Phosphorus-nitrogen flame retardant as well as preparation method and application thereof

Abstract

The invention provides an environment-friendly phosphorus-nitrogen flame retardant as well as a preparation method and application thereof. The phosphorus-nitrogen flame retardant disclosed by the invention has larger molecular weight on a chemical structure, higher coating property on fabrics and better flame-retardant effect. According to the preparation method, waste wool is used as a raw material and is convenient and easy to obtain, and a wool keratin solution (WK) obtained through treatment and a phenylphosphonic acid solution (PPOA) are mixed and react to obtain the flame-retardant solution. Nitrogen and phosphorus elements in the flame retardant are arranged in a staggered mode in long-chain molecules and are evenly distributed, the synergistic effect of the nitrogen and phosphorus elements can form a protective carbon layer on the surface of a substrate material, the heat stability of the substrate material is improved, low-temperature carbonization of the material can be promoted, and the excellent flame retardant effect is achieved; the limit oxygen index of the obtained flame-retardant cotton fabric can reach 29.6% at most, the damaged length is smaller than 7 cm, the standard is met, and the flame-retardant cotton fabric has excellent flame-retardant performance; meanwhile, the components do not contain harmful elements such as halogen, so that the environment-friendly and non-toxic advantages are also realized during use.

Description

Technical Field

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

[0002] Flame retardants are a type of material used to improve the fire resistance of materials. The application of such materials can effectively prevent the combustion of combustibles or slow the spread of fire. There are many types of flame retardants. From the perspective of composition, they are mainly divided into inorganic flame retardants and organic flame retardants. Generally speaking, organic flame retardants are mostly made of materials containing halogens, nitrogen, phosphorus, silicon and composites of multiple elements. They have a strong flame retardant effect and are added in small amounts. However, some organic flame retardants (such as halogen-containing flame retardants) release a large amount of harmful gases during the combustion process, which limits their use in certain fields. Inorganic flame retardants are mostly made of materials such as oxides, hydroxides or inorganic salts. They have the advantages of simple preparation process, low price, no smoke release at high temperatures and non-toxic materials, but they need to be added in larger amounts to achieve a flame retardant effect.

[0003] Phosphorus-nitrogen synergistic flame retardants offer excellent flame retardancy and are emerging as the most promising flame retardants of the future. They combine the advantages of nitrogen- and phosphorus-based flame retardants, achieving a more efficient flame retardant effect through their synergistic effect. Phosphorus primarily functions in the condensed phase, forming a stable phosphorus-containing carbon layer, while nitrogen generates a flame-retardant gas at high temperatures that dilutes combustible gases and oxygen. For example, patent CN118878801A discloses a method for preparing a phosphorus-nitrogen synergistic structural flame retardant for polyester. The method involves first preparing melamine diphenyl phosphite, which is then mixed with terephthalic acid and ethylene glycol for an esterification reaction. Finally, a melamine diphenyl phosphite-ethylene glycol solution is added to the mixed solution to produce a structural flame retardant with excellent thermal stability, while also improving the tensile strength and impact resistance of polyester materials. Patent CN118852256A provides a method for preparing a reactive phosphorus-nitrogen flame retardant. This method uses filtration, extraction, drying, and vacuum distillation to produce a flame retardant suitable for use in polyurethane foam. Li Xu et al. (Li Xu, Liu Xiangji, Jin Xin, et al. Preparation of durable and efficient phosphorus / nitrogen synergistic flame retardant and its application on cotton fabrics [J]. Journal of Textile Research, 2024, 45(07): 121-129.) used phosphorus pentoxide and ethanolamine to prepare phosphoramide ammonium salt (AHPA), and applied it to cotton fabric using a padding and baking method. The combustion pathway and thermal degradation process of the flame-retardant treated cotton fabric changed, and the thermal stability was significantly improved. Patent CN118754912A provides a method for preparing a small molecule phosphorus-nitrogen polyol derivative. The intermediate product is obtained by mixing an alcohol amine with dichloromethane and adding phosphorus dichloride dropwise under vacuum. The intermediate product is then reacted with phenylenediamine for a secondary reaction to obtain a small molecule phosphorus-nitrogen polyol derivative with high thermal stability. The products prepared in the above-mentioned prior art method are mostly of low molecular weight structure, but the low molecular weight flame retardant has a poor effect on fabric coating, resulting in poor flame retardancy; and the preparation process requires a lot of instruments and equipment, the preparation process is cumbersome, and the economy is not high.

[0004] Therefore, how to prepare a flame retardant with strong fabric coating and good flame retardancy has become a technical problem to be solved urgently in this field. Summary of the Invention

[0005] In view of this, in order to address the technical problem of poor flame retardancy of small molecule phosphorus-nitrogen flame retardants, the present invention proposes an environmentally friendly phosphorus-nitrogen flame retardant, a preparation method and application thereof. The molecular structure of the environmentally friendly phosphorus-nitrogen flame retardant is rich in phosphorus and nitrogen elements. The synergistic effect of the two can not only form a protective carbon layer on the surface of the base material, improve the thermal stability of the base material, but also promote low-temperature carbonization of the material, achieving excellent flame retardant effect.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0007] The present invention provides a phosphorus-nitrogen flame retardant, the structural formula of the phosphorus-nitrogen flame retardant is shown in Formula I:

[0008]

[0009] Wherein, n=20-100, R1, R2, and R3 are each independently an amino acid residue.

[0010] Preferably, the amino acid residue is -CH2-SH, -CH2-OH, -CH2-CH2-CO-NH2, -CH2-COOH, -CH2-CH(CH3)2.

[0011] The preparation method of the phosphorus-nitrogen flame retardant comprises the following steps:

[0012] The phenylphosphonic acid solution and the wool keratin solution are subjected to a nucleophilic substitution reaction to obtain the phosphorus-nitrogen flame retardant;

[0013] Preferably, the concentration of the phenylphosphonic acid solution is 2-14 wt %, and the mass ratio of the phenylphosphonic acid solution to the wool keratin solution is (1-9):(9-1).

[0014] Preferably, the reaction temperature of the nucleophilic substitution reaction is 80-100° C., and the reaction time is 6-7 h.

[0015] Preferably, the wool keratin solution is prepared by a reduction method, comprising the following steps:

[0016] A reducing agent, an auxiliary agent, a surfactant and a solvent are mixed to obtain a treatment liquid, and wool is dissolved in the treatment liquid to obtain a keratin solution;

[0017] Preferably, the mass ratio of the reducing agent, auxiliary agent, surfactant and solvent is (0.5-1): (4.4-5): (0.3-0.9): (16-20); and / or,

[0018] The mass ratio of the wool to the treatment liquid is 1:(21.5-25).

[0019] Preferably, the reducing agent is selected from one or more of sodium bisulfite, sodium sulfide, thioglycolic acid and β-mercaptoethanol; and / or,

[0020] The auxiliary agent is urea or guanidine hydrochloride; and / or,

[0021] The surfactant is one of sodium lauryl sulfate, Triton X-100, Tween 20, and Tween 80; and / or,

[0022] The solvent is water.

[0023] The phosphorus-nitrogen flame retardant or the phosphorus-nitrogen flame retardant prepared by the above preparation method is used for finishing cotton fabrics.

[0024] The present invention provides an environmentally friendly phosphorus-nitrogen flame retardant, a preparation method and application thereof. The phosphorus-nitrogen flame retardant of the present invention has a larger molecular weight in chemical structure, stronger coating properties on fabrics, and better flame retardant effect. The preparation method uses waste wool as raw material, which is convenient and easy to obtain. The wool keratin solution (WK) obtained through treatment is mixed with a phenylphosphonic acid solution (PPOA) to obtain a flame retardant solution. In the flame retardant of the present application, nitrogen and phosphorus elements are staggered in the long-chain molecules, and the elements are evenly distributed. The synergistic effect of the two can not only form a protective carbon layer on the surface of the base material, improve the thermal stability of the base material, but also promote the low-temperature carbonization of the material, achieving excellent flame retardant effect. After treating the cotton fabric, the limiting oxygen index of the resulting flame retardant cotton fabric can reach up to 29.6%, and the damaged length is less than 7 cm, which meets the standard and has excellent flame retardant properties; at the same time, because the composition does not contain harmful elements such as halogens, it also has the advantages of being environmentally friendly and non-toxic when used. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a process flow chart for the preparation of the environmentally friendly phosphorus-nitrogen flame retardant of the present invention and its flame retardant finishing on cotton fabric;

[0026] Figure 2 The vertical combustion test diagram of the environmentally friendly phosphorus-nitrogen flame retardant of the present invention is shown in FIG. 1 , wherein ad represents Examples 1-4, fi represents Examples 5-8, e represents Comparative Example 1, and j and k represent Comparative Examples 2 and 3;

[0027] Figure 3 The flame retardant performance test diagram of the environmentally friendly phosphorus-nitrogen flame retardant of the present invention is shown in Figure A, which is a heat release rate diagram of cotton fabric synergistically finished with phenylphosphonic acid at different concentrations, and Figure B is a heat release rate diagram of cotton fabric synergistically finished with phenylphosphonic acid at different ratios;

[0028] Figure 4 It is the carbon residue diagram after combustion of Comparative Examples 2 and 3 of the present invention. DETAILED DESCRIPTION

[0029] The present invention provides a phosphorus-nitrogen flame retardant, the structural formula of the phosphorus-nitrogen flame retardant is shown in Formula I:

[0030]

[0031] Where n = 20-100, R1, R2, and R3 are each independently an amino acid residue. Generally speaking, an amino acid residue refers to an incomplete amino acid; a complete amino acid includes a carboxyl group (—COOH), an amino group (—NH2), an H group, and an R group. Missing any of these parts is considered an amino acid residue, and does not include peptide bonds.

[0032] In the present invention, the amino acid residue is preferably -CH2-SH, -CH2-OH, -CH2-CH2-CO-NH2, -CH2-COOH, or -CH2-CH(CH3)2.

[0033] The preparation method of the phosphorus-nitrogen flame retardant of the present invention comprises the following steps:

[0034] The phosphorus-nitrogen flame retardant is obtained by subjecting a phenylphosphonic acid solution and a wool keratin solution to a nucleophilic substitution reaction.

[0035] In the present invention, the concentration of the phenylphosphonic acid solution is preferably 2-14 wt%, and the mass ratio of the phenylphosphonic acid solution to the wool keratin solution is preferably (1-9):(9-1). Phenylphosphonic acid, also known as phenylphosphonic acid or PPOA, is an important organophosphorus compound with a molecular formula of C6H7O3P. It is commonly used as a flame retardant additive for unsaturated polyester and polyurethane resins, and can also be used to increase the degree of polymerization of nylon and the flame retardancy of fibers.

[0036] In the present invention, the reaction temperature of the nucleophilic substitution reaction is preferably 80-100° C., and the reaction time is preferably 6-7 h.

[0037] In the present invention, the wool keratin solution is prepared by a reduction method, comprising the following steps:

[0038] A reducing agent, an auxiliary agent, a surfactant and a solvent are mixed to obtain a treatment liquid, and wool is dissolved in the treatment liquid to obtain a keratin solution.

[0039] In the present invention, after the wool is dissolved in the treatment liquid for reaction, the process further comprises: filtering the treatment liquid to obtain a keratin solution; the filtration is preferably performed using a circulating water vacuum pump.

[0040] In the present invention, the mass ratio of the reducing agent, auxiliary agent, surfactant and solvent is preferably (0.5-1): (4.4-5): (0.3-0.9): (16-20); and / or,

[0041] The mass ratio of the wool to the treatment liquid is preferably 1:(21.5-25).

[0042] In the present invention, the reducing agent is selected from one or more of sodium bisulfite, sodium sulfide, thioglycolic acid and β-mercaptoethanol;

[0043] The auxiliary agent is urea or guanidine hydrochloride;

[0044] The surfactant is one of sodium lauryl sulfate, Triton X-100, Tween 20, and Tween 80;

[0045] The solvent is water.

[0046] In the present invention, unless otherwise specified, the above-mentioned reducing agents, auxiliary agents, surfactants and other agents are all of analytical grade.

[0047] In the present invention, the reaction formula of the wool and the treatment liquid is as follows:

[0048] C6H5PO3H2+H2N-keratin→C6H5PO3H-NH-keratin+H2O (Formula 1);

[0049] C6H5PO3H2+H2N-keratin→C6H5PO3H - · + H3N-keratin (Formula 2);

[0050] C6H5PO3H2+HO-keratin→C6H5PO3H-O-keratin+H2O (Formula 3).

[0051] In the present invention, the wool is preferably washed and shredded to facilitate subsequent reactions. In the present invention, the wool is preferably wool with a fineness of ≤25 μm that has not been excessively chemically treated.

[0052] The phosphorus-nitrogen flame retardant or the phosphorus-nitrogen flame retardant prepared by the above preparation method is used for finishing cotton fabrics. In the present invention, the cotton fabric is not particularly limited, and can be, for example, pure cotton, canvas, twill, or poplin.

[0053] In the present invention, the method of using phosphorus-nitrogen flame retardant to finish cotton fabric specifically includes: soaking the cotton fabric in the flame retardant to fully diffuse the flame retardant inside the fiber, padding with a roller, and drying to obtain the flame-retardant finished cotton fabric.

[0054] In the present invention, the phosphorus-nitrogen flame retardant is used to finish cotton fabrics, specifically comprising: placing the cotton fabric in a flame retardant at 80-100°C, soaking for 15-30 minutes to allow the flame retardant to fully diffuse inside the fiber, dipping and rolling with a roller twice, and baking at 80°C for 5-25 minutes to obtain a flame-retardant finished cotton fabric.

[0055] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions of the present invention. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0056] Example 1

[0057] A method for preparing an environmentally friendly phosphorus-nitrogen flame retardant, the reaction process is shown in Formula I:

[0058]

[0059] The specific steps are as follows:

[0060] (1) Preparation of experimental materials: phenylphosphonic acid; sodium bisulfite; urea; sodium dodecyl sulfate; wool.

[0061] (2) preparing a keratin solution by preparing a treatment solution of sodium bisulfite: urea: sodium lauryl sulfate: water in a mass ratio of 0.8:4.4:0.3:16, dissolving shredded wool in the treatment solution in a mass ratio of 1:21.5, heating and stirring at 80° C. for 4 h, and filtering with a circulating water vacuum pump to obtain a keratin solution.

[0062] (3) Prepare a phenylphosphonic acid solution with a concentration of 2 wt%.

[0063] (4) The prepared keratin solution and phenylphosphonic acid solution were uniformly mixed in a mass ratio of 1:1, heated to 100° C., and magnetically stirred for 6 h to allow them to fully react to obtain a flame retardant.

[0064] (5) The cotton fabric was placed in a flame retardant (the temperature was maintained at about 100°C) and soaked for 20 minutes to allow the flame retardant to fully diffuse inside the fiber. The fabric was then dipped twice with a roller and baked at 80°C for 10 minutes to obtain a flame-retardant finished cotton fabric.

[0065] Example 2

[0066] A method for preparing an environmentally friendly phosphorus-nitrogen flame retardant, comprising the following steps:

[0067] (1) Preparation of experimental materials: phenylphosphonic acid; sodium bisulfite; urea; sodium dodecyl sulfate; wool.

[0068] (2) preparing a keratin solution by preparing a treatment solution of sodium bisulfite: urea: sodium lauryl sulfate: water in a mass ratio of 0.8:4.4:0.3:16, dissolving shredded wool in the treatment solution in a mass ratio of 1:21.5, heating and stirring at 80° C. for 4 h, and filtering with a circulating water vacuum pump to obtain a keratin solution.

[0069] (3) Prepare a phenylphosphonic acid solution with a concentration of 8 wt %.

[0070] (4) The prepared keratin and phenylphosphonic acid solution were uniformly mixed in a mass ratio of 1:1, heated to 100°C, and magnetically stirred for 6 hours to allow them to fully react to obtain a flame retardant.

[0071] (5) The cotton fabric was placed in a flame retardant (the temperature was maintained at about 100°C) and soaked for 20 minutes to allow the flame retardant to fully diffuse inside the fiber. The fabric was then dipped twice with a roller and baked at 80°C for 10 minutes to obtain a flame-retardant finished cotton fabric.

[0072] Example 3

[0073] A method for preparing an environmentally friendly phosphorus-nitrogen flame retardant, comprising the following steps:

[0074] (1) Experimental materials: phenylphosphonic acid; sodium bisulfite; urea; sodium dodecyl sulfate; wool;

[0075] (2) preparing a keratin solution by preparing a treatment solution of sodium bisulfite: urea: sodium lauryl sulfate: water in a mass ratio of 0.8:4.4:0.3:16, dissolving shredded wool in the treatment solution in a mass ratio of 1:21.5, heating and stirring at 80° C. for 4 h, and filtering with a circulating water vacuum pump to obtain a keratin solution.

[0076] (3) Prepare a phenylphosphonic acid solution with a concentration of 12 wt%.

[0077] (4) The prepared keratin and phenylphosphonic acid solution were uniformly mixed in a mass ratio of 1:1, heated to 100°C, and magnetically stirred for 6 hours to allow them to fully react to obtain a flame retardant.

[0078] (5) The cotton fabric was placed in a flame retardant (the temperature was maintained at about 100°C) and soaked for 20 minutes to allow the flame retardant to fully diffuse inside the fiber. The fabric was then dipped twice with a roller and baked at 80°C for 10 minutes to obtain a flame-retardant finished cotton fabric.

[0079] Example 4

[0080] A method for preparing an environmentally friendly phosphorus-nitrogen flame retardant, comprising the following steps:

[0081] (1) Experimental materials: phenylphosphonic acid; sodium bisulfite; urea; sodium dodecyl sulfate; wool;

[0082] (2) preparing a keratin solution by preparing a treatment solution of sodium bisulfite: urea: sodium lauryl sulfate: water in a mass ratio of 0.8:4.4:0.3:16, dissolving shredded wool in the treatment solution in a mass ratio of 1:21.5, heating and stirring at 80° C. for 4 h, and filtering with a circulating water vacuum pump to obtain a keratin solution.

[0083] (3) Prepare a phenylphosphonic acid solution with a concentration of 14 wt%.

[0084] (4) The prepared keratin and phenylphosphonic acid solution were uniformly mixed in a mass ratio of 1:1, heated to 100°C, and magnetically stirred for 6 hours to allow them to fully react to obtain a flame retardant.

[0085] (5) The cotton fabric was placed in a flame retardant (the temperature was maintained at about 100°C) and soaked for 20 minutes to allow the flame retardant to fully diffuse inside the fiber. The fabric was then dipped twice with a roller and baked at 80°C for 10 minutes to obtain a flame-retardant finished cotton fabric.

[0086] Example 5

[0087] A method for preparing an environmentally friendly phosphorus-nitrogen flame retardant, comprising the following steps:

[0088] (1) Experimental materials: phenylphosphonic acid; sodium bisulfite; urea; sodium dodecyl sulfate; wool;

[0089] (2) preparing a keratin solution by preparing a treatment solution of sodium bisulfite: urea: sodium lauryl sulfate: water in a mass ratio of 0.8:4.4:0.3:16, dissolving shredded wool in the treatment solution in a mass ratio of 1:21.5, heating and stirring at 80° C. for 4 h, and filtering with a circulating water vacuum pump to obtain a keratin solution.

[0090] (3) Prepare a phenylphosphonic acid solution with a concentration of 8 wt %.

[0091] (4) The prepared keratin and phenylphosphonic acid solution were uniformly mixed in a mass ratio of 1:9, heated to 100° C., and magnetically stirred for 6 h to allow them to fully react to obtain a flame retardant.

[0092] (5) The cotton fabric was placed in a flame retardant (the temperature was maintained at about 100°C) and soaked for 20 minutes to allow the flame retardant to fully diffuse inside the fiber. The fabric was then dipped twice with a roller and baked at 80°C for 10 minutes to obtain a flame-retardant finished cotton fabric.

[0093] Example 6

[0094] A method for preparing an environmentally friendly phosphorus-nitrogen flame retardant, comprising the following steps:

[0095] (1) Experimental materials: phenylphosphonic acid; sodium bisulfite; urea; sodium dodecyl sulfate; wool;

[0096] (2) preparing a keratin solution by preparing a treatment solution of sodium bisulfite: urea: sodium lauryl sulfate: water in a mass ratio of 0.8:4.4:0.3:16, dissolving shredded wool in the treatment solution in a mass ratio of 1:21.5, heating and stirring at 80° C. for 4 h, and filtering with a circulating water vacuum pump to obtain a keratin solution.

[0097] (3) Prepare a phenylphosphonic acid solution with a concentration of 8 wt %.

[0098] (4) The prepared keratin and phenylphosphonic acid solution were uniformly mixed in a mass ratio of 9:1, heated to 100°C, and magnetically stirred for 6 hours to allow them to fully react to obtain a flame retardant.

[0099] (5) The cotton fabric was placed in a flame retardant (the temperature was maintained at about 100°C) and soaked for 20 minutes to allow the flame retardant to fully diffuse inside the fiber. The fabric was then dipped twice with a roller and baked at 80°C for 10 minutes to obtain a flame-retardant finished cotton fabric.

[0100] Example 7

[0101] A method for preparing an environmentally friendly phosphorus-nitrogen flame retardant, comprising the following steps:

[0102] (1) Experimental materials: phenylphosphonic acid; sodium bisulfite; urea; sodium dodecyl sulfate; wool;

[0103] (2) preparing a keratin solution by preparing a treatment solution of sodium bisulfite: urea: sodium lauryl sulfate: water in a mass ratio of 0.8:4.4:0.3:16, dissolving shredded wool in the treatment solution in a mass ratio of 1:21.5, heating and stirring at 80° C. for 4 h, and filtering with a circulating water vacuum pump to obtain a keratin solution.

[0104] (3) Prepare a phenylphosphonic acid solution with a concentration of 8 wt %.

[0105] (4) The prepared keratin and phenylphosphonic acid solution were uniformly mixed in a mass ratio of 2:3, heated to 100° C., and magnetically stirred for 6 h to allow them to fully react to obtain a flame retardant.

[0106] (5) The cotton fabric was placed in a flame retardant (the temperature was maintained at about 100°C) and soaked for 20 minutes to allow the flame retardant to fully diffuse inside the fiber. The fabric was then dipped twice with a roller and baked at 80°C for 10 minutes to obtain a flame-retardant finished cotton fabric.

[0107] Example 8

[0108] A method for preparing an environmentally friendly phosphorus-nitrogen flame retardant, comprising the following steps:

[0109] (1) Experimental materials: phenylphosphonic acid; sodium bisulfite; urea; sodium dodecyl sulfate; wool;

[0110] (2) preparing a keratin solution by preparing a treatment solution of sodium bisulfite: urea: sodium lauryl sulfate: water in a mass ratio of 0.8:4.4:0.3:16, dissolving shredded wool in the treatment solution in a mass ratio of 1:21.5, heating and stirring at 80° C. for 4 h, and filtering with a circulating water vacuum pump to obtain a keratin solution.

[0111] (3) Prepare a phenylphosphonic acid solution with a concentration of 8 wt %.

[0112] (4) The prepared keratin and phenylphosphonic acid solution were uniformly mixed in a mass ratio of 3:2, heated to 100°C, and magnetically stirred for 6 hours to allow them to fully react to obtain a flame retardant.

[0113] (5) The cotton fabric was placed in a flame retardant (the temperature was maintained at about 100°C) and soaked for 20 minutes to allow the flame retardant to fully diffuse inside the fiber. The fabric was then dipped twice with a roller and baked at 80°C for 10 minutes to obtain a flame-retardant finished cotton fabric.

[0114] Comparative Example 1

[0115] The cotton fabric was placed in a 2% NaOH solution, heated in a water bath at 80°C, and soaked for 2 hours. In addition, the solution was stirred every 10 minutes to allow the inside of the fabric to be more thoroughly soaked, thereby achieving the desizing effect and obtaining the finished cotton fabric.

[0116] Comparative Example 2

[0117] (1) Preparation of experimental materials: phosphoric acid; sodium bisulfite; urea; sodium lauryl sulfate; wool.

[0118] (2) preparing a keratin solution by preparing a treatment solution of sodium bisulfite: urea: sodium lauryl sulfate: water in a mass ratio of 0.8:4.4:0.3:16, dissolving shredded wool in the treatment solution in a mass ratio of 1:21.5, heating and stirring at 80° C. for 4 h, and filtering with a circulating water vacuum pump to obtain a keratin solution.

[0119] (3) Prepare a phosphoric acid solution with a concentration of 8 wt%.

[0120] (4) The prepared keratin solution and phosphoric acid solution were uniformly mixed in a mass ratio of 1:1, heated to 100° C., and magnetically stirred for 6 h to allow them to fully react to obtain a flame retardant.

[0121] (5) The cotton fabric was placed in a flame retardant (the temperature was maintained at about 100°C) and soaked for 20 minutes to allow the flame retardant to fully diffuse inside the fiber. The fabric was then dipped twice with a roller and baked at 80°C for 10 minutes to obtain a flame-retardant finished cotton fabric.

[0122] Comparative Example 3

[0123] (1) Experimental materials: phosphorous acid; sodium bisulfite; urea; sodium lauryl sulfate; wool.

[0124] (2) preparing a keratin solution by preparing a treatment solution of sodium bisulfite: urea: sodium lauryl sulfate: water in a mass ratio of 0.8:4.4:0.3:16, dissolving shredded wool in the treatment solution in a mass ratio of 1:21.5, heating and stirring at 80° C. for 4 h, and filtering with a circulating water vacuum pump to obtain a keratin solution.

[0125] (3) Prepare a phosphorous acid solution with a concentration of 8 wt%.

[0126] (4) The prepared keratin solution and phosphorous acid solution were uniformly mixed in a mass ratio of 1:1, heated to 100° C., and magnetically stirred for 6 h to allow them to fully react to obtain a flame retardant.

[0127] (5) The cotton fabric was placed in a flame retardant (the temperature was maintained at about 100°C) and soaked for 20 minutes to allow the flame retardant to fully diffuse inside the fiber. The fabric was then dipped twice with a roller and baked at 80°C for 10 minutes to obtain a flame-retardant finished cotton fabric.

[0128] Comparative Example 4

[0129] (1) Preparation of sericin solution: Silk cocoons were crushed after removing impurities, and the crushed silk cocoons were placed in a sodium hydroxide solution with a liquid-to-solid ratio of 20:1 (mL / g). The solution was stirred and extracted at 60°C for 3 hours, and insoluble impurities were removed by filtration to obtain a sericin solution.

[0130] (2) Prepare a phosphorous acid solution with a concentration of 8 wt%.

[0131] (3) The prepared sericin solution and phosphorous acid solution were uniformly mixed in a mass ratio of 1:1, heated to 100° C., and magnetically stirred for 6 h to allow them to fully react to obtain a flame retardant.

[0132] (4) The cotton fabric was placed in a flame retardant (the temperature was maintained at about 100°C) and soaked for 20 minutes to allow the flame retardant to fully diffuse inside the fiber. The fabric was then dipped twice with a roller and baked at 80°C for 10 minutes to obtain a flame retardant finished cotton fabric.

[0133] The samples prepared in Examples 1-8 and Comparative Examples 1-4 were tested, and the corresponding performance index testing methods were as follows:

[0134] Vertical burning damage length: Refer to GB / T 5455-2014 "Textiles - Combustion performance - Determination of vertical damage length, smoldering and afterflaming time" and cut the fabric into 80mm x 300mm pieces. Test on the LFY-601 vertical burning tester. Observe the molten droplets and smoke produced during the burning of the fabric. Repeat the test twice and take the average value.

[0135] Limiting oxygen index test: According to GB / T 5454-1997 "Textile combustion performance test - Limiting oxygen index method", the fabric was cut into 60mm × 80mm size and tested using a limiting oxygen index tester. The test was repeated 4 times and the average value was taken.

[0136] A micro combustion calorimeter was used in accordance with ASTM D7309-19a "Standard Test Method for Flammability of Plastics and Other Solid Materials Using Micro Combustion Calorimetry". The experimental conditions were set according to ASTM D-7309 standard. The sample was cut into foam and weighed 5 mg.

[0137] Table 1 Test results of PPOA standard samples with different concentrations

[0138] Sample PPOA concentration (wt%) Weight gain (%) Damaged length (cm) Limiting oxygen index (%) Example 1 2 13.8 30 22.7 Example 2 8 14.7 10.8 26.6 Example 3 12 19.4 7.5 28.4 Example 4 14 22 7 29.6 Comparative Example 1 0 0 30 17

[0139] Table 2 Test results of standard samples with different mass ratios

[0140] Sample WK:PPOA Weight gain (%) Damaged length (cm) Limiting oxygen index (%) Example 5 1:9 17.5 10 28.0 Example 6 9:1 35％ 12 31.7 Example 7 2:3 22.9 8 29.5 Example 8 3:2 25.1 9.5 28.5 Comparative Example 1 0 0 30 17

[0141] Table 3 Test results of different types of synergistic samples

[0142] Sample type Weight gain (%) Damaged length (cm) Limiting oxygen index (%) Comparative Example 1 0 0 30 17 Example 2 PPOA 14.7 10.8 26.6 Comparative Example 2 <![CDATA[H3PO3]]> 33 15 26.0 Comparative Example 3 <![CDATA[H3PO4]]> 30 16.2 25.4 Comparative Example 4 Sericin 17.9 14.5 25.9

[0143] The above test results are as follows Figure 2-3 As shown in Tables 1, 2, and 3, it can be concluded from Table 1 that, compared with Comparative Example 1, as the concentration of phenylphosphonic acid added increases in Examples 1-4, the anti-combustion performance and limiting oxygen index are significantly improved, indicating that the environmentally friendly phosphorus-nitrogen synergistic flame retardant has high carbonization and high thermal stability, and can effectively improve the flame retardant effect. A moderate concentration of 8% phenylphosphonic acid was selected to explore the flame retardant effect of keratin and phenylphosphonic acid at different synergistic ratios. As can be seen from Table 2, when the compounding ratio is 2:3, the compatibility between the two is the best, and at this time the flame retardant effect is optimal, the limiting oxygen index is as high as 29.5%, and the damaged length is only 8 cm. From the above Figure 3It can be seen that the maximum heat release rate and maximum heat release rate temperature of flame-retardant treated cotton fabrics both show a significant downward trend. During the thermal oxidation process, the PPOA deposited on the cotton fabric degrades at low temperatures, generating phenolic hydroxyl radicals and phosphate groups. This inhibits the free radical chain reaction and, in turn, slows heat release. The flame retardant acts simultaneously in the gas and condensed phases, accelerating the low-temperature carbonization of the fabric and achieving excellent flame retardancy. Furthermore, cotton fabrics treated with a composite finish of keratin and phenylphosphonic acid exhibit significant improvements in tensile strength. Because the groups in the environmentally friendly flame retardant structure cross-link the hydroxyl groups on the cotton fabric, the molecular crystallinity increases, thereby enhancing mechanical strength. Figure 4 Since the surface of the cotton fabric treated by the comparative example is white, the agglomerates are light yellow (lighter in color) and are not easy to see on the (unburned) fabric, the carbon residue after combustion is used to make it easier to see the agglomerates formed on the surface of the fabric after treatment. Figure 4 It can be seen that in Comparative Examples 2 and 3, when phenylphosphonic acid is replaced with phosphonic acid and phosphorous acid, the flame retardant effect is lower than the synergistic effect of phenylphosphonic acid, and agglomerates will adhere to the surface of the fabric, which is easy to fall off, affecting the appearance, comfort and mechanical properties of the fabric.

[0144] Flame retardancy tests in Example 2 and Comparative Example 4 show that wool keratin outperforms sericin in flame retardancy. This may be due to its higher nitrogen content, which is 16%-17% higher than sericin's 12%-15%. Nitrogen promotes charring, enhancing flame retardancy. Furthermore, wool keratin contains numerous disulfide bonds, releasing flame-flammable gases like SO₂ at high temperatures, whereas sericin contains virtually no sulfur. Related literature indicates that wool keratin's β-sheet and α-helical structures are more stable, resulting in a denser charred layer at high temperatures. However, sericin is highly hydrophilic and has poorer thermal stability.

[0145] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A phosphorus-nitrogen flame retardant, characterized in that: The structural formula of the phosphorus-nitrogen flame retardant is shown in Formula I: Wherein, n=20-100, R1, R2, and R3 are each independently an amino acid residue.

2. The phosphorus-nitrogen flame retardant according to claim 1, characterized in that The amino acid residues are -CH2-SH, -CH2-OH, -CH2-CH2-CO-NH2, -CH2-COOH, -CH2-CH(CH3)2.

3. The method for preparing the phosphorus-nitrogen flame retardant according to claim 1 or 2, characterized in that: The following steps are involved: The phenylphosphonic acid solution and the wool keratin solution are subjected to a nucleophilic substitution reaction to obtain the phosphorus-nitrogen flame retardant; The concentration of the phenylphosphonic acid solution is 2-14 wt %, and the mass ratio of the phenylphosphonic acid solution to the wool keratin solution is (1-9): (9-1).

4. The preparation method according to claim 3, characterized in that The reaction temperature of the nucleophilic substitution reaction is 80-100° C., and the reaction time is 6-7 hours.

5. The preparation method according to claim 3, characterized in that The wool keratin solution is prepared by a reduction method, comprising the following steps: A reducing agent, an auxiliary agent, a surfactant and a solvent are mixed to obtain a treatment liquid, and wool is dissolved in the treatment liquid to obtain a keratin solution; Wherein, the mass ratio of the reducing agent, auxiliary agent, surfactant and solvent is (0.5-1): (4.4-5): (0.3-0.9): (16-20); and / or, The mass ratio of the wool to the treatment liquid is 1:(21.5-25).

6. The preparation method according to claim 5, characterized in that The reducing agent is selected from one or more of sodium bisulfite, sodium sulfide, thioglycolic acid and β-mercaptoethanol; and / or, The auxiliary agent is urea or guanidine hydrochloride; and / or, The surfactant is one of sodium lauryl sulfate, Triton X-100, Tween 20, and Tween 80; and / or, The solvent is water.

7. Use of the phosphorus-nitrogen flame retardant according to claim 1 or 2 or the phosphorus-nitrogen flame retardant prepared by the preparation method according to claims 3-6, characterized in that: The phosphorus-nitrogen flame retardant is used for finishing cotton fabrics.

8. The use according to claim 7, characterized in that The method of using the phosphorus-nitrogen flame retardant to finish the cotton fabric specifically comprises: soaking the cotton fabric in the flame retardant to fully diffuse the flame retardant inside the fiber, padding with a roller, and drying to obtain the flame-retardant finished cotton fabric.

9. The use according to claim 8, characterized in that The method of using phosphorus nitrogen flame retardant to finish cotton fabric specifically comprises: placing cotton fabric in 80-100°C flame retardant, soaking for 15-30 minutes to allow the flame retardant to fully diffuse inside the fiber, padding with a roller, and baking at 80°C for 5-25 minutes to obtain flame retardant finished cotton fabric.

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