CN115746404B - Surface modified hexagonal boron nitride nanosheet, modification method thereof and epoxy composite material - Google Patents
Surface modified hexagonal boron nitride nanosheet, modification method thereof and epoxy composite material Download PDFInfo
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- 239000002135 nanosheet Substances 0.000 title claims abstract description 79
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- 239000002131 composite material Substances 0.000 title claims abstract description 48
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- 238000002715 modification method Methods 0.000 title claims abstract description 12
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- 125000003700 epoxy group Chemical group 0.000 claims abstract description 16
- 239000007788 liquid Substances 0.000 claims abstract description 15
- 239000006185 dispersion Substances 0.000 claims abstract description 14
- 238000001132 ultrasonic dispersion Methods 0.000 claims abstract description 13
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- 238000001291 vacuum drying Methods 0.000 claims abstract description 3
- 238000003828 vacuum filtration Methods 0.000 claims abstract description 3
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 claims description 44
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- 238000000034 method Methods 0.000 claims description 17
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- 239000002253 acid Substances 0.000 claims description 6
- KRKNYBCHXYNGOX-UHFFFAOYSA-N citric acid Chemical compound OC(=O)CC(O)(C(O)=O)CC(O)=O KRKNYBCHXYNGOX-UHFFFAOYSA-N 0.000 claims description 6
- 239000003795 chemical substances by application Substances 0.000 claims description 5
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- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 claims description 4
- 235000006408 oxalic acid Nutrition 0.000 claims description 4
- 150000008064 anhydrides Chemical class 0.000 claims description 3
- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 claims description 2
- 235000011054 acetic acid Nutrition 0.000 claims description 2
- 229910000147 aluminium phosphate Inorganic materials 0.000 claims description 2
- 235000015165 citric acid Nutrition 0.000 claims description 2
- 229910017604 nitric acid Inorganic materials 0.000 claims description 2
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- AHDSRXYHVZECER-UHFFFAOYSA-N 2,4,6-tris[(dimethylamino)methyl]phenol Chemical compound CN(C)CC1=CC(CN(C)C)=C(O)C(CN(C)C)=C1 AHDSRXYHVZECER-UHFFFAOYSA-N 0.000 description 5
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- VYKXQOYUCMREIS-UHFFFAOYSA-N methylhexahydrophthalic anhydride Chemical compound C1CCCC2C(=O)OC(=O)C21C VYKXQOYUCMREIS-UHFFFAOYSA-N 0.000 description 5
- 239000002105 nanoparticle Substances 0.000 description 4
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- Epoxy Resins (AREA)
Abstract
The invention relates to a surface modified hexagonal boron nitride nano-sheet, a modification method thereof and an epoxy composite material, wherein the modification method comprises the following steps: (1) Adding hexagonal boron nitride powder into a homogeneous aqueous solution of an epoxy group-containing silane coupling agent, performing ultrasonic dispersion to obtain hexagonal boron nitride dispersion liquid, and adjusting the pH value to 0-6; (2) Transferring the dispersion liquid obtained in the step (1) into a ball milling tank, ball milling for 1-48 hours at 100-2000 rpm, performing vacuum suction filtration after ball milling, and drying the powder obtained by suction filtration to obtain the hexagonal boron nitride nano-sheet with the surface functionalized by epoxy groups; (3) Adding the hexagonal boron nitride nano-sheet obtained in the step (2) into an aqueous solution of branched polyethylenimine, performing ultrasonic dispersion, reacting for 1-48 hours at 0-80 ℃, and performing vacuum filtration and drying to obtain the surface modified hexagonal boron nitride nano-sheet. The surface modified hexagonal boron nitride nano-sheet of the invention obviously improves the heat conduction and mechanical properties of the epoxy composite material.
Description
Technical Field
The invention belongs to the field of nano composite materials, and particularly relates to a surface modified hexagonal boron nitride nano sheet, a modification method thereof and an epoxy composite material.
Background
With the development of modern power electronics in the direction of miniaturization, high integration and high power density, the problem of thermal management of electronic components inside the device is becoming more and more prominent. The electronic components with high integration density can generate a large amount of heat under the working state, so that the temperature of the components is rapidly increased, and finally the performance and the service life of the electronic equipment are seriously affected. In order to timely conduct out accumulated heat and ensure long-time stable operation of electronic components, it is necessary to fill heat conducting materials between the electronic components. Epoxy resins are a class of thermosetting resins having good comprehensive properties (mechanical strength, adhesive strength, insulating properties, chemical stability, etc.), and are widely used as encapsulating materials for electronic components. However, pure epoxy resin has a low thermal conductivity (about 0.2W/m·k) and cannot effectively diffuse heat of electronic components in time. Therefore, the development of the epoxy packaging material with high heat conduction and excellent comprehensive performance has important practical significance.
It is currently most common practice to improve the thermal conductivity of epoxy resin by introducing a highly thermally conductive filler into the epoxy resin matrix. As an inorganic filler having a high thermal conductivity and excellent mechanical properties, hexagonal boron nitride (h-BN), particularly, exfoliated h-BN nanoplatelets, are widely used for manufacturing various high thermal conductivity composite materials. Notably, the simple and coarse addition of the h-BN filler to the matrix generally results in uneven dispersion within the matrix and a large number of interfacial voids between the filler and the matrix, reducing the thermal conductivity of the composite. The patent document with the publication number of CN110922719A discloses a high-heat-conductivity boron nitride/epoxy resin composite material, a preparation method and application thereof, wherein h-BN nano particles are used as raw materials, surface modification h-BN nano sheets are obtained through ultrasonic stripping and surface modification of a silane coupling agent, and finally the surface modification h-BN nano sheets are compounded with epoxy resin, so that the steps of the prepared surface modification h-BN nano sheets are complicated, and the interfacial compatibility between the h-BN nano sheets and the epoxy resin is limited. The patent document with the publication number of CN113969040A takes hyperbranched polyethylene polymer as a modification molecule, carries out surface modification on h-BN through pi-pi and other non-covalent actions, effectively improves the dispersibility of h-BN nano particles and the interface compatibility of the h-BN nano particles with an epoxy matrix, but the non-covalent actions make the binding force between the modification molecule and the h-BN weak, and chemical connection cannot be generated between the modification molecule and the epoxy matrix, so that the obtained epoxy composite material has still unsatisfactory heat conduction performance and mechanical performance.
Disclosure of Invention
Based on the defects and shortcomings in the prior art, the invention provides a surface modified hexagonal boron nitride nano-sheet, a modification method thereof and an epoxy composite material. The method aims to obtain the surface modified h-BN nano sheet through simple steps, improve the dispersibility of the h-BN, enable the surface of the modified h-BN nano sheet to have abundant active groups, simultaneously perform an interfacial chemical reaction with epoxy molecules and a curing agent, improve the interfacial compatibility of a filler-matrix, and finally improve the heat conduction performance and the mechanical performance of the epoxy composite material.
In order to achieve the aim of the invention, the invention adopts the following technical scheme:
the modification method of the surface modified hexagonal boron nitride nanosheets comprises the following steps:
(1) Adding hexagonal boron nitride powder into a homogeneous aqueous solution of an epoxy group-containing silane coupling agent, performing ultrasonic dispersion to obtain hexagonal boron nitride dispersion liquid, and adjusting the pH value to 0-6;
(2) Transferring the dispersion liquid obtained in the step (1) into a ball milling tank, ball milling for 1-48 hours at 100-2000 rpm, performing vacuum suction filtration after ball milling, and drying the powder obtained by suction filtration to obtain the hexagonal boron nitride nano-sheet with the surface functionalized by epoxy groups;
(3) Adding the hexagonal boron nitride nano-sheet obtained in the step (2) into an aqueous solution of branched polyethylenimine, performing ultrasonic dispersion, reacting for 1-48 hours at 0-80 ℃, and performing vacuum filtration and drying to obtain the surface modified hexagonal boron nitride nano-sheet.
In the preferred scheme, in the step (1), KH560 is selected as the epoxy group-containing silane coupling agent, and the homogeneous aqueous solution is a water/ethanol mixed solution.
Preferably, in the step (1), the hexagonal boron nitride powder is dispersed in the water/ethanol mixed solution at a concentration of 0.5 to 50 mg/mL -1 The method comprises the steps of carrying out a first treatment on the surface of the The mass fraction of KH560 in the water/ethanol mixed solution is 0.01-30wt%; the volume ratio of the water/ethanol mixed solution is 1/(0.1-10).
Preferably, in the step (1), the ultrasonic dispersion time is 5-120 min; the pH of the hexagonal boron nitride dispersion was adjusted by an acid solution.
Preferably, the acid liquid is at least one of hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, oxalic acid, acetic acid, oxalic acid and citric acid;
the molar concentration of the acid solution is 0.01 to 10 mol.L -1 。
Preferably, in the step (2), the drying temperature is 30-150 ℃ and the drying time is 1-48 h.
Preferably, the molecular weight of the branched polyethyleneimine is 200-100000, and the concentration of the branched polyethyleneimine aqueous solution is 0.01-30wt%.
The invention also provides the surface modified hexagonal boron nitride nano-sheet obtained by modification by the modification method according to any scheme.
The invention also provides an epoxy composite material, the preparation process of which comprises the following steps:
(1) Adding the surface modified hexagonal boron nitride nano-sheet according to claim 8 into ethanol, and performing ultrasonic dispersion for 5-120 min to obtain the nano-sheet with the concentration of 0.5-50 mg.mL -1 Is a nanosheet dispersion of (a);
(2) Stirring and mixing the nano-sheet dispersion liquid, epoxy resin and a curing agent uniformly, and then distilling under reduced pressure to remove ethanol to obtain a mixed liquid;
(3) And stirring and mixing the mixed solution and the accelerator uniformly at normal temperature, standing and defoaming under vacuum, pouring the mixed solution onto a die after the bubbles are removed, and curing to obtain the epoxy composite material.
Wherein, E-51 epoxy resin is used as a matrix, methyl hexahydrophthalic anhydride (MHHPA) is used as a curing agent, 2,4, 6-tri (dimethylaminomethyl) phenol (DMP-30) is used as an accelerator, and the mass ratio of the two is E-51: MHHPA: DMP-30=100: (70-100) 0.1-2); the curing temperature is 80-180 ℃ and the curing time is 1-24 h.
As a preferable scheme, the content of the surface modified hexagonal boron nitride nano-sheet in the epoxy composite material is 1-40 wt%.
Compared with the prior art, the invention has the beneficial effects that:
the surface modified hexagonal boron nitride nano-sheet is prepared by dispersing hexagonal boron nitride nano-particles in a homogeneous aqueous solution of an epoxy group-containing silane coupling agent, and performing wet ball milling on the mixture to directly obtain the surface epoxy group-functionalized hexagonal boron nitride nano-sheet; and further obtaining the BPEI modified hexagonal boron nitride through the reaction of amino and epoxy.
The surface modified hexagonal boron nitride nanosheets prepared by the modification method have high yield and uniform size, rich amino groups exist on the surface, and the surface modified hexagonal boron nitride nanosheets can be well dispersed in an epoxy matrix, and good interface compatibility is generated between the filler and the matrix; and can be covalently combined with epoxy groups of epoxy molecular chains, so that the crosslinking degree is improved, and the heat conduction and mechanical properties of the epoxy composite material are enhanced.
The modification method disclosed by the invention is simple in process, low in cost, environment-friendly, suitable for large-scale production and capable of being widely used for enhancing the heat conduction and mechanical properties of various thermosetting and thermoplastic polymers.
Drawings
FIG. 1 is an SEM photograph of a nano-powder according to example 1 of the present invention. Wherein panel a, raw BN powder (noted BN); panel B shows BN nano-sheets (BNNS); panel C shows BN nano-sheets (designated KH 560-BNNS) obtained by ball milling with a solution containing KH560; panel D shows BPEI surface-modified BN nanosheets (designated BPEI-KH 560-BNNS);
FIG. 2 is a FTIR spectrum of the relevant nanopowder referred to in example 1 of the present invention. Wherein a is BN; b is BNNS; c is KH560-BNNS; d is BPEI-KH560-BNNS; e is KH560; f is BPEI.
FIG. 3 is a TGA curve of related nanopowders referred to in example 1 of the present invention. Wherein a is BN; b is BNNS; c is KH560-BNNS; d is BPEI-KH560-BNNS.
Detailed Description
The technical scheme of the invention is further explained by the following specific examples.
Example 1:
the preparation method of the surface modified BN nano-sheet comprises the following steps:
1) 2g BN powder was added to 120mL of a 1wt% KH560 mixed solution of water/ethanol (water: ethanol=1:4), after 30min of ultrasonic dispersion, by 8mol·l -1 Adjusting the pH value of BN dispersion liquid to 4 by hydrochloric acid solution; transferring BN dispersion liquid into a tungsten carbide ball milling tank, and adding 30 tungsten carbide grinding balls; ball milling for 24 hours at 600 rpm;
2) After ball milling is finished, carrying out vacuum suction filtration on the solution; then drying the powder obtained by suction filtration at 80 ℃ for 12 hours to obtain the surface epoxy group functionalized BN nano-sheet;
3) Adding the epoxy functionalized BN nano-sheet obtained in the step 2) into an aqueous solution containing 1wt% of BPEI, and performing ultrasonic dispersion for 30min; then reacting for 12 hours at 50 ℃, and obtaining the surface modified BN nano-sheet through vacuum suction filtration and drying.
The preparation method of the epoxy composite material of the embodiment comprises the following steps:
4) Adding the surface modified BN nano-sheet into ethanol, and performing ultrasonic dispersion for 30min to obtain the nano-sheet with the concentration of 10 mg/mL -1 BN nanosheet dispersion liquid;
5) Mixing above BN dispersion with E-51 epoxy resin and MHHPA under stirring for 2 hr, and distilling at 60deg.C under reduced pressure for 12 hr to remove ethanol solvent;
6) Stirring and mixing the solution obtained in the step 5) with DMP-30 for 0.5h at normal temperature, standing and defoaming for 1h under vacuum, pouring the mixed solution onto a die after the bubbles are removed, and curing for 4h at 120 ℃ to obtain the surface modified BN nano-sheet/epoxy composite material.
Wherein the mass fraction of the surface modified BN nano sheet in the epoxy composite material is 15wt%; e-51: MHHPA: DMP-30=100:82:0.6.
The epoxy composite of this example was cast into a standard sample to test the thermal conductivity and mechanical properties of the composite.
Preparation of surface-modified BN nanoplatelets (i.e. BPEI-KH 560-BNNS) is the first step in the preparation of epoxy nanocomposites. As shown in fig. 1A, BN exhibits irregular morphology and a tightly packed layered structure. After the ball milling process, a distinct nanoplatelet structure was observed, as shown in fig. 1B, mainly due to the shear forces during ball milling that peeled off the stacked nanoplatelets. Fig. 1C shows that the addition of KH560 does not have a significant effect on the structure of the BN nanoplatelets obtained by ball milling. Also, fig. 1D shows that post-modification with BPEI does not have a significant effect on the structure of BN nanoplatelets.
To determine the chemical structure of the surface modified BN nanoplatelets, infrared spectra were recorded. As shown in FIG. 2, KH560-BNNS was 2933cm compared to BN and BNNS -1 And 1091cm -1 Two new absorption bands are present at this point, respectively attributed to the stretching vibration of the C-H and Si-O bonds in KH560 molecules. Whereas for BPEI-KH560-BNNS, the length is 2933cm -1 And 1091cm -1 The two absorption bands are at 1460cm -1 There is a new absorption band, ascribed to the stretching vibration of the C-N bond in the BPEI molecule, which indicates that the BPEI molecule realizes surface modification of KH560-BNNS.
To determine the thermal stability of the surface modified BN nanoplatelets, thermogravimetric analysis was performed. As shown in FIG. 3, the weight loss of BN over the entire temperature range (30-800 ℃ C.) is only 0.27% while the weight loss of BNNS is estimated to be 2.85% mainly due to the removal of-OH and adsorbed water molecules from the BNNS surface. After KH560 modification, the loss rate of KH560-BNNS is 4.99%. When KH560-BNNS is further modified by BPEI, the weight loss rate of BPEI-KH560-BNNS reaches 9.43%, mainly due to thermal decomposition of surface KH560 and BPEI molecules at high temperature.
Comparative example 1:
this comparative example differs from example 1 in that:
ball milling is carried out in the step 1) by using a water/ethanol mixed solution without KH560;
other steps and process conditions were the same as in example 1.
The epoxy composites of this comparative example were cast into standard samples to test the thermal conductivity and mechanical properties of the composites.
Comparative example 2:
this comparative example differs from example 1 in that:
in the step 1), ball milling is carried out in a water/ethanol mixed solution without KH560, so as to obtain BN nano-sheets;
in step 2), BN nanoplatelets are added to a water/ethanol mixed solution containing 1wt% kh560 (water: ethanol=1:4), by 8mol·l -1 Adjusting the pH value of the BN dispersion liquid to 4 by using a hydrochloric acid solution, and stirring and reacting for 24 hours to obtain a functionalized BN nano-sheet;
other steps and process conditions were the same as in example 1.
The epoxy composites of this comparative example were cast into standard samples to test the thermal conductivity and mechanical properties of the composites.
Comparative example 3:
this comparative example differs from example 1 in that:
during the step 1), adding BN powder into the mixed solution of water and ethanol containing KH560 for mechanical stirring;
other steps and process conditions were the same as in example 1.
The epoxy composites of this comparative example were cast into standard samples to test the thermal conductivity and mechanical properties of the composites.
Comparative example 4:
this comparative example differs from example 1 in that:
in step 1), KH560 in the water/ethanol mixed solution is replaced by KH550, KH550 has no epoxy group;
other steps and process conditions were the same as in example 1.
The epoxy composites of this comparative example were cast into standard samples to test the thermal conductivity and mechanical properties of the composites.
Comparative example 5:
this comparative example differs from example 1 in that:
adding the surface epoxy functionalized BN nano-sheet in the step 3) into the BPEI solution, and stirring and mixing for 12 hours at room temperature;
other steps and process conditions were the same as in example 1.
The epoxy composites of this comparative example were cast into standard samples to test the thermal conductivity and mechanical properties of the composites.
Comparative example 6:
this comparative example differs from example 1 in that:
replacing the Branched Polyethylenimine (BPEI) in the solution in step 3) with a Linear Polyethylenimine (LPEI) of the same molecular weight, the LPEI having no amino side chains;
other steps and process conditions were the same as in example 1.
The epoxy composites of this comparative example were cast into standard samples to test the thermal conductivity and mechanical properties of the composites.
Comparative example 7:
this comparative example differs from example 1 in that:
the surface-modified BN nanoplatelets in example 1 were replaced with BN nanopowder of commercial origin;
other steps and process conditions were the same as in example 1.
The epoxy composites of this comparative example were cast into standard samples to test the thermal conductivity and mechanical properties of the composites.
Comparative example 8:
this comparative example differs from example 1 in that:
the surface-modified BN nanoplatelets in example 1 were replaced with BN nanoplatelets of commercial origin;
other steps and process conditions were the same as in example 1.
The epoxy composites of this comparative example were cast into standard samples to test the thermal conductivity and mechanical properties of the composites.
Comparative example 9:
this comparative example differs from example 1 in that:
omitting step (3), replacing the surface modified BN nanosheets in example 1 with surface epoxy functionalized BN nanosheets (i.e. KH560 modified BN nanosheets);
other steps and process conditions were the same as in example 1.
The epoxy composites of this comparative example were cast into standard samples to test the thermal conductivity and mechanical properties of the composites.
The epoxy composites of example 1 and comparative examples 1-9, as well as the pure epoxy materials, were tested for thermal conductivity, tensile strength, and impact strength, and the specific test results are shown in table 1.
Table 1 thermal conductivity, tensile Strength and impact Strength of samples of examples and comparative examples
| Sample name | Coefficient of thermal conductivity (W/m.K) | Tensile Strength (MPa) | Impact Strength (kJ/m) 2 ) |
| Pure epoxy | 0.21 | 48.3 | 9.2 |
| Example 1 | 1.14 | 95.1 | 24.5 |
| Comparative example 1 | 0.49 | 59.6 | 13.1 |
| Comparative example 2 | 0.68 | 71.9 | 17.7 |
| Comparative example 3 | 0.45 | 53.3 | 12.2 |
| Comparative example 4 | 0.56 | 63.8 | 15.9 |
| Comparative example 5 | 0.79 | 82.7 | 18.6 |
| Comparative example 6 | 0.72 | 72.4 | 17.3 |
| Comparative example 7 | 0.41 | 50.2 | 11.5 |
| Comparative example 8 | 0.54 | 57.6 | 13.3 |
| Comparative example 9 | 0.61 | 62.7 | 16.4 |
In comparative example 1, BPEI produced non-covalent modification of BN nanoplatelets. Comparison with example 1 shows that the BPEI covalent modified BN nano-sheet has better heat conduction and mechanical improvement effect than the BPEI non-covalent modified BN nano-sheet;
in comparative example 2, the epoxy-functionalized BN nanosheets were obtained by stepwise modification using KH 560. Compared with the comparison result of the embodiment 1, the epoxy group functionalized BN nano-sheet obtained by BPEI modification and one-step ball milling has better heat conduction and mechanical improvement effects than the epoxy group functionalized BN nano-sheet obtained by BPEI modification and one-step modification;
in comparative example 3, BN was not ball milled and no nanoplatelet structure could be obtained. Comparison with example 1 shows that the BPEI surface modified BN nano-sheet has better heat conduction and mechanical improvement effect than the BPEI surface modified BN powder;
in comparative example 4, KH550 was used instead of KH560, and the obtained BN nanosheets functionalized with amino groups could not be further covalently bonded to BPEI. Compared with the BN nano-sheet modified by KH550, the BPEI surface modified BN nano-sheet has better heat conduction and mechanical lifting effects as shown by the comparison result with the example 1;
in comparative example 5, BPEI reacted to a lesser extent with epoxy BN nanoplatelets at room temperature. Compared with the BPEI surface modified BN nano-sheet prepared at a certain temperature, the BPEI surface modified BN nano-sheet prepared at normal temperature has better heat conduction and mechanical improvement effects;
in comparative example 6, the linear polyethylenimine LPEI surface modified BN nanoplatelets had a lower number of amino groups, resulting in a lower degree of cross-linking with the epoxy matrix. Comparison with example 1 shows that the BPEI surface modified BN nano-sheet has better heat conduction and mechanical improvement effect than the LPEI surface modified BN nano-sheet;
comparison results of comparative examples 7, 8 and 9 with example 1 show that BPEI surface modified BN nano-sheets have better heat conduction and mechanical promotion effects than commercial BN powder, BN nano-sheets and KH560 modified BN nano-sheets at the same addition ratio.
The chemical modification principle of the surface modified BN of the invention is as follows:
1. the BN powder is stripped into BN nano-sheets under the action of shearing force in the ball milling process; simultaneously, hydroxyl on the surface of the BN nano-sheet reacts with the hydrolyzed KH560 to obtain the epoxy functionalized BN nano-sheet, and a connection point is provided for further modification of BPEI;
2. the BPEI containing rich amino groups and epoxy groups of the epoxy functionalized BN nano-sheet undergo a ring-opening reaction to obtain the BPEI surface modified BN nano-sheet; after BPEI surface modification, the surface of the BN nano-sheet contains rich amino groups, can simultaneously react with epoxy groups in an epoxy resin matrix and anhydride groups in an anhydride curing agent to generate firm chemical connection, and improves the dispersibility and interface compatibility of the BN nano-sheet.
In the above embodiments and alternatives thereof, the process parameters related to each raw material and the modification method can be determined according to practical application requirements within a defined range.
In view of the numerous embodiments of the present invention, all components, component contents and process parameters can be determined according to application requirements within corresponding ranges, experimental data of each embodiment are huge and numerous, and are not suitable for one-by-one enumeration and description herein, but the content of each embodiment to be verified and the obtained final conclusion are close.
The foregoing is only illustrative of the preferred embodiments and principles of the present invention, and changes in specific embodiments will occur to those skilled in the art upon consideration of the teachings provided herein, and such changes are intended to be included within the scope of the invention as defined by the claims.
Claims (7)
1. The epoxy composite material is characterized in that the preparation process comprises the following steps:
(a) Adding the surface modified hexagonal boron nitride nano-sheet into ethanol, and performing ultrasonic dispersion for 5-120 min to obtain the nano-sheet with the concentration of 0.5-50 mg.mL -1 Is a nanosheet dispersion of (a);
(b) Stirring and mixing the nano-sheet dispersion liquid, epoxy resin and an anhydride curing agent uniformly, and then distilling under reduced pressure to remove ethanol to obtain a mixed liquid;
(c) Stirring and mixing the mixed solution and the accelerator uniformly at normal temperature, standing and defoaming under vacuum, pouring the mixed solution onto a mold after the bubbles are removed, and curing to obtain an epoxy composite material;
wherein the content of the surface modified hexagonal boron nitride nano-sheet in the epoxy composite material is 1-40wt%;
the modification method of the surface modified hexagonal boron nitride nanosheets comprises the following steps:
(1) Adding hexagonal boron nitride powder into a homogeneous aqueous solution of an epoxy group-containing silane coupling agent, performing ultrasonic dispersion to obtain hexagonal boron nitride dispersion liquid, and adjusting the pH value to 0-6;
(2) Transferring the dispersion liquid obtained in the step (1) into a ball milling tank, ball milling for 1-48 hours at 100-2000 rpm, performing vacuum suction filtration after ball milling, and drying the powder obtained by suction filtration to obtain the hexagonal boron nitride nano-sheet with the surface functionalized by epoxy groups;
(3) Adding the hexagonal boron nitride nano-sheet obtained in the step (2) into an aqueous solution of branched polyethylenimine, performing ultrasonic dispersion, reacting at 0-80 ℃ for 1-48 h, and performing vacuum filtration and drying to obtain the surface modified hexagonal boron nitride nano-sheet.
2. The epoxy composite material according to claim 1, wherein in the step (1), the epoxy group-containing silane coupling agent is KH560, and the homogeneous aqueous solution is a water/ethanol mixed solution.
3. The epoxy composite material according to claim 2, wherein in the step (1), the dispersion concentration of the hexagonal boron nitride powder in the water/ethanol mixed solution is 0.5 to 50 mg/mL -1 The method comprises the steps of carrying out a first treatment on the surface of the The mass fraction of KH560 in the water/ethanol mixed solution is 0.01-30wt%; the volume ratio of the water/ethanol mixed solution is 1/(0.1-10).
4. The epoxy composite of claim 1, wherein in step (1), the duration of ultrasonic dispersion is from 5 to 120 minutes; the pH of the hexagonal boron nitride dispersion was adjusted by an acid solution.
5. The epoxy composite of claim 4, wherein the acid solution is at least one of hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, oxalic acid, acetic acid, oxalic acid, and citric acid;
the molar concentration of the acid solution is 0.01 to 10 mol.L -1 。
6. The epoxy composite of claim 1 wherein in step (2), the drying temperature is 30 to 150 ℃ and the drying time period is 1 to 48h.
7. The epoxy composite of claim 1, wherein the branched polyethylenimine has a molecular weight of 200 to 100000 and the concentration of the aqueous branched polyethylenimine solution is 0.01 to 30wt%.
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