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

Abstract

The invention discloses a high-enthalpy-value flexible phase change material as well as a preparation method and application thereof, and relates to the technical field of polymer composite materials. The preparation method comprises the following steps: preparing a graft-modified thermoplastic elastomer by taking maleic anhydride as a grafting agent and a polyolefin thermoplastic elastomer as a grafting object; and adding a cross-linking agent and a phase change material into the graft-modified thermoplastic elastomer, and carrying out melt blending to obtain the high-enthalpy-value flexible phase change material. According to the preparation method disclosed by the invention, a three-dimensional cross-linked network is constructed, so that the three-dimensional cross-linked network is more excellent in flexibility, the three-dimensional cross-linked network is constructed by introducing anhydride-alcohol ester dynamic bonds, and reinforcing and toughening of the organic solid-liquid phase change material are realized; due to the introduction of a cross-linked network, the polymer supporting structure can better coat the phase change material, so that the content of the phase change material is ensured, namely the high energy storage density is given.

Description

Technical Field

[0001] The present invention relates to the technical field of polymer composite materials, and particularly relates to a high-enthalpy flexible phase change material, a preparation method thereof, and an application thereof. Background Art

[0002] With the development of electronic devices towards miniaturization, high power, and high integration, a large amount of heat accumulates. If efficient heat dissipation is not carried out in a timely manner, it will accelerate their failure. Phase change materials (hereinafter referred to as PCMs) can absorb or release heat in the form of latent heat during the phase change process and maintain the temperature relatively stable. When the phase change material is used as a thermal management component, it can not only control the device temperature to prevent thermal runaway, but also make the temperature distribution more uniform to prevent heat accumulation. Traditional organic solid-liquid phase change materials have received extensive attention due to their advantages such as large energy storage density, low supercooling degree, wide phase change temperature range, and good chemical stability. However, they are prone to brittle fracture and cannot be adapted to application scenarios that require flexibility, such as thermal management of flexible electronic devices and wearable technologies. Therefore, improving the mechanical properties, especially the flexibility, of organic solid-liquid phase change materials is crucial for their development and practical applications.

[0003] Currently, the strategies for preparing flexible phase change materials can be roughly divided into flexible porous support materials, flexible shell encapsulation, and polymer network structures. Compared with high-cost porous materials and flexible shell encapsulation, polymers represented by polyolefin elastomers (POE) as the support materials of flexible phase change materials have the advantages of simple process, low cost, and rich raw material sources, and have the potential for large-scale preparation. However, further performance optimization still needs to be carried out through polymer network structure design to achieve the balance of 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] Aiming at the above defects, the present application provides a preparation method of a high-enthalpy flexible phase change material with enhanced mechanical properties. The obtained phase change material realizes the enhancement of mechanical properties while ensuring the energy storage density by regulating the crosslinking network density. Moreover, due to the formation of the crosslinking structure, the thermoplastic elastomer matrix realizes better encapsulation of the phase change component, ensuring that the phase change component will not leak under high-temperature conditions and enhancing the shape stability of the composite material at high temperatures. The present invention prepares a flexible phase change material with high enthalpy and super toughness through the synergistic effect of the crosslinking reaction of anhydride-alcohol ester and polyolefin-coated paraffin, and the preparation method of the phase change material can realize large-scale industrial production.

[0006] To achieve the above object, on the one hand, the present invention provides a preparation method of a high-enthalpy flexible phase change material, which includes the following steps:

[0007] S1. Using maleic anhydride as a grafting agent and a thermoplastic elastomer as a 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 graft-modified thermoplastic elastomer and melt-blended to obtain a high-enthalpy flexible phase change material, wherein the crosslinking agent is an alcohol compound that undergoes an esterification reaction with the maleic anhydride grafted onto the thermoplastic elastomer, and the phase change material is selected as paraffin.

[0009] The mechanism involved in the preparation of the high-enthalpy flexible phase change material in the present invention is as follows: In the present invention, grafting refers to maleic anhydride being grafted onto a polyolefin chain. Ethylene-octene copolymer, ethylene-butene copolymer, olefin block copolymer, styrene-ethylene-butene-styrene block copolymer, etc. are selected as grafting targets. Among these block copolymers, maleic anhydride grafting is more likely to occur on non-ethylene blocks because the free radicals formed by these blocks have higher stability. This reaction has great similarity and can be expressed as: the initiator decomposes and attacks the polyolefin chain segment to form a macromolecular free radical, and then the macromolecular free radical reacts with maleic anhydride to form a graft structure. Crosslinking in the present invention is the reaction of an alcohol with the maleic anhydride grafted onto the chain. The side reaction in the present invention mainly occurs during the grafting process because the subsequent crosslinking belongs to an esterification reaction and does not involve free radicals, and will not affect the macromolecular chain segments. For the listed polyolefin copolymers, their side reactions are more related to the dosage of the initiator and maleic anhydride. If the dosage is too small, the grafting amount may be small, and the crosslinking density after crosslinking is low, which cannot achieve the effect of coating the phase change component and improving the mechanical properties; while if the dosage is too large, it will cause the degradation of the polyolefin, resulting in a decrease in molecular weight and strength. Therefore, in practical applications, appropriate dosages of the initiator and maleic anhydride are required to obtain a high-enthalpy flexible phase change material with enhanced mechanical properties.

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

[0011] Thermoplastic elastomer: 10 - 30 parts by weight;

[0012] Phase change material: 70 - 90 parts by weight;

[0013] Grafting agent: 1 - 4 parts by weight;

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

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

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

[0017] As a further preferred technical solution 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 step S1 and step S2 are carried out in a mixer or an extruder; and / or, the temperature for carrying out the corresponding operations in step S1 and step S2 is 140-160 °C, such as 140 °C, 145 °C, 150 °C, 155 °C, 160 °C, etc.

[0019] As a further preferred technical solution of the present invention, in step S1, a peroxide is used as an initiator, and maleic anhydride is grafted onto the thermoplastic elastomer by melt blending. The peroxide initiator can be selected from one or more of dicumyl peroxide (DCP), di-tert-butyl peroxide, and benzoyl peroxide, and the di-tert-butyl peroxide can be di-tert-butyl peroxyisopropylbenzene, 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 is adopted: adding the crosslinking agent for crosslinking first and then adding the phase change material to be blended evenly, or adding the phase change material to be blended evenly first and then adding the crosslinking agent for 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 still 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 forms a flexible phase change film by a forming method such as hot pressing, blown film, 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 crosslinked network: more excellent flexibility, a three-dimensional crosslinked network is constructed by introducing anhydride-alcohol ester dynamic bonds, realizing the enhancement and toughening of organic solid-liquid phase change materials; high energy storage density, the introduction of the crosslinked network enables the polymer support structure to better encapsulate the phase change material, ensuring the content of the phase change material, that is, endowing 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 crosslinked network enhances the melt strength of the composite phase change material. Therefore, the flexible phase change material has excellent processing performance and can realize large-scale industrial preparation. Brief Description of the Drawings

[0026] The present invention will be further described in detail below in conjunction with the drawings and specific embodiments.

[0027] Figure 1 It is a reaction and preparation mechanism diagram of the high-enthalpy flexible phase change material in the present invention. First, a crosslinked thermoplastic elastomer is prepared through grafting and crosslinking reactions, and then the phase change material is introduced into the crosslinked network of the crosslinked thermoplastic elastomer to obtain the high-enthalpy flexible phase change material.

[0028] Figure 2 It is the mechanical property curve of the flexible phase change film obtained in Example 1. From 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, realizing the enhancement and toughening of the material.

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

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

[0031] The realization of the object, functional characteristics and advantages of the present invention will be further described in conjunction with the embodiments with reference to the drawings. Specific Embodiments

[0032] The specific embodiments of the present invention will be described in detail below in conjunction with the drawings. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0033] Unless otherwise defined, the technical terms used in the following embodiments have the same meaning as commonly understood by those skilled in the art to which the present invention pertains. The test reagents used in the following embodiments are all conventional biochemical reagents unless otherwise specified; the experimental methods are all conventional methods unless otherwise specified.

[0034] The mechanical properties, thermal properties and microstructures of the film samples with the same specifications and dimensions prepared in each embodiment were characterized by a tensile machine, a differential scanning calorimeter, a scanning electron microscope, etc.

[0035] Example 1:

[0036] The preparation of a flexible phase change film based on flexible phase change material pellets provided in this example has a chemical reaction mechanism as Figure 1 shown, and the specific preparation method is as follows:

[0037] 1) Polyolefin POE8150 of thermoplastic elastomer, initiator DCP, and grafting agent maleic anhydride MA were mixed at a mass ratio of 100:0.2:2, and melt-blended at 160 °C for 5 - 10 min to obtain maleic anhydride-grafted polyolefin POE8150.

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

[0039] 3) The crosslinked polyolefin elastomer POE8150 and paraffin were melt-blended at a mass ratio of 30:70 at 160 °C for 10 - 20 min to obtain flexible phase change material pellets with a crosslinked structure;

[0040] 4) The phase change material pellets 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: due to different dosage ratios of the grafting agent, four groups of samples were prepared respectively

[0042] 1) Polyolefin POE8150 of thermoplastic elastomer, initiator DCP, and grafting agent maleic anhydride MA were mixed at a mass ratio of 100:0.2:0 / 0.5 / 1 / 3, and melt-blended at 160 °C for 5 - 10 min to obtain a series of polyolefin POE8150 grafted with different ratios of maleic anhydride.

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

[0044] 3) The series of polyolefin POE8150 with different degrees of crosslinking were respectively melt-blended with paraffin at a mass ratio of 30:70 at 160 °C for 10 - 20 min to obtain a series of flexible phase change material pellets with a crosslinked structure;

[0045] 4) The series of phase change material pellets were hot-pressed at a temperature of 160 °C to obtain a series of flexible phase change films, denoted as: Example 2 - 0MA, Example 2 - 0.5MA, Example 2 - 1MA, Example 2 - 3MA.

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

[0047] Mix the olefin copolymer OBC of thermoplastic elastomer, initiator DCP and grafting agent maleic anhydride MA in a mass ratio of 100:0.2:2, and melt-blend at 160 °C for 5 - 10 min to obtain maleic anhydride-grafted olefin block copolymer OBC.

[0048] Then add glycerol with a molar ratio of groups equal to that of maleic anhydride as a cross-linking agent, and melt-blend for 5 - 10 min to obtain olefin block copolymers OBC with different cross-linking degrees.

[0049] Mix olefin block copolymers OBC with different cross-linking degrees and paraffin in a mass ratio of 30:70 and melt-blend at 160 °C for 10 - 20 min to obtain flexible phase change material pellets with a cross-linked structure; perform hot pressing on the phase change material pellets, and the hot pressing temperature is 160 °C to obtain a flexible phase change film.

[0050] Compared with Example 1, Example 3 only changes the type of thermoplastic elastomer, and the mechanical properties and thermal properties show a similar change trend.

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

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

[0053] 2) Mix the polyolefin elastomer POE8150 grafted with maleic anhydride and paraffin in a mass ratio of 30:70 and melt-blend at 160 °C for 10 - 20 min to obtain composite phase change material pellets with only a grafted structure and no cross-linking;

[0054] 3) Perform hot pressing on the phase change material pellets, and the hot pressing temperature is 160 °C to obtain a flexible phase change film, denoted as: comparative sample.

[0055] Figure 2 It is the mechanical property curve of the flexible phase change film obtained in Example 1. As Figure 2 shown, the comparative sample is a blend sample of a thermoplastic elastomer with only grafting and no cross-linking and paraffin, and the example sample is a blend sample of a grafted and cross-linked thermoplastic elastomer and paraffin in Example 1; it can be seen that the dynamic cross-linked structure constructed in Example 1 can achieve the enhancement and toughening of the composite phase change material.

[0056] Figure 3 It is the DSC curve of the flexible phase change film in Example 1. FromFigure 3 It can be seen that the crystallization temperature of the comparative sample (Comparative Example 1) is 38.2 °C, and the crystallization enthalpy is 144.5 J / g; the melting temperature is 52.8 °C, and the melting enthalpy is 152.1 J / g. Since the phase change components of the sample of Example 1 are the same as those of the comparative sample, the phase change temperature and phase change enthalpy values are similar. The crystallization temperature is 38.7 °C, and the crystallization enthalpy can reach 149.2 J / g; the melting temperature is 51.3 °C, and the melting enthalpy can reach 156.5 J / g.

[0057] Figure 4 The electron microscope photograph after etching off the paraffin of the sample of Example 1 shows that the paraffin is evenly coated in the cross-linked thermoplastic elastomer.

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

[0059] Table 1

[0060]

[0061]

[0062] As can be seen from Table 1, different grafting agents and cross-linking agents have a great influence on the cross-linking density of the composite phase change material, and thus there are great differences in the mechanical properties of different samples. With the increase in the content of the grafting agent and the cross-linking agent, the cross-linking density of the composite phase change material increases, and the tensile stress and tensile strain increase; then, with the further increase in the content of the grafting agent and the cross-linking agent, the excessive cross-linking density leads to a decrease in the tensile strain of the composite phase change material. At the same time, too much grafting agent also leads to an increase in side reactions, resulting in the fracture of the thermoplastic elastomer chain segments and a decrease in the tensile stress. In short, as in Example 1, when the masses of the grafting agent and the cross-linking agent respectively account for 2% of the mass of the polyolefin, the composite phase change material exhibits the best mechanical properties.

[0063] The thermal property data of the above examples and comparative examples are summarized in Table 2 as follows:

[0064] Table 2

[0065]

[0066] As can be seen from Table 2, for the sample without grafting and cross-linking of the thermoplastic elastomer (Example 2-0MA), the restriction on the chain movement of the phase change components is smaller, and the crystallization enthalpy and melting enthalpy are higher; while for the samples with grafting and cross-linking, due to the adverse effects of the grafting and cross-linking networks on the paraffin phase change, the crystallization enthalpy and phase change enthalpy of the thermally conductive flexible phase change material decrease. However, the sample of Example 1 with the best mechanical properties still has a high phase change enthalpy of 149.2 J / g for crystallization enthalpy and 156.5 J / g for melting enthalpy.

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

Claims

1. A preparation method of a high-enthalpy flexible phase change material, characterized in that, It includes the following steps: S1. Using maleic anhydride as a grafting agent and a thermoplastic elastomer as a grafting object, a graft-modified thermoplastic elastomer is prepared, where 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 graft-modified thermoplastic elastomer and melt-blended to obtain a high-enthalpy flexible phase change material, where the crosslinking agent is an alcohol compound that undergoes an esterification reaction with the maleic anhydride grafted onto the thermoplastic elastomer, and the phase change material is selected as paraffin wax.

2. The preparation method of the high-enthalpy flexible phase change material according to claim 1, wherein By weight, the dosages of each component are as follows: Thermoplastic elastomer: 10 - 30 parts by weight; Phase change material: 70 - 90 parts by weight; Grafting agent: 1 - 4 parts by weight; Crosslinking agent: 1 - 4 parts by weight.

3. The preparation method of the high-enthalpy flexible phase change material according to claim 1, characterized in that Both step S1 and step S2 are carried out in a mixer or an extruder.

4. The preparation method of the high-enthalpy flexible phase change material according to claim 3, characterized in that, The temperature for the blending treatment in step S1 and step S2 is 150 - 160 °C.

5. The preparation method of the high-enthalpy flexible phase change material according to claim 1, characterized in that The crosslinking agent is selected from at least one of glycerol, propylene glycol, and hexanediol.

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

7. The preparation method of the high-enthalpy flexible phase change material according to any one of claims 1-6, characterized in that, In step S2, the following is adopted: adding the crosslinking agent for crosslinking first and then adding the phase change material and blending evenly, or adding the phase change material and blending evenly first and then adding the crosslinking agent for crosslinking.

8. A high-enthalpy flexible phase change material prepared by the method according to any one of claims 1 - 7.

9. The application of the high-enthalpy flexible phase change material according to claim 8, characterized in that Using the high-enthalpy flexible phase change material to prepare a flexible phase change film.

10. The application according to claim 8, characterized in that The high-enthalpy flexible phase change material forms a flexible phase change film through a forming method such as hot pressing, blown film, or casting.

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