Radiation refrigeration waterborne polyurethane film with moisture resistance and preparation method of radiation refrigeration waterborne polyurethane film

Abstract

The invention discloses a preparation method of a radiation refrigeration waterborne polyurethane film with moisture resistance in the field of composite materials, and aims to overcome the defects that waterborne polyurethane is easy to absorb moisture and poor in radiation refrigeration performance after being molded, and the preparation method comprises the following steps: firstly, preparing a metal organic framework material by a solution coprecipitation method; uniformly dispersing the metal organic framework material in the aqueous polyurethane solution to obtain a homogeneous dispersion liquid; a silane modifier is dissolved in an ethanol / deionized water solution and fully stirred. And then mixing the treated silane modifier with the aqueous polyurethane / metal organic framework material dispersion liquid, and carrying out drying and heat treatment processes to prepare the radiation refrigeration aqueous polyurethane film with moisture resistance. The waterborne polyurethane material obtained by the preparation method can be widely applied to the fields of automobile coatings, energy-saving coatings and the like.

Description

Technical Field

[0001] The present invention belongs to the field of polyurethane film preparation, and particularly relates to a radiation cooling waterborne polyurethane film with moisture resistance and a preparation method thereof. Background Art

[0002] In recent years, with the advancement of global environmental protection policies, waterborne polyurethane (WPU), as a green material, has gradually replaced traditional solvent-based polyurethane due to its low toxicity, non-flammability, and environmental friendliness, and is widely used in coatings, packaging, textiles and other fields. Its core advantage lies in using water as the dispersion medium, avoiding the use of organic solvents, thereby reducing the harm to the human body and the environment. However, waterborne polyurethane still faces two key challenges in practical applications.

[0003] The moisture resistance of waterborne polyurethane is insufficient. Since hydrophilic groups need to be introduced into its molecular chain to achieve water dispersibility, polar regions exist inside the cured material, which are prone to adsorb water in a high-humidity environment, leading to swelling and degradation of mechanical properties. For example, the coating may soften and the adhesion may decrease in a humid environment, restricting its application in scenarios that require long-term moisture protection or underwater environments. Although the moisture resistance can be improved by chemical crosslinking or adding inorganic fillers, existing methods often lead to the complication of the preparation process or an increase in material cost, making it difficult to achieve industrial balance.

[0004] Secondly, waterborne polyurethane lacks the function of radiative cooling. Radiative cooling materials achieve energy-free cooling through infrared radiation in a specific band, which is a research hotspot in the field of energy and materials in recent years. However, the molecular structure of waterborne polyurethane itself is difficult to match the vibration modes required for infrared radiation, and conventional nanoscale fillers (such as metal oxides) are prone to affect the optical properties due to poor dispersibility. In contrast, other polymers (such as polydimethylsiloxane) have shown excellent sunlight reflection and infrared emission capabilities, while waterborne polyurethane coatings have not yet broken through the performance bottleneck in such functional applications. This defect not only restricts its application in high-end scenarios such as building energy conservation and outdoor equipment protection, but also restricts the improvement of its added value. Summary of the Invention

[0005] Aiming at the defects of waterborne polyurethane in the prior art, the present invention proposes a radiation cooling waterborne polyurethane film with moisture resistance and a preparation method thereof. MOF-303 and cetyltrimethoxysilane are introduced into the waterborne polyurethane. Cetyltrimethoxysilane can not only improve the water resistance of the waterborne polyurethane, but also the Si-O-C groups inside it will undergo strong stretching vibrations after receiving the radiant energy of external sunlight. The electrons in the high energy band will transition to the low energy band, thereby releasing photons. Finally, heat can be radiated outward in the form of electromagnetic waves in the mid-infrared region to achieve the effect of radiative cooling.

[0006] Specifically, the present invention obtains a radiation-cooling waterborne polyurethane film with moisture-resistant performance through the following technical means: (1) Prepare metal-organic framework material MOF-303; MOF-303 is a white granular material with a relatively wide bandgap. Due to its wide bandgap characteristics, it has a low absorption rate within the solar irradiation wavelength range (0.3–2.5 μm). Under sunlight irradiation, it can effectively inhibit the absorption of photons and reduce its surface temperature, achieving a cooling effect.

[0007] (2) Uniformly disperse MOF-303 powder in a 15-35 wt% waterborne polyurethane solution to obtain a waterborne polyurethane / MOF-303 dispersion; the mass ratio of the solid content of MOF-303 to waterborne polyurethane is 1:3-14; (3) Add a cetyltrimethoxysilane solution to the waterborne polyurethane / MOF-303 dispersion, stir until uniform, and obtain a film by low-temperature volatilization at 25-50 °C for 24-48 h, and then heat-treat at 80-90 °C for 1.5 - 3 h to prepare a radiation-cooling waterborne polyurethane film with moisture-resistant performance; The volume ratio of the cetyltrimethoxysilane solution to the waterborne polyurethane / MOF-303 dispersion is 15:27 - 50; The solvent of the cetyltrimethoxysilane solution is a mixed solution with a volume ratio of ethanol to deionized water of 1:2-3; The volume ratio of cetyltrimethylsilane to the ethanol / deionized water solution is 1:30-40.

[0008] After low-temperature volatilization at 25-50 °C for 24-48 h, the solvent in the mixture of the cetyltrimethoxysilane solution and the waterborne polyurethane / MOF-303 dispersion is volatilized completely to form a film. Subsequently, heating promotes the condensation reaction of the silane, making the silane adhere more firmly and forming a more stable hydrophobic layer.

[0009] Further, the preparation method of MOF-303 in step 1 is: (1) Dissolve 3,5-pyrazoledicarboxylic acid monohydrate in a sodium hydroxide solution; the mass ratio of sodium hydroxide to 3,5-pyrazoledicarboxylic acid monohydrate is 216:625-1250; (2) Then add aluminum chloride hexahydrate to the solution, heat and react at 120-140 °C for 10 - 12 h. After the reaction ends, wash to obtain a precipitate; the mass ratio of sodium hydroxide to aluminum chloride hexahydrate is 81:325-650; (3) Dry the obtained precipitate, and then heat-treat at 150-170 °C for 6-8 h to obtain the metal-organic framework material MOF-303.

[0010] Further, the concentration of the sodium hydroxide solution in Step 1 for preparing MOF-303 is 0.09 - 0.18 wt%.

[0011] Further, the cleaning method in Step 2 for preparing MOF-303 is to clean with deionized water and methanol.

[0012] Further, the drying method in Step 3 for preparing MOF-303 is to dry in a vacuum drying oven at 30 - 50 °C for 10 - 24 h.

[0013] During the process of co-blending aqueous polyurethane (WPU), MOF-303, and hydrolyzed hexadecyltrimethoxysilane (HDS) into a film, the intermolecular forces between the components mainly include a chemical bond and non-bond cooperative mechanism. The chemical bond action stems from the condensation reaction of the silanol (Si–OH) generated by the hydrolysis of HDS with the hydroxyl group (–OH) on the WPU molecular chain or the metal hydroxyl group of the MOF-303 framework, forming stable Si–O–C or Si–O–M covalent bonds, thereby strengthening the interfacial bonding; the non-bond interaction is manifested as a multiple hydrogen bond network and hydrophobic association effect: on the one hand, the polar groups (–NH, –COO–) of WPU, the surface hydroxyl groups of MOF-303, and the silanol of HDS form crosslinks through hydrogen bonds, enhancing the interfacial adhesion and stress transfer efficiency; on the other hand, the hexadecyl long chain of HDS associates with the hydrophobic segment of WPU through van der Waals forces, further improving the component compatibility and the structural stability of the material.

[0014] The present invention also provides a radiation-cooling aqueous polyurethane film with moisture resistance prepared by the above method.

[0015] The beneficial effects of the present invention are as follows: (1) The present invention broadens the application scope of aqueous polyurethane. By combining it with MOF-303 and hexadecyltrimethoxysilane, it not only solves the drawback of poor moisture resistance of aqueous polyurethane after film formation but also broadens its application in the field of radiation cooling.

[0016] (2) The preparation process of the aqueous polyurethane film in the present invention is simple. While improving its radiation cooling performance, it also enhances the moisture resistance and thermal stability. Description of the Drawings

[0017] Figure 1 It is a physical photograph of MOF-303 in Example 1; Figure 2 It is a temperature difference comparison chart of the radiation cooling performance of the modified aqueous polyurethane films in Example 2, Example 3, and Example 4; Figure 3 It is the contact angle of the pure aqueous polyurethane film in Comparative Example 1; Figure 4 is the contact angle of the modified waterborne polyurethane film in Example 1. DETAILED DESCRIPTION

[0018] The following examples are used to further illustrate the present invention, and their purpose is to illustrate the present invention and should not be construed as limiting the scope of the present invention. Unless otherwise specified, all parts by weight and weight percentages are used below.

[0019] The raw materials used in the present invention, unless otherwise specified, are conventional commercially available products; the methods used in the present invention, unless otherwise specified, are conventional methods in the art.

[0020] The embodiments of the present invention are further described below with reference to a plurality of embodiments.

[0021] It should be clear that 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 ordinary technicians in the field without creative work are within the scope of protection of the present application.

[0022] The terms used in the embodiments of the present application are only for the purpose of describing specific embodiments, and are not intended to limit the present application. The singular forms "a", "said" and "the" used in the embodiments of the present application and the appended claims are also intended to include plural forms, unless the context clearly indicates other meanings.

[0023] Example 1 (1) Dissolve 1.875 g of 3,5-pyrazoledicarboxylic acid monohydrate in 360 mL of sodium hydroxide (0.18 wt%) solution;

[0024] (2) Add 2.6 g of aluminum chloride hexahydrate to the solution and heat and stir at 120 °C for 10 h. After the reaction is completed, wash the precipitate with deionized water and methanol; (3) The obtained precipitate was placed in a vacuum drying oven and dried at 30 °C for 24 h, and then heated in an oven at 150 °C for 6 h to obtain MOF-303.

[0025] (4) Add 1 mL of hexadecyltrimethoxysilane to 30 mL of ethanol / deionized water solution (volume ratio of 1:2), stir and fully hydrolyze to obtain a hexadecyltrimethoxysilane solution; (5) Add 0.35 g of MOF-303 into 7.5 mL of deionized water and obtain a uniform MOF-303 dispersion by ultrasonic treatment; (6) Add the MOF-303 dispersion into 9.5 mL of aqueous polyurethane (35 wt%) and stir well to obtain the aqueous polyurethane / MOF-303 dispersion; (7) Add 15 mL of cetyltrimethoxysilane solution into the aqueous polyurethane / MOF-303 dispersion, continue stirring until homogeneous, pour it into a petri dish, volatilize at 50 °C for 24 h until dry to form a film, and heat the dry film at 80 °C for 3 h to obtain the modified aqueous polyurethane film.

[0026] Example 2 (1) Dissolve 1.875 g of 3,5-pyrazoledicarboxylic acid monohydrate in 360 mL of sodium hydroxide (0.18 wt%) solution;

[0027] (2) Add 2.6 g of aluminum chloride hexahydrate to the solution, heat and stir at 120 °C for 10 h. After the reaction, wash the precipitate with deionized water and methanol; (3) Place the obtained precipitate in a vacuum drying oven, dry at 30 °C for 24 h, and then heat in an oven at 150 °C for 6 h to obtain MOF-303.

[0028] (4) Add 1 mL of cetyltrimethoxysilane to 30 mL of ethanol / deionized water solution (volume ratio 1:2), stir well for hydrolysis to obtain the cetyltrimethoxysilane solution; (5) Add 0.3 g of MOF-303 to 15 mL of deionized water, and obtain a uniform MOF-303 dispersion by ultrasonic treatment; (6) Add the MOF-303 dispersion into 12 mL of aqueous polyurethane (35 wt%) and stir well to obtain the aqueous polyurethane / MOF-303 dispersion; (7) Add 15 mL of cetyltrimethoxysilane solution into the aqueous polyurethane / MOF-303 dispersion, continue stirring until homogeneous, pour it into a petri dish, volatilize at 50 °C for 24 h until dry to form a film, and heat the dry film at 80 °C for 3 h to obtain the modified aqueous polyurethane film.

[0029] Example 3 (1) Dissolve 1.875 g of 3,5-pyrazoledicarboxylic acid monohydrate in 360 mL of sodium hydroxide (0.18 wt%) solution;

[0030] (2) Add 2.6 g of aluminum chloride hexahydrate to the solution, heat and stir at 120 °C for 10 h. After the reaction, wash the precipitate with deionized water and methanol; (3) Place the obtained precipitate in a vacuum drying oven and dry it at 30 °C for 24 h, then place it in an oven and heat it at 150 °C for 6 h to obtain MOF-303.

[0031] (4) Add 1 mL of cetyltrimethoxysilane to 30 mL of an ethanol / deionized water solution (volume ratio 1:2), stir well for hydrolysis to obtain a cetyltrimethoxysilane solution; (5) Add 0.7 g of MOF-303 to 15 mL of deionized water and obtain a uniform MOF-303 dispersion through ultrasonic treatment; (6) Add the MOF-303 dispersion to 12 mL of aqueous polyurethane (35 wt%) and stir well to obtain an aqueous polyurethane / MOF-303 dispersion; (7) Add 15 mL of the cetyltrimethoxysilane solution to the aqueous polyurethane / MOF-303 dispersion, continue stirring until uniform, pour it into a petri dish, volatilize at 50 °C for 24 h until dry to form a film, and heat the dry film at 80 °C for 3 h to obtain a modified aqueous polyurethane film.

[0032] Example 4 (1) Dissolve 1.875 g of 3,5-pyrazoledicarboxylic acid monohydrate in 360 mL of sodium hydroxide (0.18 wt%) solution;

[0033] (2) Add 2.6 g of aluminum chloride hexahydrate to the solution, heat and stir at 120 °C for 10 h. After the reaction, wash the precipitate with deionized water and methanol; (3) Place the obtained precipitate in a vacuum drying oven and dry it at 30 °C for 12 h, then place it in an oven and heat it at 150 °C for 6 h to obtain MOF-303.

[0034] (4) Add 1 mL of cetyltrimethoxysilane to 30 mL of an ethanol / deionized water solution (volume ratio 1:2), stir well for hydrolysis to obtain a cetyltrimethoxysilane solution; (5) Add 1.3 g of MOF-303 to 15 mL of deionized water and obtain a uniform MOF-303 dispersion through ultrasonic treatment; (6) Add the MOF-303 dispersion to 12 mL of aqueous polyurethane (35 wt%) and stir well to obtain an aqueous polyurethane / MOF-303 dispersion; (7) Add 15 mL of cetyltrimethoxysilane solution to the aqueous polyurethane / MOF-303 dispersion, continue stirring until homogeneous, and pour it into a petri dish. Volatilize at 50 °C for 8 h until dry to form a film, and heat the dry film at 80 °C for 3 h to obtain a modified aqueous polyurethane film.

[0035] Example 5 (1) Dissolve 1.875 g of 3,5-pyrazoledicarboxylic acid monohydrate in 360 mL of sodium hydroxide (0.09 wt%) solution; (2) Add 2.6 g of aluminum chloride hexahydrate to the solution, and heat and stir at 140 °C for 12 h. After the reaction, wash the precipitate with deionized water and methanol; (3) Place the obtained precipitate in a vacuum drying oven, dry at 50 °C for 10 h, and then place it in an oven and heat at 170 °C for 4 h to obtain MOF-303.

[0036] (4) Add 1 mL of cetyltrimethoxysilane to 40 mL of ethanol / deionized water solution (volume ratio 1:3), stir to hydrolyze fully to obtain a cetyltrimethoxysilane solution; (5) Add 1.75 g of MOF-303 to 15 mL of deionized water, and obtain a homogeneous MOF-303 dispersion by ultrasonic treatment; (6) Add the MOF-303 dispersion to 35 mL of aqueous polyurethane (15 wt%) and stir well to obtain an aqueous polyurethane / MOF-303 dispersion; (7) Add 15 mL of cetyltrimethoxysilane solution to the aqueous polyurethane / MOF-303 dispersion, continue stirring until homogeneous, and pour it into a petri dish. Volatilize at 25 °C for 48 h until dry to form a film, and heat the dry film at 70 °C for 1.5 h to obtain a modified aqueous polyurethane film.

[0037] Comparative Example 1 (1) Pour 12 mL of aqueous polyurethane (35 wt%) into a petri dish until dry to form a film.

[0038] The above examples and comparative examples are preferred cases of this patent and are not used to limit the protection scope of this patent.

[0039] Figure 1 It is a physical picture of MOF-303 in Comparative Example 1. Figure 2It is a comparison chart of radiative cooling performance. It can be seen from the chart that as the addition amount of MOF-303 increases, the modified waterborne polyurethane films of Example 2, Example 3, and Example 4 can reduce the temperature of the target space by approximately 2.6 °C, 2.3 °C, and 5.6 °C respectively. However, Comparative Example 1 did not reduce the temperature of the target space, which is mainly due to the high light transmittance of the pure waterborne polyurethane film, and the light can directly pass through the pure waterborne polyurethane film and heat the target space.

[0040] As Figure 3 shown, the contact angle of the pure waterborne polyurethane film in Comparative Example 1 is 83 °, showing significant hydrophilic characteristics, resulting in too high interfacial wettability and severely restricting its practical application in humid environments. The contact angle of the modified waterborne polyurethane film in Example 1 is increased to 112° ( Figure 4 ), and the water resistance performance is greatly improved. This performance improvement is due to the following two aspects: on the one hand, cetyltrimethoxysilane effectively reduces the surface energy of the waterborne polyurethane film through surface energy regulation; on the other hand, the MOF-303 particles form a rough micro-nano surface structure on the surface of the waterborne polyurethane film matrix. The combination of the two effectively improves the hydrophobic performance of the modified waterborne polyurethane film and enhances its water resistance and moisture resistance.

[0041] The above embodiments have detailed the structure, characteristics, and function effects of the present invention. The above are only the preferred embodiments of the present invention. Any changes made according to the concept of the present invention, or modified into equivalent embodiments with equivalent changes, still within the scope covered by the specification, shall be within the protection scope of the present invention.

Claims

1. A preparation method of a radiation-cooling waterborne polyurethane film with moisture resistance performance, characterized in that, It has the following steps: (1) Prepare the metal-organic framework material MOF-303; (2) Uniformly disperse the MOF-303 powder in an aqueous polyurethane solution with a concentration of 15-35 wt% to obtain an aqueous polyurethane / MOF-303 dispersion; the mass ratio of the solid content of MOF-303 to aqueous polyurethane is 1:3-14; (3) Add a cetyltrimethoxysilane solution to the aqueous polyurethane / MOF-303 dispersion, stir until uniform, and obtain a film by low-temperature volatilization at 25-50 °C for 8-48 h, and then heat-treat at 70-80 °C for 1.5-3 h to prepare a radiation-cooling aqueous polyurethane film with moisture-resistant performance; The volume ratio of the cetyltrimethoxysilane solution to the aqueous polyurethane / MOF-303 dispersion is 15:17-50; The solvent of the cetyltrimethoxysilane solution is a mixed solution with a volume ratio of ethanol to deionized water of 1:2-3; The volume ratio of cetyltrimethylsilane to the ethanol / deionized water solution is 1:30-40.

2. The method according to claim 1, characterized in that, The preparation method of the MOF-303 described in step 1 is: (1) Dissolve 3,5-pyrazoledicarboxylic acid monohydrate in a sodium hydroxide solution; wherein the mass ratio of sodium hydroxide to 3,5-pyrazoledicarboxylic acid monohydrate is 216:625-1250; (2) Then add aluminum chloride hexahydrate to the solution, heat and react at 120-140 °C for 10-12 h. After the reaction is completed, wash to obtain a precipitate; the mass ratio of sodium hydroxide to aluminum chloride hexahydrate is 81:325-650; (3) Dry the obtained precipitate, and then heat-treat at 150-170 °C for 6-8 h to obtain the metal-organic framework material MOF-303.

3. The method according to claim 2, wherein The concentration of the sodium hydroxide solution described in step 1 is 0.09-0.18 wt%.

4. The method according to claim 2, wherein The washing method described in step 2 is to wash with deionized water and methanol.

5. The method according to claim 2, wherein The drying method described in step 3 is to dry in a vacuum drying oven at 30-50 °C for 10-24 h.

6. A radiation-cooling aqueous polyurethane film with moisture-resistant performance prepared by the method according to claim 1.

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