A dual-crosslinked self-healing hydrogel and a preparation method thereof

Abstract

This invention discloses a double-crosslinked self-healing hydrogel and its preparation method. The method first uses a combined approach of mixed acid hydrolysis and ultrasonic treatment to process microcrystalline cellulose into nanocellulose, followed by hydrogel preparation. Specifically: PVA is first dissolved in water to prepare a PVA solution; then, the obtained nanocellulose is added to the prepared PVA solution to obtain mixture A, where the mass fraction of nanocellulose in mixture A is 2.5 wt% to 3.5 wt%; finally, anhydrous sodium tetraborate is dissolved in water to prepare an anhydrous sodium tetraborate solution with a mass fraction of 4% to 8%, and this solution is added to mixture A to obtain the nanocellulose-based hydrogel. The porous composite hydrogel prepared by this invention has low cost, mild reaction, high yield efficiency, good biocompatibility, and high mechanical strength, and has broad application prospects in biomedicine, intelligent detection, and environmental purification.

Description

Technical Field

[0001] This invention belongs to the field of biomaterials technology, specifically relating to a double-crosslinked self-healing hydrogel and its preparation method. Background Technology

[0002] Nanocellulose-based hydrogels are a class of materials with excellent water absorption and retention capabilities, formed by cross-linking nanocellulose through a three-dimensional network structure. In aqueous solutions, nanocellulose forms a stable three-dimensional network structure through physical entanglement and intermolecular hydrogen bonding. The hydrophilicity and large specific surface area of ​​nanocellulose allow this network structure to lock in a large amount of water, thus forming a hydrogel. Cellulose-based hydrogels have a wide range of applications, showing promising prospects in environmental remediation, wearable electronic devices, human-computer interfaces, and health and medical testing. However, common drawbacks of current hydrogel preparations include the toxicity of the cross-linking agents, poor biocompatibility, and irreversible degradation, making them unsuitable for self-healing or biodegradable applications. Furthermore, common free radical polymerization methods for hydrogel preparation require long reaction times and have low efficiency. Therefore, improving the preparation efficiency of hydrogels and developing hydrogels with good biocompatibility and mechanical properties is of great significance. Summary of the Invention

[0003] This invention addresses the shortcomings of existing technologies by employing a combination of acid hydrolysis and mechanical processing to nanoscale microcrystalline cellulose. The resulting nanocellulose exhibits both spherical and rod-like morphologies with an average diameter of 10-35 nm. When this nanocellulose is incorporated into the preparation of hydrogels, the resulting cellulose-based hydrogels demonstrate excellent biocompatibility. Furthermore, based on their unique structure and composition, these hydrogels possess superior self-healing and stretchability. The method employed in this invention is simple to operate, low in cost, and highly efficient, making it suitable for large-scale industrial production while effectively ensuring product quality and expanding the applications of hydrogels.

[0004] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0005] This invention first provides a method for preparing a double-crosslinked self-healing hydrogel, the method comprising the following steps:

[0006] S1. Nanostructuring of microcrystalline cellulose: Microcrystalline cellulose is processed into nanocellulose using a combined method of mixed acid hydrolysis and ultrasonic treatment, specifically including the following sub-steps:

[0007] S11. Prepare a mixed acid solution with a volume fraction of 60% by adding deionized water using sulfuric acid and hydrochloric acid in a volume ratio of 3:1.

[0008] S12. Add microcrystalline cellulose to the mixed acid solution prepared in step S11 at a ratio of 1-2 grams of microcrystalline cellulose per 100 ml of mixed acid solution and stir until homogeneous to obtain a cellulose acid hydrolysis solution;

[0009] S13. Use a 120W ultrasonic cleaner to ultrasonically treat the cellulose acid hydrolysate obtained in step S12 for 8 hours. During this period, ice or water needs to be added to ensure that the temperature does not exceed 80°C.

[0010] S14. Neutralize the ultrasonically treated suspension to make it neutral;

[0011] S15. After centrifugation in step S14, the liquid portion of the neutralized solution is removed to obtain solid-phase nanocellulose.

[0012] S16. Add water to the nanocellulose obtained in step S15 and shake well to obtain a nanocellulose suspension. Use an ultrasonic cell disruptor with a power of 600W to perform ultrasonic treatment on the suspension for 15 minutes. During this process, keep the temperature of the suspension below 60°C to finally obtain a uniformly dispersed nanocellulose suspension.

[0013] S2. Preparation of hydrogels, including preparation of hydrogel precursor solutions and hydrogel synthesis, specifically including the following sub-steps:

[0014] S21. Add water to PVA to prepare a PVA solution with a mass fraction of 5wt%~20wt%;

[0015] S22. The nanocellulose obtained in step S16 is added to the PVA solution prepared in step S21 to obtain mixture A, wherein the mass fraction of nanocellulose in mixture A is 2.5 wt%~3.5 wt%;

[0016] S23. Prepare an anhydrous sodium tetraborate solution with a mass fraction of 4%~8% by adding water. Add the obtained anhydrous sodium tetraborate solution to the mixture A obtained in step S22. The mass ratio of the anhydrous sodium tetraborate solution with a mass fraction of 4%~8% to the mixture A is 5:4 to obtain nanocellulose-based hydrogel.

[0017] Furthermore, the preparation method of the double crosslinked self-healing hydrogel also includes a step of removing impurities from the solid phase nanocellulose obtained in step S15. Specifically, deionized water is added to the solid phase nanocellulose obtained in step S15, the mixture is shaken well, and then centrifuged. This operation is repeated 3 times.

[0018] Furthermore, the sulfuric acid used in step S11 is concentrated sulfuric acid with a mass fraction of 98%, and the hydrochloric acid is hydrochloric acid with a mass fraction of 37%.

[0019] Furthermore, in step S14, the neutralization treatment involves adding sodium hydroxide with a mass fraction of 15%.

[0020] Furthermore, the preparation of the PVA solution in step S21 requires stirring at 80±5℃ for 1.5 hours.

[0021] Further, in step S22, the nanocellulose obtained in step S16 is added to the PVA solution prepared in step S21 to obtain mixture A, which needs to be stirred at 80±5℃ for 0.5 hours.

[0022] Furthermore, the anhydrous sodium tetraborate solution prepared in step S23 is prepared by stirring at 70±5℃.

[0023] The present invention also provides a double cross-linked self-healing hydrogel prepared by the above method.

[0024] Beneficial effects

[0025] 1. This invention proposes a highly efficient method for nano-forming microcrystalline cellulose, comprising acid hydrolysis and ultrasonic disruption. In the acid hydrolysis, a mixture of sulfuric acid and hydrochloric acid is used to treat the microcrystalline cellulose. Sulfuric acid can break the acid-sensitive β-1,4-glycosidic bonds in the microcrystalline cellulose, reducing the degree of polymerization and effectively removing amorphous regions. Replacing part of the sulfuric acid with hydrochloric acid not only removes impurities from the microcrystalline cellulose but also reduces the adverse effects of sulfuric acid on the product's thermal stability. This method achieves efficient preparation of nano-cellulose while ensuring product quality. The acid treatment process is combined with ultrasonic treatment. The energy, localized high temperature, high pressure, and cavitation effect generated by ultrasound can increase the surface area of ​​cellulose, promoting contact and reaction between the reagent and cellulose, and increasing the hydrolysis rate. Furthermore, the prepared nano-cellulose undergoes ultrasonic disruption for a certain period. The energy generated by high-intensity ultrasound can break down the cellulose. Appropriate ultrasonic disruption can avoid particle carbonization caused by localized high temperatures during ultrasonic disruption and further reduce the particle size. This invention prepares nano-cellulose with a sufficiently small diameter, reaching 10 nm. Compared with traditional single processing methods, the experimental conditions involved are simple and controllable, the cost is low, and the yield of nanocellulose is high.

[0026] 2. In the preparation of the hydrogel of this invention, anhydrous sodium tetraborate and polyvinyl alcohol (PVA) are used. Anhydrous sodium tetraborate dissociates in aqueous solution to release anhydrous sodium tetraborate ions (B4O7²⁻) and sodium ions (Na⁺). The anhydrous sodium tetraborate ions can form dynamic anhydrous sodium tetraborate ester bonds (BO-) with the hydroxyl groups (-OH) in PVA. This is a reversible covalent bond, which gives the prepared hydrogel self-healing properties. Furthermore, the hydroxyl groups on the surface of the nanocellulose can form hydrogen bonds and anhydrous sodium tetraborate ester bonds with PVA and anhydrous sodium tetraborate ions, respectively, exhibiting certain intermolecular forces. The nanocellulose prepared in this invention has both rod-shaped and spherical forms. The rod-shaped nanocellulose has physical entanglement with the PVA molecular chains, forming the network framework structure of the hydrogel, while the spherical nanocellulose can fully fill the pores of the hydrogel, further increasing the mechanical strength of the hydrogel.

[0027] 3. The nanocellulose particles prepared by this invention have uniform size, good thermal stability, and high crystallinity.

[0028] 4. The hydrogel prepared by this invention has excellent self-healing and stretchability. After being broken and then touched again, the hydrogel can recover in as little as 25 seconds, and when kneaded into a sphere, it can completely unfold in as little as 5 minutes and 39 seconds. Furthermore, the hydrogel can be stretched to a maximum of 2985% of its original size.

[0029] 5. The hydrogel prepared by this invention can be applied to fields such as environmental purification, wearable electronic devices, human-computer interaction interfaces, and health and medical testing. Attached Figure Description

[0030] Figure 1 This is a TEM image of the nanocellulose prepared in this invention. Figure 1 In the image, (a) is a TEM image of rod-shaped nanocellulose, and (b) is a TEM image of spherical nanocellulose.

[0031] Figure 2 X-ray diffraction pattern of the nanocellulose prepared in this invention;

[0032] Figure 3 Prepared for the present invention Figure 3 Thermogravimetric analysis diagram of nanocellulose;

[0033] Figure 4 Figure 2 shows the self-healing and tensile test results of the hydrogel in Example 2.

[0034] Figure 5 Figure 3 shows the self-healing and tensile test results of the hydrogel in Example 3.

[0035] Figure 6 The diagram shows the self-healing and stretching test results of the hydrogel in Example 4. Detailed Implementation

[0036] The invention will be further described below with reference to specific embodiments.

[0037] Example 1:

[0038] This embodiment describes a method for preparing a double-crosslinked self-healing hydrogel, which includes the following steps:

[0039] S1. Nanostructuring of microcrystalline cellulose: Microcrystalline cellulose is processed into nanocellulose using a combined method of mixed acid hydrolysis and ultrasonic treatment, specifically including the following sub-steps:

[0040] S11. To prepare a mixed acid solution, mix 45 ml of sulfuric acid and 15 ml of hydrochloric acid and add deionized water to bring the volume to 100 ml. The sulfuric acid used is concentrated sulfuric acid with a mass fraction of 98% and the hydrochloric acid is hydrochloric acid with a mass fraction of 37%.

[0041] S12. Add 2g of microcrystalline cellulose to the above mixed acid solution and stir until homogeneous to obtain a cellulose acid hydrolysis solution;

[0042] S13. Use a 120W ultrasonic cleaner to ultrasonically treat the solution described in step S12 for 8 hours. During this period, ice or water should be added or the water changed to avoid the temperature from getting too high.

[0043] S14. Neutralize the suspension after ultrasonic treatment by adding an appropriate amount of alkaline solution to the suspension.

[0044] S15. After centrifugation in step S14, the solution after neutralization is centrifuged to remove the liquid portion, and the resulting solid phase is nanocellulose containing certain impurities. Deionized water is added to the solid product, and the mixture is shaken and centrifuged again. This operation is repeated 3 times to obtain nanocellulose after impurity removal. The yield of nanocellulose obtained according to the above process is 50% ± 5%.

[0045] S16. Add water to the purified nanocellulose from S15 and shake well to obtain a nanocellulose suspension. Use a 600W ultrasonic cell disruptor to sonicate the suspension for 15 minutes, repeating this process three times with 15-minute intervals between each treatment. During this process, maintain the temperature of the suspension below 60℃ to obtain nanocellulose as shown. Figure 1 As shown. According to the applicant's testing, the cellulose nanospheres have a diameter of 13-38 nm, the rods have a diameter of 10-35 nm, and a length of approximately 200 nm. Figure 2 The X-ray diffraction pattern of the nanocellulose is shown, revealing a crystallinity of 82.75%. Furthermore, compared to nanocellulose prepared by traditional sulfuric acid hydrolysis, the nanocellulose of this invention exhibits better thermal stability. The thermogravimetric analysis (TGA) diagram of the nanocellulose is shown below. Figure 3The nanocellulose did not exhibit any sealing effect after being left at room temperature for 2 months, demonstrating its long-term stable dispersibility.

[0046] S2. Preparation of hydrogels, including preparation of hydrogel precursor solutions and hydrogel synthesis, specifically including the following sub-steps:

[0047] S21. Take 1.7g of PVA, add water to make up to 17g, stir at 80℃ for 1.5 hours to obtain a PVA solution with a mass fraction of 10wt%.

[0048] S22. Add 0.3g of the nanocellulose obtained in step S16 above to the PVA solution and stir at 80°C for 0.5 hours to obtain mixture A.

[0049] S23. Take 2g of anhydrous sodium tetraborate and add water to a final volume of 25g. Stir at 70℃ until the anhydrous sodium tetraborate is completely dissolved, obtaining a 4% (w / w) anhydrous sodium tetraborate solution. Add the anhydrous sodium tetraborate solution to mixture A to obtain a nanocellulose-based hydrogel. The nanocellulose-based hydrogel prepared in this embodiment, according to the applicant's testing, can recover from breakage and re-contact within 25 seconds, and when kneaded into a spherical shape, it can completely unfold within 5 minutes and 39 seconds. Furthermore, the hydrogel can be stretched up to 510% of its original size.

[0050] Example 2:

[0051] The difference between this embodiment and Embodiment 1 is that step S2. hydrogel preparation in this embodiment includes hydrogel precursor solution preparation and hydrogel synthesis, specifically including the following sub-steps:

[0052] Take 1.7g of PVA, add water to make up to 17g, stir at 80℃ for 1.5 hours to obtain a PVA solution with a mass fraction of 10wt%.

[0053] Add 0.5g of the nanocellulose obtained in step S16 above to the PVA solution and stir at 80°C for 0.5 hours to obtain mixture A.

[0054] Take 1g of anhydrous sodium tetraborate and add water to make up to 25g. Stir at 70℃ until the anhydrous sodium tetraborate is completely dissolved to obtain an anhydrous sodium tetraborate solution with a mass fraction of 4%. Add the anhydrous sodium tetraborate solution to mixture A to obtain nanocellulose-based hydrogel.

[0055] According to the applicant's tests, the hydrogel, after being broken and then re-contaminated, can recover in as little as 3 minutes and 19 seconds; when molded into a sphere, it can completely unfold in as little as 11 minutes and 51 seconds. Furthermore, the hydrogel can be stretched to a maximum of 720% of its original size. The unfolding process and stretching test results of the hydrogel are shown below. Figure 4 .

[0056] Example 3:

[0057] The difference between this embodiment and Embodiment 1 is that step S2. hydrogel preparation in this embodiment includes hydrogel precursor solution preparation and hydrogel synthesis, specifically including the following sub-steps:

[0058] Take 1.7g of PVA, add water to make up to 17g, stir at 80℃ for 1.5 hours to obtain a PVA solution with a mass fraction of 10wt%.

[0059] Add 0.5g of the nanocellulose obtained in step S16 above to the PVA solution and stir at 80°C for 0.5 hours to obtain mixture A.

[0060] Take 2g of anhydrous sodium tetraborate and add water to make up to 25g. Stir at 70℃ until the anhydrous sodium tetraborate is completely dissolved to obtain an 8% anhydrous sodium tetraborate solution. Add the anhydrous sodium tetraborate solution to mixture A to obtain nanocellulose-based hydrogel.

[0061] According to the applicant's tests, the hydrogel, after being broken and then re-contaminated, can recover in as little as 51 seconds, and when molded into a sphere, it can completely unfold in as little as 13 minutes and 17 seconds. Furthermore, the hydrogel can be stretched to a maximum of 1111% of its original size. The unfolding process and stretching test results of the hydrogel are shown in [link to details]. Figure 5 .

[0062] Example 4:

[0063] The difference between this embodiment and Embodiment 1 is that step S2. hydrogel preparation in this embodiment includes hydrogel precursor solution preparation and hydrogel synthesis, specifically including the following sub-steps:

[0064] Take 1.7g of PVA, add water to make up to 17g, stir at 80℃ for 1.5 hours to obtain a PVA solution with a mass fraction of 10wt%.

[0065] Add 1g of the nanocellulose obtained in step S16 above to the PVA solution and stir at 80°C for 0.5 hours to obtain mixture A.

[0066] Take 2g of anhydrous sodium tetraborate and add water to make up to 25g. Stir at 70℃ until the anhydrous sodium tetraborate is completely dissolved to obtain an 8% anhydrous sodium tetraborate solution. Add the anhydrous sodium tetraborate solution to mixture A to obtain nanocellulose-based hydrogel.

[0067] According to the applicant's tests, the hydrogel, after being broken and then re-contaminated, can recover in as little as 25 seconds, and when molded into a sphere, it can completely unfold in as little as 7 minutes and 39 seconds. Furthermore, the hydrogel can be stretched to a maximum of 2985% of its original size. The unfolding process and stretching test results of the hydrogel are shown below. Figure 6 .

[0068] The hydrogel prepared by this invention can be used in environmental purification, wearable electronic devices, human-computer interaction interfaces, health and medical testing and other fields, and participates in the preparation as a matrix material.

Claims

1. A method for preparing a double-crosslinked self-healing hydrogel, characterized in that, The method includes the following steps: S1. Nanostructuring of microcrystalline cellulose: Microcrystalline cellulose is processed into nanocellulose using a combined method of mixed acid hydrolysis and ultrasonic treatment, specifically including the following sub-steps: S11. Prepare a mixed acid solution with a volume fraction of 60% by adding deionized water using sulfuric acid and hydrochloric acid in a volume ratio of 3:

1. S12. Add microcrystalline cellulose to the mixed acid solution prepared in step S11 at a ratio of 1-2 grams of microcrystalline cellulose per 100 ml of mixed acid solution and stir until homogeneous to obtain a cellulose acid hydrolysis solution; S13. Use a 120W ultrasonic cleaner to ultrasonically treat the cellulose acid hydrolysate obtained in step S12 for 8 hours. During this period, ice or water needs to be added to keep the temperature below 80°C. S14. Neutralize the ultrasonically treated suspension to make it neutral; S15. After centrifugation in step S14, the liquid portion of the neutralized solution is removed to obtain nanocellulose; S16. Add water to the nanocellulose obtained in step S15 and shake well to obtain a nanocellulose suspension. Use an ultrasonic cell disruptor with a power of 600W to perform ultrasonic treatment on the suspension for 15 minutes. During this process, keep the temperature of the suspension below 60°C to finally obtain a uniformly dispersed nanocellulose suspension. S2. Preparation of hydrogels, including preparation of hydrogel precursor solutions and hydrogel synthesis, specifically including the following sub-steps: S21. Add water to PVA to prepare a PVA solution with a mass fraction of 5wt%~20wt%; S22. The nanocellulose obtained in step S16 is added to the PVA solution prepared in step S21 to obtain mixture A, wherein the mass fraction of nanocellulose in mixture A is 2.5 wt%~3.5 wt%; S23. Prepare an anhydrous sodium tetraborate solution with a mass fraction of 4%~8% by adding water. Add the obtained anhydrous sodium tetraborate solution to the mixture A obtained in step S22. The mass ratio of the anhydrous sodium tetraborate solution with a mass fraction of 4%~8% to the mixture A is 5:4 to obtain nanocellulose-based hydrogel. The method also includes a step of removing impurities from the solid phase nanocellulose obtained in step S15. Specifically, deionized water is added to the solid phase nanocellulose obtained in step S15, the mixture is shaken well, and then centrifuged. This operation is repeated 3 times.

2. The method for preparing a double-crosslinked self-healing hydrogel according to claim 1, characterized in that, The sulfuric acid used in step S11 is concentrated sulfuric acid with a mass fraction of 98%, and the hydrochloric acid is hydrochloric acid with a mass fraction of 37%.

3. The method for preparing a double-crosslinked self-healing hydrogel according to claim 1, characterized in that, In step S14, a sodium hydroxide solution with a mass fraction of 15% is added for the neutralization treatment.

4. The method for preparing a double-crosslinked self-healing hydrogel according to claim 1, characterized in that, The preparation of the PVA solution in step S21 requires stirring at 80±5℃ for 1.5 hours.

5. The method for preparing a double-crosslinked self-healing hydrogel according to claim 1, characterized in that, In step S22, the nanocellulose obtained in step S16 is added to the PVA solution prepared in step S21 to obtain mixture A, which needs to be stirred at 80±5℃ for 0.5 hours.

6. The method for preparing a double-crosslinked self-healing hydrogel according to claim 1, characterized in that, The anhydrous sodium tetraborate solution prepared in step S23 is prepared by stirring at 70±5℃.

7. A double-crosslinked self-healing hydrogel prepared by the method according to any one of claims 1-6.

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