Thermochromic radiative cooling wood and methods of making and using the same

Abstract

The present application belongs to the technical field of wood-based functional materials and passive thermal management, and particularly relates to a thermochromic radiative cooling wood material, a preparation method and application thereof. The preparation method comprises the following steps: firstly, performing delignification treatment on natural wood to obtain a delignified wood template with high porosity and high whiteness; then, impregnating a thermochromic microcapsule dispersion liquid into the delignified wood template and drying to load the thermochromic microcapsule inside the wood; again, impregnating the obtained template into a precursor solution containing a polymer, and performing pre-drying and multi-stage solution replacement treatment to form a porous polymer structure inside the wood; finally, performing freeze-drying to obtain the thermochromic radiative cooling wood material. The wood material has good sunlight reflection performance, mid-infrared emission performance and temperature response color change performance, and can adjust the surface color according to the change of the ambient temperature, and has good application prospects in the fields of building energy saving, intelligent temperature control and green low-carbon materials.

Description

Technical Field

[0001] This invention relates to the fields of wood-based functional materials and passive thermal management technology, and in particular to a thermochromic radiation-cooled wood, its preparation method, and its application. Background Technology

[0002] With the increasing demand for building energy conservation, outdoor thermal management, and intelligent decorative materials, functional materials that combine aesthetics, environmental responsiveness, and thermal regulation capabilities have received widespread attention. Radiative cooling technology is a passive cooling method that achieves temperature reduction without additional energy consumption. Its basic principle is that the material reduces solar energy absorption by highly reflecting solar radiation, and radiates heat outward through high emissivity in the mid-infrared atmospheric window band, thereby achieving a cooling effect below ambient temperature. Therefore, radiative cooling materials have promising application prospects in building energy conservation, outdoor facility thermal management, and functional decorative materials.

[0003] Wood, as a natural and renewable biomass material, boasts advantages such as wide availability, light weight, ease of processing, good mechanical properties, and environmental friendliness, making it widely used in construction, furniture, and decoration. However, natural wood contains lignin and other color-producing components, which strongly absorb sunlight, hindering the achievement of high solar reflectivity and thus limiting its application in radiation cooling materials. To improve the optical properties of wood, existing technologies typically employ delignification treatment to remove some of the lignin components, enhance wood whiteness, and utilize the porous structure formed after delignification to improve its ability to scatter sunlight.

[0004] Existing technologies already include solutions for wood-based radiative cooling materials. For example, Chinese patent CN118181435B, "A Method for Preparing Colored Radiative Cooling Wood," discloses a method for preparing colored radiative cooling wood by delignifying wood and further introducing a fluorescent dye / methyl methacrylate system. This solution utilizes the porous structure of the wood after delignification to improve the material's light scattering ability, thus balancing the decorative and radiative cooling properties of the wood to some extent. However, the color in this solution mainly comes from dye coloring, and the resulting material typically exhibits a preset static color, lacking the thermochromic function that reversibly changes with ambient temperature. Therefore, it still has certain limitations in intelligent display and dynamic decorative applications.

[0005] Furthermore, existing technologies already include methods for introducing thermochromic components into delignified wood. For example, Chinese patent CN120924263A, "A Composite Material Based on a Reversible Thermochromic Flame-Retardant Mixture and Its Preparation Method," discloses a wood composite material using delignified wood as a porous carrier and introducing reversible thermochromic components through vacuum impregnation, thus giving the resulting material thermochromic properties. This technical solution demonstrates that thermochromic components can be loaded within delignified wood, thereby endowing the wood with certain temperature response capabilities. However, these technical solutions primarily focus on functions such as flame retardancy, phase change energy storage, or information response, with relatively little consideration given to the synergistic design of high solar reflectivity and high mid-infrared emissivity required for radiative cooling. Therefore, there is still room for improvement in balancing thermochromic functionality and radiative cooling performance.

[0006] In summary, existing technologies have explored color modification of wood-based radiation cooling materials and thermochromic wood composites, but there is still a lack of wood-based functional materials and their preparation methods that can stably load thermochromic components inside delignified wood and further construct porous structures that are conducive to solar light scattering and mid-infrared thermal radiation, thereby simultaneously possessing thermochromic functions, high solar reflectivity, and high mid-infrared emission performance. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of the existing technology and to propose a thermochromic radiation-cooled wood, its preparation method and application.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing thermochromic radiation-cooled wood, the method comprising the following steps: Step 1: Place the wood in an acidic sodium chlorite solution for delignification treatment. After treatment, wash until neutral to obtain delignified wood. Step 2: Immerse the delignified wood in a thermochromic microcapsule dispersion for loading treatment, and freeze-dry after loading to obtain a delignified wood template loaded with thermochromic microcapsules. Step 3: The delignified wood template loaded with thermochromic microcapsules is impregnated in a polymer-containing precursor solution, allowing the precursor solution to enter the internal pores of the wood. After impregnation, the sample is pre-dried, and then the sample is immersed in a non-solvent, allowing the non-solvent to gradually replace the residual solvent inside the wood, thereby forming a porous polymer structure inside the wood. Subsequently, it is freeze-dried to obtain thermochromic radiation-cooled wood.

[0009] Preferably, in step 1, the wood is balsa wood, poplar wood, or fir wood.

[0010] Preferably, in step 1, the concentration of the acidic sodium chlorite solution is 1 wt%, the pH is 4-5, and the treatment temperature is 80 °C.

[0011] Preferably, in step 2, the color-changing temperature of the thermochromic microcapsule is 20–35 °C.

[0012] Preferably, in step 2, the concentration of the thermochromic microcapsule dispersion is 0.1 wt% to 1 wt%.

[0013] Preferably, in step 2, the thermochromic microcapsule is a blue thermochromic microcapsule or a red thermochromic microcapsule.

[0014] Preferably, in step 3, the polymer is polymethyl methacrylate; the precursor solution is composed of polymethyl methacrylate, an organic solvent, and a co-solvent; the organic solvent is acetone, and the co-solvent is ethanol.

[0015] Preferably, in step 3, the non-solvent is deionized water.

[0016] Preferably, in step 3, the pre-drying temperature is 25 °C for 1 h, and the sample is immersed in a non-solvent for 12 h for displacement treatment.

[0017] Preferably, in step 3, the impregnation is vacuum impregnation, with a vacuum gauge pressure of -0.08 MPa to -0.1 MPa and an impregnation time of 20 min to 40 min.

[0018] Preferably, in steps 2 and 3, the freeze-drying conditions are: freezing at -20 ℃ for 8 to 12 h, followed by drying at -40 ℃ to -60 ℃ for 24 to 48 h.

[0019] A thermochromic radiation-cooled wood, prepared by the above-described method, comprises: a delignified wood skeleton with hierarchical channels; thermochromic microcapsules loaded on the inner wall of the channels of the wood skeleton; and a porous polymer network filling the channels of the wood skeleton; wherein the wood exhibits a first color below the color change temperature and a second color above the color change temperature, and the emissivity of the wood in the 8-13 μm atmospheric window is ≥90%.

[0020] Compared with the prior art, the beneficial effects of the present invention are: (1) The present invention removes the main coloring components in wood by delignification treatment, improves the whiteness of wood, and retains the natural multi-level pore structure of wood, which is beneficial to enhance the ability to scatter sunlight. (2) By introducing thermochromic microcapsules, the present invention enables wood to have the function of changing color in response to temperature, which can take into account both decorative and environmental response characteristics. (3) The present invention constructs a porous polymer structure inside the wood through multi-stage solution displacement treatment, which is beneficial to improve the solar reflectivity and mid-infrared emissivity of the material, thereby enhancing the radiative cooling effect; (4) The wood used in the preparation process of this invention is widely available and has the advantages of being renewable and environmentally friendly; (5) The thermochromic radiation-cooled wood prepared by this invention has good application prospects in the fields of building energy conservation, outdoor thermal management and decorative wood products. Attached Figure Description

[0021] Figure 1 The images show the color changes of the thermochromic radiation-cooled wood obtained in Example 1 of this invention at different temperatures. The left image shows the appearance at temperatures below 25°C, and the right image shows the appearance at temperatures above 25°C. Figure 2 Scanning electron microscope images of natural wood (a, a1), delignified wood loaded with thermochromic microcapsules (b, b1), and thermochromic radiation-cooled wood (c, c1) obtained in Example 1 of the present invention. Figure 3 This is a test image of the reflectivity of thermochromic radiation-cooled wood obtained in Example 1 of the present invention in the solar radiation band. Figure 4 This is a test image of the emissivity of thermochromic radiation-cooled wood obtained in Example 1 of the present invention in the mid-infrared band. Detailed Implementation

[0022] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0023] The blue thermochromic microcapsules used in this embodiment were purchased from Shenzhen Huancai Color Changing Technology Co., Ltd., and the product name is thermochromic powder, model number HCBS-98621. The color-changing temperature of these microcapsules is 25 ℃, and they have reversible thermochromic properties, specifically exhibiting blue color below 25 ℃ and colorless (white) color above 25 ℃.

[0024] Specific Implementation Method 1: The preparation method of thermochromic radiation-cooled wood in this implementation method is carried out according to the following steps: (1) Preparation of delignified wood: Wood is placed in an acidic sodium chlorite solution for delignification treatment. After the treatment, it is washed until neutral to obtain delignified wood. (2) Loading of thermochromic microcapsules: Delignified wood was immersed in thermochromic microcapsule dispersion for loading treatment. After loading was completed, it was freeze-dried to obtain delignified wood template loaded with thermochromic microcapsules. (3) Multi-stage solution replacement treatment: The delignified wood template loaded with thermochromic microcapsules was immersed in a precursor solution containing polymer, so that the precursor solution entered the internal pores of the wood; after immersion, the sample was pre-dried to allow the volatile components in the precursor solution to volatilize preferentially and to promote changes in the composition of the residual solvent inside the wood; then the sample was immersed in a non-solvent, so that the non-solvent and the residual solvent inside the wood were gradually replaced, thereby forming a porous polymer structure inside the wood; then it was freeze-dried to obtain thermochromic radiation-cooled wood.

[0025] In this embodiment, the wood is preferably wood with a natural porous structure.

[0026] In this embodiment, the thermochromic microcapsules are preferably microcapsules that undergo reversible color change in the range of 20 to 35 °C.

[0027] In this embodiment, the polymer is preferably polymethyl methacrylate.

[0028] Specific implementation method two: The difference between this implementation method and specific implementation method one is that the wood in step (1) is balsa wood, poplar wood, fir wood or other wood with natural pore structure.

[0029] Specific implementation method three: This implementation method differs from specific implementation method one or two in that: in step (1), the concentration of the acidic sodium chlorite solution is 1wt%, the pH is 4-5, and the treatment temperature is 80℃.

[0030] Specific implementation method four: This implementation method differs from one of the specific implementation methods one to three in that the color-changing temperature of the thermochromic microcapsules in step (2) is 20 to 35 ℃.

[0031] Specific Implementation Method 5: This implementation method differs from Specific Implementation Methods 1 to 4 in that the concentration of the thermochromic microcapsule dispersion in step (2) is 0.1wt% to 1wt%.

[0032] Specific implementation method six: This implementation method differs from one of the specific implementation methods one to five in that: in step (2), the thermochromic microcapsules are blue thermochromic microcapsules and red thermochromic microcapsules.

[0033] Specific Implementation Method Seven: This implementation method differs from Specific Implementation Methods One to Six in that the polymer in step (3) is polymethyl methacrylate.

[0034] Specific implementation method eight: This implementation method differs from one of the specific implementation methods one to seven in that: in step (3), the precursor solution is composed of polymethyl methacrylate, an organic solvent and a co-solvent, the organic solvent is acetone and the co-solvent is ethanol.

[0035] Specific implementation method nine: This implementation method differs from one of the specific implementation methods one to eight in that the non-solvent in step (3) is water, preferably deionized water.

[0036] Specific Implementation Method 10: This implementation method differs from Specific Implementation Methods 1 to 9 in that the pre-drying time in step (3) is 0.5 to 2 hours, and the solution replacement time is 6 to 24 hours. During the pre-drying process, acetone preferentially evaporates, and then deionized water gradually replaces the ethanol and residual acetone inside the wood.

[0037] Specific embodiments and comparative examples are given below.

[0038] Example 1: The preparation method of thermochromic radiation-cooled wood in this example is carried out according to the following steps: (1) Preparation of delignified wood: Balsa wood chips with longitudinal sections were selected as the substrate, with dimensions of 50 mm × 50 mm × 5 mm. A 1 wt% sodium chlorite solution was prepared, and the pH of the solution was adjusted to 4.6 using glacial acetic acid. The balsa wood chips were completely immersed in the above acidic sodium chlorite solution and delignified at 80 ℃ for 24 h. The acidic sodium chlorite solution was replaced every 6 h during the treatment until the sample turned completely white. After the treatment, the wood was repeatedly washed with deionized water until the washing solution was neutral, thus obtaining delignified wood.

[0039] (2) Loading of thermochromic microcapsules: A blue thermochromic microcapsule dispersion with a concentration of 0.2 wt% was prepared. The thermochromic microcapsules change color around 25 °C, remaining blue below 25 °C and colorless above 25 °C. The obtained delignified wood was completely immersed in the thermochromic microcapsule dispersion and soaked at 80 °C for one week. After soaking, the sample was removed and frozen at -20 °C for 12 h, followed by freeze-drying at -50 °C for 48 h to obtain delignified wood templates loaded with blue thermochromic microcapsules.

[0040] (3) Multi-stage solution displacement treatment: Weigh 15 g of polymethyl methacrylate (PMMA) and add it to 90 g of acetone at 40 ℃ and stir until completely dissolved. Then add 90 g of ethanol and continue stirring until homogeneous to obtain a precursor solution. Immerse the delignified wood template loaded with blue thermochromic microcapsules completely in the precursor solution and vacuum impregnate it for 30 min under a vacuum gauge pressure of -0.08 MPa to allow the precursor solution to fully enter the internal pores of the wood. After impregnation, remove the sample and pre-dry it at room temperature for 1 h to allow acetone to evaporate preferentially and adjust the composition of residual solvent inside the wood. Then, immerse the pre-dried sample in deionized water for 12 h. During this process, the deionized water gradually replaces the ethanol and residual acetone inside the wood, thereby inducing PMMA to form a porous structure in the wood pores. Finally, freeze the sample at -20 ℃ for 12 h and then freeze-dry it at -50 ℃ for 48 h to obtain thermochromic radiation-cooled wood.

[0041] Example 2: The preparation method of thermochromic radiation-cooled wood in this example is carried out according to the following steps: (1) Preparation of delignified wood: Balsa wood chips with longitudinal sections were selected as the substrate, with dimensions of 50 mm × 50 mm × 5 mm. A 1 wt% sodium chlorite solution was prepared, and the pH of the solution was adjusted to 4.6 using glacial acetic acid. The balsa wood chips were completely immersed in the above acidic sodium chlorite solution and delignified at 80 ℃ for 24 h. The acidic sodium chlorite solution was replaced every 6 h during the treatment until the sample turned completely white. After the treatment, the wood was repeatedly washed with deionized water until the washing solution was neutral, thus obtaining delignified wood.

[0042] (2) Loading of thermochromic microcapsules: A red thermochromic microcapsule dispersion with a concentration of 0.2 wt% was prepared. The thermochromic microcapsules change color around 25 ℃, appearing red below 25 ℃ and colorless above 25 ℃. The obtained delignified wood was completely immersed in the thermochromic microcapsule dispersion and soaked at 80 ℃ for one week. After soaking, the sample was removed and frozen at -20 ℃ for 12 h, followed by freeze-drying at -50 ℃ for 48 h to obtain delignified wood templates loaded with red thermochromic microcapsules.

[0043] (3) Multi-stage solution displacement treatment: Weigh 15 g of polymethyl methacrylate (PMMA) and add it to 90 g of acetone at 40 ℃ and stir until completely dissolved. Then add 90 g of ethanol and continue stirring until homogeneous to obtain a precursor solution. Immerse the delignified wood template loaded with red thermochromic microcapsules completely in the precursor solution and vacuum impregnate it for 30 min under a vacuum gauge pressure of -0.08 MPa to allow the precursor solution to fully enter the internal pores of the wood. After impregnation, remove the sample and pre-dry it at room temperature for 1 h to allow acetone to evaporate preferentially and adjust the composition of residual solvent inside the wood. Then, immerse the pre-dried sample in deionized water for 12 h. During this process, the deionized water gradually replaces the ethanol and residual acetone inside the wood, thereby inducing PMMA to form a porous structure in the wood pores. Finally, freeze the sample at -20 ℃ for 12 h and then freeze-dry it at -50 ℃ for 48 h to obtain thermochromic radiation-cooled wood.

[0044] Comparative Example 1: The preparation method of the thermochromic radiation-cooled wood of this comparative example is carried out according to the following steps: Unlike Example 1, delignification treatment is not performed in step (1), and natural wood is directly used as template. The remaining steps are the same as in Example 1, and comparative example sample 1 is obtained.

[0045] (1) The wood is not treated with delignification by acidic sodium chlorite solution.

[0046] (2) Loading of thermochromic microcapsules: A blue thermochromic microcapsule dispersion with a concentration of 0.2 wt% was prepared. The thermochromic microcapsules change color around 25 ℃, remaining blue below 25 ℃ and colorless above 25 ℃. The obtained natural wood was completely immersed in the thermochromic microcapsule dispersion and soaked at 80 ℃ for one week. After soaking, the sample was removed and frozen at -20 ℃ for 12 h, followed by freeze-drying at -50 ℃ for 48 h to obtain a natural wood template loaded with blue thermochromic microcapsules.

[0047] (3) Multi-stage solution displacement treatment: Weigh 15 g of polymethyl methacrylate (PMMA) and add it to 90 g of acetone at 40 ℃ and stir until completely dissolved. Then add 90 g of ethanol and continue stirring until homogeneous to obtain a precursor solution. The natural wood template loaded with blue thermochromic microcapsules was completely immersed in the precursor solution and vacuum impregnated for 30 min under a vacuum gauge pressure of -0.08 MPa to allow the precursor solution to fully enter the internal pores of the wood. After impregnation, the sample was taken out and pre-dried at room temperature for 1 h to allow acetone to evaporate preferentially and adjust the composition of residual solvent inside the wood. Subsequently, the pre-dried sample was immersed in deionized water for 12 h. During this process, the deionized water gradually replaced the ethanol and residual acetone inside the wood, thereby inducing PMMA to form a porous structure in the wood pores. Finally, the sample was frozen at -20 ℃ for 12 h and then freeze-dried at -50 ℃ for 48 h to obtain comparative sample 1.

[0048] Comparative Example 2: The preparation method of the thermochromic radiation-cooled wood in this comparative example is carried out according to the following steps: Unlike Example 1, the thermochromic microcapsule loading treatment is not performed in step (2), and the remaining steps are the same as in Example 1, to obtain comparative example sample 2.

[0049] (1) Preparation of delignified wood: Longitudinal balsa wood chips with dimensions of 50 mm × 50 mm × 5 mm were selected as the substrate. A sodium chlorite solution with a mass concentration of 1 wt% was prepared, and the pH of the solution was adjusted to 4.6 using glacial acetic acid. The balsa wood chips were completely immersed in the above acidic sodium chlorite solution and delignified at 80 ℃ for 24 h. The acidic sodium chlorite solution was replaced every 6 h during the treatment until the sample turned white. After the treatment, the sample was repeatedly washed with deionized water until the washing solution was neutral. The sample was then removed and frozen at -20 ℃ for 12 h, and then freeze-dried at -50 ℃ for 48 h to obtain delignified wood templates.

[0050] (2) Delignified wood templates are not loaded with thermochromic microcapsules.

[0051] (3) Multi-stage solution displacement treatment: Weigh 15 g of polymethyl methacrylate (PMMA) and add it to 90 g of acetone at 40 ℃ and stir until completely dissolved. Then add 90 g of ethanol and continue stirring until homogeneous to obtain a precursor solution. Immerse the delignified wood template completely in the precursor solution and vacuum impregnate it for 30 min under a vacuum gauge pressure of -0.08 MPa to allow the precursor solution to fully enter the internal pores of the wood. After impregnation, remove the sample and pre-dry it at room temperature for 1 h to allow acetone to evaporate preferentially and adjust the composition of residual solvent inside the wood. Then, immerse the pre-dried sample in deionized water for 12 h. During this process, the deionized water gradually replaces the ethanol and residual acetone inside the wood, thereby inducing PMMA to form a porous structure in the wood pores. Finally, freeze the sample at -20 ℃ for 12 h and then freeze-dry it at -50 ℃ for 48 h to obtain comparative sample 2.

[0052] Comparative Example 3: The preparation method of the thermochromic radiation-cooled wood of this comparative example is carried out according to the following steps: Unlike Example 1, no polymer loading treatment is performed in step (3), and comparative example sample 3 is obtained directly.

[0053] (1) Preparation of delignified wood: Balsa wood chips with longitudinal sections were selected as the substrate, with dimensions of 50 mm × 50 mm × 5 mm. A 1 wt% sodium chlorite solution was prepared, and the pH of the solution was adjusted to 4.6 using glacial acetic acid. The balsa wood chips were completely immersed in the above acidic sodium chlorite solution and delignified at 80 ℃ for 24 h. The acidic sodium chlorite solution was replaced every 6 h during the treatment until the sample turned completely white. After the treatment, the wood was repeatedly washed with deionized water until the washing solution was neutral, thus obtaining delignified wood.

[0054] (2) Loading of thermochromic microcapsules: A blue thermochromic microcapsule dispersion with a concentration of 0.2 wt% was prepared. The thermochromic microcapsules change color around 25 °C, remaining blue below 25 °C and colorless above 25 °C. The obtained delignified wood was completely immersed in the thermochromic microcapsule dispersion and soaked at 80 °C for one week. After soaking, the sample was removed and frozen at -20 °C for 12 h, followed by freeze-drying at -50 °C for 48 h to obtain delignified wood templates loaded with blue thermochromic microcapsules.

[0055] (3) No polymer loading treatment: The delignified wood template loaded with blue thermochromic microcapsules was no longer subjected to polymethyl methacrylate precursor solution impregnation, pre-drying and deionized water replacement treatment, and directly obtained comparative sample 3.

[0056] Comparative Example 4: The preparation method of the thermochromic radiation-cooled wood in this comparative example is carried out according to the following steps: Unlike Example 1, in step (3), after the delignified wood template loaded with thermochromic microcapsules is immersed in the precursor solution, it is not subjected to deionized water replacement treatment, but is directly dried to obtain comparative example sample 4.

[0057] (1) Preparation of delignified wood: Balsa wood chips with longitudinal sections were selected as the substrate, with dimensions of 50 mm × 50 mm × 5 mm. A 1 wt% sodium chlorite solution was prepared, and the pH of the solution was adjusted to 4.6 using glacial acetic acid. The balsa wood chips were completely immersed in the above acidic sodium chlorite solution and delignified at 80 ℃ for 24 h. The acidic sodium chlorite solution was replaced every 6 h during the treatment until the sample turned completely white. After the treatment, the wood was repeatedly washed with deionized water until the washing solution was neutral, thus obtaining delignified wood.

[0058] (2) Loading of thermochromic microcapsules: A blue thermochromic microcapsule dispersion with a concentration of 0.2 wt% was prepared. The thermochromic microcapsules change color around 25 ℃, appearing blue below 25 ℃ and colorless above 25 ℃. The obtained delignified wood was completely immersed in the thermochromic microcapsule dispersion and soaked at 80 ℃ for one week. After soaking, the sample was removed and frozen at -20 ℃ for 12 h, followed by freeze-drying at -50 ℃ for 48 h to obtain delignified wood templates loaded with blue thermochromic microcapsules.

[0059] (3) Polymer loading treatment: Weigh 15 g of polymethyl methacrylate, add it to 90 g of acetone at 40 ℃ and stir until completely dissolved, then add 90 g of ethanol and continue stirring until homogeneous to obtain a precursor solution. Completely immerse the delignified wood template loaded with blue thermochromic microcapsules in the precursor solution and vacuum impregnate it for 30 min under a vacuum gauge pressure of -0.08 MPa to allow the precursor solution to fully penetrate the internal pores of the wood. After impregnation, take out the sample and pre-dry it at room temperature for 1 h, then freeze it directly at -20 ℃ for 12 h, and then freeze-dry it at -50 ℃ for 48 h without deionized water replacement treatment to obtain comparative sample 4.

[0060] The solar reflectance of the samples was measured using an ultraviolet / visible spectrometer, and the emissivity was measured using a Fourier transform infrared spectrometer equipped with an integrating sphere. To evaluate the daytime radiative cooling performance of the samples, outdoor testing was conducted. The testing location was Nanjing Forestry University, and the testing time was from 9:00 to 13:00 under clear, cloudless weather conditions. The test samples were placed on a foam insulation board, the outer surface of which was covered with aluminum foil to reduce conductive heat input to the substrate and minimize external thermal radiation interference. A transparent polyethylene film was placed above the testing device to reduce the influence of air convection on the test results while ensuring sunlight transmission and the infrared radiation heat dissipation process within the samples.

[0061] The testing system includes a multi-channel temperature recorder, a solar irradiance meter, an anemometer, a hygrometer, foam insulation panels, a transparent polyethylene film, and a computer. The multi-channel temperature recorder is a HuiPu TCP-400X, used to record the sample surface temperature and the air temperature inside the test chamber covered by the transparent polyethylene film in real time; the solar irradiance meter is a TES-1333R, used to record solar irradiance intensity; the anemometer is a Biaozhi GT8913, used to record the outdoor wind speed around the test platform; and the hygrometer is a TH40G4-EX, used to record the outdoor relative humidity around the test platform.

[0062] During the test, the air temperature inside the test chamber covered by the transparent polyethylene film was recorded as AT, which is the local air temperature around the sample, not the outdoor ambient temperature. During the test, AT was approximately 42–58 °C, and the solar irradiance was approximately 830–1120 W / m². 2 The relative humidity was approximately 20–27%, and the wind speed was approximately 0–6.8 m / s, mostly below 2 m / s. The cooling effect of the samples was evaluated by the temperature difference between the sample surface temperature and the AT (temperature attenuation). The average cooling rate was the average of the temperature difference between the AT and the sample surface temperature over the test period. The test results are shown in Table 1.

[0063] Table 1. Optical properties of thermochromic radiation-cooled wood The structure and performance analysis of the sample obtained in Example 1 are as follows.

[0064] like Figure 1 As shown, the thermochromic radiation-cooled wood obtained in Example 1 of this invention exhibits significant color change behavior under different temperature conditions. Figure 1 As shown in Figure a, the sample turns blue when the temperature is below 25 ℃; Figure 1As shown in Figure b, when the temperature exceeds 25 °C, the sample color gradually fades and becomes white or nearly colorless. These results indicate that thermochromic microcapsules can maintain good thermal response properties within a wood matrix and impart significant reversible thermochromic properties to the resulting material. Simultaneously, the sample maintains high whiteness at high temperatures, which is beneficial for enhancing its ability to reflect solar radiation.

[0065] like Figure 2 As shown, natural wood (a, a1) retains a relatively complete and regular natural porous framework structure, with cell cavities and vessel channels arranged along the wood growth direction. In delignified wood loaded with thermochromic microcapsules (b, b1), a large number of near-spherical particles distributed on the cell wall surface and inside the pores were observed, indicating that the thermochromic microcapsules successfully entered the delignified wood and achieved effective loading. In thermochromic radiation-cooled wood (c, c1), while retaining the natural porous structure of the wood, a network or sponge-like porous polymer structure further formed inside the pores. These results demonstrate that a porous polymer network can be successfully constructed inside the natural template of wood through precursor impregnation, pre-drying, and non-solvent replacement treatment, thus providing a structural basis for improving light scattering ability and radiation cooling performance.

[0066] like Figure 3 As shown, the thermochromic radiation-cooled wood obtained in Example 1 of this invention exhibits high reflectivity within the solar radiation band, with an average solar reflectivity of 90.80%. Furthermore, its reflectivity is significantly higher than that of natural wood under both high and low temperature conditions. This indicates that after delignification treatment, thermochromic microcapsule loading, and the construction of a porous polymer structure, the material's absorption of solar radiation is significantly reduced, while still maintaining high solar reflectivity during temperature changes.

[0067] like Figure 4 As shown, the thermochromic radiation-cooled wood obtained in Example 1 of this invention maintains a high level of emissivity within the 8–13 μm atmospheric window range, with an average emissivity of 94.98%. Compared with natural wood, the thermochromic radiation-cooled wood exhibits a higher overall emissivity or maintains a high level in this wavelength range, indicating that the material of this invention has excellent mid-infrared thermal radiation capability and can effectively release its own heat to the outside world in the form of radiation, thereby facilitating passive radiation cooling.

[0068] In summary, the present invention achieves a good passive radiative cooling effect by constructing a porous polymer structure through delignification treatment, thermochromic microcapsule loading, and solution displacement, thereby enabling the obtained thermochromic radiative-cooled wood to simultaneously possess significant thermochromic properties, high solar reflectivity (90.80%), and excellent mid-infrared emissivity (94.98%).

Claims

1. A method for preparing thermochromic radiation-cooled wood, characterized in that, The preparation method includes the following steps: Step 1: Place the wood in an acidic sodium chlorite solution for delignification treatment. After treatment, wash until neutral to obtain delignified wood. Step 2: Immerse the delignified wood in a thermochromic microcapsule dispersion for loading treatment, and freeze-dry after loading to obtain a delignified wood template loaded with thermochromic microcapsules. Step 3: The delignified wood template loaded with thermochromic microcapsules is impregnated in a polymer-containing precursor solution, allowing the precursor solution to enter the internal pores of the wood. After impregnation, the sample is pre-dried, and then the sample is immersed in a non-solvent, allowing the non-solvent to gradually replace the residual solvent inside the wood, thereby forming a porous polymer structure inside the wood. Subsequently, it is freeze-dried to obtain thermochromic radiation-cooled wood.

2. The preparation method according to claim 1, characterized in that, In step 1, the wood is balsa wood, poplar wood, or fir wood.

3. The preparation method according to claim 1, characterized in that, In step 1, the concentration of the acidic sodium chlorite solution is 1 wt%, the pH is 4-5, and the treatment temperature is 80 ℃.

4. The preparation method according to claim 1, characterized in that, In step 2, the color-changing temperature of the thermochromic microcapsules is 20–35 °C.

5. The preparation method according to claim 1, characterized in that, In step 2, the concentration of the thermochromic microcapsule dispersion is 0.1 wt% to 1 wt%.

6. The preparation method according to claim 1, characterized in that, In step 2, the thermochromic microcapsules are either blue or red thermochromic microcapsules.

7. The preparation method according to claim 1, characterized in that, In step 3, the polymer is polymethyl methacrylate; the precursor solution is composed of polymethyl methacrylate, an organic solvent, and a co-solvent; the organic solvent is acetone, and the co-solvent is ethanol.

8. The preparation method according to claim 1, characterized in that, In step 3, the non-solvent is deionized water.

9. The preparation method according to claim 1, characterized in that, In step 3, the pre-drying temperature is 25 °C for 1 h, and the sample is immersed in a non-solvent for 12 h for displacement treatment.

10. A thermochromic radiation-cooled wood, characterized in that, The thermochromic radiation-cooled wood is prepared by the method described in any one of claims 1 to 9, comprising: a delignified wood skeleton with hierarchical channels; thermochromic microcapsules loaded on the inner wall of the channels of the wood skeleton; and a porous polymer network filling the channels of the wood skeleton; wherein the wood exhibits a first color below the color change temperature and a second color above the color change temperature, and the emissivity of the wood in the 8-13 μm atmospheric window is ≥90%.

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