Heat-resistant and oil-resistant polyvinyl alcohol-based hydrophilic sponge material and preparation method thereof

Abstract

The invention discloses a heat-resistant oil-stain-resistant polyvinyl alcohol-based hydrophilic sponge material and a preparation method thereof.The polyvinyl alcohol-based hydrophilic sponge material is prepared from, 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 through reaction of the following raw material system, and polyvinyl alcohol-based sponge is prepared from, 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 obtained polyvinyl alcohol-based hydrophilic sponge is of a hierarchical pore structure, the average pore size is 0.1-30 microns, the polyvinyl alcohol-based hydrophilic sponge can be used for reclaimed water reuse of high-temperature oil and water, and the evaporation performance of the polyvinyl alcohol-based hydrophilic sponge can be stably kept for at least 60 days in water or oil and water at the temperature of 50-90 DEG C; the interface evaporation water purification rate is greater than 3kg m <-2 > h <-1 > under the irradiation of one time of sunlight intensity.

Description

Technical Field

[0001] The 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 a preparation method thereof. Background Art

[0002] In modern industrial production processes, especially in the fields of petroleum, chemical industry, metal processing and catering, high-temperature oily wastewater is a common type of wastewater. This type of wastewater contains a large amount of grease, suspended solids, organic matter, and possible heavy metals and harmful chemicals. The discharge of these wastewaters not only causes serious pollution to the water body and affects the water quality, but may also cause the death of aquatic organisms and damage the ecosystem. In addition, this type of wastewater has a high temperature, and cooling it down before processing will cause serious energy loss. When treating high-temperature oily wastewater, traditional treatment methods include physical separation, chemical treatment and biodegradation. Physical separation methods such as sedimentation, filtration and centrifugal separation can effectively remove suspended solids and some grease; chemical treatment methods such as flocculation and oxidation can further remove soluble organic matter and some grease; biodegradation methods use microorganisms to decompose organic matter and are suitable for treating biodegradable organic matter. However, these methods have certain limitations when treating high-temperature oily wastewater, especially when facing high temperature and high grease content, the treatment efficiency and effect will be affected, and serious corrosion and scaling problems will occur. Therefore, the development of new treatment technologies, especially those that can adapt to high temperature environments and effectively remove oil and other pollutants, has become an important research direction in the field of water treatment.

[0003] Polymer hydrophilic sponge material is a new type of porous material with the characteristics of high water absorption, high porosity, low cost and long service life. Therefore, it shows great application potential in water purification fields such as interfacial evaporation water treatment. In the water treatment process, the hydrophilic properties of the sponge can effectively filter suspended particles, organic pollutants, large particles such as salts in the water and water selectively to achieve the water purification process. Polyvinyl alcohol is a water-soluble polymer material that has been widely studied and applied due to its excellent chemical stability, biocompatibility and degradability. Especially in environmental protection materials, the field of medicine and water treatment technology, the application prospects of polyvinyl alcohol are very broad. However, traditional polyvinyl alcohol materials have poor stability in high temperature and oily environments. After long-term work in the above environment, they are prone to structural collapse and corrosion. Not only does it damage the service life of the polyvinyl alcohol material itself, but the components that are not fully combined will pollute the water quality, limiting its application in the field of industrial water reuse. Therefore, the development of polyvinyl alcohol-based materials with heat and oil resistance has become an important research direction.

[0004] Attempts to make polymer hydrophilic sponge materials durable in high-temperature oily wastewater include appropriate pore size distribution design, water delivery microchannel structure, chemical modification and / or multi-layer design. Current research has found that the above attempts still have obvious defects. For example, attempts to meet the oil and high temperature resistance of polyvinyl alcohol sponge through component compounding or chemical modification usually seriously sacrifice its own hydrophilicity; when adding composite components such as surfactants, a large amount of metal ions or organic impurities are introduced, making subsequent treatments such as cleaning more cumbersome. Summary of the invention

[0005] In view of this, the present invention provides a heat-resistant and oil-resistant polyvinyl alcohol-based hydrophilic sponge material and a preparation method thereof. Based on polyvinyl alcohol raw materials, a hydrophilic porous sponge material with heat-resistant and oil-resistant properties is prepared by utilizing the synergistic effect of multiple aldehydes, foaming agents and flavonoid compounds. The polyvinyl alcohol-based hydrophilic sponge material can be used for the reuse of reclaimed water from interface evaporation of high-temperature oily sewage, with an average pore size of 0.5-30 μm; under irradiation with one times the intensity of sunlight, the interface evaporation rate is greater than 3 kg m -2 h -1 ; Under irradiation with ten times the intensity of sunlight, the interface evaporation rate is greater than 30 kg m -2 h -1 ; Under the action of 3m / s convection wind, the evaporation rate is greater than 8kg m -2 h -1 After long-term treatment in high-temperature oily wastewater for more than 30 days, the sponge morphology and structure did not change significantly, and the interfacial evaporation rate remained above 95%.

[0006] To achieve the above-mentioned purpose of the invention, the technical solution provided by the present invention is as follows: a heat-resistant and oil-resistant polyvinyl alcohol-based hydrophilic sponge material is obtained by reacting the following raw material system, which includes the following raw material components in parts by weight: 100 parts of polyvinyl alcohol, 100-150 parts of foaming agent, 50-90 parts of formaldehyde solution, 20-50 parts of sulfuric acid, 5-20 parts of flavonoid compounds, and 500-850 parts of 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 a starch foaming agent, sodium bicarbonate, one of sodium carbonate and sodium dodecyl sulfate and a composite thereof. Considering the foaming properties and the morphology after sponge molding, any one or more of starch foaming agent and sodium bicarbonate are preferred, and starch foaming agent is further preferred.

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

[0011] The flavonoid compound can be any one of quercetin, hesperetin, taxifolin, catechin, epicatechin, anthocyanidin and proanthocyanidin. In view of cost, chemical binding ability and water solubility, one of hesperetin, catechin, epicatechin, anthocyanidin and proanthocyanidin is preferred, and anthocyanidin or catechin is further preferred.

[0012] The non-core groups of flavonoid compounds usually contain abundant hydroxyl groups, which can be added to the ring-forming process during the cross-linking ring-opening process and combined with the polyvinyl alcohol molecular chain. The strong hydrophilicity of the hydroxyl group can reduce the attenuation of the hydrophilicity of the polyvinyl alcohol sponge material after the addition of the enhancer. The core of the flavonoid compound has a benzene ring structure. The interaction between the benzene rings can achieve the combination between the polycyclic rings, further complicate the molecular chain structure, and improve the tolerance of the obtained polyvinyl alcohol sponge in high-temperature sewage. Flavonoid compounds can combine with each other in an aldehyde and sulfuric acid environment to form oligomers with a longer molecular chain structure, which enriches the combination mode of flavonoid compounds and polyvinyl alcohol, makes the molecular network more complex, and improves the heat resistance of the polyvinyl alcohol sponge.

[0013] Sulfuric acid provides an acidic environment during the synthesis. If the amount of sulfuric acid is too little, the acetalization and cross-linking reaction between polyvinyl alcohol, aldehyde and flavonoid compounds will be slow, and since the acidic environment is weakened, cross-linking cannot be fully carried out, and the obtained sponge will gel, and therefore, it will not be resistant to heat and oil stains.

[0014] Preferably, 0.1-1 part of an aqueous solution of aliphatic dialdehyde is also included.

[0015] If the total amount of aldehyde compounds is too little, the cross-linking of the polyvinyl alcohol material cannot be complete, and the sponge softens and becomes gel-like; if aldehydes are added continuously, the sponge becomes too hard and its hydrophilicity decreases, which is manifested in a decrease in evaporation performance and long-term oil pollution resistance during the interfacial evaporation of high-temperature oily wastewater.

[0016] The preferred amount of the aliphatic dialdehyde aqueous solution is 0.3-0.7 parts. The aliphatic dialdehyde may be one of glutaraldehyde, 3-methylglutaraldehyde and 3-methyl-2-butenal. From the viewpoint of reaction activity, hydrophilicity of the prepared sponge and evaporation performance, glutaraldehyde and 3-methylglutaraldehyde are preferred, and glutaraldehyde is further preferred.

[0017] Preferably, 0.1-0.5 parts of aromatic dialdehyde are also included. The aromatic dialdehyde may be one of o-phthalaldehyde, isophthalaldehyde and terephthalaldehyde. In view of the reaction activity, hydrophilicity and evaporation performance of the prepared sponge, o-phthalaldehyde and terephthalaldehyde are preferred, and o-phthalaldehyde is further preferred.

[0018] Due to the simple molecular structure of formaldehyde, it usually preferentially condenses with adjacent hydroxyl groups in the polyvinyl alcohol molecular chain network to form a five-membered ring or six-membered ring structure; aliphatic dialdehydes usually have long chains, which can enrich the cross-linking methods on the polyvinyl alcohol molecular chain, reduce the molecular chain spacing, and make the structure more complex; the aldehyde functional group of aromatic dialdehydes relies on the aromatic ring, usually cross-linking with the adjacent hydroxyl groups of the polyvinyl alcohol molecule, and through the weak interaction π-π stacking in the aromatic ring, the condensed ring structure interacts with each other to further complicate the polyvinyl alcohol molecular network, which plays a role in further enhancing the heat resistance of polyvinyl alcohol. In addition, very small amounts of aliphatic dialdehydes and aromatic dialdehydes can change the sponge structure and performance.

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

[0020] Step 1, 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;

[0021] Step 2, mixing the polyvinyl alcohol aqueous solution, the foaming agent solution and the flavonoid solution at 40-70° C., adding the formaldehyde solution and sulfuric acid, and stirring to obtain a pre-reaction mixed solution;

[0022] Step 3: then transferring the pre-reaction mixed solution into a mold, and placing it in a 50-70° C. oven for curing for 12-36 hours; after demolding, cleaning and drying are performed to obtain the polyvinyl alcohol-based hydrophilic sponge material.

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

[0024] Preferably, the viscosity of the polyvinyl alcohol is 3-10 mPa·s, preferably 4.6-5.4 mPa·s; the alcoholysis degree is 80-99%, preferably 86.5-89%; and the polymerization degree 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, and the aromatic dialdehyde is any one of o-phthalaldehyde, isophthalaldehyde and terephthalaldehyde.

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

[0028] The beneficial effects of the present invention are as follows: by modifying by adding flavonoid compounds and regulating the proportion of ingredients, the sponge material finally obtained has a porous network structure, strong hydrophilicity, stable structure, high interface evaporation performance, and can be stable for a long time in high-temperature oily wastewater, meeting the actual service requirements of high-temperature water purification.

[0029] (1) Compared with the unmodified and traditional polyvinyl alcohol-based sponge materials, the present invention uses flavonoid compounds to modify the hydrophilic resin sponge, which can solve the problem of polyvinyl alcohol-based hydrophilic sponge materials' tolerance to high temperature and oily wastewater. After the addition of flavonoid compounds, polyvinyl alcohol participates in the acetalization and cross-linking ring formation process in a sulfuric acid environment, enhances the cross-linking reaction of the polyvinyl alcohol sponge, enriches the ring structure in the polyvinyl alcohol molecular chain, and the aromatic ring structure enhances the interaction between the molecular chains, thereby improving the heat resistance of the sponge material.

[0030] (2) The synergistic addition of multiple aldehydes can also enhance the tolerance of sponge materials in high-temperature oily wastewater. In the process of ring-opening crosslinking 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 the polyvinyl alcohol-based resin sponge to solve its heat resistance and oil resistance problems, and can obtain a polyvinyl alcohol-based hydrophilic resin sponge material with obvious cost advantages and simple preparation methods.

[0031] (3) By adding a foaming agent and flavonoid compounds, the pore size distribution of the sponge structure can be controlled. After the flavonoid compounds are added, the viscosity of the solution is increased, so that the sponge retains a small pore structure during stirring, and a bimodal pore microstructure of the sponge is achieved, with a large pore size of 3-30 μm and a small pore size of 0.5-3 μm; and a special structure of bimodal pores and through-holes within the skeleton is prepared, which is beneficial to the water reuse process in the interfacial evaporation base.

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

[0033] (5) The raw materials of the present invention are easily available, the cost is low, the preparation method is simple, it is suitable for large-scale batch production, and has a wide range of applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is a scanning electron microscope image of the heat-resistant and oil-resistant polyvinyl alcohol-based hydrophilic sponge material prepared in Example 1.

[0035] Figure 2 This is a scanning electron microscope image of the interior of the skeleton 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 of heat-resistant and oil-resistant polyvinyl alcohol-based hydrophilic sponge material under different environmental conditions.

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

[0038] The embodiment of the present invention provides a heat-resistant and oil-resistant polyvinyl alcohol-based hydrophilic sponge material and a preparation method thereof, which solves the problem that common water purification materials are easy to scale, easy to corrode and have poor heat resistance in high-temperature oily sewage, and successfully prepares a heat-resistant and oil-resistant water purification material based on polyvinyl alcohol. Unless otherwise specified, the raw materials used in the embodiments of the present invention are all commonly used raw materials, and the methods described in the embodiments are conventional material preparation methods.

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

[0040] Evaporation rate: The flux of water evaporation per unit evaporation area per unit time under a specific environment is called the evaporation rate of the material under that environment, usually expressed in terms of evaporated mass. Cut the completely wetted polyvinyl alcohol-based sponge into regular square samples, and determine and measure the evaporation surface area of ​​the material. Under specific evaporation environmental conditions, the sponge material is fixed and floated above the test water body. Then, a balance is used to measure the overall mass change over a certain period of time. The specific evaporation conditions are one times the intensity of sunlight, ten times the intensity of sunlight, and 3m / s of convection wind. Each sponge is tested 5 times, and the evaporation rate results can be calculated using the following formula:

[0041]

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

[0043] Pore ​​size distribution: Analyze the sponge SEM images for statistics to obtain the pore size distribution of the sponge. Select 5 different sponge samples for each sponge, and select 3 SEM photos in different directions to comprehensively analyze the pore size distribution and calculate the average pore size.

[0044] Long-term tolerance: Test the heat and oil resistance of the sponge. Cut the sponge material into specific sizes and measure the evaporation rate. Then, soak the sponge material in 90°C oily wastewater for 30 and 60 days. The oily wastewater is high-temperature produced water from oil fields. Measure the evaporation rate of the sponge after soaking. Each sponge is tested 3 times, and the tolerance is calculated by the following evaporation rate retention rate:

[0045]

[0046] where η 30 and η 60 They are the evaporation rate decay rate of the sponge after it has been immersed in high-temperature oily wastewater for 30 days and 60 days; is the initial evaporation rate of the sponge; and are the evaporation rates of the sponge after 30 and 60 days of immersion, respectively; and Calculated by the evaporation rate formula. The higher the evaporation rate retention rate, the better the long-term tolerance 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] Dissolve 100 g of polyvinyl alcohol PVA0588, 150 g of starch foaming agent and 20 g of anthocyanidin in deionized water to obtain corresponding polyvinyl alcohol aqueous solution, starch solution and anthocyanidin solution respectively;

[0050] Then, the three solutions were mixed at 50° C., and 90 g of 37 wt % formaldehyde solution, 0.4 g of 50 wt % glutaraldehyde, 0.1 g of o-phthalaldehyde and 50 g of 98 wt % sulfuric acid solution were added, and the mixture was stirred to obtain a pre-reaction mixed solution; the total mass of deionized water in the mixed solution was 850 g;

[0051] The mixed reaction solution is then transferred to a mold, and placed in a 60° C. oven for curing for 18 hours; after demolding, the mold is 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] Dissolve 10 g of polyvinyl alcohol PVA0588, 10 g of starch foaming agent and 0.5 g of catechin in a certain mass of deionized water to obtain corresponding polyvinyl alcohol aqueous solution, starch solution and catechin solution respectively;

[0055] Then, the three solutions were mixed at 55° C., and 5 g of 37 wt % formaldehyde solution, 0.01 g of 50 wt % glutaraldehyde, 0.05 g of o-phthalaldehyde and 5 g of 98 wt % sulfuric acid solution were added, and the mixture was stirred to obtain a pre-reaction mixed solution; the total mass of deionized water in the mixed solution was 50 g;

[0056] The mixed reaction solution is then transferred to a mold, and placed in a 60° C. oven for curing for 18 hours; after demolding, the mold is 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] Dissolve 100 g of polyvinyl alcohol PVA0588, 100 g of starch foaming agent, 8 g of catechins and 8 g of anthocyanidins in a certain amount of deionized water to obtain corresponding polyvinyl alcohol aqueous solution, starch solution, catechins and anthocyanidins solutions respectively;

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

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

[0062] Comparative Example 1

[0063] A method for preparing a hydrophilic composite sponge is as follows, which is different from Example 1 in that anthocyanin is not added, and the rest is the same as Example 1.

[0064] Comparative Example 2

[0065] A method for preparing a heat-resistant, oil-resistant and hydrophilic composite sponge is as follows. The difference from Example 1 is that the mass of anthocyanin is 5 g, and the rest is the same as Example 1.

[0066] Comparative Example 3

[0067] A method for preparing a heat-resistant, oil-resistant and hydrophilic composite sponge is as follows. The difference from Example 1 is that the mass of anthocyanin is 40 g, and the rest is the same as Example 1.

[0068]

[0069] The pore size distribution of Examples 1 to 3 is 0.5 to 10 μm, the average pore size is 1.5 to 3.5 μm, and the evaporation rate under one-fold light intensity is greater than 6 kg m -2 h -1 The evaporation rate under ten times the sunlight intensity is greater than 75 kg m -2 h -1, the evaporation rate under 3m / s convection wind is greater than 8kg m -2 h -1 , after 60 days of high temperature oily wastewater treatment, the evaporation rate can still be maintained at more than 96%. The SEM photo of the pore size distribution in Example 1 is shown in Figure 1 The SEM images of the pore size and water channels in the sponge skeleton are shown in Figure 2 The performance test proves that the polyvinyl alcohol-based hydrophilic composite sponge of the present invention has high evaporation performance, pore size distribution that is conducive to evaporation, and excellent heat resistance and oil resistance.

[0070] In Examples 1 to 3, except for selecting different types of flavonoid compounds of equal mass, the other synthetic components are the same, and the flavonoid compounds are selected as anthocyanin, catechin and an equal mixture of the two. In comparison, anthocyanin has a higher evaporation rate under high concentration conditions and better heat resistance and oil resistance; catechin has a higher evaporation rate under one times the intensity of sunlight. Considering the high temperature environment of actual sponge application, Example 1 achieves the best effect.

[0071] Except that no flavonoid compound is added, the other preparation processes of Comparative Example 1 are the same as those of Examples 1 to 3. Comparative Example 1 cannot withstand high temperature, and the sponge structure collapses and softens at high temperature, and cannot be durable in a high temperature environment.

[0072] A longitudinal comparison of Example 1 and Comparative Examples 2 to 3 shows that, except for the different quality of anthocyanins, the other components are the same, namely, appropriate, small and excessive amounts of anthocyanins added. A reduction in the quality of anthocyanins will reduce the evaporation performance; although excessive anthocyanin quality can improve heat resistance and oil resistance, the evaporation rate will generally decrease, affecting the evaporation effect. Flavonoid compounds that are not parent nuclei usually have abundant hydroxyl groups, which can be added to the ring-forming process during the cross-linking ring-opening process and combined with the polyvinyl alcohol molecular chain, and the strong hydrophilicity of the hydroxyl group can reduce the attenuation of the hydrophilicity of the polyvinyl alcohol sponge material by the addition of the enhancer. The parent nucleus of the flavonoid compound has a benzene ring, and its interaction can realize the combination of polycyclic rings, further complicate the molecular chain structure, and improve the tolerance of the prepared polyvinyl alcohol sponge in high-temperature sewage. Flavonoid compounds can combine with each other in an aldehyde and sulfuric acid environment to form oligomers, have a longer molecular chain structure, enrich the combination of flavonoid compounds and polyvinyl alcohol, make the molecular network more complex, and improve the heat resistance of the polyvinyl alcohol sponge. Excessive amounts of flavonoids are more conducive to the self-binding of flavonoids to form oligomeric compounds, which increases the length and complexity of the molecular chain and thus has better heat resistance. However, in the process of cross-linking with the polyvinyl alcohol molecular chain, the oligomeric compounds will form larger molecular rings and inhibit the ring formation process, thereby increasing the pore size. In addition, the hydrophilic functional groups are lost during the binding process of the oligomeric compounds, which reduces the evaporation rate.

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

[0074] Example 5 A method for preparing a heat-resistant and oil-resistant polyvinyl alcohol-based hydrophilic sponge material is as follows. The difference from Example 1 is that no o-phthalaldehyde is added, and the rest is the same as 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. The difference from Example 1 is that the mass of the formaldehyde solution is 30 g, and the rest is the same as 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. The difference from Example 1 is that the mass of the formaldehyde solution is 150 g, and the rest is the same as Example 1.

[0077]

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

[0079] Comparing Example 1 and Comparative Examples 4 and 5, the greater the mass of the formaldehyde solution, the smaller the average pore size. This is because when the amount of aldehyde cross-linking agents such as formaldehyde is increased, the number of cross-linking points on the molecules of the polyvinyl alcohol chain increases, which deepens the degree of cross-linking and reduces the pore size. However, after cross-linking, hydrophilic groups such as hydroxyl groups are lost, so the increase in the mass of aldehydes will weaken the evaporation rate.

[0080] As in Comparative Example 4, the quality of the formaldehyde solution is too low, and the sponge cannot be completely cross-linked to form a gel-like intermediate substance, which lacks the high evaporation performance of the sponge material. This is because there are too few cross-linking points to form a polyvinyl alcohol cross-linked molecular chain, and it becomes a gel, and the incomplete cross-linked segments are unstable in a high-temperature water environment and cannot be durable.

[0081] Due to the simple molecular structure of formaldehyde, it usually condenses with adjacent hydroxyl groups in the polyvinyl alcohol molecular chain network to form a five-membered ring or six-membered ring structure; aliphatic dialdehydes usually have long chains, which can enrich the cross-linking methods on the polyvinyl alcohol molecular chain, reduce the molecular chain spacing, and make the structure more complex; the aldehyde functional group of aromatic dialdehydes relies on the aromatic ring, usually cross-linking with the adjacent hydroxyl groups of the polyvinyl alcohol molecule, and through the weak interaction π-π stacking in the aromatic ring, the condensed ring structure interacts with each other to further complicate the polyvinyl alcohol molecular network, which plays a role in further enhancing the heat resistance of polyvinyl alcohol. In addition, very small amounts of aliphatic dialdehydes and aromatic dialdehydes can change the sponge structure and performance.

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

[0083] Example 7: A method for preparing a heat-resistant and oil-resistant polyvinyl alcohol-based hydrophilic sponge material is as follows. The difference from Example 1 is that: 125 g of starch and 25 g of sodium bicarbonate are used to prepare a mixed solution of starch and sodium bicarbonate, and the rest is the same as 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. The difference from Example 1 is that the mass of starch is 200g, and the rest is the same as 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. The difference from Example 1 is that the mass of sodium bicarbonate is 125 g, and a sodium bicarbonate aqueous solution is prepared. The rest is the same as 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. The difference from Example 1 is that 25 g of sodium bicarbonate is used and a sodium bicarbonate aqueous solution is prepared. The rest is the same as Example 1.

[0087]

[0088] Comparing Examples 1, 6 and 7 vertically, the additional addition of sodium bicarbonate foaming agent in the presence of starch additives has little effect on the evaporation rate and heat and oil resistance of the polyvinyl alcohol-based sponge, but the average pore size increases. The pore size distribution of the sponge using additional sodium bicarbonate foaming agent still has a small pore portion of the sponge using only starch foaming agent, and additional large pores of 5 to 13 μm are added. Comparative Examples 7 and 8 use different masses of sodium bicarbonate foaming agent alone. Although the heat and oil resistance are similar to Example 1, the evaporation rate is significantly reduced, and the average pore size is significantly larger than the sponge made with only starch foaming agent. Comparing Example 1 and Comparative Example 6, the excessive starch additive affects the evaporation rate of the polyvinyl alcohol hydrophilic sponge under high temperature and concentrated light conditions.

[0089] Sodium bicarbonate foaming agent can cooperate with starch foaming agent to adjust the pore size of polyvinyl alcohol sponge, but using it alone will weaken the evaporation rate of polyvinyl alcohol sponge. This is due to the different foaming mechanisms of starch and sodium bicarbonate: the expansion and gelatinization degree of starch foaming agent are regulated by temperature; sodium bicarbonate releases hydrogen during heating. Therefore, the pore size of the sponge is different. Starch is a hydrophilic foaming agent, which is easier to maintain the hydrophilicity of the sponge than sodium bicarbonate during the curing and cross-linking process of the sponge, thereby ensuring the high evaporation rate of the polyvinyl alcohol sponge. Excessive starch additives will make the sponge soft. This is because the excess starch reacts with the polyvinyl alcohol molecular chain and flavonoid compounds during the cross-linking process, affecting the mechanical properties and high temperature stability of the sponge material.

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

Claims

1. A heat-resistant and oil-resistant polyvinyl alcohol-based hydrophilic sponge material, characterized in that: The invention is obtained by reacting the following raw material system, which comprises the following raw material components by weight: 100 parts of polyvinyl alcohol, 100-150 parts of foaming agent, 50-90 parts of formaldehyde solution, 20-50 parts of sulfuric acid, 5-20 parts of flavonoid compound and 500-850 parts of deionized water.

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

3. The heat-resistant and oil-resistant polyvinyl alcohol-based hydrophilic sponge material according to claim 1, characterized in that: The flavonoid compound is any one or more of quercetin, hesperetin, taxifolin, catechin, epicatechin, anthocyanidin and proanthocyanidin.

4. The heat-resistant and oil-resistant polyvinyl alcohol-based hydrophilic sponge material according to claim 1, characterized in that: It also includes 0.1-1 part of an aqueous solution of aliphatic dialdehyde.

5. The heat-resistant and oil-resistant polyvinyl alcohol-based hydrophilic sponge material according to claim 1, characterized in that: It also contains 0.1-0.5 parts of aromatic dialdehyde.

6. A method for preparing the heat-resistant and oil-resistant polyvinyl alcohol-based hydrophilic sponge material according to any one of claims 1 to 5, characterized in that: The following steps are involved: Step 1, 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; Step 2, mixing the polyvinyl alcohol aqueous solution, the foaming agent solution and the flavonoid solution at 40-70° C., adding the formaldehyde solution and sulfuric acid, and stirring to obtain a pre-reaction mixed solution; Step 3: then transferring the pre-reaction mixed solution into a mold, and placing it in a 50-70° C. oven for curing for 12-36 hours; after demolding, cleaning and drying are performed to obtain the polyvinyl alcohol-based hydrophilic sponge material.

7. The method for preparing the heat-resistant and oil-resistant polyvinyl alcohol-based hydrophilic sponge material according to claim 6, characterized in that: The concentration of the formaldehyde solution is 35-40wt%; the concentration of the sulfuric acid is 96-99wt%.

8. The method for preparing the heat-resistant and oil-resistant polyvinyl alcohol-based hydrophilic sponge material according to claim 6, characterized in that: In step 2, an aliphatic dialdehyde aqueous solution is added, and the concentration of the aliphatic dialdehyde aqueous solution is 2-50 wt %.

9. The method for preparing the heat-resistant and oil-resistant polyvinyl alcohol-based hydrophilic sponge material according to claim 6, characterized in that: In step 2, an aromatic dialdehyde is added, and the aromatic dialdehyde is any one of o-phthalaldehyde, isophthalaldehyde and terephthalaldehyde.

10. The method for preparing the heat-resistant and oil-resistant polyvinyl alcohol-based hydrophilic sponge material according to claim 8, characterized in that: The aliphatic dialdehyde is any one of glutaraldehyde, 3-methylglutaraldehyde and 3-methyl-2-butenal.

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