Preparation method of PVA-based composite hydrogel

Abstract

The invention relates to the field of preparation and processing of advanced materials, and discloses a preparation method of PVA-based composite hydrogel, the PVA-based composite hydrogel is prepared through a solution casting and solvent evaporation method, PVA molecules and other added substances can be fully and uniformly mixed in a solution, all components in a system can also be relatively uniformly distributed, and the PVA-based composite hydrogel is prepared. The finally formed composite hydrogel is uniform in internal structure, stable in performance and free of obvious local difference. In a solution state, PVA molecular chains and other added functional substances can fully contact and interact with each other, and the interaction can be further enhanced in the process of forming the hydrogel through solvent evaporation, so that good interface bonding is formed between PVA and additives, and the comprehensive performance of the composite hydrogel is effectively improved. Afterwards, sodium hydroxide is utilized to attack alcoholic hydroxyl groups and destroy the formation of hydrogen bonds. The sodium hydroxide is further washed out with deionized water, so that hydrogen bonds are formed again to control the actuation of the hydrogel.

Description

Technical Field

[0001] The present invention relates to the technical field of advanced material preparation and processing, and specifically to a preparation method of a PVA-based composite hydrogel. Background Art

[0002] The ever-changing materials have greatly promoted the rapid development of humanity and society. Especially some high-performance polymer materials, such as polyphenylene sulfide resin, polyimide, aromatic polyamide, etc., exhibit excellent high-temperature resistance, radiation resistance, corrosion resistance, flame retardancy, insulation and mechanical properties, etc., and play a crucial role in the fields of aerospace, transportation, energy and power, industrial separation, etc. PVA is a water-soluble polymer, with acid and alkali resistance, film-forming property, barrier property and good chemical stability, and good biocompatibility. Its performance is between that of plastics and rubbers. It is one of the most widely used and largest-volume synthetic polymers globally in the past century. Compared with traditional silicon-based materials, PVA-based hydrogels have the advantages of good softness, high biocompatibility, excellent stretchability, etc. It is expected to become a candidate material for the preparation of flexible strain sensors in the future, thus promoting the development and application of flexible electronic products.

[0003] In the process of implementing the present invention, the inventors found that the prior art has at least the following problems: The mechanical properties of PVA gel materials are generally achieved by adjusting the formation and size of the crystalline domain structure. For example, the freeze-thaw method is one of the common methods to improve the mechanical properties of PVA hydrogels. It induces the formation of crystalline domains through intermolecular and intramolecular hydrogen bonds, thereby crosslinking the gel network structure. However, this method is time-consuming and easily affected by environmental factors. As the most widely used synthetic polymer, PVA is involved in all aspects of human production and life. This also means that seeking more regulation strategies has important strategic significance. Currently, the strategies for controlling the actuation of hydrogels mainly focus on the optimization of the solvent diffusion process, which dominates in most hydrogel actuators. Therefore, methods such as constructing solvent channels and reducing the material size have been proposed. However, due to their fixed driving mechanism, these strategies are still troubled by the trade-off between low driving strength or response speed and material size. Therefore, it is urgent to invent a new mechanism for regulating the mechanical properties and actuation of PVA-based composite hydrogels. Summary of the Invention

[0004] To solve the above technical problems, the present invention discloses a preparation method of a PVA-based composite hydrogel and a new mechanism for controlling the actuation of the hydrogel by the protonation-deprotonation process. The PVA-based composite hydrogel is prepared by the solution casting and solvent evaporation method. PVA molecules and other added substances can be fully mixed and homogenized in the solution, and the components in the system can also be more evenly distributed. Finally, the formed composite hydrogel has a uniform internal structure, stable performance, and no obvious local differences. Then, sodium hydroxide is used to attack the alcohol hydroxyl group to destroy the formation of hydrogen bonds. Further, sodium hydroxide is washed out with deionized water to reform the hydrogen bonds to achieve the control of the actuation of the hydrogel. It shows unique advantages in the preparation method of the PVA-based composite hydrogel and proposes a new mechanism for the actuation of the hydrogel.

[0005] To achieve the above object, the present invention is realized by the following technical solutions: A preparation method of a PVA-based composite hydrogel, comprising the following steps:

[0006] S1. Pretreatment of PVA: Add 2.5 g of PVA powder to 20 g of deionized water, and heat it in a 90 °C water bath with magnetic stirring until completely dissolved;

[0007] S2. Crosslinking and reduction: After cooling the pretreated PVA solution to 60 °C, slowly add 18 g - 19 g of CA solution. Finally, drop 1.875 g - 3.125 g of AgNO3 solution into the PVA / CA solution and stir for 1.5 hours;

[0008] S3. Film formation: Pour the mixture solution into a circular glass mold, and dry it in an oven at 40 °C for 12 hours. Peel the formed PVA-based composite hydrogel from the circular glass mold. During this period, AgNO3 is in-situ reduced to form AgNPs.

[0009] Preferably, the mass of the PVA powder in S1 is 2.5 g, the mass of the deionized water is 20 g, and the water bath heating temperature is 90 °C.

[0010] Preferably, the cooling temperature in S2 is 60 °C, the mass of the CA solution is 19 g, the mass of the AgNO3 solution is 3.125 g, and the stirring time is 1.5 hours.

[0011] Preferably, the drying temperature in the drying oven in S3 is 40 °C, and the drying time is 12 hours.

[0012] Preferably, it further includes a new mechanism for controlling the actuation of the hydrogel by the protonation-deprotonation process. The new mechanism for controlling the actuation of the hydrogel by the protonation-deprotonation process comprises the following steps:

[0013] A1. Immerse the PVA-based composite hydrogel in a high-concentration strong alkaline hydroxide (NaOH) solution. Use sodium hydroxide to attack the alcohol hydroxyl groups and disrupt the formation of hydrogen bonds. Partial deprotonation of the alcohol hydroxyl groups in the PVA-based composite hydrogel reduces the intramolecular hydrogen bonds. Since the oxygen anions cause electrostatic repulsion between adjacent segments, the polymer chains become more extended;

[0014] A2. Immerse the stretched PVA-based composite hydrogel in deionized water, and further wash out sodium hydroxide with deionized water. The hydrogen bonds will reform, the sodium ions and O+- will be reprotonated, resulting in the regeneration of the previously interrupted hydrogen bonds. This process leads to the recovery of the plastic elongation rate, achieving the control of hydrogel actuation using the protonation-deprotonation process.

[0015] Preferably, the concentration of NaOH in A1 is 6 mol, and the soaking time is 30 min.

[0016] The present invention provides a preparation method of a PVA-based composite hydrogel. It has the following beneficial effects:

[0017] 1. Through the solution casting and solvent evaporation method, the present invention can more easily obtain a PVA-based composite hydrogel with uniform pore size and regular distribution by precisely controlling parameters such as the evaporation rate of the solvent and the solution concentration. It has higher biological safety, a simpler preparation process, lower cost, and less impact on material properties, laying a good foundation for the preparation of PVA-based composite hydrogels.

[0018] 2. The present invention uses a CA solution to reduce silver ions in AgNO3 to silver nanoparticles under relatively mild conditions. Compared with some methods that require high temperature, high pressure, or strong reducing agents, this method is simpler and safer to operate, has lower requirements for equipment, and can effectively avoid the adverse effects of severe reaction conditions on the structure and properties of silver nanoparticles and hydrogels. Moreover, it can more precisely control the particle size and distribution of silver nanoparticles, which is very important for ensuring the performance stability and uniformity of the hydrogel.

[0019] 3. The present invention utilizes a new mechanism of controlling hydrogel actuation through the protonation-deprotonation process, which leads to the recovery of plastic elongation rate and releases the stored energy. The method of storing and releasing elastic potential energy in the hydrogel has high actuation strength, fast actuation speed, and high energy density. The protonation-deprotonation strategy can broaden the existing driving mechanisms of hydrogel actuators and significantly break through their upper limit efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a schematic diagram of the SEM photograph of the PVA-based composite hydrogel prepared in Example 1 of the present invention before soaking in NaOH;

[0021] Figure 2Schematic diagram of SEM photograph of the PVA-based composite hydrogel prepared in Example 1 of the present invention after being soaked in NaOH;

[0022] Figure 3 Schematic diagram of SEM photograph of the PVA-based composite hydrogel prepared in Example 1 of the present invention after being soaked in deionized water;

[0023] Figure 4 Tensile stress-strain curves of the PVA-based composite hydrogel prepared in Example 1 of the present invention before soaking in NaOH, after soaking in NaOH, and after soaking in deionized water;

[0024] Figure 5 Schematic diagram of the curve of the shrinkage strength of the PVA-based composite hydrogel prepared in Example 1 of the present invention after being soaked in NaOH varying with time under different tensile multiples when soaked in deionized water;

[0025] Figure 6 Schematic diagram of the relative resistance change and the corresponding GF coefficient under tensile strain of the PVA-based composite hydrogel prepared in Example 1 of the present invention before soaking in NaOH;

[0026] Figure 7 Schematic diagram of the relative resistance change and the corresponding GF coefficient under tensile strain of the PVA-based composite hydrogel prepared in Example 1 of the present invention after being soaked in NaOH;

[0027] Figure 8 Schematic diagram of the relative resistance change and the corresponding GF coefficient under tensile strain of the PVA-based composite hydrogel prepared in Example 1 of the present invention after being soaked in deionized water;

[0028] Figure 9 Schematic diagram of the relative resistance change of the PVA-based composite hydrogel prepared in Example 1 of the present invention under repeated stretching at 50% strain before soaking in NaOH;

[0029] Figure 10 Schematic diagram of the relative resistance change of the PVA-based composite hydrogel prepared in Example 1 of the present invention under repeated stretching at 50% strain after being soaked in NaOH;

[0030] Figure 11 Schematic diagram of the relative resistance change of the PVA-based composite hydrogel prepared in Example 1 of the present invention under repeated stretching at 50% strain after being soaked in deionized water;

[0031] Figure 12 Schematic diagram of the tensile and recovery lengths of the PVA-based composite hydrogel prepared in the present invention before and after soaking in NaOH;

[0032] Figure 13 Flow chart of the preparation method of a PVA-based composite hydrogel of the present invention;

[0033] Figure 14 It is a flow chart of a new mechanism for controlling the actuation of a hydrogel by using a protonation-deprotonation process in the present invention. Specific embodiments

[0034] Next, in combination with the accompanying drawings of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without making creative efforts shall fall within the protection scope of the present invention.

[0035] Embodiment 1:

[0036] Please refer to the attached Figure 1 - attached Figure 14 , the embodiment of the present invention provides a preparation method of a PVA-based composite hydrogel, including the following steps:

[0037] S1. Pretreatment of PVA: Add 2.5 g of PVA powder to 20 g of deionized water, and heat it in a water bath at 90 °C with magnetic stirring until completely dissolved;

[0038] S2. Crosslinking and reduction: After cooling the pretreated PVA solution to 60 °C, slowly add 17 g of CA solution. Finally, drop 2.125 g of AgNO3 solution into the PVA / CA solution and stir for 1.5 hours;

[0039] S3. Film formation: Pour the mixture solution into a circular glass mold, and dry it in an oven at 40 °C for 12 hours. Peel the formed PVA-based composite hydrogel from the circular glass mold. During this period, AgNO3 is in-situ reduced to form AgNPs.

[0040] A preparation method of a PVA-based composite hydrogel further includes: a new mechanism for controlling the actuation of a hydrogel by using a protonation-deprotonation process;

[0041] A new mechanism for controlling the actuation of a hydrogel by using a protonation-deprotonation process includes the following steps:

[0042] A1. Immerse the PVA-based composite hydrogel in a NaOH solution with a concentration of 3 mol for 15 min. Use sodium hydroxide to attack the alcohol hydroxyl group and destroy the formation of hydrogen bonds. The partial deprotonation of the alcohol hydroxyl group in the PVA-based composite hydrogel reduces the intra-chain hydrogen bonds. Because the oxygen anions cause electrostatic repulsion between adjacent segments, the polymer chains are more extended;

[0043] A2. Immerse the stretched PVA-based composite hydrogel in deionized water, and further wash out sodium hydroxide with deionized water to reform hydrogen bonds. The sodium ions and O⁺⁻ will be reprotonated, resulting in the regeneration of the previously interrupted hydrogen bonds. This process leads to the recovery of the plastic elongation rate and realizes the process of controlling the actuation of the hydrogel using the protonation-deprotonation process.

[0044] The SEM images of the PVA-based composite hydrogel prepared in Example 1 are as Figure 1 、 2 and Figure 3. It can be seen from Figure 1 that the surface of the prepared PVA-based composite hydrogel is relatively flat, indicating that the prepared material has good uniformity and stability, and the crystal structure is complete, meeting the expected effect. Figure 2 After soaking in NaOH, it can be seen that the surface roughness increases and obvious patterns appear, indicating that deprotonation occurs inside the hydrogel after soaking in NaOH, and the change of functional groups leads to the change of the arrangement and interaction of surface molecules. Figure 3 It can be seen that the flatness of the material surface partially recovers after soaking in deionized water, and some grooves become shallower, indicating that some chemical bonds inside the material recover, and the molecular chains return to a relatively more ordered state similar to the initial state.

[0045] The tensile stress-strain curves of the PVA-based composite hydrogel prepared in Example 1 before soaking in NaOH, after soaking in NaOH, and after soaking in deionized water are as Figure 4 shown. It can be seen that both the fracture stress and strain of the material after soaking in NaOH are much higher than those before soaking in NaOH. After soaking in deionized water, both the fracture stress and strain of the material decrease, but are still higher than those before soaking in NaOH, proving that the hydrogen bond breakage and formation are successfully regulated to enhance the mechanical properties of the material.

[0046] The graph showing the change of the shrinkage strength of the PVA-based composite hydrogel prepared in Example 1 with time after soaking in deionized water at different stretching multiples after soaking in NaOH is as Figure 5 shown. It can be clearly seen that as the stretching ratio increases, at the same soaking time in deionized water, the shrinkage strength increases with the increase of the stretching ratio, and basically reaches the maximum value at 60 s.

[0047] The sensing performance of the material was also tested in the experiment. The relative resistance change and the corresponding GF coefficient under tensile strain of the PVA-based composite hydrogel prepared in Example 1 before soaking in NaOH, after soaking in NaOH, and after soaking in deionized water are as Figure 6 、 7As shown in Figs. 8, it can be seen from the figure that the GF value remains relatively stable, indicating that there is a good linear relationship between the relative resistance or other physical quantities of the hydrogel and the tensile strain. Moreover, the sensitivity of the material after soaking in NaOH is higher than that before soaking in NaOH. Although the sensitivity of the material decreases after soaking in deionized water, it is still higher than that before soaking in NaOH.

[0048] The relative resistance changes during repeated stretching at 50% strain of the PVA-based composite hydrogel prepared in Example 1 before soaking in NaOH, after soaking in NaOH, and after soaking in deionized water are as Figure 9 , 10 and Figs. 11. At the same strain, the value of ΔR / R0 remains unchanged, reflecting the sensing performance of the material with stable output, reliable performance, high repeatability, and stable sensitivity.

[0049] Although the embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A preparation method of a PVA-based composite hydrogel, characterized in that, It includes the following steps: S1. Pretreatment of PVA: Add PVA powder to deionized water, and heat it in a water bath and stir magnetically until it is completely dissolved; S2. Crosslinking and reduction: After cooling the pretreated PVA solution, slowly add the CA solution. Finally, drop the AgNO3 solution into the PVA / CA solution and stir; S3. Film formation: Pour the mixture solution into a circular glass mold, and dry it in an oven. Peel the formed PVA-based composite hydrogel from the circular glass mold. During this period, AgNO3 is in-situ reduced to form AgNPs.

2. The preparation method of a PVA-based composite hydrogel according to claim 1, characterized in that, In step S1, the mass of the PVA powder used is 2.5 g, the mass of the deionized water is 20 g, and the temperature during water bath heating is 90 °C.

3. The preparation method of a PVA-based composite hydrogel according to claim 1, characterized in that, In step S2, the cooling temperature of the PVA solution is 60 °C, the mass of the CA solution used is 18 g - 19 g, the mass of AgNO3 is 1.875 g - 3.125 g, and the magnetic stirring time is 1.5 hours.

4. The preparation method of a PVA-based composite hydrogel according to claim 1, characterized in that, In step S3, the drying time in the oven is 12 hours, and the drying temperature is 40 °C.

5. The preparation method of a PVA-based composite hydrogel according to claim 1, characterized in that, It also includes a new mechanism for controlling the actuation of the hydrogel by using the protonation-deprotonation process. The new mechanism for controlling the actuation of the hydrogel by using the protonation-deprotonation process includes the following steps: A1. Immerse the PVA-based composite hydrogel in a high-concentration strong alkaline hydroxide (NaOH) solution. Use sodium hydroxide to attack the alcohol hydroxyl group and destroy the formation of hydrogen bonds. The partial deprotonation of the alcohol hydroxyl group in the PVA-based composite hydrogel reduces the intra-chain hydrogen bonds. Because the oxygen anion causes electrostatic repulsion between adjacent segments, the polymer chain becomes more extended; A2. Immerse the stretched PVA-based composite hydrogel in deionized water, and further wash out sodium hydroxide with deionized water. The hydrogen bonds will re-form, the sodium ions and O+- will be reprotonated, resulting in the regeneration of the previously interrupted hydrogen bonds. This process leads to the recovery of the plastic elongation rate to achieve the actuation control of the hydrogel by using the protonation-deprotonation process.

6. The new mechanism for controlling the actuation of a hydrogel by using a protonation-deprotonation process, characterized in that, In step A1, when the PVA-based composite hydrogel is immersed in a high-concentration strong alkaline hydroxide (NaOH) solution, the concentration of NaOH used is 2 - 6 mol, and the soaking time is 10 - 40 min.

Images