Lignin-cellulose nanofiber-based composite membrane, preparation method and application

Abstract

The present invention relates to the technical field of composite film preparation, and in particular to a lignin-cellulose nanofiber-based composite film, a preparation method and an application. The preparation method includes: mixing a carboxylated cellulose nanofiber aqueous solution, a polyvinyl alcohol aqueous solution and an ethanol solution of 4-phenylazophenol, pouring the mixture into a mold, and drying the mixture to obtain a basement membrane; using polyimide and dealkalized lignin as raw materials, using polyethylene glycol diglycidyl ether as a cross-linking agent, and carrying out a condensation reaction in the presence of a solvent to obtain a dealkalized lignin-polyimide composite solution, applying the solution to a basement membrane, and drying the solution to obtain a lignin-cellulose nanofiber-based composite film. The lignin-cellulose nanofiber-based composite film obtained by the preparation method of the present invention not only has excellent light-to-heat conversion and humidity gradient change performance, but also has excellent wet responsiveness and light responsiveness, overcoming the defects of the prior art.

Description

Technical Field

[0001] The present invention relates to the technical field of composite membrane preparation, and in particular to a lignin-cellulose nanofiber-based composite membrane, a preparation method and applications. Background Art

[0002] Inspired by biological adaptive mechanisms, stimuli-responsive actuators can sense external environmental signals such as light, heat, electricity, magnetic fields, and organic solvents and vapors to produce mechanical deformation or complex motions, thus showing significant application potential in soft robotics, wearable devices, biomedicine, and agricultural production. Among them, actuators that can respond to multiple environmental inputs can achieve multimodal actuation to adapt to complex environmental changes and meet multifunctional needs. Multi-stimulus-responsive systems are particularly valuable for adapting to dynamic environments, but the development of actuators that can achieve precise, reversible, and multimodal actuation under simple control remains challenging.

[0003] Among numerous environmental stimuli, photoactuators have attracted considerable attention for their rapid response and wet actuators for their extensive low-energy actuation capabilities. However, their synergistic integration faces significant material limitations. Traditional petroleum-based actuators suffer from poor biocompatibility and complex processing, while emerging biomass material systems often sacrifice response speed or interfacial stability for the sake of sustainability.

[0004] Achieving fast response, directional controllability and reversible drive is crucial to the design of intelligent actuators. For wet-responsive actuators, the rational construction of a double-layer heterostructure, that is, a composite structure consisting of an active layer and a passive layer, can provide an effective way to improve its performance. Among them, the gradient structure of the passive layer can simultaneously improve the response speed and deformation amplitude. Directional drive is achieved through alignment, patterning and gradient design, while reversible drive relies on the reversible expansion or contraction mechanism of the material. Studies have shown that the construction of asymmetric double-layer or multi-layer structures can effectively integrate the above characteristics and achieve complex structural deformation. Although a series of fruitful results have been achieved, there are still key problems such as poor interface compatibility, insufficient controllability of the response direction and difficulty in achieving complex programmable deformation. Summary of the Invention

[0005] In response to the shortcomings of the existing technology, the present invention provides a lignin-cellulose nanofiber-based composite membrane, preparation method and application. The present invention uses carboxylated cellulose nanofibers, polyvinyl alcohol and 4-phenylazophenol as base raw materials to obtain a base membrane; uses polyimide and dealkalized lignin as raw materials, and polyethylene glycol diglycidyl ether as a cross-linking agent to obtain a lignin-polyimide composite solution through a condensation reaction; then obtains a lignin-cellulose nanofiber-based composite membrane by coating the base membrane with the lignin-polyimide composite solution multiple times. The present invention integrates carboxylated cellulose nanofibers with excellent wet responsiveness, dealkalized lignin with photothermal conversion effect and UV shielding properties, and 4-phenylazophenol with UV-visible light responsiveness through a coating strategy to obtain an asymmetric lignin-cellulose nanofiber-based composite membrane with excellent interfacial compatibility, overcoming the shortcomings of the existing technology and making it have a wider application prospect in the fields of flexible electronics, smart materials and programmable actuators.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is:

[0007] The first object of the present invention is to provide a method for preparing a lignin-cellulose nanofiber-based composite film, comprising the following steps:

[0008] S1. After mixing the carboxylated cellulose nanofiber aqueous solution, the polyvinyl alcohol aqueous solution and the 4-phenylazophenol ethanol solution, the mixture is poured into a mold, and after drying, a basement membrane is formed by utilizing the hydrogen bond cross-linking effect of the carboxylated cellulose nanofiber, polyvinyl alcohol and 4-phenylazophenol.

[0009] S2. Using polyimide and dealkalized lignin as raw materials and polyethylene glycol diglycidyl ether as a cross-linking agent, a condensation reaction is carried out in the presence of a solvent. Under the action of the cross-linking agent, the dealkalized lignin is in situ cross-linked in the polyimide to form oligomers, thereby obtaining a dealkalized lignin-polyimide composite solution. The oligomer is a dealkalized lignin gel formed by the dealkalized lignin cross-linked with the polyethylene glycol diglycidyl ether.

[0010] S3. Coating the dealkalized lignin-polyimide composite solution on the base film, and drying it to obtain a lignin-cellulose nanofiber-based composite film.

[0011] Preferably, in the basement membrane, the mass ratio of 4-phenylazophenol to carboxylated cellulose nanofibers is 0.5-2:10, and the added amount of polyvinyl alcohol accounts for 10 wt % to 30 wt % of the total solid content of the basement membrane.

[0012] Preferably, the coating times are 1 to 4 times.

[0013] Preferably, the thickness of the basement membrane is 55 μm to 59 μm.

[0014] Preferably, the mass ratio of polyimide to dealkalized lignin is 1:0.5-3.

[0015] Preferably, the condensation reaction is carried out under stirring at 50° C. to 60° C. for 2 h to 2.5 h.

[0016] Preferably, when preparing the basement membrane, the drying treatment conditions are: drying at 50° C. to 60° C. for 6 h to 8 h.

[0017] Preferably, when preparing the lignin-cellulose nanofiber-based composite membrane, the drying treatment conditions are: drying at 50° C. to 60° C. for 0.5 h to 1 h.

[0018] Preferably, the solvent is selected from N,N-dimethylformamide.

[0019] Preferably, the polyimide is prepared according to the following steps:

[0020] 4,4′-methylenebis(2-ethyl-6-methylaniline) and 4,4′-(hexafluoroisopropylidene)diphthalic anhydride are dissolved in N,N-dimethylformamide and subjected to polycondensation reaction to obtain a polyamic acid precursor solution; the polyamic acid precursor solution is first cured at 100°C for 2 hours, then cured at 180°C for 2 hours, and finally cured at 250°C for 2 hours to obtain polyimide; wherein the molar ratio of 4,4′-methylenebis(2-ethyl-6-methylaniline) to 4,4′-(hexafluoroisopropylidene)diphthalic anhydride is 1:0.8~1.2.

[0021] Preferably, in the process of preparing polyimide, the conditions of the polycondensation reaction are: first stirring the reaction at -5°C to 5°C for 0.5h to 1h, and then stirring the reaction at room temperature for 8h.

[0022] The second object of the present invention is to provide a lignin-cellulose nanofiber-based composite membrane prepared by the above preparation method.

[0023] Preferably, the lignin-cellulose nanofiber-based composite membrane has an asymmetric structure.

[0024] The third object of the present invention is to provide a programmable actuator made of the above-mentioned lignin-cellulose nanofiber-based composite film.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] 1. The present invention provides a method for preparing a lignin-cellulose nanofiber-based composite membrane, comprising the following steps: mixing a carboxylated cellulose nanofiber aqueous solution, a polyvinyl alcohol aqueous solution, and an ethanol solution of 4-phenylazophenol, and placing the mixture in a mold. After drying, a base membrane is formed by utilizing the hydrogen bond cross-linking effect of the carboxylated cellulose nanofiber, polyvinyl alcohol, and 4-phenylazophenol; using polyimide and dealkalized lignin as raw materials and polyethylene glycol diglycidyl ether as a cross-linking agent, a condensation reaction is carried out in the presence of a solvent; under the action of the cross-linking agent, the dealkalized lignin is in situ cross-linked in the polyimide to form oligomers, thereby obtaining a dealkalized lignin-polyimide composite solution; coating the dealkalized lignin-polyimide composite solution on the base membrane, and drying the mixture to obtain a lignin-cellulose nanofiber-based composite membrane. The present invention utilizes the heat resistance and hydrophobicity of polyimide, as well as the excellent compatibility of dealkalized lignin, polyimide and the base film, to increase the interface structure of the lignin-cellulose nanofiber-based composite membrane, thereby forming a lignin-cellulose nanofiber-based composite membrane structure with excellent light-to-heat conversion and humidity gradient changes. This not only overcomes the problems of complex process, poor interface compatibility of the composite structure, and uncontrollable light response and moisture response directions in the prior art, but also significantly improves the mechanical properties of the lignin-cellulose nanofiber-based composite membrane, and enables it to have multi-response and programmable functions, providing a fast and scalable method for the development of programmable actuators, giving it broader application prospects in the fields of flexible electronics, smart materials and programmable actuators.

[0027] 2. The lignin-cellulose nanofiber-based composite film of the present invention has excellent photothermal conversion effect, wet responsiveness and photoresponsiveness, and the photoresponsiveness includes ultraviolet light and infrared light. In terms of preparation process, the base film is prepared by solution casting, and the lignin-cellulose nanofiber-based composite film is prepared by coating a dealkalized lignin-polyimide composite solution, which enhances the interface bonding performance between the layers; in terms of material selection and function assignment, 4-phenylazophenol with ultraviolet-visible light responsiveness is introduced into the base film to give it ultraviolet light responsiveness; dealkalized lignin with photothermal conversion effect and ultraviolet shielding properties is introduced into polyimide for in-situ crosslinking to obtain a dealkalized lignin-polyimide composite solution, which has infrared light conversion properties; in addition, carboxylated cellulose nanofibers have wet responsiveness, and carboxylated cellulose nanofibers are introduced into the base film to give it wet responsiveness.

[0028] 3. The lignin-cellulose nanofiber-based composite membrane of the present invention has programmable multi-responsive stimulus deformation characteristics, and can achieve controllable transformation from a two-dimensional planar structure to a predetermined three-dimensional structure driven by external stimuli through patterning processing, which makes it show significant application potential in the field of developing programmable actuators.

[0029] 4. The lignin-cellulose nanofiber-based composite membrane prepared by the present invention has the characteristics of good interface bonding, uniform thickness and simple operation steps. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 Infrared spectra of LIG oligomers, dealkalized lignin powder, and polyethylene glycol diglycidyl ether solution.

[0031] Figure 2 PI, CNF-Azo of Comparative Example 2, and S of Example 1 10 and S 10 -Infrared spectrum of 1PL-3.

[0032] Figure 3 is S of Example 1 10 and S 10 -0.5PL-3, S 10 -1PL-3、S 10 -2PL-3 and S 10 -3PL-3 U-surface SEM image, where a is the S of Example 1 10 , b is S 10 -0.5PL-3, c is S 10 -1PL-3, d is S 10 -2PL-3, e is S 10 -3PL-3.

[0033] Figure 4 For S 10 -1PL-3 and S 20 -1PL-3 D-surface SEM image, where a is S 10 -1PL-3, b is S 20 -1PL-3.

[0034] Figure 5 is S of Example 1 10 、S 10 -1PL-3 and S 20 -1PL-3 EDS diagram, where a is S of Example 1 10 , a1 is nitrogen, a2 is fluorine, b is S 10 -1PL-3 U-face, b1 is nitrogen, b2 is fluorine, c is S 20 -1PL-3 U-face, c1 is nitrogen, c2 is fluorine, d is S 10 -1PL-3 D face, d1 is nitrogen, d2 is fluorine, e is S 20 -1PL-3 D-plane, e1 is nitrogen, and e2 is fluorine.

[0035] Figure 6 is S of Example 1 10、S 10 -1PL-3 and S 20 -1PL-3 cross-section SEM image, where a is the SEM image of Example 1 10 , b is S 10 -1PL-3, c is S 20 -1PL-3.

[0036] Figure 7 is S of Example 1 10 、S 10 -1PL-1、S 10 -1PL-2, S 10 -1PL-3 and S 10 -1PL-4 U-surface light-to-heat conversion diagram.

[0037] Figure 8 S0, S in Example 1 10 、S 10 -1PL-3、S 20 UV-visible spectrum of -1PL-3.

[0038] Figure 9 For S 10 -0.5PL-3, S 10 -1PL-3、S 10 -2PL-3 and S 10 -3PL-3 U-surface light-to-heat conversion diagram.

[0039] Figure 10 For S 10 -1PL-3 U-surface and D-surface 60s light-to-heat conversion diagram and thermal imaging diagram, where a is the surface temperature change diagram and b is the thermal imaging diagram.

[0040] Figure 11 is S of Example 1 10 、S 10 -L and S 10 -1PL-3 thermogravimetric analysis diagram, wherein the illustration is S of Example 1 10 、S 10 -L and S 10 -1PL-3 thermogravimetric analysis diagram of the local enlargement at 80℃~115℃.

[0041] Figure 12 is S of Example 1 10 、S 10 -0.5PL-3, S 10 -1PL-3、S 10 -2PL-3 and S 10-3PL-3 D surface humidification 10s deformation angle result diagram and actual diagram, where a is the deformation angle result diagram, b is the deformation angle actual diagram, b1 is the S of Example 1 10 , b2 is S 10 -0.5PL-3, b3 is S 10 -1PL-3, b4 is S 10 -2PL-3, b5 is S 10 -3PL-3.

[0042] Figure 13 For S 10 Actual images of the D-surface 2 / 3 of -1PL-3 before and after deformation after contact with a water droplet, where a is the initial image after contact with a water droplet, and b is the deformation image after contact with a water droplet.

[0043] Figure 14 For S 10 -1PL-3 curvature change diagram under different humidity conditions.

[0044] Figure 15 For S 10 -1PL-3 recovery speed diagram after humidification deformation under near-infrared lamp, natural light, and LED light, where a is near-infrared lamp, a1 is 0s, a2 is 20s, a3 is 40s, a4 is 70s, and a5 is 120s; b is natural light, b1 is 0s, b2 is 20s, b3 is 40s, b4 is 70s, and b5 is 120s; c is LED light, c1 is 0s, c2 is 20s, c3 is 40s, c4 is 70s, and c5 is 120s.

[0045] Figure 16 For S 20 -1PL-3's D surface deformed after contact with a water droplet and then recovered and bent in the opposite direction after exposure to ultraviolet light. (a) shows the initial image after contact with a water droplet, (b) the deformation image after contact with a water droplet, (c) the initial image just after exposure to ultraviolet light, and (d) the deformation image after exposure to ultraviolet light.

[0046] Figure 17 For S 10 -1PL-3's D-surface 1 / 2 contact water drop twisting and end contact water drop folding diagram, where a is the initial diagram of the contact water drop at 1 / 2, b is the deformation diagram after contact with the water drop, c is the twisting and opening diagram after illumination, d is the initial diagram of the end contact water drop, e is the folding change diagram of the end contact water drop, and f is the folding and unfolding diagram after illumination.

[0047] Figure 18 For S 10 -1PL-3 weight-lifting diagram, where a is the initial diagram, b is the weight-lifting diagram after the humidifier humidifies the D surface, and c is the weight-lifting diagram after the humidifier is removed and the U surface is irradiated with a near-infrared lamp.

[0048] Figure 19 For S 10 -1PL-3 grasping diagram, where a is the initial diagram, b is the diagram of the humidifier grasping the object on the D surface while humidifying, c is the diagram of the humidifier being removed and the object being lifted, and d is the diagram of the object being released after being exposed to light and falling off.

[0049] Figure 20 For the S of Application Example 1 10 The obtained cross-shaped deformation diagram, where a is the initial diagram, b is the deformation diagram after water spraying, and c is the recovery and reverse deformation diagram after sunlight exposure.

[0050] Figure 21 For S 10 Programmable cross-bonding deformation diagram of -1PL-3, where a is the initial diagram, b is the deformation diagram after water spraying, and c is the recovery and reverse deformation diagram after sunlight exposure. DETAILED DESCRIPTION

[0051] The technical solutions of the present invention will be described clearly and completely below in conjunction with the data in the embodiments of the present invention. Obviously, the embodiments described are only a part of the embodiments of the present invention, rather than all of the embodiments. It should be noted that the professional terms used in the present invention are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention. Unless otherwise specified, the various raw materials, reagents, instruments and equipment used in the following embodiments of the present invention can be purchased from the market or prepared by existing methods.

[0052] Among them, carboxylated cellulose nanofibers, denoted as CNF, with a carboxyl content of 1.18 mmol / g and a carboxyl content of 4.5% ± 0.5%, were purchased from Zhongshan Nanofiber New Materials Co., Ltd.; 4-phenylazophenol, denoted as Azo, 98 wt%, was purchased from Shanghai MacLean Biochemical Technology Co., Ltd.; polyethylene glycol diglycidyl ether, denoted as PEGDE, with a molecular weight of 500, and dealkalized lignin, denoted as LIG, were both purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.; polyvinyl alcohol, denoted as PVA, of analytical grade, was purchased from Tianjin Damao Chemical Reagent Factory; 4,4′-methylenebis(2-ethyl-6-methylaniline), denoted as ME-MDA, was purchased from Yuanda Chemical Co., Ltd.; 4,4′-(hexafluoroisopropylidene)diphthalic anhydride, denoted as 6FDA, was purchased from Tianjin Zotye Material Technology Co., Ltd.; anhydrous ethanol and NN, dimethylformamide, denoted as DMF, were both purchased from Tianjin Fuyu Fine Chemical Co., Ltd. All reagents and solvents were used directly without further purification.

[0053] In the existing technology, although progress has been made in achieving wet- and light-responsive actuation by constructing asymmetric bilayer or multilayer structures, there are still key problems such as poor interface compatibility, insufficient controllability of the response direction, and difficulty in achieving complex programmable deformation.

[0054] The present invention addresses the poor interfacial compatibility issues of existing technologies by employing a hydrogen-bonded crosslinked basement membrane and a crosslinker-mediated in-situ condensation coating strategy. Specifically, a dense basement membrane is formed by utilizing a hydrogen-bonded network between carboxylated cellulose nanofibers, polyvinyl alcohol, and 4-phenylazophenol. Polyethylene glycol diglycidyl ether is then used to in-situ crosslink dealkalized lignin in polyimide, forming a dealkalized lignin-polyimide composite solution as the coating layer. This significantly enhances interlayer bonding and compatibility, resolving the issue of poor interfacial compatibility.

[0055] The present invention addresses the limited controllability of response direction in existing technologies by combining asymmetric gradient structure design with the targeted integration of functional components and precise control of coating thickness. Specifically, the base film imparts both wet and UV responsiveness, while the coating layer provides infrared light-to-heat conversion and UV shielding, creating a dual-response gradient for both light and wetness. By controlling the number of coatings, the coating layer thickness and distribution are adjusted, effectively controlling the direction of both wet and light-responsive deformation, such as bidirectional bending and twisting.

[0056] To address the difficulties in achieving complex programmable deformations in existing technologies, the present invention overcomes this problem by integrating multiple stimulus response mechanisms and utilizing patterned coating or localized stimulation. Specifically, the UV-light isomerization of 4-phenylazophenol in the basement membrane, the wet expansion or contraction of carboxylated cellulose nanofibers, and the infrared photothermal effect of dealkalized lignin in the coating layer work synergistically to drive rapid, reversible deformation. Patterning treatment, achieved through mask exposure or selective coating of a dealkalized lignin-polyimide composite solution, enables the lignin-cellulose nanofiber-based composite membrane to controllably transform from a two-dimensional plane to a complex three-dimensional structure according to a preset program under specific light or wet stimulation, achieving programmable deformation.

[0057] In order to enable those skilled in the art to more clearly understand the technical solution of the present invention, the following will be described in detail with reference to specific embodiments:

[0058] The polyimide in the embodiment of the present invention is prepared according to the following method:

[0059] Method 1: Add 7.05 g of ME-MDA to 55.5 g of DMF. After it is fully dissolved, add 11.325 g of 6FDA, and stir the reaction in a water bath at -5°C for 0.5 h, and then stir the reaction at room temperature for 8 h to obtain a polyamic acid precursor solution, i.e., PAA solution; wherein the molar ratio of ME-MDA to 6FDA is 1:1.02; pour the PAA solution into a culture dish and place it in an oven for gradient temperature curing, i.e., first cure at 100°C for 2 h, then cure at 180°C for 2 h, and then cure at 250°C for 2 h to obtain polyimide, which is recorded as PI.

[0060] Method 2: Add 7.05 g of ME-MDA to 55.5 g of DMF. After it is fully dissolved, add 13.324 g of 6FDA, and stir the reaction in a -5°C water bath for 0.5 h, and then stir the reaction at room temperature for 8 h to obtain a polyamic acid precursor solution, i.e., PAA solution; wherein the molar ratio of ME-MDA to 6FDA is 1:1.2; pour the PAA solution into a Petri dish and place it in an oven for gradient temperature curing, i.e., first cure at 100°C for 2 h, then cure at 180°C for 2 h, and then cure at 250°C for 2 h to obtain polyimide, recorded as PI.

[0061] Method 3: Add 7.05 g of ME-MDA to 55.5 g of DMF. After it is fully dissolved, add 8.882 g of 6FDA, and stir the reaction in a 5°C water bath for 0.5 h, and then stir the reaction at room temperature for 8 h to obtain a polyamic acid precursor solution, i.e., PAA solution; wherein the molar ratio of ME-MDA to 6FDA is 1:0.8; pour the PAA solution into a Petri dish and place it in an oven for gradient temperature curing, i.e., first cure at 100°C for 2 h, then cure at 180°C for 2 h, and then cure at 250°C for 2 h to obtain polyimide, recorded as PI.

[0062] The PI in Examples 1 to 10 of the present invention were all prepared by Method 1.

[0063] Example 1

[0064] A method for preparing a lignin-cellulose nanofiber-based composite film comprises the following steps:

[0065] S1. Dissolve 0.02 g of Azo in 2 mL of anhydrous ethanol and stir for 30 min to obtain an Azo solution for later use; weigh 4.4 g of CNF and disperse it in 5.56 g of deionized water and stir to mix evenly to obtain a CNF aqueous solution with a solid content of 2 wt%, for later use.

[0066] The CNF aqueous solution with a solid content of 2 wt%, the Azo solution and 5 g of PVA aqueous solution with a solid content of 4 wt% were mixed, stirred thoroughly for 1 h, and then ultrasonicated for 1 h. The mixture was then taken out and poured into a 10 cm 5cm silicon film mold, and placed it in an oven and dried at 50℃ for 6h to obtain a basement membrane, which was recorded as S 10 .

[0067] S2. Weigh 0.2 g of PI and add it to 0.91 mL of DMF. After fully dissolving, obtain an 18 wt% PI solution; weigh 0.2 g of LIG and dissolve it in 2 mL of DMF. Add 0.225 g of PEGDE and mix with the PI solution. Place in a water bath and stir at 50°C for 2.5 h to obtain a dealkalized lignin-polyimide composite solution, recorded as PL composite solution.

[0068] S3, evenly coat the PL composite solution on S 10 After coating for 3 times, the membrane was dried at 50 °C for 1 h to obtain a lignin-cellulose nanofiber composite membrane, which was recorded as S 10 -1PL-3.

[0069] Example 2

[0070] A method for preparing a lignin-cellulose nanofiber-based composite membrane is the same as the preparation steps in Example 1, except that the mass of Azo in S1 is replaced from 0.02 g to 0.03 g, comprising the following steps:

[0071] S1. Dissolve 0.03 g of Azo in 2 mL of anhydrous ethanol and stir for 30 min to obtain an Azo solution for later use; weigh 4.4 g of CNF and disperse it in 5.56 g of deionized water and stir to mix evenly to obtain a CNF aqueous solution with a solid content of 2 wt%, for later use.

[0072] The CNF aqueous solution with a solid content of 2 wt%, the Azo solution and 5 g of PVA aqueous solution with a solid content of 4 wt% were mixed, stirred thoroughly for 1 h, and then ultrasonicated for 1 h. The mixture was then taken out and poured into a 10 cm 5cm silicon film mold, and placed it in an oven and dried at 50℃ for 6h to obtain a basement membrane, which was recorded as S 15 .

[0073] S2. Weigh 0.2 g of PI and add it to 0.91 mL of DMF. After fully dissolving, obtain an 18 wt% PI solution; weigh 0.2 g of LIG and dissolve it in 2 mL of DMF. Add 0.225 g of PEGDE and mix with the PI solution. Place in a water bath and stir at 50°C for 2.5 h to obtain a dealkalized lignin-polyimide composite solution, recorded as PL composite solution.

[0074] S3, evenly coat the PL composite solution on S 15 After coating for 3 times, the membrane was dried at 50 °C for 1 h to obtain a lignin-cellulose nanofiber composite membrane, which was denoted as S 15 -1PL-3.

[0075] Example 3

[0076] A method for preparing a lignin-cellulose nanofiber-based composite membrane is the same as the preparation steps in Example 1, except that the mass of Azo in S1 is replaced from 0.02 g to 0.04 g, comprising the following steps:

[0077] S1. Dissolve 0.04 g of Azo in 2 mL of anhydrous ethanol and stir for 30 min to obtain an Azo solution for later use; weigh 4.4 g of CNF and disperse it in 5.56 g of deionized water and stir to mix evenly to obtain a CNF aqueous solution with a solid content of 2 wt%, for later use.

[0078] The CNF aqueous solution with a solid content of 2 wt%, the Azo solution and 5 g of PVA aqueous solution with a solid content of 4 wt% were mixed, stirred thoroughly for 1 h, and then ultrasonicated for 1 h. The mixture was then taken out and poured into a 10 cm 5cm silicon film mold, and placed it in an oven and dried at 50℃ for 6h to obtain a basement membrane, which was recorded as S 20 .

[0079] S2. Weigh 0.2 g of PI and add it to 0.91 mL of DMF. After fully dissolving, obtain an 18 wt% PI solution; weigh 0.2 g of LIG and dissolve it in 2 mL of DMF. Add 0.225 g of PEGDE and mix with the PI solution. Place in a water bath and stir at 50°C for 2.5 h to obtain a dealkalized lignin-polyimide composite solution, recorded as PL composite solution.

[0080] S3, evenly coat the PL composite solution on S 20 After coating for 3 times, the membrane was dried at 50 °C for 1 h to obtain a lignin-cellulose nanofiber composite membrane, which was denoted as S 20 -1PL-3.

[0081] Example 4

[0082] A method for preparing a lignin-cellulose nanofiber-based composite membrane is the same as the preparation steps in Example 1, except that the mass of Azo in S1 is replaced from 0.02 g to 0.01 g, comprising the following steps:

[0083] S1. Dissolve 0.01 g of Azo in 2 mL of anhydrous ethanol and stir for 30 min to obtain an Azo solution for later use; weigh 4.4 g of CNF and disperse it in 5.56 g of deionized water and stir to mix evenly to obtain a CNF aqueous solution with a solid content of 2 wt%, for later use.

[0084] The CNF aqueous solution with a solid content of 2 wt%, the Azo solution and 5 g of PVA aqueous solution with a solid content of 4 wt% were mixed, stirred thoroughly for 1 h, and then ultrasonicated for 1 h. The mixture was then taken out and poured into a 10 cm 5 cm silicon film mold, and placed it in an oven and dried at 50 ° C for 6 h to obtain a basement membrane, which was recorded as S5.

[0085] S2. Weigh 0.2 g of PI and add it to 0.91 mL of DMF. After fully dissolving, obtain an 18 wt% PI solution; weigh 0.2 g of LIG and dissolve it in 2 mL of DMF. Add 0.225 g of PEGDE and mix with the PI solution. Place in a water bath and stir at 50°C for 2.5 h to obtain a dealkalized lignin-polyimide composite solution, recorded as PL composite solution.

[0086] S3, the PL composite solution was evenly coated on S5, after coating 3 times, it was dried at 50 ° C for 1 h to obtain a lignin-cellulose nanofiber-based composite film, which was recorded as S5-1PL-3.

[0087] Example 5

[0088] A method for preparing a lignin-cellulose nanofiber-based composite membrane is the same as the preparation steps in Example 2, except that the mass ratio of PI to LIG in S2 is replaced from 1:1 to 1:0.5. The method comprises the following steps:

[0089] S1. Dissolve 0.02 g of Azo in 2 mL of anhydrous ethanol and stir for 30 min to obtain an Azo solution for later use; weigh 4.4 g of CNF and disperse it in 5.56 g of deionized water and stir to mix evenly to obtain a CNF aqueous solution with a solid content of 2 wt%, for later use.

[0090] The CNF aqueous solution with a solid content of 2 wt%, the Azo solution and 5 g of PVA aqueous solution with a solid content of 4 wt% were mixed, stirred thoroughly for 1 h, and then ultrasonicated for 1 h. The mixture was then taken out and poured into a 10 cm 5cm silicon film mold, and placed it in an oven and dried at 50℃ for 6h to obtain a basement membrane, which was recorded as S 10 .

[0091] S2. Weigh 0.2 g of PI and add it to 0.91 mL of DMF. After fully dissolving, obtain an 18 wt% PI solution; weigh 0.1 g of LIG and dissolve it in 2 mL of DMF. Add 0.225 g of PEGDE and mix with the PI solution. Place in a water bath and stir at 50 ° C for 2.5 h to obtain a dealkalized lignin-polyimide composite solution, recorded as PL composite solution.

[0092] S3, evenly coat the PL composite solution on S 10 After coating for 3 times, the membrane was dried at 50 °C for 1 h to obtain a lignin-cellulose nanofiber composite membrane, which was denoted as S 10 -0.5PL-3.

[0093] Example 6

[0094] A method for preparing a lignin-cellulose nanofiber-based composite membrane is the same as the preparation steps in Example 2, except that the mass ratio of PI to LIG in S2 is replaced from 1:1 to 1:2. The method comprises the following steps:

[0095] S1. Dissolve 0.02 g of Azo in 2 mL of anhydrous ethanol and stir for 30 min to obtain an Azo solution for later use; weigh 4.4 g of CNF and disperse it in 5.56 g of deionized water and stir to mix evenly to obtain a CNF aqueous solution with a solid content of 2 wt%, for later use.

[0096] The CNF aqueous solution with a solid content of 2 wt%, the Azo solution and 5 g of PVA aqueous solution with a solid content of 4 wt% were mixed, stirred thoroughly for 1 h, and then ultrasonicated for 1 h. The mixture was then taken out and poured into a 10 cm 5cm silicon film mold, and placed it in an oven and dried at 50℃ for 6h to obtain a basement membrane, which was recorded as S 10 .

[0097] S2. Weigh 0.2 g of PI and add it to 0.91 mL of DMF. After fully dissolving, obtain an 18 wt% PI solution. Weigh 0.4 g of LIG and dissolve it in 2 mL of DMF. Add 0.225 g of PEGDE and mix with the PI solution. Place in a water bath and stir at 50°C for 2.5 h to obtain a dealkalized lignin-polyimide composite solution, recorded as PL composite solution.

[0098] S3, evenly coat the PL composite solution on S 10 After coating for 3 times, the membrane was dried at 50 °C for 1 h to obtain a lignin-cellulose nanofiber composite membrane, which was denoted as S 10 -2PL-3.

[0099] Example 7

[0100] A method for preparing a lignin-cellulose nanofiber-based composite membrane is the same as the preparation steps in Example 2, except that the mass ratio of PI to LIG in S2 is replaced from 1:1 to 1:3. The method comprises the following steps:

[0101] S1. Dissolve 0.02 g of Azo in 2 mL of anhydrous ethanol and stir for 30 min to obtain an Azo solution for later use; weigh 4.4 g of CNF and disperse it in 5.56 g of deionized water and stir to mix evenly to obtain a CNF aqueous solution with a solid content of 2 wt%, for later use.

[0102] The CNF aqueous solution with a solid content of 2 wt%, the Azo solution and 5 g of PVA aqueous solution with a solid content of 4 wt% were mixed, stirred thoroughly for 1 h, and then ultrasonicated for 1 h. The mixture was then taken out and poured into a 10 cm 5cm silicon film mold, and placed it in an oven and dried at 50℃ for 6h to obtain a basement membrane, which was recorded as S 10 .

[0103] S2. Weigh 0.2 g of PI and add it to 0.91 mL of DMF. After fully dissolving, obtain an 18 wt% PI solution; weigh 0.6 g of LIG and dissolve it in 2 mL of DMF. Add 0.225 g of PEGDE and mix with the PI solution. Place in a water bath and stir at 50°C for 2.5 h to obtain a dealkalized lignin-polyimide composite solution, recorded as PL composite solution.

[0104] S3, evenly coat the PL composite solution on S 10 After coating for 3 times, the membrane was dried at 50 °C for 1 h to obtain a lignin-cellulose nanofiber composite membrane, which was denoted as S 10 -3PL-3.

[0105] Example 8

[0106] A method for preparing a lignin-cellulose nanofiber composite membrane is the same as the preparation steps in Example 1, except that the number of coating times in S3 is replaced from 3 times to 1 time, comprising the following steps:

[0107] S1. Dissolve 0.02 g of Azo in 2 mL of anhydrous ethanol and stir for 30 min to obtain an Azo solution for later use; weigh 4.4 g of CNF and disperse it in 5.56 g of deionized water and stir to mix evenly to obtain a CNF aqueous solution with a solid content of 2 wt%, for later use.

[0108] The CNF aqueous solution with a solid content of 2 wt%, the Azo solution and 5 g of PVA aqueous solution with a solid content of 4 wt% were mixed, stirred thoroughly for 1 h, and then ultrasonicated for 1 h. The mixture was then taken out and poured into a 10 cm 5 cm silicon film mold, and placed it in an oven and dried at 60 ° C for 8 h to obtain a basement membrane, which was recorded as S 10 .

[0109] S2. Weigh 0.2 g of PI and add it to 0.91 mL of DMF. After fully dissolving, obtain an 18 wt% PI solution. Weigh 0.2 g of LIG and dissolve it in 2 mL of DMF. Add 0.225 g of PEGDE and mix with the PI solution. Place the mixture in a water bath and stir at 50°C for 2.5 h to obtain a dealkalized lignin-polyimide composite solution, recorded as PL composite solution.

[0110] S3, evenly coat the PL composite solution on S 10 After coating once, the membrane was dried at 50 °C for 0.5 h to obtain a lignin-cellulose nanofiber composite membrane, which was recorded as S 10 -1PL-1.

[0111] Example 9

[0112] A method for preparing a lignin-cellulose nanofiber composite membrane is the same as the preparation steps in Example 1, except that the number of coating times in S3 is replaced from 3 times to 2 times, comprising the following steps:

[0113] S1. Dissolve 0.02 g of Azo in 2 mL of anhydrous ethanol and stir for 30 min to obtain an Azo solution for later use; weigh 4.4 g of CNF and disperse it in 5.56 g of deionized water and stir to mix evenly to obtain a CNF aqueous solution with a solid content of 2 wt%, for later use.

[0114] The CNF aqueous solution with a solid content of 2 wt%, the Azo solution and 5 g of PVA aqueous solution with a solid content of 4 wt% were mixed, stirred thoroughly for 1 h, and then ultrasonicated for 1 h. The mixture was then taken out and poured into a 10 cm 5 cm silicon film mold, and placed it in an oven and dried at 60 ° C for 8 h to obtain a basement membrane, which was recorded as S 10 .

[0115] S2. Weigh 0.2 g of PI and add it to 0.91 mL of DMF. After fully dissolving, obtain an 18 wt% PI solution; weigh 0.2 g of LIG and dissolve it in 2 mL of DMF. Add 0.225 g of PEGDE and mix with the PI solution. Place in a water bath and stir at 50°C for 2.5 h to obtain a dealkalized lignin-polyimide composite solution, recorded as PL composite solution.

[0116] S3, evenly coat the PL composite solution on S 10 After coating twice, the membrane was dried at 60 °C for 0.5 h to obtain a lignin-cellulose nanofiber composite membrane, which was denoted as S 10 -1PL-2.

[0117] Example 10

[0118] A method for preparing a lignin-cellulose nanofiber-based composite membrane is the same as the preparation steps in Example 1, except that the number of coating times in S3 is replaced by 4 times from 3 times, comprising the following steps:

[0119] S1. Dissolve 0.02 g of Azo in 2 mL of anhydrous ethanol and stir for 30 min to obtain an Azo solution for later use; weigh 4.4 g of CNF and disperse it in 5.56 g of deionized water and stir to mix evenly to obtain a CNF aqueous solution with a solid content of 2 wt%, for later use.

[0120] The CNF aqueous solution with a solid content of 2 wt%, the Azo solution and 5 g of PVA aqueous solution with a solid content of 4 wt% were mixed, stirred thoroughly for 1 h, and then ultrasonicated for 1 h. The mixture was then taken out and poured into a 10 cm 5cm silicon film mold, and placed it in an oven to dry at 50℃ for 8h to obtain the basement membrane, which was recorded as S 10 .

[0121] S2. Weigh 0.2 g of PI and add it to 0.91 mL of DMF. After fully dissolving, obtain an 18 wt% PI solution; weigh 0.2 g of LIG and dissolve it in 2 mL of DMF, and add 0.225 g of PEGDE and mix with the PI solution. Place it in a water bath and stir at 50°C for 2.5 hours to obtain a dealkalized lignin-polyimide composite solution, recorded as PL composite solution.

[0122] S3, evenly coat the PL composite solution on S 10 After coating 4 times, the membrane was dried at 60 °C for 1 h to obtain a lignin-cellulose nanofiber composite membrane, which was recorded as S 10 -1PL-4.

[0123] Comparative Example 1

[0124] A method for preparing a cellulose nanofiber composite membrane comprises the following steps:

[0125] S1. Weigh 4.4 g of CNF and disperse it in 5.56 g of deionized water, stirring and mixing to obtain a CNF aqueous solution with a solid content of 2 wt%, which is set aside.

[0126] S2, weigh 5g of PVA aqueous solution with a solid content of 4wt% and the above CNF aqueous solution with a solid content of 2wt%, mix them, stir them thoroughly for 1h, then ultrasonicate them for 1h, then take them out and pour them into a 10cm The cellulose nanofiber composite membrane was prepared by placing it in a 5 cm silicon membrane mold and drying it in an oven at 50 °C for 6 h to obtain a cellulose nanofiber composite membrane, which was recorded as S0.

[0127] Comparative Example 2

[0128] A method for preparing a cellulose nanofiber membrane comprises the following steps:

[0129] S1. Dissolve 0.02 g of Azo in 2 mL of anhydrous ethanol and stir for 30 min to obtain an Azo solution for later use; weigh 4.4 g of CNF and disperse it in 5.56 g of deionized water and stir evenly to obtain a CNF aqueous solution with a solid content of 2 wt% for later use.

[0130] S2, the CNF aqueous solution with a solid content of 2 wt% and the Azo solution were mixed, stirred for 1 h, then ultrasonicated for 1 h, and then taken out and poured into a 10 cm The cellulose nanofiber membrane was prepared by placing the membrane into a 5 cm silicon membrane mold and drying it in an oven at 50 °C for 6 h to obtain a cellulose nanofiber membrane, which was designated as CNF-Azo.

[0131] Comparative Example 3

[0132] A method for preparing a lignin oligomer composite film comprises the following steps:

[0133] S1. Dissolve 0.02 g of Azo in 2 mL of anhydrous ethanol and stir for 30 min to obtain an Azo solution for later use; weigh 4.4 g of CNF and disperse it in 5.56 g of deionized water and stir to mix evenly to obtain a CNF aqueous solution with a solid content of 2 wt%, for later use.

[0134] Weigh 5g of PVA aqueous solution with a solid content of 4wt%, the above CNF aqueous solution with a solid content of 2wt% and the above Azo solution, mix them, stir them thoroughly for 1h, then ultrasonicate them for 1h, and then take them out and pour them into a 10cm 5cm silicon film mold, and placed it in an oven and dried at 50℃ for 6h to obtain a basement membrane, which was recorded as S 10 .

[0135] S2. Weigh 0.2 g of LIG and dissolve it in 2 mL of DMF. Add 0.225 g of PEGDE, and place the mixture in a water bath at 50° C. and stir for 2.5 h to obtain a lignin oligomer solution, i.e., LIG ​​oligomer.

[0136] S3, LIG ​​oligomer is evenly coated on S 10 After coating for 3 times, the film was dried at 50℃ for 1h to obtain a lignin oligomer composite film, which was recorded as S 10 -L.

[0137] For ease of analysis, the side of the lignin-cellulose nanofiber-based composite membrane coated with the PL composite solution was marked as the U side, and the side not coated with the PL composite solution was marked as the D side.

[0138] LIG oligomers are formed by the etherification reaction between the epoxy bond of PEGDE and the phenolic hydroxyl group of LIG. Figure 1 It is concluded that the epoxy group in PEGDE is at 758 cm-1 、845cm -1 and 911cm -1 The characteristic peak at 1027 cm in LIG disappears in the LIG oligomer film. -1 The stretching vibration peak of -COC- is significantly reduced in the LIG oligomer film, indicating that LIG oligomers are generated.

[0139] observe Figure 2 It is concluded that PI is at 2936cm -1 The peak mainly comes from CH stretching vibration, 1783cm -1 and 1721cm -1 The peak at 1366 cm is the -C=O stretching vibration peak on the imide. -1 The stretching vibration peak of the CN bond is 724 cm -1 The peak at 1104 cm is the stretching vibration peak of the imine ring. -1 The stretching vibration peak of CF is shown in Figure 3, which indicates that PI was successfully prepared.

[0140] For CNF-Azo, at 3333 cm -1 The broad absorption band near 2900 cm -1 The peaks near 1052 cm are due to the stretching vibration of OH and -CH-. -1 、897cm -1 and 1162cm -1 The absorption peaks at 1602 cm represent the stretching vibration of COC, β-glycosidic bond and pyranose ring skeleton vibration, which are characteristic peaks unique to the cellulose macromolecular structure; -1 and 1031cm -1 Indicates the stretching vibration of C=O and CO. 1588cm -1 The -N=N- absorption peak in the azobenzene molecule is at 10 At 3333cm -1 The peak intensity near 838 cm -1 The absorption peak at 3333 cm is the CC stretching vibration in PVA. After coating the PL composite solution, the lignin-cellulose nanofiber-based composite film -1 The intensity of the stretching vibration peak nearby increases, and the peaks related to PI and LIG oligomers can be found.

[0141] from Figure 3 It is concluded that S of Example 1 10 The surface of the lignin-cellulose nanofiber-based composite membrane is relatively flat, with protrusions in some areas. After coating with the PL composite solution, a large number of flake and granular aggregates appear on the surface of the lignin-cellulose nanofiber-based composite membrane, resulting in a significant increase in surface roughness. 10-0.5PL-3,S 10 -1PL-3 has improved surface smoothness. As the LIG mass in the PL composite solution increases further, such as S 10 -2PL-3 and S 10 -3PL-3 surface roughness is relatively improved. 20 -1PL-3 surface SEM Figure 4 As shown, when the mass of Azo in the basement membrane increases, compared with S 10 -1PL-3,S 20 The amount of flake and block protrusions on the -1PL-3D surface increased significantly.

[0142] Combined with Table 1 and Figure 5 Further analysis revealed that the S 10 、S 10 -1PL-3 and S 20 -1PL-3 positive D surface EDS results show that compared with the S in Example 1 10 , S 10 -1PL-3 and S 20 -1PL-3 has a significant increase in the content of F and N elements, and S 10 -1PL-3 and S 20 The F and N content of the U-surface of -1PL-3 was significantly higher than that of its D-surface. It was concluded that a lignin-cellulose nanofiber-based composite membrane with an asymmetric structure was successfully prepared by the coating method.

[0143] Table 1 S of Example 1 10 and S 10 -1PL-3 and S 20 -1PL-3 U-face and D-face element mass percentage table

[0144]

[0145] from Figure 6 It is concluded that S of Example 1 10 The cross section is relatively flat and the thickness is 55 μm. After coating the PL composite solution, S 10 -1PL-3 and S 20 The cross section of -1PL-3 became rough and multi-level holes appeared, but no obvious delamination was observed, and the thickness increased to 57μm and 59μm, respectively.

[0146] from Figure 7 It is concluded that S of Example 1 10The surface temperature of the lignin-cellulose nanofiber-based composite membrane increased from an initial 30°C to 35°C and then remained constant over time. However, after coating with the PL composite solution, the surface temperature of the lignin-cellulose nanofiber-based composite membrane increased significantly, reaching a maximum temperature of 64.07°C on the U surface within 60 seconds. This indicates that the temperature increase of the lignin-cellulose nanofiber-based composite membrane is caused by photothermal conversion, not by heating from the near-infrared light.

[0147] like Figure 8 As shown in FIG, S0 has an obvious absorption peak at 360 nm, which is due to the absorption of ultraviolet light by cellulose. When the wavelength is greater than 556 nm, the light absorption of the lignin-cellulose nanofiber-based composite film is close to 0. 10 、S 10 -1PL-3 and S 20 -1PL-3 not only shows high absorption in the ultraviolet region, but also has a significantly increased absorption rate in the visible light region and near infrared region. 10 , S 10 The absorption of -1PL-3 in the visible and near-infrared regions increased, and the light absorption of the lignin-cellulose nanofiber-based composite film increased significantly with the increase in Azo mass. In addition, a clear absorption peak was observed at 897nm, which is related to the characteristic absorption of dealkalized lignin.

[0148] As the number of coating times of PL composite solution increases, S 10 The temperature of -1PL-3 surface is the highest. This is because the more times of coating, the higher the content of dealkalized lignin, and the more obvious the light-heat conversion. When the number of coatings reaches 4 times, the surface temperature of the lignin-cellulose nanofiber-based composite membrane decreases significantly. This is because the fluorinated PI tends to accumulate on the surface, and its thermal conductivity is low, which leads to a decrease in the surface temperature of the lignin-cellulose nanofiber-based composite membrane. When the relative mass of PI and LIG oligomer is adjusted, the surface temperature of the lignin-cellulose nanofiber-based composite membrane decreases. Figure 9 As can be seen, S 10 -1PL-3 has the highest temperature rise, S 10 -2PL-3 and S 10 -3PL-3 has a lower temperature rise, which is consistent with the 10 -2PL-3 and S 10 The relatively high content of LIG oligomers in -3PL-3 leads to the decrease of PI surface enrichment photothermal performance. 10 -1PL-3 has the best light-to-heat conversion effect.

[0149] from Figure 10 It was observed that when 100mW near-infrared lamp was used to irradiate S 10-1PL-3, the surface temperature of the U surface is significantly higher than that of the D surface, which further proves that the lignin-cellulose nanofiber-based composite membrane of the present invention has an asymmetric structure. 10 , S 10 The surface temperature of the D surface of -1PL-3 increased to 47.2℃ within 60s, indicating that the dealkalized lignin diffused into the interior of the basement membrane. At the same time, the addition of PL composite solution can effectively improve the heat resistance of the lignin-cellulose nanofiber-based composite membrane. When the S of Example 1 was irradiated with a 500mW near-infrared laser lamp, the heat resistance of the S 10 When the PL composite solution is applied, the temperature rises rapidly and burns through, while the lignin-cellulose nanofiber-based composite film heats up rapidly but does not burn through after being coated. Figure 11 The TGA test results were consistent with those of

[0150] Table 2 S of Example 1 10、 PI and S 10 -L and S 10 -Thermogravimetric analysis data sheet of 1PL-3

[0151]

[0152] Combine Figure 11 From Table 2, it can be seen that the S of Example 1 10 T 5% and T max They are 101.9℃, 318.1℃, S 10 -1PL-3 T 5% and T max 103.8 and 321.5 °C, respectively, and the maximum thermal weight loss rate decreased, indicating that the thermal stability of the lignin-cellulose nanofiber-based composite film was improved after coating with the PL composite solution.

[0153] From the beginning of humidification, the D surface of the lignin-cellulose nanofiber-based composite membrane quickly bends and deforms toward the U surface, and after the humidification is removed, the lignin-cellulose nanofiber-based composite membrane continues to bend until it reaches the maximum deformation. Figure 12 As can be seen from the figure, the S 10 The maximum bending angle reaches 50°, S 10 The deformation angle of -0.5PL-3 decreased to 25°, and with the increase of PL composite solution, the maximum deformation angle reached 60°. After the PL composite solution was applied, the thickness of the lignin-cellulose nanofiber-based composite film increased, and the humidity gradient change increased; however, the dealkalized lignin is rich in rigid benzene ring structures, which inhibited deformation. It can be concluded that the deformation amplitude of the lignin-cellulose nanofiber-based composite film is the result of the combined action of multiple factors. Under the same conditions, S 10-1PL-3 has the best wet response effect, and subsequent application test characterization is mainly based on S 10 -1PL-3 as an example.

[0154] S 10 -1PL-3 was cut into strips with a length of 3 cm and a width of 5 mm to obtain a lignin-cellulose nanofiber-based composite membrane strip actuator, referred to as a strip actuator. The strip actuator was pasted into different shapes according to test requirements and performance tests were performed:

[0155] like Figure 13 As shown in the figure, when approximately one-third of the strip actuator contacts a water droplet, its two ends rapidly lift up, supporting each other to form a droplet shape. This is because the cellulose and PVA on the D surface of the strip actuator are rich in hydrophilic groups, while the U surface is less hydrophilic due to the enrichment of PI. When the D surface of the strip actuator is humidified, water molecules diffuse inward, forming a humidity gradient. This causes the strip actuator to absorb water and expand to varying degrees along this gradient, resulting in responsive deformation.

[0156] observe Figure 14 It is found that in the range of 50%~90% RH, under different relative humidity conditions, the curvature of the D surface of the strip actuator ranges from 0.714cm to -1 Increased to 8.59cm -1 , that is 0.2055cm -1 % RH -1 , and then when the relative humidity drops to 50% RH, its curvature returns to 0.94 cm -1 , indicating that the strip actuator has excellent deformation and recovery capabilities.

[0157] observe Figure 15 Figure a shows that during the 20-second humidification of the strip actuator's D surface by the humidifier, the strip actuator bends toward the U surface; then, under near-infrared light irradiation, the strip actuator's bending angle decreases and eventually recovers to 6°, indicating that the strip actuator has a dual-response deformation characteristic of moisture and light. At the same time, the strip actuator also has a responsive deformation characteristic under natural light or LED light irradiation, but its response speed is lower than that of near-infrared light source, and the degree of recovery is lower, as shown in Figure 5. Figure 15 As shown in Figures b and c.

[0158] S 20 -1PL-3 is cut into strips with a length of 3 cm and a width of 5 mm to obtain S 20 -1PL-3 actuator. Observation Figure 16 It is concluded that S 20 After the wet response bending of the -1PL-3 actuator, the D surface can be asymmetrically restored by irradiating it with ultraviolet light, indicating that the S 20-1PL-3 actuator also has UV-visible light responsiveness. This is because when wet response deformation occurs and near-infrared light is irradiated, the dealkalized lignin absorbs near-infrared light and undergoes photothermal conversion, accelerating S 20 -1PL-3 actuator internal water evaporation, making S 20 -1PL-3 actuator recovers deformation. It is worth noting that since dealkalized lignin has ultraviolet light absorption properties, and 4-phenylazophenol has ultraviolet-visible light response recovery properties. Therefore, S 20 The -1PL-3 actuator can only respond when the D surface is irradiated with ultraviolet light and bend toward the U surface. And only when the Azo mass is high can there be relatively obvious deformation. However, the dealkalized lignin is mainly enriched on the U surface, and the photothermal conversion effect is more obvious. Therefore, although S 20 The U and D surfaces of the S-1PL-3 actuator both have wet response characteristics, but the U surface responds more obviously when irradiated with near-infrared light, indicating that the S 20 The -1PL-3 actuator has light-responsive deformation direction controllability.

[0159] When different positions of the strip actuator contact a water droplet, its deformation is different. Figure 17 As shown, a water droplet is placed on a glass plate. The middle of a strip actuator contacts the droplet, causing it to rapidly spread across the contact surface, twisting the strip. When illuminated by light, the kink untwists and the ends tilt upward. When the end of the strip actuator contacts the water droplet, the droplet spreads, soaking half of the actuator. The unsoaked side bends 180°, then recovers to approximately 60° upon illumination.

[0160] Based on the asymmetric response of the two sides of the strip actuator to the same stimulus, the strip actuator can be designed as an actuator with programmable deformation. Figure 18 As shown, a strip actuator is glued to a plastic rod, with a sponge block attached at each end. The rod is held horizontally, simulating the process of lifting a heavy object. Applying moisture to the center of the D-surface of the strip actuator causes its ends to bend upward, thereby lifting the sponge block. Subsequently, a near-infrared light is applied in the opposite direction, causing the strip actuator to return to its horizontal position.

[0161] like Figure 19 As shown, strip actuators are cross-fixed on plastic rods, acting as grippers to simulate the process of a robotic arm grasping and unloading a heavy object. When moisture is applied to the gripper's surface, the gripper deforms, allowing it to grasp a sponge without dropping it. Once the robotic arm reaches its destination, light stimulation releases the gripper, allowing the sponge to be unloaded.

[0162] In addition, programmable deformation can also be achieved by locally spraying PL composite solution on the substrate membrane or using the asymmetric responsiveness of lignin-cellulose nanofiber-based composite membrane to prepare a combined actuator using wet-heat response. Figure 20 As shown, the S of Example 1 10 Strips 3 cm long and 5 mm wide were cut and pasted into a cross shape. The PL composite solution of Example 1 was applied from 1 / 2 of the non-overlapping portion to the area near the overlapping portion. A small amount of water was then sprayed on the cross-shaped surface. The cross-shaped surface was bent downward, and after being exposed to light, it first returned to flatness and then bent upward. This process can simulate the working process of an actuated hinge.

[0163] like Figure 21 As shown, a composite actuator was fabricated by cross-pasting strip actuators with their U and D sides facing upwards, leveraging the asymmetric responsiveness of a lignin-cellulose nanofiber-based composite membrane. After humidification, the strip actuators with their U sides facing upwards deformed significantly. However, when the composite actuator was supported and exposed to light, the strip actuators with their U sides facing upwards recovered and even reversed their shape, forming a three-dimensional structure. This suggests that the lignin-cellulose nanofiber-based composite membrane of the present invention can transform stimulus-driven actuation from a two-dimensional planar structure to a three-dimensional structure, demonstrating its potential for the preparation and application of programmable actuators.

[0164] It should be noted that when the present invention involves numerical ranges, it should be understood that both endpoints of each numerical range and any value between the two endpoints can be selected. Since the steps and methods used are the same as those in the embodiments, in order to avoid redundancy, the present invention describes preferred embodiments. Although preferred embodiments of the present invention have been described, those skilled in the art will be able to make additional changes and modifications to these embodiments once they understand the basic inventive concepts. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

Claims

1. A method for preparing a lignin-cellulose nanofiber-based composite film, characterized in that: The following steps are involved: A carboxylated cellulose nanofiber aqueous solution, a polyvinyl alcohol aqueous solution and a 4-phenylazophenol ethanol solution are mixed and dried, and a basement membrane is formed by utilizing hydrogen bonding cross-linking between the carboxylated cellulose nanofiber, the polyvinyl alcohol and the 4-phenylazophenol; Using polyimide and dealkalized lignin as raw materials and polyethylene glycol diglycidyl ether as a cross-linking agent, a condensation reaction is carried out in the presence of a solvent. Under the action of the cross-linking agent, the dealkalized lignin is in situ cross-linked in the polyimide to form oligomers, thereby obtaining a dealkalized lignin-polyimide composite solution. The dealkalized lignin-polyimide composite solution is coated on a base film and dried to obtain a lignin-cellulose nanofiber-based composite film.

2. The method for preparing a lignin-cellulose nanofiber-based composite film according to claim 1, wherein: In the basement membrane, the mass ratio of 4-phenylazophenol to the carboxylated cellulose nanofibers in the carboxylated cellulose nanofiber aqueous solution is 0.5-2:10, and the mass of the polyvinyl alcohol in the polyvinyl alcohol aqueous solution accounts for 10wt%-30wt% of the total solid content of the basement membrane.

3. The method for preparing the lignin-cellulose nanofiber-based composite film according to claim 1, characterized in that: The thickness of the basement membrane is 55μm~59μm.

4. The method for preparing a lignin-cellulose nanofiber-based composite film according to claim 1, wherein: The mass ratio of polyimide to dealkalized lignin is 1:0.5~3.

5. The method for preparing the lignin-cellulose nanofiber-based composite film according to claim 1, characterized in that: The condensation reaction conditions are: stirring at 50°C~60°C for 2h~2.5h.

6. The method for preparing a lignin-cellulose nanofiber-based composite film according to claim 1, wherein: When preparing the basement membrane, the drying conditions are: drying at 50°C to 60°C for 6h to 8h.

7. The method for preparing a lignin-cellulose nanofiber-based composite film according to claim 1, characterized in that: Polyimide was prepared according to the following steps: 4,4′-methylenebis(2-ethyl-6-methylaniline) and 4,4′-(hexafluoroisopropylidene)diphthalic anhydride are dissolved in N,N-dimethylformamide to carry out polycondensation reaction to obtain a polyamic acid precursor solution; The polyamic acid precursor solution was first cured at 100°C for 2 h, then cured at 180°C for 2 h, and finally cured at 250°C for 2 h to obtain polyimide; The molar ratio of 4,4′-methylenebis(2-ethyl-6-methylaniline) to 4,4′-(hexafluoroisopropylidene)diphthalic anhydride is 1:0.8-1.

2.

8. A lignin-cellulose nanofiber-based composite membrane, characterized in that The lignin-cellulose nanofiber-based composite membrane is prepared by the preparation method of the lignin-cellulose nanofiber-based composite membrane according to any one of claims 1 to 7.

9. The lignin-cellulose nanofiber-based composite membrane according to claim 8, characterized in that The lignin-cellulose nanofiber-based composite membrane exhibits an asymmetric structure.

10. A programmable actuator, characterized in that: It is prepared using the lignin-cellulose nanofiber-based composite membrane according to claim 8.

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