Microcapsule corrosion inhibitor with pH response and slow release effects as well as preparation method and application of microcapsule corrosion inhibitor

Abstract

The invention belongs to the technical field of microcapsule corrosion inhibitors, and discloses a microcapsule corrosion inhibitor with pH response and slow release effects and a preparation method and application thereof. The method comprises the following steps: 1) preparing syringaldehyde modified methionine; (2) preparing the octenyl succinic anhydride modified chitosan; 3) dissolving the octenyl succinic anhydride modified chitosan in an acetic acid solution to serve as an internal water phase, and dissolving polylactic acid and syringaldehyde modified methionine in an organic solvent to serve as an oil phase; mixing the internal water phase and the oil phase, and performing ultrasonic treatment to obtain a primary emulsion; polyvinyl alcohol and water are mixed to serve as an outer water phase; adding the external water phase into the primary emulsion, and stirring to obtain a final emulsion; and removing the solvent, removing impurities and drying to obtain the microcapsule. The microcapsule corrosion inhibitor disclosed by the invention has a continuous and stable slow release effect, excellent encapsulation performance and relatively good corrosion resistance and pH response. The corrosion inhibitor disclosed by the invention is used for metal corrosion prevention and anticorrosive paint.

Description

Technical Field

[0001] This invention belongs to the technical field of microcapsule corrosion inhibitors, specifically relating to a microcapsule corrosion inhibitor with pH response and sustained-release effect, its preparation method, and its application. Background Technology

[0002] Metal corrosion is a widespread problem in modern industrial production, causing significant economic losses and environmental threats annually. Metal corrosion is a common electrochemical process involving chemical reactions between metals and their surrounding environment. Corrosion not only leads to material loss and structural integrity degradation but can also cause safety accidents and environmental pollution. This problem also exists in liquid cooling technologies such as automotive engine cooling systems, battery thermal management systems, and data center cooling systems. Due to its availability and cost advantages, water has become an indispensable cooling medium in metal piping systems, most of which are made of alloy materials such as carbon steel, aluminum alloys, and copper alloys. These alloy materials typically undergo significant corrosion during long-term contact with water-based coolants. In addition, water corrosion of metals frequently occurs in water treatment, metal processing, marine engineering, and infrastructure construction. To effectively inhibit corrosion, corrosion inhibitors are commonly added to water-based corrosive media such as coolants during production.

[0003] However, ordinary corrosion inhibitors have the following problems in reducing environmental pollution and ensuring long-term corrosion inhibition: (1) Inorganic corrosion inhibitors (nitrates, phosphates, chromates) and traditional organic corrosion inhibitors (phosphates and benzotriazoles) have certain toxicity and are difficult to degrade naturally; (2) Adding corrosion inhibitors directly to coolants will cause the release rate of corrosion inhibitor molecules to be uncontrolled, resulting in short action time and low efficiency; (3) The release rate of traditional corrosion inhibitors cannot respond to the pH changes of water-based corrosive media; (4) Some corrosion inhibitors are difficult to prepare, have high raw material costs, low economic benefits, and are difficult to use on a large scale. Summary of the Invention

[0004] To overcome the shortcomings and deficiencies of existing technologies, the present invention aims to provide a microcapsule corrosion inhibitor with pH responsiveness and sustained-release effect, and its preparation method. The microcapsule corrosion inhibitor of the present invention exhibits a sustained-release effect, excellent encapsulation performance, excellent mechanical properties, and good anti-corrosion properties.

[0005] Another object of the present invention is to provide applications of the microencapsulated corrosion inhibitor. These microencapsulated corrosion inhibitors are used in the field of corrosion prevention, particularly in metal corrosion prevention, such as in water treatment, water-based coolants, and anti-corrosion coatings. The microencapsulated corrosion inhibitors of the present invention are also used in coatings, adhesives, coolants, and other fields.

[0006] To achieve the above-mentioned objectives, the technical solution adopted by this invention is as follows:

[0007] A method for preparing a microcapsule corrosion inhibitor with pH responsiveness and sustained-release effect includes the following steps:

[0008] 1) Preparation of syringaldehyde-modified methionine:

[0009] Using an organic solvent as the reaction medium, 1 part by weight of methionine and 1.5-2 parts by weight of syringaldehyde are reacted under the action of an alkaline catalyst to obtain syringaldehyde-modified methionine; the organic solvent is ethanol; the mass ratio of the alkaline catalyst to methionine is 0.2-0.4:1; the reaction conditions are: stirring at 55-70℃ for 4-8 hours.

[0010] 2) Preparation of octenyl succinic anhydride modified chitosan:

[0011] 0.6-0.8 parts by weight of chitosan were dissolved in 0.62-0.77 parts by weight of acid and 61-82 parts by weight of water to obtain a chitosan solution. Using an organic solvent as the reaction medium, the chitosan solution was reacted with 0.33-0.57 parts by weight of octenyl succinic anhydride, and the pH was adjusted to 7-8 to obtain octenyl succinic anhydride-modified chitosan. The acid was glacial acetic acid; the organic solvent was anhydrous ethanol; and the reaction conditions were stirring at 35-45°C for 2-4 hours.

[0012] 3) Preparation of microcapsule corrosion inhibitor: Octenyl succinic anhydride-modified chitosan was dissolved in acetic acid solution as the inner aqueous phase, and 0.47-0.84 parts by weight of polylactic acid and methionine modified with eugenol were dissolved in 13.2-35.8 parts by weight of organic solvent as the oil phase; the inner aqueous phase and oil phase were mixed and ultrasonically treated to obtain a primary emulsion; 0.53-0.79 parts by weight of polyvinyl alcohol and 57-77 parts by weight of water were mixed as the outer aqueous phase; then the outer aqueous phase was added to the primary emulsion and stirred to obtain the final emulsion; the solvent was removed, impurities were removed, and the mixture was dried to obtain microcapsules.

[0013] In step 3), the mass ratio of chitosan in octenyl succinic anhydride-modified chitosan, methionine in eugenol-modified methionine, and polylactic acid is 0.6-0.8:1:0.47-0.84.

[0014] The specific preparation steps of syringaldehyde-modified methionine described in step 1) are as follows:

[0015] One part by weight of methionine and 0.2-0.4 parts by weight of an alkaline catalyst were dissolved in ethanol to obtain a methionine solution. 1.5-2 parts by weight of syringaldehyde were dissolved in ethanol to obtain a syringaldehyde solution. The methionine solution was added dropwise to the syringaldehyde solution, and the mixture was stirred at 55-70℃ for 4-8 hours. After cooling, centrifugation, washing, and drying, syringaldehyde-modified methionine was obtained. The mass ratio of methionine to ethanol in the methionine solution was 1:(14.3-18.5). The mass ratio of syringaldehyde to ethanol in the syringaldehyde solution was (1.5-2):(10-15).

[0016] The alkaline catalyst is one or more of sodium hydroxide, potassium hydroxide, ammonium hydroxide, potassium carbonate, and ethanolamine.

[0017] Methionine and the basic catalyst were dissolved in anhydrous ethanol under stirring at 50-65°C. The washing process involved washing with ethanol and water. The drying process was carried out at 55-65°C for 1-3 days.

[0018] The structural formula of methionine modified with eugenol:

[0019]

[0020] Step 2) Specific preparation steps of octenyl succinic anhydride modified chitosan:

[0021] Mix 0.6-0.8 parts by weight of chitosan and 61-82 parts by weight of water, add 0.62-0.77 parts by weight of glacial acetic acid, stir and dissolve at 35-50℃, then dilute with 45-58 parts by weight of anhydrous ethanol to obtain a chitosan solution; dissolve 0.33-0.57 parts by weight of octenesuccinic anhydride in 8-20 parts by weight of anhydrous ethanol to obtain an octenesuccinic anhydride solution; then slowly add the octenesuccinic anhydride solution to the chitosan solution over 1-3 hours, stir at 35-45℃ for 2-4 hours, adjust the pH of the solution to 7-8 using a pH adjuster, wash the precipitate with water and anhydrous ethanol, and finally dry at 55-70℃ for 1-3 days to obtain alkenyl succinic anhydride modified chitosan.

[0022] The pH adjuster is one or more of the following: sodium hydroxide, calcium hydroxide, sodium carbonate, potassium hydroxide, ammonia, and triethylamine.

[0023] The acetic acid solution in step 3) has a mass concentration of 45-55%; the organic solvent is one or more of dichloromethane, acetone, chloroform, ethyl acetate, and n-hexane. The mass ratio of the octenyl succinic anhydride-modified chitosan to the acetic acid solution is 0.27-0.39:25-44. The molecular weight of polylactic acid is 1000-60000.

[0024] The molecular weight of the polyvinyl alcohol is 15,000 to 20,000.

[0025] The stirring described in step 3) is: stirring at 6000-12000 rpm for 25-45 minutes.

[0026] The specific steps for step 3) are as follows:

[0027] Octenyl succinic anhydride-modified chitosan was dissolved in acetic acid solution as the inner aqueous phase (w1), and polylactic acid and eugenol-modified methionine were dissolved in an organic solvent as the oil phase (o). The inner aqueous phase and oil phase were mixed and sonicated for 10-20 minutes to obtain a primary emulsion. Polyvinyl alcohol and water were mixed and dissolved as the outer aqueous phase (w2). w2 was added to the primary emulsion and stirred at 6000-12000 rpm for 25-45 minutes to obtain the final emulsion. The emulsion was stirred at 50-75℃ for 2-6 hours to evaporate the solvent, washed with water, and then freeze-dried under vacuum to obtain microcapsule powder.

[0028] The microcapsule corrosion inhibitor can be used in the preparation of adhesives and coatings, and the amount added is 1-25% of the total mass.

[0029] Preferably, the amount added during use is 5-15% of the total mass.

[0030] This invention uses polylactic acid / octenyl succinate-chitosan as the microcapsule corrosion inhibitor shell, which has a continuous and stable sustained-release effect, excellent encapsulation performance, excellent mechanical properties, and wide applications.

[0031] The principle of this invention is as follows: (1) Methionine and eugenol undergo a Schiff base reaction under slightly alkaline conditions to generate eugenol-modified methionine; (2) Octenyl succinic acid and chitosan undergo an amidation reaction under slightly acidic conditions to modify chitosan; (3) PLA capsules are prepared by water-oil-water re-emulsion and solvent evaporation and the core material is loaded into them.

[0032] Compared with the prior art, the present invention has the following advantages:

[0033] 1) The microcapsule corrosion inhibitor prepared by this invention consists of white or off-white uniform spheres with an average particle size of 0.5-500 μm; a moisture content of ≤3% by mass; a critical stress of 0-700 mN; and good mechanical properties.

[0034] 2) The microcapsule corrosion inhibitor prepared by the present invention controls the slow release rate of the core material through microcapsule encapsulation, has pH response characteristics, and ensures the quality stability and storage stability of the product.

[0035] 3) The preparation method of microcapsule corrosion inhibitors can be used for the formulation optimization of various coatings, coolants, etc., and the raw materials are widely available and inexpensive;

[0036] 4) The preparation process is simple, and the produced microcapsule corrosion inhibitors can be used in water treatment, water-based coolants, anti-corrosion coatings and other fields. Attached Figure Description

[0037] Figure 1 Impedance curves (Requisite curve phase angle diagrams) of the microcapsule corrosion inhibitors prepared in Example 1, Comparative Example 1, and Comparative Example 2;

[0038] Figure 2 The Bode modulus diagrams are for the microcapsule corrosion inhibitors prepared in Example 1, Comparative Example 1, and Comparative Example 2. Detailed Implementation

[0039] The present invention will be described in further detail below with reference to specific embodiments, but the implementation of the present invention is not limited thereto.

[0040] The microcapsule corrosion inhibitor of the present invention is mainly composed of the following parts by weight:

[0041]

[0042]

[0043] It also includes a pH adjuster, used to adjust the pH value of the reaction system.

[0044] Example 1

[0045] A microcapsule corrosion inhibitor, mainly composed of the following parts by weight,

[0046] Components weight / g Methionine 1 Syringaldehyde 1.5 Chitosan 0.6 Octenylsuccinic anhydride 0.4 Polylactic acid 0.7 Polyvinyl alcohol 0.6 glacial acetic acid 0.7 n-Hexane 35 water 150

[0047] The specific preparation method is as follows:

[0048] Step 1: Dissolve 1 g of methionine powder and 0.3 g of sodium hydroxide in 16 g of anhydrous ethanol solution and stir at 60°C until completely dissolved. Then, dissolve 1.5 g of eugenol powder in 15 g of anhydrous ethanol. Add the methionine ethanol solution dropwise to the eugenol ethanol solution and stir continuously in a 60°C water bath for 6 hours. Finally, cool the mixture to room temperature, centrifuge, wash three times with ethanol and deionized water, and dry the product at 60°C for 2 days to obtain eugenol-modified methionine.

[0049] Step 2: Add 0.6g of chitosan and 80g of deionized water to the reaction vessel and mechanically stir until homogeneous. Add 0.7g of glacial acetic acid and stir in a 50°C water bath until the chitosan is completely dissolved. Then dilute with 50% anhydrous ethanol. Dissolve 0.4g of octenyl succinic anhydride in 10mL of anhydrous ethanol and slowly add it to the reaction vessel over 2 hours. After stirring at 40°C for 3 hours, adjust the pH of the solution to 7.5 using a pH adjuster; the reaction product will precipitate. Wash the precipitate three times with deionized water and five times with anhydrous ethanol to remove unreacted OSA and other substances. Finally, dry at 70°C for 2 days to obtain alkenyl succinic anhydride-modified chitosan.

[0050] Step 3: Dissolve the octenyl succinic anhydride-modified chitosan from Step 2 in a 50% (w / w) acetic acid solution (the mass ratio of octenyl succinic anhydride-modified chitosan to acetic acid solution is 0.3:30) as the inner aqueous phase (w1). Dissolve 0.8 g of polylactic acid (molecular weight 20000) and methionine modified with eugenol from Step 1 in 35 g of n-hexane as the oil phase (o). Mix the inner aqueous phase and oil phase and sonicate for 15 minutes to obtain a primary emulsion. Next, dissolve 0.6 g of polyvinyl alcohol (molecular weight 18000) in 70 g of deionized water as the outer aqueous phase (w2). Add w2 to the primary emulsion and stir at 10000 rpm for 40 minutes to obtain the final emulsion. Stir the mixture at 70°C for 5 hours to evaporate the solvent. Finally, wash three times with deionized water to remove impurities and obtain microcapsule powder by vacuum freeze drying.

[0051] Electrochemical impedance spectroscopy analysis: Q325 carbon steel was immersed in four groups of 3.5% NaCl solutions. One group was treated with a methionine microcapsule corrosion inhibitor modified with syringaldehyde (Example 1), another group was treated with a methionine microcapsule corrosion inhibitor (Comparative Example 2), and the third group was treated with a syringaldehyde microcapsule corrosion inhibitor (Comparative Example 1). The impedance curves were analyzed. The test results are as follows: Figure 1 As shown, Q350 exhibits significantly improved corrosion resistance compared to microcapsules without corrosion inhibitors.

[0052] At pH 5, the release rate was 52.47% after 80 hours; at pH 7, the release rate reached 56.96% after 80 hours. The encapsulation efficiency was 85.2% as measured by UV spectrophotometer.

[0053] Figure 2 The Bode modulus diagrams are for the microcapsule corrosion inhibitors prepared in Example 1, Comparative Example 1, and Comparative Example 2.

[0054] Comparative Example 1

[0055] A microcapsule corrosion inhibitor, mainly composed of the following parts by weight,

[0056] Components weight / g Methionine 0 Syringaldehyde 1.5 Chitosan 0.6 Octenylsuccinic anhydride 0.4 Polylactic acid 0.7 Polyvinyl alcohol 0.6 glacial acetic acid 0.7 n-Hexane 35 water 150

[0057] The specific preparation method is the same as steps two and three of Example 1, except that the methionine modified with eugenol in the above steps is replaced with eugenol. This comparative example yields a eugenol microcapsule corrosion inhibitor.

[0058] Electrochemical impedance spectroscopy analysis, such as Figure 1 As shown, the product still has some corrosion resistance, but the effect is poor.

[0059] Comparative Example 2

[0060] A microcapsule corrosion inhibitor, mainly composed of the following parts by weight,

[0061] Components weight / g Methionine 1 Syringaldehyde 0 Chitosan 0.6 Octenylsuccinic anhydride 0.4 Polylactic acid 0.7 Polyvinyl alcohol 0.6 glacial acetic acid 0.7 n-Hexane 35 water 150

[0062] The specific preparation method is the same as steps two and three of Example 1, except that the methionine modified with eugenol in the above steps is replaced with methionine. This comparative example yields a methionine microcapsule corrosion inhibitor.

[0063] Electrochemical impedance spectroscopy analysis, such as Figure 1 As shown, the product still has some corrosion resistance, but the effect is poor.

[0064] Example 2

[0065] A microcapsule corrosion inhibitor, mainly composed of the following parts by weight,

[0066] Components weight / g Methionine 1 Syringaldehyde 1.8 Chitosan 0.7 Octenylsuccinic anhydride 0.5 Polylactic acid 0.8 Polyvinyl alcohol 0.7 glacial acetic acid 0.6 solvent 20 water 130

[0067] For the specific preparation method, refer to Example 1, simply replace the corresponding substances by weight.

[0068] Electrochemical impedance spectroscopy analysis showed that its anti-corrosion performance was significantly improved compared with Comparative Example 2.

[0069] At pH 5, the sustained-release rate was 53.76% after 80 hours; at pH 7, the sustained-release rate reached 57.03% after 80 hours. The encapsulation efficiency, measured by UV spectrophotometer, was 79.1%.

[0070] Example 3

[0071] A microcapsule corrosion inhibitor, comprising the following components in parts by weight:

[0072] Components weight / g Methionine 1 Syringaldehyde 2.0 Chitosan 0.8 Octenylsuccinic anhydride 0.55 Polylactic acid 0.5 Polyvinyl alcohol 0.55 glacial acetic acid 0.75 dichloromethane 15 water 140

[0073] For the specific preparation method, refer to Example 1, and simply replace the corresponding weight percentages of the substances.

[0074] Chemical impedance spectroscopy analysis showed that its anti-corrosion performance was significantly improved compared with comparative example 2.

[0075] At pH=5, the sustained release rate was 53.76% after 80 hours, and at pH=7, the sustained release rate reached 57.03% after 80 hours.

[0076] Example 4

[0077] A water-based acrylic anti-corrosion coating, comprising the following components in parts by weight:

[0078]

[0079] Among them, the Products manufactured by Wanhua Chemical Company are selected, while EFKA4585 is manufactured by Ciba Fine Chemicals (Shanghai) Co., Ltd.

[0080] The method for preparing the acrylic anti-corrosion coating is to dissolve 100g of EFKA4585 in 50g of water, and then add it at 1200r / min. A suitable amount of ammonia, 7g of isopropanol, and 6.8-16g of microcapsule corrosion inhibitor are mixed and dispersed. The preparation method of the microcapsule corrosion inhibitor is as described in Example 1. Chemical impedance spectroscopy analysis (detection methods and standards according to national regulations) shows that, compared to not adding microcapsule corrosion inhibitor, adding 8g of microcapsule corrosion inhibitor can increase the corrosion resistance of the cured material by 15%; adding 14g of microcapsule corrosion inhibitor can increase the corrosion resistance of the cured material by 30%.

[0081] At pH=5, the sustained release rate decreased to 46.54% after 80 hours, while at pH=7, the sustained release rate increased to 61.20% after 80 hours.

[0082] Example 5

[0083] An epoxy anti-corrosion coating is made from the following components in parts by weight:

[0084] Components Number of weights E-44 epoxy resin 100 Talc powder (500 mesh) 10 Diethylenetriamine 13 Microencapsulated corrosion inhibitor prepared in Example 1 5.2-17

[0085] The epoxy anti-rust coating is prepared by mixing and dispersing 1000g of E-44 epoxy resin, 100g of talc powder (500 mesh), 130g of diethylenetriamine, and 52-170g of microcapsule corrosion inhibitor. The preparation method of the microcapsule corrosion inhibitor is described in Example 1. Chemical impedance spectroscopy analysis shows that, compared to not adding microcapsule corrosion inhibitor, adding 63g of microcapsule corrosion inhibitor increases the corrosion resistance of the cured product by 15%; adding 150g of microcapsule corrosion inhibitor increases the corrosion resistance of the cured product by 35%.

[0086] At pH=5, the sustained release rate was 49.33% after 80 hours, and at pH=7, the sustained release rate reached 61.71% after 80 hours.

[0087] Example 6

[0088] A polyurethane anti-corrosion coating is mainly composed of the following components in parts by weight:

[0089] Components Number of weights Polyether DL-4000D 50 Polyether EP6000 50 Diphenylmethane diisocyanate (MDI) 40 Curing agent YH-88 8 Talc powder (1250 mesh) 50 Microencapsulated corrosion inhibitor prepared in Example 1 4.6-13.0 solvent 30

[0090] The polyether DL-4000D, the polyether EP6000, and the diphenylmethane diisocyanate are all products manufactured by Lanxing Dongda Company.

[0091] The preparation method of the polyurethane anti-rust coating is as follows: At 80-110℃ and 900 r / min, add 50g of polyether polyol and 50g of talc powder and stir for 0.5h. Then cool to 75℃, add 40g of diphenylmethane diisocyanate, stir for 0.5h, then heat to 80-90℃ and react for 2.5h. After cooling to 60℃, add 4.6-13.0g of microcapsule corrosion inhibitor powder and mix evenly. The preparation method of the microcapsule corrosion inhibitor is as described in Example 1. Chemical impedance spectroscopy analysis shows that compared to not adding microcapsule corrosion inhibitor, adding 5.3 parts by weight of microcapsule corrosion inhibitor can increase the corrosion resistance of the cured product by 20%; adding 10 parts by weight of microcapsule corrosion inhibitor can increase the corrosion resistance of the cured product by 30%.

[0092] At pH=5, the sustained release rate was 50.12% after 80 hours, and at pH=7, the sustained release rate reached 59.87% after 80 hours.

Claims

1. A method for preparing a microcapsule corrosion inhibitor with pH response and sustained-release effect, characterized in that: The method comprises the following steps: 1) Preparation of methionine modified with syringaldehyde: 1 part by weight of methionine is reacted with 1.5-2 parts by weight of syringaldehyde in the presence of an alkaline catalyst in an organic solvent to obtain methionine modified with syringaldehyde; the organic solvent is ethanol; the mass ratio of the alkaline catalyst to methionine is 0.2-0.4:1; the reaction conditions are stirring at 55-70℃ for 4-8 hours; 2) Preparation of chitosan modified with octenyl succinic anhydride: 0.6-0.8 parts by weight of chitosan is dissolved in 0.62-0.77 parts by weight of acid and 61-82 parts by weight of water to obtain a chitosan solution; the chitosan solution is reacted with 0.33-0.57 parts by weight of octenyl succinic anhydride in an organic solvent, and the pH is adjusted to 7-8 to obtain chitosan modified with octenyl succinic anhydride; the acid is glacial acetic acid; the organic solvent is anhydrous ethanol; the reaction conditions are stirring at 35-45℃ for 2-4 hours; 3) Preparation of microcapsulated corrosion inhibitor: chitosan modified with octenyl succinic anhydride in step 2) is dissolved in an acetic acid solution as an internal aqueous phase, 0.47-0.84 parts by weight of polylactic acid and methionine modified with syringaldehyde in step 1) are dissolved in 13.2-35.8 parts by weight of an organic solvent as an oil phase; the internal aqueous phase and the oil phase are mixed and ultrasonically treated to obtain a primary emulsion; 0.53-0.79 parts by weight of polyvinyl alcohol and 57-77 parts by weight of water are mixed as an external aqueous phase; then the external aqueous phase is added to the primary emulsion and stirred to obtain a final emulsion; the solvent is removed, impurities are removed, and the product is dried to obtain the microcapsules.

2. The method for preparing the pH-responsive and sustained-release microcapsule corrosion inhibitor according to claim 1, characterized in that: The specific preparation steps of the methionine modified with syringaldehyde in step 1) are as follows: 1 part by weight of methionine is dissolved in 0.2-0.4 parts by weight of an alkaline catalyst in ethanol to obtain a methionine solution; 1.5-2 parts by weight of syringaldehyde is dissolved in ethanol to obtain a syringaldehyde solution; The methionine solution is added dropwise to the syringaldehyde solution, and the mixture is stirred at 55-70℃ for 4-8 hours, cooled, centrifuged, washed, and dried to obtain methionine modified with syringaldehyde.

3. The method for preparing the pH-responsive and sustained-release microcapsule corrosion inhibitor according to claim 2, characterized in that: The mass ratio of methionine to ethanol in the methionine solution is 1:(14.3-18.5); the mass ratio of syringaldehyde to ethanol in the syringaldehyde solution is (1.5-2):(10-15); The alkaline catalyst is one or more of sodium hydroxide, potassium hydroxide, ammonium hydroxide, potassium carbonate, and ethanolamine; The methionine and the alkaline catalyst are dissolved in anhydrous ethanol by stirring at 50-65℃; the washing refers to washing with ethanol and water; and the drying is performed at 55-65℃ for 1-3 days.

4. The method for preparing the pH-responsive and sustained-release microcapsule corrosion inhibitor according to claim 1, characterized in that: The specific preparation steps of the chitosan modified with octenyl succinic anhydride in step 2) are as follows: The chitosan and 61-82 parts by weight of water are mixed, 0.62-0.77 parts by weight of glacial acetic acid is added, and the mixture is dissolved by stirring at 35-50℃, 45-58 parts by weight of anhydrous ethanol is added for dilution, to obtain a chitosan solution; 0.33-0.57 parts by weight of octenyl succinic anhydride is dissolved in 8-20 parts by weight of anhydrous ethanol to obtain an octenyl succinic anhydride solution; then the octenyl succinic anhydride solution is slowly added to the chitosan solution within 1-3 hours, and after stirring at 35-45℃ for 2-4 hours, a pH regulator is used to adjust the pH of the solution to 7-8, the precipitate is washed with water and anhydrous ethanol, and finally dried at 55-70℃ for 1-3 days to obtain the octenyl succinic anhydride modified chitosan.

5. The method for preparing the pH-responsive and sustained-release microcapsule corrosion inhibitor according to claim 4, characterized in that: The pH regulator is one or more of sodium hydroxide, calcium hydroxide, sodium carbonate, potassium hydroxide, ammonia, and triethylamine.

6. The method for preparing the pH-responsive and sustained-release microcapsule corrosion inhibitor according to claim 1, characterized in that: The mass concentration of the acetic acid solution in step 3) is 45-55%; the organic solvent is one or more of dichloromethane, acetone, chloroform, ethyl acetate, and n-hexane; The mass ratio of the octenyl succinic anhydride modified chitosan to the acetic acid solution is 0.27-0.39:25-44; The molecular weight of the polylactic acid is 1000-60000; The stirring in step 3) is at 6000-12000 rpm for 25-45 minutes.

7. The method for preparing the microcapsule corrosion inhibitor with pH response and sustained-release effect according to claim 1, characterized in that: The specific steps of step 3) are as follows: the octenyl succinic anhydride modified chitosan is dissolved in the acetic acid solution as an internal water phase w1, and the polylactic acid and the allyl isothiocyanate are dissolved in the organic solvent as an oil phase o; the internal water phase and the oil phase are mixed and ultrasonically treated for 10-20 minutes to obtain a primary emulsion; the polyvinyl alcohol and water are mixed and dissolved as an external water phase w2; w2 is added to the primary emulsion, and the mixture is stirred at 6000-12000 rpm for 25-45 minutes to obtain a final emulsion; the solvent is evaporated by stirring at 50-75℃ for 2-6 hours, the mixture is washed with water, and the microcapsule powder is obtained by vacuum freeze-drying.

8. A microcapsule corrosion inhibitor with pH response and sustained release effect, prepared by the method of any one of claims 1-7.

9. The use of the microcapsulated corrosion inhibitor with pH response and slow release effect according to claim 8, characterized in that: The microcapsule corrosion inhibitor with pH response and sustained release effect is used for metal corrosion prevention.

10. The use of the microcapsulated corrosion inhibitor with pH response and slow release effect according to claim 8, characterized in that: The microcapsule corrosion inhibitor with pH response and sustained release effect is used for preparing a corrosion-resistant coating. The microcapsule corrosion inhibitor with pH response and sustained release effect is used for preparing a corrosion-resistant coating.

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