Flexible environment-friendly heat-conducting composite film and preparation method thereof

Abstract

The invention provides a flexible environment-friendly heat-conducting composite film and a preparation method thereof. The preparation method comprises the following steps: (1) adding cotton linters into a urine alkali system, and dissolving to obtain a cellulose solution; (2) adding MXene nanosheets and epichlorohydrin into the cellulose solution, stirring, centrifugally defoaming, putting into a mold, and standing to obtain MXene / cellulose hydrogel; and (3) sequentially stretching, fixing, hot-pressing and vulcanizing the MXene / cellulose hydrogel to obtain the flexible environment-friendly heat-conducting composite film. Through the synergistic effect of five steps of low-temperature urea alkali dissolution, EPI crosslinking, stretching, dilute sulphuric acid fixation and hot-pressing vulcanization, high in-plane orientation of MXene nanosheets in a cellulose network is achieved, the in-plane heat conductivity coefficient is increased, meanwhile, the flexibility is improved through an epichlorohydrin crosslinking network, an orientation structure is locked through dilute sulphuric acid, the porosity is reduced to 0.5% or below through hot pressing, and the heat conductivity coefficient of the MXene nanosheets is increased. And the in-plane heat conductivity coefficient and the flexibility of the conductive composite film are synchronously improved.

Description

Technical Field

[0001] The present invention relates to the technical field of flexible composite films, and in particular to a flexible, environmentally friendly, thermally conductive composite film and a preparation method thereof. Background Art

[0002] As electronic devices evolve towards miniaturization and higher power, composite films that combine high thermal conductivity, excellent flexibility, and environmental friendliness have become a research hotspot. Traditional polymer-based films, such as polyimide films, have low intrinsic thermal conductivity, so high proportions of ceramic fillers are often added, which significantly reduces flexibility. Metal-based materials, while excellent thermal conductors, are also dense, prone to corrosion, and difficult to decompose.

[0003] Currently available bio-based composite films, such as Chinese patent CN118271660A nanocellulose-MXene composite film and preparation method thereof, and pressure-humidity dual-mode sensor, disclose MXene / cellulose composite films. However, they adopt a physical blending method, in which the MXene nanosheets agglomerate due to van der Waals forces and hydrogen bonding, resulting in the problem of local thermal conductivity interruption. At the same time, they rely on natural casting to form films and lack active orientation control. The MXene nanosheets are randomly arranged, resulting in low in-plane thermal conductivity. In addition, the hot air drying process causes the cellulose molecular chains to shrink, resulting in a loss of orientation. The rapid evaporation of moisture at the interface will form micropores, affecting the flexibility and service life of the film.

[0004] Therefore, in view of the problems in the existing technology such as the difficulty in achieving single-layer dispersion of MXene in the cellulose matrix and the inability to construct a long-range ordered thermal conductive network, a new preparation process is urgently needed to solve the above problems. Summary of the Invention

[0005] (1) Technical problems solved

[0006] In view of the deficiencies in the prior art, the present invention provides a flexible, environmentally friendly, thermally conductive composite film and a preparation method thereof, which solves the problems raised in the above-mentioned background technology.

[0007] (2) Technical solution

[0008] To achieve the above objectives, the present invention is implemented through the following technical solutions:

[0009] According to a first aspect of the present invention, a method for preparing a flexible, environmentally friendly, thermally conductive composite film is provided, comprising the following steps:

[0010] (1) adding cotton linters into a urea-alkali system and dissolving them to obtain a cellulose solution;

[0011] (2) adding MXene nanosheets and epichlorohydrin to the cellulose solution, stirring, centrifuging to remove bubbles, placing in a mold, and allowing to stand to obtain a MXene / cellulose hydrogel;

[0012] (3) The MXene / cellulose hydrogel is sequentially stretched, fixed, and hot-pressed and vulcanized to obtain the flexible, environmentally friendly, thermally conductive composite film.

[0013] In the present invention, cellulose with a degree of polymerization greater than 1800 is first prepared by dissolving cotton linters with urea alkali at low temperature, providing a long molecular chain basis for subsequent stretching. Then, the epoxy groups of epichlorohydrin react with the hydroxyl groups of cellulose to form a three-dimensional network, stabilizing the interlayer spacing of the MXene nanosheets at 2 to 5 nm. Finally, after stretching, fixation, and hot-pressing vulcanization, the surface hydroxyl groups of the MXene nanosheets are protonated, and the electrostatic repulsion locks the oriented structure. Hot-pressing dehydration simultaneously achieves interfacial fusion, and the porosity can be lower than 0.5%, resulting in a flexible composite film with low conductivity.

[0014] Preferably, in step (1), the urea-alkali system is an aqueous solution containing urea and lithium hydroxide, wherein the mass fraction of urea in the urea-alkali system is 15-20 wt %, and the mass fraction of lithium hydroxide is 4.5-15 wt %;

[0015] The volume ratio of the added amount of the cotton linters to the urea-alkali system is 1 g: 20-40 mL.

[0016] Preferably, in step (1), the dissolution temperature is -12°C. The present invention can protect the degree of polymerization of cellulose to be greater than 1800 by dissolving cotton linters with urea alkali at low temperature, thereby avoiding molecular chain breakage.

[0017] Preferably, in step (2), the volume ratio of the mass of the MXene nanosheets to the cellulose solution is 0.1-5 g:50 mL;

[0018] The volume ratio of the epichlorohydrin to the cellulose solution is 1 to 2:50.

[0019] Preferably, in step (2), the MXene nanosheets are obtained by etching the MAX phase with lithium fluoride and concentrated sulfuric acid;

[0020] The MXene nanosheets have a sheet diameter of 50 to 800 nm.

[0021] Preferably, in step (2), the stirring speed is 1000-2000 rpm, and the stirring time is 40-60 min;

[0022] The standing condition is standing at 5° C. for 12 to 24 hours.

[0023] Preferably, in step (3), the stretching ratio is 2 to 3 times;

[0024] The fixing method is to fix with dilute sulfuric acid with a concentration of 5wt%;

[0025] The temperature of the hot pressing vulcanization is 90-110°C.

[0026] In this application, the surface hydroxyl groups of the stretched MXene nanosheets can be protonated by fixation treatment with dilute sulfuric acid, and the oriented structure after stretching can be permanently fixed by enhanced electrostatic repulsion, which can prevent the shrinkage problem caused by hot air drying in the prior art; through hot pressing vulcanization, the cellulose molecular chains and the MXene nanosheets form CO-Ti covalent bonds, which can eliminate the interfacial thermal resistance and improve the thermal conductivity efficiency.

[0027] According to a second aspect of the present invention, a flexible thermally conductive composite film prepared according to the above method is provided, comprising a three-dimensional network structure formed by epichlorohydrin and cellulose and MXene nanosheets embedded in the three-dimensional network structure.

[0028] Preferably, the content of MXene nanosheets in the flexible, environmentally friendly, thermally conductive composite film is 1 to 5 wt%;

[0029] The content of cellulose in the flexible, environmentally friendly, thermally conductive composite film is 10-20 wt %.

[0030] Preferably, the in-plane thermal conductivity of the flexible environmentally friendly thermally conductive composite film is 2 to 8 W·m -1 ·K -1 , tensile strength is 10-70 MPa, Young's modulus is 0.5-5.5 GPa, and toughness is 0.2-0.42 MJ·m -3 .

[0031] Beneficial effects

[0032] The present invention provides a flexible, environmentally friendly, thermally conductive composite film and a preparation method thereof. It has the following beneficial effects:

[0033] (1) This solution provides a method for preparing a flexible, environmentally friendly, thermally conductive composite film. The present invention achieves a high degree of in-plane orientation of MXene nanosheets in a cellulose network through the synergistic effect of low-temperature urea-alkali dissolution + EPI cross-linking + stretching + dilute sulfuric acid fixation + hot pressing vulcanization, thereby increasing the in-plane thermal conductivity to 7.36 W·m -1 ·K -1 In addition, the epichlorohydrin cross-linking network improves flexibility, the dilute sulfuric acid locks the oriented structure, and the hot pressing reduces the porosity to below 0.5%, thereby simultaneously improving the in-plane thermal conductivity and flexibility of the conductive composite film.

[0034] (2) This solution provides a method for preparing a flexible, environmentally friendly, thermally conductive composite film. MXene nanosheets are embedded in a three-dimensional network structure formed by epichlorohydrin and cellulose. Through the optimization of the technical solution, the in-plane thermal conductivity can reach 7.36 W·m -1 ·K -1 , the tensile strength can reach 69.87MPa, the Young's modulus can reach 5.21GPa, and the toughness can reach 0.23MJ·m -3 . BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 This is an infrared surface image of the flexible, environmentally friendly, thermally conductive composite film prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0036] In order to better illustrate the content of the present invention, a detailed description is given below in conjunction with specific embodiments.

[0037] Unless otherwise specified, the raw materials used in the examples of the present invention were purchased from commercial sources.

[0038] Example 1

[0039] A method for preparing a flexible, environmentally friendly, thermally conductive composite film comprises the following steps:

[0040] Step 1: Add 9.47 g of urea and 2.85 g of lithium hydroxide to 50 mL of water and mix well to obtain a urea-alkali system;

[0041] Step 2: Add 2 g of cotton linters to the urea-alkali system and dissolve in an ice bath at -12°C to obtain a cellulose solution;

[0042] Step 3: Add 0.4 g of MXene nanosheets with a sheet diameter of 0.5 μm and 2 mL of epichlorohydrin to the cellulose solution, stir at 2000 rpm for 50 min, mix thoroughly, centrifuge to remove bubbles, place in a square mold, and then transfer to a 5°C refrigerator for standing to obtain a MXene / cellulose hydrogel;

[0043] Step 4: After stretching the MXene / cellulose hydrogel by 1 times using a spiral test bench, it was immersed in 5 wt% dilute sulfuric acid to fix it, remove excess alkali, and then the stretched and fixed hydrogel was washed with deionized water;

[0044] Step 5: Place the stretched and fixed hydrogel in a hot press and vulcanize it at 110° C. to obtain a flexible, environmentally friendly, thermally conductive composite film.

[0045] The infrared characterization of the flexible environmentally friendly thermally conductive composite film prepared in Example 1 is as follows Figure 1As shown in the figure, it can be seen that MXene and cellulose are successfully composited, and hydrogen bonds are formed between MXene and cellulose.

[0046] Example 2

[0047] A method for preparing a flexible, environmentally friendly, thermally conductive composite film comprises the following steps:

[0048] Step 1: Add 9.47 g of urea and 2.85 g of lithium hydroxide to 50 mL of water and mix well to obtain a urea-alkali system;

[0049] Step 2: Add 2 g of cotton linters to the urea-alkali system and dissolve in an ice bath at -12°C to obtain a cellulose solution;

[0050] Step 3: Add 0.4 g of MXene nanosheets with a sheet diameter of 0.5 μm and 2 mL of epichlorohydrin to the cellulose solution, stir at 2000 rpm for 50 min, mix thoroughly, centrifuge to remove bubbles, place in a square mold, and then transfer to a 5°C refrigerator for standing to obtain a MXene / cellulose hydrogel;

[0051] Step 4: After stretching the MXene / cellulose hydrogel by 2 times using a spiral test bench, it was immersed in 5 wt% dilute sulfuric acid to fix it, remove excess alkali, and then the stretched and fixed hydrogel was washed with deionized water;

[0052] Step 5: Place the stretched and fixed hydrogel in a hot press and vulcanize it at 110° C. to obtain a flexible, environmentally friendly, thermally conductive composite film.

[0053] Example 3

[0054] A method for preparing a flexible, environmentally friendly, thermally conductive composite film comprises the following steps:

[0055] Step 1: Add 9.47 g of urea and 2.85 g of lithium hydroxide to 50 mL of water and mix well to obtain a urea-alkali system;

[0056] Step 2: Add 2 g of cotton linters to the urea-alkali system and dissolve in an ice bath at -12°C to obtain a cellulose solution;

[0057] Step 3: Add 0.4 g of MXene nanosheets with a sheet diameter of 0.5 μm and 2 mL of epichlorohydrin to the cellulose solution, stir at 2000 rpm for 50 min, mix thoroughly, centrifuge to remove bubbles, place in a square mold, and then transfer to a 5°C refrigerator for standing to obtain a MXene / cellulose hydrogel;

[0058] Step 4: After stretching the MXene / cellulose hydrogel 3 times using a spiral test bench, it was fixed by immersing it in 5 wt% dilute sulfuric acid to remove excess alkali, and then the stretched and fixed hydrogel was washed with deionized water;

[0059] Step 5: Place the stretched and fixed hydrogel in a hot press and vulcanize it at 110° C. to obtain a flexible, environmentally friendly, thermally conductive composite film.

[0060] Comparative Example 1

[0061] Step 1: Add 9.47 g of urea and 2.85 g of lithium hydroxide to 50 mL of water and mix well to obtain a urea-alkali system;

[0062] Step 2: Add 2 g of cotton linters to the urea-alkali system and dissolve at 0° C. to obtain a cellulose solution;

[0063] Step 3: Add 0.4 g of MXene nanosheets with a sheet diameter of 0.5 μm to the cellulose solution, stir at a speed of 2000 rpm for 50 minutes, cast into a film, and then dry with hot air at 60°C for 2 hours to obtain a composite film.

[0064] Performance Testing

[0065] The in-plane thermal conductivity, tensile strength, Young's modulus and toughness of the composite films prepared in Examples 1 to 3 and Comparative Example 1 were measured respectively. The test results are shown in Table 1.

[0066] Table 1

[0067]

[0068] According to the data in Table 1, as the degree of stretching increases, the in-plane thermal conductivity and mechanical properties of the flexible, environmentally friendly, thermally conductive composite film gradually improve. Compared with Comparative Example 1, the in-plane thermal conductivity and flexibility of the composite film prepared by the preparation process of the present invention can be improved simultaneously.

[0069] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a flexible, environmentally friendly, thermally conductive composite film, characterized by: This includes the following methods: (1) adding cotton linters into a urea-alkali system and dissolving them to obtain a cellulose solution; (2) adding MXene nanosheets and epichlorohydrin to the cellulose solution, stirring, centrifuging to remove bubbles, placing in a mold, and allowing to stand to obtain a MXene / cellulose hydrogel; (3) The MXene / cellulose hydrogel is sequentially stretched, fixed, and hot-pressed and vulcanized to obtain the flexible, environmentally friendly, thermally conductive composite film.

2. The method for preparing a flexible, environmentally friendly, thermally conductive composite film according to claim 1, wherein: In step (1), the urea-alkali system is an aqueous solution containing urea and lithium hydroxide, wherein the mass fraction of urea in the urea-alkali system is 15-20 wt %, and the mass fraction of lithium hydroxide is 4.5-15 wt %; The volume ratio of the added amount of the cotton linters to the urea-alkali system is 1 g: 20-40 mL.

3. The method for preparing a flexible, environmentally friendly, thermally conductive composite film according to claim 1, wherein: In step (1), the dissolving temperature is -12°C.

4. The method for preparing a flexible, environmentally friendly, thermally conductive composite film according to claim 1, wherein: In step (2), the volume ratio of the mass of the MXene nanosheets to the cellulose solution is 0.1-5 g:50 mL; The volume ratio of the epichlorohydrin to the cellulose solution is 1 to 2:

50.

5. The method for preparing a flexible, environmentally friendly, thermally conductive composite film according to claim 1, wherein: In step (2), the MXene nanosheets are obtained by etching the MAX phase with lithium fluoride and concentrated sulfuric acid; The MXene nanosheets have a sheet diameter of 50 to 800 nm.

6. The method for preparing a flexible, environmentally friendly, thermally conductive composite film according to claim 1, wherein: In step (2), the stirring speed is 1000-2000 rpm, and the stirring time is 40-60 min; The standing condition is standing at 5° C. for 12 to 24 hours.

7. The method for preparing a flexible, environmentally friendly, thermally conductive composite film according to claim 1, wherein: In step (3), the stretching ratio is 2 to 3 times; The fixing method is to fix with dilute sulfuric acid with a concentration of 5wt%; The temperature of the hot pressing vulcanization is 90-110°C.

8. A flexible, environmentally friendly, thermally conductive composite film obtained by the preparation method according to any one of claims 1 to 7, characterized in that: The invention comprises a three-dimensional network structure formed by epichlorohydrin and cellulose and MXene nanosheets embedded in the three-dimensional network structure.

9. The flexible, environmentally friendly, thermally conductive composite film according to claim 8, characterized in that: The content of MXene nanosheets in the flexible, environmentally friendly, thermally conductive composite film is 1 to 5 wt%; The content of cellulose in the flexible, environmentally friendly, thermally conductive composite film is 10-20 wt %.

10. The flexible, environmentally friendly, thermally conductive composite film according to claim 8, characterized in that: The in-plane thermal conductivity of the flexible environmentally friendly thermally conductive composite film is 2 to 8 W·m -1 ·K -1 , tensile strength is 10-70 MPa, Young's modulus is 0.5-5.5 GPa, and toughness is 0.2-0.42 MJ·m -3 .

Images