Thermally conductive flexible composite phase change material, and preparation method and application thereof

Abstract

The application relates to the technical field of heat-conducting composite materials, and discloses a heat-conducting flexible composite phase change material as well as a preparation method and application thereof. The method comprises the following steps: modifying a thermoplastic elastomer by grafting maleic anhydride as a grafting agent; modifying a heat-conducting filler by surface hydroxylation with a strong base as a surface modifier; melt blending the grafted thermoplastic elastomer with a phase change material, and adding the surface-modified heat-conducting filler to crosslink, so as to obtain the heat-conducting flexible composite phase change material. By regulating and controlling the micro-interface structure of the filler-matrix, the interface interaction between the filler and the matrix is enhanced, the heat-conducting-support integrated structure is constructed, the interaction between the filler and the matrix is improved, the dispersion of the filler in the matrix is improved, the interface phonon scattering is reduced, the heat-conducting flexible composite phase change material has good heat-conducting performance, and meanwhile, the heat-conducting flexible composite phase change material also has strong mechanical performance and high energy storage density.

Description

A thermally conductive flexible composite phase change material, its preparation method and application Technical Field

[0001] This invention relates to the field of thermally conductive composite materials technology, specifically to a thermally conductive flexible composite phase change material, its preparation method, and its application. Background Technology

[0002] Phase change materials (PCMs) can reversibly absorb and release large amounts of heat energy while maintaining relatively stable temperatures, making them widely used in energy storage and conversion, heat management, and other fields. However, traditional organic solid-liquid PCMs are prone to melt leakage and brittle fracture, making them unsuitable for applications requiring flexibility. Flexible PCMs can be easily prepared based on polymer network structures, such as thermoplastic elastomers like styrene-butadiene-styrene block copolymers (SBS), olefin block copolymers (OBC), and polyurethane (PU). Moreover, this method utilizes inexpensive raw materials, involves simple processes, and produces flexible PCMs with good processability.

[0003] Furthermore, the low thermal conductivity of traditional organic phase change materials severely limits their heat transfer rate in applications. Dispersing nanofillers with high thermal conductivity and thermal stability (such as graphite and hexagonal boron nitride) into organic phase change materials to prepare high thermal conductivity composite phase change materials is a simple and feasible approach. However, the introduction of thermally conductive fillers often significantly deteriorates the mechanical properties of the composite material, making it difficult to simultaneously improve the material's flexibility and thermal conductivity.

[0004] Therefore, it is crucial to optimize the microstructure of the filler-matrix interface and balance or simultaneously improve the material's flexibility and thermal conductivity. Summary of the Invention

[0005] To address the aforementioned shortcomings, this invention provides a thermally conductive flexible composite phase change material, its preparation method, and its application. By controlling the microscopic interface structure of the filler-matrix, the obtained phase change material not only achieves enhanced mechanical properties but also further improves the thermal conductivity of the composite phase change material. Furthermore, the preparation method of this thermally conductive composite phase change material has the potential for large-scale industrial production.

[0006] To achieve the above objectives, the present invention provides a method for preparing a thermally conductive flexible composite 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. The thermally conductive filler is modified by surface hydroxylation using a strong alkali as a surface modifier to generate reactive groups on the surface of the thermally conductive filler, wherein the thermally conductive filler is at least one of hexagonal boron nitride, alumina, graphene, and carbon nanotubes.

[0009] S3. Select paraffin wax as the phase change material, melt-blend the grafted modified thermoplastic elastomer obtained in step S1 with the phase change material, and add the surface-modified thermally conductive filler obtained in step S2 for cross-linking to obtain a thermally conductive flexible composite phase change material.

[0010] As a further preferred embodiment of the present invention, the amounts of each component by weight are as follows:

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

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

[0013] 2.5-10 parts by weight of thermally conductive filler;

[0014] 1-4 parts by weight of grafting agent.

[0015] In a further preferred embodiment, the thermoplastic elastomer comprises 30 parts by weight, the phase change material comprises 70 parts by weight, and the grafting agent comprises 2 parts by weight.

[0016] As a further preferred embodiment of the present invention, the strong alkali is at least one of sodium hydroxide and potassium hydroxide, and the surface hydroxylation modification is performed using an aqueous solution of the strong alkali.

[0017] As a further preferred embodiment of the present invention, step S1 specifically includes: using a peroxide as an initiator, and grafting maleic anhydride onto the thermoplastic elastomer through melt blending, wherein the melt blending processing temperature is 150-160°C. The peroxide initiator may be selected from one or more of dicumyl peroxide (DCP), di-tert-butyl peroxide, and benzoyl peroxide, wherein di-tert-butyl peroxide may be di-tert-butylperoxyisopropylbenzene, 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane, etc.

[0018] As a further preferred technical solution of the present invention, step S2 specifically includes: placing the thermally conductive filler in a strong alkaline solution with a concentration of 4-5M for heating modification, and the reaction temperature is 100-120℃.

[0019] As a further preferred technical solution of the present invention, in step S3, the melt blending processing temperature is 150-160°C.

[0020] According to another aspect of the present invention, a thermally conductive flexible composite phase change material is also provided, which is prepared by the above-described method.

[0021] According to another aspect of the present invention, an application of a thermally conductive flexible composite phase change material in the preparation of a thermally conductive composite phase change film is also provided. Specifically, the thermally conductive flexible composite phase change material is formed into a thermally conductive composite phase change film by hot pressing, blown film blowing, or casting.

[0022] This invention enhances the interfacial interaction between the filler and matrix by controlling the microscopic interface structure, thus constructing an integrated thermally conductive and support structure. Compared with existing technologies, it has the following advantages: excellent thermal conductivity; the interaction between the filler and matrix improves the dispersion of the filler within the matrix, reduces interfacial phonon scattering, and gives the thermally conductive flexible composite phase change material good thermal conductivity; enhanced mechanical properties; on the one hand, the introduction of rigid filler enhances the fracture strength of the thermally conductive flexible phase change material; on the other hand, the interaction between the filler and matrix allows force to be distributed between the filler and the matrix, avoiding stress concentration, resulting in extremely high elongation at break of the thermally conductive flexible composite phase change material; high latent heat; the low content of thermally conductive filler in this thermally conductive flexible composite phase change material ensures the content of the phase change components, and the interaction between the filler and matrix does not affect the phase change process of the phase change components, giving the thermally conductive flexible composite phase change material high energy storage density. Attached Figure Description

[0023] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0024] Figure 1 shows the mechanical property curves of the thermally conductive flexible composite phase change film obtained in Example 1.

[0025] Figure 2 shows the DSC curve of the thermally conductive flexible composite phase change film obtained in Example 1.

[0026] Figure 3 shows the thermal conductivity of the thermally conductive flexible composite phase change film obtained in Example 1.

[0027] Figure 4 is an SEM image of the thermally conductive flexible composite phase change film obtained in Example 1.

[0028] 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

[0029] 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.

[0030] 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.

[0031] The mechanical properties, thermal properties, thermal conductivity, and structure 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.

[0032] Example 1: Preparation of thermally conductive composite phase change film

[0033] 1) First, prepare a 5M sodium hydroxide solution, then add the thermally conductive filler hexagonal boron nitride (BN) to the sodium hydroxide solution at a ratio of 1 gram per 100 ml, and heat and stir at 120℃ for 24 h to obtain hydroxylated modified boron nitride filler (BNOH).

[0034] 2) Mix thermoplastic elastomer polyolefin POE, 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 POE.

[0035] 3) The maleic anhydride-grafted polyolefin POE and paraffin are melt-blended at 160℃ for 10-20 min at a mass ratio of 30:70 to obtain a flexible phase change material; then 5 parts by mass of hydroxylated modified boron nitride BNOH are added and melt-blended for 5-10 min to obtain thermally conductive flexible composite phase change material granules.

[0036] 4) The thermally conductive flexible composite phase change material granules are hot-pressed at a temperature of 160℃ to obtain a thermally conductive composite phase change film.

[0037] Example 2:

[0038] 1) First, prepare a 5M sodium hydroxide solution, then add the thermally conductive filler hexagonal boron nitride (BN) to the sodium hydroxide solution at a ratio of 1 gram per 100 ml, heat and stir at 120℃ for 24 h to obtain the hydroxylated modified boron nitride filler.

[0039] 2) Maleic anhydride-grafted polyolefin POE is prepared by mixing thermoplastic elastomer polyolefin POE, initiator DCP and grafting agent maleic anhydride MA in a mass ratio of 100:0.2:2 and melting and blending at 160℃ for 5-10 min.

[0040] 3) POE grafted with maleic anhydride and paraffin are melt-blended at 160℃ for 10-20 min at a mass ratio of 30:70 to obtain a flexible phase change material; then 2.5 parts by mass of hydroxylated modified boron nitride (BNOH) are added and melt-blended for 5-10 min to obtain thermally conductive flexible composite phase change material granules.

[0041] 4) The thermally conductive flexible composite phase change material granules are hot-pressed at a temperature of 160℃ to obtain a thermally conductive composite phase change film.

[0042] Example 3:

[0043] 1) First, prepare a 5M sodium hydroxide solution, then add the thermally conductive filler BN at a ratio of 1 gram per 100 ml to the sodium hydroxide solution, heat and stir at 120℃ for 24 h to obtain the hydroxylated modified boron nitride filler.

[0044] 2) Maleic anhydride-grafted polyolefin POE is prepared by mixing thermoplastic elastomer polyolefin POE, initiator DCP and grafting agent maleic anhydride MA in a mass ratio of 100:0.2:2 and melting and blending at 160℃ for 5-10 min.

[0045] 3) The grafted maleic anhydride POE and paraffin are melt-blended at 160℃ for 10-20 min at a mass ratio of 30:70 to obtain a flexible phase change material; then 10 parts by mass of hydroxylated modified boron nitride (BNOH) are added and melt-blended for 5-10 min to obtain thermally conductive flexible composite phase change material granules.

[0046] 4) The thermally conductive flexible composite phase change material granules are hot-pressed at a temperature of 160℃ to obtain a thermally conductive composite phase change film.

[0047] Comparative Example 1:

[0048] First, thermoplastic elastomer polyolefin (POE) and initiator DCP are melt-blended at 160℃ for 5-10 minutes at a mass ratio of 100:0.2. Then, paraffin wax (paraffin to polyolefin mass ratio of 70:30) is added and melt-blended for 10-20 minutes to obtain flexible phase change material granules. Finally, the flexible phase change material granules are hot-pressed at 160℃ to obtain a composite phase change film.

[0049] Comparative Example 2:

[0050] First, thermoplastic elastomer polyolefin (POE) and crosslinking agent DCP are melt-blended at 160℃ for 5-10 min at a mass ratio of 100:0.2. Then, paraffin wax (paraffin to polyolefin mass ratio of 70:30) is added and melt-blended for 10-20 min to obtain a flexible phase change material. Finally, 5 parts by mass of boron nitride are added and melt-blended for 5-10 min to obtain thermally conductive flexible phase change material granules. Finally, the thermally conductive flexible phase change material granules are hot-pressed at 160℃ to obtain a thermally conductive composite phase change film.

[0051] Figure 1 shows the mechanical property curves of the thermally conductive composite phase change film obtained in Example 1 (marked as the sample of Example 1 in the figure). As shown in Figure 1, Comparative Sample 1 is the thermally conductive composite phase change film without the addition of thermally conductive filler, Comparative Sample 2 is the thermally conductive composite phase change film with the addition of unmodified thermally conductive filler, and the example sample is the sample of Example 1 described in this application. It can be seen that the integrated thermally conductive-support structure constructed by the present invention can enhance the strength and elongation at break of the thermally conductive flexible composite phase change material. The elongation at break increased from 891% in Comparative Example 1 and 240% in Comparative Example 2 to 2191%, and the tensile strength at break also increased from 1.69 MPa in Comparative Example 1 and 3.09 MPa in Comparative Example 2 to 3.36 MPa.

[0052] Figure 2 shows the DSC curve of the thermally conductive composite phase change film obtained in Example 1 (marked as the sample of Example 1 in the figure). As can be seen from Figure 2, the integrated thermally conductive-support structure of the example sample did not adversely affect the crystallization of the comparative components. The crystallization temperature of the example sample was 40.72℃, and the enthalpy of crystallization reached 134.9 J / g; the melting temperature was 49.84℃, and the enthalpy of melting reached 145.2 J / g, which are similar to those of Comparative Examples 1 and 2.

[0053] Figure 3 shows the thermal conductivity of the thermally conductive composite phase change film obtained in Example 1 (labeled as the sample of Example 1 in the figure). As can be seen from Figure 3, the interaction between the filler and the matrix in the example samples improved the thermal conductivity enhancement effect of the thermally conductive filler. The thermal conductivity of the sample of Example 1 increased from 0.32 W / mK in Comparative Example 1 and 0.97 W / mK in Comparative Example 2 to 1.44 W / mK.

[0054] Figure 4 shows a cross-sectional SEM image of the paraffin-etched sample from Example 1. As can be seen from the SEM in Figure 4, the phase change component and the polymer support component have good compatibility, allowing the phase change material to be uniformly dispersed in the polymer matrix; the thermally conductive filler is oriented along the horizontal direction, imparting high in-plane thermal conductivity to the phase change material.

[0055] The mechanical and thermal conductivity data of the above embodiments and comparative examples are summarized in Table 1.

[0056] Table 1

[0057]

[0058] As shown in Table 1, the integrated thermally conductive and support structure constructed in this patent can simultaneously improve the mechanical and thermal conductivity of the composite material. With the increase of the thermally conductive filler content, the internal thermally conductive network of the composite phase change material becomes more complete but introduces more defects. Therefore, the mechanical properties of the composite phase change material show a trend of first increasing and then decreasing, while the thermal conductivity gradually increases. However, compared with Comparative Examples 1-2, it can be found that this structure endows the composite phase change material with superior mechanical and thermal properties. A comparison of Examples 1-3 shows that by changing the proportion of BNOH, the mechanical and thermal properties change significantly, with Example 1 exhibiting the best overall performance.

[0059] The phase transformation properties of the comparative examples and embodiments are not significantly different, and the crystallization temperature and melting temperature are similar. However, the phase transformation enthalpy and melting enthalpy show the same trend as the change in filler content. As the filler content increases, the phase transformation component content decreases relatively, and the phase transformation enthalpy and melting enthalpy decrease.

[0060] 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 thermally conductive flexible composite phase change material, characterized in that, Includes the following steps: S1. Using maleic anhydride as a grafting agent, thermoplastic elastomer as the grafting target, and peroxide as an initiator, maleic anhydride is grafted onto the thermoplastic elastomer through melt blending at a temperature of 150-160 °C to obtain a grafted modified thermoplastic elastomer; 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. Using a strong base as a surface modifier, the thermally conductive filler is surface-hydroxylated to generate reactive groups on the surface of the thermally conductive filler; wherein the thermally conductive filler is at least one of hexagonal boron nitride, graphene, and carbon nanotubes; S3. Paraffin wax is selected as a phase change material, and the grafted modified thermoplastic elastomer obtained in step S1 is melt-blended with the phase change material at a temperature of 150-160 °C. °C, and crosslink the surface-modified thermally conductive filler obtained in step S2 to obtain a thermally conductive flexible composite phase change material; by weight, the amounts of each component in step S3 are as follows: thermoplastic elastomer 10-30 parts by weight; phase change material 70-90 parts by weight; thermally conductive filler 2.5-10 parts by weight; grafting agent 1-4 parts by weight.

2. The method for preparing the thermally conductive flexible composite phase change material according to claim 1, characterized in that, The strong base is at least one of sodium hydroxide and potassium hydroxide.

3. The method for preparing the thermally conductive flexible composite phase change material according to claim 1, characterized in that, Step S2 specifically includes: placing the thermally conductive filler in a strong alkaline solution with a concentration of 4~5 M for heating modification, with a reaction temperature of 100~120 °C.

4. A thermally conductive flexible composite phase change material, characterized in that, It is prepared by the method described in any one of claims 1-3.

5. The application of the thermally conductive flexible composite phase change material according to claim 4 in the preparation of thermally conductive composite phase change films.

6. The application according to claim 5, characterized in that, The thermally conductive flexible composite phase change material is formed into a thermally conductive composite phase change film by hot pressing, blown film or casting molding methods.

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