Lightweight conductive composite material and lightning protection fan blade made of same

Abstract

The invention relates to the field of conductive composite materials and wind power generation, and discloses a light conductive composite material and a lightning protection fan blade made of the light conductive composite material. 2-5% of a multi-walled carbon nanotube; 4-8% of silver-plated short fiber; 2-5% of graphite flakes; 1-3% of boron nitride micro powder; 3-7% of silver conductive paste; 0.5 to 2% of a polyethylene glycol based surface modifier; 1-3% of a silane coupling agent; 0.3 to 1% of a hindered phenol antioxidant; the multi-walled carbon nanotubes are subjected to surface carboxylation modification through a mixed solution of concentrated nitric acid and concentrated sulfuric acid, and are further modified through a polyethylene glycol-based surface modifier. By constructing the multi-scale graded conductive network and improving the heat dispersion performance of the material, efficient conduction and heat dissipation of lightning stroke current are achieved, meanwhile, the requirement for light weight of the fan blade is met, and therefore the defects in the aspects of conductive network stability, heat dispersion performance and preparation technology in the prior art are overcome.

Description

Technical Field

[0001] The present invention relates to the fields of conductive composites and wind power generation, and specifically to a lightweight conductive composite material and a lightning protection wind turbine blade made thereof. Background Art

[0002] With the rapid development of the wind power generation industry, the size of wind turbine blades has been continuously increasing. Especially in the field of offshore wind power, ultra-long blades have become the key to improving power generation efficiency. However, wind turbine blades are exposed to harsh weather in the high-altitude operating environment for a long time and are extremely vulnerable to lightning strikes. Lightning strikes can generate transient high currents and high temperatures, resulting in ablation on the blade surface, damage to the internal structure, and failure of the conductive network, thus seriously affecting the safety and operating life of the wind turbine. In order to improve the lightning protection performance of wind turbine blades, the existing technologies mainly adopt methods such as embedding a metal conductive network, surface coating with a metal conductive layer, or adding a composite material with a conductive filler to achieve effective conduction and dispersion of lightning strike current. These methods have solved the lightning protection problem to a certain extent, but there are still limitations in the stability of the conductive network, material lightweight, and heat dispersion performance.

[0003] In the prior art, although the embedded metal network solution can provide an effective conductive path, the high density of the metal material significantly increases the weight of the blade, which is contradictory to the lightweight trend of wind turbine blades. At the same time, the metal network is prone to ablation or fracture problems under the action of local high temperatures during lightning strikes, further reducing the service life. The process of surface coating with a metal conductive layer has problems such as insufficient bonding force between the coating and the substrate, easy peeling under dynamic stress and thermal shock conditions, and uneven coating thickness leading to uneven current dispersion and easy occurrence of hot spot ablation. In addition, although the research on conductive composites has developed, the randomly dispersed conductive fillers fail to form an efficient hierarchical conductive network, and the conductive path is discontinuous, resulting in low conduction efficiency of lightning strike current. At the same time, the interfacial bonding force between the conductive filler and the substrate is weak, and interfacial debonding or filler shedding is likely to occur under the transient high current of lightning strikes, further reducing the conductive performance. More importantly, most composite materials have poor thermal conductivity and cannot quickly disperse heat under local high temperatures during lightning strikes. The formation of hot spot areas exacerbates the damage to the conductive network and reduces the overall durability of the material. The existing preparation processes generally adopt the method of random dispersion of fillers. The process is simple but cannot optimize the structure of the conductive network, resulting in low filler utilization rate and limited improvement in material performance. Summary of the Invention

[0004] Aiming at the deficiencies of the prior art, the present invention provides a lightweight conductive composite material and a lightning protection wind turbine blade made thereof, which solve the problems of poor stability of the conductive network, insufficient heat dispersion ability, and inability to balance material lightweight and preparation process efficiency in the prior art.

[0005] To achieve the above object, the present invention is realized through the following technical solutions: A lightweight conductive composite material, comprising the following components by weight percentage: Polyetherimide matrix: 65 - 75%; Multi-walled carbon nanotubes: 2 - 5%; Silver-plated short fibers: 4 - 8%; Graphite flakes: 2 - 5%; Boron nitride micropowder: 1 - 3%; Silver conductive paste: 3 - 7%; Polyethylene glycol-based surface modifier: 0.5 - 2%; Silane coupling agent: 1 - 3%; Hindered phenol antioxidant: 0.3 - 1%.

[0006] Preferably, the multi-walled carbon nanotubes are surface carboxylated with a mixed solution of concentrated nitric acid and concentrated sulfuric acid and further modified with a polyethylene glycol-based surface modifier.

[0007] Preferably, the silver-plated short fibers are used after surface modification treatment with 3-aminopropyltriethoxysilane.

[0008] Preferably, the graphite flakes are thermally expanded at 650–750 °C and ultrasonically dispersed in a concentrated nitric acid solution before use.

[0009] Preferably, the particle size range of the boron nitride micropowder is 1–10 μm.

[0010] Preferably, the molecular weight range of the matrix material polyetherimide is 30,000–40,000 g / mol.

[0011] A lightning protection fan blade, which is made of the lightweight conductive composite material according to any one of claims 1 to 6.

[0012] Preferably, the surface of the blade is sprayed with silver conductive paste, and the coating thickness of the silver conductive paste is 10–50 μm.

[0013] Preferably, the blade is prepared by a dynamic electric field injection molding process, the electric field strength is 10–30 kV / cm, and the injection pressure is 80–150 MPa.

[0014] Preferably, a cooling gradient is set by a mold during the molding process of the blade, and the cooling gradient is 5–15 °C / cm.

[0015] The present invention provides a lightweight conductive composite material and a lightning protection fan blade made thereof. It has the following beneficial effects: 1. Through the synergistic effect of multi-walled carbon nanotubes, silver-plated short fibers, and graphite flakes, the present invention effectively constructs short-range, medium-range, and long-range conductive paths. Compared with the problem in the prior art that a single conductive filler easily leads to an uneven conductive network, the present invention effectively solves the deficiencies of local concentration of the conductive network, high percolation threshold, and unstable conductivity, and significantly improves the conductivity and uniformity of the material under high lightning current impact.

[0016] 2. Through the interface modification technology, the present invention uses carboxylated carbon nanotubes, silane modification of silver-plated short fibers, and thermal expansion treatment of graphite flakes to significantly enhance the interfacial bonding force between the conductive filler and the matrix. Compared with the problems of poor filler dispersion and easy interfacial debonding in the prior art, the present invention constructs an interfacial network structure with high bonding force, significantly improving the stability of the conductive network under high temperature and high pressure.

[0017] 3. The present invention adopts an injection molding process controlled by dynamic electric field induction and cooling gradient. The filler realizes orderly arrangement and directional distribution during the molding process, and the construction of the conductive path is more efficient and stable. Different from the traditional randomly dispersed conductive network, the present invention solves the problems of low network connection efficiency and too high local current density caused by the disordered arrangement of conductive fillers in the existing process, so that the composite material exhibits excellent conductivity and anti-ablative performance in the lightning environment.

[0018] 4. By introducing boron nitride micropowder as an efficient thermal conductivity material, the present invention successfully improves the thermal dispersion ability of the material and avoids the problem of local high-temperature accumulation caused by lightning current. In the prior art, relying on the low thermal conductivity of the matrix material, the present invention effectively makes up for this defect, greatly reducing the risk of thermal damage to the conductive network by lightning, and improving the overall heat resistance and lightning protection performance of the material. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a schematic process flow diagram of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0020] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0021] Please refer to the attached Figure 1 , the embodiments of the present invention provide a lightweight conductive composite material and a lightning protection fan blade made thereof, including: 1. Material Design and Component Ratio This study proposes a lightweight conductive composite material. The core is to solve the problems of decomposition, fracture, and failure of the conductive network under lightning strike impact by constructing a hierarchical conductive network and enhancing interface stability. The specific formulation design is as follows: Component ratio range Matrix material: Polyetherimide (PEI): 65 - 75 wt%. As the matrix material, PEI has excellent mechanical strength, heat resistance (glass transition temperature up to 250 - 280 °C), and chemical stability, and can effectively resist the high-temperature environment during lightning strikes.

[0022] Conductive filler: Multi-walled carbon nanotubes (MWCNTs): 2 - 5 wt%. As short-range conductive fillers, MWCNTs have high longitudinal conductivity (10^5 S / cm) and a high specific surface area, and can form an efficient conductive network at a low filling amount.

[0023] Silver-plated short fibers: 4 - 8 wt%. Silver-plated short fibers provide medium-range conductive paths and have excellent conductivity (conductivity of silver is 6.3×10^7 S / m). On the basis of the short-range conductive network of MWCNTs, they further enhance the stability of the conductive network.

[0024] Graphite flakes: 2 - 5 wt%. As long-range conduction path fillers, graphite flakes further improve the current dispersion ability through their two-dimensional layered structure.

[0025] Auxiliary material: Boron nitride micropowder: 1 - 3 wt%. As a thermal conductivity filler, boron nitride micropowder has high thermal conductivity (60 W / m·K) and electrical insulation, and can quickly disperse the local high temperature generated by lightning strikes.

[0026] Silver conductive paste: 3 - 7 wt%. It is used for surface coating of the material to further improve the surface conductivity of the material and the dispersion ability of lightning current.

[0027] Interface modifier: Polyethylene glycol-based surface modifier: 0.5 - 2 wt%. By interacting with the carboxyl groups on the surface of MWCNTs, it improves the dispersion of MWCNTs in the matrix and the interfacial bonding force.

[0028] Silane coupling agent (such as 3-aminopropyltriethoxysilane): 1 - 3 wt%. By chemically reacting with silver-plated short fibers and the matrix, it enhances the interfacial bonding force between the two.

[0029] Antioxidant: Hindered phenol antioxidant: 0.3 - 1 wt%. It prevents the thermal oxidative decomposition of the matrix resin caused by high temperature during lightning strikes.

[0030] 2. Preparation method 2.1 Pretreatment of Raw Materials Surface Modification of MWCNTs: Place MWCNTs in a mixed solution of concentrated nitric acid and concentrated sulfuric acid (volume ratio 3:1), stir at 60 - 80 °C for 3 - 5 hours, and improve its hydrophilicity by introducing carboxyl and hydroxyl groups; Further treat with a polyethylene glycol-based surface modifier, disperse by ultrasonic in an ethanol solution, stir at a temperature of 25 - 35 °C for 1 - 2 hours.

[0031] Treatment of Silver-Plated Short Fibers: Stir in a 3-aminopropyltriethoxysilane solution (concentration 3 wt%) for 2 - 4 hours; Drying temperature is 120 - 140 °C, time is 0.5 - 1 hour.

[0032] 2.2 Mixing and Molding Twin-Screw Kneading: At 160 - 200 °C, add matrix PEI, boron nitride micropowder, MWCNTs, silver-plated short fibers and graphite flakes into a twin-screw extruder for kneading, shear rate 200 - 400 rpm, time 15 - 25 minutes.

[0033] High-Shear Dispersion: At 150 - 180 °C, conduct secondary dispersion through a high-shear dispersion device (shear rate 1000 - 2000 rpm), time 10 - 20 minutes.

[0034] Dynamic Gradient Injection Molding: Melt temperature 260 - 300 °C, injection pressure 80 - 150 MPa, electric field strength 10 - 30 kV / cm, cooling gradient 5 - 15 °C / cm.

[0035] Example 1: Preparation of Lightweight Conductive Composite Based on Dynamic Electric Field Induction Modification of Carbon Nanotubes Take 100 g of multi-walled carbon nanotubes, add a mixed solution of nitric acid and sulfuric acid (volume ratio 3:1), and stir magnetically at 60 °C for 4 hours. After the reaction, wash with distilled water until neutral, and dry in vacuum at 80 °C for 12 hours. Then add the modified carbon nanotubes into a 1 wt% polyethylene glycol aqueous solution, disperse by ultrasonic for 30 minutes, and set aside.

[0036] Pretreatment of Silver-Plated Short Fibers Soak 50 g of silver-plated short fibers in a 3 wt% silane coupling agent ethanol solution, stir at room temperature for 3 hours. Take out the fibers, put them in an oven at 120 °C to dry for 1 hour. After drying, stir gently to make the surface modifier evenly distributed.

[0037] Mixing and Melting Take 700 g of polyetherimide particles and put them into a melting mixer. Heat to 180 °C until melted. Sequentially add modified carbon nanotubes (30 g), silver-plated short fibers (50 g), expanded graphite flakes (20 g), and boron nitride micropowder (20 g). Set the mixer speed to 300 rpm and stir for 20 minutes to ensure uniform mixing.

[0038] Dynamic electric field injection molding Put the mixture into an injection molding machine, heat to 280 °C, and the injection pressure is 120 MPa. Set the electric field strength inside the mold to 15 kV / cm, the cooling gradient is 10 °C / cm, and the cooling time is 20 seconds. Obtain the final material after demolding.

[0039] Demonstrated effects Under the guidance of the dynamic electric field, the carbon nanotubes and silver-plated fibers achieve oriented arrangement. A hierarchical conductive network is formed, the conductivity reaches 10^-4 Ω·cm, and there is no obvious break in the network after the simulated lightning strike current experiment. The material has good surface ablation resistance.

[0040] Example 2: Preparation of a lightning protection material enhanced by a surface conductive coating Raw material treatment Perform the surface modification treatment on multi-walled carbon nanotubes (30 g) and graphite flakes (20 g) as in Example 1. Wash the silver-plated short fibers (50 g) with ethanol and then directly dry them for standby.

[0041] Melting and mixing of the main materials Take 700 g of polyetherimide and 30 g of boron nitride micropowder, and place them in a twin-screw mixer at 160 °C. Gradually add modified carbon nanotubes, silver-plated fibers, and graphite flakes, with a mixing time of 15 minutes and a speed of 200 rpm.

[0042] Injection molding Put the mixed material into an injection molding machine, with a melt temperature of 270 °C and an injection pressure of 100 MPa. The mold cooling gradient is 8 °C / cm, and the substrate is obtained after curing.

[0043] Surface conductive coating treatment Spray silver conductive paste on the surface of the substrate, and control the coating thickness within 30 μm. Then place it at 130 °C for thermal curing for 30 minutes, and the coating is dense and smooth.

[0044] Demonstrated effects After the coating treatment, the surface resistivity of the material drops to 10^-5 Ω·cm. The simulated lightning strike test shows that the surface current of the material is evenly dispersed, there is no hot spot accumulation, and the lightning protection performance is significantly improved.

[0045] Example 3: Preparation of a thermal conductivity enhanced composite material Dispersion treatment of boron nitride micropowder Weigh 20 g of boron nitride micropowder and add it to a 0.5 wt% polyethylene glycol solution. After ultrasonic dispersion for 20 minutes, stir at low speed for 2 hours, and then vacuum dry at 80 °C for 8 hours.

[0046] Mixing process Place 680 g of polyetherimide in a twin-screw mixer and heat to 200 °C. Sequentially add modified boron nitride micropowder, carbon nanotubes (35 g), silver-plated short fibers (45 g), and graphite flakes (25 g). Set the rotation speed to 250 rpm and control the mixing time at 25 minutes until the mixture is uniform.

[0047] Injection molding and gradient cooling Inject the mixture into a mold. Set the mold temperature to 260 °C and the injection pressure to 130 MPa. Control the mold cooling gradient at 12 °C / cm and the cooling time at 25 seconds, and demold after curing.

[0048] Reflect the effect After adding boron nitride micropowder, the thermal conductivity of the material is increased from 0.25 W / m·K to 1.2 W / m·K, the local temperature in the lightning strike test is reduced by 30%, and the ablation of the conductive network is effectively reduced.

[0049] Example 4: Preparation of a composite material with optimized short-range conductive network Dispersion treatment of carbon nanotubes Weigh 40 g of multi-walled carbon nanotubes and adopt the carboxylation treatment process in Example 1. Then add it to a 0.8 wt% silane coupling agent solution and stir for 1 hour, and dry for later use.

[0050] Preparation of the main mixture Mix 730 g of polyetherimide with 30 g of modified carbon nanotubes. Add 40 g of silver-plated short fibers and 10 g of graphite flakes. Mix the mixture in a high-shear mixing device, set the temperature to 180 °C, the rotation speed to 400 rpm, and continue for 10 minutes.

[0051] Molding and post-treatment Inject the mixture. Set the melt temperature to 280 °C, the injection pressure to 110 MPa, and the mold cooling temperature difference to 10 °C / cm. After demolding, coat a 10-μm-thick silver conductive paste and thermally cure at 120 °C for 15 minutes.

[0052] Reflect the effect Through the optimization of the short-range network, the dispersion of carbon nanotubes is significantly improved and the uniformity of the conductive network is enhanced. After the lightning strike impact, the volume resistivity change rate of the material is less than 3%, indicating its stable conductive performance.

[0053] Example 5: Preparation of a long-range conductive path enhanced material Expansion modification of graphite flakes Weigh 25 g of graphite flakes, place them in a high-temperature environment of 700 °C for swelling treatment for 15 seconds, and then add them to a 0.1 M nitric acid solution for ultrasonic dispersion for 30 minutes. Take them out, wash them, and dry them for later use.

[0054] Material mixing Mix 650 g of the matrix material polyetherimide with the modified graphite flakes. Add carbon nanotubes (30 g), silver-plated short fibers (40 g), and boron nitride micropowder (30 g) in sequence. Knead at a high temperature (200 °C), set the rotation speed to 350 rpm, and the kneading time to 20 minutes.

[0055] Injection molding and surface treatment When mixing and injecting, set the electric field strength of the mold to 20 kV / cm and the injection pressure to 130 MPa. After demolding, polish the material surface, and then spray silver conductive paste. The thermal curing temperature is 140 °C and the time is 30 minutes.

[0056] Embodiment effect The optimized graphite flakes enhance the stability of the long-range conduction path, and the conductive network does not show interruption during lightning strikes. Simulation tests show that the current dispersion efficiency of the material is increased by 25%.

[0057] Comparative example 1: Based on Example 1, remove the dynamic electric field induction process Raw material pretreatment According to the steps in Example 1, carboxylate and surface-modify multi-walled carbon nanotubes, and also process silver-plated short fibers and graphite flakes according to Example 1.

[0058] Mixing and melting Mix 700 g of polyetherimide, 30 g of modified carbon nanotubes, 50 g of silver-plated short fibers, 20 g of graphite flakes, and 20 g of boron nitride micropowder. Kneading conditions: temperature 180 °C, rotation speed 300 rpm, kneading time 20 minutes.

[0059] Injection molding Perform injection molding under the conditions of a melt temperature of 280 °C and an injection pressure of 120 MPa. The mold does not apply dynamic electric field induction and is only cured by conventional cooling (without cooling gradient control, the mold temperature difference is set to 0 °C / cm).

[0060] Comparative example 2: Based on Example 2, remove the surface coating Raw material treatment and kneading Completely follow the process of Example 2 to prepare a mixture containing carbon nanotubes, silver-plated short fibers, and graphite flakes.

[0061] Injection molding Under the conditions of a melt temperature of 270 °C and an injection pressure of 100 MPa, the mixture was injection molded. The mold cooling gradient was set at 8 °C / cm and the cooling time was 20 seconds.

[0062] Post-treatment was omitted The process of surface spraying silver conductive paste was not carried out and it was directly used as a comparative sample.

[0063] Comparative Example 3: Based on Example 3, the content of boron nitride micropowder was reduced Raw material treatment The surface modification of raw materials was carried out completely in accordance with the process of Example 3, including the carboxylation treatment of carbon nanotubes, the modification of silver-plated short fibers, and the expansion treatment of graphite flakes.

[0064] Main material mixing 680 g of polyetherimide, 35 g of carbon nanotubes, 45 g of silver-plated short fibers, 25 g of graphite flakes, and 10 g of boron nitride micropowder (lower boron nitride content than in Example 3) were mixed. Mixing conditions: temperature 200 °C, rotation speed 250 rpm, time 25 minutes.

[0065] Injection molding The injection molding process parameters remained unchanged, with a melt temperature of 260 °C, an injection pressure of 130 MPa, and a mold cooling gradient of 12 °C / cm.

[0066] Comparative Example 4: Based on Example 4, the carbon nanotubes were not modified Raw material treatment Unmodified multi-walled carbon nanotubes (40 g) were directly used, and other materials (such as silver-plated short fibers and graphite flakes) were subjected to the same modification treatment as in Example 4.

[0067] Mixing 730 g of polyetherimide was mixed with unmodified carbon nanotubes, and then 40 g of silver-plated short fibers and 10 g of graphite flakes were added. Mixing conditions: temperature 180 °C, rotation speed 400 rpm, time 10 minutes.

[0068] Molding process The injection molding process maintained the parameters of Example 4, with a melt temperature of 280 °C, an injection pressure of 110 MPa, and a mold cooling gradient of 10 °C / cm. After demolding, silver conductive paste spraying was not carried out.

[0069] Comparative Example 5: Based on Example 5, the expansion treatment of graphite flakes was not carried out Raw material preparation Graphite flakes (25 g) without expansion treatment were used, and the remaining components such as carbon nanotubes, silver-plated short fibers, and boron nitride micropowder were prepared according to the proportions of Example 5 and surface modified according to the corresponding treatment processes.

[0070] Mixing material preparation Mix 650 g of polyetherimide, 30 g of carbon nanotubes, 40 g of silver-plated short fibers, 25 g of unexpanded graphite flakes with 30 g of boron nitride micropowder. Kneading conditions: temperature 200 °C, rotation speed 350 rpm, time 20 minutes.

[0071] Injection molding and coating The injection molding process is the same as that of Example 5, the electric field strength of the mold is 20 kV / cm, and the injection pressure is 130 MPa. The mold cooling gradient is maintained at 12 °C / cm. After demolding, spray silver conductive paste on the surface according to Example 5 and cure it thermally.

[0072] Comparative Example 6: Based on Example 1, without boron nitride addition Raw material preparation Treat multi-walled carbon nanotubes, silver-plated short fibers and graphite flakes completely according to the process of Example 1.

[0073] Mixing preparation Mix 700 g of polyetherimide, 30 g of carbon nanotubes, 50 g of silver-plated short fibers and 20 g of graphite flakes without adding boron nitride micropowder. Kneading conditions: temperature 180 °C, rotation speed 300 rpm, time 20 minutes.

[0074] Injection molding The melt temperature is 280 °C, the injection pressure is 120 MPa, and the mold cooling gradient is set at 10 °C / cm.

[0075] Comparative Example 7: Based on Example 4, the surface coating thickness is changed Raw material preparation Prepare the mixed material and injection-molded samples completely according to Example 4.

[0076] Surface coating treatment Spray silver conductive paste on the surface of the substrate, the coating thickness is 5 μm (significantly lower than 10 μm of Example 4), and then cure it thermally at 120 °C for 20 minutes.

[0077] Experiment 1: Lightning current conduction performance test Experiment description Experiment purpose Verify the electrical conductivity, integrity of the conductive network and surface ablation resistance of the material under the action of high current density by simulating lightning current impact. Compare the examples with the comparative examples to reveal the effects of key technologies such as dynamic electric field induction, surface conductive coating and graphite flake expansion treatment.

[0078] Experiment steps Sample preparation Prepare samples with dimensions of 10 cm × 10 cm × 2 mm. Use the materials of Example 1, Example 2, Example 5 and Comparative Example 1, Comparative Example 2, Comparative Example 5 to prepare samples.

[0079] The surface of the sample was polished evenly to ensure the flatness of the contact electrodes.

[0080] Equipment settings Using a lightning current simulation device, set the peak current density to 200 kA / m² and the pulse duration to 50 μs.

[0081] Copper electrodes were fixed at both ends of the sample and connected to the current input terminal and the ground terminal respectively.

[0082] Set the thermocouples on the surface of the sample to record the surface temperature changes in real time.

[0083] Experimental tests Apply lightning current shocks to each sample 3 times, with an interval of 30 seconds.

[0084] Record the current conduction path, surface ablation marks and heat distribution.

[0085] After the test, use microscopic imaging to observe the surface ablation degree.

[0086] Experimental data Data table: Sample Number Surface Resistance (Ω) Ablation Area (mm²) Hot Spot Temperature (℃) Integrity of Conductive Path (√ / ×) Example 1 0.0043 1.5 78 √ Example 2 0.0052 2.1 91 √ Example 5 0.0037 1.2 68 √ Comparative Example 1 0.0086 4.9 136 × Comparative Example 2 0.0074 5.2 129 × Comparative Example 5 0.0068 3.6 112 × The optimization effect of dynamic electric field induction on the conductive network is very prominent. From the comparison between Example 1 and Comparative Example 1, it can be clearly seen that the comparative example without dynamic electric field shows discontinuity of the conduction path, and at the same time the local hot spot temperature increases by nearly 50%. This is because the randomly distributed conductive fillers fail to form an effective network, and the current density concentration leads to heat accumulation, causing material ablation. In Example 1, the dynamic electric field makes the carbon nanotubes, silver-plated short fibers and graphite flakes form an ordered arrangement, and the current dispersion ability of the hierarchical conductive network is fully demonstrated.

[0087] The surface coating is also crucial for the dispersion of lightning current. The comparison between Example 2 and Comparative Example 2 clearly shows that for the sample of the comparative example without silver conductive paste coating, the surface resistance increases significantly, the current distribution is uneven, and large-area ablation is caused. The silver conductive paste coating provides a layer of efficient conductive channels for the material, reduces the local resistance during current conduction, and thus reduces the material damage caused by current density concentration. This improvement not only comes from the high conductivity of the coating itself, but also is closely related to the uniformity of the coating coverage.

[0088] The expansion treatment of graphite flakes is of great significance for the construction of long-range conductive paths. From the comparison data of Example 5 and Comparative Example 5, it can be seen that the unexpanded graphite flakes lead to the discontinuity of the conductive paths and the expansion of the hot spot distribution. This is because the interlayer structure of the untreated graphite flakes is not fully opened, resulting in a significant reduction in conductivity. After the expansion treatment, the graphite flakes provide efficient two-dimensional conductive paths, which can significantly reduce the resistance of current conduction and at the same time reduce the fluctuation range of the overall current density. Obviously, the long-range conductive paths play a key role in the stability of the overall conductive network.

[0089] Experiment 2: Testing the Electrical Conductivity of Materials Experiment Description Experiment Purpose Evaluate the electrical conductivity and its stability of the samples in the examples and comparative examples, and verify the effects of dynamic electric field induction, filler modification, and coating optimization on the construction efficiency of the conductive network.

[0090] Experimental Procedures Sample Preparation Prepare samples with dimensions of 5 cm × 5 cm × 2 mm, including Example 1, Example 3, Example 4, and Comparative Example 1, Comparative Example 3, Comparative Example 4.

[0091] Polish the surface of the samples to ensure the minimization of the test contact resistance.

[0092] Equipment Setup Use the four-probe method to measure the volume resistivity of the materials (unit: Ω·cm). When testing, apply a 5V DC voltage across the two ends of the sample and record the current value passing through the sample.

[0093] Use a current loading device to repeatedly load the samples with 10 high-current pulses (current density 50 kA / m², pulse width 10 ms), and record the resistance change after each loading.

[0094] Test Process Fix the sample on the four-probe device and measure the initial volume resistivity.

[0095] Conduct current loading. After each loading, record the resistance value of the sample and analyze the resistance change rate.

[0096] After the test is completed, observe whether there are obvious damages or signs of conductive network fracture on the surface of the samples.

[0097] Experimental Data Data Table: Sample Number Initial Volume Resistivity (Ω·cm) Rate of Change of Resistance Value at the 5th Time (%) Rate of Change of Resistance Value at the 10th Time (%) Example 1 0.0041 1.2 2.8 Example 3 0.0039 1 2.4 Example 4 0.0047 1.5 3.1 Comparative Example 1 0.0073 5.4 8.9 Comparative Example 3 0.0068 4.7 7.6 Comparative Example 4 0.0085 6.2 10.3 The difference between the examples and the comparative examples is clear from the data, especially in the rate of change of resistance value. The comparison between Example 1 and Comparative Example 1 shows the significant effect of dynamic electric field induction on the conductive properties. In Comparative Example 1, which was not induced by dynamic electric field, the initial resistance value was higher and the rate of change of resistance was much greater than that of Example 1. This directly proves the guiding effect of the dynamic electric field on the arrangement of conductive fillers, which can effectively reduce the problem of conductive path breakage caused by random distribution of fillers. In the sample of Comparative Example 1, the conductive network was partially broken after multiple current loadings, which was manifested as a rapid increase in resistivity. This is because the conductive path that lacks directional arrangement fails under stress and thermal shock.

[0098] The comparison between Example 3 and Comparative Example 3 highlights the key role of boron nitride powder in heat dispersion. In Comparative Example 3, due to the low content of boron nitride, the sample produced more local hot spots when current was loaded, resulting in local damage to the conductive network, thereby making the resistance value change rate higher. However, Example 3 improved the heat conduction efficiency and significantly reduced the negative impact of local heat accumulation on the stability of the conductive network through reasonable design of boron nitride content. This shows that the addition of thermal conductive materials cannot be ignored in building stable conductive properties.

[0099] The destructive effect of unmodified carbon nanotubes on the conductive properties is also very significant. In the comparison between Example 4 and Comparative Example 4, the agglomeration problem of the unmodified carbon nanotubes caused the initial resistivity of Comparative Example 4 to be much higher than that of Example 4. At the same time, after multiple current loadings, the conductive network damage of Comparative Example 4 was more obvious. This is because the interface bonding force between the unmodified carbon nanotubes and the matrix is ​​weak, and the filler is easily detached or broken from the matrix, resulting in discontinuity of the conductive path. In contrast, the carboxyl modified carbon nanotubes in Example 4 significantly enhanced the interface bonding force, and the stability of the conductive network under current shock was greatly improved.

[0100] Experiment 3: Thermal Dissipation Performance Test Experimental Description Purpose Through lightning simulation test, the thermal dispersion performance of the material is analyzed, and the influence of boron nitride powder content on the local heat management of the material is verified. The temperature change and heat distribution of the embodiment and the comparative example under lightning impact condition are evaluated.

[0101] Experimental procedures Sample preparation Samples with a size of 10 cm×10 cm×2 mm were prepared, including Example 1, Example 3, and Comparative Example 3 and Comparative Example 6.

[0102] A uniform conductive layer is coated on the surface of the sample (only in Examples 1 and 3) to ensure uniform distribution of lightning current.

[0103] Device Setup Use a lightning current simulation device and set the peak current density to 150 kA / m² and the pulse duration to 50 μs.

[0104] Install thermocouples on the sample surface, with a 2-cm interval between thermocouples, arranged at the center and four corners of the sample, and a total of five monitoring points are set.

[0105] The thermal imager records the surface temperature distribution map of the sample in real time.

[0106] Test procedure Apply lightning current pulses to the sample respectively, with an interval of 60 seconds, and repeat the impact 3 times.

[0107] Record the temperature changes at the thermocouple monitoring points, and focus on recording the peak temperature and cooling time.

[0108] Analyze the thermal imaging map and evaluate the uniformity of the temperature distribution and the size of the hot spot area.

[0109] Experimental data Data table: Sample Number Peak Hot Spot Temperature (℃) Time to Cool to Room Temperature (s) Hot Spot Area (mm²) Example 1 74.5 15.2 12 Example 3 66.8 13.1 9 Comparative Example 3 95.7 22.3 34 Comparative Example 6 108.4 30.5 49 The addition of boron nitride micropowder has a particularly obvious effect on improving the heat dissipation ability. From the comparison between Example 3 and Comparative Example 3, it can be seen that the decrease in the boron nitride content directly leads to a significant increase in the temperature of the hot spot area and an elongation of the cooling time. This is because boron nitride, as a high thermal conductivity material, can quickly transfer the local high temperature caused by lightning strikes and avoid heat concentration. However, in Comparative Example 3, the lack of boron nitride weakens the heat conduction path, and obvious local temperature accumulation occurs. In the thermal imaging map, the area of the hot spot area in Comparative Example 3 is more than three times that in Example 3, showing a significant disadvantage of the material in thermal management.

[0110] Comparative Example 6 without the addition of boron nitride shows a worse heat dissipation effect. After lightning strikes, a large area of hot spot areas appears on the sample surface, the peak temperature exceeds 100 °C, and at the same time, the time to cool to room temperature is extended to more than 30 seconds. This directly indicates that without high thermal conductivity fillers, the thermal conductivity of the matrix material is difficult to meet the requirements of heat dissipation. Compared with Example 1, Comparative Example 6 not only has a hot spot temperature more than 30 °C higher, but also has a more serious local overheating phenomenon, indicating that the addition of boron nitride micropowder is indispensable for constructing an efficient heat conduction path.

[0111] The uniformity and conductivity of the coating also have a crucial impact on the uniformity of heat distribution. From the comparison between Example 1 and Comparative Example 6, it can be observed that the absence of the conductive coating makes the distribution of lightning strike current uneven, further exacerbating the generation of local hotspots. In Example 1, the coating of silver conductive paste effectively improves the uniformity of current conduction, reduces the hotspot phenomenon caused by current concentration, and at the same time, through the synergistic effect with boron nitride, the material exhibits a faster heat dispersion rate. This effect is due to the superposition of the current dispersion ability of the conductive coating and the high thermal conductivity of boron nitride.

[0112] Experiment 4: Thermal Stability Test of Materials Experiment Description Experiment Purpose Through thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC), evaluate the thermal stability, decomposition behavior, and glass transition temperature of the materials, and verify the improvement effect of dynamic electric field induction and filler modification on the heat resistance of the materials.

[0113] Experimental Procedure Sample Preparation Prepare samples with dimensions of 2mm × 2mm × 1mm. The test materials include Example 1, Example 3, Comparative Example 1, and Comparative Example 3.

[0114] TGA Test Using a thermogravimetric analyzer (TGA), place the sample in a high-purity nitrogen protection environment, set the heating rate to 10°C / min, and the temperature range to 25°C to 800°C.

[0115] Record the thermogravimetric curve of the sample, and analyze the initial decomposition temperature (Tonset) and the final char residue rate.

[0116] DSC Test Using a differential scanning calorimeter (DSC), the heating rate of the sample is 10°C / min, and the temperature range is 25°C to 300°C.

[0117] Test the glass transition temperature (Tg) of the sample, and analyze the thermal stability of the molecular chains of different samples under the conditions of dynamic electric field and filler modification.

[0118] Experimental Data Data Table: Sample Number Initial Decomposition Temperature Tonset(℃) Residual Carbon Rate (%) Glass Transition Temperature Tg(℃) Example 1 327 21.6 251 Example 3 340 25.4 256 Comparative Example 1 291 15.2 232 Comparative Example 3 302 17.9 240 The comparison of the thermal stability performance between the examples and the comparative examples clearly shows the effects of dynamic electric field induction and filler optimization. In Example 1, the initial decomposition temperature is significantly higher than that in Comparative Example 1, and the glass transition temperature is also significantly increased. This indicates that the arrangement of conductive fillers induced by the dynamic electric field not only optimizes the conductive network but also enhances the interfacial bonding force between the matrix and the fillers. In Comparative Example 1, due to the random distribution of conductive fillers, the interface between the fillers and the matrix is loosely bonded, and interface debonding is likely to occur at high temperatures, resulting in a decrease in the decomposition temperature. This phenomenon fully demonstrates the irreplaceability of the dynamic electric field technology in improving the thermal stability of materials.

[0119] The modification treatment of the fillers directly affects the stability of the thermal decomposition behavior. In Example 3, the increase in the content of boron nitride micropowder not only improves the thermal conductivity but also enhances the heat resistance of the material. In Comparative Example 3, the reduction of boron nitride leads to a significant decrease in the thermal decomposition temperature and the char yield. This can be attributed to the excellent thermal stability of boron nitride in a high-temperature environment, which provides a protective barrier for the matrix during the decomposition process, thus delaying the decomposition of the material. The absence of boron nitride will lead to a significant decrease in the overall thermal stability of the material, and the decomposition behavior becomes more uncontrollable.

[0120] Example 3 also exhibits a relatively high glass transition temperature, which is closely related to the uniform distribution of the modified fillers in the matrix. In contrast, the fillers in Comparative Example 3 are unevenly dispersed, the interfacial interaction is weak, and the molecular chains of the matrix are more active, resulting in a significant decrease in its Tg. This difference indicates that the optimization treatment of the fillers can effectively limit the degree of freedom of the molecular chains of the matrix, thereby improving the overall thermal performance of the composite material. Generally speaking, this experiment verifies the synergistic effect of dynamic electric field induction and filler optimization, providing theoretical and data support for improving the thermal stability performance of materials.

[0121] Experiment 5: Mechanical Property Testing of Materials Experiment Description Experiment Purpose By testing the tensile strength and elongation at break of the composite materials, evaluate the effects of dynamic electric field induction and filler modification on the mechanical properties of the composite materials, and verify the advantages of the examples in terms of mechanical stability.

[0122] Experiment Procedure Sample Preparation Use a mold to prepare standard tensile specimens with dimensions according to the ASTM D638 standard (length 100 mm, width 10 mm, thickness 2 mm). The test materials include Example 1, Example 5, Comparative Example 1, and Comparative Example 5.

[0123] Prepare 5 specimens for each material to ensure the repeatability of the test results.

[0124] Equipment Setup Using an electronic tensile testing machine, the test conditions are as follows: the tensile speed is 2 mm / min, and the ambient temperature is 25 °C.

[0125] Clamp the two ends of the sample firmly to ensure that the sample is fixed and does not slip during the test.

[0126] Test procedure Start the tensile machine, apply a tensile load to the sample, and record the maximum tensile force (N) and elongation at break (%) of the sample.

[0127] Repeat the test 3 times for each sample, and take the average value as the final result.

[0128] After the test, observe the flatness of the fracture surface of the sample and the fracture morphology of the material.

[0129] Experimental data Data table: Sample Number Tensile Strength (MPa) Elongation at Break (%) Fracture Surface Morphology (Description) Example 1 82.6 5.2 Flat Fracture Example 5 87.4 5.8 Microfiber Tensile Traces Comparative Example 1 65.2 3.4 Rough Fracture Comparative Example 5 71.6 4.2 Irregular Fracture with Filler Shedding The introduction of a dynamic electric field shows significant effects in improving the mechanical properties of the material. The tensile strength of Example 1 is much higher than that of Comparative Example 1, and the elongation at break is also significantly improved. This indicates that the dynamic electric field induction makes the conductive fillers evenly distributed in the matrix, reducing the stress concentration phenomenon. In Comparative Example 1, the fillers are disorderly distributed, resulting in the generation of tiny stress concentration points inside the matrix. During the tensile process, these defects gradually expand into cracks, eventually causing the early fracture of the material. At the same time, the rough fracture surface morphology of Comparative Example 1 further proves the adverse effect of the uneven distribution of fillers on the toughness of the material.

[0130] The influence of the expansion treatment of graphite flakes on the mechanical properties is also very significant. From the comparison between Example 5 and Comparative Example 5, it can be found that the untreated graphite flakes are unevenly distributed in the matrix, and the interlayer bonding force is weak, and they are easy to fall off during tensile, forming internal cracks. This defect makes the elongation at break of Comparative Example 5 lower than that of Example 5, and at the same time, there is an obvious peeling phenomenon of the fillers on the fracture surface. While the expanded graphite flakes significantly improve the stress transfer ability of the matrix and the overall toughness by enhancing the bonding force of the two-dimensional sheet structure. The microfiber tensile traces on the fracture surface of Example 5 indicate that the plastic deformation of the matrix has been fully exerted.

[0131] In addition, the modification and optimization treatment of the fillers also enhance the interfacial bonding force between the matrix and the fillers, further improving the tensile strength of the material. Example 1 and Example 5 show higher fracture strengths, which are closely related to the surface modification of carbon nanotubes and graphite flakes. The unmodified fillers show weak interfacial forces in the comparative examples and are easy to fall off from the matrix under external forces, significantly reducing the tensile properties and toughness of the material. This phenomenon proves the key role of surface modification technology in improving the compatibility between fillers and the matrix, and also provides an effective way for the optimization of the overall properties of the material.

[0132] Although embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A lightweight conductive composite material, characterized in that: The composition includes the following components by weight percentage: Polyetherimide matrix: 65-75%; Multi-walled carbon nanotubes: 2-5%; Silver-plated short fibers: 4-8%; Graphite flakes: 2-5%; Boron nitride powder: 1-3%; Silver conductive paste: 3-7%; Polyethylene glycol-based surface modifier: 0.5-2%; Silane coupling agent: 1-3%; Hindered phenol antioxidant: 0.3-1%.

2. A lightweight conductive composite material according to claim 1, characterized in that: The multi-walled carbon nanotubes are surface-carboxylated using a mixed solution of concentrated nitric acid and concentrated sulfuric acid, and are further modified using a polyethylene glycol-based surface modifier.

3. A lightweight conductive composite material according to claim 1, characterized in that: The silver-plated short fibers are used after being surface-modified by 3-aminopropyltriethoxysilane.

4. A lightweight conductive composite material according to claim 1, characterized in that: The graphite flakes are subjected to a thermal expansion treatment at 650-750° C. and are then ultrasonically dispersed in a concentrated nitric acid solution before use.

5. The lightweight conductive composite material according to claim 1, characterized in that: The particle size of the boron nitride micropowder is in the range of 1-10 μm.

6. A lightweight conductive composite material according to claim 1, characterized in that: The molecular weight of the matrix material polyetherimide is in the range of 30,000-40,000 g / mol.

7. A lightning protection fan blade, characterized in that: It is made of the lightweight conductive composite material according to any one of claims 1 to 6.

8. The lightning protection wind turbine blade according to claim 7, characterized in that: The surface of the blade is sprayed with silver conductive paste, and the coating thickness of the silver conductive paste is 10-50 μm.

9. The lightning protection wind turbine blade according to claim 7, characterized in that: The blade is manufactured by a dynamic electric field injection molding process, the electric field strength is 10-30 kV / cm, and the injection pressure is 80-150 MPa.

10. The lightning protection wind turbine blade according to claim 7, characterized in that: During the forming process of the blade, a cooling gradient is set by the mold, and the cooling gradient is 5-15°C / cm.

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