Preparation method of nickel hydroxide loaded graphite phase carbon nitride based fireproof coating

Abstract

The invention discloses a preparation method of a nickel hydroxide loaded graphite phase carbon nitride based fireproof coating. The preparation method comprises the following steps: (1) preparing a base material; (2) preparing a CPH-coated Ni (OH) 2 composite flame retardant; (3) preparing a nickel hydroxide loaded graphite phase carbon nitride based fireproof coating; according to the invention, the synergistic effect of graphite phase carbon nitride, phosphonitrilic chloride trimer and metal catalytic char formation is fully utilized, and the self-char formation capability of the polymer at high temperature is improved by doping phosphonitrilic chloride trimer (HCCP); meanwhile, metal nickel ions with the performance of catalyzing carbon formation are introduced into the compound, and the multifunctional novel CPH-Ni (OH) 2 composite flame retardant is obtained. Finally, the composite flame retardant is added into an epoxy resin matrix, and the ultra-thin epoxy intumescent fireproof coating with good fireproof performance and smoke suppression effect is successfully prepared.

Description

Technical Field

[0001] The invention belongs to the field of preparation of water-based ultra-thin epoxy intumescent fire-retardant coatings, and in particular relates to a method for preparing a nickel hydroxide-loaded graphite-phase carbon nitride-based fire-retardant coating. Background Art

[0002] Steel structures have been widely used in various fields due to their many excellent properties, such as high strength and stability. Unfortunately, due to the good thermal conductivity of the steel substrate itself, when encountering flames, the surface temperature of the steel will quickly rise to more than 600°C, which will seriously damage the strength of the steel substrate and cause safety accidents. In order to further improve the safety of steel structure buildings, it is essential to carry out fire protection on steel structures. Fire retardant coatings have become the most widely used fire protection method due to their advantages such as low cost, convenient construction and good fire resistance. Although intumescent fire retardant coatings have developed rapidly in recent years, their low carbon layer strength and tendency of carbon layer cracking, as well as their limited barrier capacity and low expansion height, make it impossible to achieve the desired flame retardant effect; nanomaterials have been proven to effectively improve the flame retardant and smoke suppression properties of polymers at low content, and also have an improvement effect on mechanical properties. Graphitic carbon nitride (g-C3N4) is a two-dimensional nanomaterial with excellent thermal stability. It can act as a physical insulator, slow down the transfer of heat, and prolong the conduction of smoke. At the same time, its molecular structure contains a large number of triazine ring structures. As the temperature rises, the non-flammable gas produced by the thermal decomposition of CN can dilute the concentration of combustible cracking gas and oxygen to achieve flame retardancy. Therefore, we propose to improve the flame retardant properties of epoxy resin matrix based on graphitic carbon nitride. Summary of the invention

[0003] Hexachlorocyclotriphosphazene (HCCP), as one of the main raw materials for synthesizing phosphorus-nitrogen flame retardants, is a cyclic inorganic-organic hybrid compound composed of alternating nitrogen and phosphorus atoms. It contains high content of nitrogen and phosphorus elements, has the advantages of low toxicity and low smoke, and exhibits excellent flame retardant effect. In addition, the polymer combustion carbonization process includes a series of complex pyrolysis reactions, including dehydrogenation, hydrogen transfer, condensation, aromatization, isomerization, etc. Transition metals can cause the pyrolysis products of polymers to deposit in the condensed phase and catalyze cracking into small molecules, which are further dehydrogenated (or dehydrated), aromatized, and isomerized. The invention makes full use of the synergistic effect of graphite phase carbon nitride, hexachlorocyclotriphosphazene and metal catalytic carbonization, and improves the self-carbonization ability of the polymer at high temperature by doping hexachlorocyclotriphosphazene (HCCP); at the same time, metal nickel ions with catalytic carbonization performance are introduced into the composite to obtain a multifunctional new composite flame retardant; finally, the composite flame retardant is added to the epoxy resin matrix to successfully prepare an ultra-thin epoxy intumescent fire retardant coating with good fire resistance and smoke suppression effect.

[0004] To achieve the above purpose, the technical solution adopted by the present invention to solve its technical problem is.

[0005] A method for preparing a nickel hydroxide-loaded graphite-phase carbon nitride-based fireproof coating comprises the following steps.

[0006] 1. Preparation of base material.

[0007] A waterborne epoxy resin (EP), a curing agent, and an expansion system are weighed and stirred until uniform to obtain a uniformly mixed base material, wherein the expansion system includes polyphosphate (APP), pentaerythritol (PER), and melamine (MEL).

[0008] 2. Preparation of CPH@Ni(OH)2 composite flame retardant.

[0009] (1) First, 10 g of melamine was calcined in a muffle furnace at 550 °C for 1 hour, and then taken out and ground into fine powder after cooling to room temperature. The ground fine powder was then spread on the surface of a crucible, and calcined at 550 °C for 15 minutes and then cooled to room temperature to obtain graphite phase carbon nitride (g-C3N4) nanosheets;

[0010] (2) 0.2 g of g-C3N4 nanosheets were ultrasonically dispersed in 100 mL of deionized water, 0.15 g of Tris-hydrochloric acid was added to the g-C3N4 dispersion under stirring, and the pH value was adjusted to 8.5 with sodium hydroxide (0.1 M) solution; then, 0.3 g of dopamine hydrochloride was added to the g-C3N4 dispersion, and the reaction was continued under stirring at room temperature for 16 hours; the reaction mixture was repeatedly centrifuged and washed to remove unreacted dopamine monomers, and finally a graphite phase carbon nitride@polydopamine (g-C3N4 / PDA) composite was obtained.

[0011] (3) 0.5 g of g-C3N4 / PDA composite was ultrasonically dispersed in 100 mL of tetrahydrofuran (THF) solvent, and then the suspension was transferred to a three-necked flask and 1.5 g of hexachlorocyclotriphosphazene (HCCP) and 10 mL of triethylamine (TEA) were added in sequence. The mixture was stirred in an oil bath at 50 °C for 24 h and then washed and centrifuged repeatedly to obtain a graphite phase carbon nitride@polydopamine@hexachlorocyclotriphosphazene (CPH) hybrid.

[0012] (4) 0.3 g of CPH hybrid was ultrasonically dispersed in 150 mL of deionized water; then the uniformly dispersed suspension was transferred to a three-necked flask and 0.2 g of nickel nitrate hexahydrate (Ni(NO3)2·6H2O), 0.07 g of trisodium citrate and 0.25 g of urea were added in sequence, and the mixture was stirred in an oil bath at 100°C for 7 hours; the precipitate was repeatedly washed by centrifugation with a mixed solution of deionized water and ethanol to obtain a graphite phase carbon nitride@polydopamine@hexachlorocyclotriphosphazene@nickel hydroxide (CPH@Ni(OH)2) composite flame retardant. The schematic diagram of the preparation of the CPH@Ni(OH)2 composite flame retardant is shown in FIG. Figure 1 shown.

[0013] 3. Preparation of nickel hydroxide loaded graphite phase carbon nitride based fire retardant coating.

[0014] Weigh the CPH@Ni(OH)2 composite flame retardant and mix it with the base material, stir it mechanically to form a uniform coating system; then, brush the evenly mixed CPH@Ni(OH)2-based water-based intumescent fire-retardant coating on the surface of a steel sheet with a pretreatment grade of Sa2. After brushing, cure it at room temperature for 7 days to obtain a nickel hydroxide-loaded graphite phase carbon nitride-based fire-retardant coating.

[0015] Furthermore, in step 1, the mass ratio of epoxy resin to 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, in step 1, the curing agent 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(2), the mass ratio of g-C3N4 to dopamine hydrochloride is 1:1-2.

[0020] Furthermore, in step 2(2), the mass ratio of Tris-hydrochloric acid to dopamine hydrochloride is 1:2.

[0021] Furthermore, in step 2(3), the mass ratio of g-C3N4 / PDA to hexachlorocyclotriphosphazene is 1:3-5.

[0022] Furthermore, in step 2(3), the mass volume ratio (g / mL) of g-C3N4 / PDA to triethylamine is 1:15-25.

[0023] Furthermore, in step 2(4), the mass ratio of g-C3N4@PDA@HCCP to nickel nitrate hexahydrate is 3:2-4.

[0024] Furthermore, in step 2(4), the mass ratio of trisodium citrate to nickel nitrate hexahydrate is 3-5:10.

[0025] Furthermore, in step 2(4), the mass ratio of nickel nitrate hexahydrate to urea is 3-5:5.

[0026] Furthermore, in step 3, the CPH@Ni(OH)2 composite flame retardant accounts for 2.0-5.0% of the total mass of the base coating system and the CPH@Ni(OH)2 composite flame retardant.

[0027] The present invention provides a method for preparing a nickel hydroxide-loaded graphite-phase carbon nitride-based fire-retardant coating, which has the following beneficial effects.

[0028] (1) The two-dimensional lamellar structure of graphite carbon nitride can increase the path for oxygen to enter and the escape path of combustible gases produced by polymer pyrolysis, reduce the contact time between oxygen and combustible gases, and improve the flame retardant properties of polymers.

[0029] (2) Hexachlorocyclotriphosphazene (HCCP) has a molecular structure with high content of N and P elements. The nitrogen-containing structure will produce non-combustible gases and free radicals during thermal decomposition, which will reduce the content of combustible gases in the combustion zone and block the combustion chain reaction. The strong dehydration property of phosphorus elements during combustion will dehydrate the polymer matrix into carbon, forming a phosphorus-rich glassy substance covering the surface of the matrix, which becomes a protective layer to isolate heat and oxygen transfer.

[0030] (3) Transition metal nickel can cause the pyrolysis products of the polymer to deposit in the condensed phase and catalyze cracking into small molecules, which are further dehydrogenated (or dehydrated), aromatized, and then cross-linked into carbon, thereby inhibiting the production of organic matter and catalyzing its carbonization, thereby improving the quality of the carbon layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 Schematic diagram of the preparation process of CPH@Ni(OH)2 composite flame retardant.

[0032] Figure 2 FT-IR spectra of CN, CN / PDA, CPH and CPH@Ni(OH)2.

[0033] Figure 3 XRD spectra of CN, CN / PDA, CPH and CPH@Ni(OH)2.

[0034] Figure 4 SEM images of different samples, including (a, b) CN, (c, d) CPH, (e, f)

[0035] CPH@Ni(OH)2.

[0036] Figure 5 This is the XPS spectrum of CPH@Ni(OH)2 composite flame retardant.

[0037] Figure 6 This is a curve diagram of the temperature change on the back of the steel sheet and the coating sample.

[0038] Figure 7 are the expansion height and expansion rate of different samples.

[0039] Figure 8 (a) Absorbance curve and (b) smoke density ratio of different samples.

[0040] Fig. 9 XRD spectra of the carbon layer after combustion of different coatings.

[0041] Fig.10 SEM morphology and EDS spectra of the remaining carbon layer after combustion test of different samples, including SEM images of carbon layer of (a) EP, (b) CN / EP, (c) CN / PDA / EP, (d) CPH / EP, (e, f) Ni(OH)2 / EP and (g) CPH@Ni(OH)2 / EP and EDS-Mapping photo of (hl) CPH@Ni(OH)2 / EP. DETAILED DESCRIPTION

[0042] Example 1.

[0043] A method for preparing a nickel hydroxide-loaded graphite-phase carbon nitride-based fireproof coating comprises the following steps.

[0044] 1. Preparation of base material.

[0045] A waterborne epoxy resin (EP), a curing agent, and an expansion system are weighed and stirred until uniform to obtain a uniformly mixed base material, wherein the expansion system includes polyphosphate (APP), pentaerythritol (PER), and melamine (MEL).

[0046] 2. Preparation of CPH@Ni(OH)2 composite flame retardant.

[0047] (1) First, 10 g of melamine was calcined in a muffle furnace at 550 °C for 1 hour, and then taken out and ground into fine powder after cooling to room temperature. The ground fine powder was then spread on the surface of a crucible, and calcined at 550 °C for 15 minutes and then cooled to room temperature to obtain graphite phase carbon nitride (g-C3N4) nanosheets;

[0048] (2) 0.2 g of g-C3N4 nanosheets were ultrasonically dispersed in 100 mL of deionized water, 0.15 g of Tris-hydrochloric acid was added to the g-C3N4 dispersion under stirring, and the pH value was adjusted to 8.5 with sodium hydroxide (0.1 M) solution; then, 0.3 g of dopamine hydrochloride was added to the g-C3N4 dispersion, and the reaction was continued under stirring at room temperature for 16 hours; the reaction mixture was repeatedly centrifuged and washed to remove unreacted dopamine monomers, and finally a graphite phase carbon nitride@polydopamine (g-C3N4 / PDA) composite was obtained.

[0049] (3) 0.5 g of g-C3N4 / PDA composite was ultrasonically dispersed in 100 mL of tetrahydrofuran (THF) solvent, and then the suspension was transferred to a three-necked flask and 1.5 g of hexachlorocyclotriphosphazene (HCCP) and 10 mL of triethylamine (TEA) were added in sequence. The mixture was stirred in an oil bath at 50 °C for 24 h and then washed and centrifuged repeatedly to obtain a graphite phase carbon nitride@polydopamine@hexachlorocyclotriphosphazene (CPH) hybrid.

[0050] (4) 0.3 g of CPH hybrid was ultrasonically dispersed in 150 mL of deionized water; then the uniformly dispersed suspension was transferred to a three-necked flask and 0.2 g of nickel nitrate hexahydrate (Ni(NO3)2·6H2O), 0.07 g of trisodium citrate and 0.25 g of urea were added in sequence, and the mixture was stirred in an oil bath at 100°C for 7 hours; the precipitate was repeatedly washed by centrifugation with a mixed solution of deionized water and ethanol to obtain a graphite phase carbon nitride@polydopamine@hexachlorocyclotriphosphazene@nickel hydroxide (CPH@Ni(OH)2) composite flame retardant. The schematic diagram of the preparation of the CPH@Ni(OH)2 composite flame retardant is shown in FIG. Figure 1 shown.

[0051] 3. Preparation of nickel hydroxide loaded graphite phase carbon nitride based fire retardant coating.

[0052] Weigh 2g of CPH@Ni(OH)2 composite flame retardant and mix it with the base material, stir it mechanically to form a uniform coating system; then, brush the evenly mixed CPH@Ni(OH)2-based water-based intumescent fire retardant coating on the surface of a steel sheet with a pretreatment grade of Sa2. After brushing, cure it at room temperature for 7 days to obtain a nickel hydroxide-loaded graphite phase carbon nitride-based fire retardant coating.

[0053] Table 1 Composition of different intumescent fire retardant coatings

[0054]

[0055] Experimental example 1.

[0056] This experimental example demonstrates the relevant experimental analysis results of a method for preparing a nickel hydroxide-loaded graphite-phase carbon nitride-based fire retardant coating.

[0057] 2.0wt.% CN, CN / PDA, CPH, Ni(OH)2 and CPH@Ni(OH)2 hybrids were uniformly mixed with the matrix coating system to prepare 2.0wt.% CN / EP, CN / PDA / EP, CPH / EP, Ni(OH)2 / EP and CPH@Ni(OH)2 / EP coatings, respectively; then, the evenly dispersed coating system was brushed on the surface of steel sheets with a pretreatment grade of Sa2. After brushing, the coating was cured at room temperature for 7 days and baked at 40°C for 3 days to obtain the sample coating; in addition, the experiment used pure EP coating as a control.

[0058] (1) Figure 2 The infrared spectra of CN, CN / PDA, CPH, and CPH@Ni(OH)2 hybrid materials are shown; for pure CN, 807 cm -1 The sharp absorption peaks at 1201 and 1682 cm -1 A series of characteristic peaks between 3000-3450cm -1 The broad peaks in the range can be attributed to the -NH2 and -NH vibrations at the CN structural defects and the -OH vibrations in the absorbed water; for CN / PDA, the peaks are located at 644 and 671 cm -1 Two new characteristic peaks appeared at 1133 cm-1, which mainly corresponded to the bending vibration of CO in the PDA structure; for the CPH hybrid, -1 The peak at 603 cm-1 is attributed to the vibration absorption of P=N in cyclotriphosphazene, while the peaks at 603 cm-1 and 562 cm-1 are attributed to the vibration absorption of P=N in cyclotriphosphazene. -1 The characteristic peak at 985cm-1 is mainly attributed to the vibration absorption of P-Cl in HCCP monomer. In general, after HCCP is grafted onto the PDA shell, the nucleophilic substitution reaction between P-Cl bond and hydroxyl group is formed. -1 New COP chemical bonds are formed near the CPH@Ni(OH)2 hybrid. In addition to the characteristic absorption peaks of CN, PDA, and HCCP structures, a peak at 660 cm -1 A new absorption peak is found at the CPH@Ni(OH)2 structure, which is mainly related to the bending vibration of Ni-OH in the CPH@Ni(OH)2 structure.

[0059] (2) The crystal structures of CN, CN / PDA, CPH and CPH@Ni(OH)2 hybrid materials were tested by X-ray diffractometer (XRD). Figure 3As shown; pure CN presents a sharp characteristic peak at 2θ=27.8°, which is mainly attributed to the (002) crystal plane of CN; for CN / PDA and CPH hybrids, the characteristic diffraction peaks of CN can be observed, indicating that PDA and HCCP will not change the structure of CN during the modification process, so its diffraction peaks remain unchanged; however, the peak intensity at 2θ=27.8° is reduced, which is mainly attributed to the formation of a PDA layer on the surface of CN; for CPH@Ni(OH)2 composite flame retardant, all characteristic peaks of CN and Ni(OH)2 can be detected simultaneously, among which 2θ=19.4°, 32.7°, 38.2° and 52.3° belong to the (001), (100), (101) and (102) crystal planes of Ni(OH)2, respectively.

[0060] (3) The microstructures of CN, CPH and CPH@Ni(OH)2 hybrids were observed by SEM. Figure 4 shown; from Figure 4 (ab) It can be seen that pure CN shows ultrathin nanosheet morphology and obvious corrugations; Figure 4 (cd) It can be seen that after the addition of PDA and HCCP, the micromorphology of CN nanosheets changed and its surface became rough, indicating the successful introduction of PDA and HCCP; from the micromorphology of CPH@Ni(OH)2 composite flame retardant, it can be seen (4(ef)) that the surface of CPH presents obvious particles, which is mainly attributed to the presence of Ni(OH)2.

[0061] (4) X-ray photoelectron spectroscopy (XPS) was used to characterize the elemental composition and chemical bond state of the CPH@Ni(OH)2 composite flame retardant. Figure 5 shown; from Figure 5 (a) In the full spectrum, we can see that there are signal peaks of five elements, namely C, N, O, P, and Ni, in the CPH@Ni(OH)2 hybrid, which confirms the successful doping of CPH and Ni ions. Figure 5 In (b), the high-resolution spectrum of C 1s can be decomposed into three peaks at 284.7 eV, 285.6 eV and 286.3 eV, which correspond to CC / C=C, CN and CO chemical bonds respectively; O 1s spectrum ( Figure 5 (c)) can be fitted into three clear peaks, of which 530.6 eV, 531.7 eV and 532.4 eV are attributed to CO-Ni, C=O / O-Ni and CNP / C-OH, respectively; Figure 5 The N1s spectrum in (d) mainly includes three peaks at 398.5eV, 399.6eV and 400.7eV, which correspond to -NH2 / CN=C, -NH- / N(C)3, and NH chemical bonds, respectively; the spectrum of P 2p ( Figure 5(e)) is mainly decomposed into three peaks at 132.4eV, 133.2eV and 134.1eV, which belong to PC, PN and CO-PO3 chemical bonds respectively. This is consistent with the chemical bond state of P in CPH molecule; for Ni 2p spectrum ( Figure 5 (f)), the two main peaks located at 855.5 eV and 873.4 eV are related to the formation of Ni2p3 / 2, Ni2p1 / 2 and Ni2p3 / 2, Ni2p1 / 2 salts, respectively.

[0062] (5) The thermal insulation performance of the coating can be directly reflected by recording the back temperature of the steel plate; Figure 6 The changes in the back temperature of different samples during the combustion process were recorded; it is not difficult to find from the figure that the back temperature of the uncoated steel plate rises to nearly 500°C in a short period of time, which seriously damages the strength of the steel plate itself; for the steel plate coated with pure EP coating, it can be found that the rate of increase of its back temperature is significantly reduced, and finally stabilized at 265.9°C, which shows that EP has an effective thermal protection effect; after adding CN, the back temperature of the steel plate is finally reduced to 204.8°C, which shows that the barrier property of CN nanosheets can improve the thermal insulation performance of the coating; for the CN / PDA / EP composite coating, its back temperature is further reduced to 194.9°C, which shows that the introduction of PDA can improve the dispersibility of CN, and the ammonia and water vapor produced by the pyrolysis of PDA can reduce to a certain extent The concentration of combustibles and the combustion temperature achieve a gas phase flame retardant effect, thereby further improving the thermal insulation performance of the coating; for the CPH / EP coating, the back temperature is further reduced to 177.3°C, which indicates that the thermal protection performance of CPH is further improved, which is mainly attributed to the gas phase flame retardant effect of HCCP with high content of P and N elements; for the Ni(OH)2 composite coating samples, by comparing the back temperature of CPH, it can be found that the thermal protection performance of Ni(OH)2 has decreased, but it is also better than the thermal protection performance of pure EP, indicating that it can also improve the thermal protection performance of the coating; for CPH@Ni(OH)2, the back temperature drops to the lowest (168.6°C), which can be attributed to the synergistic enhancement of CPH and Ni ions. At this time, the coating has the best thermal protection performance.

[0063] (6) The expansion parameters obtained from the experiment are as follows Figure 7As shown in the figure, by comparison, it is found that pure EP has the worst expansion height and expansion rate, which is consistent with the worst thermal insulation performance of pure epoxy coating. After adding CN, the expansion height and expansion rate of CN / EP increased significantly, reaching 12.9mm and 10.24 respectively, indicating that the addition of CN can effectively promote the formation of residual carbon. For the composite coating of CN / PDA / EP, the expansion height and expansion rate continued to increase to 17.3mm and 13.62, which is mainly because PDA decomposes at high temperature, and the ammonia and water vapor produced by the decomposition can reduce the thermal insulation performance to a certain extent. Low combustible concentration and combustion temperature; for the CPH-based EP composite coating, the expansion height and expansion rate became 21.7 mm and 17.36, while for the Ni(OH)2 / EP composite coating, the expansion height and expansion rate were 19.5 mm and 15.35, respectively. This is because metallic nickel catalyzes the conversion of organic cracking products to carbon during combustion; for the CPH@Ni(OH)2 / EP composite flame retardant, its expansion height and expansion rate both reached the maximum value (24.1 mm, 18.83), indicating that the effect is best when CPH and Ni ions work together.

[0064] (7) The smoke release performance of pure epoxy coatings and other composite coatings during combustion was tested through smoke density experiments. The data results are as follows: Figure 8 shown; from Figure 8 (a) It can be found that the light absorption rate of pure epoxy coating during combustion is significantly higher than that of other composite coating samples, which means that pure epoxy coating has a higher smoke release rate; after the introduction of CN, the light absorption rate of the composite coating sample has been significantly reduced; the specific smoke density level of each sample is as follows Figure 8 (b) shows that the smoke density level of pure epoxy coating reaches the maximum value (66.7%). After adding CN, the smoke density level is reduced to 57.8%, which indicates that CN has an inhibitory effect on the release of smoke. For the CN / PDA / EP composite coating sample, the smoke density level is further reduced to 52.3%. This is because the phosphoric acid molecules produced by the thermal decomposition of CN / PDA prevent the organic matter from degrading into small molecules and then continuing to decompose. For the CPH@Ni(OH)2 / EP composite coating, it has the lowest smoke density level. This is attributed to the catalytic effect of Ni ions on residual carbon. Similar to the previous experimental results, the samples with CPH and Ni(OH)2 hybrid materials added separately also show an increase in smoke density level, indicating that only the combined effect of the two can achieve the best effect.

[0065] (8) The crystal structure of the residual carbon layer was analyzed by XRD. Fig. 9As shown in the figure, only a broad and weak diffraction peak was observed at 2θ=24.7° for the carbon layer of the pure epoxy coating after combustion, which is basically consistent with the characteristic peak of amorphous carbon; the XRD spectra of the carbon layer of the CN / EP, CPH / EP and CN / PDA / EP composite coatings after combustion are not significantly different from those of the pure epoxy coating, which indicates that the introduction of CN, CN / PDA and CPH has no obvious effect on the crystal composition of the residual carbon; from the XRD of the carbon layer of the Ni(OH)2 / EP and CPH@Ni(OH)2 composite coatings, a series of diffraction peaks at 2θ=37.3°, 43.3°, 62.8° and 75.5° can be observed, which is consistent with the characteristic peaks of the (111), (200), (220), (311) and (222) crystal planes of nickel oxide (NiO), indicating that the doped Ni ions are converted into NiO during the combustion process, which promotes the catalytic carbonization of the polymer and effectively improves the quality of the residual carbon.

[0066] (9) The morphology and integrity of the carbon layer after the composite coating is burned are closely related to its thermal insulation performance. Fig.10 shown; from Fig.10 It is not difficult to find in (a) that the surface of the carbon layer obtained after the combustion of pure epoxy coating contains a large number of voids and cracks, which indicates that it is not effective in blocking external heat and preventing the leakage of internal smoke; after adding CN to EP ( Fig.10 (b)), due to the reinforcing effect of CN on the residual carbon, it can be found that there are almost no large holes on the surface of the carbon layer, but there are still many cracks; for the sample of CN / PDA composite coating ( Fig.10 (c)), large pores and cracks appeared on the surface of the carbon layer again; while the carbon layer of CPH / EP ( Fig.10 (d)) There are almost no large voids and cracks on its surface, but there are small holes and cracks; this is consistent with the previous fire performance test results; for Ni(OH)2 / EP( Fig.10 (e,f)) coating, the residual carbon layer obtained after combustion has holes and cracks, but the number is small, which has a certain effect on blocking external heat; after adding CPH@Ni(OH)2 composite flame retardant, the composite coating has a residual carbon layer after combustion ( Fig.10 (g)) There are no gaps or cracks on the surface, which can effectively prevent the spread of external heat and the leakage of smoke, so it has the best protection performance; from the element distribution of the CPH@Ni(OH)2 / EP residual carbon layer, it can be seen that C, N, P, O, and Ni elements are evenly distributed in the residual carbon.

Claims

1. A method for preparing a nickel hydroxide-supported graphite-phase carbon nitride-based fire-retardant coating, comprising the following steps: (1) Preparation of base material 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); (2) CPH@Ni(OH) 2 Preparation of composite flame retardant a. First, 10 g of melamine was calcined in a muffle furnace at 550 ° C for 1 hour, and then taken out and ground into fine powder after cooling to room temperature. Then, the ground fine powder was spread on the surface of the crucible, and calcined at 550 ° C for 15 minutes and then cooled to room temperature to obtain graphite phase carbon nitride (gC 3 N 4 ) nanosheets; b. Add 0.2g gC 3 N 4 The nanosheets were ultrasonically dispersed in 100 mL of deionized water and stirred to gC 3 N 4 0.15 g of Tris-hydrochloric acid was added to the dispersion, and the pH value was adjusted to 8.5 using a 0.1 mol / L sodium hydroxide solution; then, 0.3 g of dopamine hydrochloride was added to the dispersion. 3 N 4 The dispersion was stirred and reacted for 16 hours at room temperature; the reaction mixture was repeatedly centrifuged and washed to remove the unreacted dopamine monomer, and finally graphite carbon nitride@polydopamine (gC 3 N 4 / PDA) complex; c. Add 0.5g gC 3 N 4 The gC / PDA complex was ultrasonically dispersed in 100 mL of tetrahydrofuran solvent, and then 3 N 4 The / PDA suspension was transferred to a three-necked flask, and then 1.5 g of hexachlorocyclotriphosphazene (HCCP) and 10 mL of triethylamine (TEA) were added in sequence. The mixture was stirred in an oil bath at 50 °C for 24 hours, and then washed and centrifuged repeatedly to obtain a graphite phase carbon nitride@polydopamine@hexachlorocyclotriphosphazene (CPH) hybrid. d. Ultrasonic dispersion of 0.3 g CPH hybrid was performed in 150 mL deionized water. The uniformly dispersed suspension was then transferred to a three-necked flask and 0.2 g nickel nitrate hexahydrate (Ni(NO 3 ) 2 6H 2 O), 0.07 g trisodium citrate and 0.25 g urea, and stirred in an oil bath at 100 ° C for 7 hours; the precipitate was repeatedly washed by centrifugation with a mixed solution of deionized water and ethanol to obtain graphite phase carbon nitride @ polydopamine @ hexachlorocyclotriphosphazene @ nickel hydroxide (CPH@Ni(OH) 2 ) Composite flame retardant (3) Preparation of nickel hydroxide-loaded graphite-phase carbon nitride-based fire retardant coating Weigh 2g CPH@Ni(OH) 2 The composite flame retardant is mixed with the base material and mechanically stirred to form a uniform coating system; then, the uniformly mixed CPH@Ni(OH) 2 The water-based intumescent fire retardant coating is brushed on the surface of a steel sheet with a pretreatment grade of Sa2, and cured at room temperature for 7 days after the brushing is completed to obtain a nickel hydroxide-supported graphite phase carbon nitride-based fire retardant coating; Step 2(b) gC 3 N 4 The mass ratio of Tris-hydrochloric acid to dopamine hydrochloride is 1:1-2; the mass ratio of Tris-hydrochloric acid to dopamine hydrochloride is 1:2; in step 2(c), gC 3 N 4 / The mass ratio of PDA to hexachlorocyclotriphosphazene is 1:3-5; gC 3 N 4 The mass volume ratio (g / mL) of PDA to triethylamine is 1:15-25; the mass ratio of CPH to nickel nitrate hexahydrate in step 2(d) is 3:2-4; the mass ratio of trisodium citrate to nickel nitrate hexahydrate is 3-5:10; the mass ratio of nickel nitrate hexahydrate to urea is 3-5:5; the mass ratio of CPH@Ni(OH) 2 Composite flame retardant accounts for the base coating system and CPH@Ni(OH) 2 2.0-5.0% of the total mass of the composite flame retardant.

2. A nickel hydroxide-loaded graphite-phase carbon nitride-based fire-retardant coating prepared by the method of claim 1.

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