Preparation method and application method of vanillin-containing DOPO-based flame retardant

Abstract

The invention relates to a preparation method and an application method of a vanillin-containing DOPO-based flame retardant, and relates to a preparation method and an application method of an epoxy resin flame retardant, the method comprises the following steps: synthesizing a Schiff base intermediate by using vanillin (3-methoxy-4-hydroxybenzaldehyde) and 5-aminotetrazole as raw materials, and then carrying out substitution reaction on the intermediate and DOPO to obtain the vanillin-containing DOPO-based flame retardant. And synthesizing to obtain the novel vanillin DOPO-based halogen-free flame retardant. The structural formula is shown in the figure. According to the application of the flame retardant, the synthesized novel vanillin-containing DOPO flame retardant and epoxy resin are cured under the action of a DDM curing agent (4, 4-diamino diphenylmethane), an epoxy resin cured product containing the vanillin-containing DOPO flame retardant is obtained, and the obtained flame retardant modified epoxy resin has good flame retardant performance, little smoke is released in the combustion process, and the charring property is good. A compact carbon layer can be formed, and heat and combustible gas are isolated. The vertical combustion grade and the limit oxygen index of the epoxy resin are obviously improved.

Description

Technical Field

[0001] The invention relates to a preparation method of a DOPO-based flame retardant containing vanillin and an application method thereof, and in particular to a preparation method of an epoxy resin flame retardant and an application method thereof. Background Art

[0002] Epoxy resin (EP) is a key polymer material with low cost, low shrinkage, excellent mechanical properties, good insulation and strong chemical resistance. It is widely used in many fields such as surface coating, bonding, microelectronics and high-performance composites. However, EP is flammable and often needs to be added with flame retardants to improve its flame retardancy. Phosphorus-containing flame retardants have attracted much attention for their excellent flame retardant properties because they can effectively remove active free radicals in the combustion gas phase to block chain reactions and promote the formation of condensed phase carbon layers to prevent further combustion of materials.

[0003] 9,10-Dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) is a reactive phosphorus-based flame retardant with excellent performance, small addition amount and good flame retardant effect. It is widely used in the field of flame retardant polymers because of its non-toxicity and high phosphorus content, and has great development potential. However, when DOPO is added alone, the ideal flame retardant effect can only be achieved at a high content, and the mechanical properties of the material will be significantly reduced. DOPO has significant advantages in molecular structure design and synthesis. Its highly reactive PH bond can introduce flame retardant elements such as nitrogen, sulfur, silicon, and boron. DOPO derivatives designed based on this show better flame retardant efficiency for EP. In addition, lignin is the second largest natural resource in the world and is widely distributed in various plants. In recent years, vanillin and eugenol extracted from lignin have great potential in the design and synthesis of thermosetting plastics and intrinsic flame retardants. The ether bond in the vanillin structure can be cracked at high temperature to produce non-flammable gases such as carbon dioxide and water vapor. The rigid benzene ring structure gives its synthetic material excellent thermal stability. The material is easy to modify and environmentally friendly, making it one of the high-quality choices for the design and synthesis of flame retardant molecules. Summary of the invention

[0004] The purpose of the present invention is to provide a preparation method of a DOPO-based flame retardant containing vanillin and an application method thereof. The vanillin-containing DOPO flame retardant is introduced into an epoxy resin system to impart excellent flame retardant properties to the epoxy resin, exhibit good charring performance in the combustion process, and can generate a dense char layer, which greatly improves the limiting oxygen index LOI of the epoxy resin, has good thermal stability, and has significant flame retardant effect.

[0005] The technical solution of the present invention is:

[0006] A method for preparing a DOPO-based flame retardant containing vanillin, the method comprising the following steps:

[0007] First, a DOPO-based halogen-free flame retardant is prepared, vanillin and 5-aminotetrazole are added to a solvent in a molar ratio of 1:1, and then an acid binding agent is added so that the reaction process is carried out in an alkaline environment. The reaction system is placed in a three-necked flask equipped with a magnetic stirrer and a reflux condenser; the reaction temperature is controlled to be 60-80°C, and the temperature is maintained for 8-10 hours under constant stirring; then a DOPO solution is added, and stirring is continued for 8-12 hours at a temperature of 60-80°C and under the protection of nitrogen; a crude product is obtained by rotary evaporation, recrystallized in anhydrous ethanol, filtered, and washed with deionized water for 3 times; then the product is dried in an oven at 70°C to constant weight to obtain a white powder flame retardant;

[0008] Its structural formula is:

[0009]

[0010] In the method for preparing a DOPO-based flame retardant containing vanillin, the acid-binding agent comprises at least one of potassium hydroxide, sodium hydroxide, pyridine, imidazole, triethylamine, potassium tert-butoxide, sodium ethoxide, sodium methoxide and diethylamine.

[0011] In the method for preparing a DOPO-based flame retardant containing vanillin, the organic solvent comprises one of acetonitrile, hexamethylphosphoric triamide, dimethylacetamide, tetrahydrofuran, cyclopentanone, dichloromethane, chloroform, carbon tetrachloride, methanol, ethanol, and N-methylpyrrolidone.

[0012] The method for preparing a DOPO-based flame retardant containing vanillin, wherein the organic solvent includes any one of acetonitrile, hexamethylphosphoric triamide, dimethylacetamide, tetrahydrofuran, cyclopentanone, dichloromethane, chloroform, carbon tetrachloride, methanol, ethanol, and N-methylpyrrolidone and DOPO mixed at a molar ratio of 2:1.

[0013] In the method for preparing a DOPO-based flame retardant containing vanillin, the solvent comprises at least one of methanol, ethanol, chloroform, dimethylamide, dioxane, and isopropanol.

[0014] An application of a DOPO-based flame retardant containing vanillin. The flame retardant is applied to the flame retardant modification of epoxy resin. The vanillin DOPO flame retardant and epoxy resin are cured under the action of a DDM (4,4-diaminodiphenylmethane) curing agent to obtain a flame retardant epoxy resin.

[0015] The application of the vanillin-containing DOPO-based flame retardant, the type of epoxy resin includes one of E51, E44, DGEBF, and F-51.

[0016] The application of the vanillin-containing DOPO-based flame retardant is that the addition amount of the vanillin-containing DOPO flame retardant is 3%.

[0017] The beneficial effects of the present invention are:

[0018] 1. The synthesis route of the vanillin-containing DOPO flame retardant is simple, the reaction conditions are easy to control, it has a high yield, and it is easy to purify.

[0019] 2. The new vanillin-containing DOPO flame retardant is introduced into the epoxy resin system, which gives the epoxy resin excellent flame retardant properties, exhibits good charring performance in the combustion process, and can generate a dense char layer, greatly improving the limiting oxygen index LOI of the epoxy resin, with good thermal stability and significant flame retardant effect.

[0020] 3. When the addition amount of vanillin DOPO flame retardant in flame retardant epoxy resin is 3%, UL-94 test reaches V-0 level, the limiting oxygen index reaches 31%, the glass transition temperature reaches Tg=140℃, and it also shows good thermal stability in the thermogravimetric analysis of the composite material and has good transparency. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 The structural formula of the vanillin DOPO-based halogen-free flame retardant of the present invention;

[0022] Figure 2 This is the infrared spectrum of the vanillin-containing DOPO-based halogen-free flame retardant of the present invention;

[0023] Figure 3 The nuclear magnetic resonance hydrogen spectrum (a) and phosphorus spectrum (b) of the vanillin DOPO-based halogen-free flame retardant of the present invention;

[0024] Figure 4 The thermogravimetric analysis diagrams of epoxy resins modified with vanillin DOPO-based halogen-free flame retardants of different components of the present invention and pure epoxy resin samples;

[0025] Figure 5 The present invention provides a novel vanillin-containing DOPO-based halogen-free flame retardant modified epoxy resin and a glass transition temperature Tg analysis diagram of a pure epoxy resin sample. DETAILED DESCRIPTION

[0026] The technical solution of the present invention will be clearly and completely explained below through specific implementation cases. It is clear that the embodiments mentioned are only part of the many embodiments of the present invention and do not cover all of them. According to the embodiments included in the present invention, all other embodiments obtained by ordinary technicians in this field without carrying out creative work are within the protection scope of the present invention.

[0027] The present invention provides a novel vanillin-containing DOPO-based halogen-free flame retardant, the structural formula of which is:

[0028]

[0029] Please refer to the attached Figure 1-5 .

[0030] On the basis of the structural framework of the vanillin-containing DOPO flame retardant molecule being basically unchanged, the environmentally friendly bio-based material vanillin with excellent thermal stability and compatibility and the molecular structure with high nitrogen content (5-aminotetrazolyl) are introduced. Adding them into the epoxy resin system gives the epoxy resin excellent flame retardant properties, exhibits good carbonization performance in the combustion process, can generate a dense carbon layer, greatly improves the limiting oxygen index LOI of the epoxy resin, has good thermal stability, and has significant flame retardant effect.

[0031] The present invention also provides a method for preparing the novel vanillin-containing DOPO flame retardant, comprising the following steps:

[0032] Step 1: A simple one-pot method was used to prepare the DOPO-based halogen-free flame retardant, and vanillin and 5-aminotetrazole were added to the solvent in a molar ratio of 1:1.

[0033] Step 2: Add an appropriate amount of acid-binding agent (so that the reaction process is carried out in an alkaline environment), and place the reaction system in a three-necked flask equipped with a magnetic stirrer and a reflux condenser. Control the reaction temperature to 60-80°C and maintain the temperature for 8-10 hours under constant stirring.

[0034] Step 3: Finally, add DOPO solution and continue stirring at 60-80°C under nitrogen protection for 8-12 hours. Rotary evaporation to obtain a crude product, recrystallize in anhydrous ethanol, filter, and wash with deionized water three times. Then dry the product in an oven at 70°C to constant weight to obtain a white powder.

[0035] The synthetic route in the preparation method is as follows:

[0036]

[0037] In the preparation method of the novel vanillin-containing DOPO-based halogen-free flame retardant, the acid-binding agent comprises at least one of potassium hydroxide, sodium hydroxide, pyridine, imidazole, triethylamine, potassium tert-butoxide, sodium ethoxide, sodium methoxide and diethylamine.

[0038] The preparation method of the novel vanillin-containing DOPO-based halogen-free flame retardant, the organic solvent includes one of acetonitrile, hexamethylphosphoric triamide, dimethylacetamide, tetrahydrofuran, cyclopentanone, dichloromethane, chloroform, carbon tetrachloride, methanol, ethanol, and N-methylpyrrolidone.

[0039] The DOPO solution, the solvent includes at least one of methanol, ethanol, chloroform, dimethylformamide, dioxane, and isopropanol.

[0040] The preparation method of the novel vanillin-containing DOPO-based halogen-free flame retardant, the organic solvent includes any one of acetonitrile, hexamethylphosphoric triamide, dimethylacetamide, tetrahydrofuran, cyclopentanone, dichloromethane, chloroform, carbon tetrachloride, methanol, ethanol, N-methylpyrrolidone and DOPO mixed at a molar ratio of 2:1.

[0041] The main absorption peak of the infrared absorption spectrum of the novel vanillin-containing DOPO halogen-free flame retardant synthesized by the present invention is: 3156cm -1 , 1205cm -1 , 927cm -1 and 752cm -1 . Nuclear magnetic resonance hydrogen spectrum: 6.7-6.9ppm, 5.0-5.3ppm, 9.0ppm and 6.2-8.2ppm. Nuclear magnetic resonance phosphorus spectrum: 28.7ppm and 30.0ppm

[0042] Example 1

[0043] This embodiment provides a method for preparing a novel vanillin-containing DOPO-based halogen-free flame retardant, comprising the following steps:

[0044] A simple one-pot method was used to prepare DOPO-based halogen-free flame retardant. Vanillin (0.04 mol, 6.08 g) and 5-aminotetrazolyl (0.04 mol, 3.40 g) were added to a 250 mL three-necked flask equipped with a magnetic stirrer and a reflux condenser, and potassium hydroxide (0.04 mol, 2.24 g) was added as an acid-binding agent to the reaction system. The reaction temperature was controlled to 60 ° C and maintained at this temperature for 8 h under constant stirring.

[0045] Finally, DOPO ethanol solution (0.04 mol, 11.04 g) was added and stirred for 8 h at 60 ° C under nitrogen (10 mL / min). The crude product was obtained by rotary evaporation, recrystallized in anhydrous ethanol, filtered, and washed with deionized water three times. The product was then dried in an oven at 70 ° C to constant weight to obtain 15.4 g of white powder with a yield of 89%.

[0046] Example 2

[0047] This embodiment provides a method for preparing a novel vanillin-containing DOPO-based halogen-free flame retardant, comprising the following steps:

[0048] A simple one-pot method was used to prepare DOPO-based halogen-free flame retardant. Vanillin (0.04 mol, 6.08 g) and 5-aminotetrazolyl (0.04 mol, 3.40 g) were added to a 250 mL three-necked flask equipped with a magnetic stirrer and a reflux condenser, and sodium hydroxide (0.04 mol, 1.6 g) was added as an acid binding agent to the reaction system. The reaction temperature was controlled to 70 ° C and maintained at this temperature for 9 h under constant stirring.

[0049] Finally, DOPO ethanol solution (0.04 mol, 11.04 g) was added and stirred for 10 h at 70 ° C under nitrogen (10 mL / min). The crude product was obtained by rotary evaporation, recrystallized in anhydrous ethanol, filtered, and washed with deionized water three times. The product was then dried in an oven at 70 ° C to constant weight to obtain 16.0 g of white powder with a yield of 92%.

[0050] Example 3

[0051] This embodiment provides a method for preparing a novel vanillin-containing DOPO-based halogen-free flame retardant, comprising the following steps:

[0052] A simple one-pot method was used to prepare DOPO-based halogen-free flame retardant. Vanillin (0.04 mol, 6.08 g) and 5-aminotetrazolyl (0.04 mol, 3.40 g) were added to a 250 mL three-necked flask equipped with a magnetic stirrer and a reflux condenser, and potassium hydroxide (0.04 mol, 2.24 g) was added as an acid-binding agent to the reaction system. The reaction temperature was controlled to 80 ° C and maintained at this temperature for 10 h under constant stirring.

[0053] Finally, DOPO ethanol solution (0.04 mol, 11.04 g) was added and stirred for 12 h at 80 ° C under nitrogen (10 mL / min). The crude product was obtained by rotary evaporation, recrystallized in anhydrous ethanol, filtered, and washed with deionized water three times. The product was then dried in an oven at 70 ° C to constant weight to obtain 16.5 g of white powder with a yield of 95%.

[0054] The novel vanillin-containing DOPO-based halogen-free flame retardant prepared in Examples 1-3 was added to the epoxy resin matrix in different proportions (the specific control group proportions are shown in Table 1) to obtain several groups of different flame-retardant epoxy resin composite materials, which were then subjected to combustion performance tests, thermogravimetric analysis tests and heat resistance tests.

[0055] Combustion performance test: Take 50g of epoxy resin and put it into a 200mL beaker. When heated to 120°C, add the flame retardants prepared in Examples 1-3 into the beaker in three different proportions of 3%, 6%, and 9% and stir to mix evenly. When the temperature drops to 80°C, continue to add DDM curing agent (4,4-diaminodiphenylmethane), stir vigorously for 5 minutes, and after mixing evenly, vacuum degassing for 5 minutes, and finally quickly pour it into the national standard mold for limiting oxygen index (130×6.5×3mm) and the national standard mold for vertical combustion (130×12.7×3mm). Pre-cure at 100°C for 1h, cure at 120°C for 2h, and finally cure at 150°C for 3h. After curing, naturally cool to room temperature and demold to obtain the flame-retardant epoxy resin sample to be tested. The limiting oxygen index was determined using a JF-3 oxygen index meter, and the UL-94 vertical combustion performance test was performed using a CZF-5 vertical combustion instrument. The results are summarized in Table 1:

[0056] Table 1 Summary of flame retardant test data of epoxy resin composite materials

[0057]

[0058] The determination of the limiting oxygen index in Table 1 refers to the national standard method GB / T2406.2-2009, and the UL-94 vertical burning test adopts the GB / T2408-2008 standard;

[0059] Existing studies have shown that unmodified pure EP is extremely flammable, and severe dripping will occur in the UL-94 test, and no flame retardant grade can be obtained. As shown in Example 1, as the flame retardant content in pure EP increases, the epoxy resin composite material exhibits good flame retardant properties. When the addition amount is only 3%, the V-1 grade is achieved in the UL-94 test, and the LOI value reaches 31.1%. When the addition amount is 6%, the V-0 grade is achieved in the UL-94 test, and the LOI value is as high as 32.6%. When the addition amount is 9%, the V-0 grade is achieved in the UL-94 test, and the LOI value is as high as 33.2%. These data are sufficient to show that the flame retardant DAVN can give epoxy resin a higher flame retardant grade and significantly improve the flame retardant properties of epoxy resin.

[0060] Thermogravimetric analysis tests were carried out on the samples in Table 1 using a thermogravimetric analyzer (Q5000IR, TA Instruments, USA). The test was carried out in a nitrogen atmosphere (flow rate of 10 mL / min), with a set temperature range of 30-700°C and a heating rate of 10°C / min. It can be seen from the thermogravimetric test graph that with the continuous increase in the flame retardant content in samples No. 1, 2, and 3, the temperature corresponding to the mass loss rate of 5% gradually advances. This phenomenon is attributed to the presence of some weak chemical bonds such as O=PO, PC, etc. in the new vanillin-containing DOPO-based halogen-free flame retardant. These weak bonds cause the flame retardant to decompose early. Furthermore, with the increase in the flame retardant content, the residual carbon content at 700°C also gradually increases, among which the residual carbon content of sample No. 3 is as high as 18.4% of vanillin.

[0061] The test of heat resistance was carried out with the aid of the DSCQ20 differential scanning calorimeter of the American TA Vanillin Instrument Company (TaInstruments). The test was carried out under nitrogen atmosphere, and the heating rate was set to 10°C / min. The temperature range was between 40-250°C for the vanillin smoke density (DS) test operation. It can be seen from the test spectrum that the glass transition temperature (Tg) of pure EP is 135.1°C for vanillin. In the flame retardant-modified epoxy resin system involved in the present invention, with the gradual increase of the flame retardant content, the Tg of the 1 vanillin sample was increased to 140.2°C. However, when the flame retardant content was further increased, the Tg temperature showed a slightly decreasing trend, but it was still better than pure epoxy resin. This phenomenon may be due to the fact that the introduction of excessive flame retardants has an adverse effect on the compatibility between the flame retardant and the matrix, and the addition of excessive rigid structures interferes with the curing behavior of the epoxy resin.

Claims

1. A method for preparing a DOPO-based flame retardant containing vanillin, characterized in that: The method comprises the following steps: First, a DOPO-based halogen-free flame retardant is prepared, vanillin and 5-aminotetrazole are added to a solvent in a molar ratio of 1:1, and then an acid binding agent is added so that the reaction process is carried out in an alkaline environment. The reaction system is placed in a three-necked flask equipped with a magnetic stirrer and a reflux condenser; the reaction temperature is controlled to be 60-80°C, and the temperature is maintained for 8-10 hours under constant stirring; then a DOPO solution is added, and stirring is continued for 8-12 hours at a temperature of 60-80°C and under the protection of nitrogen; a crude product is obtained by rotary evaporation, recrystallized in anhydrous ethanol, filtered, and washed with deionized water for 3 times; then the product is dried in an oven at 70°C to constant weight to obtain a white powder flame retardant; Its structural formula is:

2. The method for preparing a DOPO-based flame retardant containing vanillin according to claim 1, characterized in that: The acid binding agent includes at least one of potassium hydroxide, sodium hydroxide, pyridine, imidazole, triethylamine, potassium tert-butoxide, sodium ethoxide, sodium methoxide and diethylamine.

3. The method for preparing a DOPO-based flame retardant containing vanillin according to claim 1, characterized in that: The organic solvent includes one of acetonitrile, hexamethylphosphoric acid triamide, dimethylacetamide, tetrahydrofuran, cyclopentanone, dichloromethane, chloroform, carbon tetrachloride, methanol, ethanol, and N-methylpyrrolidone.

4. The method for preparing a DOPO-based flame retardant containing vanillin according to claim 3, characterized in that: The organic solvent includes any one of acetonitrile, hexamethylphosphoric acid triamide, dimethylacetamide, tetrahydrofuran, cyclopentanone, dichloromethane, chloroform, carbon tetrachloride, methanol, ethanol, and N-methylpyrrolidone mixed with DOPO at a molar ratio of 2:

1.

5. The method for preparing a DOPO-based flame retardant containing vanillin according to claim 1, characterized in that: The solvent includes at least one of methanol, ethanol, chloroform, dimethylformamide, dioxane and isopropanol.

6. An application of a DOPO-based flame retardant containing vanillin, characterized in that: The flame retardant is used in the flame retardant modification of epoxy resin, and the contained vanillin DOPO flame retardant and epoxy resin are cured under the action of DDM (4,4-diaminodiphenylmethane) curing agent to obtain flame retardant epoxy resin.

7. The use of a DOPO-based flame retardant containing vanillin according to claim 6, characterized in that: The epoxy resin includes one of E51, E44, DGEBF, and F-51.

8. The use of a DOPO-based flame retardant containing vanillin according to claim 6, characterized in that: The added amount of the vanillin-containing DOPO flame retardant is 3%.

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