High-enthalpy flexible phase change material, and preparation method and application thereof

Abstract

The application discloses a high-enthalpy flexible phase change material and a preparation method and application thereof, and relates to the technical field of high polymer composite materials.The preparation method comprises the following steps: taking maleic anhydride as a grafting agent, and polyolefin thermoplastic elastomer as a grafting object to prepare a grafting modified thermoplastic elastomer; adding a crosslinking agent and a phase change material into the grafting modified thermoplastic elastomer, and melt blending to obtain the high-enthalpy flexible phase change material.The preparation method has the following advantages: more excellent flexibility, the three-dimensional crosslinking network is constructed through the introduction of anhydride-ester dynamic bond, and the organic solid-liquid phase change material is reinforced and toughened; high energy storage density; the introduction of the crosslinking network enables the polymer support structure to better coat the phase change material, and the content of the phase change material is ensured, that is, the high energy storage density is provided.

Description

Technical Field

[0001] This invention relates to the field of polymer composite materials technology, specifically to a high enthalpy flexible phase change material, its preparation method, and its applications. Background Technology

[0002] As electronic devices evolve towards miniaturization, high power, and high integration, significant heat accumulation occurs, which can accelerate failure if not dissipated efficiently and promptly. Phase change materials (PCMs) can absorb or release heat in the form of latent heat during phase transitions, maintaining a relatively stable temperature. When used as thermal management components, PCMs can not only control device temperature and prevent thermal runaway but also ensure more uniform temperature distribution, preventing heat buildup. Traditional organic solid-liquid phase change materials have attracted widespread attention due to their advantages such as high energy density, low supercooling, wide phase transition temperature range, and good chemical stability. However, they are prone to brittle fracture, making them unsuitable for applications requiring flexibility, such as thermal management of flexible electronic devices and wearable technology. Therefore, improving the mechanical properties, especially the flexibility, of organic solid-liquid phase change materials is crucial for their development and practical application.

[0003] Currently, strategies for preparing flexible phase change materials can be broadly categorized into flexible porous support materials, flexible shell encapsulation, and polymer network-based structures. Compared to high-cost porous materials and flexible shell encapsulation, polymers, represented by polyolefin elastomers (POEs), offer advantages such as simple processing, low cost, and abundant raw material sources, and possess the potential for large-scale production. However, further performance optimization through polymer network structure design is still needed to achieve a balance between material energy storage density, flexibility, and processing performance.

[0004] Therefore, it is of great significance to develop a phase change material with excellent mechanical properties and high energy storage density and its large-scale preparation strategy. Summary of the Invention

[0005] To address the aforementioned deficiencies, this application provides a high-enthalpy flexible phase change material with enhanced mechanical properties and its preparation method. The resulting phase change material, by controlling the density of the crosslinked network, achieves enhanced mechanical properties while maintaining energy storage density. Furthermore, due to the formation of the crosslinked structure, the thermoplastic elastomer matrix achieves better encapsulation of the phase change components, ensuring that the phase change components do not leak under high-temperature conditions and enhancing the shape stability of the composite material at high temperatures. This invention prepares a flexible phase change material with high enthalpy and ultra-toughness through the synergistic effect of the crosslinking reaction of acid anhydride-alcohol ester and the coating of polyolefin with paraffin. Moreover, this phase change material preparation method can achieve large-scale industrial production.

[0006] To achieve the above objectives, the present invention provides a method for preparing a high-enthalpy flexible phase change material, comprising the following steps:

[0007] S1. Using maleic anhydride as a grafting agent and thermoplastic elastomer as the grafting target, a graft-modified thermoplastic elastomer is prepared; wherein the thermoplastic elastomer is selected from at least one of ethylene-octene copolymer, ethylene-butene copolymer, olefin block copolymer, and styrene-ethylene-butene-styrene block copolymer.

[0008] S2. A crosslinking agent and a phase change material are added to the grafted modified thermoplastic elastomer and melt-blended to obtain a high enthalpy flexible phase change material. The crosslinking agent is an alcohol compound that undergoes an esterification reaction with maleic anhydride grafted onto the thermoplastic elastomer. The phase change material is selected as paraffin wax.

[0009] The mechanism involved in the preparation of high-enthalpy flexible phase change materials in this invention includes the following: Grafting in this invention refers to the attachment of maleic anhydride to polyolefin chains. Ethylene-octene copolymers, ethylene-butene copolymers, olefin block copolymers, and styrene-ethylene-butene-styrene block copolymers are selected as grafting targets. Among these block copolymers, maleic anhydride grafting tends to be applied to non-ethylene blocks because the free radicals formed by these blocks have higher stability. This reaction is highly similar and can be represented as follows: the initiator decomposes and attacks the polyolefin chain segments to form macromolecular free radicals, which then react with maleic anhydride to form the grafted structure. Crosslinking in this invention involves the reaction of the alcohol with the maleic anhydride grafted onto the chain. The side reactions in this invention mainly occur during the grafting process because the subsequent crosslinking is an esterification reaction, which does not involve free radicals and will not affect the macromolecular chain segments. For the listed polyolefin copolymers, the side reactions are more related to the amount of initiator and maleic anhydride used. Insufficient dosage may result in low grafting density and ineffective coating of the phase change component and improvement of mechanical properties after crosslinking; while excessive dosage may cause degradation of the polyolefin, leading to a decrease in molecular weight and strength. Therefore, in practical applications, a suitable dosage of initiator and maleic anhydride is required to obtain a high-enthalpy flexible phase change material with enhanced mechanical properties.

[0010] In a preferred embodiment, the amounts of each component in the above preparation method are as follows:

[0011] 10-30 parts by weight of thermoplastic elastomer;

[0012] 70-90 parts by weight of phase change material;

[0013] 1-4 parts by weight of grafting agent;

[0014] Crosslinking agent 1-4 parts by weight.

[0015] Furthermore, the thermoplastic elastomer comprises 30 parts by weight, and the phase change material comprises 70 parts by weight.

[0016] As a further preferred embodiment of the present invention, the thermoplastic elastomer is selected from ethylene-octene copolymer.

[0017] As a further preferred embodiment of the present invention, the crosslinking agent is selected from at least one of glycerol, propylene glycol, and hexanediol.

[0018] As a further preferred technical solution of the present invention, both steps S1 and S2 are carried out in a mixer or an extruder; and / or, the temperature at which the corresponding operations are carried out in steps S1 and S2 is 140 to 160°C, for example 140°C, 145°C, 150°C, 155°C, 160°C, etc.

[0019] As a further preferred embodiment of the present invention, in step S1, a peroxide is used as an initiator, and maleic anhydride is grafted onto the thermoplastic elastomer through melt blending. The peroxide initiator can be selected from one or more of dicumyl peroxide (DCP), di-tert-butyl peroxide, and benzoyl peroxide, wherein di-tert-butyl peroxide can be di-tert-butylperoxyisopropylbenzene, 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane, etc.

[0020] As a further preferred technical solution of the present invention, in step S2, the following methods are adopted: first add a crosslinking agent to perform crosslinking and then add a phase change material to mix evenly, or first add a phase change material to mix evenly and then add a crosslinking agent to perform crosslinking.

[0021] According to another aspect of the present invention, the present invention also provides a high-enthalpy flexible phase change material prepared by the above method.

[0022] According to another aspect of the present invention, the present invention also provides an application of a high-enthalpy flexible phase change material for preparing a flexible phase change film. The high-enthalpy flexible phase change material is used to form a flexible phase change film by hot pressing, blown film blowing, or casting.

[0023] Compared with the prior art, the present invention can achieve the following beneficial effects:

[0024] 1) The present invention has the following advantages by constructing a three-dimensional cross-linked network: better flexibility, the three-dimensional cross-linked network is constructed by introducing the dynamic bond of acid anhydride-alcohol ester, which realizes the enhancement and toughening of organic solid-liquid phase change material; high energy storage density, the introduction of cross-linked network enables the polymer support structure to better encapsulate the phase change material, ensuring the content of phase change material, that is, giving it a high energy storage density.

[0025] 2) The present invention has excellent processing performance. On the one hand, the melt blending processing method has the potential for large-scale processing. On the other hand, the cross-linked network enhances the melt strength of the composite phase change material. Therefore, the flexible phase change material has excellent processing performance and can be prepared on a large scale in industry. Attached Figure Description

[0026] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0027] Figure 1 This diagram illustrates the reaction and preparation mechanism of the high-enthalpy flexible phase change material in this invention. First, a cross-linked thermoplastic elastomer is prepared through grafting and cross-linking reactions. Then, the phase change material is introduced into the cross-linked network of the thermoplastic elastomer to obtain the high-enthalpy flexible phase change material.

[0028] Figure 2 The mechanical property curves are shown for the flexible phase change film obtained in Example 1. Figure 1 It can be seen that the tensile stress and tensile strain of the sample in Example 1 are significantly enhanced compared with the uncrosslinked control sample, thus achieving the enhancement and toughening of the material.

[0029] Figure 3 The image shows the DSC curve of the flexible phase change film obtained in Example 1. Figure 2 It can be seen that the crystallization temperature of the sample in Example 1 is 38.7℃, and the enthalpy of crystallization can reach 149.2J / g; the melting temperature is 51.3℃, and the enthalpy of melting can reach 156.5J / g.

[0030] Figure 4 This is an SEM image of the flexible phase change film obtained in Example 1. Figure 3 The SEM image shown is a cross-sectional scanning electron microscope image of the paraffin-etched sample from Example 1. Figure 3 It can be seen that, in addition to providing excellent mechanical properties, the crosslinking network of the sample in Example 1 can also enable the thermoplastic elastomer support material to well encapsulate the paraffin and prevent paraffin leakage.

[0031] The objectives, features, and advantages of this invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0032] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0033] Unless otherwise defined, the technical terms used in the following embodiments have the same meanings as commonly understood by those skilled in the art to which this invention pertains. Unless otherwise specified, the experimental reagents used in the following embodiments are conventional biochemical reagents; and the experimental methods described are conventional methods.

[0034] The mechanical properties, thermal properties, and microstructure of the thin film samples of the same specifications and dimensions prepared in each embodiment were characterized using a stretching machine, differential scanning calorimeter, and scanning electron microscope.

[0035] Example 1:

[0036] This embodiment provides a method for preparing a flexible phase change film based on flexible phase change material particles, the chemical reaction mechanism of which is as follows: Figure 1 As shown, the specific preparation method is as follows:

[0037] 1) Mix thermoplastic elastomer polyolefin POE8150, initiator DCP and grafting agent maleic anhydride MA in a mass ratio of 100:0.2:2, and melt-blend at 160℃ for 5-10 min to obtain maleic anhydride-grafted polyolefin POE8150.

[0038] 2) Then, glycerol with a molar ratio of maleic anhydride groups to maleic anhydride is added to the maleic anhydride-grafted polyolefin POE8150 as a crosslinking agent, and the mixture is melt-blended for 5-10 minutes to obtain the crosslinked polyolefin elastomer POE8150.

[0039] 3) Crosslinked polyolefin elastomer POE8150 and paraffin wax were melt-blended at 160℃ for 10-20 min at a mass ratio of 30:70 to obtain flexible phase change material granules with a crosslinked structure.

[0040] 4) The phase change material granules were hot-pressed at a temperature of 160°C to obtain a flexible phase change film, denoted as: Example 1-2MA.

[0041] Example 2: Based on Example 1, the difference is that four groups of samples were prepared with different proportions of grafting agent.

[0042] 1) A series of polyolefins POE8150 with different proportions of maleic anhydride grafted were prepared by mixing thermoplastic elastomer polyolefin POE8150, initiator DCP and grafting agent maleic anhydride MA in a mass ratio of 100:0.2:0 / 0.5 / 1 / 3 and melting and blending at 160℃ for 5-10 min.

[0043] 2) Glycerol with a molar ratio of maleic anhydride grafted to polyolefin POE8150 of different proportions was added as a crosslinking agent, and the mixture was melt-blended for 5-10 min to obtain a series of polyolefin elastomers POE8150 with different degrees of crosslinking.

[0044] 3) A series of polyolefins POE8150 with different degrees of crosslinking were melt-blended with paraffin at a mass ratio of 30:70 at 160℃ for 10-20 min to obtain a series of flexible phase change material granules with crosslinking structure;

[0045] 4) The series of phase change material granules were hot-pressed at a temperature of 160°C to obtain a series of flexible phase change films, which are respectively named: Example 2-0MA, Example 2-0.5MA, Example 2-1MA, and Example 2-3MA.

[0046] Example 3: Based on Example 1, the difference is that the type of thermoplastic elastomer is changed.

[0047] Maleic anhydride-grafted olefin block copolymer OBC is prepared by mixing thermoplastic elastomer olefin copolymer OBC, initiator DCP and grafting agent maleic anhydride MA in a mass ratio of 100:0.2:2 and melt blending at 160℃ for 5-10 min.

[0048] Then, glycerol with a molar ratio equal to that of maleic anhydride is added as a crosslinking agent, and the mixture is melt-blended for 5-10 minutes to obtain olefin block copolymers OBC with different degrees of crosslinking.

[0049] Olefin block copolymers (OBC) with different degrees of crosslinking are melt-blended with paraffin at a mass ratio of 30:70 at 160°C for 10-20 minutes to obtain flexible phase change material granules with a crosslinked structure; the phase change material granules are hot-pressed at 160°C to obtain a flexible phase change film.

[0050] Compared with Example 1, Example 3 only changed the type of thermoplastic elastomer, and the mechanical and thermal properties showed similar changing trends.

[0051] Comparative Example: As a control experiment for Example 1, the difference is that the crosslinking step is omitted.

[0052] 1) Mix thermoplastic elastomer polyolefin POE8150, initiator DCP and grafting agent maleic anhydride MA in a mass ratio of 100:0.2:2, and melt-blend at 160℃ for 5-10 min to obtain maleic anhydride-grafted polyolefin POE8150.

[0053] 2) The maleic anhydride-grafted polyolefin elastomer POE8150 and paraffin wax were melt-blended at 160°C for 10-20 min at a mass ratio of 30:70 to obtain composite phase change material granules with only grafted structure and no crosslinking.

[0054] 3) The phase change material granules were hot-pressed at a temperature of 160℃ to obtain a flexible phase change film, which was denoted as the control sample.

[0055] Figure 2 The mechanical property curves are those of the flexible phase change film obtained in Example 1. Figure 2 As shown, the comparative sample is a blend of thermoplastic elastomer and paraffin that is grafted but not crosslinked, while the example sample is a blend of grafted and crosslinked thermoplastic elastomer and paraffin from Example 1. It can be seen that the dynamic crosslinking structure constructed in Example 1 can achieve the enhancement and toughening of composite phase change materials.

[0056] Figure 3 The image shows the DSC curve of the flexible phase change film in Example 1. Figure 3 It can be seen that the crystallization temperature of the comparative sample (Comparative Example 1) is 38.2℃, and the enthalpy of crystallization is 144.5 J / g; the melting temperature is 52.8℃, and the enthalpy of melting is 152.1 J / g. The sample of Example 1, because it has the same phase transition composition as the comparative sample, has a similar phase transition temperature and enthalpy. Its crystallization temperature is 38.7℃, and the enthalpy of crystallization can reach 149.2 J / g; its melting temperature is 51.3℃, and the enthalpy of melting can reach 156.5 J / g.

[0057] Figure 4 The electron microscope image of the sample from Example 1 after the paraffin was etched away shows that the paraffin was uniformly coated in the cross-linked thermoplastic elastomer.

[0058] The mechanical property data of the above embodiments and comparative examples are summarized in Table 1:

[0059] Table 1

[0060]

[0061]

[0062] As shown in Table 1, different grafting agents and crosslinking agents have a significant impact on the crosslinking density of the composite phase change material, resulting in significant differences in the mechanical properties of different samples. With increasing content of grafting and crosslinking agents, the crosslinking density, tensile stress, and tensile strain of the composite phase change material increase. However, with further increases in the content of grafting and crosslinking agents, excessive crosslinking density leads to a decrease in the tensile strain of the composite phase change material. Simultaneously, excessive grafting agent also leads to an increase in side reactions, causing the thermoplastic elastomer chain segments to break and reducing tensile stress. In summary, as in Example 1, when the mass of grafting agent and crosslinking agent each accounts for 2% of the polyolefin mass, the composite phase change material exhibits the best mechanical properties.

[0063] The thermal performance data of the above embodiments and comparative examples are summarized in Table 2:

[0064] Table 2

[0065]

[0066] As shown in Table 2, the sample without grafting or crosslinking of the thermoplastic elastomer (Example 2-0MA) exhibits less restriction on the chain movement of the phase change components, resulting in higher enthalpy of crystallization and enthalpy of melting. However, the sample with grafting and crosslinking exhibits lower enthalpy of crystallization and enthalpy of phase change due to the adverse effects of the grafting and crosslinking network on the paraffin phase change. Nevertheless, the sample of Example 1, with the best mechanical properties, still possesses a high enthalpy of phase change: 149.2 J / g for crystallization and 156.5 J / g for melting.

[0067] While specific embodiments of the present invention have been described above, those skilled in the art should understand that these are merely illustrative examples, and various changes or modifications can be made to these embodiments without departing from the principles and essence of the present invention. The scope of protection of the present invention is defined only by the appended claims.

Claims

1. A method for preparing a high-enthalpy flexible phase change material, characterized in that, Includes the following steps: S1. Using maleic anhydride as a grafting agent and thermoplastic elastomer as the grafting target, a graft-modified thermoplastic elastomer is prepared, wherein the thermoplastic elastomer is selected from at least one of ethylene-octene copolymer, ethylene-butene copolymer, olefin block copolymer, and styrene-ethylene-butene-styrene block copolymer. S2. A crosslinking agent and a phase change material are added to the grafted modified thermoplastic elastomer and melt-blended to obtain a high enthalpy flexible phase change material. The crosslinking agent is an alcohol compound that undergoes an esterification reaction with maleic anhydride grafted onto the thermoplastic elastomer. The phase change material is selected as paraffin wax, and the crosslinking agent is selected from at least one of glycerol, propylene glycol, and hexanediol. The amounts of each component, by weight, are as follows: 10-30 parts by weight of thermoplastic elastomer; 70-90 parts by weight of phase change material; 1-4 parts by weight of grafting agent; Crosslinking agent 1-4 parts by weight.

2. The method for preparing a high-enthalpy flexible phase change material according to claim 1, characterized in that, Both steps S1 and S2 are carried out in a mixer or an extruder.

3. The method for preparing a high-enthalpy flexible phase change material according to claim 1, characterized in that, The temperature for blending in steps S1 and S2 is 150~160 °C.

4. The method for preparing a high-enthalpy flexible phase change material according to claim 1, characterized in that, Step S1 specifically includes: using peroxide as an initiator and grafting maleic anhydride onto the thermoplastic elastomer through melt blending.

5. The method for preparing a high-enthalpy flexible phase change material according to any one of claims 1-4, characterized in that, In step S2, the following methods may be adopted: first add the crosslinking agent to perform crosslinking, and then add the phase change material and mix evenly; or first add the phase change material to perform crosslinking, and then add the crosslinking agent to perform crosslinking.

6. The high enthalpy flexible phase change material prepared by the preparation method according to any one of claims 1-5.

7. The application of the high enthalpy flexible phase change material according to claim 6, characterized in that, The high-enthalpy flexible phase change material is used to prepare flexible phase change membranes.

8. The application according to claim 7, characterized in that, The high enthalpy flexible phase change material is formed into a flexible phase change film by hot pressing, blown film or casting molding methods.

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