Polyacrylonitrile-based pre-oxidized fiber and preparation method thereof, multifunctional composite fabric

Abstract

The application discloses a kind of multifunctional composite fabric based on gradient pre-oxidized yarn and its preparation method, belong to functional textile material technical field.The present application aims at solving the problems of poor mechanical properties, single function and difficulty in effectively integrating electromagnetic shielding and infrared stealth of traditional pre-oxidized yarn fabric.The scheme realizes the integration of mechanical properties, electromagnetic shielding and infrared stealth through the synergistic design of gradient pre-oxidation process and in-situ composite of functional filler, builds gradient structure with increasing cyclization degree in the fiber, and in-situ composites carbon nanotubes and nano zinc oxide in the fiber matrix, realizes the integration of mechanical properties, electromagnetic shielding and infrared stealth.The obtained fabric has high efficient X-band electromagnetic shielding efficiency and excellent infrared stealth performance.The scheme has clear process parameters, strong designability, has the potential of large-scale production, and can be widely used in special protective clothing, military camouflage equipment and electronic equipment shielding fields.

Description

Technical Field

[0001] This application relates to the field of functional textile materials technology, and in particular to a polyacrylonitrile-based pre-oxidized fiber and its preparation method, and a multifunctional composite fabric; specifically, it relates to a polyacrylonitrile-based pre-oxidized filament and its application in the preparation of high-performance flame-retardant, heat-insulating, electromagnetic shielding, and infrared stealth multifunctional integrated composite fabrics, which are particularly suitable for special protection, military camouflage and electronic security fields. Background Technology

[0002] Polyacrylonitrile pre-oxidized filament, as a precursor to carbon fiber, has been explored for application in protective clothing and thermal insulation materials due to its inherent flame retardancy, heat resistance, and chemical stability. Typically, polyacrylonitrile pre-oxidized fiber is a black fiber material prepared by oxidizing polyacrylonitrile fibers in air at a specific temperature. However, pre-oxidized filaments and fabrics prepared using traditional homogeneous pre-oxidation processes have significant limitations, including: the pursuit of high flame retardancy often leads to increased fiber brittleness and a significant decrease in mechanical properties, affecting durability and wearing comfort; its function is mostly limited to single passive flame retardancy or thermal insulation, making it difficult to effectively integrate multifunctional modern needs such as electromagnetic shielding without sacrificing the main performance characteristics.

[0003] In existing technologies, functional fillers are typically added through finishing coatings or simple blending to achieve multifunctional fiber fabrics. However, this often leads to the functional layers being prone to peeling off or becoming uneven, resulting in poor durability and mutual constraints between the various properties. Summary of the Invention

[0004] To address the shortcomings of existing technologies that struggle to balance mechanical properties and multifunctionality in pre-oxidized fiber fabrics, this invention aims to provide a polyacrylonitrile-based pre-oxidized fiber, its preparation method, and a multifunctional composite fabric. Based on the provided polyacrylonitrile-based pre-oxidized fiber, the fabric can simultaneously achieve excellent mechanical properties, high flame retardancy, and efficient electromagnetic shielding, resolving the contradiction between functional integration and durability.

[0005] This application provides a method for preparing polyacrylonitrile-based pre-oxidized fibers, comprising the following steps:

[0006] S1. Polyacrylonitrile powder is dissolved in a solvent to obtain a matrix solution, which is then mixed with carbon nanotubes and nano zinc oxide and dispersed to obtain a composite spinning solution.

[0007] S2. The composite spinning solution is wet-spun and then solidified to obtain nascent fibers.

[0008] S3. The nascent fibers are first subjected to a first-stage oxidation treatment in an oxygen-containing atmosphere below 210°C, and then subjected to a second-stage oxidation treatment in a phosphorus-containing and oxygen-containing atmosphere above 230°C to obtain polyacrylonitrile-based pre-oxidized fibers.

[0009] Preferably, in step S1, the intrinsic viscosity of the polyacrylonitrile powder is 1.4-1.8 dL / g; and the solvent is N,N-dimethylformamide.

[0010] The carbon nanotubes are silane-modified carbon nanotubes, obtained by the following operation: the carbon nanotubes are surface-modified with a silane coupling agent, wherein the amount of the silane coupling agent is 2%-5% of the mass of the carbon nanotubes.

[0011] Preferably, in step S1, the amount of carbon nanotubes used is 1%-5% of the mass of polyacrylonitrile powder; the amount of nano zinc oxide used is 2%-8% of the mass of polyacrylonitrile powder; and the dispersion treatment is carried out by alternating shear emulsification and ultrasonic treatment.

[0012] Preferably, in step S2, the wet spinning uses a spinneret with an aperture of 0.06-0.1 mm; and the coagulation is carried out in a coagulation bath at a temperature of 35-45°C.

[0013] Preferably, in step S3, the temperature of the first stage oxidation treatment is 190~210℃, the heating rate is 1~3℃ / min, and the holding time is 20-40 minutes;

[0014] The second stage of oxidation treatment uses a nitrogen-air mixture containing gasified triphenyl phosphate in the phosphorus and oxygen atmosphere. The treatment temperature is 230~260℃, the heating rate is 0.5~1.5℃ / min, and the holding time is 50-70 minutes.

[0015] Preferably, in step S3, the process tension of the first stage oxidation treatment and the second stage oxidation treatment is controlled to be 5-20 cN / tex, respectively.

[0016] The present invention provides polyacrylonitrile-based pre-oxidized fibers obtained by the preparation method described above, which are in filament form.

[0017] The present invention provides a multifunctional composite fabric, comprising the aforementioned polyacrylonitrile-based pre-oxidized fiber.

[0018] Preferably, the multifunctional composite fabric is a fabric layer formed by twisting pre-oxidized polyacrylonitrile fibers into yarn and weaving them.

[0019] Preferably, the multifunctional composite fabric further includes: other fiber layers bonded together by sewing and / or bonding.

[0020] Compared with existing technologies, this invention first incorporates carbon nanotubes and nano-oxidation wires in situ into the fiber matrix through blend spinning; then, a specific gradient pre-oxidation process is introduced to construct a certain gradient microstructure within the polyacrylonitrile-based pre-oxidized fiber. This invention effectively alleviates the internal stress of the pre-oxidized fiber, thereby significantly improving the fiber's flexibility and mechanical strength, and resolving the contradiction between high flame retardancy and high mechanical properties. Simultaneously, the in-situ composite carbon nanotubes form a durable and efficient conductive network, ensuring the fabric's electromagnetic shielding effectiveness (SE) in the X-band (8.2-12.4 GHz) remains stable above 30 dB; while the uniform distribution of nano-zinc oxide within the fiber reduces the fabric's infrared emissivity in the 8-14 μm band to below 0.6, facilitating the durable integration of dual stealth and flame retardant functions, and avoiding the problems of easy wear and peeling of post-treatment coatings.

[0021] Furthermore, the preparation method described herein has clearly defined process parameters, and the gradient structure can be flexibly controlled through temperature and atmosphere. The resulting fiber fabric possesses the characteristics of being lightweight, flexible, and multifunctional, and can be widely used in advanced special protective clothing, military camouflage systems, shielding of precision electronic equipment, and aerospace interior materials, demonstrating significant practical value and market potential. Attached Figure Description

[0022] Figure 1 The images show a comparison of infrared thermal images of the fabric (left) of Embodiment 3 and the comparative fabric (right) under the same heat source irradiation.

[0023] Figure 2 This is a diagram showing the burning of the fabric in embodiment 3 of the present invention on an alcohol lamp;

[0024] Figure 3 This is a diagram showing the electromagnetic shielding effectiveness of the fabric in the X-band of Embodiment 3 of the present invention. Detailed Implementation

[0025] The technical solutions in the embodiments of this application are described clearly and completely below. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0026] This application provides a method for preparing polyacrylonitrile-based pre-oxidized fibers, comprising the following steps:

[0027] S1. Polyacrylonitrile powder is dissolved in a solvent to obtain a matrix solution, which is then mixed with carbon nanotubes and nano zinc oxide and dispersed to obtain a composite spinning solution.

[0028] S2. The composite spinning solution is wet-spun and then solidified to obtain nascent fibers.

[0029] S3. The nascent fibers are first subjected to a first-stage oxidation treatment in an oxygen-containing atmosphere below 210°C, and then subjected to a second-stage oxidation treatment in a phosphorus-containing and oxygen-containing atmosphere above 230°C to obtain polyacrylonitrile-based pre-oxidized fibers.

[0030] The embodiments of the present invention can prepare polyacrylonitrile-based pre-oxidized fibers with excellent mechanical properties, high flame retardancy and efficient electromagnetic shielding, which is beneficial for forming durable multifunctional composite fabrics.

[0031] To achieve the above objectives, the technical solution adopted in this embodiment of the invention first involves preparing the composite spinning solution. Preferably, in this embodiment, polyacrylonitrile powder is mixed with N,N-dimethylformamide (DMF) solvent, and mechanically stirred at 60-70°C for 4-8 hours until completely dissolved, yielding a homogeneous matrix solution with a solid content of 15-20%. The polyacrylonitrile powder is a commercially available product with an intrinsic viscosity of 1.4-1.8 dL / g.

[0032] In a preferred embodiment of the present invention, carbon nanotubes and nano-zinc oxide are respectively surface-modified to improve their dispersibility; then, they are added to the polyacrylonitrile matrix solution and dispersed by alternating high-speed shear emulsification and ultrasonic treatment until a uniform, stable composite spinning solution without visible agglomerates is obtained. Its viscosity range is 40-120 Pa·s (60℃), which is suitable.

[0033] The carbon nanotubes are lightweight and possess functional properties such as electrical conductivity. Their preferred addition amount is 1%-5% (e.g., 1%, 2%, 2.5%, 3%, 4%, 5%) of the polyacrylonitrile powder mass. The nano-zinc oxide is UV resistant, highly active, and synergistically plays a multifunctional role; its preferred addition amount is 2%-8% or 3-6% of the polyacrylonitrile powder mass. Specifically, the carbon nanotubes (CNTs, 20-40 nm in diameter) and nano-zinc oxide (ZnO, 50 nm in particle size) can be surface-modified using the silane coupling agent KH-550 (3-aminopropyltriethoxysilane).

[0034] More preferably, raw CNT powder (20-40 nm in diameter) is weighed and treated with an acid solution to obtain hydroxylated carbon nanotubes. Silane coupling agent KH550 is dissolved in an ethanol / water mixture, and the pH is adjusted to 4-6 with acetic acid. The mixture is stirred and hydrolyzed for 30 minutes to obtain a KH550 modification solution with a mass fraction of 1-3%. Subsequently, hydroxylated carbon nanotubes and nano-zinc oxide (50 nm in particle size) are added separately to the KH550 modification solution, and the mixture is mechanically stirred in a water bath at 70-90°C for 9-12 hours. After the reaction, the mixture is centrifuged and then vacuum dried at 60°C for 12 hours to obtain KH550-modified carbon nanotubes and nano-zinc oxide, respectively, facilitating in-situ addition and synergistic effect of functional fillers.

[0035] In this embodiment of the invention, the composite spinning solution obtained in the above steps is subjected to wet spinning, followed by coagulation and shaping to obtain nascent fibers. The wet spinning and nascent fiber shaping specifically include: the spinning solution is precisely delivered by a gear metering pump and extruded through a spinneret. The spinneret has multiple circular spinneret holes, preferably with a diameter of 0.06-0.10 mm; the extruded solution stream enters a coagulation bath at a temperature of 35-45°C. The coagulation bath is a mixed solution of N,N-dimethylformamide and water (generally deionized water), wherein the mass fraction of N,N-dimethylformamide is 55%-65%, more preferably 60%; after undergoing a double diffusion process in the coagulation bath, nascent fibers are obtained, which can be drawn out by guide rollers and washed with deionized water to remove residual solvent. The preferred draw ratio of the guide rollers is 1.2-1.8:1.

[0036] In a preferred embodiment of the present invention, the washed nascent fibers are placed in a temperature-controlled muffle furnace or a multi-stage pre-oxidation furnace for gradient pre-oxidation treatment under continuous tension. The specific stages are as follows:

[0037] The first stage of oxidation treatment (low-temperature pre-stabilization): In an air atmosphere, the temperature is increased from room temperature (20-30℃) to 190-210℃ at a rate of 1-3℃ / min, and held at this temperature for 20-40 minutes; in this stage, the cyclization reaction mainly begins, forming a preliminary stable cortical structure.

[0038] The second stage of oxidation treatment (high temperature deep cyclization and cross-linking): switch the atmosphere to a nitrogen-air mixed atmosphere containing triphenyl phosphate, and continue to heat to 230-260℃ (e.g., 240-250℃) at a heating rate of 0.5-1.5℃ / min, and hold at this temperature for 50-70 minutes.

[0039] Cooling and setting stage: The heat source is turned off and the fiber is naturally cooled to room temperature in the air atmosphere to obtain a black, multifunctional pre-oxidized fiber with a gradient structure of increasing cyclization degree and crosslinking density from the skin to the core. The internal stress of the fiber is effectively relieved, which is beneficial for its application.

[0040] Preferably, the first stage oxidation treatment atmosphere is an air atmosphere; the second stage atmosphere is a nitrogen-air mixture with a volume ratio of 1:4, containing a trace amount of vaporized triphenyl phosphate (TPP). In this stage, while promoting deep cyclization and cross-linking of the core layer, the introduction of TPP synergistically enhances the flame retardancy of the final fiber. The volume concentration of the triphenyl phosphate vapor can be 0.3%-1.0%, and the nitrogen-to-air volume ratio is preferably 1:4.

[0041] Furthermore, the process tension of the first-stage oxidation treatment and the second-stage oxidation treatment is controlled at 5-20 cN / tex, respectively.

[0042] The present invention provides polyacrylonitrile-based pre-oxidized fibers obtained by the preparation method described above, which can be called multifunctional pre-oxidized fibers, multifunctional gradient pre-oxidized fibers, etc., and are in filament form.

[0043] This invention provides a multifunctional composite fabric comprising the aforementioned polyacrylonitrile-based pre-oxidized fibers. The multifunctional composite fabric of this invention comprises at least one functional layer, which is composed of polyacrylonitrile fibers that have undergone gradient pre-oxidation treatment, and the fibers are internally composited with carbon nanotubes and nano-zinc oxide.

[0044] The gradient pre-oxidation treatment includes a low-temperature stage and a high-temperature stage performed sequentially. The preferred temperature for the low-temperature stage is 190-210℃, and the preferred temperature for the high-temperature stage is 230-260℃. This gradient pre-oxidation treatment results in a gradient structure within the fiber, with increasing cyclization degree and crosslinking density from the cortex to the core. Furthermore, the polyacrylonitrile-based pre-oxidized fiber incorporates carbon nanotubes and nano-zinc oxide via a blending spinning process. The mass fraction of carbon nanotubes can be 1%-5% of polyacrylonitrile, and the mass fraction of nano-zinc oxide can be 2%-8% of polyacrylonitrile.

[0045] Specifically, the preparation method includes: (1) preparing a polyacrylonitrile composite spinning solution containing carbon nanotubes and nano zinc oxide; (2) wet spinning to obtain nascent fibers; (3) subjecting the nascent fibers to a gradient pre-oxidation treatment including a low-temperature stage of 190-210℃ and a high-temperature stage of 230-260℃ to form a gradient structure with increasing cyclization and crosslinking density from the skin to the core; (4) weaving the obtained multifunctional pre-oxidized fibers into fabrics. The embodiments of the present invention mainly utilize the synergy of gradient structure and functional fillers to enable the fabric to simultaneously possess multifunctional integrated characteristics such as high mechanical strength, excellent flame retardancy, efficient electromagnetic shielding (X-band SE > 30dB) and low infrared emissivity ( < 0.6), making it suitable for special protection and military camouflage fields.

[0046] In some embodiments of the present invention, fabric forming and compounding can be performed: the obtained multifunctional pre-oxidized yarn is twisted into yarn (multifunctional pre-oxidized yarn yarn) and used as warp and / or weft yarn, and woven into a single-layer functional fabric by machine weaving or knitting process; when machine weaving process is used, the fabric structure can be plain weave, twill weave or square plain weave.

[0047] Alternatively, the multifunctional composite fabric can also be a multi-layered fabric made by weaving, knitting, or composite processes using the multifunctional gradient pre-oxidized yarn and other functional yarns. In some specific embodiments, the multifunctional composite fabric is preferably a multi-layered structure, including an outer protective layer made of the multifunctional pre-oxidized yarn and an inner comfort layer or intermediate functional layer made of flame-retardant fibers. Further, the fabric woven from the multifunctional pre-oxidized yarn serves as the outer functional protective layer (the areal density of the outer functional protective layer is preferably 150-250 g / m²). 2 Multi-layered multifunctional composite fabrics are made by combining a middle functional layer or inner comfort layer composed of flame-retardant viscose, aramid, and phase change material composite yarns with a stitching, hot-pressing, or lamination process.

[0048] In a specific embodiment of the present invention, the preparation method of the multifunctional composite fabric may include the following steps: (1) preparing composite spinning solution: dissolving polyacrylonitrile powder in a solvent, adding surface-modified carbon nanotubes and nano zinc oxide, and dispersing the solution to obtain a uniform composite spinning solution; (2) obtaining nascent fibers through wet spinning and coagulation; (3) performing a gradient pre-oxidation treatment on the nascent fibers with programmed temperature rise: first performing a first-stage oxidation treatment at 190-210℃, and then performing a second-stage oxidation treatment at 230-260℃ to obtain multifunctional gradient pre-oxidized yarn; (4) making the multifunctional gradient pre-oxidized yarn into the composite fabric.

[0049] Tests have shown that the multifunctional composite fabric possesses stable flame retardant, heat insulation, electromagnetic shielding, and infrared stealth properties, making it particularly suitable for special protection, military camouflage, and electronic security applications. For example, it can be used in the manufacture of special protective clothing, military camouflage equipment, or shielding covers for electronic equipment.

[0050] To better understand the technical content of this application, specific embodiments are provided below for further explanation. The substances used in these embodiments may be commercially available.

[0051] Example 1:

[0052] (1) Preparation of composite spinning solution

[0053] Polyacrylonitrile powder with an intrinsic viscosity of 1.6 dL / g was mixed with N,N-dimethylformamide solvent at a mass ratio of 18:82 and mechanically stirred at 65°C for 6 hours to obtain a homogeneous matrix solution with a solid content of 18%. The viscosity of the matrix solution was measured to be 75 Pa·s at 60°C using a rotational viscometer.

[0054] 10 g of raw CNT powder (20-40 nm in diameter) was weighed and added to 1000 mL of a 3:1 mixture of concentrated H₂SO₄ and concentrated HNO₃. The mixture was refluxed at 70 °C for 5 h. After the reaction, the powder was washed with deionized water until neutral, centrifuged, and then vacuum dried at 100 °C to obtain hydroxylated carbon nanotubes. Silane coupling agent KH550 was dissolved in an ethanol / water mixture (95:5, volume ratio), and the pH was adjusted to approximately 5.0 with acetic acid. The mixture was stirred and hydrolyzed for 30 min to prepare a 2% (w / w) KH550 modification solution. Subsequently, hydroxylated carbon nanotubes and zinc oxide nanoparticles (50 nm in diameter) were added separately to the KH550 modification solution and mechanically stirred in an 80 °C water bath for 10 h. After the reaction, the mixture was centrifuged and vacuum dried at 60 °C for 12 h to obtain KH550-modified carbon nanotubes and zinc oxide nanoparticles, respectively. The mass ratio of CNT to KH550 is 100:3, and the mass ratio of ZnO to KH550 is 100:2.

[0055] KH-550 surface-modified carbon nanotubes and nano-zinc oxide were added to the above matrix solution at 3 wt% and 5 wt% of the mass of polyacrylonitrile powder, respectively. The mixture was treated in a high-speed shear emulsifier (10,000 rpm) for 15 minutes, and then transferred to a probe-type ultrasonic cell disruptor and ultrasonically treated at 500W for 15 minutes. This process was repeated 4 times (for a total of 2 hours) to obtain a composite spinning solution with uniformly dispersed filler and a viscosity of 95 Pa·s at 60°C.

[0056] (2) Continuous preparation of nascent fibers

[0057] The uniformly dispersed composite spinning solution is extruded through a spinneret (0.08 mm orifice) and placed in a coagulation bath at 40°C (DMF aqueous solution, 60% concentration). The solution is then drawn and shaped (guide roller draw ratio 1.2-1.8) to obtain nascent fibers. The fibers are then thoroughly washed with deionized water to remove residual solvent.

[0058] (3) Perform multi-stage pre-oxidation treatment on nascent fibers

[0059] The nascent fibers are placed in a programmed temperature muffle furnace, subjected to a constant tension of 10 cN / tex, and processed according to the following procedure:

[0060] First step: In an air atmosphere, heat from room temperature to 200℃ at a rate of 2℃ / min and hold at that temperature for 30 minutes.

[0061] Second stage: Switch the atmosphere to a nitrogen-air mixture (nitrogen:air = 1:4) containing trace amounts of triphenyl phosphate vapor (TPP, volume concentration of 0.3-0.5%), and continue heating to 240°C at a heating rate of 1°C / min, and hold at that temperature for 60 minutes.

[0062] The heat source is turned off, and the furnace is allowed to cool naturally to room temperature in the air, thus obtaining black multifunctional gradient pre-oxidized fiber.

[0063] Comparative Example 1:

[0064] The preparation steps of the traditional homogeneous pre-oxidized fiber are basically the same as those in Example 1, except that the gradient pre-oxidation treatment is changed to: directly heating to 240°C at 5°C / min in an air atmosphere, and maintaining the temperature at 240°C for 90 minutes, followed by natural cooling.

[0065] The pre-oxidized yarn obtained in Comparative Example 1 was twisted into 80 S / 2 strands and used as warp and weft yarns. The yarn was then woven into a plain weave fabric using a rapier loom, with an areal density of 200 g / m². 2 .

[0066] Example 2:

[0067] (1) Preparation of composite spinning solution

[0068] Polyacrylonitrile powder with an intrinsic viscosity of 1.6 dL / g was mixed with N,N-dimethylformamide solvent at a mass ratio of 18:82 and mechanically stirred at 65°C for 6 hours to obtain a homogeneous matrix solution with a solid content of 18%. The viscosity of the matrix solution was measured to be 75 Pa·s at 60°C using a rotational viscometer.

[0069] 10 g of raw CNT powder (20-40 nm in diameter) was added to 1000 mL of a 3:1 mixture of concentrated H₂SO₄ and concentrated HNO₃ and refluxed at 70 °C for 5 h. After the reaction, the powder was washed with deionized water until neutral, centrifuged, and then vacuum dried at 100 °C to obtain hydroxylated carbon nanotubes. Silane coupling agent KH550 was dissolved in an ethanol / water mixture (95:5, volume ratio), and the pH was adjusted to approximately 5.0 with acetic acid. The mixture was stirred and hydrolyzed for 30 minutes to prepare a 2% (w / w) KH550 modification solution. Subsequently, hydroxylated carbon nanotubes and zinc oxide nanoparticles (50 nm in diameter) were added separately to the KH550 modification solution and mechanically stirred in an 80 °C water bath for 10 h. After the reaction, the mixture was centrifuged and vacuum dried at 60 °C for 12 h to obtain KH550-modified carbon nanotubes and zinc oxide nanoparticles, respectively. The mass ratio of CNT to KH550 is 100:3, and the mass ratio of ZnO to KH550 is 100:2.

[0070] KH-550 surface-modified carbon nanotubes and nano-zinc oxide were added to the above matrix solution at 2 wt% and 2.5 wt% of the mass of polyacrylonitrile powder, respectively. The mixture was treated in a high-speed shear emulsifier (10,000 rpm) for 15 minutes, and then transferred to a probe-type ultrasonic cell disruptor and ultrasonically treated at 500W for 15 minutes. This process was repeated 4 times (for a total of 2 hours) to obtain a composite spinning solution with uniformly dispersed filler and a viscosity of 87 Pa·s at 60°C.

[0071] (2) Continuous preparation of nascent fibers

[0072] The uniformly dispersed composite spinning solution is extruded through a spinneret (0.08 mm orifice) and placed in a coagulation bath at 40°C (DMF aqueous solution, 60% concentration). The solution is then drawn and shaped (guide roller draw ratio 1.2-1.8) to obtain nascent fibers. The fibers are then thoroughly washed with deionized water to remove residual solvent.

[0073] (3) Perform multi-stage pre-oxidation treatment on nascent fibers

[0074] The nascent fibers are placed in a programmed temperature muffle furnace, subjected to a constant tension of 10 cN / tex, and processed according to the following procedure:

[0075] First step: In an air atmosphere, heat from room temperature to 200℃ at a rate of 2℃ / min and hold at that temperature for 30 minutes.

[0076] Second stage: Switch the atmosphere to a nitrogen-air mixture (nitrogen:air = 1:4) containing trace amounts of triphenyl phosphate vapor (volume concentration of 0.3-0.5%), and continue heating to 240°C at a heating rate of 1°C / min, and hold at that temperature for 60 minutes.

[0077] The heat source is turned off, and the furnace is allowed to cool naturally to room temperature in the air, thus obtaining black multifunctional gradient pre-oxidized fiber.

[0078] Example 3:

[0079] The preparation of multilayer composite fabrics is as follows:

[0080] The gradient pre-oxidized yarn obtained in Example 1 was twisted into 80 S / 2 strands and used as warp and weft yarns. The yarn was then woven into a plain weave fabric using a rapier loom, with an areal density of 210 g / m². 2 Furthermore, this plain-weave woven fabric is used as the outer functional layer.

[0081] A plain knit fabric, made of 32S flame-retardant combed cotton yarn, is knitted on a 34-inch 18-needle weft knitting machine as the inner comfort layer. The fabric has a weight of 240 g / m². 2 The vertical density is approximately 65 rows / 5cm, and the horizontal density is approximately 55 columns / 5cm.

[0082] Subsequently, reactive polyurethane hot melt adhesive (PUR) was used as the adhesive, and the PUR hot melt adhesive was applied at a rate of 8-12 g / m² using a dot-coating process. 2 The coating is dotted on the inner surface of the outer functional layer, and then hot-pressed with the inner comfort layer at 120-130℃. After curing at room temperature, a double-layer composite fabric (multifunctional composite fabric) is obtained.

[0083] Fabric performance testing

[0084] The fabric samples obtained in Example 3, the fabric with the same structure woven from the fibers of Comparative Example 1 (referred to as Comparative Fabric A), and the fabric obtained by coating the surface of the fabric of Comparative Example 1 with the same amount of CNT / ZnO coating (referred to as Comparative Fabric B) were characterized by mechanical properties (GB / T 3923.1-2013), limiting oxygen index (GB / T 5454-1997), X-band electromagnetic shielding effectiveness (ASTM D4935-18), infrared emissivity (GJB 2039A-2011), and performance stability after multiple washes.

[0085] Figure 1 The images show a comparison of infrared thermal images of the fabric of Embodiment 3 (left) and the comparative fabric (right) under the same heat source irradiation. As can be seen from the images, the surface temperature of the fabric of the present invention is significantly lower than that of the comparative fabric, with a maximum temperature of 93.9℃, while the surface temperature of the comparative fabric is 110.12℃. Combined with its infrared emissivity of only 0.58, this indicates that the fabric of the present invention has superior infrared stealth performance and can effectively suppress the thermal radiation characteristics of the target.

[0086] Figure 2This is a combustion diagram of the fabric of Embodiment 3 of the present invention on an alcohol lamp. The diagram shows that the fabric of Embodiment 3 of the present invention does not burn at all on an alcohol lamp and retains its structural integrity, indicating that the gradient pre-oxidation structure imparts superior flame-retardant properties to the fabric.

[0087] Figure 3 The figure shows the electromagnetic shielding effectiveness of the fabric of Example 3 of the present invention in the X-band. The figure shows that the shielding effectiveness of the fabric of Example 3 of the present invention is significantly higher than that of the comparative fabric (which is essentially 0 dB) throughout the entire test frequency band, with an average shielding effectiveness of 32.1 dB, meeting the requirements for commercial electromagnetic shielding materials (≥30 dB). This demonstrates that the in-situ composite conductive network is more complete and efficient.

[0088] The multifunctional composite fabric of this invention exhibits a breaking strength ≥2.5 cN / dtex, compared to fabric A ≤1.9 cN / dtex. The fabric of this invention demonstrates an X-band electromagnetic shielding effectiveness ≥32 dB, an infrared emissivity ≤0.58, and an electromagnetic shielding effectiveness retention rate ≥90% after 10 washes. Thermogravimetric analysis data proves that the gradient structure fabric has a higher high-temperature char residue rate and superior heat resistance.

[0089] As can be seen from the above embodiments, the embodiments of the present invention mainly utilize the synergistic design of "gradient pre-oxidation structure" and "in-situ composite of functional fillers" to successfully prepare a multifunctional composite fiber / fabric that combines high strength, high flame retardancy, efficient electromagnetic shielding, and infrared stealth. Its performance is comprehensively superior to traditional homogeneous pre-oxidized filament fabrics and surface-coated fabrics, demonstrating significant synergistic effects and technological advancements.

[0090] The above embodiments are only for illustrating the technical concept and features of this application, and are intended to enable those skilled in the art to understand the content of this application and implement it accordingly. They should not be construed as limiting the scope of protection of this application. All equivalent changes or modifications made in accordance with the spirit and essence of this application should be included within the scope of protection of this application. The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values; these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of various ranges, the endpoint values ​​of various ranges and individual point values, and individual point values ​​can be combined to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

Claims

1. A method for preparing polyacrylonitrile-based pre-oxidized fibers, characterized in that, Includes the following steps: S1. Polyacrylonitrile powder is dissolved in a solvent to obtain a matrix solution, which is then mixed with carbon nanotubes and nano-zinc oxide. After dispersion treatment, a composite spinning solution is obtained. The carbon nanotubes are silane-modified carbon nanotubes, obtained by the following steps: the carbon nanotubes are surface-modified with a silane coupling agent, wherein the amount of the silane coupling agent is 2%-5% of the mass of the carbon nanotubes; the amount of the carbon nanotubes is 1%-5% of the mass of the polyacrylonitrile powder; and the amount of nano-zinc oxide is 2%-8% of the mass of the polyacrylonitrile powder. S2. The composite spinning solution is wet-spun and then solidified to obtain nascent fibers. S3. The nascent fibers are first subjected to a first-stage oxidation treatment in an oxygen-containing atmosphere below 210°C, and then subjected to a second-stage oxidation treatment in a phosphorus-containing and oxygen-containing atmosphere above 230°C to obtain polyacrylonitrile-based pre-oxidized fibers.

2. The preparation method according to claim 1, characterized in that, In step S1, the intrinsic viscosity of the polyacrylonitrile powder is 1.4-1.8 dL / g; the solvent is N,N-dimethylformamide.

3. The preparation method according to claim 1, characterized in that, In step S1, the dispersion process is carried out by alternating shear emulsification and ultrasonic treatment.

4. The preparation method according to any one of claims 1-3, characterized in that, In step S2, the wet spinning uses a spinneret with an aperture of 0.06-0.1 mm; the coagulation is carried out in a coagulation bath at a temperature of 35-45℃.

5. The preparation method according to any one of claims 1-3, characterized in that, In step S3, the temperature of the first stage oxidation treatment is 190~210℃, the heating rate is 1~3℃ / min, and the holding time is 20-40 minutes; The second stage of oxidation treatment uses a nitrogen-air mixture containing gasified triphenyl phosphate in the phosphorus and oxygen atmosphere. The treatment temperature is 230~260℃, the heating rate is 0.5~1.5℃ / min, and the holding time is 50-70 minutes.

6. The preparation method according to claim 5, characterized in that, In step S3, the process tension of the first stage oxidation treatment and the second stage oxidation treatment is controlled to be 5-20 cN / tex, respectively.

7. The polyacrylonitrile-based pre-oxidized fiber obtained by the preparation method according to any one of claims 1-6 is in filament form.

8. A multifunctional composite fabric, characterized in that, Includes the polyacrylonitrile-based pre-oxidized fiber as described in claim 7.

9. The multifunctional composite fabric according to claim 8, characterized in that, The multifunctional composite fabric is a fabric layer formed by twisting pre-oxidized polyacrylonitrile fibers into yarn and weaving them.

10. The multifunctional composite fabric according to claim 9, characterized in that, The multifunctional composite fabric also includes other fiber layers bonded together by stitching and / or bonding.

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