Halogen-free flame-retardant benzoxazine-epoxy / aramid fiber composite material and preparation method thereof

Abstract

The invention discloses a halogen-free flame-retardant benzoxazine-epoxy / aramid fiber composite material and a preparation method thereof, and belongs to the technical field of polymer composite materials. The composite material is obtained by heating and curing main chain type phosphorus-containing benzoxazine, epoxy resin and aramid fiber according to the mass fraction ratio of (1%-50%): (40%-70%): (30%-70%); the main chain type phosphorus-containing benzoxazine is prepared by carrying out Mannich condensation reaction on phosphorus-containing diamine, bisphenol and paraformaldehyde according to the molar ratio of 1: 1: (4.1-4.4). According to the prepared composite material, main chain type phosphorus-containing benzoxazine modified epoxy resin serves as a matrix, the matrix and aramid fibers are subjected to heating curing to prepare the composite material, benzoxazine is crosslinked with the aramid fibers and the epoxy resin when subjected to ring opening polymerization, the interface bonding performance between the aramid fibers and the epoxy resin can be remarkably improved, and the composite material can be used for preparing the aramid fibers and the epoxy resin. The mechanical property of the composite material can be effectively improved; meanwhile, benzoxazine contains phosphorus, so that the flame retardant property of the composite material can be improved, and the application field of the aramid fiber composite material is expanded.

Description

Technical Field

[0001] The invention relates to the technical field of polymer composite materials, and in particular to a halogen-free flame-retardant benzoxazine-epoxy / aramid fiber composite material and a preparation method thereof. Background Art

[0002] Epoxy-aramid fiber composite materials have become core structural materials in cutting-edge fields such as aerospace, military equipment and new energy vehicles due to their light weight, high strength, high temperature resistance and excellent fatigue resistance. In the aviation field, this material is widely used in solid rocket engine casings, radar fairings, and load-bearing components such as aircraft main wings and flaps; in the military field, the specific modulus of the aramid-aluminum composite armor made of it is more than 10 times that of aluminum alloy, and the anti-ballistic performance is improved by 40%; in the field of new energy vehicles, the battery pack shell using this material can take into account both electromagnetic shielding and lightweight requirements. However, traditional epoxy-aramid composite materials show high heat release rate and high total heat release when burning, which easily leads to fire risks. Therefore, improving its flame retardant properties has become a hot topic of research.

[0003] Traditional flame retardant methods mainly use halogen flame retardants, such as bromine and chlorine. Although these flame retardants can improve the flame retardant properties of materials, they will release toxic halogenated gases, dioxins and other toxic substances when burned, causing serious harm to the environment and human health. Therefore, the development of halogen-free flame retardant composite materials has important practical significance.

[0004] Since benzoxazine contains N in its structure, the introduction of flame retardant elements (such as P, B, Si, S, etc.) into its molecular structure can achieve the effect of multi-element synergistic flame retardancy, and it can be used as a new type of halogen-free flame retardant. Phosphorus-containing benzoxazine has the advantages of environmental protection, high efficiency, and low toxicity. Using it to modify epoxy-aramid fiber composite materials can effectively improve the flame retardant properties of the material.

[0005] The present invention synthesizes a main chain phosphorus-containing benzoxazine from the perspective of molecular design, then mixes it with epoxy resin, and uses the resin system and aramid fiber to press into a composite material; when benzoxazine undergoes ring-opening polymerization, it cross-links with aramid fiber and epoxy resin, thereby enhancing the interfacial bonding force between aramid fiber and epoxy resin, thereby optimizing the comprehensive performance of the composite material. At the same time, due to the introduction of the main chain phosphorus-containing benzoxazine, the urgent demand for high-performance halogen-free flame-retardant composite materials in various fields can be met. Therefore, the material has broad application prospects in the fields of aerospace, electronic information, national defense and military industry, sports equipment, and automobile industry. Summary of the invention

[0006] The present invention mainly improves the interface bonding force between aramid fiber and matrix material and simultaneously improves the flame retardant performance of the composite material, and proposes a halogen-free flame retardant benzoxazine-epoxy / aramid fiber composite material and a preparation method thereof.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions: A halogen-free flame-retardant benzoxazine-epoxy / aramid fiber composite material, characterized in that the composite material is obtained by heating and curing a main chain type phosphorus-containing benzoxazine, an epoxy resin and an aramid fiber, wherein the mass fraction ratio of the main chain type phosphorus-containing benzoxazine, the epoxy resin and the aramid fiber is 1%~50%: 40%~70%: 30%~70%; the main chain type phosphorus-containing benzoxazine is prepared by a Mannich condensation reaction of a phosphorus-containing diamine, a dihydric phenol and polyformaldehyde in a molar ratio of 1:1:4.1~4.4, and the general structural formula is as follows: ; In the formula, R 1 The structure is one or more of the following: ; Among them, the value range of m is 1-40; In the formula, R 2 The structure is one or more of the following: .

[0008] Furthermore, the halogen-free flame-retardant benzoxazine-epoxy / aramid fiber composite material is characterized in that the aramid fiber is selected from one or more of meta-aramid, aramid II and aramid III.

[0009] Furthermore, the halogen-free flame-retardant benzoxazine-epoxy / aramid fiber composite material is characterized in that the epoxy resin is selected from one or more of bisphenol A epoxy resin, glycidylamine epoxy resin and alicyclic epoxy resin with a degree of polymerization of 4 to 10; and the curing agent is methyltetrahydrophthalic anhydride.

[0010] Furthermore, the method for preparing the halogen-free flame-retardant benzoxazine-epoxy / aramid fiber composite material is characterized by comprising the following steps: S1 Preparation of main chain phosphorus-containing benzoxazine: under the protection of inert gas, dihydric phenol, phosphorus-containing diamine and polyformaldehyde are added into a three-necked flask equipped with a stirrer, a thermometer and a condenser in a molar ratio of 1:1:4.1-4.4, and uniformly mixed in toluene, ethanol in a volume ratio of 2:1 or 1,4-dioxane solvent, heated to 90-110 °C for reaction for 10-36 h. After the reaction is completed, the main chain phosphorus-containing benzoxazine is obtained by post-treatment; S2 Preparation of benzoxazine-modified epoxy / aramid fiber composites: Main chain phosphorus-containing benzoxazine and epoxy resin are evenly mixed at room temperature, and then the resin system is evenly impregnated on the aramid fiber, wherein the mass fraction ratio of benzoxazine, epoxy resin and aramid fiber is 1%~50%: 40%~70%: 30%~70%. Then, it is placed in a mold and heated and cured at 120~240℃ and 5~20 MPa for 6~12 h to obtain a composite material.

[0011] Compared with the prior art, the present invention is beneficial in that: First, the present invention synthesizes a main-chain phosphorus-containing benzoxazine from the perspective of molecular design, which has the characteristics of PN synergistic flame retardancy, and modifies it into an epoxy-aramid fiber composite material. The obtained composite material has excellent halogen-free flame retardant properties, meets the requirements of green chemistry and sustainable development, and provides innovative solutions for safety upgrades in the fields of aerospace, electronic packaging, automotive industry, building materials, etc.

[0012] Secondly, the present invention uses a main-chain phosphorus-containing benzoxazine to modify the epoxy-aramid fiber composite material. When the temperature is increased and cured, the benzoxazine undergoes a ring-opening reaction and a cross-linking reaction with the benzene rings in the aramid fiber and the epoxy resin, which significantly improves the interfacial bonding force between the aramid fiber and the epoxy resin, thereby improving the overall performance and service life of the composite material.

[0013] Other advantages, objectives and features of the present invention will be embodied in part through the following description, and in part will be understood by those skilled in the art through study and practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 Implementation Case 1 Main Chain Phosphorus-containing Benzoxazine (BA-SSiO) main )’s FTIR curve; Figure 2 Implementation Case 1 Main Chain Phosphorus-containing Benzoxazine (BA-SSiO) main )of 1 H-NMR curve diagram; Figure 3 Implementation Case 1 Main Chain Phosphorus-containing Benzoxazine (BA-SSiO) main )’s DSC curve; Figure 4 . Implementation Case 1 Main Chain Phosphorus-containing Benzoxazine (BA-SSiO) main ) Stress-strain curve of modified epoxy-aramid fiber composite material; Figure 5 Implementation Case 1 Main Chain Phosphorus-containing Benzoxazine (BA-SSiO) main)Comparison of tensile strength and tensile modulus of modified epoxy-aramid fiber composites; Figure 6 Example 1: Vertical combustion diagram of main chain phosphorus-containing benzoxazine ((BA-SSiO)main) modified epoxy-aramid fiber composite material; Figure 7 Implementation Case 2 Main Chain Phosphorus-containing Benzoxazine (BA-SD230) main )’s FTIR curve; Figure 8 Implementation Case 2 Main Chain Phosphorus-containing Benzoxazine (BA-SD230) main )of 1 H-NMR curve diagram; Fig. 9 Implementation Case 2 Main Chain Phosphorus-containing Benzoxazine (BA-SD230) main )’s DSC curve. DETAILED DESCRIPTION

[0015] The preferred implementation cases of the present invention are described below in conjunction with the accompanying drawings. It should be understood that the preferred implementation cases described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0016] Implementation Case 1: A halogen-free flame-retardant benzoxazine-epoxy / aramid fiber composite material and a preparation method thereof, comprising the following steps: S1. Preparation of phosphorus-containing diamines: 2 Under protection, 6.81 g of pentaerythritol and 42.17 g of phosphorus oxychloride were added to a three-necked flask equipped with a stirrer, a thermometer, a condenser and a tail gas absorption device, heated to 110 °C, and reacted for 6 h. After the reaction, a structure containing phosphorus oxychloride at both ends (SPDPC) was obtained by post-treatment; then 5.94 g of SPDPC, 9.94 g of 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane and 5.5 mL of triethylamine were added to a three-necked flask equipped with a stirrer, a thermometer and a condenser, heated to 80 °C, and reacted for 8 h. After the reaction, a phosphorus-containing diamine (SSiO) was obtained by post-treatment. The reaction equation is as follows: ; S2. Preparation of main chain phosphorus-containing benzoxazine: 2 Under the protection of 1% paraformaldehyde, 2.28 g bisphenol A, 7.21 g phosphorus-containing diamine (SSiO) and 1.32 g paraformaldehyde were added into a three-necked flask equipped with a stirrer, a thermometer and a condenser, uniformly mixed in a solvent of toluene and ethanol with a volume ratio of 2:1, heated to 110 °C for 20 h, and after the reaction, the main chain phosphorus-containing benzoxazine (BA-SSiO) was obtained by post-treatment.main ), the reaction equation is as follows: ; Figure 1 , Figure 2 , Figure 3 They are main chain phosphorus-containing benzoxazine (BA-SSiO main ) of FTIR, 1 H-NMR and DSC spectra, by Figure 1 It can be seen that 916 cm -1 The characteristic peak of oxazine ring is 1074 cm -1 and 1224 cm -1 The characteristic peak of COC is 1178 cm -1 is the characteristic peak of CNC, 1313 cm -1 It is the characteristic peak of P=O, 1022 cm -1 is the characteristic peak of POC, 1121 cm -1 The characteristic peak of Si-O-Si is 966 cm -1 The characteristic peak of Si-O-Si is 2961 cm -1 and 2899 cm -1 -CH 3 、-CH 2 - characteristic peak; Figure 2 It can be seen that 4.61~4.68 ppm is N-CH 2 -O chemical shift, 3.83~3.98 ppm is Ar-CH 2 -N chemical shift, combined with FTIR and 1 H-NMR spectra can prove that the main chain phosphorus-containing benzoxazine (BA-SSiO main ) was successfully synthesized; Figure 3 for (BA-SSiO) main The DSC curve of the solidification peak is around 290 °C; S3. Preparation of benzoxazine-modified epoxy / polyester fiber composites: 30 wt.% of the main chain phosphorus-containing benzoxazine (BA-SSiO) main ) was mixed evenly with 70 wt.% of epoxy resin, and then the resin system was evenly impregnated on aramid II fiber, wherein the mass ratio of resin to aramid fiber was 60%:40%, and then placed in a mold and heated and cured in a hot press at 120~260 ℃ and 10 MPa for 10 h to obtain a composite material; at the same time, the aramid II fiber was impregnated with epoxy resin, and a blank control group was prepared according to the above process.

[0017] Figure 4 for Figure 5The stress-strain curve and tensile strength and tensile modulus comparison of benzoxazine-modified epoxy-aramid fiber composites are shown in the figure. The data in the figure show that the main chain phosphorus-containing benzoxazine (BA-SSiO main ) modified aramid fiber composite material (AFRP-Bz) has a tensile strength increased by 80 MPa and a tensile modulus increased by 869 MPa compared to the unmodified aramid fiber composite material (AFRP); this indicates that the use of main chain phosphorus-containing benzoxazine modified epoxy-aramid fiber composite materials can effectively improve the mechanical meshing and chemical bonding between aramid fiber and resin matrix, and also significantly improve the interfacial bonding performance between the two. Figure 6 Main chain phosphorus-containing benzoxazine (BA-SSiO main ) vertical combustion diagram of modified aramid fiber composite material (AFRP-Bz). It can be seen from the figure that the first ignition is 10 s and the fire is extinguished 4 s away from the fire source. At the same time, the second ignition is 10 s and the fire is extinguished 3 s away from the fire source without any material dripping, so it is UL94 V-0 flame retardant.

[0018] Implementation Case 2: A halogen-free flame-retardant benzoxazine-epoxy / aramid fiber composite material and a preparation method thereof, comprising the following steps: S1. Preparation of phosphorus-containing diamine: The preparation of SPDPC is the same as that of Example 1; 5.94 g of SPDPC, 9.2 g of polyetheramine D230 and 5.5 mL of triethylamine are added to a three-necked flask equipped with a stirrer, a thermometer and a condenser, heated to 80 °C, and reacted for 8 h. After the reaction is completed, phosphorus-containing diamine (SD230) is obtained by post-treatment. The reaction equation is as follows: ; S2. Preparation of main chain phosphorus-containing benzoxazine: 2 Under the protection of 1% paraformaldehyde, 2.28 g bisphenol A, 6.83 g phosphorus-containing diamine (SD230) and 1.32 g paraformaldehyde were added into a three-necked flask equipped with a stirrer, a thermometer and a condenser, uniformly mixed in a solvent of toluene and ethanol with a volume ratio of 2:1, heated to 110 °C for 20 h, and after the reaction, the main chain phosphorus-containing benzoxazine (BA-SD230) was obtained by post-treatment. main ), the reaction equation is as follows: ; Figure 7 , Figure 8 , Fig. 9 They are respectively main chain phosphorus-containing benzoxazine (BA-SD230) main ) of FTIR, 1 H-NMR and DSC spectra, by Figure 7 It can be seen that 921 cm -1The characteristic peak of oxazine ring is 1084 cm -1 and 1228 cm -1 The characteristic peak of COC is 1187 cm -1 is the characteristic peak of CNC, 1313 cm -1 It is the characteristic peak of P=O, 1022 cm -1 is the characteristic peak of POC, 2971 cm -1 and 2894 cm -1 -CH 3 、-CH 2 - characteristic peak; Figure 8 It can be seen that 4.61~4.63 ppm is N-CH 2 -O chemical shift, 3.86~3.95 ppm is the Ar-CH 2 -N chemical shift, combined with FTIR and 1 H-NMR spectra can prove that the main chain phosphorus-containing benzoxazine (BA-SSiO main ) was successfully synthesized; Fig. 9 For (BA-SD230) main The DSC curve of the solidification peak is around 270 °C; S3. Preparation of benzoxazine-modified epoxy / polyester fiber composites: 30 wt.% of the main chain phosphorus-containing benzoxazine (BA-SD230) main ) was mixed evenly with 70 wt.% of epoxy resin, and then the resin system was evenly impregnated on aramid II fiber, wherein the mass ratio of resin to aramid fiber was 60%:40%. Then it was placed in a mold and heated and cured in a hot press at 120~260 ℃ and 10 MPa for 8 h to obtain a composite material.

[0019] Implementation Case 3: A halogen-free flame-retardant benzoxazine-epoxy / aramid fiber composite material and a preparation method thereof, comprising the following steps: S1. Preparation of phosphorus-containing diamine: The preparation of SPDPC is the same as that of Example 1; 5.94 g of SPDPC, 6.89 g of decanediamine and 5.5 mL of triethylamine are added to a three-necked flask equipped with a stirrer, a thermometer and a condenser, heated to 50 °C, and reacted for 6 h. After the reaction is completed, phosphorus-containing diamine (SDDA) is obtained by post-treatment. The reaction equation is as follows: ; S2. Preparation of main chain phosphorus-containing benzoxazine: 2Under the protection of 1% paraformaldehyde, 2.28 g bisphenol A, 5.69 g phosphorus-containing diamine (SDDA) and 1.32 g paraformaldehyde were added into a three-necked flask equipped with a stirrer, a thermometer and a condenser, uniformly mixed in a solvent of toluene and ethanol with a volume ratio of 2:1, heated to 110 °C for 20 h, and after the reaction, the main chain phosphorus-containing benzoxazine (BA-ESiO) was obtained by post-treatment. main ), the reaction equation is as follows: ; S3. Preparation of benzoxazine-modified epoxy / polyester fiber composites: 40 wt.% of the main chain phosphorus-containing benzoxazine (BA-SDDA) main ) was mixed evenly with 60 wt.% of epoxy resin, and then the resin system was evenly impregnated on aramid II fiber, wherein the mass ratio of resin to aramid fiber was 60%:40%. Then, it was placed in a mold and heated and cured in a hot press at 120~240 ℃ and 10 MPa for 12 h to obtain a composite material.

[0020] Implementation Case 4: A halogen-free flame-retardant benzoxazine-epoxy / aramid fiber composite material and a preparation method thereof, comprising the following steps: S1. Preparation of phosphorus-containing diamine: The preparation of SPDPC is the same as that of Example 1; 5.66 g of SPDPC, 16 g of polyetheramine D400 and 5.5 mL of triethylamine are added to a three-necked flask equipped with a stirrer, a thermometer and a condenser, heated to 80 °C, and reacted for 6 h. After the reaction is completed, phosphorus-containing diamine (SD400) is obtained by post-treatment; S2. Preparation of main chain phosphorus-containing benzoxazine: 2 Under the protection of 1% paraformaldehyde, 2.28 g bisphenol S, 7.07 g phosphorus-containing diamine (SD400) and 1.32 g paraformaldehyde were added into a three-necked flask equipped with a stirrer, a thermometer and a condenser, uniformly mixed in a solvent of toluene and ethanol with a volume ratio of 2:1, heated to 110 °C for 20 h, and after the reaction, the main chain phosphorus-containing benzoxazine (BS-SD400) was obtained by post-treatment. main ), the reaction equation is as follows: ; S3. Preparation of benzoxazine-modified epoxy / polyester fiber composites: 35 wt.% of main chain phosphorus-containing benzoxazine (BS-SD400) main ) was mixed evenly with 65 wt.% of epoxy resin, and then the resin system was evenly impregnated on aramid II fiber, wherein the mass ratio of resin to aramid fiber was 55%:45%. Then, it was placed in a mold and heated and cured in a hot press at 120~260 ℃ and 10 MPa for 10 h to obtain a composite material.

[0021] Implementation Case 5: A halogen-free flame-retardant benzoxazine-epoxy / aramid fiber composite material and a preparation method thereof, comprising the following steps: S1. Preparation of phosphorus-containing diamine: Same as Example 1 S2. Preparation of main chain phosphorus-containing benzoxazine: 2 Under the protection of 1% paraformaldehyde, 2.5 g bisphenol S, 7.21 g phosphorus-containing diamine (SSiO) and 1.32 g paraformaldehyde were added into a three-necked flask equipped with a stirrer, a thermometer and a condenser, uniformly mixed in a solvent of toluene and ethanol with a volume ratio of 2:1, heated to 110 °C for 20 h, and after the reaction, the main chain phosphorus-containing benzoxazine (BS-SSiO) was obtained by post-treatment. main ), the reaction equation is as follows: ; S3. Preparation of benzoxazine-modified epoxy / polyester fiber composites: 45 wt.% of the main chain phosphorus-containing benzoxazine (BS-SSiO) main ) was mixed evenly with 55 wt.% of epoxy resin, and then the resin system was evenly impregnated on aramid II fiber, wherein the mass ratio of resin to aramid fiber was 55%:45%. Then it was placed in a mold and heated and cured in a hot press at 120~260 ℃ and 10 MPa for 12 h to obtain a composite material.

[0022] In summary, the present invention synthesizes main chain phosphorus-containing benzoxazines with different structures from the perspective of molecular design, and then presses the resin system mixed with epoxy resin and aramid fiber into a composite material; the benzoxazines undergo ring-opening polymerization and cross-link with aramid fiber and epoxy resin, thereby enhancing the interfacial bonding force between the aramid fiber and the epoxy resin, thereby optimizing the comprehensive performance of the composite material; at the same time, due to the introduction of the main chain phosphorus-containing benzoxazines, the urgent needs of various fields for high-performance halogen-free flame-retardant composite materials can be met, and the application scope of aramid fiber epoxy resin composite materials is further expanded.

[0023] The above is only a preferred implementation case of the present invention, and does not constitute any form of limitation to the present invention. Although the present invention has been disclosed as a preferred implementation case as above, it is not used to limit the present invention. Any technician familiar with this profession can make some changes or modifications to equivalent implementation cases with equivalent changes by using the technical contents disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modification, equivalent change and modification made to the above implementation cases based on the technical essence of the present invention without departing from the content of the technical solution of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A halogen-free flame-retardant benzoxazine-epoxy / aramid fiber composite material, characterized in that: The composite material is obtained by heating and curing a main chain type phosphorus-containing benzoxazine, an epoxy resin and an aramid fiber, wherein the mass fraction ratio of the main chain type phosphorus-containing benzoxazine, the epoxy resin and the aramid fiber is 1%-50%: 40%-70%: 30%-70%; the main chain type phosphorus-containing benzoxazine is prepared by a Mannich condensation reaction of a phosphorus-containing diamine, a dihydric phenol and polyformaldehyde in a molar ratio of 1:1:4.1-4.4, and the general structural formula is as follows: ； In the formula, the structure of R1 is one or more of the following: ； Among them, the value range of m is 1-40; In the formula, the structure of R2 is one or more of the following: 。 2. A halogen-free flame-retardant benzoxazine-epoxy / aramid fiber composite material according to claim 1, characterized in that: The aramid fiber is selected from one or more of meta-aramid, aramid II and aramid III.

3. A halogen-free flame-retardant benzoxazine-epoxy / aramid fiber composite material according to claim 1, characterized in that: The epoxy resin is selected from one or more of bisphenol A epoxy resin, glycidylamine epoxy resin and alicyclic epoxy resin with a polymerization degree of 4 to 10; the curing agent is methyltetrahydrophthalic anhydride.

4. A method for preparing a halogen-free flame-retardant benzoxazine-epoxy / aramid fiber composite material according to any one of claims 1 to 3, characterized in that: The following steps are involved: S1 Preparation of main chain phosphorus-containing benzoxazine: under the protection of inert gas, dihydric phenol, phosphorus-containing diamine and polyformaldehyde are added into a three-necked flask equipped with a stirrer, a thermometer and a condenser in a molar ratio of 1:1:4.1-4.4, and uniformly mixed in toluene, ethanol in a volume ratio of 2:1 or 1,4-dioxane solvent, heated to 90-110 °C for reaction for 10-36 h. After the reaction is completed, the main chain phosphorus-containing benzoxazine is obtained by post-treatment; S2 Preparation of benzoxazine-modified epoxy / aramid fiber composites: Main chain phosphorus-containing benzoxazine and epoxy resin are evenly mixed at room temperature, and then the resin system is evenly impregnated on the aramid fiber, wherein the mass fraction ratio of benzoxazine, epoxy resin and aramid fiber is 1%~50%: 40%~70%: 30%~70%. Then, it is placed in a mold and heated and cured at 120~240 ℃ and 5~20 MPa for 6~12 h to obtain a composite material.

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