Phosphogypsum-based heat-insulation fireproof coating and preparation method thereof

Abstract

The invention relates to the technical field of coating compositions, and particularly discloses an ardealite-based heat-insulation fireproof coating and a preparation method thereof.The ardealite-based heat-insulation fireproof coating is prepared from titanium dioxide modified ardealite, hollow glass beads, styrene-acrylic emulsion, modified composite flame-retardant fibers, calcium sulfate whiskers, microencapsulated red phosphorus, redispersible latex powder, deionized water, a dispersing agent and a defoaming agent; the preparation method comprises the following steps: firstly, preparing titanium dioxide modified phosphogypsum, secondly, modifying the composite flame-retardant fiber, and finally, mixing and stirring all the components. Through the synergistic effect of the titanium dioxide modified phosphogypsum and the composite flame-retardant fiber and in combination with an ultrasonic-assisted preparation process, a double heat-insulating barrier and a synergistic flame-retardant mechanism is formed; and calcium sulfate whiskers are matched for toughening, so that the fireproof heat-insulating performance and the structural stability of the coating are improved, and the problem that the coating is easy to crack is solved.

Description

Technical Field

[0001] The present invention relates to the technical field of coating compositions, and in particular to a phosphogypsum-based heat-insulating and fire-retardant coating and a preparation method thereof. Background Art

[0002] Due to its environmental friendliness, thermal insulation performance and fireproof function, phosphogypsum-based thermal insulation and fireproof coatings have extremely broad application prospects in the construction field in the fire prevention of steel structures. Although steel structures have advantages such as high strength in buildings, they have poor fire resistance. When a fire occurs, they are very likely to lose their bearing capacity due to high temperature, which in turn causes the collapse of the building structure. Phosphogypsum-based thermal insulation and fireproof coatings can form an effective protective layer on the surface of the steel structure. When a fire occurs, this protective layer can effectively prevent heat transfer and slow down the heating rate of the steel structure. Therefore, the research and application of phosphogypsum-based thermal insulation and fireproof coatings are of great significance.

[0003] Based on the above application requirements, in the existing technology, the patent number CN202510358012.X proposes a gypsum fire-retardant coating and a preparation method thereof. The coating is composed of powder materials, inorganic substances, additives, flame retardants, thermal insulation materials and polymer emulsions. By adding acrylic resin as the main component of the polymer emulsion, the weather resistance, water resistance and adhesion of the coating are improved. At the same time, the good water solubility of natural gypsum ore is utilized to accelerate material mixing and improve production efficiency.

[0004] However, although this technology has improved the stability of the coating, it still has shortcomings in its fireproofing and heat-insulating properties. Specifically, the flame retardants of the above-mentioned gypsum fire-retardant coating only rely on ammonium chloride and ammonium phosphate in terms of fireproofing properties, and lack a variety of flame-retardant synergistic mechanisms. When faced with high-temperature flames, it is difficult to quickly form an effective expansion insulation layer, and it is unable to block heat conduction and flame spread for a long time. At the same time, the above-mentioned coating has not chemically modified the raw materials such as gypsum, and the interfacial bonding force between the components is weak, resulting in the coating being prone to cracking, peeling and other problems during actual use, further weakening its fireproofing and heat-insulating properties. Summary of the Invention

[0005] In view of the technical defects existing in the background technology, the present invention proposes a phosphogypsum-based thermal insulation and fire retardant coating and a preparation method thereof, which solves the above technical problems and meets practical needs. The specific technical solution is as follows: A phosphogypsum-based heat-insulating fire-retardant coating comprises the following components, measured in parts by weight: 80-100 parts of titanium dioxide-modified phosphogypsum, 10-20 parts of hollow glass microspheres, 50-60 parts of styrene-acrylic emulsion, 20-25 parts of modified composite flame-retardant fibers, 1-5 parts of calcium sulfate whiskers, 5-8 parts of microencapsulated red phosphorus, 10-15 parts of redispersible latex powder, 10-20 parts of deionized water, 1-5 parts of a dispersant, and 1-5 parts of a defoaming agent.

[0006] As a further technical solution of the present invention, the titanium dioxide modified phosphogypsum is prepared by ultrasonically loading titanium dioxide on the surface of phosphogypsum particles and then calcining them. The particle size of the phosphogypsum particles is 200-300 μm, the loading amount of titanium dioxide on the surface of the phosphogypsum particles is 1-5%, and the titanium dioxide after calcination is rutile titanium dioxide.

[0007] As a further technical solution of the present invention, the modified composite flame-retardant fiber is obtained by immersing the carbon source fiber in a melamine-ammonium polyphosphate mixed solution, the carbon source fiber is any one of PVA fiber, polyester fiber, polyamide fiber, and polypropylene fiber, and the length of the carbon source fiber is 3-6 mm and the diameter is 15-25 μm.

[0008] As a further technical solution of the present invention, the dispersant is selected from any one of sodium lauryl sulfate, polycarboxylate hyperdispersants, and dodecyltrimethylammonium bromide, and the defoamer is selected from any one of polydimethylsiloxane and polyether-modified silane defoamers.

[0009] A method for preparing a phosphogypsum-based thermal insulation and fire retardant coating comprises the following steps: S1, preparing titanium dioxide modified phosphogypsum; The phosphogypsum particles were added to 5 times the volume of anhydrous ethanol, ultrasonically dispersed for 10 minutes, and the activated silane coupling agent solution was added. The mixture was heated and stirred at 70°C for 30 minutes, and ultrasonic-assisted mixing was performed with an ultrasonic power of 300W. Then, a tetrabutyl titanate-ethanol solution was slowly added dropwise at a rate of 1 mL / min. The ultrasonic power was maintained. After the tetrabutyl titanate-ethanol solution was added dropwise, deionized water was slowly added dropwise. The mixture was ultrasonically heated at 70°C for 1 hour. The mixture was filtered and washed with 5°C ice water and anhydrous ethanol in sequence. The mixture was vacuum-dried at 60°C for 12 hours. After grinding and sieving, the mixture was calcined in an air atmosphere at 700°C for 2-3 hours at a heating rate of 5°C / min to obtain titanium dioxide-modified phosphogypsum. S2. preparing modified composite flame retardant fiber; Deionized water was heated to 40-50°C, and ammonium polyphosphate and melamine were slowly added in sequence under stirring. After the solid was dissolved until the solution was transparent, the mixture was dispersed at a high speed of 2000 rpm for 10 minutes. A wetting agent was then added, and the mixture was stirred and mixed at a low speed of 500 rpm to obtain a melamine-ammonium polyphosphate mixed solution. The carbon source fiber and the melamine-ammonium polyphosphate mixed solution were immersed for a period of time at a solid-liquid ratio of 1:10, and then drained and dried to obtain a modified composite flame-retardant fiber. S3, preparing heat-insulating fire-retardant coating; 100 parts of titanium dioxide modified phosphogypsum, 10 parts of hollow glass microspheres, 60 parts of styrene acrylic emulsion, and 20 parts of modified composite flame retardant fiber were added into a stirring kettle and stirred at 300 r / min for 10 minutes. Then, 5 parts of calcium sulfate whiskers, 8 parts of microencapsulated red phosphorus, 15 parts of redispersible latex powder, 1 part of dispersant, and 1 part of defoaming agent were added and stirred at 800 r / min for 15 minutes. Finally, 10 parts of deionized water were added and stirred at 300 r / min for 5 minutes to obtain a thermal insulation and fire retardant coating.

[0010] As a further technical solution of the present invention, in step S1, a silane coupling agent is dissolved in 15 times the mass of a 98% ethanol solution, a small amount of acetic acid is added to adjust the pH to 4-5, and the solution is stirred at room temperature for 15 minutes to obtain an activated silane coupling agent solution, wherein the silane coupling agent is selected from any one of γ-methacryloxypropyltrimethoxysilane and vinyltriethoxysilane, and the amount of the silane coupling agent is 1-10% of the mass of the phosphogypsum particles.

[0011] As a further technical solution of the present invention, in step S1, tetrabutyl titanate is dissolved in 5 times the volume of anhydrous ethanol to obtain a tetrabutyl titanate-ethanol solution, wherein the amount of the tetrabutyl titanate is 5-25% of the mass of the phosphogypsum particles, and then the solution is slowly dripped into the reaction system of step S1, while maintaining ultrasound, and then deionized water is dripped, and the dripping speed of the deionized water is controlled to be 1-2 mL / min, and the molar ratio of the dripped deionized water to the tetrabutyl titanate in the tetrabutyl titanate-ethanol solution is (15-20):1.

[0012] As a further technical solution of the present invention, in step S2, the mass percentage range of each component in the melamine-ammonium polyphosphate mixed solution is: 10-15wt% ammonium polyphosphate, 3-5wt% melamine, 79.7-86.9wt% deionized water, and 0.1-0.3wt% wetting agent, the ammonium polyphosphate is a water-soluble ammonium polyphosphate with a polymerization degree >1000, and the wetting agent is an alkylphenol polyoxyethylene ether.

[0013] As a further technical solution of the present invention, in step S2, the carbon source fiber and the melamine-ammonium polyphosphate mixed solution are added to a sealed container in a ratio of 1:10 and shaken at a constant temperature, immersed in shaking at 25°C for 30-50 minutes, and manually stirred every 10 minutes.

[0014] As a further technical solution of the present invention, in step S2, the impregnated carbon source fiber is drained with a sieve to remove excess liquid, the carbon source fiber is lightly pressed until there are no continuous droplets, and then dried with hot air at 40°C for 1 hour, and then vacuum dried at 60°C and -0.08MPa for 2 hours to obtain a modified composite flame-retardant fiber.

[0015] The beneficial effects of the present invention are: The synergistic effect of titanium dioxide-modified phosphogypsum and composite flame-retardant fibers significantly improves the fireproof and heat-insulating properties and structural stability of the coating. The ultrasonic-assisted preparation process enables titanium dioxide to evenly coat the phosphogypsum particles, enhancing the high-temperature resistance of the phosphogypsum and forming a double thermal insulation barrier with the hollow glass microspheres. The modified flame-retardant fiber rapidly forms a dense carbonized layer at high temperatures through the synergistic flame retardant mechanism of the melamine-ammonium polyphosphate expansion system and microencapsulated red phosphorus, effectively isolating flames and heat. The silane coupling agent on the surface of the titanium dioxide-modified phosphogypsum strengthens its own interfacial bonding strength, and combined with the toughening effect of calcium sulfate whiskers, solves the problem of easy cracking of the coating. DETAILED DESCRIPTION

[0016] The following describes the implementation of the present invention in conjunction with relevant embodiments. The implementation of the present invention is not limited to the following embodiments, and the present invention relates to relevant necessary components in this technical field and should be regarded as a well-known technology in this technical field, which can be known and mastered by technical personnel in this technical field.

[0017] A phosphogypsum-based heat-insulating fire-retardant coating comprises the following components, measured in parts by weight: 80-100 parts of titanium dioxide-modified phosphogypsum, 10-20 parts of hollow glass microspheres, 50-60 parts of styrene-acrylic emulsion, 20-25 parts of modified composite flame-retardant fibers, 1-5 parts of calcium sulfate whiskers, 5-8 parts of microencapsulated red phosphorus, 10-15 parts of redispersible latex powder, 10-20 parts of deionized water, 1-5 parts of a dispersant, and 1-5 parts of a defoaming agent.

[0018] In terms of component formula, the present invention has the following components: the rutile titanium dioxide in the titanium dioxide-modified phosphogypsum can effectively reflect heat, and can form a good thermal insulation barrier when combined with hollow glass microspheres. The synergistic effect of the two can effectively improve the thermal insulation performance of the coating. After the carbon source fiber is impregnated with a melamine-ammonium polyphosphate mixed solution, it can work together with microencapsulated red phosphorus to exert a synergistic flame retardant effect. When a fire occurs, it can flame retard through multiple mechanisms such as expansion, heat absorption, and oxygen isolation, thereby enhancing the fireproof ability of the coating. The calcium sulfate whiskers and the modified composite flame-retardant fibers work synergistically to effectively improve the internal structure of the coating, reduce coating cracking, and improve the overall stability and durability of the coating. The styrene-acrylic emulsion serves as a base material to provide bonding force, and the redispersible latex powder can further optimize the film-forming property and flexibility of the coating. The dispersant and defoamer ensure that the components are evenly dispersed to avoid bubbles affecting the performance. Deionized water adjusts the viscosity of the system. The components cooperate with each other, so that the coating has excellent thermal insulation, fire resistance, crack resistance and construction performance, forming a thermal insulation and fireproof coating with balanced performance.

[0019] It should be noted that styrene acrylic emulsion is mainly composed of styrene, acrylates, initiators (potassium persulfate), emulsifiers (sodium lauryl sulfate) and other components. It is a polymer emulsion with good film-forming and adhesion properties. It serves as a base material in phosphogypsum-based thermal insulation and fire-retardant coatings to bond the various components and form a continuous coating.

[0020] It should be noted that microencapsulated red phosphorus is a flame retardant formed by coating red phosphorus particles with microcapsules (e.g., polymer films, inorganic coatings, etc.). In this invention, it serves as a flame-retardant component in the coating. Red phosphorus itself is a highly effective flame retardant. Upon combustion, it releases phosphates, forming a glassy insulating layer on the coating surface. This layer achieves flame retardancy by absorbing heat, diluting oxygen, and suppressing the release of combustible gases. The microencapsulation process effectively improves red phosphorus's hygroscopicity, reduces its toxicity and dust explosion risk, and enhances its thermal stability and compatibility with other components. In the coating, the microencapsulated red phosphorus and modified composite flame-retardant fibers form a synergistic flame-retardant system. At high temperatures, the microcapsules rupture to release the red phosphorus, exerting its flame retardant effect. The modified composite flame-retardant fibers then expand and carbonize to form an insulating carbon layer. The combination creates a multi-layered fire barrier on the coating surface: a barrier that absorbs heat and suppresses flames, enhancing the coating's fire resistance and safety. Furthermore, the microencapsulation process ensures a more uniform dispersion within the coating system, resulting in more stable performance over long-term use.

[0021] As one of the preferred embodiments of the present invention, the titanium dioxide modified phosphogypsum is prepared by ultrasonically loading titanium dioxide on the surface of phosphogypsum particles and then calcining them. The particle size of the phosphogypsum particles is 200-300 μm, the loading amount of titanium dioxide on the surface of the phosphogypsum particles is 1-5%, and the titanium dioxide after calcination is rutile titanium dioxide.

[0022] Specifically, the loading amount of titanium dioxide on the surface of phosphogypsum particles is preferably 5%. It should be noted that the loading amount = (mass of loaded TiO2 / mass of phosphogypsum particles) × 100%, that is, 5% loading amount: 100g of phosphogypsum needs to load 5g of TiO2.

[0023] The rutile titanium dioxide ultrasonically loaded on the surface of phosphogypsum particles can effectively block heat conduction by utilizing its high refractive index and strong reflection properties for infrared light. Phosphogypsum and hollow glass microspheres work together to construct a porous thermal insulation network, enhancing heat reflection and thermal resistance effects. When combined with base materials such as styrene acrylic emulsion, it forms a continuous thermal insulation barrier without affecting the synergistic effect of components such as modified composite flame retardant fibers, thereby optimizing the overall thermal insulation and fireproof performance of the coating.

[0024] It should be noted that after the surface of the phosphogypsum particles is ultrasonically loaded with titanium dioxide and calcined, the phosphogypsum particles are converted into anhydrous calcium sulfate particles, and the loaded titanium dioxide is converted into rutile titanium dioxide. After the phosphogypsum particles are converted into anhydrous calcium sulfate particles, when the fire retardant coating is applied to the surface of the substrate, the anhydrous calcium sulfate particles cooperate with the calcium sulfate whiskers and react with the deionized water in the coating to undergo hydration, thereby increasing the hardness of the coating while shortening the drying time of the coating.

[0025] As one of the preferred embodiments of the present invention, the modified composite flame-retardant fiber is obtained by immersing the carbon source fiber in a melamine-ammonium polyphosphate mixed solution, the carbon source fiber is any one of PVA fiber, polyester fiber, polyamide fiber, and polypropylene fiber, and the length of the carbon source fiber is 3-6 mm and the diameter is 15-25 μm.

[0026] Specifically, the carbon source fiber is preferably a PVA fiber with a length of 3 mm and a diameter of 25 μm.

[0027] After the carbon source fibers are impregnated with a melamine-ammonium polyphosphate solution, an intumescent flame retardant system is formed. At high temperatures, the melamine and ammonium polyphosphate decompose to produce phosphoric acid, which carbonizes with the PVA fibers to form an insulating char layer. This layer absorbs heat and blocks oxygen, achieving flame retardancy. In the coating, the PVA fibers serve as a framework to support the char layer structure. They also synergize with calcium sulfate whiskers to enhance the coating's toughness and reduce cracking. Furthermore, they work in conjunction with microencapsulated red phosphorus to create a dual fire protection mechanism: a "char layer barrier and flame retardant release." This creates a dense fire barrier during combustion, combining flame retardancy with mechanical stability.

[0028] As one of the preferred embodiments of the present invention, the dispersant is selected from any one of sodium lauryl sulfate, polycarboxylate hyperdispersants, and dodecyltrimethylammonium bromide, and the defoamer is selected from any one of polydimethylsiloxane and polyether-modified silane defoamers.

[0029] Specifically, the dispersant is preferably sodium lauryl sulfate, and the defoaming agent is preferably polydimethylsiloxane.

[0030] The use of dispersants such as sodium lauryl sulfate can reduce the surface tension of each component in the coating system, so that solid particles such as titanium dioxide modified phosphogypsum and hollow glass microspheres are evenly dispersed in the liquid phase, avoiding agglomeration and ensuring the uniformity of coating performance; defoaming agents such as polydimethylsiloxane can destroy the bubble film produced during the stirring process, eliminate bubbles introduced during the polymerization or stirring of styrene acrylic emulsion, and prevent the coating from having problems such as porosity and strength loss due to the presence of bubbles.

[0031] A method for preparing a phosphogypsum-based thermal insulation and fire retardant coating comprises the following steps: S1, preparing titanium dioxide modified phosphogypsum; The phosphogypsum particles were added to 5 times the volume of anhydrous ethanol, ultrasonically dispersed for 10 minutes, and the activated silane coupling agent solution was added. The mixture was heated and stirred at 70°C for 30 minutes, and ultrasonic-assisted mixing was performed with an ultrasonic power of 300W. Then, a tetrabutyl titanate-ethanol solution was slowly added dropwise at a rate of 1 mL / min. The ultrasonic power was maintained. After the tetrabutyl titanate-ethanol solution was added dropwise, deionized water was slowly added dropwise. The mixture was ultrasonically heated at 70°C for 1 hour. The mixture was filtered and washed with 5°C ice water and anhydrous ethanol in sequence. The mixture was vacuum-dried at 60°C for 12 hours. After grinding and sieving, the mixture was calcined in an air atmosphere at 700°C for 2-3 hours at a heating rate of 5°C / min to obtain titanium dioxide-modified phosphogypsum. S2. preparing modified composite flame retardant fiber; Deionized water was heated to 40-50°C, and ammonium polyphosphate and melamine were slowly added in sequence under stirring. After the solid was dissolved until the solution was transparent, the mixture was dispersed at a high speed of 2000 rpm for 10 minutes. A wetting agent was then added, and the mixture was stirred and mixed at a low speed of 500 rpm to obtain a melamine-ammonium polyphosphate mixed solution. The carbon source fiber and the melamine-ammonium polyphosphate mixed solution were immersed for a period of time at a solid-liquid ratio of 1:10, and then drained and dried to obtain a modified composite flame-retardant fiber. S3, preparing heat-insulating fire-retardant coating; 100 parts of titanium dioxide modified phosphogypsum, 10 parts of hollow glass microspheres, 60 parts of styrene acrylic emulsion, and 20 parts of modified composite flame retardant fiber were added into a stirring kettle and stirred at 300 r / min for 10 minutes. Then, 5 parts of calcium sulfate whiskers, 8 parts of microencapsulated red phosphorus, 15 parts of redispersible latex powder, 1 part of dispersant, and 1 part of defoaming agent were added and stirred at 800 r / min for 15 minutes. Finally, 10 parts of deionized water were added and stirred at 300 r / min for 5 minutes to obtain a thermal insulation and fire retardant coating.

[0032] In the preparation method of the present invention, in step S1, titanium dioxide is uniformly loaded on the surface of phosphogypsum through ultrasonic dispersion, silane coupling agent activation and tetrabutyl titanate hydrolysis, and the organic end of the silane coupling agent reacts with the styrene acrylic emulsion to enhance its compatibility and bonding with the coating system; in step S2, the carbon source fiber is impregnated with a melamine-ammonium polyphosphate solution and dried to form a high-efficiency flame retardant system, while maintaining the modified composite flame retardant fiber in fiber form, ensuring its role in enhancing mechanical properties and reducing cracking in the coating; step S3 adopts a step-by-step stirring process, first premixing the basic components at a low speed, then dispersing and adding the functional components at a high speed, and finally adjusting the viscosity to ensure that the materials are evenly dispersed, avoid agglomeration and bubbles, and give full play to the synergistic effect of the components, and finally prepare a coating with good thermal insulation and fireproofing stability and excellent mechanical properties.

[0033] As one of the preferred embodiments of the present invention, in step S1, a silane coupling agent is dissolved in 15 times the mass of a 98% ethanol solution, a small amount of acetic acid is added to adjust the pH to 4-5, and the solution is stirred at room temperature for 15 minutes to obtain an activated silane coupling agent solution, wherein the silane coupling agent is selected from any one of γ-methacryloxypropyltrimethoxysilane and vinyltriethoxysilane, and the amount of the silane coupling agent is 1-10% of the mass of the phosphogypsum particles.

[0034] Specifically, in step S1, the silane coupling agent is preferably γ-methacryloxypropyltrimethoxysilane, and the amount of the silane coupling agent is 5% of the mass of the phosphogypsum particles. When preparing the activated silane coupling agent solution, first weigh the corresponding amount of silane coupling agent according to 6% of the mass of the phosphogypsum particles, dissolve it in 15 times the mass of 90% ethanol solution, then add a small amount of acetic acid to adjust the pH value of the solution to 4-5, and continue stirring at room temperature for 15 minutes to obtain the activated silane coupling agent solution.

[0035] As one of the preferred embodiments of the present invention, in step S1, tetrabutyl titanate is dissolved in 5 times the volume of anhydrous ethanol to obtain a tetrabutyl titanate-ethanol solution, wherein the amount of the tetrabutyl titanate is 5-25% of the mass of the phosphogypsum particles, and then the solution is slowly dripped into the reaction system of step S1, while maintaining ultrasound, and then deionized water is dripped, wherein the dripping speed of the deionized water is controlled to be 1-2 mL / min, and the molar ratio of the dripped deionized water to the tetrabutyl titanate in the tetrabutyl titanate-ethanol solution is (15-20):1.

[0036] Specifically, the molar ratio of the deionized water added dropwise to the tetrabutyl titanate in the tetrabutyl titanate-ethanol solution is 15:1, and the amount of tetrabutyl titanate used is preferably 10% of the mass of the phosphogypsum particles.

[0037] The loading process of titanium dioxide on the surface of phosphogypsum particles is based on the bridging effect and step-by-step hydrolysis mechanism of the silane coupling agent. During the loading process, the activated silane coupling agent first condenses with the hydroxyl groups on the surface of the phosphogypsum through the partially hydrolyzed silanol groups, achieving surface modification of the phosphogypsum. The subsequent addition of deionized water not only hydrolyzes tetrabutyl titanate to produce titanium dioxide nanoparticles, but also changes the alcohol-water ratio of the system, promoting the hydrolysis of the remaining alkoxy groups of the silane coupling agent. The newly generated silanol groups combine with the hydroxyl groups on the surface of titanium dioxide, thereby loading titanium dioxide on the surface of the phosphogypsum. This ensures that the silane coupling agent can both effectively connect to the phosphogypsum and form a stable chemical bond with titanium dioxide, ultimately forming a "phosphogypsum-silane coupling agent-titanium dioxide" composite structure. During the subsequent coating film formation process, the vinyl groups on the organic end of the silane coupling agent can undergo free radical-induced cross-linking reactions with the vinyl groups in the styrene-acrylic emulsion, further strengthening the interfacial bonding between the titanium dioxide-modified phosphogypsum and the polymer matrix, thereby improving the structural stability and thermal insulation and fireproofing properties of the coating.

[0038] As one of the preferred embodiments of the present invention, in step S2, the mass percentage range of each component in the melamine-ammonium polyphosphate mixed solution is: 10-15wt% ammonium polyphosphate, 3-5wt% melamine, 79.7-86.9wt% deionized water, and 0.1-0.3wt% wetting agent, the ammonium polyphosphate is a water-soluble ammonium polyphosphate with a polymerization degree >1000, and the wetting agent is an alkylphenol polyoxyethylene ether.

[0039] Specifically, the mass percentages of the components in the melamine-ammonium polyphosphate mixed solution are: 15 wt % ammonium polyphosphate, 5 wt % melamine, 79.9 wt % deionized water, and 0.1 wt % wetting agent.

[0040] As one of the preferred embodiments of the present invention, in step S2, the carbon source fiber and the melamine-ammonium polyphosphate mixed solution are added to a sealed container in a ratio of 1:10 and shaken at a constant temperature at 25°C for 30-50 minutes, and manually stirred every 10 minutes.

[0041] In step S2, the carbon source fiber and the melamine-ammonium polyphosphate mixed solution are immersed in a constant temperature oscillation of 1:10 at 25°C for 30-50 minutes and stirred regularly, so that the melamine-ammonium polyphosphate is uniformly adsorbed on the fiber surface and pores to form an "acid source (ammonium polyphosphate)-carbon source (fiber)-gas source (melamine)" intumescent flame retardant system. Ammonium polyphosphate decomposes at high temperature to generate phosphoric acid substances, which promotes the carbonization of the carbon source fiber to form a carbon layer. Melamine decomposes to produce non-combustible gases such as ammonia, which causes the carbon layer to expand, thereby constructing a heat-insulating and oxygen-isolating barrier. At the same time, after the fiber is impregnated with ammonium polyphosphate, the surface polar groups form hydrogen bonds or ionic bonds with the ammonium polyphosphate, thereby enhancing the binding force of the flame-retardant components.

[0042] As one of the preferred embodiments of the present invention, in step S2, the impregnated carbon source fiber is drained with a screen to remove excess liquid, the carbon source fiber is lightly pressed until there are no continuous droplets, and then dried with hot air at 40°C for 1 hour, and then vacuum dried at 60°C and -0.08MPa for 2 hours to obtain a modified composite flame-retardant fiber.

[0043] During drying, the treatment adopts a combination of step-by-step temperature control and vacuum environment: 40℃ hot air drying for 1 hour can gently remove free water on the fiber surface to avoid high temperature-induced decomposition of melamine-ammonium polyphosphate or fiber deformation; then 60℃, -0.08MPa vacuum drying for 2 hours, the negative pressure lowers the boiling point of the solvent, completely removes residual water and a small amount of ethanol in the fiber pores, and at the same time promotes further cross-linking and curing of ammonium polyphosphate and the polar groups on the fiber surface, thereby ensuring the integrity of the ammonium polyphosphate coating layer.

[0044] Example 1

[0045] Preparation method of phosphogypsum-based thermal insulation and fire retardant coating S1. Preparation of titanium dioxide modified phosphogypsum Add 200-300 μm phosphogypsum particles into 5 volumes of anhydrous ethanol and disperse them ultrasonically for 10 minutes. Weigh 5% of the mass of phosphogypsum particles to form γ-methacryloxypropyltrimethoxysilane (silane coupling agent) and dissolve it in 15 times the mass of 90% ethanol solution. Add a small amount of acetic acid to adjust the pH to 4-5 and stir at room temperature for 15 minutes to obtain an activated silane coupling agent solution. Add the activated silane coupling agent solution into the phosphogypsum dispersion system, heat and stir at 70°C for 30 minutes with 300W ultrasonic assistance. Weigh 10% of the mass of phosphogypsum particles to form tetrakis(titanate) Butyl titanate was dissolved in 5 times the volume of anhydrous ethanol to obtain tetrabutyl titanate-ethanol solution, which was slowly added to the reaction system at a drop rate of 1 mL / min while maintaining ultrasound; the amount of deionized water was calculated based on 15 times the molar amount of tetrabutyl titanate, and was added at a drop rate of 1 mL / min, and ultrasonic heating was performed at 70°C for 1 hour; after the reaction, it was filtered, washed with 5°C ice water and anhydrous ethanol in sequence, and vacuum dried at 60°C for 12 hours. After grinding and sieving, the temperature was increased to 700°C at 5°C / min and calcined in air atmosphere for 2-3 hours to obtain anhydrous calcium sulfate particles loaded with 5% rutile titanium dioxide (titanium dioxide modified phosphogypsum).

[0046] S2. Preparation of modified composite flame-retardant fiber Deionized water is heated to 40-50°C, and 15wt% of ammonium polyphosphate with a degree of polymerization greater than 1000 and 5wt% of melamine are added in sequence with stirring. After dissolving until transparent, the mixture is dispersed at a high speed of 2000 rpm for 10 minutes, and 0.1wt% of alkylphenol polyoxyethylene ether (wetting agent) is added. The mixture is stirred at a low speed of 500 rpm to obtain a melamine-ammonium polyphosphate mixed solution. PVA fibers (carbon source fibers) with a length of 3 mm and a diameter of 25 μm are added to the mixed solution at a solid-liquid ratio of 1:10, and the mixture is immersed in a sealed container at a constant temperature of 25°C for 30-50 minutes (manually stirred every 10 minutes). After immersion, the mixture is drained through a sieve and lightly pressed until there are no continuous droplets. The mixture is dried with hot air at 40°C for 1 hour, and then vacuum dried at 60°C and -0.08 MPa for 2 hours to obtain a modified composite flame-retardant fiber.

[0047] S3. Preparation of thermal insulation and fire retardant coating 100 parts of titanium dioxide modified phosphogypsum, 10 parts of hollow glass microspheres, 60 parts of styrene acrylic emulsion, and 20 parts of modified composite flame retardant fiber were added into a stirring kettle and stirred at 300 r / min for 10 min; 5 parts of calcium sulfate whiskers, 8 parts of microencapsulated red phosphorus, 15 parts of redispersible latex powder, 1 part of sodium lauryl sulfate (dispersant), and 1 part of polydimethylsiloxane (defoaming agent) were added and stirred at 800 r / min for 15 min; finally, 10 parts of deionized water were added and stirred at 300 r / min for 5 min to obtain a phosphogypsum-based thermal insulation and fire retardant coating.

[0048] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that titanium dioxide-modified phosphogypsum is not used, and ordinary phosphogypsum (not loaded with titanium dioxide and not calcined) is directly used. The other components and preparation method are the same as those in Example 1.

[0049] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that no modified composite flame-retardant fiber is used, and PVA fiber (length 3 mm, diameter 25 μm) not impregnated with melamine-ammonium polyphosphate is directly used. The other components and preparation methods are the same as those in Example 1.

[0050] Comparative Example 3 The difference between Comparative Example 3 and Example 1 is that no microencapsulated red phosphorus is added, and the remaining components and preparation method are the same as those of Example 1.

[0051] Comparative Example 4 The difference between Comparative Example 4 and Example 1 is that no dispersant (sodium lauryl sulfate) and defoaming agent (polydimethylsiloxane) are added, and the remaining components and preparation method are the same as those of Example 1.

[0052] Comparative Example 5 The difference between Comparative Example 5 and Example 1 is that no calcination treatment is performed when preparing titanium dioxide-modified phosphogypsum (that is, only ultrasonically loaded titanium dioxide is not calcined), and the remaining components and preparation method are the same as those in Example 1.

[0053] According to GB14907-2018 (expansion type), Example 1 and Comparative Examples 1-5 were tested for drying time (surface dry) / h, initial drying crack resistance, bonding strength / MPa, heat exposure resistance, freeze-thaw cycle resistance, and ultraviolet radiation resistance; according to GB12441-2018, Example 1 and Comparative Examples 1-5 were tested for flame retardancy time / min. The test results are shown in the following table:

[0054] By comparing the test results of Example 1 and Comparative Example 1, it can be seen that Comparative Example 1 does not use titanium dioxide modified phosphogypsum, and directly uses ordinary phosphogypsum. Its surface drying time is extended from 3 hours in Example 1 to 4 hours, and the bonding strength is reduced from 1.15 MPa to 0.85 MPa. In the heat resistance test, the coating delaminates and slightly falls off. In the freeze-thaw cycle resistance test, the coating delaminates and falls off. In the ultraviolet radiation resistance test, the coating delaminates, and the flame retardant time is shortened from 65 minutes to 45 minutes. It can be seen that titanium dioxide modified phosphogypsum can significantly improve the drying speed, bonding strength, weather resistance and fire resistance of the coating. This is because rutile titanium dioxide has a high refractive index and strong reflection properties for infrared light, can effectively block heat conduction, and cooperates with hollow glass microspheres to construct a porous insulation structure. At the same time, the phosphogypsum is converted into anhydrous calcium sulfate particles after calcination, cooperates with calcium sulfate whiskers, and undergoes hydration reaction with deionized water in the coating, thereby increasing the hardness of the coating while shortening the drying time of the coating.

[0055] Comparing the test results of Example 1 and Comparative Example 2, Comparative Example 2 did not use modified composite flame-retardant fibers, but directly used PVA fibers that were not impregnated with melamine-ammonium polyphosphate. Its initial drying crack resistance showed fine cracks, and the bonding strength dropped to 0.95 MPa. In the heat exposure resistance, freeze-thaw cycle resistance, and ultraviolet radiation resistance tests, the coating did not delaminate or fall off, but had fine cracks, and the flame retardant time was shortened to 50 minutes. This shows that the modified composite flame-retardant fiber can effectively improve the crack resistance and fire resistance of the coating. The carbon source fiber is impregnated with a melamine-ammonium polyphosphate solution to form an intumescent flame retardant system. Under high temperature, melamine and ammonium polyphosphate decompose to produce phosphoric acid substances, which carbonize with the PVA fiber to form an insulating carbon layer, which achieves flame retardancy by absorbing heat and blocking oxygen. At the same time, the PVA fiber acts as a skeleton to support the carbon layer structure, and can synergize with calcium sulfate whiskers to enhance the toughness of the coating and reduce cracking.

[0056] Analysis of the test data of Example 1 and Comparative Example 3 shows that no microencapsulated red phosphorus is added to Comparative Example 3, and its flame retardant time is shortened from 65 min to 55 min. Although the coating does not delaminate or fall off in the heat resistance, freeze-thaw cycle resistance and ultraviolet radiation resistance tests, the thermal insulation efficiency attenuation is increased compared with Example 1. This shows that the microencapsulated red phosphorus forms a synergistic flame retardant system with the modified composite flame retardant fiber in the coating. At high temperature, the microcapsules rupture to release red phosphorus, and the red phosphorus burns to release phosphoric acid substances to form a glassy insulation layer on the coating surface, which achieves flame retardancy by absorbing heat, diluting oxygen and inhibiting the release of combustible gases. The modified composite flame retardant fiber forms an insulating carbon layer by expansion and carbonization. The combination of the two constructs a multiple fire barrier of "barrier-heat absorption-flame suppression" on the coating surface, thereby improving the fire resistance limit and fire safety of the coating.

[0057] Comparing the test results of Example 1 and Comparative Example 4, no dispersant and defoaming agent were added to Comparative Example 4, and its surface drying time was extended to 5h. The initial drying crack resistance caused cracks due to obvious bubbles, and the bonding strength dropped to 0.9MPa. In the heat exposure resistance, freeze-thaw cycle resistance and ultraviolet radiation resistance tests, the coating showed hollowing, cracking or delamination due to bubbles, and the thermal insulation efficiency attenuation increased significantly. This fully demonstrates the important role of dispersants and defoaming agents in coatings. Dispersants can reduce the surface tension of each component in the coating system, uniformly disperse the solid particles in the liquid phase, avoid agglomeration, and ensure the uniformity of coating performance; defoaming agents can destroy the bubble film generated during the stirring process, eliminate bubbles, and prevent the coating from having pores and strength reduction due to the presence of bubbles, thereby ensuring the construction performance and integrity of the coating.

[0058] Comparing the test results of Example 1 and Comparative Example 5, the titanium dioxide-modified phosphogypsum was prepared without calcination, and its bonding strength dropped to 0.9 MPa. In the heat resistance, freeze-thaw cycle resistance and ultraviolet radiation resistance tests, the coating did not delaminate or fall off, but had slight cracks, and the flame retardant time was shortened to 55 min. This shows that calcination is crucial to the performance of titanium dioxide-modified phosphogypsum. After calcination, titanium dioxide is converted into rutile, which enhances the heat reflection properties and effectively blocks heat conduction. At the same time, the phosphogypsum particles are converted into anhydrous calcium sulfate particles, which react with calcium sulfate whiskers and undergo hydration reaction with deionized water in the coating, thereby increasing the hardness of the coating and shortening the drying time of the coating. The calcination treatment also strengthens the interfacial bonding force of the titanium dioxide-modified phosphogypsum surface, and cooperates with the toughening effect of calcium sulfate whiskers to solve the problem of easy cracking of the coating, thereby improving the comprehensive performance of the coating.

[0059] The above description is only a preferred embodiment of the present invention. It should be pointed out that ordinary technicians in this technical field can make several improvements and modifications without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A phosphogypsum-based thermal insulation and fire retardant coating, characterized in that: The invention comprises the following components in parts by weight: 80-100 parts of titanium dioxide modified phosphogypsum, 10-20 parts of hollow glass microspheres, 50-60 parts of styrene acrylic emulsion, 20-25 parts of modified composite flame retardant fiber, 1-5 parts of calcium sulfate whiskers, 5-8 parts of microencapsulated red phosphorus, 10-15 parts of redispersible latex powder, 10-20 parts of deionized water, 1-5 parts of dispersant and 1-5 parts of defoaming agent.

2. A phosphogypsum-based thermal insulation and fire retardant coating according to claim 1, characterized in that: The titanium dioxide modified phosphogypsum is prepared by ultrasonically loading titanium dioxide on the surface of phosphogypsum particles and then calcining them. The particle size of the phosphogypsum particles is 200-300 μm, the loading amount of the titanium dioxide on the surface of the phosphogypsum particles is 1-5%, and the titanium dioxide after calcination is rutile titanium dioxide.

3. A phosphogypsum-based thermal insulation and fire retardant coating according to claim 1, characterized in that: The modified composite flame-retardant fiber is obtained by immersing a carbon source fiber in a melamine-ammonium polyphosphate mixed solution. The carbon source fiber is any one of PVA fiber, polyester fiber, polyamide fiber, and polypropylene fiber. The carbon source fiber has a length of 3-6 mm and a diameter of 15-25 μm.

4. The phosphogypsum-based thermal insulation and fire retardant coating according to claim 1, characterized in that: The dispersant is selected from any one of sodium lauryl sulfate, polycarboxylate superdispersants, and dodecyltrimethylammonium bromide; and the defoamer is selected from any one of polydimethylsiloxane and polyether-modified silane defoamers.

5. A method for preparing the phosphogypsum-based thermal insulation and fire retardant coating according to any one of claims 1 to 4, characterized in that: The following steps are involved: S1, preparing titanium dioxide modified phosphogypsum; The phosphogypsum particles were added to 5 times the volume of anhydrous ethanol, ultrasonically dispersed for 10 minutes, and the activated silane coupling agent solution was added. The mixture was heated and stirred at 70°C for 30 minutes, and ultrasonically assisted mixing was performed with an ultrasonic power of 300W. Then, the tetrabutyl titanate-ethanol solution was slowly added dropwise at a drop rate of 1.0 mL / min. The ultrasonic power was maintained. After the tetrabutyl titanate-ethanol solution was added dropwise, deionized water was slowly added dropwise. The mixture was ultrasonically heated at 70°C for 1 hour. The mixture was filtered and washed with 5°C ice water and anhydrous ethanol in sequence. The mixture was vacuum dried at 60°C for 12 hours. After grinding and sieving, the mixture was calcined in an air atmosphere at 700°C for 2-3 hours at a heating rate of 5°C / min to obtain titanium dioxide modified phosphogypsum. S2. preparing modified composite flame-retardant fiber; Deionized water was heated to 40-50°C, and ammonium polyphosphate and melamine were slowly added in sequence under stirring. After the solid was dissolved until the solution was transparent, the mixture was dispersed at a high speed of 2000 rpm for 10 minutes. A wetting agent was then added, and the mixture was stirred and mixed at a low speed of 500 rpm to obtain a melamine-ammonium polyphosphate mixed solution. The carbon source fiber and the melamine-ammonium polyphosphate mixed solution were immersed for a period of time at a solid-liquid ratio of 1:10, and then drained and dried to obtain a modified composite flame-retardant fiber. S3, preparing heat-insulating fire-retardant coating; 100 parts of titanium dioxide modified phosphogypsum, 10 parts of hollow glass microspheres, 60 parts of styrene acrylic emulsion, and 20 parts of modified composite flame retardant fiber were added into a stirring kettle and stirred at 300 r / min for 10 minutes. Then, 5 parts of calcium sulfate whiskers, 8 parts of microencapsulated red phosphorus, 15 parts of redispersible latex powder, 1 part of dispersant, and 1 part of defoaming agent were added and stirred at 800 r / min for 15 minutes. Finally, 10 parts of deionized water were added and stirred at 300 r / min for 5 minutes to obtain a thermal insulation and fire retardant coating.

6. The method for preparing the phosphogypsum-based thermal insulation and fire retardant coating according to claim 5, characterized in that: In step S1, the silane coupling agent is dissolved in 15 times the mass of 98% ethanol solution, a small amount of acetic acid is added to adjust the pH to 4-5, and stirred at room temperature for 15 minutes to obtain an activated silane coupling agent solution, wherein the silane coupling agent is selected from any one of γ-methacryloxypropyltrimethoxysilane and vinyltriethoxysilane, and the amount of the silane coupling agent is 1-10% of the mass of the phosphogypsum particles.

7. The method for preparing the phosphogypsum-based thermal insulation and fire retardant coating according to claim 5, characterized in that: In step S1, tetrabutyl titanate is dissolved in 5 times the volume of anhydrous ethanol to obtain a tetrabutyl titanate-ethanol solution, wherein the amount of the tetrabutyl titanate is 5-25% of the mass of the phosphogypsum particles, and then the solution is slowly dripped into the reaction system of step S1 while maintaining ultrasound, and then deionized water is dripped. The deionized water is dripped at a rate of 1-2 mL / min, and the molar ratio of the deionized water to the tetrabutyl titanate in the tetrabutyl titanate-ethanol solution is (15-20):

1.

8. The method for preparing the phosphogypsum-based thermal insulation and fire retardant coating according to claim 5, characterized in that: In step S2, the mass percentage range of each component in the melamine-ammonium polyphosphate mixed solution is: 10-15wt% ammonium polyphosphate, 3-5wt% melamine, 79.7-86.9wt% deionized water, and 0.1-0.3wt% wetting agent, the ammonium polyphosphate is a water-soluble ammonium polyphosphate with a degree of polymerization greater than 1000, and the wetting agent is an alkylphenol polyoxyethylene ether.

9. The method for preparing the phosphogypsum-based thermal insulation and fire retardant coating according to claim 5, characterized in that: In step S2, the carbon source fiber and the melamine-ammonium polyphosphate mixed solution are added to a sealed container in a ratio of 1:10 and shaken at a constant temperature at 25° C. for 30-50 minutes, and manually stirred every 10 minutes.

10. The method for preparing the phosphogypsum-based thermal insulation and fire retardant coating according to claim 5, characterized in that: In step S2, the impregnated carbon source fiber is drained with a sieve to remove excess liquid, the carbon source fiber is lightly pressed until there are no continuous droplets, and then dried with hot air at 40°C for 1 hour, and then vacuum dried at 60°C and -0.08 MPa for 2 hours to obtain a modified composite flame retardant fiber.

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