A method for preparing a nano-lignin cellulose flexible conductive composite gel

Abstract

This invention provides a method for preparing a flexible conductive composite gel of nano-lignin-cellulose. The extraction method includes the following steps: (1) cooking the biomass raw material with a metal salt-based eutectic solvent, and then preparing a nano-lignin-containing nano-lignin-cellulose eutectic solvent dispersion by mechanical processing; (2) adjusting the pH of the nano-lignin-containing nano-lignin-cellulose eutectic solvent dispersion to 8.5; (3) adding polymerizable monomers and initiators to the above dispersion, and rapidly initiating the polymer at room temperature through a nano-lignin-metal ion redox reaction to obtain a flexible conductive composite gel of nano-lignin-cellulose. This paper uses lignin-cellulose as raw material, and performs efficient nano-sizing treatment on the biomass raw material using a metal salt-based eutectic solvent of polyol / choline chloride / metal salt to obtain a high aspect ratio nano-lignin-cellulose eutectic solvent dispersion; then, a one-pot preparation of a flexible conductive composite gel of nano-lignin-cellulose is carried out through a redox reaction between in-situ generated or exogenously added nano-lignin and metal ions, which can be used in flexible sensing, supercapacitors, stretchable devices and other fields. The method of this invention does not require complex solvent replacement, is mild and efficient, and produces gels with excellent mechanical properties and high ionic conductivity.

Description

Technical Field

[0001] This invention relates to the field of nano-lignocellulose conductive gel materials, specifically to a method for preparing nano-lignocellulose flexible conductive composite gel by nano-sizing of biomass raw materials and their in-situ redox reaction in a metal salt-based eutectic solvent system. Background Technology

[0002] Conductive gels have attracted widespread attention in fields such as flexible sensing, batteries and supercapacitors due to their mechanical flexibility and environmental stability. However, they also suffer from poor mechanical properties and difficulty in improving conductivity in practical applications.

[0003] Nanocellulose possesses advantages such as large specific surface area, high degree of chemical modification, good biocompatibility, and high mechanical strength. High aspect ratio nanocellulose can act as a reinforcing phase in the gel polymer backbone to improve gel mechanical properties. Nanocellulose can be prepared using a eutectic solvent (DES), and conductive polymers or monomers can be introduced to prepare nanocellulose conductive gels. However, DES used for cellulose nanodispersion are typically carboxylic acid-based solvent systems (e.g., lactic acid / choline chloride, oxalic acid / choline chloride, citric acid / choline chloride, etc.), which have low conductivity and cannot meet the electrochemical performance requirements of conductive gels. Therefore, this technology utilizes a metal salt-based eutectic solvent of polyol / choline chloride / metal salt to achieve efficient nano-sizing of biomass raw materials and the preparation of highly conductive nanocellulose conductive composite gels.

[0004] Since nanocellulose exhibits poor dispersion in high-salt environments, the concentration of the metal salt is crucial in the construction of a metal-based eutectic solvent of polyol / choline chloride / metal salt. It is essential to ensure that the hydrated ions of the metal salt can penetrate the biomass feedstock, enhancing the dispersion and diffusion capabilities of the entire eutectic solvent, while also maintaining sufficient metal ion migration capacity during subsequent gel preparation to improve the conductivity of the composite gel. Furthermore, lignin possesses high redox properties and abundant active functional groups such as methoxy and phenolic hydroxyl groups. CN118256006A proposed using the redox reaction between lignin and metal ions under alkaline conditions to prepare lignin conductive gels via free radical-initiated polymerization. However, this approach suffers from problems such as heterogeneous lignin structure, poor solvent dispersibility, and insufficient catalytic activity. Compared to disordered fragmented lignin, nano-lignin offers advantages such as uniform size, strong surface charge, and regular morphology, which are beneficial for improving its reactivity. In the gel network, it acts as a reinforcing and toughening agent, significantly enhancing the mechanical stability of the gel. Furthermore, the hemicellulose in the solvent contains abundant hydroxyl, carbonyl, and aldehyde groups, which can act as a stabilizer for nano-lignin, significantly improving the dispersibility of nano-lignin in the gel network and ensuring its high reactivity with metal ions to enhance the conductivity of the gel.

[0005] In summary, using a metal-based eutectic solvent (polyol / choline chloride / metal salt) to treat biomass feedstock simultaneously achieves the nano-sizing of cellulose and lignin. This not only overcomes the poor dispersibility problem caused by high salt content, but also allows hemicellulose in biomass to encapsulate nano-lignin, improving the dispersibility of nano-lignin in the gel network, enhancing its redox activity, and achieving efficient in-situ polymerization of the gel, while simultaneously strengthening and toughening the composite conductive gel. Preparing nano-lignin-cellulose conductive composite gels in metal-based eutectic solvents simplifies the process, fully utilizes the advantages of nano-lignin-cellulose, and overcomes the imbalance between mechanical and electrical properties in traditional conductive gels. Therefore, this invention is proposed. Summary of the Invention

[0006] Objective of the Invention: Traditional conductive gel preparation processes suffer from complex reactions, poor biocompatibility, and imbalances between mechanical and electrical properties under stress-strain transfer. This invention utilizes lignocellulose as a raw material, employing a high-aspect-ratio nano-sized lignocellulose nanofiber dispersion obtained through a metal-based eutectic solvent of polyol / choline chloride / metal salt. Subsequently, a one-pot redox reaction between in-situ generated or exogenously added nano-lignin and metal ions prepares a flexible conductive composite gel from lignocellulose nanofiber. The efficient encapsulation of lignin by hemicellulose ensures highly efficient catalytic activity and gel-enhancing effects. The entire system fully leverages the advantages of each component to prepare a conductive composite gel from lignocellulose nanofiber with high mechanical properties and high electrical conductivity. Furthermore, this invention features mild reaction conditions, a simple and efficient preparation process, high component utilization, and excellent product performance.

[0007] Technical solution: To achieve the above-mentioned objectives, the technical solution adopted by this invention is as follows: 1. A method for preparing a flexible conductive composite gel made of nano-lignocellulose, characterized by comprising the following steps: S1. A nano-lignin-containing lignocellulose eutectic solvent dispersion is prepared by cooking biomass raw materials using a metal salt-based eutectic solvent and then mechanically processed; the biomass raw materials are any one or a combination of two or more of hemp, wood, grass, and bamboo. S2. Adjust the pH of the eutectic solvent of nano-lignin cellulose to 8.5, add polymerizable monomers and initiators to the dispersion prepared in step S1, and rapidly initiate the polymer at room temperature through the nano-lignin-metal ion redox reaction to obtain nano-lignin cellulose flexible conductive composite gel.

[0008] 2. The method for preparing a flexible conductive composite gel of nano-lignin cellulose according to claim 1, characterized in that additional nano-cellulose or additional nano-lignin is added to the nano-lignin-containing eutectic solvent dispersion of nano-lignin in step S1; wherein the additional nano-cellulose is any one of hemp nano-cellulose, wood nano-cellulose, grass nano-cellulose, and bamboo nano-cellulose; and the additional nano-lignin is any one of homologous lignin, alkali lignin, eutectic solvent lignin, and lignin sulfonate in biomass raw materials.

[0009] 3. A method for preparing a flexible conductive composite gel of nano-lignocellulose according to claim 1 or 2, characterized in that the metal salt-based eutectic solvent in step S1 is a polyol / choline chloride / metal salt, wherein the polyol is any one or a combination of two or more selected from glycerol, ethylene glycol, propylene glycol, butanediol, hexanediol, and neopentyl glycol, and the metal salt is any one selected from aluminum chloride, ferric chloride, zinc chloride, copper chloride, magnesium chloride, lithium chloride, and potassium chloride. The molar ratio of polyol / choline chloride / metal salt is 2:1:0.2, and the solid-liquid ratio of biomass raw material to eutectic solvent is 1:6-1:10.

[0010] 4. The method for preparing a nano-lignin-cellulose flexible conductive composite gel according to claim 1 or 2, characterized in that the cooking conditions in step S1 are 80-140 °C. o C, heat preservation time 1-5 hours.

[0011] 5. A method for preparing a flexible conductive composite gel of nano-lignocellulose according to claim 1 or 2, characterized in that, in the nano-lignocellulose eutectic solvent dispersion in step S1, the diameter of the nanocellulose is 20-100 nm and the content is 0.1-10%, and the particle size of the nanolignin is 50-200 nm and the content is 0.1-5%.

[0012] 6. A method for preparing a flexible conductive composite gel of nano-lignocellulose, characterized in that the polymerizable monomer in step S2 is any one or a combination of two or more of acrylamide, acrylic acid, and glycidyl methacrylate; the initiator in step S2 is any one or a combination of two or more of ammonium persulfate, 2,2'-azo(2-methylpropylamidine) dihydrochloride, potassium persulfate, and benzoyl peroxide; the mass of the polymerizable monomer accounts for 20 wt% of the eutectic solvent of nano-lignocellulose at pH=8.5, and the amount of the initiator accounts for 0.5 wt% of the polymerizable monomer.

[0013] 7. A flexible conductive composite gel made of nano-lignocellulose, characterized in that it is prepared by the method described in any one of claims 1 to 6. The flexible conductive composite gel made of nano-lignocellulose has a high conductivity of 5-26.1 mS / cm.

[0014] 8. The nano-lignocellulose flexible conductive composite gel according to claim 7, characterized in that the nano-lignocellulose flexible conductive composite gel has excellent mechanical properties, with a tensile stress of 60-485 kPa and a tensile strain of 300-1400%.

[0015] 9. Application of nano-lignocellulose flexible conductive composite gel, characterized in that the nano-lignocellulose flexible conductive composite gel as described in claims 7-8 is used in the fields of supercapacitors, batteries, flexible sensors, soft robots, and stretchable components.

[0016] Beneficial effects: Compared with the prior art, the advantages of the present invention include: 1) This invention uses a metal salt-based eutectic solvent for the nano-sizing of lignocellulose, resulting in the mild and efficient preparation of nano-lignocellulose with high aspect ratio and good dispersion properties. This avoids the fiber-cutting effect of traditional carboxylic acid-based eutectic solvents.

[0017] 2) By using a metal salt-based eutectic solvent containing nano-lignocellulose as a gel precursor, a complex solvent replacement process is avoided, and a high-strength, high-toughness, high-ionic-conductivity flexible conductive composite gel is prepared while ensuring the full utilization of the system components.

[0018] 3) Metal salt-based eutectic solvents can not only efficiently prepare nano-lignin cellulose, but also construct nano-lignin-metal ion redox reactions to prepare flexible conductive composite gels without the need for additional energy, thus achieving green and efficient material construction.

[0019] 4) The nano-lignocellulose flexible conductive composite gel prepared by this invention has excellent toughness and conductivity, and can be used in the electrolyte part of supercapacitors, as well as in the conduction of flexible electronic devices, and in real-time detection of minute human movements, such as joint movements. It provides broad application prospects for the high-value utilization of cellulose in eutectic solvent systems. Attached Figure Description

[0020] Figure 1 This is the preparation process of nano-lignocellulose flexible conductive composite gel; Figure 2 These are scanning electron microscope images and particle size distributions of the prepared nano-lignocellulose; Figure 3This is based on the controllable preparation of nano-lignin nanocellulose DES dispersion and the scanning electron microscope images and particle size distribution of nano-lignin. Figure 4 These are X-ray photoelectron spectra and infrared spectra obtained from the preparation of nano-lignin-metal redox process; Figure 5 This is a photograph of the prepared nano-lignocellulose flexible conductive composite gel; Figure 6 The stress-strain curve of the prepared nano-lignocellulose flexible conductive composite gel is shown. Figure 7 The conductivity of the prepared nano-lignocellulose flexible conductive composite gel; Figure 8 This is the application of the prepared nano-lignocellulose flexible conductive composite gel in flexible sensing; Figure 9 This describes the application of the prepared nano-lignocellulose flexible conductive composite gel in supercapacitor gel electrolytes. Detailed Implementation

[0021] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings, technical process steps, specific implementation conditions and materials in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0022] The nano-lignocellulose used in this invention can be prepared by mechanical dispersion such as colloid mill, ultrasonic crushing, disc mill, PFI mill, ultrafine grinding, and high pressure homogenization. The following examples illustrate the invention by preparing nano-lignocellulose by mechanical dispersion using a colloid mill.

[0023] Example 1 Take 5 g of bast fiber cellulose raw material and mix it evenly with a eutectic solvent of glycerol / choline chloride / aluminum chloride at a solid-liquid ratio of 1:6. Then, cook the mixture in an oil bath at 100°C. o The mixture was kept at temperature C for 2 h. After grinding in a colloid mill for 40 min, a eutectic solvent dispersion containing nano-lignocellulose was obtained. The pH was adjusted to 8.5, and 20 wt% acrylamide monomer and 0.5 wt% ammonium persulfate were added to the dispersion to prepare a flexible conductive composite gel containing nano-lignocellulose at room temperature. Mechanical and electrical properties of the flexible conductive composite gel containing nano-lignocellulose were characterized by measurements at 100 kPa and 738%, respectively, and the conductivity was 7.4 mS / cm.

[0024] Example 2 Take 5 g of bast fiber cellulose raw material and mix it evenly with a eutectic solvent of glycerol / choline chloride / aluminum chloride at a solid-liquid ratio of 1:6. Then, cook the mixture in an oil bath at 100°C. o The mixture was kept at C for 2 h. After grinding in a colloid mill for 40 min, a eutectic solvent dispersion containing nano-lignin was obtained. 1 wt% homologous nano-lignin was added, the pH was adjusted to 8.5, 20 wt% acrylamide monomer was added to the dispersion, and 0.5 wt% ammonium persulfate was added to prepare a nano-lignin flexible conductive composite gel at room temperature. Mechanical and electrical properties of the nano-lignin flexible conductive composite gel were characterized by mechanical and electrical measurements. The stress-strain ratios were 455 kPa and 800%, respectively, and the conductivity was 18.7 mS / cm. The effect of different amounts of nano-lignin added on the gel properties was investigated, and the results are shown in the table below. Homologous lignin exhibits good dispersibility in metal-based eutectic solvents. The uniform filling of the gel interior provides reinforcement. However, with increasing lignin content, the large amount of lignin filling the gel interior hinders the uniform construction of the network, leading to decreased internal uniformity and performance degradation.

[0025]

[0026] Example 3 Take 5 g of bast fiber cellulose raw material and mix it evenly with a eutectic solvent of glycerol / choline chloride / aluminum chloride at a solid-liquid ratio of 1:6. Then, cook the mixture in an oil bath at 100°C. o The mixture was kept at C for 2 h. After grinding in a colloid mill for 40 min, a eutectic solvent dispersion containing nano-lignin was obtained. Then, 1 wt% of homologous nano-lignin (average particle size 50 nm) was added. The pH was adjusted to 8.5, and 20 wt% acrylamide monomer and 0.5 wt% ammonium persulfate were added to the dispersion to prepare a flexible conductive composite gel of nano-lignin at room temperature. Mechanical and electrical properties of the flexible conductive composite gel of nano-lignin were characterized by measurements. The stress-strain ratios were 455 kPa and 800%, respectively, and the conductivity was 18.7 mS / cm. The influence of different average nano-lignin particle sizes on the gel properties was investigated, and the results are shown in the table below: the larger the average nano-lignin particle size, the worse the dispersibility in the gel, and the uneven gel network leads to a decrease in performance.

[0027]

[0028] Example 4 Take 5 g of bast fiber cellulose raw material and mix it evenly with a eutectic solvent of glycerol / choline chloride / aluminum chloride at a solid-liquid ratio of 1:6. Then, cook the mixture in an oil bath at 100°C. oThe mixture was kept at C for 2 h. After grinding in a colloid mill for 40 min, a eutectic solvent dispersion containing lignocellulose nanoparticles was obtained. Then, 1 wt% alkali lignin (average particle size 50 nm) was added. The pH was adjusted to 8.5, and 20 wt% acrylamide monomer and 0.5 wt% ammonium persulfate were added to the dispersion to prepare a flexible conductive composite gel of lignocellulose nanoparticles at room temperature. Mechanical and electrical properties of the flexible conductive composite gel of lignocellulose nanoparticles were characterized by measurements at 350 kPa and 1000%, respectively, and the conductivity was 16.2 mS / cm. The effect of different lignin types on the gel properties was investigated, and the results are shown in the table below: homologous lignin was obtained by pretreatment with a metal salt eutectic solvent, alkali lignin was obtained by alkali pulping, and lignin sulfonate was obtained by sulfurous acid pulping. Due to the presence of polyols, homologous lignin can regenerate the exfoliated lignin macromolecules into nano-lignin. Nano-lignin with high compatibility and good dispersibility can significantly improve gel performance. Alkali lignin and lignin sulfonate require solvent regeneration, and their size is uneven and their dispersibility is poor, so their improvement on gel performance is limited.

[0029]

[0030] Example 5 Take 5 g of bast fiber cellulose raw material and mix it evenly with a eutectic solvent of glycerol / choline chloride / aluminum chloride at a solid-liquid ratio of 1:6. Then, cook the mixture in an oil bath at 100°C. o The mixture was kept at C for 2 h. After grinding in a colloid mill for 40 min, a eutectic solvent dispersion containing nano-lignin cellulose was obtained. An additional 2 wt% of 20 nm diameter nano-cellulose was added. The pH was adjusted to 8.5, and 20 wt% acrylamide monomer and 0.5 wt% ammonium persulfate were added to the dispersion to prepare a flexible conductive composite gel containing nano-lignin cellulose at room temperature. Mechanical and electrical properties of the flexible conductive composite gel were characterized by mechanical and electrical measurements. The stress and strain were 452 kPa and 1000%, respectively, and the conductivity was 19.3 mS / cm. The effect of adding different amounts of nano-cellulose on the gel properties was investigated, and the results are shown in the table below. Nano-lignin can act as a rigid filler to enrich the internal network of the gel. Uniformly distributed nano-lignin plays a positive role in gel performance, but excessive nano-lignin will destroy the uniformity of the gel network, resulting in a decrease in gel performance.

[0031]

[0032] Example 6 Take 5 g of bast fiber cellulose raw material and mix it evenly with a eutectic solvent of glycerol / choline chloride / aluminum chloride at a solid-liquid ratio of 1:6. Then, cook the mixture in an oil bath at 100°C. oThe mixture was kept at C for 2 h. After grinding in a colloid mill for 40 min, a eutectic solvent dispersion containing lignocellulose nanoparticles was obtained. An additional 1 wt% homologous lignin (average particle size 50 nm) and 2 wt% lignocellulose nanoparticles with an average diameter of 50 nm were added. The pH was adjusted to 8.5, and 20 wt% acrylamide monomer and 0.5 wt% ammonium persulfate were added to the dispersion to prepare a flexible conductive composite gel of lignocellulose nanoparticles at room temperature. Mechanical and electrical properties of the flexible conductive composite gel of lignocellulose nanoparticles were characterized by measurements. The stress-strain ratios were 380 kPa and 850%, respectively, and the conductivity was 17.3 mS / cm. The effect of adding lignocellulose nanoparticles of different diameters on the gel properties was investigated. The results are shown in the table below: the larger the diameter of the lignocellulose nanoparticles and the smaller the aspect ratio, the more uniformly the lignocellulose nanoparticles are distributed in the gel network, and the more significant the improvement in gel properties.

[0033]

[0034] Example 7 Take 5 g of bast fiber cellulose raw material and mix it evenly with a eutectic solvent of glycerol / choline chloride / aluminum chloride at a solid-liquid ratio of 1:6. Then, cook the mixture in an oil bath at 100°C. o The mixture was kept at C for 2 h. After milling in a colloid mill for 40 min, a eutectic solvent dispersion containing lignocellulose nanoparticles was obtained. An additional 1 wt% homologous lignin (average particle size 50 nm) and 2 wt% 20 nm lignocellulose nanoparticles were added. The pH was adjusted to 8.5, and 20 wt% acrylamide monomer and 0.5 wt% ammonium persulfate were added to the dispersion to prepare a flexible conductive composite gel of lignocellulose nanoparticles at room temperature. Mechanical and electrical properties of the flexible conductive composite gel of lignocellulose nanoparticles were characterized by mechanical and electrical measurements. The stress-strain ratios were 485 kPa and 1300%, respectively, and the conductivity was 26.1 mS / cm.

[0035] Example 8 Take 5 g of poplar lignocellulose raw material and mix it evenly with a eutectic solvent of glycerol / choline chloride / aluminum chloride at a solid-liquid ratio of 1:6. Then, cook the mixture in an oil bath at 100°C. oThe mixture was kept at C for 2 h. After grinding in a colloid mill for 40 min, a eutectic solvent dispersion containing nano-lignin was obtained. An additional 1 wt% homologous lignin (average particle size 50 nm) and 2 wt% nano-cellulose with a size of 20 nm were added. The pH was adjusted to 8.5, and 20 wt% acrylamide monomer and 0.5 wt% ammonium persulfate were added to the dispersion to prepare a flexible conductive composite gel of nano-lignin at room temperature. Mechanical and electrical properties of the flexible conductive composite gel of nano-lignin were characterized by measurements. The stress-strain ratios were 168 kPa and 665%, respectively, and the conductivity was 18.2 mS / cm. The effects of different biomass raw materials on the gel properties were investigated, and the results are shown in the table below: Hemp raw materials are lightweight, with fine and long fibers, making them excellent nanofillers for enhancing the gel's performance; poplar and bamboo raw materials have high hardness, short fibers, limited pretreatment effects, and low fiber aspect ratios, resulting in limited enhancement of the gel's performance.

[0036]

[0037] Example 9 Take 5 g of bast fiber cellulose raw material and mix it evenly with a eutectic solvent of glycerol / zinc chloride / aluminum chloride at a solid-liquid ratio of 1:6. Then, cook the mixture in an oil bath digester at 100°C. o The mixture was kept at C for 2 h. After milling in a colloid mill for 40 min, a eutectic solvent dispersion containing nano-lignin was obtained. An additional 1 wt% homologous lignin (average particle size 50 nm) and 2 wt% nano-cellulose with a size of 20 nm were added. The pH was adjusted to 8.5, and 20 wt% acrylamide monomer and 0.5 wt% ammonium persulfate were added to the dispersion to prepare a flexible conductive composite gel of nano-lignin at room temperature. Mechanical and electrical properties of the flexible conductive composite gel of nano-lignin were characterized by measurements. The stress-strain ratios were 320 kPa and 850%, respectively, and the conductivity was 23.2 mS / cm. The effects of different eutectic solvents on gel performance were investigated, and the results are shown in the table below. Choline chloride, as a common hydrogen bond acceptor in eutectic solvents, can significantly reduce the viscosity of eutectic solvents and improve liquid stability. Low-viscosity eutectic solvents have stronger penetration effects and higher pretreatment efficiency. Uniform eutectic solvent dispersions are beneficial to improving gel performance. When zinc chloride and lithium chloride are used as hydrogen bond acceptors, the solution viscosity is higher and the time required is longer, which is not conducive to improving gel performance.

[0038]

[0039] Example 10 Take 5 g of bast fiber cellulose raw material and mix it evenly with a eutectic solvent of glycerol / choline chloride / aluminum chloride at a solid-liquid ratio of 1:6. Then, cook the mixture in an oil bath at 140°C. o The mixture was kept at C for 2 h. After grinding in a colloid mill for 40 min, a eutectic solvent dispersion containing nano-lignocellulose was obtained. An additional 1 wt% homologous lignin (average particle size 50 nm) and 2 wt% nano-cellulose with a size of 20 nm were added. The pH was adjusted to 8.5, and 20 wt% acrylamide monomer and 0.5 wt% ammonium persulfate were added to the dispersion to prepare a nano-lignocellulose flexible conductive composite gel at room temperature. Mechanical and electrical properties of the nano-lignocellulose flexible conductive composite gel were characterized by measurements. The stress and strain were 320 kPa and 800%, respectively, and the conductivity was 16.7 mS / cm. The effect of cooking temperature on gel performance was investigated, and the results are shown in the table below: Increasing the cooking temperature improves the penetration of the liquid into the biomass raw material, resulting in a highly dispersed and uniform eutectic solvent dispersion, effectively improving gel performance; excessively high cooking temperatures exacerbate the degradation of the biomass raw material, making it difficult for the eutectic solvent dispersion to maintain gel performance.

[0040]

[0041] Example 11 Take 5 g of bast fiber cellulose raw material and mix it evenly with a eutectic solvent of glycerol / choline chloride / aluminum chloride at a solid-liquid ratio of 1:6. Then, cook the mixture in an oil bath at 100°C. o The mixture was kept at C for 1 h. After grinding in a colloid mill for 40 min, a eutectic solvent dispersion containing nano-lignocellulose was obtained. An additional 1 wt% homologous lignin (average particle size 50 nm) and 2 wt% nano-cellulose with a size of 20 nm were added. The pH was adjusted to 8.5, and 20 wt% acrylamide monomer and 0.5 wt% ammonium persulfate were added to the dispersion to prepare a flexible conductive composite gel of nano-lignocellulose at room temperature. Mechanical and electrical properties of the flexible conductive composite gel of nano-lignocellulose were characterized by mechanical and electrical measurements. The stress-strain ratios were 325 kPa and 605%, respectively, and the conductivity was 16.7 mS / cm. The effect of different holding times on gel performance was investigated, and the results are shown in the table below: Extending the holding time resulted in more uniform mixing of the eutectic solvent and biomass raw materials, yielding a highly dispersible eutectic solvent dispersion, effectively improving gel performance; excessively long holding times degraded the biomass raw materials, making it difficult to further improve gel performance.

[0042]

[0043] Example 12 Take 5 g of bast fiber cellulose raw material and mix it evenly with a eutectic solvent of glycerol / choline chloride / aluminum chloride at a solid-liquid ratio of 1:8. Then, cook the mixture in an oil bath at 100°C. o The mixture was kept at C for 2 h. After grinding in a colloid mill for 40 min, a eutectic solvent dispersion containing nano-lignocellulose was obtained. An additional 1 wt% homologous lignin (average particle size 50 nm) and 2 wt% nano-cellulose with a size of 20 nm were added. The pH was adjusted to 8.5. 20 wt% acrylamide monomer and 0.5 wt% ammonium persulfate were added to the dispersion to prepare a nano-lignocellulose flexible conductive composite gel at room temperature. Mechanical and electrical properties of the nano-lignocellulose flexible conductive composite gel were characterized by stress and strain of 280 kPa and 825%, respectively, and the conductivity was 19.2 mS / cm. The effect of different solid-liquid ratios on gel properties was investigated, and the results are shown in the table below: As the solid-liquid ratio decreased, the biomass raw material content decreased, and the low lignocellulose content was unfavorable for gel network construction, resulting in a decrease in gel performance.

[0044]

[0045] Comparative Example 1 Take 5 g of hemp lignocellulose raw material and mix it evenly with glycerol / choline chloride eutectic solvent at a solid-liquid ratio of 1:6. Then, cook the mixture in an oil bath digester at 100°C. o Incubation at C for 2 h. Grinding in a colloid mill for 40 min failed to yield a eutectic solvent dispersion containing nano-lignocellulose. This demonstrates that using a eutectic solvent without metal salts cannot successfully prepare lignocellulose nanoparticles, ultimately failing to produce a flexible conductive composite gel containing nano-lignocellulose.

[0046] Comparative Example 2 Take 5 g of cellulose raw material and mix it evenly with a eutectic solvent of glycerol / choline chloride / aluminum chloride at a solid-liquid ratio of 1:6. Then, cook the mixture in an oil bath digester at 100°C. o The mixture was kept at temperature C for 2 h. After grinding in a colloid mill for 40 min, a eutectic solvent dispersion of nanocellulose was obtained. Adjusting the pH to 8.5 and adding 20 wt% acrylamide monomer and 0.5 wt% ammonium persulfate to the dispersion failed to produce a metal-based eutectic solvent nanocellulose flexible conductive composite gel at room temperature. This demonstrates that a nanocellulose flexible conductive composite gel cannot be successfully prepared at room temperature without nanolignin.

[0047] Comparative Example 3 Take 5 g of cellulose raw material and mix it evenly with a eutectic solvent of glycerol / choline chloride / aluminum chloride at a solid-liquid ratio of 1:6. Then, cook the mixture in an oil bath digester at 100°C. oThe mixture was kept at C for 2 h. After grinding in a colloid mill for 40 min, a eutectic solvent dispersion of nanocellulose was obtained. Adding additional lignin, adjusting the pH to 8.5, and then adding 20 wt% acrylamide monomer and 0.5 wt% ammonium persulfate to the dispersion failed to produce a flexible conductive composite gel of nanocellulose at room temperature. This indicates that the fragmented lignin particles are uneven and have low nanoscale size, resulting in poor polymerization activity and preventing the successful preparation of a flexible conductive composite gel of nanocellulose at room temperature.

[0048] Comparative Example 4 Take 5 g of cellulose raw material and 1 g of lignin, mix them evenly with a eutectic solvent of glycerol / choline chloride / aluminum chloride at a solid-liquid ratio of 1:6, and cook in an oil bath digester at 100°C. o The mixture was kept at C for 2 h. After grinding in a colloid mill for 40 min, a eutectic solvent dispersion of nano-lignin cellulose was obtained. The pH was adjusted to 8.5, and 20 wt% acrylamide monomer and 0.5 wt% ammonium persulfate were added to the dispersion at room temperature to prepare a flexible conductive composite gel of nano-lignin cellulose. Mechanical and electrical properties of the flexible conductive composite gel of nano-lignin cellulose were characterized by measurements. The stress and strain were 80 kPa and 525%, respectively, and the conductivity was 5 mS / cm. This indicates that the absence of hemicellulose makes it difficult for lignin to form uniformly sized nano-lignin in a eutectic solvent. Poor polymerization activity and uneven polymerization during gel preparation lead to poor performance of the prepared flexible conductive composite gel of nano-lignin cellulose.

[0049] Comparative Example 5 Take 5 g of cellulose raw material, 1 g of lignin, and 1 g of xylan, and mix them thoroughly with a eutectic solvent of glycerol / choline chloride / aluminum chloride at a solid-liquid ratio of 1:6. Cook the mixture in an oil bath at 100°C. o The mixture was kept at C for 2 h. After grinding in a colloid mill for 40 min, a eutectic solvent dispersion of nano-lignin cellulose was obtained. The pH was adjusted to 8.5, and 20 wt% acrylamide monomer and 0.5 wt% ammonium persulfate were added to the dispersion at room temperature to prepare a flexible conductive composite gel of nano-lignin cellulose. Mechanical and electrical properties of the flexible conductive composite gel of nano-lignin cellulose were characterized by measurements. Its stress-strain ratio was 105 kPa and 638%, respectively, and its conductivity was 6.2 mS / cm. This indicates that the addition of exogenous hemicellulose has a limited effect on the formation of nano-lignin, and it is necessary to directly prepare the gel using a one-pot method with natural biomass raw materials and a eutectic solvent.

[0050] Scanning electron microscope images and particle size distributions of lignocellulose raw materials and nano-lignocellulose prepared in Example 1 are shown below. Figure 2As shown. Example 1: Scanning electron microscope images and particle size distribution of controllable preparation of lignin nanocellulose in DES dispersion are shown in the figure. Figure 3 As shown, this indicates that high aspect ratio nano-lignin-cellulose and uniformly dispersed nano-lignin can be efficiently prepared by cooking with a metal salt-based eutectic solvent and mechanical treatment.

[0051] The X-ray photoelectron spectrum of the redox reaction between nano-lignin in nano-lignocellulose and metal ions in Example 1 is shown below. Figure 4 As shown in ab, the introduction of metals leads to an increase in the C=O peak area, indicating that the -OH and -OCH3 groups on the surface of nano-lignin are oxidized to quinones / semiquinones. Figure 4 c indicates that nano-lignin is at 1265 cm⁻¹ -1 The weakening of the -OH peak at this point is due to the effective oxidation of the methoxy groups in the nano-lignin. This indicates that the presence of metal ions successfully oxidizes the phenolic hydroxyl and methoxy groups in the nano-lignin, forming a quinone / semiquinone structure.

[0052] The flexible conductive composite gel made of lignocellulose nanoparticles in Example 1 is as follows: Figure 5 As shown, this demonstrates that the excellent combination of metal salt-based eutectic solvent and wood fiber raw material endows the flexible conductive composite gel with flexible and wide-ranging application characteristics.

[0053] The stress-strain curves of the nano-lignocellulose flexible conductive composite gels prepared in Examples 3, 5, and 7 are shown below. Figure 6 As shown, due to the good interfacial compatibility between the metal salt-based eutectic solvent and the wood nanocellulose, the stress-strain ratio increases to 483.08 kPa and 1294.67% as the content of nanolignin and nanocellulose increases.

[0054] The conductivity of the nano-lignocellulose flexible conductive composite gels prepared in Examples 3, 5, and 7 is as follows: Figure 7 As shown, due to the high ionic conductivity of the metal salt-based eutectic solvent, the increased content of nano-lignin and nano-cellulose provides more ion transport channels, and the conductivity is increased to 26.1 mS / cm.

[0055] The flexible conductive composite gel made of lignocellulose nanoparticles prepared in Example 7 was subjected to constant voltage charging to test its ability to recognize subtle human movements. Figure 8 As shown, the nano-lignocellulose flexible conductive composite gel can accurately detect subtle human movements and transmit stable electrical signals. This indicates that the present invention has excellent application prospects in the fields of flexible electronic devices and wearable devices.

[0056] The nano-lignocellulose flexible conductive composite gel prepared in Example 7 was assembled into a flexible supercapacitor, such as... Figure 9 As shown, the flexible supercapacitor exhibits excellent specific capacitance and remains stable during multiple charge-discharge cycles. This indicates that the present invention has broad application prospects in the field of energy storage.

Claims

1. A method for preparing a nano-lignin-cellulose flexible conductive composite gel, characterized in that, Includes the following steps: S1. A nano-lignin-containing lignocellulose eutectic solvent dispersion is prepared by cooking biomass raw materials using a metal salt-based eutectic solvent and then mechanically processed; the biomass raw materials are any one or a combination of two or more of hemp, wood, grass, and bamboo. The metal salt-based eutectic solvent is a polyol / choline chloride / metal salt, wherein the polyol is any one or a combination of two or more of glycerol, ethylene glycol, propylene glycol, butanediol, hexanediol, and neopentyl glycol, and the metal salt is any one of aluminum chloride, ferric chloride, zinc chloride, copper chloride, magnesium chloride, lithium chloride, and potassium chloride, and the molar ratio of polyol / choline chloride / metal salt is 2:1:0.

2. S2. Adjust the pH of the eutectic solvent of nano-lignin cellulose to 8.5, add polymerizable monomers and initiators to the dispersion prepared in step S1, and rapidly initiate polymerization at room temperature through nano-lignin-metal ion redox reaction to obtain nano-lignin cellulose flexible conductive composite gel. The polymerizable monomer is any one or a combination of two or more of acrylamide, acrylic acid, and glycidyl methacrylate.

2. The preparation method according to claim 1, characterized in that, Add additional nanocellulose or additional nanolignin to the nano-lignin-containing eutectic solvent dispersion in step S1; wherein the additional nanocellulose is any one of hemp nanocellulose, wood nanocellulose, grass nanocellulose, and bamboo nanocellulose; and the additional nanolignin is any one of homologous lignin, alkali lignin, eutectic solvent lignin, and lignin sulfonate in biomass raw materials.

3. The preparation method according to claim 1 or 2, characterized in that, In step S1, the solid-liquid ratio of the biomass feedstock to the eutectic solvent is 1:6-1:10; the cooking conditions are 80-140°C. o C, heat preservation time 1-5 hours.

4. The preparation method according to claim 2, characterized in that, In step S1, the additional nanocellulose in the eutectic solvent dispersion has a diameter of 20-100 nm and a content of 1-10%; and the additional nanolignin in the dispersion has a particle size of 50-200 nm and a content of 0.1-5%.

5. The preparation method according to claim 1, characterized in that, The initiator in step S2 is any one or a combination of two or more of ammonium persulfate, 2,2'-azo(2-methylpropylamidine) dihydrochloride, potassium persulfate, and benzoyl peroxide; the mass of the polymerizable monomer accounts for 20 wt% of the eutectic solvent of nano-lignocellulose at pH=8.5, and the amount of initiator accounts for 0.5 wt% of the polymerizable monomer.

6. A flexible conductive composite gel made of nano-lignocellulose, characterized in that, It is prepared by the preparation method according to any one of claims 1-5.

7. The nano-lignocellulose flexible conductive composite gel according to claim 6, characterized in that, The nano-lignocellulose flexible conductive composite gel has an electrical conductivity of 5-26.1 mS / cm, a tensile stress of 60-485 kPa, and a tensile strain of 300-1400%.

8. The application of the nano-lignocellulose flexible conductive composite gel according to claim 6 or 7 in the preparation of supercapacitors, batteries, flexible sensing devices, soft robots or stretchable components.

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