A method for preparing a brick structure hemp fiber-based fabric flexible radiative cooling coating

Abstract

The application relates to a preparation method of a brick mud structure hemp fiber-based fabric flexible radiation refrigeration coating, and belongs to the technical field of flexible fabric radiation refrigeration functional coating. In order to solve the problems of the existing biomass-based radiation refrigeration material, such as complicated process, weak interlayer bonding force, easy delamination and peeling, easy cracking when being bent, poor water washing resistance and poor environmental protection, a method for directly forming a brick mud structure hemp fiber-based flexible radiation refrigeration coating on a fabric surface in situ is provided. The radiation refrigeration material is combined with the fabric substrate closely without independent film forming and complicated process. The radiation refrigeration material has the advantages of bionic structure, high efficiency, high flexibility, water washing resistance, bending resistance and green degradable characteristics, and fills the application blank of the biomass-based radiation refrigeration coating in the flexible fabric field.

Description

Technical Field

[0001] This invention belongs to the field of flexible fabric radiation cooling functional coating technology, specifically relating to a method for preparing a flexible radiation cooling coating for a brick-and-mortar structure hemp fiber-based fabric. Background Technology

[0002] Radiative cooling technology, with its core advantages of zero energy consumption, zero carbon emissions, and passive cooling, has broad application prospects in fields such as building energy conservation, outdoor equipment, electronic thermal management, and textiles and apparel. Currently, mainstream radiative cooling materials are mainly self-supporting membranes made from petroleum-based polymers such as PET, PMMA, and PVDF. However, these materials suffer from drawbacks such as non-renewable raw materials, reliance on organic solvents in preparation, difficulty in degradation after disposal, and poor environmental friendliness.

[0003] Existing biomass-based radiative cooling materials are still mainly in the form of self-supporting membranes, which generally suffer from defects such as low mechanical strength, easy breakage, poor optical performance stability, and insufficient weather resistance. In addition, the independent membrane body needs to be combined with the fabric through lamination, bonding, hot pressing and other methods, which has problems such as complicated process, weak interlayer bonding, easy delamination and peeling, easy cracking when bent, and poor water resistance. It cannot meet the core requirements of flexible fabrics such as bending, rubbing, washing and long-term outdoor use.

[0004] Industrial hemp waste, a byproduct of hemp processing, is characterized by low cost, complete biodegradability, and excellent mechanical properties. Bacterial cellulose possesses advantages such as ultra-high mechanical strength, a three-dimensional network cross-linked structure, and good biocompatibility. The combination of these two materials makes for an excellent matrix for preparing green radiative cooling materials. However, existing radiative cooling materials are all self-supporting membranes, failing to achieve in-situ integrated coating construction with fabric substrates, severely limiting the application of biomass-based radiative cooling materials in flexible wearables, outdoor fabrics, and other scenarios. Summary of the Invention

[0005] To address the problems of existing biomass-based radiation cooling materials, such as cumbersome processes, weak interlayer bonding, easy delamination and peeling, easy cracking when bent, poor water resistance, and poor environmental performance, this invention provides a method for directly forming a brick-and-mortar structure hemp fiber-based flexible radiation cooling coating on the fabric surface. This method eliminates the need for separate film formation and complex processes, and the radiation cooling material bonds tightly to the fabric substrate. It also possesses advantages such as biomimetic structure, high-efficiency cooling, high flexibility, water resistance, bending resistance, and green biodegradability, filling the application gap of biomass-based radiation cooling coatings in the field of flexible fabrics.

[0006] The preparation method of the flexible radiation-cooling coating for hemp fiber-based fabric with brick-and-mortar structure of the present invention is carried out according to the following steps:

[0007] Step 1: Preparation of hemp fiber aqueous suspension:

[0008] The industrial hemp fibers are cleaned of impurities, washed with deionized water, and dried at 80-100℃. Then, they are subjected to lignin removal treatment, alkali-oxygen one-bath treatment, H2O2 / TAED activation treatment, and degumming treatment with deionized water. The hemp fibers are then dispersed in water and homogenized to obtain a hemp fiber aqueous suspension with a mass concentration of 1-2%.

[0009] Step 2: Preparation of bacterial cellulose aqueous suspension:

[0010] The bacterial cellulose wet film was subjected to surface modification, alkali washing, and water washing in sequence. Then, the bacterial cellulose wet film was dispersed in water and homogenized to obtain a bacterial cellulose aqueous suspension with a bacterial cellulose mass concentration of 1-2%.

[0011] The surface modification process is as follows: placing the bacterial cellulose wet film in a 0.5-2 mol / L NaOH solution and treating it at 60-80℃ for 30-60 min; after surface modification, a large number of hydroxyl functional groups are introduced into the surface of the bacterial cellulose, which enhances the hydrogen bonding force with hemp fiber and nanoparticles.

[0012] Step 3: Pretreatment of hydrophobic nanoparticles:

[0013] Barium sulfate nanoparticles and hollow silica nanoparticles were respectively modified with silane coupling agents to make their surfaces hydrophobic. After modification, the particle surface changed from hydrophilic to hydrophobic, resulting in better dispersibility and less agglomeration, while also giving the coating intrinsic hydrophobicity.

[0014] Step 4: Preparation of the lower layer mixture:

[0015] Aqueous suspensions of hemp fiber, bacterial cellulose, and hydrophobically modified barium sulfate nanoparticles were mixed, mechanically stirred for 30-60 minutes, and then ultrasonically dispersed for 15-30 minutes to obtain a uniform lower layer mixture.

[0016] Step 5: Preparation of the upper layer mixture:

[0017] Aqueous suspensions of hemp fiber, bacterial cellulose, and hydrophobically modified hollow silica nanoparticles were mixed, mechanically stirred for 30-60 minutes, and then ultrasonically dispersed for 15-30 minutes to obtain a uniform upper mixture.

[0018] Step Six: Preparation of Spraying Liquid:

[0019] Thickeners are added to the lower layer mixture and the upper layer mixture respectively to obtain the lower layer spray coating and the upper layer spray coating;

[0020] Step 7: Fabric substrate pretreatment:

[0021] The fabric substrate is sequentially treated with degreasing, washing, and drying to remove surface impurities and grease, thereby improving coating adhesion.

[0022] The fabric base is polyester or nylon;

[0023] Step 8: In-situ spray coating and molding

[0024] Using a high-pressure spray gun at 0.4 MPa, the lower coating liquid is evenly sprayed onto the surface of the fabric substrate, and then dried at 60℃ for 2 hours to form a lower adhesion layer with a thickness of 70-80 μm. Using a high-pressure spray gun at 0.4 MPa, the upper coating liquid is evenly sprayed onto the surface of the lower adhesion layer, and then dried at 60℃ for 2 hours to form an upper functional layer with a thickness of 170-180 μm, thus completing the process.

[0025] The lower attachment layer contains industrial hemp fiber, bacterial cellulose, and barium sulfate nanoparticles in a mass ratio of 40-50:20-30:15-20; the thickness of the lower attachment layer is 70-80 μm. The upper functional layer contains industrial hemp fiber, bacterial cellulose, and barium sulfate nanoparticles in a mass ratio of 40-50:20-30:15-20; the thickness of the upper functional layer is 170-180 μm. The lower attachment layer is firmly bonded to the fabric substrate, providing short-wave solar light scattering, basic mechanical support, and improving the overall adhesion of the coating. The upper functional layer achieves high reflection of sunlight across the entire wavelength range, high infrared radiation cooling through an 8-13 μm atmospheric window, and hydrophobic surface protection, improving weather resistance and self-cleaning ability.

[0026] The beneficial effects of this invention are as follows:

[0027] 1. The preparation process of this invention is completely different from the vacuum-assisted filtration and freeze-drying film-forming process of radiation-cooling membranes. Instead, it uses a water-based formulation-thickening slurry-in-situ fabric spraying-low-temperature drying process to achieve a self-hydrophobic brick-and-mortar structure hemp fiber-based radiation-cooling coating on the fabric surface, eliminating the need for additional hydrophobic post-treatment. The brick-and-mortar structure hemp fiber-based flexible radiation-cooling coating of this invention is a two-layer composite functional coating directly attached to the surface of the fabric substrate. It does not have an independent self-supporting membrane and is composed of a lower attachment layer and an upper functional layer tightly bonded to the textile substrate, forming an integrated structure with the fabric.

[0028] 2. The flexible radiation cooling coating of hemp fiber-based fabric with brick-and-mortar structure has an overall imitation mother-of-pearl interlocking brick-and-mortar structure. That is, industrial hemp fiber is used as the "brick" phase, providing mechanical support, structural skeleton and bending resistance; bacterial cellulose-nanoparticle composite is used as the "mortar" phase, realizing functional enhancement, structural bonding, particle dispersion and interlayer interlocking; interlayer interlocking and intralayer interweaving, the flexibility and bonding stability are far superior to traditional composite membranes.

[0029] 3. This invention completely abandons the self-supporting membrane structure and is the first to create a fabric-attached radiation cooling coating. It has no independent membrane body and is integrated with the fabric, achieving morphological and structural innovation. It solves the problems of traditional membrane body delamination, peeling, bending and cracking, and can be extended to flexible wearable and outdoor fabric scenarios.

[0030] 4. This invention adopts a coating process of spraying and low temperature drying to replace the vacuum filtration and freeze drying process of radiation cooling membrane; the bacterial cellulose and nanoparticles are pre-modified for hydrophobicity, so that the spraying and forming process has hydrophobic effect by itself, eliminating the need for post-processing steps such as high pressure gas phase, impregnation and baking, and is more suitable for continuous fabric production.

[0031] 5. The interlocking brick-and-mortar structure of the present invention, which imitates mother-of-pearl, enables nanoparticles to be evenly dispersed and firmly bonded. The average reflectivity of the 500-1500nm solar radiation core band is ≥92%, and the outdoor temperature reduction can reach more than 12℃. At the same time, it has the flexible characteristics of adhesion level 1, no cracking after 1000 bends, and no performance degradation after 10 washes, which is fully compatible with the requirements of fabric use.

[0032] 6. This invention uses industrial hemp waste as the core matrix, with water as the dispersion medium throughout the process, no organic solvents used, and the material is completely biodegradable, which is in line with the development concept of low carbon, energy saving, green and environmental protection.

[0033] 7. This invention can be directly attached to a variety of textile substrates and is suitable for outdoor clothing, flexible equipment, agricultural greenhouse fabrics, flexible heat dissipation fabrics for electronic devices, etc., breaking through the application limitations of self-supporting films and expanding application scenarios. Detailed Implementation

[0034] The technical solution of the present invention is not limited to the specific embodiments listed below, but also includes any reasonable combination of the specific embodiments.

[0035] Specific Implementation Method 1: The preparation method of the flexible radiation-cooling coating for hemp fiber-based fabric with brick-and-mortar structure in this implementation method is carried out according to the following steps:

[0036] Step 1: Preparation of hemp fiber aqueous suspension:

[0037] The industrial hemp fibers are cleaned of impurities, washed with deionized water, and dried at 80-100℃. Then, they are subjected to lignin removal treatment, alkali-oxygen one-bath treatment, H2O2 / TAED activation treatment, and degumming treatment with deionized water. The hemp fibers are then dispersed in water and homogenized to obtain a hemp fiber aqueous suspension with a mass concentration of 1-2%.

[0038] Step 2: Preparation of bacterial cellulose aqueous suspension:

[0039] The bacterial cellulose wet film was subjected to surface modification, alkali washing, and water washing in sequence. Then, the bacterial cellulose wet film was dispersed in water and homogenized to obtain a bacterial cellulose aqueous suspension with a bacterial cellulose mass concentration of 1-2%.

[0040] The surface modification process is as follows: placing the bacterial cellulose wet film in a 0.5-2 mol / L NaOH solution and treating it at 60-80℃ for 30-60 min; after surface modification, a large number of hydroxyl functional groups are introduced into the surface of the bacterial cellulose, which enhances the hydrogen bonding force with hemp fiber and nanoparticles.

[0041] Step 3: Pretreatment of hydrophobic nanoparticles:

[0042] Barium sulfate nanoparticles and hollow silica nanoparticles were respectively modified with silane coupling agents to make their surfaces hydrophobic. After modification, the particle surface changed from hydrophilic to hydrophobic, resulting in better dispersibility and less agglomeration, while also giving the coating intrinsic hydrophobicity.

[0043] Step 4: Preparation of the lower layer mixture:

[0044] Aqueous suspensions of hemp fiber, bacterial cellulose, and hydrophobically modified barium sulfate nanoparticles were mixed, mechanically stirred for 30-60 minutes, and then ultrasonically dispersed for 15-30 minutes to obtain a uniform lower layer mixture.

[0045] Step 5: Preparation of the upper layer mixture:

[0046] Aqueous suspensions of hemp fiber, bacterial cellulose, and hydrophobically modified hollow silica nanoparticles were mixed, mechanically stirred for 30-60 minutes, and then ultrasonically dispersed for 15-30 minutes to obtain a uniform upper mixture.

[0047] Step Six: Preparation of Spraying Liquid:

[0048] Thickeners are added to the lower layer mixture and the upper layer mixture respectively to obtain the lower layer spray coating and the upper layer spray coating;

[0049] Step 7: Fabric substrate pretreatment:

[0050] The fabric substrate is sequentially treated with degreasing, washing, and drying to remove surface impurities and grease, thereby improving coating adhesion.

[0051] The fabric base is polyester or nylon;

[0052] Step 8: In-situ spray coating and molding

[0053] Using a high-pressure spray gun at 0.4 MPa, the lower coating liquid is evenly sprayed onto the surface of the fabric substrate, and then dried at 60℃ for 2 hours to form a lower adhesion layer with a thickness of 70-80 μm. Using a high-pressure spray gun at 0.4 MPa, the upper coating liquid is evenly sprayed onto the surface of the lower adhesion layer, and then dried at 60℃ for 2 hours to form an upper functional layer with a thickness of 170-180 μm, thus completing the process.

[0054] The lower attachment layer contains industrial hemp fiber, bacterial cellulose, and barium sulfate nanoparticles in a mass ratio of 40-50:20-30:15-20; the thickness of the lower attachment layer is 70-80 μm. The upper functional layer contains industrial hemp fiber, bacterial cellulose, and barium sulfate nanoparticles in a mass ratio of 40-50:20-30:15-20; the thickness of the upper functional layer is 170-180 μm. The lower attachment layer is firmly bonded to the fabric substrate, providing short-wave solar light scattering, basic mechanical support, and improving the overall adhesion of the coating. The upper functional layer achieves high reflection of sunlight across the entire wavelength range, high infrared radiation cooling through an 8-13 μm atmospheric window, and hydrophobic surface protection, improving weather resistance and self-cleaning ability.

[0055] This embodiment has the following beneficial effects:

[0056] 1. The preparation process of this embodiment is completely different from the vacuum-assisted filtration and freeze-drying film-forming process of radiation-cooling membranes. Instead, it adopts a coating process of water-based preparation, thickening into a slurry, in-situ spraying onto the fabric, and low-temperature drying to achieve an in-situ hydrophobic brick-and-mortar structure hemp fiber-based radiation-cooling coating on the fabric surface, without the need for additional hydrophobic post-treatment. The flexible radiation-cooling coating of hemp fiber-based fabric with brick-and-mortar structure in this embodiment is a two-layer composite functional coating that is directly attached to the surface of the fabric substrate. It does not have an independent self-supporting membrane. It is composed of a lower attachment layer and an upper functional layer tightly bonded to the textile substrate, forming an integrated structure with the fabric.

[0057] 2. The flexible radiation cooling coating of hemp fiber-based fabric with brick-and-mortar structure has an overall imitation mother-of-pearl interlocking brick-and-mortar structure. That is, industrial hemp fiber is used as the "brick" phase, providing mechanical support, structural skeleton and bending resistance; bacterial cellulose-nanoparticle composite is used as the "mortar" phase, realizing functional enhancement, structural bonding, particle dispersion and interlayer interlocking; interlayer interlocking and intralayer interweaving, the flexibility and bonding stability are far superior to traditional composite membranes.

[0058] 3. This implementation method completely abandons the self-supporting membrane structure and is the first to use a fabric-attached radiation cooling coating. It has no independent membrane body and is integrated with the fabric, achieving morphological and structural innovation. It solves the problems of traditional membrane body delamination, peeling, bending and cracking, and can be extended to flexible wearable and outdoor fabric scenarios.

[0059] 4. This implementation method adopts a coating-specific process of spraying and low-temperature drying to replace the vacuum filtration and freeze-drying process of radiation cooling membrane; the bacterial cellulose and nanoparticles are pre-modified for hydrophobicity, so that the spraying and forming process has a hydrophobic effect, eliminating the need for post-processing steps such as high-pressure gas phase, impregnation and baking, and is more suitable for continuous fabric production.

[0060] 5. The imitation mother-of-pearl interlocking brick and mortar structure of this embodiment makes the nanoparticles uniformly dispersed and firmly bonded. The average reflectivity of the 500-1500nm solar radiation core band is ≥92%, and the outdoor temperature reduction can reach more than 12℃. At the same time, it has the flexible characteristics of adhesion level 1, no cracking after 1000 bends, and no performance degradation after 10 washes, which is fully compatible with the requirements of fabric use.

[0061] 6. This implementation method uses industrial hemp waste as the core matrix, uses water as the dispersion medium throughout the process, does not use any organic solvents, and the material is completely biodegradable, which is in line with the development concept of low carbon, energy saving and green environmental protection.

[0062] 7. This embodiment can be directly attached to a variety of textile substrates and is suitable for outdoor clothing, flexible equipment, agricultural greenhouse film fabrics, flexible heat dissipation fabrics for electronic devices, etc., breaking through the application limitations of self-supporting films and expanding application scenarios.

[0063] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that the lignin removal treatment method described in step one involves sequentially using acid washing, alkali washing, and deionized water washing.

[0064] Specific Implementation Method 3: This implementation method differs from Specific Implementation Method 1 or 2 in that: the H2O2 / TAED activation treatment process in step 1 is as follows: weigh the industrial hemp fibers after alkaline oxygen one-bath degumming into the activation reagent, with a solid-liquid mass ratio of 1:20-40, activate at 70-90℃ for 20-40 minutes, and finally wash and dry; the content of H2O2 in the activation reagent is 4-6 g / L, the content of NaOH is 1-3 g / L, and the content of tetraacetylethylenediamine is 1-2 g / L.

[0065] Specific Implementation Method Four: This implementation method differs from one of the specific implementation methods one to three in that the industrial hemp fibers mentioned in step one have a length of 0.2-1 mm and a diameter of 2-5 μm.

[0066] Specific Implementation Method 5: This implementation method differs from one of the specific implementation methods 1 to 4 in that the diameter of the bacterial cellulose described in step 2 is 50-100 nm.

[0067] Specific Implementation Method Six: This implementation method differs from Specific Implementation Methods One to Five in that the silane coupling agent mentioned in step three is KH-570.

[0068] Specific Implementation Method Seven: This implementation method differs from Specific Implementation Methods One to Six in that the hollow silica nanoparticles described in step three have a particle size of 600-1000 nm and a wall thickness of 40-50 nm.

[0069] Specific Implementation Method Eight: This implementation method differs from one of Specific Implementation Methods One to Seven in that the particle size of the barium sulfate nanoparticles described in step three is 100-200 nm.

[0070] Specific Implementation Method Nine: This implementation method differs from Specific Implementation Methods One to Eight in that: First, hexadecyltrimethylammonium bromide is added to a mixed solvent of anhydrous ethanol and water, with an addition amount of 1-5 g / L;

[0071] Then, ammonia water was added dropwise to adjust the pH of the solution to 9-11. Next, tetraethyl orthosilicate was added, with a molar ratio of tetraethyl orthosilicate to hexadecyltrimethylammonium bromide of 5-10:1. The hydrolysis-condensation reaction was carried out at room temperature for 12-24 hours. After the reaction was completed, the product was collected by centrifugation and washed 3-5 times each with ethanol and deionized water.

[0072] Finally, vacuum dry at 60-80℃ for 6-12 hours.

[0073] Specific Implementation Method Ten: This implementation method differs from Specific Implementation Methods One through Nine in that: the thickener mentioned in step six is ​​a polyurethane associative thickener and fumed silica, and the amount of thickener added is 2 wt.% of the lower or upper layer mixture.

[0074] The mass ratio of the polyurethane associative thickener to fumed silica is 2:1.

[0075] Example 1

[0076] The preparation method of the flexible radiation-cooling coating of hemp fiber-based fabric with brick-and-mortar structure in this embodiment is carried out according to the following steps:

[0077] Step 1: Preparation of hemp fiber aqueous suspension:

[0078] Industrial hemp fibers were cleaned of impurities, washed with deionized water, and dried at 80°C. Then, they were subjected to lignin removal treatment, alkali-oxygen one-bath treatment, H2O2 / TAED activation treatment, and degumming treatment with deionized water. Finally, the hemp fibers were dispersed in water and homogenized to obtain an aqueous suspension of hemp fibers with a mass concentration of 1.5%.

[0079] The lignin removal treatment method consists of sequential acid washing, alkali washing, and deionized water washing.

[0080] The H2O2 / TAED activation process is as follows: industrial hemp fibers after alkaline oxygen one-bath degumming are weighed into an activation reagent at a solid-liquid mass ratio of 1:30, activated at 90℃ for 25 minutes, and finally washed and dried; the activation reagent contains 6 g / L of H2O2, 1 g / L of NaOH, and 1 g / L of tetraacetylethylenediamine.

[0081] The industrial hemp fibers have a length of 0.2-1 mm and a diameter of 2-5 μm.

[0082] Step 2: Preparation of bacterial cellulose aqueous suspension:

[0083] The bacterial cellulose wet film was subjected to surface modification, alkali washing, and water washing in sequence. Then, the bacterial cellulose wet film was dispersed in water and homogenized to obtain a bacterial cellulose aqueous suspension with a bacterial cellulose mass concentration of 1%.

[0084] The surface modification process is as follows: the bacterial cellulose wet film is placed in a 1 mol / L NaOH solution and treated at 70°C for 45 min; after surface modification, a large number of hydroxyl functional groups are introduced on the surface of the bacterial cellulose, which enhances the hydrogen bonding force with hemp fiber and nanoparticles.

[0085] The diameter of the bacterial cellulose is 50-100 nm;

[0086] Step 3: Pretreatment of hydrophobic nanoparticles:

[0087] Barium sulfate nanoparticles and hollow silica nanoparticles were respectively modified with silane coupling agents to make their surfaces hydrophobic. After modification, the particle surface changed from hydrophilic to hydrophobic, resulting in better dispersibility and less agglomeration, while also giving the coating intrinsic hydrophobicity.

[0088] The silane coupling agent is KH-570;

[0089] The hollow silica nanoparticles have a particle size of 600-1000 nm and a wall thickness of 40-50 nm.

[0090] The barium sulfate nanoparticles have a particle size of 100-200 nm;

[0091] The hollow silica nanoparticle preparation process is as follows: hexadecyltrimethylammonium bromide is added to a mixed solvent of anhydrous ethanol and water at a concentration of 3 g / L; ammonia water is added dropwise to adjust the pH of the solution to 10, and then tetraethyl orthosilicate is added, with a molar ratio of tetraethyl orthosilicate to hexadecyltrimethylammonium bromide of 8:1. The hydrolysis and polycondensation reaction is carried out at room temperature for 18 h; after the reaction is completed, the product is collected by centrifugation, washed four times each with ethanol and deionized water, and finally dried under vacuum at 70 °C for 8 h.

[0092] Step 4: Preparation of the lower layer mixture:

[0093] Aqueous suspensions of hemp fiber, bacterial cellulose, and hydrophobically modified barium sulfate nanoparticles were mixed, mechanically stirred for 40 minutes, and then ultrasonically dispersed for 20 minutes to obtain a uniform lower layer mixture.

[0094] Step 5: Preparation of the upper layer mixture:

[0095] Aqueous suspensions of hemp fiber, bacterial cellulose, and hydrophobically modified hollow silica nanoparticles were mixed, mechanically stirred for 40 minutes, and then ultrasonically dispersed for 20 minutes to obtain a uniform upper mixture.

[0096] Step Six: Preparation of Spraying Liquid:

[0097] Thickeners are added to the lower layer mixture and the upper layer mixture respectively to obtain the lower layer spray coating and the upper layer spray coating;

[0098] The thickener is a polyurethane associative thickener and fumed silica, with the amount of thickener added being 2 wt.% of the lower or upper layer mixture; the mass ratio of polyurethane associative thickener to fumed silica is 2:1. The polyurethane associative thickener mainly provides rheological regulation to ensure coating formation, while the fumed silica mainly provides thixotropic structure and adhesion enhancement, while also assisting in thickening and preventing coating flow. After adding the thickener, the viscosity of the lower and upper spray liquids reaches 850 mPa•s, respectively preparing lower and upper spray liquids suitable for fabric spraying, meeting the rheological and adhesion requirements for coating formation.

[0099] Step 7: Fabric substrate pretreatment:

[0100] The fabric substrate is sequentially treated with degreasing, washing, and drying to remove surface impurities and grease, thereby improving coating adhesion.

[0101] The fabric base is polyester;

[0102] Step 8: In-situ spray coating and molding

[0103] The lower coating liquid is uniformly sprayed onto the surface of the fabric substrate using a high-pressure spray gun at a pressure of 0.4 MPa, and then dried at 60°C for 2 hours to form a lower adhesion layer with a thickness of 75 μm. The upper coating liquid is uniformly sprayed onto the surface of the lower adhesion layer using a high-pressure spray gun at a pressure of 0.4 MPa, and then dried at 60°C for 2 hours to form an upper functional layer with a thickness of 175 μm, thus completing the process.

[0104] The lower attachment layer contains industrial hemp fiber, bacterial cellulose, and barium sulfate nanoparticles in a mass ratio of 45:25:20; the upper functional layer also contains the same mass ratio. The lower attachment layer is firmly bonded to the fabric substrate, providing short-wavelength solar light scattering, basic mechanical support, and enhancing the overall adhesion of the coating. The upper functional layer achieves high reflection of sunlight across the entire wavelength range, infrared high-radiation cooling through an 8-13μm atmospheric window, and surface hydrophobic protection, thus improving weather resistance and self-cleaning capabilities.

[0105] Figure 1 The image shows the surface microstructure of the flexible radiation-cooling coating prepared in Example 1. In Example 1, the substrate is a polyester textile fabric with a large number of nano / micron-sized inorganic particles uniformly distributed on the surface. The particles are dispersed and do not show obvious agglomeration. The particles are well bonded to the substrate fibers and there is no large-area shedding or agglomeration. This uniformly distributed micro / nano structure is the key to achieving efficient light scattering and high reflectivity, providing a microstructural basis for radiation-cooling performance.

[0106] Figure 2 The infrared reflectance spectrum of the flexible radiation-cooling coating prepared in Example 1 is shown in Figure 1. Figure 2 The coating's reflectivity in the mid-visible-near-infrared region (400-250 nm) remains stable at over 90%. In the visible (400-700 nm) and near-infrared (700-2500 nm) bands, where solar energy is concentrated, high reflectivity can directly reduce the material's absorption of solar radiation and reduce heat input.

[0107] Figure 3The figure shows the actual outdoor temperature test results of the flexible radiative cooling coating prepared in Example 1. In the figure, Room represents the temperature curve inside the simulated house model, Paper represents the temperature curve of ordinary paper placed outdoors, and Back represents the temperature curve of the flexible radiative cooling coating prepared in Example 1. The test results show that during periods of strong sunlight during the day, the temperature inside the model (Room curve) reaches a maximum of nearly 60°C, and the surface temperature of ordinary paper (Paper curve) reaches a maximum of about 50°C. The surface temperature of the flexible radiative cooling coating in Example 1 (Back curve) is significantly lower than the former two, with the highest temperature being more than 10°C lower than the ambient temperature and about 5°C lower than that of ordinary paper, demonstrating excellent daytime radiative cooling effect. During periods of no sunlight at night, the temperatures of all three curves drop to about 20-25°C. The coating temperature is basically the same as that of ordinary paper and slightly lower than the temperature inside the model, indicating that the coating can still effectively dissipate heat at night. After sunlight resumes the next day, the coating temperature is again significantly lower than that of the environment and ordinary paper, verifying its stable cooling performance under sunlight conditions. Overall test results show that the flexible radiation cooling coating prepared by this invention can effectively reduce the surface temperature in real outdoor environments and has excellent and stable radiation cooling performance.

[0108] Example 2

[0109] The preparation method of the flexible radiation-cooling coating of hemp fiber-based fabric with brick-and-mortar structure in this embodiment is carried out according to the following steps:

[0110] Step 1: Preparation of hemp fiber aqueous suspension:

[0111] Industrial hemp fibers were cleaned of impurities, washed with deionized water, and dried at 80°C. Then, they were subjected to lignin removal treatment, alkali-oxygen one-bath treatment, H2O2 / TAED activation treatment, and degumming treatment with deionized water. Finally, the hemp fibers were dispersed in water and homogenized to obtain an aqueous suspension of hemp fibers with a mass concentration of 1.5%.

[0112] The lignin removal treatment method consists of sequential acid washing, alkali washing, and deionized water washing.

[0113] The H2O2 / TAED activation process is as follows: industrial hemp fibers after alkaline oxygen one-bath degumming are weighed into an activation reagent at a solid-liquid mass ratio of 1:30, activated at 90℃ for 25 minutes, and finally washed and dried; the activation reagent contains 6 g / L of H2O2, 1 g / L of NaOH, and 1 g / L of tetraacetylethylenediamine.

[0114] The industrial hemp fibers have a length of 0.2-1 mm and a diameter of 2-5 μm.

[0115] Step 2: Preparation of bacterial cellulose aqueous suspension:

[0116] The bacterial cellulose wet film was subjected to surface modification, alkali washing, and water washing in sequence. Then, the bacterial cellulose wet film was dispersed in water and homogenized to obtain a bacterial cellulose aqueous suspension with a bacterial cellulose mass concentration of 1%.

[0117] The surface modification process is as follows: the bacterial cellulose wet film is placed in a 1 mol / L NaOH solution and treated at 70°C for 45 min; after surface modification, a large number of hydroxyl functional groups are introduced on the surface of the bacterial cellulose, which enhances the hydrogen bonding force with hemp fiber and nanoparticles.

[0118] The diameter of the bacterial cellulose is 50-100 nm;

[0119] Step 3: Pretreatment of hydrophobic nanoparticles:

[0120] Barium sulfate nanoparticles and hollow silica nanoparticles were respectively modified with silane coupling agents to make their surfaces hydrophobic. After modification, the particle surface changed from hydrophilic to hydrophobic, resulting in better dispersibility and less agglomeration, while also giving the coating intrinsic hydrophobicity.

[0121] The silane coupling agent is KH-570;

[0122] The hollow silica nanoparticles have a particle size of 600-1000 nm and a wall thickness of 40-50 nm.

[0123] The barium sulfate nanoparticles have a particle size of 100-200 nm;

[0124] The hollow silica nanoparticle preparation process is as follows: hexadecyltrimethylammonium bromide is added to a mixed solvent of anhydrous ethanol and water at a concentration of 3 g / L; ammonia water is added dropwise to adjust the pH of the solution to 10, and then tetraethyl orthosilicate is added, with a molar ratio of tetraethyl orthosilicate to hexadecyltrimethylammonium bromide of 8:1. The hydrolysis and polycondensation reaction is carried out at room temperature for 18 h; after the reaction is completed, the product is collected by centrifugation, washed four times each with ethanol and deionized water, and finally dried under vacuum at 70 °C for 8 h.

[0125] Step 4: Preparation of the lower layer mixture:

[0126] Aqueous suspensions of hemp fiber, bacterial cellulose, and hydrophobically modified barium sulfate nanoparticles were mixed, mechanically stirred for 40 minutes, and then ultrasonically dispersed for 20 minutes to obtain a uniform lower layer mixture.

[0127] Step 5: Preparation of the upper layer mixture:

[0128] Aqueous suspensions of hemp fiber, bacterial cellulose, and hydrophobically modified hollow silica nanoparticles were mixed, mechanically stirred for 40 minutes, and then ultrasonically dispersed for 20 minutes to obtain a uniform upper mixture.

[0129] Step Six: Preparation of Spraying Liquid:

[0130] Thickeners are added to the lower layer mixture and the upper layer mixture respectively to obtain the lower layer spray coating and the upper layer spray coating;

[0131] The thickener is a polyurethane associative thickener and fumed silica. The amount of thickener added is 2 wt.% of the lower or upper mixture. The mass ratio of polyurethane associative thickener to fumed silica is 2:1. After adding the thickener, the viscosity of the lower and upper spray liquids reaches 850 mPa•s, thus preparing lower and upper spray liquids suitable for fabric spraying, which meet the rheological and adhesion requirements of coating formation.

[0132] Step 7: Fabric substrate pretreatment:

[0133] The fabric substrate is sequentially treated with degreasing, washing, and drying to remove surface impurities and grease, thereby improving coating adhesion.

[0134] The fabric base is nylon;

[0135] Step 8: In-situ spray coating and molding

[0136] The lower coating liquid is uniformly sprayed onto the surface of the fabric substrate using a high-pressure spray gun at a pressure of 0.4 MPa, and then dried at 60°C for 2 hours to form a lower adhesion layer with a thickness of 72 μm. The upper coating liquid is uniformly sprayed onto the surface of the lower adhesion layer using a high-pressure spray gun at a pressure of 0.4 MPa, and then dried at 60°C for 2 hours to form an upper functional layer with a thickness of 172 μm, thus completing the process.

[0137] The lower attachment layer contains industrial hemp fiber, bacterial cellulose, and barium sulfate nanoparticles in a mass ratio of 48:27:20; the upper functional layer also contains the same mass ratio. The lower attachment layer is firmly bonded to the fabric substrate, providing short-wavelength solar light scattering, basic mechanical support, and enhancing the overall adhesion of the coating. The upper functional layer achieves high reflection of sunlight across the entire wavelength range, high infrared radiation cooling through an 8-13μm atmospheric window, and hydrophobic surface protection, thus improving weather resistance and self-cleaning capabilities.

[0138] Figure 4The image shows the surface microstructure of the flexible radiation-cooling coating prepared in Example 2. The coating forms a uniform and continuous covering layer on the surface of a nylon fabric substrate, with no obvious cracks or defects. Micro- and nano-particles are uniformly dispersed in the coating matrix without large-area aggregation. The particle distribution density is comparable to that of the polyester substrate coating, forming an ideal micro- and nano-scattering structure. The particles are tightly bonded to the nylon substrate fibers, and the coating effectively encapsulates the fibers. This structure provides a foundation for efficient light scattering and high reflectivity.

[0139] Figure 5 The image shows the infrared reflectance spectrum of the flexible radiation-cooling coating prepared in Example 2. The reflectance in the visible light region (400-70 nm) increases rapidly, reaching a peak of approximately 95% near 500 nm, demonstrating excellent reflectivity for visible light and effectively reducing heat absorption in the visible light band. In the near-infrared region (700-2500 nm), the reflectance remains above 85% overall, with only slight fluctuations near 1500 nm and 2000 nm (due to the intrinsic absorption / scattering characteristics of the material). The reflectance at 2500 nm remains around 60%, exhibiting overall high solar spectral reflectance characteristics.

Claims

1. A method for preparing a flexible radiation-cooling coating on a brick-and-mortar structure hemp fiber-based fabric, characterized in that: The preparation method of the flexible radiation-cooling coating for hemp fiber-based fabrics with brick-and-mortar structure is carried out according to the following steps: Step 1: Preparation of hemp fiber aqueous suspension: The industrial hemp fibers are cleaned of impurities, washed with deionized water, and dried at 80-100℃. Then, they are subjected to lignin removal treatment, alkali-oxygen one-bath treatment, H2O2 / TAED activation treatment, and degumming treatment with deionized water. The hemp fibers are then dispersed in water and homogenized to obtain a hemp fiber aqueous suspension with a mass concentration of 1-2%. Step 2: Preparation of bacterial cellulose aqueous suspension: The bacterial cellulose wet film was subjected to surface modification, alkali washing, and water washing in sequence. Then, the bacterial cellulose wet film was dispersed in water and homogenized to obtain a bacterial cellulose aqueous suspension with a bacterial cellulose mass concentration of 1-2%. The surface modification process is as follows: placing the bacterial cellulose wet film in a 0.5-2 mol / L NaOH solution and treating it at 60-80℃ for 30-60 min; Step 3: Pretreatment of hydrophobic nanoparticles: Barium sulfate nanoparticles and hollow silica nanoparticles were respectively modified with silane coupling agents to achieve hydrophobicity. Step 4: Preparation of the lower layer mixture: Aqueous suspensions of hemp fiber, bacterial cellulose, and hydrophobically modified barium sulfate nanoparticles were mixed, mechanically stirred for 30-60 minutes, and then ultrasonically dispersed for 15-30 minutes to obtain a uniform lower layer mixture. Step 5: Preparation of the upper layer mixture: Aqueous suspensions of hemp fiber, bacterial cellulose, and hydrophobically modified hollow silica nanoparticles were mixed, mechanically stirred for 30-60 minutes, and then ultrasonically dispersed for 15-30 minutes to obtain a uniform upper mixture. Step Six: Preparation of Spraying Liquid: Thickeners are added to the lower layer mixture and the upper layer mixture respectively to obtain the lower layer spray coating and the upper layer spray coating; Step 7: Fabric substrate pretreatment: The fabric base is sequentially treated with degreasing, washing and drying; To remove surface impurities and grease, and improve coating adhesion; The fabric base is polyester or nylon; Step 8: In-situ spray coating and molding Using a high-pressure spray gun at 0.4 MPa, the lower coating liquid is evenly sprayed onto the surface of the fabric substrate, and then dried at 60℃ for 2 hours to form a lower adhesion layer with a thickness of 70-80 μm. Using a high-pressure spray gun at 0.4 MPa, the upper coating liquid is evenly sprayed onto the surface of the lower adhesion layer, and then dried at 60℃ for 2 hours to form an upper functional layer with a thickness of 170-180 μm, thus completing the process. The lower attachment layer contains industrial hemp fiber, bacterial cellulose, and barium sulfate nanoparticles in a mass ratio of 40-50:20-30:15-20; the thickness of the lower attachment layer is 70-80 μm. The upper functional layer contains industrial hemp fiber, bacterial cellulose, and barium sulfate nanoparticles in a mass ratio of 40-50:20-30:15-20; the thickness of the upper functional layer is 170-180 μm.

2. The method for preparing the flexible radiation-cooling coating on hemp fiber-based fabric with brick-and-mortar structure according to claim 1, characterized in that: The lignin removal process described in step one involves sequentially washing with acid, alkali, and deionized water.

3. The method for preparing the flexible radiation-cooling coating on hemp fiber-based fabric with brick-and-mortar structure according to claim 1, characterized in that: The H2O2 / TAED activation treatment process described in step one is as follows: weigh the industrial hemp fiber after alkaline oxygen one-bath degumming into the activation reagent, with a solid-liquid mass ratio of 1:20-40, activate it at 70-90℃ for 20-40 minutes, and finally wash and dry it. The activating reagent contains 4-6 g / L of H2O2, 1-3 g / L of NaOH, and 1-2 g / L of tetraacetylethylenediamine.

4. The method for preparing the flexible radiation-cooling coating on the brick-and-mortar structure hemp fiber-based fabric according to claim 1, characterized in that: The industrial hemp fibers mentioned in step one have a length of 0.2-1 mm and a diameter of 2-5 μm.

5. The method for preparing a flexible radiation-cooling coating for a brick-and-mortar structure hemp fiber-based fabric according to claim 1, characterized in that: The bacterial cellulose described in step two has a diameter of 50-100 nm.

6. The method for preparing a flexible radiation-cooling coating for a brick-and-mortar structure hemp fiber-based fabric according to claim 1, characterized in that: The silane coupling agent mentioned in step three is KH-570.

7. The method for preparing a flexible radiation-cooling coating for a brick-and-mortar structure hemp fiber-based fabric according to claim 1, characterized in that: The hollow silica nanoparticles described in step three have a particle size of 600-1000 nm and a wall thickness of 40-50 nm.

8. The method for preparing the flexible radiation-cooling coating on the brick-and-mortar structure hemp fiber-based fabric according to claim 1, characterized in that: The barium sulfate nanoparticles described in step three have a particle size of 100-200 nm.

9. The method for preparing the flexible radiation-cooling coating on a brick-and-mortar structure hemp fiber-based fabric according to claim 1, characterized in that: The hollow silica nanoparticle preparation process described in step three is as follows: First, add hexadecyltrimethylammonium bromide to a mixed solvent of anhydrous ethanol and water at a concentration of 1-5 g / L; Then, ammonia water was added dropwise to adjust the pH of the solution to 9-11. Next, tetraethyl orthosilicate was added, with a molar ratio of tetraethyl orthosilicate to hexadecyltrimethylammonium bromide of 5-10:

1. The hydrolysis-condensation reaction was carried out at room temperature for 12-24 hours. After the reaction was completed, the product was collected by centrifugation and washed 3-5 times each with ethanol and deionized water. Finally, vacuum dry at 60-80℃ for 6-12 hours.

10. The method for preparing the flexible radiation-cooling coating on a brick-and-mortar structure hemp fiber-based fabric according to claim 1, characterized in that: The thickener mentioned in step six is ​​a polyurethane associative thickener and fumed silica, and the amount of thickener added is 2 wt.% of the lower or upper layer mixture. The mass ratio of the polyurethane associative thickener to fumed silica is 2:1.

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