Phase change composite material and preparation method thereof

Abstract

The invention belongs to the technical field of energy conservation and storage, and particularly discloses a phase change composite material and a preparation method thereof. The phase-change composite material provided by the invention comprises an organic phase-change material and acidified sepiolite fibers, wherein the acidified sepiolite fiber is prepared by carrying out ultrasonic treatment on sepiolite in a mixed acid solution; the mixed acid solution comprises organic weak acid and inorganic strong acid. Wherein when sepiolite is treated by using a specific mixed acid solution under an ultrasonic condition, the activation rate of sepiolite fibers is increased, the acidification reaction time is shortened, and production energy is saved; the acidification reaction and the ultrasonic treatment are carried out at the same time, impurities in the sepiolite can be effectively removed, the sepiolite is further dispersed into a fiber net structure, more mesopores are formed, the specific surface area of the sepiolite is increased, the sepiolite can load more organic phase change materials subsequently, and the combination is firmer. The acidified sepiolite fiber subjected to specific treatment can obviously improve the latent heat performance, the stability and the service life of the phase change composite material.

Description

Technical Field

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

[0002] A phase change material is a material that can absorb or release a large amount of heat while its own temperature remains unchanged or changes very little during a phase transition. Due to the fact that the phase change material can absorb or release a large amount of latent heat and maintain a constant temperature during the phase transition process, it shows great application potential in many fields, such as clothing fabrics, phase change heat storage devices, building decoration, fresh food and cold chain preservation, etc., and can adjust temperature and provide heat insulation.

[0003] Among the numerous inorganic, organic, and their mixture phase change materials that have been studied, inorganic phase change materials are prone to supercooling and phase separation phenomena, generally have toxicity or corrosiveness, and are not conducive to being contained in containers. These characteristics limit the application of inorganic compounds in phase change energy storage systems. Compared with inorganic phase change energy storage materials, organic phase change energy storage materials have the advantages of no supercooling precipitation, stable performance, non-toxicity, and non-corrosiveness. However, there are still many technical bottlenecks in existing organic phase change composite materials: on the one hand, the compatibility between organic phase change composite materials and matrix materials is poor, and phase separation is prone to occur, resulting in a significant decline in the performance of the phase change material after multiple phase change cycles; on the other hand, the thermal conductivity of some phase change composite materials is relatively low, which restricts their application in scenarios with rapid heat response. Even when adding heat conduction enhancing fillers, agglomeration is often caused due to uneven dispersion of the fillers, which may instead reduce the overall thermal stability of the material; in addition, the mechanical strength of some organic phase change composite materials is insufficient, and they are prone to deformation and cracking under high temperature or external force, restricting the scope of their practical engineering applications; at the same time, some composite systems lack effective means to inhibit the leakage of organic phase change materials, posing potential safety hazards and environmental pollution risks. These problems seriously hinder the large-scale popularization and high-performance development of organic composite phase change materials. Therefore, it is of great significance to provide a phase change material with excellent latent heat performance, good thermal stability, and long service life. Summary of the Invention

[0004] Aiming at the problems of poor latent heat performance, poor thermal stability and short service life of existing phase change materials, the present invention provides a phase change composite material and a preparation method thereof. The present invention uses an organic phase change material and acidified sepiolite fiber to prepare a phase change composite material. Among them, when treating sepiolite with a specific mixed acid solution under ultrasonic conditions, the activation rate of 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 sepiolite, further disperse sepiolite into a fiber network structure, form more mesopores, increase its specific surface area, enable it to adsorb more organic phase change materials subsequently, and the combination is more firm. The acidified sepiolite fiber treated by a specific treatment can significantly improve the latent heat performance, stability and service life of the phase change composite material.

[0005] To solve the above technical problems, the technical solution provided by the present invention is: The first aspect of the present invention provides a phase change composite material, including an organic phase change material and acidified sepiolite fiber; wherein, the acidified sepiolite fiber is prepared by ultrasonic treatment of sepiolite in a mixed acid solution; the mixed acid solution includes an organic weak acid and an inorganic strong acid.

[0006] During the research process, the inventors found that the following problems may exist when only ultrasonic treatment is performed on sepiolite: on the one hand, impurities such as carbonates and metal oxides contained in sepiolite may block the pores of sepiolite or occupy the adsorption sites, thereby reducing the effective adsorption area, and the residual impurities may interfere with the adsorption process of the organic phase change material and reduce the stability of the phase change material during repeated use; on the other hand, the surface active sites of sepiolite after only ultrasonic treatment are insufficient, reducing its adsorption performance for the organic phase change material, thereby affecting the comprehensive performance of the phase change material; in addition, although ultrasonic treatment can disperse sepiolite fiber, the adsorption capacity of sepiolite after treatment is limited, thereby reducing the adsorption capacity and adsorption rate of sepiolite, and its stability will also be limited.

[0007] The following problems may exist when only acidification treatment is performed on sepiolite: on the one hand, the increase in the amount of active sites of sepiolite treated only by acidification is relatively limited, restricting the adsorption capacity of sepiolite; on the other hand, the pore connectivity of sepiolite treated only by acidification is poor, its pores are blocked, preventing the molecular diffusion and penetration of the organic phase change material; in addition, sepiolite treated only by acidification will have problems such as insufficient surface roughness, fragile local structure and weak surface affinity. These factors will all affect the adsorption performance of sepiolite for the organic phase change material, thereby affecting the latent heat performance, thermal stability and service life of the phase change material.

[0008] Compared with the prior art, in the phase change composite material provided by the present invention, the matrix material is defined as sepiolite treated with a mixed acid solution under ultrasonic conditions. Ultrasonic treatment can disperse the fibers of sepiolite and dredge the pores of sepiolite. Acidification treatment can remove the surface impurities of sepiolite, increase the adsorption sites by increasing the hydroxyl content on the surface of acidified sepiolite fibers. The two treatment methods act synergistically to increase the adsorption amount of acidified sepiolite fibers to the organic phase change material, thereby improving the latent heat performance of the phase change composite material; ultrasonic treatment can expose more hydrophobic groups on the sepiolite fibers, and 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, sepiolite forms a fiber network structure. During the heating process of the phase change material, it can inhibit the disordered migration of the organic phase change material and avoid the collapse of the structure of the phase change composite material caused by excessive migration of the organic phase change material; impurities such as carbonates and metal oxides act as catalytic sites for the thermal decomposition reaction of the phase change material. Acidification treatment inhibits the thermal decomposition reaction of the phase change composite material under high temperature conditions by removing the above impurities. At the same time, acidifying and ultrasonic treating 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 acidification, resulting in fracture or pore collapse of the phase change composite material, and retain a complete fiber network structure. Acidification treatment can ensure the uniform distribution of pores on sepiolite. The two work together to significantly extend the service life of the phase change composite material.

[0009] When only using inorganic strong acid to perform ultrasonic acidification on sepiolite, the problem of sepiolite collapse is likely to occur, thereby inhibiting the improvement of the performance of the phase change composite material. The inventor accidentally discovered during the research process that when using a mixed acid solution with inorganic strong acid and organic weak acid as solutes to perform acidification ultrasonic treatment on sepiolite, the organic weak acid and the inorganic strong acid act simultaneously, which can avoid excessive acidification during the removal and dispersion of the associated minerals of sepiolite fibers by a single inorganic strong acid, resulting in the problem of pore structure collapse of the fibers. The pore structure of sepiolite fibers is optimized, and the loading amount of sepiolite to the organic phase change material is increased; and the organic weak acid provides organic groups, improving its effective adsorption and adsorption stability to the organic phase change material, thereby greatly improving the latent heat performance, thermal stability and service life of the phase change composite material.

[0010] Preferably, the mass ratio of the acidified sepiolite fibers to the organic phase change material is 1:(1.5 - 2).

[0011] Preferably, the organic phase change material is paraffin.

[0012] Preferably, the concentration of the organic weak acid in the mixed acid solution is 5 mol / L - 5.5 mol / L.

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

[0014] The preferred concentrations of the inorganic strong acid and the organic weak acid are conducive to further optimizing the pore structure of the acidified sepiolite fiber, and avoiding over-etching or insufficient etching that may affect the performance of the phase change composite material.

[0015] Preferably, the inorganic strong acid is at least one of hydrochloric acid and nitric acid.

[0016] Preferably, the organic weak acid is at least one of acetic acid and citric acid.

[0017] By further defining the specific substances of the inorganic strong acid and the organic weak acid, it is conducive to further improving the optimization effect of the pore structure on the sepiolite fiber, and thus improving the performance of the phase change composite material.

[0018] Preferably, the method for preparing the acidified sepiolite fiber includes the following steps: adding sepiolite into the mixed acid solution, and performing ultrasonic treatment at 30°C - 35°C to obtain the acidified sepiolite fiber.

[0019] The preparation process of the acidified sepiolite fiber provided by the present invention is simple. By performing ultrasonic acidification treatment on sepiolite at a specific temperature, the pore structure of the acidified sepiolite fiber can be optimized, forming a uniform fiber network structure, improving its loading capacity and loading stability for the organic phase change material, and enhancing the latent heat performance, thermal stability and service life of the phase change composite material.

[0020] Preferably, the mass-volume ratio of the sepiolite to the mixed acid solution is (95 - 105) g:1 L.

[0021] Preferably, the power of the ultrasonic treatment is 350 W - 370 W.

[0022] Preferably, the time of the ultrasonic treatment is 1 h - 1.2 h.

[0023] The preferred ultrasonic treatment conditions enable sepiolite to form a uniform fiber network structure, further improving the service life of the phase change composite material.

[0024] It should be further noted that the sepiolite treated by ultrasonic treatment needs to be washed with water until the pH is 6 - 7, and then dried to obtain the acidified sepiolite fiber.

[0025] The second aspect of the present invention provides a method for preparing the above-mentioned phase change composite material, including the following steps: Step 1: Mix the weighed acidified sepiolite fiber and the organic phase change material, and perform the first heat preservation at 75°C - 85°C to obtain a mixed material; Step 2: Keep the mixed material at 100°C - 105°C for the second heat preservation to obtain the phase change composite material.

[0026] The preparation method of the phase change composite material provided by the present invention is simple, has a short preparation time, and the preparation raw materials are non-toxic and harmless, with a wide range of applications.

[0027] Preferably, in Step 1, the time for the first heat preservation is 30 min - 35 min.

[0028] It should be further noted that in Step 1, the first heat preservation is a water bath constant temperature heat preservation, and stirring treatment is also required during the first heat preservation.

[0029] Preferably, in Step 2, the time for the second heat preservation is 6 h - 6.5 h.

[0030] It should be further noted that in Step 2, the condition for the second heat preservation is to carry out the heat preservation in a vacuum constant temperature oven.

[0031] It should be further noted that after the second heat preservation in Step 2, the material also needs to be wrapped with filter paper and placed in a constant temperature drying oven to remove the excess paraffin at 80°C - 90°C.

[0032] Compared with the prior art, the present invention has the following beneficial effects: (1) Using a specific mixed acid solution to treat sepiolite under ultrasonic conditions can not only remove impurities in sepiolite, further disperse sepiolite fibers, but also form more mesopores on the acidified sepiolite fibers, increasing its specific surface area. The specific treatment method greatly reduces the reaction time, and acidified sepiolite fibers with good performance can be obtained in a short time; (2) Acidified sepiolite fibers can not only better combine with organic phase change materials, but also adsorb more organic phase change materials. The maximum loading capacity of acidified sepiolite fibers for organic phase change materials 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. It can generate a larger enthalpy value, has better thermal stability, and better heat absorption and heat preservation effects; (3) After the phase change composite material provided by the present invention is used for 30 thermal cycles in the temperature range from room temperature to 200°C, its melting latent heat and crystallization latent heat can still reach 108.55 J / g and 109.50 J / g. And after cyclic use, it also has good chemical structure, crystal structure and shape stability, and has a long service life. Description of the Drawings

[0033] Figure 1 It is the SEM diagram of the acidified sepiolite fibers prepared in Example 1 of the present invention; Figure 2 SEM image of the phase change composite material prepared in Example 1 of the present invention. Detailed implementation manners

[0034] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to embodiments and the accompanying drawings. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0035] Example 1 This example provides a phase change composite material, including paraffin wax and acidified sepiolite fibers. The mass ratio of acidified sepiolite fibers to paraffin wax is 1:2; The preparation method of the acidified sepiolite fibers includes the following steps: adding sepiolite into a mixed acid solution, performing ultrasonic treatment at 30 °C and 360 W for 1 h, washing with water until the pH is 6 to obtain acidified sepiolite fibers; The mass-volume ratio of sepiolite to the 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; This example also provides a preparation method of the above phase change composite material, including the following steps: Step 1: Mix the weighed acidified sepiolite fibers and the organic phase change material, perform water bath constant temperature insulation at 75 °C, control the insulation time to be 30 min, and stir during the insulation to obtain a mixed material; Step 2: Place the mixed material in a vacuum constant temperature oven at 100 °C for insulation, control the insulation time to be 6 h, then wrap the material with filter paper, place it in a constant temperature drying oven, and remove the excess paraffin wax at 90 °C to obtain the phase change composite material.

[0036] Example 2 This example provides a phase change composite material, including paraffin wax and acidified sepiolite fibers. The mass ratio of acidified sepiolite fibers to paraffin wax is 1:1.5; The preparation method of the acidified sepiolite fibers includes the following steps: adding sepiolite into a mixed acid solution, performing ultrasonic treatment at 35 °C and 350 W for 1.2 h, washing with water until the pH is 7 to obtain acidified sepiolite fibers; The mass-volume ratio of sepiolite to the 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; This example also provides a preparation method of the above phase change composite material, including the following steps: Step 1: Mix the weighed acidified sepiolite fibers and the organic phase change material, perform water bath constant temperature insulation at 85 °C, control the insulation time to be 35 min, and stir during the insulation to obtain a mixed material; Step 2: Place the mixed material in a vacuum constant temperature oven at 105°C for heat preservation, control the heat preservation time to be 6.5 h, then wrap the material with filter paper, place it in a constant temperature drying oven, and remove the excess paraffin at 80°C to obtain the phase change composite material.

[0037] Example 3 This example provides a phase change composite material, including paraffin and acidified sepiolite fibers, and the mass ratio of acidified sepiolite fibers to paraffin is 1:2; The preparation method of the acidified sepiolite fibers includes the following steps: Add sepiolite to the mixed acid solution, perform ultrasonic treatment at 32°C and 370 W for 1 h, wash with water until the pH is 7 to obtain acidified sepiolite fibers; The mass-volume ratio of sepiolite to the 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; This example also provides the preparation method of the above phase change composite material, including the following steps: Step 1: Mix the weighed acidified sepiolite fibers and the organic phase change material, perform water bath constant temperature heat preservation at 80°C, control the heat preservation time to be 35 min, and stir during heat preservation to obtain the mixed material; Step 2: Place the mixed material in a vacuum constant temperature oven at 100°C for heat preservation, control the heat preservation time to be 6 h, then wrap the material with filter paper, place it in a constant temperature drying oven, and remove the excess paraffin at 90°C to obtain the phase change composite material.

[0038] Comparative Example 1 This comparative example provides a phase change composite material, which is different from Example 1 in that only sepiolite is acidified with hydrochloric acid solution; specifically as follows: It includes paraffin and acidified sepiolite fibers, and the mass ratio of acidified sepiolite fibers to paraffin is 1:2; The preparation method of the acidified sepiolite fibers includes the following steps: Add sepiolite to the mixed acid solution, perform ultrasonic treatment at 30°C and 360 W for 1 h, wash with water until the pH is 6 to obtain acidified sepiolite fibers; The mass-volume ratio of sepiolite to the hydrochloric acid solution with a concentration of 5 mol / L is 100 g:1 L; This comparative example also provides the preparation method of the above phase change composite material, including the following steps: Step 1: Mix the weighed acidified sepiolite fibers and the organic phase change material, perform water bath constant temperature heat preservation at 75°C, control the heat preservation time to be 30 min, and stir during heat preservation to obtain the mixed material; Step 2: Place the mixed material in a vacuum constant temperature oven at 100°C for heat preservation, control the heat preservation time to be 6 hours, then wrap the material with filter paper, place it in a constant temperature drying oven, and remove the excess paraffin at 90°C to obtain the phase change composite material.

[0039] Comparative Example 2 This comparative example provides a phase change composite material, which is different from Example 1 in that only sepiolite is acidified with acetic acid solution; specifically as follows: It includes paraffin and acidified sepiolite fibers, and the mass ratio of acidified sepiolite fibers to paraffin is 1:2; The preparation method of acidified sepiolite fibers includes the following steps: Add sepiolite to a mixed acid solution, perform ultrasonic treatment at 30°C and 360W for 1 hour, wash with water until the pH is 6 to obtain acidified sepiolite fibers; The mass-volume ratio of sepiolite to acetic acid solution with a concentration of 5mol / L is 100g:1L; This comparative example also provides the preparation method of the above phase change composite material, including the following steps: Step 1: Mix the weighed acidified sepiolite fibers and the organic phase change material, perform water bath constant temperature heat preservation at 75°C, control the heat preservation time to be 30 minutes, and stir during heat preservation to obtain a mixed material; Step 2: Place the mixed material in a vacuum constant temperature oven at 100°C for heat preservation, control the heat preservation time to be 6 hours, wrap the material with filter paper, place it in a constant temperature drying oven, and remove the excess paraffin at 90°C to obtain the phase change composite material.

[0040] Comparative Example 3 This comparative example provides a phase change composite material, which is different from Example 1 in that sepiolite is first subjected to ultrasonic treatment and then acidified treatment; specifically as follows: This example provides a phase change composite material, including paraffin and acidified sepiolite fibers, and the mass ratio of acidified sepiolite fibers to paraffin is 1:2; The preparation method of acidified sepiolite fibers includes the following steps: Subject sepiolite to ultrasonic treatment at 30°C and 360W for 1 hour, then add the treated sepiolite to a mixed acid solution, react at 30°C for 1 hour, wash with water until the pH is 6 to obtain acidified sepiolite fibers; The mass-volume ratio of sepiolite to the mixed acid solution is 100g:1L, the concentration of hydrochloric acid in the mixed acid solution is 5mol / L, and the concentration of acetic acid in the mixed acid solution is 5mol / L; This comparative example also provides the preparation method of the above phase change composite material, including the following steps: Step 1: Mix the weighed acidified sepiolite fibers and the organic phase change material, perform water bath constant temperature heat preservation at 75°C, control the heat preservation time to be 30 minutes, and stir during heat preservation to obtain a mixed material; Step 2: Place the mixed material in a vacuum constant temperature oven at 100 °C for heat preservation, control the heat preservation time to be 6 h, then wrap the material with filter paper, place it in a constant temperature drying oven, and remove the excess paraffin at 90 °C to obtain the phase change composite material.

[0041] Comparative Example 4 This comparative example provides a phase change composite material, which is different from Example 1 in that only ultrasonic treatment is carried out and acidification treatment is not carried out. The specific steps are as follows: The preparation method of acidified sepiolite fiber includes the following steps: Ultrasonically treat sepiolite at 30 °C and 360 W for 1 h, wash it with water until the pH is 6 to obtain acidified sepiolite fiber; This comparative example also provides the preparation method of the above phase change composite material, including the following steps: Step 1: Mix the weighed acidified sepiolite fiber and organic phase change material, carry out water bath constant temperature heat preservation at 75 °C, control the heat preservation time to be 30 min, and stir during heat preservation to obtain a mixed material; Step 2: Place the mixed material in a vacuum constant temperature oven at 100 °C for heat preservation, control the heat preservation time to be 6 h, wrap the material with filter paper, place it in a constant temperature drying oven, and remove the excess paraffin at 90 °C to obtain the phase change composite material.

[0042] Comparative Example 5 This comparative example provides a phase change composite material, which is different from Example 1 in that acetic acid is replaced with an equal amount of metasilicic acid; Other components and preparation methods are the same as those in Example 1.

[0043] Effect Example Detect the specific surface area, pore structure of the acidified sepiolite fiber prepared in Examples 1 - 3 and Comparative Examples 1 - 5, and the paraffin loading, latent heat performance and thermal stability of the phase change composite material; Among them, the structural performance test of the acidified sepiolite fiber is as follows: Use a BET specific surface area tester (Micromeritics ASAP 2020) to characterize the specific surface area and pore structure of sepiolite by gas adsorption method; The detection method of paraffin loading is as follows: Adopt thermogravimetric analysis (TGA), observe the thermal decomposition behavior of the phase change composite material to determine the paraffin loading, and analyze it in an inert nitrogen atmosphere with a flow rate of 50 mL / min and a heating rate of 10 °C / min.

[0044] The thermal performance test is as follows: 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; Thermal stability performance test is as follows: 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. Where, ηm (%) = |ΔHm b −ΔHm a | / ΔHm b ×100%; ηc (%) = |ΔHc b –ΔHc a | / ΔHcb×100%; 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; Specific test indicators and test results are shown in Table 1: Table 1 Performance test results of phase change composite materials and acidified sepiolite fibers

[0045] Table 2 Performance test results of phase change composite materials after 30 cycles

[0046] 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.

[0047] 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. 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. 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. 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. 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.

[0048] 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: It includes an organic phase change material and acidified sepiolite fibers; wherein, the acidified sepiolite fibers are prepared by subjecting sepiolite to ultrasonic treatment in a mixed acid solution; the mixed acid solution includes an organic weak acid and an inorganic strong acid.

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

3. The phase change composite material according to claim 1, wherein The concentration of the organic weak acid in the mixed acid solution is 5 mol / L - 5.5 mol / L.

4. The phase change composite material according to claim 1, wherein The concentration of the inorganic strong acid in the mixed acid solution is 5 mol / L - 5.5 mol / L.

5. The phase change composite material according to claim 1 or 3, characterized in that The organic weak acid is at least one of acetic acid or citric acid.

6. The phase change composite material according to claim 1 or 4, characterized in that The inorganic strong acid is at least one of hydrochloric acid or nitric acid.

7. The phase change composite material according to claim 1, wherein The preparation method of the acidified sepiolite fibers includes the following steps: Adding sepiolite into the mixed acid solution, and carrying out ultrasonic treatment at 30°C - 35°C to obtain the acidified sepiolite fibers.

8. The phase change composite material according to claim 7, wherein The mass-volume ratio of the sepiolite to the mixed acid solution is (95 - 105) g:1 L; and / or The power of the ultrasonic treatment is 350 W - 370 W; and / or The time of the ultrasonic treatment is 1 h - 1.2 h.

9. A method for preparing the phase change composite material according to any one of claims 1-8, characterized in that, It includes the following steps: Step 1: Mixing the weighed acidified sepiolite fibers and the organic phase change material, and carrying out the first heat preservation at 75°C - 85°C to obtain a mixed material; Step 2: Carrying out the second heat preservation on the mixed material at 100°C - 105°C to obtain a phase change composite material.

10. The preparation method of the phase change composite material according to claim 9, characterized in that, In Step 1, the time of the first heat preservation is 30 min - 35 min; and / or In Step 2, the time of the second heat preservation is 6 h - 6.5 h.

Images