Aluminum hypophosphite crystal and preparation method and application thereof
By controlling the crystal structure of aluminum phosphite using crystallization-directing agents, the problem of easy decomposition of aluminum phosphite during polymer processing was solved, enabling the preparation of high-purity and high-thermal-stability aluminum phosphite that meets heat resistance requirements and can be applied in the fields of plastics and coatings.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- PRESAFER QINGYUAN PHOSPHOR CHEM
- Filing Date
- 2023-12-20
- Publication Date
- 2026-06-19
Smart Images
Figure CN117923442B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of flame retardant materials technology, and specifically relates to a crystalline aluminum phosphite, its preparation method, and its application. Background Technology
[0002] The mesoscopic state of solid substances includes two aggregate states: crystalline and amorphous. During preparation, due to the influence of process conditions such as temperature and pressure, the same chemical substance may exhibit either a crystalline or amorphous state. Different aggregate states of the same chemical substance will have certain effects on its physical and chemical properties, such as melting point and solubility. Therefore, different aggregate states can be selected according to different requirements.
[0003] Aluminum phosphite, as an inorganic additive flame retardant, exhibits excellent flame-retardant properties and is commonly used in the plastics and coatings industries. Aluminum phosphite is studied and utilized due to its porous and three-dimensional structure. In its preparation, nitrogen-containing compounds are typically used as structure-directing agents to generate crystalline compounds under high temperature and pressure conditions. However, when used as a flame retardant, it requires good heat resistance to prevent thermal decomposition during plastic processing. Nitrogen-containing compounds often fail to meet these requirements, making them prone to thermal decomposition during plastic processing. Furthermore, nitrogen compounds are difficult to completely remove during crystallization, easily forming porous products that absorb water from the crystal lattice, resulting in high moisture content in the powder. This leads to hydrolytic degradation of the polymer material, affecting its use in the flame-retardant field. Patents CN104093663B and CN111661830A use a kneader to heat and melt phosphorous acid, then add aluminum hydroxide to react and prepare aluminum phosphite. However, the dry aluminum production method requires high dosage and is prone to incomplete reaction, resulting in acid residue. Patent CN113460984A uses aluminum hydrogen phosphite and aluminum salt to react and produce crystalline aluminum phosphite, but its preparation process is complex and costly. Patent TWI765102B uses alumina hydrate and phosphorous acid to react at temperatures above 50°C to prepare aluminum phosphite, but the plastic prepared by this method has a low thermal decomposition temperature, which cannot meet the processing requirements of polymer materials with high heat resistance.
[0004] Therefore, there is an urgent need to provide a crystalline aluminum phosphite with high purity, which can be used in the preparation of plastics to give the plastics good thermal stability and flame retardant properties, and meet the processing requirements of polymer materials with high heat resistance. Summary of the Invention
[0005] This invention aims to solve one or more technical problems existing in the prior art, and at least provide a beneficial alternative or create conditions. This invention provides a crystalline aluminum phosphite with high purity, which, when used in the preparation of plastics, imparts good thermal stability and flame retardant properties to the plastics, meeting the processing requirements of polymer materials with high heat resistance requirements, and the preparation process is simple.
[0006] The inventive concept of this invention: The crystallization-directing agent of this invention has a cross-linked state and high activity. During the preparation of crystalline aluminum phosphite, it can cause the reaction product to grow along the structure of the crystallization-directing agent, thereby improving the crystal structure of the product and reducing crystal defects. The XRD pattern of the prepared crystalline aluminum phosphite shows diffraction peaks at 2θ of 12.0, 14.0, 15.0, 15.5, 16.0, 17.5, 20.0, 22.5, 23.5, 29.0, 30.0, 30.5, 31.0, 32.0, 33.0, 36.5, 38.5, and 45.0 ± 0.2°. When used in the preparation of plastics, this crystalline aluminum phosphite results in a 2% decomposition temperature as high as 440°C, and a flame retardant rating of V0. It exhibits good thermal stability and flame retardant properties, effectively meeting the processing requirements of polymer materials with high heat resistance.
[0007] Therefore, a first aspect of the present invention provides a crystalline aluminum phosphite.
[0008] Specifically, the XRD pattern of the crystalline aluminum phosphite shows diffraction peaks at 2θ of 12.0, 14.0, 15.0, 15.5, 16.0, 17.5, 20.0, 22.5, 23.5, 29.0, 30.0, 30.5, 31.0, 32.0, 33.0, 36.5, 38.5, and 45.0 ± 0.2°.
[0009] Preferably, the XRD pattern of the crystalline aluminum phosphite also shows diffraction peaks at 2θ of 22, 25.0, 27.5, 48.0, 51.0, 52.0, 57, 68 ± 0.2°.
[0010] Preferably, the crystalline aluminum phosphite has a particle size of 1-110 μm; more preferably, the crystalline aluminum phosphite has a particle size of 1-100 μm; and even more preferably, the crystalline aluminum phosphite has a particle size of 5-20 μm.
[0011] Preferably, the decomposition temperature of the crystalline aluminum phosphite is ≥400℃; more preferably, the decomposition temperature of the crystalline aluminum phosphite is ≥430℃.
[0012] Specifically, the decomposition temperature is the 2% decomposition temperature.
[0013] A second aspect of the present invention provides a method for preparing the crystalline aluminum phosphite described in the first aspect of the present invention.
[0014] Specifically, the raw materials for preparing the crystalline aluminum phosphite include a crystallization directing agent, phosphorous acid, aluminum and / or aluminum compounds; the raw materials for preparing the crystallization directing agent include phosphite and phosphorous acid.
[0015] Preferably, the raw materials for preparing the crystallization directing agent include phosphite, hydrogen phosphite, and phosphorous acid.
[0016] Preferably, the aluminum compound is selected from at least one of aluminum carbonate, aluminum acetate, aluminum hydroxide, and aluminum oxide.
[0017] Preferably, the phosphite is selected from at least one of aluminum phosphite, iron phosphite, zinc phosphite, and calcium phosphite; the hydrogen phosphite is selected from at least one of aluminum hydrogen phosphite and zinc hydrogen phosphite.
[0018] Preferably, in the raw materials for preparing aluminum phosphite, the crystallization directing agent accounts for 1-50% of the total mass of the crystallization directing agent, phosphorous acid, aluminum and / or aluminum compounds.
[0019] More preferably, in the raw materials for preparing aluminum phosphite, the crystallization directing agent accounts for 1-10% of the total mass of the crystallization directing agent, phosphorous acid, aluminum and / or aluminum compounds.
[0020] Preferably, the particle size of the crystallization directing agent is 0.1-110 μm; more preferably, the particle size of the crystallization directing agent is 0.1-100 μm; and even more preferably, the particle size of the crystallization directing agent is 0.1-50 μm.
[0021] Preferably, the pH of the aqueous suspension of the crystallization directing agent is 1-6.5; more preferably, the pH of the aqueous suspension of the crystallization directing agent is 1-6.
[0022] Specifically, water is added to the crystallization directing agent to obtain an aqueous suspension. The crystallization directing agent is a suspended particle. By limiting the pH of the aqueous suspension of the crystallization directing agent, the reaction system can be well regulated, so that the reaction is sufficient and complete.
[0023] Preferably, in the raw materials for preparing aluminum phosphite, the molar ratio of phosphorous acid, aluminum and / or aluminum compounds is (2.5-3.5):2.
[0024] More preferably, in the raw materials for preparing aluminum phosphite, the molar ratio of phosphorous acid, aluminum and / or aluminum compounds is (3.0-3.1):2.
[0025] Preferably, the method for preparing the crystalline aluminum phosphite includes the following steps:
[0026] The raw material components of crystalline aluminum phosphite are mixed and reacted to obtain the crystalline aluminum phosphite.
[0027] Preferably, the crystallization directing agent is first added to the reaction vessel, then water and phosphorous acid are added, stirred, and finally aluminum and / or aluminum compounds are added to react and obtain the crystalline aluminum phosphite.
[0028] Preferably, the stirring speed is 100-1000 r / min; the stirring time is 0.1-10 h.
[0029] More preferably, the stirring speed is 300-700 r / min; the stirring time is 0.2-2 h.
[0030] Preferably, the reaction temperature is 55-155℃; the reaction time is 1-12h.
[0031] More preferably, the reaction temperature is 60-150℃; the reaction time is 1-11h.
[0032] More preferably, the reaction temperature is 75-120°C; the reaction time is 1-10 hours.
[0033] Preferably, the reaction further includes solid-liquid separation, and the resulting solid is dried to obtain the crystalline aluminum phosphite.
[0034] Preferably, the solid-liquid separation is performed by centrifugation.
[0035] Preferably, the solid after solid-liquid separation is dried in a dryer.
[0036] Preferably, the drying temperature is 90-260℃, the drying time is 0.1-30h, and the drying pressure is -0.11 to 0.11MPa.
[0037] More preferably, the drying temperature is 100-250℃; the drying time is 0.5-20h; and the drying pressure is -0.1 to 0.1MPa.
[0038] More preferably, the drying temperature is 150-200℃; the drying time is 1-8h; and the drying pressure is 0-0.1MPa.
[0039] Preferably, the liquid after solid-liquid separation can be recycled and used in the reaction to prepare crystalline aluminum phosphite, thus saving resources.
[0040] Preferably, the method for preparing the crystallization directing agent includes the following steps:
[0041] The raw material components of the crystallization directing agent are mixed and reacted to obtain the crystallization directing agent.
[0042] Specifically, phosphites or mixtures of phosphites and hydrogen phosphites undergo a cross-linking reaction upon treatment with phosphorous acid, forming cross-linked phosphites or mixtures of phosphites and hydrogen phosphites, i.e., crystallization directing agents. Because of their cross-linked state, these crystallization directing agents are highly active and can guide the reaction products to grow along their structure, thereby improving the crystal structure of the product and reducing crystal defects. Furthermore, phosphorous acid is used during acid treatment to ensure product purity and avoid introducing other acids.
[0043] Specifically, the phosphite is in a non-crystalline amorphous form before acid treatment.
[0044] Preferably, when the phosphite is treated with phosphorous acid, the mass ratio of the phosphite to the phosphorous acid is 1:(0.09-1.1); more preferably, the mass ratio of the phosphite to the phosphorous acid is 1:(0.1-1).
[0045] Preferably, when the mixture of phosphite and hydrogen phosphite is treated with phosphorous acid, the mass ratio of the mixture of phosphite and hydrogen phosphite to phosphorous acid is 1:(0.09-1.1); more preferably, the mass ratio of the mixture of phosphite and hydrogen phosphite to phosphorous acid is 1:(0.1-1).
[0046] Preferably, when preparing the crystallization directing agent, the reaction after mixing the raw material components is carried out under heating and stirring conditions.
[0047] Preferably, the heating and stirring temperature is 55-155℃; the heating and stirring time is 0.1-10h; and the heating and stirring speed is 100-1000r / min.
[0048] More preferably, the heating and stirring temperature is 60-150℃; the heating and stirring time is 0.5-1h; and the heating and stirring speed is 300-700r / min.
[0049] Preferably, the reaction is followed by solid-liquid separation, and the solid obtained after separation is the crystallization directing agent.
[0050] Preferably, solid-liquid separation is performed by centrifugation at a rate of 100-1000 r / min for a time of 0.1-1 h.
[0051] A third aspect of the present invention provides a flame retardant.
[0052] Specifically, the flame retardant includes the crystalline aluminum phosphite described in the first aspect of this invention.
[0053] Compared with the prior art, the beneficial effects of the technical solution provided by the present invention are as follows:
[0054] (1) The present invention reacts non-crystalline amorphous phosphite or a mixture of phosphite and hydrogen phosphite with phosphoric acid to obtain a crystallization directing agent with a cross-linked state. The crystallization directing agent has high activity and can make the product generated by the reaction grow along the structure of the crystallization directing agent, thereby improving the crystal structure of the product, reducing crystal defects, reducing the content of the by-product aluminum hydrogen phosphite, and making the prepared crystalline aluminum phosphite with high purity, good thermal stability and good flame retardant properties, which can meet the processing requirements of polymer materials with high heat resistance.
[0055] (2) The present invention uses liquid phase reaction. A small amount of residual acid radicals are separated with the liquid and solid products during solid-liquid separation. Compared with solid phase reaction, the residual acid radicals can be greatly reduced. The polymer is not easily degraded during processing, which can improve mechanical properties.
[0056] (3) The process of this invention is simple, easy to implement, and economically beneficial. Attached Figure Description
[0057] Figure 1 The XRD pattern of the crystalline aluminum phosphite prepared in Example 1 of this invention;
[0058] Figure 2 The image shows the XRD pattern of aluminum phosphite prepared in Comparative Example 1 of this invention.
[0059] Figure 3 This is a TGA image of the crystalline aluminum phosphite prepared in Example 1 of the present invention;
[0060] Figure 4 This is a TGA image of the aluminum phosphite prepared in Comparative Example 1 of this invention. Detailed Implementation
[0061] To enable those skilled in the art to more clearly understand the technical solutions described in this invention, the following embodiments are provided for illustration. It should be noted that the following embodiments do not constitute a limitation on the scope of protection claimed by this invention.
[0062] Unless otherwise specified, the raw materials, reagents or devices used in the following examples are available from conventional commercial sources or can be obtained by existing known methods.
[0063] Example 1
[0064] A crystalline aluminum phosphite, wherein the raw materials for preparing the crystalline aluminum phosphite include a crystallization directing agent, phosphorous acid, and aluminum hydroxide, wherein the crystallization directing agent is an aluminum phosphite crystallization directing agent.
[0065] A method for preparing crystalline aluminum phosphite includes the following steps:
[0066] 7.5 kg of aluminum phosphite crystallization directing agent was added to a reactor, followed by 220 L of water and 136.53 kg of 98% phosphoric acid. The mixture was stirred at 300 r / min for 0.5 h. After mixing, 85 kg of aluminum hydroxide was added, and the mixture was heated to 95 °C and reacted at 95 °C for 3 h. Solid-liquid separation was performed to obtain a solid product. The solid product was placed in a dryer and dried at 150 °C for 8 h at a pressure of -0.09 MPa, yielding 159 kg of crystalline aluminum phosphite with a yield of 95%.
[0067] The preparation method of the aluminum phosphite crystallization directing agent includes the following steps:
[0068] 7.8 kg of amorphous aluminum phosphite was added to a reaction vessel, along with 8 kg of water and 0.55 kg of 98% phosphoric acid. The mixture was heated to 90 °C and stirred at 300 r / min for 2 h. Then, it was centrifuged at 500 r / min for 30 min to obtain 7.5 kg of solid aluminum phosphite crystallization directing agent.
[0069] Example 2
[0070] A crystalline aluminum phosphite, wherein the raw materials for preparing the crystalline aluminum phosphite include a crystallization directing agent, phosphorous acid, and aluminum hydroxide, wherein the crystallization directing agent is an aluminum phosphite crystallization directing agent.
[0071] A method for preparing crystalline aluminum phosphite includes the following steps:
[0072] 7.5 kg of aluminum phosphite crystallization directing agent was added to a reactor, followed by 220 L of water and 141.08 kg of 98% phosphoric acid. The mixture was stirred at 700 r / min for 0.5 h. After mixing, 85 kg of aluminum hydroxide was added, and the mixture was heated to 100 °C and reacted at 100 °C for 2 h. Solid-liquid separation was performed to obtain a solid product. The solid product was placed in a dryer and dried at 200 °C for 10 h at a pressure of -0.05 MPa, yielding 158.28 kg of crystalline aluminum phosphite, with a yield of 94.5%.
[0073] The preparation method of the aluminum phosphite crystallization directing agent is the same as in Example 1.
[0074] Example 3
[0075] A crystalline aluminum phosphite, wherein the raw materials for preparing the crystalline aluminum phosphite include a crystallization directing agent, phosphoric acid, and aluminum hydroxide, wherein the crystallization directing agent is a zinc phosphite crystallization directing agent.
[0076] A method for preparing crystalline aluminum phosphite includes the following steps:
[0077] 16 kg of zinc phosphite crystallization directing agent was added to a reaction vessel, followed by 220 L of water and 136.53 kg of 98% phosphoric acid. The mixture was stirred at 400 r / min for 1 h. After mixing, 85 kg of aluminum hydroxide was added, and the temperature was raised to 75 °C. The reaction was carried out at 75 °C for 10 h. Solid-liquid separation was performed to obtain a solid product. The solid product was placed in a dryer and dried at 250 °C for 8 h at a pressure of 0.05 MPa, yielding 170 kg of crystalline aluminum phosphite with a yield of 96%.
[0078] The preparation method of the zinc phosphite crystallization directing agent includes the following steps:
[0079] 17 kg of amorphous zinc phosphite was added to a reaction vessel, along with 34 kg of water and 1.7 kg of 98% phosphoric acid. The mixture was heated to 90 °C and stirred at 700 r / min for 2 h. Then, it was centrifuged at 800 r / min for 6 min to obtain 16 kg of solid zinc phosphite crystals.
[0080] Comparative Example 1
[0081] 220L of water was added to the reactor, along with 136.53Kg of 98% phosphorous acid. The mixture was stirred, and then 85Kg of aluminum hydroxide was added. The temperature was raised to 95℃, and the reaction was carried out at 95℃ for 3 hours. After solid-liquid separation, a solid product was obtained. The solid product was placed in a dryer and dried at 200℃ for 12 hours under a drying pressure of -0.09MPa, yielding 147.2Kg of aluminum phosphite, with a yield of 92%.
[0082] Performance testing
[0083] 1. XRD Test
[0084] The products prepared in Example 1 and Comparative Example 1 were subjected to XRD tests, and the XRD curves were obtained as shown below. Figure 1 and Figure 2 As shown, the horizontal axis 2θ represents the diffraction angle, and the vertical axis Intensity (au) represents the diffraction intensity. (From...) Figure 1 It can be seen that, Figure 1 The XRD pattern shows sharp, high-precision diffraction peaks characteristic of crystalline structures, confirming that the aluminum phosphite prepared in Example 1 is crystalline. Furthermore, the XRD pattern exhibits diffraction peaks at 2θ values of 12.0, 14.0, 15.0, 15.5, 16.0, 17.5, 20.0, 22.5, 23.5, 29.0, 30.0, 30.5, 31.0, 32.0, 33.0, 36.5, 38.5, and 45.0 ± 0.2°. Figure 2It can be seen that no crystallization directing agent was added in Comparative Example 1, which resulted in the aluminum phosphite prepared in Comparative Example 1 being in an amorphous state.
[0085] 2. Decomposition temperature determination
[0086] The decomposition temperatures of the aluminum phosphite prepared in Examples 1-3 and Comparative Example 1 were determined. The 2% decomposition temperature test was conducted in accordance with GB / T 27761-2011, and the heating rate under nitrogen atmosphere was 10℃ / min.
[0087] Thermogravimetric analysis curves of aluminum phosphite prepared in Example 1 and Comparative Example 1 are shown below. Figure 3 , 4 As shown, the left vertical axis TG / % represents the change in mass.
[0088] The 2% decomposition temperature test results of the aluminum phosphite prepared in Example 1 and Comparative Example 1 are shown in Table 1.
[0089] Table 1: 2% decomposition temperature of aluminum phosphite in Example 1 and Comparative Example 1
[0090] Examples / Comparative Examples 2% decomposition temperature / ℃ Example 1 441 Example 2 435 Example 3 440 Comparative Example 1 319
[0091] The 2% decomposition temperature of the crystalline aluminum phosphite in Examples 1-3 is relatively high, and the 2% decomposition temperature of the crystalline aluminum phosphite in Example 1 can reach as high as 441°C, indicating that the crystalline aluminum phosphite prepared by the present invention has good thermal stability.
[0092] 3. Flame retardant performance and mechanical property testing
[0093] The flame retardant and mechanical properties of the aluminum phosphite prepared in Examples 1-3 and Comparative Example 1 were tested. Specifically, by weight percentage, 6% aluminum phosphite, 10% aluminum diethylphosphinate, 30% glass fiber, and 54% nylon 66 prepared in Examples 1-3 and Comparative Example 1 were mixed evenly and processed by extrusion using a twin-screw extruder. The feeding section temperature was 240℃, the mixing and compression section temperature was 260℃, the melting section temperature was 265℃, the homogenization section temperature was 255℃, and the die head temperature was 255℃ to obtain plastic granules. The performance of the plastic granules was tested, and the results are shown in Table 2. The performance testing methods are as follows:
[0094] Flame retardancy rating: Tested in accordance with UL94 flame retardancy test methods and standards;
[0095] Tensile strength: Tested according to ASTM D638, the method for determining the tensile properties of plastics.
[0096] Table 2: Test results of flame retardant and mechanical properties of aluminum phosphite in Examples 1-3 and Comparative Example 1
[0097] Examples / Comparative Examples Flame retardant rating (UL94) 50mm tensile strength / MPa Example 1 V0 145 Example 2 V0 139 Example 3 V0 142 Comparative Example 1 V2 109
[0098] As shown in Table 2, when the crystalline aluminum phosphite prepared in Examples 1-3 of this invention is applied to plastics, the plastics exhibit good mechanical properties and flame retardancy.
[0099] The flame retardant properties and tensile strength of Comparative Example 1 were significantly reduced, indicating that the poor temperature resistance of aluminum phosphite in Comparative Example 1 led to degradation during processing, which in turn caused polymer degradation and reduced strength.
[0100] The main difference between Comparative Example 1 and Example 1 is that no crystallization directing agent was added in Comparative Example 1, resulting in the aluminum phosphite prepared in Comparative Example 1 being in an amorphous state (e.g., ...). Figure 2 As shown in the XRD pattern, when applied to plastics, the 2% decomposition temperature, flame retardancy rating, and mechanical properties of the plastic particles were significantly lower than those in Example 1. This indicates that the addition of a highly active, cross-linked crystallization-directing agent causes the reaction product to grow along the crystallization-directing agent structure, thereby improving the crystal structure of the aluminum phosphite product, reducing crystal defects, and thus increasing the 2% decomposition temperature of the product. This makes the plastic less susceptible to thermal decomposition during processing and improves the flame retardancy and mechanical properties of the plastic. Furthermore, the presence of byproducts and crystal defects leads to a decrease in the 2% decomposition temperature of the product. The crystalline aluminum phosphite of this invention exhibits a higher 2% decomposition temperature, indicating that the crystalline aluminum phosphite of this invention has high purity and fewer crystal defects.
[0101] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.
Claims
1. A method for preparing aluminum phosphite, characterized in that, The raw materials for preparing the aluminum phosphite consist of a crystallization directing agent, phosphorous acid, aluminum and / or aluminum compounds, and water; the raw materials for preparing the crystallization directing agent include phosphite and phosphorous acid. The preparation method is as follows: first, a crystallization directing agent is added to a reaction vessel, then water and phosphorous acid are added, stirred, and finally aluminum and / or aluminum compounds are added, reacted, separated from solids, and dried to obtain the aluminum phosphite; The aluminum compound is selected from at least one of aluminum carbonate, aluminum acetate, aluminum hydroxide, and aluminum oxide; The XRD pattern of the aluminum phosphite shows diffraction peaks at 2θ of 12.0, 14.0, 15.0, 15.5, 16.0, 17.5, 20.0, 22.5, 23.5, 29.0, 30.0, 30.5, 31.0, 32.0, 33.0, 36.5, 38.5, and 45.0 ± 0.2°.
2. The production method according to claim 1, characterized by, The XRD pattern also shows diffraction peaks at 2θ of 22, 25.0, 27.5, 48.0, 51.0, 52.0, 57.0, and 68.0 ± 0.2°.
3. The production method according to claim 1, characterized by, The aluminum phosphite has a particle size of 1-110 μm; and / or, the aluminum phosphite has a decomposition temperature ≥400℃.
4. The method of claim 1, wherein, The raw materials for preparing the crystallization directing agent include phosphite, hydrogen phosphite, and phosphorous acid.
5. The preparation method according to claim 1, characterized in that, In the raw materials for preparing aluminum phosphite, the crystallization directing agent accounts for 1-50% of the total mass of the crystallization directing agent, phosphorous acid, aluminum and / or aluminum compounds.
6. The method of claim 1, wherein, In the raw materials for preparing aluminum phosphite, the molar ratio of phosphorous acid, aluminum and / or aluminum compounds is (2.5-3.5):
2.
7. The preparation method according to claim 1, characterized in that, The preparation method of the crystallization directing agent includes the following steps: The raw material components are mixed and reacted to obtain the crystallization directing agent.
8. A flame retardant characterized by, Includes aluminum phosphite prepared by the preparation method according to any one of claims 1-7.