Radiation refrigeration coupling heat-insulation flame-retardant gas gel material and preparation method thereof

Abstract

The invention relates to a radiation refrigeration coupled heat-insulation flame-retardant flexible aerogel material. The radiation refrigeration coupled heat-insulation flame-retardant aerogel material PCCS-NCCPT is prepared from cellulose, polyvinyl alcohol (PVA), citric acid (CA), sodium hypophosphite (SHP), nano calcium carbonate (NCC), polyvinylpyrrolidone (PVP) and tween-80 through a melt blending method and a freeze drying method. The specific preparation process comprises the following steps: step 1, modifying and dispersing nano calcium carbonate; 2, preparing a radiation refrigeration coupling heat-insulating and flame-retardant solution; and step 3, forming the radiation refrigeration coupling heat-insulating flame-retardant aerogel. The aerogel material has excellent radiation refrigeration effect, heat insulation and flame retardance. The PCCS-coated 4NCCPT has the solar reflectivity of 98.11% in the solar spectrum range (0.3 to 2.5 mu m); the thermal emissivity is 98.35% in an atmospheric transparent window wave band (8-13 [mu] m); the heat conductivity coefficient is 0.0091 W m <-1 > K <-1 >; the flame retardance meets the UL-94 V-1 grade; the material has wide application prospects in the fields of electronic packaging, infrared stealth, energy automobiles and the like.

Description

Technical Field

[0001] This invention relates to the fields of radiative cooling, heat insulation, and flame retardancy, specifically to a radiative cooling coupled heat insulation and flame retardant gel material and its preparation method. Background Technology

[0002] Currently, energy waste and the depletion of traditional energy sources make the development of sustainable energy sources an urgent priority. With the rapid development of artificial intelligence, big data, high-performance computing, and new energy vehicles, chip power density is constantly increasing, with the power consumption of a single personal processor reaching 200-250W and system heat dissipation power reaching 1KW. Refrigeration plays a vital role in all aspects of daily life and industrial production, while simultaneously placing higher demands on refrigeration systems.

[0003] However, traditional refrigeration methods consume vast amounts of energy and cause environmental pollution, hindering their ability to meet future cooling demands. For example, air conditioning, a traditional and common refrigeration method, is inherently energy-intensive and inefficient. This is because, during operation, air conditioners consume a significant amount of electricity to cool the entire space. This method not only consumes a large amount of energy but also merely transfers heat without effectively addressing the fundamental problem of heat generation. Radiant cooling, on the other hand, requires no external energy input and consumes no additional energy. It cools objects by reflecting sunlight and mid-infrared radiant heat, making it a green and ideal alternative to air conditioning. By spontaneously reflecting sunlight through atmospheric transparent windows, excess heat is radiated into outer space for passive cooling. Its energy-saving and environmentally friendly characteristics have garnered widespread attention.

[0004] In recent years, radiative cooling technology has made significant progress, from improving cooling capacity to enhancing control over cooling effects and increasing durability. Currently, radiative cooling technology has matured to the point of practical application, showing great promise in fields such as construction, vehicles, energy equipment, electronic packaging, and personal thermal management. It fundamentally solves the problems of high energy consumption and heavy pollution associated with traditional refrigeration methods. Radiative cooling materials need to possess both high reflectivity and high emissivity, be energy-efficient, avoid greenhouse gas emissions, and be environmentally friendly. Therefore, developing inexpensive and efficient cooling materials that can mitigate global energy demand and climate impacts is becoming increasingly important. Summary of the Invention

[0005] The purpose of this invention is to provide a radiation-cooling coupled thermal insulation and flame-retardant gas gel material and its preparation method, which is obtained by melt blending and freeze-drying.

[0006] The present invention adopts the following technical solution:

[0007] This invention provides a radiation-cooling coupled thermal insulation and gas-resistant aerogel material, wherein the aerogel material PCCS@4NCCPT has a three-dimensional porous network structure.

[0008] The PCCS@4NCCPT is prepared from cellulose, polyvinyl alcohol (PVA), citric acid (CA), sodium hypophosphite (SHP), nano-calcium carbonate (NCC), polyvinylpyrrolidone (PVP), and Tween 80 (T-80).

[0009] Preferably, cellulose, polyvinyl alcohol (PVA), and citric acid (CA) undergo esterification and crosslinking reactions at a temperature of 140-160°C to generate new C=O, COC, and hydrogen-bonded covalent networks.

[0010] Preferably, the radiation-cooling coupled thermal insulation and flame-retardant gel material obtained after adding nano-calcium carbonate (NCC) exhibits a uniform, isotropically grown three-dimensional porous network structure.

[0011] This invention provides a method for preparing a radiation-cooling coupled thermal insulation and gas-resistant gas gel material, comprising the following steps:

[0012] Step 1: Modification and dispersion of nano-calcium carbonate;

[0013] First, weigh 10g of dry nano-calcium carbonate powder into a three-necked flask, add 100mL of anhydrous ethanol / water mixed solvent and stir evenly. Then, sonicate the mixed solution for a certain time to perform preliminary dispersion. Next, place the three-necked flask in a constant temperature water bath and stir, while equipping it with a condenser and funnel. Adjust its pH with ammonia water to obtain solution A.

[0014] Weigh a certain amount of KH-550 and dissolve it in 20 ml of anhydrous ethanol / water mixed solution. Adjust the pH of the solution with glacial acetic acid and let it stand for later use to obtain solution B.

[0015] Under vigorous stirring of solution A, solution B is slowly added dropwise to solution A over a certain period of time, and the reaction is carried out at a constant temperature for a certain period of time.

[0016] After heating is stopped, the mixture is allowed to cool naturally to room temperature, then transferred to centrifuge tubes and centrifuged under certain conditions using a high-speed centrifuge. The supernatant is discarded, and the mixture is washed repeatedly with anhydrous ethanol a certain number of times to remove KH-550, resulting in well-dispersible modified nano-calcium carbonate, denoted as NCC.

[0017] Step 2: Preparation of radiation-cooling coupled heat-insulating and flame-retardant gel solution; Take an appropriate amount of polyvinyl alcohol solution of a certain concentration, add a certain amount of cellulose, citric acid and sodium hypophosphite, stir evenly and then carry out esterification crosslinking at a certain temperature, then stir for a certain time at a certain temperature and stirring speed, add a certain proportion of the well-dispersible modified nano calcium carbonate prepared in Step 1 and stir for a certain time at a certain speed, finally, adjust the speed, add a certain proportion of polyvinylpyrrolidone and Tween-80, stir for a certain time to obtain radiation-cooling coupled heat-insulating and flame-retardant material, denoted as PCCS@NCCPT solution;

[0018] Step 3: Forming of radiation-cooled coupled heat-insulating and flame-retardant gas gel; Under certain conditions, the PCCSP / NCC solution obtained in step 2 is freeze-dried to finally obtain the radiation-cooled coupled heat-insulating and flame-retardant gas gel material, denoted as PCCS@NCCPT.

[0019] Preferably, in step 1, the ratio of anhydrous ethanol to water in 100 mL of anhydrous ethanol / water mixed solvent is 9:1, and the initial ultrasonic dispersion time is 15-20 min; the constant temperature water bath temperature is 60-70℃, the pH of solution A is adjusted to 9-10 with ammonia, and the pH of solution B is adjusted to 4-5 with glacial acetic acid; solution B is slowly added dropwise to solution A over 30-40 min, and the constant temperature reaction time is 2-3 h; the high-speed centrifuge speed is 4500 r, the centrifugation time is 5 min, and the solution is washed repeatedly with anhydrous ethanol 3-4 times. The obtained modified nano-calcium carbonate particles have a size of 30-50 nm and do not exhibit agglomeration.

[0020] Preferably, in step 2, the concentration of the polyvinyl alcohol solution is 5 wt%, the addition amount is 70 ml, the addition amounts of cellulose, citric acid, and sodium hypophosphite are 5 g, 5 g, and 2.5 g, respectively, the stirring conditions are 300 RPM, the esterification crosslinking reaction temperature is 140-150℃, the stirring conditions after crosslinking are 40℃, and the stirring time is 12 h; the proportion of modified nano-calcium carbonate added is 2%-4%, the stirring conditions are 500 RPM, and the stirring time is 1-2 h; the proportions of polyvinylpyrrolidone and Tween added are 1-2 wt% and 4-6 wt%, respectively, the stirring conditions are 700 RPM, and the stirring time is 15 min.

[0021] Preferably, in step 3, the freeze-drying conditions are freezing at -20°C for 5-12 hours and the freeze-drying time is 48-72 hours.

[0022] Preferably, the aerogel material has a solar reflectance of 98.11% and an emissivity of 98.35%.

[0023] Preferably, the flame retardant properties of the aerogel material reach UL-94 V1 level;

[0024] Preferably, the thermal insulation performance of the aerogel material is characterized by a thermal conductivity of 0.0091 W / m. -1 K -1 .

[0025] Therefore, the present invention has the following advantages over the prior art:

[0026] 1. Cellulose and PVA form an interwoven network, which is cross-linked through citric acid esterification to form a strong covalent network, fixing the three-dimensional network structure and achieving a mechanical synergy of "rigidity and flexibility";

[0027] 2. Modified nano-calcium carbonate is introduced. Citric acid introduces carboxyl functional groups onto the surface of the nano-calcium carbonate particles, improving its compatibility with cellulose, preventing agglomeration, and ensuring uniform distribution within the framework. Simultaneously, to enhance mechanical properties, whiten the material, and increase solar reflectivity due to the inherent properties of nano-calcium carbonate, scattering points are introduced. The numerous dispersed nanoparticles become phonon and photon scattering centers, further suppressing heat conduction and radiation. Its inherently low thermal conductivity hinders heat flow, working synergistically with cellulose insulation materials.

[0028] 3. Thanks to the "expansion-ceramication synergistic flame retardant system" constructed from "citric acid-sodium hypophosphite-nano calcium carbonate", ultra-high efficiency flame retardancy is achieved;

[0029] 4. The long molecular chain structure of PVP can further organize the re-aggregation of nano-calcium carbonate through steric hindrance, and can finely regulate the formation of gel network through interaction with cellulose and nano-calcium carbonate.

[0030] 5. Tween-80, as a surfactant, is used to homogenize the final solution, driving the regularization of the morphology of ice crystals during freezing. Attached Figure Description

[0031] Figure 1 The XRD pattern is shown in Example 1.

[0032] Figure 2 The FTIR plot of Example 1;

[0033] Figure 3 This is the SEM image of Comparative Example 1; where, Figure 3 (ac) is a cross-sectional SEM image of PCCSPT. Figure 3 (df) is the longitudinal section SEM image of PCCSPT;

[0034] Figure 4 Here is the SEM image of Example 1; where, Figure 4 (ac) is a cross-sectional SEM image of PCCS@4NCCPT. Figure 4(df) is the longitudinal section SEM image of PCCS@4NCCPT;

[0035] Figure 5 The EDS spectrum of Example 1;

[0036] Figure 6 These are the flexibility and resilience test diagrams for Example 1 and Comparative Example 1; wherein, Figure 6 (a) is a flexibility test diagram of PCCSPT in Comparative Example 1. Figure 6 (b) is a flexibility test diagram of PCCS@4NCCPT in Example 1. Figure 6 (cd) is the rebound performance test diagram of PCCS@4NCCPT in Example 1;

[0037] Figure 7 The solar reflectivity and thermal emissivity curves for Example 1, Comparative Example 1, and Example 2 are shown below;

[0038] Figure 8 The figures show vertical combustion test results for Example 1, Comparative Example 1, and Example 2.

[0039] Figure 9 The thermal conductivity diagrams are for Example 1, Comparative Example 1, and Example 2.

[0040] Figure 10 This is a scan image of nano-calcium carbonate NCC from Example 1; wherein, Figure 10 (a) is a scan image of the modified nano-calcium carbonate (NCC). Figure 10 (b) is a scan of unmodified nano-calcium carbonate (NCC). Detailed Implementation

[0041] The present invention will be further described in detail through embodiments and with reference to the accompanying drawings, but this is not intended to limit the scope of the invention.

[0042] Example 1

[0043] A method for preparing a radiation-cooled coupled thermally insulating and flame-retardant gas gel material specifically includes the following steps:

[0044] Step 1: Modification and Dispersion of Nano-Calcium Carbonate. First, weigh 10g of dried nano-calcium carbonate powder and place it in a three-necked flask. Add 100mL of anhydrous ethanol / water mixed solvent (9:1 ratio) and stir until homogeneous. Then, sonicate the solution for 15min for preliminary dispersion. Next, place the three-necked flask in a 65℃ constant temperature water bath with stirring, equipped with a condenser and funnel. Adjust the pH of solution A to 9 with ammonia water to obtain solution A. Weigh a certain amount of KH-550 and dissolve it in 20mL of anhydrous ethanol / water mixed solution (9:1 ratio). Adjust the pH of the solution to 5 with glacial acetic acid and let it stand for later use to obtain solution B.

[0045] Under vigorous stirring of solution A, solution B was slowly added dropwise to solution A over a period of 30 minutes, and the reaction was carried out at a constant temperature for 2.5 hours. After heating was stopped, the mixture was allowed to cool naturally to room temperature, transferred to centrifuge tubes, and centrifuged at a high speed of 4500 rpm for 5 minutes. The supernatant was discarded, and the mixture was washed four times with anhydrous ethanol to remove KH-550, yielding well-dispersible modified nano-calcium carbonate, denoted as NCC.

[0046] Step 2, Preparation of the radiation-cooling coupled heat-insulating and flame-retardant solution. Take 70 ml of a 5 wt% polyvinyl alcohol solution, add 5 g of cellulose, 5 g of citric acid, and 2.5 g of sodium hypophosphite. Stir at 300 RPM until homogeneous, then perform esterification crosslinking at 145 °C. Then, after stirring at 40 °C for 12 h, add 4% of the well-dispersible modified nano-calcium carbonate prepared in Step 1 and stir at 500 RPM for 1 h. Finally, adjust the stirring speed to 700 RPM, add 2 wt% polyvinylpyrrolidone and 5 wt% Tween-80, and stir for 15 min to obtain the radiation-cooling coupled heat-insulating and flame-retardant solution, denoted as PCCS@4NCCPT solution.

[0047] Step 3: Molding of the radiation-cooled coupled heat-resistant and flame-retardant aerogel material. The PCCS@4NCCPT solution obtained in Step 2 was freeze-dried for 72 hours after being frozen at -20℃ for 8 hours, finally yielding a radiation-cooled coupled synergistic flame-retardant and heat-resistant aerogel, denoted as PCCS@4NCCPT.

[0048] To further confirm the composition of PCCS@4NCCPT, XRD tests were performed. The test results are as follows: Figure 1 As shown, PCCS@NCCPT aerogel was successfully synthesized;

[0049] To verify the composition of PCCS@4NCCPT, FTIR testing was performed. The test results are as follows: Figure 2As shown, the chemical structures of each component and the aerogel were analyzed. PCCSPT, PCCS@2NCCPT, and PCCS@4NCCPT all have a range of ~1729.19 cm⁻¹. -1 A new, relatively sharp C=O stretching vibration absorption peak appears at ~1239.15 cm⁻¹, which is a characteristic peak of the ester bond (-CO-O-) formed by the esterification reaction. The COC stretching vibration of the newly formed ester bond and ether bond at ~1239.15 cm⁻¹ proves that the esterification reaction was successfully carried out.

[0050] To demonstrate the microstructure of PCCS@4NCCPT, SEM testing was performed on PCCS@4NCCPT. The SEM test results are as follows: Figure 4 As shown in the figure. Meanwhile, to further compare and confirm the changes in microstructure during the preparation process, SEM testing was performed on PCCSPT without the addition of modified nano-calcium carbonate. The SEM test results are shown in the figure. Figure 3 As shown.

[0051] SEM test results of PCCSPT are as follows Figure 3 As shown, Figure 3 (ac) is a cross-sectional SEM image of PCCSPT. Figure 3 (df) is a longitudinal section SEM image of PCCSPT; the cross-sectional scan of PCCSPT shows that the aerogel exhibits a relatively uniform hierarchical porous structure, while the longitudinal section scan of PCCSPT shows anisotropy. This is because when the system is frozen, the ice crystals preferentially and directionally grow along the temperature gradient direction (longitudinal direction), forming a highly ordered sheet or channel structure.

[0052] To demonstrate whether the modified nano-calcium carbonate (NCC) can be uniformly dispersed and is not prone to aggregation, SEM characterization was performed on the nano-calcium carbonate before and after modification. The test results are as follows: Figure 10 As shown, Figure 10 (a) A scan image of the modified nano-calcium carbonate NCC. The particle size of the modified nano-calcium carbonate NCC is 30-50 nm, compared to the unmodified NCC. Figure 10 (b) In terms of family reunions, the phenomenon has significantly decreased.

[0053] The SEM test results of PCCS@4NCCPT are as follows: Figure 4 As shown, the PCCS@4NCCPT structure has a coarser framework compared to PCCSPT, and exhibits isotropy. This is due to the introduction of a large number of uniformly dispersed nano-calcium carbonate particles, which act as "heterogeneous nucleating agents" and "physical crosslinking points / inhibitors," disrupting the directional growth of ice crystals.

[0054] To demonstrate the elemental distribution of PCCS@4NCCPT, an EDS test was performed on PCCS@4NCCPT. The EDS test results are as follows: Figure 5 As shown in the figure. EDS spectroscopy further confirms the uniform introduction of nano-calcium carbonate;

[0055] To demonstrate the flexibility and resilience properties of PCCS@4NCCPT, flexibility and resilience tests were conducted on both PCCS@4NCCPT and PCCSPT. The test results are as follows: Figure 6 As shown. Among them, Figure 6 (a) is a flexibility test diagram of PCCSPT. Figure 6 (b) is the flexibility test diagram of PCCS@4NCCPT. Figure 6 (cd) shows the resilience performance test results of PCCS@4NCCPT. The test results demonstrate that both PCCS@4NCCPT and PCCSPT possess flexibility and good shape malleability. Furthermore, PCCS@4NCCPT retains good resilience even under heavy pressure.

[0056] To demonstrate the radiative cooling effect of PCCS@4NCCPT, solar reflectivity and thermal emissivity were tested on PCCS@4NCCPT, PCCS@2NCCPT, and PCCSPT. The test results are as follows: Figure 7 As shown. Test results show that PCCS@4NCCPT has a solar reflectance of 98.11% in the solar spectral range (0.3-2.5μm); and a thermal emissivity of 98.35% in the atmospheric transparency window band (8-13μm).

[0057] To demonstrate the flame-retardant properties of PCCS@4NCCPT, vertical burning tests were conducted on PCCS@4NCCPT, PCCS@2NCCPT, and PCCSPT. The test results are as follows: Figure 8 As shown in Table 1.

[0058] Table 1. UL-94 Vertical Burning Test Results

[0059]

[0060] Vertical burning tests showed that PCCS@4NCCPT self-extinguished within 2 seconds after the flame was removed, achieving the UL-94 V-1 rating;

[0061] To demonstrate the thermal insulation performance of PCCS@4NCCPT, its thermal conductivity was tested. Simultaneously, to further confirm the variation in thermal conductivity, thermal conductivity tests were conducted on PCCSPT and PCCS@2NCCPT as a reference. The test results are as follows: Figure 9 As shown.

[0062] The thermal conductivity of PCCSPT is 0.0210 W / m. -1 K -1 ;

[0063] The thermal conductivity of PCCS@2NCCPT is 0.1382 W / m. -1 K -1 ;

[0064] The thermal conductivity of PCCS@4NCCPT is 0.0091 W / m². -1 K -1 ;

[0065] Test results show that thermal conductivity decreases with the addition of NCC. This is because hydrogen bonds form between cellulose and citric acid molecules. Hydrogen bonds have much lower bond energies, and when vibrations (phonons) are transmitted through these hydrogen bonds, they frequently collide and scatter with hydrogen bonds, the ends of molecular chains, and local structural distortions caused by hydrogen bonding. Each scattering changes the direction of phonon propagation and may even convert its energy into other forms (such as heat dissipation), leading to a sharp shortening of the phonon's mean free path. Furthermore, the interconnected hydrogen bond network forms a three-dimensional but highly disordered structure, further exacerbating phonon scattering. This makes it difficult for heat to form an effective directional transfer path, and most of the energy is absorbed and dissipated by hydrogen bonds, resulting in a significant reduction in vibrational transmission efficiency and a decrease in thermal conductivity.

[0066] To demonstrate the effect of NCC on aerogel properties, Comparative Example 1 is provided, a radiation-cooling coupled synergistic flame-retardant and heat-insulating aerogel without NCC doping.

[0067] Comparative Example 1

[0068] A radiation-cooling coupled heat-insulating and flame-retardant gas gel material without NCC dopant is prepared from cellulose, polyvinyl alcohol (PVA), citric acid (CA), sodium hypophosphite (SHP), polyvinylpyrrolidone (PVP), and Tween 80 P-80. Unless otherwise specified, the steps are the same as in Example 1, except that the NCC material in step 2 is not added to obtain the radiation-cooling coupled heat-insulating and flame-retardant gas gel material without NCC dopant, denoted as PCCSPT.

[0069] SEM test results of PCCSPT are as follows Figure 3 As shown, Figure 3 (ac) is a cross-sectional SEM image of PCCSPT. Figure 3(df) is a longitudinal section SEM image of PCCSPT; the cross-sectional scan of PCCSPT shows that the aerogel exhibits a relatively uniform hierarchical porous structure, while the longitudinal section scan of PCCSPT shows anisotropy. This is because when the system is frozen, the ice crystals preferentially and directionally grow along the temperature gradient direction (longitudinal direction), forming a highly ordered sheet or channel structure.

[0070] To demonstrate the radiative cooling effect of PCCSPT, solar reflectivity and thermal emissivity were tested. The test results are as follows: Figure 7 As shown. Test results show that PCCSPT has a solar reflectivity of 97.55% in the solar spectral range (0.3-2.5μm); and a thermal emissivity of 96.65% in the atmospheric transparency window band (8-13μm).

[0071] To demonstrate the flame-retardant properties of PCCSPT, the vertical burning test results of PCCSPT are as follows: Figure 8 As shown in Table 1, the test results show that after the flame was removed following a first 10-second ignition, PCCSPT exhibited a burning time of 32.6 seconds; after the flame was removed following a second 10-second ignition, PCCSPT exhibited a burning time of 153.2 seconds. Compared with Example 1, PCCSPT exhibits poorer flame retardancy.

[0072] To demonstrate the thermal insulation performance of PCCSPT, its thermal conductivity was tested. The test results are as follows: Figure 9 As shown, the thermal conductivity of PCCSPT is 0.0210 W / m. -1 K -1 ;

[0073] To demonstrate the effect of the NCC addition ratio on the properties of PCCS@NCCPT aerogel, Example 2 is provided, which is a radiation-cooling coupled thermal insulation and gas-resistant aerogel material with an added mass ratio of 2% NCC.

[0074] Example 2

[0075] A method for preparing a radiation-cooling coupled thermal insulation and flame-retardant gas gel material with an added amount of 2% NCC. The steps not specifically described are the same as those in Example 1, except that 2% of the well-dispersible modified nano-calcium carbonate prepared in step 1 is added in step 2. The resulting material is denoted as PCCS@2NCCPT.

[0076] To demonstrate the radiative cooling effect of PCCS@2NCCPT, solar reflectivity and thermal emissivity were tested on PCCS@2NCCPT. The test results are as follows: Figure 7As shown. Test results show that PCCS@2NCCPT has a solar reflectance of 97.97% in the solar spectral range (0.3-2.5μm); and a thermal emissivity of 98.26% in the atmospheric transparency window band (8-13μm).

[0077] To demonstrate the flame-retardant properties of PCCS@2NCCPT, the vertical burning test results of PCCS@2NCCPT are as follows: Figure 8 As shown in Table 1, the test results show that after the flame was removed following a first 10-second ignition, PCCS@2NCCPT exhibited a burning time of 13.4 seconds; after the flame was removed following a second 10-second ignition, PCCS@2NCCPT exhibited a burning time of 76.9 seconds. Compared with Example 1, PCCS@2NCCPT exhibits a certain degree of flame retardancy.

[0078] To demonstrate the thermal insulation performance of PCCS@2NCCPT, its thermal conductivity was tested. The test results are as follows: Figure 9 As shown, the thermal conductivity of PCCS@2NCCPT is 0.1382 W / m. -1 K -1 ;

[0079] Based on the above examples 1, 1 comparative example and 2, the following conclusions can be drawn:

[0080] Conclusion 1: Regarding radiative cooling performance.

[0081] The results of radiative cooling performance tests show that adding NCC improves the solar reflectivity and thermal emissivity of aerogel materials. NCC has excellent light scattering properties, and doping it can significantly improve the reflectivity of the material to the solar spectrum (0.2-2.5μm). At the same time, its own infrared radiation properties, in synergy with the porous structure of cellulose aerogel, can enhance the infrared emissivity of the 8-13μm atmospheric window, achieving a dual improvement in optical performance of "high reflectivity + high emissivity", laying the foundation for efficient radiative cooling.

[0082] Conclusion 2, regarding flame retardant performance.

[0083] Based on the flame retardant performance test results, it can be seen that adding NCC will improve the flame retardant performance of aerogel materials, thanks to the "expansion-ceramization synergistic flame retardant system" constructed by "citric acid-sodium hypophosphite-nano calcium carbonate".

[0084] Conclusion 3, regarding thermal insulation performance.

[0085] The thermal conductivity test results show that adding NCC reduces the thermal conductivity of the aerogel material. Hydrogen bonds form between cellulose and citric acid molecules, creating a three-dimensional but highly disordered structure. This further intensifies phonon scattering, making it difficult for heat to form an effective directional transfer path. Most of the energy is absorbed and dissipated by the hydrogen bonds, resulting in a significant reduction in vibrational transmission efficiency and a decrease in thermal conductivity. NCC doping, combined with Tween-80 modulation, can guide the formation of a regular porous structure in cellulose aerogels. High porosity can significantly reduce the material's thermal conductivity and enhance its thermal insulation performance.

[0086] The radiative cooling coupled with thermal insulation and flame-retardant aerogel material proposed in this patent exhibits excellent radiative cooling performance, flame retardancy, and thermal insulation properties. It provides a novel, low-carbon, and sustainable cooling solution for infrared stealth, building and device thermal management, and other facilities, while also possessing flame-retardant and thermal insulation properties. Compared to traditional active cooling technologies, this aerogel, without requiring external energy input, enhances radiative cooling and synergistically improves thermal insulation performance, thereby effectively reducing reliance on air conditioning and refrigeration equipment. This provides strong support for addressing global climate change and achieving carbon neutrality goals.

Claims

1. A radiation-cooling coupled thermal insulation and flame-retardant gas gel material, characterized in that, The aerogel material PCCS@4NCCPT is prepared from cellulose, polyvinyl alcohol (PVA), citric acid (CA), sodium hypophosphite (SHP), nano-calcium carbonate (NCC), polyvinylpyrrolidone (PVP), and Tween 80 (T-80), and has a three-dimensional porous network structure.

2. The radiative cooling coupled thermal insulation and flame-retardant gas gel material according to claim 1, characterized in that, Cellulose, polyvinyl alcohol (PVA), and citric acid (CA) undergo esterification and crosslinking reactions at 140-160℃ to generate new C=O, COC, and hydrogen covalent bond networks.

3. The radiative cooling coupled thermal insulation and gas-resistant gel material according to claim 1, characterized in that, The radiation-cooling coupled thermal insulation and gas-resistant gel material obtained by adding nano-calcium carbonate (NCC) exhibits a uniform, isotropically grown three-dimensional porous network structure.

4. A method for preparing a radiation-cooled coupled thermal insulation and flame-retardant gas gel material, characterized in that, Includes the following steps: Step 1: Modification and dispersion of nano-calcium carbonate; First, weigh 10g of dry nano-calcium carbonate powder into a three-necked flask, add 100mL of anhydrous ethanol / water mixed solvent and stir evenly. Then, sonicate the mixed solution for a certain time to perform preliminary dispersion. Next, place the three-necked flask in a constant temperature water bath and stir, while equipping it with a condenser and funnel. Adjust its pH with ammonia water to obtain solution A. Weigh a certain amount of KH-550 and dissolve it in 20 ml of anhydrous ethanol / water mixed solution. Adjust the pH of the solution with glacial acetic acid and let it stand for later use to obtain solution B. Under vigorous stirring of solution A, solution B is slowly added dropwise to solution A over a certain period of time, and the reaction is carried out at a constant temperature for a certain period of time. After heating is stopped, the mixture is allowed to cool naturally to room temperature, then transferred to centrifuge tubes and centrifuged under certain conditions using a high-speed centrifuge. The supernatant is discarded, and the mixture is washed repeatedly with anhydrous ethanol a certain number of times to remove KH-550, resulting in well-dispersible modified nano-calcium carbonate, denoted as NCC. Step 2: Preparation of radiation-cooling coupled heat-insulating and flame-retardant gel solution; Take an appropriate amount of polyvinyl alcohol solution of a certain concentration, add a certain amount of cellulose, citric acid and sodium hypophosphite, stir evenly and then carry out esterification crosslinking at a certain temperature, then stir for a certain time at a certain temperature and stirring speed, add a certain proportion of the well-dispersible modified nano calcium carbonate prepared in Step 1 and stir for a certain time at a certain speed, finally, adjust the speed, add a certain proportion of polyvinylpyrrolidone and Tween-80, stir for a certain time to obtain radiation-cooling coupled heat-insulating and flame-retardant material, denoted as PCCS@NCCPT solution; Step 3: Forming of radiation-cooled coupled heat-insulating and flame-retardant gas gel; Under certain conditions, the PCCSP / NCC solution obtained in step 2 is freeze-dried to finally obtain the radiation-cooled coupled heat-insulating and flame-retardant gas gel material, denoted as PCCS@NCCPT.

5. The preparation method according to claim 4, characterized in that: In step 1, the ratio of anhydrous ethanol to water in 100 mL of anhydrous ethanol / water mixed solvent is 9:1, and the ultrasonic time for initial dispersion is 15-20 min. The temperature of the constant temperature water bath is 60-70℃. The pH of solution A is adjusted to 9-10 with ammonia water; the pH of solution B is adjusted to 4-5 with glacial acetic acid. Solution B is slowly added dropwise to solution A for 30-40 minutes, and the constant temperature reaction time is 2-3 hours. The speed of the high-speed centrifuge is 4500 r, the centrifugation time is 5 minutes, and the solution is washed repeatedly with anhydrous ethanol 3-4 times. The obtained modified nano-calcium carbonate has a particle size of 30-50 nm and does not exhibit agglomeration.

6. The preparation method according to claim 4, characterized in that: In step 2, the concentration of the polyvinyl alcohol solution is 5 wt%, the addition amount is 70 ml, the addition amounts of cellulose, citric acid, and sodium hypophosphite are 5 g, 5 g, and 2.5 g, respectively, the stirring conditions are 300 RPM, the esterification crosslinking reaction temperature is 140-150℃, the stirring conditions after crosslinking are 40℃, and the stirring time is 12 h; the proportion of modified nano-calcium carbonate added is 2%-4%, the stirring conditions are 500 RPM, and the stirring time is 1-2 h; the proportions of polyvinylpyrrolidone and Tween added are 1-2 wt% and 4-6 wt%, respectively, the stirring conditions are 700 RPM, and the stirring time is 15 min.

7. The preparation method according to claim 4, characterized in that: In step 3, the freeze-drying conditions are freezing at -20℃ for 5-12 hours and the freeze-drying time is 48-72 hours.

8. The preparation method according to claim 4, characterized in that: The aerogel material has a solar reflectance of 98.11% and an emissivity of 98.35%.

9. The preparation method according to claim 4, characterized in that: The flame retardant properties of the aerogel material reach UL-94 V1 level.

10. The preparation method according to claim 4, characterized in that: The aerogel material has a thermal insulation performance, with a thermal conductivity of 0.0091 W / m. -1 K -1 .

Images