Composite modification method of high-insulativity carbon fiber cloth suitable for light aircraft

Abstract

The invention discloses a composite modification method of high-insulativity carbon fiber cloth suitable for a light aircraft, which comprises the following steps: S1, plasma pretreatment (Ar / Omixed gas pulse treatment, and increasing the surface oxygen content to 18.6 at% + / -0.5); s2, performing sol-gel modification on the upper surface (electrostatic spraying and gradient curing of SiOsol containing a phosphorus-nitrogen flame retardant to form a nanocapsule structure); s3, carrying out double-gradient fluorosilane treatment; and S4, carrying out supercritical CO composite reinforcement. Implanting a silver nanowire anti-lightning strike grid through laser etching; double-gradient fluorosilane ice dredging coating is adopted; and the compatibility of the fuel oil is enhanced. The material has the advantages of high insulation, flame retardance, lightning stroke resistance and environmental adaptability, meets the airworthiness requirements of the FAR 23 / 25 part, and is particularly suitable for aviation parts such as wing skins and fuel tank interlayers.

Description

Technical Field

[0001] This invention relates to the field of high-performance fiber material modification technology, and in particular to a composite modification method for high-insulation carbon fiber cloth suitable for light aircraft. Background Technology

[0002] Existing technologies for insulating carbon fiber cloth: Carbon fiber cloth, due to its high specific strength and conductivity, has significant advantages as a structural-functional integrated material in power equipment. However, the breakdown voltage of raw carbon fiber cloth is typically below 10kV / mm (see *Composites Science and Technology*, 2022, Vol. 217, 109094), which cannot meet high-voltage insulation requirements. Traditional solutions mainly fall into three categories: 1. Sol-gel coating method: For example, CN109722851A uses SiO2 sol coating on one side, which can improve the voltage to 25kV / mm, but there are problems such as easy cracking of the coating (the insulation performance decreases by 40% after 5 bends) and no flame retardant function. 2. Plasma fluorination method: For example, JP 2020-045312 uses CF4 plasma treatment to reduce surface energy, but it can only achieve single-sided modification and the breakdown voltage improvement is limited (about 18kV / mm). 3. Flame retardant blending method: US2021007102 Adding aluminum hydroxide to the resin matrix results in an increase in material density of more than 15% and affects the conductive pathway of the fiber.

[0003] Analysis of existing technological deficiencies: 1. Insufficient interfacial bonding: The difference in thermal expansion coefficients between conventional sol-gel and carbon fiber (SiO2: 0.5×10⁻) 6 / ℃ vs. carbon fiber: -0.1×10⁻ 6 / ℃) leads to the formation of microcracks during temperature cycling; 2. Single function: Existing modification methods often only focus on a single property such as insulation or flame retardancy (see Applied Surface Science 2021, Vol. 542, 148647), which cannot meet the requirements of synergistic multi-indicator performance of aerospace-grade materials; 3. Process contamination: Wet fluorination processes require the use of persistent contaminants such as perfluorooctanoic acid (PFOA) (which has been banned by the IEC 61249-2-21 standard).

[0004] Therefore, a plasma sol-gel composite modification method for high-insulation carbon fiber cloth with a double-sided asymmetric structure design, plasma activation synergistic effect, and in-situ composite of nano flame retardants is needed. Summary of the Invention

[0005] The present invention aims to provide a plasma sol-gel composite modification method for high-insulation carbon fiber cloth with a double-sided asymmetric structure design, plasma activation synergistic effect, and in-situ composite of nano flame retardants.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: a composite modification method for high-insulation carbon fiber cloth suitable for light aircraft, comprising the following stages: S1 plasma pretreatment stage ① Arrange carbon fibers in a vacuum plasma reaction chamber and evacuate to 0.1 Pa~0.5 Pa; ② Introduce an Ar / O2 mixed gas with a volume ratio of 7:3 to 9:1, and maintain the gas pressure at 10 Pa to 30 Pa; ③ Apply a pulsed radio frequency power supply with a frequency of 12MHz~15MHz and a power of 300~500W for 5~15 minutes; control the fiber surface roughness Ra to 0.8μm~1.2μm; S2 Surface Sol-Gel Modification Stage ① Prepare a SiO2 sol with a molar ratio of tetraethyl orthosilicate: ethanol: water = 1:8:4; A phosphorus-nitrogen flame retardant containing a cyclic phosphate ester complex with melamine cyanurate (0.5 wt% by mass) was added, and the pH value was adjusted to 3.5-4.0. ② A liquid film with a thickness of 20μm to 50μm is formed on the surface of the fiber cloth by electrostatic spraying at a voltage of 15kV to 20kV; ③ Gradient curing: 80℃ / 30min→120℃ / 20min→180℃ / 10min; Creative feature: Flame retardant is embedded in the gel network in the form of nanocapsules with a particle size of 80nm~120nm, forming a Si-OC chemical bonding interface, and the bonding force reaches the GB / T9286-1998 standard level 1. S3 Dual-gradient Fluorosilane Treatment Stage ① First, spray the lower surface with a perfluoropolyether solution, with a solute concentration of 5wt% and a droplet size of 1μm~5μm; ② Electron beam crosslinking with an energy of 50 kGy and a scanning speed of 2 m / min was performed under a vacuum of 10⁻² Pa; ③ The upper surface is spin-coated with an organosilicon modified coating containing carbon nanotubes, the carbon nanotube content in the coating is 0.05wt%, and the spin-coating speed is 3000rpm; S4 Composite Performance Enhancement Stage ① The modified fibers are arranged in a supercritical CO2 device. The operating parameters of the device are pressure 8MPa~12MPa and temperature 40℃~60℃. ② Inject an ethanol solution containing 0.1~0.3wt% silane coupling agent and maintain the pressure for 30min~60min; ③Relieve pressure to atmospheric pressure at a rate of 0.15 MPa / min to 0.25 MPa / min; ④ Laser etching of microgrooves with a width of 40μm~50μm and a depth of 65μm~80μm on the surface of carbon fiber cloth, with a groove grid spacing of 1.5mm~2mm×1.5mm~2mm; ⑤ A conductive network is formed by filling the trench with silver nanowires with a diameter of 25 nm to 40 nm and an aspect ratio of ≥200 using electrophoretic deposition. ⑥ Cover with a UV-curable transparent polyurethane protective layer with a thickness of 10μm~15μm and a dielectric constant ≤3.2; S5 performance testing phase ① The breakdown voltage was tested using a three-electrode system (GB / T1408.1-2016). ② The flame retardant performance was determined by a cone calorimeter (peak heat release rate ≤ 65 kW / m²). ③ XPS analysis of surface elemental composition (F1s peak at 689.5 eV, Si2p peak at 103.4 eV). Compared with existing technologies, this invention has the following advantages due to the use of innovative technologies such as plasma activation, double-sided asymmetric modification, and in-situ composite of nano flame retardants: 1. High insulation performance, with a breakdown voltage of up to 50kV / mm (1) This invention adopts a double-sided asymmetric modification design, breaking through the limitations of single modification methods. Traditional modification methods (such as sol-gel coating or fluorination) can only improve one aspect of the performance of carbon fiber cloth. However, this invention innovatively adopts a double-sided asymmetric structure of upper surface SiO2 sol-gel + lower surface fluorination treatment, which increases the breakdown voltage from <10kV / mm of conventional carbon fiber cloth to 50.3±1.2kV / mm (GB / T1408.1-2016 test standard), which is better than existing technologies (such as 25kV / mm of CN109722851A and 18kV / mm of JP JP2020-045312). Upper surface SiO2 sol-gel: Through optimized sol formulation (tetraethyl orthosilicate: ethanol: water = 1:8:4) and gradient curing process (80℃→120℃→180℃), a dense and defect-free nano-SiO2 layer is formed, which effectively blocks the electrical breakdown path. Lower surface fluorination treatment: CF4 plasma fluorination is used, combined with an axial magnetic field (0.3-0.5T) to enhance the penetration of fluorine radicals, forming a low surface energy (12.3mN / m) CF / CF2 alternating structure, which suppresses surface discharge.

[0007] (2) Plasma pretreatment enhances interfacial bonding and avoids coating peeling. Traditional sol-gel coatings are prone to cracking due to mismatch in thermal expansion coefficients (performance decreases by 40% after 5 bends). This invention uses Ar / O2 mixed gas plasma pretreatment (7:3~9:1 volume ratio) to increase the oxygen content on the carbon fiber surface to 18.6at%±0.5, forming a large number of carboxyl groups (-COOH) and hydroxyl groups (-OH), which are bonded to the sol-gel layer through Si-OC chemical bonds. The interfacial bonding force reaches 28.7N / cm (GB / T9286-1998 standard level 1), which is more than 3 times higher than that of conventional treatment (9.5N / cm).

[0008] 2. It has excellent flame retardant properties, meets UL94V-0 rating, and does not affect insulation. (1) Nanoencapsulated phosphorus and nitrogen flame retardants achieve uniform dispersion. Traditional flame retardant modification (such as aluminum hydroxide blending) will reduce the insulation of the material (dielectric loss increases by more than 50%). This invention innovatively uses cyclic phosphate ester + melamine cyanurate composite flame retardant and embeds it in the form of nanocapsules (80-120nm) into the sol network to achieve: UL94V-0 flame retardancy (self-extinguishing time of 1.6mm thick sample <3s); peak heat release rate ≤65kW / m² (cone calorimeter test), which is 67% lower than that of unmodified carbon fiber cloth (≥200kW / m²); does not affect insulation performance, dielectric constant is stable at 2.8 (at 1MHz), and dielectric loss is only 2.1×10⁻³.

[0009] (2) Supercritical CO2-assisted infiltration improves the uniformity of flame retardant distribution. Conventional impregnation methods result in uneven distribution of flame retardants (EDS surface scan uniformity <70%). This invention uses supercritical CO2 (8-12MPa, 40-60℃) to load the flame retardant, achieving a uniform distribution of 92%±3% (EDS analysis) at the fiber / gel interface, thus avoiding the problem of increased conductivity caused by excessively high local concentrations.

[0010] 3. The process is environmentally friendly and efficient, leaving no harmful residues. (1) Dry process to avoid PFOA pollution. Traditional wet fluorination requires the use of perfluorooctanoic acid (PFOA) (a prohibited substance in IEC 61249-2-21). This invention uses CF4 plasma dry fluorination, which produces no liquid waste throughout the process, and GC-MS testing shows no PFOA residue, complying with RoHS directive requirements.

[0011] (2) Pulsed plasma treatment, energy saving and no damage to fibers. Conventional continuous plasma can easily cause thermal damage to carbon fibers (strength reduction of 15%). This invention uses a pulsed radio frequency power supply (duty cycle 1:5), which ensures activation effect while reducing fiber tensile strength by only <3% (ASTM D3039 test).

[0012] 4. Excellent mechanical durability and environmental adaptability (1) Excellent bending resistance, with insulation attenuation of <5% after 500 bends. Traditional sol-gel coatings show a decrease in insulation performance of >30% after 100 bends (radius 5mm). This invention uses supercritical CO2 to strengthen the interface and gradient curing process, so that the modified layer still retains more than 95% of its original insulation performance after 500 bends.

[0013] (2) Resistant to damp heat aging, the breakdown voltage retention rate after 1000h test is >90%. After aging for 1000h at 85℃ / 85%RH, the breakdown voltage of the modified carbon fiber cloth of this invention only decreased by 9.2%, which is far better than the comparative example (sol-gel method decreased by 35%, fluorination method decreased by 28%), and is suitable for high humidity environments (such as offshore wind power equipment).

[0014] 5. The technical effects achieved by curing an environment-adaptive anti-icing coating are as follows: ice adhesion strength ≤20kPa (meeting the requirements of FAA airworthiness clause 25.1419), hydrophobic angle >150° at -40℃, and static dissipation function with surface resistance of 1-10kΩ / sq achieved by CNT network.

[0015] 6. Technical effects achieved through lightning strike resistant mesh implantation: lightning strike resistance meets SAEARP5412B standard (can disperse 100kA lightning current), surface density increases by <8g / m², solving the weight increase problem of traditional copper mesh (comparative weight reduction of 60%).

[0016] 7. Broad application prospects The modified carbon fiber cloth of this invention can be applied to: high-voltage motor slot insulation (replacing traditional mica tape, reducing weight by more than 30%); electromagnetic shielding layer for aerospace vehicles (meeting DO-160G standard lightning protection requirements); and fireproof membrane for new energy battery packs (possessing both high insulation and flame retardant properties). Detailed Implementation

[0017] Example 1: Lightning-resistant composite material for wing skin Application scenario: Main load-bearing skin of light aircraft wings (must meet FAR Part 23 lightning protection requirements) Implementation steps: S1 plasma pretreatment Parameters: Ar / O2=8:2, gas pressure 20Pa, pulse power 400W (duty cycle 1:5), processing time 10min; Measured data: Surface oxygen content 19.1 at%, Ra=1.05μm; S2 sol-gel modification Sol formulation: TEOS:EtOH:H2O=1:8:4 + 0.6wt% phosphorus-nitrogen flame retardant (melamine polyphosphate). Spraying parameters: 18kV, liquid film thickness 35μm; Post-curing performance: Flame retardant layer hardness 6H (pencil hardness), peak heat release rate 58kW / m²; S3 dual-gradient fluorosilane treatment Bottom surface: PFPE electron beam crosslinked (55kGy); Top surface: 0.08wt% CNT-silicone coating; Ice-repellent properties: -30℃ water droplet freezing time 412s (ASTM D7334); S4 lightning protection mesh implantation Laser parameters: 532nm wavelength, 100ns pulse width, 75μm trench depth; Silver nanowires have an areal density of 0.8 g / m² and a resistivity of 0.6 Ω / sq. Supercritical treatment Parameters: 10MPa / 50℃, containing 0.2wt% KH-550 silane coupling agent; Interface bonding strength: 4.8 N / mm (ISO 8510-1).

[0018] Validation data: Lightning strike test: Passes 100kA / 10μs waveform (compliant with DO-160G Section 23) Surface density: 217g / m² (52% weight reduction compared to traditional aluminum skin) Example 2: Fireproof material for fuel tank partition Application scenario: Fire barrier between composite fuel tank and engine compartment The main body is the same as in Example 1, the difference being: S2 Stage Enhanced Flame Retardancy The structure adopts a two-layer sol structure: the bottom layer contains 5 wt% expanded graphite (particle size 20 μm), and the top layer contains 1 wt% zinc borate; The peak heat release rate was reduced to 42 kW / m² (ISO 5660-1). S4 Stage Fuel Compatibility Treatment Add 0.3 wt% fluorinated silane (heptadecyltrimethoxysilane) to the supercritical fluid. After being soaked in fuel oil, the volume expansion rate was 0.3%, and the tensile strength retention rate was 97%. In stage S3, the anti-icing coating is removed and replaced with full-surface fluorocarbon plasma treatment (CF4 / C2F4=3:1). Special Test: Passed the 60-second flame penetration test (FAR 25.981 Appendix B). Fuel vapor permeability: 0.007 g / m²·h (NACA standard) Example 3: Lightweight Skin for All-Motion Horizontal Tail Application scenario: Movable wing surfaces of highly maneuverable light aircraft (with consideration for both weight reduction and fatigue resistance) The main body is the same as in Example 1, the difference being: S1 stage gradient processing: The Ar / O2 ratio was changed three times (9:1→7:3→5:5) to obtain gradient oxygen content (12at%~22at%). Fatigue life increased to 2.1×10 6 (R=0.1, 100MPa stress amplitude) S2 / S3 collaborative optimization: Adding 0.1 wt% carbon nanofibers (150 nm in diameter) to the sol on the upper surface improves conductivity to 10³ Ω / sq. The lower surface is coated with a PFPE / PDMS hybrid coating, reducing the coefficient of friction to 0.15 (ASTM D1894). S4 stage low-temperature supercritical The parameters were optimized to 7MPa / 35℃ to avoid pre-curing of the resin matrix. Interlaminar shear strength reaches 89 MPa (ASTM D2344). Weight loss effect: When the finished product thickness is 0.25mm, the following conditions must be met: Bending stiffness ≥18 N·m (FAR 23.305) Surface density 195g / m² (58% weight reduction compared to aluminum alloy) Comparison Table of Implementation Examples Example 1 (wing) Example 2 (fuel tank) Example 3 (horizontal stabilizer) Surface density (g / m²): 217, 245, 195 Lightning protection capability (kA): 100 - 30 Heat release rate (kW / m²): 58, 42, 65 Fatigue life (cycles): 1.5 × 10⁻⁶ 6 - 2.1×10 6 Special functions include ice removal, conductive fuel sealing, high fatigue resistance, and weight reduction. Note: All embodiments meet the corresponding material certification requirements in the CCAR-25-R4 airworthiness provisions. The above description of the disclosed embodiments is merely intended to enable those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A composite modification method for high-insulation carbon fiber cloth suitable for light aircraft, characterized in that... Includes the following stages: S1 plasma pretreatment stage ① Arrange carbon fibers in a vacuum plasma reaction chamber and evacuate to 0.1 Pa~0.5 Pa; ② Introduce an Ar / O2 mixed gas with a volume ratio of 7:3 to 9:1, and maintain the gas pressure at 10 Pa to 30 Pa; ③ Apply a pulsed radio frequency power supply with a frequency of 12MHz~15MHz and a power of 300~500W for 5~15 minutes; control the fiber surface roughness Ra to 0.8μm~1.2μm; S2 Surface Sol-Gel Modification Stage ① Prepare a SiO2 sol with a molar ratio of tetraethyl orthosilicate: ethanol: water = 1:8:4; A phosphorus-nitrogen flame retardant containing a cyclic phosphate ester complex with melamine cyanurate (0.5 wt% by mass) was added, and the pH value was adjusted to 3.5-4.

0. ② A liquid film with a thickness of 20μm to 50μm is formed on the surface of the fiber cloth by electrostatic spraying at a voltage of 15kV to 20kV; ③ Gradient curing: 80℃ / 30min→120℃ / 20min→180℃ / 10min; Creative feature: Flame retardant is embedded in the gel network in the form of nanocapsules with a particle size of 80nm~120nm, forming a Si-OC chemical bonding interface, and the bonding force reaches the GB / T9286-1998 standard level 1. S3 Dual-gradient Fluorosilane Treatment Stage ① First, spray the lower surface with a perfluoropolyether solution, with a solute concentration of 5wt% and a droplet size of 1μm~5μm; ② Electron beam crosslinking with an energy of 50 kGy and a scanning speed of 2 m / min was performed under a vacuum of 10⁻² Pa; ③ The upper surface is spin-coated with an organosilicon modified coating containing carbon nanotubes, the carbon nanotube content in the coating is 0.05wt%, and the spin-coating speed is 3000rpm; S4 Composite Performance Enhancement Stage ① The modified fibers are arranged in a supercritical CO2 device. The operating parameters of the device are pressure 8MPa~12MPa and temperature 40℃~60℃. ② Inject an ethanol solution containing 0.1~0.3wt% silane coupling agent and maintain the pressure for 30min~60min; ③Relieve pressure to atmospheric pressure at a rate of 0.15 MPa / min to 0.25 MPa / min; ④ Laser etching of microgrooves with a width of 40μm~50μm and a depth of 65μm~80μm on the surface of carbon fiber cloth, with a groove grid spacing of 1.5mm~2mm×1.5mm~2mm; ⑤ A conductive network is formed by filling the trench with silver nanowires with a diameter of 25 nm to 40 nm and an aspect ratio of ≥200 using electrophoretic deposition. ⑥ Cover with a UV-curable transparent polyurethane protective layer with a thickness of 10μm~15μm and a dielectric constant ≤3.2; S5 performance testing phase ① The breakdown voltage was tested using a three-electrode system (GB / T1408.1-2016). ② The flame retardant performance was determined by a cone calorimeter (peak heat release rate ≤ 65 kW / m²). ③ XPS analysis of surface elemental composition (F1s peak at 689.5 eV, Si2p peak at 103.4 eV).