A reversible thermochromic composite material and its preparation method

Abstract

This invention discloses a reversible thermochromic composite material, belonging to the technical field of thermochromic composite materials. It is a multi-component system formed by using 2,6-monosubstituted linear phenolic resin as a color developer, combined with crystal violet lactone, a monohydric alcohol mixture, and natural rubber. The 2,6-monosubstituted linear phenolic resin is polymerized using bisphenol A, glyoxal, and glutaraldehyde as comonomers. The monohydric alcohol mixture is formed by mixing hexadecyl alcohol and octadecyl alcohol. This method minimizes interference with H+ while preserving the OH group. + The reversible thermochromic composite film prepared by using 2,6-monosubstituted linear phenolic resin (GA-BPA-GDA) as a color developer exhibits good thermal stability and recyclability.

Description

Technical Field

[0001] This invention belongs to the field of thermochromic composite material technology, and particularly relates to a reversible thermochromic composite material and its preparation. Background Technology

[0002] Reversible thermochromic materials that track ambient temperature and generate color responses have been extensively studied and widely applied in fields such as smart windows, sensors, and printing. These materials typically consist of an electron donor, an electron acceptor, a melting limit regulator, and a film-forming agent. Electron donors are fluoranes and triphenylmethanes with lactone rings, serving as leucochromic agents; however, fluoranes are prone to decarboxylation and denaturation upon exposure to light. Electron acceptors include phenols and acids, serving as chromogenic agents. Phenols are too reactive and potentially harmful, while acidic systems have high color-changing temperatures, limiting their application in environments far from human habitation. Therefore, organic systems based on bisphenol A (BPA) and crystal violet lactone (CVL) have become a key research focus.

[0003] When the temperature reaches the melting limit of the system, the phenolic hydroxyl groups lose or regain H. + The lactone ring either gains or loses H. + By modulating visible light absorption through tautomerism between the lactone ring and quinone, rapid and significant reversible color change can be achieved. To meet the requirements of temperature measurement, certain types and proportions of higher fatty alcohols can be added to adjust the melting limit, i.e., the color change range, of the system.

[0004] Furthermore, the stability of these materials can be improved by refining preparation methods, including compounding and microencapsulation. The former directly combines the aforementioned components, but is prone to leakage. Therefore, encapsulating multiple components in a flexible, spherical polymer shell offers stability and environmental friendliness, attracting widespread attention from researchers. The disadvantage of microencapsulation is the risk of BPA exposure after the polymer shell degrades or is damaged. Summary of the Invention

[0005] To address the above issues and overcome the shortcomings of existing technologies, this invention provides a reversible thermochromic composite material and its preparation method. A 2,6-monosubstituted linear phenolic resin (GA-BPA-GDA) is prepared using BPA, GA, and GDA as comonomers, minimizing interference with H+ without damaging the OH groups. + The reversible thermochromic composite film prepared by using 2,6-monosubstituted linear phenolic resin (GA-BPA-GDA) as a color developer exhibits good thermal stability and recyclability.

[0006] The technical solution adopted in this invention is as follows:

[0007] In a first aspect, the present invention provides a reversible thermochromic composite material, a multi-component system formed by using 2,6-monosubstituted linear phenolic resin as a colorimetric agent, combined with crystal violet lactone, a mixture of monohydric alcohols, and natural rubber. The 2,6-monosubstituted linear phenolic resin is polymerized using bisphenol A, glyoxal, and glutaraldehyde as comonomers, and the monohydric alcohol mixture is a mixture of hexadecyl alcohol and octadecyl alcohol. The relative molecular mass and distribution of the prepared 2,6-monosubstituted linear phenolic resin are characterized by GPC. 1 H-NMR spectrum, 13 C-NMR spectroscopy confirmed that it is a 2,6-monosubstituted linear phenolic resin.

[0008] Furthermore, polarized light microscopy analysis of the composite film prepared from the above-mentioned raw materials showed that the composite film has tunable and reversible thermochromic properties because the cryptic colorant, monohydric alcohol mixture, and natural rubber in the composite film affect the formation of the co-crystallized phase.

[0009] Furthermore, the mass ratio of the crystal violet lactone, 2,6-monosubstituted linear phenolic resin, monohydric alcohol mixture, and natural rubber component is 1:(1.0-3.5):(10-60):(10-60). Within this range, the ΔE of the prepared reversible color-changing composite material is approximately 50-75. Experimental data show that with the increase of GA-BPA-GDA, ΔE / t, crystallization limit, and ΔH... m and ΔH c The appropriate ratio of CVL, GA-BPA-GDA, monohydric alcohol mixture (hexadecyl alcohol + octadecyl alcohol), and natural rubber, obtained by first reducing and then increasing, is beneficial to improving the ΔE of the composite film.

[0010] Thermochromic properties of reversible thermochromic composite materials prepared under different ratios were tested. Preferably, the mass ratio of crystal violet lactone, 2,6-monosubstituted linear phenolic resin, monohydric alcohol mixture, and natural rubber component was 1:(1.5-3.5):(20-60):(20-60). Most preferably, the mass ratio of crystal violet lactone, 2,6-monosubstituted linear phenolic resin, monohydric alcohol mixture, and natural rubber component was 1:2.0:20:60. According to this ratio, the composite film obtained by the casting method exhibits excellent thermochromic ability, with a ΔE of approximately 75. It reaches around 30.

[0011] Under the above-described basic formulation, the mass ratio of hexadecyl alcohol to octadecyl alcohol in the monohydric alcohol mixture is (0.03-0.12):(0.03-0.12). Preferably, the mass ratio of hexadecyl alcohol to octadecyl alcohol in the monohydric alcohol mixture is 0.06:0.09.

[0012] Furthermore, the 2,6-monosubstituted linear phenolic resin is prepared based on an open system and solution polycondensation method. The 2,6-monosubstituted linear phenolic resin with a content of 2.93×106 g / mol and a PDI of 1.49 was polymerized. Experiments showed that the 2,6-monosubstituted linear phenolic resin obtained by polymerization under certain mass ratios has good thermal stability.

[0013] In a second aspect, this invention provides a method for preparing the reversible thermochromic composite material described in the first aspect. The method involves dispersing and stirring crystal violet lactone, 2,6-monosubstituted linear phenolic resin, a monohydric alcohol mixture, and natural rubber in a solution according to appropriate mass ratios until dissolved. The resulting mixed solution is then obtained by casting and drying. Experiments using this method demonstrate that, under the appropriate mass ratios, the composite film absorbs light primarily in the 500-650 nm visible light region. The composite film obtained by the casting method exhibits excellent thermochromic ability, with a ΔE of approximately 75. It reaches around 30.

[0014] The beneficial effects of the present invention after adopting the above structure are as follows:

[0015] (1) In the experiment of reversible thermochromic composite film of 2,6-monosubstituted linear phenolic resin, it was found that GA-BPA-GDA, mixed alcohol, and natural rubber all significantly affected the ΔE / t, crystallization limit, and ΔH of the composite film. m and ΔH c The ratio of CVL, GA-BPA-GDA, a monohydric alcohol mixture (cetearyl alcohol + octadecanol), and natural rubber is 1:2.0:20:60. The composite film obtained by the casting method exhibits excellent thermochromic properties, with a ΔE of approximately 75. Reaching around 30;

[0016] (2) Analysis of polarized light microscopy images showed that the formation of the co-crystallized phase was affected by the cryptic colorant, monohydric alcohol mixture and natural rubber in the composite film, which gave it adjustable and reversible thermochromic properties.

[0017] (3) Composite films of 2,6-monosubstituted linear phenolic resins have good thermal stability and recyclability. Attached Figure Description

[0018] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the embodiments of the invention to explain the invention and do not constitute a limitation thereof.

[0019] Figure 1 For GA-BPA-GDA 1 H-NMR spectrum;

[0020] Figure 2 For GA-BPA-GDA 13 C-NMR spectrum;

[0021] Figure 3 The curve is GA-BPA-GDATG-DTG.

[0022] Figure 4 The TG-DTG curve of the composite membrane;

[0023] Figure 5 The DSC curve for GA-BPA-GDA;

[0024] Figure 6 The DSC curve of the composite membrane;

[0025] Figure 7 To investigate the absorption region of light waves by composite films prepared with CVL:GA-BPA-GDA at different ratios;

[0026] Figure 8 To investigate the absorption region of light waves in composite films prepared with CVL (hexadecyl alcohol + octadecyl alcohol) at different ratios;

[0027] Figure 9 To investigate the absorption region of light waves in composite films prepared with CVL (chemical viscosity level) of natural rubber at different proportions;

[0028] Figure 10 To investigate the absorption region of light waves in composite films prepared with cetyl alcohol and octadecyl alcohol at different ratios;

[0029] Figure 11 The curve shows the number of DSC cycles for the membrane phase transition. Detailed Implementation

[0030] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0031] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0032] This invention designs a reversible thermochromic composite material. Addressing the shortcomings of microencapsulation and compounding methods, it focuses on the 2,6-substituted activity of BPA. By introducing monomers such as glyoxal (GA) and glutaraldehyde (GDA), which have good chain structure adjustment capabilities, it controllably synthesizes polymers with BPA. This process minimizes interference with H+ activity while preserving OH groups. Furthermore, the composite film preparation process is optimized, improving the compatibility and stability of the multi-component system. Building upon this foundation, a further method is employed: using BPA, GA, and GDA as comonomers, and employing an open system and solution polycondensation method, microwave-assisted preparation of a 2,6-monosubstituted linear phenolic resin (GA-BPA-GDA) is carried out. The resin is then used as a color developer to prepare a reversible thermochromic composite film.

[0033] Corresponding experiments were conducted to analyze and verify the optimal formulation and function of the reversible thermochromic composite membrane. Specifically, the effects of factors such as the leucochromic agent, film-forming substance, and monohydric alcohol mixture on the color-changing properties of the composite membrane were investigated. 1 H-NMR, 13 The resin structure was analyzed by C-NMR, and the thermal stability of the resin and composite film was studied. In addition, the film morphology and thermal cycling stability were also investigated.

[0034] The reagents and main instruments used in the above experiments are as follows:

[0035] Bisphenol A (chemically pure), 40% glyoxal aqueous solution (chemically pure), 25% glutaraldehyde aqueous solution (biological reagent), n-butanol (analytical grade), NaOH (analytical grade), methanol (analytical grade), anhydrous ethanol (analytical grade), cetyl alcohol (chemically pure), octadecyl alcohol (chemically pure), and crystal violet lactone (97%) were purchased from Shanghai Titan Technology Co., Ltd.; dichloromethane (analytical grade) and acetone (analytical grade) were purchased from Sinopharm Chemical Reagent Co., Ltd.; natural rubber was provided by Jiangsu Gefei New Materials Co., Ltd.; and alcohol-free gasoline (commercially available).

[0036] Microwave reactor (M1-L213B, Guangdong Midea Kitchen Appliances Manufacturing Co., Ltd.); Gel permeation chromatograph (GPC, PL-GPC 50, Agilent Technologies); Nuclear magnetic resonance spectrometer ( 1 H-NMR, 13 C-NMR (Avance Neo 500, Bruker Ltd.); Thermal analyzer (DSC, Q20, Waters Instruments Ltd.); Thermogravimetric analyzer (TG, Q50, Waters Instruments Ltd.); Spectrophotometer (CS-420, Hangzhou Caipu Technology Co., Ltd.); Polarizing microscope (PM, BX53P, Olympus Imaging Ltd.).

[0037] Example 1: Preparation of GA-BPA-GDA

[0038] Add 4.56 g bisphenol A (0.020 mol), 10.00 mL n-butanol, 0.57 mL 40% glyoxal aqueous solution (0.0050 mol, calculated as 1.265 g / cm3), 5.67 mL 25% glutaraldehyde aqueous solution (0.015 mol, calculated as 1.06 g / cm3), and 0.10 mL 1% (mass) NaOH solution to a 100 mL beaker in sequence. Sonicate at 60 °C for 5 min to obtain a transparent homogeneous liquid.

[0039] The beaker was placed in a microwave reactor, the power was set to 385W, and the microwave reaction was carried out for 4 minutes to obtain a crude product. The crude product was then removed by vacuum rotary evaporation at 80℃ to remove water, n-butanol, and unreacted monomers. The obtained product was dissolved in 10.00 mL of acetone and the low molecular weight substances were extracted by sonication for 5 minutes. 22.00 mL of a water-methanol (volume ratio 10:1) mixture was slowly added, and the layers were separated. The bottom organic phase was retained and dried to obtain 5.23 g of pale yellow resin, with a yield of 92% based on BPA.

[0040] Example 2: Preparation method of reversible thermochromic composite film

[0041] The basic formulation consists of CVL, GA-BPA-GDA, a mixture of monohydric alcohols (cetearyl alcohol + octadecanol), and natural rubber, in appropriate mass ratios. Typical conditions for preparing the composite membrane are as follows: CVL, GA-BPA-GDA, cetyl alcohol, octadecanol, and natural rubber are added in appropriate proportions to a V-beaker. Dichloromethane, acetone, and alcohol-free gasoline are added, and the mixture is stirred and dispersed at 60°C until dissolved, yielding a mixed solution. Glass slides are alternately washed three times each with deionized water and anhydrous ethanol. The membrane is then formed by casting and drying at 80°C.

[0042] Example 3

[0043] The preparation methods of GA-BPA-GDA and the reversible thermochromic composite membrane in Examples 1 and 2 were described. The prepared GA-BPA-GDA and the composite membrane were tested and characterized. Specifically, GPC was used to characterize the relative molecular mass and distribution of GA-BPA-GDA, with CHCl3 (chromatographic grade) as the solvent and PS as the internal standard. 1 H-NMR, 13 Chain structure was characterized by C-NMR using DMSO-d6 as solvent; thermal properties were studied by TG and DSC under N2 atmosphere at a heating / cooling rate of 10.00 °C / min. Thermal history was eliminated by one heating / cooling cycle before DSC thermal cycling.

[0044] refer to Figure 1-2 Number-average and weight-average relative molecular masses of GA-BPA-GDA The GPC results were 2.93×10⁶ and 4.39×10⁶ g / mol, and the dispersion index PDI = 1.49.

[0045] in, Figure 1 It is GA-BPA-GDA 1 ¹H-NMR spectrum. The asymmetric triplet at 9.65 ppm was obtained by long-range coupling splitting of ¹H with ³H and ⁴H, confirming it as a 2,6-monosubstituted linear phenolic resin. The peak area ratio of 2H to 3H, ⁴H is 1.00:2.00, consistent with an atomic ratio of 1:2. The peak area ratio of 8H to 5H, ⁶H is 3.82:1.91, consistent with the theoretical molar ratio of 1:3 for the comonomers GA and GDA.

[0046] Figure 2 It is GA-BPA-GDA 13 C-NMR spectrum. 153.3 ppm is an asymmetric triplet of 1C, confirming it as a 2,6-monosubstituted linear phenolic resin. No signal is observed for C≡C due to a high longitudinal relaxation time T1. No signal is observed for the quaternary carbon in CH3-C-CH3 because the rapid rotation of CH3 eliminates the relaxation between 8H and the quaternary carbon.

[0047] refer to Figure 3 and 4 The GA-BPA-GDA composite membrane exhibits two weight loss peaks. Below 304℃, 85% of the mass loss is attributed to the breakage of carbon dioxide (CC), while the 6% loss between 304-359℃ corresponds to the CO dehydration process. The composite membrane shows three weight loss peaks. Between 147-320℃, 36% of the loss is due to the volatilization of high-boiling fractions from gasoline; between 320-466℃, 62% is due to the cracking of natural rubber molecules; and between 466-525℃, the loss is attributed to the degradation of refractory carbon residue. This indicates that both the resin and the composite membrane possess good thermal stability below 50℃.

[0048] refer to Figure 5 and 6 The GA-BPA-GDA composite film exhibits two endothermic peaks. The peaks between 97-162℃ are attributed to melting, resulting from the dissociation of OH groups in intermolecular associations. This aligns with the lack of weight loss observed in TG-DTG analysis at this temperature. The peaks after 170℃ are due to the gradual breaking and disintegration of C-C bonds within the resin molecules. The composite film shows four endothermic peaks. The melting peak of the GA-BPA-GDA composite film disappears. Peak 1 corresponds to the melting of the co-crystallized phase of the cryptic agent and monohydric alcohol mixture. Peak 2 is attributed to the amorphous transformation of the natural rubber molecular backbone. The broad peak 3 is caused by resin cracking and the volatilization of high-boiling-point fractions from gasoline, with a relatively low thermal effect. The sharp peak 4 is due to the evaporation of small molecules from the breakage of natural rubber molecules.

[0049] The preparation process of the composite membrane is as follows: The basic formulation consists of CVL, GA-BPA-GDA, a monohydric alcohol mixture (cetearyl alcohol + octadecyl alcohol), and natural rubber, in a mass ratio of 0.0075:0.015:0.15 (0.06:0.09):0.45 (g). Typical conditions for preparing the composite membrane are as follows: In a 50 mL beaker, add 0.0075 g CVL, 0.015 g GA-BPA-GDA, 0.060 g cetyl alcohol, 0.090 g octadecyl alcohol, and 0.45 g natural rubber. Add 5.00 mL dichloromethane, 5.00 mL acetone, and 10.00 mL alcohol-free gasoline. Stir and disperse at 60 °C until dissolved to obtain a mixed solution. Wash the glass slides alternately with deionized water and anhydrous ethanol three times each. The membrane is then formed by casting and drying at 80 °C.

[0050] Example 4

[0051] The study included testing the color-changing properties of the composite membrane, comparing the thermochromic properties of the color-changing membranes prepared with different formulations, evaluating their thermal cycling stability, and analyzing polarized microscopic images of the composite membrane. The study encompassed the following two aspects:

[0052] (1) The lightness difference (ΔL) and color difference (Δa, Δb) of the composite film were measured using a spectrophotometer, and the total color difference was calculated. The membrane was heated to 80°C on a hot stage and then allowed to cool naturally at an ambient temperature of approximately 10°C. The time for complete color change was visually observed, and the color change rate was calculated. The crystallization limit and ΔH were obtained from the DSC curve. m and ΔH c Measure the spectral reflectance R before and after complete color change, according to the Kubelka-Munk law. calculate Value. Perform the above experiment three times in parallel.

[0053] (2) The phase transition process was observed using PM. The membrane was cut into particles, sandwiched between polarizers, and laid flat at the center of the light-transmitting hole on a high-temperature hot and cold stage. The temperature was raised to 60°C at a constant rate, equilibrated for 1 minute, and then cooled to 24°C to observe the changes in the membrane microstructure.

[0054] Specifically, the composite films prepared with different mass ratios (preparation methods are described in Examples 1-3) have thermochromic properties as shown in Table 1. It can be seen that with the increase of GA-BPA-GDA, ΔE / t, crystallization limit, and ΔH... m and ΔH c The initial decrease followed by an increase may be because the crystallization limit and latent heat of the eutectic phase are both low, and a suitable GA-BPA-GDA ratio is beneficial to the growth of the eutectic phase.

[0055] As the amount of monohydric alcohol mixture increases, ΔE / t and crystallization limit first decrease and then increase, while ΔH... m and ΔH c The principle of increasing first and then decreasing is due to the higher latent heat of monohydric alcohol mixtures. However, monohydric alcohol mixtures are amphiphilic small molecules. When in excess, they separate from the matrix phase, resulting in uneven films with poor mechanical properties.

[0056] Natural rubber, which exhibits high elasticity and slight plasticity at room temperature, was selected as the film material. With the increase in the amount of natural rubber, the crystallization limit first increased and then decreased, while ΔE / t increased, and ΔH... m and ΔH c The principle of reducing first and then increasing may be because rubber is a highly elastic molecule with a higher melting limit, which participates in and is conducive to the formation of a co-crystallized phase with lower latent heat. However, excessive rubber will also increase the difficulty of blending, dissolving and film making.

[0057] As the amount of octadecyl alcohol increases, the low-temperature range of the crystallization limit first decreases and then increases, along with ΔE / t, the high-temperature range of the crystallization limit, and ΔH. m and ΔH c The reason for this increase is that the monohydric alcohol mixture participates in the formation of the low-temperature eutectic phase at a lower eutectic point.

[16] This is due to the higher melting point and latent heat of octadecyl alcohol.

[0058] It is an important parameter in the Kubelka-Munk law. A higher value indicates a darker color. (Combined with...) Figure 7-10 As you can see, the absorption of light waves by the composite film is mainly located in the 500-650nm visible light region. When the appropriate mass ratio of CVL, GA-BPA-GDA, monohydric alcohol mixture (cetearyl alcohol + octadecanol) and natural rubber is 1:2.0:20:60, that is, 0.0075:0.015:0.15 (0.06:0.09):0.45 (g), it is beneficial to improve the ΔE of the composite film.

[0059] Furthermore, cycle stability is an important indicator for evaluating the practicality and economic efficiency of composite membranes. Figure 11 It can be seen that the DSC curves of the five thermal cycles are completely consistent after the second cycle, and the latent heat of phase change and peak temperature do not change. The composite membrane changes reversibly between blue and light yellow, which indicates that the membrane has a certain reusability and is suitable for occasions with frequent temperature rises and falls.

[0060] Analysis of polarized light micrographs of the composite film, such as Figure 12 At around 45°C, a pale yellow honeycomb pattern appears in a black field of view. This is due to the transformation of natural rubber molecules from a viscous flow state to an amorphous state, participating in the formation of a eutectic phase at high temperatures, which has a light blue hue. At 36°C, the pale yellow color deepens and the honeycomb becomes denser, as the rubber molecules gradually complete their transformation. At 27°C, the surface of the honeycomb-shaped rubber crystals is coated with a deep blue, which is the result of the co-crystallization of the luminescent agent and monohydric alcohol mixture at low temperatures during the cooling of the composite film. Below 27°C, the color of the film continues to deepen to some extent.

[0061] Table 1. Thermochromic properties of the composite film

[0062]

[0063]

[0064] The above experiments show that, using bisphenol A, glyoxal, and glutaraldehyde as comonomers, and based on an open system and solution polycondensation method, microwave-assisted preparation was achieved. 2.93×10 6 2,6-monosubstituted linear phenolic resin with g / mol and PDI of 1.49 was obtained through... 1 H-NMR, 13 C-NMR confirmed its structure. A reversible thermochromic composite film was prepared using resin as the colorimetric agent. When the mass ratio of crystal violet lactone, resin, a mixture of monohydric alcohols (cetetrazol + octadecanol), and natural rubber was 1:2.0:20:60, i.e., 0.0075:0.015:0.15 (0.06:0.09):0.45 (g), the ΔE of the composite film obtained by the casting method reached approximately 75. The temperature reaches around 30, exhibiting good thermal and cyclic stability. Furthermore, polarized light microscopy analysis indicates that the formation of the co-crystallized phase is influenced by the cryptic colorant, monohydric alcohol mixture, and natural rubber in the composite film, giving it tunable and reversible thermochromic properties.

[0065] Although embodiments of the present invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents. In conclusion, if those skilled in the art, inspired by this description, design similar structural methods and embodiments without departing from the inventive spirit of the invention, such designs should fall within the protection scope of the present invention.

Claims

1. A reversible thermochromic composite material, characterized in that: A multi-component system is formed using 2,6-monosubstituted linear phenolic resin as a colorimetric agent, combined with crystal violet lactone, a mixture of monohydric alcohols, and natural rubber. The 2,6-monosubstituted linear phenolic resin is polymerized using bisphenol A, glyoxal, and glutaraldehyde as comonomers. The 2,6-monosubstituted linear phenolic resin is prepared based on an open system and solution polycondensation method. 2.93×10 6 2,6-monosubstituted linear phenolic resin with g / mol, PDI of 1.49, and a yield of 92% based on BPA; The monohydric alcohol mixture is formed by mixing hexadecyl alcohol and octadecyl alcohol; The composite material is prepared by stirring and dispersing crystal violet lactone, 2,6-monosubstituted linear phenolic resin, monohydric alcohol mixture and natural rubber in a solution until dissolved, and then obtaining a mixed solution by casting and drying.

2. The reversible thermochromic composite material according to claim 1, characterized in that, The mass ratio of the crystal violet lactone, 2,6-monosubstituted linear phenolic resin, monohydric alcohol mixture and natural rubber component is 1:(1.0-3.5):(10-60):(10-60).

3. The reversible thermochromic composite material according to claim 1, characterized in that: The mass ratio of the crystal violet lactone, 2,6-monosubstituted linear phenolic resin, monohydric alcohol mixture and natural rubber component is 1:(1.5-3.5):(20-60):(20-60).

4. The reversible thermochromic composite material according to claim 1, characterized in that: The mass ratio of the crystal violet lactone, 2,6-monosubstituted linear phenolic resin, monohydric alcohol mixture and natural rubber component is 1:2.0:20:

60.

5. The reversible thermochromic composite material according to claim 1, characterized in that: The mass ratio of hexadecyl alcohol and octadecyl alcohol in the monohydric alcohol mixture is (0.03-0.12):(0.03-0.12).

6. The reversible thermochromic composite material according to claim 1, characterized in that: The mass ratio of hexadecyl alcohol to octadecyl alcohol in the monohydric alcohol mixture is 0.06:0.09.

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