Multifunctional flame retardant based on anisaldehyde and preparation method and application thereof

Abstract

The application discloses a multifunctional flame retardant based on p-anisaldehyde and a preparation method and application thereof, and the preparation method comprises the following steps: fully mixing and reacting p-anisaldehyde with 1,5-pentanediamine and an organic solvent; after cooling, adding DOPO into a reaction system to obtain the multifunctional flame retardant PDP based on p-anisaldehyde after reaction; the multifunctional flame retardant PDP has excellent flame retardant performance and thermal stability, can significantly improve the tensile strength, bending strength and impact strength of an epoxy resin curing product, and solves the problems of poor flame retardant performance and mechanical properties of a traditional bisphenol A type epoxy resin; meanwhile, the biomass p-anisaldehyde is used as a raw material, dependence of a plastic, coating and other industry on a petrochemical industry is reduced, and problems such as environmental pollution, excessive consumption and excessive emission of carbon compounds in the conversion process of fossil resources are relieved; the preparation method is simple to operate, is beneficial to realize industrialized large-scale production, and has an excellent popularization and application prospect.

Description

Technical Field

[0001] This invention relates to the field of flame retardant technology for polymer materials, specifically to multifunctional flame retardants based on anisaldehyde, their preparation methods, and applications. Background Technology

[0002] Epoxy resin, with its excellent adhesion, corrosion resistance, mechanical properties, and electrical insulation, has become one of the most widely used polymer materials in the industrial field, and is widely used in coatings, adhesives, composite materials, electronic packaging, and other fields. However, its inherent flammability can generate a large amount of heat and toxic fumes in a short time, which brings serious fire safety problems. Currently, adding flame retardants is a common method for flame-retardant modification of epoxy resin. Although some flame retardants can improve the flame retardant properties of epoxy resin, it is difficult to simultaneously optimize other properties (such as mechanical properties and thermal stability), resulting in a limited improvement in the overall performance of epoxy resin. Therefore, the development of a multifunctional flame retardant that can achieve high flame retardancy while improving the mechanical strength and thermal stability of epoxy resin, thereby achieving a balance in the overall performance of epoxy resin, is of great research value.

[0003] In line with the current concept of green and sustainable development, flame retardants derived from biomass materials are receiving increasing attention from researchers due to their renewable source and environmentally friendly, low-toxicity properties. Given the ban on halogen-based flame retardants, using biomass materials as a raw material for flame retardant synthesis undoubtedly meets the current needs of green development. Although the synthesis of biomass flame retardants has received considerable attention, improvements in the mechanical properties and thermal stability of epoxy resins are still lacking.

[0004] Therefore, providing a multifunctional flame retardant that is renewable in origin, has a high biomass content, and also possesses good flame retardant properties, excellent mechanical strength, and thermal stability has extremely high practical significance and application prospects. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a multifunctional flame retardant, its preparation method, and its application. The invention involves fully mixing and reacting p-anisaldehyde with 1,5-pentanediamine and an organic solvent; after cooling, adding DOPO to the reaction system to obtain a multifunctional flame retardant PDP based on p-anisaldehyde. The multifunctional flame retardant PDP exhibits excellent flame retardant properties and thermal stability, while significantly improving the tensile strength, flexural strength, and impact strength of cured epoxy resins, thus solving the problem of poor flame retardant and mechanical properties of traditional bisphenol A type epoxy resins.

[0006] To achieve the above technical effects, the following technical solution is adopted: A multifunctional flame retardant based on anisaldehyde, wherein the molecular structure of the multifunctional flame retardant is as follows: ; Wherein, R is an aromatic hydrocarbon group or an aliphatic hydrocarbon group with 4 to 12 carbon atoms; This invention also provides a method for preparing a multifunctional flame retardant based on anisaldehyde, comprising the following steps: Step S1: p-Anisaldehyde, 1,5-pentanediamine, and an organic solvent are thoroughly mixed and reacted in a nitrogen atmosphere to obtain a Schiff base compound with the following structural formula: ; Wherein, R is an aromatic hydrocarbon group or an aliphatic hydrocarbon group with 4 to 12 carbon atoms; Step S2: After cooling the preparation system containing Schiff base compounds obtained in step S1 to a certain temperature, add 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide DOPO and continue the reaction. After the reaction is completed, dry to obtain the multifunctional flame retardant based on anisaldehyde. Furthermore, the mass ratio of anisaldehyde, 1,5-pentanediamine, and DOPO is 10-50:5-20:20-50; Furthermore, in step S1, the reaction temperature of anisaldehyde and 1,5-pentanediamine in an organic solvent is 70-100℃, and the reaction time is 3-6h. Furthermore, in step S2, after cooling the preparation system containing Schiff base compounds obtained in step S1 to 40-60°C, DOPO is added and the reaction continues for 6-10 hours. Furthermore, the organic solvent mentioned in step S1 is one or a combination of alcohols, aromatic hydrocarbons, ketones, and ethers; Furthermore, the alcohol organic solvent is ethanol; the aromatic hydrocarbon organic solvent is N,N-dimethylacetamide or N-methylpyrrolidone; the ketone organic solvent is acetone; and the ether organic solvent is petroleum ether or tetrahydrofuran. Furthermore, after the reaction is completed, step S2 is dried in a forced-air drying oven at 80-100°C to obtain the multifunctional flame retardant based on anisaldehyde. The present invention also provides the application of the above-mentioned multifunctional flame retardant based on anisaldehyde in epoxy resin, and the application method is as follows: the multifunctional flame retardant based on anisaldehyde is mixed with epoxy resin and curing agent to prepare epoxy resin cured product. Furthermore, the amount of the multifunctional flame retardant based on anisaldehyde added to the epoxy resin is 1-10 wt.

[0007] The beneficial effects of this invention are as follows: 1) This invention uses biomass anisaldehyde, which can be produced on a large scale, as raw material, reducing the dependence of industries such as plastics and coatings on the petrochemical industry, while alleviating problems such as environmental pollution, excessive consumption and excessive carbon emissions during the conversion of fossil resources. 2) This invention obtains a multifunctional flame retardant through molecular structure design and a simple synthesis process. The biomass-based anisaldehyde and 1,5-pentanediamine contribute to the high biomass content of the flame retardant, enhancing its environmental friendliness. The multifunctional flame retardant PDP based on anisaldehyde prepared in this invention has no hydroxyl groups, and the molecules are bonded by van der Waals forces, resulting in a more stable thermal decomposition process. Simultaneously, the dense cross-linked network can uniformly transmit impact stress, avoiding localized stress concentration. The multifunctional flame retardant PDP can simultaneously improve the mechanical strength, flame retardant efficiency, and thermal stability of E44 epoxy cured products. Compared with the vanillin-based phosphorus nitrogen flame retardant toughening agent VH-DOPO prepared in Comparative Example 3, the multifunctional flame retardant PDP based on anisaldehyde prepared in this invention significantly improves the mechanical properties, flame retardant properties, and thermal stability of E44 epoxy resin cured products. 3) The preparation method of the multifunctional flame retardant provided in this application is highly operable, controllable, economically cost-effective, easy to implement, and has good prospects for promotion and use, which is conducive to large-scale industrial production. Attached Figure Description

[0008] 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. The drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0009] Figure 1 The molecular structural formula of the multifunctional flame retardant in the embodiments of the present invention is shown below; Figure 2 This is a flowchart of the flame retardant preparation method in an embodiment of the present invention; Figure 3 The infrared spectrum of the multifunctional flame retardant prepared in Example 1 of this invention; Figure 4 The TGA curves of the epoxy resin cured products prepared in Examples 2-3 and Comparative Examples 1-4 of this invention under N2 are shown. Figure 5 The heat release rate curves are for the epoxy resin cured products prepared in Examples 2-3 and Comparative Examples 1-4 of this invention. Figure 6 The total heat release curves are for the epoxy resin cured products prepared in Examples 2-3 and Comparative Examples 1-4 of this invention. Figure 7The smoke generation rate curves are shown for the epoxy resin cured products prepared in Examples 2-3 and Comparative Examples 1-4 of this invention. Figure 8 The total smoke production curves are for the epoxy resin cured products prepared in Examples 2-3 and Comparative Examples 1-4 of this invention. Detailed Implementation

[0010] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0011] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0012] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments of the present invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, and / or combinations thereof.

[0013] In the following examples, unless otherwise specified, all reagents and consumables were purchased from conventional reagent manufacturers in the art; unless otherwise specified, the experimental methods and techniques used are conventional methods and techniques in the art.

[0014] The following examples illustrate the multifunctional flame retardant and its preparation method provided by the present invention. The scope of protection of the present invention is not limited by the following examples.

[0015] Please see Figures 1-8 This invention provides a technical solution: a multifunctional flame retardant, which has the following molecular structure: Figure 1 As shown.

[0016] On the other hand, a method for preparing the aforementioned multifunctional flame retardant is provided, the preparation process as follows: Figure 2 As shown, it specifically includes: Anisaldehyde, 1,5-pentanediamine, and an organic solvent were thoroughly mixed and reacted in a nitrogen atmosphere at 70-100°C for 4-6 hours. After cooling to 40-60°C, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) was added to the same reaction system, and the mixture was reacted at 40-60°C for 8-10 hours. The resulting mixture was then dried in a forced-air oven to obtain a multifunctional flame retardant with properties such as... Figure 1 The molecular structural formula shown; Furthermore, the mass ratio of anisaldehyde, 1,5-pentanediamine, DOPO and organic solvent is 10-50:5-20:20-50:300-500; Furthermore, in the drying step, a blower drying oven is used to dry the organic liquid to remove moisture and organic impurities from the organic liquid; Furthermore, the drying temperature in the vacuum drying oven is 80-100℃; Furthermore, the organic solvent is one or a combination of alcohols, aromatic hydrocarbons, ketones, and ethers; Furthermore, the alcohol organic solvent is ethanol; the aromatic hydrocarbon organic solvent is N,N-dimethylacetamide (DMAC) and N-methylpyrrolidone (NMP); the ketone organic solvent is acetone; and the ether organic solvent is petroleum ether and tetrahydrofuran.

[0017] Example 1 20 g of anisaldehyde, 8.54 g of 1,5-pentanediamine, and 300 ml of anhydrous ethanol were mixed in a 500 ml three-necked flask. Nitrogen gas was introduced to create a mild reaction environment. The mixture was then heated to 80 °C and reacted for 4 hours with mechanical stirring to obtain a Schiff base compound with the following structural formula: .

[0018] Subsequently, after cooling to 60°C, 31.75 g of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) was added to the reaction system, and the reaction was continued for 8 hours. The entire reaction system was then poured into a container and dried in an 80°C oven for 48 hours. The resulting solid product was ground into a white powder, which is the multifunctional flame retardant (PDP), possessing the following structural formula: .

[0019] The infrared spectrum of the multifunctional flame retardant PDP is as follows: Figure 3 As shown; Figure 3 An absorption peak of the NH structure appeared (3061 cm⁻¹). -1 And the PDP is 1246 cm. -1 (P=O stretching vibration) and 1073 cm -1 The appearance of new characteristic peaks at (PO stretching vibration) confirms the successful synthesis of PDP.

[0020] Example 2 The multifunctional flame retardant PDP (5 g) prepared in Example 1 was mixed with epoxy resin E44 (100 g) at 120°C. The temperature was then lowered to 70°C, and curing agent DDM (21.8 g) was added. Stirring continued until the mixture became homogeneous, and the mixture was poured into a polytetrafluoroethylene mold. The mold was then placed in an oven for curing at 120°C (2 h), 150°C (2 h), and 180°C (2 h). The sample was slowly cooled to room temperature to obtain the flame-retardant epoxy resin cured product 5-PDP / EP. The vertical burning flame retardancy rating of this cured product, measured according to ASTM D3801-20, reached UL-94 V-0. The limiting oxygen index of this cured product, measured according to ASTM D2863, was 35.7%, an improvement of 63.8% compared to pure epoxy resin. The thermal stability of the epoxy resin cured product 5-PDP / EP was tested using a thermogravimetric analyzer under a nitrogen atmosphere, according to the test standard GB / T27761-2011; Figure 4 It can be seen that the char residue of 5-PDP / EP is 23.8%, which is 27.3% higher than that of E44 epoxy resin (700℃). A cone calorimeter was used at 35 kW / m². 2 The flame retardant properties of 5-PDP / EP epoxy resin cured products were tested under radiation intensity, according to the test standard GB / T 16172-2007; Figures 5-8 It can be seen that the peak heat release rate, total heat release, peak smoke production rate, and total smoke production of the 5-PDP / EP are 351.3 kW / m³. 2 53.9 MJ / m 2 0.14m 2 / s, 23.8 m 2 Compared with E44 epoxy resin, the peak heat release rate of the cured epoxy resin 5-PDP / EP decreased by 58.9%, the total heat release decreased by 42.1%, the peak smoke generation rate decreased by 44.0%, and the total smoke generation decreased by 23.7%. These results indicate that epoxy resin containing 5 wt.% PDP has better thermal stability and superior flame retardant properties. The tensile and flexural strengths of the cured product were tested using a universal testing machine according to GB / T 16491-2022; the tensile strength was measured to be 50.2 MPa and the flexural strength to be 161.4 MPa, representing increases of 15.1% and 67.0% respectively compared to pure epoxy resin. The impact strength of the cured product was tested using a cantilever beam impact tester according to ASTM D256; the impact strength was measured to be 93.7 kJ / m². 2Compared to pure epoxy resin, the performance was improved by 122.0%. Test results show that the flame retardant and mechanical properties of the cured epoxy resin 5-PDP / EP are significantly improved compared to pure epoxy resin.

[0021] Example 3 The PDP (3 g) prepared in Example 1 was mixed with E44 (100 g) at 120°C, and then the temperature was lowered to 70°C. Curing agent DDM (21.8 g) was added, and stirring continued until the mixture became homogeneous. The mixture was then poured into a polytetrafluoroethylene mold. The mold was then placed in an oven for curing, with the curing sequence being 120°C (2 h), 150°C (2 h), and 180°C (2 h). The sample was slowly cooled to room temperature to obtain the flame-retardant epoxy resin cured product 3-PDP / EP. The vertical burning flame retardancy rating of this cured product, measured according to ASTM D3801-20, reached UL-94 V-1. The limiting oxygen index of this cured product, measured according to ASTM D2863, was 32.5%, an improvement of 49.1% compared to pure epoxy resin. The thermal stability of the epoxy resin cured product 3-PDP / EP was tested using a thermogravimetric analyzer under a N2 atmosphere, according to GB / T 27761-2011. Figure 4 It can be seen that the char residue of 3-PDP / EP is 21.3%, which is 13.9% higher than that of E44 epoxy resin (700℃). A cone calorimeter was used at 35 kW / m². 2 The flame retardant properties of epoxy resin cured product 3-PDP / EP were tested under radiation intensity, according to the test standard GB / T 16172-2007; Figures 5-8 It can be seen that the peak heat release rate, total heat release, peak smoke production rate, and total smoke production of the 3-PDP / EP are 407.7 kW / m³. 2 52.5 MJ / m 2 0.17 m 2 / s, 22.3 m 2Compared with E44 epoxy resin, the peak heat release rate of the cured epoxy resin 3-PDP / EP decreased by 52.3%, the total heat release decreased by 43.6%, the peak smoke generation rate decreased by 32.0%, and the total smoke generation decreased by 28.8%. These results indicate that epoxy resin containing 3 wt.% PDP has better thermal stability and flame retardant properties. The tensile and flexural strengths of the cured product were tested using a universal testing machine according to GB / T 16491-2022; the tensile strength was measured to be 46.1 MPa and the flexural strength to be 138.0 MPa, representing increases of 5.7% and 42.7% respectively compared to pure epoxy resin. The impact strength of the cured product was tested using a cantilever beam impact tester according to ASTM D256; the impact strength was measured to be 88.7 kJ / m². 2 Compared to pure epoxy resin, the flame retardancy was improved by 110.2%. These results indicate that the flame retardant and mechanical properties of the cured epoxy resin 3-PDP / EP are significantly improved compared to pure epoxy resin.

[0022] Comparative Example 1 100g of E44 epoxy resin was mixed evenly with 21.8g of 4,4'-diaminodiphenylmethane (DDM), and the mixture was poured into a polytetrafluoroethylene mold. Then, it was placed in an oven for curing, with the curing process sequentially at 120℃ (2h), 150℃ (2h), and 180℃ (2h) to obtain the epoxy cured product E44-DDM. According to standard ASTM D3801-20, the UL-94 test result for this cured product E44-DDM was unrated. According to standard ASTM D2863, the limiting oxygen index of this cured product E44-DDM was 21.8%. The thermal stability of the epoxy resin cured product E44-DDM was tested using a thermogravimetric analyzer under a N2 atmosphere, according to standard GB / T 27761-2011. Figure 4 It can be seen that its char residue rate at 700℃ is 18.7%. A cone calorimeter was used at 35 kW / m³. 2 The flame retardant properties of epoxy resin cured product E44-DDM were tested under radiation intensity, according to the test standard GB / T 16172-2007; Figures 5-8 It can be seen that the peak heat release rate, total heat release, peak smoke production rate, and total smoke production of E44-DDM are 854.4 kW / m³. 2 93.1 MJ / m 2 0.25 m 2 / s and 31.3 m 2The tensile and flexural strengths of the cured material were tested using a universal testing machine, according to GB / T 16491-2022; the measured tensile and flexural strengths were 43.6 MPa and 96.7 MPa, respectively. The impact strength of the cured material was tested using a cantilever beam impact tester, according to ASTM D256; the measured impact strength was 42.2 kJ / m. 2 The above experimental results show that E44-DDM has a low carbon residue, is prone to combustion, generates a large amount of heat and toxic and harmful fumes during combustion, and has poor mechanical properties.

[0023] Comparative Example 2 100g of E44 epoxy resin was mixed thoroughly with 21.8g of 4,4'-diaminodiphenylmethane (DDM) and 5g of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO), and the mixture was poured into a polytetrafluoroethylene mold. The mold was then placed in a drying oven for curing at 120℃ (2 h), 150℃ (2 h), and 180℃ (2 h) to obtain the cured epoxy compound 5-DOPO / EP. The cured compound met UL-94 V-2 standards according to ASTM D3801-20, and its limiting oxygen index was 30.6% according to ASTM D2863. The thermal stability of the cured epoxy resin compound 5-DOPO / EP was tested using a thermogravimetric analyzer under a N2 atmosphere, according to GB / T 27761-2011. Figure 4 It can be seen that its char residue rate at 700℃ is 21.5%, which is 15.0% higher than that of pure epoxy resin. A cone calorimeter was used at 35 kW / m². 2 The flame retardant properties of the epoxy resin cured product 5-DOPO / EP were tested under radiation intensity, according to the test standard GB / T 16172-2007; Figures 5-8 It can be seen that the peak heat release rate, total heat release, peak smoke production rate, and total smoke production of 5-DOPO / EP are 523.0 kW / m³. 2 67.4 MJ / m 2 0.28 m 2 / s and 37.6m 2Compared to E44 epoxy resin, the peak heat release rate of the cured epoxy resin 5-DOPO / EP decreased by 38.8%, the total heat release decreased by 27.6%, the peak smoke generation rate increased by 12.0%, and the total smoke generation increased by 20.1%. The tensile and flexural strengths of the cured product were tested using a universal testing machine according to GB / T16491-2022; the measured tensile and flexural strengths were 40.5 MPa and 92.2 MPa, respectively. The impact strength of the cured product was tested using a cantilever beam impact tester according to ASTM D256; the measured impact strength was 45.7 kJ / m. 2 The above experimental results show that although the flame retardant properties of the cured product prepared by directly mixing E44 epoxy resin with 5 wt.% DOPO can be slightly improved, it produces more toxic and harmful gases than pure epoxy resin and has poorer mechanical properties.

[0024] Comparative Example 3 Vanillin-based phosphorus-nitrogen flame retardant toughening agent was prepared according to Example 1 of patent CN119930694A: Vanillin (0.04 mol) and 1,6-hexanediamine (0.02 mol) were added to a 250 mL four-necked flask, and 150 mL of N,N-dimethylacetamide was added under nitrogen protection. When the temperature reached 80 °C, the mixture was stirred continuously for 5 h, and then cooled to 25 °C. The mixture was then slowly poured into distilled water, allowed to stand, and filtered to obtain the reaction product. This product was dried in a vacuum drying oven at 80 °C for 24 h to obtain a yellow powder, which is the precursor containing a Schiff base structure. The prepared precursor containing a Schiff base structure (0.1 mol), DOPO (0.2 mol), and 300 mL of anhydrous ethanol were mixed in a 500 mL three-necked flask. The mixture was then stirred continuously under reflux at 60 °C for 5 h, and then allowed to cool naturally to room temperature. The reaction product was separated by vacuum filtration and washed with anhydrous ethanol, and then dried in a vacuum drying oven at 80°C for 24 hours to obtain a brownish-yellow powder, which is the vanillin-based phosphorus nitrogen flame retardant toughening agent (VH-DOPO).

[0025] VH-DOPO (5 g) and E44 (100 g) were mixed at 120°C, and the temperature was lowered to 70°C. Then, DDM (21.8 g) curing agent was added, and stirring continued until the mixture became homogeneous. The mixture was then poured into a PTFE mold. The mold was then placed in an oven for curing, with the curing sequence being 120°C (2 h), 150°C (2 h), and 180°C (2 h). The sample was slowly cooled to room temperature to obtain the flame-retardant epoxy resin cured product 5-VH-DOPO / EP. The vertical burning flame retardancy rating of this cured product, measured according to ASTM D3801-20, reached UL-94 V-1. The limiting oxygen index of this cured product, measured according to ASTM D2863, was 32.1%. The thermal stability of the epoxy resin cured product 5-VH-DOPO / EP was tested using a thermogravimetric analyzer under a N2 atmosphere, according to GB / T 27761-2011. Figure 4 It can be seen that the char residue of 5-VH-DOPO / EP is 26.0%. A cone calorimeter was used at 35 kW / m³. 2 The flame retardant properties of the epoxy resin cured product 5-VH-DOPO / EP were tested under radiation intensity, according to the test standard GB / T 16172-2007; Figures 5-8 It can be seen that the peak heat release rate, total heat release, peak smoke production rate, and total smoke production of 5-VH-DOPO / EP are 724.3 kW / m³. 2 108.6 MJ / m 2 0.32 m 2 / s and 40.8 m 2 The tensile and flexural strengths of the cured material were tested using a universal testing machine, according to GB / T 16491-2022; the tensile strength was measured to be 43.5 MPa and the flexural strength to be 140.3 MPa. The impact strength of the cured material was tested using a cantilever beam impact tester, according to ASTM D256; the impact strength was measured to be 77.5 kJ / m². 2 Compared with the 5-VH-DOPO / EP prepared in Comparative Example 3, the 5-PDP / EP epoxy resin cured product prepared in Example 2 showed a 51.5% reduction in peak heat release rate, a 50.3% reduction in total heat release, a 56.3% reduction in peak smoke generation rate, a 41.7% reduction in total smoke generation, an 11.2% increase in limiting oxygen index, and increases in tensile strength, flexural strength, and impact strength by 15.2%, 15.0%, and 20.8%, respectively.

[0026] Comparative Example 4 The Schiff base compound PD (5 g) obtained from the reaction of anisaldehyde and 1,5-pentanediamine in Example 1 was mixed with E44 (100 g) at 120°C. The temperature was then lowered to 70°C, and curing agent DDM (21.8 g) was added. Stirring continued until the mixture became homogeneous, and the mixture was poured into a polytetrafluoroethylene mold. The mold was then placed in a drying oven for curing, with the curing sequence being 120°C (2 h), 150°C (2 h), and 180°C (2 h). The sample was slowly cooled to room temperature to obtain the epoxy cured product 5-PD / EP. According to ASTM D3801-20, the cured product has a UL-94 rating of no rating, and according to ASTM D2863, the limiting oxygen index is 24.4%. The thermal stability of the epoxy cured product 5-PD / EP was tested using a thermogravimetric analyzer under a N2 atmosphere and a cone calorimeter at 35 kW / m². 2 The flame retardant properties of the epoxy-cured compound 5-PD / EP were tested under radiation intensity. The char residue of the epoxy-cured compound 5-PD / EP under N2 was 20.3% (700℃). The peak heat release rate, total heat release, peak smoke generation rate, and total smoke generation of the epoxy-cured compound 5-PD / EP were 724.2 kW / m³. 2 95.0 MJ / m 2 0.22m 2 / s and 31.2 m 2 The tensile and flexural strengths of the cured material were tested using a universal testing machine, according to GB / T16491-2022; the measured tensile and flexural strengths were 44.8 MPa and 115.7 MPa, respectively. The impact strength of the cured material was tested using a cantilever beam impact tester, according to ASTM D256; the measured impact strength was 69.2 kJ / m. 2 These results indicate that the thermal stability, flame retardancy, and mechanical properties of the epoxy-cured 5-PD / EP are significantly inferior to those of 5-PDP / EP.

[0027] The experimental results above show that the anisaldehyde-based multifunctional flame retardant PDP prepared in Example 2 of this application, using anisaldehyde as a raw material, significantly improves the mechanical properties and flame retardant properties of E44 epoxy resin cured products compared to the vanillin-based phosphorus-nitrogen flame retardant toughening agent VH-DOPO prepared in Comparative Example 3. This may be because the vanillin-based phosphorus-nitrogen flame retardant toughening agent VH-DOPO contains hydroxyl groups, which are more likely to trigger a dehydration reaction in the early stage of combustion, destroy the continuity of the char layer, and reduce the flame retardant efficiency. The hydroxyl groups of vanillin will weaken the thermal stability of the aromatic ring, and the hydroxyl groups of vanillin may lead to uneven distribution of crosslinking sites and low crosslinking density. In contrast, the anisaldehyde-based multifunctional flame retardant PDP prepared in this application has no hydroxyl groups in its molecules, and the molecules are bonded by van der Waals forces. Its thermal decomposition process is more stable, and the dense crosslinking network can uniformly transmit impact stress and avoid local stress concentration. The anisaldehyde-based multifunctional flame retardant PDP prepared in this invention has excellent tensile strength, flexural strength, impact strength, and thermal stability.

[0028] Therefore, those skilled in the art will recognize that although embodiments of the present invention have been shown and described in detail herein, many other variations or modifications conforming to the principles of the present invention can be directly determined or derived from the disclosure of the present invention without departing from the spirit and scope of the invention. Therefore, the scope of the present invention should be understood and recognized as covering all such other variations or modifications.

Claims

1. A multifunctional flame retardant based on anisaldehyde, characterized in that, The molecular structure of the multifunctional flame retardant is as follows: ； Wherein, R is an aromatic hydrocarbon group or an aliphatic hydrocarbon group with 4 to 12 carbon atoms.

2. The method for preparing a multifunctional flame retardant based on anisaldehyde as described in claim 1, characterized in that, Step S1: p-Anisaldehyde, 1,5-pentanediamine, and an organic solvent are thoroughly mixed and reacted in a nitrogen atmosphere to obtain a Schiff base compound with the following structural formula: ； Wherein, R is an aromatic hydrocarbon group or an aliphatic hydrocarbon group with 4 to 12 carbon atoms; Step S2: After cooling the preparation system containing Schiff base compounds obtained in step S1 to a certain temperature, add 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide DOPO and continue the reaction. After the reaction is completed, dry to obtain the multifunctional flame retardant based on anisaldehyde.

3. The method for preparing a multifunctional flame retardant based on anisaldehyde as described in claim 2, characterized in that, The mass ratio of anisaldehyde, 1,5-pentanediamine and DOPO is 10-50:5-20:20-50.

4. The method for preparing a multifunctional flame retardant based on anisaldehyde as described in claim 2, characterized in that, In step S1, the reaction temperature of anisaldehyde and 1,5-pentanediamine in an organic solvent is 70-100℃, and the reaction time is 3-6h.

5. The method for preparing a multifunctional flame retardant based on anisaldehyde as described in claim 2, characterized in that, In step S2, after cooling the Schiff base compound preparation system obtained in step S1 to 40-60°C, DOPO is added and the reaction continues for 6-10 hours.

6. The method for preparing a multifunctional flame retardant based on anisaldehyde as described in claim 2, characterized in that, The organic solvent mentioned in step S1 is one or a combination of alcohols, aromatic hydrocarbons, ketones, and ethers.

7. The method for preparing a multifunctional flame retardant based on anisaldehyde as described in claim 6, characterized in that, The alcohol organic solvent is ethanol; the aromatic hydrocarbon organic solvent is N,N-dimethylacetamide or N-methylpyrrolidone; the ketone organic solvent is acetone; and the ether organic solvent is petroleum ether or tetrahydrofuran.

8. The method for preparing a multifunctional flame retardant based on anisaldehyde as described in claim 2, characterized in that, Step S2 involves drying the product in a forced-air drying oven at 80-100°C after the reaction is complete, yielding the multifunctional flame retardant based on anisaldehyde.

9. The application of the multifunctional flame retardant as described in claim 1 or the multifunctional flame retardant prepared by the preparation method described in claims 2-8 in epoxy resin, characterized in that, A multifunctional flame retardant was mixed with epoxy resin and a curing agent to prepare a cured epoxy resin product.

10. The application of the multifunctional flame retardant as described in claim 9 in epoxy resin, characterized in that, The amount of the multifunctional flame retardant added to the epoxy resin is 1-10 wt.%.

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