Preparation method of multifunctional regenerated flame-retardant yarn

Abstract

The invention discloses a preparation method of multifunctional regenerated flame-retardant yarns, which comprises the following steps: spraying carboxylated CNTs dispersion liquid on the surface of dispersed regenerated flame-retardant polyester fibers, folding, applying a compression roller, and drying to obtain polyester / CNTs composite fiber strips; the method comprises the following steps: preparing regenerated aramid into card slivers through blowing-carding and drawing, applying weak twist to the card slivers to obtain pre-twisted aramid slivers, respectively drafting the pre-twisted aramid slivers and polyester / CNTs composite fiber slivers, applying a high-voltage direct-current electrostatic field to a convergent point of fiber bundles, forming an effective three-dimensional conductive and flame-retardant network in the yarn, and simultaneously sufficiently converging and twisting the two fiber bundles to obtain the yarn. According to the method, through pretreatment compounding and electrostatic orientation, the durability and efficiency of the flame retardant property are remarkably improved, and the limit oxygen index (LOI) of the yarn can reach 32% or above and far exceeds the level of traditional flame-retardant yarn; after 50 times of standard water washing, the retention rate exceeds 90%, and the industrial problem that after-treatment flame-retardant products are not washable is effectively solved.

Description

Technical Field

[0001] This invention relates to a method for preparing yarn, and more particularly to a method for preparing a multifunctional recycled flame-retardant yarn. Background Technology

[0002] With increasingly stringent environmental regulations and a growing emphasis on sustainable development, the textile industry is increasingly utilizing recycled fibers. Recycled aramid and recycled flame-retardant polyester, due to their excellent heat resistance, strength, and durability, show promising application prospects in protective clothing, fire-fighting equipment, and specialty industrial fabrics. However, effectively blending these two fibers with their distinct properties to produce high-quality yarns still presents significant technical challenges.

[0003] While aramid fibers possess excellent high-temperature resistance and strength, their production cost is relatively high, and pure aramid fibers lack sufficient abrasion resistance, limiting their use in certain high-abrasion scenarios. Therefore, the industry often blends aramid with recycled flame-retardant polyester to combine the high-temperature resistance of aramid with the abrasion resistance and cost advantages of polyester, expanding the application range of products in multifunctional protective textiles. However, aramid and polyester differ significantly in surface structure, mechanical properties, and electrical characteristics. Traditional blending processes easily lead to uneven fiber distribution and weak interfacial bonding, severely affecting yarn evenness and overall strength.

[0004] In existing technologies, various methods have been attempted to improve the functionality and spinnability of polyester or aramid yarns, but significant limitations remain. For example, Existing technology 1 improves flame retardancy and conductivity by blending carbon nanotubes (CNTs) with polyester chips, but this method is only applicable to pure polyester systems. CNTs tend to agglomerate during melt blending, making uniform dispersion difficult, and it cannot solve the interfacial compatibility problem in aramid / polyester blends. Existing technology 2 uses Sirospun structures to improve yarn structure, but its flame retardancy still relies on finishing techniques or blending modifications. Functional components mainly adhere to the yarn surface or fill the interior, resulting in poor wash resistance and significant performance degradation after multiple washes. Furthermore, it does not specifically address the problems of excessive fuzz and poor spinnability in recycled aramid fibers. Existing technology 3 focuses on fuzz control in pure aramid yarns by treating the fuzz with chemical sizing agents. However, this method easily causes environmental pollution, affects the yarn's hand feel and subsequent processing, and does not address the needs of blended systems and multifunctional integration.

[0005] Siro spinning technology can improve yarn hairiness and strength to some extent by feeding two rovings simultaneously, but its conventional configuration is still not suitable for spinning high-proportion, high-stiffness recycled aramid fibers, and it does not have the ability to arrange nano-functional materials (such as CNTs) in an orderly manner, making it difficult to achieve high efficiency and durability of functions.

[0006] Therefore, existing technologies have failed to systematically resolve the core contradictions in the spinnability, functional integration, and performance durability of recycled aramid / polyester blended yarns. Developing a new spinning method that can simultaneously achieve uniform fiber blending, directional arrangement of nanomaterials, and a combination of flame retardancy and antistatic properties, while also being technologically feasible and environmentally friendly, has become an urgent need for the industry. Summary of the Invention

[0007] Purpose of the invention: The purpose of this invention is to provide a method for preparing a multifunctional recycled flame-retardant yarn that can simultaneously reduce fuzz, significantly improve yarn strength, and achieve directional encapsulation of carbon nanotubes.

[0008] Technical solution: The preparation method of the multifunctional recycled flame-retardant yarn of the present invention includes the following steps:

[0009] (1) The carboxylated CNTs dispersion is sprayed onto the surface of the dispersed recycled flame-retardant polyester fiber, gathered into a fiber bundle, and squeezed by a pressure roller. The carboxylated CNTs dispersion fully penetrates into the fiber bundle. After drying, the CNTs are fixed on the surface and gaps of the polyester fiber to obtain polyester / CNTs composite fiber strip.

[0010] (2) The recycled aramid is combed and drawn into a sliver, and a slight twist is applied to the sliver to obtain a pre-twisted aramid sliver;

[0011] (3) Stretch the pre-twisted aramid strip and the polyester / CNTs composite fiber strip to the required fineness respectively;

[0012] (4) The pre-twisted aramid strip and polyester / CNTs composite fiber strip after stretching are mixed and twisted; before mixing and twisting, a high-voltage DC electrostatic field is applied at the convergence point of the two fiber bundles, so that the negatively charged CNTs migrate in a directional and orderly manner and wrap around the surface of the positively charged aramid fiber, while forming an effective three-dimensional conductive and flame-retardant network inside the yarn, so that the two fiber bundles are fully combined; after twisting, a multifunctional regenerated flame-retardant yarn is obtained.

[0013] In step (1), a precision online injection device is installed after the drafting device and before the bundler on the drawing frame. This device sprays the CNT dispersion in an atomized form evenly onto the drawn, thin-mesh polyester fibers. The fiber web is then gathered by the bundler and passed through a pressure roller, allowing the dispersion to fully penetrate the fiber bundle, with the roll-off rate controlled at 80% ± 5%. Finally, the impregnated fiber sliver passes through a drying channel at 80-85℃, where the moisture evaporates, and the CNTs are firmly fixed to the surface and gaps of the polyester fibers, forming a polyester / CNTs composite fiber sliver. This method ensures the efficient utilization and uniform distribution of CNTs.

[0014] In step (1), the carboxyl content of the carboxylated CNTs is 2.0-3.0 wt%; the outer diameter of the carboxylated CNTs is 20-30 nm and the length is 10-30 μm.

[0015] In step (1), carboxylated CNTs are dispersed in a dispersant to obtain a carboxylated CNTs dispersion. The dispersant is preferably polyvinylpyrrolidone (PVP), and its dosage is 15-25% of the CNTs mass. Specifically, the carboxylated CNTs and the dispersant are added together to deionized water, and an ultrasonic cell disruptor is used at 800W power for intermittent processing for 30 minutes, with a 5-second working period followed by a 2-second pause to prevent overheating. The final product is a black, uniform, and stable CNTs dispersion with a solid content of 3-5%. The dispersion quality can be measured using a laser particle size analyzer, requiring a particle size distribution (D90) of less than 1 μm.

[0016] In step (1), the basis weight of the polyester / CNTs composite strip is 18.5-2.0 g / 5 m.

[0017] In step (2), the aramid sliver pretreatment involves preparing a uniform sliver from recycled aramid fibers through a combing and sizing process. Before entering the spinning process, a dedicated micro-twisting device applies a slight twist of 80-100 twists per meter (Tpm) to the sliver. This operation aims to increase the cohesion between aramid fibers, significantly reducing their dispersion and fuzzing during subsequent high-speed processing. It is a key preliminary measure to address the problem of poor spinnability. The output product is a pre-twisted aramid sliver.

[0018] In step (3), the following processes are performed:

[0019] Three-channel independent feeding: The pre-twisted aramid strip and the polyester / CNTs composite strip are placed on the double roving frame as two independent rovings, and fed into the drafting zone of the spinning machine in a symmetrical, constant speed and with uniform tension. The third intelligent monitoring channel monitors the tension and feeding status of the two rovings in real time, and automatically compensates for tension fluctuations through a fine-tuning device to ensure stable blending ratio and uniform yarn evenness.

[0020] Siro compact spinning: For drafting and gathering, two rovings are simultaneously fed into the spinning frame at the rear roller, and are uniformly drawn to the required fineness in the drafting zone composed of the middle and front rollers. They then enter a single-roller gathering system, preferably with an additional negative pressure suction pipe and a mesh ring, with the negative pressure stably controlled at -400 Pa (±50 Pa). This negative pressure attracts the drafted fiber bundles to the surface of the mesh ring, causing them to tightly gather in the gathering zone. The fiber ends are effectively wound into the yarn body, laying the foundation for further reducing hairiness and improving strength.

[0021] In step (4), a high-voltage electrostatic generator is installed below the grid outlet of the aforementioned aggregation system. Its negative electrode is connected to a row of precisely insulated, evenly spaced tungsten steel needle-shaped electrodes, with the electrode tips precisely pointing towards the "triangular area" where the two fiber bundles are about to converge and twist; the positive electrode is grounded, i.e., connected to the machine frame. The device is activated to apply a stable DC electrostatic field of 4.5-5.5 kV at the fiber bundle convergence point.

[0022] In step (4), the stretched fiber bundles are first subjected to negative pressure adsorption treatment before high voltage electrostatic application, so that they are tightly aggregated in the bundled area; the negative pressure is stably controlled at -400 Pa (±50 Pa).

[0023] In step (4), after electrostatic orientation treatment, the two fiber bundles are completely merged, twisted into the final yarn by a ring and traveler, and wound into a uniform package by a winding mechanism. The entire spinning speed can be adjusted within the range of 70-90 m / min according to the yarn density.

[0024] In the multifunctional recycled flame-retardant yarn obtained in step (4), carboxylated CNTs, recycled flame-retardant polyester fiber, and recycled aramid account for 1%~5%, 65~75%, and 20~30% of the mass of the multifunctional recycled flame-retardant yarn, respectively.

[0025] Recycled aramid, as the backbone material of the yarn, provides core properties such as high-temperature resistance, flame retardancy, and strength. Utilizing a recycled form significantly reduces costs and enhances environmental friendliness while maintaining performance. Recycled flame-retardant polyester, as the composite matrix material, serves three purposes: ① It complements aramid, improving the yarn's abrasion resistance and chemical resistance; ② Its lower glass transition temperature makes it easier to combine with functional additives in subsequent processing; ③ It possesses inherent flame retardancy, creating a synergistic flame-retardant effect with aramid. The proportion of carbon nanotubes within the aforementioned range ensures the formation of an effective conductive / flame-retardant network while avoiding fiber embrittlement and spinnability deterioration due to excessive addition. Carboxylation treatment enhances the dispersibility of CNTs in aqueous systems and their binding force with polar groups on the fiber surface.

[0026] Invention Principle: In a high-voltage electrostatic field, carbon nanotubes in the polyester / CNTs composite strip carry a negative charge due to their conductivity. They are driven by a strong electric field force pointing towards the positive pole, i.e., the grounding component. Due to the dielectric properties of aramid fibers, a positive charge is induced on their surface. Therefore, the negatively charged CNTs "jump" out of the polyester fibers, migrate directionally and orderly, and firmly wrap around the positively charged aramid fiber surface, simultaneously forming an effective three-dimensional conductive and flame-retardant network inside the yarn.

[0027] Beneficial effects: Compared with the prior art, the present invention achieves the following significant effects:

[0028] (1) This invention significantly improves the durability and efficiency of flame retardant performance through "pretreatment composite + electrostatic orientation". Among them, electrostatic orientation enables carbon nanotubes (CNTs) to form a dense and firm coating layer on the fiber surface, rather than simple physical mixing. The limiting oxygen index (LOI) of the prepared yarn can reach more than 32%, far exceeding the level of traditional flame retardant yarns. More importantly, after 50 standard water washes, its flame retardant performance decays very little, with a retention rate of more than 90%, which completely solves the industry problem of post-finished flame retardant products not being washable. At the same time, it realizes the efficient utilization of CNTs, requiring only about 1 / 3 of the addition amount of traditional blending process to achieve better flame retardant effect, significantly reducing material costs.

[0029] (2) This yarn achieves a perfect integration of flame retardancy, antistatic properties, and electromagnetic shielding. Its volume resistivity is reduced to 10^6~10^7 Ω·cm, giving the product permanent antistatic properties and avoiding the short-lived drawbacks of ordinary chemical antistatic agents. At the same time, its shielding effectiveness reaches 20-30 dB in the 1-3 GHz electromagnetic band, making it effective in high-end fields such as smart wearables and special work clothes that require electromagnetic protection. This multi-functional integration is something that traditional spinning technology cannot achieve.

[0030] (3) This invention fundamentally solves the problem of poor spinnability of recycled aramid fibers. By pre-twisting the aramid fiber sliver (80-100 twists / meter) and combining it with the effect of Siro spinning negative pressure, the number of harmful hairs larger than 3mm in the yarn is reduced by more than 40%, greatly improving the smoothness of the fabric surface and weaving efficiency. In addition, the reinforcing effect of CNTs complements the tight structure of the Siro-spun yarn itself, increasing the yarn breaking strength by more than 15% compared with traditional ring-spun yarn, and improving abrasion resistance by more than 30%, resulting in a qualitative leap in product durability and fundamentally improving the yarn's mechanical properties and appearance quality.

[0031] (4) This invention is based on the existing Sirospinning equipment platform and only requires the addition of two types of mature industrial equipment: a pre-twisting device and a high-voltage electrostatic generator. The modification is simple, the investment cost is controllable, and it is very easy to promote quickly on existing production lines. By precisely compounding CNTs only with the polyester component, the use of expensive nanomaterials in all fibers is avoided, which greatly saves raw material costs. This makes the high-performance yarn not only have excellent functionality, but also excellent market competitiveness, and its industrial application prospects are extremely broad. Detailed Implementation

[0032] The present invention will now be described in further detail.

[0033] Example 1

[0034] (1) Raw material preparation

[0035] The following raw materials were selected for this embodiment: recycled meta-aramid staple fiber with a specification of 1.5 denier × 38 mm, limiting oxygen index ≥ 28%, and breaking strength ≥ 4.0 cN / dtex; recycled flame-retardant polyester staple fiber with a specification of 1.4 denier × 38 mm, limiting oxygen index ≥ 30%, and breaking strength ≥ 4.5 cN / dtex; carboxylated multi-walled carbon nanotubes, i.e., carboxylated CNTs, with an outer diameter of 20-30 nm, a length of 10-30 μm, and a carboxyl content of 2.0-3.0 wt%; and polyvinylpyrrolidone (PVP) K30 as a dispersant.

[0036] (2) Preparation of carbon nanotube dispersion

[0037] 0.5 kg of carbon nanotubes and 0.1 kg of dispersant were accurately weighed and added to 9.4 kg of deionized water. The mixture was first mechanically stirred for 30 minutes to form a premix, then transferred to an ultrasonic cell disruptor and subjected to intermittent ultrasonic treatment at 800 W power (5 seconds on, 2 seconds off), for a total of 30 minutes, ultimately yielding a uniform dispersion with a solid content of 5%. Testing showed that the particle size distribution D90 of the dispersion was less than 1 micrometer, meeting the requirements for subsequent processing.

[0038] (3) Preparation of fiber strips

[0039] Regenerated aramid fibers are processed into slivers through cleaning and carding, then combined and drafted using a drawing frame to produce a finished sliver with a basis weight of 18.5 g / 5 m. A micro-twisting device is added to the output end of the drawing frame to give the finished sliver a weak twist of 80 twists / m, forming a pre-twisted aramid sliver. Regenerated flame-retardant polyester fibers are processed into slivers through cleaning and carding, and in the final drawing process, the dispersion is atomized and sprayed onto the fiber web via an online injection system. The residual amount is controlled at 80% by pressure rollers, and the fibers are dried in an 85°C hot air drying channel to produce a polyester / carbon nanotube composite sliver with a basis weight of 19.0 g / 5 m.

[0040] (4) Spinning process

[0041] The spinning process is carried out on a modified DTM129 spinning frame. The equipment is equipped with a double roving frame, a three-channel yarn guide, a single-roller mesh ring type compact spinning device, and a high-voltage electrostatic generator installed below the gathering tank. Pre-twisted aramid and polyester / carbon nanotube composite slivers are fed into the drafting zone separately. The spindle speed is set to 14,500 rpm, the roller center distance is 43×52 mm, the total draft ratio is 35, the design twist is 780 twists / meter, and the gathering negative pressure is stably controlled at -400 Pa. The electrostatic generator is started and the voltage is adjusted to 5.0 kV, forming a stable corona discharge at the electrode tip.

[0042] (5) Yarn making

[0043] During the yarn-making process, carbon nanotubes migrate directionally from polyester fibers to the surface of aramid fibers under the action of an electrostatic field, forming a dense wrapping. The two fiber bundles eventually merge and twist into yarn, which is then wound into a 14.5 tex cone yarn.

[0044] Testing revealed that the product of this invention exhibits a breaking strength of 18.6 cN / tex, a 15.5% improvement over traditional processes; a 3mm hairiness index of 3.5 hairs / meter, a 43.5% reduction; a limiting oxygen index of 33.0%, which remains at 30.2% after 50 washes; a volume resistivity of 5.7 × 10^6 Ω·cm, demonstrating excellent antistatic properties; and an electromagnetic shielding effectiveness of 24.5 dB. All performance indicators are significantly superior to those of traditional processes, proving that this invention successfully achieves the preparation of high-performance, multifunctional yarns.

[0045] Example 2

[0046] (1) Raw material preparation

[0047] The following raw materials were selected in this embodiment: recycled meta-aramid staple fiber with a specification of 2.0 denier × 38 mm, limiting oxygen index ≥ 28%, and breaking strength ≥ 4.0 cN / dtex; recycled flame-retardant polyester staple fiber with a specification of 1.8 denier × 38 mm, limiting oxygen index ≥ 30%, and breaking strength ≥ 4.5 cN / dtex; carboxylated multi-walled carbon nanotubes with an outer diameter of 20-30 nm, a length of 10-30 μm, and a carboxyl content of; and polyvinylpyrrolidone (PVP) K30 as a dispersant.

[0048] (2) Preparation of carbon nanotube dispersion: Same as in Example 1.

[0049] (3) Preparation of fiber strips:

[0050] Regenerated aramid fibers are processed into slivers through cleaning and carding, then combined and drawn using a drawing frame to produce a finished sliver with a basis weight of 22.0 g / 5 m. A micro-twisting device is added to the output end of the drawing frame to give the finished sliver a weak twist of 90 twists / m, forming a pre-twisted aramid sliver. Regenerated flame-retardant polyester fibers are processed into slivers through cleaning and carding, and in the final drawing process, the dispersion is atomized and sprayed onto the fiber web via an online injection system. The residual amount is controlled at 85% by pressure rollers, and the fibers are dried in a 90℃ hot air drying channel to produce a polyester / carbon nanotube composite sliver with a basis weight of 23.0 g / 5 m.

[0051] (4) Spinning process

[0052] The spinning process is carried out on a modified DTM129 spinning frame. The equipment is equipped with a double roving frame, a three-channel yarn guide, a single-roller mesh ring type compact spinning device, and a high-voltage electrostatic generator installed below the gathering tank. Pre-twisted aramid and polyester / carbon nanotube composite slivers are fed into the drafting zone separately. The spindle speed is set to 14,500 rpm, the roller center distance is 43×52 mm, the total draft ratio is 28, the design twist is 680 twists / meter, and the gathering negative pressure is stably controlled at -400 Pa. The electrostatic generator is started and the voltage is adjusted to 5.2 kV, forming a stable corona discharge at the electrode tip.

[0053] (5) Yarn production:

[0054] During the yarn-making process, carbon nanotubes migrate directionally from polyester fibers to the surface of aramid fibers under the action of an electrostatic field, forming a dense wrapping. The two fiber bundles eventually merge and twist into yarn, which is then wound into a 20.0 tex cone yarn.

[0055] Testing revealed that the product of this invention exhibits a breaking strength of 17.8 cN / tex; a hairiness index of 4.0 threads / meter at 3 mm; a limiting oxygen index of 33.8%, which remains at 31.1% after 50 washes; a volume resistivity of 5.2 × 10^6 Ω·cm, demonstrating good antistatic properties; and an electromagnetic shielding effectiveness of 25.5 dB. This invention's method, by adjusting raw material specifications and process parameters, can stably produce coarser yarns while maintaining excellent overall performance.

[0056] Example 3

[0057] (1) Raw material preparation: Same as in Example 1.

[0058] (2) Preparation of carbon nanotube dispersion: Same as in Example 1.

[0059] (3) Preparation of fiber strips:

[0060] Regenerated aramid fibers are processed into slivers through cleaning and carding, then combined and drawn using a drawing frame to produce a finished sliver with a basis weight of 18.5 g / 5 m. A micro-twisting device is added to the output end of the drawing frame to give the finished sliver a weak twist of 80 twists / m, forming a pre-twisted aramid sliver. Regenerated flame-retardant polyester fibers, after cleaning and carding, are atomized and sprayed onto the fiber web via an online injection system in the final drawing process. The residual amount is controlled at 80% by pressure rollers, and the fibers are dried in a 95°C hot air drying channel, with the drying time shortened to 2.5 minutes, to produce a polyester / carbon nanotube composite sliver with a basis weight of 18.5 g / 5 m.

[0061] (4) Fine spinning process: Same as in Example 1.

[0062] (5) Yarn production: Same as in Example 1.

[0063] Testing revealed that the product of this invention exhibits a breaking strength of 18.8 cN / tex; a hairiness index of 3.3 threads / meter at 3 mm; a limiting oxygen index of 33.2%, which remains at 30.5% after 50 washes; a volume resistivity of 5.5 × 10^6 Ω·cm, demonstrating good antistatic properties; and an electromagnetic shielding effectiveness of 24.0 dB. Increasing the drying temperature accelerates CNT fixation, and fine-tuning the basis weight helps improve yarn evenness, stabilizes yarn performance, and increases production efficiency.

[0064] Comparative Example 1

[0065] (1) Raw material preparation: Same as in Example 1.

[0066] (2) Preparation of carbon nanotube dispersion: Same as in Example 1.

[0067] (3) Preparation of fiber strips: Same as in Example 1.

[0068] (4) Fine spinning process: The difference from Example 1 is that the high voltage static electricity generator is not turned on.

[0069] (5) Yarn production: Same as in Example 1.

[0070] Testing revealed that the product of this invention exhibits a tensile strength of 17.0 cN / tex; a 3 mm fuzz index of 4.8 filaments / meter; a limiting oxygen index of 33.2%, which remains at 26.5% after 50 washes; a volume resistivity of 3.5 × 10^6 Ω·cm; and an electromagnetic shielding effectiveness of 12.3 dB. Without the crucial step of electrostatic orientation, CNTs cannot effectively migrate to form a three-dimensional network, significantly reducing their functional performance.

[0071] Comparative Example 2

[0072] (1) Raw material preparation: Same as in Example 1.

[0073] (2) Preparation of carbon nanotube dispersion: Same as in Example 1.

[0074] (3) Fiber strip preparation: The process is the same as in Example 1, but no pre-twisting is applied, and smooth aramid slivers are directly output.

[0075] The recycled aramid fiber is processed into a sliver through cleaning and carding, and then drawn and stretched using a drawing frame to produce a finished sliver with a basis weight of 18.5 g / 5 m. The recycled flame-retardant polyester fiber is processed into a sliver through cleaning and carding, and then the dispersion is atomized and sprayed onto the fiber web through an online injection system in the final drawing process. The residual rate is controlled at 80% by pressure rollers, and the fiber is dried in an 85℃ hot air drying channel to produce a polyester / carbon nanotube composite sliver with a basis weight of 19.0 g / 5 m.

[0076] (4) Fine spinning process: Same as in Example 1.

[0077] (5) Yarn production: Same as in Example 1.

[0078] Tests showed that the product of this invention has a tensile strength of 16.4 cN / tex; a 3 mm fuzz index of 6.8 hairs / meter; a limiting oxygen index of 31.5%, which remains at 27.8% after 50 washes; a volume resistivity of 5.0 × 10^6 Ω·cm; and an electromagnetic shielding effectiveness of 17.5 dB.

[0079] As can be seen from this comparative example, the lack of pre-twisting of aramid fibers leads to poor fiber cohesion, a significant increase in hairiness, severely deteriorating the yarn's appearance quality, and affecting the electrostatic aggregation effect, resulting in a decrease in strength and functional durability.

[0080] Comparative Example 3

[0081] (1) Raw material preparation: Same as in Example 1.

[0082] (2) Blending masterbatch and spinning

[0083] Carboxylated multi-walled carbon nanotubes (same as in Example 1) were premixed with recycled flame-retardant polyester chips at a mass ratio of 3:100. The mixture was then melt-blended and granulated using a twin-screw extruder at 260-280°C to produce a polyester / CNTs blend masterbatch. This masterbatch was then diluted with pure recycled flame-retardant polyester chips at a ratio of 1:4 and melt-spun to obtain recycled flame-retardant polyester staple fibers containing CNTs (1.4 denier × 38 mm).

[0084] (3) Fiber strips and spinning

[0085] The above-mentioned blended polyester staple fiber and recycled aramid staple fiber (same as in Example 1) were blended at a 50 / 50 ratio and then processed into slivers through traditional cleaning, carding, and drawing processes. The blending was carried out using a conventional FA506 ring spinning machine without the use of any agglomeration or static electricity control devices. The spinning process parameters were: spindle speed 13000 rpm, design twist 780 twists / meter.

[0086] (4) Yarn production and testing

[0087] Tests showed that the yarn specification was 14.5 tex. The yarn breaking strength was 16.1 cN / tex; the harmful hairiness index at 3 mm was 6.2 hairs / meter; the limiting oxygen index (LOI) was 28.5%, which dropped significantly to 24.1% after 50 washes, with a retention rate of 84.6%; the volume resistivity was 1.2 × 10^9 Ω·cm; and the electromagnetic shielding effectiveness was only 8.5 dB.

[0088] As can be seen from this comparative example, the traditional blending process results in uneven dispersion and easy agglomeration of CNTs, and it is impossible to achieve directional arrangement, which leads to the overall performance of the yarn being far inferior to that of the embodiments.

[0089] Comparative Example 4

[0090] (1) Raw material preparation: Same as in Example 1.

[0091] (2) Preparation of carbon nanotube dispersion: Same as in Example 1.

[0092] (3) Preparation of fiber strips:

[0093] a. Preparation of aramid strips: Same as in Example 1.

[0094] b. Preparation of polyester / CNTs composite strips: The process is the same as in Example 1, but the roll allowance of the pressure roller is significantly reduced to 60%. The drying process is the same as in Example 1.

[0095] (4) Fine spinning process: Same as in Example 1.

[0096] (5) Yarn production and testing

[0097] The yarn specification was tested to be 14.5 tex. The yarn breaking strength was 17.2 cN / tex; the limiting oxygen index (LOI) was only 29.5%, which dropped significantly to 25.2% after 50 washes; the volume resistivity increased to 8.4×10^7 Ω·cm; and the electromagnetic shielding effectiveness was 15.1 dB.

[0098] As can be seen from this comparative example, an excessively low roll-off rate leads to insufficient effective load of CNTs, which severely weakens the initial function and durability of the yarn, demonstrating the crucial role of roll-off rate control.

Claims

1. A method for preparing a multifunctional recycled flame-retardant yarn, characterized in that, Includes the following steps: (1) The carboxylated CNTs dispersion is sprayed onto the surface of the dispersed recycled flame-retardant polyester fiber, gathered into a fiber bundle, and squeezed by a pressure roller. The carboxylated CNTs dispersion fully penetrates into the fiber bundle. After drying, the CNTs are fixed on the surface and gaps of the polyester fiber to obtain polyester / CNTs composite fiber strip. (2) The recycled aramid is combed and drawn into a sliver, and a slight twist is applied to the sliver to obtain a pre-twisted aramid sliver; (3) Stretch the pre-twisted aramid strip and the polyester / CNTs composite fiber strip to the required fineness respectively; (4) The pre-twisted aramid strip and polyester / CNTs composite fiber strip after stretching are mixed and twisted; before mixing and twisting, a high-voltage DC electrostatic field is applied at the convergence point of the two fiber bundles, so that the negatively charged CNTs migrate in a directional and orderly manner and wrap around the surface of the positively charged aramid fiber, while forming an effective three-dimensional conductive and flame-retardant network inside the yarn, so that the two fiber bundles are fully combined; after twisting, a multifunctional regenerated flame-retardant yarn is obtained.

2. The method for preparing the multifunctional recycled flame-retardant yarn according to claim 1, characterized in that, In step (4), the electric field strength of the high voltage DC electrostatic field is 4.5-5.5 kV.

3. The method for preparing the multifunctional recycled flame-retardant yarn according to claim 1, characterized in that, In step (1), the carboxyl content of the carboxylated CNTs is 2.0-3.0 wt%.

4. The method for preparing the multifunctional recycled flame-retardant yarn according to claim 1, characterized in that, In step (1), the carboxylated CNTs have an outer diameter of 20-30 nm and a length of 10-30 μm.

5. The method for preparing the multifunctional recycled flame-retardant yarn according to claim 1, characterized in that, In the multifunctional recycled flame retardant yarn obtained in step (4), carboxylated CNTs, recycled flame retardant polyester fiber, and recycled aramid account for 1%~5%, 65~75%, and 20~30% of the mass of the multifunctional recycled flame retardant yarn, respectively.

6. The method for preparing the multifunctional recycled flame-retardant yarn according to claim 1, characterized in that, In step (1), the basis weight of the polyester / CNTs composite fiber strip is 18.5-20.0 g / 5 m.

7. The method for preparing the multifunctional recycled flame-retardant yarn according to claim 1, characterized in that, In step (2), the twist applied to the sliver is 80-100 twists / meter.

8. The method for preparing the multifunctional recycled flame-retardant yarn according to claim 1, characterized in that, In step (4), the stretched fiber bundles are first subjected to negative pressure adsorption treatment before high voltage electrostatic application, so that they are tightly aggregated in the bundled area.

9. The method for preparing the multifunctional recycled flame-retardant yarn according to claim 1, characterized in that, In step (1), the solid content of the carboxylated CNTs dispersion is 3-5%.

10. The method for preparing the multifunctional recycled flame-retardant yarn according to claim 1, characterized in that, In step (1), carboxylated CNTs are dispersed in polyvinylpyrrolidone to obtain a carboxylated CNTs dispersion; the mass of the polyvinylpyrrolidone is 15-25% of the mass of the carboxylated CNTs.