DOPO-based s-triazine-bridged thiazole flame-retardant epoxy resin and preparation method thereof

Abstract

The present invention belongs to the technical field of flame-retardant epoxy resin materials, specifically DOPO-based triazine-bridged thiazole flame-retardant epoxy resin and a preparation method thereof, wherein the preparation method comprises: 1) reacting a nitrogen-containing five-membered heterocycle or a derivative thereof with p-hydroxybenzaldehyde to obtain an intermediate product I; 2) adding DOPO and a catalyst to the intermediate product I and reacting for 12 hours to obtain an intermediate product II; 3) reacting the intermediate product II with cyanuric chloride to obtain a DOPO-based triazine-bridged thiazole flame retardant; 4) uniformly mixing the obtained flame retardant with a bisphenol A epoxy resin; adding 4,4'-diaminodiphenylmethane after the temperature of the mixed liquid drops to 90°C, and finally obtaining a DOPO-based triazine-bridged thiazole flame-retardant epoxy resin through a thermal curing reaction. Due to the introduction of the DOPO-based triazine-bridged thiazole flame retardant, the epoxy resin material of the present invention has excellent flame retardant properties and mechanical properties.

Description

Technical Field

[0001] The invention relates to the technical field of flame-retardant epoxy resins, and in particular to a DOPO-based s-triazine-bridged thiazole flame-retardant epoxy resin and a preparation method thereof. Background Art

[0002] Epoxy resin is a widely used thermosetting polymer material. After fully reacting with a curing agent, the epoxy resin material formed has good physical and chemical properties, good electrical insulation, low shrinkage, and good wear resistance. It has been widely used in bonding various materials, electrical insulation materials, polymer-based composite materials, etc. It plays an important role in microelectronics, chemical corrosion protection, aerospace and other industrial fields, and is an indispensable basic material in the modern industrial field. However, like most polymer materials, epoxy resin materials are extremely flammable, with a limiting oxygen index of only 19.8%, and usually need to be flame-retardant modified to meet higher usage requirements.

[0003] 9,10-Dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) is an organophosphorus intermediate. Since the DOPO molecular structure contains biphenyl and phenanthrene ring structures, it has higher thermal and chemical stability than other organophosphorus compounds. At the same time, the DOPO molecular structure contains a highly active PH bond, which has high reactivity to olefins, epoxy groups, carbonyl groups and other groups, and can be used to prepare a variety of DOPO-based flame retardants through chemical reactions. In current research reports, reactive organophosphorus flame retardants generally have higher flame retardant efficiency than additive organophosphorus flame retardants. Based on the good synergistic flame retardant effect between phosphorus and nitrogen elements, the performance characteristics of DOPO can be used to construct reactive DOPO-based flame retardants containing phosphorus-nitrogen elements in the molecule.

[0004] In the prior art, various structures of DOPO-based flame retardants have been reported. For example, Qian et al. synthesized a DOPO-based flame retardant HAP-DOPO and added it to the curing system of epoxy resin and 4,4'-diaminodiphenyl sulfone. When the phosphorus content of the epoxy resin material is 2wt%, the flame retardant level can reach UL-94V-0. However, the initial decomposition temperature and glass transition temperature of the epoxy resin material are greatly negatively affected, and they are reduced by 71°C and 44°C respectively compared with the unflame-retardant modified epoxy resin material. In addition, Ding et al. used 1,2-divinyl-1,1,2,2-tetramethylsiloxane, 1,2-divinyl-1,2-dimethyl-1,2-diphenylsiloxane and DOPO as raw materials, and synthesized DOPO-based flame retardants DOPO-TMDS and DOPO-DMDP containing both phosphorus and silicon elements through the addition reaction of DOPO and C=C double bonds. When the two are added to the curing system of epoxy resin and linear phenolic resin respectively, the flame retardant level of the epoxy resin material can reach UL-94V-0 when the phosphorus content in the two flame retardant epoxy materials is 2wt%. Due to the introduction of the more flexible silicone segment, the glass transition temperature of the epoxy resin material is greatly reduced. The glass transition temperature of the epoxy resin material containing DOPO-TMDS and DOPO-DMDP when reaching UL-94V-0 level is reduced from 177℃ to 141℃ and 138℃, respectively, with a drop of up to 36℃ and 39℃. Although the structures of the above-mentioned DOPO-based flame retardants all contain phosphorus elements compounded with nitrogen elements or silicon elements, theoretically, phosphorus-nitrogen or phosphorus-silicon synergistic flame retardant effects can be formed, however, these structures do not have active reaction functional groups to react with the epoxy resin matrix, and belong to additive DOPO-based flame retardants. Such flame retardants are prone to flame retardant migration and precipitation problems, and the dispersibility in the epoxy resin matrix will be greatly affected, thereby seriously weakening its flame retardant efficiency, so that the flame retardant epoxy resin material can only reach UL-94V-0 level when the phosphorus content is high, and other properties such as thermal properties or mechanical properties of the material are also sacrificed. The DOPO-based triazine-bridged thiazole flame retardant of the present invention is a reactive DOPO-based flame retardant, which is introduced into the curing network of the epoxy resin in the form of a co-curing agent, so that the cured epoxy resin material has higher flame retardant properties, and other properties are less affected, which can avoid the problems that often occur in the processing and use of the above-mentioned additive DOPO-based flame retardants, and give the epoxy resin material a lasting and stable flame retardant property without reducing the mechanical properties. Summary of the invention

[0005] In view of the above problems, the present invention provides a DOPO-based s-triazine-bridged thiazole flame-retardant epoxy resin and a preparation method thereof. The prepared DOPO-based s-triazine-bridged thiazole flame-retardant epoxy resin material has good flame retardant properties and mechanical properties.

[0006] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0007] The present invention first provides a method for preparing a DOPO-based s-triazine-bridged thiazole flame-retardant epoxy resin, comprising the following steps:

[0008] (1) Using 1,4-dioxane as solvent, adding a nitrogen-containing five-membered heterocyclic ring or its derivatives and p-hydroxybenzaldehyde to react at room temperature for 5 hours, utilizing the amino group in the nitrogen-containing five-membered heterocyclic ring or its derivatives to react with the aldehyde group of p-hydroxybenzaldehyde to generate an intermediate product I containing a Schiff base structure;

[0009] (2) adding DOPO to the intermediate product I obtained in step (1), using palladium carbon as a catalyst, stirring evenly and reacting at 80° C. for 12 h, using the active PH bond on DOPO to react with the C=N bond on the intermediate product I to prepare an intermediate product II containing a DOPO structure;

[0010] (3) adding cyanuric chloride to the intermediate product II obtained in step (2), using N,N-dimethylformamide as solvent, utilizing the phenolic hydroxyl group in the intermediate product II to react with cyanuric chloride at 120° C. under nitrogen protection for 6 hours to prepare a DOPO-based s-triazine-bridged thiazole flame retardant; after the reaction is completed, the reaction solution is naturally cooled to room temperature, poured into an ice water bath, washed with water to precipitate a crude product, which is the crude product of the DOPO-based s-triazine-bridged thiazole flame retardant;

[0011] (4) filtering the crude product, washing it with a solvent to remove unreacted raw materials and impurities, and finally drying it in a vacuum drying oven to obtain the final product of the DOPO-based s-triazine-bridged thiazole flame retardant;

[0012] (5) The DOPO-based triazine-bridged thiazole flame retardant is named CE, and the total equivalent weight of the active hydrogen on CE and the active hydrogen on the curing agent 4,4'-diaminodiphenylmethane is equal to the total equivalent weight of the epoxy groups on the bisphenol A epoxy resin (DGEBA). By changing the amount of CE added, flame-retardant epoxy resin materials with phosphorus contents of 0.50wt%, 0.75wt%, and 1.00wt% are prepared. According to the different phosphorus contents, the above flame-retardant epoxy resin materials are marked as CE-EP-0.5, CE-EP-0.75, and CE-EP-1 in the present invention, and the detailed formulas are listed in Table 1. The specific preparation process of the flame-retardant epoxy resin material is as follows: the DOPO-based triazine-bridged thiazole flame retardant finally obtained in step (4) and the epoxy resin are stirred at 130° C. under nitrogen protection for 15 minutes to completely dissolve the DOPO-based triazine-bridged thiazole flame retardant in DGEBA; then, the temperature of the mixed solution is reduced to 90° C., and the curing agent 4,4'-diaminodiphenylmethane is added, and the mixture is continuously stirred to completely dissolve it to form a uniform mixed solution, and then the mixed solution is poured into a pre-heated mold, and degassed in a vacuum drying oven to remove bubbles in the sample; then the mold is placed in an electric blast drying oven, and a thermal curing reaction is carried out according to a pre-set heating program; finally, the mold is naturally cooled to room temperature to obtain the DOPO-based triazine-bridged thiazole flame-retardant epoxy resin material.

[0013] Table 1 Formula of flame retardant epoxy resin

[0014]

[0015] Preferably, the nitrogen-containing five-membered heterocycle or its derivative is 2-aminothiazole, 2-aminobenzothiazole, 2-aminoimidazole or 2-aminobenzimidazole.

[0016] Preferably, the nitrogen-containing five-membered heterocycle or its derivative, p-hydroxybenzaldehyde, solvent 1,4-dioxane, DOPO and palladium-carbon catalyst are used in a ratio of 1 g:1.22 g:30 ml:2.16 g:0.05 g.

[0017] Preferably, in step (3), the usage ratio of the intermediate product II, cyanuric chloride and solvent N,N-dimethylformamide is 12.6 g:1.85 g:50 ml.

[0018] Preferably, the washing in step (4) is performed by washing twice with ethanol and twice with dichloromethane respectively.

[0019] Preferably, the final product of the DOPO-based s-triazine-bridged thiazole flame retardant in step (4) has the following chemical structural formula:

[0020]

[0021] Preferably, in step (5), the mass ratio of the bisphenol A epoxy resin, the DOPO-based s-triazine-bridged thiazole flame retardant and the curing agent 4,4'-diaminodiphenylmethane is 100:9-21:20-26.

[0022] Preferably, the pre-set temperature rising program in step (5) is 80°C×1h, 100°C×1h, 120°C×1h, 150°C×3h, 180°C×2h.

[0023] The present invention also provides a DOPO-based s-triazine-bridged thiazole flame-retardant epoxy resin prepared according to the preparation method of the DOPO-based s-triazine-bridged thiazole flame-retardant epoxy resin.

[0024] By adopting the above technical solution, the beneficial effects of the present invention are:

[0025] The present invention prepares a DOPO-based s-triazine-bridged thiazole flame retardant by first preparing a DOPO-based s-triazine-bridged thiazole flame retardant, and then uses the DOPO-based s-triazine-bridged thiazole flame retardant as a co-curing agent of 4,4'-diaminodiphenylmethane to react with DGEBA to prepare a DOPO-based s-triazine-bridged thiazole flame retardant epoxy resin. Through testing, it is found that the flame retardant performance of the flame retardant epoxy resin is significantly improved after the DOPO-based s-triazine-bridged thiazole flame retardant is added. When the phosphorus content in the flame retardant epoxy resin is 0.75wt%, the flame retardant level of CE-EP-0.75 can reach UL-94V-0 level, and the peak heat release rate, total heat release rate and effective combustion calorific value of CE-EP-0.75 are 735kW / m 2 、164MJ / m 2, 24.6MJ / kg, which are 22.1%, 21.9% and 15.8% lower than those of the non-flame retardant epoxy resin material. At the same time, the addition of DOPO-based triazine-bridged thiazole flame retardant significantly improves the flexural modulus and tensile modulus of the flame retardant epoxy resin. Among them, the flexural modulus and tensile modulus of CE-EP-0.75 are 3.55±0.11GPa and 3.77±0.16GPa, respectively, and the flexural modulus and tensile modulus of CE-EP-1 are 3.64±0.13GPa and 3.84±0.28GPa, respectively, which are 19.1%, 23.6% and 22.1%, 25.9% higher than those of the non-flame retardant epoxy resin material CE-EP-0, respectively, showing that the DOPO-based triazine-bridged thiazole flame retardant has a good synergistic stiffening effect. In addition, after the introduction of DOPO-based triazine-bridged thiazole flame retardant, the flexural strength and tensile strength of the flame-retardant epoxy resin were also significantly improved. Among them, the flexural strength and tensile strength of CE-EP-0.5 were 132.4±3.1MPa and 85.1±2.2MPa, and the flexural strength and tensile strength of CE-EP-0.75 were 139.5±5.6MPa and 84.8±3.2MPa, which were 2.8MPa, 4.6MPa and 9.9MPa, 4.3MPa higher than those of CE-EP-0, respectively, indicating that the prepared DOPO-based triazine-bridged thiazole flame-retardant epoxy resin has good mechanical properties. In addition, the test results of thermal stability show that the introduction of DOPO-based triazine-bridged thiazole flame retardant can increase the residual carbon rate of epoxy resin materials and improve the thermal stability at high temperatures, thus playing a key role in improving flame retardant properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a digital photo of a DOPO-based s-triazine-bridged thiazole flame-retardant epoxy resin of the present invention after being subjected to a UL-94 vertical combustion test;

[0027] Figure 2 This is a heat release rate diagram of a DOPO-based s-triazine-bridged thiazole flame-retardant epoxy resin of the present invention;

[0028] Figure 3 This is a total heat release rate diagram of a DOPO-based s-triazine-bridged thiazole flame-retardant epoxy resin of the present invention;

[0029] Figure 4 A digital photograph of carbon residue after cone calorimetry test of a DOPO-based s-triazine-bridged thiazole flame-retardant epoxy resin of the present invention;

[0030] Figure 5 This is a SEM image of a DOPO-based s-triazine-bridged thiazole flame-retardant epoxy resin after cone calorimetry test of the present invention;

[0031] Figure 6This is a storage modulus diagram of a DOPO-based s-triazine-bridged thiazole flame-retardant epoxy resin of the present invention;

[0032] Figure 7 A loss tangent diagram of a DOPO-based s-triazine-bridged thiazole flame-retardant epoxy resin of the present invention;

[0033] Figure 8 This is a TGA curve of a DOPO-based s-triazine-bridged thiazole flame-retardant epoxy resin in a nitrogen atmosphere according to the present invention;

[0034] Fig. 9 This is a DTG curve of a DOPO-based s-triazine-bridged thiazole flame-retardant epoxy resin in a nitrogen atmosphere according to the present invention. DETAILED DESCRIPTION

[0035] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0036] Example 1

[0037] A method for preparing a DOPO-based s-triazine-bridged thiazole flame-retardant epoxy resin comprises the following steps:

[0038] (1) Using 1,4-dioxane as solvent, 1 g of 2-aminothiazole and 1.22 g of p-hydroxybenzaldehyde were added to 30 mL of 1,4-dioxane solvent, stirred evenly, and reacted at room temperature for 5 h, using the amino group in 2-aminothiazole to react with the aldehyde group of p-hydroxybenzaldehyde to generate an intermediate product I containing a Schiff base structure;

[0039] (2) Add 2.16 g of DOPO and 0.05 g of palladium carbon to the intermediate product I obtained in step (1), use palladium carbon as a catalyst, stir evenly, and react at 80° C. for 12 h, using the active PH bond on DOPO to react with the C=N bond on the intermediate product I to prepare an intermediate product II containing a DOPO structure;

[0040] Wherein, step (1) and step (2) adopt a one-pot method, that is, the same solvent is used, and the intermediate product I obtained in step (1) does not need to be dried, and no additional solvent needs to be added in step (2), which simplifies the preparation process and improves the preparation efficiency.

[0041] (3) drying the intermediate product II obtained in step (2), adding cyanuric chloride to the dried intermediate product II, using N,N-dimethylformamide as solvent, utilizing the phenolic hydroxyl group in the intermediate product II to react with cyanuric chloride at 120° C. under nitrogen protection for 6 hours to prepare a DOPO-based s-triazine-bridged thiazole flame retardant with a triazine structure as the core and a five-membered heterocyclic structure; after the reaction is completed, the reaction solution is naturally cooled to room temperature, poured into an ice water bath, washed and precipitated, and a crude product of the DOPO-based s-triazine-bridged thiazole flame retardant is obtained; wherein the amounts of the intermediate product II, cyanuric chloride and solvent N,N-dimethylformamide are 12.6 g, 1.85 g and 50 ml, respectively;

[0042] (4) The crude product was filtered and washed twice with ethanol and dichloromethane respectively to remove unreacted raw materials and impurities. Finally, it was placed in a vacuum drying oven and vacuum dried at 85° C. for 24 h to obtain the final product of DOPO-based triazine-bridged thiazole flame retardant. The product was a yellow solid powder (molecular weight 1338) with a yield of 85.2%.

[0043] The typical reaction equation is:

[0044]

[0045]

[0046] (5) Preparation steps of CE-EP-0.5 sample: First, 9.8 g of CE and 100 g of DGEBA were stirred at 130 °C under nitrogen protection for 15 min to completely dissolve CE in DGEBA to form a mixed solution. Subsequently, the temperature of the mixed solution was lowered to 90 °C, and 23.1 g of 4,4'-diaminodiphenylmethane was added and stirred continuously to completely dissolve it to form a uniform mixed solution. The uniform mixed solution was then poured into a mold preheated at 85 °C and degassed in a vacuum drying oven for 15 min to remove bubbles in the sample. Then, the mold was placed in an electric blast drying oven and thermally cured according to the pre-set heating program of 80 °C × 1 h, 100 °C × 1 h, 120 °C × 1 h, 150 °C × 3 h, and 180 °C × 2 h. Finally, the mold was cooled naturally to room temperature to obtain the DOPO-based triazine-bridged thiazole flame-retardant modified epoxy resin, which was polished into a material of a specific size for subsequent experimental testing.

[0047] Example 2

[0048] A method for preparing a DOPO-based s-triazine-bridged thiazole flame-retardant epoxy resin comprises the following steps:

[0049] (1) Using 1,4-dioxane as solvent, 1 g of 2-aminothiazole and 1.22 g of p-hydroxybenzaldehyde were added to 30 mL of 1,4-dioxane solvent, stirred evenly, and reacted at room temperature for 5 h, using the amino group in 2-aminothiazole to react with the aldehyde group of p-hydroxybenzaldehyde to generate an intermediate product I containing a Schiff base structure;

[0050] (2) Add 2.16 g of DOPO and 0.05 g of palladium carbon to the intermediate product I obtained in step (1), use palladium carbon as a catalyst, stir evenly, and react at 80° C. for 12 h, using the active PH bond on DOPO to react with the C=N bond on the intermediate product I to prepare an intermediate product II containing a DOPO structure;

[0051] Wherein, step (1) and step (2) adopt a one-pot method, that is, the same solvent is used, and the intermediate product I obtained in step (1) does not need to be dried, and no additional solvent needs to be added in step (2), which simplifies the preparation process and improves the preparation efficiency.

[0052] (3) drying the intermediate product II obtained in step (2), adding cyanuric chloride to the dried intermediate product II, using N,N-dimethylformamide as solvent, utilizing the phenolic hydroxyl group in the intermediate product II to react with cyanuric chloride at 120° C. under nitrogen protection for 6 hours to prepare a DOPO-based s-triazine-bridged thiazole flame retardant with a triazine structure as the core and a five-membered heterocyclic structure; after the reaction is completed, the reaction solution is naturally cooled to room temperature, poured into an ice water bath, washed and precipitated, and a crude product of the DOPO-based s-triazine-bridged thiazole flame retardant is obtained; wherein the amounts of the intermediate product II, cyanuric chloride and solvent N,N-dimethylformamide are 12.6 g, 1.85 g and 50 ml, respectively;

[0053] (4) The crude product was filtered and washed twice with ethanol and dichloromethane respectively to remove unreacted raw materials and impurities. Finally, it was placed in a vacuum drying oven and vacuum dried at 85° C. for 24 h to obtain the final product of DOPO-based triazine-bridged thiazole flame retardant. The product was a yellow solid powder (molecular weight 1338) with a yield of 85.2%.

[0054] The typical reaction equation is the same as that in Example 1.

[0055] (5) Preparation steps of CE-EP-0.75 sample: First, 14.8 g of CE and 100 g of DGEBA were stirred at 130 °C under nitrogen protection for 15 min to completely dissolve CE in DGEBA to form a mixed liquid. Subsequently, the temperature of the mixed liquid was lowered to 90 °C, and 21.8 g of 4,4'-diaminodiphenylmethane was added and stirred continuously to completely dissolve it into a uniform mixed liquid. The uniform mixed solution was then poured into a mold preheated at 85 °C and degassed in a vacuum drying oven for 15 min to remove bubbles in the sample. The mold was then placed in an electric blast drying oven and thermally cured according to the pre-set temperature program of 80 °C × 1 h, 100 °C × 1 h, 120 °C × 1 h, 150 °C × 3 h, and 180 °C × 2 h. Finally, when the mold is naturally cooled to room temperature, the DOPO-based triazine-bridged thiazole flame-retardant modified epoxy resin is obtained, which is polished into a material of a specific size for subsequent experimental testing.

[0056] Example 3

[0057] A method for preparing a DOPO-based s-triazine-bridged thiazole flame-retardant epoxy resin comprises the following steps:

[0058] (1) Using 1,4-dioxane as solvent, 1 g of 2-aminothiazole and 1.22 g of p-hydroxybenzaldehyde were added to 30 mL of 1,4-dioxane solvent, stirred evenly, and reacted at room temperature for 5 h, using the amino group in 2-aminothiazole to react with the aldehyde group of p-hydroxybenzaldehyde to generate an intermediate product I containing a Schiff base structure;

[0059] (2) Add 2.16 g of DOPO and 0.05 g of palladium carbon to the intermediate product I obtained in step (1), use palladium carbon as a catalyst, stir evenly, and react at 80° C. for 12 h, using the active PH bond on DOPO to react with the C=N bond on the intermediate product I to prepare an intermediate product II containing a DOPO structure;

[0060] Wherein, step (1) and step (2) adopt a one-pot method, that is, the same solvent is used, and the intermediate product I obtained in step (1) does not need to be dried, and no additional solvent needs to be added in step (2), which simplifies the preparation process and improves the preparation efficiency.

[0061] (3) drying the intermediate product II obtained in step (2), adding cyanuric chloride to the dried intermediate product II, using N,N-dimethylformamide as solvent, utilizing the phenolic hydroxyl group in the intermediate product II to react with cyanuric chloride at 120° C. under nitrogen protection for 6 hours to prepare a DOPO-based s-triazine-bridged thiazole flame retardant with a triazine structure as the core and a five-membered heterocyclic structure; after the reaction is completed, the reaction solution is naturally cooled to room temperature, poured into an ice water bath, washed and precipitated, and a crude product of the DOPO-based s-triazine-bridged thiazole flame retardant is obtained; wherein the amounts of the intermediate product II, cyanuric chloride and solvent N,N-dimethylformamide are 12.6 g, 1.85 g and 50 ml, respectively;

[0062] (4) The crude product was filtered and washed twice with ethanol and dichloromethane respectively to remove unreacted raw materials and impurities. Finally, it was placed in a vacuum drying oven and vacuum dried at 85° C. for 24 h to obtain the final product of DOPO-based triazine-bridged thiazole flame retardant. The product was a yellow solid powder (molecular weight 1338) with a yield of 85.2%.

[0063] The typical reaction equation is the same as that in Example 1.

[0064] (5) Preparation steps of CE-EP-1 sample: First, 20.4 g of CE and 100 g of DGEBA were stirred at 130 °C under nitrogen protection for 15 min to completely dissolve CE in DGEBA to form a mixed solution. Subsequently, the temperature of the mixed solution was lowered to 90 °C, and 20.6 g of 4,4'-diaminodiphenylmethane was added and stirred continuously to completely dissolve it into a uniform mixed solution. The uniform mixed solution was then poured into a mold preheated at 85 °C and degassed in a vacuum drying oven for 15 min to remove bubbles in the sample. Then, the mold was placed in an electric blast drying oven and thermally cured according to the pre-set heating program of 80 °C × 1 h, 100 °C × 1 h, 120 °C × 1 h, 150 °C × 3 h, and 180 °C × 2 h. Finally, the mold was cooled naturally to room temperature to obtain the DOPO-based triazine-bridged thiazole flame-retardant modified epoxy resin material, which was polished into a material of a specific size for subsequent experimental testing.

[0065] Comparative Example

[0066] The preparation method of the non-flame retardant modified epoxy resin material comprises the following specific preparation steps: adding 25.3 g of 4,4'-diaminodiphenylmethane to 100 g of DGEBA at 90°C, stirring continuously to mix the two evenly, pouring the evenly mixed sample into a mold preheated at 85°C, and degassing in a vacuum drying oven for 15 minutes to remove bubbles in the sample. Then, the mold is placed in an electric blast drying oven, and a thermal curing reaction is performed according to a pre-set heating program of 80°C×1h, 100°C×1h, 120°C×1h, 150°C×3h, and 180°C×2h. Finally, when the mold is naturally cooled to room temperature, the non-flame retardant modified epoxy resin material is obtained, and the material is polished into a material of a specific size for subsequent experimental testing. According to the mass fraction of phosphorus content in the epoxy resin material, the non-flame retardant modified epoxy resin material is marked as CE-EP-0.

[0067] In order to verify the performance of the DOPO-based s-triazine-bridged thiazole flame-retardant epoxy resin of the present application, the applicant conducted the following performance verification on the DOPO-based s-triazine-bridged thiazole flame-retardant epoxy resin prepared in the above embodiments and comparative examples:

[0068] 1. Flame retardant properties of epoxy resin materials:

[0069] 1.UL-94 vertical combustion and limiting oxygen index test

[0070] The flame retardant properties of DOPO-based triazine-bridged thiazole flame-retardant epoxy resin were characterized by UL-94 vertical combustion and limiting oxygen index tests, and the test results are listed in Table 2. In addition, the digital photos of the specimens after the UL-94 vertical combustion test are shown in Table 2. Figure 1 According to the data in Table 2 and Figure 1 It was found that CE-EP-0 continued to burn after ignition, failed to reach any flame retardant level, and the limiting oxygen index value did not increase. It was also found that the flame retardant properties of epoxy resin materials were significantly improved with the increase of CE content. When the phosphorus content of the epoxy resin material was 0.50wt%, the total burning time (t1+t2) of CE-EP-0.5 was 11.4±1.5s, the flame retardant level could reach UL-94V-1, and the limiting oxygen index value was 35.3%. Continue to increase the content of CE in the epoxy resin material. When the phosphorus content of the epoxy resin material is 0.75wt%, the flame retardant level of CE-EP-0.75 can reach UL-94V-0. The above flame retardant test results show that the flame retardant properties of epoxy resin materials are significantly improved after the addition of CE.

[0071] Table 2 UL-94 vertical combustion and limiting oxygen index test results of epoxy resin materials

[0072]

[0073] t1: total burning time after the first ignition of the spline

[0074] t2: total burning time after the second ignition of the spline

[0075] 2. Cone calorimetry test

[0076] The combustion behavior of DOPO-based s-triazine-bridged thiazole flame-retardant epoxy resin was characterized by cone calorimetry test. The relevant data are listed in Table 3. Figure 2 and Figure 3 They are the heat release rate (HRR) curve and total heat release rate (THR) curve of epoxy resin materials. It can be found that the ignition time (TTI) of epoxy resin materials is not much different, while the peak heat release rate (P-HRR), total heat release rate and effective heat of combustion (EHC) of CE-EP-0 are as high as 944kW / m 2 and 210MJ / m 2 , 29.2MJ / kg, obviously no flame retardant ability. However, with the increase of CE content in epoxy resin material, the heat release rate continues to decrease. When the phosphorus content of epoxy resin material is 0.50wt%, the peak heat release rate, total heat release rate and effective combustion calorific value of CE-EP-0.5 are 778kW / m 2 、166MJ / m 2 When the flame retardant level of epoxy resin material reaches UL-94V-0, the peak heat release rate, total heat release rate and effective combustion heat value of CE-EP-0.75 are 735kW / m 2 、164MJ / m 2 , 24.6MJ / kg, which are 22.1%, 21.9% and 15.8% lower than those of CE-EP-0, respectively. The test results show that the introduction of CE significantly improves the flame retardant properties, making the DOPO-based triazine-bridged thiazole flame-retardant epoxy resin obtain ideal flame retardant properties.

[0077] Table 3 Cone calorimetry test results of epoxy resin materials

[0078]

[0079] 2. Analysis of carbon residue after combustion of epoxy resin materials

[0080] 1. Digital photos

[0081] Digital photos of carbon residues in epoxy resin materials after cone calorimetry testing Figure 4 As shown. Figure 4It can be seen that CE-EP-0 only has a small amount of residual carbon after combustion, and obviously has no flame retardant ability. With the addition of DOPO-based triazine-bridged thiazole flame retardant CE, the amount of carbon after combustion increases significantly, and the residual carbon of the epoxy resin material shows a significantly expanded honeycomb carbon layer structure, indicating that the addition of CE changes the morphology of the carbon layer, so that the DOPO-based triazine-bridged thiazole flame retardant epoxy resin has excellent flame retardant properties.

[0082] 2. SEM images

[0083] In order to explore the reasons for the excellent flame retardant performance, the inventors further analyzed the effect of introducing CE on the microscopic morphology of the residual carbon of epoxy resin materials by SEM. The results are as follows: Figure 5 As shown in the figure, CE-EP-0 presents a structure of large flaky debris, which cannot prevent the migration of flames and heat to the substrate, so it fails to reach any flame retardant level in the UL-94 vertical burning test. The microscopic morphology of CE-EP-0.5 still has a small number of holes, and it is not dense locally. This is one of the reasons why the flame retardant level of CE-EP-0.5 fails to reach the UL-94 V-0 level. As the CE content in the epoxy resin material continues to increase, the microscopic morphology of its residual carbon tends to become dense, and the pore structure in the carbon layer structure begins to gradually decrease. In CE-EP-0.75, it also presents a sticky and dense morphology locally, indicating that a stable carbon layer structure begins to form. CE-EP-1 finally presents a dense and regular carbon layer morphology, which can effectively block the heat exchange between the flame zone and the substrate, thereby improving the flame retardant properties of DOPO-based triazine-bridged thiazole flame-retardant epoxy resin.

[0084] 3.XPS analysis

[0085] The residual carbon was analyzed by XPS test method, and the results are listed in Table 4. It can be seen from the table that the phosphorus content of the residual carbon also increases with the increase of the phosphorus content in the DOPO-based triazine-bridged thiazole flame-retardant epoxy resin. When the phosphorus content is 0.50wt%, the phosphorus and nitrogen contents in the CE-EP-0.5 residual carbon are 0.50wt% and 3.20wt% respectively; when the phosphorus content is 0.75wt%, the phosphorus and nitrogen contents in the CE-EP-0.75 residual carbon are 1.25wt% and 3.00wt% respectively; when the phosphorus content is 1wt%, the phosphorus and nitrogen contents in the CE-EP-1 residual carbon are 1.41wt% and 2.25wt% respectively. The experimental results show that the introduction of CE changes the elemental composition ratio of the residual carbon of DOPO-based triazine-bridged thiazole flame-retardant epoxy resin, increases the enrichment of phosphorus and nitrogen in the residual carbon, thereby enhancing the catalytic carbonization efficiency of phosphorus in the condensed phase, and further improves the flame retardant properties of DOPO-based triazine-bridged thiazole flame-retardant epoxy resin.

[0086] Table 4 XPS analysis of carbon residue after cone calorimetry test

[0087]

[0088] 3. Dynamic mechanical properties and T of epoxy resin materials g

[0089] Figure 6 The relationship between the storage modulus and temperature of epoxy resin materials. It can be observed from the figure that the storage modulus of CE-EP-0 is only 2864MPa. When CE is introduced into epoxy resin materials, the storage modulus is significantly improved. When the flame retardant level of DOPO-based triazine-bridged thiazole flame-retardant epoxy resin reaches UL-94V-0, the storage modulus of CE-EP-0.75 is as high as 3575MPa, which is 24.4% higher than that of CE-EP-0. The test results show that CE has a good stiffening effect, which is consistent with the changing trend of the bending modulus and tensile modulus in the mechanical properties test.

[0090] The glass transition temperature (T) of epoxy resin materials was measured by DMA method. g ), the test results are listed in Table 5, Figure 7 is the relationship between the loss tangent of epoxy resin material and temperature. Combining the chart, it can be found that the T g With the addition of CE, the flame retardant level reaches UL-94V-0 level CE-EP-0.75 T g It still remains above 151.6℃, maintaining at a relatively high level.

[0091] Table 5 Dynamic mechanical test results of epoxy resin materials

[0092]

[0093] 4. Mechanical properties of epoxy resin materials

[0094] Table 6 shows the bending and tensile properties data of epoxy resin materials. It can be observed from the table that the changing trends of the bending and tensile properties are generally similar. After adding CE, the bending modulus and tensile modulus of the epoxy resin material are significantly improved. Among them, the bending modulus and tensile modulus of CE-EP-0.75 are 3.55GPa and 3.77GPa, respectively, and the bending modulus and tensile modulus of CE-EP-1 are 3.64GPa and 3.84GPa, respectively, which are 19.1% and 23.6% higher than CE-EP-0 and 22.1% and 25.9% higher, respectively, showing that CE has a good synergistic stiffening effect. At the same time, with the introduction of CE, the bending strength and tensile strength of the epoxy resin material have also been significantly improved. The bending strength and tensile strength of CE-EP-0 are 129.6MPa and 80.5MPa, the bending strength and tensile strength of CE-EP-0.5 are 132.4MPa and 85.1MPa, and the bending strength and tensile strength of CE-EP-0.75 with flame retardant grade reaching UL-94V-0 are 139.5MPa and 84.8MPa, which are 2.8MPa, 4.6MPa, 9.9MPa, 4.3MPa higher than those of CE-EP-0, respectively. This indicates that the bending strength and tensile strength of DOPO-based triazine-bridged thiazole flame-retardant epoxy resin have a certain enhancement effect when the phosphorus content is 0.50wt% and 0.75wt%.

[0095] The results of mechanical property tests show that the addition of CE significantly improves the mechanical properties of epoxy resin materials. CE increases the free volume between molecular chain segments, making the free movement between molecular chains less restricted, and molecular chain segments more likely to displace. When pulled by tensile stress, they can better transfer energy between chains, which is reflected in the increase of fracture energy from a macroscopic perspective. Unlike ordinary plasticizers that improve the toughness of materials while having a negative impact on the rigidity and strength of materials, CE can improve the toughness, strength and rigidity of materials at the same time, just like some surface-grafted inorganic nano-enhanced toughening materials, so that DOPO-based triazine-bridged thiazole flame-retardant epoxy resins have excellent comprehensive mechanical properties.

[0096] Table 6 Bending properties and tensile properties of epoxy resin materials

[0097]

[0098] 5. Thermal stability of epoxy resin materials

[0099] The effect of introducing CE on the thermal stability of epoxy resin materials was analyzed by thermogravimetric test under nitrogen atmosphere. The corresponding TGA curve and DTG curve are shown in Figure 2. Figure 8 and Fig. 9 As shown, the 5% thermal weight loss temperature (T d5％ )、50% thermal weight loss temperature (T d50％), maximum thermal weight loss rate temperature (T dmax ) and the carbon residue rate (Residue) at 800℃ are listed in Table 7. d5％ As the initial decomposition temperature of the epoxy resin material. From the TGA curve, it can be seen that the epoxy resin material has only one main thermal weight loss stage. The initial decomposition temperature and other temperature parameters of DOPO-based triazine-bridged thiazole flame-retardant epoxy resin, the difference in thermal stability is mainly reflected in the residual carbon rate. The residual carbon rate of CE-EP-0 is only 17.8%, while the residual carbon rate of CE-EP-0.75, which has a flame retardant grade of UL-94V-0, reaches 21%. In addition, it can be observed from the corresponding DTG curve that the decomposition rate of DOPO-based triazine-bridged thiazole flame-retardant epoxy resin also decreases significantly with the increase of phosphorus content. The decomposition rates of CE-EP-0.5 and CE-EP-1 are only 13.5% / ℃ and 11.8% / ℃, respectively, showing that DOPO-based triazine-bridged thiazole flame-retardant epoxy resin has a good inhibitory effect on thermal degradation. The test results of thermal stability show that the introduction of CE has a certain negative impact on the initial decomposition temperature of epoxy resin materials, but it can increase the residual carbon rate of epoxy resin materials and improve the thermal stability at high temperatures, thereby playing a certain role in improving the flame retardant properties.

[0100] Table 7 Thermal weight loss properties of epoxy resin materials in nitrogen atmosphere (table to be on the same page)

[0101]

[0102] The above description is a detailed description of the preferred feasible embodiments of the present invention, but the embodiments are not intended to limit the scope of the patent application of the present invention. All equivalent changes or modified changes completed under the technical spirit suggested by the present invention should fall within the patent scope covered by the present invention.

Claims

1. A method for preparing a DOPO-based s-triazine-bridged thiazole flame-retardant epoxy resin, characterized in that: The steps include: (1) Using 1,4-dioxane as solvent, adding a nitrogen-containing five-membered heterocyclic ring or its derivatives and p-hydroxybenzaldehyde to react at room temperature for 5 hours, utilizing the amino group in the nitrogen-containing five-membered heterocyclic ring or its derivatives to react with the aldehyde group of p-hydroxybenzaldehyde to generate an intermediate product I containing a Schiff base structure; (2) adding DOPO to the intermediate product I obtained in step (1) and adding palladium carbon as a catalyst, stirring evenly and reacting at 80° C. for 12 hours, using the active PH bond on DOPO to react with the C=N bond on the intermediate product I to prepare an intermediate product II containing a DOPO structure; The nitrogen-containing five-membered heterocyclic ring or its derivative, p-hydroxybenzaldehyde, solvent 1,4-dioxane, DOPO and palladium-carbon catalyst are used in a ratio of 1 g: 1.22 g: 30 ml: 2.16 g: 0.05 g; (3) adding cyanuric chloride to the intermediate product II obtained in step (2), using N,N-dimethylformamide as solvent, utilizing the phenolic hydroxyl group in the intermediate product II to react with cyanuric chloride at 120° C. under nitrogen protection for 6 hours to prepare a DOPO-based s-triazine-bridged thiazole flame retardant; after the reaction is completed, the reaction solution is naturally cooled to room temperature, poured into an ice water bath, washed with water to precipitate a crude product, which is the crude product of the DOPO-based s-triazine-bridged thiazole flame retardant; the amount ratio of the intermediate product II, cyanuric chloride and the solvent N,N-dimethylformamide is 12.6 g:1.85 g:50 ml; (4) filtering the crude product, washing it with a solvent to remove unreacted raw materials and impurities, and finally drying it in a vacuum drying oven to obtain the final product of the DOPO-based s-triazine-bridged thiazole flame retardant; The washing is specifically washing twice with ethanol and dichloromethane respectively; The final product of the DOPO-based s-triazine-bridged thiazole flame retardant has the following chemical structural formula: (5) The DOPO-based s-triazine-bridged thiazole flame retardant finally obtained in step (4) and bisphenol A epoxy resin are stirred at 130° C. under nitrogen protection for 15 minutes to completely dissolve the DOPO-based s-triazine-bridged thiazole flame retardant in the bisphenol A epoxy resin; then, the temperature of the mixed solution is reduced to 90° C., and a curing agent 4,4'-diaminodiphenylmethane is added and continuously stirred to completely dissolve the mixture to form a uniform mixed solution, and then the mixed solution is poured into a preheated mold, and the mold containing the mixed solution is degassed; then, the mold is subjected to a thermal curing reaction according to a pre-set heating program; finally, the mold is naturally cooled to room temperature to obtain a DOPO-based s-triazine-bridged thiazole flame retardant epoxy resin; the mass ratio of the bisphenol A epoxy resin, the DOPO-based s-triazine-bridged thiazole flame retardant and the curing agent 4,4'-diaminodiphenylmethane is 100:9-21:20-26.

2. The method for preparing the DOPO-based s-triazine-bridged thiazole flame-retardant epoxy resin according to claim 1, characterized in that: The nitrogen-containing five-membered heterocyclic ring or its derivative is 2-aminothiazole, 2-aminobenzothiazole, 2-aminoimidazole or 2-aminobenzimidazole.

3. The method for preparing the DOPO-based s-triazine-bridged thiazole flame-retardant epoxy resin according to claim 1, characterized in that: The pre-set temperature rising program described in step (5) is 80°C×1h, 100°C×1h, 120°C×1h, 150°C×3h, and 180°C×2h.

4. A DOPO-based s-triazine-bridged thiazole flame-retardant epoxy resin prepared according to the method for preparing a DOPO-based s-triazine-bridged thiazole flame-retardant epoxy resin according to any one of claims 1 to 3.

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