Flame retardant fiber and its preparation method and application

Abstract

The present invention provides a flame-retardant fiber, its preparation method, and application, belonging to the technical field of flame-retardant fibers. A flame retardant is produced by reacting a vitamin composition with phosphoric acid and urea. This is then grafted onto acid-treated and oxidized palm fiber to produce a flame-retardant natural fiber. The fiber is then surface-modified with polydopamine, added to a Mg-doped silicon / aluminum mixed solution, and ammonia is added dropwise. The mixture is stirred and uniformly mixed, the solvent evaporated, washed, and dried to produce the flame-retardant fiber. The flame-retardant fiber produced by the present invention exhibits low smoke generation, is non-melting and non-shrinking, and retains its original shape after combustion. It also exhibits advantages such as moisture absorption and breathability, easy dyeing, and excellent wearing comfort. It also exhibits excellent mechanical properties, flame retardancy, and high-temperature resistance, and has broad application prospects.

Description

Technical Field

[0001] The present invention relates to the technical field of flame-retardant fibers, and in particular to a flame-retardant fiber and a preparation method and application thereof. Background Art

[0002] Flame retardant technology has been developed to adapt to the needs of social development, prevent and control fires, and protect human life and property. It is a scientific method for suppressing combustion based on the laws governing the occurrence and development of fires and the principles of combustion. Flame retardant technology utilizes the combustion characteristics of combustible materials to transform them into flame-retardant or non-combustible materials, reducing their combustion rate and preventing the spread of fires.

[0003] Flame-retardant fabrics are crucial to national economy and people's livelihoods, serving as a crucial safeguard for the safety of life, property, and personnel of both the military and civilians. To meet the fire safety requirements of various countries and the needs of social development, fiber manufacturers worldwide are continuously developing their own flame-retardant fiber products. Currently, synthetic fibers dominate the flame-retardant fiber market due to their competitive price. However, they suffer from numerous performance drawbacks, such as poor breathability, poor water absorption, and secondary damage from melt droplets. Plant-based flame-retardant fibers are poised to become increasingly obsolete.

[0004] Regenerated flame-retardant cellulose fiber (viscose fiber) is favored by consumers and widely used in various fields due to its unique luster, good moisture absorption, breathability, and antistatic properties. Currently, the international industrial production of flame-retardant regenerated cellulose fiber mainly involves grafting cellulose with vinyl monomers containing phosphorus, silicon, and halogen elements.

[0005] When halogen-containing flame-retardant fibers burn, they decompose to produce hydrogen halide gas and release highly toxic and corrosive substances such as dioxins and dibenzofurans, which complicate the recycling of finished products. Such products have been eliminated.

[0006] Phosphorus-based flame-retardant regenerated cellulose fibers contain phosphorus and sulfur, which can cause eutrophication of water bodies after degradation, which is detrimental to the environment. Furthermore, they produce a large amount of harmful smoke after combustion, which has limited their development. These include Lenging (Austria), Polynosic (Japan), and HFG (Japan).

[0007] Silicone-based flame-retardant regenerated cellulose fibers have low tensile strength, a brittle feel, and a high defect rate, making them difficult to weave and therefore useful only as fillers. Patents include "Cellulose Polysilicate Flame-Retardant Fiber and Production Method Thereof" (Patent No. ZL94110065.0) and "Preparation Method for Regenerated Cellulose / Nano-SiO2 Flame-Retardant Composite Materials" (Patent No. ZL20051004231409).

[0008] To address the aforementioned shortcomings of current flame-retardant regenerated cellulose fibers, the team at Beijing Saiolan Flame Retardant Fiber Co., Ltd., after over ten years of research and development, using unique patented technology and a domestically produced viscose fiber pilot line, has successfully developed a novel silicon-nitrogen flame retardant and a new generation of silicon-nitrogen flame-retardant regenerated cellulose fibers. These fibers are safe, non-toxic, and naturally biodegradable, without causing water pollution. They offer high flame retardancy, are washable, and offer a long-lasting flame retardant effect. Furthermore, they exhibit excellent colorability, antibacterial properties, and are comfortable to wear. While this fiber overcomes the shortcomings of the aforementioned fibers, it also suffers from the drawbacks of requiring a large dosage and a single flame-retardant mechanism. These include patents such as "An Environmentally Friendly Flame Retardant, Its Preparation Method, and Application" (Patent No. ZL201410292939.X) and "An Environmentally Friendly High-Temperature-Resistant and Durable Flame-Retardant Fiber, Its Preparation Method" (Patent No. ZL201410039251.0). Summary of the Invention

[0009] The purpose of the present invention is to propose a flame-retardant fiber and its preparation method and application, which has the characteristics of low smoke emission, no melting, no shrinkage, and the ability to maintain the original shape after burning. It has the advantages of moisture absorption and breathability, easy dyeing and good wearing comfort. It has good mechanical properties, flame retardant properties and high temperature resistance, and has broad application prospects.

[0010] The technical solution of the present invention is achieved as follows:

[0011] The present invention provides a method for preparing flame-retardant fiber. The method comprises the following steps: reacting a vitamin composition with phosphoric acid and urea to obtain a flame retardant, grafting the flame retardant onto acid-treated and oxidized palm fiber to obtain flame-retardant natural fiber. The flame retardant fiber is surface-modified with polydopamine, added to a Mg-doped silicon / aluminum mixed solution, dropwise added with ammonia water, stirred and mixed uniformly, evaporating the solvent, washing, and drying to obtain the flame-retardant fiber.

[0012] As a further improvement of the present invention, the following steps are included:

[0013] S1. Preparation of a flame retardant: Mixing a vitamin C and vitamin B composition and phosphoric acid, heating to a first temperature, stirring the reaction, then adding urea and water, heating to a second temperature, stirring the reaction, filtering while hot, precipitating, washing, and drying to obtain a flame retardant;

[0014] S2. Pretreatment of palm fiber: soaking the palm fiber in acid, filtering, washing, and drying to obtain pretreated palm fiber;

[0015] S3. Preparation of palm fibrils: The pretreated palm fiber obtained in step S2 was added to PBS buffer, urea and hydrogen peroxide were added, the reaction was heated with stirring, filtered, washed, and dried to obtain palm fibrils;

[0016] S4 flame retardant natural fiber preparation: the palm fiber prepared in step S3 is added to a solvent, the flame retardant prepared in step S1 is added, a water absorbent and a catalyst, the reaction is heated with stirring, filtered, washed, and dried to obtain a flame retardant natural fiber;

[0017] S5 polydopamine modification: The flame-retardant natural fiber obtained in step S4 was added to water, dopamine hydrochloride and a catalyst were added, and the reaction was heated and stirred to obtain a modified flame-retardant natural fiber;

[0018] S6. Preparation of Mg-doped silicon / aluminum mixed solution: dissolving a soluble magnesium salt, an alkyl orthosilicate, and aluminum isopropoxide in an ethanol aqueous solution and stirring to mix uniformly to obtain a Mg-doped silicon / aluminum mixed solution;

[0019] S7. Preparation of flame-retardant fiber: The modified flame-retardant natural fiber obtained in step S5 is added to the Mg-doped silicon / aluminum mixed solution obtained in step S6, aqueous ammonia is added dropwise, stirred and mixed uniformly, the solvent is evaporated, washed, and dried to obtain a flame-retardant fiber.

[0020] As a further improvement of the present invention, the vitamin B composition in step S1 is selected from at least one of vitamin B2, vitamin B5, vitamin B6, and vitamin B8, preferably a mixture of vitamin B2 and vitamin B8, with a mass ratio of 3-5:2. The mass ratio of the vitamin C, vitamin B composition, phosphoric acid, urea, and water is 3-5:7-10:30-50:15-17:10-20. The first temperature is 120-140°C, and the second temperature is 105-115°C.

[0021] As a further improvement of the present invention, the acid solution in step S2 is a 5-7wt% hydrochloric acid or sulfuric acid solution, the solid-to-liquid ratio of the palm fiber to the acid solution is 1:5-7g / mL, and the immersion time is 30-40min; the pH of the PBS buffer in step S3 is 9.5-10.5, the mass ratio of the pretreated palm fiber, urea, and hydrogen peroxide is 7-10:3-5:4-6, the concentration of the hydrogen peroxide is 32-35wt%, and the heating and stirring reaction temperature is 75-85°C and the time is 20-30min.

[0022] As a further improvement of the present invention, the solvent in step S4 is pyridine or N-methylpyrrolidone, the water absorbent is N,N-dicyclohexylcarbodiimide, the catalyst is selected from at least one of 4-dimethylaminopyridine, triethylenediamine, and 1,8-diazabicyclo[5.4.0]undec-7-ene, the mass ratio of the palm fiber, flame retardant, water absorbent and catalyst is 10:5-7:12-17:0.2-0.5, and the temperature of the heating and stirring reaction is 60-80°C and the time is 2-4 hours.

[0023] As a further improvement of the present invention, the mass ratio of the flame-retardant natural fiber, dopamine hydrochloride and catalyst in step S5 is 10-12:15-17:0.5-1, the catalyst is a Tris-HCl solution with a pH of 8.5-9, the temperature of the heating and stirring reaction is 40-45°C, and the time is 2-3h; the alkyl orthosilicate in step S6 is methyl orthosilicate or ethyl orthosilicate, the soluble magnesium salt is selected from at least one of magnesium chloride, magnesium sulfate and magnesium nitrate, the mass ratio of the soluble magnesium salt, alkyl orthosilicate and aluminum isopropoxide is 2-3:12-15:7-10, and the concentration of the ethanol aqueous solution is 50-70wt%.

[0024] As a further improvement of the present invention, in step S7, the mass ratio of the modified flame-retardant natural fiber, the Mg-doped silicon / aluminum mixed solution, and the ammonia water is 15-20:17-22:3-5, and the concentration of the ammonia water is 22-25 wt%.

[0025] 11. As a further improvement of the present invention, the following steps are specifically included:

[0026] S1. Preparation of a flame retardant: 3-5 parts by weight of vitamin C and 7-10 parts by weight of a vitamin B composition and 30-50 parts by weight of phosphoric acid are mixed, heated to 120-140°C, stirred for 1-3h, then 15-17 parts by weight of urea and 10-20 parts by weight of water are added, heated to 105-115°C, stirred for 1-3h, filtered while hot, precipitated with ethanol, washed, and dried to obtain a flame retardant;

[0027] The vitamin B composition is a mixture of vitamin B2 and vitamin B8 in a mass ratio of 3-5:2;

[0028] S2. Pretreatment of palm fiber: The palm fiber was placed in a 5-7wt% hydrochloric acid or sulfuric acid solution and soaked for 30-40min, the solid-liquid ratio of the palm fiber and the acid was 1: 5-7g / mL, filtered, washed, and dried to obtain pretreated palm fiber;

[0029] S3. Preparation of palm fibrils: 7-10 parts by weight of the pretreated palm fiber obtained in step S2 was added to 50 parts by weight of PBS buffer having a pH of 9.5-10.5, 3-5 parts by weight of urea and 4-6 parts by weight of 32-35wt% hydrogen peroxide were added, heated to 75-85°C, stirred for 20-30min, filtered, washed, and dried to obtain palm fibrils;

[0030] S4. Preparation of flame-retardant natural fiber: 10 parts by weight of the palm fiber obtained in step S3 was added to 100 parts by weight of pyridine or N-methylpyrrolidone, 5-7 parts by weight of the flame retardant obtained in step S1, 12-17 parts by weight of N,N-dicyclohexylcarbodiimide and 0.2-0.5 parts by weight of a catalyst, heated to 60-80 ° C, stirred for 2-4h, filtered, washed, and dried to obtain a flame-retardant natural fiber;

[0031] S5 polydopamine modification: 10-12 parts by weight of the flame-retardant natural fiber obtained in step S4 is added to 100 parts by weight of water, 15-17 parts by weight of dopamine hydrochloride and 0.5-1 parts by weight of a catalyst are added, heated to 40-45 ° C, and the reaction is stirred for 2-3h to obtain a modified flame-retardant natural fiber;

[0032] The catalyst is a Tris-HCl solution with a pH of 8.5-9;

[0033] S6. Preparation of Mg-doped silicon / aluminum mixed solution: 2-3 parts by weight of a soluble magnesium salt, 12-15 parts by weight of an alkyl orthosilicate, and 7-10 parts by weight of aluminum isopropoxide are dissolved in 100 parts by weight of a 50-70 wt% aqueous ethanol solution, and the mixture is stirred and mixed to obtain a Mg-doped silicon / aluminum mixed solution;

[0034] S7. Preparation of flame-retardant fiber: 15-20 parts by weight of the modified flame-retardant natural fiber obtained in step S5 is added to 17-22 parts by weight of the Mg-doped silicon / aluminum mixed solution obtained in step S6, 3-5 parts by weight of 22-25wt% ammonia is added dropwise, the mixture is stirred and mixed uniformly, the solvent is evaporated, washed, and dried to obtain a flame-retardant fiber.

[0035] The present invention further protects a flame retardant fiber prepared by the above preparation method.

[0036] The present invention further protects a use of the flame retardant fiber in preparing flame retardant fabrics.

[0037] The present invention has the following beneficial effects: the vitamin B composition is a mixture of vitamin B2 and vitamin B8, vitamin B2 is riboflavin, which contains rich hydroxyl structures, vitamin B8 is inositol, which is a hexol of cyclohexane, and vitamin C is ascorbic acid. Since the three contain multiple reactive hydroxyl groups that are easy to be modified, and vitamin B2 contains nitrogen elements that can serve as a potential gas source, and the presence of the ring structure means good thermal stability, these vitamins can be modified, reacted with phosphoric acid, and then ammonium salted to prepare a flame retardant. Since the amount of urea added is not large, a small number of hydroxyl groups in these vitamins do not react with urea to form ammonium salts after reacting with phosphoric acid, thereby retaining the phosphate groups for subsequent grafting reaction with palm fibrils.

[0038] Palm fiber is an excellent green natural fiber with the characteristics of low density, biodegradability, abundant sources and low price. The surface of palm fiber is covered with a large amount of silica, hemicellulose and lignin. Depending on the different solubility of different components in acidic solution and alkaline buffer solution, the surface-covered hemicellulose, lignin and other colloid substances can be removed, and the silica embedded in it can be removed to obtain purer cellulose fiber. At the same time, through the oxidation of hydrogen peroxide, a large number of hydroxyl, carboxyl and other groups are formed on the surface of the palm fiber, which facilitates the subsequent graft esterification reaction with the flame retardant, so that the flame retardant can be evenly and stably fixed on the fiber, achieving a good flame retardant effect.

[0039] The flame retardant prepared by the present invention is a phosphorus- and nitrogen-containing flame retardant with a long-lasting waterproof and flame-retardant effect. It is halogen-free, generates smoke slowly, and contains no toxic components. The phosphorus-containing portion loses water upon heating and becomes metaphosphoric acid, which then polymerizes into stable polyphosphoric acid, which covers the surface of the burning material and isolates it from oxygen in the air. The phosphoric acid also promotes dehydration and carbonization of the fibers, forming a carbonized protective film to achieve a flame-retardant effect. The nitrogen-containing portion effectively suppresses the emission of fire smoke and is easily recyclable, maintaining high stability even at high temperatures. In the gas phase, it can resist the spread of fire by releasing stable nitrogen-based molecules. In the condensed phase, it can form complex nitrogen compounds that generate carbon to protect the polymer material and prevent its decomposition under fire. Simultaneously, the nitrogen-containing portion can release a nitrogen mixed gas, weakening the gas phase and thereby suppressing the combustion process.

[0040] Furthermore, the present invention performs polydopamine modification on the surface of the prepared flame-retardant natural fiber. On the one hand, the nitrogen content of the flame-retardant fiber can be greatly increased, thereby improving the flame retardant effect. On the other hand, after the polydopamine modification, a large number of hydroxyl groups, amino groups, carboxyl groups and the like are formed on the fiber surface, which can facilitate hydrogen bonding with Mg ions, alkyl orthosilicates and aluminum isopropoxide in the subsequent Mg-doped silicon / aluminum mixed solution. Under the action of ammonia water, a sol-gel reaction occurs, thereby forming a porous inorganic flame retardant layer on the fiber surface. The presence of MgO enhances the flame retardant effect, the presence of aluminum oxide simultaneously enhances the flame retardant and high-temperature resistance, and the presence of silicon oxide improves the mechanical properties and flame retardant properties of the fiber.

[0041] The densely distributed pore structure of the inorganic flame retardant layer isolates the fiber combustion system from the outside air, thereby inhibiting combustion. Due to the high content of inorganic components in the inorganic flame retardant layer, a dense carbonized layer is formed when the fiber burns. The fiber can maintain its original shape and has good carbon layer stability.

[0042] Generally, the addition of flame retardants affects the physical and mechanical properties of viscose fibers. However, the addition of flame retardants by the grafting method of the present invention and the simultaneous coating of the surface with an inorganic flame retardant layer are beneficial to improving the mechanical properties of the flame retardant fibers.

[0043] The flame-retardant fiber prepared by the present invention has the characteristics of low smoke emission, no melting, no shrinkage, and the ability to maintain the original shape after burning. It has the advantages of moisture absorption and breathability, easy dyeing and good wearing comfort. It has good mechanical properties, flame retardant properties and high temperature resistance, and has broad application prospects. DETAILED DESCRIPTION

[0044] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0045] Palm fiber was purchased from Taishan Heli Coconut Palm Products Co., Ltd.

[0046] Example 1

[0047] This embodiment provides a method for preparing a flame-retardant fiber, which specifically includes the following steps:

[0048] S1. Preparation of a flame retardant: 3 parts by weight of vitamin C and 7 parts by weight of a vitamin B composition and 30 parts by weight of phosphoric acid were mixed, heated to 120°C, stirred for 1 hour, and then 15 parts by weight of urea and 10 parts by weight of water were added, heated to 105°C, stirred for 1 hour, filtered while hot, precipitated with ethanol, washed, and dried to obtain a flame retardant;

[0049] The vitamin B composition is a mixture of vitamin B2 and vitamin B8 in a mass ratio of 3:2;

[0050] S2. Pretreatment of palm fiber: The palm fiber was immersed in a 5wt% hydrochloric acid solution for 30min, the solid-liquid ratio of the palm fiber and 5wt% hydrochloric acid was 1:5g / mL, filtered, washed, and dried to obtain pretreated palm fiber;

[0051] S3. Preparation of palm fiber: 7 parts by weight of the pretreated palm fiber prepared in step S2 was added to 50 parts by weight of PBS buffer at pH = 9.5, 3 parts by weight of urea and 4 parts by weight of 32wt% hydrogen peroxide were added, heated to 75 ° C, stirred for 20 minutes, filtered, washed, and dried to obtain palm fiber; after testing the infrared spectrum, it was found that the palm fiber had an average wavelength of 3410 cm -1 The strong absorption peak at 2910 cm represents the stretching vibration absorption peak of OH. It can be seen that the palm fiber forms a large number of hydroxyl structures.-1 The absorption peak at 1635cm represents the stretching vibration of CH and C-H2; -1 The absorption peak at 1387 cm represents the stretching vibration of C=O in the acetyl group of cellulose; -1 The absorption peak at 1157 cm represents the CH symmetrical bending vibration in palm fiber; -1 The absorption peak at represents the stretching vibration of the C=O ether bond in palm fiber glucose.

[0052] S4. Preparation of flame-retardant natural fiber: 10 parts by weight of palm fiber prepared in step S3 was added to 100 parts by weight of pyridine, 5 parts by weight of the flame retardant prepared in step S1, 12 parts by weight of N,N-dicyclohexylcarbodiimide and 0.2 parts by weight of 4-dimethylaminopyridine were added, heated to 60 ° C, stirred for 2h, filtered, washed, and dried to obtain a flame-retardant natural fiber; after testing the infrared spectrum, it was found that 3407cm -1 The absorption at 2902 cm represents the stretching vibration of OH. -1 The absorption peak at 1651 cm represents the stretching vibration of -CH. -1 and 1627cm -1 The absorption peak at 1302 cm represents the C=O stretching vibration of the acetyl group, representing the newly formed ester group and the unreacted cellulose acetyl group. -1 The absorption peak at represents the CH symmetric bending vibration in the palm fiber, which shows that the flame retardant molecules of the present invention are successfully grafted onto the palm fiber molecules.

[0053] S5 polydopamine modification: 10 parts by weight of the flame-retardant natural fiber obtained in step S4 was added to 100 parts by weight of water, 15 parts by weight of dopamine hydrochloride and 0.5 parts by weight of a catalyst were added, heated to 40 ° C, and the reaction was stirred for 2h to obtain a modified flame-retardant natural fiber;

[0054] The catalyst is a Tris-HCl solution with a pH of 8.5;

[0055] S6. Preparation of Mg-doped silicon / aluminum mixed solution: 2 parts by weight of magnesium chloride, 12 parts by weight of methyl orthosilicate, and 7 parts by weight of aluminum isopropoxide were dissolved in 100 parts by weight of a 50 wt% aqueous ethanol solution and stirred for 20 minutes to obtain a Mg-doped silicon / aluminum mixed solution;

[0056] S7. Preparation of flame-retardant fiber: 15 parts by weight of the modified flame-retardant natural fiber obtained in step S5 was added to 17 parts by weight of the Mg-doped silicon / aluminum mixed solution obtained in step S6, 3 parts by weight of 22wt% ammonia water was added dropwise, stirred and mixed for 60 minutes, the solvent was evaporated, washed, and dried to obtain a flame-retardant fiber.

[0057] Example 2

[0058] This embodiment provides a method for preparing a flame-retardant fiber, which specifically includes the following steps:

[0059] S1. Preparation of a flame retardant: 5 parts by weight of vitamin C and 10 parts by weight of a vitamin B composition and 50 parts by weight of phosphoric acid were mixed, heated to 140°C, stirred for 3 hours, and then 17 parts by weight of urea and 20 parts by weight of water were added, heated to 115°C, stirred for 3 hours, filtered while hot, precipitated with ethanol, washed, and dried to obtain a flame retardant;

[0060] The vitamin B composition is a mixture of vitamin B2 and vitamin B8 in a mass ratio of 5:2;

[0061] S2. Pretreatment of palm fiber: The palm fiber was immersed in a 7wt% sulfuric acid solution for 40min, the solid-liquid ratio of the palm fiber and 7wt% sulfuric acid solution was 1:7g / mL, filtered, washed, and dried to obtain pretreated palm fiber;

[0062] S3. Preparation of palm fibrils: 10 parts by weight of the pretreated palm fiber obtained in step S2 was added to 50 parts by weight of PBS buffer at pH = 10.5, 5 parts by weight of urea and 6 parts by weight of 35wt% hydrogen peroxide were added, heated to 85 ° C, stirred for 30 min, filtered, washed, and dried to obtain palm fibrils;

[0063] S4. Preparation of flame-retardant natural fiber: 10 parts by weight of the palm fiber obtained in step S3 was added to 100 parts by weight of N-methylpyrrolidone, 7 parts by weight of the flame retardant obtained in step S1, 17 parts by weight of N,N-dicyclohexylcarbodiimide and 0.5 parts by weight of triethylenediamine were added, heated to 80 ° C, stirred for 4h, filtered, washed, and dried to obtain a flame-retardant natural fiber;

[0064] S5 polydopamine modification: 12 parts by weight of the flame-retardant natural fiber obtained in step S4 was added to 100 parts by weight of water, 17 parts by weight of dopamine hydrochloride and 1 part by weight of a catalyst were added, heated to 45 ° C, and the reaction was stirred for 3h to obtain a modified flame-retardant natural fiber;

[0065] The catalyst is a Tris-HCl solution with a pH of 9;

[0066] S6. Preparation of Mg-doped silicon / aluminum mixed solution: 3 parts by weight of magnesium sulfate, 15 parts by weight of tetraethyl orthosilicate, and 10 parts by weight of aluminum isopropoxide were dissolved in 100 parts by weight of a 70 wt% aqueous ethanol solution and stirred for 20 minutes to obtain a Mg-doped silicon / aluminum mixed solution;

[0067] S7. Preparation of flame-retardant fiber: 20 parts by weight of the modified flame-retardant natural fiber obtained in step S5 was added to 22 parts by weight of the Mg-doped silicon / aluminum mixed solution obtained in step S6, 5 parts by weight of 25wt% ammonia solution was added dropwise, the mixture was stirred for 60 minutes, the solvent was evaporated, washed, and dried to obtain a flame-retardant fiber.

[0068] Example 3

[0069] This embodiment provides a method for preparing a flame-retardant fiber, which specifically includes the following steps:

[0070] S1. Preparation of a flame retardant: 4 parts by weight of vitamin C and 8.5 parts by weight of a vitamin B composition and 40 parts by weight of phosphoric acid were mixed, heated to 130°C, stirred for 2 hours, and then 16 parts by weight of urea and 15 parts by weight of water were added, heated to 110°C, stirred for 2 hours, filtered while hot, precipitated with ethanol, washed, and dried to obtain a flame retardant;

[0071] The vitamin B composition is a mixture of vitamin B2 and vitamin B8 in a mass ratio of 4:2;

[0072] S2. Pretreatment of palm fiber: The palm fiber was placed in a 6wt% hydrochloric acid solution and soaked for 35min, the solid-liquid ratio of the palm fiber and 6wt% hydrochloric acid solution was 1: 6g / mL, filtered, washed, and dried to obtain pretreated palm fiber;

[0073] S3. Preparation of palm fibrils: 8.5 parts by weight of the pretreated palm fiber obtained in step S2 was added to 50 parts by weight of PBS buffer at pH = 10, 4 parts by weight of urea and 5 parts by weight of 34wt% hydrogen peroxide were added, heated to 80 ° C, stirred for 25 min, filtered, washed, and dried to obtain palm fibrils;

[0074] S4. Preparation of flame-retardant natural fiber: 10 parts by weight of the palm fiber obtained in step S3 was added to 100 parts by weight of N-methylpyrrolidone, 6 parts by weight of the flame retardant obtained in step S1, 15 parts by weight of N,N-dicyclohexylcarbodiimide and 0.35 parts by weight of 1,8-diazabicyclo[5.4.0]undec-7-ene were added, heated to 70 ° C, stirred for 3h, filtered, washed, and dried to obtain a flame-retardant natural fiber;

[0075] S5 polydopamine modification: 11 parts by weight of the flame-retardant natural fiber obtained in step S4 was added to 100 parts by weight of water, 16 parts by weight of dopamine hydrochloride and 0.7 parts by weight of a catalyst were added, heated to 42 ° C, and the reaction was stirred for 2.5h to obtain a modified flame-retardant natural fiber;

[0076] The catalyst is a Tris-HCl solution with a pH of 8.7;

[0077] S6. Preparation of Mg-doped silicon / aluminum mixed solution: 2.5 parts by weight of magnesium nitrate, 13.5 parts by weight of tetraethyl orthosilicate, and 8.5 parts by weight of aluminum isopropoxide were dissolved in 100 parts by weight of a 60 wt% aqueous ethanol solution and stirred for 20 minutes to prepare a Mg-doped silicon / aluminum mixed solution;

[0078] S7. Preparation of flame-retardant fiber: 17 parts by weight of the modified flame-retardant natural fiber obtained in step S5 was added to 20 parts by weight of the Mg-doped silicon / aluminum mixed solution obtained in step S6, 4 parts by weight of 23.5wt% ammonia solution was added dropwise, stirred and mixed for 60 minutes, the solvent was evaporated, washed, and dried to obtain a flame-retardant fiber.

[0079] Example 4

[0080] Compared with Example 3, the difference is that the vitamin B composition is a single vitamin B2.

[0081] Example 5

[0082] Compared with Example 3, the difference is that the vitamin B composition is a single vitamin B8.

[0083] Example 6

[0084] The difference compared with Example 3 is that the vitamin B composition is not added.

[0085] The details are as follows:

[0086] S1. Preparation of flame retardant: Mix 12.5 parts by weight of vitamin C and 40 parts by weight of phosphoric acid, heat to 130°C, stir and react for 2 hours, then add 16 parts by weight of urea and 15 parts by weight of water, heat to 110°C, stir and react for 2 hours, filter while hot, precipitate with ethanol, wash, and dry to obtain a flame retardant.

[0087] Example 7

[0088] Compared with Example 3, the difference is that vitamin C is not added.

[0089] The details are as follows:

[0090] S1. Preparation of a flame retardant: 12.5 parts by weight of a vitamin B composition and 40 parts by weight of phosphoric acid were mixed, heated to 130°C, stirred for 2 hours, and then 16 parts by weight of urea and 15 parts by weight of water were added, heated to 110°C, stirred for 2 hours, filtered while hot, precipitated with ethanol, washed, and dried to obtain a flame retardant;

[0091] The vitamin B composition is a mixture of vitamin B2 and vitamin B8 in a mass ratio of 4:2.

[0092] Comparative Example 1

[0093] Compared with Example 3, the difference is that urea is not added in step S1.

[0094] The details are as follows:

[0095] S1. Preparation of flame retardant: 4 parts by weight of vitamin C and 8.5 parts by weight of vitamin B composition, 40 parts by weight of phosphoric acid were mixed, heated to 130 ° C, stirred for 2h, filtered while hot, precipitated with acetone, washed, and dried to obtain a flame retardant;

[0096] The vitamin B composition is a mixture of vitamin B2 and vitamin B8 in a mass ratio of 4:2.

[0097] Comparative Example 2

[0098] Compared with embodiment 3, the difference is that step S2 is not performed.

[0099] The details are as follows:

[0100] S1. Preparation of a flame retardant: 4 parts by weight of vitamin C and 8.5 parts by weight of a vitamin B composition and 40 parts by weight of phosphoric acid were mixed, heated to 130°C, stirred for 2 hours, and then 16 parts by weight of urea and 15 parts by weight of water were added, heated to 110°C, stirred for 2 hours, filtered while hot, precipitated with ethanol, washed, and dried to obtain a flame retardant;

[0101] The vitamin B composition is a mixture of vitamin B2 and vitamin B8 in a mass ratio of 4:2;

[0102] S2. Preparation of palm fibrils: 8.5 parts by weight of palm fiber were added to 50 parts by weight of PBS buffer (pH = 10), 4 parts by weight of urea and 5 parts by weight of 34wt% hydrogen peroxide were added, heated to 80°C, stirred for 25min, filtered, washed, and dried to obtain palm fibrils;

[0103] S3. Preparation of flame-retardant natural fiber: 10 parts by weight of the palm fiber obtained in step S2 was added to 100 parts by weight of N-methylpyrrolidone, 6 parts by weight of the flame retardant obtained in step S1, 15 parts by weight of N,N-dicyclohexylcarbodiimide and 0.35 parts by weight of 1,8-diazabicyclo[5.4.0]undec-7-ene, heated to 70 ° C, stirred for 3h, filtered, washed, and dried to obtain a flame-retardant natural fiber;

[0104] S4 polydopamine modification: 11 parts by weight of the flame-retardant natural fiber obtained in step S3 was added to 100 parts by weight of water, 16 parts by weight of dopamine hydrochloride and 0.7 parts by weight of a catalyst were added, heated to 42 ° C, and the reaction was stirred for 2.5h to obtain a modified flame-retardant natural fiber;

[0105] The catalyst is a Tris-HCl solution with a pH of 8.7;

[0106] S5. Preparation of Mg-doped silicon / aluminum mixed solution: 2.5 parts by weight of magnesium nitrate, 13.5 parts by weight of ethyl orthosilicate, and 8.5 parts by weight of aluminum isopropoxide were dissolved in 100 parts by weight of a 60 wt% aqueous ethanol solution and stirred for 20 minutes to obtain a Mg-doped silicon / aluminum mixed solution;

[0107] S6. Preparation of flame-retardant fiber: 17 parts by weight of the modified flame-retardant natural fiber obtained in step S4 was added to 20 parts by weight of the Mg-doped silicon / aluminum mixed solution obtained in step S5, 4 parts by weight of 23.5wt% ammonia was added dropwise, stirred and mixed for 60 minutes, the solvent was evaporated, washed, and dried to obtain a flame-retardant fiber.

[0108] Comparative Example 3

[0109] Compared with embodiment 3, the difference is that step S3 is not performed.

[0110] The details are as follows:

[0111] S1. Preparation of a flame retardant: 4 parts by weight of vitamin C and 8.5 parts by weight of a vitamin B composition and 40 parts by weight of phosphoric acid were mixed, heated to 130°C, stirred for 2 hours, and then 16 parts by weight of urea and 15 parts by weight of water were added, heated to 110°C, stirred for 2 hours, filtered while hot, precipitated with ethanol, washed, and dried to obtain a flame retardant;

[0112] The vitamin B composition is a mixture of vitamin B2 and vitamin B8 in a mass ratio of 4:2;

[0113] S2. Pretreatment of palm fiber: The palm fiber was placed in a 6wt% hydrochloric acid solution and soaked for 35min, the solid-liquid ratio of the palm fiber and 6wt% hydrochloric acid solution was 1: 6g / mL, filtered, washed, and dried to obtain pretreated palm fiber;

[0114] S3. Preparation of flame-retardant natural fiber: 10 parts by weight of the pretreated palm fiber prepared in step S2 was added to 100 parts by weight of N-methylpyrrolidone, 6 parts by weight of the flame retardant prepared in step S1, 15 parts by weight of N,N-dicyclohexylcarbodiimide and 0.35 parts by weight of 1,8-diazabicyclo[5.4.0]undec-7-ene were added, heated to 70 ° C, stirred for 3h, filtered, washed, and dried to obtain a flame-retardant natural fiber;

[0115] S4 polydopamine modification: 11 parts by weight of the flame-retardant natural fiber obtained in step S3 was added to 100 parts by weight of water, 16 parts by weight of dopamine hydrochloride and 0.7 parts by weight of a catalyst were added, heated to 42 ° C, and the reaction was stirred for 2.5h to obtain a modified flame-retardant natural fiber;

[0116] The catalyst is a Tris-HCl solution with a pH of 8.7;

[0117] S5. Preparation of Mg-doped silicon / aluminum mixed solution: 2.5 parts by weight of magnesium nitrate, 13.5 parts by weight of ethyl orthosilicate, and 8.5 parts by weight of aluminum isopropoxide were dissolved in 100 parts by weight of a 60 wt% aqueous ethanol solution and stirred for 20 minutes to obtain a Mg-doped silicon / aluminum mixed solution;

[0118] S6. Preparation of flame-retardant fiber: 17 parts by weight of the modified flame-retardant natural fiber obtained in step S4 was added to 20 parts by weight of the Mg-doped silicon / aluminum mixed solution obtained in step S5, 4 parts by weight of 23.5wt% ammonia was added dropwise, stirred and mixed for 60 minutes, the solvent was evaporated, washed, and dried to obtain a flame-retardant fiber.

[0119] Comparative Example 4

[0120] Compared with embodiment 3, the difference is that step S5 is not performed.

[0121] The details are as follows:

[0122] S1. Preparation of a flame retardant: 4 parts by weight of vitamin C and 8.5 parts by weight of a vitamin B composition and 40 parts by weight of phosphoric acid were mixed, heated to 130°C, stirred for 2 hours, and then 16 parts by weight of urea and 15 parts by weight of water were added, heated to 110°C, stirred for 2 hours, filtered while hot, precipitated with ethanol, washed, and dried to obtain a flame retardant;

[0123] The vitamin B composition is a mixture of vitamin B2 and vitamin B8 in a mass ratio of 4:2;

[0124] S2. Pretreatment of palm fiber: The palm fiber was placed in a 6wt% hydrochloric acid solution and soaked for 35min, the solid-liquid ratio of the palm fiber and 6wt% hydrochloric acid solution was 1: 6g / mL, filtered, washed, and dried to obtain pretreated palm fiber;

[0125] S3. Preparation of palm fibrils: 8.5 parts by weight of the pretreated palm fiber obtained in step S2 was added to 50 parts by weight of PBS buffer at pH = 10, 4 parts by weight of urea and 5 parts by weight of 34wt% hydrogen peroxide were added, heated to 80 ° C, stirred for 25 min, filtered, washed, and dried to obtain palm fibrils;

[0126] S4. Preparation of flame-retardant natural fiber: 10 parts by weight of the palm fiber obtained in step S3 was added to 100 parts by weight of N-methylpyrrolidone, 6 parts by weight of the flame retardant obtained in step S1, 15 parts by weight of N,N-dicyclohexylcarbodiimide and 0.35 parts by weight of 1,8-diazabicyclo[5.4.0]undec-7-ene were added, heated to 70 ° C, stirred for 3h, filtered, washed, and dried to obtain a flame-retardant natural fiber;

[0127] S5. Preparation of Mg-doped silicon / aluminum mixed solution: 2.5 parts by weight of magnesium nitrate, 13.5 parts by weight of ethyl orthosilicate, and 8.5 parts by weight of aluminum isopropoxide were dissolved in 100 parts by weight of a 60 wt% aqueous ethanol solution and stirred for 20 minutes to obtain a Mg-doped silicon / aluminum mixed solution;

[0128] S6. Preparation of flame-retardant fiber: 17 parts by weight of the flame-retardant natural fiber obtained in step S4 was added to 20 parts by weight of the Mg-doped silicon / aluminum mixed solution obtained in step S5, 4 parts by weight of 23.5wt% ammonia was added dropwise, stirred and mixed for 60min, the solvent was evaporated, washed, and dried to obtain a flame-retardant fiber.

[0129] Comparative Example 5

[0130] Compared with Example 3, the difference is that magnesium nitrate is not added in step S6.

[0131] The details are as follows:

[0132] S6. Preparation of Mg-doped silicon / aluminum mixed solution: 13.5 parts by weight of tetraethyl orthosilicate and 8.5 parts by weight of aluminum isopropoxide were dissolved in 100 parts by weight of a 60 wt% ethanol aqueous solution, and the mixture was stirred for 20 minutes to obtain a silicon / aluminum mixed solution.

[0133] Comparative Example 6

[0134] Compared with Example 3, the difference is that no ethyl orthosilicate is added in step S6.

[0135] The details are as follows:

[0136] S6. Preparation of Mg-doped silicon / aluminum mixed solution: 2.5 parts by weight of magnesium nitrate and 22 parts by weight of aluminum isopropoxide were dissolved in 100 parts by weight of a 60 wt% ethanol aqueous solution, and stirred for 20 minutes to obtain a Mg-doped aluminum mixed solution.

[0137] Comparative Example 7

[0138] Compared with Example 3, the difference is that aluminum isopropoxide is not added in step S6.

[0139] The details are as follows:

[0140] S6. Preparation of Mg-doped silicon / aluminum mixed solution: 2.5 parts by weight of magnesium nitrate and 22 parts by weight of tetraethyl orthosilicate were dissolved in 100 parts by weight of a 60 wt% ethanol aqueous solution, and stirred for 20 minutes to obtain a Mg-doped silicon mixed solution.

[0141] Comparative Example 8

[0142] Compared with Example 3, the difference is that steps S1 and S4 are not performed.

[0143] The details are as follows:

[0144] S1. Pretreatment of palm fiber: The palm fiber was placed in a 6wt% hydrochloric acid solution and soaked for 35min, the solid-liquid ratio of the palm fiber and 6wt% hydrochloric acid solution was 1:6g / mL, filtered, washed, and dried to obtain pretreated palm fiber;

[0145] S2. Preparation of palm fibrils: 8.5 parts by weight of the pretreated palm fiber obtained in step S1 was added to 50 parts by weight of PBS buffer at pH = 10, 4 parts by weight of urea and 5 parts by weight of 34wt% hydrogen peroxide were added, heated to 80°C, stirred for 25min, filtered, washed, and dried to obtain palm fibrils;

[0146] S3 polydopamine modification: 11 parts by weight of the palm fiber obtained in step S2 was added to 100 parts by weight of water, 16 parts by weight of dopamine hydrochloride and 0.7 parts by weight of a catalyst were added, heated to 42 ° C, and stirred for 2.5h to obtain a modified fiber;

[0147] The catalyst is a Tris-HCl solution with a pH of 8.7;

[0148] S4. Preparation of Mg-doped silicon / aluminum mixed solution: 2.5 parts by weight of magnesium nitrate, 13.5 parts by weight of tetraethyl orthosilicate, and 8.5 parts by weight of aluminum isopropoxide were dissolved in 100 parts by weight of a 60 wt% aqueous ethanol solution and stirred for 20 minutes to prepare a Mg-doped silicon / aluminum mixed solution;

[0149] S5. Preparation of flame-retardant fiber: 17 parts by weight of the modified fiber obtained in step S3 was added to 20 parts by weight of the Mg-doped silicon / aluminum mixed solution obtained in step S4, 4 parts by weight of 23.5wt% ammonia was added dropwise, stirred and mixed for 60min, the solvent was evaporated, washed, and dried to obtain a flame-retardant fiber.

[0150] Comparative Example 9

[0151] Compared with embodiment 3, the difference is that steps S5 to S7 are not performed.

[0152] The details are as follows:

[0153] S1. Preparation of a flame retardant: 4 parts by weight of vitamin C and 8.5 parts by weight of a vitamin B composition and 40 parts by weight of phosphoric acid were mixed, heated to 130°C, stirred for 2 hours, and then 16 parts by weight of urea and 15 parts by weight of water were added, heated to 110°C, stirred for 2 hours, filtered while hot, precipitated with ethanol, washed, and dried to obtain a flame retardant;

[0154] The vitamin B composition is a mixture of vitamin B2 and vitamin B8 in a mass ratio of 4:2;

[0155] S2. Pretreatment of palm fiber: The palm fiber was placed in a 6wt% hydrochloric acid solution and soaked for 35min, the solid-liquid ratio of the palm fiber and 6wt% hydrochloric acid solution was 1: 6g / mL, filtered, washed, and dried to obtain pretreated palm fiber;

[0156] S3. Preparation of palm fibrils: 8.5 parts by weight of the pretreated palm fiber obtained in step S2 was added to 50 parts by weight of PBS buffer at pH = 10, 4 parts by weight of urea and 5 parts by weight of 34wt% hydrogen peroxide were added, heated to 80 ° C, stirred for 25 min, filtered, washed, and dried to obtain palm fibrils;

[0157] S4. Preparation of flame-retardant natural fiber: 10 parts by weight of palm fiber prepared in step S3 was added to 100 parts by weight of N-methylpyrrolidone, 6 parts by weight of the flame retardant prepared in step S1, 15 parts by weight of N,N-dicyclohexylcarbodiimide and 0.35 parts by weight of 1,8-diazabicyclo[5.4.0]undec-7-ene were added, heated to 70°C, stirred for 3 hours, filtered, washed, and dried to obtain a flame-retardant natural fiber.

[0158] Comparative Example 10

[0159] Compared with Example 3, the difference is that only steps S2 and S3 are included.

[0160] The details are as follows:

[0161] S1. Pretreatment of palm fiber: The palm fiber was placed in a 6wt% hydrochloric acid solution and soaked for 35min, the solid-liquid ratio of the palm fiber and 6wt% hydrochloric acid solution was 1:6g / mL, filtered, washed, and dried to obtain pretreated palm fiber;

[0162] S2. Preparation of palm fibrils: 8.5 parts by weight of the pretreated palm fiber obtained in step S1 was added to 50 parts by weight of PBS buffer at pH = 10, 4 parts by weight of urea and 5 parts by weight of 34wt% hydrogen peroxide were added, heated to 80°C, stirred for 25 minutes, filtered, washed, and dried to obtain palm fibrils.

[0163] Test Example 1

[0164] The fibers prepared in Examples 1-7 of the present invention and Comparative Examples 1-10 were subjected to performance tests.

[0165] Mechanical properties test:

[0166] Fiber tensile strength and elongation at break were tested using a single-filament tensiometer according to GB / T 14463-2022, "Viscose Staple Fibers." The fiber clamping length was 20 mm, and the tensile rate was 5 mm / min. Each fiber sample was tested 20 times, and the results were averaged. Test conditions: temperature 20°C, relative humidity 60 ± 5%.

[0167] Limiting oxygen index test:

[0168] The fiber limiting oxygen index test was performed using ASTM D2863 (oxygen index method) according to GB / T 5454-1997. Fibers were weighed as spinning samples for fabric production, with a yarn linear density of no more than 60 tex. Fabric samples measuring 150 mm x 58 mm were prepared as test samples.

[0169] Flame retardant durability test:

[0170] The fabric sample was washed in a 0.15 wt% sodium dodecylbenzenesulfonate solution at 45° C. for 10 min, rinsed with tap water for 10 s, dried to constant weight, and then flame retarded again for a limiting oxygen index test.

[0171] The results are shown in Table 1.

[0172] Table 1

[0173]

[0174] It can be seen from the above table that the flame-retardant fibers prepared in Examples 1-3 of the present invention have good mechanical properties, flame-retardant properties and durability.

[0175] Compared with Example 3, Examples 4 and 5 differ in that the vitamin B composition is a single vitamin B2 or vitamin B8. Compared with Example 3, Example 6 differs in that no vitamin B composition is added. Compared with Example 3, Example 7 differs in that no vitamin C is added. The flame retardant performance decreases. The vitamin B composition is a mixture of vitamin B2 and vitamin B8. Vitamin B2 is riboflavin, which contains rich hydroxyl structures. Vitamin B8 is inositol, a hexol of cyclohexane. Vitamin C is ascorbic acid. Since the three contain multiple reactive hydroxyl groups, they are easily modified. At the same time, vitamin B2 contains nitrogen elements that can serve as a potential gas source, and the presence of the ring structure means good thermal stability. Therefore, these vitamins can be modified and reacted with phosphoric acid to undergo ammonium salt reaction to prepare flame retardants. Since the amount of urea added is not large, a small number of hydroxyl groups in these vitamins do not react with urea to form ammonium salts after reacting with phosphoric acid, thereby retaining the phosphate groups that can undergo subsequent grafting reaction with palm fibrils.

[0176] Compared with Example 3, Comparative Example 1 is different in that urea is not added in step S1. Compared with Example 3, Comparative Example 8 is different in that steps S1 and S4 are not performed. Flame retardant performance and flame retardant durability are reduced. The flame retardant prepared by the present invention is a phosphorus and nitrogen-containing flame retardant, which has a lasting waterproof and flame retardant effect, is halogen-free, generates smoke slowly, and has no toxic components. The phosphorus-containing part loses water when heated and becomes metaphosphoric acid, which repolymerizes into stable polyphosphoric acid, covering the surface of the burning object to isolate the oxygen in the air. At the same time, phosphoric acid can promote the dehydration and carbonization of the fiber to form a carbonized protective film to achieve a flame retardant effect, and the nitrogen-containing part can effectively suppress the emission of fire smoke, and is easy to recycle and reuse. Even at high temperatures, it maintains very high stability. In the gas phase, it can resist the spread of fire by releasing stable nitrogen-based molecules. In the condensed phase, it can form complex nitrogen compounds, which can generate carbon to protect the polymer material and prevent it from decomposing under fire. At the same time, the nitrogen-containing part can release nitrogen mixed gas, weakening the gas phase, thereby suppressing the combustion process.

[0177] Compared with Example 3, Comparative Example 2 is different in that step S2 is not performed. Compared with Example 3, Comparative Example 3 is different in that step S3 is not performed. Mechanical properties and flame retardant durability are reduced. Palm fiber has the characteristics of low density, biodegradability, abundant sources and low price. It is an excellent green natural fiber. The surface of palm fiber is covered with a large amount of silica, hemicellulose and lignin. Depending on the different solubility of different components in acidic solution and alkaline buffer solution, the colloid substances such as hemicellulose and lignin covering the surface can be removed, and the silica embedded therein can be fallen off to obtain purer cellulose fiber. At the same time, through the oxidation of hydrogen peroxide, a large number of hydroxyl groups, carboxyl groups and other groups are formed on the surface of the obtained palm fibrils, which are convenient for the subsequent grafting esterification reaction with the flame retardant, so that the flame retardant can be evenly and stably fixed on the fiber, achieving a good flame retardant effect.

[0178] Comparative Example 4 differs from Example 3 in that step S5 is not performed. Mechanical properties and flame retardancy durability are reduced. The present invention modifies the surface of the prepared flame-retardant natural fiber with polydopamine. This, on the one hand, greatly increases the nitrogen content of the flame-retardant fiber and improves the flame retardant effect. On the other hand, after polydopamine modification, a large number of hydroxyl, amino, and carboxyl groups are formed on the fiber surface, which facilitates hydrogen bonding with Mg ions, alkyl orthosilicates, and aluminum isopropoxide in the subsequent Mg-doped silicon / aluminum mixed solution.

[0179] Compared with Example 3, Comparative Example 5 is different in that magnesium nitrate is not added in step S6. Compared with Example 3, the difference between Comparative Examples 6 and 7 is that no ethyl orthosilicate or aluminum isopropoxide is added in step S6. Compared with Example 3, the difference between Comparative Example 9 and Example 3 is that steps S5 to S7 are not performed. Mechanical properties, flame retardant properties, and flame retardant durability are reduced. After modification with polydopamine, a large number of hydroxyl, amino, carboxyl and other groups are formed on the surface of the fiber, which can facilitate hydrogen bonding with Mg ions, alkyl orthosilicates, and aluminum isopropoxide in the subsequent Mg-doped silicon / aluminum mixed solution. Under the action of ammonia water, a sol-gel reaction occurs, thereby forming a porous inorganic flame retardant layer on the surface of the fiber. The presence of MgO enhances the flame retardant effect, and the presence of aluminum oxide simultaneously enhances the flame retardant and high temperature resistance. The presence of silicon oxide improves the mechanical properties and flame retardant properties of the fiber. The densely distributed pore structure of the inorganic flame-retardant layer isolates the fiber combustion system from the outside air, thereby inhibiting combustion. Due to the high inorganic content of the inorganic flame-retardant layer, a dense carbonized layer forms when the fiber burns, allowing the fiber to maintain its original shape and exhibit good carbon layer stability. While the addition of flame retardants typically affects the physical and mechanical properties of viscose fiber, the grafting method of the present invention, while simultaneously adding a flame retardant and coating the surface with an inorganic flame-retardant layer, improves the mechanical properties of the flame-retardant fiber.

[0180] Comparative Example 10 differs from Example 3 in that it only includes steps S2 and S3. Mechanical properties, flame retardancy, and flame retardancy durability are significantly reduced. This indicates that the flame-retardant fiber produced by the modification method of the present invention significantly improves the flame retardancy, mechanical properties, and durability of palm fiber.

[0181] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a flame retardant fiber, characterized in that: A flame retardant is prepared by reacting a vitamin composition with phosphoric acid and urea, and then grafted onto acid-treated and oxidized palm fiber to produce a flame-retardant natural fiber. The flame-retardant natural fiber is surface-modified with polydopamine, added to a Mg-doped silicon / aluminum mixed solution, and ammonia water is added dropwise. The mixture is stirred and mixed uniformly, the solvent is evaporated, washed, and dried to produce the flame-retardant fiber. The Mg-doped silicon / aluminum mixed solution is prepared by dissolving a soluble magnesium salt, an alkyl orthosilicate, and aluminum isopropoxide in an ethanol aqueous solution, stirring and mixing uniformly to produce the Mg-doped silicon / aluminum mixed solution. The vitamin composition is a mixture of vitamin C and a vitamin B composition, and the vitamin B composition is a mixture of vitamin B2 and vitamin B8.

2. The preparation method according to claim 1, characterized in that The following steps are involved: S1. Preparation of a flame retardant: Mixing a vitamin C and vitamin B composition and phosphoric acid, heating to a first temperature, stirring the reaction, then adding urea and water, heating to a second temperature, stirring the reaction, filtering while hot, precipitating, washing, and drying to obtain a flame retardant; S2. Pretreatment of palm fiber: soaking the palm fiber in acid, filtering, washing, and drying to obtain pretreated palm fiber; S3. Preparation of palm fibrils: The pretreated palm fiber obtained in step S2 was added to PBS buffer, urea and hydrogen peroxide were added, the reaction was heated with stirring, filtered, washed, and dried to obtain palm fibrils; S4 flame retardant natural fiber preparation: the palm fiber prepared in step S3 is added to a solvent, the flame retardant prepared in step S1 is added, a water absorbent and a catalyst, the reaction is heated with stirring, filtered, washed, and dried to obtain a flame retardant natural fiber; S5 polydopamine modification: The flame-retardant natural fiber obtained in step S4 was added to water, dopamine hydrochloride and a catalyst were added, and the reaction was heated and stirred to obtain a modified flame-retardant natural fiber; S6. Preparation of Mg-doped silicon / aluminum mixed solution: dissolving a soluble magnesium salt, an alkyl orthosilicate, and aluminum isopropoxide in an ethanol aqueous solution and stirring to mix uniformly to obtain a Mg-doped silicon / aluminum mixed solution; S7. Preparation of flame-retardant fiber: The modified flame-retardant natural fiber obtained in step S5 is added to the Mg-doped silicon / aluminum mixed solution obtained in step S6, aqueous ammonia is added dropwise, stirred and mixed uniformly, the solvent is evaporated, washed, and dried to obtain a flame-retardant fiber.

3. The preparation method according to claim 2, characterized in that In step S1, the mass ratio of vitamin B2 and vitamin B8 is 3-5:2, the mass ratio of vitamin C, vitamin B composition, phosphoric acid, urea and water is 3-5:7-10:30-50:15-17:10-20, the first temperature is 120-140°C, and the second temperature is 105-115°C.

4. The preparation method according to claim 2, characterized in that The acid solution in step S2 is a 5-7wt% hydrochloric acid or sulfuric acid solution, the solid-liquid ratio of the palm fiber and the acid solution is 1:5-7g / mL, and the immersion time is 30-40min; the pH of the PBS buffer in step S3 is 9.5-10.5, the mass ratio of the pretreated palm fiber, urea and hydrogen peroxide is 7-10:3-5:4-6, the concentration of the hydrogen peroxide is 32-35wt%, the temperature of the heating and stirring reaction is 75-85°C, and the time is 20-30min.

5. The preparation method according to claim 2, characterized in that In step S4, the solvent is pyridine or N-methylpyrrolidone, the water absorbent is N,N-dicyclohexylcarbodiimide, the catalyst is selected from at least one of 4-dimethylaminopyridine, triethylenediamine, and 1,8-diazabicyclo[5.4.0]undec-7-ene, the mass ratio of the palm fiber, flame retardant, water absorbent and catalyst is 10:5-7:12-17:0.2-0.5, the temperature of the heating and stirring reaction is 60-80°C, and the time is 2-4 hours.

6. The preparation method according to claim 2, characterized in that In step S5, the mass ratio of the flame-retardant natural fiber, dopamine hydrochloride, and catalyst is 10-12:15-17:0.5-1, the catalyst is a Tris-HCl solution with a pH of 8.5-9, the temperature of the heating and stirring reaction is 40-45° C., and the time is 2-3 hours; in step S6, the alkyl orthosilicate is methyl orthosilicate or ethyl orthosilicate, the soluble magnesium salt is selected from at least one of magnesium chloride, magnesium sulfate, and magnesium nitrate, the mass ratio of the soluble magnesium salt, alkyl orthosilicate, and aluminum isopropoxide is 2-3:12-15:7-10, and the concentration of the ethanol aqueous solution is 50-70wt%.

7. The preparation method according to claim 2, characterized in that In step S7, the mass ratio of the modified flame-retardant natural fiber, the Mg-doped silicon / aluminum mixed solution, and the ammonia water is 15-20:17-22:3-5, and the concentration of the ammonia water is 22-25 wt%.

8. The preparation method according to claim 2, characterized in that The specific steps include: S1. Preparation of a flame retardant: 3-5 parts by weight of vitamin C and 7-10 parts by weight of a vitamin B composition and 30-50 parts by weight of phosphoric acid are mixed, heated to 120-140°C, stirred for 1-3h, then 15-17 parts by weight of urea and 10-20 parts by weight of water are added, heated to 105-115°C, stirred for 1-3h, filtered while hot, precipitated with ethanol, washed, and dried to obtain a flame retardant; The vitamin B composition is a mixture of vitamin B2 and vitamin B8 in a mass ratio of 3-5:2; S2 palm fiber pretreatment: the palm fiber was placed in a 5-7wt% hydrochloric acid or sulfuric acid solution and soaked for 30-40min, the solid-liquid ratio of the palm fiber and the acid was 1: 5-7g / mL, filtered, washed, and dried to obtain pretreated palm fiber; S3. Preparation of palm fibrils: 7-10 parts by weight of the pretreated palm fiber obtained in step S2 was added to 50 parts by weight of PBS buffer having a pH of 9.5-10.5, 3-5 parts by weight of urea and 4-6 parts by weight of 32-35wt% hydrogen peroxide were added, heated to 75-85°C, stirred for 20-30min, filtered, washed, and dried to obtain palm fibrils; S4. Preparation of flame-retardant natural fiber: 10 parts by weight of the palm fiber obtained in step S3 was added to 100 parts by weight of pyridine or N-methylpyrrolidone, 5-7 parts by weight of the flame retardant obtained in step S1, 12-17 parts by weight of N,N-dicyclohexylcarbodiimide and 0.2-0.5 parts by weight of a catalyst, heated to 60-80 ° C, stirred for 2-4h, filtered, washed, and dried to obtain a flame-retardant natural fiber; S5 polydopamine modification: 10-12 parts by weight of the flame-retardant natural fiber obtained in step S4 is added to 100 parts by weight of water, 15-17 parts by weight of dopamine hydrochloride and 0.5-1 parts by weight of a catalyst are added, heated to 40-45 ° C, and the reaction is stirred for 2-3h to obtain a modified flame-retardant natural fiber; The catalyst is a Tris-HCl solution with a pH of 8.5-9; S6. Preparation of Mg-doped silicon / aluminum mixed solution: 2-3 parts by weight of a soluble magnesium salt, 12-15 parts by weight of an alkyl orthosilicate, and 7-10 parts by weight of aluminum isopropoxide are dissolved in 100 parts by weight of a 50-70 wt% ethanol aqueous solution and stirred to mix uniformly to obtain a Mg-doped silicon / aluminum mixed solution; S7. Preparation of flame-retardant fiber: 15-20 parts by weight of the modified flame-retardant natural fiber obtained in step S5 is added to 17-22 parts by weight of the Mg-doped silicon / aluminum mixed solution obtained in step S6, 3-5 parts by weight of 22-25wt% ammonia water is added dropwise, the mixture is stirred and mixed evenly, the solvent is evaporated, washed, and dried to obtain a flame-retardant fiber.

9. A flame-retardant fiber produced by the preparation method according to any one of claims 1 to 8.

10. Use of the flame-retardant fiber according to claim 9 in preparing flame-retardant fabrics.

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