A phosphorus-nitrogen synergistic flame-retardant biomass flame retardant and its application

Abstract

The present invention relates to the technical field of flame retardants, and in particular to a phosphorus-nitrogen synergistic flame-retardant biomass flame retardant and its application. Conventional reactive phosphorus-nitrogen flame retardants have a bulky structure and large steric hindrance, and cannot be completely dissolved in epoxy resin material systems. The obtained flame-retardant epoxy resin has poor transparency and greatly reduced mechanical properties. In response to the above problems, the present invention provides a phosphorus-nitrogen synergistic flame-retardant biomass flame retardant, which is obtained by a simple one-pot synthesis reaction of furfural and furfural derivatives with 2-amino-1,3,4-thiadiazole and DOPO. The flame retardant has a simple structure, small steric hindrance, and is easily completely dissolved in epoxy resin. The obtained flame-retardant epoxy resin has better transparency, flame retardancy and mechanical properties.

Description

Technical Field

[0001] The present invention relates to the technical field of flame retardants, and in particular to a phosphorus-nitrogen synergistic flame-retardant biomass flame retardant and application thereof. Background Art

[0002] Epoxy resins are widely used in electronics, aerospace, and high-performance coatings due to their excellent mechanical properties, chemical resistance, and durability. However, general-purpose epoxy resins are prone to combustion and produce significant smoke and dripping during combustion, posing a significant safety hazard. Therefore, research on improving the flame retardancy of epoxy resins is of great significance.

[0003] There are many types of flame retardants, among which halogen-containing flame retardants have a clear advantage in improving the flame retardancy of epoxy resins and are widely used in polymer composites. However, halogen-containing flame retardants produce large amounts of toxic and harmful gases during combustion, which pose significant risks to the environment and human health. Replacing halogens with high-efficiency, low-toxicity, and low-smoke halogen-free environmentally friendly flame retardants and new flame-retardant epoxy resin materials has become a hot topic of research for scholars both domestically and internationally. Among these, phosphorus and nitrogen compounds, as a new type of flame retardant, have attracted considerable attention due to their advantages in improving the flame retardancy and thermal stability of epoxy resins while minimizing the impact on the mechanical properties and transparency of the substrate material.

[0004] However, while current phosphorus-nitrogen flame retardants can improve the flame retardancy of epoxy resins, they can significantly reduce transparency and mechanical properties. Such modifications particularly impact the high-end applications of flame-retardant epoxy resins. For example, Chinese patent CN105837636A discloses a phosphorus-nitrogen synergistic flame retardant compound, its preparation method, and application. It utilizes a divinyl-terminated quaternary ammonium compound and DOPO to produce a phosphaphenanthrene-structured reactive flame retardant. Although this phosphorus-nitrogen flame retardant has secondary amino groups that react with the epoxy groups of the epoxy resin, its bulky structure and large steric hindrance prevent it from fully reacting with the epoxy groups. Consequently, the flame retardant cannot be completely dissolved in the epoxy resin, resulting in opacity in the flame-retardant epoxy resin after curing and a significant impact on mechanical properties. Summary of the Invention

[0005] The problem with the existing technology is that conventional reactive phosphorus-nitrogen flame retardants are bulky and have large steric hindrance, making them insoluble in epoxy resin systems. The resulting flame-retardant epoxy resin has poor transparency and significantly reduced mechanical properties. To address these issues, the present invention provides a biomass flame retardant with phosphorus-nitrogen synergistic flame retardancy, the chemical structure of which is as follows:

[0006]

[0007] The R groups in the above structural formula include hydrogen atoms, C1-C 12At least one of a straight-chain alkyl group, a hydroxyl group, a hydroxymethyl group, a hydroxyethyl group, a hydroxypropyl group, a nitro group, an aldehyde group, a dimethylamino group, a boronic acid group, a carboxyl group, a formyloxy group, an acetoxy group, and a propionyloxy group.

[0008] Preferably, the preparation method of the phosphorus-nitrogen synergistic flame-retardant biomass flame retardant comprises the following steps:

[0009] (1) Furfural or a furfural derivative reacts with 2-amino-1,3,4-thiadiazole to form a Schiff base intermediate, the structural formula of the Schiff base intermediate is as follows:

[0010]

[0011] In the above chemical structure, the R group includes hydrogen atoms, C1-C 12 At least one of a straight-link alkyl group, a hydroxyl group, a hydroxymethyl group, a hydroxyethyl group, a hydroxypropyl group, a nitro group, an aldehyde group, a dimethylamino group, a boric acid group, a carboxyl group, a formyloxy group, an acetoxy group, and a propionyloxy group;

[0012] (2) The Schiff base intermediate reacts with DOPO to form the target product.

[0013] Preferably, the furfural derivatives include at least one of 5-hydroxyfurfural, 5-nitrofurfural, 5-methylfurfural, 5-ethylfurfural, 5-propylfurfural, 5-butylfurfural, 5-hydroxymethylfurfural, 5-hydroxyethylfurfural, 5-hydroxypropylfurfural, 5-dimethylamino-2-furfural, 5-carboxy-2-furfural, 2,5-furandicarboxaldehyde, formaldehyde furan-2-boric acid, 5-acetylmethyl-2-furfural, and 5-propionylmethyl-2-furfural.

[0014] Preferably, the solvent used in step (1) includes one or more of anhydrous ethanol, 1,2-propylene glycol, 1,3-propylene glycol, 1,4-butanediol, 1,2-butanediol, 1,3-butanediol, dichloromethane, dichloroethane, chloroform, ethyl acetate, benzene, toluene, and 1,4-dioxane.

[0015] Preferably, the reaction temperature in step (1) is 40-100° C., and the reaction time is 8-12 h.

[0016] Preferably, in step (1), the molar ratio of furfural or furfural derivative to 2-amino-1,3,4-thiadiazole is 1-1.1:1.

[0017] Preferably, the molar ratio of the Schiff base intermediate to DOPO in step (2) is 1:1-1.1.

[0018] Preferably, the reaction temperature in step (2) is 40-100° C., and the reaction time is 12-24 h.

[0019] A transparent flame-retardant epoxy resin, the preparation method of which comprises the following steps:

[0020] (1) Heat the epoxy resin to 140-160° C., add an appropriate amount of the biomass flame retardant, stir until the biomass flame retardant is completely dissolved in the epoxy resin, and keep warm for 8-20 minutes;

[0021] (2) After cooling the mixed solution obtained in step (1) to 80-100° C., an epoxy curing agent is added to the reaction system, and the mixture is stirred at a constant temperature until the epoxy curing agent is completely dissolved. The reaction system is quickly poured into a mold preheated to the curing temperature and thermally cured to obtain a transparent flame-retardant epoxy resin.

[0022] Preferably, the epoxy curing agent includes 4,4'-diaminodiphenyl sulfone or 4,4'-diaminodiphenylmethane.

[0023] The present invention has the following beneficial effects:

[0024] (1) The present invention obtains a biomass flame retardant with phosphorus and nitrogen synergistic flame retardancy, which is a reactive phosphorus and nitrogen flame retardant. There is a secondary amino group in its molecular structure. Under heating conditions, the flame retardant can react with the epoxy group in the epoxy resin structure, and finally form a network cross-linked structure through the aminoamide bond. The flame retardant has better compatibility with the epoxy resin and better solubility in the epoxy resin. The obtained flame-retardant epoxy resin has better transparency, flame retardancy and mechanical properties.

[0025] (2) The phosphorus-nitrogen synergistic flame retardant biomass flame retardant obtained by the present invention is obtained by a simple one-pot synthesis reaction of furfural and furfural derivatives with 2-amino-1,3,4-thiadiazole and DOPO in sequence. Furfural and furfural derivatives are bio-based raw materials, which are renewable and meet the needs of green and sustainable development.

[0026] (3) MBFA, a Schiff base intermediate generated by the reaction of furfural and furfural derivatives with 2-amino-1,3,4-thiadiazole, has a simple structure and low steric hindrance, allowing the phosphorus-hydrogen addition reaction to proceed more fully and under milder reaction conditions;

[0027] (4) Compared with other types of reactive flame retardants, the flame retardant obtained by the present invention has better flame retardant stability and less influence on the mechanical properties of epoxy resin. The flame retardant in the present invention is synthesized by low temperature, normal pressure and two-step one-pot method. The reaction is simple and efficient. The solvent and anhydrous ethanol in the reaction and purification stages are easier to recycle and reuse, and the economic benefits are more considerable. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 : is the infrared spectrum of MBFAP obtained in Example 1 of the present invention.

[0029] Figure 2: is the MBFAP obtained in Example 1 of the present invention 1 H-NMR nuclear magnetic spectrum.

[0030] Figure 3 : is the MBFAP obtained in Example 1 of the present invention 31 P-NMR nuclear magnetic spectrum.

[0031] Figure 4 : These are the residual carbon morphologies and SEM images of the residual carbon of EP, EP / MBFAP (2 wt.%), and EP / MBFAP (4 wt.%) in Example 1 of the present invention after cone calorimetry testing.

[0032] Figure 5 : This is a transmittance test chart of EP, EP / MBFAP (2 wt.%), and EP / MBFAP (4 wt.%) in Example 1 of the present invention. DETAILED DESCRIPTION

[0033] The present invention will be described in detail below with reference to the following examples. However, it should be understood that the following examples are merely illustrative of the embodiments of the present invention and are not intended to limit the scope of the present invention.

[0034] Example 1

[0035] The preparation method of a phosphorus-nitrogen synergistic flame-retardant biomass flame retardant is as follows:

[0036] (1) Add 15.16 g of 2-amino-1,3,4-thiadiazole and 14.41 g of furfural to a 500 mL four-necked flask equipped with a reflux condenser, a thermometer, and a mechanical stirring paddle. Then add 200 mL of anhydrous ethanol as a solvent to the four-necked flask, stir and heat to 80°C, and react at this temperature for 8 hours. Take a sample at the control center to confirm that 2-amino-1,3,4-thiadiazole is completely converted and the reaction is complete.

[0037] (2) After the reaction in step (1) was completed, 33.10 g of DOPO was added to the system, and the mixture was stirred at a constant temperature of 80° C. for 12 h. During the stirring reaction, a crude product was precipitated, and the reaction liquid became a turbid suspension. After the reaction was completed, the obtained reaction liquid was filtered and washed three times with anhydrous ethanol. The obtained solid product was vacuum dried at 80° C. for 24 h to obtain a biomass flame retardant, which was recorded as MBFAP. The yield of MBFAP was 81.20%.

[0038] As the instruction manual Figure 1 The infrared spectrum of flame retardant MBFAP is shown in the figure. The spectrum analysis results are: -NH-(33226cm -1 ); P=O(1240cm -1 ); PO-Ar(1214cm -1 ); PC(758cm-1 ).

[0039] As the instruction manual Figure 2 The following is the nuclear magnetic hydrogen spectrum of the flame retardant MBFAP, and the analysis results are: 1 H NMR (DMSO-d6, 500MHz), δ (ppm): 6.90~8.91(Ar-H); 6.31~6.65(NH); 5.55~6.21(C*-H).

[0040] As the instruction manual Figure 3 The following is the nuclear magnetic resonance phosphorus spectrum of the flame retardant MBFAP, and the analysis results are: 31 PNMR (DMS0-d6, 300MHz), (ppm): 26.81ppm, 27.60ppm (PC).

[0041] Specific applications

[0042] A method for preparing a transparent flame retardant epoxy resin is as follows:

[0043] The epoxy resin (E51, epoxy equivalent weight 0.51) was heated to 160° C., and then the MBFAP obtained in Example 1 was added and stirred until the MBFAP was completely dissolved in the epoxy resin. The mixture was then stirred at a constant temperature for 8 minutes. After that, the temperature was lowered to 90° C., and 4,4'-diaminodiphenylmethane was added while stirring. The mixture was stirred until the 4,4'-diaminodiphenylmethane was completely dissolved in the reaction system. The mixture was then quickly transferred to a mold preheated to 100° C. and cured in a blast oven at 100° C. for 2 hours, and then cured at 150° C. for 3 hours to obtain the product.

[0044] When the mass percentage of MBFAP in the epoxy resin system is 2 wt.%, and the mass percentage of 4,4'-diaminodiphenylmethane in the epoxy resin system is 19.57 wt.%, the obtained flame retardant epoxy resin is recorded as EP / MBFAP (2 wt.%). The flame retardant properties of the obtained transparent flame retardant epoxy resin are shown in Table 1, and the mechanical properties are shown in Table 2.

[0045] When the mass percentage of MBFAP in the epoxy resin system is 4 wt.%, and the mass percentage of 4,4'-diaminodiphenylmethane in the epoxy resin system is 18.97 wt.%, the obtained flame retardant epoxy resin is recorded as EP / MBFAP (4 wt.%). The flame retardant properties of the obtained transparent flame retardant epoxy resin are shown in Table 1, and the mechanical properties are shown in Table 2.

[0046] The flame retardant properties of pure epoxy resin are also shown in Table 1, and the mechanical properties are shown in Table 2.

[0047] Table 1

[0048]

[0049] In Table 1, "None" means that the sample burned to the fixture and did not meet the UL-94 grade standard. A flame retardant grade of "NO" means that there was no droplet phenomenon during the combustion process, and "Yes" means that there was droplet phenomenon during the combustion process.

[0050] As shown in Table 1, pure epoxy resin exhibits dripping and cannot meet the UL94 test standard grade. It also has a low LOI index and is easily burned in the air. However, it was found that after the biomass flame retardant MBFAP was added, the dripping disappeared. When 2 wt% MBFAP was added to the epoxy resin, the flame retardancy grade reached V-1. When 4 wt% MBFAP was added to the epoxy resin, the UL94 standard test reached V-0. This indicates that MBFAP can achieve high flame retardancy in epoxy resin at extremely low addition levels.

[0051] In Table 1, the limiting oxygen index standard is ASTM D2863, and the sample size is 130×6.5×3 mm. The vertical burning test standard is ASTM D3801, and the sample size is 130×13×3 mm.

[0052] The mechanical property test results of EP, EP / MBFAP (2 wt.%), and EP / MBFAP (4 wt.%) are shown in Table 2.

[0053] Mechanical properties: The test standards are ASTM D638 (tensile properties) and ASTM D790 (bending stiffness and strength properties of materials).

[0054] Table 2

[0055]

[0056] As shown in Table 2, when 2wt% or 4wt% of MBFAP is added to epoxy resin, the mechanical properties of the flame-retardant epoxy resin obtained are similar to those of pure EP, and some properties are even slightly improved, which indicates that MBFAP has little effect on the mechanical properties of epoxy resin.

[0057] Instructions attached Figure 4The images and SEM images of the char residues from cone calorimetry (CCT) tests are shown. Images a1-a3, b1-b3, and c1-c3 are for pure EP, EP / MBFAP (2 wt.%), and EP / MBFAP (4 wt.%), respectively. The images show that the char residue morphology and carbon layer expansion height of EP / MBFAP (2 wt.%) and EP / MBFAP (4 wt.%) are superior to those of pure EP. Furthermore, increasing the amount of MBFAP added to the epoxy resin improves the integrity and expansion height of the carbon layer of the resulting flame-retardant epoxy resin. The SEM images further confirm that the addition of MBFAP significantly improves the density and continuity of the char layer after combustion. Therefore, the addition of MBFAP results in a more stable carbon layer after combustion, effectively blocking oxygen and preventing combustible gases generated by pyrolysis from escaping into the combustion zone, resulting in a more effective flame retardant effect.

[0058] Instructions attached Figure 5 UV-visible transmission spectra of pure EP, EP / MBFAP (2 wt.%), and EP / MBFAP (4 wt.%) with a thickness of 3 mm were measured in the 300-800 nm range. The images show that the transmittance of EP / MBFAP (2 wt.%) and EP / MBFAP (4 wt.%) decreases slightly compared to pure EP, but still maintains high transmittance. This indicates that the addition of MBFAP to epoxy resin has little impact on its transparency.

[0059] Example 2

[0060] A method for preparing a transparent flame retardant epoxy resin is as follows:

[0061] (1) Add 15.16 g of 2-amino-1,3,4-thiadiazole and 16.81 g of 5-hydroxyfurfural to a 500 mL four-necked flask equipped with a reflux condenser, a thermometer, and a mechanical stirring paddle. Then add 200 mL of anhydrous ethanol as a solvent to the reaction system. Raise the temperature of the reaction system to 80 ° C and stir for 12 h. Take a central control sample to confirm that 2-amino-1,3,4-thiadiazole is completely converted and the reaction is complete.

[0062] (2) 32.41 g of DOPO was added to the reaction solution obtained in step (1), and the mixture was stirred at a constant temperature of 80° C. for 12 h. During the reaction, a crude product precipitated and the reaction solution became a turbid suspension. After the reaction, the reaction solution was filtered, and the obtained solid product was washed three times with anhydrous ethanol. Finally, the solid product was vacuum-dried at 80° C. for 24 h to obtain the target product, which was designated as MBFAP with a yield of 80.71%.

[0063] Specific applications

[0064] A method for preparing a transparent flame retardant epoxy resin is as follows:

[0065] The epoxy resin (E51, epoxy equivalent weight 0.51) was heated to 160° C., and then the MBFAP obtained in Example 1 was added and stirred until the MBFAP was completely dissolved in the epoxy resin. The mixture was then stirred at a constant temperature for 8 minutes. After that, the temperature was lowered to 90° C., and 4,4'-diaminodiphenylmethane was added while stirring. The mixture was stirred until the 4,4'-diaminodiphenylmethane was completely dissolved in the reaction system. The mixture was then quickly transferred to a mold preheated to 100° C. and cured in a blast oven at 100° C. for 2 hours, and then cured at 150° C. for 3 hours to obtain the product.

[0066] When the mass percentage of MBFAP in the epoxy resin system is 2 wt.%, and the mass percentage of 4,4'-diaminodiphenylmethane in the epoxy resin system is 16.35 wt.%, the scheme is recorded as EP / MBFAP (2 wt.%). The flame retardant properties of the obtained transparent flame-retardant epoxy resin are shown in Table 3, and the mechanical properties are shown in Table 4.

[0067] When the mass percentage of MBFAP in the epoxy resin system is 4 wt.%, and the mass percentage of 4,4'-diaminodiphenylmethane in the epoxy resin system is 15.92 wt.%, the scheme is recorded as EP / MBFAP (4 wt.%). The flame retardant properties of the obtained transparent flame-retardant epoxy resin are shown in Table 3, and the mechanical properties are shown in Table 4.

[0068] Table 3

[0069]

[0070] In Table 3, the limiting oxygen index standard is ASTM D2863, and the sample size is 130×6.5×3 mm. The vertical burning test standard is ASTM D3801, and the sample size is 130×13×3 mm.

[0071] The mechanical property test results of EP, EP / MBFAP (2 wt.%), and EP / MBFAP (4 wt.%) are shown in Table 2.

[0072] Mechanical properties: The test standards are ASTM D638 and ASTM D790.

[0073] Table 4

[0074]

[0075] Example 3

[0076] A method for preparing a transparent flame retardant epoxy resin is as follows:

[0077] (1) Add 15.16 g of 2-amino-1,3,4-thiadiazole and 21.16 g of 5-nitrofurfural to a 500 mL four-necked flask equipped with a reflux condenser, a thermometer, and a mechanical stirring paddle, then add 200 ml of anhydrous ethanol as a solvent, heat to 80 ° C, stir and react for 10 h, and take a central control sample to confirm that 2-amino-1,3,4-thiadiazole is completely converted, and the reaction is complete;

[0078] (2) 32.41 g of DOPO was added to the reaction solution obtained in step (1), and the mixture was stirred at a constant temperature of 80° C. for 12 h. During the reaction, a crude product precipitated and the reaction solution became a turbid suspension. After the reaction, the reaction solution was filtered, and the obtained solid product was washed three times with anhydrous ethanol. Finally, it was vacuum-dried at 80° C. for 24 h to obtain the target product, which was recorded as MBFAP, with a yield of 79.92%.

[0079] Specific applications

[0080] A method for preparing a transparent flame retardant epoxy resin is as follows:

[0081] The epoxy resin (E51, epoxy equivalent weight 0.51) was heated to 160° C., and then the MBFAP obtained in Example 1 was added and stirred until the MBFAP was completely dissolved in the epoxy resin. The mixture was then stirred at a constant temperature for 8 minutes. After that, the temperature was lowered to 90° C., and 4,4'-diaminodiphenylmethane was added while stirring. The mixture was stirred until the 4,4'-diaminodiphenylmethane was completely dissolved in the reaction system. The mixture was then quickly transferred to a mold preheated to 100° C. and cured in a blast oven at 100° C. for 2 hours, and then cured at 150° C. for 3 hours to obtain the product.

[0082] When the mass percentage of MBFAP in the epoxy resin system is 2 wt.%, and the mass percentage of 4,4'-diaminodiphenylmethane in the epoxy resin system is 16.36 wt.%, the scheme is recorded as EP / MBFAP (2 wt.%). The flame retardant properties of the obtained transparent flame-retardant epoxy resin are shown in Table 5, and the mechanical properties are shown in Table 6.

[0083] When the mass percentage of MBFAP in the epoxy resin system is 4 wt.%, and the mass percentage of 4,4'-diaminodiphenylmethane in the epoxy resin system is 15.93 wt.%, the scheme is recorded as EP / MBFAP (4 wt.%). The flame retardant properties of the obtained transparent flame-retardant epoxy resin are shown in Table 5, and the mechanical properties are shown in Table 6.

[0084] Table 5

[0085]

[0086] In Table 5, the limiting oxygen index standard is ASTM D2863, and the sample size is 130×6.5×3 mm. The vertical burning test standard is ASTM D3801, and the sample size is 130×13×3 mm.

[0087] Mechanical properties: The test standards are ASTM D638 and ASTM D790.

[0088] Table 6

[0089]

[0090] Example 4

[0091] A method for preparing a transparent flame retardant epoxy resin is as follows:

[0092] (1) Add 15.16 g of 2-amino-1,3,4-thiadiazole and 16.52 g of 5-methylfurfural to a 500 mL four-necked flask equipped with a reflux condenser, a thermometer, and a mechanical stirring paddle, then add 200 mL of anhydrous ethanol as a solvent, heat to 80 ° C, stir and react for 8 h, and take a central control sample to confirm that 2-amino-1,3,4-thiadiazole is completely converted, and the reaction is complete;

[0093] (2) 32.41 g of DOPO was added to the reaction solution obtained in step (1), and the mixture was stirred at a constant temperature of 80° C. for 12 h. During the reaction, a crude product precipitated and the reaction solution became a turbid suspension. After the reaction, the reaction solution was filtered, and the obtained solid product was washed three times with anhydrous ethanol. Finally, it was vacuum-dried at 80° C. for 24 h to obtain the target product, which was recorded as MBFAP, with a yield of 82.1%.

[0094] Specific applications

[0095] A method for preparing a transparent flame retardant epoxy resin is as follows:

[0096] The epoxy resin (E51, epoxy equivalent weight 0.51) was heated to 160° C., and then the MBFAP obtained in Example 1 was added and stirred until the MBFAP was completely dissolved in the epoxy resin. The mixture was then stirred at a constant temperature for 8 minutes. After that, the temperature was lowered to 90° C., and 4,4'-diaminodiphenylmethane was added while stirring. The mixture was stirred until the 4,4'-diaminodiphenylmethane was completely dissolved in the reaction system. The mixture was then quickly transferred to a mold preheated to 100° C. and cured in a blast oven at 100° C. for 2 hours, and then cured at 150° C. for 3 hours to obtain the product.

[0097] When the mass percentage of MBFAP in the epoxy resin system is 2 wt.%, and the mass percentage of 4,4'-diaminodiphenylmethane in the epoxy resin system is 16.35 wt.%, the scheme is recorded as EP / MBFAP (2 wt.%). The flame retardant properties of the obtained transparent flame-retardant epoxy resin are shown in Table 7, and the mechanical properties are shown in Table 8.

[0098] When the mass percentage of MBFAP in the epoxy resin system is 4 wt.%, and the mass percentage of 4,4'-diaminodiphenylmethane in the epoxy resin system is 15.90 wt.%, the scheme is recorded as EP / MBFAP (4 wt.%). The flame retardant properties of the obtained transparent flame-retardant epoxy resin are shown in Table 7, and the mechanical properties are shown in Table 8.

[0099] Table 7

[0100]

[0101] In Table 7, the limiting oxygen index standard is: ASTM D2863, and the sample size is: 130×6.5×3 mm.

[0102] Vertical burning test standard: ASTM D3801, specimen size: 130×13×3mm.

[0103] Mechanical properties: The test standards are ASTM D638 and ASTM D790.

[0104] Table 8

[0105]

[0106] Example 5

[0107] A method for preparing a transparent flame retardant epoxy resin is as follows:

[0108] (1) Add 15.16 g of 2-amino-1,3,4-thiadiazole and 18.92 g of 5-hydroxymethylfurfural to a 500 mL four-necked flask equipped with a reflux condenser, a thermometer, and a mechanical stirring paddle, then add 200 mL of anhydrous ethanol as a solvent, heat to 80 ° C, stir and react for 8 h, and take a central control sample to confirm that 2-amino-1,3,4-thiadiazole is completely converted, and the reaction is complete;

[0109] (2) 32.41 g of DOPO was added to the reaction solution obtained in step (1), and the mixture was stirred at a constant temperature of 80° C. for 12 h. During the reaction, a crude product precipitated and the reaction solution became a turbid suspension. After the reaction, the reaction solution was filtered, and the obtained solid product was washed three times with anhydrous ethanol. Finally, it was vacuum-dried at 80° C. for 24 h to obtain the target product, which was recorded as MBFAP, with a yield of 85.2%.

[0110] Specific applications

[0111] A method for preparing a transparent flame retardant epoxy resin is as follows:

[0112] The epoxy resin (E51, epoxy equivalent weight 0.51) was heated to 160° C., and then the MBFAP obtained in Example 1 was added and stirred until the MBFAP was completely dissolved in the epoxy resin. The mixture was then stirred at a constant temperature for 8 minutes. After that, the temperature was lowered to 90° C., and 4,4'-diaminodiphenylmethane was added while stirring. The mixture was stirred until the 4,4'-diaminodiphenylmethane was completely dissolved in the reaction system. The mixture was then quickly transferred to a mold preheated to 100° C. and cured in a blast oven at 100° C. for 2 hours, and then cured at 150° C. for 3 hours to obtain the product.

[0113] When the mass percentage of MBFAP in the epoxy resin system is 2 wt.%, and the mass percentage of 4,4'-diaminodiphenylmethane in the epoxy resin system is 16.35 wt.%, the scheme is recorded as EP / MBFAP (2 wt.%). The flame retardant properties of the obtained transparent flame-retardant epoxy resin are shown in Table 9, and the mechanical properties are shown in Table 10.

[0114] When the mass percentage of MBFAP in the epoxy resin system is 4 wt.%, and the mass percentage of 4,4'-diaminodiphenylmethane in the epoxy resin system is 15.91 wt.%, the scheme is recorded as EP / MBFAP (4 wt.%). The flame retardant properties of the obtained transparent flame-retardant epoxy resin are shown in Table 9, and the mechanical properties are shown in Table 10.

[0115] Table 9

[0116]

[0117] In Table 9, the limiting oxygen index standard is ASTM D2863, and the sample size is 130×6.5×3 mm. The vertical burning test standard is ASTM D3801, and the sample size is 130×13×3 mm.

[0118] Mechanical properties: The test standards are ASTM D638 and ASTM D790.

[0119] Table 10

[0120]

[0121] With the above-described preferred embodiments of the present invention as a guide, and with reference to the above description, relevant personnel are fully capable of making various changes and modifications without departing from the technical scope of this invention. The technical scope of this invention is not limited to the contents of the specification and must be determined according to the scope of the claims.

Claims

1. A phosphorus-nitrogen synergistic flame retardant biomass flame retardant, characterized in that: The chemical structure is as follows: ， In the above chemical structural formula, the R group is a hydrogen atom.

2. The phosphorus-nitrogen synergistic flame retardant biomass flame retardant according to claim 1, characterized in that: The preparation method comprises the following steps: (1) Furfural reacts with 2-amino-1,3,4-thiadiazole to form a Schiff base intermediate, the structural formula of which is as follows: ， In the above chemical formula, the R group is a hydrogen atom; (2) The Schiff base intermediate reacts with DOPO to form the target product.

3. The phosphorus-nitrogen synergistic flame retardant biomass flame retardant according to claim 2, characterized in that: The solvent used in step (1) is one or more of anhydrous ethanol, 1,2-propylene glycol, 1,3-propylene glycol, 1,4-butanediol, 1,2-butanediol, 1,3-butanediol, dichloromethane, dichloroethane, chloroform, ethyl acetate, benzene, toluene, and 1,4-dioxane.

4. The phosphorus-nitrogen synergistic flame retardant biomass flame retardant according to claim 2, characterized in that: The reaction temperature in step (1) is 40-100°C, and the reaction time is 8-12h.

5. The phosphorus-nitrogen synergistic flame retardant biomass flame retardant according to claim 2, characterized in that: In step (1), the molar ratio of furfural to 2-amino-1,3,4-thiadiazole is 1-1.1:

1.

6. The phosphorus-nitrogen synergistic flame-retardant biomass flame retardant according to claim 2, characterized in that: In step (2), the molar ratio of the Schiff base intermediate to DOPO is 1:1-1.

1.

7. The phosphorus-nitrogen synergistic flame-retardant biomass flame retardant according to claim 2, characterized in that: The reaction temperature in step (2) is 40-100°C, and the reaction time is 12-24h.

8. A transparent flame retardant epoxy resin, characterized in that: The preparation method comprises the following steps: (1) Heat the epoxy resin to 140-160°C, add an appropriate amount of the biomass flame retardant obtained according to any one of claims 1-7, stir until the biomass flame retardant is completely dissolved in the epoxy resin, and keep the temperature for 8-20 minutes; (2) After cooling the mixed solution obtained in step (1) to 80-100°C, an epoxy curing agent is added to the reaction system, and the mixture is stirred at a constant temperature until the epoxy curing agent is completely dissolved. The reaction system is quickly poured into a mold preheated to the curing temperature and thermally cured to obtain a transparent flame-retardant epoxy resin.

9. The transparent flame-retardant epoxy resin according to claim 8, characterized in that: The epoxy curing agent is 4,4'-diaminodiphenyl sulfone or 4,4'-diaminodiphenylmethane.

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