Flame-retardant hydrophobic tunnel coating and preparation method thereof

Abstract

The invention provides a flame-retardant hydrophobic tunnel coating and a preparation method thereof. The invention discloses a flame-retardant hydrophobic tunnel coating. A flame-retardant bottom layer is prepared from the following components in parts by weight: 30-50 parts of water-based resin emulsion, 15-30 parts of phosphorylated modified biomass filler, 5-10 parts of an inorganic flame-retardant synergist, 0.5-1 part of a dispersing agent and 10-20 parts of water; the self-cleaning brightening surface layer is prepared from the following components in parts by weight: 40-60 parts of transparent water-based resin emulsion, 5-15 parts of polysiloxane grafted modified pearl powder, 1-3 parts of a coalescing agent, 0.2-0.5 part of a defoaming agent and 10-20 parts of water; the phosphorylation modified biomass filler is prepared by carrying out esterification reaction on plant fiber powder through a phosphorus-containing modifier under an acidic catalysis condition. According to the invention, tunnel fire safety is met, and long-acting self-cleaning is realized.

Description

Technical Field

[0001] This invention relates to a flame-retardant coating and its preparation method, specifically to a flame-retardant hydrophobic tunnel coating and its preparation method, belonging to the field of functional coatings technology. Background Technology

[0002] The tunnel's tubular, semi-enclosed structure results in a damp and poorly ventilated interior environment. Furthermore, the constant exposure to vehicle exhaust and dust accumulation makes the walls highly susceptible to oil stains, significantly reducing light reflectivity and severely impacting driving safety. In the event of a fire, the tunnel's temperature rises extremely rapidly due to the chimney effect, placing extremely high demands on the fire resistance of the tunnel walls.

[0003] To balance the requirements of high flame retardancy and easy cleaning, existing technologies typically employ a double-layer composite coating solution. A thicker fireproof underlayer is first coated on the surface of the tunnel substrate to provide heat insulation and flame retardancy, and after drying, a thinner decorative top layer is applied to provide gloss enhancement, stain resistance, and water repellency.

[0004] While this layered functional design approach addresses the shortcomings of single-coat performance to some extent, existing topcoats typically achieve hydrophobic effects through the physical addition of low surface energy substances. This physical mixing system lacks the anchoring effect of chemical bonds, causing the hydrophobic agent to tend to migrate to the coating surface. In the high-humidity environment of tunnels and under repeated high-pressure water jet cleaning, the hydrophobic molecules on the surface are easily lost or worn away. Furthermore, ordinary pearlescent powder added for gloss enhancement has a hydrophilic surface and easily attracts oil, leading to the failure of the coating's self-cleaning function.

[0005] In existing double-layer coating processes, the base coat is typically required to be completely dry before the top coat is applied. However, fire-resistant base coats often have a rough surface and high polarity to achieve high filler content, while hydrophobic top coats aim for low surface energy and non-polarity. This significant difference in surface energy and polarity relies primarily on intermolecular forces for adhesion, resulting in weak adhesion. Under the long-term effects of traffic vibrations, temperature variations, and moisture erosion in tunnels, stress concentration can easily occur between the layers, leading to peeling or even large-area delamination of the top coat, severely impacting the coating's protective lifespan and aesthetics.

[0006] Furthermore, in response to environmental protection requirements, the use of agricultural waste such as rice husks and straw as biomass charring agents to replace traditional inorganic fillers has gradually become an industry trend. However, the surface of natural biomass contains a large amount of wax and silica, which has poor compatibility with the resin matrix. Simple physical addition leads to defects in the fire-retardant coating interface, and the char layer formed during combustion is loose and porous, unable to effectively block oxygen and heat, resulting in low flame-retardant efficiency. This makes it difficult to apply agricultural waste, a natural and environmentally friendly material, to tunnel fire-retardant coatings, and thus cannot effectively reduce the environmental impact. Summary of the Invention

[0007] Based on the above background, the purpose of this invention is to provide a flame-retardant hydrophobic tunnel coating and its preparation method, thereby solving the technical problems of low flame-retardant efficiency of biomass fillers, poor durability of hydrophobic coatings, and easy peeling of double-layer structures in existing tunnel coatings.

[0008] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0009] A flame-retardant and hydrophobic tunnel coating includes a flame-retardant underlayer and a self-cleaning and brightening toplayer coated on the surface of the flame-retardant underlayer.

[0010] The flame-retardant bottom layer is made of the following components in parts by weight: 30-50 parts of water-based resin emulsion, 15-30 parts of phosphorylated modified biomass filler, 5-10 parts of inorganic flame-retardant synergist, 0.5-1 parts of dispersant, and 10-20 parts of water.

[0011] The self-cleaning and brightening surface layer is made of the following components in parts by weight: 40-60 parts of transparent water-based resin emulsion, 5-15 parts of polysiloxane grafted modified pearl powder, 1-3 parts of film-forming aid, 0.2-0.5 parts of defoamer, and 10-20 parts of water.

[0012] The phosphorylated modified biomass filler is prepared by esterification of plant fiber powder with a phosphorus-containing modifier under acidic catalytic conditions, and its surface is grafted with phosphate ester groups; the polysiloxane grafted modified pearlescent powder is prepared by chemically bonding polydimethylsiloxane or its derivatives to the surface of flake pearlescent pigment after treatment with a coupling agent.

[0013] Preferably, the raw materials for preparing the phosphoric acid modified biomass filler include a phosphorus-containing modifier and agricultural waste powder with a particle size of 200-400 mesh. The phosphorus-containing modifier is selected from at least one of phytic acid, phosphoric acid, polyphosphoric acid, or diammonium hydrogen phosphate, and the agricultural waste powder is selected from at least one of rice husk powder, straw powder, corn cob powder, or wood powder.

[0014] Preferably, the raw materials for preparing the polysiloxane grafted modified pearlescent powder include mica-based pearlescent powder, a surface modifier, and a silane coupling agent, wherein the surface modifier is selected from one of hydroxyl silicone oil, hydrogen-containing silicone oil, or vinyl-terminated polydimethylsiloxane.

[0015] Preferably, the inorganic flame retardant synergist is selected from at least one of zinc borate, magnesium hydroxide, aluminum hydroxide, or expanded graphite; the aqueous resin emulsion is selected from one of aqueous acrylic emulsion, aqueous polyurethane emulsion, or aqueous epoxy emulsion; and the transparent aqueous resin emulsion is selected from one of aqueous acrylic emulsion, aqueous polyurethane emulsion, or aqueous epoxy emulsion.

[0016] The present invention also provides a method for preparing the above-mentioned flame-retardant and hydrophobic tunnel coating, the method comprising the following steps:

[0017] S1. Preparation of phosphoric acid modified biomass filler: Disperse plant fiber powder in a solvent, add phosphorus-containing modifier, react at 60-90℃ for 2-5 hours, filter, wash and dry to obtain phosphoric acid modified biomass filler;

[0018] S2. Preparation of polysiloxane grafted modified pearlescent powder: Disperse pearlescent pigment in an ethanol aqueous solution, adjust the pH value to 3-5, add silane coupling agent for hydrolysis treatment, add polydimethylsiloxane or its derivative dropwise, carry out grafting reaction at 70-100℃, and obtain polysiloxane grafted modified pearlescent powder after drying.

[0019] S3. Preparation of flame-retardant underlayer slurry: According to the weight parts described in claim 1, the aqueous resin emulsion, the phosphorylated modified biomass filler obtained in step S1, the inorganic flame retardant synergist, the dispersant and water are mixed and dispersed at high speed to a fineness of less than 50 μm to obtain the flame-retardant underlayer slurry.

[0020] S4. Preparation of self-cleaning gloss-enhancing surface layer slurry: According to the weight parts described in claim 1, the transparent waterborne resin emulsion, the polysiloxane grafted modified pearl powder obtained in step S2, the film-forming aid, the defoamer and water are mixed and stirred at low speed until uniform to obtain the self-cleaning gloss-enhancing surface layer slurry.

[0021] S5. Coating construction: Apply the flame-retardant underlayer slurry from step S3 to the surface of the tunnel substrate. After drying, a flame-retardant underlayer is formed. Apply the self-cleaning and brightening toplayer slurry from step S4 to the surface of the flame-retardant underlayer and allow it to dry and cure.

[0022] Preferably, in step S1, the mass ratio of the plant fiber powder to the phosphorus-containing modifier is 1:0.5-1.5, and the solvent is water or ethanol.

[0023] Preferably, in step S2, the mass ratio of the pearlescent pigment, silane coupling agent, and polydimethylsiloxane is 100:1-3:5-10.

[0024] Preferably, prior to step S1, the method further includes the following steps:

[0025] Soak the plant fiber powder in a 2-5% sodium hydroxide solution, stir at 40-60℃ for 1-2 hours, filter and wash until neutral, and dry for later use.

[0026] Preferably, in step S2, the grafting reaction is carried out using the following stepwise feeding method:

[0027] Add the silane coupling agent to the pearlescent pigment dispersion and react at 40-50℃ for 30-60 minutes;

[0028] Then the temperature is raised to 70-80℃, and polydimethylsiloxane or its derivatives are added dropwise, and the reaction is carried out for 1-2 hours.

[0029] Finally, heat-treat and cure at 105-120℃ for 1-2 hours.

[0030] Compared with the prior art, the present invention has the following advantages:

[0031] The present invention provides a flame-retardant and hydrophobic tunnel coating that combines a modified biomass flame-retardant underlayer with a modified pearlescent powder hydrophobic toplayer. The underlayer provides fire protection by forming a dense carbon layer through phosphorylated biomass, while the toplayer provides superhydrophobicity and long-lasting gloss by constructing a micro-nano rough structure through pearlescent powder grafted with polydimethylsiloxane. This not only meets the requirements of tunnel fire safety but also achieves long-term self-cleaning.

[0032] To address the issues of poor compatibility and loose char formation in biomass fillers, this invention employs an acid-catalyzed esterification reaction to chemically graft phosphorus-containing groups onto the surface of plant fibers. When this phosphorylated modified biomass filler is heated during combustion, the phosphate ester bonds on its surface preferentially decompose to produce phosphoric acid, directly catalyzing the dehydration of the biomass skeleton into char, rather than the traditional gas-phase flame retardant method. This results in a dense, continuous, and hard char layer formed after combustion, improving the limiting oxygen index of the bottom layer.

[0033] To address the issue of easy loss of physically added polydimethylsiloxane, this invention uses coupling agent bridging and stepwise grafting processes to directionally grow polydimethylsiloxane molecular brushes on the surface of flake pearlescent pigments. This modification not only endows the pearlescent powder with superhydrophobicity, but also constructs a rough structure of pearlescent powder skeleton plus polydimethylsiloxane segments on the coating surface. Even after multiple high-pressure water washes, the hydrophobic effect remains long-lasting and it is not easy to attract oil stains.

[0034] The present invention discloses a method for preparing a flame-retardant hydrophobic tunnel coating, which effectively removes the wax on the surface of plant fibers through alkaline activation pretreatment, exposes reactive sites, and improves the grafting rate; the step-by-step feeding and thermosetting process in the preparation of the surface layer ensures the orderly formation of hydrophobic micro-nano structures. Attached Figure Description

[0035] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0036] Figure 1Here is a SEM microstructure image of the surface of the flame-retardant hydrophobic tunnel coating prepared in Example 1;

[0037] Figure 2 This is a SEM microstructure image of the coating surface prepared in Comparative Example 1.

[0038] Figure 3 The image shows the SEM microstructure of the coating surface prepared in Comparative Example 2.

[0039] Figure 4 This is a SEM microstructure image of the coating surface prepared in Comparative Example 3. Detailed Implementation

[0040] The technical solution of the present invention will be further described in detail below through specific embodiments and in conjunction with the accompanying drawings. It should be understood that the implementation of the present invention is not limited to the following embodiments, and any modifications and / or alterations made to the present invention will fall within the protection scope of the present invention.

[0041] In this invention, unless otherwise specified, all parts and percentages are by weight, and the equipment and raw materials used are commercially available or commonly used in the art. Unless otherwise specified, the methods in the following embodiments are conventional methods in the art. Unless otherwise specified, the components or equipment in the following embodiments are general standard parts or components known to those skilled in the art, and their structures and principles can be learned by those skilled in the art through technical manuals or conventional experimental methods.

[0042] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings. In this detailed description, numerous specific details are set forth to facilitate explanation and provide a thorough understanding of the embodiments of the present invention. However, one or more embodiments may be practiced by those skilled in the art without these specific details.

[0043] Raw material description:

[0044] Waterborne resin emulsion: A waterborne acrylic emulsion with a solid content of 48% is selected.

[0045] Transparent waterborne resin emulsion: Waterborne polyurethane varnish with a solid content of 45% is selected.

[0046] Plant fiber powder: rice husk powder with a particle size of 300 mesh.

[0047] Pearlescent powder: Mica titanium pearlescent powder with a particle size of 10-60μm.

[0048] Phosphorus-containing modifier: 85% phosphoric acid solution.

[0049] Example 1

[0050] A flame-retardant and hydrophobic tunnel coating is prepared by the following method:

[0051] Preparation of phosphorylated modified biomass fillers:

[0052] Alkali activation: 100g of rice husk powder was soaked in 2L of 4% NaOH solution and stirred at 50℃ for 1.5 hours. The mixture was then filtered, washed with deionized water until neutral, and dried. This step removed the silica and wax layers from the surface of the rice husk, exposing the cellulose hydroxyl groups.

[0053] Esterification reaction: Disperse the activated rice husk powder in water, add 80g of phosphoric acid (mass ratio 1:0.8), and react at 85℃ for 4 hours.

[0054] Post-processing: The product is filtered, washed, and dried to obtain phosphorylated modified biomass filler with phosphate ester groups grafted onto its surface.

[0055] Preparation of polysiloxane-grafted modified pearlescent powder:

[0056] Coupling agent base layer: Disperse 100g of pearlescent powder in an ethanol aqueous solution (pH=4), add 2g of silane coupling agent, and react at 45℃ for 45 minutes to form a monolayer of coupling agent on the surface of pearlescent powder.

[0057] Grafting reaction: Heat to 75℃, add 8g of polydimethylsiloxane, and react for 1.5 hours.

[0058] Thermosetting: After filtration, the product is heat-treated in an oven at 110℃ for 1.5 hours to obtain polysiloxane-grafted modified pearlescent powder.

[0059] Preparation of flame-retardant underlayer slurry:

[0060] Take 40 parts of waterborne resin emulsion, 25 parts of phosphorylated modified biomass filler, 8 parts of magnesium hydroxide, 0.8 parts of dispersant and 15 parts of water, and disperse at 2000 rpm for 30 minutes until the fineness is <50 μm.

[0061] Preparation of self-cleaning and brightening surface coating slurry:

[0062] Take 50 parts of transparent water-based resin emulsion, 10 parts of polysiloxane grafted modified pearl powder, 2 parts of film-forming aid, 0.3 parts of defoamer and 15 parts of water, and stir at low speed until uniform.

[0063] Coating application:

[0064] Apply a base coat of slurry to the cement board substrate and allow it to cure semi-cured (not sticky to the touch but not fully hardened). Then apply a top coat of slurry. Next, bake at 45°C for 30 minutes, then cure completely at 90°C.

[0065] See Figure 1The surface of this flame-retardant and hydrophobic tunnel coating exhibits a dense and uniform wrinkled micro-nano structure. This rough structure with a high specific surface area is the key to achieving superhydrophobicity. Water droplets cannot wet the inside of the grooves, thus exhibiting an extremely high contact angle.

[0066] Example 2

[0067] A flame-retardant and hydrophobic tunnel coating is prepared using the same method as in Example 1, except that:

[0068] Preparation of flame-retardant underlayer slurry:

[0069] Prepare the mixture by mixing 30 parts of water-based resin emulsion, 15 parts of phosphorylated modified biomass filler, 5 parts of magnesium hydroxide, 0.5 parts of dispersant and 10 parts of water.

[0070] Preparation of self-cleaning and brightening surface coating slurry:

[0071] Prepare the mixture by mixing 40 parts of transparent waterborne resin emulsion, 5 parts of polysiloxane grafted modified pearl powder, 1 part of film-forming aid, 0.2 parts of defoamer and 10 parts of water.

[0072] Example 3

[0073] A flame-retardant and hydrophobic tunnel coating is prepared using the same method as in Example 1, except that:

[0074] Prepare the mixture by mixing 50 parts of water-based resin emulsion, 30 parts of phosphorylated modified biomass filler, 10 parts of magnesium hydroxide, 1 part of dispersant and 20 parts of water.

[0075] Preparation of self-cleaning gloss-enhancing surface layer slurry: Take 60 parts of transparent water-based resin emulsion, 15 parts of polysiloxane grafted modified pearl powder, 3 parts of film-forming aid, 0.5 parts of defoamer and 20 parts of water and mix them together.

[0076] Comparative Example 1

[0077] It uses commercially available ordinary water-based acrylic paint without adding any fillers.

[0078] See Figure 2 The coating surface is flat and smooth without any micro-texture. Although the surface is smooth, it lacks the roughness required for hydrophobicity. Water droplets will spread on the surface, the contact angle is low, and it is not flame retardant.

[0079] Comparative Example 2

[0080] A coating, prepared by the same method as in Example 1, except that:

[0081] The flame-retardant base layer uses untreated and unmodified raw rice husk powder, and an equal amount of phosphoric acid is directly and physically mixed into the resin.

[0082] See Figure 3 The coating has a loose surface structure, with obvious lamellar separation and large pores. This is because the unmodified rice husk powder has a waxy surface, which has extremely poor compatibility with the resin, resulting in weak interfacial bonding. This loose structure allows oxygen to easily penetrate, preventing the formation of a dense char layer during combustion and severely affecting the flame-retardant effect.

[0083] Comparative Example 3

[0084] A coating, prepared by the same method as in Example 1, except that:

[0085] The self-cleaning gloss-enhancing surface layer uses unmodified ordinary pearlescent powder, which is directly mixed with an equal amount of polydimethylsiloxane emulsion without grafting reaction or thermal curing.

[0086] See Figure 4 The coating surface exhibits obvious agglomeration, mainly manifested as large, lumpy particles, lacking... Figure 1 The pearlescent powder exhibits fine micro- and nano-folds. This is because, without the bridging of a coupling agent, polydimethylsiloxane underwent self-condensation and failed to disperse uniformly on the pearlescent powder surface. This structure not only exhibits poor hydrophobicity but also makes the aggregates prone to detachment during friction.

[0087] The coatings prepared in Examples 1-3 and Comparative Examples 1-3 were subjected to performance tests, and the results are shown in Table 1.

[0088] Table 1 Performance Test Results

[0089]

[0090] The limiting oxygen index of Example 1 was as high as 35.2%, far exceeding that of Comparative Example 2. Figure 1 and Figure 3 The comparison shows that chemical modification makes the filler more evenly dispersed and more tightly bonded to the matrix, and can quickly form a dense char layer during combustion, while physical mixing has a significantly reduced flame retardant efficiency due to interface defects.

[0091] Example 1 achieved an initial contact angle of superhydrophobicity, with almost no decrease after 5000 washes. In contrast, Comparative Example 3, although having a decent initial contact angle, rapidly decreased to a hydrophilic state after washing. This strongly demonstrates that chemical bonding and micro / nano structures play a decisive role in long-lasting hydrophobicity.

[0092] In Comparative Example 3, the aggregation of polydimethylsiloxane led to increased diffuse reflection and a significant decrease in gloss on the coating surface. In contrast, Example 1, through graft modification, maintained the directional arrangement of pearlescent powder, resulting in excellent gloss.

[0093] In summary, this invention has successfully prepared a tunnel coating that combines excellent flame retardancy, superhydrophobicity, and high weather resistance through unique component modification and structural design.

[0094] This article uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. It should be noted that those skilled in the art can make several improvements and modifications to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims

1. A flame-retardant and hydrophobic tunnel coating, comprising a flame-retardant underlayer and a self-cleaning and brightening toplayer coated on the surface of the flame-retardant underlayer, characterized in that: The flame-retardant bottom layer is made of the following components in parts by weight: 30-50 parts of water-based resin emulsion, 15-30 parts of phosphorylated modified biomass filler, 5-10 parts of inorganic flame-retardant synergist, 0.5-1 parts of dispersant, and 10-20 parts of water. The self-cleaning and brightening surface layer is made of the following components in parts by weight: 40-60 parts of transparent water-based resin emulsion, 5-15 parts of polysiloxane grafted modified pearl powder, 1-3 parts of film-forming aid, 0.2-0.5 parts of defoamer, and 10-20 parts of water. The phosphorylated modified biomass filler is prepared by esterification of plant fiber powder with a phosphorus-containing modifier under acidic catalytic conditions, and its surface is grafted with phosphate ester groups; the polysiloxane grafted modified pearlescent powder is prepared by chemically bonding polydimethylsiloxane or its derivatives to the surface of flake pearlescent pigment after treatment with a coupling agent.

2. The flame-retardant and hydrophobic tunnel coating according to claim 1, characterized in that: The raw materials for preparing the phosphoric acid modified biomass filler include a phosphorus-containing modifier and agricultural waste powder with a particle size of 200-400 mesh. The phosphorus-containing modifier is selected from at least one of phytic acid, phosphoric acid, polyphosphoric acid, or diammonium hydrogen phosphate, and the agricultural waste powder is selected from at least one of rice husk powder, straw powder, corn cob powder, or wood powder.

3. The flame-retardant and hydrophobic tunnel coating according to claim 1, characterized in that: The raw materials for preparing the polysiloxane grafted modified pearlescent powder include mica-based pearlescent powder, surface modifier, and silane coupling agent. The surface modifier is selected from one of hydroxyl silicone oil, hydrogen-containing silicone oil, or vinyl-terminated polydimethylsiloxane.

4. The flame-retardant and hydrophobic tunnel coating according to claim 1, characterized in that: The inorganic flame retardant synergist is selected from at least one of zinc borate, magnesium hydroxide, aluminum hydroxide, or expanded graphite; the aqueous resin emulsion is selected from one of aqueous acrylic emulsion, aqueous polyurethane emulsion, or aqueous epoxy emulsion; and the transparent aqueous resin emulsion is selected from one of aqueous acrylic emulsion, aqueous polyurethane emulsion, or aqueous epoxy emulsion.

5. A method for preparing a flame-retardant and hydrophobic tunnel coating as described in any one of claims 1-4, characterized in that: The method includes the following steps: S1. Preparation of phosphoric acid modified biomass filler: Disperse plant fiber powder in a solvent, add phosphorus-containing modifier, react at 60-90℃ for 2-5 hours, filter, wash and dry to obtain phosphoric acid modified biomass filler; S2. Preparation of polysiloxane grafted modified pearlescent powder: Disperse pearlescent pigment in an ethanol aqueous solution, adjust the pH value to 3-5, add silane coupling agent for hydrolysis treatment, add polydimethylsiloxane or its derivative dropwise, carry out grafting reaction at 70-100℃, and obtain polysiloxane grafted modified pearlescent powder after drying. S3. Preparation of flame-retardant underlayer slurry: According to the weight parts described in claim 1, the aqueous resin emulsion, the phosphorylated modified biomass filler obtained in step S1, the inorganic flame retardant synergist, the dispersant and water are mixed and dispersed at high speed to a fineness of less than 50 μm to obtain the flame-retardant underlayer slurry. S4. Preparation of self-cleaning gloss-enhancing surface layer slurry: According to the weight parts described in claim 1, the transparent waterborne resin emulsion, the polysiloxane grafted modified pearl powder obtained in step S2, the film-forming aid, the defoamer and water are mixed and stirred at low speed until uniform to obtain the self-cleaning gloss-enhancing surface layer slurry. S5. Coating construction: Apply the flame-retardant underlayer slurry from step S3 to the surface of the tunnel substrate. After drying, a flame-retardant underlayer is formed. Apply the self-cleaning and brightening topcoat slurry from step S4 to the surface of the flame-retardant underlayer and allow it to dry and cure.

6. The flame-retardant and hydrophobic tunnel coating according to claim 5, characterized in that: In step S1, the mass ratio of the plant fiber powder to the phosphorus-containing modifier is 1:0.5-1.5, and the solvent is water or ethanol.

7. The flame-retardant and hydrophobic tunnel coating according to claim 5, characterized in that: In step S2, the mass ratio of the pearlescent pigment, silane coupling agent, and polydimethylsiloxane is 100:1-3:5-10.

8. The flame-retardant and hydrophobic tunnel coating according to claim 5, characterized in that: Before step S1, the method further includes the following steps: Soak the plant fiber powder in a 2-5% sodium hydroxide solution, stir at 40-60℃ for 1-2 hours, filter and wash until neutral, and dry for later use.

9. The flame-retardant and hydrophobic tunnel coating according to claim 5, characterized in that: In step S2, the grafting reaction is carried out using the following stepwise feeding method: Add the silane coupling agent to the pearlescent pigment dispersion and react at 40-50℃ for 30-60 minutes; Then the temperature is raised to 70-80℃, and polydimethylsiloxane or its derivatives are added dropwise, and the reaction is carried out for 1-2 hours. Finally, heat-treat and cure at 105-120℃ for 1-2 hours.

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