A method for preparing a core-shell structured boron nitride@vinylidene fluoride polymer

Abstract

The present invention relates to the technical field of high thermal conductivity fillers, and in particular to a method for preparing a high thermal conductivity core-shell structured boron nitride@vinylidene fluoride based polymer filler. The present invention synthesizes a core-shell structured boron nitride by an innovative phase separation method, successfully modifies a vinylidene fluoride based copolymer on the interface of BN, and increases the compatibility of the two-dimensional high thermal conductivity filler in a polymer matrix; therefore, the high thermal conductivity filler prepared in the present invention has broad application prospects in the fields of electronic packaging systems, high voltage electrical insulation equipment, and high dielectric capacitors.

Description

Technical Field

[0001] The invention relates to the field of high thermal conductivity materials and high electrical insulation materials, and in particular to a method for preparing a thermally conductive filler with a core-shell structure. Background Art

[0002] BN, also known as "white graphite", is widely used in thermal electronic packaging systems, high-voltage electrical insulation equipment, and high-dielectric capacitors because of its excellent electrical insulation properties and high thermal conductivity. Since two-dimensional boron nitride powder is easy to agglomerate, it is extremely difficult to disperse it into organic resins during use. Boron nitride is prone to agglomeration in polymer composite systems, which greatly reduces the mechanical properties and thermal conductivity of the material. In view of this shortcoming, it is necessary to design a core-shell structured boron nitride powder filler and preparation method.

[0003] Patent ZL202210546747.1 discloses a method for preparing a core-shell structured boron nitride material, which uses negatively charged phytic acid and then adds positively charged polyethyleneimine. This is a physical electrostatically adsorbed core-shell structure with poor shell stability, and is easily washed away by water or organic solvents. Summary of the invention

[0004] In view of the above problems, the present invention provides a method for preparing a boron nitride@vinylidene fluoride polymer having a core-shell structure, and successfully grafts the vinylidene fluoride copolymer onto the BN surface by a phase separation method to solve the disadvantage that the high thermal conductivity BN filler is difficult to disperse in the prior art. The specific technical scheme is as follows:

[0005] A method for preparing boron nitride with a core-shell structure, the specific steps are as follows:

[0006] Step 1: Ultrasonic dispersion of BN two-dimensional sheet material in N,N-dimethylformamide or N,N-dimethylacetamide solvent;

[0007] Step 2: dissolving the vinyl fluoride copolymer in N,N-dimethylformamide or N,N-dimethylacetamide solvent, and stirring at 50-70° C. for 5-7 hours;

[0008] Step 3: Mix the solutions in step 1 and step 2, and stir at below 60° C. for 24 hours;

[0009] Step 4: Slowly add n-octanol to the mixed solution in step 3 through a constant pressure separatory funnel, maintain the temperature at 60°C, and continue stirring for 24 hours;

[0010] Step 5: removing the solvent from the mixed solution in step 4 by evaporating to obtain a core-shell structured boron nitride filler;

[0011] Step 6: Centrifuge the filler obtained in step 5, and wash it with ethanol, methanol or propanol for 3-6 times. Place the obtained filler in a vacuum oven at 100 degrees Celsius and dry it for 5-8 hours to obtain boron nitride with a core-shell structure.

[0012] A further improvement is characterized in that the solvents in step 1 and step 2 are both DMF solvents.

[0013] A further improvement is characterized in that the vinyl fluoride-based copolymer is poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene), polyvinylidene fluoride, poly(vinylidene fluoride-trifluoroethylene), poly(vinylidene fluoride-chlorotrifluoroethylene), and poly(vinylidene fluoride-hexafluoropropylene).

[0014] A further improvement is characterized in that the vinyl fluoride-based copolymer is poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene).

[0015] A further improvement is characterized in that the mass ratio of the BN two-dimensional sheet material to the mass ratio of poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) is 3:1 to 1:3, and the higher the mass of poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene), the greater the shell thickness.

[0016] A further improvement is characterized in that the mass ratio of the BN two-dimensional sheet material to the solvent DMF solvent in step 1 is 1:50-1:70.

[0017] A further improvement is characterized in that the mass ratio of n-octanol in step 4 to the mass ratio of the BN two-dimensional sheet material is 60:1 to 80:1.

[0018] A further improvement is characterized in that the stirring speed in step three is 400-900 rpm.

[0019] Beneficial effects of the invention: The invention provides a method for preparing a core-shell structured boron nitride@vinylidene fluoride based polymer, and successfully characterizes its shell structure. The successful modification of the shell structure of the vinylidene fluoride based copolymer changes the binding ability between the BN surface and the matrix material, and can improve the dispersibility of the two-dimensional thermal conductive filler in the polymer matrix; for the first time, a fluorine-containing polymer is used to graft on the surface of BN by phase separation combined with a chemical bonding method at high temperature. The obtained shell has strong stability and will not fall off in aqueous solutions and organic solvents, greatly improving the dispersibility and thermal conductivity of the BN two-dimensional sheet material in the matrix resin. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Schematic diagram of the preparation process of the thermal conductive filler BN@P (VDF-TrFE-CFE) with a core-shell structure in the present invention;

[0021] Figure 2 TEM image and elemental analysis EDS of pure BN in Example 1 of the present invention;

[0022] Figure 3 TEM image and elemental analysis EDS of the thermal conductive filler BN@P (VDF-TrFE-CFE) in Example 1 of the present invention;

[0023] Figure 4 : The infrared absorption spectra of the thermal conductive filler BN and BN@P (VDF-TrFE-CFE) in Example 1 of the present invention;

[0024] Figure 5 XRD diagrams of the thermal conductive filler BN and BN@P (VDF-TrFE-CFE) prepared in Example 1 of the present invention;

[0025] Figure 6 This is the thermogravimetric curve of the thermal conductive filler BN@P (VDF-TrFE-CFE) with a core-shell structure prepared in Example 1 of the present invention;

[0026] Figure 7 It is the water contact angle of the thermal conductive filler BN@P (VDF-TrFE-CFE) with core-shell structure prepared in Example 1. DETAILED DESCRIPTION

[0027] In order to deepen the understanding of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. The embodiments are only used to explain the present invention and do not limit the scope of protection.

[0028] Example 1

[0029] In this embodiment, poly (vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) is used as the core-shell material to prepare a core-shell structure thermal conductive filler BN@P (VDF-TrFE-CFE), and the specific preparation method includes the following steps:

[0030] S1. Ultrasonic dispersion of 0.5 g of BN two-dimensional sheet material in 30 g of N,N-dimethylformamide (DMF) for 0.5 h. Next, 0.25 g of poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) [P(VDF-TrFE-CFE)] was dissolved in 3.5 g of DMF and stirred at 60 degrees Celsius for 6 hours. In this process, it should be noted that the mass ratio of BN two-dimensional sheet material and P(VDF-TrFE-CFE) should be 2:1. Subsequently, the two solutions were mixed and stirred at 400 rpm at 60 degrees Celsius for 24 hours.

[0031] S2. Slowly add 35 g of n-octanol into the mixture of the first step through a constant pressure separatory funnel, maintain the temperature at 60 degrees Celsius, and continue stirring for 24 hours.

[0032] S3. The mixture was evaporated at 160 degrees Celsius to remove DMF to obtain a core-shell structured BN@P (VDF-TrFE-CFE) filler. Then, the obtained nanoparticles were centrifuged and washed with ethanol 5 times to remove residual n-octanol and residual matrix P (VDF-TrFE-CFE). Finally, the dried nanoparticles were dried in a vacuum oven at 100 degrees Celsius for 6 hours to remove residual liquid.

[0033] The schematic diagram of the preparation process of the core-shell structure filler BN@P (VDF-TrFE-CFE) obtained in this example is as follows Figure 1 As shown in the figure, TEM and elemental analysis EDS, infrared absorption spectrum and XRD analysis of traditional thermal conductive filler BN and core-shell structure filler BN@P (VDF-TrFE-CFE) are shown in the figure. Figure 2-5 Then the two substances were subjected to thermogravimetric analysis to obtain a curve reference Figure 6 .

[0034] Test method:

[0035] X-Ray diffraction method (XRD): Pure BN and the powder samples prepared in Example 1 were placed on a sample table, flattened, and then scanned using an X-ray diffractometer (SmartLab9KW) with a scanning angle of 10-90° and a scanning speed of 5° / min.

[0036] Transmission electron microscopy (TEM): Pure BN and the powder sample prepared in Example 1 were dissolved in water and dispersed by ultrasonic wave for 15 min. A small drop of liquid was placed on the carbon film. Finally, the surface morphology and elemental analysis of the core-shell structured BN@P (VDF-TrFE-CFE) nanoparticles were performed using a transmission electron microscope (TEM, ThermoFisher Talos F200S).

[0037] Thermogravimetric analysis (TGA): 10 mg of pure BN and the powder prepared in Example 1 were weighed and placed in an alumina crucible, and tested using a thermogravimetric analyzer (Mettler) with a heating rate of 20° / min and a heating range of 25-600°C.

[0038] Infrared spectrum: A FT-IR spectrometer (Smart OMNI-Transmission, Thermo scientific) equipped with an intelligent iTR plug-in was used for characterization, with a scanning resolution of 2 cm-1, a scanning range of 400 to 4000 cm-1, and 32 scans to ensure the accuracy and reliability of the records.

[0039] Water contact angle test: The German KRUSS standard DSA25 contact angle goniometer is used to measure the water contact angle. The surface tension and contact angle of the liquid can be measured at -30℃-160℃. The contact angle measurement range is 0-180o. The results are shown in Figure 7 .

[0040] Data Analysis:

[0041] The characterization results of transmission electron microscopy show that typical core-shell structures are found in both successfully prepared BN@P(VDF-TrFE-CFE)NSs nanoparticles. The characteristic size of the original BN two-dimensional sheet material is 5-10μm, and its outer edges are very smooth without shell structure. The EDS element distribution shows that it only contains two elements, B and N, and its color contrast is high. After nano-coating modification to core-shell structure nanoparticles, the shell thickness of BN@P(VDF-TrFE-CFE) is about 50nm. EDS element analysis can clearly observe the chlorine and fluorine elements in the shell containing P(VDF-TrFE-CFE), indicating that it has been successfully grafted on the surface of BN.

[0042] In the FTIR spectrum and XRD spectrum, an absorption peak at 855cm-1 was found in BT@P(VDF-TrFE-CFE), which is one of the characteristic absorption peaks of P(VDF-TrFE-CFE), while other characteristic peaks are covered by BN and are difficult to observe. The typical crystal structure of BN can be observed in the XRD spectrum of BN@P(VDF-TrFE-CFE). For pure BT@TP NPs, there is a new relaxation phase peak of the P(VDF-TrFE-CFE) shell at 18.9o.

[0043] From the analysis of the thermogravimetric analysis spectrum, pure BN has almost no mass loss when heated from room temperature to about 900 degrees, indicating that BN has good thermal stability; when the BN@P(VDF-TrFE-CFE) shell is modified, when the temperature rises to about 550℃, an obvious heat loss peak appears, which is caused by the thermal decomposition of the polymer. Therefore, it can be estimated that the grafting degree of the shell P(VDF-TrFE-CFE) is about 17.6g / 100g.

[0044] According to the water contact angle test results, the contact angle of pure BN filler is only about 12.7°, indicating that BN itself is rich in hydrophilic groups and has good hydrophilicity. However, when the P(VDF-TrFE-CFE) shell material is modified on its surface, its surface hydrophilicity becomes worse, and its contact angle is about 65.3°.

Claims

1. A method for preparing a boron nitride@vinylidene fluoride polymer having a core-shell structure, the specific steps are as follows: Step 1: Ultrasonic dispersion of BN two-dimensional sheet material in N,N-dimethylformamide or N,N-dimethylacetamide solvent; Step 2: dissolving the vinyl fluoride copolymer in N,N-dimethylformamide or N,N-dimethylacetamide solvent, and stirring at 50-70° C. for 5-7 hours; Step 3: Mix the solutions in step 1 and step 2, and stir at below 60° C. for 24 hours; Step 4: Slowly add n-octanol to the mixed solution in step 3 through a constant pressure separatory funnel, maintain the temperature at 60°C, and continue stirring for 24 hours; Step 5: removing the solvent from the mixed solution in step 4 by evaporating to obtain a core-shell structured boron nitride filler; Step 6: Centrifuge the filler obtained in step 5, and wash it with ethanol, methanol or propanol for 3-6 times. Place the obtained filler in a vacuum oven at 100 degrees Celsius and dry it for 5-8 hours to obtain boron nitride with a core-shell structure.

2. The method for preparing a core-shell structured boron nitride@vinylidene fluoride polymer according to claim 1, characterized in that: The solvents in step 1 and step 2 are both DMF solvents.

3. The method for preparing a core-shell structured boron nitride@vinylidene fluoride polymer according to claim 1, characterized in that: The vinylidene fluoride-based copolymer is poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene), polyvinylidene fluoride, poly(vinylidene fluoride-trifluoroethylene), poly(vinylidene fluoride-chlorotrifluoroethylene), and poly(vinylidene fluoride-hexafluoropropylene).

4. The method for preparing a core-shell structured boron nitride@vinylidene fluoride polymer according to claim 3, characterized in that: The vinylidene fluoride-based copolymer is poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene).

5. The method for preparing a core-shell structured boron nitride@vinylidene fluoride polymer according to claim 4, characterized in that: The mass ratio of the BN two-dimensional sheet material to poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) is 3:1 to 1:

3.

6. The method for preparing a core-shell structured boron nitride@vinylidene fluoride polymer according to claim 2, characterized in that: In the step 1, the mass ratio of the BN two-dimensional sheet material to the DMF solvent is 1:50-1:

70.

7. The method for preparing a core-shell structured boron nitride@vinylidene fluoride polymer according to claim 1, characterized in that: The mass ratio of the n-octanol in the step 4 to the BN two-dimensional sheet material is 60:1 to 80:

1.

8. The method for preparing a core-shell structured boron nitride@vinylidene fluoride polymer according to claim 1, characterized in that: The stirring speed in step 3 is 400-900 rpm.

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