Polymer-assisted exfoliated boron nitride nanosheet / aramid nanofiber composite thermal conductive film and preparation method thereof

Abstract

The application discloses a polymer-assisted exfoliated boron nitride nanosheet / aramid nanofiber composite heat-conducting film and a preparation method thereof. Hexagonal boron nitride is dispersed into sodium carboxymethyl cellulose aqueous solution and hydroxyethyl cellulose aqueous solution respectively to obtain first and second suspensions. Then, the polymers in the suspensions are homogenized and separated under a pressure of 75-90 MPa. The obtained dispersion liquid is mixed with aramid nanofiber dispersion liquid to form a film to obtain the boron nitride nanosheet / aramid nanofiber composite heat-conducting film. In the application, h-BN is introduced into CMC aqueous solution and HEC aqueous solution, and h-BN is exfoliated under a certain pressure. The coating degree of h-BN can be changed by changing the viscosity, and the collision force and shear force of h-BN on the homogenization channel in the homogenization process can be changed, so that BNNS with high aspect ratio and low defects is prepared, the intrinsic thermal conductivity of BNNS is improved, and the thermal conductivity of the boron nitride nanosheet / aramid nanofiber composite film is finally improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of heat-conducting films, and particularly relates to a polymer-assisted stripping boron nitride nanosheet / aramid nanofiber composite heat-conducting film and a preparation method thereof. BACKGROUND

[0002] The high integration and high power of electronic devices result in heat accumulation of the electronic devices, which is difficult to dissipate, and seriously endangers the performance and service life of the electronic devices. In order to effectively assist the heat dissipation of the electronic devices, people begin to prepare various insulating heat-conducting materials for heat conduction. In recent years, two-dimensional materials have attracted the attention of technical personnel due to their excellent physical and chemical properties. Fillers with high thermal conductivity are filled into film-forming substances to prepare thin films with high insulation and high thermal conductivity for heat transfer.

[0003] Boron nitride (BN) has excellent chemical and thermal stability, insulation, wave transmission, low dielectric, low density, easy modification, processing, and can be compounded with polymers, and is the highest thermal conductivity ceramic material, and thus is an insulating and heat-conducting filler with excellent performance. When combined with a polymer substrate, a composite heat-conducting film is formed, which becomes one of the important ways to solve the auxiliary heat dissipation of electronic devices and rapidly develops in the field of insulating and heat-conducting materials. According to related reports, when the thickness of hexagonal boron nitride (h-BN) reaches a single layer or multiple layers, boron nitride nanosheets (BNNS) can better exhibit their excellent performance in all aspects. However, there are some problems in the stripping process of BN, such as the existence of many lattice defects in the prepared BNNS, the introduction of new functional groups, and the inability to have a large aspect ratio, which leads to the poor thermal conductivity of the current boron nitride nanosheet-based heat-conducting film.

[0004] In order to improve the thermal conductivity of the boron nitride nanosheet-based heat-conducting film, it is necessary to ensure that the BNNS can better exhibit the excellent performance of BN and reduce the lattice defects and the intervention of functional groups in the preparation process of the BNNS. However, in the current methods for stripping BN, the ball milling stripping method, the liquid phase ultrasonic method, the surface activation method and the interlayer volume expansion method obtain BNNS with small size, high thickness and small aspect ratio, and there are still many lattice defects, which are easy to introduce new functional groups, and are not conducive to the subsequent preparation of high-performance boron nitride nanosheet-based heat-conducting films. SUMMARY

[0005] In view of the problems in the prior art, the application provides a polymer-assisted exfoliated boron nitride nanosheet / aramid nanofiber composite heat-conducting film and a preparation method, h-BN is introduced into a CMC aqueous solution and an HEC aqueous solution, h-BN is exfoliated under a certain pressure, the coating degree of h-BN can be changed by changing the viscosity, and then the collision force and the shearing force of h-BN on a homogenization channel in the homogenization process are changed, so that BNNS with a high aspect ratio and low defects is prepared, the intrinsic thermal conductivity of the BNNS is improved, and finally the thermal conductivity of the boron nitride nanosheet / aramid nanofiber composite film is improved.

[0006] The application is realized by the following technical scheme:

[0007] The application provides a preparation method of a polymer-assisted exfoliated boron nitride nanosheet / aramid nanofiber composite heat-conducting film, which comprises the following steps:

[0008] S1, dispersing hexagonal boron nitride into a sodium carboxymethyl cellulose aqueous solution, the mass ratio of sodium carboxymethyl cellulose to deionized water in the sodium carboxymethyl cellulose aqueous solution is (0.5-1.5):100, to obtain a first suspension;

[0009] S2, homogenizing the first suspension under 75-90 MPa, and then separating sodium carboxymethyl cellulose therefrom to obtain a first dispersion;

[0010] S2, homogenizing the first suspension under 75-90 MPa, and then separating sodium carboxymethyl cellulose therefrom to obtain a first dispersion;

[0011] S2, homogenizing the first suspension under 75-90 MPa, and then separating sodium carboxymethyl cellulose therefrom to obtain a first dispersion;

[0012] S3, mixing the first dispersion and the second dispersion with an aramid nanofiber dispersion liquid uniformly, the aramid nanofiber is a polymer substrate, and the boron nitride nanosheet in the dispersion liquid is a heat-conducting filler, and then performing a film-forming process to obtain a boron nitride nanosheet / aramid nanofiber composite heat-conducting film.

[0013] Preferably, in S1, the mass ratio of hexagonal boron nitride to sodium carboxymethyl cellulose is 1:(2-6), and the mass ratio of hexagonal boron nitride to hydroxyethyl cellulose is 1:(2-6).

[0014] Preferably, in S1, the hexagonal boron nitride is added into the sodium carboxymethyl cellulose aqueous solution, and then stirred for 40-50 hours to obtain the first suspension; and the hexagonal boron nitride is added into the hydroxyethyl cellulose aqueous solution, and then stirred for 40-50 hours to obtain the second suspension.

[0015] Preferably, S2 obtains the first dispersion liquid and the second dispersion liquid by the following process, respectively:

[0016] The homogenized first suspension liquid is centrifuged at 7000-9000 rpm, and then the supernatant is discarded and washed with deionized water for 1-2 times to obtain the first dispersion liquid;

[0017] The homogenized second suspension liquid is centrifuged at 7000-9000 rpm, and then the supernatant is discarded and washed with deionized water for 1-2 times to obtain the second dispersion liquid.

[0018] Further, S2 obtains the first dispersion liquid and the second dispersion liquid by the same deionized water washing process, and the deionized water washing process is as follows:

[0019] During each washing, deionized water is first added, and then centrifuged at 3000-4000 rpm for 10-20 min, and then the supernatant is discarded.

[0020] Preferably, the aramid nanofiber dispersion liquid in S3 is obtained by the following process:

[0021] The para-aramid fiber and KOH are dispersed into DMSO in a ratio of 1g:1.5g:500mL to obtain an aramid nanofiber dispersion liquid with a concentration of 2mg / mL.

[0022] Further, the mass ratio of the boron nitride nanosheet in the first dispersion liquid to the aramid nanofiber in the corresponding aramid nanofiber dispersion liquid in S3 is 4:1, and the mass ratio of the boron nitride nanosheet in the second dispersion liquid to the aramid nanofiber in the corresponding aramid nanofiber dispersion liquid is 4:1.

[0023] Preferably, the film forming process in S3 is vacuum filtration and hot pressing in sequence.

[0024] Further, the hot pressing is performed at 210-230℃ for 8-12min.

[0025] A boron nitride nanosheet / aramid nanofiber composite heat-conducting film prepared by the preparation method of the polymer-assisted exfoliated boron nitride nanosheet / aramid nanofiber composite heat-conducting film according to any one of the above.

[0026] Compared with the prior art, the present application has the following beneficial technical effects:

[0027] The application discloses a preparation method of a polymer-assisted exfoliated boron nitride nanosheet / aramid nanofiber composite heat-conducting film, which is characterized by the following steps: dispersing h-BN into CMC and HEC aqueous solutions, adjusting the concentration of the two polymer aqueous solutions, and then adjusting the coating degree of the solution to h-BN, so as to avoid the polymerization of h-BN, and relying on the inner wall of the impact homogenizing channel and the shearing force in the exfoliation process to prepare the BNNS with high aspect ratio and low defects, and to improve the intrinsic thermal conductivity of the BNNS. The more viscous solution, the larger the coating surface of h-BN, and the more capable of protecting h-BN from impact, the less conducive to exfoliating h-BN and obtaining the BNNS with high aspect ratio, and the more capable of maintaining the lateral size of the BNNS, therefore, the mass ratio of the two to deionized water is adjusted to 1.5% to balance the interaction between the coating and the exfoliation under high shearing rate, and the mass ratio is less than 0.5% to have poor coating effect and easy polymerization of h-BN. The application makes full use of the characteristics that CMC and HEC are easily dissolved in water and thickened to improve the viscosity of the solution, and the aqueous solution has good dispersibility, so that the dispersity and stability of the two polymer particles in water are effectively improved, the dispersion of h-BN in the homogenization process is ensured, and the flow of the system in the homogenization process is ensured. The thickening property of CMC is relatively high, a proper viscosity can be provided at a low concentration, the stability is good under high shearing rate, and the homogeneity and stability of the system are maintained; the thickening property of HEC is relatively low, a proper viscosity can be provided under high shearing rate, and HEC is a non-ionic polymer and is not charged, so that it is highly compatible and does not cause adverse reactions. The application uses aramid nanofiber (ANF) as a polymer substrate and BNNS as a heat-conducting filler, exfoliates h-BN as much as possible without damaging the lateral size, obtains boron nitride nanosheets with large size and small thickness, improves the intrinsic thermal conductivity of the BNNS, builds a boron nitride heat-conducting channel in the filling process, the establishment of the heat-conducting channel is conducive to the phonon transmission, heat is rapidly diffused, and finally the thermal conductivity of the boron nitride nanosheet / aramid nanofiber composite film is improved. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 SEM image of BNNS obtained by the HEC aqueous solution in Example 1 of the application under the condition of homogenization at 75 MPa.

[0029] Figure 2 XRD images of two kinds of BNNS in Example 3 and Example 6 of the application.

[0030] Figure 3 Thermal conductivity images of two kinds of BNNS / ANF composite films in Example 1 to Example 3 of the application.

[0031] Figure 4 Thermal conductivity images of two kinds of BNNS / ANF composite films in Example 4 to Example 6 of the application. DETAILED DESCRIPTION

[0032] The application will be further described in detail below in connection with specific examples, which are intended to explain but not limit the application.

[0033] The preparation method of the polymer-assisted exfoliated boron nitride nanosheet / aramid nanofiber composite heat-conducting film of the application is as follows:

[0034] Step (1), sodium carboxymethyl cellulose is added to three portions of 75 g deionized water respectively, wherein the ratio of sodium carboxymethyl cellulose to deionized water is 0.5%, 1% and 1.5% respectively, and the stirring time is 2 h, to obtain three portions of completely dissolved CMC aqueous solution for standby use;

[0035] Hydroxyethyl cellulose is added to three portions of 75 g deionized water respectively, wherein the ratio of hydroxyethyl cellulose to deionized water is 0.5%, 1% and 1.5% respectively, and the stirring time is 2 h, to obtain three portions of completely dissolved HEC aqueous solution for standby use;

[0036] Step (2), 1 g of para-aramid fiber and 1.5 g of KOH are weighed and dispersed in 500 mL of DMSO to obtain an aramid nanofiber dispersion solution with a concentration of 2 mg / mL.

[0037] Step (3), 0.5 g of hexagonal boron nitride (h-BN) is weighed and evenly divided into two portions, which are added to a CMC aqueous solution and an HEC aqueous solution of the same specification prepared in step (1) respectively, and stirred for 48 h to fully mix, to obtain suspension a1 and suspension a2.

[0038] Step (4), the suspension a1 and the suspension a2 prepared in step (3) are each subjected to homogenization by a microfluidic high-pressure homogenizer under a pressure of 75-90 MPa to realize an exfoliation process, to prepare BNNS suspension a1 and BNNS suspension a2.

[0039] Step (5), the BNNS suspension a1 and the BNNS suspension a2 prepared in step (4) are each subjected to centrifugation at 7000-9000 rpm, followed by centrifugal washing with deionized water for 1-2 times to remove the polymers CMC and HEC respectively, and the centrifugal washing with deionized water is specifically carried out by centrifugation at 3000-4000 rpm for 10-20 min, and the supernatant is discarded and the precipitate is retained, to obtain two portions of BNNS dispersion.

[0040] Step (6), the two portions of BNNS dispersion prepared in step (5) are each mixed with 6 mL of the aramid nanofiber dispersion solution prepared in step (2) to obtain two portions of BNNS / ANF composite film by vacuum filtration in sequence and hot pressing at 220℃ for 10 min, wherein the BNNS is 48 mg.

[0041] Example 1

[0042] The preparation method of the polymer-assisted exfoliated boron nitride nanosheet / aramid nanofiber composite heat-conducting film according to the present application is as follows:

[0043] Step (1), 1.125g of CMC and HEC solid particles were weighed respectively, and each was dissolved in 75g of water, stirred for 2h to obtain a CMC aqueous solution and a HEC aqueous solution.

[0044] Step (2), 1g of para-aramid fiber and 1.5g of KOH were weighed and dispersed in 500mL of DMSO to obtain an aramid nanofiber dispersion solution with a concentration of 2mg / mL.

[0045] Step (3), 0.5g of h-BN was weighed and evenly divided into two parts, which were added to the CMC aqueous solution and the HEC aqueous solution prepared in step (1) respectively, and stirred for 48h to fully mix, to obtain a h-BN / CMC water suspension and a h-BN / HEC water suspension.

[0046] Step (4), the h-BN / CMC water suspension and the h-BN / HEC water suspension prepared in step (3) were taken and homogenized by a microfluidic high-pressure homogenizer at 75MPa to realize the exfoliation process, to prepare a BNNS suspension.

[0047] Step (5), the BNNS suspension prepared in step (4) was centrifuged at 8000rpm, and then washed with deionized water twice to remove the polymers CMC and HEC, and the deionized water was centrifuged at 3500rpm for 15min, the supernatant was discarded, and the precipitate was retained to obtain two portions of BNNS dispersion.

[0048] Step (6), the two portions of BNNS dispersion prepared in step (5) were mixed with 6mL of the aramid nanofiber dispersion solution prepared in step (5) respectively, wherein the BNNS was 48mg, vacuum filtration was carried out in sequence, and hot pressing was carried out at 220℃ for 10min, to finally obtain two portions of BNNS / ANF composite film.

[0049] Example 2

[0050] The preparation method of the polymer-assisted exfoliated boron nitride nanosheet / aramid nanofiber composite heat-conducting film according to the present application is as follows:

[0051] Step (1), 0.75g of CMC and HEC solid particles were weighed respectively, and each was dissolved in 75g of water, stirred for 2h to obtain a CMC aqueous solution and a HEC aqueous solution.

[0052] Step (2), 1 g of para-aramid fiber and 1.5 g of KOH were weighed and dispersed in 500 mL of DMSO to obtain an aramid nanofiber dispersion solution with a concentration of 2 mg / mL.

[0053] Step (3), 0.5 g of h-BN was weighed and evenly divided into two parts, which were added to the CMC aqueous solution and HEC aqueous solution prepared in step (1), respectively, and stirred for 48 h to fully mix, to obtain h-BN / CMC aqueous suspension and h-BN / HEC aqueous suspension.

[0054] Step (4), the h-BN / CMC aqueous suspension and the h-BN / HEC aqueous suspension prepared in step (3) were taken and homogenized by a micro-fluid high-pressure homogenizer at 75 MPa to realize the exfoliation process, to prepare a BNNS suspension.

[0055] Step (5), the BNNS suspension prepared in step (4) was centrifuged at 8000 rpm, and then washed with deionized water twice to remove the polymers CMC and HEC, and the deionized water was centrifuged at 3500 rpm for 15 min, the supernatant was discarded, and the precipitate was retained, to obtain two BNNS dispersions.

[0056] Step (6), the two BNNS dispersions prepared in step (5) were mixed with 6 mL of the aramid nanofiber dispersion prepared in step (5) to obtain two BNNS / ANF composite films.

[0057] Example 3

[0058] The application discloses a preparation method of a polymer-assisted exfoliated boron nitride nanosheet / aramid nanofiber composite heat-conducting film.

[0059] Step (1), 0.375 g of CMC and HEC solid particles were weighed respectively and dissolved in 75 g of water, and stirred for 2 h to obtain a CMC aqueous solution and an HEC aqueous solution.

[0060] Step (2), 1 g of para-aramid fiber and 1.5 g of KOH were weighed and dispersed in 500 mL of DMSO to obtain an aramid nanofiber dispersion solution with a concentration of 2 mg / mL.

[0061] Step (3), 0.5 g of h-BN was weighed and evenly divided into two parts, which were added to the CMC aqueous solution and HEC aqueous solution prepared in step (1), respectively, and stirred for 48 h to fully mix, to obtain h-BN / CMC aqueous suspension and h-BN / HEC aqueous suspension.

[0062] Step (4), take the h-BN / CMC water suspension and the h-BN / HEC water suspension prepared in step (3), and homogenize them by a microfluidic high-pressure homogenizer at 75 MPa, respectively, to realize the exfoliation process, to prepare a BNNS suspension.

[0063] Step (5), take the BNNS suspension prepared in step (4), and centrifuge it at 8000 rpm, and then wash it with deionized water twice to remove the polymers CMC and HEC, and the deionized water centrifugal washing is specifically 3500 rpm centrifugation for 15 min, and the supernatant is poured off, and the precipitate is retained, to obtain two BNNS dispersions.

[0064] Step (6), take the two BNNS dispersions prepared in step (5), and mix each with 6 mL of the aramid nanofiber dispersion prepared in step (5) uniformly, wherein the BNNS is 48 mg, and then vacuum filtration is sequentially performed, and hot pressing is performed at 220 DEG C for 10 min, to finally obtain two BNNS / ANF composite films.

[0065] Example 4

[0066] The application discloses a preparation method of a polymer-assisted exfoliated boron nitride nanosheet / aramid nanofiber composite heat-conducting film.

[0067] Step (1), 1.125 g of CMC and HEC solid particles are respectively taken, and each is dissolved in 75 g of water to be stirred for 2 h, to obtain a CMC aqueous solution and an HEC aqueous solution.

[0068] Step (2), 1 g of para-aramid fiber and 1.5 g of KOH are taken, and are dispersed in 500 mL of DMSO to obtain an aramid nanofiber dispersion with a concentration of 2 mg / mL.

[0069] Step (3), 0.5 g of h-BN is taken, and is evenly divided into two parts, and is added into the CMC aqueous solution and the HEC aqueous solution prepared in step (1) respectively, and is stirred for 48 h to be mixed fully, to obtain a h-BN / CMC water suspension and a h-BN / HEC water suspension.

[0070] Step (4), take the h-BN / CMC water suspension and the h-BN / HEC water suspension prepared in step (3), and homogenize them by a microfluidic high-pressure homogenizer at 90 MPa, respectively, to realize the exfoliation process, to prepare a BNNS suspension.

[0071] Step (5), take the BNNS suspension prepared in step (4), and centrifuge it at 8000 rpm, and then wash it with deionized water twice to remove the polymers CMC and HEC, and the deionized water centrifugal washing is specifically 3500 rpm centrifugation for 15 min, and the supernatant is poured off, and the precipitate is retained, to obtain two BNNS dispersions.

[0072] Step (6), take the two portions of BNNS dispersion prepared in step (5), respectively, and mix them evenly with 6 mL of aramid nanofiber dispersion prepared in step (5), wherein the BNNS is 48 mg each, sequentially vacuum filtration, and hot pressing at 220 DEG C for 10 min, finally obtaining two portions of BNNS / ANF composite film.

[0073] Example 5

[0074] The application discloses a preparation method of a polymer-assisted exfoliated boron nitride nanosheet / aramid nanofiber composite heat-conducting film.

[0075] Step (1), respectively, take 0.75 g of CMC and HEC solid particles, respectively, dissolve them in 75 g of water, and stir for 2 h to obtain a CMC aqueous solution and an HEC aqueous solution.

[0076] Step (2), take 1 g of para-aramid fiber and 1.5 g of KOH, disperse them in 500 mL of DMSO to obtain an aramid nanofiber dispersion with a concentration of 2 mg / mL.

[0077] Step (3), take 0.5 g of h-BN, evenly divide it into two portions, and respectively add it to the CMC aqueous solution and the HEC aqueous solution prepared in step (1), and stir for 48 h to fully mix, to obtain an h-BN / CMC water suspension and an h-BN / HEC water suspension.

[0078] Step (4), take the h-BN / CMC water suspension and the h-BN / HEC water suspension prepared in step (3), and respectively pass them through a microjet high-pressure homogenizer at 90 MPa to realize an exfoliation process, to prepare BNNS suspensions.

[0079] Step (5), take the BNNS suspensions prepared in step (4), centrifuge them at 8000 rpm, and then wash them twice with deionized water to remove the polymers CMC and HEC, wherein the deionized water centrifugal washing is performed at 3500 rpm for 15 min, the supernatant is discarded, and the precipitate is retained, to obtain two portions of BNNS dispersions.

[0080] Step (6), take the two portions of BNNS dispersions prepared in step (5), respectively, and mix them evenly with 6 mL of aramid nanofiber dispersion prepared in step (5), wherein the BNNS is 48 mg each, sequentially vacuum filtration, and hot pressing at 220 DEG C for 10 min, finally obtaining two portions of BNNS / ANF composite film.

[0081] Example 6

[0082] The application discloses a preparation method of a polymer-assisted exfoliated boron nitride nanosheet / aramid nanofiber composite heat-conducting film.

[0083] In step (1), 0.375 g of CMC and HEC solid particles are respectively taken, and each is dissolved in 75 g of water to be stirred for 2 h to obtain a CMC aqueous solution and an HEC aqueous solution.

[0084] In step (2), 1 g of para-aramid fiber and 1.5 g of KOH are taken and dispersed in 500 mL of DMSO to obtain an aramid nanofiber dispersion liquid with a concentration of 2 mg / mL.

[0085] In step (3), 0.5 g of h-BN is taken and evenly divided into two parts, which are respectively added into the CMC aqueous solution and the HEC aqueous solution prepared in step (1) and stirred for 48 h to be fully mixed to obtain h-BN / CMC water suspension and h-BN / HEC water suspension.

[0086] In step (4), the h-BN / CMC water suspension and the h-BN / HEC water suspension prepared in step (3) are taken and subjected to homogenization by a microjet high-pressure homogenizer under 90 MPa to realize an exfoliation process and prepare BNNS suspensions.

[0087] In step (5), the BNNS suspensions prepared in step (4) are taken and centrifuged under 8000 rpm, and then washed with deionized water twice to remove the polymers CMC and HEC, wherein the deionized water is centrifuged at 3500 rpm for 15 min, the supernatant is poured out, and the precipitate is reserved to obtain two portions of BNNS dispersions.

[0088] In step (6), the two portions of BNNS dispersions prepared in step (5) are taken and mixed with 6 mL of the aramid nanofiber dispersion liquid prepared in step (5) to be uniformly mixed, wherein the BNNS is 48 mg, and vacuum filtration and hot pressing at 220 DEG C for 10 min are sequentially performed to finally obtain two portions of BNNS / ANF composite films.

[0089] From Figure 1 It can be seen that, by adding the polymer-assisted exfoliation, the h-BN can be exfoliated into BNNS with a larger lateral size, and therefore, the homogenization can obtain the BNNS with a larger lateral-to-vertical ratio.

[0090] From Figure 2 It can be seen that, the XRD peaks of all the BNNS powder samples are offset from the peak (26.8°) of the standard h-BN, which indicates that the h-BN is indeed exfoliated and sheared into flakes by the method.

[0091] From Figure 3It can be seen that under the pressure of 75 MPa, the thermal conductivity of the prepared film increases with the decrease of the concentration of polymer, which shows that reducing the concentration of CMC and BNNS can increase the aspect ratio of BNNS in the homogenization process, and then increase the thermal conductivity of the film assembled into the film.

[0092] From Figure 4 It can be seen that under the pressure of 90 MPa, the thermal conductivity of the prepared film increases with the decrease of the concentration of HEC solution, and under the same conditions, the thermal conductivity of the film is lower than that under the pressure of 75 MPa, which shows that the BNNS prepared under 75 MPa is relatively better; and with the decrease of the concentration of CMC solution, the thermal conductivity of the prepared film decreases, which is due to the obvious electrostatic interaction between CMC and BNNS under the pressure of 90 MPa, and CMC is modified on BNNS. It is found by thermogravimetric detection that the higher the concentration of CMC, the higher the modification amount, and since new functional groups are introduced on BNNS, the higher the modification amount, the more conducive to the improvement of the thermal conductivity of the film.

Claims

1. A method for preparing a polymer-assisted exfoliated boron nitride nanosheet / aramid nanofiber composite thermally conductive film, characterized in that, Includes the following steps: S1, hexagonal boron nitride is dispersed in an aqueous solution of sodium carboxymethyl cellulose, the mass ratio of sodium carboxymethyl cellulose to deionized water in the aqueous solution of sodium carboxymethyl cellulose is (0.5~1.5):100, and the mass ratio of hexagonal boron nitride to sodium carboxymethyl cellulose is 1:(2~6), to obtain the first suspension; Hexagonal boron nitride was dispersed in an aqueous solution of hydroxyethyl cellulose, wherein the mass ratio of hydroxyethyl cellulose to deionized water in the aqueous solution was (0.5~1.5):100, and the mass ratio of hexagonal boron nitride to hydroxyethyl cellulose was 1:(2~6), to obtain a second suspension; S2, the first suspension is homogenized at 75~90 MPa using a microfluidic high-pressure homogenizer, then centrifuged at 7000~9000 rpm, the supernatant is discarded and the solution is washed 1~2 times with deionized water to obtain the first dispersion. The second suspension was homogenized at 75-90 MPa using a microfluidic high-pressure homogenizer, then centrifuged at 7000-9000 rpm, the supernatant was discarded, and the solution was washed 1-2 times with deionized water to obtain the second dispersion. S2 uses the same deionized water washing process to obtain the first dispersion and the second dispersion. The deionized water washing process is as follows: Each time you wash, first add deionized water, then centrifuge at 3000-4000 rpm for 10-20 min, and then discard the supernatant. S3, para-aramid fibers and KOH were dispersed in DMSO at a ratio of 1 g: 1.5 g: 500 mL to obtain an aramid nanofiber dispersion with a concentration of 2 mg / mL. The first and second dispersions were mixed evenly with the aramid nanofiber dispersion. The mass ratio of boron nitride nanosheets in the first dispersion to aramid nanofibers in the corresponding aramid nanofiber dispersion was 4:1, and the mass ratio of boron nitride nanosheets in the second dispersion to aramid nanofibers in the corresponding aramid nanofiber dispersion was 4:

1. Then, a film-forming process was carried out, which consisted of vacuum filtration and hot pressing, to obtain a boron nitride nanosheet / aramid nanofiber composite thermally conductive film.

2. The method for preparing the polymer-assisted exfoliated boron nitride nanosheet / aramid nanofiber composite thermally conductive film according to claim 1, characterized in that, In S1: Hexagonal boron nitride is added to an aqueous solution of sodium carboxymethyl cellulose and stirred for 40-50 h to obtain a first suspension; hexagonal boron nitride is added to an aqueous solution of hydroxyethyl cellulose and stirred for 40-50 h to obtain a second suspension.

3. The method for preparing the polymer-assisted exfoliated boron nitride nanosheet / aramid nanofiber composite thermally conductive film according to claim 1, characterized in that, The hot pressing is carried out at 210~230 ℃ for 8~12 min.

4. A boron nitride nanosheet / aramid nanofiber composite thermally conductive film obtained by the method for preparing a polymer-assisted exfoliated boron nitride nanosheet / aramid nanofiber composite thermally conductive film according to any one of claims 1 to 3.

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