A PVA-PVP hydrogel composite fatty acid flexible phase change film and its preparation method

Abstract

This invention proposes a PVA-PVP hydrogel composite fatty acid flexible phase change film and its preparation method. Utilizing the polar groups such as the hydroxyl groups on the PVA molecular chain and the carbonyl groups on the PVP molecular chain, strong intermolecular hydrogen bonds are formed between the fatty acid molecules and the carboxyl groups at the ends of the fatty acid molecules, stably anchoring the fatty acid within the hydrogel network. Even after the fatty acid melts, its macroscopic flow is restricted by the network structure, thus achieving intrinsic morphological stability and leak-proof function. Simultaneously, PVP, as an amphiphilic polymer, effectively improves the interfacial compatibility between the hydrophobic fatty acid and the hydrophilic PVA / PVP gel network, avoiding phase separation during long-term use. Furthermore, a dense intermolecular hydrogen bond network is formed between PVA and PVP, with PVA acting as a rigid framework and PVP as a flexible modifier. Their synergistic effect ensures that the composite gel network maintains structural stability while possessing excellent bending and tensile properties.

Description

Technical Field

[0001] This invention relates to the field of phase change thermal storage materials and flexible thermal management technology, and in particular to a PVA-PVP hydrogel composite fatty acid flexible phase change film and its preparation method. Background Technology

[0002] As electronic devices evolve towards higher power density, integration, and flexibility, heat dissipation has become a key bottleneck restricting their performance, lifespan, and reliability. This is particularly true in wearable devices, flexible displays, and smartphones, where not only are efficient heat dissipation requirements placed on thermal management materials, but also stringent demands are placed on their flexibility, thinness, and portability.

[0003] Phase change materials (PCMs) are widely used in thermal management and energy storage due to their ability to absorb or release large amounts of latent heat at constant temperatures. Among them, fatty acid-based PCMs (such as decanoic acid, lauric acid, and stearic acid) are ideal candidates for medium- and low-temperature thermal management because of their advantages, including suitable phase change temperature, high latent heat, low supercooling, non-toxicity, non-corrosiveness, good chemical stability, and wide availability. However, fatty acids inevitably transform into a mobile liquid state during the phase change process, and their unstable shape, which is prone to leakage, is a major problem hindering their practical application. After crystallization, they are hard and brittle, lacking flexibility, and cannot be directly used in flexible electronic devices that require bending and folding.

[0004] To address leakage issues, existing technologies typically employ microencapsulation or adsorption with porous materials (such as carbon foam, expanded graphite, and metal foam) to prepare shaped phase change materials. However, in practical applications, while rigid porous frameworks (such as carbon foam and metal foam) can adsorb molten fatty acids through capillary forces, the resulting composite materials exhibit high overall hardness and poor flexibility, making bending or folding impossible. Traditional surface coating encapsulation (such as epoxy resin coating) can further prevent leakage, but due to the mismatch in thermal expansion coefficients between the coating and the core material, interfacial delamination or coating cracking is prone to occur during repeated thermal cycling. Furthermore, existing composite materials are often thick and lack flexibility, making it difficult to conform to human skin or irregular curved surfaces.

[0005] Therefore, developing a phase change film that combines high thermal storage capacity, excellent flexibility, zero leakage, and good interfacial bonding performance has become a technical challenge that urgently needs to be solved in this field. Summary of the Invention

[0006] In view of this, this invention proposes a PVA-PVP hydrogel composite fatty acid flexible phase change film and its preparation method. The polar groups, such as the hydroxyl groups on the polyvinyl alcohol (PVA) molecular chain and the carbonyl groups on the polyvinylpyrrolidone (PVP) molecular chain, form strong intermolecular hydrogen bonds with the carboxyl groups at the ends of fatty acid molecules, stably anchoring the fatty acids within the hydrogel network. Even after the fatty acids melt, their macroscopic flow is restricted by the network structure, thus achieving intrinsic morphological stability and leak-proof function. Simultaneously, PVP, as an amphiphilic polymer, effectively improves the interfacial compatibility between the hydrophobic fatty acids and the hydrophilic PVA / PVP gel network, avoiding phase separation during long-term use. Furthermore, a dense intermolecular hydrogen bond network is formed between PVA and PVP, with PVA acting as a rigid framework and PVP as a flexible modifier. Their synergistic effect ensures that the composite gel network maintains structural stability while possessing excellent bending and tensile properties.

[0007] The technical solution of this invention is implemented as follows: In a first aspect, the present invention provides a PVA-PVP hydrogel composite fatty acid flexible phase change film, the raw materials of which include polyvinylpyrrolidone, polyvinyl alcohol and fatty acids.

[0008] Existing fatty acids exhibit high fluidity after melting, easily contaminating equipment. This invention aims to provide an effective encapsulation strategy to ensure the film maintains shape stability above the phase change temperature, preventing the precipitation of liquid fatty acids. It overcomes the shortcomings of rigid porous materials (such as carbon foam and metal foam) as supports, which prevent the bending of shaped phase change composite materials and hinder their application in flexible devices, enabling the prepared phase change film to possess bendable and foldable mechanical flexibility. Furthermore, it avoids coating peeling or cracking due to differences in thermal expansion coefficients, improving the structural stability and service life of the composite material during long-term thermal cycling.

[0009] This invention uses polyvinyl alcohol (PVA) and polyvinylpyrrolidone (PVP) as a mixed matrix to construct a hydrogel with a three-dimensional network structure through chemical or physical crosslinking. Utilizing the numerous polar groups such as hydroxyl and carbonyl groups in the PVA / PVP hydrogel network, molten fatty acid molecules are adsorbed and immobilized through hydrogen bonding. After introducing fatty acids into the hydrogel network, a flexible composite phase change film is formed through drying or partial dehydration. PVA provides excellent film-forming properties and mechanical strength. PVA forms strong intermolecular hydrogen bonds with the carboxyl groups (-COOH) at the ends of fatty acid molecules, promoting uniform dispersion of fatty acids in the PVA matrix and effectively inhibiting the macroscopic flow of liquid fatty acids, achieving intrinsic morphological stability and leak-proof function. The strong hydrogen bond interaction between the polar groups of PVP and fatty acids improves the interfacial compatibility between the hydrophobic fatty acids and the hydrophilic PVA hydrogel network, ensuring stability. PVA and PVP form a dense intermolecular hydrogen bond network. PVA acts as a rigid framework, and PVP acts as a flexible modifier; their synergy allows the composite gel network to maintain structural stability while possessing excellent bending and tensile properties.

[0010] Based on the above technical solutions, the fatty acid further includes at least one of stearic acid, decanoic acid, palmitic acid, and lauric acid.

[0011] Using the aforementioned fatty acids as phase change materials offers several advantages. Firstly, these four fatty acids represent typical compounds with different carbon chain lengths, and their combination can cover most medium- and low-temperature applications. Secondly, when formulating binary, ternary, or quaternary eutectic systems, the phase change temperature can be precisely controlled within the range of 18°C ​​to 26°C by adjusting the ratio of decanoic acid to lauric acid. This temperature range corresponds to the comfortable ambient temperature for the human body. Simultaneously, palmitic acid and stearic acid can provide high phase change enthalpy, excellent crystallinity, and structural rigidity support under high-temperature conditions.

[0012] Based on the above technical solution, the ratio of the mass of the fatty acid to the total mass of polyvinylpyrrolidone and polyvinyl alcohol is further (1~5):2.

[0013] When the mass ratio of fatty acids to the total mass of polyvinylpyrrolidone and polyvinyl alcohol is less than 1:2, the content of phase change components in the system is low, resulting in a significant decrease in the latent heat storage capacity of the material and an insignificant phase change temperature regulation effect, making it difficult to demonstrate the functional advantages of phase change materials. When the mass ratio of fatty acids to the total mass of polyvinylpyrrolidone and polyvinyl alcohol is greater than 5:2, the fatty acid content in the system is too high, making it prone to phase change separation or leakage in the hydrogel network. This leads to reduced structural stability of the composite film and deterioration of its mechanical properties, affecting the practical application performance of the material.

[0014] Based on the above technical solution, the mass ratio of polyvinylpyrrolidone to polyvinyl alcohol is further (1~3):5.

[0015] When the mass ratio of polyvinylpyrrolidone to polyvinyl alcohol is less than 1:5, the PVP content is low, resulting in insufficient interfacial compatibility and flexibility regulation between the hydrophobic fatty acids and the hydrophilic PVA network. This can easily lead to uneven dispersion of fatty acids and a decrease in film flexibility. When the mass ratio is higher than 3:5, the relative PVA content is low, leading to a decrease in the strength of the network skeleton and film stability. This is not conducive to maintaining the structural integrity, morphological stability, and comprehensive mechanical properties of the composite film.

[0016] Secondly, the present invention also provides a method for preparing a PVA-PVP hydrogel composite fatty acid flexible phase change film, comprising the following steps: S1, mixing polyvinylpyrrolidone and polyvinyl alcohol to obtain a first mixture; S2. Mix the first mixture with the fatty acid to obtain the second mixture; S3. The second mixture is cast onto the substrate surface to obtain the PVA-PVP hydrogel composite fatty acid flexible phase change film.

[0017] Based on the above technical solution, step S1 further includes: mixing polyvinyl alcohol with water, then adding polyvinylpyrrolidone, heating, and stirring to obtain a first mixture.

[0018] Based on the above technical solution, the mass ratio of polyvinyl alcohol to water is 1:(9~12), and the degree of alcoholysis of polyvinyl alcohol is 98%~99% (mol / mol).

[0019] Based on the above technical solution, the mass ratio of polyvinyl alcohol to water is further 1:10.

[0020] Based on the above technical solution, the stirring speed is further specified as 800~1200 r / min, and the stirring time is 0.4~0.6 h.

[0021] Based on the above technical solution, the heating temperature is further specified to be between 85 and 95°C.

[0022] Based on the above technical solution, further, the fatty acid in step S2 is a molten fatty acid.

[0023] Based on the above technical solution, the method for preparing the molten fatty acid further includes: heating and stirring the fatty acid to obtain the molten fatty acid.

[0024] Based on the above technical solutions, when the fatty acid is stearic acid, the heating temperature is 70~80℃; when the fatty acid is palmitic acid, the heating temperature is 60~70℃; when the fatty acid is n-decanoic acid, the heating temperature is 40~50℃; and when the fatty acid is lauric acid, the heating temperature is 50~60℃. When the fatty acid is a dicarboxylic acid system of decanoic acid and stearic acid, the mass ratio of decanoic acid to stearic acid is 9:1, and the heating temperature is 80~90℃. When the fatty acid is a tricarboxylic acid system of decanoic acid, stearic acid and palmitic acid, the mass ratio of decanoic acid, stearic acid and palmitic acid is 77.4:8.6:14, and the heating temperature is 70~80℃.

[0025] Based on the above technical solutions, the substrate further includes any one of glass plate, polyester release film, polytetrafluoroethylene plate or stainless steel plate.

[0026] Based on the above technical solution, step S3 further includes: casting the second mixture onto the substrate surface and drying it at room temperature for 48-72 hours to obtain the PVA-PVP hydrogel composite fatty acid flexible phase change film.

[0027] Compared with the prior art, the present invention has the following beneficial effects: (1) Compared with traditional fixed phase change materials with rigid foam carbon or porous ceramic as the skeleton, the present invention uses polymer hydrogel as the network to prepare a film with excellent flexibility. It can be bent, folded or even twisted without breaking. It can be perfectly attached to the surface of flexible electronic devices or human skin, thus broadening the application prospects of phase change materials in the wearable field.

[0028] (2) Thanks to the strong hydrogen bonding and physical confinement effect between the PVA / PVP three-dimensional network and fatty acid molecules, no liquid fatty acid seeps out even when the film is heated to a temperature far above the melting point of fatty acids and held for a certain period of time. Its encapsulation effect is better than simple surface coating, and there is no risk of coating peeling.

[0029] (3) By using hydrogen bond network confinement rather than chemical modification to destroy the fatty acid molecular structure, the fatty acids in the composite film retain their original high latent heat of phase transition (up to 100 J / g or more). Even after hundreds of thermal cycles, the phase transition temperature and latent heat value of the film decrease very little, exhibiting excellent thermal cycling stability.

[0030] (4) As an amphiphilic polymer, PVP plays a "bridging" role. It is compatible with PVA and can stabilize fatty acids through polarity, which significantly improves the interfacial binding force between the hydrophilic gel network and the hydrophobic fatty acids, thus avoiding phase separation during long-term use.

[0031] (5) The preparation process of this invention mainly uses water as a solvent, with no organic solvent involved throughout the process. The process is simple, the conditions are mild (low temperature or room temperature), the cost is low, and it is easy to achieve large-scale production. Attached Figure Description

[0032] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0033] Figure 1 This is a scanning electron microscope image of the PVA-PVP hydrogel composite fatty acid flexible phase change film of Example 1. Figure 2 Infrared spectra of the PVA-PVP hydrogel composite fatty acid flexible phase change film and the DA / SA binary fatty acid system of Example 1 and Comparative Example 1. Figure 3 The images are DSC diagrams of the PVA-PVP hydrogel composite fatty acid flexible phase change films of Examples 1-15. Figure 4 Thermogravimetric analysis (TGA) diagrams of the PVA-PVP hydrogel composite fatty acid flexible phase change films of Example 9 and Comparative Example 2 are shown. Figure 5 The tensile stress diagrams are for the PVA-PVP hydrogel composite fatty acid flexible phase change films of Examples 2, 7, 12, and Comparative Example 1. Figure 6 The image shows the bending and recovery of the PVA-PVP hydrogel composite fatty acid flexible phase change film of Example 1. Detailed Implementation

[0034] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0035] In the following specific implementation, PVA was purchased from Shanghai Maclean Biochemical Technology Co., Ltd., with product number P815725; The PVP was purchased from Shanghai McLean Biochemical Technology Co., Ltd., with item number P816208.

[0036] In the following specific implementation, the room temperature refers to 15~25℃.

[0037] Example 1 This embodiment provides a PVA-PVP hydrogel composite fatty acid flexible phase change film and its preparation method.

[0038] 1. Raw materials It includes PVA, PVP, deionized water, and fatty acids, wherein the fatty acids include decanoic acid and stearic acid, wherein the mass ratio of PVP to PVA is 1:5, the mass ratio of decanoic acid to stearic acid is 9:1, the ratio of the total mass of fatty acids to the total mass of PVA and PVP is 1:2, and the mass ratio of PVA to deionized water is 1:10.

[0039] 2. Preparation method The process includes the following steps: S1. Weigh 50g of PVA and add it to a beaker containing deionized water. Stir at a speed of 1000r / min for 0.5h at room temperature until swelling occurs. Simultaneously, weigh 10g of PVP and slowly add it to the beaker. After stirring, place the beaker in a water bath and heat and stir at 95℃ with a stirring speed of 800r / min for 1h until completely dissolved (if there are bubbles, let it stand in a water bath at 95℃ for 0.5h to defoam), resulting in a homogeneous and transparent PVA / PVP solution.

[0040] S2. Weigh out n-decanoic acid and stearic acid and add them to another beaker. Stir them in a water bath at 85°C until they are completely melted and a clear, homogeneous, and transparent liquid is obtained, which is a fatty acid solution.

[0041] S3. Slowly add the fatty acid solution dropwise to the PVA / PVP solution that is being heated and stirred. Stir vigorously at a constant temperature of 95℃ for 2 hours at a stirring rate of 1200 r / min to form a stable white homogeneous mixture.

[0042] S4. The mixture obtained in step S3 is cast onto a flat glass substrate. Before pouring the mixture, a thin layer of glycerin is applied to the substrate surface. The mixture is dried at room temperature for 56 hours to obtain a PVA-PVP hydrogel composite fatty acid flexible phase change film.

[0043] The obtained PVA-PVP hydrogel composite fatty acid flexible phase change film was observed by scanning electron microscopy, and the results are as follows: Figure 1 As shown, by Figure 1It can be seen that the composite film exhibits an interwoven porous network structure. This structural feature directly reflects the phase behavior and micro-dispersion state between the phase change component (DA / SA) and the PVA-PVP hydrogel matrix.

[0044] The infrared absorption spectrum of the obtained PVA-PVP hydrogel composite fatty acid flexible phase change film was detected, and the results are as follows: Figure 2 As shown, by Figure 2 It can be seen that the superposition of the spectra of DA / SA dicarboxylic acid and PVP / PVA hydrogel, without the appearance of new characteristic peaks, indicates that the formation of phase change composite hydrogel film is a physical change.

[0045] The bending and recovery of the obtained PVA-PVP hydrogel composite fatty acid flexible phase change film were captured by digital images, as shown below. Figure 6 As shown, by Figure 6 It can be seen that when the prepared sample is rolled up at room temperature, it does not break after being bent at 1080° and can recover after the external force is removed, without affecting the performance of the sample, indicating that the composite phase change film has good flexibility.

[0046] Example 2 This embodiment provides a PVA-PVP hydrogel composite fatty acid flexible phase change film and its preparation method.

[0047] 1. Raw materials It includes PVA, PVP, deionized water, and fatty acids, wherein the fatty acids include decanoic acid and stearic acid, wherein the mass ratio of PVP to PVA is 1:5, the mass ratio of decanoic acid to stearic acid is 9:1, the total mass ratio of fatty acids to the total mass of PVA and PVP is 1:1, and the mass ratio of PVA to deionized water is 1:8.

[0048] 2. Preparation method The process includes the following steps: S1. Weigh 50g of PVA and add it to a beaker containing deionized water. Stir at a speed of 1000r / min for 0.5h at room temperature until swelling occurs. Simultaneously, weigh 10g of PVP and slowly add it to the beaker. After stirring, place the beaker in a water bath and heat and stir at 95℃ with a stirring speed of 800r / min for 1h until completely dissolved (if there are bubbles, let it stand in a water bath at 95℃ for 0.5h to defoam), resulting in a homogeneous and transparent PVA / PVP solution.

[0049] S2. Weigh out n-decanoic acid and stearic acid and add them to another beaker. Stir them in a water bath at 85°C until they are completely melted and a clear, homogeneous, and transparent liquid is obtained, which is a fatty acid solution.

[0050] S3. Slowly add the fatty acid solution dropwise to the PVA / PVP solution that is being heated and stirred. Stir vigorously at a constant temperature of 95℃ for 2 hours at a stirring rate of 1200 r / min to form a stable white homogeneous mixture.

[0051] S4. The mixture obtained in step S3 is cast onto a flat polytetrafluoroethylene (PTFE) substrate. A thin layer of glycerin is applied to the substrate surface before pouring the mixture. The mixture is dried at room temperature for 48 hours to obtain a PVA-PVP hydrogel composite fatty acid flexible phase change film.

[0052] Example 3 This embodiment provides a PVA-PVP hydrogel composite fatty acid flexible phase change film and its preparation method.

[0053] 1. Raw materials It includes PVA, PVP, deionized water, and fatty acids, wherein the fatty acids include decanoic acid and stearic acid, wherein the mass ratio of PVP to PVA is 1:5, the mass ratio of decanoic acid to stearic acid is 9:1, the ratio of the total mass of fatty acids to the total mass of PVA and PVP is 3:2, and the mass ratio of PVA to deionized water is 1:12.

[0054] 2. Preparation method The process includes the following steps: S1. Weigh 50g of PVA and add it to a beaker containing deionized water. Stir at a speed of 1000r / min for 0.5h at room temperature until swelling occurs. Simultaneously, weigh 10g of PVP and slowly add it to the beaker. After stirring, place the beaker in a water bath and heat and stir at 95℃ with a stirring speed of 800r / min for 1h until completely dissolved (if there are bubbles, let it stand in a water bath at 95℃ for 0.5h to defoam), resulting in a homogeneous and transparent PVA / PVP solution.

[0055] S2. Weigh out n-decanoic acid and stearic acid and add them to another beaker. Stir them in a water bath at 85°C until they are completely melted and a clear, homogeneous, and transparent liquid is obtained, which is a fatty acid solution.

[0056] S3. Slowly add the fatty acid solution dropwise to the PVA / PVP solution that is being heated and stirred. Stir vigorously at a constant temperature of 95℃ for 2 hours at a stirring rate of 1200 r / min to form a stable white homogeneous mixture.

[0057] S4. The mixture obtained in step S3 is cast onto a flat stainless steel substrate. Before pouring the mixture, a thin layer of glycerin is applied to the substrate surface. The mixture is dried at room temperature for 72 hours to obtain a PVA-PVP hydrogel composite fatty acid flexible phase change film.

[0058] Example 4 This embodiment provides a PVA-PVP hydrogel composite fatty acid flexible phase change film and its preparation method. The difference from Example 1 is that the ratio of the total mass of fatty acids to the total mass of PVA and PVP is 2:1.

[0059] Example 5 This embodiment provides a PVA-PVP hydrogel composite fatty acid flexible phase change film and its preparation method. The difference from Example 1 is that the ratio of the total mass of fatty acids to the total mass of PVA and PVP is 5:2.

[0060] Example 6 This embodiment provides a PVA-PVP hydrogel composite fatty acid flexible phase change film and its preparation method. The difference from Example 1 is that the mass ratio of PVP to PVA is 2:5, and the ratio of the total mass of fatty acids to the total mass of PVA and PVP is 1:2.

[0061] Example 7 This embodiment provides a PVA-PVP hydrogel composite fatty acid flexible phase change film and its preparation method. The difference from Example 1 is that the mass ratio of PVP to PVA is 2:5, and the ratio of the total mass of fatty acids to the total mass of PVA and PVP is 1:1.

[0062] Example 8 This embodiment provides a PVA-PVP hydrogel composite fatty acid flexible phase change film and its preparation method. The difference from Example 1 is that the mass ratio of PVP to PVA is 2:5, and the ratio of the total mass of fatty acids to the total mass of PVA and PVP is 3:2.

[0063] Example 9 This embodiment provides a PVA-PVP hydrogel composite fatty acid flexible phase change film and its preparation method. The difference from Example 1 is that the mass ratio of PVP to PVA is 2:5, and the ratio of the total mass of fatty acids to the total mass of PVA and PVP is 2:1.

[0064] Example 10 This embodiment provides a PVA-PVP hydrogel composite fatty acid flexible phase change film and its preparation method. The difference from Example 1 is that the mass ratio of PVP to PVA is 2:5, and the ratio of the total mass of fatty acids to the total mass of PVA and PVP is 5:2.

[0065] Example 11 This embodiment provides a PVA-PVP hydrogel composite fatty acid flexible phase change film and its preparation method. The difference from Example 1 is that the mass ratio of PVP to PVA is 3:5, and the ratio of the total mass of fatty acids to the total mass of PVA and PVP is 1:2.

[0066] Example 12 This embodiment provides a PVA-PVP hydrogel composite fatty acid flexible phase change film and its preparation method. The difference from Example 1 is that the mass ratio of PVP to PVA is 3:5, and the ratio of the total mass of fatty acids to the total mass of PVA and PVP is 1:1.

[0067] Example 13 This embodiment provides a PVA-PVP hydrogel composite fatty acid flexible phase change film and its preparation method. The difference from Example 1 is that the mass ratio of PVP to PVA is 3:5, and the ratio of the total mass of fatty acids to the total mass of PVA and PVP is 3:2.

[0068] Example 14 This embodiment provides a PVA-PVP hydrogel composite fatty acid flexible phase change film and its preparation method. The difference from Example 1 is that the mass ratio of PVP to PVA is 3:5, and the ratio of the total mass of fatty acids to the total mass of PVA and PVP is 2:1.

[0069] Example 15 This embodiment provides a PVA-PVP hydrogel composite fatty acid flexible phase change film and its preparation method. The difference from Example 1 is that the mass ratio of PVP to PVA is 3:5, and the ratio of the total mass of fatty acids to the total mass of PVA and PVP is 5:2.

[0070] Example 16 This embodiment provides a PVA-PVP hydrogel composite fatty acid flexible phase change film and its preparation method. The difference from Example 1 is that the fatty acids are decanoic acid, stearic acid and palmitic acid, the mass ratio of decanoic acid, stearic acid and palmitic acid is 77.4:8.6:14, and the temperature in step S2 is 75℃.

[0071] The ratio of the total mass of fatty acids to the total mass of PVA and PVP is 2:1.

[0072] Example 17 This embodiment provides a PVA-PVP hydrogel composite fatty acid flexible phase change film and its preparation method. The difference from Example 1 is that the fatty acid used is n-decanoic acid. The ratio of the total mass of fatty acids to the total mass of PVA and PVP is 5:2.

[0073] Example 18 This embodiment provides a PVA-PVP hydrogel composite fatty acid flexible phase change film and its preparation method. The difference from Example 1 is that the mass ratio of PVP to PVA is 2:5. The fatty acid is stearic acid, and the temperature in step S2 is 65°C. The ratio of the total mass of fatty acids to the total mass of PVA and PVP is 1:2.

[0074] Example 19 This embodiment provides a PVA-PVP hydrogel composite fatty acid flexible phase change film and its preparation method. The difference from Example 1 is that the mass ratio of PVP to PVA is 2:5. The fatty acid is palmitic acid, and the temperature in step S2 is 65°C. The ratio of the total mass of fatty acids to the total mass of PVA and PVP is 1:2.

[0075] Example 20 This embodiment provides a PVA-PVP hydrogel composite fatty acid flexible phase change film and its preparation method. The difference from Example 1 is that the mass ratio of PVP to PVA is 2:5. The fatty acid is lauric acid, the temperature in step S2 is 55℃, and the ratio of the total mass of fatty acid to the total mass of PVA and PVP is 1:1.

[0076] Example 21 This embodiment provides a PVA-PVP hydrogel composite fatty acid flexible phase change film and its preparation method. The difference from Example 1 is that the fatty acids are stearic acid, decanoic acid, palmitic acid, and lauric acid, and the mass ratio of stearic acid, decanoic acid, palmitic acid, and lauric acid is 5:70:10:15. The temperature in step S2 is 75°C.

[0077] Comparative Example 1 The difference between this comparative example and Example 1 is that it does not contain fatty acids.

[0078] When fatty acids are lacking in the system, the main phase change heat storage component no longer exists in the composite film. Therefore, the heat absorption and release process of the material is mainly manifested as the sensible heat change of the ordinary polymer matrix, and the latent heat of phase change is significantly reduced or even basically disappears, resulting in a significant weakening of the film's thermal buffering and temperature regulation capabilities.

[0079] Comparative Example 2 The difference between this comparative example and Example 1 is that it does not contain fatty acids, and the mass ratio of PVP to PVA is 2:5.

[0080] When fatty acids are lacking in the system, the film lacks the functions of phase change heat absorption and release, as well as latent heat energy storage, and its thermal regulation performance is significantly weakened. At the same time, with the increase of PVP content, the proportion of flexible segments in the system increases, and the molecular chain mobility is enhanced, which is beneficial to improving the flexibility and ductility of the film; however, due to the decrease in the relative proportion of PVA as a supporting framework, the structural rigidity and mechanical support of the film are weakened.

[0081] Comparative Example 3 The difference between this comparative example and Example 1 is that it does not contain fatty acids, and the mass ratio of PVP to PVA is 3:5.

[0082] When fatty acids are lacking in the system, the film lacks the functions of phase change heat absorption and release, as well as latent heat energy storage, and its thermal regulation performance is significantly weakened. At the same time, with the increase of PVP content, the proportion of flexible segments in the system increases, and the molecular chain mobility is enhanced, which is beneficial to improving the flexibility and ductility of the film; however, due to the decrease in the relative proportion of PVA as a supporting framework, the structural rigidity and mechanical support of the film are weakened.

[0083] Comparative Example 4 The difference between this comparative example and Example 1 is that it does not contain PVA.

[0084] When PVA is absent in the system, the composite system lacks the main film-forming framework and support network, making it difficult to form a stable and continuous three-dimensional confined structure. This weakens the fixation and embedding of fatty acids, easily leading to decreased structural integrity, insufficient mechanical strength, and increased risk of fatty acid leakage.

[0085] Comparative Example 5 The difference between this comparative example and Example 1 is that it does not contain PVP.

[0086] When PVP is absent in the system, the interfacial compatibility between hydrophobic fatty acids and hydrophilic PVA networks decreases, the dispersion uniformity of fatty acids in the matrix deteriorates, and local aggregation or phase separation easily occurs, which in turn affects the flexibility, structural stability and long-term recycling performance of the composite film.

[0087] Performance testing 1. The phase change thermal storage properties of the PVA-PVP hydrogel composite fatty acid flexible phase change films prepared in Examples 1-15 were tested using differential scanning calorimetry. The results are as follows: Figure 3 As shown. By Figure 3 It can be seen that when the mass ratio of PVP to PVA is (1~3):5, ΔHm shows a trend of first increasing and then decreasing with the increase of DA / SA. The phase transition enthalpy is highest when the diacid accounts for 2.0% of the total PVP / PVA, which are 106.6J / g, 102.9J / g, and 96.42J / g, respectively. When the proportion is 2.5, the phase transition enthalpy decreases. Excessive DA / SA may lead to phase separation or incomplete crystallization, resulting in a decrease in ΔH.

[0088] 2. The thermal stability of the PVA-PVP hydrogel composite fatty acid flexible phase change films prepared in Example 9 and Comparative Example 2 was tested using a thermogravimetric analyzer. The results are as follows: Figure 4 As shown. By Figure 4It can be seen that the DA / SA dicarboxylic acid undergoes rapid and intense thermal degradation around 200℃, and is completely pyrolyzed at 250℃. The first relatively rapid pyrolysis range (peak location) of the composite phase change film is close to the high-speed pyrolysis range of DA / SA, and the second and third rapid pyrolysis ranges are close to the pyrolysis range of PVA / PVP. This indicates that the hydrogen bond crosslinking network constructed by the composite phase change film does not affect the thermal degradation of DA / SA and has excellent thermal stability.

[0089] 4. Mechanical tests were performed on the PVA-PVP hydrogel composite fatty acid flexible phase change films prepared in Examples 2, 7, 12, and Comparative Example 1. The results are as follows: Figure 5 As shown. By Figure 5 It is known that PVA / PVP, as a high molecular weight polymer, has relatively low plasticity and fractures at a strain of less than 15 mm. Composite phase change films, as a composite material, inherit some of the high mechanical strength of PVA / PVP and also have better plasticity. Their maximum tensile stress can reach 20.9 N, the maximum deformation reaches 24 mm, and the deformation rate reaches 240%. They can generate greater deformation under tensile force without fracture, which increases the practicality of composite phase change films.

[0090] In summary, this invention provides a PVA-PVP hydrogel composite fatty acid flexible phase change film and its preparation method. Utilizing the polar groups such as the hydroxyl groups on the PVA molecular chain and the carbonyl groups on the PVP molecular chain, strong intermolecular hydrogen bonds are formed between them and the carboxyl groups at the ends of the fatty acid molecules, stably anchoring the fatty acid within the hydrogel network. Even after the fatty acid melts, its macroscopic flow is restricted by the network structure, thus achieving intrinsic morphological stability and leak-proof function. Simultaneously, PVP, as an amphiphilic polymer, effectively improves the interfacial compatibility between the hydrophobic fatty acid and the hydrophilic PVA / PVP gel network, avoiding phase separation during long-term use. Furthermore, a dense intermolecular hydrogen bond network is formed between PVA and PVP, with PVA acting as a rigid framework and PVP as a flexible modifier. Their synergistic effect ensures that the composite gel network maintains structural stability while possessing excellent bending and tensile properties.

[0091] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A PVA-PVP hydrogel composite fatty acid flexible phase change film, characterized in that, Its raw materials consist of polyvinylpyrrolidone, polyvinyl alcohol, fatty acids and water; The mass ratio of polyvinylpyrrolidone to polyvinyl alcohol is (1~3):5; The fatty acids include at least one of stearic acid, decanoic acid, palmitic acid, and lauric acid; The ratio of the mass of the fatty acid to the total mass of polyvinylpyrrolidone and polyvinyl alcohol is (1~5):

2.

2. The method for preparing the PVA-PVP hydrogel composite fatty acid flexible phase change film as described in claim 1, characterized in that, The process includes the following steps: S1, mixing polyvinylpyrrolidone and polyvinyl alcohol to obtain a first mixture; S2. Mix the first mixture with the fatty acid to obtain the second mixture; S3. The second mixture is cast onto the substrate surface to obtain the PVA-PVP hydrogel composite fatty acid flexible phase change film.

3. The preparation method according to claim 2, characterized in that, Step S1 includes: mixing polyvinyl alcohol with water, then adding polyvinylpyrrolidone, heating, and stirring to obtain a first mixture.

4. The preparation method according to claim 3, characterized in that, The mass ratio of polyvinyl alcohol to water is 1:8~12.

5. The preparation method according to claim 3, characterized in that, The heating temperature is between 85 and 95°C.

6. The preparation method according to claim 2, characterized in that, The fatty acids in step S2 are fatty acids in a molten state.

7. The preparation method according to claim 2, characterized in that, The substrate includes any one of glass plate, polyester release film, polytetrafluoroethylene plate or stainless steel plate.

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