Phase change composite material and preparation method thereof

Abstract

The present invention belongs to the field of energy-saving and energy storage technology, and specifically discloses a phase change composite material and a preparation method thereof. The phase change composite material provided by the present invention comprises an organic phase change material and an acidified sepiolite fiber; wherein, the acidified sepiolite fiber is prepared by ultrasonically treating sepiolite in a mixed acid solution; the mixed acid solution comprises an organic weak acid and an inorganic strong acid. wherein, when sepiolite is treated with a specific mixed acid solution under ultrasonic conditions, the activation rate of the sepiolite fiber is accelerated, the acidification reaction time is shortened, and production energy is saved; the acidification reaction and ultrasonic treatment are carried out simultaneously, which can effectively remove impurities in the sepiolite, further disperse the sepiolite into a fibrous network structure, form more mesopores, increase its specific surface area, and enable it to subsequently load more organic phase change materials, and the combination is more firm. The acidified sepiolite fibers that have undergone specific treatment can significantly improve the latent heat performance, stability and service life of the phase change composite material.

Description

Technical Field

[0001] The present invention relates to the technical field of energy-saving and energy storage technology, and in particular to a phase-change composite material and a preparation method thereof. Background Art

[0002] Phase change materials (PCMs) are materials that can absorb or release large amounts of heat during phase transitions, with minimal or no change in their own temperature. Because they can absorb or release large amounts of latent heat while maintaining a constant temperature, PCMs have enormous potential for application in a wide range of fields, including clothing fabrics, phase change thermal storage devices, building decoration, and the fresh produce and cold chain, enabling temperature regulation and insulation.

[0003] Among the many inorganic, organic, and mixed phase-change materials studied, inorganic phase-change materials are prone to supercooling and phase separation, are generally toxic or corrosive, and are difficult to store in containers. These characteristics limit the application of inorganic compounds in phase-change energy storage systems. Compared to inorganic phase-change energy storage materials, organic phase-change energy storage materials offer advantages such as no supercooling precipitation, stable performance, and are non-toxic and non-corrosive. Existing organic phase-change composites (PCCs) face numerous technical bottlenecks. First, they suffer from poor compatibility with matrix materials, making them prone to phase separation and resulting in significant performance degradation after multiple phase-change cycles. Second, some PCCs suffer from low thermal conductivity, limiting their application in rapid thermal response scenarios. Even with the addition of thermally conductive fillers, the uneven dispersion of these fillers often leads to agglomeration, potentially reducing the overall thermal stability of the material. Furthermore, some PCCs lack mechanical strength and are susceptible to deformation and cracking under high temperatures or external forces, limiting their practical engineering applications. Finally, some composite systems lack effective means to prevent leakage of the PCCs, posing potential safety hazards and environmental risks. These challenges significantly hinder the large-scale promotion and high-performance development of organic composite PCCs. Therefore, it is crucial to develop a PCC material with excellent latent heat performance, good thermal stability, and a long service life. Summary of the Invention

[0004] To address the problems of existing phase change materials, such as poor latent heat performance, thermal stability, and short service life, the present invention provides a phase change composite material and a method for preparing the same. The present invention utilizes an organic phase change material and acidified sepiolite fibers to prepare the phase change composite material. The method utilizes a specific mixed acid solution to treat the sepiolite under ultrasonic conditions, accelerating the activation rate of the sepiolite fibers and shortening the acidification reaction time, thereby saving production energy. The simultaneous acidification reaction and ultrasonic treatment effectively remove impurities from the sepiolite, further dispersing the sepiolite into a fibrous network structure, forming more mesopores and increasing its specific surface area, enabling it to subsequently absorb more organic phase change material with a stronger bond. The specifically treated acidified sepiolite fibers significantly improve the latent heat performance, stability, and service life of the phase change composite material.

[0005] In order to solve the above technical problems, the technical solution provided by the present invention is:

[0006] The first aspect of the present invention provides a phase change composite material, comprising an organic phase change material and acidified sepiolite fibers; wherein the acidified sepiolite fibers are prepared by ultrasonically treating sepiolite in a mixed acid solution; the mixed acid solution comprises an organic weak acid and an inorganic strong acid.

[0007] During the research process, the inventors discovered that ultrasonic treatment of sepiolite alone may have the following problems: on the one hand, impurities such as carbonates and metal oxides contained in the sepiolite may clog the pores of the sepiolite or occupy adsorption sites, thereby reducing the effective adsorption area, and residual impurities may interfere with the adsorption process of the organic phase change material, reducing the stability of the phase change material during repeated use; on the other hand, the surface active sites of the sepiolite after ultrasonic treatment alone are insufficient, which reduces its adsorption performance for organic phase change materials and thus affects the overall performance of the phase change material; in addition, although ultrasonic treatment can disperse sepiolite fibers, the adsorption capacity of the treated sepiolite is limited, thereby reducing the adsorption capacity and adsorption rate of the sepiolite, and its stability is also limited.

[0008] Acidification treatment of sepiolite alone may result in the following problems: on the one hand, the increase in active sites of sepiolite treated only with acid is relatively limited, which limits the adsorption capacity of sepiolite; on the other hand, the pore connectivity of sepiolite treated only with acid is poor, and its pores are blocked, which hinders the diffusion and penetration of organic phase change material molecules; in addition, sepiolite treated only with acid will have problems such as insufficient surface roughness, fragile local structure and weak surface affinity. These factors will affect the adsorption performance of sepiolite on organic phase change materials, and thus affect the latent heat performance, thermal stability and service life of the phase change materials.

[0009] Compared with the prior art, the phase change composite material provided by the present invention defines the matrix material as sepiolite treated with a mixed acid solution under ultrasonic conditions. The ultrasonic treatment can disperse the sepiolite fibers and unclog the pores of the sepiolite. The acidification treatment can remove impurities on the surface of the sepiolite. By increasing the hydroxyl content on the surface of the acidified sepiolite fibers, the adsorption sites are increased. The two treatment methods work synergistically to increase the adsorption capacity of the acidified sepiolite fibers on the organic phase change material, thereby improving the latent heat performance of the phase change composite material. The ultrasonic treatment can expose more hydrophobic groups on the sepiolite fibers, and the acidification treatment can adjust the surface charge. The two treatment methods synergistically enhance the binding force between the acidified sepiolite fibers and the organic phase change material, thereby improving the thermal stability and latent heat performance of the phase change composite material. After ultrasonic treatment, the sepiolite forms a fiber network. The network structure can inhibit the disordered migration of organic phase change materials during the heating process of the phase change material, and avoid the collapse of the phase change composite material structure caused by excessive migration of organic phase change materials; impurities such as carbonates and metal oxides serve as catalytic sites for the thermal decomposition reaction of the phase change material. Acidification treatment removes the above impurities and thus inhibits the thermal decomposition reaction of the phase change composite material under high temperature conditions. At the same time, acidification and ultrasonic treatment of sepiolite can effectively improve the latent heat performance and thermal stability of the phase change composite material; ultrasonic treatment can avoid the problem of excessive etching of sepiolite fibers during the acidification process, which may cause the phase change composite material to break or collapse in pores, and retain the complete fiber network structure. Acidification treatment can ensure the uniform distribution of pores on the sepiolite. The synergistic effect of the two significantly extends the service life of the phase change composite material.

[0010] Ultrasonic acidification of sepiolite using only strong inorganic acids can easily lead to collapse, which in turn inhibits the performance improvement of the phase change composite material. During their research, the inventors accidentally discovered that when ultrasonic acidification of sepiolite using a mixed acid solution containing strong inorganic acids and weak organic acids as solutes, the simultaneous action of the weak organic acid and the strong inorganic acid can prevent excessive acidification by a single strong inorganic acid during the removal and dispersion of associated minerals from sepiolite fibers, which can lead to pore structure collapse in the fibers. The pore structure of the sepiolite fibers is optimized, increasing the loading capacity of the sepiolite for organic phase change materials. Furthermore, the weak organic acid, by providing organic groups, improves its effective adsorption and adsorption stability for organic phase change materials, thereby greatly improving the latent heat performance, thermal stability, and service life of the phase change composite material.

[0011] Preferably, the mass ratio of the acidified sepiolite fiber to the organic phase change material is 1:(1.5-2).

[0012] Preferably, the organic phase change material is paraffin.

[0013] Preferably, the concentration of the organic weak acid in the mixed acid solution is 5 mol / L-5.5 mol / L.

[0014] Preferably, the concentration of the inorganic strong acid in the mixed acid solution is 5 mol / L-5.5 mol / L.

[0015] The preferred concentrations of the inorganic strong acid and the organic weak acid are beneficial to further improving the optimization of the pore structure of the acidified sepiolite fiber by the mixed acid solution, and avoiding excessive etching or inadequate etching that affects the performance of the phase change composite material.

[0016] Preferably, the inorganic strong acid is at least one of hydrochloric acid or nitric acid.

[0017] Preferably, the organic weak acid is at least one of acetic acid or citric acid.

[0018] By further limiting the specific substances of the inorganic strong acid and the organic weak acid, it is beneficial to further improve the optimization effect of the pore structure on the sepiolite fiber, thereby improving the performance of the phase change composite material.

[0019] Preferably, the method for preparing the acidified sepiolite fiber comprises the following steps: adding sepiolite into a mixed acid solution, and performing ultrasonic treatment at 30° C.-35° C. to obtain the acidified sepiolite fiber.

[0020] The preparation process of the acidified sepiolite fiber provided by the present invention is simple. It only requires ultrasonic acidification treatment of the sepiolite at a specific temperature to optimize the pore structure of the acidified sepiolite fiber, so that it forms a uniform fiber network structure, increases its loading capacity and loading stability for organic phase change materials, and improves the latent heat performance, thermal stability and service life of the phase change composite material.

[0021] Preferably, the mass-to-volume ratio of the sepiolite to the mixed acid solution is (95-105) g:1 L.

[0022] Preferably, the power of the ultrasonic treatment is 350W-370W.

[0023] Preferably, the ultrasonic treatment time is 1 h-1.2 h.

[0024] The preferential ultrasonic treatment conditions enable the sepiolite to form a uniform fiber network structure, further improving the service life of the phase change composite material.

[0025] It should be further explained that the sepiolite treated with ultrasound needs to be washed with water until the pH value is 6-7, and then dried to obtain acidified sepiolite fibers.

[0026] A second aspect of the present invention provides a method for preparing the above-mentioned phase change composite material, comprising the following steps:

[0027] Step 1: mixing the weighed acidified sepiolite fiber and the organic phase change material, and performing a first heat preservation at 75° C.-85° C. to obtain a mixed material;

[0028] Step 2: heat-insulating the mixed material at 100° C.-105° C. for a second time to obtain a phase change composite material.

[0029] The preparation method of the phase change composite material provided by the present invention is simple and convenient, has a short preparation time, and the raw materials used are non-toxic and harmless, and has a wide range of applications.

[0030] Preferably, in step 1, the first insulation time is 30 min-35 min.

[0031] It should be further explained that, in step 1, the first heat preservation is a water bath constant temperature heat preservation, and stirring is required during the first heat preservation.

[0032] Preferably, in step 2, the second insulation time is 6h-6.5h.

[0033] It should be further explained that, in step 2, the second heat preservation condition is to place the mixture in a vacuum thermostat for heat preservation.

[0034] It should be further explained that in step 2, after the second insulation is completed, the material needs to be wrapped with filter paper and placed in a constant temperature drying oven at 80°C-90°C to remove excess paraffin.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] (1) Using a specific mixed acid solution to treat sepiolite under ultrasonic conditions can not only remove impurities in sepiolite and further disperse the sepiolite fibers, but also form more mesopores on the acidified sepiolite fibers, increasing their specific surface area. The specific treatment method greatly reduces the reaction time, and acidified sepiolite fibers with good performance are obtained in a short time.

[0037] (2) The acidified sepiolite fiber can not only better combine with the organic phase change material, but also absorb more organic phase change material. The maximum loading capacity of the acidified sepiolite fiber for organic phase change material reaches 67.97%. The maximum melting latent heat and crystallization latent heat of the phase change composite material are 110.98 J / g and 109.54 J / g, respectively. The larger enthalpy value it can generate has better thermal stability and better heat absorption and thermal insulation effect.

[0038] (3) After the phase change composite material provided by the present invention is thermally cycled 30 times in the temperature range from room temperature to 200°C, its latent heat of melting and latent heat of crystallization can still reach 108.55 J / g and 109.50 J / g, and after being recycled, it still has good chemical structure, crystal structure and shape stability, and has a long service life. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 This is a SEM image of the acidified sepiolite fiber prepared in Example 1 of the present invention;

[0040] Figure 2 This is an SEM image of the phase change composite material prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0041] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments and drawings. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0042] Example 1

[0043] This embodiment provides a phase change composite material, including paraffin wax and acidified sepiolite fibers, wherein the mass ratio of the acidified sepiolite fibers to the paraffin wax is 1:2;

[0044] The preparation method of acidified sepiolite fiber comprises the following steps: adding sepiolite into a mixed acid solution, ultrasonically treating the solution at 30°C and 360W for 1 hour, and washing the solution with water until the pH value reaches 6 to obtain the acidified sepiolite fiber;

[0045] The mass volume ratio of sepiolite to mixed acid solution is 100 g:1 L, the concentration of hydrochloric acid in the mixed acid solution is 5 mol / L, and the concentration of acetic acid is 5 mol / L;

[0046] This embodiment also provides a method for preparing the above-mentioned phase change composite material, comprising the following steps:

[0047] Step 1: Mix the weighed acidified sepiolite fiber and the organic phase change material, and heat them in a water bath at 75° C. for 30 minutes. Stir them during the heat preservation to obtain a mixed material;

[0048] Step 2: Place the mixed material in a vacuum constant temperature box at 100°C for insulation, and control the insulation time to be 6 hours. Then wrap the material with filter paper, place it in a constant temperature drying box, and remove excess paraffin at 90°C to obtain a phase change composite material.

[0049] Example 2

[0050] This embodiment provides a phase change composite material, including paraffin wax and acidified sepiolite fibers, wherein the mass ratio of the acidified sepiolite fibers to the paraffin wax is 1:1.5;

[0051] The preparation method of acidified sepiolite fiber comprises the following steps: adding sepiolite to a mixed acid solution, ultrasonically treating the solution at 35° C. and 350W for 1.2 hours, and washing the solution with water until the pH reaches 7 to obtain the acidified sepiolite fiber;

[0052] The mass volume ratio of sepiolite to mixed acid solution is 95 g:1 L, the concentration of nitric acid in the mixed acid solution is 5 mol / L, and the concentration of acetic acid is 5.5 mol / L;

[0053] This embodiment also provides a method for preparing the above-mentioned phase change composite material, comprising the following steps:

[0054] Step 1: Mix the weighed acidified sepiolite fiber and the organic phase change material, and heat them in a water bath at 85° C. for 35 minutes while stirring to obtain a mixed material;

[0055] Step 2: Place the mixed material in a vacuum constant temperature box at 105°C for insulation, and control the insulation time to be 6.5 hours. Then wrap the material with filter paper and place it in a constant temperature drying box. Remove excess paraffin at 80°C to obtain a phase change composite material.

[0056] Example 3

[0057] This embodiment provides a phase change composite material, including paraffin wax and acidified sepiolite fibers, wherein the mass ratio of the acidified sepiolite fibers to the paraffin wax is 1:2;

[0058] The preparation method of acidified sepiolite fiber comprises the following steps: adding sepiolite to a mixed acid solution, ultrasonically treating the solution at 32° C. and 370W for 1 hour, and washing the solution with water until the pH reaches 7 to obtain the acidified sepiolite fiber;

[0059] The mass volume ratio of sepiolite to mixed acid solution is 105 g:1 L, the concentration of hydrochloric acid in the mixed acid solution is 5.5 mol / L, and the concentration of citric acid is 5 mol / L;

[0060] This embodiment also provides a method for preparing the above-mentioned phase change composite material, comprising the following steps:

[0061] Step 1: Mix the weighed acidified sepiolite fiber and the organic phase change material, and keep them in a water bath at 80° C. for 35 minutes while stirring to obtain a mixed material;

[0062] Step 2: Place the mixed material in a vacuum constant temperature box at 100°C for insulation, and control the insulation time to be 6 hours. Then wrap the material with filter paper, place it in a constant temperature drying box, and remove excess paraffin at 90°C to obtain a phase change composite material.

[0063] Comparative Example 1

[0064] This comparative example provides a phase change composite material, which differs from Example 1 in that only hydrochloric acid solution is used to acidify the sepiolite; the details are as follows:

[0065] The invention comprises paraffin wax and acidified sepiolite fiber, wherein the mass ratio of the acidified sepiolite fiber to the paraffin wax is 1:2;

[0066] The preparation method of acidified sepiolite fiber comprises the following steps: adding sepiolite into a mixed acid solution, ultrasonically treating the solution at 30°C and 360W for 1 hour, and washing the solution with water until the pH value reaches 6 to obtain the acidified sepiolite fiber;

[0067] The mass volume ratio of sepiolite and 5 mol / L hydrochloric acid solution is 100 g:1 L;

[0068] This comparative example also provides a method for preparing the above-mentioned phase change composite material, comprising the following steps:

[0069] Step 1: Mix the weighed acidified sepiolite fiber and the organic phase change material, and heat them in a water bath at 75° C. for 30 minutes. Stir them during the heat preservation to obtain a mixed material;

[0070] Step 2: Place the mixed material in a vacuum constant temperature box at 100°C for insulation, and control the insulation time to be 6 hours. Then wrap the material with filter paper, place it in a constant temperature drying box, and remove excess paraffin at 90°C to obtain a phase change composite material.

[0071] Comparative Example 2

[0072] This comparative example provides a phase change composite material, which differs from Example 1 in that only acetic acid solution is used to acidify the sepiolite; the details are as follows:

[0073] The invention comprises paraffin wax and acidified sepiolite fiber, wherein the mass ratio of the acidified sepiolite fiber to the paraffin wax is 1:2;

[0074] The preparation method of acidified sepiolite fiber comprises the following steps: adding sepiolite into a mixed acid solution, ultrasonically treating the solution at 30°C and 360W for 1 hour, and washing the solution with water until the pH value reaches 6 to obtain the acidified sepiolite fiber;

[0075] The mass volume ratio of sepiolite and 5 mol / L acetic acid solution is 100 g:1 L;

[0076] This comparative example also provides a method for preparing the above-mentioned phase change composite material, comprising the following steps:

[0077] Step 1: Mix the weighed acidified sepiolite fiber and the organic phase change material, and heat them in a water bath at 75° C. for 30 minutes. Stir them during the heat preservation to obtain a mixed material;

[0078] Step 2: Place the mixed material in a vacuum constant temperature box at 100°C for insulation, control the insulation time to 6 hours, wrap the material with filter paper, place it in a constant temperature drying box, remove excess paraffin at 90°C, and obtain a phase change composite material.

[0079] Comparative Example 3

[0080] This comparative example provides a phase change composite material, which differs from Example 1 in that the sepiolite is first subjected to ultrasonic treatment and then to acidification treatment; the details are as follows:

[0081] This embodiment provides a phase change composite material, including paraffin wax and acidified sepiolite fibers, wherein the mass ratio of the acidified sepiolite fibers to the paraffin wax is 1:2;

[0082] The preparation method of acidified sepiolite fiber comprises the following steps: ultrasonically treating sepiolite at 360W at 30°C for 1 hour, adding the treated sepiolite into a mixed acid solution, reacting at 30°C for 1 hour, and washing with water until the pH reaches 6, thereby obtaining the acidified sepiolite fiber;

[0083] The mass volume ratio of sepiolite to mixed acid solution is 100 g:1 L, the concentration of hydrochloric acid in the mixed acid solution is 5 mol / L, and the concentration of acetic acid in the mixed acid solution is 5 mol / L;

[0084] This comparative example also provides a method for preparing the above-mentioned phase change composite material, comprising the following steps:

[0085] Step 1: Mix the weighed acidified sepiolite fiber and the organic phase change material, and heat them in a water bath at 75° C. for 30 minutes. Stir them during the heat preservation to obtain a mixed material;

[0086] Step 2: Place the mixed material in a vacuum constant temperature box at 100°C for insulation, and control the insulation time to be 6 hours. Then wrap the material with filter paper, place it in a constant temperature drying box, and remove excess paraffin at 90°C to obtain a phase change composite material.

[0087] Comparative Example 4

[0088] This comparative example provides a phase change composite material, which is different from Example 1 in that only ultrasonic treatment is performed without acidification treatment, as follows:

[0089] The preparation method of the acidified sepiolite fiber comprises the following steps: treating the sepiolite with ultrasound at 360W at 30°C for 1 hour, washing with water until the pH value is 6, and obtaining the acidified sepiolite fiber;

[0090] This comparative example also provides a method for preparing the above-mentioned phase change composite material, comprising the following steps:

[0091] Step 1: Mix the weighed acidified sepiolite fiber and the organic phase change material, and heat them in a water bath at 75° C. for 30 minutes. Stir them during the heat preservation to obtain a mixed material;

[0092] Step 2: Place the mixed material in a vacuum constant temperature box at 100°C for insulation, control the insulation time to 6 hours, wrap the material with filter paper, place it in a constant temperature drying box, remove excess paraffin at 90°C, and obtain a phase change composite material.

[0093] Comparative Example 5

[0094] This comparative example provides a phase change composite material, which differs from Example 1 in that acetic acid is replaced by an equal amount of metasilicic acid;

[0095] Other ingredients and preparation methods are the same as those in Example 1.

[0096] Effect Examples

[0097] The specific surface area, pore structure, paraffin loading, latent heat performance, and thermal stability of the acidified sepiolite fibers prepared in Examples 1-3 and Comparative Examples 1-5 were tested;

[0098] Among them, the structural performance tests of acidified sepiolite fiber are as follows:

[0099] The specific surface area and pore structure of sepiolite were characterized by gas adsorption method using a BET surface area tester (Micromeritics ASAP 2020);

[0100] The paraffin loading was determined as follows:

[0101] Thermogravimetric analysis (TGA) was used to observe the thermal decomposition behavior of the phase change composites to determine the loading amount of paraffin wax. The analysis was carried out in an inert nitrogen atmosphere with a flow rate of 50 mL / min and a heating rate of 10 °C / min.

[0102] Thermal performance tests are as follows:

[0103] The thermal properties of the composite phase change materials were measured using differential scanning calorimetry (DSC, TGA / DSC3+, Mettler-Toledo) with a heating / cooling rate of 10 °C / min and a temperature range of 25–150 °C;

[0104] Thermal stability performance test is as follows:

[0105] The thermal properties of the composite phase change materials were measured using differential scanning calorimetry (DSC, TGA / DSC3+, Mettler-Toledo) at a heating / cooling rate of 10°C / min over a temperature range of 25°C–150°C. Accelerated thermal cycling tests were performed to evaluate the thermal reliability and reusability of the phase change composites. The samples were heated to 80°C for 1 hour and then cooled to room temperature for 30 cycles.

[0106] Where, ηm (%) = |ΔHm b −ΔHm a | / ΔHm b ×100%;

[0107] ηc (%) = |ΔHc b –ΔHc a | / ΔHcb×100%;

[0108] ηm is the melting coefficient, ηc is the crystallization coefficient, ΔHm b is the latent heat of fusion before the cycle, ΔHm a is the latent heat of melting after cycling, Tm b is the melting temperature before cycling, Tm a is the melting temperature after the cycle, ΔHc a is the latent heat of crystallization after the cycle, ΔHc b is the latent heat of crystallization before cycling, Tc a is the crystallization temperature after cycling, Hcb is the crystallization temperature before cycling;

[0109] Specific test indicators and test results are shown in Table 1:

[0110] Table 1 Performance test results of phase change composite materials and acidified sepiolite fibers

[0111]

[0112] Table 2 Performance test results of phase change composite materials after 30 cycles

[0113]

[0114] In summary, it can be seen from Tables 1-2 of the present invention that the acidified sepiolite fiber provided by the embodiments of the present invention has an excellent specific surface area, and ultrasonic acidification improves the pore structure of the sepiolite fiber, so that the acidified sepiolite fiber has a suitable specific surface area, pore volume and pore diameter. The combined effect of these factors improves the adsorption capacity of the acidified sepiolite fiber for paraffin, thereby increasing the paraffin loading amount, thereby preparing a phase change composite material with excellent latent heat performance and thermal stability.

[0115] In Comparative Example 1 of the present invention, only hydrochloric acid solution was used to acidify the sepiolite during ultrasound treatment. Although the specific surface area was increased, the acidification was excessive, which destroyed the pore structure and reduced the pore size, making it unfavorable for the adsorption of paraffin. After thermal cycling, the paraffin was also easily lost, resulting in poor thermal stability.

[0116] In Comparative Example 2 of the present invention, only acetic acid solution was used to acidify the sepiolite while ultrasonicating. Although the pore size was appropriate, the specific surface area and pore volume were relatively small, and the paraffin loading was lower than that in Example 1, thereby reducing its latent heat performance and thermal stability.

[0117] Comparative Example 3 of the present invention adopts a method of first ultrasonically treating the sepiolite and then performing an acidification treatment. The initial ultrasound only physically disperses the sepiolite fibers. During the subsequent acidification, due to the lack of ultrasonic synergistic treatment, the acidification is insufficient, impurities such as calcite and talc are removed less, and the fibers are not well dispersed, resulting in a small specific surface area and a large pore size. The acidified sepiolite fibers have a low paraffin loading capacity, thereby reducing the latent heat performance and thermal stability of the phase change composite material.

[0118] Comparative Example 4 of the present invention uses ultrasonic treatment on sepiolite. Impurities in the sepiolite are not removed, and the sepiolite fibers are basically not dispersed. Some impurities may clog the pores of the sepiolite or occupy adsorption sites, resulting in a small specific surface area, small pore volume, large pore diameter, and few active sites of the sepiolite, which is not conducive to the adsorption of paraffin. Most of the paraffin remains on the fiber surface and is easily lost during preparation, resulting in poor latent heat performance and thermal stability.

[0119] In Comparative Example 5 of the present invention, ultrasound combined with a mixed acid treatment consisting of hydrochloric acid and the inorganic weak acid metasilicic acid removed impurities such as calcite and talc. However, the acidified sepiolite fibers had larger pore sizes, a lower paraffin loading, a lower enthalpy value, and poorer latent heat performance. Later thermal stability tests revealed a significant decrease in thermal stability compared to Experimental Example 1.

[0120] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions or improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A phase change composite material, characterized in that: including organic phase change materials and acidified sepiolite fibers; The preparation method of the acidified sepiolite fiber comprises the following steps: adding sepiolite to a mixed acid solution and performing ultrasonic treatment at 30° C.-35° C. to obtain the acidified sepiolite fiber; The mixed acid solution comprises 5 mol / L-5.5 mol / L of an organic weak acid and 5 mol / L-5.5 mol / L of an inorganic strong acid; the organic weak acid is at least one of acetic acid or citric acid; the inorganic strong acid is at least one of hydrochloric acid or nitric acid; The mass volume ratio of the sepiolite and the mixed acid solution is (95-105) g:1 L; The power of the ultrasonic treatment is 350W-370W; The ultrasonic treatment time is 1 h-1.2 h.

2. The phase change composite material according to claim 1, wherein The mass ratio of the acidified sepiolite fiber to the organic phase change material is 1:(1.5-2).

3. A method for preparing the phase change composite material according to any one of claims 1 to 2, characterized in that: The steps include: Step 1: mixing the weighed acidified sepiolite fiber and the organic phase change material, and performing a first heat preservation at 75° C.-85° C. to obtain a mixed material; Step 2: heat-insulating the mixed material at 100° C.-105° C. for a second time to obtain a phase change composite material.

4. The method for preparing a phase change composite material according to claim 3, wherein: In step 1, the first insulation time is 30 min-35 min; and / or In step 2, the second insulation time is 6h-6.5h.

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