A modified melamine polyphosphate resistant to precipitation, and a preparation method and application thereof

Abstract

The application discloses a precipitation-resistant modified melamine polyphosphate and a preparation method and application thereof, and belongs to the field of phosphorus-nitrogen halogen-free flame retardants. The preparation method of the precipitation-resistant modified melamine polyphosphate comprises the following steps: (1) mixing phosphoric acid and formula (a) in deionized water at normal temperature, heating under stirring until the temperature is higher than 80 DEG C, adding melamine, and reacting for 1-4 hours to obtain a modified intermediate; (2) performing dehydration on the obtained modified intermediate, then heating to 300-350 DEG C to perform a polycondensation reaction, and the reaction time is 4-10 hours to obtain a polycondensate; and (3) crushing the obtained polycondensate, then adding a coupling agent, uniformly dispersing, heating to 150-250 DEG C, and reacting for 1-3 hours to obtain a precipitation-resistant modified melamine polyphosphate product. The application can effectively reduce the solubility of melamine polyphosphate in water, and solves the problems of poor dispersibility and easy precipitation of melamine polyphosphate in the application process.

Description

Technical Field

[0001] This invention relates to a phosphorus-nitrogen-based halogen-free flame retardant, specifically to a precipitation-resistant modified melamine polyphosphate, its preparation method, and its application. Background Technology

[0002] In recent decades, polymer materials have been increasingly widely used, becoming an important material in the industrial field alongside metals and inorganic non-metals. Many polymer materials, especially high-molecular materials represented by plastics, have high carbon content and are inherently flammable. When the material surface is exposed to heat radiation, it may spontaneously combust, or even ignite upon direct contact with an open flame. If the combustion is not controlled in time and space, a fire will occur. Therefore, flame-retardant modification of polymer materials is necessary. Currently, the most widely used and effective flame retardants are halogenated flame retardants. Although a small amount can achieve a high flame retardancy rating, their combustion produces toxic and corrosive gases. Some halogenated flame retardants also produce carcinogenic dioxins, posing significant harm to the environment and human health.

[0003] Melamine polyphosphate (MPP) is an environmentally friendly and highly efficient nitrogen-phosphorus flame retardant. It is characterized by low toxicity, excellent flame retardant effect, good thermal stability, small addition amount, and low water solubility, and is widely used.

[0004] Currently, there are three main methods for producing MPP: solvent method, one-step solid-phase method, and two-step solid-phase method. While the solvent method produces MPP with high purity and excellent performance, its high production cost, complex process, and high safety risks prevent its application in large-scale industrial production. The one-step solid-phase method requires sophisticated equipment because localized overheating during pyrolysis can lead to inconsistent reaction rates and ultimately poor product purity. The two-step solid-phase method is currently the most commonly used production method in China, offering milder conditions and simpler operation. However, during the first step of MP synthesis, the reaction between the solid and liquid phases can cause phosphoric acid to aggregate locally during the addition of phosphoric acid, forming lumps that are difficult to control. This can result in localized or side reactions, leading to a product with similarly low purity, containing significant amounts of MP and oligomeric melamine polyphosphate, exhibiting poor thermal stability, high solubility, and poor compatibility with various materials.

[0005] To address the aforementioned issues, relevant patents report methods for improving the quality of melamine polyphosphate flame retardants by adding modifiers. For example, Chinese invention patent CN106831625A discloses a metal ion-modified melamine polyphosphate, its preparation method, and its application. This patent involves mixing polyphosphoric acid with melamine, heating to 80–300°C, and reacting for 1–10 hours to obtain a melamine polyphosphate prepolymer. A metal compound is then added to the melamine polyphosphate prepolymer, mixed, heated to 270–350°C, and reacted for 0.5–5 hours to obtain the metal ion-modified melamine polyphosphate. Chinese invention patent CN111285817A discloses a melamine polyphosphate and its application. This patent first prepares a dimelamine pyrophosphate intermediate from melamine, sodium pyrophosphate, and an inorganic acid, and then dries and calcines the intermediate to obtain the melamine polyphosphate.

[0006] Although the aforementioned patented solutions improved the thermal stability of melamine polyphosphate to some extent and enhanced the flame retardant properties of materials such as nylon and resin, Patent 1 did not effectively improve the water solubility of MPP, and the problem of easy precipitation still existed in the materials. While Patent 2 improved the solubility of MPP to some extent, its reaction process involved adding all reactants such as melamine and sodium pyrophosphate together, making the reaction process difficult to control. The first step product contained byproducts and had low purity. Summary of the Invention

[0007] Based on the above-mentioned technical problems, this invention proposes a precipitation-resistant modified melamine polyphosphate, as well as the preparation method and application of the melamine polyphosphate.

[0008] The technical solution adopted in this invention is:

[0009] A precipitation-resistant modified melamine polyphosphate, having the following structural formula:

[0010]

[0011] Among them, M1 and M2 are both Or M1 is M2 is hydrogen;

[0012] n≥1, m≥2, and both are integer values.

[0013] The preparation method of the precipitation-resistant modified melamine polyphosphate as described above includes the following steps:

[0014] (1) At room temperature, phosphoric acid and formula (a) are mixed in deionized water, and the temperature is raised to above 80°C while stirring. Melamine is added and the reaction is carried out for 1 to 4 hours to obtain the modified intermediate.

[0015]

[0016] In formula (a), R1 and R2 are selected from hydrogen, hydroxyl, C1-C4 alkyl, and phenyl, respectively; and R1 and R2 cannot be selected from hydrogen at the same time.

[0017] (2) The modified intermediate obtained in step (1) is heated and dehydrated, and then heated to 300-350°C for polycondensation reaction for 4-10 hours to obtain the polycondensate.

[0018] (3) Crush the condensate obtained in step (2), then add a coupling agent, disperse evenly, heat to 150-250℃, and react for 1-3 hours to obtain a precipitation-resistant modified melamine polyphosphate product.

[0019] Preferably, the coupling agent is one or a combination of two of the coupling agents S4-3047 and 208C.

[0020] Preferably, the amount of coupling agent added accounts for 0.1% to 3% of the mass fraction of the condensate.

[0021] Preferably, the properties of the obtained modified melamine polyphosphate product are: solubility in water at 80°C less than 10 mg / 100 mL; phosphorus content > 15.8%.

[0022] Preferably, the structural formula of the condensation polymer obtained in step (2) is as follows:

[0023]

[0024] Among them, M1 and M2 are both Or M1 is M2 is hydrogen;

[0025] Where n≥1, m≥2, and both take integer values.

[0026] Preferably, in step (1): the molar ratio of formula (a) to phosphoric acid is (1-20):10; the molar ratio of melamine to phosphoric acid is greater than or equal to 1:1.

[0027] Preferably, when R2 is a hydroxyl group, the structural formula of formula (b) is transformed into formula (b1):

[0028]

[0029] In equation (b1), n≥1, m≥2, and both are integers;

[0030] When neither R1 nor R2 is a hydroxyl group, the structural formula of formula (b) is transformed into formula (b2):

[0031]

[0032] In equation (b2), n≥2, and the value of n in equation (b2) does not have to be the same as that of n in equation (b) and equation (b1).

[0033] In step (2) above, dehydration condensation is preferably carried out under a nitrogen atmosphere. The equipment used includes, but is not limited to, high-temperature ovens, kneaders, internal mixers, muffle furnaces, and tube furnaces.

[0034] The above describes the flame-retardant application of a precipitation-resistant modified melamine polyphosphate in polymers.

[0035] Preferably, the polymer is at least one selected from nylon, polyester, polyolefin, polyurethane, thermoplastic elastomer, polycarbonate, and epoxy resin.

[0036] The beneficial technical effects of this invention are:

[0037] This invention modifies melamine polyphosphate to resist precipitation by replacing part of the phosphoric acid with organic structures such as benzene rings. This effectively reduces the solubility of melamine polyphosphate in water, solving problems such as poor dispersibility, poor compatibility with materials, high water solubility, and easy precipitation that exist in the application of melamine polyphosphate. This invention can improve the product quality of melamine polyphosphate. The modified melamine polyphosphate, when used as an additive flame retardant in the flame retardancy of polymers, exhibits good flame retardant effect, low solubility, good polymer compatibility, good dispersibility, and resistance to precipitation.

[0038] Specifically, the present invention has the following advantages:

[0039] This invention provides a precipitation-resistant modified melamine polyphosphate, which has the characteristics of good dispersion, good polymer compatibility, low solubility, precipitation resistance, and excellent flame retardant properties.

[0040] This invention provides a method for preparing precipitation-resistant modified melamine polyphosphate. This method has the advantages of simple process steps, readily available raw materials, mild reaction conditions, stable reaction process, high safety, and low energy consumption.

[0041] This invention also provides an application of precipitation-resistant modified melamine polyphosphate in polymers for flame retardant modification, which has excellent flame retardant effect, better compatibility, and significant advantages in mechanical strength. Attached Figure Description

[0042] Figure 1 The exudation of the flame retardant strip is shown, where 1# represents the blank control sample, and the others correspond to Examples 1-4 and Comparative Examples 1-3, respectively.

[0043] Figure 2The infrared spectrum of the precipitate-resistant modified melamine polyphosphate obtained in Example 1 of this invention;

[0044] Figure 3 Infrared spectrum of commercially available melamine polyphosphate. Detailed Implementation

[0045] The present invention will be further described below with reference to specific embodiments.

[0046] Example 1

[0047] (1) Phenylenic acid and phosphoric acid were weighed in a molar ratio of 1:2, added to a reaction vessel, and water was added to 2 / 3 of the volume. The mixture was stirred and heated. Melamine was added in three batches under stirring conditions, with a molar ratio of melamine to phosphoric acid of 1.03:1. The mixture was heated to 90°C and reacted for 4 hours to obtain a white powdery intermediate.

[0048] (2) Take 100g of the intermediate, place it in a covered porcelain crucible, put it in an oven, slowly heat it to above 100℃ to dehydrate for 2 hours, then gradually heat it to 300℃ to carry out a polycondensation reaction. After reacting for 8 hours, cool it to obtain the polycondensate.

[0049] (3) After crushing the condensate, add 0.3% by mass of coupling agent, disperse evenly, heat to 200℃, and react for 2 hours to obtain a modified melamine polyphosphate product with resistance to precipitation and low solubility.

[0050] Example 2

[0051] (1) Diphenylphosphonic acid and phosphoric acid were weighed in a molar ratio of 1:1, added to a reaction vessel, and water was added to 2 / 3 of the volume. The mixture was stirred and heated. Melamine was added in three batches under stirring conditions, with a molar ratio of melamine to phosphoric acid of 1.03:1. The mixture was heated to 90°C and reacted for 4 hours to obtain a white powdery intermediate.

[0052] (2) Take 100g of the intermediate, place it in a covered porcelain crucible, place it in an oven, slowly heat it to above 100℃ to dehydrate for 2 hours, then gradually heat it to 350℃ to carry out a polycondensation reaction. After reacting for 8 hours, cool it to obtain the polycondensate.

[0053] (3) After crushing the condensate, add 0.3% by mass of coupling agent, disperse evenly, heat to 200℃, and react for 2 hours to obtain a melamine polyphosphate product with resistance to precipitation and low solubility.

[0054] Example 3

[0055] (1) Methylphosphonic acid and phosphoric acid were weighed in a molar ratio of 1:2, added to a reaction vessel, and water was added to 2 / 3 of the volume. The mixture was stirred and heated. Melamine was added in three batches under stirring conditions, with a molar ratio of melamine to phosphoric acid of 1.03:1. The mixture was heated to 90°C and reacted for 4 hours to obtain a white powdery intermediate.

[0056] (2) Take 100g of the intermediate, place it in a covered porcelain crucible, place it in an oven, slowly heat it to above 100℃ to dehydrate for 2 hours, then gradually heat it to 350℃ to carry out a polycondensation reaction. After reacting for 8 hours, cool it to obtain the polycondensate.

[0057] (3) After crushing the condensate, add 3% by mass of coupling agent, disperse evenly, heat to 250℃, and react for 2 hours to obtain melamine polyphosphate product with resistance to precipitation and low solubility.

[0058] Example 4

[0059] (1) Dimethylphosphoric acid and phosphoric acid were weighed in a molar ratio of 1:10, added to a reaction vessel, and water was added to 2 / 3 of the volume. The mixture was stirred and heated. Melamine was added in three batches under stirring conditions. The molar ratio of melamine to phosphoric acid was 1.03:1. The mixture was heated to 90°C and reacted for 4 hours to obtain a white powdery intermediate.

[0060] (2) Take 100g of the intermediate, place it in a covered porcelain crucible, put it in an oven, slowly heat it to above 100℃ to dehydrate for 2 hours, then gradually heat it to 300℃ to carry out a polycondensation reaction. After reacting for 8 hours, cool it to obtain the polycondensate.

[0061] (3) After crushing the condensate, add 0.3% by mass of coupling agent, disperse evenly, heat to 150℃, and react for 2 hours to obtain melamine polyphosphate product with resistance to precipitation and low solubility.

[0062] Comparative Example 1

[0063] Melamine and phosphate were weighed in a 1:1 molar ratio, heated to above 80°C and reacted for 3 hours, then dehydrated and dried to obtain melamine phosphate intermediate; the intermediate was heated to 300°C and reacted for a period of time, then pulverized to obtain melamine polyphosphate.

[0064] Comparative Example 2

[0065] (1) Melamine, sodium pyrophosphate and hydrochloric acid were weighed in a molar ratio of 2:1:4 and added to a reaction vessel containing deionized water under stirring. The liquid occupied 60% of the container volume. The mixed liquid was reacted at 85°C for 2.0 h, dehydrated, washed and dried at 100°C for 48 h to obtain an intermediate.

[0066] (2) Heat the intermediate at 170°C for 1 hour, then heat it to 300°C for 2 hours, cool and crush it to obtain melamine polyphosphate.

[0067] Comparative Example 3

[0068] Melamine and cyanuric acid were weighed at a molar ratio of 1:1.05. Deionized water was added to the reactor, filling 60% of the reactor volume. Cyanuric acid was then added to the reactor, and the mixture was stirred and heated to 85°C. Melamine and a polymeric nucleating agent were then added, and the mixture was stirred and reacted at 85°C for 2 hours to obtain a white slurry. The slurry was dehydrated, dried, and pulverized to obtain white melamine cyanurate powder with a particle size of 15–100 μm.

[0069] The performance of the melamine polyphosphates prepared in Examples 1-4 and Comparative Examples 1-3 was tested. Thermal stability was tested using thermogravimetric analysis (TGA). Small amounts of samples from Examples 1-4 and Comparative Examples 1-3 were taken for TGA testing. For water solubility testing, small amounts of samples from Examples 1-4 and Comparative Examples 1-3 were dissolved in a certain amount of water to form saturated solutions, and the solubility of the samples in water was measured. The comparative data of thermal stability and solubility are shown in Table 1 below.

[0070] Table 1

[0071]

[0072]

[0073] As shown in Table 1, the melamine polyphosphate prepared by this invention has excellent properties such as good thermal stability and low water solubility.

[0074] The melamine polyphosphate flame retardants prepared in the above embodiments and comparative examples were extruded as follows and tested experimentally. Mechanical properties were tested according to GB / T1843 for impact strength and GB / T1040 for tensile strength; vertical burning tests were conducted according to GB / T2408-2008; and oxygen index (LOI) tests were conducted according to GB / T2406.1-2008.

[0075] Step 1: Place PBT and melamine polyphosphate flame retardant in an 80℃ vacuum oven and dry for 4 hours. Then mix them evenly and extrude them into granules using a twin-screw extruder to obtain PBT flame retardant granules. Place the obtained PBT flame retardant granules in an 80℃ vacuum oven and dry for 4 hours for later use.

[0076] Step 2: Use an injection molding machine to injection mold completely dried PBT flame retardant granules into flame retardant strips (1.6mm), and test the flame retardant performance after placing them at 25℃ and 50% humidity for 24 hours.

[0077] Step 3: Use an injection molding machine to injection mold the completely dried PBT flame retardant granules into flame retardant strips (1.6mm), and observe their precipitation after placing them at 85℃ and 85% humidity for 48 hours.

[0078] Figure 1 This shows the precipitation pattern of the flame-retardant strip. From Figure 1 It can be seen that the modified melamine polyphosphate product prepared by the present invention has a significant advantage in terms of precipitation resistance compared with traditional MPP products.

[0079] Table 2 shows the component data and flame retardant performance test results of melamine polyphosphate flame retardant PBT prepared in Examples 1-4 and Comparative Examples 1-3.

[0080] Table 2

[0081]

[0082] NC: Unrated.

[0083] As shown in Table 2, in the glass fiber reinforced PBT flame retardant system, the compound system of modified melamine polyphosphate and aluminum diethylphosphinate (ADP) can achieve a UL-94 V-0 rating, while the same ratio of ADP, traditional melamine polyphosphate, and melamine cyanurate and ADP compound systems do not achieve this effect. Therefore, the flame retardant provided by this invention has a significant flame retardant effect and improves the limiting oxygen index of the material.

[0084] Modified melamine polyphosphate (MPP) flame-retardant PP plastic:

[0085] Step 1: Dry polypropylene (PP) plastic granules and flame retardant in an 80℃ vacuum oven for 4 hours. Weigh 100 parts of PP plastic granules and mix them with 18 parts of melamine polyphosphate flame retardant. Then, extrude and granulate the mixture using a twin-screw extruder to obtain PP flame-retardant granules. Place the obtained PP flame-retardant granules in an 80℃ vacuum oven for 4 hours for later use.

[0086] Step 2: Use an injection molding machine to injection mold the completely dried PP flame retardant granules into flame retardant strips (1.6mm), and test the flame retardant performance and mechanical properties after placing them at 25℃ and 50% humidity for 24 hours, as shown in Table 3 below.

[0087] Table 3

[0088]

[0089] As shown in Table 3, the addition of a certain amount of zinc oxide to the piperazine pyrophosphate compound system, along with the embodiments of the present invention and other comparative examples, achieves good flame retardant effects. In particular, the product of Example 1 achieves an LOI of 31.7 and a UL-94 rating of V-0, demonstrating excellent performance. The modified melamine polyphosphate product prepared in the embodiments of the present invention exhibits superior compatibility with plastics, thus demonstrating a significant advantage in mechanical strength.

[0090] Flame-retardant epoxy resin system:

[0091] Weigh 100 parts by weight of epoxy resin, then add the flame retardant prepared in the examples and comparative proportions according to the formula. Mix at 150°C for 3-5 minutes until it reaches a fluid state. While still hot, add the curing agent and other ingredients according to the formula, and stir again at 150°C for 5 minutes. After stirring evenly, place in a vacuum drying oven to remove air bubbles, then pour while hot into a standard mold and cure at 120°C for 2 hours and then at 180°C for 2 hours. After demolding, the flame-retardant epoxy resin material is obtained.

[0092] The component dosage data and flame retardant performance test results for the examples and comparative examples are shown in Table 4 below.

[0093] Table 4

[0094]

[0095] Table 4 shows that the addition of aluminum diethylphosphonate (ADP) alone only improves the UL-94 flame retardancy of bisphenol A epoxy resin to V-1 level. While the traditional melamine polyphosphate and ADP blend can achieve a UL-94 V-0 level, its limiting oxygen index is lower compared to the modified melamine polyphosphate and ADP blend. In summary, the melamine polyphosphate and ADP blend flame retardant system shows a significant advantage over other flame retardant systems.

[0096] pass Figure 2 and Figure 3 The comparison of the infrared spectra shown indicates that the infrared spectra of the modified melamine polyphosphate in Example 1 do not completely match those of commercially available conventional melamine polyphosphate. The infrared spectrum of the modified melamine polyphosphate in Example 1 (e.g.) Figure 3 (As shown) 3403cm is not included. -1 The NC stretching vibration peak appeared, but a 710 cm peak was observed. -1 and 750cm -1 The monosubstituted benzene ring peak and 1010 cm⁻¹ -1 The absorption peak at PC differs from that of melamine polyphosphate, indicating a structural change; in other words, through... Figure 2 and Figure 3In comparison, it can be seen that the modified melamine polyphosphate in this invention has a different structure from the commercially available conventional melamine polyphosphate.

Claims

1. A precipitation-resistant modified melamine polyphosphate, characterized in that... It has the following structural formula (b): ； Among them, M1 and M2 are both Or M1 is M2 is hydrogen; R1 and R2 are selected from hydrogen, hydroxyl, C1-C4 alkyl, and phenyl, respectively; and R1 and R2 cannot both be hydrogen. n≥1, m≥2, and both are integer values.

2. The preparation method of the precipitation-resistant modified melamine polyphosphate as described in claim 1, characterized in that... Includes the following steps: (1) At room temperature, phosphoric acid and formula (a) are mixed in deionized water, and the temperature is raised to above 80°C while stirring. Melamine is added and the reaction is carried out for 1 to 4 hours to obtain the modified intermediate. （a） In formula (a), R1 and R2 are selected from hydrogen, hydroxyl, C1-C4 alkyl, and phenyl, respectively; and R1 and R2 cannot be selected from hydrogen at the same time. (2) The modified intermediate obtained in step (1) is heated to dehydrate, and then heated to 300-350°C to carry out a polycondensation reaction for 4-10 hours to obtain the polycondensate; (3) Crush the condensate obtained in step (2), then add a coupling agent, disperse evenly, heat to 150-250℃, react for 1-3 hours, and obtain the precipitation-resistant modified melamine polyphosphate product.

3. The preparation method of the precipitation-resistant modified melamine polyphosphate as described in claim 2, characterized in that: The amount of coupling agent added is 0.1% to 3% of the mass fraction of the condensate.

4. The preparation method of the precipitation-resistant modified melamine polyphosphate as described in claim 2, characterized in that, The properties of the obtained modified melamine polyphosphate product are as follows: at 80℃, the solubility in water is less than 10 mg / 100 mL; the phosphorus content is greater than 15.8%.

5. The preparation method of the precipitation-resistant modified melamine polyphosphate as described in claim 2, characterized in that, In step (1): the molar ratio of formula (a) to phosphoric acid is (1-20):10; the molar ratio of melamine to phosphoric acid is greater than or equal to 1:

1.

6. The flame-retardant application of the precipitation-resistant modified melamine polyphosphate as described in claim 1 in polymers.

7. The application as described in claim 6, characterized in that: The polymer is at least one of nylon, polyester, polyolefin, polyurethane, thermoplastic elastomer, and epoxy resin.

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