Composite material based on reversible thermochromic flame-retardant mixture and preparation method thereof

Abstract

The invention discloses a reversible thermochromic flame-retardant mixture which is prepared by taking tetradecanol TD as a phase change material, a cosolvent and a surface modifier, crystal violet lactone CVL and bisphenol A BPA as an electron donor and an electron acceptor and nanoCaCO3 as a flame-retardant additive through a melt blending method. The preparation method comprises the following steps: 1, preparing a reversible thermochromic blend; and 2, preparing the reversible thermochromic flame-retardant mixture. The invention further discloses a reversible thermochromic composite material with the flame retardant property, delignification wood DW serves as a porous carrier, the reversible thermochromic flame retardant mixture CTBC is adsorbed through a vacuum impregnation method, and the reversible thermochromic composite material with the flame retardant property is obtained and has the phase change energy storage property, the reversible thermochromic property, the flame retardant property, the information storage property and the temperature self-response property at the same time. The preparation method comprises the following steps: carrying out first and second lignin removal treatment on poplar RW, carrying out freeze drying to obtain delignified wood DW, and carrying out vacuum impregnation on the DW in a CTBC blend.

Description

Technical Field

[0001] This invention relates to the fields of thermal management and reversible thermochromism, specifically to the preparation of a composite material based on a reversible thermochromic flame-retardant mixture. Background Technology

[0002] Reversible thermochromic materials are characterized by specific color changes that occur with temperature variations. These color changes can indicate the temperature of an object or environment, making them suitable for use as functional sensing materials in intelligent temperature measurement. The basic principle of reversible thermochromic materials is that, with the melting and solidification of the solvent, the lactone ring in the crystal violet lactone molecule opens and closes, resulting in electron transfer between the electron donor and electron acceptor. This shifts the absorption spectrum between the ultraviolet and visible light regions, causing a color change within the visible light range, thus exhibiting reversible thermochromic properties.

[0003] In common reversible thermochromic materials, crystal violet lactone (CVL) acts as an electron donor, bisphenol A (BPA) acts as an electron acceptor, and tetradecyl alcohol (TD), a phase change material, acts as a cosolvent. For example, existing literature 1 (Haiyue Yang, Yazhou Wang, Qianqian Yu, et al. Composite phase change materials with good reversible thermochromic ability in delignified wood substrate for thermal energy storage. Applied Energy, 2018, 212:455-464) adds crystal violet lactone and bisphenol A to molten 1-tetradecyl alcohol and stirs and dissolves at 90°C for 1 h to obtain a thermochromic compound. Then, the thermochromic compound is added to delignified wood chips by vacuum-assisted impregnation to obtain a thermochromic delignified composite phase change material. The thermochromic delignified composite phase change material obtained by this technical solution has good reversible thermochromic ability, and the phase change process and temperature can be intuitively displayed through color changes. However, these reversible thermochromic materials applied to delignified wood are all flammable, posing a safety hazard.

[0004] To address the safety issue of flammability in delignified wood, conventional methods involve using flame-retardant coatings to improve its flame-retardant properties. For example, in our previous work, existing literature 2 (application number 2024100586651, "A PCS-based Flame-Retardant Urea-Formaldehyde Resin and Its Preparation Method and Application") used phytic acid-chitosan composite polymer PCS as the bio-based flame-retardant component, urea and formaldehyde as the main raw materials, melamine and polyvinyl alcohol-124 as additives, dioctyl phthalate (DOP) as a plasticizer, and ammonium chloride and ammonium polyphosphate as composite curing agents to prepare a milky-white flame-retardant urea-formaldehyde resin based on PCS. This resin was then used for flame retardancy in wood, achieving excellent flame-retardant properties. However, this technical solution has created new technical problems when applied to reversible thermochromic materials. Since conventional flame-retardant coatings do not need to consider color development and are not transparent, an opaque coating is formed on the wood surface after applying a conventional flame-retardant coating. As a result, the color development phenomenon of the reversible thermochromic material cannot be observed through the coating. In other words, such conventional flame-retardant coatings are not suitable for reversible thermochromic materials.

[0005] Besides the aforementioned technical solutions, other existing flame-retardant technologies for wood also suffer from similar technical problems. For example, existing literature 3 (Yingnan Zhang, Mingju Jing, Muchen Zhang, et al. Preparation and Properties of Silica Gel Foam as Fire-Retardant with High Water Retention for Wood. Fire Technology, 2022, 58:3597-3621) prepared a novel high-water-retention silicone foam by mixing a composite foaming agent composed of sodium dodecylbenzenesulfonate and sodium dodecyl sulfate with foam stabilizers sodium polyacrylate, sodium silicate, sodium bicarbonate, aluminum citrate, and glucono-δ-lactone. This technical solution improves the flame-retardant properties of wood by forming a thermally stable layer of SiO2 in the wood through the silicone foam and adsorbing water molecules using hydrophilic groups. However, the silicone foam formed by this technical solution also significantly reduces the visibility of reversible heat-induced discoloration materials. Furthermore, when applied in the field of energy buildings, this technical solution also suffers from insufficient service life. Summary of the Invention

[0006] To address the aforementioned problems in existing technologies, this invention provides a method for preparing a composite material based on a reversible thermochromic flame-retardant mixture. The reversible thermochromic blend is compounded with flame-retardant nanoCaCO3, and then combined with delignified wood. This achieves both reversible thermochromic properties and flame-retardant properties in the composite material. The main technical principle is as follows:

[0007] 1. Tetradecyl alcohol plays a role in the technical solution mainly in two aspects:

[0008] 1.1 In terms of reversible thermochromic properties, tetradecyl alcohol acts as both a phase change material and a cosolvent, i.e., it dissolves CVL and BPA and realizes the reversible thermochromic function of the composite material.

[0009] 1.2 In terms of flame retardant properties, tetradecyl alcohol can modify the surface of nanoCaCO3, increase the hydrophobicity and oleophilicity of nanoCaCO3, thereby improving the compatibility of nanoCaCO3 with composite materials and achieving composite;

[0010] 2. The role of nanoCaCO3 in the technical solution is that it can be simultaneously incorporated into the DW pore structure along with the thermochromic mixture, achieving flame retardant effect without affecting the thermochromic function.

[0011] To achieve the above-mentioned objectives, the technical solution adopted by this invention is as follows:

[0012] A reversible thermochromic flame retardant mixture, comprising tetradecanol TD as a phase change material, cosolvent and surface modifier, crystal violet lactone CVL and bisphenol A BPA as electron donor and electron acceptor, and nanoCaCO3 as a flame retardant additive, was prepared by melt blending.

[0013] The nanoCaCO3 has a size of 50-70 nm.

[0014] A method for preparing a reversible thermochromic flame retardant blend includes the following steps: Step 1, preparation of the reversible thermochromic blend, wherein crystal violet lactone (CVL): bisphenol A (BPA): tetradecyl alcohol (TD) meets a certain mass ratio. First, under certain conditions, TD is heated and melted into a liquid state. Then, under certain conditions, CVL and BPA are added to TD in sequence, and the mixture is stirred under certain conditions until it is uniformly mixed to obtain the reversible thermochromic blend TBC.

[0015] In step 1, the mass ratio of CVL:BPA:TD is 1:4:50;

[0016] In step 1, the conditions for heating and melting TD are: heating temperature is 50℃; the conditions for adding CVL and BPA are: maintaining the temperature at 50℃ and stirring for 30-60 minutes.

[0017] Step 2, preparation of reversible thermochromic flame retardant mixture: Under certain temperature conditions, a certain amount of nano-calcium carbonate nanoCaCO3 is added to TBC and stirred under certain conditions until the mixture is uniform, thus obtaining reversible thermochromic flame retardant mixture CTBC.

[0018] In step 2, the amount of nanoCaCO3 added is 7-14 wt%, and the conditions for adding nanoCaCO3 are: maintaining the temperature at 50℃ and stirring for 30-60 min.

[0019] A reversible thermochromic composite material with flame-retardant properties was prepared by adsorbing a reversible thermochromic flame-retardant mixture CTBC using delignified wood (DW) as a porous carrier and a vacuum impregnation method. It is referred to as CTBC / DW.

[0020] The resulting CTBC / DW simultaneously possesses phase change energy storage performance, reversible thermochromic performance, flame retardant performance, information storage, and temperature self-response performance;

[0021] The function of the DW is to provide a porous structure for the composite material;

[0022] The phase change thermal storage performance has a thermal density of 168.97 J / g. -1 ;

[0023] The flame retardant properties were demonstrated by the composite material maintaining a relatively intact shape even after a 50-second test.

[0024] The reversible thermochromic property is characterized by the following color change: the thermochromic temperature is 38°C, the color is dark blue below the phase transition temperature, and light wood color above the phase transition temperature, and this process is reversible.

[0025] The information storage and temperature self-response performance, achieved through the use of barcodes made of composite materials, allows for information reading and concealment via temperature control; the composite material can also report the temperature range inside the cup from the outside of the cup wall, enabling visual reading.

[0026] A method for preparing a reversible thermochromic composite material with flame-retardant properties includes the following steps:

[0027] First, poplar RW was placed in a mixed treatment solution of NaOH and Na2SO3 of a certain concentration and heated under certain conditions to remove lignin for the first time. After the heating treatment was completed, RW was placed in deionized water and heated and washed under certain conditions to obtain RW-1.

[0028] The NaOH concentration in the mixed treatment solution is 2.5 mol / L. -1 The concentration of Na2SO3 is 0.5 mol / L. -1 ;

[0029] The conditions for the first lignin removal heat treatment are: heating to 100°C and boiling, with a heat treatment time of 6-8 hours;

[0030] After the first heat treatment to remove lignin, the conditions for heat washing are: heating to 100°C and boiling, each heat washing time is 1 hour, and the number of heat washing cycles is 8-10.

[0031] Then, RW-1 was placed in a H2O2 solution of a certain concentration and soaked under certain conditions to achieve the second removal of lignin. After the soaking treatment was completed, RW-1 was placed in deionized water and heated and washed under certain conditions to obtain RW-2.

[0032] The H2O2 concentration in the H2O2 solution is 2.5 mol / L. -1 ;

[0033] The conditions for the second lignin removal soaking treatment are: soaking temperature of 25℃ and soaking time of 2-4 hours;

[0034] After the second lignin removal soaking treatment, the heating and washing conditions are as follows: heating to 100°C and boiling, each heating and washing time is 1 hour, and the number of heating and washing cycles is 8-10.

[0035] Then, under certain conditions, RW-2 was freeze-dried to obtain delignified wood DW;

[0036] The freeze-drying conditions are as follows: freeze-drying temperature is -52℃, and freeze-drying time is 27-48h;

[0037] Finally, DW is placed in the CTBC blend and vacuum impregnated under certain conditions to obtain a reversible thermochromic composite material with flame retardant properties, referred to as CTBC / DW.

[0038] The vacuum impregnation conditions are as follows: impregnation temperature is 60°C, and impregnation time is 24-36 hours.

[0039] The technical effects of this invention have been tested and verified, and the specific details are as follows:

[0040] According to FT-IR testing, there is no strong chemical interaction between DW, BPA, CVL, nanoCaCO3 and TD, and the components are physically mixed.

[0041] The present invention, as shown by SEM testing, has the following characteristics: DW has high porosity, multi-channel cell structure and nanopores between wood cells, which is beneficial for impregnation of flame-retardant thermochromic composite materials. The longitudinal section of 10CTBC / DW is filled with CTBC, which makes the tubular DW pore structure smooth. Furthermore, it is shown that the size of conventional calcium carbonate does not meet the conditions for addition into the pores of DW.

[0042] Differential scanning calorimetry (DSC) analysis of this invention revealed that the melting temperature of the 10CTBC / DW composite material is 35.56℃, and the phase transition enthalpy is 168.97 J / g. -1 .

[0043] According to the reversible thermochromic function test of this invention, when the temperature of the 10CTBC / DW composite material is raised from 20°C to 50°C on a constant temperature heating table, the color of the sample gradually changes from dark blue to light wood color as the temperature rises, completing the thermochromic process, and this process is reversible.

[0044] The leak-proof effect test of this invention shows that the 10CTBC / DW composite material is a stable solid at room temperature, and retains its initial form after being heated for 60 minutes at 45°C.

[0045] The flame retardant effect test of this invention shows that the 10CTBC / DW composite material still maintains a good shape when the test time is 50s, indicating that it has a certain flame retardant function.

[0046] In summary, the present invention has the following advantages:

[0047] 1. This invention combines carbon-based porous carrier delignified wood (DW) with reversible thermochromic material and flame-retardant material nanoCaCO3, adding flame-retardant functional material without affecting the reversible thermochromic phenomenon, thus achieving dual-function application;

[0048] 2. Using nanoCaCO3 with a size of 50-70nm, CaCO3 was added to the DW pore structure;

[0049] 3. In this invention, tetradecyl alcohol is used as a phase change material and a co-solvent to provide a reaction environment for crystal violet lactone and bisphenol A to accept open-ring electrons and release closed-ring electrons.

[0050] 4. The long carbon chain structure and hydroxyl groups of tetradecyl alcohol are used to modify the surface of nanoCaCO3 to increase its hydrophobicity and oleophilicity, improve the compatibility between materials, prevent liquid phase leakage of phase change materials, and endow it with high adsorption rate and phase change enthalpy.

[0051] 5. The present invention uses the phase transition temperature of tetradecyl alcohol, 38°C, as the dividing line. Below the phase transition temperature, the composite material appears dark blue. During the heating stage, it exhibits a color change process from dark blue to light wood color. During the cooling stage, a reversible color change process from light wood color to dark blue occurs. Attached Figure Description

[0052] Figure 1 The thermochromic properties of TBC in Example 1 are shown in the diagram.

[0053] Figure 2 The FTIR plot of Example 1;

[0054] Figure 3 Here are the SEM images of RW, DW, and nanoCaCO3 in Example 1;

[0055] Figure 4 This is a SEM image of Example 1;

[0056] Figure 5 Crystallization and melting curves for Examples 1, 2, 3, and Comparative Example 3;

[0057] Figure 6 These are test images of reversible thermochromic heating in Examples 1, 2, 3, and Comparative Example 3.

[0058] Figure 7 These are the reversible thermochromic cooling test diagrams for Examples 1, 2, 3, and Comparative Example 3;

[0059] Figure 8 The flame retardant test diagrams are for Examples 1, 2, 3, Comparative Example 3, and DW.

[0060] Figure 9 This is a leak resistance test diagram of Example 1 and tetradecyl alcohol;

[0061] Figure 10 The barcode information display and hiding test and temperature response test diagrams are from Example 1;

[0062] Figure 11 The image shows a reversible thermochromic test result for Comparative Example 1.

[0063] Figure 12 The image shows the reversible thermochromic pattern of Comparative Example 2.

[0064] Figure 13 This is a diagram of the leakage resistance test for Comparative Example 2;

[0065] Figure 14 This is a SEM image of conventional CaCO3 in Comparative Example 4. Detailed Implementation

[0066] The present invention will be further described in detail through embodiments and with reference to the accompanying drawings, but this is not intended to limit the scope of the invention.

[0067] Example 1

[0068] A method for preparing a reversible thermochromic flame retardant mixture includes the following steps:

[0069] Step 1, Preparation of reversible thermochromic blend: With a mass ratio of crystal violet lactone (CVL): bisphenol A (BPA): tetradecyl alcohol (TD) of 1:4:50, firstly, 3.5g of TD was heated and melted into a liquid state at a heating temperature of 50℃. Then, while maintaining the temperature at 50℃, 0.07g of CVL and 0.28g of BPA were added to TD sequentially, and the mixture was stirred for 30 minutes until it was uniformly mixed, thus obtaining the reversible thermochromic blend TBC.

[0070] To demonstrate the reversible thermochromic function of TBC, a reversible thermochromic test was conducted. The test results are as follows: Figure 1 As shown, TBC appears dark blue at 20℃; as the temperature increases, TBC changes color in the range of 35-40℃; TBC appears white at 50℃ and changes from a solid state to a molten state.

[0071] Step 2, preparation of reversible thermochromic flame retardant mixture: keep the temperature at 50℃, add 0.43g of nano-calcium carbonate nanoCaCO3 to TBC, stir for 30min until uniformly mixed, and the reversible thermochromic flame retardant mixture CTBC is obtained. In specific example 1, the amount of nanoCaCO3 added is 10wt%, so it is named 10CTBC.

[0072] A method for preparing a reversible thermochromic composite material with flame-retardant properties, i.e., the application of the reversible thermochromic flame-retardant mixture, includes the following steps:

[0073] First, poplar wood RW was placed in NaOH with a concentration of 2.5 mol / L. -1 The concentration of Na2SO3 is 0.5 mol / L. -1 The RW was heated in the mixed treatment solution to boiling at 100°C for 8 hours to achieve the first removal of lignin. After the heating treatment was completed, the RW was placed in deionized water and heated to boiling at 100°C for 1 hour each time, and the number of heating and washing cycles was 10 times to obtain RW-1.

[0074] Then, RW-1 was placed in an environment with an H2O2 concentration of 2.5 mol L. -1 The lignin was removed by soaking in H2O2 solution at a soaking temperature of 25℃ for 3 hours. After soaking, RW-1 was placed in deionized water and heated to 100℃ boiling point for 1 hour each time, and the number of times the heating and washing was carried out was 10 times to obtain RW-2.

[0075] Subsequently, RW-2 was freeze-dried at a freeze-drying temperature of -52℃ for 36 hours to obtain delignified wood DW.

[0076] Finally, DW is placed in 10CTBC blend and vacuum impregnated at an impregnation temperature of 60°C for 24 hours to obtain a reversible thermochromic composite material with flame retardant properties, abbreviated as CTBC / DW. The CTBC / DW obtained in Specific Example 1 is named 10CTBC / DW.

[0077] To verify the composition of 10CTBC / DW, FTIR testing was performed. Simultaneously, to demonstrate the successful addition of RW, DW, CVL, BPA, TD, and nanoCaCO3 to the composite material, FTIR testing of RW, DW, CVL, BPA, TD, and nanoCaCO3 was conducted as a baseline comparison.

[0078] FTIR test results are as follows Figure 2 As shown, 10CTBC / DW simultaneously contains the characteristic absorption peaks of DW, CVL, BPA, TD, and nanoCaCO3, and no new absorption peaks are generated, indicating that the characteristic absorption peaks of 10CTBC / DW and TD are similar. The test results show that DW, CVL, BPA, and nanoCaCO3 do not affect the crystal structure of TD, and there are no strong chemical interactions between DW, BPA, CVL, nanoCaCO3, and TD, meaning that the components are physically mixed.

[0079] To demonstrate the microstructure of 10CTBC / DW, SEM tests were performed on 10CTBC / DW. Meanwhile, to further confirm the changes in microstructure during the preparation process, SEM tests were performed on the raw material RW, the DW obtained in Example 1, and nanoCaCO3.

[0080] SEM test results of nanoCaCO3 are as follows: Figure 3 e and Figure 3 As shown in f, the size of nanoCaCO3 is 50-70 nm;

[0081] The SEM test results of the longitudinal section of RW are as follows: Figure 3 a and Figure 3 As shown in b, it exhibits a longitudinal tubular aperture structure;

[0082] The SEM test results of the longitudinal section of DW are as follows: Figure 3 c and Figure 3As shown in d, DW has a highly oriented macroporous structure, and in addition, micropores with a diameter of 10 μm are uniformly distributed around the macroporous structure. The test results compared with RW show that, due to the removal of lignin, DW has higher porosity, multi-channel cell structure and nanopores between wood cells. This porous structure is more conducive to the impregnation of flame-retardant thermochromic composite materials.

[0083] SEM test results of the longitudinal section of 10CTBC / DW are as follows: Figure 4 As shown, the tubular DW pore structure becomes smooth due to the filling with 10CTBC.

[0084] To demonstrate the thermal storage performance of 10CTBC / DW, differential scanning calorimetry (DSC) tests were performed. To further confirm the phase change properties of the composite material, DSC tests were conducted on TD as a baseline comparison.

[0085] The test results of the melt curve of TD are as follows: Figure 5 As shown in b and Table 1, within the test temperature range of -10 to 90℃, the melting process exhibits an endothermic peak at 39.25℃, with a latent heat value of 242.25 J / g. -1 ;

[0086] The test results of the crystallization curve of TD are as follows: Figure 5 As shown in a and Table 1, within the test temperature range of -10 to 90℃, the crystallization process exhibits an exothermic peak at 30.20℃, with a latent heat value of 241.15 J / g. -1 ;

[0087] The test results of the melt profile of 10CTBC / DW are as follows: Figure 5 As shown in b and Table 1, within the test temperature range of -10 to 90℃, the melting process exhibits an endothermic peak at 35.56℃, with a latent heat value of 168.97 J / g. -1 ;

[0088] The crystallization curve test results of 10CTBC / DW are as follows: Figure 5 As shown in a and Table 1, within the test temperature range of -10 to 90℃, the crystallization process exhibits an exothermic peak at 25.09℃, with a latent heat value of 168.22 J / g. -1 ;

[0089] Test results show that the T of 10CTBC / DW m Both are lower than pure TD, which is attributed to the reduced thermal resistance of DW after being filled with flame-retardant thermochromic material due to its excellent carbon network structure, allowing 10CTBC / DW to undergo phase transition behavior earlier. During crystallization, 10CTBC / DW has a lower T value compared to pure TD. cThe temperature dropped by 5.11℃ because the highly open macroporous structure of the DW network made it difficult for TD to nucleate on the DW framework, thus leading to a decrease in its 10CTBC / DW crystallization temperature.

[0090] Table 1. Thermophysical properties of TD and CTBC / DW with different nanoCaCO3 mass fractions.

[0091]

[0092]

[0093] To demonstrate the reversible thermochromic function of the 10CTBC / DW, a reversible thermochromic test was conducted. The test results are as follows: Figure 6 and Figure 7 As shown,

[0094] The heat-induced color change process of 10CTBC / DW is as follows: Figure 6 As shown, 10CTBC / DW appears dark blue at 20℃. As the temperature rises, 10CTBC / DW changes color in the range of 35-40℃. When the temperature is above 40℃, 10CTBC / DW appears light wood color.

[0095] The cooling discoloration process of 10CTBC / DW is as follows: Figure 7 As shown, at 45℃, 10CTBC / DW appears light wood color. As the temperature decreases, 10CTBC / DW undergoes color change behavior in the range of 40-35℃. When the temperature is below 35℃, 10CTBC / DW appears dark blue.

[0096] The following conclusions can be drawn from the reversible thermochromic function test and phase change thermal storage performance test of 10CTBC / DW: The 10CTBC / DW prepared in this invention has both reversible thermochromic function and phase change function, and the difference between the reversible thermochromic temperature and the phase change temperature is less than 5℃.

[0097] To demonstrate the flame retardant properties of 10CTBC / DW, a combustion performance test was conducted on it, and a combustion test was also performed on DW as a baseline comparison.

[0098] DW's combustion test results are as follows Figure 8 As shown, after 50 seconds of testing, DW had completely turned into black charcoal;

[0099] The combustion test results of 10CTBC / DW are as follows: Figure 8 As shown, when the test time is 50s, the surface of 10CTBC / DW is partially blackened, but the wood itself still maintains a good shape.

[0100] Combustion test results show that the composite material with added nanoCaCO3 has flame-retardant properties.

[0101] To demonstrate the shape stability of the 10CTBC / DW, a leak resistance test was conducted. Simultaneously, a leak resistance test was performed on the TD as a baseline comparison.

[0102] TD's leakage resistance test results are as follows Figure 9 As shown, under the conditions of heating temperature of 45℃ and heating time of 20min, TD has completely melted;

[0103] The leakage resistance test results of 10CTBC / DW are as follows: Figure 9 As shown, under the same conditions, namely a heating temperature of 45°C and the same sample volume, and a heating time of 60 min, the 10CTBC / DW maintained its original block shape, and no TD leakage was observed.

[0104] Leakage resistance test results show that 10CTBC / DW maintains a stable solid state after phase transition, exhibiting good shape stability and meeting leakage prevention requirements.

[0105] To demonstrate that the 10CTBC / DW has information storage and temperature self-reporting functions, barcode information display and hiding tests and temperature response tests were conducted.

[0106] The barcode information display and hiding test results for 10CTBC / DW are as follows: Figure 10 As shown, at room temperature, the 10CTBC / DW is dark blue and can be scanned to read barcode information; when the temperature is 38℃, which is the phase transition temperature, the 10CTBC / DW undergoes a thermochromic change, turning into a light wood color, and the barcode information cannot be scanned, thus achieving information hiding.

[0107] The temperature response test results of 10CTBC / DW are as follows: Figure 10 As shown, the 10CTBC / DW is attached to the outer wall of the cup. If the 10CTBC / DW is dark blue, it indicates that the water temperature inside the cup is lower than the phase change temperature; if the 10CTBC / DW is light wood color, it indicates that the water temperature inside the cup is higher than the phase change temperature.

[0108] The above experiments have demonstrated that the 10CTBC / DW possesses leak-proof, phase change heat storage, reversible thermochromic, and flame-retardant properties.

[0109] To demonstrate the role of tetradecyl alcohol in the technical solution, Comparative Example 1 is provided, a mixture prepared without the addition of tetradecyl alcohol.

[0110] Comparative Example 1

[0111] A method for preparing a mixture without adding tetradecyl alcohol, the specific steps of which are the same as the method for preparing the reversible thermochromic flame retardant mixture in Example 1, the difference being that tetradecyl alcohol is not added in step 1, and the resulting mixture is named 10BC.

[0112] The reversible thermochromic test results of 10BC are as follows: Figure 11 As shown, at 50°C, 10BC is off-white, indicating no thermochromic phenomenon. Furthermore, 10BC remains in a solid particle state, making subsequent vacuum impregnation impossible and thus preventing the preparation of a reversible thermochromic composite material with flame-retardant properties. Comparison of the test results with Example 1 shows that without the addition of tetradecyl alcohol, the mixture does not possess thermochromic properties. In addition, tetradecyl alcohol acts as a co-solvent in the mixture, ensuring its liquid state.

[0113] To further confirm the role of tetradecyl alcohol in the technical solution, Comparative Example 2 is provided, which is a composite material prepared by adding n-octadecane. The reason and purpose is that since tetradecyl alcohol is a common phase change material, n-octadecane, another common phase change material, is used to simply replace tetradecyl alcohol.

[0114] Comparative Example 2

[0115] A method for preparing a composite material with added n-octadecane, the specific steps of which are the same as the preparation methods of the reversible thermochromic flame retardant mixture and the reversible thermochromic composite material in Example 1, the difference being that n-octadecane (OD) is used instead of tetradecyl alcohol in step 1, and the resulting composite material is named 10COBC / DW.

[0116] The reversible thermochromic test results of 10COBC / DW are as follows: Figure 12 As shown, at 50°C, 10COBC / DW appears blue, indicating that no thermochromic phenomenon occurred. Comparing the test results with Example 1, it can be seen that while adding OD (alkane-based phase change material) can act as a co-solvent, similar to TD, to liquefy the mixture and allow for subsequent vacuum impregnation to prepare the composite material, the resulting composite material does not possess reversible thermochromic properties. In other words, adding alkane-based phase change materials cannot achieve thermochromic properties.

[0117] The leak resistance test results of 10COBC / DW are as follows: Figure 13 As shown, leakage occurred in the 10COBC / DW mixture after heating at 45℃ for 10 minutes. The test results indicate that adding alkane-based phase change materials cannot achieve anti-leakage performance. This is because TD, in its technical solution, not only acts as a phase change material and co-solvent, but also modifies the surface of nanoCaCO3, making it oleophilic, thereby enhancing the interaction between the components and ultimately improving anti-leakage performance.

[0118] Based on the experimental results of Example 1 and Comparative Examples 1 and 2, it can be concluded that:

[0119] 1. Mixing CVL and BPA below their respective melting points will not achieve reversible thermochromic properties;

[0120] 2. In this composite phase change material, tetradecyl alcohol not only serves as an energy storage agent but also as a co-solvent in the technology system. It can dissolve CVL and BPA, thereby realizing the reversible thermochromic function of the composite phase change material and endowing it with phase change heat storage performance.

[0121] 3. Tetradecyl alcohol is selected as the phase change material and co-solvent. At the same time, the long carbon chain structure and hydroxyl groups of tetradecyl alcohol are used to modify the surface of nanoCaCO3 to increase its hydrophobicity and oleophilicity, improve the compatibility of the composite phase change energy storage material, better adsorb the phase change material, and improve the heat storage capacity.

[0122] To demonstrate the role of nanoCaCO3 in the technical solution, Comparative Example 3 is provided, a composite material prepared without the addition of nanoCaCO3; at the same time, to further demonstrate the influence of nanoCaCO3 size on the technical effect, i.e. the difference from conventional CaCO3, Comparative Example 4 is provided, a mixture prepared with the addition of conventional CaCO3.

[0123] Comparative Example 3

[0124] A method for preparing a composite material without adding nanoCaCO3 is identical in specific steps to the preparation methods of the reversible thermochromic flame retardant mixture and the reversible thermochromic composite material in Example 1, except that nanoCaCO3 is not added in step 2, and the resulting composite material is named TBC / DW.

[0125] The combustion test results of TBC / DW are as follows: Figure 8 As shown, after 50 seconds of testing, TBC / DW had completely turned into black charcoal. Comparison of the test results with Example 1 shows that adding nanoCaCO3 can give the composite material flame-retardant properties.

[0126] Comparative Example 4

[0127] A method for preparing a mixture with added conventional CaCO3, the specific steps of which are the same as the preparation method of the reversible thermochromic flame retardant mixture in Example 1, the difference being that in step 2, conventional CaCO3 is obtained by grinding solid CaCO3, and conventional CaCO3 is used instead of nanoCaCO3, the resulting mixture is named C-CTBC.

[0128] SEM test results of conventional CaCO3 are as follows Figure 14 As shown, the size of conventional CaCO3 is 10-15 μm and is uneven. Comparison of the test results with Example 1 shows that nanoCaCO3 is 1000 times smaller than conventional CaCO3. Therefore, doping conventional CaCO3 is difficult, making subsequent vacuum impregnation difficult and thus preventing the preparation of reversible thermochromic composite materials with flame-retardant properties.

[0129] Based on the experimental results of Example 1 and Comparative Example 4, it can be seen that only by using nanoCaCO3 can it be doped into the pore structure of DW and ultimately achieve flame retardant function.

[0130] To demonstrate the effect of nanoCaCO3 addition on the phase change thermal storage and flame retardant properties of the composite material, Examples 2 and 3 are provided, with composite materials containing 7% and 14% nanoCaCO3, respectively.

[0131] Example 2

[0132] A method for preparing a composite material with a nanoCaCO3 addition of 7wt% is provided. The steps not specifically described are the same as those in Example 1, except that the amount of nanoCaCO3 added in step 2 is 0.29g, and the resulting composite material is named 7CTBC / DW.

[0133] The thermal storage performance test results of 7CTBC / DW are as follows:

[0134] The test results of the melt profile of 7CTBC / DW are as follows: Figure 5 As shown in b and Table 1, within the test temperature range of -10 to 90℃, the melting process exhibits an endothermic peak at 35.48℃, with a latent heat value of 171.40 J / g. -1 ;

[0135] The test results of the crystallization curve of 7CTBC / DW are as follows: Figure 5 As shown in a and Table 1, within the test temperature range of -10 to 90℃, the crystallization process exhibits an exothermic peak at 24.89℃, with a latent heat value of 169.17 J / g. -1 ;

[0136] The combustion test results of 7CTBC / DW are as follows: Figure 8 As shown, when the test time is 50s, the middle part of the 7CTBC / DW composite material is mostly black, but the DW is retained, which has a certain flame retardant effect.

[0137] Example 3

[0138] A method for preparing a composite material with a nanoCaCO3 addition amount of 14wt% is provided. The steps not specifically described are the same as those in Example 1, except that the amount of nanoCaCO3 added in step 2 is 0.63g, and the resulting composite material is named 14CTBC / DW.

[0139] The thermal storage performance test results of 14CTBC / DW are as follows:

[0140] The test results of the melt curve of 14CTBC / DW are as follows: Figure 5 As shown in b and Table 1, within the test temperature range of -10 to 90℃, the melting process exhibits an endothermic peak at 35.78℃, with a latent heat value of 142.70 J / g. -1 ;

[0141] The crystallization curve test results of 14CTBC / DW are as follows: Figure 5 As shown in a and Table 1, within the test temperature range of -10 to 90℃, the crystallization process exhibits an exothermic peak at 24.77℃, with a latent heat value of 141.99 J g. -1 ;

[0142] The combustion test results of 14CTBC / DW are as follows: Figure 8 As shown, when the test time is 50s, the 14CTBC / DW composite material exhibits an intact morphology, indicating that the composite material has good flame retardant properties.

[0143] Based on the experimental results of Examples 1, 2, and 3, it can be concluded that:

[0144] 1. From Figure 5 The DSC curves show that all nCTBC / DW have melting and crystallization peaks similar to TD, indicating that TD adsorbed in the DW channels maintains its original crystallization behavior.

[0145] 2. As can be seen from the data in Table 1, the more nanoCaCO3 is added per unit mass, the lower the phase change enthalpy of the composite phase change material.

[0146] 3. When the nanoCaCO3 content is 14wt%, the flowability of the flame-retardant thermochromic blend deteriorates and the impregnation rate decreases. Adding nanoCaCO3 has a certain flame-retardant effect; comparison shows that the flame-retardant effect improves with increasing nanoCaCO3 content.

Claims

1. A reversible thermochromic flame retardant mixture, characterized in that: Tetradecyl alcohol TD was prepared by melt blending as a phase change material, cosolvent and surface modifier, crystal violet lactone CVL and bisphenol ABPA as electron donor and electron acceptor and nanoCaCO3 as flame retardant additive. The nanoCaCO3 has a size of 50-70 nm.

2. A method for preparing a reversible thermochromic flame-retardant mixture, characterized in that... The process includes the following steps: Step 1, preparation of reversible thermochromic blend, with crystal violet lactone (CVL): bisphenol A (BPA): tetradecyl alcohol (TD) in a certain mass ratio. First, under certain conditions, TD is heated and melted into a liquid state. Then, under certain conditions, CVL and BPA are added to TD in sequence and stirred under certain conditions until the mixture is uniform, thus obtaining the reversible thermochromic blend TBC. Step 2, preparation of reversible thermochromic flame retardant mixture: Under certain temperature conditions, a certain amount of nano-calcium carbonate (nanoCaCO3) is added to TBC and stirred under certain conditions until the mixture is uniform, thus obtaining reversible thermochromic flame retardant mixture CTBC.

3. The method for preparing the reversible thermochromic flame retardant mixture according to claim 2, characterized in that: In step 1, the mass ratio of CVL:BPA:TD is 1:4:50; In step 1, the conditions for heating and melting TD are: heating temperature is 50℃; the conditions for adding CVL and BPA are: maintaining the temperature at 50℃ and stirring for 30-60 minutes. In step 2, the amount of nanoCaCO3 added is 7-14 wt%, and the conditions for adding nanoCaCO3 are: maintaining the temperature at 50℃ and stirring for 30-60 min.

4. A reversible thermochromic composite material with flame-retardant properties, characterized in that: The mixture CTBC / DW was prepared by adsorbing a reversible thermochromic flame retardant mixture using delignified wood (DW) as a porous carrier via vacuum impregnation.

5. The reversible thermochromic composite material with flame-retardant properties according to claim 4, characterized in that: The CTBC / DW simultaneously possesses phase change energy storage performance, reversible thermochromic performance, flame retardant performance, information storage, and temperature self-response performance. The function of the DW is to provide a porous structure for the composite material.

6. The reversible thermochromic composite material with flame-retardant properties according to claim 5, characterized in that: The phase change thermal storage performance has a thermal density of 168.97 J / g. -1 ; The flame retardant properties were demonstrated by the composite material maintaining a relatively intact shape even after a 50-second test.

7. The reversible thermochromic composite material with flame-retardant properties according to claim 5, characterized in that: The reversible thermochromic property is characterized by the following color change: the thermochromic temperature is 38℃, the color is dark blue below the phase transition temperature, and light wood color above the phase transition temperature, and this process is reversible.

8. The reversible thermochromic composite material with flame-retardant properties according to claim 5, characterized in that: The information storage and temperature self-response performance, achieved through the use of barcodes made of composite materials, allows for information reading and concealment via temperature control; the composite material can also report the temperature range inside the cup from the outside of the cup wall, enabling visual reading.

9. A method for preparing a reversible thermochromic composite material with flame-retardant properties, characterized in that... Includes the following steps: First, poplar RW was placed in a mixed treatment solution of NaOH and Na2SO3 of a certain concentration and heated under certain conditions to remove lignin for the first time. After the heating treatment was completed, RW was placed in deionized water and heated and washed under certain conditions to obtain RW-1. Then, RW-1 was placed in a H2O2 solution of a certain concentration and soaked under certain conditions to achieve the second removal of lignin. After the soaking treatment was completed, RW-1 was placed in deionized water and heated and washed under certain conditions to obtain RW-2. Then, under certain conditions, RW-2 was freeze-dried to obtain delignified wood DW; Finally, DW is placed in the CTBC blend and vacuum impregnated under certain conditions to obtain a reversible thermochromic composite material with flame-retardant properties, referred to as CTBC / DW.

10. The method for preparing the reversible thermochromic composite material with flame-retardant properties according to claim 9, characterized in that: The NaOH concentration in the mixed treatment solution is 2.5 mol / L. -1 The concentration of Na2SO3 is 0.5 mol / L. -1 ; The conditions for the first lignin removal heat treatment are: heating to 100°C and boiling, with a heat treatment time of 6-8 hours; After the first heat treatment to remove lignin, the conditions for heat washing are: heating to 100°C and boiling, each heat washing time is 1 hour, and the number of heat washing cycles is 8-10. The H2O2 concentration in the H2O2 solution is 2.5 mol / L. -1 ; The conditions for the second lignin removal soaking treatment are: soaking temperature of 25℃ and soaking time of 2-4 hours; After the second lignin removal soaking treatment, the heating and washing conditions are as follows: heating to 100°C and boiling, each heating and washing time is 1 hour, and the number of heating and washing cycles is 8-10. The freeze-drying conditions are as follows: freeze-drying temperature is -52℃, and freeze-drying time is 27-48h; The vacuum impregnation conditions are as follows: impregnation temperature is 60°C, and impregnation time is 24-36 hours.

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