Preparation method of directionally-arranged boron nitride-based self-expansion epoxy flame-retardant material

Abstract

The invention discloses a preparation method of a directionally-arranged boron nitride-based self-expanding epoxy flame-retardant material. The preparation method comprises the following steps: (1) preparing a BN / Fe3O4-coated PATP nano composite flame retardant; (2) preparing the directionally-arranged boron nitride-based self-expansion epoxy flame-retardant material; according to the invention, the flame retardance is improved by utilizing the heat transfer anisotropic characteristic after oriented arrangement of BN; an ATP monomer expanding agent and a magnetic transition metal oxide (ferroferric oxide) are used for synergistically modifying BN, so that a way is provided for magnetically inducing oriented arrangement of BN nanosheets, and meanwhile, the effect of expanding a carbon layer of a non-expansive resin matrix is achieved; in the combustion process, the directionally-arranged boron nitride-based self-expanding epoxy flame-retardant material has the lowest PHRR (833.92 kW / m < 2 >), THR (24.35 MJ / m < 2 >), PSPR (0.121 m < 2 > / s) and TSP value (3.6 m < 2 >), and shows the best flame retardance and smoke suppression effect.

Description

Technical Field

[0001] The invention belongs to the technical field of preparation of epoxy flame retardant materials, and particularly relates to a method for preparing a directionally arranged boron nitride-based self-expanding epoxy flame retardant material. Background Art

[0002] Epoxy resin (EP), as a high-performance thermosetting polymer, is widely used in aerospace, electronic packaging and other fields, but its molecular chain is rich in carbon, hydrogen and oxygen combustible groups, resulting in significant flammability; under high temperature or open flame conditions, EP is prone to thermal degradation and releases large amounts of combustible gases, posing a serious fire risk; current flame retardant technology mainly reduces the heat release rate (HRR) by adding halogen / phosphorus flame retardants or inorganic fillers, but the improvement in extending the ignition time is limited, and it is difficult to suppress casualties caused by smoke diffusion in the early stage of the fire; ideally, the inorganic flame retardant used for the polymer should have higher and lower thermal conductivity coefficients in the transverse plane and longitudinal section respectively, thereby reducing the peak temperature of the polymer, exerting a "de-thermalization concentration" effect, and achieving the purpose of improving ignition performance.

[0003] Hexagonal boron nitride (BN), as an additive inorganic flame retardant, can modify the pyrolysis behavior, heat absorption, and anti-melting properties of polymers, thereby improving their thermal stability, inhibiting flame propagation, and reducing the heat release rate. More importantly, BN exhibits a completely different thermal anisotropy from other nanomaterials. At room temperature, the thermal conductivity of BN in the AB (transverse) plane is as high as 390 W / (m·K), while the thermal conductivity along the C (longitudinal) axis is as low as 2 W / (m·K). This thermal anisotropy gives the material the dual functions of "avoiding high-temperature hot spots" and "directional rapid heat dissipation," making it one of the more valuable inorganic nano-flame retardants for research. However, the disordered arrangement of BN in the resin matrix makes it difficult to fully exert its thermal protective effect of "transverse heat dissipation and longitudinal heat suppression." Furthermore, as one of the most important flame retardant methods at high temperatures, the quality and morphology of the carbon layer are key factors affecting the flame retardant properties of polymers. Compared with ordinary carbon layers, the thermal conductivity of the honeycomb carbon foam layer is approximately 2.326×10 -5 W / (m·K), which is much smaller than that of the general carbon layer (1.163×10 -4 ~8.141×10 -4 W / (m·K)), which can directly change the process of heat flow transfer; therefore, the present invention focuses on the dual goals of "delayed ignition" and "highly effective flame retardancy" and invents a directionally arranged boron nitride-based self-expanding epoxy flame retardant material. Summary of the Invention

[0004] The present invention utilizes the anisotropic heat transfer properties of BN in different directions after highly ordered and oriented arrangement to delay the ignition time of epoxy resin. Furthermore, adenosine triphosphate (ATP) monomer biomass expansion agent and magnetic transition metal oxide (ferroferric oxide) are used to synergistically modify BN, providing a pathway for magnetically induced oriented arrangement of BN nanosheets while simultaneously achieving the purpose of expanding the carbon layer of a non-expandable resin matrix. ATP contains structural components of an acid source, a carbon source, and a nitrogen-containing gas source. When heated, the phosphoric acid released by decomposition can undergo an esterification reaction with the carbon source hydroxyl group to form a carbon layer. As the reaction proceeds, the foaming agent decomposes to generate water vapor and other nitrogen-containing non-flammable gases, causing the system to expand under the promotion of the gas and ultimately forming a foamed carbon layer. Furthermore, the transition metal can cause the polymer to pyrolyze and deposit in a condensed phase, catalyzing cracking into small molecules that are further dehydrogenated (or dehydrated), aromatized, and then cross-linked to form carbon, thereby inhibiting the generation of organic matter and catalyzing its carbonization, promoting the formation of amorphous carbon from the polymer, and improving the quality and strength of the residual carbon layer.

[0005] To achieve the above-mentioned purpose, the technical solution adopted by the present invention to solve its technical problem is.

[0006] A method for preparing an oriented boron nitride-based self-expanding epoxy flame retardant material comprises the following steps.

[0007] 1. Preparation of BN / Fe3O4@PATP nanocomposite flame retardant.

[0008] (1) First, BN powder was ultrasonically dispersed in 100 mL of deionized water for 1 h, and Tris-HCl buffer was added and stirred for 20 min to obtain a BN dispersion. Then, dopamine (DA) was added to the BN dispersion and stirred for 20 min. The pH of the BN dispersion was adjusted to 8.5 with 0.1 M NaOH and reacted at room temperature for 24 h. The BN / PDA composite material was obtained after washing with deionized water and ethanol. Then, BN@PDA was ultrasonically dispersed in 100 mL of deionized water, and ferrous chloride tetrahydrate (FeCl2·4H2O) and ferric chloride hexahydrate (FeCl3·6H2O) were added to the BN@PDA dispersion in sequence. The pH of the BN@PDA dispersion was adjusted to 11 with 0.1 M NaOH, and the dispersion was stirred at 65 °C for 2 h and then aged for 2 h. Finally, the BN / Fe3O4 composite material was obtained by centrifugal washing with deionized water.

[0009] (2) BN / Fe3O4 powder was ultrasonically dispersed in 100 mL of deionized water, and then Tris-HCl buffer was added and stirred for 20 min to obtain a BN / Fe3O4 dispersion. Then, dopamine (DA) and adenosine triphosphate (ATP) were added to the BN / Fe3O4 dispersion and stirred for 20 min. The pH was adjusted to 8.5 with 0.1 M NaOH and the mixture was reacted at room temperature for 24 h. Finally, the mixture was washed three times with deionized water to remove unreacted monomers to obtain a BN / Fe3O4@PATP nanocomposite flame retardant. The specific preparation scheme is as follows: Figure 1 shown.

[0010] 2. Preparation of oriented boron nitride-based self-expanding epoxy flame retardant materials.

[0011] First, the BN / Fe3O4@PATP nanocomposite flame retardant was ultrasonically dispersed in deionized water to obtain a BN / Fe3O4@PATP suspension. Then, an aqueous epoxy resin emulsion and a curing agent were added to a glass beaker and stirred for 20 minutes to obtain an epoxy resin mixture. Subsequently, the BN / Fe3O4@PATP suspension was added to the epoxy resin mixture and stirred for 30 minutes to obtain a uniformly mixed BN / Fe3O4@PATP epoxy resin slurry. Finally, the BN / Fe3O4@PATP epoxy resin slurry was poured into a polytetrafluoroethylene mold (size 100×100×5mm) and cured at 40°C for 2 hours and then at 80°C for 2 hours. During the step-by-step curing process, a magnetic field generator was used to apply a horizontal uniform magnetic field to drive the in-plane orientation of the h-BN nanosheets to obtain a directional arranged boron nitride-based self-expanding epoxy flame retardant material.

[0012] Furthermore, in step 1(1), hexagonal boron nitride can be replaced by graphene, carbon nitride, or two-dimensional MXene.

[0013] Furthermore, in step 1(1), the molar ratio of FeCl2·4H2O to FeCl3·6H2O is 1:1-1.2.

[0014] Furthermore, in step 1(1), the mass ratio of FeCl2·4H2O to BN@PDA is 1:2-3.

[0015] Furthermore, in step 1(2), the mass ratio of DA to BN / Fe3O4 is 2-4:5.

[0016] Furthermore, the mass ratio of DA to ATP in step 1(2) is 1:1.5-3.

[0017] Furthermore, in step 2, the mass ratio of epoxy resin to curing agent is 2:1-1.2.

[0018] Furthermore, the curing agent in step 2 can be ethylenediamine, diethylenetriamine, or triethylenetetramine.

[0019] Furthermore, in step 2, the BN / Fe3O4@PATP nanocomposite flame retardant accounts for 2.0-5.0 wt.% of the total mass of the waterborne epoxy resin emulsion, the curing agent and the BN / Fe3O4@PATP nanocomposite flame retardant.

[0020] Furthermore, in step 2, the magnetic induction intensity is 0.5-1.5T.

[0021] The present invention provides a method for preparing a directionally arranged boron nitride-based self-expanding epoxy flame-retardant material. Based on a new macro / micro synergistic flame-retardant concept, it organically combines the macro flame-retardant principle of the expanded carbon layer with the micro heat transfer anisotropy of the directionally arranged BN. It proposes to utilize the combined effects of ATP to promote the expansion and carbonization of the polymer surface and the thermal protection properties of the directionally arranged BN, namely "lateral heat dissipation and longitudinal heat suppression", to construct a multifunctional, high-performance composite flame-retardant material system.

[0022] In addition, the present invention provides a method for preparing a directionally arranged boron nitride-based self-expanding epoxy flame retardant material, which has the following beneficial effects.

[0023] (1) The present invention replaces the traditional mixed expansion system of physical mixing of acid source, carbon source and gas source, and adopts ATP monomer expansion agent with embedded three-source functional groups, which effectively avoids the problems of poor compatibility and reaction rate mismatch caused by multi-component compounding; and ATP can quickly construct an expanded carbon layer through the advantages of its own synchronous pyrolysis and metal ion matching of the three-source reaction rate.

[0024] (2) The present invention constructs a directional heat conduction structure in the BN surface through magnetic field induction technology, and utilizes its significant anisotropy of high lateral thermal conductivity and low longitudinal thermal conductivity to achieve heat flow path regulation. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Schematic diagram of the preparation process of BN / Fe3O4@PATP nanocomposite flame retardant.

[0026] Figure 2 FT-IR images of BN, Fe3O4, BN / Fe3O4 and BN / Fe3O4@PATP.

[0027] Figure 3 XRD spectra of BN, Fe3O4, BN / Fe3O4 and BN / Fe3O4@PATP.

[0028] Figure 4 This is the XPS spectrum of BN / Fe3O4@PATP nanocomposite flame retardant.

[0029] Figure 5 SEM images of (a,h) EP, (b,i) BN / EP, (c,j) Fe3O4 / EP, (d,k) BN / Fe3O4 / EP, (e,l) BN / Fe3O4 / EP(MF), (f,m) BN / Fe3O4@PATP / EP, and (g,n) BN / Fe3O4@PATP / EP(MF) samples.

[0030] Figure 6 CCT spectra of EP, BN / EP, Fe3O4 / EP, BN / Fe3O4 / EP, BN / Fe3O4 / EP(MF), BN / Fe3O4@PATP / EP, and BN / Fe3O4@PATP / EP(MF) samples, including (a) peak heat release rate, (b) total heat release rate, (c) peak smoke rate, (d) total smoke emission, (e) CO peak emission, and (f) CO2 peak emission.

[0031] Figure 7 XRD spectra of the carbon layer after combustion of different coatings.

[0032] Figure 8 SEM morphology and EDS spectra of the remaining carbon layer after combustion test of different samples, including (a) EP, (b) BN / EP, (c) Fe3O4 / EP, (d) BN / Fe3O4 / EP, (e) BN / Fe3O4 / EP(MF), (f) BN / Fe3O4@PATP / EP, (g) BN / Fe3O4@PATP / EP SEM images of carbon layer, (ho) EDS-Mapping photo of BN / Fe3O4@PATP. DETAILED DESCRIPTION

[0033] Example 1.

[0034] A method for preparing an oriented boron nitride-based self-expanding epoxy flame retardant material comprises the following steps.

[0035] 1. Preparation of BN / Fe3O4@PATP nanocomposite flame retardant.

[0036] (1) First, 0.5 g of BN powder was ultrasonically dispersed in 100 mL of deionized water for 1 h, and 0.16 g of Tris-HCl buffer was added and stirred for 20 min to obtain a BN dispersion. Then, 0.3 g of dopamine (DA) was added to the BN dispersion and stirred for 20 min. The pH of the BN dispersion was adjusted to 8.5 with 0.1 M NaOH and reacted at room temperature for 24 h. The BN / PDA composite material was obtained after washing with deionized water and ethanol. Then, 0.5 g of BN@PDA was ultrasonically dispersed in 100 mL of deionized water, and 0.2 g of ferrous chloride tetrahydrate (FeCl2·4H2O) and 0.54 g of ferric chloride hexahydrate (FeCl3·6H2O) were added to the BN@PDA dispersion in sequence. The mixture was stirred for 20 min with 0.1 M NaOH. The pH of the BN@PDA dispersion was adjusted to 11 with NaOH, and the mixture was stirred at 65 °C for 2 h and then aged for 2 h. Finally, the BN / Fe3O4 composite material was prepared by centrifugal washing with deionized water.

[0037] (2) 0.25 g of BN / Fe3O4 powder was ultrasonically dispersed in 100 mL of deionized water, and then 0.16 g of Tris-HCl buffer was added and stirred for 20 min to obtain a BN / Fe3O4 dispersion. Then, 0.15 g of dopamine (DA) and 0.3 g of adenosine triphosphate (ATP) were added to the BN / Fe3O4 dispersion and stirred for 20 min. The pH was adjusted to 8.5 with 0.1 M NaOH and the mixture was reacted at room temperature for 24 h. Finally, the mixture was washed three times with deionized water to remove unreacted monomers to obtain a BN / Fe3O4@PATP nanocomposite flame retardant. The specific preparation scheme is as follows: Figure 1 shown.

[0038] 2. Preparation of oriented boron nitride-based self-expanding epoxy flame retardant materials.

[0039] First, 4 g of BN / Fe3O4@PATP nanocomposite flame retardant was ultrasonically dispersed in deionized water to obtain a BN / Fe3O4@PATP suspension. Then, 64 g of water-based epoxy resin emulsion and 32 g of curing agent were added to a glass beaker and stirred for 20 min to obtain an epoxy resin mixture. Subsequently, the BN / Fe3O4@PATP suspension was added to the epoxy resin mixture and stirred for 30 min to obtain a uniformly mixed BN / Fe3O4@PATP epoxy resin slurry. Finally, the BN / Fe3O4@PATP epoxy resin slurry was poured into a polytetrafluoroethylene mold (100×100×5 mm) and cured at 40°C for 2 h and then at 80°C for another 2 h. During the step-by-step curing process, a magnetic field generator was used to apply a horizontal uniform magnetic field to drive the in-plane orientation of the h-BN nanosheets to obtain an oriented h-BN-based epoxy composite material.

[0040] Experimental example 1.

[0041] This experimental example shows the relevant experimental analysis results of an oriented boron nitride-based self-expanding epoxy flame retardant material.

[0042] 2.0 wt.% BN, Fe3O4, BN / Fe3O4 and BN / Fe3O4@PATP hybrids were mixed and stirred with epoxy resin for 30 minutes to prepare BN / EP, Fe3O4 / EP, BN / Fe3O / EP and BN / Fe3O4@PATP / EP slurries, respectively. The evenly dispersed slurries were then poured into a polytetrafluoroethylene mold (100×100×5 mm) and cured at 40°C for 2 hours and then at 80°C for another 2 hours. A magnetic field generator was used to apply a horizontal uniform magnetic field throughout the step-by-step curing process to obtain different types of epoxy flame-retardant materials. In addition, pure EP was used as a control in the experiment.

[0043] (1) FT-IR spectra of pure BN, Fe3O4, BN / Fe3O4 and BN / Fe3O4@PATP Figure 2 As shown; it can be seen that BN at 1376cm -1 and 819cm -1 There are characteristic absorption peaks at 580 cm-1, corresponding to the in-plane and out-of-plane vibrations of the BN bond; Fe3O4 -1 The characteristic absorption peaks of Fe-O-Fe appeared at 1604 cm-1. For the BN / Fe3O4 composite material, the characteristic peaks of BN and Fe3O4 were observed at the same time, confirming the successful synthesis of Fe3O4. For the BN / Fe3O4@PATP sample, in addition to the characteristic peaks of BN and Fe3O4, the characteristic peaks of BN and Fe3O4 were observed at 1604 cm-1. -1 、1066cm -1 、482cm -1 and 721cm -1 Four characteristic absorption peaks were observed at the C—N bond, P—O bond and (PO4) of PDA. 3- chemical bonds; these findings further confirmed the successful synthesis of BN / Fe3O4@PATP.

[0044] (2) The crystal structures of pure BN, Fe3O4, BN / Fe3O4 and BN / Fe3O4@PATP were tested by XRD. Figure 3As shown in the figure, pure BN exhibits characteristic diffraction peaks at 2θ=26.63°, 41.52°, 43.83°, 50.22° and 55.24°, corresponding to the (002), (100), (101), (004) and (110) crystal planes of BN; similarly, Fe3O4 exhibits obvious peaks at 30.12°, 35.52°, 43.48°, 53.52°, 57.24° and 62.76°, corresponding to the (220 ), (311), (400), (511), (422) and (440) planes; for BN / Fe3O4 and BN / Fe3O4@PATP samples, the characteristic diffraction peaks of BN and Fe3O4 can be clearly observed, but the peak intensity in BN / Fe3O4@PATP is significantly reduced, which is mainly attributed to the shielding effect of the PATP organic coating layer; the experimental results indirectly prove the successful preparation of BN / Fe3O4@PATP.

[0045] (3) The chemical bonding state and type of BN / Fe3O4@PATP composite flame retardant were determined by XPS, such as Figure 4 shown; from Figure 4 As can be seen in (a), BN / Fe3O4@PATP is mainly composed of C1s, N 1s, O 1s, B 1s, P 2p and Fe 2p, which is consistent with the elemental composition of BN / Fe3O4@PATP; Figure 4 In (b), the high-resolution spectrum of C 1s can be decomposed into four peaks at 284.7eV, 285.8eV, 286.5eV and 287.9eV (O=CO), which are derived from CC, CN, CO, C=O and O=CO respectively; for the high-resolution spectrum of N1s ( Figure 4 (c)), the three peaks at 397.38eV, 398.68eV and 400.18eV correspond to NB, CN and NP / NH, respectively, among which CN and NH are derived from the PDA structure, thus confirming the successful incorporation of PDA; while O1s( Figure 4 (d)) consists of three fitting signals, namely 530.5eV (Fe-O), 531.6eV (PO) and 532.5eV (P=O / POP); for the P2p high-resolution spectrum ( Figure 4 (e)) captures two signals at 133.1eV and 134.1eV, corresponding to (PO4) in the ATP structure. 3- and (PO3) - group; in the Fe 2p spectrum ( Figure 4 (f)), the peaks at 710.98 eV, 712.88 eV, 723.88 eV, and 728.88 eV are attributed to Fe 3+ 2p 3 / 2, Fe 2+ 2p 3 / 2 , Fe 3+ 2p 1 / 2 and Fe 2+ 2p 1 / 2 ; The signals of Fe 2p and P 2p confirmed the successful synthesis of BN / Fe3O4@PATP.

[0046] (4) Cross-sectional SEM of boron nitride-based epoxy composites Figure 5 As shown, the cross section of pure EP ( Figure 5 (a, h)) are smooth, indicating poor crack resistance; in contrast, all BN-filled EP composites exhibit significantly rougher fracture surfaces with distinct grooves and wrinkles, indicating a ductile fracture mechanism. The increased surface complexity effectively hinders heat transfer through the resin matrix, which is beneficial to the thermal management of the material; BN / EP composites ( Figure 5 (b, i)) showed many micron-sized aggregates on the fracture surface, indicating that the unmodified BN nanosheets were not dispersed sufficiently in the epoxy matrix; BN / Fe3O4 / EP composites ( Figure 5 (d, k)) also show visible particle agglomeration, indicating that the improvement of dispersion efficiency is limited. This non-uniform distribution creates local weaknesses in the thermal barrier and provides a preferential path for heat penetration, which is not conducive to the flame retardancy of the material. For the disordered BN / Fe3O4@PATP / EP composite material ( Figure 5 (f, m)), where the PATP organic layer significantly improved the uniformity of BN dispersion, confirming the effectiveness of surface functionalization in enhancing the compatibility of nanofillers with epoxy resin matrix; while the oriented BN / Fe3O4 / EP ( Figure 5 (e, l)) and BN / Fe3O4@PATP / EP( Figure 5 The (g, n) nanocomposite flame retardant exhibits a uniformly wrinkled fracture surface, and the BN nanosheets show oriented arrangement within the matrix. This ordered microstructure combines excellent dispersibility with structural anisotropy, which can maximize the thermal insulation performance of heat insulation and flame penetration.

[0047] (5) The cone calorimeter test (CCT) was used to simulate the combustion risk of pure EP and composite materials in a real fire. The test results are as follows: Figure 6 The relevant combustion data are shown in Table 1; the peak heat release rate (PHRR) of pure EP is 1399.51kW / m 2 , the total heat release rate (THR) is 36.53MJ / m 2, which means it has a higher thermal risk; with the introduction of inorganic nano flame retardants, the PHRR and THR values ​​of EP composites gradually decreased, which proves that nanomaterials have a positive effect on the flame retardant safety of composites; among all the tested samples, the directional BN / Fe3O4@PATP / EP can form an insulating structure that inhibits heat conduction and volatile release, thereby significantly improving the flame retardant efficiency and showing the lowest PHRR (833.92kW / m 2 ) and THR (24.35MJ / m 2 ) value; In addition, the peak smoke rate (PSPR) and total smoke volume (TSP) of EP were 0.165m 2 / s and 7.6m 2 , which is significantly higher than other composite materials; with the addition of nanofillers, the smoke release gradually decreases; among them, the oriented boron nitride-based self-expanding epoxy flame retardant material (BN / Fe3O4@PATP / EP) shows the lowest PSPR and TSP values, which are 0.121m 2 / s and 3.6m 2 , with the most excellent smoke suppression performance; this enhancement is due to three synergistic mechanisms: (1) the physical barrier effect of BN nanosheets, (2) the catalytic carbonization of Fe3O4, and (3) the phosphide in ATP promoting the dehydration of the epoxy matrix, inducing carbonization and scavenging free radicals.

[0048] Table 1 Cone calorimeter combustion data

[0049]

[0050] (6) The crystal structure of the residual carbon was analyzed by XRD, such as Figure 7 As shown in Figure 2, the diffraction peak of amorphous carbon was detected at 2θ=24.7° for pure EP. In contrast, the residual carbon of BN / EP showed diffraction peaks at 26.6°, 41.6°, 43.8°, 50.2° and 55.1°, corresponding to the (002), (100), (101), (102) and (004) crystal planes of BN, respectively. These peaks confirmed the preservation of BN nanosheets in the carbonaceous matrix after combustion. The residual carbon of Fe3O4 / EP showed diffraction peaks at 30.2°, 35.6°, 43.2°, 54.1° and 56.3°, corresponding to the (002), (100), (101), (102) and (004) crystal planes of BN, respectively. Characteristic peaks are shown at .2°, 57.3° and 62.8°, corresponding to the (220), (311), (400), (422), (511) and (440) planes of Fe3O4, respectively, which match well with JCPDS no.85-1436; in BN / Fe3O4 / EP and BN / Fe3O4@PATP / EP samples, the characteristic diffraction peaks of BN and Fe3O4 appear simultaneously, indicating that BN and Fe3O4 have a synergistic enhancing effect on the integrity and stability of the carbon layer.

[0051] (7) SEM and EDS analysis were performed on the carbon layers after combustion of different samples, such as Figure 8 As shown; Figure 8 As shown in (a), the surface of the carbon layer of pure EP shows large cavities and cracks, which cannot block the heat from the outside, resulting in poor thermal insulation performance; BN / EP ( Figure 8 b) and Fe3O4 / EP( Figure 8 c) The composites showed a relatively more stable carbon structure than pure EP, with fewer pores and cracks, but still obvious, indicating that their thermal insulation effect and structural stability were limited; for BN / Fe3O4 / EP and BN / Fe3O4@PATP / EP composites ( Figure 8 (d, f)), the residual carbon layer is denser, with only tiny local pores and slight cracks, which significantly improves the continuity and strength of the residual carbon; most notably, the magnetically oriented BN / Fe3O4@PATP / EP composite ( Figure 8 (g, h)) shows a highly compact and continuous carbon surface without obvious structural defects, providing a stable thermal barrier at high temperatures, effectively inhibiting heat conduction and flame penetration, and the flame retardant performance is significantly better than other samples; Figure 8 (io) It can be seen that C, O, N, B, P and Fe elements are evenly distributed in the carbon layer without obvious agglomeration; these findings confirm that BN nanosheets, phosphorus and nitrogen components in ATP and Fe3O4 nanoparticles are effectively retained after combustion and synergistically embedded in the carbonaceous carbon network. This synergistic embedding enhances the thermal stability and mechanical strength of the residual carbon, ultimately significantly improving the flame retardant properties of the composite material.

Claims

1. A method for preparing an oriented boron nitride-based self-expanding epoxy flame retardant material, comprising the following steps: (1) Preparation of BN / Fe3O4@PATP nanocomposite flame retardant a. First, BN powder was ultrasonically dispersed in 100 mL of deionized water for 1 h, and Tris-HCl buffer was added and stirred for 20 min to obtain a BN dispersion. Then, dopamine (DA) was added to the BN dispersion and stirred for 20 min. The pH of the BN dispersion was adjusted to 8.5 with 0.1 M NaOH and reacted at room temperature for 24 h. The BN / PDA composite material was obtained after washing with deionized water and ethanol. Then, BN@PDA was ultrasonically dispersed in 100 mL of deionized water, and ferrous chloride tetrahydrate (FeCl2·4H2O) and ferric chloride hexahydrate (FeCl3·6H2O) were added to the BN@PDA dispersion in sequence. The pH of the BN@PDA dispersion was adjusted to 11 with 0.1 M NaOH, and the mixture was stirred at 65°C for 2 h and then aged for 2 h. Finally, the BN / Fe3O4 composite material was obtained after centrifugal washing with deionized water. b. Ultrasonic dispersion of BN / Fe3O4 powder in 100 mL of deionized water was followed by addition of Tris-HCl buffer and stirring for 20 min to obtain a BN / Fe3O4 dispersion. Next, dopamine (DA) and adenosine triphosphate (ATP) were added to the BN / Fe3O4 dispersion and stirred for 20 min. The pH was then adjusted to 8.5 with 0.1 M NaOH and the mixture was reacted at room temperature for 24 h. Finally, the mixture was washed three times with deionized water to remove unreacted monomers to obtain a BN / Fe3O4@PATP nanocomposite flame retardant. (2) Preparation of oriented boron nitride-based self-expanding epoxy flame retardant materials First, the BN / Fe3O4@PATP nanocomposite flame retardant was ultrasonically dispersed in deionized water to obtain a BN / Fe3O4@PATP suspension. Then, a water-based epoxy resin emulsion and a curing agent were added to a glass beaker and stirred for 20 minutes to obtain an epoxy resin mixture. Subsequently, the BN / Fe3O4@PATP suspension was added to the epoxy resin mixture and stirred for 30 minutes to obtain a uniformly mixed BN / Fe3O4@PATP epoxy resin slurry. Finally, the BN / Fe3O4@PATP epoxy resin slurry was poured into a polytetrafluoroethylene mold (100×100×5mm in size) and cured at 40°C for 2 hours and then at 80°C for another 2 hours. During the step-by-step curing process, a magnetic field generator was used to apply a horizontal uniform magnetic field to drive the in-plane orientation of the h-BN nanosheets, thereby obtaining a directional arranged boron nitride-based self-expanding epoxy flame retardant material. In step (1) a, hexagonal boron nitride can be replaced by graphene, carbon nitride, or two-dimensional MXene; the molar ratio of FeCl2·4H2O and FeCl3·6H2O is 1:1-1.2; the mass ratio of FeCl2·4H2O to BN@PDA is 1:2-3; in step (1) b, the mass ratio of DA to BN / Fe3O4 is 2-4:5; the mass ratio of DA to ATP is 1:1.5-3; in step (2), the BN / Fe3O4@PATP nanocomposite flame retardant accounts for 2.0-5.0 wt.% of the total mass of the water-based epoxy resin emulsion, the curing agent, and the BN / Fe3O4@PATP nanocomposite flame retardant; and the magnetic induction intensity is 0.5-1.5 T.

2. An oriented boron nitride-based self-expanding epoxy flame retardant material prepared by the method according to claim 1.

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