Microcapsule flame retardant, flame-retardant unsaturated polyester resin and preparation method of flame-retardant unsaturated polyester resin

Abstract

The invention discloses a novel microcapsule flame retardant and a preparation method thereof, and relates to the technical field of flame retardants. According to the novel microcapsule flame retardant, a novel biological matrix material is prepared from carboxymethyl chitosan. Then taking NF-grade cholesterol and a novel biological matrix material NF-carboxymethyl chitosan derivative as a shell material, and taking phosphoric acid metal salt as a capsule core; the novel biological matrix material carboxymethyl chitosan derivative shell material is low in cost, green and non-toxic, and is emulsified and cross-linked with NF-grade cholesterol, so that the flame retardant can be better coated, the surface of the flame retardant can be modified, and the microcapsule flame retardant has excellent and lasting flame retardant property. The flame retardant can be used for flame retardant modification of unsaturated polyester resin, the vertical combustion grade of the obtained flame retardant unsaturated polyester resin reaches V1, the limit oxygen index is 33%, and the flame retardant unsaturated polyester resin has good flame retardance, is suitable for high flame retardant requirements, has the smoke density grade of 58, and is low in smoke density and environmentally friendly.

Description

Technical Field

[0001] The present invention belongs to the technical field of flame retardants, and particularly 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. It has easily available raw materials, low price, good chemical corrosion resistance, excellent mechanical properties, and a wide processing temperature range. It can be cured at normal temperature and pressure and is widely used in many fields such as industry, transportation, construction, and national defense. However, UPR is mainly composed of carbon and hydrogen elements, with a limiting oxygen index of only 19.6%, being extremely flammable, having poor flame retardancy and heat resistance. When burning, it will produce a large amount of harmful thick smoke, and the char-forming ability of the resin itself is very poor, with a char residue rate of only 1.16% at 700 °C. Flame retardant modification of UPR can significantly reduce the combustion risk of unsaturated polyester resin, reduce fire losses, and at the same time meet the requirements of various industries for the flame retardancy of materials, which has important social and economic value. Therefore, researchers at home and abroad have conducted a large number of studies on improving the flame retardancy of UPR. However, there are still problems such as poor flame retardant effect and a large amount of smoke generated during combustion. Therefore, the innovative invention of a new type of flame retardant is extremely necessary.

[0003] At present, there are the following two methods for flame retardants of unsaturated polyester resin: one is additive flame retardant modification, that is, adding a flame retardant during the UPR forming process; the other is reactive flame retardant modification, that is, using an intermediate containing a flame retardant element as a raw material to synthesize flame retardant UPR. Additive flame retardants are the mainstream choice in the field of flame retardant materials, including halogen-based flame retardants, nitrogen-based flame retardants, phosphorus-based flame retardants, etc. Among them, phosphorus-based flame retardants have a large variety and wide uses. Inorganic phosphorus-based flame retardants mainly include ammonium polyphosphate, red phosphorus, and phosphates; organic phosphorus-based flame retardants mainly include phosphates, phosphites, and organic phosphates. In recent years, the mainly studied ones are ammonium polyphosphate, phosphates, and phosphazene flame retardants, etc. Phosphorus-based flame retardants generate substances such as phosphoric acid and polyphosphoric acid during combustion, promoting the formation of a carbon layer on the polymer surface, blocking heat and oxygen, thereby effectively inhibiting combustion. And compared with halogen-based flame retardants, phosphorus-based flame retardants produce less smoke and toxic gases during combustion, with less harm to the environment and the human body. Most phosphorus-based flame retardants do not contain halogens, meet environmental protection requirements, and are easy to degrade. Phosphorus-based flame retardants can not only be used as gas-phase flame retardants but also as condensed-phase flame retardants. At the same time, phosphorus-based flame retardants have good synergistic effects with nitrogen-based and silicon-based flame retardants, which can significantly improve the flame retardant efficiency.

[0004] In the prior art, the microencapsulation technology is often adopted to encapsulate the flame retardant, reduce its water solubility, enhance its compatibility with materials, improve the thermal stability of the flame retardant, and cover up the defects of the flame retardant itself. The common types on the market at present include ammonium polyphosphate microcapsules, phosphate ester microcapsules, phosphazene microcapsules, etc. These products also have more or less problems such as less than ideal flame retardant effect, too much smoke during combustion, and greatly reduced mechanical properties after adding the microcapsule flame retardant to unsaturated polyester resin. 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 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, the microcapsule flame retardant has a core-shell structure, including a shell layer and a core; the material of the shell layer includes derivatives of cyclopentane polyhydrophenanthrene and NF-carboxymethyl chitosan derivatives, and the derivative of cyclopentane polyhydrophenanthrene is NF-grade cholesterol; the material of the core includes metal phosphate salts.

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

[0008] Preferably, the preparation raw materials of the NF-carboxymethyl chitosan derivative include chitosan, halide, catalyst and activator.

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

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

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

[0012] Preferably, the crosslinking agent includes glutaraldehyde or genipin.

[0013] Preferably, the method for preparing the microcapsule flame retardant further includes the following steps: Step S1: Stir and disperse chitosan in isopropanol. Slowly add an NaOH solution to the chitosan suspension, and stir until the chitosan is fully swollen and activated. Dissolve an appropriate amount of chloroacetic acid in isopropanol, and slowly drip it into the chitosan suspension while keeping stirring. After heating and stirring the reaction mixture until 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 it to obtain O-carboxymethyl chitosan; Step S2: Dissolve O-carboxymethyl chitosan in water and adjust the pH to weakly alkaline. Dissolve phthalic anhydride in an organic solvent, and slowly add it to the O-carboxymethyl chitosan solution and stir for reaction. Slowly add an appropriate amount of hydroxy compound solution to the carboxymethyl chitosan solution, and then add an activator. After heating and stirring the reaction mixture until the reaction is completed, add N2H4 and ethanol to the solution and continue heating and stirring. After the reaction is completed, centrifuge the reaction mixture, wash and dry it to obtain an NF-carboxymethyl chitosan derivative.

[0014] A flame-retardant unsaturated polyester resin, which comprises an unsaturated polyester resin, the microcapsule flame retardant as described above, an accelerator and a curing agent. The curing agent comprises methyl ethyl ketone peroxide; the accelerator comprises cobalt naphthenate.

[0015] A preparation method of a flame-retardant unsaturated polyester resin. After adding the unsaturated polyester resin into a container and heating it until its fluidity is enhanced, successively add a flame retardant, an accelerator and a curing agent and stir. After removing the stirring bubbles, pour the mixture into a mold and cure it at room temperature. After secondary curing, a flame-retardant unsaturated polyester resin is obtained.

[0016] Among them, the NF-carboxymethyl chitosan derivative is rich in hydroxyl and amino groups in its molecular chain, and is prone to dehydration reaction at high temperature, which can promote carbonization to form a dense carbon layer. During the decomposition process of the metal phosphate, incombustible gases are released, diluting the concentrations of oxygen and combustible gases. The nitrogen-containing structure of the NF-carboxymethyl chitosan derivative can release nitrogen free radicals at high temperature, capture the active free radicals in the combustion chain reaction, and inhibit flame propagation. The compound system of the NF-carboxymethyl chitosan derivative and the metal phosphate realizes a synergistic effect through the intumescent flame retardant mechanism of "acid source - carbon source - gas source". At the same time, derivatives of cyclopentane polyhydrophenanthrene are used. The polycyclic aromatic hydrocarbon derivatives can be cracked at high temperature to generate stable aromatic free radicals, and cooperate with the NF-carboxymethyl chitosan derivative to inhibit flame propagation by terminating the combustion chain reaction. And due to its high thermal stability, it can form a graphitized carbon layer during combustion, and can also cooperate with the metal phosphate and the NF-carboxymethyl chitosan derivative to enhance the compactness 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 generated by incomplete combustion, and reduce the environmental pollution of the flame retardant.

[0017] A novel microcapsule flame retardant of the present invention has an obvious flame retardant effect. The vertical burning grade of the unsaturated polyester resin added with the microcapsule flame retardant reaches V1, and the limiting oxygen index is 33%, showing good flame retardancy and being suitable for high flame retardant requirements, which is superior to the existing products on the market. At the same time, the smoke density grade is 58, which is a low smoke density and environmentally friendly. And the tensile property test of the unsaturated polyester resin shows that the tensile strength of the unsaturated polyester resin without adding the microcapsule flame retardant is 32.85 / MPa, and the tensile strength of the flame retardant unsaturated polyester resin added with an appropriate amount of the microcapsule flame retardant is 32.25 / MPa, indicating that the microcapsule flame retardant has little effect on the mechanical properties of the unsaturated polyester resin. Description of the Drawings

[0018] Figure 1 It is the preparation flow chart of the microcapsule flame retardant.

[0019] Figure 2 It is the infrared spectrum diagram of the microcapsule flame retardant.

[0020] Figure 3 It is the scanning electron microscope image of the microcapsule flame retardant.

[0021] Figure 4 It is the thermogravimetric analysis diagram of the microcapsule flame retardant.

[0022] Figure 5 It is the particle size distribution diagram of the microcapsule flame retardant.

[0023] Figure 6 It is the heat release rate curve diagram of the flame retardant unsaturated polyester resin. Detailed Embodiments

[0024] The following further describes the present invention in combination with Figure 1-6 Examples 1-3.

[0025] In the method for preparing the microcapsule flame retardant, the preparation of the preliminary raw materials includes but is not limited to the following steps: Step S1: Disperse chitosan in isopropanol, stir evenly, slowly add NaOH solution to the chitosan suspension, stir until the chitosan is fully swollen and activated, dissolve chloroacetic acid with a ratio of 1:1.5 to chitosan in a small amount of isopropanol, slowly drop it into the chitosan suspension while keeping stirring, heat the reaction mixture to 60°C, continuously stir and react for 4 hours. After the reaction is completed, adjust to pH 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; Step S2: Dissolve O-carboxymethyl chitosan in water, adjust the pH to weakly alkaline, dissolve phthalic anhydride in an organic solvent, slowly add it to the O-carboxymethyl chitosan solution, stir and react at 60 °C for 6 hours. Dissolve the hydroxyl-containing compound in the same organic solvent, slowly add it to the carboxymethyl chitosan solution, use carbodiimide and N-hydroxysuccinimide as activators, heat the reaction mixture to 65 °C, and continuously stir and react for 8 hours. After the reaction is completed, add N2H4 and ethanol to the solution and continue to heat and stir for 4 hours. After the reaction, centrifuge the reaction mixture, wash and dry it to obtain the NF-carboxymethyl chitosan derivative.

[0026] Example 1: Dissolve 2 g of NF-grade cholesterol in 12 g of ethyl acetate as the oil phase. Dissolve 10 g of NF-carboxymethyl chitosan derivative in 200 g of water, and then add 5 g of triphenyl phosphate to 300 g of water. Mix the two solutions and stir evenly as the water phase. According to the volume ratio of the oil phase to the water phase of 1:5, slowly add the oil phase to the water phase, and stir 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 cure the shell layer. Centrifuge or filter the emulsion to collect the microcapsules. Wash with distilled water to remove unreacted substances. Finally, dry to obtain the microcapsule powder. Add 10 g of unsaturated polyester resin to a beaker, heat it at 110 °C. After its viscosity decreases and fluidity increases, add 2 g of flame retardant and quickly stir magnetically for a period of time to disperse the flame retardant evenly in the unsaturated polyester resin. Add the accelerator cobalt naphthenate and continue to stir evenly, then add the curing agent methyl ethyl ketone peroxide and stir, and evacuate to remove the bubbles generated by stirring. Then pour the mixture into a mold and cure it at room temperature, and post-cure it at 80 °C for 2 h to obtain the specimen.

[0027] Performance test: Limiting oxygen index (LOI): Tested according to the provisions of GB / 8624-2012, that is, under the specified conditions, the lowest oxygen concentration at which the specimen maintains equilibrium combustion in a nitrogen-oxygen mixed gas; Vertical burning performance: Tested according to the provisions of GB2409-84; Smoke density grade: Tested according to the provisions of GB / T 8323-2008; Tensile strength: Determined according to the provisions of GB / T 1040-2006; The above performance test results Table 1: Effects of CMCS derivative-TPP microcapsule flame retardant on the limiting oxygen index, vertical burning grade and smoke density grade of unsaturated polyester resin

[0028]

[0029] Table 2 Influence of CMCS Derivative - TPP Mass Fraction on Tensile Strength of Unsaturated Polyester Resin

[0030]

[0031] Example 2: Dissolve 1 g of NF - grade cholesterol in ethyl acetate as the oil phase. Dissolve 5 g of NF - carboxymethyl chitosan derivative in 100 g of water, and add 2 g of ammonium dihydrogen phosphate to 150 g of water. Mix the two solutions and stir evenly as the water phase. Slowly add the oil phase to the water phase at a ratio of 1:5 of the oil phase to the water phase, and stir at 3000 rpm for 20 minutes to form a stable oil - in - water emulsion. Add the cross - linker glutaraldehyde and stir at 50 °C for 1.5 hours to cross - link and cure the shell layer. Centrifuge or filter the emulsion to collect the microcapsules. Wash with distilled water to remove unreacted substances. Finally, dry to obtain microcapsule powder. Add 5 g of unsaturated polyester resin to a beaker, heat it at 110 °C. After its viscosity decreases and fluidity increases, add 1 g of flame retardant and stir rapidly with a magnetic stirrer for a period of time to disperse the flame retardant evenly in the unsaturated polyester resin. Add the accelerator cobalt naphthenate and continue to stir evenly, then add the curing agent methyl ethyl ketone peroxide and stir, and evacuate to remove the bubbles generated by stirring. Then pour the mixture into a mold and cure it at room temperature, and post - cure it at 80 °C for 2 h to obtain the specimen.

[0032] Performance testing is as in Example 1.

[0033] Table 3: Influence of CMCS Derivative - DAP Microcapsule Flame Retardant on Limiting Oxygen Index, Vertical Burning Grade and Smoke Density Grade of Unsaturated Polyester Resin

[0034]

[0035] Table 4: Influence of CMCS Derivative - DAP Mass Fraction on Tensile Strength of Unsaturated Polyester Resin

[0036]

[0037] Example 3: Dissolve 1 g of NF-grade cholesterol in ethyl acetate as the oil phase. Dissolve 5 g of NF-carboxymethyl chitosan derivative in 100 g of water, and dissolve 2 g of aluminum diethyl phosphate in 150 g of water. Mix the two solutions and stir evenly as the water phase. Slowly add the oil phase to the water phase at a ratio of 1:5 of the oil phase to the water phase, and stir at 3000 rpm for 20 minutes to form a stable oil-in-water emulsion. Add the cross-linking agent glutaraldehyde and stir at 50 °C for 1.5 hours to cross-link and cure the shell layer. Centrifuge or filter the emulsion to collect the microcapsules. Wash with distilled water to remove unreacted substances. Finally, dry to obtain microcapsule powder. Add 5 g of unsaturated polyester resin to a beaker and heat it at 110 °C. After its viscosity decreases and fluidity increases, add 1 g of flame retardant and stir rapidly with a magnetic stirrer for a period of time to disperse the flame retardant evenly in the unsaturated polyester resin. Add the accelerator cobalt naphthenate and continue to stir evenly, then add the curing agent methyl ethyl ketone peroxide and stir, and evacuate to remove the bubbles generated by stirring. Then pour the mixture into a mold and cure it at room temperature, and post-cure it at 80 °C for 2 h to obtain a specimen.

[0038] The performance test was carried out as in Example 1.

[0039] Table 5 Effect of CMCS derivative-OP mass fraction on the tensile strength of unsaturated polyester resin

[0040]

[0041] As Figure 2 shown, the infrared spectrum of the microcapsule flame retardant was used to confirm its composition.

[0042] As Figure 3 shown is the scanning electron micrograph of the microcapsule flame retardant. Direct observation shows that there are no cracks and pores on the surface of the microcapsule flame retardant, indicating good coating effect.

[0043] Figure 4 Shown is the thermogravimetric analysis chart of the microcapsule flame retardant, indicating that the microcapsule flame retardant has excellent thermal stability.

[0044] Figure 5 Shown is the particle size distribution chart of the microcapsule flame retardant, indicating that the microcapsule flame retardant has a narrow and uniform particle size distribution and a stable preparation process.

[0045] Figure 6 Shown is the heat release rate curve of the flame-retardant unsaturated polyester resin. The vertical coordinate HHR is the heat release rate, indicating that the microcapsule flame retardant effectively inhibits combustion.

[0046] Where Figure 4 and Figure 6 CMCSAHP in is the abbreviation of the 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 material of the shell layer includes derivatives of cyclopentane polyhydrophenanthrene and NF-carboxymethyl chitosan derivatives, and the derivative of cyclopentane polyhydrophenanthrene is NF-grade cholesterol; the material of the core includes metal phosphate salts.

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

3. The microcapsule flame retardant according to claim 1, characterized in that: The preparation raw materials of the NF-carboxymethyl chitosan derivative include chitosan, halide, catalyst and activator.

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

5. The microcapsule flame retardant according to claim 1, characterized in that: The metal phosphate salt is aluminum hypophosphite, triphenyl phosphate or 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 the emulsification-crosslinking method, and the specific steps include: dissolving NF-grade cholesterol in ethyl acetate as the oil phase; first dissolving the NF-carboxymethyl chitosan derivative in water, then stirring or ultrasonically dispersing the metal phosphate salt in water, and then mixing the two solutions and stirring evenly as the water phase, slowly mixing the oil phase and the water phase and stirring to form an oil-in-water emulsion, adding a crosslinking agent and then stirring, centrifuging, washing and drying to obtain the microcapsule flame retardant powder.

7. The method for preparing the microcapsule flame retardant according to claim 6, wherein: The crosslinking agent includes glutaraldehyde or genipin.

8. The method for preparing the microcapsule flame retardant according to claim 6, wherein, The preparation of the NF-carboxymethyl chitosan derivative includes the following steps: Step S1: Stir and disperse chitosan in isopropanol, slowly add NaOH solution to the chitosan suspension, stir until the chitosan is fully swollen and activated, dissolve an appropriate amount of chloroacetic acid in isopropanol, slowly drop it into the chitosan suspension while keeping stirring, heat and stir the reaction mixture until the reaction is completed, adjust to pH 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; Step S2: Dissolve O-carboxymethyl chitosan in water, adjust the pH to weakly alkaline, dissolve phthalic anhydride in an organic solvent, slowly add it to the O-carboxymethyl chitosan solution and stir to react, slowly add an appropriate amount of hydroxy compound solution to the carboxymethyl chitosan solution, then add an activator and heat and stir the reaction mixture until the reaction is completed, add N2H4 and ethanol to the solution and continue to heat and stir until the reaction is completed, then centrifuge the reaction mixture, wash and dry to obtain the NF-carboxymethyl chitosan derivative.

9. A flame-retardant unsaturated polyester resin, characterized in that: The flame-retardant unsaturated polyester resin includes unsaturated polyester resin, the microcapsule flame retardant as described in any one of claims 1-5, accelerator and curing agent, the curing agent includes methyl ethyl ketone peroxide; the accelerator includes cobalt naphthenate.

10. A method for preparing the flame-retardant unsaturated polyester resin according to claim 9, characterized in that: After adding the unsaturated polyester resin into a container and heating until its fluidity is enhanced, successively add the flame retardant, accelerator and curing agent and stir, remove the stirring bubbles, then pour the mixture into a mold and cure it at room temperature, and obtain the flame-retardant unsaturated polyester resin after secondary aging.

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