High-transparency ultraviolet-resistant lignin-pva hydrogel, and preparation method and application thereof

Abstract

The application discloses a kind of high transparency ultraviolet-resistant lignin-PVA hydrogel and its preparation method and application.It is prepared by the method of alkali dissolution and acid deposition to prepare nano lignin, and modified lignin is prepared by Mannich reaction with hydrochloric acid dopamine;Modified lignin is uniformly dispersed in PVA aqueous solution, and lignin / PVA hydrogel is prepared by freeze-thaw method.Curative effect is as follows: the performance test result of high transparency ultraviolet-resistant lignin-PVA hydrogel prepared by the application: the antibacterial rate of S.aureus is 96%, the visible light transmittance at 750 nm is 67%, and the DPPH free radical scavenging rate is 96%.

Description

Technical Field

[0001] This invention relates to the field of biomass UV-resistant materials technology, specifically to a highly transparent UV-resistant lignin-PVA hydrogel, its preparation method, and its applications. Background Technology

[0002] With the depletion of the Earth's ozone layer, more and more ultraviolet (UV) radiation reaches the Earth's surface, and excessive UV exposure can cause significant harm to human production and daily life. UV radiation is considered a contributing factor to skin cancer, and it also causes adverse effects such as food spoilage, paper yellowing, and plastic aging. Therefore, UV-resistant materials have broad development prospects in medical protection, daily chemicals, building materials, and food packaging. Medical wound dressings, especially hydrogels, require direct observation of wound healing and infection status without removing the dressing, while also needing UV resistance to prevent damage to new skin tissue and pigmentation. Therefore, a hydrogel dressing that is opaque and lacks UV protection would severely affect clinical monitoring results and may lead to aesthetic and functional problems, making it unacceptable to the market.

[0003] In the prior art: CN104497341A discloses a method for preparing a photocrosslinked polyvinyl alcohol / lignin (PVA / lignin) composite film, belonging to the field of polymer materials and photosensitive materials. This invention first adds the natural polymer lignin, which crosslinks with PVA through hydrogen bonding. Then, it adds hydroxyethyl methacrylate (HEMA) molecules containing carbon-carbon double bonds and hydroxyl groups. HEMA undergoes a hydrogen bonding reaction with PVA, and simultaneously polymerizes under ultraviolet light irradiation to obtain a photocrosslinked PVA / lignin composite film. This composite film exhibits excellent water resistance, mechanical properties, and thermal stability, making its application in the field of biodegradable packaging materials possible.

[0004] CN110564096A discloses an anti-ultraviolet nano-lignin composite film and its preparation method. The composite film is composed of nano-lignin composite particles and a polymer carrier, wherein the mass ratio of nano-lignin composite particles to polymer carrier is 1:100800.

[0005] Currently, the UV protection properties of hydrogels are mainly achieved through two basic approaches: intrinsic UV protection and the addition of UV-resistant components. Intrinsic UV protection primarily utilizes polymers with conjugated structures such as benzene rings as the backbone or a dense, physically cross-linked hydrogel network with strong hydrogen bonds and crystalline microregions. However, these two methods are costly or offer weak UVA protection. Adding UV-resistant components is the most important and flexible method, including organic UV absorbers, inorganic UV shielding agents, and natural UV-resistant extracts. Huang et al. (ACS Appl. Mater. Interfaces 2023, 15, 14, 18300–18310) introduced benzotriazole organic UV absorbers into the polyurethane chain via in-situ polymerization, preparing a high-performance, colorless, and transparent UV-resistant film. However, its biocompatibility and long-term stability were not investigated, significantly limiting its application in wound dressings. Lignin, as a natural UV-resistant extract, possesses biocompatibility, antioxidant properties, and anti-inflammatory activities, showing strong application potential in the medical field. Lu et al. (International Journal of Biological Macromolecules 280 (2024) 135942) prepared a lignin / dopamine-based nano-Fe3O4 hydrogel, which exhibited good antibacterial and antioxidant activities. However, the addition of lignin and Fe3O4 resulted in a significant reduction in the transparency of the hydrogel.

[0006] In summary, in order to solve the problems of the prior art, the present invention provides a high-transparency, UV-resistant lignin-PVA hydrogel, its preparation method, and its application. Summary of the Invention

[0007] The purpose of this invention is to provide a highly transparent, UV-resistant lignin-PVA hydrogel, its preparation method, and its applications.

[0008] This invention uses an alkali-dissolution-acid-precipitation method to prepare nano-lignin particles (LNP), grafts dopamine (DA) onto LNP via the Mannich reaction to prepare dopamine-modified nano-lignin particles (LNP-DA), and uniformly disperses them in a polyvinyl alcohol (PVA) aqueous solution. PVA / LNP-DA composite hydrogels are then prepared by a cyclic freeze-thaw method.

[0009] The prepared PVA / LNP-DA composite hydrogel can balance high UV resistance and high visible light transmittance, and improve the antioxidant and antibacterial properties of lignin.

[0010] To achieve the above objectives, the following technical solutions are used: A method for preparing lignin-PVA hydrogel involves preparing nano-lignin by alkali dissolution and acid precipitation, and then preparing modified lignin by reacting it with dopamine hydrochloride via the Mannich reaction. Modified lignin was uniformly dispersed in PVA aqueous solution, and lignin / PVA hydrogel was prepared by cyclic freeze-thaw method.

[0011] As a further improvement to this solution, the following specific steps are included: S1 mechanically crushes unpurified lignin raw material, sieves it to obtain micron-sized lignin fine powder LMP, disperses it in deionized water, prepares nano-lignin by alkali dissolution and acid precipitation, and obtains lignin nanoparticle LNP water-based dispersion system by centrifugation purification. S2 mixes a uniformly dispersed lignin dispersion with dopamine hydrochloride, adjusts the pH of the system with dilute hydrochloric acid, then adds a trace amount of aldehyde under heating and heat preservation conditions, reacts under anaerobic conditions, and finally obtains dopamine-modified lignin powder by centrifugation purification. S3 prepared a PVA aqueous solution by mixing PVA powder with ultrapure water under high temperature conditions with continuous stirring, and then introduced dopamine-modified lignin powder with different contents to prepare a composite hydrogel by cyclic freeze-thaw method. in, The ratio of nano-lignin to dopamine hydrochloride is between 1:0.1 and 1:5; The ratio of nano-lignin to aldehydes is between 104:1 and 103:1; In step (3), the ratio of PVA powder to dopamine-modified lignin powder is 100:1-10:1.

[0012] As a further improvement to this scheme, the nano-lignin is at least one of alkali lignin, sulfonate lignin, enzymatically hydrolyzed lignin, and organic solvent lignin.

[0013] As a further improvement to this scheme, the aldehydes mentioned in step (2) are at least one of glyoxal, glutaraldehyde, and terephthalaldehyde.

[0014] As a further improvement to this scheme, the heating reaction temperature in step (2) is 50-110 ℃ and the time is 1-8h.

[0015] As a further improvement to this scheme, the mixing temperature of PVA and ultrapure water in step (3) is 60-120 ℃ and the time is 0.5-6 h.

[0016] As a further improvement to this scheme, the mixing temperature of the PVA aqueous solution and the dopamine-modified lignin in step (3) is 15-50 °C and the time is 1-45 min.

[0017] As a further improvement to this scheme, the freezing temperature of the cyclic freeze-thaw method in step (3) is -10~-50 ℃, the time is 2-10 h, the thawing temperature is 5-28 ℃, the time is 0.5-5 h, and the freeze-thaw cycle is completed at least 2 times.

[0018] A lignin-PVA hydrogel, wherein the lignin-PVA hydrogel is prepared by the method for preparing lignin-PVA hydrogel according to any one of claims 1 to 8.

[0019] An application of lignin-PVA hydrogel: The preparation method of lignin-PVA hydrogel yields lignin-PVA hydrogels for use in antibacterial and anti-inflammatory biomaterials, drug delivery, and medical materials.

[0020] The high-transparency, UV-resistant lignin-PVA hydrogel of the present invention has the following beneficial effects: (1) This invention uses lignin as raw material. Lignin is abundant and is the second most abundant organic compound in the world, second only to cellulose. It is plentiful and green and recyclable. At the same time, it uses the biocompatible drug dopamine hydrochloride as a reactant, water as a solvent, and PVA as a hydrogel matrix. The reaction conditions are mild and there are no toxic byproducts, which conforms to the principles of green chemistry. In addition, it improves the UV resistance while increasing the transmittance of visible light.

[0021] (2) The modified nano-lignin particles of the present invention do not require the addition of other functional fillers. Since the raw material itself contains multiple phenolic hydroxyl groups, it has biological activity, such as ultraviolet shielding performance and free radical scavenging (anti-inflammatory) performance. In addition, the synthesized modified nano-lignin particles and hydrogels are environmentally friendly and in line with the general trend of sustainable development.

[0022] (3) Existing natural UV-resistant extracts are mostly tannic acid, gallic acid, tea polyphenols, etc. These raw materials have been used efficiently in other fields such as food and papermaking and have high utilization value. Lignin is inexpensive and has not been well utilized, which can effectively improve the utilization rate of lignin.

[0023] (4) The performance test results of the high transparency and UV-resistant lignin-PVA hydrogel prepared by the present invention are as follows: the antibacterial rate of S. aureus increased to 96%, the visible light transmittance at 750 nm increased to 67%, and the DPPH free radical scavenging rate increased to 96%. Attached Figure Description

[0024] Figure 1 The image shows the Fourier transform infrared (FTIR) spectrum of dopamine hydrochloride-modified lignin nanoparticles. The FTIR spectrum shows that the benzene ring content of the lignin nanoparticles increases and the stretching vibration of the conjugated double bonds of the benzene rings is enhanced, which proves that the Mannich reaction successfully prepared dopamine hydrochloride-modified lignin nanoparticles.

[0025] Figure 2 The visible-ultraviolet transmittance spectrum of lignin / PVA hydrogel is shown.

[0026] Figure 3 The UV absorption curves of lignin / PVA hydrogel for ABTS free radicals are shown. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described below in conjunction with embodiments and accompanying drawings: Unless otherwise specified, all the raw materials used in this invention are commercially available.

[0028] The enzymatically hydrolyzed lignin used in the following examples was purchased from Shandong Longli Biotechnology Co., Ltd. Sodium hydroxide and hydrochloric acid were purchased from Sinopharm Chemical Reagent Co., Ltd., dopamine hydrochloride and polyvinyl alcohol were purchased from Shanghai Aladdin Biochemical Technology Co., Ltd., and glyoxal was purchased from Adamas Reagent Co., Ltd.

[0029] The UV shielding performance of each group of samples was analyzed using a UV-Vis-NIR spectrophotometer (UV-3600 plus, Tsushima, Japan) in transmission mode. During the test, the scanning speed was medium, and the scanning range was 280-780 nm.

[0030] The antioxidant properties were tested by determining the free radical scavenging rate using the DPPH method. Specifically, the sample was dissolved and mixed with DPPH solution, with the solvent used as a blank control, and the absorbance of the mixed solution was tested. 200.0 mg of ABTS and 34.4 mg of potassium persulfate were weighed and dissolved in 50.0 mL of distilled water. After standing at room temperature in the dark for 24 h, this was used as the ABTS stock solution. An appropriate amount of the ABTS stock solution was taken and diluted with 95% ethanol to an absorbance value within 0.70 ± 0.02 (OD734) to obtain the ABTS assay solution. This solution should be prepared fresh before use. 3 g of the hydrogel material prepared from PVA and its composite system was cut and 10 g of ethanol was added, and the mixture was allowed to stand in the dark for 72 h to obtain the hydrogel leachate sample solution. The ABTS system was mixed at a 9:1 ratio (3.6 mL + 0.4 mL) and treated in the dark for 5 min, with pure solvent (ethanol) used as a blank control. Three parallel scans were performed in the wavelength range of 600-900 nm using a double-beam UV-Vis spectrophotometer (TU-1950, Presee, China). The free radical scavenging efficiency (RSA) of each group of samples was calculated using the following formula: ,in and The figures represent the fitted areas of the absorbance curves of the blank control and the sample solution within a specific wavelength range (fitting range: 726-776 nm).

[0031] Antimicrobial properties were tested using a Gram-positive bacteria (Staphylococcus aureus) test, characterized by bacterial colony counting. The glycerol tubes were frozen at -80°C. S Aureus was inoculated into liquid medium and cultured at 37 °C with shaking at 200 rpm for 12 h until the logarithmic growth phase (1 × 10⁻⁶). 8 CFU / mL). The activated bacterial solution was serially diluted tenfold with sterile PBS to 1×10⁻⁶ CFU / mL. 5 CFU / mL; the hydrogel sample extract was sterilized by UV and mixed with 1 mL of bacterial solution, and cultured at 37 ℃ and 200 rpm for 3 h with shaking; 50 μL of culture solution was evenly spread on agar plates, and after incubation at 37 ℃ for 24 h, the surviving colonies were counted; an equal volume of PBS buffer (pH=7.4) was used as a control group to replace the sample solution and cultured with the bacterial solution; the antibacterial rate (A) was calculated by formula (3-1): ,in and These represent the colony counts in the culture media of the control group and the sample group, respectively.

[0032] Example 1 (1) The lignin raw material was mechanically pulverized and then sieved to obtain micron-sized lignin fine powder (LMP). 8g of the sieved product was weighed and placed in 400 mL of deionized water for dispersion. Under magnetic stirring, 2 mol / L sodium hydroxide solution was added dropwise until the reaction medium reached a stable alkaline environment (pH=12). This homogenization process was carried out continuously in a constant temperature environment of 25±2 ℃. After alkalization, the mixture was stirred for 60 min, and then impurities were removed by filtration. Then, 0.5 mol / L dilute hydrochloric acid was slowly added dropwise until pH=2 to precipitate the nano-lignin particles. A water-based dispersion system of lignin nanoparticles (LNP) with pH=7.0 was obtained after three centrifugation-washing processes. (2) Weigh the LNP colloidal solution containing 0.8 g of solid particles and sonicate for 30 min. Then add 0.8 g of dopamine monomer and mix thoroughly under magnetic stirring. Add 0.5 mol / L dilute hydrochloric acid dropwise to adjust the pH of the system to 2.0, then purge with nitrogen to establish an anaerobic environment, and then add 480 μL of glyoxal. Continue the reaction under a constant temperature oil bath at 70℃ for 4 h. After centrifugation and washing three times, remove the supernatant to obtain dopamine hydrochloride modified lignin suspension (LNP-DA). (3) Weigh 5 g of PVA powder and mix it with 45 g of ultrapure water. Stir continuously at 90 ℃ for 2 h to prepare a 10 wt% PVA aqueous solution. When the solution temperature drops to 50-60 ℃, introduce 0.05 g of LNP-DA into 50 g of PVA base solution and stir at 25 ℃ for 10 min. Inject the composite sol into a special aluminum alloy mold (Φ4.8 cm×H1.8 cm) to implement a cyclic freeze-thaw crosslinking process. Each cycle includes alternating processes of -20 ℃ deep cryogenic treatment for 6 h and thawing at 25 ℃ for 2 h. A total of three complete freeze-thaw cycles are completed to finally obtain the composite hydrogel.

[0033] Example 2 Referring to Example 1, the pH value of the alkaline environment in step (1) was changed to 10, the pH value of the acidic environment was changed to 3, and the other conditions remained unchanged.

[0034] Example 3 Referring to Example 1, the amount of glyoxal added in step (2) was changed to 120 μL, while the other conditions remained unchanged.

[0035] Example 4 Referring to Example 1, the amount of dopamine added in step (2) was changed to 0.2 g, while the other conditions remained unchanged.

[0036] Example 5 Referring to Example 1, step (2) was changed to a continuous reaction under a constant temperature oil bath at 80°C for 6 hours, while the other conditions remained unchanged.

[0037] Example 6 Referring to Example 1, step (2) was changed to introduce 0.25 g of LNP-DA into 50 g of PVA base solution, while the other conditions remained unchanged.

[0038] Comparative Example 1 Referring to Example 1, steps (1, 2) were modified as follows: 0.8 g of micron-sized lignin powder (LMP) obtained by mechanical pulverization and sieving, and 0.8 g of dopamine monomer were dispersed in an aqueous solution and thoroughly mixed under magnetic stirring. 0.5 mol / L dilute hydrochloric acid was added dropwise to adjust the pH of the system to 2.0. Then, nitrogen gas was introduced to establish an anaerobic environment, followed by the addition of 480 μL of glyoxal. The reaction was continued for 4 h under a constant temperature oil bath at 70°C. After three cycles of centrifugation and washing, the supernatant was removed to obtain a dopamine hydrochloride-modified lignin suspension (LNP-DA). The conditions for step (3) remained unchanged.

[0039] Comparative Example 2 Referring to Example 1, step (2) is omitted, and 0.05 g of LNP is introduced into 50 g of PVA base liquid in step (3), while the other conditions remain unchanged.

[0040] Comparative Example 3 Referring to Example 1, glyoxal was not added in step (2), and the other conditions remained unchanged.

[0041] Comparative Example 4 Weigh 5 g of PVA powder and mix it with 45 g of ultrapure water. Stir continuously at a constant temperature of 90 ℃ for 2 h to prepare a 10 wt% PVA aqueous solution. PVA was then injected into a specially made aluminum alloy mold (Φ4.8 cm × H1.8 cm) and subjected to a cyclic freeze-thaw crosslinking process. Each cycle consisted of alternating processes of deep cryogenic treatment at -20 ℃ for 6 h and thawing at 25 ℃ for 2 h. A total of three complete freeze-thaw cycles were completed to finally obtain the hydrogel.

[0042] Comparative Example 5 Referring to Example 1, in step (2), the dopamine monomer was replaced with phenylethylamine, while the other conditions remained unchanged.

[0043] Table 1. Comparison of the properties of the high-transparency, UV-resistant lignin / PVA hydrogels prepared in this invention. Figure 1 The infrared spectrum of dopamine hydrochloride-modified nanolignin prepared by the method of the present invention in Example 1 is shown. In the infrared spectrum, 1600-1450 cm⁻¹ -1 The four characteristic peaks at 1125 cm⁻¹ are attributed to the stretching vibrations of the conjugated double bonds in the benzene ring. Dopamine contains a benzene ring, and the benzene ring content in the LNP molecule increases after modification with dopamine, thus enhancing the stretching vibrations of the conjugated double bonds in the benzene ring. -1 The characteristic peaks at the α-ray peaks are attributed to the CN stretching vibrations of primary or secondary amines. The Mannich reaction grafts the amine source dopamine onto the LNP molecule, enhancing the CN stretching vibrations of the modified molecule. Combined infrared analysis confirms the successful preparation of LNP-DA via the Mannich reaction.

[0044] Examples 1-6 investigated the changes in visible and ultraviolet light transmittance by varying reaction time, temperature, pH, and reactant amounts, revealing significant performance differences. This may be due to varying degrees of lignin modification, resulting in different contents of phenolic hydroxyl groups and catechol structures that contribute to antibacterial and antioxidant activity, as well as differences in the content of hydrophilic and adhesive groups that improve the compatibility between lignin and PVA, thus affecting visible light transmittance and leading to performance variations.

[0045] Comparative Example 5 is a pure PVA hydrogel, which exhibits almost no antibacterial activity, very poor antioxidant capacity, and high UV transmittance at 340 nm. Comparative Example 2 is an unmodified dopamine-based lignin hydrogel, where dopamine modification significantly impacts its antibacterial, antioxidant, and visible light transmittance properties compared to Example 1. S The antibacterial rate of *Aureus* decreased from 96% to 62%, the visible light transmittance at 750 nm decreased from 67% to 53%, and the DPPH free radical scavenging rate decreased from 96% to 86%. Comparative Example 5, by grafting LNP with phenethylamine, did not show improved antioxidant (89%) and antibacterial (63%) properties due to the lack of phenolic hydroxyl structures in phenethylamine; the results were similar to Comparative Example 2.

[0046] This invention discloses a method for preparing a high-transparency, UV-resistant lignin / PVA hydrogel using lignin, dopamine hydrochloride, and PVA as raw materials. Lignin is chemically modified via the Mannich reaction to obtain an LNP-DA derivative, which is then added to the hydrogel system to regulate UV and visible light transmittance, resulting in a high-transparency, UV-resistant lignin / PVA hydrogel. This method further clarifies the UV-visible light transmittance of lignin. The lignin / PVA hydrogel of this invention exhibits good antioxidant and antibacterial properties.

[0047] Based on the above tests, the high-transparency, UV-resistant lignin / PVA hydrogel prepared in this invention exhibits good antioxidant and antibacterial properties. This may be because lignin itself contains chromophores such as aromatic rings, phenolic hydroxyl groups, and carbonyl groups, which can absorb ultraviolet light. During the dopamine modification process, dopamine monomers react with lignin nanoparticles under acidic conditions (pH=2) and the action of glyoxal, introducing catechol groups and potentially forming polydopamine-like structures. These new groups have a wider ultraviolet absorption band, effectively absorbing ultraviolet light in both the UVA and UVB regions, thus significantly enhancing the UV shielding capability of the composite hydrogel. Simultaneously, the reaction between dopamine and lignin may form an extended conjugated system, further reducing ultraviolet light transmittance. Under acidic conditions of pH=2, dopamine tends to covalently crosslink with lignin rather than self-polymerize, but can still form structures with ultraviolet absorption capabilities. Unmodified lignin (LNP) readily aggregates in a PVA matrix. Due to refractive index mismatch, these aggregates cause strong light scattering, leading to reduced transmittance in the visible light region (especially 600–800 nm). After dopamine modification, the LNP-DA surface is coated with dopamine derivatives. These hydrophilic and adhesive groups improve the interfacial compatibility between lignin and PVA, resulting in more uniform particle dispersion within the PVA, reducing particle size and aggregation, and thus lowering light scattering. Dopamine coating on the lignin surface may also make the LNP-DA surface smoother, reducing diffuse reflection at the interface and further improving transparency. Nano-lignin itself contains phenolic hydroxyl groups; after dopamine grafting, the phenolic hydroxyl groups and catechol groups work together to form a synergistic antioxidant effect, significantly improving free radical scavenging efficiency. Furthermore, the small size of nano-lignin improves its dispersibility in the medium, allowing for more complete exposure of antioxidant groups, increasing contact opportunities with free radicals, and thus enhancing reaction kinetics. The phenolic hydroxyl structure of lignin and the catechol structure of dopamine can generate reactive oxygen species (ROS). These ROS exceed the scavenging capacity of bacterial antioxidant systems, oxidizing lipids, proteins, and nucleic acids in bacterial cell membranes, leading to cell membrane rupture and metabolic dysfunction, ultimately resulting in cell death. The high specific surface area of ​​nano-lignin enhances its contact efficiency with bacteria, while its small particle size may directly penetrate the bacterial cell wall or membrane, causing physical damage. This effect, combined with chemical action, can significantly improve antibacterial efficiency.

[0048] The above description is only a preferred embodiment of the present invention and does not limit the patent scope of the present invention. All equivalent modifications made using the present invention are within the patent protection scope of the present invention.

Claims

1. A method for preparing a lignin-PVA hydrogel, characterized in that, Nano-lignin was prepared by alkali dissolution and acid precipitation, and modified lignin was prepared by reaction with dopamine hydrochloride. Modified lignin was uniformly dispersed in PVA aqueous solution, and lignin / PVA hydrogel was prepared by cyclic freeze-thaw method.

2. The method for preparing lignin-PVA hydrogel according to claim 1, characterized in that, The specific steps include the following: S1 mechanically crushes unpurified lignin raw material, sieves it to obtain micron-sized lignin fine powder LMP, disperses it in deionized water, prepares nano-lignin by alkali dissolution and acid precipitation, and obtains lignin nanoparticle LNP water-based dispersion system by centrifugation purification. S2 mixes a uniformly dispersed lignin dispersion with dopamine hydrochloride, adjusts the pH of the system with dilute hydrochloric acid, then adds a trace amount of aldehyde under heating and heat preservation conditions, reacts under anaerobic conditions, and finally obtains dopamine-modified lignin powder by centrifugation purification. S3 prepared a PVA aqueous solution by mixing PVA powder with ultrapure water under high temperature conditions with continuous stirring, and then introduced dopamine-modified lignin powder with different contents to prepare a composite hydrogel by cyclic freeze-thaw method. The ratio of nano-lignin to dopamine hydrochloride is between 1:0.1 and 1:

5. The ratio of nano-lignin to aldehyde is 10. 4 :1-10 3 Between 1 and 2; In step (3), the ratio of PVA powder to dopamine-modified lignin powder is 100:1-10:

1.

3. The method for preparing lignin-PVA hydrogel according to claim 2, characterized in that, The nano-lignin is at least one of alkali lignin, sulfonate lignin, enzymatically hydrolyzed lignin, and organic solvent lignin.

4. The method for preparing lignin-PVA hydrogel according to claim 2, characterized in that, The aldehydes mentioned in step (2) are at least one of glyoxal, glutaraldehyde, and terephthalaldehyde.

5. The method for preparing lignin-PVA hydrogel according to claim 2, characterized in that, The heating reaction in step (2) is carried out at a temperature of 50-110 ℃ for 1-8 hours.

6. The method for preparing lignin-PVA hydrogel according to claim 2, characterized in that, In step (3), the PVA is mixed with ultrapure water at a temperature of 60-120 ℃ for a time of 0.5h-6h.

7. The method for preparing lignin-PVA hydrogel according to claim 2, characterized in that, In step (3), the PVA aqueous solution and dopamine-modified lignin are mixed at a temperature of 15-50 °C for 1 min-45 min.

8. The method for preparing lignin-PVA hydrogel according to claim 2, characterized in that, In step (3), the freezing temperature of the cyclic freeze-thaw method is -10 to -50 ℃, the time is 2-10h, the thawing temperature is 5-28 ℃, the time is 0.5-5h, and the freeze-thaw cycle is completed at least 2 times.

9. A lignin-PVA hydrogel, characterized in that, The lignin-PVA hydrogel is prepared by the method for preparing lignin-PVA hydrogel according to any one of claims 1 to 8.

10. An application of a lignin-PVA hydrogel, characterized in that, The lignin-PVA hydrogel prepared by any one of claims 1 to 8 can be used in antibacterial and anti-inflammatory biomaterials, drug delivery, and medical materials.

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