Preparation and Application of a Layer-by-Layer Self-Assembled MOFs Intumescent High-Efficiency Fire-Retardant Coating

Abstract

This invention discloses the preparation and application of a layer-by-layer self-assembled MOFs intumescent high-efficiency fire-retardant coating, belonging to the field of fire-retardant coating technology. The preparation method includes the following steps: (1) preparation of flame-retardant functionalized MOFs nanomaterials using the LBL method; (2) preparation of an intumescent high-efficiency fire-retardant coating based on the LBL-based flame-retardant functionalized MOFs nanomaterials. In this invention, flame-retardant functionalization modification of MOFs nanomaterials is achieved through layer-by-layer self-assembly, and the flame-retardant functionalized MOFs nanomaterials and the intumescent flame-retardant system are synergistically introduced into the coating matrix, promoting the expansion of the char layer, enhancing the flame-retardant effect, and significantly improving the char layer strength. Furthermore, the preparation is simple and environmentally friendly.

Description

Technical Field

[0001] This invention relates to the field of fire-retardant coating technology, and in particular to the preparation and application of a layer-by-layer self-assembled MOFs intumescent high-efficiency fire-retardant coating. Background Technology

[0002] Fires pose a significant threat to human life and property. While continuous economic and technological development has improved humanity's disaster prevention and firefighting capabilities, the risks associated with fires are also rapidly increasing. The frequent occurrence of fires has drawn widespread attention, making the development of efficient flame-retardant protection measures imperative. Fire-retardant coatings, also known as flame-retardant paints, are one of the earliest, simplest, and most effective methods for protecting substrates. Intumescent fire-retardant coatings are widely used for fire protection of combustible substrate surfaces. Intumescent flame retardants include acid sources, carbon sources, and gas sources, and are rich in phosphorus and nitrogen elements, playing a highly efficient synergistic flame-retardant role. During heating, the acid source in the system decomposes and releases inorganic acids, primarily phosphoric acid. The carbon source and polymer matrix undergo dehydration reactions to form coke, while the gas source decomposes to produce non-combustible gases such as ammonia and water vapor, causing the molten carbon layer to expand and form a foam-like structure. This loose, porous foam-like structure reduces the system's thermal conductivity, isolates heat and oxygen, and effectively reduces the combustion performance of the substrate material.

[0003] However, intumescent flame retardants suffer from problems such as uneven foaming, poor thermal stability, and difficulty in compatibility with composite materials. Studies have shown that adding inorganic fillers to intumescent flame retardant systems can effectively improve these defects and enhance flame retardant performance, demonstrating promising application prospects. Metal-organic frameworks (MOFs) are organic-inorganic hybrid porous nanomaterials that have attracted widespread attention in the flame retardant field due to their excellent catalytic oxidation and char formation properties resulting from their ordered porous structure and active metal centers. However, compared to traditional, well-developed flame retardants, the flame retardant effect of MOFs alone has certain limitations; therefore, it is necessary to find a suitable method to apply MOF materials to flame retardant materials. Summary of the Invention

[0004] To address the aforementioned issues, this invention utilizes LBL technology to load positive and negative electrolytes with good flame retardant and heat resistance properties onto the surface of MOF nanomaterials in layers, thereby achieving flame retardant modification of MOF nanomaterials. Then, the LBL-modified MOF nanomaterials are used as fillers and compounded with intumescent fire-retardant coatings and resin materials to obtain composite materials with enhanced flame retardant properties.

[0005] Layer-by-layer self-assembly (LBL) technology is an emerging material functionalization modification technique. It involves repeatedly immersing a substrate in solutions of positive and negative charges, depositing functional materials on its surface through the interaction of these charges to achieve substrate functionalization. LBL technology uses aqueous solutions as solvents, effectively avoiding pollution during implementation and making it environmentally friendly. Furthermore, the technology boasts a short, simple, and efficient process, thus attracting considerable attention in the field of flame retardancy.

[0006] Analysis shows that imparting flame-retardant properties to MOFs materials through LBL technology is feasible and advanced, although no related research has been conducted yet. This invention will be a significant expansion of environmentally friendly and efficient flame-retardant technology, and will also provide new ideas for the modification of MOFs materials.

[0007] The first aspect of this invention provides a method for preparing flame-retardant modified MOF nanomaterials using the LBL method, comprising the following steps:

[0008] 1. Preparation of MOFs micro / nano materials: The transition metal salt compound and the organic ligand are dissolved in appropriate solvents and mixed evenly. The mixture is reacted under certain temperature conditions to obtain a suspension. The suspension is collected by centrifugation and washed. Finally, the obtained solid is dried. The product is the MOFs micro / nano material.

[0009] 2. Preparation of positive and negative electrolyte solutions.

[0010] Positive electrolytes are dissolved in appropriate solvents to prepare positive electrolyte solutions of a certain concentration; negative electrolytes are dissolved in appropriate solvents to prepare negative electrolyte solutions of a certain concentration.

[0011] 3. Preparation of flame-retardant modified MOF nanomaterials by LBL method.

[0012] (1) The obtained MOFs micro-nano materials were immersed in a positive electrolyte solution. After a certain period of time, the particulate precipitate was collected and washed to remove the unadsorbed positive electrolyte.

[0013] (2) Immerse the precipitate washed in (1) in the prepared negative electrolyte solution. After a certain period of time, collect the particulate precipitate and wash it to remove the unadsorbed negative electrolyte and complete the first layer of layer-by-layer self-assembly.

[0014] (3) Repeat the assembly process of steps (1) to (2) until 1 to 8 layers are reached.

[0015] Furthermore, the transition metal salt compound mentioned in step 1 is one or more of the transition metal salts such as cobalt nitrate, zirconium chloride, zirconium sulfate, and zirconium acetate.

[0016] Further, the organic ligand mentioned in step 1 is terephthalic acid, pyromellitic acid, or dimethylimidazole.

[0017] Further, the solvent in step 1 is one or more of water, methanol, anhydrous ethanol and N,N-dimethylformamide.

[0018] Furthermore, the concentration of the transition metal salt compound in the suspension in step 1 is 0.15–0.25 mol / L.

[0019] Furthermore, the concentration of dimethylimidazole in the suspension in step 1 is 0.2–0.3 mol / L.

[0020] Furthermore, the specific temperature mentioned in step 1 is 100–180°C, and the reaction time is 10–48 h.

[0021] Furthermore, the centrifugation speed in step 1 is 1000-9000 r / min, and the centrifugation time is 3-10 min.

[0022] Furthermore, the drying temperature in step 1 is 45–120°C, and the drying time is 1–8 hours.

[0023] Furthermore, the positive electrolyte in step 2 includes polyethyleneimine (PEI), chitosan (CS), and amino acids.

[0024] Furthermore, the negative electrolyte in step 2 includes phytic acid (PA), sodium alginate (SA), and amino acids.

[0025] Further, the solvent mentioned in step 2 is one or more of water, acetic acid, and N,N-dimethylformamide.

[0026] Furthermore, the concentration of the positive electrolyte solution in step 2 is 0.5–3 wt%.

[0027] Furthermore, the concentration of the negative electrolyte solution in step 2 is 0.5–10 wt%.

[0028] Furthermore, in step 3, the soaking time described in steps (1) and (2) is 1 to 10 minutes.

[0029] Furthermore, in step 3, the number of layers in the assembly process is 1 to 8.

[0030] This invention provides flame-retardant modified MOF nanomaterials prepared according to the above method.

[0031] The application of flame-retardant modified MOF nanomaterials provided by this invention in the field of flame-retardant material preparation.

[0032] A second aspect of the present invention provides a method for preparing an intumescent fire-retardant coating based on flame-retardant modified MOF nanomaterials, comprising the following steps:

[0033] S1. Preparation of base material: Take the film-forming agent, curing agent and intumescent flame retardant system and stir until uniform to obtain a uniformly mixed base material;

[0034] S2. Preparation of reinforced intumescent fire-retardant coating based on flame-retardant modified MOFs: Weigh a certain mass of base material and the flame-retardant modified MOFs nanomaterials prepared by the above method, mix and stir to form a uniformly dispersed system, thus obtaining the intumescent fire-retardant coating.

[0035] Furthermore, the film-forming agent in step S1 includes one or more of epoxy resin, polyurethane, acrylic acid, waterborne silicone-acrylic emulsion, and butadiene resin.

[0036] Further, the curing agent in step S1 includes one or more combinations of ethylenediamine, diethylenetriamine, triethylenetetramine, polyamides, liquid acid anhydrides, aliphatic polyamines, cashew phenol-modified amine curing agents, diethylenediamine, hexamethylenediamine, diethylaminopropylamine, ketimine compounds, diaminodiphenylmethane, m-phenylenediamine, and diketone acrylamide adducts.

[0037] Furthermore, the intumescent flame retardant system described in step S1 includes a dehydrating agent, a charring agent, and a foaming agent.

[0038] Further, the dehydrating agent in step S1 is an inorganic acid or a compound that can generate acid in situ during combustion, including one or more of phosphoric acid, polyphosphoric acid, pyrophosphate, ammonium phosphate, ammonium polyphosphate, melamine, ammonium dihydrogen phosphate, melamine phosphate, melamine pyrophosphate, and black phosphorus.

[0039] Furthermore, the charring agent in step S1 is a high-carbon-content polyhydroxy compound, including one or more of starch, pentaerythritol and its derivatives, epoxy resin, dextrin, chitin, triazine charring agent, sorbitol, chitosan and its derivatives, cellulose and its derivatives, and pentaerythritol and its derivatives.

[0040] Further, the foaming agent in step S1 is a polyamino compound, including one or more of ammonium phosphate, ammonium dihydrogen phosphate, ammonium polyphosphate, dicyandiamide, melamine, urea, glycine, guanidines, polyurea, and ammonium molybdate.

[0041] Specifically, the intumescent flame retardant system described in step S1 is a mixture of ammonium polyphosphate and calcium gluconate in a mass ratio of 2 to 4:1.

[0042] Furthermore, the ratio of film-forming agent to curing agent in step S1 is 1.5:1 to 5:1.

[0043] Furthermore, the intumescent flame retardant system described in step S1 accounts for 0.5% to 10% of the base material.

[0044] Furthermore, in step S2, the base material accounts for 97.5% to 99.0% of the total weight of the uniformly dispersed system.

[0045] Furthermore, in step S2, the flame-retardant modified MOF nanomaterials account for 0.5–4% of the total weight of the uniformly dispersed system.

[0046] Preferably, in step S2, the flame-retardant modified MOF nanomaterials account for 0.5% to 2% of the total weight of the uniformly dispersed system.

[0047] This invention provides an intumescent fire-retardant coating prepared by the above method.

[0048] The intumescent fire-retardant coating provided by this invention is applied in the fields of fire prevention and fire-retardant product preparation.

[0049] Furthermore, the application includes the following steps:

[0050] The intumescent fire-retardant coating is brushed onto the substrate surface and cured for 1–7 days after application. Then, it is baked at 40–100℃ for 1–5 days to obtain a high-temperature resistant modified MOFs hybrid material-reinforced intumescent fire-retardant coating.

[0051] Furthermore, the substrate includes buildings, vehicles, boards, and various objects that require fire protection.

[0052] Beneficial effects:

[0053] (1) This invention is the first to use LBL modification technology to prepare flame-retardant functionalized MOF nanomaterials. It is effective and reliable. While enhancing the flame-retardant properties of MOF nanomaterials, it also improves the compatibility between MOF nanomaterials and the matrix and improves the defects of easy agglomeration and easy migration of nanomaterials.

[0054] (2) In this invention, flame-retardant functionalized MOFs are combined with traditional intumescent flame-retardant systems to exert a synergistic flame-retardant effect, have excellent smoke suppression and toxicity reduction effects, promote char formation, enhance the intumescent flame-retardant effect, and effectively improve the flame-retardant performance of composite materials.

[0055] (3) The LBL flame retardant modification technology in this invention uses aqueous solution as solvent, which is safe and non-toxic; the modification process is easy to operate, simple and efficient, and conforms to the current development trend. Attached Figure Description

[0056] Figure 1 The images show the infrared spectra of ZIF-67 before and after modification.

[0057] Figure 2 The images show the XRD patterns of ZIF-67 before and after modification.

[0058] Figure 3The images show SEM images of ZIF-67 before and after modification, where a represents the flame-retardant modification before modification and b represents the flame-retardant modification after modification. Detailed Implementation

[0059] The present invention will be further explained and described below with reference to the appendix and embodiments, but the scope of protection of the present invention is not limited to the following embodiments.

[0060] Example 1

[0061] A method for preparing flame-retardant modified ZIF-67 nanomaterials using the LBL method includes the following steps:

[0062] 1. Preparation of ZIF-67 micro / nano materials:

[0063] 1.092 g of cobalt nitrate and 0.616 g of dimethylimidazole were dissolved in 15 mL of anhydrous methanol solution and mixed evenly. The mixture was reacted at 120 °C for 12 h to obtain a clear suspension. The precipitate was collected by centrifugation and washed repeatedly with anhydrous methanol and deionized water. Finally, the obtained solid was dried in an oven. The product obtained is ZIF-67 micro / nano material.

[0064] 2. Preparation of positive and negative electrolyte solutions:

[0065] Polyethyleneimine (PEI) was dissolved in deionized water to prepare a 2 wt% positive electrolyte solution; sodium alginate (SA) was dissolved in deionized water to prepare a 0.5 wt% negative electrolyte solution.

[0066] 3. Preparation of flame-retardant modified ZIF-67 nanomaterials by the LBL method:

[0067] (1) Immerse the ZIF-67 sample in 100 mL of prepared positive electrolyte solution. After 5 min, collect the particulate precipitate and wash it with deionized water to remove the unadsorbed positive electrolyte.

[0068] (2) The precipitate obtained in (1) is immersed in 100 mL of prepared negative electrolyte solution. After 5 min, the particulate precipitate is collected and washed with deionized water to remove the unadsorbed negative electrolyte and complete the first layer of layer-by-layer self-assembly.

[0069] (3) Repeat the assembly process of steps (1) to (2), with an immersion time of 1 minute, until the number of self-assembled modified layers reaches 5, and obtain flame-retardant modified ZIF-67 nanomaterial.

[0070] A method for preparing an intumescent fire-resistant composite material based on LBL-modified ZIF-67 nanomaterials includes the following steps:

[0071] S1. Preparation of base material:

[0072] Weigh 45.327g of epoxy resin (EP), 9.873g of 4,4-diaminodiphenylmethane, and 3g of intumescent flame retardant system (ammonium polyphosphate: calcium gluconate = 3:1, w / w) and stir until a uniformly mixed base material is formed.

[0073] S2. Preparation of reinforced intumescent fire-retardant coating based on LBL method for flame-retardant modification of ZIF-67:

[0074] The base material from step 1 was mixed with 1.8g of flame-retardant modified ZIF-67 nanomaterial and mechanically stirred and dispersed for 5 hours to form a uniformly dispersed intumescent fire-retardant coating based on flame-retardant modified ZIF-67. Then, the uniformly mixed fire-retardant coating was brushed onto the surface of a pretreated substrate. After brushing, it was cured at room temperature for 1 day and then baked at 100℃ for 1 day to obtain a high-temperature resistant modified MOF hybrid material-reinforced intumescent fire-retardant composite material.

[0075] Example 2

[0076] A method for preparing flame-retardant modified ZIF-67 nanomaterials using the LBL method includes the following steps:

[0077] 1. Preparation of ZIF-67 micro / nano materials: Performed according to step 1 in Example 1;

[0078] 2. Preparation of positive and negative electrolyte solutions: Refer to step 2 in Example 1;

[0079] 3. Preparation of flame-retardant modified ZIF-67 nanomaterials by LBL method: Refer to step 3 in Example 1;

[0080] A method for preparing an intumescent fire-resistant composite material based on LBL-modified ZIF-67 nanomaterials includes the following steps:

[0081] S1. Preparation of base material:

[0082] Weigh 45.82g of epoxy resin (EP), 9.98g of 4,4-diaminodiphenylmethane, and 3g of intumescent flame retardant system (ammonium polyphosphate: calcium gluconate = 3:1, w / w) and stir until a uniformly mixed base material is formed.

[0083] S2. Preparation of reinforced intumescent fire-retardant coating based on LBL method for flame-retardant modification of ZIF-67:

[0084] The base material weighed in step 1 was mixed with 1.2g of flame-retardant modified ZIF-67 nanomaterial and mechanically stirred and dispersed for 5 hours to form a uniformly dispersed intumescent fire-retardant coating based on flame-retardant modified ZIF-67. Then, the uniformly mixed fire-retardant coating was brushed onto the surface of the pretreated substrate. After brushing, it was cured at room temperature for 1 day and baked at 100℃ for 1 day to obtain a high-temperature resistant modified MOF hybrid material-reinforced intumescent fire-retardant composite material.

[0085] Example 3

[0086] A method for preparing flame-retardant modified ZIF-67 nanomaterials using the LBL method includes the following steps:

[0087] 1. Preparation of ZIF-67 micro / nano materials: Performed according to step 1 in Example 1;

[0088] 2. Preparation of positive and negative electrolyte solutions: Refer to step 2 in Example 1;

[0089] 3. Preparation of flame-retardant modified ZIF-67 nanomaterials by LBL method: Refer to step 3 in Example 1;

[0090] A method for preparing an intumescent fire-retardant composite coating based on LBL-modified ZIF-67 nanomaterials includes the following steps:

[0091] 1. Preparation of base material:

[0092] Weigh 46.313g of epoxy resin (EP), 10.087g of 4,4-diaminodiphenylmethane, and 3g of intumescent flame retardant system (ammonium polyphosphate: calcium gluconate = 3:1, w / w) and stir until a uniformly mixed base material is formed.

[0093] 2. Preparation of reinforced intumescent fire-retardant coating based on LBL method for flame-retardant modification of ZIF-67:

[0094] The base material weighed in step 1 was mixed with 0.6g of flame-retardant modified ZIF-67 nanomaterial and mechanically stirred and dispersed for 5 hours to form a uniformly dispersed intumescent fire-retardant coating based on flame-retardant modified ZIF-67. Then, the uniformly mixed fire-retardant coating was brushed onto the surface of the pretreated substrate. After brushing, it was cured at room temperature for 1 day and baked at 100℃ for 1 day to obtain a high-temperature resistant modified MOF hybrid material-reinforced intumescent fire-retardant composite material.

[0095] Example 4

[0096] A method for preparing flame-retardant modified ZIF-67 nanomaterials using the LBL method includes the following steps:

[0097] 1. Preparation of ZIF-67 micro / nano materials: Performed according to step 1 in Example 1;

[0098] 2. Preparation of positive and negative electrolyte solutions: Refer to step 2 in Example 1;

[0099] 3. Preparation of flame-retardant modified ZIF-67 nanomaterials by LBL method: Refer to step 3 in Example 1;

[0100] A method for preparing an intumescent fire-resistant composite material based on LBL-modified ZIF-67 nanomaterials includes the following steps:

[0101] 1. Preparation of base material:

[0102] Weigh 46.559g of epoxy resin (EP), 10.141g of 4,4-diaminodiphenylmethane, and 3g of intumescent flame retardant system (ammonium polyphosphate: calcium gluconate = 3:1, w / w) and stir until a uniformly mixed base material is formed.

[0103] 2. Preparation of reinforced intumescent fire-retardant coating based on LBL method for flame-retardant modification of ZIF-67:

[0104] The base material weighed in step 1 was mixed with 0.3g of flame-retardant modified ZIF-67 nanomaterial and mechanically stirred and dispersed for 5 hours to form a uniformly dispersed intumescent fire-retardant coating based on flame-retardant modified ZIF-67. The uniformly mixed fire-retardant coating was then brushed onto the surface of the pretreated substrate. After brushing, it was cured at room temperature for 1 day and baked at 100℃ for 1 day to obtain a high-temperature resistant modified MOF hybrid material-reinforced intumescent fire-retardant composite material.

[0105] Comparative Example 1

[0106] Weigh 49.269g of epoxy resin (EP) and 10.731g of 4,4-diaminodiphenylmethane and stir until a uniformly mixed base material is formed. Apply the uniformly mixed fire-retardant coating to the surface of the pretreated substrate. After application, cure at room temperature for 1 day and bake at 100℃ for 1 day to obtain the composite material.

[0107] Comparative Example 2

[0108] Weigh 46.806g of epoxy resin (EP), 10.194g of 4,4-diaminodiphenylmethane, and 3g of intumescent flame retardant system (ammonium polyphosphate: calcium gluconate = 3:1, w / w), and stir until a uniformly dispersed intumescent fire retardant coating is formed. The uniformly mixed fire retardant coating is then brushed onto the surface of the pretreated substrate. After brushing, the coating is cured at room temperature for 1 day and then baked at 100℃ for 1 day to obtain an intumescent flame retardant fire retardant composite material.

[0109] Comparative Example 3

[0110] 1. Weigh 45.820g of epoxy resin (EP), 9.980g of 4,4-diaminodiphenylmethane, and 3g of intumescent flame retardant system (ammonium polyphosphate: calcium gluconate = 3:1, w / w) and stir until a uniformly mixed base material is formed.

[0111] 2. The base material weighed in step 1 is mixed with 1.2g of the ZIF-67 nanomaterial prepared in step 1 of Example 1, and mechanically stirred and dispersed for 5 hours to form a uniformly dispersed intumescent fire-retardant coating based on ZIF-67. Then, the uniformly mixed fire-retardant coating is brushed onto the surface of the pretreated substrate. After brushing, it is cured at room temperature for 1 day and baked at 100℃ for 1 day to obtain a high-temperature resistant modified MOF hybrid material-reinforced intumescent fire-retardant composite material.

[0112] Comparative Example 4

[0113] A method for preparing flame-retardant modified ZIF-67 nanomaterials using the LBL method includes the following steps:

[0114] 1. Preparation of ZIF-67 micro / nano materials: Performed according to step 1 in Example 1;

[0115] 2. Preparation of positive and negative electrolyte solutions: Refer to step 2 in Example 1;

[0116] 3. Preparation of flame-retardant modified ZIF-67 nanomaterials by LBL method: Refer to step 3 in Example 1;

[0117] A method for preparing an intumescent fire-resistant composite material based on LBL-modified ZIF-67 nanomaterials includes the following steps:

[0118] 1. Preparation of base material:

[0119] Weigh 48.283g of epoxy resin (EP) and 10.517g of 4,4-diaminodiphenylmethane and stir until a uniformly mixed base is formed.

[0120] 2. Preparation of reinforced intumescent fire-retardant coating based on LBL method for flame-retardant modification of ZIF-67:

[0121] The base material weighed in step 1 was mixed with 1.2g of flame-retardant modified ZIF-67 nanomaterial and mechanically stirred and dispersed for 5 hours to form a uniformly dispersed intumescent fire-retardant coating based on flame-retardant modified ZIF-67. The uniformly mixed fire-retardant coating was then brushed onto the surface of the pretreated substrate. After brushing, it was cured at room temperature for 1 day and baked at 100℃ for 1 day to obtain a high-temperature resistant modified MOF hybrid material-reinforced intumescent fire-retardant composite material.

[0122] Table 1. Formulation of Comparative Examples 1-3 and Examples 1-3

[0123]

[0124] Cone calorimetry test procedure:

[0125] Fire-resistant composite material samples prepared in Examples 1-4 and Comparative Examples 1-4 were respectively installed on the test apparatus. The power of the radiation cone was set to 35 kW. The cone calorimeter was started to perform thermal radiation and collect test data in real time. Parameters such as the heat release rate (PHRR), total heat release (THR), total smoke release (TSR), and real-time mass (MASS) of the material were calculated. After the preset test time was reached, the thermal radiation of the radiation cone was stopped, and the following data were obtained:

[0126] Table 2. Cone calorimetry test data for Comparative Examples 1-4 and Examples 1-3

[0127]

[0128] PHRR is an important fire characteristic parameter of materials, reflecting their combustion intensity. Combined with data such as THR, it allows for a better evaluation of the material's combustion performance. Compared to pure epoxy resin (Comparative Example 1) and uniformly dispersed conventional intumescent coatings (Comparative Example 2), the uniformly dispersed intumescent fire-retardant coatings based on flame-retardant modified ZIF-67 (Examples 1-4) showed a significantly lower PHRR value during combustion, indicating that flame-retardant modified ZIF-67 can effectively improve the flame-retardant performance of the resin material. The PHRR value of the uniformly dispersed intumescent fire-retardant coating based on ZIF-67 (Comparative Example 3) was higher than that of Examples 1-4, strongly demonstrating that the flame-retardant performance of the modified ZIF-67 was effectively enhanced. For Examples 2-4, the PHRR value during combustion decreased with increasing amounts of flame-retardant modified ZIF-67, suggesting that increased amounts enhance the flame-retardant performance of the composite material. However, when the amount of flame-retardant modified ZIF-67 reached 1.8g, the PHRR value during combustion increased instead of decreasing, possibly due to agglomeration caused by excessive nanomaterial addition.

[0129] Therefore, the uniformly dispersed intumescent fire-retardant coating based on flame-retardant modified ZIF-67 can impart better flame-retardant properties to the composite material. Furthermore, within a certain range, the higher the addition amount, the better the effect. Therefore, the mass fraction of the flame-retardant modified ZIF-67 nanomaterial prepared in this invention in the intumescent fire-retardant coating should be 1–2.5%. These conclusions are also verified in subsequent results. In addition, the total heat release (THR) refers to the total heat released by the material from ignition to flame extinguishing; the higher the value, the more intense the combustion reaction. Real-time mass reflects the trend of weight loss during material decomposition during combustion; the greater the weight loss, the more intense the combustion reaction. It can also be seen that the products obtained in Examples 2 and 3 have superior flame-retardant properties.

[0130] The embodiments provided above are not intended to limit the scope of the invention, nor are the described steps intended to limit the order of execution. Any obvious modifications made to the invention by those skilled in the art based on existing common knowledge also fall within the scope of protection defined by the claims.

Claims

1. A method for preparing an intumescent fire-retardant coating based on LBL-modified MOF nanomaterials, characterized in that, Includes the following steps: S1. Preparation of base material: Take the film-forming agent, curing agent and intumescent flame retardant system and stir them evenly to obtain the base material; the intumescent flame retardant system is a mixture of ammonium polyphosphate and calcium gluconate salt in a mass ratio of 2~4:1; S2. Preparation of reinforced intumescent fire-retardant coating based on LBL method flame-retardant modified MOFs: Weigh the base material and flame-retardant modified MOFs nanomaterials obtained in step S1, mix and stir to form a uniform dispersion system, and thus obtain the intumescent fire-retardant coating. In step S2, the flame-retardant modified MOF nanomaterials account for 0.5-2.0% of the total weight of the uniformly dispersed system; The preparation method of the flame-retardant modified MOF nanomaterials in step S2 includes the following steps: I. Preparation of MOFs micro / nanomaterials: A transition metal salt compound and an organic ligand are dissolved in a solvent and mixed evenly. The mixture is then reacted at a certain temperature to obtain a suspension. The suspension is centrifuged to collect the precipitate, which is then washed. Finally, the obtained solid is dried, and the product is the MOFs micro / nanomaterial. The transition metal salt compound is cobalt nitrate, and the organic ligand is dimethylimidazole. II. Preparation of positive and negative electrolyte solutions: Dissolve the positive electrolyte in a solvent to prepare a positive electrolyte solution of a certain concentration; dissolve the negative electrolyte in a solvent to prepare a negative electrolyte solution of a certain concentration; the positive electrolyte is polyethyleneimine; the negative electrolyte is sodium alginate; III. Preparation of flame-retardant modified MOF nanomaterials by the LBL method: (1) The obtained MOFs micro-nano materials were immersed in a positive electrolyte solution. After a certain period of time, the particulate precipitate was collected and washed to remove the unadsorbed positive electrolyte. (2) Immerse the precipitate washed in (1) in the prepared negative electrolyte solution. After a certain period of time, collect the particulate precipitate and wash it to remove the unadsorbed negative electrolyte and complete the first layer of layer-by-layer self-assembly. (3) Repeat the assembly process of steps (1) to (2) until 1 to 8 layers are reached to obtain flame-retardant modified MOF nanomaterials.

2. The preparation method according to claim 1, characterized in that, The film-forming agent mentioned in step S1 includes one or more of epoxy resin, polyurethane, acrylic acid, waterborne silicone-acrylic emulsion, and butadiene resin.

3. The preparation method according to claim 1, characterized in that, The curing agent mentioned in step S1 includes one or more of the following: ethylenediamine, diethylenetriamine, triethylenetetramine, polyamides, liquid acid anhydrides, cashew phenol-modified amine curing agents, diethylenediamine, hexamethylenediamine, diethylaminopropylamine, ketimine compounds, diaminodiphenylmethane, m-phenylenediamine, and diketone acrylamide adducts.

4. The preparation method according to claim 1, characterized in that, In step I, the concentration of the transition metal salt compound in the suspension is 0.15 ~ 0.25 mol / L; the concentration of dimethylimidazole in the suspension is 0.2 ~ 0.3 mol / L.

5. The preparation method according to claim 1, characterized in that, In step II, the solvent is one or more of water, acetic acid, and N,N-dimethylformamide; the concentration of the positive electrolyte solution is 0.5-3 wt%; and the concentration of the negative electrolyte solution is 0.5-10 wt%.

6. The preparation method according to claim 1, characterized in that, In step III, the immersion time described in steps (1) and (2) is 1 to 10 minutes.

7. An intumescent fire-retardant coating, characterized in that, The intumescent fire-retardant coating is prepared by the method described in any one of claims 1 to 6.

8. The application of the intumescent fire-retardant coating as described in claim 7 in the fields of fire prevention and fire-retardant product preparation.

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