Ionic liquid pretreated graphene conductive filler and method of making

Abstract

The application relates to a kind of ionic liquid pretreatment graphene conductive filler and its preparation method, belong to high polymer material technical field, including the following steps: preparation graphene oxide, then by ultrasonic stripping or chemical reduction obtains reduced graphene oxide;Graphene dispersion liquid is mixed with ionic liquid, stirring ultrasonic treatment is carried out, so that ionic liquid is adsorbed on the surface of graphene by ion-pi interaction and charge transfer;The pretreated graphene is compounded with polymer matrix;The material after compounding is controlled forming processing, and the morphology and distribution of graphene are regulated;Cooling, cutting, packaging, obtain conductive filler;The application also includes ionic liquid recovery technology, and recovery efficiency is greater than or equal to 95%. Ionic liquid is firmly adsorbed on the surface of graphene by ion-pi interaction, which not only avoids agglomeration, but also enhances electron transmission as a conductive bridge, the technology makes the conductivity of composite material increase by 20-60%, improves the mechanical properties, and the process is compatible with existing equipment, and the cost is reduced by more than 30%.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials technology, specifically referring to an ionic liquid pretreated graphene conductive filler and its preparation method. Background Technology

[0002] With the development of the electronic information and new energy industries, the demand for polymer conductive composite materials is increasing due to their combination of the processability and conductivity of polymer materials. Among them, graphene stands out for its excellent intrinsic conductivity (approximately 10⁻⁶ ohms). 3 -10 4 (S / cm) makes it an ideal conductive filler; however, the strong van der Waals forces between graphene sheets make them prone to agglomeration and difficult to disperse uniformly in the polymer matrix, resulting in a decrease in the conductivity of the composite material.

[0003] In existing technologies, the mainstream solution to the graphene dispersion problem is "surfactant or organic solvent pretreatment - polymer composite". The specific process involves: preparing graphene through chemical oxidation or mechanical exfoliation; pretreating the graphene with surfactants such as sodium dodecyl sulfate (SDS) or organic solvents such as N,N-dimethylformamide (DMF); and then composited with a polymer matrix such as epoxy resin or polyolefin through solution mixing or melt blending (e.g., published patent CN102120303A). However, this solution has significant limitations: Poor dispersion stability: The surfactant adheres to the graphene surface only through physical adsorption and is easily desorbed during processing, causing the graphene to re-aggregate. Conductivity loss: Surfactants are insulators, and when they cover the graphene surface, they hinder electron transport, resulting in the conductivity of the composite material only increasing by 10-15%. Environmental and cost issues: Organic solvents are volatile and toxic, which does not meet the requirements of green manufacturing; and existing graphene preparation methods (such as chemical vapor deposition CVD) are expensive, while liquid phase exfoliation has low yield (concentration is usually < 1 mg / mL), making it difficult to apply on a large scale. Insufficient interfacial compatibility and performance controllability: The weak interfacial bonding between graphene and the polymer matrix leads to a decline in the mechanical properties of the composite material; moreover, the process parameters lack systematic optimization, the morphology and distribution of fillers are random, and the performance fluctuates greatly.

[0004] Lowering the threshold: The conductivity of graphene / polymer composites in existing technologies is typically around 10. -2 -10 2 Within the S / cm range, the conductivity increases non-linearly with increasing graphene content, exhibiting a significant percolation threshold effect. However, this invention, through ionic liquid pretreatment, can achieve a conductivity improvement of 2-3 orders of magnitude at low addition levels (≤2wt%).

[0005] To address the aforementioned issues, there is an urgent need in this field for a polymer conductive filler preparation technology that can simultaneously achieve the high dispersibility and high conductivity of graphene, while also being environmentally friendly, low-cost, and having controllable performance. Summary of the Invention

[0006] To overcome some of the problems mentioned in the background above, the present invention provides an ionic liquid pretreated graphene conductive filler and its preparation method, so as to at least partially solve the above problems.

[0007] According to the technical solution of the present invention, a method for preparing ionic liquid pretreated graphene conductive filler is provided, comprising the following steps: Step 1: Natural graphite powder is reacted with reagents such as concentrated sulfuric acid and potassium permanganate under ice bath conditions to prepare graphene oxide. Then, reduced graphene oxide is obtained by ultrasonic exfoliation or chemical reduction. It is dispersed in N-methylpyrrolidone or deionized water to form a graphene dispersion with a concentration of 0.1-5 mg / mL. Step 2: Mix the graphene dispersion and the ionic liquid at a mass ratio of 1:0.1-1:1, mechanically stir at room temperature for 30-60 minutes, and then sonicate at 100-500W power for 30-120 minutes to allow the ionic liquid to adsorb onto the graphene surface; the ionic liquid includes one or more of 1-butyl-3-methylimidazolium tetrafluoroborate, 1-ethyl-3-methylimidazolium tetrafluoroborate, 1-allyl-3-methylimidazolium chloride, or 1-hydroxyethyl-3-methylimidazolium tetrafluoroborate. Step 3: Combine the pretreated graphene with the polymer matrix at a graphene addition amount of 0.1-10 wt%, and the combination method is solution blending, melt blending or surface in-situ polymerization. Step 4: Perform controlled molding processing on the composite material. When granulating by extruder, control the temperature at 180-220℃ and the screw speed at 100-300rpm, or when injection molding, control the pressure at 50-100MPa and the mold temperature at 40-80℃. Step 5: Cooling, cutting, and packaging yields a highly dispersible and highly conductive polymeric conductive filler; The polymer matrix includes one or more of polyethylene, polypropylene, polystyrene, polylactic acid, natural rubber, silicone rubber, epoxy acrylate, waterborne polyurethane, or acrylic emulsion.

[0008] Furthermore, the ionic liquid and graphene form a stable pretreatment layer through ion-π interactions and charge transfer, with an interfacial binding energy of -150 to -175 kJ / mol, which is determined by density functional theory calculation or isothermal titration calorimetry.

[0009] Furthermore, in the solution blending method, the polymer is dissolved in toluene or chloroform organic solvent, and the pretreated graphene dispersion is added, stirred and mixed, and then the solvent is evaporated to remove it; the melt blending method is carried out in a twin-screw extruder or internal mixer, with a mixing temperature of 150-250℃, a rotation speed of 50-200rpm, and a time of 5-20 minutes.

[0010] Furthermore, it also includes an ionic liquid recovery step, which uses magnetic-assisted recovery technology to introduce Fe3O4 nanoparticles, or surfactant synergistic separation technology to use nonionic surfactants to regulate the surface charge of graphene, with an ionic liquid recovery efficiency of ≥95%, and can be recycled ≥7 times without significant reduction in activity.

[0011] Furthermore, the ionic liquid and graphene are bonded by dynamic covalent bonds, which are reversible bonds formed by the Diels-Alder reaction, achieving bonding at 75°C and dissociation at 120°C.

[0012] Furthermore, during the controllable molding process, graphene is induced to curl into a curved structure by high-pressure micro-jet, or a spherical composite is formed by microemulsion method, with the graphene interlayer spacing controlled at 0.4-0.8 nm and the dispersion ≥95%.

[0013] Furthermore, the method for reducing graphene oxide in step 1 includes electrochemical reduction, photocatalytic reduction, or multi-component synergistic reduction, with a reduction time ≤ 30 minutes and a reduced graphene conductivity ≥ 1000 S / cm.

[0014] Furthermore, when the polymer matrix is ​​replaced with natural rubber, silicone rubber, epoxy acrylate, waterborne polyurethane, or acrylic emulsion, the tensile strength of the composite material increases by ≥8.36%, and the flexural modulus increases by ≥12.76%. The pretreatment method in step 2 is replaced by microwave-assisted pretreatment, mechanochemical pretreatment or ultrasonic-assisted pretreatment, wherein the mechanochemical pretreatment adopts ball milling, sand milling or three-roll milling.

[0015] Furthermore, the interfacial bonding energy between the ionic liquid and graphene is -155 to -165 kJ / mol, and the conductivity of the composite material satisfies the formula σ = σ0・(1 + k・φ). Where σ is the conductivity of the composite material (S / cm), σ0 is the conductivity of the matrix, φ is the dispersion (0.5-0.98), and k is the ionic liquid control coefficient (0.3-0.6). When φ increases from 0.7 to 0.95 and k increases from 0.3 to 0.6, the conductivity increases by 40-60%. The formula is applicable to polyolefin or polyester matrix composites with graphene content of 0.1-5 wt%, and the test conditions are 25℃ and 1 kHz AC signal.

[0016] On the other hand, the present invention also provides an ionic liquid pretreated graphene conductive filler, which is a graphene conductive filler obtained by the above-mentioned method for preparing ionic liquid pretreated graphene conductive filler.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: The ionic liquid of this invention is firmly adsorbed onto the graphene surface through ion-π interaction, which not only avoids agglomeration but also acts as a conductive bridge to enhance electron transport, thereby increasing the conductivity of the composite material by 20-60%.

[0018] The ionic liquid of this invention is non-toxic and non-volatile, and can be recycled more than 7 times through recycling technology. The cost per use is reduced to less than 80% of that of traditional dispersants, thus reducing environmental pollution. At the same time, the pretreatment and compounding process is compatible with existing polymer processing equipment, eliminating the need for expensive equipment.

[0019] The ionic liquid of this invention acts as a molecular bridge to improve the interfacial bonding force between graphene and the polymer matrix, thereby enhancing the mechanical properties of the composite material. By adjusting the type of ionic liquid, pretreatment conditions, and molding parameters, the interlayer spacing, dispersion, and morphology of graphene can be precisely controlled to meet the needs of different scenarios such as lithium-ion batteries and electromagnetic shielding materials. At the same time, it can also expand the multifunctionality of thermal conductivity, flame retardancy, and self-healing. Attached Figure Description

[0020] Figure 1 This is a transmission electron microscope (TEM) image of the [Amim]Cl pretreated graphene / ABS composite filler in Example 2 of the present invention. Figure 2 This is a TEM image of the [HAIM]BF4 pretreated graphene / natural rubber composite filler after high-pressure microfluidic treatment in Example 3 of the present invention.

[0021] Figure 3 This is a SEM image of pure reduced graphene oxide (rGO) before in-situ surface polymerization in Example 4 of the present invention; Figure 4 This is a SEM image of composite particles of PMMA grown on the surface of graphene after in-situ polymerization in Example 4 of the present invention. Figure 5 This is a SEM image of the interface between the surface in-situ polymerized composite particles and PLA after melt blending in Example 4 of the present invention. Figure 6 This is a high-magnification SEM image of the graphene and PLA composite material after in-situ surface polymerization in Example 4 of the present invention. Detailed Implementation

[0022] The technical solutions in the embodiments will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection.

[0023] This invention aims to solve four core problems existing in the preparation technology of graphene-based polymer conductive fillers: The contradiction between dispersibility and conductivity: Traditional pretreatment methods cannot simultaneously achieve stable dispersion and high conductivity retention of graphene. Process complexity and high cost - Existing preparation and pretreatment processes require high-performance equipment, consume a lot of energy, and are difficult to scale up; Poor interfacial compatibility and stability – the bonding force between graphene and the polymer matrix is ​​weak, and the long-term performance of the composite material is unstable. Uncontrollable performance – lack of precise control over the morphology and dispersion state of graphene, making it impossible to meet the customized needs of different application scenarios.

[0024] The core of this invention lies in utilizing the amphiphilic properties of ionic liquids: the cationic portion is firmly adsorbed onto the graphene surface through ion-π interactions, while the anionic portion is compatible with the polymer matrix, forming a molecular bridging structure. Density functional theory (DFT) calculations show that the adsorption energy of 1-butyl-3-methylimidazolium cations with graphene is approximately -162.58 kJ / mol, far higher than that of traditional surfactants (approximately -40 to -60 kJ / mol). Simultaneously, the ionic liquid itself possesses ionic conductivity (1-10 mS / cm), which can serve as an electron transport channel, compensating for the interlayer contact resistance of graphene sheets and forming a continuous conductive network of "graphene-ionic liquid-graphene". This invention provides a method for preparing a highly dispersible and highly conductive polymeric conductive filler. Through ionic liquid pretreatment, multi-process synergistic compounding, and controllable molding, highly efficient compatibility between graphene and the polymer matrix is ​​achieved. The specific steps are as follows: Preparation of graphene dispersion: Graphene oxide (GO) was prepared using a modified Hummers method: Natural graphite powder was reacted with concentrated sulfuric acid and potassium permanganate under ice bath conditions to generate graphene oxide; subsequently, reduced graphene oxide (rGO) was obtained by ultrasonic exfoliation or chemical reduction (such as hydrazine hydrate reduction), and dispersed in a solvent (N-methylpyrrolidone or deionized water) to form a graphene dispersion with a concentration of 0.1-5 mg / mL; ultrasonic treatment was performed for 30-60 minutes to ensure that the graphene was in a monolayer or few-layer dispersion state.

[0025] Ionic liquid pretreatment: The obtained graphene dispersion is mixed with an ionic liquid at a mass ratio of 1:0.1-1:1; the ionic liquid is selected from imidazoles (such as 1-butyl-3-methylimidazolium tetrafluoroborate [BMIM][BF4], 1-ethyl-3-methylimidazolium tetrafluoroborate [EMIM][BF4], [Amim]Cl, [HAIM]BF4), quaternary ammonium salts, pyridines, or phosphates, and the anion can be tetrafluoroborate (BF4). 4- ), hexafluorophosphate (PF6) 6- ), dinitrileamine (N(CN)2) - ) or acetate (CH3COO - (For aqueous systems, choose acetate; for organic systems, choose fluoride anions.)

[0026] Mechanically stir at room temperature for 30-60 minutes, then ultrasonically treat with 100-500W power for 30-120 minutes to allow the ionic liquid to adsorb onto the graphene surface through ion-π interactions and charge transfer, forming a stable pretreated layer. If it is necessary to improve the pretreatment efficiency, it can be replaced with microwave-assisted pretreatment (microwave radiation accelerates intercalation), mechanochemical pretreatment (ball milling, sand milling and three-roll milling to achieve large-scale uniform pretreatment) or low-frequency ultrasonic (20-40kHz) assisted pretreatment (cavitation effect promotes the entry of ionic liquid into the graphite interlayer).

[0027] Composite with a polymer matrix: Pretreated graphene is composited with a polymer matrix at a graphene addition rate of 0.1-10 wt%. The polymer matrix is ​​selected from polyethylene (PE), polypropylene (PP), polystyrene (PS), polylactic acid (PLA), natural rubber (NR), silicone rubber, epoxy acrylate, waterborne polyurethane, or acrylic emulsion. The composite methods include: Solution blending method: The polymer is dissolved in an organic solvent such as toluene or chloroform, a pretreated graphene dispersion is added, the mixture is stirred and then the solvent is evaporated to obtain a composite film or powder; Melt blending method: In a twin-screw extruder or internal mixer, pretreated graphene and polymer melt are mixed at 150-250℃, at a speed of 50-200 rpm, for 5-20 minutes to achieve uniform dispersion.

[0028] Surface in-situ polymerization: Pretreated graphene is dispersed in polymer monomers such as acrylate and styrene, and initiators such as ammonium persulfate and azobisisobutyronitrile are added. In-situ polymerization is initiated at 60-80℃, so that polymer chains grow on the graphene surface and form covalent bonds, further enhancing the interfacial bonding force; polymerization time is 2-6 hours.

[0029] Controlled molding process: The composite material is molded to control the shape and size of the filler. If granular fillers are to be prepared: granulate using a single-screw or twin-screw extruder, controlling the temperature at 180-220℃ and the screw speed at 100-300 rpm; To prepare conductive components of a specific shape: injection molding is used, with a pressure of 50-100 MPa and a mold temperature of 40-80℃. To optimize the conductive path: use high-pressure microfluidics (pressure 30MPa, shear rate 10). 4 s -1 Inducing graphene to curl into a curved structure, or forming a spherical composite through microemulsion / sol-gel method, so that the graphene interlayer spacing is controlled at 0.4-0.8nm and the dispersion is ≥95%.

[0030] Ionic liquid recovery: Ionic liquids can be recovered and recycled using any of the following technologies: Magnetic-assisted recovery technology: Fe3O4 nanoparticles are introduced into the pretreatment of ionic liquids. After the pretreatment is completed, the ionic liquids are quickly recovered by an external magnetic field (strength 0.5 T). The recovery efficiency is ≥95%, and the liquids can be recycled more than 7 times without significant reduction in activity. Surfactant-assisted separation technology: Utilizing nonionic surfactants (such as SDS) to regulate the surface charge of graphene, enhancing centrifugal separation efficiency, with ionic liquid recovery rate ≥98%; Dynamic covalent bond recovery technology: Reversible covalent bonds formed by the Diels-Alder reaction are introduced between ionic liquid and graphene. Bonding is achieved at 75℃, and the complex is dissociated at 120℃ to recover the ionic liquid with a recovery rate of ≥95%.

[0031] Post-processing and finished products: The molded products are cooled, cut and packaged to obtain highly dispersible and highly conductive polymer conductive fillers.

[0032] Example 1 Preparation of graphene dispersion: Graphene oxide was reduced with hydrazine hydrate to obtain rGO, which was dispersed in deionized water and ultrasonically treated for 45 minutes to form a graphene dispersion with a concentration of 2 mg / mL. Ionic liquid pretreatment: The graphene dispersion was mixed with [BMIM][BF4] at a mass ratio of 1:0.5, mechanically stirred at room temperature for 45 minutes, and then ultrasonically treated with 300W power for 60 minutes; Melt blending: Add pretreated graphene and PP to a twin-screw extruder at a graphene addition rate of 2wt%, mix at 200℃, speed of 100rpm, and time of 10 minutes; Controlled molding: Granulation is performed using a single-screw extruder at a temperature of 200℃ and a screw speed of 200 rpm; Post-processing: After cooling, the material is cut and packaged to obtain PP-based conductive filler.

[0033] Performance testing: The filler has a dispersion of 96%, its conductivity is 35% higher than that of untreated graphene and PP composites, and its tensile strength is 7.2% higher than that of pure PP.

[0034] Example 2 Preparation of graphene dispersion: Graphene oxide was ultrasonically exfoliated and dispersed in N-methylpyrrolidone at a concentration of 1 mg / mL; Ionic liquid pretreatment: Add [Amim]Cl (mass ratio 1:0.3), and simultaneously add Fe3O4 nanoparticles, mechanically stir for 30 minutes, and then sonicate at 500W for 45 minutes; Solution blending: Dissolve ABS in chloroform, add pretreated graphene dispersion, stir and evaporate to remove solvent; Injection molding: Injection molding into sheet-like parts at 50MPa pressure and 60℃ mold temperature; Ionic liquid recovery: [Amim]Cl was recovered with an external 0.5 T magnetic field, achieving a recovery rate of 97%. Post-processing: After cooling, cut and package.

[0035] Performance testing: The sheet-like component exhibits a volumetric conductivity of 15.7 S / cm (measured using the four-probe method), which is 42 times higher than the control sample without ionic liquid and 3.8 times higher than the sample treated with traditional sodium dodecyl sulfate (SDS). The thermal conductivity is 0.249 W / (m·K), and after 7 cycles of ionic liquid recycling, the filler retains 88% of its conductivity.

[0036] like Figure 1 The graphene shown is uniformly dispersed in the ABS matrix without obvious agglomerates (agglomerate size <50nm), and the graphene sheets are tightly bonded to the ABS matrix interface. This proves that the ionic liquid pretreatment effectively solves the dispersion and interfacial compatibility problems of graphene, providing a structural basis for high conductivity and mechanical properties.

[0037] Example 3 Preparation of graphene dispersion: Graphene oxide was electrochemically reduced to obtain rGO (electrolyte was BMIMHSO4, negative potential was applied), and dispersed in deionized water at a concentration of 0.5 mg / mL. Ionic liquid pretreatment: Add [HAIM] BF4 at a mass ratio of 1:0.8 to graphene and perform microwave-assisted pretreatment (500W power, 10 minutes). Melt blending: Mix with natural rubber at 180°C and 150 rpm for 15 minutes (graphene addition 1.5 wt%). Controllable molding: High-pressure micro-jet (30MPa) treatment induces graphene to form a curved structure; Post-processing: cooling and cutting to obtain flexible conductive filler.

[0038] Performance testing: Filler dispersion 98%, tear strength 48.6kN / m, 14.9% higher than pure natural rubber (42.3kN / m); elongation at break 820%, 13.9% higher than pure natural rubber (720%); volumetric conductivity 2.3S / cm, 36 times higher than untreated sample, suitable for wearable devices.

[0039] like Figure 2 The graphene shown forms a curved structure in a natural rubber matrix, which confirms the effect of controllable molding and processing steps on the morphology of graphene. This structure can significantly improve the conductivity and flexibility of the composite material, which meets the application requirements of wearable devices.

[0040] Example 4 Preparation of graphene dispersion: Graphene oxide was photocatalytically reduced to rGO under TiO2 photocatalyst and ultraviolet light irradiation for 20 minutes, and then dispersed in deionized water at a concentration of 1.2 mg / mL. Ionic liquid pretreatment: [BMIM][BF4] with a mass ratio of 1:0.7 to graphene was added, and Fe3O4 nanoparticles were introduced at the same time. The mixture was stirred at room temperature for 60 minutes and then sonicated at 400W for 90 minutes. In-situ surface polymerization: Pretreated graphene was dispersed in methyl methacrylate (MMA) monomer, and azobisisobutyronitrile (AIBN) initiator (0.8% of monomer mass) was added. Polymerization was carried out at 70°C for 4 hours, with a monomer conversion rate of 92%, forming composite particles of PMMA grown in-situ on the graphene surface.

[0041] Melt blending: Graphene-PMMA composite particles after in-situ surface polymerization were compounded with PLA at a graphene addition of 2.5 wt% in a twin-screw extruder at a temperature of 190℃, a speed of 180 rpm, and a time of 15 minutes.

[0042] Controlled molding: Injection molding is performed under a pressure of 80MPa and a mold temperature of 60℃ to produce standard mechanical specimens.

[0043] Post-processing: Cooling and cutting to obtain PLA-based conductive filler.

[0044] Performance testing: The filler dispersion was 99%, and the volumetric conductivity reached 9.8 S / cm; the tensile strength reached 51.2 MPa (15.3% higher than that of pure PLA), and the flexural modulus reached 2380 MPa (18.6% higher than that of pure PLA); the interfacial bonding energy was calculated to be -165.3 kJ / mol by DFT, which was significantly higher than that of the non-in-situ polymerized sample (-98.7 kJ / mol).

[0045] like Figure 3The pure rGO shown exhibits a typical lamellar structure with clear lamellar edges and no obvious polymer adhesion. There is slight stacking between the lamellars, but after ultrasonic dispersion, it can form a monolayer or few-layer structure, providing a clean reaction surface for subsequent in-situ surface polymerization. like Figure 4 The graphene sheet surface shown is coated with a uniform polymer film (PMMA) with a thickness of about 50-100 nm, proving that the polymer monomers were successfully polymerized in situ on the graphene surface; the polymerized composite particles showed no obvious agglomeration and excellent dispersion, verifying the further improvement effect of surface in situ polymerization on the dispersibility of graphene. like Figure 5 The PMMA layer grown on the graphene surface forms a tight interface bond with the PLA matrix, with no obvious voids or desorption phenomena. The graphene sheets are uniformly embedded in the PLA matrix, and the PMMA transition layer achieves efficient compatibility between graphene and PLA, explaining the structural root of the synergistic improvement of the mechanical and electrical properties of the composite material. like Figure 6 The graphene sheets shown form a continuous conductive network in the PLA matrix with uniform interlayer spacing (approximately 0.6 nm) and no obvious agglomerates (agglomerate size <30 nm). The polymer chains formed by in-situ polymerization on the surface form a bridging structure between the graphene sheets, which not only hinders the stacking of the sheets but also reduces the contact resistance, further verifying the structural basis for the improved conductivity.

[0046] Comparative Example 1 The difference from Example 2 is as follows: Graphene was treated by replacing the ionic liquid with the traditional SDS surfactant Sigma-Aldrich S5136.

[0047] Comparative Example 2 The difference from Example 2 is as follows: The ionic liquid and graphene dispersion were initially mixed uniformly by manually stirring with a glass rod for 10 minutes, without room temperature mechanical stirring or ultrasonic treatment, and without a full induction process of ion-π interactions.

[0048] The performance of Example 2, Comparative Example 1, and Comparative Example 2 was tested respectively, and the test results are shown in Table 1 below: Table 1

[0049] As shown in Table 1 above, Example 2 is significantly better than Comparative Example 1 and Comparative Example 2 in terms of conductivity, mechanical properties, dispersibility, and ionic liquid recovery rate, demonstrating the synergistic effect of specific pretreatment process and recovery technology for ionic liquids, and solving the core pain points of existing technologies.

[0050] Ionic liquid recovery of ABS-based conductive filler prepared using process parameters in Example 2: After the composite material is crushed, deionized water is added, ultrasonic dispersion is performed for 30 minutes, a magnetic field of 0.6T is applied, ionic liquid containing Fe3O4 is separated, water is removed by rotary evaporation, and vacuum drying is performed at 60°C. Recycling: The recycled ionic liquid was used for the pretreatment of the next batch of graphene, repeated 7 times. The performance test results are shown in Table 1 below. Table 2

[0051] As shown in Table 2 above, the ionic liquid recovery efficiency decreases slowly with the increase of the number of cycles, but it still remains above 94.7% after 7 cycles. The conductivity of the composite material decreases by no more than 22%, which proves the feasibility and stability of the recovery technology of this invention.

[0052] It should be noted that the performance difference between Example 2 and Example 4 is due to the fact that ABS matrix is ​​an amorphous polymer with high molecular chain freedom, making it easier for graphene sheets to form a continuous conductive network within the matrix. PLA, on the other hand, is a crystalline polymer, and the crystalline regions physically block the conductive pathways, resulting in a slightly lower conductivity for the same amount of graphene added. However, the mechanical properties of the PLA-based composite material are significantly improved, with a 15.3% increase in tensile strength. This is because PLA has better compatibility with PMMA and stronger interfacial bonding, meeting the performance requirements of different application scenarios.

[0053] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing graphene conductive filler pretreated with ionic liquid, characterized in that, Includes the following steps: Step 1: Reduced graphene oxide is obtained by ultrasonic exfoliation or chemical reduction of graphene oxide, and then dispersed in N-methylpyrrolidone or deionized water to form a graphene dispersion with a concentration of 0.1-5 mg / mL. Step 2: Mix the graphene dispersion and the ionic liquid at a mass ratio of 1:0.1-1:1, mechanically stir at room temperature for 30-60 minutes, and then sonicate at 100-500W power for 30-120 minutes to allow the ionic liquid to adsorb onto the graphene surface; the ionic liquid includes one or more of 1-butyl-3-methylimidazolium tetrafluoroborate, 1-ethyl-3-methylimidazolium tetrafluoroborate, 1-allyl-3-methylimidazolium chloride, or 1-hydroxyethyl-3-methylimidazolium tetrafluoroborate. Step 3: Combine the pretreated graphene with the polymer matrix at a graphene addition amount of 0.1-10 wt%, and the combination method is solution blending, melt blending or surface in-situ polymerization. Step 4: Perform controlled molding processing on the composite material. When granulating by extruder, control the temperature at 180-220℃ and the screw speed at 100-300rpm, or when injection molding, control the pressure at 50-100MPa and the mold temperature at 40-80℃. Step 5: Cooling, cutting, and packaging yields a highly dispersible and highly conductive polymeric conductive filler; The polymer matrix includes one or more of polyethylene, polypropylene, polystyrene, polylactic acid, natural rubber, silicone rubber, epoxy acrylate, waterborne polyurethane, or acrylic emulsion.

2. The method for preparing ionic liquid pretreated graphene conductive filler according to claim 1, characterized in that, During the mixing process of the ionic liquid and graphene, the mechanical stirring speed is 200-500 rpm and the ultrasonic treatment frequency is 20-40 kHz, forming a stable pretreatment layer through ion-π interaction and charge transfer.

3. The method for preparing ionic liquid pretreated graphene conductive filler according to claim 1, characterized in that, In the solution blending method, the polymer is dissolved in toluene or chloroform organic solvent, and the pretreated graphene dispersion is added, stirred and mixed, and then the solvent is evaporated to remove it; the melt blending method is carried out in a twin-screw extruder or internal mixer, with a mixing temperature of 150-250℃, a speed of 50-200rpm, and a time of 5-20 minutes.

4. The method for preparing ionic liquid pretreated graphene conductive filler according to claim 1, characterized in that, It also includes an ionic liquid recovery step, which uses magnetic-assisted recovery technology to introduce Fe3O4 nanoparticles, or surfactant synergistic separation technology to regulate the surface charge of graphene using nonionic surfactants. The ionic liquid recovery efficiency is ≥95%, and the number of cycles is ≥7 times with no significant reduction in activity.

5. The method for preparing ionic liquid pretreated graphene conductive filler according to claim 1, characterized in that, The ionic liquid and graphene are bonded by dynamic covalent bonds, which are reversible bonds formed by the Diels-Alder reaction, achieving bonding at 75°C and dissociation at 120°C.

6. The method for preparing ionic liquid pretreated graphene conductive filler according to claim 1, characterized in that, During the controllable molding process, graphene is induced to curl into a curved structure by high-pressure micro-jet, or a spherical composite is formed by microemulsion method, with the graphene interlayer spacing controlled at 0.4-0.8 nm.

7. The method for preparing ionic liquid pretreated graphene conductive filler according to claim 1, characterized in that, The method for reducing graphene oxide in step 1 includes electrochemical reduction, photocatalytic reduction, or multi-component synergistic reduction, with a reduction time ≤ 30 minutes and a graphene conductivity ≥ 1000 S / cm after reduction.

8. The method for preparing ionic liquid pretreated graphene conductive filler according to claim 1, characterized in that, The polymer matrix is ​​replaced with natural rubber, silicone rubber, epoxy acrylate, waterborne polyurethane or acrylic emulsion, and the tensile strength of the composite material is increased by at least 8% and the flexural modulus is increased by at least 12% after the composite is formed. The pretreatment method in step 2 is replaced by microwave-assisted pretreatment, mechanochemical pretreatment or ultrasonic-assisted pretreatment, wherein the mechanochemical pretreatment adopts ball milling, sand milling or three-roll milling.

9. A graphene conductive filler pretreated with ionic liquid, characterized in that, The graphene conductive filler obtained by the preparation method of graphene conductive filler pretreated with ionic liquid according to any one of claims 1-8.

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