Preparation and application of reactive nano-silica inorganic-organic core-shell structure sizing agent

Abstract

The patent relates to preparation and application of a reactive nano-SiO2 inorganic-organic core-shell structure sizing agent. An intermediate is prepared by amine group modification of epoxy resin, SiO2 precursor and silicon coupling agent KH570 are added into the intermediate solution, stirred uniformly, then acid and water are added, and the nano-SiO2 inorganic-organic core-shell structure carbon fiber sizing agent emulsion containing double bonds on the surface is prepared by stirring and emulsification. The free radicals generated by thermal decomposition of the carboxyl group at the interface of the carbon fiber are used to graft the nano-SiO2 sizing agent containing double bonds on the surface to the surface of the carbon fiber. After sizing, the nano-SiO2 can repair the groove defects on the surface of the carbon fiber, improve the uniformity and stability of the nano-SiO2 on the surface of the carbon fiber, increase the tensile strength and surface roughness of the carbon fiber after sizing, improve the interlocking force and bonding force between the interface of the carbon fiber and the resin matrix, and thus improve the interlaminar shear strength of the carbon fiber reinforced epoxy resin matrix composite material.

Description

TECHNICAL FIELD

[0001] The patent belongs to the technical field of preparation of high-performance carbon fiber sizing agent, in particular to a kind of carbon fiber surface reactive nano-SiO2 Inorganic-Organic Core-Shell Structure Sizing Agent Preparation Method and Its Application in Epoxy Resin Based Carbon Fiber Composite Material. BACKGROUND

[0002] Carbon fiber is a kind of carbon material with carbon content of more than 90%, and high carbon element determines its surface inertness. Especially high-performance carbon fiber is produced by dry spraying wet spinning process, which not only shows inertness, but also has a smooth and dense surface. Therefore, carbon fiber and resin matrix have poor wetting and bonding properties, so it is necessary to size the carbon fiber during production to improve the compatibility of sized carbon fiber and resin matrix, which is beneficial to the rapid wetting and uniform coverage of resin matrix on the interface of carbon fiber, and realizes the effective transmission of load stress between resin matrix and fiber, thereby improving the mechanical properties of carbon fiber resin matrix composite material, especially interlaminar shear strength. The inventor of the present patent has proposed a kind of self-assembled self-emulsifying amphiphilic cationic epoxy resin type high-performance fiber sizing agent / impregnant / film-forming agent and its preparation method in patent CN109251305A. The compatibility of sized carbon fiber and epoxy resin matrix and the interfacial adhesion of composite material are improved by the electrostatic force between the sizing agent and the interface of carbon fiber. However, this electrostatic force has a very limited effect on the improvement of the performance of the composite material, especially the interlaminar shear strength. Therefore, the inventor of the present patent has proposed in-situ synthesis and application of nano-oxide reinforced carbon fiber sizing agent and basalt fiber impregnant in patent CN109972397A. The surface roughness of sized carbon fiber is improved by nano-oxide modified sizing agent, the interlocking adhesion between carbon fiber and resin matrix is improved, and the interlaminar shear strength of carbon fiber reinforced epoxy resin matrix composite material is further improved. In order to further optimize the nano-oxide modified sizing agent, improve the stability of nano-SiO2 on the surface of sized carbon fiber, avoid the migration and aggregation of nano-oxide, and improve the interfacial adhesion between carbon fiber and sizing agent, the present patent invents a method of grafting methacrylate unsaturated double bond to the surface of nano-SiO2 by silane coupling agent KH570, and then using the free radicals generated by the decomposition of carboxyl groups on the surface of carbon fiber at high temperature to initiate the grafting reaction of methacrylate unsaturated double bond. Thus, nano-SiO2 is connected to the surface of carbon fiber through covalent bond. At the same time, due to the formation of positive and negative charge interaction between the silicic acid group (Si-OH) on the surface of nano-SiO2 and the amine group in the intermediate of amine modified epoxy resin (SiO - --- + NHR3), further enhancing the interfacial adhesion between nano-SiO2 Inorganic-Organic Core-Shell Structure Sizing Agent and carbon fiber surface, thereby improving the mechanical properties of carbon fiber and its epoxy resin matrix composite material, especially the interlaminar shear strength. SUMMARY

[0003] In view of the deficiencies of the prior art, the present application aims to provide a preparation method of a reactive nano-SiO2 inorganic-organic core-shell structure sizing agent, the product and application thereof. First, an amphiphilic intermediate (as shown in Figure 1 The SiO2 precursor is uniformly mixed with the amine-modified intermediate, a salting agent, glacial acetic acid and water is added for emulsification to prepare an emulsion of the organic phase containing the SiO2 precursor. Under acidic conditions, the nano-SiO2 precursor is hydrolyzed, and a nano-SiO2 inorganic core and an amine-modified epoxy resin intermediate shell are prepared through a sol-gel reaction, that is, a nano-SiO2 inorganic-organic core-shell structure sizing agent (as shown in Figure 2 The present application aims to provide a method for grafting a methacrylate unsaturated double bond to the surface of the nano-SiO2 core through a silane coupling agent KH570, and then using the free radicals generated by the decomposition of the carboxyl groups on the surface of the carbon fiber at high temperature to initiate the grafting reaction of the methacrylate unsaturated double bond, so as to covalently bond the nano-SiO2 to the surface of the carbon fiber (as shown in Figure 3 The present application aims to provide a method for grafting a methacrylate unsaturated double bond to the surface of the nano-SiO2 core through a silane coupling agent KH570, and then using the free radicals generated by the decomposition of the carboxyl groups on the surface of the carbon fiber at high temperature to initiate the grafting reaction of the methacrylate unsaturated double bond, so as to covalently bond the nano-SiO2 to the surface of the carbon fiber (as shown in

[0004] A preparation and application of a reactive nano-SiO2 inorganic-organic core-shell structure sizing agent, characterized in that an intermediate is prepared by amine-modified epoxy resin, the SiO2 precursor and the silicon coupling agent KH570 are added to the intermediate solution, stirred uniformly, then the salting agent acid and distilled water are added, stirred and emulsified, and the sizing agent emulsion of the nano-SiO2 surface containing the inorganic-organic core-shell structure double bond is prepared after heating and aging. After sizing, the carbon fiber is applied to the preparation of an epoxy resin-based composite material (as shown in Figure 4 The specific steps are as follows:

[0005] 1) The amine-modified epoxy resin intermediate is dissolved in dry acetone;

[0006] 2) The SiO2 precursor tetraethyl orthosilicate and the silicon coupling agent KH570 are added under stirring at room temperature, and after being fully stirred and uniformly mixed under alkaline conditions, the acid is added for salting reaction;

[0007] 3) Deionized water is added, stirred and emulsified to in-situ synthesize the sizing agent emulsion of the nano-SiO2 surface containing the inorganic-organic core-shell structure unsaturated double bond;

[0008] 4) The acetone is removed by stirring under air atmosphere and heating to 80°C, and the sizing agent emulsion is prepared after cooling to room temperature;

[0009] 5) After diluting the nano-SiO2 inorganic-organic core-shell structure reactive sizing agent with deionized water, the surface of the carbon fiber is sized and modified;

[0010] 6) The sized carbon fiber is dried at 110°C to 170°C.

[0011] As a further optimization of the present application, the step 1) acetone is dried by 4A molecular sieve, the purpose is to avoid the SiO2 precursor hydrolysis under the basic conditions of the amine group modified epoxy resin, resulting in the organic phase of the SiO2 inorganic same amine group modified epoxy resin intermediate phase separation.

[0012] As a further optimization of the present application, in step 2), the SiO2 precursor is methyl orthosilicate, ethyl orthosilicate or propyl orthosilicate, the best choice is ethyl orthosilicate. The fatty alcohol orthosilicate hydrolysis reaction occurs under acidic conditions, and the hydrolysis reaction rate decreases with the increase of the volume of the fatty alcohol, that is, the hydrolysis rate of methyl orthosilicate > the hydrolysis rate of ethyl orthosilicate > the hydrolysis rate of propyl orthosilicate. Since the hydrolysis rate of methyl orthosilicate in aqueous acetic acid is too fast, therefore, in the mixture of the amine group modified epoxy resin intermediate and methyl orthosilicate, when water is added for emulsification, SiO2 precipitate has been formed before the formation of emulsion micelles, resulting in inorganic-organic phase separation; the hydrolysis rate of propyl orthosilicate in aqueous acetic acid is too slow, therefore, in the mixture of the amine group modified epoxy resin intermediate and propyl orthosilicate, when water is added for emulsification, there is enough time to form oil-in-water emulsion micelles, propyl orthosilicate is coated inside the emulsion micelles by the amine group modified epoxy resin intermediate, acetic acid and tertiary amine group of the amine group modified epoxy resin intermediate form a salt, and due to the steric shielding effect of the propyl group, it is difficult for propyl orthosilicate to hydrolyze into orthosilicic acid (Si(OH)4), that is, SiO2 cannot be formed by sol-gel.

[0013] As a further optimization of the present application, in step 2), the amount of SiO2 precursor, ethyl orthosilicate, accounts for 10% to 40% of the weight of the amine group modified epoxy resin intermediate.

[0014] As a further optimization of the present application, in step 2), the amount of silicon coupling agent KH570 accounts for 10% to 130% of the weight of the SiO2 precursor, ethyl orthosilicate, the more suitable amount is 70% to 110%, and the best amount is 90%.

[0015] As a further optimization of the present application, in step 4), the removal of acetone must be carried out in air, and O2 in the air can prevent the thermal polymerization of methyl methacrylate on the surface of the nano-SiO2 core.

[0016] As a further optimization of the present application, in step 4), the removal of acetone is carried out at a temperature of 80°C, which is beneficial to the hydrolysis and sol-gel reaction of the SiO2 precursor, ethyl orthosilicate, inside the emulsion micelles, and the preparation of nano-SiO2 inorganic-organic core-shell structure sizing agent.

[0017] As a further optimization of the present application, step 5) after the nano-SiO2 inorganic-organic core-shell structure sizing agent is diluted with deionized water, the carbon fiber surface is modified by sizing. The solid content of the sizing agent is generally 2% to 5% in the sizing tank, ensuring that the sizing rate of the carbon fiber is 0.8% to 1.5%, depending on the carbonization process such as drawing and winding speed, sizing tank length, carbon fiber surface roughness, and carbon fiber end application.

[0018] As a further optimization of the present application, step 6) after sizing, the carbon fiber is dried at medium-high temperature (110°C to 170°C). The carbon fiber surface contains carboxyl groups, which are prone to decomposition at medium-high temperature to generate free radicals. The methyl methacrylate unsaturated double bonds on the surface of nano-SiO2 will undergo double bond grafting reaction through the carbon fiber surface free radicals and self-crosslinking reaction of the methyl methacrylate unsaturated double bonds on the surface of SiO2 (as shown in Figure 2

[0019] The present patent addresses the shortcomings of the prior art and invents a reactive nano-SiO2 inorganic-organic core-shell structure sizing agent. The free radical reaction of the methyl methacrylate double bonds grafted on the surface of nano-SiO2 is covalently bonded to the surface of carbon fiber through the decomposition of carboxyl groups on the surface of carbon fiber at high temperature, improving the stability and uniformity of nano-SiO2 coating on the surface of carbon fiber after sizing, avoiding the migration and aggregation of nano-SiO2, and further enhancing the adhesion of nano-SiO2 inorganic-organic core-shell structure sizing agent to the surface of carbon fiber due to the formation of positive and negative charges (SiO - --- + NHR3) between the silicon acid groups (Si-OH) on the surface of nano-SiO2 and the tertiary amine groups of the amine-modified epoxy resin intermediate, thereby further enhancing the adhesion of the nano-SiO2 inorganic-organic core-shell structure sizing agent to the surface of carbon fiber, and improving the mechanical properties of carbon fiber and epoxy resin-based composite materials, especially the interlaminar shear strength. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 Synthesis of amine-modified epoxy resin polymer;

[0021] Figure 2 Synthesis of reactive nano-SiO2 inorganic-organic core-shell structure sizing agent;

[0022] Figure 3 Grafting reaction of methyl methacrylate double bonds on the surface of nano-SiO2 with the interface of carbon fiber;

[0023] Figure 4 Carbon fiber sizing, drying and winding process. DETAILED DESCRIPTION

[0024] Example 1:

[0025] ​Example 1 : 26.6 g of octadecylamine, 24.7 g of polyetheramine (molecular weight 1000) were dissolved using 30 g of acetone, 49.1 g of E-1 NT type epoxy resin (epoxy equivalent weight 185 g / eq) was added into a reaction kettle, after installing sealing, condensing device and purging with nitrogen, the temperature was set to 40°C, after the temperature reached 40°C and stabilized for 10 min, a water separator was added, the temperature was set to 70°C, after no solvent was evaporated, the water separator device was removed, the temperature was slowly increased to 100°C, reacted for 1 h, then increased to 130°C, kept constant for 3 h, then decreased to 50°C, 100.4 g of 4A molecular sieve dried acetone was added, after cooling to room temperature, it was sealed and used.

[0026] Example 2:

[0027] The amine-modified epoxy resin intermediate prepared in Example 1 and tetraethyl orthosilicate (TEOS) were added into a reaction kettle with sealing, condensing device installed and purging with nitrogen, after stirring uniformly at room temperature, 7.6 g of glacial acetic acid and water were added, an emulsion was prepared by high-speed stirring and stabilized for 30 min, a water separator was added, the temperature was set to 80°C, after no solvent was evaporated, the water separator device was removed, the temperature was maintained at 80°C, aged for 1 h, and then sealed after cooling to room temperature.

[0028] Table 1

[0029] Comparative Example 2-1:

[0030] The amine-modified epoxy resin intermediate prepared in Example 1, 100 g of acetone (industrial grade) and 25 g of tetraethyl orthosilicate (TEOS) were added into a reaction kettle with sealing and condensing device installed, after stirring uniformly at room temperature, 7.6 g of glacial acetic acid was added, a small amount of white precipitate was produced; high-speed stirring, adding water, a large amount of precipitate was produced.

[0031] Comparative Example 2-2:

[0032] The amine-modified epoxy resin intermediate prepared in Example 1, 100 g of acetone (industrial grade) and 31.7 g of tetrapropyl orthosilicate were added into a reaction kettle with sealing and condensing device installed, after stirring uniformly at room temperature, 7.6 g of glacial acetic acid was added, an emulsion was prepared by high-speed stirring and stabilized for 30 min, a water separator was added, the temperature was set to 80°C, after no solvent was evaporated, the water separator device was removed, the temperature was maintained at 80°C, aged for 1 h, and then sealed after cooling to room temperature.

[0033] Example 3:

[0034] Into a reactor equipped with a seal, condenser and nitrogen inlet, 100 g (100% solid content) of the amine-modified epoxy resin intermediate prepared in Example 1, 25 g of tetraethyl orthosilicate (TEOS) and 0.5 g of silane coupling agent KH570 were added. After stirring uniformly at room temperature, 0.5 g of glacial acetic acid was added, and water was added under high-speed stirring to prepare an emulsion, which was stabilized for 30 min. A water separator was added, and the temperature was set to 80°C. After no solvent was evaporated, the water separator was removed, and the temperature was maintained at 80°C. The reaction was aged for 1 h, and then the temperature was lowered to room temperature. The product was sealed and stored for use.

[0035] Table 2

[0036]

[0037] Comparative Example 3

[0038] Into a reactor equipped with a seal and a condenser, 100 g (100% solid content) of the amine-modified epoxy resin intermediate prepared in Example 1, 100 g of acetone (industrial grade), 25 g of tetraethyl orthosilicate (TEOS) and 22.5 g of silane coupling agent KH570 were added. After stirring uniformly at room temperature, 7.6 g of glacial acetic acid was added, and a small amount of white precipitate was produced. Water was added under high-speed stirring, and a large amount of precipitate was produced.

[0039] Example 4

[0040] 1. Carbon fiber sizing process

[0041] The carbon fiber tows were immersed in a sizing agent tank containing the sizing agent of Example 2 or 3, and the sizing process was completed by continuously pulling the CF into the tank and immersing it in combination with an automatic flushing device. The solid content of the sizing agent in the sizing agent tank was 2.5%, and the sizing rate was about 1%. As shown in FIG. 1, the sized CF was then immediately dried at 110°C to 170°C for 2 h to evaporate water. Figure 4

[0042] 2. Preparation of epoxy resin composite

[0043] A unidirectional carbon fiber-reinforced epoxy resin composite for interlaminar shear strength testing was prepared by a hot press molding method. A sample having a size of 2*6*200 mm was prepared by impregnating carbon fibers with a resin using a hand lay-up method. The weight ratio of Dow epoxy resin 550E and curing agent 555H was 100:105. The mixture of 550E and 555H was stirred uniformly, and the mixture of the epoxy resin and the curing agent was applied to the unidirectional carbon fiber tows at 35°C to 40°C and was degassed for 10 min. Then, the resin-impregnated unidirectional carbon fiber tows were placed in a mold that was preheated and treated with a release agent at 150°C, the mold was closed, and then the mold was placed in an oven at 150°C for 30 min, and then was naturally cooled to room temperature.

[0044] Example 5:​

[0045] The carbon fiber reinforced epoxy resin matrix composite samples were prepared according to Example 4(2) respectively, and the sizing agents were S0, S1, S2, S3, S4 and S5. The interlaminar shear strength (ILSS) test of the composite material was carried out according to GB / T30969-2014, and the test method for the three-point short beam shear strength of the polymer matrix composite. The interlaminar shear strength (ILSS) of the carbon fiber reinforced epoxy resin matrix composite after sizing was tested. The results are shown in Table 4.

[0046] Table 4

[0047] Sizing agent [S0] [SI] [S2] [S3] [S4] [S5] 550E / 555H ILSS (MPa) 59.4 66.2 68.6 69.4 65.2 62.7

[0048] Example 6:

[0049] The carbon fiber reinforced epoxy resin matrix composite samples were prepared according to Example 4(2) respectively, and the sizing agents were SK0, SK 10 , SK 30 , SK 50 , SK 70 , SK 90 , SK 110 and SK 130 . The interlaminar shear strength (ILSS) test results of the composite material are shown in Table 5.

[0050] Table 5

[0051] Sizing agent SK0 SK 10 ]] SK 30 ]]> SK 50 ]] SK 70 ]] SK 90 ]] SK 110 ]]> SK 130 ]] 550E / 555H ILSS (MPa) 69.4 69.5 69.5 69.9 73.2 80.4 75.7 69.8

Claims

1. A method for preparing a reactive nano-SiO2 inorganic-organic core-shell structure sizing agent, characterized in that, This method includes the following synthesis steps: 1) The amine-modified epoxy resin intermediate was dissolved in acetone and dried using a 4A molecular sieve; 2) Add tetraethyl orthosilicate, a SiO2 precursor, and KH570, a silicon coupling agent, at room temperature and with stirring. After stirring evenly, add acid to carry out a salt formation reaction. 3) Add deionized water, stir and emulsify, and synthesize in situ a reactive sizing agent emulsion with nano-SiO2 inorganic-organic core-shell structure containing unsaturated double bonds on the surface. 4) Stir in air, heat to 80°C to remove acetone, cool to room temperature, and prepare the sizing agent emulsion.

2. The method for preparing a reactive nano-SiO2 inorganic-organic core-shell structure sizing agent according to claim 1, characterized in that, The SiO2 precursor, tetraethyl orthosilicate, is used in an amount that accounts for 10% to 40% of the weight of the amine-modified epoxy resin intermediate.

3. A method for preparing a reactive nano-SiO2 inorganic-organic core-shell structure sizing agent according to any one of claims 1 to 2, characterized in that, In step 2), the amount of silicon coupling agent KH570 is 10% to 130% of the weight of SiO2 precursor tetraethyl orthosilicate.

4. The method for preparing a reactive nano-SiO2 inorganic-organic core-shell structure sizing agent according to claim 3, characterized in that, In step 2), the amount of silicon coupling agent KH570 accounts for 90% of the weight of SiO2 precursor and tetraethyl orthosilicate.

5. The method for preparing a reactive nano-SiO2 inorganic-organic core-shell structure sizing agent according to claim 1, characterized in that, In step 4), O2 in the air is used as an inhibitor of unsaturated double bonds.

6. The nano-SiO2 inorganic-organic core-shell structure reactive sizing agent prepared by any one of the preparation methods according to claims 1 to 5.

7. The application of the nano-SiO2 inorganic-organic core-shell structure reactive sizing agent according to claim 6, characterized in that, During the medium-high temperature drying of carbon fibers after sizing, the methacrylate double bonds contained in the nano-SiO2 inorganic-organic core-shell structure sizing agent undergo a free radical grafting reaction with the carbon fiber interface, and the double bonds in the sizing agent molecules simultaneously undergo a self-crosslinking reaction. The specific steps are as follows: 1) The nano-SiO2 inorganic-organic core-shell structure reactive sizing agent was diluted with deionized water and then used to sizing and modify the surface of carbon fibers. 2) Dry the sized carbon fiber at 110℃~170℃.

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