Composite phase change material, and preparation method and application thereof

Abstract

The application belongs to the technical field of energy storage, and relates to a composite phase change material and a preparation method and application thereof.The composite phase change material comprises a paraffin base body and a heat-conducting phase change material dispersed in the paraffin base body; the heat-conducting phase change material comprises at least one of biomass-based graphene, copper nanowire foam and Fe3O4 modified biomass-based graphene. Bamboo powder is converted into few-layer graphene through sandwich microwave plasma technology, then is modified by Fe3O4 nanoparticles, is compounded with paraffin, and finally is packaged with copper nanowire foam to construct a synergistic structure of 'two-dimensional heat-conducting network-three-dimensional metal skeleton-nano light absorber'. The prepared composite phase change material has a photo-thermal conversion efficiency of 73.47%, a heat conductivity of 3.157 W·m ‑1 ·K ‑1 , a phase change enthalpy retention rate of >98% and no leakage. The composite phase change material is suitable for solar heat storage, intelligent building and electronic device heat management, and is produced in a green and low-cost manner through biomass waste resource utilization.

Description

Technical Field

[0001] This invention belongs to the field of energy storage technology, specifically relating to a composite phase change material, its preparation method, and its application. Background Technology

[0002] Paraffin (PW), as a typical organic solid-liquid phase change material, has become a research hotspot in the field of thermal energy storage due to its high latent heat of phase change (180-230 J / g, about 5 times that of water), suitable phase change temperature (25-80 ℃, highly compatible with solar thermal utilization, building heating and other scenarios), and excellent chemical stability (phase change enthalpy decay rate <5% after 500 thermal cycles and no supercooling phenomenon). However, paraffin faces three technical bottlenecks in practical applications: (1) The intrinsic thermal conductivity of paraffin is only 0.2-0.4 W·m -1 ·K -1 (1) This leads to slow heat transfer during the charging process, and a significant temperature gradient during heat release, increasing the risk of local overheating; (2) Pure paraffin has an absorbance of <0.1 in the ultraviolet-visible-near-infrared band (200-2500 nm), and cannot directly absorb solar energy; (3) The phase change volume change rate of paraffin is 15-30%, and liquid leakage leads to a decrease in heat storage capacity (the phase change enthalpy decreases by 12% after 50 cycles) and equipment corrosion.

[0003] Existing technologies often improve thermal conductivity by adding carbon-based additives, metal-based additives, traditional photothermal materials, microencapsulation, and metal foam encapsulation. However, carbon-based additives such as carbon nanotubes (CNTs) suffer from severe agglomeration due to their high specific surface area; adding 1 wt% CNTs only increases the thermal conductivity of paraffin by 30.3%, and graphene oxide (GO) offers limited improvement in thermal conductivity due to its oxygen-containing groups (1 wt% GO only achieves 0.32 W·m). -1 ·K -1 Metal-based additives such as copper nanoparticles (Cu NPs) exhibit significant phonon scattering at the paraffin interface; adding 10 wt% only increases thermal conductivity by 46.3% and readily catalyzes paraffin oxidation. Traditional photothermal materials such as carbon black have an absorbance <0.5 in the near-infrared band; adding 10 wt% results in a photothermal conversion efficiency of only 60.1%. Fe3O4 nanoparticles, due to their poor thermal conductivity (5.9 W·m), further hinder this process. -1 ·K -1 This leads to localized overheating; the thermal conductivity of the polymer shell of the microcapsule in the encapsulation technology is only 0.15 W·m. -1 ·K -1 The thermal conductivity of the 50% filling rate system only increased by 12%, and the leakage rate of expanded graphite (EG) encapsulation reached 3.2% at 70 °C. Furthermore, the system has problems such as complex preparation process and poor interfacial compatibility. Summary of the Invention

[0004] The purpose of this invention is to provide a composite phase change material, its preparation method, and its application, which solves the problems of low thermal conductivity, low photothermal conversion efficiency, and phase change leakage of paraffin. It develops a paraffin-based composite phase change material that combines high-efficiency photothermal-thermal conductivity, low-cost preparation, and reliable encapsulation, becoming a key to breaking through the large-scale utilization of solar energy.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows:

[0006] In a first aspect, the present invention provides a composite phase change material, comprising a paraffin matrix and a thermally conductive phase change material dispersed within the paraffin matrix; the thermally conductive phase change material is selected from at least one of biomass-based graphene, copper nanowire foam, and Fe3O4-modified biomass-based graphene.

[0007] This invention uses paraffin (PW) as the matrix phase change material, making full use of its advantages such as high latent heat of phase change, chemical stability, low cost, environmental friendliness and adjustable phase change temperature. The addition of thermally conductive phase change materials such as biomass-based graphene (BMPG), copper nanowire foam (CNF) and Fe3O4 modified biomass-based graphene (BMPG-Fe3O4) to the paraffin matrix can significantly improve the thermal conductivity and photothermal conversion efficiency. This is because biomass-based graphene (BMPG) has a two-dimensional network structure composed of few stacked single-atom carbon layers, low defects, and high graphitization properties; copper nanowire foam (CNF) has a three-dimensional copper nanowire framework structure with capillary adsorption in its pores; in Fe3O4-modified biomass-based graphene (BMPG-Fe3O4), the "nano-thermal bridge" formed by Fe3O4, biomass-based graphene, and copper nanowire foam optimizes the phonon transport path, solving the three major contradictions of low-cost graphene preparation and high crystallinity, improved photothermal conversion efficiency and retention of latent heat of phase change, and enhanced thermal conductivity and reliable encapsulation. This has led to the development of a paraffin-based composite phase change material that combines high-efficiency photothermal-thermal conductivity, low-cost preparation, and reliable encapsulation.

[0008] In some other embodiments, the composite phase change material is selected from one of the following: paraffin / biomass-based graphene composite phase change material, paraffin / copper nanowire foam composite phase change material, paraffin / biomass-based graphene / copper nanowire foam composite phase change material, and paraffin / Fe3O4 modified biomass-based graphene / copper nanowire foam composite phase change material.

[0009] The thermal conductivity of the paraffin / biomass-based graphene composite phase change material is at least 2.25 times higher than that of pure paraffin, and the photothermal conversion efficiency can reach up to 61.97%. The thermal conductivity of the paraffin / biomass-based graphene / copper nanowire foam composite phase change material is at least 11 times higher than that of pure paraffin, reaching 2.772 W·m. -1 ·K -1Furthermore, it maintains good thermal and morphological stability after 50 heating and cooling cycles. The photothermal conversion efficiency of the paraffin / Fe3O4 modified biomass-based graphene / copper nanowire foam composite phase change material can reach up to 73.47%, and the thermal conductivity can reach up to 3.157 W·m. -1 ·K -1 It is 12.6 times stronger than pure paraffin. The paraffin / Fe3O4 modified biomass-based graphene / copper nanowire foam composite exhibits optimal performance due to its synergistic thermal conduction mechanism of "two-dimensional network + three-dimensional framework + nano-thermal bridge" constructed through phase transition. In practical applications, one or more of these composite materials can be selected for use in combination to meet specific application requirements.

[0010] In some other embodiments, the content of biomass-based graphene in the paraffin / biomass-based graphene composite phase change material is 0.1 wt%-0.5 wt%; for example, the content of biomass-based graphene is 0.1 wt%, 0.3 wt%, and 0.5 wt%. Biomass-based graphene exhibits optimal dispersion performance, thermal conductivity, and photothermal conversion efficiency in paraffin within this range.

[0011] Alternatively, in paraffin / copper nanowire foam composite phase change materials, the content of copper nanowire foam is 30 wt%-35 wt%; within this range, the copper nanowire foam exhibits the best dispersion performance, thermal conductivity, and photothermal conversion efficiency in paraffin.

[0012] Alternatively, in the paraffin / biomass-based graphene / copper nanowire foam composite phase change material, the content of biomass-based graphene is 0.1 wt%-0.5 wt%, and the content of copper nanowire foam is 30 wt%-35 wt%. Optionally, the content of copper nanowire foam is 30 wt%, 32 wt%, 34 wt%, and 35 wt%. Within this range, the biomass-based graphene / copper nanowire foam exhibits the best dispersion performance, thermal conductivity, and photothermal conversion efficiency in paraffin.

[0013] Alternatively, in the paraffin / Fe3O4-modified biomass-based graphene / copper nanowire foam composite phase change material, the content of Fe3O4-modified biomass-based graphene is 0.1 wt%-0.5 wt%, and the content of copper nanowire foam is 30 wt%-35 wt%; optionally, the content of copper nanowire foam is 30 wt%, 32 wt%, 34 wt%, and 35 wt%. Within this range, the Fe3O4-modified biomass-based graphene / copper nanowire foam exhibits the best dispersion performance, thermal conductivity, and photothermal conversion efficiency in paraffin.

[0014] In Fe3O4-modified biomass-based graphene, the mass ratio of biomass-based graphene to Fe3O4 is 1: (1-3). In Fe3O4-modified biomass-based graphene, the surface plasmon resonance effect of Fe3O4 grown in situ on biomass-based graphene enhances light capture and reverses the efficiency decrease caused by the introduction of CNF.

[0015] In some other embodiments, the biomass-based graphene is a two-dimensional network composed of 2-8 stacked single-atom carbon layers, Raman spectroscopy I 2D / I G The value is 0.70-0.82, I D / I G <0.58; This structure has few layers, low defects and high graphitization characteristics. The highly crystalline biomass-based graphene has an absorption rate of 92.7% in the 800-2500 nm light band, realizing efficient photothermal conversion.

[0016] Alternatively, copper nanowire foam has a three-dimensional copper nanowire framework structure with a particle size of 50-100 nm. This structure of CNF can enhance the composite interface with PW / BMPG. At the same time, due to the capillary adsorption effect of CNF pores, the composite phase change material is leak-free and has improved thermal conductivity.

[0017] Alternatively, Fe3O4-modified biomass-based graphene, with Fe3O4 nanoparticles (uniform and well-crystallized) loaded on the surface of biomass-based graphene. The composite structure formed by Fe3O4 nanoparticles and graphene synergistically enhances the light energy capture and conversion efficiency of the composite phase change material by increasing light absorption capacity (broad-spectrum light capture) and thermal conductivity efficiency (reducing interfacial thermal resistance).

[0018] Secondly, this invention provides a method for preparing the composite phase change material described in the first aspect, comprising the following steps: heating and melting a paraffin matrix, then adding a thermally conductive phase change material, mixing uniformly, and then cooling and molding to obtain the composite phase change material; the thermally conductive phase change material includes at least one of biomass-based graphene, copper nanowire foam, and Fe3O4-modified biomass-based graphene. The preparation method of this invention is simple to operate, low in cost, and has good application prospects.

[0019] In some other embodiments, the paraffin matrix is ​​heated to melt at a temperature of 65-85 °C, and the mixing method is selected from ultrasonic dispersion and vacuum impregnation; for example, the paraffin matrix is ​​heated to melt at a temperature of 70 or 80 °C.

[0020] The composite phase change material contains 0.1 wt% to 0.5 wt% thermally conductive phase change material. Within this range, the thermally conductive phase change material exhibits good dispersion, significantly improving photothermal conversion efficiency and thermal conductivity while reducing production costs.

[0021] In some other embodiments, the preparation method of biomass-based graphene is as follows: carbonizing a nitrogen source under inert protection to obtain a carbonized nitrogen source; mixing the carbonized nitrogen source with biochar and then performing microwave plasma conversion treatment under inert protection to obtain biomass-based graphene.

[0022] Alternatively, the preparation method of the copper nanowire foam is as follows: Copper foam is sequentially cleaned with anhydrous ethanol, water, and hydrochloric acid, then rinsed with water, dried with nitrogen, and then baked to obtain clean copper foam; the clean copper foam is immersed in an alkaline solution to react and obtain modified copper foam; polytetrafluoroethylene, natural graphite, and anhydrous ethanol are mixed to prepare a suspension; the suspension is drop-coated onto the surface of the modified copper foam, and after drying, heat treatment under inert gas protection, and cooling, copper nanowire foam is obtained.

[0023] Alternatively, the preparation method of the Fe3O4-modified biomass-based graphene is as follows: after mixing biomass-based graphene with a solvent, adding soluble iron salt and mixing, then adding sodium acetate and stirring, and carrying out a hydrothermal reaction to obtain Fe3O4-modified biomass-based graphene.

[0024] In some other embodiments, in the method for preparing biomass-based graphene, the nitrogen source is selected from at least one of urea, dicyandiamide, melamine foam, and aniline; the carbonization temperature is 800-1000 ℃, and the carbonization time is 1-2 h; the mixing ratio of the carbonized nitrogen source to biochar is (2-3):1; the biochar is at least one of bamboo powder, straw powder, and fruit shell; the particle size of the biochar is 50-500 μm; the power of the microwave plasma conversion treatment is 700-900 W, the frequency is 2-3 GHz, and the time is 5-15 seconds.

[0025] Preferably, the nitrogen source is melamine foam; the carbonization treatment temperature is 900 ℃, and the carbonization treatment time is 1 h; the mixing ratio of the carbonized nitrogen source to biochar is 2.4:1; the biochar is bamboo powder; the microwave plasma conversion treatment power is 800 W, the frequency is 2.45 GHz, and the time is 10 seconds.

[0026] Alternatively, in the preparation method of copper nanowire foam, the concentration of hydrochloric acid is 15-25 wt%, the drying temperature is 75-85℃, the alkaline solution includes sodium hydroxide and ammonium persulfate, the concentration of sodium hydroxide is 2-3 M, the concentration of ammonium persulfate is 0.1-0.2 M, and the reaction time in the alkaline solution is 20-30 minutes; the mixing ratio of polytetrafluoroethylene, natural graphite and anhydrous ethanol is 1 mg:(450-550) mg:(250-350) mL; the drying temperature is 45-55 ℃, and the drying time is 3-5 h; the heat treatment atmosphere is nitrogen, the temperature is increased to 350-450 ℃ at 3-5 ℃ / min, and the temperature is held for 1.5-2.5 h;

[0027] Preferably, in the method for preparing the copper nanowire foam, the concentration of hydrochloric acid is 20 wt%, the drying temperature is 80℃, the concentration of sodium hydroxide in the alkaline solution is 2.5 M, the concentration of ammonium persulfate is 0.15 M, and the reaction time in the alkaline solution is 25 minutes; the mixing ratio of polytetrafluoroethylene, natural graphite, and anhydrous ethanol is 1 mg: 500 mg: 300 mL; the drying temperature is 50℃, and the drying time is 4 hours; the heat treatment atmosphere is nitrogen, with the temperature increased to 400℃ at 5℃ / min and held for 2 hours.

[0028] Alternatively, in the preparation method of Fe3O4 modified biomass-based graphene, after adding biomass-based graphene to a solvent, adding soluble iron salt and mixing, then adding sodium acetate, and carrying out a hydrothermal reaction, Fe3O4 modified biomass-based graphene is obtained.

[0029] The solvent is a mixed solvent composed of diethylene glycol and ethylene glycol, with a volume ratio of (30-40):10.

[0030] The ratio of biomass-based graphene to solvent is 10 mg : (40-50) mL;

[0031] The soluble iron salt is one of FeCl3, ferric nitrate, and ferric sulfate;

[0032] The mass ratio of biomass-based graphene to soluble iron salt is 1:(1-3); for example, the mass ratio of biomass-based graphene to soluble iron salt is 1:1, 1:2, or 1:3.

[0033] The mass ratio of biomass-based graphene to sodium acetate is 10: (75-85);

[0034] The hydrothermal reaction temperature is 180-220 ℃, and the hydrothermal reaction time is 10-15 h;

[0035] Preferably, the volume ratio of diethylene glycol to ethylene glycol in the solvent is 35:10;

[0036] The ratio of biomass-based graphene to solvent is 10 mg : 45 mL;

[0037] The soluble iron salt is FeCl3;

[0038] The mass ratio of biomass-based graphene to FeCl3 is 1:3;

[0039] The mass ratio of biomass-based graphene to sodium acetate is 10:80;

[0040] The hydrothermal reaction was carried out at a temperature of 200 °C for 12 h.

[0041] In some other embodiments, the composite phase change material is selected from one of the following: paraffin / biomass-based graphene composite phase change material, paraffin / copper nanowire foam composite phase change material, paraffin / biomass-based graphene / copper nanowire foam composite phase change material, and paraffin / Fe3O4 modified biomass-based graphene / copper nanowire foam composite phase change material.

[0042] The preparation method of the paraffin / biomass-based graphene composite phase change material is as follows:

[0043] The paraffin matrix is ​​heated and melted, then vacuum-dried biomass-based graphene is added, and the mixture is ultrasonically dispersed and heated and stirred. After cooling and molding, the paraffin / biomass-based graphene composite phase change material is obtained.

[0044] Preferably, the temperature at which the paraffin matrix is ​​heated and melted is 60-80 ℃, the temperature at which the ultrasonic dispersion is performed is 60-80 ℃, and the ultrasonic dispersion time is 0.5-1.5 h; the temperature at which the heating and stirring is performed is 90-110 ℃, and the heating and stirring time is 1-3 h.

[0045] The composite phase change material has a thermally conductive phase change material content of 0.1 wt%-0.5 wt%.

[0046] Alternatively, the preparation method of the paraffin / copper nanowire foam composite phase change material is as follows:

[0047] The paraffin matrix is ​​heated and melted, then copper nanowire foam is added, and the mixture is mixed by vacuum impregnation. After cooling and molding, the paraffin / copper nanowire foam composite phase change material is obtained.

[0048] In the paraffin / copper nanowire foam composite phase change material, the content of copper nanowire foam is 30 wt%-35 wt%.

[0049] Preferably, the vacuum impregnation method is performed at a temperature of 75-85 ℃ for 1-2 h.

[0050] Alternatively, the preparation method of the paraffin / biomass-based graphene / copper nanowire foam composite phase change material is as follows: heat and melt paraffin / biomass-based graphene, then add copper nanowire foam, mix by vacuum impregnation, and cool and shape to obtain the paraffin / biomass-based graphene / copper nanowire foam composite phase change material.

[0051] Alternatively, in the paraffin / biomass-based graphene / copper nanowire foam composite phase change material, the content of biomass-based graphene is 0.1 wt%-0.5 wt%, and the content of copper nanowire foam is 30 wt%-35 wt%.

[0052] Preferably, the vacuum impregnation method is performed at a temperature of 75-85 ℃ for 1-2 h.

[0053] Alternatively, the preparation method of the paraffin / Fe3O4 modified biomass-based graphene / copper nanowire foam composite phase change material is as follows:

[0054] Paraffin wax is heated and melted, and then Fe3O4-modified biomass-based graphene and copper nanowire foam are added. The mixture is then mixed using a vacuum impregnation method and cooled to form a composite phase change material of paraffin wax / Fe3O4-modified biomass-based graphene / copper nanowire foam.

[0055] In the paraffin / Fe3O4-modified biomass-based graphene / copper nanowire foam composite phase change material, the content of Fe3O4-modified biomass-based graphene is 0.1 wt%-0.5 wt%, and the content of copper nanowire foam is 30 wt%-35 wt%.

[0056] Preferably, the vacuum impregnation method is mixed at a temperature of 75-85 ℃ for 1-2 h.

[0057] Thirdly, the present invention provides the application of the composite phase change material described in the first aspect in solar water heater heat storage, intelligent temperature-controlled building walls, and thermal management of electronic devices.

[0058] The beneficial effects of this invention are:

[0059] (1) This invention uses paraffin (PW) as the matrix phase change material, making full use of its advantages such as high latent heat of phase change, chemical stability, low cost, environmental friendliness and adjustable phase change temperature. The thermally conductive phase change materials added to the paraffin matrix can significantly improve the thermal conductivity and photothermal conversion efficiency. This is because biomass-based graphene (BMPG) has a two-dimensional network structure formed by stacking a few single-atom carbon layers, low defects and high graphitization characteristics, and copper nanowire foam (CNF) has a three-dimensional copper nanowire skeleton structure with capillary adsorption effect in its pores. In Fe3O4 modified biomass-based graphene (BMPG-Fe3O4), Fe3O4 forms a "nano thermal bridge" with biomass-based graphene and copper nanowire foam, which optimizes the phonon transport path and solves the three major contradictions of low-cost graphene preparation and high crystallinity, photothermal conversion efficiency improvement and phase change latent heat retention, and thermal conductivity enhancement and packaging reliability. This invention develops a paraffin-based composite phase change material with high efficiency photothermal-thermal conductivity, low cost preparation and reliable packaging.

[0060] (2) The preparation method of the present invention is simple in operation and low in cost, and has good application prospects. Among them, the sandwich-type carbon foam-induced microwave plasma conversion technology is used, with bamboo powder as raw material and melamine foam (CMF) as induction medium. Microwave plasma treatment is carried out under a nitrogen atmosphere. The obtained BMPG has excellent crystallinity and conductivity, and its Raman spectrum I 2D / I D It can reach a maximum of 0.82;

[0061] A PW / BMPG composite phase change material was prepared by melt blending BMPG and paraffin wax, followed by ultrasonic dispersion, heating and stirring, and cooling to form the final product. The addition of BMPG significantly improved the thermal conductivity and photothermal conversion efficiency of paraffin wax; when the BMPG content was 0.5 wt%, the thermal conductivity of paraffin wax reached 0.841 W·m. -1 ·K -1 The photothermal conversion efficiency reached 61.97%.

[0062] Copper nanowire foam (CNF) was prepared by in-situ growth of copper nanoparticles on the surface of copper foam. Using CNF as an encapsulation medium, the CNF was introduced into a PW / BMPG system via vacuum impregnation. The addition of CNF effectively solved the leakage problem during the paraffin phase transition process and further improved the thermal conductivity of the composite material to 2.772 W·m. -1 ·K -1 However, this reduced the photothermal conversion efficiency by 19.57%.

[0063] Using BMPG as a carrier, Fe3O4 nanoparticles were grown in situ on its surface via a solvothermal method. Modified BMPG-Fe3O4 was then introduced into a paraffin and CNF system to prepare PW / BMPG-Fe3O4 / CNF. The introduction of Fe3O4 nanoparticles significantly improved the photothermal conversion efficiency of the composite phase change material, reaching a maximum of 73.47%, while maintaining good cyclic thermal stability.

[0064] In summary, this invention utilizes biomass waste to prepare BMPG, prepares copper nanowire foam (CNF) by in-situ growing copper nanoparticles on the surface of copper foam, and uses BMPG as a carrier to in-situ grow Fe3O4 nanoparticles on its surface via a solvothermal method. The modified BMPG-Fe3O4 is then introduced into the paraffin and CNF system to construct a synergistic structure of "two-dimensional thermally conductive network - three-dimensional metal framework - nano-light absorber". The resulting composite phase change material achieves a photothermal conversion efficiency of 73.47% (217% higher than pure paraffin) and a thermal conductivity of 3.157 W·m. -1 ·K -1 (12.6 times that of pure paraffin), with a phase change enthalpy retention rate >98% and no leakage. This achieves efficient resource utilization and green conversion. The prepared composite phase change material, while maintaining high heat storage capacity, significantly improves photothermal conversion efficiency and thermal conductivity, solves the leakage problem of paraffin phase change, and has a simple and low-cost preparation process, showing good application prospects. It can be widely used in fields such as solar photothermal conversion and storage, and human body thermal management. Attached Figure Description

[0065] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0066] Figure 1 This is a schematic diagram of the preparation process of biomass-based graphene (BMPG) in Example 1, where a is a schematic diagram of the sandwich-type carbon foam-induced microwave plasma conversion process, b is a quartz reactor, c is a schematic diagram of the induction period in the microwave plasma conversion process, and d is a schematic diagram of the plasma generation process.

[0067] Figure 2 These are TEM and HRTEM images of the BMPG obtained in Example 1;

[0068] Figure 3 The XRD pattern of the BMPG obtained in Example 1;

[0069] Figure 4 The Raman spectrum of the BMPG prepared in Example 1 and I 2D / I G and I D / IG The fluctuation range diagram shows that, where a is the Raman spectrum of BMPG obtained from ten parallel experiments, and b is the I spectrum corresponding to different numbers of experiments. 2D / I G and I D / I G The ratio;

[0070] Figure 5 The XRD pattern of PW / BMPG-Fe3O4 / CNF obtained in Example 9;

[0071] Figure 6 The TEM and mapping images of BMPG-Fe3O4 obtained in Example 8 are shown.

[0072] Figure 7 SEM images of CNF obtained in Example 4 and PW / BMPG / CNF obtained in Example 5, where a is the SEM image of CNF obtained in Example 4 and b is the SEM image of PW / BMPG / CNF obtained in Example 5.

[0073] Figure 8 This is a flexible display diagram of the PW / BMPG-Fe3O4 / CNF prepared in Example 9;

[0074] Figure 9 The graphs show the thermal energy release curves of the upper and lower surfaces of pure PW and PW / BMPG-Fe3O4 / CNF prepared in Example 9. Detailed Implementation

[0075] Those skilled in the art will understand that the following embodiments are for illustrative purposes only and should not be construed as limiting the scope of the invention. Specific conditions not specified in the embodiments are performed under conventional conditions or conditions recommended by the manufacturer. Components whose manufacturers are not specified are all commercially available conventional products.

[0076] Solar energy is a renewable energy source with abundant reserves (annual total radiation of 5.6 × 10⁻⁶). 24 J, which is more than 10,000 times the global annual energy consumption, has enormous potential in building heating, industrial heating, and other fields. However, it is characterized by intermittency (radiation intensity fluctuates more than 20 times between day and night) and low density (average 1 kW / m² on the Earth's surface). 2 This leads to a mismatch between the supply and demand of heat energy in time and space. Conventional sensible heat storage (energy density 0.2-0.5 MJ / m³) 3 The inability to meet continuous energy supply requirements, while phase change materials (PCMs) offer advantages due to their high energy storage density (100-300 MJ / m³). 3 ) becomes key.

[0077] Although paraffin-based phase change materials have been applied in fields such as solar thermal storage, they face three major technical bottlenecks: ① Low intrinsic thermal conductivity (0.2-0.4 W / m·K), resulting in a heating time of up to 4.5 h for solar heating systems (2.1 h longer than metal foam systems) and a large heat release temperature difference; ② Absorbance in the ultraviolet-near-infrared band <0.1, relying on an external black chrome coating (costing $200 / m²). 2 ① Energy loss > 30%); ② Leakage due to 15-30% phase change volume change (12% enthalpy drop after 50 cycles of phase change). Existing microcapsule / metal foam encapsulation has problems such as limited improvement in thermal conductivity or complex processes.

[0078] The specific solution adopted in this invention is as follows:

[0079] Embodiments of the present invention provide a composite phase change material, comprising a paraffin matrix and a thermally conductive phase change material dispersed within the paraffin matrix; the thermally conductive phase change material includes at least one of biomass-based graphene, copper nanowire foam, and Fe3O4-modified biomass-based graphene. Optionally, the composite phase change material is selected from one of the following: paraffin / biomass-based graphene composite phase change material, paraffin / copper nanowire foam composite phase change material, paraffin / biomass-based graphene / copper nanowire foam composite phase change material, and paraffin / Fe3O4-modified biomass-based graphene / copper nanowire foam composite phase change material.

[0080] Some other embodiments of the present invention provide a method for preparing composite phase change materials, wherein the method for preparing paraffin / biomass-based graphene composite phase change materials is as follows: a nitrogen source is carbonized under inert protection to obtain a carbonized nitrogen source; the carbonized nitrogen source is mixed with biomass char and then subjected to microwave plasma conversion treatment under inert protection to obtain biomass-based graphene; a paraffin matrix is ​​heated and melted, and then vacuum-dried biomass-based graphene is added, followed by ultrasonic dispersion and heating and stirring, and then cooled and shaped to obtain the paraffin / biomass-based graphene composite phase change material.

[0081] The preparation method of paraffin / copper nanowire foam composite phase change material is as follows: Copper foam is sequentially cleaned with anhydrous ethanol, water, and hydrochloric acid, then rinsed with water, dried with nitrogen, and finally baked to obtain clean copper foam; the clean copper foam is immersed in an alkaline solution to react and obtain modified copper foam; polytetrafluoroethylene, natural graphite, and anhydrous ethanol are mixed to prepare a suspension; the suspension is drop-coated onto the surface of the modified copper foam, and after drying, heat treatment under inert gas protection, and cooling, copper nanowire foam is obtained.

[0082] The paraffin matrix is ​​heated and melted, then copper nanowire foam is added, and the mixture is mixed using a vacuum impregnation method. After cooling and molding, the paraffin / copper nanowire foam composite phase change material is obtained.

[0083] The preparation method of paraffin / biomass-based graphene / copper nanowire foam composite phase change material is as follows: paraffin / biomass-based graphene is heated and melted, then copper nanowire foam is added, mixed by vacuum impregnation, and cooled and shaped to obtain paraffin / biomass-based graphene / copper nanowire foam composite phase change material.

[0084] The preparation method of paraffin / Fe3O4 modified biomass-based graphene / copper nanowire foam composite phase change material is as follows: After adding biomass-based graphene to a solvent, add soluble iron salt and mix, then add sodium acetate and carry out hydrothermal reaction to obtain Fe3O4 modified biomass-based graphene.

[0085] Paraffin wax is heated and melted, and then Fe3O4-modified biomass-based graphene and copper nanowire foam are added. The mixture is then mixed using a vacuum impregnation method and cooled to form a composite phase change material of paraffin wax / Fe3O4-modified biomass-based graphene / copper nanowire foam.

[0086] To address the challenges of low thermal conductivity, low photothermal conversion efficiency, and phase change leakage associated with paraffin wax, this invention utilizes biomass waste to prepare BMPG, constructing a "BMPG-Fe3O4-copper nanowire foam" composite system. While maintaining high heat storage capacity, this system achieves a synergistic improvement in photothermal conversion efficiency (73.47%) and thermal conductivity (3.157 W / m·K), while simultaneously resolving leakage issues through a three-dimensional metal framework. This green and low-cost process can be widely applied in fields such as solar thermal storage and human body thermal management.

[0087] The preparation method and characteristics of the composite phase change material of the present invention are further described below with reference to specific embodiments:

[0088] Example 1

[0089] A method for preparing a paraffin / biomass-based graphene composite phase change material (PW / BMPG) includes the following steps:

[0090] Preparation of biomass-based graphene (BMPG): Melamine foam (from Henan Zhongyuan Dahua Group Co., Ltd.) was placed in a tube furnace and carbonized at 900 °C for 1 hour under nitrogen protection to obtain carbonized melamine foam (CMF), which was then cut into pieces for later use. The carbonized melamine foam (CMF) and bamboo powder (100 mesh) were placed in a quartz reactor at a mass ratio of 2.4:1. Two pieces of CMF were placed parallel to each other with a 3 mm gap inside the quartz reactor. After purging with nitrogen and removing air, the reactor was treated with microwave plasma (800 W, 2.45 GHz) for 10 seconds. After the reaction, the mixture was washed with ethanol, dried with concentrated sulfuric acid, and the residual acid on the surface was removed with sodium hydroxide to obtain biomass-based graphene, labeled BMPG.

[0091] Take an appropriate amount of BMPG and vacuum dry it at 80 ℃ for 2 hours. Heat paraffin (PW) to 70 ℃ to melt it, and add a certain amount of petroleum ether to make a dispersion (the amount added is about 3 times the mass of paraffin). Add BMPG at a mass ratio of PW:BMPG of 999:1. After ultrasonic dispersion at 70 ℃ for 1 hour, heat and stir at 100 ℃ for 2 hours to volatilize the petroleum ether. After cooling and molding, the paraffin / biomass-based graphene composite phase change material is obtained. The obtained product is labeled as PW / BMPG (BMPG content 0.1wt%).

[0092] Example 2

[0093] A method for preparing a paraffin / biomass-based graphene composite phase change material (PW / BMPG) differs from Example 1 in that BMPG is added at a mass ratio of PW:BMPG of 997:3. The other preparation steps are the same as in Example 1, and the resulting product is labeled as PW / BMPG (BMPG content 0.3 wt%).

[0094] Example 3

[0095] A method for preparing a paraffin / biomass-based graphene composite phase change material (PW / BMPG) differs from Example 2 in that BMPG is added at a mass ratio of PW:BMPG of 995:5, while the other preparation steps are the same as in Example 1. The resulting product is labeled as PW / BMPG (BMPG content 0.5 wt%).

[0096] Example 4

[0097] A method for preparing a paraffin / copper nanowire foam composite phase change material (PW / CNF) includes the following steps:

[0098] First, cut the foamed copper (Suzhou Keshenghe Metal Material, specification: 130 ppi) into 20×20×2 mm pieces. 3 The cube was sequentially ultrasonically cleaned with anhydrous ethanol for 1 hour, rinsed with deionized water, ultrasonically cleaned with 20 wt% hydrochloric acid for 5 minutes, rinsed with deionized water again, dried with nitrogen and baked at 80 ℃. Then, it was immersed in an alkaline solution containing 2.5 M sodium hydroxide and 0.15 M ammonium persulfate for 25 minutes to prepare modified copper foam. Polytetrafluoroethylene and natural graphite were dissolved in anhydrous ethanol (300 mL) at a mass ratio of 1:500, stirred for 30 minutes, and then dripped onto the surface of the modified copper foam and dried at 50 ℃ for 4 hours. Subsequently, under nitrogen protection, the temperature was increased to 400 ℃ at 5 ℃ / min and held for 2 hours. After cooling, copper nanowire foam (CNF) was obtained.

[0099] The vacuum impregnation method was used to melt paraffin wax (PW) under vacuum at 80 °C, and CNF was immersed in the molten paraffin wax for 1 hour (the mass ratio of PW to CNF was 2:1). After cooling and molding, the resulting product was marked as PW / CNF.

[0100] Example 5

[0101] A method for preparing a paraffin / biomass-based graphene / copper nanowire foam composite phase change material (PW / BMPG / CNF) includes the following steps:

[0102] The PW / BMPG (BMPG content 0.1 wt%) prepared in Example 1 was vacuum melted at 80 °C and impregnated with CNF prepared in Example 4 for 1 hour (the mass ratio of PW / BMPG to CNF was 2:1). After cooling and molding, the paraffin / biomass-based graphene / copper nanowire foam composite phase change material was obtained. The obtained product was labeled as PW / BMPG / CNF.

[0103] Example 6

[0104] A method for preparing a paraffin / biomass-based graphene / copper nanowire foam composite phase change material (PW / BMPG / CNF) includes the following steps:

[0105] The PW / BMPG (BMPG content 0.3 wt%) prepared in Example 2 was vacuum melted at 80°C and impregnated with CNF prepared in Example 4 for 1 hour (the mass ratio of PW / BMPG to CNF was 2:1). After cooling and molding, the paraffin / biomass-based graphene / copper nanowire foam composite phase change material was obtained. The obtained product was labeled as PW / BMPG / CNF.

[0106] Example 7

[0107] A method for preparing a paraffin / biomass-based graphene / copper nanowire foam composite phase change material (PW / BMPG / CNF) includes the following steps:

[0108] The PW / BMPG (BMPG content 0.5 wt%) prepared in Example 3 was vacuum melted at 80°C and impregnated with CNF prepared in Example 4 for 1 hour (the mass ratio of PW / BMPG to CNF was 2:1). After cooling and molding, the paraffin / biomass-based graphene / copper nanowire foam composite phase change material was obtained. The obtained product was labeled as PW / BMPG / CNF.

[0109] Example 8

[0110] A method for preparing a paraffin / Fe3O4 modified biomass-based graphene / copper nanowire foam composite phase change material (PW / BMPG-Fe3O4 / CNF) includes the following steps:

[0111] Preparation of BMPG-Fe3O4: 10 mg of BMPG obtained in Example 1 was added to a mixed solvent (a mixed solvent consisting of 35 mL of diethylene glycol and 10 mL of ethylene glycol) and ultrasonically dispersed. Anhydrous FeCl3 was added and ultrasonication continued (the mass ratio of BMPG to anhydrous FeCl3 was 1:1). The mixture was then transferred to an oil bath and heated (heating temperature 120 °C). 80 mg of sodium acetate was added and stirred for 1 h. The mixture was then transferred to an autoclave and reacted at 200 °C for 12 h to obtain BMPG-Fe3O4.

[0112] BMPG-Fe3O4 was introduced into the PW / CNF system prepared in Example 4, wherein the mass ratio of PW / CNF to BMPG-Fe3O4 was 997:3. After cooling and molding, the paraffin / Fe3O4 modified biomass-based graphene / copper nanowire foam composite phase change material was obtained, and the resulting product was labeled as PW / BMPG-Fe3O4 / CNF-1.

[0113] Example 9

[0114] A method for preparing a paraffin / Fe3O4 modified biomass-based graphene / copper nanowire foam composite phase change material (PW / BMPG-Fe3O4 / CNF) includes the following steps:

[0115] Unlike Example 8, in the preparation of BMPG-Fe3O4, the mass ratio of BMPG to anhydrous FeCl3 was 1:2; the other preparation steps were the same as in Example 8, and the resulting product was labeled as PW / BMPG-Fe3O4 / CNF-2.

[0116] Example 10

[0117] A method for preparing a paraffin / Fe3O4 modified biomass-based graphene / copper nanowire foam composite phase change material (PW / BMPG-Fe3O4 / CNF) includes the following steps:

[0118] Unlike Example 8, in the preparation of BMPG-Fe3O4, the mass ratio of BMPG to anhydrous FeCl3 was 1:3; the other preparation steps were the same as in Example 8, and the resulting product was labeled as PW / BMPG-Fe3O4 / CNF-3.

[0119] Comparative Example 1

[0120] A method for preparing a paraffin / biomass-based graphene composite phase change material (PW / BMPG) differs from Example 1 in that melamine foam and bamboo powder are directly mixed, nitrogen gas is introduced to purge air, and then microwave plasma treatment (800W microwave oven, 2.45GHz frequency) is performed for 10 seconds. The specific preparation steps are as follows:

[0121] Preparation of biomass-based graphene (BMPG): Melamine foam (Henan Zhongyuan Dahua Group Co., Ltd.) and bamboo powder (100 mesh) were placed in a quartz reactor at a specific spacing and mass ratio (two pieces of CMF were placed parallel to each other in a quartz dish with a 3 mm spacing, and the mass ratio was 2.4:1). After nitrogen gas was introduced to purge the air, the reaction was subjected to microwave plasma treatment (800W power, 2.45GHz frequency) for 10 seconds. After the reaction was completed, the mixture was washed and dried to obtain biomass-based graphene, labeled as BMPG.

[0122] Take an appropriate amount of BMPG and vacuum dry it at 80℃ for 2 hours. Heat paraffin (PW) to 70℃ to melt it, and add a certain amount of petroleum ether to make a dispersion (the amount added is about 3 times the mass of paraffin). Add BMPG at a mass ratio of PW:BMPG of 999:1. After ultrasonic dispersion at 70℃ for 1 hour, heat and stir at 100℃ for 2 hours to volatilize the petroleum ether. After cooling and molding, the paraffin / biomass-based graphene composite phase change material is obtained. The obtained product is labeled as PW / BMPG (BMPG content 0.1wt%).

[0123] Comparative Example 2

[0124] A method for preparing a paraffin / copper nanowire foam composite phase change material (PW / CNF) differs from Example 4 in that the addition of polytetrafluoroethylene and natural graphite is omitted. Instead, modified copper foam is directly heated to 400 °C at a rate of 5 °C / min under nitrogen protection, held at that temperature for 2 hours, and then cooled to obtain copper nanowire foam (CNF). The specific preparation steps are as follows:

[0125] First, cut the foamed copper (Suzhou Keshenghe Metal Material, specification: 130 ppi) into 20×20×2mm pieces. 3 The cube was sequentially ultrasonically cleaned with anhydrous ethanol for 1 hour, rinsed with deionized water, ultrasonically cleaned with 20 wt% hydrochloric acid for 5 minutes, rinsed with deionized water again, dried with nitrogen and then dried at 80°C. Next, it was immersed in an alkaline solution containing 2.5M sodium hydroxide and 0.15M ammonium persulfate for 25 minutes to obtain modified copper foam. Subsequently, under nitrogen protection, the temperature was increased to 400°C at 5°C / min and held for 2 hours. After cooling, copper nanowire foam (CNF) was obtained.

[0126] The vacuum impregnation method is used to melt paraffin wax (PW) in a vacuum at 80 °C, and then immerse CNF in the molten paraffin wax (PW:CNF mass ratio of 2:1) for 1 hour. After cooling and molding, the resulting product is marked as PW / CNF.

[0127] Performance testing

[0128] The samples prepared in the embodiments and comparative examples of this invention were subjected to Raman spectrum, thermal conductivity, TEM, mapping, and X-ray powder diffraction tests, respectively. The results are as follows: Figures 1-9 As shown, BMPG is the sample prepared in Example 1, PW / BMPG is the sample prepared in Examples 1-3 with different mass ratios of biomass-based graphene and paraffin, PW / CNF is the sample prepared in Example 4 with different mass ratios of biomass-based graphene and paraffin, PW / BMPG / CNF is the sample prepared in Examples 5-7 with different mass ratios of biomass-based graphene and paraffin, and PW / BMPG-Fe3O4 / CNF is the sample prepared in Examples 8-10 with different mass ratios of BMPG and anhydrous FeCl3 introduced into the PW / CNF system.

[0129] Figure 1 This is a schematic diagram of the preparation process of biomass-based graphene (BMPG) in Example 1, where a is a schematic diagram of the sandwich-type carbon foam-induced microwave plasma conversion process, b is a quartz reactor, c is the microwave plasma conversion process, and d is a schematic diagram of the plasma generation process. Figure 1 From a and b, it can be seen that two pieces of carbonized melamine foam (CMF) are placed parallel to each other in a quartz dish with a spacing of 3 mm, and are placed in a quartz reactor with bamboo powder at a mass ratio of 2.4:1. Figure 1 In step b), after nitrogen is introduced and air is purged, the material is treated with microwave plasma, cleaned with ethanol, dried with concentrated sulfuric acid, and the residual acid on the surface is removed with sodium hydroxide to obtain biomass-based graphene. The top cover and base of the quartz reactor are airtightly connected by a rubber sealing ring and elastic strap, and a quartz wool insulation layer is pre-placed at the bottom. A small quartz reaction vessel is installed inside to assemble the reactants in a sandwich configuration. A three-stage gas scrubbing device is used to treat the waste gas, which can precisely control parameters such as nitrogen flow rate and reaction position to ensure concentrated plasma generation and a stable reaction atmosphere under the microwave field, making it suitable for efficient thermal conversion of biomass.

[0130] Depend on Figure 1 As shown in section c, CMF initiates the initial thermal effect through microwave absorption, providing the energy basis for subsequent plasma generation. However, the temperature at this stage is insufficient to directly generate graphene, requiring further energy accumulation. Figure 1 As shown in section d, the plasma formation period is the core stage of graphene synthesis. The ultra-high temperature environment enables rapid reconstruction of the carbon source, verifying that the sandwich-type CMF structure can efficiently induce plasma, and confirming that the microwave plasma method can directly prepare few-layer graphene from biomass (Raman spectroscopy shows I). 2D / I G It achieves a yield of 0.82, and the process requires no catalyst or substrate, giving it a green and low-cost advantage.

[0131] Figure 2These are TEM and HRTEM images of the BMPG obtained in Example 1. From... Figure 2 The images show that BMPG consists of 2-8 layers of flakes with a wrinkled structure at the edge layers. The interlayer spacing is 0.345 nm, consistent with the calculated results of the (002) crystal plane diffraction peaks in the subsequent XRD pattern. The wrinkled structure at the edge provides abundant defect sites. This few-layer structure reduces phonon scattering, while the wrinkled defects provide anchoring points for subsequent Fe3O4 loading, laying the foundation for subsequent interface modification.

[0132] Figure 3 The image shows the XRD pattern of the BMPG obtained in Example 1. Figure 3 The graphite (002) peak at 26.0° (interlayer spacing 3.45 Å) indicates that the turbine-like layered structure of BMPG has a larger interlayer spacing than conventional graphite (3.35 Å), which is caused by interlayer distortion introduced by microwave plasma treatment. This structural feature enhances the thermal conductivity of BMPG.

[0133] Figure 4 The Raman spectrum of the BMPG prepared in Example 1 and I 2D / I G and I D / I G The fluctuation range diagram shows that, where a is the Raman spectrum of BMPG obtained from ten parallel experiments, and b is the I spectrum corresponding to different numbers of experiments. 2D / I G and I D / I G The ratio. From Figure 4 As can be seen from 'a', the characteristic peaks of graphene include: the D peak (~1350 cm⁻¹). -1 , originating from sp 3 Hybridized carbon and lattice defects), G peak (~1580 cm⁻¹) -1 (Generated by the stretching vibrations of C-C bonds and C=C double bonds) and 2D peak (~2700 cm⁻¹) -1 The second-order characteristic peak of two-phonon resonance Raman scattering is related to the stacking mode and number of carbon atoms. It is usually represented by I... 2D / I G The ratio determines the number of layers (the larger the ratio, the fewer the layers). D / I G Reflects defect density (a larger ratio indicates more defects and lower graphitization) (Chem Soc Rev, 2018, 47 (5): 1822-1873). From Figure 4 As can be seen from b, the BMPG spectrum exhibits a high-intensity sharp 2D peak and a low-intensity D peak, I 2D / I G Up to 0.82, I D / IG With an average value as low as 0.58, BMPG exhibits characteristics of few layers, low defects, and high graphitization, indicating that it is a high-quality graphene material. This characteristic is directly related to photothermal efficiency, enabling highly efficient photothermal conversion.

[0134] Figure 5 The image shows the XRD pattern of PW / BMPG-Fe3O4 / CNF obtained in Example 9. Figure 5 It can be seen that, in addition to the graphite peak (002) of BMPG, new Fe3O4 crystal plane peaks (220) and (311) (2θ=30.1°, 35.4°) are added, proving that Fe3O4 was successfully loaded. The introduction of Fe3O4 increases the thermal conductivity by 3.157 W·m. -1 ·K -1 This is attributed to the "nano-thermal bridge" formed between Fe3O4 and BMPG and CNF, which optimizes the phonon transport path.

[0135] Figure 6 The image shows the TEM and mapping images of BMPG-Fe3O4 obtained in Example 8. Figure 6 It can be seen that 5-10 nm Fe3O4 particles are uniformly distributed on the BMPG surface, and the nanoparticles exhibit clear lattice fringes with a lattice spacing of 0.253 nm, corresponding to the (311) crystal plane of Fe3O4 (PDF#89-0691), confirming the crystallinity and phase purity of the Fe3O4 nanoparticles. The Fe and O element mapping shows good interfacial compatibility. This structure improves the photothermal efficiency of PW / BMPG-Fe3O4 / CNF. The surface plasmon resonance effect of Fe3O4 enhances light capture, reversing the efficiency decrease caused by the introduction of CNF.

[0136] Figure 7 SEM images of CNF obtained in Example 4 and PW / BMPG / CNF obtained in Example 5 are shown, where a is the SEM image of CNF obtained in Example 4 and b is the SEM image of PW / BMPG / CNF obtained in Example 5. Figure 7 As shown in section a, the diameter of the three-dimensional copper nanowire framework of CNF is 50-100 nm. From... Figure 7 As shown in Figure b, the three-dimensional copper nanowire framework of CNF is tightly bonded to the PW / BMPG composite interface. This structure is directly related to the leak-free properties, attributed to the capillary adsorption effect of the CNF pores, while the three-dimensional framework enhances the thermal conductivity.

[0137] Figure 8This is a diagram illustrating the flexibility of the PW / BMPG-Fe3O4 / CNF prepared in Example 9. The diagram shows the flexible properties of the composite phase change material cut to a size of 4 × 6 × 2 cm. The material can be bent and deformed without breaking, attributed to the synergistic effect of the three-dimensional copper nanowire foam (CNF) framework and biomass-based graphene (BMPG): the metallic network of CNF provides structural support, while the two-dimensional sheets of BMPG impart flexibility to the material, and paraffin (PW) fills the pores to form a flexible matrix. This property makes it suitable for the fit requirements of wearable thermal management devices.

[0138] Figure 9 The graphs show the heat release curves of the upper and lower surfaces of pure PW and the PW / BMPG-Fe3O4 / CNF prepared in Example 9. Pure PW has a low thermal conductivity (0.251 W·m). -1 ·K -1 After the bottom of the device came into contact with a simulated skin interface at 35°C, the temperature dropped sharply from 67°C to below 40°C within 400 seconds, while the top remained above 55°C, resulting in an axial temperature difference of over 15°C and uneven heat release. The PW / BMPG-Fe3O4 / CNF system utilizes the highly efficient thermally conductive network formed by BMPG-Fe3O4 and CNF (thermal conductivity 3.157 W·m). -1 ·K -1 The curve trend verifies the synergistic heat conduction mechanism of "two-dimensional network + three-dimensional skeleton + nano thermal bridge". The temperature difference between the upper and lower surfaces is ≤ 2.5 ℃, and the effective heat therapy temperature range of 40~70 ℃ is maintained for about 800 s. The heat release time is extended by 95% compared with pure PW, which shows that the composite heat conduction network optimizes the temperature uniformity and continuous heat release capacity, meeting the needs of wearable heat therapy.

[0139] To further verify the photothermal conversion performance of a series of composite phase change materials prepared from bamboo powder using sandwiched carbon foam-induced microwave plasma conversion technology, their application effects were tested as follows:

[0140] Thermal conductivity test

[0141] Test method: A hot-wire thermal conductivity meter (model TA612C) was used. The sample was processed into a circular disc with a diameter of 20 mm and a thickness of 2 mm. A constant heat flow was applied between the hot and cold plates. The thermal conductivity was calculated by measuring the temperature difference between the upper and lower surfaces. The formula is: The results are shown in Tables 1 and 2.

[0142] in, λ Thermal conductivity (W·m) -1 ·K -1 ), Q h and Q cHeat flow output of upper and lower thermal sensors (W·m) -2 ), L For sample thickness (m), Δ t The temperature difference is in K.

[0143] Table 1 Thermal conductivity of paraffin composite phase change materials containing BMPG and other graphene-based materials

[0144]

[0145] Among them, the graphite nanosheets in Table 1 (Applied Energy, 2013, 110: 163-172), multi-walled carbon nanotubes (Applied Energy, 2013, 110: 163-172), graphene (The Journal of Physical Chemistry C, 2011, 115(17): 8753-8758.), randomly arranged graphite nanosheets (Composites Part A: Applied Science and Manufacturing, 2013, 44: 40-46), and oriented graphite nanosheets (Composites Part A: Applied Science and Manufacturing, 2013, 44: 40-46).

[0146] As can be seen from Table 1, compared with other graphene-based materials, the thermal conductivity of BMPG in Example 3 at an addition amount of 0.5 wt% is 0.913 W·m. -1 ·K -1 The concentration was significantly higher than that of graphite nanosheets (0.322 W·m). -1 ·K -1 ), multi-walled carbon nanotubes (0.257 W·m) -1 ·K -1 This verifies that the BMPG prepared by sandwich microwave plasma in Example 3 has a better thermal conductivity enhancement effect.

[0147] Table 2 Comparison of Thermal Conductivity and Photothermal Conversion Efficiency

[0148]

[0149] In Table 2, the improvement rate of photothermal conversion efficiency is the improvement rate of the photothermal conversion efficiency of PW / BMPG-Fe3O4 / CNF in Examples 8-10 compared to that of PW / BMPG / CNF in Example 6.

[0150] As shown in Table 2, the thermal conductivity of pure paraffin (PW) is 0.251 W·m. -1 ·K-1 The properties are consistent with those of conventional organic phase change materials. In the PW / BMPG system, the thermal conductivity significantly increases with increasing BMPG content (Examples 1-3). When the BMPG content is 0.5 wt% (Example 3), the thermal conductivity reaches 0.913 W·m. -1 ·K -1 The thermal conductivity is 3.64 times higher than that of pure PW. This is attributed to the two-dimensional layered structure of BMPG forming a continuous thermally conductive network, reducing interfacial thermal resistance. The thermal conductivity of PW / CNF reaches 2.220 W·m. -1 ·K -1 (8.84 times higher than pure PW), originating from a metal thermally conductive network constructed from a 50-100 nm three-dimensional copper nanowire framework, but the photothermal efficiency is only 32.21% due to the metal reflection effect and the lack of photothermal components (Example 4). PW / BMPG / CNF system: After introducing copper nanowire foam (CNF) (Examples 5-7), the thermal conductivity is further improved to 2.772 W·m. -1 ·K -1 (11-fold improvement, Example 6), the three-dimensional metallic framework of CNF and BMPG form a synergistic thermal conduction path. PW / BMPG-Fe3O4 / CNF system: After modification with Fe3O4 nanoparticles (Examples 8-10), the thermal conductivity reaches a maximum of 3.157 W·m. -1 ·K -1 The thermal conductivity of Fe3O4 is 12.58 times higher than that of pure PW (Example 9). Fe3O4 also exhibits high thermal conductivity (5.9 W·m³). -1 ·K -1 It forms a "nano thermal bridge" with BMPG and CNF networks to optimize phonon transport.

[0151] The thermal conductivity of Comparative Example 1 is 0.315 W·m. -1 ·K -1 The thermal conductivity of Comparative Example 2 is 1.523 W·m. -1 ·K -1 This is because Comparative Example 1 did not undergo carbonization treatment of the melamine foam, resulting in a significant increase in the defect density of the biomass-based graphene induced by microwave plasma. The layers were stacked disordered and could not form a continuous thermally conductive network, resulting in a 35.2% decrease in thermal conductivity compared to Example 1. Comparative Example 2 did not add polytetrafluoroethylene and natural graphite, resulting in uneven growth of copper nanowires on the surface of the copper foam and fractures in the framework structure, increased interfacial thermal resistance, and a 31.4% decrease in thermal conductivity compared to Example 4.

[0152] Photothermal conversion efficiency test

[0153] Test method: A 300 W xenon lamp was used to simulate sunlight (intensity 1500 W·m). -2The sample was placed in an insulated chamber, and the temperature change at the center was recorded using thermocouples. The test results are shown in Table 2. Photothermal conversion efficiency η The calculation formula is:

[0154]

[0155] in, m For sample mass (g), Δ H m Phase transition enthalpy (J·g) -1 ), P Light intensity (m W·cm) -2 ), S Light-illuminated area (cm²) 2 ), Δ t The phase transition time is denoted as s.

[0156] As shown in Table 2, in the PW / BMPG system, with the increase of BMPG content (Examples 1-3), the broad-spectrum light absorption characteristics of BMPG significantly improve the photothermal efficiency, reaching 61.97% at a content of 0.5 wt% (Example 3), achieving a breakthrough compared to pure PW (which cannot directly absorb light energy). In the PW / BMPG / CNF system, after the introduction of copper nanowire foam (CNF) (Examples 5-7), the metallic reflection effect of CNF causes the photothermal efficiency to drop to 49.84% (Example 6), but this trend can be reversed by Fe3O4 modification.

[0157] PW / BMPG-Fe3O4 / CNF system: The surface plasmon resonance effect of Fe3O4 nanoparticles enhances the light-harvesting ability (Examples 8-10). When BMPG : FeCl3 = 1 : 3, the photothermal efficiency reaches 73.47%, which is 47.4% higher than PW / BMPG / CNF (specifically compared to Example 6) (Example 9), and is superior to the single modification effect of carbon black (60.1%) and Fe3O4 nanoparticles (47.9%) in the literature.

[0158] Thermal stability and latent heat of phase change testing

[0159] Test method: Differential scanning calorimetry (DSC) was used at 10℃·min under N2 atmosphere. -1 The enthalpy of fusion (ΔH m) was tested by heating and cooling rates, and thermal stability was evaluated by thermogravimetric analysis (TGA) in the range of 30-600℃. The test results are shown in Table 3.

[0160] Table 3 Comparison of latent heat of phase change and thermal stability tests

[0161]

[0162] As shown in Table 3, the differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) results indicate that the enthalpy of fusion of pure paraffin (PW) is 199.86 J·g. -1 The thermal decomposition initiation temperature was 200 °C; as the biomass-based graphene (BMPG) doping content increased from 0.1 wt% to 0.5 wt% (Examples 1-3), the melting enthalpy of the PW / BMPG system decreased to 168.69 J·g. -1 The thermal decomposition initiation temperature was increased to 210 °C, and the enthalpy of melting retention exceeded 97.9% after 50 cycles (Example 3); after introducing copper nanowire foam (CNF) encapsulation (Examples 4-7), the enthalpy of melting of PW / CNF (Example 4) was 165.72 J·g. -1 Enthalpy of solidification: 155.23 J·g -1 The thermal decomposition initiation temperature reached 210 °C, the complete pyrolysis temperature was 345 °C, the residual mass at 600 °C was 29.63%, and the enthalpy of fusion retention rate after 50 cycles was 97.5%, confirming that the three-dimensional framework structure of CNF not only increased the thermal decomposition temperature but also maintained the heat storage capacity of paraffin through physical encapsulation. The enthalpy of fusion of the PW / BMPG / CNF system (Examples 5-7) was further reduced to 115.48 J·g. -1 The thermal decomposition initiation temperature reaches 215 ℃, which is attributed to the synergistic effect of BMPG and CNF, which both reduces the paraffin content and improves thermal stability through the metal network of CNF.

[0163] When Fe3O4 nanoparticles are modified on the surface of BMPG (BMPG:FeCl3 = 1:3), the enthalpy of melting of PW / BMPG-Fe3O4 / CNF is maintained at 116.57 J·g. -1 To meet energy storage requirements (Example 10), the thermal decomposition initiation temperature was raised to 220 °C, and the enthalpy retention rate after 50 cycles reached 98.3%, achieving synergistic optimization of latent heat of phase change and thermal stability.

[0164] Application examples

[0165] To evaluate the applicability of composite phase change materials in human thermal management, heat release tests were conducted within the effective thermotherapy temperature range of 40–70°C. Wearable units of PW / BMPG-Fe3O4 / CNF were cut into 4×6×2 cm pieces, heated to 67°C by light irradiation, and then placed on a 35°C silicone plate (simulating the skin interface). The temperatures of the upper and lower surfaces were monitored simultaneously. Pure PW of equal mass, electrically heated to 67°C, served as a control. Figure 9 As shown, pure PW has a low thermal conductivity (0.251 W·m). -1 ·K -1The first material exhibits significant temperature hysteresis – the temperature at the bottom drops sharply to below 40°C within 400 seconds after contacting the platform, while the top, due to its low internal thermal conductivity, remains above 55°C, indicating that heat is primarily transferred through air convection, with axial thermal conduction failing. In contrast, the PW / BMPG-Fe3O4 / CNF (Example 9), thanks to its BMPG-Fe3O4-CNF composite thermally conductive network, maintains an axial temperature difference ΔT ≤ 2.5°C between the upper and lower surfaces, remaining within the effective thermotherapy temperature range for nearly 800 seconds. This extends the effective heat release time at the contact surface by 95% compared to pure PW. This material achieves efficient and uniform continuous thermal energy management, providing crucial material support for wearable solar thermotherapy devices.

[0166] In summary, this invention utilizes biomass waste to prepare BMPG, prepares copper nanowire foam (CNF) by in-situ growing copper nanoparticles on the surface of copper foam, and uses BMPG as a carrier to in-situ grow Fe3O4 nanoparticles on its surface via a solvothermal method. The modified BMPG-Fe3O4 is then introduced into the paraffin and CNF system, achieving efficient resource utilization and green conversion. The prepared composite phase change material, while possessing high heat storage capacity, significantly improves photothermal conversion efficiency and thermal conductivity, solves the leakage problem of paraffin phase change, and features a simple and low-cost preparation process. It has promising application prospects and can be widely used in fields such as solar photothermal conversion and storage, and human body thermal management.

[0167] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A composite phase change material, characterized in that, The composite phase change material comprises a paraffin matrix and a heat-conducting phase change material dispersed in the paraffin matrix, wherein the heat-conducting phase change material is at least one selected from biomass-based graphene, copper nanowire foam and Fe3O4 modified biomass-based graphene. The biomass-based graphene is prepared by the following method: a nitrogen source is carbonized under inert protection to obtain carbonized nitrogen source; the carbonized nitrogen source is mixed with biomass charcoal, and then subjected to microwave plasma conversion treatment under inert protection to obtain biomass-based graphene. The copper nanowire foam is prepared by the following method: foam copper is sequentially cleaned with anhydrous ethanol, water and hydrochloric acid, and then washed with water, dried with nitrogen and dried in an oven to obtain clean foam copper; the clean foam copper is immersed in an alkaline solution to obtain modified foam copper; polytetrafluoroethylene, natural graphite and anhydrous ethanol are mixed to obtain a suspension; the suspension is drop-coated on the surface of the modified foam copper, and then dried, heat-treated under inert gas protection and cooled to obtain the copper nanowire foam. The Fe3O4 modified biomass-based graphene is prepared by the following method: biomass-based graphene is mixed with a solvent, and then mixed with a soluble iron salt and stirred after adding sodium acetate, and then subjected to hydrothermal reaction to obtain the Fe3O4 modified biomass-based graphene.

2. The composite phase change material of claim 1, wherein, The composite phase change material is selected from one of paraffin / biomass-based graphene composite phase change material, paraffin / copper nanowire foam composite phase change material, paraffin / biomass-based graphene / copper nanowire foam composite phase change material and paraffin / Fe3O4 modified biomass-based graphene / copper nanowire foam composite phase change material.

3. The composite phase change material of claim 2, wherein, In the paraffin / biomass-based graphene composite phase change material, the content of biomass-based graphene is 0.1 wt%-0.5 wt%.

4. The composite phase change material of claim 2, wherein, In the paraffin / copper nanowire foam composite phase change material, the content of copper nanowire foam is 30 wt%-35 wt%.

5. The composite phase change material of claim 2, wherein, In the paraffin / biomass-based graphene / copper nanowire foam composite phase change material, the content of biomass-based graphene is 0.1 wt%-0.5 wt%, and the content of copper nanowire foam is 30 wt%-35 wt%.

6. The composite phase change material of claim 2, wherein, In the paraffin / Fe3O4 modified biomass-based graphene / copper nanowire foam composite phase change material, the content of Fe3O4 modified biomass-based graphene is 0.1 wt%-0.5 wt%, and the content of copper nanowire foam is 30 wt%-35 wt%. In the Fe3O4 modified biomass-based graphene, the mass ratio of biomass-based graphene to Fe3O4 is 1: (1-3).

7. The composite phase change material of claim 1, wherein, The biomass-based graphene is a two-dimensional network of 2-8 layers of single-atom carbon layers stacked together, and the Raman spectrum I 2D / I G is 0.70-0.82, I D / I G <0.

58.

8. The composite phase change material of claim 1, wherein, The copper nanowire foam has a three-dimensional copper nanowire skeleton structure, and the particle size is 50-100 nm.

9. The composite phase change material of claim 1, wherein, In the Fe3O4 modified biomass-based graphene, Fe3O4 particles are distributed on the surface of biomass-based graphene, and the particle size of the Fe3O4 particles is 5-10 nm.

10. A method of producing the composite phase change material according to any one of claims 1 to 9, characterized by, The method comprises the following steps: The paraffin matrix is heated and melted, then the heat-conducting phase change material is added, and the mixture is uniformly mixed, cooled and formed to obtain the composite phase change material. The heat-conducting phase change material includes at least one of biomass-based graphene, copper nanowire foam and Fe3O4 modified biomass-based graphene.

11. The method of claim 10, wherein the composite phase change material is prepared by a process comprising: The temperature of the paraffin matrix is 65-85 ℃, and the mixing method is selected from one of ultrasonic dispersion and vacuum impregnation. The content of the heat-conducting phase change material in the composite phase change material is 0.1 wt%-0.5 wt%.

12. The method of claim 10, wherein the composite phase change material is prepared by a process comprising: In the preparation method of the biomass-based graphene, the nitrogen source is at least one of urea, dicyandiamide, melamine foam and aniline; the carbonization treatment temperature is 800-1000 ℃, and the carbonization treatment time is 1-2 h. The mixing mass ratio of the carbonized nitrogen source and the biomass charcoal is (2-3): 1; the biomass charcoal is at least one of bamboo powder, straw powder and fruit shell; and the particle size of the biomass charcoal is 50-500 μm. The microwave plasma conversion treatment power is 700-900 W, the frequency is 2-3 GHz, and the time is 5-15 seconds.

13. The method of claim 12, wherein the composite phase change material is prepared by a process comprising: In the preparation method of the biomass-based graphene, the nitrogen source is melamine foam; the carbonization treatment temperature is 900 ℃, the carbonization treatment time is 1 h; the mixing mass ratio of the carbonized nitrogen source and the biomass charcoal is 2.4:1; the biomass charcoal is bamboo powder; the microwave plasma conversion treatment power is 800 W, the frequency is 2.45 GHz, and the time is 10 seconds.

14. The method of claim 10, wherein the composite phase change material is prepared by a process comprising: In the preparation method of the copper nanowire foam, the concentration of hydrochloric acid is 15-25 wt%, the drying temperature is 75-85 ℃, the alkaline solution includes sodium hydroxide and ammonium persulfate, the concentration of sodium hydroxide is 2-3 M, the concentration of ammonium persulfate is 0.1-0.2 M, the reaction time in the alkaline solution is 20-30 minutes; the mixing ratio of polytetrafluoroethylene, natural graphite and anhydrous ethanol is 1 mg:(450-550) mg:(250-350) mL; the drying temperature is 45-55 ℃, and the drying time is 3-5 h; the heat treatment atmosphere is nitrogen, the temperature is raised to 350-450 ℃ at a rate of 3-5 ℃ / min, and the temperature is kept for 1.5-2.5 h.

15. The method of claim 14, wherein the composite phase change material is prepared by a process comprising: In the preparation method of the copper nanowire foam, the concentration of hydrochloric acid is 20 wt%, the drying temperature is 80 ℃, the concentration of sodium hydroxide in the alkaline solution is 2.5 M, the concentration of ammonium persulfate is 0.15 M, and the reaction time in the alkaline solution is 25 minutes; the mixing ratio of polytetrafluoroethylene, natural graphite and anhydrous ethanol is 1 mg:500 mg:300 mL; the drying temperature is 50 ℃, the drying time is 4 h; the heat treatment atmosphere is nitrogen, the temperature is raised to 400 ℃ at a rate of 5 ℃ / min, and the temperature is kept for 2 h.

16. The method of claim 10, wherein the composite phase change material is prepared by a process comprising: In the preparation method of the Fe3O4 modified biomass-based graphene, after the biomass-based graphene is added into a solvent, a soluble iron salt is added and mixed, and then sodium acetate is added, and then the hydrothermal reaction is performed to obtain the Fe3O4 modified biomass-based graphene. The solvent is a mixed solvent composed of diethylene glycol and ethylene glycol, and the volume ratio of diethylene glycol to ethylene glycol is (30-40) : 10; The ratio of biomass-based graphene to solvent is 10 mg : (40-50) mL; The soluble iron salt is one of FeCl3, ferric nitrate and ferric sulfate; The mass ratio of biomass-based graphene to soluble iron salt is 1 : (1-3) ; The mass ratio of biomass-based graphene to sodium acetate is 10 : (75-85) ; The temperature of the hydrothermal reaction is 180-220 ℃, and the time of the hydrothermal reaction is 10-15 h; The ratio of biomass-based graphene to solvent is 10 mg : 45 mL; The soluble iron salt is FeCl3; The mass ratio of biomass-based graphene to FeCl3 is 1 : 3; The mass ratio of biomass-based graphene to sodium acetate is 10 : 80; The temperature of the hydrothermal reaction is 200 ℃, and the time of the hydrothermal reaction is 12 h.

17. The method of claim 16, wherein the composite phase change material is prepared by a process comprising: In the preparation method of the Fe3O4 modified biomass-based graphene, the volume ratio of diethylene glycol to ethylene glycol in the solvent is 35 :

10.

18. The method of claim 10, wherein the composite phase change material is prepared by a process comprising: The composite phase change material is selected from one of paraffin / biomass-based graphene composite phase change material, paraffin / copper nanowire foam composite phase change material, paraffin / biomass-based graphene / copper nanowire foam composite phase change material, and paraffin / Fe3O4 modified biomass-based graphene / copper nanowire foam composite phase change material. The preparation method of the paraffin / biomass-based graphene composite phase change material is as follows: The paraffin matrix is heated and melted, then the biomass-based graphene after vacuum drying is added, ultrasonic dispersion and heating stirring are performed, and after cooling and molding, the paraffin / biomass-based graphene composite phase change material is obtained. The content of the composite phase change material is 0.1 wt%-0.5 wt%.

19. The method of claim 18, wherein In the preparation method of the paraffin / biomass-based graphene composite phase change material, the temperature of the heating and melting of the paraffin matrix is 60-80 ℃, the temperature of the ultrasonic dispersion is 60-80 ℃, and the time of the ultrasonic dispersion is 0.5-1.5 h; the temperature of the heating and stirring is 90-110 ℃, and the time of the heating and stirring is 1-3 h.

20. The method of claim 18, wherein the composite phase change material is prepared by a process comprising: The preparation method of the paraffin / copper nanowire foam composite phase change material is as follows: The paraffin matrix is heated and melted, then the copper nanowire foam is added, and vacuum impregnation is adopted for mixing, and after cooling and molding, the paraffin / copper nanowire foam composite phase change material is obtained. In the paraffin / copper nanowire foam composite phase change material, the content of the copper nanowire foam is 30 wt%-35 wt%.

21. The method of claim 20, wherein the composite phase change material is prepared by a process comprising: In the preparation method of the paraffin / copper nanowire foam composite phase change material, the temperature of the vacuum impregnation is 75-85 ℃, and the time is 1-2 h.

22. The method of claim 18, wherein the composite phase change material is prepared by a process comprising: The preparation method of the paraffin / biomass-based graphene / copper nanowire foam composite phase change material is as follows: the paraffin / biomass-based graphene is heated and melted, then the copper nanowire foam is added, and vacuum impregnation is adopted for mixing, and after cooling and molding, the paraffin / biomass-based graphene / copper nanowire foam composite phase change material is obtained.

23. The method of claim 22, wherein the composite phase change material is prepared by a process comprising: The content of the biomass-based graphene in the paraffin / biomass-based graphene / copper nanowire foam composite phase change material is 0.1 wt%-0.5 wt%, and the content of the copper nanowire foam is 30 wt%-35 wt%.

24. The method of claim 22, wherein the composite phase change material is prepared by a process comprising: The temperature of the vacuum impregnation method is 75-85 ℃, and the time is 1-2 h.

25. The method of claim 18, wherein the composite phase change material is prepared by a process comprising: The preparation method of the paraffin / Fe3O4 modified biomass-based graphene / copper nanowire foam composite phase change material is as follows: The paraffin / Fe3O4 modified biomass-based graphene / copper nanowire foam composite phase change material is obtained by heating and melting the paraffin, then adding the Fe3O4 modified biomass-based graphene and the copper nanowire foam, and mixing by the vacuum impregnation method, and then cooling and forming. The content of the Fe3O4 modified biomass-based graphene in the paraffin / Fe3O4 modified biomass-based graphene / copper nanowire foam composite phase change material is 0.1 wt%-0.5 wt%, and the content of the copper nanowire foam is 30 wt%-35 wt%.

26. The method of claim 25, wherein the composite phase change material is prepared by a process comprising: The temperature of the vacuum impregnation method is 75-85 ℃, and the time is 1-2 h.

27. The application of the composite phase change material of any one of claims 1-9 in solar water heater heat storage, intelligent temperature control building wall and electronic device heat management.

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