Microcapsule flame retardant, flame retardant unsaturated polyester resin and preparation method thereof

Abstract

The present invention discloses a novel microcapsule flame retardant and a preparation method thereof, and relates to the technical field of flame retardants. The novel microcapsule flame retardant utilizes carboxymethyl chitosan to prepare a novel biomatrix material. Then, NF-grade cholesterol and a novel biomatrix material NF-carboxymethyl chitosan derivative are used as shell materials, and a phosphate metal salt is used as the capsule core. The novel biomatrix material carboxymethyl chitosan derivative shell material is low-cost, green and non-toxic, and is emulsified and cross-linked with NF-grade cholesterol, which can not only better encapsulate the flame retardant, but also modify the surface of the flame retardant, thereby making the microcapsule flame retardant have excellent and lasting flame retardant properties. At the same time, it can be used for flame retardant modification of unsaturated polyester resin. The obtained flame retardant unsaturated polyester resin has a vertical combustion grade of V1 and a limiting oxygen index of 33%, has good flame retardancy, is suitable for high flame retardancy requirements, and has a smoke density grade of 58, which is low smoke density and environmentally friendly.

Description

Technical Field

[0001] The present invention belongs to the technical field of flame retardants, and in particular relates to a microcapsule flame retardant, a flame retardant unsaturated polyester resin and a preparation method thereof. Background Art

[0002] Unsaturated polyester resin (UPR) is one of the most widely used thermosetting resins. Its raw materials are readily available and inexpensive, and it offers good chemical resistance, excellent mechanical properties, and a wide processing temperature range. It can be cured at room temperature and pressure, making it widely used in various fields, including industry, transportation, construction, and defense. However, UPR is primarily composed of carbon and hydrogen, with a limiting oxygen index of only 19.6%, making it highly flammable. Its flame retardancy and heat resistance are poor, producing large amounts of noxious smoke during combustion. Furthermore, the resin itself has a very poor char formation ability, with a residual char rate of only 1.16% at 700°C. Flame-retardant modification of UPR can significantly reduce the combustion risk and minimize fire damage, while also meeting the flame retardant requirements of various industries. This has significant social and economic value. Consequently, researchers both domestically and internationally have conducted extensive research on improving the flame retardancy of UPR. However, the flame retardant effect remains poor, and combustion produces significant smoke. Therefore, the development of new flame retardants is highly desirable.

[0003] Currently, there are two methods for creating flame retardants for unsaturated polyester resins: additive flame retardant modification, which involves adding flame retardants during the UPR molding process; and reactive flame retardant modification, which involves synthesizing flame-retardant UPR using intermediates containing flame retardant elements. Additive flame retardants are the mainstream choice in the flame retardant material field, and include halogen-based, nitrogen-based, and phosphorus-based flame retardants. Phosphorus-based flame retardants are numerous and widely used. Inorganic phosphorus-based flame retardants primarily include ammonium polyphosphate, red phosphorus, and phosphates; while organic phosphorus-based flame retardants primarily include phosphate esters, phosphites, and organic phosphates. In recent years, ammonium polyphosphate, phosphate esters, and phosphazene flame retardants have received significant research. Phosphorus-based flame retardants generate substances such as phosphoric acid and polyphosphoric acid during combustion, which promote the formation of a char layer on the polymer surface, blocking heat and oxygen, thereby effectively inhibiting combustion. Furthermore, compared to halogen-based flame retardants, phosphorus-based flame retardants produce less smoke and toxic gases during combustion, posing less harm to the environment and health. Most phosphorus-based flame retardants are halogen-free, environmentally friendly, and easily degradable. They can function not only as vapor-phase flame retardants but also as condensed-phase flame retardants. They also exhibit synergistic effects with nitrogen- and silicon-based flame retardants, significantly improving flame retardancy.

[0004] Existing technologies often utilize microencapsulation technology to encapsulate flame retardants, reducing their water solubility, enhancing compatibility with materials, improving their thermal stability, and masking their inherent defects. Common types currently on the market include ammonium polyphosphate microcapsules, phosphate ester microcapsules, and phosphazene microcapsules. These products also suffer from various issues, including less-than-ideal flame retardancy, excessive smoke generation during combustion, and significantly reduced mechanical properties of unsaturated polyester resins after adding microencapsulated flame retardants. Summary of the Invention

[0005] The purpose of the present invention is to provide a novel microcapsule flame retardant, a flame retardant unsaturated polyester resin and a preparation method thereof, so as to overcome the problems of poor flame retardant effect, large combustion smoke and poor compatibility with UPR in the prior art.

[0006] A microcapsule flame retardant has a core-shell structure, comprising a shell layer and a core; the shell layer is made of a derivative of cyclopentane polyhydrophenanthrene and a NF-carboxymethyl chitosan derivative, wherein the derivative of cyclopentane polyhydrophenanthrene is NF-grade cholesterol; and the core is made of a metal phosphate.

[0007] Preferably, the mass ratio of the NF-grade cholesterol, the NF-carboxymethyl chitosan derivative and the metal phosphate is 1:(4-5):(2-3).

[0008] Preferably, the raw materials for preparing the NF-carboxymethyl chitosan derivative include chitosan, a halide, a catalyst and an activator.

[0009] Preferably, the halide comprises chloroacetic acid; the catalyst comprises concentrated sulfuric acid or p-toluenesulfonic acid; and the activator comprises diimine and N-hydroxysuccinimide.

[0010] Preferably, the metal phosphate is aluminum hypophosphite, triphenyl phosphate or aluminum hypophosphite.

[0011] A method for preparing the microcapsule flame retardant is an emulsification-crosslinking method, and specifically comprises the following steps: dissolving NF-grade cholesterol in ethyl acetate as an oil phase; first dissolving an NF-carboxymethyl chitosan derivative in water, then stirring or ultrasonically dispersing a phosphate metal salt in water, then mixing and stirring the two solutions evenly as an aqueous phase, slowly mixing and stirring the oil phase and the aqueous phase to form an oil-in-water emulsion, adding a crosslinking agent, stirring, centrifuging, washing and drying to obtain microcapsule flame retardant powder.

[0012] Preferably, the cross-linking agent comprises glutaraldehyde or genipin.

[0013] Preferably, the method for preparing the microcapsule flame retardant further comprises the following steps:

[0014] Step S1: Chitosan is stirred and dispersed in isopropanol, a NaOH solution is slowly added to the chitosan suspension, and the mixture is stirred until the chitosan is fully swollen and activated. An appropriate amount of chloroacetic acid is dissolved in isopropanol and the mixture is slowly added dropwise to the chitosan suspension while stirring. The reaction mixture is heated and stirred until the reaction is complete, and the pH is adjusted to 7-8 with dilute hydrochloric acid or acetic acid to terminate the reaction. The reaction mixture is filtered or centrifuged, washed, and dried to obtain O-carboxymethyl chitosan.

[0015] Step S2: dissolving O-carboxymethyl chitosan in water, adjusting the pH to weak alkalinity, dissolving phthalic anhydride in an organic solvent, slowly adding the solution to the O-carboxymethyl chitosan and stirring the reaction, slowly adding an appropriate amount of hydroxyl compound solution to the carboxymethyl chitosan solution, then adding an activator and heating the reaction mixture with stirring until the reaction is complete, adding N2H4 and ethanol to the solution, continuing to heat and stir the reaction, and after the reaction is complete, centrifuging the reaction mixture, washing, and drying to obtain a NF-carboxymethyl chitosan derivative.

[0016] A flame-retardant unsaturated polyester resin comprises an unsaturated polyester resin, the microcapsule flame retardant, an accelerator and a curing agent, wherein the curing agent comprises methyl ethyl ketone peroxide; and the accelerator comprises cobalt naphthenate.

[0017] A method for preparing a flame-retardant unsaturated polyester resin comprises the following steps: adding the unsaturated polyester resin into a container and heating it until the fluidity is enhanced; then successively adding a flame retardant, an accelerator and a curing agent and stirring; removing the stirring bubbles; pouring the mixture into a mold and curing it at room temperature; and obtaining the flame-retardant unsaturated polyester resin after secondary aging.

[0018] NF-carboxymethyl chitosan derivatives, due to their rich hydroxyl and amino groups in their molecular chains, readily undergo dehydration reactions at high temperatures, promoting carbonization and forming a dense carbon layer. The decomposition of metal phosphates releases non-combustible gases, diluting the concentrations of oxygen and combustible gases. The nitrogen-containing structure of NF-carboxymethyl chitosan derivatives releases nitrogen-containing free radicals at high temperatures, trapping active free radicals in the combustion chain reaction and inhibiting flame propagation. The combined system of NF-carboxymethyl chitosan derivatives and metal phosphates achieves a synergistic effect through an intumescent flame retardant mechanism characterized by an "acid source-carbon source-gas source" mechanism. Furthermore, derivatives of cyclopentane polyhydrophenanthrene, which utilize polycyclic aromatic hydrocarbons to cleave at high temperatures to generate stable aromatic free radicals, synergistically inhibit flame propagation by terminating the combustion chain reaction and synergizing with NF-carboxymethyl chitosan derivatives. Their high thermal stability allows them to form a graphitized carbon layer during combustion, and they synergize with metal phosphates and NF-carboxymethyl chitosan derivatives to enhance the density of the carbon layer. Moreover, the aromatization tendency of the polycyclic structure of the derivatives of cyclopentane polyhydrophenanthrene can reduce the smoke and toxic gases produced by incomplete combustion and reduce the pollution of flame retardants to the environment.

[0019] The present invention creates a new type of microcapsule flame retardant with a significant flame retardant effect. The vertical combustion rating of the unsaturated polyester resin to which the microcapsule flame retardant is added reaches V1, and the limiting oxygen index is 33%. It has good flame retardancy and is suitable for high flame retardancy requirements, which is superior to the products currently available on the market. At the same time, the smoke density level is 58, which is low smoke density and environmentally friendly. In addition, the tensile properties of the unsaturated polyester resin were tested. The tensile strength without the addition of microcapsule flame retardant was 32.85 / MPa, while the tensile strength of the flame-retardant unsaturated polyester resin with an appropriate amount of microcapsule flame retardant was 32.25 / MPa, indicating that the microcapsule flame retardant has little effect on the mechanical properties of the unsaturated polyester resin. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is the preparation flow chart of microcapsule flame retardant.

[0021] Figure 2 This is the infrared spectrum of the microcapsule flame retardant.

[0022] Figure 3 This is a scanning electron microscope image of the microcapsule flame retardant.

[0023] Figure 4 This is the thermogravimetric analysis diagram of the microcapsule flame retardant.

[0024] Figure 5 This is the particle size distribution diagram of microcapsule flame retardant.

[0025] Figure 6 This is the heat release rate curve of flame retardant unsaturated polyester resin. DETAILED DESCRIPTION

[0026] The following is combined with Figure 1-6 The present invention is further described with reference to Examples 1-3.

[0027] The preparation of raw materials in the preparation method of microcapsule flame retardant includes but is not limited to the following steps:

[0028] Step S1: Disperse chitosan in isopropanol and stir evenly. Slowly add NaOH solution to the chitosan suspension and stir until the chitosan is fully swollen and activated. Dissolve chloroacetic acid in a small amount of isopropanol at a ratio of 1:1.5 to chitosan and slowly add it dropwise to the chitosan suspension while stirring. Heat the reaction mixture to 60°C and continue stirring for 4 hours. After the reaction is completed, adjust the pH to 7-8 with dilute hydrochloric acid or acetic acid to terminate the reaction. Filter or centrifuge the reaction mixture, wash, and dry to obtain O-carboxymethyl chitosan.

[0029] Step S2: dissolving O-carboxymethyl chitosan in water and adjusting the pH to weak alkalinity; dissolving phthalic anhydride in an organic solvent and slowly adding the solution to the O-carboxymethyl chitosan; stirring and reacting at 60°C for 6 hours; dissolving a hydroxyl-containing compound in the same organic solvent and slowly adding the solution to the carboxymethyl chitosan; using carbodiimide and N-hydroxysuccinimide as activators; heating the reaction mixture to 65°C; stirring and reacting for 8 hours; after the reaction is completed, adding N2H4 and ethanol to the solution and continuing heating and stirring for 4 hours; after the reaction is completed, centrifuging the reaction mixture, washing and drying to obtain a NF-carboxymethyl chitosan derivative.

[0030] Example 1: Dissolve 2g of NF-grade cholesterol in 12g of ethyl acetate to form the oil phase. Dissolve 10g of NF-carboxymethyl chitosan derivative in 200g of water, then add 5g of triphenyl phosphate to 300g of water. Mix the two solutions and stir until evenly mixed to form the water phase. Slowly add the oil phase to the water phase at a ratio of 1:5 by volume, stirring at 4000 rpm for 15 minutes to form a stable oil-in-water emulsion. Add the crosslinking agent glutaraldehyde and stir at 40°C for 1.5 hours to crosslink and solidify the shell. Collect the microcapsules by centrifugation or filtration. Wash with distilled water to remove unreacted material. Finally, dry to obtain a microcapsule powder. Add 10g of unsaturated polyester resin to a beaker and heat at 110°C. Once the viscosity decreases and the fluidity increases, add 2g of flame retardant and stir rapidly with a magnetic stirrer for a period of time to evenly disperse the flame retardant in the unsaturated polyester resin. Add the accelerator cobalt naphthenate and continue stirring until uniform. Then add the curing agent methyl ethyl ketone peroxide and stir. Vacuum to remove bubbles generated by stirring. The mixture is then poured into a mold and cured at room temperature. After secondary aging at 80°C for 2 hours, the sample is obtained.

[0031] Performance testing:

[0032] Limiting Oxygen Index (LOI): Tested in accordance with the provisions of GB / 8624-2012, that is, under specified conditions, the minimum oxygen concentration for the sample to maintain balanced combustion in a nitrogen and oxygen mixture;

[0033] Vertical burning performance: tested according to the provisions of GB2409-84;

[0034] Smoke density level: tested according to the provisions of GB / T 8323-2008;

[0035] Tensile strength: measured according to GB / T 1040-2006;

[0036] The above performance test results

[0037] Table 1: Effects of CMCS derivative-TPP microcapsule flame retardant on limiting oxygen index, vertical burning grade and smoke density grade of unsaturated polyester resin

[0038]

[0039] Table 2 Effect of CMCS derivative-TPP mass fraction on the tensile strength of unsaturated polyester resin

[0040]

[0041] Example 2: Dissolve 1g of NF-grade cholesterol in ethyl acetate to form the oil phase. Dissolve 5g of NF-carboxymethyl chitosan derivative in 100g of water. Add 2g of ammonium dihydrogen phosphate to 150g of water, mix the two solutions, and stir until evenly mixed to form the water phase. Slowly add the oil phase to the water phase at a ratio of 1:5, stirring at 3000 rpm for 20 minutes to form a stable oil-in-water emulsion. Add the crosslinking agent glutaraldehyde and stir at 50°C for 1.5 hours to crosslink and solidify the shell. Centrifuge or filter the emulsion to collect the microcapsules. Wash with distilled water to remove unreacted substances. Finally, dry to obtain a microcapsule powder. Add 5g of unsaturated polyester resin to a beaker and heat at 110°C. Once the viscosity decreases and the fluidity increases, add 1g of flame retardant and apply rapid magnetic stirring for a period of time to evenly disperse the flame retardant in the unsaturated polyester resin. Add the accelerator cobalt naphthenate and continue stirring until uniform. Then add the curing agent methyl ethyl ketone peroxide and stir. Vacuum to remove bubbles generated by stirring. The mixture is then poured into a mold and cured at room temperature. After secondary aging at 80°C for 2 hours, the sample is obtained.

[0042] The performance test is the same as in Example 1.

[0043] Table 3: Effect of CMCS derivative-DAP microcapsule flame retardant on limiting oxygen index, vertical burning grade and smoke density grade of unsaturated polyester resin

[0044]

[0045] Table 4: Effect of CMCS derivative-DAP mass fraction on tensile strength of unsaturated polyester resin

[0046]

[0047] Example 3: Dissolve 1g of NF-grade cholesterol in ethyl acetate to form the oil phase. Dissolve 5g of NF-carboxymethyl chitosan derivative in 100g of water. Add 2g of diethyl aluminum phosphate to 150g of water, mix the two solutions, and stir until evenly mixed to form the water phase. Slowly add the oil phase to the water phase at a ratio of 1:5, stirring at 3000 rpm for 20 minutes to form a stable oil-in-water emulsion. Add the crosslinking agent glutaraldehyde and stir at 50°C for 1.5 hours to crosslink and solidify the shell. Centrifuge or filter the emulsion to collect the microcapsules. Wash with distilled water to remove unreacted substances. Finally, dry to obtain a microcapsule powder. Add 5g of unsaturated polyester resin to a beaker and heat at 110°C. Once the viscosity decreases and the fluidity increases, add 1g of flame retardant and rapidly magnetically stir for a period of time to evenly disperse the flame retardant in the unsaturated polyester resin. Add the accelerator cobalt naphthenate and continue stirring until uniform. Then add the curing agent methyl ethyl ketone peroxide and stir. Vacuum to remove bubbles generated by stirring. The mixture is then poured into a mold and cured at room temperature. After secondary aging at 80°C for 2 hours, the sample is obtained.

[0048] The performance test is the same as in Example 1.

[0049] Table 5 Effect of CMCS derivative-OP mass fraction on the tensile strength of unsaturated polyester resin

[0050]

[0051] like Figure 2 The infrared spectrum of the microcapsule flame retardant shown is used to confirm the composition of the microcapsule flame retardant.

[0052] like Figure 3 This is a scanning electron microscope image of the microcapsule flame retardant. Direct observation shows that there are no cracks or pores on the surface of the microcapsule flame retardant, indicating that the coating effect is good.

[0053] Figure 4 This is the thermogravimetric analysis diagram of the microcapsule flame retardant, which shows that the microcapsule flame retardant has excellent thermal stability.

[0054] Figure 5 This is the particle size distribution diagram of the microcapsule flame retardant, which shows that the microcapsule flame retardant has a narrow and uniform particle size distribution and a stable preparation process.

[0055] Figure 6 The heat release rate curve of flame retardant unsaturated polyester resin is shown in FIG. 1 , where the vertical coordinate HHR is the heat release rate, indicating that the microcapsule flame retardant effectively inhibits combustion.

[0056] in Figure 4 and Figure 6 CMCSAHP is the abbreviation of microcapsule flame retardant, that is, CMCS is carboxymethyl chitosan derivative, and AHP is aluminum hypophosphite.

Claims

1. A microcapsule flame retardant, characterized in that: The microcapsule flame retardant has a core-shell structure, including a shell layer and a core; the shell layer comprises a derivative of cyclopentane polyhydrogen phenanthrene and a NF-carboxymethyl chitosan derivative, wherein the derivative of cyclopentane polyhydrogen phenanthrene is NF-grade cholesterol; the core comprises a metal phosphate, triphenyl phosphate or ammonium dihydrogen phosphate; and the preparation of the NF-carboxymethyl chitosan derivative comprises the following steps: Step S1: Chitosan is stirred and dispersed in isopropanol, a NaOH solution is slowly added to the chitosan suspension, and the mixture is stirred until the chitosan is fully swollen and activated. An appropriate amount of chloroacetic acid is dissolved in isopropanol and the mixture is slowly added dropwise to the chitosan suspension while stirring. The reaction mixture is heated and stirred until the reaction is complete, and the pH is adjusted to 7-8 with dilute hydrochloric acid or acetic acid to terminate the reaction. The reaction mixture is filtered or centrifuged, washed, and dried to obtain O-carboxymethyl chitosan. Step S2: dissolving O-carboxymethyl chitosan in water, adjusting the pH to weak alkalinity, dissolving phthalic anhydride in an organic solvent, slowly adding the solution to the O-carboxymethyl chitosan and stirring the reaction, slowly adding an appropriate amount of hydroxyl compound solution to the carboxymethyl chitosan solution, then adding an activator and heating the reaction mixture with stirring until the reaction is complete, adding N2H4 and ethanol to the solution, continuing to heat and stir the reaction, and after the reaction is complete, centrifuging the reaction mixture, washing, and drying to obtain a NF-carboxymethyl chitosan derivative.

2. The microcapsule flame retardant according to claim 1, characterized in that: The mass ratio of the NF-grade cholesterol, the NF-carboxymethyl chitosan derivative and the phosphate metal salt is 1:(4-5):(2-3).

3. The microcapsule flame retardant according to claim 1, characterized in that: The raw materials for preparing the NF-carboxymethyl chitosan derivative include a catalyst.

4. The microcapsule flame retardant according to claim 3, characterized in that: The catalyst includes concentrated sulfuric acid or p-toluenesulfonic acid; and the activator includes carbodiimide and N-hydroxysuccinimide.

5. The microcapsule flame retardant according to claim 1, characterized in that: The metal phosphate is aluminum hypophosphite.

6. A method for preparing the microcapsule flame retardant according to any one of claims 1 to 5, characterized in that: The method is an emulsification-crosslinking method, which specifically comprises the following steps: dissolving NF-grade cholesterol in ethyl acetate as an oil phase; first dissolving a NF-carboxymethyl chitosan derivative in water, then stirring or ultrasonically dispersing a metal phosphate, triphenyl phosphate or ammonium dihydrogen phosphate in water, then mixing and stirring the two solutions evenly as an aqueous phase, slowly mixing and stirring the oil phase and the aqueous phase to form an oil-in-water emulsion, adding a crosslinking agent, then stirring, centrifuging, washing and drying to obtain a microcapsule flame retardant powder.

7. The method for preparing a microcapsule flame retardant according to claim 6, wherein: The cross-linking agent includes glutaraldehyde or genipin.

8. A flame retardant unsaturated polyester resin, characterized in that: The flame-retardant unsaturated polyester resin comprises an unsaturated polyester resin, the microcapsule flame retardant according to any one of claims 1 to 5, an accelerator and a curing agent, wherein the curing agent comprises methyl ethyl ketone peroxide; and the accelerator comprises cobalt naphthenate.

9. A method for preparing the flame-retardant unsaturated polyester resin according to claim 8, characterized in that: Unsaturated polyester resin is added into a container and heated until fluidity is enhanced, and then flame retardant, accelerator and curing agent are added successively and stirred. After removing stirring bubbles, the mixture is poured into a mold and cured at room temperature. After secondary aging, flame retardant unsaturated polyester resin is obtained.

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