Controllable low-temperature energy storage fatty acid methyl ester / epoxy microcapsule and preparation method thereof

Abstract

This invention discloses a controllable low-temperature energy storage fatty acid methyl ester / epoxy microcapsule and its preparation method. The fatty acid methyl ester / epoxy microcapsule comprises a core material and a shell. The core material is a fatty acid methyl ester phase change material, selected from a binary eutectic mixture formed by methyl laurate and methyl myristate, methyl laurate, a binary eutectic mixture formed by methyl myristate and methyl palmitate, or methyl myristate. The peak melting points of the four core materials are -0.3℃, 7.0℃, 13.9℃, and 20.6℃, respectively, forming a series of phase change materials covering a temperature range of -0.3℃ to 20.6℃. The shell is epoxy resin E51, coated onto the surface of the core material via interfacial polymerization. The resulting microcapsules have a peak melting point of -1.5℃ to 19.0℃ and a phase change enthalpy of 104.6–121.3 J / g. The microcapsule phase change temperature of this invention can be precisely controlled and has stable heat storage performance, showing good application prospects in fields such as food and pharmaceuticals that require low-temperature energy storage.

Description

Technical Field

[0001] This invention relates to the field of phase change energy storage materials technology, and to a low-temperature energy storage microcapsule with controllable phase change temperature through a eutectic strategy and its preparation method, particularly a fatty acid methyl ester / epoxy microcapsule with controllable low-temperature energy storage and its preparation method. Background Technology

[0002] Phase change materials (PCMs) are energy storage media capable of absorbing a large amount of latent heat of phase change at a near-constant temperature when there is excess heat. This characteristic allows them to serve as passive cold sources, maintaining a stable low-temperature environment without consuming additional energy. The core functional parameter of PCMs is their phase change temperature, which determines the material's temperature control range. This is of great significance for cold chain logistics of temperature-sensitive items such as fresh produce, fruits and vegetables, and vaccines.

[0003] Currently, common low-temperature organic phase change materials are mainly alkanes. Fatty acid methyl esters, as a common type of fatty acid ester, have a phase change temperature significantly lower than that of fatty acids and fatty alcohols with the same number of carbon atoms due to the weakening of intermolecular hydrogen bonding by the methyl ester group (-COOCH3) introduced at the molecular end. This makes them highly promising low-temperature phase change materials. However, the phase change temperature of fatty acid methyl esters with a single number of carbon atoms is fixed, resulting in a temperature gap. This temperature gap makes it difficult to meet the precise temperature control requirements of different low-temperature energy storage scenarios, such as cold chain logistics fields like fresh food refrigeration (-5-0℃) and tropical fruit and vegetable preservation (10-18℃). To expand the temperature application range of phase change materials, researchers have attempted to physically composite phase change materials with different melting points through a eutectic strategy to obtain eutectic systems with adjustable phase change temperatures. Binary eutectic systems of methyl laurate and methyl myristate, and methyl myristate and methyl palmitate have been reported. However, existing research has only focused on the thermal properties characterization of the eutectic system itself, and has not yet further developed it into a practically applicable phase change energy storage material, let alone combined it with packaging technology.

[0004] On the other hand, regardless of whether it is a single component or a eutectic system, organic phase change materials face the risk of morphological instability and leakage during the solid-to-liquid phase transition, limiting their application. Microencapsulation technology is an effective means to solve the above-mentioned leakage problem. By encapsulating the phase change material in a micron-sized shell, its phase change process can be confined in a closed space, effectively preventing core material leakage, while improving the material's cycle stability and processing applicability. Epoxy resin, as a high-performance thermosetting resin, possesses excellent mechanical properties, thermal stability, and good compatibility with fatty acid methyl ester core materials, making it an ideal candidate material for preparing phase change microcapsule shells.

[0005] Therefore, how to use fatty acid methyl esters as raw materials, fill the temperature gap of single components through eutectic strategy, achieve precise control of phase change temperature, and further use microencapsulation technology to solve the leakage problem in the solid-liquid phase change process, so as to obtain low-temperature phase change microcapsules with adjustable phase change temperature and stable heat storage performance to meet the diverse needs of different cold chain scenarios for phase change temperature, is an urgent technical problem to be solved in this field. Summary of the Invention

[0006] In view of this, the present invention provides a controllable low-temperature energy storage fatty acid methyl ester / epoxy microcapsule and its preparation method. First, using fatty acid methyl ester as raw material, a series of phase change materials with peak melting points covering the temperature range of -0.3-20.6℃ are constructed through a eutectic strategy to achieve precise and controllable adjustment of the phase change temperature; then, using interfacial polymerization, the above-mentioned core material is encapsulated with epoxy resin E51 as a shell to prepare a low-temperature energy storage phase change microcapsule with adjustable phase change temperature.

[0007] This invention is achieved through the following scheme:

[0008] A controllable low-temperature energy storage fatty acid methyl ester / epoxy microcapsule includes a core material and a shell coating the core material; the core material is a fatty acid methyl ester phase change material with a peak melting point of -0.3℃ to 20.6℃; the shell is epoxy resin E51. The fatty acid methyl ester / epoxy microcapsule has a smooth surface and a clear core-shell structure.

[0009] The microcapsules with the above structure have a peak melting point of -1.5℃ to 19.0℃ and a phase transition enthalpy of 104.6 J / g to 121.3 J / g.

[0010] Preferably, the core material is selected from one of methyl lauryl (ML) and methyl myristate (MM), or a binary eutectic mixture (ML-MM) formed by methyl lauryl and methyl myristate, or a binary eutectic mixture (MM-MP) formed by methyl myristate and methyl palmitate.

[0011] Preferably, in the binary eutectic mixture of methyl laurate and methyl myristate, the mass ratio of the two is 3:1, and the peak melting point is -0.3℃; in the binary eutectic mixture of methyl myristate and methyl palmitate, the mass ratio of the two is 4:1, and the peak melting point is 13.9℃.

[0012] Preferably, the average particle size D50 of the microcapsules is 18.7-22.8 μm.

[0013] The controllable low-temperature energy storage fatty acid methyl ester / epoxy microcapsules with the above characteristics were prepared by the following method:

[0014] Step 1, oil phase preparation: Mix fatty acid methyl ester phase change material with epoxy resin E51, heat and stir to form a homogeneous oil phase;

[0015] Step 2, Aqueous phase preparation: Emulsifier SMA, co-emulsifier NaOH are mixed with water, and heated and stirred to form a suspension aqueous phase;

[0016] Step 3, Emulsification: The oil phase and the aqueous phase are mixed and emulsified to obtain a stable O / W type emulsion;

[0017] Step 4, Polymerization and Post-processing: A curing agent is added to the emulsion to carry out an interfacial polymerization reaction. After the reaction is completed, the phase change microcapsules are obtained through post-processing.

[0018] In the above method, the heating and stirring temperature in step one is 70°C.

[0019] In the above method, in step two, the emulsifier SMA is a styrene-maleic anhydride copolymer, and the co-emulsifier is NaOH; the ratio of SMA, NaOH and deionized water is 0.12 g : 0.4 g : 40 mL.

[0020] In the above method, step three, the emulsification treatment includes sequential mechanical stirring pre-emulsification and homogenization; the mechanical stirring pre-emulsification conditions are 55-65℃ and 600-800 r / min for 40-60 minutes, and Tween 80 is added as an auxiliary emulsifier during the pre-emulsification process; the homogenization conditions are 11000-13000 r / min for 3-5 minutes. As a preferred embodiment, the emulsification treatment includes sequential mechanical stirring pre-emulsification and homogenization; the mechanical stirring pre-emulsification conditions are 60℃ and 700 r / min for 40 minutes; the homogenization conditions are 12000 r / min for 3 minutes; and Tween 80 is added as an auxiliary emulsifier during the emulsification process at a dosage of 0.06 g.

[0021] In the above method, in step four, the curing agent is m-phenylenediamine (MXDA); the temperature of the interfacial polymerization reaction is 55-65℃, and the time is 5-7 hours; the post-treatment includes centrifugation, washing, and drying; the washing uses a mixed solvent of ethanol and petroleum ether.

[0022] In this invention, fatty acid methyl ester core materials with different phase transition temperatures are first constructed using a eutectic strategy, and then encapsulated with epoxy resin E51 using an interfacial polymerization method. The preparation process is simple and environmentally friendly. By controlling the composition of the core material, the phase transition temperature of the microcapsules can be precisely controlled within the range of -1.5 to 19°C. The epoxy resin shell provides good mechanical properties and sealing performance, ensuring the cycling stability of the microcapsules.

[0023] The beneficial effects of this invention can be summarized as follows:

[0024] (1) Precise and controllable phase change temperature: This invention uses a eutectic strategy to physically compound fatty acid methyl esters with different carbon chain lengths and combine them with pure fatty acid methyl esters to obtain a series of phase change materials with peak melting points covering the temperature range of -1.5℃ to 19.0℃. The interval between adjacent melting points is only 6.7-7.3℃, realizing continuous and precise controllable adjustment of phase change temperature within this range.

[0025] (2) Good encapsulation effect: The core material is encapsulated by using the interface polymerization method with epoxy resin E51 as the shell layer. The resulting microcapsules have a clear core-shell structure, which can effectively prevent core material leakage and improve the cycle stability of the material.

[0026] (3) Simple preparation process: The method of the present invention does not require complex equipment, the process conditions are mild, and it is suitable for industrial production. Attached Figure Description

[0027] Figure 1 The above are DSC curves of the fatty acid methyl ester core materials of Comparative Example 1, Comparative Example 2, and Examples 1 and 2 of the present invention.

[0028] Figure 2 The DSC curves are for different phase change microcapsules prepared in Examples 3-6 of this invention.

[0029] Figure 3 This is a scanning electron microscope (SEM) image of the phase change microcapsules prepared in Example 3 of the present invention.

[0030] Figure 4 This is a scanning electron microscope (SEM) image of the phase change microcapsules prepared in Example 4 of the present invention.

[0031] Figure 5 This is a scanning electron microscope (SEM) image of the phase change microcapsules prepared in Example 5 of the present invention.

[0032] Figure 6 This is a scanning electron microscope (SEM) image of the phase change microcapsules prepared in Example 6 of the present invention.

[0033] Figure 7 This is a scanning electron microscope (SEM) image of the fragmented phase change microcapsules of the present invention, showing their core-shell structure.

[0034] Figure 8 The particle size distribution diagrams are for the phase change microcapsules prepared in Examples 3-6 of this invention.

[0035] Figure 9 The following are the Fourier Transform Infrared (FTIR) spectra of the phase change microcapsules of Examples 3-6 of this invention. Detailed Implementation

[0036] To make the technical problems, technical solutions, and beneficial effects of this invention clearer, the technical solutions in the embodiments of this invention will be further described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are only for explaining this invention and are not intended to limit the technical solutions of this invention. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0037] To facilitate understanding, this invention first provides two pure component core materials as comparative benchmarks through Comparative Examples 1 and 2, showcasing their thermal properties. Two binary eutectic core materials were prepared and their thermal properties were tested through Examples 1 and 2. Based on this, microcapsules with different fatty acid methyl ester phase change materials as core materials were prepared through Examples 3 to 6.

[0038] Comparative Example 1

[0039] The thermal properties of the above core material were tested using differential scanning calorimetry (DSC) with methyl lauryl ester (ML, purity ≥99%). Test conditions: nitrogen atmosphere, heating rate 10℃ / min, heating temperature range -25~35℃. Test results are shown below. Figure 1 See Table 1.

[0040] Comparative Example 2

[0041] The thermal properties of the above core material were tested using differential scanning calorimetry (DSC) with methyl myristate (MM, purity ≥98%). Test conditions: nitrogen atmosphere, heating rate 10℃ / min, heating temperature range -20~40℃. Test results are shown below. Figure 1 See Table 1.

[0042] Example 1

[0043] Methyl lauryl acid (ML, purity ≥99%) and methyl myristate (MM, purity ≥98%) were weighed and mixed in a mass ratio of 3:1 (ML:MM) in a beaker. The beaker was placed in a 60℃ constant temperature water bath and heated while being magnetically stirred at 150 r / min for 30 minutes until the mixture was completely melted and formed a homogeneous transparent liquid. Heating was stopped, and the resulting eutectic product was sealed in a sample vial, allowed to cool naturally to room temperature, and then refrigerated at -25℃. This product was labeled as methyl lauryl acid-methyl myristate eutectic core material. The thermal properties of the eutectic core material prepared above were tested using differential scanning calorimetry (DSC). The test conditions were the same as those in Comparative Example 1, and the test results are shown in [Figure 1]. Figure 1 See Table 1.

[0044] Example 2

[0045] Methyl myristate (MM, purity ≥98%) and methyl palmitate (MP, purity ≥98%) were weighed and mixed in a mass ratio of 4:1 (MM:MP) in a beaker. The beaker was placed in a 60℃ constant temperature water bath and heated while being magnetically stirred at 150 r / min for 30 minutes until the mixture was completely melted and formed a homogeneous transparent liquid. Heating was stopped, and the resulting eutectic product was sealed in a sample vial and allowed to cool naturally to room temperature, labeled as methyl myristate-methyl palmitate eutectic core material. The thermal properties of the eutectic core material prepared above were tested using differential scanning calorimetry (DSC). The test conditions were the same as those in Comparative Example 2, and the test results are shown in [Figure 2]. Figure 1 See Table 1. Figure 1 (a) is the DSC curve of the microcapsules prepared in Comparative Example 1; (b) is the DSC curve of the microcapsules prepared in Comparative Example 2; (c) is the DSC curve of the microcapsules prepared in Example 1; and (d) is the DSC curve of the microcapsules prepared in Example 2.

[0046] Example 3

[0047] Step 1, Oil Phase Preparation: Preheat 2 g of epoxy resin E51 at 70℃. Take 6 g of methyl laurate and methyl myristate eutectic as the core material and mix it with the preheated E51. Stir continuously at 70℃ until a homogeneous oil phase is formed.

[0048] Step 2, Aqueous Phase Preparation: Mix 0.12 g of styrene-maleic anhydride copolymer (SMA), 0.4 g of NaOH, and 40 g of deionized water, and stir at 70°C until homogeneous to form an aqueous suspension. NaOH is used to neutralize the maleic anhydride units in SMA, converting them into carboxylate salts and enhancing emulsifying ability.

[0049] Step 3, Emulsification: Combine the oil and water phases and pre-emulsify for 40 minutes at 60°C and 700 r / min with mechanical stirring. After 20 minutes of pre-emulsification, add 0.06 g of Tween 80 as an auxiliary emulsifier and continue stirring for another 20 minutes. Transfer the resulting emulsion to a homogenizer and homogenize at 12000 r / min for 3 minutes to obtain a stable O / W type pre-emulsion.

[0050] Step 4, Polymerization and Post-treatment: Add 0.42g of curing agent m-phenylenediamine (MXDA) to the emulsion and react at 60℃ for 6 hours. After the reaction, centrifuge to collect the concentrated microcapsule suspension, dry it at room temperature, wash it twice with a mixed solvent of ethanol and petroleum ether, and finally dry it at room temperature to obtain phase change microcapsules with methyl laurate-methyl myristate eutectic as the core material.

[0051] Example 4

[0052] The difference from Example 3 is that in step one, 6g of methyl laurate was used instead of the methyl laurate-methyl myristate eutectic as the core material. The remaining steps are the same as in Example 3, resulting in phase change microcapsules with pure methyl laurate as the core material.

[0053] Example 5

[0054] The difference from Example 3 is that in step one, 6g of methyl myristate-methyl palmitate eutectic is used instead of methyl laurate-methyl myristate eutectic as the core material. The remaining steps are the same as in Example 3, resulting in phase change microcapsules with methyl myristate-methyl palmitate eutectic as the core material.

[0055] Example 6

[0056] The difference from Example 3 is that in step one, 6 g of methyl myristate was used instead of methyl laurate-methyl myristate eutectic. The remaining steps are the same as in Example 3, resulting in phase change microcapsules with methyl myristate as the core material.

[0057] The performance characterization and results of the microcapsules prepared in Examples 3-6 are as follows.

[0058] (1) Thermal storage performance: The phase transition temperature and phase transition enthalpy of the microcapsules were tested using differential scanning calorimetry (DSC) under a nitrogen atmosphere at a heating rate of 10℃ / min. In Example 3, the heating range was -25-35℃; in Example 4, the heating range was -30-30℃; and in Examples 5-6, the heating range was -20-40℃. The results are shown in Table 2 and... Figure 2 . Figure 2 (a) is the DSC curve of the microcapsules prepared in Example 3, (b) is the DSC curve of the microcapsules prepared in Example 4, (c) is the DSC curve of the microcapsules prepared in Example 5, and (d) is the DSC curve of the microcapsules prepared in Example 6.

[0059] (2) Morphology and particle size: The morphology of the microcapsules was observed using scanning electron microscopy (SEM). Figures 3-7 All microcapsules had relatively smooth surfaces and a clear core-shell structure. This typical core-shell structure is the morphological basis for the microcapsules' function: the continuous epoxy shell acts as a physical barrier, tightly sealing the core material (fatty acid methyl ester) within a micron-sized cavity, effectively preventing leakage during molten operation; simultaneously, the shell, with sufficient mechanical strength, buffers internal stress changes during phase transitions, protecting the core material from external environmental interference, thus ensuring the structural integrity and thermal stability of the microcapsules during repeated phase transition cycles. Particle size distribution was determined using a laser particle size analyzer; the results are shown in Table 2. Figure 8 .

[0060] (3) Chemical structure analysis: from Figure 9The Fourier transform infrared (FTIR) spectrum shows that the microcapsule sample simultaneously exhibits the core material (1740 cm⁻¹). -1 , ester group C=O) and shell (1608 cm -1 and 1508 cm -1 The characteristic absorption peaks of benzene rings, and the characteristic epoxy groups of epoxy resins (916 cm⁻¹) -1 The significant decrease in the peak value and the absence of new peaks indicate that the epoxy resin successfully coated the fatty acid methyl ester core material.

[0061] Table 1 Thermal performance parameters of different core materials

[0062]

[0063] As shown in Table 1, the peak melting points of Comparative Example 1 and Comparative Example 2 are 7.0℃ and 20.6℃, respectively, with a temperature gap of over 13℃ between them, which is insufficient to meet the precise temperature control requirements of diverse low-temperature energy storage scenarios. In contrast, the methyl laurate-methyl myristate eutectic (Example 1) and methyl myristate-methyl palmitate eutectic (Example 2) prepared by the present invention using a eutectic strategy have peak melting points of -0.3℃ and 13.9℃, respectively. These provide phase transition temperatures near 0℃ and in the middle temperature range, respectively. Together with the pure components, they form a series of phase transition temperatures covering -0.3℃ to 20.6℃, with adjacent melting points only 6.7-7.3℃ apart, achieving continuous and precise control within this temperature range.

[0064] Table 2 Performance parameters of phase change microcapsules prepared in different embodiments

[0065]

[0066] Based on the successful achievement of precise control of the phase change temperature of the core material, epoxy resin E51 was further used as the shell layer to microencapsulate the above series of fatty acid methyl ester core materials, and corresponding phase change microcapsules were prepared (Examples 3-6). The performance parameters of the prepared microcapsules are shown in Table 2. The peak melting points of the obtained microcapsules are -1.5℃, 4.8℃, 12.5℃ and 19.0℃, respectively, covering the temperature range of -1.5℃ to 19.0℃. The phase change enthalpy is 104.6-121.3 J / g and the average particle size D50 is 18.7-22.8μm.

[0067] In summary, the fatty acid methyl ester / epoxy microcapsules provided by this invention achieve precise control of the phase change temperature of the core material through a eutectic strategy and effective encapsulation of the core material through an epoxy resin shell. The resulting product has an adjustable phase change temperature, stable thermal storage performance, and uniform particle size distribution, which can meet the diverse phase change temperature requirements of scenarios such as fresh food cold storage (-5-0℃), vaccine transportation (2-8℃), tropical fruit and vegetable preservation (10-15℃), and cooked food transportation (18-25℃), and has good application prospects in the field of low-temperature energy storage.

[0068] The above-described embodiments are merely examples of several feasible implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. For those skilled in the art, various modifications and improvements can be made without departing from the concept of the present invention. All equivalent implementations or changes that do not depart from the scope of the present invention should be included within the protection scope of the present invention.

Claims

1. A fatty acid methyl ester / epoxy microcapsule for controllable low-temperature energy storage, characterized in that: It includes a core material and a shell covering the core material; the core material is derived from fatty acid methyl ester phase change materials, and its peak melting point can be controllably adjusted within the range of -0.3℃ to 20.6℃ through a eutectic strategy; the shell is epoxy resin E51; the fatty acid methyl ester / epoxy microcapsules have a smooth surface and a clear core-shell structure.

2. The fatty acid methyl ester / epoxy microcapsule for controllable low-temperature energy storage according to claim 1, characterized in that: The core material is selected from one of the following: a binary eutectic mixture of methyl laurate and methyl myristate, methyl laurate, a binary eutectic mixture of methyl myristate and methyl palmitate, or methyl myristate.

3. The fatty acid methyl ester / epoxy microcapsule for controllable low-temperature energy storage according to claim 2, characterized in that: The binary eutectic mixture of methyl laurate and methyl myristate has a mass ratio of 3:1 and a peak melting point of -0.3℃; the binary eutectic mixture of methyl myristate and methyl palmitate has a mass ratio of 4:1 and a peak melting point of 13.9℃.

4. The fatty acid methyl ester / epoxy microcapsule for controllable low-temperature energy storage according to claim 1, characterized in that: The microcapsules have a peak melting point of -1.5℃ to 19.0℃ and a phase transition enthalpy of 104.6 J / g to 121.3 J / g.

5. The fatty acid methyl ester / epoxy microcapsule for controllable low-temperature energy storage according to claim 1, characterized in that: The average particle size D50 of the microcapsules is 18.7~22.8 μm.

6. The method for preparing the controllable low-temperature energy storage fatty acid methyl ester / epoxy microcapsules according to any one of claims 1 to 5, characterized in that, Includes the following steps: Step 1: Oil phase preparation: Mix fatty acid methyl ester phase change material with epoxy resin E51, heat and stir to form a homogeneous oil phase; Step 2: Aqueous phase preparation: Mix emulsifier, co-emulsifier and water, heat and stir to form a homogeneous aqueous phase; Step 3: Emulsification: The oil phase and the aqueous phase are mixed and emulsified to obtain a stable O / W type emulsion; Step 4: Polymerization and post-treatment: Add a curing agent to the emulsion to carry out an interfacial polymerization reaction. After the reaction is completed, post-treatment is performed to obtain the phase change microcapsules.

7. The preparation method according to claim 6, characterized in that: In step two, the emulsifier is styrene-maleic anhydride copolymer (SMA), and the co-emulsifier is NaOH.

8. The preparation method according to claim 6, characterized in that: In step four, the curing agent is m-phenylenediamine.

9. The preparation method according to claim 6, characterized in that: In step three, the emulsification process includes sequential mechanical stirring pre-emulsification and homogenization. The mechanical stirring pre-emulsification is performed at 55-65°C and 600-800 r / min for 40-60 minutes, with Tween 80 added as an auxiliary emulsifier during the pre-emulsification process. The homogenization is performed at 11000-13000 r / min for 3-5 minutes.

10. The preparation method according to claim 6, characterized in that: In step four, the interfacial polymerization reaction is carried out at a temperature of 55-65°C for 5-7 hours; the post-treatment includes centrifugation, washing, and drying.

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