A space-division multiplexing multi-core optical fiber cable and its fabrication method

Abstract

This invention relates to the field of optical fiber manufacturing technology and discloses a space-division multiplexing multi-core optical fiber cable and its preparation method. The optical fiber cable contains multi-core optical fiber units and a functionally graded sheath layer. The functionally graded sheath layer uses an end-group reactive liquid crystal polymer as a matrix and is doped with a "core-shell-crown" three-dimensional hybrid filler, which is distributed in a radially gradient increasing manner. The preparation method includes stepwise preparation of core-shell structured CNC@SiO2, three-dimensional hybrid filler, and high-concentration masterbatch, followed by multi-layer co-extrusion molding and three-stage gradient cooling and shaping to achieve integrated low-temperature molding of the gradient sheath layer. This invention solves the problems of weak sheath interfaces, high-temperature damage to optical fibers, and uneven performance in existing systems through filler interface modification, gradient structure design, and process optimization. The sheath layer exhibits excellent mechanical, thermal, and dielectric properties, outstanding optical fiber transmission stability and long-term weather resistance, and the preparation process is controllable and suitable for large-scale production.

Description

Technical Field

[0001] This invention relates to the field of optical fiber manufacturing technology, specifically to a space-division multiplexing multi-core optical fiber cable and its preparation method. Background Technology

[0002] Space division multiplexing (SDM) technology, by integrating multiple fiber cores into a single optical fiber, breaks through the capacity limit of single-mode fiber and is a key technology for next-generation optical communication networks. However, multi-core optical fibers are extremely sensitive to mechanical stress and changes in ambient temperature. Traditional loose tube structures or ordinary polymer sheaths (such as PE and PBT) are prone to hardening and embrittlement at low temperatures, leading to microbending loss due to lateral pressure on the fiber. In high-temperature and high-humidity environments, ordinary sheaths are prone to hydrolysis or thermal expansion coefficient mismatch, causing changes in the fiber core spacing and resulting in a sharp increase in crosstalk. Existing liquid crystal polymers (LCPs), although possessing low thermal expansion and high strength, lack sufficient toughness and have weak interfacial bonding with inorganic fillers, making them prone to cracking under bending or impact when directly used as fiber sheaths. Therefore, developing a novel sheath material that combines high strength and high modulus, excellent low-temperature flexibility, and a low coefficient of thermal expansion is crucial. Summary of the Invention

[0003] The purpose of this invention is to provide a space-division multiplexing multi-core optical fiber cable and its preparation method to solve the problems mentioned in the background art.

[0004] To achieve the above objectives, on the one hand, the present invention provides a space-division multiplexing multi-core optical fiber cable, comprising a multi-core optical fiber unit and a functionally graded sheath layer covering the outside thereof. The matrix of the functionally graded sheath layer is an end-group reactive liquid crystal polymer, and the molecular chain ends contain at least one active functional group selected from carboxyl, hydroxyl, or epoxy groups. The functionally graded sheath layer contains dispersed three-dimensional hybrid nanofillers, which include a core, an intermediate shell, and an outer crown. The core is a cellulose nanofiber (CNC), the intermediate shell is a dense silica shell grown on the surface of the cellulose nanofiber, and the outer crown is a functionalized graphene sheet covalently grafted onto the surface of the silica layer by a silane coupling agent. The functionalized graphene sheet is partially reduced graphene oxide with a carbon-to-oxygen ratio of (4-8):1. The functionally graded sheath layer extends radially from the inner surface to the outer surface, and the volume fraction of the three-dimensional hybrid nanofiller increases in a gradient, with a volume fraction of 1%-3% on the inner surface and 8%-15% on the outer surface.

[0005] The CNC core provides high-strength rigid support, the SiO2 shell ensures low dielectric loss and insulation stability, and the functionalized graphene crown improves thermal conductivity and interface compatibility. The radial filler gradient achieves inner flexibility and outer rigidity in the sheath. The low filler content in the inner layer adapts to the flexible protection requirements of optical fibers, while the high filler content in the outer layer enhances mechanical impact resistance and environmental resistance. At the same time, the gradient distribution alleviates interface stress concentration, avoids sheath cracking, and balances optical fiber transmission stability and mechanical protection.

[0006] Silane coupling agents enable covalent grafting of functionalized graphene with SiO2 shells, preventing sheet detachment and ensuring the integrity of the filler structure. Oxygen-containing functional groups on the graphene surface form covalent / hydrogen bonds with the active functional groups at the ends of the reactive liquid crystal polymer, significantly improving the interfacial bonding force between the filler and the matrix, enhancing the mechanical properties and thermal stability of the sheath, while ensuring uniform dielectric properties and avoiding interference from space-division multiplexed optical fiber signals.

[0007] Preferably, the average length of the nanocellulose whiskers is 80-150 nm and the diameter is 5-15 nm.

[0008] Preferably, the silica shell is generated by the sol-gel reaction of tetraethyl orthosilicate on the surface of nanocellulose whiskers, and the silica mass accounts for 8%-15% of the total mass of the three-dimensional hybrid nanofiller.

[0009] Preferably, the functionally graded sheath layer further contains 0.5%-1.5% by mass of a high molecular weight hindered phenolic antioxidant and 0.3%-1.0% by mass of a carbodiimide anti-hydrolysis agent. The antioxidants and anti-hydrolysis agents enhance the long-term weather resistance and environmental stability of the sheath layer. The high molecular weight hindered phenolic antioxidant inhibits the thermo-oxidative aging of the end-group reactive liquid crystal polymer during high-temperature processing and long-term service, preventing matrix degradation and embrittlement; the carbodiimide anti-hydrolysis agent blocks the matrix hydrolysis reaction, adapting to harsh service environments such as humidity and high temperature, extending the service life of the optical fiber cable, and ensuring long-term transmission reliability.

[0010] Preferably, the increasing volume fraction of the packing material satisfies the following functional relationship: ,in i This refers to the volume fraction of the filler on the inner surface. 0 represents the volume fraction of the outer surface filler, r i Let r0 be the inner diameter of the functionally graded sheath layer, r0 be the outer diameter of the functionally graded sheath layer, and n be the gradient exponent, ranging from 0.5 to 2.0. The gradient exponent of 0.5-2.0 allows for flexible adjustment of the gradient increase rate, adapting to the performance requirements of different application scenarios. This ensures both the flexibility of the inner layer with low filler content and the high strength of the outer layer with high filler content, precisely balancing sheath flexibility, mechanical strength, and thermal conductivity, thus improving the versatility and controllability of the solution.

[0011] On the other hand, the present invention discloses a method for preparing the above-mentioned space-division multiplexing multi-core optical fiber cable, comprising the following steps: (1) A dense silica shell was grown on the surface of nanocellulose whiskers to obtain CNC@SiO2; (2) CNC@SiO2 was dispersed in an organic solvent, a silane coupling agent was added, and the reaction was carried out at 70℃-85℃ for 4-8h. Then, a partially reduced graphene oxide dispersion was added and the reaction was carried out for 12-24h. After centrifugation, washing, and freeze-drying, a three-dimensional hybrid nanofiller was obtained. (3) Mix the three-dimensional hybrid nanofiller, end-group reactive liquid crystal polymer and compatibilizer in a mass ratio of (20-30):(68-79):(1-5), melt blend and extrude granulate to obtain a high-concentration masterbatch with a filler mass fraction of 20%-30%. (4) The end-reactive liquid crystal polymer and high-concentration masterbatch are melted and extruded separately. The extruded melt is compounded by a multi-layer co-extrusion die and extruded onto the outer periphery of the multi-core optical fiber unit to form a functional gradient sheath layer. The extruded cable is shaped by three-stage temperature-controlled cooling and traction to obtain the space-division multiplexing multi-core optical fiber cable.

[0012] Preferably, in step (1), the growth of a dense silica shell on the surface of nanocellulose whiskers to obtain CNC@SiO2 includes: Cellulose nanofibers were dispersed in an ethanol / water mixed solvent, the pH was adjusted to 8-10, tetraethyl orthosilicate was added dropwise, and the reaction was carried out at 40℃-60℃ for 6-12 hours. After washing and drying, CNC@SiO2 was obtained.

[0013] Preferably, in step (2), before adding the silane coupling agent, an ultrasonic dispersion step is also included, with an ultrasonic power of 200-400W and a dispersion time of 15-30min. Ultrasonic dispersion effectively breaks up the agglomeration of nanofillers, improves the uniformity of the filler dispersion in the matrix, and avoids local stress concentration.

[0014] Preferably, in step (4), the process of melting and extruding the end-group reactive liquid crystal polymer and the high-concentration masterbatch separately, and then compounding the extruded melt through a multi-layer co-extrusion die and extruding it onto the outer periphery of the multi-core optical fiber unit to form a functionally graded sheath layer includes: The main extruder extrudes end-reactive liquid crystal polymer melt, while the auxiliary extruder extrudes high-concentration masterbatch melt. The extruded melts pass through a multi-layer co-extrusion die with 3-8 independent annular flow channels. Adjusting the feed rate of the auxiliary extruder controls the concentration of each layer of three-dimensional hybrid nanofiller. After the end-reactive liquid crystal polymer melt and the high-concentration masterbatch melt converge at the exit of the multi-layer co-extrusion die, they partially diffuse, forming a functionally graded sheath layer around the multi-core optical fiber unit. The 3-8 independent annular flow channels enable precise control of the melt concentration in each layer, and the feed rate adjustment achieves a stepped gradient distribution. The partial diffusion after melt convergence forms a continuous gradient, adapting to different gradient requirements.

[0015] Preferably, in step (4), the three-stage temperature-controlled cooling traction shaping includes: The first cooling section uses an oil bath / high-pressure steam temperature control at 160℃-200℃ and is 5-15m long; the second cooling section uses a water bath temperature control at 80℃-120℃ and is 10-30m long; the third cooling section uses a water bath temperature control at 15℃-30℃ and is 5-10m long; the traction speed is 5-20m / min. The first cooling section slowly lowers the temperature to suppress stress concentration, the second cooling section gradually shapes the structure and improves crystallinity regularity, and the third cooling section rapidly cools and locks in the structure. By matching the length, temperature, and traction speed of the cooling sections, the radial crystallinity distribution of the sheath is precisely controlled, further enhancing gradient performance, preventing sheath deformation and warping, and improving dimensional accuracy and performance stability.

[0016] In step (2), partially reduced graphene oxide is prepared by reducing it at 80℃-95℃ for 1-3 hours using hydrazine hydrate or ascorbic acid. By precisely controlling the carbon-oxygen ratio under mild reduction conditions and with varying amounts of reducing agent, an appropriate amount of oxygen-containing functional groups on the graphene surface is retained to ensure its reactivity with silane coupling agents and end-group reactive liquid crystal polymer matrices. At the same time, the electrical and thermal conductivity of graphene is improved, avoiding excessive reduction that could lead to the loss of functional groups and a decrease in interfacial bonding. This precise control of the degree of graphene functionalization optimizes the overall performance of the filler.

[0017] The beneficial effects of this invention are as follows: This invention uses end-group reactive liquid crystal polymers as the matrix and leverages the multi-component synergistic effect of a "core-shell-crown" three-dimensional hybrid filler. CNC provides rigid support, SiO2 ensures low dielectric insulation, and functionalized graphene enhances thermal conductivity and interfacial activity. The three-dimensional hybrid filler and end-group reactive liquid crystal polymers are bridged by a compatibilizer, resulting in a strong interfacial bond, uniform filler dispersion, and significantly improved sheath tensile strength and heat distortion temperature, with high performance retention after thermo-oxidative aging. The radial filler gradient design achieves a performance gradient distribution of inner flexibility and outer rigidity in the sheath, alleviating interfacial stress and balancing flexible protection with mechanical strength. The low-temperature multilayer co-extrusion + three-stage gradient cooling process avoids optical fiber thermal damage and precisely controls the crystallinity and gradient structure of the sheath, ultimately achieving synergistic optimization of optical fiber cable mechanical protection, thermal stability, dielectric stability, and transmission reliability.

[0018] Other features and advantages of the present invention will be described in detail in the following detailed description section. Detailed Implementation

[0019] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0020] It should be noted that all reagents and raw materials used in this invention are commercially available, and the reagents are of analytical grade.

[0021] The liquid crystal polymer was purchased from Dongguan Suguang Plastic Raw Materials Co., Ltd., model Vectra A950. The cellulose nanofiber whiskers (CNC) were from Guilin Qihong Technology Co., Ltd., model CNC-C99. The graphene oxide powder was from Jiangsu Xianfeng Nanomaterials Technology Co., Ltd., model XF002-2. The multifunctional epoxy resin compatibilizer was purchased from Gabette (Guangzhou) New Materials Co., Ltd., model BASF Joncryl® ADR 4468. The maleic anhydride-grafted POE compatibilizer was from Ningbo Nengzhiguang New Materials Technology Co., Ltd., model MC509.

[0022] Example 1

[0023] 1. Preparation of end-group reactive liquid crystal polymer (raw materials by mass): Weigh 100 parts of liquid crystal polymer, 1.2 parts of hydroxyl end-capping agent (p-hydroxybenzoic acid), and 0.08 parts of antimony trioxide catalyst, put them into a high-speed mixer for premixing for 5 min, and then transfer them to a twin-screw extruder. Nitrogen protection and screw zone temperature control: Zone 1 285℃, Zone 2 290℃, Zone 3 295℃, Zone 4 295℃, Zone 5 290℃, Zone 6 285℃, screw speed 180 r / min, vacuum degree -0.098 MPa. After the extruder die produces molten strip, immediately send it to a room temperature cooling water bath for water cooling and shaping to quickly terminate the melting reaction and solidify the strip. Cut into pellets, and then place the pellets in a vacuum drying oven and dry at 140℃ for 6 h to completely remove moisture. After crushing and sieving, the end-group reactive liquid crystal polymer with hydroxyl active functional groups at the end of the molecular chain is obtained. 2. Preparation of core-shell structured CNC@SiO2: 2.0 g of CNC particles with an average length of 110 nm and an average diameter of 10 nm were weighed and dispersed in 1000 mL of ethanol / water (volume ratio 7:3) mixed solvent. The mixture was mechanically stirred and ultrasonically dispersed at 250 W for 30 min until a uniform suspension was formed. Ammonia was added dropwise to adjust the pH to 9, and 8.5 g of tetraethyl orthosilicate was added dropwise. The sol-gel reaction was carried out at 50 °C with stirring for 9 h. The reaction product was centrifuged, washed three times alternately with ethanol and deionized water, and vacuum dried at 60 °C for 12 h to obtain CNC@SiO2 core-shell particles. The SiO2 shell thickness was measured to be 6 nm, and its mass accounted for 11% of the total mass of the filler. 3. Preparation of partially reduced graphene oxide dispersion: Graphene oxide powder was dispersed in deionized water to prepare a uniform dispersion with a concentration of 2 mg / mL. Hydrazine hydrate was used as a reducing agent, and the reducing agent was added at a mass ratio of graphene oxide to hydrazine hydrate of 1:0.8. The dispersion was reduced at 90℃ and 300 rpm for 2 h. Samples were taken every 30 min during the reduction process, and the carbon-oxygen ratio was tested by X-ray photoelectron spectroscopy (XPS). The reaction was terminated immediately when the carbon-oxygen ratio stabilized at 6:1. The reduction reaction was quenched by rapid cooling in an ice-water bath. Unreacted reagents were removed by centrifugation and washing to obtain a partially reduced graphene oxide dispersion with a sheet size of 1.2 μm, which was then used for later use. 4. Preparation of three-dimensional hybrid nanofiller: Weigh 3.0g of the above CNC@SiO2 core-shell particles, disperse them in 800mL of N,N-dimethylformamide solvent, and ultrasonically disperse them at 250W for 20min until uniform. Add 0.36g of KH550 silane coupling agent, heat to 80℃ and stir for 6h. Then add 300mL of the partially reduced graphene oxide dispersion prepared in step 3, and continue to stir for 18h. The reaction product is centrifuged at high speed, washed three times alternately with N,N-dimethylformamide and deionized water, and freeze-dried for 24h to obtain the "core-shell-crown" three-dimensional hybrid nanofiller. 5. Preparation of high-concentration masterbatch: Three-dimensional hybrid nanofiller, end-group reactive liquid crystal polymer, and maleic anhydride-grafted POE compatibilizer are mixed at a mass ratio of 25:73:2, melt-blended and extruded in a twin-screw extruder, with zoned temperature control in the twin-screw extruder: zone 1 265℃, zone 2 270℃, zone 3 275℃, zone 4 275℃, zone 5 270℃, and zone 6 265℃, to obtain a high-concentration masterbatch with a filler mass fraction of 25%; 6. Multi-layer co-extrusion molding: The main extruder conveys end-group reactive liquid crystal polymer, and two auxiliary extruders convey high-concentration masterbatch. The die head is equipped with 5 independent annular flow channels. The feed rate of the main extruder is 10 kg / h and remains constant throughout the process. The feed rate of the first auxiliary extruder (middle flow channel) is adjusted to 3 kg / h. After the melt pressure stabilizes at 10 MPa and the output is uniform, the feed rate of the second auxiliary extruder (outer flow channel) is finely adjusted to 5 kg / h, so that the volume fraction of the inner layer filler is 2% and that of the outer layer is 11%, with a gradient index n=1.2. The die head extrusion temperature is 275℃. The extrusion is applied to the outer periphery of the multi-core optical fiber unit to obtain an extruded cable with a functionally gradient sheath layer. 7. Three-stage gradient cooling and traction shaping: The extruded cable is subjected to three-stage temperature-controlled traction cooling and shaping. The first cooling stage is an oil bath at 180℃ with a length of 10m, the second cooling stage is a water bath at 100℃ with a length of 20m, and the third cooling stage is a water bath at 25℃ with a length of 8m. The traction speed is 12m / min, and an optical fiber cable is produced.

[0024] Example 2

[0025] 1. Preparation of end-group reactive liquid crystal polymer (raw materials by mass): Weigh 100 parts of liquid crystal polymer, 1.5 parts of carboxyl end-capping agent (pyromellitic dianhydride), and 0.1 parts of catalyst antimony trioxide, put them into a high-speed mixer for premixing for 6 min, and then transfer them to a twin-screw extruder. Nitrogen protection and screw zone temperature control: Zone 1 275℃, Zone 2 280℃, Zone 3 285℃, Zone 4 285℃, Zone 5 280℃, Zone 6 275℃, screw speed 150 r / min, vacuum degree -0.095 MPa. After the extruder die produces molten strip, immediately send it to a room temperature cooling water bath for water cooling and shaping to quickly terminate the melting reaction and solidify the strip. Cut into pellets, and then place the pellets in a vacuum drying oven and dry at 140℃ for 6 h to completely remove moisture. After crushing and sieving, the end-group reactive liquid crystal polymer with carboxyl active functional groups at the end of the molecular chain is obtained. 2. Preparation of core-shell structured CNC@SiO2: 1.5g of CNC with an average length of 80nm and an average diameter of 5nm was weighed and dispersed in 800mL of ethanol / water (volume ratio 7:3) mixed solvent. The mixture was mechanically stirred and ultrasonically dispersed at 250W for 25min until a uniform suspension was obtained. Ammonia was added dropwise to adjust the pH to 8, and 5.2g of tetraethyl orthosilicate was added dropwise. The sol-gel reaction was carried out at 40℃ with stirring for 12h. The reaction product was centrifuged, washed three times alternately with ethanol and deionized water, and vacuum dried at 60℃ for 12h to obtain CNC@SiO2 core-shell particles. The SiO2 shell thickness was measured to be 2nm, and its mass accounted for 8% of the total mass of the filler. 3. Preparation of partially reduced graphene oxide dispersion: Graphene oxide powder was dispersed in deionized water to prepare a uniform dispersion with a concentration of 1.5 mg / mL. Ascorbic acid was used as a reducing agent, and the reducing agent was added at a mass ratio of graphene oxide to ascorbic acid of 1:1.2. The dispersion was reduced at 80℃ and 300 rpm for 3 h. Samples were taken every 30 min during the reduction process, and the carbon-oxygen ratio was tested by X-ray photoelectron spectroscopy (XPS). The reaction was terminated immediately when the carbon-oxygen ratio stabilized at 4:1. The reduction reaction was quenched by rapid cooling in an ice-water bath. Unreacted reagents were removed by centrifugation and washing to obtain a partially reduced graphene oxide dispersion with a sheet size of 0.3 μm, which was then used for later use. 4. Preparation of three-dimensional hybrid nanofiller: Weigh 2.5g of the above CNC@SiO2 core-shell particles, disperse them in 600mL of toluene solvent, and ultrasonically disperse them at 200W for 30min until uniform. Add 0.24g of KH560 silane coupling agent, heat to 70℃ and stir for 8h. Then add 330mL of the partially reduced graphene oxide dispersion prepared in step 3, and continue to stir for 24h. The reaction product is centrifuged at high speed, washed three times with toluene and deionized water alternately, and freeze-dried for 24h to obtain the "core-shell-crown" three-dimensional hybrid nanofiller. 5. Preparation of high-concentration masterbatch: Three-dimensional hybrid nanofiller, end-group reactive liquid crystal polymer, and multifunctional epoxy resin compatibilizer are mixed at a mass ratio of 20:79:1, melt-blended and extruded in a twin-screw extruder, with zoned temperature control in the twin-screw extruder: zone 1 255℃, zone 2 260℃, zone 3 265℃, zone 4 265℃, zone 5 260℃, and zone 6 255℃, to obtain a high-concentration masterbatch with a filler mass fraction of 20%; 6. Multi-layer co-extrusion molding: The main extruder conveys end-group reactive liquid crystal polymer, and the auxiliary extruder conveys high-concentration masterbatch. The die head is equipped with 3 independent annular flow channels. The feed rate of the main extruder is 8 kg / h and remains constant throughout the process, while the feed rate of the auxiliary extruder is adjusted to 2 kg / h. The melt pressure is kept stable at 9 MPa throughout the process, so that the filler volume fraction of the inner layer of the sheath is 1% and that of the outer layer is 8%, with a gradient index n=0.5. The die head extrusion temperature is 260℃. The sheath is extruded around the periphery of the multi-core optical fiber unit to obtain an extruded cable with a functional gradient sheath layer. 7. Three-stage gradient cooling and traction shaping: The extruded cable is subjected to three-stage temperature-controlled traction cooling and shaping. The first cooling stage is high-pressure steam at 160℃ and 5m in length. The second cooling stage is water bath at 80℃ and 10m in length. The third cooling stage is water bath at 15℃ and 5m in length. The traction speed is 5m / min to produce the optical fiber cable.

[0026] Example 3

[0027] 1. Preparation of end-group reactive liquid crystal polymer (raw materials by mass): Weigh 100 parts of liquid crystal polymer, 1.0 part of epoxy end-capping agent (4,4'-biphenyl diepoxyglycerol ether), and 0.06 parts of antimony trioxide catalyst, put them into a high-speed mixer for premixing for 4 min, and then transfer them to a twin-screw extruder. Nitrogen protection and screw zone temperature control: Zone 1 290℃, Zone 2 295℃, Zone 3 300℃, Zone 4 300℃, Zone 5 295℃, Zone 6 290℃, screw speed 200 r / min, vacuum degree -0.099 MPa. After the extruder die produces molten strip, immediately send it to a room temperature cooling water bath for water cooling and shaping to quickly terminate the melting reaction and solidify the strip. Cut into pellets, and then place the pellets in a vacuum drying oven and dry at 140℃ for 6 h to completely remove moisture. After crushing and sieving, the end-group reactive liquid crystal polymer with epoxy active functional groups at the end of the molecular chain is obtained. 2. Preparation of core-shell structured CNC@SiO2: 2.5g of CNC with an average length of 150nm and an average diameter of 15nm was weighed and dispersed in 1200mL of ethanol / water (volume ratio 7:3) mixed solvent. The mixture was mechanically stirred and ultrasonically dispersed at 250W for 35min until a uniform suspension was obtained. Ammonia was added dropwise to adjust the pH to 10, and 12.8g of tetraethyl orthosilicate was added dropwise. The sol-gel reaction was carried out at 60℃ with stirring for 6h. The reaction product was centrifuged, washed three times alternately with ethanol and deionized water, and vacuum dried at 60℃ for 12h to obtain CNC@SiO2 core-shell particles. The SiO2 shell thickness was measured to be 10nm, and its mass accounted for 15% of the total mass of the filler. 3. Preparation of partially reduced graphene oxide dispersion: Graphene oxide powder was dispersed in deionized water to prepare a uniform dispersion with a concentration of 2.5 mg / mL. Hydrazine hydrate was used as a reducing agent, and the reducing agent was added at a mass ratio of graphene oxide to hydrazine hydrate of 1:1.05. The dispersion was reduced at 95℃ and 300 rpm for 1 h. Samples were taken every 30 min during the reduction process, and the carbon-oxygen ratio was tested by X-ray photoelectron spectroscopy (XPS). The reaction was terminated immediately when the carbon-oxygen ratio stabilized at 8:1. The reduction reaction was quenched by rapid cooling in an ice-water bath. Unreacted reagents were removed by centrifugation and washing to obtain a partially reduced graphene oxide dispersion with a sheet size of 2 μm, which was then used for later use. 4. Preparation of three-dimensional hybrid nanofillers: Weigh 3.5g of the above CNC@SiO2 core-shell particles, disperse them in 1000mL of N,N-dimethylformamide solvent, and sonicate at 300W for 15min until uniform. Add 0.48g of KH550 silane coupling agent, heat to 85℃ and stir for 4h. Then add 280mL of the partially reduced graphene oxide dispersion prepared in step 3, and continue to stir for 12h. The reaction product is centrifuged at high speed, washed three times alternately with N,N-dimethylformamide and deionized water, and freeze-dried for 24h to obtain the "core-shell-crown" three-dimensional hybrid nanofiller. 5. Preparation of high-concentration masterbatch: Three-dimensional hybrid nanofiller, end-group reactive liquid crystal polymer, and maleic anhydride-grafted POE compatibilizer are mixed at a mass ratio of 30:68:2, melt-blended and extruded in a twin-screw extruder, with zoned temperature control in the twin-screw extruder: zone 1 280℃, zone 2 285℃, zone 3 290℃, zone 4 290℃, zone 5 285℃, and zone 6 280℃, to obtain a high-concentration masterbatch with a filler mass fraction of 30%; 6. Multi-layer co-extrusion molding: The main extruder conveys end-group reactive liquid crystal polymer, and three auxiliary extruders convey high-concentration masterbatch. The die head is equipped with eight independent annular flow channels. The main extruder feed rate is 15 kg / h and remains constant throughout the process. The three auxiliary extruders are speed-adjusted step by step in the order of "inner layer → middle layer → outer layer". The feed rate of the first auxiliary extruder is adjusted to 4 kg / h, the feed rate of the second auxiliary extruder is adjusted to 5 kg / h, and the feed rate of the third auxiliary extruder (outer layer) is adjusted to 6 kg / h, gradually increasing the rate difference and concentration difference. The melt pressure is controlled at 12 MPa throughout the process, so that the filler volume fraction of the inner layer of the sheath is 3% and that of the outer layer is 15%, with a gradient index n=2. The die head extrusion temperature is 290℃. The sheath is extruded around the periphery of the multi-core optical fiber unit to obtain an extruded cable with a functional gradient sheath layer. 7. Three-stage gradient cooling and traction shaping: The extruded cable is subjected to three-stage temperature-controlled traction cooling and shaping. The first cooling stage is high-pressure steam at 200℃ and 15m in length. The second cooling stage is water bath at 120℃ and 30m in length. The third cooling stage is water bath at 30℃ and 10m in length. The traction speed is 20m / min to produce the optical fiber cable.

[0028] Example 4

[0029] 1. Preparation of end-group reactive liquid crystal polymer (raw materials by mass): Weigh 100 parts of liquid crystal polymer, 1.3 parts of hydroxyl end-capping agent (p-hydroxybenzoic acid), and 0.09 parts of catalyst tetrabutyl titanate, put them into a high-speed mixer for premixing for 5 min, and then transfer them to a twin-screw extruder. Nitrogen protection and screw zone temperature control: Zone 1 280℃, Zone 2 285℃, Zone 3 290℃, Zone 4 290℃, Zone 5 285℃, Zone 6 280℃, screw speed 170 r / min, vacuum degree -0.097 MPa. After the extruder die produces molten strip, immediately send it to a room temperature cooling water bath for water cooling and shaping to quickly terminate the melting reaction and solidify the strip. Cut into pellets, and then place the pellets in a vacuum drying oven and dry at 140℃ for 6 h to completely remove moisture. After crushing and sieving, the end-group reactive liquid crystal polymer with hydroxyl active functional groups at the end of the molecular chain is obtained. 2. Preparation of core-shell structured CNC@SiO2: 2.2g of CNC particles with an average length of 120nm and an average diameter of 8nm were weighed and dispersed in 900mL of ethanol / water (volume ratio 7:3) mixed solvent. The mixture was mechanically stirred and ultrasonically dispersed at 250W for 30min until a uniform suspension was obtained. Ammonia was added dropwise to adjust the pH to 9, and 9.6g of tetraethyl orthosilicate was added dropwise. The sol-gel reaction was carried out at 55℃ with stirring for 8h. The reaction product was centrifuged, washed three times alternately with ethanol and deionized water, and vacuum dried at 60℃ for 12h to obtain CNC@SiO2 core-shell particles. The SiO2 shell thickness was measured to be 7nm, and its mass accounted for 12% of the total mass of the filler. 3. Preparation of partially reduced graphene oxide dispersion: Graphene oxide powder was dispersed in deionized water to prepare a uniform dispersion with a concentration of 2 mg / mL. Ascorbic acid was used as a reducing agent, and the reducing agent was added at a mass ratio of graphene oxide to ascorbic acid of 1:1.0. The dispersion was reduced at 85℃ and 300 rpm for 2.5 h. During the reduction process, samples were taken every 30 min. The carbon-oxygen ratio was tested by X-ray photoelectron spectroscopy (XPS). The reaction was terminated immediately when the carbon-oxygen ratio stabilized at 5:1. The reduction reaction was quenched by rapid cooling in an ice-water bath. Unreacted reagents were removed by centrifugation and washing to obtain a partially reduced graphene oxide dispersion with a sheet size of 1 μm, which was then used for later use. 4. Preparation of three-dimensional hybrid nanofiller: Weigh 2.8g of the above CNC@SiO2 core-shell particles, disperse them in 700mL of toluene solvent, and ultrasonically disperse them at 260W for 20min until uniform. Add 0.30g of KH550 silane coupling agent, heat to 75℃ and stir for 5h. Then add 280mL of the partially reduced graphene oxide dispersion prepared in step 3, and continue to stir for 20h. The reaction product is centrifuged at high speed, washed three times with toluene and deionized water alternately, and freeze-dried for 24h to obtain the "core-shell-crown" three-dimensional hybrid nanofiller. 5. Preparation of high-concentration masterbatch: Three-dimensional hybrid nanofiller, end-group reactive liquid crystal polymer, and maleic anhydride-grafted POE compatibilizer are mixed at a mass ratio of 24:71:5. At the same time, 1% of antioxidant 1010 and 0.6% of N,N'-bis(2,6-diisopropylphenyl)carbodiimide are added to the mixture. The mixture is melt-blended and extruded and granulated using a twin-screw extruder. The twin-screw extruder is divided into zones with temperature control: zone 1 255℃, zone 2 260℃, zone 3 265℃, zone 4 265℃, zone 5 260℃, and zone 6 255℃ to obtain a high-concentration masterbatch with a filler mass fraction of 24%. 6. Multi-layer co-extrusion molding: The main extruder conveys end-group reactive liquid crystal polymer, and two auxiliary extruders convey high-concentration masterbatch. The die head is equipped with 6 independent annular flow channels. The feed rate of the main extruder is 12 kg / h and remains constant throughout the process. The feed rate of the first auxiliary extruder is adjusted to 3.5 kg / h, and the feed rate of the second auxiliary extruder is adjusted to 5.5 kg / h. The melt pressure is controlled at 10 MPa throughout the process, so that the filler volume fraction of the inner layer of the sheath is 2.5% and that of the outer layer is 12%, with a gradient index n=1.5. The die head extrusion temperature is 270℃. The extrusion is applied to the outer periphery of the multi-core optical fiber unit to obtain an extruded cable with a functionally gradient sheath layer. 7. Three-stage gradient cooling and traction shaping: The extruded cable is subjected to three-stage temperature-controlled traction cooling and shaping. The first cooling stage is an oil bath at 170℃ with a length of 12m, the second cooling stage is a water bath at 90℃ with a length of 25m, and the third cooling stage is a water bath at 22℃ with a length of 7m. The traction speed is 15m / min to produce the optical fiber cable.

[0030] Comparative Example 1 Compared with Example 1, the difference is that steps 2-5 are omitted, and in step 6, the end-group reactive liquid crystal polymer is directly extruded by a twin-screw extruder.

[0031] Comparative Example 2 Compared with Example 1, the difference is that steps 3 and 4 are omitted, and in step 5, the core-shell structure CNC@SiO2 is directly mixed with the end-group reactive liquid crystal polymer and the epoxy-modified liquid crystal polymer compatibilizer at a mass ratio of 25:73:2.

[0032] Comparative Example 3 Compared with Example 1, the difference is that in step 5, the three-dimensional hybrid nanofiller, end-group reactive liquid crystal polymer, and epoxy-modified liquid crystal polymer compatibilizer are mixed at a mass ratio of 11:87:2 to prepare a masterbatch with a concentration of 11%. In step 6, the masterbatch with a concentration of 11% is directly extruded onto the outer periphery of the multi-core optical fiber unit using an extruder.

[0033] Comparative Example 4 Compared with Example 1, the difference is that step 1 is omitted and the end-group reactive liquid crystal polymer is replaced with a common liquid crystal polymer.

[0034] Comparative Example 5 The difference from Example 1 is that no silane coupling agent is added in step 4.

[0035] Comparative Example 6 The difference from Example 1 is that in step 7, room temperature water cooling is used directly.

[0036] The samples obtained in Examples 1-4 were subjected to relevant performance tests. The test methods and standards are as follows: 1. Tensile strength and elongation at break (GB / T 1040.1-2025 Determination of tensile properties of plastics - Part 1: General): The specimens were prepared using a dumbbell-shaped cutter with a gauge length of 50 mm, a width of 10 mm, and a thickness of 2 mm. Five parallel specimens were tested in each group. The test environment was 23±2℃ and the relative humidity was 50±5%. The tensile speed was uniformly set to 50 mm / min and the tensile speed was uniform throughout. The maximum load and gauge length elongation at the time of specimen breakage were recorded. After removing outliers, the average value was taken, and the tensile strength and elongation at break were calculated respectively.

[0037] 2. Heat distortion temperature (GB / T 1634.2-2019 "Determination of load distortion temperature of plastics - Part 2: Plastics and hard rubber"): The sample size is 80mm×10mm×4mm, and 3 parallel samples are tested in each group; a three-point bending support method is adopted with a span of 64mm, a constant load of 1.82MPa is applied, and the heating rate is 120℃ / h; the deformation of the sample is monitored in real time, and when the deformation of the sample reaches 0.34mm, the corresponding temperature is recorded as the heat distortion temperature, and the average value of 3 groups of samples is taken.

[0038] 3. Dielectric constant (1GHz, GB / T 1408.1-2016 "Test Methods for Electrical Strength of Insulating Materials - Part 1: Test at Power Frequency"): The sample is a circular sheet with a diameter of 50mm and a thickness of 1.5mm. The surface is polished smooth without burrs or scratches. Before testing, it is dried in a vacuum drying oven at 80℃ for 2 hours. A dielectric constant tester is used, with a test frequency of 1GHz, an ambient temperature of 25℃, and a relative humidity of 45%. Four test points are used for each group. After removing values ​​with excessive deviation, the average value is taken.

[0039] 4. Fiber transmission attenuation increment (ITU-T G.650.1-2024 "Definition and test methods for linear and deterministic properties of single-mode optical fibers and cables"): The optical time domain reflectometer (OTDR) is used for testing at wavelengths of 1310nm and 1550nm. The initial transmission attenuation value of the sample is tested first, and then the sample is placed in a constant temperature and humidity chamber at 85℃ and 95%RH for 2000h for damp heat aging. After being removed and restored to room temperature, the transmission attenuation value is measured again. The difference in attenuation before and after aging is calculated, which is the transmission attenuation increment. Three fiber samples are tested in each group, and the average value is taken.

[0040] 5. Retention rate of tensile strength after thermo-oxidative aging: The dumbbell-shaped specimens used for tensile property testing are placed in a thermo-oxidative aging chamber at 150℃ for 1000 hours. After being taken out and cooled to room temperature, the tensile strength is retested according to the tensile property testing method described above. The retention rate of tensile strength is calculated by formula: (tensile strength after aging / tensile strength before aging) × 100%.

[0041] The performance test results are shown in Table 1.

[0042] Table 1 Performance Test Results

[0043] As shown in the table above, there is little difference in mechanical properties, thermal stability, dielectric properties, and optical fiber transmission stability among Examples 1-4. Example 4, due to the addition of antioxidants and anti-hydrolysis agents, has the greatest long-term weather resistance and anti-aging ability. Its strength retention rate after thermo-oxidative aging is the highest among the four examples, and its optical fiber transmission attenuation is the smallest under humid and hot conditions. It can meet the needs of conventional use scenarios and is also suitable for harsh service environments such as high temperature and high humidity. It is the optimal choice that takes into account basic performance, long-term stability, and environmental adaptability, unlike the basic examples which can only meet conventional basic needs.

[0044] Comparative Example 1 uses a pure end-group reactive liquid crystal polymer matrix without the addition of three-dimensional hybrid fillers and compatibilizers. The lack of core designs for filler reinforcement and interface modification leads to a significant decrease in the tensile strength and heat distortion temperature of the sheath, resulting in extremely poor mechanical support and high-temperature deformation resistance. At the same time, the dielectric constant of the pure end-group reactive liquid crystal polymer is relatively high, and the matrix is ​​easily degraded after hygrothermal aging, resulting in a sharp increase in fiber transmission attenuation. The performance retention rate after thermo-oxidative aging is extremely low, which fully demonstrates the role of the three-dimensional hybrid filler compound system in improving the overall performance of the sheath.

[0045] Comparative Example 2 uses only CNC@SiO2 core-shell filler, abandoning the functionalized graphene crown modification. Without the interface strengthening and thermal conductivity enhancement effects brought by graphene, the interfacial bonding force between the filler and the matrix is ​​insufficient, and interface debonding and filler agglomeration problems are prone to occur. Not only are the mechanical properties and thermal stability lower than those of Example 1, but micro-defects are also prone to occur inside the sheath under humid and hot conditions, which aggravates the attenuation of optical fiber transmission, highlighting the necessity of the "core-shell-crown" three-dimensional hybrid filler structure.

[0046] Comparative Example 3 eliminated the radial filler gradient distribution design and used a single concentration filler for uniform extrusion. This failed to achieve the performance gradient of inner flexibility and outer rigidity of the sheath. Excessive rigidity of the inner layer easily squeezed the optical fiber, while insufficient strength of the outer layer resulted in poor protection and a significant decline in mechanical properties and thermal stability. At the same time, the lack of gradient control led to large fluctuations in the dielectric properties of the sheath, and the transmission loss increased significantly after humid heat aging. This proves that the radial gradient distribution structure is the key to balancing the flexibility, strength and transmission stability of the sheath.

[0047] Comparative Example 4 uses a common liquid crystal polymer matrix without end-group reactive modification. The matrix molecular chain has no active functional groups and cannot form an effective interface with the three-dimensional hybrid filler. The filler has poor dispersibility and is prone to agglomeration, resulting in weak overall performance of the sheath. In addition, the common liquid crystal polymer has poor processing fluidity and thermal stability compared to the end-group reactive liquid crystal polymer, making it prone to defects during extrusion molding and resulting in low performance retention after thermo-oxidative aging.

[0048] Comparative Example 5, without the addition of silane coupling agent, lacked interfacial coupling modification of the three-dimensional hybrid filler. The filler-matrix interface compatibility was poor, and interfacial separation easily occurred under external force, resulting in a significant decrease in mechanical properties and thermal stability. At the same time, interfacial defects caused fluctuations in dielectric properties, exacerbating optical fiber transmission loss. This indicates that silane coupling agent interfacial modification is a necessary means to ensure uniform filler dispersion and strengthen interfacial bonding.

[0049] Comparative Example 6 eliminated the three-stage gradient cooling process and directly cooled the sheath melt at room temperature, resulting in rapid cooling and the generation of large internal stress. The uneven distribution of crystallinity not only resulted in low elongation at break and impaired mechanical properties, but also made the sheath prone to warping and dimensional deviations. The release of internal stress and micro-defects affected the stability of optical fiber transmission, and the increase in transmission attenuation was higher than that in Example 1, which confirms the importance of the gradient cooling process in eliminating internal stress and improving product stability.

[0050] In summary, this invention effectively addresses the performance shortcomings of existing optical fiber cable sheaths through the synergistic effect of core technologies such as "core-shell-crown" three-dimensional hybrid filler compounding, end-group reactive liquid crystal polymer matrix modification, radial filler gradient distribution, and gradient cooling shaping. Each embodiment balances excellent mechanical properties, thermal stability, low dielectric loss, and high transmission reliability, adapting to the stringent service requirements of space-division multiplexing multi-core optical fibers. Example 4 adds additional antioxidants and anti-hydrolysis agents, further improving the long-term weather resistance and thermo-oxidative aging performance of the sheath, and optimizing the overall service life of the product.

[0051] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details of the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, and these simple modifications all fall within the protection scope of the present invention. Furthermore, it should be noted that the various specific technical features described in the above embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, the present invention will not further describe the various possible combinations.

[0052] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. A space-division multiplexing multi-core optical fiber cable, characterized in that, It includes a multi-core optical fiber unit and a functionally graded sheath layer covering the outside of it. The matrix of the functionally graded sheath layer is an end-group reactive liquid crystal polymer, and the molecular chain ends contain at least one active functional group selected from carboxyl, hydroxyl or epoxy groups. The functionally graded sheath layer contains dispersed three-dimensional hybrid nanofillers, which include a core, an intermediate shell, and an outer crown. The core is a nanocellulose whisker, the intermediate shell is a dense silica shell grown on the surface of the nanocellulose whisker, and the outer crown is a functionalized graphene sheet covalently grafted onto the surface of the silica layer by a silane coupling agent. The functionalized graphene sheet is partially reduced graphene oxide with a carbon-to-oxygen ratio of (4-8):

1. The functionally graded sheath layer extends radially from the inner surface to the outer surface, and the volume fraction of the three-dimensional hybrid nanofiller increases in a gradient, with a volume fraction of 1%-3% on the inner surface and 8%-15% on the outer surface. The increasing gradient of the packing volume fraction satisfies the functional relationship: ,in This refers to the volume fraction of the filler on the inner surface. r represents the volume fraction of the filler on the outer surface. i r0 is the inner diameter of the functionally graded sheath layer, r0 is the outer diameter of the functionally graded sheath layer, and n is the gradient exponent, which takes a value of 0.5-2.

0.

2. The space-division multiplexing multi-core optical fiber cable according to claim 1, characterized in that, The average length of the nanocellulose whiskers is 80-150 nm, and the diameter is 5-15 nm.

3. The space-division multiplexing multi-core optical fiber cable according to claim 1, characterized in that, The silica shell is generated by the sol-gel reaction of tetraethyl orthosilicate on the surface of nanocellulose whiskers, and the silica mass accounts for 8%-15% of the total mass of the three-dimensional hybrid nanofiller.

4. The space-division multiplexing multi-core optical fiber cable according to claim 1, characterized in that, The functionally graded sheath layer also contains 0.5%-1.5% by mass of high molecular weight hindered phenolic antioxidants and 0.3%-1.0% by mass of carbodiimide anti-hydrolysis agents.

5. A method for preparing a space-division multiplexing multi-core optical fiber cable according to any one of claims 1-4, characterized in that, Includes the following steps: (1) A dense silica shell was grown on the surface of nanocellulose whiskers to obtain CNC@SiO2; (2) CNC@SiO2 was dispersed in an organic solvent, a silane coupling agent was added, and the reaction was carried out at 70℃-85℃ for 4-8h. Then, a partially reduced graphene oxide dispersion was added and the reaction was carried out for 12-24h. After centrifugation, washing, and freeze-drying, a three-dimensional hybrid nanofiller was obtained. (3) Mix the three-dimensional hybrid nanofiller, end-group reactive liquid crystal polymer and compatibilizer in a mass ratio of (20-30):(68-79):(1-5), melt blend and extrude granulate to obtain a high-concentration masterbatch with a filler mass fraction of 20%-30%. (4) The end-reactive liquid crystal polymer and high-concentration masterbatch are melted and extruded separately. The extruded melt is compounded by a multi-layer co-extrusion die and extruded onto the outer periphery of the multi-core optical fiber unit to form a functional gradient sheath layer. The extruded cable is shaped by three-stage temperature-controlled cooling and traction to obtain the space-division multiplexing multi-core optical fiber cable.

6. The method for preparing a space-division multiplexed multi-core optical fiber cable according to claim 5, characterized in that, In step (1), the growth of a dense silica shell on the surface of nanocellulose whiskers to obtain CNC@SiO2 includes: Cellulose nanofibers were dispersed in an ethanol / water mixed solvent, the pH was adjusted to 8-10, tetraethyl orthosilicate was added dropwise, and the reaction was carried out at 40℃-60℃ for 6-12 hours. After washing and drying, CNC@SiO2 was obtained.

7. The method for preparing a space-division multiplexed multi-core optical fiber cable according to claim 5, characterized in that, In step (2), before adding the silane coupling agent, there is also an ultrasonic dispersion step, with an ultrasonic power of 200-400W and a dispersion time of 15-30min.

8. The method for preparing a space-division multiplexed multi-core optical fiber cable according to claim 5, characterized in that, In step (4), the end-group reactive liquid crystal polymer and high-concentration masterbatch are melt-extruded separately, and the extruded melt is compounded by a multi-layer co-extrusion die and extruded onto the outer periphery of the multi-core optical fiber unit to form a functionally graded sheath layer, including: The main extruder extrudes end-reactive liquid crystal polymer melt, while the auxiliary extruder extrudes high-concentration masterbatch melt. The extruded melt passes through a multi-layer co-extrusion die with 3-8 independent annular flow channels. The feed rate of the auxiliary extruder is adjusted to control the concentration of each layer of three-dimensional hybrid nanofiller. After the end-reactive liquid crystal polymer melt and the high-concentration masterbatch melt merge at the outlet of the multi-layer co-extrusion die, they partially diffuse to form a functionally graded sheath layer on the outer periphery of the multi-core optical fiber unit.

9. The method for preparing a space-division multiplexed multi-core optical fiber cable according to claim 5, characterized in that, In step (4), the three-stage temperature-controlled cooling traction shaping includes: The first cooling section is an oil bath / high-pressure steam temperature controlled at 160℃-200℃ and 5-15m in length; the second cooling section is a water bath temperature controlled at 80℃-120℃ and 10-30m in length; the third cooling section is a water bath temperature controlled at 15℃-30℃ and 5-10m in length; the traction speed is 5-20m / min.

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