A super-hydrophobic, zero-energy cooling dual-functional phosphogypsum coating and its preparation method

Abstract

This invention discloses a method for preparing a phosphogypsum coating with superhydrophobic and radiative cooling properties. The coating's main components include phosphogypsum (PG), a silane coupling agent, polymethyl methacrylate (PMMA), stearic acid (SA), polydimethylsiloxane (PDMS), and a curing agent. A simple blending method is used to prepare a slurry, followed by a doctor blade coating process. This results in a phosphogypsum coating with excellent superhydrophobic and radiative cooling properties.

Description

Technical Field

[0001] The present invention belongs to the technical field of functional coatings, and in particular relates to a method for preparing a phosphogypsum coating with super-hydrophobic and radiation cooling functions. Background Art

[0002] Phosphogypsum, a major byproduct of the production of high-concentration phosphate fertilizers, compound fertilizers, and wet-process phosphoric acid, has a massive annual output and contains numerous impurities, including phosphorus, fluorine, and organic matter. This limits its direct use and results in a low resource utilization rate. Statistics show that China emits enormous quantities of phosphogypsum annually, with surface stockpiles exceeding hundreds of millions of tons. This not only occupies significant arable land but also damages the surface ecosystem. Therefore, the efficient utilization of phosphogypsum has become a global challenge, and increasing its utilization rate is an urgent need.

[0003] Superhydrophobic modification of phosphogypsum is an effective way to increase the value of phosphogypsum. Through superhydrophobic modification, the water absorption rate of phosphogypsum products can be significantly reduced, and their water resistance and durability can be improved, thereby expanding the application range of phosphogypsum in fields such as building materials. Among various superhydrophobic modification methods, organic modification of phosphogypsum improves the hydrophobicity of phosphogypsum products without affecting the aesthetic appearance of phosphogypsum products and is currently a commonly used modification method. However, organic hydrophobic agents usually only affect gypsum with small pore size and low porosity, and have little effect on phosphogypsum with large pore size and high porosity.

[0004] Meanwhile, radiative cooling is a highly attractive new zero-energy cooling technology. This technique uses electromagnetic waves to release heat energy from surface objects into outer space, where temperatures are near absolute zero, through an atmospheric window (such as the 8-13 μm band), thereby achieving self-cooling. To achieve optimal zero-energy cooling, the cooling material typically requires high reflectivity in the solar spectrum (0.3-2.5 μm) to prevent heat absorption, and high emissivity in the atmospheric window (ATW) (8-13 μm) to transfer heat to the cold outer space. This minimizes heat absorption while efficiently dissipating the existing heat through radiation, achieving silent, power-free cooling. Modifying phosphogypsum to improve its cooling properties, resulting in a zero-energy cooling version, would further expand its applications and promote its high-value utilization. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for preparing a phosphogypsum coating with super-hydrophobicity and radiation cooling functions, so as to solve the problems of existing phosphogypsum disposal and efficient utilization.

[0006] The technical solution of the present invention:

[0007] The synergistic effect of polydimethylsiloxane (PDMS), stearic acid (SA) and polymethyl methacrylate (PMMA) is utilized to reduce the surface energy of PG and make its surface hydrophobic. At the same time, PMMA and SA give PG a significant cooling effect under the action of ultrasound.

[0008] A method for preparing a phosphogypsum coating having super-hydrophobic and radiative cooling functions comprises the following steps:

[0009] Step 1: Add PG, NaOH, and Na2SO4 into deionized water in proportion, and stir to disperse to obtain a mixed suspension;

[0010] Step 2: Filter, wash and dry the mixed suspension obtained in step 1 to obtain hydroxylated PG powder;

[0011] Step 3: Add the silane coupling agent to a mixed solvent of deionized water and anhydrous ethanol, heat and stir to obtain a dispersant;

[0012] Step 4: adding the hydroxylated PG powder obtained in step 2 to the dispersant obtained in step 3, and stirring to obtain a mixed suspension;

[0013] Step 5: filtering, washing and drying the mixed suspension obtained in step 4 to obtain hydrophobically modified PG powder;

[0014] Step 6: Grind the hydrophobically modified PG powder obtained in step 5 and pass it through a sieve to obtain hydrophobically modified PG powders of different particle sizes;

[0015] Step 7: Add PMMA and SA in proportion to a mixed solvent of N,N-dimethylformamide (DMF) and tetrahydrofuran (THF), and stir thoroughly to obtain a cooling modifier;

[0016] Step 8: Add the hydrophobically modified PG powder obtained in step 6 to the cooling modifier obtained in step 7, stir thoroughly, and then ultrasonicate, and then add PDMS and its curing agent to obtain a super-hydrophobic-radiation cooling dual-functional modified phosphogypsum coating;

[0017] Step 9: The coating obtained in step 8 is coated on the substrate using a doctor blade method, and after the solvent is dried, a phosphogypsum coating with super-hydrophobicity and radiation cooling functions is obtained.

[0018] In the step 1, the mass concentration of PG is 0.1-0.5 g / mL, the mass concentration of NaOH is 0.05-0.25 g / mL, the mass concentration of Na2SO4 is 0.005-0.04 g / mL, the stirring temperature is room temperature, and the stirring time is 20-30 min.

[0019] In step 2, the drying temperature is 60° C. and the drying time is 12 h.

[0020] In step 3, the silane coupling agent is any one of KH550, KH560, and KH570; the volume ratio of deionized water to anhydrous ethanol is 3:4-6, and the mass concentration of the silane coupling agent in the silane coupling agent mixture is 0.03-0.06 g / mL.

[0021] In step 4, the stirring temperature is 60-80° C., and the stirring time is 1.0-2.5 h.

[0022] In step 5, the drying temperature is 60-80° C. and the drying time is 10-12 hours.

[0023] In step 6, the mesh size of the sieve is 90-110 meshes.

[0024] In step 7, the volume ratio of DMF to THF in the mixed solvent is 1:1-5, the mass concentration of PMMA added is 0.015-0.1 g / mL, and the mass concentration of SA is 0.02-0.1 g / mL.

[0025] In step 8, the mass ratio of hydrophobically modified PG powder to cooling modifier is 1:3-4, the PDMS mass concentration is 0.03-0.1 g / ml, the ultrasonic power is 50-100 W, preferably 80 W, the ultrasonic time is 5-30 minutes, preferably 10 minutes, the stirring temperature is room temperature, and the stirring time is 3-10 minutes, preferably 5 minutes.

[0026] In step 9, the scraping film thickness of the scraping method is 300-400 μm, and the material of the substrate includes any one of a glass sheet, an aluminum sheet, a copper sheet, and a carbon steel sheet.

[0027] Beneficial effects of the present invention:

[0028] 1. Good water resistance. Silane coupling agent is used to modify the surface of small-pore particles of phosphogypsum to make them hydrophobic, while PMMA and SA are used to penetrate into the large pores. This makes the phosphogypsum have excellent super-hydrophobic and anti-water seepage properties, thus extending the service life of the phosphogypsum material.

[0029] 2. Good zero-energy cooling effect. The synergistic effect of PMMA and SA is used to optimize the reflectivity and emissivity of phosphogypsum, significantly improving the zero-energy cooling effect of phosphogypsum. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 Graphs showing the water droplet contact angle test results for the coatings in Examples 1, 2, 3, 4, and 5.

[0031] Figure 2 Graphs showing the water droplet rolling angle test results for the coatings in Examples 1, 2, 3, 4, and 5.

[0032] Figure 3 This is a graph showing the temperature change results of the radiant cooling test of the coatings in Examples 1, 2, and 3 on the same day.

[0033] Figure 4 This is a comparison chart of the radiant cooling test temperature and cavity temperature of the coatings in Examples 1, 2, and 3 on the same day.

[0034] Figure 5 Graph showing temperature change results of the radiant cooling test on the coatings in Examples 1, 4, and 5 on the same day.

[0035] Figure 6 This is a comparison chart of the radiant cooling test temperature and cavity temperature of the coatings in Examples 1, 4, and 5 on the same day.

[0036] Figure 7 Graph showing the test results of water drop contact angle and rolling angle of the coating in Example 1 during a cyclic impact test with 20g gravel at a height of 40cm.

[0037] Figure 8 Graph showing the test results of water drop contact angle and rolling angle of the coating in Example 1 during a cyclic friction test on 1000-grit sandpaper with a load of 100 g.

[0038] Figure 9 Graph showing the test results of water drop contact angle and rolling angle in a water drop impact test of the coating in Example 1 at a position 30 cm below a faucet with a droplet falling speed adjusted to 1 drop / s. DETAILED DESCRIPTION

[0039] In order to further understand the content and features of the present invention, examples of the present invention are given below. It should be understood that these examples are only used to illustrate the present invention and are not used to limit the scope of the present invention.

[0040] The experimental methods in the following examples are conventional methods unless otherwise specified.

[0041] Example 1

[0042] A method for preparing a phosphogypsum coating having super-hydrophobic and radiative cooling functions comprises the following steps:

[0043] Step 1: Add 6 g PG, 3 g NaOH, and 0.5 g Na2SO4 to 30 g deionized water and stir magnetically at room temperature for 30 min to obtain a mixed suspension;

[0044] Step 2: The mixed suspension obtained in step 1 was filtered, washed three times with deionized water and anhydrous ethanol, and dried at 60°C for 12 h to obtain 4.2 g of hydroxylated PG powder;

[0045] Step 3: Add 0.43 g of KH570 to a mixed solvent of 1 mL of deionized water and 13.4 mL of anhydrous ethanol, and heat at 60 °C with magnetic stirring for 10 min to obtain a dispersant;

[0046] Step 4: Grind 4.2 g of hydroxylated PG powder obtained in step 2 and add it to the dispersant obtained in step 3. Heat at 60° C. with magnetic stirring for 2.5 h to obtain a mixed suspension;

[0047] Step 5: The mixed suspension obtained in step 4 was filtered, washed three times with deionized water and anhydrous ethanol, and dried at 60° C. for 12 h to obtain hydrophobically modified PG powder;

[0048] Step 6: Grind the hydrophobically modified PG powder obtained in step 5 and pass it through a 90-mesh sieve to obtain a hydrophobically modified PG powder with a particle size of 90 mesh;

[0049] Step 7: Add 0.6 g of PMMA and 1.0 g of SA to a mixed solvent of 10 mL of DMF and 10 mL of THF, and stir at room temperature until all the solids are dissolved to obtain a cooling modifier;

[0050] Step 8: Add 0.5 g of the hydrophobically modified PG powder obtained in step 6 to the cooling modifier obtained in step 7, use a magnetic stirrer, stir at room temperature at a speed of 500-700 r / min for 10 min, and then perform ultrasonic treatment with an ultrasonic power of 80 w and an ultrasonic time of 10 min to obtain a super hydrophobic coating;

[0051] Step 9: Add 0.6 g of PDMS and 0.06 g of curing agent to 0.5 g of hydrophobically modified PG powder obtained in step 8, and add it to the cooling modifier obtained in step 7. Use a magnetic stirrer to stir at room temperature at a speed of 500-700 r / min for 10 minutes, and then perform ultrasonic treatment with an ultrasonic power of 80 w and an ultrasonic time of 10 minutes to obtain a super-hydrophobic-radiation cooling dual-functional modified phosphogypsum coating;

[0052] Step 10: Place the aluminum substrate in a plasma cleaning machine and clean it for 2 minutes. At room temperature, use a scraper with a height of 400 μm to scrape the film. Place it in an 80°C oven to dry for 4 hours. Place it at room temperature for 3 days to obtain a phosphogypsum coating with superhydrophobicity and radiation cooling functions.

[0053] Through the above steps, the water contact angle of the coating prepared on the aluminum substrate reached a maximum of 160.2° ( Figure 1 ), the roll angle is 2.25° ( Figure 2 ).

[0054] Compared with the ambient temperature, the temperature difference ΔT on the sample surface of this embodiment can reach up to 24.5℃, and the average temperature drop is 20℃ ( Figure 5 、 Figure 6 ), has excellent cooling effect.

[0055] Compared with the surface temperature of commercial white paint, the temperature difference ΔT of the sample surface in this embodiment can reach up to 8°C, and the average temperature drop is 5.38°C ( Figure 5 、 Figure 6 ), has excellent cooling effect.

[0056] The sample of this embodiment has passed 30 cycles ( Figure 7 ) can maintain a contact angle of about 155° and a rolling angle of about 6°; in a cyclic friction test with a load of 100g on 1000 grit sandpaper, after 22 cycles ( Figure 8 ) can maintain a contact angle of about 155° and a rolling angle of less than 10°; at 30 cm below the faucet, the droplet falling speed is adjusted to 1 drop / s, and the time is within 10 hours ( Figure 9 ) can maintain a contact angle of about 155° and a rolling angle of about 5°.

[0057] Example 2

[0058] The method and steps are the same as those in Example 1, except that 1.5 g of SA is added in step 6. The rest is the same as in Example 1. The water contact angle of the coating was tested to be 157.74° ( Figure 1 ), rolling angle 2° ( Figure 2 ).

[0059] Compared with the ambient temperature, the surface temperature difference ΔT of the samples in this embodiment can reach up to 18.8℃, and the average temperature drop is 13.2℃ ( Figure 3 、 Figure 4 ).

[0060] Compared with the surface temperature of commercial white paint, the temperature difference ΔT of the sample surface in this embodiment can reach up to 6.7℃, and the average temperature drop is 4.86℃ ( Figure 3 、 Figure 4 ).

[0061] Example 3

[0062] The method and steps are the same as those in Example 1, except that 2.0 g of SA is added in step 6. The rest is the same as in Example 1. The water contact angle of the coating was tested to be 159° ( Figure 1 ), rolling angle 2° ( Figure 2 ).

[0063] Compared with the ambient temperature, the surface temperature difference ΔT of the samples in this embodiment can reach up to 19.99℃, and the average temperature drop is 13.99℃ ( Figure 3 、 Figure 4 ).

[0064] Compared with the surface temperature of commercial white paint, the temperature difference ΔT of the sample surface in this embodiment can reach up to 7.9℃, and the average temperature drop is 5.53℃ ( Figure 3 、 Figure 4 ).

[0065] Example 4

[0066] The method and steps are the same as those in Example 1, except that 1.0 g of PMMA is added in step 7. The rest is the same as in Example 1. The water contact angle of the coating was tested to be 158.29° ( Figure 1 ), rolling angle 3.25° ( Figure 2 ).

[0067] Compared with the ambient temperature, the surface temperature difference ΔT of the samples in this embodiment can reach up to 21.9℃, and the average temperature drop is 18.08℃ ( Figure 5 、 Figure 6 ).

[0068] Compared with the surface temperature of commercial white paint, the temperature difference ΔT of the sample surface in this embodiment can reach up to 6.8℃, and the average temperature drop is 4℃ ( Figure 5 、 Figure 6 ).

[0069] Example 5

[0070] The method and steps are the same as those in Example 1, except that a scraper with a height of 400 μm is used for scraping in step 7, and the film is placed at room temperature for 5 days to obtain a phosphogypsum radiation cooling multifunctional super hydrophobic coating. The rest is the same as in Example 1. The water contact angle of the coating is tested to be 149.04° ( Figure 1 ), rolling angle 18° ( Figure 2 ).

[0071] Compared with the ambient temperature, the surface temperature difference ΔT of the samples in this embodiment can reach up to 24.3℃, and the average temperature drop is 19.45℃ ( Figure 5 、 Figure 6 ), has excellent cooling effect.

[0072] Compared with the surface temperature of commercial white paint, the temperature difference ΔT of the sample surface in this embodiment can reach up to 8.1℃, and the average temperature drop is 5.93℃ ( Figure 5 、 Figure 6 ), has excellent cooling effect.

Claims

1. A method for preparing a phosphogypsum coating having super-hydrophobic and radiation cooling functions, characterized in that: The following steps are involved: Step 1: Add phosphogypsum PG, NaOH, and Na2SO4 into deionized water in proportion, and stir and disperse to obtain a mixed suspension; Step 2: Filter, wash and dry the mixed suspension obtained in step 1 to obtain hydroxylated PG powder; Step 3: Add the silane coupling agent to a mixed solvent of water and anhydrous ethanol, heat and stir to obtain a dispersant; Step 4: adding the hydroxylated PG powder obtained in step 2 to the dispersant obtained in step 3, and stirring to obtain a mixed suspension; Step 5: filtering, washing and drying the mixed suspension obtained in step 4 to obtain hydrophobically modified PG powder; Step 6: Grind the hydrophobically modified PG powder obtained in step 5 and pass it through a sieve to obtain hydrophobically modified PG powders of different particle sizes; Step 7: Add PMMA and SA in proportion to a mixed solvent of N,N-dimethylformamide and tetrahydrofuran, and stir thoroughly to obtain a cooling modifier; Step 8: adding the hydrophobically modified PG powder obtained in step 6 to the cooling modifier obtained in step 7, stirring thoroughly, ultrasonically treating, and then adding PDMS and its curing agent to obtain a phosphogypsum coating with super-hydrophobic and radiation cooling functions; Step 9: The coating obtained in step 8 is scraped onto the substrate using a scraper method, and after the solvent is dried, a phosphogypsum coating with super-hydrophobicity and radiation cooling functions is obtained.

2. The method for preparing a phosphogypsum coating having super-hydrophobicity and radiation cooling function according to claim 1, wherein In the step 1, the mass concentration of PG is 0.1-0.5 g / mL, the mass concentration of NaOH is 0.05-0.25 g / mL, the mass concentration of Na2SO4 is 0.005-0.04 g / mL, the stirring temperature is room temperature, and the stirring time is 20-30 min.

3. The method for preparing a phosphogypsum coating having super-hydrophobicity and radiation cooling function according to claim 1, wherein In step 2, the drying temperature is 60-80° C., and the drying time is 10-12 hours.

4. The method for preparing a phosphogypsum coating having super-hydrophobicity and radiation cooling function according to claim 1, wherein In step 3, the silane coupling agent is any one of KH550, KH560, and KH570; by volume, water: anhydrous ethanol = 3:4-6, and the mass concentration of the silane coupling agent is 0.03-0.06 g / mL.

5. The method for preparing the phosphogypsum coating having super-hydrophobicity and radiation cooling function according to claim 1, wherein In step 4, the stirring temperature is 60-80° C., and the stirring time is 1.0-2.5 h.

6. The method for preparing the phosphogypsum coating having super-hydrophobicity and radiation cooling function according to claim 1, wherein In step 5, the drying temperature is 60-80° C. and the drying time is 10-12 hours.

7. The method for preparing the phosphogypsum coating having super-hydrophobicity and radiation cooling function according to claim 1, wherein In step 6, the mesh size of the sieve is 90-110 meshes.

8. The method for preparing the phosphogypsum coating having super-hydrophobicity and radiation cooling function according to claim 1, wherein In step 7, the volume ratio of DMF to THF in the mixed solvent is 1:1-5, the mass concentration of PMMA added is 0.015-0.1 g / mL, and the mass concentration of SA is 0.02-0.1 g / mL.

9. The method for preparing the phosphogypsum coating having super-hydrophobicity and radiation cooling function according to claim 1, wherein In step 8, the mass ratio of hydrophobically modified PG powder to cooling modifier is 1:3-4, the PDMS mass concentration is 0.03-0.1 g / ml, the ultrasonic power is 50-100 W, the ultrasonic time is 5-30 minutes, the stirring temperature is room temperature, and the stirring time is 3-10 minutes.

10. The method for preparing the phosphogypsum coating having super-hydrophobicity and radiation cooling function according to claim 1, wherein: In step 9, the scraping film thickness of the scraping method is 300-400 μm, and the material of the substrate includes any one of a glass sheet, an aluminum sheet, a copper sheet, and a carbon steel sheet.

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