Recyclable solid-solid phase change material with high enthalpy and preparation method thereof

Abstract

This invention discloses a recyclable solid-solid phase change material with high enthalpy and its preparation method, belonging to the field of phase change energy storage material preparation technology. The solid-solid phase change material uses polyethylene glycol as the soft segment of the phase change process, and isophorone diisocyanate, a monoisocyanate-modified tetrahydrobonded intermediate (UPy-NCO), 4,4'-diaminodiphenyl sulfide, and melamine as comonomers, which are cross-linked and polymerized to form a polyurethane network. The process includes the following steps: first, synthesizing the UPy-NCO intermediate, then reacting it with the remaining monomers through prepolymerization, chain extension, and cross-linking reactions, and finally obtaining the target material through precipitation and drying. The material of this invention possesses both high phase change enthalpy and excellent cycling thermal stability. Furthermore, the material can be pulverized and heated in an oven to self-melt and reassemble without external pressure, achieving convenient and efficient recyclability. This material is suitable for long-term energy storage applications such as thermal management of electronic devices, battery pack heat dissipation, and building energy conservation.

Description

Technical Field

[0001] This invention relates to the field of phase change energy storage material preparation technology, and in particular to a recyclable solid-solid phase change material with high enthalpy and its preparation method. Background Technology

[0002] With the continuous growth of global energy demand and the increasingly severe environmental pressure brought about by fossil fuel consumption, the efficient use of renewable energy has become a focus of attention for all countries. Phase change energy storage materials can absorb or release a large amount of latent heat during the phase change process while maintaining a constant temperature, showing broad application prospects in fields such as solar energy storage, waste heat recovery, building energy conservation, and thermal management of electronic devices. Phase change energy storage materials can be classified into solid-liquid phase change materials and solid-solid phase change materials according to their physical state during the phase change process. Among them, solid-solid phase change materials maintain solid-state characteristics during the phase change process and have outstanding advantages such as small volume change during the phase change, no leakage risk, no need for complex packaging, and good cycle stability. In recent years, they have attracted more and more attention from researchers.

[0003] Polyethylene glycol (PEG) is an ideal candidate material for preparing solid-solid phase change materials (SCMs) due to its high phase transition enthalpy, wide range of adjustable phase transition temperatures with molecular weight, and good chemical stability. However, PEG itself is a solid-liquid SCM, which melts and flows above the phase transition temperature, making it prone to leakage and limiting its direct application. To solve this problem, researchers usually graft PEG into the polymer backbone through chemical bonds to construct polymer-based solid-solid SCMs. Polyurethane, due to its strong structural designability, significant microphase separation characteristics of soft and hard segments, and excellent mechanical properties, has become an ideal matrix material for preparing SCMs. By introducing PEG as the soft segment of polyurethane into the polyurethane molecular chain through chemical bonding, the leakage problem of PEG during the phase transition process can be effectively solved. However, traditional polyurethane-based SCMs are mostly thermosetting cross-linked structures, which cannot be reprocessed once molded and are difficult to recycle after the material's life cycle, resulting in resource waste and environmental pressure.

[0004] To address the challenge of recycling thermosetting polyurethane materials, researchers have begun to explore the introduction of dynamic covalent bonds into the polyurethane network. However, while dynamic covalent bond systems impart recyclability to materials, they often present two problems: first, the introduction of dynamic covalent bonds may disrupt the crystallization of phase transition units, thus affecting the phase transition enthalpy; second, the exchange process of dynamic covalent bonds requires the addition of external catalysts or heating to high temperatures, posing risks of harsh reaction conditions and the generation of active substances that could lead to a decline in performance after recycling. In other words, achieving a good balance between "recyclability" and "high enthalpy" remains a pressing technical challenge.

[0005] In summary, existing polyurethane-based solid-solid phase change materials (PSCs) face the following technical shortcomings. Firstly, due to limitations in PEG loading, some traditional PSCs have low enthalpy values ​​for phase transition, making them unsuitable for high-energy-density applications. Secondly, most existing polyurethane PSCs are thermosetting network structures, making them difficult to reprocess and recycle once formed, resulting in resource waste. Thirdly, attempts to introduce dynamic covalent bonds to impart recyclability often sacrifice enthalpy values ​​for phase transition, making it difficult to balance high enthalpy change with recyclability. To address these issues, there is an urgent need to develop a polyurethane-based PSC that combines high enthalpy with recyclability to meet the growing demands for efficient energy storage and environmentally friendly practices. Summary of the Invention

[0006] In view of the shortcomings of the prior art, the present invention aims to provide a recyclable solid-solid phase change material with high enthalpy and its preparation method. It solves the technical contradiction that existing polyurethane solid-solid phase change materials cannot simultaneously achieve high phase change enthalpy and recyclability. Through the synergistic effect of quadruple hydrogen bonds and dynamic disulfide bonds and the structural matching of melamine crosslinking network, while maintaining the high crystallinity of PEG soft segments to ensure the phase change enthalpy, it endows the material with the ability of dynamic bonds to break and recombine reversibly under thermal stimulation. This achieves the unity of high energy storage density and full life cycle recyclability, effectively extending the service life of the material and reducing the pressure on the environment after disposal.

[0007] The method for preparing a recyclable solid-solid phase change material with high enthalpy value according to the present invention specifically includes the following steps: S1. 2-Amino-4-hydroxy-6-methylpyrimidine (UPy) and hexamethylene diisocyanate (HDI) are added to a three-necked flask in a preset ratio. Under a nitrogen protective atmosphere and heating conditions, the mixture is stirred thoroughly to obtain a viscous homogeneous fluid. S2. The homogeneous fluid prepared in S1 is washed, centrifuged and dried to obtain a monoisocyanate-modified tetrahydrobonded intermediate, namely UPy-NCO. S3. After dehydration treatment, PEG and IPDI are added to a three-necked flask and stirred and mixed. Then, dibutyltin dilaurate catalyst is added. Under nitrogen protection and heating conditions, the mixture is stirred and reacted thoroughly to obtain isocyanate-terminated prepolymer, namely PEG-IPDI. S4. After cooling the prepolymer prepared in S3, add diaminodiphenyl sulfide dissolved in N,N-dimethylformamide (DMF), stir and mix evenly, then add UPy-NCO intermediate dissolved in DMF and melamine powder, and after heating and reaction, obtain a viscous light yellow homogeneous fluid. S5. The light yellow homogeneous fluid prepared in S4 is slowly added dropwise to anhydrous ethanol, stirred, washed, and centrifuged to dry to obtain the product. The obtained product is placed in a polytetrafluoroethylene mold, dried and shaped to obtain a recyclable solid-solid phase change material with high enthalpy, namely PCM.

[0008] As a further improvement of the present invention, the preset ratio of UPy and HDI in step S1 is a molar ratio of 1:(5~10); the heating in step S1 is specifically carried out in a constant temperature oil bath at 80℃~120℃ for a constant temperature reaction time of 10h~12h.

[0009] As a further improvement of the present invention, the washing in step S2 is specifically performed by washing three times with 20 ml of n-hexane; the centrifugation in step S2 is specifically performed by a rotation speed of 8000 rpm for 8 min; and the drying treatment in step S2 is specifically performed by vacuum drying at a temperature of 60°C for 8 h.

[0010] As a further improvement of the present invention, the polyethylene glycol in step S3 has a molecular weight of 4000; the dehydration treatment in step S3 specifically involves vacuum drying of polyethylene glycol 4000 at a temperature of 100°C for 3 hours; the stirring and mixing in step S3 specifically involves magnetic stirring at a speed of 400 rpm for 30 minutes; and the heating in step S3 specifically involves a constant temperature oil bath at 70°C for a reaction time of 3 hours.

[0011] As a further improvement of the present invention, the stirring and mixing described in step S4 is specifically carried out at a temperature of 40°C for a time of 30 minutes; the heating described in step S4 is specifically carried out in a constant temperature oil bath at 70°C for a constant temperature reaction time of 10 hours.

[0012] As a further improvement of the present invention, the stirring and washing described in step S5 is specifically carried out at room temperature with mechanical stirring at 400 rpm for 20 min; the drying and molding described in step S5 is specifically carried out at a temperature of 40℃~80℃ for 12h~36h.

[0013] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention synthesizes recyclable solid-solid phase change material with high enthalpy value by prepolymer method. The phase change enthalpy value can reach more than 154.56 J / g. After 50 DSC heating and cooling cycle tests, the melting enthalpy retention rate of the material is still greater than 85%, indicating that its phase change performance has almost no decay during long-term repeated heat absorption and release, which can meet the requirements of energy storage devices for long-term service stability. This shows that the material has high phase change enthalpy and excellent cycle thermal stability.

[0014] (2) The recyclable solid-solid phase change material with high enthalpy value prepared by the present invention has convenient and efficient recycling and repair capabilities; after use, the material is cut into pieces and placed directly in an oven and heated at 70°C for 2 hours. It can melt and recombine into a complete material without external pressure, demonstrating the excellent recyclability of the material based on the reversible recombination mechanism of dynamic disulfide bond and quadruple hydrogen bond synergy. Attached Figure Description

[0015] Figure 1 This is a flowchart illustrating the preparation process of a recyclable solid-solid phase change material with high enthalpy value and its preparation method according to the present invention. Figure 2 The infrared spectrum of the solid-solid phase change material obtained by this invention is shown below. Figure 3 The infrared spectrum of the UPy-NCO intermediate obtained in Example 1; Figure 4 The DSC characterization curves for the thermal cycling stability of the solid-solid phase change material prepared in Example 1 are shown. Figure 5 Differential scanning calorimetry (DSC) curves of the solid-solid phase change material prepared in Example 1 under different thermal cycles; Figure 6 These are photographs of the solid-solid phase change material prepared in Example 1 before and after recycling. Figure 7 The X-ray diffraction (XRD) patterns are those of pure PEG4000 and PCM-C1 prepared in Example 1. Detailed Implementation

[0016] This invention provides a recyclable solid-solid phase change material with high enthalpy and a method for preparing the same. To make the objectives, technical solutions and advantages of this invention clearer and more explicit, the invention will be further described in conjunction with specific embodiment 1 and the accompanying drawings.

[0017] Example 1: As Figure 1 As shown, the present invention discloses a method for preparing a recyclable solid-solid phase change material with high enthalpy, which is prepared by the following steps.

[0018] Step 1: Add 2.0 g of 2-amino-4-hydroxy-6-methylpyrimidine (UPy) and 14.2 ml of HDI to a three-necked flask. Under a nitrogen atmosphere, stir the mixture thoroughly at 100 °C for 16 h to obtain a viscous homogeneous fluid. Wash the homogeneous fluid three times with n-hexane and centrifuge for 8 min at 8000 rpm. Dry the lower solid obtained by centrifugation in an oven at 60 °C for 24 h to obtain a white powder, i.e., the UPy-NCO intermediate.

[0019] Step 2: Add 15g of dehydrated polyethylene glycol 4000 and 1.12ml of isophorone diisocyanate (IPDI) to a three-necked flask and stir to mix. Then add 50µL of dibutyltin dilaurate catalyst and stir thoroughly at 70°C for 3 hours under a nitrogen protective atmosphere to obtain the isocyanate-terminated prepolymer, namely PEG-IPDI.

[0020] Step 3: Cool the PEG-IPDI prepolymer to 40℃, dissolve 0.45 g of diaminodiphenyl sulfide in 10 mL of DMF, add it to the reaction system, stir at 40℃ for 30 min, then dissolve 0.33 g of UPy-NCO intermediate in 8 mL of DMF and add it to the reaction system, finally add 0.25 g of melamine, continue stirring, raise the temperature to 70℃, and react for 10 h.

[0021] Step 4: Slowly add the light yellow homogeneous fluid obtained in Step 3 to anhydrous ethanol with mechanical stirring at 400 rpm, stir and wash, then centrifuge the mixture in a centrifuge at 8000 rpm for 8 min, discard the supernatant to obtain the product, place the obtained product in a polytetrafluoroethylene mold, and vacuum dry at 60℃ for 24 h to constant weight to obtain a solid-solid phase change film.

[0022] The solid-solid phase change thin film prepared in Example 1 was subjected to Fourier transform infrared spectroscopy to characterize the chemical structure of the sample. The results are as follows: Figure 2 As shown.

[0023] from Figure 2 It can be seen that it is approximately 3439cm -1 The peak of the NH stretching vibration is located at approximately 2890 cm⁻¹. -1 The peak at this location is the CH stretching vibration peak, approximately 1113 cm⁻¹. -1 The strong absorption peak at approximately 1633 cm⁻¹ corresponds to the COC ether bond and is attributed to the main chain structure of the PEG soft segment; -1 The presence of a carbonyl (C=O) stretching vibration absorption peak at approximately 2270 cm⁻¹ indicates that the isocyanate group and hydroxyl group have successfully reacted to form a polyurethane structure. This peak is attributed to the urethane bond (-NH₃COO₃), suggesting that the isocyanate group and hydroxyl group have successfully reacted to form a polyurethane structure. -1 The absence of characteristic absorption peaks for isocyanate (-NCO) in the vicinity indicates that the isocyanate groups have completely reacted. These results confirm the successful synthesis of a solid-solid phase change material with PEG as the soft segment and polyurethane as the matrix.

[0024] The UPy-NCO intermediate prepared in Example 1 was subjected to Fourier transform infrared spectroscopy to characterize the chemical structure of the sample. The results are as follows: Figure 3 As shown.

[0025] Figure 3It can be seen that it is approximately 3435cm -1 The peak of the NH stretching vibration is located at approximately 2938 cm⁻¹. -1 and 2858cm -1 The peak of CH stretching vibration is located at approximately 1661 cm⁻¹. -1 The peak of the stretching vibration at C=O / C=N is approximately 1590 cm⁻¹. -1 The peak at this location represents the NH bending vibration; the above results indicate that the UPy-NCO intermediate was successfully synthesized.

[0026] The solid-solid phase change film (PCM) prepared in Example 1 was subjected to 50 thermal cycles. The test conditions were: temperature range -10 to 70°C, heating / cooling rate of 5°C / min. Samples were taken from the 1st (before recycling), 10th, 30th, and 50th cycles, with the 10th, 30th, and 50th cycles being samples after recycling. Differential scanning calorimetry (DSC) was performed sequentially for characterization. The results are as follows: Figure 4 and Figure 5 As shown.

[0027] Figure 4 The differential scanning calorimetry (DSC) curves of the PCM samples under different thermal cycles can be seen. PCM-C1 represents the sample before recycling, while PCM-C10, PCM-C30, and PCM-C50 correspond to the samples after 10, 30, and 50 thermal cycles, respectively. As shown in the figure, the samples exhibit a significant endothermic peak around 40°C during the heating process and an exothermic peak around 60°C during the cooling process, both in the initial state and after multiple thermal cycles. This indicates that the solid-solid phase transition behavior is stable, with no significant shift in phase transition temperature before and after cycling, and no significant change in the phase transition peak shape. This result demonstrates that the phase change material prepared in this invention possesses good thermal cycling stability and can maintain stable phase change performance even after multiple uses, meeting the requirements for long-term thermal storage applications.

[0028] Figure 5 It can be seen that all samples exhibited a significant endothermic peak in the 39-40℃ range during the heating process, corresponding to their solid-solid phase change melting process; and an exothermic peak appeared near 60℃ during the cooling process, corresponding to the crystallization process. Specifically, the melting peak temperatures of PCM-C50, PCM-C30, PCM-C10, and PCM-C1 were 39.93℃, 39.64℃, 39.03℃, and 39.21℃, respectively, and the crystallization peak temperatures were 59.83℃, 61.39℃, 60.92℃, and 61.17℃, respectively. The above results indicate that the phase change material prepared by this invention has stable solid-solid phase change behavior and a suitable phase change temperature, which can meet the requirements of thermal storage applications.

[0029] Table 1 shows the phase transition enthalpy values ​​of the samples from Example 1 at different numbers of thermal cycles:

[0030] Combination Figure 4 and Figure 5 The DSC curve shows that the enthalpy retention rate of the sample is still above 85% after 50 cycles, indicating that the phase change material of the present invention has excellent thermal cycling stability and can maintain stable heat storage performance after multiple uses, making it suitable for long-term cyclic use.

[0031] The solid-solid phase change film prepared in Example 1 was cut into small pieces with scissors, placed in a polyvinyl fluoride mold, and heated in a 70°C oven for 2 hours. After removal, the material melted and re-aggregated into a complete film, as shown below. Figure 6 As shown, this indicates that the material has good thermally induced repair and recyclable molding capabilities.

[0032] X-ray diffraction patterns of the PCM-C1 sample prepared in Example 1 and pure PEG4000 were analyzed. The scanning range was 5°~70°, and the scanning rate was 5° / min. The results are as follows: Figure 7 As shown.

[0033] Figure 7 It can be seen that pure PEG4000 exhibits two sharp characteristic diffraction peaks at 2θ = 19.2° and 23.4°, corresponding to its typical crystal structure. In the XRD pattern of the PCM sample, characteristic diffraction peaks consistent with those of pure PEG also appear at the same 2θ position, with complete peak shapes and no obvious shift. The above results indicate that the crystal structure of PEG is completely preserved in the polyurethane solid-solid phase change film prepared in this invention, without any crystal transformation. At the same time, the diffraction peak intensity of the PCM sample is lower than that of pure PEG, indicating that PEG is successfully immobilized in the polyurethane matrix. The matrix plays a certain role in constraining the crystallization of PEG, but does not destroy its crystallization ability. Therefore, the sample still has good phase change heat storage performance.

[0034] In summary, this embodiment successfully prepared a recyclable solid-solid phase change material with high enthalpy. The material uses PEG as the soft segment of the phase change and forms a cross-linked network through copolymerization of IPDI, UPy-NCO intermediate, diaminodiphenyl sulfide, and melamine. Infrared spectroscopy confirmed the successful introduction of the PEG soft segment, urethane bonds, and UPy units. XRD patterns confirmed that the crystallinity of PEG was not damaged. DSC testing showed that the material has a high phase change enthalpy and excellent cyclic thermal stability. Recycling experiments demonstrated that the material can be melted and reassembled spontaneously after being pulverized and heated in an oven, achieving convenient recyclability. This invention simultaneously achieves high phase change enthalpy, excellent cyclic stability, and easy recyclability.

Claims

1. A method for preparing a recyclable solid-solid phase change material with high enthalpy, characterized in that, Includes the following steps: S1. 2-Amino-4-hydroxy-6-methylpyrimidine (UPy) and hexamethylene diisocyanate (HDI) are added to a three-necked flask in a preset ratio. Under a nitrogen protective atmosphere and heating conditions, the mixture is stirred thoroughly to obtain a viscous homogeneous fluid. S2. The homogeneous fluid prepared in S1 is washed, centrifuged and dried to obtain a monoisocyanate-modified tetrahydrobonded intermediate, namely UPy-NCO. S3. After dehydration treatment, polyethylene glycol and isophorone diisocyanate (IPDI) are added to a three-necked flask and stirred and mixed. Then, dibutyltin dilaurate catalyst is added. Under nitrogen protection and heating conditions, the mixture is stirred and reacted thoroughly to obtain isocyanate-terminated prepolymer, namely PEG-IPDI. S4. After cooling the prepolymer prepared in S3, add diaminodiphenyl sulfide dissolved in DMF, stir and mix evenly, then add UPy-NCO intermediate dissolved in DMF and melamine powder. After heating and reaction, a light yellow homogeneous fluid with viscosity is obtained. S5. The light yellow homogeneous fluid prepared in S4 is slowly added dropwise to anhydrous ethanol, stirred, washed, and centrifuged to dry to obtain the product. The obtained product is placed in a polytetrafluoroethylene mold, dried and shaped to obtain a recyclable solid-solid phase change material with high enthalpy, namely PCM.

2. The method for preparing a recyclable solid-solid phase change material with high enthalpy value according to claim 1, characterized in that, The preset ratio of UPy and HDI in step S1 is 1:7 molar ratio; the heating in step S1 is specifically carried out in a constant temperature oil bath at 80℃~120℃ for 10h~12h.

3. The method for preparing a recyclable solid-solid phase change material with high enthalpy value according to claim 1, characterized in that, The washing described in step S2 is specifically performed by washing three times with 20 ml of n-hexane; the centrifugation described in step S2 is specifically performed by centrifugation at 8000 rpm for 8 min; the drying treatment described in step S2 is specifically performed by vacuum drying at 60°C for 8 h.

4. The method for preparing a recyclable solid-solid phase change material with high enthalpy value according to claim 1, characterized in that, The polyethylene glycol in step S3 has a molecular weight of 4000; the dehydration treatment in step S3 specifically involves vacuum drying of polyethylene glycol 4000 at 100°C for 3 hours; the stirring and mixing in step S3 specifically involves magnetic stirring at 400 rpm for 30 minutes; and the heating in step S3 specifically involves a constant temperature oil bath at 70°C for 3 hours.

5. The method for preparing a recyclable solid-solid phase change material with high enthalpy value according to claim 1, characterized in that, The stirring and mixing described in step S4 is carried out at a temperature of 40°C for 30 minutes; the heating described in step S4 is carried out in a constant temperature oil bath at 70°C for 10 hours.

6. The method for preparing a recyclable solid-solid phase change material with high enthalpy value according to claim 1, characterized in that, The stirring and washing described in step S5 is carried out under the following conditions: mechanical stirring at 400 rpm for 20 min at room temperature; the drying and molding described in step S5 is carried out under the following conditions: temperature 40℃~80℃ and drying time 12h~36h.

7. A recyclable solid-solid phase change material with high enthalpy, characterized in that, It is prepared by the preparation method described in any one of claims 1 to 6.

8. A recyclable solid-solid phase change material with high enthalpy value according to claim 7, characterized in that, The material has a high phase transition enthalpy and can be recycled after being crushed and heated in an oven. Even after recycling, it still maintains a high phase transition enthalpy.

Images