A strong stretchable hydrogel based on aromatic eutectic ionic liquid amphoteric lignin nanoparticles and its preparation method

Abstract

The present invention belongs to the field of biomass technology, and specifically discloses a strong stretchable hydrogel based on aromatic low eutectic ionic liquid amphoteric lignin nanoparticles and a preparation method thereof. The preparation steps are as follows: dissolve lignin in aromatic low eutectic ionic liquid, uniformly mix with gelatin solution, acrylic acid, and initiator at a certain temperature and time, and then transfer the mixed solution to a mold and polymerize in an oven to obtain a hydrogel. Mechanical tests show that the synthesized hydrogel has super strong tensile properties (1457%). The present invention significantly improves the tensile properties of the hydrogel by amphotericizing the surface charge of lignin nanoparticles through the supramolecular interaction between aromatic low eutectic ionic liquid and lignin. The present invention has the advantages of being green and environmentally friendly, low cost, simple steps, and safe process, and has broad application prospects in the fields of stretchable sensors, flexible sensing, tissue engineering, etc.

Description

Technical Field

[0001] The invention relates to a strong stretchable hydrogel based on aromatic eutectic ionic liquid amphoteric lignin nanoparticles and a preparation method thereof, belonging to the technical field of biomass. Background Art

[0002] Hydrogel is a polymer material with a three-dimensional cross-linked structure and has a wide range of applications in many fields, but its fragility has always been considered a fatal flaw of traditional hydrogels. Lignin, as a natural renewable polymer biomass resource with abundant reserves and huge potential, has attracted increasing attention. In particular, preparing lignin into nano-sized particles can provide a rigid three-dimensional network structure for hydrogels. However, due to the inherent heterogeneity of lignin nanoparticles (LNPs), they have poor compatibility with the cross-linked matrix, making the hydrogel prone to stress points and breakage during stretching, which limits its application in large strain scenarios. Therefore, enhancing the interaction between LNPs and the cross-linked matrix will significantly improve the tensile properties of hydrogels and expand the application scenarios of hydrogels.

[0003] Modifying the surface charge of amphiphilic LNPs is considered an effective solution. Previous studies have shown that introducing amphiphilic charges into hydrogels can form additional dipole-dipole interactions with polymer chain groups, thereby enhancing the stretchability of the hydrogel. Therefore, modifying the surface charge of amphiphilic LNPs is also expected to significantly improve the stretchability of hydrogels. However, research on amphiphilic LNPs is currently very limited. Most existing studies have utilized negatively charged lignin to crosslink with other positively charged matrices to synergistically construct amphiphilic hydrogels. For example, in a recent study by Sun et al. (Chemical Engineering Journal, 2024, 495:153781), sulfonic acid groups were introduced into lignin and quaternary ammonium groups into chitosan via a grafting method. Using these two as raw materials, they developed an amphiphilic hydrogel with excellent tensile properties, achieving a tensile strain of 927.32%. However, this preparation process often requires the use of toxic reagents such as concentrated alkali and acetone, which pose significant health risks to humans. Furthermore, the complex grafting reactions, dialysis, and freeze-thaw cycles required complicated preparation processes and long production cycles. Therefore, finding green, harmless and easy-to-operate methods for preparing amphoteric LNPs and exploring new ways to efficiently prepare amphoteric LNPs have important research significance and application value.

[0004] To address the above issues, amphiphilic LNPs can be self-assembled into them through self-assembly behavior in solution and the use of supramolecular interactions between molecules. As a green ionic liquid, low eutectic solvents can form hydrogen bonds and electrostatic interactions with monomers, providing an opportunity to realize the above concept. In particular, because the structure of aromatic low eutectic ionic liquids contains positively charged aromatic groups, they can form π-π interactions with the aromatic rings in LNPs and spontaneously attach to the surface of LNPs. At the same time, because LNPs contain groups such as carboxyl groups, they themselves have a certain degree of negative charge. Therefore, through the above-mentioned self-assembly method based on π-π interactions, it is expected to synthesize amphiphilic LNPs.

[0005] Based on this, the present invention uses supramolecular interactions between an aromatic eutectic ionic liquid and lignin to amphotericize the surface charge of lignin nanoparticles, significantly improving the tensile properties of the hydrogel. This method is environmentally friendly, low-cost, simple, and safe, and has broad application prospects in stretchable sensors, flexible sensing, tissue engineering, and other fields. Summary of the Invention

[0006] The purpose of the present invention is to provide a new method for strengthening the tensile properties of hydrogels by using amphoteric lignin nanoparticles based on aromatic low eutectic ionic liquid.

[0007] The technical solution adopted by the present invention is: dissolving lignin into an aromatic low-melting ionic liquid, uniformly mixing it with a gelatin solution, acrylic acid, and an initiator at a certain temperature and time, and then transferring the mixed solution into a mold and polymerizing it in an oven to obtain a hydrogel.

[0008] Furthermore, the aromatic eutectic ionic liquid is one or a combination of benzyltrimethylammonium chloride, benzyltrimethylammonium bromide, benzyltrimethylammonium iodide, benzyltriethylammonium chloride, benzyltriethylammonium bromide, and benzyltriethylammonium iodide.

[0009] Furthermore, the lignin is one of alkali lignin, enzymatic lignin, and lignin sulfonate.

[0010] Furthermore, the initiator is one or more of potassium persulfate, sodium persulfate, and ammonium persulfate.

[0011] Furthermore, in the experiment, the mass ratio of lignin: eutectic ionic liquid: gelatin: water: acrylic acid: initiator = 0.01-0.04 g: 1-5 g: 0.5-2.5 g: 4-9 mL: 6-11 mL: 0.1 g.

[0012] Furthermore, in the experiment, the temperature of the heating polymerization is 40 to 80° C., and the time is 1 to 7 hours.

[0013] The beneficial effects of the present invention are:

[0014] 1. Developed a new method for preparing amphoteric lignin nanoparticles: This invention utilizes the supramolecular interaction between aromatic low-melting ionic liquids and LNPs to amphotericize the surface charge of LNPs, and developed a green and simple one-step method for preparing amphoteric LNPs, providing a new idea for the purposeful construction of LNPs with relevant structure and performance.

[0015] 2. A new method for synthesizing highly stretchable hydrogels has been developed: The present invention introduces amphoteric LNPs into hydrogels, significantly improving the tensile properties of the hydrogel by strengthening the dipole-dipole interaction. A new method for synthesizing highly stretchable hydrogels has been developed, which has broad application prospects in the fields of stretchable sensors, flexible sensing, tissue engineering, etc.

[0016] 3. Broadens the application of eutectic ionic liquids: This invention leverages the aromatic properties of aromatic eutectic ionic liquids to zwitterionize the surface charge of LNPs through π-π interactions with the aromatic rings of lignin, enabling microscopic control of LNP properties. This invention transcends the traditional use of eutectic ionic liquids as solvents and provides an important technical reference for novel functional applications of eutectic ionic liquids. DETAILED DESCRIPTION

[0017] For a better understanding of the present invention, the present invention is further described below with reference to examples, but the embodiments of the present invention are not limited thereto.

[0018] Example 1

[0019] 0.02g of enzymatically hydrolyzed lignin was completely dissolved in 3g of a eutectic ionic liquid (benzyltrimethylammonium chloride and ethylene glycol mixed in a 1:3 molar ratio). The mixture was then mixed at 60°C with a gelatin solution (0.5g of gelatin added to 5ml of water), 8ml of acrylic acid, and 0.1g of potassium persulfate. The mixed solution was transferred to a mold and polymerized in an oven at 55°C for 6h to produce a lignin-acrylic acid-based hydrogel. Mechanical testing showed a tensile strain of 667%.

[0020] Example 2

[0021] 0.02g of enzymatically hydrolyzed lignin was completely dissolved in 3g of a eutectic ionic liquid (benzyltrimethylammonium chloride and ethylene glycol mixed in a 1:3 molar ratio). The mixture was then mixed at 60°C with a gelatin solution (2.5g of gelatin added to 5ml of water), 8ml of acrylic acid, and 0.1g of potassium persulfate. The resulting mixture was transferred to a mold and polymerized in an oven at 55°C for 6h to produce a lignin-acrylic acid-based hydrogel. Mechanical testing showed a tensile strain of 681%.

[0022] Example 3

[0023] 0.02g of enzymatically hydrolyzed lignin was completely dissolved in 3g of a eutectic ionic liquid (benzyltrimethylammonium chloride and ethylene glycol mixed in a 1:3 molar ratio). The mixture was then mixed at 60°C with a gelatin solution (1.5g of gelatin added to 5ml of water), 6mL of acrylic acid, and 0.1g of potassium persulfate. The mixed solution was transferred to a mold and polymerized in an oven at 55°C for 6h to produce a lignin-acrylic acid-based hydrogel. Mechanical testing showed a tensile strain of 900%.

[0024] Example 4

[0025] 0.02g of enzymatically hydrolyzed lignin was completely dissolved in 3g of a eutectic ionic liquid (benzyltrimethylammonium chloride and ethylene glycol mixed in a 1:3 molar ratio). The mixture was then mixed at 60°C with a gelatin solution (1.5g of gelatin added to 5ml of water), 11ml of acrylic acid, and 0.1g of potassium persulfate. The resulting mixture was transferred to a mold and polymerized in an oven at 55°C for 6 hours to produce a lignin-acrylic acid-based hydrogel. Mechanical testing showed a tensile strain of 494%.

[0026] Example 5

[0027] 0.02g of enzymatically hydrolyzed lignin was completely dissolved in 3g of a eutectic ionic liquid (benzyltrimethylammonium chloride and ethylene glycol mixed in a 1:3 molar ratio). The mixture was then mixed at 60°C with a gelatin solution (1.5g of gelatin added to 4ml of water), 8ml of acrylic acid, and 0.1g of potassium persulfate. The mixed solution was transferred to a mold and polymerized in an oven at 55°C for 6h to produce a lignin-acrylic acid-based hydrogel. Mechanical testing showed a tensile strain of 957%.

[0028] Example 6

[0029] 0.02g of enzymatically hydrolyzed lignin was completely dissolved in 3g of a eutectic ionic liquid (benzyltrimethylammonium chloride and ethylene glycol mixed in a 1:3 molar ratio). The mixture was then mixed at 60°C with a gelatin solution (1.5g of gelatin added to 9ml of water), 8ml of acrylic acid, and 0.1g of potassium persulfate. The mixed solution was transferred to a mold and polymerized in an oven at 55°C for 6h to produce a lignin-acrylic acid-based hydrogel. Mechanical testing showed a tensile strain of 615%.

[0030] Example 7

[0031] 0.02g of enzymatically hydrolyzed lignin was completely dissolved in 1g of a eutectic ionic liquid (benzyltrimethylammonium chloride and ethylene glycol mixed in a 1:3 molar ratio). The mixture was then mixed at 60°C with a gelatin solution (1.5g of gelatin added to 5ml of water), 8ml of acrylic acid, and 0.1g of potassium persulfate. The mixed solution was transferred to a mold and polymerized in an oven at 55°C for 6 hours to produce a lignin-acrylic acid-based hydrogel. Mechanical testing showed a tensile strain of 509%.

[0032] Example 8

[0033] 0.02g of enzymatically hydrolyzed lignin was completely dissolved in 5g of a eutectic ionic liquid (benzyltrimethylammonium chloride and ethylene glycol mixed in a 1:3 molar ratio). The mixture was then mixed at 60°C with a gelatin solution (1.5g of gelatin added to 5ml of water), 8ml of acrylic acid, and 0.1g of potassium persulfate. The resulting mixture was transferred to a mold and polymerized in an oven at 55°C for 6 hours to produce a lignin-acrylic acid-based hydrogel. Mechanical testing showed a tensile strain of 1297%.

[0034] Example 9

[0035] 0.015g of enzymatically hydrolyzed lignin was completely dissolved in 3g of a eutectic ionic liquid (benzyltrimethylammonium chloride and ethylene glycol mixed in a 1:3 molar ratio). The mixture was then mixed at 60°C with a gelatin solution (1.5g of gelatin added to 5ml of water), 8ml of acrylic acid, and 0.1g of potassium persulfate. The resulting mixture was transferred to a mold and polymerized in an oven at 55°C for 6h to produce a lignin-acrylic acid-based hydrogel. Mechanical testing showed a tensile strain of 1268%.

[0036] Example 10

[0037] 0.02g of enzymatically hydrolyzed lignin was completely dissolved in 3g of a eutectic ionic liquid (benzyltrimethylammonium chloride and ethylene glycol mixed in a 1:3 molar ratio). The mixture was then mixed at 60°C with a gelatin solution (1.5g of gelatin added to 5ml of water), 8ml of acrylic acid, and 0.1g of potassium persulfate. The mixed solution was transferred to a mold and polymerized in an oven at 55°C for 6h to produce a lignin-acrylic acid-based hydrogel. Mechanical testing showed a tensile strain of 1457%.

[0038] Comparative Example 1

[0039] 0.015g of enzymatically hydrolyzed lignin was completely dissolved in 3g of a eutectic ionic liquid (choline chloride and ethylene glycol mixed in a 1:3 molar ratio). The mixture was then mixed at 60°C with a gelatin solution (1.5g of gelatin added to 5ml of water), 8ml of acrylic acid, and 0.1g of potassium persulfate. The resulting mixture was transferred to a mold and polymerized in an oven at 55°C for 6 hours to produce a lignin-acrylic acid-based hydrogel. Mechanical testing showed a tensile strain of 934%.

[0040] In summary, Example 10 achieved an optimal tensile strain of 1457% for the hydrogel. This is due to the synergistic effects of the introduction of amphiphilic LNPs into the hydrogel, which form additional dipole-dipole interactions with the polymer chain groups, and the formation of hydrogen bonds and electrostatic interactions between the deep eutectic solvent and the monomers. In Comparative Example 1, the addition of non-amphiphilic LNPs to the hydrogel reduced the tensile strain, but this is because the non-amphiphilic LNPs do not provide dipole-dipole interactions and therefore do not impart superior tensile properties to the hydrogel.

[0041] The above is an exemplary description of the present invention. Without departing from the core of the present invention, any simple deformation, modification, substitution, combination, and simplification are equivalent replacement methods and are included in the scope of protection of the present invention.

Claims

1. A highly stretchable hydrogel based on aromatic eutectic ionic liquid amphoteric lignin nanoparticles, characterized by: The lignin is dissolved in an aromatic eutectic ionic liquid, and uniformly mixed with a gelatin solution, acrylic acid, and an initiator at a certain temperature and time. The mixed solution is then transferred to a mold and polymerized in an oven to obtain a hydrogel. The aromatic eutectic ionic liquid is obtained by uniformly mixing benzyltrimethylammonium chloride and ethylene glycol in a molar ratio of 1:

3. According to the mass volume ratio, lignin: low eutectic ionic liquid: gelatin: water: acrylic acid: initiator = 0.01-0.04g: 1-5g: 0.5-2.5g: 4-9mL: 6-11mL: 0.1g.

2. The strong stretchable hydrogel based on aromatic eutectic ionic liquid amphoteric lignin nanoparticles according to claim 1, characterized in that: The lignin is enzymatically hydrolyzed lignin.

3. The strong stretchable hydrogel based on aromatic eutectic ionic liquid amphoteric lignin nanoparticles according to claim 1, characterized in that: The initiator is one or more of potassium persulfate, sodium persulfate and ammonium persulfate.

4. The strong stretchable hydrogel based on aromatic eutectic ionic liquid amphoteric lignin nanoparticles according to claim 1, characterized in that: The temperature of the heating polymerization is 40 to 80° C., and the time is 1 to 7 hours.