Prismatic aluminum hypophosphite compound, and preparation method and application thereof

Abstract

The present application belongs to the technical field of flame-retardant materials, and particularly relates to a prismatic aluminum hypophosphite compound, a preparation method and application thereof. The prismatic aluminum hypophosphite compound comprises aluminum hypophosphite, layered montmorillonite and nano-silicon dioxide, wherein the weight percentage of the layered montmorillonite is 0.043-0.087 wt% and the weight percentage of the nano-silicon dioxide is 0.0036-0.0181 wt% based on 100% of the weight of the aluminum hypophosphite; the D10 particle size of the prismatic aluminum hypophosphite compound is 1-3 microns, the D50 particle size is 5-8 microns, the D90 particle size is 10-15 microns, and the D97 particle size is less than 20 microns; and the prismatic aluminum hypophosphite compound has a single prismatic crystal structure or a regular structure in which multiple prismatic crystals are embedded with each other. The prismatic aluminum hypophosphite compound has a specific morphology and is particularly suitable for a polyurethane flame-retardant system.

Description

Technical Field

[0001] This invention relates to the field of flame retardant materials technology, and in particular to a prismatic aluminum hypophosphite composite, its preparation method, and its application in flame retardant polyurethane materials. Background Technology

[0002] Most commonly used aluminum hypophosphite (AHP) has an amorphous structure, with indistinct particle edges, relatively large particle size, and uneven particle size distribution. This can lead to uneven dispersion of flame retardant particles in the polymer during processing, and may even seriously affect various performance indicators of the polymer. This problem is particularly prominent in the application of aluminum hypophosphite in polyurethane (PU) resins. Specifically, this is related to the morphology and particle size of the AHP used. The more regular the morphology, the lower the probability of agglomeration, the easier it is to achieve uniform dispersion in the polymer, the less impact on the polymer itself, and the higher the overall flame retardant efficiency. Furthermore, when AHP itself is highly dispersed and does not agglomerate, the overall flame retardant effect of the compounded product will also be significantly improved.

[0003] However, although existing technologies have explored different morphologies of aluminum hypophosphite, none have been developed specifically for polyurethane, and its dispersion effect in polyurethane remains unknown. For example, Chinese patent application CN103613084A discloses a method for preparing spherical aluminum hypophosphite, which mainly uses melamine cyanurate as a seed crystal and organic compounds such as polyacrylamide, sodium dodecylbenzenesulfonate, and citric acid as dispersants. Chinese patent application CN119306193A discloses a rough-surfaced spherical aluminum hypophosphite, which is mainly obtained by dissolving sodium hypophosphite monohydrate in deionized water and ethylene glycol to prepare a solution. Summary of the Invention

[0004] The purpose of this invention is to provide an aluminum hypophosphite composite exhibiting a regular structure with a single prismatic crystal structure or a plurality of prismatic crystals interlocked, and a method and application for preparing the aluminum hypophosphite composite based on a supergravity reactor.

[0005] This invention is achieved through the following technical solution:

[0006] A prismatic aluminum hypophosphite composite comprises aluminum hypophosphite, layered montmorillonite, and nano-silica, wherein, based on the weight of aluminum hypophosphite (100%), the weight percentage of layered montmorillonite is 0.043~0.087 wt%, and the weight percentage of nano-silica is 0.0036~0.0181 wt%. The prismatic aluminum hypophosphite composite has a D10 particle size of 1~3 micrometers, a D50 particle size of 5~8 micrometers, a D90 particle size of 10~15 micrometers, and a D97 particle size <20 micrometers. Furthermore, the morphology of the prismatic aluminum hypophosphite composite exhibits a single prismatic crystal structure or a regular structure in which multiple prismatic crystals are interlocked.

[0007] A method for preparing a prismatic aluminum hypophosphite complex includes the following steps:

[0008] Step 1: Mix sodium hypophosphite aqueous solution with sodium lignosulfonate and layered montmorillonite and add the mixture as the base liquid to the centrifugal reactor, maintaining the temperature at 70~80℃;

[0009] Step 2: Add aluminum sulfate aqueous solution to the supergravity reactor over a period of 0.1 to 0.5 hours, then add an aqueous dispersion of polyvinyl alcohol and nano-silica, and react at 70 to 80°C to precipitate aluminum hypophosphite crystals. The reaction time is 3 to 4 hours to obtain a slurry containing aluminum hypophosphite.

[0010] Step 3: Separate the slurry from Step 2, wash it, and obtain a filter cake;

[0011] Step 4: Place the filter cake in a desiccator to dry, and obtain a prismatic aluminum hypophosphite composite.

[0012] The preparation method of the prismatic aluminum hypophosphite composite of the present invention uses layered montmorillonite as seed crystals to provide a large number of active sites with high specific surface area. When the aluminum sulfate aqueous solution is gradually added to the hypergravity reactor, the generated aluminum hypophosphite molecules preferentially adsorb, arrange, and grow at these sites, reducing the nucleation energy barrier and making the nucleation process more controllable and uniform. The interlayer nanospace can limit the growth dimension of the crystal, promote the formation of small-sized crystals, and prevent excessive crystal growth. The aluminum sulfate aqueous solution is added for 0.1 to 0.5 hours. Through slow addition, the crystal growth proceeds slowly and orderly, enabling it to grow into a single prismatic crystal structure or a regular structure of multiple prismatic crystals interlocking as described in the present invention. Polyvinyl alcohol and nano-silica, while acting as a dispersant, are adsorbed on the crystal surface or interspersed between crystals during crystal growth, preventing crystal growth through physical spatial barriers. Through close contact and fusion, sodium lignosulfonate can adsorb onto the surface of crystals and seed crystals, increasing the surface negative charge and stabilizing particles through electrostatic repulsion. Simultaneously, it improves the wettability and dispersion uniformity of all solid components (aluminum hypophosphite, seed crystals, and nano-silica) in the reaction system. Therefore, the combination of polyvinyl alcohol, nano-silica, and sodium lignosulfonate achieves a dual stabilization mechanism of "steric hindrance + electrostatic repulsion," effectively preventing crystal aggregation. Under the high shear environment of a hypergravity field, it can more effectively maintain the independent existence of crystal nuclei and microcrystals, ultimately obtaining a regular structure with a single prismatic crystal structure or multiple prismatic crystals interlocking. After the washing step, sodium lignosulfonate and polyvinyl alcohol are removed, and the prismatic aluminum hypophosphite composite includes aluminum hypophosphite, layered montmorillonite, and nano-silica. These three components can also play a synergistic role in the field of flame retardants, resulting in good flame retardant performance.

[0013] The material-liquid separation step in step 3 above can be performed using a filter press, centrifuge, vacuum filter, etc. The dryer in step 4 can be a rake dryer, and the drying temperature can be 60~120℃. After drying, due to the excellent dispersibility of the prismatic aluminum hypophosphite of this invention, no grinding is required to obtain a prismatic aluminum hypophosphite composite product with a D10 particle size of 1~3 micrometers, a D50 particle size of 5~8 micrometers, a D90 particle size of 10~15 micrometers, and a D97 particle size <20 micrometers.

[0014] The particle size distribution of the prismatic aluminum hypophosphite composite was tested using a Bettersize 2600 laser particle size analyzer. The test system was turned on for ultrasonic and rotational testing, with the rotation speed set to 1200 r and the ultrasonic frequency set to 50 w for baseline adjustment. Then, diluted sample (1.0 g of sample powder was diluted with 8 g of pure water and ultrasonicated for 2 min) was added for particle size testing.

[0015] In step 1, the sodium hypophosphite aqueous solution is prepared from sodium hypophosphite monohydrate, with a weight ratio of sodium hypophosphite monohydrate to deionized water of 1:(2~2.25). In step 2, the aluminum sulfate aqueous solution is prepared from aluminum sulfate octadecade, with a weight ratio of aluminum sulfate octadecade to deionized water of 1:(1.5~1.75), and the weight ratio of sodium hypophosphite monohydrate to aluminum sulfate octadecade is 1:(1.03~1.08). These proportions ensure complete reaction between sodium hypophosphite monohydrate and aluminum sulfate octadecade. The optimal concentrations of the sodium hypophosphite aqueous solution and the aluminum sulfate octadecade aqueous solution during the reaction are chosen to control the reaction rate during the slow addition of the aluminum sulfate aqueous solution, thus further controlling the particle size distribution and morphology of the final aluminum hypophosphite.

[0016] The degree of sulfonation of sodium lignosulfonate is 0.4~1.0 mmol / g, more preferably 0.5~0.7 mmol / g, and the amount of sodium lignosulfonate added is 0.01~0.05 wt% of the amount of sodium hypophosphite monohydrate added. Since sodium lignosulfonate acts as a surfactant and disperses, excessively high or low sulfonation will result in poor dispersion, further affecting its anti-agglomeration effect on aluminum hypophosphite, thus affecting the morphology of the aluminum hypophosphite complex.

[0017] The median particle size (D50) of the layered montmorillonite is 1-5 micrometers, and the addition amount is 0.03-0.06 wt% of the amount of sodium hypophosphite monohydrate added in the reactor. If the content of layered montmorillonite is too low, there will be insufficient seed crystals and growth sites for aluminum hypophosphite, which is not conducive to the formation of the special morphology of the aluminum hypophosphite composite of this invention. If the content is too high, it is also not conducive to its effect as a seed crystal and is not conducive to crystal growth.

[0018] In the aqueous dispersion of polyvinyl alcohol and nano silica, the median particle size of nano silica is 200~500 nm, and the amount added is 0.0025~0.0125 wt% of the amount of sodium hypophosphite monohydrate added; the molecular weight Mw of polyvinyl alcohol is 40000~80000, and the amount added is 0.02~0.06 wt% of the amount of sodium hypophosphite monohydrate added; the weight ratio of nano silica to deionized water is 1:(10~100).

[0019] In steps 1 and 2, the temperature difference between the sodium hypophosphite aqueous solution and the aluminum sulfate aqueous solution should not exceed ±2℃. By controlling the temperature difference between the sodium hypophosphite aqueous solution and the aluminum sulfate aqueous solution, the temperature of the reaction system can be kept stable when aluminum sulfate aqueous solution is added to the original sodium hypophosphite aqueous solution. This ensures that crystal growth is carried out in a stable temperature environment. If the system temperature fluctuates too much, it can easily affect the crystal growth process, thereby affecting the crystal growth effect, making it difficult to control the crystal size and morphology, and even causing agglomeration.

[0020] The stirring speed of the centrifugal reactor is 2000~4000 r / min. The dryer is a rake dryer with a drying temperature of 60~120℃.

[0021] Step 3 specifically involves filtering the slurry containing aluminum hypophosphite, rinsing the filter cake with deionized water at a temperature of 40-70°C, and ensuring the rinsing is completed when the conductivity of the filtrate is <100 mS / cm.

[0022] The prismatic aluminum hypophosphite composite of the present invention is used to prepare flame-retardant polyurethane materials; the end application is automotive interior leather.

[0023] The present invention has the following beneficial effects:

[0024] First, under the high-gravity environment generated by stirring at 2000-4000 rpm, the liquid is cut into extremely thin films or tiny droplets, and the reactants are instantly and uniformly mixed at the micron or even nanoscale. This avoids the localized excessive concentration caused by uneven mixing in traditional stirred tanks, thus effectively suppressing explosive nucleation and crystal aggregation. Furthermore, the extremely fast mixing speed allows the supersaturation of the entire reaction system to reach a uniform and controllable high level in a very short time, which is conducive to the formation of a large number of uniform crystal nuclei.

[0025] Secondly, this invention provides a large number of high specific surface area active sites through layered montmorillonite. Aluminum hypophosphite molecules preferentially adsorb, align, and grow at these sites, lowering the nucleation energy barrier and making the nucleation process more controllable and uniform. Its interlayer nanospaces can restrict the growth dimension of crystals, promote the formation of small-sized crystals, and prevent excessive crystal growth.

[0026] Third, polyvinyl alcohol and nano-silica particles dispersed in the solution adsorb onto the crystal surface or interpenetrate between crystals during crystal growth, preventing close contact and fusion between crystals through physical spatial barrier. Sodium lignosulfonate adsorbs onto the crystal and seed crystal surfaces, increasing the surface negative charge and stabilizing the particles through electrostatic repulsion. Simultaneously, it improves the wettability and dispersion uniformity of all solid components (aluminum hypophosphite, seed crystals, and nano-silica) in the reaction system. The combination of these two elements achieves a dual stabilization mechanism of "steric hindrance + electrostatic repulsion," more effectively maintaining the independent existence of crystal nuclei and microcrystals under the high shear environment of a hypergravity field, ultimately resulting in a regular structure exhibiting a single prismatic crystal structure or multiple interlocking prismatic crystals.

[0027] Fourth, since the prismatic aluminum hypophosphite of this invention has excellent dispersibility, it can be obtained after drying without grinding, with D10 particle size of 1~3 micrometers, D50 particle size of 5~8 micrometers, D90 particle size of 10~15 micrometers, and D97 particle size of <20 micrometers.

[0028] Fifth, furthermore, the prismatic aluminum hypophosphite composite of the present invention exhibits excellent dispersibility when applied to flame-retardant polyurethane materials, effectively improving the flame retardancy of polyurethane, and also provides a smooth surface and good toughness for polyurethane leather. Attached Figure Description

[0029] Figure 1 SEM image of the prismatic aluminum hypophosphite composite powder in Example 1. Morphologically, it exhibits a regular structure in which single or multiple prismatic crystals are interlocked, with a smooth surface and no cracks or breaks (5 μm).

[0030] Figure 2 SEM image of the prismatic aluminum hypophosphite composite powder in Example 1, showing a regular structure (20 μm) of single or multiple prismatic crystals interlocked.

[0031] Figure 3 SEM image (20 μm) of amorphous agglomerated aluminum hypophosphite powder obtained in Comparative Example 1. Detailed Implementation

[0032] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention. These all fall within the scope of protection of the present invention.

[0033] The raw materials used in this invention are sourced from the following sources:

[0034] Aluminum sulfate octahydrate: purity > 98%, commercially available;

[0035] Sodium hypophosphite monohydrate: purity > 98%, commercially available;

[0036] Polyvinyl alcohol A: Molecular weight Mw=47000, Aladdin;

[0037] Polyvinyl alcohol B: Molecular weight Mw=67000, Aladdin;

[0038] Sodium lignosulfonate A: sulfonation degree 0.43 mmol / g, self-made;

[0039] Sodium lignosulfonate B: sulfonation degree 0.51 mmol / g, self-made;

[0040] Sodium lignosulfonate C: sulfonation degree 0.70 mmol / g, self-made;

[0041] Sodium lignosulfonate D: sulfonation degree 0.96 mmol / g, self-made;

[0042] Sodium lignosulfonate E: sulfonation degree 0.33 mmol / g, self-made;

[0043] Sodium lignosulfonate F: sulfonation degree 1.20 mmol / g, self-made;

[0044] Alkali lignin: purchased from Shanghai Nazhifu Chemical Technology Co., Ltd.;

[0045] The above-mentioned sodium lignin sulfonate is prepared by the sulfate method commonly used in this field. The preparation method is as follows: alkali lignin and a measured amount of sodium sulfite are heated to above 120°C under pH=10~12 conditions (the pH is adjusted by sodium hydroxide) to induce sulfonation of the hydroxyl groups. After concentration and drying, sodium lignin sulfonate with different degrees of sulfonation is obtained.

[0046] Test method for degree of sulfonation:

[0047] Weigh 5g of sodium lignosulfonate, dissolve it in distilled water, filter, and dilute the filtrate to 250mL. Add 15mL of the filtrate to an anion exchange resin tube to begin the exchange process. Elute with deionized water at a flow rate of 15-20 drops / second, allowing the lignosulfonate solution to flow slowly through the anion exchange resin first, then through the cation exchange resin. When the solution reaches approximately 10cm from the bottom of the cation exchange resin burette, begin collecting the eluent until it becomes colorless and neutral. Titrate the eluent with 0.01 mmol / mL NaOH standard solution, and measure the change in conductivity of the solution during the titration using a conductivity meter. Plot the conductivity against the volume of NaOH consumed (V), with the midpoint of the curve representing the equivalence point. Calculate the degree of sulfonation (mmol / g) using the following formula.

[0048] The calculation formula is: Degree of sulfonation = (N) NaOH ×VNaOH ×M)÷(W s -W r );

[0049] Where: N NaOH The molar concentration of the standard NaOH solution is given in mmol / mL.

[0050] V NaOH The volume of NaOH consumed during the titration process, in ml;

[0051] M is the magnification factor, which is 250 / 15 in this test;

[0052] W s The mass of sodium lignosulfonate taken is in grams;

[0053] W r For the quality of the filter residue;

[0054] The above experiment was repeated three times, and the average value was taken.

[0055] Nano silica: D50 particle size 0.2-0.5μm, commercially available;

[0056] Layered montmorillonite: D50 particle size is 2-3 μm, commercially available;

[0057] Melamine cyanurate: D50 particle size is 0.2-0.5μm, commercially available;

[0058] Sodium dodecyl sulfate: Commercially available;

[0059] Deionized water: conductivity <10mS / cm.

[0060] After washing with deionized water, the conductivity of the above nano-silica, layered montmorillonite, and melamine cyanurate is ≤200mS / cm.

[0061] The supergravity reactors used in the examples and comparative examples have a capacity of 500L and an adjustable rotation speed range of 2000~4000 rpm.

[0062] Examples 1-6

[0063] The preparation method of aluminum hypophosphite is as follows:

[0064] Preliminary steps: Prepare an aqueous solution of sodium hypophosphite monohydrate (the weight ratio of sodium hypophosphite monohydrate to deionized water is 1:2.1), prepare an aqueous solution of aluminum sulfate octadecade (the weight ratio of aluminum sulfate octadecade to deionized water is 1:1.6), wherein the weight ratio of sodium hypophosphite monohydrate to aluminum sulfate octadecade is 1:1.05, and prepare an aqueous dispersion of polyvinyl alcohol and nano silica (the weight ratio of nano silica to deionized water is 1:30).

[0065] Step 1: The stirring speed is 3000 r / min. The sodium hypophosphite monohydrate aqueous solution, sodium lignosulfonate (see Table 1 below for the selection of sodium lignosulfonate and the specific amount added) and layered montmorillonite (see Table 1 below for the specific amount added) are mixed evenly and added to the supergravity reactor as the bottom liquid, and the temperature is maintained at 75℃.

[0066] Step 2: Aqueous aluminum sulfate octadeca solution at 75±2℃ is continuously and slowly added to the hypergravity reactor over a period of 20 minutes. Then, an aqueous dispersion of polyvinyl alcohol (polyvinyl alcohol A is used in Examples 1-3, and polyvinyl alcohol B is used in Examples 4-6) and nano silica is added (the specific amounts of polyvinyl alcohol and nano silica added in different examples are shown in Table 1 below, and the specific amounts of polyvinyl alcohol and nano silica added in different comparative proportions are shown in Table 2 below). The mixture is then reacted at 75±2℃ to precipitate aluminum hypophosphite crystals over a period of 3 hours to obtain a slurry containing regular small-particle-size aluminum hypophosphite.

[0067] Step 3: Separate the slurry from Step 2 using a filter press, and wash it with deionized water at 50°C until the conductivity of the filtrate is <100mS / cm to obtain the filter cake.

[0068] Step 4: Place the filter cake in a rake dryer and dry it at 90°C to obtain aluminum hypophosphite composite.

[0069] Table 1. Raw materials and product parameters used in the preparation process of aluminum phosphate in this example.

[0070]

[0071] In Table 1 above, the amounts of sodium lignosulfonate, layered montmorillonite, nano silica, and polyvinyl alcohol added are weight percentages relative to the amount of sodium hypophosphite monohydrate added (based on the weight of sodium hypophosphite monohydrate being 100%).

[0072] The weight percentages of layered montmorillonite and nano-silica in the aluminum hypophosphite composite were calculated based on the amount added before the reaction. Since sodium lignosulfonate and polyvinyl alcohol were removed after the washing step, the prismatic aluminum hypophosphite composite includes aluminum hypophosphite, layered montmorillonite, and nano-silica. The content of layered montmorillonite in the composite is calculated using the following formula, with aluminum hypophosphite weight as 100%.

[0073] Layered montmorillonite wt% in the composite = Layered montmorillonite addition amount ÷ Aluminum hypophosphite weight × 100wt%

[0074] The content of nano-silica in the composite is calculated using the following formula:

[0075] The wt% of nano-silica in the composite is calculated as: (Amount of nano-silica added ÷ Weight of aluminum hypophosphite) × 100wt%.

[0076] The difference between Comparative Example 1 and Example 1 is that the experiment was conducted in a conventional reactor, and the resulting product had an amorphous aggregate morphology (as shown in the instruction manual). Figure 3 ).

[0077] The difference between Comparative Example 2 / 3 and Example 1 is that sodium lignosulfonate was selected from E and F respectively. The process was the same, and the resulting product morphology was also amorphous agglomerate.

[0078] The difference between Comparative Examples 4 / 5 / 6 and Example 1 is that they do not contain sodium lignosulfonate / nano silica / polyvinyl alcohol, but the processes are the same and the resulting products are amorphous aggregates.

[0079] The difference between Comparative Example 7 and Example 1 is that melamine cyanurate is used instead of montmorillonite as crystal. The process is the same, and the resulting product has an amorphous aggregate morphology.

[0080] The difference between Comparative Example 8 and Example 1 is that sodium dodecyl sulfate is used instead of sodium lignosulfonate. The process is the same, and the product morphology is also amorphous agglomerate.

[0081] Table 2 Comparative Aluminum Hypophosphite Product Parameters

[0082]

[0083] As can be seen from the above embodiments and comparative examples, the aluminum hypophosphite product obtained by the method of the present invention has a finer particle size and exhibits a regular structure in terms of morphology, consisting of a single prismatic crystal or multiple prismatic crystals interlocking. In contrast, the comparative examples only yielded amorphous products, and the particle size was larger if not ground.

[0084] The aluminum hypophosphite products obtained in the above examples and comparative examples were combined with melamine cyanurate as a compound flame retardant to prepare flame-retardant polyurethane, wherein the formulation is as follows:

[0085] Material A: Polypropylene glycol, 50 parts;

[0086] Material B: Toluene-2,4-diisocyanate, 50 parts;

[0087] Catalyst: 0.05 parts of dibutyltin dilaurate;

[0088] Aluminum hypophosphite: 25 parts;

[0089] Melamine cyanurate: 25 parts.

[0090] The preparation process of flame-retardant polyurethane is as follows: Component A and the compounded flame retardant (composed of aluminum hypophosphite and melamine cyanurate) are added to a high-speed mixer and mixed at a speed of 500-1000 r / min for 10-15 min. Then, a catalyst is added and mixed evenly. Component B of the PU is then added, and the mixture is continued to be mixed at a speed of 500-1000 r / min for 10-15 min. The mixture is then discharged to obtain a composite material. The composite material is placed in an oven at a temperature of 120-160℃ and baked for 10-15 min to obtain flame-retardant polyurethane.

[0091] Test items:

[0092] (1) Flame retardancy: Tested in accordance with GB 8410-2006 "Combustion characteristics of automotive interior materials".

[0093] (2) Surface smoothness of flame-retardant polyurethane parts: Observe whether there are white spots on the surface, count the number of white spots within a range of 100×100mm. The more white spots there are, the worse the dispersion performance of the flame retardant.

[0094] Table 3 Test results of flame-retardant polyurethane in the examples

[0095]

[0096] Table 4 Test results of comparative flame-retardant polyurethane

[0097]

[0098] As can be seen from the test results of the above embodiments and comparative examples, the prismatic aluminum hypophosphite composite of the present invention has excellent dispersibility in polyurethane, resulting in a short semi-drying time, no white spots visible to the naked eye, and good flame retardant performance. The aluminum hypophosphite obtained in the comparative examples has poor dispersibility in polyurethane, a long semi-drying time, a large number of white spots, and its flame retardant performance can only reach level B.

[0099] Specifically, the test results of Examples 4 and 5 show that the prismatic aluminum hypophosphite composite prepared with sodium lignosulfonate of the preferred degree of sulfonation has better dispersibility, and the flame-retardant polyurethane prepared from it has better test results.

Claims

1. A prismatic aluminum hypophosphite composite, characterized in that, The composite material comprises aluminum hypophosphite, layered montmorillonite, and nano-silica, wherein, based on the weight of aluminum hypophosphite (100%), the weight percentage of layered montmorillonite is 0.043–0.087 wt%, and the weight percentage of nano-silica is 0.0036–0.0181 wt%. The prismatic aluminum hypophosphite composite has a D10 particle size of 1–3 μm, a D50 particle size of 5–8 μm, a D90 particle size of 10–15 μm, and a D97 particle size <20 μm. Furthermore, the prismatic aluminum hypophosphite composite exhibits a single prismatic crystal structure or a regular structure of multiple prismatic crystals interlocking. The prismatic aluminum hypophosphite composite is prepared through the following steps: Step 1: Mix sodium hypophosphite aqueous solution with sodium lignosulfonate and layered montmorillonite and add it as the bottom liquid to the supergravity reactor, maintaining the temperature at 70~80℃. The sodium hypophosphite aqueous solution is prepared with sodium hypophosphite monohydrate. Step 2: Add the aluminum sulfate aqueous solution into the supergravity reactor over a period of 0.1 to 0.5 hours, then add the aqueous dispersion of polyvinyl alcohol and nano-silica, and react at 70 to 80°C to precipitate aluminum hypophosphite crystals. The reaction time is 3 to 4 hours to obtain a slurry containing aluminum hypophosphite. The aluminum sulfate aqueous solution is prepared with aluminum sulfate octadecahydrate. Step 3: Separate the slurry from Step 2, wash it, and obtain a filter cake; Step 4: Place the filter cake in a desiccator to dry, and obtain a prismatic aluminum hypophosphite complex; The weight ratio of sodium hypophosphite monohydrate to aluminum sulfate octadecade is 1:(1.03~1.08); the degree of sulfonation of sodium lignosulfonate is 0.4~1.0 mmol / g, and the amount added is 0.01~0.05 wt% of the amount of sodium hypophosphite monohydrate; the median particle size of layered montmorillonite is 1~5 micrometers, and the amount added is 0.03~0.06 wt% of the amount of sodium hypophosphite monohydrate; the stirring speed of the centrifugal reactor is 2000~4000 r / min; the amount of nano-silica added is 0.0025~0.0125 wt% of the amount of sodium hypophosphite monohydrate; the molecular weight (Mw) of polyvinyl alcohol is 40000~80000, and the amount added is 0.02~0.06 wt% of the amount of sodium hypophosphite monohydrate.

2. The prismatic aluminum hypophosphite composite according to claim 1, characterized in that, In step 1, the weight ratio of sodium hypophosphite monohydrate to deionized water is 1:(2~2.25), and in step 2, the weight ratio of aluminum sulfate octadechydrate to deionized water is 1:(1.5~1.75).

3. The prismatic aluminum hypophosphite composite according to claim 1, characterized in that, The degree of sulfonation of the sodium lignosulfonate is 0.5~0.7 mmol / g.

4. The prismatic aluminum hypophosphite composite according to claim 1, characterized in that, In the aqueous dispersion of polyvinyl alcohol and nano silica, the median particle size of nano silica is 200-500 nanometers; the weight ratio of nano silica to deionized water is 1:(10-100).

5. The prismatic aluminum hypophosphite composite according to claim 2, characterized in that, The temperature difference between the sodium hypophosphite aqueous solution in step 1 and the aluminum sulfate aqueous solution in step 2 shall not exceed ±2℃.

6. The prismatic aluminum hypophosphite composite according to claim 1, characterized in that, The dryer is a rake dryer with a drying temperature of 60~120℃.

7. The prismatic aluminum hypophosphite composite according to claim 1, characterized in that, Step 3 specifically involves filtering the slurry containing aluminum hypophosphite, rinsing the filter cake with deionized water at a temperature of 40-70°C, and ensuring the rinsing is completed when the conductivity of the filtrate is <100 mS / cm.

8. The application of the prismatic aluminum hypophosphite complex according to claim 1, characterized in that, Used to prepare flame-retardant polyurethane materials; the end application is automotive interior leather.

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