Green lignin-based fiber membrane as well as preparation method and application thereof

Abstract

The invention discloses a green lignin-based fiber membrane as well as a preparation method and application thereof, and the method comprises the following steps: 1, mixing choline chloride and lactic acid, and magnetically stirring at 60-80 DEG C to obtain transparent DES liquid; 2, adding the wheat straw powder into DES liquid, reacting at 110-150 DEG C for 3-12 hours, filtering, and collecting DES filtrate rich in lignin; 3, adding water into the DES filtrate rich in lignin, and magnetically stirring to obtain a green and nontoxic precursor electrostatic spinning solution; 4, adding polyvinyl alcohol into the precursor electrostatic spinning solution, and stirring at 90-105 DEG C until the polyvinyl alcohol is completely dissolved to obtain a uniform and viscous electrostatic spinning solution; and 5, adding the electrostatic spinning solution into an injector of electrostatic spinning equipment, and preparing the green lignin-based fiber membrane through electrostatic spinning at room temperature. The raw materials are easy to obtain, the preparation process is simple, and the prepared lignin-based fiber membrane has the advantages of being non-toxic, degradable, adjustable in porosity and excellent in mechanical property.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials technology, specifically a green lignin-based fiber membrane, its preparation method, and its application. Background Technology

[0002] Traditional electrolyte membranes mostly use polyolefin materials, which have stable electrochemical performance, but have the following problems: First, they are non-degradable and have poor environmental compatibility; second, they are prone to shrinkage at high temperatures, leading to the risk of battery short circuits; third, they have low surface polarity, making it difficult to achieve uniform electrolyte wetting; fourth, most polyolefin materials are made from petroleum-based raw materials, which are non-renewable and exacerbate the problem of resource scarcity. Therefore, there is an urgent need to develop sustainable alternative materials.

[0003] Lignin, as one of the main components of plant cell walls, has a three-dimensional network structure and abundant hydroxyl functional groups, which can provide a natural channel for ion transport. However, existing lignin-based materials have technical bottlenecks such as difficulty in fiber film formation and insufficient mechanical strength, making it difficult to meet the dual requirements of membranes for porosity and mechanical properties. Currently, researchers have tried to improve the performance of lignin through blending modification, but the proportion of biomass components often decreases, losing the core advantages of non-toxicity and biodegradability of renewable materials.

[0004] Therefore, there is an urgent need to explore a novel method for preparing lignin-based films that can improve their mechanical properties while maintaining the biomass component content. Summary of the Invention

[0005] The purpose of this invention is to provide a green lignin-based fiber membrane, its preparation method, and its application. The raw materials are readily available, the preparation process is simple, and the prepared lignin-based fiber membrane has the characteristics of being non-toxic, biodegradable, having adjustable porosity, and excellent mechanical properties, which can meet the performance requirements of electrolyte membranes.

[0006] This invention is achieved through the following technical solution:

[0007] A method for preparing a green lignin-based fiber membrane includes the following steps:

[0008] Step 1: Mix choline chloride and lactic acid in a molar ratio of 1:(1~2) and stir magnetically at 60~80℃ to obtain a transparent DES liquid;

[0009] Step 2: According to the mass ratio of wheat straw powder to DES liquid of 1:10, add wheat straw powder to DES liquid, react at 110-150℃ for 3-12 hours, filter, and collect DES filtrate rich in lignin.

[0010] Step 3: Add water to the lignin-rich DES filtrate according to the mass ratio of water to lignin-rich DES filtrate (1-5):1, stir magnetically, and obtain a green and non-toxic precursor electrospinning solution.

[0011] Step 4: Add polyvinyl alcohol to the electrospinning solution of the precursor and stir at 90-105°C until the polyvinyl alcohol is completely dissolved to obtain a uniform and viscous electrospinning solution, wherein the weight fraction of polyvinyl alcohol in the electrospinning solution is 8-12 wt%.

[0012] Step 5: Add the electrospinning solution to the syringe of the electrospinning equipment, and prepare a green lignin-based fiber membrane by electrospinning at room temperature.

[0013] Furthermore, the magnetic stirring time in step 1 is 6 hours.

[0014] Furthermore, step 2 also includes passing the wheat straw powder through a 40-mesh sieve.

[0015] Furthermore, in step 3, the mass ratio of water to lignin-rich DES filtrate is 2:1.

[0016] Furthermore, the magnetic stirring time in step 3 is 3 hours.

[0017] Furthermore, the parameters for electrospinning in step 5 are: voltage of 15-20kV, collection distance of 7-12cm, and injection pump propulsion rate of a constant rate of 2.5-5mL / h.

[0018] Furthermore, the room temperature in step 5 is 24±2℃.

[0019] A green lignin-based fiber membrane.

[0020] Application of a green lignin-based fiber membrane as an electrolyte separator for supercapacitors.

[0021] The present invention has the following beneficial technical effects:

[0022] 1) This invention utilizes the strong hydrogen bonding between the hydroxyl groups of polyvinyl alcohol and the hydrophilic groups of lignin. By adding polyvinyl alcohol to lignin-rich DES filtrate, it imparts excellent film-forming properties. Combined with electrospinning technology, a non-toxic, biodegradable, inexpensive, and mechanically superior flexible lignin-based fiber membrane can be prepared. In this process, by adjusting the electrospinning process parameters, the PVA addition ratio, and the concentration of lignin-rich DES filtrate, the intermolecular interactions in the lignin-based fiber membrane system can be controlled, thereby regulating the porosity and mechanical strength of the lignin-based fiber membrane. In short, by controlling the intermolecular interactions and cross-linking degree of the system, this invention prepares a green lignin-based fiber membrane that not only retains the core advantages of recycled materials but also meets the requirements of electrolyte membranes for porosity and mechanical properties, showing broad application prospects.

[0023] 2) The raw materials of this invention are inexpensive, readily available, and non-toxic, and the preparation process is simple, efficient, and environmentally friendly. Attached Figure Description

[0024] Figure 1 These are physical images of the green lignin-based fiber membranes prepared in Examples 1 to 3 of this invention;

[0025] Figure 2 The images are scanning electron microscope (SEM) images of the green lignin-based fiber membranes prepared in Examples 1 to 3 of this invention. Detailed Implementation

[0026] The present invention will be further described in detail below with reference to specific embodiments. These descriptions are for explanation purposes only and are not intended to limit the scope of the invention.

[0027] Example 1

[0028] Step 1: Mix choline chloride and lactic acid in a molar ratio of 1:1 and stir magnetically at 60°C for 6 hours to obtain a transparent DES liquid.

[0029] Step 2: First, take wheat straw powder and pass it through a 40-mesh sieve. Then, according to the mass ratio of wheat straw powder to DES liquid of 1:10, add wheat straw powder to DES liquid, react at 110℃ for 12 hours, filter, and collect DES filtrate rich in lignin.

[0030] Step 3: Add water to the lignin-rich DES filtrate at a mass ratio of 1:1, and stir magnetically for 3 hours to obtain a green and non-toxic precursor electrospinning solution.

[0031] Step 4: Add polyvinyl alcohol to the precursor electrospinning solution and stir at 95°C for 12 hours to completely dissolve the polyvinyl alcohol, obtaining a uniform and viscous electrospinning solution, wherein the weight fraction of polyvinyl alcohol in the electrospinning solution is 10 wt%.

[0032] Step 5: First, add the electrospinning solution to a 10mL syringe. At 24℃, the syringe pump pushes the syringe at a constant feed rate of 3mL / h and applies a high voltage electrostatic field of 18kV. Electrospinning is performed using a 19G needle. Release paper is wrapped around a roller, and the fiber filaments are collected at a distance of 10cm from the needle to prepare a green lignin-based fiber membrane.

[0033] Example 2

[0034] Step 1: Mix choline chloride and lactic acid in a molar ratio of 1:1.5 and stir magnetically at 70°C for 6 hours to obtain a transparent DES liquid.

[0035] Step 2: First, take wheat straw powder and pass it through a 40-mesh sieve. Then, according to the mass ratio of wheat straw powder to DES liquid of 1:10, add wheat straw powder to DES liquid, react at 130℃ for 8 hours, filter, and collect DES filtrate rich in lignin.

[0036] Step 3: Add water to the lignin-rich DES filtrate at a mass ratio of 2:1, and stir magnetically for 3 hours to obtain a green and non-toxic precursor electrospinning solution.

[0037] Step 4: Add polyvinyl alcohol to the precursor electrospinning solution and stir at 95°C for 12 hours to completely dissolve the polyvinyl alcohol, obtaining a uniform and viscous electrospinning solution, wherein the weight fraction of polyvinyl alcohol in the electrospinning solution is 10 wt%.

[0038] Step 5: First, add the electrospinning solution to a 10mL syringe. At 24℃, the syringe pump pushes the syringe at a constant feed rate of 3mL / h and applies a high voltage electrostatic field of 18kV. Electrospinning is performed using a 19G needle. Release paper is wrapped around a roller, and the fiber filaments are collected at a distance of 10cm from the needle to prepare a green lignin-based fiber membrane.

[0039] Example 3

[0040] Step 1: Mix choline chloride and lactic acid in a molar ratio of 1:2 and stir magnetically at 80°C for 6 hours to obtain a transparent DES liquid.

[0041] Step 2: First, take wheat straw powder and pass it through a 40-mesh sieve. Then, according to the mass ratio of wheat straw powder to DES liquid of 1:10, add wheat straw powder to DES liquid, react at 150℃ for 3 hours, filter, and collect DES filtrate rich in lignin.

[0042] Step 3: Add water to the lignin-rich DES filtrate at a mass ratio of 3:1, and stir magnetically for 3 hours to obtain a green and non-toxic precursor electrospinning solution.

[0043] Step 4: Add polyvinyl alcohol to the electrospinning solution of the precursor and stir at 100°C for 12 hours to completely dissolve the polyvinyl alcohol, so as to obtain a uniform and viscous electrospinning solution. The weight fraction of polyvinyl alcohol in the electrospinning solution is 10 wt%.

[0044] Step 5: First, add the electrospinning solution to a 10mL syringe. At 24℃, the syringe pump pushes the syringe at a constant feed rate of 4mL / h and applies a high voltage electrostatic field of 18kV. Electrospinning is performed using a 19G needle. Release paper is wrapped around a roller, and the fiber filaments are collected at a distance of 10cm from the needle to prepare a green lignin-based fiber membrane.

[0045] Example 4

[0046] Step 1: Mix choline chloride and lactic acid in a molar ratio of 1:2 and stir magnetically at 75°C for 6 hours to obtain a transparent DES liquid.

[0047] Step 2: First, take wheat straw powder and pass it through a 40-mesh sieve. Then, according to the mass ratio of wheat straw powder to DES liquid of 1:10, add wheat straw powder to DES liquid, react at 120℃ for 3 hours, filter, and collect DES filtrate rich in lignin.

[0048] Step 3: Add water to the lignin-rich DES filtrate at a mass ratio of 4:1, and stir magnetically for 3 hours to obtain a green and non-toxic precursor electrospinning solution.

[0049] Step 4: Add polyvinyl alcohol to the precursor electrospinning solution and stir at 90°C for 12 hours to completely dissolve the polyvinyl alcohol, obtaining a uniform and viscous electrospinning solution, wherein the weight fraction of polyvinyl alcohol in the electrospinning solution is 12 wt%.

[0050] Step 5: First, add the electrospinning solution to a 10mL syringe. At 22℃, the syringe pump pushes the syringe at a constant advance rate of 2.5mL / h and applies a high voltage electrostatic field of 20kV. Electrospinning is performed using a 19G needle. Release paper is wrapped on a roller, and the fiber filaments are collected at a distance of 7cm from the needle to prepare a green lignin-based fiber membrane.

[0051] Example 5

[0052] Step 1: Mix choline chloride and lactic acid in a molar ratio of 1:1 and stir magnetically at 65°C for 6 hours to obtain a transparent DES liquid.

[0053] Step 2: First, take wheat straw powder and pass it through a 40-mesh sieve. Then, according to the mass ratio of wheat straw powder to DES liquid of 1:10, add wheat straw powder to DES liquid, react at 140℃ for 5 hours, filter, and collect DES filtrate rich in lignin.

[0054] Step 3: Add water to the lignin-rich DES filtrate at a mass ratio of 5:1, and stir magnetically for 3 hours to obtain a green and non-toxic precursor electrospinning solution.

[0055] Step 4: Add polyvinyl alcohol to the electrospinning solution of the precursor and stir at 105°C for 12 hours to completely dissolve the polyvinyl alcohol, so as to obtain a uniform and viscous electrospinning solution, wherein the weight fraction of polyvinyl alcohol in the electrospinning solution is 8 wt%.

[0056] Step 5: First, add the electrospinning solution to a 10mL syringe. At 26℃, use a syringe pump to push the syringe at a constant feed rate of 5mL / h and apply a 15kV high-voltage electrostatic field. Use a 19G needle to perform electrospinning. Wrap the release paper around the roller and collect the fiber filaments at a distance of 12cm from the needle to prepare a green lignin-based fiber membrane.

[0057] Figure 1 Photographs of the green lignin-based fiber membranes prepared in Examples 1 to 3 are shown. It can be seen that when water and lignin-rich DES filtrate are mixed at a mass ratio of 1:1, the surface of the prepared lignin-based fiber membrane is slightly rough, with a small number of discretely distributed droplets. This indicates that the water content needs to be appropriately increased to improve the compatibility of the lignin-rich filtrate with the PVA blend system, thereby inhibiting macroscopic phase separation. When water and lignin-rich DES filtrate are mixed at a mass ratio of 2:1, the surface of the prepared lignin-based fiber membrane is very smooth, exhibiting a homogeneous brownish-yellow film. This indicates that the electrospinning solution has reached dynamic equilibrium, with the solvent evaporation rate matching the polymer chain relaxation rate, forming a dense fiber membrane structure. When water and lignin-rich DES filtrate are mixed at a mass ratio of 3:1, a network-like shrinkage texture appears on the surface of the prepared lignin-based fiber membrane. This is because excessive deionized water molecules accelerate solvent evaporation, leading to rapid surface solidification and a mismatch between the inner layer's shrinkage stress, causing buckling instability.

[0058] Figure 2Images (a), (b), and (c) show SEM images of the green lignin-based fiber membranes prepared in Examples 1 through 3, respectively. It can be seen that the green lignin-based fiber membrane prepared in Example 1 exhibits an interwoven network structure with a fiber diameter of 400 nm and large voids. This loose structure is due to phase separation caused by the high lignocellulose content in the spinning solution. In Example 2, the fiber diameter of the green lignin-based fiber membrane increases to 1 μm, the complexity of the interwoven network significantly increases, and the void size decreases and becomes more uniformly distributed. This indicates that an appropriate amount of water can improve the rheological properties of the spinning solution and promote hydrogen bonding between the fibers and PVA. In Example 3, the fiber structure of the green lignin-based fiber membrane undergoes significant densification, forming a tightly packed stripe pattern 250 nm wide. The porosity decreases, attributed to the increased water content accelerating solvent evaporation, leading to rapid consolidation and recombination of the polymer chains.

[0059] Commercial supercapacitor separator MPF30AC (NKK, Japan) and green lignin-based fiber membranes prepared in Examples 1 to 3 were used as electrolyte separators, respectively. These were then assembled into supercapacitors with symmetrical carbon electrodes, and their electrochemical performance was tested.

[0060] The supercapacitor assembled from commercially available diaphragms exhibits a capacitance of 171.9 F / g at a low current density of 0.5 A / g and a capacitance of 93.6 F / g at a high current density of 2 A / g, with a capacitance retention of 54.5%.

[0061] The supercapacitor assembled from the green lignin-based fiber membrane prepared in real-time Example 1 exhibits a capacitance of 170.9 F / g at a low current density of 0.5 A / g and 116.7 F / g at a high current density of 2 A / g, with a capacitance retention of 68.3%. Compared with a commercially available membrane-assembled supercapacitor, the capacitance values ​​are comparable at a low current density of 0.5 A / g, while the capacitance is increased by 24.7% at a high current density of 2 A / g.

[0062] The supercapacitor assembled from the green lignin-based fiber membrane prepared in real-time Example 2 has a capacitance of 197.1 F / g at a low current density of 0.5 A / g and a capacitance of 116.8 F / g at a high current density of 2 A / g, which represents an increase of 14.7% and 24.8% respectively compared to the supercapacitor assembled from a commercially available membrane.

[0063] The supercapacitor assembled from the green lignin-based fiber membrane prepared in real-time Example 3 has a capacitance of 164.5 F / g at a low current density of 0.5 A / g and a capacitance of 98.4 F / g at a high current density of 2 A / g, which is similar to the capacitance of the supercapacitor assembled from the commercial membrane.

[0064] The electrochemical performance test results above show that the performance of the green lignin-based fiber membranes prepared in Examples 1 to 3 is close to that of commercial membranes, indicating that they can meet the requirements of electrolyte membranes.

Claims

1. A method for preparing a green lignin-based fiber membrane, characterized in that, Includes the following steps: Step 1: Mix choline chloride and lactic acid in a molar ratio of 1:(1~2) and stir magnetically at 60~80℃ to obtain a transparent DES liquid; Step 2: According to the mass ratio of wheat straw powder to DES liquid of 1:10, add wheat straw powder to DES liquid, react at 110-150℃ for 3-12 hours, filter, and collect DES filtrate rich in lignin. Step 3: Add water to the lignin-rich DES filtrate according to the mass ratio of water to lignin-rich DES filtrate (1-5):1, stir magnetically, and obtain a green and non-toxic precursor electrospinning solution. Step 4: Add polyvinyl alcohol to the electrospinning solution of the precursor and stir at 90-105°C until the polyvinyl alcohol is completely dissolved to obtain a uniform and viscous electrospinning solution, wherein the weight fraction of polyvinyl alcohol in the electrospinning solution is 8-12 wt%. Step 5: Add the electrospinning solution to the syringe of the electrospinning equipment, and prepare a green lignin-based fiber membrane by electrospinning at room temperature.

2. The method for preparing the green lignin-based fiber membrane according to claim 1, characterized in that, The magnetic stirring time in step 1 is 6 hours.

3. The method for preparing the green lignin-based fiber membrane according to claim 1, characterized in that, Step 2 also includes passing the wheat straw powder through a 40-mesh sieve.

4. The method for preparing a green lignin-based fiber membrane according to claim 1, characterized in that, In step 3, the mass ratio of water to lignin-rich DES filtrate is 2:

1.

5. The method for preparing a green lignin-based fiber membrane according to claim 1, characterized in that, The magnetic stirring time in step 3 is 3 hours.

6. The method for preparing a green lignin-based fiber membrane according to claim 1, characterized in that, The parameters for electrospinning in step 5 are: voltage of 15-20kV, collection distance of 7-12cm, and injection pump push rate of 2.5-5mL / h at a constant rate.

7. The method for preparing a green lignin-based fiber membrane according to claim 1, characterized in that, The room temperature in step 5 is 24±2℃.

8. A green lignin-based fiber membrane prepared by the method according to any one of claims 1 to 7.

9. The application of the green lignin-based fiber membrane according to claim 8 as an electrolyte membrane for supercapacitors.

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