A flame retardant, a flame-retardant lyocell fiber and a preparation method and application thereof

Abstract

The application discloses a kind of flame retardant, flame-retardant Lyocell fiber and its preparation method and application.The flame retardant compound of the application has the structure as shown in formula I: Wherein, R1 is selected from-OCH3, -OCH2CH3, -OCH2CH2CH3, R2 is selected from-NHCH2COOH, -NHCH2CH2COOH, complex flame retardant includes the flame-retardant compound and inorganic flame-retardant auxiliary agent;The inorganic flame-retardant auxiliary agent is graphene or graphene derivative.The flame retardant compound of the application contains flame-retardant elements phosphorus and nitrogen, and contains carboxyl structure, can be combined with the hydroxyl on cellulose, can improve the firmness of combination with fiber, and has good flame retardancy, can form complex flame retardant system with inorganic flame-retardant auxiliary agent, is added into fiber spinning dope to prepare flame-retardant Lyocell fiber, and flame-retardant performance is excellent, good durability, while flame-retardant agent is less in amount, need not add emulsifying agent, dispersing agent and other auxiliary agents, and spinning process is green and environment-friendly.

Description

Technical Field

[0001] This invention belongs to the field of textile fiber preparation, specifically, it relates to a flame retardant, flame retardant Lyocell fiber, its preparation method and application. Background Technology

[0002] Lyocell fiber is made from natural cellulose as raw material and N-methylmorpholine-N-oxide (NMMO) as solvent through dry and wet spinning, followed by coagulation, stretching, and winding processes. Its production process is simple, the solvent is non-toxic and recyclable, making it a truly green fiber. Lyocell fabrics possess a variety of excellent properties, including comfort, breathability, and a soft hand feel, thus finding wide application in clothing, home textiles, and many other fields. However, Lyocell fiber is flammable, and fires caused by its products have become one of the major disasters in modern society, limiting its application in fields with high flame-retardant requirements.

[0003] Therefore, flame-retardant modification of Lyocell fibers is an effective way to solve these problems. Currently, the modification of flame-retardant Lyocell fibers is mainly done through blending, which results in a large amount of flame retardant entering the coagulation bath, making solvent recovery difficult. Not only is the amount of flame retardant added large, but the mechanical properties of the fiber are also significantly reduced. Furthermore, considering the compatibility of the flame retardant with the spinning solution, emulsifiers and dispersants are needed to address issues such as easy agglomeration of the flame retardant. After repeated use and washing, the flame-retardant performance of the fiber product will be greatly reduced. Therefore, how to prepare flame-retardant Lyocell fibers with high flame-retardant performance that can permanently maintain its flame-retardant properties is a key focus of research and attention.

[0004] In view of this, the present invention is proposed. Summary of the Invention

[0005] The technical problem this invention aims to solve is to overcome the shortcomings of existing technologies and provide a flame retardant, flame-retardant Lyocell fiber, its preparation method, and its applications. This invention simultaneously introduces phosphorus and nitrogen, elements with flame-retardant properties, and carboxyl groups that can react with hydroxyl groups on cellulose into a compound to obtain a flame retardant compound. This compound can form a complex flame retardant system with inorganic synergistic flame retardant additives (i.e., inorganic flame retardant additives). The flame-retardant Lyocell fiber prepared by adding the complex flame-retardant system to the fiber spinning solution exhibits excellent flame-retardant properties and good durability. Furthermore, the amount of flame retardant added is small, and no emulsifiers, dispersants, or other additives are required, making the spinning process green and environmentally friendly.

[0006] To solve the above-mentioned technical problems, the basic concept of the technical solution adopted by the present invention is as follows:

[0007] The first object of the present invention is to provide a flame retardant compound having a structure as shown in Formula I:

[0008]

[0009] Wherein, R1 is selected from -OCH3, -OCH2CH3, -OCH2CH2CH3, and R2 is selected from -NHCH2COOH, -NHCH2CH2COOH.

[0010] In a further embodiment, the structure of the flame retardant monomer is shown in Formula II, or Formula III, or Formula IV:

[0011]

[0012] The flame retardant compound of this invention is a phosphazene compound. On the one hand, it contains both the flame-retardant elements phosphorus and nitrogen, which have a good effect on inhibiting the combustion of fibers. On the other hand, the carboxyl groups introduced on the phosphazene compound can interact with the hydroxyl groups on cellulose through hydrogen bonds, resulting in a strong bond between the flame retardant compound and the fiber, preventing the flame retardant from seeping out of the fiber during the coagulation and washing stage. Thus, not only can the mechanical properties of flame-retardant fibers be improved, but the durability of flame-retardant Lyocell fibers can also be enhanced, while avoiding the use of emulsifiers and dispersants.

[0013] A second objective of this invention is to provide a compound flame retardant comprising the flame retardant compound and an inorganic flame retardant additive as described above; wherein the inorganic flame retardant additive is graphene or a graphene derivative.

[0014] In this invention, the above-mentioned phosphazene compound containing a carboxyl group (the flame retardant compound is used as the main flame retardant) is further compounded with an inorganic flame retardant auxiliary to obtain a compound flame retardant, which can work synergistically. The main flame retardant phosphazene compound, as a phosphorus and nitrogen flame retardant system, has a good effect on inhibiting the combustion of fibers. The addition of inorganic flame retardant auxiliaries can work with the main flame retardant to inhibit the combustion of fibers, and can change the fiber's pyrolysis, heat conduction, heat absorption, viscosity and dripping properties, which is beneficial to improving the mechanical properties and durability of flame retardant fibers.

[0015] A third object of the present invention is to provide a method for preparing the flame-retardant compound as described above, comprising:

[0016] (1) Mix a benzene solution, a monohydric alcohol solution and an organic amine compound of hexachlorocyclotriphosphazene and carry out a nucleophilic substitution reaction to obtain a trioxy-trichlorocyclotriphosphazene compound;

[0017] (2) The trioxy-trichlorocyclotriphosphazene compound, amino acid compound, catalyst and reaction solvent are mixed and subjected to nucleophilic substitution reaction. The trioxy-acid aminocyclotriphosphazene compound is obtained by neutralization, extraction, vacuum distillation, recrystallization and drying.

[0018] In a further embodiment, in step (1), the molar ratio of the hexachlorocyclotriphosphazene compound, the monohydric alcohol compound, and the organic amine compound is 1:(3-5):(7-9).

[0019] In a further embodiment, the concentration of hexachlorocyclotriphosphazene in the benzene solution is 0.2–0.8 g / mL.

[0020] In a further embodiment, the monohydric alcohol solution is selected from one or more of methanol, ethanol, and n-propanol.

[0021] In a further embodiment, the organic amine compound is selected from one or more of triethylamine and trimethylamine.

[0022] In a further embodiment, the benzene solvent in the hexachlorocyclotriphosphazene benzene solution is selected from one or more of cumene, biphenyl, toluene, or xylene.

[0023] In a further scheme, in step (1), the nucleophilic substitution reaction is carried out at a temperature of 70-120℃ for 8-12 hours.

[0024] In a further embodiment, in step (2), the molar ratio of the trioxy-acid aminocyclotriphosphazene compound, the amino acid compound, the catalyst, and the reaction solvent is 1:(5-7):(6-9):(10-12).

[0025] In a further embodiment, the amino acid compound has the structural formula NH2-R3-COOH, where R3 is selected from -CH2-.

[0026] -CH2CH2-,

[0027] In a further embodiment, the catalyst is selected from one or more of potassium carbonate, cesium carbonate, cesium fluoride, lithium carbonate, or sodium hydride.

[0028] In a further embodiment, the reaction solvent is selected from one or more of dimethyl sulfoxide, N-methylpyrrolidone, N,N-dimethylformamide, or N,N-dimethylacetamide.

[0029] In a further scheme, in step (2), the nucleophilic substitution reaction temperature is 100-150℃ and the time is 8-16h.

[0030] In a further step, in step (2), the neutralizing agent used during neutralization is selected from one or more of sodium carbonate, potassium carbonate, calcium carbonate, sodium bicarbonate, potassium bicarbonate, and ammonium bicarbonate.

[0031] In a further embodiment, in step (2), the organic solvent used for extraction is selected from one or more of dichloromethane, trichloromethane, carbon tetrachloride, ethyl acetate, and petroleum ether.

[0032] In a further embodiment, step (2) involves recrystallization as follows: adding the vacuum distillation product to an aqueous solution of N,N-dimethylformamide or N,N-dimethylacetamide with a mass fraction of 80%, heating under reflux and then cooling to obtain a supersaturated solution, and then using hydrothermal crystallization to precipitate a trioxy-acid aminocyclotriphosphazene compound at a high temperature and high pressure of 200-230℃ and 0.2-0.5GPa.

[0033] A fourth objective of this invention is to provide the application of the flame-retardant compound or the compounded flame-retardant described above in the preparation of flame-retardant fibers; preferably, in the preparation of flame-retardant Lyocell fibers.

[0034] The fifth objective of this invention is to provide a flame-retardant Lyocell fiber comprising a flame-retardant compound, an inorganic flame-retardant additive, and cellulose as shown in Formula I, II, III, or IV above, wherein the mass ratio of the flame-retardant compound, the inorganic flame-retardant additive, and cellulose is 1:(0.02 to 0.04):(10 to 20).

[0035] Preferably, the inorganic flame retardant is graphene or a graphene derivative.

[0036] In this invention, the inorganic flame retardant additive can also be called an inorganic synergistic flame retardant additive. The flame-retardant Lyocell fiber prepared by mixing and dissolving flame retardant compounds and inorganic flame retardant additives with cellulose pulp and then spinning, requires only a small amount of flame retardant compounds and inorganic flame retardant additives, and does not require the addition of emulsifiers, dispersants, or other additives. The fiber exhibits excellent flame retardant properties, good durability, and high mechanical properties.

[0037] Preferably, the flame retardant compound has an average particle size of 5 μm;

[0038] Preferably, the average particle size of the inorganic flame retardant is 400-800 nm, and more preferably, the average particle size is 500-700 nm.

[0039] By controlling the average particle size of flame retardant compounds and inorganic flame retardant auxiliaries, a more uniform spinning solution can be obtained, which is beneficial to improving the mechanical properties of flame retardant fibers, and to better combining flame retardant compounds and inorganic flame retardant auxiliaries with cellulose, thereby improving the flame retardancy and durability of the fibers.

[0040] The sixth objective of this invention is to provide a method for preparing the flame-retardant Lyocell fiber as described above, comprising:

[0041] (1) Mix the flame retardant compound, inorganic flame retardant additive and NMMO aqueous solution as described above, and stir to obtain NMMO mixed solution of flame retardant compound system;

[0042] (2) The NMMO mixed solution, antioxidant, stabilizer and cellulose pulp flakes of the flame retardant compound system are mechanically stirred and swollen, and then dissolved under vacuum to prepare the spinning solution;

[0043] (3) The spinning solution is spun by a dry-wet method, and the fibers are formed in a coagulation bath after passing through a spinneret. Then, flame-retardant Lyocell fibers are obtained by stretching, washing, and drying.

[0044] Preferably, in the NMMO aqueous solution of step (1), the mass concentration of NMMO is 70-78%, the temperature is 50-80℃, and the stirring time is 1-3h.

[0045] Preferably, in step (1), the mass ratio of the flame retardant compound, the inorganic flame retardant additive, and the NMMO aqueous solution is 1:

[0046] (0.025-0.04): (55-75).

[0047] A further approach involves preparing the dried cellulose pulp into uniformly sized cellulose pulp flakes before processing; the size of the cellulose pulp flakes is (0.5–2 cm) × (0.5–2 cm), which facilitates swelling and dissolution.

[0048] In a further embodiment, the mass ratio of the cellulose pulp to the spinning solution is 5–20:100;

[0049] In other words, the dry matter content of cellulose in the spinning solution is 5%-20%.

[0050] In a further embodiment, the antioxidant is hydroxylamine and the stabilizer is n-propyl gallate;

[0051] In a further embodiment, the temperature of the dry-wet spinning process is 85–110°C, and the pressure is 5–15 kPa.

[0052] The temperature of the coagulation bath is 10-30℃, and the coagulation bath is an aqueous solution containing NMMO, wherein the mass percentage content of NMMO in the coagulation bath is 0-30%.

[0053] After the spinning solution is prepared by the present invention, it can be spun using existing spinning equipment, methods and conditions. The above is only one embodiment provided by the present invention.

[0054] By adopting the above technical solution, the present invention has the following beneficial effects compared with the prior art:

[0055] 1. The flame retardant compound provided by this invention is a trioxy-acid aminocyclotriphosphazene compound. By introducing a carboxyl group into the phosphazene compound, a phosphazene compound containing the flame retardant elements nitrogen and phosphorus is obtained. This compound can not only play a good flame retardant role, but the carboxyl group can also interact with the hydroxyl groups on cellulose, so that the flame retardant has a good binding strength with the fiber, preventing the flame retardant from seeping out of the fiber during the coagulation and washing stage. This not only improves the mechanical properties of the flame retardant fiber, but also improves the durability of the flame retardant Lyocell fiber.

[0056] 2. In this invention, the above-mentioned trioxy-aminocyclotriphosphazene compound containing a carboxyl group is further compounded with an inorganic synergistic flame retardant to obtain a compound flame retardant; the obtained compound flame retardant system is further mixed with pulp and dissolved and spun to obtain flame-retardant Lyocell fiber. The main flame retardant, the phosphazene compound, as a phosphorus-nitrogen flame retardant system, has a good effect on inhibiting fiber combustion; the carboxyl group contained in the phosphazene compound is firmly bound to the fiber, and the addition of the inorganic synergistic agent can work synergistically with the main flame retardant to jointly inhibit fiber combustion, and can change the fiber's pyrolysis, heat conduction, heat absorption, viscosity, and dripping properties.

[0057] The resulting flame-retardant Lyocell fiber also contains nitrogen and phosphorus flame-retardant elements, as well as inorganic synergistic flame-retardant additives. Moreover, the carboxyl groups on the phosphazene compound can interact with the hydroxyl groups on the cellulose through hydrogen bonds, which can ensure that the flame retardant is effectively incorporated into the fiber, increasing the incorporation rate of the flame retardant in the fiber. Even with a small amount of flame retardant added, the fiber still has excellent flame-retardant properties and washability, improving the durability and mechanical properties of the flame-retardant Lyocell fiber. The small amount of flame retardant added also avoids the use of emulsifiers and dispersants.

[0058] The specific embodiments of the present invention will now be described in further detail with reference to the accompanying drawings. Attached Figure Description

[0059] The accompanying drawings, as part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments and descriptions of the invention are used to explain the invention, but do not constitute an undue limitation of the invention. Obviously, the drawings described below are merely some embodiments, and those skilled in the art can obtain other drawings based on these drawings without creative effort. In the drawings:

[0060] Figure 1 This is the infrared spectrum of the trimethoxy-triacetic acid aminocyclotriphosphazene compound prepared in Example 1 of this invention.

[0061] It should be noted that these accompanying drawings and textual descriptions are not intended to limit the scope of the invention in any way, but rather to illustrate the concept of the invention to those skilled in the art by referring to specific embodiments. Detailed Implementation

[0062] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments will be clearly and completely described below with reference to the accompanying drawings. The following embodiments are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0063] Unless otherwise specified, all raw materials required for preparation in this invention are commercially available products well known in the art.

[0064] In this invention, unless otherwise specified, the process or method of solution mixing can be carried out according to processes and conditions known in the art that can mix the raw materials evenly.

[0065] The flame retardant compound provided by this invention has the structure shown in Formula I:

[0066]

[0067] Wherein, R1 is selected from -OCH3, -OCH2CH3, -OCH2CH2CH3, and R2 is selected from -NHCH2COOH, -NHCH2CH2COOH.

[0068] The preparation method of the flame retardant compound as described in Formula I includes:

[0069] (1) Mix a benzene solution, a monohydric alcohol solution and an organic amine compound of hexachlorocyclotriphosphazene and carry out a nucleophilic substitution reaction to obtain a trioxy-trichlorocyclotriphosphazene compound;

[0070] (2) The trioxy-trichlorocyclotriphosphazene compound, amino acid compound, catalyst and reaction solvent are mixed and subjected to nucleophilic substitution reaction. The trioxy-acid aminocyclotriphosphazene compound is obtained by neutralization, extraction, vacuum distillation, recrystallization and drying.

[0071] In this invention, the substitution reaction process is as follows:

[0072]

[0073] In this invention, R1 includes, but is not limited to, -OCH3, -OCH2CH3, and -OCH2CH2CH3, and R2 includes, but is not limited to, -NHCH2COOH and -NHCH2CH2COOH.

[0074] Example 1

[0075] Preparation of trimethoxy-trichlorocyclotriphosphazene compounds:

[0076] 1 kg of hexachlorocyclotriphosphazene and 1.5 L of toluene were added to a 2 L reactor equipped with a mechanical stirrer. The temperature was increased to 80 °C at a rate of 5 °C / min, and stirring was continued until the hexachlorocyclotriphosphazene was fully dissolved. Then, 0.5 L of methanol was added and stirring was continued while nitrogen was introduced for protection. The temperature was increased to 90 °C at a rate of 2 °C / min, and 3 L of triethylamine was slowly added dropwise. When white fumes were produced in the system, the reaction was continued for 8 hours. The reactor was cooled, and the precipitate formed in the reactor was filtered. The crude product was placed in a vacuum tube furnace and heated to 200 °C to sublimate the crude product. The sublimation product was collected. The yield of the trimethoxy-trichlorocyclotriphosphazene compound was 86%, and the structure of the obtained product is as follows:

[0077]

[0078] Preparation of trimethoxy-triacetic acid aminocyclotriphosphazene compounds:

[0079] In a 2L reactor equipped with a mechanical stirrer, under stirring and nitrogen protection conditions, 0.5 kg of trimethoxy-trichlorocyclotriphosphazene compound, 1.3 L of N,N-dimethylformamide, and 1.5 kg of potassium carbonate catalyst were added as reactants. The system was slowly heated to 120°C, and then 0.6 kg of glycine was added. The reaction was carried out for 10 h, followed by a gentle heating to 50°C for 1 h. Sodium bicarbonate was added to neutralize the acidity of the reaction system. After extraction with dichloromethane and removal of organic solvent by vacuum distillation, the solution was heated to reflux with an 80% N,N-dimethylformamide aqueous solution to obtain a supersaturated solution. After cooling, the supersaturated solution was concentrated under high temperature and high pressure at 220°C and 0.3 GPa to precipitate trimethoxy-triacetic acid aminocyclotriphosphazene compound. The yield of trimethoxy-triacetic acid aminocyclotriphosphazene compound was 75%, and the structure of the obtained product is as follows:

[0080]

[0081] Example 2

[0082] Preparation of triethoxy-trichlorocyclotriphosphazene compounds:

[0083] 1 kg of hexachlorocyclotriphosphazene and 1.25 L of toluene were added to a 2 L reactor equipped with a mechanical stirrer. The temperature was increased to 100 °C at a rate of 4 °C / min, and stirring was continued until the hexachlorocyclotriphosphazene was fully dissolved. Then, 0.6 L of ethanol was added and stirring was continued while nitrogen was introduced for protection. The temperature was increased to 100 °C at a rate of 2 °C / min, and 3.2 L of triethylamine was slowly added dropwise. When white fumes were produced in the system, the reaction was continued for 12 h. The reactor was cooled and the precipitate formed in the reactor was filtered. The crude product was placed in a vacuum tube furnace and heated to 280 °C to sublimate the crude product. The sublimation product was collected. The yield of the triethoxy-trichlorocyclotriphosphazene compound was 80%, and the structure of the obtained product is as follows:

[0084]

[0085] Preparation of triethoxy-tripropionic acid aminocyclotriphosphazene compounds:

[0086] In a 2L reactor equipped with a mechanical stirrer, under stirring and nitrogen protection conditions, 0.6 kg of triethoxy-trichlorocyclotriphosphazene compound, 1.2 L of dimethyl sulfoxide, and 0.3 kg of sodium hydride catalyst were added as reactants. The system was slowly heated to 120°C, and then 0.8 kg of beta-amino acid was added. The reaction was carried out for 15 h, followed by a gentle heating to 55°C for 2 h. Potassium bicarbonate was added to neutralize the acidity of the reaction system. After extraction with carbon tetrachloride and removal of organic solvent by vacuum distillation, the solution was heated to reflux with an 80% N,N-dimethylformamide aqueous solution to obtain a supersaturated solution. After cooling, the supersaturated solution was concentrated under high temperature and high pressure at 20°C and 0.3 GPa to precipitate triethoxy-tripropionic acid aminocyclotriphosphazene compound. The yield of triethoxy-tripropionic acid aminocyclotriphosphazene compound was 77%. The structure of the obtained product is as follows:

[0087]

[0088] Example 3

[0089] Preparation of tripropoxy-trichlorocyclotriphosphazene compounds:

[0090] 1 kg of hexachlorocyclotriphosphazene and 1.4 L of toluene were added to a 2 L reactor equipped with a mechanical stirrer. The temperature was increased to 120 °C at a rate of 5 °C / min, and stirring was continued until the hexachlorocyclotriphosphazene was fully dissolved. Then, 0.8 L of n-propanol was added and stirring was continued while nitrogen was introduced for protection. The temperature was increased to 120 °C at a rate of 2 °C / min, and 3.6 L of trimethylamine was slowly added dropwise. When white fumes were produced in the system, the reaction was continued for 12 h. The reactor was cooled and the precipitate formed in the reactor was filtered. The crude product was placed in a vacuum tube furnace and heated to 240 °C to sublimate the crude product. The sublimation product was collected. The yield of the tripropoxy-trichlorocyclotriphosphazene compound was 78%, and the structure of the obtained product is as follows:

[0091]

[0092] Preparation of tripropoxy-triacetic acid aminocyclotriphosphazene compounds:

[0093] In a 2L reactor equipped with a mechanical stirrer, under stirring and nitrogen protection conditions, 0.6 kg of tripropoxy-trichlorocyclotriphosphazene compound, 1.3 L of N,N-dimethylformamide, and 1.6 kg of cesium fluoride catalyst were added as reactants. The system was slowly heated to 130°C, and then 0.65 kg of glycine was added. The reaction was carried out for 12 h, followed by a gentle heating to 60°C for 2 h. Sodium bicarbonate was added to neutralize the acidity of the reaction system. The mixture was extracted with ethyl acetate, and the organic solvent was removed by vacuum distillation. After heating to reflux with an 80% N,N-dimethylformamide aqueous solution, a supersaturated solution was obtained. The solution was then cooled and concentrated under high temperature and high pressure at 200°C and 0.2 GPa to precipitate tripropoxy-triacetic acid aminocyclotriphosphazene compound. The yield of tripropoxy-triacetic acid aminocyclotriphosphazene compound was 72%. The structure of the obtained product is as follows:

[0094]

[0095] Example 4

[0096] Preparation of flame-retardant Lyocell fibers containing trimethoxy-triacetic acid aminocyclotriphosphazene compounds:

[0097] First, the pulp dried for 12 hours was pulverized into 1.5cm × 1.5cm flakes. 1 kg of the pulverized pulp was weighed out, and then 140 g of the main flame retardant trimethoxy-triacetic acid aminocyclotriphosphazene compound prepared in Example 1 was added to 10 kg of a 75% NMMO aqueous solution. The main flame retardant accounted for 14% of the pulp by mass. The mixture was vigorously stirred at 70°C for 1 hour, and then 4.2 g of graphene was added. Stirring continued at this temperature for 0.5 hours to obtain an NMMO mixture containing the flame retardant. Then, the pulp flakes, the NMMO mixture containing the flame retardant, hydroxylamine, and n-propyl gallate were mixed and stirred until swollen for 0.5 hours. Simultaneously, a vacuum was applied at 100°C for 5 hours to obtain the spinning solution.

[0098] The spinning solution is metered by a metering pump at a pressure of 5 kPa and a temperature of 90°C and then extruded through a spinneret for spinning. After passing through a 30 cm long air gap section, it enters a NMMO water coagulation bath at a temperature of 19°C and a mass fraction of 15%. After stretching, washing, and drying, flame-retardant Lyocell fiber I is obtained.

[0099] Example 5

[0100] Preparation of flame-retardant Lyocell fibers containing triethoxy-tripropionic acid aminocyclotriphosphazene compounds:

[0101] First, the Cosmo pulp dried for 12 hours was pulverized into 1.5cm × 1.5cm flakes. 1 kg of the pulverized pulp was weighed out, and then 180 g of the main flame retardant, triethoxy-tripropionic acid aminocyclotriphosphazene compound prepared in Example 2, was added to 10 kg of a 75% NMMO aqueous solution. The main flame retardant accounted for 18% of the pulp by mass. The mixture was vigorously stirred at 70°C for 1 hour, and then 5.4 g of graphene was added. Stirring continued at this temperature for 0.5 hours to obtain an NMMO mixture containing the flame retardant. The pulp flakes, the NMMO mixture containing the flame retardant, and hydroxylamine and n-propyl gallate were then mixed and stirred until swollen for 0.5 hours. Simultaneously, a vacuum was applied at 100°C for 5 hours to obtain the spinning solution.

[0102] The spinning solution is metered by a metering pump at a pressure of 5 kPa and a temperature of 90°C and then extruded through a spinneret for spinning. After passing through a 30 cm long air gap section, it enters a NMMO water coagulation bath at a temperature of 19°C and a mass fraction of 15%. After stretching, washing, and drying, flame-retardant Lyocell fiber II is obtained.

[0103] Example 6

[0104] Preparation of flame-retardant Lyocell fibers containing tripropoxy-triacetic acid aminocyclotriphosphazene compounds:

[0105] First, the Cosmo pulp dried for 12 hours was pulverized into 1.5cm × 1.5cm flakes. 0.8 kg of the pulverized pulp was weighed out. Then, 118 g of the main flame retardant, tripropoxy-triacetic acid aminocyclotriphosphazene compound prepared in Example 3, was added to 8 kg of a 75% NMMO aqueous solution. The main flame retardant accounted for 14% of the pulp by mass. The mixture was vigorously stirred at 70°C for 1 hour. Then, 3.54 g of graphene was added, and stirring continued at this temperature for 0.5 hours to obtain an NMMO mixture containing the flame retardant. The pulp flakes, the NMMO mixture containing the flame retardant, were then mixed with hydroxylamine and n-propyl gallate and stirred until swollen for 0.5 hours. Simultaneously, a vacuum was applied at 100°C for 5 hours to obtain the spinning solution.

[0106] The spinning solution is metered by a metering pump at a pressure of 5 kPa and a temperature of 90°C and then extruded through a spinneret for spinning. After passing through a 30 cm long air gap section, it enters a NMMO water coagulation bath at a temperature of 19°C and a mass fraction of 15%. After stretching, washing, and drying, flame-retardant Lyocell fiber III is obtained.

[0107] Comparative Example 1: No flame retardant added

[0108] First, the pulp dried for 12 hours was pulverized into 1.5cm×1.5cm flakes. 1kg of the pulverized pulp was weighed and added to 10kg of 75% NMMO aqueous solution. Then, hydroxylamine and n-propyl gallate were mixed, stirred and swollen and added to the system. The system was heated to 90℃ and maintained at this temperature for 40min. Then, vacuum was applied at 100℃ for 5h to obtain the spinning solution.

[0109] The spinning solution is metered by a metering pump at a pressure of 5 kPa and a temperature of 100°C and then extruded through a spinneret for spinning. After passing through a 30 cm long air gap section, it enters a NMMO water coagulation bath at a temperature of 19°C and a mass fraction of 15%. After stretching, washing, and drying, Lyocell fiber I0 is obtained.

[0110] Comparative Example 2: Flame-retardant Lyocell fibers were prepared by adding a trimethoxy-triacetic acid aminocyclotriphosphazene compound without adding a graphene synergistic flame retardant.

[0111] First, the pulp dried for 12 hours was pulverized into 1.5cm × 1.5cm flakes. 1 kg of the pulverized pulp was weighed out, and then 144.2 g of the main flame retardant, trimethoxy-triacetic acid aminocyclotriphosphazene compound prepared in Example 1, was added to 10 kg of a 75% NMMO aqueous solution. The main flame retardant accounted for 14.42% of the pulp by mass. The mixture was vigorously stirred at 70°C for 1 hour, and then stirred for another 0.5 hours at the same temperature to obtain an NMMO mixture containing the flame retardant. The pulp flakes, the NMMO mixture containing the flame retardant, were then mixed with hydroxylamine and n-propyl gallate and stirred until swollen for 0.5 hours. Simultaneously, a vacuum was applied at 100°C for 5 hours to obtain the spinning solution.

[0112] The spinning solution is metered by a metering pump at a pressure of 5 kPa and a temperature of 90°C and then extruded through a spinneret for spinning. After passing through a 30 cm long air gap section, it enters a NMMO water coagulation bath at a temperature of 19°C and a mass fraction of 15%. After stretching, washing, and drying, flame-retardant Lyocell fiber I1 is obtained.

[0113] Comparative Example 3: Flame-retardant Lyocell fibers prepared by adding graphene as a synergistic flame retardant but without adding the main flame retardant.

[0114] First, the pulp dried for 12 hours was pulverized into 1.5cm × 1.5cm flakes. 1 kg of the pulverized pulp was weighed out, and then 144.2 g of graphene was added to 10 kg of a 75% NMMO aqueous solution. The mixture was vigorously stirred at 70°C for 1 hour, and then stirred for another 0.5 hours at the same temperature to obtain an NMMO mixture containing graphene flame retardant. The pulp flakes, the NMMO mixture containing flame retardant, and hydroxylamine and n-propyl gallate were then mixed and stirred until swollen for 0.5 hours. Simultaneously, a vacuum was applied at 100°C for 5 hours to obtain the spinning solution.

[0115] The spinning solution is metered by a metering pump at a pressure of 5 kPa and a temperature of 90°C and then extruded through a spinneret for spinning. After passing through a 30 cm long air gap section, it enters a NMMO water coagulation bath at a temperature of 19°C and a mass fraction of 15%. After stretching, washing, and drying, flame-retardant Lyocell fiber I2 is obtained.

[0116] Performance testing

[0117] 1) The trimethoxy-triacetic acid aminocyclotriphosphazene prepared in Example 1 was characterized by infrared spectroscopy, and the results are shown in the figure. Figure 1 The spectrum shows that the C=O stretching vibration peak on the carboxyl group is at 1736 cm⁻¹. -1 The stretching absorption peak of NH on the substituent appears at 3371 cm⁻¹. -1 The discovery of this finding proves the successful synthesis of the target trimethoxy-triacetic acid aminocyclotriphosphazene.

[0118] 2) The dry breaking strength (CN / dtex) of the flame-retardant Lyocell fibers prepared in Examples 4 to 6 was tested according to GB / T14337 Test Method for Tensile Properties of Short Fibers;

[0119] 3) The dry breaking elongation (%) of the flame-retardant Lyocell fibers prepared in Examples 4 to 6 was tested according to GB / T14337 Test Method for Tensile Properties of Short Fibers.

[0120] 4) The wet breaking strength (CN / dtex) of the flame-retardant Lyocell fibers prepared in Examples 4 to 6 was tested according to GB / T14337 Test Method for Tensile Properties of Short Fibers;

[0121] 5) The wet breaking elongation (%) of the flame-retardant Lyocell fibers prepared in Examples 4-6 was tested according to GB / T14337 Test Method for Tensile Properties of Short Fibers.

[0122] 6) The limiting oxygen index (LOI, %) of the flame-retardant Lyocell fibers prepared in Examples 4 to 6 was tested according to the test method of FZT50016-2011, which describes the flame-retardant performance test method of viscose staple fibers.

[0123] 7) The performance testing methods for Lyocell fibers prepared in Comparative Examples 1-3 are the same as above.

[0124] The test results for the above performance are shown in Table 1.

[0125] Table 1. Test performance indicators of Lyocell fibers prepared in Examples 4-6 and Comparative Examples 1-4

[0126]

[0127]

[0128] As shown in Table 1, the introduction of compound flame retardants into the fiber, and the presence of carboxyl groups on the flame retardants that can interact with cellulose, ensures that the flame retardants are effectively incorporated into the fiber, increasing the incorporation rate of the flame retardants in the fiber. Even with a small amount of flame retardant added, the fiber still has excellent flame retardant properties and washability. After 30 high-temperature machine washes, the LOI value of the flame-retardant Lyocell fiber is still above 28%.

[0129] Furthermore, based on the content ratio of flame-retardant elements P and N in the main flame retardant, the flame-retardant element content of the flame retardant in Example 6 is less than that in Example 4, and the flame-retardant element content of the flame retardant in Example 4 is less than that in Example 5. It can be seen that the flame-retardant performance of the flame-retardant Lyocell fiber improves with the increase of the amount of flame-retardant elements in the flame retardant. A relatively small amount of flame retardant is sufficient to give the fiber good flame-retardant properties.

[0130] As shown in Table 1, the mechanical properties of the flame-retardant Lyocell fibers prepared by the method of the present invention did not decrease significantly. This is because the flame retardant has a good bond strength with the fiber, thereby reducing the impact of the addition of the flame retardant on the mechanical properties of the Lyocell fibers.

[0131] Compared with Comparative Example 2, the flame-retardant Lyocell fibers of Examples 4-6 all had higher LOI values. Moreover, after 30 washes, the LOI values ​​of the flame-retardant fibers of Examples 4-6 were still higher than those of Comparative Example 2, proving that the addition of synergistic flame-retardant additives can not only improve the LOI value of flame-retardant fibers, but also play a positive role in improving the wash resistance of flame-retardant Lyocell fibers.

[0132] Compared with Comparative Example 3, the flame-retardant Lyocell fibers of Examples 4-6 have higher LOI values. After 30 washes, the flame-retardant Lyocell fibers prepared in Examples 4-6 still have the property of self-extinguishing after being removed from the flame, while the LOI of the fiber of Comparative Example 3 is only 18%, showing the phenomenon of burning when exposed to fire. This proves that the main flame retardant plays an important role in improving the flame retardancy of flame-retardant Lyocell fibers and strengthening the bonding strength between the flame retardant and the fiber.

[0133] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-described technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A flame-retardant compound, characterized in that, The flame-retardant compound has a structure as shown in Formula I: Formula I Among them, R1 is selected from -OCH3, -OCH2CH3, -OCH2CH2CH3, and R2 is selected from -NHCH2COOH, -NHCH2CH2COOH.

2. The flame retardant compound according to claim 1, characterized in that, The structure of the flame retardant compound is shown in Formula II, or Formula III, or Formula IV: Formula II Formula III Formula IV.

3. A compound flame retardant, characterized in that, It includes the flame retardant compound and inorganic flame retardant additive as described in claim 1 or 2; wherein the inorganic flame retardant additive is graphene.

4. A method for preparing the flame-retardant compound as described in claim 1 or 2, characterized in that, include: (1) A benzene solution, a monohydric alcohol solution, and an organic amine compound of hexachlorocyclotriphosphazene were mixed and subjected to a nucleophilic substitution reaction to obtain a trioxy-trichlorocyclotriphosphazene compound with the structural formula: ; The benzene solvent in the hexachlorocyclotriphosphazene benzene solution is selected from one or more of cumene, biphenyl, toluene or xylene; the organic amine compound is selected from one or more of triethylamine and trimethylamine. (2) The trioxy-trichlorocyclotriphosphazene compound, amino acid compound, catalyst and reaction solvent are mixed and subjected to nucleophilic substitution reaction. The flame retardant compound is obtained by neutralization, extraction, vacuum distillation, recrystallization and drying. The amino acid compound has the structural formula NH2-R3-COOH, where R3 is selected from -CH2- and -CH2CH2-.

5. The preparation method according to claim 4, characterized in that, In step (1), the molar ratio of hexachlorocyclotriphosphazene, monohydric alcohol solution, and organic amine compound is 1:(3-5):(7-9).

6. The preparation method according to claim 4, characterized in that, In step (1), the concentration of hexachlorocyclotriphosphazene in the benzene-based solution is 0.2 to 0.8 g / mL.

7. The preparation method according to claim 4, characterized in that, In step (1), the monohydric alcohol solution is selected from one or more of methanol, ethanol, and n-propanol.

8. The preparation method according to claim 4, characterized in that, In step (1), the nucleophilic substitution reaction is carried out at a temperature of 70-120℃ for 8-12 hours.

9. The preparation method according to any one of claims 4-8, characterized in that, In step (2), the molar ratio of the trioxy-trichlorocyclotriphosphazene compound, the amino acid compound, the catalyst, and the reaction solvent is 1:(5-7):(6-9):(10-12).

10. The preparation method according to any one of claims 4-8, characterized in that, In step (2), the catalyst is selected from one or more of potassium carbonate, cesium carbonate, cesium fluoride, lithium carbonate or sodium hydride.

11. The preparation method according to any one of claims 4-8, characterized in that, In step (2), the reaction solvent is selected from one or more of dimethyl sulfoxide, N-methylpyrrolidone, N,N-dimethylformamide or N,N-dimethylacetamide.

12. The preparation method according to any one of claims 4-8, characterized in that, In step (2), the nucleophilic substitution reaction temperature is 100-150℃ and the time is 8-16h.

13. The preparation method according to any one of claims 4-8, characterized in that, In step (2), recrystallization includes: adding the vacuum distillation product to an aqueous solution of N,N-dimethylformamide or N,N-dimethylacetamide with a mass fraction of 80%, heating under reflux and then cooling to obtain a supersaturated solution, and using hydrothermal crystallization to precipitate the flame retardant compound at a high temperature and high pressure of 200-230℃ and 0.2-0.5GPa.

14. The preparation method according to any one of claims 4-8, characterized in that, In step (2), the neutralizing agent used during neutralization is selected from one or more of sodium carbonate, potassium carbonate, calcium carbonate, sodium bicarbonate, potassium bicarbonate, and ammonium bicarbonate.

15. The preparation method according to any one of claims 4-8, characterized in that, In step (2), the organic solvent used for extraction is selected from one or more of dichloromethane, trichloromethane, carbon tetrachloride, ethyl acetate, and petroleum ether.

16. The use of a flame retardant compound as described in claim 1 or 2, or a compounded flame retardant as described in claim 3, in the preparation of flame retardant Lyocell fibers.

17. A flame-retardant Lyocell fiber, characterized in that, Flame-retardant Lyocell fiber comprises the flame-retardant compound, inorganic flame-retardant additive and cellulose as described in claim 1 or 2, wherein the mass ratio of the flame-retardant compound, inorganic flame-retardant additive and cellulose is 1:(0.02-0.04):(10-20), and the inorganic flame-retardant additive is graphene.

18. The flame-retardant Lyocell fiber according to claim 17, characterized in that, The flame retardant compound has an average particle size of 5 μm.

19. The flame-retardant Lyocell fiber according to claim 17, characterized in that, The average particle size of the inorganic flame retardant additive is 400–800 nm.

20. The flame-retardant Lyocell fiber according to claim 17, characterized in that, The average particle size of the inorganic flame retardant additive is 500–700 nm.

21. A method for preparing flame-retardant Lyocell fiber as described in any one of claims 17-20, characterized in that, include: (1) Mix the flame retardant compound, inorganic flame retardant additive and NMMO aqueous solution as described in claim 1 or 2, and stir to obtain NMMO mixed solution of flame retardant compound system; (2) The NMMO mixed solution, antioxidant, stabilizer and cellulose pulp flakes of the flame retardant compound system are mechanically stirred and swollen, and then dissolved under vacuum to prepare the spinning solution; (3) The spinning solution is spun by a dry-wet method, and the fibers are formed in a coagulation bath through a spinneret. Then, the fibers are drawn, washed, and dried to obtain flame-retardant Lyocell fibers.

22. The method for preparing flame-retardant Lyocell fiber according to claim 21, characterized in that, In step (1), the mass ratio of flame retardant compound, inorganic flame retardant additive and NMMO aqueous solution is 1:(0.025-0.04):(55-75).

23. The method for preparing flame-retardant Lyocell fiber according to claim 21, characterized in that, In step (1), the NMMO aqueous solution has a mass concentration of 70-78%, a temperature of 50-80℃, and a stirring time of 1-3h.

24. The method for preparing flame-retardant Lyocell fiber according to claim 21, characterized in that, In step (2), the mass ratio of the cellulose pulp to the spinning solution is 5-20:100.

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