Waterborne polyurethane graphene fiber sizing agent and sizing method for graphene fibers

Abstract

This invention belongs to the field of graphene fiber surface modification technology, and relates to a water-based polyurethane graphene fiber sizing agent and a method for sizing graphene fibers. The water-based polyurethane graphene fiber sizing agent comprises a cationic polyether polyurethane sizing agent, a volatile ester co-solvent, and water; the boiling point and solubility of the volatile ester co-solvent are strictly controlled. The method for sizing the graphene fibers is as follows: after impregnating the graphene fibers in the sizing agent, the liquid content is controlled by an extrusion roller or scraper, followed by drying and curing, thus completing the sizing of the graphene fibers; the sizing agent used is the aforementioned water-based polyurethane graphene fiber sizing agent. The sizing agent of this invention can achieve deep wetting and strong interfacial bonding of graphene fibers, while maintaining their electrical and thermal conductivity, thus improving weaving and processing performance.

Description

Technical Field

[0001] This invention belongs to the field of graphene fiber surface modification technology, and relates to a water-based polyurethane graphene fiber sizing agent and a sizing method for graphene fibers. Background Technology

[0002] Graphene fiber, as a novel high-performance carbon-based material, possesses excellent electrical conductivity, mechanical strength, and thermal stability, and has been widely used in composite materials, conductive fabrics, and other fields. However, graphene fibers are mostly in a multifilament state, and their surface inertness, hydrophobicity, and the rough morphology formed by wrinkles easily lead to the peeling of monofilament sheets during spinning and weaving, resulting in problems such as fuzzing, loose fibers, and breakage. This affects the consistency of the fiber bundle and mechanical properties, making continuous and stable weaving impossible and severely restricting its industrialization process. Sizing, as a key technology to improve fiber bundle properties, wettability, and interfacial compatibility, is an important way to achieve efficient fiber processing.

[0003] Existing fiber sizing agents can be mainly divided into three categories: solvent-based, emulsion-based, and water-based. Among them, solvent-based sizing agents (such as DMF or NMP-based systems) have a good wetting effect on fibers, but the volatile organic solvents in the system can easily cause environmental pollution and pose significant safety hazards. They have been gradually phased out by the market and industry standards. Emulsion-based sizing agents (such as polyurethane emulsions) have the disadvantage of poor system stability. They are prone to demulsification and stratification during storage or use. At the same time, their formulations contain a large amount of surfactants, which are prone to migration during subsequent high-temperature processing, thereby causing fiber interface defects and affecting the final application performance.

[0004] Water-based sizing agents have become the mainstream choice in the current fiber sizing field due to their advantages of being both environmentally friendly and low-cost, and related technologies have been extensively researched and applied. For example, patent CN110468591B discloses a sizing agent for graphene fibers and its preparation method. In this sizing agent, graphene accounts for 0.5-5% of the total organic matter, and the overall solid content is 0.5-3%. Its epoxy resin emulsion ingredients, by weight, contain 37-50 parts of liquid bisphenol A epoxy resin, 8-10 parts of epoxy resin emulsifier, and 40-55 parts of deionized water. The chain extender used is diphenylmethane diisocyanate or toluene diisocyanate. This technology aims to protect graphene fibers through sizing treatment, optimize their surface physicochemical structure, and improve the interfacial properties between the fiber and the polymer matrix. Another example is patent application CN120590628A, which discloses a preparation method and application of a water-based polyamic acid sizing agent, which involves adding 5-10 wt% of... The solvents used are low-grade esters or low-grade ketones, wherein the low-grade ester solvents can be selected from one of ethyl acetate, ethyl formate, ethyl propionate, ethyl butyrate, propyl acetate, and butyl acetate. By using such solvents to intervene in the interaction between water molecules and polyamic acid molecules, the conformation of polyamic acid molecules is changed, and the intermolecular forces are weakened, thereby achieving rapid, stable, and uniform dissolution of polyamic acid in water. For example, patent application CN117903430A discloses a main slurry polymer, a water-soluble sizing agent, a composite material, and a preparation method. This technology adds a small amount of hydroxides such as potassium hydroxide as a co-solvent to promote the ionization of modified polyarylene ether nitrile resin, thereby achieving complete dissolution of the resin in water. After coating, the co-solvent can be removed by a brief hot water wash to improve the moisture and heat resistance of the composite material.

[0005] However, existing water-based sizing agents have the inherent drawback of high surface tension. Their wetting of graphene fiber bundles can only remain on the surface, failing to penetrate into the interior of the bundle. This easily leads to a "skin-core" structure on the fiber surface, resulting in a high fuzz content after fiber bundling. This causes frequent fraying during subsequent weaving, resulting in low processing efficiency and severely impacting the fiber's application performance. Furthermore, due to the inherent inertness and highly wrinkled morphology of graphene fibers, sizing agent molecules struggle to achieve uniform adsorption and form a complete, dense sizing film layer on their surface. Therefore, even after bundled treatment, fibers can still break at stress concentration points, failing to meet the requirements for basic mechanical properties in applications such as composite material preparation and conductive fabric weaving.

[0006] To address the issue of insufficient wettability of water-based sizing agents, existing technologies have attempted to use nonionic surfactants, fatty acid ester smoothers (such as patent application CN117385643A), or alcohol additives such as isopropanol and ethylene glycol to enhance the wettability. However, these additives suffer from uneven evaporation rates. If evaporation is too rapid, the additives tend to accumulate on the fiber surface, affecting the sizing film performance. If evaporation is too slow, it will significantly increase the energy consumption of subsequent drying processes. Furthermore, these additives have a negative impact on the stability of the polyurethane emulsion system, and still cannot achieve deep and uniform wettability of the graphene fiber bundles.

[0007] Therefore, it is necessary to provide a novel waterborne polyurethane graphene fiber sizing agent and a corresponding sizing method to solve the problems of insufficient wetting of graphene fibers, weak interfacial bonding, and easy formation of fuzz and brittleness of fibers after bundling by existing sizing agents. This will enable the sizing agent to quickly and completely wet the graphene fiber interface and achieve stable fiber bundling, thus ensuring the continuity of subsequent fiber processing and the stability of application performance. Summary of the Invention

[0008] The purpose of this invention is to solve the problems existing in the prior art and to provide a water-based polyurethane graphene fiber sizing agent and a sizing method for graphene fibers.

[0009] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0010] A waterborne polyurethane-based graphene fiber sizing agent comprises a cationic polyether-based polyurethane sizing agent, a volatile ester co-solvent, and water;

[0011] The volatile ester cosolvent has a boiling point of 146-156℃ and a solubility in water at 20℃ of ≥19.8g / 100mL.

[0012] The sizing agent of this invention is based on a dual strategy of cationic electrostatic anchoring and volatile ester-assisted wetting, aiming to balance the bundle properties and lubricity of graphene fibers, and solve the problems of difficult wetting and weak interfacial bonding of traditional sizing agents. Specific details are as follows:

[0013] Since the surface of graphene fibers is usually negatively charged, positively charged cationic polyether polyurethane can be used as the main film-forming material. Through strong electrostatic attraction and hydrogen bonding, the sizing agent can be directionally adsorbed and stably anchored on the fiber surface.

[0014] The volatile ester cosolvents are highly miscible with water, which significantly reduces the surface tension of the sizing agent (to 25-30 mN / m). This allows the sizing agent to overcome capillary resistance and quickly penetrate into the interior of the graphene fiber, solving the problem of wetting the graphene fiber.

[0015] Volatile ester co-solvents have boiling points between 146-156℃, corresponding to relatively low saturated vapor pressures and evaporation rates slightly lower than water. This gradient evaporation characteristic allows moisture to evaporate preferentially in the initial drying stage, while the ester solvent remains to maintain the leveling of the wet film, avoiding surface skinning caused by excessively rapid evaporation of low-boiling-point solvents. Simultaneously, this boiling point range ensures complete solvent escape without residue during subsequent heat setting processes, avoiding the plasticizing effect caused by high-boiling-point solvents. Furthermore, volatile ester co-solvents do not degrade the stability of cationic polyether polyurethane slurries (specifically, the sizing agent emulsion remains highly stable across a wide temperature range of -5℃ to 40℃, without demulsification or stratification), ensuring film uniformity.

[0016] Therefore, the sizing agent of this invention can achieve rapid and good wetting of graphene fibers, strong interfacial adsorption, excellent film-forming cohesion and stability, and significantly enhance the interfacial shear strength (IFSS), flexural strength and tensile strength of the bundled fibers. In addition, while the sized graphene fibers undergo multi-scale mechanical enhancement, their electrical conductivity and thermal conductivity remain unchanged.

[0017] As a preferred technical solution:

[0018] The waterborne polyurethane graphene fiber sizing agent described above uses one or more of the following volatile ester co-solvents: ethyl lactate (CAS: 97-64-3), propylene glycol methyl ether acetate (CAS: 108-65-6), and ethylene glycol ethyl ether acetate (CAS: 111-15-9).

[0019] The waterborne polyurethane graphene fiber sizing agent described above contains the following components and contents in the cationic polyether polyurethane sizing agent: 75wt%-92wt% cationic polyether polyurethane, 0.5wt%-2wt% functional additives, and 6wt%-24.5wt% water.

[0020] The waterborne polyurethane graphene fiber sizing agent described above contains the following components and contents in the cationic polyether polyurethane reaction raw materials: polyether polyol 55wt%-75wt%, isocyanate 18wt%-30wt%, cationic hydrophilic chain extender 2wt%-5wt%, nonionic chain extender 2wt%-7wt%, and neutralizer (used to neutralize the cationic hydrophilic chain extender) 1wt%-3wt%.

[0021] The waterborne polyurethane graphene fiber sizing agent described above uses polytetramethylene ether glycol (PTMG-2000, CAS: 25190-06-1) or polyoxypropylene glycol (PPG-2000, CAS: 25322-69-4).

[0022] The isocyanate is isophorone diisocyanate (IPDI, CAS: 4098-71-9) or 1,6-hexamethylene diisocyanate (HDI, CAS: 822-06-0).

[0023] The cationic hydrophilic chain extender is N-methyldiethanolamine (MDEA, CAS: 105-59-9).

[0024] The nonionic chain extender is 1,4-butanediol (BDO, CAS: 110-63-4) or ethylenediamine (EDA, CAS: 107-15-3).

[0025] The neutralizing agent is acetic acid (CAS: 64-19-7) or lactic acid (CAS: 50-21-5).

[0026] As described above, the waterborne polyurethane graphene fiber sizing agent comprises two or more of the following functional additives: penetrant, defoamer, and rheology / thickening agent. In the cationic polyether polyurethane sizing agent, the penetrant content is 0.4wt%-1.0wt%, the defoamer content is 0.1wt%-0.5wt%, and the rheology / thickening agent content is 0wt%-0.5wt%. The penetrant is either isotridecyl alcohol polyoxyethylene ether (TO-10, CAS: 69011-36-5) or fatty alcohol polyoxyethylene ether (AEO-9, CAS: 68131-39-5). The defoamer is either BYK-028 (a commercial product manufactured by BYK Chemicals AG, Germany) or Tego-810 (a commercial product from Evonik Industries' Tego additives series). The rheology / thickening agent is either Rheovis PU 1190 (a commercial product from BASF, Germany) or WT-105A (a commercial product from the Elementis Group).

[0027] The waterborne polyurethane graphene fiber sizing agent described above contains a cationic polyether polyurethane sizing agent with a content of 0.5wt%-20wt% and a volatile ester co-solvent to water mass ratio of 1:4-20.

[0028] The present invention also provides a method for sizing graphene fibers, wherein the graphene fibers are impregnated in a sizing agent, and the liquid content is controlled by an extrusion roller or a scraping device, followed by drying and curing to complete the sizing of the graphene fibers. The sizing agent is a water-based polyurethane graphene fiber sizing agent as described in any of the preceding claims.

[0029] As a preferred technical solution:

[0030] The sizing method for graphene fibers described above involves an impregnation temperature of 5-40℃ and a time of 5-60s; and a drying and curing temperature of 100-200℃ and a time of 30-180s.

[0031] The graphene fiber sizing method described above has graphene fiber specifications of 20-1000tex / 1000-50000F (i.e., the linear density of graphene fiber is 20-1000tex, composed of 1000-50000 monofilaments), the contact angle of the sizing agent on the graphene fiber is <30°, and the penetration time is <5s.

[0032] After sizing, the graphene fiber has a wettability of >98%, surface hairs of <10 fibers / m, good bundle properties, moderate flexibility, no fraying or breakage during weaving, and a retention rate of >92% for both electrical conductivity and thermal conductivity. The functionality is not significantly reduced due to the introduction of the sizing layer. The interfacial shear strength (IFSS) is increased by 60%-120%, the flexural strength by 20%-80%, and the tensile strength by 40%-120%. The increase rate is calculated as (value after sizing - value before sizing) / value before sizing × 100%.

[0033] Beneficial effects:

[0034] (1) By adding specific volatile ester co-solvents, the present invention can significantly reduce the surface tension of water-based polyurethane graphene fiber sizing agent, enabling it to overcome capillary resistance and penetrate into the interior of graphene fiber bundles. This solves the problem that traditional water-based sizing agents can only wet the surface and easily form a core-sheath structure, thus achieving deep and uniform wetting of graphene fibers.

[0035] (2) The present invention uses cationic polyether polyurethane slurry as the main film-forming material, which can achieve directional adsorption and stable anchoring on the surface of graphene fiber by means of electrostatic attraction and hydrogen bonding. This solves the problem of uneven adsorption of slurry agent and non-dense slurry film caused by the inertness and wrinkles on the surface of graphene fiber, strengthens the interfacial bonding force of fiber, and avoids fiber breakage at stress concentration points after bundling.

[0036] (3) The volatile ester co-solvent selected in this invention has a specific boiling point range and can achieve gradient evaporation. It can maintain the leveling of the wet film and avoid surface skinning, and can completely escape without residue in the subsequent heat setting process. At the same time, the co-solvent will not destroy the stability of the cationic polyether polyurethane slurry, thus ensuring the uniformity of film formation and the stability of use of the sizing agent.

[0037] (4) The sizing agent of the present invention can improve the bundle properties and mechanical properties of graphene fibers while ensuring that the electrical conductivity and thermal conductivity of the fibers remain unchanged and will not reduce their functionality due to the introduction of the sizing layer.

[0038] (5) The graphene fiber sizing method of the present invention utilizes the process of impregnation-controlling liquid-drying and curing to give full play to the technical advantages of the above-mentioned sizing agent, achieve stable sizing of graphene fiber, improve its weaving and processing performance, and avoid the occurrence of loose or broken fibers during processing. Attached Figure Description

[0039] Figure 1 In Figure a, it is a schematic diagram of the bonding state between the sizing agent and graphene fiber in Comparative Example 1, and in Figure b, it is a schematic diagram of the bonding state between the sizing agent and graphene fiber in Example 3; wherein, 1 is graphene fiber, 2 is the sizing agent in Comparative Example 1, and 3 is the sizing agent in Example 3.

[0040] Figure 2 This is a diagram showing the broken and flying filaments after the graphene fibers in Comparative Example 1 were bundled and knotted.

[0041] Figure 3 This is a diagram showing the state of a small number of broken filaments after the graphene fibers in Example 3 were bundled and knotted. Detailed Implementation

[0042] The present invention will be further described below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0043] The following are the test methods for the relevant performance indicators in each embodiment and comparative example:

[0044] Boiling point: Tested according to GB / T 615-2006 "General Method for Determination of Boiling Range of Chemical Reagents".

[0045] Solubility: Tested according to GB / T 21845-2008 "Test for water solubility of chemicals".

[0046] Specifications: Tested according to ISO 1889:2009 "Reinforcement yarns - Determination of linear density".

[0047] Contact angle and penetration time of waterborne polyurethane graphene fiber sizing agent on graphene fibers: Graphene fiber bundles were arranged closely and parallel with the same tension and fixed on a glass slide to form a relatively flat surface. 2 μL of waterborne polyurethane graphene fiber sizing agent was added to the fiber surface using a microsyringe under ambient temperature and pressure. After standing for 10-30 seconds to allow the droplet shape to stabilize, the droplet outline was captured by an optical camera and the equilibrium contact angle was calculated using contact angle analysis software. Simultaneously, the penetration time from the droplet contacting the fiber surface to the complete disappearance of the three-phase contact line and the absence of obvious droplet residue on the fiber surface (i.e., the contact angle drops to 0° or the droplet completely penetrates into the fiber bundle) was recorded.

[0048] Wetting rate: After embedding the sized fiber bundles, samples were prepared by cryosectioning or liquid nitrogen brittle fracture. The sample surface was then sputtered with gold, and the cross-sectional morphology was observed under a scanning electron microscope. To ensure statistical representativeness, at least five different fields of view (including the edge, middle, and core areas of the bundle) were randomly selected on the fiber bundle cross-section and photographed at 1000-3000x magnification. A continuously visible sizing coating or a sizing-mediated inter-filament adhesion structure was considered a validly wetted filament. The total number of filaments N in all fields of view was counted. total And the number of effectively wetted monofilaments, N wet The wetting rate is calculated according to the formula. : =(∑N wet / ∑N total )×100%.

[0049] Surface hairiness: The BT-2 online hairiness tester was used for measurement, with the detection threshold set to hair length ≥2mm. The graphene fiber bundle was passed through the detection channel at a speed of 10m / min. The instrument automatically recorded the number of light-blocking pulses using a photoelectric sensor. After 100m of continuous testing, the instrument automatically output the average number of hairs (hairs / m) to characterize the density of hairiness on the fiber surface.

[0050] Conductivity: Lay the sample flat on the insulating film and fix both ends with conductive double-sided tape, ensuring that the sample and the contact section of the four probes are straight and without bending; in the fiber test mode of the four-probe conductivity tester, press the probes down onto the sample surface, apply a current of 10μA, and read the voltage value. Calculate the resistance value according to the formula "resistance value R = voltage value / current value"; then calculate the conductivity (S / cm) according to the formula "conductivity = 4l × 10 / (R•πd²)", where: R is the resistance value (Ω), l is the probe spacing (1.59 mm), and d is the sample diameter (mm).

[0051] Thermal conductivity: According to GB / T 22588-2008 "Measurement of Thermal Diffusion Coefficient or Thermal Conductivity by Flash Method", the laser flare method (LFA) was used for determination. A Netzsch LFA 467 laser thermal conductivity meter was used to test the thermal diffusion coefficient (α) of the sample at 25℃. The sample preparation method was as follows: fiber bundles were bundled together, tightly wrapped with PI tape, cut by a cutting machine, and then arranged unidirectionally and tightly in a sample stage with an inner diameter of 12.7 mm, ensuring that the fiber axis was parallel to the heat flow direction. The thermal conductivity was determined by combining the sample density (ρ, unit kg / m³) and specific heat capacity (C). p (Unit: J / (kg·K)), according to the formula λ=α·ρ·C p The thermal conductivity of the filament bundle (λ, unit W / (m·K)) was calculated.

[0052] Interfacial shear strength: This was determined using the microdroplet debonding method. Single fibers were randomly selected from the graphene fiber bundles before and after sizing, and fixed flat onto a U-shaped paper frame. A resin mixture was prepared with E-51 epoxy resin (epoxy value 0.51) and curing agent (m-phenylenediamine, CAS No.: 108-45-2) at a mass ratio of 100:14. The resin mixture was then drop-coated onto the surface of the single fiber using a microsyringe, forming independent microdroplets (single fibers) encapsulating the fiber. (Droplet volume controlled at 0.1-0.5 μL); place the fiber sample with microdroplets in an oven, first at 80℃ for 2 hours, then at 120℃ for 2 hours to complete curing; using a composite material interface evaluation instrument, under microscope assistance, clamp the microdroplets onto a specially designed micro-blade or clamp, and stretch the fiber along the fiber axis at a constant rate of 0.05 mm / min until the microdroplets detach (peel) from the fiber surface; record the maximum load F at the moment of microdroplet detachment. max (Unit: N), and the effective embedding length L (unit: mm) of the microdroplet and fiber and the fiber diameter D (unit: mm) were measured using a microscope, and the interfacial shear strength (IFSS, unit: MPa) was calculated: IFSS = F max / (π•D•L).

[0053] Bending strength: According to GB / T 3362-2017 standard, a 500mm sample was wound on a multifilament frame, immersed in resin solution at 25℃ (prepared according to GB / T 3362-2017 standard A.3.3) and left to stand for 5 minutes. Then, it was placed in a 120℃ electric heating drying oven for curing to obtain the sample composite material specimen. The bending strength (unit: MPa) of the specimen was tested according to GB / T 1449-2005 "Test Method for Bending Properties of Fiber Reinforced Plastics".

[0054] Tensile strength: Tested according to GB / T 3362-2017 "Test Method for Tensile Properties of Carbon Fiber Multifilament" (the adhesive used in the test was prepared according to A.3.3 of the standard).

[0055] In the following embodiments, the preparation process of the graphene fibers is basically the same, except that the diameter of the fiber bundle and the number of filaments are controlled by adjusting the pore size and number parameters of the spinneret. The specific preparation process is as follows: First, a spinning solution of graphene oxide (GO) / N,N-dimethylformamide (DMF) with a concentration of 10 mg / g is prepared, wherein the transverse dimension of GO is 10~50 μm and the thickness is 1~5 nm; then, the solution is wet-spun, and ethyl acetate is used as the coagulation bath. After the solution is extruded through the spinneret, phase separation and solidification are completed in the coagulation bath to obtain graphene oxide fiber bundles; then, the fiber bundles are immersed in a mixture of hydroiodic acid and ethanol with a volume ratio of 1:3, and chemical reduction is completed at 60°C to obtain chemically reduced graphene fiber bundles; finally, the chemically reduced graphene fiber bundles are subjected to hot stretching treatment at 1200°C to obtain graphene fiber bundles with different diameters and numbers.

[0056] Example 1

[0057] A sizing method for graphene fibers, the specific steps of which are as follows:

[0058] (1) Material preparation;

[0059] Polyether polyol: Polytetramethylene ether diol;

[0060] Isocyanate: Isophorone diisocyanate;

[0061] Cationic hydrophilic chain extender: N-methyldiethanolamine;

[0062] Nonionic chain extender: 1,4-butanediol;

[0063] Neutralizing agent: acetic acid;

[0064] Penetrant: Isotridecyl alcohol polyoxyethylene ether;

[0065] Defoamer: BYK-028;

[0066] Substance X and substance Y: Both are water;

[0067] Volatile ester cosolvent: Ethyl lactate (miscible with water at 20°C in any proportion), boiling point 154°C;

[0068] Graphene fiber: Specifications are 20tex / 1000F, electrical conductivity is 1500S / cm, thermal conductivity is 300W / m·K, interfacial shear strength is 25MPa, flexural strength is 800MPa, and tensile strength is 950MPa.

[0069] (2) Preparation of cationic polyether polyurethane;

[0070] First, the polyether polyol was vacuum dehydrated at 105℃ and -0.095MPa for 1.5h, then cooled to 60℃ and added isocyanate, and the temperature was raised to 85℃ for 2.5h to obtain a prepolymer. Then, the prepolymer was cooled to 65℃, and cationic hydrophilic chain extenders and nonionic chain extenders were added sequentially, and the temperature was raised to 75℃ for 2h of chain extension reaction. Then, the temperature was lowered to 45℃, and a neutralizing agent was added for 20min of neutralization reaction to completely ionize the tertiary amine groups on the molecular chain, thus obtaining cationic polyether polyurethane.

[0071] The contents of each component in the reaction raw materials of cationic polyether polyurethane are as follows: polyether polyol 75wt%, isocyanate 18wt%, cationic hydrophilic chain extender 2wt%, nonionic chain extender 3wt%, and neutralizer 2wt%;

[0072] (3) Prepare cationic polyether polyurethane slurry;

[0073] The cationic polyether polyurethane slurry is composed of cationic polyether polyurethane, penetrant, defoamer, and substance X; the content of each component in the cationic polyether polyurethane slurry is as follows: cationic polyether polyurethane 75wt%, penetrant 0.4wt%, defoamer 0.1wt%, and substance X 24.5wt%.

[0074] (4) Prepare water-based polyurethane graphene fiber sizing agent;

[0075] The waterborne polyurethane graphene fiber sizing agent is composed of cationic polyether polyurethane slurry, volatile ester co-solvent, and substance Y. In the waterborne polyurethane graphene fiber sizing agent, the content of cationic polyether polyurethane slurry is 0.5wt%, and the mass ratio of volatile ester co-solvent to substance Y is 1:4.

[0076] (5) Sizing of graphene fibers;

[0077] After impregnating graphene fibers in an aqueous polyurethane graphene fiber sizing agent, the amount of liquid is controlled by an extrusion roller or scraper, followed by drying and curing to complete the sizing of the graphene fibers. The impregnation temperature is 5℃ and the time is 5s; the drying and curing temperature is 100℃ and the time is 30s.

[0078] Tests show that the waterborne polyurethane graphene fiber sizing agent has a contact angle of 29° and a penetration time of 4.5s on graphene fibers. After sizing, the wetting rate of graphene fibers is 98.5%, the surface hairs are 9 hairs / m, the electrical conductivity retention rate is 93%, the thermal conductivity retention rate is 93%, the interfacial shear strength improvement rate is 60%, the flexural strength improvement rate is 20%, and the tensile strength improvement rate is 40%.

[0079] Example 2

[0080] A sizing method for graphene fibers, the specific steps of which are as follows:

[0081] (1) Material preparation;

[0082] Polyether polyol: Polypropylene glycol;

[0083] Isocyanate: 1,6-hexamethylene diisocyanate;

[0084] Cationic hydrophilic chain extender: N-methyldiethanolamine;

[0085] Nonionic chain extender: ethylenediamine;

[0086] Neutralizing agent: lactic acid;

[0087] Penetrant: Fatty alcohol polyoxyethylene ether;

[0088] Defoamer: Tego-810;

[0089] Rheology modifier / thickener: Rheovis PU 1190;

[0090] Substance X and substance Y: Both are water;

[0091] Volatile ester cosolvent: Propylene glycol methyl ether acetate, boiling point 146℃, solubility in water at 20℃ is 19.8 g / 100 mL;

[0092] Graphene fiber: Specifications are 250tex / 12500F, electrical conductivity is 925S / cm, thermal conductivity is 192W / m·K, interfacial shear strength is 22MPa, flexural strength is 563MPa, and tensile strength is 766MPa.

[0093] (2) Preparation of cationic polyether polyurethane;

[0094] First, the polyether polyol was vacuum dehydrated at 105℃ and -0.095MPa for 1.5h, then cooled to 60℃ and added isocyanate, and the temperature was raised to 85℃ for 2.5h to obtain a prepolymer. Then, the prepolymer was cooled to 65℃, and cationic hydrophilic chain extenders and nonionic chain extenders were added sequentially, and the temperature was raised to 75℃ for 2h of chain extension reaction. Then, the temperature was lowered to 45℃, and a neutralizing agent was added for 20min of neutralization reaction to completely ionize the tertiary amine groups on the molecular chain, thus obtaining cationic polyether polyurethane.

[0095] The contents of each component in the reaction raw materials of cationic polyether polyurethane are as follows: polyether polyol 55wt%, isocyanate 30wt%, cationic hydrophilic chain extender 5wt%, nonionic chain extender 7wt%, and neutralizer 3wt%;

[0096] (3) Prepare cationic polyether polyurethane slurry;

[0097] The cationic polyether polyurethane slurry is composed of cationic polyether polyurethane, penetrant, defoamer, rheology / thickening agent, and substance X; the content of each component in the cationic polyether polyurethane slurry is as follows: cationic polyether polyurethane 79wt%, penetrant 0.6wt%, defoamer 0.2wt%, rheology / thickening agent 0.1wt%, and substance X 20.1wt%.

[0098] (4) Prepare water-based polyurethane graphene fiber sizing agent;

[0099] The waterborne polyurethane graphene fiber sizing agent is composed of cationic polyether polyurethane slurry, volatile ester co-solvent, and substance Y. In the waterborne polyurethane graphene fiber sizing agent, the content of cationic polyether polyurethane slurry is 5wt%, and the mass ratio of volatile ester co-solvent to substance Y is 1:8.

[0100] (5) Sizing of graphene fibers;

[0101] After impregnating graphene fibers in an aqueous polyurethane graphene fiber sizing agent, the amount of liquid is controlled by an extrusion roller or scraper, followed by drying and curing to complete the sizing of the graphene fibers; the impregnation temperature is 10℃ and the time is 20s; the drying and curing temperature is 125℃ and the time is 60s.

[0102] Tests show that the waterborne polyurethane graphene fiber sizing agent has a contact angle of 22° and a penetration time of 3.5s on graphene fibers. After sizing, the wetting rate of graphene fibers is 98.8%, the surface hairs are 7 hairs / m, the electrical conductivity retention rate is 95%, the thermal conductivity retention rate is 95%, the interfacial shear strength improvement rate is 75%, the flexural strength improvement rate is 35%, and the tensile strength improvement rate is 60%.

[0103] Example 3

[0104] A sizing method for graphene fibers, the specific steps of which are as follows:

[0105] (1) Material preparation;

[0106] Polyether polyol: Polytetramethylene ether diol;

[0107] Isocyanate: Isophorone diisocyanate;

[0108] Cationic hydrophilic chain extender: N-methyldiethanolamine;

[0109] Nonionic chain extender: 1,4-butanediol;

[0110] Neutralizing agent: acetic acid;

[0111] Penetrant: Isotridecyl alcohol polyoxyethylene ether;

[0112] Defoamer: BYK-028;

[0113] Rheology modifier / thickener: Rheovis PU 1190;

[0114] Substance X and substance Y: Both are water;

[0115] Volatile ester cosolvent: ethylene glycol ethyl ether acetate, boiling point 156℃, solubility in water at 20℃ is 23.0 g / 100 mL;

[0116] Graphene fiber: Specifications are 510tex / 25500F, electrical conductivity is 800S / cm, thermal conductivity is 180W / m·K, interfacial shear strength is 20MPa, flexural strength is 498MPa, and tensile strength is 698MPa.

[0117] (2) Preparation of cationic polyether polyurethane;

[0118] First, the polyether polyol was vacuum dehydrated at 105℃ and -0.095MPa for 1.5h, then cooled to 60℃ and added isocyanate, and the temperature was raised to 85℃ for 2.5h to obtain a prepolymer. Then, the prepolymer was cooled to 65℃, and cationic hydrophilic chain extenders and nonionic chain extenders were added sequentially, and the temperature was raised to 75℃ for 2h of chain extension reaction. Then, the temperature was lowered to 45℃, and a neutralizing agent was added for 20min of neutralization reaction to completely ionize the tertiary amine groups on the molecular chain, thus obtaining cationic polyether polyurethane.

[0119] The contents of each component in the reaction raw materials of cationic polyether polyurethane are as follows: polyether polyol 65wt%, isocyanate 24wt%, cationic hydrophilic chain extender 3.5wt%, nonionic chain extender 5wt%, and neutralizer 2.5wt%.

[0120] (3) Prepare cationic polyether polyurethane slurry;

[0121] The cationic polyether polyurethane slurry is composed of cationic polyether polyurethane, penetrant, defoamer, rheology / thickening agent, and substance X. The content of each component in the cationic polyether polyurethane slurry is as follows: cationic polyether polyurethane 83.5 wt%, penetrant 0.7 wt%, defoamer 0.3 wt%, rheology / thickening agent 0.2 wt%, and substance X 15.3 wt%.

[0122] (4) Prepare water-based polyurethane graphene fiber sizing agent;

[0123] The waterborne polyurethane graphene fiber sizing agent is composed of cationic polyether polyurethane slurry, volatile ester co-solvent, and substance Y. In the waterborne polyurethane graphene fiber sizing agent, the content of cationic polyether polyurethane slurry is 10wt%, and the mass ratio of volatile ester co-solvent to substance Y is 1:12.

[0124] (5) Sizing of graphene fibers;

[0125] After impregnating graphene fibers in an aqueous polyurethane graphene fiber sizing agent, the amount of liquid applied is controlled by an extrusion roller or scraper, followed by drying and curing to complete the sizing of the graphene fibers. The impregnation temperature is 22.5℃ and the time is 32.5s; the drying and curing temperature is 150℃ and the time is 105s.

[0126] Tests show that the waterborne polyurethane graphene fiber sizing agent has a contact angle of 15° and a penetration time of 2.5s on graphene fibers. After sizing, the wetting rate of graphene fibers is 99.2%, the surface hairs are 5 hairs / m, the electrical conductivity retention rate is 96%, the thermal conductivity retention rate is 96%, the interfacial shear strength improvement rate is 90%, the flexural strength improvement rate is 50%, and the tensile strength improvement rate is 80%.

[0127] Example 4

[0128] A sizing method for graphene fibers, the specific steps of which are as follows:

[0129] (1) Material preparation;

[0130] Polyether polyol: Polypropylene glycol;

[0131] Isocyanate: 1,6-hexamethylene diisocyanate;

[0132] Cationic hydrophilic chain extender: N-methyldiethanolamine;

[0133] Nonionic chain extender: ethylenediamine;

[0134] Neutralizing agent: lactic acid;

[0135] Penetrant: Fatty alcohol polyoxyethylene ether;

[0136] Defoamer: Tego-810;

[0137] Rheology modifier / thickener: Rheovis PU 1190;

[0138] Substance X and substance Y: Both are water;

[0139] Volatile ester cosolvent: ethylene glycol ethyl ether acetate, boiling point 156℃, solubility in water at 20℃ is 23.0 g / 100 mL;

[0140] Graphene fiber: Specifications are 750tex / 37500F, electrical conductivity is 700S / cm, thermal conductivity is 165W / m·K, interfacial shear strength is 20MPa, flexural strength is 450MPa, and tensile strength is 650MPa.

[0141] (2) Preparation of cationic polyether polyurethane;

[0142] First, the polyether polyol was vacuum dehydrated at 105℃ and -0.095MPa for 1.5h, then cooled to 60℃ and added isocyanate, and the temperature was raised to 85℃ for 2.5h to obtain a prepolymer. Then, the prepolymer was cooled to 65℃, and cationic hydrophilic chain extenders and nonionic chain extenders were added sequentially, and the temperature was raised to 75℃ for 2h of chain extension reaction. Then, the temperature was lowered to 45℃, and a neutralizing agent was added for 20min of neutralization reaction to completely ionize the tertiary amine groups on the molecular chain, thus obtaining cationic polyether polyurethane.

[0143] The contents of each component in the reaction raw materials of cationic polyether polyurethane are as follows: 60wt% polyether polyol, 28wt% isocyanate, 4wt% cationic hydrophilic chain extender, 6wt% nonionic chain extender, and 2wt% neutralizer;

[0144] (3) Prepare cationic polyether polyurethane slurry;

[0145] The cationic polyether polyurethane slurry is composed of cationic polyether polyurethane, penetrant, defoamer, rheology / thickening agent, and substance X; the content of each component in the cationic polyether polyurethane slurry is as follows: cationic polyether polyurethane 87wt%, penetrant 0.9wt%, defoamer 0.4wt%, rheology / thickening agent 0.3wt%, and substance X 11.4wt%.

[0146] (4) Prepare water-based polyurethane graphene fiber sizing agent;

[0147] The waterborne polyurethane graphene fiber sizing agent is composed of cationic polyether polyurethane slurry, volatile ester co-solvent, and substance Y. In the waterborne polyurethane graphene fiber sizing agent, the content of cationic polyether polyurethane slurry is 15wt%, and the mass ratio of volatile ester co-solvent to substance Y is 1:16.

[0148] (5) Sizing of graphene fibers;

[0149] After impregnating graphene fibers in an aqueous polyurethane graphene fiber sizing agent, the amount of liquid is controlled by an extrusion roller or scraper, followed by drying and curing to complete the sizing of the graphene fibers. The impregnation temperature is 30℃ and the time is 45s; the drying and curing temperature is 175℃ and the time is 140s.

[0150] Tests show that the waterborne polyurethane graphene fiber sizing agent has a contact angle of 8° and a penetration time of 1.5s on graphene fibers. After sizing, the wetting rate of graphene fibers is 99.5%, the surface hairs are 3 hairs / m, the electrical conductivity retention rate is 97%, the thermal conductivity retention rate is 97%, the interfacial shear strength improvement rate is 105%, the flexural strength improvement rate is 65%, and the tensile strength improvement rate is 100%.

[0151] Example 5

[0152] A sizing method for graphene fibers, the specific steps of which are as follows:

[0153] (1) Material preparation;

[0154] Polyether polyol: Polytetramethylene ether diol;

[0155] Isocyanate: Isophorone diisocyanate;

[0156] Cationic hydrophilic chain extender: N-methyldiethanolamine;

[0157] Nonionic chain extender: 1,4-butanediol;

[0158] Neutralizing agent: acetic acid;

[0159] Penetrant: Isotridecyl alcohol polyoxyethylene ether;

[0160] Defoamer: BYK-028;

[0161] Rheology modifier / thickener: Rheovis PU 1190;

[0162] Substance X and substance Y: Both are water;

[0163] Volatile ester cosolvent: A mixture of ethyl lactate (miscible with water at 20°C in any proportion, boiling point 154°C) and propylene glycol methyl ether acetate (boiling point 146°C, solubility in water at 20°C 19.8 g / 100 mL) in a volume ratio of 1:1.

[0164] Graphene fiber: Specifications are 1000tex / 50000F, electrical conductivity is 600S / cm, thermal conductivity is 150W / m·K, interfacial shear strength is 18MPa, flexural strength is 400MPa, and tensile strength is 600MPa.

[0165] (2) Preparation of cationic polyether polyurethane;

[0166] First, the polyether polyol was vacuum dehydrated at 105℃ and -0.095MPa for 1.5h, then cooled to 60℃ and added isocyanate, and the temperature was raised to 85℃ for 2.5h to obtain a prepolymer. Then, the prepolymer was cooled to 65℃, and cationic hydrophilic chain extenders and nonionic chain extenders were added sequentially, and the temperature was raised to 75℃ for 2h of chain extension reaction. Then, the temperature was lowered to 45℃, and a neutralizing agent was added for 20min of neutralization reaction to completely ionize the tertiary amine groups on the molecular chain, thus obtaining cationic polyether polyurethane.

[0167] The contents of each component in the reaction raw materials of cationic polyether polyurethane are as follows: polyether polyol 70wt%, isocyanate 22.5wt%, cationic hydrophilic chain extender 2.5wt%, nonionic chain extender 3.5wt%, and neutralizer 1.5wt%.

[0168] (3) Prepare cationic polyether polyurethane slurry;

[0169] The cationic polyether polyurethane slurry is composed of cationic polyether polyurethane, penetrant, defoamer, rheology / thickening agent, and substance X; the content of each component in the cationic polyether polyurethane slurry is as follows: cationic polyether polyurethane 92wt%, penetrant 1wt%, defoamer 0.5wt%, rheology / thickening agent 0.5wt%, and substance X 6wt%.

[0170] (4) Prepare water-based polyurethane graphene fiber sizing agent;

[0171] The waterborne polyurethane graphene fiber sizing agent is composed of cationic polyether polyurethane slurry, volatile ester co-solvent, and substance Y. In the waterborne polyurethane graphene fiber sizing agent, the content of cationic polyether polyurethane slurry is 20wt%, and the mass ratio of volatile ester co-solvent to substance Y is 1:20.

[0172] (5) Sizing of graphene fibers;

[0173] After impregnating graphene fibers in an aqueous polyurethane graphene fiber sizing agent, the amount of liquid applied is controlled by an extrusion roller or scraper, followed by drying and curing to complete the sizing of the graphene fibers. The impregnation temperature is 40℃ and the time is 60s; the drying and curing temperature is 200℃ and the time is 180s.

[0174] Tests show that the waterborne polyurethane graphene fiber sizing agent has a contact angle of 2° and a penetration time of 1s on graphene fibers. After sizing, the wetting rate of graphene fibers is 99.9%, the surface hair count is 1 hair / m, the electrical conductivity retention rate is 99%, the thermal conductivity retention rate is 99%, the interfacial shear strength improvement rate is 120%, the flexural strength improvement rate is 80%, and the tensile strength improvement rate is 120%.

[0175] Comparative Example 1

[0176] A sizing method for graphene fibers differs from Example 3 in that the waterborne polyurethane graphene fiber sizing agent does not contain volatile ester co-solvents.

[0177] Tests show that the waterborne polyurethane graphene fiber sizing agent has a contact angle of 70° and a penetration time of 60s on graphene fibers. After sizing, the graphene fiber wettability is 60%, the surface hairs are 60 hairs / m, the electrical conductivity retention rate is 80%, the thermal conductivity retention rate is 80%, the interfacial shear strength improvement rate is 30%, the flexural strength improvement rate is 20%, and the tensile strength improvement rate is 25%.

[0178] Comparing Example 3 and Comparative Example 1, it can be seen that volatile ester co-solvents are a key factor affecting wetting performance: when the waterborne polyurethane graphene fiber sizing agent contains volatile ester co-solvents, the co-solvents can reduce the surface tension of the sizing agent, resulting in a smaller contact angle and shorter penetration time on the graphene fiber, leading to a high wetting rate of the graphene fiber; when the waterborne polyurethane graphene fiber sizing agent does not contain volatile ester co-solvents, the sizing agent has a high surface tension, a large contact angle, and a long penetration time, resulting in a low wetting rate of the graphene fiber, which cannot overcome capillary resistance and presents a significant wetting problem. This further leads to relatively limited improvement or maintenance of other performance indicators of the graphene fiber after sizing. The binding effect of the two sizing agents on the graphene fiber surface differs significantly, such as... Figure 1 As shown, the coating and bonding effect of sizing agent 2 on the surface of graphene fiber 1 in Comparative Example 1 is weaker than that of sizing agent 3 in Example 3 on graphene fiber 1. From... Figure 2 and Figure 3 As can be seen, in Comparative Example 1, the graphene fibers were knotted after being bundled, resulting in obvious broken and flying fibers; while in Example 3, the graphene fibers were knotted after being bundled, with only a small number of broken fibers, demonstrating better bundle properties and mechanical toughness.

[0179] Comparative Example 2

[0180] A sizing method for graphene fibers differs from Example 3 in that the volatile ester co-solvent is replaced with propylene carbonate.

[0181] Tests show that the waterborne polyurethane graphene fiber sizing agent has a contact angle of 32° and a penetration time of 6.5s on graphene fibers. After sizing, the wetting rate of graphene fibers is 88.5%, the surface hair count is 25 hairs / m, the electrical conductivity retention rate is 92%, the thermal conductivity retention rate is 91%, the interfacial shear strength improvement rate is 35%, the flexural strength improvement rate is 15%, and the tensile strength improvement rate is 30%.

[0182] Compared to Comparative Example 2 and Example 3, the wetting and penetration performance of the sizing agent deteriorated, manifested as an increased contact angle, prolonged penetration time, and a significant increase in the number of surface hairs. Furthermore, the fiber mechanical reinforcement effect after sizing was significantly reduced, particularly the improvement in interfacial shear strength and tensile strength. This is because the co-solvent in Comparative Example 2 is non-volatile, with a boiling point (242°C) far exceeding the drying and curing temperature of 150°C. This resulted in the solvent failing to evaporate during film formation and remaining in large quantities in the polyurethane coating. The residual propylene carbonate acts as a "plasticizer" in the cationic polyether polyurethane film system, reducing the modulus and cohesive strength of the polyurethane film, making it soft and sticky, and unable to form a dense, rigid protective layer on the graphene fiber surface. In addition, the solvent residue hindered the tight bonding between the polyurethane molecular chains and the graphene fiber surface, severely weakening the effective stress transfer efficiency at the interface.

[0183] Comparative Example 3

[0184] A method for sizing graphene fibers differs from Example 3 in that the volatile ester co-solvent is replaced with methyl acetate, which has a boiling point of 57°C and a solubility of 24.5 g / 100 mL in water at 20°C.

[0185] Tests show that the waterborne polyurethane graphene fiber sizing agent has a contact angle of 28° and a penetration time of 4.2s on graphene fibers. After sizing, the wetting rate of graphene fibers is 92.5%, the surface hair count is 18 hairs / m, the electrical conductivity retention rate is 94%, the thermal conductivity retention rate is 93%, the interfacial shear strength improvement rate is 65%, the flexural strength improvement rate is 30%, and the tensile strength improvement rate is 55%.

[0186] Compared to Example 3, although the penetration performance of the sizing agent in Comparative Example 3 was acceptable, the surface hairiness of the fibers increased after sizing, and the improvement in various mechanical properties was not as significant as in Example 3, especially the enhancement effect on interfacial shear strength and tensile strength. This is because the boiling point of the co-solvent in Comparative Example 3 was too low. In the initial stage of high-temperature drying and curing at 150°C, the evaporation rate of the co-solvent was too fast, causing rapid skinning to occur on the surface of the fiber before the sizing agent had fully leveled and penetrated. This rapid phase separation disrupted the continuity and density of the polyurethane film, leaving some pore defects inside the coating and at the interface, thus failing to provide a uniform and tough interfacial bonding layer like that in Example 3.

[0187] Comparative Example 4

[0188] A method for sizing graphene fibers differs from Example 3 in that the volatile ester co-solvent is replaced with ethylene glycol diacetate, which has a boiling point of 190°C and a solubility of 21.3 g / 100 mL in water at 20°C.

[0189] Tests show that the waterborne polyurethane graphene fiber sizing agent has a contact angle of 24° and a penetration time of 4.5s on graphene fibers. After sizing, the graphene fiber wettability is 94.5%, the surface hairs are 10 hairs / m, the electrical conductivity retention rate is 95%, the thermal conductivity retention rate is 95%, the interfacial shear strength improvement rate is 72%, the flexural strength improvement rate is 35%, and the tensile strength improvement rate is 65%.

[0190] Compared with Example 3, Comparative Example 4 showed a decrease in the improvement of interfacial shear strength and tensile strength, and the number of fiber hairs was greater than that in Example 3. This is because the boiling point of the cosolvent in Comparative Example 4 was too high, which caused the residual ethylene glycol diacetate inside the fiber bundle to produce a liquid bridge effect during the high-temperature curing and drying process. This induced severe filament bundling and adhesion between monofilaments, hindering the formation of an independent and uniform film layer on the surface of the monofilaments, resulting in a decrease in the overall improvement of the fiber bundle's flexibility and strength.

[0191] Comparative Example 5

[0192] A method for sizing graphene fibers differs from Example 2 in that the volatile ester co-solvent is replaced with n-butyl propionate, which has a boiling point of 146°C and a solubility of 0.15 g / 100 mL in water at 20°C.

[0193] Tests show that the waterborne polyurethane graphene fiber sizing agent has a contact angle of 45° and a penetration time of 12.5s on graphene fibers. After sizing, the wettability of graphene fibers is 78.5%, the surface hair count is 35 hairs / m, the electrical conductivity retention rate is 90%, the thermal conductivity retention rate is 88%, the interfacial shear strength is increased by 25%, the flexural strength is increased by 10%, and the tensile strength is increased by 10%.

[0194] Compared to Example 2, Comparative Example 5 exhibited severely deteriorated sizing performance, with the contact angle increasing to 45°, the penetration time being several times longer, and the improvement in mechanical properties being relatively small. This is because the co-solvent in Comparative Example 5 has extremely low solubility and exhibits strong hydrophobicity. In the waterborne polyurethane system, this co-solvent cannot be effectively dispersed in the aqueous phase to form a homogeneous phase as the co-solvent in Example 2, instead resulting in macroscopic or microscopic oil-water separation. This not only prevents the surface tension of the sizing agent from being effectively reduced, but also hinders the wetting of the graphene fiber bundles by the sizing agent.

Claims

1. A method for sizing graphene fibers, characterized in that, After the graphene fiber is impregnated in the sizing agent, the amount of liquid is controlled by the extrusion roller or scraper, and then dried and cured to complete the sizing of the graphene fiber. The sizing agent is a water-based polyurethane graphene fiber sizing agent. The waterborne polyurethane graphene fiber sizing agent is composed of cationic polyether polyurethane sizing agent, volatile ester co-solvent and water; The components and contents of the cationic polyether polyurethane slurry are as follows: cationic polyether polyurethane 75wt%-92wt%, functional additives 0.5wt%-2wt%, and water 6wt%-24.5wt%. The volatile ester cosolvent has a boiling point of 146-156℃ and a solubility in water at 20℃ of ≥19.8g / 100mL.

2. The sizing method for graphene fibers according to claim 1, characterized in that, The volatile ester cosolvents are one or more of ethyl lactate, propylene glycol methyl ether acetate, and ethylene glycol ethyl ether acetate.

3. The sizing method for graphene fibers according to claim 1, characterized in that, The components and contents of the reaction raw materials for cationic polyether polyurethane are as follows: polyether polyol 55wt%-75wt%, isocyanate 18wt%-30wt%, cationic hydrophilic chain extender 2wt%-5wt%, nonionic chain extender 2wt%-7wt%, and neutralizer 1wt%-3wt%.

4. The sizing method for graphene fibers according to claim 3, characterized in that, The polyether polyol is polytetramethylene ether glycol or polyoxypropylene glycol; The isocyanate is isophorone diisocyanate or 1,6-hexamethylene diisocyanate; The cationic hydrophilic chain extender is N-methyldiethanolamine; The nonionic chain extender is 1,4-butanediol or ethylenediamine; The neutralizing agent is acetic acid or lactic acid.

5. The sizing method for graphene fibers according to claim 1, characterized in that, In waterborne polyurethane graphene fiber sizing agents, the content of cationic polyether polyurethane sizing agent is 0.5wt%-20wt%, and the mass ratio of volatile ester co-solvent to water is 1:4-20.

6. The sizing method for graphene fibers according to claim 1, characterized in that, The impregnation temperature is 5-40℃ and the time is 5-60s; the drying and curing temperature is 100-200℃ and the time is 30-180s.

7. The sizing method for graphene fibers according to claim 1, characterized in that, The specifications of the graphene fiber are 20-1000tex / 1000-50000F, the contact angle of the sizing agent on the graphene fiber is <30°, and the penetration time is <5s; After sizing, the graphene fiber wettability is >98%, the surface hairs are <10 hairs / m, the retention rate of electrical conductivity and thermal conductivity is >92%, the interfacial shear strength is increased by 60%-120%, the flexural strength is increased by 20%-80%, and the tensile strength is increased by 40%-120%.

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