Flame retardant and anticorrosive coating and preparation method thereof

Abstract

This application discloses a flame-retardant anticorrosion coating and its preparation method, relating to the field of coating technology. The coating is prepared from the following components by weight: 95-105 parts of a benzoxazine oligomer, 1-10 parts of nanocellulose, 0.5-5 parts of graphene oxide, and 3-7 parts of a catalyst. By designing a benzoxazine oligomer, co-polymerizing the nanocellulose, graphene oxide, and catalyst under heating conditions to form a dense coating, the application improves the adhesion, mechanical, flame retardancy, and corrosion resistance of the flame-retardant anticorrosion coating, reduces the difficulty of curing the flame-retardant anticorrosion coating, and improves the toughness of the flame-retardant anticorrosion coating.

Description

Technical Field

[0001] The present application relates to the field of coating technology, and in particular to a flame retardant and anti-corrosion coating and a preparation method thereof. Background Art

[0002] Metal corrosion is a common and serious problem inherent in metal equipment. Corrosion-induced damage to equipment and facilities results in significant losses. To protect metals, an organic protective film is typically applied to the metal surface to prevent direct contact with corrosive media in the environment, thereby reducing the likelihood of chemical or electrochemical reactions.

[0003] Currently, the main components of commonly used coatings are phenolic resins and benzoxazine resins. Benzoxazine resins are synthesized from inexpensive raw materials, release no small molecules during the curing process, exhibit low volume shrinkage, and possess excellent heat resistance, flame retardancy, dielectric properties, and mechanical properties. However, benzoxazine resin coatings suffer from high curing temperatures, difficulty in film formation, brittleness of the cured product, and inconvenient processing. Summary of the Invention

[0004] In view of the shortcomings of the above-mentioned related technologies, the present application provides a flame-retardant anti-corrosion coating and a preparation method thereof. By designing a benzoxazine oligomer, nanocellulose, graphene oxide, and a catalyst, and copolymerizing them under heating conditions to form a dense coating, the flame-retardant anti-corrosion coating improves its adhesion, mechanical, and anti-corrosion properties, reduces the difficulty of curing the flame-retardant anti-corrosion coating, and improves its toughness.

[0005] On the one hand, the present application provides a flame retardant and anti-corrosion coating that adopts the following technical solution:

[0006] A flame retardant and anti-corrosion coating is prepared from the following components in parts by weight: 95-105 parts of benzoxazine oligomer, 1-10 parts of nanocellulose, 0.5-5 parts of graphene oxide, and 3-7 parts of a catalyst.

[0007] Preferably, the benzoxazine oligomer is obtained by reacting a benzoxazine monomer containing a phosphazene ring with cardanol.

[0008] Preferably, the benzoxazine monomer containing a phosphazene ring is prepared by the following steps: adding benzoxazine containing a phenolic hydroxyl group to a mixed system containing hexachlorocyclotriphosphazene, activated potassium carbonate, and acetonitrile, reacting at room temperature for 2.5-3.5 hours under an inert gas atmosphere, and heating and refluxing for 3-5 hours to obtain an intermediate mixture; adding an acetonitrile solution of (4-hydroxy-phenyl)-diethyl phosphate to the intermediate mixture, heating and refluxing for 11-13 hours, cooling to room temperature, filtering, vacuum rotary evaporation, washing, and drying to obtain the benzoxazine monomer containing a phosphazene ring.

[0009] Preferably, the benzoxazine monomer containing a phosphazene ring is prepared by the following steps: adding benzoxazine containing a phenolic hydroxyl group to a mixed system containing hexachlorocyclotriphosphazene, activated potassium carbonate, and acetonitrile, reacting at room temperature for 3 hours under an inert gas atmosphere, and heating and refluxing for 4 hours to obtain an intermediate mixture; adding an acetonitrile solution of (4-hydroxy-phenyl)-diethyl phosphate to the intermediate mixture, heating and refluxing for 12 hours, cooling to room temperature, filtering, vacuum rotary evaporation, washing, and drying to obtain the benzoxazine monomer containing a phosphazene ring.

[0010] Preferably, the washing comprises dissolving the product obtained by rotary evaporation under reduced pressure in chloroform or ethyl acetate, and washing the product three times with 10% sodium hydroxide solution-water in sequence.

[0011] Preferably, the molar ratio of the hexachlorocyclotriphosphazene to the benzoxazine containing a phenolic hydroxyl group is 1:1-5.

[0012] Preferably, the molar ratio of the hexachlorocyclotriphosphazene to the benzoxazine containing a phenolic hydroxyl group is 1:2-5.

[0013] Preferably, the molar ratio of the hexachlorocyclotriphosphazene to the benzoxazine containing a phenolic hydroxyl group is 1:2-4.

[0014] Preferably, the molar ratio of the hexachlorocyclotriphosphazene to the benzoxazine containing a phenolic hydroxyl group is 1:2.

[0015] Preferably, the molar ratio of the hexachlorocyclotriphosphazene to the (4-hydroxy-phenyl)-diethyl phosphate is 1:1-5.

[0016] Preferably, the molar ratio of the hexachlorocyclotriphosphazene to the (4-hydroxy-phenyl)-diethyl phosphate is 1:1-4.

[0017] Preferably, the molar ratio of the hexachlorocyclotriphosphazene to the (4-hydroxy-phenyl)-diethyl phosphate is 1:2-4.

[0018] Preferably, the molar ratio of the hexachlorocyclotriphosphazene to the (4-hydroxy-phenyl)-diethyl phosphate is 1:4.

[0019] Preferably, the structural formula of the benzoxazine containing phenolic hydroxyl group includes the following formula

[0020] H: .

[0021] Preferably, the benzoxazine containing phenolic hydroxyl groups is prepared by the following steps:

[0022] The first intermediate is obtained by mixing p-aminophenol, salicylaldehyde, and anhydrous ethanol, stirring continuously under argon protection, and reflux reaction at 60-70°C for 3-5 hours. After the reaction, the mixture is evaporated under reduced pressure, cooled in an ice-water bath for crystallization, filtered, washed with ethanol, and dried under vacuum to obtain the first intermediate. The first intermediate is then weighed and dissolved in anhydrous ethanol, and NaBH4 is added in batches and stirred at 28-32°C. After the reaction is complete, distilled water is slowly added to form a precipitate, which is filtered to obtain the second intermediate. The second intermediate, paraformaldehyde, dioxane, and molecular sieves are stirred continuously, heated to 95-105°C, and refluxed for 3-5 hours. After the reaction is complete, the mixture is filtered, decompressed, rotary evaporated, and recrystallized to obtain the benzoxazine containing phenolic hydroxyl groups.

[0023] Preferably, the structural formula of the benzoxazine monomer containing a phosphazene ring includes the following formula:

[0024] M1: 、

[0025] M2: and

[0026] M3: One or more of .

[0027] Preferably, the structural formula of the benzoxazine monomer containing a phosphazene ring is as follows:

[0028] M1: .

[0029] Preferably, the structural formula of the cardanol includes the following formula

[0030] C: ;in:

[0031] .

[0032] Preferably, the benzoxazine oligomer is prepared by the following steps: mixing a benzoxazine monomer containing a phosphazene ring with cardanol, heating the mixture to 62-68° C., and continuing the reaction for 4-8 hours to obtain the benzoxazine oligomer.

[0033] Preferably, the benzoxazine oligomer is prepared by the following steps: mixing a benzoxazine monomer containing a phosphazene ring with cardanol, heating the mixture to 65° C., and continuing the reaction for 6 hours to obtain the benzoxazine oligomer.

[0034] Preferably, the structural formula of the benzoxazine oligomer includes the following formula

[0035] P1: 、

[0036] P2: and

[0037] P3: One or more of the following, where:

[0038] 、 .

[0039] Preferably, the molar ratio of the benzoxazine monomer containing a phosphazene ring to the cardanol is 1:1-5.

[0040] Preferably, the molar ratio of the benzoxazine monomer containing a phosphazene ring to the cardanol is 1:2-4.

[0041] Preferably, the molar ratio of the benzoxazine monomer containing a phosphazene ring to the cardanol is 1:2.

[0042] On the other hand, the present application provides a method for preparing a flame retardant and anti-corrosion coating using the following technical solution:

[0043] A method for preparing a flame retardant and anti-corrosion coating comprises the following steps: mixing the nanocellulose, the graphene oxide, the benzoxazine oligomer and the catalyst and uniformly coating the mixture on a surface to be coated; pre-curing the mixture at 100-110° C. for 1-3 hours; then heating the mixture to 145-155° C. and curing the mixture for 3-5 hours to obtain the flame retardant and anti-corrosion coating.

[0044] Preferably, the method comprises the following steps: mixing the nanocellulose, the graphene oxide, the benzoxazine oligomer and the catalyst and uniformly coating the mixture on the surface to be coated, pre-curing the mixture at 100-110° C. for 2 hours, then heating the mixture to 150° C. and curing the mixture for 4 hours to obtain the flame retardant and anti-corrosion coating.

[0045] Preferably, the mixing comprises: adding the catalyst to the benzoxazine oligomer for standby use; mixing the graphene oxide, the nanocellulose and a solvent to obtain a mixture; dropwise adding the benzoxazine oligomer to which the catalyst is added to the mixture, stirring for 1-3 hours, and distilling under reduced pressure.

[0046] Preferably, the mixing comprises: adding the catalyst to the benzoxazine oligomer for later use; mixing the graphene oxide, the nanocellulose and a solvent to obtain a mixture; dropwise adding the benzoxazine oligomer to which the catalyst is added to the mixture, stirring for 2 hours, and distilling under reduced pressure.

[0047] Preferably, the specific steps of mixing the graphene oxide, the nanocellulose and the solvent are as follows: dissolving the nanocellulose in the solvent to obtain a nanocellulose solution, dispersing the graphene oxide in the solvent by ultrasonic stirring for 20-40 minutes to obtain a graphene oxide dispersion, and adding the graphene oxide dispersion dropwise to the nanocellulose solution by ultrasonic stirring for 20-40 minutes.

[0048] Preferably, the weight ratio of the graphene oxide to the nanocellulose is 1:1.5-2.5.

[0049] Preferably, the weight ratio of the graphene oxide to the nanocellulose is 1:2.

[0050] In summary, this application includes at least one of the following beneficial technical effects:

[0051] 1. By designing a benzoxazine oligomer, combining it with nanocellulose, graphene oxide, and a catalyst to copolymerize under heating conditions to form a dense coating, the flame-retardant anti-corrosion coating's adhesion, mechanical, and anti-corrosion properties are improved. The difficulty of curing the flame-retardant anti-corrosion coating is also reduced, and the impact strength of the flame-retardant anti-corrosion coating is increased.

[0052] 2. At the same time, the introduction of the phosphazene ring can graft multiple benzoxazine functional groups containing phenolic hydroxyl groups, thereby copolymerizing and cross-linking with cardanol, which is conducive to forming a dense coating and improving the flame retardant properties of the coating.

[0053] 3. At the same time, a low-melting-point benzoxazine monomer containing a phosphazene ring was prepared by design, and a benzoxazine oligomer was prepared by reacting the phosphazene ring-containing benzoxazine monomer with cardanol, which reduced the reaction temperature, reduced the preparation difficulty, and mildened the reaction conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Figure 1 1 and 2 are the nuclear magnetic resonance phosphorus spectrum (a) and nuclear magnetic resonance hydrogen spectrum (b) of the benzoxazine monomer containing a phosphazene ring prepared in Preparation Example 2 of the present application.

[0055] Figure 2 1 and 2 are the nuclear magnetic resonance phosphorus spectrum (a) and nuclear magnetic resonance hydrogen spectrum (b) of the benzoxazine monomer containing a phosphazene ring prepared in Preparation Example 4 of the present application.

[0056] Figure 3 1 and 2 are the nuclear magnetic resonance phosphorus spectrum (a) and nuclear magnetic resonance hydrogen spectrum (b) of the benzoxazine monomer containing a phosphazene ring prepared in Preparation Example 6 of the present application.

[0057] Figure 4 It is a comparison diagram of the Tafel curves of the flame retardant and anti-corrosion coatings prepared in Examples 1-3 and Comparative Example 1.

[0058] Figure 5 It is a comparison chart of the thermogravimetric curves of the flame retardant and anti-corrosion coatings prepared in Examples 1-3 of the present application. DETAILED DESCRIPTION

[0059] The present application is described in further detail below in conjunction with Examples. The following examples are only used to illustrate the present invention and should not be construed as limiting the scope of the present invention. In the following examples, if specific conditions are not specified, they are carried out according to conventional conditions or the conditions recommended by the manufacturer. The methods used are conventional methods well known in the art unless otherwise specified, and the consumables and reagents used are commercially available unless otherwise specified. Unless otherwise indicated, the professional and scientific terms used herein have the same meaning as those familiar to those skilled in the art. In addition, any method or material similar or equivalent to the described content may also be applied to the present invention.

[0060] The raw materials used in the examples and comparative examples can all be obtained commercially.

[0061] Preparation Example 1

[0062] Preparation Example 1 of the present application provides a benzoxazine containing a phenolic hydroxyl group, which is prepared by the following steps: p-aminophenol (21.80 g, 0.2 mol), salicylaldehyde (24.40 g, 0.2 mol) and anhydrous ethanol (200 mL) are added in sequence to a 500 mL three-necked flask, and the mixture is continuously stirred under argon protection and refluxed at 60°C. After the reaction for 4 hours, the mixture is distilled under reduced pressure to about 100 mL, cooled in an ice-water bath for crystallization, filtered, washed with a small amount of ethanol, and dried in vacuo at 50°C to obtain 39.00 g of the first intermediate (whose structural formula is Formula A1, light brown crystals, with a yield of 90.6%). The first intermediate (25.00 g, 0.12 mol) was weighed and dissolved in anhydrous ethanol (200 mL). NaBH4 (2.30 g, 0.06 mol) was added in batches and the reaction was stirred at 30°C. TLC (petroleum ether: ethyl acetate = 2:1) monitored the completion of the reaction of the first intermediate. 400 mL of distilled water was slowly added under stirring to produce a precipitate. The second intermediate (21.88 g of the second intermediate having the structural formula of Formula A2, an off-white powder, and a yield of 84.2%) was obtained by filtration. The second intermediate (11.00 g, 0.05 mol), paraformaldehyde (1.80 g, 0.06 mol), dioxane (150 mL) and a small amount of 4A molecular sieves were added sequentially to a 250 mL three-necked flask. The mixture was stirred continuously, heated to 100°C, and refluxed for 4 h. The reaction was complete as monitored by TLC (petroleum ether:ethyl acetate = 2:1). The mixture was filtered off and the dioxane was removed by rotary evaporation under reduced pressure to obtain a yellow solid. The solid was recrystallized in a dichloromethane / petroleum ether system (dichloromethane:petroleum ether = 1:10) and filtered off to obtain 10.80 g of benzoxazine containing a phenolic hydroxyl group (HO-BOZ) (whose structural formula is Formula H, white needle-shaped crystals, yield 95.0%).

[0063] The reaction equation of Preparation Example 1 is as follows:

[0064] .

[0065] Preparation Example 2

[0066] Preparation Example 2 of the present application provides a benzoxazine monomer containing a phosphazene ring, which is prepared by the following steps:

[0067] A benzoxazine containing a phenolic hydroxyl group (1.32 g, 0.0058 mol) and an acetonitrile solution (21 mL) were mixed to obtain an acetonitrile solution of the benzoxazine containing a phenolic hydroxyl group. Hexachlorocyclotriphosphazene (1.00 g, 0.0029 mol), activated potassium carbonate (5.00 g, 0.03 mol), and acetonitrile (40 mL) were then slowly added dropwise to the mixture under an argon atmosphere. The mixture was allowed to react at room temperature for 3 h, then heated to reflux for 4 h to obtain an intermediate mixture. The mixture was cooled to room temperature, and an acetonitrile solution of (4-hydroxyphenyl)-diethyl phosphate (DPP) (2.21 g, 0.0096 mol) was added dropwise to the intermediate mixture. The mixture was then heated to reflux for 12 h to terminate the reaction. After cooling, the K2CO3 and generated KCl were removed by filtration. The filtrate was evaporated under reduced pressure at 40°C to remove acetonitrile to obtain a light yellow block solid. The solid was dissolved in chloroform and washed three times with 10% sodium hydroxide solution-water. The solid was dried over anhydrous magnesium sulfate to obtain a benzoxazine monomer containing a phosphazene ring (structural formula M1, a transparent oil, 90% yield).

[0068] The reaction equation for the preparation of benzoxazine monomers containing a phosphazene ring is as follows:

[0069] .

[0070] Preparation Example 3

[0071] Preparation Example 3 of the present application provides a benzoxazine oligomer, which is prepared by the following steps: 10.00 g of a benzoxazine monomer containing a phosphazene ring (structural formula: M1, 7.27 mmol) and 4.39 g of cardanol (structural formula: C, 14.53 mmol) are weighed and added to a 100 mL three-necked flask and stirred continuously. Under an argon atmosphere, the mixture is heated to 40° C. in an oil bath and thoroughly mixed, and then the mixture is heated to 65° C. to continue the reaction. After reacting for 6 h, a sample is taken and the mixture is stirred using a flask. 1 The ring-opening of the oxazine ring was monitored by HNMR. After the oxazine ring disappeared, heating was stopped and the mixture was cooled to room temperature to obtain a benzoxazine oligomer (structural formula P1, a reddish-brown viscous liquid, with a yield of 91%).

[0072] The reaction equation for the preparation of benzoxazine oligomers is as follows:

[0073] .

[0074] Preparation Example 4

[0075] Preparation Example 4 of the present application provides a benzoxazine monomer containing a phosphazene ring. The difference between Preparation Example 4 and Preparation Example 2 is that in the preparation process of Preparation Example 4, benzoxazine containing a phenolic hydroxyl group (1.98 g, 0.0087 mol) and hexachlorocyclotriphosphazene (1.00 g, 0.0029 mol) are used to prepare a benzoxazine monomer containing a phosphazene ring having the structural formula of Formula M2 , a transparent viscous liquid.

[0076] Preparation Example 5

[0077] Preparation Example 5 of the present application provides a benzoxazine oligomer. The difference between Preparation Example 5 and Preparation Example 3 is that in the preparation process of Preparation Example 5, the molar ratio of the weighed phosphazene ring-containing benzoxazine monomer (structural formula: Formula M2) and cardanol (structural formula: Formula C) is 1:3, and the structural formula of the obtained benzoxazine oligomer is Formula P2 .

[0078] Preparation Example 6

[0079] Preparation Example 6 of the present application provides a benzoxazine monomer containing a phosphazene ring. The difference between Preparation Example 6 and Preparation Example 2 is that in the preparation process of Preparation Example 6, benzoxazine containing a phenolic hydroxyl group (2.64 g, 0.0116 mol) and hexachlorocyclotriphosphazene (1.00 g, 0.0029 mol) are used to prepare a benzoxazine monomer containing a phosphazene ring having the structural formula of Formula M3 , a transparent viscous substance.

[0080] Preparation Example 7

[0081] Preparation Example 7 of the present application provides a benzoxazine oligomer. The difference between Preparation Example 7 and Preparation Example 2 is that in the preparation process of Preparation Example 7, the molar ratio of the weighed benzoxazine monomer containing a phosphazene ring (structural formula: Formula M3) and the cardanol (structural formula: Formula C) is 1:4, and the structural formula of the obtained benzoxazine oligomer is Formula P3 .

[0082] Example 1

[0083] Example 1 of the present application provides a flame-retardant and anti-corrosion coating prepared by the following steps: 100 parts by weight of the benzoxazine oligomer prepared in Preparation Example 3 and 5 parts by weight of a catalyst (cobalt naphthenate) are mixed and set aside. 0.5 parts by weight of graphene oxide (GO) and 1 part by weight of nanocellulose (CNC) are dissolved in N,N-dimethylformamide to obtain a nanocellulose solution; the graphene oxide is dispersed in the N,N-dimethylformamide by ultrasonic stirring for 30 minutes to obtain a graphene oxide dispersion; the graphene oxide dispersion is dropwise added to the nanocellulose solution by ultrasonic stirring for 30 minutes; the mixture is allowed to stand at room temperature for 8 hours until substantially no stratification occurs, thereby obtaining a mixture. The benzoxazine oligomer prepared in Preparation Example 3 with the addition of a catalyst (cobalt cyclohexane) was added dropwise to the mixture and stirred for 2 hours. The solvent was removed by distillation under reduced pressure to obtain a flame retardant anti-corrosion coating (black viscous liquid). The flame retardant anti-corrosion coating was evenly coated on the pretreated tinplate using a coating rod, and pre-cured at 100-110°C for 2 hours. The temperature was then raised to 150°C and cured for 4 hours to obtain a flame retardant anti-corrosion coating (maroon coating).

[0084] Example 2

[0085] Example 2 of the present application provides a flame retardant and anti-corrosion coating. The difference between Example 2 and Example 1 is that Example 2 uses 1 part by weight of graphene oxide (GO) and 2 parts by weight of nanocellulose (CNC) during the preparation process.

[0086] Example 3

[0087] Example 3 of the present application provides a flame retardant and anti-corrosion coating. The difference between Example 3 and Example 1 is that Example 3 uses 2 parts by weight of graphene oxide (GO) and 4 parts by weight of nanocellulose (CNC) during the preparation process.

[0088] Comparative Example 1

[0089] Comparative Example 1 provides a flame retardant and anti-corrosion coating. The difference between Comparative Example 1 and Example 1 is that: in the preparation process of Comparative Example 1, graphene oxide (GO) and nanocellulose (CNC) are not added.

[0090] Comparative Example 2

[0091] Comparative Example 2 provides a flame retardant mixed system. The difference between Comparative Example 2 and Example 1 is that: in the preparation process of Comparative Example 1, 3 parts by weight of graphene oxide (GO) and 6 parts by weight of nanocellulose (CNC) are used.

[0092] Test and Inspection

[0093] (1) The benzoxazine monomers containing phosphazene rings prepared in Preparation Examples 2, 4 and 6 were subjected to nuclear magnetic resonance phosphorus and hydrogen spectrum tests. Figure 1-3 As shown, Figure 1 a is the nuclear magnetic resonance phosphorus spectrum of the benzoxazine monomer containing a phosphazene ring obtained in Preparation Example 2, Figure 1 b is the H NMR spectrum of the benzoxazine monomer containing a phosphazene ring obtained in Preparation Example 2; Figure 2 a is the nuclear magnetic resonance phosphorus spectrum of the benzoxazine monomer containing a phosphazene ring obtained in Preparation Example 4, Figure 2 b is the H NMR spectrum of the benzoxazine monomer containing a phosphazene ring obtained in Preparation Example 4; Figure 3 a is the nuclear magnetic resonance phosphorus spectrum of the benzoxazine monomer containing a phosphazene ring obtained in Preparation Example 6, Figure 3 b is the hydrogen nuclear magnetic resonance spectrum of the benzoxazine monomer containing a phosphazene ring prepared in Preparation Example 6.

[0094] (2) The flame retardant anticorrosion coatings prepared in Examples 1-3 and the flame retardant mixed system of Comparative Example 2 were observed. The flame retardant anticorrosion coatings prepared in Examples 1-3 had uniform texture and good stability. After coating and curing, they successfully formed flame retardant anticorrosion coatings. However, the flame retardant mixed system of Comparative Example 2 was unevenly dispersed, produced precipitation, had poor stability, and was difficult to cure to form a uniform flame retardant anticorrosion coating after coating. This indicates that excessive addition of graphene oxide (GO) and nanocellulose (CNC) is not conducive to forming a stable and uniform flame retardant anticorrosion coating, and it is difficult to cure to form a uniform flame retardant anticorrosion coating.

[0095] (3) The flame retardant and anti-corrosion coatings prepared in Examples 1-3 and Comparative Example 1 were placed in 3.5 wt% NaCl solution, and Tafel polarization curve tests were performed to obtain Tafel curves as shown in the following figure: Figure 4 As shown, Comparative Example 1 is marked as 0%, Example 1 is marked as 0.5%, Example 2 is marked as 1%, and Example 3 is marked as 2%. The corrosion current density (Icorr) and protection efficiency (PE) are shown in Table 1.

[0096] Table 1:

[0097]

[0098] (4) The flame retardant anti-corrosion coatings prepared in Examples 1-3 and Comparative Example 1 were subjected to an adhesion test in accordance with GB / T1720-2020, the flame retardant anti-corrosion coatings prepared in Examples 1-3 were subjected to an impact resistance test in accordance with GB / T1732-2020, the flame retardant anti-corrosion coatings prepared in Examples 1-3 were subjected to a hardness test in accordance with GB / T6739-1996A, and the flame retardant anti-corrosion coatings prepared in Examples 1-3 were subjected to a gloss test in accordance with GB / T1743-1989. The data are shown in Table 2.

[0099] Table 2:

[0100]

[0101] (5) The flame retardant and anti-corrosion coatings prepared in Examples 1-3 were subjected to thermogravimetric tests, and the thermogravimetric curves were obtained as follows: Figure 5 As shown, the curve obtained by the flame retardant anti-corrosion coating prepared in Example 1 is marked as PM1; the curve obtained by the flame retardant anti-corrosion coating prepared in Example 2 is marked as PM2; and the curve obtained by the flame retardant anti-corrosion coating prepared in Example 3 is marked as PM3.

[0102] Result Analysis

[0103] The following combination Figure 1-5 , and the experimental results provided in Tables 1-2 are used to describe this application in detail.

[0104] According to Preparation Examples 2, 4 and 6 and Figure 1-3 The NMR phosphorus spectra of the three benzoxazine monomers containing a phosphazene ring show proton peaks at 7.26 and 2.05, respectively, derived from the solvents CDCl3 and acetonitrile. The peak at 8.17-9.07 ppm is attributed to the phosphorus atoms on the phosphazene ring attached to the phenolic hydroxyl group of the benzoxazine or to (4-hydroxyphenyl)-diethyl phosphate. The peak at 17.71-18.18 ppm is attributed to the phosphorus atoms of (4-hydroxyphenyl)-diethyl phosphate. Figure 1 The phosphorus atom peaks on the two structures of monomer M1 in a are located at 8.17-8.64 ppm and 17.11-17.90 ppm, respectively. Taking the three phosphorus atoms on the phosphazene ring as a reference, the area integral ratio is 3.00:4.03, which is basically consistent with the fact that the phosphazene ring and phosphate ester in one molecule of monomer M1 contain 3 and 4 phosphorus atoms, respectively. Figure 2 The phosphorus atom peaks of monomer M2 in a are located at 8.55-8.65 ppm and 18.00 ppm. Taking the three phosphorus atoms on the phosphazene ring as a reference, the area integral ratio is 3.00:3.03, which is basically consistent with the fact that the phosphazene ring and phosphate ester in one molecule of monomer M2 contain 3 and 3 phosphorus atoms respectively. Figure 3 The phosphorus peaks of monomer M3 in a are located at 8.92-9.07 ppm and 18.11-18.18 ppm. Using the three phosphorus atoms on the phosphazene ring as a reference, the area-integrated ratio is 3.00:2.00, consistent with the fact that the phosphazene ring and phosphate ester contain three and two phosphorus atoms, respectively, per molecule of monomer M3. The absence of a P-Cl peak (22-23 ppm) indicates that the chlorine atoms have been essentially completely replaced.

[0105] In the H NMR spectrum of the phosphazene-containing benzoxazine monomer M1 (1b), the chemical shifts at 1.29-1.33 ppm and 4.06-4.14 ppm correspond to the methyl and methylene proton peaks in the (4-hydroxyphenyl)-diethyl phosphate structure, respectively. The peaks at 4.59 ppm and 5.32 ppm correspond to the proton peaks of the two methylene groups, Ar-CH2-N and O-CH2-N, respectively, on the oxazine ring. The multiplets at 6.88-7.11 ppm and 7.69-7.72 ppm correspond to the hydrogen proton peaks on the phenyl ring. Using the proton peak area of ​​the Ar-CH2-N proton on the oxazine ring as a reference, the area integrated ratios of the peaks are 24.13:16.13:4.00:4.07:32.27, which is consistent with the hydrogen atom ratio of 24:16:4:4:32 in a single molecule of monomer M1.

[0106] In the H NMR spectrum of monomer M2 (2b), the chemical shifts are similar to those of M1. The area integrated ratios of the corresponding peak groups are 18.40:12.44:6.00:6.07:36.49, which is consistent with the ratio of hydrogen atoms in one molecule of monomer M2 of 18:12:6:6:36. In the H NMR spectrum of monomer M3 (3b), the chemical shifts are similar to those of M1. The area integrated ratios of the corresponding peak groups are 12.26:8.04:12.44:8.00:7.95:40.71, which is consistent with the ratio of hydrogen atoms in one molecule of monomer M3 of 12:8:8:8:40. In summary, Preparation Examples 2, 4, and 6 successfully prepared the phosphazene-ring-containing benzoxazine monomer M1, the phosphazene-ring-containing benzoxazine monomer M2, and the phosphazene-ring-containing benzoxazine monomer M3, respectively.

[0107] Refer to Table 1 and Figure 4 The corrosion current density of the flame retardant anti-corrosion coatings prepared in Examples 1-3 is much lower than the corrosion current density of the flame retardant anti-corrosion coatings prepared in Comparative Example 1 and the tinplate without coating, and the protection efficiency of the flame retardant anti-corrosion coatings prepared in Examples 1-3 is much higher than the protection efficiency of the flame retardant anti-corrosion coating prepared in Comparative Example 1, indicating that the simultaneous presence of benzoxazine polymer, graphene oxide (GO) and nanocellulose (CNC) is beneficial to reducing the corrosion current density of the flame retardant anti-corrosion coating and improving the protection efficiency. In particular, the corrosion current density data of the flame retardant anti-corrosion coating prepared in Example 3 is nearly two orders of magnitude smaller than the corrosion current density data of tinplate, and the protection rate reaches 98.99%.

[0108] Referring to Table 2, the hardness, adhesion and impact strength of the flame retardant anti-corrosion coatings prepared in Examples 1-3 are better than those of the flame retardant anti-corrosion coating prepared in Comparative Example 1, indicating that the simultaneous presence of benzoxazine oligomers, graphene oxide (GO) and nanocellulose (CNC) is beneficial to reducing the corrosion current density of the flame retardant anti-corrosion coating and improving the protection efficiency, while also helping to improve the adhesion of the flame retardant anti-corrosion coating on tinplate, and the hardness and toughness of the flame retardant anti-corrosion coating.

[0109] Reference Figure 5 The flame-retardant anti-corrosion coatings prepared in Examples 2 and 3 exhibited almost no thermal weight loss below 300°C. When the temperature rose to 400-500°C, the TG curves experienced a significant dip, indicating significant thermal weight loss. The fastest thermal weight loss occurred at 410-430°C, demonstrating superior thermal stability. At 800°C, the residual char rates of the flame-retardant anti-corrosion coatings prepared in Examples 1, 2, and 3 were 28%, 46%, and 48%, respectively. According to the empirical formula for the limiting oxygen index (LOI): LOI = 17.5% + 0.4Yc (residual char rate), the calculated oxygen indices were 28.7%, 35.9%, and 36.7%, respectively. All of these were greater than 27%, making them flame-retardant materials. This is attributed to the inorganic phosphazene ring backbone and the cyclotriphosphazene structure, which provide a stable crosslinking support core for the flame-retardant anti-corrosion coating's crosslinked network. Combined with graphene oxide (GO) and nanocellulose, the flame-retardant anti-corrosion coatings exhibit enhanced high-temperature resistance, flame retardancy, and thermal stability.

[0110] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make non-creative modifications to the present embodiment as needed, but as long as they are within the scope of the claims of the present application, they are protected by the patent law.

Claims

1. A flame retardant and anti-corrosion coating, characterized by: The invention relates to a method for preparing a benzoxazine oligomer comprising the following components in parts by weight: 95-105 parts of a benzoxazine oligomer, 1-4 parts of nanocellulose, 0.5-2 parts of graphene oxide, and 3-7 parts of a catalyst; the benzoxazine oligomer is obtained by reacting a benzoxazine monomer containing a phosphazene ring with cardanol; the benzoxazine monomer containing a phosphazene ring is prepared by the following steps: adding a benzoxazine containing a phenolic hydroxyl group to a mixed system containing hexachlorocyclotriphosphazene, activated potassium carbonate, and acetonitrile, reacting at room temperature for 2.5-3.5 hours under an inert gas atmosphere, and then heating and refluxing for 3-5 hours to obtain a benzoxazine oligomer; An intermediate mixture; an acetonitrile solution of (4-hydroxy-phenyl)-diethyl phosphate is added to the intermediate mixture, and the mixture is heated and refluxed for 11-13 hours. After cooling to room temperature, the mixture is filtered, evaporated under reduced pressure, washed, and dried to obtain the benzoxazine monomer containing a phosphazene ring; the molar ratio of the hexachlorocyclotriphosphazene to the benzoxazine containing a phenolic hydroxyl group is 1:2-4; the molar ratio of the hexachlorocyclotriphosphazene to the (4-hydroxy-phenyl)-diethyl phosphate is 1:2-4; the structural formula of the benzoxazine monomer containing a phosphazene ring includes M1： 、 M2: and M3: One or more of .

2. The flame retardant and anti-corrosion coating according to claim 1, characterized in that: The benzoxazine oligomer is prepared by the following steps: mixing a benzoxazine monomer containing a phosphazene ring with cardanol, heating the mixture to 62-68° C., and continuing the reaction for 4-8 hours to obtain the benzoxazine oligomer.

3. The flame retardant and anti-corrosion coating according to claim 2, characterized in that: The molar ratio of the benzoxazine monomer containing a phosphazene ring to the cardanol is 1:1-5.

4. A method for preparing a flame retardant and anti-corrosion coating according to any one of claims 1 to 3, characterized in that: The method comprises the following steps: mixing the nanocellulose, the graphene oxide, the benzoxazine oligomer and the catalyst and uniformly coating the mixture on the surface to be coated, pre-curing the mixture at 100-110° C. for 1-3 hours, then heating the mixture to 145-155° C. and curing the mixture for 3-5 hours to obtain the flame retardant and anti-corrosion coating.

5. The method for preparing a flame retardant and anti-corrosion coating according to claim 4, characterized in that: The mixing includes: adding the catalyst to the benzoxazine oligomer for standby use; mixing the graphene oxide, the nanocellulose and a solvent to obtain a mixture; and dropwise adding the benzoxazine oligomer to which the catalyst is added to the mixture, stirring for 1-3 hours, and performing reduced pressure distillation.

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