Expandable microsphere and preparation method thereof

Abstract

The preparation method of the expandable microspheres comprises the following steps: firstly, dissolving a certain amount of a calcium source in a certain amount of deionized water, dissolving a certain amount of a phosphorus source in a certain amount of deionized water, dropwise adding a phosphoric acid solution into calcium hydroxide at a proper speed at a proper rotating speed, and stirring to obtain a mixed solution; a hydroxyl calcium phosphate solution is obtained; adding a dispersing aid into hydroxyl calcium phosphate to obtain a water phase; mixing a reaction monomer, an initiator, a cross-linking agent and a foaming agent to obtain an oil phase; adding the oil phase into the water phase, and stirring at a high speed to obtain an emulsion; stirring and reacting for 10 to 16 hours at the reaction temperature; and filtering and drying to obtain expandable microsphere powder. According to the preparation method, agglomeration in the synthesis process of the expandable microspheres can be effectively prevented, the usage amount of the organic dispersing agent and the dispersing auxiliary can be reduced, and the prepared expandable microspheres are uniform in particle size distribution and excellent in expansion performance.

Description

Technical Field

[0001] The present invention relates to the field of functional materials technology, and specifically to a method for preparing expandable microspheres with hydroxy calcium phosphate (HAP) as a dispersed phase, which is applicable to the fields of biomedical materials, smart packaging, thermal insulation materials, etc. Background Art

[0002] Expandable microspheres are core-shell microspheres composed of a thermoplastic polymer shell encapsulating a volatile expansion agent, such as a low-boiling-point hydrocarbon organic compound. Their particle size ranges from 5 to 75 microns. When heated, the thermoplastic shell softens, and the low-boiling-point organic compound within the microsphere vaporizes, increasing the internal pressure. The gas expands, expanding the shell. After expansion, the volume of the microspheres can increase by tens or even hundreds of times. Expandable microspheres have been successfully used as both lightweight and heavy fillers in the foam industry, coating printing, ultra-light clay, printing pastes, and CMP polishing pads.

[0003] In the preparation of expandable microspheres, dispersants play a decisive role in the uniformity of microsphere particle size, the stability of the polymerization process, and the ductility of the expandable behavior. In the currently disclosed patents, dispersants used for the preparation of expandable microspheres can be divided into two categories: high molecular organic polymers and inorganic dispersants. Among them, high molecular organic polymers include polyvinyl pyrrolidone, polyethylene glycol, lignin, etc., while inorganic dispersants include silicon dioxide and magnesium hydroxide, etc. Patent document with publication number CN119708601 discloses the preparation of expandable microspheres using a dispersed aqueous phase composed of polyvinyl pyrrolidone and colloidal silica. Patent document with publication number 118240262 discloses the preparation of expandable microspheres with short temperature range and fast foaming using water-soluble polymers and nano-silica as dispersants. Publication number CN115197519A reports that the salt resistance and dispersibility of microspheres are improved by introducing hydrophilic organic modified colloidal silica. Furthermore, patent publication number CN119463273 discloses the preparation of expandable microspheres using only an emulsifier composed of organic salts, without the use of any inorganic dispersants. However, when using only high-molecular-weight organic polymers or emulsifiers, the dosage is often very large, which will put pressure on sewage treatment and environmental protection. While using silica as a dispersant can reduce the dosage of high-molecular-weight organic polymers or emulsifiers, it often requires the addition of multiple substances such as sodium chloride and hydrochloric acid to form the dispersed phase.

[0004] In summary, there is an urgent need for an environmentally friendly and simple method for preparing expandable microspheres. Summary of the Invention

[0005] To address the above-mentioned issues, the present invention provides, in one aspect, a method for preparing expandable microspheres. The present invention utilizes an acid-base neutralization method to prepare a hydroxy calcium phosphate dispersant. This dispersant, when applied to the preparation of expandable microspheres by suspension polymerization, can reduce the use of organic dispersants to a certain extent, resulting in expandable microspheres with uniform particle size distribution and excellent expansion properties.

[0006] A method for preparing expandable microspheres comprises the following steps:

[0007] A. First, a certain amount of calcium source is dissolved in a certain amount of deionized water, and a certain amount of phosphorus source is dissolved in a certain amount of deionized water. At an appropriate speed, the phosphoric acid solution is added dropwise to the calcium hydroxide to obtain a hydroxy calcium phosphate solution.

[0008] B; adding a dispersant to calcium hydroxyphosphate to obtain an aqueous phase;

[0009] C; mixing the reaction monomer, initiator, crosslinking agent and foaming agent to obtain an oil phase;

[0010] D; adding the above oil phase to the water phase and stirring at high speed to obtain an emulsion;

[0011] E; stirring the reaction at the reaction temperature for 10-16 h;

[0012] F; filtration and drying to obtain expandable microsphere powder;

[0013] The calcium source is selected from one or more of calcium carbonate, calcium nitrate, calcium hydroxide, and calcium chloride, and the mass fraction of the calcium source dissolved in water is 1%-20%, preferably 5%-10%;

[0014] The phosphoric acid source is selected from one or more of phosphoric acid, sodium phosphate, phosphorus trichloride, and phosphorus trioxide. The mass fraction of the phosphorus source dissolved in water is 0.5%-20%, preferably 1%-5%.

[0015] Furthermore, the stirring speed of the calcium source in step A is 500-2000 rpm.

[0016] Furthermore, in step A, the phosphorus source should be slowly added to the calcium source. Adding too quickly will result in a reduced amount of produced calcium hydroxyphosphate, larger particle size, and a significant decrease in dispersibility.

[0017] Furthermore, the pH value of the hydroxy calcium phosphate solution is 7-9, and the particle size is 0.01-5 μm.

[0018] Furthermore, the dispersant is selected from one or more of polyvinyl pyrrolidone, methyl cellulose, lignin, polyvinyl alcohol, dodecyl sulfonate, gelatin, sodium alkyl sulfate, polyethylene oxide, and alkyl dimethylaminoacetic acid betaine, and the amount of the dispersant is 0.01%-5% of the total mass of the aqueous phase, preferably 0.05%-1%.

[0019] Furthermore, the reactive monomer is one or more of acrylonitrile, methacrylonitrile, methyl methacrylate, methacrylic acid, styrene, hydroxypropyl acrylate, vinyl acetate, vinyl laurate, vinyl stearate, vinyl halide, vinylidene halide, vinyl dihalide, acrylamide, ethylstyrene, halostyrene, methyl acrylate, ethyl acrylate, ethyl methacrylate, propyl acrylate, hydroxypropyl methacrylate, propyl methacrylate, butyl acrylate, butyl methacrylate, isobornyl methacrylate, hydroxyethyl methacrylate, hydroxyethyl acrylate, methacrylamide and hydroxyethyl methacrylate.

[0020] Further, the cross-linking agent is selected from one or more of divinylbenzene, di(ethylene glycol) di(meth)acrylate, triethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, glycerol di(meth)acrylate, neopentyl glycol di(meth)acrylate, 1,10-decanediol di(meth)acrylate, dipentaerythritol hexa(meth)acrylate, triallyl formal tri(meth)acrylate, allyl methacrylate, divinyl ether, ethylene glycol divinyl ether, diethylene glycol divinyl ether or tetraethylene glycol divinyl ether.

[0021] Furthermore, the initiator is selected from one or more of dioctyl peroxydicarbonate, diisopropyl peroxydicarbonate, tert-butyl peroxypivalate, azobisisobutyronitrile, azobisisovaleronitrile, azobisisoheptonitrile, dilauroyl peroxide, dibenzoyl peroxide, tert-butyl peroxyisobutyrate, bis(4-tert-butylcyclohexyl)peroxydicarbonate, and di-tert-butyl peroxide.

[0022] Furthermore, the foaming agent is selected from one or more of butane, isobutane, pentane, isopentane, hexane, cyclohexane, octane, isooctane, ethyl acetate, petroleum ether, ether, benzene, toluene and methyl chloride.

[0023] Furthermore, the oil phase accounts for 20%-50% of the total mass of the water phase and the oil phase.

[0024] Furthermore, the reaction temperature of step E is 40-70° C., and a suitable reaction temperature needs to be selected according to the initiator used.

[0025] Another aspect of the present invention provides expandable microspheres, which are prepared by the above method.

[0026] Furthermore, the particle size of the expandable microspheres is normally distributed, and D50 is 1-100 μm.

[0027] The beneficial technical effects of the present invention are as follows:

[0028] This invention uses an acid-base neutralization method to rapidly prepare calcium hydroxyphosphate for use in the synthesis of expandable microspheres. Calcium hydroxyphosphate effectively prevents agglomeration during the synthesis of expandable microspheres and reduces the amount of organic dispersants and dispersing aids used. The resulting expandable microspheres exhibit uniform particle size distribution and excellent expansion properties. DETAILED DESCRIPTION

[0029] The present invention will be further described below by means of specific examples. The examples described in the present invention are only for illustration of the present invention and do not limit the scope of the present invention.

[0030] The main test instruments and methods used in the embodiments and comparative examples are:

[0031] Laser particle size analyzer: Model LS13320 particle size distribution laser diffraction analyzer produced by Bekman Coulter Company, the test method is wet method, the shading rate selected for the test is 5%-20%, and the test medium is water.

[0032] TMA: Q-400 Thermomechanical Analyzer from TA Instruments. The test method involves increasing the sample temperature from ambient to 280°C at a rate of 20°C / min while applying a probe force of 0.1 N. Analysis is performed by measuring the vertical displacement of the probe.

[0033] Example 1

[0034] The steps for preparing expandable microspheres are as follows:

[0035] A: Weigh 10.26 g of calcium hydroxide and dissolve it in 200 g of deionized water. Weigh 9.58 g of 85% phosphoric acid and dissolve it in 800 g of deionized water. Stir the calcium hydroxide at 2000 rpm and add the phosphoric acid solution dropwise to the calcium hydroxide at a rate of 30 mL / min. After the addition is complete, let the mixture stand for 5 minutes to obtain a hydroxy calcium phosphate solution.

[0036] B: Weigh 300 g of calcium hydroxyphosphate solution, 0.25 g of polyvinylpyrrolidone and 0.25 g of lignin to prepare the aqueous phase;

[0037] C: 53 g acrylonitrile, 4 g methyl methacrylate, 15 g methacrylic acid, 17 g isopentane, 9 g isooctane, 0.1 g divinylbenzene crosslinker, and 1 g polymerization initiator dioctyl peroxydicarbonate were weighed and added to a reaction flask to prepare an oil phase;

[0038] D: Add the above oil phase to the water phase and stir at 1200 rpm for 10 min to form an emulsion;

[0039] E: The emulsion was polymerized at 50 °C and 350 rpm for 16 h;

[0040] F: After the reaction is completed, the filter cake is obtained by filtration, which is then dried in a 50°C oven and passed through a 150-mesh sieve to obtain expandable microsphere powder.

[0041] The relevant test data are listed in Table 1.

[0042] Example 2

[0043] The steps for preparing expandable microspheres are as follows:

[0044] A: Weigh 10.26 g of calcium hydroxide and dissolve it in 800 g of deionized water. Weigh 9.58 g of 85% phosphoric acid and dissolve it in 200 g of deionized water. Stir the calcium hydroxide at 2000 rpm and add the phosphoric acid solution dropwise to the calcium hydroxide at a rate of 30 mL / min. After the addition is complete, let the mixture stand for 5 minutes to obtain a hydroxy calcium phosphate solution.

[0045] B: Weigh 300 g of calcium hydroxyphosphate solution, 0.25 g of polyvinylpyrrolidone and 0.25 g of lignin to prepare the aqueous phase;

[0046] C: 53 g acrylonitrile, 4 g methyl methacrylate, 15 g methacrylic acid, 17 g isopentane, 9 g isooctane, 0.1 g divinylbenzene crosslinker, and 1 g polymerization initiator dioctyl peroxydicarbonate were weighed and added to a reaction flask to prepare an oil phase;

[0047] D: Add the above oil phase to the water phase and stir at 1200 rpm for 10 min to form an emulsion;

[0048] E: The emulsion was polymerized at 50 °C and 350 rpm for 16 h;

[0049] F: After the reaction is completed, the filter cake is obtained by filtration, which is then dried in a 50°C oven and passed through a 150-mesh sieve to obtain expandable microsphere powder.

[0050] The relevant test data are listed in Table 1.

[0051] Example 3

[0052] The steps for preparing expandable microspheres are as follows:

[0053] A: Weigh 10.26 g of calcium hydroxide and dissolve it in 200 g of deionized water. Weigh 9.58 g of 85% phosphoric acid and dissolve it in 800 g of deionized water. Stir the calcium hydroxide at 2000 rpm and add the phosphoric acid solution dropwise to the calcium hydroxide at a rate of 90 mL / min. After the addition is complete, let the mixture stand for 5 minutes to obtain a hydroxy calcium phosphate solution.

[0054] B: Weigh 300 g of calcium hydroxyphosphate solution, 0.25 g of polyvinylpyrrolidone and 0.25 g of lignin to prepare the aqueous phase;

[0055] C: 53 g acrylonitrile, 4 g methyl methacrylate, 15 g methacrylic acid, 17 g isopentane, 9 g isooctane, 0.1 g divinylbenzene crosslinker, and 1 g polymerization initiator dioctyl peroxydicarbonate were weighed and added to a reaction flask to prepare an oil phase;

[0056] D: Add the above oil phase to the water phase and stir at 1200 rpm for 10 min to form an emulsion;

[0057] E: The emulsion was polymerized at 50 °C and 350 rpm for 16 h;

[0058] F: After the reaction is completed, the filter cake is obtained by filtration, which is then dried in a 50°C oven and passed through a 150-mesh sieve to obtain expandable microsphere powder.

[0059] The relevant test data are listed in Table 1.

[0060] Comparative Example 1

[0061] The difference from Example 1 is that commercially available calcium hydroxyphosphate powder produced by Shaanxi Jiatian Biological was directly used as the dispersed phase component.

[0062] The steps for preparing expandable microspheres are as follows:

[0063] A: Weigh 10 g of 200 nm calcium hydroxyphosphate powder (produced by Shaanxi Jiatian Biological) and dissolve it in 1000 g of deionized water. Stir at 2000 rpm for 5 min and let it stand for 5 minutes to obtain a calcium hydroxyphosphate solution.

[0064] B: Weigh 300 g of calcium hydroxyphosphate solution, 0.25 g of polyvinylpyrrolidone and 0.25 g of lignin to prepare the aqueous phase;

[0065] C: 53 g acrylonitrile, 4 g methyl methacrylate, 15 g methacrylic acid, 17 g isopentane, 9 g isooctane, 0.1 g divinylbenzene crosslinker, and 1 g polymerization initiator dioctyl peroxydicarbonate were weighed and added to a reaction flask to prepare an oil phase;

[0066] D: Add the above oil phase to the water phase and stir at 1200 rpm for 10 min to form an emulsion;

[0067] E: The emulsion was polymerized at 50 °C and 350 rpm for 16 h;

[0068] F: After the reaction is completed, the filter cake is obtained by filtration, which is then dried in a 50°C oven and passed through a 150-mesh sieve to obtain expandable microsphere powder.

[0069] The relevant test data are listed in Table 1.

[0070] Comparative Example 2

[0071] The difference from Example 1 is that calcium hydroxyphosphate is not used as a dispersant, and only polyvinyl pyrrolidone and lignin are used as dispersants, and the amount of polyvinyl pyrrolidone used is increased.

[0072] The steps for preparing expandable microspheres are as follows:

[0073] A: Weigh 300 g of water, 5 g of polyvinylpyrrolidone, and 0.25 g of lignin to prepare the aqueous phase;

[0074] B: 53 g acrylonitrile, 4 g methyl methacrylate, 15 g methacrylic acid, 17 g isopentane, 9 g isooctane, 0.1 g divinylbenzene crosslinker, and 1 g polymerization initiator dioctyl peroxydicarbonate were weighed and added to a reaction flask to prepare an oil phase;

[0075] C: Add the above oil phase to the water phase and stir at 1200 rpm for 10 min to form an emulsion;

[0076] D: The emulsion was polymerized at 50 °C and 350 rpm for 16 h;

[0077] E: After the reaction is completed, the filter cake is obtained by filtration, which is then dried in a 50°C oven and passed through a 150-mesh sieve to obtain expandable microsphere powder.

[0078] The relevant test data are listed in Table 1.

[0079] Table 1. Test data of microspheres obtained in Examples and Comparative Examples:

[0080] example Proportion of material on 150 mesh sieve D50 / µm Span Initial expansion temperature / ℃ Maximum expansion temperature / ℃ Example 1 0.2% 38.87 1.32 161.6 197.9 Example 2 15% 56.91 2.86 157.5 194.3 Example 3 80% 70.25 2.65 / / Comparative Example 1 86% 197.56 5.06 / / Comparative Example 2 0.3% 39.95 1.25 160.4 196.3

[0081] By comparing the relevant data in Table 1, the method of preparing calcium hydroxyphosphate by acid-base neutralization and applying it to the preparation of expandable microspheres proposed in the present invention not only has more significant dispersion protection than commercially available calcium hydroxyphosphate, but also can significantly reduce the amount of organic dispersant used. The prepared expandable microspheres have excellent particle size distribution and expandability. In addition, different calcium source concentrations, phosphorus source concentrations, and addition speeds were compared. Calcium hydroxyphosphate prepared at excessively high phosphorus source concentrations and addition speeds reduced the dispersion protection effect during the synthesis of expandable microspheres. Therefore, it is shown that the method for preparing expandable microspheres based on the dispersed phase of calcium hydroxyphosphate provided by the present invention has broad market prospects.

[0082] The preferred embodiments of the present invention disclosed above are intended only to help illustrate the present invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the present invention to the specific embodiments described. Obviously, many modifications and variations are possible based on the content of this specification. These embodiments are selected and described in detail in this specification to better explain the principles and practical applications of the present invention, thereby enabling those skilled in the art to better understand and utilize the present invention. The present invention is limited only by the claims and their full scope and equivalents.

Claims

1. A method for preparing expandable microspheres, comprising the following steps: A. First, a certain amount of calcium source is dissolved in a certain amount of deionized water, and a certain amount of phosphorus source is dissolved in a certain amount of deionized water. At an appropriate speed, the phosphoric acid solution is added dropwise to the calcium hydroxide to obtain a hydroxy calcium phosphate solution. B; adding a dispersant to calcium hydroxyphosphate to obtain an aqueous phase; C; mixing the reaction monomer, initiator, crosslinking agent and foaming agent to obtain an oil phase; D; adding the above oil phase to the water phase and stirring at high speed to obtain an emulsion; E; stirring the reaction at the reaction temperature for 10-16 h; F; filtration and drying to obtain expandable microsphere powder; The calcium source is selected from one or more of calcium carbonate, calcium nitrate, calcium hydroxide, and calcium chloride, and the mass fraction of the calcium source dissolved in water is 1%-20%; The phosphoric acid source is selected from one or more of phosphoric acid, sodium phosphate, phosphorus trichloride, and phosphorus trioxide, and the mass fraction of the phosphorus source dissolved in water is 0.5%-20%.

2. The method for preparing expandable microspheres according to claim 1, wherein: The pH value of the hydroxy calcium phosphate solution is 7-9, and the particle size is 0.01-5 μm.

3. The method for preparing expandable microspheres according to claim 1, wherein: The dispersant is selected from one or more of polyvinyl pyrrolidone, methyl cellulose, lignin, polyvinyl alcohol, dodecyl sulfonate, gelatin, sodium alkyl sulfate, polyethylene oxide, and alkyl dimethylamino acetic acid betaine. The amount of the dispersant is 0.01%-5% of the total mass of the aqueous phase.

4. The method for preparing expandable microspheres according to claim 1, wherein: The reactive monomer is one or more of acrylonitrile, methacrylonitrile, methyl methacrylate, methacrylic acid, styrene, hydroxypropyl acrylate, vinyl acetate, vinyl laurate, vinyl stearate, vinyl halide, vinylidene halide, vinyl dihalide, acrylamide, ethylstyrene, halostyrene, methyl acrylate, ethyl acrylate, ethyl methacrylate, propyl acrylate, hydroxypropyl methacrylate, propyl methacrylate, butyl acrylate, butyl methacrylate, isobornyl methacrylate, hydroxyethyl methacrylate, hydroxyethyl acrylate, methacrylamide and hydroxyethyl methacrylate.

5. The method for preparing expandable microspheres according to claim 1, wherein: The cross-linking agent is selected from one or more of divinylbenzene, di(ethylene glycol) di(meth)acrylate, triethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, glycerol di(meth)acrylate, neopentyl glycol di(meth)acrylate, 1,10-decanediol di(meth)acrylate, dipentaerythritol hexa(meth)acrylate, triallyl formal tri(meth)acrylate, allyl methacrylate, divinyl ether, ethylene glycol divinyl ether, diethylene glycol divinyl ether or tetraethylene glycol divinyl ether.

6. The method for preparing expandable microspheres according to claim 1, wherein: The foaming agent is selected from one or more of butane, isobutane, pentane, isopentane, hexane, cyclohexane, octane, isooctane, ethyl acetate, petroleum ether, ether, benzene, toluene and methyl chloride.

7. The method for preparing expandable microspheres according to claim 1, wherein: The reaction temperature of step E is 40-70°C.

8. An expandable microsphere, characterized in that: The expandable microspheres are prepared by the method according to claims 1-6.