A flexible phase change material with double network packaging and a three-step mixing and room temperature pressing method thereof

Abstract

The present invention discloses a flexible phase change material with double network encapsulation and a three-step mixing and room temperature pressing method thereof. The materials include: water, expanded graphite, sodium polyacrylate, polyethylene glycol octylphenyl ether and borax. The method is as follows: water is taken and stirred with sodium polyacrylate to obtain a binary composite material with high molecular polymer network encapsulation; polyethylene glycol octylphenyl ether, a surfactant, is added to the expanded graphite and fully mixed, and then stirred with the binary composite material to obtain a ternary composite material; the ternary composite material is then fully mixed with borax to obtain a quaternary composite material, and hot pressed at 30°C to allow the sodium polyacrylate in the composite material to fully infiltrate the pores of the expanded graphite. The method has a simple process and high efficiency. The prepared material overcomes the problems of liquid leakage and low thermal conductivity of traditional phase change materials, and has the advantages of high enthalpy value, high thermal conductivity and good flexibility. It is suitable for application scenarios such as refrigerated transportation, cold compress and cold therapy, and human thermal management textiles.

Description

Technical Field

[0001] The present invention relates to the field of phase change cold storage, and in particular to a double-network-encapsulated low-temperature phase change material and a three-step mixing and room-temperature pressing method thereof. Background Art

[0002] As global average temperatures rise and people's quality of life improves, demand for cooling is rapidly increasing. At the same time, carbon emissions from refrigeration and air-conditioning systems are increasing, and their electricity consumption accounts for up to 15% of global electricity consumption. Faced with the trend of rapidly increasing cooling energy consumption, vigorously developing renewable energy sources such as solar and wind power is the key to solving the future cooling energy gap. However, renewable energy sources suffer from intermittent and highly volatile power generation, which can easily lead to a mismatch between power generation and power consumption. Phase change materials can absorb and release energy through phase changes, shifting energy peaks and filling valleys. This significantly addresses the energy mismatch between time and space, helps alleviate grid load, and contributes to energy conservation.

[0003] Water is a common and important inorganic phase change material with a phase change temperature of 0°C and a latent heat of 334 J / g. Compared to other commonly used phase change materials, it offers advantages such as high phase change enthalpy, non-toxicity, low price, and stable performance. However, water is liquid at room temperature and prone to leakage and evaporation. It requires well-sealed packaging containers for storage, resulting in high production costs. Furthermore, its low thermal conductivity results in a slow cooling rate, requiring a long recharge time after use.

[0004] CN1408736A discloses a method for improving the water retention of materials using hydrogels. By cross-linking acrylic acid and acrylamide, a super absorbent resin is prepared, and it is applied to long-term water retention scenarios to effectively reduce water loss. However, the thermal conductivity of super absorbent resin is low, which is not conducive to heat transfer, and its thermal conductivity needs to be improved. CN111548771A discloses a method for making a low-temperature phase change material using tetradecane and expanded graphite. By adsorbing the phase change material by expanded graphite, the leakage of tetradecane can be reduced, ensuring stability during use. However, the enthalpy value of the phase change material used is up to 201.4 J / g, which is low in enthalpy and insufficient in energy storage density. CN106967390A discloses a low-temperature inorganic composite phase change heat storage material and its preparation method. By soaking expanded graphite in the adsorption of barium hydroxide octahydrate, the thermal conductivity of barium hydroxide octahydrate with a thermal conductivity of 1.14 W / (m·K) is increased to 1.99-4.22 W / (m·K), effectively improving the thermal conductivity of the phase change material. The addition of expanded graphite further stabilizes the performance of the composite phase-change material, ensuring long-term use. However, the phase transition temperature of the barium hydroxide octahydrate used is between 75°C and 80°C, making it unsuitable for cold storage and cooling applications below 25°C. Furthermore, the process of modifying the expanded graphite uses large amounts of anhydrous ethanol, which poses significant environmental risks, high energy consumption, and safety risks during production. A new method with simpler processes and lower production costs is needed to address the issues of water leakage and low thermal conductivity and expand its application in various fields. Summary of the Invention

[0005] The present invention aims to provide an organic-inorganic dual network encapsulated phase change material and a three-step mixing and room temperature pressing method thereof. This method has a simple process and high efficiency. The prepared material overcomes the problems of liquid leakage and low thermal conductivity of traditional phase change materials, and has the advantages of high enthalpy value, high thermal conductivity and good flexibility. It is suitable for application scenarios such as refrigerated transportation, cold compress and cold therapy, and human thermal management textiles.

[0006] The technical solutions of the present invention are as follows.

[0007] The present invention provides a double-network-encapsulated flexible phase-change material and a three-step mixing and room-temperature pressing method thereof, comprising the following steps:

[0008] (1) Mixing of binary composite materials: first, water is heated, and then sodium polyacrylate is added and stirred to allow the water to be fully absorbed in the sodium polyacrylate to obtain a gel-like composite material;

[0009] (2) Mixing the ternary composite material: uniformly mixing the expanded graphite and polyethylene glycol octylphenyl ether, and after the sodium polyacrylate hydrogel obtained in step (1) is cooled to room temperature, adding the surface-modified expanded graphite and fully mixing and stirring to allow the sodium polyacrylate hydrogel to fully adhere to the pores of the expanded graphite;

[0010] (3) mixing the quaternary composite material: adding borax to the mixture obtained in step (2), mixing and stirring thoroughly to allow the borax to be completely dispersed in the sodium polyacrylate to obtain the quaternary composite material;

[0011] (4) Compression molding: The mixture obtained in step (3) is introduced into a mold and pressed at a temperature of 20-50° C. and a pressure of 5-15 MPa to shape the expanded graphite into a block;

[0012] (5) Material demoulding: The pressed material is removed from the mold to obtain a shaped double-network encapsulated water / expanded graphite / sodium polyacrylate / borax composite phase change material.

[0013] Preferably, in step (1), the mixing temperature is 40-80° C., and the mixing time is 10-30 minutes. The mixing process is continued until all the water is absorbed into the sodium polyacrylate without any residue, and the sodium polyacrylate has no agglomeration phenomenon, and the whole is a transparent and clear gel.

[0014] Preferably, the mixing temperature in step (2) is 20-40° C., and the mixing time is 10-30 minutes. The mixing process is continued until all the water and sodium polyacrylate are adhered to the expanded graphite without any residue.

[0015] Preferably, the mixing temperature in step (3) is 20-40° C., and the mixing time is 10-30 minutes. The mixing process is continued until the borax fully enters the gaps between the expanded graphite and the sodium polyacrylate, and no agglomeration occurs.

[0016] Preferably, the hot pressing time in step (4) is 20 to 60 minutes.

[0017] Preferably, in the flexible phase change material, the composite material comprises, by mass fraction, 40%-90% water, 4%-30% expanded graphite, 4%-30% sodium polyacrylate, and 0.5%-2% borax.

[0018] A flexible phase-change material with a double-network encapsulation comprises the following components, calculated by percentage: 40%-90% water, 4%-30% expanded graphite, 4%-30% sodium polyacrylate, and 0.5%-2% borax. The water acts as the phase-change material, with a phase-change temperature between -5°C and 0°C. Due to the double network encapsulation of expanded graphite and sodium polyacrylate, the resulting composite phase-change material is leak-proof during use and exhibits high thermal conductivity, high enthalpy, high compressive strength, and flexibility.

[0019] Furthermore, the flexible phase change material with double network packaging is characterized in that the thermal conductivity of the flexible phase change material can reach up to 4.62W / m·K or more, and the thermal impedance is as low as 10.20K·cm 2 / W, its phase change temperature is -5-0℃, and the phase change enthalpy can reach up to 331.5kJ / kg or more.

[0020] Furthermore, the double-network-encapsulated flexible phase change material is characterized in that the minimum water surface contact angle of the flexible phase change material is 0°, the maximum compressive load is 44.90 kPa, the time required for 50% water loss in a constant temperature environment of 45°C is extended to 18.1 hours, and the time required for 90% water loss is extended to 72.4 hours.

[0021] Furthermore, the sodium polyacrylate is a white powder at room temperature, and has an average relative molecular mass of 3 million to 10 million.

[0022] Furthermore, the expanded graphite is a worm-like loose porous three-dimensional network structure, which acts as a matrix to absorb water and sodium polyacrylate, plays a shaping role and constructs a heat-conducting network, and can improve the material's resistance to pressure and impact.

[0023] Furthermore, the sodium polyacrylate has strong water retention, certain flexibility and viscosity, and can form a high molecular polymer cross-linked network after pressure pressing, which can effectively improve the water retention and flexibility of the composite phase change material.

[0024] Furthermore, the polyethylene glycol octylphenyl ether is a surfactant, which is grafted onto the surface of the expanded graphite to introduce hydrophilic groups such as hydroxyl groups, thereby improving the hydrophilicity of the expanded graphite and better absorbing and accommodating water.

[0025] Furthermore, the borax is a cross-linking agent that can generate chemical bonds and hydrogen bonds between linear sodium polyacrylate molecules, connecting the linear molecules to each other, making the three-dimensional network structure more complete, thereby enhancing the mechanical strength and elasticity of the material, and improving the thermal impedance of the material and reducing the contact thermal resistance.

[0026] Furthermore, the double-network-encapsulated flexible phase change material is characterized in that the prepared quaternary composite phase change material has greatly increased water retention under the combined action of hydrogen bonds and mutually entangled high-polymerization molecular chains, and has given the material better flexibility and compressive resistance.

[0027] The flexible phase-change material described in the present invention has the following characteristics: Water, as the phase-change material, has a phase-change temperature between -5°C and 0°C, with an enthalpy value of up to 331.5 kJ / kg or higher, resulting in a suitable phase-change temperature and a high phase-change enthalpy. Expanded graphite is modified with the surfactant polyethylene glycol octylphenyl ether, introducing hydroxyl groups on its surface to increase its hydrophilicity. Hydrogen bonds and capillary action bind water within the pores of the expanded graphite, preventing leakage. The expanded graphite used is a high-thermal-conductivity material, and after compression molding, it forms a thermally conductive network, effectively improving the overall thermal conductivity of the material. Sodium polyacrylate contains a large number of hydrophilic groups. Upon contact with water, the polymer network gradually swells from its intertwined state, generating osmotic pressure within and outside the network structure. This allows water molecules to diffuse into the network by osmosis, effectively adsorbing water within the network. This gives the sodium polyacrylate excellent water absorption and water retention, as well as a certain degree of flexibility. However, when sodium polyacrylate molecules are not cross-linked, their mechanical strength is low and they are difficult to shape. Borax cross-linking agents can generate chemical bonds and hydrogen bonds between linear molecules, connecting the linear molecules together to form a network structure, thereby improving the mechanical strength and elasticity of the material. In addition, expanded graphite and sodium polyacrylate can form a double encapsulation network together, which can improve the thermal conductivity of the composite material while preventing water leakage during use and having a certain degree of flexibility. The thermal conductivity of the composite phase change material can reach up to 4.62W / (m·K) and the lowest thermal impedance is 10.20K·cm 2 / W, the maximum pressure load is 44.90kPa, the minimum water surface contact angle is 0°, and the time taken to lose 50% of the water in a constant temperature environment of 45℃ is extended to 18.1h, and the time taken to lose 90% of the water is extended to 72.4h.

[0028] Compared with the prior art, the advantages of the organic-inorganic composite phase change material prepared by the method provided by the present invention are:

[0029] (1) This method has a simple process flow and high preparation efficiency. Water is adsorbed in sodium polyacrylate, and sodium polyacrylate can adhere to expanded graphite. The block can be formed at room temperature of 30°C without the need for high-temperature curing.

[0030] (2) After the addition of sodium polyacrylate, the material's flexibility is significantly improved, and it has a certain viscosity, allowing it to fit tightly onto thermal management objects of different shapes. Furthermore, sodium polyacrylate can act as a water-retaining agent, effectively delaying the evaporation of water in the phase change material, and has excellent water-retaining properties.

[0031] (3) This material also has the characteristics of high thermal conductivity, high enthalpy value, good water retention, and good compression performance. It can be used in thermal management fields such as refrigerators, battery heat dissipation, and smart textiles.

[0032] (4) The present invention utilizes the three-dimensional interconnected network of expanded graphite as a matrix, adds sodium polyacrylate as a polymer filler, and forms a high molecular polymer network through high-pressure pressing. While retaining the thermal conductive network of the expanded graphite itself, a flexible network is introduced to improve the overall mechanical properties of the composite material. While having high thermal conductivity, the material's ability to resist pressure shock is also improved, which is beneficial for resisting the pressure shock caused by bulging and side wall rupture caused by thermal runaway of the battery, and preventing the composite material from breaking and affecting the heat storage performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 1 is the relationship between the surface water contact angle of the composite material obtained in Example 1 and the ratio of surfactant to hydrophilic material.

[0034] Figure 2 This is an SEM image of the composite material obtained in Example 2 of the present invention.

[0035] Figure 3 This is the relationship between the thermal impedance of the composite material obtained in Example 3 of the present invention and the proportion of the cross-linking agent borax.

[0036] Figure 4 This is the relationship between the maximum load of the composite material obtained in Example 4 of the present invention and the ratio of expanded graphite to sodium polyacrylate.

[0037] Figure 5 This is the relationship between the maximum load of the composite material obtained in Example 4 of the present invention and the proportion of the cross-linking agent borax.

[0038] Table 1 shows the relationship between the enthalpy value of the composite material obtained in Example 5 of the present invention and the water ratio.

[0039] Figure 6 3. The relationship between the enthalpy value of the composite material obtained in Example 5 of the present invention and the water ratio.

[0040] Figure 7 This is the relationship between the water retention performance of the composite material obtained in Example 6 of the present invention and the proportion of sodium polyacrylate.

[0041] Figure 8 This is the relationship between the thermal conductivity of the composite material obtained in Example 7 of the present invention and the proportion of expanded graphite. DETAILED DESCRIPTION

[0042] The technical solutions of the present invention are further specifically described below by means of specific examples and in conjunction with the accompanying drawings. The embodiments cannot be described one by one here, but the embodiments of the present invention are not therefore limited to the following examples. In the present invention, unless otherwise specified, all equipment and raw materials can be purchased from the market or are commonly used in the industry. The methods in the following embodiments, unless otherwise specified, are conventional methods in the art. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0043] The present invention provides a double-network-encapsulated flexible phase-change material and a three-step mixing and room-temperature pressing method thereof, comprising the following steps:

[0044] (1) Mixing of binary composite materials: First, heat water, then add sodium polyacrylate and stir to mix, so that the water is fully absorbed in the sodium polyacrylate to obtain a gel composite material.

[0045] (2) Ternary composite material mixing: Expanded graphite and polyethylene glycol octylphenyl ether are uniformly mixed in a certain proportion. After the sodium polyacrylate hydrogel obtained in step (1) is cooled to room temperature, the surface-modified expanded graphite is added and mixed thoroughly to allow the sodium polyacrylate hydrogel to fully adhere to the pores of the expanded graphite.

[0046] (3) Mixing the quaternary composite material: adding borax to the mixture obtained in step (2), mixing and stirring thoroughly to allow the borax to be completely dispersed in the sodium polyacrylate to obtain the quaternary composite material.

[0047] (4) Compression molding: The mixture obtained in step (3) is introduced into a mold and heated at 20-50 ° C.

[0048] The expanded graphite is pressed at a temperature of 5-15 MPa to form a block.

[0049] (5) Material demoulding: The pressed material is removed from the mold to obtain a shaped double-network encapsulated water / expanded graphite / sodium polyacrylate / borax composite phase change material.

[0050] The present invention encapsulates water with a double network composed of expanded graphite and sodium polyacrylate. The loose, porous expanded graphite with a three-dimensional interconnected network structure serves as a matrix to adsorb water and sodium polyacrylate. Polyethylene glycol octylphenyl ether serves as a surfactant to introduce hydroxyl groups, thereby improving the hydrophilicity of the expanded graphite and enhancing the compatibility between the expanded graphite, water and sodium polyacrylate. Borax serves as a cross-linking agent to connect the expanded graphite and sodium polyacrylate. The formed double encapsulation network can prevent water leakage during use while improving the thermal conductivity of the composite material, and has certain flexibility and pressure resistance. It is suitable for application scenarios such as refrigerated transportation, cold compresses and cold therapy, and human thermal management textiles.

[0051] Example 1

[0052] Set the briquetting density to 1000kg / m 3 A briquetting mold with an outer diameter of 60mm, an inner diameter of 40mm, and a height of 10mm was selected, and the total mass of the briquetting material was determined to be 12.57g. The mass ratio of sodium polyacrylate and surface-modified expanded graphite was first set to 10%, followed by a mass ratio of 79.5% for the aqueous phase change material, 0.5% for borax, and a mass ratio of 100:1 for expanded graphite and polyethylene glycol octylphenyl ether. The details are as follows:

[0053] (1) Drying of expanded graphite: Place the expanded graphite in an oven at 75°C for 2 hours to fully dry it.

[0054] (2) Surface modification of expanded graphite: 5 g of fully dried expanded graphite was weighed and added to a beaker. The mixture was stirred at a constant speed of 150 rad / min for 30 min. 0.05 g of polyethylene glycol octylphenyl ether was added and stirred at a constant speed of 150 rad / min for 30 min at 50°C to allow the surfactant to be grafted onto the surface of the expanded graphite.

[0055] (3) Binary composite material mixing: 10% (1.26 g) of sodium polyacrylate and 79.5% (9.99 g) of water were weighed and mixed, and stirred for 30 min at a speed of 150 rad / min to allow water to be adsorbed in the sodium polyacrylate through hydrogen bonding.

[0056] (4) Compounding of ternary composite materials: 10% (1.26 g) of surface-modified expanded graphite was weighed and added to the mixture obtained in step (3). The mixture was stirred for 30 min at a speed of 150 rad / min to allow the aqueous sodium polyacrylate to be adsorbed into the pores of the surface-modified expanded graphite.

[0057] (5) Quaternary composite material compounding: 0.5% (0.06 g) of borax was weighed and added to the mixture obtained in step (4), and stirred for 30 min at a speed of 150 rad / min. The borax promoted the cross-linking between the sodium polyacrylate molecular chains to form a three-dimensional network structure.

[0058] (6) Compression molding: The surface-modified expanded graphite obtained in step (5) was filled into a mold with a diameter of 40 mm and a height of 10 mm, and briquetting was performed at a pressure of 10 MPa and a temperature of 25° C. to shape the surface-modified expanded graphite.

[0059] (7) Material demoulding: removing the pressed material from the mold.

[0060] The water / expanded graphite / sodium polyacrylate composite phase change material prepared in Example 1 of the present invention was tested by a surface tension and surface contact angle tester. Figure 1 As shown in the figure, the surfactant polyethylene glycol octylphenyl ether was successfully grafted onto the surface of expanded graphite. Its hydrophilic groups improved the hydrophobicity of the expanded graphite. In addition, sodium polyacrylate contains a large number of carboxyl and hydroxyl hydrophilic groups, which improve the compatibility of the composite material and the aqueous phase change material, and help to absorb and accommodate more water.

[0061] Example 2

[0062] Set the briquetting density to 1000kg / m 3 A briquetting mold with an outer diameter of 60mm, an inner diameter of 40mm, and a height of 10mm was selected, and the total mass of the briquetting material was determined to be 12.57g. The mass ratio of sodium polyacrylate and surface-modified expanded graphite was first set at 10%, followed by a mass ratio of 77% for the aqueous phase change material and 3% for borax. The details are as follows:

[0063] (1) Mixing of binary composite materials: 10% (1.26 g) of sodium polyacrylate and 77% of water were weighed and mixed, and stirred for 30 min at a speed of 150 rad / min to allow water to be adsorbed in the sodium polyacrylate through hydrogen bonding.

[0064] (2) Compounding of ternary composite materials: 10% (1.26 g) of surface-modified expanded graphite was weighed and added to the mixture obtained in step (1). The mixture was stirred for 30 min at a speed of 150 rad / min to allow the aqueous sodium polyacrylate to be adsorbed into the pores of the surface-modified expanded graphite.

[0065] (3) Quaternary composite material compounding: 3% (0.38 g) of borax was weighed and added to the mixture obtained in step (2), and stirred for 30 min at a speed of 150 rad / min. Borax promoted the cross-linking between the sodium polyacrylate molecular chains to form a three-dimensional network structure.

[0066] (4) Compression molding: The mixture obtained in step (3) is filled into a mold with a diameter of 40 mm and a height of 10 mm, and pressed into blocks at a pressure of 10 MPa and a temperature of 25° C. to shape the surface-modified expanded graphite.

[0067] (5) Material demoulding: removing the pressed material from the mold.

[0068] The composite phase change material prepared in Example 2 of the present invention was examined by scanning electron microscopy. Figure 2As shown, Figures a and b are electron microscope images of expanded graphite, and Figures c and d are electron microscope images of expanded graphite / sodium polyacrylate composite materials, indicating that an organic-inorganic three-dimensional interconnected network is formed between the surface modified expanded graphite and sodium polyacrylate, which together play the role of encapsulating the aqueous phase change material and bonding support to improve the mechanical properties of the material.

[0069] Example 3

[0070] Set the briquetting density to 1000kg / m 3 A briquetting mold with an outer diameter of 60mm, an inner diameter of 40mm, and a height of 10mm was selected, and the total mass of the briquetting material was determined to be 12.57g. First, the mass proportion of sodium polyacrylate was set to 5%, and the mass proportion of surface-modified expanded graphite was set to 10%. Subsequently, a series of step-by-step changes in the mass proportions of borax were formulated: 0%, 0.5%, 1%, 1.5%, and 2%. A series of step-by-step changes in the mass proportions of the aqueous phase change material were formulated: 85%, 84.5%, 84%, 83.5%, and 83%. The details are as follows:

[0071] (1) Mixing of binary composite materials: Sodium polyacrylate with a mass ratio of 5% (0.63 g) and water with a mass ratio of 85% (10.68 g), 84.5% (10.62 g), 84% (10.56 g), 83.5% (10.50 g), and 83% (10.43 g) were weighed and mixed, and stirred with an agitator at a speed of 150 rad / min for 30 min to allow water to be adsorbed in the sodium polyacrylate through hydrogen bonds.

[0072] (2) Compounding of ternary composite materials: 10% (1.26 g) of surface-modified expanded graphite was weighed and added to the mixture obtained in step (1), and stirred for 30 min at a speed of 150 rad / min to allow the aqueous sodium polyacrylate to be adsorbed into the pores of the surface-modified expanded graphite.

[0073] (3) Quaternary composite material compounding: Borax weighed in proportions of 0% (0 g), 0.5% (0.06 g), 1% (0.13 g), 1.5% (0.19 g), and 2% (0.25 g) was added to the mixture obtained in step (2), and stirred for 30 min with a stirrer at a speed of 150 rad / min. The borax promoted crosslinking between the sodium polyacrylate molecular chains to form a three-dimensional network structure.

[0074] (4) Compression molding: The mixture obtained in step (3) is filled into a mold with a diameter of 40 mm and a height of 10 mm, and briquetting is performed at a pressure of 10 MPa and a temperature of 25° C. to shape the material.

[0075] (5) Material demoulding: removing the pressed material from the mold.

[0076] The composite phase change material prepared in Example 3 of the present invention was tested by a DRL-III thermal impedance tester. Figure 3 As shown in the figure, with the increase of borax mass fraction, its thermal impedance increases from 10.74K·cm 2 / W dropped to 10.20K·cm 2 / W, a decrease of approximately 5%. This suggests that an appropriate amount of borax helps to create an interconnected network that facilitates heat transfer by strengthening cross-linking strength, thereby reducing the thermal impedance of the material. Furthermore, the material's certain degree of flexibility can also reduce contact thermal resistance. However, as the borax mass fraction increases, the thermal impedance of the material increases, indicating that excessive borax can damage the internal integrity of the material and increase contact thermal resistance.

[0077] Example 4

[0078] Set the briquetting density to 1000kg / m 3 , select a briquetting mold with an outer diameter of 60mm, an inner diameter of 40mm, and a height of 10mm, and determine the total mass of the briquetting material to be 12.57g. First, set the mass ratio of sodium polyacrylate to 5% and the mass ratio of surface-modified expanded graphite to 10%. Then, formulate a series of step-by-step changes in the mass ratio of borax to 0%, 0.5%, and 1%, and a series of step-by-step changes in the mass ratio of the aqueous phase change material to 95%, 90%, 85%, 84.5%, 84%, and 83.5%. The details are as follows:

[0079] (1) Mixing of binary composite materials: Sodium polyacrylate with a mass ratio of 5% (0.63 g) and water with a mass ratio of 95% (11.94 g), 85% (10.68 g), 84.5% (10.62 g), 84% (10.56 g), and 83.5% (10.50 g) were weighed and mixed, and stirred with an agitator at a speed of 150 rad / min for 30 min to allow water to be adsorbed in the sodium polyacrylate through hydrogen bonds.

[0080] (2) Ternary composite material compounding: 0% (0 g) and 10% (1.26 g) of surface-modified expanded graphite were weighed and added to the mixture obtained in step (1), and stirred for 30 min at a speed of 150 rad / min to allow the aqueous sodium polyacrylate to be adsorbed into the pores of the surface-modified expanded graphite.

[0081] (3) Quaternary composite material compounding: Borax weighed in proportions of 0% (0 g), 0.5% (0.06 g), 1% (0.13 g), and 1.5% (0.19 g) by mass was added to the mixture obtained in step (2), and stirred for 30 min with a stirrer at a speed of 150 rad / min. The borax promoted the crosslinking between the sodium polyacrylate molecular chains to form a three-dimensional network structure.

[0082] (4) Compression molding: The mixture obtained in step (3) is filled into a mold with a diameter of 40 mm and a height of 10 mm, and briquetting is performed at a pressure of 10 MPa and a temperature of 25° C. to shape the material.

[0083] (5) Material demoulding: removing the pressed material from the mold.

[0084] The composite phase change material prepared in Example 4 of the present invention was tested by a universal electronic testing machine. Figure 4 As shown in the figure, the maximum load of the expanded graphite / water composite phase change material is 239.76kPa, and its compressive resistance is strong. The maximum load of the sodium polyacrylate / water composite phase change material is 3.60kPa, and its compressive resistance is weak. The maximum load of the expanded graphite / sodium polyacrylate / water composite phase change material is 41.29kPa, which is 11.5 times that of the sodium polyacrylate / water composite material. This shows that the introduction of expanded graphite into sodium polyacrylate can effectively improve the overall compression performance of the material, and has a higher pressure load bearing capacity, which is conducive to resisting pressure shocks and avoiding the composite material from breaking and affecting the heat storage performance. Figure 5 As shown, the addition of an appropriate amount of borax can further improve the material's compressive load bearing capacity. The maximum loads of the composite phase change materials containing 0.5% and 1% borax were 44.90 kPa and 43.41 kPa, respectively, which are 8.7% and 5.1% higher than those of the materials without borax. This is because borax, as a crosslinking agent, can form dynamic hydrogen bonds and chemical bonds with the hydroxyl groups on sodium polyacrylate and modified expanded graphite, thereby increasing the internal crosslinking strength and providing greater structural integrity for the expanded graphite-sodium polyacrylate dual network, effectively improving the material's mechanical strength. However, excessive borax can damage the material's internal structural integrity, reducing its mechanical strength and hindering its resistance to pressure shocks.

[0085] Example 5

[0086] Set the briquetting density to 1000kg / m 3 A briquetting mold with an outer diameter of 60mm, an inner diameter of 40mm, and a height of 10mm was selected, and the total mass of the briquetting material was determined to be 12.57g. The mass ratio of sodium polyacrylate to surface-modified expanded graphite was first set at 1:1. A series of step-by-step changes in the mass ratio of the aqueous phase change material were then formulated: 97%, 87%, 77%, 67%, and 57%. Borax accounted for 3% of the total mass. The details are as follows:

[0087] (1) Mixing of binary composite materials: Sodium polyacrylate with a mass ratio of 0 (0 g), 5% (0.63 g), 10% (1.26 g), 15% (1.89 g), and 20% (2.51 g) was weighed and mixed with water with a mass ratio of 97% (12.19 g), 87% (10.94 g), 77% (9.68 g), 67% (8.55 g), and 57% (7.16 g), respectively. The mixture was stirred for 30 min at a speed of 150 rad / min to allow water to be adsorbed in the sodium polyacrylate through hydrogen bonds.

[0088] (2) Ternary composite material compounding: Surface-modified expanded graphite in weighed mass proportions of 0 (0 g), 5% (0.63 g), 10% (1.26 g), 15% (1.89 g), and 20% (2.51 g) was added to the mixture obtained in step (1), and stirred for 30 min at a speed of 150 rad / min to allow the aqueous sodium polyacrylate to be adsorbed into the pores of the surface-modified expanded graphite.

[0089] (3) Quaternary composite material compounding: 3% (0.38 g) of borax was weighed and added to the mixture obtained in step (2), and stirred for 30 min at a speed of 150 rad / min. Borax promoted the cross-linking between the sodium polyacrylate molecular chains to form a three-dimensional network structure.

[0090] (4) Compression molding: The mixture obtained in step (3) is filled into a mold with a diameter of 40 mm and a height of 10 mm, and pressed into blocks at a pressure of 10 MPa and a temperature of 25° C. to shape the surface-modified expanded graphite.

[0091] (5) Material demoulding: removing the pressed material from the mold.

[0092] The composite phase change material prepared in Example 5 of the present invention was tested by differential scanning calorimetry, as shown in Table 1 and Figure 6 As shown in the figure, with the increase of expanded graphite and sodium polyacrylate, the enthalpy value decreases from 269.4 J / g to 132.3 J / g, indicating that with the reduction of water phase change material, the enthalpy value of the composite material will decrease, and the change of enthalpy value is linearly correlated with the change of expanded graphite and sodium polyacrylate.

[0093] Table 1 Phase change characteristics of water / sodium polyacrylate / expanded graphite composite phase change materials with different water contents

[0094]

[0095] Example 6

[0096] Set the briquetting density to 1000kg / m 3A briquetting mold with an outer diameter of 60mm, an inner diameter of 40mm, and a height of 10mm was selected, and the total mass of the briquetting material was determined to be 12.57g. The surface-modified expanded graphite was first set to account for 10% of the total mass, and the borax accounted for 3% of the total mass. Subsequently, a series of step-by-step changes in the mass proportions of sodium polyacrylate were formulated: 0%, 5%, 10%, 15%, and 20%. The mass proportions of the aqueous phase change material were also formulated: 87%, 83%, 77%, 72%, and 67%, as follows:

[0097] (1) Mixing of binary composite materials: Sodium polyacrylate with a mass ratio of 0 (0 g), 5% (0.63 g), 10% (1.26 g), 15% (1.89 g), and 20% (2.51 g) was weighed and mixed with water with a mass ratio of 87% (10.94 g), 83% (10.43 g), 77% (9.68 g), 72% (9.05 g), and 67% (8.42 g), respectively. The mixture was stirred for 30 min at a speed of 150 rad / min to allow water to be adsorbed in the sodium polyacrylate through hydrogen bonds.

[0098] (2) Compounding of ternary composite materials: 10% (1.26 g) of surface-modified expanded graphite was weighed and added to the mixture obtained in step (1). The mixture was stirred for 30 min at a speed of 150 rad / min to allow the aqueous sodium polyacrylate to be adsorbed into the pores of the surface-modified expanded graphite.

[0099] (3) Quaternary composite material compounding: 3% (0.38 g) of borax was weighed and added to the mixture obtained in step (2), and stirred for 30 min at a speed of 150 rad / min. Borax promoted the cross-linking between the sodium polyacrylate molecular chains to form a three-dimensional network structure.

[0100] (4) Compression molding: The mixture obtained in step (3) is filled into a mold with a diameter of 40 mm and a height of 10 mm, and pressed into blocks at a pressure of 10 MPa and a temperature of 25° C. to shape the surface-modified expanded graphite.

[0101] (5) Material demoulding: removing the pressed material from the mold.

[0102] The composite phase change material prepared in Example 6 of the present invention was dried in a constant temperature box at 45°C for 140 hours. Figure 7As shown, the water loss rate of the composite phase-change material gradually decreases with increasing sodium polyacrylate content, and the change in water retention is directly proportional to the change in sodium polyacrylate. Water retention experiments demonstrate that sodium polyacrylate has excellent water retention properties. For composite phase-change materials with sodium polyacrylate mass fractions of 0% and 20%, the time required for 50% water loss is 9.8 hours and 18.1 hours, respectively, and the time required for 90% water loss is 45.7 hours and 72.4 hours, respectively. Sodium polyacrylate can extend the water retention time by 1.58-1.85 times.

[0103] Example 7

[0104] Set the briquetting density to 1000kg / m 3 A briquetting mold with an outer diameter of 60mm, an inner diameter of 40mm, and a height of 10mm was selected, and the total mass of the briquetting material was determined to be 12.57g. The mass proportion of sodium polyacrylate was first set at 5%, followed by a series of step-by-step changes in the mass proportions of surface-modified expanded graphite: 0%, 5%, 10%, 15%, and 20%. The mass proportions of the aqueous phase change material were also set at 92%, 87%, 82%, 77%, and 72%. Borax accounted for 3% of the total mass. The details are as follows:

[0105] (1) Mixing of binary composite materials: Sodium polyacrylate with a mass ratio of 5% (0.63 g) and water with a mass ratio of 92% (11.56 g), 87% (10.94 g), 82% (10.31 g), 77% (9.68 g), and 72% (9.05 g) were weighed and mixed, and stirred with an agitator at a speed of 150 rad / min for 30 min to allow water to be adsorbed in the sodium polyacrylate through hydrogen bonds.

[0106] (2) Ternary composite material compounding: 0% (0 g), 5% (0.63 g), 10% (1.26 g), 15% (1.89 g), and 20% (2.51 g) of surface-modified expanded graphite were added to the mixture obtained in step (1), and stirred for 30 min at a speed of 150 rad / min to allow the aqueous sodium polyacrylate to be adsorbed into the pores of the surface-modified expanded graphite.

[0107] (3) Quaternary composite material compounding: 3% (0.38 g) of borax was weighed and added to the mixture obtained in step (2), and stirred for 30 min at a speed of 150 rad / min. Borax promoted the cross-linking between the sodium polyacrylate molecular chains to form a three-dimensional network structure.

[0108] (4) Compression molding: The mixture obtained in step (3) is filled into a mold with a diameter of 40 mm and a height of 10 mm, and pressed into blocks at a pressure of 10 MPa and a temperature of 25° C. to shape the surface-modified expanded graphite.

[0109] (5) Material demoulding: removing the pressed material from the mold.

[0110] The composite phase change material prepared in Example 7 of the present invention was tested by the Hot-disk method. Figure 8 As shown in the figure, with the increase of the proportion of expanded graphite, the thermal conductivity of the composite phase change material increases from 1.47W / m·K to 4.62W / m·K, indicating that with the increase of the proportion of expanded graphite, the thermal conductivity of the composite phase change material will increase, and the change in thermal conductivity is directly proportional to the change in expanded graphite.

[0111] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be appropriately modified or replaced by equivalents without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A three-step mixing and room temperature pressing method for a double network encapsulated flexible phase change material, characterized in that: The following steps are involved: (1) Mixing of binary composite materials: First, heat water, then add sodium polyacrylate and stir to make the water fully absorbed in the sodium polyacrylate to obtain a gel composite material; (2) Mixing the ternary composite material: uniformly mix the expanded graphite and polyethylene glycol octylphenyl ether, and after the sodium polyacrylate hydrogel obtained in step (1) cools to room temperature, add the surface-modified expanded graphite and mix and stir thoroughly to allow the sodium polyacrylate hydrogel to fully adhere to the pores of the expanded graphite; (3) Mixing the quaternary composite material: adding borax to the mixture obtained in step (2), and mixing and stirring thoroughly to allow the borax to be completely dispersed in the sodium polyacrylate to obtain the quaternary composite material; (4) Pressing: The mixture obtained in step (3) is introduced into a mold and pressed at a temperature of 20-50°C and a pressure of 5-15 MPa to shape the expanded graphite into a block; (5) Material demolding: removing the pressed material from the mold to obtain a double-network encapsulated water / expanded graphite / sodium polyacrylate / borax composite phase change material; The raw materials in the above preparation method include the following components by mass percentage: 40%-90% water, 4%-30% expanded graphite, 4%-30% sodium polyacrylate, and 0.5%-2% borax.

2. The three-step mixing and room temperature pressing method of the double network encapsulated flexible phase change material according to claim 1 is characterized in that: In step (1), the mixing and stirring temperature is 40-80° C., and the mixing and stirring time is 10-30 minutes; the mixing process is carried out until all the water is absorbed into the sodium polyacrylate without any residue, and the mixture is evenly dispersed without agglomeration.

3. The three-step mixing and room temperature pressing method of the double network encapsulated flexible phase change material according to claim 1 is characterized in that: In step (2), the mixing and stirring temperature is 20-40° C., the mixing and stirring time is 10-30 minutes, and the mixing process is carried out until all the water and sodium polyacrylate are adhered to the expanded graphite without any residue.

4. The three-step mixing and room temperature pressing method of the double network encapsulated flexible phase change material according to claim 1 is characterized in that: In step (3), the mixing and stirring temperature is 20-40°C, and the mixing and stirring time is 10-30 minutes.

5. The three-step mixing and room temperature pressing method of the double network encapsulated flexible phase change material according to claim 1 is characterized in that: In step (4), the hot pressing time is 20 to 60 minutes.

6. A double-network-encapsulated flexible phase change material prepared by the method according to any one of claims 1 to 5, characterized in that: The water is a phase change material, and its phase change temperature is -5-0°C.

7. The double-network-encapsulated flexible phase change material according to claim 6, characterized in that: The sodium polyacrylate is a white powder at room temperature, and has an average relative molecular mass of 3 million to 10 million.

8. The double-network-encapsulated flexible phase change material according to claim 6, characterized in that: The thermal conductivity of the flexible phase change material is above 4.62 W / m·K, and the minimum thermal impedance is 10.20 K·cm 2 / W, its phase change temperature is -5-0℃, and the maximum phase change enthalpy is above 331.5kJ / kg.

9. The double-network-encapsulated flexible phase change material according to claim 6, characterized in that: The flexible phase change material has a minimum water surface contact angle of 0° and a maximum compressive load of 44.90 kPa. In a constant temperature environment of 45°C, the time required for 50% water loss is extended to 18.1 hours, and the time required for 90% water loss is extended to 72.4 hours.

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