A polyvinyl alcohol-based foam material and its preparation method

Abstract

This invention provides a polyvinyl alcohol-based foam material and its preparation method, belonging to the field of porous polymer materials. The method includes the following steps: S1, mixing cellulose and an acid solution and reacting them, then terminating the reaction by passing cold water below the reaction temperature to obtain a solution containing cellulose nanocrystals; S2, mixing the solution containing cellulose nanocrystals, polyvinyl alcohol, and aldehyde to obtain a mixed solution, placing the mixed solution in a mold, and reacting and curing it at a temperature of 20-60°C to obtain the polyvinyl alcohol-based foam material. This preparation process does not require additional mechanical stirring to introduce gas for foaming, and does not involve the addition of any pore-forming agents, foaming agents, or surfactants. The reaction conditions are mild, and the method is simple. The resulting foam material has good performance; it is easy to clean, has no surfactant residue, and its pore size and porosity are adjustable.

Description

Technical Field

[0001] This invention belongs to the field of porous polymer materials and relates to a polyvinyl alcohol-based foam material and its preparation method. Background Technology

[0002] Polyvinyl alcohol (PVA) foam is generally a porous polymer material with a large-pore open-cell structure. It has excellent mechanical properties in the dry state and good wear resistance and biocompatibility in the wet state. It is mainly used in cleaning and beauty, filtration and sound absorption, functional medical, biological carrier and biodegradable fields.

[0003] Currently, the foaming methods for polyvinyl alcohol (PVA) based foam materials can be mainly divided into four types: pore-forming agent foaming, mechanical foaming, chemical foaming, and physical foaming. Pore-forming agent foaming generally uses starch as a pore-forming agent, which is removed after the PVA has cured and cross-linked. Mechanical foaming involves injecting air into the PVA solution to form liquid foam, adding a certain surfactant to stabilize the cell structure, and then curing and cross-linking to form the foam material. Chemical foaming typically uses inorganic foaming agents (sodium carbonate, sodium bicarbonate, potassium carbonate, calcium carbonate, etc.) or organic foaming agents (azodicarbonamide, benzenesulfonyl hydrazine, etc.) added to the PVA solution. Through chemical reaction or thermal decomposition, gases such as CO2, N2, or NH3 are released, thereby forming a porous structure in the PVA system. The physical foaming method involves adding low-boiling-point soluble liquids or easily sublimable solid foaming agents to a PVA solution. Through the adjustment and transformation of the external environment, gas is generated and encapsulated by the PVA system during the evaporation process, forming a certain porous structure.

[0004] Each of the aforementioned foaming methods has its advantages and disadvantages. Pore-forming agent foaming is simple and easy to implement, but the pore-forming agents used, such as starch, are difficult to remove completely, resulting in high water consumption, high production costs, water pollution, and susceptibility to mold growth. Mechanical foaming requires a certain amount of surfactant to stabilize the wet foam, which is difficult to remove completely during cleaning, making it unsuitable for applications with high requirements, such as medical and hygiene fields. Furthermore, the long washing cycle leads to high production costs. Existing physical foaming methods use foaming agents such as alkanes and fluorocarbons, which are flammable or toxic, requiring sophisticated equipment, and fluorocarbons have a certain degree of environmental toxicity. Chemical foaming methods, on the other hand, struggle to precisely control the reaction temperature and time of the foaming agent, making it difficult to meet the required appearance and performance of the foam material. Summary of the Invention

[0005] In view of this, the present invention provides a polyvinyl alcohol-based foam material and its preparation method. The polyvinyl alcohol-based foam material provided by the present invention is easy to clean, has no surfactant residue, and has adjustable pore size and / or porosity. It also has excellent thermal stability, is simple to prepare, and has low cost.

[0006] This invention provides a method for preparing polyvinyl alcohol-based foam material, comprising the following steps:

[0007] S1. After mixing cellulose and acid solution, the reaction is terminated by passing cold water below the reaction temperature to obtain a solution containing cellulose nanocrystals.

[0008] S2. The solution containing cellulose nanocrystals, polyvinyl alcohol, and aldehyde are mixed to obtain a mixed solution. The mixed solution is placed in a mold and reacted and cured at a temperature of 20-60°C to obtain a polyvinyl alcohol-based foam material.

[0009] In an embodiment of the present invention, the acid in the acid solution of step S1 is sulfuric acid or hydrochloric acid; the cellulose is cellulose powder or slurry.

[0010] In an embodiment of the present invention, step S1 includes: dispersing cellulose in a sulfuric acid solution, reacting at 40-50°C for 40-50 minutes, and then adding an equal volume of cold water at a temperature lower than the reaction temperature to terminate the reaction, thereby obtaining a solution containing cellulose nanocrystals.

[0011] In an embodiment of the present invention, in step S1, the volume ratio of the sulfuric acid solution to the mass of cellulose is (5-13) mL: 1 g.

[0012] In an embodiment of the present invention, the polyvinyl alcohol in step S2 is PVA1799 and / or PVA2499; the aldehyde is one or more of formaldehyde, glutaraldehyde and paraformaldehyde.

[0013] In an embodiment of the present invention, step S2 includes: adding the solution containing cellulose nanocrystals to a polyvinyl alcohol aqueous solution, wherein the concentration of the polyvinyl alcohol aqueous solution is 6-18 wt%; then adding an aldehyde solution of 8-16 wt% relative to the amount of polyvinyl alcohol solution, stirring and ultrasonically defoaming to obtain a mixed solution.

[0014] In an embodiment of the present invention, in step S2, the stirring time is 10-30 min and the ultrasonic defoaming time is 2-10 min.

[0015] In an embodiment of the present invention, step S2 includes: placing the mixed solution in an acid-resistant mold, reacting and curing it at a temperature of 40-60°C for 3-24 hours, and then washing and drying it to obtain a polyvinyl alcohol-based foam material.

[0016] The present invention provides a polyvinyl alcohol-based foam material with a porosity of 34-90% obtained by the preparation method described above.

[0017] In an embodiment of the present invention, the pore size of the polyvinyl alcohol-based foam material is 3 to 55 μm.

[0018] In this invention, PVA and cellulose are used as the main raw materials. First, cellulose is oxidized to cellulose nanocrystals (CNC) in an acidic solution, which can act as a pore stabilizer and foam reinforcing agent. Then, the remaining acid continues to act as a catalyst, causing PVA to undergo a curing and crosslinking reaction with aldehydes at a certain temperature. By controlling the multiphase separation during the curing process, a foam material with an alcohol-aldehyde crosslinking chemical network structure is obtained. This preparation process does not require additional mechanical stirring to introduce gas for foaming, and does not involve the addition of any pore-forming agents, foaming agents, or surfactants. The reaction conditions are mild (temperature can be 40-60℃). The resulting foam material relies on the hydrogen bonding interaction between cellulose nanocrystals and polyvinyl alcohol to stabilize the three-dimensional network structure, preventing the collapse of the pore network structure while expelling liquid water to form pores. It is easy to clean, leaves no surfactant residue, and has adjustable pore size and porosity. Compared to traditional PVA foam, the polyvinyl alcohol-based foam material described above exhibits superior thermal stability. Attached Figure Description

[0019] Figure 1 This is a product photograph of Embodiment 1 of the present invention;

[0020] Figure 2 This is a product photograph of Comparative Example 1 of the present invention. Detailed Implementation

[0021] To provide a clearer understanding of the technical features, objectives, and effects of the present invention, the technical solution of the present invention will now be described in detail with reference to specific embodiments. The described embodiments are only some embodiments of the present invention, and not all embodiments.

[0022] This invention provides a method for preparing polyvinyl alcohol-based foam material, comprising the following steps:

[0023] S1. After mixing cellulose and acid solution, the reaction is terminated by passing cold water below the reaction temperature to obtain a solution containing cellulose nanocrystals.

[0024] S2. The solution containing cellulose nanocrystals, polyvinyl alcohol, and aldehyde are mixed to obtain a mixed solution. The mixed solution is placed in a mold and reacted and cured at a temperature of 20-60°C to obtain a polyvinyl alcohol-based foam material.

[0025] The polyvinyl alcohol-based foam material provided by this invention is easy to clean, has no surfactant residue, and has adjustable pore size and / or porosity. It also has excellent thermal stability, is simple to prepare, and has low cost.

[0026] In this embodiment of the invention, one or more polyvinyl alcohols can be prepared into a polyvinyl alcohol aqueous solution with a concentration of 6wt%-18wt%, further wherein the concentration is 8-12wt%, preferably 9-11wt%; cooled to room temperature for later use. The degree of polymerization of the polyvinyl alcohol (PVA) is preferably 1700-2400, and the degree of alcoholysis is 88%-99%, more preferably commercially available polyvinyl alcohol PVA1799, PVA2499, or a mixture thereof.

[0027] In some embodiments, PVA1799 or PVA2499 can be used; in other embodiments, PVA1799 and PVA2499 are used. The pore structure can be controlled by changing the ratio of PVA1799 to PVA2499, for example, a mass ratio of 1:1. Generally, because PVA2499 has a longer molecular chain than PVA1799, under the same conditions, a higher proportion of PVA2499 in the solution leads to more severe entanglement between polymer chains, resulting in more severe shrinkage of the formed foam material, smaller pore size, and lower porosity.

[0028] Furthermore, in this embodiment of the invention, a certain mass of cellulose is added to an acid solution, dispersed evenly, and preferably reacted at 40–50°C for 40–50 minutes to form cellulose nanocrystals (CNC). Then, an equal volume of cold water below the reaction temperature is added to terminate the reaction, yielding a solution containing cellulose nanocrystals. The cellulose is cellulose powder or slurry; generally, the cellulose powder has a particle size ≤25-300 μm, and the slurry has a solid content of 10%–50%. The acid used in the acid solution can be sulfuric acid or hydrochloric acid, preferably sulfuric acid.

[0029] Specifically, the concentration of the sulfuric acid solution can be 60-70 wt% (specifically 65 wt%), and its volume to cellulose mass ratio is preferably (5-13) mL:1 g, more preferably (6-12) mL:1 g, and further preferably (8-12) mL:1 g. In this embodiment of the invention, the foam pore structure can be controlled by adjusting the ratio of sulfuric acid to cellulose. When the amount of cellulose added decreases, the pore size of the foam material increases, and the porosity improves. This invention can also control the pore structure by changing the amount of cold water added; preferably, an equal volume of cold water is added (temperature range 0-10℃, preferably 0℃, with the same volume as the acid solution). When no cold water is added, the formed foam pore structure easily collapses and becomes a gel after drying.

[0030] Then, in this embodiment of the invention, the solution containing cellulose nanocrystals is added to a polyvinyl alcohol aqueous solution, followed by the addition of an aldehyde solution. The mixture is stirred for 10–30 minutes, and then ultrasonically defoamed for 2–10 minutes (all at room temperature) to obtain a more uniform and stable mixed solution. The aldehyde solution, as a crosslinking agent, can be one or more of formaldehyde, glutaraldehyde, and paraformaldehyde, and more specifically, a formaldehyde solution; its addition amount can be 8–16 wt% of the polyvinyl alcohol solution (e.g., using a 37 wt% formaldehyde aqueous solution).

[0031] Finally, in this embodiment of the invention, the above-mentioned mixed solution is poured into an acid-resistant mold and cured in a constant temperature oven at 20–60°C for 3–48 hours; the preferred temperature is 40–60°C, and the preferred time is 3–24 hours. CNC interacts with the hydrogen bonds of polyvinyl alcohol, stabilizing the wet foam and improving the thermal stability of the foam material. The remaining acid solution can act as a catalyst for the next acetal reaction of polyvinyl alcohol, causing PVA and aldehyde to undergo a curing and cross-linking reaction at a certain temperature. By controlling the multiphase separation during the curing process, liquid water is discharged to form pores, resulting in a chemical network structure of alcohol-aldehyde cross-linking. In this embodiment of the invention, the product can be obtained by washing with water (usually using deionized water) and drying.

[0032] Existing methods for preparing polyvinyl alcohol-based foam materials generally require the addition of foaming agents, pore-forming agents, and other pore-forming functional reagents, resulting in complex preparation steps, high costs, and significant energy consumption. The method of this invention does not use any pore-forming agents, foaming agents, or surfactants. The preparation process is simple, the reaction conditions are mild, and mechanical stirring is unnecessary for foaming. The resulting foam material has a high open-cell ratio, is easy to clean, exhibits high product purity, and demonstrates excellent thermal stability.

[0033] This invention provides a polyvinyl alcohol-based foam material prepared by the method described above, which has uniform pores and no macropore defects; its porosity can be 34-90% and its pore size can be 3-55μm, which is beneficial for application.

[0034] To better illustrate the present invention, further examples are provided below. In the examples, all original reagents and materials are commercially available, and experimental methods without specific experimental conditions are conventional methods and conditions well known in the art.

[0035] Example 1: PVA 1799 (v sulfuric acid solution:m cellulose = 6:1)

[0036] 7.2g of PVA1799 was added to 64.8g of water, stirred, and heated to 95℃. The mixture was kept at this temperature for 5 hours to prepare a 10wt% polyvinyl alcohol aqueous solution. The solution was then cooled to room temperature and set aside. 6.0g of cellulose (powder particle size 250μm, the same in the following examples) was added to 36.0mL of 65wt% sulfuric acid solution and dispersed evenly. The reaction was carried out at 45℃ for 45 minutes, and then 36.0mL of cold water was added to terminate the reaction, resulting in a solution containing cellulose nanocrystals. This cellulose nanocrystal-containing solution was then added to the aforementioned polyvinyl alcohol aqueous solution and stirred for 10 minutes. Next, 6.65mL of 37wt% formaldehyde solution was added, and the mixture was stirred for 30 minutes. The mixture was then ultrasonically defoamed for 10 minutes to obtain a mixed solution. Finally, the mixed solution was poured into an acid-resistant mold and cured in a constant temperature oven at 50℃ for 5 hours. After washing with deionized water and drying, the target polyvinyl alcohol-based foam material was obtained. Its cells are uniform and free of macropore defects. Figure 1 As shown.

[0037] The performance of the obtained foam material was tested as follows (the same applies to the following examples).

[0038] Pore ​​size and porosity: determined using a Micromeritics Autopore IV 9500 fully automated mercury porosimeter.

[0039] Water absorption rate: At 20℃, accurately weigh a certain amount of the above foam material and record it as m. 干态 Soak the sample in deionized water until saturated, then remove it and place it on a filter screen for 30 seconds to remove surface water. Weigh the sample and record the weight as m. 饱和 Calculation formula: Water absorption rate = (m 饱和 -m 干态 ) / m 干态 The process was repeated three times, and the average value was taken as the aspiration rate.

[0040] Thermal stability: Tested using TGA (TA, Q500), and the thermal stability was recorded. d5％ Temperature range: room temperature - 800℃; heating rate: 10℃·min -1 N2 atmosphere, flow rate 50 mL / min -1 .

[0041] The above sample was tested and found to have a pore size of 18 μm, a porosity of 78%, a water absorption rate of 14.7 g / g, and a T... d5％ The temperature is 349℃.

[0042] Example 2: PVA 1799 (v sulfuric acid solution:m cellulose = 8:1)

[0043] 7.2g of PVA1799 was added to 64.8g of water, stirred, and heated to 95℃, held at this temperature for 5 hours to prepare a 10wt% polyvinyl alcohol aqueous solution. The solution was then cooled to room temperature and set aside. 4.5g of cellulose was added to 36.0mL of 65wt% sulfuric acid solution and dispersed evenly. The reaction was carried out at 45℃ for 45 minutes, and then 36.0mL of cold water was added to terminate the reaction, yielding a solution containing cellulose nanocrystals. This solution containing cellulose nanocrystals was added to the aforementioned polyvinyl alcohol aqueous solution and stirred for 10 minutes. Then, 6.65mL of 37wt% formaldehyde solution was added, and the mixture was stirred for 30 minutes. The mixture was then ultrasonically defoamed for 10 minutes to obtain a mixed solution. Finally, the mixed solution was poured into an acid-resistant mold and cured in a constant temperature oven at 50℃ for 5 hours. After washing with deionized water and drying, the target product was obtained, exhibiting uniform pores and no macropore defects.

[0044] The performance of the sample provided in Example 2 of this invention was tested using the test method provided in Example 1. The test results were as follows: pore size 53 μm, porosity 87%, water absorption rate 11.2 g / g, T d5％ The temperature is 349℃.

[0045] Example 3: PVA 1799 (v sulfuric acid solution:m cellulose = 12:1)

[0046] 7.2g of PVA1799 was added to 64.8g of water, stirred, and heated to 95℃, held at that temperature for 5 hours to prepare a 10wt% polyvinyl alcohol aqueous solution. The solution was then cooled to room temperature and set aside. 3.0g of cellulose was added to 36.0mL of 65wt% sulfuric acid solution and dispersed evenly. The reaction was carried out at 45℃ for 45 minutes, and then 36.0mL of cold water was added to terminate the reaction, yielding a solution containing cellulose nanocrystals. This solution containing cellulose nanocrystals was added to the aforementioned polyvinyl alcohol aqueous solution and stirred for 10 minutes. Then, 6.65mL of 37wt% formaldehyde solution was added, and the mixture was stirred for 30 minutes. The mixture was then ultrasonically defoamed for 10 minutes to obtain a mixed solution. Finally, the mixed solution was poured into an acid-resistant mold and cured in a constant temperature oven at 50℃ for 5 hours. After washing with deionized water and drying, the target product was obtained, exhibiting uniform pores and no macropore defects.

[0047] The performance of the sample provided in Example 3 of this invention was tested using the test method provided in Example 1. The test results were as follows: pore size 55 μm, porosity 85%, water absorption rate 10.3 g / g, T d5％ The temperature is 349℃.

[0048] Example 4: PVA 2499 (ν sulfuric acid solution: m cellulose = 10:1)

[0049] 7.2g of PVA2499 was added to 64.8g of water, stirred, and heated to 95℃, held at this temperature for 5 hours to prepare a 10wt% polyvinyl alcohol aqueous solution. The solution was then cooled to room temperature and set aside. 3.6g of cellulose was added to 36.0mL of 65wt% sulfuric acid solution and dispersed evenly. The reaction was carried out at 45℃ for 45 minutes, and then 36.0mL of cold water was added to terminate the reaction, yielding a solution containing cellulose nanocrystals. This solution containing cellulose nanocrystals was added to the aforementioned polyvinyl alcohol aqueous solution and stirred for 10 minutes. Then, 6.65mL of 37wt% formaldehyde solution was added, and the mixture was stirred for 30 minutes. The mixture was then ultrasonically defoamed for 2 minutes to obtain a mixed solution. Finally, the mixed solution was poured into an acid-resistant mold and cured in a constant temperature oven at 50℃ for 5 hours. After washing with deionized water and drying, the target product was obtained, exhibiting uniform cell structure without large pore defects.

[0050] The performance of the sample provided in Example 4 of this invention was tested using the test method provided in Example 1. The test results were as follows: pore size 3 μm, porosity 34%, water absorption rate 11.8 g / g, T d5％ The temperature is 334℃.

[0051] Example 5: PVA 1799 / PVA2499 (ν sulfuric acid solution: m cellulose = 10:1)

[0052] 3.6g of PVA1799 and 3.6g of PVA2499 were added to 64.8g of water, stirred, and heated to 95℃, maintaining this temperature for 5 hours to prepare a 10wt% polyvinyl alcohol aqueous solution. The solution was then cooled to room temperature and set aside. Next, 3.6g of cellulose was added to 36.0mL of 65wt% sulfuric acid solution and dispersed evenly. The reaction was carried out at 45℃ for 45 minutes, and then 36.0mL of cold water was added to terminate the reaction, yielding a solution containing cellulose nanocrystals. This solution containing cellulose nanocrystals was added to the aforementioned polyvinyl alcohol aqueous solution and stirred for 10 minutes. Then, 6.65mL of 37wt% formaldehyde solution was added, and the mixture was stirred for 30 minutes. The mixture was then ultrasonically defoamed for 2 minutes to obtain a mixed solution. Finally, the mixed solution was poured into an acid-resistant mold and cured in a constant temperature oven at 50℃ for 5 hours. After washing with deionized water and drying, the target product was obtained, exhibiting uniform pores and no macropore defects.

[0053] The performance of the sample provided in Example 5 of this invention was tested using the test method provided in Example 1. The test results were as follows: pore size 14 μm, porosity 78%, water absorption rate 8.7 g / g, T d5％ The temperature was 341℃. Comparative Example 1: PVA1799 (without added cellulose)

[0054] 7.2g of PVA1799 was added to 64.8g of water, stirred, and heated to 95℃. The mixture was kept at this temperature for 5 hours to prepare a 10wt% polyvinyl alcohol aqueous solution. The solution was then cooled to room temperature and set aside. 36.0mL of 65wt% sulfuric acid solution and 36.0mL of cold water were mixed thoroughly. This mixture was then added to the polyvinyl alcohol aqueous solution and stirred for 10 minutes. Next, 6.65mL of 37wt% formaldehyde solution was added, and the mixture was stirred for 30 minutes. The mixture was then ultrasonically defoamed for 10 minutes. Finally, the liquid was poured into an acid-resistant mold and cured in a constant temperature oven at 50℃ for 5 hours. After washing with deionized water and drying, the target product was obtained. The product exhibited uneven cell structure, partial collapse, and significant macropore defects, such as… Figure 2 As shown.

[0055] The performance of the provided sample was tested using the test method provided in Example 1. Test results: pore size and porosity were not measured due to pore structure inhomogeneity; water absorption rate was 8.1 g / g; T d5％ At 322℃, its thermal stability is not as good as the sample with added cellulose.

[0056] Comparative Example 2: PVA1799 (without added cellulose and cold water)

[0057] 7.2g of PVA1799 was added to 64.8g of water, stirred, and heated to 95℃, held at that temperature for 5 hours to prepare a 10wt% polyvinyl alcohol aqueous solution. The solution was then cooled to room temperature and set aside. Next, 36.0mL of 65wt% sulfuric acid solution was added to the polyvinyl alcohol aqueous solution, and the mixture was stirred for 10 minutes. Then, 6.65mL of 37wt% formaldehyde solution was added, and the mixture was stirred for 30 minutes, followed by ultrasonic defoaming for 5 minutes. Finally, the liquid was poured into an acid-resistant mold and cured in a constant temperature oven at 50℃ for 5 hours. After washing with deionized water and drying, the target product was obtained. The product exhibited almost no pores, with most of the pores collapsed, indicating the absence of a porous structure and forming a non-porous dry gel (the sample performance was not tested using the test method provided in Example 1).

[0058] As can be seen from the above embodiments, the preparation reaction conditions of the foam material in the embodiments of the present invention are mild (40-60℃), the method is simple and easy to implement, energy consumption is low, and it is environmentally friendly. The obtained foam material has uniform pores, is easy to clean, and has a water absorption rate of over 8.7g / g. Moreover, its pore size and porosity are adjustable, and it has better thermal stability than traditional PVA foam (the foam material of the present invention has T...). d5％ It can reach 341-349℃ and has broad application prospects.

[0059] The above examples are only used to illustrate the technical features and implementation process of the present invention, and are not intended to limit the technical solutions of the present invention. It should be noted that those skilled in the art can still make modifications or equivalent substitutions to the present invention without departing from the principle of the present invention, and all such modifications or substitutions are covered by the protection of the present invention.

Claims

1. A method for preparing a polyvinyl alcohol-based foam material, characterized in that, Includes the following steps: S1. A mixture of cellulose and an acid solution is reacted, wherein the cellulose is cellulose powder and the acid in the acid solution is sulfuric acid or hydrochloric acid; the reaction is then terminated by passing cold water below the reaction temperature to obtain a solution containing cellulose nanocrystals and containing the remaining acid. S2. The solution containing cellulose nanocrystals is added to a polyvinyl alcohol aqueous solution with a concentration of 6-18 wt%; then, an aldehyde solution of 8-16 wt% relative to the volume of the polyvinyl alcohol solution is added, stirred and ultrasonically defoamed to obtain a mixed solution. The mixed solution was placed in an acid-resistant mold and reacted and cured at a temperature of 40~60℃ for 3~24h. After washing and drying, polyvinyl alcohol-based foam material was obtained. The aldehyde in the aldehyde solution is one or more of formaldehyde, glutaraldehyde, and paraformaldehyde.

2. The preparation method according to claim 1, characterized in that, Step S1 includes: dispersing cellulose in sulfuric acid solution, reacting at 40-50°C for 40-50 minutes, and then adding an equal volume of cold water below the reaction temperature to terminate the reaction, thereby obtaining a solution containing cellulose nanocrystals.

3. The preparation method according to claim 2, characterized in that, In step S1, the volume ratio of the sulfuric acid solution to the mass of cellulose is (5~13) mL: 1 g.

4. The preparation method according to any one of claims 1-3, characterized in that, The polyvinyl alcohol in step S2 is PVA1799 and / or PVA2499.

5. The preparation method according to claim 4, characterized in that, In step S2, the stirring time is 10-30 minutes, and the ultrasonic defoaming time is 2-10 minutes.

6. The polyvinyl alcohol-based foam material obtained by the preparation method according to any one of claims 1-5 has a porosity of 34-90%.

7. The polyvinyl alcohol-based foam material according to claim 6, characterized in that, The pore size of the polyvinyl alcohol-based foam material is 3~55μm.

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