Dopo phosphorus-nitrogen durable flame retardant and preparation method thereof

Abstract

The application belongs to the technical field of functional auxiliaries, and particularly relates to a DOPO phosphorus-nitrogen durable flame retardant and a preparation method thereof. The DOPO and alkenyl phenol are mixed in anhydrous ethanol, heated, stirred and reacted to generate a solid intermediate in a protective atmosphere, then phosphoric acid and urea solution are added, stirred, heated, refluxed and reacted to prepare the flame retardant. The alkenyl phenol is used as a carbon source, the DOPO and phosphoric acid are used as acid sources, and the phosphorus ammonium group is used as a gas source, so that the ternary integration of the alkenyl phenol flame retardant is completed: the acid source catalyzes carbonization, the carbon source increases the number of protective carbon layers, the gas source generates non-combustible gas, the conversion rate of the alkenyl phenol is above 96%, and the synthesized flame retardant can effectively improve the flame retardance of cotton fabric. The preparation method is simple, the conditions are easy to realize, the solvent toluene used can be recycled and reused, environmental pollution is reduced, and the cost is reduced.

Description

Technical Field

[0001] This invention belongs to the field of functional additives technology, specifically relating to a DOPO phosphorus-nitrogen durable flame retardant and its preparation method. Background Technology

[0002] Cotton fabric, as a typical natural fiber, is widely used in textiles, clothing, home and automotive interiors, and industrial applications due to its softness, comfort, breathability, and availability. However, cotton fabric solutions can be ignited under high temperatures, posing a serious threat to human life and property safety. Therefore, flame-retardant functional treatment of cotton fabrics is essential.

[0003] Currently, the main applications of flame retardants still focus on halogenated flame retardants. However, halogenated flame retardants release large amounts of toxic gases during the flame retardation process, which does not meet the requirements of green development. Furthermore, halogenated flame retardants have poor durability and tend to gradually lose their flame retardant properties with increasing service life. Therefore, developing a bio-based, green, and long-lasting flame retardant is extremely urgent.

[0004] Alkenylphenols (such as eugenol) are typical natural compounds found in various plants and essential oils. In the theory of intumescent ternary flame retardants, they can serve as a carbon source, effectively increasing the thickness and yield of the protective char layer, thereby mitigating the negative effects of high temperatures and combustion-supporting gases. Furthermore, the phenolic hydroxyl groups in alkenylphenols can react with phosphoric acid through etherification, and can further undergo ammoniation with NH3 produced during the high-temperature decomposition of urea, transforming into phosphatidyl groups. These phosphatidyl groups can achieve durable fire-retardant treatment of fibers through POC covalent bonds. DOPO (9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide) is a highly efficient phosphorus-based flame retardant commonly used in resins and plastics, and is an effective alternative to halogen products. It can not only catalyze char formation in the solid phase but also generate free radicals such as HPO· and PO· in the gas phase to quench high-energy free radicals and terminate chain reactions. The synergistic complementarity between alkenylphenols, phosphatidyl groups, and DOPO will effectively achieve durable fire-retardant functional treatment for cotton fabrics. Summary of the Invention

[0005] The technical problem to be solved by this invention is to provide a DOPO phosphorus-nitrogen durable flame retardant and its preparation method. The method uses alkenylphenol as the carbon source, DOPO and phosphoric acid as acid sources, and phosphate ammonium groups as the gas source, thus completing a ternary integrated DOPO phosphorus-nitrogen durable flame retardant for bio-based applications. The toluene used in the preparation process is recyclable, and the flame retardant exhibits good water solubility and high flame retardant efficiency.

[0006] The technical solution adopted is as follows:

[0007] A DOPO phosphorus-nitrogen durable flame retardant, the chemical structure of which is shown below:

[0008]

[0009] In the formula, R1 represents hydrogen, methyl, ethyl, methoxy, ethoxy, trifluoromethyl, or hydroxyl.

[0010] A method for preparing a DOPO phosphorus-nitrogen durable flame retardant includes the following synthesis steps:

[0011] (1) Add DOPO and alkenylphenol to anhydrous ethanol and stir until the mixture becomes a homogeneous solution;

[0012] (2) Transfer the mixed solution in step (1) to the reaction apparatus, introduce protective gas until the air in the apparatus is completely removed, heat the reaction system and stir it to generate a pale yellow precipitate; when the precipitate no longer continues to be generated, pour out the mixture, filter it, wash it, purify it and dry it to obtain a pale yellow powdery solid intermediate.

[0013] (3) Add phosphoric acid to a three-necked flask containing solvent and solid intermediate, mix, heat and stir until no more droplets evaporate from the reaction apparatus;

[0014] (4) After the reaction apparatus in step (3) has cooled down, add urea solution, stir, heat, reflux, and react.

[0015] (5) The solvent in the solution that has completed the reaction in step (4) is removed by vacuum rotary evaporator to obtain a viscous oily target flame retardant.

[0016] Preferably, step (1) is performed at room temperature, and the molar ratio of DOPO to alkenylphenol is 4 to 1:1.

[0017] Preferably, in step (1), the total mass ratio of DOPO and alkenylphenol to anhydrous ethanol is 1:5 to 15.

[0018] Preferably, in step (1), the alkenylphenol is any one of eugenol, 3-allylphenol, 2-allylphenol, 4-allylphenol, 2-vinylphenol, 3-vinylphenol, 4-vinylphenol, and 4-vinyl-3-methylphenol.

[0019] Preferably, the protective gas in step (2) is nitrogen or high-purity argon.

[0020] Preferably, in step (2), the heating temperature is 50-200℃, the stirring time is 1-20h, and the reaction temperature is maintained at 50-200℃.

[0021] Preferably, the solvent used for washing in step (2) is anhydrous ethanol or anhydrous methanol, and the washing is repeated 3 to 5 times.

[0022] Preferably, in step (3), 85% phosphoric acid is used, and the molar ratio of phosphoric acid to solid intermediate is 1:0.5-2; the heating temperature is 85-120°C.

[0023] Preferably, the solvent used is toluene, and the mass ratio of toluene to phosphoric acid is 10 to 3:1.

[0024] Preferably, in step (4), urea is dissolved in water to form a urea solution, the reaction apparatus is cooled to below 80°C, and the urea solution is added; the molar ratio of the added urea to phosphoric acid is 4 to 2:1; the reaction temperature is 130 to 150°C, and the reaction time is 2 to 4 hours.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0026] This invention provides a DOPO phosphorus-nitrogen durable flame retardant, which uses alkenylphenol as a carbon source, DOPO and phosphoric acid as acid sources, and phosphate ammonium groups as gas sources to complete the three-in-one bio-based flame retardant: the acid source catalyzes the formation of carbon, the carbon source increases the number of protective carbon layers, and the gas source generates non-flammable gas. The alkenylphenol conversion rate is over 96%, and the synthesized flame retardant can effectively improve the flame retardancy of cotton fabrics.

[0027] The preparation method of this invention is simple and the conditions are easy to achieve. The solvent toluene used can be recycled and reused, reducing environmental pollution and lowering costs. Attached Figure Description

[0028] Figure 1 Scanning electron microscope images of pure cotton fabric (a1-a3), treated cotton fabric (b1-b3), and char residue (c1-c3) after combustion of a DOPO phosphorus-nitrogen durable flame retardant prepared in Example 1 of the present invention.

[0029] Figure 2 The curve showing the limiting oxygen index of cotton fabric treated with the DOPO phosphorus-nitrogen durable flame retardant synthesized in Example 1 of this invention as a function of fabric weight gain is shown.

[0030] Figure 3 The curves showing the limiting oxygen index changes of cotton fabrics treated with the DOPO phosphorus-nitrogen durable flame retardant synthesized in Example 1 of this invention under different washing cycles are shown. Detailed Implementation

[0031] The accompanying drawings are for illustrative purposes only; it should be understood that common knowledge or prior art in the embodiments may be omitted; the examples mentioned below are only used to explain the present invention, in order to facilitate the description of the present invention and simplify the description, and therefore should not be construed as limiting the present invention.

[0032] The present invention will now be described in detail with reference to the embodiments.

[0033] Example 1

[0034] At 25°C, 0.04 mol DOPO and 0.02 mol eugenol were added to 60 mL of anhydrous ethanol and stirred until the liquid was homogeneous and transparent. Then the mixture was transferred to a three-necked flask and nitrogen gas was introduced for 5 minutes. The gas vent and outlet were then sealed, and the temperature of the reaction system was raised to 70°C. The mixture was stirred continuously for 3 hours until no more pale yellow precipitate was produced in the solution.

[0035] The mixture was poured out and filtered. The filtered product was washed three times with anhydrous ethanol and then transferred to a forced-air drying oven and dried at 60°C for 12 hours to obtain a solid intermediate. The solid intermediate was then mixed with 5 g of toluene and 2.3 g of 85% phosphoric acid and stirred at 120°C for 1 hour.

[0036] Dissolve 2.4g of urea in 20mL of water and add it to the slightly cooled three-necked flask. Adjust the heating temperature to 130℃, stir and reflux. After 3 hours, transfer the solution to a flask and remove the solvent water using a rotary evaporator to obtain 9.49g of the target flame retardant with a eugenol conversion rate of 96%.

[0037] like Figure 1 As shown, Figure 1 Images (a1-a3) are scanned electronic images of pure cotton fabric. The surface of pure cotton fibers is relatively smooth, showing natural folds and bends. After burning, the pure cotton fabric is almost completely consumed and cannot be photographed using SEM. Figure 1 Images (b1-b3) are microscopic images of cotton fibers after treatment with flame retardant. Clearly, the treated fibers exhibit a large number of rough structures on their surface, indicating that the flame retardant has successfully adhered to and modified the fibers. Figure 1 (c1-c3) are SEM images of the char residue after burning of cotton fabric treated with flame retardant. First, the fiber structure of the cotton fabric is well protected by the presence of flame retardant and still shows a basic intact structure. The uniformly distributed small particles formed on the fiber surface are polyphosphoric acid formed by the decomposition of flame retardant.

[0038] Figure 2The display shows the limiting oxygen index (LOI) curves for cotton fabrics and cotton fabrics with weight gains of 10%, 15%, and 20% after treatment with flame retardants. Untreated pure cotton has an LOI value of 18.0%, making it easily ignited. The treated cotton fabrics show a significant increase in LOI: the LOI of the 10% weight gain cotton fabric is 27.1%, and the LOI value gradually increases with increasing weight gain, reaching 36.8% for the 20% weight gain cotton fabric. This demonstrates the effectiveness of the flame retardant treatment on cotton fabrics.

[0039] Figure 3 The data demonstrates the wash durability of samples treated with flame retardant. Clearly, after 10 washes, the limiting oxygen index (LOI) of the cotton fabric showed a significant decrease, as the unreacted flame retardant left the fiber surface during washing. In subsequent washes, the LOI decreased more slowly, due to the formation of a strong point of contact (POC) between the flame retardant and the fiber, enhancing its durability. Finally, after 50 washes, the cotton fabric with a 20% weight gain still exhibited an LOI of 25.1%. These data illustrate that the presence of flame retardant significantly improves the flame retardancy and wash durability of cotton fabrics.

[0040] Example 2

[0041] At 25°C, 0.1 mol DOPO and 0.025 mol 4-allylphenol were added to 60 mL of anhydrous ethanol and stirred until the liquid was homogeneous and transparent. Then, the mixture was transferred to a three-necked flask, and argon gas was introduced for 5 minutes. The gas vent and outlet were then sealed, and the temperature of the reaction system was raised to 65°C. The mixture was stirred continuously for 2.5 h until no more pale yellow precipitate was produced in the solution.

[0042] The mixture was poured out and filtered. The filtered product was washed three times with anhydrous methanol and then transferred to a vacuum drying oven and dried at 60°C for 12 hours to obtain a solid intermediate. The solid intermediate was then mixed with 6.5 g of toluene and 2.9 g of 85% phosphoric acid and stirred at 105°C for 1.5 hours.

[0043] Dissolve 6g of urea in 25mL of water and add it to the slightly cooled three-necked flask. Adjust the heating temperature to 150℃, stir and reflux. After 2.5h, transfer the solution to a flask and remove the solvent water by rotary evaporation to obtain 10.7g of the target flame retardant with a 4-allylphenol conversion rate of 92%.

[0044] Example 3

[0045] At 25°C, 0.06 mol DOPO and 0.025 mol 3-allylphenol were added to 60 mL of anhydrous ethanol and stirred until the liquid was homogeneous and transparent. Then, the mixture was transferred to a three-necked flask, and argon gas was introduced for 5 minutes. The gas vent and outlet were then sealed, and the temperature of the reaction system was raised to 60°C. The mixture was stirred continuously for 2.5 h until no more pale yellow precipitate was produced in the solution.

[0046] The mixture was poured out and filtered. The filtered product was washed three times with anhydrous methanol and then transferred to a vacuum drying oven and dried at 60°C for 12 hours to obtain a solid intermediate. The solid intermediate was then mixed with 6.0 g toluene and 2.9 g 85% phosphoric acid and stirred at 105°C for 1.5 hours.

[0047] Dissolve 4.5g of urea in 18mL of water and add it to the slightly cooled three-necked flask. Adjust the heating temperature to 145℃, stir and reflux. After 2 hours, transfer the solution to a flask and remove the solvent water using a rotary evaporator to obtain 10.4g of the target flame retardant with a 3-allylphenol conversion rate of 90%.

[0048] Example 4

[0049] At 25°C, 0.25 mol DOPO and 0.1 mol 2-allylphenol were added to 60 mL of anhydrous ethanol and stirred until the liquid was homogeneous and transparent. Then, the mixture was transferred to a three-necked flask and argon gas was introduced for 5 minutes. The gas vent and outlet were then sealed, and the temperature of the reaction system was raised to 55°C. The mixture was stirred continuously for 3 hours until no more pale yellow precipitate was produced in the solution.

[0050] The mixture was poured out and filtered. The filtered product was washed three times with anhydrous methanol and then transferred to a vacuum drying oven and dried at 60°C for 16 hours to obtain a solid intermediate. The solid intermediate was then mixed with 17.6 g of toluene and 11.5 g of 85% phosphoric acid and stirred at 110°C for 1 hour.

[0051] Dissolve 18g of urea in 50mL of water and add it to the slightly cooled three-necked flask. Adjust the heating temperature to 145℃, stir and reflux. After 2 hours, transfer the solution to a flask and remove the solvent water using a rotary evaporator to obtain 39.9g of the target flame retardant with a 2-allylphenol conversion rate of 86%.

[0052] Example 5

[0053] At 25℃, 0.28 mol DOPO and 0.08 mol 2-vinylphenol were added to 60 mL of anhydrous ethanol and stirred until the liquid was homogeneous and transparent. Then, the mixture was transferred to a three-necked flask and argon gas was introduced for 5 minutes. The gas vent and outlet were then sealed, and the temperature of the reaction system was raised to 70℃. The mixture was stirred continuously for 2.5 h until no more pale yellow precipitate was produced in the solution.

[0054] The mixture was poured out and filtered. The filtered product was washed three times with anhydrous ethanol and then transferred to a vacuum drying oven and dried at 60°C for 15 hours to obtain a solid intermediate. The solid intermediate was then mixed with 12.8 g of toluene and 9.2 g of 85% phosphoric acid and stirred at 115°C for 1 hour.

[0055] Dissolve 7.2g of urea in 25mL of water and add it to the slightly cooled three-necked flask. Adjust the heating temperature to 140℃, stir and reflux. After 3 hours, transfer the solution to a flask and remove the solvent water using a rotary evaporator to obtain 31.6g of the target flame retardant with a 2-vinylphenol conversion rate of 88%.

[0056] Example 6

[0057] At 25℃, 0.28 mol DOPO and 0.08 mol 3-vinylphenol were added to 60 mL of anhydrous ethanol and stirred until the liquid was homogeneous and transparent. Then, the mixture was transferred to a three-necked flask and argon gas was introduced for 5 minutes. The gas vent and outlet were then sealed, and the temperature of the reaction system was raised to 70℃. The mixture was stirred continuously for 2.5 h until no more pale yellow precipitate was produced in the solution.

[0058] The mixture was poured out and filtered. The filtered product was washed three times with anhydrous ethanol and then transferred to a vacuum drying oven and dried at 60°C for 15 hours to obtain a solid intermediate. The solid intermediate was then mixed with 12.8 g of toluene and 9.2 g of 85% phosphoric acid and stirred at 115°C for 1 hour.

[0059] Dissolve 7.2g of urea in 25mL of water and add it to the slightly cooled three-necked flask. Adjust the heating temperature to 140℃, stir and reflux. After 3 hours, transfer the solution to a flask and remove the solvent water using a rotary evaporator to obtain 32.7g of the target flame retardant with a 3-vinylbenzene conversion rate of 91%.

[0060] Example 7

[0061] At 25°C, 0.28 mol DOPO and 0.08 mol 4-vinylphenol were added to 60 mL of anhydrous ethanol and stirred until the liquid was homogeneous and transparent. The mixture was then transferred to a three-necked flask, and argon gas was introduced for 5 minutes. The gas vent and outlet were then sealed, and the temperature of the reaction system was raised to 70°C. The mixture was stirred continuously for 2.5 h until no more pale yellow precipitate was produced in the solution.

[0062] The mixture was poured out and filtered. The filtered product was washed three times with anhydrous ethanol and then transferred to a vacuum drying oven and dried at 60°C for 15 hours to obtain a solid intermediate. The solid intermediate was then mixed with 12.8 g of toluene and 9.2 g of 85% phosphoric acid and stirred at 115°C for 1 hour.

[0063] Dissolve 7.2g of urea in 25mL of water and add it to the slightly cooled three-necked flask. Adjust the heating temperature to 140℃, stir and reflux. After 3 hours, transfer the solution to a flask and remove the solvent water using a rotary evaporator to obtain 32.4g of the target flame retardant with a 4-vinylbenzene conversion rate of 90%.

[0064] Example 8

[0065] At 25°C, 0.28 mol DOPO and 0.08 mol 4-vinyl-3-methylphenol were added to 60 mL of anhydrous ethanol and stirred until the liquid was homogeneous and transparent. The mixture was then transferred to a three-necked flask, and argon gas was introduced for 5 minutes. The gas vent and outlet were then sealed, and the temperature of the reaction system was raised to 70°C. The mixture was stirred continuously for 2.5 h until no more pale yellow precipitate was produced in the solution.

[0066] The mixture was poured out and filtered. The filtered product was washed three times with anhydrous ethanol and then transferred to a vacuum drying oven and dried at 60°C for 15 hours to obtain a solid intermediate. The solid intermediate was then mixed with 12.8 g of toluene and 9.2 g of 85% phosphoric acid and stirred at 115°C for 1 hour.

[0067] Dissolve 7.2g of urea in 25mL of water and add it to the slightly cooled three-necked flask. Adjust the heating temperature to 140℃, stir and reflux. After 3 hours, transfer the solution to a flask and remove the solvent water using a rotary evaporator to obtain 31.9g of the target flame retardant with a 4-vinyl-3-methylphenol conversion rate of 86%.

[0068] The reaction apparatus used in each example is conventional reaction equipment used in actual operation, such as a three-necked flask, and therefore will not be described in detail.

[0069] Of course, the above description is not intended to limit the present invention, and the present invention is not limited to the examples given above. Any changes, modifications, additions or substitutions made by those skilled in the art within the scope of the present invention should also fall within the protection scope of the present invention.

Claims

1. A DOPO phosphorus-nitrogen durable flame retardant, characterized in that, The chemical structure of the DOPO phosphorus-nitrogen durable flame retardant is shown below: In the formula, R1 represents hydrogen, methyl, ethyl, methoxy, ethoxy, trifluoromethyl, or hydroxyl.

2. The preparation method of the DOPO phosphorus-nitrogen durable flame retardant as described in claim 1, characterized in that, The synthesis steps include the following: (1) Add DOPO and alkenylphenol to anhydrous ethanol and stir until the mixture becomes a homogeneous solution; (2) Transfer the mixed solution in step (1) to the reaction apparatus, introduce protective gas until the air in the apparatus is completely removed, heat the reaction system and stir it to generate a pale yellow precipitate; when the precipitate no longer continues to be generated, pour out the mixture, filter it, wash it, purify it and dry it to obtain a pale yellow powdery solid intermediate. (3) Add phosphoric acid to a three-necked flask containing solvent and solid intermediate, mix, heat and stir until no more droplets evaporate from the reaction apparatus; (4) After the reaction apparatus in step (3) has cooled down, add urea solution, stir, heat, reflux, and react. (5) The solvent in the solution that has completed the reaction in step (4) is removed by vacuum rotary evaporator to obtain a viscous oily target flame retardant.

3. The preparation method of a DOPO phosphorus-nitrogen durable flame retardant according to claim 2, characterized in that, Step (1) is performed at room temperature, with a molar ratio of DOPO to alkenylphenol of 4 to 1:1; and a mass ratio of the total mass of DOPO and alkenylphenol to the mass of anhydrous ethanol of 1:5 to 15.

4. The preparation method of a DOPO phosphorus-nitrogen durable flame retardant according to claim 2, characterized in that, In step (1), the alkenylphenol is any one of eugenol, 2-allylphenol, 3-allylphenol, 4-allylphenol, 2-vinylphenol, 3-vinylphenol, 4-vinylphenol, and 4-vinyl-3-methylphenol.

5. The preparation method of a DOPO phosphorus-nitrogen durable flame retardant according to claim 2, characterized in that, The protective gas in step (2) is nitrogen or high-purity argon.

6. The method for preparing a DOPO phosphorus-nitrogen durable flame retardant according to claim 2, characterized in that, In step (2), the heating temperature is 50-200℃, the stirring time is 1-20h, and the reaction temperature is maintained at 50-200℃.

7. The method for preparing a DOPO phosphorus-nitrogen durable flame retardant according to claim 2, characterized in that, In step (2), the solvent used for washing is anhydrous ethanol or anhydrous methanol, and the washing is repeated 3 to 5 times.

8. The method for preparing a DOPO phosphorus-nitrogen durable flame retardant according to claim 2, characterized in that, In step (3), 85% phosphoric acid is used, and the molar ratio of phosphoric acid to solid intermediate is 1:0.5-2; the heating temperature is 85-120℃.

9. The method for preparing a DOPO phosphorus-nitrogen durable flame retardant according to claim 8, characterized in that, The solvent used is toluene, and the mass ratio of toluene to phosphoric acid is 10 to 3:

1.

10. The method for preparing a DOPO phosphorus-nitrogen durable flame retardant according to claim 2, characterized in that, In step (4), urea is dissolved in water to form a urea solution. The reaction apparatus is cooled to below 80°C, and the urea solution is added. The molar ratio of the added urea to phosphoric acid is 4 to 2:

1. The reaction temperature is 130 to 150°C, and the reaction time is 2 to 4 hours.

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