PVA hydrogel with high tensile strength and preparation method thereof

Abstract

The invention discloses high-tensile-strength PVA hydrogel and a preparation method thereof, and relates to the technical field of hydrogel, the high-tensile-strength PVA hydrogel comprises hydrogel, the microstructure of the hydrogel is provided with shrinkage lines oriented in multiple directions, and the hydrogel is prepared from the following components in percentage by mass: 8-15% of PVA, 5-15% of PVA, 5-15% of PVA, 5-15% of PVA and the balance of water. 75%-87% of a good solvent, wherein the good solvent is dimethyl sulfoxide (DMSO) or N-methyl pyrrolidone (NMP); the replacement solution is 5%-15%, the replacement solution is an aqueous solution containing sodium ions or an organic solution containing hydroxyl, and the concentration of the sodium ions is 0.4-1.6 mol / L. The PVA hydrogel has the advantages that the tensile strength and the elongation at break of the PVA hydrogel are remarkably improved through the synergistic effect of an optimized solvent system, the concentration gradient of a replacement solution and a freeze thawing process.

Description

Technical Field

[0001] The present invention relates to the technical field of hydrogels, and specifically relates to a high tensile strength PVA hydrogel and a preparation method thereof. Background Art

[0002] Polyvinyl alcohol (PVA) is an amphiphilic macromolecule composed of a hydrophobic (CH2-CH2) backbone and hydrophilic (-OH) side groups. It has a simple molecular structure and many outstanding advantages such as biodegradability, biocompatibility, and non-toxicity. These advantages make PVA an ideal polymer example for systematically studying the effects of various cations and anions on the hydrogel network. Scientists have developed hydrogels with a wide range of adjustable mechanical, structural, and physical properties through various methods such as freeze-thawing, chemical cross-linking, and mechanical training. A hydrogel is a hydrophilic three-dimensional network structure gel, usually with high elasticity and a transparent and bright appearance. Polyvinyl alcohol (PVA) hydrogel is a polymer hydrogel composed of a non-covalent interaction network, and has received extensive attention due to its broad composition regulation range and biocompatibility, etc., and is widely used in various fields such as the medical industry, manufacturing, and industry.

[0003] Polyvinyl alcohol (PVA) hydrogels are widely used in medical, industrial and other fields due to their advantages such as biocompatibility and degradability. However, their traditional preparation methods have problems such as low tensile strength (usually below 1 MPa) and insufficient mechanical properties. In the prior art, although the performance can be improved by adding fillers or chemical cross-linking, there are defects such as complex processes and introduction of toxic substances. To solve the above problems, a high tensile strength PVA hydrogel and a preparation method thereof are proposed. Summary of the Invention

[0004] To solve the above technical problems, the present invention provides a high tensile strength PVA hydrogel and a preparation method thereof, which solve the problems that the current polyvinyl alcohol (PVA) hydrogels are widely used in medical, industrial and other fields due to their advantages such as biocompatibility and degradability, but their traditional preparation methods have problems such as low tensile strength (usually below 1 MPa) and insufficient mechanical properties. In the prior art, although the performance can be improved by adding fillers or chemical cross-linking, there are defects such as complex processes and introduction of toxic substances.

[0005] To achieve the above object, the technical solution adopted by the present invention is: a high tensile strength PVA hydrogel, including a hydrogel, and the hydrogel is composed of the following components in mass percentage:

[0006] Polyvinyl alcohol (PVA): 8% - 15%;

[0007] Good solvent: 75% - 87%, and the good solvent is dimethyl sulfoxide (DMSO) or N-methylpyrrolidone (NMP);

[0008] Displacement solution: 5% - 15%, and the displacement solution is an aqueous solution containing sodium ions or an organic solution containing hydroxyl groups, where the sodium ion concentration is 0.4 - 1.6 mol / L.

[0009] Preferably, the microstructure of the hydrogel has multi-directionally oriented shrinkage lines, and the cross-linked network is regular and orderly, with a tensile strength ≥ 3.0 MPa and an elongation at break ≥ 300%.

[0010] A method for preparing a high-tensile-strength PVA hydrogel, which is used to prepare the above-mentioned high-tensile-strength PVA hydrogel, includes the following steps:

[0011] S1: Preparation of PVA (polyvinyl alcohol) solution. Dissolve PVA (polyvinyl alcohol) in dimethyl sulfoxide (DMSO) and stir to form a homogeneous solution under heating conditions.

[0012] S2: Perform repeated freeze-thaw treatment on the solution obtained in step S1 to form a physical cross-linked network.

[0013] S3: Immerse the freeze-thawed sample in a sodium sulfate solution, remove the solvent by gradient concentration displacement method, and complete the strengthening of the non-covalent cross-linked network through the Hofmeister effect.

[0014] S4: Wash and dry to obtain a high-tensile-strength PVA hydrogel.

[0015] Preferably, the preparation of the PVA solution is to add PVA particles to a good solvent, magnetically stir at 100 - 130 °C in an oil bath for 0.5 - 1.5 hours, with a stirring rate of 500 - 700 rpm, to form a homogeneous solution with a concentration of 8% - 15% (w / v) and a transparency higher than 90%.

[0016] Preferably, the repeated freeze-thaw treatment is to pour the PVA solution into a mold, freeze at -50 °C to -70 °C for 5 - 10 hours, then thaw at 20 - 30 °C for 2 - 4 hours, and repeat the freeze-thaw cycle 2 - 4 times to form a preliminarily cross-linked hydrogel precursor.

[0017] Preferably, the gradient concentration displacement method is to immerse the freeze-thawed hydrogel precursor in a sodium sulfate solution, with the volume ratio of the sodium sulfate solution to the hydrogel precursor being 5:1 - 10:1, change the sodium sulfate solution every 6 - 10 hours, and continue the displacement for 12 - 36 hours. The concentration of the sodium sulfate solution is 0.4 - 1.6 mol / L, and the solution concentration of the gradient concentration displacement method increases from 0.4 mol / L to 1.6 mol / L, with each stage of displacement time being 6 - 10 hours.

[0018] Preferably, the temperature of the sodium sulfate solution is 5-30°C. When the temperature rises to 30-50°C, the solubility of sodium sulfate increases to above 1.8 mol / L, which can further enhance the Hofmeister effect, increase the tensile strength to above 4.0 MPa and the elongation at break to above 350%.

[0019] Preferably, the cleaning is performed using deionized water or ethanol to remove residual salt on the surface, and the drying is freeze-drying or vacuum drying, with the temperature controlled at -50°C to 25°C for 6 to 48 hours.

[0020] Preferably, the replacement solution includes sodium sulfate or potassium sulfate or glucose solution or ethanol solution. During the replacement process, ions promote the formation of hydrogen bonds between PVA chains through the Hofmeister effect and induce the densification of the polymer network.

[0021] Compared with the prior art, the advantages of the present invention are as follows: the present invention induces the PVA chain to form a composite cross-linking unit of "ion bridge-hydrogen bond cluster" by respectively competing with hydrogen bonds through electrostatic action by Na⁺ and SO4²⁻ in sodium sulfate, so that the breaking energy of each cross-linking point is increased to 2.3 times that of traditional physical cross-linking; the high polarity of DMSO inhibits the aggregation of PVA chains in the dissolution stage, and reduces the polarity through gradient concentration in the replacement stage, prompting the chain segments to change from "stretched state" to "folded state", forming a high-density cross-linking network; the continuous freeze-thaw system controls the cooling rate (5℃ / min) to form nano-scale ice crystals, preventing large ice crystals from piercing the gel network, thereby maintaining the stability of the microstructure while improving production capacity. By optimizing the solvent system, replacing the solution concentration gradient and the synergistic effect of the freeze-thaw process, the optimized solvent system and concentration gradient make the PVA hydrogel show a significant improvement in tensile strength and elongation at break, increasing its carrying capacity in practical applications. The synergistic effect of the freeze-thaw process improves the ductility of the hydrogel and reduces its brittleness, making the material more flexible during use. Due to the improvement of tensile strength and elongation at break, PVA hydrogel can be widely used in medicine, sensors, soft robots and other fields, especially in environments that need to withstand stretching and strain. The optimized process improves the physical stability of the hydrogel, allowing it to maintain good mechanical properties and durability during long-term use. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 The present invention is a flow chart of the preparation method of the high tensile strength PVA hydrogel.

[0023] Figure 2 Schematic diagram of the effect of different concentrations of sodium sulfate solution on the cross-sectional structure of PVA hydrogel in the present invention.

[0024] Figure 3Schematic diagram of the influence of different replacement solutions on the tensile strength and elongation at break of PVA hydrogels in the present invention. Detailed implementation manners

[0025] The following description is used to disclose the present invention so that those skilled in the art can implement the present invention. The preferred embodiments in the following description are only examples, and other obvious variations can be conceived by those skilled in the art.

[0026] Example 1

[0027] A high-tensile-strength PVA hydrogel, including a hydrogel, which is composed of the following components in mass percentage:

[0028] Polyvinyl alcohol (PVA): 8% - 15%. This ratio range can ensure that the hydrogel has a sufficient polymer chain density to form a stable cross-linked network, while avoiding excessive viscosity of the solution due to too high PVA content, which affects the processing performance. Preferably, the concentration is 10%;

[0029] Good solvent: 75% - 87%. The good solvent is dimethyl sulfoxide (DMSO) or N-methylpyrrolidone (NMP). As a strong hydrogen bond acceptor, DMSO forms stronger solvent-polymer interactions with the hydroxyl groups of PVA and is more likely to induce the directional disentanglement of PVA chain segments during the replacement process, forming a regular cross-linked network. In contrast, NMP has a weaker hydrogen bond accepting ability and a high randomness of chain segment arrangement, resulting in significantly lower mechanical properties than the DMSO system. Therefore, DMSO solvent is preferably used when preparing the hydrogel;

[0030] Replacement solution: 5% - 15%. The replacement solution is an aqueous solution containing sodium ions or an organic solution containing hydroxyl groups, where the sodium ion concentration is 0.4 - 1.6 mol / L.

[0031] The microstructure of the hydrogel has multi-directionally oriented shrinkage lines, and the cross-linked network is regular and orderly. The tensile strength ≥ 3.0 MPa, and the elongation at break ≥ 300%.

[0032] Example 2

[0033] Referring to Figure 1 As shown, a preparation method of a high-tensile-strength PVA hydrogel for preparing the above-mentioned high-tensile-strength PVA hydrogel includes the following steps:

[0034] S1: Preparation of PVA (polyvinyl alcohol) solution. Dissolve PVA (polyvinyl alcohol) in dimethyl sulfoxide (DMSO) and stir to form a homogeneous solution under heating conditions;

[0035] S2: Perform repeated freeze-thaw treatment on the solution obtained in step S1 to form a physical cross-linked network;

[0036] S3: Immerse the freeze-thawed sample in a sodium sulfate solution, remove the solvent by gradient concentration replacement method, and complete the strengthening of the non-covalent cross-linked network through the Hofmeister effect;

[0037] S4: Perform cleaning and drying treatments to obtain a PVA hydrogel with high tensile strength.

[0038] The PVA solution is prepared by adding PVA particles into a good solvent, magnetically stirring for 0.5 - 1.5 hours under the condition of oil bath heating at 100 - 130 °C, with a stirring rate of 500 - 700 rpm, to form a homogeneous solution with a concentration of 8% - 15% (w / v) and a transparency higher than 90%.

[0039] The repeated freeze-thaw treatment is to pour the PVA solution into a mold, freeze it at -50 °C to -70 °C for 5 - 10 hours, then thaw it at 20 - 30 °C for 2 - 4 hours, and repeat the freeze-thaw cycle 2 - 4 times to form a preliminarily cross-linked hydrogel precursor.

[0040] The gradient concentration replacement method is to immerse the freeze-thawed hydrogel precursor in a sodium sulfate solution, with the volume ratio of the sodium sulfate solution to the hydrogel precursor being 5:1 - 10:1, replace the sodium sulfate solution every 6 - 10 hours, continuously replace for 12 - 36 hours, the concentration of the sodium sulfate solution is 0.4 - 1.6 mol / L, and the solution concentration of the gradient concentration replacement method increases from 0.4 mol / L to 1.6 mol / L, with the replacement time for each stage being 6 - 10 hours. For the influence of sodium sulfate solutions with different concentrations on the cross-sectional structure of the PVA hydrogel with DMSO as the solvent, please refer to Figure 2 as shown, where a. D-Na0.4, b. D-Na0.8, c. D-Na1.2, d. D-Na1.6.

[0041] Furthermore, it is concluded that as the concentration of sodium sulfate in the sodium sulfate solution increases, the shrinkage lines gradually decrease and fade, and the structure is relatively flat. The structure of the D-Na0.4 sample is complex, with obvious and deep shrinkage lines. This is because when the replacement solution is added, due to the presence of the sodium sulfate solution in the pores originally filled with the solvent, the solvent is replaced, resulting in the collapse or protrusion of the pores, forming shrinkage lines of varying depths. As the concentration of sodium sulfate in the sodium sulfate solution increases, the shrinkage lines gradually become uniform, shallower, and more regular.

[0042] Refine step S3:

[0043] The first stage: Immerse the freeze-thawed hydrogel precursor in a 0.4 mol / L sodium sulfate solution for 8 hours at a solution temperature of 25°C with a volume ratio of 8:1. At this time, Na⁺ initially penetrates into the gel interior, inducing local ordered arrangement of PVA chain segments, increasing the hydrogen bond density to 15 mJ / m², and the tensile strength reaches 1.2 MPa, which is 80% higher than the tensile strength obtained by the traditional process under the sample preparation conditions of 10% PVA concentration, DMSO solvent, single freeze-thaw cycle, and direct water washing to replace the solvent.

[0044] The second stage: Replace it with a 1.2 mol / L sodium sulfate solution for 10 hours while maintaining the temperature at 25°C. The high-concentration SO4²⁻ enhances the salting-out effect through the Hofmeister effect, promoting the formation of ionic bonds between PVA chains, and the tensile strength is increased to 2.8 MPa.

[0045] The third stage: Finally, replace it with a 1.6 mol / L sodium sulfate solution for 12 hours, raise the solution temperature to 35°C, and the solubility is increased to 1.8 mol / L. At this time, the synergistic effect of Na⁺ and SO4²⁻ makes the hydrogen bond and ionic bond densities reach equilibrium, the gel structure is flat, the tensile strength reaches 3.6 MPa, and the elongation at break is 330%.

[0046] Here, gradient concentration replacement is adopted to avoid gel cracking caused by the instantaneous penetration of high-concentration salt solution. By stepwise strengthening the cross-linked network, the mechanical properties are improved while maintaining the structural uniformity. The increase in temperature increases the ionic activity, further activating the Hofmeister effect and breaking through the strength limit at room temperature. The sample preparation conditions of the traditional process are: 10% PVA concentration, DMSO solvent, single freeze-thaw cycle, and direct water washing to replace the solvent to obtain the basic value of the tensile strength.

[0047] The temperature of the sodium sulfate solution is 5 - 30°C. When the temperature rises to 30 - 50°C, the solubility of sodium sulfate increases to more than 1.8 mol / L, which can further enhance the Hofmeister effect, increasing the tensile strength to more than 4.0 MPa and the elongation at break to more than 350%.

[0048] The cleaning is carried out with deionized water or ethanol to remove the residual salts on the surface, and the drying is freeze-drying or vacuum drying, with the temperature controlled at -50°C to 25°C for 6 - 48 hours.

[0049] Example 3

[0050] The replacement solution includes sodium sulfate or potassium sulfate or glucose solution or ethanol solution. During the replacement process, ions promote the formation of hydrogen bonds between PVA chains through the Hofmeister effect and simultaneously induce densification of the polymer network.

[0051] Dissolve PVA in DMSO. Denote pure water as the D-S group, 3M (3 mol / L) glucose solution (dissolved in deionized water) as the D-P group, ethanol solution with a mass fraction > 99.8% as the D-J group, and 1.6M (1.6 mol / L) sodium sulfate solution (dissolved in deionized water) as the D-Na1.6 group. The aim is to explore the effect of solution replacement of various replacement solutions on the tensile strength and elongation at break of PVA hydrogel with DMSO as the solvent. For details, please refer to Figure 3 as shown.

[0052] The tensile test adopts the standard test method for the tensile properties of plastics ASTM / D638 - 91. The test specimens are directly punched from the hydrogel along the flow direction. The test specimens adopt the ASTM / D638 standard and are made into dumbbell shapes with a length of 165 mm and a width of 13 mm. The test speed is 5 mm / min. At least five samples are prepared for each scale and the average value is taken to ensure the accuracy of the test. This is the prior art and will not be elaborated here.

[0053] The elongation at break is calculated based on the data in the tensile test, and its specific calculation formula is as follows:

[0054] Calculation formula for elongation at break (ε):

[0055] ε = × 100%;

[0056] In the formula, is the original gauge length of the test specimen (unit: mm or in); is the final gauge length of the test specimen at break (unit: mm or in).

[0057] Furthermore, a conclusion is drawn. Keeping other factors unchanged and changing the type of replacement solution, discuss the effect of different replacement solutions on the tensile strength and elongation at break of PVA hydrogel. From Figure 3It can be seen that the effects of different replacement solutions from high to low are D-Na1.6 > D-J > D-P > D-S. Among them, the tensile strength of D-Na1.6 is as high as 3.6 MPa, and the elongation at break is as high as 330%. For common hydrogels, its mechanical strength is significantly improved, which verifies the characteristic that Na+ causes the Hofmeister effect in PVA gels. In contrast, although the tensile strength of D-J is as high as 1.5 MPa, its elongation at break is significantly lower, only 92%. And although the tensile strength of D-P is only 1.1 MPa, its elongation at break is as high as 220%. It can be seen that carrying multiple hydroxyl groups in the replacement solution is not the main reason for the increase in tensile strength. The tensile strength of D-S is extremely low, and its elongation at break is close to that of D-J. And the D-P group has a relatively high elongation at break, indicating that glucose has a significant effect on unilaterally increasing the elongation at break of PVA hydrogels. The presence of ethanol molecules simultaneously increases the tensile strength and elongation at break of PVA hydrogels, and the presence of sodium sulfate crystals significantly increases both the tensile strength and elongation at break of PVA hydrogels due to the Hofmeister effect.

[0058] Working principle: Na⁺ and SO4²⁻ in sodium sulfate respectively compete through electrostatic interaction and hydrogen bond, inducing PVA chains to form "ion bridge - hydrogen bond cluster" composite cross-linking units, increasing the fracture energy of each cross-linking point to 2.3 times that of traditional physical cross-linking. The high polarity of DMSO inhibits the aggregation of PVA chains during the dissolution stage, and reduces the polarity through gradient concentration during the replacement stage, prompting the chain segments to turn from the "stretched state" to the "folded state" to form a high-density cross-linking network. The continuous freeze-thaw system forms nano-scale ice crystals by controlling the cooling rate (5°C / min), avoiding large ice crystals from piercing the gel network, thereby maintaining the microstructural stability while increasing production capacity.

[0059] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments. What is described in the above embodiments and the specification is only the principle of the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements all fall within the scope of the present invention claimed. The scope of protection claimed by the present invention is defined by the appended claims and their equivalents.

Claims

1. A high tensile strength PVA hydrogel, characterized in that: Comprising a hydrogel, the hydrogel is composed of components in the following mass percentages: Polyvinyl alcohol (PVA): 8% - 15%; Good solvent: 75% - 87%, the good solvent is dimethyl sulfoxide (DMSO) or N-methylpyrrolidone (NMP); Displacement solution: 5% - 15%, the displacement solution is an aqueous solution containing sodium ions or an organic solution containing hydroxyl groups, where the sodium ion concentration is 0.4 - 1.6 mol / L.

2. The high tensile strength PVA hydrogel according to claim 1, wherein: The microstructure of the hydrogel has multi-directionally oriented shrinkage marks, and the cross-linked network is regular and orderly, with a tensile strength ≥ 3.0 MPa and an elongation at break ≥ 300%.

3. A method for preparing a high tensile strength PVA hydrogel, which is used to prepare the high tensile strength PVA hydrogel described in any one of claims 1-3, and is characterized in that, Including the following steps: S1: Preparation of PVA (polyvinyl alcohol) solution, dissolving PVA (polyvinyl alcohol) in dimethyl sulfoxide (DMSO), and stirring to form a homogeneous solution under heating conditions; S2: Subjecting the solution obtained in step S1 to repeated freeze-thaw treatment to form a physical cross-linked network; S3: Immersing the freeze-thawed sample in a sodium sulfate solution, removing the solvent by gradient concentration displacement method, and completing the strengthening of the non-covalent cross-linked network through the Hofmeister effect; S4: Cleaning and drying treatment to obtain a PVA hydrogel with high tensile strength.

4. The preparation method of a high tensile strength PVA hydrogel according to claim 4, characterized in that: The preparation of the PVA solution is to add PVA particles to a good solvent, magnetically stir for 0.5 - 1.5 hours under the condition of oil bath heating at 100 - 130 °C, with a stirring rate of 500 - 700 rpm, to form a homogeneous solution with a concentration of 8% - 15% (w / v) and a transparency higher than 90%.

5. The preparation method of a high tensile strength PVA hydrogel according to claim 4, characterized in that: The repeated freeze-thaw treatment is to pour the PVA solution into a mold, freeze it at -50 °C to -70 °C for 5 - 10 hours, and then thaw it at 20 - 30 °C for 2 - 4 hours, repeating the freeze-thaw cycle 2 - 4 times to form a preliminarily cross-linked hydrogel precursor.

6. The preparation method of a high tensile strength PVA hydrogel according to claim 4, characterized in that: The gradient concentration displacement method is to immerse the freeze-thawed hydrogel precursor in a sodium sulfate solution, with the volume ratio of the sodium sulfate solution to the hydrogel precursor being 5:1 - 10:1, replacing the sodium sulfate solution every 6 - 10 hours, and continuously displacing for 12 - 36 hours. The concentration of the sodium sulfate solution is 0.4 - 1.6 mol / L, and the solution concentration of the gradient concentration displacement method increases from 0.4 mol / L to 1.6 mol / L, with each stage of displacement time being 6 - 10 hours.

7. The preparation method of a high tensile strength PVA hydrogel according to claim 4, characterized in that: The temperature of the sodium sulfate solution is 5 - 30 °C. When the temperature rises to 30 - 50 °C, the solubility of sodium sulfate increases to more than 1.8 mol / L, which can further enhance the Hofmeister effect and increase the tensile strength to more than 4.0 MPa and the elongation at break to more than 350%.

8. The preparation method of a high tensile strength PVA hydrogel according to claim 4, characterized in that: The cleaning is carried out using deionized water or ethanol to remove the residual salts on the surface, and the drying is freeze-drying or vacuum drying, with the temperature controlled at -50 °C to 25 °C for 6 - 48 hours.

9. The preparation method of a high tensile strength PVA hydrogel according to claim 4, characterized in that: The displacement solution includes sodium sulfate or potassium sulfate or glucose solution or ethanol solution. During the displacement process, ions promote the formation of hydrogen bonds between PVA chains through the Hofmeister effect and simultaneously induce the densification of the polymer network.

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