Preparation method of high-nitrogen phosphorus flower-like hydrotalcite-based fireproof coating

Abstract

The application discloses a preparation method of a high-nitrogen phosphorus flower-like hydrotalcite-based fireproof coating, and the preparation steps are as follows: (1) preparation of a base; (2) preparation of an LDH / PCP@ZHS flower-like heterostructure composite flame retardant; and (3) preparation of the high-nitrogen phosphorus flower-like hydrotalcite-based fireproof coating. In the application, the LDH has a metal catalytic charring effect, and the released CO2 and H2O in the decomposition process can reduce the combustible gas concentration and play a gas-phase flame-retardant role. The HCCP thermal degradation produces free radicals to block the combustion chain reaction. The synergistic effect with the PDA forms a stable C-N-P network to prevent heat penetration. The metal oxides (Al2O3, NiO) and ZnSnO3 generated in the combustion process of the ZHS are filled into the carbon layer, which can further enhance the structural strength and heat insulation property of the carbon layer. Therefore, the high-nitrogen phosphorus flower-like hydrotalcite-based fireproof coating has the best flame retardancy and smoke suppression effect.

Description

Technical Field

[0001] This invention belongs to the field of preparation of water-based ultrathin epoxy intumescent fire-retardant coatings, specifically relating to a method for preparing a high-nitrogen-phosphorus flower-shaped hydrotalcite-based fire-retardant coating. Background Technology

[0002] Steel structures are widely used in large-span buildings; however, due to steel's excellent thermal conductivity, its fire resistance is relatively low. Under fire conditions, the surface temperature of steel rises sharply, leading to collapse and causing casualties and property damage. Intumescent fire-retardant coatings are widely used for passive fire protection of steel structures due to their unique advantages. Typically, intumescent fire-retardant coatings consist of intumescent components (carbon, acid, and gas sources), polymers, and fillers. Their protective mechanism is that under high-temperature conditions, they form a charred carbon layer, which acts as an insulating barrier between the fire and the substrate, delaying heat transfer and providing protection. Although intumescent fire-retardant coatings have seen rapid development in recent years, their low carbon layer strength, tendency for carbon layer cracking, limited barrier capacity, and low expansion height prevent them from achieving the desired flame-retardant effect. Adding flame retardants has been proven to be an economical, efficient, and environmentally friendly method to reduce the fire risk of polymers. Compared to halogenated flame retardants, which are harmful to the environment and human health, nanomaterials have been shown to effectively improve the flame-retardant and smoke-suppressing properties of polymers at low concentrations, and also improve mechanical properties.

[0003] Layered bimetallic hydroxides (LDHs) can decompose into water and carbon dioxide in high-temperature environments, exhibiting gas-phase flame retardant properties. The decomposed metal residues can effectively block the transfer of heat and combustible gases, thus being considered an effective inorganic flame retardant. Furthermore, studies have shown that the flower-like hierarchical three-dimensional structure has a large specific surface area, extending the heat transfer path and creating a "maze" effect, thereby increasing the adsorption and interaction of degradation products. Moreover, the flower-like hierarchical nanostructure, while ensuring that its own structure and morphology are not destroyed, prevents the aggregation of low-dimensional nanostructures, effectively enhancing the dispersibility and interfacial interaction forces of nanomaterials in EP, thereby effectively improving the strength and toughness of EP. Summary of the Invention

[0004] Zinc hydroxystannate (ZHS) is a highly efficient flame retardant. The zinc ions in its structure can promote the conversion of thermal degradation products into carbon residues during combustion, which is beneficial for improving the flame retardant properties of polymers. This invention utilizes the reinforcing effect of Ni-Al / LDH on the char layer, the gas-phase flame retardant effect of ZHS, and the synergistic effect of catalytic carbonization to obtain a multifunctional composite fireproof coating with better flame retardant effect. First, high-nitrogen polydopamine (PDA) is loaded onto the surface of flower-shaped nickel-aluminum bimetallic hydroxide (Ni-Al / LDH) to impart excellent hydrophilicity and abundant reactive groups. Then, high-phosphorus... Hexachlorocyclotriphosphazene (HCCP) was grafted onto the LDH / PDA surface to ensure the introduction of a large amount of phosphorus, which is crucial for improving the flame retardancy of the composite material. Next, zinc hydroxystannate (ZHS) was anchored onto the LDH / PDA / HCCP (abbreviated as LDH / PCP) surface via co-precipitation, resulting in a highly efficient LDH / PCP@ZHS flower-like heterostructure composite flame retardant. Finally, the LDH / PCP@ZHS flower-like heterostructure composite flame retardant was added to an epoxy resin matrix to successfully prepare an ultra-thin epoxy intumescent fire-retardant coating with good fire resistance and smoke suppression effects.

[0005] To achieve the above objectives, the technical solution adopted by the present invention to solve its technical problems is as follows.

[0006] A method for preparing a high-nitrogen-phosphorus flower-shaped hydrotalcite-based fire-retardant coating includes the following steps.

[0007] 1. Preparation of base material.

[0008] Weigh out waterborne epoxy resin (EP), curing agent, and expansion system and stir until uniform to obtain a uniformly mixed base material, wherein the expansion system includes polyphosphate (APP), pentaerythritol (PER), and melamine (MEL).

[0009] 2. Preparation of LDH / PCP@ZHS flower-like heterogeneous composite flame retardant.

[0010] (1) First, nickel nitrate hexahydrate, aluminum nitrate nonahydrate, urea and ammonium fluoride were dissolved in deionized water to obtain a mixed solution. Then, the mixed solution was transferred to a high-pressure reactor and hydrothermally reacted at 110°C for 12 hours. Subsequently, the green solid obtained by centrifugation was repeatedly washed with deionized water to obtain nickel-aluminum flower-shaped LDH.

[0011] (2) Nickel-aluminum flower-shaped LDH was uniformly dispersed in deionized water by ultrasonication, and Tris-HCl was added to the nickel-aluminum flower-shaped LDH dispersion. The pH value was adjusted to 8.5 by NaOH solution, and dopamine hydrochloride was added to it. The resulting mixture was stirred at room temperature for 16 hours, and then the solid was repeatedly washed with deionized water and centrifuged to obtain hydrotalcite / polydopamine (LDH / PDA) hybrid.

[0012] (3) LDH / PDA and hexachlorocyclotriphosphazene (HCCP) were added to tetrahydrofuran (THF) solvent and stirred to obtain a homogeneous mixed solution. The mixed solution was then transferred to a three-necked flask, and triethylamine (TEA) was added to the three-necked flask. After reacting at 50°C for 24 hours, the solid was repeatedly washed and centrifuged with tetrahydrofuran solvent to obtain LDH / PDA / HCCP (abbreviated as: LDH / PCP) hybrid. Finally, LDH / PCP was uniformly dispersed in 150 ml of deionized water again by ultrasonic treatment to obtain LDH / PCP dispersion. ZnSO4·7H2O was added to the dispersion, and after stirring at room temperature for 30 minutes, Na2SnO3 was added to the dispersion and reacted for another 2 hours. The obtained solid product was repeatedly washed and centrifuged, and freeze-dried to obtain LDH / PCP@ZHS flower-like heterostructure composite flame retardant. The entire experimental process is as follows: Figure 1 As shown.

[0013] 3. Preparation of high nitrogen and phosphorus content flower-shaped hydrotalcite-based fireproof coating.

[0014] Weigh out LDH / PCP@ZHS flower-shaped heterogeneous composite flame retardant and mix with the base material, and mechanically stir evenly to form a uniform coating system; then, brush the evenly mixed water-based intumescent fire retardant coating onto the surface of a steel sheet with a pretreatment grade of Sa2, and cure at room temperature for 7 days after brushing to obtain a high nitrogen and phosphorus content flower-shaped hydrotalcite-based fire retardant coating.

[0015] Furthermore, in step 1, the mass ratio of epoxy resin to the expansion system is 1:1-1.2.

[0016] Furthermore, in step 1, the mass ratio of epoxy resin to curing agent is 2:1-1.2.

[0017] Furthermore, the curing agent in step 1 can be ethylenediamine, diethylenetriamine, or triethylenetetramine.

[0018] Furthermore, in step 1, the ratio of polyphosphate, pentaerythritol, and melamine is 5.5-6.5 : 2.5-3.5 : 1-1.2.

[0019] Furthermore, in step 2(1), the molar ratio of nickel nitrate hexahydrate to aluminum nitrate nonahydrate is 2:1-1.5.

[0020] Furthermore, in step 2(1), the molar ratio of nickel nitrate hexahydrate to urea is 1:10-15.

[0021] Furthermore, in step 2(1), the molar ratio of nickel nitrate hexahydrate to ammonium fluoride is 1:3-5.

[0022] Furthermore, in step 2(2), the mass ratio of LDH to Tris-HCl is 2:3-4.

[0023] Furthermore, in step 2(2), the mass ratio of dopamine hydrochloride to Tris-HCl is 4:3-4.

[0024] Furthermore, in step 2 (3), the mass ratio of LDH / PDA to hexachlorocyclotriphosphine is 1:2-3.

[0025] Furthermore, in step 2 (3), the mass-to-volume ratio (g / mL) of LDH / PDA to triethylamine is 1:15-20.

[0026] Furthermore, in step 2 (3), the mass ratio of LDH / PCP to ZnSO4·7H2O is 5:3-4.

[0027] Furthermore, in step 2 (3), the mass ratio of ZnSO4·7H2O to Na2SnO3 is 3:1.5-2.5.

[0028] Furthermore, in step 3, the LDH / PCP@ZHS nanocomposite flame retardant accounts for 2.0-5.0% of the total mass of the matrix coating system and the LDH / PCP@ZHS hybrid.

[0029] The present invention provides a high nitrogen and phosphorus content flower-shaped hydrotalcite-based fireproof coating, which has the following beneficial effects.

[0030] The layered structure of LDH makes the heat penetration path tortuous, slowing down the combustion of the polymer matrix. In addition, the catalytic effect of Ni and Al in LDH enables the intermediates to degrade and transform into residual carbon more quickly at high temperatures. The CO2 and H2O released during the decomposition process can reduce the concentration of combustible gases in the combustion zone, carry away some heat, and play a role in gas phase flame retardancy.

[0031] The thermal degradation of HCCP generates free radicals such as PO2·, HPO2·, and HPO·. These free radicals react with reactive free radicals (H·, OH·, CH3·) generated by the resin during the thermal degradation process, thereby preventing combustion. At the same time, the synergistic effect of PDA and HCCP forms a stable CNP network, preventing heat penetration.

[0032] ZHS plays a similar role as a gas coalescing phase flame retardant during combustion, further improving the conversion rate of residual carbon, slowing down the decomposition of the resin matrix, and the metal oxides (Al2O3, NiO) and ZnSnO3 produced by pyrolysis fill the carbon layer, which can further enhance the structural strength and heat insulation of the carbon layer. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of the preparation process of LDH / PCP@ZHS flower-like heterostructure composite flame retardant.

[0034] Figure 2 SEM images of different samples are shown, where (a, b) LDH, (c, d) LDH / PDA, (e, f) LDH / PCP, and (g, h) LDH / PCP@ZHS.

[0035] Figure 3 FT-IR spectra of LDH, LDH / PDA, LDH / PCP, ZHS, and LDH / PCP@ZHS.

[0036] Figure 4 XRD spectra of LDH, LDH / PDA, LDH / PCP, ZHS and LDH / PCP@ZHS.

[0037] Figure 5 XPS spectra of the LDH / PCP@ZHS hybrid.

[0038] Figure 6 This is a graph showing the temperature change on the back side of the steel sheet and the coated sample.

[0039] Figure 7 The expansion height and expansion rate of different samples.

[0040] Figure 8 (a) Absorbance curves and (b) Smoke density ratios for different samples.

[0041] Figure 9 The images show the XRD patterns of the carbon layers after combustion of different coatings.

[0042] Figure 10 SEM images and EDS spectra of the remaining char layers after combustion tests of different samples are shown, including SEM images of the char layers of (a) EP, (b) LDH / EP, (c) LDH / PDA / EP, (d) LDH / PCP / EP, (e) ZHS / EP, (g) LDH / PCP@ZHS / EP and EDS-Mapping image of (hl) LDH / PCP@ZHS / EP. Detailed Implementation

[0043] Example 1: A method for preparing a high-nitrogen-phosphorus flower-shaped hydrotalcite-based fireproof coating, comprising the following steps.

[0044] 1. Preparation of base material.

[0045] Weigh 38g of waterborne epoxy resin (EP), 19g of curing agent, and 40g of expansion system and stir until uniform to obtain a uniformly mixed base material, wherein the expansion system includes 20g of polyphosphate (APP), 10g of pentaerythritol (PER), and 10g of melamine (MEL).

[0046] 2. Preparation of LDH / PCP@ZHS flower-like heterogeneous composite flame retardant.

[0047] (1) First, 0.58g nickel nitrate hexahydrate, 0.3751g aluminum nitrate nonahydrate, 1.8g urea and 0.3g ammonium fluoride were dissolved in 60mL of deionized water to obtain a mixed solution. Then, the mixed solution was transferred to an autoclave and hydrothermally reacted at 110℃ for 12 hours. Subsequently, the green solid obtained by centrifugation was repeatedly washed with deionized water to obtain nickel-aluminum flower-shaped LDH.

[0048] (2) 0.2 g LDH was uniformly dispersed in 100 mL of deionized water by ultrasonication, and 0.32 g Tris-HCl was added to the LDH dispersion. The pH value was adjusted to 8.5 by NaOH solution, and 0.4 g dopamine hydrochloride was added to it. The resulting mixture was stirred at room temperature for 16 hours, and then the solid was repeatedly washed with deionized water and centrifuged to obtain the hydrotalcite / polydopamine (LDH / PDA) hybrid.

[0049] (3) 0.5 g LDH / PDA and 1.5 g hexachlorocyclotriphosphazene (HCCP) were added to 100 mL of tetrahydrofuran solvent and stirred to obtain a homogeneous mixed solution. The mixed solution was then transferred to a three-necked flask, and 10 mL of triethylamine (TEA) was added to the three-necked flask. After reacting at 50 °C for 24 hours, the solid was repeatedly washed and centrifuged with tetrahydrofuran solvent to obtain the LDH / PDA / HCCP (abbreviated as: LDH / PCP) hybrid. Finally, 0.5 g LDH / PCP was uniformly dispersed in 150 mL of deionized water again by ultrasonic treatment to obtain an LDH / PCP dispersion. 30 mL of ZnSO4·7H2O (0.01 g / mL) solution was added to the dispersion, and after stirring at room temperature for 30 minutes, 20 mL of ZnSO4·7H2O solution was added. Na2SnO3 (0.01 g / mL) solution was added to the dispersion and reacted for 2 hours. The resulting solid product was repeatedly washed and centrifuged, and then freeze-dried to obtain LDH / PCP@ZHS flower-like heterostructure composite flame retardant.

[0050] 3. Preparation of high nitrogen and phosphorus content flower-shaped hydrotalcite-based fireproof coating.

[0051] Weigh 3g of LDH / PCP@ZHS flower-shaped heterostructure composite flame retardant and mix it with the base material. Stir it evenly with mechanical stirring to form a uniform coating system. Then, brush the uniformly mixed water-based intumescent fire retardant coating onto the surface of a steel sheet with a pretreatment grade of Sa2. After brushing, cure at room temperature for 7 days to obtain a high nitrogen and phosphorus flower-shaped hydrotalcite-based fire retardant coating.

[0052] ;

[0053] Experimental Example 1: This experimental example demonstrates the experimental analysis results related to the preparation method of a high nitrogen and phosphorus content flower-shaped hydrotalcite-based fireproof coating.

[0054] 3.0 wt.% of LDH, LDH / PDA, LDH / PCP, and LDH / PCP@ZHS flower-like heterostructure composite flame retardants were uniformly mixed with the matrix coating system to prepare 3.0 wt.% LDH / EP, LDH / PDA / EP, LDH / PCP / EP, and LDH / PCP@ZHS / EP coatings, respectively. Then, the uniformly dispersed coating system was brushed onto the surface of a steel sheet with a pretreatment grade of Sa2. After brushing, the coating was cured at room temperature for 7 days and baked at 40℃ for 3 days to obtain the sample coating. In addition, a pure EP coating was used as a control in the experiment.

[0055] (1) The microstructure of LDH, LDH / PDA, LDH / PCP hybrid and LDH / PCP@ZHS flower-like heterostructure composite flame retardant was observed by SEM. The results are as follows: Figure 2 As shown; in Figure 2 In (a, b), spherical materials with uniform size and flower-like surface can be observed, confirming the correct preparation process of LDH; for the LDH / PDA sample ( Figure 2 (c, d)), the morphology still exhibits a uniformly sized sphere, but from the magnified image (segment 2(d) of Figure), the stripes on the LDH surface are covered, which is caused by the load of the PDA; in Figure 2 In (e, f), the surface deposits on LDH / PCP are significantly increased compared to LDH / PDA, which demonstrates the accumulation of HCCP on the LDH / PDA surface; Figure 2 (g, h) shows that the surface of the flower-like material is uniformly loaded with a large number of cubic particles, indicating that ZHS is fixed on LDH / PCP by chemical bonds. The presence of these chemical bonds effectively avoids the self-polymerization of ZHS and improves the stability of the LDH / PCP@ZHS flower-like heterostructure composite flame retardant, which provides favorable conditions for its multifunctional flame retardancy.

[0056] (2) The composition and structure of LDH, LDH / PDA, LDH / PCP and LDH / PCP@ZHS were detected by Fourier transform infrared spectroscopy (FT-IR), and the results are as follows: Figure 3 As shown; in the case of LDH, 3488cm -1 The broad peak nearby is attributed to the -OH group in the metal hydroxide, 1641 cm⁻¹ -1 The broad peak in the vicinity is attributed to the vibration of water molecules in the LDH interlayer, 1365 cm⁻¹. -1 and 770cm -1 Nearby peaks and CO3 formation in LDH interlayers 2- Related; with 580 and 419 cm -1 The peak centered at 1501 cm⁻¹ is attributed to metal oxides (Ni-O and Al-O); for the LDH / PDA sample, a peak at 1501 cm⁻¹ can be observed. -1 1394 cm -1 The newly appearing peaks nearby are attributed to the tensile vibrations of the NH and CN backbones in LDH / PDA, indicating that PDA has been successfully loaded onto LDH; for LDH / PCP, at 1185 cm⁻¹... -1 The broad peak nearby is attributed to the stretching vibration of the P=N group in HCCP, 978 cm⁻¹ -1 The broad peaks nearby originate from the tensile vibrations of COP, indicating that PDA has reacted with HCCP; for ZHS, the peak at 1179 cm⁻¹... -1 The characteristic peak at 787 cm⁻¹ is attributed to the OH stretching vibration. -1 and 543 cm -1 The absorption peaks are attributed to the characteristic tensile vibrations of Sn-O and Zn-O. By comparison, it was found that the typical absorption peaks of LDH, PDA, HCCP and ZHS also appeared in the FT-IR curve of LDH / PCP@ZHS, which is strong evidence of the successful preparation of composite materials.

[0057] (3) The crystal structures of LDH, LDH / PDA, LDH / PCP hybrids and LDH / PCP@ZHS flower-like heterostructure composite flame retardants were detected by X-ray diffraction (XRD). The results are as follows: Figure 4As shown; the synthesized LDH exhibited a series of sharp peaks at 11.4° (003), 23.2° (006), 34.9° (012), 39.5° (015), 46.9° (018), 60.9° (110), and 62.1° (113), demonstrating its high purity; LDH / PDA and LDH / PCP similarly showed LDH-specific diffraction peaks, indicating that the layered structure of LDH was not destroyed by PDA and HCCP, but the characteristic peak intensity of LDH was slightly reduced, which may be due to the encapsulation effect of organic matter; ZH S exhibits some sharp peaks at 19.6°, 22.9°, 32.6°, 40.2°, 46.8°, 52.7°, 58.3°, 68.2°, and 73.3°, which are highly consistent with JCPDS:NO.74-1825. This also proves that the obtained ZHS particles have high purity and a good crystalline structure. In the LDH / PCP@ZHS flower-like heterostructure composite flame retardant, all the sharp peaks of LDH and ZHS appear in the same diffraction pattern, which proves that LDH and ZHS maintain their complete crystal forms during the bonding process.

[0058] (4) The elemental composition and chemical bond states of the LDH / PCP@ZHS flower-like heterostructure composite flame retardant were characterized by X-ray photoelectron spectroscopy (XPS), and the results are as follows: Figure 5 As shown; from Figure 5 (a) It can be observed that signals of Zn, Ni, O, Sn, N, C, P and Al were detected, revealing the main constituent elements of the composite material; in the C1s spectrum ( Figure 5 (b) The four signals located at 284.7 eV, 285.8 eV, 286.3 eV, and 288.6 eV belong to CC / C=C, CN, OC=O, and CO bonds, respectively; Figure 5 In (c), the N1s spectrum decomposes into three peaks at 398.1 eV, 399.5 eV, and 400.9 eV, corresponding to -NH2, -NH, and =N bonds, respectively; in the O1s spectrum ( Figure 5 In (d), signals at four positions—530.4 eV, 531.4 eV, 532.5 eV, and 533.3 eV—can be clearly detected, belonging to the -OH / Zn-O, -PO, C=O, and CO bonds, respectively; Figure 5 In (e), the P2p spectrum mainly consists of PC (132.3 eV), PN (133.4 eV), and CO-PO3 (134.7 eV), which is further evidence of the successful doping of HCCP into LDH / PDA; Figure 5 In (f), five peaks can be detected in the Ni2p spectrum, namely Ni2p3 / 2 (856.6 eV), Ni 3+(858.6 eV); Ni 3+ The presence of Ni may be due to the reaction process. 2+ Caused by oxidation; in Figure 5 In (g), the Al2p spectrum mainly shows peaks at Al2p3 / 2 (68.5 eV) and Al2p1 / 2 (74.4 eV), while the peaks at 70.1 eV and 71.5 eV mainly originate from satellites; Figure 5 In (h), the Sn3d spectrum shows Sn at 486.9 eV and 495.5 eV, respectively. 2+ The Sn 3d5 / 2 and Sn 3d3 / 2 peaks; in addition, in Figure 5 In (i), the absorption peaks at 1022.5 eV and 1045.6 eV in the Zn2p spectrum belong to the internal electron binding energies of Zn2p3 / 2 and Zn2p1 / 2, respectively.

[0059] (5) The temperature change trend of the back side of different coatings during combustion is as follows: Figure 6 As shown in the figure, it is clear that the uncoated steel plate rapidly heats to over 500℃ within 10 minutes, an irreversible process that severely damages the steel plate and affects its performance. After applying the EP coating, the temperature rise on the back side is significantly reduced compared to the pure steel plate, eventually stabilizing at 265.9℃, proving that the addition of EP contributes to the temperature barrier. After adding LDH, the final temperature of the LDH / EP combination remains at 206.4℃, indicating that the addition of LDH is significantly effective in enhancing the thermal insulation performance of the intumescent coating. Compared to LDH / EP, the temperature of the LDH / PDA / EP combination is reduced by 17.1℃, indicating that the PDA coating has a certain effect. This is beneficial for improving the thermal insulation performance of the composite coating. For the LDH / PCP / EP sample, the final temperature stabilized at 178.2℃, which is related to the formation of a stable CNP network structure by the reaction of high phosphorus and high nitrogen content groups in PCP during combustion. In the case of the ZHS / EP sample, the equilibrium temperature on the back of the steel plate dropped to 197.6℃, which may be related to the gas-phase flame retardant effect and catalytic carbonization effect of ZHS. The back temperature of the LDH / PCP@ZHS / EP sample was the lowest among all samples (162.6℃). This significant reduction indicates that this nanocomposite material can give full play to the advantages of each component and improve the flame retardant effect of the composite coating.

[0060] (6) The expansion behavior of different composite coatings was studied through in-furnace experiments. The expansion height and expansion rate of different samples after calcination at 800℃ are as follows: Figure 7As shown in the test results, the swelling height and swelling rate of pure EP are 8.6 mm and 6.56, respectively, and only a small portion of swelling was observed, so it is not particularly effective in protecting steel. After adding LDH filler, the swelling height and swelling rate of the carbon layer increased to 14.2 mm and 11.01, respectively. This is mainly attributed to the fact that LDH effectively prevents the foaming gas from diffusing outward, thereby promoting the volatilization of molten carbon. For the LDH / PDA / EP and LDH / PCP / EP samples, the maximum expansion height and expansion rate of the carbon layer reached 20.4 mm and 22.3 mm, and 16.19 and 17.56, respectively, confirming that the introduction of N and P elements is beneficial to improving the carbon formation ability of the polymer during combustion, thereby limiting gas overflow and improving the expansion properties of the carbon layer. The expansion height and expansion rate of the ZHS / EP sample coating were 18.7 mm and 14.5, respectively, significantly higher than that of pure EP. This is attributed to the expansion caused by the decomposition of ZHS under high temperature conditions to generate water vapor. At the same time, the zinc stannate nanoparticles remaining in the carbon layer allow more residual carbon to be retained by the generated gas, thereby improving the foaming effect. For the LDH / PCP@ZHS / EP sample, the expansion height and expansion rate of the carbon layer reached the maximum expansion values ​​of 29.6 mm and 23.13, respectively, which can be attributed to the synergistic effect of LDH, LDH / PDA, LDH / PCP and ZHS. The results confirm that this composite material can effectively improve swelling performance.

[0061] (7) The smoke suppression performance of different samples was evaluated through smoke density testing, such as... Figure 8 As shown; from Figure 8(a) It can be seen that during combustion, the light absorption rate of pure EP is always higher than that of other samples, while LDH / PCP@ZHS / EP has the lowest light absorption, indicating that it releases the least amount of smoke during the entire combustion process; in addition, the smoke density levels of EP, LDH / EP, LDM / PDA / EP, LDN / PCP / EP, ZHS / EP and LDH / PCP@ZHS / EP are 66.7%, 55.4%, 49.6%, 41.1%, 46.6% and 35.7%, respectively; the decrease in the smoke density level of LDH / EP is attributed to the fact that LDH prevents smoke from escaping to the outside, and LDH The metal ions in the carbon help to convert intermediate products into stable ones, thereby reducing the smoke release rate. The further reduction in smoke density ratings of LDH / PDA / EP and LDH / PCP / EP is mainly due to the formation of more stable CN / NP / CNP compounds during combustion, which improves the heat resistance of the entire char layer and thus reduces the release of volatiles. The reduced smoke density of ZHS / EP is based on ZHS's ability to convert more pyrolysis products into stable carbon during combustion to reduce further decomposition and thus reduce smoke generation. The lowest smoke density rating of LDH / PCP@ZHS / EP is direct evidence of its excellent smoke suppression performance.

[0062] (8) XRD tests of residual char layer after combustion tests of different samples are as follows: Figure 9 As shown, for the pure EP coating, the diffraction peak near 24.7° of the residual carbon layer confirms its amorphous carbon structure; for LDH / EP, LDH / PDA / EP, and LDH / PCP / EP, some sharp diffraction peaks can be detected, among which the characteristic peaks at 37.8°, 44.3°, and 63.5° belong to the (111), (200), and (220) crystal planes of NiO; in addition, the diffraction peak at 51.8° mainly comes from Al2O3, indicating that LDH is converted into metal oxide during calcination, which is conducive to the formation of residual carbon; for ZHS / EP, there is a broad diffraction peak near 33.6° in the carbonized coke layer that belongs to the characteristic signal of zinc stannate, which confirms that ZHS is converted into zinc stannate; the spectrum of LDH / PCP@ZHS / EP shows that the intensity of the diffraction peaks of NiO and Al2O3 decreases, which is due to the relatively small amount of LDH in the hybrid material.

[0063] (9) The microstructure of the residual char layer after combustion tests of different samples is as follows: Figure 10 As shown; it can be seen that the carbon layer surface of EP has large voids and cracks, which allows heat and combustible gases to reach the surface of the substrate, thus determining its poor thermal insulation performance and ineffective protection of the substrate; after introducing LDH filler ( Figure 10(b) The reduced porosity on the carbon layer surface is attributed to the enhancing effect of Ni and Al metal oxides in catalytic carbon formation; however, long cracks still exist, demonstrating the limited thermal insulation performance of introducing LDH alone; for Figure 10 (c) Crack propagation on the surface of the residual carbon layer in LDH / PDA / EP was significantly improved, which has a positive impact on the thermal insulation of the residual carbon; for Figure 10 (d) The cracks on the surface of the LDH / PCP / EP residual char have disappeared, and the size of the surface dispersed pores has been significantly reduced. This means that the introduction of N and P flame-retardant elements has an effective reinforcing effect on the structure of the residual char. Figure 10 In (e), the surface of the residual carbon layer in ZHS / EP shows no cracks, but some large voids exist, which determines its limited thermal barrier capability; Figure 10 In (f), the residual carbon on the surface of LDH / PCP@ZHS / EP is relatively intact, with no obvious adverse defects, indicating good thermal insulation performance; furthermore, Figure 10 (gl) shows that P, Ni, Al, Zn and Sn elements are uniformly dispersed in LDH / PCP@ZHS / EP residual carbon, forming a high-strength and high-barrier insulating layer to resist the penetration of external heat.

Claims

1. A method for preparing a high-nitrogen-phosphorus flower-shaped hydrotalcite-based fire-retardant coating, comprising the following steps: (1) Preparation of base material Weigh out waterborne epoxy resin (EP), curing agent, and expansion system and stir until uniform to obtain a uniformly mixed base material, wherein the expansion system includes polyphosphate (APP), pentaerythritol (PER), and melamine (MEL). (2) Preparation of LDH / PCP@ZHS flower-like heterostructure composite flame retardant a. First, nickel nitrate hexahydrate, aluminum nitrate nonahydrate, urea and ammonium fluoride are dissolved in deionized water to obtain a mixed solution. Then, the mixed solution is transferred to an autoclave and hydrothermally reacted at 110°C for 12 hours. Subsequently, the green solid obtained by centrifugation is repeatedly washed with deionized water to obtain nickel-aluminum flower-shaped LDH. b. Nickel-aluminum flower-shaped LDH was uniformly dispersed in deionized water by ultrasonication, and Tris-HCl was added to the nickel-aluminum flower-shaped LDH dispersion; the pH value was adjusted to 8.5 using NaOH solution, and dopamine hydrochloride was added to it. The resulting mixture was stirred at room temperature for 16 hours, and then the solid was repeatedly washed with deionized water and centrifuged to obtain the hydrotalcite / polydopamine (LDH / PDA) hybrid. c. LDH / PDA and hexachlorocyclotriphosphazene (HCCP) were added to tetrahydrofuran (THF) solvent and stirred to obtain a homogeneous mixed solution. The mixed solution was then transferred to a three-necked flask, and triethylamine (TEA) was added to the flask. After reacting at 50°C for 24 hours, the solid was repeatedly washed and centrifuged with tetrahydrofuran solvent to obtain the LDH / PDA / HCCP (abbreviated as LDH / PCP) hybrid. Finally, LDH / PCP was re-dispersed uniformly in 150 ml of deionized water by ultrasonic treatment to obtain an LDH / PCP dispersion. ZnSO4·7H2O was added to the dispersion, and after stirring at room temperature for 30 minutes, Na2SnO3 was added to the dispersion and the reaction was continued for another 2 hours. The resulting solid product was repeatedly washed and centrifuged, and then freeze-dried to obtain the LDH / PCP@ZHS flower-like heterostructure composite flame retardant. (3) Preparation of high nitrogen and phosphorus content flower-shaped hydrotalcite-based fireproof coating Weigh out LDH / PCP@ZHS flower-shaped heterogeneous composite flame retardant and mix with the base material, and mechanically stir evenly to form a uniform coating system; then, brush the uniformly mixed water-based intumescent fire retardant coating onto the surface of a steel sheet with a pretreatment grade of Sa2, and cure at room temperature for 7 days after brushing to obtain a high nitrogen and phosphorus flower-shaped hydrotalcite-based fire retardant coating. In step (2)a, the molar ratio of nickel nitrate hexahydrate to aluminum nitrate nonahydrate is 2:1-1.5; the molar ratio of nickel nitrate hexahydrate to urea is 1:10-15; the molar ratio of nickel nitrate hexahydrate to ammonium fluoride is 1:3-5; in step (2)b, the mass ratio of LDH to Tris-HCl is 2:3-4; the mass ratio of dopamine hydrochloride to Tris-HCl is 4:3-4; in step (2)c, the mass ratio of LDH / PDA to hexachlorocyclotriphosphate is 1:2-3; LD The mass-to-volume ratio (g / mL) of H / PDA to triethylamine is 1:15-20; the mass ratio of LDH / PCP to ZnSO4·7H2O is 5:3-4; the mass ratio of ZnSO4·7H2O to Na2SnO3 is 3:1.5-2.5; in step (3), the LDH / PCP@ZHS flower-shaped heterostructure composite flame retardant accounts for 2.0-5.0% of the total mass of the matrix coating system and the LDH / PCP@ZHS flower-shaped heterostructure composite flame retardant.

2. The high nitrogen and phosphorus content flower-shaped hydrotalcite-based fireproof coating prepared by the method described in claim 1.

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