Preparation method of moldable wood-based composite phase change material and strength switching method thereof
Moldable wood-based composite phase change materials were prepared by inducing phase separation through water-polyethylene glycol solvent exchange, which solved the problems of formability and structural stability, realized the soft-hard switching of materials and improved mechanical properties, and is suitable for structural thermal management materials and is biodegradable.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- NORTHEAST FORESTRY UNIV
- Filing Date
- 2024-05-21
- Publication Date
- 2026-07-14
AI Technical Summary
Existing phase change materials have poor formability and structural stability, making it difficult to meet the requirements for complex shapes and high mechanical strength.
Moldable wood-based composite phase change materials were prepared by water-polyethylene glycol solvent exchange-induced phase separation. The reversible change of hydrogen bonds between cellulose and polyvinyl alcohol was utilized to achieve the switching between soft and hard properties of the material, thereby enhancing its mechanical properties.
It has achieved a moldable, strength-switchable phase change material that can maintain complex shapes and has excellent mechanical properties. It is suitable for structural thermal management materials and is biodegradable.
Smart Images
Figure CN118559826B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of phase change materials. Background Technology
[0002] Humans urgently need various thermal regulation technologies to improve the comfort of life. Among them, phase change materials (PCMs) have attracted widespread attention due to their ability to store and release heat energy in the form of latent heat during phase change. However, traditional PCMs suffer from poor formability and mechanical properties. The final step in material processing is often material forming, especially for structural components which must be made from physically formable materials to meet specific shape requirements. For example, structural materials such as those used in electronic devices, building structures, and aerospace equipment housings not only require thermal management but also complex shapes. To address these key issues, flexible PCMs with stretchability, foldability, and bendability have emerged, meeting the need for shape changes in thermal management materials and facilitating installation and disassembly. However, even though flexible PCMs can be bent into large angles or molded into various desired shapes, they quickly return to their original shape once the external force is removed. In conclusion, the formability and structural stability (mechanical strength) of materials are necessary conditions for the preparation of high-performance structural thermal management materials. Summary of the Invention
[0003] This invention aims to address the problems of poor formability and structural stability of existing phase change materials, and thus provides a method for preparing a moldable wood-based composite phase change material and a method for switching its strength.
[0004] A method for preparing a moldable wood-based composite phase change material comprises the following steps:
[0005] 1. Impregnate the delignified wood in an aqueous solution of polyvinyl alcohol to obtain wood impregnated with polyvinyl alcohol solution;
[0006] The polyvinyl alcohol in the aqueous solution is 5% to 30% by mass.
[0007] 2. Freeze the wood impregnated with polyvinyl alcohol solution, then thaw it to obtain a soft wood hydrogel;
[0008] 3. Immerse the soft wood hydrogel in liquid polyethylene glycol until the liquid polyethylene glycol displaces the water in the soft wood hydrogel, thus obtaining a hard moldable wood-based composite phase change material.
[0009] A method for strength switching of a moldable wood-based composite phase change material, comprising the following steps:
[0010] 1. Immerse the rigid moldable wood-based composite phase change material in water until the water displaces the polyethylene glycol in the phase change material to obtain a soft wood hydrogel.
[0011] 2. Immerse the soft wood hydrogel in liquid polyethylene glycol until the polyethylene glycol displaces the water in the hydrogel, thus obtaining a hard, moldable wood-based composite phase change material.
[0012] Third, repeat steps one and two multiple times to complete the intensity switching method.
[0013] The beneficial effects of this invention are:
[0014] This invention develops a moldable phase change material with switchable strength through a unique water-polyethylene glycol solvent exchange-induced phase separation. In the presence of water, the hydrogen bonds between cellulose and polyvinyl alcohol (PVA) are weak, resulting in a soft gel with excellent formability. In the presence of polyethylene glycol, cellulose and PVA form strong hydrogen bonds, leading to a wood gel with excellent mechanical properties. Since the soft wood hydrogel can be bent into various shapes, when it is fixed in a certain shape and placed in liquid polyethylene glycol, the resulting wood-based composite phase change material exhibits excellent mechanical properties and retains its previously fixed shape well. This gives the wood gel excellent moldability, and through repeated cycles, the wood-based composite phase change material can switch between soft and hard states and continuously change shape.
[0015] This invention utilizes polyethylene glycol, which not only enhances wood gels but is also a phase change material. This solvent-responsive strategy allows for the design of wood gels with complex shapes to meet the needs of structural thermal management materials. Furthermore, this biodegradable material holds promise as a replacement for traditional plastics and some thermal management materials. Attached Figure Description
[0016] Figure 1 The following is a schematic diagram of the mechanism of the rigid moldable wood-based composite phase change material of the present invention: (a) a schematic diagram of hydrogen bonds between PVA and cellulose fibers in the PEG / PVA / W composite material; (b) a schematic diagram of the reversible breaking and formation of hydrogen bonds between cellulose and polyvinyl alcohol through water-polyethylene glycol solvent exchange.
[0017] Figure 2 The images show the physical samples of PVA / W prepared in step two of Example 1 and PEG / PVA / W prepared in step three.
[0018] Figure 3 The stress-strain curves of PVA / W prepared in step two of Example 1 and PEG / PVA / W prepared in step three are parallel to the (L) wood growth direction.
[0019] Figure 4 Stress-strain curves of PVA / W prepared in step two of Example 1 and PEG / PVA / W prepared in step three, perpendicular to the (T) wood growth direction;
[0020] Figure 5 The images are scanning electron microscope images. a is the longitudinal (L) and tangential (T) direction of the log (without lignin), b is the longitudinal section of the log (without lignin), c is the cross section of the PEG / PVA / W prepared in step three of Example 1, and d is the longitudinal section of the PEG / PVA / W prepared in step three of Example 1.
[0021] Figure 6 The images show physical examples of PED / PVA / W in different forms, as shown in step three of Example 1.
[0022] Figure 7 Differential scanning calorimetry (DSC) was used to determine the crystallization and melting curves of the PEG / PVA / W prepared in step three of Example 1 before and after 100 heating-cooling cycles;
[0023] Figure 8 Differential scanning calorimetry (DSC) was used to determine the crystallization and melting curves of PEG / PVA / W prepared with polyethylene glycol of different molecular weights before and after 100 heating-cooling cycles in step three of Example 3.
[0024] Figure 9 This is a photograph of the PEG / PVA / W prepared from various hardwoods and softwoods in step three of Example 4.
[0025] Figure 10 The biodegradability of PEG / PVA / W prepared in step three of Example 1;
[0026] Figure 11 This is a photograph of the rigid moldable wood-based composite phase change material in Example 2 after repeated hard-soft switching under the action of water and polyethylene glycol for the tenth time.
[0027] Figure 12 This is a graph showing the mechanical properties of the rigid moldable wood-based composite phase change material in Example 2 after repeated hard-soft switching under the action of water and polyethylene glycol for the tenth time. Detailed Implementation
[0028] Specific Implementation Method 1: This implementation method provides a method for preparing a moldable wood-based composite phase change material, which is prepared according to the following steps:
[0029] 1. Impregnate the delignified wood in an aqueous solution of polyvinyl alcohol to obtain wood impregnated with polyvinyl alcohol solution;
[0030] The polyvinyl alcohol in the aqueous solution is 5% to 30% by mass.
[0031] 2. Freeze the wood impregnated with polyvinyl alcohol solution, then thaw it to obtain a soft wood hydrogel;
[0032] 3. Immerse the soft wood hydrogel in liquid polyethylene glycol until the liquid polyethylene glycol displaces the water in the soft wood hydrogel, thus obtaining a hard moldable wood-based composite phase change material.
[0033] The hard, moldable wood-based composite phase change material prepared in step three of this specific implementation method is a PEG / PVA / W composite material.
[0034] Figure 1 This is a schematic diagram of the mechanism of the rigid moldable wood-based composite phase change material of the present invention. (a) Schematic diagram of hydrogen bonds between PVA and cellulose fibers in the PEG / PVA / W composite material; (b) Schematic diagram of the reversible breaking and formation of hydrogen bonds between cellulose and polyvinyl alcohol through water-polyethylene glycol solvent exchange. As shown in the diagram, polyvinyl alcohol (PVA) and cellulose form cellulose-cellulose, cellulose-PVA, and PVA-PVA interactions. Water, as a good solvent for PVA, results in weak hydrogen bonds between cellulose and PVA, making the wood gel very soft. Polyethylene glycol, as a poor solvent for PVA, forms strong hydrogen bonds between cellulose and PVA under the action of water, with PVA molecular chains tightly wrapped around cellulose molecular chains, thus strengthening the mechanical properties of the gel. The mechanical properties of the gel can be repeatedly switched between soft and hard by repeatedly replacing water or polyethylene glycol.
[0035] The beneficial effects of this embodiment are:
[0036] This embodiment develops a moldable phase change material with switchable strength through a unique water-polyethylene glycol solvent exchange-induced phase separation. In the presence of water, the hydrogen bonds between cellulose and polyvinyl alcohol (PVA) are weak, resulting in a soft gel with excellent formability. In the presence of polyethylene glycol, cellulose and PVA form strong hydrogen bonds, leading to a wood gel with excellent mechanical properties. Since the soft wood hydrogel can be bent into various shapes, when it is fixed in a certain shape and placed in liquid polyethylene glycol, the resulting wood-based composite phase change material exhibits excellent mechanical properties and retains its previously fixed shape well. This gives the wood gel excellent moldability, and through repeated cycles, the wood-based composite phase change material can switch between soft and hard states and continuously change shape.
[0037] In this embodiment, polyethylene glycol not only reinforces wood gels but is also a phase change material. This solvent-responsive strategy allows for the design of wood gels with complex shapes to meet the needs of structural thermal management materials. Furthermore, this biodegradable material holds promise as a replacement for traditional plastics and some thermal management materials.
[0038] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that the delignified wood described in step one is prepared according to the following steps: Wood chips are placed in a de-hemicellulose solution, and then kept at a temperature of 60℃~120℃ for 5h~24h to obtain de-hemicellulose wood. The de-hemicellulose wood is washed and placed in a hydrogen peroxide solution, and then kept at a temperature of 25℃~80℃ until the wood turns white. It is then washed and dried to obtain delignified wood. The de-hemicellulose solution is a mixed solution of NaOH and Na2SO3, and the concentration of NaOH in the de-hemicellulose solution is 1mol / L~3mol / L, and the concentration of Na2SO3 in the de-hemicellulose solution is 0.1mol / L~1mol / L. The mass percentage of the hydrogen peroxide solution is 2.5%~30%. Everything else is the same as in Specific Implementation Method One.
[0039] Specific Implementation Method Three: This implementation method differs from Specific Implementation Method One or Two in that the impregnation described in step one is specifically carried out at room temperature for 12 to 24 hours. Everything else is the same as in Specific Implementation Method One or Two.
[0040] Specific Implementation Method Four: This implementation method differs from Specific Implementation Methods One to Three in that the freezing described in step two is specifically carried out at a temperature of -5℃ to -40℃ for 6 to 48 hours. Everything else is the same as in Specific Implementation Methods One to Three.
[0041] Specific Implementation Method Five: This implementation method differs from Specific Implementation Methods One to Four in that, in step three, the soft wood hydrogel is immersed in liquid polyethylene glycol for 12 to 24 hours at a temperature ranging from room temperature to 80°C. Everything else is the same as in Specific Implementation Methods One to Four.
[0042] Specific Implementation Method Six: This implementation method provides a strength switching method for a moldable wood-based composite phase change material, which is carried out according to the following steps:
[0043] 1. Immerse the rigid moldable wood-based composite phase change material in water until the water displaces the polyethylene glycol in the phase change material to obtain a soft wood hydrogel.
[0044] 2. Immerse the soft wood hydrogel in liquid polyethylene glycol until the liquid polyethylene glycol displaces the water in the hydrogel, thus obtaining a hard moldable wood-based composite phase change material.
[0045] Third, repeat steps one and two multiple times to complete the intensity switching method.
[0046] Specific Implementation Method Seven: This implementation method differs from Specific Implementation Method Six in that, in step one, the rigid moldable wood-based composite phase change material is immersed in water for 2 to 3 hours at a temperature ranging from room temperature to 80°C. Everything else is the same as in Specific Implementation Method Six.
[0047] Specific Implementation Method Eight: This implementation method differs from Specific Implementation Method Six or Seven in that: in step two, the soft wood hydrogel is immersed in liquid polyethylene glycol for 2 to 12 hours at room temperature to 80°C. Everything else is the same as in Specific Implementation Method Six or Seven.
[0048] Specific Implementation Method Nine: This implementation method differs from Specific Implementation Methods Six to Eight in that: in step one, the shape of the soft wood hydrogel is adjusted; in step two, the shaped soft wood hydrogel is immersed in liquid polyethylene glycol for shaping, resulting in a shape-adjusted phase change material. Everything else is the same as in Specific Implementation Methods Six to Eight.
[0049] Specific Implementation Method Ten: This implementation method differs from Specific Implementation Methods Six to Nine in that step three repeats steps one to two 10 times. Everything else is the same as in Specific Implementation Methods Six to Nine.
[0050] The beneficial effects of the present invention are verified using the following embodiments:
[0051] Example 1:
[0052] A method for preparing a moldable wood-based composite phase change material comprises the following steps:
[0053] 1. Impregnate the delignified wood in an aqueous solution of polyvinyl alcohol to obtain wood impregnated with polyvinyl alcohol solution;
[0054] The aqueous solution of polyvinyl alcohol contains 10% polyvinyl alcohol by mass.
[0055] 2. Freeze the wood impregnated with polyvinyl alcohol solution, and then thaw it to obtain a soft wood hydrogel (PVA / W);
[0056] 3. Immerse the soft wood hydrogel in liquid polyethylene glycol until the liquid polyethylene glycol displaces the water in the soft wood hydrogel, thus obtaining the hard moldable wood-based composite phase change material (PEG / PVA / W).
[0057] The delignified wood described in step one is prepared according to the following steps: wood chips are placed in a de-hemicellulose solution and kept at 100℃ for 7 hours to obtain de-hemicellulose wood. The de-hemicellulose wood is washed and placed in a hydrogen peroxide solution and kept at 40℃ until the wood turns white. It is then washed and dried to obtain delignified wood. The de-hemicellulose solution is a mixed solution of NaOH and Na2SO3, with a NaOH concentration of 2.5 mol / L and a Na2SO3 concentration of 0.4 mol / L. The hydrogen peroxide solution has a mass percentage of 7.5%. The wood chips are rotary-cut linden wood with a thickness of 0.2 mm.
[0058] The immersion described in step one is specifically performed at room temperature for 24 hours.
[0059] The freezing process described in step two specifically involves freezing at a temperature of -20°C for 12 hours.
[0060] The liquid polyethylene glycol mentioned in step three is PEG400.
[0061] In step three, the soft wood hydrogel is immersed in liquid polyethylene glycol for 12 hours at room temperature.
[0062] Example 2:
[0063] The strength switching method for the moldable wood-based composite phase change material prepared in Example 1 is carried out according to the following steps:
[0064] 1. The rigid moldable wood-based composite phase change material prepared in Example 1 was immersed in water until the water displaced the polyethylene glycol in the phase change material to obtain a soft wood hydrogel (PVA / W).
[0065] 2. Immerse the soft wood hydrogel in liquid polyethylene glycol until the liquid polyethylene glycol displaces the water in the hydrogel to obtain a hard moldable wood-based composite phase change material (PEG / PVA / W).
[0066] 3. Repeat steps one and two 10 times to complete the intensity switching method.
[0067] In step one, the rigid moldable wood-based composite phase change material is immersed in water for 2 hours at room temperature.
[0068] The liquid polyethylene glycol mentioned in step two is PEG400.
[0069] In step two, the soft wood hydrogel is immersed in liquid polyethylene glycol PEG400 for 6 hours at room temperature.
[0070] In step one, the shape of the soft wood hydrogel is adjusted. In step two, the shaped soft wood hydrogel is immersed in liquid polyethylene glycol for shaping, thus obtaining the shape-adjusted phase change material.
[0071] Example 3: This example differs from Example 1 in that the polyethylene glycol used in step 3 is PEG1000, PEG2000, PEG4000, PEG6000, PEG8000, and PEG10000. When the polyethylene glycol is PEG1000, the flexible wood hydrogel is immersed in liquid polyethylene glycol at 60°C for 12 hours in step 3. When the polyethylene glycol is PEG2000, the flexible wood hydrogel is immersed in liquid polyethylene glycol at 80°C for 12 hours in step 3. When the polyethylene glycol is PEG4000... In step three, the flexible wood hydrogel is immersed in liquid polyethylene glycol at 80°C for 12 hours. This process is repeated for all cases: when the polyethylene glycol is PEG6000, PEG8000, and PEG10000. All other steps are the same as in Example 1.
[0072] Example 4: This example differs from Example 1 in that the wood chips used are spruce, New Zealand pine, and birch, respectively. Everything else is the same as in Example 1.
[0073] Figure 2 The images show the physical samples of PVA / W prepared in step two of Example 1 and PEG / PVA / W prepared in step three. The soft wood gel (0.5 mm thick) could not lift the reactor (0.9238 kg), and the soft PVA / W was directly destroyed due to the weight of the reactor. In contrast, the hard PEG / PVA / W (0.2 mm thick) could easily lift the reactor, indicating that PEG / PVA / W has excellent mechanical properties.
[0074] Figure 3 The stress-strain curves of PVA / W prepared in step two of Example 1 and PEG / PVA / W prepared in step three are parallel to the (L) wood growth direction. Figure 4The figures show the stress-strain curves of PVA / W prepared in step two of Example 1 and PEG / PVA / W prepared in step three, perpendicular to the (T) wood growth direction. As can be seen from the figures, under the influence of polyethylene glycol, PEG / PVA / W exhibits excellent tensile strength (80.86 MPa in the L direction and 4.77 MPa in the T direction), even exceeding the tensile strength of the original wood (un-ligninized) at 60.70 MPa (L direction) and 3.49 MPa (T direction). In contrast, PVA / W, due to its high water content, has low mechanical strength (11.3 MPa in the L direction and 0.15 MPa in the T direction), indicating that the mechanical properties of the wood gel undergo a weak-to-strong transformation under the influence of water and polyethylene glycol, respectively.
[0075] Figure 5 The images are scanning electron microscope (SEM) images. a) shows the longitudinal (L) and tangential (T) directions of the un-lignin-treated log; b) shows the longitudinal section of the un-lignin-treated log; c) shows the cross section of the PEG / PVA / W prepared in step three of Example 1; and d) shows the longitudinal section of the PEG / PVA / W prepared in step three of Example 1. As can be seen from the images, linden wood has a natural porous structure, while the porous structure of the wood in the PEG / PVA / W is filled with polyethylene glycol and polyvinyl alcohol.
[0076] The soft wood hydrogel prepared in step two of Example 1 can be shaped by adjusting its shape and then soaking it in liquid polyethylene glycol for fixation, thus creating a variety of shapes. Figure 6 The images show physical pictures of PED / PVA / W in different forms in step three of Example 1. As can be seen from the pictures, it can be made into a variety of shapes, such as honeycomb structures (honeycomb structures are often used in load-bearing structures in daily life) or bags (indicating that wood gel is expected to replace traditional plastic products).
[0077] Figure 7 Differential scanning calorimetry (DSC) was used to determine the crystallization and melting curves of PEG / PVA / W prepared in step three of Example 1 before and after 100 heating-cooling cycles. As shown in the figure, PEG / PVA / W exhibited a significant endothermic peak during heating and a significant exothermic peak during cooling, indicating that PEG / PVA / W has good phase transition properties (see Table 1 below). Furthermore, it remained stable after 100 heating-cooling cycles, demonstrating good stability (see Table 1 below).
[0078] Figure 8Differential scanning calorimetry (DSC) was used to determine the crystallization and melting curves of PEG / PVA / W prepared using polyethylene glycol of different molecular weights in Example 3, before and after 100 heating-cooling cycles. As shown in the figure, PEG / PVA / W exhibited obvious endothermic peaks during heating and obvious exothermic peaks during cooling, indicating that PEG / PVA / W using polyethylene glycol of different molecular weights possesses excellent phase transition properties (see Table 1 below). Furthermore, the molecular weight and melting point of polyethylene glycol also differ, allowing for the selection of appropriate molecular weight polyethylene glycol based on actual environmental needs. The PEG / PVA / W remained stable after 100 heating-cooling cycles, demonstrating excellent stability (see Table 1 below).
[0079]
[0080]
[0081] In the table, a) represents the melting temperature; b) represents the latent heat of melting; c) represents the crystallization temperature; and d) represents the latent heat of crystallization.
[0082] Figure 9 The image shows the actual PEG / PVA / W prepared from various hardwoods and softwoods in step three of Example 4. As can be seen from the image, PEG / PVA / W exhibits good plasticity and can be made not only from linden wood but also from a variety of other types of wood, indicating that this preparation method is universal.
[0083] The PEG / PVA / W prepared in step three of Example 1 and common plastics (including polyvinyl chloride (PVC, widely used in the construction industry and consumer goods) and polyethylene (PE, often used in agricultural and packaging applications) were buried in the soil at a depth of 10 cm. Figure 10 The figure shows the biodegradability of PEG / PVA / W prepared in step three of Example 1. As can be seen from the figure, cellulose, PVA, and PEG in PEG / PVA / W can be directly degraded by microorganisms, and are completely biodegraded after 4 months of burial. In contrast, PVC and PE retain their original form and show no signs of change after the same burial time, reflecting the non-degradability of traditional plastics and their tendency to cause environmental pollution. The excellent biodegradability of PEG / PVA / W indicates that it has the potential to become a sustainable, biodegradable, and efficient plastic in the future, avoiding long-term environmental pollution after its final use.
[0084] Figure 11 This is a photograph of the rigid moldable wood-based composite phase change material in Example 2 after repeated hard-soft switching under the action of water and polyethylene glycol for the tenth time. Figure 12This image shows the mechanical properties of the rigid moldable wood-based composite phase change material in Example 2 after ten cycles of repeated hard-soft switching under the influence of water and polyethylene glycol. After ten cycles, PVA / W remained very soft (tensile strength in the L direction 5.60 MPa) and maintained its shape intact without damage. The mechanical properties of PEG / PVA / W (tensile strength in the L direction 85.63 MPa) also remained good. The mechanical properties of PVA / W and PEG / PVA / W after ten cycles did not change significantly from their initial values, indicating good stability.
Claims
1. A method for preparing a moldable wood-based composite phase change material, characterized in that... It is prepared according to the following steps:
1. Impregnate the delignified wood in an aqueous solution of polyvinyl alcohol to obtain wood impregnated with polyvinyl alcohol solution; The polyvinyl alcohol in the aqueous solution contains 5% to 30% by mass.
2. Freeze the wood impregnated with polyvinyl alcohol solution, then thaw it to obtain a soft wood hydrogel; 3. Immerse the soft wood hydrogel in liquid polyethylene glycol until the liquid polyethylene glycol displaces the water in the soft wood hydrogel, thus obtaining a hard moldable wood-based composite phase change material.
2. The method for preparing a moldable wood-based composite phase change material according to claim 1, characterized in that... The delignified wood described in step one is prepared according to the following steps: wood chips are placed in a de-hemicellulose solution and kept at a temperature of 60℃~120℃ for 5h~24h to obtain de-hemicellulose wood. The de-hemicellulose wood is washed and placed in a hydrogen peroxide solution and kept at a temperature of 25℃~80℃ until the wood turns white. It is then washed and dried to obtain delignified wood. The de-hemicellulose solution is a mixed solution of NaOH and Na2SO3, and the concentration of NaOH in the de-hemicellulose solution is 1mol / L~3mol / L, and the concentration of Na2SO3 in the de-hemicellulose solution is 0.1mol / L~1mol / L. The mass percentage of the hydrogen peroxide solution is 2.5%~30%.
3. The method for preparing a moldable wood-based composite phase change material according to claim 1, characterized in that... The soaking described in step one is specifically performed at room temperature for 12 to 24 hours.
4. The method for preparing a moldable wood-based composite phase change material according to claim 1, characterized in that... The freezing process described in step two specifically involves freezing at a temperature of -5℃ to -40℃ for 6 to 48 hours.
5. The method for preparing a moldable wood-based composite phase change material according to claim 1, characterized in that... In step three, the soft wood hydrogel is immersed in liquid polyethylene glycol for 12 to 24 hours at room temperature to 80°C.
6. A method for intensity switching of a moldable wood-based composite phase change material prepared according to claim 1, characterized in that... It is done in the following steps:
1. Immerse the rigid moldable wood-based composite phase change material in water until the water displaces the polyethylene glycol in the phase change material to obtain a soft wood hydrogel.
2. Immerse the soft wood hydrogel in liquid polyethylene glycol until the liquid polyethylene glycol displaces the water in the hydrogel, thus obtaining a hard moldable wood-based composite phase change material. Third, repeat steps one and two multiple times to complete the intensity switching method.
7. The strength switching method for a moldable wood-based composite phase change material according to claim 6, characterized in that... In step one, the rigid moldable wood-based composite phase change material is immersed in water for 2 to 3 hours at room temperature to 80°C.
8. The method for strength switching of a moldable wood-based composite phase change material according to claim 6, characterized in that... In step two, the soft wood hydrogel is immersed in liquid polyethylene glycol for 2 to 12 hours at room temperature to 80°C.
9. The strength switching method for a moldable wood-based composite phase change material according to claim 6, characterized in that... In step one, the shape of the soft wood hydrogel is adjusted. In step two, the shaped soft wood hydrogel is immersed in liquid polyethylene glycol for shaping, thus obtaining the shape-adjusted phase change material.
10. The strength switching method for a moldable wood-based composite phase change material according to claim 6, characterized in that... Step 3: Repeat steps 1 to 2 1 to 10 times.