阅读说明：本技术 一种高透明聚乙烯醇水凝胶及其制备方法和应用 (High-transparency polyvinyl alcohol hydrogel and preparation method and application thereof ) 是由 王莉莉 田心语 赵现伟 张宪胜 耿存珍 夏延致 于 2020-12-21 设计创作，主要内容包括：本发明提供一种高透明聚乙烯醇水凝胶及其制备方法和应用。本发明所述高透明聚乙烯醇水凝胶以聚乙烯醇和无机盐为原料,以水为溶剂,其中,聚乙烯醇的浓度为3-30wt％,无机盐的浓度为0.5-29.9wt％。本发明的方法绿色环保,且制备得到的聚乙烯醇水凝胶兼具高透明性、粘附性,超低温抗冻性,同时具有弹性、延展性、离子导电性及保湿性,克服了聚乙烯醇水凝胶在应用时的不透明、无粘附性、不抗冻等问题,可应用于医药、材料以及传感器等领域。(The invention provides a high-transparency polyvinyl alcohol hydrogel and a preparation method and application thereof. The high-transparency polyvinyl alcohol hydrogel takes polyvinyl alcohol and inorganic salt as raw materials and water as a solvent, wherein the concentration of the polyvinyl alcohol is 3-30 wt%, and the concentration of the inorganic salt is 0.5-29.9 wt%. The method is environment-friendly, and the prepared polyvinyl alcohol hydrogel has high transparency, adhesiveness, ultralow-temperature frost resistance, elasticity, ductility, ionic conductivity and moisture retention, overcomes the problems of opaqueness, non-adhesiveness, non-frost resistance and the like of the polyvinyl alcohol hydrogel during application, and can be applied to the fields of medicines, materials, sensors and the like.)

1. A high transparent polyvinyl alcohol hydrogel is prepared from polyvinyl alcohol and inorganic salt as raw materials, and water as solvent, wherein the concentration of polyvinyl alcohol is 3-30 wt%, and the concentration of inorganic salt is 0.5-29.9 wt%; the visible light transmittance is not less than 80%.

2. The highly transparent polyvinyl alcohol hydrogel according to claim 1, wherein the concentration of the polyvinyl alcohol is 10 to 20 wt%; the concentration of the inorganic salt is 10-20 wt%.

3. The highly transparent polyvinyl alcohol hydrogel according to claim 1 or 2, wherein the polyvinyl alcohol has a number average molecular weight of 40000-180000 and a degree of alcoholysis of 70-99.9%;

preferably, the inorganic salt is selected from one or more of calcium chloride, zinc chloride, lithium chloride, sodium phosphate, potassium acetate.

4. A method of preparing the highly transparent polyvinyl alcohol hydrogel of any one of claims 1 to 3, comprising: preparing a polyvinyl alcohol/inorganic salt mixed solution, defoaming the mixed solution, and then transferring the mixed solution to a mold for freezing and thawing.

5. The method of claim 4, wherein the debubbling process comprises sonication, vacuum, or standing still.

6. The method as claimed in claim 4, wherein the freezing and thawing operation is a freezing and thawing cycle method comprising freezing the mixed solution of the defoamed polyvinyl alcohol and the inorganic salt at-10 ℃ to-150 ℃ for 1 to 48 hours, and then thawing at-10 ℃ to 50 ℃ for 0 to 48 hours.

7. A composite hydrogel comprising the high-transparency polyvinyl alcohol hydrogel according to any one of claims 1 to 3 as a matrix material;

preferably, the composite hydrogel comprises a macromolecule/polyvinyl alcohol composite hydrogel and a nano filler/polyvinyl alcohol composite hydrogel.

8. A polyvinyl alcohol dry film which is produced from the highly transparent polyvinyl alcohol hydrogel according to any one of claims 1 to 3.

9. A polyvinyl alcohol aerogel starting from the highly transparent polyvinyl alcohol hydrogel according to any one of claims 1 to 3.

10. Use of the highly transparent polyvinyl alcohol hydrogel according to any one of claims 1 to 3, or the composite hydrogel according to claim 7, or the polyvinyl alcohol dry film according to claim 8, or the polyvinyl alcohol aerogel according to claim 9 as a medical or pharmaceutical material in the medical field and in the field of sensors;

preferably, the medical or medicinal material comprises an artificial cornea material, a material directly contacting the eye, a wound dressing, an antipyretic patch, a drug delivery material, an artificial cartilage material, an artificial skin material.

Technical Field

The invention relates to the field of high polymer materials, and in particular relates to a high-transparency polyvinyl alcohol hydrogel and a preparation method and application thereof.

Background

The information in this background section is only for enhancement of understanding of the general background of the invention and is not necessarily to be construed as an admission or any form of suggestion that this information forms the prior art that is already known to a person of ordinary skill in the art.

The polyvinyl alcohol is a water-soluble high molecular polymer, has the advantages of biodegradability, good biocompatibility and the like, and is a green chemical material. The polyvinyl alcohol can be prepared into the polyvinyl alcohol hydrogel through a physical or chemical crosslinking method, and the polyvinyl alcohol hydrogel has important application prospects in the fields of artificial cartilage, engineering scaffold composition and biosensors due to the non-toxicity and excellent mechanical properties.

The polyvinyl alcohol hydrogel is usually prepared by a chemical crosslinking method, a physical crosslinking method, a radiation crosslinking method and the like. Wherein, the chemical crosslinking method usually uses toxic reagents such as glutaraldehyde, boric acid, epichlorohydrin and the like as crosslinking agents, the toxic crosslinking agents are difficult to eliminate, and the biocompatibility of the polyethylene hydrogel is greatly reduced due to trace residual crosslinking agents; the radiation crosslinking method adopts radiation or ultraviolet light to induce the crosslinking of polyvinyl alcohol hydrogel, although the synthesis efficiency of the method is high, the method has higher requirements on crosslinking equipment, and the high-energy rays cause weaker mechanical properties; the freeze-thaw cycle method is one of the most common physical crosslinking methods for preparing polyvinyl alcohol hydrogels, and is a common method for preparing polyvinyl alcohol hydrogels for medical use. However, the polyvinyl alcohol hydrogel prepared by the method has the defects of low adhesion, opacity, no freezing resistance and the like when being used like most of hydrogels, and the use requirements of the polyvinyl alcohol hydrogel in the biomedical field and in low-temperature environments are severely limited.

Chinese patent No. 202010508542.5 discloses a preparation method of polyvinyl alcohol ionic conduction hydrogel with high strength and high sensitivity, which comprises soaking polyvinyl alcohol hydrogel prepared by freezing-thawing method in sodium chloride aqueous solution to obtain ionic conduction, but the hydrogel obtained by the method is opaque and has no adhesiveness.

Chinese patent No. 201910718777.4 discloses a method for preparing a transparent polyvinyl alcohol hydrogel eye patch. The defect that polyvinyl alcohol hydrogel is turbid and opaque is made up by performing irradiation crosslinking on the frozen and thawed semi-gel product. But the irradiation crosslinking operation is inconvenient and expensive, and the popularization and the application are not easy.

Disclosure of Invention

In order to overcome the defects in the prior art, the invention provides a high-transparency polyvinyl alcohol hydrogel and a preparation method and application thereof. The preparation method disclosed by the invention is simple in raw materials, green and environment-friendly, easy to implement and popularize and capable of realizing large-scale industrial application; the polyvinyl alcohol hydrogel prepared by the invention has the performances of elasticity, ductility, ionic conductivity, moisture retention and the like, and also has high transparency, adhesion and ultralow temperature frost resistance, and is suitable for the fields of medicines, materials and sensors.

In a first aspect of the present invention, the present invention provides a highly transparent polyvinyl alcohol hydrogel, which uses polyvinyl alcohol and an inorganic salt as raw materials, and water as a solvent, wherein the concentration of the polyvinyl alcohol is 3 to 30 wt%, and the concentration of the inorganic salt is 0.5 to 29.9 wt%.

In an embodiment of the present invention, the high transparent polyvinyl alcohol hydrogel of the present invention has a light transmittance of not less than 80% in the visible light range and a freezing resistance temperature as low as-80 ℃.

Conventional polyvinyl alcohol gels are opaque and often require the use of organic solvents such as dimethyl sulfoxide to obtain transparency, which often must be completely removed from the gel, which is difficult to achieve, and which is toxic. The invention takes water as solvent, adopts polyvinyl alcohol with specific concentration and inorganic salt with specific concentration and kind to obtain the high-transparency polyvinyl alcohol hydrogel, the high-transparency polyvinyl alcohol hydrogel can realize transparency higher than 80%, and the polyvinyl alcohol hydrogel has ultralow temperature anti-freezing function and adhesiveness.

In some embodiments of the invention, the concentration of polyvinyl alcohol is 10 to 20 wt%, preferably 15 to 20 wt%; the concentration of the inorganic salt is 10-20 wt%.

In some embodiments of the invention, the polyvinyl alcohol has a number average molecular weight of 40000-180000 and a degree of alcoholysis of 70 to 99.9%.

In an embodiment of the present invention, the inorganic salt is selected from one or more of calcium chloride, zinc chloride, lithium chloride, sodium phosphate and potassium acetate, and the addition of these inorganic salts can inhibit the crystallization of polyvinyl alcohol and improve the macroscopic properties of polyvinyl alcohol hydrogel. In some embodiments of the invention, more preferred inorganic salts are calcium chloride and lithium chloride. When the two inorganic salts are selected, the prepared polyvinyl alcohol hydrogel has better transparency, adhesiveness and ultralow temperature frost resistance.

It should be noted that although inorganic salts such as sodium chloride, sodium oleate, potassium chloride and the like are commonly used as metal inorganic salts, when they are used in combination with polymer molecules, they tend to enhance the crosslinking between polymer molecules and molecular chains and the solvent needs to contain an organic solvent such as dimethyl sulfoxide or polyethylene glycol, and in the embodiment of the present invention, the inventors found that when inorganic salts such as sodium chloride, sodium oleate, potassium chloride and the like are used in combination with polyvinyl alcohol, polyvinyl alcohol is easily precipitated from an aqueous solution at a concentration of, for example, more than 5% by weight, and that the resulting polyvinyl alcohol hydrogel does not have transparency when these inorganic salts are used.

In the present embodiment, the inventors found that when the concentration of polyvinyl alcohol is too high, for example, more than 30 wt%, the polyvinyl alcohol is difficult to dissolve in water, when the concentration is too low, for example, less than 3 wt%, the polyvinyl alcohol cannot form a hydrogel, and when the concentration of inorganic salt is too high, the polyvinyl alcohol is saturated and cannot dissolve. In some preferred embodiments of the invention, the concentration of polyvinyl alcohol is from 15 to 20 wt%. In addition, the kind and concentration of the inorganic salt play an especially important role in the performance of the polyvinyl alcohol hydrogel of the present invention, and in the embodiment of the present invention, when the concentration of the inorganic salt is 10 to 20 wt%, the obtained polyvinyl alcohol hydrogel has higher transparency and better comprehensive performance; in particular, in some embodiments, the polyvinyl alcohol hydrogels of the present invention have a transmittance of greater than 90% in the visible range and a freezing point of up to-80 ℃ when the polyvinyl alcohol concentration is 15 to 20 wt%, the inorganic salt is calcium chloride or lithium chloride, and the concentration is 10 to 20 wt%.

In some embodiments of the present invention, the inventors have also tried a method comprising dissolving polyvinyl alcohol in DMSO at normal temperature with a polyvinyl alcohol concentration of 10 wt%, and then exchanging by soaking in deionized water, and the prepared polyvinyl alcohol gel has a transmittance of only 80% in the visible light range, and DMSO is toxic and difficult to remove in hydrogel; the method comprises the steps of adopting sodium chloride as inorganic salt, preparing a polyvinyl alcohol/sodium chloride (10 wt%) aqueous solution at a high temperature, and obtaining the hydrogel through a freezing-unfreezing method, wherein the transmittance of the hydrogel in a visible light range is only 30%, the hydrogel has no adhesiveness, and the freezing resistance temperature is only-5 ℃; and preparing polyvinyl alcohol solution at high temperature, freezing and thawing to obtain hydrogel, soaking the hydrogel in sodium chloride aqueous solution to obtain hydrogel with transmittance of 20% in visible light range, no adhesion and freezing resistance of-5 deg.C.

In a second aspect of the present invention, the present invention provides a method for preparing the highly transparent polyvinyl alcohol hydrogel described in the first aspect above, comprising: preparing a polyvinyl alcohol/inorganic salt mixed solution, defoaming the mixed solution, and transferring the mixed solution to a mold for freezing. In the present invention, the polyvinyl alcohol/inorganic salt mixed solution is a mixed aqueous solution of polyvinyl alcohol and an inorganic salt, unless otherwise specified.

In the present embodiment, the defoaming treatment may be performed by a method commonly used in the art, but in some embodiments of the present invention, ultrasonic treatment, vacuum treatment or standing treatment is more preferable, and particularly, ultrasonic defoaming is performed.

In some embodiments of the present invention, the freezing operation is a freeze-thaw cycle method, which comprises freezing the mixed solution of the deaerated polyvinyl alcohol and the inorganic salt at-10 ℃ to-150 ℃ for 1 to 48 hours, and then thawing at-10 ℃ to 50 ℃ for 0 to 48 hours, preferably 6 to 12 hours.

In some embodiments of the invention, the freezing temperature is from-20 ℃ to-80 ℃, preferably from-20 ℃ to-50 ℃, and the thawing temperature is from 4 ℃ to 20 ℃; the times of circulating freezing and thawing are 1-10.

In some embodiments of the present invention, the way of freezing operation can affect the characteristics of the polyvinyl alcohol hydrogel, and in the research of the present invention, the inventor finds that when the freezing temperature is-20 ℃ to-50 ℃, the thawing temperature is 4 ℃ to 20 ℃, and the freezing and thawing treatment is cycled at least once, the obtained polyvinyl alcohol hydrogel has better transparency and frost resistance.

The method effectively realizes the transparency, adhesiveness, elasticity, ionic conductivity, low-temperature frost resistance, moisture retention and the like of the obtained polyvinyl alcohol hydrogel by controlling the type and content of the inorganic salt and the freezing temperature, and particularly solves the problems of the traditional polyvinyl alcohol hydrogel, such as opacity, non-adhesiveness, non-frost resistance and the like.

In a third aspect of the present invention, there is provided a composite hydrogel comprising the highly transparent polyvinyl alcohol hydrogel as described in the first aspect as a matrix material.

In some embodiments of the invention, the composite hydrogel comprises a polymer/polyvinyl alcohol composite hydrogel, a nanofiller/polyvinyl alcohol composite hydrogel.

In some embodiments of the present invention, the composite hydrogel may be a polyvinyl alcohol/chitosan composite hydrogel, a polyvinyl alcohol/seaweed composite hydrogel, a polyvinyl alcohol/polyacrylamide composite hydrogel, a polyvinyl alcohol/polyvinylpyrrolidone composite hydrogel, a carbon nanotube/polyvinyl alcohol composite hydrogel, a graphene/polyvinyl alcohol composite hydrogel, an MXene/polyvinyl alcohol composite hydrogel, a montmorillonite/polyvinyl alcohol composite hydrogel, a silica/polyvinyl alcohol composite hydrogel, a hydroxyapatite/polyvinyl alcohol composite hydrogel, or a cellulose nanocrystal/polyvinyl alcohol composite hydrogel.

In a fourth aspect of the present invention, there is provided a dry polyvinyl alcohol film using the highly transparent polyvinyl alcohol hydrogel described in the first aspect as a raw material.

The polyethylene dry film of the present invention can be obtained by treating the highly transparent polyvinyl alcohol hydrogel of the first aspect of the present invention described above by conventional methods in the art, such as by evaporation of water, such as in some embodiments at a temperature of 5-60 ℃.

In a fifth aspect of the present invention, the present invention provides a polyvinyl alcohol aerogel which is prepared from the highly transparent polyvinyl alcohol hydrogel described in the first aspect.

The polyvinyl alcohol aerogel of the present invention can be obtained by processing the high transparent polyvinyl alcohol hydrogel of the first aspect of the present invention by conventional methods in the art, such as by freeze-drying, for example, in some embodiments, quenching the high transparent polyvinyl alcohol hydrogel in liquid nitrogen followed by drying in a freeze-dryer.

In a sixth aspect, the present invention provides the use of the polyvinyl alcohol hydrogel according to the first aspect, the composite hydrogel according to the third aspect, the dry polyvinyl alcohol film according to the fourth aspect, or the polyvinyl alcohol aerogel according to the fifth aspect as a medical or pharmaceutical material in the medical field and in the field of sensors.

For example, the medical or medicinal material may include artificial corneal lamella material, material that directly contacts the eye, wound dressing, cooling patch, drug delivery material, artificial cartilage material, artificial skin material, and the like.

Compared with the prior art, the invention has the advantages that: the raw materials used in the method for producing the polyvinyl alcohol hydrogel do not relate to any toxic materials, and the preparation process is green and environment-friendly; the polyvinyl alcohol hydrogel prepared by the method has high transparency, adhesiveness and ultralow-temperature frost resistance, and simultaneously has the performances of elasticity, ductility, ionic conductivity, moisture retention and the like, so that the problems of non-transparency, non-adhesiveness, non-frost resistance and the like of the polyvinyl alcohol hydrogel prepared by the method in the prior art are solved; the polyvinyl alcohol hydrogel prepared by the method has good comprehensive performance, can be applied to artificial cornea, materials contacting eyes, wound dressings, can be used as an adhesive to prepare an antipyretic patch, and can be used in the fields of drug delivery, artificial cartilage, artificial skin, sensors and the like.

Drawings

The accompanying drawings, which are incorporated in and constitute a part of this application, illustrate embodiments of the application and, together with the description, serve to explain the application and are not intended to limit the application. Embodiments of the invention are described in detail below with reference to the attached drawing figures, wherein:

FIG. 1 shows the transparency of the polyvinyl alcohol hydrogel obtained in example 1, the polyvinyl alcohol hydrogel with the thickness of 2mm prepared in example 1 is covered on the school badge of Qingdao university, the figure, the font and the color of the school badge are clearly visible and are hardly influenced, and the polyvinyl alcohol hydrogel has adhesiveness and is well adhered to the school badge below.

FIG. 2 is a graph showing the transparency of the polyvinyl alcohol hydrogel obtained in comparative example 5, wherein the polyvinyl alcohol hydrogel having a thickness of 2mm obtained in example 5 was applied on a school badge of the university of Qingdao, the figure, the font, and the color of the school badge were completely hidden, and the hydrogel had almost no transparency.

FIG. 3 is a drawing cycle curve of the transparent polyvinyl alcohol hydrogel obtained in example 1, which shows the stretch recovery property of the polyvinyl alcohol hydrogel of the present invention, and it can be seen from the drawing that the length of the polyvinyl alcohol is completely recovered to the original length after the polyvinyl alcohol is stretched to 1 time or 2 times of the original length and the stretching force is unloaded, which proves that the material has good resilience.

Fig. 4 shows the sensing performance (strain of 50%) of the transparent polyvinyl alcohol hydrogel obtained in example 1, and it can be seen from the graph that when the strain is stretched to 50%, the resistance of the hydrogel changes significantly, which proves that the hydrogel is very sensitive to strain and can be used as a good sensing material.

FIG. 5 shows the effect of adhesion of the polyvinyl alcohol hydrogel obtained in example 7 to glass, from which it can be seen that the gel has low transparency and is capable of bonding two sheets of glass; and when the two pieces of glass are separated by force, the gel exhibits stringiness and adhesion to the glass.

Detailed Description

The invention will be further illustrated with reference to the following specific examples. It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the present invention. The experimental procedures, in which specific conditions are not noted in the following examples, are generally carried out according to conventional conditions or according to conditions recommended by the manufacturers.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. The reagents or starting materials used in the present invention can be purchased from conventional sources, and unless otherwise specified, the reagents or starting materials used in the present invention can be used in a conventional manner in the art or in accordance with the product specifications. In addition, any methods and materials similar or equivalent to those described herein can be used in the methods of the present invention. The preferred embodiments and materials described herein are intended to be exemplary only. Unless otherwise specified, the elevated temperatures described in the following examples of the invention are from 90 to 100 ℃.

Example 1

Preparing a mixed solution of polyvinyl alcohol (M70000) with the concentration of 20 wt% and calcium chloride with the concentration of 20 wt% at a high temperature, uniformly mixing, ultrasonically defoaming, adding the obtained mixed solution into a mold, putting the mold into a refrigerator for freezing at the freezing temperature of-50 ℃ for 24 hours, and unfreezing at the temperature of 4 ℃ for 6 hours, wherein the number of freezing and unfreezing cycles is 1. Through detection, the transmittance of the prepared polyvinyl alcohol hydrogel in a visible light range is 91%, and the lowest freezing resistance temperature is-25 ℃. The transparency is schematically shown in fig. 1, the stretch recovery properties are shown in fig. 3, and the sensing properties are shown in fig. 4.

Example 2

Preparing a polyvinyl alcohol (M140000) solution with the concentration of 10 wt% at a high temperature, continuously adding 20 wt% of calcium chloride, uniformly mixing, ultrasonically defoaming, adding the obtained mixed solution into a mold, putting the mold into a refrigerator for freezing at the freezing temperature of-40 ℃ for 24 hours, and unfreezing at the temperature of 4 ℃ for 6 hours, wherein the number of freezing and unfreezing cycles is 2. Through detection, the transmittance of the prepared polyvinyl alcohol hydrogel in a visible light range is 90%, and the lowest freezing resistance temperature is-25 ℃. The stretch recovery and sensory properties were similar to those of the polyvinyl alcohol hydrogel of example 1.

Example 3

Preparing a polyvinyl alcohol (M ═ 70000) solution with the concentration of 10 wt% at a high temperature, uniformly mixing, defoaming by ultrasonic, adding the obtained mixed solution into a mold, putting the mold into a refrigerator for freezing at the freezing temperature of-50 ℃ for 24 hours, and unfreezing at the temperature of 4 ℃ for 6 hours, wherein the number of freezing and unfreezing cycles is 3. Through detection, the transmittance of the prepared polyvinyl alcohol hydrogel in a visible light range is 92%, and the lowest freezing resistance temperature is-80 ℃. The sensory properties were similar to those of the polyvinyl alcohol hydrogel of example 1, but the stretch recovery properties were inferior to those of example 1.

Example 4

Preparing a mixed solution of polyvinyl alcohol (M110000) with the concentration of 10 wt% and calcium chloride (15 wt%) at a high temperature, uniformly mixing, ultrasonically defoaming, adding the obtained mixed solution into a mold, putting the mold into a refrigerator for freezing at the freezing temperature of-20 ℃ for 24 hours, and unfreezing for 12 hours at the temperature of 20 ℃, wherein the number of freezing and unfreezing cycles is 1. Through detection, the visible light range transmittance of the prepared polyvinyl alcohol hydrogel is 81%, and the lowest freezing resistance temperature is-10 ℃. The stretch recovery and sensing properties were similar to those of the polyvinyl alcohol hydrogel of example 3.

Example 5

Preparing a mixed solution of polyvinyl alcohol (M70000) with the concentration of 10 wt% and calcium chloride with the concentration of 0.2 wt% at a high temperature, continuously adding the mixed solution, uniformly mixing, ultrasonically defoaming, adding the obtained mixed solution into a mold, putting the mold into a refrigerator for freezing at the freezing temperature of-20 ℃ for 24 hours, unfreezing the mixed solution at the temperature of 4 ℃ for 6 hours, and controlling the number of freezing and unfreezing cycles to be 3. Through detection, the visible light range transmittance of the prepared polyvinyl alcohol hydrogel is 10%, and the lowest freezing resistance temperature is 0 ℃. The transparency of which is schematically shown in fig. 2.

Example 6

Preparing a polyvinyl alcohol (M70000) solution with the concentration of 10 wt% at a high temperature, wherein dimethyl sulfoxide is used as a solvent, uniformly mixing, ultrasonically defoaming, adding the obtained mixed solution into a mold, and then soaking the mold into enough deionized water to obtain the polyvinyl alcohol hydrogel. The transmittance of the prepared polyvinyl alcohol hydrogel in a visible light range is 78%, and toxic solvents are easy to remain in the hydrogel.

Example 7

Preparing a mixed solution of polyvinyl alcohol (M70000) with the concentration of 20 wt% and calcium chloride with the concentration of 40 wt% at a high temperature, uniformly mixing, ultrasonically defoaming, adding the obtained mixed solution into a mold, putting the mold into a refrigerator for freezing at the freezing temperature of-20 ℃ for 24 hours, and unfreezing at the temperature of 4 ℃ for 6 hours, wherein the number of freezing and unfreezing cycles is 3. The polyvinyl alcohol hydrogel obtained by the preparation method has a low transmittance of only 20% in a visible light range, but has stronger adhesiveness, and the transparency and adhesiveness are shown in fig. 5.

Example 8

Preparing a solution of polyvinyl alcohol (M70000) with the concentration of 10 wt% and sodium chloride with the concentration of 10 wt% at a high temperature, uniformly mixing, defoaming by ultrasonic, adding the obtained mixed solution into a mold, putting the mold into a refrigerator for freezing at the freezing temperature of-20 ℃ for 24 hours, and unfreezing at the temperature of 4 ℃ for 6 hours, wherein the number of freezing and unfreezing cycles is 3. Through detection, the visible light range transmittance of the prepared polyvinyl alcohol hydrogel is 30%, and the lowest freezing resistance temperature is-5 ℃.

Examples9

Preparing a mixed solution of polyvinyl alcohol (M70000) with the concentration of 20 wt% and calcium chloride with the concentration of 20 wt% at a high temperature, uniformly mixing, defoaming by ultrasonic, adding the obtained mixed solution into a mold, and putting the mold into a refrigerator for freezing at the freezing temperature of-50 ℃ for 24 hours. The detection shows that the performance of the prepared polyvinyl alcohol hydrogel is better and is equivalent to that of the polyvinyl alcohol hydrogel in example 4.

Example 10

Preparing a mixed solution of polyvinyl alcohol (M70000) with the concentration of 10 wt% and calcium chloride with the concentration of 10 wt% at a high temperature, uniformly mixing, ultrasonically defoaming, adding the obtained mixed solution into a mold, putting the mold into a refrigerator for freezing at the freezing temperature of-20 ℃ for 24 hours, and unfreezing at the temperature of 4 ℃ for 6 hours, wherein the number of freezing and unfreezing cycles is 1. And (3) putting the obtained sample into a 45 ℃ oven for drying until constant weight is achieved, thus obtaining the polyvinyl alcohol dry film.

Example 11

Preparing a mixed solution of polyvinyl alcohol (M70000) with the concentration of 10 wt% and lithium chloride with the concentration of 10 wt% at a high temperature, uniformly mixing, ultrasonically defoaming, adding the obtained mixed solution into a mold, putting the mold into a refrigerator for freezing at the freezing temperature of-20 ℃ for 24 hours, and unfreezing at the temperature of 4 ℃ for 6 hours, wherein the number of freezing and unfreezing cycles is 1. And (3) putting the obtained sample into a 45 ℃ oven for drying until constant weight is achieved, thus obtaining the polyvinyl alcohol dry film.

Example 12

Preparing a mixed solution of polyvinyl alcohol (M90000) with the concentration of 20 wt% and calcium chloride with the concentration of 20 wt% at a high temperature, uniformly mixing, ultrasonically defoaming, adding the obtained mixed solution into a mold, putting into a refrigerator for freezing at the freezing temperature of-30 ℃ for 24 hours, and unfreezing at the temperature of 4 ℃ for 6 hours, wherein the number of freezing and unfreezing cycles is 1. And quenching the obtained sample in liquid nitrogen for 30min, and then placing the sample in a freeze dryer for freeze drying for 48h to obtain the polyvinyl alcohol aerogel.

Although the present invention has been described in detail with reference to the foregoing embodiments, it will be apparent to those skilled in the art that changes may be made in the embodiments and/or equivalents thereof without departing from the spirit and scope of the invention. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.