A functionalized MXene-based waterborne fire-retardant coating, its preparation method and application

Abstract

This invention discloses a functionalized MXene-based waterborne fire-retardant coating, its preparation method, and its application, belonging to the field of fire-retardant coating technology. This invention combines the advantages of functionalized MXene materials, such as high dispersibility, high temperature resistance, and excellent flame-retardant properties, using waterborne polyurethane as the resin matrix, ammonium citrate as the acid source, and MXene materials as nanostructured flame retardants to develop an environmentally friendly, high-performance reinforced waterborne fire-retardant coating. The MXene materials can be obtained through chemical modification with different functional groups (such as silane coupling agents, calixarenes, and MOFs) to introduce polar groups onto the surface. The fire-retardant coating prepared using functionalized MXene materials achieves UL-94 V-0 flame retardancy through a dual mechanism of physical barrier and "catalytic char formation," while also possessing high mechanical strength and thermal stability, making it suitable for protecting substrates such as metals and wood.

Description

Technical Field

[0001] This invention belongs to the field of fire-retardant coating technology, and in particular relates to a functionalized MXene-type water-based fire-retardant coating and its preparation method. Background Technology

[0002] Fire-retardant coatings are functional coatings specifically designed for the surface of flammable substrates. They significantly reduce the flammability of the substrate surface, effectively prevent the rapid spread of fire, and improve the fire resistance limit of the substrate. They are crucial for ensuring personnel safety and evacuation during a fire. Fire-retardant coatings can be adhered to the substrate surface using adhesives, forming a passive fire barrier. When heated, they can significantly inhibit heat and mass transfer between the condensed phase and the gas phase, thus providing thermal insulation. However, commonly used solvent-based fire-retardant coatings often use low-flash-point organic solvents such as toluene, xylene, and 200# solvent oil. These solvents easily form flammable gases, which can easily cause combustion or explosion. Furthermore, they release harmful substances such as benzene, toluene, xylene, and halogenated hydrocarbons, which not only harm human health but also pose serious environmental pollution risks. With increasing safety and environmental protection requirements, solvent-based fire-retardant coatings are gradually transitioning to water-based formulations to avoid the environmental and worker health hazards caused by the release of volatile organic compounds (VOCs) during the production and application of traditional solvent-based coatings.

[0003] In the structural system of water-based fire-retardant coatings, functional nano-flame retardants are the key components for achieving flame retardancy, heat insulation, and adhesion. Currently, the preparation of water-based fire-retardant coatings mainly involves introducing nano-structured flame retardants with high specific surface area and excellent flame-retardant properties into the coating, effectively improving the fire resistance of the water-based coating by leveraging the non-combustible and barrier properties of these nano-structured flame retardants. However, existing nano-flame retardants suffer from poor dispersibility in water-based resin matrices, and some even exhibit severe agglomeration, leading to decreased crack resistance during the curing process. Furthermore, commonly used nano-structured flame retardants (such as graphene oxide, carbon nanotubes, and silicon dioxide) still lag behind solvent-based fire-retardant coatings in improving their flame-retardant properties. Summary of the Invention

[0004] To address the issues of poor dispersibility and insufficient flame retardant performance of nanostructured flame retardants in current water-based fire-retardant coatings, this invention selects MXene materials and their derivatives as nanostructured flame retardants to prepare a functionalized MXene-type water-based fire-retardant coating. When applied to the protection of flammable substrates such as metals and wood, it can solve the problems of poor dispersibility and insufficient flame retardant performance of nanostructured flame retardants in existing water-based fire-retardant coatings.

[0005] MXene materials are a class of two-dimensional inorganic compounds composed of transition metal carbides, nitrides, or carbonitrides with a thickness of several atomic layers, and their surfaces contain hydroxyl or terminal oxygen functional groups. This invention leverages the characteristic of MXene nanomaterials being rich in –OH, –O, and –F functional groups, enabling them to form hydrogen bonds or covalent bonds with other components in coatings. This enhances the interfacial compatibility of waterproof coatings, thereby improving dispersibility and preventing agglomeration. Simultaneously, the two-dimensional layered structure of MXene nanomaterials can spread uniformly within the polymer matrix, creating a "maze effect" that delays the migration and aggregation of flame retardants, improving the dispersion stability of waterproof coatings. Furthermore, the structural and performance characteristics of MXene nanomaterials allow them to induce directional carbonization of the aqueous resin matrix during combustion, forming a dense char layer. This char layer acts as a physical barrier, blocking contact between the substrate and external heat and oxygen, delaying further polymer pyrolysis; it also prevents combustible small molecules generated by internal thermal decomposition from entering the gas phase and participating in the combustion reaction, thus inhibiting the transmission of the combustion chain reaction at its source. Furthermore, the dense char layer contains a large number of pores and cracks, which can extend the heat transfer path through the "maze effect" and slow down the heat conduction efficiency, thereby further improving the fire resistance of the functionalized MXene-type water-based fire retardant coating of the present invention.

[0006] The present invention discloses a functionalized MXene-type water-based fire-retardant coating, which is prepared by mixing the following raw materials in a certain order of addition and stirring until homogeneous:

[0007] 1 part of MXene nanostructured flame retardant;

[0008] 1-10 parts of waterborne polyurethane;

[0009] Ammonium citrate 0.5-5 parts;

[0010] 2-12 parts of titanium dioxide;

[0011] Water 0.2 to 1 part.

[0012] Preferably, the MXene nanostructure flame retardant is any one of MXene material, silane coupling agent functionalized MXene material, calixarene functionalized MXene material, or MOFs / MXene composite material.

[0013] The functionalized MXene-type waterborne fire-retardant coating provided by this invention is prepared by the following steps:

[0014] (1) Weigh a certain amount of MXene nanomaterial flame retardant and disperse it evenly in water to obtain the first mixed liquid.

[0015] (2) Add a certain amount of ammonium citrate to the first mixed liquid obtained in step (1) and stir at room temperature for 5 to 20 minutes until completely dissolved to obtain the second mixed liquid.

[0016] (3) A certain amount of waterborne polyurethane is placed as the resin matrix in the second mixed liquid obtained in step (2), and stirred at room temperature for 10-20 min. Then a certain amount of titanium dioxide is added, and stirred at room temperature for 15-40 min until all components are completely mixed and homogeneous to obtain functionalized MXene type waterborne fireproof coating.

[0017] Preferably, the MXene nanostructure flame retardant in step (1) can be any one of MXene material, silane coupling agent functionalized MXene material, calixarene functionalized MXene material, or MOFs / MXene composite material.

[0018] Preferably, in step (1), the mass ratio of MXene nanostructured flame retardant to water is 1:1 to 5:1. More preferably, the water is deionized water or ultrapure water.

[0019] Preferably, the mass ratio of MXene nanostructure flame retardant to ammonium citrate in step (2) is 2:1 to 1:5.

[0020] Preferably, in step (3), the mass ratio of MXene nanostructure flame retardant to waterborne epoxy resin is 1:1 to 1:10.

[0021] Preferably, in step (3), the mixing system after adding waterborne epoxy resin is stirred for 10-20 minutes at room temperature.

[0022] Preferably, in step (3), the mass ratio of MXene nanostructure flame retardant to titanium dioxide is 1:2 to 1:12.

[0023] Preferably, in step (3), the mixing time of the mixed solution 3 at room temperature is 15-40 min.

[0024] The present invention also relates to a functionalized MXene-type waterborne fire-retardant coating prepared by the above-described preparation method.

[0025] When using, the functionalized MXene-type waterborne fire retardant coating obtained by the above method is applied to the surface of the substrate to be protected and cured at room temperature for 12~24 h, thereby forming a functionalized MXene-type waterborne fire retardant coating on the surface of the substrate.

[0026] The functionalized MXene-type water-based fire-retardant coating of the present invention is particularly suitable for the protection of flammable substrates such as metals and wood.

[0027] Compared with the prior art, the beneficial technical effects of the present invention are mainly reflected in the following aspects.

[0028] (1) The MXene nanomaterial flame retardant selected in the water-based fireproof coating of the present invention utilizes its typical high specific surface area and two-dimensional layered structure and surface rich in functional groups such as –OH, –O and –F. It can interact with the polyurethane resin matrix to enhance interfacial compatibility. On the one hand, it improves the dispersibility of the nanostructure flame retardant in the resin, and on the other hand, it constructs a dense layered physical barrier in the polyurethane matrix to prevent heat, oxygen and substrate from contacting each other.

[0029] (2) The water-based fireproof coating of the present invention uses MXene nanostructure flame retardant. When it is ignited and burning, MXene nanostructure flame retardant can also induce water-based resin to undergo directional carbonization, forming a dense char layer, which isolates the heat source and adsorbs combustible components. The flame retardant performance is achieved through the dual mechanism of "physical barrier" and "catalytic carbonization".

[0030] (3) In the water-based fireproof coating of the present invention, the acid source is ammonium citrate. Compared with the conventional acid sources containing phosphorus and halogen commonly used in conventional fireproof coatings, when the ammonium citrate is ignited and burned, the thermal decomposition products are mainly ammonia, carbon dioxide and water, without toxic halogenated gases or persistent pollutants. Furthermore, the ammonia in the decomposition products is difficult to ignite, while carbon dioxide and water are not flammable, which is in line with the development trend of green flame retardants.

[0031] (4) The fireproof coating prepared by the functionalized MXene water-based fireproof coating of the present invention can achieve UL-94 V-0 flame retardancy and the limiting oxygen index can reach up to 35.2%, and its fireproof performance is significantly better than that of similar fireproof coating products. Attached Figure Description

[0032] Figure 1 The graphs show the thermal stability test curves of the fire-retardant coatings made from the MXene nanostructure flame retardants prepared in Examples 1, 2, and 3.

[0033] Figure 2 Limiting oxygen index and UL-94 test bar chart of the functionalized MXene-type waterborne fire retardant coating prepared for embodiments of the present invention.

[0034] Figure 3 UL-94 flame retardancy test of the A1-coated PP test plate prepared in Example 1.

[0035] Figure 4 UL-94 flame retardancy test of the A2-coated PP test plate prepared in Example 2.

[0036] Figure 5 UL-94 flame retardancy test of the A3-coated PP test plate prepared in Example 3.

[0037] Figure 6 UL-94 flame retardancy test of uncoated PP test panels. Detailed Implementation

[0038] The preparation and performance of the functionalized MXene-type waterborne fire-retardant coating of the present invention will be further described below with reference to the accompanying drawings in the embodiments of the present invention.

[0039] (I) Preparation of Functionalized MXene-type Waterborne Fire-retardant Coatings

[0040] Example 1

[0041] (1) Weigh 1.0 g of MXene nanostructure flame retardant and disperse it evenly in 1.0 mL of ultrapure water to obtain the first mixed dispersion.

[0042] (2) Weigh 5.0 g of ammonium citrate and add it to the first mixed dispersion in batches. Stir the mixture at room temperature for 20 min to obtain the second mixed solution.

[0043] (3) Weigh 10.0 g of waterborne polyurethane and place it in the second mixed solution, then stir at room temperature for 20 min; then add 12.0 g of titanium dioxide in batches, and continue to stir the mixed system at room temperature for 40 min until the components in the system are evenly dispersed, and obtain a viscous functionalized MXene type waterborne fireproof coating.

[0044] (4) The obtained functionalized MXene water-based fire retardant coating is applied to the surface of the protected substrate and cured at room temperature for 24 hours to obtain a functionalized MXene water-based fire retardant coating, labeled as A1.

[0045] Example 2

[0046] (1) Weigh 1.0 g of MXene nanostructure flame retardant and disperse it evenly in 0.4 mL of ultrapure water to obtain the first mixed dispersion.

[0047] (2) Weigh 4.0 g of ammonium citrate and add it to the first mixed dispersion in batches. Stir the mixture at room temperature for 15 min to obtain the second mixed solution.

[0048] (3) Weigh 8.0 g of waterborne polyurethane and place it in the second mixed solution, then stir at room temperature for 18 min; then add 10.0 g of titanium dioxide gradually, and continue to stir the mixed system at room temperature for 30 min until the components in the system are evenly dispersed, and obtain a viscous functionalized MXene type waterborne fireproof coating.

[0049] (4) The obtained functionalized MXene water-based fire retardant coating is applied to the surface of the protected substrate and cured at room temperature for 20 hours to obtain a functionalized MXene water-based fire retardant coating, labeled as A2.

[0050] Example 3

[0051] (1) Weigh 1.0 g of MXene nanostructure flame retardant and disperse it evenly in 0.6 mL of ultrapure water to obtain the first mixed dispersion.

[0052] (2) Weigh 3.0 g of ammonium citrate and add it to the first mixed dispersion in batches. Stir the mixture at room temperature for 10 min to obtain the second mixed solution.

[0053] (3) Weigh 6.0 g of waterborne polyurethane and place it in the second mixed solution, then stir at room temperature for 15 min; then add 8.0 g of titanium dioxide in batches, and continue to stir the mixed system at room temperature for 25 min until the components in the system are evenly dispersed, and obtain a viscous functionalized MXene type waterborne fireproof coating.

[0054] (4) The obtained functionalized MXene water-based fire retardant coating is applied to the surface of the protected substrate and cured at room temperature for 18 hours to obtain a functionalized MXene water-based fire retardant coating, labeled as A3.

[0055] Example 4

[0056] (1) Weigh 1.0 g of MXene nanostructure flame retardant and disperse it evenly in 0.4 mL of ultrapure water to obtain the first mixed dispersion.

[0057] (2) Weigh 2.0 g of ammonium citrate and add it to the first mixed dispersion in batches. Stir the mixture at room temperature for 5 min to obtain the second mixed solution.

[0058] (3) Weigh 4.0 g of waterborne polyurethane and place it in the second mixed solution, then stir at room temperature for 10 min; then add 6.0 g of titanium dioxide in batches, and continue to stir the mixed system at room temperature for 20 min until the components in the system are evenly dispersed, and obtain a viscous functionalized MXene type waterborne fireproof coating.

[0059] (4) The obtained functionalized MXene water-based fire retardant coating is applied to the surface of the protected substrate and cured at room temperature for 12 hours to obtain a functionalized MXene water-based fire retardant coating, marked as A4.

[0060] Example 5

[0061] (1) Weigh 1.0 g of MXene nanostructure flame retardant material and disperse it evenly in 0.2 mL of ultrapure water to obtain the first mixed dispersion.

[0062] (2) Weigh 1.0 g of ammonium citrate and add it to the first mixed dispersion in batches. Stir the mixture at room temperature for 20 min to obtain the second mixed solution.

[0063] (3) Weigh 2.0 g of waterborne polyurethane and place it in the second mixed solution, then stir for 5 min at room temperature; then add 4.0 g of titanium dioxide in batches, and continue stirring the mixed system at room temperature for 15 min until the components in the system are evenly dispersed, and obtain a viscous functionalized MXene type waterborne fireproof coating.

[0064] (4) The obtained functionalized MXene water-based fire retardant coating is applied to the surface of the protected substrate and cured at room temperature for 24 hours to obtain a functionalized MXene water-based fire retardant coating, which is marked as A5.

[0065] Example 6

[0066] (1) Weigh 1.0 g of silane coupling agent functionalized MXene material and disperse it evenly in 0.8 mL of ultrapure water to obtain the first mixed dispersion.

[0067] (2) Weigh 0.5 g of ammonium citrate and add it to the first mixed dispersion in batches. Stir the mixture at room temperature for 10 min to obtain the second mixed solution.

[0068] (3) Weigh 1.0 g of waterborne polyurethane and place it in the second mixed solution, then stir at room temperature for 20 min; then add 2.0 g of titanium dioxide gradually, and continue to stir the mixed system at room temperature for 40 min until the components in the system are evenly dispersed, and obtain a viscous functionalized MXene type waterborne fireproof coating.

[0069] (4) The obtained functionalized MXene water-based fire retardant coating is applied to the surface of the protected substrate and cured at room temperature for 16 hours to obtain a functionalized MXene water-based fire retardant coating, which is marked as A6.

[0070] Example 7

[0071] (1) Weigh 1.0 g of calixarene-functionalized MXene material and disperse it evenly in 1.0 mL of ultrapure water to obtain the first mixed dispersion.

[0072] (2) Weigh 1.0 g of ammonium citrate and add it to the first mixed dispersion in batches. Stir the mixture at room temperature for 5 min to obtain the second mixed solution.

[0073] (3) Weigh 10.0 g of waterborne polyurethane and place it in the second mixed solution, then stir at room temperature for 20 min; then add 6.0 g of titanium dioxide in batches, and continue to stir the mixed system at room temperature for 15 min until the components in the system are evenly dispersed, and obtain a viscous functionalized MXene type waterborne fireproof coating.

[0074] (4) The obtained functionalized MXene water-based fire retardant coating is applied to the surface of the protected substrate and cured at room temperature for 14 hours to obtain a functionalized MXene water-based fire retardant coating, which is marked as A7.

[0075] Example 8

[0076] (1) Weigh 1.0 g of MOFs / MXene composite material and disperse it evenly in 0.2 mL of ultrapure water to obtain the first mixed dispersion.

[0077] (2) Weigh 3.0 g of ammonium citrate and add it to the first mixed dispersion in batches. Stir the mixture at room temperature for 5 min to obtain the second mixed solution.

[0078] (3) Weigh 5.0 g of waterborne polyurethane and place it in the second mixed solution, then stir at room temperature for 10 min; then add 12.0 g of titanium dioxide in batches, and continue to stir the mixed system at room temperature for 40 min until the components in the system are evenly dispersed, and obtain a viscous functionalized MXene type waterborne fireproof coating.

[0079] (4) The obtained functionalized MXene water-based fire retardant coating is applied to the surface of the protected substrate and cured at room temperature for 12 hours to obtain a functionalized MXene water-based fire retardant coating, marked as A8.

[0080] (II) Product performance testing and characterization analysis

[0081] To verify the flame-retardant effect of the functionalized MXene-type waterborne fire-retardant coatings described in the above embodiments, the inventors conducted tests and characterization analyses on the structure and properties of the functionalized MXene-type waterborne fire-retardant coatings with different component ratios in Examples 1 to 8. The test and characterization methods and results are as follows.

[0082] (1) Test of thermal stability of functionalized MXene-type waterborne fire retardant coatings

[0083] The thermal stability of the functionalized MXene-based waterborne fire-retardant coatings prepared in Examples 1, 2, and 3 was tested using thermogravimetric analysis (TGA), and the results are as follows: Figure 1 As shown. From Figure 1It can be seen that: 1) the MXene-based functionalized fire-retardant coatings in Examples 1-3 begin to degrade and undergo charring at 160℃; 2) the char residue rate of the coating increases with the increase of the MXene nanostructure flame retardant content, while the maximum mass loss rate gradually decreases. This indicates that MXene promotes the charring of water-based resins during the flame-retardant process of fire-retardant coatings, forming a dense char residue layer and improving the flame-retardant performance of the fire-retardant coating.

[0084] (2) Limiting oxygen index test and UL-94 flammability test of functionalized MXene waterborne fire-retardant coatings

[0085] Limiting oxygen index (LOI) tests were conducted on PP test panels (25*100*2 mm) coated with MXene-modified fire-retardant coating using a limiting oxygen index (LOI) tester. The oxygen pressure was 0.3 MPa and the nitrogen pressure was 0.6 MPa. By adjusting the oxygen and nitrogen concentration ratios during the test, and with an ignition time of 10 s, the minimum oxygen concentration required for the sample to ignite was determined as the LIO of that sample. Each group of samples underwent three tests, and the average value was taken as the LIO of that group of fire-retardant coatings. The experimental results are as follows: Figure 2 As shown. By Figure 2 It can be seen that in Examples 1 to 5 of this invention, the fire-retardant coatings (A1, A2, A3, A4, A5) prepared by adjusting the different proportions of MXene material with aqueous solution, ammonium citrate, polyurethane, and titanium dioxide have a limiting oxygen index between 25.4% and 33.5%, and the fire-retardant coatings all achieve a V-0 fire rating. Furthermore, in Examples 6 to 8 of this patent, the fire-retardant coatings prepared by using silane coupling agent-functionalized MXene material, calixarene-functionalized MXene material, or MOFs / MXene composite materials as nanostructured flame retardants have limiting oxygen indices of 33.9%, 34.5%, and 35.2%, respectively, and all achieve a V-0 fire rating.

[0086] The fire resistance performance of the functionalized MXene-type waterborne fire-retardant coatings prepared in Examples 1, 2, and 3 was tested using the UL-94 national standard test method. PP test panels coated with the fire-retardant coating were fixed using a bracket. A butane spray gun was used to continuously heat the center of one side. The duration of combustion and the presence or absence of molten droplets ignited cotton 30 cm below the surface, and the experimental results were recorded. As a control experiment, PP test panels without the fire-retardant coating were tested using the same method, and the results were recorded. The results are shown below. Figures 3 to 6 .

[0087] Experimental results show that the PP test panel coated with A1 paint extinguished its flame within 2 seconds after the first 10-second burning test, and extinguished its flame within 5 seconds after the second 10-second burning test without any molten droplets falling. Figure 3 According to the UL-94 fire rating standard, a flame that extinguishes within 30 seconds after two 10-second burning tests and has no burning material dripping off can be classified as V-0.

[0088] Similar to the results above, the PP test panels coated with A2 paint ( Figure 4 ) and PP test panels coated with A3 paint ( Figure 5 The fire resistance test results show that the fire resistance rating of this coating can reach V-0 level.

[0089] As a control, the PP test board without a fire-retardant coating began to burn fully within 5 seconds, and the flame increased in size after 15 seconds, with molten droplets igniting the cotton 30 cm below. This indicates that the PP test board material itself cannot withstand the burning of a high-temperature flame. Figure 6 ).

[0090] The above experimental results show that the fire-retardant coatings prepared from the MXene material and its derivatives provided in this patent as nanostructured flame retardants all have good fire-retardant properties.

Claims

1. A functionalized MXene-type water-based fire-retardant coating, characterized in that, It is prepared by mixing the following raw materials in a certain order of addition and stirring until homogeneous: 1 part of MXene nanostructured flame retardant; 1-10 parts of waterborne polyurethane; Ammonium citrate 0.5-5 parts; 2-12 parts of titanium dioxide; Water 0.2 to 1 part.

2. The functionalized MXene-type water-based fire-retardant coating as described in claim 1, characterized in that, The MXene nanostructure flame retardant is any one of MXene material, silane coupling agent-functionalized MXene material, calixarene-functionalized MXene material, or MOFs / MXene composite material.

3. A method for preparing a functionalized MXene-type waterborne fire-retardant coating, characterized in that: (1) Disperse MXene nanomaterials in the prescribed amount of water to obtain a first mixed liquid; (2) Add the prescribed amount of ammonium citrate to the first mixed liquid and stir until completely dissolved to obtain the second mixed liquid; (3) Add the amount of waterborne polyurethane in the formula to the second mixed liquid, stir evenly, then add the amount of titanium dioxide in the formula, and continue stirring until the components are completely mixed evenly to obtain functionalized MXene type waterborne fireproof coating.

4. The preparation method of the MXene-modified and reinforced waterborne fire-retardant coating as described in claim 1, characterized in that: The MXene nanostructure flame retardant is any one of MXene material, silane coupling agent-functionalized MXene material, calixarene-functionalized MXene material, or MOFs / MXene composite material.

5. The preparation method of the functionalized MXene-type waterborne fire-retardant coating as described in claim 1, characterized in that: The mass ratio of the MXene nanostructured flame retardant to water is 1:1 to 5:

1.

6. The preparation method of the functionalized MXene-type waterborne fire-retardant coating as described in claim 1, characterized in that: The mass ratio of the MXene nanostructured flame retardant to ammonium citrate is 2:1 to 1:

5.

7. The preparation method of the functionalized MXene-type waterborne fire-retardant coating as described in claim 1, characterized in that: The mass ratio of MXene nanostructured flame retardant to waterborne polyurethane is 1:1 to 1:

10.

8. The preparation method of the functionalized MXene-type waterborne fire-retardant coating as described in claim 1, characterized in that: The mass ratio of MXene nanostructured flame retardant to titanium dioxide is 1:2 to 1:

12.

9. The application of a functionalized MXene-type waterborne fire-retardant coating according to any one of claims 1 or 2, characterized in that, The functionalized MXene-type waterborne fire-retardant coating is applied to the surface of the substrate to be protected and cured at room temperature for 12-24 hours to obtain the functionalized MXene-type waterborne fire-retardant coating.

10. The application as described in claim 9, characterized in that, The protected substrate is metal or wood.

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