Epoxy resin heat-conducting composite material with three-dimensional polyion liquid functionalized boron nitride skeleton

Abstract

The invention discloses an epoxy resin heat-conducting composite material with a three-dimensional poly (ionic liquid) functionalized boron nitride skeleton, which is prepared by the following steps: by taking acrylic acid and 1-vinyl-3-ethylimidazolium bromide as monomers, preparing a poly (ionic liquid) functionalized boron nitride nanosheet heat-conducting filler by adopting an in-situ polymerization method; preparing the cellulose aqueous solution and the heat-conducting filler into a three-dimensional skeleton by an ice template method, and pouring epoxy resin to obtain the epoxy resin heat-conducting composite material. Compared with a three-dimensional framework prepared by loading boron nitride on a micromolecule modifier, the three-dimensional framework has the advantages that the macromolecular modifier is introduced in situ, so that more interaction is generated between the filler and a matrix, the interface thermal resistance is further reduced, and better heat-conducting property is realized.

Description

Technical Field

[0001] The present invention belongs to the field of thermally conductive composite materials, and in particular relates to an epoxy resin thermally conductive composite material having a three-dimensional polyionic liquid functionalized boron nitride skeleton. Background Art

[0002] With the rapid development of science and technology, the power density and integration of modern devices are constantly increasing. During operation, a large amount of heat is inevitably generated inside these devices. If it is not released in time, it will reduce the device's operating efficiency and even shorten its service life. Polymer-based materials are widely used in sealing and interfacial bonding of various electronic devices due to their advantages such as processability, scalability, flexibility, lightweight, high pressure resistance and low cost, and can transfer heat out of the device. By adding highly thermally conductive inorganic fillers to polymer matrices with poor thermal conductivity, polymer composites with better thermal conductivity can be prepared, further solving the heat dissipation problem. However, since the filler particles are not in direct contact with each other, the low thermal conductivity of the polymer matrix between them hinders the formation of a continuous heat transfer path, thereby affecting the thermal conductivity of the material. In addition, since most highly thermally conductive inorganic fillers lack functional groups, it is often difficult to achieve good dispersion in polymer matrices with different polarities, which also affects the improvement of thermal conductivity. Summary of the Invention

[0003] Based on the problems existing in the above-mentioned prior art, the present invention aims to provide an epoxy resin thermal conductive composite material with a three-dimensional polyionic liquid functionalized boron nitride skeleton, prepare polyionic liquid functionalized boron nitride nanosheet thermal conductive filler by in situ polymerization, prepare cellulose aqueous solution and thermal conductive filler into a three-dimensional skeleton by ice template method, and then infuse epoxy resin to obtain an epoxy resin thermal conductive composite material, so as to solve the problem of excessively high thermal resistance at the interface between the epoxy resin matrix and the filler skeleton.

[0004] In order to achieve the above object, the present invention adopts the following technical solutions:

[0005] The present invention first provides a method for preparing a polyionic liquid functionalized boron nitride nanosheet thermal conductive filler, comprising the following steps:

[0006] Step 1: Exfoliate hexagonal boron nitride to prepare boron nitride nanosheets. The specific process is as follows:

[0007] Hexagonal boron nitride powder and ball milling beads are uniformly mixed with a dispersion solution and then ultrasonically milled. The resulting dispersion solution is centrifuged, washed, and freeze-dried to produce thin boron nitride nanosheets. The dispersion solution is a mixture of isopropyl alcohol and deionized water, and the mass ratio of the dispersion solution to the hexagonal boron nitride powder is 200:1. The ball milling beads are zirconia ball milling beads with diameters of 0.15 mm and 0.3 mm, with the mass ratio of the 0.15 mm and 0.3 mm zirconia ball milling beads being 1:1. The mass ratio of the ball milling beads to the hexagonal boron nitride powder is 1:5. The ultrasonic milling time is 18 to 24 hours.

[0008] Step 2: blending acrylic acid, 1-vinyl-3-ethylimidazolium bromide and boron nitride nanosheets, and then obtaining polyionic liquid functionalized boron nitride nanosheets by copolymerization of acrylic acid and 1-vinyl-3-ethylimidazolium bromide. The specific process is as follows:

[0009] Acrylic acid and 1-vinyl-3-ethylimidazolium bromide were stirred and dissolved in deionized water, and then boron nitride nanosheets were added. The mixture was stirred and ultrasonicated under nitrogen protection until uniformly dispersed. Then, the temperature was raised to 80-90°C in a nitrogen atmosphere, and an aqueous ammonium persulfate solution was added as an initiator. The mixture was stirred and reacted for 6-8 hours. After the reaction, the product was centrifuged, washed with water, and freeze-dried to obtain polyionic liquid-functionalized boron nitride nanosheets, which were recorded as PIL@BNNS.

[0010] Preferably, the molar ratio of acrylic acid to 1-vinyl-3-ethylimidazolium bromide is 1:1; the mass of ammonium persulfate accounts for 25-30% of the total mass of acrylic acid and 1-vinyl-3-ethylimidazolium bromide; the ratio of the mass of deionized water to the total mass of acrylic acid and 1-vinyl-3-ethylimidazolium bromide is 13-15:0.27; and the ratio of the mass of boron nitride nanosheets to the total mass of acrylic acid and 1-vinyl-3-ethylimidazolium bromide is 0.12-0.15:0.27.

[0011] Preferably, the freeze-drying temperature is -60 to -50°C, the pressure is 30 to 50 Pa, and the time is 24 to 36 hours.

[0012] The present invention further provides a method for preparing an epoxy resin thermally conductive composite material having a three-dimensional polyionic liquid functionalized boron nitride skeleton, specifically:

[0013] The polyionic liquid functionalized boron nitride nanosheet thermal conductive filler and the carboxylated cellulose aqueous solution are uniformly mixed to obtain a mixed solution; the mixed solution is prepared into a three-dimensional skeleton by an ice template method, and then epoxy resin is poured and cured to obtain a polyionic liquid functionalized boron nitride nanosheet / epoxy resin thermal conductive composite material.

[0014] Preferably, the mass concentration of the carboxylated cellulose aqueous solution is 1%, and the mass ratio of the polyionic liquid functionalized boron nitride nanosheet thermal conductive filler to the carboxylated cellulose aqueous solution is 0.08-0.4:2.

[0015] Preferably, the steps of the ice template method are: pouring the mixed liquid into a mold, placing the mold in liquid nitrogen, and performing directionally freezing from bottom to top using liquid nitrogen, and then placing it in a freeze dryer for freeze drying (freeze drying temperature is -60 to -50°C, pressure is 30 to 50Pa, and time is 24 to 36h) to obtain a three-dimensional skeleton.

[0016] Preferably, the curing conditions are: first treating at 60-80° C. for 1-2 hours, and then treating at 120-150° C. for 1-2 hours.

[0017] Preferably, the polyionic liquid functionalized boron nitride nanosheet thermal conductive filler accounts for 5 to 20% of the total mass of the composite material.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] 1. The present invention uses acrylic acid and 1-vinyl-3-ethylimidazolium bromide as monomers to prepare a polyionic liquid-functionalized boron nitride nanosheet thermally conductive filler through an in-situ polymerization method. A cellulose aqueous solution and the thermally conductive filler are then formed into a three-dimensional framework using an ice-templating method. This framework is then infused with epoxy resin to produce an epoxy resin thermally conductive composite material. The imidazole rings in the selected imidazole salt bind to the hexagonal lattice on the boron nitride surface through π-π interactions, reducing phonon scattering. Furthermore, the carboxyl groups in the polyionic liquid form a hydrogen bond network with the hydroxyl groups of the epoxy matrix, while the anionic portion of the polyionic liquid also generates electrostatic interactions with the polar groups of the epoxy molecular chains. This improves interfacial compatibility and reduces interfacial thermal resistance, thereby further increasing the interfacial heat transfer efficiency of the composite material.

[0020] 2. The present invention mixes boron nitride nanosheets non-covalently functionalized with polyionic liquid and a carboxylated cellulose aqueous solution, and utilizes the carboxyl groups in the polyionic liquid to produce a large number of hydrogen bonds with the hydroxyl groups of cellulose to achieve good dispersion, which helps to form an aerogel skeleton with a clear orientation structure and stability through the ice template method, thereby improving the continuity of the thermal conductivity path.

[0021] 3. The operation steps of the present invention are easy to control, the processing cost is low, and industrial production is expected to be realized. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0023] Figure 1 Scanning electron microscopy images of BNNS (a) and PIL@BNNS (b) prepared in Example 1;

[0024] Figure 2 is the NMR spectrum of the polyionic liquid in Comparative Example 2;

[0025] Figure 3 Thermogravimetric analysis of the PIL@BNNS obtained in Example 1 and the PIL / BNNS obtained in Comparative Example 2;

[0026] Figure 4 3D images of the three-dimensional skeletons prepared in Examples 1 to 4 are scanning electron microscope images, where a to d correspond to Examples 1 to 4, respectively.

[0027] Figure 5 Graph showing thermal conductivity of samples obtained in various embodiments of the present invention and comparative example 1. DETAILED DESCRIPTION

[0028] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0029] Example 1

[0030] This embodiment provides a method for preparing an epoxy resin thermally conductive composite material having a three-dimensional polyionic liquid functionalized boron nitride skeleton, which is carried out according to the following steps:

[0031] 1. Preparation of polyionic liquid functionalized boron nitride nanosheet thermal conductive filler:

[0032] To a 100mL mixture of isopropanol and deionized water (1:1 by volume), 0.05g each of 0.15mm and 0.3mm diameter zirconium oxide ball milling beads and 0.5g of hexagonal boron nitride powder were added. After stirring and mixing thoroughly, the mixture was placed in an ultrasonic machine and ball milled at a frequency of 60kHz for 24 hours. After ball milling, the resulting dispersion was centrifuged at 2000rpm for 10 minutes, and the supernatant was retained and centrifuged at 9500rpm for 15 minutes. The resulting precipitate was washed three times with water and then freeze-dried to obtain boron nitride nanosheets (BNNS).

[0033] 1 mmol (0.07 g) of acrylic acid and 1 mmol (0.20 g) of 1-vinyl-3-ethylimidazolium bromide (VEIMBr) were dissolved in 13 g of water, and 0.12 g of BNNS was added. The mixture was stirred and ultrasonicated under nitrogen protection until uniformly dispersed. Then, the temperature was raised to 80°C in a nitrogen atmosphere, and 8 mL of a 1 wt% ammonium persulfate aqueous solution was added as an initiator. The mixture was stirred and reacted for 8 hours. After the reaction, the dispersion was centrifuged at 9000 rpm for 15 minutes, washed twice with water to remove free boron nitride nanosheets and polyionic liquid (PIL), and then freeze-dried (freeze-drying temperature: -50°C, pressure: 30 Pa, time: 24 hours) to obtain hydrophilic PIL@BNNS.

[0034] The SEM images of BNNS and PIL@BNNS obtained in this example are shown in Figure 2. Figure 1 As shown in (a) and (b), it can be seen that the PIL is successfully in situ loaded on the BNNS surface.

[0035] 2. 80 mg of the synthesized PIL@BNNS was dispersed into 2 g of a 1 wt% aqueous solution of carboxylated cellulose. The mixture was evenly dispersed by alternating sonication and stirring to obtain a mixture. The mixture was poured into a mold, which was then placed in liquid nitrogen and subjected to bottom-up freezing for 15 minutes. The mold was then freeze-dried in a freeze dryer (freeze-drying at -50°C, 30 Pa, and 24 hours) to obtain a three-dimensional framework.

[0036] 3. Liquid EP, catalyst (2,4,6-tris(dimethylhydrogenphenol, MeH-HPA), and curing agent (methylhexahydrophthalic anhydride, TAP) were mixed in a mass ratio of 5:5:0.25 and placed in an oven under vacuum at room temperature for 30 minutes to remove bubbles. After that, the mixture was injected into a mold containing a three-dimensional skeleton. The mold was then placed in a vacuum oven under vacuum at 30°C for 12 hours to ensure that the epoxy resin could be completely impregnated into the three-dimensional skeleton. Finally, the oven was heated to 80°C for curing for 2 hours, and then heated to 120°C for curing for 2 hours. After curing, the sample was removed and polished to remove excess resin outside the skeleton to obtain a PIL@BNNS / EP composite material. The mass fraction of the filler in the composite material was determined to be 6.4% by weight.

[0037] Example 2

[0038] In this example, a PIL@BNNS / EP composite material was prepared in the same manner as in Example 1, except that 160 mg of PIL@BNNS was added in step 2. The mass fraction of filler in the PIL@BNNS / EP composite material obtained in this example was 8.9%.

[0039] Example 3

[0040] In this example, a PIL@BNNS / EP composite material was prepared in the same manner as in Example 1, except that 240 mg of PIL@BNNS was added in step 2. The mass fraction of filler in the PIL@BNNS / EP composite material obtained in this example was 11.9%.

[0041] Example 4

[0042] In this example, a PIL@BNNS / EP composite material was prepared in the same manner as in Example 1, except that 320 mg of PIL@BNNS was added in step 2. The mass fraction of filler in the PIL@BNNS / EP composite material obtained in this example was 14.3%.

[0043] Example 5

[0044] In this example, a PIL@BNNS / EP composite material was prepared in the same manner as in Example 1, except that 400 mg of PIL@BNNS was added in step 2. The mass fraction of filler in the PIL@BNNS / EP composite material obtained in this example was 17.9%.

[0045] Comparative Example 1

[0046] This comparative example prepared EP according to the following steps:

[0047] 5 g of curing agent (methylhexahydrophthalic anhydride) and 0.25 g of catalyst (2,4,6-tris(dimethylhydrogenated cresol)) were dissolved in 5 g of epoxy resin and stirred for 30 min to obtain an epoxy resin mixed solution. The solution was then poured into a mold and placed in a vacuum oven at 30°C for 12 h to remove bubbles. The solution was then heated to 80°C for curing for 2 h, and then heated to 120°C for curing for 2 h. After curing, the sample was taken out to obtain the epoxy resin material EP.

[0048] Comparative Example 2

[0049] In this comparative example, a sample of a physical mixture of polyionic liquid and BNNS was prepared for comparison. The specific steps were as follows:

[0050] 1. Preparation of polyionic liquids

[0051] Dissolve 1 mmol of acrylic acid and 1 mmol of 1-vinyl-3-ethylimidazolium bromide (VEIMBr) in 13 g of water. Then, under a nitrogen atmosphere, heat to 80°C and add 8 mL of a 1 wt% aqueous solution of ammonium persulfate as an initiator. Stir and react for 8 hours. After the reaction, the solution is rotary evaporated, and the resulting liquid is precipitated into anhydrous ethanol. The solution is allowed to stand for 24 hours, and the precipitate is centrifuged, washed, and freeze-dried to obtain a polyionic liquid powder. The synthetic reaction formula is as follows:

[0052]

[0053] The NMR characterization of the obtained polyionic liquid is as follows Figure 2 As shown, the signal peaks at 9.42 and 7.95 ppm correspond to the imidazolium ring protons of [>NCHN<] and [>NCHCHN<], and the signal peaks at 2.02 ppm and 4.28 ppm correspond to the -(CH2) n -, and the sharp peaks of -CH=CH2 at 5.85ppm and 5.31ppm belonging to 1-vinyl-3-ethylimidazolium bromide and the sharp peaks of -CH=CH2 at 6.25ppm, 5.92ppm and 5.85ppm belonging to acrylic acid disappeared, proving that the two monomers were successfully polymerized into a polyionic liquid.

[0054] 2. Physical mixing of polyionic liquid and BNNS

[0055] The polyionic liquid obtained in step 1 was physically mixed with 0.12g of boron nitride nanosheets BNNS, and the resulting material was recorded as PIL / BNNS. The thermogravimetric analysis of the PIL@BNNS obtained in Example 1 and the PIL / BNNS obtained in this comparative example is shown in FIG. Figure 3As shown in the figure, the grafting rate of functionalized boron nitride nanosheets obtained by first synthesizing the polyionic liquid and then directly blending it with the boron nitride nanosheets is only 1.2%, while the grafting rate of functionalized boron nitride nanosheets obtained by in-situ polymerization can reach 5.9%. The high grafting rate of the polyionic liquid and the boron nitride nanosheets can maintain a stable structure when forming a three-dimensional framework, thereby improving thermal conductivity.

[0056] Figure 4 (a), (b), (c), and (d) are scanning electron microscopic cross-sectional images of the PIL@BNNS three-dimensional skeleton obtained in Examples 1, 2, 3, and 4 of the present invention. It can be seen that the composite material has a clear oriented structure.

[0057] Figure 5 The thermal conductivity diagram of the samples obtained in Examples 1, 2, 3, 4, and 5 of the present invention and Comparative Example 1 shows that when the corresponding PIL@BNNS filler mass fraction is 17.9 wt%, the thermal conductivity of the composite material can reach 1.8923 W / (m·K), which is 786% higher than that of pure EP in Comparative Example 1.

[0058] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A method for preparing a polyionic liquid functionalized boron nitride nanosheet thermal conductive filler, characterized in that: The steps include: Step 1: exfoliating hexagonal boron nitride to prepare boron nitride nanosheets; Step 2: blending acrylic acid, 1-vinyl-3-ethylimidazolium bromide and boron nitride nanosheets, and then obtaining polyionic liquid functionalized boron nitride nanosheets through copolymerization of acrylic acid and 1-vinyl-3-ethylimidazolium bromide.

2. The preparation method according to claim 1, characterized in that The specific process in step 2 is: Acrylic acid and 1-vinyl-3-ethylimidazolium bromide were stirred and dissolved in deionized water, and then boron nitride nanosheets were added. The mixture was stirred and ultrasonicated under nitrogen protection until uniformly dispersed. Then, the temperature was raised to 80-90°C in a nitrogen atmosphere, and an aqueous ammonium persulfate solution was added as an initiator. The mixture was stirred and reacted for 6-8 hours. After the reaction, the product was centrifuged, washed with water, and freeze-dried to obtain polyionic liquid-functionalized boron nitride nanosheets, which were recorded as PIL@BNNS.

3. The preparation method according to claim 2, characterized in that The molar ratio of acrylic acid to 1-vinyl-3-ethylimidazolium bromide is 1:1; the mass of ammonium persulfate accounts for 25-30% of the total mass of acrylic acid and 1-vinyl-3-ethylimidazolium bromide; the ratio of the mass of deionized water to the total mass of acrylic acid and 1-vinyl-3-ethylimidazolium bromide is 13-15:0.27; and the ratio of the mass of boron nitride nanosheets to the total mass of acrylic acid and 1-vinyl-3-ethylimidazolium bromide is 0.12-0.15:0.

27.

4. The preparation method according to claim 2, characterized in that The freeze-drying temperature is -60 to -50°C, the pressure is 30 to 50 Pa, and the time is 24 to 36 hours.

5. A polyionic liquid functionalized boron nitride nanosheet thermal conductive filler prepared by the preparation method according to any one of claims 1 to 4.

6. A method for preparing an epoxy resin thermally conductive composite material having a three-dimensional polyionic liquid functionalized boron nitride framework, characterized in that: The polyionic liquid functionalized boron nitride nanosheet thermal conductive filler described in claim 5 and the carboxylated cellulose aqueous solution are evenly mixed to obtain a mixed solution; the mixed solution is prepared into a three-dimensional skeleton by an ice template method, and then epoxy resin is poured into it, and after curing, a polyionic liquid functionalized boron nitride nanosheet / epoxy resin thermal conductive composite material is obtained.

7. The preparation method according to claim 6, characterized in that The mass concentration of the carboxylated cellulose aqueous solution is 1%, and the mass ratio of the polyionic liquid functionalized boron nitride nanosheet thermal conductive filler to the carboxylated cellulose aqueous solution is 0.08-0.4:

2.

8. The preparation method according to claim 6, characterized in that The curing conditions are: first treating at 60-80° C. for 1-2 hours, and then treating at 120-150° C. for 1-2 hours.

9. The preparation method according to claim 6, characterized in that The polyionic liquid functionalized boron nitride nanosheet heat-conducting filler accounts for 5 to 20% of the total mass of the composite material.

10. An epoxy resin thermally conductive composite material having a three-dimensional polyionic liquid functionalized boron nitride skeleton, prepared by the preparation method according to any one of claims 6 to 9.

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