Preparation method and application of PMMA (polymethyl methacrylate) composite microspheres

Abstract

The invention belongs to the technical field of new energy adhesives, and provides a preparation method and application of PMMA (polymethyl methacrylate) composite microspheres, the preparation method of the PMMA composite microspheres comprises the following steps: S1, soaking PMMA microspheres with isopropanol and acetone, centrifuging, and taking precipitate to obtain pretreated PMMA microspheres; s2, adding the modified magnesium hydroxide into isopropanol, performing ultrasonic treatment, sequentially adding acetic acid and polyethylene glycol, performing ultrasonic treatment, and taking an upper-layer suspension to obtain a magnesium hydroxide suspension; and S3, soaking the pretreated PMMA microspheres in a magnesium hydroxide suspension under ultrasonic conditions, centrifuging, washing, repeatedly soaking for 3-5 times, drying, and grinding to obtain the PMMA composite microspheres. The PMMA composite microsphere disclosed by the invention is good in stability, uniform in particle size distribution and good in flame retardance, and can be applied to the field of binders of battery diaphragms.

Description

Technical Field

[0001] The present invention belongs to the technical field of new energy binders, and provides a preparation method and application of PMMA composite microspheres. Background Art

[0002] Polymethyl methacrylate (PMMA) is a polymer with good transparency, chemical stability and high mechanical strength. PMMA composite microspheres are microsphere materials composed of polymethyl methacrylate and other materials. There are various preparation methods for PMMA composite microspheres, including emulsion polymerization, suspension polymerization, dispersion polymerization, seed swelling polymerization, etc. Through these methods, composite microspheres with different structures and functions can be prepared, such as core-shell structure, multi-layer core-shell structure, porous structure, pomegranate-like structure and yolk-shell structure, etc. These composite microspheres can have special properties, such as heat insulation, antibacterial, water resistance, etc.

[0003] Due to its excellent properties, PMMA is widely used in construction, optical fiber manufacturing, sanitary ware, various lamps, etc., and has become an indispensable material in modern society. However, like most thermoplastic polymer materials, it is extremely flammable, with a large heat release rate, high calorific value, fast flame propagation speed and difficult to extinguish during combustion, which greatly limits its application in many occasions. Therefore, in order to fully exert the application potential of polymethyl methacrylate materials in the field of battery separator binders, it is necessary to study the improvement of its flame retardancy.

[0004] Chinese Patent CN104356285 B discloses a synthesis method of PMMA microspheres with low hardness and high crosslinking degree. The dispersant is heated and dissolved, and methyl methacrylate, crosslinking agent, initiator, pore-forming agent and co-dispersant are added and mixed evenly to prepare PMMA microspheres; the PMMA microspheres are heated and stirred in an air bath together with tetraethylenepentamine and xylene, and the product is washed and filtered to obtain aminated PMMA microspheres; epichlorohydrin and triethylamine are stirred and reacted at room temperature, and a small amount of concentrated hydrochloric acid is added during the reaction, and the obtained product is filtered, washed and dried to obtain white crystals; the obtained white crystals and aminated PMMA microspheres are added to an appropriate amount of ethanol, stirred, washed, filtered and dried to obtain the target product. The microspheres prepared by this invention have low hardness and high crosslinking degree, and have certain mechanical strength and wear resistance; however, the PMMA microspheres of this invention do not involve the research on flame retardancy, which limits its application in the field of battery separator binders.

[0005] Therefore, it is urgent to develop a PMMA composite microsphere with good flame retardancy. Summary of the Invention

[0006] Aiming at the existing technical problems, the purpose of the present invention is to provide a preparation method and application of PMMA composite microspheres. The PMMA composite microspheres of the present invention have good stability, uniform particle size distribution, good flame retardancy, and can be used in the field of adhesives.

[0007] In order to achieve the above purpose, the technical scheme adopted by the present invention is as follows:

[0008] The present invention firstly provides a preparation method of PMMA composite microspheres, which comprises the following steps:

[0009] S1. Soak the PMMA microspheres in isopropyl alcohol and acetone, centrifuge, and take the precipitate to obtain pretreated PMMA microspheres for standby;

[0010] S2. Add modified magnesium hydroxide to isopropyl alcohol, ultrasonicate to obtain a suspension, then sequentially add acetic acid and polyethylene glycol, ultrasonicate, and take the upper suspension to obtain a magnesium hydroxide suspension for standby;

[0011] S3. Immerse the pretreated PMMA microspheres obtained in step S1 in the magnesium hydroxide suspension obtained in step S2 under ultrasonication, centrifuge, wash, repeat the immersion 3-5 times, and after drying and grinding, obtain PMMA composite microspheres.

[0012] The reaction mechanism and function of the present invention are as follows:

[0013] 1. The PMMA microspheres of the present invention have uniform size and good stability. On the one hand, the applicant selects a suitable dispersant, polyvinylpyrrolidone, which can effectively prevent the agglomeration phenomenon that occurs during the preparation of the core layer emulsion structure of PMMA microspheres, thereby obtaining a more uniform particle size distribution; further, the applicant selects an emulsifier with a specific mass ratio to control the particle size distribution of PMMA microspheres and improve the stability of PMMA microspheres; at the same time, epoxy resin, as a thermosetting resin, has good adhesive properties and heat resistance, and using it as part of the emulsifier can enhance the mechanical strength and heat resistance of the final PMMA microspheres. On the other hand, the present invention limits the mass ratio of styrene, methyl methacrylate, N-methylacetamide, and 2-hydroxyethyl methacrylate so that the core layer emulsion structure has better mechanical strength and crosslinking degree, which can reduce the swelling performance of PMMA microspheres; further, the applicant limits the mass ratio of 2-hydroxyethyl acrylate, β-(acryloyloxy) propionic acid, ethylene glycol dimethacrylate, and hydroxymethylacrylamide so that the high-temperature resistance of the shell layer emulsion structure is improved, and at the same time, the flame retardancy of PMMA microspheres is effectively improved.

[0014] 2. Magnesium hydroxide itself has good high-temperature resistance and flame retardancy, but its compatibility with polymers is poor.

[0015] The magnesium hydroxide pretreated by coupling agent modification in the present invention can be evenly dispersed in the system, so that the burning rate of PMMA microspheres is slowed down and the flame retardancy is improved. At the same time, the modified magnesium hydroxide endows the PMMA composite microspheres with better mechanical properties. Further, the applicant makes an effective isolation network formed on the surface of the modified magnesium hydroxide by limiting the mass ratio of tricyclodecane dimethanol dimethacrylate, 4-hydroxybutyl acrylate and 2-methylene butyrolactone, so that the prepared PMMA composite microspheres can absorb heat in time, rapidly cool down and isolate air, which is beneficial to improving the flame retardancy of the PMMA composite microspheres.

[0016] In addition, the applicant controls the mass ratio of the modified magnesium hydroxide, acetic acid and polyethylene glycol, so that a new flame retardant layer is formed on the surface of the PMMA microspheres by the magnesium hydroxide suspension, realizing the hindrance effect on the transfer of oxygen and volatile gases and the barrier effect on heat flow, and obtaining excellent flame retardant performance.

[0017] In some embodiments, the preparation method of the PMMA microspheres in step S1 includes the following steps:

[0018] Q1. Add a dispersant, ethanol and pure water into a reaction kettle, stir, and then add a mixture of styrene, methyl methacrylate, N-methylacetamide and 2-hydroxyethyl methacrylate, heat to 60-70 °C, add a first initiator, and stir and react to obtain a core layer emulsion;

[0019] Q2. Mix 2-hydroxyethyl acrylate, β-(acryloyloxy)propionic acid, ethylene glycol dimethacrylate, hydroxymethylacrylamide and an emulsifier, and stir well to obtain a shell layer emulsion; when the temperature of the reaction kettle rises to 75-90 °C, add the core layer emulsion obtained in step Q1 and a second initiator, and carry out a polymerization reaction to obtain PMMA microspheres.

[0020] In some embodiments, the dispersant in step Q1 is polyvinylpyrrolidone.

[0021] Preferably, the dosage of the dispersant in step Q1 is 3-4% of the total mass of styrene, methyl methacrylate, N-methylacetamide and 2-hydroxyethyl methacrylate.

[0022] In some embodiments, the emulsifier in step Q2 is a composition of sodium dodecyl sulfonate and epoxy resin.

[0023] Preferably, the mass ratio of sodium dodecyl sulfonate to epoxy resin is (1.5-2.5):1.

[0024] Preferably, the dosage of the emulsifier in step Q2 is 3-5% of the total mass of 2-hydroxyethyl acrylate, β-(acryloyloxy)propionic acid, ethylene glycol dimethacrylate and hydroxymethylacrylamide.

[0025] In some embodiments, the mass ratio of styrene, methyl methacrylate, N-methylacetamide, and 2-hydroxyethyl methacrylate described in step Q1 is 1:(0.6 - 0.9):(0.3 - 0.6):(0.2 - 0.4).

[0026] In some embodiments, the mass ratio of 2-hydroxyethyl acrylate, β-(acryloyloxy)propionic acid, ethylene glycol dimethacrylate, and hydroxymethylacrylamide described in step Q2 is 1:(0.15 - 0.35):(0.45 - 0.75):(0.1 - 0.2).

[0027] Preferably, the first initiator described in step Q1 is azobisisobutyronitrile, and the second initiator described in step Q2 is sodium persulfate.

[0028] In some embodiments, the mass ratio of the modified magnesium hydroxide, acetic acid, and polyethylene glycol described in step S2 is 1:(0.6 - 1.2):(0.1 - 0.3).

[0029] Preferably, the mass ratio of the modified magnesium hydroxide, acetic acid, and polyethylene glycol described in step S2 is 1:0.9:0.2.

[0030] In some embodiments, the preparation method of the modified magnesium hydroxide described in step S2 comprises the following steps:

[0031] T1. Add magnesium hydroxide, deionized water, and absolute ethanol to the reaction kettle in sequence, dropwise add the coupling agent, heat to 45 - 55 °C, stir and react for 10 - 12 h, filter, wash, dry, and grind to obtain an intermediate;

[0032] T2. Add the intermediate obtained in step T1, tricyclodecane dimethanol dimethacrylate, 4-hydroxybutyl acrylate, 2-methylene butyrolactone, and azobisisobutyronitrile to the reaction kettle, heat to 70 - 85 °C, react for 3 - 4 h, filter, wash, and dry to obtain the modified magnesium hydroxide.

[0033] In some embodiments, the mass ratio of tricyclodecane dimethanol dimethacrylate, 4-hydroxybutyl acrylate, and 2-methylene butyrolactone described in step T2 is (3.5 - 5):1:(0.3 - 0.4).

[0034] Preferably, the mass ratio of the coupling agent to magnesium hydroxide in step (3) is 1:(15 - 18).

[0035] In some embodiments, the soaking time in step S3 is 3 - 8 min; the centrifugation speed is 5000 - 8000 r / min, and the centrifugation time is 10 - 15 min.

[0036] Second, the present invention provides an application of the PMMA composite microspheres obtained by the preparation method in the field of binders for battery separators.

[0037] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0038] 1. The PMMA composite microspheres of the present invention have good stability, uniform particle size distribution, good flame retardancy, can be used in the field of binders, and have high market value.

[0039] 2. The present invention selects specific dispersants and emulsifiers to make the particle size distribution of PMMA microspheres uniform, and further selects monomers with specific parts by weight to make the PMMA microspheres have appropriate crosslinking degree, and have better high-temperature resistance and mechanical strength.

[0040] 3. The modified magnesium hydroxide of the present invention has good dispersibility, making the PMMA composite microspheres have good mechanical properties, high-temperature resistance and flame retardancy. Specific Embodiments

[0041] The following will describe the present invention in conjunction with specific implementation examples. It should be noted that the following examples are examples of the present invention, only used to illustrate the present invention, rather than to limit the present invention. Without departing from the gist or scope of the present invention, other combinations and various improvements within the concept of the present invention can be made.

[0042] According to the raw material ratios and production methods specified in the following examples and comparative examples, various PMMA composite microspheres are produced.

[0043] For the convenience of those skilled in the art to implement the present invention, the manufacturers of some raw materials in the examples and comparative examples are described as follows:

[0044] Polyethylene glycol: purchased from Shandong Baihua Chemical Co., Ltd., model PEG-1000;

[0045] Polyvinylpyrrolidone: purchased from Huzhou Shenhua High Polymer Materials Co., Ltd., model K30;

[0046] Epoxy resin: purchased from Zhengzhou Wubao Tong Trading Co., Ltd., brand CYDW-100;

[0047] PMMA microspheres: purchased from Dongguan Hongyu Plastic Co., Ltd., brand DNT-3;

[0048] For other raw materials, without special instructions, they can all be purchased from the market.

[0049] Preparation Example 1

[0050] The preparation method of modified magnesium hydroxide A includes the following steps:

[0051] T1. Add 60 g of magnesium hydroxide, 90 g of water, and 90 g of ethanol to the reaction kettle in sequence. Dropwise add 3.6 g of vinyltrimethoxysilane, heat to 50 °C, stir and react for 12 h, filter, wash with ethanol three times, dry to constant weight at 80 °C, and grind to an average particle size of 0.5 μm to obtain an intermediate;

[0052] T2. Add 36 g of the intermediate obtained in step T1, 25.5 g of tricyclodecane dimethanol dimethacrylate, 6 g of 4-hydroxybutyl acrylate, 2.1 g of 2-methylene butyrolactone, and 0.3 g of azobisisobutyronitrile to the reaction kettle, heat to 75 °C, react for 4 h, filter, wash with deionized water three times, and dry at 105 °C for 10 h to obtain modified magnesium hydroxide A.

[0053] Preparation Example 2

[0054] The preparation method of modified magnesium hydroxide B is the same as that of Preparation Example 1, except that the addition amount of tricyclodecane dimethanol dimethacrylate in step T2 is 19.8 g.

[0055] Preparation Example 3

[0056] The preparation method of modified magnesium hydroxide C is the same as that of Preparation Example 1, except that the addition amount of 2-methylene butyrolactone in step T2 is 1.62 g.

[0057] Preparation Example 4

[0058] The preparation method of modified magnesium hydroxide D includes the following steps:

[0059] Add 60 g of magnesium hydroxide, 90 g of water, and 90 g of ethanol to the reaction kettle in sequence. Dropwise add 3.6 g of vinyltrimethoxysilane, heat to 50 °C, stir and react for 12 h, filter, wash with ethanol three times, dry to constant weight at 80 °C, and grind to obtain modified magnesium hydroxide D.

[0060] Preparation Example 5

[0061] The preparation method of PMMA microsphere A includes the following steps:

[0062] Q1. Add 1.8 g of polyvinylpyrrolidone, 150 ml of ethanol, and 50 ml of pure water to the reaction kettle, stir for 15 min, then add a mixture of 20 g of styrene, 15 g of methyl methacrylate, 9 g of N-methylacetamide, and 6 g of 2-hydroxyethyl methacrylate, heat to 65 °C, stir for 30 min, add 0.2 g of azobisisobutyronitrile, and stir and react for 1.5 h to obtain a core layer emulsion;

[0063] Q2. Under the protection of nitrogen, 6 g of 2-hydroxyethyl acrylate, 1.5 g of β-(acryloyloxy)propionic acid, 3.6 g of ethylene glycol dimethacrylate, 0.9 g of hydroxymethylacrylamide, 0.32 g of sodium dodecylsulfonate, and 0.16 g of epoxy resin were mixed and stirred thoroughly to obtain a shell layer emulsion; when the temperature of the reaction kettle rose to 80 °C, a mixed solution of 38 g of the core layer emulsion obtained in step Q1 and 0.4 g of sodium persulfate was added, and a polymerization reaction was carried out for 24 h to obtain PMMA microspheres A.

[0064] Preparation Example 6

[0065] The preparation method of PMMA microspheres B is the same as that of Preparation Example 5, except that 0.48 g of sodium dodecylsulfonate was used to replace 0.32 g of sodium dodecylsulfonate and 0.16 g of epoxy resin.

[0066] Preparation Example 7

[0067] The preparation method of PMMA microspheres C is the same as that of Preparation Example 5, except that the addition amount of methyl methacrylate is 10 g.

[0068] Preparation Example 8

[0069] The preparation method of PMMA microspheres D is the same as that of Preparation Example 5, except that the addition amount of ethylene glycol dimethacrylate is 2.1 g.

[0070] Example 1

[0071] A preparation method of PMMA composite microspheres comprises the following steps:

[0072] S1. The PMMA microspheres A were immersed in a mixed solution of isopropanol and acetone with a volume ratio of 2:1 for 2 min, centrifuged at 6000 r / min for 15 min, and the precipitate was taken to obtain pretreated PMMA microspheres for standby;

[0073] S2. 8 g of modified magnesium hydroxide A was added to 500 ml of isopropanol, ultrasonicated at a power of 400 W for 4 h, then 7.2 g of acetic acid and 1.6 g of PEG-1000 were added in sequence, and ultrasonicated at a power of 400 W for 4 h. The upper suspension was taken to obtain a magnesium hydroxide suspension for standby;

[0074] S3. The pretreated PMMA microspheres obtained in step S1 were ultrasonically immersed in the magnesium hydroxide suspension obtained in step S2 for 6 min, centrifuged at 6000 r / min for 15 min, washed twice with deionized water, the immersion process was repeated 4 times, dried at 60 °C to constant weight, and ground into powder to obtain PMMA composite microspheres.

[0075] Example 2

[0076] A preparation method of PMMA composite microspheres comprises the following steps:

[0077] S1. Immerse PMMA microspheres A in a mixed solution of isopropanol and acetone with a volume ratio of 2:1 for 2 min, centrifuge at 6000 r / min for 15 min, take the precipitate to obtain pretreated PMMA microspheres, and set aside;

[0078] S2. Add 8 g of modified magnesium hydroxide A to 500 ml of isopropanol, ultrasonicate at a power of 400 W for 4 h, then sequentially add 4.8 g of acetic acid and 0.8 g of PEG-1000, ultrasonicate at a power of 400 W for 4 h, take the upper suspension to obtain a magnesium hydroxide suspension, and set aside;

[0079] S3. Immerse the pretreated PMMA microspheres obtained in step S1 in the magnesium hydroxide suspension obtained in step S2 under ultrasonication at a power of 400 W for 3 min, centrifuge at 8000 r / min for 10 min, wash twice with deionized water, repeat the immersion process 4 times, dry at 60 °C to constant weight, and grind into powder to obtain PMMA composite microspheres.

[0080] Example 3

[0081] A method for preparing PMMA composite microspheres comprises the following steps:

[0082] S1. Immerse PMMA microspheres A in a mixed solution of isopropanol and acetone with a volume ratio of 2:1 for 2 min, centrifuge at 6000 r / min for 15 min, take the precipitate to obtain pretreated PMMA microspheres, and set aside;

[0083] S2. Add 8 g of modified magnesium hydroxide A to 500 ml of isopropanol, ultrasonicate at a power of 400 W for 4 h, then sequentially add 9.6 g of acetic acid and 2.4 g of PEG-1000, ultrasonicate at a power of 400 W for 4 h, take the upper suspension to obtain a magnesium hydroxide suspension, and set aside;

[0084] S3. Immerse the pretreated PMMA microspheres obtained in step S1 in the magnesium hydroxide suspension obtained in step S2 under ultrasonication at a power of 400 W for 8 min, centrifuge at 5000 r / min for 15 min, wash twice with deionized water, repeat the immersion process 4 times, dry at 60 °C to constant weight, and grind into powder to obtain PMMA composite microspheres.

[0085] Example 4

[0086] A method for preparing PMMA composite microspheres, the specific implementation manner is the same as that of Example 1, the difference is that an equal amount of modified magnesium hydroxide B is used to replace modified magnesium hydroxide A.

[0087] Example 5

[0088] A preparation method of PMMA composite microspheres, the specific implementation manner is the same as that of Example 1, except that an equal amount of modified magnesium hydroxide C is used to replace modified magnesium hydroxide A.

[0089] Example 6

[0090] A preparation method of PMMA composite microspheres, the specific implementation manner is the same as that of Example 1, except that an equal amount of modified magnesium hydroxide D is used to replace modified magnesium hydroxide A.

[0091] Example 7

[0092] A preparation method of PMMA composite microspheres, the specific implementation manner is the same as that of Example 1, except that an equal amount of PMMA microspheres B is used to replace PMMA microspheres A.

[0093] Example 8

[0094] A preparation method of PMMA composite microspheres, the specific implementation manner is the same as that of Example 1, except that an equal amount of PMMA microspheres C is used to replace PMMA microspheres A.

[0095] Example 9

[0096] A preparation method of PMMA composite microspheres, the specific implementation manner is the same as that of Example 1, except that an equal amount of PMMA microspheres D is used to replace PMMA microspheres A.

[0097] Comparative Example 1

[0098] A preparation method of PMMA composite microspheres and its preparation method, the specific implementation manner is the same as that of Example 1, except that an equal amount of commercially available magnesium hydroxide is used to replace modified magnesium hydroxide A.

[0099] Comparative Example 2

[0100] A preparation method of PMMA composite microspheres and its preparation method, the specific implementation manner is the same as that of Example 1, except that an equal amount of commercially available PMMA microspheres is used to replace PMMA microspheres A.

[0101] Effect evaluation:

[0102] The PMMA composite microspheres prepared in the above Examples 1 - 9 and Comparative Examples 1 - 2 were tested and analyzed, and the specific results are shown in Table 1.

[0103] Performance test:

[0104] (1) Flame retardant grade: The flame retardant performance was tested according to GB / T 2408 - 2021 "Test Methods for Flammability of Plastics - Horizontal and Vertical Methods".

[0105] (2) Heat resistance test: Test the initial median particle size of the PMMA composite microspheres, then place the PMMA composite microspheres in an environment of 160 °C for 4 h. After taking them out, retest the median particle size, and calculate the thermal shrinkage rate according to the following formula:

[0106] Thermal shrinkage rate (%) = (M 1 - M 2 ) / M 1 × 100%;

[0107] Wherein, M 1 is the initial median particle size of the PMMA composite microspheres, and M 2 is the median particle size of the PMMA composite microspheres after thermal shrinkage;

[0108] Table 1

[0109] Serial number Flame retardancy Heat shrinkage rate / % Example 1 V0 0 Example 2 V0 0 Example 3 V0 0 Example 4 V0 0.3 Example 5 V0 0.2 Example 6 V1 0.7 Example 7 V0 0.4 Example 8 V0 1.1 Example 9 V0 0.8 Comparative example 1 V2 1.6 Comparative example 2 V1 3.2

[0110] From the results in Table 1, it can be seen that the PMMA composite microspheres prepared in Examples 1-3 have good flame retardancy and small thermal shrinkage, that is, good high-temperature stability.

[0111] Compared with Example 1, in the preparation of modified magnesium hydroxide in Examples 4-6 and Comparative Example 1, in Examples 4-5, the mass ratios of tricyclodecane dimethanol dimethacrylate, 4-hydroxybutyl acrylate and 2-methylene butyrolactone were changed, resulting in weakened heat resistance. In Example 6, there was no step T2, resulting in weakened heat resistance and poor flame retardancy, which would all affect the flame retardancy and high-temperature stability; in Comparative Example 1, an equal amount of commercially available magnesium hydroxide was used to replace modified magnesium hydroxide A, resulting in poor dispersion stability, which would all affect the flame retardancy and high-temperature stability.

[0112] Compared with Example 1, in the preparation of PMMA microspheres in Examples 7-9 and Comparative Example 2, in Example 7, the type of emulsifier was changed, resulting in poor heat stability. In Example 8, the mass ratios of styrene, methyl methacrylate, N-methylacetamide and 2-hydroxyethyl methacrylate were changed. In Example 9, the mass ratios of 2-hydroxyethyl acrylate, β-(acryloyloxy)propionic acid, ethylene glycol dimethacrylate and hydroxymethylacrylamide were changed, all of which would result in uneven particle size distribution of the PMMA microspheres, and thus would all result in a decrease in high-temperature stability; in Comparative Example 2, an equal amount of commercially available PMMA microspheres was used to replace PMMA microsphere A, resulting in poor dispersion compatibility, which would all affect the flame retardancy and high-temperature stability.

[0113] As described above, it is only the preferred embodiment of the present invention, and it does not impose any form of limitation on this application. Although this application is disclosed as the preferred embodiment above, it is not intended to limit this application. Any person skilled in the relevant art, without departing from the scope of the technical solution of this application, making some changes or modifications using the technical content disclosed above is equivalent to equivalent implementation cases. However, as long as it does not depart from the content of the technical solution of the present invention, any simple modification, equivalent change, and modification made to the above embodiments based on the technical essence of the present invention still fall within the scope of the technical solution.

Claims

1. A method for preparing PMMA composite microspheres, characterized in that: The following steps are included: S1. Soak the PMMA microspheres with isopropanol and acetone, centrifuge, and take the precipitate to obtain pretreated PMMA microspheres for later use; S2. The modified magnesium hydroxide was added to isopropanol, ultrasonicated, and then acetic acid and polyethylene glycol were added successively, ultrasonicated, and the upper suspension was taken to obtain a magnesium hydroxide suspension for later use; S3. The pretreated PMMA microspheres obtained in step S1 are immersed in the magnesium hydroxide suspension obtained in step S2 under ultrasound, centrifuged, washed, and immersed 3-5 times repeatedly, dried, and ground to obtain PMMA composite microspheres.

2. The method for preparing PMMA composite microspheres according to claim 1, characterized in that: The method for preparing PMMA microspheres in step S1 comprises the following steps: Q1. Add dispersant, ethanol and pure water into a reactor, stir, then add a mixture of styrene, methyl methacrylate, N-methylacetamide and hydroxyethyl methacrylate, heat to 60-70°C, add the first initiator, stir and react to obtain a core layer emulsion; Q2. Mix 2-hydroxyethyl acrylate, β-(acryloyloxy) propionic acid, ethylene glycol dimethacrylate, hydroxymethyl acrylamide and an emulsifier, and stir them thoroughly to obtain a shell emulsion; when the temperature of the reactor is raised to 75-90°C, add the core emulsion obtained in step Q1 and the second initiator, and perform a polymerization reaction to obtain PMMA microspheres.

3. The method for preparing PMMA composite microspheres according to claim 2, characterized in that: The dispersant in step Q1 is polyvinyl pyrrolidone.

4. The method for preparing PMMA composite microspheres according to claim 2, characterized in that: The emulsifier in step Q2 is a composition of sodium dodecyl sulfate and epoxy resin.

5. The method for preparing PMMA composite microspheres according to claim 2, characterized in that: In step Q1, the mass ratio of styrene, methyl methacrylate, N-methylacetamide and hydroxyethyl methacrylate is 1:(0.6-0.9):(0.3-0.6):(0.2-0.4).

6. The method for preparing PMMA composite microspheres according to claim 2, characterized in that: In step Q2, the mass ratio of 2-hydroxyethyl acrylate, β-(acryloyloxy)propionic acid, ethylene glycol dimethacrylate, and hydroxymethyl acrylamide is 1:(0.15-0.35):(0.45-0.75):(0.1-0.2).

7. The method for preparing PMMA composite microspheres according to claim 1, characterized in that: The mass ratio of the modified magnesium hydroxide, acetic acid and polyethylene glycol in step S2 is 1:(0.6-1.2):(0.1-0.3).

8. The method for preparing PMMA composite microspheres according to claim 1, characterized in that: The preparation method of the modified magnesium hydroxide described in step S2 comprises the following steps: T1. Magnesium hydroxide, deionized water and anhydrous ethanol are added to the reaction kettle in sequence, a coupling agent is added dropwise, the reaction is heated to 45-55°C, stirred for 10-12h, filtered, washed, dried and ground to obtain an intermediate; T2. Add the intermediate obtained in step T1, tricyclodecane dimethanol dimethacrylate, 4-hydroxybutyl acrylate, 2-methylbutyrolactone and azobisisobutyronitrile to a reaction kettle, heat to 70-85°C, react for 3-4h, filter, wash and dry to obtain modified magnesium hydroxide.

9. The method for preparing PMMA composite microspheres according to claim 8, characterized in that: The mass ratio of tricyclodecane dimethanol dimethacrylate, 4-hydroxybutyl acrylate and 2-methylbutyrolactone in step T2 is (3.5-5):1:(0.3-0.4).

10. An application of PMMA composite microspheres obtained by the preparation method according to any one of claims 1 to 9, characterized in that: Used in the field of adhesives for battery separators.