A method for preparing a polyvinyl alcohol-based composite film with water resistance and high mechanical strength
By introducing polyphenolic compounds and iron salts into polyvinyl alcohol films to form hydrogen bond networks and metal coordination crosslinking, PVA-TA-Fe composite films were prepared. This solved the problem of polyvinyl alcohol films easily absorbing moisture and swelling in humid environments, achieving high mechanical strength and water resistance, and enhancing the stability and antibacterial properties of the films.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- SICHUAN UNIV
- Filing Date
- 2026-04-10
- Publication Date
- 2026-05-29
AI Technical Summary
Polyvinyl alcohol films are prone to absorbing moisture and swelling in humid environments, which leads to a decline in their mechanical properties and affects their practical application in fields such as waterproof coatings.
By introducing polyphenolic compounds and iron salts into polyvinyl alcohol films to form hydrogen bond networks and metal coordination crosslinks, the water resistance and mechanical strength of the materials are improved. PVA-TA-Fe composite films are prepared by solution casting.
It significantly improves the water resistance and mechanical strength of the film, imparts antibacterial properties, and enhances its stability and service life in humid environments.
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Figure CN122103640A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of polymer materials technology, and in particular to a method for preparing a polyvinyl alcohol-based composite film that combines water resistance and high mechanical strength. Background Technology
[0002] Polyvinyl alcohol (PVA), as an environmentally friendly polymer material with good biocompatibility and biodegradability, can decompose into water and carbon dioxide in the natural environment, making it an ideal material for solving the problem of plastic pollution. PVA possesses various properties, but the requirements for PVA differ in different situations. Modifying PVA according to specific needs is a common and efficient way to utilize it. For example, when PVA is used in packaging materials, waterproof coatings, and other applications requiring moisture protection, its molecular chain contains abundant hydroxyl groups. These hydroxyl groups easily react with water vapor to form hydrogen bonds, leading to moisture absorption and swelling, decreased mechanical strength, or softening and failure of the coating, severely restricting practical applications. Therefore, hydrophobic modification of polyvinyl alcohol materials is necessary to improve the material's service life and reduce costs. Summary of the Invention
[0003] To address the problems of easy moisture absorption and swelling, and degradation of mechanical properties in polyvinyl alcohol (PVA) materials, this invention provides a method for preparing a PVA-based composite film that combines water resistance and high mechanical strength.
[0004] The polyvinyl alcohol-based composite film with both water resistance and high mechanical strength provided by this invention is prepared by the following method: S1. Dissolve polyvinyl alcohol (PVA), polyphenolic compounds and iron salts in an organic solvent, heat to 70-90℃ and stir for 4-5 h to obtain a composite solution.
[0005] The amount of the polyphenolic compound used is 0.5-5% of the mass of polyvinyl alcohol, and the amount of iron salt used is 0.5-2% of the mass of polyvinyl alcohol; the organic solvent is a polar aprotic solvent.
[0006] S2. The composite film is prepared by solution casting: The specific method is to pour the composite solution into the film-forming container and dry it at 50-60℃ until the film is formed, so as to obtain the PVA-TA-Fe composite film, which is the polyvinyl alcohol-based composite film with both water resistance and high mechanical strength.
[0007] Preferably, the specific method of step S1 is as follows: first, polyvinyl alcohol and polyphenolic compounds are dissolved in an organic solvent, heated to 70-90℃, and stirred at a constant temperature for 4-4.5 h, then iron salt is added and stirred at a constant temperature for 10-20 min to obtain a composite solution.
[0008] A further preferred method is as follows: the organic solvent is divided into three parts, and polyvinyl alcohol, polyphenolic compounds, and iron salts are dissolved in the three parts of the organic solvent respectively to obtain polyvinyl alcohol solution, polyphenolic compound solution, and iron salt solution; then the polyvinyl alcohol solution and polyphenolic compound solution are mixed, stirred evenly, and heated to 70-90℃, and stirred at a constant temperature for 4-4.5 h; then the iron salt solution is added, and the mixture is stirred at a constant temperature for 10-20 min to obtain a composite solution.
[0009] The polyphenolic compound is preferably tannic acid (TA). The iron salt is preferably ferric chloride. The organic solvent is preferably dimethyl sulfoxide. The amount of tannic acid is preferably 1.25% of the mass of polyvinyl alcohol, and the amount of ferric chloride is preferably 1.0% of the mass of polyvinyl alcohol, to prepare a PVA-TA-Fe composite film material. Compared with the prior art, the advantages of the present invention are: (1) This invention is based on the hydrogen bond-metal coordination synergistic mechanism, through the formation of a multiple hydrogen bond network between the phenolic hydroxyl groups of polyphenolic compounds (natural polyphenols) and the PVA molecular chain, and the introduction of Fe 3+ Metal coordination crosslinking with the hydroxyl groups of PVA occupies hydrophilic sites, thereby synergistically improving the water resistance and mechanical properties (mechanical strength) of the material, thus preparing PVA-TA-Fe composite thin film materials.
[0010] (2) Thermogravimetric analysis showed that the thermal stability of the PVA-TA-Fe composite film was significantly improved compared with that of the pure PVA film.
[0011] (3) Antibacterial performance tests confirmed that the PVA-TA-Fe composite film exhibited significant antibacterial effects against both Gram-negative and Gram-positive bacteria. This invention utilizes the introduction of TA and Fe... 3+ It not only improves the mechanical strength and water resistance of PVA materials, but also endows them with antibacterial properties.
[0012] (4) The composite film prepared by the solution casting method of the present invention exhibits good film-forming characteristics. The film has a uniform and dense structure, and the film surface is smooth and uniform, without defects and agglomeration.
[0013] Other advantages, objectives and features of the present invention will become apparent in part from the following description, and in part from those skilled in the art through study and practice of the invention. Attached Figure Description
[0014] Figure 1The figures show the mechanical property test results of PVA-TA composite films prepared with different TA contents in Example 1. Among them, (a) is the stress-strain curve of the composite films prepared with different TA contents, (b) is the tensile strength of the composite films prepared with different TA contents, and (c) is the elongation at break of the composite films prepared with different TA contents.
[0015] Figure 2 This is a flowchart of the preparation method for PVA-TA-Fe composite films.
[0016] Figure 3 Different Fe contents in Example 2 3+ The mechanical properties of the prepared PVA-TA-Fe composite films are shown in the figure. (a) shows the mechanical properties of films with different Fe contents. 3+ The stress-strain curves of the prepared composite films, (b) showing the curves with different Fe contents. 3+ The tensile strength of the prepared composite film, (c) represents the tensile strength of films with different Fe contents. 3+ Elongation at break of the prepared composite film.
[0017] Figure 4 Water contact angle diagrams for pure PVA film, PVA-TA composite film, and PVA-TA-Fe composite film.
[0018] Figure 5 The graph shows the water absorption test results for pure PVA film, PVA-TA composite film, and PVA-TA-Fe composite film.
[0019] Figure 6 Stress-strain curves of pure PVA film, PVA-TA composite film, and PVA-TA-Fe composite film after immersion.
[0020] Figure 7 The stress-strain curves are from the wet pressing bonding experiment of PVA-TA-Fe composite films.
[0021] Figure 8 The thermogravimetric analysis results of pure PVA film and PVA-TA-Fe composite film are shown in the figures. (a) is the TG figure and (b) is the DTG figure.
[0022] Figure 9 The figures show the results of the antibacterial test. Among them, (a) shows the results of the Escherichia coli test, and (b) shows the results of the Staphylococcus aureus test.
[0023] Figure 10 The stress-strain curves of the PVA-TA-Fe composite film after initial loading and multiple recycling cycles are shown. Detailed Implementation
[0024] The preferred embodiments of the present invention will be described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.
[0025] The preparation methods for the polyvinyl alcohol solution, polyphenol compound solution, and iron salt solution used in the following examples are as follows: Preparation of PVA solution: Weigh 4500 mg of granular PVA solid into an Erlenmeyer flask, add 150 mL of DMSO to the flask, and heat in an oil bath at 90 °C for about 5 hours until the PVA is completely dissolved to obtain a 30 mg / mL PVA solution.
[0026] Preparation of TA solution: Weigh 45 mg of tannic acid (TA) solid powder and put it into a 3 mL centrifuge tube. Then add 1.5 mL of DMSO into the tube, vortex and sonicate for a certain time to completely dissolve the solid, and obtain a TA solution of 30 mg / mL.
[0027] Preparation of FeCl3 solution: Weigh a certain amount of ferric chloride hexahydrate solid into a 3 mL centrifuge tube, add DMSO solution into the tube, vortex and sonicate to completely dissolve the solid, and prepare a 30 mg / mL FeCl3 solution.
[0028] Example 1 A method for preparing a polyvinyl alcohol-based composite film (PVA-TA composite film) is as follows: A 30 mg / mL PVA solution was placed in a container and stirred continuously in an 80 °C oil bath. A TA solution was then added, and the mixture was stirred for 4 hours in the 80 °C oil bath. The solution was then poured into a film-forming container and dried at 50 °C in a blower dryer until a film was formed. By changing the amount of TA solution used, the percentage of TA to PVA mass was adjusted to 0.625%, 1.25%, 2.5%, and 5.0%, respectively. The composite films containing different proportions of TA were named PVA-TA. x , where x = 0.625, 1.25, 2.5, 5.0. When no TA solution is added, the resulting film is a pure PVA film.
[0029] The mechanical properties of the above five films were tested using a servo-controlled computer system tensile testing machine. Strips approximately 5 mm wide were cut from the obtained films and tested at a speed of 10 mm / min to compare the effects of different TA contents on the film's tensile strength, elongation at break, and other mechanical properties. The test results are shown below. Figure 1In the figure, (a) represents the stress-strain curves of composite films prepared with different TA contents, (b) represents the tensile strength of composite films prepared with different TA contents, and (c) represents the elongation at break of composite films prepared with different TA contents. PT1, PT2, PT3, and PT4 in the figure represent PVA-TA films, respectively. 0.625 PVA-TA 1.25 PVA-TA 2.5 PVA-TA 5.0 .
[0030] It can be seen that the tensile strength of pure PVA film is approximately 36 MPa, and the elongation at break is 470%. After adding 0.625% TA, the tensile strength and ductility of the PVA-TA composite film increase. The optimal values are achieved at a TA content of 1.25%, with the tensile strength increasing by approximately 25% and the elongation at break increasing by approximately 40% compared to pure PVA film. This is because the phenolic hydroxyl groups of TA interact with multiple aliphatic hydroxyl groups of PVA to form hydrogen bonds, enhancing the interaction between molecular chains. Further increasing the TA content leads to a decrease in the mechanical properties of the PVA-TA composite film. Excessive TA molecules, due to the high density of hydroxyl groups, tend to aggregate in the PVA matrix, leading to decreased compatibility between the two phases and disrupting the film's uniformity. Simultaneously, excessive TA may also compete with PVA molecules for hydrogen bonds, weakening the interaction between the PVA backbone chains and creating stress concentration points within the film, resulting in a decrease in tensile strength. Therefore, the PVA-TA composite film with a TA content of 1.25% exhibits the best mechanical properties, with a tensile strength close to 45 MPa and an elongation at break exceeding 650%.
[0031] Example 2 A method for preparing a polyvinyl alcohol-based composite film (PVA-TA-Fe composite film) is as follows: Figure 2 As shown, the details are as follows: A 30 mg / mL PVA solution was placed in a container and stirred continuously in an 80°C oil bath. A TA solution was then added, with the TA concentration accounting for 1.25% of the PVA mass. The mixture was stirred for 4 hours in an 80°C oil bath. Then, a FeCl3 solution was added, and the mixture was stirred for another 15 minutes in an 80°C oil bath. Finally, the solution was poured into a film-forming container and dried in a forced-air dryer at 50°C until a film was formed, yielding a PVA-TA-Fe composite film. This method utilizes different amounts of FeCl3 solution, with the FeCl3 concentration accounting for 0.5%, 1.0%, and 2.0% of the PVA mass, to achieve different concentrations of Fe... 3+ The composite films were named PVA-TA. 1.25 -Fe y , where y = 0.5, 1.0, 2.0.
[0032] Scanning electron microscopy revealed that the PVA-TA-Fe composite film exhibits a uniform and dense structure with a smooth and uniform surface free of defects and agglomeration.
[0033] Fe with different mass fractions was processed using the same method as in Example 1. 3+ Mechanical properties of the PVA-TA-Fe composite film were tested, and it was also compared with PVA-TA. 1.25 The performance of the composite films was compared. The test results are shown below. Figure 3 Where (a) represents different contents of Fe 3+ The stress-strain curves of the prepared composite films, (b) showing the curves with different Fe contents. 3+ The tensile strength of the prepared composite film, (c) represents the tensile strength of films with different Fe contents. 3+ The elongation at break of the prepared composite film. In the figure, PT, PTF1, PTF2, and PTF3 represent the PVA-TA film, respectively. 1.25 PVA-TA 1.25 -Fe 0.5 PVA-TA 1.25 -Fe 1.0 PVA-TA 1.25 -Fe 2.0 It can be seen that among the four composite films with a TA content of 1.25%, the composite film with an iron ion content of 1.0% exhibits the best mechanical properties, compared to PVA-TA. 1.25 The performance of the composite thin film is significantly improved. This is because of the introduction of Fe. 3+ After that, Fe 3+ As a multi-coordination center, it can form strong coordination bonds with the phenolic hydroxyl groups in the TA molecule. At appropriate concentrations, the coordination crosslinking strengthens the network structure of the PVA matrix, resulting in a higher tensile strength of the film compared to PVA-TA. 1.25 The membrane achieves a more significant improvement. When Fe 3+ When the concentration is too low, the crosslinking strengthening effect on the PVA matrix is limited, and the effect on the tensile strength and elongation at break of the film is small. When Fe... 3+ When the concentration is too high, stress concentration points are easily generated within the film, disrupting structural uniformity and resulting in uneven stress during weighing, thus reducing the film's mechanical strength. Simultaneously, excessively high coordination crosslinking density restricts the movement of PVA molecular chains, reducing the film's ductility, which manifests as a decrease in elongation at break during testing. Therefore, in the above three different Fe... 3+ The PVA-TA-Fe composite film of a certain concentration contains 1.0% Fe. 3+ It achieves the best effect in regulating the mechanical properties of thin films, and can achieve synergistic optimization of the strength and toughness of film materials.
[0034] The following uses pure PVA film and PVA-TA.1.25 Composite film, PVA-TA 1.25 -Fe 1.0 The composite film was used as the research object, and various performance tests were conducted. For ease of description, PVA-TA was used. 1.25 Composite film, PVA-TA 1.25 -Fe 1.0 The composite films are referred to as PVA-TA composite films and PVA-TA-Fe composite films, respectively.
[0035] (1) Water contact angle analysis Pure PVA films, PVA-TA composite films, and PVA-TA-Fe composite films were cut into small pieces, ensuring the sample surfaces were dry, clean, and free of foreign matter. The static water contact angle of the samples was then measured at room temperature using a contact angle meter, with approximately 4 μL of deionized water added dropwise each time, and droplet images were captured.
[0036] Test results are available Figure 4 The results showed that the water contact angles of pure PVA film, PVA-TA composite film, and PVA-TA-Fe composite film were 57.86°, 73.75°, and 104.79°, respectively. The static water contact angle of pure PVA film was relatively small, mainly because the PVA molecular chain contains a large number of hydrophilic hydroxyl groups, exhibiting strong hydrophilicity. Compared with pure PVA film, the water contact angle of PVA-TA composite film was increased. This is because TA contains phenolic hydroxyl groups, which can combine with the alcohol hydroxyl groups in PVA to form hydrogen bonds, reducing the binding of water molecules to PVA and improving the hydrophobicity of the material. Simultaneously, the aromatic ring structure in TA also has a certain degree of hydrophobicity, further enhancing the hydrophobicity of the PVA-TA composite film and increasing its static water contact angle. The static water contact angle of the PVA-TA-Fe composite film was approximately 81.1% higher than that of pure PVA. This is because Fe... 3+ It forms coordination bonds with hydroxyl groups on the TA and PVA molecular chains, occupying more hydrophilic hydroxyl sites on the material surface, effectively reducing the number of exposed hydrophilic hydroxyl groups on the film surface, thereby further enhancing the surface hydrophobicity of the membrane material and increasing the water contact angle.
[0037] In practical applications, improved hydrophobicity helps enhance the water resistance of the membrane during actual use, improves its stability in humid environments, and increases its service life. Furthermore, the TA used in this embodiment is a natural biomass material, widely available and low in cost. Using it to modify PVA aligns with the principles of green chemistry, contributing to the high-value utilization of biomass resources and the development of sustainable materials.
[0038] (2) Water absorption performance analysis Pure PVA film, PVA-TA composite film, and PVA-TA-Fe composite film were dried in an oven until their weights were constant. Then, the films were cut into small pieces (10 mm × 10 mm) of similar size and thickness using scissors. The initial weight was recorded as W0 using an electronic balance. The cut pieces of PVA film, PVA-TA composite film, and PVA-TA-Fe composite film were then immersed in the same volume of deionized water. After soaking for a period of time, the films were removed with tweezers, excess water was absorbed from the surface, and the films were weighed. The weight was recorded as W. S Calculate the water absorption rate of the membrane. Then, immerse the membrane in deionized water and repeat the above steps. The water absorption rate of the membrane is calculated using the following method.
[0039] M A = ×100% Where: M A W represents water absorption rate. S W0 represents the mass of the film after immersion in deionized water, while W0 represents the mass of the film after drying in an oven.
[0040] Test results are as follows Figure 5 As shown, the water absorption rate of the pure PVA film reaches its maximum at 236.11% after 30 minutes. Subsequently, the PVA water absorption rate begins to decrease. Based on the PVA molecular structure analysis, this decrease is mainly due to the partial dissolution of PVA. Water molecules bind to the hydroxyl groups on the PVA chains through hydrogen bonds, inducing local untangling and network relaxation of the molecular chains. With increasing immersion time, water molecules further penetrate into the amorphous region, increasing the mobility of the molecular chains and slowly dissolving into the water. The water absorption rate of the PVA-TA composite film stabilizes at 225.12% after 30 minutes, lower than that of the pure PVA film. The maximum water absorption rate of the PVA-TA-Fe composite film is 212.22%, a further decrease compared to the PVA-TA composite film. The main reason is that the pure PVA molecular chain contains a large number of hydrophilic hydroxyl groups, while TA is rich in multiple phenolic hydroxyl groups, which form hydrogen bonds with PVA, reducing the number of hydroxyl groups on the PVA molecular chain that can bind to water molecules. Simultaneously, it increases the cross-linking density of the polymer network, limiting the addition of water molecules. The simultaneous introduction of TA and Fe... 3+ Subsequently, the hydroxyl groups coordinate and complex with the PVA matrix, forming a more complex three-dimensional network structure, making the structure between PVA molecular chains more compact and further restricting the entry of water molecules. The pure PVA film begins to partially dissolve after reaching its maximum water absorption rate, while the composite film's water absorption rate remains stable for a certain period. This result is consistent with the water contact angle test results, further demonstrating that the composite film of this invention exhibits improved water resistance and enhanced mechanical properties in humid environments.
[0041] (3) Mechanical property test after soaking Pure PVA film, PVA-TA composite film, and PVA-TA-Fe composite film were cut into strips of 5 mm × 20 mm using scissors. These strips were placed in headspace vials and immersed in an equal volume of deionized water for 24 hours at room temperature. After immersion, the surface moisture was removed, and the mechanical properties of the immersed films were tested using a servo-controlled computer system tensile testing machine. The test results are as follows: Figure 6 As shown, after soaking in deionized water for 24 hours, the PVA-TA-Fe composite film exhibits the best mechanical properties, maintaining a certain degree of support and bending even in water. The pure PVA film and the PVA-TA composite film show no significant support. Stress-strain curve analysis reveals that the pure PVA film exhibits poor mechanical properties after 24 hours of immersion in water, with a tensile strength of approximately 2 MPa and an elongation at break of approximately 200%. The PVA-TA composite film shows a significant improvement in mechanical properties, with a tensile strength reaching 6.5 MPa and an elongation at break approaching 1000%. The PVA-TA-Fe composite film achieves a tensile strength of 11 MPa and an elongation at break of 1300%. This further confirms that the dynamic cross-linking system constructed by hydrogen bonds and coordination interactions within the PVA-TA-Fe composite film plays a synergistic role, enhancing the film's water resistance and stability in water to a certain extent, maintaining a certain mechanical strength even after prolonged immersion.
[0042] (4) Wet pressing adhesion test The PVA-TA-Fe composite film was cut into strips 10 mm wide and approximately 40 mm long using scissors. These strips were then immersed in hot water at approximately 80 °C for 5 minutes. Two strips were then partially overlapped, forming a square with both sides measuring 10 mm. Pressure was applied to the overlap. The bonded film was dried in a 50 °C oven, and its mechanical properties were tested using a servo-controlled computer-controlled tensile testing machine. A pure PVA film was tested using the same method as a control.
[0043] Experimental results show that pure PVA film almost dissolves after being immersed in 80 ℃ hot water for three minutes, making it unsuitable for wet pressing. Due to the reversibility of hydrogen bonding and coordination interactions, PVA-TA-Fe composite film can be bonded using hot water, generating new hydrogen and covalent bonds at the bonding site and exhibiting a certain degree of mechanical strength. This indicates that the stability of PVA-TA-Fe composite film in hot water is significantly higher than that of pure PVA film.
[0044] The mechanical properties of the PVA-TA-Fe composite film were tested as follows: Figure 7As shown, it can still maintain a tensile strength of 21.6 MPa. The hydrogen bonds and coordination interactions within the PVA-TA-Fe composite film strips are disrupted by water and heat, and then at the contact surface of the two strips, PVA, TA, and Fe... 3+ Hydrogen bonds and coordination interactions will re-form between them. After cooling to room temperature, the wet-pressed strips exhibit certain mechanical properties.
[0045] (5) Thermogravimetric analysis The thermal properties of pure PVA film and PVA-TA-Fe composite film were analyzed and tested using thermogravimetric analysis (TGA). No more than 5 mg of pure PVA film and PVA-TA-Fe composite film were placed in an alumina dry pot, then placed in the testing instrument. The heating rate was set to 10 °C / min, the temperature range was 35 ~ 800 °C, and nitrogen gas was introduced during the test. The obtained TG and DTG curves are shown below. Figure 8 As shown, (a) is the TG curve and (b) is the DTG curve.
[0046] As shown in the figure, the main weight loss stage of the film is between 240 ℃ and 480 ℃. For pure PVA film, its weight loss is mainly divided into four stages. The first stage is from 50 ℃ to 240 ℃, where the weight loss rate is relatively slow, mainly due to the evaporation of water and solvent within the film. The second stage mainly occurs from 240 ℃ to 360 ℃, where PVA begins to decompose, resulting in significant weight loss. The weight loss rate is highest at 290 ℃, and the weight loss is greatest in this stage. The third stage mainly occurs from 360 ℃ to 480 ℃, where the PVA weight loss rate decreases and the film decomposition slows down. The fourth stage mainly occurs after 480 ℃, where PVA decomposition almost stops, the weight becomes nearly constant, and some solid residue remains. The decomposition of PVA-TA-Fe composite film can also be divided into four stages, but in the main weight loss region, the thermal stability of PVA-TA-Fe composite film is significantly higher than that of PVA film. The first stage is from 50℃ to 290℃, during which the weight loss of the membrane is slow. The second stage is from 290℃ to 360℃, which is the main weight loss region, where the composite film decomposes rapidly, and the weight loss rate is the highest, reaching its peak at 340℃. The third stage is from 360℃ to 480℃, during which the weight loss rate of the composite film decreases, and the decomposition of the composite film slows down. The fourth stage is after 480℃, where the decomposition of the PVA-TA-Fe composite film almost stops, and the weight tends to be constant. Comparative analysis of the two figures shows that, in the main weight loss stage, for the same weight loss, the temperature required for the PVA-TA-Fe composite film is higher than that for the pure PVA film. This is mainly because of the addition of TA and Fe to PVA. 3+This increases the number of coordination bonds and hydrogen bonds within the supramolecular material, significantly enhancing the intermolecular binding force. Higher energy is required to break these bonds, resulting in higher temperatures and thus improving the material's thermal stability.
[0047] (6) Antibacterial test Pure PVA membranes, PVA-TA composite membranes, and PVA-TA-Fe composite membranes were completely dissolved in deionized water at 80 °C to prepare a liquid state for later use. Solid culture media required for bacterial growth were prepared. After the solid culture media solidified, holes were punched in the media using a standardized punching tool. PBS buffer and pure PVA were set up as control groups, while PVA-TA and PVA-TA-Fe were set up as experimental groups. Equal volumes of control and experimental group liquids were added to the holes, and the growth of colonies in the solid culture media was observed after 24 hours of incubation. Using *Escherichia coli* as a representative of Gram-negative bacteria and *Staphylococcus aureus* as a representative of Gram-positive bacteria, the antibacterial properties of PVA-TA composite membranes, PVA-TA-Fe composite membranes, and pure PVA membranes were compared under the same conditions. Experimental results are shown below. Figure 9 In the figures, (a) shows the experimental results for *Escherichia coli*, and (b) shows the experimental results for *Staphylococcus aureus*. The inhibition zones of the colonies clearly show that *E. coli* grows into visible colonies in pure PVA and PBS buffer, without any inhibition zones; however, no obvious colonies grow in PVA-TA and PVA-TA-Fe buffer, and inhibition zones of a certain size are observed. Similarly, *Staphylococcus aureus* grows colonies in PVA and PBS buffer without inhibition zones, but exhibits inhibition zones of a certain size in PVA-TA and PVA-TA-Fe buffer. This demonstrates that the composite film of this invention has a certain antibacterial effect, inhibiting bacterial growth and reproduction, and reducing the risk of infection caused by bacterial proliferation during use.
[0048] (7) Recyclability test The PVA-TA-Fe composite film was shredded and placed in a headspace vial. An appropriate amount of DMSO solution was added, and the shredded film was dissolved in an 80 °C oil bath. After complete dissolution, the liquid was poured into a film-forming container and dried in a forced-air dryer at 50 °C until a film was formed, thus regenerating the composite film. This process was repeated three times. The recast film was then subjected to tensile testing using a servo-controlled computer system tensile testing machine. The test results are as follows: Figure 10As shown in the stress-strain curves, after three cycles of regeneration, the PVA-TA-Fe composite film still maintains strength comparable to its original mechanical properties, with a tensile strength between 40 MPa and 45 MPa and an elongation at break greater than 500%. This is because the composite film is a supramolecular plastic dynamically cross-linked internally through hydrogen bonds and coordination interactions. The reversibility of these dynamic hydrogen bonds and coordination interactions allows the film to reconstruct itself after dissolving at high temperatures, restoring its original mechanical strength. This characteristic endows the material with good recyclability and reprocessing capabilities, potentially enabling the recycling of waste materials through simple treatment, reducing resource consumption, and extending the material's service life.
[0049] In summary, the PVA-based composite film material (PVA-TA-Fe composite film) prepared by this invention has excellent mechanical properties, water resistance, thermal stability, and antibacterial properties, as well as outstanding recyclability, making it suitable for a wide range of applications in packaging, medical fields, and other areas.
[0050] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.
Claims
1. A method for preparing a polyvinyl alcohol-based composite film possessing both water resistance and high mechanical strength, characterized in that, It includes the following two steps: S1. Polyvinyl alcohol, polyphenolic compounds, and iron salts are dissolved in an organic solvent, heated to 70-90℃, and stirred for 4-5 hours to obtain a composite solution; wherein the amount of polyphenolic compounds is 0.5-5% of the mass of polyvinyl alcohol, and the amount of iron salts is 0.5-2% of the mass of polyvinyl alcohol; the organic solvent is a polar aprotic solvent. S2. The composite solution is prepared into a thin film by solution casting to obtain a PVA-TA-Fe composite film, which has both water resistance and high mechanical strength.
2. The method for preparing a polyvinyl alcohol-based composite film with both water resistance and high mechanical strength as described in claim 1, characterized in that, The specific method for step S1 is as follows: First, dissolve polyvinyl alcohol and polyphenolic compounds in an organic solvent, heat to 70-90℃, and stir at a constant temperature for 4-4.5 h. Then, add iron salt and continue stirring at a constant temperature for 10-20 min to obtain a composite solution.
3. The method for preparing a polyvinyl alcohol-based composite film with both water resistance and high mechanical strength as described in claim 1, characterized in that, The specific method for step S1 is as follows: the organic solvent is divided into three parts, and polyvinyl alcohol, polyphenolic compounds, and iron salts are dissolved in the three parts of the organic solvent respectively to obtain polyvinyl alcohol solution, polyphenolic compound solution, and iron salt solution; then the polyvinyl alcohol solution and polyphenolic compound solution are mixed, stirred evenly, and heated to 70-90℃, and stirred at a constant temperature for 4-4.5 h; then the iron salt solution is added, and the mixture is stirred at a constant temperature for 10-20 min to obtain a composite solution.
4. The method for preparing a polyvinyl alcohol-based composite film with both water resistance and high mechanical strength as described in claim 3, characterized in that, The polyphenolic compound is tannic acid.
5. The method for preparing a polyvinyl alcohol-based composite film with both water resistance and high mechanical strength as described in claim 4, characterized in that, The iron salt is ferric chloride.
6. The method for preparing a polyvinyl alcohol-based composite film with both water resistance and high mechanical strength as described in claim 5, characterized in that, The organic solvent is dimethyl sulfoxide.
7. The method for preparing a polyvinyl alcohol-based composite film with both water resistance and high mechanical strength as described in claim 6, characterized in that, The amount of tannic acid used is 1.25% of the mass of polyvinyl alcohol, and the amount of ferric chloride used is 1.0% of the mass of polyvinyl alcohol.
8. The method for preparing a polyvinyl alcohol-based composite film with both water resistance and high mechanical strength as described in claim 1, characterized in that, Step S2 specifically involves pouring the composite solution into a film-forming container and drying it at 50-60°C until a film is formed, thus obtaining a PVA-TA-Fe composite film.
9. A polyvinyl alcohol-based composite film possessing both water resistance and high mechanical strength, characterized in that, It is prepared by the method described in any one of claims 1-8.