An environmentally friendly porous material for exterior wall thermal insulation and its preparation method

Abstract

The present invention discloses an environmentally friendly porous material for exterior wall thermal insulation and its preparation method, which relates to the technical field of heat insulation materials; the environmentally friendly porous material for exterior wall thermal insulation is composed of a flame-retardant pore-forming composite, a geopolymer filler based on gasified fly ash, nanocellulose, methyltrimethoxysilane, and polyvinyl alcohol; the flame-retardant pore-forming composite and methyltrimethoxysilane are modified by a solution method to obtain a multi-dimensional pore-modified aerogel solution, and then the geopolymer filler based on gasified fly ash is further used to fill the pore structure of the aerogel, which not only increases the stability of the aerogel structure, but also increases the complexity of the pores, making the pore structure of the material porous, multi-dimensional and multi-level, thus significantly enhancing the thermal insulation performance, and at the same time also having certain hydrophobic and flame-retardant properties, which can play the role of waterproofing and fire prevention, and enhance the applicability and durability of the exterior wall material.

Description

Technical Field

[0001] The present invention belongs to the technical field of thermal insulation materials, and specifically refers to an environmentally friendly exterior wall thermal insulation porous material and a preparation method thereof. Background Art

[0002] The external wall thermal insulation technology is one of the important means of building energy conservation. The performance and configuration of thermal insulation materials will directly affect the thermal insulation effect of the external wall; in the traditional thermal insulation industry, common thermal insulation materials, such as polyurethane and expanded polystyrene, are derived from non-renewable fossil raw materials. Therefore, it is urgent to seek environmentally friendly and sustainable thermal insulation materials.

[0003] Aerogel materials have a unique three-dimensional porous structure, showing characteristics of low density, high porosity and low thermal conductivity, and have become an ideal substitute for traditional petroleum-based foam thermal insulation materials; cellulose not only has the advantages of good biocompatibility, renewable, biodegradable, economical, non-toxic, etc., but also has the advantages of high corrosion resistance, high strength, high modulus, etc. Therefore, cellulose aerogel, as a representative of the third generation of biomass aerogels, not only inherits the advantages of large specific surface area and high porosity of traditional aerogels, but also overcomes the disadvantages of poor mechanical properties of inorganic aerogels, cumbersome preparation steps of organic aerogels and non-degradability. As a new type of green material, cellulose aerogel not only shows great potential in thermal insulation applications, but also better meets the requirements of sustainable development, providing a new solution for reducing global energy consumption.

[0004] The current existing technologies mainly have the following problems:

[0005] The stability of cellulose aerogel is poor and it is easy to collapse in structure, which will have an adverse impact on the thermal insulation performance of the material. Summary of the Invention

[0006] In view of the above situation, in order to overcome the defects of the existing technologies, the present invention provides an environmentally friendly exterior wall thermal insulation porous material, which comprises the following components in parts by weight: 10-20 parts of a flame-retardant pore-forming composite, 30-40 parts of a gasified fly ash-based geopolmer filler, 4-5 parts of nanocellulose, 8-10 parts of methyltrimethoxysilane, and 8-10 parts of polyvinyl alcohol.

[0007] The flame-retardant pore-forming composite comprises the following components in parts by weight: 10-20 parts of phosphorus-doped graphitic carbon nitride, and 30-40 parts of ZIF-8 zeolitic imidazolate framework material.

[0008] The gasified fly ash-based geopolmer filler is a thermal insulation filler obtained by calcining and activating gasified fly ash as a raw material, preparing an alkali activator with sodium hydroxide, sodium silicate and deionized water, and mixing and stirring the activated material, the alkali activator, a hydrogen peroxide foaming agent and an oleic acid foam stabilizer for synergistic modification.

[0009] The preparation method of the flame-retardant pore-forming composite specifically includes the following steps:

[0010] (1) Add urea and diammonium hydrogen phosphate into 200 - 300 mL of deionized water. The addition amount of urea is 5.0 g. Stir magnetically for 3 - 4 h at a stirring speed of 500 - 600 rpm until it is completely dissolved. Place the clarified solution in a refrigerator at -18 °C for freezing for 10 - 12 h, then freeze-dry to remove moisture, grind it into a powder, add it to a sealed ceramic crucible, and then calcine it in a muffle furnace at 500 - 550 °C for 3 - 4 h. The heating-up time is controlled within 100 min. Collect the yellow product and grind it. Phosphorus atoms are doped to replace the carbon sites in the graphitic carbon nitride oxide framework, without destroying the basic morphology of graphitic carbon nitride oxide. However, after phosphorus doping, the two-dimensional layered structure shows micron-sized wrinkles, and the nanosheet layers are larger and more obvious, obtaining phosphorus-doped graphitic carbon nitride;

[0011] (2) Pour 80 - 100 mg of zinc nitrate hexahydrate and the phosphorus-doped graphitic carbon nitride obtained in step (1) into a methanol solution, ultrasonically disperse it to form a uniform dispersion, and then pour the dispersion into a 10 mL methanol solution of 2-methylimidazole. The methanol solution of 2-methylimidazole contains 1.0 - 1.2 g of 2-methylimidazole. Stir at room temperature for 2 h, then let it stand for precipitation, filter and wash, and dry. The zinc nitrate hexahydrate and 2-methylimidazole form a ZIF-8 zeolitic imidazolate framework material. The ZIF-8 particles are evenly distributed on the surface of the phosphorus-doped graphitic carbon nitride and are tightly combined, obtaining the flame-retardant pore-forming composite, which not only reduces the agglomeration of ZIF-8 particles but also is beneficial to the pore-forming uniformity and multi-level nature of the subsequent cross-linking reaction. Moreover, the porous protective film of the composite itself also has certain flame-retardant and waterproof properties, which is beneficial to the safety and durability of the use of exterior wall building materials;

[0012] Preferably, in step (1), the addition amount of diammonium hydrogen phosphate is 0.3 - 0.5 g. The addition of diammonium hydrogen phosphate provides phosphorus elements, which is beneficial to improving the flame-retardant and waterproof properties of graphitic carbon nitride oxide;

[0013] Preferably, in step (2), the zinc atom content in the flame-retardant pore-forming composite is 5.4 - 6.8%. The presence of zinc elements has a good smoke suppression effect, can combine with phosphorus and nitrogen elements to exert better flame-retardant performance, and at the same time, zinc elements can form an oxide protective film on the material surface, thus having good waterproof performance.

[0014] The preparation method of the gasified fly ash-based geopolymers filler specifically includes the following steps:

[0015] a. Put the gasified fly ash into a muffle furnace at 700 - 800 °C and calcine it until the mass no longer changes. Then grind it. There are a large number of glass microspheres on the surface of the gasified fly ash particles, and its main components are silicon dioxide and alumina. Under the action of high temperature, the original stable and ordered structure is destroyed, generating more amorphous monomers, which is conducive to the alkali activation reaction of the gasified fly ash, leaching out the silicon and aluminum elements in the fly ash, thereby preparing a polymer with higher strength, more uniform and dense structure, and obtaining the calcined and activated material;

[0016] b. Mix sodium hydroxide, sodium silicate with 25 mL of deionized water and stir evenly. The addition amount of sodium hydroxide is 2.0 g. Then weigh 30.0 g of the obtained alkali activator and the calcined and activated material described in step a and mix and stir them. Add 0.6 - 0.7 g of oleic acid foam stabilizer and 0.6 - 0.7 g of hydrogen peroxide foaming agent, and stir rapidly for 1 - 2 min. The stirring speed is 800 - 1000 rpm, and the shear speed is 8000 - 10000 rpm. Then pour the slurry into a mold and place it in a standard curing box at 60 °C for 3 days. Under the action of sodium hydroxide, the Si - O and Al - O covalent bonds in the gasified fly ash are broken, and recombined and polycondensed to form a polysialic acid compound with a bonding network structure based on -SiO 4 -AlO 4 which can increase the compressive strength of the polymer and also form a large number of closed small pores inside the geopolymers, effectively improving the porosity and enhancing the heat insulation performance. Therefore, the gasified fly ash is modified by this process method to prepare a geopolymer thermal insulation material with fire resistance, high temperature resistance and high compressive strength, improving the current situation that organic thermal insulation materials are easy to age and inorganic materials have poor heat insulation, and obtaining a gasified fly ash - based geopolymer filler;

[0017] Preferably, in step b, the addition amount of sodium silicate is 5.5 - 6.5 g. Sodium silicate can effectively adjust the silicon - aluminum ratio in the reaction system, which is conducive to the uniform and stable formation of bubble pores and has good heat insulation performance.

[0018] The present invention also provides a preparation method of an environmentally friendly exterior wall thermal insulation porous material, which specifically includes the following steps:

[0019] S1. Add 0.8 - 1.0 g of nanocellulose to 100 mL of deionized water, then add 1.6 - 2.0 g of polyvinyl alcohol, and magnetically stir for 24 h at room temperature. Add methyltrimethoxysilane liquid to the mixture of polyvinyl alcohol and nanocellulose, stir to disperse it evenly, then add the flame-retardant pore-forming composite, and magnetically stir for 1 - 2 h. Under the further cross-linking action of the flame-retardant pore-forming composite, the network structure of the aerogel becomes denser, significantly enhancing the pore-forming uniformity and multi-levelness, being able to effectively capture and store energy, enhancing the heat insulation performance, and the incorporation of phosphorus, nitrogen, and zinc elements in the flame-retardant pore-forming composite improves the flame-retardant and waterproof properties of the aerogel, obtaining a multi-dimensional pore modified aerogel solution;

[0020] S2. Pour the multi-dimensional pore modified aerogel solution obtained in step S1 into a silicone mold, first pre-freeze it in a refrigerator at 4 °C for 1 - 2 h, add the gasified fly ash-based geopolymers filler and stir, then perform ultrasonic treatment for 1 - 2 h, with the ultrasonic temperature of 5 - 6 °C and the ultrasonic power of 600 - 800 W, so that the gasified fly ash-based geopolymers filler can fully enter the pores of the aerogel, further filling the pore structure of the aerogel, providing abundant mesopores for the aerogel and increasing the complexity of the pores, making the micron-scale pore structure porous, multi-dimensional, and multi-level, thus significantly enhancing the heat insulation, waterproof, and flame-retardant properties. The network bonding structure of the gasified fly ash-based geopolymers filler also enhances the compressive strength of the aerogel, can act as a stabilizer to reduce the collapse of pores in the aerogel, is conducive to better exerting the heat insulation, waterproof, and fireproof characteristics, and improves the durability of the material use. Then vacuum freeze-dry at -70 °C for 24 - 48 h, and place the obtained aerogel in an oven at 70 - 80 °C and dry for 3 - 4 h to obtain an environmentally friendly exterior wall thermal insulation porous material;

[0021] Preferably, in step S1, the addition amount of methyltrimethoxysilane is 1.6 - 2.0 g. Methyltrimethoxysilane is both a hydrophobic modifier and a cross-linking agent, coating on the aerogel skeleton, making the connection between fibers tighter, improving the mechanical properties and structural stability of the aerogel, reducing the occurrence of pore collapse in the cellulose aerogel, and methyltrimethoxysilane can generate a silica carbon layer at high temperature, and this carbon layer can isolate heat and oxygen, thus playing a flame-retardant role.

[0022] The beneficial effects obtained by the present invention are as follows:

[0023] In the present invention, a multi-dimensional pore modified aerogel solution is obtained by modifying a flame retardant pore-forming composite and methyltrimethoxysilane using a solution method. Then, a gasification fly ash-based geopolmer filler is further used to fill the pore structure of the aerogel, which not only increases the stability of the aerogel structure but also increases the complexity of the pores, making the pore structure of the material porous, multi-dimensional, and multi-level, thus significantly enhancing the thermal insulation performance. At the same time, it also has certain hydrophobic and flame retardant properties, which can play the role of waterproofing and fire prevention, enhancing the applicability and durability of the exterior wall material; in the multi-dimensional pore modified aerogel solution, the polyvinyl alcohol and nano-cellulose aerogel are modified with a flame retardant pore-forming composite and methyltrimethoxysilane. Methyltrimethoxysilane, as a cross-linking agent and hydrophobic modifier, is coated on the aerogel skeleton, enhancing the structural stability, reducing the risk of collapse of the cellulose aerogel, and endowing it with hydrophobic and flame retardant properties. Then, the flame retardant pore-forming composite further cross-links to enhance the uniformity and multi-level nature of pore formation, and can effectively capture and store energy, thereby enhancing the thermal insulation performance. Among them, the flame retardant pore-forming composite is that ZIF-8 zeolitic imidazolate framework material is uniformly distributed on the surface of phosphorus-doped graphitic carbon nitride, which not only reduces the agglomeration of ZIF-8 particles but also introduces phosphorus, nitrogen, and zinc elements, thus improving the flame retardant performance and waterproof performance of the aerogel; in the gasification fly ash-based geopolmer filler, the gasification fly ash is modified to obtain a polysialic acid compound with a bonding network structure based on -SiO 4 -AlO 4 . Then it is filled into the multi-dimensional pore modified aerogel solution, increasing the surface pore structure and compressive strength of the aerogel, making the pore structure of the aerogel porous, multi-dimensional, and multi-level, significantly enhancing the thermal insulation performance, waterproof performance, and flame retardant performance of the material. The gasification fly ash-based geopolmer filler can also act as a stabilizer to reduce the collapse of pores in the aerogel, which is beneficial to better exerting the properties of thermal insulation, waterproofing, and fire prevention; the present invention uses a flame retardant pore-forming composite, a gasification fly ash-based geopolmer filler, nano-cellulose, methyltrimethoxysilane, and polyvinyl alcohol to prepare an environmentally friendly exterior wall thermal insulation porous material, which has excellent thermal insulation performance, fire prevention performance, and waterproof performance, enhancing the applicability, safety, and durability of the exterior wall material. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a scanning electron microscope image of the environmentally friendly exterior wall thermal insulation porous material prepared in Example 1 of the present invention;

[0025] Figure 2 It is a graph of the thermal conductivity results of Examples 1-4 and Comparative Examples 1-3 of the present invention;

[0026] Figure 3 It is a graph of the limiting oxygen index results of Examples 1-4 and Comparative Examples 1-3 of the present invention;

[0027] Figure 4 This is the contact angle result diagram of Examples 1-4 and Comparative Examples 1-3 of the present invention;

[0028] Figure 5 This is the scanning electron microscope image of the phosphorus-doped graphitic carbon nitride prepared in Example 1 of the present invention. Detailed implementation manners

[0029] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments; based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0030] Unless otherwise defined, all professional and scientific terms used herein have the same meaning as those familiar to those skilled in the art. In addition, any methods and materials similar or equivalent to the described content can be applied to the present invention. The preferred implementation methods and materials described herein are only for illustration purposes and cannot limit the content of this application.

[0031] The experimental methods in the following embodiments are all conventional methods unless otherwise specified; the test materials used in the following embodiments are all obtained from commercial channels unless otherwise specified.

[0032] Example 1

[0033] This example provides an environmentally friendly exterior wall thermal insulation porous material, which includes the following components in parts by weight: 20 parts of a flame-retardant pore-forming composite, 40 parts of a gasification fly ash-based geopolmer filler, 5 parts of nanocellulose, 10 parts of methyltrimethoxysilane, and 10 parts of polyvinyl alcohol.

[0034] The flame-retardant pore-forming composite includes the following components in parts by weight: 20 parts of phosphorus-doped graphitic carbon nitride and 40 parts of ZIF-8 zeolitic imidazolate framework material.

[0035] The gasification fly ash-based geopolmer filler is a thermal insulation filler obtained by calcining and activating gasification fly ash as a raw material, preparing an alkali activator with sodium hydroxide, sodium silicate and deionized water, and mixing and stirring the activated material, the alkali activator, a hydrogen peroxide foaming agent and an oleic acid foam stabilizer for synergistic modification.

[0036] The preparation method of the flame-retardant pore-forming composite specifically includes the following steps:

[0037] (1) Urea and diammonium hydrogen phosphate were added to 300 mL of deionized water. The addition amount of urea was 5.0 g, and it was magnetically stirred for 4 h at a stirring speed of 600 rpm until it was completely dissolved. The addition amount of diammonium hydrogen phosphate was 0.5 g. The addition of diammonium hydrogen phosphate provided phosphorus element, which was beneficial to improving the flame retardancy and waterproof performance of graphitic carbon nitride oxide. The clarified solution was placed in a refrigerator at -18 °C and frozen for 12 h, then freeze-dried to remove water, ground into a powder and added to a sealed ceramic crucible, and then calcined in a muffle furnace at 550 °C for 4 h. The heating-up time was controlled within 100 min. The yellow product was collected and ground. The phosphorus atoms doped and replaced the carbon sites in the graphitic carbon nitride oxide framework, without destroying the basic morphology of graphitic carbon nitride oxide. However, after phosphorus doping, the two-dimensional layered structure presented micron-sized wrinkles, and the lamellae of the nanosheets were larger and more obvious, obtaining phosphorus-doped graphitic carbon nitride;

[0038] (2) 100 mg of zinc nitrate hexahydrate and the phosphorus-doped graphitic carbon nitride described in step (1) were poured into a methanol solution, and ultrasonic dispersion was carried out to form a uniform dispersion liquid. Then the dispersion liquid was poured into a 10 mL methanol solution of 2-methylimidazole. The methanol solution of 2-methylimidazole contained 1.2 g of 2-methylimidazole. It was stirred at room temperature for 2 h, then allowed to stand for precipitation, filtered, washed, and dried. ZIF-8 zeolitic imidazole framework material was formed with zinc nitrate hexahydrate and 2-methylimidazole. The ZIF-8 particles were evenly distributed on the surface of the phosphorus-doped graphitic carbon nitride and tightly combined, obtaining a flame-retardant pore-forming composite, which not only reduced the aggregation of ZIF-8 particles but also was beneficial to the pore-forming uniformity and multi-level nature of the subsequent cross-linking reaction. Moreover, the porous protective film of the composite itself also had certain flame retardancy and waterproof performance, which was beneficial to the safety and durability of the use of exterior wall building materials. The zinc atom content in the flame-retardant pore-forming composite was 6.8%. The presence of zinc element had a good smoke suppression effect and could combine with phosphorus and nitrogen elements to exert a more excellent flame retardancy. At the same time, the zinc element could form an oxide protective film on the material surface, thus having good waterproof performance.

[0039] A preparation method of a gasification fly ash-based geopolmer filler specifically includes the following steps:

[0040] a. The gasification fly ash was placed in a muffle furnace at 800 °C and calcined until the mass no longer changed, and then ground. There were a large number of glass microspheres on the surface of the gasification fly ash particles, and their main components were silica and alumina. Under the action of high temperature, the original stable and orderly structure was destroyed, generating more amorphous monomers, which was beneficial to the alkali activation reaction of the gasification fly ash, leaching out the silicon and aluminum elements in the fly ash, thereby preparing a polymer with higher strength, more uniform and dense structure, obtaining a calcined and activated material;

[0041] b. Mix sodium hydroxide, sodium silicate with 25 mL of deionized water, and stir evenly. The addition amount of sodium hydroxide is 2.0 g, and the addition amount of sodium silicate is 6.5 g. Sodium silicate can effectively adjust the silicon-aluminum ratio in the reaction system, which is beneficial to the formation of uniform and stable bubble pores and has good heat preservation performance. Then, weigh 30.0 g of the alkali activator obtained above and the calcined and activated material described in step a for mixing and stirring, add 0.7 g of oleic acid foam stabilizer and 0.7 g of hydrogen peroxide foaming agent, and stir rapidly for 2 min at a stirring speed of 1000 rpm and a shear speed of 10000 rpm. Then pour the slurry into a mold and place it in a standard curing box at 60 °C for 3 days. Under the action of sodium hydroxide, the Si-O and Al-O covalent bonds in the gasified fly ash are broken, and they are recombined and polycondensed to form -SiO 4 -AlO 4 -based polyaluminum silicate compound with a bonded network structure, which can increase the compressive strength of the polymer, and can also form a large number of closed small holes inside the geopolymers, effectively improving the porosity and enhancing the heat preservation performance. Therefore, the gasified fly ash is modified by this process method to prepare a geopolymer thermal insulation material with fire resistance, high temperature resistance and high compressive strength, improving the current situation that organic thermal insulation materials are prone to aging and inorganic materials have poor heat insulation, and obtaining a gasified fly ash-based geopolymer filler.

[0042] This embodiment provides a preparation method of an environmentally friendly exterior wall thermal insulation porous material, which specifically includes the following steps:

[0043] S1. Add 1.0 g of nanocellulose to 100 mL of deionized water, then add 2.0 g of polyvinyl alcohol, and stir magnetically at room temperature for 24 h. Add methyltrimethoxysilane liquid to the mixture of polyvinyl alcohol and nanocellulose. The addition amount of methyltrimethoxysilane is 2.0 g. Methyltrimethoxysilane is both a hydrophobic modifier and a crosslinking agent, which coats on the aerogel skeleton, making the connection between fibers tighter, improving the mechanical properties and structural stability of the aerogel, reducing the occurrence of pore collapse of the cellulose aerogel, and methyltrimethoxysilane can generate a silicon dioxide carbon layer at high temperature, which can isolate heat and oxygen, thus playing a flame retardant role. Stir to make it disperse evenly, then add a flame retardant pore-forming composite, and stir magnetically for 2 h. Under the further crosslinking action of the flame retardant pore-forming composite, the network structure of the aerogel is denser, significantly enhancing the pore-forming uniformity and multi-levelness, being able to effectively capture and store energy, enhancing the heat preservation performance, and the incorporation of phosphorus, nitrogen, and zinc elements in the flame retardant pore-forming composite improves the flame retardant performance and waterproof performance of the aerogel, obtaining a multi-dimensional pore modified aerogel solution;

[0044] S2. Pour the multi-dimensional pore modified aerogel solution described in step S1 into a silica gel mold. First, pre-freeze it in a refrigerator at 4°C for 2 h, add the gasified fly ash-based geopolmer filler and stir, then perform ultrasonic treatment for 2 h at an ultrasonic temperature of 6°C and an ultrasonic power of 800 W, so that the gasified fly ash-based geopolmer filler can fully enter the pores of the aerogel, further filling the pore structure of the aerogel, providing rich mesopores for the aerogel and increasing the complexity of the pores, making the micron-scale pore structure porous, multi-dimensional and multi-level, thus significantly enhancing the heat insulation performance, waterproof performance and flame retardant performance. The network bonding structure of the gasified fly ash-based geopolmer filler also enhances the compressive strength of the aerogel, can act as a stabilizer to reduce the collapse of pores in the aerogel, is conducive to better exerting the heat insulation, waterproof and fireproof characteristics, improves the durability of the material use, and then vacuum freeze-dry at -70°C for 48 h. Place the obtained aerogel in an oven at 80°C and dry for 4 h to obtain the environmentally friendly exterior wall thermal insulation porous material.

[0045] In this example, the environmentally friendly exterior wall thermal insulation porous material prepared was subjected to scanning electron microscopy to observe its microscopic morphology. Figure 1 It is the SEM image magnified 400 times of the environmentally friendly exterior wall thermal insulation porous material prepared in Example 1, as Figure 1 , the pore structure of the environmentally friendly exterior wall thermal insulation porous material prepared in this example shows dense complexity.

[0046] In this example, the phosphorus-doped graphitic carbon nitride prepared was subjected to scanning electron microscopy to observe its microscopic morphology. Figure 5 It is the SEM image magnified 100,000 times of the phosphorus-doped graphitic carbon nitride prepared in Example 1, as Figure 5 , the lamellae of the phosphorus-doped graphitic carbon nitride prepared in this example are larger and more obvious.

[0047] Example 2

[0048] This example proposes an environmentally friendly exterior wall thermal insulation porous material, which includes the following components in parts by weight: 10 parts of flame retardant pore-forming composite, 30 parts of gasified fly ash-based geopolmer filler, 4 parts of nanocellulose, 8 parts of methyltrimethoxysilane, and 8 parts of polyvinyl alcohol.

[0049] The flame retardant pore-forming composite includes the following components in parts by weight: 10 parts of phosphorus-doped graphitic carbon nitride and 30 parts of ZIF-8 zeolitic imidazole framework material.

[0050] The gasified fly ash-based geopolmer filler is a thermal insulation filler obtained by calcining and activating gasified fly ash as raw materials, preparing an alkali activator with sodium hydroxide, sodium silicate and deionized water, and mixing and stirring the activated material, alkali activator, hydrogen peroxide foaming agent and oleic acid foam stabilizer for synergistic modification.

[0051] Preparation method of flame-retardant pore-forming composite, specifically including the following steps:

[0052] (1) Add urea and diammonium hydrogen phosphate into 200 mL of deionized water. The addition amount of urea is 5.0 g, and stir magnetically for 3 h at a stirring speed of 500 rpm until it is completely dissolved. The addition amount of diammonium hydrogen phosphate is 0.3 g. The addition of diammonium hydrogen phosphate provides phosphorus element, which is beneficial to improving the flame-retardant and waterproof properties of graphitic carbon nitride oxide. Place the clarified solution in a refrigerator at -18 °C for 10 h, then freeze-dry to remove moisture, grind it into powder and add it into a sealed ceramic crucible, and then calcine it in a muffle furnace at 500 °C for 3 h. The heating-up time is controlled within 100 min. Collect the yellow product and grind it. The phosphorus atoms are doped to replace the carbon sites in the graphitic carbon nitride oxide framework, without destroying the basic morphology of graphitic carbon nitride oxide. However, after phosphorus doping, the two-dimensional layered structure presents micron-sized wrinkles, and the layers of the nanosheets are larger and more obvious, obtaining phosphorus-doped graphitic carbon nitride;

[0053] (2) Pour 80 mg of zinc nitrate hexahydrate and the phosphorus-doped graphitic carbon nitride described in step (1) into a methanol solution, and ultrasonically disperse it to form a uniform dispersion. Then pour the dispersion into a 10 mL methanol solution of 2-methylimidazole. The methanol solution of 2-methylimidazole contains 1.0 g of 2-methylimidazole. Stir at room temperature for 2 h, then let it stand for precipitation, filter and wash, and dry. Zinc nitrate hexahydrate and 2-methylimidazole form ZIF-8 zeolite imidazole framework material. The ZIF-8 particles are evenly distributed on the surface of the phosphorus-doped graphitic carbon nitride and are tightly combined, obtaining the flame-retardant pore-forming composite, which not only reduces the agglomeration of ZIF-8 particles, but also is beneficial to the pore-forming uniformity and multi-levelness of the subsequent cross-linking reaction. Moreover, the porous protective film of the composite itself also has certain flame-retardant and waterproof properties, which is beneficial to the safety and durability of the use of exterior wall building materials. The zinc atom content in the flame-retardant pore-forming composite is 5.4%. The presence of zinc element has a good smoke suppression effect and can combine with phosphorus and nitrogen elements to exert more excellent flame-retardant properties. At the same time, zinc element can form an oxide protective film on the material surface, thus having good waterproof properties.

[0054] Preparation method of gasification fly ash-based geopolymers filler, specifically including the following steps:

[0055] a. Put the gasification fly ash into a muffle furnace at 700 °C and calcine it until the mass no longer changes, then grind it. There are a large number of glass microspheres on the surface of the gasification fly ash particles, and its main components are silicon dioxide and alumina. Under the action of high temperature, the original stable and ordered structure is destroyed, generating more amorphous monomers, which is beneficial to the alkali activation reaction of the gasification fly ash, leaching out the silicon and aluminum elements in the fly ash, so as to prepare a polymer with higher strength, more uniform and dense structure, obtaining the calcined and activated material;

[0056] b. Mix sodium hydroxide, sodium silicate with 25 mL of deionized water and stir evenly. The addition amount of sodium hydroxide is 2.0 g, and the addition amount of sodium silicate is 5.5 g. Sodium silicate can effectively adjust the silicon-aluminum ratio in the reaction system, which is beneficial to the formation of uniform and stable bubble pores and has good heat insulation performance. Then, weigh 30.0 g of the obtained alkali activator and the calcined and activated material described in step a for mixing and stirring, add 0.6 g of oleic acid foam stabilizer and 0.6 g of hydrogen peroxide foaming agent, and quickly stir for 1 min at a stirring speed of 800 rpm and a shear speed of 8000 rpm. Then pour the slurry into a mold and place it in a standard curing box at 60 °C for 3 days. Under the action of sodium hydroxide, the Si-O and Al-O covalent bonds in the gasified fly ash are broken, and recombined and polycondensed to form a -SiO 4 -AlO 4 -based adhesive network structure polysialic acid compound, which can increase the compressive strength of the polymer, and can also form a large number of closed small holes inside the geopolymers, effectively improving the porosity and enhancing the heat insulation performance. Therefore, the gasified fly ash is modified by this process method to prepare a geopolymer thermal insulation material with fire resistance, high temperature resistance and high compressive strength, improving the current situation that organic thermal insulation materials are easy to age and inorganic materials have poor heat insulation, and obtaining a gasified fly ash-based geopolymer filler.

[0057] This embodiment provides a preparation method of an environmentally friendly exterior wall thermal insulation porous material, which specifically includes the following steps:

[0058] S1. Add 0.8 g of nanocellulose to 100 mL of deionized water, then add 1.6 g of polyvinyl alcohol, and magnetically stir at room temperature for 24 h. Add methyltrimethoxysilane liquid to the mixed solution of polyvinyl alcohol and nanocellulose. The addition amount of methyltrimethoxysilane is 1.6 g. Methyltrimethoxysilane is both a hydrophobic modifier and a cross-linking agent, which coats on the aerogel skeleton, making the connection between fibers tighter, improving the mechanical properties and structural stability of the aerogel, reducing the occurrence of pore collapse of the cellulose aerogel, and methyltrimethoxysilane can generate a silicon dioxide carbon layer at high temperature, and this carbon layer can isolate heat and oxygen, thus playing a flame retardant role. Stir to make it evenly dispersed, then add a flame retardant pore-forming composite and magnetically stir for 1 h. Under the further cross-linking action of the flame retardant pore-forming composite, the network structure of the aerogel is more dense, significantly enhancing the pore-forming uniformity and multi-levelness, being able to effectively capture and store energy, enhancing the heat insulation performance, and the incorporation of phosphorus, nitrogen and zinc elements in the flame retardant pore-forming composite improves the flame retardant performance and waterproof performance of the aerogel, obtaining a multi-dimensional pore modified aerogel solution;

[0059] S2. Pour the multi-dimensional porous modified aerogel solution described in step S1 into a silica gel mold. First, pre-freeze it in a refrigerator at 4°C for 1 h, add the gasified fly ash-based geopolmer filler and stir, then perform ultrasonic treatment for 1 h at an ultrasonic temperature of 5°C and an ultrasonic power of 600 W, so that the gasified fly ash-based geopolmer filler can fully enter the pores of the aerogel, further filling the pore structure of the aerogel, providing rich mesopores for the aerogel and increasing the complexity of the pores, making the micron-scale pore structure porous, multi-dimensional and multi-level, thus significantly enhancing the thermal insulation performance, waterproof performance and flame retardant performance. The network bonding structure of the gasified fly ash-based geopolmer filler also enhances the compressive strength of the aerogel, can act as a stabilizer to reduce the collapse of pores in the aerogel, is conducive to better exerting the characteristics of thermal insulation, waterproof and fire prevention, improves the durability of material use, and then vacuum freeze-dry at -70°C for 24 h. Place the obtained aerogel in an oven at 70°C and dry for 3 h to obtain an environmentally friendly exterior wall thermal insulation porous material.

[0060] Example 3

[0061] This example presents an environmentally friendly exterior wall thermal insulation porous material, which includes the following components in parts by weight: 15 parts of flame retardant pore-forming composite, 35 parts of gasified fly ash-based geopolmer filler, 4.5 parts of nanocellulose, 9 parts of methyltrimethoxysilane, and 9 parts of polyvinyl alcohol.

[0062] The flame retardant pore-forming composite includes the following components in parts by weight: 15 parts of phosphorus-doped graphitic carbon nitride and 35 parts of ZIF-8 zeolitic imidazolate framework material.

[0063] The gasified fly ash-based geopolmer filler is a thermal insulation filler obtained by calcining and activating gasified fly ash as raw material, preparing an alkali activator with sodium hydroxide, sodium silicate and deionized water, and mixing and stirring the activated material, the alkali activator, hydrogen peroxide foaming agent and oleic acid foam stabilizer for synergistic modification.

[0064] The preparation method of the flame retardant pore-forming composite specifically includes the following steps:

[0065] (1) Urea and diammonium hydrogen phosphate were added to 250 mL of deionized water. The amount of urea added was 5.0 g, and it was magnetically stirred for 3.5 h at a stirring speed of 550 rpm until completely dissolved. The amount of diammonium hydrogen phosphate added was 0.4 g. The addition of diammonium hydrogen phosphate provided phosphorus elements, which was beneficial to improving the flame retardancy and waterproof performance of graphitic carbon nitride oxide. The clarified solution was placed in a refrigerator at -18 °C and frozen for 11 h, then freeze-dried to remove water, ground into a powder, added to a sealed ceramic crucible, and then calcined in a muffle furnace at 525 °C for 3.5 h. The heating-up time was controlled within 100 min. The yellow product was collected and ground. Phosphorus atom doping replaced the carbon sites in the graphitic carbon nitride oxide framework without destroying the basic morphology of graphitic carbon nitride oxide. However, after phosphorus doping, the two-dimensional layered structure showed micron-sized wrinkles, and the nanosheet layers were larger and more obvious, obtaining phosphorus-doped graphitic carbon nitride;

[0066] (2) 90 mg of zinc nitrate hexahydrate and the phosphorus-doped graphitic carbon nitride described in step (1) were poured into a methanol solution, and ultrasonic dispersion was carried out to form a uniform dispersion. Then the dispersion was poured into a 10 mL methanol solution of 2-methylimidazole, and the methanol solution of 2-methylimidazole contained 1.1 g of 2-methylimidazole. It was stirred at room temperature for 2 h, then allowed to stand for precipitation, filtered, washed, and dried. ZIF-8 zeolitic imidazole framework material was formed with zinc nitrate hexahydrate and 2-methylimidazole. ZIF-8 particles were evenly distributed on the surface of the phosphorus-doped graphitic carbon nitride and tightly bonded, obtaining a flame-retardant pore-forming composite, which not only reduced the aggregation of ZIF-8 particles but also was beneficial to the pore-forming uniformity and multi-level nature of the subsequent cross-linking reaction. Moreover, the porous protective film of the composite itself also had certain flame retardancy and waterproof performance, which was beneficial to the safety and durability of exterior wall building materials. The zinc atom content in the flame-retardant pore-forming composite was 6.1%. The presence of zinc element had a good smoke suppression effect and could combine with phosphorus and nitrogen elements to exhibit more excellent flame retardancy. At the same time, zinc element could form an oxide protective film on the material surface, thus having good waterproof performance.

[0067] A preparation method of a gasification fly ash-based geopolymer filler specifically includes the following steps:

[0068] a. The gasification fly ash was placed in a muffle furnace at 750 °C and calcined until the mass no longer changed, and then ground. There were a large number of glass microspheres on the surface of the gasification fly ash particles, and their main components were silicon dioxide and alumina. Under the action of high temperature, the original stable and ordered structure was destroyed, generating more amorphous monomers, which was beneficial to the alkali activation reaction of the gasification fly ash, leaching out the silicon and aluminum elements in the fly ash, thereby preparing a polymer with higher strength, more uniform and dense structure, and obtaining a calcined and activated material;

[0069] b. Mix sodium hydroxide, sodium silicate with 25 mL of deionized water and stir evenly. The addition amount of sodium hydroxide is 2.0 g, and the addition amount of sodium silicate is 6.0 g. Sodium silicate can effectively adjust the silicon-aluminum ratio in the reaction system, which is beneficial to the formation of uniform and stable bubble pores and has good heat preservation performance. Then, weigh 30.0 g of the alkali activator obtained above and the calcined and activated material described in step a for mixing and stirring, add 0.65 g of oleic acid foam stabilizer and 0.65 g of hydrogen peroxide foaming agent, and stir rapidly for 1.5 min at a stirring speed of 900 rpm and a shear speed of 9000 rpm. Then pour the slurry into a mold and place it in a standard curing box at 60 °C for 3 days. Under the action of sodium hydroxide, the Si-O and Al-O covalent bonds in the gasified fly ash are broken, and recombined and polycondensed to form a -SiO 4 -AlO 4 -based adhesive network-structured polysialic acid compound, which can increase the compressive strength of the polymer and also form a large number of closed small holes inside the geopolymers, effectively improving the porosity and enhancing the heat preservation performance. Therefore, by using this process method to modify the gasified fly ash, a geopolymers thermal insulation material with fire prevention, high temperature resistance, and high compressive strength is prepared, improving the current situation that organic thermal insulation materials are prone to aging and inorganic materials have poor heat insulation, and obtaining a gasified fly ash-based geopolymers filler.

[0070] This embodiment provides a preparation method of an environmentally friendly exterior wall thermal insulation porous material, which specifically includes the following steps:

[0071] S1. Add 0.9 g of nanocellulose to 100 mL of deionized water, then add 1.8 g of polyvinyl alcohol, and magnetically stir at room temperature for 24 h. Add methyltrimethoxysilane liquid to the mixed solution of polyvinyl alcohol and nanocellulose. The addition amount of methyltrimethoxysilane is 1.8 g. Methyltrimethoxysilane is both a hydrophobic modifier and a cross-linking agent, which coats the aerogel skeleton, making the connection between fibers tighter, improving the mechanical properties and structural stability of the aerogel, reducing the occurrence of pore collapse of the cellulose aerogel, and methyltrimethoxysilane can generate a silica carbon layer at high temperature, which can isolate heat and oxygen, thus playing a flame retardant role. Stir to make it evenly dispersed, then add a flame retardant pore-forming composite, and magnetically stir for 1.5 h. Under the further cross-linking action of the flame retardant pore-forming composite, the network structure of the aerogel becomes denser, significantly enhancing the pore-forming uniformity and multi-levelness, being able to effectively capture and store energy, enhancing the heat preservation performance, and the incorporation of phosphorus, nitrogen, and zinc elements in the flame retardant pore-forming composite improves the flame retardant and waterproof properties of the aerogel, obtaining a multi-dimensional pore modified aerogel solution;

[0072] S2. Pour the multi-dimensional pore modified aerogel solution described in step S1 into a silica gel mold. First, pre-freeze it in a refrigerator at 4°C for 1.5 h, add the gasified fly ash-based geopolymers filler and stir, then perform ultrasonic treatment for 1.5 h at an ultrasonic temperature of 5.5°C and an ultrasonic power of 700 W, so that the gasified fly ash-based geopolymers filler can fully enter the pores of the aerogel, further filling the pore structure of the aerogel, providing rich mesopores for the aerogel and increasing the complexity of the pores, making the micron-scale pore structure porous, multi-dimensional and multi-level, thus significantly enhancing the thermal insulation performance, waterproof performance and flame retardant performance. The network bonding structure of the gasified fly ash-based geopolymers filler also enhances the compressive strength of the aerogel, can act as a stabilizer to reduce the collapse of the pores in the aerogel, is beneficial to better exert the characteristics of thermal insulation, waterproof and fire prevention, improves the durability of the material use, and then vacuum freeze-dry at -70°C for 36 h. Place the obtained aerogel in an oven at 75°C and dry for 3.5 h to obtain the environmentally friendly exterior wall thermal insulation porous material.

[0073] Example 4

[0074] This example presents an environmentally friendly exterior wall thermal insulation porous material, including the following components in parts by weight: 10 parts of flame retardant pore-forming composite, 30 parts of gasified fly ash-based geopolymers filler, 5 parts of nanocellulose, 8 parts of methyltrimethoxysilane, and 10 parts of polyvinyl alcohol.

[0075] The flame retardant pore-forming composite includes the following components in parts by weight: 20 parts of phosphorus-doped graphitic carbon nitride and 40 parts of ZIF-8 zeolitic imidazolate framework material.

[0076] The gasified fly ash-based geopolymers filler is a thermal insulation filler obtained by calcining and activating gasified fly ash as raw materials, preparing an alkali activator with sodium hydroxide, sodium silicate and deionized water, and mixing and stirring the activated material, the alkali activator, a hydrogen peroxide foaming agent and an oleic acid foam stabilizer for synergistic modification.

[0077] The preparation method of the flame retardant pore-forming composite specifically includes the following steps:

[0078] (1) Add urea and diammonium hydrogen phosphate to 300 mL of deionized water. The addition amount of urea is 5.0 g. Stir magnetically for 3 h at a stirring speed of 600 rpm until it is completely dissolved. The addition amount of diammonium hydrogen phosphate is 0.5 g. The addition of diammonium hydrogen phosphate provides phosphorus elements, which is beneficial to improving the flame retardancy and waterproof performance of graphitic carbon nitride oxide. Place the clarified solution in a refrigerator at -18 °C and freeze it for 10 h, then freeze-dry to remove the moisture, grind it into a powder and add it to a sealed ceramic crucible, and then calcine it in a muffle furnace at 550 °C for 3 h. Control the heating time within 100 min, collect the yellow product and grind it. The phosphorus atoms are doped to replace the carbon sites in the graphitic carbon nitride oxide framework, without destroying the basic morphology of graphitic carbon nitride oxide. However, after phosphorus doping, the two-dimensional layered structure shows micron-sized wrinkles, and the nanosheets are larger and more obvious, obtaining phosphorus-doped graphitic carbon nitride;

[0079] (2) Pour 100 mg of zinc nitrate hexahydrate and the phosphorus-doped graphitic carbon nitride described in step (1) into a methanol solution, and ultrasonically disperse it to form a uniform dispersion. Then pour the dispersion into a 10 mL methanol solution of 2-methylimidazole. The methanol solution of 2-methylimidazole contains 1.2 g of 2-methylimidazole. Stir at room temperature for 2 h, then let it stand for precipitation, filter and wash, and dry. Zinc nitrate hexahydrate and 2-methylimidazole form a ZIF-8 zeolitic imidazolate framework material. The ZIF-8 particles are evenly distributed on the surface of the phosphorus-doped graphitic carbon nitride and are tightly combined, obtaining a flame-retardant pore-forming composite, which not only reduces the agglomeration of ZIF-8 particles, but also is beneficial to the pore-forming uniformity and multi-levelness of the subsequent cross-linking reaction. Moreover, the porous protective film of the composite itself also has certain flame retardancy and waterproof performance, which is beneficial to the safety and durability of exterior wall building materials. The zinc atom content in the flame-retardant pore-forming composite is 6.8%. The presence of zinc element has a good smoke suppression effect and can combine with phosphorus and nitrogen elements to exert a more excellent flame retardancy. At the same time, zinc element can form an oxide protective film on the material surface, thus having good waterproof performance.

[0080] A preparation method of a geopolymer filler for gasification fly ash base, specifically comprising the following steps:

[0081] a. Place the gasification fly ash in a muffle furnace at 800 °C and calcine it until the mass no longer changes, then grind it. There are a large number of glass microspheres on the surface of the gasification fly ash particles, and its main components are silicon dioxide and alumina. Under the action of high temperature, the original stable and ordered structure is destroyed, generating more amorphous monomers, which is beneficial to the alkali activation reaction of the gasification fly ash and leaching of silicon and aluminum elements in the fly ash, thereby preparing a polymer with higher strength, more uniform and dense structure, and obtaining a calcined activated material;

[0082] b. Mix sodium hydroxide, sodium silicate with 25 mL of deionized water and stir evenly. The addition amount of sodium hydroxide is 2.0 g, and the addition amount of sodium silicate is 6.5 g. Sodium silicate can effectively adjust the silicon-aluminum ratio in the reaction system, which is beneficial to the formation of uniform and stable bubble pores and has good heat preservation performance. Then, weigh 30.0 g of the obtained alkali activator and the calcined and activated material described in step a and mix and stir them. Add 0.7 g of oleic acid foam stabilizer and 0.7 g of hydrogen peroxide foaming agent, and quickly stir for 1 min at a stirring speed of 1000 rpm and a shear speed of 10000 rpm. Then pour the slurry into a mold and place it in a standard curing box at 60 °C for 3 days. Under the action of sodium hydroxide, the Si-O and Al-O covalent bonds in the gasified fly ash are broken, and recombined and polycondensed to form a -SiO 4 -AlO 4 -based adhesive network-structured polysialic compound, which can increase the compressive strength of the polymer, and can also form a large number of closed small holes inside the geopolymers, effectively improving the porosity and enhancing the heat preservation performance. Therefore, the gasified fly ash is modified by this process method to prepare a geopolymer thermal insulation material with fire resistance, high temperature resistance and high compressive strength, improving the current situation that organic thermal insulation materials are prone to aging and inorganic materials have poor heat insulation, and obtaining a gasified fly ash-based geopolymer filler.

[0083] This embodiment provides a preparation method of an environmentally friendly exterior wall thermal insulation porous material, which specifically includes the following steps:

[0084] S1. Add 1.0 g of nanocellulose to 100 mL of deionized water, then add 2.0 g of polyvinyl alcohol, and magnetically stir at room temperature for 24 h. Add methyltrimethoxysilane liquid to the mixed solution of polyvinyl alcohol and nanocellulose. The addition amount of methyltrimethoxysilane is 1.6 g. Methyltrimethoxysilane is both a hydrophobic modifier and a cross-linking agent, which is coated on the aerogel skeleton to make the connection between fibers tighter, improving the mechanical properties and structural stability of the aerogel, reducing the occurrence of pore collapse of the cellulose aerogel, and methyltrimethoxysilane can generate a silica carbon layer at high temperature, which can isolate heat and oxygen, thus playing a flame retardant role. Stir to make it evenly dispersed, then add a flame retardant pore-forming composite and magnetically stir for 1 h. Under the further cross-linking action of the flame retardant pore-forming composite, the network structure of the aerogel becomes denser, significantly enhancing the pore-forming uniformity and multi-levelness, being able to effectively capture and store energy, enhancing the heat preservation performance, and the incorporation of phosphorus, nitrogen, and zinc elements in the flame retardant pore-forming composite improves the flame retardant and waterproof properties of the aerogel, obtaining a multi-dimensional pore-modified aerogel solution;

[0085] S2. Pour the multi-dimensional pore modified aerogel solution described in step S1 into a silica gel mold, first pre-freeze it in a refrigerator at 4°C for 1 h, add the gasified fly ash-based geopolmer filler and stir, then perform ultrasonic treatment for 1 h at an ultrasonic temperature of 6°C and an ultrasonic power of 800 W, so that the gasified fly ash-based geopolmer filler can fully enter the pores of the aerogel, further filling the pore structure of the aerogel, providing abundant mesopores for the aerogel and increasing the complexity of the pores, making the micron-scale pore structure porous, multi-dimensional and multi-level, thus significantly enhancing the heat insulation performance, waterproof performance and flame retardant performance. The network bonding structure of the gasified fly ash-based geopolmer filler also enhances the compressive strength of the aerogel, can act as a stabilizer to reduce the collapse of the pores in the aerogel, is conducive to better exerting the heat insulation, waterproof and fireproof characteristics, improves the durability of the material use, and then vacuum freeze-dry it at -70°C for 24 h. Place the obtained aerogel in an oven at 80°C and dry it for 3 h to obtain an environmentally friendly exterior wall thermal insulation porous material.

[0086] Comparative Example 1

[0087] This comparative example provides an environmentally friendly exterior wall thermal insulation porous material, which is different from Example 1 in that the flame retardant pore-forming composite does not contain phosphorus-doped graphitic carbon nitride; the preparation method of the flame retardant pore-forming composite does not include step (1); the preparation method of the gasified fly ash-based geopolmer filler is the same as that in Example 1; the preparation method of the environmentally friendly exterior wall thermal insulation porous material is the same as that in Example 1.

[0088] Comparative Example 2

[0089] This comparative example provides an environmentally friendly exterior wall thermal insulation porous material, which is different from Example 1 in that the gasified fly ash in the gasified fly ash-based geopolmer filler is not calcined and activated; the preparation method of the flame retardant pore-forming composite is the same as that in Example 1; the preparation method of the gasified fly ash-based geopolmer filler does not include step a; the preparation method of the environmentally friendly exterior wall thermal insulation porous material is the same as that in Example 1.

[0090] Comparative Example 3

[0091] This comparative example provides an environmentally friendly exterior wall thermal insulation porous material, which is different from Example 1 in that the multi-dimensional pore modified aerogel solution does not contain methyltrimethoxysilane; the preparation method of the flame retardant pore-forming composite is the same as that in Example 1; the preparation method of the gasified fly ash-based geopolmer filler is the same as that in Example 1; in step S1 of the preparation method of the environmentally friendly exterior wall thermal insulation porous material, methyltrimethoxysilane liquid is not added to the mixed solution of polyvinyl alcohol and nanocellulose.

[0092] Experimental Example 1

[0093] Heat insulation performance experiment

[0094] Test samples: The environmentally friendly exterior wall thermal insulation porous materials prepared in Examples 1-4 and Comparative Examples 1-3.

[0095] Test method: Use a Tci thermal conductivity measuring instrument to measure the thermal conductivity (mW·m −1 ·K −1 ) of the test samples. The test is carried out in accordance with ISO22007-2.2. standard. The test method is the transient plane heat source method (TPS). Under normal temperature and pressure conditions, 3 parallel samples are tested for each sample, and the results are averaged. The smaller the thermal conductivity, the better the thermal insulation performance.

[0096] Figure 2 Fig. is the graph of the thermal conductivity results of Examples 1-4 and Comparative Examples 1-3; as shown in the figure, the thermal conductivity of Examples 1-4 is 33.1-34.8 mW·m −1 ·K −1 , indicating good thermal insulation performance; the thermal conductivity of Comparative Examples 1-3 is 42.5-48.9 mW·m −1 ·K −1 , indicating poor thermal insulation performance; the flame-retardant pore-forming composite in Comparative Example 1 does not contain phosphorus-doped graphitic carbon nitride, which cannot reduce the agglomeration of ZIF-8 particles, is not conducive to the uniformity and hierarchy of pore formation, and results in poor thermal insulation performance; the gasified fly ash-based geopolymers filler in Comparative Example 2 does not calcine and activate the gasified fly ash, and cannot better leach out the silicon and aluminum elements in the fly ash, which is not conducive to the alkali activation reaction of the gasified fly ash, and thus is not conducive to the formation of a uniform and dense polymer, resulting in poor thermal insulation performance; the multi-dimensional pore-modified aerogel solution in Comparative Example 3 does not contain methyltrimethoxysilane, which cannot play the role of a cross-linking agent, is not conducive to the stability of the aerogel structure, and is not conducive to further cross-linking reactions, weakening the complexity of the pores and resulting in poor thermal insulation performance.

[0097] Experimental Example 2

[0098] Flame retardancy experiment

[0099] Test samples: The environmentally friendly exterior wall thermal insulation porous materials prepared in Examples 1-4 and Comparative Examples 1-3.

[0100] Test method: Use a JF-5 limiting oxygen index tester to measure the limiting oxygen index (LOI) of the test samples. The test is carried out in accordance with GB / T8924-2005. 5 samples are tested in each group, and the results are averaged. The larger the limiting oxygen index, the stronger the flame retardancy.

[0101] Figure 3Graph of limiting oxygen index results for Examples 1-4 and Comparative Examples 1-3; as shown in the figure, the limiting oxygen index of Examples 1-4 is 40.3-42.1%, indicating strong flame retardancy; the limiting oxygen index of Comparative Examples 1-3 is 31.8-37.6%, indicating weak flame retardancy; the flame-retardant pore-forming composite of Comparative Example 1 does not contain phosphorus-doped graphitic carbon nitride, and phosphorus and nitrogen elements cannot be introduced to play a flame-retardant role, nor is it conducive to the uniform dispersion of ZIF-8, limiting the flame retardancy of the ZIF-8 zeolitic imidazolate framework material and resulting in weak flame retardancy; the gasified fly ash-based geopolymers filler of Comparative Example 2 does not calcine and activate the gasified fly ash, which is not conducive to the formation of a bonding network structure of polysialate compounds, cannot better fill the pore structure of the aerogel, and is not conducive to increasing the complexity of the pores, resulting in weak flame retardancy; the multi-dimensional pore-modified aerogel solution of Comparative Example 3 does not contain methyltrimethoxysilane, which can neither play its own flame-retardant role nor is it conducive to the stability and porosity of the aerogel structure, resulting in weak flame retardancy.

[0102] Experimental Example 3

[0103] Waterproof performance experiment

[0104] Test samples: The environmentally friendly exterior wall thermal insulation porous materials prepared in Examples 1-4 and Comparative Examples 1-3.

[0105] Test method: Use an OCA15EC type contact angle tester to measure the water contact angle of the test samples. Using the sessile drop method, deposit 5 μL of water droplets on the surface of the samples, take horizontal photos of the droplets from 4 directions, measure the surface water contact angle 3 times in parallel, and take the average value. The larger the contact angle, the better the waterproof performance.

[0106] Figure 4 Graph of contact angle results for Examples 1-4 and Comparative Examples 1-3; as shown in the figure, the contact angle of Examples 1-4 is 135.3-138.2°, indicating good waterproof performance; the contact angle of Comparative Examples 1-3 is 116.5-124.7°, indicating average waterproof performance; the flame-retardant pore-forming composite of Comparative Example 1 does not contain phosphorus-doped graphitic carbon nitride, and water cannot be isolated through the wrinkled nanosheet structure, nor is it conducive to the hydrophobicity of the ZIF-8 zeolitic imidazolate framework material, resulting in average waterproof performance; the gasified fly ash-based geopolymers filler of Comparative Example 2 does not calcine and activate the gasified fly ash, which is not conducive to the formation of a bonding network structure of polymers, so that the pore structure of the aerogel cannot have porosity, multi-dimensionality and multi-levelness, weakening the barrier to moisture and resulting in average waterproof performance; the multi-dimensional pore-modified aerogel solution of Comparative Example 3 does not contain methyltrimethoxysilane, which cannot perform hydrophobic modification on the polyvinyl alcohol and nanocellulose aerogel, nor is it conducive to the stability and porosity of the aerogel structure, thus limiting the barrier effect on moisture and resulting in average waterproof performance.

[0107] The above experimental results show that the heat preservation performance, flame retardant performance and waterproof performance of Examples 1-4 of the present invention are significantly better than those of the samples of Comparative Examples 1-3. Among them, Example 1 using the flame retardant pore-forming composite and the gasified fly ash-based geopolymers filler has better heat preservation performance, stronger flame retardant performance and better waterproof performance. The polyvinyl alcohol and nanocellulose aerogel are modified with the flame retardant pore-forming composite and methyltrimethoxysilane. Methyltrimethoxysilane is used as a cross-linking agent and a hydrophobic modifier to coat on the aerogel skeleton, which enhances the structural stability and endows it with hydrophobicity and flame retardancy. Then, the flame retardant pore-forming composite further cross-links to enhance the uniformity and multi-level nature of pore formation, which can effectively capture and store energy and enhance the heat preservation performance. The gasified fly ash is modified to obtain a polysialic compound with a bonding network structure based on -SiO 4 -AlO 4 and filled into the multi-dimensional pore modified aerogel solution, which increases the surface pore structure and compressive strength of the aerogel, making the pore structure of the aerogel porous, multi-dimensional and multi-level. The gasified fly ash-based geopolymers filler can also be used as a stabilizer to reduce the collapse of pores in the aerogel, significantly enhancing the heat preservation performance, waterproof performance and flame retardant performance of the material.

[0108] Although the embodiments of the present invention have been shown and described, for those of ordinary skill in the art, it can be understood that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention.

[0109] The present invention and its implementation manners have been described above. This description is not restrictive. What is shown in the drawings is only one of the implementation manners of the present invention, and the actual application is not limited thereto. Generally speaking, if those of ordinary skill in the art are inspired by it and design similar ways and embodiments to this technical solution without creative work without departing from the purpose of the present invention, they shall fall within the protection scope of the present invention.

Claims

1. An environmentally friendly exterior wall thermal insulation porous material, characterized by: The environmentally friendly exterior wall thermal insulation porous material comprises the following components in parts by weight: 10-20 parts of a flame retardant pore-forming compound, 30-40 parts of a gasified fly ash-based geopolymer filler, 4-5 parts of nanocellulose, 8-10 parts of methyltrimethoxysilane, and 8-10 parts of polyvinyl alcohol; the flame retardant pore-forming compound comprises the following components in parts by weight: 10-20 parts of phosphorus-doped graphite-like carbon nitride, and 30-40 parts of a ZIF-8 zeolite imidazole framework material; the gasified fly ash-based geopolymer filler is a thermal insulation filler obtained by calcining and activating gasified fly ash as a raw material, using sodium hydroxide, sodium silicate and deionized water to form an alkali activator, mixing and stirring the activated material, the alkali activator, a hydrogen peroxide foaming agent and an oleic acid foam stabilizer, and synergistically modifying the material.

2. A method for preparing the environmentally friendly exterior wall thermal insulation porous material according to claim 1, characterized in that: The specific steps include: S1. Add 0.8-1.0 g of nanocellulose to 100 mL of deionized water, then add 1.6-2.0 g of polyvinyl alcohol, and stir magnetically at room temperature for 24 h. Add methyltrimethoxysilane liquid to the mixture of polyvinyl alcohol and nanocellulose, stir to make it evenly dispersed, then add the flame-retardant pore-forming composite, and stir magnetically for 1-2 h to obtain a multidimensional pore-modified aerogel solution. S2. Pour the multidimensional pore modified aerogel solution described in step S1 into a silica gel mold, pre-freeze it in a refrigerator at 4°C for 1-2h, add gasified fly ash-based geopolymer filler and stir it, then ultrasonically treat it for 1-2h, the ultrasonic temperature is 5-6°C, the ultrasonic power is 600-800W, and then vacuum freeze-dried at -70°C for 24-48h. The obtained aerogel is placed in an oven at 70-80°C and dried for 3-4h to obtain an environmentally friendly exterior wall thermal insulation porous material.

3. The method for preparing the environmentally friendly exterior wall thermal insulation porous material according to claim 2, characterized in that: In step S1, the amount of methyltrimethoxysilane added is 1.6-2.0 g.

4. The method for preparing the environmentally friendly exterior wall thermal insulation porous material according to claim 3, characterized in that: The method for preparing the flame-retardant pore-forming composite specifically comprises the following steps: (1) Urea and diammonium hydrogen phosphate are added to 200-300 mL of deionized water, the amount of urea added is 5.0 g, and magnetic stirring is performed for 3-4 hours at a stirring speed of 500-600 rpm to completely dissolve the urea. The clarified solution is placed in a refrigerator at -18°C for 10-12 hours, and then freeze-dried to remove moisture. The powder is added to a sealed ceramic crucible, and then calcined in a muffle furnace at 500-550°C for 3-4 hours, and the heating time is controlled within 100 minutes. The yellow product is collected and ground to obtain phosphorus-doped graphite-like carbon nitride; (2) Pour 80-100 mg of zinc nitrate hexahydrate and the phosphorus-doped graphite-like carbon nitride described in step (1) into a methanol solution, disperse them by ultrasonication to form a uniform dispersion, then pour the dispersion into 10 mL of a 2-methylimidazole methanol solution containing 1.0-1.2 g of 2-methylimidazole, stir at room temperature for 2 h, then allow to stand and precipitate, filter, wash, and dry to obtain a flame-retardant pore-forming composite.

5. The method for preparing the environmentally friendly exterior wall thermal insulation porous material according to claim 4, characterized in that: In step (1), the amount of diammonium hydrogen phosphate added is 0.3-0.5 g.

6. The method for preparing the environmentally friendly exterior wall thermal insulation porous material according to claim 5, characterized in that: In step (2), the content of zinc atoms in the flame retardant pore-forming composite is 5.4-6.8%.

7. The method for preparing the environmentally friendly exterior wall thermal insulation porous material according to claim 6, characterized in that: The method for preparing the gasified fly ash-based geopolymer filler specifically comprises the following steps: a. Place the gasified fly ash in a muffle furnace at 700-800°C and calcine until the mass no longer changes, then grind to obtain a calcined activated material; b. Mix sodium hydroxide and sodium silicate with 25 mL of deionized water and stir evenly. The amount of sodium hydroxide added is 2.0 g. Then weigh 30.0 g of the obtained alkali activator and the calcined activated material described in step a and mix and stir. Add 0.6-0.7 g of oleic acid foam stabilizer and 0.6-0.7 g of hydrogen peroxide foaming agent. Stir rapidly for 1-2 min at a stirring speed of 800-1000 rpm and a shear rate of 8000-10000 rpm. Then pour the slurry into a mold and put it into a standard curing box at 60° C. for curing for 3 days to obtain a gasified fly ash-based geopolymer filler.

8. The method for preparing the environmentally friendly exterior wall thermal insulation porous material according to claim 7, characterized in that: In step b, the amount of sodium silicate added is 5.5-6.5 g.

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