A surface-hydrophobically modified gypsum-aerogel composite thermal insulation material, its preparation method and application

Abstract

This invention discloses a method for preparing a surface-hydrophobically modified gypsum-aerogel composite thermal insulation material. The method includes the following steps: calcining and aging gypsum (CaSO4·2H2O) to obtain gypsum powder (CaSO4·0.5H2O); mixing the gypsum powder (CaSO4·0.5H2O) with hydrophilic aerogel powder (0.01–0.02 W / (m·K) by mass ratio of 3–6, adding water, molding, curing, and drying to obtain a hydrophilic gypsum-aerogel composite material; immersing the hydrophilic gypsum-aerogel composite material in a silane coupling agent solution, and drying after modification to obtain a surface-hydrophobic gypsum-aerogel composite material. This invention overcomes the problems of difficult mixing and poor compatibility between traditional hydrophobic aerogels and gypsum, achieving surface hydrophobic modification without affecting thermal insulation performance and strength, increasing the softening coefficient of gypsum, and broadening the application range of gypsum-based materials in humid environments.

Description

Technical Field

[0001] This invention belongs to the field of solid waste resource utilization technology, specifically relating to a surface-hydrophobically modified gypsum-aerogel composite thermal insulation material, its preparation method and application. Background Technology

[0002] With the continuous development of my country's industry, the output of industrial by-product gypsum has been increasing year by year, currently reaching approximately 220 million tons annually, with accumulated stockpiles exceeding 1 billion tons, causing serious land occupation problems and posing potential environmental pollution risks. Using industrial by-product gypsum as a raw material to prepare gypsum-based building materials is a relatively mature resource utilization method. Compared to cement, lime, and other cementing materials, it has lower energy consumption, lower carbon emissions, and certain thermal insulation properties, with a thermal conductivity of approximately 0.3-0.5 W / (m·K). However, this still falls short of the performance requirements for building insulation materials. Composites of gypsum as the main material with lightweight aggregates can enhance the thermal insulation performance of gypsum-based materials, resulting in lightweight insulation materials that have gained recognition and application in the construction field. Compared to traditional lightweight aggregates, aerogels exhibit excellent thermal insulation performance, with a thermal conductivity as low as 0.02 W / (m·K), effectively improving the thermal insulation performance of gypsum products, enabling them to meet the standards of thermal insulation building materials, and realizing the resource utilization of industrial by-product gypsum.

[0003] Chinese invention patent (publication number CN1 13461404A) discloses a SiO2 aerogel-gypsum-based thermal insulation material and its preparation method. This method does not use any other additives; it directly incorporates hydrophobic SiO2 aerogel into gypsum for co-hydration, and after drying, obtains a SiO2 aerogel-gypsum-based thermal insulation material with good thermal insulation performance. However, during the mixing process, the aerogel tends to float and aggregate, exhibiting poor compatibility with gypsum. The resulting product contains numerous honeycomb pores, has poor aesthetics, and is unsuitable for direct use.

[0004] Chinese invention patent (publication number CN1 13429184A) discloses a paper-faced gypsum board and its preparation method. This method involves mixing and granulating aerogel with clay, then incorporating the resulting aerogel particles into gypsum building materials, thus solving the problem of poor compatibility between aerogel and the gypsum matrix. The resulting aerogel gypsum board has a dense structure and good thermal insulation performance. However, granulating aerogel powder is difficult, requiring the addition of various binders and foaming agents, making the process complex.

[0005] Chinese invention patent (publication number CN1 16143486A) discloses a thermal insulation gypsum and its preparation method. This method, with the assistance of a retarder and an air-entraining agent, achieves uniform dispersion of aerogel in the gypsum through a combination of vacuum stirring and atmospheric pressure stirring, thus enhancing the material's thermal insulation performance. However, the material's hydrophobicity remains unimproved; water absorption easily leads to a decrease in mechanical strength and thermal insulation performance, limiting its application in humid environments.

[0006] In summary, in practical applications, hydrophobic aerogels are typically chosen as raw materials to ensure that gypsum-based composites maintain high thermal insulation performance in humid environments. However, hydrophobic aerogels and gypsum have several drawbacks during mixing, including easy floating, difficulty in co-hydration, and poor compatibility. Furthermore, the addition of hydrophobic aerogels does not alter the overall hydrophilicity of the composite material, and water absorption can lead to a decrease in mechanical strength and thermal insulation performance, thus limiting their application in humid environments. Summary of the Invention

[0007] To address the shortcomings of existing technologies, this invention provides a surface-modified hydrophobic gypsum-aerogel composite insulation material, its preparation method, and its application. The purpose is to circumvent the technical problems in existing technologies, such as poor compatibility between hydrophobic aerogel and gypsum, and the reduction in mechanical strength and insulation performance of the product after water absorption. The result is a gypsum-aerogel composite insulation material with good insulation performance, a smooth surface, and hydrophobicity.

[0008] According to a first aspect of the present invention, a method for preparing a surface-hydrophobically modified gypsum-aerogel composite thermal insulation material is provided, characterized by comprising the following steps:

[0009] (1) Mix gypsum powder with a purity of 85% to 95% CaSO4·0.5H2O and hydrophilic aerogel powder with a thermal conductivity of 0.01 to 0.02 W / (m·K) at a mass ratio of 3 to 6, then add water, mold and cure, and then dry at 40 to 60°C to obtain a hydrophilic gypsum-aerogel composite material.

[0010] (2) The hydrophilic gypsum-aerogel composite material is modified by immersing it in a silane coupling agent solution and then dried to obtain a hydrophobic gypsum-aerogel composite material.

[0011] Preferably, the CaSO4·0.5H2O gypsum powder is obtained by calcining and aging gypsum containing CaSO4·2H2O, wherein the calcination temperature is 140-180℃, the calcination time is 1-4 hours, and the aging time is 1-3 days.

[0012] Preferably, the gypsum containing CaSO4·2H2O is one or more of desulfurized gypsum, phosphogypsum, fluorogypsum, and citric acid gypsum.

[0013] Preferably, the hydrophilic aerogel powder material is selected from one or more of silica aerogel, alumina aerogel, and carbon aerogel, and the pore size of the hydrophilic aerogel powder is 20-40 nm.

[0014] Preferably, in step (1), the ratio of the volume of water added to the sum of the weights of the gypsum powder of CaSO4·0.5H2O and the hydrophilic aerogel powder is 1.2-1.8 mL / g.

[0015] Preferably, in step (1), the curing conditions for injection molding are: curing temperature of 15-25℃, relative humidity of 80%-90%, and curing time of 1-3 days.

[0016] Preferably, in step (2), the silane coupling agent solution is prepared by adding a silane coupling agent to a solvent, wherein the silane coupling agent is selected from one or more of trimethylchlorosilane, octadecyltrichlorosilane, and methyltrimethoxysilane, and the volume ratio of the solvent to the silane coupling agent is 80 to 100.

[0017] Preferably, in step (2), the mass-to-volume ratio of the hydrophilic gypsum-aerogel composite material to the silane coupling agent solution is 1.0–1.5 g / mL, and the soaking time is 3–5 h.

[0018] According to another aspect of the present invention, a method for preparing the surface-hydrophobic modified gypsum-aerogel composite thermal insulation material is provided to obtain a surface-hydrophobic gypsum-aerogel composite material.

[0019] According to another aspect of the invention, the application of the aforementioned hydrophobic gypsum-aerogel composite material is provided, wherein the hydrophobic gypsum-aerogel composite material is used as an interior insulation material for buildings.

[0020] The principle of this invention is as follows: First, industrial by-product gypsum rich in CaSO4·2H2O is calcined, aged, and then dehydrated to obtain industrial by-product building gypsum powder rich in CaSO4·0.5H2O. This CaSO4·0.5H2O-rich industrial by-product building gypsum powder is then mixed with hydrophilic aerogel powder, and water is added. The hydrophilic aerogel powder is physically incorporated into the CaSO4·0.5H2O-rich industrial by-product building gypsum powder. The hydrophilic aerogel does not participate in the hydration of the gypsum and remains in a nano-network structure. After the CaSO4·0.5H2O-rich industrial by-product building gypsum powder is added to water and undergoes complete hydration, all of the CaSO4·0.5H2O is converted to CaSO4·2H2O. The resulting hydrophilic gypsum-aerogel composite material is then impregnated and modified using a silane coupling agent solution. The water of crystallization in the gypsum can interact with water molecules or other polar molecules in the air through hydrogen bonds to form hydroxyl groups. The Si-Cl bond in the silane coupling agent molecule can be hydrolyzed to generate Si-OH groups. The generated Si-OH groups can dehydrate with the hydroxyl groups on the gypsum surface to form stable Si-O-Si bonds. In this way, the hydrophobic alkyl network on the silane coupling agent is grafted onto the gypsum surface, thereby obtaining a hydrophobic gypsum-aerogel composite material.

[0021] In summary, compared with the prior art, the above-described technical solutions conceived by this invention mainly possess the following technical advantages:

[0022] (1) This invention mixes a hydrophilic aerogel with a thermal conductivity of 0.01–0.02 W / (m·K) with industrial by-product building gypsum rich in CaSO4·0.5H2O. By externally adding the low thermal conductivity hydrophilic aerogel, the thermal insulation performance of the gypsum substrate is improved. Since the hydrophilic aerogel combines with the industrial by-product gypsum in the form of physical doping, the hydrophilic aerogel does not participate in the hydration of the gypsum. Therefore, the hydrophilic aerogel still exists in a nano-network structure, increasing the heat transfer path and resulting in a larger overall thermal resistance of the material, which can significantly improve the thermal insulation performance of the gypsum substrate. This method aims to improve the thermal insulation performance of gypsum materials. The hydrophilic aerogel with a pore size distribution of 20–40 nm is chosen because this pore size is smaller than the mean free path of air under standard conditions (69 nm). These nanoscale pores severely restrict the free movement of molecules, thereby significantly reducing the thermal conductivity of the gas and improving the material's thermal insulation performance. Furthermore, due to the good compatibility between hydrophilic aerogel and gypsum, uniform mixing of the aerogel and gypsum can be achieved without the addition of external chemical reagents, solving the problems of difficult mixing and poor compatibility between hydrophobic aerogel and gypsum.

[0023] (2) The present invention achieves hydrophobic modification of the surface of the hydrophilic gypsum-aerogel composite material by adding an external hydrophobic modifier silane coupling agent for soaking treatment, thereby achieving overall hydrophobicity of the composite material. At the same time, the modification process does not involve the destruction of the internal structure of the material, so it does not have a significant impact on the mechanical strength and thermal insulation performance of the composite material.

[0024] (3) The purpose of preparing industrial by-product building gypsum powder of CaSO4·0.5H2O is to obtain a material with high mechanical strength. CaSO4·0.5H2O has a fast hydration rate and the generated crystals are intersected by faults, which is the main source of strength of industrial by-product gypsum. When the content of dihydrate gypsum is high, it will significantly reduce the strength of desulfurized building gypsum. When the content of anhydrous gypsum is too high, it will lead to the initial setting of desulfurized building gypsum being too short, making it impossible to process and use the calcined gypsum. Since aerogel does not have structural strength, the mechanical strength of the composite material is reduced accordingly after being mixed with gypsum. Therefore, the use of CaSO4·0.5H2O is crucial to the strength of the composite material after molding.

[0025] (4) This invention selects industrial by-product gypsum rich in CaSO4·2H2O as the raw material for surface hydrophobic modified gypsum-aerogel composite thermal insulation material, thereby making resource utilization of industrial by-product gypsum and avoiding resource waste. At the same time, the prepared thermal insulation material can be used in the field of building thermal insulation, providing a new choice for building energy-saving materials in my country.

[0026] (5) The hydrophobic gypsum-aerogel composite material obtained by this invention has a thermal conductivity as low as 0.08 W / (m·K), while its compressive and flexural strengths remain above 1.8 MPa and 0.7 MPa, respectively, meeting the Type II standard specified in GB / T20473-2021 "Building Thermal Insulation Mortar". Simultaneously, the static water contact angle can reach 120°, and the softening coefficient can reach above 0.8, sufficient to resist humid environments. Furthermore, the resulting hydrophobic gypsum-aerogel composite material has a smooth surface, free of irregular pores, and exhibits good aesthetics. Attached Figure Description

[0027] Figure 1 This is a process flow diagram of the present invention;

[0028] Figure 2 The diagram illustrates the principle of surface hydrophobic modification of hydrophilic gypsum-aerogel composites, using trimethylchlorosilane and octadecyltrichlorosilane as examples.

[0029] Figure 3 (a) Morphology of the hydrophobic gypsum-aerogel composite material prepared in Example 1, and (b) Static water contact angle of the surface;

[0030] Figure 4(a) Morphology of the gypsum-aerogel composite material prepared for Comparative Example 3, and (b) Static water contact angle of the surface.

[0031] Figure 5 XRD pattern of surface-hydrophobically modified gypsum-aerogel composite insulation material Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0033] Example 1:

[0034] Preparation of surface-hydrophobically modified gypsum-aerogel composite insulation materials:

[0035] (1) Desulfurized gypsum (from Lanxi Power Plant in Zhejiang Province, the same below) was calcined in an oven at 160°C for 3 hours and then aged in an environment at 20°C and 80% relative humidity for 2 days to obtain desulfurized building gypsum powder.

[0036] (2) After dry mixing and stirring the desulfurized building gypsum powder and silica hydrophilic aerogel powder (thermal conductivity of 0.018 W / (m·K)) evenly, mix them according to the water-to-powder ratio (V 水 :m (脱硫建筑石膏粉+亲水气凝胶粉末) Add water at a concentration of 1.8 mL / g and stir to obtain a gypsum-aerogel mixture.

[0037] (3) After the gypsum-aerogel mixture is poured into a mold, it is cured in an environment of 20°C and 80% relative humidity for 3 days and then dried to obtain a hydrophilic gypsum-aerogel composite material.

[0038] (4) Octadecyltrichlorosilane was dissolved in n-hexane to obtain an octadecyltrichlorosilane solution. The hydrophilic gypsum-aerogel composite material was immersed in the octadecyltrichlorosilane solution for 5 hours at a mass-volume ratio of 1.0 g / mL. The volume ratio of the solvent n-hexane to octadecyltrichlorosilane was 80 v / v. After modification, the gypsum-aerogel composite material with a hydrophobic surface was obtained by drying.

[0039] Example 2:

[0040] The difference between this embodiment and Embodiment 1 is that the phosphogypsum, calcination temperature, calcination time, aging time, and water-to-powder ratio were selected.

[0041] (1) Phosphogypsum (from Hubei Xingfa Group, the same below) was calcined in an oven at 140°C for 4 hours and then aged in an environment at 20°C and 80% relative humidity for 1 day to obtain phosphogypsum powder.

[0042] (2) Phosphorus building gypsum powder and silica hydrophilic aerogel (purchased from Wuzhen Technology Group Hebei Co., Ltd., the same below) with a thermal conductivity of 0.018W / (m·K) were dry-mixed and stirred evenly. Water was added at a water-powder ratio of 1.2mL / g and stirred to obtain gypsum-aerogel mixed slurry.

[0043] (3) After the gypsum-aerogel mixture is poured into a mold, it is cured in an environment of 20°C and 80% relative humidity for 3 days and then dried to obtain a hydrophilic gypsum-aerogel composite material.

[0044] (4) Octadecyltrichlorosilane was dissolved in n-hexane to obtain an octadecyltrichlorosilane solution. The hydrophilic gypsum-aerogel composite material was immersed in the octadecyltrichlorosilane solution for 5 hours at a mass-volume ratio of 1.0 g / mL. The volume ratio of the solvent n-hexane to octadecyltrichlorosilane was 80 v / v. After modification, the gypsum-aerogel composite material with a hydrophobic surface was obtained by drying.

[0045] Example 3:

[0046] The difference between this embodiment and Embodiment 1 is that different calcination temperatures, aging times, curing times, silane coupling agents, and impregnation times were selected.

[0047] (1) Desulfurized gypsum was calcined in an oven at 180°C for 3 hours and then aged in an environment at 20°C and 80% relative humidity for 3 days to obtain desulfurized building gypsum powder.

[0048] (2) After dry mixing and stirring the desulfurized building gypsum powder and silica hydrophilic aerogel (thermal conductivity of 0.018 W / (m·K)) evenly, add water at a water-powder ratio of 1.8 mL / g and stir to obtain gypsum-aerogel mixed slurry;

[0049] (3) After the gypsum-aerogel mixture is poured into a mold, it is cured in an environment of 20°C and 80% relative humidity for 1 day and then dried to obtain a hydrophilic gypsum-aerogel composite material.

[0050] (4) Trimethylchlorosilane was dissolved in n-hexane to obtain a trimethylchlorosilane solution. The hydrophilic gypsum-aerogel composite material was soaked in the trimethylchlorosilane solution for 5 hours at a mass-volume ratio of 1.0 g / mL. The volume ratio of the solvent n-hexane to trimethylchlorosilane was 80 v / v. After modification, the gypsum-aerogel composite material with a hydrophobic surface was obtained by drying.

[0051] Example 4:

[0052] The difference between this embodiment and Embodiment 1 is that different calcination times, water-to-powder ratios, hydrophobic modifier ratios, hydrophobic modifier addition mass-to-volume ratios, and impregnation times were selected.

[0053] (1) Desulfurized gypsum was calcined in an oven at 160°C for 1 hour and then aged in an environment at 20°C and 80% relative humidity for 2 days to obtain desulfurized building gypsum powder.

[0054] (2) After dry mixing and stirring the desulfurized building gypsum powder and silica hydrophilic aerogel (thermal conductivity of 0.018 W / (m·K)) evenly, add water at a water-powder ratio of 1.2 mL / g and stir to obtain gypsum-aerogel mixed slurry;

[0055] (3) After the gypsum-aerogel mixture is poured into a mold, it is cured in an environment of 20°C and 80% relative humidity for 3 days and then dried to obtain a hydrophilic gypsum-aerogel composite material.

[0056] (4) Octadecyltrichlorosilane was dissolved in n-hexane to obtain an octadecyltrichlorosilane solution. The hydrophilic gypsum-aerogel composite material was immersed in the octadecyltrichlorosilane solution for 5 hours at a mass-volume ratio of 1.5 g / mL. The volume ratio of the solvent n-hexane to octadecyltrichlorosilane was 100 v / v. After modification, the gypsum-aerogel composite material with a hydrophobic surface was obtained by drying.

[0057] Comparative Example 1:

[0058] The difference between this comparative example and Example 1 is that no hydrophilic aerogel was added. The specific steps are as follows:

[0059] (1) Desulfurized gypsum was calcined in an oven at 160°C for 3 hours and then aged in an environment at 20°C and 80% relative humidity for 2 days to obtain desulfurized building gypsum powder.

[0060] (2) Add water to the desulfurized building gypsum powder at a water-to-powder ratio of 0.6 mL / g and stir to obtain gypsum slurry;

[0061] (3) After the gypsum slurry is poured into the mold, it is cured in an environment of 20°C and 80% relative humidity for 2 days and then dried to obtain a gypsum material with a hydrophilic surface.

[0062] (4) Octadecyltrichlorosilane was dissolved in n-hexane to obtain an octadecyltrichlorosilane solution. The hydrophilic gypsum-aerogel composite material was immersed in the octadecyltrichlorosilane solution for 5 hours at a mass-volume ratio of 1.0 g / mL. The volume ratio of the solvent n-hexane to octadecyltrichlorosilane was 80 v / v. After modification, the gypsum-aerogel composite material was dried to obtain a hydrophobic gypsum-aerogel composite material.

[0063] Comparative Example 2:

[0064] The difference between this comparative example and Example 1 is that the hydrophobic impregnation modification step is not performed. The specific steps are as follows:

[0065] (1) Desulfurized gypsum was calcined in an oven at 160°C for 3 hours and then aged in an environment at 20°C and 80% relative humidity for 2 days to obtain desulfurized building gypsum powder.

[0066] (2) After dry mixing and stirring the desulfurized building gypsum powder and silica hydrophilic aerogel (thermal conductivity of 0.018 W / (m·K)) evenly, add water at a water-powder ratio of 1.8 mL / g and stir to obtain gypsum-aerogel mixed slurry;

[0067] (3) After the gypsum-aerogel mixture is molded, it is cured for 2 days at 20°C and 80% relative humidity and then dried to obtain a gypsum-aerogel composite material with a hydrophilic surface.

[0068] Comparative Example 3:

[0069] The difference between this comparative example and Example 1 is that a silica hydrophobic aerogel (purchased from Needleless Technology Group Hebei Co., Ltd.) was added, and the hydrophobic impregnation modification step was not performed. The specific steps are as follows:

[0070] (1) Desulfurized gypsum was calcined in an oven at 160°C for 3 hours and then aged in an environment at 20°C and 80% relative humidity for 2 days to obtain desulfurized building gypsum powder.

[0071] (2) After dry mixing and stirring the desulfurized building gypsum powder and hydrophobic aerogel (thermal conductivity of 0.015 W / (m·K)) evenly, add water at a water-powder ratio of 0.9 mL / g and stir to obtain gypsum-aerogel mixed slurry;

[0072] (3) After the gypsum-aerogel mixture is cast into a mold, it is cured for 2 days at 20°C and 80% relative humidity and then dried to obtain the gypsum-aerogel composite material.

[0073] The silica hydrophilic aerogel used in Examples 1-4 and the silica hydrophobic aerogel used in Comparative Example 3 have the following data on density, thermal conductivity and pore structure: Table 1.

[0074] Table 1. Aerogel density, thermal conductivity, and pore structure data

[0075]

[0076] Note: S BET - Specific surface area (m²) 2 / g); V T - Pore volume (cm³) 3 / g); D - average pore size (nm).

[0077] Comparative analysis of experimental results: Table 2 shows the mechanical strength, density, thermal conductivity, softening coefficient, and surface water contact angle of the gypsum-aerogel composite materials prepared in Examples 1-4 and Comparative Examples 1-3. By adding hydrophilic aerogel, the thermal conductivity of the gypsum material decreased from 0.491 W / (m·K) to 0.080 W / (m·K), a reduction of over 80%, resulting in a significant improvement in thermal insulation performance. Simultaneously, the compressive and flexural strengths remained above 1.8 and 0.7 MPa, respectively. Through hydrophobic impregnation modification, the hydrophobic properties of the gypsum-aerogel composite material were significantly improved, with the softening coefficient increasing from 0.34 to over 0.80 and the contact angle increasing from 0° to over 120°, without significantly affecting the mechanical and thermal insulation properties of the gypsum-aerogel composite material. Compared to existing processes that directly incorporate hydrophobic aerogel into gypsum to obtain composite materials, the finished industrial by-product gypsum-aerogel composite insulation material obtained by this method has a smooth surface, no irregular pores, good aesthetics, and excellent hydrophobic properties, which are sufficient to resist humid environments. Figure 3 (a) shows the morphology of the surface-modified hydrophobic gypsum-aerogel composite insulation material prepared in Example 1. Figure 3 (b) shows the static water contact angle of the surface of the hydrophobically modified gypsum-aerogel composite insulation material prepared in Example 1; Figure 4 (a) shows the morphology of the industrial by-product gypsum-hydrophobic aerogel composite insulation material prepared in Comparative Example 3. Figure 4 (b) shows the static water contact angle of the surface of the industrial by-product gypsum-hydrophobic aerogel composite insulation material prepared in Comparative Example 3; Figure 5 The XRD characterization diagram of the surface-hydrophobically modified gypsum-aerogel composite insulation material shows that hydrophilic CaSO4·2H2O exists in the surface-hydrophobically modified gypsum-aerogel composite insulation material.

[0078] Table 2. Mechanical strength, density, thermal conductivity, softening coefficient, and surface water contact angle of gypsum-aerogel composite materials prepared in different embodiments.

[0079]

[0080]

[0081] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a surface-hydrophobically modified gypsum-aerogel composite thermal insulation material, characterized in that, Includes the following steps: (1) Mix CaSO4·0.5H2O gypsum powder with a purity of 85%~95% with hydrophilic aerogel powder with a thermal conductivity of 0.01~0.02 W / (m·K) at a mass ratio of 3~6, ​​then add water, mold and cure, and then dry at 40-60℃ to obtain a hydrophilic gypsum-aerogel composite material; the ratio of the volume of water added to the sum of the weights of the CaSO4·0.5H2O gypsum powder and the hydrophilic aerogel powder is 1.2~1.8 mL / g; (2) The hydrophilic gypsum-aerogel composite material is modified by immersing it in a silane coupling agent solution and then dried to obtain a hydrophobic gypsum-aerogel composite material. The hydrophilic aerogel powder material is selected from one or more of silica aerogel, alumina aerogel, and carbon aerogel, and the pore size of the hydrophilic aerogel powder is 20~40nm.

2. The method for preparing a surface-modified hydrophobic gypsum-aerogel composite thermal insulation material according to claim 1, characterized in that, The CaSO4·0.5H2O gypsum powder is obtained by calcining and aging gypsum containing CaSO4·2H2O. The calcination temperature is 140~180℃, the calcination time is 1~4 h, and the aging time is 1~3 days.

3. The preparation method of a surface-hydrophobically modified gypsum-aerogel composite thermal insulation material according to claim 2, characterized in that, The gypsum containing CaSO4·2H2O is one or more of desulfurized gypsum, phosphogypsum, fluorogypsum, and citric acid gypsum.

4. The method for preparing a surface-hydrophobically modified gypsum-aerogel composite thermal insulation material according to claim 3, characterized in that, In step (1), the curing conditions for injection molding are: curing temperature of 15~25 ℃, relative humidity of 80%~90%, and curing time of 1~3 days.

5. The preparation method of a surface-modified hydrophobic gypsum-aerogel composite thermal insulation material according to claim 4, characterized in that, In step (2), the silane coupling agent solution is prepared by adding the silane coupling agent to a solvent. The silane coupling agent is selected from one or more of trimethylchlorosilane, octadecyltrichlorosilane, and methyltrimethoxysilane. The volume ratio of the solvent to the silane coupling agent is 80-100.

6. The method for preparing a surface-hydrophobically modified gypsum-aerogel composite thermal insulation material according to claim 5, characterized in that, In step (2), the mass-to-volume ratio of the hydrophilic gypsum-aerogel composite material to the silane coupling agent solution is 1.0~1.5 g / mL, and the soaking time is 3~5 h.

7. The method for preparing a surface-hydrophobic modified gypsum-aerogel composite thermal insulation material according to any one of claims 1 to 6 yields a surface-hydrophobic gypsum-aerogel composite material.

8. The application of the hydrophobic gypsum-aerogel composite material according to claim 7, wherein the hydrophobic gypsum-aerogel composite material is used as an interior thermal insulation material for buildings.

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