sizing agent in this example is 9g.

[0084] Example 13

[0085] The carbon fiber sizing agent in this embodiment is basically the same as that in Example 11, except that the emulsifier used to prepare the carbon fiber sizing agent in this example is 12g.

[0086] Comparative Example

[0087] The sizing agent used for the carbon fiber in this comparative example is basically the same as that in Example 11, except that no curing agent was added to the modified epoxy resin used in this example.

[0088] In Examples 1-13 and the comparative examples, the carbon fiber tows were subjected to microdroplet adhesion experiments to test the interfacial shear capacity of the samples. The microdroplets were made of 10g of epoxy resin TDE-85 and 3g of curing agent DDS. The curing temperatures were 140℃ for 1h, 180℃ for 2h, and 200℃ for 0.5h. The length of the microdroplets was between 40-60um.

[0089] The interfacial shear strength data of the micro-debonded samples prepared in Examples 1-13 and the comparative examples are shown in Table 1.

[0090] Table 1. Interfacial shear strength of carbon fibers in Examples 1-13 and Comparative Examples

[0091]

[0092] As can be seen from the interfacial shear strength data of carbon fibers in Examples 1-13 and the comparative example in Table 1, the interfacial shear strength of carbon fibers in Examples 1-13 is significantly higher than that of the comparative example, indicating that the carbon fiber emulsifier composed in this invention can improve the interfacial shear strength of the material.

[0093] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0094] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A sizing agent for carbon fiber, characterized in that, It comprises 20-60 parts by weight of modified epoxy resin, 1-20 parts by weight of emulsifier and 50-300 parts by weight of deionized water. The modified epoxy resin is prepared by reacting a first epoxy resin with a curing agent and a first catalyst. The emulsifier is prepared by grafting hydrophilic PEG epoxy resin.

2. The sizing agent for carbon fiber according to claim 1, characterized in that, The modified epoxy resin is prepared by using a mass ratio of the first epoxy resin to the curing agent and the first catalyst of (20-60):(1-10):(0-5).

3. The sizing agent for carbon fiber according to claim 1 or 2, characterized in that, The first epoxy resin includes one or more of E51, E44, E20, TDE-85, AG-80, AFG-90, ethylene glycol diglycidyl ether, and glycerol triglycidyl ether; Optionally, the curing agent includes one or more of diethylenetriamine, DDM, DDS, m-phenylenediamine, phthalic anhydride, and tetrahydrophthalic anhydride; Optionally, the first catalyst comprises one of ammonium persulfate, potassium persulfate, tetrabutylammonium bromide, triphenylphosphine bromide, and boron trifluoride diethyl ether.

4. The sizing agent for carbon fiber according to claim 1, characterized in that, The method for preparing the modified epoxy resin using a first epoxy resin, a curing agent, and a first catalyst includes: The first epoxy resin, curing agent and first catalyst were added to a three-necked flask equipped with a reflux condenser and stirred. The three-necked flask was placed in an oil bath and heated at 120℃-170℃ for 3-4 hours.

5. The sizing agent for carbon fiber according to claim 1 or 4, characterized in that, Methods for preparing emulsifiers using hydrophilic segment PEG-grafted epoxy resin include: The hydrophilic PEG segment, the second epoxy resin, and the second catalyst were added to a three-necked flask equipped with a reflux condenser and stirred. The three-necked flask was then placed in an oil bath and heated at 100-140°C for 1-4 hours.

6. The method according to claim 5, characterized in that, The mass ratio of the hydrophilic PEG segment, the second epoxy resin, and the second catalyst is (50-100):(5-10):(0.5-1); Optionally, the hydrophilic PEG segment includes one or more of PEG-2000, PEG-4000, and PEG-6000; Optionally, the second epoxy resin includes one or more of E51, E44, E20, TDE-85, AG-80, AFG-90, ethylene glycol diglycidyl ether, and glycerol triglycidyl ether. Optionally, the second catalyst comprises one or more of ammonium persulfate, potassium persulfate, tetrabutylammonium bromide, triphenylphosphine bromide, and boron trifluoride diethyl ether.

7. A method for preparing a sizing agent for carbon fibers according to any one of claims 1-6, characterized in that, include: The modified epoxy resin was mixed with an emulsifier to obtain a mixture. The mixture is emulsified using a high-speed shear emulsifier, and deionized water is added to the high-speed shear emulsifier to obtain a sizing agent for carbon fibers.

8. The method according to claim 7, characterized in that, The stirring rate during the emulsification process of the mixture is 1500-2500 rpm using a high-speed shear emulsifier; Optionally, deionized water is added to the high-speed shear emulsifier using a peristaltic pump at a rate of 5-10 g / min.

9. A method for sizing carbon fibers, characterized in that, include: Carbon fibers are sized with a carbon fiber sizing agent, and the sized carbon fibers are dried. The carbon fiber sizing agent includes any one of the carbon fiber sizing agents according to claims 1-6 or a carbon fiber sizing agent obtained by the method according to claim 7 or 8.

10. The method according to claim 9, characterized in that, The sizing time is 15-60 seconds; Optionally, the sizing temperature is 20-50℃; Optionally, the drying time is 3-10 minutes; Optionally, the sizing agent for the carbon fiber has a sizing amount of 0.5-1.5 wt%. Optionally, the carbon fiber includes high-modulus carbon fiber M40J.

Images