Preparation method and application of boron nitride nanosheet and composite material thereof

Abstract

The application discloses a method for preparing functionalized boron nitride nanosheets by means of sugar-assisted ball milling-microjet cooperative stripping and application thereof. Hexagonal boron nitride powder, a sugar additive and water are mixed, and after pretreatment by mechanical ball milling, the mixture is subjected to high-pressure microjet deep stripping, and functionalized BNNSs are obtained by stepwise centrifugal purification; the functionalized BNNSs are blended with epoxy resin to be cured, and a composite anticorrosion coating and a heat-conducting sheet are prepared. The obtained nanosheets have a thickness of 2.6-3.6 nm and a yield of 63.87%. The 0.5 wt% anticorrosion coating has a corrosion inhibition efficiency of 99.85%, and the salt spray T3% is up to 43 days; the 30 wt% heat-conducting sheet has a heat conductivity coefficient of 1.1341 W / (m.K), which is increased by 516.69% compared with that of pure epoxy resin.

Description

Technical Field

[0001] This invention belongs to the field of inorganic nanomaterial synthesis and composite material application, specifically involving a method for preparing functionalized boron nitride nanosheets using sugars as exfoliation aids and functionalizing reagents through a stepwise synergistic strategy of "mechanical ball milling pretreatment - high-pressure micro-jet deep exfoliation", and the application of the functionalized boron nitride nanosheets in oily epoxy resin systems to construct composite anti-corrosion coatings and composite thermally conductive sheets.

[0002] This invention relates to IPC classifications: C01B 35 / 14 (Preparation of boron nitride); C09D 163 / 00 (Epoxy resin coating composition); C09D 5 / 08 (Anti-corrosion coating); C09D 7 / 62 (Filler for coating); C08K 3 / 38 (Boron-containing inorganic compound filler); C08L 63 / 00 (Epoxy resin composition). Background Technology

[0003] With the increasing demand for multifunctional materials in high-power-density electronic devices and complex industrial environments, the application of polymer-based composite materials in thermal management and corrosion protection faces severe challenges. Traditional encapsulation materials and anti-corrosion coatings, such as epoxy resin (EP), are widely used due to their excellent insulation, corrosion resistance, and processability. However, pure epoxy resin has inherent defects such as microporosity after curing, which allows corrosive media to easily penetrate and cause under-film corrosion; at the same time, its intrinsic thermal conductivity is extremely low (approximately 0.18 W / (m·K)), making it difficult to meet the heat dissipation requirements of modern highly integrated electronic devices.

[0004] Among numerous two-dimensional nanofillers, hexagonal boron nitride (h-BN) and its exfoliated boron nitride nanosheets (BNNSs) possess ultra-high intrinsic thermal conductivity (theoretical value approximately 2000 W / (m·K)), excellent electrical insulation (band gap approximately 5.9 eV), and chemical inertness (oxidation resistance in air up to 850℃). Introducing them into polymer matrices can simultaneously construct a dense physical barrier "labyrinth network" that resists media penetration, as well as highly efficient phonon transport channels.

[0005] In practical applications of two-dimensional nanofillers, the number of filler layers and their thickness have a specific correlation with the enhancement effect on different properties. On the one hand, in corrosion protection applications, ultrathin BNNSs with a large aspect ratio can construct a dense, tortuous "labyrinth effect" physical barrier network within the coating, greatly extending the barrier life of corrosive media (H2O, O2, Cl-). -The permeation path of h-BN is thus directly interrupted, thereby cutting off the formation of corrosion galvanic cells. On the other hand, in thermal conductivity applications, considering the characteristics of the mean free path of h-BN phonons, its intrinsic thermal conductivity increases with the number of layers within a certain range. Therefore, by utilizing functionalized nanosheets with an appropriate number of layers and a continuous two-dimensional network structure, continuous and efficient heat conduction pathways can be constructed within the resin matrix, while functionalization modification can effectively reduce the interfacial thermal resistance between the filler and the matrix.

[0006] However, BNNSs are currently severely limited in practical applications: on the one hand, the interlayer van der Waals forces and "Lip-Lip" polar interactions of h-BN are strong (interlayer binding energy is about 56.7 meV / atom), the yield of traditional liquid-phase ultrasonic exfoliation is low (usually <10%), long-term ball milling is prone to damaging the lattice and often uses toxic organic solvents (such as N-methylpyrrolidone, dimethylformamide); on the other hand, the surface of unmodified BNNSs lacks active groups, which are very easy to recombine and agglomerate in the resin, resulting in extremely poor interfacial compatibility. The introduced thermal resistance and voids will degrade the performance of the composite material.

[0007] In the prior art, Chen et al. (Chen S, Xu R, Liu J, et al., , Advanced Materials A 2019 paper reported a sucrose-assisted mechanochemical exfoliation (SAMCE) method, using sucrose as a ball milling aid to simultaneously exfoliate and functionalize h-BN nanosheets via planetary ball milling for 8 hours, achieving a yield of 87.3%. This method uses sucrose as a water-soluble, green aid, making it environmentally friendly. However, the pure ball milling method has the following drawbacks: the direct impact of the milling beads during long-term ball milling can easily introduce lattice defects into the BNNSs, affecting the lattice integrity of the nanosheets; the resulting BNNSs have a wide thickness distribution; and the process control freedom is limited, making it difficult to independently optimize the degree of exfoliation and functionalization.

[0008] Guerra et al. (Guerra V, Wan C, et al., , Nanoscale (2018) first reported a method for preparing BNNSs using an industrial-grade high-pressure homogenizer, but this method directly uses untreated h-BN as raw material, resulting in limited stripping efficiency and no surface functionalization involved.

[0009] Wang et al. Nano Research (2022) reported a glucose-assisted ball milling-ultrasound combination strategy, but ultrasound and microfluidics have fundamental differences in stripping mechanism, scalability and product uniformity.

[0010] Furthermore, in the field of BNNSs / epoxy resin composite anti-corrosion coatings, existing technologies (such as polypyrrole-functionalized BNNSs / epoxy coatings, BNNSs-carbon dot hybrid / epoxy coatings, etc.) mostly employ synthetic polymers or nano-hybrid materials to functionalize BNNSs, resulting in complex preparation processes. The problem of achieving long-lasting, high-barrier anti-corrosion performance with extremely low filler addition (e.g., 0.5 wt%) while maintaining coating adhesion has not yet been fully resolved.

[0011] In the field of BNNSs / epoxy resin thermally conductive composites, existing technologies either modify h-BN using the SAMCE method to directly fill epoxy resin, resulting in limited improvement in thermal conductivity (e.g., a thermal conductivity of approximately 0.51 W / (m·K) at a 15 wt% filler content); or achieve higher thermal conductivity by constructing a three-dimensional BNNSs framework, but this process is complex and not conducive to large-scale production. There is still room for improvement in simple methods that achieve higher thermal conductivity without relying on complex three-dimensional framework construction and only through simple blending.

[0012] Therefore, developing a green preparation process that balances high yield, high quality, surface functionalization, and environmental friendliness, and on this basis, achieving the simple preparation of high-performance anti-corrosion coatings and thermally conductive composite materials, is the core technological challenge for promoting the large-scale application of BNNSs. Summary of the Invention

[0013] This invention proposes a method for preparing functionalized boron nitride nanosheets and their composite materials. Natural and environmentally friendly sugar molecules are used as exfoliation aids and functionalizing agents. A stepwise synergistic strategy of "mechanical ball milling-high-pressure microfluidic homogenization" is employed to achieve hydroxyl functionalization of h-BN surface simultaneously through green exfoliation. Subsequently, the functionalized BNNSs are introduced into an oil-based epoxy resin system, effectively solving the problems of easy agglomeration and poor interfacial compatibility of inorganic fillers. The raw materials used in this invention are widely available and inexpensive, and the process is stable and easily scaled up.

[0014] I. Technical problems to be solved In view of the shortcomings of the prior art, the technical problem to be solved by the present invention is: (1) On the premise of ensuring the integrity of the BNNSs lattice, an efficient, green and scalable method for preparing functional boron nitride nanosheets is provided to overcome the problems of large lattice damage, uneven thickness and limited control freedom of the existing pure ball milling method, as well as the limited exfoliation efficiency and inability to simultaneously functionalize the pure high pressure homogenization method. (2) Using sugars as the sole stripping agent and functionalizing reagent, and water as the sole stripping medium, the use of organic solvents and toxic reagents is avoided, thus achieving green preparation; (3) Provides an epoxy resin composite anti-corrosion coating based on sugar functionalized BNNSs, which has excellent long-term anti-corrosion performance (corrosion inhibition efficiency ≥99.85%, salt spray T3% ≥40 days) and good coating adhesion at ultra-low filler addition (0.5 wt%). (4) Provides an epoxy resin composite thermally conductive sheet based on sugar functionalized BNNSs, which can achieve a thermal conductivity of ≥1.0 W / (m·K) through a simple blending process.

[0015] II. Technical Solution The objective of this invention can be achieved through the following technical solutions: (I) Preparation of Functionalized Boron Nitride Nanosheets This invention provides a method for preparing functionalized boron nitride nanosheets, comprising the following steps: (1) Hexagonal boron nitride powder, a sugar auxiliary agent, and deionized water are mixed to obtain a mixed suspension. The preferred mass ratio of h-BN powder, sugar auxiliary agent, and deionized water is 1:5:40. The sugar auxiliary agent is selected from at least one of sucrose or glucose, preferably sucrose. Sugar molecules contain abundant hydroxyl functional groups, which can be grafted onto the surface and edges of BNNSs through mechanochemical action during ball milling, simultaneously achieving exfoliation and surface hydroxyl functionalization.

[0016] (2) The mixed suspension is subjected to mechanical ball milling pretreatment to obtain a pre-modified suspension. The mechanical ball milling pretreatment is carried out in a planetary ball mill, preferably with grinding beads added as the grinding medium. The ball milling speed is 200-350 rpm, preferably 300 rpm; the ball milling time is 3-12 h, preferably 12 h. In this step, the ball milling process mainly plays the role of pre-modification and preliminary exfoliation: sugar molecules are grafted to the interlayer and edge of h-BN under the mechanical force of the grinding beads, while partial exfoliation is achieved.

[0017] (3) The pre-modified suspension is introduced into a high-pressure microjets homogenizer for multiple cycles (the pressure of the cycles is 150-300 MPa) to obtain a dispersion containing functionalized boron nitride nanosheets. The number of cycles is 10-20 times, preferably 15 times. The microjets process utilizes the cavitation effect, high-speed shearing, and turbulent collisions generated when high-speed fluid passes through micro-channels to deeply exfoliate and homogenize the ball-milled pre-modified BNNSs, while avoiding lattice damage caused by direct impact from the milling beads.

[0018] The synergistic effect between ball milling pre-modification and microfluidic deep exfoliation is the core feature that distinguishes this invention from existing single exfoliation methods (pure ball milling, pure ultrasound, pure high-pressure homogenization): the ball milling step completes the pre-intercalation and initial exfoliation of sugars, providing the subsequent microfluidic process with an h-BN precursor weakened by sugar molecule intercalation; the microfluidic step completes deep exfoliation and homogenization with non-contact fluid shear force, protecting the lattice integrity of BNNSs while ensuring exfoliation efficiency. The independent adjustability of the two process parameters (ball milling time + number of microfluidic cycles) provides greater controllability for optimizing product performance.

[0019] (4) The dispersion is separated and purified to obtain saccharide-functionalized boron nitride nanosheets. The separation and purification includes: centrifuging the dispersion at 2000-4000 rpm (preferably 3000 rpm, 10 min) to remove large unpeeled precipitate particles; taking the supernatant from the first centrifugation and centrifuging it at 8000-12000 rpm (preferably 10000 rpm, 10 min) to collect the precipitate; washing the precipitate 2-3 times with anhydrous ethanol and then vacuum drying it.

[0020] Preferably, the unstripped large particle precipitate obtained from the first centrifugation is recovered and mixed into the mixed suspension of the next batch in step (1) for recycling, so as to improve the utilization rate of raw materials and the economic efficiency of the process.

[0021] The functionalized boron nitride nanosheets (Sucrose-BNNSs) prepared by the above method have a thickness of 2.6–3.6 nm (approximately 7–11 atomic layers) and a lateral dimension of 100–300 nm, with a yield of 63.87% (sucrose system); the functionalized boron nitride nanosheets (Glucose-BNNSs) have a thickness of 3.3–5.5 nm (approximately 10–17 atomic layers) and a lateral dimension of 100–300 nm, with a yield of 59.37% (glucose system). The obtained BNNSs contain hydroxyl functional groups derived from sugar molecules on their surface, exhibiting good water dispersion stability and interfacial compatibility with the polymer matrix.

[0022] (II) Preparation of Functionalized Boron Nitride Nanosheets / Epoxy Resin Composite Anticorrosive Coating This invention provides a method for preparing a composite anti-corrosion coating, which further includes the following steps after obtaining functionalized BNNSs by the above method: The obtained functionalized BNNSs were ultrasonically dispersed in anhydrous ethanol to obtain a nanosheet dispersion. An oily epoxy resin (preferably bisphenol A type epoxy resin E-51) was heated to 40–60°C (preferably 50°C), and the nanosheet dispersion was slowly added dropwise under stirring. The temperature was maintained and stirring continued until the anhydrous ethanol completely evaporated. The temperature was lowered to 30–50°C (preferably 40°C), and a curing agent (preferably polyamide curing agent 650) was added and stirred until homogeneous, wherein the mass ratio of epoxy resin to curing agent was approximately 1:1. After standing to remove bubbles, the mixture was coated onto the surface of a metal substrate (such as carbon steel plate). The coating was cured at 50–70°C (preferably 60°C) for 2–4 h (preferably 3 h) to obtain a composite anti-corrosion coating.

[0023] When preparing the composite anti-corrosion coating, the mass ratio of the functionalized boron nitride nanosheets to the epoxy resin is 1-2:100; preferably, the amount of functionalized boron nitride nanosheets added is 0.5 wt% of the total mass of epoxy resin and curing agent.

[0024] At an ultra-low addition level of 0.5 wt%, the hydroxyl functional groups on the surface of sugar-functionalized BNNSs enhanced their interfacial compatibility with the epoxy resin matrix, enabling the nanosheets to be uniformly dispersed in the matrix and forming a dense "maze effect" physical barrier network. This significantly extended the barrier life of the nanosheets against corrosive media (H2O, O2, Cl). - The penetration path of ).

[0025] (III) Preparation of Functionalized Boron Nitride Nanosheets / Epoxy Resin Composite Thermally Conductive Sheets This invention provides a method for preparing composite thermally conductive thin films, which further includes the following steps after obtaining functionalized BNNSs by the above method: The obtained functionalized BNNSs were ultrasonically dispersed in anhydrous ethanol to obtain a nanosheet dispersion. An oily epoxy resin (preferably bisphenol A type epoxy resin E-51) was heated to 40–60°C (preferably 50°C), and a dispersant and the nanosheet dispersion were added under stirring. The temperature was maintained and stirring continued until the anhydrous ethanol completely evaporated. The temperature was lowered to 30–50°C (preferably 40°C), and a curing agent (preferably polyamide curing agent 650) was added and stirred until homogeneous, wherein the mass ratio of epoxy resin to curing agent was approximately 1:1. After standing to remove bubbles, the mixture was poured into a mold (such as a polytetrafluoroethylene mold). It was cured at 50–70°C (preferably 60°C) for 2–4 h (preferably 3 h) to obtain a composite thermally conductive sheet.

[0026] The dispersant is selected from at least one of DISPERBYK 111, DISPERBYK 163, and DISPERBYK 164, with DISPERBYK 163 being preferred. The mass ratio of the dispersant, functionalized boron nitride nanosheets, and epoxy resin is 1–5:20–90:100. When preparing the composite thermally conductive sheet, the amount of functionalized boron nitride nanosheets added is 10–30 wt% of the total mass of epoxy resin and curing agent. At an addition amount of 30 wt%, the thermal conductivity can reach 1.1341 W / (m·K).

[0027] At higher filler content (30 wt%), functionalized BNNSs construct a continuous phonon transport network in the matrix, while surface hydroxyl functionalization effectively reduces the interfacial thermal resistance (phonon scattering) between the filler and the matrix, thereby achieving a significant improvement in thermal conductivity.

[0028] III. Beneficial Effects Compared with the prior art, the present invention has the following beneficial effects: (1) Green synergistic exfoliation and functionalization: Inexpensive and environmentally friendly sucrose or glucose were used instead of toxic organic solvents, with water as the sole exfoliation medium. A stepwise synergistic strategy of "ball milling pre-intercalation / pre-modification + high-pressure microfluidic deep exfoliation" was employed to increase the yield of BNNSs to 63.87% (sucrose system), achieving large-scale green preparation. The polyhydroxyl structure of sugar molecules was coated onto the surface of BNNSs through mechanochemical action, not only endowing the nanosheets with excellent colloidal dispersion stability but also perfectly preserving the intrinsic two-dimensional crystal structure (HRTEM showed continuous and straight lattice fringes). The resulting functionalized BNNSs had a thickness of 2.6–3.6 nm and a lateral dimension of 100–300 nm.

[0029] (2) Excellent anti-corrosion performance: In anti-corrosion coating applications, an ultra-low addition of only 0.5 wt% forms a dense "maze effect" barrier network within the coating. Experimental data show that the corrosion current density Icorr of the 0.5 wt% Sucrose-BNNSs / EP composite anti-corrosion coating is 3.02 × cm⁻¹. 2 A / cm 2 Pureer EP coating (2.04×10) -7 A / cm 2 The corrosion rate was reduced by approximately three orders of magnitude, achieving a corrosion inhibition efficiency of 99.85%; the corrosion rate was 3.51 × 10⁻⁶. -6 mm / year, purer EP coating (2.37×10) -3The corrosion rate was reduced by about three orders of magnitude per year; in a continuous salt spray test with 5 wt% NaCl, the corrosion area after 14 days was only 1.299% (compared to 33.571% for pure EP), and the failure time (T3%) to reach 3% surface corrosion area was as long as 43 days; at the same time, the coating adhesion increased from 7.82 MPa for pure EP to 9.31 MPa (an increase of 19.1%), achieving a simultaneous improvement in corrosion resistance and adhesion.

[0030] (3) Excellent thermal conductivity: In the application of thermally conductive composite materials, the thermal conductivity of the 30 wt% Sucrose-BNNSs / EP composite thermally conductive sheet reaches 1.1341 W / (m·K), which is 516.69% higher than that of pure epoxy resin (0.1839 W / (m·K)). At the same 30 wt% filler content, the thermal conductivity of unmodified h-BN / EP is only 0.4918 W / (m·K) (an improvement of 167.43%), and the thermal conductivity enhancement effect of functionalized BNNSs is significantly better than that of unmodified h-BN (the improvement is about 3 times that of the latter). This invention does not rely on complex three-dimensional skeleton construction, and can achieve a thermal conductivity of >1 W / (m·K) simply through solution blending and casting curing.

[0031] (4) Simple process and easy to scale up: The method of this invention uses water as solvent and sugar as auxiliary agent, and the raw materials are cheap and readily available; the planetary ball mill and high-pressure micro-jet homogenizer are both mature and common industrial equipment; the unstripped precipitate can be recycled; the process steps are simple and the conditions are mild, and it has good industrial applicability. Attached Figure Description

[0032] Figure 1 A process flow diagram for the preparation of functionalized boron nitride nanosheets and their composites; Figure 2 This is a transmission electron microscope (TEM) image of the boron nitride nanosheets (Sucrose-BNNSs) prepared in Example 1; Figure 3 Atomic force microscopy (AFM) image of the boron nitride nanosheets (Sucrose-BNNSs) prepared in Example 1; Figure 4 The image shows the actual product of the composite anti-corrosion coating (0.5 wt% Sucrose-BNNSs / EP) prepared in Example 2. Figure 5 The image shows the actual composite thermally conductive sheet (30 wt% Sucrose-BNNSs / EP) prepared in Example 3. Detailed Implementation

[0033] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0034] In the following embodiments, unless otherwise specified, the raw materials, reagents or processing techniques are all conventional commercial products or conventional processing techniques in the art.

[0035] Raw material and equipment information The main raw materials used in the specific embodiments of the present invention include: - Hexagonal boron nitride powder: particle size of about 1 μm; - Sucrose: analytical grade; - Glucose: analytical grade; - Deionized water: laboratory-made; - Anhydrous ethanol: analytical grade; - Bisphenol A type epoxy resin E-51; - Type 650 polyamide curing agent; - DISPERBYK 163 dispersant.

[0036] The main equipment used includes: - a planetary ball mill with agate grinding jars and zirconium oxide (ZrO2) grinding beads; - a high-pressure micro-jet homogenizer (ultra-high pressure nano-crusher); - a high-speed centrifuge; - a vacuum drying oven; - an ultrasonic cleaner / ultrasonic disperser.

[0037] Testing and Characterization Methods Transmission electron microscopy (TEM) analysis: used to observe the morphology, size, and lattice fringes of BNNSs.

[0038] Atomic force microscopy (AFM) analysis: used to measure the thickness and lateral dimensions of BNNSs.

[0039] Electrochemical tests were performed using a three-electrode system in a 3.5 wt% NaCl solution. Tafel polarization curves were scanned over a range of ±250 mV relative to the open-circuit potential at a scan rate of 1 mV / s. Electrochemical impedance spectroscopy (EIS) was performed in the frequency range of 100 kHz to 0.01 Hz with a perturbation amplitude of 10 mV.

[0040] Salt spray test: Perform a continuous accelerated corrosion test with 5 wt% NaCl according to ASTM B117 standard, and record the change in corrosion area on the coating surface and the time when 3% of the rust area appears (T3%).

[0041] Adhesion test: The adhesion between the coating and the metal substrate is measured using a pull-out adhesion tester, and the test is conducted strictly in accordance with the ASTM D4541-22 standard.

[0042] Thermal conductivity testing: The laser flare method was used, and the test was conducted strictly in accordance with ASTM E1461 standard. The test sample was a thin sheet, approximately 3 mm thick.

[0043] Corrosion rate calculation: The corrosion rate (CR) is expressed in mm / year and is calculated using the following formula: CR = (M × Icorr × T × 10) / (n × ρ × F) Where M is the molar mass of Fe (55.85 g / mol), and Icorr is the measured corrosion current density (A / cm). 2 T is the total number of seconds in a year (31,536,000 s), n is the ionic valence state of Fe (usually taken as 2), and ρ is the density of the metal matrix (7.85 g / cm³). 3 F is the Faraday constant (96485 C / mol).

[0044] Corrosion inhibition efficiency calculation: Corrosion inhibition efficiency (IE) is expressed as a percentage (%) and is calculated using the following formula: IE = (I 0 corr - Icorr) / I 0 corr × 100% Among them, I 0 corr is the corrosion current density of the pure epoxy resin coating (Comparative Example 1), and Icorr is the corrosion current density of the coating to be tested.

[0045] Example Example 1: Preparation of sucrose-modified boron nitride nanosheets (Sucrose-BNNSs) Dissolve 5 g of sucrose in 40 g of deionized water, add 1 g of bulk h-BN powder (h-BN:sucrose:water = 1:5:40), and stir to disperse evenly. Transfer the mixture to an agate ball mill jar, add zirconium oxide (ZrO2) milling beads, and pre-treat by ball milling at 300 rpm for 12 h in a planetary ball mill to obtain a pre-modified suspension (product A).

[0046] The pre-modified suspension was transferred to a high-pressure micro-jet homogenizer (ultra-high pressure nano-crusher) and circulated 15 times to obtain a dispersion containing functionalized boron nitride nanosheets (product B).

[0047] The resulting dispersion was first centrifuged at 3000 rpm for 10 min to remove large particles that had not been separated from the precipitate; the supernatant was then centrifuged at 10000 rpm for 10 min to collect the precipitate. The precipitate was washed three times with anhydrous ethanol and then vacuum dried to obtain sucrose-functionalized boron nitride nanosheets (Sucrose-BNNSs).

[0048] The unremoved large particle precipitate collected during the first centrifugation (3000 rpm) can be recovered and mixed into the next batch of h-BN / sucrose / water mixed suspension for recycling.

[0049] Observational tests using TEM and AFM (see...) Figure 2 , Figure 3 The prepared Sucrose-BNNSs particles were confirmed to have a size range of 100–300 nm and a thickness range of 2.6–3.6 nm (corresponding to approximately 7–11 atomic layers). HRTEM images showed that the nanosheet lattice fringes were continuous and straight, indicating that the microfluidic treatment effectively protected the lattice integrity of the BNNSs while achieving deep exfoliation. Zeta potential testing showed that the Zeta potential of Sucrose-BNNSs was approximately -42.7 mV, indicating that the nanosheets exhibited excellent colloidal stability in aqueous dispersions. The yield of this example was approximately 63.87%.

[0050] Example 2: Preparation of composite anti-corrosion coating (0.5 wt% Sucrose-BNNSs / EP) 0.1 g of Sucrose-BNNSs obtained in Example 1 (approximately 0.5 wt% of the total mass of epoxy resin and curing agent) was dispersed in anhydrous ethanol and ultrasonically dispersed for 20 min to obtain a uniform nanosheet anhydrous ethanol dispersion. 10 g of bisphenol A type epoxy resin E-51 was heated to 50°C in a water bath and magnetically stirred. The above dispersion was slowly added dropwise to the epoxy resin. The temperature was maintained and stirring continued until the ethanol completely evaporated and no bubbles remained. The temperature was then lowered to 40°C, and 10 g of 650 type polyamide curing agent (epoxy resin to curing agent mass ratio of 1:1) was added and mixed thoroughly. After standing to remove bubbles, the mixture was uniformly coated onto the surface of a sanded and acetone-washed carbon steel plate using a wire rod coater. The plate was cured at 60°C for 3 h to obtain a 0.5 wt% Sucrose-BNNSs / EP composite anti-corrosion coating.

[0051] The resulting composite anti-corrosion coating has a pale yellow appearance (see...). Figure 4 ).

[0052] Example 3: Preparation of composite thermally conductive sheet (30 wt% Sucrose-BNNSs / EP) Following the preparation process of Example 2, the mass ratio of functionalized nanosheets was adjusted. 8.57 g of Sucrose-BNNSs prepared in Example 1 (approximately 30 wt% of the total mass of epoxy resin and curing agent) was ultrasonically dispersed in anhydrous ethanol. 10 g of bisphenol A type epoxy resin E-51 was heated in a water bath to 50°C and magnetically stirred. Before adding the nanosheet dispersion, 0.2 g of dispersant BYK-163 was added (dispersant:Sucrose-BNNSs:epoxy resin ≈ 1:43:50, i.e., approximately 2:86:100), and then the nanosheet dispersion was slowly added dropwise. The temperature was maintained and stirring continued until the ethanol completely evaporated. The temperature was then lowered to 40°C, and 10 g of 650 type polyamide curing agent was added and stirred until homogeneous. After standing and degassing, the mixture was poured into a polytetrafluoroethylene mold and cured at 60°C for 3 h to obtain a 30 wt% Sucrose-BNNSs / EP composite thermally conductive sheet.

[0053] The resulting composite thermally conductive sheet has an off-white appearance (see...). Figure 5 According to the ASTM E1461 standard, the thermal conductivity of the composite thermally conductive sheet (approximately 3 mm thick) in this embodiment reached 1.1341 W / (m·K) after rigorous testing using the laser scintillation method.

[0054] Example 4: Preparation of glucose-modified boron nitride nanosheets (Glucose-BNNSs) Glucose was used instead of sucrose as a stripping agent and functionalizing agent, and other conditions were the same as in Example 1.

[0055] The specific operation is as follows: 5 g of glucose is dissolved in 40 g of deionized water, 1 g of bulk h-BN powder is added, and after stirring and dispersing evenly, it is transferred to an agate ball mill jar and ball milled at 300 rpm for 12 h in a planetary ball mill. After that, it is circulated 15 times by a high-pressure micro-jet homogenizer, and after stepwise centrifugation, washing with anhydrous ethanol 3 times and vacuum drying, glucose-functionalized boron nitride nanosheets (Glucose-BNNSs) are obtained.

[0056] According to the test, the yield of Glucose-BNNSs obtained in this embodiment is about 59.37%, the thickness is 3.3 to 5.5 nm (about 10 to 17 atomic layers), and the lateral dimension is 100 to 300 nm.

[0057] Example 5: Preparation of composite anti-corrosion coating (0.5 wt% Glucose-BNNSs / EP) The Glucose-BNNSs prepared in Example 4 were used to replace Sucrose-BNNSs as the functional filler, and the amount added was about 0.5 wt% of the total mass of epoxy resin and curing agent. Other steps were the same as in Example 2.

[0058] Testing showed that the corrosion current density of the glucose-BNNSs / EP composite anti-corrosion coating obtained in this embodiment was approximately 3.31 × cm⁻¹. 2 A / cm 2 .

[0059] Example 6: Preparation of composite thermally conductive sheet (30 wt% Glucose-BNNSs / EP) The Glucose-BNNSs prepared in Example 4 were used to replace Sucrose-BNNSs as the functional filler, and the amount added was about 30 wt% (about 8.57 g) of the total mass of epoxy resin and curing agent. The other steps were the same as in Example 3.

[0060] According to the laser scintillation method, the thermal conductivity of the glucose-BNNSs / EP composite thermally conductive sheet obtained in this embodiment is approximately 1.0163 W / (m·K), which is about 452.64% higher than that of pure EP (0.1839 W / (m·K)).

[0061] Example 7: Preparation with different ball milling times The method is the same as in Example 1, except that the ball milling time in step (2) is 3 hours, while other conditions remain unchanged. The yield of Sucrose-BNNSs obtained in this example is 53.7%.

[0062] Example 8: Preparation of microfluidic cycles with different numbers of cycles The method is the same as in Example 1, except that the number of microjets cyclically is 20 in step (3), while other conditions remain unchanged. The Zeta potential of the Sucrose-BNNSs obtained in this example is approximately -39.3 mV.

[0063] Comparative Example Comparative Example 1: Pure epoxy resin coating (pure EP) A pure epoxy resin coating was prepared as a blank control using bisphenol A type epoxy resin E-51 and polyamide curing agent 650 (mass ratio 1:1). The preparation process was the same as in Example 2, but without the addition of functionalized BNNSs dispersion. The corrosion current density of the pure EP coating was tested to be 2.04 × 10⁻⁶. -7 A / cm 2 The corrosion rate is 2.37 × 10⁻⁶. -3 mm / year.

[0064] Comparative Example 2: Pure epoxy resin film (pure EP) Pure epoxy resin sheets were prepared as a blank control using bisphenol A type epoxy resin E-51 and polyamide type 650 curing agent (mass ratio 1:1) under the same curing conditions. The preparation process was the same as in Example 3, but without the addition of functionalized BNNSs and dispersants. The thermal conductivity of the pure EP sheet was measured by laser scintillation method to be 0.1839 W / (m·K).

[0065] Comparative Example 3: Unmodified h-BN / epoxy resin composite anti-corrosion coating (0.5 wt% h-BN / EP) Functionalized BNNSs were replaced with untreated, unprocessed h-BN powder at an addition rate of 0.5 wt% (approximately 0.1 g) of the total mass of epoxy resin and curing agent, with other steps identical to those in Example 2. The corrosion current density of the 0.5 wt% h-BN / EP composite coating was tested to be 8.13 × 10⁻⁶. -9 A / cm 2 The corrosion rate is 9.45 × 10⁻⁶. -5 mm / year.

[0066] Comparative Example 4: Unmodified h-BN / epoxy composite thermally conductive sheet (30 wt% h-BN / EP) Functionalized BNNSs were replaced with untreated, unprocessed h-BN powder at an addition rate of 30 wt% (approximately 8.57 g) of the total mass of epoxy resin and curing agent, with other steps identical to those in Example 3. Testing showed that the thermal conductivity of 30 wt% h-BN / EP was only 0.4918 W / (m·K), an improvement of only 167.43% compared to pure EP, significantly lower than that of Example 3 (516.69%).

[0067] Application Examples Application Example 1: Corrosion Resistance and Salt Spray Resistance Test Electrochemical polarization curve analysis and neutral salt spray test were performed on the composite anti-corrosion coating (0.5 wt% Sucrose-BNNSs / EP) prepared in Example 2, with Comparative Example 1 (pure EP coating) as a blank control.

[0068] Tafel polarization curve testing: Tafel polarization curves were measured using a three-electrode system in a 3.5 wt% NaCl solution. The test results are summarized in the table below.

[0069] Table 1. Results of Tafel polarization curve testing and corrosion rate calculation in 3.5 wt% NaCl solution. As shown in Table 1, the corrosion current density of the 0.5 wt% Sucrose-BNNSs / EP composite anti-corrosion coating prepared in Example 2 was reduced by approximately three orders of magnitude compared to the pure EP coating, achieving a corrosion inhibition efficiency of 99.85%; the corrosion rate decreased from 2.37 × 10⁻⁶. -3 mm / year decreased to 3.51×10 -6 The corrosion rate is reduced by approximately three orders of magnitude, with a rate of mm / year. The corrosion rate of the 0.5 wt% h-BN / EP composite coating is 9.45 × 10⁻⁶ mm / year. -5 mm / year, an order of magnitude higher than the 0.5 wt% Sucrose-BNNSs / EP composite anti-corrosion coating. This result indicates that ultra-low addition of sugar-functionalized BNNSs forms a highly efficient and dense physical barrier network in the epoxy coating, significantly inhibiting the penetration of corrosive media and the occurrence of corrosion electrochemical reactions.

[0070] Furthermore, the corrosion current density of 0.5 wt% Glucose-BNNSs / EP (Example 5) was approximately 3.31 × cm⁻¹. 2 A / cm 2 The corrosion inhibition efficiency is about 99.85%, indicating that glucose, as a substitute for sugars, can also achieve excellent anti-corrosion effects.

[0071] Salt spray test: Accelerated corrosion treatment with 5 wt% NaCl was performed according to ASTM B117 standard. The test results are shown in Table 2.

[0072] Table 2 Comparison of corrosion area in continuous salt spray test with 5 wt% NaCl As shown in Table 2, after 14 consecutive days of salt spray testing, the surface corrosion area of ​​the pure EP coating reached as high as 33.571%. The 0.5 wt% h-BN / EP prepared in Comparative Example 3 had a certain protective effect, but it was limited. In contrast, the surface of the 0.5 wt% Sucrose-BNNSs / EP coating prepared in Example 2 remained smooth and dense, without blistering, and the corrosion area after 14 days was only 1.299%. The T3% (failure time when the surface corrosion area reaches 3%) of the coating in Example 2 was as long as about 43 days, indicating that it has a long-lasting and durable physical barrier against ion penetration.

[0073] Electrochemical impedance spectroscopy (EIS) analysis: EIS testing was performed on the coated samples after immersion in 3.5 wt% NaCl solution for 30 days. The 30-day low-frequency impedance modulus (|Z|0.05) of Example 2 (0.5 wt% Sucrose-BNNSs / EP) is shown. 01 (Hz) remained at approximately 7.07 × 10 9 Ω·cm 2This indicates that the coating maintains good barrier protection performance even after immersion for up to 30 days. Example 5 (0.5wt% Glucose-BNNSs / EP) 30-day |Z|0. 01 The Hz is approximately 9.85 × 10⁻⁶. 8 Ω·cm 2 .

[0074] Table 3. EIS test results in 3.5 wt% NaCl solution Adhesion test: The adhesion of the coating was tested using the pull-out method. The adhesion of the pure EP coating (Comparative Example 1) was approximately 7.82 MPa; the adhesion of Example 2 (0.5 wt% Sucrose-BNNSs / EP) was approximately 9.31 MPa, an improvement of 19.1% compared to pure EP. The adhesion test results indicate that the hydroxyl functional groups on the surface of sugar-functionalized BNNSs enhance the interfacial bonding between the coating and the metal substrate, achieving a simultaneous improvement in corrosion resistance and adhesion.

[0075] Application Example 2: Thermal Conductivity Test The thermal conductivity of the composite thermally conductive sheets prepared in Examples 3, 6, and Comparative Examples 2 and 4 was tested. The tests were conducted using the laser flare method, strictly following the ASTM E1461 standard. The test samples were sheet-like, approximately 3 mm thick. The test results are shown in Table 4.

[0076] Table 4. Thermal conductivity test results (sheet thickness approximately 3 mm) As shown in Table 4, the thermal conductivity of Example 3 (30 wt% Sucrose-BNNSs / EP) reached 1.1341 W / (m·K), which is 516.69% higher than that of pure EP (0.1839 W / (m·K)), approximately 6.2 times that of pure EP. The thermal conductivity of Example 6 (30 wt% Glucose-BNNSs / EP) was 1.0163 W / (m·K), an improvement of 452.64%.

[0077] Compared with Comparative Example 4 (unmodified h-BN / EP, 30 wt%), the thermal conductivity improvement of Example 3 was approximately three times that of Comparative Example 4 (516.69% vs 167.43%). This significant difference is attributed to: (1) the hydroxyl functional groups on the surface of sugar-functionalized BNNSs enhanced the interfacial compatibility between the nanosheets and the epoxy resin matrix, reducing interfacial phonon scattering and interfacial thermal resistance; (2) the good dispersion of functionalized BNNSs in the matrix facilitated the construction of a more continuous phonon transport pathway; and (3) the few-layer, high aspect ratio nanosheets obtained by microfluidic deep exfoliation could form a more efficient thermally conductive network at the same filling amount.

[0079] (2) In the application of anti-corrosion coatings, an ultra-low addition of only 0.5 wt% can reduce the corrosion current density of the composite coating by about 3 orders of magnitude (2.04 × 10⁻⁶). -7 → 3.02×cm 2 A / cm 2 The corrosion inhibition efficiency reached 99.85%, and the corrosion rate was also reduced by about three orders of magnitude (2.37 × 10⁻⁶). -3 → 3.51×10 -6 (mm / year), salt spray T3% lasts for about 43 days, and coating adhesion is improved by 19.1% simultaneously.

[0080] (3) In the application of thermally conductive composite materials, the thermal conductivity reaches 1.1341 W / (m·K) with an addition of 30 wt%, which is 516.69% higher than that of pure EP. The thermal conductivity enhancement effect of functionalized BNNSs is about 3 times that of unmodified h-BN with the same filling amount.

[0081] The above description of the embodiments is provided to enable those skilled in the art to understand and use the present invention. It will be apparent to those skilled in the art that various modifications can be easily made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the present invention should be within the protection scope of the present invention.

Claims

1. A method for preparing functionalized boron nitride nanosheets and their composite materials, characterized in that, Includes the following steps: Hexagonal boron nitride powder, sugar additives and deionized water were mixed and then subjected to mechanical ball milling pretreatment to obtain a pre-modified suspension; The pre-modified suspension was introduced into a high-pressure microfluidic homogenizer for multiple cycles to obtain a dispersion containing functionalized boron nitride nanosheets; the dispersion was separated and purified to obtain sugar-functionalized boron nitride nanosheets; the obtained functionalized boron nitride nanosheets were dispersed in an organic solvent and blended with an oily epoxy resin matrix; after the organic solvent evaporated, a curing agent was added and the mixture was cured to obtain a composite material.

2. The preparation method according to claim 1, characterized in that, The mass ratio of the hexagonal boron nitride powder, the sugar additive, and the deionized water is 1:5:

40.

3. The preparation method according to claim 1, characterized in that, The sugar additive is selected from at least one of sucrose or glucose.

4. The preparation method according to claim 1, characterized in that, The mechanical ball milling pretreatment is carried out in a planetary ball mill at a speed of 200–350 rpm, preferably 300 rpm; the ball milling time is 3–12 h.

5. The preparation method according to claim 1, characterized in that, The high-pressure micro-jet homogenizer is used for 10 to 20 cycles, preferably 15 cycles; the cycle pressure is 150 to 300 MPa.

6. The preparation method according to claim 1, characterized in that, The mass ratio of the oily epoxy resin to the curing agent is approximately 1:

1.

7. The preparation method according to claim 1, characterized in that, The separation and purification process includes: centrifuging the dispersion at 2000–4000 rpm for the first time to remove large particles of precipitate that have not been removed; taking the supernatant from the first centrifugation and centrifuging it a second time at 8000–12000 rpm to collect the precipitate; washing the precipitate with an organic solvent and then drying it.

8. The preparation method according to claim 7, characterized in that, The large, unstripped precipitate obtained from the first centrifugation is recovered and mixed into the next batch of raw material suspension for recycling.

9. The preparation method according to claim 1, characterized in that, When preparing the composite anti-corrosion coating, the mass ratio of the functionalized boron nitride nanosheets to the epoxy resin is 1-2:100; preferably, the amount of functionalized boron nitride nanosheets added is 0.5 wt% of the total mass of epoxy resin and curing agent.

10. The preparation method according to claim 1, characterized in that, In the preparation of composite thermally conductive sheets, a dispersant is also added in the blending step; the dispersant is selected from at least one of DISPERBYK 111, DISPERBYK 163, and DISPERBYK 164; the mass ratio of the dispersant, functionalized boron nitride nanosheets and epoxy resin is 1-5:20-90:

100.

11. A functionalized boron nitride nanosheet, characterized in that, It is prepared by the separation and purification step in the preparation method according to any one of claims 1-5 and 7-8.

12. A composite anti-corrosion coating, characterized in that, The product comprises an oily epoxy resin matrix and functionalized boron nitride nanosheets as described in claim 11 dispersed in the matrix.

13. The composite anti-corrosion coating according to claim 12, characterized in that, The amount of the functionalized boron nitride nanosheets added is 0.1 to 1.0 wt% of the total mass of epoxy resin and curing agent, preferably 0.5 wt%.

14. The composite anti-corrosion coating according to claim 12, characterized in that, The corrosion current density of the composite anti-corrosion coating is no higher than 5 × 10⁻⁶. -10 cm 2 The corrosion inhibition efficiency is not less than 99.5% (determined by Tafel polarization curve of 3.5 wt% NaCl solution); the failure time (T3%) of the composite anti-corrosion coating when the surface corrosion area reaches 3% in the continuous salt spray test of 5 wt% NaCl is not less than 40 days.

15. A composite thermally conductive sheet, characterized in that, The product comprises an oily epoxy resin matrix and functionalized boron nitride nanosheets as described in claim 11 dispersed in the matrix.

16. The composite thermally conductive sheet according to claim 15, characterized in that, The amount of functionalized boron nitride nanosheets added is 10 to 30 wt% of the total mass of epoxy resin and curing agent.

17. The composite thermally conductive sheet according to claim 16, characterized in that, The amount of functionalized boron nitride nanosheets added is 30 wt%, and the thermal conductivity of the composite thermally conductive sheet is not less than 1.0 W / (m·K).

Images