Red phosphorus-based halogen-free flame retardant, and preparation method and application thereof

Abstract

The application discloses a red phosphorus-based halogen-free flame retardant and a preparation method and application thereof, and belongs to the technical field of halogen-free flame retardants. The red phosphorus-based halogen-free flame retardant takes red phosphorus as a base body, and is coated twice in a preparation process. The first coating is helpful to improve the mechanical properties of red phosphorus-based halogen-free flame retardant particles, the morphology of the pre-coated red phosphorus microspheres is more regular, and the surface is more rough, which is helpful to improve the coating effect of subsequent polymer second coating. The outer layer of the red phosphorus-based halogen-free flame retardant particle is polystyrene, which is helpful to improve the compatibility with other polymer base bodies and increase the use effect. The flame-retardant modified polyvinyl alcohol in the second coating process contains an organic phosphorus flame retardant, which is helpful to improve the effective phosphorus content of the red phosphorus-based halogen-free flame retardant. The reaction-type organic phosphorus flame retardant is grafted with polyvinyl alcohol, which is helpful to avoid the migration of the reaction-type organic phosphorus flame retardant, can reduce the hydroxyl groups in the polyvinyl alcohol, avoid the moisture failure of the red phosphorus-based halogen-free flame retardant, and has good flame-retardant effect.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of halogen-free flame retardants, and particularly relates to a red phosphorus-based halogen-free flame retardant and a preparation method and application thereof. BACKGROUND

[0002] Red phosphorus is an amorphous powder of purple red or slightly brown, which is one of the allotropes of phosphorus. China is a big country of phosphorus resources in the world, and the resources are relatively rich. Red phosphorus is an inorganic substance, and has a low cost advantage. Due to the high flame retardant efficiency, low cost and halogen-free, red phosphorus has been applied in the domestic market to a certain extent.

[0003] In recent years, environmentally friendly flame retardants, especially those with halogen-free, low smoke and low toxicity characteristics, have become the target of widespread attention and pursuit in the industry. Many flame retardant suppliers and application enterprises show a high enthusiasm for the halogen-free trend of flame-retardant materials, and have invested a large amount of resources in the research and development of halogen-free flame retardants and related materials. According to relevant analysis, the main categories of halogen-free flame retardants include phosphorus-based flame retardants and inorganic hydrates, among which the important members of phosphorus-based flame retardants include red phosphorus flame retardants. Microencapsulated red phosphorus flame retardants have good use effect.

[0004] Microencapsulated red phosphorus has the characteristics of small particle size, good dispersibility, high fluidity and excellent flame retardant performance, and can be widely used as a new type of halogen-free flame retardant in various plastic, rubber, fiber and other products. Microencapsulated red phosphorus flame retardant reduces the activity of red phosphorus and solves the compatibility with the matrix, but the content of red phosphorus is about 85%, and the effective phosphorus content is not as high as that of red phosphorus alone. Therefore, how to improve the effective phosphorus content of microencapsulated red phosphorus flame retardant and improve its flame retardant effect has certain application prospect. SUMMARY

[0005] The purpose of the present application is to provide a red phosphorus-based halogen-free flame retardant and a preparation method and application thereof. The mechanical properties of the red phosphorus-based halogen-free flame retardant particles are improved by first coating, the compatibility with other polymer matrices is improved by second coating, the use effect is increased, the flame-retardant modified polyvinyl alcohol in the second coating process contains an organic phosphorus flame retardant, which helps to improve the effective phosphorus content of the red phosphorus-based halogen-free flame retardant, has good flame-retardant effect, and meets the application in polyurethane foaming materials by reducing the moisture absorption performance.

[0006] The purpose of the present application can be achieved by the following technical solutions:

[0007] A preparation method of a red phosphorus-based halogen-free flame retardant, comprising the following steps:

[0008] Step one: uniformly mix red phosphorus powder and deionized water according to a mass ratio of 1:2, and ultrasonically disperse for 10-15 min to obtain a red phosphorus dispersion liquid;

[0009] Tannic acid, deionized water and copper acetate are added into the reaction kettle, stirred at 300-500 r / min for 10-15 min, then copper-based nano metal organic framework is added into the reaction kettle, ultrasonic dispersion is carried out for 20-25 min, to obtain a prepolymer dispersion liquid;

[0010] Step two: the red phosphorus dispersion liquid and the prepolymer dispersion liquid are added into the reaction kettle according to a volume ratio of 1:2, stirred at 200-300 r / min for 5-10 min, then the pH value is adjusted to 8.5-9 by using a 0.05 mol / L sodium hydroxide solution, stirred and reacted under ultrasonic assistance for 10-15 min, centrifugal filtration is carried out, the filter cake is washed with deionized water for 3-5 times, vacuum drying is carried out at 50-60℃, to obtain the pre-coated red phosphorus microspheres.

[0011] Step three: the flame-retardant modified polyvinyl alcohol is dissolved with deionized water and transferred into the reaction kettle, then the pre-coated red phosphorus microspheres are added into the reaction kettle, stirred at 30-35℃ for 1 h, ultrasonic dispersion is carried out for 10-15 min, then styrene, diphenyl ethylene, magnesium aluminum silicate and sodium dodecyl sulfonate are added into the reaction kettle, stirred at 60-65℃ and 500-800 r / min for 20-30 min, potassium persulfate is added, stirred and reacted at 80-90℃ for 2.5-3 h, suction filtration is carried out, the filter cake is washed with anhydrous ethanol for 2-3 times, vacuum drying is carried out, to obtain the red phosphorus-based halogen-free flame retardant.

[0012] Further, the amount ratio of tannic acid, deionized water, copper acetate and copper-based nano metal organic framework is 0.5 g:25-30 mL:0.025 g:0.05 g.

[0013] Further, the power of ultrasonic assistance is 450-500 W, and the frequency is 35-40 kHz.

[0014] Further, the amount ratio of flame-retardant modified polyvinyl alcohol, deionized water, pre-coated red phosphorus microspheres, styrene, diphenyl ethylene, magnesium aluminum silicate, sodium dodecyl sulfonate and potassium persulfate is 2.5-3 g:400-450 mL:50-55 g:25 mL:0.75-1 mL:1-1.2 g:1-1.2 g:0.25 g.

[0015] Further, the copper-based nano metal organic framework is prepared by the following steps:

[0016] 3,5-pyrazole dicarboxylic acid monohydrate, copper nitrate trihydrate and N,N-dimethylformamide are added into the reaction kettle, stirred at 200-300 r / min for 20-30 min, then stirred and reacted at 90-100℃ for 6-8 h, the product is washed with anhydrous ethanol by centrifugation for 4-5 times, the precipitate is vacuum dried, to obtain the copper-based nano metal organic framework.

[0017] Further, the usage ratio of 3,5-pyrazole dicarboxylic acid monohydrate, copper nitrate trihydrate and N,N-dimethylformamide is 1.8-2 g: 0.24-0.25 g: 40-50 mL.

[0018] Further, the flame-retardant modified polyvinyl alcohol is prepared by the following steps:

[0019] The polyvinyl alcohol, the reactive organic phosphorus flame retardant, the dicyandiamide and the deionized water are added into a reaction kettle, stirred and reacted at 65-75°C for 1-1.5 h, then the reaction solution is transferred into anhydrous methanol to precipitate the precipitate, which is filtered, washed with anhydrous methanol for 2-3 times, and vacuum dried to obtain the flame-retardant modified polyvinyl alcohol.

[0020] Further, the usage ratio of the polyvinyl alcohol, the reactive organic phosphorus flame retardant, the dicyandiamide and the deionized water is 4 g: 3.5-4 g: 1 g: 20 mL.

[0021] Further, the reactive organic phosphorus flame retardant is prepared by the following steps:

[0022] Step 1: DOPO, sodium p-aminobenzoate, phenylacetaldehyde and anhydrous ethanol as a solvent are added into a reaction kettle according to a mass ratio of 26: 18-20: 14-15: 400-500, stirred at 65-70°C and 200-300 r / min for 15-20 min, then formic acid is added dropwise into the reaction kettle, and the reaction is carried out at 90-95°C under nitrogen protection for 5-6 h, the solvent is removed by rotary evaporation, and the product is ground and crushed to obtain a phosphorus-nitrogen-sodium salt intermediate. The reaction process is shown as follows:

[0023]

[0024] Step 2: The phosphorus-nitrogen-sodium salt intermediate and hydrochloric acid with a molar concentration of 0.1 mol / L are added into a reaction kettle according to a mass ratio of 1: 15-20, stirred at 25-30°C for 8-10 h, centrifugally washed for 3-5 times, and the filter cake is vacuum dried to obtain a carboxyl-terminated intermediate. The reaction process is shown as follows:

[0025]

[0026] Step 3: The carboxyl-terminated intermediate and phosphoric acid are added into a reaction kettle according to a mass ratio of 2: 1, and the reaction is carried out at 140-150°C for 4-5 h, then urea is added into the reaction kettle, and the reaction is continued for 1.5-2 h, and the product is centrifugally washed with anhydrous ethanol for 3-5 times and vacuum dried to obtain the reactive organic phosphorus flame retardant. The reaction process is shown as follows:

[0027]

[0028] The beneficial effects of the present application are:

[0029] 1、The red phosphorus-based halogen-free flame retardant takes red phosphorus as a matrix, and is prepared by twice coating. The first coating helps to improve the mechanical properties of the red phosphorus-based halogen-free flame retardant particles, the morphology of the pre-coated red phosphorus microspheres is more regular, and the surface is more rough, which helps to improve the coating effect of the subsequent second coating of the polymer, and the outer layer of the red phosphorus-based halogen-free flame retardant particles is polystyrene, which helps to improve the compatibility with other polymer matrices and increase the use effect.

[0030] 2、In the first coating process of the red phosphorus-based halogen-free flame retardant, the red phosphorus can adsorb copper ions, and then a shell formed by the copper-based nano metal organic framework and the copper ion chelate is coated on the surface of the red phosphorus particles by using the chelating effect of tannic acid, which helps to improve the rigidity and stability of the pre-coated red phosphorus microspheres. The introduced copper ions can form copper oxide in the combustion process, which helps to promote the formation of residual carbon in the polymer combustion process and prevent the further combustion of the polymer, and the copper-based nano metal organic framework helps to inhibit the release of smoke in the combustion process, which has application prospects in low-smoke and low-toxicity flame retardation.

[0031] 3、In the second coating process of the red phosphorus-based halogen-free flame retardant, a layer of flame-retardant modified polyvinyl alcohol is coated on the surface of the pre-coated red phosphorus microspheres, which helps to further improve the regularity of the red phosphorus-based halogen-free flame retardant particles and helps to coat the polystyrene shell in the subsequent reaction. The outermost polystyrene shell plays a barrier role, which helps to reduce the hygroscopicity of the red phosphorus-based halogen-free flame retardant, thereby improving its stability and long-lasting flame retardation effect.

[0032] The P(=O)(O - NH4 + ) active group at the end of the reactive organic phosphorus flame retardant can form a covalent bond with the hydroxyl group in the polyvinyl alcohol, thereby grafting the reactive organic phosphorus flame retardant with the polyvinyl alcohol, which helps to avoid the migration of the reactive organic phosphorus flame retardant, and can reduce the hydroxyl group in the polyvinyl alcohol, reduce its hydrophilicity, avoid the moisture failure of the red phosphorus-based halogen-free flame retardant, thereby further improving its stability, and helps to be applied in porous and hygroscopic polymer foam materials. DETAILED DESCRIPTION

[0033] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments of the present application, all other embodiments obtained by a person of ordinary skill in the art without creative effort belong to the protection scope of the present application.

[0034] Embodiment 1: The present embodiment provides a red phosphorus-based halogen-free flame retardant, which is prepared by the following method:

[0035] S1: DOPO (9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide), sodium p-aminobenzoate, phenylacetaldehyde and anhydrous ethanol as a solvent are added into a reaction kettle according to a mass ratio of 26:18:14:400, stirred at 65℃ and 200r / min for 15min, formic acid is added dropwise into the reaction kettle, and the reaction is kept at 90℃ for 5h under the protection of nitrogen, the solvent is removed by rotary evaporation, and the product is ground and crushed to obtain a phosphorus-nitrogen-sodium salt intermediate.

[0036] S2: The phosphorus-nitrogen-sodium salt intermediate and hydrochloric acid with a molar concentration of 0.1mol / L are added into a reaction kettle according to a mass ratio of 1:15, stirred at 25℃ for 8h, centrifuged and washed for 3 times, and the filter cake is vacuum dried to obtain a carboxyl-terminated intermediate.

[0037] S3: The carboxyl-terminated intermediate and phosphoric acid are added into a reaction kettle according to a mass ratio of 2:1, and the reaction is kept at 140℃ for 4h, then urea is added into the reaction kettle, and the reaction is continued for 1.5h, and the product is naturally cooled, centrifuged and washed with anhydrous ethanol for 3 times, and vacuum dried to obtain a reactive organic phosphorus flame retardant.

[0038] S4: 4kg of polyvinyl alcohol, 3.5kg of the reactive organic phosphorus flame retardant, 1kg of dicyandiamide and 20L of deionized water are added into a reaction kettle, and the reaction is stirred at 65℃ for 1h, then the reaction solution is transferred into anhydrous methanol to precipitate a precipitate, the precipitate is filtered, washed with anhydrous methanol for 2 times, and vacuum dried to obtain a flame-retardant modified polyvinyl alcohol.

[0039] S5: 18kg of 3,5-pyrazole dicarboxylic acid monohydrate, 2.4kg of copper nitrate trihydrate and 400L of N,N-dimethylformamide are added into a reaction kettle, stirred at 200r / min for 20min, and then the reaction is stirred at 90℃ for 6h, the product is centrifuged and washed with anhydrous ethanol for 4 times, and the precipitate is vacuum dried to obtain a copper-based nano metal organic framework.

[0040] S6: 10 kg of red phosphorus powder and 20 kg of deionized water were uniformly mixed and ultrasonically dispersed for 10 min to obtain a red phosphorus dispersion liquid; 5 kg of tannic acid, 250 L of deionized water and 250 g of copper acetate were added into a reaction kettle, stirred at 300 r / min for 10 min, then 500 g of copper-based nano metal organic framework was added into the reaction kettle and ultrasonically dispersed for 20 min to obtain a prepolymer dispersion liquid.

[0041] S7: The red phosphorus dispersion liquid and the prepolymer dispersion liquid were added into a reaction kettle according to a volume ratio of 1:2, stirred at 200 r / min for 5 min, then a sodium hydroxide solution with a molar concentration of 0.05 mol / L was used to adjust the pH value to 8.5, and stirring reaction was carried out under ultrasonic assistance with a power of 450 W and a frequency of 35 kHz for 10 min, then centrifugal filtration was carried out, the filter cake was washed with deionized water for 3 times, and vacuum drying was carried out at 50℃ to obtain pre-coated red phosphorus microspheres.

[0042] S8: 250 g of flame-retardant modified polyvinyl alcohol was dissolved with 40 L of deionized water and transferred into a reaction kettle, then 5 kg of pre-coated red phosphorus microspheres were added into the reaction kettle, stirred at 30℃ for 1 h, ultrasonically dispersed for 10 min, then 2.5 L of styrene, 75 mL of diphenyl ethylene, 100 g of magnesium aluminum silicate and 100 g of sodium dodecyl sulfonate were added into the reaction kettle, stirred at 60℃ and 500 r / min for 20 min, 25 g of potassium persulfate was added, and stirring reaction was carried out at 80℃ for 2.5 h, then suction filtration was carried out, the filter cake was washed with anhydrous ethanol for 2 times, and vacuum drying was carried out to obtain a red phosphorus-based halogen-free flame retardant.

[0043] Example 2: The present example provides a red phosphorus-based halogen-free flame retardant, which is prepared by the following method:

[0044] S1: DOPO, sodium p-aminobenzoate, phenylacetaldehyde and anhydrous ethanol as a solvent were added into a reaction kettle according to a mass ratio of 26:19:14.5:450, stirred at 68℃ and 250 r / min for 18 min, then formic acid was added dropwise into the reaction kettle, and stirring reaction was carried out under nitrogen protection and at 92℃ for 5.5 h, then the solvent was removed by rotary evaporation, and grinding and crushing were carried out to obtain a phosphorus-nitrogen-sodium salt intermediate.

[0045] S2: The phosphorus-nitrogen-sodium salt intermediate and hydrochloric acid with a molar concentration of 0.1 mol / L were added into a reaction kettle according to a mass ratio of 1:18, stirred at 28℃ for 9 h, centrifugal washed 4 times, and the filter cake was vacuum dried to obtain a carboxyl-terminated intermediate.

[0046] S3: The carboxyl-terminated intermediate and phosphoric acid were added into a reaction kettle in a mass ratio of 2:1, and reacted at 145°C for 4.5 h. Then, urea was added into the reaction kettle, and the reaction was continued for 1.8 h. The product was washed with anhydrous ethanol by centrifugation for 4 times, and dried under vacuum to obtain the reactive organic phosphorus flame retardant.

[0047] S4: 4 kg of polyvinyl alcohol, 3.8 kg of the reactive organic phosphorus flame retardant, 1 kg of dicyandiamide, and 20 L of deionized water were added into a reaction kettle, and stirred at 70°C for 1.2 h. Then, the reaction solution was transferred into anhydrous methanol to precipitate the product. The precipitate was filtered, washed with anhydrous methanol for 2 times, and dried under vacuum to obtain the flame-retardant modified polyvinyl alcohol.

[0048] S5: 19 kg of 3,5-pyrazole dicarboxylic acid monohydrate, 2.45 kg of copper nitrate trihydrate, and 450 L of N,N-dimethylformamide were added into a reaction kettle, and stirred at 250 r / min for 25 min. Then, the reaction was carried out at 95°C for 7 h. The product was washed with anhydrous ethanol by centrifugation for 4 times, and the precipitate was dried under vacuum to obtain the copper-based nano-metal organic framework.

[0049] S6: 10 kg of red phosphorus powder and 20 kg of deionized water were uniformly mixed and ultrasonically dispersed for 12 min to obtain a red phosphorus dispersion liquid. 5 kg of tannic acid, 280 L of deionized water, and 250 g of copper acetate were added into a reaction kettle, and stirred at 400 r / min for 12 min. Then, 500 g of the copper-based nano-metal organic framework was added into the reaction kettle, and ultrasonically dispersed for 22 min to obtain a prepolymer dispersion liquid.

[0050] S7: The red phosphorus dispersion liquid and the prepolymer dispersion liquid were added into a reaction kettle in a volume ratio of 1:2, and stirred at 250 r / min for 8 min. Then, the pH value was adjusted to 8.5 by using a sodium hydroxide solution with a molar concentration of 0.05 mol / L. The reaction was carried out under ultrasonic assistance at a power of 480 W and a frequency of 38 kHz for 12 min. The filter cake was washed with deionized water for 4 times, and dried under vacuum at 55°C to obtain the pre-coated red phosphorus microspheres.

[0051] S8: 280 g of the flame-retardant modified polyvinyl alcohol was dissolved in 42 L of deionized water and transferred into a reaction kettle. Then, 5.2 kg of the pre-coated red phosphorus microspheres was added into the reaction kettle, and stirred at 32°C for 1 h. The reaction was ultrasonically dispersed for 12 min. Then, 2.5 L of styrene, 85 mL of diphenyl ethylene, 110 g of magnesium aluminum silicate, and 110 g of sodium dodecyl sulfonate were added into the reaction kettle, and stirred at 62°C and 650 r / min for 25 min. 25 g of potassium persulfate was added, and the reaction was carried out at 85°C for 2.8 h. The filter cake was washed with anhydrous ethanol for 2 times, and dried under vacuum to obtain the red phosphorus-based halogen-free flame retardant.

[0052] Embodiment 3: The embodiment provides a red phosphorus-based halogen-free flame retardant, which is prepared by the following method.

[0053] S1: DOPO, sodium p-aminobenzoate, phenylacetaldehyde and anhydrous ethanol as a solvent are added into a reaction kettle according to a mass ratio of 26:20:15:500, stirred at 70 DEG C and 300 r / min for 20 min, formic acid is added dropwise into the reaction kettle, and reaction is carried out under the conditions of nitrogen protection and 95 DEG C for 6 h, the solvent is removed by rotary evaporation, and grinding and crushing are carried out to obtain a phosphorus-nitrogen-sodium salt intermediate.

[0054] S2: The phosphorus-nitrogen-sodium salt intermediate and hydrochloric acid with a molar concentration of 0.1 mol / L are added into a reaction kettle according to a mass ratio of 1:20, stirred at 30 DEG C for 10 h, centrifugal washing is carried out for 5 times, the filter cake is vacuum dried to obtain a terminal carboxyl intermediate.

[0055] S3: The terminal carboxyl intermediate and phosphoric acid are added into a reaction kettle according to a mass ratio of 2:1, reaction is carried out under the condition of 150 DEG C for 5 h, then urea is added into the reaction kettle, and reaction is continued for 2 h, natural cooling is carried out, the product is centrifugal washed with anhydrous ethanol for 5 times, and vacuum drying is carried out to obtain a reaction-type organic phosphorus flame retardant.

[0056] S4: 4 kg of polyvinyl alcohol, 4 kg of the reaction-type organic phosphorus flame retardant, 1 kg of dicyandiamide and 20 L of deionized water are added into a reaction kettle, stirring reaction is carried out at 75 DEG C for 1.5 h, then the reaction solution is transferred into anhydrous methanol to precipitate a precipitate, the precipitate is filtered, washed with anhydrous methanol for 3 times, and vacuum dried to obtain a flame-retardant modified polyvinyl alcohol.

[0057] S5: 20 kg of 3,5-pyrazole dicarboxylic acid monohydrate, 2.5 kg of copper nitrate trihydrate and 500 L of N,N-dimethylformamide are added into a reaction kettle, stirring is carried out at 300 r / min for 30 min, then reaction is carried out at 100 DEG C for 8 h, the product is centrifugal washed with anhydrous ethanol for 5 times, and the precipitate is vacuum dried to obtain a copper-based nano metal organic framework.

[0058] S6: 10 kg of red phosphorus powder and 20 kg of deionized water are uniformly mixed, and ultrasonic dispersion is carried out for 15 min to obtain a red phosphorus dispersion liquid; 5 kg of tannic acid, 300 L of deionized water and 250 g of copper acetate are added into a reaction kettle, stirring is carried out at 500 r / min for 15 min, then 500 g of the copper-based nano metal organic framework is added into the reaction kettle, and ultrasonic dispersion is carried out for 25 min to obtain a prepolymer dispersion liquid.

[0059] S7: The red phosphorus dispersion liquid and the prepolymer dispersion liquid were added into the reaction kettle at a volume ratio of 1:2, stirred at 300 r / min for 10 min, then the pH value was adjusted to 9 with a sodium hydroxide solution with a molar concentration of 0.05 mol / L, and stirred for 15 min under ultrasonic assistance with a power of 500 W and a frequency of 40 kHz, centrifugal filtration was performed, the filter cake was washed with deionized water for 5 times, and vacuum drying was performed at 60 DEG C to obtain the pre-coated red phosphorus microspheres.

[0060] S8: 300 g of the flame-retardant modified polyvinyl alcohol was dissolved in 45 L of deionized water and transferred into the reaction kettle, then 5.5 kg of the pre-coated red phosphorus microspheres was added into the reaction kettle, stirred at 35 DEG C for 1 h, ultrasonic dispersion was performed for 15 min, then 2.5 L of styrene, 100 mL of diphenyl ethylene, 120 g of magnesium aluminum silicate and 120 g of sodium dodecyl sulfonate were added into the reaction kettle, stirred at 65 DEG C and 800 r / min for 30 min, 25 g of potassium persulfate was added, and stirred at 90 DEG C for 3 h, filtration was performed, the filter cake was washed with anhydrous ethanol for 3 times, and vacuum drying was performed to obtain the red phosphorus-based halogen-free flame retardant.

[0061] Comparative Example 1: On the basis of Example 3, without the pre-coating operation in step S7, the pre-coated red phosphorus microspheres in step S8 were replaced by red phosphorus with the same mass, and the remaining steps were unchanged, to prepare a red phosphorus-based halogen-free flame retardant.

[0062] Comparative Example 2: On the basis of Example 3, the pre-coated red phosphorus microspheres in step S7 were directly used as the final red phosphorus-based halogen-free flame retardant.

[0063] Comparative Example 3: On the basis of Example 3, no copper-based nano metal organic framework was added when preparing the prepolymer dispersion liquid in step S6, and the amount of copper acetate was increased to 500 g, and the remaining steps were unchanged, to prepare a red phosphorus-based halogen-free flame retardant.

[0064] Comparative Example 4: On the basis of Example 3, the flame-retardant modified polyvinyl alcohol in step S8 was replaced by polyvinyl alcohol with the same mass, and the remaining steps were unchanged, to prepare a red phosphorus-based halogen-free flame retardant.

[0065] Comparative Example 5: On the basis of Example 3, the polyvinyl alcohol and the phosphorus-nitrogen sodium salt intermediate were directly kneaded with a double screw extruder at a mass ratio of 1:1 in step S4 to obtain a composite polyvinyl alcohol, and the same mass of the composite polyvinyl alcohol was used to replace the flame-retardant modified polyvinyl alcohol in step S8, and the remaining steps were unchanged, to prepare a red phosphorus-based halogen-free flame retardant.

[0066] The above-mentioned red phosphorus-based halogen-free flame retardant was applied to a polymer foaming material, and the addition amount of the red phosphorus-based halogen-free flame retardant could be appropriately adjusted according to the application. Taking a two-component polyurethane foaming material as an example:

[0067] The A component comprises by mass fraction: propylene glycol polyether with a molecular weight of 2000 60 parts, polyoxypropylene triol with a molecular weight of 4000 25 parts, propylene glycol 3 parts, pentaerythritol 2 parts, triethylamine catalyst 1 part, deionized water 0.5 parts.

[0068] The B component comprises by mass fraction: propylene glycol polyether with a molecular weight of 2000 45 parts, polyoxypropylene triol with a molecular weight of 4000 20 parts, isophorone diisocyanate 40 parts, triethylamine catalyst 0.2 parts, red phosphorus-based halogen-free flame retardant 2 parts.

[0069] The A component and the B component are mixed in a mass ratio of 3:2, transferred to a mold for foaming and molding, vacuum dried at 60°C, and the polyurethane foam material is obtained.

[0070] The polyurethane foam materials containing different red phosphorus-based halogen-free flame retardants of Examples 1-3 and Comparative Examples 1-5 are tested for performance, samples are prepared according to the corresponding test standards, the combustion performance of different samples is tested by the vertical method in GB / T2408-2021, the results include V-0, V-1, V-2, wherein V-0 indicates the best flame retardant effect; the limiting oxygen index (LOI) of different samples is tested according to GB / T2406; the flame retardant performance of different samples is tested again after being soaked in deionized water at 80°C for 24h. The results are shown in the following table:

[0071] Table 1: Flame retardant performance results of each sample before and after soaking

[0072] As can be seen from Table 1, the samples in Examples 1-3 have good flame retardant performance before and after soaking. Combined with the data in Comparative Example 1 and Comparative Example 3, the flame retardant effect of the red phosphorus-based halogen-free flame retardant after pre-coating is better, because the copper-based nano metal organic framework and the like coating helps to improve the rigidity and stability of the red phosphorus-based halogen-free flame retardant particles, and the pre-coating can improve the surface roughness, which is helpful for secondary coating.

[0073] The flame retardant performance in Comparative Example 2 and Comparative Example 4-5 is poor, which indicates that the reaction type organic phosphorus flame retardant can improve the flame retardant effect of the red phosphorus-based halogen-free flame retardant, and the flame retardant performance of the corresponding sample further decreases after soaking, which may be because the coating effect is not good, the hydroxyl group in the polyvinyl alcohol combined after the reaction of the reaction type organic phosphorus flame retardant is reduced, the hydrophilicity is reduced, which can avoid the red phosphorus-based halogen-free flame retardant from being invalid due to moisture, and further improve its stability.

[0074] It is to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting; it is not intended to exclude myriad other embodiments of the present application that other inventors can develop based on the same general inventive concepts embodied by the described embodiments. That is, although the present application is described in terms of particular embodiments and illustrative figures, it should be apparent that the scope of the present application is not limited to these specific embodiments.

[0075] While the embodiments of the application have been shown and described herein, it will be understood by those skilled in the art that many changes, modifications, substitutions and alterations to these embodiments can be made without departing from the principles and spirits of the application, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A process for the preparation of red phosphorus-based halogen-free flame retardants, characterized in that, Comprising the following steps: Step one: uniformly mix red phosphorus powder and deionized water according to a mass ratio of 1:2, ultrasonic dispersion for 10-15 min, to obtain a red phosphorus dispersion liquid; add tannic acid, deionized water and copper acetate into a reaction kettle, stir at 300-500 r / min for 10-15 min, then add copper-based nano metal organic framework, ultrasonic dispersion for 20-25 min, to obtain a prepolymer dispersion liquid; Step two: add the red phosphorus dispersion liquid and the prepolymer dispersion liquid into a reaction kettle according to a volume ratio of 1:2, stir at 200-300 r / min for 5-10 min, then adjust the pH value to 8.5-9 with a 0.05 mol / L sodium hydroxide solution, stir and react under ultrasonic assistance for 10-15 min, centrifugal filtration, wash the filter cake with deionized water for 3-5 times, vacuum drying at 50-60℃, to obtain pre-coated red phosphorus microspheres; the power of the ultrasonic assistance is 450-500 W, and the frequency is 35-40 kHz; Step three: dissolve the flame-retardant modified polyvinyl alcohol with deionized water and transfer it into a reaction kettle, then add the pre-coated red phosphorus microspheres, stir at 30-35℃ for 1 h, ultrasonic dispersion for 10-15 min, then add styrene, diphenyl ethylene, magnesium aluminum silicate and sodium dodecyl sulfonate, stir at 60-65℃ and 500-800 r / min for 20-30 min, add potassium persulfate, stir and react at 80-90℃ for 2.5-3 h, suction filtration, wash the filter cake with anhydrous ethanol for 2-3 times, vacuum drying, to obtain a red phosphorus-based halogen-free flame retardant; The flame-retardant modified polyvinyl alcohol is prepared by the following steps: Add polyvinyl alcohol, reactive organic phosphorus flame retardant, dicyandiamide and deionized water into a reaction kettle, stir and react at 65-75℃ for 1-1.5 h, then transfer the reaction liquid into anhydrous methanol to precipitate, filter, wash the precipitate with anhydrous methanol for 2-3 times, vacuum drying, to obtain the flame-retardant modified polyvinyl alcohol; The reactive organic phosphorus flame retardant is prepared by the following steps: Add carboxyl-terminated intermediate and phosphoric acid into a reaction kettle according to a mass ratio of 2:1, heat at 140-150℃ for 4-5 h, then add urea, continue to react for 1.5-2 h, natural cooling, centrifugal washing of the product with anhydrous ethanol for 3-5 times, vacuum drying, to obtain the reactive organic phosphorus flame retardant; The carboxyl-terminated intermediate is prepared by the following steps: Add phosphorus-nitrogen sodium salt intermediate and 0.1 mol / L hydrochloric acid into a reaction kettle according to a mass ratio of 1:15-20, stir at 25-30℃ for 8-10 h, centrifugal washing for 3-5 times, vacuum drying of the filter cake, to obtain the carboxyl-terminated intermediate; The phosphorus-nitrogen sodium salt intermediate is prepared by the following steps: The DOPO, sodium p-aminobenzoate, phenylacetaldehyde and anhydrous ethanol as a solvent are added into a reaction kettle according to a mass ratio of 26:18-20:14-15:400-500, stirred at 65-70 DEG C and 200-300 r / min for 15-20 min, then formic acid is added dropwise into the reaction kettle, and the reaction is carried out under the conditions of nitrogen protection and 90-95 DEG C for 5-6 h, the solvent is removed by rotary evaporation, and grinding is carried out to obtain a phosphorus-nitrogen-sodium salt intermediate.

2. The method for preparing a red phosphorus-based halogen-free flame retardant according to claim 1, characterized in that, The tannic acid, deionized water, copper acetate and copper-based nanometer metal organic framework in step one are used in a ratio of 0.5 g:25-30 mL:0.025 g:0.05 g.

3. The method for preparing a red phosphorus-based halogen-free flame retardant according to claim 1, characterized in that, The flame-retardant modified polyvinyl alcohol, deionized water, pre-coated red phosphorus microspheres, styrene, diphenyl ethylene, magnesium aluminum silicate, sodium dodecyl sulfonate and potassium persulfate in step three are used in a ratio of 2.5-3 g:400-450 mL:50-55 g:25 mL:0.75-1 mL:1-1.2 g:1-1.2 g:0.25 g.

4. The method for preparing a red phosphorus-based halogen-free flame retardant according to claim 1, characterized in that, The copper-based nanometer metal organic framework in step one is prepared by the following steps: 3,5-pyrazole dicarboxylic acid monohydrate, copper nitrate trihydrate and N,N-dimethylformamide are added into a reaction kettle, stirred at 200-300 r / min for 20-30 min, then the reaction is carried out under the conditions of 90-100 DEG C and stirring for 6-8 h, the product is washed by centrifugation with anhydrous ethanol for 4-5 times, and the precipitate is vacuum dried to obtain a copper-based nanometer metal organic framework; The 3,5-pyrazole dicarboxylic acid monohydrate, copper nitrate trihydrate and N,N-dimethylformamide are used in a ratio of 1.8-2 g:0.24-0.25 g:40-50 mL.

5. The method for preparing a red phosphorus-based halogen-free flame retardant according to claim 1, characterized in that, The polyvinyl alcohol, reactive organic phosphorus flame retardant, dicyandiamide and deionized water are used in a ratio of 4 g:3.5-4 g:1 g:20 mL.

6. A red phosphorus-based halogen-free flame retardant characterized by comprising: The red phosphorus-based halogen-free flame retardant is prepared by the preparation method in any one of claims 1-5.

7. The use of the red phosphorus-based halogen-free flame retardant in claim 6 as a flame-retardant filler in a polymer foaming material.

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