Environment-friendly halogen-free flame-retardant epoxy resin composite material and preparation method thereof

Abstract

The invention relates to an environment-friendly halogen-free flame-retardant epoxy resin composite material and a preparation method thereof, the main raw materials of the composite material comprise epoxy resin and bio-based benzoxazine resin, and based on 100 phr of the epoxy resin and the bio-based benzoxazine resin, 5-10 phr of the bio-based benzoxazine resin is contained. The scheme provided by the invention has the advantages that by arranging the Bio-based BOZ resin, the mechanical property of the composite material can be effectively improved while the efficient flame retardant property can be realized.

Description

Technical Field

[0001] This application belongs to the technical field of flame-retardant resins, and relates to an environmentally friendly halogen-free flame-retardant epoxy resin composite material and a preparation method thereof. Background Technique

[0002] As a typical thermosetting polymer material, epoxy resin (EP) is widely used in national major strategic demand fields such as wind power, infrastructure, electronics and electrical, aerospace, and military due to its good processing characteristics, adhesion, mechanical properties, chemical stability, low shrinkage rate and other properties. However, pure EP resin usually starts to decompose at about 300 °C, and then shows strong combustion behavior, accompanied by a large amount of heat, combustible volatiles and smoke until the flame goes out and leaves a certain amount of char. Therefore, the limiting oxygen index (LOI) of pure EP is only 18.4%, and it has the disadvantages of being easy to burn, unable to self-extinguish and poor thermal stability of the carbon layer. Moreover, a large amount of heat and toxic fumes are released during combustion, seriously endangering the lives and property safety of personnel, and greatly restricting its use in high-safety fields such as aviation, military, railway transportation and marine engineering. Therefore, the flame-retardant modification technology of epoxy resin has attracted the attention of researchers around the world.

[0003] Based on the understanding of the combustion and thermal degradation process of EP resin, the key to the research on EP resin flame retardancy lies in improving the stability of the EP resin structure, or delaying its decomposition rate to improve char formation while reducing the release of combustibles, or capturing the highly active free radical compounds released during its degradation process to disrupt the combustion process of EP resin.

[0004] As a new type of phenolic resin, benzoxazine (BOZ) resin has good mechanical properties, high thermal stability and char-forming ability. Its oxazine ring structure undergoes a cross-linking reaction with epoxy groups under heating conditions, and can be used as a char-forming modifier to improve the stability of the carbon layer of EP resin for the purpose of flame retardant modification. Bio-based benzoxazine (Bio-based BOZ) resin prepared from bio-based compounds has rich functional groups (such as carboxyl group, aldehyde group, double bond, furan ring, etc.), which significantly promotes the ring-opening reaction of the oxazine ring. At the same time, it can also increase the hydrogen bond sites and cross-linking points in the structure, and improve the cross-linking density of the resin to achieve the purpose of improving char-forming ability. Therefore, Bio-based BOZ resin is far better than fossil-based BOZ resin in terms of char-forming performance, and through structural design, its curing temperature and high-temperature char residue rate can be regulated between 160 °C and 250 °C and between 30% and 63% respectively, and then it is easier to obtain a high-char-forming BOZ resin that matches the curing of EP resin. At the same time, the oxazine ring, carboxyl group, aldehyde group, olefin bond, and furan ring in the monomer structure of Bio-based BOZ resin can also undergo chemical cross-linking reactions with the epoxy groups in epoxy resin and the flame retardant 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) to form a "three-dimensional network structure", which can replace part of the curing agent to participate in the curing cross-linking reaction of EP resin and obtain excellent processing performance with lower temperature curing. Therefore, as long as the curing reaction is reasonably regulated to achieve the control of the "three-dimensional network structure", the goal of improving the poor carbon layer stability of the EP resin system and effectively enhancing the dispersibility and durability of the flame retardant DOPO can be achieved. At the same time, the "three-dimensional network structure" formed in the system makes the components form very tight hydrogen bond and chemical cross-linking interactions, greatly enhancing the ability of the EP / Bio-based BOZ / DOPO system to resist external stimuli, and thus can exhibit more excellent flame retardant and strengthening effects. It can be seen that the application of Bio-based BOZ resin in the field of flame retardant modification of EP resin has more obvious advantages, can obtain more excellent processing characteristics and char-forming ability, and is expected to improve the carbon layer stability of EP resin and achieve the balance of its high-efficiency flame retardancy and other comprehensive properties.

[0005] Therefore, by virtue of the advantages of Bio-based BOZ resin in char-forming performance, using the "three-dimensional network structure" constructed by Bio-based BOZ resin, EP resin, and flame retardant to solve the stubborn problems such as poor carbon layer stability of EP resin and difficulty in balancing flame retardancy and other comprehensive properties, and obtaining a flame retardant EP resin composite product with good flame retardant performance and mechanical properties has become an urgent technical problem in this field. Summary of the Invention

[0006] The objective of this application is to address the above problems existing in the prior art, and a halogen-free environmentally friendly flame-retardant epoxy resin composite material is proposed. By setting Bio-based BOZ resin, it can achieve high-efficiency flame-retardant performance while effectively improving the mechanical properties of the composite material.

[0007] To solve the above technical problems, the technical solution adopted in this application is as follows: An environmentally friendly halogen-free flame-retardant epoxy resin composite material. The main raw materials of this composite material include epoxy resin (EP) and bio-based benzoxazine (Bio-based BOZ) resin. Calculated based on 100 phr of EP / BOZ resin (100 phr of EP / BOZ resin means the sum of epoxy resin and bio-based benzoxazine (Bio-based BOZ) resin is 100 phr), it contains 5 - 10 phr of bio-based benzoxazine resin (that is, 5 - 10 parts by weight of bio-based benzoxazine resin are added relative to every 100 parts by weight of EP / BOZ resin).

[0008] Further, the epoxy resin (EP) includes: E-51 epoxy resin and MTHPA (methyltetrahydrophthalic anhydride) curing agent.

[0009] Further, this composite material also includes: DMP-30 (2,4,6-tris(dimethylaminomethyl)phenol) curing accelerator.

[0010] Further, calculated based on 100 phr of EP / BOZ resin, this composite material contains 54 - 58 phr of E-51 epoxy resin, 36 - 42 phr of MTHPA (methyltetrahydrophthalic anhydride) curing agent, and 0.180 - 0.200 phr of DMP-30 (2,4,6-tris(dimethylaminomethyl)phenol) curing accelerator.

[0011] Even further, calculated based on 100 phr of EP / BOZ resin, this composite material contains 5 - 10 phr of bio-based benzoxazine resin.

[0012] Further, the bio-based benzoxazine (Bio-based BOZ) resin includes one or more of PHA-fa, DPA-fa, PTL-fa, DZ-fa. The structural formulas (monomer structures, which form the polymerized resin after subsequent curing reactions) of the above bio-based benzoxazine (Bio-based BOZ) resins are shown as follows:

[0013]

[0014] Furthermore, the halogen-free environmentally friendly flame-retardant EP resin composite further comprises: 5-15 phr of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide flame retardant (DOPO) (i.e., 5-15 parts by weight of the flame retardant DOPO is added relative to every 100 parts by weight of the EP / BOZ resin).

[0015] Furthermore, the raw materials of the halogen-free environmentally friendly flame-retardant EP resin composite include: 54-58 phr of E-51 epoxy resin, 36-42 phr of MTHPA curing agent, 0.180-0.200 phr of DMP-30 curing accelerator, 5-10 phr of bio-based benzoxazine resin, and 5-15 phr of DOPO flame retardant.

[0016] This application also provides a preparation method of a halogen-free environmentally friendly flame-retardant epoxy resin composite, comprising:

[0017] (1) First, dry various raw materials for preparing the composite at a temperature of 80-100 °C for 4-5 h;

[0018] (2) Then, at 80-90 °C, add the bio-based BOZ resin to the EP-51 epoxy resin (EP-51), stir until completely dissolved, then add 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide flame retardant (DOPO) and stir until completely dissolved. Cool down to 50-60 °C and add the MTHPA curing agent and DMP-30 curing accelerator, and stir at a constant temperature for 5-15 min to obtain an EP mixture;

[0019] (4) Put the EP mixture obtained in step (3) into a vacuum oven to remove air bubbles; after completion, pour the EP mixture into a preheated mold and complete curing in a forced-air oven; finally, cold-press to room temperature to remove the mold release to obtain the composite.

[0020] Further, the raw materials for preparing the composite in step (1) include: 54-58 phr of E-51 resin, 36-42 phr of the curing agent MTHPA, 0.180-0.200 phr of the curing accelerator DMP-30, 5-10 phr of bio-based benzoxazine resin, and 5-15 phr of the flame retardant DOPO.

[0021] Further, the temperature in the vacuum oven in step (4) is 50-70 °C, and air bubbles are removed for 10-20 min.

[0022] Further, the curing temperature program corresponding to step (4) is 80 - 120°C for 3 - 5 h, then 120 - 140°C for 1 - 3 h, then 160 - 190°C for 1 - 3 h, and finally 190 - 220°C for 1 - 3 h; or 90 - 120°C for 3 - 5 h, then 120 - 140°C for 1 - 3 h, then 170 - 190°C for 1 - 3 h, then 190 - 220°C for 1 - 3 h, and finally 240 - 260°C for 1 - 3 h.

[0023] Advantages and beneficial effects of this application:

[0024] 1. This application selects a specific type of Bio-based BOZ resin, which can undergo a co-curing reaction with the EP resin and promotes the curing reaction of the epoxy resin, resulting in a decrease in its curing temperature; therefore, the environmentally friendly halogen-free flame-retardant EP resin composite material of this application has more excellent processing performance.

[0025] 2. The environmentally friendly halogen-free flame-retardant EP resin composite material of this application contains Bio-based BOZ resin. During the curing reaction process, the oxazine ring, carboxyl group, and furan ring (adjacent to the O atom) in it can undergo cross-linking reactions with the EP resin and the flame retardant DOPO, forming a three-dimensional network structure, thereby further increasing the cross-linking density of the composite material system and the compatibility of the flame retardant in the system, effectively improving its char-forming property and the durability of flame retardant modification.

[0026] 3. The selected Bio-based BOZ resin and flame retardant compound system in this application has excellent charring synergistic effect on the EP resin system, can significantly improve the charring property of the EP resin, and its char residue at 800°C under nitrogen conditions can be increased from 5.7% to 18.8%; in particular, by limiting the dosage of the Bio-based BOZ resin in this application, excellent charring synergistic effect can be effectively ensured within this dosage range.

[0027] 4. The limiting oxygen index (LOI) of the environmentally friendly halogen-free flame-retardant EP resin composite material prepared in this application is increased from 18.4% to 46.8%, the vertical burning test reaches UL94 V0 level, the ignition time (TTI) is extended to 53.0 s, and the fire safety index (FPI) is also increased from 0.07 to 0.17, with an increase amplitude as high as 142.9%, and the flame retardant modification effect is very significant.

[0028] 5. The oxazine ring, carboxyl group, and furan ring in the monomer structure of the selected Bio-based BOZ resin in this application can also undergo chemical cross-linking reactions with the epoxy groups in the epoxy resin and the flame retardant DOPO, constructing a "three-dimensional network structure" (specific reference Figure 2-3As shown in the figure, very strong hydrogen bonds and chemically cross-linked interactions are formed among its various components, greatly enhancing the ability of the EP / BOZ composite material system to resist external stimuli, and thus more excellent strengthening and toughening effects can be demonstrated. Therefore, the present invention enables the EP resin to maintain excellent mechanical properties while achieving excellent flame retardant modification effects.

[0029] 6. The preparation method of the environmentally friendly halogen-free flame retardant EP resin composite material of the present application is simple, flexible, has good stability, and low cost; it further expands the application fields of the Bio-based BOZ resin. Brief Description of the Drawings

[0030] Figure 1 It is the DSC curve of the flame retardant EP / BOZ resin composite materials prepared in the examples and comparative examples of the present application.

[0031] Figure 2 It is the in-situ FTIR diagram of the cross-linking reaction among several components in the flame retardant EP / BOZ resin composite materials prepared in the examples and comparative examples of the present application: (a) EP (E-51 / MTHPA / DMP-30); (b) 5DPA-fa / 10DOPO; (c) EP / 5DPA-fa; (d) EP / 10DOPO;

[0032] Figure 3 It is the schematic diagram of the cross-linked structure after curing of the flame retardant EP / BOZ resin composite materials prepared in the examples and comparative examples of the present application.

[0033] Figure 4 It is the TG (a) and DTG (b) curves of the flame retardant EP / BOZ resin composite materials prepared in the examples and comparative examples of the present application under N2 atmosphere.

[0034] Figure 5 It is the TG (a) and DTG (b) curves of the flame retardant EP / BOZ / DOPO resin composite materials prepared in the examples and comparative examples of the present application under N2 atmosphere. Detailed Embodiments

[0035] The following are specific examples of the present application, which further describe the technical solutions of the present application, but the present application is not limited to these examples.

[0036] For every 100 parts by weight of the EP / BOZ resin of the present application, 100 parts of the resin is the sum of three components: E-51, MTHPA curing agent, and Bio-based BOZ resin, which is 100 parts.

[0037] The PHA-fa of the present application can be obtained by the preparation method of the monomer of the biobased benzoxazine resin shown in Formula (I) in CN201911321743.8; the DPA-fa can be obtained by the synthesis method of the monomer of the biomass bisphenol acid-furfurylamine type benzoxazine resin in CN201810013847.1; the PTL-fa can be obtained by the synthesis method of the monomer of the biomass phenolphthalein-furfurylamine type benzoxazine resin in CN201810014012.8; the DZ-fa used can be obtained by the method involved in Biobased Benzoxazine Derived from Daidzein and Furfurylamine: Microwave-Assisted Synthesis and Thermal Properties Investigation (ChemSusChem, 2018, 11(18): 3175-3183).

[0038] Example 1

[0039] The halogen-free flame-retardant EP resin composite in this example contains 55 phr of EP resin (EP-51), 38 phr of curing agent MTHPA, 0.186 phr of curing accelerator DMP-30, and 7 phr of Bio-based BOZ resin (PHA-fa). The preparation process is as follows:

[0040] Add the PHA-fa resin monomer to the epoxy resin (EP-51) at 80 °C, stir until completely dissolved, cool down to 50 °C, then add the curing agent MTHPA and the curing accelerator DMP-30, and stir at a constant temperature for 5 min to obtain an EP mixture; then place the obtained EP mixture in a vacuum oven at 60 °C to remove air bubbles for about 10 min. After completion, pour the EP mixture into a mold preheated to 80 °C in advance, and complete the curing in a forced-air oven according to the curing temperature program of 100 °C / 4 h + 130 °C / 2 h + 180 °C / 2 h + 200 °C / 2 h + 250 °C / 2 h; finally, cold press to room temperature to remove the mold, and obtain a spline for test analysis. The specific properties are shown in Table 2-5.

[0041] Example 2

[0042] The halogen-free flame-retardant EP resin composite in this example contains 55 phr of EP resin (EP-51), 38 phr of curing agent MTHPA, 0.186 phr of curing accelerator DMP-30, and 7 phr of Bio-based BOZ resin (DPA-fa).

[0043] Compared with Example 1, the difference is that the raw material Bio-based BOZ resin in the halogen-free flame-retardant EP resin composite material is DPA-fa, and the preparation process of this composite material is as follows:

[0044] Add the DPA-fa resin monomer to the epoxy resin (EP-51) at 80 °C, stir until completely dissolved, cool down to 50 °C, then add the curing agent MTHPA and the curing accelerator DMP-30, and stir at a constant temperature for 5 min. Then put the obtained EP mixture into a vacuum oven at 60 °C to remove air bubbles for about 10 min. After completion, pour the EP mixture into a mold preheated to 80 °C in advance, and complete the curing in a forced-air oven according to the curing temperature program of 100 °C / 4 h + 130 °C / 2 h + 180 °C / 2 h + 200 °C / 2 h + 250 °C / 2 h. Finally, cold press to room temperature to remove the mold, and obtain the test specimens for analysis. The specific properties are shown in Table 2-5.

[0045] Example 3

[0046] This halogen-free flame-retardant EP resin composite material contains 55 phr of EP resin (EP-51), 38 phr of curing agent MTHPA, 0.186 phr of curing accelerator DMP-30, and 7 phr of Bio-based BOZ resin (PTL-fa).

[0047] Compared with Example 1, the difference is that the Bio-based BOZ resin of the halogen-free flame-retardant EP resin composite material is PTL-fa, and its preparation process is as follows:

[0048] Add the PTL-fa resin monomer to the epoxy resin (EP-51) at 80 °C, stir until completely dissolved, cool down to 50 °C, then add the curing agent MTHPA and the curing accelerator DMP-30, and stir at a constant temperature for 5 min. Then put the obtained EP mixture into a vacuum oven at 60 °C to remove air bubbles for about 10 min. After completion, pour the EP mixture into a mold preheated to 80 °C in advance, and complete the curing in a forced-air oven according to the curing temperature program of 100 °C / 4 h + 130 °C / 2 h + 180 °C / 2 h + 200 °C / 2 h + 250 °C / 2 h. Finally, cold press to room temperature to remove the mold, and obtain the test specimens for analysis. The specific properties are shown in Table 2-5.

[0049] Example 4

[0050] This halogen-free flame-retardant EP resin composite material contains 55 phr of EP resin (EP-51), 38 phr of curing agent MTHPA, 0.186 phr of curing accelerator DMP-30, and 7 phr of Bio-based BOZ resin (DZ-fa).

[0051] Compared with Example 1, the difference is that the Bio-based BOZ resin used in the halogen-free flame-retardant EP resin composite is DZ-fa, and the preparation process of the composite is as follows:

[0052] Add the DZ-fa resin monomer to the epoxy resin (EP-51) at 80 °C, stir until completely dissolved, cool down to 50 °C, then add the curing agent MTHPA and the curing accelerator DMP-30, and stir at a constant temperature for 5 min. Then put the obtained EP mixture into a vacuum oven at 60 °C to remove air bubbles for about 10 min. After completion, pour the EP mixture into a mold preheated to 80 °C in advance, and complete the curing in a forced-air oven according to the curing temperature program of 100 °C / 4 h + 130 °C / 2 h + 180 °C / 2 h + 200 °C / 2 h + 250 °C / 2 h. Finally, cold press to room temperature to remove the mold release, and obtain the test specimens for analysis. The specific properties are shown in Table 2-5.

[0053] Example 5

[0054] This halogen-free flame-retardant EP resin composite contains 56 phr of EP resin (EP-51), 39 phr of curing agent MTHPA, 0.190 phr of curing accelerator DMP-30, and 5 phr of Bio-based BOZ resin (PHA-fa).

[0055] Compared with Example 1, the difference is the change in the dosage of the Bio-based BOZ resin (PHA-fa) in the halogen-free flame-retardant EP resin composite, and the preparation process of the composite is as follows:

[0056] Add the PHA-fa resin monomer to the epoxy resin (EP-51) at 80 °C, stir until completely dissolved, cool down to 50 °C, then add the curing agent MTHPA and the curing accelerator DMP-30, and stir at a constant temperature for 5 min. Then put the obtained EP mixture into a vacuum oven at 60 °C to remove air bubbles for about 10 min. After completion, pour the EP mixture into a mold preheated to 80 °C in advance, and complete the curing in a forced-air oven according to the curing temperature program of 100 °C / 4 h + 130 °C / 2 h + 180 °C / 2 h + 200 °C / 2 h + 250 °C / 2 h. Finally, cold press to room temperature to remove the mold release, and obtain the test specimens for analysis. The specific properties are shown in Table 2-5.

[0057] Example 6

[0058] This halogen-free flame-retardant EP resin composite contains 54 phr of EP resin (EP-51), 36 phr of curing agent MTHPA, 0.180 phr of curing accelerator DMP-30, and 10 phr of Bio-based BOZ resin (PHA-fa).

[0059] Compared with Example 1, the difference lies in the change in the dosage of the Bio-based BOZ resin (PHA-fa) in the halogen-free flame-retardant EP resin composite. The preparation process of the composite is as follows:

[0060] Add the PHA-fa resin monomer to the epoxy resin (EP-51) at 80 °C, stir until completely dissolved, cool down to 50 °C, then add the curing agent MTHPA and the curing accelerator DMP-30, and stir at a constant temperature for 10 min. Then put the obtained EP mixture into a vacuum oven at 60 °C to remove air bubbles for about 10 min. After completion, pour the EP mixture into a mold preheated to 80 °C in advance, and complete the curing in a forced-air oven according to the curing temperature program of 100 °C / 4 h + 130 °C / 2 h + 180 °C / 2 h + 200 °C / 2 h + 250 °C / 2 h. Finally, cold press to room temperature to remove the mold, and obtain the test specimens for analysis. The specific properties are shown in Table 2-5.

[0061] Example 7

[0062] The halogen-free flame-retardant EP resin composite in this example contains 56 phr of epoxy resin (EP-51), 39 phr of curing agent MTHPA, 0.190 phr of curing accelerator DMP-30, 5 phr of Bio-based BOZ resin (PHA-fa), and 10 phr of flame retardant DOPO.

[0063] Compared with Example 1, the differences are as follows: 5 phr of the Bio-based BOZ resin (PHA-fa) with the same structure is used, and an additional 10 phr of flame retardant DOPO is also used. The preparation process is as follows:

[0064] Add the PHA-fa resin monomer to the epoxy resin (EP-51) at 90 °C, stir until completely dissolved, then add DOPO and stir until completely dissolved. Cool down to 60 °C, then add the curing agent MTHPA and the curing accelerator DMP-30, and stir at a constant temperature for 15 min. Then put the EP mixture into a vacuum oven at 60 °C to remove air bubbles for about 20 min. After completion, pour the EP mixture into a mold preheated to 80 °C in advance, and complete the curing in a forced-air oven according to the curing temperature program of 100 °C / 4 h + 130 °C / 2 h + 180 °C / 2 h + 200 °C / 2 h + 250 °C / 2 h. Finally, cold press to room temperature to remove the mold, and obtain the test specimens for analysis. The specific properties are shown in Table 2-5.

[0065] Example 8

[0066] The halogen-free flame-retardant EP resin composite material of this example contains 55 phr EP resin (EP-51), 38 phr curing agent MTHPA, 0.186 phr curing accelerator DMP-30, 7 phr Bio-based BOZ resin (PHA-fa), and 10 phr flame retardant DOPO.

[0067] Compared with Example 1, the difference is that: 7 phr of Bio-based BOZ resin (PHA-fa) with the same structure is used, and additionally 10 phr of flame retardant DOPO is used. The preparation process is as follows:

[0068] The PHA-fa resin monomer is added to the epoxy resin (EP-51) at 90 °C and stirred until completely dissolved. Then DOPO is added and stirred until completely dissolved. After cooling to 60 °C, the curing agent MTHPA and the curing accelerator DMP-30 are added, and the mixture is stirred at a constant temperature for 15 min. Then the EP mixture is placed in a vacuum oven at 60 °C to remove air bubbles for about 20 min. After completion, the EP mixture is poured into a mold preheated to 80 °C in advance and cured in a forced-air oven according to the curing temperature program of 100 °C / 4 h + 130 °C / 2 h + 180 °C / 2 h + 200 °C / 2 h + 250 °C / 2 h. Finally, it is cold-pressed to room temperature to remove the mold, and a spline for test analysis is obtained. The specific properties are shown in Table 2-5.

[0069] Example 9

[0070] The halogen-free flame-retardant EP resin composite material of this example contains 54 phr EP resin (EP-51), 36 phr curing agent MTHPA, 0.180 phr curing accelerator DMP-30, 10 phr Bio-based BOZ resin (PHA-fa), and 10 phr flame retardant DOPO.

[0071] Compared with Example 1, the difference is that: 10 phr of Bio-based BOZ resin (PHA-fa) with the same structure is used, and in addition, 10 phr of flame retardant DOPO is used. The preparation process is as follows:

[0072] The PHA-fa resin monomer was added to the epoxy resin (EP-51) at 90 °C and stirred until completely dissolved. Then DOPO was added and stirred until completely dissolved. After cooling to 60 °C, the curing agent MTHPA and the curing accelerator DMP-30 were added, and the mixture was stirred at a constant temperature for 15 min. Then the EP mixture was placed in a vacuum oven at 60 °C to remove air bubbles for about 20 min. After completion, the EP mixture was poured into a mold preheated to 80 °C in advance and cured in a forced-air oven according to the curing temperature program of 100 °C / 4 h + 130 °C / 2 h + 180 °C / 2 h + 200 °C / 2 h + 250 °C / 2 h. Finally, it was cold-pressed to room temperature to remove the mold release, and a test specimen for analysis was obtained. The specific properties are shown in Table 2-5.

[0073] Example 10

[0074] The halogen-free flame-retardant EP resin composite in this example contains 55 phr of EP resin (EP-51), 38 phr of curing agent MTHPA, 0.186 phr of curing accelerator DMP-30, 7 phr of Bio-based BOZ resin (DPA-fa), and 10 phr of flame retardant DOPO.

[0075] Compared with Example 1, the difference is that 7 phr of Bio-based BOZ resin (DPA-fa) with a different structure was used. In addition, 10 phr of flame retardant DOPO was additionally used. The preparation process is as follows:

[0076] The DPA-fa resin monomer was added to the epoxy resin (EP-51) at 90 °C and stirred until completely dissolved. Then DOPO was added and stirred until completely dissolved. After cooling to 60 °C, the curing agent MTHPA and the curing accelerator DMP-30 were added, and the mixture was stirred at a constant temperature for 15 min. Then the EP mixture was placed in a vacuum oven at 60 °C to remove air bubbles for about 20 min. After completion, the EP mixture was poured into a mold preheated to 80 °C in advance and cured in a forced-air oven according to the curing temperature program of 100 °C / 4 h + 130 °C / 2 h + 180 °C / 2 h + 200 °C / 2 h + 250 °C / 2 h. Finally, it was cold-pressed to room temperature to remove the mold release, and a test specimen for analysis was obtained. The specific properties are shown in Table 2-5.

[0077] Example 11

[0078] The halogen-free flame-retardant EP resin composite in this example contains 55 phr of EP resin (EP-51), 38 phr of curing agent MTHPA, 0.186 phr of curing accelerator DMP-30, 7 phr of Bio-based BOZ resin (PTL-fa), and 10 phr of flame retardant DOPO.

[0079] Compared with Example 1, the difference is that the raw materials of the halogen-free flame-retardant EP resin composite include: 7 phr of Bio-based BOZ resin (PTL-fa) with different structures and 10 phr of flame retardant DOPO. The preparation process is as follows:

[0080] Add the PTL-fa resin monomer to the epoxy resin (EP-51) at 90 °C, stir until completely dissolved, then add DOPO and stir until completely dissolved. Cool down to 60 °C and then add the curing agent MTHPA and the curing accelerator DMP-30, and stir at a constant temperature for 15 min. Then put the EP mixture into a vacuum oven at 60 °C to remove air bubbles for about 20 min. After completion, pour the EP mixture into a mold preheated to 80 °C in advance, and complete the curing in a forced-air oven according to the curing temperature program of 100 °C / 4 h + 130 °C / 2 h + 180 °C / 2 h + 200 °C / 2 h + 250 °C / 2 h. Finally, cold press to room temperature to remove the mold release, and obtain the test specimens for analysis. The specific properties are shown in Table 2-5.

[0081] Example 12

[0082] The halogen-free flame-retardant EP resin composite in this example contains 55 phr of EP resin (EP-51), 38 phr of curing agent MTHPA, 0.186 phr of curing accelerator DMP-30, 7 phr of Bio-based BOZ resin (DZ-fa), and 10 phr of flame retardant DOPO.

[0083] Compared with Example 1, the differences are as follows: 7 phr of Bio-based BOZ resin (DZ-fa) with different structures is used, and in addition, 10 phr of flame retardant DOPO is additionally added. The preparation process is as follows:

[0084] Add the DZ-fa resin monomer to the epoxy resin (EP-51) at 90 °C, stir until completely dissolved, then add DOPO and stir until completely dissolved. Cool down to 60 °C and then add the curing agent MTHPA and the curing accelerator DMP-30, and stir at a constant temperature for 15 min. Then put the EP mixture into a vacuum oven at 60 °C to remove air bubbles for about 20 min. After completion, pour the EP mixture into a mold preheated to 80 °C in advance, and complete the curing in a forced-air oven according to the curing temperature program of 100 °C / 4 h + 130 °C / 2 h + 180 °C / 2 h + 200 °C / 2 h + 250 °C / 2 h. Finally, cold press to room temperature to remove the mold release, and obtain the test specimens for analysis. The specific properties are shown in Table 2-5.

[0085] Comparative Example 1

[0086] In this comparative example, the halogen-free flame-retardant EP resin composite contains 58 phr of EP resin (EP-51), 42 phr of curing agent MTHPA, and 0.200 phr of curing accelerator DMP-30;

[0087] Compared with Example 1, the difference is that it does not contain Bio-based BOZ resin. The preparation process is as follows:

[0088] The curing agent MTHPA and the curing accelerator DMP-30 were added to the epoxy resin (EP-51) at 60 °C and stirred at a constant temperature for 5 min. Then the EP mixture was placed in a vacuum oven at 60 °C to remove air bubbles for about 10 min. After completion, the EP mixture was poured into a polytetrafluoroethylene mold preheated to 80 °C in advance and cured in a forced-air oven according to the curing temperature program of 100 °C / 4 h + 130 °C / 2 h + 180 °C / 2 h + 200 °C / 2 h. Finally, it was cold-pressed to room temperature to remove the mold, and the test specimens for analysis were obtained. The specific properties are shown in Table 2-5.

[0089] Comparative Example 2

[0090] In this comparative example, the halogen-free flame-retardant EP resin composite contains 58 phr of EP resin (EP-51), 42 phr of curing agent MTHPA, 0.200 phr of curing accelerator DMP-30, and 10 phr of flame retardant DOPO;

[0091] Compared with Example 1, the difference is that no bio-based benzoxazine resin was added, and only 10 phr of flame retardant DOPO was added. The preparation process is as follows:

[0092] DOPO was added to the epoxy resin (EP-51) at 90 °C and stirred until completely dissolved. After cooling to 60 °C, the curing agent MTHPA and the curing accelerator DMP-30 were added, and the mixture was stirred at a constant temperature for 15 min. Then the EP mixture was placed in a vacuum oven at 60 °C to remove air bubbles for about 20 min. After completion, the EP mixture was poured into a mold preheated to 80 °C in advance and cured in a forced-air oven according to the curing temperature program of 100 °C / 4 h + 130 °C / 2 h + 180 °C / 2 h + 200 °C / 2 h. Finally, it was cold-pressed to room temperature to remove the mold, and the test specimens for analysis were obtained. The specific properties are shown in Table 2-5.

[0093] The formulations of the flame-retardant EP resin composites corresponding to the above examples and comparative examples are shown in Table 1 below:

[0094] Table 1. Formulations of flame-retardant EP resin composites

[0095]

[0096] For the samples prepared in the examples and comparative examples of this application, the specific test results of various properties are shown in Table 2-5 below:

[0097] Table 2 Characteristic Temperatures of DSC Curves of Flame-Retardant EP Resin Composites

[0098]

[0099] Table 3 TG Data of Flame-Retardant EP Resin Composites

[0100]

[0101] Table 4 Flame Retardancy of Flame-Retardant EP Resin Composites

[0102]

[0103] Table 5 Mechanical Properties of Flame-Retardant EP Resin Composites

[0104]

[0105]

[0106] In Table 2-5:

[0107] T p1 and T p2 were measured by a differential scanning calorimeter (DSC) under a nitrogen atmosphere and a heating rate of 10 °C / min;

[0108] T 5％ 、T max 、Peak Value and the char residue amount Y c at 800 °C were measured by a thermogravimetric analyzer (TG) under a nitrogen atmosphere and a heating rate of 20 °C / min;

[0109] The test standard for the limiting oxygen index test (LOI) is GB / T 2406.2-2009;

[0110] The test standard for the vertical burning test is ASTM D6413;

[0111] The data of ignition time (TTI), peak heat release (pHRR) and total heat release enthalpy (THR) were obtained by cone calorimetry (Cone) test, and its test standard is ISO 5660-1:2002;

[0112] The fire safety index (FPI) was calculated based on the TTI and pHRR data measured by Cone: FPI = TTI / pHRR;

[0113] The test standard for tensile strength test is GB / T 1040.2-2006;

[0114] The test standard for impact strength test is GB / T 1843-2008.

[0115] According to Figure 1 and Table 2, it can be seen that for Comparative Example 1 pure EP resin, there is only one exothermic peak in the curing reaction in the presence of curing agent MTHPA and accelerator DMP-30, and its curing temperature is 162 °C. After adding 7 phr of the four Bio-based BOZ resins (PHA-fa, DPA-fa, PTL-fa, and DZ-fa) of this application to the EP / BOZ composites in Examples 1-4, the curing reaction of the EP / BOZ composites contains two exothermic peaks. The first curing temperature is reduced to between 140-150 °C, indicating that these four Bio-based BOZ resins have a co-curing reaction with epoxy resin and play a promoting role in the curing reaction of epoxy resin, resulting in a decrease in its curing temperature. At the same time, a small exothermic peak also appears between 230-260 °C, which is mainly due to the exothermic peak generated by the structural rearrangement of the Bio-based BOZ resin.

[0116] From Figure 2 (a), it can be seen that in the EP (E-51 / MTHPA / DMP-30) system, as the temperature increases, the absorption peaks of anhydride in MHHPA (at 1850 cm -1 and 1780 cm -1 , corresponding to the C=O and C-O stretching vibrations of cyclic anhydride) decrease with the increase of temperature, and completely disappear at 180 °C; at the same time, the absorption peak of epoxy group at 922 cm -1 decreases with the increase of curing temperature. At the same time, the absorption peak of C=O in the ester group at 1730 cm -1 increases with the increase of temperature. The changes of these peaks confirm that the epoxy groups in the EP resin react with the anhydride in the MTHPA curing agent to form a curing crosslinking reaction. From Figure 2 (b), it can be seen that in the 5DPA-fa / 10DOPO system, the absorption peak of carbonyl (carboxyl group) in the DPA-fa structure at 1714 cm -1 decreases with the increase of temperature, the characteristic peak of oxazine ring shifts from 939 cm -1 to 910 cm -1 , and decreases with the increase of temperature. The Ar-O-C stretching vibration peak at 1234 cm -1 connected to the oxazine ring and the characteristic peak of 1,2,4-trisubstituted benzene ring skeleton stretching vibration at 1498 cm -1 also decrease sharply. At the same time, the P-O-Ph of DOPO at 752 cm -1The absorption peaks also decreased significantly. These results fully demonstrate that the carboxyl group and oxazine ring structure in the DPA-fa structure underwent a co-curing crosslinking reaction with DOPO. From Figure 2 (c), it can be seen that in the EP / 5DPA-fa system, similar to the pure EP resin system, the absorption peaks at 1850 cm -1 and 1780 cm -1 decreased with the increase of the curing temperature, while the absorption peak at 1730 cm -1 increased. The characteristic peak of the oxazine ring in the DPA-fa structure at 939 cm -1 coincided with the absorption peak of the epoxy group at 922 cm -1 , and the peak area further decreased with the increase of temperature. At the same time, the absorption peaks of Ar-O-C at 1240 cm -1 and the 1,2,4-trisubstituted benzene ring at 1509 cm -1 both decreased with the increase of temperature. These results fully illustrate that co-curing reaction also occurred between EP and DPA-fa. The absorption peak of the furan ring in the DPA-fa structure at 1602 cm -1 broadened with the increase of temperature, indicating that substitution reaction occurred on the furan ring structure, further demonstrating that the furan ring participated in the crosslinking reaction during heating, thereby increasing the crosslinking density of the structure. From Figure 2 (d), it can be seen that in the EP / 10DOPO system, the absorption peaks of the epoxy group (922 cm -1 ) and P-O-Ph (754 cm -1 ) in the DOPO structure decreased with the increase of temperature, indicating that DOPO also underwent a crosslinking reaction with the epoxy group. It can be speculated from this that in the EP / DPA-fa / DOPO system, crosslinking reactions will occur between the epoxy group in the epoxy resin, the oxazine ring, furan ring, carboxyl group in the bio-based benzoxazine resin structure, and DOPO during curing, and a dense three-dimensional network structure can be formed (as shown in Figure 3 ).

[0117] According to Figure 4 , 5 and Table 3, for Comparative Example 1, the initial decomposition temperature T 5％ of the pure EP resin was 387.5 °C, the temperature T max at the maximum decomposition rate and the decomposition rate Peak Value were 422.4 °C and -26.2% / min respectively, and the char residue amount Y c at 800 °C was only 5.7%. In Comparative Example 2, after adding 10 phr of the flame retardant DOPO, T 5％ and T max decreased to 376.4 °C and 406.0 °C respectively due to the decomposition of DOPO, but Y cIt has been increased to 13.5%, indicating that the addition of DOPO can significantly slow down the decomposition rate of EP resin. After adding 7 phr of the four Bio-based BOZ resins (PHA-fa, DPA-fa, PTL-fa, and DZ-fa) of this application in Examples 1 to 4, the T of the EP / BOZ composite material 5％ has also decreased to a certain extent due to the co-curing between the Bio-based BOZ resin and the epoxy resin, but its Peak Value has decreased significantly, and its Y c has been greatly improved. After further adding 10 phr of the flame retardant DOPO in Examples 8, 10 to 12, the Y of the EP / BOZ composite material c has been further greatly improved. These results fully illustrate that the four Bio-based BOZ resins involved in this application can significantly improve the charring property of EP resin to achieve the purpose of improving the stability of its carbon layer, and at the same time, when compounded with the flame retardant DOPO, it shows excellent synergistic effect in improving the charring property of EP resin.

[0118] As can be seen from Table 4, the limiting oxygen index (LOI) of the neat EP resin in Comparative Example 1 was only 18.4, and there was no rating in the UL94 vertical burning test. After adding 10 phr of the flame retardant DOPO in Comparative Example 2, the LOI increased to 30.1%, and the UL94 vertical burning reached the V1 rating, indicating that DOPO had a certain flame retardant effect on the EP resin. After adding 7 phr of the four Bio-based BOZ resins (PHA-fa, DPA-fa, PTL-fa, and DZ-fa) of the present application in Examples 1 to 4, the LOI of the EP / BOZ composites also increased to some extent compared with Comparative Example 1, but there was still no rating in the UL94 vertical burning test. The results of Examples 1, 5, and 6 showed that as the addition amount of PHA-fa increased, the LOI of the EP / BOZ composites would further increase. After adding 10 phr of the flame retardant DOPO and 7 phr of the Bio-based BOZ resin in Examples 8, 10 to 12, the LOI of the EP / BOZ composites increased significantly again, and the UL94 vertical burning reached the V0 rating for all of them. The results of Examples 7 to 9 showed that further increasing the addition amount of the Bio-based BOZ resin was beneficial to improving the flame retardant performance of the EP / BOZ composites. At the same time, the results of Comparative Example 1, Comparative Example 2, Example 1, and Example 8 also showed that the compounding of DOPO and the Bio-based BOZ resin could significantly prolong the ignition time (TTI) of the EP resin, reduce the peak heat release rate (pHRR) and the total heat release enthalpy (THR) of the EP resin, and effectively improve the fire safety index (FPI) of the EP / BOZ composites. These results fully demonstrated that the four Bio-based BOZ resins involved in the present application could improve the flame retardant performance of the EP resin, and the compounding with the flame retardant DOPO showed excellent synergistic effects in improving the flame retardant performance of the EP resin. This was mainly because BOZ mainly acted through the condensed-phase flame retardant mechanism, while DOPO mainly acted through the gas-phase flame retardant mechanism. The compounding of the two in the EP resin system combined the condensed-phase and gas-phase flame retardant mechanisms and exhibited excellent flame retardant synergistic effects.

[0119] As can be seen from Table 5, the tensile strength and impact strength of the neat EP resin in Comparative Example 1 were 62.8 MPa and 8.9 kJ / m 2 , respectively. The tensile strength of Comparative Example 2 with 10 phr of the flame retardant DOPO added decreased to 53.4 MPa, while the impact strength increased to 10.8 kJ / m 2, indicating that DOPO causes significant damage to the tensile properties of the EP resin system. After adding 7 phr of the four Bio-based BOZ resins (PHA-fa, DPA-fa, PTL-fa, and DZ-fa) of this application in Examples 1 to 4, the tensile strength and impact strength of the EP / BOZ composites are significantly improved, and high mechanical properties can be maintained when added at 5 - 10 phr (Examples 1, 5, and 6), indicating that the crosslinking of Bio-based BOZ resin and EP resin is beneficial to improving the mechanical properties of EP resin. From the results of Examples 7 to 12, it can be seen that adding 10 phr of the flame retardant DOPO also causes a decrease in the tensile strength and impact strength of the EP / BOZ composites, but compared with Comparative Example 1, its tensile strength and impact strength are still improved to a certain extent. These results show that Bio-based BOZ resin can effectively improve the mechanical properties of the flame-retardant EP resin system. This is mainly because the oxazine ring, carboxyl group, and furan ring in the monomer structure of Bio-based BOZ resin can also undergo chemical crosslinking reactions with the epoxy groups in epoxy resin and the flame retardant DOPO, and a "three-dimensional network structure" can be constructed in the system, enabling very strong hydrogen bonding and chemically crosslinked interactions to form between its components, greatly enhancing the ability of the EP / BOZ composite system to resist external stimuli, and thus showing more excellent strengthening and toughening effects.

[0120] In summary, the environmentally friendly halogen-free flame-retardant EP resin system of the present application can effectively improve its curing process and the stability of the carbon layer, achieving a dual improvement in the flame retardancy and mechanical properties of the EP resin composite, and solving the technical problems of poor carbon layer stability and difficulty in balancing flame retardancy and other comprehensive properties in the flame-retardant modification of EP resin.

[0121] The specific embodiments described herein are merely illustrative of the spirit of the present application. Those skilled in the art of the present application can make various modifications or supplements to the described specific embodiments or use similar methods for substitution, but will not deviate from the spirit of the present application or exceed the scope defined by the appended claims.

Claims

1. An environmentally friendly halogen-free flame-retardant epoxy resin composite material, characterized in that: The main raw materials of the composite material include epoxy resin and bio-based benzoxazine resin. Calculated based on 100 phr of epoxy resin and bio-based benzoxazine resin, it contains 5 - 10 phr of bio-based benzoxazine resin.

2. The environmentally friendly halogen-free flame-retardant epoxy resin composite material according to claim 1, wherein: The epoxy resin mentioned above includes E-51 epoxy resin and MTHPA curing agent.

3. The environmentally friendly halogen-free flame-retardant epoxy resin composite material according to claim 2, wherein: The composite material also includes DMP-30 curing accelerator.

4. The environmentally friendly halogen-free flame-retardant epoxy resin composite material according to claim 3, wherein: Calculated based on 100 phr of epoxy resin and bio-based benzoxazine resin, the composite material contains 54 - 58 phr of E-51 epoxy resin, 36 - 42 phr of MTHPA curing agent, and 0.180 - 0.200 phr of DMP-30 curing accelerator.

5. The environmentally friendly halogen-free flame-retardant epoxy resin composite material according to claim 1, wherein: The bio-based benzoxazine resin includes one or more of PHA-fa, DPA-fa, PTL-fa, DZ-fa. The structural formulas of the above-mentioned bio-based benzoxazine resins are shown as follows:

6. The environmentally friendly halogen-free flame-retardant epoxy resin composite material according to any one of claims 1-5, characterized in that: The raw materials of the composite material also include: 5 - 15 phr of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide flame retardant.

7. The environmentally friendly halogen-free flame-retardant epoxy resin composite material according to claim 6, wherein: The raw materials of the composite material include: 54 - 58 phr of E-51 epoxy resin, 36 - 42 phr of MTHPA curing agent, 0.180 - 0.200 phr of DMP-30 curing accelerator, 5 - 10 phr of bio-based benzoxazine resin, and 5 - 15 phr of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide flame retardant.

8. A preparation method of the environmentally friendly halogen-free flame-retardant epoxy resin composite material according to claim 7, characterized in that: Including: (1) First, dry various raw materials for preparing the composite material at a temperature of 80 - 100 °C for 4 - 5 h respectively; (2) Then, at 80 - 90 °C, add the bio-based BOZ resin to the EP-51 epoxy resin and stir until completely dissolved. Then add the 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide flame retardant and stir until completely dissolved. Cool down to 50 - 60 °C and then add the MTHPA curing agent and DMP-30 curing accelerator, and stir at a constant temperature for 5 - 15 min to obtain an EP mixture; (4) Put the EP mixture obtained in step (3) into a vacuum oven to remove air bubbles; after completion, pour the EP mixture into a preheated mold and complete curing in a forced-air oven; finally, cold-press to room temperature to remove the mold release to obtain the composite material.

9. The preparation method of the environment-friendly halogen-free flame-retardant epoxy resin composite material according to claim 8, wherein: The various raw materials for preparing the composite material mentioned in step (1) include: 54 - 58 phr of E-51 epoxy resin, 36 - 42 phr of MTHPA curing agent, 0.180 - 0.200 phr of DMP-30 curing accelerator, 5 - 10 phr of bio-based benzoxazine resin, and 5 - 15 phr of DOPO flame retardant.

10. The preparation method of the environment-friendly halogen-free flame-retardant epoxy resin composite material according to claim 8, wherein: The temperature in the vacuum oven described in step (4) is 50 - 70°C, and air bubbles are evacuated for 10 - 20 min; the curing temperature program described in step (4) is 80 - 120°C for 3 - 5 h, then 120 - 140°C for 1 - 3 h, then 160 - 190°C for 1 - 3 h, and finally 190 - 220°C for 1 - 3 h; or 90 - 120°C for 3 - 5 h, then 120 - 140°C for 1 - 3 h, then 170 - 190°C for 1 - 3 h, then 190 - 220°C for 1 - 3 h, and finally 240 - 260°C for 1 - 3 h.

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