DOPO phosphorus-nitrogen durable flame retardant and preparation method thereof

Abstract

The invention belongs to the technical field of functional aids, and particularly relates to a DOPO phosphorus-nitrogen durable flame retardant and a preparation method thereof. The preparation method comprises the following steps: adding DOPO and alkenyl phenol into absolute ethyl alcohol, mixing, heating, stirring and reacting in a protective atmosphere to generate a solid intermediate, then adding phosphoric acid and a urea solution, stirring, heating, refluxing and reacting to prepare the flame retardant. Ternary integration of the alkenyl phenol flame retardant is completed by taking alkenyl phenol as a carbon source, DOPO and phosphoric acid as an acid source and an ammonium phosphate group as a gas source: the acid source catalyzes charring, the carbon source increases the number of protective carbon layers, the gas source generates incombustible gas, the conversion rate of alkenyl phenol is 96% or above, and the synthesized flame retardant can effectively improve the flame retardance of cotton fabrics. The preparation method is simple, the conditions are easy to realize, and the used solvent toluene can be recycled, so that the environmental pollution is reduced, and the cost is reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of functional additives, and specifically relates to a DOPO phosphorus-nitrogen durable flame retardant and a preparation method thereof. Background Art

[0002] As a typical natural fiber, cotton fabric is widely used in textiles and clothing, home and car decoration, and industrial applications due to its softness, comfort, breathability, and easy availability. However, cotton fabric solution is affected by high temperature environment and then ignites, which causes serious harm and negative impact on people's life and property safety. Therefore, it is necessary to perform flame retardant functional treatment on cotton fabric.

[0003] At present, the main application types of flame retardants are still concentrated on halogen flame retardants, but halogen flame retardants will release a large amount of toxic gases during the flame retardant process, which does not meet the requirements of green development. In addition, halogen flame retardants have poor durability and tend to gradually lose their flame retardancy as the service life increases. Therefore, it is extremely urgent to develop a bio-based green and long-lasting flame retardant.

[0004] Vinylphenol (such as eugenol) is a typical natural compound found in many plants and essential oils. In the intumescent ternary flame retardant theory, it can be used as a carbon source to effectively increase the thickness and yield of the protective carbon layer, thereby alleviating the negative effects of high temperature and combustion-supporting gases. In addition, the phenolic hydroxyl group in vinylphenol can react with phosphoric acid through etherification, and can continue to undergo ammoniation reaction with NH3 produced by urea during high temperature decomposition to convert into phosphate ammonium group. The phosphate ammonium group can achieve durable fireproof 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 substitute for halogen products. It can not only catalyze carbonization 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 vinylphenol, phosphate ammonium group and DOPO will effectively achieve durable fireproof functional treatment of cotton fabrics. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a DOPO phosphorus-nitrogen durable flame retardant and a preparation method thereof, using alkenylphenol as a carbon source, DOPO and phosphoric acid as an acid source, and ammonium phosphate group as a gas source to complete a ternary integrated DOPO phosphorus-nitrogen durable flame retardant of a bio-based flame retardant. The toluene used in the preparation process of the flame retardant can be recycled, and the flame retardant has good water solubility and high flame retardant efficiency.

[0006] The technical solutions adopted are:

[0007] A DOPO phosphorus-nitrogen durable flame retardant, the chemical structure of the DOPO phosphorus-nitrogen durable flame retardant is as follows:

[0008]

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

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

[0011] (1) adding DOPO and alkenylphenol into anhydrous ethanol and stirring until the mixture becomes a homogeneous solution;

[0012] (2) transferring the mixed solution in step (1) to a reaction device, introducing a protective gas until the air in the device is completely expelled, heating the reaction system and stirring it to generate a light yellow precipitate in the reaction system; when the precipitate no longer continues to be generated, pouring out the mixture, filtering with suction, washing, purifying, and drying to obtain a light yellow powdery solid intermediate;

[0013] (3) adding phosphoric acid to a three-necked flask containing the solvent and the solid intermediate, mixing, heating and stirring until no liquid droplets evaporate in the reaction device;

[0014] (4) After the reaction device in step (3) is cooled, urea solution is added, stirred, heated, refluxed, and reacted;

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

[0016] Preferably, the 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 mass ratio of the total mass of DOPO and alkenylphenol to anhydrous ethanol is 1:5-15.

[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°C, the stirring time is 1-20h, and the reaction temperature is maintained at 50-200°C.

[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 the solid intermediate is 1:0.5-2; and 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 device 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 present invention has the following beneficial effects:

[0026] The invention provides a DOPO phosphorus-nitrogen durable flame retardant, which adopts alkenylphenol as a carbon source, DOPO and phosphoric acid as acid sources, and ammonium phosphate group as a gas source, thereby completing the ternary integration of the bio-based flame retardant: the acid source catalyzes carbonization, the carbon source increases the number of protective carbon layers, and the gas source generates non-flammable gas. The alkenylphenol conversion rate is above 96%, and the synthesized flame retardant can effectively improve the flame retardancy of cotton fabrics.

[0027] The preparation method of the invention is simple, the conditions are easy to implement, and the used solvent toluene can be recycled and reused repeatedly, thereby reducing environmental pollution and lowering costs. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0029] Figure 2 is a curve of the limiting oxygen index of the cotton fabric treated with the DOPO phosphorus-nitrogen durable flame retardant synthesized in Example 1 of the present invention with respect to the weight gain of the fabric;

[0030] Figure 3 The limiting oxygen index change curve of cotton fabric treated with the DOPO phosphorus-nitrogen durable flame retardant synthesized in Example 1 of the present invention at different washing times. DETAILED DESCRIPTION

[0031] The accompanying drawings are only for illustrative purposes; it should be understood that common knowledge or prior art in the embodiments may be omitted; the cases 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, cannot be understood as limiting the present invention.

[0032] The present invention is described in detail below with reference to the embodiments.

[0033] Example 1

[0034] At 25°C, add 0.04 mol DOPO and 0.02 mol eugenol into 60 mL anhydrous ethanol and stir until the liquid is homogeneous and transparent. Then add it into a three-necked flask and pass nitrogen for 5 minutes. Then seal the air tube and the outlet, raise the temperature of the reaction system to 70°C, and continue stirring for 3 hours until no light yellow precipitate continues to form in the solution.

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

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

[0037] like Figure 1 As shown, Figure 1 (a1-a3) are scanning electron images of pure cotton fabric. The surface of pure cotton fiber is relatively smooth, showing natural folds and bends. After the pure cotton is burned, the pure cotton fabric is almost consumed and cannot be photographed by SEM. Figure 1 (b1-b3) are microscopic images of cotton fabrics treated with flame retardants. Obviously, a large number of rough structures appear on the surface of the treated fibers, which indicates that the flame retardant has successfully attached to and modified the fibers. Figure 1 (c1-c3) are SEM images of the carbon residue after combustion of cotton fabric treated with flame retardant. First, the fiber structure of cotton fabric is well protected due to the presence of flame retardant and still shows a basic complete structure. The evenly distributed small particles formed on the fiber surface are polyphosphoric acid formed by the decomposition of flame retardant.

[0038] Figure 2The graph shows the changing curves of the limiting oxygen index (LOI) of cotton fabric and cotton fabric with weight gain of 10%, 15% and 20% after being treated with flame retardant. The LOI value of untreated pure cotton is 18.0%, which is easy to ignite. The LOI of treated cotton fabric has been greatly improved: the LOI of cotton fabric with weight gain of 10% is 27.1%, and as the weight gain increases, the LOI value of the sample is also gradually increasing. When the weight gain is 20%, the LOI of cotton fabric is 36.8%, which shows the effectiveness of flame retardant treatment of cotton fabric.

[0039] Figure 3 The washing durability of the samples treated with flame retardants is shown. It is obvious that after 10 washes, the limiting oxygen index of cotton fabric has dropped significantly, which is because the flame retardant that has not reacted with the fiber leaves the fiber surface with the wash. In the subsequent washing process, the LOI value decreases slowly, which is due to the formation of a strong POC between the flame retardant and the fiber, which enhances the durability of the flame retardant. Finally, the cotton fabric with a weight gain of 20% after 50 washes still shows an LOI value of 25.1%. The above data show that the presence of flame retardants greatly improves the flame retardancy and washing 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 added to a three-necked flask and argon was introduced for 5 minutes. Then, the air permeable tube and the air outlet were sealed, the temperature of the reaction system was raised to 65°C, and stirring was continued for 2.5 h until no more light yellow precipitate was produced in the solution.

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

[0043] 6 g of urea was dissolved in 25 mL of water and added to the slightly cooled three-necked flask. The heating temperature was adjusted to 150°C and stirred under reflux. After 2.5 h, the solution was transferred to an eggplant-shaped bottle and the solvent water was removed by a rotary evaporator to obtain 10.7 g of the target flame retardant. The conversion rate of 4-allylphenol was 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 added to a three-necked flask and argon was introduced for 5 minutes. Then, the air permeable tube and the air outlet were sealed, the temperature of the reaction system was raised to 60°C, and stirring was continued for 2.5 h until no more light yellow precipitate was produced in the solution.

[0046] The mixture was poured out and filtered, and the product obtained by filtration was washed three times with anhydrous methanol, and then transferred to a vacuum drying oven and dried at 60° C. for 12 h 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 h.

[0047] Dissolve 4.5 g of urea in 18 mL of water and add it to the slightly cooled three-necked flask. Adjust the heating temperature to 145 ° C. Stir and reflux. After 2 hours, transfer the solution to an eggplant-shaped bottle and remove the solvent water by a rotary evaporator to obtain 10.4 g of the target flame retardant. The conversion rate of 3-allylphenol is 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 added to a three-necked flask and argon was introduced for 5 minutes. Then, the air permeation tube and the air outlet were sealed, the temperature of the reaction system was raised to 55°C, and stirring was continued for 3 h until no light yellow precipitate continued to form in the solution.

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

[0051] 18 g of urea was dissolved in 50 mL of water and added to the slightly cooled three-necked flask. The heating temperature was adjusted to 145 ° C. and stirred under reflux. After 2 hours, the solution was transferred to an eggplant-shaped bottle and the solvent water was removed by a rotary evaporator to obtain 39.9 g of the target flame retardant. The conversion rate of 2-allylphenol was 86%.

[0052] Example 5

[0053] At 25°C, 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 added to a three-necked flask and argon was introduced for 5 minutes. Then, the air permeable tube and the air outlet were sealed, and the temperature of the reaction system was raised to 70°C. Stirring was continued for 2.5 h until no more light yellow precipitate was produced in the solution.

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

[0055] 7.2 g of urea was dissolved in 25 mL of water and added to the slightly cooled three-necked flask. The heating temperature was adjusted to 140°C and stirred under reflux. After 3 h, the solution was transferred to an eggplant-shaped bottle and the solvent water was removed by a rotary evaporator to obtain 31.6 g of the target flame retardant. The conversion rate of 2-vinylphenol was 88%.

[0056] Example 6

[0057] At 25°C, 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 added to a three-necked flask and argon was introduced for 5 minutes. Then, the air permeable tube and the air outlet were sealed, and the temperature of the reaction system was raised to 70°C. Stirring was continued for 2.5 h until no more light yellow precipitate was produced in the solution.

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

[0059] Dissolve 7.2 g of urea in 25 mL of water and add it to the slightly cooled three-necked flask. Adjust the heating temperature to 140 ° C. Stir and reflux. After 3 hours, transfer the solution to an eggplant-shaped bottle and remove the solvent water by a rotary evaporator to obtain 32.7 g of the target flame retardant. The conversion rate of 3-vinylbenzene is 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. Then, the mixture was added to a three-necked flask and argon was introduced for 5 minutes. Then, the air permeable tube and the air outlet were sealed, and the temperature of the reaction system was raised to 70°C. Stirring was continued for 2.5 h until no more light yellow precipitate was produced in the solution.

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

[0063] Dissolve 7.2 g of urea in 25 mL of water and add it to the slightly cooled three-necked flask. Adjust the heating temperature to 140°C and stir under reflux. After 3 hours, transfer the solution to an eggplant-shaped bottle and remove the solvent water by a rotary evaporator to obtain 32.4 g of the target flame retardant. The conversion rate of 4-vinylbenzene is 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. Then, the mixture was added to a three-necked flask and argon was introduced for 5 minutes. Then, the air permeation tube and the air outlet were sealed, the temperature of the reaction system was raised to 70°C, and stirring was continued for 2.5 h until no light yellow precipitate continued to form in the solution.

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

[0067] 7.2 g of urea was dissolved in 25 mL of water and added to the slightly cooled three-necked flask. The heating temperature was adjusted to 140 ° C. Stir and reflux. After 3 hours, the solution was transferred to an eggplant-shaped bottle and the solvent water was removed by a rotary evaporator to obtain 31.9 g of the target flame retardant. The conversion rate of 4-vinyl-3-methylphenol was 86%.

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

[0069] Of course, the above description is not a limitation of the present invention, and the present invention is not limited to the above examples. Changes, modifications, additions or substitutions made by technicians in this technical field within the essential 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 is hydrogen, methyl, ethyl, methoxy, ethoxy, trifluoromethyl or hydroxy.

2. The method for preparing a DOPO phosphorus-nitrogen durable flame retardant according to claim 1, characterized in that: The method comprises the following synthesis steps: (1) adding DOPO and alkenylphenol into anhydrous ethanol and stirring until the mixture becomes a homogeneous solution; (2) transferring the mixed solution in step (1) to a reaction device, introducing a protective gas until the air in the device is completely expelled, heating the reaction system and stirring it to generate a light yellow precipitate in the reaction system; when the precipitate no longer continues to be generated, pouring out the mixture, filtering with suction, washing, purifying, and drying to obtain a light yellow powdery solid intermediate; (3) adding phosphoric acid to a three-necked flask containing the solvent and the solid intermediate, mixing, heating and stirring until no liquid droplets evaporate in the reaction device; (4) After the reaction device in step (3) is cooled, urea solution is added, stirred, heated, refluxed, and reacted; (5) The solution obtained by the reaction in step (4) is subjected to a vacuum rotary evaporator to remove the solvent to obtain a viscous oily target flame retardant.

3. The method for preparing a DOPO phosphorus-nitrogen durable flame retardant according to claim 2, characterized in that: The step (1) is carried out at room temperature, the molar ratio of DOPO to alkenyl phenol is 4-1:1, and the mass ratio of the total mass of DOPO and alkenyl phenol to anhydrous ethanol is 1:5-15.

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

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

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 10-3:

1.

10. The method for preparing a DOPO phosphorus-nitrogen durable flame retardant according to claim 2, characterized in that: In the step (4), urea is dissolved in water to form a urea solution, the reaction device 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.

Images