Chitosan phosphoric acid modified flame retardant and its application in preparing flame-retardant lyocell fiber

Abstract

The application provides a chitosan phosphoric acid modified flame retardant and application thereof in preparation of flame-retardant lyocell fibers, wherein the chitosan phosphoric acid modified flame retardant is obtained by reacting a phosphoric acid aqueous solution and chitosan at 120 DEG C for 1-2 hours, and the structure is shown as formula I; by controlling the accurate attack of phosphoric acid groups on C6-OH at a specific 120 DEG C, the similar structure with cellulose molecules can be kept, the hydrogen bond crosslinking between the flame retardant and the cellulose molecules is strengthened, and the complete amine radical is kept, and the gas phase flame retardant capacity is kept. The flame-retardant lyocell fibers prepared by using the chitosan phosphoric acid modified flame retardant have good flame-retardant effect, the biomass material is environment-friendly and non-polluted, halogen-free and formaldehyde-free, the synthesis process is simple, and the compatibility with a lyocell dissolving solution is good.

Description

Technical Field

[0001] This invention belongs to the field of flame retardant technology, and in particular relates to a chitosan phosphate modified flame retardant and its application in the preparation of flame retardant lyocell fibers. Background Technology

[0002] Chitosan, as a typical biomass flame retardant, possesses many unique advantages. It contains abundant active functional groups such as amino and hydroxyl groups, which readily attach to flame-retardant elements like nitrogen and phosphorus. Furthermore, the amino groups on chitosan themselves contain nitrogen, forming nitrogen-phosphorus flame retardants. These retardants can undergo various chemical reactions during combustion, such as dehydration and cross-linking, forming a char layer with heat-insulating and oxygen-barrier properties, effectively preventing the spread of flames. However, current chitosan-based flame retardants mostly rely on amine group reactions, losing effective flame-retardant elements and resulting in decreased flame-retardant efficiency.

[0003] Lyocell fiber is a novel, green, regenerated cellulose fiber produced from natural plant fibers through solvent spinning. It possesses advantages such as good moisture absorption and breathability, high strength, and beautiful luster, and is widely used in the textile, apparel, and chemical industries. Furthermore, compared to other regenerated cellulose fibers, lyocell fiber exhibits superior mechanical properties. Therefore, flame-retardant modification of lyocell fiber must be carried out while preserving its original properties.

[0004] Given the flammability of lyocell fiber, modifying it with biomass materials to impart durable flame retardancy, thus enabling it to meet various application scenarios, without compromising its advantages such as green recyclability and high strength, is currently a research hotspot and challenge. At present, there is no method for preparing flame-retardant lyocell fiber using chitosan phosphate modified flame retardants. Summary of the Invention

[0005] In view of this, the present invention aims to provide a chitosan-phosphate modified flame retardant and its application in the preparation of flame-retardant lyocell fibers. The flame-retardant lyocell fibers prepared using this chitosan-phosphate modified flame retardant have durable and excellent flame-retardant effects.

[0006] To achieve the above objectives, the technical solution of the present invention is implemented as follows: A chitosan-phosphate modified flame retardant, wherein the chitosan-phosphate modified flame retardant has the structure of Formula I: Equation I, where n is a positive integer; The chitosan-phosphate modified flame retardant is obtained by reacting an aqueous solution of phosphoric acid and chitosan at 120°C for 1-2 hours, and the reaction equation is as follows: .

[0007] Furthermore, the mass concentration of the phosphoric acid aqueous solution is 85%, and the molar ratio of chitosan to phosphoric acid is 1:(1-3).

[0008] Furthermore, the preparation method of chitosan-phosphate modified flame retardant is as follows: chitosan is first dissolved in a solvent, and then an aqueous solution of phosphoric acid is added for mixing; the resulting mixture is first kept at 100°C for 30 minutes, and then heated to 120°C for reaction; after the reaction is completed, it is cooled to room temperature, and the filtered product is washed with acetone and water to remove residual raw materials and reaction by-products, and finally dried at 80°C to obtain the flame retardant.

[0009] Furthermore, the solvent is N,N-dimethylformamide, dichloromethane, or tetrahydrofuran.

[0010] This invention also provides the application of the chitosan phosphate modified flame retardant as described above in the preparation of flame retardant lyocell fibers.

[0011] Furthermore, the preparation method of flame-retardant lyocell fiber is as follows: chitosan phosphoric acid modified flame retardant is mixed with lyocell fiber solution and allowed to stand for 1-3 hours to ensure the formation of ammonium ions, thereby obtaining flame-retardant lyocell spinning solution; after the flame-retardant lyocell spinning solution is defoamed, flame-retardant lyocell fiber is prepared by wet spinning process; wherein, the lyocell fiber solution is prepared by DMAC aqueous solution, cellulose and LiCl powder.

[0012] Furthermore, the preparation method of the lyocell fiber dissolving solution is as follows: DMAC aqueous solution and cellulose are placed in a three-necked flask at a liquid-to-solid ratio of (16-18):1 mL / g, and activated by heating and stirring in an oil bath at 110-150℃ for 2-5 hours; then cooled to room temperature, LiCl powder is added, and the mass ratio of LiCl powder to cellulose is (1-3):1, and the mixture is heated to 110℃ and stirred until the cellulose is completely dissolved, and then cooled to room temperature.

[0013] Furthermore, the chitosan phosphate modified flame retardant has a mass percentage of 25-30 wt% relative to the flame retardant lyocell fiber.

[0014] Preferably, the chitosan phosphate modified flame retardant has a mass percentage of 25 wt% relative to the flame-retardant lyocell fiber. That is, the ratio of chitosan phosphate modified flame retardant to lyocell fiber solution is 25:75 = 1:3.

[0015] Furthermore, the average particle size of the chitosan phosphoric acid modified flame retardant is 30 μm.

[0016] Furthermore, the wet spinning process uses water as the coagulation bath medium, with a coagulation bath temperature of 25℃-30℃ and a time of 24 hours, after which the fibers are removed and air-dried naturally.

[0017] Compared with existing technologies, the chitosan-phosphate modified flame retardant of the present invention and its application in the preparation of flame-retardant lyocell fibers have the following advantages: (1) The chitosan-phosphate modified flame retardant of the present invention is generated at a specific temperature of 120°C, and the phosphate groups are precisely controlled to attack C6-OH to obtain phosphorylated chitosan. This flame retardant can maintain a structure similar to that of cellulose molecules, and the introduced phosphate groups strengthen the hydrogen bond crosslinking between the flame retardant and cellulose molecules. The molecular structure of the flame retardant maintains the complete amine group, and the gas-phase flame retardant ability is preserved.

[0018] (2) The chitosan-phosphate modified flame retardant of this invention is essentially a phosphorus-nitrogen type flame retardant with a molecular structure similar to cellulose. It has good compatibility with lyocell fiber liquid and can be uniformly dispersed in the fiber system, ensuring the uniformity and stability of the modification effect. The flame retardant acts in the condensed phase, promoting the formation of stable carbonaceous residues (i.e., so-called coke) on the surface, acting as a barrier to prevent gaseous products from diffusing into the flame and protecting the polymer surface from the effects of heat and air. The flame retardant decomposes into an inert gas (nitrogen in this invention) at high temperatures, thereby diluting the polymer and reducing the concentration of combustible gases derived from decomposition. In addition, the bio-based flame retardant itself has the advantages of being environmentally friendly and easily degradable, without affecting the properties of the lyocell material itself, and meets the requirements for ecological textile processing.

[0019] (3) The chitosan-phosphate modified flame retardant of the present invention can form a lithium salt ammonium complex with LiCl in the lyocell fiber dissolution system, thereby fixing metal ions in the flame-retardant lyocell fiber. This not only realizes the construction of a phosphorus-based / metal ion dual-catalytic flame retardant system, but also reduces the emission of lithium ions and reduces the pressure of subsequent procedures such as wastewater treatment.

[0020] (4) The lyocell fiber dissolving solution used in this invention is a dimethylacetamide (DMAC) / lithium chloride (LiCl) system with relatively mild dissolving conditions. During the cellulose membrane forming process, it forms ammonium ions with phosphorylated chitosan, fixes lithium ions, constructs a dual catalytic flame retardant system of phosphorus and metal ions, and maintains the strength of lyocell fiber.

[0021] (5) This invention uses chitosan-phosphate modified flame retardant to prepare flame-retardant lyocell fibers. Testing its limiting oxygen index and afterflame retention revealed that adding this flame retardant significantly improves the flame-retardant efficiency and durability of the membrane. The phosphorus and nitrogen elements in this flame retardant have a synergistic flame-retardant effect, greatly promoting the combustion of the membrane material into char, resisting flame and heat erosion, and reducing the release of toxic gases. Therefore, the prepared flame-retardant fibers have low toxicity. Thanks to the structural design of the flame retardant, the similar structure of chitosan and cellulose polysaccharides enhances the bonding force between the flame retardant and the cellulose matrix, resulting in good compatibility. Compared with pure lyocell fibers, the prepared flame-retardant lyocell membrane suffers less strength damage.

[0022] (6) The flame-retardant lyocell fiber prepared by the chitosan-phosphate modified flame retardant of this invention eliminates the disadvantage of lyocell base film material being highly flammable, avoids problems such as poor durability and severe strength damage, and improves the flame retardancy of lyocell fiber. It has excellent flame-retardant properties of low toxicity, halogen-free, environmentally friendly, and durable. Therefore, while maintaining the properties of lyocell fiber, this invention provides a simple, environmentally friendly, and efficient method for preparing flame-retardant lyocell fiber. The obtained lyocell fiber is a halogen-free, environmentally friendly, highly efficient, and high-strength flame-retardant fiber. Attached Figure Description

[0023] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings: Figure 1 The FTIR spectrum of the chitosan-phosphate modified flame retardant prepared in Example 1; Figure 2 Comparison of tensile strength between Example 1 and Comparative Examples 3, 4, and 7; Figure 3 This is a diagram illustrating the open flame ignition process of the flame-retardant lyocell fiber membrane prepared in Example 1. Figure 4 This is a diagram showing the open flame ignition process of the ordinary Lyocell fiber membrane prepared by Comparative Example 7. Detailed Implementation

[0024] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

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

[0026] Example 1 1. Preparation of chitosan-phosphate modified flame retardant 1 mol of chitosan powder was added to a three-necked flask equipped with a spherical condenser, thermometer, and magnetic stirrer, and dispersed in 60 mL of DMF solvent system. 3 mol of 85 wt% aqueous phosphoric acid solution (chitosan to phosphoric acid molar ratio 1:3) was added. The resulting mixture was kept at 100 °C for 30 min, then heated to 120 °C under oil bath conditions with continuous stirring for 1.5 h. After the reaction, the mixture was cooled to room temperature, and solid-liquid separation was achieved by pressure filtration. Unreacted raw materials and reaction byproducts were removed by continuous washing with acetone and water. The mixture was then vacuum dried at 80 °C and ground to obtain a chitosan-phosphate modified flame retardant with an average particle size of 30 μm. The structural formula is shown in Formula I. Formula I; The reaction equation is as follows: .

[0027] Figure 1 The image shows the FTIR spectrum of the chitosan-phosphate modified flame retardant obtained in this embodiment. As can be seen from the image, chitosan (CS) exhibits a distinct absorption peak located at 3384 cm⁻¹. -1 -OH / NH peak, 2987 cm⁻¹ -1 CH peak, 1650cm -1 The vibrational absorption peak of amide I around 1541m -1 The NH absorption peak is located at 1361 cm⁻¹. -1 CH bending vibration peak, and 1000cm -1 The C6-OH peak disappears in the modified phosphorylated chitosan (PCS) sample, i.e., the chitosan phosphoric acid modified flame retardant prepared in this example, indicating that H3PO4 reacts with the hydroxyl group at the C6 position. In the figure, PCS is shown at 3200 cm⁻¹. -1 The broad peaks around the 1260 cm⁻¹ indicate the presence of hydrogen bonds in the flame retardant structure. The peak at 1260 cm⁻¹ is particularly prominent. -1 The P=O bond absorption peak at 1628 cm⁻¹ and the absorption peak at 1628 cm� -1 -NH at the location 3+ The absorption peaks indicate that the amino group in CS was successfully protonated, proving that this embodiment successfully obtained a chitosan phosphoric acid modified flame retardant with the structure of Formula I.

[0028] 2. Preparation of flame-retardant lyocell fibers (1) Preparation of Lyocell fiber dissolving solution Weigh 75 mL of DMAC aqueous solution and 4.5 g of cellulose, place them in a three-necked flask, heat and stir in an oil bath at 110 °C for 2 h to activate; then cool to room temperature, add 9 g of LiCl powder, continue heating to 110 °C and stirring, and then cool until the cellulose is completely transparent and dissolved with no obvious fibrous structure, indicating that the lyocell fiber is completely dissolved.

[0029] (2) Preparation of flame-retardant Lyocell spinning solution Weigh 80g of lyocell fiber solution and mix it with 25wt% (relative to flame-retardant lyocell fiber) of chitosan phosphate modified flame retardant. Stir at room temperature to ensure that the flame retardant and lyocell solution are evenly mixed and allowed to stand for 1 hour to ensure the formation of ammonium ions. Then, degas under vacuum to prepare flame-retardant lyocell spinning solution.

[0030] (3) Fiber spinning The flame-retardant lyocell spinning solution is sprayed through a spinneret into a coagulation bath to obtain nascent fibers. The spinning speed is 110 m / min and the air gap length is 5 cm. The fibers are then drawn, washed, dried and wound to obtain flame-retardant fibers.

[0031] The wet spinning process uses water as the coagulation bath medium, with a coagulation bath temperature of 25℃-30℃ and a time of 24 hours, after which the fibers are removed and air-dried naturally.

[0032] The obtained flame-retardant lyocell fiber was tested for its limiting oxygen index (LOI) (%) according to GB / T 5454-1997 "Textiles - Test for Burning Performance - Oxygen Index Method GB / T 2408-2021". The test results are shown in Table 1 below.

[0033] Example 2 1. The preparation of chitosan-phosphate modified flame retardant is the same as in Example 1.

[0034] 2. Preparation of flame-retardant lyocell fibers Step (1) is the same as in Example 1.

[0035] (2) Preparation of flame-retardant Lyocell spinning solution Weigh 80g of lyocell fiber solution, add 30wt% (relative to flame-retardant lyocell fiber) of chitosan phosphoric acid modified flame retardant, stir at room temperature to ensure uniform mixing of flame retardant and lyocell solution, and let stand for 1 hour to ensure the formation of ammonium ions. Then, degas under vacuum to prepare flame-retardant lyocell spinning solution.

[0036] Step (3) is the same as in Example 1.

[0037] The obtained flame-retardant lyocell fiber was tested for its limiting oxygen index (LOI) (%) according to GB / T 5454-1997 "Textiles - Test for Burning Performance - Oxygen Index Method GB / T 2408-2021". The test results are shown in Table 1 below.

[0038] Example 3 1. Preparation of chitosan-phosphate modified flame retardant 1 mol of chitosan powder was added to a three-necked flask equipped with a spherical condenser, thermometer, and magnetic stirrer, and dispersed in 60 mL of DMF solvent system. 2 mol of 85 wt% phosphoric acid aqueous solution (chitosan to phosphoric acid molar ratio of 1:2) was added. The resulting mixture was kept at 100 °C for 30 min, then heated to 120 °C under oil bath conditions with continuous stirring for 2 h. After the reaction, the mixture was cooled to room temperature, and solid-liquid separation was achieved by pressure filtration. Unreacted raw materials and reaction byproducts were removed by continuous washing with acetone and water. The mixture was then vacuum dried at 80 °C and ground to obtain a chitosan-phosphate modified flame retardant with an average particle size of 30 μm and a structural formula as shown in Formula I.

[0039] 2. Preparation of flame-retardant lyocell fibers (1) Preparation of Lyocell fiber dissolving solution Weigh 70 mL of DMAC aqueous solution and 4 g of cellulose, place them in a three-necked flask, heat and stir in an oil bath at 120 °C for 2.5 h to activate; then cool to room temperature, add 10 g of LiCl powder, continue heating to 110 °C and stirring, then cool until the cellulose is completely transparent and dissolved, with no obvious fibrous structure, indicating that the lyocell fiber is completely dissolved.

[0040] (2) Preparation of flame-retardant Lyocell spinning solution Weigh 80g of lyocell fiber solution and mix it with 25wt% (relative to flame-retardant lyocell fiber) of chitosan phosphate modified flame retardant. Stir at room temperature to ensure that the flame retardant and lyocell solution are evenly mixed and allowed to stand for 1.5h to ensure the formation of ammonium ions. Then, degas under vacuum to prepare flame-retardant lyocell spinning solution.

[0041] (3) Fiber spinning The flame-retardant lyocell spinning solution is sprayed through a spinneret into a coagulation bath to obtain nascent fibers. The spinning speed is 110 m / min and the air gap length is 5 cm. The fibers are then drawn, washed, dried and wound to obtain flame-retardant fibers.

[0042] The wet spinning process uses water as the coagulation bath medium, with a coagulation bath temperature of 25℃-30℃ and a time of 24 hours, after which the fibers are removed and air-dried naturally.

[0043] The obtained flame-retardant lyocell fiber was tested for its limiting oxygen index (LOI) (%) according to GB / T 5454-1997 "Textiles - Test for Burning Performance - Oxygen Index Method GB / T 2408-2021". The test results are shown in Table 1 below.

[0044] Comparative Example 1: Synthesis of Flame Retardant at 150℃ 1. Preparation of chitosan-phosphate modified flame retardant 1 mol of chitosan powder was added to a three-necked flask equipped with a spherical condenser, thermometer, and magnetic stirrer, and dispersed in 60 mL of DMF solvent. 3 mol of 85 wt% aqueous phosphoric acid solution (chitosan to phosphoric acid molar ratio of 1:3) was added. The resulting mixture was kept at 100 °C for 30 min, then heated to 150 °C under oil bath conditions with continuous stirring for 1.5 h. After the reaction was complete, the mixture was cooled to room temperature, and solid-liquid separation was achieved by pressure filtration. Unreacted raw materials and reaction byproducts were removed by continuous washing with acetone and water. The mixture was then vacuum dried at 80 °C and ground to obtain the flame retardant.

[0045] 2. The preparation of flame-retardant lyocell fibers is the same as in Example 1.

[0046] The obtained flame-retardant lyocell fiber was tested for its limiting oxygen index (LOI) (%) according to GB / T 5454-1997 "Textiles - Test for Burning Performance - Oxygen Index Method GB / T 2408-2021". The test results are shown in Table 1 below.

[0047] Comparative Example 2: Synthesis of Flame Retardant at 110℃ 1. Preparation of chitosan-phosphate modified flame retardant 1 mol of chitosan powder was added to a three-necked flask equipped with a spherical condenser, thermometer, and magnetic stirrer, and dispersed in 60 mL of DMF solvent. 3 mol of 85 wt% phosphoric acid aqueous solution (chitosan to phosphoric acid molar ratio of 1:3) was added. The resulting mixture was kept at 100 °C for 30 min, then heated to 110 °C under oil bath conditions with continuous stirring for 1.5 h. After the reaction was complete, the mixture was cooled to room temperature, and solid-liquid separation was achieved by pressure filtration. Unreacted raw materials and reaction byproducts were removed by continuous washing with acetone and water. The mixture was then vacuum dried at 80 °C and ground to obtain the flame retardant.

[0048] 2. The preparation of flame-retardant lyocell fibers is the same as in Example 1.

[0049] The obtained flame-retardant lyocell fiber was tested for its limiting oxygen index (LOI) (%) according to GB / T 5454-1997 "Textiles - Test for Burning Performance - Oxygen Index Method GB / T 2408-2021". The test results are shown in Table 1 below.

[0050] Comparative Example 3: Less Flame Retardant 1. The preparation of chitosan-phosphate modified flame retardant is the same as in Example 1.

[0051] 2. Preparation of flame-retardant lyocell fibers Step (1) is the same as in Example 1.

[0052] (2) Preparation of flame-retardant Lyocell spinning solution Weigh 80g of lyocell fiber solution and mix it with 15wt% (relative to flame-retardant lyocell fiber) of chitosan phosphoric acid modified flame retardant. Stir at room temperature to ensure that the flame retardant and lyocell solution are evenly mixed and allowed to stand for 1 hour to ensure the formation of ammonium ions. Then, degas under vacuum to prepare flame-retardant lyocell spinning solution.

[0053] Step (3) is the same as in Example 1.

[0054] The obtained flame-retardant lyocell fiber was tested for its limiting oxygen index (LOI) (%) according to GB / T 5454-1997 "Textiles - Test for Burning Performance - Oxygen Index Method GB / T 2408-2021". The test results are shown in Table 1 below.

[0055] Comparative Example 4: Less Flame Retardant 1. The preparation of chitosan-phosphate modified flame retardant is the same as in Example 1.

[0056] 2. Preparation of flame-retardant lyocell fibers Step (1) is the same as in Example 1.

[0057] (2) Preparation of flame-retardant Lyocell spinning solution Weigh 80g of lyocell fiber solution, add 20wt% (relative to flame-retardant lyocell fiber) of chitosan phosphate modified flame retardant, stir at room temperature to ensure uniform mixing of flame retardant and lyocell solution, and let stand for 1 hour to ensure the formation of ammonium ions. Then, degas under vacuum to prepare flame-retardant lyocell spinning solution.

[0058] Step (3) is the same as in Example 1.

[0059] The obtained flame-retardant lyocell fiber was tested for its limiting oxygen index (LOI) (%) according to GB / T 5454-1997 "Textiles - Test for Burning Performance - Oxygen Index Method GB / T 2408-2021". The test results are shown in Table 1 below.

[0060] Comparative Example 5: No 100℃ insulation 1. Preparation of chitosan-phosphate modified flame retardant 1 mol of chitosan powder was added to a three-necked flask equipped with a spherical condenser, thermometer, and magnetic stirrer, and dispersed in 60 mL of DMF solvent system. 3 mol of 85 wt% aqueous phosphoric acid solution (chitosan to phosphoric acid molar ratio of 1:3) was added, and the resulting mixture was stirred continuously in an oil bath at 120 °C for 1.5 h. After the reaction, the mixture was cooled to room temperature, and solid-liquid separation was achieved by pressure filtration. Unreacted raw materials and reaction byproducts were removed by continuous washing with acetone and water. The mixture was then vacuum dried at 80 °C to obtain a chitosan-phosphate modified flame retardant with the structural formula shown in Formula I.

[0061] 2. The preparation of flame-retardant lyocell fibers is the same as in Example 1.

[0062] The obtained flame-retardant lyocell fiber was tested for its limiting oxygen index (LOI) (%) according to GB / T 5454-1997 "Textiles - Test for Burning Performance - Oxygen Index Method GB / T 2408-2021". The test results are shown in Table 1 below.

[0063] Comparative Example 6: Different Lyocell Fiber Dissolving Solutions 1. The preparation of chitosan-phosphate modified flame retardant is the same as in Example 1.

[0064] 2. Preparation of flame-retardant lyocell fibers (1) Preparation of Lyocell fiber dissolving solution A conventional NMMO solvent system was used, in which cellulose was dissolved in NMMO to obtain a lyocell cellulose solution.

[0065] Steps (2)-(3) are the same as in Example 1.

[0066] The obtained flame-retardant lyocell fiber was tested for its limiting oxygen index (LOI) (%) according to GB / T 5454-1997 "Textiles - Test for Burning Performance - Oxygen Index Method GB / T 2408-2021". The test results are shown in Table 1 below.

[0067] Comparative Example 7: Ordinary Lyocell Fiber The difference from Example 1 is that no flame retardant is added, and ordinary lyocell fiber is obtained.

[0068] The obtained flame-retardant lyocell fiber was tested for its limiting oxygen index (LOI) (%) according to GB / T 5454-1997 "Textiles - Test for Burning Performance - Oxygen Index Method GB / T 2408-2021". The test results are shown in Table 1 below.

[0069] Table 1. Performance Comparison of Various Examples and Comparative Examples

[0070] As shown in Table 1, after adding chitosan-phosphate modified flame retardant in Examples 1-3, the LOI value was >31%, and the fibers were self-extinguishing upon ignition with an open flame. This indicates that the lyocell fiber exhibits excellent flame retardant performance after adding the chitosan-phosphate modified flame retardant prepared in this invention, reaching the level of flame-retardant materials. Furthermore, when the flame retardant content increased from 25wt% to 30wt%, the increase in LOI value was not significant enough. Considering cost control in practical applications, the optimal addition concentration can be set at 25wt%.

[0071] The flame retardants used in Comparative Examples 1 and 2 were prepared at 150℃ and 110℃, respectively. Their flame retardant effects were significantly inferior to those prepared at 120℃. At the specific temperature of 120℃, the phosphate groups could be precisely controlled to attack C6-OH, resulting in phosphorylated chitosan with superior performance. Furthermore, the flame retardant in Comparative Example 1 underwent severe carbonization at higher temperatures, leading to a decreased ability to form hydrogen bonds with cellulose molecules, resulting in poor compatibility and significant damage to fiber strength.

[0072] Comparative Examples 3 and 4 used flame retardant content below 25%, resulting in significantly poorer flame retardant performance and a lack of self-extinguishing properties. Furthermore, Figure 2 A comparison of breaking forces is given, illustrating that insufficient flame retardant content also affects mechanical properties. In Example 1, the increased amount of flame retardant resulted in a denser hydroxyl crosslinking network between the flame retardant and the Lyocell matrix. Example 1 maintained the same strength as Lyocell, better preserving the inherent advantages of Lyocell fiber.

[0073] In Comparative Example 5, the chitosan molecules were poorly infiltrated and expanded under conditions of no heat preservation during the preparation process, resulting in low flame retardant efficiency.

[0074] In Comparative Example 6, the flame retardant is easily lost in the NMMO solution system, while in the DMAC / LiCl system, ammonium ions and lithium ions form lithium salt ammonium ions, which can stably exist in the solution system and fix the metal ions, ensuring the metal-catalyzed flame retardant mechanism. During combustion, the flame retardant itself forms char and catalyzes the char formation of lyocell fibers, thus forming a condensed phase char layer. The formation of the lithium salt ammonium complex consolidates the catalytic effect of the flame retardant, strengthens the char layer, slows down the transfer of oxygen and heat between the combustible material and the outside environment, and releases non-combustible gases to dilute the fuel and oxygen concentration in the combustion system, exhibiting good flame retardant efficiency for lyocell materials.

[0075] Since there is no reliable standard for small-fire ignition of fibers, the performance of flame-retardant Lyocell fibers is demonstrated by testing the corresponding fiber membranes. Figure 3 and Figure 4 The images show the ignition process of the fiber membranes prepared from Lyocell fibers in Example 1 and Comparative Example 7, respectively. It can be seen that the flame-retardant Lyocell fiber membrane prepared in Example 1 self-extinguishes after being ignited twice, thus achieving flame retardancy. This indicates that the flame-retardant Lyocell fiber prepared according to the present invention has good flame-retardant properties.

[0076] 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 within the protection scope of the present invention.

Claims

1. A method for preparing flame-retardant lyocell fiber, characterized in that, Chitosan phosphoric acid modified flame retardant was mixed with lyocell fiber solution and allowed to stand for 1-3 hours to ensure the formation of ammonium ions, thus obtaining flame retardant lyocell spinning solution. After the flame retardant lyocell spinning solution was defoamed, flame retardant lyocell fiber was prepared by wet spinning process. The lyocell fiber solution was prepared from DMAC aqueous solution, cellulose and LiCl powder. The chitosan phosphoric acid modified flame retardant has the structure of Formula I: Equation I, where n is a positive integer; The chitosan-phosphate modified flame retardant is obtained by reacting an aqueous solution of phosphoric acid and chitosan at 120°C for 1-2 hours, and the reaction equation is as follows: 。 2. The method for preparing flame-retardant lyocell fiber according to claim 1, characterized in that, The mass concentration of the phosphoric acid aqueous solution is 85%, and the molar ratio of chitosan to phosphoric acid is 1:(1-3).

3. The method for preparing flame-retardant lyocell fiber according to claim 1, characterized in that, The preparation method of chitosan-phosphate modified flame retardant is as follows: chitosan is first dissolved in a solvent, and then an aqueous solution of phosphoric acid is added for mixing; the resulting mixture is first kept at 100℃ for 30 min, and then heated to 120℃ for reaction; after the reaction is completed, it is cooled to room temperature, and the filtered product is washed with acetone and water to remove residual raw materials and reaction by-products, and finally dried at 80℃ to obtain the flame retardant.

4. The method for preparing flame-retardant lyocell fiber according to claim 3, characterized in that, The solvent is N,N-dimethylformamide, dichloromethane, or tetrahydrofuran.

5. The method for preparing flame-retardant lyocell fiber according to claim 1, characterized in that, The preparation method of lyocell fiber dissolving solution is as follows: DMAC aqueous solution and cellulose are placed in a three-necked flask at a liquid-to-solid ratio of (16-18):1, and activated by heating and stirring in an oil bath at 110-150℃ for 2-5 hours; then cooled to room temperature, LiCl powder is added, and the mass ratio of LiCl powder to cellulose is (1-3):1, and the mixture is heated to 110℃ and stirred until the cellulose is completely dissolved, and then cooled to room temperature.

6. The method for preparing flame-retardant lyocell fiber according to claim 1, characterized in that, The chitosan-phosphate modified flame retardant has a mass percentage of 25-30 wt% relative to the flame-retardant lyocell fiber.

7. The method for preparing flame-retardant lyocell fiber according to claim 1, characterized in that, The average particle size of the chitosan phosphoric acid modified flame retardant is 30 μm.

8. The method for preparing flame-retardant lyocell fiber according to claim 1, characterized in that, The wet spinning process uses water as the coagulation bath medium, with a coagulation bath temperature of 25℃-30℃ and a time of 24 hours, after which the fibers are removed and air-dried naturally.

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