Carbonized composite phase change material as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of phase change materials, and particularly relates to a carbonized composite phase change material and a preparation method and application thereof. Filamentous fibers are softened and then gathered into bundles for hot pressing, self-assembly occurs in the hot pressing process, and filamentous fiber blocks are obtained; carbonizing the filamentous fiber block in protective gas to obtain a carbonized framework; performing vacuum impregnation on the carbonized framework in impregnation liquid to obtain a carbonized composite phase change material; the impregnation liquid comprises a phase-change material or comprises the phase-change material and a filler. The carbonized framework prepared by the method has a multi-scale pore structure, high porosity and a remarkable transverse and longitudinal difference structure, and the carbonized composite phase change material prepared from the carbonized framework has high phase change material loading rate, high thermal conductivity, high heat storage density and high anisotropy.

Description

Technical Field

[0001] The present invention belongs to the technical field of phase change materials, and particularly relates to a carbonized composite phase change material, a preparation method thereof, and an application thereof. Background Art

[0002] A phase change material (PCM) is a substance that undergoes a morphological change with temperature variation and can absorb or release latent heat. PCMs have been widely recognized for their unique thermoelectric properties and have become an effective solution for thermal energy storage applications. PCMs exhibit excellent capabilities in terms of energy storage density and heat recovery efficiency, while maintaining high environmental compatibility to ensure practicality. According to the state changes occurring during the phase change process, PCMs can be classified into gas-liquid PCMs, solid-liquid PCMs, and solid-solid PCMs. Among them, solid-liquid PCMs have become the most practical phase change energy storage materials due to their high phase change latent heat, stable performance, and suitability for industrial applications.

[0003] From the current research progress, it can be seen that although composite phase change materials (CPCMs) with stable anisotropic shapes have excellent thermal management properties, their transformation in practical applications lags behind relatively. There are three core problems causing this lag. Firstly, the substrate materials (such as carbon fibers) used to manufacture these anisotropic PCMs are costly, restricting their widespread application. Secondly, the manufacturing processes for achieving the desired anisotropic porous structures are usually complex and rely on chemical reagents, such as those used in aerogel production, thereby increasing production costs and potentially causing harm to the environment. Thirdly, the long-term durability problem of PCMs has not been effectively solved, limiting their reliability and stability during long-term use. Therefore, finding more cost-effective alternative materials has become the focus of research.

[0004] As a renewable resource with natural anisotropy, biomass materials have become an ideal choice for substrate materials due to their unique advantages such as renewable nature, easy processability, recyclability and degradability, and environmental friendliness. Using biomass materials as the substrate for CPCMs can not only make full use of their inherent advantages but also address the challenges faced by existing materials. Although there have been studies using biomass resources such as sugarcane, poplar, and pine as substrate materials (with anisotropy degrees of 1.25, 1.88, and 1.43 respectively), the thermal conductivity and heat storage density of the composite phase change materials prepared from these materials are still poor. Summary of the Invention

[0005] In view of this, the purpose of the present invention is to provide a carbonized composite phase change material, a preparation method thereof, and an application thereof. The carbonized skeleton prepared by the present invention has a multi-scale pore structure, high porosity, and a significant transverse and longitudinal difference structure. The carbonized composite phase change material prepared therefrom has a high phase change material loading rate, high thermal conductivity, high heat storage density, and high anisotropy degree.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] The present invention provides a method for preparing a carbonized composite phase change material, comprising the following steps:

[0008] After softening the filamentous fibers, they are assembled into bundles and hot-pressed. Self-assembly occurs during the hot-pressing process to obtain a filamentous fiber block;

[0009] Carbonize the filamentous fiber block in a protective gas to obtain a carbonized skeleton;

[0010] Vacuum impregnate the carbonized skeleton in an impregnating solution to obtain a carbonized composite phase change material;

[0011] The impregnating solution includes a phase change material or includes a phase change material and a filler.

[0012] Preferably, the filamentous fibers include one or more of bamboo fibers, sugarcane fibers, and ramie fibers.

[0013] Preferably, the pressure of the hot-pressing is 3-15 MPa, the temperature is 70-300 °C, and the heat preservation and pressure holding time is 1-15 min.

[0014] Preferably, the temperature of the carbonization is 600-1200 °C, and the heat preservation time is 2-10 h.

[0015] Preferably, the phase change material includes an organic phase change material and / or an inorganic phase change material; the organic phase change material includes one or more of paraffin, polyols, and fatty acids; the inorganic phase change material includes dodecahydrate sulfate and / or nitrate.

[0016] Preferably, the filler includes one or more of carbon materials, metal-organic framework materials, zeolitic imidazolate framework materials, and covalent organic framework materials.

[0017] Preferably, the temperature of the softening is 70-100 °C, the heat preservation time is 3-30 min; the softening is carried out under ultrasonic conditions; the power of the ultrasonic is 200-2000 W.

[0018] Preferably, the method for preparing the filamentous fibers is to draw the biomass raw material containing filamentous fibers; the drawing is to beat the biomass raw material containing filamentous fibers into filamentous fibers after heating; the heating is to 70-300 °C.

[0019] The present invention also provides a carbonized composite phase change material prepared by the preparation method described in the above technical solutions, including a carbonized skeleton and a phase change material adsorbed in the pore structure of the carbonized skeleton, or including a carbonized skeleton and a phase change material and a filler adsorbed in the pore structure of the carbonized skeleton.

[0020] The present invention also provides an application of the carbonized composite phase change material described in the above technical solution in thermal energy storage.

[0021] The present invention provides a preparation method of a carbonized composite phase change material, comprising the following steps: after softening the filamentous fibers, aggregating them into bundles and performing hot pressing, self-assembly occurs during the hot pressing process to obtain a filamentous fiber block; carbonizing the filamentous fiber block in a protective gas to obtain a carbonized skeleton; performing vacuum impregnation on the carbonized skeleton in an impregnating solution to obtain a carbonized composite phase change material; the impregnating solution includes a phase change material or includes a phase change material and a filler. In the present invention, the softened filamentous fibers are longitudinally arranged and aggregated into bundles, and the filamentous fibers are arranged in parallel and then hot pressed. During the hot pressing process, uneven chemical adhesive bonding and mechanical interlocking occur between the lignin, cellulose, and hemicellulose between the filamentous fibers for self-assembly, forming a multi-scale pore structure, strengthening the phonon transmission ability in the axial direction (along the direction of the filamentous fibers) of the carbonized skeleton obtained by carbonization, weakening the connection in the radial direction (perpendicular to the direction of the filamentous fibers), weakening phonon heat transfer. The high anisotropy obtained by hot pressing the parallel arrangement of the filamentous fibers leads to this difference in axial and radial thermal conductivity, reducing heat loss during the heat transfer process, improving the heat transfer efficiency, and enhancing the thermal conductivity. The carbonized composite phase change material prepared by the present invention has a multi-scale pore structure, and the proportion of macropores (pore diameter above 50 nm) is large, the porosity is high, and the connectivity is strong, improving the distribution uniformity and loading rate of the phase change material in the carbonized skeleton, thereby improving the heat storage density of the carbonized composite phase change material and enhancing the heat storage performance. Description of the Drawings

[0022] Figure 1 Schematic flow chart for preparing the carbonized bamboo-based composite phase change material in the example;

[0023] Figures 2 to 4 Respectively, size distribution diagrams of macropores, mesopores, and micropores in the carbonized bamboo-based skeleton prepared in Example 1;

[0024] Figure 5 Schematic heat transfer diagram of the carbonized bamboo-based composite phase change material prepared in Example 1;

[0025] Figure 6 Paraffin loading diagrams of different biomass materials;

[0026] Figure 7 Thermal conductivity diagrams of different composite phase change materials. Detailed Description of the Invention

[0027] The present invention provides a preparation method of a carbonized composite phase change material, comprising the following steps:

[0028] After softening the filamentous fibers, they are assembled into bundles and hot-pressed. Self-assembly occurs during the hot-pressing process to obtain a filamentous fiber block.

[0029] The filamentous fiber block is carbonized in a protective gas to obtain a carbonized framework.

[0030] The carbonized framework is subjected to vacuum impregnation in an impregnating solution to obtain a carbonized composite phase change material.

[0031] The impregnating solution contains a phase change material or contains a phase change material and a filler.

[0032] Unless otherwise specified, the present invention has no special requirements for the sources of the raw materials used, and commercially available products well-known to those skilled in the art can be used.

[0033] In the present invention, after softening the filamentous fibers, they are assembled into bundles and hot-pressed. Self-assembly occurs during the hot-pressing process to obtain a filamentous fiber block.

[0034] As an embodiment, the filamentous fibers include one or more of bamboo fibers, sugarcane fibers, and ramie fibers, and are bamboo fibers in specific embodiments.

[0035] As an embodiment, the preparation method of the filamentous fibers is to draw the biomass raw material containing filamentous fibers; the biomass raw material containing filamentous fibers includes one or more of bamboo, sugarcane, and ramie, and is bamboo in specific embodiments.

[0036] As an embodiment, before the drawing, it further includes: pre-treating the biomass raw material containing filamentous fibers; the pre-treatment is to remove the outer skin of the biomass raw material containing filamentous fibers and divide it into two parts longitudinally. When the biomass raw material containing filamentous fibers is bamboo, the internode septum of the divided bamboo also needs to be removed.

[0037] As an embodiment, the drawing is to heat the biomass raw material containing filamentous fibers and beat it into filamentous fibers; the heating is to 70 - 300 °C, and is 100 - 200 °C in specific embodiments; before the heating, it further includes: cutting the pre-treated biomass raw material containing filamentous fibers into slices to facilitate subsequent beating and drawing; the thickness of the slices is 0.1 - 100 mm, and is 0.1 - 10 mm in specific embodiments.

[0038] As an embodiment, the softening temperature is 70 - 100 °C, and is 80 - 100 °C in specific embodiments, and the heat preservation time is 3 - 30 min, and is 5 - 10 min in specific embodiments; the softening is carried out under ultrasonic conditions; the power of the ultrasonic wave is 200 - 2000 W, and is 500 - 1000 W in specific embodiments; the equipment used for the ultrasonic wave is an ultrasonic cleaner. In the present invention, the filamentous fibers are softened while being cleaned under ultrasonic conditions.

[0039] As an implementation manner, the pressure of the hot pressing is 3 to 15 MPa, and in specific embodiments, it is 3 to 10 MPa; the temperature is 70 to 300 °C, and in specific embodiments, it is 100 to 200 °C; the heat preservation and pressure maintaining time is 1 to 15 min, and in specific embodiments, it is 1 to 10 min.

[0040] In the present invention, the filamentous fibers are stacked and arranged longitudinally in parallel to form a bundle and then hot pressed. The present invention has no special limitation on the size of the filamentous fiber block obtained by the hot pressing, which depends on the required application scenario.

[0041] The present invention sets the pressure, temperature and time of the hot pressing within the above ranges, which is conducive to the mutual adhesion between lignin and cellulose and hemicellulose in the filamentous fibers of biomass to form a multi-scale pore structure.

[0042] After obtaining the filamentous fiber block, the present invention carbonizes the filamentous fiber block in a protective gas to obtain a carbonized skeleton.

[0043] As an implementation manner, the protective gas is nitrogen or an inert gas, and in specific embodiments, it is nitrogen; the inert gas is helium or argon; the temperature of the carbonization is 600 to 1200 °C, and in specific embodiments, it is 800 to 1000 °C; the heat preservation time is 2 to 10 h, and in specific embodiments, it is 3 to 6 h; the heating rate for heating to the temperature of the carbonization is 5 to 15 °C / min, and in specific embodiments, it is 5 to 10 °C / min. The present invention sets the carbonization temperature and time within the above ranges, which can increase the proportion of pores with a pore diameter of more than 50 nm (macropores) in the carbonized skeleton, make the pore diameter of the macropores larger, and thus increase the loading amount of the phase change material on the carbonized skeleton.

[0044] After obtaining the carbonized skeleton, the present invention performs vacuum impregnation on the carbonized skeleton in an impregnating solution to obtain a carbonized composite phase change material.

[0045] As an implementation mode, the impregnating solution includes a phase change material or includes a phase change material and a filler; the phase change material includes an organic phase change material and / or an inorganic phase change material, specifically paraffin wax in a specific embodiment; the organic phase change material includes one or more of paraffin wax, polyhydric alcohol and fatty acid, specifically paraffin wax in a specific embodiment; the polyhydric alcohol includes polyethylene glycol; the inorganic phase change material includes dodecahydrate sulfate and / or nitrate, specifically dodecahydrate sulfate in a specific embodiment; the dodecahydrate sulfate includes one or more of potassium alum dodecahydrate (KAl(SO4)2·12H2O), potassium chromic sulfate dodecahydrate (KCr(SO4)2·12H2O) and ammonium iron(II) sulfate dodecahydrate (NH4Fe(SO4)2·12H2O), specifically potassium alum dodecahydrate in a specific embodiment; the nitrate includes one or more of sodium nitrate (NaNO3), potassium nitrate (KNO3) and magnesium nitrate (Mg(NO3)2), specifically sodium nitrate in a specific embodiment; the preparation method of the impregnating solution is: heating the phase change material to melt and then adding the filler; the heating is carried out under the condition of magnetic stirring. The present invention has no special limitation on the heating temperature, time and the rate of magnetic stirring, as long as the phase change material can be melted.

[0046] As an implementation mode, the filler includes one or more of carbon materials, metal-organic framework materials (MOF), zeolitic imidazolate framework materials (ZIF) and covalent organic framework materials (COF), specifically carbon materials in a specific embodiment; the particle size of the carbon material is from nanometer to micrometer level, specifically 1 nm to 2 μm in a specific embodiment; the particle sizes of the metal-organic framework, zeolitic imidazolate framework material and covalent organic framework material are at the nanometer level, specifically 10 to 500 nm in a specific embodiment; the carbon material includes one or more of graphene, graphite and carbon nanotubes, specifically graphene in a specific embodiment; the mass of the filler accounts for 1 to 10% of the mass of the phase change material, specifically 1 to 5% in a specific embodiment. The function of the filler in the present invention is to enhance heat transfer.

[0047] As an implementation mode, the vacuum impregnation is carried out in a vacuum drying oven; the time of the vacuum impregnation is 3 to 10 h, specifically 5 to 8 h in a specific embodiment. The present invention has no special limitation on the temperature and vacuum degree of the vacuum impregnation, as long as the phase change material is in a molten state.

[0048] Figure 1 It is a schematic flow chart for preparing the carbonized bamboo-based composite phase change material in the embodiment. As Figure 1As shown in the figure, the steps of the present invention include cutting, wire drawing, self-assembly, carbonization, and vacuum impregnation. Specifically: First, the original bamboo is removed the diaphragm and then cut into bamboo slices. After the bamboo slices are beaten into bamboo filaments, they are softened. After the bamboo filaments are assembled into bundles, they are hot-pressed, carbonized at high temperature in a nitrogen atmosphere, and finally the phase change material is vacuum-adsorbed to obtain the carbonized bamboo-based composite phase change material. The carbonized composite phase change material prepared by the above steps of the present invention has high porosity, high anisotropy degree, and excellent thermal conductivity, effectively solving the problems of low anisotropy degree, poor thermal conductivity, the need to rely on chemical reagents for pore opening, and uneven impregnation of the phase change material existing in the traditional biomass-based composite phase change material skeleton, significantly improving the efficient heat transport and storage capacity of the composite phase change material in the processes of photothermal, electrothermal, etc., and at the same time greatly reducing the heat loss.

[0049] The preparation method provided by the present invention not only has the characteristics of simple and easy process flow and high mechanization degree, but also does not need to use chemical reagents, avoiding the environmental pollution problem, and showing good large-scale industrial production potential. The present invention provides a new technical route for the preparation and application of biomass-based composite phase change materials, having important academic research value and broad application prospects.

[0050] The present invention also provides a carbonized composite phase change material prepared by the preparation method described in the above technical solution, including a carbonized skeleton and an impregnating solution adsorbed in the pore structure of the carbonized skeleton;

[0051] The impregnating solution includes a molten solution of the phase change material, or a molten solution of the phase change material and a filler.

[0052] As an implementation manner, the carbonized composite phase change material has a multi-scale pore structure, including macropores with a pore diameter of more than 50 nm, micropores with a pore diameter of 20-50 nm, and mesopores with a pore diameter of ≤1 nm. The pore diameter of the macropores is concentrated in 100-1000 μm. Among them, the proportion of macropore pores is 60-80%, the proportion of micropore pores is <10%, and the proportion of mesopore pores is 10-30%.

[0053] The present invention also provides an application of the carbonized composite phase change material described in the above technical solution in heat energy storage.

[0054] The present invention has no special limitation on the application of the carbonized composite phase change material in heat energy storage, and the well-known heat energy storage applications in the art can be adopted.

[0055] Next, the technical solutions in the present invention will be clearly and completely described in combination with the embodiments in the present invention, but they cannot be understood as a limitation on the protection scope of the present invention.

[0056] Example 1

[0057] Step 1: After removing the outer skin of fresh bamboo, divide the bamboo into two equal parts longitudinally. Subsequently, remove the inner septum in the internodes of the bamboo to achieve uniformity. Then, heat the bamboo in a steaming box to 110 °C;

[0058] Step 2: After pounding the bamboo containing the residual heat of the steaming box into bamboo fibers, put the prepared bamboo fibers into an ultrasonic cleaner with hot water at 100 °C and clean and soften them at 500 W for 10 min. Finally, hot-press the longitudinally arranged and bundled bamboo fibers at a pressure of 3 MPa and a temperature of 180 °C for 3 min to obtain bamboo fiber blocks;

[0059] Step 3: Place the above-mentioned bamboo fiber blocks in a nitrogen environment, heat them to 1000 °C at a heating rate of 5 °C / min, and carry out carbonization for 6 h. Then, naturally cool them to room temperature to obtain a carbonized bamboo-based framework;

[0060] Step 4: Weigh the paraffin wax block and press it into small pieces for rapid heating and melting. Then, put the small pieces of paraffin wax into a beaker, place the beaker on a magnetic stirring heater, stir and heat it to melting. Finally, put the above-mentioned carbonized bamboo-based framework into the beaker, and put the beaker into a vacuum drying oven, and carry out vacuum impregnation for 6 h in the molten state of paraffin wax to obtain a carbonized bamboo-based composite phase change material.

[0061] Example 2

[0062] The difference from Example 1 is that before heating the bamboo, the bamboo is cut into slices with a thickness of 1 mm for subsequent pounding and filament extraction. The rest is the same as Example 1.

[0063] Example 3

[0064] The difference from Example 1 is that the pressure of the hot pressing is 5 MPa, the temperature is 120 °C, and the heat preservation and pressure holding time is 1 min. The rest is the same as Example 1.

[0065] Example 4

[0066] The difference from Example 1 is that the paraffin wax in Example 1 is replaced by polyethylene glycol. The rest is the same as Example 1.

[0067] Example 5

[0068] The difference from Example 1 is that graphene (particle size of 1.2 μm) is added to the paraffin wax in Example 1, and the mass of graphene is 1% of the mass of the paraffin wax. The rest is the same as Example 1.

[0069] Comparative Examples 1-11

[0070] Use the composite phase change materials prepared by the following existing technologies as comparative examples.

[0071] The indexing information of the prior art is as follows:

[0072] [1]Chin O C,Yang X,Paul C S,et al.Development ofthermal energystorage lightweight concrete using paraffin-oil palm kernel shell-activatedcarbon composite[J]Journal ofCleanerProduction,2020,261121227-121227.

[0073] [2]Yin Q,Zhu G,Wang R,et al.Enhancement ofthe thermal propertiesofthe phase change composite ofacid-base modified biochar / paraffin wax[J].Solar Energy Materials and Solar Cells,2024,269112802-.

[0074] [3]XianfengY,Rong Z,Xiaobei J,et al.Bamboo-derivedphase changematerial with hierarchical structure for thermal energy storage of building[J].Journal of Energy Storage,2023,62.

[0075] [4]Das D,Bordoloi U,Muigai H H,et al.A novel form stable PCM basedbio composite material for solar thermal energy storage applications[J].Journal of Energy Storage,2020,30.

[0076] [5]Yue L,Feng Z,Chongchong L,et al.Biomass-based shape-stable phasechange materials supported by garlic peel-derived porous carbon for thermalenergy storage[J].Journal ofEnergy Storage,2022,46.

[0077] [6]Kunyang Y,Yushi L,Minjie J,et al.Bio-Based Dual-FunctionalizedPhase Change Composite:Ultrafast Solar-to-Thermal Conversion and ReinforcedHeat Storage Capacity[J].Energy&Fuels,2021,35(19):16162-16173.

[0078] [7]Sheng N,Nomura T,Zhu C,et al.Cotton-derived carbon sponge assupport for formstabilized composite phase change materials with enhancedthermal conductivity[J].Solar Energy Materials and Solar Cells,2019,192:8-15.

[0079] [8]Zhang W,Zhang X,Zhang X,et al.Lauric-stearic acid eutecticmixture / carbonized biomass waste corn cob composite phase change materials:Preparation and thermal characterization[J].ThermochimicaActa,2019,674:21-27.

[0080] [9] Hu X, Huang H, Hu Y, et al. Novel bio-based composite phase change materials with reduced graphene oxide-functionalized spent coffee grounds for efficient solar-tothermal energy storage[J]. Solar Energy Materials and Solar Cells, 2021, 219: 110790.

[0081]

[10] Li X, Zhu Z, Yang P, et al. Carbonized wood loaded with carbon dots for preparation long-term shape-stabilized composite phase change materials with superior thermal energy conversion capacity[J]. Renewable Energy, 2021, 174: 19 - 30.

[0082]

[11] Feng N, Kang Z, Hu D. Shape-stabilized and antibacterial composite phase change materials based on wood-based cellulose micro-framework, erythritol-urea or erythritolthiourea for thermal energy storage[J]. Solar Energy, 2021, 223: 19 - 32.

[0083] The biomass materials used in the above prior arts [1 - 6] are in sequence: palm shell [1] , coffee granules [2] , bamboo powder [3] , water hyacinth [4] , garlic skin [5] , rice husk [6] .

[0084] The phase change materials prepared in the above prior arts [7 - 11] are in sequence: cotton / paraffin [7] , corn / lauric acid / stearic acid [8] , coffee powder / PEG[9] , Wood flour / PEG

[10] , Paulownia wood chips / erythritol-urea (7:3)

[11] , Paulownia wood chips / erythritol-urea (7:3)

[11] .

[0085] The prior art includes the biological template method and the foaming technology, and these methods involve the following steps: peeling, slicing, freeze-drying, impregnation; activation, soaking, pyrolysis, melting, grinding, activation, impregnation, cleaning with water / acid / alkali solution, drying, mixing phase change materials (PCM), tabletting, etc.

[0086] It can be found that the main process flow of the present invention is controlled within 5 steps, while the process flow of the prior art is between 6 and 10 steps. In addition, the prior art uses chemical reagents to develop the substrate material, which increases the risk and complexity of the preparation process. Therefore, the increase in cost is mainly reflected in the cost of chemical reagents, which is $2.90 - $5.24 higher than the cost of each kilogram of substrate material developed by the present invention. The price of bamboo raw materials is about $70 per ton, but the price of carbon nanomaterials such as boron nitride and expanded graphite is $50 - $150 per kilogram. Compared with the biomass-based composite phase change material, the cost of preparing the pure carbon fiber composite phase change material is much higher. The cost of preparing the biomass-based composite phase change material using carbon nanomaterials will also increase with the increase of the additional addition amount.

[0087] Comparative Example 12

[0088] The difference from Example 2 is that the bamboo slices are directly softened and hot-pressed without going through the step of being beaten into bamboo fibers, and the rest is the same as in Example 2.

[0089] Performance test

[0090] (1) Figures 2 to 4 They are the pore size distribution diagrams of macropores, mesopores, and micropores in the carbonized bamboo-based framework prepared in Example 1 respectively.

[0091] From Figure 2 it can be seen that the proportion of macropores with a pore diameter of more than 50 nm in the carbonized bamboo-based framework prepared by the present invention is 60 - 80%, and the macropore diameter mostly concentrates in 100 - 1000 μm.

[0092] From Figure 3 it can be seen that the mesopore diameter in the carbonized bamboo-based framework prepared by the present invention mostly distributes in 20 - 50 nm, and the proportion of mesopores is 10 - 30%.

[0093] From Figure 4 it can be seen that the micropore diameter in the carbonized bamboo-based framework prepared by the present invention mostly concentrates in ≤1 nm, and the proportion of micropores is <10%.

[0094] As can be seen from the above, the carbonized bamboo-based framework prepared by the present invention has a multi-scale pore structure, mainly because uneven chemical adhesive bonding and mechanical interlocking occur between lignin and cellulose and hemicellulose among bamboo fibers during the hot pressing process, thus realizing the characteristics of a multi-scale pore structure.

[0095] (2) Figure 5 It is a heat transfer schematic diagram of the carbonized bamboo-based composite phase change material prepared in Example 1, where (a) is radial heat transfer and (b) is axial heat transfer.

[0096] From Figure 5 it can be seen that in the carbonized bamboo-based composite phase change material prepared by the present invention, the direction along the bamboo fibers is axial / longitudinal, and the direction perpendicular to the bamboo fibers is transverse / radial. The carbonized bamboo-based composite phase change material prepared by the present invention has a high degree of anisotropy, mainly because axial heat transfer is along the direction parallel to the bamboo fibers, with continuous phonon transmission channels, which also results in relatively high axial thermal conductivity (0.763 W·m -1 ·K -1 ), while in the radial direction, bamboo fibers and phase change materials alternate, weakening phonon transmission (0.325 W·m -1 ·K -1 ), thus forming a high degree of anisotropy. The degree of anisotropy of the carbonized bamboo-based framework prepared by the present invention can reach 2.35.

[0097] (3) Figure 6 It is a graph of the paraffin loading of different biomass materials. From Figure 6 it can be seen that the paraffin loading of the carbonized bamboo-based framework prepared in Example 1 of the present invention is significantly higher than that of the biomass materials used in the prior art [1-6].

[0098] (4) Figure 7 It is a graph of the thermal conductivity of different composite phase change materials. From Figure 7 it can be seen that the thermal conductivity of the carbonized bamboo-based composite phase change material prepared in Example 1 of the present invention is significantly higher than that of the composite phase change materials prepared by the prior art [7-11].

[0099] Although the above embodiments have described the present invention in detail, they are only a part of the embodiments of the present invention rather than all embodiments. People can also obtain other embodiments without creative efforts based on these embodiments, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A preparation method of a carbonized composite phase change material, characterized in that, It includes the following steps: After softening the filamentous fibers, they are assembled into bundles and hot-pressed. Self-assembly occurs during the hot-pressing process to obtain a filamentous fiber block; The filamentous fiber block is carbonized in a protective gas to obtain a carbonized framework; The carbonized framework is subjected to vacuum impregnation in an impregnating solution to obtain a carbonized composite phase change material; The impregnating solution contains a phase change material or contains a phase change material and a filler.

2. The preparation method according to claim 1, characterized in that, The filamentous fibers include one or more of bamboo fibers, sugarcane fibers, and ramie fibers.

3. The preparation method according to claim 1, characterized in that, The pressure of the hot-pressing is 3 to 15 MPa, the temperature is 70 to 300 °C, and the heat preservation and pressure holding time is 1 to 15 min.

4. The preparation method according to claim 1, characterized in that, The temperature of the carbonization is 600 to 1200 °C, and the heat preservation time is 2 to 10 h.

5. The preparation method according to claim 1, characterized in that, The phase change material includes an organic phase change material and / or an inorganic phase change material; the organic phase change material includes one or more of paraffin, polyols, and fatty acids; the inorganic phase change material includes dodecahydrate sulfate and / or nitrate.

6. The preparation method according to claim 1, characterized in that, The filler includes one or more of carbon materials, metal-organic framework materials, zeolitic imidazolate framework materials, and covalent organic framework materials.

7. The preparation method according to claim 1, characterized in that, The temperature of the softening is 70 to 100 °C, and the heat preservation time is 3 to 30 min; the softening is carried out under ultrasonic conditions; the power of the ultrasonic is 200 to 2000 W.

8. The preparation method according to claim 1, characterized in that, The preparation method of the filamentous fibers is to draw the biomass raw material containing the filamentous fibers; the drawing is to heat the biomass raw material containing the filamentous fibers and then beat it into filamentous fibers; the heating is to 70 to 300 °C.

9. The carbonized composite phase change material prepared by the preparation method according to any one of claims 1 to 8, characterized in that, It includes a carbonized framework and a phase change material adsorbed in the pore structure of the carbonized framework, or includes a carbonized framework and a phase change material and a filler adsorbed in the pore structure of the carbonized framework.

10. Application of the carbonized composite phase change material according to claim 9 in thermal energy storage.

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