Preparation method of epoxy resin coating for hydrotalcite nanocontainers modified with novel choline-based ionic liquids

Abstract

This invention discloses a choline salt ionic liquid, the molecular structure of which is shown below. This invention not only provides a method for preparing the choline salt ionic liquid ([Ch][Benzoic Acid]), but also a method for preparing an epoxy resin coating using a modified hydrotalcite nanocontainer. The method includes: preparing [Ch][Benzoic Acid] using a simple neutralization method; using the prepared [Ch][Benzoic Acid]-modified hydrotalcite nanocontainer (CB-LDH), finally doping it with epoxy resin, and then preparing an anti-corrosion coating (CB-LDH / EP coating) on ​​the treated substrate surface using spin coating. The preparation process of this invention is simple and environmentally friendly, and the prepared CB-LDH / EP coating exhibits excellent corrosion resistance and good self-healing properties, showing broad application prospects in the field of corrosion protection.

Description

Technical Field

[0001] This invention belongs to the field of chemical materials and metal corrosion protection technology, specifically relating to a novel choline-based ionic liquid, its preparation method, and a method for preparing an epoxy resin coating of a hydrotalcite nanocontainer modified by the novel choline-based ionic liquid. Background Technology

[0002] Magnesium and its alloys possess excellent strength-to-weight ratio and biocompatibility, making them promising lightweight metal materials for applications in aerospace, automotive, and biomedical fields. However, the extremely high chemical reactivity of magnesium results in poor corrosion resistance in magnesium alloys, limiting their further applications. To improve the corrosion resistance of magnesium alloys, researchers have developed various surface protection technologies, such as chemical conversion coatings, electrochemical plating, organic coatings, and plasma electrolytic oxidation coatings. Among these, organic coating systems can act as a protective barrier for metals and their alloys, preventing corrosive elements (such as water and chlorides) from extensively corroding the metal surface, thus providing corrosion protection. However, organic coatings are prone to degradation under prolonged immersion or when scratched, a drawback that severely limits their application. Therefore, it is worth considering improving this situation by using a carrier doped with a corrosion inhibitor.

[0003] In recent years, commonly used nanocomposites include halloysite, organic nanocomposites, carbon nanotubes (CNTs), metal-organic frameworks (MOFs), and hydrotalcites (LDHs). Among them, LDHs have many advantages, such as abundant raw materials and low manufacturing costs. Therefore, they have become one of the most widely used nanocomposites.

[0004] Ionic liquids possess characteristics such as high polarity, low melting point, low toxicity, high chemical stability, and minimal harm to the environment and organisms. As a green and environmentally friendly compound, ionic liquids can be widely used in the study of metal corrosion. Modifying LDHs with ionic liquids and doping them into organic coatings can impart better corrosion resistance and self-healing properties to the coatings. Summary of the Invention

[0005] In order to overcome the shortcomings of the existing technology, the present invention aims to provide a novel choline ionic liquid that is green and environmentally friendly and has good corrosion inhibition properties, and to provide a method for preparing a hydrotalcite nanocontainer modified with it and doped into an epoxy resin coating.

[0006] The present invention also provides an epoxy resin coating based on the novel choline-based ionic liquid modified hydrotalcite nanocontainer, and applies it to the corrosion protection of metals, especially magnesium alloys.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A choline-based ionic liquid [Ch][Benzoic Acid] has the following molecular structure:

[0009] .

[0010] A method for preparing the above-mentioned choline-based ionic liquid, which is synthesized through a simple acid-base neutralization reaction, specifically: reacting choline hydroxide with excess benzoic acid at room temperature for 20-28 h in the presence of water as a solvent. This choline-based ionic liquid [Ch][Benzoic Acid] can be used as a corrosion inhibitor.

[0011] Specifically, the preferred molar ratio of choline hydroxide to benzoic acid is 1:1.1 to 1.4.

[0012] This invention provides a method for preparing an epoxy resin coating of a hydrotalcite nanocontainer modified with the above-mentioned choline-based ionic liquid, comprising the following steps:

[0013] (1) Synthesis of hydrotalcite nano-container filler

[0014] Dissolve 1–3 mmol of Mg(NO3)2·6H2O and 1–3 mmol of Al(NO3)3·9H2O in 60–100 mL of deionized water, and adjust the pH to 10.3 ± 0.2 with NaOH, which is called solution A. Then weigh 1–2 mmol of choline-based ionic liquid and add it to 30–50 mL of deionized water to prepare solution B of a certain concentration. Add solution B dropwise to solution A. The entire dropwise addition process is carried out under nitrogen protection to prevent carbon dioxide in the air from being converted into carbonate ions and inserted into the interlayer of CB-LDH. After continuous stirring, centrifugation, washing, and drying, the hydrotalcite nanocomposite packing CB-LDH is obtained.

[0015] (2) Preparation of anti-corrosion coating

[0016] Take 0.26-0.78g of hydrotalcite nanocontainer filler CB-LDH and disperse it uniformly in a mixed solvent of ethyl acetate and acetone (the volume ratio of ethyl acetate and acetone is controlled at 3:1~1.4). Then add 10~12g of epoxy resin, sonicate, and then add 4~8g of polyamide curing agent. Stir evenly. The mass percentage of hydrotalcite nanocontainer filler CB-LDH in the system is 1.0~3.0wt.%. Finally, spin-coat it onto the pretreated magnesium alloy surface and dry it to obtain the epoxy resin coating CB-LDH / EP based on the novel choline-based ionic liquid modified hydrotalcite nanocontainer.

[0017] Specifically, the stirring reaction temperature in step (1) is 50~100 ℃, and the time is 9~24 h. During centrifugation, the rotation speed is 5000~10000 r / min, and the time is 3~9 min.

[0018] Furthermore, in step (2), the spin coating speed is 1000~3000 r / min and the time is 10~100 s.

[0019] Specifically, in step (2), the drying oven temperature is 30~90 ℃ and the time is 12~36 h.

[0020] The present invention also provides an epoxy resin coating CB-LDH / EP based on a novel choline-based ionic liquid modified hydrotalcite nanocontainer prepared by the above preparation method.

[0021] This invention also provides the application of the above-mentioned epoxy resin coating CB-LDH / EP based on a novel choline-based ionic liquid-modified hydrotalcite nanocontainer in metal corrosion protection. Further, the metal is preferably a magnesium alloy.

[0022] The epoxy resin coating based on a novel choline-based ionic liquid-modified hydrotalcite nanocontainer provided by this invention serves as an anti-corrosion coating for metals and their alloys. Compared with existing technologies, the beneficial effects of this invention are as follows:

[0023] This invention discloses a method for preparing an epoxy resin coating based on a novel choline-based ionic liquid-modified hydrotalcite nanocontainer. In this invention, a choline-based ionic liquid is synthesized using a simple neutralization reaction. This liquid is then used to modify LDH nanocontainer fillers. The CB-LDH nanocontainers are uniformly dispersed in epoxy resin, and a CB-LDH / EP coating is successfully prepared on the surface of AZ31B magnesium alloy by spin coating. The uniform dispersion of CB-LDH gives the coating not only excellent corrosion resistance but also good self-healing properties. The epoxy resin coating based on a novel choline-based ionic liquid-modified hydrotalcite nanocontainer provided by this invention shows great promise for mitigating the corrosion of metals and their alloys. Attached Figure Description

[0024] Figure 1 The images show the electrochemical impedance spectroscopy (EIS) results of different coatings prepared on the surface of AZ31B magnesium alloy, where a is the Nyquist plot, b~c are further magnified Nyquist plots, and d is the Bode plot.

[0025] Figure 2 Figure showing the results of a long-term corrosion resistance study on different coatings prepared on the surface of AZ31B magnesium alloy;

[0026] Figure 3Figure 1 shows the test results of the self-healing performance of the CB-LDH / EP coating prepared on the surface of AZ31B magnesium alloy. Detailed Implementation

[0027] The technical solution of the present invention will be further described in detail below with reference to the embodiments, but the scope of protection of the present invention is not limited thereto.

[0028] Unless otherwise specified, all raw materials used in the following embodiments are commercially available products that can be directly purchased or prepared using conventional techniques in the art. Room temperature refers to 25±5 ℃.

[0029] The pretreatment process for magnesium alloys can employ conventional techniques in this field, such as the following:

[0030] (1) The AZ31B magnesium alloy was machined into a sample with a size of 1.0 cm × 1.0 cm × 0.6 cm, and the substrate was coated with silicone rubber, leaving only a 1.0 cm × 1.0 cm working surface;

[0031] (2) The AZ31B magnesium alloy sample was then polished with 180, 600, 1500 and 3000 grit sandpaper in sequence, and then polished with W3.5 diamond polishing paste (Veiyee, model PG);

[0032] (3) Finally, use distilled water and anhydrous ethanol respectively for ultrasonic cleaning for 10 min each, and then air dry.

[0033] Example 1:

[0034] (1) Synthesis of ionic liquid corrosion inhibitors

[0035] The preparation method of choline-based ionic liquid choline benzoic acid [Ch][Benzoic Acid] includes the following steps:

[0036] (a) 2.52 g (10 mmol) of choline hydroxide solution (47%–50%), 40 mL of water, and 1.46 g (12 mmol) of benzoic acid were added to a single-necked flask and reacted at room temperature for 24 h. The solvent was removed by rotary evaporation at 65 °C to obtain a pale yellow viscous crude product.

[0037] (b) The crude product obtained in step (a) was dissolved in 50 mL of methanol and refrigerated overnight (12 h) to remove excess benzoic acid. After a white solid precipitated, the benzoic acid was removed by vacuum filtration. This step was repeated three times to ensure the purity of the final product.

[0038] (c) The solution obtained in step (b) was subjected to rotary evaporation at 45 °C to obtain a viscous liquid. The product was further dried in a vacuum drying oven at 60 °C for 24 h. The resulting pale yellow viscous liquid was the choline-based ionic liquid [Ch][BenzoicAcid] (yield: 95.0%); its structural formula and spectral information are shown below:

[0039] ;

[0040] 1H NMR (400 MHz, DMSO-d6) δ 7.88~7.85 (m, 2H), 7.28 (m, 3H), 3.91 (m, 2H), 3.51~3.47 (m, 2H), 3.17 (s, 9H).

[0041] (2) Synthesis of hydrotalcite nano-container filler

[0042] Synthesizing CB-LDH and CO3 using a simple method 2- -LDH. Taking the synthesis of CB-LDH as an example, 2 mmol of Mg(NO3)2·6H2O and 1 mmol of Al(NO3)3·9H2O were dissolved in 80 mL of deionized water, and the pH was adjusted to 10.3±0.1 with NaOH, which was called solution A. Then, 2.0 mmol of [Ch][Benzoic Acid] was weighed and added to 40 mL of deionized water to prepare a solution of a certain concentration, which was called solution B. Solution B was added dropwise to solution A. The entire dropwise addition process was carried out under nitrogen protection to prevent carbon dioxide in the air from being converted into carbonate ions and inserted into the interlayer of CB-LDH. The mixture was stirred continuously at 65 °C for 10 h. It was centrifuged at 8000 r / min for 5 min and washed with deionized water. Finally, it was dried in an oven at 70 °C for 12 h to obtain the hydrotalcite nanocontainer filler CB-LDH.

[0043] Synthetic CO3 2- The method for preparing LDH hydrotalcite nanocontainer filler is similar to the method described above. Solution B consists of 2.0 mmol Na2CO3 added to 40 mL of deionized water to prepare a solution of a certain concentration. Other operating steps are the same as described above.

[0044] (3) Preparation of anti-corrosion coating

[0045] 0.26 g of the prepared hydrotalcite nanocontainer filler CB-LDH was added to a mixed solvent of ethyl acetate and acetone (volume ratio of ethyl acetate to acetone: 3:1) and ultrasonically treated for 10 min to achieve uniform dispersion. Then, 12 g of epoxy resin (E44) was added and ultrasonically treated for 20 min. 6 g of polyamide curing agent (651) was added to the above mixture and stirred for 10 min to achieve uniform mixing. At this point, the mass percentage of hydrotalcite nanocontainer filler CB-LDH in the system was 1.0 wt.%. The final mixture was spin-coated onto the pretreated AZ31B magnesium alloy surface using a compact spin coater (EZ4) at 2000 rpm for 50 s. The resulting coating was dried at 60 ℃ for 24 h to obtain the epoxy resin coating CB-LDH / EP based on a novel choline-based ionic liquid modified hydrotalcite nanocontainer.

[0046] Pure epoxy resin coating (EP coating) and CO3 2- The preparation method of the -LDH / EP coating is similar, except that the EP coating does not contain hydrotalcite nano-capsule filler, and CO3... 2- CO3 is added to the LDH / EP coating. 2- -LDH hydrotalcite nano-container packing, other operating steps are the same as described above.

[0047] Corrosion test

[0048] A typical three-electrode electrolytic cell was used, with a saturated calomel electrode (SCE) as the reference electrode, a platinum black electrode as the auxiliary electrode, and a magnesium alloy electrode as the working electrode. Corrosion resistance tests were conducted in a 3.5 wt.% NaCl solution. The EIS test results are as follows: Figure 1 As shown, Figure 1 Images a through d are, in order: (a) Nyquist plot; (b through c) magnified Nyquist plot; and (d) Bode plot. Three coatings were prepared using the examples, and the three coatings |Z|... 0.01Hz The order from lowest to highest is: EP coating (9.12×10 6 Ω cm 2 ) < CO3 2- -LDH / EP coating (1.62×10 7 Ω cm 2 ) < CB-LDH / EP (4.36×10 8 Ω cm 2 The CB-LDH / EP coating described in this invention has the best protective effect because CB-LDH plays an active protective role in preventing corrosive ions from diffusing through the coating to the surface of the metal substrate, effectively improving the interface barrier effect of the coating.

[0049] Figure 2 Long-term corrosion resistance tests were conducted on three coatings: EP coating, CO3 coating, and others. 2- Photographs of samples with -LDH / EP coating and CB-LDH / EP coating immersed in 3.5 wt.% NaCl solution for different times. Figure 2 The results showed that the EP coating developed corrosion pits after 5 days of immersion, and these pits gradually increased in size with prolonged immersion time; CO3 2- The -LDH / EP coating showed elongated corrosion after 3 days of immersion, and by 15 days, corrosion had occurred on almost the entire substrate surface. In contrast, the CB-LDH / EP coating of this invention only showed some corrosion after 15 days of immersion, and the coating surface showed no obvious changes before 15 days. This indicates that the CB-LDH / EP coating of this invention showed corrosion the latest and with the lowest degree of corrosion, demonstrating the best long-term corrosion resistance.

[0050] Figure 3 The potentiodynamic polarization curves of the CB-LDH / EP coating after scratch testing are presented. Figure 3 It can be seen that the corrosion current density decreases with increasing immersion time, indicating that CB-LDH plays a positive role in preventing further corrosion of the coating when it is damaged.

[0051] In summary, the CB-LDH / EP coating of this invention has a simple preparation method and not only has a low |Z| 0.01Hz It has good long-term corrosion resistance and self-healing properties, and can form a protective barrier between the magnesium alloy surface and the corrosive medium, thereby reducing the corrosion rate of the magnesium alloy.

[0052] The above embodiments are merely preferred embodiments of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-substantial changes and substitutions made by those skilled in the art based on the present invention shall fall within the scope of protection claimed by the present invention.

Claims

1. The application of choline-based ionic liquids in the preparation of epoxy resin coatings for modified hydrotalcite nanocontainers, characterized in that, The molecular structure of the choline-based ionic liquid is shown below: 。 2. The application of the choline-based ionic liquid of claim 1 in the preparation of epoxy resin coatings for modified hydrotalcite nanocontainers, characterized in that, The choline-based ionic liquid is prepared by reacting choline hydroxide with excess benzoic acid at room temperature for 20-28 hours in the presence of water as a solvent.

3. The application of the choline-based ionic liquid as described in claim 2 in the preparation of epoxy resin coatings for modified hydrotalcite nanocontainers, characterized in that, The molar ratio of choline hydroxide to benzoic acid is 1:1.1~1.

4.

4. A method for preparing an epoxy resin coating of a choline-based ionic liquid-modified hydrotalcite nanocontainer according to claim 1, characterized in that, Includes the following steps: (1) Synthesis of hydrotalcite nano-container filler 1–3 mmol of Mg(NO3)2·6H2O and 1–3 mmol of Al(NO3)3·9H2O were dissolved in deionized water, and the pH was adjusted to 10.3 ± 0.2, which was called solution A. Then, 1–2 mmol of choline-based ionic liquid was weighed and added to deionized water to prepare solution B of a certain concentration. Solution B was added to solution A. The entire addition process was carried out under nitrogen protection with continuous stirring. After centrifugation, washing, and drying, the hydrotalcite nanocontainer packing was obtained. (2) Preparation of anti-corrosion coating Take 0.26-0.78g of hydrotalcite nano-container filler and disperse it evenly in a mixed solvent of ethyl acetate and acetone. Then add 10-12g of epoxy resin, sonicate, and then add 4-8g of polyamide curing agent. Stir evenly. The mass percentage of hydrotalcite nano-container filler in the system is 1.0-3.0 wt.%. Finally, spin-coat it onto the pretreated magnesium alloy surface and dry it to obtain the final product.

5. The method for preparing the epoxy resin coating of the hydrotalcite nanocontainer modified with choline-based ionic liquid as described in claim 4, characterized in that, The stirring reaction temperature in step (1) is 50~100 ℃ and the time is 9~24 h.

6. The method for preparing the epoxy resin coating of the hydrotalcite nanocontainer modified with choline-based ionic liquid as described in claim 4, characterized in that, In step (2), the spin coating speed is 1000~3000 r / min and the time is 10~100 s.

7. The method for preparing the epoxy resin coating of the hydrotalcite nanocontainer modified with choline-based ionic liquid as described in claim 4, characterized in that, During the drying process in step (2), the oven temperature is 30~90 ℃ and the time is 12~36 h.

8. An epoxy resin coating based on a novel choline-based ionic liquid-modified hydrotalcite nanocontainer prepared by any of the preparation methods described in claims 4 to 7.

9. The application of the epoxy resin coating based on the novel choline-based ionic liquid modified hydrotalcite nanocontainer as described in claim 8 in metal corrosion protection.

10. The application of the epoxy resin coating based on the novel choline-based ionic liquid-modified hydrotalcite nanocontainer as described in claim 9 in metal corrosion protection, characterized in that, The metal is a magnesium alloy.

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