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

Abstract

The invention discloses a vanillin-based phosphorus-nitrogen flame-retardant toughening agent and a preparation method thereof. The preparation method of the flame-retardant toughening agent comprises the following steps: fully mixing vanillin and binary aliphatic amine in an organic solvent to react to form a precursor substance containing a Schiff base structure; the obtained Schiff base compound and DOPO are fully mixed and reacted in an organic solvent, and the vanillin-based phosphorus-nitrogen flame-retardant toughening agent is obtained through separation, drying and other purification processes. The invention solves the problems of poor flame retardant property and low toughness of the traditional bisphenol A type epoxy resin raw material, biomass vanillin with wide source and low cost is used as the raw material, and a novel vanillin-based phosphorus-nitrogen flame retardant toughening agent is synthesized by forming a Schiff base structure and introducing DOPO on the structure; the flame-retardant toughening agent is added into the epoxy resin, so that the flame retardance and toughness of cured epoxy are remarkably improved, the preparation method is simple and convenient to operate, and large-scale production can be realized.

Description

Technical Field

[0001] The invention relates to the technical field of flame retardant polymer materials, and in particular to a vanillin-based phosphorus-nitrogen flame retardant toughening agent and a preparation method thereof. Background Art

[0002] Epoxy resin is a polymer material with a wide range of applications, and is widely used in coatings, adhesives, composite materials and other fields. However, the flammability and brittleness of epoxy resin limit the expansion of its application areas. Epoxy resin itself has high flammability, especially when it comes into contact with a fire source, it is easy to burn, and it releases a large amount of heat and toxic gases during its combustion 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 retardancy, low smoke and low toxicity, and high toughness. Biomass-based flame retardants can not only improve the flame retardant properties of epoxy resin, but also improve its environmental friendliness.

[0003] Biomass-based flame retardants use natural materials and can better meet the requirements of modern environmental regulations. Vanillin is a platform compound of lignin, the second largest natural renewable resource. In the existing technology, there are also methods of preparing vanillin-based flame retardants by reacting vanillin with phosphate compounds, and synthesizing coatings with flame retardant effects by reacting vanillin with polyol compounds, all of which show certain flame retardant properties for polymer materials. However, in the existing flame retardant technology, there is still the problem of improving both flame retardant effect and toughness simultaneously.

[0004] Therefore, there is an urgent need to develop a vanillin-based flame retardant with excellent flame retardancy and high toughness, as well as a simple preparation method, low production cost, and easy large-scale production. Summary of the invention

[0005] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a vanillin-based phosphorus-nitrogen flame retardant and toughening agent. The vanillin, an aromatic compound derived from lignin that can be mass-produced, is used as a raw material. A DOPO structure is introduced into the formed Schiff base structure to achieve the purpose of improving the flame retardancy and toughness of the epoxy resin at the same time, thereby solving the problems mentioned in the above-mentioned background technology.

[0006] In order 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 of which is:

[0008]

[0009] Wherein, R is an aliphatic straight chain having 4 to 12 carbon atoms and its derivatives;

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

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

[0012] Step S1: Preparation of precursor material containing Schiff base structure

[0013] Vanillin and dibasic fatty amine 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. The molecular structure of the precursor substance containing a Schiff base structure is as follows:

[0014]

[0015] Wherein, R is an aliphatic straight chain having 4 to 12 carbon atoms and its derivatives;

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

[0017] 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 reacted in a reaction container; the mixture after the reaction is subjected to a purification process to obtain the vanillin-based phosphorus-nitrogen flame retardant and toughening agent, and the molecular structure of the vanillin-based phosphorus-nitrogen flame retardant and toughening agent is as follows:

[0018]

[0019] Wherein, R is an aliphatic straight chain having 4 to 12 carbon atoms and its derivatives.

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

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

[0022] Furthermore, in step S1, the dibasic fatty 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 their derivatives.

[0023] Furthermore, in step S1, the organic solvent is one or more combinations of alcohols, aromatic hydrocarbons, ketones, and ethers; 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] Furthermore, in the step S2, the mass ratio of the precursor 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.

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

[0026] Furthermore, in step S2, the purification process includes separation and drying steps.

[0027] Furthermore, the separation step is specifically: using a vacuum filter to extract the organic solvent and washing it with anhydrous ethanol; the drying step is specifically: drying the organic liquid in a vacuum drying oven to remove moisture and organic impurities in the organic liquid; the drying temperature in the vacuum drying oven is 50-80°C

[0028] The beneficial effects of the present invention are:

[0029] 1. The present invention uses vanillin, an aromatic compound derived from lignin that can be mass-produced, as a raw material, which reduces the dependence of industries such as plastics and coatings on the petrochemical industry, and alleviates the problems of environmental pollution, excessive consumption and excessive carbonized material emissions during the conversion of fossil resources;

[0030] 2. Through molecular structure design and simple synthesis process, a precursor substance containing Schiff base structure is obtained, and the Schiff base structure of the flexible chain segment is reacted with DOPO to achieve the rigidity and flexibility of the flame retardant molecular structure, which not only improves the flame retardant efficiency of epoxy cured products, but also increases the toughness of epoxy resin cured products at the same time;

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

[0032] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. The drawings in the following description are merely embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying any creative work.

[0033] Figure 1 is the molecular structural formula of the precursor substance containing the Schiff base structure in the present invention;

[0034] Figure 2 is the molecular structural formula of the vanillin-based phosphorus-nitrogen flame retardant toughening agent of the present invention;

[0035] Figure 3 It is a flow chart of the steps of the preparation method of the present invention;

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

[0037] Figure 5 For Examples 2-4 and Comparative Example 1, N 2 TGA curve below;

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

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

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

[0041] Fig. 9 It is the total smoke production curve of Examples 2-4 of the present invention and Comparative Example 1. DETAILED DESCRIPTION

[0042] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0043] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0044] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, it indicates 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 field; unless otherwise specified, the experimental methods and technical means used were conventional methods and means in the field.

[0046] The starch-based epoxy resin and the preparation method thereof provided by the present invention are described below in conjunction with the embodiments, but the protection scope of the present invention is not limited by the following embodiments.

[0047] See also Figure 1-Figure 9 The present invention provides a technical solution: a vanillin-based phosphorus-nitrogen flame retardant toughening agent having a molecular structure such as Figure 2 shown.

[0048] On the other hand, a method for preparing the vanillin-based phosphorus-nitrogen flame retardant toughening agent is provided, and the preparation process is as follows: Figure 3 As shown, specifically including:

[0049] In the first stage, vanillin and dibasic fatty amine are fully mixed in an organic solvent, and reacted in a reaction vessel at 50-120° C. under nitrogen protection for 1-6 hours to obtain a precursor substance containing a Schiff base structure, which has the following characteristics: Figure 1 The molecular structure shown;

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

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

[0052] Furthermore, the mass ratio of vanillin, dibasic fatty amine and organic solvent is 5-100:1-50:50-500.

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

[0054] Furthermore, the purification process is to separate and dry the mixture system after the reaction.

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

[0056] Furthermore, in the drying step, a vacuum drying oven is used to dry the organic liquid to remove moisture and organic impurities in the organic liquid.

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

[0058] Furthermore, the dibasic fatty amines include, but are 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] Furthermore, the organic solvent is one or more combinations of alcohols, aromatic hydrocarbons, ketones, and ethers.

[0060] 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.

[0061] Embodiment 1:

[0062] Add vanillin (0.04 mol) and 1,6-hexanediamine (0.02 mol) to a 250 mL four-necked flask, and add 150 mL of N,N-dimethylacetamide under nitrogen protection. When the temperature reaches 80°C, continue stirring for 5 hours, and then cool the reaction system to 25°C. Then, slowly pour the mixed liquid into distilled water, let it stand and filter to obtain the reaction product, place it in a vacuum drying oven at 80°C and dry it for 24 hours to obtain a yellow powder, which is a precursor substance containing a Schiff base structure, with the following structural formula:

[0063]

[0064] The above-obtained precursor substance containing 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, stirring was continued for 5 h under reflux conditions at 60 ° C, and then naturally cooled to room temperature. The reaction product was separated by suction filtration, washed with anhydrous ethanol, and placed in a vacuum drying oven at 80 ° C for 24 h to obtain a brown-yellow powder, which is a vanillin-based phosphorus-nitrogen flame retardant toughening agent (VH-DOPO), which has the following structural formula:

[0065]

[0066] The infrared spectrum of the vanillin-based phosphorus-nitrogen flame retardant toughening agent is as follows Figure 4 As shown. Figure 4 It can be seen that in the spectrum of VH-DOPO, 754 cm -1 (PC) and 1297cm -1 The absorption peak of (CN) and the pH characteristic peak of DOPO are 2436cm -1 and VH C=N characteristic peak 1644cm -1 No, which indicates that vanillin first reacts with 1,6-hexanediamine through dehydration condensation to form a Schiff base structure, and then the active PH bond of DOPO and the Schiff base structure undergo an addition reaction, and the vanillin-based phosphorus-nitrogen flame retardant and toughening agent VH-DOPO is successfully prepared.

[0067] Embodiment 2:

[0068] After VH-DOPO (5g) and E51 epoxy resin (100g) were stirred and mixed at 140°C, the temperature was lowered to 80°C, and the curing agent 4,4'-diaminodiphenylmethane (DDM) (25g) was added. The mixture was stirred until it became uniform, and the mixture was poured into a polytetrafluoroethylene mold. Then, it was placed in a drying oven for curing reaction. The curing procedure was 120°C (2h), 150°C (2h), and 170°C (2h). The sample was slowly cooled to room temperature to obtain a flame retardant epoxy resin cured product VD-5. According to the standard ASTM D3801-20, this cured product reached UL-94V0 level. A thermogravimetric analyzer was used at N 2 The thermal stability of epoxy cured material VD-5 was tested in a cone calorimeter at 35kW / m 2 The flame retardant properties of epoxy cured material VD-5 were tested under radiation intensity. Figure 5-Figure 9 It can be seen that compared with E51 epoxy resin, the residual carbon rate of epoxy cured product VD-5 increased by 37.0% (800℃), the peak heat release rate decreased by 14.6%, the total heat release decreased by 12.0%, the peak smoke production rate decreased by 7.1%, and the total smoke production decreased by 30.4%, which shows that epoxy cured product VD-5 has good thermal stability and excellent flame retardant properties. According to the standard GB / T 1843-2008 test, the cantilever beam impact strength of E51 epoxy cured product and VD-5 are 22.8kJ / m 2 and 79.8 kJ / m 2 , an increase of 249.6%, which shows that the epoxy cured material VD-5 has excellent toughness.

[0069] Embodiment 3:

[0070] After VH-DOPO (10g) and E51 (100g) were stirred and mixed at 140°C, the temperature was lowered to 80°C, and the curing agent 4,4'-diaminodiphenylmethane (DDM) (25g) was added. The mixture was stirred until it became uniform, and the mixture was poured into a polytetrafluoroethylene mold. Then, it was placed in a drying oven for curing reaction. The curing procedure was 120°C (2h), 150°C (2h), and 170°C (2h). The sample was slowly cooled to room temperature to obtain a flame retardant epoxy resin cured product VD-10. According to the standard ASTMD3801-20, this cured product reached UL-94V0 level. A thermogravimetric analyzer was used at N 2 The thermal stability of epoxy resin VD-10 was tested in a cone calorimeter at 35kW / m 2 The flame retardant properties of epoxy resin cured material VD-10 were tested under radiation intensity. Figure 5-Figure 9It can be seen that compared with E51 epoxy resin, the residual carbon rate of epoxy resin cured product VD-10 increased by 46.0%, the peak value of heat release rate decreased by 29.1%, the total heat release decreased by 14.5%, the peak value of smoke production rate slightly increased by 3.6%, and the total smoke production decreased by 20.7%, which shows that epoxy cured product VD-10 has better thermal stability and more excellent flame retardant properties. According to the standard GB / T 1843-2008, the cantilever beam impact strength of this cured product is 70.3kJ / m 2 , an increase of 207.8% compared with E51 epoxy resin, which shows that the epoxy cured material VD-10 has excellent toughness.

[0071] Embodiment 4:

[0072] After VH-DOPO (15g) and E51 (100g) were stirred and mixed at 140°C, the temperature was lowered to 80°C, and the curing agent 4,4'-diaminodiphenylmethane (DDM) (25g) was added. The mixture was stirred until it became uniform, and the mixture was poured into a polytetrafluoroethylene mold. Then, it was placed in a drying oven for curing reaction. The curing procedure was 120°C (2h), 150°C (2h), and 170°C (2h). The sample was slowly cooled to room temperature to obtain epoxy cured product VD-15. According to the standard ASTM D3801-20, this cured product reached UL-94V0 level. A thermogravimetric analyzer was used at N 2 The thermal stability of epoxy cured material VD-15 was tested in a cone calorimeter at 35kW / m 2 The flame retardant properties of epoxy cured material VD-15 were tested under radiation intensity. Figure 5-Figure 9 It can be seen that compared with E51 epoxy resin, the residual carbon rate of epoxy cured product VD-15 increased by 53.1%, the peak heat release rate decreased by 59.3%, the total heat release decreased by 23.5%, the peak smoke generation rate decreased by 21.4%, and the total smoke generation decreased by 17.3%, which indicates that epoxy cured product VD-15 has better thermal stability and more excellent flame retardant properties. According to the standard GB / T 1843-2008, 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 shows that the epoxy cured material VD-15 has better toughness.

[0073] Comparative Example 1:

[0074] 100g E51 epoxy resin was mixed with 25g 4,4'-diaminodiphenylmethane (DDM) and the mixture was poured into a polytetrafluoroethylene mold. Then, it was placed in a drying oven for curing reaction. The curing procedures were 120℃ (2h), 150℃ (2h), and 170℃ (2h) to obtain epoxy cured product DGEBA. According to the standard ASTM D3801-20 test, the UL-94 test result of this cured product was no grade. The thermogravimetric analyzer was used at N 2 The thermal stability of E51 was tested in a cone calorimeter at 35 kW / m 2 The flame retardant properties of E51 epoxy resin were tested under radiation intensity. Figure 5-Figure 9 It can be seen that E51 epoxy resin 2 The residual carbon rate under the condition of 13.8% was 13.8%, the peak heat release rate, total heat release, peak smoke generation rate and total smoke generation of E51 epoxy resin were 816.9kW / m 2 、85.8MJ / m 2 、0.28m 2 / s and 35.8m 2 These results show that the E51 epoxy resin has low carbon residue and is easy to burn, and generates a lot of heat and toxic and harmful smoke during the combustion process. The cantilever beam impact strength of this cured product measured according to standard GB / T 1843-2008 is 22.8kJ / m 2 , which indicates that the toughness of this cured product is poor.

[0075] Comparative Example 2:

[0076] The vanillin-based phosphorus-nitrogen flame retardant and toughening agent prepared in Example 1 was used as a reference, except that an equal amount of 1,6-hexanediamine was replaced by 1,3-propylenediamine, and other conditions remained unchanged, to obtain a vanillin-based phosphorus-nitrogen flame retardant and toughening agent 2.

[0077] After the prepared vanillin-based phosphorus-nitrogen flame retardant toughener 2 (5 g) and E51 epoxy resin (100 g) were stirred and mixed at 140 ° C, the temperature was reduced to 80 ° C, and the curing agent 4,4'-diaminodiphenylmethane (DDM) (25 g) was added. The mixture was stirred until it became uniform, and the mixture was poured into a polytetrafluoroethylene mold. Then, it was placed in a drying oven for curing reaction. The curing procedure was 120 ° C (2 h), 150 ° C (2 h), and 170 ° C (2 h). The sample was slowly cooled to room temperature to obtain a flame retardant epoxy resin cured product 2. According to the standard ASTM D3801-20, this cured product reached V2 grade. A thermogravimetric analyzer was used at N 2 The thermal stability of epoxy cured products was tested in a cone calorimeter at 35kW / m 2The flame retardant properties of epoxy cured product 2 were tested under radiation intensity. Compared with the E51 epoxy resin in comparative example 1, the residual carbon rate of epoxy cured product 2 increased by 10.6% (800°C), 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%, which indicates that the epoxy cured product has poor thermal stability and poor flame retardant properties. According to the standard GB / T 1843-2008 test, the cantilever beam impact strength of E51 epoxy cured product and epoxy cured product 2 in comparative example 2 is 22.8 kJ / m 2 and 23.3 kJ / m 2 , an increase of 2.2%, which indicates that epoxy cured material 2 does not have excellent toughness.

[0078] Comparative Example 3:

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

[0080] After the prepared vanillin-based phosphorus-nitrogen flame retardant toughener 3 (5 g) and E51 epoxy resin (100 g) were stirred and mixed at 140 ° C, the temperature was reduced to 80 ° C, and the curing agent 4,4'-diaminodiphenylmethane (DDM) (25 g) was added. The mixture was stirred until it became uniform, and the mixture was poured into a polytetrafluoroethylene mold. Then, it was placed in a drying oven for curing reaction. The curing procedure was 120 ° C (2 h), 150 ° C (2 h), and 170 ° C (2 h). The sample was slowly cooled to room temperature to obtain a flame retardant epoxy resin cured product 3. According to the standard ASTM D3801-20, this cured product reached V1 level. Thermogravimetric analyzer was used at N 2 The thermal stability of epoxy cured product 3 was tested in a cone calorimeter at 35 kW / m 2 The flame retardant properties of epoxy cured product 3 were tested under radiation intensity. Compared with the E51 epoxy resin in comparative example 1, the residual carbon rate of epoxy cured product 3 increased by 15.6% (800°C), the peak value of heat release rate decreased by 14.7%, the total heat release decreased by 11.5%, the peak value of smoke production rate decreased by 8.4%, and the total smoke production decreased by 9.5%, which indicates that the epoxy cured product has poor thermal stability and poor flame retardant properties. According to the standard GB / T 1843-2008 test, the cantilever beam impact strength of E51 epoxy cured product and epoxy cured product 3 in comparative example 3 is 22.8 kJ / m 2 and 20.4 kJ / m 2 , which decreased by 10.5%, indicating that epoxy cured product 3 does not have excellent toughness.

[0081] Comparative Example 4:

[0082] The vanillin-based phosphorus-nitrogen flame retardant and toughening agent prepared in Example 1 was used as a reference, without adding 1,6-hexanediamine, and only vanillin and DOPO were directly reacted; other conditions remained unchanged, and vanillin-based phosphorus-nitrogen flame retardant and toughening agent 4 was obtained.

[0083] After the prepared vanillin-based phosphorus-nitrogen flame retardant toughener 4 (5 g) and E51 epoxy resin (100 g) were stirred and mixed at 140 ° C, the temperature was reduced to 80 ° C, and the curing agent 4,4'-diaminodiphenylmethane (DDM) (25 g) was added. The mixture was stirred until it became uniform, and the mixture was poured into a polytetrafluoroethylene mold. Then, it was placed in a drying oven for curing reaction. The curing procedure was 120 ° C (2 h), 150 ° C (2 h), and 170 ° C (2 h). The sample was slowly cooled to room temperature to obtain a flame retardant epoxy resin cured product 4. According to the standard ASTM D3801-20, this cured product reached V1 level. Thermogravimetric analyzer was used at N 2 The thermal stability of epoxy cured products was tested in a cone calorimeter at 35kW / m 2 The flame retardant properties of epoxy cured product 4 were tested under radiation intensity. Compared with the E51 epoxy resin in comparative example 1, the residual carbon rate of epoxy cured product 4 increased by 8.1% (800°C), the peak value of heat release rate decreased by 17.3%, the total heat release decreased by 15.4%, the peak value of smoke production rate decreased by 10.7%, and the total smoke production decreased by 11.5%, which indicates that epoxy cured product 4 has poor thermal stability and poor flame retardant properties. According to the standard GB / T 1843-2008 test, the cantilever beam impact strength of E51 epoxy cured product and epoxy cured product 4 in comparative example 4 is 22.8 kJ / m 2 and 15.3 kJ / m 2 , which decreased by 32.8%, indicating that epoxy cured material 4 cannot have excellent toughness.

[0084] Comparative Example 5:

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

[0086] After the prepared vanillin-based phosphorus-nitrogen flame retardant toughener 5 (5 g) and E51 epoxy resin (100 g) were stirred and mixed at 140°C, the temperature was lowered to 80°C, and the curing agent 4,4'-diaminodiphenylmethane (DDM) (25 g) was added, and 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 procedure was 120°C (2h), 150°C (2h), and 170°C (2h). The sample was slowly cooled to room temperature to obtain a flame retardant epoxy resin cured product 5. According to the standard ASTM D3801-20, the UL-94 test result of this cured product was measured to be no grade. A thermogravimetric analyzer was used at N 2 The thermal stability of epoxy cured products was tested in a cone calorimeter at 35kW / m 2 The flame retardant properties of epoxy cured product 5 were tested under radiation intensity. Compared with the E51 epoxy resin in comparative example 1, the residual carbon rate of epoxy cured product 5 increased by 2.6% (800°C), the peak value of heat release rate decreased by 4.5%, the total heat release decreased by 5.3%, the peak value of smoke production rate decreased by 8.6%, and the total smoke production decreased by 7.8%, which indicates that epoxy cured product 5 has poor thermal stability and poor flame retardant properties. According to the standard GB / T 1843-2008 test, the cantilever beam impact strength of E51 epoxy cured product and epoxy cured product 5 in comparative example 5 is 22.8 kJ / m 2 and 26.4 kJ / m 2 , an increase of 15.8%, which indicates that epoxy cured material 5 does not have excellent toughness.

[0087] In summary, the present invention provides a vanillin-based phosphorus-nitrogen flame retardant and toughening agent and a preparation method thereof, starting from the perspectives of the flammability of traditional epoxy resins, poor environmental protection, and high toxicity of traditional flame retardants. The vanillin-based aromatic compound derived from lignin that can be mass-produced is used as a raw material, and the Schiff base group of the flexible chain segment reacts with DOPO to form a phosphorus-nitrogen structure, thereby achieving the purpose of simultaneously improving the flame retardant efficiency and toughness of the epoxy resin. The cured epoxy resin system has excellent flame retardancy and toughness, and the preparation method thereof is highly operable, controllable, easy to implement, and conducive to industrial large-scale production.

[0088] At this point, those skilled in the art recognize that, although the embodiments of the present invention have been shown and described in detail herein, many other variations or modifications that conform to the principles of the present invention can still be directly determined or derived based on the contents disclosed in the present invention without departing from the spirit and scope of the present invention. Therefore, the scope of the present invention should be understood and recognized as covering all such other variations or modifications.

Claims

1. A vanillin-based phosphorus-nitrogen flame retardant toughening agent, characterized in that: The molecular structural formula of the flame retardant toughening agent is: Wherein, R is an aliphatic straight chain having 4 to 12 carbon atoms and its derivatives; In flame retardant applications, the vanillin-based phosphorus-nitrogen flame retardant toughening agent is added in an amount of 5wt%-10wt% in the epoxy resin.

2. The method for preparing the vanillin-based phosphorus-nitrogen flame retardant toughening agent according to claim 1, characterized in that: The preparation method comprises: Step S1: Preparation of precursor material containing Schiff base structure Vanillin and dibasic fatty amine 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. The molecular structure of the precursor substance containing a Schiff base structure is as follows: Wherein, R is an aliphatic straight chain having 4 to 12 carbon atoms and its derivatives; Step S2: Preparation of vanillin-based phosphorus-nitrogen flame retardant toughening agent 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 reacted in a reaction container; the mixture after the reaction is subjected to a purification process to obtain the vanillin-based phosphorus-nitrogen flame retardant and toughening agent, and the molecular structure of the vanillin-based phosphorus-nitrogen flame retardant and toughening agent is as follows: Wherein, R is an aliphatic straight chain having 4 to 12 carbon atoms and its derivatives.

3. The method for preparing the vanillin-based phosphorus-nitrogen flame retardant toughening agent according to claim 2, characterized in that: In the step S1, the mass ratio of vanillin, dibasic fatty amine and organic solvent is 5-100:1-50:50-500.

4. The method for preparing the vanillin-based phosphorus-nitrogen flame retardant toughening agent according to claim 2, characterized in that: In the step S1, the reaction temperature is 50-120° C., and the reaction time is 1-6 hours.

5. The method for preparing the vanillin-based phosphorus-nitrogen flame retardant toughening agent according to claim 2, characterized in that: In the step S1, the dibasic fatty 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 their derivatives.

6. The method for preparing the vanillin-based phosphorus-nitrogen flame retardant toughening agent according to claim 2, characterized in that: In step S1, the organic solvent is one or more combinations of alcohols, aromatic hydrocarbons, ketones, and ethers; 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.

7. The method for preparing the vanillin-based phosphorus-nitrogen flame retardant toughening agent according to claim 2, characterized in that: In the step S2, the mass ratio of the precursor 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.

8. The method for preparing the vanillin-based phosphorus-nitrogen flame retardant toughening agent according to claim 2, characterized in that: In the step S2, the reaction temperature is 60-100° C., and the reaction time is 2-8 hours.

9. The method for preparing the vanillin-based phosphorus-nitrogen flame retardant toughening agent according to claim 2, characterized in that: In step S2, the purification process includes separation and drying steps.

10. The method for preparing the vanillin-based phosphorus-nitrogen flame retardant and toughening agent according to claim 9, characterized in that: The separation step is specifically: using a vacuum filter to extract the organic solvent and washing it with anhydrous ethanol; the drying step is specifically: drying the organic liquid in a vacuum drying oven to remove moisture and organic impurities in the organic liquid; the drying temperature in the vacuum drying oven is 50-80°C.

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