Conductive lignin-based polyurethane film, and preparation method and application thereof
By introducing dynamic covalent bonds and non-covalent interactions into a polyurethane network, a covalent adaptive network is constructed and conductive nanofillers are added. This solves the problem of preparing high-strength and tough conductive lignin-based polyurethane films using traditional methods, and realizes the preparation of high-performance, low-cost conductive films suitable for flexible wearable devices.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- JIMEI UNIV
- Filing Date
- 2026-05-12
- Publication Date
- 2026-06-30
AI Technical Summary
Existing technologies struggle to prepare conductive lignin-based polyurethane films that combine high mechanical strength and toughness, high electrical conductivity and stability, reprocessability, and low cost. Furthermore, traditional methods suffer from complex processes and are not suitable for flexible wearable devices.
By introducing dynamic covalent bonds and non-covalent interactions into a polyurethane network, a covalent adaptive network is constructed, and conductive nanofillers are added using a solution mixing method to form a dynamic covalent cross-linked network, thus preparing a conductive lignin-based polyurethane film.
It achieves high strength and toughness mechanical properties, good heat resistance and UV shielding, is reprocessable and self-healing, is compatible with flexible wearable devices, reduces production costs, and is environmentally friendly.
Smart Images
Figure CN122302337A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of polymer materials technology, and in particular to a conductive lignin-based polyurethane film, its preparation method, and its application. Background Technology
[0002] Against the backdrop of the booming development of national fitness driven by the concept of "big sports and big health," the market demand for flexible wearable sensing devices is increasing. Piezoresistive strain sensors have attracted widespread attention because they convert physical signals such as heart rate, pulse, and respiratory intensity during exercise into measurable electrical signals, such as changes in resistance, enabling real-time non-invasive measurement and health monitoring. However, traditional silicon or metal oxide-based semiconductor sensors are rigid materials, and their inherent brittleness and lack of flexibility make them difficult to apply directly in wearable devices. Polyurethane film materials, due to their advantages such as light weight, high ductility, and biocompatibility, can meet the comfort and safety requirements of wearable sensing devices. Currently, there are three main methods for combining polyurethane films with nano-conductive components: solution mixing, melt mixing, and in-situ polymerization. Solution mixing of conductive materials is simple to operate, but it requires meeting the minimum amount of conductive filler while achieving the ideal conductivity level. This is because increasing the filler content will not only impair the mechanical properties of the composite material, but also increase the product cost. During melt mixing, the increase of temperature, time and shear force may damage nanoparticles and reduce conductivity, and this method is not entirely applicable to all polyurethane systems. Introducing conductive materials through in-situ polymerization can yield uniformly dispersed conductive polyurethane, but the preparation process is complex, the polymerization reaction is difficult to control, and it affects the uniformity of the product.
[0003] Polyurethanes (PUs) are typically prepared by polymerizing polyisocyanates and polyols. Lignin molecules are rich in active groups such as phenolic and alcoholic hydroxyl groups. Replacing petroleum-based polyols with isocyanates in the synthesis of lignin-based polyurethanes (LPUs) can improve the UV resistance and heat resistance of polyurethanes, while also promoting the efficient and high-value utilization of lignin. Traditional lignin-based PUs rely on stable covalent bonds to form cross-linked networks, resulting in a chemically irreversible structure. They generally suffer from problems such as limited functionality, insufficient toughness, susceptibility to aging and wear, and difficulty in recycling and reuse.
[0004] Therefore, how to use lignin sulfonates to prepare a conductive lignin-based polyurethane film that is green and simple to process, has high mechanical strength and toughness, high electrical conductivity and stability, is reprocessable and low cost, and is suitable for flexible wearable sensors has become a technical problem that urgently needs to be solved in this field. Summary of the Invention
[0005] This invention provides a conductive lignin-based polyurethane film, its preparation method, and its applications. By introducing dynamic covalent bonds and non-covalent interactions into the polyurethane network, a covalent adaptive network is constructed. This network endows the material with self-healing and reconfigurable intelligent properties, thereby significantly broadening its application prospects in the field of flexible wearable devices. Specifically, this invention bridges the flexible chain (polyester diol as the soft segment) with isocyanate and introduces supramolecular interaction units containing dynamic disulfide bonds and hydrogen bonds into the lignin-based polyurethane (LPU) matrix to construct a dynamic covalent crosslinking network. Conductive nanofillers are added to this multiphase LPU matrix using a solution mixing method to promote the formation of the conductive network. Furthermore, the constructed dynamic covalent crosslinking network containing multiple hydrogen bonds can further improve the mechanical properties of the LPU and simultaneously endow it with repair and reconfigurability, thereby overcoming the shortcomings of the prior art mentioned in the background.
[0006] To achieve the above objectives, the technical solution of the present invention is as follows: This invention provides a method for preparing a conductive lignin-based polyurethane film, comprising the following steps: S1. Using lignin sulfonate from papermaking waste liquid as raw material, extract lignin sulfonate; S2. Liquefy lignin sulfonic acid into lignin sulfonic acid polyol; S3. Lignosulfonic acid polyol, polyester polyol, diisocyanate, chain extender containing dynamic disulfide bonds, crosslinking agent and catalyst are mixed to form a mixed system. The mixed system is subjected to polymerization reaction under an inert atmosphere. The raw materials are used to construct a dynamic covalent crosslinking network through diisocyanate and chain extender to control the degree of microphase separation, thereby obtaining polymer film liquid. S4. Add the conductive material to the polymer film liquid, mix evenly, cast into a film and cure to obtain the conductive lignin-based polyurethane film.
[0007] Further, in step S3, the lignin sulfonate polyol accounts for 10-35% of the total mass of the mixed system, the mass ratio of the diisocyanate to the polyester polyol is 0.75-2:1, the amount of the chain extender added is 1.0-6.0% of the total mass of the mixed system, and the amount of the crosslinking agent added is 0.05-0.30% of the total mass of the mixed system. The chain extender containing dynamic disulfide bonds is selected from at least one of 4,4'-diaminodiphenyl disulfide and 2,2'-dithiodibenzoic acid. The specific steps of step S3 are as follows: In a nitrogen atmosphere, lignin sulfonate polyol is mixed and reacted with diisocyanate, chain extender containing dynamic disulfide bonds and catalyst at 60~80 °C for 3~6 hours. Then, polyester polyol and crosslinking agent are added, and the polymerization reaction is continued for 3~5 hours to obtain polymer film liquid.
[0008] Further, the specific steps of step S2 are as follows: the lignin sulfonic acid obtained in step S1 is mixed with polyethylene glycol 400, glycerol and concentrated sulfuric acid in a mass ratio of (30~50):(120~200):(30~50):(3~12) and liquefied to obtain the lignin sulfonic acid polyol. The liquefaction reaction is carried out at a temperature of 100-150 °C for 90-150 min.
[0009] Further, the specific steps of step S1 are as follows: lignosulfonate from papermaking waste liquid is added to water to prepare a lignosulfonate aqueous solution. The lignosulfonate aqueous solution is then treated sequentially with activated and regenerated anion exchange resin and cation exchange resin to remove sodium ions and impurities, thereby obtaining a lignosulfonic acid solution. After drying, lignosulfonic acid is obtained. The lignin sulfonate aqueous solution has a mass fraction of 5 wt%. The lignin sulfonate aqueous solution was soaked in anion exchange resin for 72 h. The anion exchange resin is 717 resin, which is activated by soaking in NaOH solution before use; the cation exchange resin is 732 resin, which is activated by soaking in HCl solution before use. Preferably, the concentration of the NaOH solution is 2M; the concentration of the HCl solution is 2M.
[0010] Further, step S2 also includes the following steps: after the liquefaction reaction is completed, the mixture obtained from the reaction is diluted with anhydrous ethanol, neutralized with an alkaline substance, filtered, and the anhydrous ethanol in the filtrate is removed by rotary evaporation at 65 °C for 2 h. The mixture is then dehydrated under vacuum at 105 °C for 12 h to obtain the lignin sulfonate polyol. The alkaline substance includes NaOH solution.
[0011] Furthermore, the catalyst is selected from at least one of stannous octoate, dibutyltin dilaurate, di(dodecyl sulfide)dibutyltin, monobutyltin oxide, and dibutyltin oxide; The polyester polyol is selected from at least one of polycaprolactone diol and polyethylene adipate diol (PEA-diol). The crosslinking agent is selected from at least one of triethanolamine and tris(2-aminoethyl)amine; The diisocyanate is selected from at least one of hexamethylene diisocyanate, isophorone diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, and 4,4'-diphenylmethane diisocyanate.
[0012] Further, the specific steps of step S4 are as follows: add the conductive material to the polymer film liquid and stir to mix evenly, cast into the mold, and then place it in a 60~80 ℃ forced air drying oven for 12 h to cure into a film, thereby obtaining conductive lignin-based polyurethane. The conductive material is added in an amount of 0.5 to 2.5 wt% of the total mass of the polymer film solution; the conductive material is selected from any one or more of multi-walled carbon nanotubes, graphene, carbon black, Mxene, polyaniline, and polypyrrole.
[0013] In another aspect, the present invention provides a conductive lignin-based polyurethane film, characterized in that it is prepared by the aforementioned preparation method.
[0014] In another aspect, the present invention provides a flexible sensor comprising the aforementioned conductive lignin-based polyurethane film.
[0015] In another aspect, the present invention provides the application of the aforementioned conductive lignin-based polyurethane film in the fabrication of wearable flexible electronic devices.
[0016] Furthermore, wearable flexible electronic devices include: sports wristbands and heart rate monitors.
[0017] The beneficial effects of this invention are: (1) The method for preparing conductive lignin-based polyurethane film disclosed in this invention uses lignin sulfonate from papermaking waste liquid as raw material to realize the high-value utilization of industrial biomass waste; the preparation conditions are mild, the modification efficiency is high, the process is simple, and no waste is generated throughout the process, which meets the requirements of green chemical industry. (2) In the preparation method, a dynamic covalent cross-linked network is constructed, so that the film has both high strength and toughness mechanical properties, good heat resistance and ultraviolet shielding. A stable conductive path can be formed with a low amount of conductive filler, which overcomes the matrix embrittlement problem caused by high addition of traditional conductive fillers. (3) The preparation method utilizes dynamic disulfide bonds and multiple hydrogen bonds in the raw materials to give the film the ability to be reprocessed, self-repaired and reconfigurable. It has excellent conductivity stability, sensing durability and strain response sensitivity, wide detection range and rapid signal response / recovery.
[0018] (4) The raw materials for this method are inexpensive and readily available, resulting in low overall production costs; it is environmentally friendly, the raw materials are renewable, the process is simple, and the film is biodegradable.
[0019] (5) The conductive lignin-based polyurethane film prepared by this method has good biocompatibility and flexibility, and can be directly used for the preparation of flexible sensors. It can be adapted to outdoor sports wearable devices such as sports wristbands and heart rate belts, thus broadening the high-end application scenarios of lignin-based polyurethane. Attached Figure Description To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0020] Figure 1 This is a graph showing the 30-cycle test result of the conductive lignin-based polyurethane film containing 2.5 wt% CNT in Example 1 of the present invention, with a tensile deformation of 15%. Figure 2 This is a graph showing the sensing performance of the conductive lignin-based polyurethane film under three different tensile deformations in Embodiment 1 of the present invention. Figure 3 This is a stress-strain curve of the conductive lignin-based polyurethane film with CNTs added in Embodiment 1 of the present invention before and after stretching. Figure 4 This is a physical image and a real-time sensing response curve of the conductive lignin-based polyurethane film used to monitor finger joint flexion movements in Embodiment 1 of the present invention. Figure 4 a is a real-time sensing response curve of a conductive lignin-based polyurethane film used to monitor finger joint flexion movements. Figure 4 b is a photograph of a conductive lignin-based polyurethane film used to monitor finger joint bending movements when the finger is not bent. Figure 4 c is a photograph of a conductive lignin-based polyurethane film used to monitor finger joint bending movements after the finger has bent. Detailed Implementation
[0021] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0022] Example 1: A conductive lignin-based polyurethane film is prepared by the following method: S1: Extracting lignin sulfonate from papermaking waste liquor. Anion exchange resin 717 was immersed in 2M NaOH solution, and cation exchange resin 732 was immersed in 2M HCl solution for 12 h of activation and regeneration. The resins were then packed into a chromatography column and continuously washed with deionized water until neutral. A 5 wt% lignin sulfonate aqueous solution was prepared from papermaking waste liquor. This solution was first immersed in the activated anion exchange resin for 72 h, then passed through the activated cation exchange resin, and finally washed with deionized water. The solution was collected and freeze-dried to obtain lignin sulfonate powder.
[0023] S2: Preparation of lignin sulfonate polyols In a 500 mL three-necked flask, 40 g of lignin sulfonic acid, 160 g of polyethylene glycol 400, and 40 g of glycerol were added sequentially. Then, 4 g of concentrated sulfuric acid was slowly added dropwise. The mixture was heated to 120 °C in an oil bath and stirred at a constant speed for 120 min to induce a liquefaction reaction. After liquefaction, the mixture was diluted with anhydrous ethanol, neutralized with NaOH solution, and filtered. The filtrate was rotary evaporated at 65 °C for 2 h to remove anhydrous ethanol, and then dehydrated under vacuum at 105 °C for 12 h to obtain a brown, viscous lignin sulfonic acid polyol.
[0024] S3: Preparation of polymer film solution In a nitrogen atmosphere, the above-mentioned lignin sulfonate polyol (20% of the total mass of the mixture formed by all reactants in this step), hexamethylene diisocyanate (HDI), 4,4'-diaminodiphenyl disulfide (chain extender, 3% of the total mass of the mixture), and dibutyltin dilaurate (organotin catalyst) were added to a reactor and reacted at 70 °C for 4 h. Subsequently, polyethylene adipate diol (PEA-diol, polyester polyol, soft segment) and triethanolamine (crosslinking agent, 0.2% of the total mass of the mixture) were added, controlling the mass ratio of diisocyanate to polyester polyol at 1.5:1, and the polymerization reaction was continued for 4 h to obtain a polymer film solution.
[0025] S4: Preparation of conductive lignin-based polyurethane films Add 2.5 wt% of multi-walled carbon nanotubes (MWCNTs) of the polymer film solution to the above polymer film solution, and mix mechanically and ultrasonically until homogeneous. Cast the mixed film solution into a mold, place it in a 70 ℃ forced-air drying oven for 12 h to cure, and finally peel off the film to obtain a conductive lignin-based polyurethane film.
[0026] Example 2 S1: The extraction steps for lignin sulfonic acid are the same as in Example 1.
[0027] S2: Preparation of lignin sulfonate polyols: In a three-necked flask, 30 g of lignin sulfonic acid, 120 g of polyethylene glycol 400, and 30 g of glycerol were mixed. 3 g of concentrated sulfuric acid was added, and the mixture was liquefied at 100 °C for 150 min. Subsequent neutralization, filtration, rotary evaporation, and vacuum dehydration were performed as in Example 1 to obtain the lignin sulfonic acid polyol.
[0028] S3: Preparation of polymer film solution: Under a nitrogen atmosphere, lignin sulfonate polyol (10% of the total mass of the mixture formed by all reactants in this step), isophorone diisocyanate (IPDI), 2,2'-dithiodibenzoic acid (chain extender, 1% added), and stannous octoate (organotin catalyst) were mixed and reacted at 60 °C for 6 h. Subsequently, polycaprolactone diol (polyester polyol, soft segment) and tris(2-aminoethyl)amine (crosslinking agent, 0.05% added) were added, and the mass ratio of isophorone diisocyanate to polyester polyol was controlled at 0.75:1. The reaction was continued for 5 h to obtain a polymer film solution.
[0029] S4: Preparation of conductive lignin-based polyurethane films: 1.0 wt% of graphene was added to the above polymer film solution, and after uniform mixing, it was cast into a mold and cured in a 60℃ forced-air drying oven for 24 h. After peeling off the film, a conductive lignin-based polyurethane film was obtained.
[0030] Example 3 S1: The extraction steps for lignin sulfonic acid are the same as in Example 1.
[0031] S2: Preparation of lignin sulfonate polyols: In a three-necked flask, 50 g of lignin sulfonic acid, 200 g of polyethylene glycol 400, and 50 g of glycerol were mixed. 12 g of concentrated sulfuric acid was added, and the mixture was liquefied at 150 °C for 90 min. Subsequent neutralization, filtration, rotary evaporation, and vacuum dehydration were performed as in Example 1 to obtain the lignin sulfonic acid polyol.
[0032] S3: Preparation of polymer film solution: In a nitrogen atmosphere, lignin sulfonate polyol (35% of the total mass of the mixture formed by all reactants in this step), 4,4'-diphenylmethane diisocyanate (MDI), 4,4'-diaminodiphenyl disulfide (chain extender, 6% added) and dibutyltin dilaurate were reacted at 80 °C for 3 h. Polyethylene adipate diol (PEA-diol) and triethanolamine (crosslinking agent, 0.3% added) were added, and the mass ratio of 4,4'-diphenylmethane diisocyanate (MDI) to polyester polyol was controlled at 2:1. The polymerization reaction was continued for 3 h to obtain a polymer film solution.
[0033] S4: Preparation of conductive lignin-based polyurethane films: Add 2.0 wt% of MXene conductive material to the above polymer film solution, stir evenly, cast to a mold, place in an 80 ℃ forced-air drying oven for 12 h to cure, and peel off the film to obtain a conductive lignin-based polyurethane film.
[0034] Example 4 S1: The extraction steps for lignin sulfonic acid are the same as in Example 1.
[0035] S2: Preparation of lignin sulfonate polyols: In a three-necked flask, 45 g of lignin sulfonic acid, 180 g of polyethylene glycol 400, and 45 g of glycerol were mixed. 6 g of concentrated sulfuric acid was added, and the mixture was liquefied at 130 °C for 110 min. Subsequent steps were the same as in Example 1 to prepare the polyol.
[0036] S3: Preparation of polymer film solution: Under a nitrogen atmosphere, lignin sulfonate polyol (30% of the total mass of the mixture formed by all reactants in this step), 4,4'-dicyclohexylmethane diisocyanate (HMDI), 4,4'-diaminodiphenyl disulfide (chain extender, 4% added), and dibutyltin dilaurate were reacted at 80 °C for 3 h. Polyethylene adipate diol (PEA-diol) and triethanolamine (crosslinking agent, 0.3% added) were added, and the mass ratio of 4,4'-dicyclohexylmethane diisocyanate to polyester polyol was controlled at 2:1. The polymerization reaction was continued for 3 h to obtain a polymer film solution.
[0037] S4: Preparation of conductive lignin-based polyurethane films: Add 0.5 wt% carbon black conductive material to the above polymer film liquid, stir evenly, cast to a mold, place in an 80 ℃ forced-air drying oven for 12 h to cure, and peel off the film to obtain a conductive lignin-based polyurethane film.
[0038] To verify the performance of the conductive lignin-based polyurethane films prepared in Examples 1-4 of this invention, the following related tests were conducted: The conductive lignin-based polyurethane films prepared in Examples 1-4 were subjected to tensile and release cycle tests to assess their mechanical properties. Figure 1 The image shows a cyclic sensing attempt of a conductive lignin-based polyurethane film containing 2.5 wt% CNTs from Example 1, subjected to 30 cycles of tensile deformation at 15%. Figure 1As can be seen, in 30 consecutive stretch-release cycle tests, the relative resistivity change rate (ΔR / R0) of the film exhibits extremely high periodic consistency, with its peak (approximately 14%) and trough baseline remaining stable, without significant resistance signal drift, hysteresis, or attenuation. This indicates that the conductive lignin-based polyurethane film prepared in this invention possesses a stable and robust conductive network structure, endowing the sensor with extremely excellent conductivity stability and sensing durability, meeting the reliability requirements of wearable devices under long-term repeated movement.
[0039] Figure 2 The figure shows the sensing performance curves of the conductive lignin-based polyurethane composite film containing 2.5 wt% CNT in Example 1 under three different degrees of tensile deformation (10%, 15%, and 20%). Figure 2 As shown, with the gradual increase of applied tensile strain, the rate of change of relative resistance of the film increases significantly in a stepwise manner (approximately 10% at 10% strain, approximately 20% at 15% strain, and approximately 40% at 20% strain). At each set strain level, the electrical signal of the composite film maintains regular and stable periodic fluctuations, with rapid response and recovery. This fully demonstrates that the flexible composite film has high sensing sensitivity and a wide detection range for strain changes, accurately capturing, feeding back, and quantifying physical deformation signals of different degrees.
[0040] Figure 3 The image shows a comparison of the tensile strength and elongation at break of lignin-based polyurethane films containing different amounts of CNTs (no CNTs, 1%, 2.5%) before and after tensile testing. Figure 3 It is evident that the pure lignin-based polyurethane film without added conductive materials already possesses excellent initial mechanical properties, with a tensile strength of approximately 46 MPa and an elongation at break of nearly 800%. When 1% CNTs are introduced, a synergistically reinforced dynamic covalent crosslinking network is constructed within the polymer matrix, significantly increasing the tensile strength of the film to approximately 83 MPa while maintaining a high elongation at break of nearly 600%. Even when the CNT content increases to 2.5% (Example 1), its tensile strength remains at a relatively high level of approximately 68 MPa, and the elongation at break still exceeds 400%. This demonstrates that by utilizing lignin sulfonate polyols (lignin-based polyols) and supramolecular interaction units to regulate microphase separation, the polyurethane film of this invention successfully introduces conductive fillers and achieves excellent sensing performance while overcoming the defects of matrix brittleness caused by the addition of traditional conductive fillers, maintaining excellent tensile strength and ultra-high elasticity, perfectly meeting the high strength and toughness design goals of this invention.
[0041] Figure 4 The conductive lignin-based polyurethane film prepared in Example 1 of this invention is used as a flexible sensor to monitor finger joint movement. (Image and real-time sensing response curve are shown.) Figure 4 a- Figure 4 As shown in Figure c, the flexible sensor is flatly attached to the index finger joint. With the periodic "bending-straightening" movement of the finger, the rate of change of resistance (ΔR / R0) exhibits highly synchronized pulse-like fluctuations: when the finger bends, the film stretches, and the resistance rapidly increases, forming a peak; when the finger straightens, the film quickly rebounds, and the resistance instantly returns to the initial baseline. In repeated cyclic tests, the sensor demonstrates extremely fast response / recovery speed, with the signal remaining highly consistent and stable, without significant hysteresis or attenuation. This fully demonstrates that the thin film of this invention possesses excellent flexibility and superior dynamic strain sensing capabilities, accurately capturing human joint movement signals, and has enormous application potential in flexible electronics fields such as wearable health devices.
[0042] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.
Claims
1. A process for the preparation of an electrically conductive lignin-based polyurethane film, characterized in that, Includes the following steps: S1. Using lignin sulfonate from papermaking waste liquid as raw material, extract lignin sulfonate; S2. Liquefy lignin sulfonic acid into lignin sulfonic acid polyol; S3. Lignosulfonic acid polyol, polyester polyol, diisocyanate, chain extender containing dynamic disulfide bonds, crosslinking agent and catalyst are mixed to form a mixed system. The mixed system is subjected to polymerization reaction under an inert atmosphere. The raw materials are used to construct a dynamic covalent crosslinking network through diisocyanate and chain extender to control the degree of microphase separation, thereby obtaining polymer film liquid. S4. Add the conductive material to the polymer film liquid, mix evenly, cast into a film and cure to obtain the conductive lignin-based polyurethane film.
2. The process for the preparation of electrically conductive lignin-based polyurethane films according to claim 1, characterized in that, In step S3, the lignin sulfonate polyol accounts for 10-35% of the total mass of the mixed system, the mass ratio of the diisocyanate to the polyester polyol is 0.75-2:1, the amount of the chain extender added is 1.0-6.0% of the total mass of the mixed system, and the amount of the crosslinking agent added is 0.05-0.30% of the total mass of the mixed system. The chain extender containing dynamic disulfide bonds is selected from at least one of 4,4'-diaminodiphenyl disulfide and 2,2'-dithiodibenzoic acid.
3. The method for preparing the conductive lignin-based polyurethane film according to claim 1, characterized in that, The specific steps of step S3 are as follows: In a nitrogen atmosphere, lignin sulfonate polyol is mixed and reacted with diisocyanate, chain extender containing dynamic disulfide bonds and catalyst at 60~80℃ for 3~6 hours. Then, polyester polyol and crosslinking agent are added, and the polymerization reaction is continued for 3~5 hours to obtain polymer film liquid.
4. The method for preparing the conductive lignin-based polyurethane film according to claim 1, characterized in that, The specific steps of step S2 are as follows: the lignin sulfonic acid obtained in step S1 is mixed with polyethylene glycol 400, glycerol and concentrated sulfuric acid in a mass ratio of (30~50):(120~200):(30~50):(3~12) and liquefied to obtain the lignin sulfonic acid polyol. The liquefaction reaction is carried out at a temperature of 100-150 °C for 90-150 min.
5. The method for preparing the conductive lignin-based polyurethane film according to claim 1, characterized in that, The specific steps of step S1 are as follows: lignosulfonate from papermaking waste liquid is added to water to prepare a lignosulfonate aqueous solution. The lignosulfonate aqueous solution is then treated sequentially with activated and regenerated anion exchange resin and cation exchange resin to remove sodium ions and impurities, thereby obtaining a lignosulfonic acid solution. After drying, lignosulfonic acid is obtained. The lignin sulfonate aqueous solution has a mass fraction of 5 wt%. The lignin sulfonate aqueous solution was soaked in anion exchange resin for 72 h. The anion exchange resin is 717 resin, which is activated by soaking in NaOH solution before use; the cation exchange resin is 732 resin, which is activated by soaking in HCl solution before use.
6. The method for preparing the conductive lignin-based polyurethane film according to claim 4, characterized in that, Step S2 further includes the following steps: after the liquefaction reaction is completed, the mixture obtained from the reaction is diluted with anhydrous ethanol, neutralized with an alkaline substance, filtered, and the anhydrous ethanol in the filtrate is removed by rotary evaporation at 65 °C for 2 h. The mixture is then dehydrated under vacuum at 105 °C for 12 h to obtain the lignin sulfonate polyol. The alkaline substance includes NaOH solution.
7. The method for preparing a conductive lignin-based polyurethane film according to claim 1, characterized in that, The catalyst is selected from at least one of stannous octoate, dibutyltin dilaurate, di(dodecyl sulfide)dibutyltin, monobutyltin oxide, and dibutyltin oxide; The polyester polyol is selected from at least one of polycaprolactone diol and polyethylene adipate diol; The crosslinking agent is selected from at least one of triethanolamine and tris(2-aminoethyl)amine; The diisocyanate is selected from at least one of hexamethylene diisocyanate, isophorone diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, and 4,4'-diphenylmethane diisocyanate.
8. The method for preparing the conductive lignin-based polyurethane film according to claim 1, characterized in that, The specific steps of step S4 are as follows: add the conductive material to the polymer film liquid and stir to mix evenly, cast into the mold, and then place it in a 60~80 ℃ forced air drying oven for 12 h to cure into a film, thereby obtaining conductive lignin-based polyurethane. The conductive material is added in an amount of 0.5 to 2.5 wt% of the total mass of the polymer film solution; the conductive material is selected from any one or more of multi-walled carbon nanotubes, graphene, carbon black, Mxene, polyaniline, and polypyrrole.
9. A conductive lignin-based polyurethane film, characterized in that, It is prepared by any one of claims 1 to 8.
10. The application of the conductive lignin-based polyurethane film of claim 9 in the preparation of wearable flexible electronic devices.