Furyl flame-retardant toughening curing agent as well as preparation method and application thereof

Abstract

The invention discloses a furyl flame-retardant toughening curing agent as well as a preparation method and application thereof. The chemical structure of the furyl flame-retardant toughening curing agent is shown as a formula (I), wherein R1 is a hydrogen atom or methyl, and R2 is a phosphorus-containing group. The flame-retardant curing structure provided by the invention simultaneously contains a furan ring and a phosphorus element, the furan ring can promote dehydration and charring of a polymer matrix, and the phosphorus element can play a flame-retardant role when a condensed phase and a gas phase are used. The structure of the flame retardant has imino groups, so that the flame retardant can play a role of a co-curing agent when being applied to thermosetting polymers such as epoxy resin and the like. When the flame-retardant toughening curing agent is applied to epoxy resin, the flame-retardant efficiency is very high, the limit oxygen index of the prepared epoxy resin material is obviously improved, the vertical combustion reaches V-0 level, and the flame-retardant toughening curing agent has excellent tensile property and impact resistance.

Description

Technical Field

[0001] This invention belongs to the field of bio-based phosphorus-containing flame retardants, specifically relating to a furan-based flame retardant toughening curing agent, its preparation method, and its application. Background Technology

[0003] Currently, a large number of bio-based raw materials, such as vanillin, lignin, eugenol, cashew nut shell, furan, phytic acid, and itaconic acid (Progress in Organic Coatings 2024, 191, 108409; Polymer 2021, 235, 124285; Journal of Materials Science, 2023, 58(16), 7208-7195), have been used to develop bio-based flame retardants. However, bio-based flame retardants still have many drawbacks, such as insufficient thermal stability, low flame retardant efficiency, and complex synthesis steps, which limit their large-scale application in polymers, especially epoxy resin materials. Furan and its derivatives, as a relatively common bio-based raw material, are mainly derived from agricultural by-products such as wheat bran and corn cobs (Biochemical Engineering Journal 2016, 116, 166-175; Biomass Conversion and Biorefinery 2017, 7, 247-274). These compounds exhibit good reactivity, and the furan ring in their molecules undergoes aromatization under high-temperature conditions, transforming from a five-membered heterocyclic structure to a benzene ring structure (Journal of Analytical and Applied Pyrolysis 2016, 120, 252-257; RSC Advances 2019, 9(16), 9099-9105). This structural transformation process can significantly promote the charring behavior of polymers and improve the flame retardant properties of materials, showing broad application prospects in the preparation of flame retardants.

[0004] The research group of Professor Yang Wantai at Beijing University of Chemical Technology synthesized a novel furfuryl-based DOPO-containing monomer (DDFA) using raw materials such as furfurylamine, paraformaldehyde (POM), and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO). This DDFA was copolymerized with maleic anhydride (MAH) to obtain a P / N-containing flame retardant (PDM), which was then applied to epoxy resin (EP). This flame retardant can give epoxy resin composites excellent flame retardant efficiency, while also enhancing their mechanical and dielectric properties and improving the char formation efficiency of flame-retardant modified epoxy resins. However, the epoxy resin materials still suffer from a decrease in thermal stability (Chemical Engineering Journal 2025, 519, 165034). A research group at South China University of Technology synthesized a bio-based phosphorus / nitrogen synergistic furan derivative (TFAD) using raw materials such as furfurylamine, 4-hydroxybenzaldehyde, cyanuric chloride, and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO). When applied to epoxy resins, low-dose addition achieved a synergistic effect of flame retardancy and toughening. However, the introduction of the flame retardant caused a decrease in the glass transition temperature (Tg) of the epoxy resin composite material. g Significantly reduced thermal stability and mechanical strength (Macromolecular Materials and Engineering 2022, 307, 2100981).

[0005] Therefore, developing a novel furan-based flame retardant that is simple to process, low in toxicity, highly efficient in flame retardancy, and has good stability, as well as preparing epoxy resin composite materials that combine excellent flame retardancy, high mechanical strength, and good thermal stability, has become an important research direction in the field of flame retardant materials. Summary of the Invention

[0006] This invention aims to provide a furan-based flame-retardant toughening curing agent, its preparation method, and its applications. The furan ring promotes the dehydration and char formation of the polymer matrix, while phosphorus can exert a flame-retardant effect in both the condensed phase and the gas phase. In the condensed phase, the presence of phosphorus promotes char formation of the polymer during combustion, while in the gas phase, phosphorus-containing free radicals quench active free radicals during combustion. The phosphorus content and aromatic ring number of this type of flame-retardant curing agent are adjustable, making it suitable for flame-retardant treatment of different polymer matrices. Furthermore, the flame retardant structure contains imino groups, which can act as co-curing agents when applied to thermosetting polymers such as epoxy resins. This flame retardant is based on bio-based raw materials, has a simple preparation process, relatively mild conditions, and high yield, making it suitable for flame-retardant treatment and large-scale production and application of different polymer matrices, such as epoxy resins.

[0007] The furan-based flame retardant toughening curing agent of the present invention has the following chemical structure as shown in formula (I):

[0008] ;

[0009] In formula (I), R1 is selected from either hydrogen or methyl, and R2 is selected from any of the following structures:

[0010] .

[0011] The preparation method of the furan-based flame retardant toughening curing agent of the present invention includes the following steps:

[0012] Step 1: Under inert gas protection, furanyl diamine and furfural are mixed in anhydrous ethanol at a certain molar ratio and heated to 60-80°C for 8-10 hours.

[0013] The furanyl diamine is (DFDA-1) and Any of (DFDA-2).

[0014] Step 2: Slowly add the phosphorus-containing compound to the mixture obtained in Step 1. The reaction mixture is kept at a temperature of 60-80 °C under an inert gas atmosphere and stirred for 6-24 hours. After the reaction is completed, remove the solvent by rotary evaporation (liquid product) or by filtration and washing (solid product), and then dry to obtain the target product.

[0015] In step 1, the molar ratio of furanyldiamine to furfural is 1:2.

[0016] In steps 1 and 2, the inert gas is any one of nitrogen, argon, or helium.

[0017] In step 2, the phosphorus-containing compound is selected from any one of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, diphenylphosphine oxide, diphenyl phosphite, dibenzyl phosphite, dimethyl phosphite, diethyl phosphite, di-n-butyl phosphite, and di-tert-butyl phosphite.

[0018] In step 2, the molar ratio of furanyldiamine to the phosphorus-containing compound is 1:2~2.2.

[0019] The present invention relates to the application of furan-based flame-retardant toughening curing agent in the preparation of flame-retardant epoxy resin materials.

[0020] Furthermore, the furan-based flame-retardant toughening curing agent is used as a co-curing agent to partially replace conventional curing agents.

[0021] The amount of furan-based flame retardant toughening curing agent added is determined by adjusting the phosphorus content; generally, the overall phosphorus content of the system is ≤2.0 wt%.

[0022] The appropriate molecular weight and number of functional groups are crucial to the toughening effect of flame retardants. The furan-based phosphorus-containing flame retardant provided by this invention has a moderate molecular weight and contains bifunctional active NH groups, thus exhibiting a toughening effect (improved impact strength). The initial decomposition temperature (temperature at 5% weight loss) of the flame-retardant epoxy resins in Examples 7, 8, and 9 is higher than that of the unmodified epoxy resin in Comparative Example 1, indicating that the furan-based flame-retardant toughening curing agent of this invention can improve the thermal stability of epoxy resins. This is invaluable for phosphorus-containing flame-retardant epoxy resins, as most phosphorus-containing flame retardants currently lead to a decrease in the thermal stability of epoxy resins.

[0023] Compared with the prior art, the beneficial effects of the present invention are:

[0024] 1. The flame-retardant curing agent provided by this invention contains furan rings, benzene rings, and phosphorus elements in its chemical structure. Phosphorus can exert a flame-retardant effect in both the condensed phase and the gas phase. In the condensed phase, the presence of phosphorus promotes char formation of the polymer during combustion, while in the gas phase, phosphorus-containing free radicals quench active free radicals during combustion. Furthermore, the furan rings and benzene rings in the structure of this flame-retardant curing agent can promote the dehydration and char formation of the polymer matrix, significantly improving the stability of the char layer.

[0025] 2. The flame retardant curing agent provided by the present invention has imino groups in its chemical structure, which can act as a co-curing agent when applied to thermosetting polymers such as epoxy resin.

[0026] 3. The flame retardant curing agent provided by the present invention has adjustable phosphorus content and aromatic ring number in its chemical structure, and is suitable for flame retardant treatment of different polymer matrices. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 Thermogravimetric analysis curves of each sample in Comparative Example 1, Example 7, Example 8 and Example 9 of this invention.

[0029] Figure 2 The heat release rate curves of each sample in Comparative Example 1, Example 7, Example 8 and Example 9 of this invention are shown.

[0030] Figure 3 The total heat release curves for each sample in Comparative Example 1, Example 7, Example 8 and Example 9 of this invention are shown.

[0031] Figure 4 These are photographs of the carbon residue from Comparative Examples 1, 7, 8, and 9 of this invention after testing with a cone calorimeter.

[0032] Figure 5 The stress-strain curves of each sample in Comparative Example 3 and Example 8 of this invention are shown. Detailed Implementation

[0033] To further illustrate the technical solution of the present invention, preferred embodiments are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, and not for limiting the scope of the claims. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0034] Example 1:

[0035] 1. Under nitrogen protection, add DFDA-1 and furfural to the solvent at a molar ratio of 1:2, stir magnetically for 5-10 minutes, then heat the system to 80°C and react for 10 hours.

[0036] 2. Diphenylphosphine oxide was slowly added to the reaction mixture obtained in step 1, with a molar ratio of DFDA-1 to diphenylphosphine oxide of 1:2.1. Under nitrogen atmosphere and at a temperature of 80°C, the mixture was stirred for 24 hours to obtain the target product a, whose chemical structure is shown below:

[0037]

[0038] Target product a was subjected to Fourier transform infrared spectroscopy (FT-IR) and proton nuclear magnetic resonance spectroscopy (1H NMR). 1 Characterized by 1H-NMR, its chemical structure was confirmed as follows: FT-IR (KBr, cm⁻¹) -1 ): 3317 (NH), 2940, 2898 (-CH3, -CH2-), 1605,1510 (benzene ring), 1081, 738 (furan ring), 1177 (P=O), 1117 (PC). 1H-NMR(400 MHz, CDCl3-d6, ppm): 1.51 (s, 3H, (-CH3)2), 3.44-3.48 (d, 4H, (-CH2-)2), 3.69-3.73 (d, 2H, (-CH-)2), 4.90 (s, 2H, (-NH-)2), 5.96 (s, 4H, (CC-(CH)2-)2), 6.31 (s, 4H, (PC-(CH)2-)2), (m, 20H, Ar-H (Ar-P-Ar)).

[0039] Example 2:

[0040] 1. Under nitrogen protection, add DFDA-1 and furfural to the solvent at a molar ratio of 1:2, stir magnetically for 5-10 minutes, then heat the system to 70°C and react for 8 hours.

[0041] 2. 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide was slowly added to the reaction mixture obtained in step 1, with a molar ratio of DFDA-1 to 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide of 1:2.05. Under nitrogen atmosphere and at a temperature of 70°C, the mixture was stirred for 12 hours to obtain the target product b, whose chemical structure is shown below:

[0042]

[0043] Target product b was subjected to Fourier transform infrared spectroscopy (FT-IR) and proton nuclear magnetic resonance spectroscopy (1H NMR). 1 Characterized by 1H-NMR, its chemical structure was confirmed as follows: FT-IR (KBr, cm⁻¹) -1 ): 3320 (NH), 2942, 2895 (-CH3, -CH2-), 1611(Ar-Ar), 1605, 1510 (benzene ring), 1517 (P-Ar), 1081, 738 (furan ring), 1177(P=O), 1117 (PC, PO). 1H-NMR (400 MHz, DMSO-d6, ppm): 1.63 (S, 3H, -C-(CH3)2), 3.97 (dd, 1H, -NH-CH2-C), 4.20 (dt, 1H, -CH2-NH-CH-), 4.90 (dd, 1H, -NH-CH-CH(-POCO)), 6.30 (d, 1H, CH-CH=C), 6.39 (m, 1H, =CH-CH=CH-), 6.51 (dd, 1H,C=CH-C=), 7.37 (m, 1H, Ar-H), 7.47 (m, 1H, Ar-H), 7.56 (dd, 1H, Ar-H & -O-CH=C-), 7.93 (ddd, 1H, Ar-H), 8.00 (dd, 1H, Ar-H), 8.18 (ddd, 1H, Ar-H).

[0044] Example 3:

[0045] 1. Under nitrogen protection, add DFDA-1 and furfural to the solvent at a molar ratio of 1:2, stir magnetically for 5-10 minutes, then heat the system to 80°C and react for 10 hours.

[0046] 2. Diphenyl phosphite was slowly added to the reaction mixture obtained in step 1, with a molar ratio of DFDA-1 to diphenyl phosphite of 1:2.1. Under nitrogen atmosphere and at a temperature of 80°C, the mixture was stirred for 24 hours to obtain the target product c, whose chemical structure is shown below:

[0047]

[0048] The target product c was subjected to Fourier transform infrared spectroscopy (FT-IR) and proton nuclear magnetic resonance spectroscopy (1H NMR). 1 Characterized by 1H-NMR, its chemical structure was confirmed as follows: FT-IR (KBr, cm⁻¹) -1 ): 3315 (NH), 2940, 2897 (-CH3, -CH2-), 1605,1510 (benzene ring), 1080, 738 (furan ring), 1177 (P=O), 1117 (PC, PO). 1H-NMR (400 MHz, DMSO-d6, ppm): 1.63 (S, 3H, -C-(CH3)2), 3.94 (dd, 2H, -NH-CH2-C), 4.06 (dt, 1H, -CH2-NH-CH-), 4.65 (dd, 1H, -NH-CH-CH(-P)), 6.30 (d, 1H,CH-CH=C), 6.40 (m, 1H, =CH-CH=CH-), 6.57 (dd, 1H, C=CH-C=), 7.19 (m, 1H, Ar-H), 7.39 (m, 1H, Ar-H), 7.47 (t, 1H, Ar-H & -O-CH=C-).

[0049] Example 4:

[0050] 1. Under nitrogen protection, add DFDA-1 and furfural to the solvent at a molar ratio of 1:2, stir magnetically for 5-10 minutes, then heat the system to 80°C and react for 8 hours.

[0051] 2. Dimethyl phosphite was slowly added to the reaction mixture obtained in step 1, with a molar ratio of DFDA-1 to dimethyl phosphite of 1:2.1. Under nitrogen atmosphere and at a temperature of 80°C, the mixture was stirred for 24 hours to obtain the target product d, whose chemical structure is shown below:

[0052]

[0053] The target product d was subjected to Fourier transform infrared spectroscopy (FT-IR) and proton nuclear magnetic resonance spectroscopy (1H NMR). 1 Characterized by 1H-NMR, its chemical structure was confirmed as follows: FT-IR (KBr, cm⁻¹) -1 ): 3313 (NH), 2960, 2892 (-CH3, -CH2-), 1080,735 (furan ring), 1177 (P=O), 1110 (PC, PO), 907 (POC). 1H-NMR (400 MHz, DMSO-d6, ppm): 1.63 (S, 3H, -C-(CH3)2), 3.46 (dt, 1H, -CH2-NH-CH-), 3.64 (t,3H, -O-CH3), 3.94 (dd, 2H, -NH-CH2-C), 4.53 (dd, 1H, -NH-CH-CH(-P)), 6.30 (d,1H, CH-CH=C), 6.39 (m, 1H, =CH-CH=CH-), 6.54 (dd, 1H, C=CH-C=), 7.48 (t, 1H,-O-CH=C-).

[0054] Example 5:

[0055] 1. Under nitrogen protection, add DFDA-2 and furfural to the solvent at a molar ratio of 1:2, stir magnetically for 5-10 minutes, then heat the system to 80°C and react for 10 hours.

[0056] 2. Diphenylphosphine oxide was slowly added to the reaction mixture obtained in step 1, with a molar ratio of DFDA-2 to diphenylphosphine oxide of 1:2.1. Under nitrogen atmosphere and at a temperature of 80°C, the mixture was stirred for 6 hours to obtain the target product e, whose chemical structure is shown below:

[0057]

[0058] The target product e was subjected to Fourier transform infrared spectroscopy (FT-IR) and proton nuclear magnetic resonance spectroscopy (1H NMR). 1 Characterized by 1H-NMR, its chemical structure was confirmed as follows: FT-IR (KBr, cm⁻¹) -1 ): 3317 (NH), 2905 (-CH2-), 1605, 1510 (benzenering), 1080, 736 (furan ring), 1177 (P=O), 1117 (PC). 1 H-NMR (400 MHz, DMSO-d6, ppm): 3.91 (d, 2H, -NH-CH2-C), 4.06 (m, 1H, -CH2-NH-CH-), 5.07 (dd, 1H, -NH-CH-CH(-POCO)), 6.21 (d, 1H, CH-CH=C), 6.37 (m, 1H, =CH-CH=CH-), 6.46 (dd,1H, C=CH-C=), 7.50 (m, 1H, Ar-H), 7.79 (dt, 1H, Ar-H).

[0059] Example 6:

[0060] 1. Under nitrogen protection, add DFDA-2 and furfural to the solvent at a molar ratio of 1:2, stir magnetically for 5-10 minutes, then heat the system to 70°C and react for 8 hours.

[0061] 2. 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide was slowly added to the reaction mixture obtained in step 1, with a molar ratio of DFDA-2 to 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide of 1:2.05. Under nitrogen atmosphere and at a temperature of 70°C, the mixture was stirred for 24 hours to obtain the target product f, whose chemical structure is shown below:

[0062]

[0063] The target product f was subjected to Fourier transform infrared spectroscopy (FT-IR) and proton nuclear magnetic resonance spectroscopy (1H NMR). 1 Characterized by 1H-NMR, its chemical structure was confirmed as follows: FT-IR (KBr, cm⁻¹) -1 ): 3321 (NH), 2910 (-CH2-), 1611 (Ar-Ar), 1605,1510 (benzene ring), 1517 (P-Ar), 1081, 738 (furan ring), 1177 (P=O), 1117 (PC, PO). 1 H-NMR (400 MHz, DMSO-d6, ppm): 3.94-3.99 (d, 2H, C-CH2-C & (-NH-CH2-C)), 4.20 (dt, 1H, -CH2-NH-CH-), 4.90 (dd, 1H, -NH-CH-CH(-POCO)), 6.21 (d,1H, CH-CH=C), 6.39 (m, 1H, =CH-CH=CH-), 6.51 (dd, 1H, C=CH-C=), 7.37 (m, 1H,Ar-H), 7.47 (m, 1H, Ar-H), 7.56 (dd, 1H, Ar-H & -O-CH=C-), 7.93 (ddd, 1H, Ar-H), 8.00 (dd, 1H, Ar-H), 8.18 (ddd, 1H, Ar-H).

[0064] Example 7:

[0065] Accurately weigh 63.3 g of bio-based epoxy resin (DGFA), 30.3 g of curing agent (4,4'-diaminodiphenylmethane), and 6.3 g of flame-retardant curing agent a. Add DGFA and flame-retardant curing agent a to a three-necked flask, heat to 150°C, and mechanically stir for 30 minutes to obtain an epoxy resin dispersion. Add the curing agent to the above epoxy resin dispersion, heat to 70-80°C, and mechanically stir for 10-20 minutes. Immediately pour into a mold, and cure under the following conditions: 100°C / 2 hours + 150°C / 2 hours. After demolding, allow to cool naturally to room temperature to obtain a flame-retardant epoxy resin sample with a phosphorus content of 0.5% by mass.

[0066] Example 8:

[0067] Accurately weigh 59.2 g of bio-based epoxy resin (DGFA), 28.0 g of curing agent (4,4'-diaminodiphenylmethane), and 12.8 g of flame-retardant curing agent a. Add DGFA and flame-retardant curing agent a to a three-necked flask, heat to 150°C, and mechanically stir for 30 minutes to obtain an epoxy resin dispersion. Add the curing agent to the above epoxy resin dispersion, heat to 70-80°C, and mechanically stir for 10-20 minutes. Immediately pour the mixture into a mold, and cure under the following conditions: 100°C / 2 hours + 150°C / 2 hours. After demolding, allow it to cool naturally to room temperature to obtain a flame-retardant epoxy resin sample with a phosphorus content of 1.0% by mass.

[0068] Example 9:

[0069] Accurately weigh 54.7 g of bio-based epoxy resin (DGFA), 26.0 g of curing agent (4,4'-diaminodiphenylmethane), and 19.3 g of flame-retardant curing agent a. Add DGFA and flame-retardant curing agent a to a three-necked flask, heat to 150°C, and mechanically stir for 30 minutes to obtain an epoxy resin dispersion. Add the curing agent to the above epoxy resin dispersion, heat to 70-80°C, and mechanically stir for 10-20 minutes. Immediately pour the mixture into a mold, and cure under the following conditions: 100°C / 2 hours + 150°C / 2 hours. After demolding, allow it to cool naturally to room temperature to obtain a flame-retardant epoxy resin sample with a phosphorus content of 1.5% by mass.

[0070] Example 10:

[0071] Accurately weigh 58.8 g of bio-based epoxy resin (DGFA), 27.9 g of curing agent (4,4'-diaminodiphenylmethane), and 13.3 g of flame-retardant curing agent b. Add DGFA and flame-retardant curing agent b to a three-necked flask, heat to 150°C, and mechanically stir for 30 minutes to obtain an epoxy resin dispersion. Add the curing agent to the above epoxy resin dispersion, heat to 70-80°C, and mechanically stir for 10-20 minutes. Immediately pour into a mold, and cure under the following conditions: 100°C / 2 hours + 150°C / 2 hours. After demolding, allow to cool naturally to room temperature to obtain a flame-retardant epoxy resin sample with a phosphorus content of 1.0% by mass.

[0072] Example 11:

[0073] Accurately weigh 58.4 g of bio-based epoxy resin (DGFA), 27.7 g of curing agent (4,4'-diaminodiphenylmethane), and 13.9 g of flame-retardant curing agent c. Add DGFA and flame-retardant curing agent c to a three-necked flask, heat to 150°C, and mechanically stir for 30 minutes to obtain an epoxy resin dispersion. Add the curing agent to the above epoxy resin dispersion, heat to 70-80°C, and mechanically stir for 10-20 minutes. Immediately pour into a mold, and cure under the following conditions: 100°C / 2 hours + 150°C / 2 hours. After demolding, allow to cool naturally to room temperature to obtain a flame-retardant epoxy resin sample with a phosphorus content of 1.0% by mass.

[0074] Example 12:

[0075] Accurately weigh 61.1 g of bio-based epoxy resin (DGFA), 29.0 g of curing agent (4,4'-diaminodiphenylmethane), and 9.9 g of flame-retardant curing agent d. Add DGFA and flame-retardant curing agent d to a three-necked flask, heat to 150°C, and mechanically stir for 30 minutes to obtain an epoxy resin dispersion. Add the curing agent to the above epoxy resin dispersion, heat to 70-80°C, and mechanically stir for 10-20 minutes. Immediately pour into a mold, and cure under the following conditions: 100°C / 2 hours + 150°C / 2 hours. After demolding, allow to cool naturally to room temperature to obtain a flame-retardant epoxy resin sample with a phosphorus content of 1.0% by mass.

[0076] Example 13:

[0077] Accurately weigh 59.4 g of bio-based epoxy resin (DGFA), 28.2 g of curing agent (4,4'-diaminodiphenylmethane), and 12.4 g of flame-retardant curing agent e. Add DGFA and flame-retardant curing agent e to a three-necked flask, heat to 150°C, and mechanically stir for 30 minutes to obtain an epoxy resin dispersion. Add the curing agent to the above epoxy resin dispersion, heat to 70-80°C, and mechanically stir for 10-20 minutes. Immediately pour the mixture into a mold, and cure under the following conditions: 100°C / 2 hours + 150°C / 2 hours. After demolding, allow it to cool naturally to room temperature to obtain a flame-retardant epoxy resin sample with a phosphorus content of 1.0% by mass.

[0078] Example 14:

[0079] Accurately weigh 59.2 g of bio-based epoxy resin (DGFA), 28.0 g of curing agent (4,4'-diaminodiphenylmethane), and 12.8 g of flame-retardant curing agent f. Add DGFA and flame-retardant curing agent f to a three-necked flask, heat to 150°C, and mechanically stir for 30 minutes to obtain an epoxy resin dispersion. Add the curing agent to the above epoxy resin dispersion, heat to 70-80°C, and mechanically stir for 10-20 minutes. Immediately pour into a mold, and cure under the following conditions: 100°C / 2 hours + 150°C / 2 hours. After demolding, allow to cool naturally to room temperature to obtain a flame-retardant epoxy resin sample with a phosphorus content of 1.0% by mass.

[0080] Comparative Example 1:

[0081] Accurately weigh 67.7 g of bio-based epoxy resin (DGFA) and 32.3 g of curing agent (4,4'-diaminodiphenylmethane). Add the epoxy resin and curing agent to a three-necked flask, heat to 70-80°C, and mechanically stir for 10-20 minutes. Immediately pour the mixture into a mold. Curing conditions are 100°C / 2 hours + 150°C / 2 hours. After demolding, allow it to cool naturally to room temperature to obtain the epoxy resin sample.

[0082] Comparative Example 2:

[0083] Accurately weigh 60.7 g of bio-based epoxy resin (DGFA), 10.5 g of 10-(2,5-dihydroxyphenyl)-10-hydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO-HQ), and 28.8 g of curing agent (4,4'-diaminodiphenylmethane). Add the epoxy resin and DOPO-HQ to a three-necked flask, heat to 80°C, and mechanically stir for 30 minutes. Then add the curing agent and continue mechanically stirring for 10 minutes. Immediately pour the mixture into a mold and cure under the following conditions: 100°C / 2 hours + 150°C / 2 hours. After demolding, allow it to cool naturally to room temperature to obtain a flame-retardant epoxy resin sample with a phosphorus content of 1.0% by mass.

[0084] Comparative Example 3:

[0085] Accurately weigh 59.6 g of bio-based epoxy resin (DGFA), 12.2 g of furan-based flame retardant (DPO-FD, chemical structure shown below), and 28.2 g of curing agent (4,4'-diaminodiphenylmethane). Add the epoxy resin and DPO-FD to a three-necked flask, heat to 80 °C, and mechanically stir for 30 minutes. Then add the curing agent and continue mechanically stirring for 10 minutes. Immediately pour the mixture into a mold and cure under the following conditions: 100 °C / 2 hours + 150 °C / 2 hours. After demolding, allow it to cool naturally to room temperature to obtain a flame-retardant epoxy resin sample with a phosphorus content of 1.0% by mass.

[0086]

[0087] The performance test results of the products obtained in the above embodiments and comparative examples are as follows:

[0088]

[0089] The flame retardant test results in Table 1 show that the oxygen index of DGFA / DDM epoxy resin (Comparative Example 1) is only 23.0%, it has no rating in the UL-94 vertical burning test, and its tensile strength and impact strength are 80.3 MPa and 13.1 kJ / m, respectively. 2 The glass transition temperature was 104.3℃. Compared with the unmodified epoxy resin (Comparative Example 1), the tensile strength, impact strength, and glass transition temperature of each flame-retardant epoxy resin in Examples 7-14 did not decrease significantly, and the oxygen index was above 29.5%. Furthermore, each flame-retardant epoxy resin in Examples 8-14 passed the UL-94 V-0 rating. Compared with the commonly used commercially available flame retardant DOPO-HQ, when the phosphorus content was 1%, the oxygen index, UL-94 flammability rating, tensile strength, and impact strength of the flame-retardant epoxy resin obtained in Comparative Example 2 were all inferior to the performance of the furan-based flame-retardant toughening curing agent modified flame-retardant epoxy resin provided by this invention (Examples 8, 10, 11, 12, 13, and 14). Compared to monofunctional furanyl flame retardants, although the flame-retardant epoxy resin obtained in Comparative Example 3 could pass the UL-94 V-0 rating when the phosphorus content was 1%, its tensile strength, impact strength, and glass transition temperature were significantly reduced. This is because the addition of monofunctional furanyl flame retardants reduced the crosslinking density of the epoxy resin, leading to a decrease in its mechanical properties and thermal stability. Therefore, the furanyl flame-retardant toughening curing agent-modified flame-retardant epoxy resin provided by this invention is suitable for applications requiring high flame retardant and mechanical properties.

[0090] Thermogravimetric analysis curves of the samples in Comparative Example 1, Example 7, Example 8, and Example 9 under a nitrogen atmosphere are shown below. Figure 1 As shown, the initial decomposition temperature (temperature at 5% weight loss) of the flame-retardant epoxy resins in Examples 7, 8, and 9 is higher than that of the unmodified epoxy resin in Comparative Example 1, indicating that the furan-based flame-retardant toughening curing agent in this invention does not deteriorate the thermal stability of the epoxy resin. Furthermore, with the increase in the amount of furan-based flame-retardant toughening curing agent, the char residue of the flame-retardant epoxy resin increases significantly, indicating that the introduction of the furan-based flame-retardant toughening curing agent improves the charring performance of the bio-based epoxy resin.

[0091] The heat release rate curves of each sample in Comparative Example 1, Example 7, Example 8, and Example 9 are shown below. Figure 2 As shown, the peak heat release rate of the unmodified epoxy resin (Comparative Example 1) is approximately 1445 kW / m². 2 In Examples 7, 8, and 9, the peak heat release rates of the flame-retardant epoxy resins decreased to 1170, 1091, and 833 kW / m, respectively. 2 This indicates that furan-based flame retardant toughening curing agents can effectively suppress the heat release rate of bio-based epoxy resins.

[0092] The total heat release curves for each sample in Comparative Example 1, Example 7, Example 8, and Example 9 are shown below. Figure 3 As shown in the figure, it can be seen that within 0-400s, the total heat release value of the unmodified epoxy resin (Comparative Example 1) is approximately 68.8 MJ / m. 2 The total heat release values ​​of the flame-retardant epoxy resins in Examples 7, 8, and 9 were 66.4, 62.4, and 53.2 MJ / m³, respectively. 2 This indicates that furan-based flame retardant toughening curing agents can promote the formation of a char layer in bio-based epoxy resins, effectively suppressing the heat release during combustion.

[0093] Photographs of the char residue of each sample in Comparative Example 1, Example 7, Example 8, and Example 9 after testing with a cone calorimeter are shown below. Figure 4 As shown, the unmodified epoxy resin (Comparative Example 1) left almost no char residue after combustion, indicating poor oxidation resistance of the char layer. In contrast, the flame-retardant epoxy resins in Examples 7, 8, and 9 showed increasing amounts of char residue and more pronounced expansion effects, further demonstrating that the furan-based flame-retardant toughening curing agent has a good catalytic char formation effect.

[0094] The stress-strain curves of each sample in Comparative Example 3 and Example 8 are as follows: Figure 5As shown, the flame-retardant epoxy resin sample in Comparative Example 3 fractured at a strain of 13.3%, with a tensile strength of 41.9 MPa; while the flame-retardant epoxy resin in Example 8 fractured at a strain of 14.1%, with a tensile strength reaching 81.4 MPa, which is 94.3% higher than that of the flame-retardant epoxy resin sample in Comparative Example 3. This indicates that the furan-based flame-retardant toughening curing agent in this invention can effectively maintain the tensile strength of epoxy resin materials.

[0095] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A furan-based flame-retardant toughening curing agent, characterized in that... Its chemical structure is shown in formula (I): ； In formula (I), R1 is selected from either hydrogen or methyl, and R2 is selected from any of the following structures: 。 2. The preparation method of the furan-based flame retardant toughening curing agent according to claim 1, characterized in that... Includes the following steps: Step 1: Under the protection of an inert gas, furanyl diamine and furfural are mixed in anhydrous ethanol at a certain molar ratio and heated to 60-80°C for 8-10 hours. The furanyl diamine is or ; Step 2: Slowly add the phosphorus-containing compound to the mixture obtained in Step 1. The reaction mixture is kept at a temperature of 60-80 °C under an inert gas atmosphere and stirred for 6-24 hours. After the reaction is completed, remove the solvent by rotary evaporation or by filtration and washing, and then dry to obtain the target product.

3. The preparation method according to claim 2, characterized in that: In step 1, the molar ratio of furanyldiamine to furfural is 1:

2.

4. The preparation method according to claim 2, characterized in that: In steps 1 and 2, the inert gas is any one of nitrogen, argon, or helium.

5. The preparation method according to claim 2, characterized in that: In step 2, the phosphorus-containing compound is selected from any one of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, diphenylphosphine oxide, diphenyl phosphite, dibenzyl phosphite, dimethyl phosphite, diethyl phosphite, di-n-butyl phosphite, and di-tert-butyl phosphite.

6. The preparation method according to claim 2 or 5, characterized in that: The molar ratio of furanyldiamine to the phosphorus-containing compound is 1:2~2.

2.

7. The application of the furan-based flame retardant toughening curing agent according to claim 1 in the preparation of flame retardant epoxy resin materials.

8. The application according to claim 7, characterized in that: The furan-based flame-retardant toughening curing agent is used as a co-curing agent to partially replace conventional curing agents.

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