A method for preparing nanoscale uniform spherical aluminum hypophosphite based on a hydrothermal method

Abstract

The present application relates to a kind of methods for preparing nanoscale uniform spherical aluminum hypophosphite based on hydrothermal method, the present application uses aluminum chloride six-water and sodium hypophosphite monohydrate as raw material, by adding ethylene glycol, the product morphology is adjusted under lower temperature hydrothermal route, the spherical structure with regular morphology and relatively smooth surface is obtained, preparation operation is simple, synthesis step is simple, raw material cost is low, process can be completed under lower temperature, is suitable for large-scale industrialization.By introducing ethylene glycol, the supersaturation of the system is controlled to affect the generation of crystal nucleus, the solvent viscosity is increased, which is beneficial to the growth of crystal nucleus diffusion control, further uniformizes the size of product, and forms uniform spherical particles.The preparation process of the present application is simple, the aluminum hypophosphite product synthesized has excellent morphology and good dispersibility, and is helpful for subsequent modification of aluminum hypophosphite.

Description

Technical Field

[0001] This invention relates to a method for preparing nanoscale uniform spherical aluminum hypophosphite based on a hydrothermal method, belonging to the field of polymer flame retardant technology. Background Technology

[0002] With technological advancements and heightened fire safety awareness, the consumption of flame retardants is increasing, making flame-retardant materials ever more crucial. Traditional flame retardants are primarily halogenated, offering advantages such as low dosage and high efficiency. However, halogenated flame retardants have significant drawbacks, releasing harmful substances like dioxins and corrosive hydrogen halides during combustion, severely impacting human health and the environment. As environmental awareness grows, regulations concerning flame retardants are being enacted, and halogenated flame retardants are gradually being phased out. New halogen-free flame retardants are rapidly developing and gradually becoming the market mainstream.

[0003] Aluminum hypophosphite is a novel inorganic phosphorus-based flame retardant with numerous advantages, including poor water solubility, high phosphorus content, excellent thermal stability, strong flame retardant effect, and low cost. Furthermore, it is halogen-free, non-toxic, and environmentally friendly. It exhibits good mechanical properties in plastics and is suitable for flame-retardant modification of PBT, PET, TPU, and other plastics.

[0004] Currently, the synthesis of aluminum hypophosphite is relatively mature, mainly using soluble aluminum salts such as aluminum sulfate, aluminum chloride, and aluminum nitrate as aluminum sources to undergo a metathesis reaction with sodium hypophosphite to synthesize aluminum hypophosphite flame retardants. Although the synthesis route is relatively simple, the aluminum hypophosphite crystals synthesized by this method have large particle sizes, a wide particle size distribution, and irregular morphology, which is not conducive to subsequent modification of aluminum hypophosphite.

[0005] To address the aforementioned problems, Chinese patent document CN114314538A discloses a method for synthesizing ultrafine aluminum hypophosphite, using aluminum chloride and sodium hypophosphite as raw materials, and adding various dispersants to control particle size. However, it still suffers from defects such as large particle size and irregular morphology. Chinese patent document CN103613084A discloses a method for preparing spherical aluminum hypophosphite, using aluminum sulfate and sodium hypophosphite to react, while simultaneously adding a dispersant and melamine cyanurate as seed crystals. Although spherical aluminum hypophosphite can be synthesized, the uniformity is poor and the product purity is reduced. Similarly, Chinese patent document CN111116987B discloses a method for synthesizing fine-particle aluminum hypophosphite composite flame retardants, using diethylaluminum hypophosphite as seed crystals, adding surfactants to control crystal morphology, and performing a metathesis reaction to obtain aluminum hypophosphite. However, introducing surfactants into the system can cause problems in the post-processing; introducing additional substances as seed crystals does not improve the product's agglomeration phenomenon and may even reduce product purity, potentially affecting the subsequent microcapsule modification of aluminum hypophosphite.

[0006] In summary, most existing methods for preparing aluminum hypophosphite flame retardants involve metathesis reaction precipitation, which results in low product purity, large particle size, and irregular morphology, making it unfavorable for subsequent modification of aluminum hypophosphite.

[0007] Therefore, developing a novel method for preparing aluminum hypophosphite with high product purity, small particle size, spherical morphology, and without the need for dispersants or surfactants as seed crystals has significant application value. Summary of the Invention

[0008] To address the shortcomings of existing methods for preparing aluminum hypophosphite, this invention provides a method for preparing nanoscale uniform spherical aluminum hypophosphite based on a hydrothermal approach.

[0009] This invention uses aluminum chloride hexahydrate and sodium hypophosphite monohydrate as raw materials, and water and ethylene glycol as mixed solvents. A hydrothermal method is employed to synthesize aluminum hypophosphite at a relatively low temperature. Ethylene glycol induces the formation of spherical aluminum hypophosphite, resulting in well-dispersed, nano-sized, uniformly spherical aluminum hypophosphite. The preparation process of this invention is simple, and the synthesized aluminum hypophosphite product exhibits excellent morphology and good dispersibility. The spherical morphology is beneficial for subsequent modification of aluminum hypophosphite.

[0010] The technical solution of the present invention is as follows:

[0011] A method for preparing nanoscale uniform spherical aluminum hypophosphite based on a hydrothermal method includes the following steps:

[0012] (1) Under stirring conditions, aluminum chloride hexahydrate aqueous solution was slowly added dropwise to sodium hypophosphite monohydrate aqueous solution to obtain a mixed solution;

[0013] (2) Ethylene glycol was added to the mixed solution under stirring conditions to obtain an aluminum hypophosphite precursor solution;

[0014] (3) The aluminum hypophosphite precursor solution was transferred to a hydrothermal reactor and subjected to hydrothermal reaction. After natural cooling to room temperature, the product was washed with deionized water and anhydrous ethanol, centrifuged, vacuum dried, and ground to obtain nano-sized uniform spherical aluminum hypophosphite.

[0015] According to the present invention, preferably, in step (1), the concentration of the aqueous solution of aluminum chloride hexahydrate is 7-10 mg / mL;

[0016] Preferably, the concentration of the aqueous solution of aluminum chloride hexahydrate is 8.5 mg / mL.

[0017] According to the present invention, preferably, in step (1), the concentration of the sodium hypophosphite monohydrate aqueous solution is 5-25 mg / mL.

[0018] According to the present invention, preferably, in step (1), the molar ratio of sodium hypophosphite monohydrate to aluminum chloride hexahydrate is 2-6:1;

[0019] Preferably, the molar ratio of sodium hypophosphite monohydrate to aluminum chloride hexahydrate is 2-4:1;

[0020] The most preferred molar ratio is 3:1 for sodium hypophosphite monohydrate and aluminum chloride hexahydrate.

[0021] According to the present invention, preferably, in step (2), the mass-to-volume ratio of aluminum chloride hexahydrate to ethylene glycol is (40-150):(20-30), in mg / mL.

[0022] Preferably, the mass-to-volume ratio of aluminum chloride hexahydrate to ethylene glycol is (40-150):(20-24), in mg / mL.

[0023] According to the present invention, preferably, in step (3), the hydrothermal reaction temperature is 120-160°C;

[0024] Preferably, the hydrothermal reaction temperature is 140℃.

[0025] According to the present invention, preferably, in step (3), the hydrothermal reaction time is 5-9 hours;

[0026] Preferably, the hydrothermal reaction time is 7 hours.

[0027] This invention uses aluminum chloride hexahydrate and sodium hypophosphite monohydrate as raw materials, and adjusts the morphology of the product by adding ethylene glycol and using a hydrothermal approach at a lower temperature to synthesize nanoscale uniform spherical aluminum hypophosphite, resulting in a spherical structure with regular morphology and a relatively smooth surface.

[0028] The technical features and beneficial effects of this invention are as follows:

[0029] 1. This invention uses aluminum chloride hexahydrate and sodium hypophosphite monohydrate as raw materials. By adding ethylene glycol and adjusting the product morphology via a hydrothermal approach at a lower temperature, a well-formed, relatively smooth spherical structure is obtained. The preparation operation is simple, the synthesis steps are straightforward, the raw material cost is low, and the process can be completed at a relatively low temperature, making it suitable for large-scale industrialization. By introducing ethylene glycol, the supersaturation of the system is controlled to influence crystal nucleus formation. Increasing the solvent viscosity facilitates crystal nucleus diffusion and controls growth, further homogenizing the product size and forming uniform spherical particles.

[0030] 2. The method of the present invention produces aluminum hypophosphite with regular morphology, high spherical yield, and small particle size. It has excellent performance and is helpful for subsequent aluminum hypophosphite modification processes. The particle size distribution range is narrow, with the particle size mainly concentrated in 600-700 nm.

[0031] 3. The product obtained by this invention has high purity, small particle size, and spherical morphology. No additional substances such as dispersants and surfactants are required as seed crystals. The resulting spherical structure with a regular morphology and relatively smooth surface is beneficial for subsequent modification of aluminum hypophosphite, while irregular morphologies are not easy to modify in subsequent processes. Attached Figure Description

[0032] Figure 1 This is a scanning electron microscope image of aluminum hypophosphite prepared in Example 1.

[0033] Figure 2 This is a transmission electron microscope (TEM) image of aluminum hypophosphite prepared in Example 1.

[0034] Figure 3 The image shows the XRD pattern of aluminum hypophosphite prepared in Example 1.

[0035] Figure 4 This is a particle size distribution diagram of aluminum hypophosphite prepared in Example 1.

[0036] Figure 5 This is a scanning electron microscope image of the spherical aluminum hypophosphite microcapsules prepared in Example 5.

[0037] Figure 6 This is a transmission electron microscope (TEM) image of the spherical aluminum hypophosphite microcapsules prepared in Example 5.

[0038] Figure 7 The image shows the infrared spectrum of the spherical aluminum hypophosphite microcapsules prepared in Example 5.

[0039] Figure 8 This is a scanning electron microscope image of aluminum hypophosphite from Comparative Example 1.

[0040] Figure 9 This is a scanning electron microscope image of aluminum hypophosphite from Comparative Example 2.

[0041] Figure 10 This is a scanning electron microscope image of aluminum hypophosphite in Comparative Example 3.

[0042] Figure 11 This is a scanning electron microscope image of the irregular aluminum hypophosphite microcapsules in Comparative Example 4. Detailed Implementation

[0043] The present invention will be further described below with reference to specific embodiments and accompanying drawings, but is not limited thereto.

[0044] Unless otherwise specified, the experimental methods described in the examples are conventional methods; the reagents and materials used are commercially available unless otherwise specified.

[0045] Example 1

[0046] Preparation method of nanoscale uniform spherical aluminum hypophosphite:

[0047] (1) Place 51 mg of aluminum chloride hexahydrate in a beaker, add 6 mL of deionized water, and stir until the aluminum chloride hexahydrate is completely dissolved to obtain an aluminum chloride aqueous solution. Place 66.4 mg of sodium hypophosphite monohydrate in a beaker, add 6.5 mL of deionized water, and stir until the sodium hypophosphite monohydrate is completely dissolved to obtain a sodium hypophosphite aqueous solution.

[0048] (2) Aluminum chloride aqueous solution was added dropwise to sodium hypophosphite aqueous solution while stirring. 22 mL of ethylene glycol was added and stirred for 30 min to mix evenly, thus obtaining aluminum hypophosphite precursor solution. The aluminum hypophosphite precursor solution was transferred to a hydrothermal reactor with a filling degree of 70%. The reactor was reacted in an oven at 140 °C for 7 hours, and then naturally cooled to room temperature. The solid was obtained by washing with deionized water and anhydrous ethanol and centrifuging. The solid was dried in a vacuum drying oven at 60 °C for 12 hours to obtain nano-sized uniform spherical aluminum hypophosphite.

[0049] The material obtained in Example 1 was characterized by scanning electron microscopy. Figure 1 Transmission electron microscopy revealed Figure 2 ,Depend on Figure 1 Scanning electron microscope image of aluminum hypophosphite and Figure 2 Transmission electron microscopy (TEM) images of aluminum hypophosphite show that its microstructure exhibits a well-dispersed, regular spherical structure.

[0050] The XRD pattern of aluminum hypophosphite is shown below. Figure 3 ,pass Figure 3 The characteristic peaks in the XRD pattern confirm the successful synthesis of aluminum hypophosphite.

[0051] See the particle size distribution diagram of aluminum hypophosphite. Figure 4 , Figure 4 The particle size distribution diagram shows that the spherical structure particles are mainly concentrated in the range of 600-700 nm, which is small.

[0052] Example 2

[0053] Preparation method of nanoscale uniform spherical aluminum hypophosphite:

[0054] (1) Place 42 mg of aluminum chloride hexahydrate in a beaker, add 7 mL of deionized water, and stir until the aluminum chloride hexahydrate is completely dissolved to obtain an aluminum chloride aqueous solution. Similarly, place 55.4 mg of sodium hypophosphite monohydrate in a beaker, add 8 mL of deionized water, and stir until the sodium hypophosphite monohydrate is completely dissolved to obtain a sodium hypophosphite aqueous solution.

[0055] (2) Add aluminum chloride aqueous solution dropwise to sodium hypophosphite aqueous solution while stirring, add 20 mL of ethylene glycol, stir for 30 min, mix evenly to obtain aluminum hypophosphite precursor solution; transfer aluminum hypophosphite precursor solution to hydrothermal reactor with a filling degree of 70%, react in oven at 140℃ for 5 hours, then cool naturally to room temperature, wash with deionized water and anhydrous ethanol, centrifuge to obtain solid, dry in vacuum drying oven at 60℃ for 12 hours to obtain nano-sized uniform spherical aluminum hypophosphite.

[0056] Example 3

[0057] Preparation method of nanoscale uniform spherical aluminum hypophosphite:

[0058] (1) Place 90 mg of aluminum chloride hexahydrate in a beaker, add 5 mL of deionized water, and stir until the aluminum chloride hexahydrate is completely dissolved to obtain an aluminum chloride aqueous solution. Similarly, place 118 mg of sodium hypophosphite monohydrate in a beaker, add 6 mL of deionized water, and stir until the sodium hypophosphite monohydrate is completely dissolved to obtain a sodium hypophosphite aqueous solution.

[0059] (2) Aluminum chloride aqueous solution was added dropwise to sodium hypophosphite aqueous solution while stirring. 24 mL of ethylene glycol was added and stirred for 30 min to mix evenly, thus obtaining aluminum hypophosphite precursor solution. The aluminum hypophosphite precursor solution was transferred to a hydrothermal reactor with a filling degree of 70%. The reactor was dried in an oven at 150 °C for 7 hours and then naturally cooled to room temperature. The solid was obtained by washing with deionized water and anhydrous ethanol and centrifuging. The solid was dried in a vacuum drying oven at 60 °C for 12 hours to obtain nano-sized uniform spherical aluminum hypophosphite.

[0060] Example 4

[0061] Preparation method of nanoscale uniform spherical aluminum hypophosphite:

[0062] (1) Place 120 mg of aluminum chloride hexahydrate in a beaker, add 6 mL of deionized water, and stir until the aluminum chloride hexahydrate is completely dissolved to obtain an aluminum chloride aqueous solution. Similarly, place 150 mg of sodium hypophosphite monohydrate in a beaker, add 6.5 mL of deionized water, and stir until the sodium hypophosphite monohydrate is completely dissolved to obtain a sodium hypophosphite aqueous solution.

[0063] (2) Aluminum chloride aqueous solution was added dropwise to sodium hypophosphite aqueous solution while stirring. 22 mL of ethylene glycol was added and stirred for 30 min to mix evenly, thus obtaining aluminum hypophosphite precursor solution. The aluminum hypophosphite precursor solution was transferred to a hydrothermal reactor with a filling degree of 70%. The reactor was reacted in an oven at 160 °C for 9 hours, and then naturally cooled to room temperature. The solid was obtained by washing with deionized water and anhydrous ethanol and centrifuging. The solid was dried in a vacuum drying oven at 60 °C for 12 hours to obtain nano-sized uniform spherical aluminum hypophosphite.

[0064] Example 5

[0065] Modification of aluminum hypophosphite:

[0066] (1) Weigh 50 mg of the uniform spherical aluminum hypophosphite prepared in Example 1 and place it in a glass sample bottle. Add 250 mg of deionized water and stir thoroughly for 30 min to ensure uniform dispersion of the aluminum hypophosphite.

[0067] (2) Place 25 mg of melamine, 56.3 mg of 37% formaldehyde solution and 125 mg of deionized water in a glass sample bottle, adjust the pH to 8 with triethanolamine, stir thoroughly in a water bath, heat to 65°C, the melamine gradually dissolves and the solution becomes clear, and the prepolymerization reaction is carried out for 30 min.

[0068] (3) The melamine-formaldehyde prepolymer solution after the reaction in step (2) was added dropwise to the aluminum hypophosphite in step (1), the pH was adjusted to 5 with hypophosphite, the temperature was raised to 55°C, and the mixture was stirred and allowed to undergo a polycondensation reaction for 2 hours. Then the mixture was cooled to room temperature, washed with deionized water and anhydrous ethanol, and centrifuged to obtain a solid. The solid was dried in a vacuum drying oven at 60°C for 24 hours to obtain spherical aluminum hypophosphite microcapsules coated with melamine-formaldehyde resin.

[0069] The scanning electron microscope, transmission electron microscope, and infrared spectra of the spherical aluminum hypophosphite microcapsules coated with melamine-formaldehyde resin are shown in the figures below. Figure 5 , Figure 6 , Figure 7 ,pass Figure 5 , Figure 6 It can be seen that the spherical aluminum hypophosphite is uniformly coated with melamine-formaldehyde resin, indicating that the spherical aluminum hypophosphite with regular morphology and small particle size prepared by this invention is easy to modify.

[0070] Comparative Example 1

[0071] The preparation method of aluminum hypophosphite is the same as that described in Example 1, except that:

[0072] In step (2), without adding ethylene glycol, the aqueous solution of aluminum chloride is added dropwise to the aqueous solution of sodium hypophosphite while stirring. 22 ml of deionized water is added and stirred for 30 min until homogeneous. The homogeneous solution is transferred to a hydrothermal reactor with a filling degree of 70%, and reacted in an oven at 140°C for 7 hours. After natural cooling to room temperature, the solid is obtained by washing with deionized water and anhydrous ethanol, centrifuging, and then drying in a vacuum drying oven at 60°C for 12 hours to obtain aluminum hypophosphite.

[0073] The scanning electron microscope image of the aluminum hypophosphite prepared in Comparative Example 1 is shown in Figure 8. It can be seen that the aluminum hypophosphite prepared without the addition of ethylene glycol has an irregular sheet-like or blocky structure, indicating that ethylene glycol has an improving effect on the morphology of aluminum hypophosphite.

[0074] Comparative Example 2

[0075] The preparation method of aluminum hypophosphite is the same as that described in Example 1, except that:

[0076] In step (2), 5 mL of ethylene glycol is added.

[0077] The scanning electron microscope image of the aluminum hypophosphite prepared in Comparative Example 2 is shown in Figure 9. It can be seen that when the amount of ethylene glycol added is too small, the morphology of the prepared aluminum hypophosphite is a spherical and irregular elongated structure. It can be seen that an appropriate amount of ethylene glycol can improve the morphology of aluminum hypophosphite.

[0078] Comparative Example 3

[0079] The preparation method of aluminum hypophosphite is the same as that described in Example 1, except that:

[0080] In step (2), the amount of ethylene glycol added is 35 mL.

[0081] The scanning electron microscope image of the aluminum hypophosphite prepared in Comparative Example 2 is shown in Figure 10. It can be seen that when too much ethylene glycol is added, the morphology of the prepared aluminum hypophosphite is a rough micron-sized spherical structure and agglomerated small particles. It can be seen that an appropriate amount of ethylene glycol can improve the morphology of aluminum hypophosphite.

[0082] Comparative Example 4

[0083] The modification of aluminum hypophosphite as described in Example 5 differs in that:

[0084] Weigh 50 mg of the uniform spherical aluminum hypophosphite prepared in Comparative Example 1 and place it in a glass sample bottle. The rest of the process is carried out as in Example 5.

[0085] The scanning electron microscope image of the melamine-formaldehyde resin-coated aluminum hypophosphite microcapsules obtained in Comparative Example 4 is shown below. Figure 11 ,pass Figure 11 It can be seen that the irregularly shaped aluminum hypophosphite cannot be uniformly coated with melamine-formaldehyde resin, indicating that the irregularly shaped aluminum hypophosphite is not easy to modify.

[0086] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any other way. Any person skilled in the art may make changes or modifications to the above-disclosed technical content to create equivalent embodiments for application in other fields. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A method for preparing nanoscale uniform spherical aluminum hypophosphite based on a hydrothermal method, comprising the following steps: (1) Under stirring conditions, aluminum chloride hexahydrate aqueous solution is slowly added dropwise to sodium hypophosphite monohydrate aqueous solution to obtain a mixed solution; the concentration of aluminum chloride hexahydrate aqueous solution is 7-10 mg / mL; the concentration of sodium hypophosphite monohydrate aqueous solution is 5-25 mg / mL; the molar ratio of sodium hypophosphite monohydrate to aluminum chloride hexahydrate is 2-6:

1. (2) Under stirring conditions, ethylene glycol was added to the mixed solution to obtain an aluminum hypophosphite precursor solution; the mass-volume ratio of aluminum chloride hexahydrate to ethylene glycol was (40-150):(20-30), unit mg / mL; (3) The aluminum hypophosphite precursor solution was transferred to a hydrothermal reactor and subjected to hydrothermal reaction. After natural cooling to room temperature, the product was washed with deionized water and anhydrous ethanol, centrifuged, vacuum dried, and ground to obtain nano-sized uniform spherical aluminum hypophosphite. The hydrothermal reaction temperature was 120-160 °C and the hydrothermal reaction time was 5-9 hours.

2. The method according to claim 1, characterized in that, In step (1), the concentration of the aqueous solution of aluminum chloride hexahydrate is 8.5 mg / mL.

3. The method according to claim 1, characterized in that, In step (1), the molar ratio of sodium hypophosphite monohydrate to aluminum chloride hexahydrate is 2-4:

1.

4. The method according to claim 1, characterized in that, In step (2), the mass-to-volume ratio of aluminum chloride hexahydrate to ethylene glycol is (40-150):(20-24), in mg / mL.

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