Passive cooling composite material and method for manufacturing the same

Abstract

The application belongs to the field of composite material preparation, and particularly relates to a passive cooling composite material and a preparation method thereof. The passive cooling composite material has the characteristics of low ultraviolet-visible-near-infrared transmittance and high mid-infrared radiation transmittance, and the cooling effect reaches 3.79 DEG C in outdoor direct sunlight cooling test. The composite material comprises a bottom film, an intermediate film layer and a passive cooling film layer arranged from bottom to top. The intermediate film layer is composed of the following raw materials: polyester chips, modified polyester, modified kaolin, vinyl bis-stearamide, calcium stearate and antioxidant. The passive cooling film layer is composed of the following raw materials: low-density polyethylene and modified titanium dioxide nanoparticles. The composite material prepared in the application shows good cooling effect, and provides a new idea for the preparation of radiation cooling materials and functional application in the textile field.

Description

Technical Field

[0001] This invention belongs to the field of composite material preparation, specifically relating to a passive cooling composite material and its preparation method. Background Technology

[0002] With industrialization and increased human activity, greenhouse gas emissions from industrial production and vehicle exhaust have led to global warming. The Sixth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC) states that over the past century, the burning of fossil fuels and unequal and unsustainable energy and land use have caused a sustained rise in global temperatures, now exceeding pre-industrial levels by 1.1°C. This has resulted in more frequent and intense extreme weather events, increasingly endangering nature and populations worldwide. As global warming intensifies, food and water insecurity will become increasingly severe; these risks will be exacerbated if they coincide with other adverse events such as pandemics or conflicts. Against this backdrop, cities, as the core carriers of human activity and energy consumption, are experiencing a "heat island effect." Increasingly dense building clusters, paved surfaces, and limited urban green spaces contribute to significantly higher urban temperatures compared to surrounding rural areas, making summer heat waves a major public health problem threatening the health and safety of hundreds of millions of urban residents. Traditional countermeasures rely heavily on active cooling systems (such as air conditioning). While these devices provide localized cooling, they also consume about 10% of the world's electricity and emit huge amounts of greenhouse gases and waste heat, creating a vicious cycle of "surge in cooling demand - increased energy consumption and carbon emissions - further global warming - further surge in cooling demand".

[0003] Therefore, radiative cooling materials based on personal thermal management have become a research hotspot. Currently, the invention of passive cooling materials is mainly in the form of coatings, which limits their application scenarios and makes them unsuitable for use in clothing fabrics, greatly restricting the widespread application of passive cooling materials. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a passive cooling composite material and its preparation method.

[0005] The present invention adopts the following technical solution:

[0006] A passive cooling composite material includes a PET film, an intermediate film layer, and a passive cooling film layer arranged sequentially from bottom to top.

[0007] The intermediate film layer is composed of the following raw materials in parts by weight: 100 parts polyester chips, 18-25 parts modified polyester, 12-15 parts modified kaolin, 3-5 parts vinyl bis-stearamide, 5-8 parts calcium stearate, and 1-3 parts antioxidant.

[0008] The passive cooling film is composed of the following raw materials in parts by weight: 100 parts of low-density polyethylene and 5-10 parts of modified titanium dioxide nanoparticles.

[0009] The modification method for modified titanium dioxide nanoparticles is as follows:

[0010] Step A: Place titanium dioxide nanoparticles in an alkaline anhydrous ethanol solution with a pH of 8-9 and ultrasonically disperse for 8-15 min to obtain a dispersion system.

[0011] Step B: Add 20 wt% of silane coupling agent KH-570 to the dispersion system and continue to disperse for 10 minutes to obtain product 1. Place product 1 in an oil bath at 55-65℃ and continue to disperse for 7-9 hours with magnetic stirring during the dispersion process to obtain product 2.

[0012] Step C: The centrifuged precipitate of product 2 was washed three times with anhydrous ethanol and deionized water, and the dried modified titanium dioxide nanoparticles were obtained.

[0013] Preferably, the modified polyester is composed of the following raw materials in parts by weight: 100 parts polyester, 20-30 parts polypropylene, 5-8 parts maleic anhydride-grafted polypropylene, and 6-10 parts organomontmorillonite.

[0014] Preferably, the modified polyester is prepared by the following method:

[0015] S1. The polyester was vacuum dried at 120℃ for 6 hours to achieve a moisture content of ≤0.02%.

[0016] S2. Mix polypropylene and maleic anhydride-grafted polypropylene in a high-speed mixer for 5 minutes to obtain a premix.

[0017] S3. The dried polyester, premix and organomontmorillonite are fed into a twin-screw extruder for melt blending, extrusion and pelletizing, and dried at 80°C for 2 hours to obtain the modified polyester.

[0018] Preferably, the passive cooling film layer is prepared as follows:

[0019] Step 1: Place the low-density polyethylene in a dryer and dry for 6 hours to control the moisture content of the low-density polyethylene to below 20 ppm.

[0020] Step 2: The dried low-density polyethylene and modified titanium dioxide nanoparticles are premixed for 30 minutes. After thorough mixing, the mixture is fed into a twin-screw extruder for melt blending. After extrusion and pelletizing, the mixture is fed back into the twin-screw extruder for melt blending. This operation is repeated 2-5 times until the mixture is extruded into sheets. The sheets are then quickly solidified into films on cooling rollers. After traction and edge trimming, the passive cooling film layer is obtained.

[0021] Preferably, in step two, the temperature of the twin-screw extruder head is 210℃, the temperature of zone one is 210℃, the temperature of zone two is 215℃, the temperature of zone three is 220℃, the temperature of zone four is 220℃, the temperature of zone five is 220℃, the temperature of zone six is ​​210℃, the pelletizing speed is 200r / min, the main machine speed is 13Hz, and the feeding speed is 4Hz.

[0022] Preferably, the thickness of the PET film is 0.01-0.02 mm.

[0023] A method for preparing a passive cooling composite material includes the following steps:

[0024] Step 1: Apply adhesive to the PET film, then bond the intermediate film layer to the PET film under the action of hot press rollers. After cooling, send it into the curing chamber and cure at 40-50℃ for 4-6 hours.

[0025] Step 2: Apply adhesive to the intermediate film layer, and then apply the passive cooling film layer to the intermediate film layer under the action of hot rollers. After cooling, send it into the curing chamber and cure it at 50-60℃ for 24 hours. Allow it to cool naturally to room temperature to obtain the passive cooling composite material.

[0026] As can be seen from the above description of the present invention, compared with the prior art, the beneficial effects of the present invention are as follows: The composite material prepared in this application has low transmittance in ultraviolet-visible-near infrared (0.2-2.5μm) and nearly 100% transmittance in mid-infrared radiation (7-14μm), and can completely transmit mid-infrared light radiation emitted by the human body. The cooling effect in outdoor direct sunlight cooling test reaches 3.79℃. In particular, by defining the structural composition of the composite material, an intermediate film layer is added between the PET film and the passive cooling film layer to provide support for the passive cooling film layer and ensure the stability of the prepared composite material. Furthermore, the raw material composition of the intermediate film layer is further specifically defined. Modified polyester is introduced into the polyester chips in combination with other raw materials to enhance the barrier ability of the intermediate film layer against oxygen and water vapor, thereby improving the weather resistance of the prepared composite material and maintaining the stability of long-term optical and mechanical properties.

[0027] In modified polyester, polypropylene and organomontmorillonite are introduced as modifiers to improve the strength and toughness of the modified polyester, ensuring the support of the prepared intermediate film layer for the passive cooling film layer. Furthermore, the layered structure of montmorillonite can prolong the diffusion path of gas molecules in the material, significantly reducing the permeation rate of small molecules such as oxygen and water vapor, thereby improving the barrier capacity of the prepared intermediate film layer. The introduced polypropylene has excellent resistance to acids, alkalis and various solvents, which can enhance the composite material's resistance to external chemical media, thereby improving the weather resistance of the prepared composite material and maintaining the stability of its long-term optical and mechanical properties.

[0028] The passive cooling film uses low-density polyethylene as raw material and modified silica nanoparticles as an additive. The raw material composition is simple, low-cost, and free of toxic chemicals. In outdoor direct sunlight cooling tests, it achieved a cooling effect of 3.79℃. It can improve the reflectivity of the passive cooling film to sunlight, and the passive cooling film can completely transmit mid-infrared and outer infrared radiation emitted by the human body, resulting in excellent cooling performance of the composite material. This provides new ideas for the preparation of radiative cooling materials and their functional applications in the textile industry. Furthermore, the modification method of the modified silica nanoparticles is further refined. The introduced silane coupling agent KH-570 contains a polar siloxane group at one end, which can undergo a hydrolytic condensation reaction with the hydroxyl groups on the surface of the titanium dioxide nanoparticles to form a stable Ti-O-Si. One end has chemical bonds; the other end is grafted with nonpolar organic long chains, which changes the surface of the modified titanium dioxide nanoparticles from polar to nonpolar, making them more consistent with the molecular polarity of nonpolar low-density polyethylene. This increases the compatibility between titanium dioxide nanoparticles and low-density polyethylene, thus solving the problem of uneven dispersion of nanoparticles in low-density polyethylene. Attached Figure Description

[0029] Figure 1 The FTIR spectrum of sample 2 prepared in Example 2;

[0030] Figure 2 XPS image of sample 2 prepared in Example 3;

[0031] Figure 3 X-ray diffraction patterns of sample 2, LDPE film, and TiO2-NPs prepared in Example 2;

[0032] Figure 4 Infrared transmittance diagrams for samples 1-5;

[0033] Figure 5 A schematic diagram and a photo of the actual self-made testing device are provided.

[0034] Figure 6 The radiation cooling temperature curves are for samples 1-5 and the blank sample. Detailed Implementation

[0035] The present invention will be further described below through specific embodiments.

[0036] A passive cooling composite material has the characteristics of low transmittance of ultraviolet-visible-near infrared light and high transmittance of mid-infrared radiation, and the cooling effect reaches 3.79℃ in outdoor direct sunlight cooling test. Specifically, the composite material includes a PET film, an intermediate film layer and a passive cooling film layer arranged from bottom to top; wherein, the thickness of the PET film is 0.01-0.02mm.

[0037] The intermediate film layer is composed of the following raw materials in parts by weight: 100 parts polyester chips, 18-25 parts modified polyester, 12-15 parts modified kaolin, 3-5 parts vinyl bis-stearamide, 5-8 parts calcium stearate, and 1-3 parts antioxidant. Specifically, the preparation method of the intermediate film layer is as follows:

[0038] (1) Dry the polyester chips at 1200℃ for 6 hours to control the moisture content of the polyester chips to below 30ppm;

[0039] (2) The dried polyester chips, modified polyester, modified kaolin, vinyl bis-stearamide, calcium stearate and antioxidant are fed into a twin-screw extruder for melt blending and extrusion to obtain a film layer thick sheet.

[0040] (3) The obtained film layer is preheated at 90°C for 15s, then fed into a tenter frame, stretched and shaped, and heat-set at 115°C for 5s, and then rapidly cooled to obtain the intermediate film layer.

[0041] The passive cooling film layer is composed of the following raw materials in parts by weight: 100 parts low-density polyethylene and 5-10 parts modified titanium dioxide nanoparticles; specifically, the preparation method of the passive cooling film layer is as follows:

[0042] Step 1: Place the low-density polyethylene in a dryer and dry for 6 hours to control the moisture content of the low-density polyethylene to below 20 ppm.

[0043] Step 2: The dried low-density polyethylene and modified titanium dioxide nanoparticles are premixed for 30 minutes. After thorough mixing, the mixture is fed into a twin-screw extruder for melt blending. After extrusion and pelletizing, the mixture is fed back into the twin-screw extruder for melt blending. This operation is repeated 2-5 times until the mixture is extruded into sheets. The sheets are then quickly solidified into films on cooling rollers. After traction and edge trimming, the passive cooling film layer is obtained.

[0044] In step two, the temperature of the twin-screw extruder head is 210℃, the temperature of zone one is 210℃, the temperature of zone two is 215℃, the temperature of zone three is 220℃, the temperature of zone four is 220℃, the temperature of zone five is 220℃, the temperature of zone six is ​​210℃, the pelletizing speed is 200r / min, the main machine speed is 13Hz, and the feeding speed is 4Hz.

[0045] The modification method for modified titanium dioxide nanoparticles is as follows:

[0046] Step A: Place titanium dioxide nanoparticles in an alkaline anhydrous ethanol solution with a pH of 8-9 and ultrasonically disperse for 8-15 min to obtain a dispersion system.

[0047] Step B: Add 20 wt% of silane coupling agent KH-570 to the dispersion system and continue to disperse for 10 minutes to obtain product 1. Place product 1 in an oil bath at 55-65℃ and continue to disperse for 7-9 hours with magnetic stirring during the dispersion process to obtain product 2.

[0048] Step C: The centrifuged precipitate of product 2 was washed three times with anhydrous ethanol and deionized water, and the dried modified titanium dioxide nanoparticles were obtained.

[0049] The modified polyester is composed of the following raw materials in parts by weight: 100 parts polyester, 20-30 parts polypropylene, 5-8 parts maleic anhydride-grafted polypropylene, and 6-10 parts organomontmorillonite; specifically, its preparation method is as follows:

[0050] S1. The polyester was vacuum dried at 120℃ for 6 hours to achieve a moisture content of ≤0.02%.

[0051] S2. Mix polypropylene and maleic anhydride-grafted polypropylene in a high-speed mixer for 5 minutes to obtain a premix.

[0052] S3. The dried polyester, premix and organomontmorillonite are fed into a twin-screw extruder for melt blending, extrusion and pelletizing, and dried at 80°C for 2 hours to obtain the modified polyester.

[0053] A method for preparing a passive cooling composite material includes the following steps:

[0054] Step 1: Apply adhesive to the PET film, then bond the intermediate film layer to the PET film under the action of hot press rollers. After cooling, send it into the curing chamber and cure at 40-50℃ for 4-6 hours.

[0055] Step 2: Apply adhesive to the intermediate film layer, and then apply the passive cooling film layer to the intermediate film layer under the action of hot rollers. After cooling, send it into the curing chamber and cure it at 50-60℃ for 24 hours. Allow it to cool naturally to room temperature to obtain the passive cooling composite material.

[0056] Example 1

[0057] A passive cooling composite material has the characteristics of low transmittance of ultraviolet-visible-near infrared light and high transmittance of mid-infrared radiation, and the cooling effect reaches 3.79℃ in outdoor direct sunlight cooling test. Specifically, the composite material includes a PET film, an intermediate film layer and a passive cooling film layer arranged from bottom to top; wherein, the thickness of the PET film is 0.015mm.

[0058] The intermediate film layer is composed of the following raw materials in parts by weight: 100 parts polyester chips, 22 parts modified polyester, 13 parts modified kaolin, 4 parts vinyl bis-stearamide, 6 parts calcium stearate, and 2 parts antioxidant.

[0059] The passive cooling film layer is composed of the following raw materials in parts by weight: 100 parts low-density polyethylene and 6 parts modified titanium dioxide nanoparticles; specifically, the preparation method of the passive cooling film layer is as follows:

[0060] Step 1: Place the low-density polyethylene in a dryer and dry for 6 hours to control the moisture content of the low-density polyethylene to below 20 ppm.

[0061] Step 2: The dried low-density polyethylene and modified titanium dioxide nanoparticles are premixed for 30 minutes. After being thoroughly mixed, the mixture is fed into a twin-screw extruder for melt blending. After extrusion and pelletizing, the mixture is fed back into the twin-screw extruder for melt blending. This operation is repeated twice. The mixture is then extruded into sheets and quickly solidified into a film on a cooling roller. After traction and edge trimming, the passive cooling film layer is obtained.

[0062] In step two, the temperature of the twin-screw extruder head is 210℃, the temperature of zone one is 210℃, the temperature of zone two is 215℃, the temperature of zone three is 220℃, the temperature of zone four is 220℃, the temperature of zone five is 220℃, the temperature of zone six is ​​210℃, the pelletizing speed is 200r / min, the main machine speed is 13Hz, and the feeding speed is 4Hz.

[0063] The modification method for modified titanium dioxide nanoparticles is as follows:

[0064] Step A: Place titanium dioxide nanoparticles in an alkaline anhydrous ethanol solution with a pH of 8 and ultrasonically disperse for 12 min to obtain a dispersion system.

[0065] Step B: 20 ​​wt% of silane coupling agent KH-570 was added dropwise to the dispersion system and dispersed for 10 minutes to obtain product 1. Product 1 was placed in an oil bath at 60°C and dispersed for 8 hours with magnetic stirring during the dispersion process to obtain product 2.

[0066] Step C: The centrifuged precipitate of product 2 was washed three times with anhydrous ethanol and deionized water, and the dried modified titanium dioxide nanoparticles were obtained.

[0067] The modified polyester is composed of the following raw materials in parts by weight: 100 parts polyester, 25 parts polypropylene, 6 parts maleic anhydride-grafted polypropylene, and 8 parts organomontmorillonite; specifically, its preparation method is as follows:

[0068] S1. The polyester was vacuum dried at 120℃ for 6 hours to achieve a moisture content of ≤0.02%.

[0069] S2. Mix polypropylene and maleic anhydride-grafted polypropylene in a high-speed mixer for 5 minutes to obtain a premix.

[0070] S3. The dried polyester, premix and organomontmorillonite are fed into a twin-screw extruder for melt blending, extrusion and pelletizing, and dried at 80°C for 2 hours to obtain the modified polyester.

[0071] A method for preparing a passive cooling composite material includes the following steps:

[0072] Step 1: Apply adhesive to the PET film, then bond the intermediate film layer to the PET film under the action of hot rollers. After cooling, send it into the curing chamber and cure at 45°C for 5 hours.

[0073] Step 2: Apply adhesive to the intermediate film layer, and then apply the passive cooling film layer to the intermediate film layer under the action of hot rollers. After cooling, send it into the curing chamber and cure at 55°C for 24 hours. Allow it to cool naturally to room temperature to obtain the passive cooling composite material.

[0074] Example 2

[0075] A passive cooling composite material has the characteristics of low transmittance of ultraviolet-visible-near infrared light and high transmittance of mid-infrared radiation, and the cooling effect reaches 3.79℃ in outdoor direct sunlight cooling test. Specifically, the composite material includes a PET film, an intermediate film layer and a passive cooling film layer arranged from bottom to top; wherein, the thickness of the PET film is 0.015mm.

[0076] The intermediate film layer is composed of the following raw materials in parts by weight: 100 parts polyester chips, 22 parts modified polyester, 13 parts modified kaolin, 4 parts vinyl bis-stearamide, 6 parts calcium stearate, and 2 parts antioxidant.

[0077] The passive cooling film layer is composed of the following raw materials in parts by weight: 100 parts low-density polyethylene and 8 parts modified titanium dioxide nanoparticles; specifically, the preparation method of the passive cooling film layer is as follows:

[0078] Step 1: Place the low-density polyethylene in a dryer and dry for 6 hours to control the moisture content of the low-density polyethylene to below 20 ppm.

[0079] Step 2: The dried low-density polyethylene and modified titanium dioxide nanoparticles are premixed for 30 minutes. After being thoroughly mixed, the mixture is fed into a twin-screw extruder for melt blending. After extrusion and pelletizing, the mixture is fed back into the twin-screw extruder for melt blending. This operation is repeated 3 times. The mixture is then extruded into sheets and quickly solidified into a film on a cooling roller. After traction and edge trimming, the passive cooling film layer is obtained.

[0080] In step two, the temperature of the twin-screw extruder head is 210℃, the temperature of zone one is 210℃, the temperature of zone two is 215℃, the temperature of zone three is 220℃, the temperature of zone four is 220℃, the temperature of zone five is 220℃, the temperature of zone six is ​​210℃, the pelletizing speed is 200r / min, the main machine speed is 13Hz, and the feeding speed is 4Hz.

[0081] The modification method for modified titanium dioxide nanoparticles is as follows:

[0082] Step A: Place titanium dioxide nanoparticles in an alkaline anhydrous ethanol solution with a pH of 8 and ultrasonically disperse for 12 min to obtain a dispersion system.

[0083] Step B: 20 ​​wt% of silane coupling agent KH-570 was added dropwise to the dispersion system and dispersed for 10 minutes to obtain product 1. Product 1 was placed in an oil bath at 60°C and dispersed for 8 hours with magnetic stirring during the dispersion process to obtain product 2.

[0084] Step C: The centrifuged precipitate of product 2 was washed three times with anhydrous ethanol and deionized water, and the dried modified titanium dioxide nanoparticles were obtained.

[0085] The modified polyester is composed of the following raw materials in parts by weight: 100 parts polyester, 25 parts polypropylene, 6 parts maleic anhydride-grafted polypropylene, and 8 parts organomontmorillonite; specifically, its preparation method is as follows:

[0086] S1. The polyester was vacuum dried at 120℃ for 6 hours to achieve a moisture content of ≤0.02%.

[0087] S2. Mix polypropylene and maleic anhydride-grafted polypropylene in a high-speed mixer for 5 minutes to obtain a premix.

[0088] S3. The dried polyester, premix and organomontmorillonite are fed into a twin-screw extruder for melt blending, extrusion and pelletizing, and dried at 80°C for 2 hours to obtain the modified polyester.

[0089] A method for preparing a passive cooling composite material includes the following steps:

[0090] Step 1: Apply adhesive to the PET film, then bond the intermediate film layer to the PET film under the action of hot rollers. After cooling, send it into the curing chamber and cure at 45°C for 5 hours.

[0091] Step 2: Apply adhesive to the intermediate film layer, and then apply the passive cooling film layer to the intermediate film layer under the action of hot rollers. After cooling, send it into the curing chamber and cure at 55°C for 24 hours. Allow it to cool naturally to room temperature to obtain the passive cooling composite material.

[0092] Experimental verification

[0093] The passive cooling film layer prepared in this embodiment was used as the test sample.

[0094] To verify whether the silane coupling agent KH-570 was successfully grafted onto the TiO2-NPs surface and to clarify the modification effect on its surface chemical structure, Fourier transform infrared spectroscopy (FTIR) was used to characterize and analyze the changes in functional groups of TiO2-NPs before and after modification. The results are as follows: Figure 1 As shown, unmodified TiO2-NPs at 680 cm⁻¹ -1 The low transmittance at this wavelength indicates strong absorption in the material, a characteristic absorption peak of Ti-O-Ti, which is a typical structural feature of TiO2 nanoparticles; the modified TiO2-NPs exhibit low transmittance at 2930 cm⁻¹. -1 1430 cm -1 The presence of distinct absorption peaks on the left and right corresponds to the characteristic vibrations of -CH2- and CH, respectively. These functional groups match the organic functional group structure of the LDPE matrix, indicating that KH-570 was successfully grafted onto the TiO2-NPs surface, laying the structural foundation for the subsequent compatible dispersion of TiO2-NPs in the LDPE matrix. Simultaneously, at 876 cm⁻¹... -1 The presence of Ti-O-Si characteristic peaks confirms that KH-570 achieves chemical bonding with the TiO2-NPs surface through silicon-oxygen bonds, completing the surface modification of TiO2-NPs and effectively endowing TiO2-NPs with nonpolar organic functional groups compatible with LDPE.

[0095] To further verify the grafting effect of KH-570, X-ray photoelectron spectroscopy (XPS) was used to analyze the elemental composition and binding state of TiO2-NPs before and after modification. The results are shown in Figure 2. The XPS spectrum of unmodified TiO2-NPs mainly shows Ti 2p and O 1s characteristic peaks, reflecting the basic elemental composition of TiO2-NPs. After KH-570 surface modification, the intensity of Ti 2p and O 1s characteristic peaks of TiO2-NPs was significantly reduced, and clear Si 2s and Si 2p characteristic peaks appeared in the spectrum. These elements are derived from the KH-570 silane coupling agent, which directly indicates that KH-570 was successfully grafted onto the surface of TiO2-NPs. The relative reduction in the intensity of Ti 2p and O 1s peaks after modification further proves that the surface of TiO2-NPs is covered by the organic layer of KH-570, and the modification effect is significant.

[0096] To further demonstrate the successful loading of TiO2-NPs into LDPE films, refer to... Figure 3As shown in the figure, the X-ray diffraction patterns of LDPE / TiO2 film, LDPE film, and TiO2-NPs are analyzed. As can be seen from the figure, the peaks observed at 25.3°, 37.8°, 48.1°, 54.0°, and 55.1° correspond to the (101), (004), (200), (105), and (211) crystal planes of TiO2-NPs, respectively. The peaks observed at 21.5° and 23.5° correspond to the (110) and (200) crystal planes of LDPE, respectively. The LDPE / TiO2 film has characteristic peaks at 25.3°, 37.8°, 48.1°, 54.0°, and 55.1° that are different from those of LDPE, proving that TiO2-NPs were successfully loaded into the LDPE film.

[0097] Example 3

[0098] A passive cooling composite material has the characteristics of low transmittance of ultraviolet-visible-near infrared light and high transmittance of mid-infrared radiation, and the cooling effect reaches 3.79℃ in outdoor direct sunlight cooling test. Specifically, the composite material includes a PET film, an intermediate film layer and a passive cooling film layer arranged from bottom to top; wherein, the thickness of the PET film is 0.01mm.

[0099] The intermediate film layer is composed of the following raw materials in parts by weight: 100 parts polyester chips, 18 parts modified polyester, 15 parts modified kaolin, 5 parts vinyl bis-stearamide, 5 parts calcium stearate, and 1 part antioxidant.

[0100] The passive cooling film layer is composed of the following raw materials in parts by weight: 100 parts low-density polyethylene and 10 parts modified titanium dioxide nanoparticles; specifically, the preparation method of the passive cooling film layer is as follows:

[0101] Step 1: Place the low-density polyethylene in a dryer and dry for 6 hours to control the moisture content of the low-density polyethylene to below 20 ppm.

[0102] Step 2: The dried low-density polyethylene and modified titanium dioxide nanoparticles are premixed for 30 minutes. After being thoroughly mixed, the mixture is fed into a twin-screw extruder for melt blending. After extrusion and pelletizing, the mixture is fed back into the twin-screw extruder for melt blending. This operation is repeated 3 times. The mixture is then extruded into sheets and quickly solidified into a film on a cooling roller. After traction and edge trimming, the passive cooling film layer is obtained.

[0103] In step two, the temperature of the twin-screw extruder head is 210℃, the temperature of zone one is 210℃, the temperature of zone two is 215℃, the temperature of zone three is 220℃, the temperature of zone four is 220℃, the temperature of zone five is 220℃, the temperature of zone six is ​​210℃, the pelletizing speed is 200r / min, the main machine speed is 13Hz, and the feeding speed is 4Hz.

[0104] The modification method for modified titanium dioxide nanoparticles is as follows:

[0105] Step A: Place titanium dioxide nanoparticles in an alkaline anhydrous ethanol solution with a pH of 9 and ultrasonically disperse for 15 min to obtain a dispersion system.

[0106] Step B: 20 ​​wt% of silane coupling agent KH-570 was added dropwise to the dispersion system and dispersed for 10 minutes to obtain product 1. Product 1 was placed in an oil bath at 55°C and dispersed for 9 hours with magnetic stirring during the dispersion process to obtain product 2.

[0107] Step C: The centrifuged precipitate of product 2 was washed three times with anhydrous ethanol and deionized water, and the dried modified titanium dioxide nanoparticles were obtained.

[0108] The modified polyester is composed of the following raw materials in parts by weight: 100 parts polyester, 20 parts polypropylene, 8 parts maleic anhydride-grafted polypropylene, and 6 parts organomontmorillonite; specifically, its preparation method is as follows:

[0109] S1. The polyester was vacuum dried at 120℃ for 6 hours to achieve a moisture content of ≤0.02%.

[0110] S2. Mix polypropylene and maleic anhydride-grafted polypropylene in a high-speed mixer for 5 minutes to obtain a premix.

[0111] S3. The dried polyester, premix and organomontmorillonite are fed into a twin-screw extruder for melt blending, extrusion and pelletizing, and dried at 80°C for 2 hours to obtain the modified polyester.

[0112] A method for preparing a passive cooling composite material includes the following steps:

[0113] Step 1: Apply adhesive to the PET film, then bond the intermediate film layer to the PET film under the action of hot rollers. After cooling, send it into the curing chamber and cure at 40°C for 6 hours.

[0114] Step 2: Apply adhesive to the intermediate film layer, and then apply the passive cooling film layer to the intermediate film layer under the action of hot press rollers. After cooling, send it into the curing chamber and cure it at 50°C for 24 hours. Then let it cool naturally to room temperature to obtain the passive cooling composite material.

[0115] Example 4

[0116] A passive cooling composite material has the characteristics of low transmittance of ultraviolet-visible-near infrared light and high transmittance of mid-infrared radiation, and the cooling effect reaches 3.79℃ in outdoor direct sunlight cooling test. Specifically, the composite material includes a PET film, an intermediate film layer and a passive cooling film layer arranged from bottom to top; wherein, the thickness of the PET film is 0.02mm.

[0117] The intermediate film layer is composed of the following raw materials in parts by weight: 100 parts polyester chips, 25 parts modified polyester, 12 parts modified kaolin, 3 parts vinyl bis-stearamide, 8 parts calcium stearate, and 3 parts antioxidant.

[0118] The passive cooling film layer is composed of the following raw materials in parts by weight: 100 parts low-density polyethylene and 5 parts modified titanium dioxide nanoparticles; specifically, the preparation method of the passive cooling film layer is as follows:

[0119] Step 1: Place the low-density polyethylene in a dryer and dry for 6 hours to control the moisture content of the low-density polyethylene to below 20 ppm.

[0120] Step 2: The dried low-density polyethylene and modified titanium dioxide nanoparticles are premixed for 30 minutes. After being thoroughly mixed, the mixture is fed into a twin-screw extruder for melt blending. After extrusion and pelletizing, the mixture is fed back into the twin-screw extruder for melt blending. This operation is repeated 5 times. The mixture is then extruded into sheets and quickly solidified into a film on a cooling roller. After traction and edge trimming, the passive cooling film layer is obtained.

[0121] In step two, the temperature of the twin-screw extruder head is 210℃, the temperature of zone one is 210℃, the temperature of zone two is 215℃, the temperature of zone three is 220℃, the temperature of zone four is 220℃, the temperature of zone five is 220℃, the temperature of zone six is ​​210℃, the pelletizing speed is 200r / min, the main machine speed is 13Hz, and the feeding speed is 4Hz.

[0122] The modification method for modified titanium dioxide nanoparticles is as follows:

[0123] Step A: Place titanium dioxide nanoparticles in an alkaline anhydrous ethanol solution with a pH of 8.5 and ultrasonically disperse for 8 min to obtain a dispersion system;

[0124] Step B: 20 ​​wt% of silane coupling agent KH-570 was added dropwise to the dispersion system and dispersed for 10 minutes to obtain product 1. Product 1 was placed in an oil bath at 65°C and dispersed for 7 hours with magnetic stirring during the dispersion process to obtain product 2.

[0125] Step C: The centrifuged precipitate of product 2 was washed three times with anhydrous ethanol and deionized water, and the dried modified titanium dioxide nanoparticles were obtained.

[0126] The modified polyester is composed of the following raw materials in parts by weight: 100 parts polyester, 30 parts polypropylene, 5 parts maleic anhydride-grafted polypropylene, and 10 parts organomontmorillonite; specifically, its preparation method is as follows:

[0127] S1. The polyester was vacuum dried at 120℃ for 6 hours to achieve a moisture content of ≤0.02%.

[0128] S2. Mix polypropylene and maleic anhydride-grafted polypropylene in a high-speed mixer for 5 minutes to obtain a premix.

[0129] S3. The dried polyester, premix and organomontmorillonite are fed into a twin-screw extruder for melt blending, extrusion and pelletizing, and dried at 80°C for 2 hours to obtain the modified polyester.

[0130] A method for preparing a passive cooling composite material includes the following steps:

[0131] Step 1: Apply adhesive to the PET film, then bond the intermediate film layer to the PET film under the action of hot press rollers. After cooling, send it into the curing chamber and cure at 50°C for 4 hours.

[0132] Step 2: Apply adhesive to the intermediate film layer, and then apply the passive cooling film layer to the intermediate film layer under the action of hot rollers. After cooling, send it into the curing chamber and cure at 60°C for 24 hours. Allow it to cool naturally to room temperature to obtain the passive cooling composite material.

[0133] Example 5

[0134] A passive cooling composite material has the characteristics of low transmittance of ultraviolet-visible-near infrared light and high transmittance of mid-infrared radiation, and the cooling effect reaches 3.79℃ in outdoor direct sunlight cooling test. Specifically, the composite material includes a PET film, an intermediate film layer and a passive cooling film layer arranged from bottom to top; wherein, the thickness of the PET film is 0.015mm.

[0135] The intermediate film layer is composed of the following raw materials in parts by weight: 100 parts polyester chips, 22 parts modified polyester, 13 parts modified kaolin, 4 parts vinyl bis-stearamide, 6 parts calcium stearate, and 2 parts antioxidant.

[0136] The passive cooling film is composed of the following raw materials in parts by weight: 100 parts low-density polyethylene and 7 parts modified titanium dioxide nanoparticles; specifically, the preparation method of the passive cooling film is as follows:

[0137] Step 1: Place the low-density polyethylene in a dryer and dry for 6 hours to control the moisture content of the low-density polyethylene to below 20 ppm.

[0138] Step 2: The dried low-density polyethylene and modified titanium dioxide nanoparticles are premixed for 30 minutes. After being thoroughly mixed, the mixture is fed into a twin-screw extruder for melt blending. After extrusion and pelletizing, the mixture is fed back into the twin-screw extruder for melt blending. This operation is repeated 3 times. The mixture is then extruded into sheets and quickly solidified into a film on a cooling roller. After traction and edge trimming, the passive cooling film layer is obtained.

[0139] In step two, the temperature of the twin-screw extruder head is 210℃, the temperature of zone one is 210℃, the temperature of zone two is 215℃, the temperature of zone three is 220℃, the temperature of zone four is 220℃, the temperature of zone five is 220℃, the temperature of zone six is ​​210℃, the pelletizing speed is 200r / min, the main machine speed is 13Hz, and the feeding speed is 4Hz.

[0140] The modification method for modified titanium dioxide nanoparticles is as follows:

[0141] Step A: Place titanium dioxide nanoparticles in an alkaline anhydrous ethanol solution with a pH of 8 and ultrasonically disperse for 12 min to obtain a dispersion system.

[0142] Step B: 20 ​​wt% of silane coupling agent KH-570 was added dropwise to the dispersion system and dispersed for 10 minutes to obtain product 1. Product 1 was placed in an oil bath at 60°C and dispersed for 8 hours with magnetic stirring during the dispersion process to obtain product 2.

[0143] Step C: The centrifuged precipitate of product 2 was washed three times with anhydrous ethanol and deionized water, and the dried modified titanium dioxide nanoparticles were obtained.

[0144] The modified polyester is composed of the following raw materials in parts by weight: 100 parts polyester, 25 parts polypropylene, 6 parts maleic anhydride-grafted polypropylene, and 8 parts organomontmorillonite; specifically, its preparation method is as follows:

[0145] S1. The polyester was vacuum dried at 120℃ for 6 hours to achieve a moisture content of ≤0.02%.

[0146] S2. Mix polypropylene and maleic anhydride-grafted polypropylene in a high-speed mixer for 5 minutes to obtain a premix.

[0147] S3. The dried polyester, premix and organomontmorillonite are fed into a twin-screw extruder for melt blending, extrusion and pelletizing, and dried at 80°C for 2 hours to obtain the modified polyester.

[0148] A method for preparing a passive cooling composite material includes the following steps:

[0149] Step 1: Apply adhesive to the PET film, then bond the intermediate film layer to the PET film under the action of hot rollers. After cooling, send it into the curing chamber and cure at 45°C for 5 hours.

[0150] Step 2: Apply adhesive to the intermediate film layer, and then apply the passive cooling film layer to the intermediate film layer under the action of hot rollers. After cooling, send it into the curing chamber and cure at 55°C for 24 hours. Allow it to cool naturally to room temperature to obtain the passive cooling composite material.

[0151] Process testing

[0152] The composite materials prepared in Examples 1-5 were labeled as Sample 1, Sample 2, Sample 3, Sample 4 and Sample 5, respectively.

[0153] I. Optical Performance Testing

[0154] Reference Figure 4 As shown in the figure, the infrared transmittance of different composite materials reveals that, in the ultraviolet band, except for sample 1, the transmittance of the other four films is almost zero, indicating that the films almost completely block ultraviolet light, which also reflects the good anti-aging properties of the films. Overall, the figure shows that sample 1 has the highest transmittance, while samples 3 and 5 have the lowest. At a normal skin temperature of 34 ℃, the human body emits mid-infrared radiation with a wavelength of 7-14 μm. Therefore, if the mid-infrared radiation emitted by the human body can pass through, the cooling effect of the material can be significantly improved. The figure shows that samples 1-5 all have similarly good transmittance, close to 100%, which is mainly attributed to their amorphous structure. The amorphous structure of LDPE films means that there are a large number of free volumes and fewer ordered molecular chains inside, and the presence of these free volumes allows infrared spectra to pass through the material more easily.

[0155] II. Cooling Performance Test

[0156] Under direct sunlight, five films (sample 1, sample 2, sample 3, sample 4, and sample 5) were placed in a self-made experimental apparatus as a reference. A box without a sample cover was also tested simultaneously. All experiments were conducted at the same location: Quanzhou, Fujian, China (117°25′E, 24°30′N). The experimental apparatus was placed on a rooftop, facing the sky, to simulate actual conditions. The highest temperature that day was 33°C, and the test time was from 11:30 to 15:30. Schematic diagrams and actual images of the testing apparatus are shown below. Figure 5 As shown. The film temperature-time curve is as follows. Figure 6 As shown, overall, the temperatures of all five samples were lower than the ambient temperature measured in the empty chamber. However, the temperature measured under sample 3 remained consistently lower than the other samples, reaching its maximum cooling effect at 13:07, decreasing by 3.79℃ compared to the empty chamber, demonstrating a better cooling effect. The self-made testing device in this application uses polystyrene foam as the main body, covered with aluminum foil, and has a cylindrical groove at the top. A layer of polyethylene (PE) film is placed above the groove, and the sample to be tested is placed over a pre-reserved window directly above it. A temperature sensor is placed in the cavity to measure its temperature. The aluminum foil is used to wrap the surface of the foam box to create a sealed space to isolate external heat conduction and convection.

[0157] In summary, the composite material prepared in this application has low transmittance in the ultraviolet-visible-near infrared (0.2-2.5μm) range and nearly 100% transmittance in the mid-infrared radiation (7-14μm), and can completely transmit the mid-infrared radiation emitted by the human body. The cooling effect in outdoor direct sunlight cooling test reaches 3.79℃, showing good cooling effect and providing new ideas for the preparation of radiation cooling materials and their functional applications in the textile field.

[0158] The above description is merely a preferred embodiment of the present invention and should not be construed as limiting the scope of the present invention. All equivalent changes and modifications made in accordance with the scope of the patent application and the contents of the specification of the present invention should still fall within the scope of the patent of the present invention.

Claims

1. A passive cooling composite material, characterized in that: It includes, from bottom to top, a PET film, an intermediate film layer, and a passive cooling film layer; The intermediate film layer is composed of the following raw materials in parts by weight: 100 parts polyester chips, 18-25 parts modified polyester, 12-15 parts modified kaolin, 3-5 parts vinyl bis-stearamide, 5-8 parts calcium stearate, and 1-3 parts antioxidant. The passive cooling film is composed of the following raw materials in parts by weight: 100 parts of low-density polyethylene and 5-10 parts of modified titanium dioxide nanoparticles. The modification method for modified titanium dioxide nanoparticles is as follows: Step A: Place titanium dioxide nanoparticles in an alkaline anhydrous ethanol solution with a pH of 8-9 and ultrasonically disperse for 8-15 min to obtain a dispersion system. Step B: Add 20 wt% of silane coupling agent KH-570 to the dispersion system and continue to disperse for 10 minutes to obtain product 1. Place product 1 in an oil bath at 55-65℃ and continue to disperse for 7-9 hours with magnetic stirring during the dispersion process to obtain product 2. Step C: The centrifuged precipitate of product 2 was washed three times with anhydrous ethanol and deionized water, and the dried modified titanium dioxide nanoparticles were obtained. The modified polyester is composed of the following raw materials in parts by weight: 100 parts polyester, 20-30 parts polypropylene, 5-8 parts maleic anhydride-grafted polypropylene, and 6-10 parts organomontmorillonite.

2. The passive cooling composite material according to claim 1, characterized in that: The modified polyester is prepared as follows: S1. The polyester was vacuum dried at 120℃ for 6 hours to achieve a moisture content of ≤0.02%. S2. Mix polypropylene and maleic anhydride-grafted polypropylene in a high-speed mixer for 5 minutes to obtain a premix. S3. The dried polyester, premix and organomontmorillonite are fed into a twin-screw extruder for melt blending, extrusion and pelletizing, and dried at 80°C for 2 hours to obtain the modified polyester.

3. The passive cooling composite material according to claim 1, characterized in that: The method for preparing the passive cooling film layer is as follows: Step 1: Place the low-density polyethylene in a dryer and dry for 6 hours to control the moisture content of the low-density polyethylene to below 20 ppm. Step 2: The dried low-density polyethylene and modified titanium dioxide nanoparticles are premixed for 30 minutes. After thorough mixing, the mixture is fed into a twin-screw extruder for melt blending. After extrusion and pelletizing, the mixture is fed back into the twin-screw extruder for melt blending. This operation is repeated 2-5 times until the mixture is extruded into sheets. The sheets are then quickly solidified into a film on a cooling roller. After traction and edge trimming, the passive cooling film layer is obtained.

4. The passive cooling composite material according to claim 3, characterized in that: In step two, the temperature of the twin-screw extruder head is 210℃, the temperature of zone one is 210℃, the temperature of zone two is 215℃, the temperature of zone three is 220℃, the temperature of zone four is 220℃, the temperature of zone five is 220℃, the temperature of zone six is ​​210℃, the pelletizing speed is 200r / min, the main machine speed is 13Hz, and the feeding speed is 4Hz.

5. The passive cooling composite material according to claim 1, characterized in that: The thickness of the PET film is 0.01-0.02 mm.

6. A method for preparing a passive cooling composite material, used to prepare the passive cooling composite material according to any one of claims 1-5, characterized in that: Includes the following steps: Step 1: Apply adhesive to the PET film, and then bond the intermediate film layer to the PET film under the action of hot press rollers. After cooling, send it into the curing chamber and cure at 40-50℃ for 4-6 hours. Step 2: Apply adhesive to the intermediate film layer, and then apply the passive cooling film layer to the intermediate film layer under the action of hot rollers. After cooling, send it into the curing chamber and cure it at 50-60℃ for 24 hours. Allow it to cool naturally to room temperature to obtain the passive cooling composite material.

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