Method for preparing epoxy resin system with liquid oxygen compatibility based on phosphorus-containing curing agent

Abstract

The invention discloses a method for preparing an epoxy resin system with liquid oxygen compatibility based on a phosphorus-containing curing agent, and belongs to the technical field of chemical engineering and materials. A structure containing a P element and an active amino group is introduced at the same time and can react with epoxy resin in one step and be cured, so that the prepared epoxy resin system has liquid oxygen compatibility, the strength of the epoxy resin can be kept, and the toughness is improved. The preparation method comprises the following steps: reacting 10-(2, 5-dihydroxyphenyl)-10-hydrogen-9-oxa-10-phosphaphenanthrene-10-oxide (ODOPB) with nitro halide, and introducing amino through reduction of iron powder / HCl, so as to obtain a phosphorus-containing epoxy cross-linking agent taking the amino as an active group; the epoxy resin system with liquid oxygen compatibility can be obtained, has a wide application prospect in the field of aerospace, and particularly can be used for heavy rocket storage tanks and liquid oxygen storage tanks.

Description

Technical Field

[0001] The present invention relates to a method for preparing a liquid oxygen compatible epoxy resin system based on a phosphorus-containing curing agent, belonging to the technical fields of chemical engineering and materials. Background Art

[0002] Highly stable, lightweight and fully functional structural components are crucial in many space missions. As the main transportation tool for deep space, the liquid oxygen (LOX) and liquid hydrogen storage tanks of the key power system of a heavy-lift launch vehicle account for 60% of the total weight of the rocket. And as the main weight-reducing component, the lightweight development of the storage tank has become a top priority.

[0003] Statistics show that compared with traditional aluminum alloy storage tanks, liquid oxygen storage tanks made of carbon fiber reinforced resin matrix composites (CFRE), such as carbon fiber reinforced epoxy resin composites (CFRP), can reduce the weight by 27 - 35% and save 25% of the cost. Although CFRP combines the high strength and high stiffness characteristics of carbon fiber and the good adhesiveness and chemical resistance of epoxy resin, its compatibility with liquid oxygen is poor, and it will cause combustion and even explosion under external energy stimulation, which seriously hinders the application of CFRP in a liquid oxygen environment (90K). Therefore, improving the liquid oxygen compatibility of epoxy resin matrix and carbon fiber reinforced composites is the key problem to be solved at present.

[0004] At present, the methods for improving the liquid oxygen compatibility of epoxy resin in China are complex and not environmentally friendly. The literature (Zhou Z, Qian J, Zhang J, et al. Phosphorus and bromine modified epoxy resin with enhanced cryogenic mechanical properties and liquid oxygen compatibility simultaneously[J]. Polymer Testing, 2021, 94:107051.) uses halogenated substances to modify epoxy resin. For the epoxy resin system modified with phosphorus alone and the synergistic modification of phosphorus and bromine, the impact sensitivity is 20% and 5% respectively. The addition of bromine significantly reduces the impact sensitivity, but there are still flash and carbonization phenomena in this technical solution. Secondly, the introduction of halogen atoms is also not conducive to environmental protection.

[0005] The literature (Li J, Liu X, Wu Z, et al. The effect of 10-(2,5-dihydroxyphenyl)-9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide on liquid oxygen compatibility and cryogenic mechanical properties of epoxy resins[J]. High Performance Polymers, 2016, 28(7):820-830.) used phosphorus-based substances to modify epoxy resins and flame retardant monomers (DOPO) or (ODOPB) to prepare epoxy resins with liquid oxygen compatibility. 10-(2,5-Dihydroxyphenyl)-9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (ODOPB) was used to modify bisphenol A and bisphenol F epoxy resins respectively to obtain a series of epoxy resins with liquid oxygen compatibility. This technical solution prepared modified epoxy resin monomers through the high-temperature polymerization reaction of the O-H bond in ODOPB with the epoxy group. After that, a curing agent still needed to be added for further reaction to form an epoxy resin system with liquid oxygen compatibility. The preparation process was cumbersome and the temperature requirement was relatively high.

[0006] The literature (Wang Ge. Research on polymers and their composites compatible with liquid oxygen[D]. National University of Defense Technology, 2005.) used polymers to modify epoxy resins and selected diaminodiphenyl sulfone (DDS) and bisphenol A cyanate ester (CE) as epoxy resin crosslinking agents respectively. Although the impact sensitivities were 5% and 3% respectively, the epoxy resins prepared with the two crosslinking agents still belonged to the liquid oxygen incompatible system.

[0007] Patents CN109721711A and CN116515247B prepared modified epoxy resin monomers through the high-temperature polymerization reaction of the P-H or O-H bond in ODOPB or DOPO with the epoxy group. After that, a curing agent or a modified curing agent still needed to be added for further reaction to form an epoxy resin system with liquid oxygen compatibility. The preparation process was cumbersome and the temperature requirement was relatively high.

[0008] In summary, to prepare an epoxy resin system with liquid oxygen compatibility and certain strength and toughness, and to apply it as the matrix of carbon fiber reinforced composites in the aviation field while ensuring a simple operation process and cost savings is an urgent problem to be solved at present. Summary of the Invention

[0009] To solve the above problems, the present invention simultaneously introduces a structure containing P element and active amino group, which can react and cure with epoxy resin in one step, enabling the prepared epoxy resin system to have liquid oxygen compatibility while maintaining the strength of epoxy resin and improving toughness. The present invention uses 10-(2,5-dihydroxyphenyl)-10H-9-oxa-10-phosphaphenanthrene-10-oxide (ODOPB) to react with nitro halide, and introduces an amino group through reduction with iron powder / HCl, obtaining a phosphorus-containing epoxy crosslinking agent with amino group as the active group; a liquid oxygen-compatible epoxy resin system can be obtained, which has broad application prospects in the aerospace field, especially can be used for heavy rocket storage tanks and liquid oxygen storage tanks.

[0010] The first object of the present invention is to provide a method for preparing an epoxy resin composite material with both liquid oxygen compatibility and mechanical properties, and the method includes the steps:

[0011] (1) Mix 10-(2,5-dihydroxyphenyl)-10H-9-oxa-10-phosphaphenanthrene-10-oxide, fluoronitrobenzene, cesium fluoride and N,N-dimethylacetamide, stir, heat, cool, precipitate, and filter to obtain a filtered product; the filtered product is recrystallized in acetic anhydride, filtered and dried to obtain a nitro compound;

[0012] (2) Mix hydrochloric acid and absolute ethanol to obtain solution A; mix the nitro compound, reduced iron and N,N-dimethylacetamide to obtain solution B; add solution B to solution A, stir, filter and recrystallize to obtain a phosphorus-containing curing agent;

[0013] (3) Mix epoxy resin, the phosphorus-containing curing agent and diaminodiphenylmethane (DDM), heat and mix evenly to obtain an epoxy resin composite material with improved liquid oxygen compatibility and mechanical properties.

[0014] In one embodiment, the dosage ratio of 10-(2,5-dihydroxyphenyl)-10H-9-oxa-10-phosphaphenanthrene-10-oxide, fluoronitrobenzene, cesium fluoride and N,N-dimethylacetamide in step (1) is 1-5 g: 1-5 g: 0.5-5 g: 50-100 mL;

[0015] The heating in step (1) is stirring at 120-160 °C for 8-12 h at 300-500 rpm.

[0016] Optionally, the dosage ratio of 10-(2,5-dihydroxyphenyl)-10H-9-oxa-10-phosphaphenanthrene-10-oxide, fluoronitrobenzene, cesium fluoride and N,N-dimethylacetamide is 1-1.2 g: 1-1.2 g: 1-1.2 g: 80-100 mL.

[0017] In one embodiment, the volume ratio of hydrochloric acid to absolute ethanol in step (2) is 10 - 80:10 - 80;

[0018] In step (2), the dosage ratio of the nitro compound, reduced iron, and N,N-dimethylacetamide is 2.5 - 10 g:1 - 5 g:50 - 100 mL.

[0019] Optionally, the volume ratio of hydrochloric acid to absolute ethanol is 10 - 15:70 - 80;

[0020] Optionally, the dosage ratio of the nitro compound, reduced iron, and N,N-dimethylacetamide is 3 - 5 g:1 - 3 g:150 - 200 mL.

[0021] In one embodiment, in step (2), the stirring is to stir for 10 - 30 min, then heat up to 50 - 75 °C and stir for 3 - 5 h, add ammonium hydroxide solution, and continue stirring for 30 min.

[0022] In one embodiment, the chemical structural formula of the phosphorus-containing curing agent prepared in step (2) is as follows:

[0023]

[0024] Among them, the R group is:

[0025] In one embodiment, the R group of the phosphorus-containing curing agent prepared in step (2) can also be:

[0026]

[0027] Preferably, the chemical structural formula of the phosphorus-containing curing agent prepared in step (2) is:

[0028]

[0029] In one embodiment, in step (3), the mass ratio of epoxy resin, phosphorus-containing curing agent, and diaminodiphenylmethane is 100 g:0 - 65 g:0 - 25 g.

[0030] Optionally, the mass ratio of epoxy resin, phosphorus-containing curing agent, and diaminodiphenylmethane is 100 g:16 g:19 g;

[0031] Optionally, the mass ratio of epoxy resin, phosphorus-containing curing agent, and diaminodiphenylmethane is 100 g:33 g:13 g;

[0032] Preferably, the mass ratio of epoxy resin, phosphorus-containing curing agent, and diaminodiphenylmethane is 100 g:49 - 65 g:0 - 6 g;

[0033] Preferably, the mass ratio of epoxy resin, phosphorus-containing curing agent and diaminodiphenylmethane is 100 g: 49 g: 6 g;

[0034] Preferably, the mass ratio of epoxy resin, phosphorus-containing curing agent and diaminodiphenylmethane is 100 g: 65 g: 0 g.

[0035] In one embodiment, the present invention also provides the use of the above-prepared phosphorus-containing curing agent (including phosphorus-containing curing agents with different R groups) in the preparation of epoxy resin composites having liquid oxygen compatibility and mechanical properties.

[0036] The second object of the present invention is to provide an epoxy resin composite prepared by the above method.

[0037] The third object of the present invention is to provide the use of any of the above methods or the above epoxy resin composites in the field of aerospace.

[0038] In one embodiment, the application includes using the epoxy resin composite to prepare rocket fuel tanks, such as liquid oxygen tanks and liquid hydrogen tanks.

[0039] The fourth object of the present invention is to provide a carbon composite material prepared from the above epoxy resin composite.

[0040] The fifth object of the present invention is to provide a method for simultaneously improving the liquid oxygen compatibility and mechanical properties of an epoxy resin composite based on a phosphorus-containing curing agent, the method comprising the steps of:

[0041] (1) Mix 10-(2,5-dihydroxyphenyl)-10H-9-oxa-10-phosphaphenanthrene-10-oxide, fluoronitrobenzene, cesium fluoride and N,N-dimethylacetamide, stir, heat, cool, precipitate, filter to obtain a filtered product; the filtered product is recrystallized in acetic anhydride, filtered and dried to obtain a nitro compound;

[0042] (2) Mix hydrochloric acid and absolute ethanol to obtain solution A; mix the nitro compound, reduced iron and N,N-dimethylacetamide to obtain solution B; add solution B to solution A, stir, filter and recrystallize to obtain a phosphorus-containing curing agent;

[0043] (3) Mix epoxy resin, phosphorus-containing curing agent and diaminodiphenylmethane, heat and mix evenly to obtain an epoxy resin composite having both liquid oxygen compatibility and mechanical properties.

[0044] In one embodiment, in step (1), the dosage ratio of 10-(2,5-dihydroxyphenyl)-10H-9-oxa-10-phosphaphenanthrene-10-oxide, fluoronitrobenzene, cesium fluoride and N,N-dimethylacetamide is 1-5 g: 1-5 g: 0.5-5 g: 50-100 mL;

[0045] In step (1), the heating is carried out with stirring at 300 - 500 rpm and 120 - 160 °C for 8 - 12 h.

[0046] Optionally, the dosage ratio of 10-(2,5-dihydroxyphenyl)-10H-9-oxa-10-phosphaphenanthrene-10-oxide, fluoronitrobenzene, cesium fluoride and N,N-dimethylacetamide is 1 - 1.2 g : 1 - 1.2 g : 1 - 1.2 g : 80 - 100 mL.

[0047] In one embodiment, the volume ratio of hydrochloric acid to absolute ethanol in step (2) is 10 - 80 : 10 - 80;

[0048] In step (2), the dosage ratio of the nitro compound, reduced iron and N,N-dimethylacetamide is 2.5 - 10 g : 1 - 5 g : 50 - 100 mL.

[0049] Optionally, the volume ratio of hydrochloric acid to absolute ethanol is 10 - 15 : 70 - 80;

[0050] Optionally, the dosage ratio of the nitro compound, reduced iron and N,N-dimethylacetamide is 3 - 5 g : 1 - 3 g : 150 - 200 mL.

[0051] In one embodiment, in step (2), the stirring is carried out for 10 - 30 min, then the temperature is raised to 50 - 75 °C and stirring is continued for 3 - 5 h, and then ammonium hydroxide solution is added and stirring is continued for 30 min.

[0052] In one embodiment, in step (3), the mass ratio of the epoxy resin, phosphorus-containing curing agent and diaminodiphenylmethane is 100 g : 0 - 65 g : 0 - 25 g.

[0053] In one embodiment, the epoxy resin in step (3) includes one or more of bisphenol A epoxy resin, hydrogenated bisphenol A epoxy resin, bisphenol F epoxy resin, bisphenol S epoxy resin, phenolic epoxy resin, aliphatic glycidyl ether epoxy resin, alicyclic epoxy resin.

[0054] In one embodiment, the active group of the phosphorus-containing curing agent in step (3) is an amino group, and it can be used alone as an epoxy curing agent without adding other curing agents.

[0055] Beneficial effects

[0056] The present invention prepares a novel phosphorus-containing compound as a curing agent for epoxy systems, which has both ODOPB flame-retardant segments and diamine functional groups for curing epoxy resins. A series of epoxy resin matrix systems with liquid oxygen compatibility are prepared, providing a new approach for the lightweight development of liquid oxygen storage tanks and enabling epoxy resin series to have broad application prospects in liquid oxygen storage tanks and cryogenic fields. Specifically, based on the liquid oxygen compatibility (IRS) of 0, the epoxy resin composites prepared by the present invention have a mechanical strength of over 81 MPa (up to 90 MPa) and a toughness of over 0.9 (up to 1.6 MPa·m 0.5 ). BRIEF DESCRIPTION OF THE DRAWINGS

[0057] Figure 1 1H NMR spectrum of the nitro compound 1 ;

[0058] Figure 2 1H NMR spectrum of the phosphorus-containing curing agent 1 . DETAILED DESCRIPTION OF THE INVENTION

[0059] The raw materials involved in the following examples are as follows

[0060] ODOPB: ≥98%, purchased from Shanghai Macklin Biochemical Co., Ltd., CAS No. 99208-50-1

[0061] Concentrated hydrochloric acid: 36 - 38% (v / v), purchased from Sinopharm Chemical Reagent Co., Ltd

[0062] Reduced iron: particle size of 100 nm, purchased from Shanghai Macklin Biochemical Co., Ltd

[0063] Ammonium hydroxide solution: 25 - 28% (v / v), purchased from Sinopharm Chemical Reagent Co., Ltd

[0064] Fluoronitrobenzene: purchased from Shanghai Macklin Biochemical Co., Ltd., CAS No. 350-46-9

[0065] Cesium fluoride: purchased from Shanghai Macklin Biochemical Co., Ltd., CAS No. 13400-13-0

[0066] N,N-dimethylacetamide: purchased from Shanghai Macklin Biochemical Co., Ltd., CAS No. 127-19-5

[0067] Diaminodiphenylmethane: purchased from Shanghai Aladdin Biochemical Technology Co., Ltd., CAS No. 101-77-9

[0068] Glycidyl ether epoxy resin (type E51): Nantong Xingchen Synthetic Materials Co., Ltd

[0069] Unless otherwise specified, the remaining raw materials were all purchased from Shanghai Macklin Biochemical Co., Ltd.

[0070] The resin systems involved in the following examples were subjected to performance tests:

[0071] 1. Liquid oxygen compatibility test method:

[0072] Referring to the American ASTM G86 standard, the liquid oxygen compatibility of the epoxy resin sample was determined using an XCM-120 mechanical impact sensitivity tester manufactured by Changchun Xinke Experimental Instrument and Equipment Co., Ltd.

[0073] The specific test process is as follows: First, place a circular sample with a diameter of about 19.5 mm and a thickness of 2 mm in the sample cup, and put the sample cup and the striker into a Dewar flask filled with liquid oxygen; when the temperature is the same (i.e., the liquid level no longer boils), take out the sample cup and the striker, install them in the base of the sample cup, and place them in the bottom groove of the mechanical impact test device; then continuously inject liquid oxygen into the sample cup. When the liquid oxygen in the cup no longer boils, release a 9.07 kg weight from a height of 1.1 m to impact the striker, and repeat this operation 20 times. Observe and record phenomena such as explosion, combustion, and sparks during the impact process, and at the same time check whether the sample is charred after the impact. For the sample with explosion, combustion, sparks, and charring phenomena. When there are no explosion, combustion, sparks, and charring phenomena during 20 consecutive mechanical impact processes, the material can be considered compatible with liquid oxygen; or if a phenomenon occurs once during 20 mechanical impact processes, but no phenomenon occurs in the subsequent 40 tests, the material can also be considered to pass the test.

[0074] The liquid oxygen compatibility test results were evaluated using the impact reaction sensitivity coefficient (IRS) to evaluate the response intensity between the material and liquid oxygen under mechanical impact. IRS can be calculated by the following formula:

[0075]

[0076] Among them, N is the total number of tests, and n i is the total number of sensitivity reactions. ω i is the weight coefficient, where ω1 (combustion) = 1, ω2 (explosion) = 0.9, ω3 (flashing) = 0.6, ω4 (carbonization) = 0.4, ω5 (no phenomenon) = 0.0.

[0077] 2. Strength test method:

[0078] The tensile properties of the resin were tested on a universal testing machine according to ASTM D638 standard.

[0079] 3. Toughness test method:

[0080] The fracture test was carried out in accordance with 《ASTM D5045-14 Standard Test Methods for Plane-Strain Fracture Toughness and Strain Energy Release Rate of Plastic Materials》 and was conducted by a three-point bending test. During the experiment, the span was taken as 40 mm, the loading rate was 1 mm / min, and the test samples needed to be prefabricated with cracks in advance. The length of the prefabricated crack accounted for 45% - 55% of the specimen width, and the number of valid data in each group was not less than 5. The fracture toughness (K IC ) is calculated by the following formula.

[0081]

[0082] Where: K IC is the fracture strength factor for evaluating the fracture toughness of the material, P m is the maximum force (N) at which the specimen fails, b is the width (mm) of the sample, d is the thickness (mm) of the specimen, a is the length (mm) of the prefabricated crack, and Y is the geometric correction factor.

[0083] Example 1: Preparation of epoxy resin composites

[0084] 1. A method for preparing an epoxy resin composite material with both liquid oxygen compatibility and mechanical properties, comprising the following steps:

[0085] (1) Preparation of nitro compound:

[0086] Add 10 g of 10-(2,5-dihydroxyphenyl)-10H-9-oxa-10-phosphaphenanthrene-10-oxide (ODOPB), 10 g of 1,4-fluoronitrobenzene, 10 g of cesium fluoride (CsF) and 200 mL of N,N-dimethylacetamide (DMAc) into a 500 mL three-necked flask, magnetically stir and mix at a rotation speed of 200 r / min, heat in an oil bath to 160 °C, reflux for 12 h, and then cool to room temperature; after cooling, pour it into a mixed solution of 500 mL of ethanol and water (V 乙醇 :V 水 = 1:2), wait for precipitation to occur, and then filter; the filter residue is dissolved in 30 mL of acetic anhydride at 130 °C and stirred for 30 min (rotation speed 200 r / min) for recrystallization. Wait for the filtrate to cool to room temperature and filter again. Dry the filtered precipitate in a vacuum oven for 12 h to obtain the nitro compound;

[0087] (2) Preparation of phosphorus-containing curing agent:

[0088] At room temperature, mix 11 mL of HCl and 75 mL of absolute ethanol to obtain solution A;

[0089] Add the nitro compound prepared in step (1) of 5 g, 2.8 g of reduced iron with a particle size of 100 nm (Shanghai Macklin Biochemical Co., Ltd., CAS: 7439-89-6), and 200 mL of DMAc into a three-necked flask, and stir and mix at a rotation speed of 600 r / min to obtain solution B;

[0090] Slowly add solution A to solution B, stir for 30 min, raise the temperature to 50 °C, continue to stir for 4 h, then add 11 mL of ammonium hydroxide solution thereto, and continue to stir for 30 min. At this time, the pH of the filtrate is 8-9; perform hot filtration, pour the filtrate into 500 mL of water for anti-solvent crystallization, then perform vacuum filtration, dissolve the filter cake in 20 mL of methanol (60 °C), stir for 30 min (rotation speed 200 r / min) for recrystallization. Wait for the filtrate to cool to room temperature, filter again, and vacuum dry for 12 h to obtain the phosphorus-containing curing agent;

[0091] (3) Preparation of epoxy resin composite

[0092] At 80 °C, according to the molar ratio of active hydrogen to epoxy value of 1:1. Add 65 g of the phosphorus-containing curing agent obtained in Example 1 to 100 g of glycidyl ether epoxy resin (model E51), heat to 80 °C, and stir (300 r / min) until the phosphorus-containing curing agent is completely dissolved to obtain a uniformly mixed resin glue, which is the epoxy resin composite for liquid oxygen compatible environment.

[0093] 2. Take the nitro compound and the phosphorus-containing curing agent obtained in 1 for NMR detection, and the results are as follows:

[0094] Figure 1 is the 1 1H NMR spectrum of the nitro compound; its NMR data are as follows:

[0095] 1H NMR(600MHz,DMSO-d6)δ8.32(d,J=8.7Hz,2H),8.19–8.07(m,2H),7.96(d,J=8.7Hz,2H),7.81(dd,J=14.2,3.1Hz,1H),7.70(dd,J=14.7,7.6Hz,1H),7.67–7.55(m,2H),7.44(td,J=7.5,2.7Hz,1H),7.33(t,J=6.9Hz,3H),7.28(q,J=8.2Hz,,2H),7.06(d,J=8.1Hz,1H),6.53(d,J=8.7Hz,2H)

[0096] The disappearance of the -OH proton peaks at 9.17 and 9.46 ppm (the positions of the hydroxyl peaks in ODOPB), while in H 29 -H28 and H 31 -H 32 Signals were observed at the position, representing the nitro position. The proton chemical shift adjacent to the nitro position (H 32 ) was the largest, at 8.32 ppm. On the contrary, the chemical shift of H 29 was the lowest, at 6.5 ppm. This was because of the shielding effect of oxygen on the adjacent hydrogen, indicating that the phosphorus-containing nitro compound was successfully prepared.

[0097] Figure 2 is the 1 1H NMR spectrum of the phosphorus-containing curing agent; its NMR data is as follows:

[0098] 1H NMR(600MHz,DMSO-d6)δ8.21–7.96(m,2H),7.69(dt,J=23.4,7.6Hz,2H),7.52(dt,J=9.3,4.6Hz,1H),7.45–7.31(m,2H),7.30–6.99(m,3H),6.79(d,J=8.3Hz,2H),6.61(dd,J=14.3,7.8Hz,3H),6.34(d,J=8.2Hz,2H),6.13(d,J=8.3Hz,2H),4.99(s,4H)

[0099] The proton peak representing NH2 appeared at 4.96 ppm. At the same time, due to the shielding effect of the electron-donating amino group, in the nitro compound, that is, the signals of H 32 and H 28 shifted from 8.3 and 7.9 ppm at low field to 6.6 and 6.1 ppm at high field respectively, indicating that the epoxy curing agent containing active amino groups was successfully prepared.

[0100] 3. The structural formula of the above-prepared phosphorus-containing curing agent is as follows:

[0101]

[0102] 4. Perform performance tests on the epoxy resin composite material prepared in 1 for a liquid oxygen-compatible environment. The test results are shown in Table 1:

[0103] Table 1 Performance test results

[0104]

[0105] Example 2: Change the dosage of the phosphorus-containing curing agent

[0106] At 80 °C, according to the molar ratio of active hydrogen to epoxy value of 1:1, the composition of the phosphorus-containing curing agent in Example 1 was adjusted as follows: 16 g of phosphorus-containing curing agent, 19 g of diaminodiphenylmethane (DDM), with a molar ratio of 25:75; 33 g of phosphorus-containing curing agent, 13 g of DDM, with a molar ratio of 50:50; 49 g of phosphorus-containing curing agent, 6 g of DDM, with a molar ratio of 75:25; 0 g of phosphorus-containing curing agent, 25 g of DDM, with a molar ratio of 0:100. The phosphorus-containing curing agent and DDM were blended with epoxy resin, and the rest was kept the same as in Example 1 to obtain a resin system for a liquid oxygen compatible environment.

[0107] The obtained epoxy resin system was subjected to performance testing, and the test results are as follows:

[0108] Table 2 Test Results

[0109]

[0110] Example 3

[0111] The structural formula of the phosphorus-containing curing agent in Example 1 was adjusted, specifically the R group in the following structure was adjusted, and the R group structure is shown in Table 3;

[0112] A resin system for a liquid oxygen compatible environment was prepared using phosphorus-containing compounds diphenylphosphine oxide, diphenyl phosphite, and 1,2-diphenylethyl phosphate, and the rest was kept the same as in Example 1. The method is as follows:

[0113] Using a four-necked round-bottom flask as the reaction vessel, temperature control, stirring, reflux and other equipment were installed, and 2.75 g of phosphorus-containing compounds were added. The phosphorus-containing compounds were diphenylphosphine oxide (CAS: 4559-70-0, purchased from Merck Life Science Co., Ltd.), diphenyl phosphite (CAS: 4712-55-4, purchased from Shanghai Macklin Biochemical Co., Ltd.), and 1,2-diphenylethyl phosphate (CAS: 17176-77-1, purchased from Shanghai Macklin Biochemical Co., Ltd.). The phosphorus-containing compounds were dissolved in 10 ml of tetrahydrofuran at 50 °C, and a solution of 1.2 g of p-benzoquinone (Sinopharm Chemical Reagent Co., Ltd.) in tetrahydrofuran (Sinopharm Chemical Reagent Co., Ltd.) was added. Nitrogen was passed to protect the reaction, and the reaction was carried out for 8 h to obtain the R structure monomer (Table 3) in the corresponding phosphorus-containing curing agent structure. The other processes were kept the same as in Example 1 to obtain a resin system for a liquid oxygen compatible environment.

[0114] The above-prepared epoxy resin system was subjected to performance testing, and the test results are as follows:

[0115] Table 3 Test Results

[0116]

[0117]

[0118] Comparative Example 1: Preparation of epoxy resin systems with different phosphorus-containing curing agents

[0119] The R group in the structure of the epoxy curing agent was changed, and its structure is specifically shown in Table 4. The remaining steps were the same as those in Example 1, and a resin system for a liquid oxygen-compatible environment was obtained.

[0120] 1. In a 100 mL three-necked flask equipped with a reflux condenser, a mechanical stirrer (500 r / min), and a dropping funnel, under a nitrogen atmosphere at room temperature, diphenylphosphine chloride (2.37 g, 0.01 mol) and tetrahydrofuran (20 mL) were respectively introduced; then, 1-(3-aminopropyl)-imidazole (1.25 g, 0.01 mol), triethylamine TEA (1.01 g, 0.01 mol), and tetrahydrofuran (10 mL) were dropped into the flask, and continuous stirring was carried out for 1 h. After reacting at room temperature for 2 h, it was heated to 75 °C and stirred overnight to obtain a phosphorus-containing curing agent;

[0121] 100 parts of epoxy resin were mixed with 31 parts of the phosphorus-containing curing agent prepared in step (1), and then heated to 80 °C in a forced-air oven for mixing, and gradient curing was carried out in the temperature range of 120 - 240 °C to obtain an epoxy resin cured product.

[0122] 2. In a four-necked round-bottom flask equipped with a mechanical stirrer, a condenser, and a nitrogen balloon, 5 g of phenylphosphonic acid (CAS: 1571-33-1, purchased from Shanghai Macklin Biochemical Co., Ltd.), 11.75 g of ethanolamine (CAS: 141-43-5, purchased from Shanghai Macklin Biochemical Co., Ltd.), 19.48 g of triethylamine TEA, and 40 mL of tetrahydrofuran were added. The reactants were continuously stirred at room temperature for 24 h to obtain a phosphorus-containing curing agent. 100 parts of epoxy resin were mixed with 12 parts of the phosphorus-containing curing agent, and then heated to 80 °C in a forced-air oven for mixing, and gradient curing was carried out in the temperature range of 120 - 240 °C to obtain an epoxy resin cured product.

[0123] The epoxy resin systems prepared in 1 and 2 were subjected to performance tests, and the test results are shown in Table 4. The results show that when the R in the structure of the phosphorus-containing curing agent was changed, the performance of the epoxy resin system was significantly reduced, far inferior to the epoxy resin system prepared in Example 1.

[0124] Table 4 Test Results

[0125]

[0126]

[0127] Comparative Example 2: Preparation of epoxy resin systems by existing methods

[0128] It consists of a modified epoxy resin (prepared by polymerizing epoxy resin and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO)) and a modified amine curing agent (prepared by polymerizing an alicyclic amine curing agent and vinyl silane). The specific preparation method is as follows:

[0129] Preparation of the modified amine curing agent: At a temperature of 80 °C, vinyltriethoxysilane was slowly added dropwise to the alicyclic amine curing agent. The molar ratio of the alicyclic amine curing agent to vinyltriethoxysilane was 1:2. During the dropping process, the temperature of the reaction system was controlled at 80 °C. After the dropping was completed, it was kept at 80 °C for 2 h to obtain the modified amine curing agent.

[0130] Preparation of the modified epoxy resin: At a temperature of 120 °C, DOPO was added to the epoxy resin and stirred (the mass ratio of DOPO to epoxy resin was 1:13). After DOPO was completely dissolved, the temperature was raised to 160 °C and kept for 5 h to obtain the modified epoxy resin. Preparation of the liquid oxygen-compatible epoxy resin system: By mass, 100 parts of the modified epoxy resin and 12 parts of the modified amine curing agent were mixed evenly, gelled at 100 °C for 2 h, cured at 140 °C for 2 h, and post-cured at 180 °C for 4 h. The cured epoxy resin was prepared and tested according to the standard.

[0131] The obtained epoxy resin system was subjected to performance testing, and the test results are shown in Table 5.

[0132] Table 5 Test Results

[0133]

[0134] Comparative Example 3: Preparation of an epoxy resin system by the existing method

[0135] Epoxy resin, phosphorus-containing epoxy resin, and a curing agent were mixed to obtain a liquid oxygen-compatible epoxy resin system. The phosphorus-containing epoxy resin was prepared from 10-(2,5-dihydroxyphenyl)-10H-9-oxa-10-phosphaphenanthrene-10-oxide (ODOPB), epichlorohydrin, a ring-opening catalyst, and a ring-closing catalyst. The specific preparation method is as follows:

[0136] Under a nitrogen atmosphere, 10-(2,5-dihydroxyphenyl)-10H-9-oxa-10-phosphaphenanthrene-10-oxide with a molar ratio of 1:6 and epichlorohydrin were reacted in the presence of tetrabutylammonium bromide. The amount of tetrabutylammonium bromide used was 0.5 wt% of the weight of 10-(2,5-dihydroxyphenyl)-10H-9-oxa-10-phosphaphenanthrene-10-oxide. After reacting at a reaction temperature of 60 °C for 5 h, an intermediate was obtained. Sodium methoxide with a molar ratio of 2:1 was mixed with the intermediate and reacted at a reaction temperature of 50 °C for 5 h. After post-treatment, a phosphorus-containing epoxy resin was obtained. 100 parts of glycidyl ether epoxy resin and 5 parts of phosphorus-containing epoxy resin were mixed at 100 °C and stirred for 5 min to obtain a uniformly mixed resin solution. At a temperature of 90 °C, the curing agent diaminodiphenylmethane was added to the uniformly mixed resin solution. The ratio was based on the equivalent ratio of epoxy groups in the glycidyl ether epoxy resin to the active hydrogen in the curing agent of 1:0.85. Stir until the curing agent diaminodiphenylmethane was completely dissolved to obtain a resin system that can be used in a liquid oxygen environment, and cured according to the process of 90 °C / 2 h + 120 °C / 2 h + 160 °C / 2 h. The cured epoxy resin was prepared and tested according to the standard.

[0137] The obtained epoxy resin system was subjected to performance testing, and the test results are shown in Table 6:

[0138] Table 6 Test Results

[0139]

[0140] In summary, the results show that the epoxy resin system prepared by the existing method cannot have both good liquid oxygen compatibility and mechanical properties; while the epoxy resin system with liquid oxygen compatibility prepared based on the phosphorus-containing curing agent in Example 1 has stronger mechanical properties on the basis of excellent liquid oxygen compatibility.

[0141] Comparative Example 4: Preparation of an epoxy resin system from existing raw materials

[0142] A resin system for a liquid oxygen-compatible environment was prepared using a compound containing a DOPO structure, and its performance was detected. The structural formula and test results are shown in Table 7.

[0143] 1. A method for preparing a resin system for a liquid oxygen-compatible environment using a curing agent containing a DOPO structure is as follows:

[0144] In a 250 ml round-bottom flask, 20 g of DOPO (9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, CAS: 35948-25-5, purchased from Shanghai Macklin Biochemical Co., Ltd.) and 10 g of DABP (4,4'-diaminobenzophenone, CAS: 611-98-3, purchased from Shanghai Macklin Biochemical Co., Ltd.) were mixed together and heated to 180 °C while stirring for 3 h to thicken the reaction mixture. After cooling to 100 °C, toluene (CAS: 1330-20-7, purchased from Shanghai Macklin Biochemical Co., Ltd.) was added to the flask, and the formed precipitate was filtered out and washed with toluene to obtain a phosphorus-containing curing agent.

[0145] 2. A method for preparing a resin system for a liquid oxygen-compatible environment using a curing agent containing a DOPO structure is as follows:

[0146] 10.8 g of p-phenylenediamine (CAS: 106-50-3, purchased from Shanghai Macklin Biochemical Co., Ltd.) and 19.2 g of furfural (CAS: 98-01-1, purchased from Shanghai Macklin Biochemical Co., Ltd.) were added to a 1000 mL three-necked flask with 400 mL of ethanol as a solvent, and the reaction was carried out at room temperature for 6 h to obtain an intermediate. 26.4 g of the intermediate and 43.2 g of DOPO were dissolved in 600 mL of ethanol, and the reaction was carried out at 70 °C for 12 h. After the reaction was completed, the system was cooled to room temperature, and the brown product was filtered out under vacuum to obtain a phosphorus-containing curing agent.

[0147] The phosphorus-containing curing agents prepared in 1 and 2 were taken, and an epoxy resin composite material was prepared according to the method of Example 1, and its liquid oxygen compatibility, strength, and toughness were detected. The results are shown in Table 7.

[0148] The results show that although the epoxy resin composite material prepared from a conventional compound containing a DOPO structure has good liquid oxygen compatibility, it is inferior to the epoxy resin composite material prepared in Example 1 in terms of strength and toughness.

[0149] Table 7 Detection Results

[0150]

[0151] Although the present invention has been disclosed above with preferred embodiments, it is not intended to limit the present invention. Any person familiar with this technology can make various modifications and decorations without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention should be defined by the claims.

Claims

1. A method for preparing an epoxy resin composite material having both liquid oxygen compatibility and mechanical properties, characterized in that, The method includes the steps: (1) Mix 10-(2,5-dihydroxyphenyl)-10H-9-oxa-10-phosphaphenanthrene-10-oxide, fluoronitrobenzene, cesium fluoride, and N,N-dimethylacetamide, stir, heat, cool, precipitate, and filter to obtain a filtered product; Recrystallize the filtered product in acetic anhydride, filter, and dry to obtain a nitro compound; (2) Mix hydrochloric acid and absolute ethanol to obtain Solution A; mix the nitro compound, reduced iron, and N,N-dimethylacetamide to obtain Solution B; add Solution B to Solution A, stir, filter, and recrystallize to obtain a phosphorus-containing curing agent; (3) Mix epoxy resin, the phosphorus-containing curing agent, and diaminodiphenylmethane, heat and mix evenly to obtain an epoxy resin composite material with both liquid oxygen compatibility and mechanical properties.

2. The method according to claim 1, wherein In step (1), the dosage ratio of 10-(2,5-dihydroxyphenyl)-10H-9-oxa-10-phosphaphenanthrene-10-oxide, fluoronitrobenzene, cesium fluoride, and N,N-dimethylacetamide is 1-5 g: 1-5 g: 0.5-5 g: 50-100 mL; In step (1), the heating is stirring at 300-500 rpm and 120-160 °C for 8-12 h; Optionally, the dosage ratio of 10-(2,5-dihydroxyphenyl)-10H-9-oxa-10-phosphaphenanthrene-10-oxide, fluoronitrobenzene, cesium fluoride, and N,N-dimethylacetamide is 1-1.2 g: 1-1.2 g: 1-1.2 g: 80-100 mL.

3. The method according to claim 1, characterized in that, In step (2), the volume ratio of hydrochloric acid to absolute ethanol is 10-80: 10-80; In step (2), the dosage ratio of the nitro compound, reduced iron, and N,N-dimethylacetamide is 2.5-10 g: 1-5 g: 50-100 mL; Optionally, the volume ratio of hydrochloric acid to absolute ethanol is 10-15: 70-80; Optionally, the dosage ratio of the nitro compound, reduced iron, and N,N-dimethylacetamide is 3-5 g: 1-3 g: 150-200 mL.

4. The method according to claim 1, characterized in that In step (2), the stirring is to stir for 10-30 min, then raise the temperature to 50-75 °C and stir for 3-5 h, add ammonium hydroxide solution, and continue to stir for 30 min.

5. The method according to claim 1, characterized in that, In step (3), the mass ratio of epoxy resin, the phosphorus-containing curing agent, and diaminodiphenylmethane is 100 g: 0-65 g: 0-25 g; Optionally, the mass ratio of epoxy resin, the phosphorus-containing curing agent, and diaminodiphenylmethane is 100 g: 16 g: 19 g; Optionally, the mass ratio of epoxy resin, the phosphorus-containing curing agent, and diaminodiphenylmethane is 100 g: 33 g: 13 g; Preferably, the mass ratio of epoxy resin, the phosphorus-containing curing agent, and diaminodiphenylmethane is 100 g: 49-65 g: 0-6 g; Preferably, the mass ratio of epoxy resin, the phosphorus-containing curing agent, and diaminodiphenylmethane is 100 g: 49 g: 6 g; Preferably, the mass ratio of epoxy resin, the phosphorus-containing curing agent, and diaminodiphenylmethane is 100 g: 65 g: 0 g.

6. The epoxy resin composite material prepared by the method according to claims 1-5.

7. Use of the method according to any one of claims 1 to 5 or the epoxy resin composite material according to claim 6 in the field of aerospace, characterized in that, The application includes the preparation of a rocket fuel tank.

8. A carbon composite material, characterized in that, The carbon composite material is prepared from the epoxy resin composite material described in claim 6.

9. A method for simultaneously improving the liquid oxygen compatibility and mechanical properties of an epoxy resin composite based on a phosphorus-containing curing agent, characterized in that, The method comprises the steps of: (1) Mix 10-(2,5-dihydroxyphenyl)-10H-9-oxa-10-phosphaphenanthrene-10-oxide, fluoronitrobenzene, cesium fluoride and N,N-dimethylacetamide, stir, heat, cool, precipitate and filter to obtain a filtered product; The filtered product is recrystallized in acetic anhydride, filtered and dried to obtain a nitro compound; (2) Mix hydrochloric acid and absolute ethanol to obtain solution A; mix the nitro compound, reduced iron and N,N-dimethylacetamide to obtain solution B; add solution B to solution A, stir, filter and recrystallize to obtain a phosphorus-containing curing agent; (3) Mix epoxy resin, the phosphorus-containing curing agent and diaminodiphenylmethane, and heat and mix evenly to obtain an epoxy resin composite material with improved liquid oxygen compatibility and mechanical properties.

10. The method according to claim 9, wherein In step (1), the dosage ratio of 10-(2,5-dihydroxyphenyl)-10H-9-oxa-10-phosphaphenanthrene-10-oxide, fluoronitrobenzene, cesium fluoride and N,N-dimethylacetamide is 1-5 g:1-5 g:0.5-5 g:50-100 mL.

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