A preparation method of a carboxylated cellulose nanofiber (CCNF) and reduced graphene oxide-based directional high-thermal-conductivity aerogel-based composite phase change material

Abstract

This invention discloses a method for preparing a carboxylated cellulose nanofiber (CCNF) and reduced graphene oxide-based oriented high thermal conductivity aerogel-based composite phase change material, comprising the following steps: the high thermal conductivity aerogel composite phase change material includes carboxylated cellulose nanofiber (CCNF), reduced graphene oxide (rGO), and neopentyl glycol (NPG) phase change material. The aerogel (CG) is prepared from CCNF and rGO using an ice template method. The prepared aerogel (CG) exhibits a bottom-up oriented structure. After vacuum impregnation with NPG, CCNF can form hydrogen bonds with rGO and NPG, improving the dispersion of rGO and NPG. Simultaneously, the continuous thermally conductive network constructed by rGO provides an efficient heat conduction path, improving the thermal conductivity and photothermal properties of the aerogel composite phase change material (CGN). The high thermal conductivity aerogel composite phase change material prepared by this invention has high thermal conductivity and latent heat of phase change, and exhibits good photothermal synergy, showing broad application prospects in thermal management.

Description

Technical Field

[0001] This invention relates to the field of aerogel-based phase change material preparation, specifically a method for preparing a carboxylated cellulose nanofibers (CCNF) and reduced graphene oxide-based directional high thermal conductivity aerogel-based composite phase change material. This high thermal conductivity aerogel-based composite phase change material uses highly thermally conductive reduced black graphene oxide and carboxylated cellulose nanofibers (CCNF) as the aerogel substrate and neopentyl glycol (NPG) as the phase change material, and is a directional high thermal conductivity CGN composite phase change material. Background Technology

[0002] In recent years, phase change materials (PCMs) have attracted much attention in the field of thermal energy storage, and their functional PCMs have been extensively studied in applications such as solar / electric thermal energy storage, waste heat storage and utilization, and building energy conservation. However, the widespread application of most solid-liquid PCMs is limited by leakage problems and low thermal conductivity. To solve these problems, techniques such as encapsulating PCMs with high thermal conductivity filler materials are commonly used, including microencapsulation, organic and inorganic porous framework encapsulation, etc.

[0003] Carboxylated cellulose nanofibers (CCNFs), as a green and renewable nanomaterial, have demonstrated multifunctional potential in solving the aforementioned complex challenges. The abundant hydroxyl and carboxyl groups on their molecular chains not only endow them with excellent water dispersibility, effectively stabilizing and dispersing rGO sheets through steric hindrance and electrostatic repulsion, but also act as molecular bridges, significantly improving the interfacial bonding between rGO and NPG and reducing interfacial thermal resistance through their amphiphilic structure. Crucially, CCNFs' superior gelling ability makes it possible to construct precisely customized three-dimensional porous frameworks. However, traditional physical blending or random freeze-drying techniques struggle to achieve precise control over the microstructure of composite materials, resulting in randomness and incompleteness in the construction of thermally conductive pathways.

[0004] Chinese patent CN119160885 A discloses a modified graphene oxide, a modified graphene oxide aqueous dispersion, its preparation method and application. The modified graphene oxide comprises graphene oxide and grafted polyoxyethylene chains, and the chemical formula of the polyoxyethylene chains is -CH2CH(OH)CH2O(CH2CH2O). nCH2CH2OH, where n is any integer from 3 to 20; the grafting rate of polyoxyethylene chains in the modified graphene oxide is 30-50%. This modified graphene oxide exhibits good salt resistance, can withstand acid / alkali aqueous solutions, and effectively inhibits the accumulation and aggregation of graphene oxide. Chinese Patent Publication No. CN119219980 A discloses a composite thermally conductive filler, an in-situ modified graphene thermally conductive gel, and their preparation and application. The composite thermally conductive filler is a graphene oxide-encapsulated alumina composite thermally conductive filler, wherein alumina is grown in situ on the surface of graphene oxide, and then a microsphere structure of graphene oxide encapsulated on the surface of alumina oxide is formed through a special drying technique. This invention also discloses an in-situ modified graphene thermally conductive gel containing the above-mentioned composite thermally conductive filler. In the product prepared in the embodiments of the present invention, graphene is wrapped on the surface of aluminum oxide. The two overlap and cooperate with each other to form a special composite effect of two-dimensional and zero-dimensional spheres, which constructs a three-dimensional and extensive thermally conductive network structure, achieving high thermal conductivity and high extrusion rate with low filling amount.

[0005] Although the aforementioned techniques can effectively promote the dispersion of graphene oxide in the matrix and enhance the thermal conductivity of composite phase change materials through graphene oxide, the prepared aerogel substrate and phase change material still suffer from uneven dispersion and high thermal resistance. Summary of the Invention

[0006] In view of the shortcomings of the prior art, the present invention aims to provide a method for preparing a composite phase change material based on carboxylated cellulose nanofibers (CCNF) and reduced graphene oxide-based directional high thermal conductivity aerogel, solving the defects of neopentyl glycol as a phase change material, such as difficulty in dispersion with a thermally conductive medium and high thermal resistance. Furthermore, cellulose can improve the dispersion and sedimentation problems of reduced graphene oxide.

[0007] To solve the above problems, the technical solution of the present invention is as follows: This invention uses low-cost and easily processable graphene oxide and cellulose (CNF) with numerous excellent properties as basic building blocks. Carboxylated cellulose nanofibers (CCNF) and reduced graphene oxide (rGO) aerogels are prepared through ultrasonication, thermal reduction, and directional freeze-drying. Then, using neopentyl glycol as a phase change material, a CGN aerogel composite phase change material with high thermal conductivity is prepared. The prepared CGN aerogel exhibits a directional structure and a continuous thermally conductive network. Hydrogen bonds are formed between CCNF and reduced graphene oxide, which better disperses the reduced graphene oxide. After vacuum impregnation with NPG, CCNF can simultaneously form hydrogen bonds with both rGO and NPG, thereby improving the shortcomings of neopentyl glycol as a phase change material, such as difficulty in dispersion with the thermally conductive medium and high thermal resistance. Simultaneously, the continuous thermally conductive network constructed by the uniformly dispersed rGO provides an efficient heat conduction path, improving the thermal conductivity and photothermal properties of the composite phase change material. Furthermore, neopentyl glycol, as a phase change material, can absorb or release heat in response to changes in external temperature. Therefore, the prepared CGN composite phase change material has broad application prospects in thermal management.

[0008] The preparation method of a carboxylated cellulose nanofiber (CCNF) and reduced graphene oxide-based oriented highly thermally conductive aerogel-based composite phase change material according to the present invention specifically includes the following steps: S1. Mix carboxylated cellulose nanofiber aqueous dispersion and graphene oxide with ultrasonication to obtain a mixed suspension of cellulose and graphene oxide; S2. Add citric acid to the mixed suspension obtained in step S1, heat and stir to obtain CG suspension; S3. The CG suspension obtained in step S2 is directionally frozen in a liquid nitrogen environment, and then transferred to a freeze dryer for drying to obtain CG aerogel. S4. Add neopentyl glycol and the aerogel obtained in step S3 into a beaker, and place the beaker in a vacuum drying oven, heat and evacuate to perform vacuum impregnation of the phase change material. S5. Take out the product prepared in step S4, and after the product cools down, use tweezers to remove the residual neopentyl glycol on the surface, finally obtaining carboxylated cellulose nanofibers (CCNF) and reduced graphene oxide-based directional aerogel-based composite phase change material (CGN).

[0009] As a further improvement of the present invention, in step S1, the mass ratio of carboxylated cellulose nanofibers to graphene oxide is 6:1, 3:1 and 3:2, and the mixed ultrasound in step S1 is specifically performed under the following conditions: ultrasonic power 600 W, temperature 25 ℃ and ultrasonic time 90 min.

[0010] As a further improvement of the present invention, in step S2, the mass fraction ratio of citric acid to graphene oxide is 1:50; the heating and stirring in step S2 are specifically carried out at a temperature of 85°C, a time of 10 hours, and a stirring rate of 400 rpm.

[0011] As a further improvement of the present invention, the freeze-drying temperature in step S3 is -60°C and the time is 72 hours.

[0012] As a further improvement of the present invention, the vacuum degree in step S4 is less than 0.08 MPa, the vacuum impregnation temperature is 150°C, and the vacuum impregnation time is 1 hour.

[0013] As a further improvement of the present invention, a carboxylated cellulose nanofiber (CCNF) and reduced graphene oxide-based oriented high thermal conductivity aerogel-based composite phase change material is provided, wherein the high thermal conductivity aerogel composite phase change material includes carboxylated cellulose nanofiber, reduced graphene oxide and neopentyl glycol (NPG) phase change material.

[0014] As a further improvement of the present invention, the carboxylated cellulose nanofibers (CCNF) and reduced graphene oxide-based directional high thermal conductivity aerogel-based composite phase change material are provided, wherein the cellulose is carboxylated cellulose nanofibers (CCNF) with a diameter of 50 nm, a length of about 1~3 μm, and a concentration of 6% dispersion.

[0015] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention uses carboxylated cellulose nanofibers (CCNF). Since its surface is rich in hydroxyl and carboxyl groups, a large number of hydrogen bonds can be generated by CCNF and reduced graphene oxide. Therefore, the CG suspension obtained by the present invention has good colloidal stability. At the same time, since the CG suspension obtained by CCNF and reduced graphene oxide exhibits a black hue, this significantly improves its light absorption capacity. (2) The CGN high thermal conductivity aerogel composite phase change material prepared by the present invention has a high thermal conductivity and excellent photothermal properties. The continuous thermally conductive network constructed by uniformly dispersed reduced graphene oxide provides an efficient heat conduction path, which significantly enhances the heat transfer within the structure, thereby improving the thermal conductivity and photothermal properties of the composite phase change material. Attached Figure Description

[0016] Figure 1 This is a flowchart illustrating the preparation process of a carboxylated cellulose nanofiber (CCNF) and reduced graphene oxide-based directional high thermal conductivity aerogel-based composite phase change material according to the present invention. Figure 2The images (ab) show the CG suspension prepared in Example 1 of this invention, as well as the prepared carboxylated cellulose nanofibers (CCNF) and reduced graphene oxide-based oriented high thermal conductivity aerogel. Figure 3 Scanning electron microscope (SEM) of the CG aerogel prepared in Example 1. Figure 4 The axial and radial compressibility of the CG aerogel obtained in Example 1; Figure 5 Differential scanning calorimetry (DSC) and thermal conductivity (ad) of the CGN composite phase change material obtained in Example 1; Figure 6 This demonstrates the leak-proof performance of the CGN composite phase change material obtained in Example 1; Figure 7 The photothermal properties of the CGN composite phase change material obtained in Example 1 are shown. Detailed Implementation

[0017] This invention provides a method for preparing a composite phase change material based on carboxylated cellulose nanofibers (CCNF) and reduced graphene oxide-based directional high thermal conductivity aerogel. To make the objectives, technical solutions, and advantages of this invention clearer and more explicit, this invention will be further described in conjunction with specific embodiments and accompanying drawings.

[0018] Example 1: As Figure 1 As shown, the present invention discloses a method for preparing a carboxylated cellulose nanofiber (CCNF) and reduced graphene oxide-based oriented high thermal conductivity aerogel-based composite phase change material, which is prepared through the following steps: Step 1: Mix 10 g of 6% carboxylated cellulose nanofiber aqueous dispersion with 0.1 g, 0.2 g and 0.4 g of graphene oxide, and sonicate at 25 ℃ for 90 min using a 600 W ultrasonic machine to obtain a cellulose and graphene oxide suspension.

[0019] Step 2: Add 2 mg, 4 mg and 8 mg of citric acid to the cellulose and graphene oxide suspension obtained in Step 1, heat at 85 °C and stir at 400 rpm for 10 h to obtain CG suspension; Step 3: The CG suspension obtained in Step 2 is directionally frozen in a liquid nitrogen environment, and then placed in a freeze dryer for freeze drying to obtain CG aerogel; Step 4: The aerogel obtained in Step 3 and neopentyl glycol are placed in a beaker at room temperature. The beaker is placed in a vacuum drying oven and vacuum impregnated at 150°C for 1 hour. After the product cools down, the residual neopentyl glycol on the surface is removed with tweezers to finally obtain the CGN composite phase change material.

[0020] The CG-2 suspension and CG-2 aerogel prepared in Example 1 were observed in practice, and the results are as follows: Figure 2 (a) Right and Figure 2 (b) As shown on the right.

[0021] The CG-2 aerogel prepared in Example 1 was examined by scanning electron microscopy, and the results are as follows: Figure 3 As shown.

[0022] Figure 3 The study revealed that CG-2 aerogel exhibits a tubular microstructure in the longitudinal direction and a honeycomb-like microstructure in the transverse direction, with uniformly dispersed reduced graphene oxide effectively forming a continuous thermally conductive network.

[0023] Figure 4 It can be seen that CG-2 aerogel has significantly different compressibility properties in the axial and radial directions.

[0024] The CGN-2 composite phase change material prepared in Example 1 was subjected to differential scanning calorimetry (DSC) and thermal conductivity tests, and the results are as follows: Figure 5 .

[0025] Figure 5 It can be seen that the enthalpy of fusion of CGN-2 can reach 104.89 J / g, and its thermal conductivity is as high as 1.38867 W / (m·K).

[0026] Figure 6 It can be seen that CGN maintains its structural integrity above the solid-liquid phase transition temperature, with no leakage of phase change material.

[0027] Figure 7 Photothermal experiments showed that none of the CGNs leaked throughout the entire process. When the light intensity increased from 100 mW / cm², this was observed. 2 Increased to 200 mW / cm 2 At that time, the peak temperature of CGN-2 increased from 47.56 ℃ to 73.79 ℃.

[0028] Comparative Examples 2-5: A method for preparing a composite phase change material based on carboxylated cellulose nanofibers (CCNF) and reduced graphene oxide-based directional high thermal conductivity aerogel is provided. Compared with Example 1, the difference is that in step 2, the mass ratio of graphene oxide to citric acid is 100, 25, 15 and 10, respectively. The rest is roughly the same as in Example 1, and will not be repeated here.

[0029] Comparative Example 6: A method for preparing a carboxylated cellulose nanofibers (CCNF) and reduced graphene oxide-based oriented high thermal conductivity aerogel-based composite phase change material, the specific steps of which are as follows: Step 1: 10 g of 6% carboxylated cellulose nanofiber aqueous dispersion was subjected to directional freeze-drying to obtain CCNF aerogel; Step 2: Same as step 4 in Example 1, and will not be repeated here, to obtain a single CCNF aerogel composite phase change material.

[0030] Comparative Example 7: A method for preparing a composite phase change material based on carboxylated cellulose nanofibers (CCNF) and reduced graphene oxide-based directional high thermal conductivity aerogel is provided. The difference from Example 1 is that citric acid is not added in step 2. The rest is roughly the same as Example 1 and will not be described again here. A CGN composite phase change material is obtained.

[0031] Comparative Example 8: A method for preparing a composite phase change material based on carboxylated cellulose nanofibers (CCNF) and reduced graphene oxide-based directional high thermal conductivity aerogel is provided. The difference from Example 1 is that directional freezing is not performed in step 3. The rest is roughly the same as Example 1 and will not be described again here. CGW aerogel phase change material is obtained.

[0032] In summary, this invention utilizes CCNF, graphene oxide, citric acid, and neopentyl glycol as raw materials to prepare a CGN composite phase change material with excellent thermal conductivity and storage capabilities through directional freezing and vacuum impregnation. The abundant hydroxyl and carboxyl groups on the surface of CCNF effectively promote the uniform dispersion of graphene oxide, facilitating the formation of a thermally conductive network and thus achieving synergistic photothermal enhancement. Overall, CGN-based composite phase change materials offer a feasible solution to thermal management challenges, combining high efficiency with broad applicability, and can be used to improve the safety of overheating or overcooling in living environments.

Claims

1. A method for preparing a composite phase change material based on carboxylated cellulose nanofibers (CCNF) and reduced graphene oxide-based oriented high thermal conductivity aerogel, characterized in that, Includes the following steps: S1. Mix carboxylated cellulose nanofiber aqueous dispersion and graphene oxide with ultrasonication to obtain a mixed suspension of cellulose and graphene oxide; S2. Add citric acid to the mixed suspension obtained in step S1, heat and stir to obtain CG suspension; S3. The CG suspension obtained in step S2 is directionally frozen in a liquid nitrogen environment, and then transferred to a freeze dryer for drying to obtain CG aerogel. S4. Add neopentyl glycol and the aerogel obtained in step S3 into a beaker, and place the beaker in a vacuum drying oven, heat and evacuate to perform vacuum impregnation of the phase change material. S5. Take out the product prepared in step S4, remove the residual neopentyl glycol on the surface, and finally obtain carboxylated cellulose nanofibers (CCNF) and reduced graphene oxide-based directional aerogel-based composite phase change material (CGN).

2. The method for preparing a carboxylated cellulose nanofibers (CCNF) and reduced graphene oxide-based oriented high thermal conductivity aerogel-based composite phase change material according to claim 1, characterized in that, In step S1, the mass ratio of carboxylated cellulose nanofibers to graphene oxide is 6:1, 3:1, and 3:

2. The specific conditions for the mixed ultrasound in step S1 are: ultrasound power 600 W, temperature 25 ℃, and ultrasound time 90 min.

3. The method for preparing a carboxylated cellulose nanofibers (CCNF) and reduced graphene oxide-based oriented high thermal conductivity aerogel-based composite phase change material according to claim 1, characterized in that, The mass ratio of citric acid to graphene oxide in step S2 is 1:50; the heating and stirring in step S2 are specifically carried out at a temperature of 85°C, a time of 10 hours, and a stirring speed of 400 rpm.

4. The method for preparing a carboxylated cellulose nanofibers (CCNF) and reduced graphene oxide-based oriented high thermal conductivity aerogel-based composite phase change material according to claim 1, characterized in that, The freeze-drying temperature in step S3 is -60℃ and the time is 72h.

5. The method for preparing a carboxylated cellulose nanofibers (CCNF) and reduced graphene oxide-based oriented high thermal conductivity aerogel-based composite phase change material according to claim 1, characterized in that, The vacuum degree mentioned in step S4 is less than 0.08 MPa, the vacuum impregnation temperature is 150°C, and the vacuum impregnation time is 1 hour.

6. The carboxylated cellulose nanofibers (CCNF) and reduced graphene oxide-based oriented high thermal conductivity aerogel-based composite phase change material according to claim 1, characterized in that, It is prepared by the preparation method described in any one of claims 1 to 5.

7. The carboxylated cellulose nanofibers (CCNF) and reduced graphene oxide-based oriented high thermal conductivity aerogel-based composite phase change material according to claim 1, characterized in that, The high thermal conductivity aerogel composite phase change material includes carboxylated cellulose nanofibers, reduced graphene oxide, and neopentyl glycol (NPG) phase change material.

8. The carboxylated cellulose nanofibers (CCNF) and reduced graphene oxide-based oriented high thermal conductivity aerogel-based composite phase change material according to claim 7, characterized in that, The cellulose is carboxylated cellulose nanofiber (CCNF) with a diameter of 50 nm, a length of about 1~3 μm, and a concentration of 6% dispersion.

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