Flame-retardant thermal expansion microsphere and preparation method thereof

Abstract

The invention belongs to the technical field of thermal expansion microspheres, and particularly relates to flame-retardant thermal expansion microspheres and a preparation method thereof. The method comprises the following steps: firstly, dissolving methyl methacrylate, allyl methacrylate and methacrylic acid in petroleum ether and other organic solvents, adding an emulsifier and an initiator to form a stable oil phase, and then forming a water-in-oil emulsion from the oil phase and a water phase in which a flame retardant is dissolved; under the action of an emulsifier and shearing force, the flame-retardant expanded microspheres are finally obtained. The flame retardant and water are wrapped in the microspheres, and when a certain temperature is reached, the microspheres expand, so that heat transfer is reduced, and the flame-retardant effect is improved. The flame-retardant thermal expansion microspheres prepared by the method have good expansion performance and flame-retardant performance.

Description

Technical Field

[0001] The present invention belongs to the technical field of thermally expandable microspheres, and particularly relates to a flame-retardant thermally expandable microsphere and a preparation method thereof. Background Art

[0002] Thermally expandable microspheres, also known as physical foaming microspheres, generally have a size between 5 - 500 μm. Thermally expandable microspheres usually have a core-shell structure, with the core material being a low-boiling organic solvent (such as butane, pentane, etc.) and the shell material being a thermoplastic polymer (such as polyacrylonitrile, etc.). When the microspheres are heated above a certain temperature (higher than the boiling point of the organic solvent and the glass transition temperature Tg of the shell material), the outer shell of the microspheres softens and the internal low-boiling organic solvent rapidly vaporizes, generating an internal pressure that forces the outer shell of the microspheres to expand and swell, increasing the volume of the microspheres to several to dozens of times the original volume. As long as the toughness of the polymer of the microsphere outer shell matches the expansion pressure inside the shell appropriately, the microspheres can maintain the expanded state, and there will be no obvious shrinkage when returning to room temperature. However, at too high temperatures, the microspheres will be burst by the organic solvent vapor, and the collapsed structure of the microspheres will be damaged.

[0003] At home and abroad, for the thermally expandable foaming microsphere technology to meet the mechanical properties of the microspheres, polyacrylonitrile and its copolymers, as well as polyvinylidene chloride and its copolymers are mostly used as the main microsphere shell materials, encapsulating low-boiling alkanes as the inner core of the microspheres. However, low-boiling alkanes (such as butane, pentane) are volatile, flammable, and explosive hazardous chemicals, and acrylonitrile and vinylidene chloride are both flammable, highly toxic, and hazardous chemicals under control with the risk of causing distortion. These hazardous chemicals pose great safety hazards during the storage, transportation, production, and use of thermally expandable microspheres. At the same time, the waste liquid, waste residue, and waste gas generated during the production and use processes need to be discharged and treated, which has an impact on the ecological environment. Summary of the Invention

[0004] In view of the above problems existing in the prior art, the present invention provides a flame-retardant thermally expandable microsphere and a preparation method thereof, and the flame-retardant thermally expandable microsphere has good flame-retardant properties.

[0005] To achieve the above object, the technical solutions provided by the present invention are as follows:

[0006] In a first aspect, the present application provides a preparation method of a flame-retardant thermally expandable microsphere, including the following steps:

[0007] Mix petroleum ether, acrylic acid monomers, crosslinking agent, initiator, and emulsifier to obtain an oil phase;

[0008] Mix a flame retardant and deionized water to obtain an aqueous phase;

[0009] Under stirring, add the oil phase to the aqueous phase to obtain a mixed solution;

[0010] The mixture is heated under a nitrogen atmosphere to carry out a polymerization reaction, and after filtration, washing and air drying, the flame-retardant thermally expandable microspheres are obtained.

[0011] Optionally, the emulsifier includes Span 80 and Tween 80, and the mass ratio of Span 80 to Tween 80 is (3 - 4):1.

[0012] Optionally, the mass ratio of the petroleum ether, acrylic acid monomer, crosslinking agent and emulsifier is 100:(10 - 16):(1 - 2):(1 - 3).

[0013] Optionally, the flame retardant is one or more of trimethyl phosphate, triethyl phosphate and tris(xylene) phosphate.

[0014] Optionally, the acrylic acid monomer includes methyl methacrylate and methacrylic acid, and the mass ratio of methyl methacrylate to methacrylic acid is (24 - 29):2.

[0015] Optionally, the polymerization reaction temperature is 75 - 90 °C.

[0016] Optionally, the aqueous phase includes the following components in parts by mass: 0.8 - 1 part of flame retardant and 1 part of water.

[0017] On the other hand, the present application also provides a kind of flame-retardant thermally expandable microspheres prepared by the above method.

[0018] Compared with the prior art, the present application has at least the following beneficial effects:

[0019] In the method of the present invention, first, methyl methacrylate, allyl methacrylate and methacrylic acid are dissolved in an organic solvent such as petroleum ether, and an emulsifier and an initiator are added to form a stable oil phase. Then, the oil phase and the aqueous phase dissolved with the flame retardant form a "water-in-oil" emulsion. Under the action of the emulsifier and shear force, finally, flame-retardant expandable microspheres are obtained. The flame retardant and water are wrapped in the microspheres. When the temperature reaches a certain value, the microspheres expand, reducing heat transfer and improving the flame retardant effect. The flame-retardant thermally expandable microspheres prepared by the present invention have good expansion performance and flame retardant performance. Description of the Drawings

[0020] Figure 1 SEM images of the flame-retardant thermally expandable microspheres prepared in Examples 1, 2, and 3 before and after the thermal expansion experiment;

[0021] Figure 2 Schematic diagrams of the expansion of the flame-retardant thermally expandable microspheres prepared in Examples 1, 2, and 3 at different temperatures;

[0022] Figure 3 Schematic diagrams of the expansion of the flame-retardant thermally expandable microspheres prepared in Comparative Example 1 at different temperatures;

[0023] Figure 4 Schematic diagram of the flame retardant effect of the flame retardant thermally expandable microspheres prepared in Example 1 under an open flame;

[0024] Figure 5 Schematic diagram of the flame retardant effect of the flame retardant thermally expandable microspheres prepared in Comparative Example 1 under an open flame. Detailed implementation manners

[0025] The present invention will be further described in detail below with reference to the accompanying drawings:

[0026] The experimental methods used in the embodiments of the present invention are all conventional methods unless otherwise specified.

[0027] The reagent materials used in this example can be purchased conventionally. For the quantitative experiments involved in the embodiments, at least three repeated experiments are set, and the results are averaged.

[0028] Source of raw materials:

[0029] Petroleum ether: Purchased from Shanghai Yuanye Bio-Technology Co., Ltd.

[0030] Example 1

[0031] The preparation method of the flame retardant thermally expandable microspheres of the present invention is specifically as follows: (1) Mix 100 g of petroleum ether, 1.5 g of Span 80, 0.5 g of Tween 80, 13.5 g of methyl methacrylate, 1.5 g of allyl methacrylate, 1 g of methacrylic acid and 0.43 g of azobisisobutyronitrile evenly at room temperature to obtain an oil phase; (2) Mix 14.83 g of triethyl phosphate with 15 g of deionized water evenly to obtain an aqueous phase; (3) Mix the oil phase prepared in step (1) and the aqueous phase prepared in step (2), and stir at a speed of 500 rpm for 10 min at room temperature to obtain a mixed solution; (4) Heat the mixed solution obtained in step (3) to 75 °C under a nitrogen atmosphere and react for 4 h, filter to obtain microspheres, then wash with petroleum ether and filter three times by suction, and air-dry naturally under ventilation in a fume hood to obtain the flame retardant thermally expandable microspheres.

[0032] Example 2

[0033] The preparation method of the flame-retardant thermally expandable microspheres of the present invention is specifically as follows: (1) Mix 100 g of petroleum ether, 1.5 g of Span 80, 13.5 g of methyl methacrylate, 1.5 g of allyl methacrylate, 1 g of methacrylic acid and 0.43 g of azobisisobutyronitrile evenly at room temperature to obtain an oil phase; (2) Mix 14.83 g of triethyl phosphate evenly in 15 g of deionized water to obtain an aqueous phase; (3) Mix the oil phase prepared in step (1) and the aqueous phase prepared in step (2), and stir at a speed of 500 rpm for 10 min at room temperature to obtain a mixed solution; (4) Raise the temperature to 75 °C under a nitrogen atmosphere to make the mixed solution in step (3) react for 4 h, filter to obtain microspheres, then wash with petroleum ether and filter by suction three times, and air-dry naturally under ventilation in a fume hood to obtain the flame-retardant thermally expandable microspheres.

[0034] Example 3

[0035] The preparation method of the flame-retardant thermally expandable microspheres of the present invention is specifically as follows: (1) Mix 100 g of petroleum ether, 0.5 g of Tween 80, 13.5 g of methyl methacrylate, 1.5 g of allyl methacrylate, 1 g of methacrylic acid and 0.43 g of azobisisobutyronitrile evenly at room temperature to obtain an oil phase; (2) Mix 14.83 g of triethyl phosphate evenly in 15 g of deionized water to obtain an aqueous phase; (3) Mix the oil phase prepared in step (1) and the aqueous phase prepared in step (2), and stir at a speed of 500 rpm for 10 min at room temperature to obtain a mixed solution; (4) Raise the temperature to 75 °C under a nitrogen atmosphere to make the mixed solution in step (3) react for 4 h, filter to obtain microspheres, then wash with petroleum ether and filter by suction three times, and air-dry naturally under ventilation in a fume hood to obtain the flame-retardant thermally expandable microspheres.

[0036] Comparative Example 1

[0037] The preparation method of the flame-retardant thermally expandable microspheres of the present invention is specifically as follows: (1) Mix 100 g of petroleum ether, 13.5 g of methyl methacrylate, 1.5 g of allyl methacrylate, 1 g of methacrylic acid, 14.83 g of n-octane and 0.43 g of azobisisobutyronitrile evenly at room temperature to obtain an oil phase; (2) Mix 1.5 g of Span 80 and 0.5 g of Tween 80 evenly in 15 g of deionized water to obtain an aqueous phase; (3) Mix the oil phase prepared in step (1) and the aqueous phase prepared in step (2), and stir at a speed of 500 rpm for 10 min at room temperature to obtain a mixed solution; (4) Raise the temperature to 75 °C under a nitrogen atmosphere to make the mixed solution in step (3) react for 4 h, filter to obtain microspheres, then wash with petroleum ether and filter by suction three times, and air-dry naturally under ventilation in a fume hood to obtain the flame-retardant thermally expandable microspheres.

[0038] Related performance tests

[0039] The heat expansion experiment and open flame flame retardancy detection were carried out on the flame retardant thermally expandable microspheres obtained in Examples 1-3 and Comparative Example 1.

[0040] Take an equal mass of thermally expandable microspheres and conduct a heat expansion experiment. Figure 1 Figures are the SEM images of the flame retardant thermally expandable microspheres before heating and after heating at 160 °C for 2 h for the thermally expandable microspheres obtained in Examples 1-3. It can be seen that the thermally expandable microspheres in Example 1 have good thermal expansion performance.

[0041] Figure 2 In which, a, b, c, and d are the states of the thermally expandable microspheres in Examples 1-3 after heating at 30 °C, 80 °C, 140 °C, and 160 °C for 2 h respectively. From Figure 2 It can be concluded that among Examples 1, 2, and 3, the microspheres in Example 1 underwent significant expansion, indicating that Example 1 successfully formed a "water-in-oil" expandable microsphere structure. Since Tween 80 was not added in Example 2, it did not form expandable microspheres. Since Span 80 was not added in Example 3, it did not finally form expandable microspheres. It can be seen that only when both Tween 80 and Span 80 are added, the outer shell has good encapsulation of the aqueous phase, so that when the temperature rises, an inner core with increased pressure can be formed, and then the microspheres expand.

[0042] Figure 3 In which, a, b, c, and d are the states of the thermally expandable microspheres in the comparative example after heating at 30 °C, 80 °C, 140 °C, and 160 °C for 2 h respectively. From Figure 3 It can be concluded that in Comparative Example 1, the microspheres in Comparative Example 1 underwent significant expansion, indicating that Comparative Example 1 successfully formed a "oil-in-water" expandable microsphere structure.

[0043] Comparison Figure 4 and Figure 5 It can be seen that the flame retardant expandable microsphere composite prepared in Example 1 has good flame retardant effect. Under the high-temperature roasting of a blowtorch, it can well protect the carbon paper from burning; while for the flame retardant expandable microsphere composite prepared in Comparative Example 1, the carbon paper burned under the high-temperature roasting of the blowtorch, and its flame retardant performance is poor.

Claims

1. A method for preparing flame retardant heat-expandable microspheres, characterized in that: The steps include: petroleum ether, olefinic acid monomer, crosslinking agent, initiator and emulsifier are mixed to obtain an oil phase; mixing a flame retardant with deionized water to obtain an aqueous phase; Under stirring, the oil phase is added to the water phase to obtain a mixed solution; The mixed solution is heated under a nitrogen atmosphere to perform a polymerization reaction, filtered, washed, and air-dried to obtain the flame-retardant heat-expandable microspheres.

2. The method for preparing flame retardant heat-expandable microspheres according to claim 1, characterized in that: The emulsifier includes Span 80 and Tween 80, and the mass ratio of Span 80 to Tween 80 is (3-4):

1.

3. The method for preparing flame retardant heat-expandable microspheres according to claim 1, characterized in that: The mass ratio of the petroleum ether, olefinic acid monomer, crosslinking agent and emulsifier is 100: (10-16): (1-2): (1-3).

4. The method for preparing flame retardant heat-expandable microspheres according to claim 1, characterized in that: The flame retardant is one or more of trimethyl phosphate, triethyl phosphate and tri(xylene) phosphate.

5. The method for preparing flame retardant heat-expandable microspheres according to claim 1, characterized in that: The olefinic monomers include methyl methacrylate and methacrylic acid, and the mass ratio of methyl methacrylate to methacrylic acid is (24-29):

2.

6. The method for preparing flame retardant heat-expandable microspheres according to claim 1, characterized in that: The polymerization reaction temperature is 75-90°C.

7. The method for preparing flame retardant heat-expandable microspheres according to claim 1, characterized in that: The water phase includes the following components in parts by weight: 0.8-1 part of a flame retardant and 1 part of water.

8. A flame retardant heat-expandable microsphere, characterized in that: Prepared by the method according to any one of claims 1 to 7.

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