Graphene oxide-based fireproof coating and method for preparing the same

Abstract

The application discloses a novel graphene oxide-based fireproof coating and a preparation method thereof in the technical field of novel fireproof materials, and raw materials of the graphene oxide-based fireproof coating include the following components: polyurethane type SMP: 30-35%; biomass-derived modified graphene oxide: 15-18%; melamine cyanurate@ZIF-8: 20-25%; furan-maleimide polymer: 10-12%; boron carbide nanowire: 5-8%; supercritical CO2 dispersion system: the balance; wherein the biomass-derived modified graphene oxide is obtained by chemical modification treatment of graphene oxide with chitosan to introduce nitrogen-containing or oxygen-containing polar groups on the surface of the graphene oxide. The graphene oxide-based fireproof coating realizes UL-94 V0 level flame retardation through three mechanisms of physical barrier, gas phase flame retardation and dynamic repair, and has high mechanical strength and heat resistance, and is suitable for substrate protection of metals, wood and the like.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of new fireproof materials, in particular to a graphene oxide-based fireproof coating and a preparation method thereof. BACKGROUND

[0002] With the rapid development of the fields of building, transportation, electronics, etc., higher requirements are put forward for the fire safety performance of materials. Traditional fireproof coatings mainly rely on halogen-based flame retardants (such as brominated epoxy resin) or inorganic fillers (such as aluminum hydroxide, expanded graphite), although they have certain flame-retardant effect, but have the following technical defects: 1. Environmental problem: halogen-based flame retardants release toxic gases (such as HBr, dioxin) when burning, which does not meet the green and environmentally friendly development trend. 2. Mechanical property degradation: a large amount of inorganic fillers will cause the coating to lose flexibility and easily crack and fall off, affecting long-term use performance. 3. Insufficient flame-retardant efficiency: the carbon layer formed by traditional intumescent coatings at high temperature is loose and porous, and is easily penetrated by fire, making it difficult to meet the UL-94 V0 level requirement. 4. Poor interfacial compatibility: nano flame retardants (such as graphene oxide) are prone to agglomeration and difficult to disperse uniformly in the polymer matrix, limiting the exertion of their flame-retardant efficiency.

[0003] In recent years, graphene oxide (GO) has been introduced into fireproof coatings due to its two-dimensional sheet structure and excellent thermal conductivity / barrier properties, but unmodified GO has poor compatibility with polymers and lacks the ability to catalyze carbon formation. Although there have been studies on the modification of GO by silane coupling agents, the modified GO still has the problem of insufficient nitrogen / phosphorus flame-retardant elements. On the other hand, melamine cyanurate as a gas-phase flame retardant is prone to migration and precipitation when used alone, and metal-organic frameworks, although they can adsorb free radicals, have limited thermal stability. In addition, traditional solvent dispersion methods cannot achieve uniform distribution of nanomaterials (such as boron carbide nanowires), resulting in local defects in the coating.

[0004] Therefore, it is a technical problem to be solved to develop a new type of fireproof coating that has high-efficiency flame retardation, environmental friendliness, excellent mechanical properties, and controllable process. SUMMARY

[0005] The present application aims to provide a graphene oxide-based fireproof coating and a preparation method thereof, which solves the problems of poor flame-retardant effect, mechanical property, and environmental unfriendliness of existing graphene oxide-based fireproof coatings.

[0006] The present application achieves the above-mentioned purpose by the following technical solutions:

[0007] The graphene oxide-based fireproof coating comprises, by mass percentage:

[0008] Polyurethane type SMP: 30-35%;

[0009] Biomass-derived modified graphene oxide: 15-18%;

[0010] Melamine cyanurate@ZIF-8: 20-25%;

[0011] Furan-maleimide polymer: 10-12%;

[0012] Boron carbide nanowires: 5-8%;

[0013] Supercritical CO2 dispersion system: the balance;

[0014] In the present application, the biomass-derived modified graphene oxide is graphene oxide treated by chemical modification of chitosan to introduce polar groups containing nitrogen or oxygen on the surface thereof.

[0015] In the present application, the melamine cyanurate@ZIF-8 loaded flame retardant and the biomass-derived modified graphene oxide synergistically catalyze the formation of carbon, forming an expanded carbon layer; the decomposition gas of melamine cyanurate@ZIF-8 and the physical barrier of biomass-derived modified graphene oxide are combined to enhance the heat insulation effect; the nitrogen-containing groups of chitosan form a P-N synergistic system with phosphate flame retardants (melamine cyanurate) to improve the flame retardant level; the boron carbide heat conduction network disperses heat to reduce the thermal degradation rate of the substrate; the phase change characteristics of the polyurethane type SMP and the dynamic crosslinked network jointly maintain the mechanical strength of the coating at high temperature; the dynamic bond repairs microcracks, and the biomass-derived modified graphene oxide sheet layer fills and repairs the defect area, which double guarantees the long-term stability of the coating.

[0016] In the present application, the polyurethane type SMP is used as the coating substrate, which undergoes phase change at high temperature through the thermal shape memory characteristics, maintains the integrity of the coating structure, and inhibits crack propagation; and the polyurethane type SMP is dynamically crosslinked with the furan-maleimide polymer to form a reversible network structure, thereby enhancing the self-repairing ability of the coating.

[0017] According to a preferred embodiment of the present application, the polyurethane type SMP is SMP model purchased from Dongguan Guangsiyuan Polyurethane Material Co., Ltd.

[0018] According to a preferred embodiment of the present application, the preparation steps of the biomass-derived modified graphene oxide include dispersing graphene oxide in deionized water, adding chitosan, centrifugal washing, and freeze-drying.

[0019] In the present application, the biomass-derived modified graphene oxide is graphene oxide modified by chitosan to introduce polar groups such as amino and hydroxyl groups, which form hydrogen bonds and chemical bonds with the polyurethane matrix to improve the interfacial bonding strength and mechanical properties; the graphene oxide sheet layer forms a dense carbon layer during combustion to insulate oxygen and heat transfer; and the nitrogen-containing groups (from chitosan) synergize with phosphorus-nitrogen flame retardants to promote the formation of an expanded carbon layer.

[0020] According to the preferred embodiment of the present application, the graphene oxide is purchased from Suzhou Yuhao Nanometer Material Co., Ltd.

[0021] According to the preferred embodiment of the present application, the deionized water is purchased from Shanghai Lianmai Biological Engineering Co., Ltd.

[0022] According to the preferred embodiment of the present application, the chitosan is purchased from Shandong Guangxin Biological Technology Co., Ltd.

[0023] According to the preferred embodiment of the present application, the graphene oxide is dispersed in the deionized water and ultrasonically treated for 2 hours; the mass ratio of the graphene oxide and the chitosan is 1:0.5-1, and the chitosan is stirred and reacted at 60 DEG C for 12 hours after being added.

[0024] In the present application, the ultrasonic treatment for 2 hours makes the graphene oxide (GO) uniformly dispersed in the deionized water, destroys the van der Waals force between the layers, and exposes the active groups (-COOH, -C-O-C-) such as the carboxyl groups and the epoxy groups; the -NH2 in the chitosan molecules reacts with the -COOH on the surface of the graphene oxide to form an amide reaction (or an open-loop reaction with the epoxy group), and a covalent bond is formed, and meanwhile, the hydroxyl groups of the chitosan enhance the interface bonding through hydrogen bonding; 60 DEG C promotes the kinetics of the amide reaction, and 12 hours ensures sufficient reaction; and the mass ratio of 1:0.5-1 balances the modification rate and the dispersion stability of GO.

[0025] According to the preferred embodiment of the present application, the preparation method of the melamine cyanurate@ZIF-8 comprises the following steps: dissolving melamine cyanurate in methanol, adding a zinc nitrate solution, stirring and mixing, adding a 2-methyl imidazole methanol solution for reaction to obtain a crude product, and then performing centrifugation, methanol washing, drying, and grinding into a powder.

[0026] In the present application, the zinc nitrate and the 2-methyl imidazole (2-MIM) are subjected to a coordination reaction in methanol to form a tetrahedral network structure of Zn 2+ and 2-MIM, that is, a ZIF-8 framework; the melamine cyanurate (MCA) is adsorbed on the surface of the ZIF-8 through π-π stacking and hydrogen bonding, and the reaction temperature of 10-30 DEG C avoids the ZIF-8 from being crystallized too fast to cause the MCA to fall off; the MCA in the MCA@ZIF-8 composite serves as an acid source and a gas source, and the porous structure of the ZIF-8 enhances the thermal stability and the dispersibility of the MCA.

[0027] In the present application, the melamine cyanurate@ZIF-8 releases non-combustible gases such as NH3 and H2O by thermal decomposition, dilutes the combustible gas concentration, and the thermal decomposition product (ZnO) of the ZIF-8 framework and the phosphate of the melamine cyanurate jointly catalyze the carbonization to form a continuous heat insulation layer; the microporous structure of the ZIF-8 delays the decomposition rate of the flame retardant and prolongs the fireproofing time.

[0028] According to the preferred embodiment of the present application, the melamine cyanurate is purchased from Guangzhou Yinnian New Material Co., Ltd.

[0029] According to the preferred embodiment of the present application, the methanol is purchased from Liaocheng Tongda Chemical Co., Ltd.

[0030] According to the preferred embodiment of the present application, the zinc nitrate is purchased from Henan Xinzhiyuan Chemical Product Co., Ltd.

[0031] According to the preferred embodiment of the present application, the 2-methylimidazole is purchased from Zhengzhou Aikemu Chemical Co., Ltd.

[0032] In the present application, the furan-maleimide polymer forms a reversible covalent bond network through Diels-Alder reaction, which endows the coating with self-repairing ability and anti-creep property at high temperature; the dynamic bond breaks to absorb energy at high temperature, relieving thermal stress and avoiding coating peeling.

[0033] According to the preferred embodiment of the present application, the furan-maleimide polymer is purchased from Xi'an Kaixin Biological Technology Co., Ltd.

[0034] In the present application, the boron carbide nanowires construct three-dimensional heat conduction channels in the coating, quickly disperse heat and reduce local temperature rise; the nanowires are inserted into the matrix to inhibit crack propagation through bridging effect and improve the impact resistance of the coating.

[0035] According to the preferred embodiment of the present application, the boron carbide nanowires are 60 / 1000 nm boron carbide nanowires purchased from Shanghai Bikexi New Material Technology Co., Ltd.

[0036] According to the preferred embodiment of the present application, after adding the 2-methylimidazole methanol solution, the reaction is carried out at 10-30℃ for 24h.

[0037] According to the preferred embodiment of the present application, the preparation method of the supercritical CO2 dispersion system comprises the following steps: injecting liquid CO2 into a high-pressure reaction kettle, heating to 31℃ and pressurizing to 7.4MPa or above to reach a supercritical state; adding 0.5%-1% of polyether-modified siloxane and stirring to form a homogeneous dispersion medium.

[0038] In the present application, CO2 is converted into supercritical fluid (scCO2) at 31℃ and 7.4MPa or above, which has both gas diffusion and liquid solubility; the polyether-modified siloxane acts as a surfactant, its hydrophobic end is compatible with scCO2, and its hydrophilic end wraps particles (such as GO, boron carbide nanowires), reducing the interfacial energy and forming a homogeneous dispersion medium.

[0039] The low viscosity and high diffusion characteristics of supercritical CO2 in the application realize uniform dispersion of nanofiller such as boron carbide nanowires and graphene oxide, and avoid agglomeration; CO2 is rapidly volatilized in the pressure relief process, forming a microporous structure, reducing the density of the coating and improving the thermal insulation performance.

[0040] According to the preferred embodiment of the application, the liquid CO2 is purchased from Shanghai Chunyu Special Gas Co., Ltd.

[0041] According to the preferred embodiment of the application, the high-pressure reaction kettle is purchased from Weihai Xintai Chemical Machinery Co., Ltd.

[0042] According to the preferred embodiment of the application, the polyether-modified siloxane is purchased from Wuhan Huaxiang Kejie Biotechnology Co., Ltd.

[0043] The application also provides a preparation method of the graphene oxide-based fireproof coating, comprising the following steps:

[0044] S1, the polyurethane type SMP, furan-maleimide polymer is dissolved in N,N-dimethylformamide, and stirred until dissolved; biomass-derived modified graphene oxide, melamine cyanurate@ZIF-8, boron carbide nanowires are added, and high-speed shear emulsification is carried out to obtain a mixed slurry;

[0045] S2, the mixed slurry is injected into a supercritical CO2 reaction kettle, and the pressure is released to normal pressure to obtain a porous composite slurry;

[0046] S3, the slurry is scraped on the surface of the substrate, and is cured in stages: 80℃ pre-curing for 1h; 120℃ crosslinking for 2h; 150℃ heat treatment for 30h; further surface curing by ultraviolet irradiation.

[0047] In the application, the SMP soft segment relaxes in the 80℃ pre-curing stage, and a physical crosslinking network is initially formed; the furan-maleimide polymer is not completely reacted; in the 120℃ crosslinking and curing stage, the polyurethane hard segment-NCO reacts with the biomass GO-NH2 to form covalent crosslinking; Diels-Alder cycloaddition reaction occurs between furan and maleimide to construct a reversible network; 150℃ heat treatment makes MCA@ZIF-8 decompose to produce non-combustible gases such as NH3 and H2O, which cooperate with GO to form a dense carbon layer (ZnO derived from ZIF-8 promotes graphitization of the carbon layer); ultraviolet light (365nm) excites the residual double bonds (such as maleimide) on the surface of the coating to polymerize free radicals, enhancing the surface hardness.

[0048] According to the preferred embodiment of the application, in step S1, the stirring temperature is 60℃; the high-speed shear emulsification speed is 10,000rpm, and the time is 30min.

[0049] According to the preferred embodiment of the present application, in step S2, the temperature of the supercritical CO2 reactor is 35℃, the pressure is 10 MPa, and the treatment time of the mixed slurry is 2h.

[0050] According to the preferred embodiment of the present application, in step S3, the substrate is metal or wood; the wavelength of the ultraviolet light irradiation is 365nm, and the time is 10min.

[0051] In the present application, the polyurethane type SMP (shape memory polyurethane) and furan-maleimide polymer are dissolved in DMF by solvation to form a high molecular chain entanglement network; the biomass derived GO: the surface polar group reacts with the -NCO group of the polyurethane to enhance the interface compatibility; the agglomeration is broken by high-speed shearing (10,000 rpm), the metal nodes of ZIF-8 are coordinated with the polymer chain, and the boron carbide nanowires are dispersed by mechanical interlocking; scCO2 penetrates into the slurry and is dissolved in the polymer phase; CO2 is supersaturated and precipitated to form gas nuclei when the pressure is released. The growth of the gas nuclei is controlled by the polymer viscosity and the heterogeneous nucleation of the fillers (such as GO and boron carbide nanowires), and finally a closed / open composite structure is formed to improve the thermal insulation of the coating.

[0052] The present application has the following advantages:

[0053] The graphene oxide-based fireproof coating provided by the present application realizes significant performance improvement through unique formula design and preparation process. The coating exhibits excellent fireproof performance, and the synergistic effect of biomass-derived modified graphene oxide and melamine cyanurate@ZIF-8 forms a highly efficient triple flame-retardant mechanism, which can generate a dense and strong expanded carbon layer during combustion, reaching the highest level of fireproof standard. At the same time, the product has outstanding environmental characteristics, using a halogen-free formula and biomass raw materials, combined with a green and environmentally friendly supercritical CO2 dispersion process, avoiding the environmental pollution problem of traditional flame retardants. In terms of mechanical properties, the three-dimensional network constructed by boron carbide nanowires and modified graphene oxide greatly improves the mechanical strength of the coating, and the self-repairing function of furan-maleimide polymer effectively prevents the coating from cracking. The innovative preparation process ensures the uniform dispersion of nanomaterials, and the staged curing process optimizes the performance of each component. The ultraviolet light assisted curing further enhances the surface density. The coating also has shape memory function and excellent thermal insulation performance, suitable for surface protection of various substrates, solving the technical problems of easy migration and rapid performance decay of traditional fireproof coatings, maintaining high efficiency of flame retardancy while having good environmental adaptability and long-term stability, providing an innovative solution for the development of high-performance fireproof materials. DETAILED DESCRIPTION

[0054] The following detailed description is provided for the purpose of further explanation of the application, and is not to be understood as limiting the scope of the application, which is defined in the appended claims. Those skilled in the art can make some non-essential improvements and adjustments to the application according to the above application content.

[0055] I. Example

[0056] Example 1

[0057] Raw material composition:

[0058] Polyurethane type SMP: 330 g; biomass-derived modified graphene oxide: 160 g; melamine cyanurate@ZIF-8:

[0059] 230 g; furan-maleimide polymer: 110 g; boron carbide nanowire: 70 g; supercritical CO2 dispersion system: 100 g (containing 0.8 g of polyether modified siloxane);

[0060] (1) Preparation of biomass-derived modified graphene oxide: Take 10 g of graphene oxide and add it to 500 mL of deionized water. Use an ultrasonic cell crusher (power 300 W) to treat for 2 hours. Add 8 g of chitosan powder (GO: chitosan = 1:0.8) and stir magnetically in a 60°C water bath for 12 hours. After the reaction is complete, use a high-speed centrifuge to centrifuge at 8000 rpm for 10 minutes to remove unreacted chitosan, and collect the precipitate for freeze-drying for 48 hours. Repeat the above operation to obtain 160 g of modified product.

[0061] (2) Preparation of melamine cyanurate@ZIF-8: Dissolve 115 g of melamine cyanurate in 200 mL of methanol and stir for 30 minutes until completely dissolved. Slowly add 50 mL of zinc nitrate methanol solution (0.1 mol / L) and continue stirring for 10 minutes. Then add 50 mL of 2-methylimidazole methanol solution (0.2 mol / L) and react at 25°C for 24 hours. After the reaction is complete, centrifuge at 5000 rpm for 5 minutes to collect the precipitate, wash with methanol 3 times, and grind after vacuum drying at 60°C for 12 hours to obtain 230 g of powder.

[0062] (3) Preparation of supercritical CO2 dispersion system: Inject liquid CO2 into a stainless steel high-pressure reaction kettle, heat to 31°C and pressurize to 8 MPa to reach the supercritical state. Add 0.8 g of polyether modified siloxane and stir at 500 rpm for 30 minutes to form a homogeneous dispersion medium.

[0063] (4) Coating preparation: S1, 330 g of polyurethane type SMP and 110 g of furan-maleimide polymer were added into 500 mL of N,N-dimethylformamide, stirred at 60 °C for 1 hour until completely dissolved. 160 g of biomass-derived modified graphene oxide, 230 g of melamine cyanurate@ZIF-8 and 70 g of boron carbide nanowires were added in turn, and treated with a high-speed shearing emulsifier at 10,000 rpm for 30 minutes. S2, the mixed slurry was transferred to a supercritical reaction kettle, treated at 35 °C and 10 MPa for 2 hours, and slowly released to atmospheric pressure. S3, the porous slurry was scraped onto an aluminum plate, pre-cured at 80 °C for 1 hour, cross-linked and cured at 120 °C for 2 hours, heat treated at 150 °C for 30 hours, and finally irradiated with a 365 nm ultraviolet lamp for 10 minutes.

[0064] Example 2

[0065] The specific implementation is the same as that of Example 1, except that the raw material composition is: polyurethane type SMP 300 g, biomass-derived modified graphene oxide 180 g (GO: chitosan = 1:1), melamine cyanurate@ZIF-8 250 g (MCA: ZIF-8 = 1:1.2), furan-maleimide polymer 100 g, boron carbide nanowires 80 g, and supercritical CO2 dispersion system 90 g (containing 0.9 g of polyether modified siloxane). The preparation process refers to Example 1, except that the ZIF-8 synthesis temperature is 10 °C; the supercritical treatment conditions are 38 °C, 12 MPa, and 1.5 hours; and the substrate is pine, and the UV curing is extended to 15 minutes.

[0066] Example 3

[0067] The specific implementation is the same as that of Example 1, except that the raw material composition is: polyurethane type SMP 350 g, biomass-derived modified graphene oxide 150 g (GO: chitosan = 1:0.5), melamine cyanurate@ZIF-8 200 g (MCA: ZIF-8 = 1:0.8), furan-maleimide polymer 120 g, boron carbide nanowires 50 g, and supercritical CO2 dispersion system 130 g (containing 0.65 g of polyether modified siloxane). The preparation process refers to Example 1, except that the high-speed shearing speed is reduced to 8000 rpm, and the time is extended to 40 minutes; and the 150 °C heat treatment is shortened to 20 hours.

[0068] Comparative Example 1

[0069] The specific implementation is the same as that of Example 1, except that the raw material composition is: polyurethane type SMP 330 g, unmodified graphene oxide 160 g, melamine cyanurate@ZIF-8 230 g, furan-maleimide polymer 110 g, boron carbide nanowire 70 g, and supercritical CO2 dispersion system 100 g. The preparation method is the same as that of Example 1, except that the chitosan modification step of GO is omitted.

[0070] Comparative Example 2

[0071] The specific implementation is the same as that of Example 1, except that the raw material composition is: polyurethane type SMP 330 g, biomass-derived modified graphene oxide 160 g, pure melamine cyanurate 230 g, furan-maleimide polymer 110 g, boron carbide nanowire 70 g, and supercritical CO2 dispersion system 100 g. The preparation method is the same as that of Example 1, except that pure MCA is used instead of MCA@ZIF-8.

[0072] Comparative Example 3

[0073] The specific implementation is the same as that of Example 1, except that the supercritical CO2 treatment step is omitted in the preparation process, and a conventional vacuum defoaming step is used instead, followed by direct blade coating.

[0074] III. Performance Test

[0075] 1. Vertical burning test (UL-94)

[0076] Equipment: CZF-5 type horizontal and vertical burning tester; test standard: GB / T 2408; sample preparation: injection molding of 125 mm x 13 mm x 3 mm standard sample; test environment: 23 ± 2 ℃, 50 ± 5% RH; test steps: a) vertically fix the sample on the clamp; b) adjust the Bunsen burner flame height to 20 ± 1 mm; c) remove after the first ignition for 10 s, and record the afterflame time t1; d) immediately ignite for the second time after the flame is extinguished, and record the afterflame time t2; e) observe whether burning drippings are produced and whether the lower cotton pad is ignited.

[0077] 2. Limiting oxygen index test (LOI)

[0078] Equipment: HC-2C type oxygen index tester; test standard: ASTM D2863; test steps: a) sample size 100 mm x 10 mm x 3 mm; b) initial oxygen concentration set to ± 2% of the estimated value; c) mixed gas is introduced at a flow rate of 40 ± 2 mm / s; d) the lowest oxygen concentration to maintain combustion is determined by the ascending and descending method; e) take the average value of 5 samples in each group.

[0079] 3. Thermogravimetric analysis (TGA)

[0080] Equipment: TA Q500 thermogravimetric analyzer; test standard: GB / T 27761; test conditions: a) sample amount: 10 ± 0.5 mg; b) temperature range: room temperature ~ 800 ℃; c) heating rate: 10 ℃ / min; d) protective gas: high-purity nitrogen, flow rate 50 mL / min; e) reference material: α-Al2O3 empty crucible. Data processing: a) analyzed using TA Universal Analysis software; b) record 5% weight loss temperature (T5%) and maximum decomposition rate temperature (Tmax); c) calculate the carbon residue rate at 800 ℃.

[0081] 4. Tensile property test

[0082] Equipment: Instron 5967 universal material testing machine; test standard: ISO 527-2; sample preparation: a) ISO 3167 standard multipurpose sample was used; b) size: 150 mm x 10 mm x 2 mm; c) placed for 24 h after injection molding; test parameters: a) gauge length: 50 mm; b) tensile rate: 5 mm / min; c) environmental temperature: 23 ± 2 ℃; d) 5 samples were tested for each group and the average value was taken.

[0083] 5. Adhesion test

[0084] Equipment: QFH grid test instrument; test standard: ASTM D3359; test steps: a) the coating thickness was controlled at 50 ± 5 μm; b) a 1 mm x 1 mm grid was cut out using a 6-blade cutting knife; c) 3M tape was used for pasting and then quickly peeled off; d) the peeling condition was observed under a microscope and rated.

[0085] 6. Thermal insulation performance test

[0086] Equipment: self-built high-temperature test platform; test standard: GB / T 9978.1; test system composition: a) heating furnace: maximum temperature 1000 ℃; b) K-type thermocouple temperature measurement system; c) data acquisition instrument; test steps: a) sample size 100 mm x 100 mm x 3 mm; b) heat source temperature set to 500 ℃; c) sample distance from heat source 10 mm; d) record the back surface temperature change within 0-30 min; e) sampling frequency 1 Hz.

[0087] (2) Performance test results:

[0088] Table 1: Performance test results of each example and comparative example

[0089]

[0090]

[0091] Note: All tests were carried out at 23±2℃, 50±5% RH, and the average value of 5 parallel samples was taken for each group of data, with a relative standard deviation of <5%.

[0092] As can be seen from Table 1, the graphene oxide-based fireproof coating developed by the present application effectively solves the key problems of traditional graphene oxide fireproof coating in flame retardant performance, mechanical properties and environmental friendliness through innovative material design and process optimization. In terms of flame retardant performance, the limiting oxygen index (LOI) of Examples 1-3 reaches 40.2%-45.1%, which is increased by 34%-50% compared with traditional coating (about 30%), and the UL-94 grade reaches V0-V1 level, which is increased by 1-2 levels compared with the commonly used V2 level in the industry. This significant improvement is mainly due to the introduction of biomass-derived modified graphene oxide, and the nitrogen-containing groups of chitosan grafted on its surface promote the formation of a dense carbon layer during combustion, so that the carbon layer thickness reaches 2.8-3.5 mm, which is increased by 56%-250% compared with the 1.0-1.8 mm of traditional coating. At the same time, the synergistic flame retardant system of melamine cyanurate@ZIF-8 delays the decomposition of MCA through the porous structure of ZIF-8, so that the maximum decomposition temperature is increased by 30℃, the gas phase flame retardant time is extended by 50%, and the afterflame time is greatly shortened from 15.7s of the pure MCA system to 3.2s. In terms of mechanical properties, the tensile strength of the examples reaches 17.8-20.2 MPa, which is increased by 78%-102% compared with the about 10 MPa of traditional coating, which is due to the strong interfacial bonding between biomass modified GO and the polyurethane matrix, and the uniform porous structure formed by the supercritical CO2 foaming process. Adhesion tests show that all examples reach level 1 standard, proving the excellent bonding performance of the coating and the substrate. In terms of environmental friendliness, the use of biomass chitosan modification avoids harmful reagents in traditional chemical modification methods, and the supercritical CO2 process realizes solvent-free processing, with VOC emissions reduced by more than 90%. Thermogravimetric analysis shows that the 800℃ carbon residue rate of the examples reaches 48.7%-55.3%, which is increased by 39%-121% compared with the 25%-35% of traditional coating, indicating that the stability of the material at high temperature is significantly enhanced, reducing the generation of toxic smoke. In summary, this technology realizes the synergistic improvement of flame retardant performance, mechanical properties and environmental friendliness through the triple innovation of biomass modified GO enhancing carbon layer quality, MCA@ZIF-8 optimizing gas phase flame retardant, and supercritical process improving material structure, providing a reliable solution for the development of a new generation of high-performance fireproof coating.

[0093] The above examples only express several embodiments of the present application, and the description is more specific and detailed, but it cannot be understood as a limitation on the scope of the patent of the present application. It should be noted that for ordinary skilled persons in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, which are within the scope of protection of the present application.

Claims

1. A graphene oxide-based fire-retardant coating, characterized in that, By weight percentage, its raw materials include: Polyurethane SMP: 30-35%; Biomass-derived modified graphene oxide: 15-18%; Melamine cyanurate @ZIF-8: 20-25%; Furan-maleimide polymer: 10-12%; Boron carbide nanowires: 5-8%; Supercritical CO2 dispersion system: balance; The biomass-derived modified graphene oxide is obtained by chemically modifying graphene oxide with chitosan to introduce nitrogen- or oxygen-containing polar groups on its surface.

2. The graphene oxide-based fire-retardant coating according to claim 1, characterized in that, The preparation steps of the biomass-derived modified graphene oxide include: dispersing graphene oxide in deionized water, adding chitosan, centrifuging and washing, and freeze-drying.

3. The graphene oxide-based fire-retardant coating according to claim 2, characterized in that, Graphene oxide was dispersed in deionized water and ultrasonically treated for 2 hours; the mass ratio of graphene oxide to chitosan was 1:0.5-1, and after adding chitosan, the mixture was stirred at 60°C for 12 hours.

4. The graphene oxide-based fire-retardant coating according to claim 1, characterized in that, The preparation method of the melamine cyanurate@ZIF-8 includes: dissolving melamine cyanurate in methanol, adding zinc nitrate solution, stirring and mixing; then adding 2-methylimidazole methanol solution to react and obtain crude product; then centrifuging, washing with methanol, drying and grinding the crude product into powder.

5. The graphene oxide-based fire-retardant coating according to claim 4, characterized in that, After adding a methanol solution of 2-methylimidazole, the reaction was carried out at 10-30℃ for 24 hours.

6. The graphene oxide-based fire-retardant coating according to claim 1, characterized in that, The preparation method of the supercritical CO2 dispersion system includes the following steps: injecting liquid CO2 into a high-pressure reactor, heating it to 31°C and pressing it to a pressure of 7.4 MPa or higher to reach a supercritical state; adding 0.5%-1% of polyether-modified siloxane and stirring to form a homogeneous dispersion medium.

7. A method for preparing a graphene oxide-based fire-retardant coating according to any one of claims 1-5, characterized in that, Includes the following steps: S1, Dissolve polyurethane-type SMP and furan-maleimide polymer in N,N-dimethylformamide and stir until dissolved; Biomass-derived modified graphene oxide, melamine cyanurate@ZIF-8, and boron carbide nanowires were added, and high-speed shear emulsification was performed to obtain a mixed slurry; S2, the mixed slurry is injected into a supercritical CO2 reactor and depressurized to atmospheric pressure to obtain a porous composite slurry; S3, apply the slurry to the substrate surface and cure in stages: pre-curing at 80℃ for 1 hour; cross-linking at 120℃ for 2 hours; heat treatment at 150℃ for 30 hours; and further surface curing by UV irradiation.

8. The preparation method according to claim 7, characterized in that, In step S1, the stirring temperature is 60℃; the high-speed shear emulsification speed is 10,000 rpm and the time is 30 min.

9. The preparation method according to claim 7, characterized in that, In step S2, the temperature of the supercritical CO2 reactor is 35℃, the pressure is 10MPa, and the processing time of the mixed slurry is 2h.

10. The preparation method according to claim 7, characterized in that, In step S3, the substrate is metal or wood; the wavelength of ultraviolet light irradiation is 365nm and the time is 10min.

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