Preparation of a hexachlorocyclotriphosphazene bimetallic MOF microcapsule boron nitride-based fireproof coating

Abstract

The application discloses a hexachlorocyclotriphosphazene bimetallic MOF microcapsule boron nitride-based fireproof coating and a preparation method thereof, and the preparation method comprises the following steps: (1) preparing a BN@PDA-MOF@HCCP (BM@PH) flame retardant; (2) preparing a BM@PH epoxy intumescent fireproof coating; the prepared coating has the functions of the excellent barrier property of BN, the synergistic catalytic carbonization flame-retardant effect of bimetallic ions in Co / Zn-MOF and the gas-phase flame-retardant effect of the high-phosphorus and high-nitrogen HCCP flame retardant, and is a multifunctional and efficient boron nitride-based epoxy intumescent fireproof coating; during the combustion of the coating sample, the sample of the BM@PH has the lowest back temperature (163.2 DEG C), the largest intumescent height (31 mm) and the largest intumescent rate (24.2%), and the sample has the most excellent heat insulation property.

Description

Technical Field

[0001] This invention belongs to the field of epoxy waterborne intumescent fire-retardant coating preparation, specifically relating to the preparation of a hexachlorocyclotriphosphazene bimetallic MOF microcapsule boron nitride-based fire-retardant coating. Background Technology

[0002] Currently, steel structures are widely used in buildings, bridges, and tunnels due to their significant ductility and mechanical properties. However, the high thermal conductivity of steel structures leads to a high fire risk, making fire protection crucial for their safety. Among various fire protection technologies, intumescent fire-retardant coatings are popular due to their excellent performance and low price. Generally, intumescent fire-retardant coatings are mainly composed of polymers, intumescent components, and fillers. In terms of polymer components, waterborne epoxy resins have received widespread attention due to their excellent adhesion and environmental friendliness. However, like most polymer materials, waterborne epoxy resins are inherently flammable and prone to causing fires. Therefore, research on the flame retardant properties of waterborne epoxy resins has significant practical implications. Numerous studies have shown that adding inorganic nano-flame retardants can effectively improve their fire resistance. Therefore, developing a high-performance, multifunctional composite nano-flame retardant is an effective way to solve this problem. Summary of the Invention

[0003] Hexagonal boron nitride (BN), as an emerging two-dimensional layered material, is mainly composed of B and N atoms and has a two-dimensional layered structure similar to graphene. More importantly, its excellent high-temperature resistance, thermal stability, oxidation resistance, and high barrier properties can effectively block oxygen entry, volatile matter leakage, and inhibit heat / flame transfer, thus it is considered a very promising inorganic nanomaterial for flame retardancy. Metal-organic frameworks (MOFs), as a class of highly regular porous crystalline nanomaterials formed by the coordination of metal ions or metal oxides with organic linkers, possess unique pore structures and extremely high specific surface areas. This porosity facilitates the adsorption and storage of small molecules, giving it great application potential in adsorption and encapsulation technologies. Furthermore, during combustion, the metal ions in MOFs can promote the formation of residual carbon, increasing the residual carbon content and thus improving the flame-retardant effect of the char layer. Therefore... MOFs are promising encapsulation materials and precursors for metal-catalyzed flame retardants. Hexachlorocyclotriphosphazene (HCCP) is a phosphorus-containing inorganic compound with environmentally friendly and non-toxic advantages. Its molecule contains a large amount of phosphorus (approximately 26.73%). During combustion, the phosphorus free radicals generated by the decomposition of HCCP can effectively capture H- and OH- free radicals, thereby interrupting the combustion reaction. HCCP is an excellent phosphorus-containing bio-flame retardant. This invention uses a simple one-step method to encapsulate hexachlorocyclotriphosphazene (HCCP) in the pores of Co / Zn-MOFs, and then loads these hexachlorocyclotriphosphazene bimetallic MOF microcapsules onto the surface of boron nitride, thereby obtaining a novel multifunctional and efficient nanocomposite flame retardant. Then, this novel multifunctional and efficient nanocomposite flame retardant is added to an aqueous epoxy resin matrix to successfully prepare a high-performance, multifunctional epoxy intumescent fireproof coating.

[0004] To achieve the above objectives, the technical solution adopted by the present invention to solve its technical problems is as follows.

[0005] The preparation of a hexachlorocyclotriphosphazene bimetallic MOF microcapsule boron nitride-based fire-retardant coating includes the following steps.

[0006] 1. Preparation of BN@PDA-MOF@HCCP (BM@PH) flame retardant.

[0007] (1) First, boron nitride (BN) was ultrasonically dispersed in 100 mL of deionized water to obtain a uniformly dispersed boron nitride suspension. Then, tris-HCl was added to the boron nitride suspension and stirred until homogeneous. Dopamine hydrochloride was then added, and the pH of the boron nitride mixture was adjusted to 8.5 and stirred at room temperature for 24 h. Finally, the mixture was repeatedly washed with deionized water to remove excess reactants, and boron nitride / polydopamine (BN@PDA) hybrid was obtained by high-speed centrifugation.

[0008] (2) Disperse BN@PDA in 100mL of methanol solution by ultrasonication, and add Zn(NO3)2:6H2O and Co(NO3)2:6H2O powder to it and stir for 10-20min; then add HCCP to the BN@PDA dispersion and continue stirring for 5-10min, then add dimethylimidazolium (2-MIM) to the BN@PDA dispersion; after stirring for 30min, transfer the BN@PDA dispersion to a hydrothermal reactor and react at 140℃ for 16-20 hours; finally, repeatedly centrifuge and wash the precipitate with methanol to obtain BN@PDA-MOF@HCCP (BM@PH) flame retardant.

[0009] 2. Preparation of BM@PH epoxy intumescent fireproof coating.

[0010] First, melamine (MEL), pentaerythritol (PER), and ammonium polyphosphate (APP) are dispersed in deionized water and vigorously stirred until a homogeneous expansion system mixture is obtained. Then, BM@PH flame retardant is ultrasonically dispersed in deionized water to obtain a BM@PH flame retardant suspension. The BM@PH flame retardant suspension, waterborne epoxy resin emulsion, and curing agent are mixed and stirred for 10-20 minutes and then poured into the expansion system mixture in one go to obtain a homogeneously dispersed BM@PH-based waterborne epoxy slurry. Finally, the BM@PH-based waterborne epoxy slurry is uniformly coated onto a steel plate with a sandblasting grade of Sa2. After brushing, it is cured at room temperature for 7 days to obtain a BM@PH epoxy intumescent fireproof coating.

[0011] Furthermore, in step 1(1), the mass ratio of dopamine hydrochloride to boron nitride is 1:1-2.

[0012] Furthermore, in step 1(1), the mass ratio of tris-HCl to dopamine hydrochloride is 1:1-1.5.

[0013] Furthermore, in step 1(2), the mass ratio of Zn(NO3)2:6H2O to BN@PDA is 1:1-2.

[0014] Furthermore, in step 1(2), the molar ratio of Zn(NO3)2:6H2O and Co(NO3)2:6H2O is 3-1:1.

[0015] Furthermore, in step 1(2), the molar ratio of Zn(NO3)2:6H2O and 2-MIM is 1:4-8.

[0016] Furthermore, in step 1(2), the mass ratio of Zn(NO3)2:6H2O and HCCP is 1:0.4-1.

[0017] Furthermore, in step 2, the mass ratio of polyphosphate, dipentaerythritol, and melamine is 5-7:2-4:0.5-1.5.

[0018] Furthermore, in step 2, the mass ratio of epoxy resin, curing agent, and expansion system is 2-2.5:1:0.8-1.2.

[0019] Furthermore, the curing agent in step 2 is ethylenediamine, diethylenetriamine, or triethylenetetramine.

[0020] Furthermore, in step 2, the total mass of the waterborne epoxy resin emulsion, curing agent, melamine, pentaerythritol, and ammonium polyphosphate accounts for 95.0-97.0% of the total weight of the uniformly dispersed system.

[0021] Furthermore, in step 2, the BM@PH flame retardant accounts for 3.0-5.0% of the total weight of the uniformly dispersed system.

[0022] The present invention provides a boron nitride-based fire-retardant coating based on hexachlorocyclotriphosphazene bimetallic MOF microcapsules, which combines the excellent barrier properties of boron nitride (BN), the synergistic catalytic char formation and flame retardant effect of bimetallic ions in Co / Zn-MOF, and the gas-phase flame retardant effect of high phosphorus and nitrogen HCCP flame retardants. This results in a multifunctional and highly efficient boron nitride-based epoxy intumescent fire-retardant coating. The successful development of this product can promote the application of multifunctional nanocomposite flame retardants in fire-retardant coatings and has important application research value for the large-scale production of fire-retardant coatings.

[0023] Furthermore, the preparation of a boron nitride-based fire-retardant coating based on hexachlorocyclotriphosphazene bimetallic MOF microcapsules provided by the present invention has the following beneficial effects.

[0024] (1) Co / Zn-MOF microcapsules encapsulated with HCCP can be uniformly loaded on the surface of boron nitride. The porous structure and large surface area of ​​Co / Zn-MOF increase the catalytic active sites, effectively improving the ability of flame retardants to catalyze the carbonization of the resin matrix, thereby achieving the purpose of improving the flame retardant performance of polymers.

[0025] (2) Co / Zn-MOF as a microcapsule shell not only has the advantages of controllable structure and adjustable pore size, but also Co / Zn-MOF can pyrolyze at high temperature to produce metal oxides, play the role of metal catalysis to carbonization, and greatly improve the quality of residual carbon layer.

[0026] (3) The phosphorus free radicals generated by the decomposition of HCCP stored in Co / Zn-MOFs at high temperature can effectively capture H· and OH· free radicals generated during polymer combustion and play a role in gas phase flame retardancy. Attached Figure Description

[0027] Figure 1SEM images and EDS spectra of (a) BN, (b) BN@PDA, (c) Co / Zn-MOF, (d) Co / Zn-MOF@HCCP and (ef) BM@PH.

[0028] Figure 2 XRD patterns of BN, BN@PDA, Co / Zn-MOF, Co / Zn-MOF@HCCP, and BM@PH hybrids.

[0029] Figure 3 FTIR spectra of BN, BN@PDA, Co / Zn-MOF, Co / Zn-MOF@HCCP, and BM@PH hybrids.

[0030] Figure 4 TGA and DTG spectra of BN, BN@PDA, Co / Zn-MOF, Co / Zn-MOF@HCCP, and BM@PH hybrids.

[0031] Figure 5 Digital photographs of pure (a, g)EP, (b, h)BN / EP, (c, i)BN@PDA / EP, (d, j)Co / Zn-MOF / EP, (e, k)Co / Zn-MOF@HCCP / EP and (f, l)BM@PH / EP plates before and after combustion.

[0032] Figure 6 This is a graph showing the temperature variation on the back side of the steel sheet and samples with different coatings.

[0033] Figure 7 Macroscopic photographs of (a) pure EP, (b) BN / EP, (c) BN@PDA / EP, (d) Co / Zn-MOF / EP, (e) Co / Zn-MOF@HCCP / EP and (f) BM@PH / EP after expansion tests.

[0034] Figure 8 The graph shows the expansion height and expansion rate of different samples. Detailed Implementation

[0035] Example 1.

[0036] The preparation of a hexachlorocyclotriphosphazene bimetallic MOF microcapsule boron nitride-based fire-retardant coating includes the following steps.

[0037] 1. Preparation of BN@PDA-MOF@HCCP (BM@PH) flame retardant.

[0038] (1) First, 0.5 g boron nitride (BN) was ultrasonically dispersed in 100 mL of deionized water to obtain a uniformly dispersed boron nitride suspension. Then, 0.2 g tris-HCl was added to the boron nitride suspension and stirred until homogeneous. Then, 0.35 g dopamine hydrochloride was added, and the pH of the boron nitride mixture was adjusted to 8.5 and stirred at room temperature for 24 h. Finally, the mixture was repeatedly washed with deionized water to remove excess reactants, and the boron nitride / polydopamine (BN@PDA) hybrid was obtained by high-speed centrifugation.

[0039] (2) 0.5 BN@PDA was ultrasonically dispersed in 100 mL of methanol solution, and 0.5 g Zn(NO3)2:6H2O and 0.5 g Co(NO3)2:6H2O powder were added and stirred for 10-20 min. Then, 0.25 g HCCP was added to the BN@PDA dispersion and stirred for 5-10 min. Next, 0.95 g dimethylimidazole (2-MIM) was added to the BN@PDA dispersion. After stirring for 30 min, the BN@PDA dispersion was transferred to a hydrothermal reactor and reacted at 140 °C for 16-20 hours. Finally, the precipitate was repeatedly washed by centrifugation with methanol to obtain BN@PDA-MOF@HCCP (BM@PH) flame retardant.

[0040] 2. Preparation of BM@PH epoxy intumescent fireproof coating.

[0041] First, 10g of melamine (MEL), 10g of pentaerythritol (PER), and 20g of ammonium polyphosphate (APP) were dispersed in deionized water and vigorously stirred until a homogeneous expansion system mixture was obtained. Then, 4g of BM@PH flame retardant was ultrasonically dispersed in deionized water to obtain a BM@PH flame retardant suspension. The BM@PH flame retardant suspension, 38g of waterborne epoxy resin emulsion, and 19g of curing agent were mixed and stirred for 10-20 minutes and then poured into the expansion system mixture in one go to obtain a homogeneously dispersed BM@PH-based waterborne epoxy slurry. Finally, the BM@PH-based waterborne epoxy slurry was uniformly coated onto a steel plate with a sandblasting grade of Sa2. After brushing, it was cured at room temperature for 7 days to obtain a BM@PH epoxy intumescent fireproof coating. The composition of different waterborne intumescent fireproof coatings is shown in Table 1.

[0042] Table 1 Composition of different water-based intumescent fire-retardant coatings

[0043]

[0044] Experimental Example 1.

[0045] This experimental example demonstrates the experimental analysis results of a boron nitride-based fire-retardant coating based on hexachlorocyclotriphosphazene bimetallic MOF microcapsules.

[0046] BN, BN@PDA, Co / Zn-MOF, Co / Zn-MOF@HCCP, BM@PH composite flame retardants and expansion system suspensions were added to a water-based epoxy resin and curing agent mixture to prepare coatings of 4 wt.% each. Then, the uniformly dispersed coating system was brushed onto the surface of a pretreated steel sheet and cured at room temperature for 7 days to obtain the sample coating. In addition, a pure EP coating was used as a control in the experiment.

[0047] (1) The microstructure of flame retardants BN, BN@PDA, Co / Zn-MOF, Co / Zn-MOF@HCCP, and BM@PH was observed by SEM, and the results are as follows: Figure 1 As shown; from Figure 1 (a) It can be seen that pure BN does not exhibit a specific morphology and mainly exists in an aggregated state; such as Figure 1 As shown in (b), dopamine (DA) modified BN@PDA exhibits a similar structure, but is relatively more dispersed compared to BN, indicating that dopamine modification can alter the dispersion state of BN; for Co / Zn-MOF hybrids ( Figure 1 (c)) It can be clearly observed that the particles are in an octahedral state, and the particle size is between 50-100 nanometers. From Figure 1 (d) It can be seen that the Co / Zn-MOF particles coated with HCCP still exist in an octahedral state, but the particle size is 5-10 times larger than that of Co / Zn-MOFs and the surface is rougher. This indicates that HCCP is coated in the channels of Co / Zn-MOFs, increasing the volume of Co / Zn-MOFs and thus changing its microstructure; Figure 1 As shown in (e), Co / Zn-MOFs coated with HCCP are anchored on the BN@PDA surface with uniform particle distribution. This is attributed to the modification with dopamine, which improves the bonding force and dispersibility between MOFs and BN. Furthermore, the elemental distribution map of the BM@PH hybrid surface is shown in (e). Figure 1 (fl) indicates that Zn, Co, P, N, B and Cl elements are uniformly distributed throughout the BN, indicating that Zn, Co and P ions are uniformly doped into the BN structure, which is crucial for fully leveraging their synergistic effects.

[0048] (2) The XRD diffraction curves of BN, BN@PDA, MOF, HCCP, Co / Zn-MOF@HCCP and BM@PH nanohybrids are shown in the figure. Figure 2As shown; it can be clearly seen from BN and BN@PDA that a series of peaks at 26.7°, 41.6°, 43.7°, 50.1° and 55.2° are consistent with the (002), (100), (101), (004) and (110) crystal planes; the spectrum shows that Co / Zn-MOF@HCCP particles have high crystallinity and sharp diffraction peaks. The Co / Zn-MOF diffraction peaks are at 2θ = 10.3°, 12.7°, 14.6°, 16.4°, and 18.0°. The main peaks at 19.4°, 22.1°, 24.4°, 25.5°, and 26.7° are consistent with those of Co / Zn-MOF@HCCP, and the main peak of HCCP can be found in the spectrum of Co / Zn-MOF@HCCP, indicating the presence of HCCP in Co / Zn-MOF. The characteristic diffraction behavior of BN@PDA and MOF@HCCP can be simultaneously monitored in the diffraction spectrum of BM@PH nanohybrid, further confirming the successful preparation of BM@PH nanohybrid.

[0049] (3) The chemical composition of the material was detected by Fourier transform infrared spectroscopy (FT-IR), and the results are as follows: Figure 3 As shown, BN nanosheets at 1373 cm⁻¹ -1 With 815cm -1 The characteristic peak at 2921 cm⁻¹ is attributed to the stretching vibrations of the inner rings and the bending vibrations of the outer rings of the BN bond plane. However, in BN@PDA, the functional groups characteristic of the PDA layer polymerized on the BN surface cannot be clearly observed, due to their low signal intensity and being masked by the -OH, -NH and -BN bonds in the BN nanosheets. But compared to pure N, the characteristic peak at 2921 cm⁻¹ is significantly higher. -1 The stretching vibration peak of alkyl groups appeared at 1633 cm⁻¹. -1 With 1060cm -1 The stretching vibration peak of the benzene ring and the characteristic peak of the CO bond in PDA appeared at 3121 cm⁻¹, confirming the successful synthesis of BN@PDA; Co / Zn-MOF showed a peak at 3121 cm⁻¹. -1 2926cm -1 1581cm -1 1142cm -1 , and 991cm -1 The peak at 422 cm⁻¹ belongs to the stretching vibration peak of the CH,CN bond, while the peak at 422 cm⁻¹ belongs to the stretching vibration peak of the CH,CN bond. -1 and 990cm -1 The peaks at 964°C belong to the stretching vibrations of Zn-N and Co-N bonds, respectively; these data confirm the successful synthesis of Co / Zn-MOF crystals; the HCCP spectrum shows that at 964°C... -1 and 1178cm -1The PN and P=O stretching vibration peaks at the NH3 level reflect the phosphorus-containing groups in HCCP, indicating the structural characteristics of HCCP. In the spectrum of Co / Zn-MOF@HCCP, the characteristic peaks of Co / Zn-MOF and HCCP are observed to coexist, indicating that HCCP has been successfully coated on the surface of MOF, but no significant chemical bonding has occurred between the two. This physical bonding indicates that HCCP on the surface of Co / Zn-MOF is mainly attached through weak interactions. In the spectrum of BM@PH composite material, the characteristic peaks of BN, Co / Zn-MOF and HCCP are still present. Hydrogen bonds or electrostatic interactions may exist between the hydroxyl and amino functional groups of the PDA modified layer and Co / Zn-MOF and HCCP. Therefore, a more complex peak shape appears in the spectrum of BM@PH, which strongly reflects the successful formation of the composite hybrid.

[0050] (4) When exposed to high heat, the thermal mass loss state of the composite coating is as follows: Figure 4 As shown in Table 2, the thermogravimetric data for all samples exhibited two main decomposition processes within the 25-800℃ range: evaporation of adsorbed water within the 50-180℃ range and high-temperature pyrolysis of the polymer matrix between 200-550℃. Furthermore, it is clearly visible in the figures that the pyrolysis temperature increased after the addition of BN and BN@PDA, which may reflect the role of the BN nanosheet spacers. However, the maximum decomposition temperature of EP filled with Co / Zn-MOF and Co / Zn-MOF@HCCP decreased, which is due to the lower maximum decomposition temperature of Co. 2+ Zn 2+ The synergistic catalytic effect of phosphate promotes the early decomposition of the polymer; the pyrolysis temperature of BM@PH is moderate, which is the result of the synergistic effect of BN@PDA and MOF@HCCP nanosheets; the carbon residue of pure intumescent coating, BN / EP, BN@PDA / EP, MOF / EP, MOF@HCCP / EP and BM@PH / EP are 17.8%, 18.4%, 19.2%, 20.3%, 21.9% and 24.2% respectively; the increase in carbon residue of BN / EP and BN@PDA / EP composite intumescent coatings is mainly due to the blocking effect of BN nanosheets, while the higher carbon residue in BN / PDA-based EP is due to the formation of a stable CN network structure and improved dispersibility after PDA decomposition; the higher carbon residue retained by the MOF-reinforced EP swelling coating is partly attributed to the fact that MOF@HCCP nanosheets to some extent prevent the loss of cracked materials into the air, while Co 2+ Zn 2+Phosphate catalyzes more cyclization and coking of cracked small molecules, which are retained in the coke; the BM@PH-loaded EP swelling coating exhibits the highest coke retention after being subjected to a high temperature of 800°C, which is the result of the combination of the significant blocking ability of BN and the effective coke-promoting effect of MOF@HCCP.

[0051] Table 2 Thermogravimetric data of different samples

[0052]

[0053] (5) The surface condition of the composite coating before and after the large plate combustion test is as follows: Figure 5 As shown; Figure 5 As shown in (af), it can be clearly observed that all samples exhibited a smooth, flat surface without any defects before combustion; after the large plate combustion test, the surfaces of different samples showed different states; the middle part of the pure EP char layer ( Figure 5 (g) almost completely peeled off after combustion, exposing the steel substrate, which laid the foundation for its poor thermal insulation performance; the carbon layer of the BNI / EP composite coating ( Figure 5 (h) did not show significant peeling, but a small portion of the char layer still detached, which facilitated the penetration of heat and flame; for the EP composite coating filled with BN@PDA (segment 5(i) in Figure), the char layer was more completely retained, which helped block the external heat intrusion path, but pores still appeared; for the EP composite coating with added MOF ( Figure 5 (j)) Pores still appeared on the surface of the coke layer, which may be due to the absence of boron nitride, reducing its barrier effect on the external flame; after adding MOF@HCCP ( Figure 5 (k)), fine cracks still appear on the surface of the layer; when BM@PH hybrid is added to EP ( Figure 5 (l)) The carbon layer on the substrate surface did not show obvious defects, such as large holes or cracks, which determined the best blocking effect against external high temperature.

[0054] (6) The back surface temperature of the steel plate is directly related to the thermal insulation performance of the coating. The changes in back surface temperature of different samples during combustion are shown below. Figure 6As shown, the back temperature of the uncoated steel plate rapidly rises to nearly 500℃ in a short time, which will seriously damage its strength. For the pure EP coating steel plate, the rate of temperature rise on the back side is significantly reduced, eventually stabilizing at 230.8℃, demonstrating its effective protective effect. After adding BN, the back temperature of the steel plate drops to 199.4℃, indicating that BN can improve the fire resistance of the coating. For the BN@PDA-based EP composite coating, the back temperature further decreases to 190.1℃, reflecting that the introduction of BN after PDA modification can effectively improve the carbonization ability of the polymer, thereby improving its thermal insulation effect. For the MOF and MOF@HCCP-based composite coating samples, the back temperature drops to the lowest (188.6℃ and 179.2℃), which can be attributed to HCCP and Co. 2+ Zn 2+ The synergistic reinforcing effect of ions; in contrast, the back surface temperature of BN@PH composite material is 163.2℃, which fully reflects the excellent flame retardant ability of BN@PH composite material.

[0055] (7) The expansion characteristics of the composite coating are intrinsically related to the thermal insulation effect of the formed carbon layer; the appearance of the expanded carbon layer obtained after high-temperature combustion of different samples is as follows: Figure 7 As shown; the specific expansion parameters obtained are as follows: Figure 8 As shown in the figure; the comparison shows that the expansion height and expansion rate of pure EP are significantly lower than those of other composite coating samples, which is consistent with its worst insulation performance; after adding BN and BN@PDA, the expansion height and expansion rate of the coating significantly increased to 15 mm and 17 mm and 11.7 and 13.3, respectively, because BN with self-carbonizing effect is retained in the carbon layer to prevent the escape of organic pyrolysis products and gas molecules; for MOF composite coating, the expansion height and expansion rate further increased to 20 mm and 16.4, mainly due to Co 2+ Zn 2+ This result is due to the catalytic effect: for the MOF@HCCP composite coating, the expansion height and expansion ratio increase to 27 mm and 21.1 mm, respectively, which is due to Co 2+ Zn 2+ The catalytic effect and the high phosphorus content of HCCP produce phosphoric acid molecules at high temperatures to promote the formation of residual carbon. For the BM@PH-based composite coating sample, due to the high barrier properties and excellent thermal stability of BN, the catalytic effect of metal ions on the conversion of organic pyrolysis products into carbon during combustion, and the promotion of residual carbon formation by phosphorus-containing organic matter at high temperatures, the sample exhibits the largest expansion height and expansion rate (31 mm, 24.2 mm).

Claims

1. A method for preparing a boron nitride-based fire-retardant coating based on hexachlorocyclotriphosphazene bimetallic MOF microcapsules, comprising the following steps: (1) Preparation of BN@PDA-MOF@HCCP flame retardant a. First, 0.5 g of boron nitride (BN) was ultrasonically dispersed in 100 mL of deionized water to obtain a uniformly dispersed boron nitride suspension. Then, 0.2 g of tris-HCl was added to the boron nitride suspension and stirred until homogeneous. Next, 0.35 g of dopamine hydrochloride was added, and the pH of the boron nitride mixture was adjusted to 8.

5. The mixture was then stirred at room temperature for 24 h. Finally, the mixture was repeatedly washed with deionized water to remove excess reactants, and the boron nitride / polydopamine (BN)@PDA hybrid was obtained by high-speed centrifugation. b. 0.5 g of boron nitride / polydopamine (BN@PDA) hybrid was ultrasonically dispersed in 100 mL of methanol solution, and 0.5 g of Zn(NO3)2:6H2O and 0.5 g of Co(NO3)2:6H2O powder were added and stirred for 10-20 min. Then, 0.25 g of hexachlorocyclotriphosphazene (HCCP) was added to the boron nitride / polydopamine (BN@PDA) hybrid dispersion and stirred for another 5-10 min. Next, 0.95 g of dimethylimidazole was added to the dispersion. After stirring for 30 min, the dispersion was transferred to a hydrothermal reactor and reacted at 140 °C for 16-20 hours. Finally, the precipitate was repeatedly washed by centrifugation with methanol to obtain the BN@PDA-MOF@HCCP flame retardant. (2) Preparation of BN@PDA-MOF@HCCP epoxy intumescent fireproof coating First, 10g of melamine, 10g of pentaerythritol and 20g of ammonium polyphosphate were dispersed in deionized water and stirred vigorously until a uniform expansion system mixture was obtained. Then, 4g of the BN@PDA-MOF@HCCP flame retardant prepared in step (1)b was ultrasonically dispersed in deionized water to obtain a flame retardant suspension. The flame retardant suspension, 38g of waterborne epoxy resin emulsion and 19g of curing agent were mixed and stirred for 10-20 minutes and then poured into the expansion system mixture at once to obtain a uniformly dispersed waterborne epoxy slurry. Finally, the waterborne epoxy slurry was uniformly coated on a steel plate with a sandblasting grade of Sa2. After brushing, it was cured at room temperature for 7 days to obtain a BN@PDA-MOF@HCCP epoxy intumescent fireproof coating.

2. The hexachlorocyclotriphosphazene bimetallic MOF microcapsule boron nitride-based fire-retardant coating prepared by the method described in claim 1.

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