Expandable microsphere with super-large particle size and preparation method thereof

Abstract

The invention provides a super-large-particle-size expandable microsphere. The super-large-particle-size expandable microsphere comprises a water phase, a dispersing agent, a stabilizing agent and an oil phase. The buffer solution is added into the water phase, the pH of the water phase is controlled to be acidic, flocculation of silica sol is promoted, and the stability of the water phase environment is maintained; by adding a surfactant and an auxiliary agent into a water phase, the interfacial tension of oil and water is reduced, and the expansible microspheres with ultra-large particle sizes are formed. The prepared super-large-particle-size expandable microspheres have more advantages in the aspects of improving the material strength, improving the buffering performance, the damping performance, the weight reducing effect and the like, and the application field of the expandable microspheres is expanded.

Description

Technical Field

[0001] The invention belongs to the field of polymer functional materials and relates to ultra-large thermal expansion microspheres and a preparation method thereof. Background Art

[0002] Expandable microspheres are microcapsules with a core-shell structure consisting of a thermoplastic polymer as a shell and a low molecular weight hydrocarbon as a core. According to current reports, the expandable microspheres prepared by suspension polymerization generally have a particle size of 5-50 μm. When microspheres with smaller particle sizes are added to resins for molding, the product may face deficiencies in terms of smaller pores, cushioning performance, shock absorption performance, and weight reduction. There are almost no patents related to ultra-large expandable microspheres above 400 μm or even reaching the millimeter level. Microspheres with ultra-large particle sizes have a thicker shell layer, which plays a role in enhancing the strength of the material. The ultra-large size after foaming can improve the cushioning and shock absorption of the material.

[0003] The existing preparation methods of large-size expandable microspheres are reported in patents such as CN104877060A, CN116333223A, and CN113731310A. They are mainly prepared by suspension polymerization or emulsion polymerization, and finally obtain microspheres with a particle size between 1-70 μm. Patent CN104877060A provides a method for preparing large-size hollow polymer microspheres. First, a metal hydroxide colloidal dispersant is prepared by the existing technology, and then an aqueous phase and an oil phase are added in sequence for high-speed shear emulsification dispersion, and large-size hollow polymer microspheres are obtained by suspension polymerization. The method is simple to operate and has a mild reaction, but the particle size of the prepared large-size microspheres is only 1-10 μm. Patent CN116333223A provides a method for preparing large-size hollow microspheres by multi-step emulsion polymerization. The particle size distribution of the microspheres prepared by this method is uniform, but the particle size is only 5-20 μm. Patent CN113731310A provides a method for preparing ultra-large particle size expandable microspheres by suspension polymerization, which relies on the hydrogen bonding effect of N,N-dimethylamide and silica sol to change the interfacial energy of the oil-water interface and increase the adsorption of silica sol on the surface of the microspheres, thereby obtaining ultra-large particle size expandable microspheres with a particle size of more than 50 μm. However, the particle size of the microspheres in the examples is less than 70 μm.

[0004] In summary, the large-size expandable microspheres prepared by the existing patented methods are still not large enough. This patent prepares a super-large-size expandable microsphere by suspension polymerization, and successfully prepares millimeter-level super-large-size expandable microspheres by adjusting the polymer phase separation and water-oil interface energy during the polymerization process, as well as the control of the water phase Zeta potential. Summary of the invention

[0005] In order to solve the above problems, the present invention provides expandable microspheres with super large particle size and a preparation method thereof.

[0006] The present invention aims to provide a millimeter-level super-large particle size expandable microsphere, which has a uniform particle size distribution, a particle size of 0.4mm-0.5mm, and a thick shell layer, which can significantly improve the cushioning and shock absorption of the material. The millimeter-level super-large particle size expandable microsphere is prepared by Pickering emulsion suspension polymerization. The key to achieving super-large particle size is to adjust the polymer phase separation and water-oil interface energy during the polymerization process, and control the Zeta potential of the water phase.

[0007] The present invention first establishes a Pickering emulsion system, including an aqueous phase, a dispersant, a stabilizer, and an oil phase. The aqueous phase is composed of deionized water, a surfactant, a dispersant, etc., and the oil phase is formed by the mutual dissolution of oil-soluble monomers such as acrylonitrile, methacrylic acid, methyl methacrylate, and a core material, an initiator, and a crosslinking agent. The present invention controls the pH of the aqueous phase to be acidic by adding a buffer solution to the aqueous phase, promotes the flocculation of the silica sol and maintains the stability of the aqueous phase environment; and reduces the interfacial tension between the oil and water by adding a surfactant and an auxiliary agent to the aqueous phase to form microspheres with larger particle sizes.

[0008] The present invention is achieved through the following technical solutions:

[0009] The present invention provides an ultra-large-size expandable microsphere and a preparation method thereof. The microsphere is prepared by suspension polymerization. The preparation method comprises the following steps:

[0010] (1) Preparation of aqueous phase: weigh 10 kg of deionized water, 500 g of silica sol, 0.01-1% of surfactant, 500 g of inorganic salt, 0.05-1% of 0.1 M hydrochloric acid, and 0.05-1% of aqueous phase auxiliary agent, add them into a kettle, stir at 500 rpm for 0.5 h at room temperature and pressure to mix evenly to obtain a silica sol-acidic buffer solution aqueous phase;

[0011] (2) Preparation of oil phase: 0-60% of the total amount of the oil phase is a gas-tight monomer, 0-20% of an acrylic monomer, 0-20% of other functional monomers, 0.05-1% of a cross-linking agent, 1-3% of an initiator, and 10-30% of a foaming agent are dissolved in each other and added to the oil phase kettle, and stirred and mixed to obtain a usable oil phase;

[0012] (3) Preparation of expandable microspheres: The prepared oil phase and water phase are introduced into a homogenizing kettle and homogenized at a speed of 100-500 rpm. After homogenization, they are transferred to a reactor. The temperature is set between 40-80 °C according to the half-life of the initiator. The polymerization reaction is carried out at a speed of 100-300 rpm under a nitrogen pressure of 0-1 MPa. After the reaction is allowed to react for 12-16 h, the mixture is cooled to room temperature, filtered and dried to obtain white powdery expandable microspheres.

[0013] Furthermore, the buffer solution used to prepare the aqueous phase is one or more of a phosphate buffer, a citrate buffer, and an acetate buffer.

[0014] Furthermore, the phosphate buffer is phosphoric acid (H3PO4) and its salts (NaH2PO4 and Na2HPO4), the citric acid buffer is citric acid (C6H8O7) and its salts (Na3C6H5O7), and the acetate buffer is acetic acid (CH3COOH) and its salts (CH3COONa).

[0015] Furthermore, the inorganic salt is one of sodium chloride, potassium chloride and sodium sulfate, preferably sodium chloride.

[0016] Furthermore, the surfactant is any one of perfluorooctylethanol (PFOE) and polyethylene glycol-polylactide (PEG-PLA).

[0017] Furthermore, the water phase auxiliary agent is any one of ethanolamine and ethylenediamine.

[0018] Furthermore, the airtight monomer is one or more of acrylonitrile, methacrylonitrile, and vinylidene chloride; the acrylic ester monomer is one or more of methyl acrylate (MA), methacrylic acid (MAA), methyl methacrylate (MMA), and isobornyl methacrylate (IBOMA); and the other functional monomers are one or more of 4-cyclohexylstyrene (M1), 4-phenyl-1-cyclohexene (M2), and N-benzyl-2,5-dihydropyrrole (M3).

[0019] This type of functional monomer has a multi-cyclic stable structure and can form a polymer with excellent thermal stability and mechanical properties after polymerization, thereby improving the mechanical properties of the shell polymer.

[0020] Furthermore, the crosslinking agent is a multifunctional compound having two or more carbon-carbon double bonds, preferably a crosslinking agent having two carbon-carbon double bonds, specifically one or more of divinylbenzene (DVB), ethylene glycol dimethacrylate (EGDMA), and diethylene glycol dimethacrylate (DEGDMA).

[0021] Furthermore, the initiator is one or more of di(2-ethylhexyl) peroxydicarbonate (EHP), lauroyl peroxide (LPO), azobisisobutyronitrile (AIBN), and azobismethoxyisoheptanenitrile (V-70).

[0022] Furthermore, the core material is one or more of isooctane, n-pentane, isopentane, n-hexane, and n-heptane.

[0023] Another aspect of the present invention provides expandable microspheres with ultra-large particle sizes, wherein the expandable microspheres are prepared by the above method.

[0024] Furthermore, the particle size of the microspheres is 400-500um.

[0025] The beneficial technical effects of the present invention are as follows:

[0026] The present invention provides an expandable microsphere with an ultra-large particle size and a preparation method thereof. The expandable microsphere with an ultra-large particle size has advantages in improving material strength, improving cushioning and shock absorption, and reducing weight. On the other hand, since the ultra-large particle size microsphere has a thicker shell layer, it can play a role in strengthening the skeleton in the material, so that the mechanical strength and rigidity of the composite material are significantly improved, which is impossible to achieve with the existing microspheres with smaller particle sizes. The ultra-large particle size microspheres after foaming have a larger pore structure, can provide more excellent cushioning and shock absorption performance, effectively absorb and disperse external impact force, and enhance the protective ability of the material. The ultra-large particle size microsphere has a high gas content, and a large volume pore structure is formed after foaming, which significantly reduces the material density and achieves lightweight. In addition, by introducing functional monomers or modifications, the heat resistance, sound insulation, heat insulation and other properties of the microsphere preparation can also be enhanced, expanding the application field of expandable microspheres and improving the comprehensive performance of the material. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is the morphology of the ultra-large particle size expandable microspheres 10X, 92.786um / grid. DETAILED DESCRIPTION

[0028] The present invention is further described below by way of examples. In the examples listed, unless otherwise stated, all parts and percentages in the examples are parts and percentages by weight.

[0029] The polyurethane microspheres prepared by the present invention are mainly tested for particle size, dispersibility, and foaming expansion. The particle size and dispersibility of the microsphere slurry and dry powder are tested by a laser particle size analyzer, and the expansion coefficient of the microspheres is tested by a thermomechanical analyzer (TMA).

[0030] (1) Particle size distribution characteristics analysis:

[0031] The particle size distribution of the microspheres was measured by a particle size distribution laser diffraction analyzer LS13320 produced by Bekman Coulter, and the average diameter was measured as the volume average particle size.

[0032] (2) Foaming characteristics analysis:

[0033] The characteristic of heat-expandable microsphere is measured by the thermomechanical analyzer TMA Q-400 produced by TA Instrument company.The 1.0mg heat-expandable microsphere prepared sample by the aluminum pan of diameter 6.7mm and depth 4.5mm.Then, the aluminum pan of diameter 6.5mm and depth 4.0mm is sealed.According to the TMA extended probe type, the sample temperature is increased to 280 ℃ from ambient temperature with the heating rate of 20 ℃ / min, and the power of 0.1N is applied by probe.Analysis is carried out by measuring the vertical displacement of probe.

[0034] - Expansion initial temperature (Tstart): The temperature at which the probe displacement begins to increase (°C);

[0035] - Maximum foaming temperature (Tmax): the temperature (°C) when the probe displacement reaches the maximum;

[0036] - Foaming density (Dmin): the ratio of the amount of microspheres added to the volume after foaming (kg / m 3 ).

[0037] The addition amount of each component in Examples 1-3 and Comparative Examples 1-4 is recorded in Table 1, and the performance test results of the expandable microspheres prepared in Examples 1-3 and Comparative Examples 1-4 are also recorded in Table 1.

[0038] The preparation method of the super-large particle size expandable microspheres is as follows:

[0039] (1) Aqueous phase preparation: Aqueous phase preparation is divided into silica sol acidic aqueous phase (SS) preparation and silica sol-acidic buffer solution aqueous phase (SSB) preparation;

[0040] SS aqueous phase: weigh 10 kg of deionized water, 500 g of silica sol, 0.01-1% of surfactant, 500 g of inorganic salt, and 0.05-1% of 0.1M hydrochloric acid, add them into a kettle, stir at 500 rpm for 0.5 h at room temperature and pressure to obtain a silica sol acidic aqueous phase;

[0041] SSB1 aqueous phase: weigh 10 kg deionized water, 500 g silica sol, 0.01-1% surfactant, 500 g inorganic salt, 0.05-1% 0.1M buffer solution, 0.05-1% aqueous phase additive;

[0042] SSB2 aqueous phase: weigh 10 kg deionized water, 500 g silica sol, 0.01-1% surfactant, 500 g inorganic salt, 0.05-1% 0.1M hydrochloric acid, 0.05-1% aqueous phase additive;

[0043] SSB3 aqueous phase: weigh 10 kg deionized water, 500 g silica sol, 0.01-1% surfactant, 500 g inorganic salt, 0.05-1% 0.1 M buffer solution;

[0044] SSB4 water phase: weigh 10 kg deionized water, 500 g silica sol, 0.01-1% surfactant, 500 g inorganic salt, 0.05-1% water phase additive;

[0045] (2) Preparation of oil phase: 0-60% of the total amount of the oil phase is a gas-tight monomer, 0-20% of an acrylic monomer, 0-20% of other functional monomers, 0.05-1% of a cross-linking agent, 1-3% of an initiator, and 10-30% of a foaming agent are dissolved in each other and added to the oil phase kettle, and stirred and mixed to obtain a usable oil phase;

[0046] (3) Preparation of expandable microspheres: The prepared oil phase and water phase are introduced into a homogenizing kettle and homogenized at a speed of 100-500 rpm. After homogenization, they are transferred to a reactor. The temperature is set between 40-80 °C according to the half-life of the initiator. The polymerization reaction is carried out at a speed of 100-300 rpm under a nitrogen pressure of 0-1 MPa. After the reaction is allowed to react for 12-16 h, the mixture is cooled to room temperature, filtered and dried to obtain white powdery expandable microspheres.

[0047] Table 1

[0048]

[0049] The unit of each component in the embodiments and comparative examples in Table 1 is gram, wherein AN is acrylonitrile, MAN is methacrylonitrile, MAA is methacrylic acid, MMA is methyl methacrylate, IBOMA isobornyl methacrylate, M1 is 4-cyclohexylstyrene, EGDMA is ethylene glycol dimethacrylate, DVB is divinylbenzene, EHP is di(2-ethylhexyl) peroxydicarbonate, V-70 is 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile), IP is isopentane, ISO isooctane, SSB1, SSB2, SSB3, SSB4 are silica sol-acidic buffer solution aqueous phase, SS is silica sol acidic aqueous phase.

[0050] From the data of the embodiments and comparative examples in Table 1 above, it can be concluded that the particle size of the microspheres prepared by using the silica sol-acidic buffer solution aqueous phase increases, among which the particle size of the microspheres prepared by using the low-temperature initiator and the silica sol-acidic buffer solution aqueous phase is the largest, indicating that the preparation of ultra-large particle size microspheres can be achieved by adjusting the polymer phase separation, water-oil interfacial energy and water phase Zeta potential during the polymerization process, and initiating polymerization with a low-temperature initiator.

[0051] In Example 1, the particle size of the microspheres prepared by using silica sol-acidic buffer solution SSB1 containing surfactant, acidic buffer solution and aqueous phase auxiliary agent can reach 426.878 μm. In Comparative Example 1, the particle size of the microspheres prepared by using silica sol acidic aqueous phase SS is 28.326 μm. In Comparative Example 4, the polymerization experiment using silica sol aqueous phase SSB4 without hydrochloric acid and buffer solution failed. The difference between Example 1 and Comparative Example 1 and Comparative Example 4 lies in the aqueous phase. In Example 1, surfactant, acidic buffer solution and aqueous phase auxiliary agent are added to the aqueous phase, which is helpful for polymer phase separation, water-oil interfacial energy regulation, and aqueous phase Zeta potential control, thereby obtaining microspheres with ultra-large particle size with good dispersibility. In Comparative Example 1, hydrochloric acid solution is added to the aqueous phase, and aqueous phase auxiliary agent is lacking, which is not conducive to controlling the pH and Zeta potential of the aqueous phase and reducing the interfacial energy, and microspheres with conventional particle size are obtained. In Comparative Example 4, aqueous phase auxiliary agent is added to the aqueous phase, and hydrochloric acid solution or buffer solution is lacking, and silica sol cannot flocculate, resulting in poor dispersibility and polymerization failure.

[0052] Example 2 uses silica sol-acidic buffer solution SSB2 containing surfactant, hydrochloric acid solution and water phase auxiliary agent to obtain ultra-large particle size microspheres with a particle size of 284.398 μm. The difference between Example 2 and Example 1 is that the buffer acid solution in the aqueous phase is replaced by hydrochloric acid solution, which is not conducive to the control of the pH and Zeta potential of the aqueous phase, and the flocculation of the silica sol and the stability of the aqueous phase environment are also affected, thereby affecting the particle size and dispersibility of the microspheres. Comparative Example 2 uses silica sol-acidic buffer solution SSB3 (without water phase auxiliary agent) containing surfactant and acidic buffer solution to prepare microspheres with a particle size of 47.583 μm. The lack of water phase auxiliary agent in Comparative Example 2 causes the particle size of the microspheres to decrease. The water phase auxiliary agent used in this patent mainly increases the particle size by enhancing hydrogen bonding and reducing the interfacial energy, and the lack of water phase auxiliary agent is not conducive to the preparation of ultra-large particle size expandable microspheres.

[0053] In Example 3, the particle size of the microspheres prepared using the SSB1 aqueous phase and the low-temperature initiator V-70 is 468.756 μm. Compared with Example 1, the lower temperature initiator controls the polymerization rate to form microspheres with larger particle sizes, and helps to improve the dispersibility of the microspheres. Compared with Comparative Example 1, Comparative Example 3 shows that the lower temperature initiator helps to improve the dispersibility of the microspheres. In addition, the TMA test results show that the Dmin of the ultra-large particle size microspheres is about 20. The shell layer of the ultra-large particle size microspheres is too thick, which may limit the expansion space of the internal gas, resulting in a slightly larger Dmin.

[0054] In summary, this patent successfully prepared expandable microspheres with ultra-large particle sizes in the millimeter range by adjusting surfactants, buffer solutions, aqueous phase additives and initiators, regulating polymer phase separation and water-oil interfacial energy during the polymerization process, and controlling the Zeta potential of the aqueous phase. The ultra-large particle size microspheres have a thicker shell layer, which plays a role in reinforcing the skeleton in the material and can be used to improve the mechanical strength and rigidity of composite materials, which is impossible for existing microspheres with smaller particle sizes. The ultra-large particle size microspheres after foaming have a larger pore structure, which can provide better cushioning and shock absorption performance, effectively absorb and disperse external impact forces, and enhance the protective ability of the material. In addition, the introduction of functional monomers or modifications to the ultra-large particle size expandable microspheres can also enhance the heat resistance, sound insulation, heat insulation and other properties of the microspheres, expand the application field, and improve the comprehensive performance of the material.

Claims

1. A method for preparing expandable microspheres with ultra-large particle size, comprising the following steps: (1) Preparation of aqueous phase: weigh 10 kg of deionized water, 500 g of silica sol, 0.01-1% of surfactant, 500 g of inorganic salt, 0.05-1% of 0.1 M hydrochloric acid, and 0.05-1% of aqueous phase auxiliary agent, add them into a kettle, stir at 500 rpm for 0.5 h at room temperature and pressure to mix evenly to obtain a silica sol-acidic buffer solution aqueous phase; (2) Preparation of oil phase: 0-60% of the total amount of the oil phase is a gas-tight monomer, 0-20% of an acrylic monomer, 0-20% of other functional monomers, 0.05-1% of a cross-linking agent, 1-3% of an initiator, and 10-30% of a foaming agent are dissolved in each other and added to the oil phase kettle, and stirred and mixed to obtain a usable oil phase; (3) Preparation of expandable microspheres: The prepared oil phase and water phase are introduced into a homogenizing kettle and homogenized at a speed of 100-500 rpm. After homogenization, they are transferred to a reactor. The temperature is set between 40-80 °C according to the half-life of the initiator. The polymerization reaction is carried out at a speed of 100-300 rpm under a nitrogen pressure of 0-1 MPa. After the reaction is allowed to react for 12-16 h, the mixture is cooled to room temperature, filtered and dried to obtain white powdery expandable microspheres.

2. The method for preparing expandable microspheres according to claim 1, characterized in that: The buffer solution used for preparing the aqueous phase is one or more of a phosphate buffer, a citric acid buffer, and an acetic acid buffer. The phosphate buffer is phosphoric acid (H3PO4) and its salts (NaH2PO4 and Na2HPO4), the citric acid buffer is citric acid (C6H8O7) and its salts (Na3C6H5O7), and the acetate buffer is acetic acid (CH3COOH) and its salts (CH3COONa).

3. The method for preparing expandable microspheres according to claim 1, characterized in that: The inorganic salt is one of sodium chloride, potassium chloride and sodium sulfate.

4. The method for preparing expandable microspheres according to claim 1, characterized in that: The surfactant is any one of perfluorooctylethanol and polyethylene glycol-polylactide.

5. The method for preparing expandable microspheres according to claim 1, characterized in that: The water phase auxiliary agent is any one of ethanolamine and ethylenediamine.

6. The method for preparing expandable microspheres according to claim 1, characterized in that: The airtight monomer is one or more of acrylonitrile, methacrylonitrile, and vinylidene chloride; the acrylic ester monomer is one or more of methyl acrylate, methacrylic acid, methyl methacrylate, and isobornyl methacrylate; and the other functional monomers are one or more of 4-cyclohexylstyrene, 4-phenyl-1-cyclohexene, and N-benzyl-2,5-dihydropyrrole.

7. The method for preparing expandable microspheres according to claim 1, characterized in that: The crosslinking agent is a multifunctional compound having two or more carbon-carbon double bonds, preferably a crosslinking agent having two carbon-carbon double bonds, specifically one or more of divinylbenzene, ethylene glycol dimethacrylate, and diethylene glycol dimethacrylate.

8. The method for preparing expandable microspheres according to claim 1, characterized in that: The initiator is one or more of di(2-ethylhexyl) peroxydicarbonate (EHP), lauroyl peroxide (LPO), azobisisobutyronitrile (AIBN), and azobismethoxyisoheptanenitrile (V-70).

9. An expandable microsphere with an ultra-large particle size, characterized in that: The expandable microspheres are prepared by any method described in claims 1-8.

10. The expandable microsphere according to claim 9, characterized in that: The particle size of the microspheres is 400-500um.

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