Preparation method of high-temperature-resistant liquid crystal polyarylester composite nitrogen-doped graphene electromagnetic shielding fiber

Abstract

The invention relates to a preparation method of a high-temperature-resistant liquid crystal polyarylester composite nitrogen-doped graphene electromagnetic shielding fiber. The fiber prepared by the method has a skin-core composite structure, a skin layer contains 3.0-10.0 wt% of surface modified nitrogen-doped graphene, a core layer is pure liquid crystal polyarylester, and the mass ratio of the skin layer to the core layer is 3: 7-5: 5. The preparation method comprises the steps of nitrogen-doped graphene surface modification, conductive master batch preparation, sheath-core composite spinning and gradient heat setting. The electromagnetic shielding effectiveness of the obtained fiber at the frequency band of 8-40 GHz is larger than or equal to 35 dB, the tensile strength is larger than or equal to 3.0 GPa, the density is 1.42-1.45 g / cm < 3 >, and the shielding effectiveness retention rate gt after thermal aging at 250 DEG C for 500 hours is achieved; the spinning end breakage rate is 1t; 5%. The fiber and the preparation method are suitable for manufacturing 5G / 6G communication base station radio frequency cables, aerospace electronic equipment cable shielding, high-voltage wiring harnesses of new energy automobiles or shells of precise electronic parts.

Description

Technical Field

[0001] This invention relates to the field of high-performance fiber composite materials technology, specifically to a high-temperature resistant composite fiber with electromagnetic shielding function and its preparation method, which is applicable to aerospace, 5G / 6G communication equipment, precision electronic devices and new energy vehicles. Background Technology

[0002] The integrated development of 5G / 6G communication and aerospace electronic equipment has placed demands on electromagnetic shielding materials to be lightweight, heat-resistant, and high-strength. Traditional metal shielding materials are dense and easily corroded, while existing carbon-based shielding materials have insufficient temperature resistance (long-term operating temperature <150℃), making it difficult to meet the requirements of extreme environments.

[0003] Liquid crystal polyarylate (TLCP) fibers possess a rigid, fully aromatic chain structure, tensile strength ≥3.5 GPa, melting point >285℃, and moisture regain <0.1%. However, their insulating properties result in electromagnetic shielding effectiveness <5 dB, offering virtually no shielding capability. While nitrogen-doped graphene exhibits excellent conductivity, it is difficult to disperse in TLCP melts, exhibiting weak interfacial bonding. Direct lamination would lead to a mechanical property loss >30% and a spinning breakage rate >30%, making continuous production impossible. Summary of the Invention

[0004] A high-temperature resistant liquid crystal polyarylate / nitrogen-doped graphene electromagnetic shielding fiber, wherein the fiber has a core-sheath composite structure, which is formed in one step by melt spinning through a concentric spinneret, without the need for subsequent composite processes: Skin layer: Composed of liquid crystal polyarylate matrix resin, surface-modified nitrogen-doped graphene, dispersant and antioxidant. The thickness of the skin layer is 15%-35% of the total fiber diameter. The nitrogen-doped graphene in the skin layer is oriented along the fiber axis to form a continuous conductive network. Core layer: pure liquid crystal polyarylate resin, which bears the main mechanical load and ensures the high strength properties of the fiber; Based on the total fiber mass, the liquid crystal polyarylate matrix resin accounts for 85.0-95.0 wt%, the surface-modified nitrogen-doped graphene accounts for 3.0-10.0 wt%, and the dispersing agent accounts for 1.0-3.0 wt%; the mass ratio of the sheath to the core layer is 3:7 to 5:5, the fiber fineness is 50-1500 denier, the fiber cross-sectional roundness is ≥95%, and the sheath-core interface bonding strength is ≥70 MPa.

[0005] A method for preparing the above-mentioned fiber includes the following four core steps performed in sequence: S1 Nitrogen-Doped Graphene Surface Modification: Nitrogen-doped graphene was dispersed in an ethanol / water mixture (volume ratio 8:2) and treated with ultrasound at 300-500W for 30-60 minutes to prepare a suspension with a concentration of 0.5-2 mg / mL. An aminosilane coupling agent, KH-792, was added to carry out a surface grafting reaction at pH 4-5 and a temperature of 60℃ for 4-6 hours under nitrogen protection. The product was then centrifuged (first centrifugation at 8000-10000 rpm to remove large agglomerates, second centrifugation at 5000-7000 rpm to collect the modified product), washed, and dried to obtain surface-modified nitrogen-doped graphene. The modified product had an amino grafting rate of 5-12% and a particle size <500 nm in TLCP melt. Preparation of S2 conductive masterbatch: The surface-modified nitrogen-doped graphene obtained in step S1 is blended and granulated with liquid crystal polyarylate resin at a mass ratio of 3:7 in a twin-screw extruder. The twin-screw extruder has an aspect ratio (L / D) of 40:1. The screw assembly includes 3-5 kneading blocks to enhance the dispersion effect. The temperatures of each section are set as follows: feeding section 280-300℃, melting section 310-330℃, homogenization section 320-340℃, and die head 320-350℃. The screw speed is 150-200 rpm, the vacuum degree is ≤-0.08 MPa, and the material residence time is 3-8 minutes. A 30wt% conductive masterbatch is obtained, and the melt index (MI) of the masterbatch (350℃, 2.16kg) is 15-25 g / 10min. S3 Sheath-Core Composite Spinning: The conductive masterbatch from step S2 is mixed with liquid crystal polyarylate resin, dispersant, and antioxidant in a nitrogen atmosphere and vacuum dried at 120-150℃ for 4-8 hours until the moisture content is <100ppm; melt spinning is performed through a sheath-core composite spinning assembly, which includes independent sheath and core melt channels, with the ends of the channels connected by concentric spinnerets; the sheath is a composite system containing nitrogen-doped graphene, and the core is pure liquid crystal polyarylate resin, with a sheath-core mass ratio of 3:7 to 5:5; the spinning temperature is 300-320℃, the spinning pressure is 8-15MPa, the spinning speed is 800-1500m / min, and the stretching ratio of 4-8 times is achieved through 3-5 sets of hot rollers, with the hot roller temperature increasing gradually from 120-220℃; the stretching process is controlled by gradient tension; and the nascent fibers are wound into shape after cooling and solidification. S4 Gradient Heat Setting: The fiber undergoes a two-stage heat treatment under nitrogen protection with an oxygen content of <100ppm. The first stage involves treatment at 180-200℃ for 1-2 hours, with a heating rate of 2-5℃ / min and an applied tension of 0.05-0.1cN / dtex. The second stage involves treatment at 220-240℃ for 1-2 hours, with a heating rate of 1-3℃ / min and an applied tension of 0.1-0.2cN / dtex. The tension difference between the two stages is controlled within 0.05-0.1cN / dtex. The nitrogen protection system includes a gas purification device, an online oxygen content monitor, and a flow controller. The nitrogen purity is ≥99.995%, the flow rate is 5-15L / min, and the furnace pressure is maintained at a slightly positive pressure of 0.05-0.15MPa. After heat treatment, the fiber is sized with an oiling agent, dried, and wound to obtain the finished fiber. The fiber spinning breakage rate is <5%, and the batch performance fluctuation is ≤3%.

[0006] Comparative experiments have verified the technical effects of each optimized parameter range as follows: 1. Relationship between nitrogen-doped graphene content and effectiveness: When the content is below 3.0 wt% (Comparative Example 4), the shielding effectiveness is <25 dB, and an effective conductive network cannot be formed. In Example 4, the shielding effectiveness reaches 28.5 dB at the critical threshold of 3.0 wt%, which meets the basic protection requirements. When the content is 7.0 wt% (Example 1), the effectiveness is 38.5 dB. When the content is 10.0 wt% (Example 2), the effectiveness is 42.8 dB, which meets the military-grade shielding standard. When the content exceeds 10 wt%, the melt viscosity increases by >200%, the spinnability decreases sharply, the breakage rate is >15%, and the industrial value is lost.

[0007] 2. Spinning speed and process stability: When the speed is below 750 m / min (Comparative Example 5), insufficient cooling rate leads to inconsistent crystallization of the core-sheath layer, resulting in microcracks at the interface and a breakage rate >8%; when the speed is in the range of 800-1500 m / min (Examples 1-3), cooling and stress are balanced, and the breakage rate is 3.8-4.5%; when the speed exceeds 1500 m / min (Comparative Example 6), the spinneret shear rate >10 4 s⁻¹, melt degradation is accelerated, and the strength retention rate is <85%.

[0008] 3. Sheath-core mass ratio and performance balance: When the sheath content exceeds 50% (mass ratio > 5:5), the core layer has insufficient load-bearing cross-sectional area, fiber strength retention rate < 85%, and modulus decrease > 20%; when the sheath content is < 30% (mass ratio < 3:7), the surface conductive layer is too thin, and the shielding effectiveness is < 30dB (critical state of Example 3); the mass ratio range of 3:7 to 5:5 (Examples 1, 2, and 4) can achieve the optimal balance between strength and effectiveness, meeting the needs of more than 80% of application scenarios.

[0009] 4. Gradient heat setting and dimensional stability: When the temperature in the second stage is below 220℃ (Comparative Example 7), the fiber orientation degree is <0.75, the boiling water shrinkage rate is >0.3%, and the shielding effectiveness decreases by >15% under humid and hot conditions; when the temperature is above 240℃ (Comparative Example 8), the liquid crystal polyarylate begins to degrade thermally, the strength decreases by >10%, and the surface turns yellow; when the tension difference is <0.05cN / dtex, the core-sheath interface bonding strength is <60MPa, and the risk of interlayer delamination is high; when the tension difference is >0.1cN / dtex, axial microcracks appear on the fiber surface, and the bending resistance is <5000 times.

[0010] 5. Nitrogen protection and oxidation resistance: When the oxygen content is >100ppm, the fiber surface oxidizes and discolors, the color difference ΔE >3.0, and the dielectric loss tangent tanδ increases by more than 20%; when the oxygen content is <100ppm and the flow rate is 5-15L / min, there is no oxidation phenomenon, the fiber color is uniform, and the dielectric properties are stable; when the furnace pressure is <0.05MPa, external air can easily penetrate; when the pressure is >0.15MPa, the nitrogen consumption is too high, and the economy decreases. Beneficial effects

[0011] The technical effects of this invention correspond clearly to the technical features in the claims, specifically as follows: 1. Electromagnetic shielding effectiveness of 35-45dB: This is directly achieved by combining 3.0-10.0wt% surface-modified nitrogen-doped graphene in the skin layer with a skin-core mass ratio of 3:7 to 5:5 as described in claim 1. Examples 1-6 verify that this parameter range is from a lower limit of 28.5dB (Example 4) to an upper limit of 43.1dB (Example 5). Comparative Example 4 demonstrates that when the content is below 3.0wt%, the shielding effectiveness is <25dB, which does not meet the application requirements.

[0012] 2. Mechanical strength retention rate ≥90%: This is guaranteed by the mass ratio of pure liquid crystal polyarylate in the core layer to the skin layer ≤5:5 in claim 1. The tensile strength of Examples 1-6 is 3.22-3.52 GPa (retention rate 96-99%), while the strength of the homogeneous composite structure in Comparative Example 2 decreased by 34%, proving the necessity of the core-skin structure.

[0013] 3. Spinning breakage rate <5% and batch stability: The breakage rate is controlled by surface modification (KH-792 dosage 5-10%), conductive masterbatch pre-dispersion (30wt% masterbatch), and spinning speed of 800-1500m / min as described in claim 2. The breakage rate in Examples 1-6 is 3.8-4.5%, and the batch fluctuation is ≤3%. In Comparative Example 2, the unmodified system has a breakage rate of 32% and a fluctuation >15%.

[0014] 4. Density 1.42-1.45 g / cm³: Determined by the density of the matrix resin (1.41 g / cm³) and the amount of nitrogen-doped graphene added. The measured density deviation in Examples 1-6 is <2%, which meets the requirements for lightweighting.

[0015] 5. Shielding effectiveness retention rate after thermal aging >90%: This is achieved by gradient thermal setting (two-stage temperature 180-200℃, 220-240℃) + nitrogen protection system (oxygen content <100ppm) as described in claim 2. In Example 1, the shielding effectiveness retention rate is 92.3% after thermal aging at 250℃ for 500h, while in Comparative Examples 7 and 8, the retention rate is <75% when the temperature runs out.

[0016] 6. Dimensional stability (boiling water shrinkage rate <0.2%): This is ensured by the second stage temperature of 220-240℃ and the tension of 0.1-0.2cN / dtex in gradient heat setting. The boiling water shrinkage rate of Examples 1-6 is 0.08-0.12%, while the shrinkage rate of Comparative Example 7 is 0.35% due to insufficient temperature. Attached Figure Description

[0017] Figure 1 This is a flowchart of the overall preparation method.

[0018] Figure 2 This is a flowchart of the surface modification process for nitrogen-doped graphene.

[0019] Figure 3 This is a flowchart of the core-sheath composite spinning process control.

[0020] Figure 4 This is a flowchart of the gradient thermal shaping process. Detailed Implementation

[0021] Example 1: 1000g of TLCP resin (ordinary type, intrinsic viscosity 5.2dL / g, melting point 305℃) was vacuum dried at 130℃ for 8 hours. 70g of nitrogen-doped graphene (8at% doping, 5 layers, sheet diameter 1-2μm) was vacuum dried at 70℃ for 6 hours.

[0022] Nitrogen-doped graphene was dispersed in 500 mL of an ethanol / water mixture (8:2) and sonicated at 500 W for 45 minutes to prepare a 1 mg / mL suspension. 5.6 g of KH-792 coupling agent was added, and the pH was adjusted to 4.5 with acetic acid. The mixture was reacted in a 60 °C water bath for 5 hours. The product was separated by centrifugation (first centrifugation at 10000 rpm × 10 min to remove large particles, second centrifugation at 6000 rpm × 15 min to collect the product), washed three times with deionized water, and vacuum dried at 80 °C for 12 hours to obtain the modified product.

[0023] Modified nitrogen-doped graphene and TLCP resin were premixed at a mass ratio of 3:7 and fed into a twin-screw extruder (φ35mm, L / D=40, including 4 kneading blocks). The temperatures of each zone were: feeding zone 290℃, melting zone 320℃, homogenization zone 330℃, and die head 335℃. The screw speed was 180rpm, the vacuum degree was -0.08MPa, and the material residence time was 5min. Granulation yielded 30wt% conductive masterbatch with MI=18g / 10min.

[0024] The conductive masterbatch was diluted to the final formulation (TLCP 90.0wt%, N-GQDs 7.0wt%, PEI dispersant 2.0wt%, antioxidant 1.0wt%), and vacuum dried at 120℃ for 8 hours until the moisture content was 85ppm. A core-sheath composite spinning assembly was used (sheath metering pump 10rpm, core 25rpm, speed deviation ±0.5rpm), core-sheath mass ratio 4:6, spinning temperature 310℃, pressure 12MPa, spinning speed 1200m / min. The spinning process involved three stages of stretching: pre-stretching (100℃ × 2 times), hot stretching (230℃ × 4 times), and relaxation setting (260℃ × 10s), with a total stretch of 6 times. Side-blown cooling was used: air temperature 25℃, air velocity 0.4m / s.

[0025] Nascent fibers were subjected to nitrogen-protected gradient heat setting: nitrogen oxygen content 50ppm, flow rate 10L / min, furnace pressure 0.1MPa, first stage 190℃×1.5h (heating rate 3℃ / min, tension 0.08cN / dtex), second stage 230℃×1.5h (heating rate 2℃ / min, tension 0.15cN / dtex). The resulting shielding fiber had a fineness of 250D and a sheath thickness of 28%.

[0026] Performance testing: 10GHz shielding effectiveness 38.5dB, surface resistivity 8.5×10²Ω / sq, tensile strength 3.45GPa, modulus 98GPa, density 1.43g / cm³, boiling water shrinkage 0.09%, breakage rate 4.2%, batch variation 2.1%, core-skin interface strength 76MPa. Example 2

[0027] 1000g of TLCP resin (high-strength type, intrinsic viscosity 6.0 dL / g), 100g of nitrogen-doped graphene (10 at% doping, 4 layers, sheet diameter 0.5-1μm). 8g of coupling agent. Twin-screw blending temperature 310℃, speed 200 rpm, time 5 min. Temperatures in each zone: feeding section 300℃, melting section 330℃, homogenization section 340℃, die head 345℃. MI = 16g / 10min.

[0028] Final formulation: TLCP 86.0wt%, N-GQDs 10.0wt%, PPS dispersant 3.0wt%, antioxidant 1.0wt%. Sheath-core ratio 5:5, spinning temperature 315℃, pressure 14MPa, spinning speed 1000m / min, total three-stage stretching ratio 5 times (pre-stretching 110℃×2.2 times, hot stretching 240℃×3.5 times, setting 270℃×8s). Nitrogen and oxygen content 45ppm, flow rate 12L / min.

[0029] Performance: 10GHz shielding effectiveness 42.8dB, surface resistivity 2.3×10²Ω / sq, tensile strength 3.22GPa, modulus 95GPa, density 1.44g / cm³, boiling water shrinkage 0.07%, breakage rate 3.8%, batch variation 2.8%, core-skin interface strength 78MPa.

[0030] Example 3 (Aerospace Microfiber) 1000g of TLCP resin (ultra-high strength type), 45g of nitrogen-doped graphene (6at% doping, 8 layers, 2-3μm diameter), 3.6g of coupling agent, twin-screw blending temperature 300℃, speed 160rpm, MI=22g / 10min.

[0031] Final formulation: TLCP 93.0 wt%, N-GQDs 4.5 wt%, PEI 1.5 wt%, antioxidant 1.0 wt%. Sheath-to-core ratio 3:7, spinneret outer layer orifice diameter 0.20 mm, inner layer 0.18 mm, spinning speed 1500 m / min, pressure 15 MPa, total three-stage stretch ratio 8 times (pre-stretch 120℃ × 2.5 times, hot stretch 250℃ × 4.5 times, setting 275℃ × 5 s). Nitrogen and oxygen content 60 ppm.

[0032] Performance: 26GHz shielding effectiveness 36.2dB, surface resistivity 1.2×10³Ω / sq, areal density 12g / m², tensile strength 3.52GPa, modulus 102GPa, density 1.42g / cm³, boiling water shrinkage 0.05%, core-skin interface strength 82MPa, bending resistance >20000 cycles.

[0033] Example 4 (Verification of lower limit of content) 1000g TLCP resin, 30g nitrogen-doped graphene (7at% doping, 5 layers), 1.5g coupling agent, twin-screw blending temperature 295℃, speed 150rpm.

[0034] Final formulation: TLCP 95.0wt%, N-GQDs 3.0wt%, PEI 1.5wt%, antioxidant 0.5wt%. Sheath-core ratio 5:5, spinning temperature 305℃, pressure 10MPa, spinning speed 900m / min, total three-stage draw ratio 5 times. Nitrogen and oxygen content 55ppm.

[0035] Performance: 10GHz shielding effectiveness 28.5dB, surface resistivity 1.5×10³Ω / sq, tensile strength 3.28GPa, modulus 101GPa, density 1.45g / cm³, boiling water shrinkage 0.11%. When the N-GQDs content is less than 3.0wt% (Comparative Example 4), the shielding effectiveness is only 22dB, which does not meet the application requirement of ≥25dB.

[0036] Example 5 (Process Lower Limit Verification) The formulation of Example 2 was used, with a core-sheath ratio of 4:6, a spinning speed reduced to 800 m / min (lower limit), a pressure of 9 MPa, and other parameters the same as in Example 2.

[0037] Performance: Shielding effectiveness 43.1dB, surface resistivity 2.1×10²Ω / sq, tensile strength 3.31GPa, modulus 97GPa, boiling water shrinkage 0.10%, breakage rate 4.5%. When the spinning speed is below 750m / min (Comparative Example 5), the breakage rate is >8% due to insufficient cooling rate resulting in excessively low crystallinity of the skin layer.

[0038] Example 6 (Verification of Additive Replacement) The formulation of Example 1 was used, except that PEI was replaced with PAI (molecular weight 3500) at a dosage of 2.0 wt%, and other parameters were the same as in Example 1.

[0039] Performance: Shielding effectiveness 37.8dB, surface resistivity 9.8×10²Ω / sq, tensile strength 3.41GPa, modulus 99GPa, boiling water shrinkage 0.09%, batch fluctuation 2.6%, demonstrating the universality of the dispersant system.

[0040] Comparative Example 1 (Pure TLCP) Pure TLCP resin, same process as in Example 1. Performance: Shielding effectiveness <3dB, tensile strength 3.20GPa, modulus 105GPa, boiling water shrinkage 0.08%.

[0041] Comparative Example 2 (homogeneous structure) Unmodified graphene, homogeneous blend without core-skin structure, graphene content 7wt%. Properties: breakage rate 32%, shielding effectiveness fluctuation 15-28dB, tensile strength 2.10GPa, modulus 68GPa, boiling water shrinkage rate 0.28%, batch variation >12%.

[0042] Comparative Example 3 (Metal Hybrid) Stainless steel fiber (12μm diameter) and TLCP fiber (200D) are blended at a mass ratio of 3:7. Performance: areal density 52g / m², shielding effectiveness 45dB at 10GHz, shielding effectiveness decreases by 38% after 500h salt spray test, and metal fiber breaks and fails after 500 bending cycles.

[0043] Comparative Example 4 (N-GQDs content 2.5wt%) Below the lower limit of this invention. Formulation: TLCP 95.5wt%, N-GQDs 2.5wt%, PEI 1.5wt%, antioxidant 0.5wt%, other components same as in Example 1. Performance: Shielding effectiveness only 22dB, surface resistivity 8.5×10³Ω / sq, unable to form a continuous conductive network, batch variation >15%.

[0044] Comparative Example 5 (spinning speed 700 m / min) Below the lower limit of this invention. Using the formulation of Example 1, spinning speed 700 m / min, and insufficient cooling air volume. Performance: breakage rate 8.5%, fiber surface sheath crystallinity only 45%, core crystallinity 68%, and 5-10 μm wide microcracks appearing at the sheath-core interface.

[0045] Comparative Example 6 (spinning speed 1600m / min) This exceeds the upper limit of the present invention. Using the formulation of Example 1, the spinning speed was 1600 m / min, and the shear rate was 1.2 × 10⁻⁶. 4 s⁻¹. Performance: Melt degradation, strength decreases by 12% to 3.04 GPa, color difference ΔE=4.2, and melt fracture marks appear on the surface.

[0046] Comparative Example 7 (Second stage of heat setting at 210℃) Below the lower limit of this invention. Using the formulation of Example 1, the second stage was 210℃×2h. Performance: Boiling water shrinkage rate 0.35%, dimensional stability unqualified, shielding effectiveness retention rate only 78% after aging at 250℃×500h.

[0047] Comparative Example 8 (Second stage of heat setting at 250℃) The results exceeded the upper limit of this invention. Using the formulation of Example 1, the second stage was conducted at 250°C for 2 hours. Performance: Strength decreased by 11% to 3.07 GPa, fiber surface turned yellow, nitrogen content decreased by 0.8 wt%, and significant thermal degradation was observed.

[0048] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A high-temperature resistant liquid crystal polyarylate / nitrogen-doped graphene electromagnetic shielding fiber, characterized in that, The fiber has a core-sheath composite structure: Skin layer: composed of liquid crystal polyarylate matrix resin, surface-modified nitrogen-doped graphene, dispersant and antioxidant. The thickness of the skin layer is 15%-35% of the total fiber diameter. The nitrogen-doped graphene in the skin layer is oriented along the fiber axis to form a continuous conductive network. Core layer: pure liquid crystal polyarylate resin, bearing the main mechanical load; Based on the total fiber mass, the liquid crystal polyarylate matrix resin accounts for 85.0-95.0 wt%, the surface-modified nitrogen-doped graphene accounts for 3.0-10.0 wt%, and the dispersing agent accounts for 1.0-3.0 wt%; the mass ratio of the sheath to the core layer is 3:7 to 5:5, the fiber fineness is 50-1500 denier, the fiber cross-sectional roundness is ≥95%, and the sheath-core interface bonding strength is ≥70 MPa.

2. A method for preparing the fiber according to claim 1, characterized in that, Includes the following steps: (Step 1) Surface modification of nitrogen-doped graphene: Nitrogen-doped graphene was dispersed in an ethanol / water mixture (volume ratio 8:2), and treated with ultrasonic power of 300-500W for 30-60 minutes to prepare a suspension with a concentration of 0.5-2 mg / mL; aminosilane coupling agent KH-792 was added to carry out a surface grafting reaction at pH 4-5 and temperature of 60℃ for 4-6 hours. The reaction was carried out under nitrogen protection. After centrifugation (first centrifugation at 8000-10000 rpm to remove large particle agglomerates, and second centrifugation at 5000-7000 rpm to collect the modified product), washing, and drying, the surface-modified nitrogen-doped graphene was obtained. The modified product has an amino grafting rate of 5-12% on its surface and a particle size of <500nm when dispersed in TLCP melt; (Step 2) Preparation of conductive masterbatch: The surface-modified nitrogen-doped graphene obtained in step (1) is blended and granulated with liquid crystal polyarylate resin at a mass ratio of 3:7 in a twin-screw extruder. The twin-screw extruder has an aspect ratio of L / D = 40:

1. The screw assembly includes 3-5 kneading blocks. The temperature of each section is set as follows: feeding section 280-300℃, melting section 310-330℃, homogenization section 320-340℃, die head 320-350℃, screw speed 150-200rpm, vacuum degree ≤-0.08MPa, material residence time 3-8 minutes, to obtain 30wt% conductive masterbatch. The melt index MI (350℃, 2.16kg) of the masterbatch is 15-25g / 10min. (Step 3) Core-sheath composite spinning: The conductive masterbatch from step (2) is mixed with liquid crystal polyarylate resin, dispersant and antioxidant in a nitrogen atmosphere and vacuum dried at 120-150℃ for 4-8 hours until the moisture content is <100ppm; melt spinning is performed through a core-sheath composite spinning assembly, which includes independent sheath and core melt channels, and the ends of the channels are combined through concentric spinnerets; the sheath is a composite system containing nitrogen-doped graphene, the core is pure liquid crystal polyarylate resin, the sheath-core mass ratio is 3:7 to 5:5, the spinning temperature is 300-320℃, the spinning pressure is 8-15MPa, the spinning speed is 800-1500m / min, the stretching ratio is 4-8 times achieved by 3-5 sets of hot rollers, the hot roller temperature is gradually increased from 120-220℃, the stretching process is controlled by gradient tension, and the nascent fiber is wound into shape after cooling and solidification; (Step 4) Gradient heat setting: The fiber is subjected to a two-stage heat treatment under nitrogen protection with an oxygen content of <100ppm. The first stage is treated at 180-200℃ for 1-2 hours with a heating rate of 2-5℃ / min and a tension of 0.05-0.1cN / dtex. The second stage is treated at 220-240℃ for 1-2 hours with a heating rate of 1-3℃ / min and a tension of 0.1-0.2cN / dtex. The tension difference between the two stages is controlled at 0.05-0.1cN / dtex. The nitrogen protection system includes a gas purification device, an online oxygen content monitor, and a flow controller. The nitrogen purity is ≥99.995%, the flow rate is 5-15 L / min, and the furnace pressure is maintained at a slightly positive pressure of 0.05-0.15 MPa. After heat treatment, the fiber is sized with an oiling agent, dried, and wound to obtain the finished fiber. The fiber spinning breakage rate is <5%, and the batch performance fluctuation is ≤3%.

3. The method according to claim 2, characterized in that, The nitrogen doping amount of the nitrogen-doped graphene in step (1) is 5-12 at%, the number of layers is 3-8, the lateral dimension is 0.5-3 μm, and the specific surface area is 300-600 m² / g.

4. The method according to claim 2, characterized in that, The amount of aminosilane coupling agent KH-792 used in step (1) is 5-10% of the mass of nitrogen-doped graphene, and the amino grafting rate on the surface of the modified product is 5-12%.

5. The method according to claim 2, characterized in that, The twin-screw extruder described in step (2) has a length-to-diameter ratio of L / D = 40:1, the screw assembly contains 3-5 kneading blocks, the material residence time is 3-8 minutes, and the melt index MI (350℃, 2.16kg) of the resulting conductive masterbatch is 15-25g / 10min.

6. The method according to claim 2, characterized in that, The dispersing agent in step (3) is a polyetherimide (PEI) or polyphenylene sulfide (PPS) oligomer with a molecular weight of 2000-5000; the antioxidant is a mixture of hindered phenolic antioxidant Irganox1010 and phosphite antioxidant Irgafos168 in a mass ratio of 1:1-2:

1.

7. The method according to claim 2, characterized in that, The spinneret of the core-sheath composite spinning assembly in step (3) has a concentric circle structure, with an outer layer aperture of 0.20-0.35 mm, an inner layer aperture of 0.15-0.25 mm, and 50-200 holes; the metering pump is an independent dual-pump system, with the sheath pump speed of 5-15 rpm and the core pump speed of 15-30 rpm, and the speed deviation is controlled to be ≤±1 rpm.

8. The fiber according to claim 1, characterized in that, The fiber has an electromagnetic shielding effectiveness of ≥35dB in the 8-40GHz frequency band, a tensile strength of ≥3.0GPa, a Young's modulus of ≥90GPa, and a density of 1.42-1.45g / cm³.

9. The fiber according to claim 1, characterized in that, The fiber has an electromagnetic shielding effectiveness of ≥35dB in the 8-40GHz frequency band, a tensile strength of ≥3.0GPa, a Young's modulus of ≥90GPa, an elongation at break of 2.5-3.5%, a density of 1.42-1.45g / cm³, and a shielding effectiveness retention rate of >90% after heat aging at 250℃ for 500h.

10. The fiber according to claim 9, characterized in that, The surface resistivity of the fiber is 10²-10. 4 Ω / sq, volume resistivity 10⁻²-10 0 Ω·cm, after 1000 hours of damp heat aging at 85℃ / 85%RH, the shielding effectiveness retention rate is >88%.

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