CN115746404B - Surface modified hexagonal boron nitride nanosheet, modification method thereof and epoxy composite material - Google Patents

Abstract

The invention relates to surface-modified hexagonal boron nitride nanosheets and modification methods thereof, and epoxy composite materials. The modification method includes: (1) adding hexagonal boron nitride powder to an epoxy group-containing silane coupling agent In a homogeneous aqueous solution, disperse it ultrasonically to obtain a hexagonal boron nitride dispersion and adjust the pH to 0 to 6; (2) Transfer the dispersion obtained in step (1) to a ball mill tank, and ball mill at 100 to 2000 rpm for 1 to 48h, perform vacuum filtration after ball milling, and dry the powder obtained by suction filtration to obtain surface epoxy functionalized hexagonal boron nitride nanosheets; (3) Add the hexagonal boron nitride nanosheets obtained in step (2) to the branch. In an aqueous solution of polyethyleneimine, the reaction is carried out at 0 to 80°C for 1 to 48 hours after ultrasonic dispersion, followed by vacuum filtration and drying to obtain surface-modified hexagonal boron nitride nanosheets. The surface-modified hexagonal boron nitride nanosheets of the present invention significantly improve the thermal conductivity and mechanical properties of epoxy composite materials.

Description

Surface modified hexagonal boron nitride nanosheets and modification methods, epoxy composite materials

Technical field

The invention belongs to the field of nanocomposite materials, and specifically relates to surface-modified hexagonal boron nitride nanosheets and modification methods thereof, and epoxy composite materials.

Background technique

As modern power electronic devices gradually develop towards miniaturization, high integration and high power density, the thermal management problem of electronic components within the equipment has become increasingly prominent. Highly integrated electronic components will generate a large amount of heat during operation, causing the temperature of the components to rise rapidly, ultimately seriously affecting the performance and life of electronic equipment. In order to dissipate accumulated heat in time and ensure that electronic components work stably for a long time, it is necessary to fill thermally conductive materials between electronic components. Epoxy resin is a type of thermosetting resin with good comprehensive properties (mechanical strength, adhesion strength, insulation performance, chemical stability, etc.) and is widely used as packaging material for electronic components. However, pure epoxy resin has a low thermal conductivity (around 0.2W/m·K) and cannot effectively diffuse the heat from electronic components in a timely manner. Therefore, it is of great practical significance to develop epoxy packaging materials with high thermal conductivity and excellent comprehensive properties.

It is currently the most common practice to introduce high thermal conductivity fillers into the epoxy resin matrix to improve its thermal conductivity. As an inorganic filler with high thermal conductivity and excellent mechanical properties, hexagonal boron nitride (h-BN), especially the exfoliated h-BN nanosheets, is widely used to manufacture various high thermal conductivity composite materials. It is worth noting that simply and roughly adding h-BN filler to the matrix will usually cause uneven dispersion within the matrix, and there will be a large number of interface gaps between the filler and the matrix, reducing the thermal conductivity of the composite material. The patent document with publication number CN110922719A discloses a highly thermally conductive boron nitride/epoxy resin composite material and its preparation method and application. It uses h-BN nanoparticles as raw materials, and is successively subjected to ultrasonic peeling and surface modification with a silane coupling agent. Surface-modified h-BN nanosheets are obtained, and finally they are compounded with epoxy resin. The steps to prepare surface-modified h-BN nanosheets are cumbersome, and the interface between h-BN nanosheets and epoxy resin is compatible. Sexual enhancement is limited. The patent document with publication number CN113969040A uses hyperbranched polyethylene polymer as the modified molecule to modify the surface of h-BN through non-covalent interactions such as π-π, which effectively improves the dispersion of h-BN nanoparticles and their interaction with rings. Interfacial compatibility of the oxygen matrix, but the non-covalent interaction makes the binding force between the modified molecules and h-BN weak, and there is no chemical connection between the modified molecules and the epoxy matrix. The thermal conductivity and mechanical properties of the obtained epoxy composite materials are still Less than ideal.

Contents of the invention

Based on the above-mentioned shortcomings and deficiencies in the prior art, the present invention provides a surface-modified hexagonal boron nitride nanosheet, a modification method thereof, and an epoxy composite material. The purpose is to obtain surface-modified h-BN nanosheets through simple steps and improve the dispersion of h-BN. There are abundant active groups on the surface of the modified h-BN nanosheets, which can interact with epoxy molecules at the same time. And the curing agent undergoes an interfacial chemical reaction to improve the filler-matrix interface compatibility, and ultimately improve the thermal conductivity and mechanical properties of the epoxy composite material.

In order to achieve the above-mentioned object of the invention, the present invention adopts the following technical solutions:

The modification method of surface-modified hexagonal boron nitride nanosheets includes the following steps:

(1) Add hexagonal boron nitride powder to the homogeneous aqueous solution of the epoxy-containing silane coupling agent, and disperse it ultrasonically to obtain a hexagonal boron nitride dispersion and adjust the pH to 0 to 6;

(2) Transfer the dispersion obtained in step (1) to a ball milling tank, and ball mill at 100 to 2000 rpm for 1 to 48 hours. After ball milling, vacuum filtration is performed, and the powder obtained by suction filtration is dried to obtain surface epoxy functionalized hexagonal boron nitride nanosheets;

(3) Add the hexagonal boron nitride nanosheets obtained in step (2) to the aqueous solution of branched polyethyleneimine, disperse it ultrasonically, and react at 0 to 80°C for 1 to 48 hours, followed by vacuum filtration and drying to obtain Surface modified hexagonal boron nitride nanosheets.

As a preferred embodiment, in step (1), the epoxy group-containing silane coupling agent is KH560, and the homogeneous aqueous solution is a water/ethanol mixed solution.

As a preferred version, in the step (1), the dispersion concentration of hexagonal boron nitride powder in the water/ethanol mixed solution is 0.5~50 mg·mL ^-1 ; the mass fraction of KH560 in the water/ethanol mixed solution is 0.01~ 30wt%; the volume ratio of water/ethanol mixed solution is 1/(0.1~10).

As a preferred embodiment, in the step (1), the duration of ultrasonic dispersion is 5 to 120 minutes; the pH of the hexagonal boron nitride dispersion is adjusted with an acid solution.

As a preferred embodiment, 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 .

As a preferred version, in the step (2), the drying temperature is 30-150°C, and the drying time is 1-48 hours.

As a preferred embodiment, the molecular weight of the branched polyethyleneimine is 200-100000, and the concentration of the branched polyethyleneimine aqueous solution is 0.01-30wt%.

The present invention also provides surface-modified hexagonal boron nitride nanosheets modified by the modification method described in any of the above solutions.

The invention also provides epoxy composite materials, and their preparation process includes the following steps:

(1) Add the surface-modified hexagonal boron nitride nanosheets as claimed in claim 8 into ethanol and disperse them ultrasonically for 5 to 120 minutes to obtain a nanosheet dispersion with a concentration of 0.5 to 50 mg·mL ^-1 ;

(2) Stir and mix the nanosheet dispersion, epoxy resin, and curing agent evenly, and then distill under reduced pressure to remove the ethanol to obtain a mixed solution;

(3) Stir the mixed solution and accelerator evenly at room temperature, and then leave it to defoam under vacuum. After the bubbles are removed, pour the mixed solution onto the mold and solidify to obtain the epoxy composite material.

Among them, E-51 epoxy resin is used as the matrix, methylhexahydrophthalic anhydride (MHHPA) is used as the curing agent, and 2,4,6-tris(dimethylaminomethyl)phenol (DMP-30) is used as the accelerator. The mass ratio between them is E-51:MHHPA:DMP-30=100: (70～100):(0.1～2); the curing temperature is 80～180℃, and the curing time is 1～24h.

As a preferred solution, the content of the surface-modified hexagonal boron nitride nanosheets in the epoxy composite material is 1 to 40 wt%.

Compared with the prior art, the beneficial effects of the present invention are:

The surface-modified hexagonal boron nitride nanosheets of the present invention are surface epoxy groups directly obtained by dispersing hexagonal boron nitride nanoparticles in a homogeneous aqueous solution of an epoxy-containing silane coupling agent and performing wet ball milling in one step. Functionalized hexagonal boron nitride nanosheets; and further obtain BPEI-modified hexagonal boron nitride through the reaction of amino groups and epoxy groups.

The surface-modified hexagonal boron nitride nanosheets prepared by the modification method of the present invention have high yield, uniform size, abundant amino groups on the surface, can be better dispersed in the epoxy matrix, and produce good results between the filler/matrix. It has excellent interfacial compatibility; it can also form covalent bonds with the epoxy groups of the epoxy molecular chain to increase the degree of cross-linking and enhance the thermal conductivity and mechanical properties of epoxy composite materials.

The modification method of the invention is simple in process, low in cost, environmentally friendly, suitable for large-scale production, and can be widely used to enhance the thermal conductivity and mechanical properties of various thermosetting and thermoplastic polymers.

Description of the drawings

Figure 1 is an SEM photograph of the nanopowder involved in Example 1 of the present invention. Picture A shows the original BN powder (denoted as BN); Picture B shows the BN nanosheets obtained by ball milling (denoted as BNNS); Picture C shows the BN nanosheets obtained by ball milling using a solution containing KH560 (denoted as KH560-BNNS); Picture D It is BPEI surface modified BN nanosheets (denoted as BPEI-KH560-BNNS);

Figure 2 is an FTIR spectrum of the relevant nanopowder involved in Example 1 of the present invention. Among them, a is BN; b is BNNS; c is KH560-BNNS; d is BPEI-KH560-BNNS; e is KH560; f is BPEI.

Figure 3 is a TGA curve of the relevant nanopowder involved in Example 1 of the present invention. Among them, a is BN; b is BNNS; c is KH560-BNNS; d is BPEI-KH560-BNNS.

Detailed ways

The technical solution of the present invention will be further explained below through specific examples.

Example 1:

The preparation method of surface-modified BN nanosheets in this embodiment includes the following steps:

1) Add 2g BN powder to 120mL of water/ethanol mixed solution containing 1wt% KH560 (water:ethanol=1:4). After ultrasonic dispersion for 30 minutes, adjust the pH value of the BN dispersion by 8mol·L ^-1 hydrochloric acid solution. Adjust to 4; then transfer the BN dispersion to the tungsten carbide ball mill tank, and add 30 tungsten carbide grinding balls; ball mill at 600 rpm for 24 hours;

2) After the ball milling is completed, carry out vacuum filtration of the solution; then dry the powder obtained by suction filtration at 80°C for 12 hours to obtain surface epoxy functionalized BN nanosheets;

3) Add the epoxy-functionalized BN nanosheets obtained in 2) to an aqueous solution containing 1wt% BPEI, and disperse it ultrasonically for 30 minutes; then react at 50°C for 12 hours, vacuum filtrate and dry to obtain surface-modified BN nanosheets.

The preparation method of the epoxy composite material in this embodiment includes the following steps:

4) Add the surface-modified BN nanosheets to ethanol and disperse with ultrasonic for 30 minutes to obtain a BN nanosheet dispersion with a concentration of 10 mg·mL ^-1 ;

5) Stir and mix the above BN dispersion with E-51 epoxy resin and MHHPA for 2 hours, and then distill under reduced pressure at 60°C for 12 hours to remove the ethanol solvent;

6) Stir and mix the solution obtained in 5) and DMP-30 at room temperature for 0.5h, then leave it to defoam under vacuum for 1h. After the bubbles are removed, pour the mixed solution onto the mold and solidify at 120°C for 4h. Surface-modified BN nanosheet/epoxy composite material was obtained.

Among them, the mass fraction of surface-modified BN nanosheets in the epoxy composite material is 15wt%; E-51:MHHPA:DMP-30=100:82:0.6.

The epoxy composite material in this embodiment was cast into a standard sample to test the thermal conductivity and mechanical properties of the composite material.

The preparation of surface-modified BN nanosheets (i.e., BPEI-KH560-BNNS) is the first step in the preparation of epoxy nanocomposites. As shown in Figure 1A, BN exhibits an irregular morphology and a closely stacked layered structure. After the ball milling process, an obvious nanosheet structure was observed, as shown in Figure 1B, which was mainly due to the shear force during the ball milling process that peeled off the stacked nanosheets. Figure 1C shows that the addition of KH560 does not have a significant impact on the structure of BN nanosheets obtained by ball milling. Moreover, Figure 1D shows that post-modification using BPEI will not have a significant impact on the structure of BN nanosheets.

To determine the chemical structure of surface-modified BN nanosheets, infrared spectra were recorded. As shown in Figure 2, compared with BN and BNNS, KH560-BNNS has two new absorption bands at 2933cm ^-1 and 1091cm ^-1 , which are attributed to the stretching vibration of CH and Si-O bonds in the KH560 molecule respectively. For BPEI-KH560-BNNS, in addition to the two absorption bands of 2933cm ^-1 and 1091cm ^-1 , a new absorption band appears at 1460cm ^-1 , which is attributed to the stretching vibration of the CN bond in the BPEI molecule, which indicates that the BPEI molecule The surface modification of KH560-BNNS was achieved.

To determine the thermal stability of surface-modified BN nanosheets, thermogravimetric analysis was performed. As shown in Figure 3, the weight loss rate of BN in the entire temperature range (30~800°C) is only 0.27%, while the weight loss rate of BNNS is estimated to be 2.85%, which is mainly due to the migration of -OH and adsorbed water molecules on the BNNS surface. remove. After modification with KH560, the weight loss rate of KH560-BNNS was 4.99%. When KH560-BNNS was further modified by BPEI, the weight loss rate of BPEI-KH560-BNNS reached 9.43%, which was mainly due to the thermal decomposition of surface KH560 and BPEI molecules at high temperatures.

Comparative example 1:

The differences between this comparative example and Example 1 are:

In step 1), use a KH560-free water/ethanol mixed solution for ball milling;

Other steps and process conditions are the same as in Example 1.

The epoxy composite material of this comparative example was cast into a standard sample to test the thermal conductivity and mechanical properties of the composite material.

Comparative example 2:

The differences between this comparative example and Example 1 are:

In step 1), perform ball milling in a water/ethanol mixed solution without KH560 to obtain BN nanosheets;

In step 2), add BN nanosheets to a water/ethanol mixed solution containing 1wt% KH560 (water:ethanol=1:4), and adjust the pH value of the BN dispersion to 8 mol·L ^-1 hydrochloric acid solution. 4. Stir the reaction for 24 hours to obtain functionalized BN nanosheets;

Other steps and process conditions are the same as in Example 1.

The epoxy composite material of this comparative example was cast into a standard sample to test the thermal conductivity and mechanical properties of the composite material.

Comparative example 3:

The differences between this comparative example and Example 1 are:

In the process of step 1), BN powder is added to the water/ethanol mixed solution containing KH560 for mechanical stirring;

Other steps and process conditions are the same as in Example 1.

The epoxy composite material of this comparative example was cast into a standard sample to test the thermal conductivity and mechanical properties of the composite material.

Comparative example 4:

The differences between this comparative example and Example 1 are:

In step 1), replace KH560 in the water/ethanol mixed solution with KH550, which has no epoxy group;

Other steps and process conditions are the same as in Example 1.

The epoxy composite material of this comparative example was cast into a standard sample to test the thermal conductivity and mechanical properties of the composite material.

Comparative example 5:

The differences between this comparative example and Example 1 are:

In step 3), add the surface epoxy functionalized BN nanosheets to the BPEI solution and stir and mix at room temperature for 12 hours;

Other steps and process conditions are the same as in Example 1.

The epoxy composite material of this comparative example was cast into a standard sample to test the thermal conductivity and mechanical properties of the composite material.

Comparative example 6:

The differences between this comparative example and Example 1 are:

In step 3), replace the branched polyethyleneimine (BPEI) in the solution with linear polyethyleneimine (LPEI) of the same molecular weight. LPEI has no amino side chains;

Other steps and process conditions are the same as in Example 1.

The epoxy composite material of this comparative example was cast into a standard sample to test the thermal conductivity and mechanical properties of the composite material.

Comparative Example 7:

The differences between this comparative example and Example 1 are:

Use commercially sourced BN nanopowder instead of the surface-modified BN nanosheets in Example 1;

Other steps and process conditions are the same as in Example 1.

The epoxy composite material of this comparative example was cast into a standard sample to test the thermal conductivity and mechanical properties of the composite material.

Comparative example 8:

The differences between this comparative example and Example 1 are:

Use commercially sourced BN nanosheets instead of the surface-modified BN nanosheets in Example 1;

Other steps and process conditions are the same as in Example 1.

The epoxy composite material of this comparative example was cast into a standard sample to test the thermal conductivity and mechanical properties of the composite material.

Comparative example 9:

The differences between this comparative example and Example 1 are:

Step (3) is omitted, and the surface epoxy functionalized BN nanosheets (i.e., KH560 modified BN nanosheets) are used instead of the surface modified BN nanosheets in Example 1;

Other steps and process conditions are the same as in Example 1.

The epoxy composite material of this comparative example was cast into a standard sample to test the thermal conductivity and mechanical properties of the composite material.

The thermal conductivity, tensile strength and impact strength were tested on the epoxy composite materials and pure epoxy materials in Example 1 and Comparative Examples 1-9. The specific test results are shown in Table 1.

Table 1 Thermal conductivity, tensile strength and impact strength of samples in Examples and Comparative Examples

sample name 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 nanosheets. Comparative results with Example 1 show that BPEI covalently modified BN nanosheets have better thermal conductivity and mechanical improvement effects than BPEI non-covalently modified BN nanosheets;

In Comparative Example 2, epoxy functionalized BN nanosheets were obtained by step-by-step modification using KH560. The comparison results with Example 1 show that the epoxy-functionalized BN nanosheets obtained by one-step ball milling modified by BPEI have better thermal conductivity and mechanical improvement effects than the epoxy-functionalized BN nanosheets obtained by step-by-step modification by BPEI. ;

In Comparative Example 3, BN was not ball milled and the nanosheet structure could not be obtained. Comparative results with Example 1 show that BPEI surface-modified BN nanosheets have better thermal conductivity and mechanical improvement effects than BPEI surface-modified BN powder;

In Comparative Example 4, KH550 was used instead of KH560, resulting in amino-functionalized BN nanosheets that could not be further covalently linked to BPEI. Comparative results with Example 1 show that BPEI surface-modified BN nanosheets have better thermal conductivity and mechanical improvement effects than KH550-modified BN nanosheets;

In Comparative Example 5, the degree of reaction between BPEI and epoxy-based BN nanosheets is low at room temperature. Comparative results with Example 1 show that the BPEI surface-modified BN nanosheets prepared at a certain temperature have better thermal conductivity and mechanical improvement effects than the BPEI surface-modified BN nanosheets prepared at room temperature;

In Comparative Example 6, the number of amino groups on the surface-modified BN nanosheets of linear polyethyleneimine LPEI is small, resulting in a low degree of cross-linking with the epoxy matrix. Comparative results with Example 1 show that BPEI surface-modified BN nanosheets have better thermal conductivity and mechanical improvement effects than LPEI surface-modified BN nanosheets;

The comparison results of Comparative Examples 7, 8 and 9 with Example 1 show that at the same addition ratio, BPEI surface-modified BN nanosheets have better thermal conductivity and mechanical improvement than commercial BN powder, BN nanosheets and KH560 modified BN nanosheets. Effect.

The chemical modification principle of the surface-modified BN of the present invention is:

1. Under the shear force of the ball milling process, BN powder is peeled off into BN nanosheets; at the same time, the hydroxyl groups on the surface of the BN nanosheets react with the hydrolyzed KH560 to obtain epoxy-functionalized BN nanosheets, which is a further modification of BPEI. Provide connection points;

2. BPEI containing rich amino groups undergoes a ring-opening reaction with the epoxy group of the epoxy-functionalized BN nanosheets to obtain BPEI surface-modified BN nanosheets. After BPEI surface modification, the surface of BN nanosheets contains rich amino groups. , can react with the epoxy groups in the epoxy resin matrix and the anhydride groups in the anhydride curing agent at the same time to produce a strong chemical connection and improve the dispersion and interfacial compatibility of BN nanosheets.

In the above embodiments and their alternatives, each raw material and the process parameters involved in the modification method can be determined within a limited range according to actual application requirements.

In view of the numerous embodiments of the present invention, all components, component contents and process parameters can be determined within the corresponding range according to application requirements. The experimental data of each embodiment are huge and numerous, and it is not suitable to list and explain them one by one here. However, each The content that needs to be verified in the examples and the final conclusions obtained are close.

The above is only a detailed description of the preferred embodiments and principles of the present invention. For those of ordinary skill in the art, there will be changes in the specific implementation methods based on the ideas provided by the present invention, and these changes should also be made. regarded as the protection scope of the present invention.

Claims (7)

1. Epoxy composite material, characterized in that its preparation process includes the following steps: (a) Add surface-modified hexagonal boron nitride nanosheets to ethanol and disperse them ultrasonically for 5 to 120 minutes to obtain a nanosheet dispersion with a concentration of 0.5 to 50 mg·mL ^-1 ; (b) Stir and mix the nanosheet dispersion, epoxy resin, and acid anhydride curing agent evenly, and then distill under reduced pressure to remove the ethanol to obtain a mixed solution; (c) Stir the mixed solution and accelerator evenly at room temperature, and then leave it to defoam under vacuum. After the bubbles are removed, pour the mixed solution onto the mold and solidify to obtain the epoxy composite material; Wherein, the content of the surface-modified hexagonal boron nitride nanosheets in the epoxy composite material is 1 to 40wt%; The modification method of surface-modified hexagonal boron nitride nanosheets includes the following steps: (1) Add hexagonal boron nitride powder to the homogeneous aqueous solution of the epoxy-containing silane coupling agent, disperse it ultrasonically, obtain a hexagonal boron nitride dispersion and adjust the pH to 0 to 6; (2) Transfer the dispersion obtained in step (1) to a ball milling tank, and ball mill at 100 to 2000 rpm for 1 to 48 hours. After ball milling, vacuum filtration is performed, and the powder obtained by suction filtration is dried to obtain surface epoxy functionalized hexagonal boron nitride nanosheets; (3) Add the hexagonal boron nitride nanosheets obtained in step (2) to the aqueous solution of branched polyethyleneimine, disperse it ultrasonically, and react at 0 to 80°C for 1 to 48 hours, followed by vacuum filtration and drying. Surface-modified hexagonal boron nitride nanosheets were obtained. 2. The epoxy composite material according to claim 1, characterized in that 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, characterized in that in the step (1), the dispersion concentration of hexagonal boron nitride powder in the water/ethanol mixed solution is 0.5 to 50 mg·mL ^-1 ; 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 material according to claim 1, characterized in that in the step (1), the duration of ultrasonic dispersion is 5 to 120 minutes; the pH of the hexagonal boron nitride dispersion is adjusted by acid liquid. 5. The epoxy composite material according to claim 4, wherein 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 . 6. The epoxy composite material according to claim 1, characterized in that in the step (2), the drying temperature is 30-150°C, and the drying time is 1-48 h. 7. The epoxy composite material according to claim 1, wherein the molecular weight of the branched polyethyleneimine is 200-100000, and the concentration of the branched polyethyleneimine aqueous solution is 0.01-30wt%.