Heat and oil resistant polyvinyl alcohol-based hydrophilic sponge material and method of making same

Abstract

The application discloses a heat-resistant and oil-resistant polyvinyl alcohol-based hydrophilic sponge material and a preparation method thereof. The polyvinyl alcohol-based sponge comprises the following components by weight: 100 parts of polyvinyl alcohol, 100-150 parts of a foaming agent, 50-90 parts of a formaldehyde solution, 20-50 parts of sulfuric acid, 5-20 parts of a flavonoid compound and 500-850 parts of deionized water. The polyvinyl alcohol-based hydrophilic sponge has a multi-level pore structure, an average pore diameter of 0.1-30 microns, and can be used for high-temperature oil-water medium water reuse. The evaporation performance of the polyvinyl alcohol-based hydrophilic sponge remains stable for at least 60 days in 50-90 DEG C water or oil-water, and the interface evaporation water purification rate is greater than 3 kg m ‑2 h ‑1 under one-fold solar intensity irradiation.

Description

Technical Field

[0001] This invention belongs to the field of hydrophilic porous sponge materials, and relates to a heat-resistant and oil-resistant polyvinyl alcohol-based hydrophilic sponge material and its preparation method. Background Technology

[0002] In modern industrial production processes, particularly in the petroleum, chemical, metal processing, and catering industries, high-temperature oily wastewater is a common type of wastewater. This type of wastewater contains large amounts of grease, suspended solids, organic matter, and potentially heavy metals and harmful chemicals. The discharge of this wastewater not only severely pollutes water bodies and affects water quality but can also lead to the death of aquatic organisms and ecosystem damage. Furthermore, the high temperature of this type of wastewater results in significant energy loss during cooling and subsequent treatment. Traditional treatment methods for high-temperature oily wastewater include physical separation, chemical treatment, and biodegradation. Physical separation methods, such as sedimentation, filtration, and centrifugation, can effectively remove suspended solids and some grease; chemical treatment methods, such as flocculation and oxidation, can further remove dissolved organic matter and some grease; and biodegradation methods utilize microorganisms to decompose organic matter, suitable for treating biodegradable organic matter. However, these methods have certain limitations in treating high-temperature oily wastewater, especially when faced with high temperatures and high grease content, where treatment efficiency and effectiveness are affected, and serious corrosion and scaling problems can occur. Therefore, developing new treatment technologies, especially those that can adapt to high-temperature environments and effectively remove grease and other pollutants, has become an important research direction in the field of water treatment.

[0003] Hydrophilic polymer sponges are a novel type of porous material characterized by high water absorption, high porosity, low cost, and long service life, thus showing great application potential in water purification fields such as interfacial evaporation water treatment. In water treatment processes, the hydrophilic properties of sponges can effectively selectively filter large particles such as suspended particles, organic pollutants, and salts from water, achieving water purification. Polyvinyl alcohol (PVA) is a water-soluble polymer material widely studied and applied due to its excellent chemical stability, biocompatibility, and biodegradability. Especially in environmental protection materials, pharmaceuticals, and water treatment technologies, PVA has a very broad application prospect. However, traditional PVA materials have poor stability in high-temperature and oily environments. After long-term operation in these environments, they are prone to structural collapse and corrosion, which not only shortens the service life of the PVA material itself but also causes unbonded components to pollute water quality, limiting its application in industrial water reuse. Therefore, developing PVA-based materials with heat and oil resistance has become an important research direction.

[0004] Attempts to make polymeric hydrophilic sponge materials durable in high-temperature, oily wastewater have included appropriate pore size distribution design, water-transporting microchannel structures, chemical modification, and / or multilayer design. Current research has found that these attempts still have significant drawbacks. For example, attempts to achieve the oil and high-temperature resistance of polyvinyl alcohol (PVA) sponges through component compounding or chemical modification often severely sacrifice their inherent hydrophilicity; adding surfactants and other composite components introduces large amounts of metal ions or organic impurities, making subsequent treatments such as cleaning more complicated. Summary of the Invention

[0005] In view of this, the present invention provides a heat- and oil-resistant polyvinyl alcohol-based hydrophilic sponge material and its preparation method. Based on polyvinyl alcohol raw material, the invention utilizes the synergistic effect of various aldehydes, foaming agents, and flavonoid compounds to prepare a hydrophilic porous sponge material with heat and oil resistance. This polyvinyl alcohol-based hydrophilic sponge material can be used for the reuse of recycled water from high-temperature oily wastewater through interfacial evaporation. The average pore size is 0.5-30 μm; under irradiation with one times the solar intensity, the interfacial evaporation rate is greater than 3 kg m³. -2 h -1 Under ten times the intensity of sunlight, the interfacial evaporation rate exceeds 30 kg / m³. -2 h -1 Under the influence of a convective wind of 3 m / s, the evaporation rate is greater than 8 kg / m³. -2 h -1 After being treated in high-temperature oily wastewater for more than 30 days, the morphology and structure of the sponge did not change significantly, and the interfacial evaporation rate remained above 95%.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution: a heat-resistant and oil-resistant polyvinyl alcohol-based hydrophilic sponge material, obtained by reacting the following raw material system, comprising the following raw material components by weight: 100 parts polyvinyl alcohol, 100-150 parts foaming agent, 50-90 parts formaldehyde solution, 20-50 parts sulfuric acid, 5-20 parts flavonoid compound, and 500-850 parts deionized water.

[0007] The preferred amount of formaldehyde solution added is 65-80 parts.

[0008] The preferred amount of foaming agent added is 120-130 parts.

[0009] The foaming agent may be one of starch foaming agent, sodium bicarbonate, sodium carbonate and sodium dodecyl sulfate and their complexes. Considering the specific foaming characteristics and the morphology of the foam after molding, any one or more of starch foaming agent and sodium bicarbonate are preferred, and starch foaming agent is even more preferred.

[0010] The preferred amount of added flavonoid compounds is 13-16 parts.

[0011] The flavonoid compound can be any one of quercetin, hesperidin, piperidin, catechin, epicatechin, anthocyanin and proanthocyanidin. Considering cost, chemical binding ability and water solubility, hesperidin, catechin, epicatechin, anthocyanin and proanthocyanidin are preferred, and anthocyanin or catechin are further preferred.

[0012] Flavonoids typically contain abundant hydroxyl groups in their non-core groups, which can be incorporated into the cyclization process during cross-linking and ring-opening, binding with the polyvinyl alcohol (PVA) molecular chain. Furthermore, the strong hydrophilicity of hydroxyl groups can reduce the attenuation of hydrophilicity in PVA sponge materials caused by the addition of reinforcing agents. The core of flavonoids possesses a benzene ring structure, and the interactions between benzene rings can achieve multi-ring bonding, further complicating the molecular chain structure and improving the resistance of the resulting PVA sponge in high-temperature wastewater. Moreover, flavonoids can combine with each other to form oligomers in aldehyde and sulfuric acid environments, exhibiting longer molecular chain structures. This enriches the binding modes between flavonoids and PVA, making the molecular network more complex and improving the heat resistance of the PVA sponge.

[0013] Sulfuric acid provides an acidic environment during synthesis. If the amount of sulfuric acid is too small, the acetal and cross-linking reactions between polyvinyl alcohol, aldehydes, and flavonoids slow down, and due to the weakened acidic environment, the cross-linking cannot proceed completely, resulting in a gelled sponge that lacks heat and oil resistance.

[0014] Preferably, it also includes 0.1-1 parts of an aqueous solution of aliphatic dialdehyde.

[0015] If the total amount of aldehyde compounds is too small, the polyvinyl alcohol material cannot be fully cross-linked, and the sponge softens into a gel-like state. If the amount of aldehyde is continuously added, the sponge becomes too hard and its hydrophilicity decreases, which manifests as a decline in evaporation performance and long-term oil pollution resistance during the interfacial evaporation process of high-temperature oily wastewater.

[0016] The preferred amount of aliphatic dialdehyde aqueous solution added is 0.3-0.7 parts. The aliphatic dialdehyde can be one of glutaraldehyde, 3-methylglutaraldehyde, and 3-methyl-2-butenal. Considering the reactivity, hydrophilicity of the prepared sponge, and evaporation performance, glutaraldehyde and 3-methylglutaraldehyde are preferred, and glutaraldehyde is further preferred.

[0017] Preferably, it also includes 0.1-0.5 parts of an aromatic dialdehyde. The aromatic dialdehyde can be one of o-phthalaldehyde, iso-phthalaldehyde, and terephthalaldehyde. Considering the reactivity, hydrophilicity of the prepared sponge, and evaporation performance, o-phthalaldehyde and terephthalaldehyde are preferred, and o-phthalaldehyde is even more preferred.

[0018] Because formaldehyde has a simple molecular structure, it typically preferentially condenses with adjacent hydroxyl groups in the polyvinyl alcohol (PVA) molecular chain network to form five- or six-membered ring structures. Aliphatic dialdehydes usually have long chains, which can enrich the cross-linking methods on the PVA molecular chain, reducing the interchain spacing and making the structure more complex. Aromatic dialdehydes, with their aldehyde functional groups reliant on aromatic rings, typically cross-link with adjacent hydroxyl groups in the PVA molecule. Through the weak π-π stacking interactions within the aromatic rings, the already condensed ring structures interact, further complicating the PVA molecular network and enhancing its heat resistance. Furthermore, even trace amounts of aliphatic and aromatic dialdehydes can alter the structure and properties of sponges.

[0019] This invention also provides a method for preparing a heat- and oil-resistant polyvinyl alcohol-based hydrophilic sponge material, comprising the following steps:

[0020] Step 1: Dissolve polyvinyl alcohol, foaming agent and flavonoid compound in deionized water to obtain polyvinyl alcohol aqueous solution, foaming agent solution and flavonoid solution respectively;

[0021] Step 2: Mix the polyvinyl alcohol aqueous solution, foaming agent solution and flavonoid solution evenly at 40-70℃, and add formaldehyde solution and sulfuric acid. After stirring evenly, the mixture before reaction is obtained.

[0022] Step 3: Then transfer the pre-reaction mixed solution into a mold and place it in an oven at 50-70℃ to cure for 12-36 hours; after demolding, clean and dry to obtain the polyvinyl alcohol-based hydrophilic sponge material.

[0023] Preferably, the concentration of the formaldehyde solution is 35-40 wt%; and the concentration of the sulfuric acid is 96-99 wt%.

[0024] Preferably, the viscosity of polyvinyl alcohol is 3-10 mPa·s, preferably 4.6-5.4 mPa·s; the degree of alcoholysis is 80-99%, preferably 86.5-89%; and the degree of polymerization (MW) is 500-30000, preferably 500-3000.

[0025] Preferably, the concentration of the aliphatic dialdehyde aqueous solution is 2-50 wt%.

[0026] Preferably, in step 2, an aromatic dialdehyde is added, which is any one of o-phthalaldehyde, iso-phthalaldehyde, and terephthalaldehyde.

[0027] Preferably, the aliphatic dialdehyde is any one of glutaraldehyde, 3-methylglutaraldehyde, and 3-methyl-2-butenal.

[0028] The beneficial effects of this invention are as follows: by adding flavonoid compounds for modification and controlling the proportion of components, the final sponge material has a porous network structure, strong hydrophilicity, structural stability, high interfacial evaporation performance, and can be stable in high-temperature oily wastewater for a long time, meeting the actual service requirements of high-temperature water purification.

[0029] (1) Compared with unmodified and traditional polyvinyl alcohol (PVA)-based sponge materials, this invention utilizes flavonoid compounds to modify hydrophilic resin sponges, which can solve the problem of high temperature and oily wastewater tolerance in PVA-based hydrophilic sponge materials. After the addition of flavonoid compounds, they participate in the acetalization and cross-linking cyclization process of PVA in a sulfuric acid environment, enhancing the cross-linking reaction of the PVA sponge, enriching the ring structure in the PVA molecular chain, and strengthening the intermolecular forces through the aromatic ring structure, thereby improving the heat resistance of the sponge material.

[0030] (2) The synergistic addition of multiple aldehydes can also enhance the resistance of sponge materials to high-temperature oily wastewater. During the ring-opening crosslinking process of multiple aldehydes and sulfuric acid with polyvinyl alcohol, flavonoid compounds enrich the ring-forming mode in the crosslinking process, and their 2-phenylchromone groups modify polyvinyl alcohol-based resin sponges, solving the problems of heat resistance and oil resistance, and can obtain polyvinyl alcohol-based hydrophilic resin sponge materials with obvious cost advantages and simple preparation methods.

[0031] (3) By adding foaming agents and flavonoids, the pore size distribution of the sponge structure can be controlled. The addition of flavonoids increases the viscosity of the solution, so that the sponge retains the small pore structure during stirring, realizing the sponge's bimodal pore microstructure with macropore size of 3-30 μm and micropore size of 0.5-3 μm; and a special structure of bimodal pores and internal through-pores in the framework is prepared, which is beneficial to the water recycling process in the interfacial evaporation base.

[0032] (4) The overall preparation process is simple and convenient. It can be prepared by solution mixing, solidification and cleaning, and has great application value in the fields of wastewater reuse and water purification.

[0033] (5) The raw materials of this invention are readily available, the cost is low, the preparation method is simple, it is suitable for large-scale mass production, and the application range is wide. Attached Figure Description

[0034] Figure 1 The image shows a scanning electron microscope (SEM) image of the heat-resistant and oil-resistant polyvinyl alcohol-based hydrophilic sponge material prepared in Example 1.

[0035] Figure 2 The image shows a scanning electron microscope (SEM) image of the interior of the heat-resistant and oil-resistant polyvinyl alcohol-based hydrophilic sponge material prepared in Example 1.

[0036] Figure 3This is a graph showing the change in evaporation mass over time for heat-resistant and oil-resistant polyvinyl alcohol-based hydrophilic sponge material under different environmental conditions.

[0037] Figure 4 This is a cycle diagram showing the evaporation performance of heat-resistant and oil-resistant polyvinyl alcohol-based hydrophilic sponge material after long-term immersion in high-temperature oily wastewater. Detailed Implementation

[0038] This invention provides a heat- and oil-resistant polyvinyl alcohol-based hydrophilic sponge material and its preparation method, solving the problems of common water purification materials being prone to scaling, corrosion, and poor heat resistance in high-temperature oily wastewater. It successfully prepares a heat- and oil-resistant water purification material based on polyvinyl alcohol. Unless otherwise specified, the raw materials used in the embodiments of this invention are all commonly used raw materials, and the methods described in the embodiments are conventional material preparation methods.

[0039] The testing methods for evaporation rate, pore size distribution, and long-term tolerance are as follows:

[0040] Evaporation rate: The flux of water evaporated per unit evaporation area per unit time under a specific environment is called the evaporation rate of the material under that environment, usually expressed as the mass of evaporation. Fully wetted polyvinyl alcohol (PVA) sponges were cut into regular square samples to determine and measure the evaporation surface area of ​​the material. Under specific evaporation conditions, the sponge material was fixed and floated above the test water body. Then, the overall mass change over a certain period of time was measured using a balance. The specific evaporation conditions were irradiation with one times the solar radiation intensity, irradiation with ten times the solar radiation intensity, and a convective wind of 3 m / s. Each type of sponge was tested 5 times, and the evaporation rate result can be calculated using the following formula:

[0041]

[0042] in t is the evaporation rate of the sponge material under specific conditions; A is the evaporation surface area of ​​the sponge; m0 is the initial mass; m1 is the mass after evaporation for time t.

[0043] Pore ​​size distribution: The pore size distribution of the sponge was obtained by statistically analyzing the SEM images. Five different sponge samples were selected for each type of sponge, and SEM images from three different orientations were selected for each sample. The pore size distribution was analyzed comprehensively, and the average pore size was calculated.

[0044] Long-term durability: The heat and oil resistance of the sponge was tested. The sponge material was cut to specific sizes, and the evaporation rate was measured. Then, the sponge material was immersed in oily wastewater (high-temperature produced water from an oilfield) at 90°C for 30 and 60 days. The evaporation rate of the sponge after immersion was measured. Each type of sponge was tested three times, and the durability was calculated using the following evaporation rate retention rate:

[0045]

[0046] Where η 30 and η 60 These are the evaporation rate and decay rate of the sponge after immersing it in high-temperature oily wastewater for 30 days and 60 days, respectively. This is the initial evaporation rate of the sponge; and The evaporation rates of the sponges after soaking for 30 days and 60 days are respectively. and Calculated using the evaporation rate formula. The higher the evaporation rate retention rate, the better the long-term durability of the sponge.

[0047] Example 1

[0048] A method for preparing a heat-resistant and oil-resistant polyvinyl alcohol-based hydrophilic sponge material is as follows:

[0049] 100g of polyvinyl alcohol PVA0588, 150g of starch foaming agent and 20g of anthocyanin were dissolved in deionized water to obtain the corresponding polyvinyl alcohol aqueous solution, starch solution and anthocyanin solution, respectively.

[0050] Then, the three solutions were mixed evenly at 50°C, and 90g of 37wt% formaldehyde solution, 0.4g of 50wt% glutaraldehyde, 0.1g of o-phthalaldehyde and 50g of 98wt% sulfuric acid solution were added. After stirring evenly, the mixed solution before reaction was obtained; the total mass of deionized water in the mixed solution was 850g.

[0051] The mixed reaction solution was then transferred to a mold and placed in a 60°C oven to cure for 18 hours. After demolding, the mold was cleaned and dried to obtain a heat-resistant and oil-resistant polyvinyl alcohol-based hydrophilic resin sponge.

[0052] Example 2

[0053] A method for preparing a heat-resistant and oil-resistant polyvinyl alcohol-based hydrophilic sponge material is as follows:

[0054] 10g of polyvinyl alcohol PVA0588, 10g of starch foaming agent and 0.5g of catechin were dissolved in a certain mass of deionized water to obtain the corresponding polyvinyl alcohol aqueous solution, starch solution and catechin solution respectively.

[0055] Then, the three solutions were mixed evenly at 55°C, and 5g of 37wt% formaldehyde solution, 0.01g of 50wt% glutaraldehyde, 0.05g of o-phthalaldehyde and 5g of 98wt% sulfuric acid solution were added. After stirring evenly, the mixed solution before reaction was obtained; the total mass of deionized water in the mixed solution was 50g.

[0056] The mixed reaction solution was then transferred to a mold and placed in a 60°C oven to cure for 18 hours. After demolding, the mold was cleaned and dried to obtain a heat-resistant and oil-resistant polyvinyl alcohol-based hydrophilic resin sponge.

[0057] Example 3

[0058] A method for preparing a heat-resistant and oil-resistant polyvinyl alcohol-based hydrophilic sponge material is as follows:

[0059] 100g of polyvinyl alcohol PVA0588, 100g of starch foaming agent, 8g of catechin and 8g of anthocyanin were dissolved in a certain mass of deionized water to obtain the corresponding polyvinyl alcohol aqueous solution, starch solution, catechin and anthocyanin solution respectively.

[0060] Then, the above four solutions were mixed evenly at 55°C, and 50g of 37wt% formaldehyde solution, 0.1g of 50wt% glutaraldehyde, 0.5g of o-phthalaldehyde and 20g of 98wt% sulfuric acid solution were added. After stirring evenly, the mixed solution before reaction was obtained; the total mass of deionized water in the mixed solution was 850g.

[0061] The mixed reaction solution was then transferred to a mold and placed in a 60°C oven to cure for 18 hours. After demolding, the mold was cleaned and dried to obtain a heat-resistant and oil-resistant polyvinyl alcohol-based hydrophilic resin sponge.

[0062] Comparative Example 1

[0063] The preparation method of a hydrophilic composite sponge is as follows, which differs from Example 1 in that: no anthocyanins are added, but all other aspects are the same as in Example 1.

[0064] Comparative Example 2

[0065] The preparation method of a heat-resistant, oil-resistant, and hydrophilic composite sponge is as follows, which differs from Example 1 in that the anthocyanin content is 5g, while the rest are the same as in Example 1.

[0066] Comparative Example 3

[0067] The preparation method of a heat-resistant, oil-resistant, and hydrophilic composite sponge is as follows, which differs from Example 1 in that the mass of anthocyanin is 40g, while the rest are the same as in Example 1.

[0068]

[0069] The pore size distribution of Examples 1-3 ranges from 0.5 to 10 μm, with an average pore size of 1.5 to 3.5 μm, and the evaporation rate under one times the light intensity is greater than 6 kg / m³. -2 h -1 Evaporation rate greater than 75 kg / m² under ten times the intensity of sunlight. -2 h -1Under the action of a 3m / s convective wind, the evaporation rate is greater than 8 kg / m³. -2 h -1 Even after 60 days of high-temperature oily wastewater treatment, the evaporation rates remained above 96%. The SEM image of the pore size distribution in Example 1 is shown below. Figure 1 As shown, SEM images of the pore size and water channels within the sponge skeleton are as follows: Figure 2 As shown, the SEM images of the remaining embodiments are similar. Performance tests demonstrate that the polyvinyl alcohol-based hydrophilic composite sponge of the present invention has high evaporation performance, a pore size distribution conducive to evaporation, and excellent heat and oil resistance.

[0070] Examples 1-3 used the same synthetic components, except for the selection of different types of flavonoid compounds in equal mass. The flavonoid compounds were anthocyanins, catechins, and equal mixtures of both. Comparatively, anthocyanins exhibited a higher evaporation rate under high light concentration conditions and better heat and oil resistance; catechins had a higher evaporation rate under one times the sunlight intensity. Considering the high-temperature environment of actual sponge applications, Example 1 achieved the best results.

[0071] Comparative Example 1 was prepared in the same manner as Examples 1-3, except that no flavonoid compounds were added. Comparative Example 1 could not withstand high temperatures; its sponge structure collapsed and softened at high temperatures, making it unsuitable for high-temperature environments.

[0072] In a longitudinal comparison of Examples 1 and 2-3, the components were identical except for the mass of anthocyanins, representing appropriate, small, and excessive amounts of anthocyanins, respectively. A decrease in anthocyanin mass reduces evaporation performance; although excessive anthocyanin mass can improve heat and oil resistance, the evaporation rate generally decreases, affecting the evaporation effect. Flavonoids, especially non-core components, typically possess abundant hydroxyl groups, allowing them to participate in the ring-forming process during cross-linking and ring-opening, binding with the polyvinyl alcohol molecular chain. Furthermore, the strong hydrophilicity of hydroxyl groups reduces the attenuation of hydrophilicity in the polyvinyl alcohol sponge material caused by the addition of reinforcing agents. The core of flavonoids has a benzene ring, and their interactions can achieve inter-ring bonding, further complicating the molecular chain structure and improving the resistance of the resulting polyvinyl alcohol sponge in high-temperature wastewater. In aldehyde and sulfuric acid environments, flavonoids can combine to form oligomers with longer molecular chain structures, enriching the binding between flavonoids and polyvinyl alcohol, making the molecular network more complex, and improving the heat resistance of the polyvinyl alcohol sponge. Excessive amounts of flavonoids promote self-binding, forming oligomers that increase chain length and complexity, thus resulting in better heat resistance. However, during cross-linking with polyvinyl alcohol, these oligomers form larger rings, inhibiting the cyclization process and increasing pore size. Furthermore, the binding process of oligomers depletes hydrophilic functional groups, leading to a decrease in evaporation rate.

[0073] Example 4: A method for preparing a heat-resistant and oil-resistant polyvinyl alcohol-based hydrophilic sponge material is as follows, which differs from Example 1 in that glutaraldehyde and o-phthalaldehyde are not added, while the rest are the same as in Example 1.

[0074] Example 5: A method for preparing a heat-resistant and oil-resistant polyvinyl alcohol-based hydrophilic sponge material is as follows, which differs from Example 1 in that: no o-phthalaldehyde is added, while all other aspects are the same as in Example 1.

[0075] Comparative Example 4: A method for preparing a heat-resistant and oil-resistant polyvinyl alcohol-based hydrophilic sponge material is as follows, which differs from Example 1 in that the mass of the formaldehyde solution is 30g, while the rest is the same as in Example 1.

[0076] Comparative Example 5: A method for preparing a heat-resistant and oil-resistant polyvinyl alcohol-based hydrophilic sponge material is as follows, which differs from Example 1 in that the mass of the formaldehyde solution is 150g, while the rest is the same as in Example 1.

[0077]

[0078] Comparing Examples 1, 4, and 5, the addition of glutaraldehyde and o-phthalaldehyde can regulate the pore size distribution and increase the evaporation rate of polyvinyl alcohol-based sponges.

[0079] Comparing Example 1 with Comparative Examples 4 and 5, the larger the mass of the formaldehyde solution, the smaller the average pore size. This is because increasing the amount of formaldehyde and other aldehyde crosslinking agents increases the number of crosslinking points on the polyvinyl alcohol chain, resulting in a deeper degree of crosslinking and a smaller pore size. However, crosslinking also results in the loss of hydrophilic groups such as hydroxyl groups, thus increasing the mass of the aldehyde reduces the evaporation rate.

[0080] As shown in Comparative Example 4, the formaldehyde solution was of too low quality, preventing the sponge from fully cross-linking and forming a gel-like intermediate substance, thus lacking the high evaporation performance of the sponge material. This is because there were too few cross-linking points, preventing the formation of polyvinyl alcohol cross-linked molecular chains, resulting in a gel-like state. Furthermore, the incomplete cross-linked segments are unstable in high-temperature water environments and cannot withstand the test of time.

[0081] Because formaldehyde has a simple molecular structure, it typically condenses with adjacent hydroxyl groups in the polyvinyl alcohol (PVA) molecular chain network to form five- or six-membered ring structures. Aliphatic dialdehydes usually have long chains, which can enrich the cross-linking methods on the PVA molecular chain, reducing the inter-chain spacing and making the structure more complex. Aromatic dialdehydes, with their aldehyde functional groups based on aromatic rings, typically cross-link with adjacent hydroxyl groups in the PVA molecule. Through the weak π-π stacking interactions within the aromatic rings, the already condensed ring structures interact, further complicating the PVA molecular network and enhancing its heat resistance. Furthermore, even trace amounts of aliphatic and aromatic dialdehydes can alter the structure and properties of sponges.

[0082] Example 6: A method for preparing a heat-resistant and oil-resistant polyvinyl alcohol-based hydrophilic sponge material is as follows, which differs from Example 1 in that: 100g of starch and 25g of sodium bicarbonate are used to prepare a mixed solution of starch and sodium bicarbonate, and the rest is the same as in Example 1.

[0083] Example 7: A method for preparing a heat-resistant and oil-resistant polyvinyl alcohol-based hydrophilic sponge material is as follows, which differs from Example 1 in that: 125g of starch and 25g of sodium bicarbonate are used to prepare a mixed solution of starch and sodium bicarbonate; the rest is the same as in Example 1.

[0084] Comparative Example 6: A method for preparing a heat-resistant and oil-resistant polyvinyl alcohol-based hydrophilic sponge material is as follows, which differs from Example 1 in that: the starch mass is 200g, and the rest are the same as in Example 1.

[0085] Comparative Example 7: A method for preparing a heat-resistant and oil-resistant polyvinyl alcohol-based hydrophilic sponge material is as follows, which differs from Example 1 in that: 125g of sodium bicarbonate is used to prepare an aqueous solution of sodium bicarbonate, and the rest is the same as in Example 1.

[0086] Comparative Example 8: A method for preparing a heat-resistant and oil-resistant polyvinyl alcohol-based hydrophilic sponge material is as follows, which differs from Example 1 in that: 25g of sodium bicarbonate is used to prepare an aqueous solution of sodium bicarbonate, and the rest is the same as in Example 1.

[0087]

[0088] Comparing Examples 1, 6, and 7 longitudinally, the addition of sodium bicarbonate foaming agent when starch additives are present has little effect on the evaporation rate and heat and oil resistance of polyvinyl alcohol-based sponges, but increases the average pore size. The pore size distribution of sponges using additional sodium bicarbonate foaming agent still exhibits the small pore portion of sponges made only with starch foaming agent, with the addition of large pores of 5–13 μm. Comparative Examples 7 and 8, using different masses of sodium bicarbonate foaming agent alone, although exhibiting heat and oil resistance similar to Example 1, show a significantly decreased evaporation rate and a significantly larger average pore size than sponges made only with starch foaming agent. Comparing Examples 1 and 6, excessive starch additives affect the evaporation rate of polyvinyl alcohol hydrophilic sponges under high temperature and light-concentrating conditions.

[0089] Sodium bicarbonate foaming agent can synergistically regulate the pore size of polyvinyl alcohol (PVA) sponges with starch foaming agents, but using it alone will weaken the evaporation rate of the PVA sponge. This is because starch and sodium bicarbonate have different foaming mechanisms: starch foaming agents expand and gelatinize by temperature, while sodium bicarbonate releases hydrogen gas during heating. Therefore, the resulting sponges have different pore sizes. Starch, being a hydrophilic foaming agent, maintains the sponge's hydrophilicity more effectively than sodium bicarbonate during curing and cross-linking, thus ensuring a high evaporation rate for the PVA sponge. However, excessive starch additives will soften the resulting sponge because excess starch interacts with PVA molecular chains and flavonoids during cross-linking, affecting the mechanical properties and high-temperature stability of the sponge material.

[0090] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any other improvements and modifications made without departing from the principle of the present invention are included within the protection scope of the present invention.

Claims

1. A heat and oil resistant polyvinyl alcohol-based hydrophilic sponge material, characterized by, The polyvinyl alcohol-based hydrophilic sponge material is prepared by the following steps: dissolving polyvinyl alcohol, a foaming agent and a flavonoid compound in deionized water to obtain a polyvinyl alcohol aqueous solution, a foaming agent solution and a flavonoid solution respectively; mixing the polyvinyl alcohol aqueous solution, the foaming agent solution and the flavonoid solution at 40-70°C, and adding a formaldehyde solution and sulfuric acid to obtain a pre-reaction mixed solution; then transferring the pre-reaction mixed solution into a mold and placing it in an oven at 50-70°C for curing for 12-36 hours; and cleaning and drying after demolding to obtain the polyvinyl alcohol-based hydrophilic sponge material.

2. The heat and oil resistant polyvinyl alcohol-based hydrophilic sponge material according to claim 1, characterized by, The foaming agent is one or more of starch foaming agent, sodium bicarbonate, sodium carbonate and sodium dodecyl sulfate.

3. The heat and oil resistant polyvinyl alcohol-based hydrophilic sponge material according to claim 1, characterized in that, The polyvinyl alcohol-based hydrophilic sponge material is prepared by the following steps: dissolving polyvinyl alcohol, a foaming agent and a flavonoid compound in deionized water to obtain a polyvinyl alcohol aqueous solution, a foaming agent solution and a flavonoid solution respectively; mixing the polyvinyl alcohol aqueous solution, the foaming agent solution and the flavonoid solution at 40-70°C, and adding a formaldehyde solution and sulfuric acid to obtain a pre-reaction mixed solution; then transferring the pre-reaction mixed solution into a mold and placing it in an oven at 50-70°C for curing for 12-36 hours; and cleaning and drying after demolding to obtain the polyvinyl alcohol-based hydrophilic sponge material.

4. The heat and oil resistant polyvinyl alcohol-based hydrophilic sponge material according to claim 1, characterized in that, The formaldehyde solution has a concentration of 35-40 wt%.

5. The method for preparing the heat-resistant and oil-stain-resistant polyvinyl alcohol-based hydrophilic sponge material according to any one of claims 1 to 4, characterized in that, In step 2, an aqueous aliphatic dialdehyde solution is added, and the concentration of the aqueous aliphatic dialdehyde solution is 2-50 wt%. In step 2, an aromatic dialdehyde is added, and the aromatic dialdehyde is any one of o-phthaldehyde, m-phthaldehyde and p-phthaldehyde. The aliphatic dialdehyde is any one of glutaraldehyde, 3-methyl glutaraldehyde and 3-methyl-2-butenal. ​ 6. The process for preparing heat and oil resistant polyvinyl alcohol-based hydrophilic sponge material as claimed in claim 5, wherein, ​ 7. The process for preparing heat and oil resistant polyvinyl alcohol based hydrophilic sponge material as claimed in claim 5, wherein, ​ 8. The process for preparing heat and oil resistant polyvinyl alcohol based hydrophilic sponge material as claimed in claim 5, wherein, ​ 9. The process for preparing heat and oil resistant polyvinyl alcohol based hydrophilic sponge material as claimed in claim 7, wherein, ​

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