Preparation method of phase change energy storage wood with lignin-based photothermal flame retardant coating

Abstract

A method for preparing phase-change energy storage wood with a lignin-based photothermal flame-retardant coating belongs to the field of phase-change energy storage materials. The present invention aims to solve the problems of liquid leakage, flammability, and low photothermal conversion efficiency in existing organic solid-liquid phase-change energy storage materials. Method: 1. Delignification treatment to obtain a delignified mixed water solution and delignified wood; 2. Preparation of phase-change energy storage wood; 3. Preparation of purified lignin; 4. Preparation of a mixed liquid of lignin and polydimethylsiloxane prepolymer; 5. Immersion of the phase-change energy storage wood in the mixed liquid of lignin and polydimethylsiloxane prepolymer. The present invention is used for the preparation of phase-change energy storage wood with a lignin-based photothermal flame-retardant coating.

Description

Technical Field

[0001] The invention belongs to the field of phase change energy storage materials. Background Art

[0002] Organic solid-liquid phase change energy storage materials are widely used in thermal energy storage due to their high latent heat, low supercooling, non-toxicity, and non-corrosiveness, thereby alleviating energy pressure. However, organic solid-liquid phase change energy storage materials suffer from issues such as liquid leakage, flammability, and low light-to-heat conversion efficiency. To address the leakage issue of organic solid-liquid phase change energy storage materials, microencapsulation and porous material support methods are currently the most widely used methods. The microencapsulation method is complex and costly to prepare, while the porous material support method has a wider range of raw materials and a simpler preparation process, making it more widely used. To address the flammability of organic solid-liquid phase change energy storage materials, doping with flame retardants and applying flame-retardant coatings are currently common approaches. However, doping flame retardants into phase change energy storage composites requires a large amount of flame retardant to achieve flame retardancy, significantly reducing the composite's thermal storage capacity. The coating method, however, only protects the composite surface, has a minimal impact on its thermal storage capacity and provides excellent flame retardancy. Low light-to-heat conversion efficiency also affects the energy utilization of phase-change energy storage materials. Phase-change materials are often doped with materials such as graphene, carbon nanotubes, and MXene, but these materials are relatively expensive. Therefore, the development and utilization of flame-retardant, high light-to-heat conversion efficiency, and stable shape-enhancing phase-change energy storage materials with low cost and simple processing are of great significance to their development. Summary of the Invention

[0003] The present invention aims to solve the problems of liquid leakage, flammability and low photothermal conversion efficiency of existing organic solid-liquid phase change energy storage materials, and further provide a method for preparing phase change energy storage wood with a lignin-based photothermal flame retardant coating.

[0004] 1. Cooking the wood in a mixed aqueous solution of sodium hydroxide and sodium sulfite, then removing the wood to obtain a delignified mixed aqueous solution, and rinsing and freeze-drying the removed wood to obtain delignified wood;

[0005] Second, the delignified wood is impregnated into the molten phase change energy storage material by vacuum-assisted impregnation for 2 to 5 hours to obtain the phase change energy storage wood;

[0006] 3. Adjusting the pH of the mixed aqueous solution after delignification to 1-3, then filtering, washing with distilled water to neutrality and drying to obtain purified lignin;

[0007] 4. Evenly mixing the purified lignin, polydimethylsiloxane and curing agent to obtain a mixed liquid of lignin and polydimethylsiloxane prepolymer;

[0008] The mass ratio of the purified lignin to the polydimethylsiloxane prepolymer is (1-15):10;

[0009] 5. The phase change energy storage wood is immersed in a mixed liquid of lignin and polydimethylsiloxane prepolymer, and finally cured to obtain a phase change energy storage wood with a lignin-based photothermal flame retardant coating.

[0010] The beneficial effects of the present invention are:

[0011] The phase-change energy storage wood with a lignin-based photothermal flame-retardant coating prepared by this invention not only has excellent thermal energy storage capacity, but also exhibits flame retardancy and high photothermal conversion efficiency. This allows for efficient solar energy storage and alleviates energy pressure. Furthermore, its flame retardant properties can improve the fire safety of phase-change energy storage wood, broadening its scope of application. Furthermore, this invention, with its "full green utilization of wood components" design strategy, is environmentally friendly and sustainable, and is expected to be mass-produced and manufactured, contributing to the realization of the dual carbon strategy.

[0012] 1. In this specific embodiment, delignified wood is used as the supporting material, which retains the unique porous structure of wood, effectively solves the leakage problem of organic solid-liquid phase change energy storage materials, has good thermal energy storage capacity, and has the advantages of sustainable regeneration, environmental friendliness, and low cost, and has broad application prospects.

[0013] 2. The lignin purified in this embodiment has good flame retardancy and photothermal conversion efficiency.

[0014] 3. This specific implementation method proposes the concept of "green full utilization of wood components", purifies and reuses the removed lignin as a photothermal and flame-retardant coating to solve the practical application problem of phase change energy storage wood.

[0015] 4. The raw materials of this specific embodiment are easily available, the process is simple and mild, the operation cycle is short, and large-scale production and processing can be achieved.

[0016] Figures in the specification

[0017] Figure 1 This is a schematic diagram of the preparation process of phase change energy storage wood with lignin-based photothermal flame retardant coating in Example 1;

[0018] Figure 2 Macroscopic images of phase-change energy storage wood after heating on a 60°C hot plate for different times. A is polyethylene glycol 2000, B is polyethylene glycol / wood prepared in comparative experiment 1, and C is phase-change energy storage wood with a lignin-based photothermal flame-retardant coating prepared in Example 1.

[0019] Figure 3 This is the DSC curve of the phase change energy storage wood with lignin-based photothermal flame retardant coating prepared in Example 1;

[0020] Figure 4 Macroscopic images after the polyethylene glycol / wood cone calorimetry experiment prepared for comparison experiment 1;

[0021] Figure 5 For comparison, the macroscopic image of the phase change energy storage wood with PDMS coating without lignin prepared in Experiment 2 after the cone calorimetry experiment;

[0022] Figure 6 This is a macroscopic image of the phase change energy storage wood with a lignin-based photothermal flame retardant coating prepared in Example 1 after the cone calorimetry experiment;

[0023] Figure 7 is the heat release rate curve, a is the polyethylene glycol / wood prepared in comparative experiment 1, b is the phase change energy storage wood with a PDMS coating without lignin prepared in comparative experiment 2, and c is the phase change energy storage wood with a lignin-based photothermal flame retardant coating prepared in Example 1;

[0024] Figure 8 is the total heat release rate curve, a is the polyethylene glycol / wood prepared in comparative experiment 1, b is the phase change energy storage wood with a PDMS coating without lignin prepared in comparative experiment 2, and c is the phase change energy storage wood with a lignin-based photothermal flame retardant coating prepared in Example 1;

[0025] Figure 9 : These are the photothermal heating and cooling curves of phase change energy storage wood. a is the phase change energy storage wood with a lignin-based photothermal flame retardant coating prepared in Example 1, and b is the phase change energy storage wood with a PDMS coating without lignin prepared in Comparative Experiment 2. DETAILED DESCRIPTION

[0026] Specific embodiment 1: This embodiment is a method for preparing phase change energy storage wood with a lignin-based photothermal flame retardant coating, which is carried out according to the following steps:

[0027] 1. Cooking the wood in a mixed aqueous solution of sodium hydroxide and sodium sulfite, then removing the wood to obtain a delignified mixed aqueous solution, and rinsing and freeze-drying the removed wood to obtain delignified wood;

[0028] Second, the delignified wood is impregnated into the molten phase change energy storage material by vacuum-assisted impregnation for 2 to 5 hours to obtain the phase change energy storage wood;

[0029] 3. Adjusting the pH of the mixed aqueous solution after delignification to 1-3, then filtering, washing with distilled water to neutrality and drying to obtain purified lignin;

[0030] 4. Evenly mixing the purified lignin, polydimethylsiloxane and curing agent to obtain a mixed liquid of lignin and polydimethylsiloxane prepolymer;

[0031] The mass ratio of the purified lignin to the polydimethylsiloxane prepolymer is (1-15):10;

[0032] 5. The phase change energy storage wood is immersed in a mixed liquid of lignin and polydimethylsiloxane prepolymer, and finally cured to obtain a phase change energy storage wood with a lignin-based photothermal flame retardant coating.

[0033] In step three of this specific embodiment, lignin is precipitated under an acidic environment.

[0034] This specific embodiment proposes a "green utilization of all wood components" strategy, using delignified wood as a supporting material to solve the leakage problem of phase change energy storage materials. The removed lignin is usually treated as waste, which not only causes a waste of resources, but also causes serious environmental pollution. As an aromatic compound, lignin has a rich variety of functional groups (such as π-π conjugated structures, ketones, quinone structures, etc.), which not only gives it rich light absorption capacity, but also has good thermal stability and charring ability. It can form a dense carbon layer during the combustion process, isolating combustion-supporting gases such as oxygen from contact with flammable materials, and effectively stopping the combustion process. Therefore, in this specific embodiment, the removed lignin is purified and then composited with polydimethylsiloxane (PDMS) as a photothermal flame retardant coating, which is applied to the surface of phase change energy storage wood to construct a phase change energy storage wood with a lignin-based photothermal flame retardant coating.

[0035] The phase-change energy storage wood with a lignin-based photothermal flame-retardant coating produced in this embodiment not only addresses the issues of liquid leakage, flammability, and low photothermal conversion efficiency associated with organic solid-liquid phase-change energy storage materials, but also fully utilizes the wood component, aligning with the concept of green sustainability. Furthermore, the design is simple, requires mild reaction conditions, and is environmentally friendly, amenable to large-scale production and has broad application prospects.

[0036] The beneficial effects of this embodiment are:

[0037] The phase-change energy storage wood with a lignin-based photothermal flame-retardant coating prepared by this invention not only has excellent thermal energy storage capacity, but also exhibits flame retardancy and high photothermal conversion efficiency. This allows for efficient solar energy storage and alleviates energy pressure. Furthermore, its flame retardant properties can improve the fire safety of phase-change energy storage wood, broadening its scope of application. Furthermore, this invention, with its "full green utilization of wood components" design strategy, is environmentally friendly and sustainable, and is expected to be mass-produced and manufactured, contributing to the realization of the dual carbon strategy.

[0038] 1. In this specific embodiment, delignified wood is used as the supporting material, which retains the unique porous structure of wood, effectively solves the leakage problem of organic solid-liquid phase change energy storage materials, has good thermal energy storage capacity, and has the advantages of sustainable regeneration, environmental friendliness, and low cost, and has broad application prospects.

[0039] 2. The lignin purified in this embodiment has good flame retardancy and photothermal conversion efficiency.

[0040] 3. This specific implementation method proposes the concept of "green full utilization of wood components", purifies and reuses the removed lignin as a photothermal and flame-retardant coating to solve the practical application problem of phase change energy storage wood.

[0041] 4. The raw materials of this specific embodiment are easily available, the process is simple and mild, the operation cycle is short, and large-scale production and processing can be achieved.

[0042] Specific embodiment 2: This embodiment differs from specific embodiment 1 in that the concentration of sodium hydroxide in the mixed aqueous solution of sodium hydroxide and sodium sulfite in step 1 is 1 mol / L to 5 mol / L, and the concentration of sodium sulfite is 0.1 mol / L to 1 mol / L. Other steps are the same as those in specific embodiment 1.

[0043] Specific embodiment 3: This embodiment differs from either specific embodiment 1 or 2 in that, in step 1, the wood is immersed in a mixed aqueous solution of sodium hydroxide and sodium sulfite at a temperature of 70°C to 100°C for 6 to 24 hours. Other steps are the same as specific embodiments 1 or 2.

[0044] Specific embodiment 4: This embodiment differs from specific embodiments 1 to 3 in that the freeze drying in step 1 is carried out at a temperature of -50°C to -70°C and a pressure of <20 Pa for 12 to 24 hours. Other aspects are the same as specific embodiments 1 to 3.

[0045] Specific embodiment 5: This embodiment differs from specific embodiments 1 to 4 in that the wood in step 1 is poplar, basswood, birch, balsa or pine. Other aspects are the same as specific embodiments 1 to 4.

[0046] Specific embodiment 6: This embodiment differs from Specific embodiments 1 to 5 in that, in step 2, the delignified wood is impregnated into the molten phase change energy storage material using a vacuum-assisted impregnation method at a temperature of 50°C to 90°C and a pressure of 0.05 MPa to 0.08 MPa for 2 to 5 hours. Other steps are the same as Specific embodiments 1 to 5.

[0047] Specific embodiment 7: This embodiment differs from any one of specific embodiments 1 to 6 in that the phase change energy storage material in step 2 is fatty acid, fatty alcohol, polyethylene glycol or paraffin. Other aspects are the same as specific embodiments 1 to 6.

[0048] Specific embodiment 8: This embodiment differs from specific embodiments 1 to 7 in that in step 3, the pH of the mixed aqueous solution after delignification is adjusted to 1 to 3 using a hydrochloric acid solution with a concentration of 0.1 mol / L to 0.3 mol / L. Other aspects are the same as specific embodiments 1 to 7.

[0049] Specific embodiment 9: This embodiment differs from Specific embodiments 1 to 8 in that the mass ratio of polydimethylsilane to curing agent in step 4 is 10:(1-5). Other aspects are the same as Specific embodiments 1 to 8.

[0050] Specific Embodiment 10: This embodiment differs from Specific Embodiments 1 to 9 in that, in step 5, the phase change energy storage wood is immersed in a mixture of lignin and polydimethylsiloxane prepolymer at room temperature for 5 to 10 minutes; and the curing in step 5 is performed at a temperature of 25°C to 50°C for 6 to 24 hours. Other aspects are the same as Specific Embodiments 1 to 9.

[0051] The following examples are used to verify the beneficial effects of the present invention:

[0052] Example 1, combined with Figure 1 Specific instructions:

[0053] A method for preparing phase-change energy storage wood with a lignin-based photothermal flame-retardant coating is carried out according to the following steps:

[0054] 1. The wood is placed in a mixed aqueous solution of sodium hydroxide and sodium sulfite and boiled for 12 hours at a temperature of 80°C, and then the wood is taken out to obtain a delignified mixed aqueous solution. The taken out wood is rinsed and freeze-dried to obtain delignified wood;

[0055] Second, the delignified wood was impregnated into the molten phase change energy storage material by vacuum-assisted impregnation at a temperature of 60°C and a pressure of 0.08 MPa for 3 hours to obtain the phase change energy storage wood;

[0056] 3. Using a 0.1 mol / L hydrochloric acid solution, the pH of the mixed aqueous solution after delignification was adjusted to 2, and then filtered, washed with distilled water until neutral and dried to obtain purified lignin;

[0057] 4. Evenly mix the purified lignin, polydimethylsiloxane and curing agent to obtain a mixed liquid of lignin and polydimethylsiloxane prepolymer (PDMS);

[0058] The mass ratio of the purified lignin to the polydimethylsiloxane prepolymer is 12:10;

[0059] 5. At room temperature, the phase change energy storage wood was immersed in a mixed liquid of lignin and polydimethylsiloxane prepolymer for 5 minutes, and finally cured at a temperature of 30°C for 24 hours to obtain a phase change energy storage wood with a lignin-based photothermal flame retardant coating.

[0060] The concentration of sodium hydroxide in the mixed aqueous solution of sodium hydroxide and sodium sulfite described in step 1 is 2 mol / L, and the concentration of sodium sulfite is 0.5 mol / L.

[0061] The freeze drying in step 1 is specifically drying at a temperature of -55°C and a pressure of 20 Pa for 24 hours.

[0062] The wood described in step 1 is basswood.

[0063] The phase change energy storage material described in step 2 is polyethylene glycol 2000.

[0064] The mass ratio of the polydimethylsilane to the curing agent in step 4 is 10:3, and the polydimethylsilane and the curing agent are purchased from Dow Corning Company as model DC184.

[0065] Comparative Experiment 1: This comparative experiment differs from Example 1 in that steps 3 to 5 are omitted, and the phase change energy storage wood prepared in step 2 is polyethylene glycol / wood.

[0066] Comparative Experiment 2: This comparative experiment differs from Example 1 in that the addition of purified lignin is omitted in step 4, and phase change energy storage wood having a PDMS coating without lignin is obtained in step 5.

[0067] Figure 2 These are macroscopic images of phase-change energy storage wood after being heated on a 60°C hot plate for different times. A is polyethylene glycol 2000, B is polyethylene glycol / wood prepared in comparative experiment 1, and C is phase-change energy storage wood with a lignin-based photothermal flame-retardant coating prepared in Example 1. As can be seen from the figure, pure polyethylene glycol 2000 melts and becomes amorphous after heating. Polyethylene glycol / wood maintains shape stability after heating, indicating that wood as a supporting material can significantly solve the leakage problem of phase-change energy storage materials. For phase-change energy storage wood with a lignin-based photothermal flame-retardant coating, its shape stability can be completely maintained, indicating that the presence of wood and coating can limit the leakage of polyethylene glycol at high temperatures.

[0068] Figure 3This is the DSC curve of the phase change energy storage wood with a lignin-based photothermal flame retardant coating prepared in Example 1; as can be seen from the figure, its melting enthalpy is 101.63 kJ / kg and its crystallization enthalpy is 96.82 kJ / kg, indicating that it has a high phase change latent heat enthalpy and good heat storage capacity.

[0069] Figure 4 This is a macroscopic image of the polyethylene glycol / wood prepared in the first comparative experiment after the cone calorimetry test. As can be seen from the figure, the amount of residual carbon after the cone calorimetry test is small, indicating that the phase change energy storage material without coating is flammable.

[0070] Figure 5 This is a macroscopic image of the phase change energy storage wood with a PDMS coating without lignin prepared in Experiment 2 after the cone calorimetry test. As can be seen from the figure, the amount of residual carbon after the cone calorimetry test is greater than that of the phase change energy storage wood without coating, indicating that the presence of the PDMS coating improves the flame retardancy of the phase change energy storage material.

[0071] Figure 6 This is a macroscopic image of the phase change energy storage wood with a lignin-based photothermal flame-retardant coating prepared in Example 1 after the cone calorimetry experiment; as can be seen from the figure, a dense carbon layer is formed on the surface of the phase change energy storage wood, and the size remains basically unchanged, indicating that it has good flame retardancy.

[0072] Figure 7 The heat release rate curve is shown in Figure 1. a is the polyethylene glycol / wood prepared in comparative experiment 1, b is the phase change energy storage wood with a PDMS coating without lignin prepared in comparative experiment 2, and c is the phase change energy storage wood with a lignin-based photothermal flame retardant coating prepared in Example 1. As can be seen from the figure, the flame of the polyethylene glycol / wood spreads rapidly after being burned, and the heat release rate continues to increase, quickly reaching a peak of 600.41kW / m 2 With the introduction of polydimethylsiloxane, the peak heat release rate dropped significantly to 450.5kW / m 2 , verifying the flame retardancy of polydimethylsiloxane. After the lignin was introduced into Example 1, the peak heat release rate continued to decrease, and its peak heat release rate dropped to 330.1kW / m 2 .

[0073] Figure 8 The total heat release rate curve is shown in Figure 1. a is the polyethylene glycol / wood prepared in comparative experiment 1, b is the phase change energy storage wood with PDMS coating without lignin prepared in comparative experiment 2, and c is the phase change energy storage wood with lignin-based photothermal flame retardant coating prepared in Example 1. As can be seen from the figure, the polyethylene glycol / wood reaches the maximum total heat release rate (160.07 MJ / m 2) until 760 s after being ignited. 2 ), the maximum total heat release rate of the phase change energy storage wood with PDMS coating without lignin decreased to 145.37MJ / m2 In Example 1, as lignin was added, the maximum total heat release rate further decreased to 70.54 MJ / m 2 .

[0074] The relevant data measured by the cone calorimetry experiment are shown in Table 1 below:

[0075] Table 1

[0076]

[0077] At room temperature, the phase-change energy storage wood with the lignin-based photothermal flame-retardant coating prepared in Example 1 and the phase-change energy storage wood with the PDMS coating without lignin prepared in Comparative Experiment 2 were irradiated with a xenon lamp (PLS-SEX300UV, spectral band 200 nm-2500 nm, distance between the lens and the sample 50 cm); Figure 9 Figure 3 is the photothermal heating and cooling curve of phase change energy storage wood. a is the phase change energy storage wood with lignin-based photothermal flame retardant coating prepared in Example 1, and b is the phase change energy storage wood with PDMS coating without lignin prepared in comparative experiment 2. As can be seen from the figure, compared with the phase change energy storage wood without lignin coating, the sample temperature of the phase change energy storage wood with lignin-based photothermal flame retardant coating rises to 160°C after 420s of illumination, indicating that after adding lignin, solar energy can be quickly converted into thermal energy, with high photothermal conversion efficiency.

Claims

1. A method for preparing phase change energy storage wood with a lignin-based photothermal flame retardant coating, characterized in that It is carried out in the following steps:

1. The wood is placed in a mixed aqueous solution of sodium hydroxide and sodium sulfite and boiled for 12 to 24 hours at a temperature of 70°C to 100°C, and then the wood is removed to obtain a delignified mixed aqueous solution. The removed wood is rinsed and then dried at a temperature of -50°C to -70°C and a pressure of ≤20Pa for 12 to 24 hours to obtain delignified wood; The concentration of sodium hydroxide in the mixed aqueous solution of sodium hydroxide and sodium sulfite is 1 mol / L to 5 mol / L, and the concentration of sodium sulfite is 0.1 mol / L to 1 mol / L; Second, by vacuum-assisted impregnation, the delignified wood was impregnated into the molten phase change energy storage material for 2h~5h at a temperature of 50℃~90℃ and a pressure of 0.05MPa~0.08MPa to obtain the phase change energy storage wood; 3. Using a hydrochloric acid solution with a concentration of 0.1mol / L~0.3mol / L, the pH of the mixed aqueous solution after delignification is adjusted to 1~3, and then filtered, washed with distilled water until neutral and dried to obtain purified lignin; 4. Evenly mixing the purified lignin, polydimethylsiloxane and curing agent to obtain a mixed liquid of lignin and polydimethylsiloxane prepolymer; The mass ratio of the purified lignin to the polydimethylsiloxane prepolymer is (1-15):10; the polydimethylsilane and curing agent are Dow Corning DC184 models; 5. At room temperature, the phase change energy storage wood is immersed in a mixed liquid of lignin and polydimethylsiloxane prepolymer for 5 minutes to 10 minutes, and finally cured at a temperature of 25°C to 50°C for 6 hours to 24 hours to obtain a phase change energy storage wood with a lignin-based photothermal flame retardant coating.

2. The method for preparing a phase change energy storage wood with a lignin-based photothermal flame retardant coating according to claim 1, characterized in that The wood in step 1 is poplar, basswood, birch, balsa or pine.

3. The method for preparing a phase change energy storage wood with a lignin-based photothermal flame retardant coating according to claim 1, characterized in that The phase change energy storage material described in step 2 is fatty acid, fatty alcohol, polyethylene glycol or paraffin.

4. The method for preparing a phase change energy storage wood with a lignin-based photothermal flame retardant coating according to claim 1, characterized in that The mass ratio of polydimethylsilane to curing agent described in step 4 is 10:(1~5).

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