Phosphorus-nitrogen synergistic flame-retardant biomass flame retardant and application thereof

Abstract

The invention relates to the technical field of flame retardants, in particular to a phosphorus-nitrogen synergistic flame-retardant biomass flame retardant and application thereof. A conventional reaction type phosphorus-nitrogen flame retardant is huge in structure and large in steric hindrance and cannot be completely dissolved in an epoxy resin material system, the obtained flame-retardant epoxy resin is poor in transparency, and the mechanical property is greatly reduced. In order to solve the problems, the invention provides the phosphorus-nitrogen synergistic flame-retardant biomass flame retardant which is obtained by sequentially carrying out simple one-pot synthesis reaction on furfural and furfural derivatives with 2-amino-1, 3, 4-thiadiazole and DOPO, and the flame retardant is simple in structure, small in steric hindrance, easy to completely dissolve in epoxy resin, good in flame retardancy and good in flame retardance. The obtained flame-retardant epoxy resin is better in transparency, flame retardance and mechanical property.

Description

Technical Field

[0001] The 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 easy to burn, and during the combustion process, they are accompanied by a large amount of thick smoke and serious melting droplets, which poses a great safety hazard. Therefore, it is of great significance to study the energy required to improve the flame retardancy of epoxy resins.

[0003] There are many types of flame retardants, among which halogen-containing flame retardants have obvious advantages in improving the flame retardant properties of epoxy resins. They are widely used in polymer composite materials. However, halogen-containing flame retardants will produce a large amount of toxic and harmful gases during combustion, which is extremely harmful to the environment and human body. How to replace halogens and develop high-efficiency, low-toxic, low-smoke halogen-free environmentally friendly flame retardants and new flame-retardant epoxy resin materials has become a research hotspot for scholars at home and abroad. Among them, phosphorus and nitrogen compounds, as a new type of flame retardant, have the advantages of improving the flame retardancy and thermal stability of epoxy resins while having little effect on the mechanical properties and transparency of the base material, and have attracted much attention.

[0004] However, although current phosphorus-nitrogen flame retardants can improve the flame retardancy of epoxy resins, they will cause a significant reduction in transparency and mechanical properties. Such modifications particularly affect the high-end applications of flame-retardant epoxy resins. For example, Chinese patent CN105837636A discloses a phosphorus-nitrogen synergistic flame retardant compound and its preparation method and application, which uses a divinyl-terminated quaternary ammonium compound and DOPO to obtain a phosphorus-phenanthrene structure reactive flame retardant. Although the phosphorus-nitrogen flame retardant has a secondary amine group that reacts with the epoxy group of the epoxy resin, it is not easy to react completely with the epoxy group due to its bulky structure and large steric hindrance, resulting in the flame retardant being unable to completely dissolve in the epoxy resin. After curing, the flame-retardant epoxy resin is opaque and has a significant impact on the mechanical properties. Summary of the invention

[0005] The problems existing in the prior art are: conventional reactive phosphorus-nitrogen flame retardants have a bulky structure and large steric hindrance, and cannot be completely dissolved in the epoxy resin material system. The obtained flame-retardant epoxy resin has poor transparency and greatly reduced mechanical properties. In view of the above problems, the present invention provides a phosphorus-nitrogen synergistic flame-retardant biomass flame retardant, and its chemical structure 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 boric acid group, a carboxyl group, a formyloxy group, an acetyloxy 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 generate 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-linked 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 acetyloxy group, and a propionyloxy group;

[0012] (2) The Schiff base intermediate undergoes a phosphine-hydrogen addition reaction with DOPO to obtain the target product.

[0013] Preferably, the furfural derivative includes 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, formaldehydefuran-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 derivatives to 2-amino-1,3,4-thiadiazole is 1-1.1:1.

[0017] Preferably, in step (2), the molar ratio of the Schiff base intermediate to DOPO 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) heating the epoxy resin to 140-160° C., adding an appropriate amount of the biomass flame retardant, stirring until the biomass flame retardant is completely dissolved in the epoxy resin, and keeping the temperature 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 small steric hindrance, and the phosphorus-hydrogen addition reaction proceeds more fully 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 : are the residual carbon morphologies and SEM images of residual carbon of EP, EP / MBFAP (2wt.%) and EP / MBFAP (4wt.%) in Example 1 of the present invention after cone calorimetry test.

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

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

[0034] Example 1

[0035] A 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 a constant temperature for 8 hours. Take a sample at the central control to confirm that 2-amino-1,3,4-thiadiazole is completely converted and the reaction is completed;

[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 with anhydrous ethanol for 3 times. 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 below. 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 NMR hydrogen spectrum of the flame retardant MBFAP. 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 figure below shows the nuclear magnetic resonance phosphorus spectrum of the flame retardant MBFAP. 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 0.51) was heated to 160°C, and then the MBFAP obtained in Example 1 was added and stirred until MBFAP was completely dissolved in the epoxy resin, and then stirred at a constant temperature for 8 minutes. Then, the temperature was lowered to 90°C, and 4,4'-diaminodiphenylmethane was added while stirring, and stirred until 4,4'-diaminodiphenylmethane was completely dissolved in the reaction system. Then, the mixture was 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 2wt.%, and the mass percentage of 4,4'-diaminodiphenylmethane in the epoxy resin system is 19.57wt.%, the flame retardant epoxy resin obtained is recorded as EP / MBFAP (2wt.%). 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 4wt.%, and the mass percentage of 4,4'-diaminodiphenylmethane in the epoxy resin system is 18.97wt.%, the flame retardant epoxy resin obtained is recorded as EP / MBFAP (4wt.%). 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] None in Table 1 means that the sample burns to the fixture and does not meet the UL-94 grade standard; the flame retardant grade of NO means that there is no droplet phenomenon during the combustion process, and Yes means that there is droplet phenomenon during the combustion process.

[0050] As shown in Table 1, pure epoxy resin has droplets and cannot meet the UL94 test standard level, and the LOI index is low, which makes it easy to burn in the air. However, after the addition of biomass flame retardant MBFAP, the droplets disappeared. After adding 2wt% MBFAP to the epoxy resin, the flame retardant level reached V-1. After adding 4wt% MBFAP to the epoxy resin, the UL94 standard test reached V-0. This shows that MBFAP can achieve high flame retardancy of epoxy resin at extremely low addition amounts.

[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 properties test results of EP, EP / MBFAP (2wt.%) and EP / MBFAP (4wt.%) 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] From the analysis in Table 2, it can be seen that when 2wt% or 4wt% MBFAP is added to epoxy resin, the mechanical properties of the flame retardant epoxy resin obtained are not much different from those of pure EP, and some properties are even slightly improved, which shows that MBFAP has little effect on the mechanical properties of epoxy resin.

[0057] Instructions attached Figure 4The images and SEM images of the burning charcoal residues tested by the cone calorimeter (CCT) show that a1-a3, b1-b3, c1-c3 are the test images of pure EP, EP / MBFAP (2wt.%), and EP / MBFAP (4wt.%), respectively. The images show that the residual carbon morphology and carbon layer expansion height of EP / MBFAP (2wt.%) and EP / MBFAP (4wt.%) are better than those of pure EP, and as the amount of MBFAP added to the epoxy resin increases, the integrity and expansion height of the carbon layer of the flame-retardant epoxy resin are better. The SEM image further confirms that the introduction of MBFAP significantly improves the density and continuity of the carbon layer of the flame-retardant epoxy resin after combustion. Therefore, after adding MBFAP, the flame-retardant epoxy resin can form a more stable carbon layer after combustion, which can effectively block oxygen and prevent the combustible gas produced by pyrolysis from escaping to the combustion zone, thereby achieving a better flame retardant effect.

[0058] Instructions attached Figure 5 The UV-visible transmission spectra of pure EP and EP / MBFAP (2wt.%) and EP / MBFAP (4wt.%) with a thickness of 3mm were measured in the range of 300-800nm. The image shows that the transmittance of EP / MBFAP (2wt.%) and EP / MBFAP (4wt.%) is slightly lower than that of pure EP, but still maintains a high transmittance, which shows that adding MBFAP to epoxy resin does not have a significant 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, stir and react for 12 hours, and take a central control sample to confirm that 2-amino-1,3,4-thiadiazole is completely converted, and the reaction is completed;

[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 was precipitated and the reaction solution became a turbid suspension. After the reaction, the reaction solution was filtered and the 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 recorded 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 0.51) was heated to 160°C, and then the MBFAP obtained in Example 1 was added and stirred until MBFAP was completely dissolved in the epoxy resin, and then stirred at a constant temperature for 8 minutes. Then, the temperature was lowered to 90°C, and 4,4'-diaminodiphenylmethane was added while stirring, and stirred until 4,4'-diaminodiphenylmethane was completely dissolved in the reaction system. Then, the mixture was 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 2wt.%, and the mass percentage of 4,4'-diaminodiphenylmethane in the epoxy resin system is 16.35wt.%, the scheme is recorded as EP / MBFAP (2wt.%), and 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 4wt.%, and the mass percentage of 4,4'-diaminodiphenylmethane in the epoxy resin system is 15.92wt.%, the scheme is recorded as EP / MBFAP (4wt.%), and 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 properties test results of EP, EP / MBFAP (2wt.%) and EP / MBFAP (4wt.%) 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 hours, and take a central control sample to confirm that 2-amino-1,3,4-thiadiazole is completely converted, and the reaction is completed;

[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 was precipitated and the reaction solution became a turbid suspension. After the reaction, the reaction solution was filtered and the 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 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 0.51) was heated to 160°C, and then the MBFAP obtained in Example 1 was added and stirred until MBFAP was completely dissolved in the epoxy resin, and then stirred at a constant temperature for 8 minutes. Then, the temperature was lowered to 90°C, and 4,4'-diaminodiphenylmethane was added while stirring, and stirred until 4,4'-diaminodiphenylmethane was completely dissolved in the reaction system. Then, the mixture was 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 2wt.%, and the mass percentage of 4,4'-diaminodiphenylmethane in the epoxy resin system is 16.36wt.%, the scheme is recorded as EP / MBFAP (2wt.%), and 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 4wt.%, and the mass percentage of 4,4'-diaminodiphenylmethane in the epoxy resin system is 15.93wt.%, the scheme is recorded as EP / MBFAP (4wt.%), and 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 hours, 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 was precipitated and the reaction solution became a turbid suspension. After the reaction, the reaction solution was filtered and the 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 denoted as MBFAP. The yield was 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 0.51) was heated to 160°C, and then the MBFAP obtained in Example 1 was added and stirred until MBFAP was completely dissolved in the epoxy resin, and then stirred at a constant temperature for 8 minutes. Then, the temperature was lowered to 90°C, and 4,4'-diaminodiphenylmethane was added while stirring, and stirred until 4,4'-diaminodiphenylmethane was completely dissolved in the reaction system. Then, the mixture was 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 2wt.%, and the mass percentage of 4,4'-diaminodiphenylmethane in the epoxy resin system is 16.35wt.%, the scheme is recorded as EP / MBFAP (2wt.%), and 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 4wt.%, and the mass percentage of 4,4'-diaminodiphenylmethane in the epoxy resin system is 15.90wt.%, the scheme is recorded as EP / MBFAP (4wt.%), and 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 hours, 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 was precipitated and the reaction solution became a turbid suspension. After the reaction, the reaction solution was filtered and the solid product was washed three times with anhydrous ethanol. Finally, the solid product was dried under vacuum at 80° C. for 24 h to obtain the target product, which was denoted as MBFAP. The yield was 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 0.51) was heated to 160°C, and then the MBFAP obtained in Example 1 was added and stirred until MBFAP was completely dissolved in the epoxy resin, and then stirred at a constant temperature for 8 minutes. Then, the temperature was lowered to 90°C, and 4,4'-diaminodiphenylmethane was added while stirring, and stirred until 4,4'-diaminodiphenylmethane was completely dissolved in the reaction system. Then, the mixture was 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 2wt.%, and the mass percentage of 4,4'-diaminodiphenylmethane in the epoxy resin system is 16.35wt.%, the scheme is recorded as EP / MBFAP (2wt.%), and 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 4wt.%, and the mass percentage of 4,4'-diaminodiphenylmethane in the epoxy resin system is 15.91wt.%, the scheme is recorded as EP / MBFAP (4wt.%), and 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] Based on the above ideal embodiments of the present invention, the relevant staff can make various changes and modifications without departing from the technical concept of the present invention through the above description. The technical scope of the present invention is not limited to the contents of the specification, and its technical scope must be determined according to the scope of the claims.

Claims

1. A biomass flame retardant with phosphorus and nitrogen synergistic flame retardancy, characterized in that: The chemical structure is as follows: In the above chemical structure, the R group includes hydrogen atoms, C1-C 12 At 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 boric acid group, a carboxyl group, a formyloxy group, an acetyloxy group, and a propionyloxy group.

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 or a furfural derivative reacts with 2-amino-1,3,4-thiadiazole to generate a Schiff base intermediate, the structural formula of the Schiff base intermediate is as follows: In the above chemical structure, the R group includes hydrogen atoms, C1-C 12 At 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 boric acid group, a carboxyl group, an acetoxy group, and a propionyloxy group; (2) The Schiff base intermediate undergoes a phosphine-hydrogen addition reaction with DOPO to obtain the target product.

3. The phosphorus-nitrogen synergistic flame retardant biomass flame retardant according to claim 2, characterized in that: 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, formaldehydefuran-2-boric acid, 5-acetylmethyl-2-furfural, and 5-propionylmethyl-2-furfural.

4. The phosphorus-nitrogen synergistic flame retardant biomass flame retardant according to claim 2, characterized in that: 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.

5. 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 8-12 h.

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

1.

7. 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.

8. 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 12-24 h.

9. A transparent flame retardant epoxy resin, characterized in that: The preparation method comprises the following steps: (1) heating the epoxy resin to 140-160° C., adding an appropriate amount of the biomass flame retardant obtained according to any one of claims 1 to 8, stirring until the biomass flame retardant is completely dissolved in the epoxy resin, and keeping 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.

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

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