Reactive halogen-free phosphorus-nitrogen flame retardant and its preparation method and use

Abstract

The present invention relates to a reactive halogen-free phosphorus-nitrogen flame retardant and a preparation method and application thereof, which mainly solve the problems of poor flame retardant effect, easy precipitation of flame retardant elements, poor stability and environmental unfriendliness of halogen in the flame retardant in the prior art. The present invention provides a reactive halogen-free phosphorus-nitrogen flame retardant, and the preparation method thereof comprises the following steps: (1) reacting melamine and carbonate in a molar ratio of 1:6-18 at 150-200°C for 3-8h to obtain material I; (2) adding an acid binding agent and a reaction solvent to material I, and stirring the mixture in an ice bath to obtain material II; (3) dropwise adding a phosphorus-chloride compound to material II, wherein the amount of the phosphorus-chloride compound is calculated as melamine:phosphorus-chloride compound in a molar ratio of 1:1-4; (4) continuing the reaction in an ice bath for 1-3h, then heating to room temperature and continuing the reaction for 1-12h; (5) filtering, extracting, drying and distilling under reduced pressure after the reaction is completed to obtain the reactive halogen-free phosphorus-nitrogen flame retardant, which solves the technical problem well and can be used in the flame retardancy of polyurethane foam.

Description

Technical Field

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

[0002] Polyurethane (PU) is widely used in various fields, including home furnishings, construction, and daily necessities, due to its stability and aging resistance. However, polyurethane raw material molecules contain a large number of flammable hydrocarbon segments, making them highly flammable. With the frequent occurrence of fire accidents, the demand for flame retardant properties of polyurethane materials in various fields has become increasingly stringent. Consequently, the social demand for flame retardants has also been increasing year by year in recent years. Furthermore, with the growing awareness of environmental protection and sustainable development, the development of efficient, environmentally friendly, and clean flame retardants has become a new trend.

[0003] Flame retardants are primarily categorized as additive and reactive based on their principle of use. Additive flame retardants are mechanically mixed directly into the raw materials of polyurethane foam to achieve a flame-retardant effect. Their simple preparation, low cost, and wide applicability make them widely used. However, additive flame retardants generally have a plasticizing effect, which affects the mechanical properties of polyurethane materials. Furthermore, the flame retardant elements are prone to migration, affecting the flame-retardant effect of polyurethane materials. This is a fatal drawback of additive flame retardants. Reactive flame retardants, on the other hand, chemically react compounds containing flame-retardant elements such as phosphorus and nitrogen with isocyanate segments to produce flame-retardant polyurethane foam. This effectively addresses the issue of flame retardant element migration and provides long-lasting flame retardancy. Common reactive flame retardants include halogen-based reactive flame retardants, phosphorus-based reactive flame retardants, and nitrogen-based reactive flame retardants. At the same time, with growing environmental awareness, modifying compounds containing low-smoke, low-toxic flame-retardant elements such as phosphorus and nitrogen with polyol chain segments is currently a mainstream direction in flame retardant development. Phosphorus-nitrogen synergistic flame retardants, which contain both phosphorus and nitrogen and offer superior flame retardancy compared to single-element flame retardants, have garnered widespread attention. However, common reactive flame retardants on the market are expensive and unstable, and some contain halogens, significantly limiting their application.

[0004] Chinese patent application CN115679470A discloses a flame-retardant polyester fiber fabric and a preparation method thereof, wherein a dicarboxyl triazine phosphate flame retardant is synthesized. The preparation method comprises: adding 6-(N,N-dihydroxyethyl)amino-2,4-dichloro-1,3,5-triazine, serine and N,N-diisopropylethylamine to tetrahydrofuran, stirring and dissolving, heating to 60-75°C and reacting for 6-18 hours, cooling after the reaction, concentrating under reduced pressure, and recrystallizing. 6-(N,N-dihydroxyethyl)amino-2,4-serine-1,3,5-triazine is obtained; then it is reacted with 5,5-dimethyl-1,3-dioxahexanone phosphoryl chloride at 25-40°C with stirring for 12-36 hours; the obtained triazine phosphate uses the triazine ring as a nitrogen source and the tetrafunctional dioxahexanone phosphoric acid ester as a phosphorus source to form a nitrogen-phosphorus synergistic flame retardant system with good flame retardant effect, but its structural formula contains a functional carboxyl group and cannot be used in the polyurethane field. Summary of the Invention

[0005] One of the technical problems to be solved by the present invention is that the flame retardants in the prior art have the problems of poor flame retardant effect, easy precipitation of flame retardant elements, poor stability, and environmental unfriendliness due to the presence of halogens. A reactive halogen-free phosphorus-nitrogen flame retardant is provided, which has the advantages of good flame retardant effect, long-lasting flame retardant performance, being halogen-free, environmentally friendly, and having economical raw materials.

[0006] The second technical problem to be solved by the present invention is to provide a method for preparing a reactive halogen-free phosphorus and nitrogen flame retardant corresponding to the first technical problem to be solved.

[0007] The third technical problem to be solved by the present invention is to provide a use corresponding to solving one of the technical problems.

[0008] In order to solve one of the above technical problems, the technical solution adopted by the present invention is as follows: a reactive halogen-free phosphorus-nitrogen flame retardant, whose structural formula is as follows:

[0009]

[0010] wherein A1 to A6 are selected from one of -CH2CH2O- or -CH2CH(CH3)O-; 0≤m1+m2+m3+m4+m5+m6≤12, and m1 to m6 are integers; R1 to R4 are selected from -H, , and R1-R4 are not -H at the same time.

[0011] To solve the second technical problem mentioned above, the present invention adopts the following technical solution: a method for preparing a reactive halogen-free phosphorus-nitrogen flame retardant, comprising the following steps:

[0012] (1) Add melamine and carbonate in a molar ratio of 1:6-18 into a reaction vessel, stir evenly, react under normal pressure, at a reaction temperature of 150-200°C, for a reaction time of 3-8 hours, and distill under reduced pressure to obtain material I;

[0013] (2) adding an acid-binding agent and a reaction solvent to material I, stirring the mixture in an ice bath to obtain material II;

[0014] (3) adding a phosphorus-chloride compound dropwise to material II, wherein the amount of the phosphorus-chloride compound is calculated by a molar ratio of melamine to phosphorus-chloride compound = 1:1-4, to obtain material III;

[0015] (4) After the addition is completed, material III is allowed to react in an ice bath for 1 to 3 hours, then naturally warmed to room temperature and allowed to react for 1 to 12 hours to obtain material IV;

[0016] (5) After the reaction is completed, the filtrate is filtered, and the filtrate is extracted, dried, and distilled under reduced pressure to obtain the product, a reactive halogen-free phosphorus-nitrogen flame retardant.

[0017] In the above technical solution, preferably, the carbonate in step (1) is selected from at least one of ethylene carbonate and propylene carbonate.

[0018] In the above technical solution, preferably, the acid-binding agent in step (2) is selected from at least one of triethylamine and pyridine, and the molar ratio of the acid-binding agent to the phosphorus-chloriding compound is 1:1.

[0019] In the above technical solution, preferably, the reaction solvent in step (2) is selected from at least one of dichloromethane, chloroform or tetrahydrofuran.

[0020] In the above technical solution, preferably, the phosphorus-chloride compound in step (3) is selected from at least one of diphenylphosphine chloride, diphenylphosphine chloride or diphenoxyphosphine chloride.

[0021] In the above technical solution, preferably, the temperature of the ice bath is -10 to 10°C.

[0022] In the above technical solution, preferably, the filtrate in step (5) is first extracted with chloroform and sodium chloride aqueous solution, and then dried over anhydrous sodium sulfate.

[0023] In the above technical solution, preferably, the conditions for the reduced pressure distillation in step (5) are a temperature of 40 to 70° C. and a pressure of -0.08 to -0.10 MPa, measured in gauge pressure.

[0024] To solve the third of the above technical problems, the present invention adopts the following technical solution: adding the prepared reactive halogen-free phosphorus and nitrogen flame retardant to the foaming formula of polyurethane foam to participate in the reaction, so as to improve the flame retardant properties of polyurethane foam.

[0025] The present invention provides a reactive halogen-free phosphorus-nitrogen flame retardant. A phosphorus-chloride compound is grafted with a melamine derivative by a chemical reaction and then purified to obtain a phosphorus-nitrogen synergistic flame retardant compound. The compound structural formula simultaneously contains elements or groups with flame retardant effects, such as phosphorus, nitrogen, a benzene ring, and a triazine ring, and has a good flame retardant effect. The compound structural formula also contains a reactive group -OH, and is a reactive flame retardant. After being added to a polyurethane foam foaming formula, the compound can further react with -NCO in a black material. The flame retardant element is incorporated into the macromolecular structure of the polyurethane foam, is not easily migrated out, and has long-lasting flame retardant performance. The compound structural formula does not contain a halogen structure and has the advantage of being environmentally friendly. When the flame retardant is applied to the foaming of polyurethane foam, the critical oxygen index of the polyurethane foam can be increased to 27.5% by simply adding a certain amount of the flame retardant of the present invention. Good technical effects are achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Attachment Figure 1 This is the H-NMR spectrum of the reactive halogen-free phosphorus-nitrogen flame retardant S1 prepared in Example 1. DETAILED DESCRIPTION

[0027] The following are only preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. All technical solutions based on the concept of the present invention should fall within the scope of protection of the present invention. For professionals in this technical field, minor improvements and modifications to the present invention without departing from the principles of the present invention should also fall within the scope of protection of the present invention.

[0028] [Example 1]

[0029] A reactive halogen-free phosphorus-nitrogen flame retardant, the preparation method of which comprises the following steps:

[0030] (1) Melamine and ethylene carbonate were added to a reaction vessel in a molar ratio of 1:9, stirred evenly, reacted at normal pressure and 180°C for 6 hours, and distilled under reduced pressure to obtain material I;

[0031] (2) adding an acid-binding agent, triethylamine, and a reaction solvent, chloroform, to material I, wherein the molar ratio of the acid-binding agent, triethylamine, to the phosphorus-chlorided compound is 1:1, and stirring the mixture in an ice bath to obtain material II;

[0032] (3) adding diphenylphosphinic chloride dropwise to material II for 1 h, wherein the molar ratio of the added diphenylphosphinic chloride to the melamine in step (1) is 3:1, to obtain material III;

[0033] (4) After the addition was completed, the reaction was continued in an ice bath for 1 h, then the temperature was naturally raised to room temperature and the reaction was continued for 10 h to obtain material IV;

[0034] (5) After the reaction is completed, the filtrate is filtered, and the filtrate is extracted with chloroform and sodium chloride aqueous solution, dried over anhydrous sodium sulfate, and distilled under reduced pressure. The reduced pressure distillation temperature is 60° C. and the pressure is -0.098 MPa, as measured by gauge pressure, to obtain a reactive halogen-free phosphorus and nitrogen flame retardant S1. The physical properties of the product S1 are shown in Table 3, and the nuclear magnetic hydrogen spectrum characterization data are: 1 H-NMR (ppm, CDCl3), δ = 3.04 ~ 4.07 (36H, –CH2–), 7.19 ~ 7.73 (30H, Aromatic H), the area ratio of the two hydrogens in the spectrum is consistent with the structural formula of the prepared flame retardant.

[0035] [Examples 2 to 6]

[0036] Examples 2 to 6 were carried out according to the steps in Example 1, except for the differences in reaction raw materials, raw material ratios, reaction time, and reaction temperature, as shown in Table 1. The performance data of the obtained reactive halogen-free phosphorus and nitrogen flame retardant products are shown in Table 3.

[0037] Table 1 Molar ratio of raw materials and reaction conditions in the preparation of reactive halogen-free phosphorus and nitrogen flame retardants in Examples 1 to 6

[0038]

[0039]

[0040] The main structural formula of the reactive halogen-free phosphorus-nitrogen flame retardant prepared in Examples 1 to 6 is as follows: S1: S2: S3: S4: S5: S6:

[0041] [Example 7]

[0042] The reactive halogen-free phosphorus-nitrogen flame retardants prepared in Examples 1 to 6 were added to the polyurethane foaming formula to improve the flame retardant properties of the polyurethane foam. The weight proportions of the components in the formula are shown in Table 2. The flame retardant properties of the prepared polyurethane foam, i.e., the critical oxygen index data, are shown in Table 3.

[0043] Table 2 Weight percentage of each component of the flame retardant added to the polyurethane foaming formula in Examples 1 to 6 and Comparative Example 1

[0044]

[0045]

[0046] [Comparative Example 1]

[0047] The phosphorus-nitrogen flame retardant was synthesized by referring to the technical solution of Example 1 in Chinese patent application CN110283207A, and the steps are as follows:

[0048] Hexamethoxymethylmelamine (HMMM, 3.9 g, 0.01 mol) and phosphate diol (di-2-hydroxyethylaminomethyl phosphonic acid diethyl ester, FRC-6, 5.1 g, 0.02 mol) were added to a 100 mL three-necked flask, followed by the addition of p-toluenesulfonic acid (TsOH, approximately 0.005 g) and N,N-dimethylformamide (DMF, 2 g). Under nitrogen protection, the ether exchange reaction was completed at 120°C with magnetic stirring for 3 h. The reaction system was cooled to room temperature, 2 mL of ethyl acetate was added and stirred uniformly, and then 12 mL of n-hexane was added under stirring. The mixture was allowed to stand for phase separation and the supernatant was removed. After repeating this process 3 to 5 times, the viscous material in the lower layer was evaporated at 55 to 70°C to remove the solvent, obtaining a brown-yellow viscous product: phosphorus-nitrogen synergistic flame retardant S, with a yield of 95%.

[0049] The prepared flame retardant was added to the polyurethane foaming formula to improve the flame retardant properties of the polyurethane foam. The weight proportions of the components in the formula are shown in Table 2. The flame retardant properties of the prepared polyurethane foam are shown in Table 3.

[0050] Table 3 Index data of phosphorus-nitrogen flame retardants in Examples 1 to 6 and Comparative Example 1 and polyurethane foam in Example 7

[0051]

[0052] From the performance data of the critical oxygen index in Table 3, it can be seen that when the reactive halogen-free phosphorus and nitrogen flame retardants prepared in Examples 1 to 6 are added to the same polyurethane foam foaming formula in the same amount, the critical oxygen index of the obtained polyurethane foam is above 25%, and can reach 27.5%, and the flame retardant performance is much better than that of Comparative Example 1; and the flame retardant prepared by the present invention is a reactive flame retardant containing multiple flame retardant elements such as phosphorus, nitrogen, benzene ring, and triazine ring in the compound structure. The flame retardant elements are not easy to migrate out and the flame retardant performance is more lasting; the flame retardant compound structure does not contain halogen, is more environmentally friendly, has good technical effects, and can be used to improve the flame retardant performance of polyurethane foam.

Claims

1. A reactive halogen-free phosphorus-nitrogen flame retardant, the structural formula of which is as follows: in, A1 to A6 are selected from one of -CH2CH2O- or -CH2CH(CH3)O-; 0≤m1+m2+m3+m4+m5+m6≤12, and m1 to m6 are integers; R1 to R4 are selected from -H, , and R1-R4 are not -H at the same time.

2. A method for preparing the reactive halogen-free phosphorus-nitrogen flame retardant according to claim 1, comprising the following steps: (1) Add melamine and carbonate in a molar ratio of 1:6-18 into a reaction vessel, stir evenly, react under normal pressure, at a reaction temperature of 150-200°C, for a reaction time of 3-8 hours, and distill under reduced pressure to obtain material I; (2) adding an acid-binding agent and a reaction solvent to material I, stirring the mixture in an ice bath to obtain material II; (3) adding a phosphorus-chloride compound dropwise to material II, wherein the amount of the phosphorus-chloride compound is calculated by a molar ratio of melamine to phosphorus-chloride compound = 1:1-4, to obtain material III; (4) After the addition is completed, material III is allowed to react in an ice bath for 1 to 3 hours, then naturally warmed to room temperature and allowed to react for 1 to 12 hours to obtain material IV; (5) After the reaction is completed, the filtrate is filtered, and the filtrate is extracted, dried, and distilled under reduced pressure to obtain the product, a reactive halogen-free phosphorus-nitrogen flame retardant.

3. The method for preparing a reactive halogen-free phosphorus-nitrogen flame retardant according to claim 2, wherein: The carbonate in step (1) is selected from at least one of ethylene carbonate and propylene carbonate.

4. The method for preparing a reactive halogen-free phosphorus-nitrogen flame retardant according to claim 2, wherein: The acid binding agent in step (2) is selected from at least one of triethylamine and pyridine, and the molar ratio of the acid binding agent to the phosphorus-chloriding compound is 1:

1.

5. The method for preparing a reactive halogen-free phosphorus-nitrogen flame retardant according to claim 2, wherein: The reaction solvent in step (2) is selected from at least one of dichloromethane, chloroform or tetrahydrofuran.

6. The method for preparing a reactive halogen-free phosphorus-nitrogen flame retardant according to claim 2, wherein: The phosphorus-chloride compound in step (3) is selected from at least one of diphenylphosphine chloride, diphenylphosphine chloride or diphenoxyphosphine chloride.

7. The method for preparing a reactive halogen-free phosphorus-nitrogen flame retardant according to claim 2, wherein: The temperature of the ice bath is -10 to 10°C.

8. The method for preparing a reactive halogen-free phosphorus-nitrogen flame retardant according to claim 2, wherein: In the step (5), the filtrate is first extracted with chloroform and sodium chloride aqueous solution, and then dried over anhydrous sodium sulfate; the temperature of the reduced pressure distillation is 40 to 70° C., and the pressure is -0.08 to -0.10 MPa, measured in gauge pressure.

9. Use of the reactive halogen-free phosphorus-nitrogen flame retardant according to claim 1 in flame retardant polyurethane foam.

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