Functional hybrid flame retardant based on cyclodextrin-MOF, preparation method and application

Abstract

The invention discloses a functionalized hybrid flame retardant based on cyclodextrin-MOF (Metal Organic Framework) as well as a preparation method and application thereof, and belongs to the technical field of high polymer material science and flame retardance. The hybrid flame retardant (F-CD-MOF) has a core-shell structure, a core body is crystalline CD-MOF formed by self-assembly of cyclodextrin and potassium ions, and a shell layer is an organic interface layer which is formed by grafting of a silane coupling agent and contains an active functional group (-NH2 or-NCO). The preparation method comprises the steps of CD-MOF primary crystal synthesis, surface silanization functionalization and post-treatment. The flame retardant can be used as a reactive nanofiller for preparing a high-performance flame-retardant polyurea coating, a polyurea three-dimensional cross-linked network is embedded through covalent bonding, the UL-94 flame-retardant grade of the obtained coating reaches V-0 grade, the peak heat release rate is reduced by 40% or above compared with that of a pure polyurea coating, and the flame retardant has excellent mechanical properties and is suitable for industrial production. The fireproof coating is suitable for high-end fireproof fields such as building fireproof coatings and electric power facility fireproof coating materials.

Description

Technical Field

[0001] This invention relates to the interdisciplinary field of polymer materials science and flame retardant technology, and in particular to the design of a nano flame retardant based on biomass metal-organic framework (MOF) materials, a surface interface engineering modification method, and the application of the flame retardant in the preparation of high-performance intrinsically flame-retardant polyurea elastomer coatings. Background Technology

[0002] Polyurea materials have become important protective coating materials due to their excellent mechanical properties, rapid reaction molding characteristics and outstanding chemical stability. However, their intrinsic flammability limits their application in demanding fire protection scenarios such as aerospace, electronic packaging, and high-end buildings.

[0003] In existing technologies, polyurea flame retardancy mainly relies on physically blended flame retardant fillers such as aluminum hydroxide and ammonium polyphosphate (APP). To achieve UL-94V-0 flame retardancy, the filler addition amount needs to reach 30-60 wt.%, which will seriously degrade the high elasticity, high tensile strength and wear resistance of polyurea. Moreover, the interface between inorganic fillers and organic polymer matrix is ​​incompatible, which makes the fillers easy to agglomerate and migrate, affecting the flame retardant durability and accelerating material aging.

[0004] MOF materials show promise in the flame retardant field, but their direct application to polyurea systems faces challenges such as poor interfacial compatibility and low dispersion stability. Cyclodextrin-based metal-organic frameworks (CD-MOFs), as green and porous carbon sources / catalyst precursors, possess abundant hydroxyl groups on their surface, making them highly hydrophilic. However, their compatibility with hydrophobic polyurea matrices is extremely poor; direct addition leads to weak interfacial bonding and a sharp decline in mechanical properties, rendering them impractical. Therefore, there is an urgent need to develop a technical solution that achieves strong interfacial bonding between MOF flame retardants and polyurea matrices, balancing high flame retardancy with enhanced mechanical properties. Summary of the Invention

[0005] This invention aims to overcome the shortcomings of existing technologies and provide a functionalized CD-MOF hybrid flame retardant based on interface engineering, its preparation method and application. Through a covalent bonding strategy, the nano flame retardant is uniformly and stably dispersed and strongly bonded to the polyurea matrix, so that the polyurea coating has both excellent flame retardant and mechanical properties.

[0006] Therefore, the specific technical solution adopted by the present invention is as follows:

[0007] According to one aspect of the present invention, a functionalized hybrid flame retardant based on cyclodextrin-MOF is provided, characterized by having a core-shell structure: the core is a cyclodextrin-based metal-organic framework (CD-MOF) with cyclodextrin as the organic ligand and potassium ions as the metal nodes; the shell is a layer of silane coupling agent molecules grafted onto the surface of the CD-MOF by chemical bonding, wherein the general formula of the silane coupling agent is X-(CH2). n-Si(OR′)3, where X is an amino or isocyanate group, n is an integer from 3 to 6, and R′ is an alkyl group.

[0008] Preferably, the CD-MOF is a regular octahedral single crystal or polycrystalline material synthesized by a room-temperature liquid-phase method, with a BET specific surface area of ​​not less than 500 m². 2 / g; the silane coupling agent is selected from at least one of 3-aminopropyltriethoxysilane (APTES) and 3-propyltriethoxysilane (IPTS); the grafting density of the silane coupling agent molecular layer is 0.5-2.0 mmol / g (based on the total mass of the hybrid flame retardant).

[0009] A method for preparing a functionalized hybrid flame retardant based on cyclodextrin-MOF includes the following steps:

[0010] S1. Under alkaline conditions, cyclodextrin and potassium ions are self-assembled and crystallized in a mixed solvent of water and alcohol to obtain CD-MOF primary crystals; the alkaline conditions are provided by an aqueous solution of potassium hydroxide with a concentration of 0.15-0.25 mol / L, the alcohol is methanol or ethanol, and the volume ratio of water to alcohol is (2:1)-(4:1);

[0011] S2. The CD-MOF primary crystals are dispersed in an anhydrous aprotic solvent under an inert atmosphere, the silane coupling agent is added, and a reflux condensation reaction is carried out at 80-120°C for 6-24 hours to achieve surface silanization functionalization.

[0012] S3. After the reaction is complete, the solid product is separated, washed multiple times with organic solvent to remove physical adsorbates, and finally dried under vacuum to obtain the hybrid flame retardant.

[0013] Preferably, in step S1, after dissolving cyclodextrin in an aqueous potassium hydroxide solution, the trace amounts of insoluble matter are removed by pressure filtration, and then mixed with alcohol and sealed and allowed to stand, allowing self-assembly crystallization to be achieved through slow solvent evaporation.

[0014] Preferably, in step S2, the inert atmosphere is high-purity nitrogen, the anhydrous aprotic solvent is anhydrous toluene dried by molecular sieves, and the CD-MOF primary crystals are dispersed and then ultrasonically treated to form a uniform suspension.

[0015] An application of a functionalized hybrid flame retardant based on cyclodextrin-MOF, wherein the flame-retardant polyurea coating is formed by curing a two-component coating composition containing the hybrid flame retardant; wherein component A of the two-component coating composition contains a polyisocyanate with a functionality of not less than 2.2, component B contains an amino-terminated polyether with a molecular weight of 1000-5000 and a functionality of 2-3, and the hybrid flame retardant accounting for 3 wt.% to 15 wt.% of the total mass of the coating composition; in use, components A and B are mixed and cured at a ratio of isocyanate index (R value) of 1.05-1.20.

[0016] Preferably, the polyisocyanate is selected from liquefied MDI, polymeric MDI or its prepolymer; the terminal amino polyether is polyoxypropylene ether diamine or polyoxypropylene ether triamine; the B component also contains optional amine chain extenders and auxiliaries, and the hybrid flame retardant is pre-dispersed in the B component.

[0017] Preferably, in the cured flame-retardant polyurea coating, the hybrid flame retardant is chemically bonded to the three-dimensional network structure of the polyurea in the form of covalent bonds, and the coating achieves a UL-94 flame retardancy rating of V-0, with the peak heat release rate (pHRR) reduced by more than 40% compared to a pure polyurea coating without added flame retardant.

[0018] Preferably, the high-performance flame-retardant polyurea coating is used to prepare fire-retardant coatings for buildings, fire-retardant coverings for power facilities, flame-retardant interior trim for transportation vehicles, or fire-retardant layers for chemical storage tanks.

[0019] Compared with the prior art, this application has the following beneficial effects:

[0020] 1. Innovative and efficient flame retardant mechanism: For the first time, CD-MOF is applied to polyurea flame retardancy through interface engineering strategies. When F-CD-MOF burns, K... + Ion catalysis dehydrates and crosslinks the polyurea molecular chain. CD serves as a high-quality carbon source, and the gas generated by MOF decomposition helps to form an expanded and dense porous carbon layer with excellent thermal insulation and oxygen shielding effects. UL-94V-0 flame retardancy can be achieved with low addition amounts.

[0021] 2. Scientific and universal interface design: By introducing active functional groups through surface silanization, F-CD-MOF is transformed from a "physical filler" into a "reactive monomer". The covalently bonded interface design fundamentally solves the problem of dispersion and compatibility of nanomaterials in polymer matrices, providing a new paradigm for the application of other nanofunctional materials in polymers.

[0022] 3. Synergistic performance enhancement: Strong interfacial bonding avoids performance degradation, and F-CD-MOF, as a nano-crosslinking point, can also improve the tensile strength and modulus of polyurea, achieving a unified "flame retardant-enhancement" effect, breaking through the bottleneck of mutual constraints between the two in traditional flame retardant technologies.

[0023] 4. Practical and environmentally friendly products: The hybrid flame retardant uses environmentally friendly raw materials and has a stable preparation process. The resulting polyurea coating can be applied using conventional spraying equipment, has good process compatibility, is easy to industrialize, and has broad application prospects in the high-end fire protection field. Attached Figure Description

[0024] The present invention will be described in detail below with reference to the embodiments, but the scope of protection of the present invention is not limited to these embodiments.

[0025] Example 1:

[0026] Example 1: Preparation and characterization of functionalized CD-MOF hybrid flame retardant (NH2-CD-MOF)

[0027] 1. Synthesis of CD-MOF: Accurately weigh 4.000 g (approximately 3.08 mmol) of cyclodextrin (CD, purity ≥99%, Sigma-Aldrich) into a 250 mL Erlenmeyer flask, and add 40.0 mL of 0.200 mol / L potassium hydroxide (KOH, analytical grade) aqueous solution. Place the Erlenmeyer flask on a magnetic stirrer and stir at room temperature until the CD is completely dissolved, yielding a clear solution. Filter the solution under pressure using a 0.22 μm polyethersulfone (PES) aqueous microporous membrane to remove any trace insoluble matter. Transfer the filtrate to a clean 150 mL crystallizing dish, and then accurately add 12.0 mL of chromatographically pure methanol using a pipette. Gently shake the crystallizing dish to mix the solution thoroughly, and then seal the dish with Parafilm sealing film with several micropores (approximately 0.5 mm in diameter). The crystallization dish was placed stably in a constant temperature and humidity chamber (temperature: 25.0±0.5℃, relative humidity: 45±5%) to allow the solvent to evaporate slowly. After about 7-10 days, a large amount of colorless, transparent, regular octahedral crystals precipitated at the bottom of the crystallization dish. The supernatant was carefully poured off, and the crystal surface was gently rinsed with a small amount of ice-cold methanol (about 5 mL × 3 times). The obtained crystals were collected in a watch glass and placed in a vacuum drying oven at 60℃ for 12 hours to obtain a white crystalline CD-MOF product. The yield was approximately 3.45 g, and the calculated yield based on the mass of CD was 86.3%.

[0028] 2. Surface Amine Functionalization of CD-MOF (Preparation of NH2-CD-MOF): In a glove box filled with high-purity nitrogen (99.999% purity), 1.000 g of the CD-MOF prepared in the above steps was rapidly transferred to a 250 mL three-necked round-bottom flask that had been baked and dehydrated. 150 mL of [unclear - possibly a specific chemical process] was added to the flask. Anhydrous toluene (water content <50 ppm, determined by the Karl-Fischer method) was dried for at least 48 hours using molecular sieves. The flask was removed from the glove box, and the condenser, nitrogen inlet tube, and magnetic stir bar were immediately installed, ensuring the entire system was under continuous positive nitrogen pressure. The flask was ultrasonically treated for 30 minutes in an ultrasonic cleaner to fully disperse the CD-MOF crystals and form a homogeneous suspension. Subsequently, the flask was transferred to a thermostatic magnetic stirrer, and under continuous stirring and nitrogen protection, 2.20 mL (approximately 9.4 mmol) of 3-aminopropyltriethoxysilane (APTES, purity ≥98%, Sigma-Aldrich) was slowly injected through a rubber stopper using a microsyringe. The system was heated to 110 °C and refluxed at this temperature for 12 hours. After the reaction was complete, heating was stopped, and the mixture was allowed to cool naturally to room temperature. The reaction mixture was transferred to centrifuge tubes and centrifuged at 10,000 rpm for 10 minutes, collecting the solid. The sample was washed three times each with anhydrous toluene and anhydrous ethanol (50 mL each time) to completely remove physically adsorbed APTES and byproducts. The resulting white solid product was transferred to a vacuum drying oven and dried at 80 °C for 24 hours to obtain an amino-functionalized CD-MOF, denoted as NH2-CD-MOF. The yield was approximately 1.08 g.

[0029] 3. Characterization and Results

[0030] Morphology analysis (SEM): Observation was performed using field emission scanning electron microscopy (FE-SEM, Hitachi SU8220). Both functionalized and unfunctionalized samples maintained a complete octahedral crystal shape with a size distribution of 5-15 μm, indicating that the silanization reaction conditions were mild and did not damage the crystal morphology of CD-MOF.

[0031] Chemical structure analysis (FT-IR): Fourier transform infrared spectroscopy (Nicoleti S50) was used for testing, employing the KBr pellet method. Compared to the infrared spectrum of the original CD-MOF, NH2-CD-MOF showed a different structure at 2935 cm⁻¹. -1 and 2873cm -1 A distinct absorption peak appeared at 1560 cm⁻¹, which were attributed to the asymmetric and symmetric stretching vibrations of the methylene group (-CH₂-) in APTES, respectively; -1 The absorption peaks appearing nearby are attributed to the NH bending vibration of primary amines. Meanwhile, the absorption peaks at 3300-3500 cm⁻¹... -1 Within this range, the morphology of the broad and intense peaks of the hydroxyl groups in CD-MOF itself changes, overlapping and broadening with the stretching vibration peaks of the amino groups. These changes confirm that APTES has been successfully grafted onto the CD-MOF surface.

[0032] Surface elemental analysis (XPS): Tests were performed using a Thermo Scientific K-Alpha+ X-ray photoelectron spectroscopy system. Broadband scanning revealed a characteristic N1s peak in the NH2-CD-MOF, which was absent in the original CD-MOF. High-resolution scanning fitting of the N1s peak revealed a characteristic peak at 399.8 eV attributable to nitrogen in primary amines (-NH2).

[0033] Thermogravimetric analysis (TGA): Under a nitrogen atmosphere, the temperature was increased from 50°C to 800°C at a rate of 10°C / min. By comparing the weight loss difference between CD-MOF and NH2-CD-MOF between 200-600°C, the grafting amount of the organosilane layer was calculated to be approximately 8.2 wt.%.

[0034] Example 2:

[0035] Preparation of isocyanate-functionalized CD-MOF (NCO-CD-MOF)

[0036] The preparation process was exactly the same as the "surface amino functionalization" step in Example 1, the only difference being that the silane coupling agent was replaced by an equimolar amount (2.20 mL) of 3-isocyanate-propyltriethoxysilane (IPTS, purity ≥95%, TCI). A white solid product was finally obtained, denoted as NCO-CD-MOF. Its FT-IR characterization was performed at 2270 cm⁻¹. -1 The presence of a distinct characteristic peak near the isocyanate group (the typical stretching vibration absorption peak) confirms the successful grafting of IPTS.

[0037] Example 3:

[0038] Preparation and performance evaluation of high-performance flame-retardant polyurea coatings containing 5 wt.% NH2-CD-MOF

[0039] 1. Raw materials

[0040] Component A: Liquefied diphenylmethane diisocyanate (liquefied MDI, Wanhua, PM-200, NCO mass fraction 31.5%).

[0041] Component B: Amino-terminated polyoxypropylene ether (Huntsman, JEFFAMINE D-2000, number-average molecular weight Mn≈2000, functionality≈2). Amine chain extender: Diethyltoluene diamine (DETDA, Albemarle, Ethacure 100). Functionalized flame retardant: NH2-CD-MOF prepared in Example 1. Additives: Polysiloxane defoamer (BYK-Chemie, BYK-066N).

[0042] 2. Preparation of polyurea composite coating

[0043] Component B preparation: Accurately weigh the following materials according to the mass ratio: JEFFAMINE D-2000: 76.00g; DETDA: 18.00g; NH2-CD-MOF: 5.00g; BYK-066N: 1.00g. Add the above materials to a 500mL four-necked flask equipped with a mechanical stirrer, thermocouple, vacuum interface, and heating mantle. Heat the system to 100±2℃ and continuously stir and dehydrate under a vacuum of -0.098MPa (gauge pressure) for 2 hours to remove trace amounts of moisture (ensuring the moisture content is below 0.05%). Then stop heating and vacuuming, cool to below 40℃ under nitrogen protection, discharge, seal and store in a desiccator to obtain homogenized component B. Laser particle size analyzer determination shows that the particle size distribution (D90) of NH2-CD-MOF in component B is less than 20μm, indicating good dispersion.

[0044] Component A preparation: Liquefied MDI (PM-200) is used directly. Before use, its NCO content is measured and confirmed to be 31.5%.

[0045] 3. Preparation and Curing of Coating Samples Based on the designed isocyanate index (R value = amount of NCO groups / amount of NH2 groups) of 1.10, components A and B were accurately calculated and weighed. Specifically: Component A (PM-200) mass = 36.55g, Component B mass = 100.00g. Components A and B were quickly poured into a 500mL plastic beaker preheated to 60℃ and immediately stirred vigorously at 2500rpm for 60±5 seconds using a high-speed mechanical stirrer (IKA RW20digital) to ensure uniform mixing. The mixture was then quickly poured into a preheated (80℃) polytetrafluoroethylene (PTFE) mold (cavity size: 150mm×150mm×2mm). The mold was transferred to a forced-air oven and cured at 60±2°C for 4 hours. Afterwards, the mold was removed and allowed to mature for 7 days under standard experimental conditions of 23±2℃ and 50±5% relative humidity before various performance tests were conducted.

[0046] Performance Testing and Results Analysis

[0047] (1) Flame retardant performance test

[0048] Limiting Oxygen Index (LOI): The LOI of the specimen (size: 100mm × 10mm × 2mm) was determined using a Fire Testing Technology oxygen indexer according to ASTM D2863. Results: The LOI value of the coating in Example 3 was 23.8 ± 0.3%. Comparative Example 1 (pure polyurea) had an LOI of 19.5 ± 0.2%, and Comparative Example 2 (with 5 wt.% unmodified CD-MOF) had an LOI of 21.0 ± 0.3%.

[0049] UL-94 Vertical Flame Rating: The sample (size: 125mm × 13mm × 2mm) was tested using a UL94 vertical flame tester according to the ANSI / UL-94 standard. Results: In Example 3, the average afterflame time t1 after the first application of flame was 2.3s, the average afterflame time t2 after the second application was 1.1s, and the total afterflame time (t1 + t2) was < 5s. No burning droplets ignited the absorbent cotton, achieving a V-0 rating. Comparative Examples 1 and 2 could not be rated (NR).

[0050] Cone calorimetry: Performed according to ISO 5660-1 standard using a cone calorimeter at 50 kW / m³. 2 The test sample (dimensions: 100mm × 100mm × 2mm) was subjected to external radiative heat flux. Peak heat release rate (pHRR): 605 ± 25 kW / m³ in Example 3. 2 Compared with Comparative Example 1 (1210±40kW / m 2 It decreased by 50.0%, compared to control sample 2 (980±35kW / m²). 2 The total heat release (THR) decreased by 38.3% in Example 3. 2 Compared with control example 1 (82±3MJ / m 2 The total tobacco production (TSP) decreased by 45.1% in Example 3, which was 12 ± 1 m³. 2 Comparative Example 1 (20±1m) 2 It decreased by 40.0%.

[0051] (2) Thermal stability analysis (TGA) was performed under a nitrogen atmosphere at a heating rate of 10 °C / min. The carbon residue of the coating in Example 3 at 700 °C was 18.5 wt.%, which was significantly higher than that of Comparative Example 1 (5.2 wt.%) and Comparative Example 2 (9.8 wt.%), indicating that NH2-CD-MOF greatly promoted the carbonization of the polyurea matrix at high temperatures.

[0052] (3) Mechanical properties were tested according to ASTM D412 standard. The dumbbell-shaped specimen (Type V) was tested using a universal testing machine (Instron 5967) at a tensile speed of 500 mm / min.

[0053] Tensile strength: Example 3 was 20.8 ± 0.5 MPa, which was higher than Comparative Example 1's 17.5 ± 0.4 MPa, representing an increase of 18.9%. Comparative Example 2, on the other hand, showed a decrease to 13.8 ± 0.6 MPa.

[0054] Elongation at break: Example 3 was 420±15%, comparable to Comparative Example 1 (450±20%), indicating good retention of toughness. Comparative Example 2 was 380±18%.

[0055] Young's modulus (at 100% strain): 45.2 ± 1.2 MPa in Example 3, which is higher than 38.5 ± 1.0 MPa in Comparative Example 1.

[0056] The performance test results are summarized in the table below:

[0057]

[0058]

[0059] (4) Analysis of char morphology: After cone calorimetry testing, a uniform (approximately 2.5 cm) thick, dense, and hard expanded char layer was formed on the surface of the sample in Example 3. This char layer has a continuous porous network structure, which is the key to its ability to effectively block heat and mass transfer.

[0060] Comparative Example 1 (pure polyurea)

[0061] Component B contains only JEFFAMINE D-2000 (80.00 g) and DETDA (20.00 g), without any added flame retardants. The amount of component A (PM-200) is calculated according to R = 1.10. The preparation and testing methods are the same as in Example 3.

[0062] Comparative Example 2 (Polyurea with 5 wt.% unmodified CD-MOF)

[0063] 5.00 g of the unmodified CD-MOF prepared in step 1 of Example 1 was added to component B to replace an equal mass of JEFFAMINE D-2000. The component ratio for group B was: JEFFAMINE D-2000: 75.00 g; DETDA: 20.00 g; unmodified CD-MOF: 5.00 g. The preparation and testing methods were the same as in Example 3. It was noted that the viscosity of the system increased significantly during mixing, and a slight particulate feel was observed.

[0064] Example 4: Optimization of NH2-CD-MOF addition amount

[0065] Following the preparation method of Example 3, the effect of NH2-CD-MOF added to the total mass of polyurea (2 wt.%, 5 wt.%, 8 wt.%, 10 wt.%, 12 wt.%) on coating performance was systematically studied by varying only the amount added. The results are summarized in the table below:

[0066]

[0067] Conclusion: Considering flame retardancy efficiency, mechanical properties, and processability, the optimal addition amount of NH2-CD-MOF is 5 wt.% to 8 wt.%. Within this range, the coating achieves UL-94V-0 flame retardancy while simultaneously enhancing mechanical properties and exhibiting good processability.

[0068] Although the present invention has been disclosed above with reference to preferred embodiments, the embodiments are merely examples for illustrative purposes and are not intended to limit the present invention. Those skilled in the art can make various modifications and refinements without departing from the spirit and scope of the present invention. The scope of protection claimed by the present invention should be determined by the claims.

Claims

1. A functionalized hybrid flame retardant based on cyclodextrin-MOF, characterized in that, It has a core-shell structure: the core is a cyclodextrin-based metal-organic framework (CD-MOF) with cyclodextrin as the organic ligand and potassium ions as the metal nodes; the shell is a layer of silane coupling agent molecules grafted onto the surface of the CD-MOF by chemical bonding, and the general formula of the silane coupling agent is X-(CH2). n -Si(OR′)3, where X is an amino or isocyanate group, n is an integer from 3 to 6, and R′ is an alkyl group.

2. The functionalized hybrid flame retardant based on cyclodextrin-MOF according to claim 1, characterized in that, The CD-MOF is a regular octahedral single crystal or polycrystalline material synthesized by a room-temperature liquid-phase method, with a BET specific surface area of ​​not less than 500 m². 2 / g; the silane coupling agent is selected from at least one of 3-aminopropyltriethoxysilane (APTES) and 3-propyltriethoxysilane (IPTS); the grafting density of the silane coupling agent molecular layer is 0.5-2.0 mmol / g (based on the total mass of the hybrid flame retardant).

3. A method for preparing the functionalized hybrid flame retardant based on cyclodextrin-MOF as described in claim 1 or 2, characterized in that, Includes the following steps: S1. Under alkaline conditions, cyclodextrin and potassium ions are self-assembled and crystallized in a mixed solvent of water and alcohol to obtain CD-MOF primary crystals; the alkaline conditions are provided by an aqueous solution of potassium hydroxide with a concentration of 0.15-0.25 mol / L, the alcohol is methanol or ethanol, and the volume ratio of water to alcohol is (2:1)-(4:1); S2. The CD-MOF primary crystals are dispersed in an anhydrous aprotic solvent under an inert atmosphere, the silane coupling agent is added, and a reflux condensation reaction is carried out at 80-120°C for 6-24 hours to achieve surface silanization functionalization. S3. After the reaction is complete, the solid product is separated, washed multiple times with organic solvent to remove physical adsorbates, and finally dried under vacuum to obtain the hybrid flame retardant.

4. The preparation method of a functionalized hybrid flame retardant based on cyclodextrin-MOF according to claim 3, characterized in that, In step S1, cyclodextrin is dissolved in an aqueous solution of potassium hydroxide, then filtered under pressure to remove trace amounts of insoluble matter, and then mixed with alcohol and sealed and allowed to stand. Self-assembly crystallization is achieved through the slow evaporation of the solvent.

5. The preparation method of a functionalized hybrid flame retardant based on cyclodextrin-MOF according to claim 3, characterized in that, In step S2, the inert atmosphere is high-purity nitrogen, the anhydrous aprotic solvent is anhydrous toluene dried by molecular sieves, and the CD-MOF primary crystals are dispersed and then ultrasonically treated to form a uniform suspension.

6. The application of the functionalized hybrid flame retardant based on cyclodextrin-MOF as described in claim 1 or 2 in the preparation of high-performance flame-retardant polyurea coatings, characterized in that, The flame-retardant polyurea coating is formed by curing a two-component coating composition containing the hybrid flame retardant; in the two-component coating composition, component A contains a polyisocyanate with a functionality of not less than 2.2, component B contains an amino-terminated polyether with a molecular weight of 1000-5000 and a functionality of 2-3, and the hybrid flame retardant accounts for 3 wt.% to 15 wt.% of the total mass of the coating composition; when used, components A and B are mixed and cured in a ratio of isocyanate index (R value) of 1.05-1.

20.

7. The application of a functionalized hybrid flame retardant based on cyclodextrin-MOF according to claim 6 in the preparation of high-performance flame-retardant polyurea coatings, characterized in that, The polyisocyanate is selected from liquefied MDI, polymeric MDI or their prepolymers; the terminal amino polyether is polyoxypropylene ether diamine or polyoxypropylene ether triamine; the B component also contains optional amine chain extenders and auxiliaries, and the hybrid flame retardant is pre-dispersed in the B component.

8. The application of a cyclodextrin-MOF-based functionalized hybrid flame retardant according to any one of claims 6 or 7 in the preparation of high-performance flame-retardant polyurea coatings, characterized in that, In the cured flame-retardant polyurea coating, the hybrid flame retardant is chemically bonded to the three-dimensional network structure of the polyurea in the form of covalent bonds. The coating achieves a UL-94 flame retardancy rating of V-0, and the peak heat release rate (pHRR) is reduced by more than 40% compared to the pure polyurea coating without added flame retardant.

9. The application of the functionalized hybrid flame retardant based on cyclodextrin-MOF according to claim 6 in the preparation of high-performance flame-retardant polyurea coatings, characterized in that, The high-performance flame-retardant polyurea coating is used to prepare fire-retardant coatings for buildings, fire-retardant coverings for power facilities, flame-retardant interior trim for transportation vehicles, or fire-retardant layers for chemical storage tanks.

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