Vanillin-based phosphorus-nitrogen flame-retardant toughening agent and preparation method thereof

Abstract

The application discloses a vanillin-based phosphorus-nitrogen flame-retardant toughening agent and a preparation method thereof. The preparation method comprises the following steps: mixing and reacting vanillin and a binary aliphatic amine in an organic solvent to form a precursor containing a Schiff base structure; mixing and reacting the obtained Schiff base compound and DOPO in an organic solvent, and then performing separation, drying and other purification processes to obtain the vanillin-based phosphorus-nitrogen flame-retardant toughening agent. The application solves the problems of poor flame-retardant performance and low toughness of a traditional bisphenol A type epoxy resin. A new type of vanillin-based phosphorus-nitrogen flame-retardant toughening agent is synthesized by using widely-sourced and low-cost biomass vanillin as a raw material, forming a Schiff base structure and then introducing DOPO on the structure. The flame-retardant and toughness of an epoxy cured product are significantly improved by adding the flame-retardant toughening agent to the epoxy resin. The preparation method is simple to operate and can realize large-scale production.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of flame-retardant high polymer materials, and particularly relates to a vanillin-based phosphorus-nitrogen flame-retardant toughening agent and a preparation method thereof. BACKGROUND

[0002] Epoxy resin is a kind of high polymer material with wide application, which is widely used in the fields of coatings, adhesives, composite materials and the like. However, the flammability and brittleness of epoxy resin limit the expansion of its application field. Epoxy resin itself has high flammability, and is prone to burning, especially when in contact with a fire source. In addition, a large amount of heat and toxic gases are released during the burning process, which brings safety hazards when using epoxy resin. Therefore, the research on epoxy resin tends to develop in the direction of halogen-free flame retardant, low smoke and low toxicity, and high toughness. Biomass-based flame retardant not only can improve the flame retardant performance of epoxy resin, but also can improve its environmental friendliness.

[0003] Biomass-based flame retardant uses natural materials, which can better meet the requirements of modern environmental regulations. Vanillin, as the second largest natural renewable resource lignin platform compound, in the prior art, vanillin and phosphate compounds are reacted to prepare vanillin-based flame retardant, and vanillin and polyol compounds are reacted to synthesize a coating with flame retardant effect, which all show certain flame retardant performance to high polymer materials. However, in the existing flame retardant technology, there is still a problem of simultaneous improvement of flame retardant effect and toughness.

[0004] Therefore, it is urgent to develop a vanillin-based flame retardant with excellent flame retardant and high toughness, and a preparation method which is simple, low in production cost and easy to mass produce. SUMMARY

[0005] The present application aims to overcome the shortcomings of the prior art, and provides a vanillin-based phosphorus-nitrogen flame-retardant toughening agent. The vanillin-based phosphorus-nitrogen flame-retardant toughening agent uses vanillin, a lignin-derived aromatic compound, as a raw material, and introduces a DOPO structure on the formed Schiff base structure, thereby achieving the purposes of improving the flame retardant and toughness of epoxy resin, and solving the problems mentioned in the background.

[0006] To achieve the above technical effects, the following technical solutions are adopted:

[0007] A vanillin-based phosphorus-nitrogen flame-retardant toughening agent, the molecular structure formula of which is:

[0008]

[0009] wherein R is an aliphatic straight chain with a carbon atom number of 4 to 12 and derivatives thereof;

[0010] In the flame-retardant application, the addition amount of the vanillin-based phosphorus-nitrogen flame-retardant toughening agent in the epoxy resin is 5wt%-10wt%.

[0011] Further, the preparation method of the vanillin-based phosphorus-nitrogen flame-retardant toughening agent comprises the following steps:

[0012] Step S1: preparation of a precursor substance containing a Schiff base structure

[0013] The vanillin and the dibasic aliphatic amine are mixed in an organic solvent and reacted in a reaction container under nitrogen protection to obtain a precursor substance containing a Schiff base structure, and the molecular structure of the precursor substance is as follows:

[0014]

[0015] In the formula, R is an aliphatic straight chain with 4 to 12 carbon atoms and derivatives thereof.

[0016] Step S2: preparation of a vanillin-based phosphorus-nitrogen flame-retardant toughening agent

[0017] The Schiff base compound obtained in step S1 and 9,10-dihydro-9-oxa-10-phospha-phenanthrene-10-oxide DOPO are mixed in an organic solvent and reacted in a reaction container; and after the reaction, the mixture is purified to obtain the vanillin-based phosphorus-nitrogen flame-retardant toughening agent, and the molecular structure of the vanillin-based phosphorus-nitrogen flame-retardant toughening agent is as follows:

[0018]

[0019] In the formula, R is an aliphatic straight chain with 4 to 12 carbon atoms and derivatives thereof.

[0020] Further, in step S1, the mass ratio of vanillin, dibasic aliphatic amine, and organic solvent is 5-100:1-50:50-500.

[0021] Further, in step S1, the reaction temperature is 50-120°C, and the reaction time is 1-6 hours.

[0022] Further, in step S1, the dibasic aliphatic amine includes, but is not limited to, one or more combinations of 1,4-butanediamine, 1,5-pentanediamine, 1,6-hexanediamine, 1,8-octanediamine, 1,10-decanediamine, and derivatives thereof.

[0023] Further, in step S1, the organic solvent is one or more combinations of an alcohol, an aromatic hydrocarbon, a ketone, and an ether; 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.

[0024] Further, in the step S2, the mass ratio of the precursor material containing the Schiff base structure, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide DOPO and the organic solvent is 10-100:50-1000:10-300.

[0025] Further, in the step S2, the reaction temperature is 60-100 DEG C, and the reaction time is 2-8 hours.

[0026] Further, in the step S2, the purification process comprises a separation and a drying step.

[0027] Further, the separation step specifically comprises: using a vacuum filter to extract the organic solvent, and washing with anhydrous ethanol; the drying step specifically comprises: sequentially drying the organic liquid in a vacuum drying box to remove water and organic impurities in the organic liquid; and the drying temperature in the vacuum drying box is 50-80 DEG C.

[0028] The present application has the following beneficial effects:

[0029] 1. The present application uses lignin-derived aromatic compound vanillin as raw material, which can be produced on a large scale, reduces the dependence of plastic, paint and other industries on petrochemical industry, and at the same time alleviates the problems of environmental pollution, excessive consumption and excessive emission of carbon compounds in the conversion process of fossil resources;

[0030] 2. The precursor material containing the Schiff base structure is obtained through molecular structure design and simple synthesis process, the flexible chain segment of the Schiff base structure is reacted with DOPO, the rigid and flexible molecular structure of the flame retardant is realized, the flame retardant efficiency of the epoxy curing product is improved, and the toughness of the epoxy resin curing product is also increased;

[0031] 3. The preparation method of the vanillin-based phosphorus-nitrogen flame-retardant toughening agent has strong operability, good controllability, low economic cost, easy implementation and good popularization and application prospect, and is conducive to large-scale industrial production. BRIEF DESCRIPTION OF DRAWINGS

[0032] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description, and the drawings in the following description are only embodiments of the present application, and for those skilled in the art, other drawings can be obtained without creative labor on the basis of the provided drawings.

[0033] Figure 1 The molecular structure formula of the precursor material containing the Schiff base structure in the present application;

[0034] Figure 2 The molecular structure formula of the vanillin-based phosphorus-nitrogen flame-retardant toughening agent in the present application;

[0035] Figure 3 This is a flowchart of the preparation method of the present invention;

[0036] Figure 4 The infrared spectrum of the vanillin-based phosphorus nitrogen flame retardant toughening agent prepared in Example 1 of this invention;

[0037] Figure 5 The TGA curves of Examples 2-4 and Comparative Example 1 under N2 are shown.

[0038] Figure 6 The heat release rate curves of Examples 2-4 and Comparative Example 1 of the present invention are shown.

[0039] Figure 7 The total heat release curves for Examples 2-4 and Comparative Example 1 of the present invention are shown.

[0040] Figure 8 The smoke production rate curves of Examples 2-4 and Comparative Example 1 of the present invention;

[0041] Figure 9 The total smoke production curves for Examples 2-4 and Comparative Example 1 of the present invention are shown. Detailed Implementation

[0042] 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.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] The starch-based epoxy resin and its preparation method provided by the present invention will be described below with reference to the embodiments. The scope of protection of the present invention is not limited by the following embodiments.

[0047] Referring to Figures 1-9 The present application provides a technical solution: a vanillin-based phosphorus-nitrogen flame-retardant toughening agent, which has a molecular structure as shown in Figure 2 .

[0048] Another aspect provides a preparation method of the vanillin-based phosphorus-nitrogen flame-retardant toughening agent, and the preparation process is as shown in Figure 3 , and specifically includes:

[0049] In the first stage, vanillin and a binary aliphatic amine are mixed in an organic solvent, and a precursor containing a Schiff base structure is obtained by reacting at 50-120°C under nitrogen protection in a reaction container for 1-6 hours, which has a molecular structure formula as shown in Figure 1 .

[0050] In the second stage, the Schiff base compound obtained in step S1 is mixed with DOPO in an organic solvent, and the mixture is reacted in a reaction container at 60-100°C for 2-8 hours.

[0051] In the third stage, the vanillin-based phosphorus-nitrogen flame-retardant toughening agent is obtained after the mixture after reaction is purified.

[0052] Further, the mass ratio of vanillin, binary aliphatic amine, and organic solvent is 5-100:1-50:50-500.

[0053] Further, the mass ratio of the precursor containing a Schiff base structure, DOPO, and the organic solvent is 10-100:50-1000:10-300.

[0054] Further, the purification process is that the mixture system after reaction is subjected to separation, drying, etc.

[0055] Further, in the separation step, the organic solvent is extracted by a vacuum filter, and washed with anhydrous ethanol.

[0056] Further, in the drying step, the organic liquid is dried in a vacuum drying oven to remove water and organic impurities in the organic liquid.

[0057] Further, the drying temperature in the vacuum drying oven is 50-80°C.

[0058] Further, the binary aliphatic amine includes but is not limited to one or more combinations of 1,4-butanediamine, 1,5-pentanediamine, 1,6-hexanediamine, 1,8-octanediamine, 1,10-decanediamine, and derivatives thereof.

[0059] Further, the organic solvent is one or more combinations of alcohols, aromatic hydrocarbons, ketones, and ethers.

[0060] Further, the alcohol organic solvent is ethanol; the aromatic hydrocarbon organic solvent is N,N-dimethylacetamide (DMAC), N-methyl pyrrolidone (NMP); the ketone organic solvent is acetone; the ether organic solvent is petroleum ether, tetrahydrofuran.

[0061] Example 1:

[0062] 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 reaction system was continuously stirred for 5 h, and then cooled to 25°C. Then, the above mixture was slowly poured into distilled water, and after standing and suction filtration, the reaction product was obtained and placed in a vacuum drying oven at 80°C for 24 h to obtain a yellow powder, which was a precursor material containing a Schiff base structure, having the following structural formula:

[0063]

[0064] The above obtained precursor material 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. Subsequently, under the condition of reflux at 60°C, the mixture was continuously stirred for 5 h, and then naturally cooled to room temperature. The reaction product was separated by suction filtration, washed with anhydrous ethanol, and then placed in a vacuum drying oven at 80°C for 24 h to obtain a brownish yellow powder, which was a vanillin-based phosphorus-nitrogen flame-retardant toughening agent (VH-DOPO), having the following structural formula:

[0065]

[0066] The infrared spectrum of the vanillin-based phosphorus-nitrogen flame-retardant toughening agent is shown in Figure 4 As can be seen from Figure 4 , in the spectrum of VH-DOPO, absorption peaks of 754 cm -1 (P-C) and 1297 cm -1 (C-N) appear, the characteristic peak of P-H of DOPO at 2436 cm -1 and the characteristic peak of C=N of VH at 1644 cm -1 do not appear, which indicates that vanillin first reacts with 1,6-hexanediamine to generate a Schiff base structure, and then the active P-H bond of DOPO and the Schiff base structure undergo an addition reaction, successfully preparing the vanillin-based phosphorus-nitrogen flame-retardant toughening agent VH-DOPO.

[0067] Example 2:

[0068] VH-DOPO (5 g) was stirred and mixed with E51 epoxy resin (100 g) at 140 °C, the temperature was reduced to 80 °C, the curing agent 4,4'-diaminodiphenyl methane (DDM) (25 g) was added, the stirring was continued until the mixture became uniform, and the mixture was poured into a polytetrafluoroethylene mold. Then, it was placed in a drying oven for curing reaction, the curing program was 120 °C (2 h), 150 °C (2 h), 170 °C (2 h) in turn, the sample was slowly cooled to room temperature, and the flame-retardant epoxy resin cured product VD-5 was obtained. The cured product reached UL-94 V0 level according to the standard ASTM D3801-20. The thermal stability of the epoxy cured product VD-5 was tested by a thermal gravimetric analyzer under N2 atmosphere, and the flame-retardant performance of the epoxy cured product VD-5 was tested by a cone calorimeter under 35 kW / m2 radiation intensity. The results are shown in Table 1. 2 It can be seen that, compared with E51 epoxy resin, the carbon residue rate of the epoxy cured product VD-5 increased by 37.0% (800 °C), the peak heat release rate decreased by 14.6%, the total heat release amount decreased by 12.0%, the peak smoke production rate decreased by 7.1%, and the total smoke production amount decreased by 30.4%, which indicated that the epoxy cured product VD-5 had good thermal stability and excellent flame-retardant performance. According to the standard GB / T 1843-2008, the Izod impact strength of E51 epoxy cured product and VD-5 was 22.8 kJ / m2 and 79.8 kJ / m2 respectively, which increased by 249.6%, which indicated that the epoxy cured product VD-5 had excellent toughness. 2 2 Figures 5-9

[0069] Example 3:

[0070] VH-DOPO (10 g) was stirred and mixed with E51 (100 g) at 140 °C, the temperature was reduced to 80 °C, the curing agent 4,4'-diaminodiphenyl methane (DDM) (25 g) was added, the stirring was continued until the mixture became uniform, and the mixture was poured into a polytetrafluoroethylene mold. Then, it was placed in a drying oven for curing reaction, the curing program was 120 °C (2 h), 150 °C (2 h), 170 °C (2 h) in turn, the sample was slowly cooled to room temperature, and the flame-retardant epoxy resin cured product VD-10 was obtained. The cured product reached UL-94 V0 level according to the standard ASTM D3801-20. The thermal stability of the epoxy resin cured product VD-10 was tested by a thermal gravimetric analyzer under N2 atmosphere, and the flame-retardant performance of the epoxy resin cured product VD-10 was tested by a cone calorimeter under 35 kW / m2 radiation intensity. The results are shown in Table 1. 2 It can be seen that, compared with E51 epoxy resin, the carbon residue rate of the epoxy cured product VD-5 increased by 37.0% (800 °C), the peak heat release rate decreased by 14.6%, the total heat release amount decreased by 12.0%, the peak smoke production rate decreased by 7.1%, and the total smoke production amount decreased by 30.4%, which indicated that the epoxy cured product VD-5 had good thermal stability and excellent flame-retardant performance. According to the standard GB / T 1843-2008, the Izod impact strength of E51 epoxy cured product and VD-5 was 22.8 kJ / m2 and 79.8 kJ / m2 respectively, which increased by 249.6%, which indicated that the epoxy cured product VD-5 had excellent toughness. Figures 5-9 ​​​It can be seen that, compared with E51 epoxy resin, the carbon residue rate of epoxy resin cured product VD-10 increased by 46.0%, the heat release rate peak decreased by 29.1%, the total heat release decreased by 14.5%, the smoke production rate peak slightly increased by 3.6%, and the total smoke production decreased by 20.7%, which indicates that the epoxy cured product VD-10 has good thermal stability and more excellent flame retardant performance. The cantilever beam impact strength of this cured product is 70.3kJ / m 2 Compared with E51 epoxy resin, it increased by 207.8%, which indicates that the epoxy cured product VD-10 has excellent toughness.

[0071] Example 4:

[0072] After stirring and mixing VH-DOPO (15g) and E51 (100g) at 140℃, the temperature was reduced to 80℃, and curing agent 4,4'-diaminodiphenyl methane (DDM) (25g) was added, and the mixture was continuously stirred until the mixture became uniform, and the mixture was poured into a polytetrafluoroethylene mold. Then, it was put into a drying box for curing reaction, and the curing program was 120℃ (2h), 150℃ (2h), 170℃ (2h) in turn, and the sample was slowly cooled to room temperature to obtain epoxy cured product VD-15. This cured product reached UL-94 V0 level according to standard ASTM D3801-20. The thermal stability of epoxy cured product VD-15 was tested by thermogravimetric analyzer under N2 atmosphere, and the flame retardant performance of epoxy cured product VD-15 was tested by cone calorimeter under 35kW / m 2 Radiation intensity. From the Figures 5-9 It can be seen that, compared with E51 epoxy resin, the carbon residue rate of epoxy cured product VD-15 increased by 53.1%, the heat release rate peak decreased by 59.3%, the total heat release decreased by 23.5%, the smoke production rate peak decreased by 21.4%, and the total smoke production decreased by 17.3%, which indicates that the epoxy cured product VD-15 has good thermal stability and more excellent flame retardant performance. The cantilever beam impact strength of this cured product is 35.2kJ / m 2 Compared with E51 epoxy resin, it increased by 54.4%, which indicates that the epoxy cured product VD-15 has good toughness.

[0073] Comparative Example 1:

[0074] 100g of E51 epoxy resin was mixed thoroughly with 25g of 4,4'-diaminodiphenylmethane (DDM), and the mixture was poured into a polytetrafluoroethylene mold. Then, it was placed in a drying oven for curing, with the curing process sequentially at 120℃ (2h), 150℃ (2h), and 170℃ (2h) to obtain the cured epoxy compound DGEBA. According to standard ASTM D3801-20, the UL-94 test result for this cured compound was unrated. The thermal stability of E51 was tested using a thermogravimetric analyzer under a N2 atmosphere, and a cone calorimeter was used at 35kW / m³. 2 The flame retardant properties of E51 epoxy resin were tested under radiation intensity. Figures 5-9 It can be seen that the residual carbon rate of E51 epoxy resin under N2 is 13.8%, and the peak heat release rate, total heat release, peak smoke generation rate, and total smoke generation of E51 epoxy resin are 816.9 kW / m³. 2 85.8 MJ / m 2 0.28m 2 / s and 35.8m 2 These results indicate that E51 epoxy resin has a low carbon residue, is prone to combustion, and generates a large amount of heat and toxic fumes during combustion. The cantilever beam impact strength of this cured product, measured according to standard GB / T 1843-2008, is 22.8 kJ / m. 2 This indicates that the cured material has poor toughness.

[0075] Comparative Example 2:

[0076] Based on the vanillin-based phosphorus nitrogen flame retardant toughening agent prepared in Example 1, except that 1,6-hexanediamine was replaced with 1,3-propanediamine in equal amounts, while other conditions remained unchanged, vanillin-based phosphorus nitrogen flame retardant toughening agent 2 was obtained.

[0077] The prepared vanillin-based phosphorus nitrogen flame retardant toughening agent 2 (5g) was mixed with E51 epoxy resin (100g) at 140℃. The temperature was then lowered to 80℃, and curing agent 4,4'-diaminodiphenylmethane (DDM) (25g) 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℃ (2h), 150℃ (2h), and 170℃ (2h). The sample was slowly cooled to room temperature to obtain flame retardant epoxy resin cured product 2. According to standard ASTM D3801-20, this cured product reached V2 grade. The thermal stability of the epoxy cured product was tested using a thermogravimetric analyzer under N2 atmosphere and a cone calorimeter at 35kW / m². 2The flame retardant properties of epoxy cured compound 2 were tested under radiation intensity. Compared with E51 epoxy resin in Comparative Example 1, the residual char rate of epoxy cured compound 2 increased by 10.6% (800℃), the peak heat release rate decreased by 8.7%, the total heat release decreased by 7.6%, the peak smoke production rate decreased by 2.7%, and the total smoke production decreased by 3.8%. This indicates that the epoxy cured compound has poor thermal stability and poor flame retardant properties. According to standard GB / T 1843-2008, the cantilever beam impact strength of E51 epoxy cured compound and epoxy cured compound 2 in Comparative Example 2 were 22.8 kJ / m², respectively. 2 and 23.3 kJ / m 2 The increase was 2.2%, indicating that epoxy-cured compound 2 could not have excellent toughness.

[0078] Comparative Example 3:

[0079] Based on the vanillin-based phosphorus nitrogen flame retardant toughening agent prepared in Example 1, 1,6-hexanediamine was replaced with an equal amount of 4,4'-diaminodiphenylmethane, while other conditions remained unchanged, to obtain vanillin-based phosphorus nitrogen flame retardant toughening agent 3.

[0080] The prepared vanillin-based phosphorus nitrogen flame retardant toughening agent 3 (5g) was mixed with E51 epoxy resin (100g) at 140℃. The temperature was then lowered to 80℃, and curing agent 4,4'-diaminodiphenylmethane (DDM) (25g) 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℃ (2h), 150℃ (2h), and 170℃ (2h). The sample was slowly cooled to room temperature to obtain flame retardant epoxy resin cured product 3. According to standard ASTM D3801-20, this cured product reached V1 grade. The thermal stability of epoxy cured product 3 was tested using a thermogravimetric analyzer under N2 atmosphere and a cone calorimeter at 35kW / m². 2 The flame retardant properties of epoxy cured compound 3 were tested under radiation intensity. Compared with E51 epoxy resin in Comparative Example 1, the residual char rate of epoxy cured compound 3 increased by 15.6% (800℃), the peak heat release rate decreased by 14.7%, the total heat release decreased by 11.5%, the peak smoke production rate decreased by 8.4%, and the total smoke production decreased by 9.5%. This indicates that the epoxy cured compound has poor thermal stability and poor flame retardant properties. According to standard GB / T 1843-2008, the cantilever beam impact strength of E51 epoxy cured compound and epoxy cured compound 3 in Comparative Example 3 were 22.8 kJ / m², respectively. 2 and 20.4 kJ / m 2 The toughness was reduced by 10.5%, indicating that epoxy-cured compound 3 could not have excellent toughness.

[0081] Comparative Example 4:

[0082] With the vanillin-based phosphorus-nitrogen flame-retardant toughening agent prepared in Example 1 as a reference, 1,6-hexanediamine was not added, and only vanillin and DOPO were directly reacted; other conditions remained unchanged to obtain vanillin-based phosphorus-nitrogen flame-retardant toughening agent 4.

[0083] After the prepared vanillin-based phosphorus-nitrogen flame-retardant toughening agent 4 (5 g) and E51 epoxy resin (100 g) were stirred and mixed at 140°C, the temperature was reduced to 80°C, a curing agent 4,4'-diaminodiphenyl methane (DDM) (25 g) was added, and stirring was continued until the mixture became uniform, and the mixture was poured into a polytetrafluoroethylene mold. Then, it was placed in a drying oven for a curing reaction, and the curing program was 120°C (2 h), 150°C (2 h), and 170°C (2 h) in sequence. The sample was slowly cooled to room temperature to obtain a flame-retardant epoxy resin cured product 4. The cured product reached V1 level according to the standard ASTM D3801-20. The thermal stability of the epoxy cured product was tested by a thermal gravimetric analyzer under N2 atmosphere, and the flame-retardant performance of the epoxy cured product 4 was tested by a cone calorimeter under a radiation intensity of 35 kW / m2. Compared with the E51 epoxy resin in Comparative Example 1, the carbon residue rate of the epoxy cured product 4 increased by 8.1% (800°C), the peak heat release rate decreased by 17.3%, the total heat release amount decreased by 15.4%, the peak smoke production rate decreased by 10.7%, and the total smoke production amount decreased by 11.5%, which indicated that the epoxy cured product 4 had poor thermal stability and poor flame-retardant performance. According to the standard GB / T 1843-2008, the Izod impact strength of the E51 epoxy cured product and the epoxy cured product 4 in Comparative Example 4 was 22.8 kJ / m2 and 15.3 kJ / m2, respectively, which decreased by 32.8%, which indicated that the epoxy cured product 4 could not have excellent toughness. 2 The flame-retardant performance of the epoxy cured product 4 was tested under a radiation intensity. Compared with the E51 epoxy resin in Comparative Example 1, the carbon residue rate of the epoxy cured product 4 increased by 8.1% (800°C), the peak heat release rate decreased by 17.3%, the total heat release amount decreased by 15.4%, the peak smoke production rate decreased by 10.7%, and the total smoke production amount decreased by 11.5%, which indicated that the epoxy cured product 4 had poor thermal stability and poor flame-retardant performance. According to the standard GB / T 1843-2008, the Izod impact strength of the E51 epoxy cured product and the epoxy cured product 4 in Comparative Example 4 was 22.8 kJ / m2 and 15.3 kJ / m2, respectively, which decreased by 32.8%, which indicated that the epoxy cured product 4 could not have excellent toughness. 2 and 15.3 kJ / m 2 , which decreased by 32.8%, which indicated that the epoxy cured product 4 could not have excellent toughness.

[0084] Comparative Example 5:

[0085] With the vanillin-based phosphorus-nitrogen flame-retardant toughening agent prepared in Example 1 as a reference, DOPO was not added, and only vanillin and 1,6-hexanediamine were directly reacted to obtain a precursor containing a Schiff base structure; other conditions remained unchanged to obtain vanillin-based phosphorus-nitrogen flame-retardant toughening agent 5.

[0086] The prepared vanillin-based phosphorus-nitrogen flame-retardant toughening agent 5 (5 g) was mixed with E51 epoxy resin (100 g) at 140°C under stirring, the temperature was reduced to 80°C, the curing agent 4,4'-diaminodiphenyl methane (DDM) (25 g) was added, the stirring was continued until the mixture became uniform, and the mixture was poured into a polytetrafluoroethylene mold. Then, it was placed in a drying oven for curing reaction, and the curing program was 120°C (2 h), 150°C (2 h), and 170°C (2 h) in turn, the sample was slowly cooled to room temperature, and the flame-retardant epoxy resin cured product 5 was obtained. The UL-94 test result of the cured product was no rating according to the standard ASTM D3801-20. The thermal stability of the epoxy cured product was tested by a thermal gravimetric analyzer under N2 atmosphere, and the flame-retardant performance of the epoxy cured product 5 was tested by a cone calorimeter under a radiation intensity of 35 kW / m2. 2 The flame-retardant performance of the epoxy cured product 5 was tested. Compared with the E51 epoxy resin in Comparative Example 1, the carbon residue rate of the epoxy cured product 5 increased by 2.6% (800°C), the peak heat release rate decreased by 4.5%, the total heat release amount decreased by 5.3%, the peak smoke production rate decreased by 8.6%, and the total smoke production amount decreased by 7.8%, which indicated that the epoxy cured product 5 had poor thermal stability and poor flame-retardant performance. According to the standard GB / T 1843-2008, the Izod impact strength of the E51 epoxy cured product and the epoxy cured product 5 in Comparative Example 5 was 22.8 kJ / m 2 and 26.4 kJ / m 2 , respectively, which increased by 15.8%, which indicated that the epoxy cured product 5 could not have excellent toughness.

[0087] In summary, the present application provides a vanillin-based phosphorus-nitrogen flame-retardant toughening agent and a preparation method thereof from the perspective of the flammability of traditional epoxy resin, poor environmental performance, and large toxicity of traditional flame retardants. The lignin-derived aromatic compound vanillin, which can be produced on a large scale, is used as a raw material, the phosphorus-nitrogen structure is formed by the chemical reaction between the flexible chain segment Schiff base group and DOPO, and the purpose of simultaneously improving the flame-retardant efficiency and toughness of the epoxy resin is achieved. The cured epoxy resin system has excellent flame retardance and toughness, and the preparation method has strong operability, good controllability, and is easy to implement, which is conducive to large-scale industrial production.

[0088] At this point, those skilled in the art recognize that, although embodiments of the present application have been fully demonstrated and described herein, many other variations or modifications in accordance with the principles of the present application can be directly determined or deduced from the disclosure of the present application without departing from the spirit and scope of the present application. Therefore, the scope of the present application should be understood and recognized as covering all these other variations or modifications.

Claims

1. A method of using a vanillin-based compound as a toughening agent for epoxy resins, characterized in that, The molecular structure of the toughening agent is: R is a linear aliphatic chain with 6 carbon atoms; The application method is: the vanillin-based compound is used as a toughening agent to be stirred and mixed with an epoxy resin and a curing agent to prepare a toughened epoxy resin curing product, and the vanillin-based compound is added in the epoxy resin in an amount of 5wt%-10wt%; The preparation method of the vanillin-based compound comprises: Step S1: preparation of a precursor substance containing a Schiff base structure Vanillin and 1,6-hexanediamine are fully mixed in an organic solvent, and reacted in a reaction container under nitrogen protection to obtain a precursor substance containing a Schiff base structure, and the molecular structure of the precursor substance containing a Schiff base structure is as follows: R is a linear aliphatic chain with 6 carbon atoms; Step S2: preparation of a vanillin-based compound The Schiff base compound obtained in step S1 and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide DOPO are fully mixed in an organic solvent, and continuously stirred and fully reacted under reflux conditions; after the reaction, the mixture is purified to obtain the vanillin-based compound, and the molecular structure of the vanillin-based compound is as follows: ； R is a linear aliphatic chain with 6 carbon atoms.

2. The method of using a vanillin-based compound as a toughening agent for epoxy resins according to claim 1, characterized in that, In step S1, the mass ratio of vanillin, 1,6-hexanediamine and the organic solvent is 5-100:1-50:50-500.

3. The method of using a vanillin-based compound as a toughening agent for epoxy resins according to claim 1, characterized in that, In step S1, the reaction temperature is 50-120℃, and the reaction time is 1-6 hours.

4. The method of using a vanillin-based compound as a toughening agent for epoxy resins according to claim 1, characterized in that, In step S1, the organic solvent is one or more of ethanol, N,N-dimethylacetamide, N-methylpyrrolidone, acetone, petroleum ether or tetrahydrofuran.

5. The method of using a vanillin-based compound as a toughening agent for epoxy resins according to claim 1, characterized in that, In step S2, the mass ratio of the precursor substance containing a Schiff base structure, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide DOPO and the organic solvent is 10-100:50-1000:10-300.

6. The method of using a vanillin-based compound as a toughening agent for epoxy resins according to claim 1, characterized in that, In step S2, the reaction temperature is 60-100℃, and the reaction time is 2-8 hours.

7. The method of using a vanillin-based compound as a toughening agent for epoxy resins according to claim 1, characterized in that, In step S2, the purification process comprises separation and drying steps.

8. The method of using a vanillin-based compound as a toughening agent for epoxy resins according to claim 7, characterized in that, The separation step specifically comprises: using a vacuum filter to extract the organic solvent, and washing with anhydrous ethanol; the drying step specifically comprises: sequentially drying the organic liquid in a vacuum drying oven to remove water and organic impurities in the organic liquid; and the drying temperature in the vacuum drying oven is 50-80℃.

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