High-dispersity flame retardant and preparation method thereof

Abstract

The invention discloses a high-dispersity flame retardant and a preparation method thereof, and the preparation method comprises the following steps: adding an organic solvent dissolved with oleic acid into an aqueous solution of magnesium hydroxide nanoparticles, carrying out a heating reaction, and after the reaction is finished, carrying out centrifugation, washing, vacuum drying and grinding to obtain modified magnesium hydroxide nanoparticles; and dispersing the modified magnesium hydroxide nanoparticles in methyl methacrylate to prepare a suspension, adding the suspension into an organic solvent added with a dispersant, carrying out primary heating, adding an initiator, carrying out secondary heating reaction, and carrying out suction filtration, washing and vacuum drying after the reaction is finished to obtain the magnesium hydroxide / polymethacrylate composite flame retardant. The flame retardant has good dispersibility in a high polymer material matrix, and can improve the flame retardance and tensile property of the material.

Description

Technical Field

[0001] This invention relates to a highly dispersible flame retardant and its preparation method, belonging to the field of flame retardant technology. Background Technology

[0002] Magnesium hydroxide is an inorganic, halogen-free flame retardant often used as a filler in polymer materials to reduce fire hazards. When a fire occurs, magnesium hydroxide decomposes upon heating, absorbing a large amount of heat during the decomposition process to lower the ambient temperature. Simultaneously, the decomposition produces highly stable and flame-retardant magnesium oxide, which coats the surface of the material, preventing further contact between the material and air, thereby reducing the material's combustion rate. Furthermore, magnesium hydroxide flame retardants do not contain halogens and do not produce harmful gases during the flame-retardant process. They offer high safety performance, good smoke suppression, and are considered a green and environmentally friendly flame retardant, making them highly favored in the selection of flame retardants for fire safety materials.

[0003] The hydrophilic hydroxyl groups (-OH) on the surface of magnesium hydroxide give it a hydrophilic-oleophobic property, making it difficult to disperse uniformly in organic polymers. Therefore, using untreated magnesium hydroxide as a filler in polymer materials will negatively impact the processing and mechanical properties of the polymer product. To improve its dispersibility in polymers, surface modification of magnesium hydroxide is necessary to alter its natural hydrophilic-oleophobic surface properties and enhance its compatibility with polymers.

[0004] Currently, the main methods for flame-retardant modification of magnesium hydroxide are physical or chemical methods to modify its surface, changing it from hydrophilic to hydrophobic, thereby improving the compatibility between the flame retardant and the polymer matrix. For example, the common modifier silane coupling agent (KH550) contains flame-retardant elements, and the Si-OH in KH550 can bond with magnesium hydroxide, forming non-polar groups on the magnesium hydroxide surface, thus improving its hydrophobicity. However, the modified magnesium hydroxide exhibits poor dispersibility in polymer materials. Therefore, there is an urgent need for a flame retardant with excellent dispersibility in polymer materials. Summary of the Invention

[0005] The purpose of this invention is to provide a highly dispersible flame retardant and its preparation method. This polymerization inhibitor is prepared by modifying magnesium hydroxide with oleic acid and then copolymerizing it with methyl methacrylate, and it has good dispersibility in a polymer matrix.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A method for preparing a highly dispersible composite flame retardant includes the following steps:

[0008] S1. Add an organic solvent containing oleic acid to an aqueous solution of magnesium hydroxide nanoparticles, heat to react, and after the reaction is complete, centrifuge, wash, vacuum dry and grind to obtain modified magnesium hydroxide nanoparticles.

[0009] S2. Modified magnesium hydroxide nanoparticles are dispersed in methyl methacrylate to obtain a suspension. The suspension is then added to an organic solvent containing a dispersant. After a first heating, an initiator is added, followed by a second heating reaction. After the reaction is completed, the mixture is filtered, washed, and vacuum dried to obtain a magnesium hydroxide / polymethyl methacrylate composite flame retardant.

[0010] Preferably, in steps S1 and S2, the organic solvent is anhydrous ethanol.

[0011] Preferably, in step S1, the oleic acid content in the organic solvent is 3-8%;

[0012] The concentration of magnesium hydroxide nanoparticles in the aqueous solution is 0.1-0.5 g / ml;

[0013] Furthermore, the mass of oleic acid is 0.5-2% of the mass of magnesium hydroxide nanoparticles.

[0014] Preferably, in step S1, the heating reaction conditions are: under stirring, the reaction is carried out at 75-85°C for 1-1.5 hours;

[0015] The conditions for vacuum drying are: drying at 65-75℃ for 1-2 hours.

[0016] Preferably, in step S2, the mass ratio of modified magnesium hydroxide nanoparticles to methyl methacrylate in the suspension is 1:(1.5-3).

[0017] Preferably, in step S2, the dispersant is PVP;

[0018] Furthermore, the dispersant content in the organic solvent is 0.7-1.2%.

[0019] Preferably, in step S2, the mass ratio of the suspension to the organic solvent is 1:(1-2).

[0020] Preferably, in step S2, the initiator is azobisisobutyronitrile, and the amount of initiator added is 0.1-0.5% of the mass of the suspension.

[0021] Preferably, in step S2, the conditions for the first heating are: heating to 55-65°C under stirring conditions;

[0022] The conditions for the secondary heating reaction are: under a nitrogen atmosphere and with stirring, the temperature is raised to 75-85℃ and the reaction is carried out for 7-10 hours;

[0023] Vacuum drying conditions: -50℃ to -35℃, 20-25h.

[0024] A method for preparing a highly dispersible composite flame retardant is provided, wherein the flame retardant is prepared by any of the methods described above.

[0025] The beneficial effects of this invention are as follows:

[0026] The reaction between the -COOH group of oleic acid and the -OH group on the surface of magnesium hydroxide allows oleic acid to be grafted onto the magnesium hydroxide surface, while simultaneously introducing C=C unsaturated double bonds. Then, by utilizing the C=C unsaturated double bonds in the oleic acid that prevent grafting, methyl methacrylate is copolymerized to prepare a composite flame retardant with magnesium hydroxide ions as the active center. The long hydrocarbon chains after copolymerization have a certain retardant effect, which reduces the surface energy of magnesium hydroxide nanoparticles, weakens the mutual attraction between nanoparticles, prevents the aggregation of nanoparticles, and improves dispersibility. Attached Figure Description

[0027] Figure 1 Scanning electron microscope (SEM) images of (a) unmodified magnesium hydroxide and (b) modified copolymerized magnesium hydroxide. Detailed Implementation

[0028] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0029] Example 1

[0030] This embodiment provides a method for preparing a highly dispersible composite flame retardant, comprising the following steps:

[0031] 5g of dried magnesium hydroxide nanoparticles were ultrasonically dispersed in water to prepare an aqueous solution with a magnesium hydroxide nanoparticle concentration of 0.5g / ml. The solution was then heated to 75℃ at 1000rpm. Anhydrous ethanol containing 0.1g of oleic acid (5% oleic acid content) was added to the aqueous solution, and stirring was continued for 30min. After cooling to room temperature, the solution was centrifuged, washed with anhydrous ethanol, and then vacuum dried at 70℃ for 1h. The resulting product was then ground to obtain modified magnesium hydroxide nanoparticles.

[0032] 2g of modified magnesium hydroxide nanoparticles were dispersed in 6g of methyl methacrylate to prepare a suspension. The suspension was then added to 10g of anhydrous ethanol containing 1% PVP. After ultrasonic dispersion, the mixture was stirred at 500rpm and 60℃ for 30min. Then, under a nitrogen atmosphere, 0.04g of azobisisobutyronitrile was added to the above system, and the temperature was raised to 80℃ for 7h. After the reaction was completed, the mixture was cooled to room temperature, filtered, washed with water and alcohol, and then vacuum dried at -45℃ for 22h to obtain a magnesium hydroxide / polymethyl methacrylate composite flame retardant, denoted as flame retardant 1.

[0033] Figure 1Scanning electron microscope (SEM) images of unmodified magnesium hydroxide (left) and modified copolymerized magnesium hydroxide (right), from... Figure 1 As can be seen, unmodified magnesium hydroxide exhibits significant agglomeration, while the modified copolymerized magnesium hydroxide demonstrates good dispersibility. This indicates that copolymerization of oleic acid-modified magnesium hydroxide with methacrylate effectively improves the dispersibility of nano-magnesium hydroxide particles.

[0034] Comparative Example 1

[0035] The difference from Example 1 is that oleic acid was not used to modify the magnesium hydroxide nanoparticles.

[0036] Specifically, 2g of magnesium hydroxide nanoparticles were dispersed in 6g of methyl methacrylate to prepare a suspension. The suspension was then added to 10g of anhydrous ethanol containing 1% PVP. After ultrasonic dispersion, the mixture was stirred at 500rpm and 60℃ for 30min. Then, under a nitrogen atmosphere, 0.04g of azobisisobutyronitrile was added to the above system, and the temperature was raised to 80℃ for 7h. After the reaction was completed, the mixture was cooled to room temperature, filtered, washed with water and alcohol, and then vacuum dried at -45℃ for 22h to obtain flame retardant 2.

[0037] Comparative Example 2

[0038] The difference from Example 1 is that the modified magnesium hydroxide nanoparticles were not copolymerized with methyl methacrylate after obtaining them.

[0039] Specifically, 5g of dried magnesium hydroxide nanoparticles were added to water and ultrasonically dispersed to prepare an aqueous solution with a magnesium hydroxide nanoparticle concentration of 0.5g / ml. The solution was then heated to 75℃ at 1000rpm. Next, anhydrous ethanol containing 0.1g of oleic acid (5% oleic acid content) was added to the aqueous solution, and stirring was continued for 30min. After the reaction, the solution was cooled to room temperature, centrifuged, washed with anhydrous ethanol, and then vacuum dried at 70℃ for 1h. The resulting modified magnesium hydroxide nanoparticles were obtained by grinding and designated as flame retardant 3.

[0040] Flame retardants 1, 2, and 3 obtained in Example 1 and Comparative Examples 1-2 were melt-blended with polypropylene, pressed, and cured to obtain polypropylene composite flame retardant materials, which were respectively denoted as flame retardant material 1, flame retardant material 2, and flame retardant material 3; and the addition ratio of flame retardants 1, 2, and 3 in the above flame retardant materials was 30wt%.

[0041] The performance of the flame-retardant materials 1, 2, and 3 obtained above was tested, and the results are as follows:

[0042] sample Oxygen Index Tensile strength Flame retardant material 1 32.5％ 35.2MPa Flame retardant material 2 25.7％ 25.3MPa Flame retardant material 3 23.2％ 27.2MPa

[0043] As can be seen from the table above, the oxygen index and tensile strength of the flame-retardant material are significantly improved after the addition of magnesium hydroxide / polymethyl methacrylate composite flame retardant. This is because the modified magnesium hydroxide nanoparticles, after copolymerization with methyl methacrylate, form hydrocarbon long chains with a certain degree of retardant effect, which reduces the surface energy of the magnesium hydroxide nanoparticles, thereby weakening the mutual attraction between nanoparticles, preventing the aggregation of nanoparticles, and improving the dispersibility in polypropylene. Therefore, it can improve the flame-retardant performance and tensile strength of the flame-retardant material.

[0044] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a highly dispersible composite flame retardant, characterized in that, Includes the following steps: S1. Add an organic solvent containing oleic acid to an aqueous solution of magnesium hydroxide nanoparticles, heat to react, and after the reaction is complete, centrifuge, wash, vacuum dry and grind to obtain modified magnesium hydroxide nanoparticles. S2. Modified magnesium hydroxide nanoparticles are dispersed in methyl methacrylate to obtain a suspension. The suspension is then added to an organic solvent containing a dispersant. After a first heating, an initiator is added, followed by a second heating reaction. After the reaction is completed, the mixture is filtered, washed, and vacuum dried to obtain a magnesium hydroxide / polymethyl methacrylate composite flame retardant.

2. The method for preparing the highly dispersible composite flame retardant according to claim 1, characterized in that, In steps S1 and S2, the organic solvent is anhydrous ethanol.

3. The method for preparing the highly dispersible composite flame retardant according to claim 1, characterized in that, In step S1, the oleic acid content in the organic solvent is 3-8%. The concentration of magnesium hydroxide nanoparticles in the aqueous solution is 0.1-0.5 g / ml; Furthermore, the mass of oleic acid is 0.5-2% of the mass of magnesium hydroxide nanoparticles.

4. The method for preparing the highly dispersible composite flame retardant according to claim 1, characterized in that, In step S1, the heating reaction conditions are: under stirring, the reaction is carried out at 75-85℃ for 1-1.5 hours; The conditions for vacuum drying are: drying at 65-75℃ for 1-2 hours.

5. The method for preparing the highly dispersible composite flame retardant according to claim 1, characterized in that, In step S2, the mass ratio of modified magnesium hydroxide nanoparticles to methyl methacrylate in the suspension is 1:(1.5-3).

6. The method for preparing the highly dispersible composite flame retardant according to claim 5, characterized in that, In step S2, the dispersant is PVP; Furthermore, the dispersant content in the organic solvent is 0.7-1.2%.

7. The method for preparing the highly dispersible composite flame retardant according to claim 6, characterized in that, In step S2, the mass ratio of the suspension to the organic solvent is 1:(1-2).

8. The method for preparing the highly dispersible composite flame retardant according to claim 7, characterized in that, In step S2, the initiator is azobisisobutyronitrile, and the amount of initiator added is 0.1-0.5% of the mass of the suspension.

9. The method for preparing the highly dispersible composite flame retardant according to claim 1, characterized in that, In step S2, the conditions for the first heating are: heating to 55-65℃ under stirring. The conditions for the secondary heating reaction are: under a nitrogen atmosphere and with stirring, the temperature is raised to 75-85℃ and the reaction is carried out for 7-10 hours; Vacuum drying conditions: -50℃ to -35℃, 20-25h.

10. A method for preparing a highly dispersible composite flame retardant, characterized in that, It is prepared by the method described in any one of claims 1-9.

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