Graphene oxide-based fireproof coating and preparation method thereof

Abstract

The invention discloses a graphene oxide-based fireproof coating and a preparation method thereof, and belongs to the technical field of novel fireproof materials. The graphene oxide-based fireproof coating comprises the following raw materials: 30-35% of polyurethane SMP; 15 to 18% of biomass derived modified graphene oxide; 20 to 25% of melamine cyanurate (ZIF)-8; 10 to 12% of a furan-maleimide polymer; 5-8% of a boron carbide nanowire; and the balance of a supercritical CO2 dispersion system. Wherein the biomass derived modified graphene oxide is obtained by carrying out chemical modification treatment on graphene oxide through chitosan, so as to introduce a nitrogen or oxygen-containing polar group on the surface of the graphene oxide. According to the graphene oxide-based fireproof coating, UL-94V0-level flame retardance is achieved through three mechanisms of physical barrier, gas-phase flame suppression and dynamic repair, and the graphene oxide-based fireproof coating has high mechanical strength and heat resistance and is suitable for protection of base materials such as metal and wood.

Description

Technical Field

[0001] The present invention relates to the technical field of novel fireproof materials, and in particular to a graphene oxide-based fireproof coating and a preparation method thereof. Background Art

[0002] With the rapid development of fields such as construction, transportation, and electronics, higher requirements are placed on the fire safety performance of materials. Traditional fire-retardant coatings mainly rely on halogenated flame retardants (such as brominated epoxy resins) or inorganic fillers (such as aluminum hydroxide and expanded graphite). Although they have a certain flame retardant effect, they have the following technical defects: 1. Environmental protection issues: Halogenated flame retardants release toxic gases (such as HBr and dioxins) when burned, which is not in line with the development trend of green environmental protection. 2. Deterioration of mechanical properties: The addition of a large amount of inorganic fillers will cause the coating to lose flexibility, easily crack and fall off, affecting long-term performance. 3. Insufficient flame retardant efficiency: The carbon layer formed by traditional intumescent coatings at high temperatures is loose and porous, easily penetrated by flames, and difficult to meet the UL-94V0 level requirements. 4. Poor interface compatibility: Nano flame retardants (such as graphene oxide) are easy to agglomerate and difficult to disperse evenly in the polymer matrix, limiting their flame retardant performance.

[0003] In recent years, graphene oxide (GO) has been introduced into fire-retardant coatings due to its two-dimensional lamellar structure and excellent thermal conductivity / barrier properties. However, unmodified GO has poor compatibility with polymers and lacks catalytic carbonization ability. Although studies have been conducted to modify GO using silane coupling agents, the modified GO still suffers from 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 although metal-organic frameworks can adsorb free radicals, their thermal stability is limited. In addition, traditional solvent dispersion methods make it difficult to achieve uniform distribution of nanomaterials (such as boron carbide nanowires), resulting in local defects in the coating.

[0004] Therefore, developing a new type of fire-retardant coating that is highly flame-retardant, environmentally friendly, has excellent mechanical properties and is process-controllable has become a technical challenge that needs to be solved urgently. Summary of the Invention

[0005] The purpose of the present invention is to provide a graphene oxide-based fire retardant coating and a preparation method thereof, which solves the problems of existing graphene oxide-based fire retardant coatings in terms of poor flame retardancy and mechanical properties and environmental unfriendliness.

[0006] The present invention achieves the above-mentioned purpose through the following technical solutions:

[0007] The raw materials of the graphene oxide-based fire retardant coating include, by mass percentage:

[0008] Polyurethane 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: balance;

[0014] The biomass-derived modified graphene oxide is obtained by chemically modifying graphene oxide with chitosan to introduce polar groups containing nitrogen or oxygen onto its surface.

[0015] In the present invention, the flame retardant loaded with melamine cyanurate@ZIF-8 and the biomass-derived modified graphene oxide synergistically catalyze carbonization to form an expanded carbon layer; the decomposition gas of melamine cyanurate@ZIF-8 combines with the biomass-derived modified graphene oxide as a physical barrier to enhance the thermal insulation effect; the nitrogen-containing groups of chitosan and the phosphate flame retardant (melamine cyanurate) form a PN synergistic system to improve the flame retardant level; the boron carbide thermal conductive network disperses heat and reduces the thermal degradation rate of the substrate; the phase change characteristics of the polyurethane-type SMP and the dynamic cross-linking network jointly maintain the mechanical strength of the coating at high temperatures; dynamic bonds repair microcracks, and the biomass-derived modified graphene oxide sheets fill the repaired defective areas, doubly ensuring the long-term stability of the coating.

[0016] In the present invention, the polyurethane-type SMP serves as the coating matrix, which undergoes phase change at high temperature through its thermally induced shape memory properties, maintains the structural integrity of the coating, and inhibits crack propagation; it is dynamically cross-linked 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 invention, the polyurethane type SMP is purchased from Dongguan Guangsiyuan Polyurethane Material Co., Ltd.

[0018] According to a preferred embodiment of the present invention, 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.

[0019] The biomass-derived modified graphene oxide in the present invention is graphene oxide modified with chitosan to introduce polar groups such as amino groups 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 sheets form a dense carbon layer when burned, isolating oxygen and heat transfer; the nitrogen-containing groups (from chitosan) and the phosphorus-nitrogen flame retardant synergistically promote the formation of an expanded carbon layer.

[0020] According to a preferred embodiment of the present invention, the graphene oxide is purchased from Suzhou Yuhao Nanomaterials Co., Ltd.

[0021] According to a preferred embodiment of the present invention, the deionized water is purchased from Shanghai Lianmai Bioengineering Co., Ltd.

[0022] According to a preferred embodiment of the present invention, the chitosan ene is purchased from Shandong Guangxin Biotechnology Co., Ltd.

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

[0024] In the present invention, ultrasonic treatment for 2 hours allows graphene oxide (GO) to be uniformly dispersed in deionized water, destroying the van der Waals forces between the sheets and exposing surface active groups such as carboxyl and epoxy groups (-COOH, -COC-); -NH2 in the chitosan molecule undergoes an amidation reaction with -COOH on the graphene oxide surface (or a ring-opening reaction with the epoxy group) to form a covalent bond, while the hydroxyl groups of chitosan and GO enhance the interfacial bonding through hydrogen bonding; 60°C promotes the amidation reaction kinetics, and 12 hours ensures sufficient reaction; a mass ratio of 1:0.5-1 balances the modification rate and GO dispersion stability.

[0025] According to a preferred embodiment of the present invention, the preparation method of melamine cyanurate @ ZIF-8 includes: dissolving melamine cyanurate in methanol, adding zinc nitrate solution, and stirring and mixing; then adding a methanol solution of 2-methylimidazole to react to obtain a crude product; then centrifuging the crude product, washing with methanol, drying, and grinding into powder.

[0026] In the present invention, zinc nitrate and 2-methylimidazole (2-MIM) undergo coordination reaction in methanol to form Zn 2+ The tetrahedral network structure with 2-MIM, namely the ZIF-8 framework; melamine cyanurate (MCA) is adsorbed on the ZIF-8 surface through π-π stacking and hydrogen bonding, and the reaction temperature is 10-30℃ to avoid excessive crystallization of ZIF-8 and the resulting shedding of MCA; in the MCA@ZIF-8 complex, MCA acts as an acid source and a gas source, and the porous structure of ZIF-8 enhances the thermal stability and dispersibility of MCA.

[0027] In the present invention, melamine cyanurate@ZIF-8 decomposes upon heating to release non-combustible gases such as NH3 and H2O, which dilute the concentration of combustible gases. The thermal decomposition product (ZnO) of the ZIF-8 framework and the phosphate of melamine cyanurate jointly catalyze carbonization to form a continuous thermal insulation layer. The microporous structure of ZIF-8 slows the decomposition rate of the flame retardant and prolongs the fire protection period.

[0028] According to a preferred embodiment of the present invention, the melamine cyanurate is purchased from Guangzhou Yinyuan New Materials Co., Ltd.

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

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

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

[0032] The furan-maleimide polymer in the present invention forms a reversible covalent bond network through the Diels-Alder reaction, which gives the coating self-repairing ability and creep resistance at high temperatures; at high temperatures, dynamic bonds break and absorb energy, relieve thermal stress, and prevent coating peeling.

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

[0034] In the present invention, boron carbide nanowires construct three-dimensional heat conduction paths in the coating, quickly dissipate heat, and reduce local temperature rise; the nanowires are interspersed in the matrix, inhibiting crack propagation through a bridging effect, thereby improving the impact resistance of the coating.

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

[0036] According to a preferred embodiment of the present invention, after adding the methanol solution of 2-methylimidazole, the reaction is carried out at 10-30° C. for 24 hours.

[0037] According to a preferred embodiment of the present invention, 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 the pressure to above 7.4 MPa to reach a supercritical state; adding 0.5%-1% polyether-modified siloxane and stirring to form a homogeneous dispersion medium.

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

[0039] The low viscosity and high diffusion characteristics of supercritical CO2 in the present invention enable uniform dispersion of nanofillers such as boron carbide nanowires and graphene oxide, avoiding agglomeration; during the pressure release process, CO2 evaporates rapidly to form a microporous structure, reducing the coating density and improving the thermal insulation performance.

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

[0041] According to a preferred embodiment of the present invention, the high-pressure reactor was purchased from Weihai Xintai Chemical Machinery Co., Ltd.

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

[0043] The present invention also provides a method for preparing the graphene oxide-based fire retardant coating, comprising the following steps:

[0044] S1, dissolving polyurethane-type SMP and furan-maleimide polymer in N,N-dimethylformamide and stirring until dissolved; adding biomass-derived modified graphene oxide, melamine cyanurate@ZIF-8, and boron carbide nanowires, and emulsifying at high shear speed to obtain a mixed slurry;

[0045] S2, injecting the mixed slurry into a supercritical CO2 reactor and releasing the pressure to normal pressure to obtain a porous composite slurry;

[0046] S3, the slurry is scraped onto the surface of the substrate and cured in stages: pre-curing at 80°C for 1 hour; cross-linking at 120°C for 2 hours; heat treatment at 150°C for 30 hours; and further surface curing by ultraviolet light irradiation.

[0047] In the present invention, during the 80°C pre-curing stage, the SMP soft segment relaxes and initially forms a physical cross-linked network; the furan-maleimide polymer is not completely reacted; during the 120°C cross-linking curing stage, the polyurethane hard segment -NCO reacts with the -NH2 of the biomass GO to form covalent cross-links; furan and maleimide undergo a Diels-Alder cycloaddition reaction to construct a reversible network; heat treatment at 150°C causes MCA@ZIF-8 to decompose and produce non-flammable gases such as NH3 and H2O, which cooperate with GO to form a dense carbon layer (ZIF-8-derived ZnO promotes graphitization of the carbon layer); ultraviolet light (365nm) excites the free radical polymerization of residual double bonds (such as maleimide) on the coating surface, enhancing the surface hardness.

[0048] According to a preferred embodiment of the present invention, in step S1, the stirring temperature is 60° C.; the rotation speed of the high-speed shear emulsification is 10,000 rpm, and the time is 30 min.

[0049] According to a preferred embodiment of the present invention, in step S2, the temperature of the supercritical CO2 reactor is 35°C, the pressure is 10 MPa, and the processing time of the mixed slurry is 2 hours.

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

[0051] In this invention, polyurethane-based shape memory polyurethane (SMP) and furan-maleimide polymer are dissolved in DMF through solvation to form an entangled network of polymer chains. Biomass-derived GO: Surface polar groups react with the -NCO groups of the polyurethane, enhancing interfacial compatibility. High-speed shear (10,000 rpm) breaks up agglomerates, allowing the metal nodes of ZIF-8 to coordinate with the polymer chains and the boron carbide nanowires to disperse through mechanical interlocking. scCO2 infiltrates the slurry and dissolves in the polymer phase. During pressure release, CO2 supersaturates and precipitates, forming gas nuclei. The growth of the gas nuclei is controlled by the polymer viscosity and the heterogeneous nucleation of fillers (such as GO and boron carbide nanowires), ultimately forming a closed-cell / open-cell composite structure, improving the thermal insulation properties of the coating.

[0052] The beneficial effects of the present invention are:

[0053] The graphene oxide-based fire-retardant coating provided by the present invention has achieved significant performance improvements through a unique formula design and preparation process. The coating exhibits excellent fire retardant properties. The synergistic effect of biomass-derived modified graphene oxide and melamine cyanurate @ZIF-8 forms an efficient triple flame retardant mechanism, which can produce a dense and firm expanded carbon layer during combustion, reaching the highest level of fire protection standards. At the same time, the product has outstanding environmental protection characteristics. It adopts a halogen-free formula and biomass raw materials, combined with a green and environmentally friendly supercritical CO2 dispersion process, to avoid the environmental pollution problems 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, while the self-healing function of furan-maleimide polymer effectively prevents the coating from cracking. The innovative preparation process ensures the uniform dispersion of nanomaterials, the staged curing process optimizes the performance of each component, and ultraviolet light-assisted curing further enhances the surface density. The coating also has shape memory function and excellent thermal insulation performance, and is suitable for surface protection of various substrates. It solves the technical problems of easy migration and rapid performance degradation of flame retardants in traditional fire-retardant coatings. While maintaining high flame retardancy, it also has good environmental adaptability and long-term stability, providing an innovative solution for the development of high-performance fire-retardant materials. DETAILED DESCRIPTION

[0054] The following specific implementation methods are only used to further illustrate the present application and should not be understood as limiting the scope of protection of the present application. Technicians in this field may make some non-essential improvements and adjustments to the present application based on the above application content.

[0055] 1. Implementation

[0056] Example 1

[0057] Raw material composition:

[0058] Polyurethane-based SMP: 330g; Biomass-derived modified graphene oxide: 160g; Melamine cyanurate@ZIF-8:

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

[0060] (1) Preparation of biomass-derived modified graphene oxide: 10 g of graphene oxide was added to 500 mL of deionized water and treated with an ultrasonic cell disruptor (power 300 W) for 2 h. 8 g of chitosan powder (GO:chitosan = 1:0.8) was added and magnetically stirred in a 60°C water bath for 12 h. After the reaction was completed, the unreacted chitosan was removed by centrifugation at 8000 rpm for 10 min, and the precipitate was collected and freeze-dried for 48 h. The above operation was repeated to obtain 160 g of the 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) dropwise and react at a constant temperature of 25°C for 24 hours. After the reaction, centrifuge at 5000 rpm for 5 minutes to collect the precipitate, wash it three times with methanol, dry it in a vacuum at 60°C for 12 hours, and grind it to obtain 230 g of powder.

[0062] (3) Preparation of supercritical CO2 dispersion: Liquid CO2 was injected into a stainless steel autoclave, heated to 31°C, and pressurized to 8 MPa to achieve a supercritical state. 0.8 g of polyether-modified siloxane was added, and the mixture was stirred at 500 rpm for 30 minutes to form a homogeneous dispersion medium.

[0063] (4) Coating preparation: S1, add 330g polyurethane-type SMP and 110g furan-maleimide polymer to 500mL N,N-dimethylformamide, stir at 60℃ for 1 hour until completely dissolved. Add 160g biomass-derived modified graphene oxide, 230g melamine cyanurate @ZIF-8 and 70g boron carbide nanowires in sequence, and use a high-speed shear emulsifier to treat at 10000rpm for 30 minutes. S2, transfer the mixed slurry to a supercritical reactor, treat at 35℃ and 10MPa for 2 hours, and slowly release the pressure to normal pressure. S3, apply the porous slurry on an aluminum plate, pre-cure at 80℃ for 1 hour, cross-link and cure at 120℃ for 2 hours, heat treat at 150℃ for 30 hours, and finally irradiate with a 365nm UV lamp for 10 minutes.

[0064] Example 2

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

[0066] Example 3

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

[0068] Comparative Example 1

[0069] The specific implementation method is the same as that of Example 1, except that the raw materials are: 330g of polyurethane-based SMP, 160g of unmodified graphene oxide, 230g of melamine cyanurate@ZIF-8, 110g of furan-maleimide polymer, 70g of boron carbide nanowires, and 100g of supercritical CO2 dispersion. 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 method is the same as that of Example 1, except that the raw materials are: 330g of polyurethane-based SMP, 160g of biomass-derived modified graphene oxide, 230g of pure melamine cyanurate, 110g of furan-maleimide polymer, 70g of boron carbide nanowires, and 100g of supercritical CO2 dispersion. 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 method is the same as that of Example 1, except that the supercritical CO2 treatment step is omitted in the preparation process, and direct scraping after conventional vacuum degassing is performed instead.

[0074] 3. Performance Testing

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

[0076] Equipment: CZF-5 horizontal and vertical combustion tester; Test standard: GB / T 2408; Specimen preparation: Injection-molded 125 mm × 13 mm × 3 mm standard specimens; Test environment: 23 ± 2°C, 50 ± 5% RH; Test steps: a) Fix the specimen vertically in the fixture; b) Adjust the flame height of the Bunsen burner to 20 ± 1 mm; c) Ignite the burner 10 seconds after the first ignition and remove it, recording the afterflame time t1; d) Wait for the flame to go out and immediately ignite the burner a second time for 10 seconds, recording the afterflame time t2; e) Observe for the generation of burning drips and the ignition of the cotton pad below.

[0077] 2. Limiting Oxygen Index Test (LOI)

[0078] Equipment: HC-2C oxygen index meter; Test standard: ASTM D2863; Test procedures: a) Sample dimensions: 100 mm × 10 mm × 3 mm; b) Initial oxygen concentration set to ±2% of the estimated value; c) Mixed gas introduced at a flow rate of 40 ± 2 mm / s; d) Minimum oxygen concentration required to sustain combustion determined using the lift method; e) Five samples per group were tested and the average value was calculated.

[0079] 3. Thermogravimetric analysis (TGA)

[0080] Equipment: TA Q500 Thermogravimetric Analyzer; Test Standard: GB / T 27761; Test Conditions: a) Sample weight: 10 ± 0.5 mg; b) Temperature range: Room temperature to 800°C; c) Heating rate: 10°C / min; d) Protective gas: High-purity nitrogen, flow rate 50 mL / min; e) Reference material: Empty α-Al2O3 crucible. Data Processing: a) Analyze using TA Universal Analysis software; b) Record the 5% weight loss temperature (T5%) and the temperature of maximum decomposition rate (Tmax); c) Calculate the carbon residue at 800°C.

[0081] 4. Tensile performance test

[0082] Equipment: Instron 5967 universal testing machine; Test standard: ISO 527-2; Specimen preparation: a) ISO 3167 standard multi-purpose specimens; b) Dimensions: 150 mm × 10 mm × 2 mm; c) Specimens were left to rest for 24 h after injection molding; Test parameters: a) Gauge length: 50 mm; b) Tensile rate: 5 mm / min; c) Ambient temperature: 23 ± 2°C; d) Five specimens were tested in each group and the average value was calculated.

[0083] 5. Adhesion test

[0084] Equipment: QFH Cross-Hatch Tester; Test Standard: ASTM D3359; Test Procedure: a) Control coating thickness to 50 ± 5 μm; b) Use a six-blade cutter to score a 1 mm × 1 mm grid; c) Apply 3M tape and quickly remove; d) Observe and grade the peeling under a microscope.

[0085] 6. Thermal insulation performance test

[0086] Equipment: Self-built high-temperature test platform; Test standard: GB / T 9978.1; Test system components: a) Heating furnace: maximum temperature 1000°C; b) K-type thermocouple temperature measurement system; c) Data acquisition instrument; Test steps: a) Sample size 100 mm × 100 mm × 3 mm; b) Heat source temperature set to 500°C; c) Distance between sample and heat source 10 mm; d) Record backside temperature changes within 0-30 minutes; e) Sampling frequency 1 Hz.

[0087] (2) Performance test results:

[0088] Table 1: Performance test results of various embodiments and comparative examples

[0089]

[0090]

[0091] Note: All tests were conducted at 23±2℃, 50±5%RH. Each set of data was tested on 5 parallel samples and the average value was taken. The relative standard deviation was <5%.

[0092] As can be seen from Table 1, the graphene oxide-based fire retardant coating developed by the present invention effectively solves the key problems of traditional graphene oxide fire retardant coatings in terms of flame retardancy, mechanical properties and environmental friendliness through innovative material design and process optimization. In terms of flame retardancy, the limiting oxygen index (LOI) of Examples 1-3 reaches 40.2%-45.1%, which is 34%-50% higher than that of traditional coatings (about 30%), and the UL-94 rating reaches V0-V1, which is 1-2 levels higher than the common V2 level in the industry. This significant improvement is mainly due to the introduction of biomass-derived modified graphene oxide. The chitosan nitrogen-containing groups grafted on its surface promote the formation of a dense carbon layer during combustion, so that the carbon layer thickness reaches 2.8-3.5mm, which is 56%-250% thicker than the 1.0-1.8mm of traditional coatings. The synergistic flame retardant system of melamine cyanurate@ZIF-8, through the porous structure of ZIF-8, delays the decomposition of MCA, raising the maximum decomposition temperature by 30°C, extending the gas-phase flame retardancy by 50%, and significantly shortening the afterflame time from 15.7s for the pure MCA system to 3.2s. In terms of mechanical properties, the tensile strength of the examples reached 17.8-20.2 MPa, a 78%-102% increase compared to the approximately 10 MPa of conventional coatings. This is attributed to the strong interfacial bonding between the biomass-modified GO and the polyurethane matrix, as well as the uniform porous structure formed by the supercritical CO2 foaming process. Adhesion tests showed that all examples met Class 1 standards, demonstrating excellent adhesion between the coating and the substrate. Regarding environmental friendliness, the use of biomass chitosan modification avoids the harmful reagents used in traditional chemical modification methods, and the supercritical CO2 process enables solvent-free processing, reducing VOC emissions by over 90%. Thermogravimetric analysis shows that the carbon residue rate of the examples at 800°C reaches 48.7%-55.3%, an increase of 39%-121% compared to the 25%-35% of traditional coatings, indicating that the material's stability at high temperatures is significantly enhanced, reducing the generation of toxic fumes. Overall, this technology achieves a synergistic improvement in flame retardancy, mechanical properties, and environmental friendliness through the triple innovation of biomass-modified GO to enhance the quality of the carbon layer, MCA@ZIF-8 to optimize gas-phase flame retardancy, and supercritical processing to improve the material structure. This provides a reliable solution for the development of a new generation of high-performance fire-retardant coatings.

[0093] The above-described embodiments merely illustrate several implementations of the present invention. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that variations and improvements are possible without departing from the scope of the present invention, and all such variations and improvements fall within the scope of protection of the present invention.

Claims

1. A graphene oxide-based fire retardant coating, characterized in that: In terms of mass percentage, the 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 polar groups containing nitrogen or oxygen onto 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, centrifugation 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 chitosan was added, the mixture was stirred and reacted 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 melamine cyanurate@ZIF-8 comprises: dissolving melamine cyanurate in methanol, adding zinc nitrate solution, and stirring and mixing; then adding 2-methylimidazole methanol solution to react to obtain a crude product; and then centrifuging the crude product, washing with methanol, drying, and grinding 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°C 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 the pressure to above 7.4 MPa to reach a supercritical state; adding 0.5%-1% 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 to 5, characterized in that: The following steps are involved: S1, dissolving polyurethane-type SMP and furan-maleimide polymer in N,N-dimethylformamide and stirring until dissolved; Add biomass-derived modified graphene oxide, melamine cyanurate@ZIF-8, and boron carbide nanowires, and emulsify at high speed to obtain a mixed slurry; S2, injecting the mixed slurry into a supercritical CO2 reactor and releasing the pressure to normal pressure to obtain a porous composite slurry; S3, the slurry is scraped onto the surface of the substrate and cured in stages: pre-curing at 80°C for 1 hour; cross-linking at 120°C for 2 hours; heat treatment at 150°C for 30 hours; and further surface curing by ultraviolet light irradiation.

8. The preparation method according to claim 7, characterized in that In step S1, the stirring temperature is 60° C.; the rotation speed of the high-speed shear emulsification 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°C, the pressure is 10 MPa, and the processing time of the mixed slurry is 2 hours.

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 365 nm, and the time is 10 minutes.

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