Continuous aramid fiber reinforced epoxy resin composite material and preparation method thereof

Abstract

The invention discloses a continuous aramid fiber reinforced epoxy resin composite material and a preparation method thereof, and belongs to the technical field of composite materials. The composite material is obtained by heating and curing continuous aramid fibers modified by a benzoxazine-containing waterborne polyurethane emulsion sizing agent and epoxy resin, the waterborne polyurethane emulsion sizing agent containing benzoxazine is prepared from diisocyanate, long-chain diol, 2, 2-dimethylolpropionic acid, dihydric alcohol containing benzoxazine and triethylamine according to the molar ratio of 1: (0.1 to 0.5): (0.1 to 0.3): (0.3 to 0.4): (0.1 to 0.3) through reaction. The benzoxazine-containing waterborne polyurethane sizing agent is used for modifying the aramid fibers, and benzoxazine is crosslinked with the aramid fibers and the epoxy resin during ring opening polymerization, so that the interface bonding property between the aramid fibers and the epoxy resin can be remarkably improved, and the mechanical property of the composite material can be effectively improved; the application field of the aramid fiber composite material is expanded.

Description

Technical Field

[0001] The present invention relates to the technical field of composite materials, and particularly to a continuous aramid fiber reinforced epoxy resin composite material and a preparation method thereof. Background Art

[0002] Due to its high strength, high modulus, heat resistance and chemical corrosion resistance, aramid fiber is widely used in the fields of aerospace, national defense, automobiles and sports equipment. However, the surface of aramid fiber is smooth and chemically inert, resulting in poor interfacial bonding force with the matrix material, which limits the further improvement of the performance of composite materials. Therefore, improving the interfacial bonding force between aramid fiber and matrix material is a current research hotspot.

[0003] Although traditional sizing agents such as epoxy resin and phenolic resin can improve the interfacial bonding between fibers and the matrix, they have problems such as poor environmental protection and complex processes. Waterborne polyurethane sizing agent has become the focus of research due to its environmental protection, easy processing and good interfacial modification effect.

[0004] In the present invention, benzoxazine is introduced into the waterborne polyurethane sizing agent, and the sizing agent is used to modify aramid fiber. Through the ring-opening polymerization of benzoxazine and the cross-linking with aramid fiber and epoxy resin, the interfacial bonding force between aramid fiber and epoxy resin is enhanced, thereby optimizing the comprehensive performance of the composite material. Therefore, this material has broad application prospects in the fields of aerospace, electronic information, national defense industry, sports equipment, automobile industry, etc. Summary of the Invention

[0005] The main object of the present invention is to improve the interfacial bonding force between aramid fiber and matrix material and enhance the mechanical properties of the composite material, and to provide a continuous aramid fiber reinforced epoxy resin composite material and a preparation method thereof.

[0006] To achieve the above object, the present invention adopts the following technical solutions: A continuous aramid fiber reinforced epoxy resin composite material and a preparation method thereof, characterized in that the composite material is obtained by heat curing continuous aramid fiber modified by a waterborne polyurethane sizing agent containing benzoxazine and epoxy resin, and the aramid fiber, sizing agent and epoxy resin are cured in a mass fraction ratio of 30% - 70% : 0.1% - 5% : 30% - 70%.

[0007] Furthermore, the continuous aramid fiber reinforced epoxy resin composite material and a preparation method thereof are characterized in that the waterborne polyurethane sizing agent containing benzoxazine is formed by reacting diisocyanate, long-chain diol, 2,2-dimethylolpropionic acid, benzoxazine-containing diol and triethylamine in a molar ratio of 1 : 0.1 - 0.5 : 0.1 - 0.3 : 0.3 - 0.4 : 0.1 - 0.3, and the structural general formula is as follows: ; In the formula, the structure of R1 is one or more of the following: ; In the formula, the structure of R2 is one or more of the following: ; wherein, the value range of m is 1 - 20; In the formula, the structure of R3 is one or more of the following: 。

[0008] Further, in the continuous aramid fiber reinforced epoxy resin composite material and its preparation method, it is characterized in that the benzoxazine diol is obtained by reacting diphenol, ethanolamine and paraformaldehyde. The structure of the diphenol is as follows: 。

[0009] Further, in the continuous aramid fiber reinforced epoxy resin composite material and its preparation method, it is characterized in that the aramid fiber is selected from one or more of meta-aramid, aramid II, aramid III, Kevlar-29, Kevlar-49, Technora of Japan, Terlon of Russia.

[0010] Further, in the continuous aramid fiber reinforced epoxy resin composite material and its preparation method, it is characterized in that the epoxy resin is selected from one or more of bisphenol A type epoxy resins with a polymerization degree of 4 - 10, glycidylamine type epoxy resins (AG-80, MY-720) and alicyclic epoxy resins (TDE-85, ERL-4221); the curing agent is methyltetrahydrophthalic anhydride.

[0011] Further, the continuous aramid fiber reinforced epoxy resin composite material and its preparation method are characterized by comprising the following steps: S1. Preparation of benzoxazine diol: Add diphenol, ethanolamine and paraformaldehyde into a three-necked flask equipped with a stirrer, a thermometer and a glass bottle stopper according to a molar ratio of 1:2:4.1 - 4.4, uniformly mix in toluene or 1,4-dioxane solvent, heat to 90 - 110 °C and react for 10 - 36 h. After the reaction is completed, perform post-treatment to obtain a diphenol containing a benzoxazine structure; S2. Preparation of benzoxazine-containing aqueous polyurethane emulsion sizing agent: Under the protection of inert gas, diisocyanate, long-chain diol, and 2,2-dimethylolpropionic acid are added to a three-necked flask equipped with a stirrer, thermometer, and glass stopper. After uniform mixing, dibutyltin dilaurate is added as a catalyst, and the reaction is carried out at 60 - 80 °C for 2 - 3 h. After cooling to 50 - 70 °C, benzoxazine-based diol is added and the reaction is carried out for 2 - 3 h. During this period, acetone is added to reduce the viscosity. Subsequently, the temperature is cooled to 25 - 40 °C, triethylamine is added, and after reacting for 20 - 60 min, deionized water is added. After high-speed dispersion, an aqueous polyurethane emulsion is obtained; among them, diisocyanate, long-chain diol, 2,2-dimethylolpropionic acid, benzoxazine-based diol, and triethylamine are added according to a molar ratio of 1 : 0.1 - 0.5 : 0.1 - 0.3 : 0.3 - 0.4 : 0.1 - 0.3; S3. Preparation of continuous aramid fiber-reinforced epoxy resin composite: At room temperature, the benzoxazine-containing aqueous polyurethane emulsion sizing agent is sprayed on the cleaned aramid fibers, and then the solvent is dried at 80 - 120 °C to obtain sized aramid fibers; subsequently, at room temperature, the sized aramid fibers are impregnated uniformly with the epoxy component, and then placed in a mold, and heated and cured at 120 - 240 °C and 5 - 20 MPa in a hot press for 6 - 10 h to obtain the composite.

[0012] Compared with the prior art, the beneficial effects of the present invention are as follows: Firstly, the present invention uses an aqueous polyurethane emulsion containing benzoxazine as a sizing agent, which improves the interfacial bonding force between the fiber and the resin matrix. For the aramid fibers modified by the sizing agent, when the temperature rises, the benzoxazine will undergo a ring-opening reaction and cross-link with the benzene rings on the aramid fibers and epoxy, significantly improving the interfacial bonding force between the aramid fibers and the epoxy resin, thereby enhancing the overall performance of the composite material and improving the overall performance and service life of the composite material.

[0013] Secondly, the present invention uses an aqueous polyurethane emulsion as a sizing agent, avoiding the toxicity of traditional sizing agents (such as phenolic resin) using organic solvents, and having the characteristics of environmental protection and easy processing, meeting the requirements of green chemistry and sustainable development.

[0014] Other advantages, objectives, and features of the present invention will be partially reflected by the following description, and partially will be understood by those skilled in the art through the research and practice of the present invention. Description of the Drawings

[0015] Figure 1 . FTIR curve of benzoxazine-based diol (BPA-ea) in Example 1; Figure 2. DSC curve of benzoxazine-based diol (BPA-ea) in Example 1; Figure 3 . FTIR curve of aqueous polyurethane sizing agent (WPU-BPA-ea) in Example 1; Figure 4 . DSC curve of aqueous polyurethane sizing agent (WPU-BPA-ea) in Example 1; Figure 5 . Storage stability test chart of aqueous polyurethane sizing agent (WPU-BPA-ea) in Example 1; Figure 6 . SEM images of aramid fibers before and after sizing in Example 1 ((a) aramid fibers before sizing, (b) aramid fibers after sizing); Figure 7 . Comparison of stress-strain curves of sized and unsized aramid fiber composites in Example 1; Figure 8 . Comparison of tensile strength and tensile modulus of sized and unsized aramid fiber composites in Example 1. Detailed implementation mode

[0016] The preferred embodiments of the present invention will be described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are only for the purpose of illustrating and explaining the present invention, and are not intended to limit the present invention.

[0017] Example 1 A continuous aramid fiber reinforced epoxy resin composite and its preparation method, comprising the following steps: S1. Preparation of benzoxazine-based diol: 6.85 g of bisphenol A, 3.67 g of ethanolamine and 3.96 g of paraformaldehyde were added to a three-necked flask equipped with a stirrer, a thermometer and a glass bottle stopper, 40 mL of 1,4-dioxane was added, and the mixture was heated to 105 °C and reacted for 12 h. After the reaction, a diphenol with a benzoxazine structure (BPA-ea) was obtained through post-treatment. The reaction equation is as follows: Figure 1 . Figure 2 are respectively the FTIR spectrum and DCS curve of benzoxazine-based diol (BPA-ea) in Example 1. As can be seen from Figure 1 . 3342 cm -1 is the characteristic peak of -OH, 937 cm -1 is the characteristic peak of the oxazine ring, 1037 cm -1 and 1231 cm -1 are the characteristic peaks of C-O-C, 1187 cm -1is the C-N-C characteristic peak, 2962 cm -1 and 2886 cm -1 are the characteristic peaks of -CH3 and -CH2; It can be seen from Figure 2 that the curing temperature is about 244 °C. Combining the FTIR and DSC graphs, it is proved that the benzoxazine-based diol (BPA-ea) has been successfully prepared; Preparation of the benzoxazine-containing aqueous polyurethane emulsion sizing agent: Under N2 protection, 6.67 g of isophorone diisocyanate, 7.8 g of polytetrahydrofuran diol (molecular weight 1000), and 1.05 g of 2,2-dimethylolpropionic acid were added to a three-necked flask equipped with a stirrer and a glass bottle stopper, and evenly mixed; After adding 22.5 μL of dibutyltin dilaurate, the temperature was raised to 70 °C and reacted for 2 h under an N2 atmosphere; 4.06 g of BPA-ea was added to the mixed solution and reacted at 60 °C for 2 h; 0.9 mL of triethylamine was added to the round-bottom flask and reacted at 40 °C for 30 min; 100 mL of deionized water was added to the system, and an aqueous polyurethane emulsion was obtained after high-speed dispersion. The reaction equation is as follows: Figure 3 、 Figure 4 are the FTIR spectrum and DCS curve of polyurethane (WPU-BPA-ea) in Example 1 respectively. It can be seen from Figure 1 that 3323 cm -1 and 1548 cm -1 are the N-H characteristic peaks in the amide group, 1710 cm -1 is the C=O characteristic peak in the amide group, 956 cm -1 is the oxazine ring characteristic peak, 1046 cm -1 and 1243 cm -1 are the C-O-C characteristic peaks, 1109 cm -1 is the C-N-C characteristic peak, 2936 cm -1 and 2858 cm -1 are the characteristic peaks of -CH3 and -CH2; It can be seen from Figure 2 that the curing temperature is about 220 °C. Combining the FTIR and DSC graphs, it is proved that polyurethane (WPU-BPA-ea) has been successfully prepared; Figure 5 is the storage stability test chart of the aqueous polyurethane emulsion (WPU-BPA-ea) in Example 1. The above-prepared polyurethane emulsion (WPU-BPA-ea) was centrifuged at 3000 rpm for 15 min under test conditions to simulate storage stability. The results showed that there was no sedimentation phenomenon in the polyurethane emulsion after centrifugation, indicating a storage stability period of at least 6 months; S3. Preparation of continuous aramid fiber reinforced epoxy resin composite material: At room temperature, spray the waterborne polyurethane emulsion on the cleaned aramid II fiber, and then remove the solvent at 80 °C to obtain the sized aramid fiber; then at room temperature, impregnate the sized aramid fiber with the epoxy component evenly, and then place it in a mold and heat and cure it in a hot press to obtain an aramid fiber composite board. The mass fraction ratio of the aramid II fiber, epoxy resin and sizing agent is 30% : 68% : 2%. The curing process is stage curing, and the curing process is 120 °C / 1 h, 150 °C / 1 h, 180 °C / 1 h, 220 °C / 2 h, and the pressure is 8 MPa. At the same time, impregnate the unsized aramid fiber with the epoxy component and prepare a blank control group according to the above process.

[0018] Figure 6 Figures are SEM images of unsized aramid fiber and aramid fiber sized with polyurethane emulsion. Figure (a) is the aramid fiber before sizing, and Figure (b) is the aramid fiber after sizing. By comparing the two figures, it can be clearly seen that polyurethane is evenly attached to the surface of the sized aramid fiber, and the surface roughness increases, which is not only beneficial to the formation of mechanical meshing and chemical bonding between the aramid fiber and the resin matrix, but also can improve the interfacial bonding performance between the two; Figure 7 and Figure 8 are respectively the stress-strain curve, tensile strength and tensile modulus comparison diagrams of sized and unsized aramid fiber composites. The data in the figure show that compared with the unsized aramid fiber composite material (control group), the tensile strength of the aramid fiber composite material treated with polyurethane sizing increases by 75 MPa, and the tensile modulus increases by 1,003 MPa; it shows that sizing the aramid fiber with polyurethane emulsion can effectively improve the formation of mechanical meshing and chemical bonding between the aramid fiber and the resin matrix, and also significantly improves the interfacial bonding performance between the two.

[0019] Example 2 A continuous aramid fiber reinforced epoxy resin composite material and its preparation method, comprising the following steps: S1. Preparation of the benzoxazine-based diol is the same as that in Example 1; S2. Preparation of benzoxazine-containing aqueous polyurethane emulsion sizing agent: Under N2 protection, 7.86 g of 4,4'-dicyclohexylmethane diisocyanate, 12 g of polycarbonate diol (molecular weight 2000), and 1.05 g of 2,2-dimethylolpropionic acid were added to a three-necked flask equipped with a stirrer and a glass stopper and mixed evenly; after adding 22.5 μL of dibutyltin dilaurate, the temperature was raised to 70 °C and reacted for 2 h under a N2 atmosphere; 4.06 g of BPA-ea was added to the mixed solution and reacted at 60 °C for 2 h; 0.9 mL of triethylamine was added to the round-bottom flask and reacted at 40 °C for 30 min; 100 mL of deionized water was added to the system, and an aqueous polyurethane emulsion was obtained after high-speed dispersion. The reaction equation is as follows: S3. Preparation of continuous aramid fiber-reinforced epoxy resin composite: At room temperature, the aqueous polyurethane emulsion was sprayed on the cleaned aramid II fibers, and then the solvent was removed at 100 °C to obtain sized aramid fibers; then at room temperature, the sized aramid fibers were impregnated evenly with the epoxy component, and then placed in a mold and heated and cured in a hot press to obtain an aramid fiber composite board. The mass fraction ratio of the aramid II fibers, epoxy resin, and sizing agent is 50%: 46%: 4%. The curing process is stage curing, and the curing process is 120 °C / 1 h, 150 °C / 1 h, 180 °C / 1 h, 220 °C / 2 h.

[0020] Example 3 A continuous aramid fiber-reinforced epoxy resin composite and its preparation method, comprising the following steps: S1. Preparation of benzoxazine-based diol: 10.1 g of bisphenol AF, 3.67 g of ethanolamine, and 3.96 g of paraformaldehyde were added to a three-necked flask equipped with a stirrer, a thermometer, and a glass stopper, 40 mL of toluene was added, and the mixture was heated to 110 °C and reacted for 10 h. After the reaction, it was washed with deionized water and dried to obtain a benzoxazine-structured diphenol (BPAF-ea). The reaction equation is as follows: S2. Preparation of benzoxazine-containing aqueous polyurethane emulsion sizing agent: Under N2 protection, 6.67 g of isophorone diisocyanate, 7.8 g of polytetrahydrofuran diol (molecular weight 1000), and 1.05 g of 2,2-dimethylolpropionic acid were added to a three-necked flask equipped with a stirrer and a glass stopper, and evenly mixed; after adding 22.5 μL of dibutyltin dilaurate, under N2 atmosphere, the temperature was raised to 70 °C and reacted for 2 h; 5.58 g of BPAF-ea was added to the mixed solution and reacted at 60 °C for 2.5 h; 0.9 mL of triethylamine was added to the round-bottom flask and reacted at 40 °C for 30 min; 100 mL of deionized water was added to the system, and an aqueous polyurethane emulsion was obtained after high-speed dispersion. The reaction equation is as follows: S3. Preparation of continuous aramid fiber reinforced epoxy resin composite is the same as that in Example 1.

[0021] Example 4 A continuous aramid fiber reinforced epoxy resin composite and its preparation method, comprising the following steps: S1. Preparation of benzoxazine-based diol is the same as that in Example 3; S2. Preparation of benzoxazine-containing aqueous polyurethane emulsion sizing agent: Under N2 protection, 7.86 g of 4,4'-diisocyanatodicyclohexylmethane, 12 g of polycarbonate diol (molecular weight 2000), and 1.05 g of 2,2-dimethylolpropionic acid were added to a three-necked flask equipped with a stirrer and a glass stopper, and evenly mixed; after adding 22.5 μL of dibutyltin dilaurate, under N2 atmosphere, the temperature was raised to 80 °C and reacted for 2 h; 5.58 g of BPAF-ea was added to the mixed solution and reacted at 60 °C for 2.5 h; 0.9 mL of triethylamine was added to the round-bottom flask and reacted at 30 °C for 30 min; 100 mL of deionized water was added to the system, and an aqueous polyurethane emulsion was obtained after high-speed dispersion. The reaction equation is as follows: S3. Preparation of continuous aramid fiber reinforced epoxy resin composite is the same as that in Example 3.

[0022] Example 5 A continuous aramid fiber reinforced epoxy resin composite and its preparation method, comprising the following steps: S1. Preparation of benzoxazine-based diol is the same as that in Example 3; S2. Preparation of benzoxazine-containing aqueous polyurethane emulsion sizing agent: Under N2 protection, 6.67 g of isophorone diisocyanate, 12 g of polycarbonate diol (molecular weight 2000), and 1.05 g of 2,2-dimethylolpropionic acid were added to a three-necked flask equipped with a stirrer and a glass stopper, and uniformly mixed; after adding 22.5 μL of dibutyltin dilaurate, the temperature was raised to 70 °C and reacted for 2 h under N2 atmosphere; 5.58 g of BPAF-ea was added to the mixed solution and reacted at 60 °C for 2.5 h; 0.9 mL of triethylamine was added to the round-bottom flask and reacted at 30 °C for 30 min; 100 mL of deionized water was added to the system, and an aqueous polyurethane emulsion was obtained after high-speed dispersion. The reaction equation is as follows: S3. The preparation of continuous aramid fiber-reinforced epoxy resin composite is the same as that in Example 3.

[0023] In summary, in the present invention, the aqueous polyurethane of benzoxazine is used as a sizing agent to modify aramid fibers. Through the cross-linking reaction between the ring-opening curing of benzoxazine and aramid fibers and epoxy resin, the interfacial interaction between the fibers and the resin matrix is enhanced, the mechanical properties are improved, and the application range of aramid fiber epoxy resin composites is further expanded.

[0024] The above are only the preferred embodiments of the present invention, and do not limit the present invention in any form. Although the present invention has been disclosed above with the preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some changes or modifications to the above-disclosed technical content to obtain equivalent embodiments with equivalent changes, but as long as the content does not depart from the technical solution of the present invention, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A continuous aramid fiber reinforced epoxy resin composite material and a preparation method thereof, characterized in that, The composite material is obtained by heat curing continuous aramid fibers modified with a benzoxazine-containing aqueous polyurethane emulsion sizing agent and epoxy resin. The aramid fibers, sizing agent, and epoxy resin are cured in a mass fraction ratio of 30% - 70% : 0.1% - 5% : 30% - 70%.

2. A continuous aramid fiber reinforced epoxy resin composite material and a preparation method thereof according to claim 1, characterized in that, The benzoxazine-containing aqueous polyurethane emulsion sizing agent is formed by reacting diisocyanate, long-chain diol, 2,2-dimethylolpropionic acid, benzoxazine-containing diol, and triethylamine in a molar ratio of 1 : 0.1 - 0.5 : 0.1 - 0.3 : 0.3 - 0.4 : 0.1 - 0.

3. The structural general formula is as follows: ； In the formula, the structure of R1 is one or more of the following: ； In the formula, the structure of R2 is one or more of the following: ； Among them, the value range of m is 1 - 20; In the formula, the structure of R3 is one or more of the following: 。 3. A continuous aramid fiber reinforced epoxy resin composite material and a preparation method thereof according to claim 1, characterized in that, The benzoxazine-containing diol is obtained by reacting diphenol, ethanolamine, and paraformaldehyde. The structure of the diphenol is as follows: 。 4. A continuous aramid fiber reinforced epoxy resin composite material and a preparation method thereof according to claim 1, wherein, The aramid fibers are selected from one or more of meta-aramid, Aramid II, Aramid III, Kevlar-29, Kevlar-49, Technora of Japan, and Terlon of Russia.

5. A continuous aramid fiber reinforced epoxy resin composite material according to claim 1 and a preparation method thereof, characterized in that, The epoxy resin is selected from one or more of bisphenol A epoxy resins with a polymerization degree of 4 - 10, glycidylamine epoxy resins (AG-80, MY-720), and alicyclic epoxy resins (TDE-85, ERL-4221); the curing agent is methyltetrahydrophthalic anhydride.

6. A continuous aramid fiber reinforced epoxy resin composite material according to claims 1-5 and a preparation method thereof, characterized in that, It includes the following steps: S1. Preparation of benzoxazine-containing diol: Add diphenol, ethanolamine, and paraformaldehyde in a molar ratio of 1 : 2 : 4.1 - 4.4 to a three-necked flask equipped with a stirrer, thermometer, and glass bottle stopper, mix evenly in toluene or 1,4-dioxane solvent, heat to 90 - 110 °C, react for 10 - 36 h. After the reaction, through post-treatment, a diphenol containing a benzoxazine structure is obtained; S2. Preparation of benzoxazine-containing aqueous polyurethane emulsion sizing agent: Under the protection of inert gas, add diisocyanate, long-chain diol, and 2,2-dimethylolpropionic acid to a three-necked flask equipped with a stirrer, thermometer, and glass bottle stopper. After mixing evenly, add dibutyltin dilaurate as a catalyst, react at 60 - 80 °C for 2 - 3 h, cool down to 50 - 70 °C, then add benzoxazine-based diol and react for 2 - 3 h. During this period, add acetone to reduce the viscosity. Subsequently, cool down to 25 - 40 °C, add triethylamine, react for 20 - 60 min, and then add deionized water. After high-speed dispersion, an aqueous polyurethane emulsion is obtained; among them, diisocyanate, long-chain diol, 2,2-dimethylolpropionic acid, benzoxazine-based diol, and triethylamine are added in a molar ratio of 1 : 0.1 - 0.5 : 0.1 - 0.3 : 0.3 - 0.4 : 0.1 - 0.3; S3. Preparation of continuous aramid fiber reinforced epoxy resin composite: At room temperature, spray the benzoxazine aqueous polyurethane emulsion sizing agent on the cleaned aramid fibers, and then dry the solvent at 80-120 °C to obtain sized aramid fibers; subsequently, uniformly impregnate the sized aramid fibers with the epoxy component at room temperature, then place them in a mold, and heat and cure at 120-240 °C and 5-20 MPa in a hot press for 6-10 h to obtain the composite material.

Images