Flame-retardant cool filament cotton fiber and method for preparing the same

Abstract

This invention provides a flame-retardant cotton fiber and its preparation method. Based on 100% by weight, it comprises the following raw materials by weight percentage: 58%-62% polyester chips; 30%-34% nylon chips; 5%-8% flame-retardant masterbatch, wherein the flame-retardant masterbatch contains: a phosphorus-nitrogen-carbon synergistic flame retardant treated with a silane coupling agent; the phosphorus-nitrogen-carbon synergistic flame retardant is a compound system of bio-based phytic acid-urea salt and cyclotriphosphazene derivatives; 1%-2% maleic anhydride-grafted polyolefin elastomer compatibilizer; 0.1%-0.3% compound antioxidant; and 0.1%-0.3% lubricant. Through the synergistic design system among the raw materials, this invention solves the problems of poor flame-retardant effect, low washability, poor compatibility between flame retardants and polyester / nylon systems, poor environmental friendliness, unstable spinning, and hardened fiber feel in existing flame-retardant modifications of cotton fibers. It achieves a synergistic improvement in high flame retardancy, washability, environmental friendliness, stable spinning, excellent mechanical properties, and a cotton-like feel, while simultaneously reducing costs.

Description

Technical Field

[0001] This invention relates to the field of cool cotton fiber technology, and in particular to a flame-retardant cool cotton fiber and its preparation method. Background Technology

[0002] "Cool Cotton" refers to a fiber with a cotton-like feel, produced by blending or composite spinning of polyester and nylon. It combines the crispness and abrasion resistance of polyester with the softness and moisture absorption of nylon, while also possessing advantages such as quick-drying and easy dyeing. It is widely used in various textile products, including clothing, home textiles, and workwear. However, the limiting oxygen index of conventional Cool Cotton fiber is only about 18%, classifying it as a flammable material. When burning, it easily produces molten droplets and has a long afterburning time, making it difficult to meet the mandatory flame-retardant requirements for children's products, high-end workwear, and home textiles in public places, thus limiting its further expansion of applications.

[0003] Currently, flame retardant modification of Coolsilk cotton mainly involves two methods: finishing and bulk modification. Finishing is widely used due to its simple process and low cost, but it has obvious drawbacks: the flame retardant only adheres to the fiber surface, has poor durability, and loses its flame retardant effect quickly after multiple washes. Furthermore, the finishing process can easily lead to a stiffer fabric feel and reduced breathability, affecting the user experience. At the same time, some flame retardants used in finishing contain formaldehyde or halogens, which release toxic and harmful fumes when burned, posing a safety hazard and failing to meet the environmental and safety requirements of modern textile products.

[0004] Bulk modification, which involves incorporating flame retardants into fiber raw materials during spinning, can achieve long-lasting flame retardant effects. However, existing bulk modification technologies still have many problems: First, the flame retardant efficiency of a single flame retardant is low, making it difficult to achieve high flame retardant ratings. Second, conventional flame retardants have poor compatibility with polyester-nylon blends, leading to issues such as filament breakage and fuzzing during spinning, hindering stable mass production. Third, some flame retardants have poor thermal stability and are prone to decomposition at the 260-280℃ high temperatures required for polyester spinning, resulting in decreased mechanical properties and increased production costs. Fourth, it is difficult to simultaneously achieve flame retardant performance, washability, mechanical properties, and a cotton-like feel, often resulting in improved flame retardant effects but also a stiffer fiber feel and decreased strength. Summary of the Invention

[0005] To address the aforementioned technical problems, the present invention aims to provide a flame-retardant cotton fiber and its preparation method. Through a synergistic design system among the formulation raw materials, the present invention solves the problems existing in the flame-retardant modification of cotton fibers, such as poor flame retardant effect, low washability, poor compatibility of flame retardants with polyester-nylon systems, poor environmental performance, unstable spinning, and hardened fiber feel. The invention achieves a synergistic improvement in high flame retardancy, washability, environmental friendliness, stable spinning, excellent mechanical properties, and cotton-like feel, while reducing costs.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: On one hand, the present invention provides a flame-retardant cotton fiber, comprising the following raw materials by weight percentage (100%): Polyester chips 58%-62%; Nylon chips 30%-34%; The flame retardant masterbatch comprises 5%-8% of a phosphorus-nitrogen-carbon synergistic flame retardant treated with a silane coupling agent; the phosphorus-nitrogen-carbon synergistic flame retardant is a compound system of bio-based phytic acid-urea salt and cyclotriphosphazene derivatives. Maleic anhydride-grafted polyolefin elastomer 1%-2%; Compound antioxidant 0.1%-0.3%; Lubricant 0.1%-0.3%.

[0007] The purpose of this invention is to provide a flame-retardant cotton fiber and its preparation method. Through a synergistic design system among the raw materials in the formulation, this invention solves the problems of poor flame retardant effect, low washability, poor compatibility between flame retardants and polyester / nylon systems, poor environmental performance, unstable spinning, and hardened fiber feel in the existing flame-retardant modification of cotton. This invention achieves a synergistic improvement in high flame retardancy, washability, environmental friendliness, stable spinning, excellent mechanical properties, and cotton-like feel, while reducing costs.

[0008] In some embodiments, the weight ratio of the bio-based phytate-urea salt to the cyclotriphosphazene derivative is (2-3):1.

[0009] In some embodiments, the flame retardant masterbatch comprises the following parts by weight of raw materials: 40-52 parts of a phosphorus-nitrogen-carbon synergistic flame retardant coated with a silane coupling agent; 20-30 parts of polyester-nylon blended carrier resin; 5-8 parts dispersant; In the phosphorus-nitrogen-carbon synergistic flame retardant treated with silane coupling agent, the weight ratio of the phosphorus-nitrogen-carbon synergistic flame retardant to the silane coupling agent is (40-50):(0.4-1.25).

[0010] In some embodiments, the antioxidant is a compound system of hindered phenolic antioxidants and phosphite antioxidants, wherein the weight ratio of the hindered phenolic antioxidants to the phosphite antioxidants is 1:(0.8-1.2).

[0011] In some embodiments, the lubricant is butyl stearate.

[0012] On the other hand, the present invention provides a method for preparing flame-retardant cotton fiber, which, in order to obtain the flame-retardant cotton fiber as described in any of the preceding claims, includes the following preparation steps: S1 Mixed Ingredients: Polyester chips, nylon chips, flame retardant masterbatch, maleic anhydride grafted polyolefin elastomer compatibilizer, compound antioxidant and lubricant are mixed evenly according to weight percentage. S2 melt spinning: The mixed raw materials are melt spun using a spinneret, and the nascent fibers are obtained after cooling. S3 stretching and setting: The nascent fibers are stretched and heat-set in segments, and the finished product is obtained after cooling.

[0013] In some embodiments, the method for preparing the flame retardant masterbatch in step S1 includes the following steps: S11 mixes the phosphorus-nitrogen-carbon synergistic flame retardant coated with silane coupling agent, polyester-nylon blend carrier resin and dispersant in parts by weight to obtain a mixture; S12 involves melting, extruding, granulating, and drying the mixture at a temperature of 180-200℃ and a rotation speed of 200-250r / min to obtain flame-retardant masterbatch.

[0014] In some embodiments, the preparation method of the phosphorus-nitrogen-carbon synergistic flame retardant coated with silane coupling agent in step S11 includes the following steps: S111 mixes phytic acid and urea in a molar ratio of 1:(2-3) and reacts them at 60-70℃ for 2-3 hours to obtain phytic acid urea salt; S112 involves adding hexachlorocyclotriphosphazene and hydroquinone in a molar ratio of 1:(6~8) into a reaction vessel, adding an organic solvent, controlling the solid content to be 20%~30%, and then adding an alkaline catalyst with a molar ratio of alkaline catalyst to hydroquinone of (1.0~1.5):1. The mixture is stirred until homogeneous and reacted at 80~90℃ for 4~6 hours. After the reaction is complete, the product is filtered, washed, and dried to obtain the hexa(4-hydroxyphenoxy)cyclotriphosphazene. The organic solvent is at least one of toluene, xylene, tetrahydrofuran, or dioxane; the alkaline catalyst is at least one of triethylamine, pyridine, or N,N-dimethylaniline. S113 is prepared by weighing phytic acid urea salt and hexa(4-hydroxyphenoxy)cyclotriphosphazene at a weight ratio of (2-3):1. It is then mixed with 10%-15% of the total mass of bio-based phytic acid-urea salt and hexa(4-hydroxyphenoxy)cyclotriphosphazene in anhydrous ethanol and dispersed evenly. After vacuum drying and pulverization, it is passed through an 80-100 mesh sieve to obtain a phosphorus-nitrogen-carbon synergistic flame retardant. S114 is added to a silane coupling agent, the temperature is controlled at 83-87℃, the stirring speed is 150-200r / min, and the stirring is continued for 1.3-1.7h to complete the coating treatment of the phosphorus-nitrogen-carbon synergistic flame retardant by the silane coupling agent, and the phosphorus-nitrogen-carbon synergistic flame retardant coated with silane coupling agent is obtained.

[0015] In some embodiments, the temperature of melt spinning in step S2 is 260-280°C, the spinneret temperature is 270-290°C, the spinning speed is 2800-3200 m / min, and the cooling is achieved by side air cooling.

[0016] In some embodiments, the preparation method of the maleic anhydride-grafted polyolefin elastomer compatibilizer in step S1 includes the following steps: melt grafting of ethylene octene copolymer, maleic anhydride and dicumyl peroxide in a weight ratio of 100:(2-3):(0.5-1.0) to obtain a maleic anhydride-grafted polyolefin elastomer compatibilizer with a grafting rate of 1.5%-2.5%.

[0017] This invention provides a flame-retardant cotton fiber and its preparation method, which has the following beneficial effects: 1) This invention provides a flame-retardant cotton fiber and its preparation method. Through a synergistic design system among the raw materials in the formulation, it solves the problems of poor flame retardant effect, low water resistance, poor compatibility between flame retardant and polyester / nylon system, poor environmental protection, unstable spinning, and hardened fiber hand feel in the existing flame-retardant modification of cotton. It achieves a synergistic improvement in high flame retardancy, water resistance, environmental protection, stable spinning, excellent mechanical properties and cotton-like hand feel, while reducing costs.

[0018] 2) The specific mechanism is as follows: A phosphorus-nitrogen-carbon synergistic flame retardant system is formed by combining bio-based phytic acid urea salt with hexa(4-hydroxyphenoxy)cyclotriphosphazene. The two have a clear synergistic mechanism: when phytic acid urea salt burns, it releases substances such as phosphoric acid and polyphosphoric acid, which catalyze the dehydration and carbonization of fibers to form a dense char layer that blocks oxygen and heat transfer; when hexa(4-hydroxyphenoxy)cyclotriphosphazene burns, it releases nitrogen-based gases (such as ammonia and nitrogen), which dilutes the concentration of combustible gases. At the same time, its benzene ring structure can enhance the stability of the char layer. The synergistic effect of the two significantly improves the flame retardant efficiency, which is far superior to the effect of a single flame retardant. Meanwhile, the coating treatment of this phosphorus-nitrogen-carbon synergistic flame retardant by the silane coupling agent can enhance its compatibility with the polyester-nylon blend carrier resin, prevent flame retardant agglomeration, ensure uniform distribution of flame retardant effect, and prevent flame retardant loss during water washing. This results in a fiber limiting oxygen index ≥32%, achieving B1 level in vertical burning, and a limiting oxygen index ≥28% after 50 water washes, meeting the requirements for long-lasting flame retardancy and solving the problems of poor flame retardant effect and low water washability in existing technologies.

[0019] To verify the synergistic effect of the bio-based phytate urea salt and hexa(4-hydroxyphenoxy)cyclotriphosphazene compound system described in this invention, Example 1 was compared with Comparative Example 1 (single phytate urea salt) and Comparative Example 2 (single hexa(4-hydroxyphenoxy)cyclotriphosphazene). The limiting oxygen index (LOI) of Comparative Example 1 was 28.7%, and that of Comparative Example 2 was 29.2%, with an arithmetic mean of 28.95%. If only a simple additive effect existed, the LOI of the compound should be close to this average. However, in Example 1, after compounding the two at a ratio of 2.5:1, the LOI reached 33.2%, an increase of 4.25 percentage points compared to the arithmetic mean, representing a relative increase of 14.7%. This increase significantly exceeded the effect expected by those skilled in the art from a simple mixture of two known flame retardants, demonstrating a clear synergistic effect between the two. The synergistic mechanism lies in the following: phytic acid urea salt releases acidic substances such as phosphoric acid and polyphosphoric acid during combustion, catalyzing the dehydration and carbonization of fibers to form a dense char layer, which isolates oxygen and heat. Meanwhile, hexa(4-hydroxyphenoxy)cyclotriphosphazene releases nitrogen-containing gases (such as ammonia and nitrogen) at high temperatures, diluting the concentration of combustible gases. Simultaneously, the benzene ring and cyclotriphosphazene skeleton in its molecular structure can form a stable cross-linked char layer during pyrolysis, enhancing the thermal stability and density of the char layer. The two complement each other in both the condensed phase (catalytic char formation) and the gas phase (diluting combustible gases). Furthermore, the benzene ring structure of hexa(4-hydroxyphenoxy)cyclotriphosphazene can undergo esterification with the phosphoric acid substances formed by phytic acid urea salt, further promoting cross-linking and char formation, thus producing a synergistic flame-retardant effect of "1+1>2". A single flame retardant cannot simultaneously achieve the above two-phase synergistic mechanism; therefore, its flame-retardant efficiency is significantly lower than that of a compound system.

[0020] The entire system is halogen-free, with formaldehyde emissions far below the national standard Class A limit. The various raw materials work together to ensure environmental friendliness: bio-based phytic acid urea salt is derived from natural phytic acid, is environmentally friendly, non-toxic, and biodegradable; hexa(4-hydroxyphenoxy)cyclotriphosphazene has halogen-free formaldehyde emissions far below the national standard Class A limit and does not release toxic or harmful fumes during combustion; silane coupling agents, compound antioxidants, and butyl stearate are all environmentally friendly additives, releasing no toxic or harmful substances, and there are no harmful reactions between the components. Ultimately, the fiber formaldehyde emission is ≤3.6mg / kg, meeting the requirements of GB 18401-2010 Class A, making it suitable for children's products, high-end home textiles, and other applications with high environmental and safety requirements.

[0021] The compatibility problem is solved through the synergistic effect between raw materials. In the molecular chain of maleic anhydride-grafted polyolefin elastomer compatibilizer (grafting rate 1.5%-2.5%), the maleic anhydride group can form hydrogen bonds with the terminal hydroxyl and amino groups of polyester and nylon, and the polyolefin elastomer chain segment can entangle with the polyester and nylon molecular chains. At the same time, its grafting rate is within the optimal range, which can effectively improve the interfacial compatibility between polyester / nylon and flame retardant masterbatch. On the one hand, the silane coupling agent coats the flame retardant to improve its thermal stability and avoid decomposition during high-temperature spinning. On the other hand, its amino group can form a stable bond with the surface active groups of the flame retardant and the polyester / nylon blend carrier resin, further promoting the uniform dispersion of each component. The dispersant and silane coupling agent work synergistically to completely avoid flame retardant agglomeration. The three work together to ensure that there are no broken or fuzzy fibers in the spinning process, realizing continuous and stable industrial mass production without the need to modify existing spinning equipment, thus reducing production costs.

[0022] The synergistic effect of the raw material ratio balances mechanical properties and a cotton-like feel. The proportion of polyester and nylon chips by weight percentage fully utilizes the crispness and abrasion resistance of polyester and the softness and moisture absorption of nylon, laying the foundation for the cotton-like feel. The maleic anhydride-grafted polyolefin elastomer compatibilizer not only improves compatibility but also enhances fiber toughness through its flexible segments, resulting in a fiber breaking strength ≥3.5 cN / dtex. Butyl stearate, acting as a lubricant, reduces frictional resistance during spinning and, in synergy with the compatibilizer, prevents the fiber from becoming stiff. Ultimately, this improves flame retardant performance while retaining the inherent soft, cotton-like feel of Cool Silk Cotton, solving the problems of stiffening and decreased mechanical properties in existing flame-retardant modified fibers, thus enhancing the product's user experience. Crucially, the maleic anhydride-grafted polyolefin elastomer compatibilizer used in this invention allows its maleic anhydride groups to form hydrogen bonds with the terminal hydroxyl and amino groups of polyester and nylon, providing a strong anchor point for reaction with polar polyester / polyamide; while the polyolefin elastomer segments provide excellent molecular flexibility. This unique structure of "rigid anchor point + flexible chain segment" enables it to effectively transfer and buffer stress while improving interfacial compatibility, and avoid fiber embrittlement and hardening caused by the addition of flame retardants. This is the key mechanism by which the invention can retain the soft, cotton-like feel of Cool Silk Cotton while significantly improving flame retardant performance.

[0023] The raw materials are environmentally friendly and cost-controllable, and the component ratio synergistically reduces costs: The flame retardant is prepared using bio-based phytic acid, which is widely available and inexpensive. When compounded with hexa(4-hydroxyphenoxy)cyclotriphosphazene, the amount of high-priced cyclotriphosphazene can be reduced while ensuring flame retardant efficiency, thus lowering the raw material cost. At the same time, the polyester-nylon blended carrier resin has good compatibility with polyester and nylon chips, which can reduce the amount of flame retardant masterbatch used, further controlling costs. Moreover, the synergistic effect between the raw materials eliminates the need for additional high-priced additives, making the product competitive in the market.

[0024] Therefore, this application achieves a synergistic improvement in properties such as high flame retardancy, water resistance, environmental friendliness, spinning stability, excellent mechanical properties, and cotton-like feel through a synergistic system of "bio-based phytic acid urea salt and hexa(4-hydroxyphenoxy)cyclotriphosphazene compound, silane coating, and maleic anhydride grafted polyolefin elastomer compatibilizer". Detailed Implementation

[0025] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. However, those skilled in the art will understand that the embodiments described below are some embodiments of the present invention, but not all embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. 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. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0026] On one hand, the present invention provides a flame-retardant cotton fiber, comprising the following raw materials by weight percentage (100%): Polyester chips: 58%-62%, preferably textile-grade polyester chips to ensure the stiffness and abrasion resistance of the fibers. The polyester chips are made of fiber-grade polyethylene terephthalate (PET), preferably semi-dull fiber-grade polyester chips from Tongkun Group, with an intrinsic viscosity of 0.64-0.68 dL / g. Nylon chips: 30%-34%, preferably textile-grade nylon 6 or nylon 66 chips, to improve fiber softness and moisture absorption. Nylon 66 chips use textile-grade polyhexamethylene adipamide (PA66), preferably Shenma Industrial spinning-grade PA66 chips, with a relative viscosity of 2.4-2.6; Nylon 6 chips use textile-grade polycaprolactam (PA6), preferably Yongrong Jinjiang high-speed spinning semi-dull nylon 6 chips, with a relative viscosity controlled between 2.40 and 2.60. Flame retardant masterbatch: 5%-8%, as the core flame retardant component, achieves halogen-free flame retardancy and formaldehyde release far below the national standard Class A limit, while also taking into account the fiber processing performance; Maleic anhydride-grafted polyolefin elastomer compatibilizer: 1%-2%, improves the interfacial compatibility between polyester, nylon and flame retardant masterbatch, and avoids filament breakage and fuzzing during spinning. Compound antioxidant: 0.1%-0.3%, to prevent oxidative degradation of fibers during high-temperature spinning and use, and to improve the aging resistance of fibers; Lubricant: 0.1%-0.3%, reduces frictional resistance during spinning, improves spinning stability, and enhances the feel of the fiber.

[0027] Preferably, the flame retardant masterbatch comprises the following components in parts by weight: 40.4-51.25 parts of phosphorus-nitrogen-carbon synergistic flame retardant coated with silane coupling agent improve its thermal stability and compatibility with polyester-nylon blend carrier resin; Polyester-nylon blend carrier resin: 20-30 parts, with good compatibility with polyester and nylon chips, facilitating uniform dispersion of flame retardants. Preferably, the polyester-nylon blend carrier resin is a blend of polyester resin and nylon resin at a weight ratio of 6:4, a ratio highly compatible with the proportion of polyester and nylon chips in the main fiber raw materials. Using a carrier resin with a composition similar to the main raw materials minimizes the interfacial energy difference between the carrier resin and the main raw materials, allowing the flame retardant masterbatch to be uniformly dispersed at the nanoscale in the polyester and nylon matrix during melt blending. This avoids problems such as flame retardant agglomeration and uneven dispersion caused by poor compatibility between the carrier resin and the matrix resin.

[0028] Dispersant: 5-8 parts, to ensure that the flame retardant is evenly dispersed in the carrier resin, avoid agglomeration, and improve the uniformity of the flame retardant effect; In the phosphorus-nitrogen-carbon synergistic flame retardant treated with silane coupling agent, the weight ratio of the phosphorus-nitrogen-carbon synergistic flame retardant to the silane coupling agent is (40-50):(0.4-1.25).

[0029] The phosphorus-nitrogen-carbon synergistic flame retardant is a compound of bio-based phytic acid urea salt and hexa(4-hydroxyphenoxy)cyclotriphosphazene in a weight ratio of (2-3):1. The bio-based phytic acid urea salt is synthesized from phytic acid and urea in a molar ratio of 1:(2-3). Phytic acid is a bio-based material, environmentally friendly and non-toxic, and the phytic acid urea salt formed by its reaction with urea has excellent flame retardant effects. Hexa(4-hydroxyphenoxy)cyclotriphosphazene has excellent phosphorus-nitrogen flame retardant properties and thermal stability. The compound of the two forms a phosphorus-nitrogen-carbon synergistic flame retardant system, significantly improving flame retardant efficiency. Furthermore, the formaldehyde release is far below the national standard Class A limit, and it is halogen-free, meeting environmental protection requirements.

[0030] The compound antioxidant is a mixture of hindered phenolic antioxidant (such as antioxidant 1010) and phosphite antioxidant (such as antioxidant 168) in a weight ratio of 1:(0.8-1.2). The two work synergistically to effectively inhibit oxidative degradation of the fiber during high-temperature processing and use, thus extending the fiber's service life. The lubricant is butyl stearate, which has good compatibility and can effectively reduce spinning friction without affecting other fiber properties.

[0031] The maleic anhydride-grafted polyolefin elastomer compatibilizer has a grafting rate of 1.5%-2.5%. This grafting rate range ensures that the compatibilizer can effectively improve the interfacial bonding force between polyester, nylon and flame retardant masterbatch, thereby enhancing spinning stability and the mechanical properties of the fiber.

[0032] The maleic anhydride-grafted polyolefin elastomer (POE-g-MAH) compatibilizer used in this invention requires a grafting rate strictly controlled within the range of 1.5%-2.5%. If the grafting rate is too low (<1.5%), the number of maleic anhydride groups is insufficient, failing to form a sufficient number of hydrogen bonds between polyester / nylon and the flame-retardant masterbatch. This results in limited improvement in interfacial compatibility, and fiber breakage and fuzzing will still occur during spinning, along with a decrease in fiber breaking strength. If the grafting rate is too high (>2.5%), excessive maleic anhydride groups will react excessively with the terminal amino and hydroxyl groups of polyester / nylon, leading to increased crosslinking density and restricted molecular chain movement. This results in a stiff and brittle fiber feel, losing the unique soft, cotton-like feel of cotton. Furthermore, an excessively high grafting rate leads to a decrease in the molecular weight of the compatibilizer itself, resulting in poor thermal stability. During high-temperature spinning, it is prone to decomposition, producing volatiles and causing fiber breakage.

[0033] After being coated with a silane coupling agent, the phosphorus-nitrogen-carbon synergistic flame retardant has a thermal decomposition temperature of ≥280℃, which can adapt to the high-temperature environment of polyester spinning, avoid the decomposition of the phosphorus-nitrogen-carbon synergistic flame retardant during spinning, and ensure the color and mechanical properties of the fiber.

[0034] On the other hand, the present invention provides a method for preparing flame-retardant cotton fiber, comprising the following steps: S1 Raw Material Drying: Place polyester chips in a dryer and dry at 120-130℃ for 4-6 hours; place nylon chips in a dryer and dry at 80-90℃ for 3-4 hours. After drying, ensure that the moisture content of both types of chips is ≤0.03% to avoid problems such as bubbles and yarn breakage caused by moisture during spinning.

[0035] S2 Preparation of a phosphorus-nitrogen-carbon synergistic flame retardant coated with a silane coupling agent includes the following steps: S201 Phytic acid and urea were added to the reaction vessel in a molar ratio of 1:(2-3), stirred evenly, and the reaction temperature was controlled at 60-70℃ for 2-3 hours. After the reaction was completed, the mixture was cooled to room temperature to obtain phytic acid urea salt. In step S202, hexachlorocyclotriphosphazene and hydroquinone are added to a reaction vessel at a molar ratio of 1:(6~8), along with an organic solvent (at least one of toluene, xylene, tetrahydrofuran, or dioxane), controlling the solid content to be 20%~30% (i.e., the percentage of the total mass of the reactants to the total mass of the reaction system). Then, an alkaline catalyst (at least one of triethylamine, pyridine, or N,N-dimethylaniline) is added, with a molar ratio of alkaline catalyst to hydroquinone of (1.0~1.5):1. The mixture is stirred evenly and reacted at 80~90℃ for 4~6 hours. After the reaction is completed, the mixture is filtered, washed, and dried to obtain the hexa(4-hydroxyphenoxy)cyclotriphosphazene product. S203 is prepared by weighing phytic acid urea salt and hexa(4-hydroxyphenoxy)cyclotriphosphazene at a weight ratio of 2-3:1, adding 10%-15% anhydrous ethanol as a dispersant, stirring evenly and then vacuum drying. The vacuum drying conditions are: temperature 60-80℃, vacuum degree ≤-0.09MPa, drying time 8-12h. After drying, it is placed in a pulverizer for pulverization, and then passed through an 80-100 mesh sieve to ensure uniform particle size of the flame retardant, thus obtaining a phosphorus-nitrogen-carbon synergistic flame retardant. S204 mixes phosphorus-nitrogen-carbon synergistic flame retardant and silane coupling agent at a weight ratio of (40-50):(0.4-1.25) and stirs at 80-90℃ for 1-2 hours to complete the coating treatment, thereby obtaining phosphorus-nitrogen-carbon synergistic flame retardant coated with silane coupling agent. The preferred silane coupling agent is γ-aminopropyltriethoxysilane (KH-550), which raises the thermal decomposition temperature of the flame retardant to ≥280℃. S3 is used to prepare flame retardant masterbatch, including the following steps: The phosphorus-nitrogen-carbon synergistic flame retardant, polyester-nylon blended carrier resin, and dispersant prepared in step S2 are mixed evenly according to the weight ratio and fed into a twin-screw extruder. The extrusion temperature is controlled at 180-200℃ and the screw speed is 200-250 r / min. The mixture is melt-extruded and granulated. The granulated masterbatch is placed in a dryer and dried at 80-90℃ for 2-3 hours to ensure that the moisture content of the masterbatch is ≤0.05%. The masterbatch is then ready for use.

[0036] S4 prepares maleic anhydride-grafted polyolefin elastomer compatibilizers, including the following steps: Ethylene-octene copolymer (POE), maleic anhydride (MAH), and dicumyl peroxide (DCP) were added to a high-speed mixer at a weight ratio of 100:(2~3):(0.5~1.0) and mixed evenly. The mixture was then fed into a co-rotating twin-screw extruder for melt grafting reaction. The extruder temperatures were set as follows: feeding section 150~160℃, melting section 165~175℃, mixing section 170~180℃, and extrusion section 160~170℃; screw speed was 200~300 r / min; vacuum was controlled at -0.06~-0.08 MPa to remove unreacted monomers and low-molecular-weight volatiles. After the reaction, the product was extruded, water-cooled, and pelletized to obtain maleic anhydride-grafted polyolefin elastomer compatibilizer. Grafting rate determination method (acid-base titration method): Accurately weigh 0.5 g of the grafted product and dissolve it in 50 mL of xylene. Heat under reflux until completely dissolved. Add 2-3 drops of phenolphthalein indicator and titrate with 0.01 mol / L KOH-ethanol standard solution while hot until the solution turns pink and does not fade for 30 seconds. Record the volume consumed. Use ungrafted polyolefin elastomer as a blank control. The grafting rate (G) is calculated using the following formula: G (%)=[(V1-V0)×C×M / (1000×m)]×100% In the formula: V1 - Volume of KOH solution consumed by the sample, in mL; V0 - Volume of KOH solution consumed by the blank sample, in mL; Concentration of C-KOH-ethanol standard solution, mol / L; Molar mass of M-maleic anhydride, 98.06 g / mol; m - Sample mass, g.

[0037] By adjusting the feed ratio of maleic anhydride and dicumyl peroxide and the twin-screw extrusion process parameters, maleic anhydride-grafted polyolefin elastomer compatibilizers with a grafting rate in the range of 1.5% to 2.5% can be prepared for later use.

[0038] S5 Mixing and Batching: The polyester and nylon chips dried in step S1, the flame retardant masterbatch prepared in step S3, the compatibilizer prepared in step S4, and the compounded antioxidant and lubricant are added to a high-speed mixer in a weight percentage ratio. The mixing speed is 800-1000 r / min and the mixing time is 10-15 min to ensure that all raw materials are mixed evenly.

[0039] S6 Melt spinning: The material mixed in step S5 is fed into the spinning machine. The spinning temperature is controlled at 260-280℃, the spinneret temperature is 270-290℃, and the spinning speed is 2800-3200m / min. Side air cooling is used (cooling air temperature is 20-25℃, and wind speed is 0.5-1.0m / s) to quickly cool and shape the filament bundle.

[0040] S7 Segmented Stretching and Setting: The cooled and formed filament bundle is fed into a stretching machine for segmented stretching: the first segment has a stretching ratio of 1.5-1.8 times and a stretching temperature of 70-75℃; the second segment has a stretching ratio of 1.2-1.5 times and a stretching temperature of 85-90℃; after stretching, the filament bundle is fed into a heat setting machine, with a heat setting temperature of 120-130℃ and a setting time of 3-5 minutes. After setting, it is cooled to room temperature by side air at a temperature of 20-25℃ and a wind speed of 0.5-1.0 m / s to obtain the flame-retardant cool silk cotton fiber product.

[0041] Example 1

[0042] The flame-retardant cotton fiber provided in Example 1 comprises the following raw materials by weight percentage: Textile-grade polyester chips: 60.0%; Nylon 66 chips: 32.0%; Flame retardant masterbatch: 6.0%; Maleic anhydride-grafted polyolefin elastomer compatibilizer: 1.5%; Compound antioxidant (antioxidant 1010: antioxidant 168 = 1:1): 0.2%; Butyl stearate: 0.3%.

[0043] The flame retardant masterbatch contains the following components by weight: 48.82 parts of a phosphorus-nitrogen-carbon synergistic flame retardant coated with a silane coupling agent, 25 parts of a polyester-nylon blended carrier resin, and 6.5 parts of a dispersant. The polyester-nylon blended carrier resin is prepared by blending polyester resin and nylon resin at a weight ratio of 6:4. In the phosphorus-nitrogen-carbon synergistic flame retardant, the weight ratio of bio-based phytic acid urea salt to hexa(4-hydroxyphenoxy)cyclotriphosphazene is 2.5:1. The bio-based phytic acid urea salt is synthesized from phytic acid and urea at a molar ratio of 1:2.5. In the phosphorus-nitrogen-carbon synergistic flame retardant coated with a silane coupling agent, the weight ratio of the phosphorus-nitrogen-carbon synergistic flame retardant to γ-aminopropyltriethoxysilane (KH-550) is 48:0.82.

[0044] The method for preparing flame-retardant cotton fiber provided in Example 1 includes the following steps: S1. Place polyester chips in a dryer and dry at 125℃ for 5 hours; place nylon chips in a dryer and dry at 85℃ for 3.5 hours. After drying, ensure that the moisture content of both types of chips is 0.02%. S2 prepares a phosphorus-nitrogen-carbon synergistic flame retardant coated with a silane coupling agent, including the following steps: S201 Phytic acid and urea were added to a reaction vessel at a molar ratio of 1:2.5, stirred evenly, and the reaction temperature was controlled at 65℃ for 2.5h. After the reaction was completed, the mixture was cooled to room temperature to obtain phytic acid urea salt. In step S202, hexachlorocyclotriphosphazene and hydroquinone were added to a reaction vessel at a molar ratio of 1:7. Toluene organic solvent was added, and the solid content was controlled to be 25% (i.e., the percentage of the total mass of the reactants to the total mass of the reaction system). Triethylamine alkaline catalyst was then added, with a molar ratio of alkaline catalyst to hydroquinone of 1.3:1. The mixture was stirred evenly and reacted at 85°C for 5 hours. After the reaction was completed, the product was filtered, washed, and dried to obtain the hexa(4-hydroxyphenoxy)cyclotriphosphazene product. S203 was prepared by weighing phytic acid urea salt and hexa(4-hydroxyphenoxy)cyclotriphosphazene at a weight ratio of 2.5:1, and 12% by mass of anhydrous ethanol was added as a dispersant. After stirring evenly, it was vacuum dried under the following conditions: temperature 70℃, vacuum degree -0.08MPa, and drying time 10h. After drying, it was put into a pulverizer for pulverization and then passed through a 90-mesh sieve to ensure uniform particle size of the flame retardant, thus obtaining a phosphorus-nitrogen-carbon synergistic flame retardant. S204 mixes phosphorus-nitrogen-carbon synergistic flame retardant with γ-aminopropyltriethoxysilane (KH-550) at a weight ratio of 48:0.82, stirs at 85°C for 1.5 h to complete the coating treatment, and obtains phosphorus-nitrogen-carbon synergistic flame retardant coated with silane coupling agent. S3 is used to prepare flame retardant masterbatch, including the following steps: The phosphorus-nitrogen-carbon synergistic flame retardant, polyester-nylon blended carrier resin, and montan wax dispersant prepared in step S2 were mixed evenly in a weight ratio of 48.82:25:6.5 and fed into a twin-screw extruder. The extrusion temperature was controlled at 190℃ and the screw speed at 225 r / min. The mixture was melt-extruded and granulated. The granulated masterbatch was placed in a dryer and dried at 85℃ for 2.5 h to ensure that the moisture content of the masterbatch was 0.04%. The mixture was then set aside for later use. S4 prepares maleic anhydride-grafted polyolefin elastomer compatibilizers, including the following steps: Ethylene-octene copolymer (Dow Chemical ENGAGE™ 8480), maleic anhydride, and dicumyl peroxide were added to a high-speed mixer at a weight ratio of 100:2.5:0.75 and mixed evenly. The mixture was then fed into a co-rotating twin-screw extruder for melt grafting reaction. The extruder temperatures were set as follows: feeding section 155℃, melting section 160℃, mixing section 175℃, and extrusion section 165℃; screw speed was 250 r / min; vacuum was controlled at -0.07 MPa to remove unreacted monomers and low-molecular-weight volatiles. After the reaction, the mixture was extruded, water-cooled, and pelletized to obtain a maleic anhydride-grafted polyolefin elastomer compatibilizer with a grafting rate of 2%, which was then ready for use. S5 Mixing and Batching: The polyester chips and nylon chips dried in step S1, the flame retardant masterbatch prepared in step S3, the compatibilizer prepared in step S4, and the compounded antioxidant and lubricant are added to a high-speed mixer in the above weight percentage ratio. The mixing speed is 900 r / min and the mixing time is 12 min to ensure that all raw materials are mixed evenly. S6 Melt spinning: The material mixed in step S5 is fed into the spinning machine, and the spinning temperature is controlled at 270℃, the spinneret temperature is 280℃, the spinning speed is 3000m / min, and side air cooling is used (cooling air temperature is 23℃, wind speed is 0.8 m / s) to make the filament bundle cool and form quickly. S7 Segmented Stretching and Setting: The cooled and formed filament bundle is fed into a stretching machine for segmented stretching: the first segment has a stretching ratio of 1.6 times and a stretching temperature of 72℃; the second segment has a stretching ratio of 1.4 times and a stretching temperature of 88℃; after stretching, the filament bundle is fed into a heat setting machine, the heat setting temperature is 125℃, the setting time is 4min, after setting, it is cooled to room temperature by side air at a side air cooling temperature of 23℃ and a wind speed of 0.8m / s, to obtain the flame-retardant cool silk cotton fiber finished product.

[0045] Example 2

[0046] The flame-retardant cotton fiber provided in Example 2, by weight, comprises the following raw materials in the following weight percentages: textile-grade polyester chips: 60.0%; nylon 6 chips: 33.7%; flame-retardant masterbatch: 5.0%; maleic anhydride-grafted polyolefin elastomer compatibilizer: 1.0%; compound antioxidant (antioxidant 1010: antioxidant 168 = 1:1): 0.2%; butyl stearate: 0.1%. The flame retardant masterbatch comprises the following components by weight: 40.4 parts of a phosphorus-nitrogen-carbon synergistic flame retardant coated with a silane coupling agent, 20 parts of a polyester-nylon blended carrier resin, and 5 parts of a dispersant (anhydrous ethanol). The polyester-nylon blended carrier resin is prepared by blending polyester resin and nylon resin at a weight ratio of 6:4. In the phosphorus-nitrogen-carbon synergistic flame retardant, the weight ratio of bio-based phytic acid urea salt to hexa(4-hydroxyphenoxy)cyclotriphosphazene is 2:1, and the bio-based phytic acid urea salt is synthesized from phytic acid and urea at a molar ratio of 1:2. In the phosphorus-nitrogen-carbon synergistic flame retardant coated with a silane coupling agent, the weight ratio of the phosphorus-nitrogen-carbon synergistic flame retardant to γ-aminopropyltriethoxysilane (KH-550) is 40:0.4.

[0047] The preparation method of flame-retardant cotton fiber provided in Example 2 is different in that the raw material ratio is as described above by weight percentage, and the remaining preparation steps are the same as in Example 1.

[0048] Example 3

[0049] The flame-retardant cotton fiber provided in Example 3, by weight, comprises the following raw materials in the following weight percentages: textile-grade polyester chips: 58.0%; nylon 66 chips: 32.0%; flame-retardant masterbatch: 8.0%; maleic anhydride-grafted polyolefin elastomer compatibilizer: 1.5%; compound antioxidant (antioxidant 1010: antioxidant 168 = 1:1): 0.3%; butyl stearate: 0.2%.

[0050] The flame retardant masterbatch comprises the following components by weight: 51.25 parts of a phosphorus-nitrogen-carbon synergistic flame retardant coated with a silane coupling agent, 30 parts of a polyester-nylon blended carrier resin, and 8 parts of a dispersant (anhydrous ethanol). The polyester-nylon blended carrier resin is prepared by blending polyester resin and nylon resin at a weight ratio of 6:4. In the phosphorus-nitrogen-carbon synergistic flame retardant, the weight ratio of bio-based phytic acid urea salt to hexa(4-hydroxyphenoxy)cyclotriphosphazene is 2:1, and the bio-based phytic acid urea salt is synthesized from phytic acid and urea at a molar ratio of 1:2. In the phosphorus-nitrogen-carbon synergistic flame retardant coated with a silane coupling agent, the weight ratio of the phosphorus-nitrogen-carbon synergistic flame retardant to γ-aminopropyltriethoxysilane (KH-550) is 50:1.25.

[0051] The preparation method of flame-retardant cotton fiber provided in Example 3 is different in that the raw material ratio is as described above by weight percentage, and the remaining preparation steps are the same as in Example 1.

[0052] Comparative Example 1 The fiber provided in Comparative Example 1 differs from that in Example 1 in that 51.25 parts of the phosphorus-nitrogen-carbon synergistic flame retardant coated with silane coupling agent are replaced with 51.25 parts of phytic acid urea salt flame retardant coated with silane coupling agent in the weight ratio of the flame retardant masterbatch. The phytic acid urea salt flame retardant uses a single phytic acid urea salt as the flame retardant (the combination with hexa(4-hydroxyphenoxy)cyclotriphosphazene is cancelled), and the ratio of other raw materials is the same as that in Example 1.

[0053] The fiber preparation method provided in Comparative Example 1 differs in that step S2, which involves preparing a phytic acid urea salt flame retardant coated with a silane coupling agent, includes the following steps: S201: Phytic acid and urea were added to a reaction vessel at a molar ratio of 1:2.5, stirred evenly, and the reaction temperature was controlled at 65℃ for 2.5 hours. After the reaction was completed, the mixture was cooled to room temperature to obtain phytic acid urea salt flame retardant. S204: Phytic acid urea salt flame retardant and γ-aminopropyltriethoxysilane (KH-550) are mixed evenly at a weight ratio of 48:0.82 and stirred at 85°C for 1.5 h to complete the coating treatment, thus obtaining phytic acid urea salt flame retardant coated with silane coupling agent. In step S3, the phosphorus-nitrogen-carbon synergistic flame retardant treated with silane coupling agent is replaced with phytic acid urea salt flame retardant treated with silane coupling agent. The remaining preparation steps are the same as in Example 1.

[0054] Comparative Example 2 The fiber provided in Comparative Example 2 differs from that in Example 1 in that 51.25 parts of the phosphorus-nitrogen-carbon synergistic flame retardant coated with silane coupling agent are replaced with 51.25 parts of hexa(4-hydroxyphenoxy)cyclotriphosphazene flame retardant coated with silane coupling agent. The hexa(4-hydroxyphenoxy)cyclotriphosphazene flame retardant uses a single hexa(4-hydroxyphenoxy)cyclotriphosphazene as the flame retardant (the phytic acid urea salt compound is omitted), and the proportions of the remaining raw materials are the same as in Example 1.

[0055] The fiber preparation method provided in Comparative Example 2 differs in that step S2, which involves preparing a hexa(4-hydroxyphenoxy)cyclotriphosphazene flame retardant coated with a silane coupling agent, includes the following steps: In step S202, hexachlorocyclotriphosphazene and hydroquinone were added to a reaction vessel at a molar ratio of 1:7. Toluene organic solvent was added, and the solid content was controlled to be 25% (i.e., the percentage of the total mass of the reactants to the total mass of the reaction system). Triethylamine alkaline catalyst was then added, with a molar ratio of alkaline catalyst to hydroquinone of 1.3:1. The mixture was stirred evenly and reacted at 85°C for 5 hours. After the reaction was completed, the product was filtered, washed, and dried to obtain the hexa(4-hydroxyphenoxy)cyclotriphosphazene product. S204 involves mixing hexa(4-hydroxyphenoxy)cyclotriphosphazene flame retardant with γ-aminopropyltriethoxysilane (KH-550) at a weight ratio of 48:0.82, stirring at 85°C for 1.5 hours to complete the coating process, and obtaining hexa(4-hydroxyphenoxy)cyclotriphosphazene flame retardant coated with silane coupling agent. In step S3, the phosphorus-nitrogen-carbon synergistic flame retardant coated with silane coupling agent is replaced with a hexa(4-hydroxyphenoxy)cyclotriphosphazene flame retardant coated with silane coupling agent. The remaining preparation steps are the same as in Example 1.

[0056] Comparative Example 3 The fiber provided in Comparative Example 3 differs from that in Example 1 in that maleic anhydride-grafted polyolefin elastomer compatibilizer is not added in the raw material weight percentages. The raw material weight percentages are as follows: textile-grade polyester chips: 60.8%; nylon 66 chips: 32.7%; flame retardant masterbatch: 6.0%; compound antioxidant (antioxidant 1010: antioxidant 168 = 1:1): 0.2%; butyl stearate: 0.3%. The remaining raw material ratios are the same as in Example 1.

[0057] The fiber preparation method provided in Comparative Example 3 differs from that of Example 1 in that the preparation step of maleic anhydride grafted polyolefin elastomer compatibilizer in step S4 is omitted, and the compatibilizer prepared in step S4 is not added in the mixing of ingredients in step S5. The remaining preparation steps are the same as in Example 1.

[0058] Comparative Example 4 The fiber provided in Comparative Example 4 differs from that in Example 1 in that no flame retardant masterbatch is added in the raw material weight percentage. The raw material weight percentage ratio is as follows: 63.0% polyester chips, 35.0% nylon chips, 1.5% maleic anhydride grafted polyolefin elastomer compatibilizer, 0.2% compound antioxidant, 0.3% butyl stearate, and the remaining raw material ratios are the same as in Example 1.

[0059] The fiber preparation method provided in Comparative Example 4 differs from the steps of step S2 (preparing the phosphorus-nitrogen-carbon synergistic flame retardant coated with silane coupling agent) and step S3 (preparing the flame retardant masterbatch), and the flame retardant masterbatch prepared in step S3 is not added to the mixing of ingredients in step S5. The remaining preparation steps are the same as in Example 1.

[0060] The comparative sample prepared conventional cotton fiber without the addition of any flame retardant masterbatch was used as a blank control and directly subjected to subsequent performance tests without any flame retardant treatment.

[0061] Comparative Example 5 Comparative Example 5 uses a post-treatment padding method to perform flame retardant treatment on the conventional cotton fiber prepared in Comparative Example 4. The flame retardant used is a formaldehyde-containing hydroxymethylphosphazene flame retardant. The specific process steps are as follows: S1 is formulated with flame-retardant finishing liquid, prepared according to the following weight percentages: The flame retardant contains 30% formaldehyde hydroxymethylphosphazene. The formaldehyde hydroxymethylphosphazene flame retardant used is tetramethylphosphoric acid (THPC) based hydroxymethylphosphazene flame retardant, preferably Xingfa Group industrial grade tetramethylphosphoric acid (THPC), CAS No. 124-64-1. 5% crosslinking agent (including formaldehyde etherified crosslinking agent), preferably a highly etherified melamine-formaldehyde resin crosslinking agent, specifically Allnex CYMEL 303LF; Penetrant JFC 1%; The remainder is deionized water; stir well.

[0062] S2 impregnation and padding treatment: The conventional cotton fiber prepared in Comparative Example 4 was impregnated in the above flame retardant finishing liquid, and then impregnated and padded twice, with a padding rate of 75%.

[0063] S3 pre-baking involves pre-baking at 80℃ for 5 minutes to remove surface moisture.

[0064] S4 baking and curing: Baking at 155℃ for 4 minutes allows the flame retardant to cross-link and form a film on the fiber surface.

[0065] S5 is washed and dried, rinsed twice with clean water at room temperature, and dried at 80℃ to obtain flame-retardant cotton fiber after finishing.

[0066] Comparative Example 6 The fiber provided in Comparative Example 6 differs from that in Example 1 in that 48.82 parts of phosphorus-nitrogen-carbon synergistic flame retardant coated with silane coupling agent were replaced with 48.82 parts of phosphorus-nitrogen-carbon synergistic flame retardant not coated with silane coupling agent in the weight ratio of the flame retardant masterbatch. The remaining raw material ratios are the same as in Example 1.

[0067] The fiber preparation method provided in Comparative Example 6 differs in that step S2 involves preparing a phosphorus-nitrogen-carbon synergistic flame retardant without silane coupling agent coating, including the following steps: S201 Phytic acid and urea were added to a reaction vessel at a molar ratio of 1:2.5, stirred evenly, and the reaction temperature was controlled at 65℃ for 2.5h. After the reaction was completed, the mixture was cooled to room temperature to obtain phytic acid urea salt. In step S202, hexachlorocyclotriphosphazene and hydroquinone were added to a reaction vessel at a molar ratio of 1:7. Toluene organic solvent was added, and the solid content was controlled to be 25% (i.e., the percentage of the total mass of the reactants to the total mass of the reaction system). Triethylamine alkaline catalyst was then added, with a molar ratio of alkaline catalyst to hydroquinone of 1.3:1. The mixture was stirred evenly and reacted at 85°C for 5 hours. After the reaction was completed, the product was filtered, washed, and dried to obtain the hexa(4-hydroxyphenoxy)cyclotriphosphazene product. S203 was prepared by weighing phytic acid urea salt and hexa(4-hydroxyphenoxy)cyclotriphosphazene at a weight ratio of 2.5:1, and 12% by mass of anhydrous ethanol was added as a dispersant. After stirring evenly, it was vacuum dried under the following conditions: temperature 70℃, vacuum degree -0.08MPa, and drying time 10h. After drying, it was put into a pulverizer for pulverization and then passed through a 90-mesh sieve to ensure uniform particle size of the flame retardant, thus obtaining a phosphorus-nitrogen-carbon synergistic flame retardant. In step S3, the phosphorus-nitrogen-carbon synergistic flame retardant treated with silane coupling agent is replaced with the above-mentioned phosphorus-nitrogen-carbon synergistic flame retardant, and the remaining preparation steps are the same as in Example 1.

[0068] Test experimental standards and experimental methods 1) Limiting Oxygen Index (LOI) Test: The test is conducted in accordance with GB / T17932-2012 "Oxygen Index Method for Burning Performance of Textiles".

[0069] Sample preparation: The fibers were combed into a web and made into strips of 150mm×58mm with a mass of about 5g. The strips were conditioned for 24h under standard atmospheric conditions (temperature 20±2℃, relative humidity 65±4%).

[0070] Test: The sample is vertically clamped in the combustion chamber. The oxygen and nitrogen flow rates are adjusted. The lowest oxygen concentration that sustains combustion for 3 minutes after ignition at the top of the sample or reaches a combustion length of 50 mm is defined as the limiting oxygen index. Each sample is tested in parallel 5 times, and the average value is taken.

[0071] 2) Vertical flammability rating test: The test shall be conducted in accordance with GB / T 8333-2022 "Determination of vertical flammability of textiles".

[0072] Sample preparation: The fiber was spun into a fabric, and a 300mm×80mm sample was cut and conditioned under standard atmospheric conditions for 24 hours.

[0073] Test: Fix the sample vertically, ignite it with a burner with a flame height of 40mm for 12s and then remove it. Record the afterflame time, smoldering time and dripping behavior, and determine the **B1 (flame-retardant) or B2 (flammable)** rating according to the standard.

[0074] 3) Flame retardant performance test after washing: 50 standard washes were performed according to GB / T12494-2024 "Test Method for Flammability of Textiles after Washing".

[0075] Washing conditions: water temperature 40±2℃, washing for 15 minutes, standard synthetic detergent 1g / L, liquor ratio 1:30, spin speed 800r / min; rinse once after every 5 washes, and finally dry at 60±5℃.

[0076] After washing, humidify under standard atmospheric conditions for 24 hours, and then test the Limiting Oxygen Index (LOI) according to the above-mentioned Limiting Oxygen Index method.

[0077] Formaldehyde emission: According to GB18401-2010 "National Basic Safety Technical Specifications for Textile Products" (Class A), the acetylacetone spectrophotometric method was used for determination. After extraction and color development, the absorbance was measured at 412 nm, and the average value was taken from three parallel tests.

[0078] Tensile strength: According to GB / T14344-2017 "Test Method for Tensile Properties of Chemical Fibers (Short Fibers)". Tensile speed 10 mm / min, clamping distance 50 mm, 10 parallel tests and average value.

[0079] Hand feel evaluation: A combination of a stiffness-flexibility meter (objective) and sensory evaluation (subjective) was used. The stiffness-flexibility meter recorded the bending stiffness; 5 professionals scored the softness, fluffiness, and smoothness (out of 10), and an average score of ≥8 was considered soft cotton-like.

[0080] Spinning stability: After 24 hours of continuous spinning, the frequency of filament breakage and fuzzing was recorded. No filament breakage or fuzzing was considered stable; ≥3 times / hour was considered unstable; and the inability to produce continuously was considered severely unstable.

[0081] 4) Method for determining the thermal decomposition temperature of flame retardants: The test shall be conducted in accordance with GB / T 14837.2-2014 "Determination of thermal degradation of vulcanized and unvulcanized rubber by thermogravimetric analysis of rubber and rubber products".

[0082] Instrument: Thermogravimetric analyzer (TGA), such as TA Instruments Q500.

[0083] Test conditions: Sample volume 5~10mg, heating rate 10℃ / min, test temperature range 30~600℃, air atmosphere, gas flow rate 50mL / min.

[0084] The temperature at which the sample mass loss is 5% is taken as the thermal decomposition temperature (T5%). Each sample is tested in triplicate, and the average value is taken.

[0085] The performance test data of the samples from Examples 1-3 and Comparative Examples 1-6, tested using the above-mentioned test standards and methods, are shown in Table 1 below: Table 1. Experimental data on the test performance of samples from Examples 1-3 and Comparative Examples 1-6. Note: Comparative Example 4 is a blank control sample without the addition of flame retardant masterbatch, and its limiting oxygen index (LOI) was directly tested without any flame retardant treatment; Comparative Example 5 is a sample that has undergone flame retardant treatment, and its LOI is the test value after treatment. Comparative Example 3 was "unable to be formed" due to severe filament breakage, marked with " / " in the table. An explanation can be added: "Due to unstable spinning, not enough samples could be obtained for testing."

[0086] As shown in Table 1, the phosphorus-nitrogen-carbon synergistic flame retardant system formed by the bio-based phytic acid urea salt and hexa(4-hydroxyphenoxy)cyclotriphosphazene in the present invention at a ratio of 2 to 3:1 has a significantly better flame retardant effect than a single flame retardant (Comparative Examples 1 and 2). It can make the limiting oxygen index of flame-retardant cotton fiber ≥32%, achieve B1 level in vertical burning, and still have a limiting oxygen index ≥28% after 50 washes, thus achieving high efficiency and long-lasting flame retardancy and verifying the effectiveness of the phosphorus-nitrogen-carbon synergistic flame retardant mechanism.

[0087] The coating treatment of phosphorus, nitrogen and carbon synergistic flame retardants with silane coupling agent (KH-550) is the key to ensuring spinning stability and fiber performance (comparative example 6). After coating, the thermal decomposition temperature of the flame retardant is increased to ≥280℃, which can be adapted to the high-temperature spinning process of polyester, avoiding fiber breakage and mechanical property degradation caused by flame retardant decomposition. At the same time, it improves the compatibility between the flame retardant and the carrier resin and reduces flame retardant agglomeration.

[0088] Maleic anhydride-grafted polyolefin elastomer compatibilizers with a grafting rate of 1.5%-2.5% can effectively improve the interfacial compatibility between polyester, nylon, and flame-retardant masterbatch (comparative example 3), avoiding problems such as fiber breakage and fuzzing during spinning, ensuring continuous and stable industrial mass production, and simultaneously improving fiber breaking strength. Mechanistically, the maleic anhydride groups in this compatibilizer provide an anchor point for reaction with polar polyester / polyamide, achieving a strong interfacial bond; the polyolefin elastomer segments provide molecular flexibility, acting as a buffer during stress transmission. In Comparative example 3, without this compatibilizer, not only was spinning discontinuous, but the fiber also had a stiff feel and a breaking strength of only 2.9 cN / dtex, conversely demonstrating the indispensability of this synergistic mechanism of "rigid anchor point + flexible segment." Combined with butyl stearate lubricant, it can balance fiber mechanical properties with a soft, cotton-like feel.

[0089] The bulk modification method used in this invention (Examples 1-3) has significant advantages over traditional finishing flame retardant treatment (Comparative Example 5). It can not only achieve halogen-free formaldehyde release far below the national standard Class A limit environmental protection requirement (formaldehyde release ≤3.6mg / kg, in compliance with GB18401-2010 Class A requirements), but also greatly improve flame retardant durability, avoid the loss of flame retardant effect after washing, and avoid the problem of fiber stiffness.

[0090] The polyester-nylon blend carrier resin is made by compounding polyester resin and nylon resin in a 6:4 ratio (matching the main raw material ratio), which can effectively promote the uniform dispersion of flame retardants and further improve the compatibility of each component. Combined with optimized raw material ratio and spinning process, the fiber breaking strength is ≥3.5cN / dtex, taking into account flame retardant performance, processing performance and cotton-like feel.

[0091] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A flame-retardant cotton fiber, characterized in that, The ingredients are comprised of the following weight percentages based on 100% weight: Polyester chips 58%-62%; Nylon chips 30%-34%; The flame retardant masterbatch comprises 5%-8% of a phosphorus-nitrogen-carbon synergistic flame retardant treated with a silane coupling agent; the phosphorus-nitrogen-carbon synergistic flame retardant is a compound system of bio-based phytic acid-urea salt and cyclotriphosphazene derivatives. Maleic anhydride-grafted polyolefin elastomer 1%-2%; Compound antioxidant 0.1%-0.3%; Lubricant 0.1%-0.3%.

2. The flame-retardant cotton fiber according to claim 1, characterized in that, The weight ratio of the bio-based phytic acid-urea salt to the cyclotriphosphazene derivative is (2-3):

1.

3. The flame-retardant cotton fiber according to claim 1, characterized in that, The flame retardant masterbatch comprises the following raw materials in parts by weight: 40-52 parts of a phosphorus-nitrogen-carbon synergistic flame retardant coated with a silane coupling agent; 20-30 parts of polyester-nylon blended carrier resin; 5-8 parts dispersant; The weight ratio of the phosphorus-nitrogen-carbon synergistic flame retardant to the silane coupling agent in the silane coupling agent coated with the silane coupling agent is (40-50):(0.4-1.25).

4. The flame-retardant cotton fiber according to claim 1, characterized in that, The antioxidant is a compound system of hindered phenolic antioxidants and phosphite antioxidants, with the weight ratio of the hindered phenolic antioxidants to the phosphite antioxidants being 1:(0.8-1.2).

5. The flame-retardant cotton fiber according to claim 1, characterized in that, The lubricant is butyl stearate.

6. A method for preparing flame-retardant cotton fiber, characterized in that, The preparation of flame-retardant cotton fiber as described in any one of claims 1-5 comprises the following preparation steps: S1 Mixed Ingredients: Polyester chips, nylon chips, flame retardant masterbatch, maleic anhydride grafted polyolefin elastomer compatibilizer, compound antioxidant and lubricant are mixed evenly according to weight percentage. S2 melt spinning: The mixed raw materials are melt spun using a spinneret, and the nascent fibers are obtained after cooling. S3 stretching and setting: The nascent fibers are stretched and heat-set in segments, and the finished product is obtained after cooling.

7. The method for preparing flame-retardant cotton fiber according to claim 6, characterized in that, The preparation method of the flame retardant masterbatch in step S1 includes the following steps: S11 mixes the phosphorus-nitrogen-carbon synergistic flame retardant coated with silane coupling agent, polyester-nylon blend carrier resin and dispersant in parts by weight to obtain a mixture; S12 involves melting, extruding, granulating, and drying the mixture at a temperature of 180-200℃ and a rotation speed of 200-250r / min to obtain flame-retardant masterbatch.

8. The method for preparing flame-retardant cotton fiber according to claim 7, characterized in that, The preparation method of the phosphorus-nitrogen-carbon synergistic flame retardant coated with silane coupling agent as described in step S11 includes the following steps: S111 mixes phytic acid and urea in a molar ratio of 1:(2-3) and reacts them at 60-70℃ for 2-3 hours to obtain phytic acid urea salt; S112: Hexachlorocyclotriphosphazene and hydroquinone are added to a reaction vessel at a molar ratio of 1:(6~8), an organic solvent is added, and the solid content is controlled at 20%~30%. Then, an alkaline catalyst is added, with a molar ratio of alkaline catalyst to hydroquinone of (1.0~1.5):

1. The mixture is stirred evenly and reacted at 80~90℃ for 4~6 hours. After the reaction is completed, the product is filtered, washed, and dried to obtain the hexa(4-hydroxyphenoxy)cyclotriphosphazene product. S113 is prepared by weighing phytic acid urea salt and hexa(4-hydroxyphenoxy)cyclotriphosphazene at a weight ratio of (2-3):

1. It is then mixed with 10%-15% of the total mass of bio-based phytic acid-urea salt and hexa(4-hydroxyphenoxy)cyclotriphosphazene in anhydrous ethanol and dispersed evenly. After vacuum drying and pulverization, it is passed through an 80-100 mesh sieve to obtain a phosphorus-nitrogen-carbon synergistic flame retardant. S114 is added to a silane coupling agent, the temperature is controlled at 83-87℃, the stirring speed is 150-200r / min, and the stirring is continued for 1.3-1.7h to complete the coating treatment of the phosphorus-nitrogen-carbon synergistic flame retardant by the silane coupling agent, and the phosphorus-nitrogen-carbon synergistic flame retardant coated with silane coupling agent is obtained.

9. The method for preparing flame-retardant cotton fiber according to claim 6, characterized in that, In step S2, the melt spinning temperature is 260-280℃, the spinneret temperature is 270-290℃, the spinning speed is 2800-3200m / min, and the cooling is achieved by side air cooling.

10. The method for preparing flame-retardant cotton fiber according to claim 6, characterized in that, The preparation method of the maleic anhydride-grafted polyolefin elastomer compatibilizer in step S1 includes the following steps: melt grafting of ethylene octene copolymer, maleic anhydride and dicumyl peroxide in a weight ratio of 100:(2-3):(0.5-1.0) to obtain a maleic anhydride-grafted polyolefin elastomer compatibilizer with a grafting rate of 1.5%-2.5%.

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