A method for preparing a radiation cooling paper

Abstract

The application discloses a preparation method of a radiation refrigeration paper and belongs to the technical fields of optical illumination and papermaking. The preparation method comprises the following steps: 1) soaking cellulose paper in alkali water for swelling, and then soaking the paper in a hydroxyapatite (HAP) / ethanol suspension; and 2) obtaining the refrigeration paper by hot pressing the soaked paper through a hot press. The radiation refrigeration paper prepared by the method has high solar reflectivity and long-wave infrared emissivity, excellent radiation refrigeration performance, simple preparation process, and is suitable for large-scale production, and the product is degradable and recyclable, has remarkable economic and social benefits, and has a wide application prospect.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of optical illumination and papermaking technology, and particularly relates to a preparation method of a radiative cooling paper. BACKGROUND

[0002] Radiative cooling technology is a sustainable cooling technology that achieves self-sustainability by reflecting sunlight and emitting heat. Compared with traditional cooling technologies (for example, air conditioners), the radiative cooling technology does not need to consume any energy. The temperature of the earth's surface can be maintained at a relatively stable temperature of about 300 K, which is mainly caused by the balance of radiative heat flux between the incident sunlight and the heat radiation emitted to the cold universe. The global solar radiation absorbed every day is huge, and the total output heat radiation is also very large. Therefore, it is important for the radiative cooling technology to utilize the coldness of the universe as a renewable energy source.

[0003] At present, the main radiative cooling materials reported in the literature mainly include photonic crystals, high molecular polymers, porous high molecular materials and composite materials, which can achieve the effect of radiative cooling by reducing the absorption of sunlight and increasing the emissivity in the middle infrared. Under the condition of direct sunlight, the temperature of the material surface is lower than the ambient temperature. Among these materials, the preparation method of photonic crystals is complex, time-consuming, labor-intensive and energy-consuming. High molecular polymers, porous high molecular materials and composite materials are mainly composed of non-degradable and non-renewable plastics. For example, CN110042564A discloses a radiative cooling material in which radiative particles (SiO2) are randomly distributed in a polymer (one of PE, PA6, PMMA and PVDF); CN113235172A discloses a composite fiber composed of a base resin and needle-shaped magnesium phosphite. Although the above materials have the performance of radiative cooling, the production cost is high, and the products are easy to cause a large consumption of primary energy and pollution of the natural environment. SUMMARY

[0004] The purpose of the present application is to provide a preparation method of a radiative cooling paper which is easy to operate, renewable, degradable and has abundant raw material sources.

[0005] To achieve the above purpose, the technical scheme adopted by the present application is as follows:

[0006] A preparation method of a radiative cooling paper comprises the following steps:

[0007] 1) Plant fibers are soaked and mechanically beaten to obtain plant fiber slurry;

[0008] 2) The plant fiber slurry prepared in step 1) is made into paper, soaked in a sodium hydroxide solution for swelling, and then cleaned with an ethanol solution to neutralize;

[0009] 3) immersing the cellulose paper prepared in step 2) into an ethanol suspension of hydroxyapatite, and then hot-pressing to obtain the radiative cooling paper.

[0010] The plant fiber in step 1) is selected from at least one of cotton fiber, wood fiber, grass fiber, hemp fiber and bamboo fiber, and has a diameter of 50 nm to 50 μm and a length of 500 nm to 5 cm.

[0011] The beating degree of the mechanical beating in step 1) is 40 to 80 °SR.

[0012] The basis weight of the paper in step 2) is 30 to 200 g / m 2 .

[0013] The mass fraction of the sodium hydroxide solution in step 2) is 0.05 to 8 %, and the swelling time is 1 to 6 h.

[0014] The volume fraction of the ethanol solution in step 2) is 30 to 70 %.

[0015] The mass fraction of the hydroxyapatite in the suspension in step 3) is 2 to 15 %.

[0016] The particle size of the hydroxyapatite in step 3) is 50 nm to 20 μm.

[0017] The hot-pressing time in step 3) is 2 to 60 min, the pressure is 0.1 to 5 MPa, and the temperature is 60 to 90 °C.

[0018] The present application has the advantages that the HAP is uniformly dispersed on the cellulose fiber, the prepared radiative cooling paper has high solar reflectivity and long-wave infrared emissivity, excellent radiative cooling performance, simple preparation process, large-scale production, product degradation and recycling, significant economic and social benefits, and wide application prospect. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 is the SEM image of the original fiber in Example 1;

[0020] Figure 2 is the SEM image of the fiber of the radiative cooling paper in Example 1;

[0021] Figure 3 is the emissivity and emissivity curve of the radiative cooling paper in Example 1. DETAILED DESCRIPTION

[0022] The present application will be further described in conjunction with specific examples, so that those skilled in the art can better understand the present application and implement it, but the examples are not limiting to the present application.

[0023] Example 1

[0024] a. Take 5 g of coniferous wood pulp (octane dry), loosen it for 3 min, and make paper for later use;

[0025] b. Cut the coniferous cellulose paper into 80 x 120 x 0.13 mm pieces. 3 The rectangular prism was soaked in a 5% (w / w) sodium hydroxide solution for 4 hours to allow it to swell, and then washed with an ethanol / water (v / v 2:1) solution until neutral. The washed cellulose paper was then immersed in anhydrous ethanol and allowed to stand for 4 hours.

[0026] c. Soak the swollen cellulose paper in HAP / ethanol suspension (5 mg / mL) for 2 hours, and then hot press it at 1 MPa (90 °C) for 10 minutes to obtain radiation cooling paper.

[0027] The radiation-cooling paper obtained through the above steps, together with the original fibers ( Figure 1 Compared to radiation-cooled paper, the fiber fibrillation of the paper exposes more fine fibers, allowing HAP to be better dispersed on the cellulose. Figure 2 This demonstrates the high solar reflectivity and long-wave infrared emissivity of the radiation-cooled paper. Figure 3 ).

[0028] Example 2

[0029] a. Take 4.5 g of hardwood pulp (octane dry), loosen it for 5 min, and make paper for later use;

[0030] b. Cut the coniferous cellulose paper into 60 x 100 x 0.13 mm pieces. 3 The rectangular prism was soaked in a 6% (w / w) sodium hydroxide solution for 3 hours to allow it to swell, and then washed with an ethanol / water (v / v 2:1) solution until neutral. The washed cellulose paper was then immersed in anhydrous ethanol and allowed to stand for 2 hours.

[0031] c. Soak the swollen cellulose paper in HAP / ethanol suspension (10 mg / mL) for 2 h, and then hot press it at 2 MPa (80 °C) for 8 min to obtain radiation cooling paper.

[0032] Example 3

[0033] a. Take 5 g of bamboo pulp (completely dry), loosen it for 4 min, and make paper for later use;

[0034] b. Cut the coniferous cellulose paper into 50 x 100 x 0.13 mm pieces. 3of 70 x 100 x 0.13 mm; soaked in 4% (w / w) sodium hydroxide solution for 5 h, after swelling, washed to neutral with ethanol / water (v / v 1 : 1) solution. The washed cellulose paper was immersed in absolute ethanol and left for 2 hours.

[0035] c. The swollen cellulose paper was soaked in HAP / ethanol suspension (7 mg / mL) for 4 h, and then hot-pressed by a hot press at 0.5 MPa (70 °C) for 12 min to obtain the radiative cooling paper.

[0036] Example 4

[0037] a. Take 6 g of hemp pulp (absolute dry), defibrate for 3 min, and prepare for papermaking;

[0038] b. The coniferous wood cellulose paper was cut into 70 x 100 x 0.13 mm 3 cuboids; soaked in 6% (w / w) sodium hydroxide solution for 3 h, after swelling, washed to neutral with ethanol / water (v / v 1 : 1) solution. The washed cellulose paper was immersed in absolute ethanol and left for 3 hours.

[0039] c. The swollen cellulose paper was soaked in HAP / ethanol suspension (6 mg / mL) for 3 h, and then hot-pressed by a hot press at 1.5 MPa (90 °C) for 8 min to obtain the radiative cooling paper.

[0040] Example 5

[0041] a. Take 4.5 g of cotton pulp (absolute dry), defibrate for 5 min, and prepare for papermaking;

[0042] b. The coniferous wood cellulose paper was cut into 70 x 100 x 0.13 mm 3 cuboids; soaked in 4% (w / w) sodium hydroxide solution for 1.5 h, after swelling, washed to neutral with ethanol / water (v / v 2: 1) solution. The washed cellulose paper was immersed in absolute ethanol and left for 2 hours.

[0043] c. The swollen cellulose paper was soaked in HAP / ethanol suspension (5 mg / mL) for 2 h, and then hot-pressed by a hot press at 1 MPa (85 °C) for 5 min to obtain the radiative cooling paper.

[0044] Example 6

[0045] a. Take 6.5 g of grass pulp (absolute dry), defibrate for 7 min, and prepare for papermaking;

[0046] b. The coniferous wood cellulose paper was cut into 60 x 100 x 0.13 mm 3cotton cellulose paper (Whatman® 903) was cut into 2 cm x 2 cm x 0.2 cm cuboids; soaked in 6% (w / w) sodium hydroxide solution for 3 h, swelled, and washed to neutral with ethanol / water (v / v 1 : 1) solution. The washed cellulose paper was immersed in absolute ethanol and left to stand for 5 h.

[0047] c. The swelled cellulose paper was soaked in HAP / ethanol suspension (8 mg / mL) for 2 h, and hot-pressed by a hot press at 0.2 MPa pressure (80 °C) for 8 min to obtain the radiative cooling paper.

[0048] Other reagents used in the present application are commercially available or prepared according to the prior art, and are not listed again.

[0049] The above-described examples are only preferred examples for fully illustrating the present application, and the protection scope of the present application is not limited thereto. Any equivalent replacement or transformation made by the skilled in the art based on the present application is within the protection scope of the present application. The protection scope of the present application is subject to the claims.

Claims

1. A radiative cooling paper, characterized in that: The preparation method comprises the following steps: 1) plant fibers are soaked and mechanically beaten to obtain a plant fiber slurry; 2) the plant fiber slurry obtained in step 1) is made into paper, soaked in a sodium hydroxide solution for swelling, and then cleaned with an ethanol solution to neutralize; 3) the cellulose paper obtained in step 2) is immersed in an ethanol suspension of hydroxyapatite, and a hot-pressing treatment is performed to obtain the radiation cooling paper; In step 1), the beating degree of mechanical beating is 40-80 °SR; In step 3), the particle size of the hydroxyapatite is 50 nm-20 μm; In step 3), the mass fraction of the hydroxyapatite in the suspension is 2-15 %; and the immersion time of the cellulose paper is 2 h, 3 h or 4 h.

2. The radiative cooling paper of claim 1, wherein: In step 1), the plant fibers are selected from at least one of cotton fibers, wood fibers, grass fibers, hemp fibers and bamboo fibers, and have a diameter of 50 nm-50 μm and a length of 500 nm-5 cm.

3. The radiative cooling paper of claim 1, wherein: The basis weight of the paper in step 2) is 30 to 200 g / m 2 .

4. The radiative cooling paper of claim 1, wherein: In step 2), the mass fraction of the sodium hydroxide solution is 0.05-8 %, and the swelling time is 1-6 h.

5. The radiative cooling paper of claim 1, wherein: In step 2), the volume fraction of the ethanol solution is 30-70 %.

6. The radiative cooling paper of claim 1, wherein: In step 3), the hot-pressing treatment is performed for 2-60 min at a pressure of 0.1-5 MPa and a temperature of 60-90 °C.

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