Melamine phosphite / aluminum phosphite core-shell structure and method of making same

Abstract

Melamine phosphite / aluminum phosphite with core-shell structure and preparation method thereof, the present application belongs to flame retardant, in order to further improve the performance of melamine-based flame retardant, the present application synthesizes a novel flame retardant material with core-shell structure by hydrothermal method through melamine phosphite and aluminum phosphite, and the core-shell structure is formed by using surfactant.The beneficial effects of the present application are as follows: (1) the particle size D50 of melamine phosphite can be controlled in 0.8-2.0 mu m through quaternary ammonium salt type surfactant and reaction temperature, and the dispersibility of the product is enhanced; (2) the thickness of the shell can be controlled to improve the decomposition temperature of the final product, and the decomposition temperature of melamine-based flame retardant is increased from about 260 DEG C to 400-450 DEG C, and the product particle size D50 can be controlled in 15-20 mu m; (3) the release rate of gas is effectively slowed down, and the gas phase flame retardation of melamine phosphite is enhanced.

Description

Technical Field

[0001] This invention pertains to flame retardants, specifically to melamine phosphite / aluminum phosphite with a core-shell structure and its preparation method. Background Technology

[0002] Core-shell structures are ordered, nanoscale assemblies formed by one nanomaterial encapsulating another through chemical bonds or other forces. Due to their unique structural characteristics, core-shell structures integrate the properties of both the inner and outer materials, complementing each other's shortcomings. This has been a significant and enduring research direction in recent years, demonstrating how morphology determines properties. With the deepening research into flame retardants for polymer materials, additive flame retardants are mainly divided into halogenated and halogen-free flame retardants. However, halogenated flame retardants easily release toxic and harmful gases and fumes, causing adverse environmental impacts. Melamine salts are an important component of halogen-free intumescent flame retardants, forming an intumescent flame retardant system integrating char, acid, and gas sources. Melamine nitrogen-based flame retardants are halogen-free, low-smoke, stable to light and heat, have good flame retardant effects, and are inexpensive. In recent years, research and application of melamine and its salt-based halogen-free flame retardants have been extensive, resulting in the preparation of many high-performance melamine-based flame retardants that have been applied in various polymer materials. Commonly used flame retardants include melamine and melamine urea cyanate (MCA), which often require the addition of synergists. They are used in resins such as PA, PU, ​​PO, PET, PS, and PVC, with nitrogen / phosphorus being the most commonly used synergistic flame retardant system. Aluminum phosphite, on the other hand, is a newly emerging inorganic phosphorus flame retardant in China. It exhibits good dispersibility and excellent affinity with organic matrices, helping to leverage the superior properties of organic materials and preventing material damage and failure caused by localized stress. It is widely used as a single flame retardant or in combination with other flame retardants.

[0003] Since 2001, there have been numerous reports on the synthesis of microporous phosphite materials via hydrothermal methods. These reported microporous phosphite materials include many transition metal phosphites, such as one-dimensional, two-dimensional, and three-dimensional zinc phosphite, organically templated chromium fluoride phosphite, inorganic-organic hybrid cobalt phosphite, three-dimensional iron phosphite, and vanadium phosphite. There have also been reports of using the polynitrogen compound guanidine carbonate as a structure-directing agent to synthesize aluminum phosphite [Al2(HPO3)3(H2O)3]·H2O (Al-7) crystals with a three-dimensional open framework and a three-dimensional cross-pore system of 10-membered, 8-membered, and 8-membered rings via hydrothermal methods. It has been confirmed that the structure of Al-7 does not contain guanidine carbonate as an organic template, indicating that guanidine carbonate may play a role in providing a certain reaction environment and pH conditions for the synthesis of Al-7, rather than acting as an organic template. This provides theoretical support for the preparation of aluminum phosphite with a multi-dimensional framework structure under specific reaction environment and pH conditions.

[0004] Melamine and its salt flame retardants have multiple reactive functions. Composite systems with added nitrogen-based flame retardants have poor processability and poor dispersibility with resins. Because melamine decomposes at around 260℃, there are problems such as the generation of ammonia gas during high-temperature injection molding in the processing, which can corrode the mold. In addition, it has low bulk density and is prone to delamination with engineering plastics. Summary of the Invention

[0005] To further improve the performance of melamine-based flame retardants, this invention synthesizes a novel core-shell structured flame retardant material from melamine phosphite and aluminum phosphite via a hydrothermal method, using a surfactant to induce the formation of the core-shell structure. Melamine phosphite forms the core, while aluminum phosphite is deposited on the melamine surface to form a shell. After the reaction, a white powdery solid is obtained through washing, filtration, drying, and baking, which is the core-shell structured melamine phosphite / aluminum phosphite composite material. The above preparation method specifically includes the following steps:

[0006] (1) Preparation of dilute melamine phosphite solution

[0007] Step 1.1) Dissolve phosphorous acid or its salt in deionized water, turn on heating and stirring to obtain a phosphorous acid or its salt solution with a concentration of 30-50 wt%.

[0008] The phosphorous acid or its salt is phosphorous acid (H3PO3) and its various phosphites, such as sodium phosphite (Na2HPO3) and ammonium phosphite ((NH4)2HPO3). The heating temperature is set at 70-80℃ and the stirring speed is 12-17 r / min.

[0009] Step 1.2) Pour the melamine aqueous dispersion (dispersion ratio of 30-50 wt%) into the above-mentioned phosphorous acid or its salt solution in batches;

[0010] Generally, add 15-20 wt% melamine aqueous dispersion per batch. Add in batches, waiting until the solution becomes clear before continuing to add. Maintain the temperature of the mixed solution at 70-80℃ and continue stirring. During the reaction, add 1-5 parts by weight of quaternary ammonium salt surfactant. After stirring continuously for 1-2 hours, the suspension will gradually thicken. Add water and raise the temperature to 90-120℃. The reaction is complete when the suspension becomes clear. Adding in batches ensures complete reaction and prevents aggregation.

[0011] The quaternary ammonium salt surfactant includes one or a combination of two of the following: hexadecyltrimethylammonium chloride, octadecyltrimethylammonium chloride, dodecyldimethylbenzylammonium chloride, and dialkyldimethylammonium salts. The amount of quaternary ammonium salt surfactant added is 1-5 wt%.

[0012] Step 1.3) After the obtained solution is completely cooled, it is filtered and washed until the pH value is neutral, and then dried to obtain melamine phosphite; the drying temperature is 90-120℃ and the drying time is 8-12h.

[0013] Step 1.4) Dissolve the above-mentioned melamine phosphite in an aqueous solution at 80-100℃ to prepare a 15-35% dilute melamine phosphite solution.

[0014] (2) Preparation of saturated aluminum phosphite solution

[0015] Step 2.1) Dissolve phosphorous acid or its salt in a certain aqueous solution, wherein the concentration of the phosphorous acid or its salt solution is the same as that in Step 1.1).

[0016] Step 2.2) Add the measured amount of aluminum hydroxide to the above-mentioned phosphorous acid or its salt solution concentration, and start heating and stirring; the weight ratio of aluminum hydroxide to phosphorous acid or its salt is 0.5-0.8:1, the heating temperature is 70-100℃, and the stirring speed is 12-17 r / min.

[0017] Step 2.3) Adjust the above solution to a saturated state and adjust the pH to 3-3.5;

[0018] Step 2.4) Add a dispersant to the saturated aluminum phosphite solution to maintain the stability of the saturated solution. The dispersant includes at least one of barium stearate, zinc stearate, calcium stearate, cadmium stearate, magnesium stearate, copper stearate, vinyl bis-stearamide, and glyceryl tristearate, added in an amount of 0.2-2 wt% (by weight in the entire reaction system).

[0019] (3) Synthesis of melamine phosphite / aluminum phosphite with core-shell structure

[0020] Step 3.1) Add the dilute melamine phosphite solution obtained in step (1) to the saturated aluminum phosphite solution in step (2), and keep it under heating and stirring. The heating temperature is 80-100℃. The weight ratio of the dilute melamine phosphite solution to the saturated aluminum phosphite solution can be 1:1.5.

[0021] Step 3.2) Add a coupling agent to the above solution at a rate of 0.5-2 wt% to promote the combination of aluminum phosphite and melamine phosphite. Under certain temperature conditions, aluminum phosphite gradually aggregates into a shell on the surface of melamine phosphite. After the reaction is complete, a white precipitate is produced.

[0022] The coupling agent includes at least one of silane coupling agents KH550, KH560, KH570, KH792, DL602, and DL171. The reaction temperature is 90-110℃, and the mixture is continuously stirred until a white precipitate is formed.

[0023] Step 3.3) The obtained white precipitate is filtered, washed to pH 4.0-4.5, and dried to obtain a white precipitate; the drying temperature is 100-180℃ and the time is 5-8h.

[0024] Step 3.4) Place the white precipitate into a reaction vessel lined with polytetrafluoroethylene and bake it in a muffle furnace to solidify the core-shell structure of melamine phosphite / aluminum phosphite; baking temperature 200-350℃, baking time 3-5h.

[0025] Step 3.5) Grind the obtained white powder and sieve it to obtain melamine phosphite / aluminum phosphite with a core-shell structure.

[0026] This invention synthesizes a novel core-shell structured flame-retardant material from melamine phosphite and aluminum phosphite via a hydrothermal method. Melamine phosphite forms the core, with aluminum phosphite deposited on its surface to form a shell. This structure allows for control of the shell thickness by adjusting the temperature and time of the synthesis reaction, thereby increasing the decomposition temperature of the flame retardant and slowing the release rate of ammonia from the thermal decomposition of melamine phosphite, thus enhancing the flame-retardant effect of the condensed phase. Furthermore, the particle size D of the flame retardant can be controlled by adjusting the deposition time of the aluminum phosphite. 50 The particle size D is controlled at 15-20μm, which is the particle size of most flame retardants currently on the market. 50 By controlling the particle size to 30-50μm, we can stabilize it at a finer particle size, resulting in better dispersibility of the flame retardant and making it easier to add and apply to various plastics.

[0027] The present invention has the following advantages and effects compared with the prior art:

[0028] (1) The particle size D50 of melamine phosphite can be controlled between 0.8-2.0 μm by using quaternary ammonium salt surfactants and reaction temperature, which enhances the dispersibility of the product;

[0029] (2) During the melamine phosphite / aluminum phosphite surface shell formation process, the shell thickness can be controlled by adjusting different reaction temperatures and times, thereby increasing the decomposition temperature of the final product. This raises the decomposition temperature of the melamine-based flame retardant from approximately 260℃ to 400-450℃, and also controls the product particle size D. 50 At 15-20μm;

[0030] (3) The core-shell structure of melamine phosphite / aluminum phosphite has a higher decomposition temperature than melamine phosphite. When melamine phosphite is heated and decomposed, the gas source flows inside the shell, which effectively slows down the gas release rate and enhances the gas phase flame retardant effect of melamine phosphite. When the aluminum phosphite in the shell is heated, it forms a carbon layer to block the contact between the flammable gas released from the plastic decomposition and oxygen in the air, thus blocking further combustion and effectively enhancing the flame retardant effect of the condensed phase. Attached Figure Description

[0031] Figure 1 Here is a scanning electron microscope image of melamine phosphite / aluminum phosphite with a core-shell structure, as shown in Example 1.

[0032] Figure 2 Particle size distribution of melamine phosphite with different contents of quaternary ammonium salt surfactants;

[0033] Figure 3 The particle size distribution diagram is for melamine phosphite in Example 1.

[0034] Figure 4 The particle size analysis diagram of melamine phosphite in Example 2 is shown.

[0035] Figure 5 The particle size distribution diagram for Example 1 shows the core-shell structure of melamine phosphite / aluminum phosphite.

[0036] Figure 6 Thermogravimetric analysis diagram of melamine phosphite / aluminum phosphite with core-shell structure in Example 1;

[0037] Figure 7 Thermogravimetric analysis diagram of melamine phosphite / aluminum phosphite with core-shell structure for Example 2. Detailed Implementation

[0038] Example 1

[0039] (1) Preparation of dilute melamine phosphite solution

[0040] A round-bottom flask containing 100 ml of deionized water was placed in an oil bath and heated with stirring at 80°C. 50 g of phosphorous acid was weighed and added to the flask. Separately, 50 g of melamine was weighed and added to 100 ml of deionized water to disperse it. After the phosphorous acid dissolved in the phosphorous acid mixture, the melamine dispersion was added in batches, maintaining the temperature of the mixture at 80°C and stirring continuously. 2 g of the quaternary ammonium salt surfactant, dodecyl dimethyl benzyl ammonium chloride, was added, and stirring continued for 1.5 hours. The suspension gradually thickened; water was added, and the temperature was raised to 100°C. The reaction was complete when the suspension became transparent. After cooling, the precipitate was filtered, repeatedly washed until the pH was neutral, and then baked in an oven at 90°C for 10 hours to obtain melamine phosphite powder. 30 g of the powder was dissolved in 90°C deionized water to prepare a 30% melamine phosphite solution. Please refer to [reference needed]. Figure 2 The particle size distribution of melamine phosphite in the sample shows that D50 = 0.809 μm.

[0041] (2) Preparation of saturated aluminum phosphite solution

[0042] Weigh 70g of phosphorous acid and dissolve it in 120ml of water. Add 45g of aluminum hydroxide, turn on the heating and stirring, and heat the solution to 90℃. Finely adjust the content of phosphorous acid and aluminum hydroxide to make the solution saturated. Adjust the pH to 3.0. After reacting for 0.5h, add 1.5g of calcium stearate dispersant and continue stirring for 1.5h to obtain a saturated aluminum phosphite solution.

[0043] (3) Synthesis of melamine phosphite / aluminum phosphite with core-shell structure

[0044] The dilute melamine phosphite solution from step (1) was added to the saturated aluminum phosphite solution from step (2). The temperature was controlled at 90°C, and mechanical stirring was used. 2.5g of silane coupling agent KH-550 was added, and the reaction temperature was raised to 105°C. Stirring was continued until a white precipitate was formed. After reacting for 2 hours, the precipitate was filtered and washed until the pH reached 4.2. It was then dried in an oven at 110°C for 5 hours and transferred to a reaction vessel with a polytetrafluoroethylene liner. The vessel was then baked in a muffle furnace at 200°C for 3 hours. After cooling, grinding, and screening, melamine phosphite / aluminum phosphite with a core-shell structure was obtained. The thermal decomposition temperature was approximately 428.7°C.

[0045] Depend on Figure 1 The scanning electron microscope (SEM) images show that the melamine phosphite / aluminum phosphite prepared in Example 1 has a distinct core-shell structure, with excellent outer aluminum phosphite coating and crystal grain size ranging from 15 to 20 μm. Combined with... Figure 5 Particle size analysis of melamine phosphite / aluminum phosphite with a core-shell structure can further verify the particle size of the product. Figure 5Data shows the D of the product obtained in Example 1 50 It is 20.27 μm.

[0046] Example 2

[0047] (1) Preparation of dilute melamine phosphite solution

[0048] A round-bottom flask containing 100 ml of deionized water was placed in an oil bath and heated with stirring at 80°C. 50 g of phosphorous acid was weighed and added to the flask. Separately, 50 g of melamine was weighed and added to 100 ml of deionized water to disperse it. After the phosphorous acid dissolved in the phosphorous acid mixture, the melamine dispersion was added in batches, maintaining the temperature of the mixture at 80°C and stirring continuously. 2 g of the quaternary ammonium salt surfactant, hexadecyltrimethylammonium chloride, was added, and stirring continued for 1.5 hours. The suspension gradually thickened; water was added, and the temperature was raised to 110°C. The reaction was complete when the suspension became transparent. After cooling, the precipitate was filtered, repeatedly washed until the pH was neutral, and then baked in an oven at 90°C for 10 hours to obtain melamine phosphite powder. 30 g of the powder was dissolved in 90°C deionized water to prepare a 30% melamine phosphite solution. Please refer to [reference needed]. Figure 3 The particle size distribution of melamine phosphite in the sample shows that D50 = 1.911 μm.

[0049] (2) Preparation of saturated aluminum phosphite solution

[0050] Weigh 70g of phosphorous acid and dissolve it in 120ml of water. Add 45g of aluminum hydroxide, turn on the heating and stirring, and heat the solution to 95℃. Finely adjust the content of phosphorous acid and aluminum hydroxide to make the solution saturated and adjust the pH to 3.0. After reacting for 0.5h, add 0.5g of barium stearate as a dispersant and continue stirring for 1.5h to obtain a saturated aluminum phosphite solution.

[0051] (3) Synthesis of melamine phosphite / aluminum phosphite with core-shell structure

[0052] The dilute melamine phosphite solution from step (1) was added to the saturated aluminum phosphite solution from step (2). The temperature was controlled at 90°C, and mechanical stirring was used. 2.5g of silane coupling agent KH-550 was added, and the reaction temperature was raised to 100°C. Stirring was continued until a white precipitate was formed. After reacting for 3 hours, the precipitate was filtered, washed until the pH reached 4.2, and dried in an oven at 110°C for 5 hours. The precipitate was then transferred to a reaction vessel with a polytetrafluoroethylene liner and baked in a muffle furnace at 200°C for 3 hours. After cooling, grinding, and screening, melamine phosphite / aluminum phosphite with a core-shell structure was obtained. The thermal decomposition temperature was 446.6°C.

[0053] As a compound flame retardant, it replaced 30% of APP and DiPE in halogen-free flame-retardant PP (APP system) materials, achieving UL94 (V0) flame retardancy. The flame retardant performance before and after compounding was compared, and the results are shown in Table 1 below:

[0054]

[0055]

[0056] LOI: Limiting Oxygen Index. A high index indicates that the material is not easily combustible, while a low index indicates that the material is easily combustible. Generally, an oxygen index <22% is considered a flammable material, an oxygen index between 22% and 27% is considered a combustible material, and an oxygen index >27% is considered a flame-retardant material.

[0057] Afterflame time(T1+T2): The duration of the afterflame.

[0058] UL94: Flame retardant rating.

[0059] Table 2 Mechanical property test data of core-shell structured melamine phosphite / aluminum phosphite in halogen-free flame-retardant PP:

[0060]

[0061] As shown in Table 1, when melamine phosphite / aluminum phosphite with a core-shell structure is added to PP material, replacing 30% of APP and DiPE, the limiting oxygen index increases from 28% to 30.7%. The flame retardancy of the material is significantly increased, the vertical afterflame burning time increases by 1 second, and the flame retardancy rating UL94 reaches V0 level.

[0062] Table 2 shows the mechanical property test data of the core-shell structure melamine phosphite / aluminum phosphite in Example 2 applied to halogen-free flame-retardant PP. As can be seen from the data in the table, compared with the original flame-retardant formula of halogen-free flame-retardant PP, after replacing 30% APP, the tensile strength of PP material remained basically unchanged, while the bending strength and bending modulus were significantly improved, and the elongation at break increased from 18.1% to 27%.

[0063] Figure 2In the graphs, A1 and A2 represent the particle size distribution of melamine phosphite with 2 wt% and 5 wt% quaternary ammonium salt surfactants, respectively. The graphs clearly show that when the addition amount is 2 wt%, the particle size of melamine phosphite is mainly distributed between 1-2 μm; when the addition amount is 5 wt%, it is mainly distributed between 2-4 μm. The former has a smaller and more concentrated particle size distribution, indicating that the dispersibility of melamine phosphite is better when the addition amount of quaternary ammonium salt surfactant is 2 wt%. Therefore, it can be concluded that the particle size of melamine phosphite can be controlled by adjusting the addition amount of quaternary ammonium salt surfactant.

[0064] In Examples 1 and 2, the synthesis temperatures of melamine phosphite were 100°C and 110°C, respectively. Figure 3 and Figure 4 The particle size analysis results show that the particle sizes D50 of the obtained products are 0.809 μm and 1.911 μm, respectively. In the synthesis of melamine phosphite, the reaction temperature has a significant effect on the particle size. The particle size of melamine phosphite can be controlled by adjusting the amount of quaternary ammonium salt surfactant added and the reaction temperature, thereby enhancing the dispersibility.

[0065] Figure 6 and Figure 7 The thermogravimetric analysis (TGA) charts of the core-shell structured melamine phosphite / aluminum phosphite prepared in Examples 1 and 2 are shown respectively. The main difference between the two products lies in the reaction temperature and time during the shell formation process on the melamine phosphite / aluminum phosphite surface. In Example 1, the reaction temperature and time were 105°C for 2 hours, while in Example 2, the reaction temperature and time were 100°C for 3 hours. Figure 6 and Figure 7 The data shows that the thermal decomposition temperatures of the obtained products are 428.7℃ and 446.6℃, respectively, with the latter exhibiting better heat resistance. The coating rate of aluminum phosphite varies under different reaction temperatures and times, resulting in different shell thicknesses. At 100℃, increasing the reaction time leads to an increase in shell thickness, thereby raising the decomposition temperature of the final product. Further research is needed to determine the optimal reaction temperature and time.

Claims

1. A method for preparing a core-shell structured melamine phosphite / aluminum phosphite, characterized in that, The preparation method includes the following steps: (1) Preparation of dilute melamine phosphite solution Step 1.1) Dissolve phosphorous acid or its salt in deionized water and heat to obtain a phosphorous acid or its salt solution with a concentration of 30-50 wt% at a heating temperature of 70-80℃; Step 1.2) Pour the melamine aqueous dispersion with a dispersion ratio of 30-50 wt% into the above-mentioned phosphorous acid or its salt solution in batches, wherein the proportion of the melamine aqueous dispersion is 15-20 wt%. During the reaction, add 1-5 wt% of quaternary ammonium salt surfactant, stir continuously until the suspension gradually becomes viscous, add water and heat to 90-120℃, and the reaction is complete when the suspension becomes transparent. Step 1.3) After the obtained solution is completely cooled, it is filtered and washed until the pH value is neutral, and then dried to obtain melamine phosphite at a drying temperature of 90-120℃. Step 1.4) Dissolve the above-mentioned melamine phosphite in an aqueous solution at 80-100℃ to prepare a 15-35% dilute melamine phosphite solution; (2) Preparation of saturated aluminum phosphite solution Step 2.1) Dissolve phosphorous acid or its salt in deionized water, wherein the concentration of the phosphorous acid or its salt solution is the same as in step 1.1); Step 2.2) Add aluminum hydroxide to the above solution of phosphorous acid or its salt, and start heating and stirring. The weight ratio of aluminum hydroxide to phosphorous acid or its salt is 0.5-0.8:1, and the heating temperature is 70-100℃. Step 2.3) Adjust the above solution to a saturated state and adjust the pH to 3-3.5; Step 2.4) Add a dispersant to the saturated aluminum phosphite solution to maintain the stability of the saturated solution. The amount added is 0.2-2 wt%. (3) Synthesis of melamine phosphite / aluminum phosphite with core-shell structure Step 3.1) Add the dilute melamine phosphite solution obtained in step (1) to the saturated aluminum phosphite solution in step (2), and keep heating and stirring, wherein the heating temperature is 80-100℃; Step 3.2) Add coupling agent to the above solution, the amount of which is 0.5-2 wt%, the reaction temperature is 90-110℃, and stir continuously until a white precipitate is formed; Step 3.3) The obtained white precipitate is filtered, washed to pH 4.0-4.5, and dried to obtain a white precipitate at a drying temperature of 100-180℃; Step 3.4) Place the white precipitate into a reaction vessel with a polytetrafluoroethylene liner, and bake it in a muffle furnace to solidify the core-shell structure of melamine phosphite / aluminum phosphite at a baking temperature of 200-350℃. Step 3.5) Grind the obtained white powder and sieve it to obtain melamine phosphite / aluminum phosphite with a core-shell structure.

2. The method for preparing core-shell structured melamine phosphite / aluminum phosphite as described in claim 1, characterized in that, The phosphite mentioned is sodium phosphite or ammonium phosphite.

3. The method for preparing core-shell structured melamine phosphite / aluminum phosphite as described in claim 1, characterized in that, The quaternary ammonium salt surfactant is one or a combination of two of the following: hexadecyltrimethylammonium chloride, octadecyltrimethylammonium chloride, dodecyldimethylbenzylammonium chloride, and dialkyldimethylammonium salt.

4. The method for preparing core-shell structured melamine phosphite / aluminum phosphite as described in claim 1, characterized in that, The dispersant in step 2.4) includes at least one of barium stearate, zinc stearate, calcium stearate, cadmium stearate, magnesium stearate, copper stearate, vinyl bis-stearamide, and tristearate.

5. The method for preparing core-shell structured melamine phosphite / aluminum phosphite as described in claim 1, characterized in that, The coupling agent in step 3.2) includes at least one of the silane coupling agents KH550, KH560, KH570, KH792, DL602, and DL-171.

6. Melamine phosphite / aluminum phosphite prepared by the method for preparing a core-shell structured melamine phosphite / aluminum phosphite according to any one of claims 1-5.

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