A plastic composite shape-stabilized phase change material, its preparation method and application

Abstract

The application relates to a plastic composite fixed shape phase change material and a preparation method and application thereof, and belongs to the technical field of building energy-saving materials. The plastic composite fixed shape phase change material is composed of solid-liquid phase change materials, expanded graphite and calcium ion cross-linked sodium alginate three-dimensional porous support materials. The calcium ion and carboxyl functional groups on a G unit block of sodium alginate are combined through coordination chelation to construct a three-dimensional cross-linked network to in-situ load phase change materials, and a plastic composite fixed shape phase change material is prepared by combining a cold drying technology. The three-dimensional porous network structure of the calcium ion cross-linked sodium alginate improves the mechanical properties of the composite material, the composite material can be shaped and volume controlled under heating conditions, and the shape is kept unchanged after cooling. The composite material has light-thermal energy conversion and heat energy storage functions, is suitable for building heat preservation in an environment with large day-night temperature difference, can slow down the temperature fluctuation amplitude of indoor temperature at night, saves building operation energy consumption, is convenient to apply, is low in cost, and has a wide application prospect in the field of building energy saving.

Description

Technical Field

[0001] This invention relates to a plastic composite shape-stabilized phase change material, its preparation method, and its application, belonging to the field of building energy-saving materials technology. Background Technology

[0002] According to statistics from the International Energy Agency, building energy consumption currently accounts for more than 30% of total global energy consumption, and this figure continues to rise with climate change and population growth. Therefore, intelligent thermal management of buildings has attracted widespread research from the scientific and industrial communities. Phase change materials (PCMs) possess isothermal phase change characteristics and high energy storage density, which can enhance building thermal inertia, reduce maximum heat flux, transfer peak energy demand, and reduce air temperature fluctuations. Their application in thermal management within the field of building energy conservation has been extensively studied. Research results show that adding appropriate amounts of PCMs to buildings, using suitable encapsulation methods and deployment locations, can significantly improve indoor comfort conditions and reduce the energy demand of HVAC systems (BR Sahar, A. Amani, BK Rim, MS Nejla and J. Abdelmajid, Journal of Building Engineering, 2020, 32, 101563.).

[0003] Adding single phase change materials directly to building materials or mixing them into concrete can lead to problems such as phase change leakage and poor thermal conductivity. If the phase change material is deformed by pressure or other external forces, leakage will be further exacerbated. Furthermore, the inherent rigidity and brittleness of phase change materials severely limit their practical applications. To date, research and development of plastic phase change materials are limited; therefore, developing and preparing plastic composite phase change energy storage materials is of great significance. Summary of the Invention

[0004] Addressing key issues such as leakage, inherent rigidity, and brittle fracture in organic solid-liquid phase change materials (PCMs), this invention aims to design and prepare a malleable composite shape-stabilized PCM. Through an in-situ loading method, paraffin / expanded graphite is encapsulated within a gel system. A three-dimensional porous cross-linked network is formed by the coordination chelation between calcium ions and sodium alginate carboxyl groups. Combined with freeze-drying technology, porous airflow channels are constructed based on the three-dimensional support framework, providing the composite material with processable space and enabling shape malleability and volume control. Simultaneously, by combining solar radiation phenomena with the phase change heat collection characteristics of PCMs, a low-cost, processable composite shape-stabilized PCM is constructed, integrating light absorption, heat generation, and heat storage. This material can be applied to insulation in buildings and greenhouses under conditions of large diurnal temperature variations or off-seasons, saving building operating energy consumption and reducing production and living costs.

[0005] The purpose of this invention is to provide a plastic composite shape-stabilized phase change material. This material is rich in pores, possesses certain compressibility and flexibility, and integrates light-to-heat energy conversion and thermal energy storage and utilization. It has good thermal management capabilities, a simple synthesis process, and is convenient to apply, thus having broad application prospects.

[0006] A plastic composite shape-stabilized phase change material is disclosed, comprising paraffin / expanded graphite and a three-dimensional porous network support material. The three-dimensional porous network support material is formed by the coordination and crosslinking of calcium ions with carboxyl groups on the G unit blocks of sodium alginate. Under the chelating effect of the coordination bonds, the sodium alginate G units stack to form a three-dimensional porous network while the phase change component is loaded in situ. Combined with freeze-drying technology, a three-dimensional sponge-like structure is formed, giving the composite material excellent mechanical properties. It can be processed and shaped under heating conditions.

[0007] The composite shape-stabilized phase change material is composed of 75-90 wt% paraffin wax, 3-15 wt% expanded graphite, and 2-10 wt% calcium ion-crosslinked sodium alginate. The mass ratio of sodium alginate to calcium ions in the calcium ion-crosslinked sodium alginate is 1:6 to 1:5.

[0008] The organic solid-liquid phase change material is at least one of the following: paraffin wax (melting point between 20 and 50°C), n-octadecane, n-eicosane, n-dodecyl alcohol, n-tetradecyl alcohol, n-hexadecyl alcohol, palmitic acid, stearic acid, butyl stearate, methyl palmitate, methyl stearate, and polyethylene glycol (molecular weight between 2000 and 10000).

[0009] Another object of the present invention is to provide a method for preparing the above-mentioned plastic composite shape-stabilized phase change material.

[0010] A method for preparing a plastic composite shape-stabilized phase change material, the method comprising the following steps:

[0011] Step (1): Place the paraffin wax in a beaker and heat it in an electric heating mantle. After the paraffin wax has completely melted, add expanded graphite and mechanically stir to mix the paraffin wax and expanded graphite thoroughly. The paraffin wax is completely adsorbed into the porous structure of the expanded graphite. The mass ratio of paraffin wax to expanded graphite in the composite phase change material is 9:1 to 19:1.

[0012] Step (2): Grind the paraffin / expanded graphite composite phase change material into powder with a particle size of approximately 0.2–0.3 mm;

[0013] Step (3): Dissolve sodium alginate in water at 60°C to obtain sodium alginate aqueous solution, wherein the mass ratio of sodium alginate to water is 1:68.

[0014] Step (4): Under room temperature conditions, the prepared paraffin / expanded graphite composite phase change material is mixed with the sodium alginate aqueous solution obtained in step (3), mechanically stirred until uniform, calcium chloride solution is added dropwise, stirred until uniform, and then allowed to stand for 12 hours to form a paraffin / expanded graphite / calcium ion crosslinked sodium alginate composite hydrogel. The mass ratio of the paraffin / expanded graphite composite phase change material to sodium alginate is 10:1 to 20:1.

[0015] Step (5): Place it in a freeze dryer for 24 hours to remove water and obtain a plastic composite shape-stabilized phase change material suitable for building insulation in environments with large day-night temperature differences.

[0016] The shaped phase change material is composed of paraffin / expanded graphite and a three-dimensional porous network support material. The three-dimensional porous network support material is formed by cross-linking calcium ions with carboxyl groups on the G-unit blocks of sodium alginate via cryo-drying. This three-dimensional porous network support endows the composite material with plasticity. The three-dimensional cross-linked network is used to in-situ load the phase change material through the coordination and chelation of calcium ions with the carboxyl functional groups on the G-unit blocks of sodium alginate. Combined with freeze-drying technology, porous airflow channels are built based on the three-dimensional framework to obtain a sponge-like composite phase change material, providing ample room for processing and control of the composite material. It exhibits excellent mechanical properties and shape controllability; it can be shaped under heating conditions, and its shape and volume remain unchanged after cooling.

[0017] The three-dimensional porous network support material is rich in interconnected porous channels with a porosity of 82%, exhibiting compressibility and flexibility. In the composite shape-stabilized phase change material, the porous expanded graphite and the calcium ion-crosslinked sodium alginate form a three-dimensional crosslinked network support material that synergistically encapsulates the organic solid-liquid phase change material. This aforementioned plastic composite shape-stabilized phase change material maintains structural stability even after a 40% volume compression, retaining excellent shape-stabilizing properties.

[0018] The aforementioned composite shaped phase change material, suitable for building and greenhouse insulation, is lightweight, environmentally friendly, has high heat storage density, adjustable volume, and can be used in suspended or embedded applications. Depending on the phase change temperature of the material, it can be used for insulation of buildings, houses, or greenhouses in environments with large diurnal temperature variations during the season or in off-season conditions. During the day, under solar radiation, it converts solar energy into heat energy and stores it as latent heat. This reduces the dissipation of external heat during hot days, storing it as latent heat. At night, when the indoor and greenhouse temperatures drop, the stored heat is released, maintaining the indoor and greenhouse temperatures at a certain level or reducing temperature fluctuations, thus reducing building operating energy consumption.

[0019] The beneficial effects of this invention are as follows: This invention constructs a three-dimensional cross-linked network for in-situ loading of phase change materials through the coordination and chelation of calcium ions with carboxyl functional groups on the G-unit blocks of sodium alginate. Simultaneously, it combines this with cold-drying technology to prepare a plastic composite shape-stabilized phase change material. The synthesis process is simple and clean, convenient to apply, has a wide range of applications, and low energy consumption, effectively reducing production costs. The plastic composite shape-stabilized phase change material is rich in pores, possesses compressibility and flexibility, and maintains structural stability and leak-proof performance even after being compressed by 2 / 5 of its volume, while still exhibiting excellent shape-stabilizing effects. Its shape and volume can be processed and modified, broadening its practical application range.

[0020] Simultaneously, the light-to-heat conversion function is introduced into the phase change system to achieve effective utilization of solar energy. Then, it is combined with the building to construct a temperature difference-driven clean energy utilization system that integrates solar energy absorption, conversion, and storage in the building structure, thereby improving the thermal quality and thermal inertia of lightweight buildings and achieving the effect of intelligent indoor temperature regulation. Attached Figure Description

[0021] Figure 1 For example, EG, PW / EG, and Ca in Example 1 2+ -SA and PW / EG / Ca 2+ Scanning electron microscope (SEM) image of -SA (PESCs).

[0022] Figure 2 The infrared spectra (FT-IR) of EG, PW / EG, SA and PESCs in Example 1 are shown.

[0023] Figure 3 The X-ray diffraction (XRD) curves of EG, PW / EG, SA and PESCs in Example 1 are shown.

[0024] Figure 4 For Ca in Example 1 2+ Frequency-scanned rheological property curves of SA hydrogel and PESCs hydrogel.

[0025] Figure 5 Infrared thermal imaging images of the shape stability of the PW, PW / EG and PESCs composite shape-stabilized phase change materials described in Example 1.

[0026] Figure 6 The image shows the DSC curves of the PW, PW / EG, and PESCs composite shape-stabilized phase change materials described in Example 1.

[0027] Figure 7 The graph shows the heating and cooling rate curves of the PW and PESCs composite shape-stabilized phase change material described in Example 1.

[0028] Figure 8The test curves for photothermal conversion and thermal energy storage of the PW and PESCs composite shape-stabilized phase change material described in Example 1 are shown.

[0029] Figure 9 This is a plasticity test of the PESCs composite shape-stabilized phase change material described in Example 1.

[0030] Figure 10 This is a test of the shape stability of the PESCs composite shape-stabilized phase change material during compression as described in Example 1.

[0031] Figure 11 This is a schematic diagram illustrating the preparation principle of the PESCs composite shape-stabilized phase change material described in Example 1.

[0032] Figure 12 The simulation test of the application of the PESCs composite shape-stabilized phase change material described in Example 1 to greenhouse insulation (ambient temperature 15℃). (a) The figure shows the temperature change process inside the greenhouse under simulated sunlight: curve a is the temperature rise process inside the greenhouse under the blank condition without phase change material, and curve b is the temperature rise process inside the greenhouse under the condition containing PESCs composite shape-stabilized phase change material; (b) The figure shows the temperature change process inside the greenhouse under no light: curve a is the temperature drop process inside the greenhouse under the blank condition without phase change material, and curve b is the temperature drop process inside the greenhouse under the condition containing PESCs composite shape-stabilized phase change material. Detailed Implementation

[0033] The following non-limiting embodiments are intended to enable those skilled in the art to more fully understand the invention, but do not limit the invention in any way.

[0034] Unless otherwise specified, the experimental methods described in the following examples are conventional methods; the reagents and materials described are commercially available unless otherwise specified.

[0035] Example 1

[0036] 1. Place 9.0g of paraffin PW in a 50ml beaker and heat it in an electric heating mantle at 80℃. After the PW has completely melted, add 1.0g of EG and stir magnetically for 2 hours to fully mix the PW and expanded graphite (EG). The resulting PW / EG composite phase change material is cooled and ground into powder with a particle size of approximately 0.2–0.3 mm.

[0037] 2. Add 0.22g sodium alginate (SA) and 15ml deionized water to a 100ml three-necked flask, place it in a 60℃ water bath, and mechanically stir at 200r / min for 0.5h to completely dissolve SA in the deionized water to obtain an SA aqueous solution.

[0038] 3. After adjusting the water bath temperature to room temperature, weigh 2.2g of the PW / EG composite phase change material obtained in step (1) and add it to the SA aqueous solution obtained in step (2). Stir mechanically at 700r / min for 2 hours to ensure uniform mixing. Then add 10ml of 0.007mol / ml CaCl2 solution and continue stirring for 2 hours. After standing for 12 hours, calcium ions undergo a coordination crosslinking reaction with the carboxyl groups on the sodium alginate G unit block to form a gel, resulting in a PESCs composite gel system. After freeze-drying, a plastic composite shape-stabilized phase change material PESCs with photothermal conversion and thermal energy storage functions is obtained.

[0039] The morphology of the above-mentioned composite shape-stabilized phase change material was characterized by scanning electron microscopy (SEM). Figure 1 As can be seen in a, the porous structure of EG is formed by the accumulation of flake graphite. This porous network structure can give the supporting material a large specific surface area and sufficient adsorption space. Figure 1 The disappearance of the porous network structure of bEG proves the effective loading of the phase change material. Figure 1 c shows Ca 2+ The amorphous porous cage-like network structure formed by cross-linking SA has a large number of pores and internal space, which can improve the loading rate of phase change materials. Figure 1 d indicates that the PW / EG composite phase change material is effectively encapsulated in the three-dimensional cross-linked network structure, thereby achieving the shape stability of the PESCs composite phase change material before and after the phase change.

[0040] from Figure 2 The infrared spectrum of the material shows that, in addition to the characteristic vibrational peaks of PW, the obtained PESCs also contain characteristic vibrational peaks of EG and SA. No new characteristic peaks are generated, and the positions of the characteristic peaks do not change, indicating that PW is physically composited with EG and SA and no new chemical bonds are formed.

[0041] Depend on Figure 3 XRD characterization of the material shows that PW is similar to EG and Ca. 2+ The PESCs generated after SA recombination showed characteristic diffraction peaks at the same positions. Although the intensity of the characteristic peaks of PESCs decreased, they still maintained relatively good crystallinity.

[0042] At room temperature, the obtained Ca was analyzed using a rotational rheometer. 2+ The rheological properties of the SA and PESCs composite hydrogel system were characterized, such as... Figure 4 As shown, the storage modulus (G′) of the two gel systems is always higher than the loss modulus (G″), indicating that they mainly undergo elastic deformation and have a solid-like gel structure. This demonstrates that the formation of the cross-linked structure ensures the shape stability of the composite material.

[0043] The shaping effect of the composite phase change material was tested at 70℃. Figure 5 This indicates that PESCs composite shape-stabilized phase change materials have excellent shape stability and will not leak at 70°C.

[0044] Differential scanning calorimetry (DSC) was used to test the composite phase change material, and the results are as follows: Figure 6 As shown, the phase change enthalpy of PESCs composite shaped phase change material is around 155 J / g, which provides a guarantee for the practical application of greenhouse insulation.

[0045] The thermal conductivity of the composite shape-stabilized phase change material was tested under conditions ranging from room temperature to 70°C, and the results are as follows: Figure 7 As shown, compared with pure PW, the heat storage and release rates of PESCs are significantly enhanced, increasing by 62.6% and 58.0%, respectively. This indicates that the presence of EG effectively improves the thermal conductivity of the material.

[0046] The PESCs composite shape-stabilized phase change material prepared by this invention can achieve light capture, convert solar energy into thermal energy, and store it. Figure 8 (a) shows the UV-Vis absorption spectra of PW and PESCs. Compared with PW, PESCs exhibit stronger light absorption across the entire spectral range, indicating that the prepared PESCs have strong light absorption capabilities and can effectively absorb sunlight. Figure 8 (b) The temperature change curves of PW and PESCs under simulated illumination show that PESCs undergo a phase change heat storage and release process. Under the same conditions, PW did not show a melting and crystallization phase transition plateau, indicating that pure PW did not undergo a phase transition during this process because it lacks light absorption capacity and its maximum temperature does not reach the phase transition temperature.

[0047] The three-dimensional porous cross-linked network skeleton formed by the cross-linking of sodium alginate and calcium ions can effectively improve the mechanical properties of composite materials and expand their application range. The test results are as follows: Figure 9 As shown, PW / EG / Ca 2+ -SA composite hydrogels, after freeze-drying, yield sponge-like PESCs. The three-dimensional porous cross-linked network structure endows PESCs with compressibility and flexibility, overcoming the rigidity limitations of traditional phase change materials. Even with a maximum volume compressibility of 40%, they maintain good encapsulation and prevent leakage. When the volume compressibility reaches 50%, as... Figure 10 As shown in Figure d, PESCs exhibit slight exudation of phase change materials at 70°C. Therefore, within a controllable volume range, composite phase change materials possess processability during production, increasing the adhesion between the material and the device, and can be molded into the desired shape according to actual needs.

[0048] The preparation principle of PESCs composite shape-stabilized phase change materials is as follows: Figure 11 As shown, PW / EG was placed in an aqueous sodium alginate solution, introducing calcium ions. Through the cross-linking reaction between calcium ions and sodium alginate, sodium alginate molecules formed a three-dimensional network, which in turn formed a gel system, completing the in-situ encapsulation of PW / EG. Combined with freeze-drying technology, porous airflow channels were constructed based on the three-dimensional cross-linked network to obtain a porous, sponge-like composite phase change material.

[0049] Simulation test of thermal insulation of PESCs composite shape-stabilized phase change materials in greenhouses, as follows: Figure 12 As shown in (a) and (b), under simulated sunlight conditions, the heating rate inside the greenhouse of the blank group (a) in (a) is much faster than that of the experimental group (b). This is because under light radiation, the PESCs first undergo a phase change heat storage process before transferring heat into the greenhouse to maintain a relatively stable temperature. The rapid temperature rise in the blank group is due to direct solar radiation. After the light source is turned off, the temperature inside the greenhouse of the blank group (a) drops instantly, while the temperature change in the experimental group (b) is slow. The experimental group maintains a temperature above 25°C for 9.5 times longer than the blank group. This indicates that the composite phase change material releases heat during this process, maintaining a relatively stable room temperature and reducing the temperature fluctuation range inside the greenhouse.

[0050] Example 2

[0051] Paraffin wax: 90 wt%; expanded graphite: 5 wt%; calcium ion crosslinked sodium alginate three-dimensional support material: 5 wt%; other conditions are the same as in Example 1.

[0052] Example 3

[0053] Paraffin wax: 85 wt%; expanded graphite: 10 wt%; calcium ion crosslinked sodium alginate three-dimensional support material: 5 wt%; other conditions are the same as in Example 1.

[0054] Example 4

[0055] Paraffin wax: 80 wt%; expanded graphite: 10 wt%; calcium ion crosslinked sodium alginate three-dimensional support material: 10 wt%; other conditions are the same as in Example 1.

[0056] Example 5

[0057] Paraffin wax: 75 wt%; expanded graphite: 10 wt%; calcium ion crosslinked sodium alginate three-dimensional support material: 15 wt%; other conditions are the same as in Example 1.

[0058] Examples 6-10

[0059] By replacing paraffin wax with n-octadecane as the organic solid-liquid phase change material, a corresponding plastic composite shape-stabilized phase change material with photothermal conversion function was obtained, with other conditions consistent with Examples 1-5.

[0060] Examples 11-15

[0061] By replacing paraffin wax with hexadecyl alcohol as the organic solid-liquid phase change material, a corresponding plastic composite shape-stabilized phase change material with photothermal conversion function was obtained, with other conditions consistent with Examples 1-5.

[0062] Examples 16-20

[0063] Paraffin wax was replaced with butyl stearate as an organic solid-liquid phase change material to obtain a corresponding plastic composite shape-stabilized phase change material with photothermal conversion function. Other conditions were the same as in Examples 1-5.

Claims

1. A plastic composite shape-stabilized phase change material, characterized in that: The composite shaped phase change material contains 75-90 wt% solid-liquid phase change material, 3-15 wt% expanded graphite, and 2-10 wt% calcium ion crosslinked sodium alginate. The calcium ion crosslinked sodium alginate is formed by crosslinking calcium ions with carboxyl groups on the G unit block of sodium alginate and then cold drying, wherein the mass ratio of sodium alginate to calcium ions is 1:6-1:

5. The preparation method of phase change materials includes the following steps: (1) Add expanded graphite to the solid-liquid phase change material and stir to mix; the solid-liquid phase change material is adsorbed onto the expanded graphite. In the porous structure, a solid-liquid phase change material / expanded graphite composite phase change material is obtained and ground into powder with a particle size of 0.2-0.3 mm; the mass ratio of the solid-liquid phase change material to expanded graphite is 9:1-19:1; (2) Dissolve sodium alginate in water to obtain an aqueous solution of sodium alginate, wherein the mass ratio of sodium alginate to water is 1: (60-80)； (3) Mix the solid-liquid phase change material / expanded graphite composite phase change material with sodium alginate aqueous solution, stir and mix evenly, add calcium chloride solution dropwise, and let stand for 10-12 hours to form a composite hydrogel; the mass ratio of the solid-liquid phase change material / expanded graphite composite phase change material to sodium alginate is 10:1-20:

1. (4) The material is freeze-dried to remove water, and a plastic composite shaped phase change material is obtained.

2. The plastic composite shape-stabilized phase change material according to claim 1, characterized in that: The solid-liquid phase change material is at least one of paraffin wax, n-octadecane, n-eicosane, n-dodecyl alcohol, n-tetradecyl alcohol, n-hexadecyl alcohol, palmitic acid, stearic acid, butyl stearate, methyl palmitate, methyl stearate, and polyethylene glycol.

3. The application of a plastic composite shape-stabilized phase change material according to claim 1 or 2, characterized in that: The plastic composite shape-stabilized phase change material is used in buildings or greenhouses.

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