PO film with good cooling effect in summer and preparation method thereof

Abstract

The invention discloses a PO film with a good cooling effect in summer and a preparation method of the PO film, and belongs to the technical field of composite membranes, titanium-based MOF is intercalated between layers of MXene nanosheets, suspended solids of the titanium-based MOF intercalated MXene nanosheets are obtained, then ceramic heat-conducting microspheres are coated, MXene nanosheet composite heat-conducting microspheres are obtained, the high conductivity of MXene can serve as an electron acceptor, and the MXene can serve as an electron acceptor, so that the PO film with the good cooling effect in summer is prepared. The MXene nanosheet composite heat-conducting microspheres have the advantages that titanium-based MOF photo-induced electrons can be quickly transferred, electron-hole recombination can be inhibited, the photocatalytic performance of the titanium-based MOF can be promoted, accordingly, the PO film is endowed with antibacterial performance as an agricultural film, PO film pollution caused by bacterium breeding can be avoided, and the MXene nanosheet composite heat-conducting microspheres have excellent heat-conducting capacity and can be used as a reinforcing phase to increase the mechanical performance of the PO film.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of composite films, and particularly relates to a PO film with good summer cooling effect and a preparation method thereof. BACKGROUND

[0002] The PO film is a new type of agricultural film, mainly comprising a base film and a coating liquid. The base film is manufactured by adding a functional master batch to polyethylene materials such as linear low-density polyethylene (LLDPE) and low-density polyethylene (LDPE), stirring by a high-speed stirrer, and then extruding and pelletizing by a double-screw extruder. The coating liquid is formed by mixing a film-forming agent, a surfactant and other functional additives, and is coated on the surface of the base film to form a coating layer. The PO film is an upgraded product of the EVA film, and brings revolutionary improvements to the traditional agricultural greenhouse film. This high-tech coated product has the advantages of high light transmission, strong tensile force and aging resistance, and is suitable for various agricultural scenes such as greenhouse planting and orchard covering, and can significantly improve the yield and quality, especially in the planting of vegetables and fruits that require high temperature.

[0003] However, the PO film has poor dew condensation and dripping properties, especially in winter. Water generated by the respiration of crops accumulates on the greenhouse film to form water droplets, which causes the reflection or refraction of incident light from the outside, reduces the light transmittance of the greenhouse film, and affects the photosynthesis of crops. In addition, the water droplets falling on the leaves of crops form a water film, which creates conditions for the infection and development of bacteria, and causes vegetable diseases. Therefore, it is necessary to modify the coating liquid used for the PO film to improve the hydrophilicity of the film layer formed by the coating liquid, thereby reducing the surface tension of water and improving the dew condensation and dripping properties of the PO film. In addition, it is also necessary to improve the adhesion of the coating liquid on the surface of the base film to reduce the reduction of the film layer of the coating liquid caused by the long-term dripping of water droplets.

[0004] A PO composite film and a preparation method thereof are disclosed in Chinese Patent No. CN119283464B. A modified hyperbranched polymer is introduced into the coating liquid as a multi-hydroxyl non-ionic surfactant. The unique hyperbranched structure of the modified hyperbranched polymer allows the embedding of core layer organic silicon microspheres into the film layer structure after coating. The branched structure of the shell layer can spread out in the coating liquid to form a network structure, further enhancing the hydrophilicity of the surface of the composite film. The improvement of the hydrophilicity reduces the surface tension of water, which is beneficial to the spreading of water droplets on the film surface and the aggregation of adjacent water droplets to form water flow, thereby making the dew condensation and dripping of the film surface quickly flow away and avoiding the occurrence of water droplet hanging phenomenon, and further improving the dew condensation and dripping properties of the composite film. However, the PO film is in a high-temperature and high-humidity state for a long time, which is easy to breed mold, algae and bacteria. The organic acid produced by the metabolism of microorganisms can accelerate the aging of the agricultural film, resulting in a decrease in light transmittance. SUMMARY

[0005] The purpose of the present application is to provide a PO film with good summer cooling effect and a preparation method thereof. The titanium-based MOF is intercalated between the layers of MXene nanosheets to obtain a suspension of titanium-based MOF intercalated MXene nanosheets. The ceramic heat-conducting microspheres are then coated. The high conductivity of MXene can act as an electron acceptor, quickly transfer the photo-generated electrons of the titanium-based MOF, inhibit electron-hole recombination, and promote the photocatalytic performance of the titanium-based MOF. Thus, the PO film is endowed with antibacterial properties as an agricultural film, avoiding bacterial growth and contamination of the PO film.

[0006] The purpose of the present application can be achieved by the following technical solutions: A preparation method of a PO film with good summer cooling effect, comprising the following steps: Step one: ceramic heat-conducting microspheres are obtained by calcining a mixture of zirconium tetrachloride and silicon dioxide and a phenolic resin solution.

[0007] Step two: lithium fluoride reacts with hydrochloric acid to generate hydrofluoric acid, which is etched with titanium aluminum carbide to generate a suspension of multi-layer MXene nanosheets. The MXene nanosheets are ultrasonically dispersed under hydrothermal conditions, and MOF is formed by coordination of 2,5-dihydroxyterephthalic acid and titanium tetrachloride, obtaining a suspension of titanium-based MOF intercalated MXene nanosheets.

[0008] Step three: the ceramic heat-conducting microspheres are embedded in the skeleton of the suspension of titanium-based MOF intercalated MXene nanosheets by mechanical stirring to obtain MXene nanosheet composite heat-conducting microspheres coated with ceramic heat-conducting microspheres.

[0009] Step four: the MXene nanosheet composite heat-conducting microspheres are mixed with polyacrylic acid resin and deionized water to form a coating liquid, which is coated on the surface of the base film, dried, and rolled to obtain a PO film with good summer cooling effect.

[0010] Further, the specific preparation steps of the ceramic heat-conducting microspheres are as follows: Zirconium tetrachloride, silicon dioxide and acetylacetone solution are added to a reaction kettle and stirred at 20-25℃ and 500-600r / min for 20-30min, then ethanol is added and continues to stir for 20-30min to obtain a zirconium-silicon solution; the zirconium-silicon solution and the phenolic resin solution are added to the reaction kettle in a dosage ratio of 500-600mL:700-780mL, and stirred at 150-160℃ and 500-600r / min for 20-22h, filtered, the filter cake is washed with deionized water for 2-4 times, vacuum dried at 60-70℃ for 1-2h, the product is transferred to a muffle furnace, heated to 800-890℃ at a rate of 5-6℃ / min under nitrogen protection, and then heated to 1500-1600℃ at a rate of 10-12℃ / min and kept for 1-2h to obtain ceramic heat-conducting microspheres.

[0011] Further, the amount ratio of zirconium tetrachloride, silicon dioxide, acetylacetone solution and ethanol is 120-140 g: 110-120 g: 800-900 mL: 120-140 mL.

[0012] Further, the specific preparation steps of the MXene nanosheet suspension are as follows: Lithium fluoride and a hydrochloric acid solution with a mass fraction of 20-35% are added to a reaction kettle, stirred at 20-25°C and 400-500 r / min for 20-30 min, then titanium aluminum carbide is added, and stirring is continued for 48-50 h, centrifuged at 5000-6000 r / min for 3-5 min, filtered, and the filter cake is washed with deionized water and ethanol until the last washing liquid is neutral, ultrasonic stripping under an argon flow of 20-25 mL / min, centrifuged at 5000-6000 r / min for 3-5 min, to obtain the MXene nanosheet suspension.

[0013] Further, the amount ratio of lithium fluoride, hydrochloric acid solution and titanium aluminum carbide is 180-190 g: 800-900 mL: 80-90 g.

[0014] Further, the specific preparation steps of the MXene nanosheet suspension are as follows: The MXene nanosheet suspension and N,N-dimethylformamide are added to a reaction kettle lined with polytetrafluoroethylene, sealed, and ultrasonically dispersed at 130-135°C for 20-40 min, then 2,5-dihydroxyterephthalic acid and titanium tetrachloride are added, ultrasonically dispersed for 40-60 min, and stirring is continued for 24-26 h, then naturally cooled to room temperature, filtered, and the filter cake is washed with N,N-dimethylformamide and methanol for 2-3 times, respectively, and vacuum dried at 60-80°C for 1-2 h, to obtain the MXene nanosheet suspension intercalated with titanium-based MOF.

[0015] Further, the amount ratio of the MXene nanosheet suspension, N,N-dimethylformamide, 2,5-dihydroxyterephthalic acid and titanium tetrachloride is 80-90 g: 1-2 L: 40-50 g: 50-60 g.

[0016] Further, the specific preparation steps of the MXene nanosheet composite heat-conducting microsphere are as follows: The MXene nanosheet suspension intercalated with titanium-based MOF, ceramic heat-conducting microspheres and N,N-dimethylformamide are added to a reaction kettle, stirred at 20-25°C and 400-500 r / min for 4-5 h, centrifuged at 5000-6000 r / min for 10-12 min, filtered, and the filter cake is washed with deionized water and ethanol for 2-4 times, and vacuum dried at 60-70°C for 1-2 h, to obtain the MXene nanosheet composite heat-conducting microsphere.

[0017] Further, the amount ratio of the suspension of titanium-based MOF intercalated MXene nanosheet, ceramic heat-conducting microspheres and N,N-dimethylformamide is 120-140g:100-120g:1-2L.

[0018] Further, the specific preparation steps of the PO film are as follows: The MXene nanosheet composite heat-conducting microspheres, polyvinylpyrrolidone, sodium lauryl sulfate are stirred for 30-40min, then a mixed solution with a mass ratio of polyacrylic resin and deionized water of 1:10 is added to obtain a coating liquid; the coating liquid is uniformly coated on the surface of the PO film, the film layer thickness is 0.1-0.2mm, and the PO film with good summer cooling effect is obtained after drying and winding.

[0019] Further, the amount ratio of the MXene nanosheet composite heat-conducting microspheres, polyvinylpyrrolidone, sodium lauryl sulfate and the mixed solution is 100-120g:80-90mL:15-20g:150-170mL.

[0020] The beneficial effects of the present application are: 1. The PO film prepared by the present application has good heat dissipation capacity and tensile strength, is not easy to age and wrinkle, and is not easy to breed bacteria during long-term use.

[0021] 2. The PO film prepared by the present application is obtained by stirring and mixing MXene nanosheet composite heat-conducting microspheres, polyvinylpyrrolidone, sodium lauryl sulfate, polyacrylic resin and deionized water to obtain a coating liquid, which is coated on the PO film to obtain a PO film with good summer cooling effect. The MXene nanosheet composite heat-conducting microspheres have excellent heat dissipation capacity and can increase the mechanical properties of the PO film as a reinforcing phase.

[0022] 3. The MXene nanosheet composite heat-conducting microspheres of the present application are obtained by intercalating titanium-based MOF between the layers of MXene nanosheets to obtain a suspension of titanium-based MOF intercalated MXene nanosheets. The intercalation of titanium-based MOF can prevent the agglomeration of MXene nanosheets due to van der Waals force and is beneficial to the subsequent coating of MXene nanosheets on ceramic heat-conducting microspheres. MXene nanosheets form titanium vacancies during preparation, which leads to the oxidation of MXene to titanium dioxide in air. The thermal conductivity of titanium dioxide is much lower than that of MXene. During the growth of titanium-based MOF intercalation, the coordination monomer 2,5-dihydroxy terephthalic acid will form titanium-based MOF with titanium ions in the titanium vacancies, and the intercalation of titanium-based MOF can also cover the active sites on the surface of MXene, thereby preventing oxidation and maintaining the high thermal conductivity of MXene.

[0023] 4. The MXene has high electrical conductivity and can act as an electron acceptor, quickly transferring the photo-generated electrons of the titanium-based MOF, inhibiting electron-hole recombination, and promoting the photocatalytic performance of the titanium-based MOF, thereby endowing the PO film with antibacterial properties as an agricultural film and avoiding bacterial growth to cause pollution of the PO film. DETAILED DESCRIPTION

[0024] The technical solutions in the embodiments of the present application will be clearly and completely described below in combination with the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0025] Embodiment 1: A preparation method of a PO film with good summer cooling effect, comprising the following steps: S1: 120 g of zirconium tetrachloride, 110 g of silicon dioxide and 800 mL of acetylacetone solution were added to a reaction kettle, stirred at 20°C and 500 r / min for 20 min, then 120 mL of ethanol was added and continued to stir for 20 min to obtain a zirconium-silicon solution; 500 mL of the zirconium-silicon solution and 700 mL of a phenolic resin solution were added to the reaction kettle, stirred at 150°C and 500 r / min for 20 h, filtered, the filter cake was washed with deionized water for 2 times, vacuum dried at 60°C for 1 h, the product was transferred to a muffle furnace, heated to 800°C at a rate of 5°C / min under nitrogen protection, kept for 1 h, then heated to 1500°C at a rate of 10°C / min, kept for 1 h to obtain ceramic heat-conducting microspheres.

[0026] S2: 180 g of lithium fluoride and 800 mL of a 20% mass fraction hydrochloric acid solution were added to a reaction kettle, stirred at 20°C and 400 r / min for 20 min, then 80 g of titanium aluminum carbide was added and continued to stir for 48 h, centrifuged at 5000 r / min for 3 min, filtered, the filter cake was washed with deionized water and ethanol until the last washing liquid was neutral, ultrasonically peeled under an argon flow of 20 mL / min, centrifuged at 5000 r / min for 3 min to obtain a suspension of MXene nanosheets.

[0027] S3: 80 g of the suspension of MXene nanosheets and 1 L of N,N-dimethylformamide were added to a reaction kettle lined with polytetrafluoroethylene, sealed, ultrasonically dispersed at 130°C for 20 min, then 40 g of 2,5-dihydroxyterephthalic acid and 50 g of titanium tetrachloride were added, ultrasonically dispersed for 40 min, continued to stir for 24 h, naturally cooled to room temperature, filtered, the filter cake was washed with N,N-dimethylformamide and methanol for 2 times respectively, vacuum dried at 60°C for 1 h to obtain a suspension of titanium-based MOF intercalated MXene nanosheets.

[0028] S4: 120 g of a suspension of titanium-based MOF intercalated MXene nanosheets, 100 g of ceramic heat-conducting microspheres, and 1 L of N,N-dimethylformamide were added to a reaction kettle, stirred at 20 ℃ and 400 r / min for 4 h, centrifuged at 5000 r / min for 10 min, filtered, the filter cake was washed with deionized water and ethanol for 2 times, and vacuum dried at 60 ℃ for 1 h to obtain MXene nanosheet composite heat-conducting microspheres.

[0029] S5: 100 g of MXene nanosheet composite heat-conducting microspheres, 80 mL of polyvinylpyrrolidone, and 15 g of sodium lauryl sulfate were stirred for 30 min, then 150 mL of a mixed solution of polyacrylic acid resin and deionized water with a mass ratio of 1:10 was added to obtain a coating liquid; the coating liquid was uniformly coated on the surface of the PO film, the film layer thickness was 0.1 mm, and the film was dried and rolled to obtain a PO film with good summer cooling effect.

[0030] Example 2: A preparation method of a PO film with good summer cooling effect, comprising the following steps: S1: 130 g of zirconium tetrachloride, 115 g of silicon dioxide, and 850 mL of acetylacetone solution were added to a reaction kettle, stirred at 22.5 ℃ and 550 r / min for 25 min, then 130 mL of ethanol was added, and the stirring was continued for 25 min to obtain a zirconium-silicon solution; 550 mL of the zirconium-silicon solution and 740 mL of a phenolic resin solution were added to the reaction kettle, stirred at 155 ℃ and 550 r / min for 21 h, filtered, the filter cake was washed with deionized water for 3 times, vacuum dried at 65 ℃ for 1.5 h, the product was transferred to a muffle furnace, heated to 845 ℃ at a rate of 5.5 ℃ / min under nitrogen protection, kept for 1.5 h, then heated to 1550 ℃ at a rate of 11 ℃ / min, and kept for 1.5 h to obtain ceramic heat-conducting microspheres.

[0031] S2: 185 g of lithium fluoride and 850 mL of a 27.5% mass fraction hydrochloric acid solution were added to a reaction kettle, stirred at 22.5 ℃ and 450 r / min for 25 min, then 85 g of titanium aluminum carbide was added, and the stirring was continued for 49 h, centrifuged at 5500 r / min for 4 min, filtered, the filter cake was washed with deionized water and ethanol until the last washing liquid was neutral, ultrasonically peeled under an argon flow of 22.5 mL / min, and centrifuged at 5500 r / min for 4 min to obtain a suspension of MXene nanosheets.

[0032] S3: 85 g of MXene nanosheet suspension and 1.5 L of N,N-dimethylformamide were added to a reaction kettle lined with polytetrafluoroethylene, sealed, and ultrasonically dispersed at 132.5°C for 30 min. Then 45 g of 2,5-dihydroxyterephthalic acid and 55 g of titanium tetrachloride were added, ultrasonically dispersed for 50 min, and continuously stirred for 25 h. After natural cooling to room temperature, the filter cake was washed with N,N-dimethylformamide and methanol for 2.5 times, respectively, and vacuum dried at 70°C for 1.5 h to obtain a suspension of titanium-based MOF intercalated MXene nanosheets.

[0033] S4: 130 g of the suspension of titanium-based MOF intercalated MXene nanosheets, 110 g of ceramic heat-conducting microspheres, and 1.5 L of N,N-dimethylformamide were added to a reaction kettle, stirred at 22.5°C and 450 r / min for 4.5 h, centrifuged at 5500 r / min for 11 min, filtered, and the filter cake was washed with deionized water and ethanol for 3 times, and vacuum dried at 65°C for 1.5 h to obtain MXene nanosheet composite heat-conducting microspheres.

[0034] S5: 110 g of MXene nanosheet composite heat-conducting microspheres, 85 mL of polyvinylpyrrolidone, and 17.5 g of sodium lauryl sulfate were stirred for 35 min, and then a mixed solution of 160 mL of polyacrylic acid resin and deionized water in a mass ratio of 1:10 was added to obtain a coating liquid. The coating liquid was uniformly coated on the surface of the PO film with a film layer thickness of 0.15 mm, dried, and wound to obtain a PO film with good summer cooling effect.

[0035] Example 3: A preparation method of a PO film with good summer cooling effect, comprising the following steps: S1: 140 g of zirconium tetrachloride, 120 g of silicon dioxide, and 900 mL of acetylacetone solution were added to a reaction kettle, stirred at 25°C and 600 r / min for 30 min, and then 140 mL of ethanol was added and continuously stirred for 30 min to obtain a zirconium-silicon solution. 600 mL of the zirconium-silicon solution and 780 mL of a phenolic resin solution were added to the reaction kettle, stirred at 160°C and 600 r / min for 22 h, filtered, and the filter cake was washed with deionized water for 4 times, and vacuum dried at 70°C for 2 h. The product was transferred to a muffle furnace, heated to 890°C at a rate of 6°C / min under nitrogen protection for 2 h, and then heated to 1600°C at a rate of 12°C / min for 2 h to obtain ceramic heat-conducting microspheres.

[0036] S2: 190 g of lithium fluoride and 900 mL of a 35% mass fraction hydrochloric acid solution were added to a reaction kettle, stirred at 25 °C and 500 r / min for 30 min, then 90 g of titanium aluminum carbide was added, and stirring was continued for 50 h, centrifuged at 6000 r / min for 5 min, filtered, and the filter cake was washed with deionized water and ethanol until the last washing liquid was neutral, ultrasonic stripping under an argon flow of 25 mL / min, centrifuged at 6000 r / min for 5 min, to obtain a suspension of MXene nanosheets.

[0037] S3: 90 g of the suspension of MXene nanosheets and 2 LN, N-dimethylformamide were added to a polytetrafluoroethylene-lined reaction kettle, sealed, ultrasonic dispersed at 135 °C for 40 min, then 50 g of 2, 5-dihydroxyterephthalic acid and 60 g of titanium tetrachloride were added, ultrasonic dispersed for 60 min, and stirring was continued for 26 h, and then naturally cooled to room temperature, filtered, and the filter cake was washed with N, N-dimethylformamide and methanol for 3 times respectively, and vacuum dried at 80 °C for 2 h, to obtain a suspension of titanium-based MOF intercalated MXene nanosheets.

[0038] S4: 140 g of the suspension of titanium-based MOF intercalated MXene nanosheets, 120 g of ceramic heat-conducting microspheres, and 2 LN, N-dimethylformamide were added to a reaction kettle, stirred at 25 °C and 500 r / min for 5 h, centrifuged at 6000 r / min for 12 min, filtered, and the filter cake was washed with deionized water and ethanol for 4 times, and vacuum dried at 70 °C for 2 h, to obtain MXene nanosheet composite heat-conducting microspheres.

[0039] S5: 120 g of the MXene nanosheet composite heat-conducting microspheres, 90 mL of polyvinylpyrrolidone, and 20 g of sodium lauryl sulfate were stirred for 40 min, then a mixed solution of 170 mL of polyacrylic resin and deionized water in a mass ratio of 1:10 was added, to obtain a coating liquid; the coating liquid was uniformly coated on the surface of the PO film, the film layer thickness was 0.2 mm, dried, and wound, to obtain a PO film with good summer cooling effect.

[0040] Comparative Example 1: on the basis of Example 3, the MXene nanosheet composite heat-conducting microspheres in step S5 were replaced by the suspension of titanium-based MOF intercalated MXene nanosheets prepared in step S3.

[0041] Comparative Example 2: on the basis of Example 3, without the treatment in step S3, the suspension of titanium-based MOF intercalated MXene nanosheets in step S4 was replaced by the suspension of MXene nanosheets prepared in step S2.

[0042] Comparative Example 3: on the basis of Example 3, the ceramic heat-conducting microspheres in step S4 were replaced by the silicon dioxide in step S1.

[0043] The performance of the PO membranes prepared in Examples 1-3 and Comparative Examples 1-3 was tested, and the results are shown in Table 1: 1. Thermal conductivity test: The test was conducted using a Netzsch LFA447 thermal conductivity tester.

[0044] 2. Tensile strength test: Refer to GB / T13022-1991 Plastic film tensile test to test the tensile strength, record the data, and the tensile strength is the tensile strength; PO film is attached to the film surface, left to stand for 2 hours, then peeled off, then attached to the film surface again, left to stand for 2 hours, peeled off, repeat the operation 20 times, and record the tensile strength data again, which is the tensile strength.

[0045] 3. Wrinkle detection: After the PO film is attached to the film surface, it is wound up. Then, 6 wound films are stacked to form a structure of 3, 2, 1 from bottom to top, with 6 films as a group. After the 6 wound films are stacked and left for 1 day, the PO film on the film surface is peeled off. The wrinkle area of ​​the PO film on the surface of the middle film in the bottom row of 3 films is observed and the wrinkle area per unit area is recorded.

[0046] 4. Tear strength test: The tear strength of the PO film was determined by the pendulum method according to the standard ASTM D1922-08.

[0047] 5. Optical performance: The transmittance was tested in accordance with GB / T2410-2008 standard.

[0048] 6. Antibacterial test: According to the test method of GB / T20944.3-2008 "Evaluation of antibacterial properties of textiles", take 5mm×5mm sample pieces, disinfect them and put them into 70mL buffer flasks. Then add 5mL of inoculated bacterial solution and incubate for 18h (37℃, 130r / min). Finally, transfer 100μL of sample to nutrient agar plate and incubate at 37℃ for 24h. Then calculate the antibacterial rate.

[0049] 6. After each group of test samples was subjected to UV aging treatment for 72 hours, performance testing was continued.

[0050] Table 1

[0051] As can be seen from Table 1, the PO films prepared in Examples 1-3 have better thermal conductivity, tensile strength, wrinkle area, tear strength, and light transmittance than the comparative examples. This indicates that the PO films prepared in this invention have good heat dissipation capacity and tensile strength, are not prone to aging and wrinkling, and are not prone to bacterial growth after long-term use.

[0052] Comparative Example 1 replaces the MXene nanosheet composite thermal conductive microspheres in Step S5 with the suspension of titanium-based MOF intercalated MXene nanosheets prepared in Step S3, and the ceramic thermal conductive microspheres as the reinforcing phase are removed, resulting in a decrease in tensile strength, further weakening the interfacial adhesion between the coating and the PO film, and a significant increase in wrinkles after aging, with the MXene layers directly exposed, heat unable to quickly spread through the microspheres, localized overheating on the film surface, and accelerated aging.

[0053] Comparative Example 2 replaces the suspension of titanium-based MOF intercalated MXene nanosheets in Step S4 with the suspension of MXene nanosheets prepared in Step S2, with the unintercalated MXene exposed to air, titanium vacancies rapidly oxidized to titanium dioxide, a decrease in the overall thermal conductivity of the composite microspheres, MXene surface active sites not protected by the MOF, inability to act as electron acceptors after oxidation, loss of the ability to inhibit electron-hole recombination, and uneven microsphere coating due to the easy agglomeration of MXene layers due to van der Waals forces, with stress concentration in the coating.

[0054] Comparative Example 3 replaces the ceramic thermal conductive microspheres in Step S4 with silica in Step S1, with the thermal conductivity of silica significantly lower than that of ceramic thermal conductive microspheres, and silica being a brittle particle that cannot form a three-dimensional skeleton at the microsphere level, resulting in a decrease in tensile strength and brittle cracking of the coating.

[0055] Although embodiments of the present application have been shown and described, it is to be understood that various modifications, substitutions, replacements and changes can be made to these embodiments without departing from the principles and spirit of the present application, which can be understood by those of ordinary skill in the art.

Claims

1. A method for preparing a PO membrane with good cooling effect in summer, characterized in that, Includes the following steps: Step 1: Ceramic thermally conductive microspheres are obtained by mixing zirconium tetrachloride and silicon dioxide with a phenolic resin solution and then calcining. Step 2: Lithium fluoride reacts with hydrochloric acid to generate hydrofluoric acid, which is then added to etch titanium aluminum carbide to generate a suspension of multilayer MXene nanosheets; the MXene nanosheets are ultrasonically dispersed under hydrothermal conditions, and 2,5-dihydroxyterephthalic acid is coordinated with titanium tetrachloride to form MOF, resulting in a suspension of titanium-based MOF intercalated MXene nanosheets. Step 3: The ceramic thermally conductive microspheres are embedded into the suspension framework of titanium-based MOF intercalated MXene nanosheets by mechanical stirring to obtain ceramic thermally conductive microspheres coated with MXene nanosheet composite thermally conductive microspheres; Step 4: Form a coating solution by combining MXene nanosheets with thermally conductive microspheres, polyacrylic acid resin, and deionized water, coat the base film surface, dry, and roll up to obtain a PO film with good cooling effect in summer.

2. The method for preparing a PO membrane with good cooling effect in summer according to claim 1, characterized in that, The specific preparation steps of the ceramic thermally conductive microspheres are as follows: Zirconium tetrachloride, silicon dioxide and acetylacetone solution are added to a reaction vessel and stirred for 20-30 min at 20-25℃ and 500-600 r / min. Then ethanol is added and stirring is continued for 20-30 min to obtain zirconium silicon solution. Zirconium silicon solution and phenolic resin solution were added to a reaction vessel at a ratio of 500-600 mL: 700-780 mL. The mixture was stirred at 150-160℃ and 500-600 r / min for 20-22 h. After filtration, the filter cake was washed 2-4 times with deionized water and dried under vacuum at 60-70℃ for 1-2 h. The product was then transferred to a muffle furnace and heated to 800-890℃ at a rate of 5-6℃ / min under nitrogen protection and held for 1-2 h. The temperature was then increased to 1500-1600℃ at a rate of 10-12℃ / min and held for 1-2 h to obtain ceramic thermally conductive microspheres.

3. The method for preparing a PO film with good cooling effect in summer according to claim 2, characterized in that, The ratio of zirconium tetrachloride, silicon dioxide, acetylacetone solution and ethanol is 120-140g: 110-120g: 800-900mL: 120-140mL.

4. The method for preparing a PO film with good cooling effect in summer according to claim 1, characterized in that, The specific preparation steps for the MXene nanosheet suspension are as follows: Lithium fluoride and a 20-35% hydrochloric acid solution were added to a reaction vessel and stirred at 20-25℃ and 400-500 rpm for 20-30 min. Then, titanium aluminum carbide was added, and stirring was continued for 48-50 h. The mixture was centrifuged at 5000-6000 rpm for 3-5 min, filtered, and the filter cake was washed with deionized water and ethanol until the final washing solution was neutral. The mixture was then ultrasonically exfoliated at an argon flow rate of 20-25 mL / min and centrifuged at 5000-6000 rpm for 3-5 min to obtain a suspension of MXene nanosheets.

5. The method for preparing a PO membrane with good cooling effect in summer according to claim 4, characterized in that, The ratio of lithium fluoride, hydrochloric acid solution, and titanium aluminum carbide is 180-190g: 800-900mL: 80-90g.

6. The method for preparing a PO membrane with good cooling effect in summer according to claim 1, characterized in that, The specific preparation steps for the suspension of the titanium-based MOF intercalated MXene nanosheets are as follows: The suspension of MXene nanosheets and N,N-dimethylformamide were added to a polytetrafluoroethylene-lined reactor, sealed, and ultrasonically dispersed at 130-135℃ for 20-40 min. Then, 2,5-dihydroxyterephthalic acid and titanium tetrachloride were added, and ultrasonically dispersed for 40-60 min. The mixture was stirred for 24-26 h, cooled naturally to room temperature, filtered, and the filter cake was washed 2-3 times with N,N-dimethylformamide and methanol, respectively. The mixture was then vacuum dried at 60-80℃ for 1-2 h to obtain the suspension of titanium-based MOF intercalated MXene nanosheets. The ratio of the suspended matter, N,N-dimethylformamide, 2,5-dihydroxyterephthalic acid and titanium tetrachloride in the MXene nanosheets is 80-90g:1-2L:40-50g:50-60g.

7. The method for preparing a PO film with good cooling effect in summer according to claim 1, characterized in that, The specific preparation steps of the MXene nanosheet composite thermally conductive microspheres are as follows: A suspension of titanium-based MOF intercalated MXene nanosheets, ceramic thermally conductive microspheres, and N,N-dimethylformamide were added to a reaction vessel and stirred at 20-25℃ and 400-500 r / min for 4-5 h. After centrifugation at 5000-6000 r / min for 10-12 min, the mixture was filtered. The filter cake was washed 2-4 times with deionized water and ethanol and then vacuum dried at 60-70℃ for 1-2 h to obtain MXene nanosheet composite thermally conductive microspheres.

8. The method for preparing a PO film with good cooling effect in summer according to claim 7, characterized in that, The ratio of the suspended solids of the titanium-based MOF intercalated MXene nanosheets, the ceramic thermally conductive microspheres, and N,N-dimethylformamide is 120-140g: 100-120g: 1-2L.

9. The method for preparing a PO film with good cooling effect in summer according to claim 1, characterized in that, The specific preparation steps of the PO membrane are as follows: MXene nanosheets were combined with thermally conductive microspheres, polyvinylpyrrolidone, and sodium lauryl sulfate and stirred for 30-40 minutes. Then, a mixed solution of polyacrylic acid resin and deionized water at a mass ratio of 1:10 was added to obtain a coating solution. The coating solution was uniformly coated on the surface of a PO film with a film thickness of 0.1-0.2 mm. The film was then dried and wound up to obtain a PO film with good cooling effect in summer. The ratio of the MXene nanosheet composite thermally conductive microspheres, polyvinylpyrrolidone, sodium lauryl sulfate, and the mixed solution is 100-120g: 80-90mL: 15-20g: 150-170mL.

10. A PO film with good cooling effect in summer, characterized in that, It is prepared by the preparation method described in any one of claims 1-9.

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