Preparation method of heat-resistant and hydrolysis-resistant caged phosphorus-aluminum flame retardant

Abstract

The invention discloses a preparation method of a heat-resistant and hydrolysis-resistant caged phosphorus-aluminum flame retardant. Pentaerythritol and phosphorus oxychloride are used as raw materials to synthesize di-cage phosphorus oxychloride, which is then hydrolyzed and reacted with aluminum salt to obtain a phosphorus-aluminum flame retardant containing a cage structure. In the invention, the caged phosphorus-aluminum flame retardant has the characteristics of hydrolysis resistance, high temperature resistance, good compatibility with polymers, etc., avoids the risks of decomposition and agglomeration during polymer processing, and provides a feasible solution for flame-retardant modification of engineering plastics with high molding temperatures. The phosphorus and aluminum elements in the flame retardant play a role in gas-phase and solid-phase flame retardancy, and exhibit good flame retardant properties in polymers.

Description

Technical Field

[0001] The invention belongs to the technical field of polymer materials, and particularly relates to a preparation method of a heat-resistant and hydrolysis-resistant caged phosphorus-aluminum flame retardant. Background Art

[0002] Phosphorus-based flame retardants exhibit dual flame retardancy in both the gas and solid phases, offering excellent flame retardant efficiency. Compared to halogen flame retardants, phosphorus-based flame retardants are characterized by low toxicity and diverse structural designs. Consequently, phosphorus-based flame retardants have garnered widespread attention in the field of polymer flame retardancy. Common phosphorus-based flame retardants include ammonium polyphosphate and melamine polyphosphate. However, during the processing of polymers at high processing temperatures (such as engineering plastics), many phosphorus-based flame retardants either cannot withstand the high shear heat generated during processing and decompose, or require high addition levels (greater than 30 wt%) to achieve high flame retardant properties. Therefore, optimization of phosphorus-based flame retardants is necessary.

[0003] Research has discovered a synergistic flame-retardant effect between phosphorus and aluminum. During combustion, they form a dense char layer that blocks heat and oxygen transfer, further enhancing solid-phase flame retardancy. Inorganic phosphorus-aluminum flame retardants (such as aluminum hypophosphite) are an early and widely used type of phosphorus-aluminum flame retardant. While they offer excellent heat resistance, they require high dosages as flame retardants and can easily cause degradation of polymers such as polyamide during processing. Organic aluminum hypophosphite offers advantages over inorganic phosphorus-aluminum flame retardants, such as good compatibility with polymers and minimal loss of mechanical properties. The earliest organic phosphorus-aluminum flame retardant, diethyl aluminum hypophosphite, was developed by Clariant in Germany. However, due to its still-patent period and the fact that its synthesis requires a free radical addition reaction between sodium hypophosphite and gaseous ethylene under high pressure, the complex manufacturing process and demanding synthesis conditions undoubtedly increase costs.

[0004] To overcome the preparation challenges associated with high-pressure reactions, it is necessary to develop simple and efficient organoaluminum hypophosphites to meet the flame retardant requirements of engineering plastics. High-temperature-resistant organoaluminum hypophosphites are a particular research hotspot, as they not only avoid decomposition during processing but also allow for the reproducibility of flame-retardant materials. In recent years, researchers have made progress in the atmospheric-pressure synthesis of organoaluminum hypophosphites. For example, organoaluminum hypophosphites with various substituents have been synthesized using cyclohexene and isobutylene as raw materials. Their initial decomposition temperatures are all above 280°C, and they exhibit good flame retardancy in polyamides. Currently, most patents published by Clariant utilize dialkyl hypophosphites. The alkyl groups can be further optimized to enhance the flame retardancy or heat resistance of organoaluminum hypophosphites, such as phenyl groups, to improve their flame retardancy. Furthermore, the reported variety of high-temperature-resistant organoaluminum hypophosphites for engineering plastics is limited, and the synthesis routes need improvement. Summary of the Invention

[0005] In order to solve the above problems, the present invention discloses a method for preparing a heat-resistant and hydrolysis-resistant caged phosphorus-aluminum flame retardant.

[0006] To achieve the above object, the technical solution of the present invention is as follows:

[0007] A heat-resistant and hydrolysis-resistant caged phosphorus-aluminum flame retardant, characterized in that the chemical structural formula of the heat-resistant and hydrolysis-resistant caged phosphorus-aluminum flame retardant is as follows:

[0008] .

[0009] The preparation method of the heat-resistant and hydrolysis-resistant caged phosphorus-aluminum compound comprises the following specific steps:

[0010] Step (1) Synthesis of Pentaerythritol Phosphate: Add an anhydrous dioxane solution of pentaerythritol into a reactor equipped with a mechanical stirrer and a condensing reflux device, introduce nitrogen protection, and heat to 80-130°C; quickly add 50% of the total mass of phosphorus oxychloride, and then slowly add the remaining phosphorus oxychloride using a dropping funnel to react for 5-12 hours, let it stand to room temperature, filter, and then recrystallize with 100-300 mL of anhydrous ethanol, and vacuum dry to obtain a white solid, which is pentaerythritol phosphate; the reaction formula is as follows:

[0011] ;

[0012] Step (2) Synthesis of di-caged phosphoryl chloride: Anhydrous acetonitrile and phosphorus oxychloride are added to the reactor described in step (1), stirred evenly at room temperature, and passed through dry nitrogen for protection, equipped with a mechanical stirrer and a condensation reflux device; the pentaerythritol phosphate obtained in step (1) is added to the above reaction system in 6-8 portions; after the addition is completed, the system is heated to 70-90°C and refluxed for condensation reaction until no hydrogen chloride (HCl) gas escapes, and the reaction is stopped; the solvent is removed by rotary evaporation using a rotary evaporator to obtain a white powder, which is di-caged phosphoryl chloride; the reaction formula is as follows:

[0013] ;

[0014] Step (3) Synthesis of caged phosphorus-aluminum compound: add di-cage phosphoryl chloride and N,N-dimethylformamide (DMF) to a reaction apparatus, heat to 60-90 °C, add 5-20 mL of deionized water dropwise for hydrolysis reaction for 2-4 hours, then adjust the pH of the above system solution to 6-7 with sodium hydroxide aqueous solution at room temperature, slowly add aluminum salt aqueous solution dropwise, react at 60-90 °C for 4-7 hours, distill and concentrate under reduced pressure, then add acetonitrile to precipitate, filter to obtain a white solid, and vacuum dry to obtain a caged phosphorus-aluminum compound; the reaction formula is as follows: .

[0015] .

[0016] Furthermore, in step (1), the mass ratio of the pentaerythritol to the anhydrous dioxane is 1:3-5.

[0017] Furthermore, the vacuum drying time in step (1) and step (3) is 3-8 hours and the temperature is 70-90°C.

[0018] Furthermore, in step (1), the mass ratio of the anhydrous dioxane to the phosphorus oxychloride is 6-8:1.

[0019] Furthermore, the pentaerythritol phosphate in step (2) is added in batches 6 to 8 times, with an interval of 0.5 h between each addition and a temperature increase of 3 to 6°C.

[0020] Furthermore, the reflux condensation reaction time in step (2) is 20 to 30 hours.

[0021] Furthermore, in step (3), the mass ratio of the di-cage phosphoryl chloride to the N,N-dimethylformamide is 1:10-15.

[0022] Furthermore, the aluminum salt in step (3) includes any one of aluminum chloride, aluminum sulfate, and aluminum nitrate; and the concentration of the sodium hydroxide aqueous solution is 0.1-1 mol / L.

[0023] Furthermore, the concentration of the sodium hydroxide aqueous solution in step (3) is 0.1-0.3 mol / L.

[0024] The caged phosphorus-aluminum compound prepared by the present invention has a significantly higher carbon residue rate than diethylaluminum hypophosphite (39.0%) in a nitrogen atmosphere at 800° C., and both are white solids and will not affect the color of polymer products.

[0025] The beneficial effects of the present invention are:

[0026] (1) The present invention provides a method for preparing a heat-resistant and hydrolysis-resistant caged phosphorus-aluminum flame retardant, which has a simple process and is easy to operate and control;

[0027] (2) The heat-resistant and hydrolysis-resistant caged phosphorus-aluminum flame retardant provided by the present invention is as follows: Figure 1 As shown, the initial decomposition temperature (T 5wt% ) reaches 265℃, and the residual carbon rate is 53.6% at 800℃, which has a good high-temperature carbonization rate. It can be used as an additive flame retardant for halogen-free flame retardancy of engineering plastics such as nylon;

[0028] (3) When the heat-resistant and hydrolysis-resistant caged phosphorus-aluminum flame retardant provided by the present invention is used for flame retardant of PA66, when the addition amount is 10-25%, the limiting oxygen index of the flame retardant material can reach 23-29. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 The thermal gravimetric analysis (TGA) and differential thermal gravimetric analysis (DTG) curves of the caged phosphorus-aluminum flame retardant synthesized in the present invention in a nitrogen atmosphere are shown;

[0030] Figure 2 The flame retardant effect of the caged phosphorus-aluminum flame retardant synthesized by the present invention;

[0031] Figure 3 The electronic photograph of the carbon residue after the cone calorimetry test of the caged phosphorus-aluminum flame retardant synthesized by the present invention is used in nylon 66. DETAILED DESCRIPTION

[0032] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. It should be understood that the following specific embodiments are only used to illustrate the present invention and are not used to limit the scope of the present invention.

[0033] The room temperature in the following examples is 22-28°C.

[0034] Example 1

[0035] The first step is the synthesis of pentaerythritol phosphate: 140 mL of anhydrous dioxane and 34.0 g of pentaerythritol are added to a 250 mL three-necked flask, which is protected by nitrogen and equipped with a mechanical stirrer and a condenser reflux device. The temperature is raised to 95°C. After the pentaerythritol is dissolved, 19.1 g of phosphorus oxychloride is quickly added to the reaction system, and then 19.1 g of phosphorus oxychloride is slowly added dropwise to the system using a dropping funnel; the reaction system is maintained at 95°C for 10 hours; after standing to room temperature, it is filtered, and then 100 mL of anhydrous ethanol is added for recrystallization, and vacuum drying is performed to obtain a white solid with a yield of 68%.

[0036] Step 2: Synthesis of di-cage phosphoryl chloride: 500 mL of anhydrous acetonitrile and 31.9 g of phosphorus oxychloride were added to a 1 L three-necked flask and stirred evenly at room temperature. Dry nitrogen was introduced into the flask, and the flask was equipped with a mechanical stirrer and a reflux condenser. 75 g of pentaerythritol phosphate was weighed and added to the reaction system in seven portions, with a 0.5 h interval between additions. The temperature was raised by 5°C after each addition. After the addition of pentaerythritol phosphate, the system was heated to 75°C and refluxed for approximately 22 h. The reaction was stopped when no HCl gas escaped. The acetonitrile solvent was removed using a rotary evaporator to obtain a white powder solid.

[0037] Step 3: Synthesis of a caged phosphorus-aluminum compound: 46 g of di-cage phosphoryl chloride and 500 mL of N,N-dimethylformamide were weighed and added to a 1-L three-necked flask. The temperature was raised to 70°C, and 10 mL of deionized water was added dropwise for hydrolysis reaction for 4 hours. The pH of the solution was then adjusted to 7 with 0.1 mol / L sodium hydroxide aqueous solution at room temperature. Aqueous aluminum chloride solution (12.8 g of aluminum chloride hexahydrate and 38 g of water) was then added dropwise. The reaction was continued at 85°C for 6 hours. The solution was concentrated by vacuum distillation, and acetonitrile was added to precipitate the solid. The solid was filtered and dried under vacuum to obtain a white solid.

[0038] Example 2

[0039] The first step is the synthesis of pentaerythritol phosphate: 280 mL of anhydrous dioxane and 68.0 g of pentaerythritol are added to a 500 mL three-necked flask, which is protected by nitrogen and equipped with a mechanical stirrer and a condenser reflux device. The temperature is raised to 90°C. After the pentaerythritol is dissolved, 38.2 g of phosphorus oxychloride is quickly added to the reaction system, and then 38.2 g of phosphorus oxychloride is slowly added dropwise to the system using a dropping funnel; the reaction system is maintained at 90°C for 10 hours; the mixture is allowed to stand to room temperature and then filtered, then recrystallized with 300 mL of anhydrous ethanol, and dried in vacuo to obtain a white solid with a yield of 65%.

[0040] Step 2: Synthesis of di-cage phosphoryl chloride: 470 mL of anhydrous acetonitrile and 31.9 g of phosphorus oxychloride were added to a 1 L three-necked flask and stirred evenly at room temperature. Dry nitrogen was introduced into the flask, and the flask was equipped with a mechanical stirrer and a reflux condenser. 75 g of pentaerythritol phosphate was weighed and added to the reaction system in seven portions, with a 0.5 h interval between additions. The temperature was raised by 5°C after each addition. After the addition of pentaerythritol phosphate, the system was heated to 78°C and refluxed for approximately 20 h. The reaction was stopped when no HCl gas escaped. The acetonitrile solvent was removed using a rotary evaporator to obtain a white powder solid.

[0041] Step 3: Synthesis of the caged phosphorus-aluminum compound: 46 g of di-cage phosphoryl chloride and 500 mL of N,N-dimethylformamide were weighed and added to a 1-L three-necked flask. The temperature was raised to 70°C, and 10 mL of deionized water was added dropwise for hydrolysis reaction for 3 hours. The pH of the solution was then adjusted to 7 with 0.1 mol / L aqueous sodium hydroxide at room temperature. Aqueous aluminum sulfate (18.1 g aluminum sulfate and 38 g water) was then added dropwise. The reaction was continued at 80°C for 5 hours. The solution was concentrated by vacuum distillation, and acetonitrile was added to precipitate the solid. The solid was filtered and dried under vacuum to obtain a white solid.

[0042] Example 3

[0043] 10-30 parts by weight of a caged phosphorus-aluminum compound and 70-90 parts of polyamide 66 were melt-blended in a twin-screw extruder (Thermo Haake) to produce a flame-retardant polymer material. The screw diameter (D) was 16 mm, the L / D ratio (L / D) was 25 / 1, and the screw speed was 45 rpm. The temperatures from the feed section to the extrusion die were set at 265°C, 280°C, 282°C, 282°C, and 280°C, respectively.

[0044] The flame retardant properties of the flame retardant material with 30 parts of caged phosphorus-aluminum compound are as follows: the heat release rate and total heat release during combustion are reduced by 43.4% and 55.8% respectively compared with the pure polymer. The electron photo of the carbon residue after the cone calorimetry test is as follows: Figure 3 shown.

[0045] Example 4

[0046] 15-30 parts by weight of a caged phosphorus-aluminum compound and 75-85 parts of polypropylene were weighed and stirred in an internal mixer until uniformly mixed. The mixture was then extruded and pelletized using a twin-screw extruder (Thermo Haake) to produce a flame-retardant polymer material. The screw diameter (D) was 16 mm, the L / D ratio (L / D) was 25 / 1, and the screw speed was 300-400 rpm. The temperatures from the feed section to the extrusion die were set at 190°C, 205°C, 210°C, 215°C, and 205°C, respectively.

[0047] The flame retardant effect of caged phosphorus-aluminum flame retardant is as follows Figure 2 As shown in FIG, the flame retardant properties of the flame retardant material with 25 parts of diphenyl aluminum hypophosphite added are as follows: the limiting oxygen index reaches 29.1%, and the heat release rate and total heat release during combustion are reduced by 57.3% and 48.9% respectively compared with the pure polymer.

[0048] It should be noted that the above content merely illustrates the technical idea of ​​the present invention and cannot be used to limit the scope of protection of the present invention. For ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications all fall within the scope of protection of the claims of the present invention.

Claims

1. A heat-resistant and hydrolysis-resistant caged phosphorus-aluminum flame retardant, characterized in that: The chemical structural formula of the heat-resistant and hydrolysis-resistant caged phosphorus-aluminum flame retardant is as follows: 。 2. The method for preparing a heat-resistant and hydrolysis-resistant caged phosphorus-aluminum flame retardant according to claim 1, comprising the following steps: Step (1): add anhydrous dioxane of pentaerythritol into a reactor equipped with a mechanical stirrer and a condensing reflux device, introduce nitrogen protection, heat to 80-130°C, quickly add 50% of the total mass of phosphorus oxychloride, and then slowly add the remaining phosphorus oxychloride using a dropping funnel to react for 5-12 hours, let it stand to room temperature and then filter, then recrystallize with 100-300 mL of anhydrous ethanol, and vacuum dry to obtain pentaerythritol phosphate; the reaction formula is as follows: ； Step (2): add anhydrous acetonitrile and phosphorus oxychloride to the reactor described in step (1), stir evenly at room temperature, and introduce dry nitrogen for protection. Add the pentaerythritol phosphate obtained in step (1) to the above reactor in 6-8 portions. After the addition is completed, heat to 70-90°C and reflux for condensation reaction until no hydrogen chloride gas escapes. Stop the reaction; remove the solvent by rotary evaporation to obtain di-cage phosphoryl chloride. The reaction formula is as follows: ； Step (3): add di-cage phosphoryl chloride and N,N-dimethylformamide to the reaction apparatus, heat to 60-90 °C, add 5-20 mL of deionized water dropwise for hydrolysis reaction for 2-4 hours, then adjust the pH of the system to 6-7 with sodium hydroxide aqueous solution at room temperature, slowly add aluminum salt aqueous solution dropwise, react at 60-90 °C for 4-7 hours, concentrate by vacuum distillation, add acetonitrile for precipitation, filter to obtain a white solid, vacuum dry to obtain a caged phosphorus-aluminum flame retardant; the reaction formula is as follows: 。 3. The preparation method according to claim 2, characterized in that The mass ratio of the pentaerythritol to the anhydrous dioxane in step (1) is 1:3-5.

4. The preparation method according to claim 2, characterized in that The vacuum drying time in step (1) and step (3) is 3-8 hours and the temperature is 70-90°C.

5. The preparation method according to claim 2, characterized in that The mass ratio of the anhydrous dioxane to the phosphorus oxychloride in step (1) is 6-8:

1.

6. The preparation method according to claim 2, characterized in that The pentaerythritol phosphate in step (2) is added in batches 6 to 8 times, with an interval of 0.5 h between each addition and a temperature increase of 3 to 6 °C.

7. The preparation method according to claim 2, characterized in that The reflux condensation reaction time in step (2) is 20 to 30 hours.

8. The preparation method according to claim 2, characterized in that The mass ratio of the di-crystal phosphoryl chloride to the N,N-dimethylformamide in step (3) is 1:10-15.

9. The preparation method according to claim 2, characterized in that The aluminum salt in step (3) includes any one of aluminum chloride and aluminum sulfate; the concentration of the sodium hydroxide aqueous solution is 0.1-1 mol / L.

10. The preparation method according to claim 2, characterized in that: The concentration of the sodium hydroxide aqueous solution in step (3) is 0.1-0.3 mol / L.

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