Boron nitride modified waterborne polyurethane coating with high mechanical property and preparation method thereof

Abstract

The invention belongs to the technical field of high polymer materials, and particularly relates to a boron nitride modified waterborne polyurethane coating with high mechanical property and a preparation method thereof. Through in-situ polymerization of dopamine on the surface of graphene oxide, abundant active groups are introduced, and covalent crosslinking of graphene oxide and waterborne polyurethane is enhanced; meanwhile, the surfactant modified boron nitride nanosheet and the coated modified graphene oxide form a three-dimensional heterostructure through hydrogen bonds and electrostatic interaction, and a multi-stage enhanced network is constructed in a polyurethane matrix. The method not only solves the problem of dispersion of the nanofiller, but also optimizes stress distribution through a brick-mud structure, and significantly improves the mechanical properties and wear resistance of the coating. Compared with traditional single filler modification, the technology realizes the synergistic breakthrough of filler-matrix interface performance and macroscopic mechanical performance, and provides a new idea for development of high-performance waterborne polyurethane coatings.

Description

Technical Field

[0001] The invention belongs to the technical field of waterborne polyurethane coatings, and particularly relates to a boron nitride-modified waterborne polyurethane coating with high mechanical properties and a preparation method thereof. Background Art

[0002] As an environmentally friendly polymer material, waterborne polyurethane (WPU) is widely used in coatings, adhesives, leather finishing, and other fields due to its water-based dispersion medium, non-toxicity, non-flammability, and low volatile organic compound (VOC) content. However, traditional waterborne polyurethane films exhibit numerous challenges after film formation, such as poor mechanical properties, insufficient wear resistance, and limited heat resistance, which restrict their application in high-end industrial fields.

[0003] To enhance the mechanical properties of waterborne polyurethane (WPU), researchers have attempted to incorporate nanomaterials (such as carbon nanotubes, graphene, and inorganic clays) into the WPU matrix. However, these nanomaterials exhibit poor interfacial compatibility with WPU and are prone to agglomeration, resulting in uneven dispersion and, consequently, inability to fully exert their reinforcing properties. For example, while the direct addition of unmodified nanomaterials can improve WPU performance to a certain extent, dispersibility issues still hinder further optimization of its mechanical properties. Furthermore, while traditional methods improve mechanical properties, they often overlook the balance of comprehensive coating properties, such as heat resistance and corrosion resistance.

[0004] In recent years, boron nitride (BN) has been recognized as a promising nano-reinforcement material due to its excellent thermal conductivity, high mechanical strength, and chemical stability. However, the dispersibility and interfacial bonding ability of BN nanosheets in polymer matrices still require improvement through effective surface modification. While existing studies have attempted to improve the dispersibility of BN by modifying it with surfactants, these efforts have primarily focused on the introduction of a single nanomaterial and lack in-depth exploration of the synergistic enhancement mechanisms of multiple components, particularly how to comprehensively enhance the overall performance of WPU through interface design and the construction of multi-level cross-linked networks.

[0005] Therefore, developing a water-based polyurethane modification method that can effectively solve the dispersibility of nanomaterials, interfacial compatibility and synergistic improvement of multiple properties has become a technical problem that needs to be solved urgently in this field. Summary of the Invention

[0006] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a high-mechanical-performance boron nitride-modified waterborne polyurethane coating and a preparation method thereof. By in-situ polymerization of dopamine on the surface of graphene oxide, abundant active groups are introduced to enhance the covalent cross-linking between graphene oxide and waterborne polyurethane. At the same time, surfactant-modified boron nitride nanosheets form a three-dimensional heterostructure with the coated modified graphene oxide through hydrogen bonding and electrostatic interaction, thereby constructing a multi-level reinforced network in the polyurethane matrix. This method not only solves the dispersion problem of nanofillers, but also optimizes the stress distribution through the "brick-mud" structure, significantly improving the mechanical properties and wear resistance of the coating. Compared with traditional single filler modification, this technology achieves a synergistic breakthrough in the filler-matrix interface performance and macroscopic mechanical properties, providing a new approach for the development of high-performance waterborne polyurethane coatings.

[0007] The technical solutions adopted by the present invention to achieve the above-mentioned purpose are: A method for preparing a boron nitride-modified waterborne polyurethane coating with high mechanical properties comprises the following steps: Step S1: adding graphene oxide to Tris-HCl buffer, ultrasonically dispersing for 20-40 minutes, then adding dopamine hydrochloride, stirring at room temperature for 10-14 hours, centrifuging, washing, and re-dispersing to obtain a coated modified graphene oxide dispersion; Step S2: dissolving sodium dodecyl sulfate in deionized water, adding boron nitride powder, performing ultrasonic exfoliation, and centrifuging to obtain a boron nitride dispersion; uniformly mixing the coated modified graphene oxide dispersion and the boron nitride dispersion, stirring at room temperature for 0.5-2.5 hours, ultrasonicating for 20-40 minutes, centrifuging, washing, and re-dispersing to obtain a modified boron nitride dispersion; Step S3: dilute the aqueous polyurethane emulsion to a solid content of 20-25wt%, stir for 5-15 minutes to obtain a mixed solution, then add the modified boron nitride dispersion, continue stirring for 1.5-2.5 hours, add the HDI trimer after ultrasonic treatment, stir for 20-40 minutes to obtain a premixed emulsion, apply the premixed emulsion on the substrate, and heat treat to obtain the product.

[0008] The above-mentioned preparation process modifies graphene oxide (GO) with polydopamine, composites it with boron nitride (BN), and then introduces it into a waterborne polyurethane (WPU) system, ultimately forming a polyurethane composite coating with high mechanical properties. The core mechanism lies in the spontaneous polymerization of dopamine under weak alkaline conditions to form polydopamine (PDA), which tightly coats the surface of GO through π-π stacking and hydrogen bonding, significantly improving the dispersion and interfacial bonding of GO. Furthermore, after ultrasonic exfoliation, the boron nitride modified with sodium dodecyl sulfate exposes more active edge sites, which form a three-dimensional heterostructure with the polydopamine-modified GO through hydrogen bonding and electrostatic adsorption. This structure acts as a nano-reinforcement phase in the WPU matrix, effectively improving the interfacial compatibility and dispersibility of the inorganic nanomaterial with WPU, preventing agglomeration, and enhancing the performance of the composite coating through multiple mechanisms.

[0009] Furthermore, in step S1, the amount of graphene oxide added to the Tris-HCl buffer is 0.07-0.14 mg / mL, the mass ratio of graphene oxide to dopamine hydrochloride is 1:1.5-2.5, and the concentration of the coated modified graphene oxide dispersion is 0.4-0.6 mg / mL.

[0010] Furthermore, in step S2, the mass ratio of sodium lauryl sulfate, deionized water, and boron nitride powder is 5-15:950-1000:5, the volume ratio of the coated modified graphene oxide dispersion to the boron nitride dispersion is 1:10-20, and the concentration of the modified boron nitride dispersion is 0.5-1.5 mg / mL.

[0011] Furthermore, in step S3, the mass ratio of the mixed solution, the modified boron nitride dispersion, and the HDI trimer is 20:10-15:0.04-0.10.

[0012] The present invention has the following beneficial effects: The present invention modifies graphene oxide with polydopamine, compounds it with boron nitride, and then introduces a waterborne polyurethane system to ultimately form a polyurethane composite coating with excellent overall performance. Its core mechanism lies in the following aspects: (1) The catechol groups of polydopamine react with the amino / hydroxyl groups of the waterborne polyurethane chain segments to form covalent crosslinking points, while the lamellar structure of boron nitride restricts the movement of the waterborne polyurethane molecular chains through physical entanglement and hydrogen bonding, synergistically improving the crosslinking density of the coating. This multi-level crosslinking network significantly enhances the mechanical properties of the coating.

[0013] (2) Two-dimensional nanosheets of graphene oxide and boron nitride are arranged in parallel in a water-based polyurethane matrix, and the flexible polyurethane chains fill the gaps between the nanosheets to form a "brick-mud" structure. Under the action of external forces, this structure can effectively disperse stress and hinder crack propagation, thereby greatly improving the wear resistance and impact resistance of the coating.

[0014] (3) The high thermal conductivity of boron nitride can accelerate heat transfer during the curing process, promote its uniform cross-linking with HDI trimer and waterborne polyurethane, and reduce local defects. This not only improves the heat resistance of the coating, but also further enhances its mechanical properties and corrosion resistance.

[0015] In summary, the present invention significantly improves the wear resistance, mechanical properties, corrosion resistance and heat resistance of waterborne polyurethane coatings by combining polydopamine-modified graphene oxide with boron nitride, combined with the design of a multi-stage cross-linked network and a "brick-mud" structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for describing the embodiments or the prior art.

[0017] Figure 1 This is the dispersed state of the premixed emulsion prepared in Example 1 after standing at room temperature for 15 days.

[0018] Figure 2 This is the SEM image of the polyurethane coating prepared in Example 1.

[0019] Figure 3 These are the stress-strain curves of the polyurethane coatings prepared in Example 1 (BN / WPU) and Comparative Example 3 (WPU). DETAILED DESCRIPTION

[0020] The following will be combined with the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the embodiments described are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments of the present application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0021] Graphene oxide, active ingredient content > 99%, diameter 0.5-3 μm, thickness 0.55-1.2 nm, purchased from Zhongke Leiming (Beijing) Technology Co., Ltd.; boron nitride powder, purity > 99%, 50 nm, model 00878, purchased from Qinghe Chaotai Metal Materials Co., Ltd.; aqueous polyurethane emulsion, solid content 50±1%, density 1.06 g / mL, brand FS-1551, purchased from Anhui Feimiao Chemical Co., Ltd.; HDI trimer, Lanxess Trixene BI 200, pH 7-8, purchased from Guangzhou Haoyi New Materials Technology Co., Ltd. The raw materials used in the following examples are all common commercially available products.

[0022] Example 1 A method for preparing a boron nitride-modified waterborne polyurethane coating with high mechanical properties comprises the following steps: Step S1: adding graphene oxide to a Tris-HCl buffer solution with a pH of 8.5, placing the solution in an ice-water bath, and ultrasonically dispersing the solution for 30 minutes using a probe ultrasonicator (power of 200 W, pulse mode: working for 2 seconds, interval of 2 seconds, avoid overheating during the ultrasonic process, and maintain the temperature of the ice bath at ≤25°C), then adding dopamine hydrochloride, stirring the solution in the dark at room temperature and 500 rpm for 12 hours, until the color of the mixed solution gradually changes from brown to dark brown. After the reaction, the reaction mixture is transferred to a centrifuge tube and centrifuged at 8000 rpm for 15 minutes. The supernatant is discarded, and the solution is centrifuged and washed three times with deionized water. Finally, the solution is redispersed in deionized water and ultrasonically dispersed for 5 minutes at a power of 300 W to obtain a coated modified graphene oxide dispersion. The amount of graphene oxide added to the Tris-HCl buffer solution is 0.1 mg / mL, the mass ratio of graphene oxide to dopamine hydrochloride is 1:2, and the concentration of the coated modified graphene oxide dispersion is 0.5 mg / mL. Step S2: Sodium dodecyl sulfate was dissolved in deionized water, and then boron nitride powder was added. In an ice bath, the solution was ultrasonicated for 1 hour using a probe ultrasonicator (power of 300W, pulse mode: working 2s, interval 2s). After ultrasonication, the solution became a milky white homogeneous suspension (avoid overheating during ultrasonication, and the ice bath temperature was maintained at ≤25°C). The solution was centrifuged at low speed (3000rpm, 5min), and the supernatant was retained. The concentration of the supernatant was adjusted to 0.1mg / mL to obtain a boron nitride dispersion. The coated modified graphene oxide dispersion and the boron nitride dispersion were evenly mixed and stirred at 500rpm at room temperature. The mixture was stirred for 2 hours, and then further homogenized by water bath sonication for 30 minutes (power of 200 W). The reaction mixture was centrifuged at 8000 rpm for 15 minutes, the supernatant was discarded, and the mixture was centrifuged and washed three times with deionized water. Finally, the mixture was redispersed in deionized water and sonicated for 5 minutes at a power of 300 W to obtain a modified boron nitride dispersion. The mass ratio of sodium dodecyl sulfate, deionized water, and boron nitride powder was 10:990:5, the volume ratio of the coated modified graphene oxide dispersion to the boron nitride dispersion was 1:15, and the concentration of the modified boron nitride dispersion was 1 mg / mL. Step S3: diluting the aqueous polyurethane emulsion to a solid content of 20wt%, stirring at 500rpm for 10min to obtain a mixed solution, adding the modified boron nitride dispersion, continuing to stir at 1000rpm for 2h in the dark at room temperature, then ultrasonicating in a water bath for 15min (power of 100W), then adding HDI trimer, stirring at 200rpm for 30min to obtain a premixed emulsion, wiping the glass substrate with ethanol and drying, adjusting the gap of the scraper to 150μm, and evenly scraping the premixed emulsion on the substrate at a scraping speed of 5mm / s. After the scraping is completed, it is first allowed to air at room temperature for 30min, then cured at 80°C for 2h, and then treated at 120°C for 30min. The humidity is maintained at 50±5% during curing to obtain the product; wherein the mass ratio of the mixed solution, modified boron nitride dispersion, and HDI trimer is 20:15:0.08.

[0023] The premixed emulsion prepared in this example was left to stand at room temperature (25±2°C) for 15 days, and the dispersion state of the premixed emulsion was observed. The results were as follows: Figure 1 As shown. Figure 1 It can be seen that the premixed emulsion has good dispersion stability and can be maintained without sedimentation for 15 days.

[0024] Example 2 A method for preparing a boron nitride-modified waterborne polyurethane coating with high mechanical properties is prepared according to the method described in Example 1, except that the mass ratio of graphene oxide to dopamine hydrochloride in step S1 is 1:1.5.

[0025] Example 3 A method for preparing a boron nitride-modified waterborne polyurethane coating with high mechanical properties is prepared according to the method described in Example 1, except that the volume ratio of the coated modified graphene oxide dispersion to the boron nitride dispersion in step S2 is 1:20.

[0026] Example 4 A method for preparing a boron nitride-modified waterborne polyurethane coating with high mechanical properties is prepared according to the method described in Example 1, except that the mass ratio of the mixed liquid, modified boron nitride dispersion, and HDI trimer in step S3 is 20:10:0.08.

[0027] Comparative Example 1 A method for preparing a boron nitride-modified waterborne polyurethane coating with high mechanical properties is prepared according to the method described in Example 1, except that step S1 is omitted, the coated modified graphene oxide dispersion in step S2 is replaced by a graphene oxide dispersion, the concentration of the graphene oxide dispersion is 0.5 mg / mL, and the volume ratio of the graphene oxide dispersion to the boron nitride dispersion is 1:15.

[0028] Comparative Example 2 A method for preparing a boron nitride-modified waterborne polyurethane coating with high mechanical properties comprises the following steps: Sodium dodecyl sulfate was dissolved in deionized water, and then boron nitride powder was added. The mixture was ultrasonicated for 1 hour using a probe ultrasonicator (power of 300W, pulse mode: working for 2s, interval of 2s) under ice bath conditions. After ultrasonication, the solution became a milky white homogeneous suspension (avoid overheating during ultrasonication, and keep the temperature of the ice bath ≤25°C). The mixture was centrifuged at low speed (3000rpm, 5min), and the supernatant was retained. The concentration of the supernatant was adjusted to 1mg / mL to obtain a boron nitride dispersion. The aqueous polyurethane emulsion was diluted to a solid content of 20wt%, and stirred at 500rpm for 10min to obtain a mixed solution, and the boron nitride dispersion was then added. The mixture was stirred at 1000 rpm for 2 h at room temperature in the dark, then subjected to water bath ultrasound for 15 min (power of 100 W), and then HDI trimer was added and stirred at 200 rpm for 30 min. The glass substrate was wiped with ethanol and dried, and the gap of the scraper was adjusted to 150 μm. The mixed emulsion obtained by the reaction was evenly scraped on the substrate at a scraping speed of 5 mm / s. After the scraping was completed, it was allowed to air at room temperature for 30 min, and then cured at 80°C for 2 h, and then treated at 120°C for 30 min to obtain the product. The mass ratio of the mixed liquid, boron nitride dispersion, and HDI trimer was 20:15:0.08.

[0029] Comparative Example 3 A method for preparing a boron nitride-modified waterborne polyurethane coating with high mechanical properties comprises the following steps: The aqueous polyurethane emulsion was diluted to a solid content of 20 wt %, stirred at 500 rpm for 10 min to obtain a mixed solution, and then HDI trimer was added and stirred at 200 rpm for 30 min. The glass substrate was wiped with ethanol and dried, and the gap of the scraper was adjusted to 150 μm. The mixed emulsion obtained by the reaction was evenly scraped on the substrate at a scraping speed of 5 mm / s. After the scraping was completed, it was first allowed to air at room temperature for 30 min, and then cured at 80° C. for 2 h, and then treated at 120° C. for 30 min to obtain the product; wherein, the mass ratio of the mixed solution to the HDI trimer was 20:0.08.

[0030] The waterborne polyurethane coating prepared in Example 1 was subjected to SEM testing. The sample was cut into small pieces of 5 mm × 5 mm and fixed on the sample stage with conductive glue. The sample surface was gold-sprayed using an ion sputtering instrument. The micromorphology of the sample was observed using a scanning electron microscope (SEM). The results are as follows: Figure 2 As shown. Figure 2 It can be seen that there are no obvious defects on the coating surface, the nanofillers are evenly dispersed without large-size agglomerations, and they have good interface bonding with the WPU matrix and can be evenly embedded in the WPU matrix.

[0031] The mechanical properties of the polyurethane coatings prepared in Example 1 and Comparative Example 3 were tested. The coating samples were cut into dumbbell-shaped specimens according to GB / T1040.3-2006 standard with dimensions of 25 mm × 4 mm × 0.15 mm. The specimens were balanced at 23 ± 2 ° C and 50 ± 5% humidity for 24 h and tested using a universal material testing machine. The test conditions were: tensile rate 10 mm / min, gauge length 20 mm, preload force 0.1 N, and stress-strain curves were recorded. At least three parallel specimens were tested for each group of samples, and the average value was taken. The results are shown in Figure 2. Figure 3 shown. Figure 3 The stress-strain curve shows that compared with WPU (Comparative Example 3), the mechanical properties of the polyurethane coating prepared in Example 1 (BN / WPU) are significantly improved, with the Young's modulus increased by about 4 times and the tensile strength increased by about 3.6 times.

[0032] Relevant performance tests were performed on the high mechanical performance boron nitride modified waterborne polyurethane coatings prepared in Examples 1-4 and Comparative Examples 1-3. The wear resistance test was conducted in accordance with GB / T 1768-2006 "Paints and varnishes - Determination of abrasion resistance - Rotating rubber grinding wheel method" with a load of 500 g and a rotation speed of 500 rpm, and the wear volume of the sample was recorded. The impact resistance test was conducted in accordance with GB / T 19250-2013 "Polyurethane waterproof coatings" under the test conditions of 1 kg·m. The corrosion resistance test was conducted in accordance with GB / T 1771-2007 "Paints and varnishes - Determination of resistance to neutral salt spray" with a salt solution concentration of 5 wt% NaCl. The thermal stability test was conducted using a NETZSCH thermogravimetric analyzer to determine the thermal decomposition temperature of the sample. A 10 mg sample was taken and the test was conducted under nitrogen with a heating rate of 10°C / min and a temperature range of 30-500°C. The temperature corresponding to a 5% mass loss of the material was recorded as the thermal decomposition temperature (T5%) of the material. The above tests were repeated three times and the average value was obtained. The test results are shown in Table 1.

[0033] Table 1 Test results of relevant properties of polyurethane coatings Table 1 compares the coating properties of Examples 1-4 and Comparative Examples 1-3, showing that the present invention significantly improves the comprehensive properties of the waterborne polyurethane coating by composite modification of polydopamine-modified graphene oxide and boron nitride. The specific analysis is as follows: The wear losses of Examples 1-4 (7.7-8.6 mg) were significantly lower than those of the comparative examples (10.4-13.1 mg). Example 1 exhibited the best wear resistance, with a wear loss of only 58.8% of that of Comparative Example 3 (pure WPU). This is due to the two-dimensional graphene oxide (GO) and boron nitride (BN) nanosheets forming a "brick-and-mortar" structure within the WPU matrix, which disperses stress and inhibits crack propagation. Furthermore, the polydopamine-modified GO, through covalent crosslinking (catechol groups reacting with WPU amino / hydroxyl groups) and physical entanglement with BN (hydrogen bonding), increases the crosslink density and reduces molecular chain slip. The wear loss of Example 2 (GO to dopamine hydrochloride mass ratio of 1:1.5) was slightly higher than that of Example 1, indicating that insufficient dopamine hydrochloride dosage weakens GO dispersion and interfacial bonding. The wear losses of Examples 3 (GO to BN volume ratio of 1:20) and 4 (reduced modified BN dosage) increased, indicating that either excessive or insufficient BN dosage can compromise the synergistic reinforcement effect.

[0034] Examples 1-4 all withstood a 1 kg·m impact without noticeable damage, whereas Comparative Example 1 (unmodified GO) and Comparative Example 2 (unmodified BN) exhibited wrinkles, and Comparative Example 3 (pure WPU) cracked directly. This demonstrates that the multi-stage crosslinked network (covalent bonds + physical entanglement) and the "stress buffering effect" of the nanosheet layers enable the coating to effectively absorb impact energy. The unmodified GO in Comparative Example 1 easily agglomerated, leading to stress concentration; while the unmodified BN in Comparative Example 2 exhibited insufficient dispersion, weak interfacial bonding, and limited deformation resistance.

[0035] The salt spray resistance time of Examples 1-4 (2380-2450h) is significantly higher than that of Comparative Examples 1-3 (1800-2210h), among which Example 1 has the best corrosion resistance, which is 36.1% higher than that of Comparative Example 3. The chemical stability of BN and the barrier effect of GO can block corrosive media (such as Cl - ) penetration. The dense cross-linked network reduces the coating's porosity, further inhibiting corrosion pathways. The slightly lower salt spray resistance in Example 4 is due to insufficient use of modified BN, which weakens the barrier effect.

[0036] The thermal decomposition temperatures (T5%) of Examples 1-4 ranged from 299.3 to 318.8°C, significantly higher than those of Comparative Examples 1-3 (256.4 to 284.1°C). Example 1 exhibited the best heat resistance, achieving a 62.4°C improvement over Comparative Example 3. This indicates that BN's high thermal conductivity accelerates uniform heat distribution during curing, promoting full crosslinking between the HDI trimer and WPU and reducing local defects. Furthermore, polydopamine (PDA)-modified GO further enhances intermolecular forces through π-π stacking, improving the thermal stability of the composite. The lower T5% of Example 3 (GO to BN volume ratio of 1:20) is due to the high BN ratio, which reduces the dispersion of the nanofiller in the WPU matrix and weakens the synergistic effect.

[0037] In summary, both polydopamine-modified GO and surfactant-modified BN improve the dispersibility of nanofillers in WPU, preventing agglomeration and forming strong interfacial bonds (covalent bonding, hydrogen bonding, and electrostatic interactions). The polydopamine-modified GO and BN form a three-dimensional heterostructure, acting as a "nano-reinforcement phase" to increase crosslink density. This "brick-and-mortar" structure optimizes stress distribution and synergistically enhances the mechanical properties, wear resistance, corrosion resistance, and heat resistance of the composite material. This invention, through multi-component synergistic modification, overcomes the performance bottleneck of a single filler and provides an effective path for the development of high-performance waterborne polyurethane coatings.

[0038] Although the embodiments of the present application have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations may be made to these embodiments without departing from the principles and spirit of the present application, and the scope of the present application is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a high mechanical performance boron nitride modified waterborne polyurethane coating, characterized in that: The following steps are involved: Step S1: adding graphene oxide to Tris-HCl buffer, ultrasonically dispersing for 20-40 minutes, then adding dopamine hydrochloride, stirring at room temperature for 10-14 hours, centrifuging, washing, and re-dispersing to obtain a coated modified graphene oxide dispersion; Step S2: dissolving sodium dodecyl sulfate in deionized water, adding boron nitride powder, performing ultrasonic exfoliation, and centrifuging to obtain a boron nitride dispersion; uniformly mixing the coated modified graphene oxide dispersion and the boron nitride dispersion, stirring at room temperature for 0.5-2.5 hours, ultrasonicating for 20-40 minutes, centrifuging, washing, and re-dispersing to obtain a modified boron nitride dispersion; Step S3: dilute the aqueous polyurethane emulsion to a solid content of 20-25wt%, stir for 5-15 minutes to obtain a mixed solution, then add the modified boron nitride dispersion, continue stirring for 1.5-2.5 hours, add the HDI trimer after ultrasonic treatment, stir for 20-40 minutes to obtain a premixed emulsion, apply the premixed emulsion on the substrate, and heat treat to obtain the product.

2. The method for preparing the high mechanical performance boron nitride modified waterborne polyurethane coating according to claim 1, characterized in that: The amount of graphene oxide added to the Tris-HCl buffer in step S1 is 0.07-0.14 mg / mL.

3. The method for preparing the high mechanical performance boron nitride modified waterborne polyurethane coating according to claim 1, characterized in that: The mass ratio of graphene oxide to dopamine hydrochloride in step S1 is 1:1.5-2.

5.

4. The method for preparing the high mechanical property boron nitride modified waterborne polyurethane coating according to claim 1, characterized in that: The concentration of the coated modified graphene oxide dispersion in step S1 is 0.4-0.6 mg / mL.

5. The method for preparing the high mechanical performance boron nitride modified waterborne polyurethane coating according to claim 1, characterized in that: The mass ratio of sodium lauryl sulfate, deionized water, and boron nitride powder in step S2 is 5-15:950-1000:

5.

6. The method for preparing the high mechanical property boron nitride modified waterborne polyurethane coating according to claim 1, characterized in that: The volume ratio of the coated modified graphene oxide dispersion to the boron nitride dispersion in step S2 is 1:10-20.

7. The method for preparing the high mechanical property boron nitride modified waterborne polyurethane coating according to claim 1, characterized in that: The concentration of the modified boron nitride dispersion in step S2 is 0.5-1.5 mg / mL.

8. The method for preparing the high mechanical property boron nitride modified waterborne polyurethane coating according to claim 1, characterized in that: The mass ratio of the mixed solution, modified boron nitride dispersion, and HDI trimer in step S3 is 20:10-15:0.04-0.

10.

9. A boron nitride modified waterborne polyurethane coating with high mechanical properties prepared according to the method according to any one of claims 1 to 8.

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