A recyclable cellulose radiation refrigeration material and its preparation method

Abstract

The present invention discloses a recyclable cellulose radiative cooling material and a preparation method thereof, relating to the technical fields of optics and materials science and engineering. The preparation method comprises the following steps: mixing cellulose fibers and cellulose powder, stirring, to obtain a cellulose mixed suspension; coating the suspension, and drying the suspension to obtain the cellulose radiative cooling material. The refrigeration material of the present invention is prepared at room temperature, employing a simple process, exhibits high solar reflectivity and infrared thermal radiation emissivity, and can achieve excellent radiative cooling performance. Furthermore, the cellulose radiative cooling material can be recycled by simply heating and stirring, making it significantly low-cost and environmentally friendly.

Description

Technical Field

[0001] The invention discloses a recyclable cellulose radiation refrigeration material and a preparation method thereof, and belongs to the technical field of optics and material science and engineering. Background Art

[0002] Unlike nearly all other available energy technologies, the sun's radiant heat is deposited into the surrounding environment. Radiative cooling, on the other hand, is an emerging cooling technology that emits heat directly into ultra-cold outer space through the atmosphere's "transparent window" (8-13 μm) without consuming any energy. It has enormous potential for reducing building energy consumption. For daytime radiative cooling, the refrigerator also needs to incorporate a sunlight reflection mechanism and increase the emissivity of thermal radiation, thereby achieving a daytime cooling system.

[0003] Currently, reported radiative cooling coatings primarily include photonic crystals, inorganic particulate materials, and petroleum-based polymer composites. By emitting significant amounts of solar heat and increasing mid-infrared thermal emissivity, these coatings can lower the surface temperature of the material below the ambient temperature under direct sunlight, achieving a radiative cooling effect. Chinese patent CN111468378 A discloses a low-cost, large-area radiative cooling film with an average solar reflectivity of 90% and an average atmospheric window emissivity of 92%, achieving a cooling effect approximately 8°C below outdoor temperatures. However, the extensive use of precious metals (gold and silver) results in high costs. Regarding inorganic materials, Chinese patent CN113416521 A discloses a daytime radiative cooling material and its preparation method. This material utilizes inorganic particles ranging in size from 0.1 to 100 μm, sintered at high temperatures (500-3000°C). This material exhibits high solar reflectivity and high atmospheric window infrared emissivity, enabling efficient radiative cooling. However, the low bonding strength of the particles results in low tensile strength, and the high-temperature sintering process also consumes significant energy. Regarding petroleum-based polymer composites, Chinese patent CN 114481636 A discloses a textile coating with radiative cooling capabilities. The coating primarily consists of a textile layer composed of a water-based acrylic resin and a functional layer composed of inorganic particles, exhibiting excellent radiative cooling and cooling effects. Chinese patent CN 1113698641 A discloses a radiative cooling film material based on indium oxide nanocrystals, primarily obtained by drying a mixture of tin, indium oxide, and polymethyl methacrylate. The film can cover the entire atmospheric window and enhance the material's radiative cooling power. However, oil-based polymer composites are primarily composed of non-biodegradable and non-renewable plastics and often involve the use of hazardous chemicals (organic solvents), which can lead to significant primary energy consumption and environmental pollution.

[0004] Due to its excellent structural and optical properties, naturally abundant cellulose has promising prospects for the development of radiative cooling materials. Chinese patent CN 113024866 A discloses a hydrophobic cellulose material with an anisotropic structure for daytime passive radiative cooling. The material is prepared by dissolving cellulose, coating the cellulose solution on a substrate, drying it in a high-voltage electrostatic field to form a film, and then modifying it with a solution of a hydrophobic polymer to obtain a passive radiative cooling hydrophobic cellulose material, achieving daytime radiative cooling performance. However, the preparation process is relatively complex, operability is poor, and reflectivity is low. Furthermore, the aforementioned radiative cooling material is difficult to recycle, thereby increasing its cost. Summary of the Invention

[0005] In view of the above existing problems, the present invention provides a cellulose radiation refrigeration material which is recyclable, simple in process and environmentally friendly and a preparation method thereof.

[0006] To achieve the above object, the technical solution of the present invention is:

[0007] A recyclable cellulose radiation refrigeration material and a preparation method thereof, comprising the following steps:

[0008] 1) Fully mixing cellulose fibers, cellulose powder and water to prepare a cellulose suspension;

[0009] 2) The cellulose mixed suspension is coated and dried to obtain a recyclable cellulose radiation refrigeration material.

[0010] Furthermore, in step 1), the cellulose fibers and cellulose powder are both derived from at least one of natural plant fibers selected from cotton fibers, wood fibers, grass fibers, hemp fibers and bamboo fibers.

[0011] Furthermore, in step 1), the diameter of the cellulose fibers is 300-900 nm.

[0012] Furthermore, in step 1), the mass fraction of cellulose fiber is 25%-40%, the mass fraction of cellulose powder is 20%-40%, and the mass fraction of water is 25-38%, and the sum of the three is 100%.

[0013] Furthermore, in step 1), the particle size of the cellulose powder is 0.4-40 μm.

[0014] Furthermore, in step 2), the thickness of the recyclable cellulose radiation refrigeration material is greater than 50 μm.

[0015] The recyclable cellulose radiation refrigeration material of the present invention is heated and stirred in an aqueous solution to obtain a mixed suspension of cellulose fibers and cellulose powder, thereby realizing the recycling of the cellulose radiation refrigeration material.

[0016] Furthermore, the temperature of heating and stirring is 60-90°C.

[0017] The nanostructure of the cellulose fibers combined with the micro-nanostructure of the cellulose powder in the cellulose radiative cooling material prepared by the above-mentioned method creates a strong light-scattering effect, resulting in a high solar reflectivity. Cellulose contains a large number of mid-infrared absorbing chemical groups (e.g., CO and COC) in the "atmospheric window" band, which gives it excellent long-wave infrared emissivity. Cellulose radiative cooling materials are simple to prepare, have abundant sources, require no additional chemical reagents or additives, and are recyclable, making them cost-effective and environmentally friendly.

[0018] The benefits of the present invention are:

[0019] (1) The present invention proposes a method for preparing a recyclable cellulose radiative cooling material, which is simple to operate, environmentally friendly, and has high solar reflectivity and long-wave infrared emissivity.

[0020] (2) The cellulose radiation cooling material proposed in the present invention has a micro-nano fiber structure that effectively improves solar reflectivity, and the unique chemical groups provide excellent long-infrared emissivity.

[0021] (3) The cellulose radiation cooling material proposed in the present invention is recyclable. By heating and decomposing, a cellulose-cellulose powder suspension is obtained, which can be reused to construct a high-performance cellulose radiation cooling material. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 The cellulose radiation refrigeration material prepared by coating in step 1 is implemented;

[0023] Figure 2 These are SEM images of the material structures in Example 1, which are: a) cellulose radiation cooling material; b) cellulose powder; c) cellulose fiber;

[0024] Figure 3 is the reflectivity curve of the cellulose radiative cooling material, cellulose powder and cellulose fiber in embodiment 1;

[0025] Figure 4 is a Fourier transform infrared spectrum of the cellulose radiation refrigeration material in embodiment 1;

[0026] Figure 5 is the emissivity curve of the cellulose radiative cooling material, cellulose powder and cellulose fiber in embodiment 1;

[0027] Figure 6 This is a comparison chart of the cooling effects of the cellulose radiation refrigeration material in Implementation 1, cellulose fibers, and cellulose powder. DETAILED DESCRIPTION

[0028] The present invention provides a recyclable cellulose radiation refrigeration material and a preparation method thereof:

[0029] The present invention will be further described below with reference to specific examples so that those skilled in the art can better understand the present invention and implement it, but the examples are not intended to limit the present invention.

[0030] Example 1

[0031] a. Take wood fiber cellulose with a diameter of 500 nm, wood fiber cellulose powder with a diameter of 20 μm, and water and mix them evenly. The mass fractions are: cellulose fiber accounts for 35%; cellulose powder accounts for 33%; water accounts for 32%.

[0032] b. After mixing evenly, a cellulose radiative cooling material with a thickness of 50 μm was obtained by blade coating.

[0033] c. Add the collected cellulose refrigeration material into an aqueous solution and heat and stir at 70°C to prepare a mixed suspension of cellulose fiber and cellulose powder, thereby recovering the cellulose radiant refrigeration material.

[0034] The cellulose radiation refrigeration material ( Figure 1 ), where nano-scale cellulose fibers can produce a good scattering effect on nano-scale wavelength light, and micron-scale cellulose powder can produce a good scattering effect on micron-scale wavelength light. By combining the micro- and nano-structures of cellulose fibers and cellulose powder ( Figure 2 ), which can form a wide wavelength light scattering effect (0~2.5 μm), thereby greatly improving the reflectivity of cellulose radiation cooling materials to sunlight ( Figure 3 ), which is impossible to achieve with cellulose fiber or cellulose powder alone. In addition, the cellulose molecules in the cellulose material contain a large number of functional groups (CO and COC) ( Figure 4 ), giving cellulose radiative cooling materials excellent long-wave infrared emissivity ( Figure 5 ), which can achieve infrared heat exchange with the ultra-cold universe through the transparent window of the atmosphere, realizing its own cooling performance. Outdoor test results show that the temperature of cellulose radiation cooling material is 40℃, which is 4℃ lower than the outdoor temperature, while the temperature of cellulose powder is still 43℃, and the temperature of cellulose fiber is still 44℃ ( Figure 6 ). In addition, cellulose powder has poor adhesion to the substrate and is easily detached from the substrate surface.

[0035] Example 2

[0036] a. Mix 400 nm diameter cotton cellulose fibers, 20 μm diameter cotton cellulose powder, and water. The mass fraction distribution is: 30% cellulose fibers; 35% cellulose powder; and 35% water.

[0037] b. After mixing evenly, a cellulose radiative cooling material with a thickness of 200 μm was obtained by blade coating.

[0038] c. Add the collected cellulose refrigeration material into an aqueous solution and heat and stir at 80°C to prepare a mixed suspension of cellulose fiber and cellulose powder, thereby recovering the cellulose radiant refrigeration material.

[0039] Example 3

[0040] a. Mix 600 nm diameter hemp fiber, 40 μm diameter hemp fiber cellulose powder, and water. The mass fraction distribution is: 40% cellulose fiber; 30% cellulose powder; and 30% water.

[0041] b. After mixing evenly, a cellulose radiative cooling material with a thickness of 2000 μm was obtained by blade coating.

[0042] c. Add the collected cellulose refrigeration material into an aqueous solution and heat and stir at 90°C to prepare a mixed suspension of cellulose fiber and cellulose powder, thereby recovering the cellulose radiant refrigeration material.

[0043] Example 4

[0044] a. Mix 300 nm diameter grass fiber cellulose fibers, 5 μm diameter grass fiber cellulose powder, and water. The mass fraction distribution is: 32% cellulose fiber; 35% cellulose powder; and 33% water.

[0045] b. After mixing evenly, a cellulose radiative cooling material with a thickness of 1000 μm was obtained by blade coating.

[0046] c. Add the collected cellulose refrigeration material into an aqueous solution and heat and stir at 85°C to prepare a mixed suspension of cellulose fiber and cellulose powder, thereby recovering the cellulose radiant refrigeration material.

[0047] Example 5

[0048] a. Mix bamboo cellulose fibers with a diameter of 900 nm, bamboo cellulose powder with a diameter of 0.4 μm, and water. The mass fraction distribution is: cellulose fibers account for 28%, cellulose powder accounts for 35%, and water accounts for 37%.

[0049] b. After mixing evenly, a cellulose radiative cooling material with a thickness of 500 μm was obtained by blade coating.

[0050] c. Add the collected cellulose refrigeration material into an aqueous solution and heat and stir at 75°C to prepare a mixed suspension of cellulose fiber and cellulose powder, thereby recovering the cellulose radiant refrigeration material.

[0051] Other reagents used in the present invention are all reagents that can be purchased or prepared in the prior art and will not be described again.

[0052] The above embodiments are merely preferred embodiments for the purpose of fully illustrating the present invention, and the scope of protection of the present invention is not limited thereto. Equivalent substitutions or modifications made by those skilled in the art based on the present invention are within the scope of protection of the present invention. The scope of protection of the present invention shall be subject to the claims.

Claims

1. A recyclable cellulose radiation refrigeration material and a preparation method thereof, characterized in that: The following steps are involved: 1) Fully mixing cellulose fibers, cellulose powder and water to prepare a cellulose suspension; 2) The cellulose suspension is coated and dried to obtain a recyclable cellulose radiation cooling material; The diameter of the cellulose fibers in step 1) is 50-900 nm; The particle size of the cellulose powder in step 1) is 0.2-50 μm.

2. The preparation method according to claim 1, wherein: In step 1), the cellulose fiber and cellulose powder are both derived from at least one of cotton fiber, wood fiber, grass fiber, hemp fiber and bamboo fiber in natural plants.

3. The preparation method according to claim 1, wherein: The mass fraction of cellulose fibers in the cellulose suspension of step 1) is 20%-40%.

4. The preparation method according to claim 1, wherein: The mass fraction of cellulose powder in step 1) is 20%-50%.

5. The preparation method according to claim 1, wherein: The mass fraction of water in step 1) is 20-38%.

6. A recyclable cellulose radiation refrigeration material prepared by the preparation method according to any one of claims 1 to 5.

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