A flame retardant for epoxy resin, a preparation method and application thereof

Abstract

The application discloses a flame retardant for epoxy resin flame retardation, a preparation method and application of the flame retardant, the flame retardant has a nitrogen-containing phosphate structure; in the structure of the flame retardant, a nitrogen-containing group and a phosphorus-containing group are combined through an ionic bond. The flame retardant provided in the application can be well used in the flame retardation of epoxy resin, obviously improves the flame retardation of the epoxy resin (especially improves the limiting oxygen index and the vertical combustion grade), and guarantees good physical and mechanical properties.

Description

Technical Field

[0001] The present invention relates to the technical field of polymer composite material modification, and more specifically to a flame retardant for epoxy resin flame retardancy, a preparation method thereof, and an application thereof. Background Art

[0002] Epoxy resin (EP) is widely used in the fields of construction, automobiles, electronics, and aerospace due to its high mechanical strength, chemical resistance, corrosion resistance, and good electrical insulation. However, EP is flammable and releases large amounts of smoke and toxic gases when burned. At the same time, since the flames will drip and transfer along with a large number of matrix droplets, it may cause large-scale serious fires. The disadvantage of flammability causes EP materials to pose a huge fire threat to human life and property in people's daily use. With the development of the times, many industries, such as the automotive and electronics industries, have higher requirements for the flame retardancy of EP to a certain extent. Therefore, the development of efficient flame retardants for flame-retardant EP thermosetting plastics has attracted everyone's attention.

[0003] Extensive research has been conducted on flame-retardant EP, with methods categorized as reactive and additive. Additive flame retardants are favored by industry due to their simplicity, low cost, and flexible formulation. However, previous studies have often encountered issues with additive flame retardants, such as low flame retardancy, high addition levels, and poor compatibility with the EP matrix, which can compromise the mechanical properties of EP. Therefore, achieving excellent flame retardancy at low addition levels without compromising mechanical properties is crucial. Summary of the Invention

[0004] Based on the above problems, the purpose of the present invention is to provide a flame retardant for epoxy resin flame retardancy, and its preparation method and application. The flame retardant provided in the present invention can be well used in the flame retardancy of epoxy resin, while significantly improving the flame retardancy of epoxy resin (especially improving the limiting oxygen index and vertical burning grade) while ensuring its good physical and mechanical properties.

[0005] In one aspect, the present invention provides a flame retardant for epoxy resin flame retardancy, wherein the flame retardant has a nitrogen-containing phosphate structure;

[0006] In the structure of the flame retardant, the nitrogen-containing group and the phosphorus-containing group are combined through ionic bonds.

[0007] Furthermore, in the flame retardant, the molar ratio of phosphorus-containing groups to nitrogen-containing groups is 5:1-1:1, preferably 1.5:1-1:1.

[0008] Furthermore, in the flame retardant, the source of the phosphorus-containing group is one or more of phosphoric acid, hypophosphorous acid, aminotrimethylenephosphonic acid, diethylenetriaminepentamethylenephosphonic acid, polyphosphoric acid, phytic acid or tannic acid.

[0009] Further, the source of the nitrogen group in the flame retardant is one or more of melamine, piperazine hexahydrate, dicyandiamide or dimethylpropylene diamine.

[0010] In another aspect, the present application provides a method for preparing the flame retardant as described above, comprising the following steps:

[0011] The aqueous solution of the source of the nitrogen group is added dropwise to the aqueous solution of the source of the phosphorus group, and the reaction is carried out after heating. The obtained product is washed and dried to obtain the flame retardant.

[0012] Further, the temperature of the reaction is 80-90℃, and the reaction time is 5-7h.

[0013] In the reaction, the source of the nitrogen group and the source of the nitrogen group undergo supramolecular reaction, and the two are combined by ionic bond to obtain the flame retardant.

[0014] In another aspect, the present application provides a flame-retardant epoxy resin composite material, wherein the raw materials used to prepare the composite material comprise the following components:

[0015] 70-80 parts of epoxy resin, 15-20 parts of curing agent, and 2-10 parts of the flame retardant as described above.

[0016] Illustratively, the addition amount of the flame retardant in the raw materials is 3-5wt%, preferably 4-5wt%, and more preferably 5wt%.

[0017] Illustratively, the epoxy resin includes but is not limited to selected from Nantong Xingchen Synthetic Material Co., Ltd. E44, Nantong Xingchen Synthetic Material Co., Ltd. E51, Jining Huakai Resin Co., Ltd. S-28, Nanya Epoxy Resin (Kunshan) Co., Ltd. E51, Nanya Epoxy Resin (Kunshan) Co., Ltd. NPFE-170, etc.

[0018] Illustratively, the addition amount of the flame retardant includes but is not limited to selected from 3 parts, 4 parts, 5 parts, 6 parts, 7 parts, 8 parts, 9 parts, 10 parts, 2-10 parts, 2-8 parts, 2-5 parts, 2-4 parts, 3-5 parts, 4-5 parts, 2-3 parts, 3-4 parts, 5-10 parts, 5-9 parts, 5-8 parts, 4-7 parts, etc.

[0019] Further, the raw materials further comprise: 0-5 parts of a flow promoter. Illustratively, the addition amount of the flow promoter includes but is not limited to 0 parts, 0.5 parts, 1 part, 2 parts, 3 parts, 4 parts, 5 parts, 0.5-5 parts, 0.5-4 parts, 0.5-3 parts, etc. Illustratively, the flow promoter includes but is not limited to one selected from acrylate, stearate or micro-wax powder.

[0020] Furthermore, the raw materials further comprise: 0-2 parts of defoaming agent. Exemplary, the amount of the defoaming agent added includes but is not limited to 0 part, 0.2-2 parts, 0.2-1.8 parts, 0.2-1 parts, 0.2 parts, 0.4 parts, 0.6 parts, 0.8 parts, 1 part, 1.2 parts, 1.4 parts, 1.6 parts, 1.8 parts or 2 parts. From the perspective of balanced addition, 0.2 parts is preferred. Exemplary defoaming agents include but are not limited to one selected from model AKN-3386 defoaming agent, BYKA535 defoaming agent, DJ-1288 defoaming agent, DF-2211 defoaming agent or B-0790 defoaming agent.

[0021] Furthermore, the raw materials include: 75 parts of epoxy resin, 16.36 parts of curing agent, 4.84 parts of flame retardant, 0.5 parts of flow promoter, and 0.2 parts of defoaming agent. The EP composite material obtained within this range has the best flame retardant and mechanical properties.

[0022] In another aspect, the present invention provides a method for preparing the flame retardant epoxy resin composite material as described above, comprising the following steps:

[0023] After the components are uniformly mixed, the mixture is degassed at 90±10° C. under vacuum for 10 to 15 minutes, and then cured to obtain the flame-retardant epoxy resin composite material.

[0024] Furthermore, the curing method is: first curing at a temperature of 80-100° C. for 2-3 hours, and then curing at a temperature of 100-120° C. for 2-3 hours.

[0025] In another aspect, the present invention provides use of the flame retardant epoxy resin composite material described above in the preparation of construction, automobile, electronic and electrical appliances, and aerospace products.

[0026] The beneficial effects of the present invention are as follows:

[0027] The flame retardant provided by the present invention can be evenly dispersed in the epoxy resin matrix when used for flame retardancy of epoxy resin, and there is a strong interaction between the flame retardant and the epoxy resin matrix, thereby improving the crosslinking density of the matrix itself, and simultaneously improving the strength and toughness of the material. The flame retardant has an excellent flame retardant effect. When subjected to flame combustion, the flame retardant easily degrades to produce strong dehydrating agents such as phosphoric acid, metaphosphoric acid, and pyrophosphoric acid, which promote the dehydration, carbonization, and crosslinking of the EP matrix, thereby forming a protective carbon layer. The dense carbon layer can block oxygen and heat, inhibit the combustion process, and significantly reduce the heat and smoke release of the material during combustion. This solves the problem of melt dripping during combustion of epoxy resin materials, and can be quickly extinguished after leaving the fire, resulting in a flame-retardant EP composite material with excellent flame retardant and mechanical properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The specific embodiments of the present application are further described in detail below with reference to the accompanying drawings.

[0029] Figure 1 The infrared spectrum (a) and nuclear magnetic spectrum (b) of the P-N flame retardant (molar ratio 1:1) in Example 1 of the present application are shown.

[0030] Figure 2 The (a) HRR, (b) THR, (c) SPR, (d) TSP, (e) PCO PR and (f) PCO2 PR curves of the EP composite material flame-retardant modified by 5% mass fraction of the P-N flame retardant (molar ratio 1:1) in Example 1 of the present application and pure EP after the cone calorimeter test are shown.

[0031] Figure 3 The digital photos and electron microscope pictures of the EP composite material flame-retardant modified by 5% mass fraction of the P-N flame retardant (molar ratio 1:1) in Example 1 of the present application after the cone calorimeter test are shown: (a1, a2) digital photos of the EP and (b1, b2) EP / 5% PI-DTPMP samples after the cone calorimeter test; (a3, a4) SEM images of the external coke residues of the EP and (b3, b4) EP / 5% PI-DTPMP samples.

[0032] Figure 4 The mechanical data of the flame-retardant modified EP composite materials obtained in Examples 1, 2 and 3 of the present application and pure EP are shown.

[0033] Figure 5 The scanning electron microscope pictures (low magnification) of the material cross section after the tensile test of the pure EP, the flame-retardant modified EP composite materials obtained in Examples 1, 2 and 3 of the present application are shown in a-d in sequence; the scanning electron microscope pictures (high magnification) of the material cross section after the tensile test of the pure EP, the flame-retardant modified EP composite materials obtained in Examples 1, 2 and 3 of the present application are shown in a`-d` in sequence. DETAILED DESCRIPTION

[0034] In order to more clearly illustrate the present application, the present application is further described below with reference to the preferred embodiments and the accompanying drawings. Like components are denoted by the same reference numerals in the drawings. It should be understood by those skilled in the art that the specific descriptions below are illustrative rather than limiting, and the protection scope of the present application should not be limited thereby.

[0035] Example 1

[0036] The present embodiment provides a preparation method of a flame-retardant EP composite material:

[0037] Piperazine hexahydrate (PI) and diethylenetriamine pentamethylene phosphonic acid (DTPMP) were used as starting materials. PI (9.71 g) and DTPMP (57.32 g, 50% aqueous solution) were dissolved in 100 mL of deionized water at a molar ratio of 1:1. The solution of PI was added slowly into the solution of DTPMP and heated to 85 °C. The reaction was carried out for 6 h. The product was washed with a large amount of anhydrous ethanol for 3 times after removing most of the water by a rotary evaporator at 90 °C. The product was dried in a vacuum oven at 85 °C for 48 h. The light yellow product, P-N flame retardant, was obtained.

[0038] FTIR spectra of the resulting flame retardant and 1 H NMR spectra of PI-DTPMP are shown in (a) and (b), respectively. The chemical structures of PI, DTPMP and the synthesized P-N flame retardant (PI-DTPMP) at a molar ratio of 1:1 were characterized by FTIR spectroscopy. The FTIR spectra of PI, DTPMP and PI-DTPMP are shown in Figure 1 Figure 1 (a) For PI, the bands at 2961, 2851 and 1426 cm -1 near 3380 cm -1 are assigned to the stretching vibration of -OH on DTPMP. The absorption bands at 1185 and 934-1040 cm"1correspond to the stretching vibration of P=0 and P-0, respectively, which can be found in both FTIR spectra of DTPMP and PI-DTPMP. For PI-DTPMP, it is worth noting that the absorption bands of N-H at 3210 and 1554 cm -1 disappear, in addition, the new peaks at 1550-1620 cm"1belong to the N-H bending vibration of NH2 + , the peaks at 2728-2783 and 3007 cm -1 are assigned to the stretching vibration of N-H of NH2 + . The FTIR spectra preliminarily confirm the successful preparation of PI-DTPMP. The chemical structures of PI, DTPMP and PI-DTPMP were further characterized by NMR technique, as shown in Figure 1 (b). The peak at about 2.67 ppm in the proton NMR spectrum of PI belongs to the proton in -CH2-, the mass spectrum of PI-DTPMP obtained after the supramolecular reaction of PI and DTPMP is similar to that of DTPMP, but the chemical shift of the peak of -CH2- of PI changes, the peak at 2.67 ppm shifts to 3.48 ppm, which corresponds to the -CH2-proton in -CH2-NH2 + , indicating that the reaction between PI and DTPMP is complete.

[0039] ​By the weight fraction, the raw materials consist of EP 75 parts, curing agent 16.36 parts, P-N flame retardant 4.84 parts (5wt%), flow improver 0.5 parts, defoamer 0.2 parts. After the flame retardant is mixed uniformly, the flame-retardant EP composite material is obtained through the process of vacuum degassing and high-temperature curing. Specifically, the EP resin, curing agent, and synthetic P-N flame retardant are dried at 80°C for 2h to remove the water content, and then the dry components are obtained; the EP, curing agent, synthetic P-N flame retardant, flow improver, and defoamer are mixed uniformly, and then the flame-retardant EP composite material is obtained through the process of vacuum degassing and high-temperature curing. The degassing temperature and time are 90±10°C / 10-15min; the curing temperature and time are 80-100°C / 2-3h, and then 100-120°C / 2-3h.

[0040] The HRR, THR, SPR, TSP, PCOPR, and PCO2PR curves of the above-mentioned EP composite material and pure EP cone calorimeter test are shown in a-f of Figure 2 Figure 2 The cone calorimeter test data of EP and EP / 5% PI-DTPMP, including heat release rate (HRR), total heat release (THR), smoke production rate (SPR), total smoke production (TSP), CO production rate (PCOPR), and CO2 production rate (PCO2PR). Among them, EP / 5% PI-DTPMP corresponds to the composite material of Example 1, and the addition amount of flame retardant is 5% mass fraction. Figure 2 It can be seen that, compared with the pure sample, EP / 5% PI-DTPMP shows better flame retardant behavior, and the peak value of HRR, THR, and TSR is reduced by 34.7%, 44.9%, and 37.7%, respectively. At the same time, the PCOPR and PCO2PR values of EP are reduced by 38.5% and 54.5%, respectively. The reduction of toxic gas CO, smoke, and heat release during combustion is beneficial to fire rescue.

[0041] Figure 3 The macroscopic and microscopic morphology of the residual carbon of the pure EP sample and the composite material sample with 5% mass fraction of the flame retardant of Example 1 after the cone calorimeter test. It can be seen that the residual carbon amount of pure EP after the cone calorimeter test is small and the microscopic morphology is loose and porous, and the addition of 5% PI-DTPMP can obtain a thick and dense carbon layer with a height of 5.0 cm. The dense protective carbon layer inhibits the release of heat and volatile matter during the combustion process, thereby effectively interrupting the combustion cycle and preventing further combustion.

[0042] Example 2

[0043] The present embodiment provides a preparation method of a flame-retardant EP composite material:

[0044] ​Dissolve 9.71 g of piperazine hexahydrate and 57.32 g of diethylenetriamine pentamethylene phosphonic acid (50% aqueous solution) in a molar ratio of 1:1 in 100 mL of deionized water, respectively, slowly drop the piperazine aqueous solution into the diethylenetriamine pentamethylene phosphonic acid aqueous solution and heat to 85°C, react for 6h, after removing most of the water by a rotary evaporator at 90°C, add a large amount of anhydrous ethanol to wash 3 times, vacuum oven at 85°C for 48h, get a light yellow product P-N flame retardant.

[0045] According to the weight fraction, the raw materials are composed of EP 75 parts, curing agent 16.36 parts, synthetic P-N flame retardant 3.84 parts (4wt%), flow improver 0.5 parts, defoaming agent 0.2 parts. After the flame retardant is mixed uniformly, the flame retardant EP composite material is obtained through the processes of vacuum degassing and high temperature curing. Specifically, the EP resin, curing agent and synthetic P-N flame retardant are dried at 80°C for 2h to remove the water, and then the dry components are obtained; the EP, curing agent, synthetic P-N flame retardant, flow improver and defoaming agent are mixed uniformly, and then the flame retardant EP composite material is obtained through the processes of vacuum degassing and high temperature curing. The degassing temperature and time are 90±10°C / 10-15min; the curing temperature and time are 80-100°C / 2-3h, 100-120°C / 2-3h.

[0046] Example 3

[0047] The embodiment provides a preparation method of a flame-retardant EP composite material.

[0048] Dissolve 9.71 g of piperazine hexahydrate and 57.32 g of diethylenetriamine pentamethylene phosphonic acid (50% aqueous solution) in a molar ratio of 1:1 in 100 mL of deionized water, respectively, slowly drop the piperazine aqueous solution into the diethylenetriamine pentamethylene phosphonic acid aqueous solution and heat to 85°C, react for 6h, after removing most of the water by a rotary evaporator at 90°C, add a large amount of anhydrous ethanol to wash 3 times, vacuum oven at 85°C for 48h, get a light yellow product P-N flame retardant.

[0049] The flame-retardant EP composite material is composed of the following raw materials in the stated weight fractions: 75 parts EP, 16.36 parts curing agent, 2.85 parts (3 wt%) synthetic PN flame retardant, 0.5 parts flow promoter, and 0.2 parts defoamer. The flame retardants are thoroughly mixed and then subjected to vacuum degassing and high-temperature curing to obtain a flame-retardant EP composite material. Specifically, the EP resin, curing agent, and synthetic PN flame retardant are dried separately at 80°C for 2 hours to remove moisture, thereby obtaining dried components. The EP, curing agent, synthetic PN flame retardant, flow promoter, and defoamer are thoroughly mixed and then subjected to vacuum degassing and high-temperature curing to obtain a flame-retardant EP composite material. The degassing temperature and time are 90±10°C for 10-15 minutes; the curing temperature and time are 80-100°C for 2-3 hours and 100-120°C for 2-3 hours.

[0050] Example 4

[0051] This embodiment provides a method for preparing a flame-retardant EP composite material:

[0052] 19.42 g of piperazine hexahydrate and 57.32 g of diethylenetriamine penta methylenephosphonic acid (50% aqueous solution) in a molar ratio of 2:1 were dissolved in 100 mL of deionized water, and the piperazine hexahydrate aqueous solution was slowly added dropwise to the diethylenetriamine penta methylenephosphonic acid aqueous solution and heated to 85°C for 6 h. After removing most of the water from the product by a rotary evaporator at 90°C, a large amount of anhydrous ethanol was added for washing three times, and the product was dried in a vacuum oven at 85°C for 48 h to obtain a light yellow PN flame retardant.

[0053] (2) According to the weight fraction, the following raw materials are composed: 75 parts of EP, 16.36 parts of curing agent, 4.84 parts (5wt%) of synthetic PN flame retardant (molar ratio 2:1), 0.5 parts of flow promoter, and 0.2 parts of defoaming agent. After the flame retardants are fully mixed, the flame retardant EP composite material is obtained by vacuum degassing and high-temperature curing. Specifically, the EP resin, curing agent, and synthetic PN flame retardant are dried at 80°C for 2 hours, and after removing the moisture therefrom, the dried components are obtained; after the EP, curing agent, synthetic PN flame retardant, flow promoter, and defoaming agent are fully mixed, the flame retardant EP composite material is obtained by vacuum degassing and high-temperature curing. The degassing temperature and time are: 90±10°C / 10~15min; the curing temperature and time are: first 80~100°C / 2~3h, then 100~120°C / 2~3h.

[0054] Figure 4Shown are the tensile strength and impact strength (a) and stress-strain curves (b) of EP, EP / 5%PI-DTPMP, EP / 4%PI-DTPMP, and EP / 3%PI-DTPMP composites; Figure 5 SEM images of the fracture surfaces of (a, a') EP, (b, b') EP / 3% PI-DTPMP, (c, c') EP / 4% PI-DTPMP and (d, d') EP / 5% PI-DTPMP tensile specimens.

[0055] Figure 4 and Figure 5 EP / 5%PI-DTPMP, EP / 4%PI-DTPMP, and EP / 3%PI-DTPMP correspond to the composite materials of Example 1, Example 2, and Example 3, respectively, and the addition amount of the flame retardant is 5%, 4%, and 3% by mass, respectively. Figure 4 It can be seen that compared with the pure sample, the tensile strength of EP / 3%PI-DTPMP, EP / 4%PI-DTPMP and EP / 5%PI-DTPMP increased by 14.3%, 19.9% ​​and 21.2% respectively. At the same time, with the introduction of PI-DTPMP, the impact strength also showed a gradual upward trend. In addition, Figure 5 The SEM images of the fracture surface of the tensile specimen shown reveal more information. Figure 5 In Figures a and 5a', the pure EP fracture surface exhibits brittle fracture, with regular, smooth cracks. In contrast, the EP / PI-DTPMP composite exhibits a rough, rippled fracture, indicating ductile fracture. This is due to the fact that the addition of PI-DTPMP affects crack propagation, leading to crack deflection and secondary cracking. Ductile fracture consumes more energy, resulting in higher strength for the EP / PI-DTPMP composite. In summary, the addition of PI-DTPMP, at a certain dosage, improves both toughness and strength, demonstrating excellent mechanical properties.

[0056] Comparative Example 1

[0057] The comparative example provides a preparation method of a new EP composite material: the raw materials are composed of the following parts by weight fraction, EP 75 parts, curing agent 16.36 parts, piperazine hexahydrate 1.42 parts, diethylene triamine pentamethylene phosphonic acid 50% aqueous solution 8.41 parts, flow improver 0.5 parts, defoamer 0.2 parts. The molar ratio of the added piperazine hexahydrate and diethylene triamine pentamethylene phosphonic acid 50% aqueous solution is equivalent to that of the added P-N flame retardant in Example 1. After the flame retardant is uniformly mixed, vacuum degassing and high temperature curing are carried out to obtain a flame-retardant EP composite material. Specifically: the EP resin, curing agent, piperazine hexahydrate, diethylene triamine pentamethylene phosphonic acid solution are dried at 80°C for 2h, and after removing the water, dry components are obtained; after the EP, curing agent, piperazine hexahydrate, diethylene triamine pentamethylene phosphonic acid solution, flow improver, defoamer are uniformly mixed, vacuum degassing and high temperature curing are carried out to obtain a flame-retardant EP composite material. The degassing temperature and time are: 90±10°C / 10-15min; the curing temperature and time are: 80-100°C / 2-3h, 100-120°C / 2-3h.

[0058] Comparative example 2

[0059] The comparative example provides a preparation method of a new EP composite material: the raw materials are composed of the following parts by weight fraction, EP 75 parts, curing agent 16.36 parts, P-N flame retardant (molar ratio 1:1) 10.2 parts (10wt%) in Example 1, flow improver 0.5 parts, defoamer 0.2 parts. After the flame retardant is uniformly mixed, vacuum degassing and high temperature curing are carried out to obtain a flame-retardant EP composite material. Specifically: the EP resin, curing agent, P-N flame retardant are dried at 80°C for 2h, and after removing the water, dry components are obtained; after the EP, curing agent, P-N flame retardant, flow improver, defoamer are uniformly mixed, vacuum degassing and high temperature curing are carried out to obtain a flame-retardant EP composite material. The degassing temperature and time are: 90±10°C / 10-15min; the curing temperature and time are: 80-100°C / 2-3h, 100-120°C / 2-3h.

[0060] Comparative example 3

[0061] The comparative example 4 provides a preparation method of a new EP composite material: the raw materials are composed of EP 75 parts, curing agent 16.36 parts, P-N flame retardant (molar ratio 2:1) 10.2 parts (10 wt%) in example 4, flow improver 0.5 parts, defoaming agent 0.2 parts according to the weight fraction. After the flame retardant is uniformly mixed, the flame-retardant EP composite material is obtained through the processes of vacuum degassing and high-temperature curing. Specifically, the EP resin, curing agent, and synthetic P-N flame retardant are dried at 80°C for 2h respectively to remove the water in them, and then the dried components are obtained; the EP, curing agent, synthetic P-N flame retardant, flow improver, and defoaming agent are uniformly mixed, and then the flame-retardant EP composite material is obtained through the processes of vacuum degassing and high-temperature curing. The degassing temperature and time are 90±10°C / 10-15min; the curing temperature and time are 80-100°C / 2-3h, 100-120°C / 2-3h.

[0062] Comparative example 4

[0063] Example 1 is repeated, except that diethylenetriamine pentamethylene phosphonic acid is replaced by hydroxyethylidene diphosphonic acid in the preparation process of the flame retardant, and the rest of the conditions remain unchanged to prepare the flame retardant.

[0064] It is applied to the preparation of epoxy resin composite material in the manner of example 1 to obtain the flame-retardant EP composite material.

[0065] Comparative example 5

[0066] Example 1 is repeated, except that piperazine hexahydrate is replaced by N-aminoethyl piperazine hexahydrate in the preparation process of the flame retardant, and the rest of the conditions remain unchanged to prepare the flame retardant.

[0067] It is applied to the preparation of epoxy resin composite material in the manner of example 1 to obtain the flame-retardant EP composite material.

[0068] The conventional mechanical properties and combustion performance of the flame-retardant EP resin composition are tested according to the following standards, and the results are shown in Table 1.

[0069] Izod impact strength: tested according to GB / T1043.1-2018 standard, impact energy is 2.75J;

[0070] Tensile strength: tested according to GB / T1040.1-2018 standard, test speed is 5mm / min;

[0071] Combustion performance: LOI standard test is carried out according to GB / T 2406-2015 standard, and UL-94 standard test is carried out according to GB / T 2408-2008.

[0072] Table 1: Example / Comparative Example Performance Test:

[0073]

[0074] *t1 / t2 refer to the duration of the burning of the specimen after the first and second ignitions, respectively. Unless otherwise specified, the time unit is seconds.

[0075] Conclusion: A performance comparison in Table 1 shows that, compared to Comparative Example 1, the addition of 3%, 4%, and 5% of the synthetic PN flame retardant in Examples 1, 2, and 3 using piperazine-diethylenetriamine penta-methylenephosphonate increases the tensile strength of the materials by 14.3%, 19.9%, and 21.2%, respectively. Impact strength also shows a gradual upward trend. The mechanical properties of the materials in Examples 1, 2, and 3 all improve compared to Comparative Example 1. The significant impact on the mechanical properties of the material in Comparative Example 1 is due to the significant agglomeration of diethylenetriamine penta-methylenephosphonate within the epoxy resin. The synthetic PN flame retardant, produced after reaction with piperazine, forms nanosheets. Its addition affects the crack propagation process, leading to crack deflection and secondary cracking, transforming the EP material's original brittle fracture into a ductile fracture. The ductile fracture process consumes more energy, resulting in the composite's higher strength. Furthermore, the synthetic PN flame retardant is well dispersed within the EP matrix, lacking agglomeration, which also contributes to the material's excellent mechanical properties. Comparing Example 1 with Example 4, and Comparative Example 2 with Comparative Example 3, it can be seen that when the addition amount is the same, the flame retardant effect of the synthetic PN flame retardant (molar ratio 2:1) is worse than that of the synthetic PN flame retardant (molar ratio 1:1), which is mainly due to the reduced flame retardant efficiency of the former due to the reduction in P content. Comparative Examples 2 and 3 can both achieve good flame retardant effects, but compared with Examples 1 and 4, the increase in the addition amount leads to the agglomeration of the flame retardant, which significantly reduces the mechanical properties of the system. The above results show that the EP composite materials prepared using the raw materials and raw material ratios provided in the embodiments of the present invention have excellent flame retardant and mechanical properties. Comparative Examples 4 and 5 continued to burn for too long and failed the vertical combustion test.

[0076] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not limitations on the implementation methods of the present invention. For ordinary technicians in the relevant field, other different forms of changes or modifications can be made based on the above description. It is impossible to list all the implementation methods here. All obvious changes or modifications derived from the technical solution of the present invention are still within the scope of protection of the present invention.

Claims

1. A flame retardant for epoxy resin flame retardancy, characterized in that: The flame retardant has a nitrogen-containing phosphate structure; In the structure of the flame retardant, the nitrogen-containing group and the phosphorus-containing group are bonded via ionic bonds; The source of the phosphorus-containing group is diethylenetriaminepentamethylenephosphonic acid; The source of the nitrogen-containing group is piperazine hexahydrate; The molar ratio of the phosphorus-containing groups to the nitrogen-containing groups is 5:1-1:1; The preparation of the flame retardant comprises the following steps: The aqueous solution of the source of nitrogen-containing groups is added dropwise to the aqueous solution of the source of phosphorus-containing groups, and the mixture is heated to react. The resultant is washed and dried to obtain the flame retardant.

2. The flame retardant according to claim 1, characterized in that In the flame retardant, the molar ratio of phosphorus-containing groups to nitrogen-containing groups is 1.5:1-1:

1.

3. The flame retardant according to claim 1, characterized in that The reaction temperature is 80-90° C., and the reaction time is 5-7 h.

4. A flame retardant epoxy resin composite material, characterized in that: The raw materials for preparing the composite material include the following components: 70-80 parts of epoxy resin, 15-20 parts of curing agent, and 2-10 parts of the flame retardant according to any one of claims 1-3.

5. The method for preparing a flame retardant epoxy resin composite material according to claim 4, wherein: The steps include: After the components are uniformly mixed, degassing is performed at 90±10° C. under vacuum for 10 to 15 minutes, and then curing is performed to obtain the flame-retardant epoxy resin composite material.

6. The preparation method according to claim 5, characterized in that The curing method is: first curing at a temperature of 80-100° C. for 2-3 hours, and then curing at a temperature of 100-120° C. for 2-3 hours.

7. Use of the flame retardant epoxy resin composite material according to claim 4 in the preparation of construction, automobile, electronic appliance and aerospace products.

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