A paper-based antistatic separator and a method for manufacturing the same

Abstract

The application relates to the technical field of functionalized paper-based material, in particular to a paper-based antistatic diaphragm and a preparation method thereof. The method comprises the following steps: 1) subjecting coniferous wood pulp to enzymatic modification to prepare cellulose pulp; 2) subjecting the cellulose pulp to in-situ polymerization-wet papermaking forming to obtain a paper base material; and 3) coating a carbon-based slurry on one side of the paper base material and calendering to obtain the paper-based antistatic diaphragm. The diaphragm has good antistatic performance and mechanical performance, can be effectively used for the packaging of products with antistatic requirements such as medicines, electronic components and precise components, and has the potential possibility of being used as a diaphragm for a special electrochemical system due to the synergistically generated high ionic conductivity.

Description

Technical Field

[0001] This invention relates to the field of functionalized paper-based materials technology, specifically to a paper-based antistatic separator and its preparation method. Background Technology

[0002] Paper-based antistatic separators are a common and widely used separator material with antistatic properties, and they are widely used in the fields of electronics, packaging, and medical and health care.

[0003] Its most common uses are in food packaging, pharmaceutical packaging, and electronic component packaging. Especially in electronic component packaging and pharmaceutical packaging, it mainly serves to protect against static electricity and prevent problems such as impurity adsorption caused by static electricity during storage and transportation.

[0004] However, existing antistatic membranes typically suffer from several core defects: Firstly, they rely heavily on conductive fillers such as carbon black and graphene to achieve antistatic properties. This not only significantly increases material costs, but also causes uneven dispersion of fillers in the matrix, which can lead to agglomeration, thereby blocking or destroying the original uniform pore structure of the membrane. This results in a significant decrease in the gas permeability of some breathable antistatic membranes. Secondly, the preparation of the antistatic functional layer and the molding of the substrate membrane are carried out independently in separate steps. The process route is complex and lengthy, with high energy consumption and limited production efficiency. More importantly, this approach results in the antistatic layer and the polymer substrate being only physically attached or simply composited, with weak interfacial bonding strength. They are prone to delamination and peeling under aging or alternating hot and cold environments.

[0005] This results in the limited effectiveness of existing antistatic diaphragms. Summary of the Invention

[0006] This invention addresses the problems of traditional diaphragms relying on conductive fillers, having complex processes, and the tendency for antistatic treatment of diaphragms to cause imbalances and degradation in other properties. This invention provides a paper-based antistatic diaphragm and its preparation method.

[0007] The main objective of this invention is: 1. Achieve the intrinsic antistatic properties of the diaphragm substrate itself, eliminating the need for external fillers; II. Improve the bonding strength and production efficiency of the conductive layer through in-situ polymerization-papermaking integrated process; Third, construct a flexible integrated structure of "diaphragm-current collector" to ensure that the diaphragm has good mechanical properties.

[0008] To achieve the above objectives, the present invention adopts the following technical solution.

[0009] A method for preparing a paper-based antistatic separator. The method includes: 1) Enzymatically modify softwood pulp to produce cellulose pulp; 2) In-situ polymerization of cellulose pulp followed by wet papermaking is carried out to obtain paper substrate; 3) A carbon-based slurry is coated on one side of a paper substrate and then calendered to obtain a paper-based antistatic diaphragm.

[0010] As a preferred option The degree of polymerization of the softwood pulp in step 1) is 600-700, and the fiber length is 1.3-1.8 mm; Step 1) The enzymatic modification uses xylanase with an enzyme activity of 10,000 to 15,000 U / g, and the amount used is 0.5 to 1.5 wt% of the dry weight of the pulp.

[0011] As a preferred option Step 1) The enzymatic modification involves dispersing softwood pulp in an acetate-sodium acetate buffer solution with a pH of 4.8–5.2, adding xylanase, and enzymatically hydrolyzing at 50–60 °C for 120–180 min. Then, the temperature is raised to 80–90 °C to inactivate the enzyme for 10–15 min, followed by washing and concentration to a dryness of 18–22%.

[0012] As a preferred option Step 2) The in-situ polymerization-wet papermaking process is a one-step polymerization process: First, the cellulose pulp is bubbled with nitrogen for 30-40 minutes to remove oxygen from the pulp. Next, 3,4-ethylenedioxythiophene and the emulsifier Tween 80 are mixed at a mass ratio of 1:(0.3-0.5) to form a microemulsion. The microemulsion is added to the pulp system at 10-15 wt% of the cellulose pulp mass. Then, 200-220 wt% of the mass of 3,4-ethylenedioxythiophene and a 5 wt% ammonium persulfate aqueous solution are slowly added dropwise to the pulp system. The reaction is carried out under a nitrogen atmosphere, at a temperature of 23-27 ℃ and a rotation speed of 200-300 rpm for 45-55 minutes. Finally, the reaction pulp is vacuum filtered through a 25 μm pore size filter and dried with hot air at 50-60 ℃ to a basis weight of 40-60 g / m³. 2 Paper substrate.

[0013] As a preferred option Step 3) The carbon-based slurry is made by mixing graphene oxide with a diameter of 5-15 μm and carbon nanotubes with a length of 18-22 μm at a mass ratio of 3:(0.75-1.25), adding 1 wt% carboxymethyl cellulose aqueous solution, and preparing a slurry with a solid content of 8-12 wt% and a viscosity of 1000-1400 mPa·s.

[0014] As a preferred option Step 3) The coating process employs a microgravure coating technique, with a coating rate of 8–12 m / min and a coating amount of 7.5–8.5 g / m. 2 After coating, it is dried in an oven at 110–130 ℃ for 30–40 s.

[0015] As a preferred option Step 3) The calendering is performed using a silicone roller under the conditions of pressure 8-12 MPa, temperature 90-110 ℃ and linear speed 8-10 m / min. Then, it is placed in 45 vol% hydroiodic acid vapor and reduced at 60-70 ℃ for 20-30 min. After reduction treatment, it is washed in deionized water until neutral.

[0016] A paper-based antistatic separator.

[0017] The core of this invention lies in the use of enzymatic modification technology, which utilizes the specific recognition and hydrolysis capabilities of xylanase on hemicellulose in plant fibers. Xylanase catalyzes the hydrolysis and cleavage of glycosidic bonds by specifically binding its active site to the β-1,4 glycosidic bonds in xylan molecules. This enzymatic reaction has high substrate selectivity, mainly acting on hemicellulose without affecting the main chain structure of cellulose, thereby maintaining the basic mechanical properties of the fiber.

[0018] The removal of hemicellulose alters the microstructure of the fiber. Hemicellulose acts as a "cementing agent" between cellulose microfibers; its removal exposes the cellulose molecular chains more, significantly increasing the density of surface hydroxyl groups. Enzymatic hydrolysis increases the C-OH bond content on the fiber surface, providing abundant active sites for subsequent chemical modification and ion conduction. During enzymatic hydrolysis, the exposed cellulose chains undergo intramolecular dehydration under specific conditions, forming a conjugated double bond system. This process involves the dehydration condensation of adjacent hydroxyl groups in the cellulose molecular chain, forming unsaturated bonds at C2 and C3 positions. The formation of conjugated double bonds is based on the delocalization effect of π electrons, allowing electrons to move within a limited range along the molecular chain, endowing cellulose with intrinsic electronic conductivity. The conductivity mechanism of the conjugated system follows a hopping conduction model. Within conjugated segments, π electrons achieve delocalization conduction through resonance effects; between segments, electrons are transported through tunneling effects or thermally activated hopping. This conduction mechanism ensures that, although the conductivity of modified cellulose is lower than that of metallic conductors, it is sufficient to effectively dissipate static charge and prevent static accumulation. Furthermore, enzymatic modification imparts conductivity while maintaining the hydrophilic properties of the fibers. The abundant hydroxyl groups on the fiber surface interact strongly with solvent molecules in the electrolyte through hydrogen bonds, significantly reducing the surface tension at the solid-liquid interface, lowering the contact angle, and ensuring good wettability of the diaphragm in the solution system. This excellent wettability gives it superior wetting ability. In packaging diaphragm applications, it makes the paper-based diaphragm of this invention highly adaptable to further printing and secondary processing. Packaging diaphragms typically require printing, such as brand logos, product information, and barcodes. Good wettability means that inks or coatings can spread evenly on its surface, ensuring uniform color, clear edges, and strong adhesion of the printed pattern without spots or gaps. On the other hand, some packaging materials require the paper-based diaphragm to be further laminated with multiple layers of films with different functions using adhesives. If the diaphragm surface has poor wettability, the adhesive cannot fully wet its surface, resulting in low interlayer bonding strength (peel strength) after lamination, easy delamination, and causing the packaging bag to break under external force, losing its protective function. Therefore, this wetting property makes the application of the diaphragm of the present invention simpler and the secondary processing effect is excellent. On the other hand, due to the excellent performance of the paper-based diaphragm of the present invention, it also has the possibility of being used as a special conductive diaphragm, such as in some special sensors and special electrochemical environments, such as gas sensors and water electrolysis. Due to the good wettability and structural fit, good ionic conductivity is formed, making such unexpected applications possible.

[0019] Another core aspect of this invention lies in the in-situ polymerization-papermaking integrated process technology. This technology combines traditional wet papermaking with conductive polymer synthesis, utilizing a pulp dispersion system as the reaction medium. In the pulp suspension, the hydroxyl groups on the fiber surface act as nucleophilic sites, adsorbing and activating monomer molecules, providing nucleation centers for the polymerization reaction. This "template-guided" polymerization mechanism ensures uniform polymer distribution on the fiber surface. Precise control of the pulp concentration is crucial for the polymerization reaction. An appropriate concentration ensures sufficient dispersion between fibers, preventing agglomeration, while maintaining sufficient fiber surface area to provide ample reaction sites. Excessively high concentrations can lead to fiber entanglement, affecting monomer diffusion and uniform polymer coating; excessively low concentrations reduce reaction efficiency and affect polymer loading. The in-situ polymerization of 3,4-ethylenedioxythiophene follows an oxidative polymerization mechanism. Under the action of an oxidant, 3,4-ethylenedioxythiophene molecules lose electrons to form cationic free radicals, which then form dimers through α-α coupling, further polymerizing to generate poly(3,4-ethylenedioxythiophene). The use of low-temperature conditions is based on precise control of polymerization kinetics. Low temperatures reduce the polymerization rate, prolong the nucleation period, and facilitate the formation of more nucleation centers, achieving a uniform distribution of the polymer. The formation mechanism of poly(3,4-ethylenedioxythiophene) involves the construction of a π-conjugated system. The π electrons on the thiophene ring form a delocalized electron cloud through the conjugation effect, endowing the polymer with excellent electrical conductivity. The uniform coating layer formed by the poly(3,4-ethylenedioxythiophene) molecular chains on the fiber surface has a thickness that ensures sufficient conductivity while avoiding the adverse effects of excessively thick coatings on fiber flexibility.

[0020] During in-situ polymerization, weak interactions, such as hydrogen bonds or van der Waals forces, may occur between the 3,4-ethylenedioxythiophene monomer and the hydroxyl groups on the fiber surface. These interactions help the monomer to be pre-adsorbed and oriented on the fiber surface. The initiation of the polymerization reaction may involve the participation of the hydroxyl groups on the fiber surface, forming chemical bonds between the fiber and the polymer, and enhancing the interfacial bonding force.

[0021] Furthermore, in this invention, the graphene / carbon nanotube composite carbon material layer forms a mechanically interlocked structure with the membrane substrate through a calendering process. During calendering, the graphene sheets and carbon nanotubes are partially embedded in the microporous structure of the membrane surface under mechanical force, forming a mechanical connection similar to "anchoring." This interlocking structure does not rely on chemical bonding but achieves a firm bond through geometric constraints. The two-dimensional sheet structure of graphene and the one-dimensional tubular structure of carbon nanotubes form a complementary conductive network. Graphene provides an efficient in-plane electron transport path, while carbon nanotubes establish conductive bridges in the vertical direction. Together, they construct a three-dimensional conductive network. This composite structure exhibits superior conductivity compared to a single component and also possesses better mechanical stability.

[0022] The core function of graphene-based carbon material layers lies in enabling rapid lateral charge diffusion. Graphene's π-electron system possesses extremely high carrier mobility, allowing for the rapid transport of electrons and holes. When localized charges arise on the membrane surface, the graphene layer can quickly disperse the charge across the entire surface, preventing localized charge accumulation. The efficiency of charge diffusion depends on the continuity and defect density of the graphene layer. High-quality graphene possesses a complete π-conjugated structure, low defect density, and low electron transport impedance. The addition of carbon nanotubes further enhances the connectivity of the conductive network; even when gaps exist between graphene sheets, carbon nanotubes can provide effective conductive bridges.

[0023] The mechanical interlocking structure maintains the flexibility of the diaphragm while ensuring conductivity. This stability stems from the synergistic effect of multiple factors: the mechanical interlocking structure prevents the peeling of the carbon material layer; the high flexibility of graphene and carbon nanotubes allows them to adapt to the deformation of the matrix; and the redundant design of the composite conductive network ensures that the overall conductivity can still be maintained even if some conductive paths break.

[0024] The beneficial effects of this invention are as follows: The diaphragm of this invention has good antistatic and mechanical properties, and can be effectively used for packaging products with antistatic requirements such as pharmaceuticals, electronic components and precision components. Furthermore, due to the synergistic effect, it has a high ionic conductivity and also has the potential to be used as a diaphragm for special electrochemical systems. Detailed Implementation

[0025] The present invention will be further described clearly and in detail below with reference to specific embodiments. Those skilled in the art will be able to implement the present invention based on these descriptions. Furthermore, the embodiments of the present invention described below are generally only some, not all, of the embodiments of the present invention. Therefore, all other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort should fall within the scope of protection of the present invention.

[0026] Unless otherwise specified, all raw materials used in the embodiments of the present invention are commercially available or obtainable by those skilled in the art; unless otherwise specified, all methods used in the embodiments of the present invention are methods mastered by those skilled in the art.

[0027] Example 1: Preparation of a paper-based antistatic separator, The method includes: 1) Softwood pulp with a degree of polymerization of 600 and a fiber length of 1.3 mm was dispersed in an acetate-sodium acetate buffer solution at pH 4.8. Xylanase with an activity of 10000 U / g was added and enzymatically hydrolyzed at 50 °C for 180 min. The enzyme was then inactivated at 80 °C for 15 min. After washing and concentration to a dryness of 18%, cellulose pulp was produced. The amount of xylanase used was 0.5 wt% of the dry weight of the pulp. 2) First, the cellulose pulp was bubbled with nitrogen for 30 min to remove oxygen. Then, a microemulsion was prepared by mixing 3,4-ethylenedioxythiophene with emulsifier Tween 80 at a mass ratio of 1:0.3, and added to the pulp system at 10 wt% of the cellulose pulp mass. Next, a 5 wt% ammonium persulfate aqueous solution (200 wt% of 3,4-ethylenedioxythiophene mass) was slowly and uniformly added to the pulp system over 60 min. The reaction was carried out under a nitrogen atmosphere at 23 ℃ and a stirring speed of 200 rpm for 55 min. Finally, the reaction pulp was vacuum filtered through a 25 μm pore size filter and dried with hot air at 50 ℃ to a basis weight of 40 g / m³. 2 Paper substrate; 3) Mix graphene oxide with a diameter of 5 μm and carbon nanotubes with a length of 18 μm at a mass ratio of 3:0.75, add 1 wt% carboxymethyl cellulose aqueous solution, and prepare a carbon-based slurry with a solid content of 8 wt% and a viscosity of 1000 mPa·s. 3) Carbon-based paste is coated on one side of the paper substrate using a microgravure coating process at a coating rate of 8 m / min and a coating amount of 7.5 g / m. 2 After coating, the material is dried in an oven at 110 ℃ for 40 s, and then calendered using a silicone roller at a pressure of 8 MPa, a temperature of 90 ℃, and a linear speed of 8 m / min. Subsequently, it is placed in 45 vol% hydroiodic acid vapor and reduced at 60 ℃ for 30 min. After reduction treatment, it is washed in deionized water until neutral to obtain a paper-based antistatic separator.

[0028] The materials prepared in the examples were subjected to performance testing, and the specific characterization results are shown in Table 1 below.

[0029] Surface resistance characterization and testing: Referring to GB / T 15738-2023 "Test Method for Resistivity of Conductive Plastics", the four-probe method was used to conduct the test in constant current mode. A constant current of 1 mA was applied and the probe spacing was set to 1.0 mm. During the measurement process, 10 evenly distributed test points were selected on the diaphragm surface. After removing extreme data, the average value was taken as the surface resistance result.

[0030] Ion conductivity detection: The ion transport performance of the membrane was evaluated using electrochemical impedance spectroscopy. The membrane sample was immersed in 1M LiPF6 (EC:DMC volume ratio 1:1) for 24 h until fully wetted. Subsequently, the membrane was held between two stainless steel blocking electrodes, and the impedance value was measured. Ion conductivity was calculated using the formula σ=d / (R×A), where d is the membrane thickness, R is the resistance, and A is the electrode contact area (cm²). 2 Note: If a short circuit occurred during the experiment, the data from the short-circuit experimental group should be excluded.

[0031] Thermal performance index testing: The volume shrinkage rate and limiting oxygen index (LOI) are tested under constant temperature of 150 ℃ for 1 h. If the volume shrinkage rate is ≤5% and the limiting oxygen index is ≥28%, it is marked as qualified (P). If any unqualified items are found, the characterization results of the unqualified items are recorded.

[0032] Bending performance testing: The dynamic bending test method was used to evaluate the structural stability and electrochemical performance retention of the diaphragm under mechanical stress. The dynamic bending tester was used to perform 1000 bending cycles on the diaphragm sample under a curvature radius of 5 mm. The bending frequency was set to 1 Hz to simulate mechanical deformation in actual applications. The rate of change of resistance before and after bending was compared.

[0033] Mechanical strength testing: Referring to GB / T 1040.3-2006 "Test for tensile properties of plastics", the mechanical properties of the diaphragm material are evaluated by uniaxial tensile method. A dumbbell-shaped specimen with a width of 10 mm is used for testing. The longitudinal and transverse tensile strengths are measured at a constant tensile rate of 50 mm / min. The comprehensive tensile strength index of the material is obtained by taking the average value of the test results in the two directions.

[0034] Table 1: Performance Characterization Results

[0035] Analyzing the characterization results in Table 1 above, the surface resistivity is 0.82 × 10⁻⁶. 3The Ω / sq ratio is significantly lower than that of conventional separators, verifying the intrinsic antistatic properties of the cellulose substrate imparted by enzymatic modification technology: the conjugated double bond system formed during enzymatic hydrolysis achieves electron conduction through the π-electron delocalization effect, effectively dissipating surface static charge and avoiding the risk of accumulation. Simultaneously, it demonstrates the advantages of the flexible integrated "separator-current collector" structure: the three-dimensional conductive network constructed by the graphene / carbon nanotube composite carbon material layer reduces interfacial resistance, ensuring rapid charge diffusion. The ionic conductivity reaches 1.85 mS / cm, indicating that the separator has excellent wettability and ion transport efficiency in the electrolyte. This is attributed to the increased density of exposed hydroxyl groups after hemicellulose removal, enhancing solid-liquid interfacial interactions and optimizing the lithium-ion solvation structure. Furthermore, the excellent thermal performance indicators demonstrate the broad applicability and heat resistance of the membrane of this invention. The glass transition temperature of cellulose fibers (~220℃) is much higher than that of polyolefin membranes (~130℃). After selective enzymatic removal of hemicellulose, the crystallinity of cellulose type I increases, the rigidity of the molecular chains is enhanced, and the graphene / carbon nanotube composite layer forms a carbonization barrier at high temperatures, blocking oxygen diffusion and thus increasing the limiting oxygen index. The resistivity change rate after bending is only 4.5%, indicating good conductivity stability under mechanical stress. This is attributed to the mechanical interlocking structure formed by the calendering process, which firmly anchors the graphene sheets and carbon nanotubes in the micropores of the matrix, while the polymer coating layer maintains flexibility. The tensile strength of 38.7 MPa confirms the mechanical integrity of the substrate; the enzymatic treatment selectively removes hemicellulose without damaging the cellulose backbone, maintaining the basic mechanical properties of the fibers.

[0036] Example 2: Preparation of a paper-based antistatic separator, The method includes: 1) Softwood pulp with a degree of polymerization of 650 and a fiber length of 1.5 mm was dispersed in an acetate-sodium acetate buffer solution at pH 5. Xylanase with an activity of 12500 U / g was added and enzymatically hydrolyzed at 55 °C for 150 min. The enzyme was then inactivated at 85 °C for 13 min. After washing and concentration to a dryness of 20%, cellulose pulp was produced. The amount of xylanase used was 1 wt% of the dry weight of the pulp. 2) First, the cellulose pulp was bubbled with nitrogen for 35 min to remove oxygen. Then, a microemulsion was prepared by mixing 3,4-ethylenedioxythiophene with emulsifier Tween 80 at a mass ratio of 1:0.4. This microemulsion was added to the pulp system at 13 wt% of the cellulose pulp mass. Next, a 5 wt% ammonium persulfate aqueous solution (210 wt% of 3,4-ethylenedioxythiophene mass) was slowly and uniformly added to the pulp system over 60 min. The reaction was carried out under a nitrogen atmosphere at 25 ℃ and a stirring speed of 250 rpm for 50 min. Finally, the reaction pulp was vacuum filtered through a 25 μm pore size filter and dried at 55 ℃ with hot air to a basis weight of 50 g / m³. 2 Paper substrate; 3) Mix graphene oxide with a diameter of 10 μm and carbon nanotubes with a length of 20 μm at a mass ratio of 3:1, add 1 wt% carboxymethyl cellulose aqueous solution, and prepare a carbon-based slurry with a solid content of 10 wt% and a viscosity of 1200 mPa·s. 3) Carbon-based paste is coated on one side of the paper substrate using a microgravure coating process at a coating rate of 10 m / min and a coating amount of 8 g / m. 2 After coating, the material is dried in an oven at 120 ℃ for 35 s, and then calendered using a silicone roller at a pressure of 10 MPa, a temperature of 100 ℃, and a linear speed of 9 m / min. Subsequently, it is placed in 45 vol% hydroiodic acid vapor and reduced at 65 ℃ for 25 min. After reduction treatment, it is washed in deionized water until neutral to obtain a paper-based antistatic separator.

[0037] The materials prepared in the examples were subjected to performance testing, and the specific characterization results are shown in Table 2 below.

[0038] Surface resistance characterization and testing: Referring to GB / T 15738-2023 "Test Method for Resistivity of Conductive Plastics", the four-probe method was used to conduct the test in constant current mode. A constant current of 1 mA was applied and the probe spacing was set to 1.0 mm. During the measurement process, 10 evenly distributed test points were selected on the diaphragm surface. After removing extreme data, the average value was taken as the surface resistance result.

[0039] Ion conductivity detection: The ion transport performance of the membrane was evaluated using electrochemical impedance spectroscopy. The membrane sample was immersed in 1M LiPF6 (EC:DMC volume ratio 1:1) for 24 h until fully wetted. Subsequently, the membrane was held between two stainless steel blocking electrodes, and the impedance value was measured. Ion conductivity was calculated using the formula σ=d / (R×A), where d is the membrane thickness, R is the resistance, and A is the electrode contact area (cm²). 2 Note: If a short circuit occurred during the experiment, the data from the short-circuit experimental group should be excluded.

[0040] Thermal performance index testing: The volume shrinkage rate and limiting oxygen index (LOI) are tested under constant temperature of 150 ℃ for 1 h. If the volume shrinkage rate is ≤5% and the limiting oxygen index is ≥28%, it is marked as qualified (P). If any unqualified items are found, the characterization results of the unqualified items are recorded.

[0041] Bending performance testing: The dynamic bending test method was used to evaluate the structural stability and electrochemical performance retention of the diaphragm under mechanical stress. The dynamic bending tester was used to perform 1000 bending cycles on the diaphragm sample under a curvature radius of 5 mm. The bending frequency was set to 1 Hz to simulate mechanical deformation in actual applications. The rate of change of resistance before and after bending was compared.

[0042] Mechanical strength testing: Referring to GB / T 1040.3-2006 "Test for tensile properties of plastics", the mechanical properties of the diaphragm material are evaluated by uniaxial tensile method. A dumbbell-shaped specimen with a width of 10 mm is used for testing. The longitudinal and transverse tensile strengths are measured at a constant tensile rate of 50 mm / min. The comprehensive tensile strength index of the material is obtained by taking the average value of the test results in the two directions.

[0043] Table 2: Performance Characterization Results

[0044] Analysis of the characterization results in Table 2 shows a further reduction in surface resistivity compared to Example 1. This is attributed to the optimized ratio of graphene oxide sheet diameter to carbon nanotube length, which enhances the continuity of the graphene layer and the conductive bridging effect of the carbon nanotubes, effectively reducing the risk of charge accumulation. The ionic conductivity is slightly higher than in Example 1, indicating more thorough removal of hemicellulose, exposing more hydroxyl sites, and enhancing electrolyte wettability and lithium-ion transport efficiency. The resistance change rate after bending is only 4.3%, demonstrating excellent mechanical stability. This is attributed to the denser interlocking structure formed by the calendering process at higher temperatures and linear speeds, which firmly anchors the graphene sheets and carbon nanotubes to the matrix while maintaining flexibility. The tensile strength of 38.8 MPa confirms that the enzymatic hydrolysis selectively removes hemicellulose without damaging the cellulose backbone, maintaining the mechanical integrity of the substrate.

[0045] Example 3: Preparation of a paper-based antistatic separator, The method includes: 1) Softwood pulp with a degree of polymerization of 700 and a fiber length of 1.8 mm was dispersed in an acetate-sodium acetate buffer solution at pH 5.2. Xylanase with an activity of 15000 U / g was added and enzymatically hydrolyzed at 60 °C for 120 min. The enzyme was then inactivated at 90 °C for 10 min. After washing and concentration to a dryness of 22%, cellulose pulp was produced. The amount of xylanase used was 1.5 wt% of the dry weight of the pulp. 2) First, the cellulose pulp was bubbled with nitrogen for 40 min to remove oxygen from the pulp. Then, a microemulsion was prepared by mixing 3,4-ethylenedioxythiophene with the emulsifier Tween 80 at a mass ratio of 1:0.5, and added to the pulp system at 15 wt% of the cellulose pulp mass. Next, a 5 wt% ammonium persulfate aqueous solution (220 wt% of 3,4-ethylenedioxythiophene mass) was slowly and uniformly added to the pulp system over 60 min. The reaction was carried out under a nitrogen atmosphere at 27 ℃ and a stirring speed of 300 rpm for 45 min. Finally, the reaction pulp was vacuum filtered through a 25 μm pore size filter and dried with hot air at 60 ℃ to a basis weight of 60 g / m³. 2 Paper substrate; 3) Mix graphene oxide with a diameter of 15 μm and carbon nanotubes with a length of 22 μm at a mass ratio of 3:1.25, add 1 wt% carboxymethyl cellulose aqueous solution, and prepare a carbon-based slurry with a solid content of 12 wt% and a viscosity of 1400 mPa·s. 3) Carbon-based paste is coated on one side of the paper substrate using a microgravure coating process at a coating rate of 12 m / min and a coating amount of 8.5 g / m. 2 After coating, the material is dried in an oven at 130 ℃ for 30 s, and then calendered using a silicone roller at a pressure of 12 MPa, a temperature of 110 ℃, and a linear speed of 10 m / min. Subsequently, it is placed in 45 vol% hydroiodic acid vapor and reduced at 70 ℃ for 20 min. After reduction treatment, it is washed in deionized water until neutral to obtain a paper-based antistatic separator.

[0046] The materials prepared in the examples were subjected to performance testing, and the specific characterization results are shown in Table 3 below.

[0047] Surface resistance characterization and testing: Referring to GB / T 15738-2023 "Test Method for Resistivity of Conductive Plastics", the four-probe method was used to conduct the test in constant current mode. A constant current of 1 mA was applied and the probe spacing was set to 1.0 mm. During the measurement process, 10 evenly distributed test points were selected on the diaphragm surface. After removing extreme data, the average value was taken as the surface resistance result.

[0048] Ion conductivity detection: The ion transport performance of the membrane was evaluated using electrochemical impedance spectroscopy. The membrane sample was immersed in 1M LiPF6 (EC:DMC volume ratio 1:1) for 24 h until fully wetted. Subsequently, the membrane was held between two stainless steel blocking electrodes, and the impedance value was measured. Ion conductivity was calculated using the formula σ=d / (R×A), where d is the membrane thickness, R is the resistance, and A is the electrode contact area (cm²). 2 Note: If a short circuit occurred during the experiment, the data from the short-circuit experimental group should be excluded.

[0049] Thermal performance index testing: The volume shrinkage rate and limiting oxygen index (LOI) are tested under constant temperature of 150 ℃ for 1 h. If the volume shrinkage rate is ≤5% and the limiting oxygen index is ≥28%, it is marked as qualified (P). If any unqualified items are found, the characterization results of the unqualified items are recorded.

[0050] Bending performance testing: The dynamic bending test method was used to evaluate the structural stability and electrochemical performance retention of the diaphragm under mechanical stress. The dynamic bending tester was used to perform 1000 bending cycles on the diaphragm sample under a curvature radius of 5 mm. The bending frequency was set to 1 Hz to simulate mechanical deformation in actual applications. The rate of change of resistance before and after bending was compared.

[0051] Mechanical strength testing: Referring to GB / T 1040.3-2006 "Test for tensile properties of plastics", the mechanical properties of the diaphragm material are evaluated by uniaxial tensile method. A dumbbell-shaped specimen with a width of 10 mm is used for testing. The longitudinal and transverse tensile strengths are measured at a constant tensile rate of 50 mm / min. The comprehensive tensile strength index of the material is obtained by taking the average value of the test results in the two directions.

[0052] Table 3: Performance Characterization Results

[0053] Analyzing the characterization results in Table 3 above, the surface resistivity is 0.84 × 10⁻⁶. 3 The Ω / sq ratio remained at a low level, attributed to the optimized enzymatic modification parameters enhancing the conjugated double bond system of the cellulose matrix, achieving efficient charge dissipation through π-electron delocalization, although the increased graphene oxide sheet diameter to 15 μm may slightly affect conductivity continuity. The ionic conductivity reached 1.83 mS / cm, indicating excellent wettability and ion transport capabilities of the membrane in the electrolyte. This is due to the more thorough removal of hemicellulose by the enzymatic hydrolysis, exposing a higher density of hydroxyl sites, enhancing solid-liquid interface interactions, and optimizing the lithium-ion solvation structure. The change in resistance after bending was only 4.1%, superior to the previous embodiment. This is attributed to improved calendering process parameters, forming a denser mechanically interlocked structure that firmly anchors the graphene sheets and carbon nanotubes within the matrix micropores, while the polymer coating maintains flexibility. The tensile strength of 38.9 MPa confirms further enhancement of the substrate's mechanical integrity; the enzymatic hydrolysis selectively removed hemicellulose without damaging the cellulose backbone, maintaining the fiber's basic mechanical properties.

[0054] Comparative Example 1: Based on Example 2, this example only modifies the enzymatic hydrolysis modification process; the remaining steps are the same as in Example 2. Specific settings are shown in Table 4 below: Table 4: Process Adjustment Comparison Table

[0055] The performance testing method for the comparative product is completely consistent with that of Example 1. Partial performance characterization was performed, and the characterization results are shown in Table 5 below.

[0056] Table 5: Performance Characterization Results and Comparison Table

[0057] Analysis of the above characterization results shows that the low temperature and low enzyme dosage in group D1-1 resulted in hemicellulose residue, insufficient intramolecular dehydration, fewer conjugated structures, and insufficient nucleation sites for 3,4-ethylenedioxythiophene. This limited the polymerization of poly(3,4-ethylenedioxythiophene) on the fiber surface, leading to a decrease in coverage, significantly lower than in Example 2. This directly resulted in an incomplete conductive network, blocked charge transport channels, and a sharp increase in surface resistivity to 53.16 × 10⁻⁶. 3 The Ω / sq ratio is nearly two orders of magnitude higher than in Example 2. The residual hemicellulose not only hinders intramolecular dehydration and the formation of conjugated double bonds, but also reduces the hydrophilicity and wettability of the cellulose matrix to the electrolyte, indirectly affecting ion transport efficiency. Furthermore, the residual hemicellulose may disrupt the homogeneity of the matrix, weaken the hydrogen bonding between cellulose fibers, and ultimately lead to a significant deterioration in the overall mechanical properties of the material.

[0058] Comparative Example 2: Based on Example 2, this example only modifies the in-situ polymerization-wet papermaking process; the remaining steps are the same as in Example 2. Specific settings are shown in Table 6 below: Table 6: Process Adjustment Comparison Table

[0059] The performance testing method for the comparative product was completely consistent with that of Example 1. Partial performance characterization was performed, and the results are shown in Table 7 below. In addition, narrow-range thermal cycling characterization was also performed. The narrow-range thermal cycling characterization took into account the actual storage and transportation environment. The temperature cycle was -10 to 60 ℃. The sample was placed in an environment of 60 ℃ for 30 min and then cooled to -10 ℃ for 30 min. This was counted as one cycle, and a total of 168 cycles were performed. After the cycle, the sample was observed, ultrasonically cleaned in deionized water, dried, and then the mass was characterized. The mass loss rate of the sample after the cycle was calculated relative to the mass before the cycle.

[0060] Table 7: Performance Characterization Results and Comparison Table

[0061] Analysis of the characterization results in Table 7 shows that in group D2-1, high-temperature accelerated polymerization resulted in homogeneous nucleation and particle formation of 3,4-ethylenedioxythiophene. Oxygen-induced side reactions generated oligomers, disrupting the continuity of the coating and leading to uneven thickness and a loose structure in the poly(3,4-ethylenedioxythiophene) coating layer. This not only weakens the effectiveness of the conductive network but also hinders the uniform loading and bonding of the subsequent graphene oxide / carbon nanotube conductive layer. The thicker coating layer, accompanied by localized agglomeration, significantly reduced the hydrogen bonding force between fibers, weakening the matrix structure and causing the tensile strength to plummet from 38.8 MPa to 21.4 MPa. During narrow-range thermal cycling, the loose and discontinuous coating layer was more prone to structural collapse and fracture under alternating hot and cold conditions, ultimately manifesting as powdering and flaking.

[0062] Comparative Example 3: Based on Example 2, this example only modifies the carbon-based slurry composition; the remaining steps are the same as in Example 2. Specific settings are shown in Table 8 below: Table 8: Process Adjustment Comparison Table

[0063] The performance testing method for the comparative product is completely consistent with that of Example 1. Partial performance characterization was performed, and the characterization results are shown in Table 9 below.

[0064] Table 9: Performance Characterization Results and Comparison Table

[0065] Analyzing the characterization results in Table 9 above, in group D3-1, the removal of carbon nanotubes and the use of only an equal amount of graphene as a replacement significantly reduced the structural continuity of the three-dimensional conductive network. The lack of bridging connections between graphene sheets by carbon nanotubes obstructed charge transport paths, leading to an increase in surface resistivity. Simultaneously, the rate of change in resistance after bending increased significantly, attributed to the ease with which graphene sheets slip or break under mechanical stress. The lack of flexible anchoring effect from carbon nanotubes prevented the effective maintenance of the conductive network's structural integrity, resulting in a substantial increase in interfacial resistance.

[0066] Comparative Example 4: Based on Example 2, this example only modifies the calendering process; the remaining steps are the same as in Example 2. Specific settings are shown in Table 10 below: Table 10: Process Adjustment Comparison Table

[0067] The performance testing method for the comparative product is completely consistent with that of Example 1. Partial performance characterization was performed, and the characterization results are shown in Table 11 below.

[0068] Table 11: Performance Characterization Results and Comparison Table

[0069] Analysis of the characterization results shows that the D4-1 group was below the glass transition temperature of cellulose, preventing the fibers from undergoing plastic deformation. Insufficient low pressure resulted in only physical adsorption of graphene, failing to effectively embed it into the fiber network to form a mechanically interlocked structure. This led to weak bonding between the graphene layer and the substrate interface, with an embedding depth of only 0.4–0.5 μm. The loose interface was prone to slippage under thermal stress, resulting in a significant increase in the thermal shrinkage rate at 150℃. Simultaneously, the lack of effective interlocking reduced the efficiency of external force transmission, causing the tensile strength to drop from 38.8 MPa to 36.7 MPa, thus compromising the overall structural integrity of the material.

Claims

1. A method for preparing a paper-based antistatic separator, characterized in that, The method includes: 1) Enzymatically modify softwood pulp to produce cellulose pulp; 2) In-situ polymerization of cellulose pulp followed by wet papermaking is carried out to obtain paper substrate; 3) A carbon-based slurry is coated on one side of a paper substrate and then calendered to obtain a paper-based antistatic diaphragm; Step 1) The enzymatic modification uses xylanase with an enzyme activity of 10,000–15,000 U / g, and the dosage is 0.5–1.5 wt% of the dry weight of the pulp. Step 1) The enzymatic modification involves dispersing softwood pulp in an acetate-sodium acetate buffer solution with a pH of 4.8–5.2, adding xylanase, and enzymatically hydrolyzing at 50–60 °C for 120–180 min. The enzyme is then inactivated by heating to 80–90 °C for 10–15 min, followed by washing and concentration to a dryness of 18–22%. Step 2) The in-situ polymerization-wet papermaking process is a one-step polymerization process: First, the cellulose pulp is bubbled with nitrogen for 30-40 minutes to remove oxygen from the pulp. Next, 3,4-ethylenedioxythiophene and the emulsifier Tween 80 are mixed at a mass ratio of 1:(0.3-0.5) to form a microemulsion. The microemulsion is added to the pulp system at 10-15 wt% of the cellulose pulp mass. Then, 200-220 wt% of the mass of 3,4-ethylenedioxythiophene and a 5 wt% ammonium persulfate aqueous solution are slowly added dropwise to the pulp system. The reaction is carried out under a nitrogen atmosphere, at a temperature of 23-27 ℃ and a rotation speed of 200-300 rpm for 45-55 minutes. Finally, the reaction pulp is vacuum filtered through a 25 μm pore size filter and dried with hot air at 50-60 ℃ to a basis weight of 40-60 g / m³. 2 Paper substrate; Step 3) The carbon-based slurry is made by mixing graphene oxide with a diameter of 5-15 μm and carbon nanotubes with a length of 18-22 μm at a mass ratio of 3:(0.75-1.25), adding 1 wt% carboxymethyl cellulose aqueous solution, and preparing a slurry with a solid content of 8-12 wt% and a viscosity of 1000-1400 mPa·s. Step 3) The coating process employs a microgravure coating technique, with a coating rate of 8–12 m / min and a coating amount of 7.5–8.5 g / m. 2 After coating, it is dried in an oven at 110–130 ℃ for 30–40 s; Step 3) The calendering is performed using a silicone roller under the conditions of pressure 8-12 MPa, temperature 90-110 ℃ and linear speed 8-10 m / min. Then, it is placed in 45 vol% hydroiodic acid vapor and reduced at 60-70 ℃ for 20-30 min. After reduction treatment, it is washed in deionized water until neutral.

2. The method for preparing a paper-based antistatic separator according to claim 1, characterized in that, The degree of polymerization of the softwood pulp in step 1) is 600-700 and the fiber length is 1.3-1.8 mm.

3. The method for preparing a paper-based antistatic separator according to claim 1, characterized in that, Step 1) The pH of the acetate-sodium acetate buffer solution is 5, the enzyme activity of xylanase is 12500 U / g, the amount is 1 wt% of the dry weight of the pulp, the temperature of the enzymatic hydrolysis treatment is 55 ℃ and the time is 150 min, the temperature of the enzyme inactivation treatment is 85 ℃ and the time is 13 min, and the washed pulp is concentrated to a dryness of 20%.

4. The method for preparing a paper-based antistatic separator according to claim 3, characterized in that, Step 2) The cellulose pulp is bubbled with nitrogen for 35 min. 3,4-ethylenedioxythiophene and Tween 80 are mixed at a mass ratio of 1:0.4 to form a microemulsion. The microemulsion is added to the pulp system at 13 wt% of the cellulose pulp mass. The amount of the 5 wt% ammonium persulfate aqueous solution is 210 wt% of the mass of 3,4-ethylenedioxythiophene. The mixture is stirred and reacted for 50 min under a nitrogen atmosphere, at 25 ℃ and 250 rpm, and then dried with hot air at 55 ℃ to obtain the paper substrate.

5. The method for preparing a paper-based antistatic separator according to claim 4, characterized in that, Step 3) The graphene oxide sheet has a diameter of 10 μm, the carbon nanotube has a length of 20 μm, and the mass ratio of the two is 3:1; the carbon-based slurry has a solid content of 10 wt% and a viscosity of 1200 mPa·s.

6. The method for preparing a paper-based antistatic separator according to claim 5, characterized in that, Step 3) The coating rate of the microgravure coating is 10 m / min and the coating amount is 8 g / m. 2 After coating, the material was dried in an oven at 120 ℃ for 35 s, and then calendered using a silicone roller at a pressure of 10 MPa, a temperature of 100 ℃, and a linear speed of 9 m / min. After calendering, the material was placed in 45 vol% hydroiodic acid vapor and reduced at 65 ℃ for 25 min. After reduction treatment, the material was washed with deionized water until neutral.

7. A paper-based antistatic separator prepared by any one of claims 1 to 6.

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