Flame-retardant fiber having a core-hole-shell triple composite structure and a method for preparing the same

Abstract

This invention belongs to the field of polymer composite materials technology and aims to solve the problem that existing flame-retardant fibers cannot simultaneously achieve high-efficiency flame retardancy, heat insulation, good mechanical properties, and processing durability. To this end, this invention provides a flame-retardant fiber with a core-pore-shell triple composite structure and its preparation method. This flame-retardant fiber has a concentric three-layer structure: the core layer contains microencapsulated red phosphorus particles and thermoplastic polyurethane, serving as the core chemical flame-retardant layer; the middle layer covers the core layer and contains aerogel particles, nano-reinforcing fibers, and cross-linked polymers, serving as a physical heat insulation barrier; the outer shell layer covers the middle layer and contains carbon nanotubes and nylon 66, serving as a mechanical support and protective layer. The flame-retardant fiber of this invention achieves synergistic flame retardancy and heat insulation through a three-layer gradient protection design, while also considering multiple functions such as mechanical properties, durability, and antistatic properties.

Description

Technical Field

[0001] This invention relates to the field of polymer composite materials technology, specifically to a flame-retardant fiber with a core-pore-shell triple composite structure and its preparation method. Background Technology

[0002] Flame-retardant fibers are key materials used in special protection, transportation, and public buildings. Existing flame-retardant fiber preparation technologies mainly include blending modification, composite spinning, and finishing processes.

[0003] Blending modification involves directly mixing flame retardants with fiber-forming polymers during spinning. However, this method suffers from drawbacks such as high retardant dosage, easy migration and precipitation from the fiber matrix, and impact on spinning stability and mechanical properties. For example, red phosphorus is a highly efficient flame retardant, but its direct addition not only darkens the fiber color and affects its appearance but also easily migrates due to poor polymer compatibility, potentially even generating toxic gases during processing and use. Composite spinning technologies, such as core-sheath structures, typically concentrate the flame retardant in the sheath layer. While this improves flame retardant efficiency, the flame retardant in the sheath layer is easily lost after repeated washing, leading to insufficient durability of the flame retardant performance. Furthermore, if the physicochemical properties of the core and sheath layers differ significantly, interfacial delamination can easily occur during post-processing such as stretching, resulting in fiber structural damage and functional failure.

[0004] Aerogel, as an excellent thermal insulation material, has also been explored for use in the preparation of thermal insulation fibers. However, aerogel itself has a nanoporous structure, extremely poor flowability, and high brittleness, making it impossible to directly form fibers using traditional melt spinning processes. Existing technologies typically employ impregnation or coating methods to attach it to the fiber surface, but fibers produced in this way suffer from defects such as easy aerogel detachment, poor abrasion resistance, and a stiff feel.

[0005] Therefore, existing technologies still face pressing technical challenges in how to stably integrate highly efficient flame-retardant components and high-performance thermal insulation components into a single fiber while simultaneously ensuring that the fiber possesses excellent mechanical properties, processing performance, and durability. Summary of the Invention

[0006] The purpose of this invention is to provide a flame-retardant fiber with a core-pore-shell triple composite structure and its preparation method, aiming to solve the problem that existing flame-retardant fibers are difficult to simultaneously achieve high flame retardancy, heat insulation, good mechanical properties and processing durability.

[0007] To achieve the above objectives, this invention provides a flame-retardant fiber with a core-pore-shell triple composite structure. The flame-retardant fiber, viewed in cross-section, has a concentric three-layer structure, consisting of the following layers from the inside out: a core layer comprising microencapsulated red phosphorus particles and thermoplastic polyurethane, with the microencapsulated red phosphorus particles dispersed within the thermoplastic polyurethane; a middle layer covering the core layer, comprising aerogel particles, nano-reinforcing fibers, and a cross-linked polymer, with the aerogel particles and nano-reinforcing fibers dispersed within the cross-linked polymer; and an outer shell layer covering the middle layer, comprising carbon nanotubes and nylon 66, with the carbon nanotubes dispersed within the nylon 66. This three-layer structure, through functional division, utilizes the core layer as the core flame-retardant layer, employing the efficient charring effect of red phosphorus to inhibit combustion and dripping; the middle layer as a physical thermal insulation barrier, effectively blocking heat transfer using the nanoporous structure of the aerogel; and the outer shell layer as a mechanical support and protective layer, providing wear resistance, antistatic properties, and other functions. The synergistic effect of these three layers achieves a comprehensive improvement in performance.

[0008] Optionally, the core layer accounts for 20%-30% of the total mass of the flame-retardant fiber, the intermediate layer accounts for 30%-40% of the total mass of the flame-retardant fiber, and the outer shell layer accounts for 40%-50% of the total mass of the flame-retardant fiber. By controlling the mass ratio of each layer, the flame retardancy, heat insulation, and mechanical properties of the fiber can be balanced. For example, appropriately increasing the proportion of the core layer can enhance the charring effect, while ensuring that the outer shell layer has a sufficient proportion helps to maintain the overall strength and abrasion resistance of the fiber.

[0009] Optionally, the core layer further comprises pentaerythritol, a first antioxidant, a lubricant, and zinc borate; in the core layer, by mass percentage: the microencapsulated red phosphorus is 50%-65%, the thermoplastic polyurethane is 28%-40%, the pentaerythritol is 2%-5%, the first antioxidant is 1%-3%, the lubricant is 0.5%-2%, and the zinc borate is 1%-2%, wherein pentaerythritol, as a char-forming aid, synergistically works with the acid source released by the microencapsulated red phosphorus to form a denser char layer; zinc borate, as a smoke suppressant, can effectively suppress the smoke generated during combustion; the first antioxidant and the lubricant are respectively used to improve the thermo-oxidative stability and processing fluidity of the material.

[0010] Optionally, in the intermediate layer, by mass percentage: the aerogel particles comprise 60%-75%, the nano-reinforcing fibers comprise 15%-30%, and the cross-linked polymer comprises 5%-15%. The high content of aerogel particles ensures good thermal insulation performance, while the introduction of nano-reinforcing fibers constructs a three-dimensional network skeleton, significantly improving the mechanical strength and toughness of the intermediate layer and preventing cracking or detachment due to aerogel brittleness. Preferably, the aerogel particles are hydrophobic silica aerogel particles, whose hydrophobicity prevents the fibers from absorbing moisture and causing a decrease in thermal insulation performance; the nano-reinforcing fibers are basalt nanofibers, which have excellent high-temperature resistance and mechanical strength; the cross-linked polymer is an epoxy resin cross-linking cured product or polyimide, which, as a bonding matrix, can firmly fix the aerogel particles and nano-reinforcing fibers in the intermediate layer structure after curing.

[0011] Optionally, the outer shell layer further comprises aluminum diethylphosphinate, a compatibilizer, and a second antioxidant. In the outer shell layer, by mass percentage: 70%-85% nylon 66, 2%-8% carbon nanotubes, 5%-15% aluminum diethylphosphinate, 2%-5% compatibilizer, and 1%-3% second antioxidant. Aluminum diethylphosphinate is a highly efficient halogen-free flame retardant that can play a char-forming role in the condensed phase, forming a synergistic effect with the flame-retardant system of the core layer. Carbon nanotubes not only improve the mechanical strength of the outer shell layer but also construct a conductive network, imparting antistatic properties to the fibers. The compatibilizer improves the interfacial compatibility between the carbon nanotubes, flame retardant, and other fillers and the nylon 66 matrix, preventing agglomeration and ensuring uniform and stable performance. Preferably, the compatibilizer is a maleic anhydride-grafted polyolefin elastomer, which can effectively compatibilize and improve the toughness of the outer shell layer.

[0012] The present invention also provides a method for preparing the aforementioned flame-retardant fiber with a core-pore-shell triple composite structure, the method comprising: S1: Microencapsulated red phosphorus, thermoplastic polyurethane, pentaerythritol, primary antioxidant, and lubricant are mixed and then melt-blended and extruded to obtain the core masterbatch. S2: Aerogel particles, nano-reinforcing fibers, thermosetting resin and curing agent are added to a solvent and dispersed to obtain intermediate layer slurry; S3: Carbon nanotubes, nylon 66, aluminum diethylphosphinate, compatibilizer and second antioxidant are mixed and then melt-blended and extruded to obtain shell masterbatch; S4: Using a three-component composite spinning equipment, the core masterbatch, the intermediate layer slurry and the outer shell masterbatch are respectively fed into a three-layer concentric circle composite spinning assembly, and extruded through a spinneret to form a three-layer composite nascent fiber. S5: The nascent fibers are sequentially stretched and heat-set through multiple stages of hot rollers to obtain finished flame-retardant fibers.

[0013] This method involves preparing the core and shell into melt-processable masterbatches, preparing the non-meltable intermediate layer into slurry, and then combining the three materials with different physical forms and processing characteristics into an integrated three-layer fiber structure through a specially designed composite spinning process.

[0014] Optionally, in step S4, the intermediate layer slurry is delivered by a high-pressure micro-jet metering pump for quantitative injection. During the injection process, the delivery pipeline and storage tank are cooled to control the temperature between 5°C and 50°C. This low-temperature, high-pressure, and precise quantitative injection method helps to prepare an aerogel-containing intermediate layer. It not only solves the problem of poor flowability of aerogel slurry, but also effectively avoids premature evaporation of solvents or pre-curing of thermosetting resins in high-temperature spinning components through low-temperature control, thus ensuring the integrity and uniformity of the intermediate layer structure.

[0015] Optionally, in step S4, the spinning temperature is 260℃-290℃, the spinneret orifice diameter is 0.3mm-0.5mm, and the aspect ratio is 2:1-5:1. A suitable spinning temperature ensures sufficient melting of the core and outer shell masterbatches, while optimized spinneret parameters facilitate the formation of a stable three-layer composite fluid and ensure smooth extrusion. Preferably, a slow-cooling heating zone is provided below the spinneret, with a temperature of 180℃-220℃. This slow-cooling heating zone slows down the cooling rate of the nascent fibers after exiting the spinneret, allowing more time for interfacial fusion between the inner and outer layers, thereby significantly enhancing interlayer bonding and preventing delamination during subsequent stretching.

[0016] Optionally, in step S2, the solid content of the intermediate layer slurry is 15%-30%, and the viscosity is 500-1500 mPa·s. Controlling the solid content and viscosity of the slurry within a specific range is to balance the stability and processability of the slurry. If the solid content is too low, the intermediate layer will have too large a pore or an incomplete structure after fiber forming. If it is too high, the viscosity will be too high and difficult to transport. If the viscosity is too low, it will easily cause particle sedimentation. If it is too high, it will place harsh requirements on the pumping system and result in uneven flow.

[0017] Optionally, in step S5, the multi-stage hot roller stretching and heat setting includes: first-stage stretching: temperature 60℃-100℃, stretching ratio 1.5-2.5 times; second-stage stretching: temperature 130℃-160℃, stretching ratio 1.2-2.0 times; third-stage heat setting: temperature 160℃-190℃, applying 0.5%-5% relaxation shrinkage. The multi-stage stretching process allows for full orientation of the fiber molecular chains, thereby improving mechanical strength. Simultaneously, the staged heating and stretching, especially in the high-temperature zones of the second and third stages, enables simultaneous cross-linking and curing of the thermosetting resin in the intermediate layer and complete solvent evaporation, ultimately forming a stable cross-linked network structure. The final heat setting relaxation treatment helps eliminate internal fiber stress and improve dimensional stability. Attached Figure Description

[0018] The features and advantages of the invention will be more clearly understood by referring to the accompanying drawings, which are schematic and should not be construed as limiting the invention in any way. In the drawings: Figure 1 This is a schematic diagram of the cross-sectional structure of the flame-retardant fiber according to an embodiment of the present invention; Figure 2 This is a flowchart of the method for preparing flame-retardant fibers according to an embodiment of the present invention. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] Before providing a further detailed description of the embodiments of the present invention, the nouns and terms involved in the embodiments of the present invention are explained, and the nouns and terms involved in the embodiments of the present invention are subject to the following interpretations: The core-pore-shell triple composite structure refers to a three-layer concentric circle composite structure consisting of an inner core layer, an intermediate layer, and an outer shell layer from the inside out. This structure achieves a gradient distribution and synergistic effect of multiple functions such as chemical flame retardancy, physical heat insulation, and mechanical reinforcement by encapsulating components with different functions in specific layers. It aims to solve the problem of traditional flame retardant fibers having single performance and difficulty in achieving multiple indicators.

[0021] Microencapsulated red phosphorus particles: These are micron-sized particles formed by coating red phosphorus particles, which have high flame retardant efficiency but are chemically active, with polymer materials. The purpose is to passivate the activity of red phosphorus, prevent it from reacting with moisture or oxygen in the air to generate toxic gases during processing and use, and at the same time improve its compatibility with the polymer matrix and reduce its negative impact on the mechanical properties of fibers.

[0022] Aerogel particles are solid material particles with a nanoporous network structure, extremely high porosity, and extremely low density. In this invention, their core function is to use the large number of nanoscale pores inside to bind air, greatly reducing the conduction of heat through solid and gas convection, thereby building a highly efficient physical thermal insulation barrier in the middle layer of the fiber.

[0023] Nanofibers: These are fibrous materials with a diameter typically less than 1000 nm and an extremely high aspect ratio. In this invention, they are introduced into an intermediate layer composed of aerogel particles and cross-linked polymers as a reinforcing skeleton to overcome the brittleness of aerogel materials, improve the mechanical strength and toughness of the intermediate layer, and ensure the structural integrity of the fibers during stretching and use.

[0024] Crosslinked polymer: refers to a polymeric material formed by a three-dimensional network structure through a chemical reaction of linear or branched thermosetting resin precursors (such as epoxy resin and polyimide precursors used in this invention) under thermal action. In the intermediate layer of this invention, it acts as a binder to firmly fix the dispersed aerogel particles and nano-reinforcing fibers together, forming a structurally stable, solvent-resistant, and high-temperature resistant composite layer.

[0025] Carbon nanotubes are a type of one-dimensional quantum material with a special structure, consisting of hexagonal grids of carbon atoms that are rolled up. In the outer shell layer of this invention, their main function is to utilize their excellent conductivity to construct a conductive network, giving the fiber antistatic properties. At the same time, their extremely high mechanical strength can also reinforce the nylon matrix and assist in the formation of a denser carbon layer during combustion.

[0026] Masterbatch: refers to high-concentration granular material made by pre-mixing various additives (such as flame retardants, pigments, antioxidants, etc.) with carrier resin and extruding them into granules in plastic or fiber processing for ease of operation. Using masterbatch can improve the dispersion uniformity of additives, increase production efficiency, and avoid dust pollution.

[0027] like Figure 1As shown, this embodiment of the invention provides a flame-retardant fiber with a core-pore-shell triple composite structure, which solves the problem that existing flame-retardant fibers are difficult to simultaneously achieve high flame retardancy, good mechanical properties, thermal insulation, and durability. Viewed from its cross-section perpendicular to the axial direction, the flame-retardant fiber exhibits a concentric three-layer structure, consisting of a core layer 101, a middle layer 102, and an outer shell layer 103, from the inside out.

[0028] Specifically, the innermost core layer 101 is the chemical flame-retardant core of the fiber. This core layer 101 contains microencapsulated red phosphorus particles and thermoplastic polyurethane as the matrix. Structurally, a large number of microencapsulated red phosphorus particles are uniformly distributed in the continuous phase of the thermoplastic polyurethane matrix in the form of a dispersed phase, encapsulating the highly efficient phosphorus-based flame retardant in the core region of the fiber. When the fiber encounters flames or high temperatures, the core layer 101 will serve as the main chemical reaction center. Encasing the core layer 101 is the intermediate layer 102, whose main function is to act as a physical thermal insulation barrier. This intermediate layer 102 contains aerogel particles, nano-reinforcing fibers, and cross-linked polymers. Among them, the aerogel particles have extremely low thermal conductivity, and the nano-reinforcing fibers are used to enhance the structural strength. The fibers are dispersed and fixed in a cross-linked polymer within a three-dimensional network structure. This unique pore-skeleton composite structure allows the intermediate layer 102 to possess both excellent thermal insulation properties and sufficient mechanical strength to withstand the stresses of spinning stretching and daily use. The outermost shell layer 103 covers the outside of the intermediate layer 102, forming the protective shell and mechanical support of the fiber. This shell layer 103 contains carbon nanotubes and nylon 66 as the matrix. The carbon nanotubes are uniformly dispersed at the nanoscale within the nylon 66 matrix, forming a conductive and reinforcing network. The shell layer 103 is in direct contact with the external environment, and its high strength and wear resistance ensure the fiber's durability. This three-layer structure achieves a precise gradient division of labor and... In a synergistic manner, the core layer 101 plays a major role in chemical flame retardancy, the intermediate layer 102 acts as a physical heat insulation barrier, and the outer shell layer 103 provides mechanical reinforcement and protection. When the flame-retardant fiber of this invention is attacked by an external flame or heat source, the outermost shell layer 103 carbonizes upon contact with the heat source, forming a preliminary barrier. As heat is transferred inward, the porous intermediate layer 102 exerts its excellent physical heat insulation effect, greatly slowing down the speed and intensity of heat reaching the core layer, providing a time window for the chemical reaction in the core layer. When sufficient heat penetrates the intermediate layer 102, the microencapsulated red phosphorus particles in the core layer 101 decompose upon heating, releasing acidic substances such as phosphoric acid. These substances act as dehydration catalysts, promoting the dehydration of the surrounding thermoplastic polyurethane groups. The body undergoes a violent dehydration and char formation reaction, forming a fluffy and dense expanded char layer, i.e., the core layer expands into char. This process not only consumes a large amount of heat, but the expanded char layer also fills the voids that may be generated by polymer melting, and together with the char layer formed by the outer shell layer 103, it constructs a complete and denser char layer barrier. The resulting multi-layer composite char layer barrier can effectively isolate heat and oxygen, prevent the further spread of flame and the continued combustion of the matrix material, and effectively suppress the generation of molten droplets. Through this step-like, multi-mechanism synergistic flame-retardant process of initial carbonization of the outer shell, heat insulation of the middle layer, and expansion of the core layer into char, the flame-retardant fiber of the present invention achieves higher flame-retardant efficiency and safety compared to traditional single flame-retardant fiber.

[0029] This invention also provides a method for preparing the above-mentioned flame-retardant fiber, the process of which is as follows: Figure 2 As shown. This method aims to solve the technical challenge of integrating multiple components with vastly different physical properties (such as melting point and flowability), especially non-melting, brittle aerogel materials, into a single continuous fiber.

[0030] This method mainly includes: S1: Preparation of kernel masterbatch; S2: Preparation of intermediate layer slurry; S3: Preparation of shell masterbatch; S4: Three-component composite spinning; S5: Post-processing, finally obtaining the finished flame-retardant fiber.

[0031] In step S1: In the preparation of the core masterbatch, the components used to form the core layer 101, namely microencapsulated red phosphorus, thermoplastic polyurethane, pentaerythritol, first antioxidant, and lubricant, are physically premixed. Then, the mixture is fed into a melt blending device (such as a twin-screw extruder) and sheared and mixed in a heated and molten state to make the components uniformly dispersed. Finally, it is extruded through a die and pelletized to obtain a solid core masterbatch. The purpose of this step is to pre-disperse powdered red phosphorus and other additives in the polymer matrix to facilitate accurate metering and stable delivery in the subsequent spinning process.

[0032] In step S2, during the preparation of the intermediate layer slurry, since the key components of the intermediate layer 102—aerogel particles and nanofibers—cannot be melted, a wet process is employed. The aerogel particles, nanofibers, a thermosetting resin (i.e., a precursor to a cross-linked polymer), and a curing agent are added to a suitable solvent. Through high-energy dispersion methods (such as sand milling and high-speed shearing), the solid particles are uniformly suspended in the liquid, forming an intermediate layer slurry with specific solid content and viscosity. This step transforms the non-meltable thermal insulation material into a flowable liquid form, making subsequent composite spinning possible.

[0033] In step S3: Preparation of the outer shell masterbatch, similar to the preparation of the core masterbatch, the components used to form the outer shell layer 103, namely carbon nanotubes, nylon 66, aluminum diethylphosphinate, compatibilizer and second antioxidant, are prepared into a solid outer shell masterbatch by melt blending extrusion granulation. This step is also to ensure the uniform dispersion of each component in the final fiber. In particular, for carbon nanotubes that are prone to agglomeration, masterbatch technology can achieve better dispersion effect.

[0034] In step S4: In the three-component composite spinning, the three materials prepared in the first three steps—solid core masterbatch, liquid intermediate layer slurry, and solid outer shell masterbatch—are simultaneously introduced into a three-component composite spinning device. This composite spinning device has three independent inlets, corresponding to the core masterbatch inlet, the intermediate layer slurry inlet, and the outer shell masterbatch inlet, respectively. The three materials are guided and converged inside the device through a three-layer concentric circle distribution plate to form a coaxial three-layer composite melt / slurry flow. Subsequently, the composite flow is extruded together from the micropores of the spinneret, forming a nascent fiber with a three-layer structure at the moment it leaves the spinneret.

[0035] In step S5: post-processing, the newly formed nascent fibers are still soft and have poor mechanical properties. A series of post-processing operations are performed to impart their final physical and mechanical properties. The nascent fibers are guided through a stretching and heat-setting system composed of multiple sets of hot rollers. The fibers are pulled between hot rollers at different temperatures and speeds (such as the feed roller, first-stage stretching roller, second-stage stretching roller, and heat-setting roller), undergoing multi-stage stretching and heat setting. This process not only orients the polymer chains in the fibers, significantly improving their strength, but also promotes the cross-linking reaction of the heat-curable resin in the intermediate slurry, forming a stable cross-linked polymer and completely evaporating the solvent. Finally, the post-processed fibers are collected by a winding device to obtain finished fibers with good overall properties.

[0036] In a preferred embodiment, the mass ratio of the three layers is optimized to achieve synergistic effects among the functional layers. Specifically, the core layer 101 accounts for 20%-30% of the total mass of the flame-retardant fiber, the middle layer 102 accounts for 30%-40%, and the outer shell layer 103 accounts for 40%-50%. This ratio is a result of comprehensive balance. For example, when the core layer 101 accounts for 30%, the limiting oxygen index and charring performance of the fiber are good, but some mechanical properties may be slightly sacrificed; while when its proportion is 20%, more space is left for the outer shell layer with stronger mechanical properties while ensuring sufficient flame retardancy; similarly, adjusting the proportion of the outer shell layer 103 between 40%-50% can achieve a balance between the strength, abrasion resistance, and overall flame-retardant and heat-insulating performance of the fiber; a higher proportion of the outer shell layer (such as 50%) can provide stronger mechanical protection and durability, suitable for scenarios with high abrasion resistance requirements.

[0037] In the above, pentaerythritol provides a rich carbon source when heated, forming an efficient acid-carbon source expansion flame retardant system with the phosphoric acid produced by the decomposition of microencapsulated red phosphorus, significantly improving the amount and strength of the char layer. The primary antioxidant is used to prevent thermo-oxidative degradation of thermoplastic polyurethane during high-temperature melt processing, ensuring the intrinsic quality of the fiber. The lubricant can improve the fluidity of the melt, reduce processing torque, and protect the integrity of the red phosphorus microcapsules. Zinc borate can promote the cross-linking of the char layer during combustion and capture smoke particles, reducing the release of toxic and harmful fumes.

[0038] In the core layer 101, which contains various additives, the mass percentages of each component have been optimized. In a specific example, the content of microencapsulated red phosphorus is 50%-65%, thermoplastic polyurethane is 28%-40%, pentaerythritol is 2%-5%, the primary antioxidant is 1%-3%, the lubricant is 0.5%-2%, and zinc borate is 1%-2%. This formulation ensures sufficient red phosphorus as the core flame retardant, while the addition of pentaerythritol is sufficient to create a synergistic effect, and the content of other additives maximizes their auxiliary functions without significantly affecting the main performance.

[0039] In another preferred embodiment, the composition and material selection of the interlayer 102 are specifically defined. By mass percentage, the aerogel particles comprise 60%-75%, the nanofibers comprise 15%-30%, and the crosslinked polymer comprises 5%-15%. This high-solids-content formulation aims to maximize the thermal insulation and reinforcement effects of the interlayer. The aerogel particles, as the main component, ensure an extremely low thermal conductivity; the 15%-30% nanofibers act as a mechanical support network, constructing a mechanical support network in the aerogel composite material to prevent breakage or delamination during stretching; and the 5%-15% crosslinked polymer acts as a bonding matrix, firmly bonding the former two components into a single unit.

[0040] Preferably, the aerogel particles are hydrophobic silica aerogel particles. Silica aerogel is chosen because it has high temperature resistance, and hydrophobic modification (e.g., through methylation) prevents the fibers from absorbing moisture during use or washing, avoiding a sharp decline in thermal insulation performance due to moisture filling the pores, thus ensuring the durability of the fiber's performance. Meanwhile, preferably, the nano-reinforcing fibers are basalt nanofibers. Basalt fiber is a high-performance inorganic fiber with high strength, high modulus, excellent temperature resistance and chemical stability, and relatively low cost, making it an ideal nano-reinforcing material. Furthermore, the crosslinking polymer is preferably an epoxy resin crosslinking cured product or polyimide. Both polymers are known for their excellent heat resistance, mechanical properties, and good adhesion to inorganic fillers, ensuring the structural stability of the interlayer under high temperature and stress.

[0041] In the above, aluminum diethylphosphonate (ADP) has flame retardant effects in both the gas phase and the condensed phase, and can form a synergistic flame retardant effect with the red phosphorus system in the core layer, further improving the overall flame retardant level of the fiber. The addition of the compatibilizer is to solve the problem of easy agglomeration of carbon nanotubes in the nylon 66 matrix. By improving the interfacial compatibility, the carbon nanotubes can be more uniformly dispersed, thereby more effectively exerting their conductivity and reinforcing effects. The second antioxidant is used to protect the performance stability of the nylon 66 matrix during high-temperature spinning and long-term use.

[0042] In a specific outer shell formulation, by mass percentage, nylon 66 comprises 70%-85%, carbon nanotubes 2%-8%, aluminum diethylphosphinate 5%-15%, compatibilizer 2%-5%, and secondary antioxidant 1%-3%. This formulation, while ensuring that nylon 66 provides good mechanical properties as the matrix, achieves a balance of multiple functions such as flame retardancy, antistatic properties, and reinforcement through the compounding of various additives. Preferably, the compatibilizer is maleic anhydride-grafted polyolefin elastomer (POE-g-MAH). The maleic anhydride functional groups of this compatibilizer can react with the terminal amino groups of nylon 66 and the surface-treated carbon nanotubes to form chemical bonds, greatly enhancing the interfacial bonding force; while its polyolefin elastomer segments can improve the toughness of the outer shell.

[0043] In step S2, which involves preparing the intermediate layer slurry, a preferred approach is to control the slurry's solid content to be 15%-30% and its viscosity to be 500-1500 mPa·s. This parameter range is crucial for achieving stable spinning. If the solid content is too low, a large amount of solvent needs to be evaporated during spinning, which can easily lead to fiber structure collapse or the formation of voids; if the solid content is too high, the slurry will have poor fluidity, making it difficult to transport and inject evenly. Similarly, if the viscosity is too low, the slurry will be unstable in the composite flow, easily leading to mixing or flow interruption; if the viscosity is too high, it will put enormous pressure on the metering pump and make it difficult to form a uniform annular layer.

[0044] In step S4 of the composite spinning process, preferably, a high-pressure micro-jet metering pump is used to quantitatively inject the intermediate layer slurry. This pump provides a stable and precise micro-flow rate, ensuring a uniform thickness of the fine intermediate layer. Simultaneously, the delivery pipeline and storage tank are cooled during injection, with the temperature controlled between 5°C and 50°C. This measure is crucial because the intermediate layer slurry contains heat-curable resin and curing agent. Excessive temperature may cause the resin to pre-cur before entering the spinning assembly, clogging the pipeline or affecting the final cross-linking effect. Low-temperature control ensures the stability and flowability of the slurry before spinning.

[0045] Similarly, in step S4, preferably, the spinning temperature is controlled at 260℃-290℃. This temperature is necessary to ensure that the masterbatch of the core layer and the outer shell layer can be fully melted to form a melt with good fluidity, but it cannot be too high to prevent degradation of the polymer and flame retardant. The orifice diameter of the spinneret is preferably 0.3mm-0.5mm, and the aspect ratio is 2:1-5:1. The orifice diameter determines the initial diameter of the nascent fiber, while a suitable aspect ratio helps the melt flow stably before extrusion, eliminates the elastic memory effect, and improves forming stability. More preferably, a slow cooling heating zone is set below the spinneret, and its temperature is controlled at 180℃-220℃. The existence of this zone prevents the newly extruded three-layer composite fiber from being immediately and rapidly cooled by cold air, but instead keeps it at a higher temperature for a short time. This slow cooling time greatly promotes the diffusion of molecular chains and physical entanglement between the three interfaces of the core, intermediate layer, and outer shell layer, ensuring a strong bond between the three layers and effectively preventing delamination during subsequent high-ratio stretching.

[0046] In post-processing step S5, in a preferred embodiment, the process includes: a first-stage stretching, performed at a lower temperature of 60℃-100℃ with a stretch ratio of 1.5-2.5, primarily aimed at initially inducing the orientation of amorphous molecular chains; a second-stage stretching, performed at a higher temperature of 130℃-160℃ with a stretch ratio of 1.2-2.0, where the molecular chain segment mobility is enhanced and the orientation degree is further improved, and this temperature also begins to activate the cross-linking reaction of the thermosetting resin in the intermediate layer; and a third-stage heat setting, performed at an even higher temperature of 160℃-190℃, where no large stretching is applied, but rather a small amount of relaxation shrinkage of 0.5%-5%, the main purpose of which is to further improve the crystalline structure of the fiber at high temperatures, eliminate the internal stress generated by stretching, and ensure the complete cross-linking reaction of the intermediate layer, ultimately obtaining a finished fiber with stable dimensions, high strength, and moderate elongation.

[0047] In one specific embodiment, the present invention provides a finished flame-retardant fiber. The diameter of the fiber can be controlled within the range of 18-25 μm. Scanning electron microscopy reveals a clear three-layer structure in its cross-section: a core layer approximately 4-6 μm thick, a middle layer approximately 3-5 μm thick, and an outer shell approximately 10-15 μm thick. Performance testing shows that the fiber's limiting oxygen index (LOI) can reach over 40%. In vertical burning tests, it achieves the UL94 standard V-0 rating, meaning it self-extinguishes rapidly after being removed from the flame without producing molten drips. Thanks to the aerogel structure of the middle layer, its radial thermal conductivity is as low as below 0.028 W / (m·K), exhibiting excellent thermal insulation performance. Simultaneously, its mechanical properties are also excellent, with a tensile strength of not less than 4.8 cN / dtex and an elongation at break between 25% and 35%, combining strength and toughness. Due to the presence of carbon nanotubes in the outer shell, its volume resistivity is below 1 × 10⁻⁶. 8 With a strength of Ω·cm, this fiber exhibits excellent antistatic properties. More importantly, it demonstrates outstanding wash resistance; after 50 standard washing cycles, its limiting oxygen index remains above 38%, showcasing its functional durability.

[0048] The technical solution of the present invention will be fully demonstrated through a specific embodiment below. This embodiment aims to prepare a flame-retardant fiber with a core-pore-shell triple composite structure and good comprehensive performance.

[0049] Firstly, regarding the material composition, the overall weight of this fiber is divided into: a core layer of 25%, a middle layer of 35%, and an outer shell of 40%. The core layer 101 specifically consists of: 60% by weight of melamine resin-coated microencapsulated red phosphorus, and 33% by weight of thermoplastic polyurethane (BASF). The intermediate layer 102 consists of: 70% hydrophobic silica aerogel with a particle size of 5-10 μm, 20% basalt nanofibers with a diameter of 150 nm and surface-treated with KH-560 silane coupling agent, and 10% waterborne epoxy resin and latent curing agent (based on solids); the outer shell layer 103 consists of: 78% nylon 66 (model Shenma EPR27), 3% carboxylated multi-walled carbon nanotubes, 12% aluminum diethylphosphinate, 4% POE-g-MAH compatibilizer, and 3% antioxidant 1098 / 168 composite.

[0050] Secondly, the fiber is prepared using the following process: Step S1: The components of the core layer are mixed evenly in a high-speed mixer, then fed into a twin-screw extruder. The temperature distribution is set at 130℃, 170℃, 190℃, 200℃, and 195℃. The mixture is melt-blended in low-shear mode, extruded and granulated, and finally vacuum-dried at 80℃ for 8 hours to obtain the core masterbatch. Step S2: The components of the intermediate layer are added to an ethanol solvent and dispersed through a two-stage process of sand milling and high-speed shearing to prepare a uniform slurry with a solid content of 25% and a viscosity of 800 mPa·s at 25℃. Step S3: The outer shell masterbatch is prepared using a two-step method. First, 20% carbon nanotubes and 80% POE-g-MAH are mixed to form a high-concentration masterbatch. Then, this masterbatch is diluted and blended with the remaining components, such as nylon 66 and aluminum diethylphosphinate, at 260℃. Extrusion granulation at 285℃; Step S4: Feed the three materials into the composite spinning machine, set the spinning component temperature to 285℃, the spinneret orifice diameter to 0.4mm, the length-to-diameter ratio to 4:1, the core masterbatch and the outer shell masterbatch are melted and conveyed by the screw, while the intermediate layer slurry is injected at a low temperature of 10℃ by a high-pressure metering pump, and the temperature of the slow cooling zone below the spinneret is set to 200℃; Step S5: Perform four-stage hot roller post-treatment on the extruded nascent fiber, the first stage feed roller speed is 800m / min; the second stage stretching roller temperature is 90℃, speed is 1600m / min, achieving 2.0 times stretching; the third stage stretching roller temperature is 150℃, speed is 2400m / min, achieving 1.5 times stretching; the fourth stage heat setting roller temperature is 180℃, speed is about 2350m / min, about 2% relaxation is applied, and finally the finished fiber is wound.

[0051] Through the aforementioned material formulation and process control, the fiber obtained in this embodiment exhibits excellent comprehensive properties. Testing revealed a limiting oxygen index as high as 41%, a thermal conductivity as low as 0.024 W / (m·K), a breaking strength of 5.2 cN / dtex, and a volume resistivity of 5 × 10⁻⁶. 7 The LOI value remains at 40% even after 50 washes, with almost no degradation. This result fully demonstrates that the present invention integrates multiple excellent properties such as high flame retardancy, good thermal insulation, high mechanical strength, antistatic properties, and washability through the precise selection of materials in each layer, the optimization of the component ratios, and the synergistic control of various preparation process parameters.

[0052] In summary, the beneficial effects of the present invention are as follows: 1. Achieves synergistic flame retardancy and heat insulation: Through a triple-gradient protection design of core chemical charring + intermediate layer physical heat insulation + outer shell synergistic flame retardancy, the fiber can quickly form a dense char layer barrier when exposed to fire, while effectively blocking heat transfer to the interior. The limiting oxygen index (LOI) can reach more than 40%, and the radial thermal conductivity is low, achieving a unity of flame retardancy and heat insulation performance. 2. A method for composite processing of heterogeneous materials is provided: through a three-component composite spinning process of masterbatch and slurry, especially the low-temperature and high-pressure injection technology of the intermediate slurry, aerogel that cannot be melted and processed is uniformly and stably composited inside the fiber, forming a complete core-pore-shell structure, providing a feasible technical path for the use of aerogel in spinning; 3. It combines good mechanical properties and durability: The nano-reinforcing fibers in the middle layer and the carbon nanotubes in the outer shell effectively enhance the mechanical strength of the fiber, making its breaking strength no less than that of traditional fibers; at the same time, the functional components are encapsulated inside the fiber, avoiding loss due to washing and friction, giving the fiber water resistance and durability. 4. Multifunctional integration: The carbon nanotubes in the outer shell endow the fiber with good antistatic properties, broadening its application scenarios in electronics, precision instruments and other fields.

[0053] Furthermore, the flame-retardant fiber provided by this invention has application potential in multiple fields due to its excellent comprehensive properties: In the aerospace field, interior materials such as seat fabrics, carpets, and partition curtains inside aircraft have extremely high requirements for flame retardancy and lightweighting. The high LOI value and low heat release rate of the fiber of this invention can effectively suppress the spread of fire, and its good thermal insulation performance helps to maintain stable cabin temperature. At the same time, its high strength characteristics are in line with the trend of lightweight design.

[0054] In the fields of military protection and public safety, the fiber of this invention can be used to manufacture fire-fighting suits, training uniforms, and explosion-proof blankets. Its excellent heat insulation properties can protect firefighters from the high temperature heat waves during deflagration, and its non-dripping properties avoid secondary burns to the skin. When applied to seat fabrics and curtains of public transportation such as subways and high-speed trains, it can significantly improve the fire safety level of public spaces.

[0055] In the field of industrial production protection, especially for workers in industries such as welding, metallurgy, and chemicals, their work clothes need to have the functions of flame retardancy, heat insulation, wear resistance, and antistatic properties. The multifunctional integrated characteristics of the fiber of this invention can meet these needs, provide safety protection for workers, and avoid injuries caused by sparks, molten metal splashes, or static electricity ignition.

[0056] The fiber of this invention also has potential in the high-end civilian textile market. For example, it can be used to manufacture flame-retardant curtains, carpets and decorative fabrics for high-end hotels and public places, as well as pajamas for the elderly and children where safety requirements are extremely high. Its soft hand feel and good mechanical properties improve the comfort of the fabric and help to balance safety protection and comfort.

[0057] It should be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0058] The various embodiments in this invention are described in a progressive manner. Similar or identical parts between embodiments can be referred to mutually. Each embodiment focuses on describing the differences from other embodiments. In particular, the system embodiments are basically similar to the method embodiments, so the description is relatively simple; relevant parts can be referred to the descriptions in the method embodiments.

[0059] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of this disclosure is limited to these examples; within the framework of this disclosure, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of different aspects of one or more embodiments of the present invention as described above, which are not provided in detail for the sake of brevity.

[0060] Although this disclosure has been described in conjunction with specific embodiments thereof, many substitutions, modifications and variations of these embodiments will be apparent to those skilled in the art from the foregoing description.

[0061] One or more embodiments of the present invention are intended to cover all such substitutions, modifications, and variations that fall within the scope of protection of the present invention. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of one or more embodiments of the present invention should be included within the scope of protection of this disclosure.

Claims

1. A flame-retardant fiber having a core-pore-shell triple composite structure, characterized in that, The flame-retardant fiber, viewed in cross-section, has a concentric three-layer structure, consisting of the following layers from the inside out: The core layer comprises microencapsulated red phosphorus particles and thermoplastic polyurethane, wherein the microencapsulated red phosphorus particles are dispersed in the thermoplastic polyurethane. An intermediate layer, which covers the core layer, comprises aerogel particles, nanofibers, and a cross-linked polymer, wherein the aerogel particles and nanofibers are dispersed in the cross-linked polymer; An outer shell layer, which covers the intermediate layer, comprises carbon nanotubes and nylon 66, wherein the carbon nanotubes are dispersed in the nylon 66.

2. The flame retardant fiber having a core-pore-shell triple composite structure according to claim 1, wherein, The core layer accounts for 20%-30% of the total mass of the flame-retardant fiber, the intermediate layer accounts for 30%-40% of the total mass of the flame-retardant fiber, and the outer shell layer accounts for 40%-50% of the total mass of the flame-retardant fiber.

3. The flame-retardant fiber with a core-pore-shell triple composite structure according to claim 1, characterized in that, The core layer also includes pentaerythritol, a first antioxidant, a lubricant, and zinc borate; In the core layer, by mass percentage: 50%-65% microencapsulated red phosphorus, 28%-40% thermoplastic polyurethane, 2%-5% pentaerythritol, 1%-3% of the first antioxidant, 0.5%-2% of the lubricant, and 1%-2% of the zinc borate.

4. The flame-retardant fiber with a core-pore-shell triple composite structure according to claim 1, characterized in that, In the intermediate layer, by mass percentage: aerogel particles 60%-75%, nano-reinforcing fibers 15%-30%, and cross-linked polymer 5%-15%; Preferably, the aerogel particles are hydrophobic silica aerogel particles, the nano-reinforcing fibers are basalt nanofibers, and the crosslinking polymer is an epoxy resin crosslinking curing product or polyimide.

5. The flame-retardant fiber with a core-pore-shell triple composite structure according to claim 1, characterized in that, The outer shell layer also includes aluminum diethylphosphinate, a compatibilizer, and a second antioxidant; In the outer shell layer, by mass percentage: 70%-85% nylon 66, 2%-8% carbon nanotubes, 5%-15% aluminum diethylphosphinate, 2%-5% compatibilizer, and 1%-3% second antioxidant; Preferably, the compatibilizer is a maleic anhydride-grafted polyolefin elastomer.

6. A method for preparing a flame-retardant fiber having a core-pore-shell triple composite structure as described in any one of claims 1 to 5, characterized in that, The preparation method includes: S1: Microencapsulated red phosphorus, thermoplastic polyurethane, pentaerythritol, primary antioxidant, and lubricant are mixed and then melt-blended and extruded to obtain the core masterbatch. S2: Aerogel particles, nano-reinforcing fibers, thermosetting resin and curing agent are added to a solvent and dispersed to obtain intermediate layer slurry; S3: Carbon nanotubes, nylon 66, aluminum diethylphosphinate, compatibilizer and second antioxidant are mixed and then melt-blended and extruded to obtain shell masterbatch; S4: Using a three-component composite spinning equipment, the core masterbatch, the intermediate layer slurry and the outer shell masterbatch are respectively fed into a three-layer concentric circle composite spinning assembly, and extruded through a spinneret to form a three-layer composite nascent fiber. S5: The nascent fibers are sequentially stretched and heat-set through multiple stages of hot rollers to obtain finished flame-retardant fibers.

7. The method for preparing flame-retardant fiber with a core-pore-shell triple composite structure according to claim 6, characterized in that, In step S4, the intermediate layer slurry is delivered by a high-pressure micro-jet metering pump for quantitative injection. During the injection process, the delivery pipeline and storage tank are cooled to control the temperature between 5℃ and 50℃.

8. The method for preparing flame-retardant fiber with a core-pore-shell triple composite structure according to claim 6, characterized in that, In step S4, the spinning temperature is 260℃-290℃, the orifice diameter of the spinneret is 0.3mm-0.5mm, and the aspect ratio is 2:1-5:1; Preferably, a slow-cooling heating zone is provided below the spinneret, and the temperature of the slow-cooling zone is 180℃-220℃.

9. The method for preparing flame-retardant fiber with a core-pore-shell triple composite structure according to claim 6, characterized in that, In step S2, the solid content of the intermediate layer slurry is 15%-30%, and the viscosity is 500-1500 mPa·s.

10. The method for preparing flame-retardant fiber with a core-pore-shell triple composite structure according to claim 6, characterized in that, In step S5, the multi-stage hot roller stretching and heat setting includes: First stage of tensile testing: temperature 60℃-100℃, stretching ratio 1.5-2.5 times; Second-stage tensile testing: temperature 130℃-160℃, tensile ratio 1.2-2.0 times; Third-stage stretching: Temperature 160℃-190℃, apply 0.5%-5% relaxation contraction.

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