Preparation method and application of bamboo nanocellulose and bi-crosslinking hydrogel

Abstract

The invention discloses a preparation method and application of bamboo nanocellulose and bi-crosslinking hydrogel. The preparation method of the hydrogel comprises the following steps: (1) dispersing the bamboo nanocellulose; (2) preparing a lignin-Fe solution; and (3) preparation of the bi-crosslinked hydrogel: adding the bamboo nanocellulose suspension and acrylic acid into water, then adding ammonium persulfate and N, N '-methylene bisacrylamide, finally adding the lignin-Fe solution to obtain a precursor solution, and pouring the precursor solution into a mold to obtain the bi-crosslinked hydrogel. The moso bamboo is used as a raw material, cellulose is extracted from the plant which is extremely high in carbon sequestration capacity and rapid in production and then is processed into nano cellulose, a novel utilization way is provided for the moso bamboo, and the hydrogel prepared from the moso bamboo is good in environment friendliness, green, natural and non-toxic, can be in direct contact with skin, and has a good application prospect. And the application and development of the material in the fields of environmental protection, biomedical treatment, electronic skin, wearable sensors and the like are facilitated.

Description

Technical Field

[0001] The present invention relates to the technical field of hydrogels, and in particular to a preparation method and application of bamboo nanocellulose and a double-crosslinked hydrogel. Background Art

[0002] Hydrogel is a viscoelastic polymer material with a three-dimensional network structure. Due to its unique structure and easy functionalization, it has excellent swelling, biocompatibility, and adjustability. As a soft and wet material, hydrogel can maintain high strength and softness, is easy to process and shape, and has controllable shape and size. It is widely used in many fields such as soft robotics, flexible electronic devices, biomedicine, and tissue engineering. However, traditional hydrogels have very simple functions and are in many aspects insufficient to meet the complex material requirements of various fields. In addition, they lack strength and toughness, and have poor fatigue resistance, making it difficult to meet people's demand for durable materials.

[0003] Research has shown that the introduction of nanocellulose into hydrogel systems can yield a variety of ideal functional materials. Bamboo, as a unique biomass resource, is considered a potential source of cellulose fiber due to its abundant resources, high renewability, high cellulose content, and high-performance fibers.

[0004] Currently, there are various methods for preparing nanocellulose, including enzymatic hydrolysis, chemical methods, or physical and mechanical methods. Each of these methods has its own advantages and has been used to varying degrees. However, although the preparation of nanocellulose has been commercialized, these processes often have problems such as long production time, high energy consumption, toxic reagents, and high environmental pollution.

[0005] In recent years, research on the preparation of nanocellulose by treating with low eutectic solvent systems has begun to increase. Low eutectic solvents are a green solvent that is currently considered suitable for the pretreatment of nanocellulose. This type of method is an emerging technology, and whether it is universally applicable to cellulose from different sources in nature has not yet been determined. For example, citric acid, a commonly used raw material, has many carboxyl sites that can interact with the hydrogen bond structure in the cellulose molecule, effectively destroying the hydrogen bond network within the cellulose chain, while promoting the dissociation of nanofibers and carboxylating the modified nanocellulose; the steric hindrance effect of choline chloride (ChCl) can prevent the dehydration of adjacent carboxyl groups to form cyclic anhydrides, thereby retaining more free carboxyl sites and ensuring the efficiency of carboxylation, and the addition of water to adjust the protonation characteristics of the solvent not only prevents excessive hydrolysis of cellulose, but also reduces the viscosity and hydrogen bond acidity of H-DES, enhances the swelling capacity of cellulose, and promotes the stable grafting of carboxyl groups. However, excessive acid may reduce the efficiency of carboxylation and cause the nanocellulose to dissociate too quickly, thereby reducing the aspect ratio of nanocellulose. Cellulose prepared from different raw materials has certain differences in treatment effects. In this case, the most suitable low eutectic solvent for processing bamboo cellulose has not yet been determined.

[0006] Therefore, how to design and use low eutectic solvents to efficiently prepare bamboo nanocellulose with a higher aspect ratio and apply it to enhance the performance of hydrogels has become the current research focus in this field. Summary of the Invention

[0007] The main purpose of the present invention is to provide a preparation method and application of bamboo nanocellulose and double-crosslinked hydrogel, aiming to solve the technical problems of low aspect ratio of bamboo nanocellulose prepared by existing technology, dependence on exogenous energy for preparation of hydrogel, poor mechanical properties and insufficient functionality.

[0008] To achieve the above object, the present invention provides a method for preparing bamboo nanocellulose, comprising the following steps:

[0009] (1) Bamboo pretreatment

[0010] Fresh bamboo is dried, crushed into powder, added into a mixture of toluene and ethanol, extracted at a temperature of 85-95°C, and then filtered, washed, and dried to obtain pretreated bamboo powder;

[0011] (2) Extraction and bleaching of bamboo cellulose

[0012] The pretreated bamboo powder is added to an acidified sodium chlorite solution with a pH value of 4 to 4.7, heated at 80°C, and sodium chlorite is added multiple times during the heating process. The powder is then filtered and washed until neutral, and then added to a potassium hydroxide solution, heated at 90°C. Finally, the powder is filtered, washed until neutral, and dried to obtain dry bamboo cellulose.

[0013] (3) Preparation of bamboo nanocellulose

[0014] Citric acid, choline chloride and water are mixed, heated and stirred to obtain a HS solvent, dried bamboo cellulose is dispersed in the HS solvent, heated for reaction, filtered, washed to neutrality, and dried to obtain the bamboo nanocellulose.

[0015] Furthermore, in step (1), the mass ratio of bamboo powder to the mixed liquid is 1:50-100, and the mass ratio of toluene to ethanol in the mixed liquid is 2:1.

[0016] Furthermore, in step (2), the acidified sodium chlorite solution contains sodium chlorite in an amount equal to that of the pretreated bamboo powder, and the specific method of adding sodium chlorite multiple times is to add sodium chlorite in an amount equal to that of the pretreated bamboo powder every hour during the heating process.

[0017] Furthermore, in step (2), the concentration of the potassium hydroxide solution is 6 wt %.

[0018] Furthermore, in step (3), the mass ratio of citric acid, choline chloride and water is 2:1:1, and the heating and stirring treatment conditions are a temperature of 80° C. and a time of 30 minutes.

[0019] Furthermore, in step (3), the ratio of dry bamboo cellulose to HS solvent is 1 g:25 ml, and the heating reaction treatment conditions are a temperature of 130° C. and a time of 3 hours.

[0020] The present invention also provides bamboo nanocellulose, which is prepared according to the above preparation method.

[0021] The present invention also provides a method for preparing a double-crosslinked hydrogel, comprising the following steps:

[0022] (1) Dispersion of bamboo nanocellulose

[0023] The bamboo nanocellulose is added into water and dispersed to obtain a bamboo nanocellulose suspension;

[0024] (2) Preparation of lignin-Fe solution

[0025] Sodium lignin sulfonate and anhydrous ferric chloride are prepared in a mass ratio of 4:1, and then the sodium lignin sulfonate is dispersed in water in a mass ratio of 1:10 to obtain a solution A, and anhydrous ferric chloride is dispersed in water in a mass ratio of 1:10 to obtain a solution B, and the solutions A and B are mixed to obtain a lignin-Fe solution;

[0026] (3) Preparation of double-crosslinked hydrogel

[0027] The bamboo nanocellulose suspension and acrylic acid are added to water and dispersed, and then ammonium persulfate and N,N'-methylenebisacrylamide are added and dispersed. Finally, the lignin-Fe solution is added and stirred to obtain a precursor solution. The precursor solution is poured into a mold to obtain a double-crosslinked hydrogel.

[0028] Furthermore, in step (1), the concentration of the bamboo nanocellulose suspension is 1 wt %.

[0029] Furthermore, in step (3), the mass ratio of bamboo nanocellulose to acrylic acid, ammonium persulfate, and N,N'-methylenebisacrylamide in the bamboo nanocellulose suspension is 0.009-0.05:2:0.15:0.005.

[0030] The present invention also provides a double-crosslinked hydrogel prepared according to the above preparation method.

[0031] The present invention also provides an application of the double-crosslinked hydrogel in preparing a material whose electrical conductivity changes with strain.

[0032] The beneficial effects of the present invention are embodied in:

[0033] In the preparation of bamboo nanocellulose, the citric acid contained in the HS solvent is an organic acid with a high molecular weight of carboxyl groups. During the pretreatment stage, these carboxyl groups interact with the hydrogen bonds within the cellulose molecules, effectively disrupting the hydrogen-bonding network within the cellulose chains. Combined with mechanical ultrasound, this provides longitudinal shear force, promoting longitudinal separation of the cellulose bundles. Furthermore, bamboo fiber, as a medium-length fiber, naturally possesses a high aspect ratio. This characteristic ensures that the bamboo nanocellulose obtained after the pretreatment and mechanical ultrasound processes retains its excellent aspect ratio.

[0034] The present invention uses bamboo as raw material, extracts cellulose from this plant with extremely strong carbon fixation ability and rapid production, and then processes it into nanocellulose, providing a novel utilization method for bamboo, which is conducive to the implementation of "replacing plastic with bamboo". The hydrogel prepared with bamboo as raw material has good environmental friendliness, is green, natural and non-toxic, and can come into direct contact with the skin, which is conducive to its use and development in environmental protection, biomedicine, electronic skin and wearable sensors.

[0035] The present invention designs a lignin-Fe solution based on polyphenols (lignin, derived from sodium lignin sulfonate) and oxidative metal ions (iron ions, Fe 3+) complex. According to the characteristics of the lignin-Fe solution, as well as the differences in the cross-linking mode and network characteristics of the hydrogel, the present invention designs a double-cross-linked bamboo nanocellulose-based conductive hydrogel catalyzed by the lignin-Fe complex. The bamboo nanocellulose can be uniformly dispersed in the hydrogel precursor solution, thereby effectively forming a large number of hydrogen bonds with the polyacrylamide chain and forming a double-penetrating network with the polyacrylamide. In addition, based on the addition of alkali lignin and the lignin-Fe complex, a large number of free radicals are formed with ammonium persulfate, causing the hydrogel to polymerize. The large amount of phenolic hydroxyl groups and iron ions contained in the lignin-Fe complex can effectively connect the bamboo nanocellulose chains and the polyacrylamide chains, thereby improving the mechanical properties of the hydrogel and simultaneously giving the hydrogel excellent adhesion and good conductivity. When the hydrogel is subjected to external force, the energy dissipation is faster and more uniform.

[0036] Free radical polymerization is a commonly used method for preparing chemically cross-linked hydrogels. It uses free radicals as the initiator to open the double bonds of vinyl monomers and then graft them to make the chains grow continuously to carry out addition polymerization. It has the advantages of low reaction temperature, fast reaction speed, and high cross-linking density. However, free radical initiators such as persulfates are difficult to decompose and produce free radicals under normal temperature conditions, and usually require external stimulation such as activation of amine monomers, heating, UV irradiation, etc. These conditions are difficult to meet in the large-scale preparation process of hydrogels, and amine compounds are flammable and corrosive, posing a safety hazard. The present invention is based on the reaction of polyphenols (lignin) and oxidizing metal ions (iron ions, Fe 3+ In a dual-crosslinked hydrogel system using polyphenols as catalysts, polyphenols can induce a variety of non-covalent interactions, such as cation-π interactions, π-π stacking, and metal ion coordination. Polyphenols can also undergo redox reactions with metal ions or self-crosslink via Michael addition reactions in an alkaline environment. The polyphenol-metal ion complex formed by the reaction of polyphenols with metal ions can serve as a catalytic system to activate persulfate, generating sulfate and hydroxyl radicals for free radical polymerization of vinyl monomers. The redox reaction between polyphenols and metal ions can also effectively prevent over-oxidation of phenolic hydroxyl groups, thereby achieving long-term, effective adhesion. Furthermore, in the polyphenol-metal ion catalytic system, lignin polyphenols can be used synergistically with metal ions to prepare a series of adhesive hydrogels. These adhesive hydrogels do not require complex gelation initiation conditions and exhibit excellent adhesion and mechanical properties. Therefore, this polyphenol-metal ion catalytic system provides a green and environmentally friendly method for the preparation of multifunctional bamboo nanocellulose hydrogels. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 Transmission electron micrographs of the bamboo nanocellulose prepared in Example 1 and Comparative Examples 1-3.

[0038] Figure 2 4. Fourier transform infrared spectra of the bamboo nanocellulose prepared in Example 1 and Comparative Example 1.

[0039] Figure 3 This is a graph showing the yield of bamboo nanocellulose prepared in Example 1, Comparative Example 2, and Comparative Example 3.

[0040] Figure 4 The diagrams are of gelation conditions and temperature changes during the hydrogel formation process of Example 3, Comparative Example 4, Comparative Example 5, and Comparative Example 6.

[0041] Figure 5 This is a graph showing the compressive strength performance test results of the hydrogels prepared in Examples 1-3 and Comparative Example 6.

[0042] Figure 6 Graph showing the tensile strength performance test results of the hydrogels prepared in Examples 1-3 and Comparative Example 6.

[0043] Figure 7 Graph showing the adhesion performance test results of the hydrogels prepared in Examples 1-3 and Comparative Example 6.

[0044] Figure 8 Graph showing the ionic conductivity test results of the hydrogels prepared in Example 1, Comparative Examples 7, and 8.

[0045] Figure 9 This is a test graph showing the resistance change of the hydrogel prepared in Example 3 as a function of strain. DETAILED DESCRIPTION

[0046] In order to make the technical solution of the present invention more clearly understood by those skilled in the art, the following examples are given for illustration. It should be noted that the following examples do not limit the scope of protection claimed by the present invention.

[0047] Unless otherwise specified, the raw materials, reagents, or devices used in the following examples can be obtained from conventional commercial sources or by existing known methods.

[0048] Example 1

[0049] Preparation of double-crosslinked hydrogels

[0050] (1) Bamboo pretreatment: Fresh bamboo was dried at 80°C, crushed with a grinder, and passed through an 80-mesh sieve to obtain bamboo powder with a mesh size of 0.1 to 0.18 mm. The bamboo powder was added to a mixture of toluene and ethanol (the mass ratio of toluene to ethanol was 2:1), with the mass ratio of bamboo powder to the mixture being 1:50. The mixture was extracted at 85°C for 7 h, and then the bamboo powder was filtered out, washed with deionized water, and dried in an oven to obtain pretreated bamboo powder.

[0051] (2) Extraction and bleaching of bamboo cellulose: 5 g of pretreated bamboo powder was poured into 500 ml of acidified sodium chlorite solution (the solvent was deionized water, containing 5 g of sodium chlorite, and glacial acetic acid was added to adjust the pH to 4), and heated at 80 ° C for 6 hours. During the heating process, 5 g of sodium chlorite was added every hour (five times in total). Then, the bamboo powder was filtered out and washed with deionized water until neutral. Then, it was poured into a potassium hydroxide solution prepared by 500 ml of deionized water and 30 g of potassium hydroxide, and heated at 90 ° C for 2 hours. Finally, it was filtered out, and the product was washed with deionized water until neutral. It was dried in an oven to obtain dry bamboo cellulose.

[0052] (3) Preparation of bamboo nanocellulose: 20 g of anhydrous citric acid, 10 g of choline chloride, and 10 g of deionized water were mixed and stirred at 80°C for 30 minutes to prepare a HS solvent. 1 g of dry bamboo cellulose was dispersed in 25 ml of the HS solvent and reacted at 130°C for 3 hours. After the reaction, the precipitate was filtered out, washed with deionized water until neutral, and dried in an oven to obtain bamboo nanocellulose.

[0053] (4) Dispersion of bamboo nanocellulose: 1 g of bamboo nanocellulose was added to 100 g of deionized water and ultrasonicated for 30 minutes under ice bath conditions to obtain a bamboo nanocellulose suspension;

[0054] (5) Preparation of lignin-Fe solution: 4 g of sodium lignin sulfonate powder was dispersed in deionized water at a mass ratio of 1:10 to obtain solution A. 1 g of anhydrous ferric chloride was dispersed in deionized water at a mass ratio of 1:10 to obtain solution B. Solutions A and B were mixed to obtain a lignin-Fe solution.

[0055] (6) Preparation of double cross-linked hydrogel: 0.5 g of bamboo nanocellulose suspension and 2 g of acrylic acid (AA) were added to 7.5 g of deionized water and ultrasonically dispersed. Then, 150 mg of ammonium persulfate (APS) and 5 mg of N,N'-methylenebisacrylamide (MBAA) were added and ultrasonically dispersed. Finally, 0.25 ml of lignin-Fe solution was added and stirred to obtain a precursor solution. The precursor solution was quickly poured into a polytetrafluoroethylene mold to obtain a double cross-linked hydrogel.

[0056] The double-crosslinked hydrogel prepared in this embodiment has been tested to have a tensile strength of 45.42 kPa, a tensile strain of 809.98%, a compressive strength of 436.29 kPa, and good electrical conductivity (1.16 S / m) and adhesion (adhesion strength to wood reaches 27.12 kPa).

[0057] Example 2

[0058] Preparation of double-crosslinked hydrogels

[0059] (1) Bamboo pretreatment: Fresh bamboo was dried at 80°C, crushed in a grinder, and passed through an 80-mesh sieve to obtain bamboo powder with a mesh size of 0.1-0.18 mm. The bamboo powder was added to a mixture of toluene and ethanol (the mass ratio of toluene to ethanol was 2:1), with the mass ratio of bamboo powder to the mixture being 1:80. The mixture was extracted at 90°C for 6 h, and then the bamboo powder was filtered out, washed with deionized water, and dried in an oven to obtain pretreated bamboo powder.

[0060] (2) Extraction and bleaching of bamboo cellulose: 5 g of pretreated bamboo powder was poured into 500 ml of acidified sodium chlorite solution (the solvent was deionized water, containing 5 g of sodium chlorite, and glacial acetic acid was added to adjust the pH to 4.5), and heated at 80 ° C for 6 hours. During the heating process, 5 g of sodium chlorite was added every hour (five times in total). Then, the bamboo powder was filtered out and washed with deionized water until neutral. Then, it was poured into a potassium hydroxide solution prepared by 500 ml of deionized water and 30 g of potassium hydroxide, and heated at 90 ° C for 2 hours. Finally, it was filtered out and the product was washed with deionized water until neutral. It was dried in an oven to obtain dry bamboo cellulose.

[0061] (3) Preparation of bamboo nanocellulose: 20 g of anhydrous citric acid, 10 g of choline chloride, and 10 g of deionized water were mixed and stirred at 80°C for 30 minutes to prepare a HS solvent. 1 g of dry bamboo cellulose was dispersed in 25 ml of the HS solvent and reacted at 130°C for 3 hours. After the reaction, the precipitate was filtered out, washed with deionized water until neutral, and dried in an oven to obtain bamboo nanocellulose.

[0062] (4) Dispersion of bamboo nanocellulose: 1 g of bamboo nanocellulose was added to 100 g of deionized water and ultrasonicated for 30 minutes under ice bath conditions to obtain a bamboo nanocellulose suspension;

[0063] (5) Preparation of lignin-Fe solution: 4 g of sodium lignin sulfonate powder was dispersed in deionized water at a mass ratio of 1:10 to obtain solution A. 1 g of anhydrous ferric chloride was dispersed in deionized water at a mass ratio of 1:10 to obtain solution B. Solutions A and B were mixed to obtain a lignin-Fe solution.

[0064] (6) Preparation of double cross-linked hydrogel: 1 g of bamboo nanocellulose suspension and 2 g of acrylic acid (AA) were added to 7 g of deionized water and ultrasonically dispersed. Then, 150 mg of ammonium persulfate (APS) and 5 mg of N,N'-methylenebisacrylamide (MBAA) were added and ultrasonically dispersed. Finally, 0.25 ml of lignin-Fe solution was added and stirred to obtain a precursor solution. The precursor solution was quickly poured into a polytetrafluoroethylene mold to obtain a double cross-linked hydrogel.

[0065] The double-crosslinked hydrogel prepared in this embodiment has been tested to have a tensile strength of 63.92 kPa, a tensile strain of 911.74%, a compressive strength of 560.44 kPa, and good electrical conductivity (1.16 S / m) and adhesion (adhesion strength to wood reaches 35.15 kPa).

[0066] Example 3

[0067] Preparation of double-crosslinked hydrogels

[0068] (1) Bamboo pretreatment: Fresh bamboo was dried at 80°C, crushed in a grinder, and passed through an 80-mesh sieve to obtain bamboo powder with a size of >80 mesh. The size of the bamboo powder after crushing was 0.1-0.18 mm. The bamboo powder was added to a mixture of toluene and ethanol (the mass ratio of toluene to ethanol was 2:1), with the mass ratio of bamboo powder to the mixture being 1:100. The mixture was extracted at 95°C for 5 h, and then the bamboo powder was filtered out, washed with deionized water, and dried in an oven to obtain pretreated bamboo powder.

[0069] (2) Extraction and bleaching of bamboo cellulose: 5 g of pretreated bamboo powder was poured into 500 ml of acidified sodium chlorite solution (the solvent was deionized water, containing 5 g of sodium chlorite, and glacial acetic acid was added to adjust the pH to 4.7), and heated at 80 ° C for 6 hours. During the heating process, 5 g of sodium chlorite was added every hour (five times in total). Then, the bamboo powder was filtered out and washed with deionized water until neutral. Then, it was poured into a potassium hydroxide solution prepared by 500 ml of deionized water and 30 g of potassium hydroxide, and heated at 90 ° C for 2 hours. Finally, it was filtered out, and the product was washed with deionized water until neutral. It was dried in an oven to obtain dry bamboo cellulose.

[0070] (3) Preparation of bamboo nanocellulose: 20 g of anhydrous citric acid, 10 g of choline chloride, and 10 g of deionized water were mixed and stirred at 80°C for 30 minutes to prepare a HS solvent. 1 g of dry bamboo cellulose was dispersed in 25 ml of the HS solvent and reacted at 130°C for 3 hours. After the reaction, the precipitate was filtered out, washed with deionized water until neutral, and dried in an oven to obtain bamboo nanocellulose.

[0071] (4) Dispersion of bamboo nanocellulose: 1 g of bamboo nanocellulose was added to 100 g of deionized water and ultrasonicated for 30 minutes under ice bath conditions to obtain a bamboo nanocellulose suspension;

[0072] (5) Preparation of lignin-Fe solution: 4 g of sodium lignin sulfonate powder was dispersed in deionized water at a mass ratio of 1:10 to obtain solution A. 1 g of anhydrous ferric chloride was dispersed in deionized water at a mass ratio of 1:10 to obtain solution B. Solutions A and B were mixed to obtain a lignin-Fe solution.

[0073] (6) Preparation of double cross-linked hydrogel: 2 g of bamboo nanocellulose suspension and 2 g of acrylic acid (AA) were added to 6 g of deionized water and ultrasonically dispersed. Then, 150 mg of ammonium persulfate (APS) and 5 mg of N,N'-methylenebisacrylamide (MBAA) were added and ultrasonically dispersed. Finally, 0.25 ml of lignin-Fe solution was added and stirred to obtain a precursor solution. The precursor solution was quickly poured into a polytetrafluoroethylene mold to obtain a double cross-linked hydrogel.

[0074] The double-crosslinked hydrogel prepared in this embodiment has been tested to have a tensile strength of 77.37 kPa, a tensile strain of 1029.79%, a compressive strength of 697.36 kPa, and good electrical conductivity (1.16 S / m) and adhesion (adhesion strength to wood reaches 42.64 kPa).

[0075] Comparative Example 1

[0076] In this comparative example, bamboo nanocellulose was prepared using the same preparation method as in Example 1, except that no HS solvent was added.

[0077] Comparative Example 2

[0078] In this comparative example, bamboo nanocellulose was prepared by the same preparation method as in Example 1, except that the mass ratio of anhydrous citric acid, choline chloride, and water used in the prepared HS solvent was 1:1:1.

[0079] Comparative Example 3

[0080] In this comparative example, bamboo nanocellulose was prepared by the same preparation method as in Example 1, except that the mass ratio of anhydrous citric acid, choline chloride, and water used in the prepared HS solvent was 3:1:1.

[0081] Comparative Example 4

[0082] In this comparative example, bamboo nanocellulose and hydrogel were prepared by the same preparation method as in Example 1, except that no lignin-Fe solution was added in step (6).

[0083] Comparative Example 5

[0084] In this comparative example, bamboo nanocellulose and hydrogel were prepared by the same preparation method as in Example 1, except that anhydrous ferric chloride was not added in step (5).

[0085] Comparative Example 6

[0086] In this comparative example, bamboo nanocellulose and hydrogel were prepared by the same preparation method as in Example 1, except that no bamboo nanocellulose suspension was added in step (6).

[0087] Comparative Example 7

[0088] In this comparative example, bamboo nanocellulose and hydrogel were prepared by the same preparation method as in Example 1, except that in step (5), the amount of anhydrous ferric chloride added was adjusted to 0.5 g.

[0089] Comparative Example 8

[0090] In this comparative example, bamboo nanocellulose and hydrogel were prepared by the same preparation method as in Example 1, except that the lignin-Fe solution was not added in step (6), and step (7) was added: a polytetrafluoroethylene mold to which the precursor solution was added was placed in a water bath, heated at 80°C for 2 min, and then the mold was removed to obtain a hydrogel sample.

[0091] Experimental Example 1

[0092] Performance testing of bamboo nanocellulose

[0093] The bamboo nanocellulose prepared in Example 1 and Comparative Examples 1, 2 and 3 was tested by transmission electron microscopy. Figure 1 It can be seen that the diameter, length and dispersion of the nanocellulose treated under different conditions are different. Among them, Comparative Example 2 and Example 1 are dispersed in a network, while Example 1 is relatively uniformly distributed. Subsequently, the diameter, length and aspect ratio were measured as shown in Table 1. It was found that the diameter and length of Comparative Example 1 without the addition of HS solvent did not reach the nanometer level. The length of the nanocellulose prepared in Comparative Example 3 with the addition of more citric acid was significantly reduced compared with Comparative Example 1 and Example 1, while the aspect ratio of the bamboo nanocellulose prepared in Example 1 was relatively high, reaching 1023.14, which is much higher than that of other samples. The ternary low eutectic solvent effectively destroys the hydrogen bond network within the cellulose chain and promotes the dissociation of nanofibers. The bamboo nanocellulose prepared by DES with an appropriate amount of citric acid is dispersed in the liquid in a network-like manner in water and has a very high aspect ratio. Excessive citric acid will excessively dissociate the amorphous region of cellulose, significantly reducing the length of the nanocellulose, which reduces the aspect ratio of the bamboo nanocellulose.

[0094] Table 1

[0095] Diameter (nm) Length (μm) Aspect ratio Comparative Example 1 1274.17±31.1 154.22±11.5 120.35 Comparative Example 2 5.37±1.68 4.41±1.03 821.23 Comparative Example 3 3.99±0.79 1.07±0.18 268.17 Example 1 4.21±0.85 4.41±0.89 1023.14

[0096] The bamboo nanocellulose prepared in Example 1 and Comparative Example 1 was tested by Fourier transform infrared spectroscopy. Figure 2 From the spectrum, we can see that the three substances are mainly at 3350, 2900, 1729, 1640, 1510, 1246, 1070, and 897 cm -1There are obvious characteristic peak changes at 3350cm-1. Among them, the peak at 3350cm-1 is attributed to the stretching vibration of hydroxyl (-OH), which mainly comes from cellulose, hemicellulose, lignin, polysaccharide and monosaccharide molecules, and the peak at 2900cm-1 is attributed to the stretching vibration of hydroxyl (-OH). -1 The absorption peak at 1729 cm-1 can be attributed to the stretching vibration of the CH bond in α-cellulose. -1 The peak at 1640 cm is derived from the symmetrical stretching vibration in the plane of the lignin aromatic ring, the carbonyl C=O of the ester group in hemicellulose, and the C=O stretching vibration of the acidic carboxyl group, while the peak at 1640 cm -1 The peaks at 1510 cm are related to the O–H bending vibration caused by the strong adsorption of cellulose and water. These two peaks reappeared and increased in Example 1, proving that the deep eutectic solvent successfully carboxylated and modified the cellulose surface. -1 The C=C vibration of lignin is at 1246cm, and its disappearance indicates that the lignin has been effectively removed. -1 The peak at ≈1070cm represents the COC stretching vibration of the acetyl bond in lignin and hemicellulose. The peak gradually decreases and disappears, indicating that lignin and hemicellulose are effectively removed step by step during the treatment process. -1 The characteristic peak at ≈897cm represents the vibration of the cellulose COC pyranose ring, while -1 The characteristic peaks at are related to the CH swing of the β-glycosidic bond connecting the cellulose units. The increase of these two peaks in Example 1 indicates that the relative content of cellulose in the sample is increased and the sample is purified.

[0097] The yield of bamboo nanocellulose prepared in Example 1, Comparative Example 2 and Comparative Example 3 was measured, and the results are shown in Figure 3 The bamboo nanocellulose prepared by combining different proportions of low eutectic solvent with mechanical ultrasonic treatment has different yields. Comparative Example 2 has the highest yield of 91.18%, and Example 1 has a yield of 88.31%, which is only 2.87% lower than that of 1:1:1, and the decrease is very small. As the proportion of citric acid continues to increase, the yield decreases rapidly. Comparative Example 3 is 68.97%, which is 19.34% lower than that of the example. This may be because the acidity of the low eutectic solvent continues to increase with the increase of citric acid, resulting in the rapid decomposition of nanocellulose.

[0098] According to the above measurements, it is believed that the bamboo nanocellulose treated with HS solvent in a ratio of 2:1:1 (Example 1) has the best performance.

[0099] Experimental Example 2

[0100] Performance testing of hydrogels

[0101] Test 1:

[0102] Observe the gelation and temperature changes of the hydrogels in Example 1, Comparative Example 4, Comparative Example 5 and Comparative Example 6 during the static formation process. Figure 4 It can be found that both Example 1 and Comparative Example 6 gelled after 60 seconds at room temperature, while the hydrogels of Comparative Examples 4 and 5 could not gel (preparation failure), indicating that the lignin-Fe solution has a catalytic function on the performance of the hydrogel.

[0103] Test 2:

[0104] The mechanical properties of the hydrogels prepared in each example and comparative example 6 were tested according to GB / T 1040.1-2018. The results are shown in Figure 5 and Figure 6 , Figure 5 The compressive stress of Example 1 at 85% strain is shown to be 436.29 kPa, which is a significant increase of 37.93% compared to Comparative Example 6; Example 2 is 560.44 kPa, which is an increase of 28.46% compared to Example 1; and Example 3 is 697.36 kPa, which is an increase of 24.43% compared to Example 2. Figure 6 The maximum tensile breaking stress of Example 1 shown is 45.42 kPa, and the maximum tensile strain is 809.98%, which are significantly increased by 45.90% and 22.63% respectively compared to the case without adding nanocellulose (Comparative Example 6). The values ​​of Example 2 are 63.92 kPa and 911.74%, and the values ​​of Example 3 are the highest, which are 77.37 kPa and 1029.79% respectively. These situations are because the surface of nanocellulose is rich in carboxyl and hydroxyl functional groups, which make the nanocellulose uniformly dispersed in the precursor solution and can form a large number of hydrogen bonds, van der Waals forces and electrostatic interactions with functional groups such as carboxyl groups on the polyacrylic acid chains in the hydrogel, and interact with Fe 3+ The formation of coordination bonds effectively enhances the structural strength of the hydrogel. At the same time, the bamboo nanocellulose used has a relatively high aspect ratio, which helps form a three-dimensional network structure in the hydrogel. This network structure not only increases the rigidity of the hydrogel, but also effectively prevents the expansion of cracks when the hydrogel is deformed, avoiding stress concentration, thereby improving the strength and toughness of the hydrogel. However, when the nanocellulose is excessive, it will cause it to agglomerate in the hydrogel, forming nanocellulose-rich areas, destroying the microscopic uniformity of the material, leading to local stress concentration, and thus reducing the mechanical properties of the hydrogel. In addition, excessive nanocellulose may interfere with the formation of the cross-linked network of the hydrogel matrix itself, or the interaction between it and the matrix may be too strong, resulting in a decrease in the toughness of the overall system, making the material more prone to fracture when subjected to stress.

[0105] The hydrogels prepared in each example and comparative example 6 were tested for adhesion properties according to GB / T 7124-2008. The results are shown in Figure 7As shown, the wood adhesion strength of Comparative Example 6 is only 20.88 kPa, and the adhesion strength gradually increases with the increase of the amount of bamboo nanocellulose added, which is 27.12 kPa in Example 1, 35.15 kPa in Example 2, and the highest 42.64 kPa in Example 3. This difference in interfacial adhesion may be due to the different physical interactions between the substrate and the catechol groups contained in the hydrogel, the hydroxyl (-OH) and carboxyl (-COOH) groups on the nanocellulose and polyacrylic acid chains.

[0106] The hydrogels prepared in Example 1, Comparative Example 7 and Comparative Example 8 were tested for ionic conductivity according to GB / T 43343-2023. The results are shown in Table 1. Figure 8 , the conductivity of the hydrogel increases with Fe 3+ The concentration increases. Without Fe addition 3+ The conductivity of the hydrogel of Comparative Example 8 is 0.43S / m, which has certain conductive properties. This may be related to the fact that the polyacrylic acid (PAA) molecular chain contains a large number of carboxyl groups (-COOH). Under acidic or neutral conditions, the carboxyl groups can be protonated to form carboxyl groups (-COO-), and ion conductivity is achieved through proton dissociation and migration. At the same time, the pore structure inside the gel can also provide a channel for ion transport. After adding 2.5mg FeCl3, the conductivity increased significantly to 0.76S / m, an increase of 76.75%. When 5mg FeCl3 was added, the conductivity was 1.18S / m, an increase of 55.26% compared to 2.5mg. This high conductivity comes from Fe 3+ The ion migration in the hydrogel-rich porous network channels is directed, and the increase in conductivity and the free migration of Fe 3+ ion increase.

[0107] Experimental Example 3

[0108] Test of hydrogel resistance change with strain

[0109] The hydrogel prepared in Example 3 was tested for resistance variation with strain according to SJ / T 11476-2014. Figure 9 As shown, the hydrogel sensor has excellent sensing stability, fatigue resistance, high accuracy and good sensitivity, indicating its excellent application potential.

[0110] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing bamboo nanocellulose, characterized in that: The following steps are involved: (1) Bamboo pretreatment Fresh bamboo is dried, crushed into powder, added into a mixture of toluene and ethanol, extracted at a temperature of 85-95°C, and then filtered, washed, and dried to obtain pretreated bamboo powder; (2) Extraction and bleaching of bamboo cellulose The pretreated bamboo powder is added to an acidified sodium chlorite solution with a pH value of 4 to 4.7, heated at 80°C, and sodium chlorite is added multiple times during the heating process. The powder is then filtered and washed until neutral, and then added to a potassium hydroxide solution, heated at 90°C. Finally, the powder is filtered, washed until neutral, and dried to obtain dry bamboo cellulose. (3) Preparation of bamboo nanocellulose Citric acid, choline chloride and water are mixed, heated and stirred to obtain a HS solvent, dried bamboo cellulose is dispersed in the HS solvent, heated for reaction, filtered, washed to neutrality, and dried to obtain the bamboo nanocellulose.

2. The method for preparing bamboo nanocellulose according to claim 1, wherein: In step (1), the mass ratio of bamboo powder to the mixed solution is 1:50-100, and the mass ratio of toluene to ethanol in the mixed solution is 2:

1.

3. The method for preparing bamboo nanocellulose according to claim 1, wherein: In step (2), the acidified sodium chlorite solution contains sodium chlorite in an amount equal to that of the pretreated bamboo powder. The specific method of adding sodium chlorite multiple times is to add sodium chlorite in an amount equal to that of the pretreated bamboo powder every hour during the heating process.

4. The method for preparing bamboo nanocellulose according to claim 1, wherein: In step (3), the mass ratio of citric acid, choline chloride and water is 2:1:1, and the heating and stirring treatment conditions are a temperature of 80° C. and a time of 30 minutes.

5. The method for preparing bamboo nanocellulose according to claim 1, wherein: In step (3), the ratio of dry bamboo cellulose to HS solvent is 1 g:25 ml, and the heating reaction treatment conditions are a temperature of 130° C. and a time of 3 hours.

6. A bamboo nanocellulose, characterized in that Prepared according to the preparation method according to any one of claims 1 to 5.

7. A method for preparing a double-crosslinked hydrogel, characterized in that: The following steps are involved: (1) Dispersion of bamboo nanocellulose Adding the bamboo nanocellulose according to claim 6 into water, and dispersing the bamboo nanocellulose to obtain a bamboo nanocellulose suspension; (2) Preparation of lignin-Fe solution Sodium lignin sulfonate and anhydrous ferric chloride are prepared in a mass ratio of 4:1, and then the sodium lignin sulfonate is dispersed in water in a mass ratio of 1:10 to obtain a solution A, and anhydrous ferric chloride is dispersed in water in a mass ratio of 1:10 to obtain a solution B, and the solutions A and B are mixed to obtain a lignin-Fe solution; (3) Preparation of double-crosslinked hydrogel The bamboo nanocellulose suspension and acrylic acid are added to water and dispersed, and then ammonium persulfate and N,N'-methylenebisacrylamide are added and dispersed. Finally, the lignin-Fe solution is added and stirred to obtain a precursor solution. The precursor solution is poured into a mold to obtain a double-crosslinked hydrogel.

8. The method for preparing the double-crosslinked hydrogel according to claim 7, wherein: In step (3), the mass ratio of bamboo nanocellulose to acrylic acid, ammonium persulfate, and N,N'-methylenebisacrylamide in the bamboo nanocellulose suspension is 0.009-0.05:2:0.15:0.

005.

9. A double-crosslinked hydrogel, characterized in that: Prepared according to the preparation method as described in any one of claims 7 to 8.

10. Use of the double-crosslinked hydrogel according to claim 9 in preparing a material whose electrical conductivity changes with strain.

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