Functionalized boron nitride nanosheet, functionalized boron nitride nanosheet covalently grafted polyurethane and boron nitride nanosheet covalently grafted polyurethane high-thermal-conductivity composite material

Abstract

The invention discloses a functionalized boron nitride nanosheet, functionalized boron nitride nanosheet covalent grafted polyurethane, a boron nitride nanosheet covalent grafted polyurethane high-thermal-conductivity composite material, and preparation of the functionalized boron nitride nanosheet and the functionalized boron nitride nanosheet covalent grafted polyurethane. According to the boron nitride nanosheet covalently grafted polyurethane high-thermal-conductivity composite material and the preparation method thereof, operation is easy, industrial large-scale production is easy to achieve, meanwhile, excellent electrical insulation performance and mechanical performance are shown, and wide application prospects and market potential are achieved.

Description

Technical Field

[0001] The present application relates to the technical field of polymer composite materials, and in particular to a functionalized boron nitride nanosheet, a functionalized boron nitride nanosheet covalently grafted with polyurethane, and a boron nitride nanosheet covalently grafted with polyurethane high thermal conductivity composite material. Background Art

[0002] With the continuous advancement of integration and self-assembly technology, micro-integrated circuits and electronic components are rapidly developing in the direction of miniaturization, high performance, intelligence and energy saving. However, in this process, if the large amount of heat generated by the device during operation cannot be effectively discharged, it will accelerate the aging process of the electronic components, shorten their service life, and even cause safety accidents. Given that high temperatures mainly come from the accumulation of heat generated when the electronic components are working, rather than the external environment. Therefore, in order to ensure that electronic products can operate stably for a long time, it is particularly important to develop materials with excellent thermal conductivity and heat dissipation properties. As a polymer material, thermoplastic polyurethane (TPU) has excellent water resistance, elasticity and environmental protection properties. Generally speaking, TPU materials are composed of staggered hard segments and soft segments. This unique microphase separation structure gives it moderate hardness and excellent elasticity, making it an ideal choice for thermal interface materials. However, the thermal conductivity of TPU itself is relatively low (~0.22W·m -1 ·K -1 ), this characteristic limits its applicability in most semiconductor device heat dissipation applications. In order to improve the comprehensive performance of TPU materials, it is necessary to enhance its thermal conductivity by adding thermal conductive materials to meet the needs of electronic devices for efficient heat dissipation.

[0003] Boron nitride (h-BN) has been widely used in the field of heat dissipation materials for electronic devices due to its excellent mechanical strength, excellent thermal conductivity, outstanding thermal stability and low thermal expansion rate. However, single-component boron nitride (h-BN) has fewer surface chemical active sites, high structural stability, weak interaction with the substrate polymer, and is prone to agglomeration and precipitation, resulting in unsatisfactory thermal and mechanical properties of the composite material. Therefore, in the process of compounding with TPU, improving the dispersibility and compatibility of boron nitride (h-BN) is the key to preparing high thermal conductivity and high strength composite materials. Generally, the compatibility between inorganic materials and TPU matrix can be improved by functionalizing the surface of boron nitride (h-BN), thereby enhancing the bonding force between the two and reducing the contact thermal resistance to improve the thermal conductivity of the polymer substrate. Summary of the invention

[0004] In view of the limitations of the prior art, the purpose of this application is to provide an innovative preparation scheme, aiming to develop a high thermal conductivity composite material of covalently grafted polyurethane with boron nitride nanosheets. This application uses precise functional modification technology to deeply treat h-BN, and combines the structural advantages of the six-membered ring trimer of diisocyanate isocyanurate to successfully prepare functionalized boron nitride nanosheets (NCO-BNNSs-OH) materials with large spacing and high reactivity. Subsequently, the functionalized boron nitride nanosheets (NCO-BNNSs-OH) are precisely grafted onto the molecular backbone of polyurethane using in-situ polymerization technology, realizing the in-situ composite of boron nitride (h-BN) and polyurethane. This process not only significantly enhances the interfacial compatibility between boron nitride (h-BN) and polyurethane, but also greatly enhances the positive effects of boron nitride (h-BN) on the mechanical properties, thermal stability and electrical conductivity of polyurethane. To achieve the above purpose, this application provides the following technical solutions:

[0005] Specifically, according to the first aspect of the present application, a functionalized boron nitride nanosheet is provided, and the preparation method thereof comprises the following steps:

[0006] S1. Disperse the boron nitride (h-BN) powder evenly in isopropanol, then add the intercalation agent and stir for 30 to 50 minutes. Subsequently, heat the mixture to 160 to 190°C and react at this temperature for 72 to 80 hours. After the reaction is completed, lower the temperature to room temperature and stop stirring. Ultrasonicate the resulting milky white solution for further dispersion; after ultrasonic treatment, seal the solution and let it stand for one day; the next day, pour out the upper dissolved colloidal hexagonal boron nitride nanosheets (h-BNNSs) and place them in an oven to dry;

[0007] S2. adding the hexagonal boron nitride nanosheets (h-BNNSs) to an alkaline hydroxide solution of a predetermined concentration, ultrasonically treating, heating and stirring under reflux at 100 to 120° C. for 5 to 7 hours, centrifuging the product, washing with an organic solvent, and vacuum drying the obtained product to obtain hydroxylated boron nitride nanosheets (BNNSs-OH);

[0008] S3. Under nitrogen protection, the hydroxylated boron nitride nanosheets (BNNSs-OH), N,N-dimethylformamide, catalyst and modifier are stirred at 70-80°C for 6-10 hours; after the reaction is completed, the reaction mixture is repeatedly washed with a solvent, ultrasonically dispersed, and centrifuged, and the lower layer of precipitate is collected and dried to obtain the functionalized boron nitride nanosheets (NCO-BNNSs-OH).

[0009] Furthermore, in step S1, the particle size of boron nitride (h-BN) powder is 2-10 μm; the intercalation agent is LiF or NaCl; the ultrasonic treatment time is 2-3 h, and the ultrasonic treatment power is 200-500 W.

[0010] Furthermore, in step S2, the concentration of the alkaline hydroxide solution is 30 mol / L-100 mol / L, preferably 50 mol / L; the alkaline hydroxide is potassium hydroxide and / or sodium hydroxide; the ultrasonic treatment time is 1 to 2 hours, and the ultrasonic treatment power is 100 to 300 W; and the organic detergent is N,N-dimethylformamide and / or acetone.

[0011] Furthermore, in step S3, the catalyst is a combination of one or more of triethylamine, triethylenediamine, bis(dimethylaminoethyl)ether, stannous octoate, and dibutyltin dilaurate; and the modifier is hexamethylene diisocyanate isocyanurate six-membered ring trimer and / or isophorone diisocyanate isocyanurate six-membered ring trimer.

[0012] Furthermore, in the above steps S1 to S3, the weight proportions of the raw materials are as follows: 70 to 80 parts of boron nitride (h-BN), 100 to 120 parts of isopropanol, 5 to 30 parts of intercalation agent, 50 to 60 parts of hexagonal boron nitride nanosheets (h-BNNSs), 5 to 10 parts of alkaline hydroxide solution, 80 to 100 parts of organic solvent, 40 to 50 parts of hydroxylated boron nitride nanosheets (BNNSs-OH), 80 to 100 parts of N,N-dimethylformamide, 0.01 to 0.05 parts of catalyst, and 1 to 2.5 parts of modifier.

[0013] According to a second aspect of the present application, there is provided a functionalized boron nitride nanosheet covalently grafted polyurethane comprising the aforementioned functionalized boron nitride nanosheet.

[0014] Furthermore, the preparation method of functionalized boron nitride nanosheets covalently grafted with polyurethane comprises the following steps:

[0015] S1'. Add oligomer polyol monomers to a three-necked flask, raise the temperature to 120-130°C, and dehydrate under vacuum for 2-2.5h;

[0016] S2'. After the dehydration process is completed, under the protection of nitrogen, the temperature is adjusted to 60 to 85 ° C; the functionalized boron nitride nanosheets (NCO-BNNSs-OH) powder is evenly dispersed in a small amount of N-methylpyrrolidone and added dropwise to the solution; then, the diisocyanate is also added dropwise, and the addition is completed, and the reaction is kept at 85 to 90 ° C for 2 to 2.5 hours; finally, the isocyanate group (NCO) content of the generated prepolymer is determined by the toluene-di-n-butylamine method. When it is close to the theoretical value of NCO, the reaction temperature is reduced to 50 to 65 ° C; preferably, the insulation reaction temperature is 90 ° C;

[0017] S3. After the temperature drops to the set temperature, a catalyst, a diol chain extender, and a diamine chain extender are added in sequence and reacted for 3 to 4 hours; finally, a polyol with a functionality ≥ 3 is added for cross-linking and reacted for 1 to 3 hours until the NCO is 0 to obtain a functionalized boron nitride nanosheet covalently grafted polyurethane (NCO-BNNSs-OH / TPU).

[0018] Furthermore, in the step S1', the oligomer polyol monomer is one of polycarbonate diol, polyethylene glycol, polybutylene adipate, polytetramethylene glycol, polypropylene glycol, or any combination thereof.

[0019] Furthermore, in step S2', the concentration of the functionalized boron nitride nanosheet (NCO-BNNSs-OH) dispersion is 0.1-5%; the diisocyanate compound is one of toluene diisocyanate, naphthalene diisocyanate, trimethyl hexamethylene diisocyanate or trimethyl-1,6-hexamethylene diisocyanate.

[0020] Furthermore, in step S3', the catalyst is dibutyltin dilaurate; the diol chain extender is one of dimethylolpropionic acid, neopentyl glycol, dimethylolbutyric acid, 1,4-butanediol, and 1,6-hexanediol; the diamine chain extender is ethylenediamine; and the polyol compound with a functionality ≥ 3 is one of propylene glycol, pentaerythritol, and trimethylolpropane, or a combination of any of them.

[0021] Furthermore, in the above steps S1' to S3', the weight proportions of the raw materials are as follows: 60 to 70 parts of oligomer polyol, 5 to 20 parts of functionalized boron nitride nanosheets (NCO-BNNSs-OH), 20 to 80 parts of N-methylpyrrolidone, 120 to 140 parts of diisocyanate, 0.1 to 0.5 parts of catalyst, 1 to 5 parts of diol chain extender, 4 to 5 parts of diamine chain extender, and 5 to 7 parts of polyol with functionality ≥ 3.

[0022] This application adopts surface grafting technology, firstly exfoliating and surface hydroxylating boron nitride (h-BN) to increase the interlayer spacing and the content of surface hydroxyl (OH). Subsequently, the diisocyanate isocyanurate six-membered ring trimer is precisely modified on the surface of hydroxylated boron nitride nanosheets (BNNSs-OH) to prepare a product with rich reactive sites, functionalized boron nitride nanosheets (NCO-BNNSs-OH). Then, the TPU substrate is modified using functionalized boron nitride nanosheets (NCO-BNNSs-OH); in this process, the isocyanate group (NCO) modified on the surface of hydroxylated boron nitride nanosheets (BNNSs-OH) not only increases the polymer chain segments on the surface of the nanosheets, but also cleverly introduces highly heat-resistant isocyanurate six-membered ring functional groups, which significantly optimizes the dispersion state of hydroxylated boron nitride nanosheets (BNNSs-OH) in the polymer substrate and the heat resistance of the composite material. In addition, the close interaction between the surface isocyanurate hexacyclic ring and the polymer molecular chain effectively enhances the cross-linking between hydroxylated boron nitride nanosheets (BNNSs-OH) and the substrate polymer, thereby greatly improving the mechanical properties, thermal stability and excellent thermal conductivity of the composite material.

[0023] Compared with the prior art, this application has the following beneficial effects:

[0024] 1. The innovative solution provided by this application is to graft and modify boron nitride (h-BN) by diisocyanate isocyanurate six-membered ring trimer molecules. Compared with the traditional diisocyanate grafting method, this application makes the surface of boron nitride (h-BN) rich in a large number of highly active isocyanate groups, effectively overcoming the problem of chemical inertness of the surface of boron nitride (h-BN).

[0025] 2. This application uses in-situ polymerization technology to cleverly use functionalized boron nitride nanosheets (NCO-BNNSs-OH) as efficient thermal conductive fillers, and cross-links with -OH or -NH2 in TPU to generate continuous polymer chains. This innovative method effectively reduces the agglomeration of thermal conductive fillers in the polyurethane matrix and significantly enhances the compatibility and interfacial interaction between functionalized boron nitride nanosheets (NCO-BNNSs-OH) and polyurethane. Through this strategy, not only the thermal conductivity of TPU materials is greatly improved, but also composite materials with excellent performance are successfully prepared.

[0026] 3. In the present application, the covalent compounding of functionalized boron nitride nanosheets (NCO-BNNSs-OH) and TPU will not change the microphase separation structure of the TPU composite material, and effectively solves the brittleness problem that may be caused by the addition of inorganic thermal conductive fillers.

[0027] 4. The functionalized boron nitride nanosheets covalently grafted polyurethane (NCO-BNNSs-OH / TPU) thermal conductive material prepared in this application not only exhibits excellent electrical insulation and mechanical properties, but also has a simple preparation process and is easy to realize industrial large-scale production, and has broad application prospects and market potential. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the technical solution of the present disclosure, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present disclosure. For those skilled in the art, other drawings can be obtained based on these drawings without paying any creative work.

[0029] Figure 1 Schematic diagram of the preparation principle of functionalized boron nitride nanosheets (NCO-BNNSs-OH) according to one embodiment of the present application.

[0030] Figure 2 Schematic diagram of functionalized boron nitride nanosheets covalently grafted with polyurethane (NCO-BNNSs-OH / TPU) according to an embodiment of the present application.

[0031] Figure 3 1 is an infrared spectrum of boron nitride (h-BN), hydroxylated boron nitride nanosheets (BNNSs-OH) and functionalized boron nitride nanosheets (NCO-BNNSs-OH) according to an embodiment of the present application.

[0032] Figure 4 Graphs showing thermal diffusion coefficients of TPU-based nanocomposites according to Examples 1-4 and Comparative Examples 1-3 of the present application.

[0033] Figure 5 3 is a thermal conductivity diagram of the TPU-based nanocomposite materials according to Examples 1-4 and Comparative Examples 1-3 of the present application.

[0034] Figure 6 It is a graph of elongation at break of TPU-based nanocomposites according to Examples 1-4 and Comparative Examples 1-3 of the present application.

[0035] Figure 7 is a field emission scanning electron microscope (FESEM) image of the functionalized boron nitride nanosheets (NCO-BNNSs-OH) according to Example 1 of the present application.

[0036] Figure 8 is a field emission scanning electron microscope (FESEM) image of Comparative Example 2 (h-BN / TPU) of the present application. DETAILED DESCRIPTION

[0037] The technical solution of the present application will be described in detail and comprehensively with the help of the accompanying drawings and examples. It should be clear that the embodiments described in this application are only a part of the numerous implementation schemes of the present application and do not cover all of them. The present application is intended to illustrate its technical principles through the following examples, rather than to limit its scope of application. For those of ordinary skill in the art, all other embodiments derived without creative work should be regarded as the scope covered and protected by this application.

[0038] Example

[0039] Embodiment 1:

[0040] (A) Preparation of functionalized boron nitride nanosheets (NCO-BNNSs-OH):

[0041] The raw material composition includes the following components by mass: 75 parts of boron nitride (h-BN), 110 parts of isopropanol, 10 parts of intercalating agent (all are LiF), 55 parts of hexagonal boron nitride nanosheets (h-BNNSs), 8 parts of alkaline hydroxide solution (all are sodium hydroxide: 50 mol / L), 100 parts of organic solvent (all are acetone), 45 parts of hydroxylated boron nitride nanosheets (BNNSs-OH), 90 parts of N,N-dimethylformamide, 0.03 parts of catalyst (all are stannous octoate), and 1.5 parts of modifier (all are hexamethylene diisocyanate isocyanurate six-membered ring trimer).

[0042] The preparation method steps are as follows:

[0043] (S1) Boron nitride (h-BN) powder with a particle size of 8 μm is evenly dispersed in isopropanol. LiF is then added and stirred for 40 minutes; the temperature of the mixture is then raised to 190°C and reacted at this temperature for 80 hours. After the reaction is completed, the temperature is gradually lowered to room temperature and the stirring is stopped; the resulting milky white solution is placed in an ultrasonic instrument with a power setting of 300 W and subjected to ultrasonic treatment for 2.5 hours to promote its further dispersion; after the treatment is completed, the solution is sealed and allowed to stand for 24 hours; the next day, the upper layer of dissolved colloidal hexagonal boron nitride nanosheets (h-BNNSs) is poured out and placed in an oven to be thoroughly dried;

[0044] (S2) Add hexagonal boron nitride nanosheets (h-BNNSs) to a sodium hydroxide solution with a concentration of 50 mol / L, and place in an ultrasonic instrument with a power setting of 200 W for 1.5 hours of ultrasonic treatment. After the ultrasonic treatment, the mixed solution is heated to 110°C and refluxed at this temperature for 6 hours; after the reaction is completed, the product is separated by centrifugal separation technology and thoroughly washed with an appropriate amount of acetone; finally, the obtained product is placed in a vacuum environment for drying to obtain hydroxylated boron nitride nanosheets (BNNSs-OH);

[0045] (S3) In a nitrogen-protected environment, hydroxylated boron nitride nanosheets (BNNSs-OH), N,N-dimethylformamide, dibutyltin dilaurate and hexamethylene diisocyanate isocyanurate six-membered ring trimer are mixed and stirred at a temperature of 75°C for 8 hours; after the reaction is completed, the reaction mixture is repeatedly washed with a solvent, ultrasonically dispersed, and centrifuged, and the lower precipitate is collected and dried to obtain surface-grafted functionalized boron nitride nanosheets (NCO-BNNSs-OH). Figure 1 The corresponding preparation principle is shown.

[0046] (B) Preparation of functionalized boron nitride nanosheets covalently grafted with polyurethane (NCO-BNNSs-OH / TPU):

[0047] The raw material composition includes the following components by mass: 65 parts of oligomer polyol (all of which are mixtures of polycarbonate diol and polytetramethylene glycol), 10 parts of functionalized boron nitride nanosheets (NCO-BNNSs-OH), 50 parts of N-methylpyrrolidone, 130 parts of diisocyanate (all of which are naphthalene diisocyanate), 0.25 parts of catalyst (all of which are dibutyltin dilaurate), 3 parts of diol (all of which are neopentyl glycol), 4.5 parts of diamine (all of which are ethylenediamine), and 6 parts of polyol with a functionality ≥3 (all of which are propylene glycol).

[0048] The preparation method steps are as follows:

[0049] (S1') adding a mixture of polycarbonate diol and polytetrahydrofuran diol into a three-necked flask, raising the temperature to 125° C., and performing vacuum dehydration treatment for 2.5 h;

[0050] (S2') After the dehydration process is completed, the temperature is adjusted to 85°C under the protection of nitrogen. At this time, the functionalized boron nitride nanosheets (NCO-BNNSs-OH) powder is evenly dispersed in a small amount of N-methylpyrrolidone and added dropwise to the solution. Subsequently, naphthalene diisocyanate is also added dropwise, and the addition is completed. The temperature is kept at 90°C and the reaction is carried out for 2.5 hours. Finally, the isocyanate group (NCO) content of the generated prepolymer is determined by the toluene-di-n-butylamine method. When it is close to the theoretical value of NCO, the reaction temperature is reduced to 60°C;

[0051] (S3') After the temperature drops to the set temperature, dibutyltin dilaurate, neopentyl glycol, and ethylenediamine are added in sequence and reacted for 3.5 hours; finally, propylene glycol is added for crosslinking and reacted for 2 hours until the NCO content drops to 0, and finally functionalized boron nitride nanosheets covalently grafted polyurethane (NCO-BNNSs-OH / TPU) is obtained (the concrete structure is as shown in Figure 2 As shown, A is TPU and B is functionalized boron nitride nanosheets (NCO-BNNSs-OH).

[0052] Embodiment 2:

[0053] The functionalized boron nitride nanosheets (NCO-BNNSs-OH) are 20 parts. The remaining steps are the same as the process flow in Example 1.

[0054] Embodiment 3:

[0055] 2.5 parts of modifier (all hexamethylene diisocyanate isocyanurate six-membered ring trimer). The remaining steps are the same as the process flow in Example 1.

[0056] Embodiment 4:

[0057] The modifier is 2.5 parts (all hexamethylene diisocyanate isocyanurate six-membered ring trimer), and the functionalized boron nitride nanosheets (NCO-BNNSs-OH) is 20 parts. The remaining steps are the same as the process flow in Example 1.

[0058] Comparative Example 1 (unmodified TPU):

[0059] The raw material composition includes the following components by mass: 65 parts of oligomer polyol (all of which are mixtures of polycarbonate diol and polytetramethylene glycol), 130 parts of diisocyanate (all of which are naphthalene diisocyanate), 0.25 parts of catalyst (all of which are dibutyltin dilaurate), 3 parts of diol (all of which are neopentyl glycol), 4.5 parts of diamine (all of which are ethylenediamine), and 6 parts of polyol with a functionality ≥ 3 (all of which are propylene glycol).

[0060] The preparation method steps are as follows:

[0061] (1) Add a mixture of polycarbonate diol and polytetrahydrofuran diol into a three-necked flask, raise the temperature to 125° C., and perform vacuum dehydration treatment for 2.5 hours;

[0062] (2) After the dehydration process is completed, the temperature is adjusted to 85°C under the protection of nitrogen. At this time, naphthalene diisocyanate is added dropwise, and after the addition is completed, the temperature is kept at 90°C and the reaction is carried out for 2.5 hours. Finally, the isocyanate content (NCO) of the generated prepolymer is determined by the toluene-di-n-butylamine method. When it is close to the theoretical value of NCO, the reaction temperature is reduced to 60°C;

[0063] (3) After the temperature drops to the set temperature, dibutyltin dilaurate, neopentyl glycol, and ethylenediamine are added in sequence and reacted for 3.5 hours; finally, propylene glycol is added for cross-linking and reacted for 2 hours until the NCO content drops to 0, thereby obtaining unmodified TPU.

[0064] Comparative Example 2 (preparation of h-BN / TPU by modification of h-BN without stripping and functionalization modification in block form):

[0065] The functionalized boron nitride nanosheets (NCO-BNNSs-OH) in Example 1 were replaced with 10 parts of boron nitride (h-BN), and the functionalized boron nitride nanosheets (NCO-BNNSs-OH) powder in step S2' was replaced with boron nitride (h-BN) powder, and the remaining steps were the same as the process flow of steps S1' and S3' in Example 1. Finally, h-BN / TPU material was obtained.

[0066] Comparative Example 3 (modifying agent replaced by hexamethylene diisocyanate):

[0067] The hexamethylene diisocyanate isocyanurate six-membered ring trimer in step S3 of Example 1 was replaced with hexamethylene diisocyanate, and the NCO-BNNSs-OH powder in step S2' was replaced with the corresponding hexamethylene diisocyanate-modified functionalized boron nitride nanosheets, and the remaining steps were the same as the process flow in Example 1. Finally, a functionalized boron nitride nanosheet covalently grafted polyurethane elastomer (S-NCO-BNNSs-OH / TPU) material was obtained.

[0068] In this application, whether it is an embodiment or a comparative example, all prepared polyurethane film samples follow strict testing standards for performance evaluation. Specifically, the test standard for thermal diffusivity is ISO 22007-2, the test standard for thermal conductivity is ASTM D5470, and the test standard for elongation at break is GB / T1040.1-2018.

[0069] This application uses Fourier transform infrared spectroscopy (FT-IR) to conduct a detailed comparative analysis of the surface chemical functional groups of h-BN in Example 1 before and after modification, aiming to verify whether the surface of functionalized boron nitride nanosheets (NCO-BNNSs-OH) has the characteristics of isocyanate molecules. Figure 3As shown in the figure, compared with the original boron nitride (h-BN) and the hydroxylated boron nitride nanosheets (BNNSs-OH) modified with hydroxyl groups, the spectrum of the functionalized boron nitride nanosheets (NCO-BNNSs-OH) not only maintains the characteristic peaks of BN bonds (1376cm-1 and 762cm-1) and the characteristic peak of hydroxyl (-OH) (3219cm-1), but also shows several new characteristic peaks. It is worth noting that the peak near 2270cm-1 corresponds to the stretching vibration of the -NCO group. In addition, the -OH peak in the functionalized boron nitride nanosheets (NCO-BNNSs-OH) is significantly weakened compared with that of BNNSs-OH, which indicates that a chemical reaction occurs between the hydroxyl groups on the surface of the hydroxylated boron nitride nanosheets (BNNSs-OH) and the six-membered ring trimer of hexamethylene diisocyanate isocyanurate. Based on the above analysis, these newly emerged absorption peaks fully demonstrate the successful modification of hydroxylated boron nitride nanosheets (BNNSs-OH) by hexamethylene diisocyanate isocyanurate six-membered ring trimer.

[0070] This application conducts an in-depth analysis of the thermal conductivity and mechanical properties of different TPU-based nanocomposites, and compares the examples with the comparative examples (e.g. Figure 4-Figure 6 As shown in the figure, it was found that in Examples 1 to 4 (the horizontal axis is numbered 1-4), with the increasing content of hexamethylene diisocyanate isocyanurate six-membered ring trimer and modified nano inorganic particle functionalized boron nitride nanosheets (NCO-BNNSs-OH), the thermal diffusion coefficient, thermal conductivity and elongation at break of the nanocomposite material all showed a corresponding growth trend. This result shows that the functionalized boron nitride nanosheets (NCO-BNNSs-OH) have excellent compatibility with the thermoplastic polyurethane (TPU) matrix, which can promote the rapid transfer of heat flow inside the functionalized boron nitride nanosheet covalently grafted polyurethane (NCO-BNNSs-OH / TPU) system, effectively disperse stress, and significantly improve the mechanical properties of the composite material.

[0071] Comparative Examples 1 to 3 (numbered 5-7 on the horizontal axis) confirm the functional modification of boron nitride (h-BN) and the structural advantages of hexamethylene diisocyanate isocyanurate six-membered ring trimer compared to ordinary hexamethylene diisocyanate from another perspective. This modification not only increases the reactive active sites on the surface of functionalized boron nitride nanosheets (NCO-BNNSs-OH), but also promotes the cross-linking degree of TPU matrix molecules, which is more conducive to the improvement of thermal conductivity and mechanical properties of composite materials.

[0072] In addition, the field emission scanning electron microscope (FESEM) images of Example 1 and Comparative Example 2 at the same magnification show (as shown in Figure 7 and Figure 8As shown in the figure, no obvious aggregation of functionalized boron nitride nanosheets (NCO-BNNSs-OH) was observed in the TPU matrix, while boron nitride (h-BN) showed a large amount of aggregation. This observation shows that functionalized boron nitride nanosheets (NCO-BNNSs-OH) can form good interactions inside the TPU matrix and build an effective thermal conductive network, which is consistent with the above-mentioned mechanical and thermal conductivity analysis results, further confirming the positive role of functionalized boron nitride nanosheets (NCO-BNNSs-OH) in improving the performance of composite materials.

[0073] The above embodiments are only used to illustrate the technical solutions of the present disclosure, rather than to limit them. Although the present disclosure is described in detail with reference to the above embodiments, a person skilled in the art should understand that the technical solutions described in the above embodiments can still be modified, or some of the technical features can be replaced by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present disclosure.

[0074] The above description is only the preferred embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the present application may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

[0075] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the above embodiments, a person skilled in the art should understand that the technical solutions described in the above embodiments can still be modified, or some of the technical features can be replaced by equivalents; and these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A functionalized boron nitride nanosheet, characterized in that: The method for preparing the functionalized boron nitride nanosheets comprises the following steps: S1. Preparation of hexagonal boron nitride nanosheets: Boron nitride powder is uniformly dispersed in isopropanol, and then an intercalation agent is added and stirred for 30 to 50 minutes; the mixed solution is heated to 160 to 190°C and reacted at this temperature for 72 to 80 hours; after the reaction is completed, the temperature is lowered to room temperature and stirring is stopped; the resulting solution is ultrasonically treated, and then sealed and allowed to stand for a specified time; after standing, the upper layer of dissolved colloidal hexagonal boron nitride nanosheets is poured out and placed in an oven for drying; S2. Preparation of hydroxylated boron nitride nanosheets: adding the hexagonal boron nitride nanosheets obtained in step S1 to an alkaline hydroxide solution of a predetermined concentration and ultrasonically treating the solution, heating and stirring the solution under reflux at 100 to 120° C. for 5 to 7 hours, centrifuging the product, washing the product with an organic solvent, and vacuum drying the product to obtain hydroxylated boron nitride nanosheets; S3. Under nitrogen protection, the hydroxylated boron nitride nanosheets, N,N-dimethylformamide, catalyst and modifier are stirred and reacted at a temperature of 70 to 80°C for 6 to 10 hours; after the reaction is completed, the reaction mixture is repeatedly washed with a solvent, and ultrasonically dispersed and centrifuged, and the lower layer of precipitate is collected and dried to obtain the functionalized boron nitride nanosheets.

2. The functionalized boron nitride nanosheet according to claim 1, characterized in that: The weight parts of each raw material are as follows:

3. The functionalized boron nitride nanosheet according to claim 1, characterized in that: In step S1, the ultrasonic treatment time is 2 to 3 hours, and the ultrasonic treatment power is 200 to 500W; in step S2, the ultrasonic treatment time is 1 to 2 hours, and the ultrasonic treatment power is 100 to 300W.

4. The functionalized boron nitride nanosheet according to claim 1, characterized in that: In step S2, the alkaline hydroxide is potassium hydroxide and / or sodium hydroxide; the organic detergent is N,N-dimethylformamide and / or acetone.

5. The functionalized boron nitride nanosheet according to claim 1, characterized in that: In step S3, the catalyst is a combination of one or more of triethylamine, triethylenediamine, bis(dimethylaminoethyl)ether, stannous octoate, and dibutyltin dilaurate; and the modifier is hexamethylene diisocyanate isocyanurate six-membered ring trimer and / or isophorone diisocyanate isocyanurate six-membered ring trimer.

6. A functionalized boron nitride nanosheet covalently grafted with polyurethane, characterized in that: The invention comprises the functionalized boron nitride nanosheets prepared as claimed in any one of claims 1 to 5.

7. A functionalized boron nitride nanosheet covalently grafted polyurethane as claimed in claim 6, characterized in that: The preparation method of the functionalized boron nitride nanosheet covalently grafted polyurethane comprises the following steps: S1 '. Add oligomer polyol monomers to the container, raise the temperature to 120 to 130 ° C, and dehydrate under vacuum for 2 to 2.5h; S2'. Under nitrogen protection, the temperature is adjusted to 60-85 ° C; the functionalized boron nitride nanosheets are uniformly dispersed in N-methylpyrrolidone and added dropwise to the solution; then the diisocyanate is added dropwise, and the addition is completed, and the reaction is kept at 85-90 ° C for 2-2.5 hours; then the isocyanate content of the generated prepolymer is determined, and when it is close to the theoretical value, the reaction temperature is reduced to 50-65 ° C; S3'. After the temperature drops to the set temperature, a catalyst, a diol chain extender, and a diamine chain extender are added in sequence and reacted for 3 to 4 hours; finally, a polyol with a functionality ≥ 3 is added for crosslinking and reacted for 1 to 3 hours until the isocyanate group content is 0, thereby obtaining the functionalized boron nitride nanosheet grafted polyurethane.

8. The functionalized boron nitride nanosheet covalently grafted polyurethane according to claim 7, characterized in that: The weight parts of each raw material are as follows:

9. The functionalized boron nitride nanosheet grafted polyurethane according to claim 7, characterized in that: In step S1', the oligomer polyol monomer is one of polycarbonate diol, polyethylene glycol, polybutylene adipate, polytetramethylene glycol, polypropylene glycol, or any combination thereof.

10. The functionalized boron nitride nanosheet grafted polyurethane according to claim 7, characterized in that: In step S2', the concentration of the dispersion of the functionalized boron nitride nanosheets is 0.1-5%; the diisocyanate compound is one of toluene diisocyanate, naphthalene diisocyanate, trimethyl hexamethylene diisocyanate or trimethyl-1,6-hexamethylene diisocyanate.

11. The functionalized boron nitride nanosheet grafted polyurethane according to claim 7, characterized in that: In step S3', the catalyst is dibutyltin dilaurate; The diol chain extender is one of dimethylol propionic acid, neopentyl glycol, dimethylol butyric acid, 1,4-butanediol, and 1,6-hexanediol; the diamine chain extender is ethylenediamine; The polyol compound with a functionality of ≥3 is one of glycerol, pentaerythritol, trimethylolpropane, or any combination thereof.

12. A boron nitride nanosheet covalently grafted polyurethane high thermal conductivity composite material, characterized in that: The invention comprises the functionalized boron nitride nanosheets covalently grafted with polyurethane as described in claims 6 to 11.

Images