CN118772202A - Imidazole latent flame retardant and preparation method thereof and modified epoxy resin - Google Patents

Abstract

Imidazole latent flame retardant and its preparation method and modified epoxy resin, which relate to the field of new polymer material technology. The aforementioned imidazole latent flame retardant has a brand-new molecular structure, which does not contain halogen elements. It is a green halogen-free environmentally friendly flame retardant. It will not pollute the environment during thermal decomposition or combustion, which is beneficial to environmental protection and sustainable development. After the flame retardant performance test, mechanical property test and thermal stability test were carried out on the epoxy resin composite material added with the above flame retardant, it was proved that the composite material added with the above flame retardant not only has good flame retardant performance, but also has significantly improved mechanical properties and maintains good thermal stability. Compared with existing flame retardants, the above flame retardant can also ensure good flame retardant effect when the addition amount is low.

Description

Imidazole latent flame retardant and preparation method thereof and modified epoxy resin

Technical Field

The invention relates to the technical field of novel polymer materials, in particular to an imidazole latent flame retardant and a preparation method thereof and a modified epoxy resin.

Background Art

Epoxy resin is highly flammable and easily decomposes and burns at high temperatures, so flame retardants need to be added to it to make it flame retardant.

Chinese patent document CN104193967A discloses a bisphenol A-monobenzoxazine/epoxy resin copolymer containing bis-DOPO. First, DOPO and bisphenol A-bisbenzoxazine are used as raw materials to prepare intermediate I containing bisphenol A containing bis-DOPO, and then intermediate I is reacted with aniline and polyformaldehyde to obtain flame retardant bisphenol A-monobenzoxazine containing bis-DOPO, and then the obtained flame retardant is mixed with epoxy resin in proportion and heated to open the ring to obtain flame retardant material, but the amount of flame retardant added is large. Generally, adding a high dose of flame retardant will lead to a decrease in the mechanical properties of the polymer composite material, thereby limiting the applicable scenarios.

Summary of the invention

One of the purposes of the present invention is to provide an imidazole latent flame retardant with good flame retardant effect and lower additive dosage when used.

In order to achieve the above object, the present invention adopts the following technical solution:

Imidazole latent flame retardant, its structural formula is:

On the other hand, the present invention also relates to a method for preparing the above-mentioned imidazole latent flame retardant, and the preparation process comprises the following steps:

1. HPBI (2-(2'-hydroxyphenyl)-1h-benzimidazole) was prepared by the following route:

2. The imidazole latent flame retardant (DOPO-HPBI derivative) was prepared according to the following route:

Furthermore, in step 1: an appropriate amount of salicylaldehyde, NaHSO ₃ and anhydrous ethanol (EtOH) are added to a reaction container, stirred for reaction, and then an appropriate amount of o-phenylenediamine (OPD) dissolved in DMF is added to the reaction container, stirred for reaction, and then filtered, washed and dried to obtain HPBI.

Specifically, in step one:

Place appropriate amounts of salicylaldehyde, NaHSO ₃ and anhydrous ethanol (EtOH) in a three-necked flask. Equipped with a reflux condenser and a stirring bar, stir magnetically at room temperature for 2 to 6 hours (e.g., 4 hours). Then slowly add o-phenylenediamine dissolved in DMF into a three-necked flask with a constant pressure drop funnel, and stir continuously at 18 to 25°C (e.g., 20°C) for 2 to 6 hours (e.g., 4 hours). After the reaction is completed, cool the product and filter it. Then wash the filtered product repeatedly with distilled water several times and put it in an oven to dry overnight. Finally, a golden yellow powder HPBI is obtained.

Wherein, every 0.05-0.2 mol of o-phenylenediamine corresponds to 30-80 mL of DMF. Preferably, every 0.1 mol of o-phenylenediamine corresponds to 50 mL of DMF.

Furthermore, in step 2: adding appropriate amounts of HPBI, DOPO and acetone into a reaction container, stirring and reflux reaction, and then filtering, washing and drying to obtain an imidazole latent flame retardant.

Specifically, in step 2:

Add HPBI, DOPO and acetone to a three-necked flask. Stir and reflux at 18-25°C (e.g. 20°C) for 1-5h (e.g. 3h). Then take a certain amount of distilled water in a large beaker, pour the reaction solution into it, wait for all the solid matter to precipitate, filter under reduced pressure, wash the filtered product repeatedly with distilled water and anhydrous ethanol, then put it into a vacuum oven, dry it at 50-70°C (e.g. 60°C) overnight, and finally obtain a light purple solid powder, i.e. imidazole latent flame retardant.

Further, the molar ratio of salicylaldehyde, NaHSO ₃ and o-phenylenediamine is (1-4):(1-4):(1-4). Preferably, the molar ratio of salicylaldehyde, NaHSO ₃ and o-phenylenediamine is 1:1:1.

Further, the molar ratio of HPBI to DOPO is (1-4):(1-4). Preferably, the molar ratio of HPBI to DOPO is 1:1.

Further, every 0.05-0.2 mol of salicylaldehyde, 0.05-0.2 mol of NaHSO ₃ and 0.05-0.2 mol of o-phenylenediamine corresponds to 30-80 mL of anhydrous ethanol. For example, salicylaldehyde is 0.05-0.2 mol, NaHSO ₃ is 0.05-0.2 mol, o-phenylenediamine is 0.05-0.2 mol, and anhydrous ethanol is 30-80 mL.

Preferably, every 0.1 mol of salicylaldehyde, 0.1 mol of NaHSO ₃ and 0.1 mol of o-phenylenediamine corresponds to 50 mL of anhydrous ethanol. For example, salicylaldehyde is 0.1 mol, NaHSO ₃ is 0.1 mol, o-phenylenediamine is 0.1 mol, and anhydrous ethanol is 50 mL.

Further, every 0.025-0.1 mol of HPBI and 0.025-0.1 mol of DOPO corresponds to 80-120 mL of acetone. For example, HPBI is 0.025-0.1 mol, DOPO is 0.025-0.1 mol, and acetone is 80-120 mL.

Preferably, every 0.05 mol of HPBI and 0.05 mol of DOPO corresponds to 100 mL of acetone. For example, HPBI is 0.05 mol, DOPO is 0.05 mol, and acetone is 100 mL.

Finally, the present invention also relates to a modified epoxy resin, wherein the above-mentioned imidazole latent flame retardant is added.

Furthermore, the mass content (mass fraction) of the imidazole latent flame retardant in the modified epoxy resin is 3% to 7%. Preferably, the mass content of the imidazole latent flame retardant is 5% to 7%.

The imidazole latent flame retardant provided by the present invention has a new molecular structure, does not contain halogen elements, is a green halogen-free environmentally friendly flame retardant, does not cause pollution to the environment during thermal cracking or combustion, is conducive to environmental protection and sustainable development, and after the epoxy resin composite material to which the flame retardant is added is tested for flame retardancy, mechanical properties and thermal stability, it is proved that the composite material to which the flame retardant is added not only has good flame retardancy, but also has significantly improved mechanical properties and maintains good thermal stability. Compared with the flame retardant in the background technology literature, the flame retardant can also ensure a good flame retardant effect when the addition amount is low.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is an infrared spectrogram of raw materials and products of the present invention;

FIG2 is a tensile property test result of a flame retardant composite material to which the flame retardant of the present invention is added;

FIG. 3 is a thermogravimetric analysis diagram of a flame retardant composite material to which the flame retardant of the present invention is added.

DETAILED DESCRIPTION

In order to facilitate the understanding of those skilled in the art, the present invention is further described below in conjunction with the examples and drawings, and the contents mentioned in the examples are not limitations of the present invention. It should be noted in advance that the following examples were completed in the laboratory, and those skilled in the art should understand that the amounts of the components given in the examples only represent the ratio relationship between the components, rather than specific limitations.

The steps of preparing the novel imidazole latent flame retardant of the present invention mainly include two steps: the synthesis of HPBI and the preparation of DOPO-HPBI derivatives. Specifically, in the first step, salicylaldehyde and o-phenylenediamine (OPD) react to generate 2-(2'-hydroxyphenyl)-1h-benzimidazole (HPBI); in the second step, DOPO reacts with the substance obtained in the first step to generate DOPO derivatives.

1. Synthesis of HPBI.

The specific steps are as follows:

0.05-0.2 mol salicylaldehyde, 0.05-0.2 mol NaHSO ₃ and 30-80 mL anhydrous ethanol (EtOH) were placed in a three-necked flask. Equipped with a reflux condenser and a stirring rod, magnetic stirring was performed at room temperature for 2-6 hours. Then, 0.05-0.2 mol o-phenylenediamine dissolved in DMF (30-80 mL) was slowly added to the three-necked flask with a constant pressure drop funnel and stirred continuously at 18-25°C for 2-6 hours. After the reaction was completed, the product was cooled and filtered. The filtered product was then repeatedly washed with distilled water for several times and dried in an oven overnight to obtain a golden yellow powder HPBI.

The preparation route of this step is as follows:

2. Preparation of DOPO-HPBI derivatives (imidazole latent flame retardants).

The specific steps are as follows:

Add 0.025-0.1 mol HPBI, 0.025-0.1 mol DOPO and 80-120 mL acetone to a three-necked flask. Stir and reflux at 18-25°C for 1-5 hours. Then take a certain amount of distilled water in a large beaker, pour the reaction solution into it, wait for all the solid matter to precipitate, filter under reduced pressure, wash the filtered product repeatedly with distilled water and anhydrous ethanol, then put it into a vacuum oven and dry it at 50-70°C overnight, and finally obtain a light purple solid powder, i.e., imidazole latent flame retardant.

The preparation route of this step is as follows:

The following is an explanation through specific embodiments.

Example 1

1. Synthesis of HPBI.

0.1 mol salicylaldehyde, 0.1 mol NaHSO ₃ and 50 ml anhydrous ethanol (EtOH) were placed in a three-necked flask. Equipped with a reflux condenser and a stirring bar, magnetic stirring was performed at room temperature for 4 hours. Then, 0.1 mol o-phenylenediamine dissolved in DMF (50 mL) was slowly added to the three-necked flask with a constant pressure drop funnel and stirred continuously at 20°C for 4 hours. After the reaction was completed, the product was cooled and filtered. The filtered product was then repeatedly washed with distilled water for several times and placed in an oven to dry overnight. Finally, golden yellow powder HPBI was obtained.

2. Preparation of DOPO-HPBI derivatives (imidazole latent flame retardants).

Add 0.05 mol HPBI, 0.05 mol DOPO and 100 mL acetone to a three-necked flask. Stir and reflux at 20°C for 3 h. Then take a certain amount of distilled water in a large beaker and pour the reaction solution into it. After all the solid matter is precipitated, reduce the pressure and filter it. Wash the filtered product repeatedly with distilled water and anhydrous ethanol, then put it into a vacuum oven and dry it at 60°C overnight. Finally, a light purple solid powder is obtained, which is an imidazole latent flame retardant.

Example 2

1. Synthesis of HPBI.

0.05 mol salicylaldehyde, 0.05 mol NaHSO ₃ and 30 mL anhydrous ethanol (EtOH) were placed in a three-necked flask. Equipped with a reflux condenser and a stirring bar, magnetic stirring was performed at room temperature for 2 h. Then, 0.05 mol o-phenylenediamine dissolved in DMF (30 mL) was slowly added to the three-necked flask with a constant pressure drop funnel and stirred continuously at 18 ° C for 2 h. After the reaction was completed, the product was cooled and filtered. The filtered product was then repeatedly washed with distilled water for several times and placed in an oven to dry overnight. Finally, golden yellow powder HPBI was obtained.

2. Preparation of DOPO-HPBI derivatives (imidazole latent flame retardants).

Add 0.025 mol HPBI, 0.025 mol DOPO and 80 mL acetone to a three-necked flask. Stir and reflux at 18°C for 1 hour. Then take a certain amount of distilled water in a large beaker and pour the reaction solution into it. After all the solid matter is precipitated, reduce the pressure and filter it. Wash the filtered product repeatedly with distilled water and anhydrous ethanol, then put it into a vacuum oven and dry it at 50°C overnight. Finally, a light purple solid powder is obtained, which is an imidazole latent flame retardant.

Example 3

1. Synthesis of HPBI.

0.2 mol salicylaldehyde, 0.2 mol NaHSO ₃ and 80 mL anhydrous ethanol (EtOH) were placed in a three-necked flask. Equipped with a reflux condenser and a stirring bar, magnetic stirring was performed at room temperature for 6 hours. Then, 0.2 mol o-phenylenediamine dissolved in DMF (80 mL) was slowly added to the three-necked flask with a constant pressure drop funnel and stirred continuously at 25 ° C for 6 hours. After the reaction was completed, the product was cooled and filtered. The filtered product was then repeatedly washed with distilled water for several times and placed in an oven to dry overnight. Finally, golden yellow powder HPBI was obtained.

2. Preparation of DOPO-HPBI derivatives (imidazole latent flame retardants).

Add 0.1 mol HPBI, 0.1 mol DOPO and 120 mL acetone to a three-necked flask. Stir and reflux at 25°C for 5 hours. Then take a certain amount of distilled water in a large beaker and pour the reaction solution into it. After all the solid matter is precipitated, reduce the pressure and filter it. Wash the filtered product repeatedly with distilled water and anhydrous ethanol, then put it into a vacuum oven and dry it at 70°C overnight. Finally, a light purple solid powder is obtained, which is an imidazole latent flame retardant.

1. Infrared spectrum analysis of the product.

From the infrared spectrum of Figure 1, it can be seen that o-phenylenediamine has a characteristic absorption peak _{of -NH2} at 3372cm ^-1 , while the characteristic absorption peak of the amino group of product 1 (the product of step one) disappears, and the characteristic absorption peak of -C=N- bond appears at 1617cm ^-1 in product 1, and the characteristic absorption peak of -CN- appears at 1276cm- ¹ . It can be inferred that o-phenylenediamine reacts with salicylaldehyde to generate the first step product, the imidazole ring. Since the characteristic absorption peak at 1276cm ^-1 can be attributed to the p-π conjugated characteristic absorption peak in C-NH-Ar, and a strong characteristic absorption peak appears at 931.7cm ^-1 , which can be attributed to the PO-Ar characteristic absorption peak; the characteristic absorption peak at 1205cm ^-1 can be attributed to the Ar-P=O characteristic absorption peak, and the characteristic absorption peak of the PH bond appears at 2435cm ^-1 , and the PH bond disappears in product 2 (the product of step two), and there is a CP bond at 1043cm-1. ^-1 appears, and the -C=N- characteristic absorption peak of product 1 disappears, from which it can be inferred that DOPO reacts with the carbon-nitrogen double bond of product 1. The above shows that compound 1 (HPBI) and compound 2 (DOPO-HPBI derivative/imidazole latent flame retardant) have been successfully synthesized.

2. Flame retardant performance test.

The flame retardant composite material (epoxy resin added with flame retardant of Example 1) and epoxy resin without flame retardant were made into national standard oxygen index specimens (130*6.5*3) and national standard vertical combustion specimens (120*13*3.2), and the limiting oxygen index was measured by JF3-oxygen index meter in accordance with GB/T2406.2-2009, and the vertical combustion performance (UL-94) was tested by FZ-5401 vertical combustion instrument in accordance with GB/T 2408-2008. The test results are as follows:

Table 1 UL-94 test data

It can be seen from Table 1 that adding different amounts (mass content/mass fraction) of HPBI-DOPO flame retardant (flame retardant in Example 1) to EP (epoxy resin) will make the molded epoxy-based composite material have a flame retardant effect. By comparing the grade judgment criteria, it can be obtained that the flame retardant grade of EP with a flame retardant mass fraction of 1% is V-1 level; T ₁ =10s, T ₂ =2s, T ₁ +T ₂ <30s of the EP flame retardant composite material with a flame retardant mass fraction of 3%, indicating that the flame retardant grade of EP with a flame retardant mass fraction of 3% is V-0 level; T ₁ <10s, T ₂ <10s, and T ₁ +T ₂ <30s of the EP flame retardant composite strip with a flame retardant mass fraction of 5% and no dripping, so the flame retardant grade of the EP flame retardant composite material with a flame retardant mass fraction of 5% is also V-0 level; the flame retardant grade of the EP flame retardant composite material with a flame retardant mass fraction of 7% is also V-0 level. In summary, it can be seen that adding the flame retardant to EP can significantly improve the flame retardant effect of the epoxy resin. When the content (mass content/mass fraction) of the HPBI-DOPO flame retardant is 3%, the flame retardant grade of the flame retardant composite material can reach the best.

Table 2 LOI experimental data

Table 2 shows the limiting oxygen concentration of flame retardant composite materials with different contents of flame retardants. When the UL-94V-0 level is reached, the content of the flame retardant is only 3%, and the LOI concentration is 32.6%, which is 6.0% higher than the 26.6% of the blank epoxy composite material. When the flame retardant content is 5%, the LOI value of the flame retardant composite material is 34.0%; when the added HPBI-DOPO flame retardant content is 7%, the LOI value of the flame retardant composite material is 34.5%. It can be seen from the experimental data that by adding HPBI-DOPO flame retardant (flame retardant in Example 1) to epoxy resin, its limiting oxygen index can be improved to a certain extent. As the content of HPBI-DOPO flame retardant in EP increases, the flame retardant effect of the composite material is better.

3. Effect of flame retardants on the mechanical properties of epoxy resin composites.

3-1. Impact test.

By conducting comparative tests on epoxy composite materials with different contents (mass content/mass fraction) of flame retardant added, 1%, 3%, and 5%, and pure epoxy resin specimens, a certain number of complete specimens were prepared for each of the four materials.

Calculation formula: a _k =A/(bh); unit: (kJ/m ² ), where a _k represents impact strength, A is the test work value, b represents the spline thickness, and h represents the spline width.

After testing, the impact test data of four complete specimens are as follows:

Table 3 Impact test data

It can be seen from the impact test data in Table 3 that although the mass fraction of the added flame retardant is different, in general, the impact strength of the epoxy composite material with the flame retardant added is significantly improved compared with the pure epoxy material without the flame retardant added.

3-2. Tensile test.

The same size of the sample was subjected to tensile performance test, among which the blank sample broke when the ultimate tensile force was 1730N. It is not difficult to see from the test results of Figure 2 that the maximum bearing capacity of the sample with 1% flame retardant added is about 2985N, the maximum bearing capacity of the sample with 3% flame retardant added is about 2869N, the maximum bearing capacity of the sample with 5% flame retardant added is about 3366N, and the maximum bearing capacity of the sample with 7% flame retardant added is about 3264N. By comparing and analyzing the data results, it can be seen that the tensile strength and yield strength of the sample with flame retardant added are significantly improved.

4. Effect of flame retardants on the thermal stability of epoxy resin composites.

The temperature range of the thermogravimetric analyzer is 30-900℃, the system's program heating rate is 20.0 (K/min), and the test is carried out in an air atmosphere. The initial mass of the EP flame retardant composite powder sample with a flame retardant mass fraction of 1% is 7.081mg, the initial mass of the EP flame retardant composite powder sample with a flame retardant mass fraction of 3% is 8.527mg, and the initial mass of the EP flame retardant composite powder sample with a flame retardant mass fraction of 5% is 9.185mg. The initial mass of the EP flame retardant composite powder sample with a flame retardant mass fraction of 7% is 5.537mg. As shown in Figure 3, the material has two weight loss events, at about 400℃ and 600℃, respectively. When the temperature rises to about 350℃, the composite material begins to decompose due to heat. When the content of DOPO-HPBI flame retardant is 1%, it loses weight completely and there is no residue; when the content of DOPO-HPBI flame retardant is 3%, it also loses weight completely and there is still no residue; when the content of DOPO-HPBI flame retardant is 5%, it loses weight completely and there is no residue; when the content of DOPO-HPBI flame retardant is 7%, it also loses weight completely and there is no residue. Among them, when the addition amount of flame retardant is 5%, it has good thermal stability at 500℃ to 800℃.

It is also worth noting that, generally speaking, the addition of flame retardants will lead to a decrease in the mechanical properties of epoxy resins. However, through the above experiments, it can be seen that after the flame retardant prepared by the present invention is added to the epoxy resin, it not only improves the flame retardant properties of the epoxy resin and has good thermal stability, but also significantly improves the mechanical properties of the epoxy resin.

In summary, the imidazole latent flame retardant provided by the present invention has a new molecular structure, does not contain halogen elements, is a green halogen-free environmentally friendly flame retardant, does not cause pollution to the environment during thermal cracking or combustion, is conducive to environmental protection and sustainable development, and after the epoxy resin composite material to which the flame retardant of the present invention is added is tested for flame retardancy, mechanical properties and thermal stability, it is proved that the composite material to which the flame retardant of the present invention is added not only has good flame retardancy, but also has significantly improved mechanical properties and maintains good thermal stability. Compared with the existing flame retardants, the flame retardant of the present invention can also ensure a good flame retardant effect when the additive amount is low (for example, 3%, 5%, 7%). In addition, the process for preparing the imidazole latent flame retardant provided by the present invention is simple, the reaction conditions are mild, and it is easy to be produced and applied on an industrial scale.

The above embodiments are preferred implementation schemes of the present invention. In addition, the present invention may also be implemented in other ways. Any obvious replacement without departing from the concept of the present technical solution is within the protection scope of the present invention.

Finally, it should be emphasized that in order to allow ordinary technicians in the field to more easily understand the improvements of the present invention over the prior art, some descriptions of the present invention have been simplified, and for the sake of clarity, some other elements are omitted in this application document. Those skilled in the art should realize that these omitted elements may also constitute the content of the present invention.

Claims (10)

1. Imidazole latent flame retardant, characterized in that the structural formula is: 2. The method for preparing the imidazole latent flame retardant according to claim 1, characterized in that it comprises the following steps: 1. Prepare HPBI according to the following route: 2. Prepare the imidazole latent flame retardant according to the following route: 3. The preparation method according to claim 2, characterized in that in step 1: salicylaldehyde, NaHSO ₃ and anhydrous ethanol are added to a reaction container, stirred for reaction, then o-phenylenediamine dissolved in DMF is added to the reaction container, stirred for reaction, filtered, washed and dried to obtain HPBI. 4. The preparation method according to claim 2, characterized in that in step 2: HPBI, DOPO and acetone are added into a reaction container, stirred and refluxed for reaction, and then filtered, washed and dried to obtain the imidazole latent flame retardant. 5. The preparation method according to claim 3, characterized in that the molar ratio of salicylaldehyde, _NaHSO3 and o-phenylenediamine is (1-4):(1-4):(1-4). 6. The preparation method according to claim 4, characterized in that the molar ratio of HPBI to DOPO is (1-4):(1-4). 7. The preparation method according to claim 3, characterized in that every 0.05-0.2 mol of salicylaldehyde, 0.05-0.2 _mol of NaHSO3 and 0.05-0.2 mol of o-phenylenediamine corresponds to 30-80 mL of anhydrous ethanol. 8. The preparation method according to claim 4, characterized in that every 0.025-0.1 mol of HPBI and 0.025-0.1 mol of DOPO corresponds to 80-120 mL of acetone. 9. Modified epoxy resin, characterized in that the imidazole latent flame retardant according to claim 1 is added therein. 10 . The modified epoxy resin according to claim 9 , wherein the mass content of the imidazole latent flame retardant in the modified epoxy resin is 3% to 7%.