A flame-retardant superhydrophobic polyurethane containing benzoxazine and its preparation method

Abstract

The present invention discloses a flame-retardant superhydrophobic polyurethane containing benzoxazine and a preparation method thereof, belonging to the technical field of waterborne polyurethane coatings. The polyurethane is obtained by co-blending and spraying an aqueous polyurethane emulsion containing benzoxazine and modified nanoparticles in a mass ratio of 1:0.2 - 0.8 and then heating and curing at 80 - 200 °C for 4 - 8 h; the aqueous polyurethane emulsion is prepared by reacting a diisocyanate, a phosphorus-containing benzoxazine diol, a long-chain diol, 2,2-dimethylolpropionic acid, 1,4-butanediol and triethylamine in a molar ratio of 1:0.15 - 0.2:0.15 - 0.2:0.1 - 0.3:0.3 - 0.4:0.1 - 0.3. By introducing phosphorus-containing benzoxazine into the polyurethane structure and simultaneously blending with modified nanoparticles, the present invention endows the coating with excellent mechanical properties, superhydrophobic properties, flame-retardant characteristics and high adhesiveness. Spraying the polyurethane material on the surfaces of foams and fabrics can also achieve the separation of oil-water emulsions, greatly broadening the application scope of the material. The material prepared by the present invention has broad application prospects in the fields of oil-water separation, transportation, electronic industry and aerospace, etc.

Description

Technical Field

[0001] The present invention belongs to the technical field of waterborne polyurethane coatings, and particularly relates to a flame-retardant superhydrophobic polyurethane containing benzoxazine and a preparation method thereof. Background Art

[0002] Waterborne polyurethane coatings use water as a dispersion medium and have advantages such as low toxicity, no pollution, and excellent weather resistance. However, due to the large number of hydrophilic groups and low crosslinking degree in waterborne polyurethane, there are problems of poor water resistance and poor mechanical properties. At the same time, waterborne polyurethane is prone to decomposition to generate combustible substances under high-temperature conditions, severely limiting its application scenarios. Therefore, it is very important to modify waterborne polyurethane for water resistance and flame retardancy to expand the application of waterborne polyurethane.

[0003] Benzoxazine resin is a heterocyclic compound containing a six-membered oxazine ring with oxygen and nitrogen atoms, and can be synthesized by a simple condensation reaction of phenols, primary amines, and formaldehyde. Benzoxazine is considered an ideal and cost-competitive new thermosetting high-performance material, having good mechanical properties, low hygroscopicity, and low surface free energy.

[0004] Through innovative molecular design, the present invention introduces phosphorus-containing benzoxazine into the main chain of waterborne polyurethane. The prepared waterborne polyurethane emulsion has excellent stability. After the sprayed waterborne polyurethane coating is heat-treated at high temperature, the benzoxazine in the main chain is cured, increasing the crosslinking degree of waterborne polyurethane, improving the mechanical properties and adhesion properties of the waterborne polyurethane coating. At the same time, phosphorus compounds decompose at high temperature to generate acidic substances such as phosphoric acid and polyphosphoric acid, catalyzing the dehydration and crosslinking of polymer materials to form a dense carbon layer, improving the flame-retardant properties of the waterborne polyurethane coating. To further improve the water resistance of the coating, modified nanoparticles are introduced into the waterborne polyurethane emulsion, constructing a micro-nano rough structure that significantly improves the water resistance of the coating, with a hydrophobic angle greater than 150°. At the same time, the benzoxazine in the polyurethane main chain undergoes ring-opening crosslinking after high-temperature treatment to obtain a crosslinked waterborne polyurethane coating, further enhancing the mechanical properties and hydrophobic properties of the coating. This material has broad application prospects in fields such as oil-water separation, transportation, electronics industry, and aerospace. Summary of the Invention

[0005] Aiming at the disadvantages of poor water resistance, poor mechanical properties, and poor flame-retardant effect of waterborne polyurethane, the present invention prepares a waterborne polyurethane coating with flame retardancy, superhydrophobicity, and high mechanical properties by introducing phosphorus-containing benzoxazine into the main chain, thus having broad application prospects in the fields of anticorrosion materials and electronic devices.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] The provided flame-retardant superhydrophobic polyurethane containing benzoxazine is prepared by reacting a diisocyanate, a phosphorus-containing benzoxazine diol, a long-chain diol, 2,2-dimethylolpropionic acid, 1,4-butanediol, and triethylamine in a molar ratio of 1:0.15 - 0.2:0.15 - 0.2:0.1 - 0.3:0.3 - 0.4:0.1 - 0.3. It is obtained by blending and spraying with modified nanoparticles in a mass ratio of 1:0.2 - 0.8, drying the solvent, and then heating at 80 - 200 °C for 4 - 8 h.

[0008] The phosphorus-containing benzoxazine diol is prepared by reacting a phosphorus-containing long-chain diamine, p-hydroxybenzyl alcohol, and paraformaldehyde in a molar ratio of 1:2:4.1 - 4.3 at 120 °C for 12 h in a mixed solvent of toluene and ethanol with a volume ratio of 2:1.

[0009] The diisocyanate is one or more of 4,4'-dicyclohexylmethane diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, 4,4'-diphenylmethane diisocyanate, toluene-2,4-diisocyanate, etc.

[0010] The long-chain diol is one or more of polytetrahydrofuran diol, polysiloxane diol, polycaprolactone diol, polycarbonate diol, etc. with a molecular weight of 200 - 3000.

[0011] The long-chain diamine is one or more of polysiloxane diamine, polyetheramine, polyethylene glycol diamine, polyethylenediamine, etc. with a molecular weight of 200 - 2000.

[0012] The preparation method of the superhydrophobic aqueous polyurethane containing benzoxazine includes the following steps:

[0013] S1. Preparation of the phosphorus-containing benzoxazine diol: Add a phosphorus-containing long-chain diamine, p-hydroxybenzyl alcohol, and paraformaldehyde in a molar ratio of 1:2:4.1 - 4.3, and heat under reflux at 120 °C for 12 h in a mixed solvent of toluene and ethanol with a volume ratio of 2:1.

[0014] S2. Preparation of aqueous polyurethane emulsion: Under nitrogen protection, diisocyanate, phosphorus-containing benzoxazine diol, long-chain diol, and 2,2-dimethylolpropionic acid were mixed evenly, and then dibutyltin dilaurate as a catalyst was added. After reacting at 80 °C for 2 - 3 hours, the temperature was lowered to 60 °C, and then 1,4-butanediol was added to continue the reaction for 2 - 3 hours. Acetone was added during this period to reduce the viscosity. After the reaction ended, the temperature was lowered to 40 °C, triethylamine was added, and after stirring for 30 min, deionized water was added. After high-speed dispersion at 2000 rpm for 40 min, a benzoxazine-containing aqueous polyurethane emulsion was obtained; diisocyanate, phosphorus-containing benzoxazine diol, long-chain diol, 2,2-dimethylolpropionic acid, 1,4-butanediol, and triethylamine were added according to a molar ratio of 1:0.15 - 0.2:0.15 - 0.2:0.1 - 0.3:0.3 - 0.4:0.1 - 0.3;

[0015] S3. Preparation of benzoxazine-containing superhydrophobic aqueous polyurethane: The aqueous polyurethane emulsion and modified nanoparticles were mixed at a mass ratio of 1:0.2 - 0.8. The mixed solution was sprayed on the substrate using a spray gun. After drying the solvent, it was cured by gradient heating at 80 - 200 °C to obtain a flame-retardant superhydrophobic polyurethane containing benzoxazine.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0017] First, by introducing phosphorus-containing benzoxazine that can be heat-crosslinked into the main chain of aqueous polyurethane, the mechanical properties and adhesion properties of the polyurethane coating are further improved, and excellent flame-retardant properties are imparted to the material.

[0018] Second, by blending and spraying the aqueous polyurethane emulsion containing benzoxazine and modified nanoparticles, excellent superhydrophobic properties are imparted to the polyurethane coating, realizing the multifunctionalization of the coating.

[0019] Third, by spraying the polyurethane coating on the surfaces of foam and fabric, excellent oil-water emulsion separation properties are imparted to the foam and fabric through the interaction between the phenolic hydroxyl groups in benzoxazine and the emulsion particles.

[0020] Other advantages, objectives, and features of the present invention will be partially reflected by the following description, and partially will also be understood by those skilled in the art through the research and practice of the present invention. Description of the Drawings

[0021] Figure 1 . DSC test chart of phosphorus-containing benzoxazine diol in Example 1;

[0022] Figure 2 . Infrared spectrum chart of phosphorus-containing benzoxazine diol in Example 1;

[0023] Figure 31H NMR spectrum of phosphorus-containing benzoxazine diol in Example 1;

[0024] Figure 4 FTIR spectrum of the waterborne polyurethane film in Example 1;

[0025] Figure 5 Tensile property test diagrams of the waterborne polyurethane film before and after curing in Example 1;

[0026] Figure 6 Adhesion test diagram of the waterborne polyurethane in Example 1;

[0027] Figure 7 Stability test diagram of the waterborne polyurethane emulsion in Example 1;

[0028] Figure 8 Flame retardancy characteristic diagram of the waterborne polyurethane coating in Example 1;

[0029] Figure 9 Contact angle test diagram of the waterborne polyurethane coating in Example 1, Figure 9 A is the contact angle test diagram of the glass substrate, Figure 9 B is the contact angle test diagram of the waterborne polyurethane composite coating;

[0030] Figure 10 Oil-water separation test diagram of the waterborne polyurethane in Example 1; Detailed implementation method

[0031] The preferred embodiments of the present invention will be described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0032] Example 1:

[0033] A superhydrophobic waterborne polyurethane containing benzoxazine and its preparation method include the following steps:

[0034] (1) Preparation of modified nanoparticles

[0035] Prepare 30 ml of an alkaline solution with a pH of 10 - 11 using ammonia water. Add 5 g of nano-titanium dioxide to the ammonia water solution and stir magnetically for 10 min to obtain solution A; drop 0.5 mL of perfluorodecyltriethoxysilane (PFDTES) into 50 ml of an anhydrous ethanol solution, and stir magnetically at room temperature for 60 min. After completion, obtain solution B; slowly add solution A to solution B and stir magnetically at a water bath temperature of 50 °C for 12 h. The product after the reaction is centrifuged at a centrifugal speed of 10,000 rpm for 5 min, washed with anhydrous ethanol, and dried at 60 °C for 24 h. The resulting product is modified nanoparticles;

[0036] (2) Preparation of Phosphorus-Containing Benzoxazine Diol

[0037] Add 10 g of pentaerythritol and 60 ml of phosphorus oxychloride into a 250-ml three-necked flask. After setting up the tail gas removal device, use the inert gas replacement method to fill the system with nitrogen. Heat the temperature to 100 °C and react for 5 h. Wash the product after the reaction with petroleum ether and dichloromethane and then dry it to obtain intermediate product A.

[0038]

[0039] Add 4 g of product A, 6.71 g of siloxane diamine and 2.73 g of triethylamine into 60 ml of acetonitrile. React under nitrogen at 80 °C for 8 h. Separate the product after the reaction and take the lower viscous liquid. Add methanol and then rotary evaporate to dryness to obtain phosphorus-containing long-chain diamine.

[0040]

[0041] Add 8.54 g of phosphorus-containing long-chain diamine, 1.5 g of paraformaldehyde and 2.98 g of p-hydroxybenzyl alcohol into 60 ml of a solvent (toluene:ethanol = 2:1). Raise the system temperature to 120 °C and react overnight; monitor the reaction process by thin layer chromatography (TCL), then filter the solid residue, and obtain a yellow solid after washing, drying and rotary evaporation. The product is phosphorus-containing benzoxazine diol.

[0042]

[0043] Figure 1 Figure for the DSC test of the phosphorus-containing benzoxazine diol in Example 1. It can be seen from the figure that the curing temperature is between 200 and 250 °C, indicating that the benzoxazine has been successfully prepared.

[0044] Figure 2 Figure for the infrared spectrum of the phosphorus-containing benzoxazine diol in Example 1. It can be seen from the figure that at wavenumbers 1075 cm -1 and 1222.1 cm -1 belong to the symmetric and antisymmetric vibration peaks of C-O-C in the oxazine ring, and the wavenumber 1511.8 cm -1 is the stretching vibration absorption peak of C-N-C. From this, it can be inferred that the oxazine ring has been formed. The wavenumbers 1257.3 cm -1 and 1154.1 cm -1 are the characteristic absorption peaks of P-O-C and -P=O. At the same time, the wavenumber 1024.6 cm -1 is the stretching vibration peak of Si-O-Si, and at the wavenumber 3669.5 cm -1 is the characteristic absorption peak of -OH. The appearance of the above various peaks indicates that the phosphorus-containing benzoxazine diol has been successfully prepared.

[0045] Figure 3 1H NMR spectrum of the phosphorus-containing benzoxazine diol in Case 1. The proton peaks of the N-CH2-O group are at chemical shifts of 4.67 ppm to 4.75 ppm, and the proton peaks of the N-CH2-C group are at chemical shifts of 3.87 ppm to 3.81 ppm. This proves the successful synthesis of benzoxazine.

[0046] (3) Preparation of aqueous polyurethane emulsion

[0047] 5.3 g of isophorone diisocyanate, 1.3 g of phosphorus-containing benzoxazine diol, 0.6 g of 2,2-dimethylolpropionic acid, and 5.2 g of polytetrahydrofuran (molecular weight 1000) were added to a three-necked flask equipped with a stirrer and a glass stopper, and mixed evenly. After adding 15 μL of dibutyltin dilaurate, it was heated in an electric thermostatic water bath under a nitrogen atmosphere, and the temperature was raised to 80 °C for 2 h. 0.6 mL of 1,4-butanediol was added to the mixed solution and reacted at 60 °C for 2 h. 0.6 mL of triethylamine was added to the round-bottom flask and reacted at 40 °C for 30 min. 45 g of deionized water was added to the system, and after being dispersed by a high-speed disperser at 2000 rpm for 40 min, an aqueous polyurethane emulsion containing benzoxazine was obtained. It was left standing in a polytetrafluoroethylene mold at room temperature for 72 h, dried in a blast box at 55 °C for 48 h to obtain a polyurethane film, and gradient heat-cured at 80-200 °C to obtain a cured polyurethane film.

[0048] The reaction equation is as follows:

[0049]

[0050] Figure 4 FT-IR spectrum of the flame-retardant superhydrophobic polyurethane containing benzoxazine in Case 1. As can be seen from the figure, the characteristic absorption peak of C-O-C in the oxazine ring is at 1066.4 cm -1 The stretching vibration peak of the benzene ring skeleton is at 1650 cm -1 , and at the same time, the wave numbers of 2954.4 cm -1 and 2856.6 cm -1 are the antisymmetric absorption peak and symmetric absorption peak of methyl and methylene, respectively; the wave numbers of 3315.6 cm -1 and 1700.4 cm -1 are the characteristic absorption peaks of N-H and C=O on the urethane. The wave number of 1040.6 cm -1 is the characteristic absorption peak of Si-O-Si. The appearance of these various peaks indicates that the flame-retardant superhydrophobic polyurethane containing benzoxazine has been successfully prepared.

[0051] Figure 5Figure for the tensile property test of the waterborne polyurethane film and the cured waterborne polyurethane film in Case 1. A universal tensile testing machine with a capacity of 500 N was used to test the two samples at a tensile rate of 30 mm / min. The results showed that the maximum tensile strength of the waterborne polyurethane film was 6.58 MPa, and the maximum elongation at break was 331.18%; for the cured waterborne polyurethane film, the maximum tensile strength was 11.54 MPa, and the maximum elongation at break was 343.22%. This is because the ring-opening curing of benzoxazine in the waterborne polyurethane formed a three-dimensional network structure, greatly improving the tensile property.

[0052] Figure 6 Figure for the adhesion test of the waterborne polyurethane in Case 1. The shear method was used to test its adhesion. It was found that the adhesion increased from 0.23 Mpa before curing to 0.7 Mpa after curing, indicating that a large number of hydroxyl groups were exposed after the curing of benzoxazine, increasing its adhesion to the substrate.

[0053] Figure 7 Figure for the storage stability test of the flame-retardant superhydrophobic polyurethane containing benzoxazine in Case 1. The waterborne polyurethane emulsion prepared in step (3) was subjected to a centrifugal acceleration sedimentation test at 3000 rpm for 30 min to simulate storage stability. The results showed that there was no sedimentation phenomenon in the waterborne polyurethane emulsion after centrifugation, indicating a storage stability period of at least six months.

[0054] (4) Preparation of the waterborne polyurethane composite coating

[0055] The waterborne polyurethane emulsion, modified nanoparticles, and absolute ethanol were mixed at a ratio of 1:0.6:4, and the mixed solution was sprayed on the substrate using a spray gun. The dried waterborne polyurethane film was cured by heating at 80 - 200 °C for 4 - 8 h to obtain the cured flame-retardant superhydrophobic waterborne polyurethane film.

[0056] Figure 8 Figure for the flame-retardant property of the waterborne polyurethane coating in Case 1. The aerogel was immersed in the waterborne polyurethane and then dried. After ignition, it extinguished after 2 s, indicating that the coating has good flame-retardant properties.

[0057] Figure 9 Figure for the contact angle test of the waterborne polyurethane coating in Case 1. Figure 9 A is the figure for the contact angle test of the glass substrate. Figure 9 B is the figure for the contact angle test of the waterborne polyurethane composite coating. After applying the composite coating, the hydrophobic angle increased from 68° to 158°, and the coating reached the superhydrophobic state.

[0058] Figure 10Test diagram of oil-water separation of waterborne polyurethane in Implementation Case 1. The melamine foam was immersed in a mixed solution of waterborne polyurethane and modified nanoparticles. After ultrasonic treatment for 5 minutes, it was taken out and dried. The mixed emulsion of toluene and water can achieve oil-water separation through the modified foam.

[0059] Implementation Case 2

[0060] A flame-retardant superhydrophobic polyurethane containing benzoxazine and its preparation method, comprising the following steps:

[0061] (1) The preparation of the modified nanoparticles is the same as step (1) in Implementation Case 1

[0062] (2) The preparation of the phosphorus-containing benzoxazine diol is the same as step (2) in Implementation Case 1

[0063] (3) Preparation of the waterborne polyurethane emulsion

[0064] 4.18 g of toluene diisocyanate, 1.3 g of phosphorus-containing benzoxazine diol, 0.6 g of 2,2-dimethylolpropionic acid, and 5.2 g of polypropylene glycol (molecular weight 1000) were added to a three-necked flask equipped with a stirrer and a glass bottle stopper and mixed evenly. After adding 15 μL of dibutyltin dilaurate, it was heated in an electric thermostatic water bath under a nitrogen atmosphere and heated to 80 °C for 2 h. 0.6 mL of 1,4-butanediol was added to the mixed solution and reacted at 60 °C for 2 h. 0.6 mL of triethylamine was added to the round-bottom flask and reacted at 40 °C for 30 min. 45 g of deionized water was added to the system, and after being dispersed by a high-speed disperser at 2000 rpm for 40 min, a waterborne polyurethane emulsion containing benzoxazine was obtained. It was left standing at room temperature in a polytetrafluoroethylene mold for 72 h, dried in a blast box at 55 °C for 48 h to obtain a polyurethane film, and gradient heat-cured at 80-200 °C to obtain a cured polyurethane film.

[0065]

[0066] (4) The preparation of the waterborne polyurethane composite coating is the same as step (4) in Implementation Case 1

[0067] Implementation Case 3

[0068] A flame-retardant superhydrophobic polyurethane containing benzoxazine and its preparation method, comprising the following steps:

[0069] (1) The preparation of the modified nanoparticles is the same as step (1) in Implementation Case 1

[0070] (2) The preparation of the phosphorus-containing benzoxazine diol is the same as step (2) in Implementation Case 1

[0071] (3) Preparation of the waterborne polyurethane emulsion

[0072] 6 g of diphenylmethane diisocyanate, 1.3 g of phosphorus-containing benzoxazine diol, 0.6 g of 2,2-dimethylolpropionic acid and 5.2 g of polytetrahydrofuran (molecular weight 1000) were added to a three-necked flask equipped with a stirrer and a glass stopper, and mixed evenly; after adding 15 μL of dibutyltin dilaurate, it was heated in a nitrogen atmosphere using an electrothermal constant temperature water bath, and the temperature was raised to 80 °C and reacted for 2 h; 0.6 mL of 1,4-butanediol was added to the mixed solution, and the reaction was carried out at 60 °C for 2 h; 0.6 mL of triethylamine was added to the round-bottom flask, and the reaction was carried out at 40 °C for 30 min; 45 g of deionized water was added to the system, and after being dispersed by a high-speed disperser at 2000 rpm for 40 min, a waterborne polyurethane emulsion containing benzoxazine was obtained. It was left standing at room temperature in a polytetrafluoroethylene mold for 72 h, dried in a blast oven at 55 °C for 48 h to obtain a polyurethane film, and gradient heat-cured at 80-200 °C to obtain a cured polyurethane film.

[0073]

[0074] (4) The preparation of the waterborne polyurethane composite coating was the same as step (4) in Example 1.

[0075] Example 3

[0076] A flame-retardant superhydrophobic polyurethane containing benzoxazine and its preparation method, comprising the following steps:

[0077] (1) The preparation of the modified nanoparticles was the same as step (1) in Example 1.

[0078] (2) The preparation of the phosphorus-containing benzoxazine diol was the same as step (2) in Example 1.

[0079] (3) Preparation of the waterborne polyurethane emulsion

[0080] 6.3 g of 4,4'-dicyclohexylmethane diisocyanate, 1.3 g of phosphorus-containing benzoxazine diol, 0.6 g of 2,2-dimethylolpropionic acid and 5.2 g of polycaprolactone (molecular weight 1000) were added to a three-necked flask equipped with a stirrer and a glass stopper, and mixed evenly; after adding 15 μL of dibutyltin dilaurate, it was heated in a nitrogen atmosphere using an electrothermal constant temperature water bath, and the temperature was raised to 80 °C and reacted for 2 h; 0.6 mL of 1,4-butanediol was added to the mixed solution, and the reaction was carried out at 60 °C for 2 h; 0.6 mL of triethylamine was added to the round-bottom flask, and the reaction was carried out at 40 °C for 30 min; 45 g of deionized water was added to the system, and after being dispersed by a high-speed disperser at 2000 rpm for 40 min, a waterborne polyurethane emulsion containing benzoxazine was obtained. It was left standing at room temperature in a polytetrafluoroethylene mold for 72 h, dried in a blast oven at 55 °C for 48 h to obtain a polyurethane film, and gradient heat-cured at 80-200 °C to obtain a cured polyurethane film.

[0081]

[0082] (4) The preparation of the waterborne polyurethane composite coating is the same as step (4) in Example 1.

[0083] Example 4

[0084] A flame-retardant superhydrophobic polyurethane containing benzoxazine and its preparation method, comprising the following steps:

[0085] (1) The preparation of the modified nanoparticles is the same as step (1) in Example 1.

[0086] (2) The preparation of the phosphorus-containing benzoxazine diol is the same as step (2) in Example 1.

[0087] (3) Preparation of the waterborne polyurethane emulsion

[0088] 4 g of hexamethylene diisocyanate, 1.3 g of phosphorus-containing benzoxazine diol, 0.6 g of 2,2-dimethylolpropionic acid and 5.2 g of polytetrahydrofuran (molecular weight 1000) were added to a three-necked flask equipped with a stirrer and a glass stopper, and mixed evenly; after adding 15 μL of dibutyltin dilaurate, it was heated in an electric thermostatic water bath under a nitrogen atmosphere, and the temperature was raised to 80 °C and reacted for 2 h; 0.6 mL of 1,4-butanediol was added to the mixed solution, and the reaction was carried out at 60 °C for 2 h; 0.6 mL of triethylamine was added to the round-bottom flask, and the reaction was carried out at 40 °C for 30 min; 45 g of deionized water was added to the system, and after being dispersed by a high-speed disperser at 2000 rpm for 40 min, a waterborne polyurethane emulsion containing benzoxazine was obtained. It was left standing at room temperature in a polytetrafluoroethylene mold for 72 h, dried in a blast oven at 55 °C for 48 h to obtain a polyurethane film, and gradient thermally cured at 80-200 °C to obtain a cured polyurethane film.

[0089]

[0090] (4) The preparation of the waterborne polyurethane composite coating is the same as step (4) in Example 1.

[0091] In summary, the present invention introduces phosphorus-containing benzoxazine into the waterborne polyurethane structure, and the benzoxazine is cured by heating. The linear structure is transformed into a crosslinked structure, which not only endows the material with superior mechanical properties and water resistance, but also enhances the flame-retardant characteristics of the waterborne polyurethane; at the same time, the performance of the coating is enhanced after blending and spraying the prepared waterborne polyurethane emulsion with modified nano-titanium dioxide, and it has a superhydrophobic effect, avoiding the influence of environmental changes on the mechanical properties of the material, and greatly enhancing the outdoor application scenarios of the waterborne polyurethane. This material is suitable for various fields such as oil-water separation, transportation, electronics industry and aerospace.

[0092] As described above, it is only the preferred embodiment of the present invention and does not impose any formal restrictions on the present invention. Although the present invention has been disclosed as above with the preferred embodiment, it is not intended to limit the present invention. Any person skilled in the art can make some changes or modifications to equivalent embodiments of equivalent changes by using the above-disclosed technical content within the scope of the technical solution of the present invention. However, as long as it does not depart from the content of the technical solution of the present invention, any simple modification, equivalent change and modification made to the above embodiments based on the technical essence of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A flame-retardant superhydrophobic polyurethane containing benzoxazine, characterized in that, The polyurethane is obtained by blending and spraying an aqueous polyurethane emulsion containing benzoxazine and modified nanoparticles in a mass ratio of 1:0.2 - 0.8, and curing at 80 - 200 °C for 4 - 8 h; the aqueous polyurethane emulsion containing benzoxazine is prepared by reacting a diisocyanate, a phosphorus-containing benzoxazine diol, a long-chain diol, 2,2-dimethylolpropionic acid, 1,4-butanediol and triethylamine in a molar ratio of 1:0.15 - 0.2:0.15 - 0.2:0.1 - 0.3:0.3 - 0.4:0.1 - 0.

3. The general structural formula of the aqueous polyurethane containing benzoxazine is: ； In the formula, the value range of n is 2 - 30; In the formula, R1 is one or more of the following structural formulas; ； In the formula, R2 is one or more of the following structural formulas; ； In the formula, the value range of m1 is 1 - 40; In the formula, R3 is one or more of the following structural formulas; ； In the formula, the value range of m2 is 1 - 40.

2. The flame-retardant superhydrophobic polyurethane containing benzoxazine according to claim 1, characterized in that, The phosphorus-containing benzoxazine diol is prepared by reacting a phosphorus-containing long-chain diamine, p-hydroxybenzyl alcohol and paraformaldehyde in a molar ratio of 1:2:4.1 - 4.3 at 120 °C for 12 h in a mixed solvent of toluene and ethanol with a volume ratio of 2:

1.

3. The preparation method of a flame-retardant superhydrophobic polyurethane containing benzoxazine according to claim 2, characterized in that, It includes the following steps: S1. Preparation of phosphorus-containing benzoxazine diol: Add a phosphorus-containing long-chain diamine, p-hydroxybenzyl alcohol and paraformaldehyde in a molar ratio of 1:2:4.1 - 4.3, and heat and reflux at 120 °C for 12 h in a mixed solvent of toluene and ethanol with a volume ratio of 2:1 to obtain it; S2. Preparation of aqueous polyurethane emulsion containing benzoxazine: Under nitrogen protection, uniformly mix a diisocyanate, a phosphorus-containing benzoxazine diol, a long-chain diol, and 2,2-dimethylolpropionic acid, add a catalyst dibutyltin dilaurate, react at 80 °C for 2 - 3 h, then cool down to 60 °C, then add 1,4-butanediol and continue to react for 2 - 3 h, and add acetone to reduce viscosity during the reaction; after the reaction is completed, cool down to 40 °C, add triethylamine, stir for 30 min, then add deionized water, and obtain an aqueous polyurethane emulsion containing benzoxazine after high-speed dispersion at 2000 rpm for 40 min; the diisocyanate, the phosphorus-containing benzoxazine diol, the long-chain diol, 2,2-dimethylolpropionic acid, 1,4-butanediol and triethylamine are added in a molar ratio of 1:0.15 - 0.2:0.15 - 0.2:0.1 - 0.3:0.3 - 0.4:0.1 - 0.3; S3. Preparation of flame-retardant superhydrophobic polyurethane containing benzoxazine: Mix the aqueous polyurethane emulsion containing benzoxazine and modified nanoparticles in a mass ratio of 1:0.2 - 0.8, spray the mixed solution on the substrate using a spray gun, and heat at 80 - 200 °C for 4 - 8 h to obtain a flame-retardant superhydrophobic polyurethane material containing benzoxazine.

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