Preparation method of ultrahigh-temperature-resistant bio-based epoxy curing agent

Abstract

The invention relates to the technical field of epoxy resin curing agents, and discloses a preparation method of an ultrahigh-temperature-resistant bio-based epoxy curing agent, which comprises the following steps: preparing 220-240 parts by mass of cardanol in advance; 432 to 450 parts by mass of m-phenylenediamine; 300-350 parts by mass of a formaldehyde solution; the preparation method comprises the following steps: sequentially carrying out primary condensation reaction on the raw materials in parts by mass: 94-100 parts of phenol and 10-30 parts of perchloric acid solution, dissolving cardanol and m-phenylenediamine, dropwise adding a formaldehyde solution, and carrying out segmented heating, heat preservation and dehydration; carrying out primary dehydration and phenol addition, and carrying out acid catalytic reaction to crosslink the phenolic resin prepolymer; according to the preparation method, more amino cross-linking points are introduced through secondary condensation, finally, final curing and secondary dehydration are conducted, and the product is obtained. According to the preparation method, the heat resistance, rigidity, toughness, cross-linking density and toughness of the curing agent are improved by conducting multi-point grafting on a benzene ring structure amino group in anacardol molecules; and molecules contain phenolic hydroxyl groups, so that the reaction activity of the curing agent is improved, and finally, the performance requirements of high-performance materials on high temperature resistance and high strength in multiple fields are effectively met.

Description

Technical Field

[0001] The present invention relates to the technical field of epoxy resin curing agents, in particular to a method for preparing an ultra-high temperature resistant bio-based epoxy curing agent. Background Art

[0002] In modern industry, the demand for high-performance materials is growing, especially in aerospace, automotive manufacturing, electronics, and energy storage. These applications typically require materials with excellent high-temperature resistance, good mechanical strength and toughness, as well as environmental sustainability. Although traditional phenolic epoxy curing agents meet the high-temperature resistance requirements to a certain extent, they are insufficient in terms of toughness and environmental friendliness. Therefore, the development of a new type of ultra-high-temperature resistant bio-based epoxy curing agent to improve the material's heat resistance, toughness, and environmental friendliness has become an important topic in the field of materials science. Summary of the Invention

[0003] (1) Technical problems solved

[0004] In response to the shortcomings of the existing technology, the present invention provides a method for preparing an ultra-high-temperature resistant bio-based epoxy curing agent, which has the advantages of high-temperature resistance, high mechanical strength, balanced toughness and environmental sustainability. It solves the problems of traditional phenolic epoxy curing agents such as insufficient toughness, low bio-based content, and steric hindrance in the synthesis process, which makes it difficult to meet the stringent requirements of high-end application scenarios.

[0005] (2) Technical solution

[0006] To achieve the above object, the present invention provides the following technical solution: a method for preparing an ultra-high temperature resistant bio-based epoxy curing agent, comprising the following steps:

[0007] Step 1: Prepare raw materials: prepare cardanol, m-phenylenediamine, formaldehyde solution, phenol and perchloric acid solution;

[0008] Step 2, primary condensation reaction: add cardanol and m-phenylenediamine into a reactor, stir and heat to 65-70°C for complete dissolution, add formaldehyde solution dropwise, keep warm for 3.5-4 hours after the addition is complete, heat to 115-120°C and dehydrate at normal pressure for 0.8-1 hour, continue to heat to 145-150°C and keep warm for 1.5-2 hours;

[0009] Step 3: First dehydration and phenol addition: Cool to 75-80°C and perform vacuum dehydration, add phenol and stir evenly;

[0010] Step 4: Acid-catalyzed reaction: add perchloric acid solution dropwise, and heat to 85-90°C and keep warm for 4-5 hours;

[0011] Step 5, secondary condensation and heating: add the remaining m-phenylenediamine, cool to 68-70°C, then add the remaining formaldehyde solution dropwise, and perform heat preservation-heating-heating;

[0012] Step 6: Final solidification and second dehydration: Continue to heat to 175-180°C and keep warm for 1-1.2 hours; cool down and vacuum dehydrate, then discharge the material to obtain the target product.

[0013] Preferably, the raw materials and their preparation weight parts in step 1 are: 220-240 weight parts of cardanol; 432-450 weight parts of m-phenylenediamine; 300-350 weight parts of formaldehyde solution; 94-100 weight parts of phenol, and 10-30 weight parts of perchloric acid solution.

[0014] Preferably, the molar ratio of the raw materials of cardanol, m-phenylenediamine, formaldehyde and phenol is 1:4:4:1.

[0015] Preferably, the concentration of the formaldehyde solution is between 36.95% and 37.05%.

[0016] Preferably, when the formaldehyde solution is added dropwise in step 2, the solution temperature is controlled to be ≤95° C., and the initial condensation reaction formula is:

[0017] Cardanol+HCHO+m-PDA Mannich Bridge Structure + H20

[0018] In the formula, cardanol and m-phenylenediamine undergo a Mannich reaction under the action of formaldehyde to generate an intermediate containing a Mannich bridge.

[0019] Preferably, during the addition of phenol in step three, the temperature is controlled between 55-60°C.

[0020] Preferably, when the perchloric acid solution is added dropwise in step 4, the temperature is controlled to be ≤70°C.

[0021] Preferably, after the remaining formaldehyde solution is added dropwise in step 5, the temperature is kept at 90-95° C. for 2-2.1 hours; and the temperature is raised to 145-150° C. and kept for 1.8-2 hours.

[0022] Preferably, the second dehydration temperature in step six is ​​85-90°C.

[0023] Preferably, the overall chemical molecular reaction formula of steps 1 to 6 is:

[0024]

[0025] In the formula, the phenolic hydroxyl group of cardanol and the amino group of m-phenylenediamine are connected through a hydroxymethylation reaction of formaldehyde to form a Mannich bridge. Phenol and formaldehyde condense under acidic conditions to form a phenolic resin skeleton. The Mannich bridge and the phenolic network are cured at high temperature to form an interpenetrating polymer network.

[0026] Compared with the prior art, the present invention provides a method for preparing an ultra-high temperature resistant bio-based epoxy curing agent, which has the following beneficial effects:

[0027] 1. The present invention improves the heat resistance of the cured product by inserting benzene ring structure amino groups at multiple points in the cardanol molecule, so that its glass transition temperature exceeds the temperature of traditional phenolic curing agents, and the thermal weight loss temperature is also increased accordingly. Because the molecule contains phenolic hydroxyl groups, the reaction activity of the curing agent is also improved, so that the curing agent of the present invention has better thermal stability in high temperature environments. This high heat resistance makes it suitable for aircraft engine components, high-temperature reactors and other high-temperature application scenarios.

[0028] 2. The present invention introduces long side chains of cardanol to enhance the toughness of the cured product and increase the impact toughness, thereby overcoming the brittleness of traditional amine curing agents. This improvement enables the curing agent of the present invention to exhibit better performance in applications that need to withstand impact and vibration, such as carbon fiber composites and power battery packaging.

[0029] 3. The curing agent of the present invention has a high bio-based content. Cardanol is derived from cashew nut shell liquid, which is a renewable resource and shows good environmental properties. In addition, by precisely controlling the raw material ratio and reaction conditions, the side reactions in the preparation process are reduced, and the by-product content is controlled at a low level to further improve the environmental protection and purity of the curing agent. This high bio-based content and low by-product characteristics make the curing agent of the present invention have important application value in the pursuit of sustainable development and environmental protection in modern industry. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 A flow chart was prepared for the present invention. DETAILED DESCRIPTION

[0031] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0032] See also Figure 1 A method for preparing an ultra-high temperature resistant bio-based epoxy curing agent comprises the following steps:

[0033] Step 1: Raw material preparation: Prepare cardanol, m-phenylenediamine, formaldehyde solution, phenol, and perchloric acid solution. By using cardanol as the core raw material, which is derived from cashew nut shell liquid and is a renewable resource, it complies with environmental regulations and reduces dependence on petrochemical raw materials. Accurately setting the raw material mass parts and molar ratios can ensure that each reactant can fully participate in the subsequent reaction, avoid side reactions caused by excessive or insufficient raw materials, and ensure the consistency and stability of the product. By strictly controlling the concentration of the formaldehyde solution, its reaction activity can be stabilized, making the reaction process easier to control, thereby improving the yield and quality of the target product.

[0034] Step 2, primary condensation reaction: add cardanol and m-phenylenediamine to a reactor, stir and heat to 65-70°C for complete dissolution, add formaldehyde solution dropwise, keep warm for 3.5-4 hours after the addition is complete, heat to 115-120°C and dehydrate at normal pressure for 0.8-1 hour, continue to heat to 145-150°C and keep warm for 1.5-2 hours, and dissolve cardanol and m-phenylenediamine at 65-70°C. This temperature can ensure that both are fully dissolved and avoid excessive temperature causing decomposition of raw materials or premature side reactions; Adding formaldehyde solution dropwise and controlling the temperature to ≤95°C can ensure a smooth reaction, promoting a full Mannich reaction between the phenolic hydroxyl groups of cardanol and the amino groups of m-phenylenediamine under the action of formaldehyde, generating an intermediate containing a Mannich bridge. This intermediate structure lays the foundation for the subsequent formation of a polymer with excellent high-temperature resistance. The staged heating, insulation, and dehydration operations can gradually remove the water generated by the reaction, promote the reaction in the positive direction, increase the polymerization degree and purity of the intermediate, and enhance the heat resistance and rigidity of the final curing agent.

[0035] Step 3, first dehydration and phenol addition: After cooling to 75-80°C, vacuum dehydration is performed, and phenol is added and stirred evenly. Vacuum dehydration can more thoroughly remove moisture in the system, preventing residual moisture from affecting subsequent reactions. Adding phenol at a set temperature for addition reaction is conducive to the condensation reaction of phenol as a comonomer with the Mannich intermediate to form a phenolic resin prepolymer, further enriching the molecular structure of the polymer and enhancing the thermal stability and crosslinking density of the curing agent. At the same time, this temperature will not cause excessive volatilization of phenol, ensuring efficient utilization of raw materials.

[0036] Step 4, acid-catalyzed reaction: adding perchloric acid solution dropwise, raising the temperature to 85-90°C and keeping it warm for 4-5 hours after the addition is complete. Controlling the temperature of the perchloric acid addition can avoid catalyst decomposition or violent reaction caused by excessive temperature, thereby ensuring a smooth catalytic process. Carrying out the catalytic reaction under heat preservation conditions can promote the full cross-linking reaction of the phenolic resin prepolymer to form a three-dimensional network structure, thereby increasing the cross-linking density and toughness of the curing agent, and making the final cured product have better mechanical properties and high temperature resistance.

[0037] Step 5, secondary condensation and heating: Add the remaining m-phenylenediamine, cool to 68-70°C, then add the remaining formaldehyde solution dropwise, keep warm-heat-keep warm, and add m-phenylenediamine and formaldehyde solution a second time for condensation reaction, which can introduce more amino cross-linking points, further enhance the cross-linking ability of the curing agent, and improve the cross-linking density and toughness of the cured product; the staged heat preservation and temperature increase operation can fully carry out the reaction, ensure that the newly added raw materials react fully with the existing polymer, form a more complete molecular network structure, and thus improve the stability and durability of the curing agent in a high temperature environment;

[0038] Step 6. Final curing and second dehydration: Continue to heat to 175-180℃ and keep warm for 1-1.2 hours; cool down and vacuum dehydrate, then discharge the material to obtain the target product. Final curing is carried out under high temperature conditions to fully cure the cross-linked phenolic resin, forming a high-temperature resistant three-dimensional cross-linked network, and achieving the performance requirements of the curing agent's ultra-high temperature tolerance (>300℃); vacuum dehydration is carried out again to help completely remove the trace moisture and low-boiling point impurities remaining in the reaction process, improve the purity and quality of the product, and make the final ultra-high temperature resistant bio-based epoxy curing agent have excellent comprehensive performance, meeting the high-end application scenarios of aircraft structural parts and engine components.

[0039] Specifically, the raw materials and their preparation weight parts in step 1 are: 220-240 weight parts of cardanol; 432-450 weight parts of m-phenylenediamine; 300-350 weight parts of formaldehyde solution; 94-100 weight parts of phenol, and 10-30 weight parts of perchloric acid solution.

[0040] Specifically, the molar ratio of the raw materials of cardanol, m-phenylenediamine, formaldehyde and phenol is 1:4:4:1.

[0041] Specifically, the concentration of the formaldehyde solution is between 36.95% and 37.05%.

[0042] Specifically, when the formaldehyde solution is added dropwise in step 2, the solution temperature is controlled to be ≤95° C., and the initial condensation reaction formula is:

[0043] Cardanol + HCHO + m-PDA Mannich Bridge Structure + H20

[0044] In the formula, cardanol and m-phenylenediamine (m-PDA) undergo a Mannich reaction under the action of formaldehyde (HCHO) to generate an intermediate containing a Mannich bridge. The specific structure is that the phenolic hydroxyl group of cardanol and the amino group of m-phenylenediamine are connected by a methylene bridge.

[0045] Specifically, during the addition of phenol in step 3, the temperature is controlled between 55-60° C., and the reaction formula for the first dehydration and phenol addition is:

[0046] Mannich intermediate + PhOH Phenolic resin prepolymer + H2O

[0047] In the formula, phenol (PhOH) participates in the polycondensation reaction as a comonomer and further condenses with the Mannich intermediate.

[0048] Specifically, when the perchloric acid solution is added dropwise in step 4, the temperature is controlled to be ≤70° C., and the acid-catalyzed reaction formula is:

[0049] Phenolic prepolymer Cross-linked phenolic resin + H2O

[0050] In the formula, perchloric acid (HClO4) catalyzes the cross-linking reaction of phenolic resin prepolymer to form a three-dimensional network structure.

[0051] Specifically, after the remaining formaldehyde solution is added dropwise in step 5, the temperature is kept at 90-95° C. for 2-2.1 hours; the temperature is raised to 145-150° C. and kept for 1.8-2 hours. The secondary condensation reaction formula is:

[0052] m-PDA+HCHO Mannich bridge containing amino group + H2O

[0053] In the formula, the remaining m-phenylenediamine reacts with formaldehyde again to undergo a Mannich reaction, introducing more amino cross-linking points.

[0054] Specifically, the second dehydration temperature in step 6 is 85-90° C., and the curing reaction formula is:

[0055] Cross-linked phenolic resin Ultra-high temperature resistant bio-based epoxy curing agent (cured material)

[0056] In the formula, the cross-linked phenolic resin is cured at high temperature (180°C) to form a high-temperature resistant three-dimensional cross-linked network.

[0057] The advantage is that the special synthesis process of steps one and six helps to overcome the technical difficulty of being greatly affected by steric hindrance in grafting macromolecules containing benzene ring structure amino groups at multiple points in the cardanol molecule.

[0058] Specifically, the overall chemical molecular reaction formula of steps 1 to 6 is:

[0059]

[0060] In the formula, the phenolic hydroxyl group of cardanol and the amino group of m-phenylenediamine are connected through a hydroxymethylation reaction of formaldehyde to form a Mannich bridge (-CH2-NR-CH2-) with excellent heat resistance. Phenol and formaldehyde condense under acidic conditions to form a phenolic resin skeleton, enhancing thermal stability. The Mannich bridge and the phenolic network form an interpenetrating polymer network (IPN) through high-temperature curing, achieving ultra-high temperature tolerance (>300°C). Cardanol (derived from cashew nut shell liquid) and phenol (which can be partially replaced by bio-based materials) give the material renewable properties.

[0061] The advantages are: by inserting benzene ring structure amino groups at multiple points in the cardanol molecule, the heat resistance, rigidity, toughness, cross-linking density and toughness of the cured product can be greatly improved. Since the molecule contains phenolic hydroxyl groups, the reaction activity of the curing agent can also be improved.

[0062] The parameters of the curing agent prepared above were compared with existing competitive products, and the following Table 1 was obtained:

[0063] Table 1

[0064]

[0065] As shown in Table 1, in terms of typical performance parameters before curing, the curing agent of the present invention has a brown-red powder crystal appearance, which is significantly different from the light yellow powder crystals of the competing product. The nitrogen value reaches 513, which is higher than the 452 of the competing product. According to the CS113 standard, a higher nitrogen value means that it contains more nitrogen atom groups in its molecular structure. These groups can provide more active sites in the subsequent curing reaction, thereby enhancing the reaction degree between the curing agent and the epoxy resin. The active hydrogen equivalent is 43, which is lower than the 62 of the competing product. According to theoretical calculation principles, the lower the active hydrogen equivalent, the more active hydrogen is contained at the same mass. This enables the curing agent of the present invention to achieve sufficient curing with a smaller amount when reacting with the epoxy resin, thereby reducing the cost of use. Its melting point is 152°C, which is lower than the 177°C of the competing product. The lower melting point of the curing agent helps it to melt and disperse more easily during the actual processing, reduce the processing temperature requirements, and improve production efficiency.

[0066] In terms of typical performance parameters after curing, the curing agent of the present invention has more prominent advantages. Its glass transition temperature (Tg) reaches 240°C, far exceeding the 180°C of competing products. According to the GB / T40396-2021 standard, the higher Tg indicates that the material cured with the curing agent of the present invention can still maintain good mechanical properties and dimensional stability in high-temperature environments, making it more suitable for aircraft engine components, high-temperature reactors, and other high-temperature application scenarios; the tensile strength of the curing agent of the present invention is 105 MPa, which is 44% higher than the 73 MPa of competing products. According to the GB.T1040.1-2018 standard, the excellent tensile strength makes the material cured with the curing agent of the present invention less likely to break when subjected to external tensile force, and can be used to manufacture structural parts that need to withstand large tensile forces. The Shore hardness (Shore D) of the curing agent of the present invention is 95, higher than the 88 of competing products. According to the GB / T2411-2008 standard, higher hardness means that the material surface has a stronger ability to resist deformation, can effectively resist wear and scratches, and improve the durability of the material.

[0067] In summary, the key performance parameters of the curing agent of the present invention before and after curing are superior to those of competing products, showing excellent comprehensive performance, and possessing market competitiveness and application value in application fields requiring high temperature, high strength, and high hardness.

[0068] Example 1

[0069] Step 1: Prepare raw materials: prepare cardanol, m-phenylenediamine, formaldehyde solution, phenol and perchloric acid solution;

[0070] Step 2, primary condensation reaction: add 1 mol of cardanol and 2 mol of m-phenylenediamine to a reactor, stir and heat to 70°C until completely dissolved; add 2 mol of formaldehyde solution dropwise, control the temperature to ≤95°C, and keep warm for 4 hours after the addition is complete; heat to 120°C and dehydrate at normal pressure for 1 hour, then continue to heat to 150°C and keep warm for 2 hours;

[0071] Step 3: First dehydration and phenol addition: cool to 80°C and vacuum dehydrate; add 1 mol of phenol and stir evenly, controlling the temperature at 60°C;

[0072] Step 4, acid-catalyzed reaction: add perchloric acid solution dropwise, control the temperature ≤ 70°C, and raise the temperature to 90°C and keep warm for 4 hours after the addition is completed;

[0073] Step 5, secondary condensation and heating: add the remaining 2 mol of m-phenylenediamine, cool to 70°C, then add 2 mol of formaldehyde solution dropwise, keep warm at 95°C for 2 hours; heat to 150°C and keep warm for 2 hours;

[0074] Step 6: Final curing and post-treatment: Continue heating to 180°C and keep warm for 1 hour; cool to 90°C and vacuum dehydrate, then discharge the material to obtain the target product.

[0075] Example 2

[0076] Step 1: 230 parts of cardanol, 440 parts of m-phenylenediamine, 320 parts of 37% formaldehyde, 97 parts of phenol, and 20 parts of perchloric acid. Step 2: Dissolve at 65°C, add formaldehyde dropwise in three steps (85 / 90 / 95°C), dehydrate at 120°C for 0.8h, and keep warm at 148°C for 1.8h.

[0077] Step 3: vacuum dehydration at 78°C, adding phenol in two batches;

[0078] Step 4: perchloric acid catalysis in stages (65→75℃);

[0079] Step 5: The secondary condensation was carried out by temperature programming (70 → 90 °C / 2h → 150 °C / 1.5h);

[0080] Step 6: Final curing at 175°C, vacuum dehydration temperature at 88°C.

[0081] Example 3

[0082] Step 1, 240 parts of cardanol, 432 parts of m-phenylenediamine, 350 parts of 37% formaldehyde, 100 parts of phenol, and 30 parts of perchloric acid;

[0083] Step 2: Dissolve at 70°C, pre-cool to 50°C, and then add formaldehyde dropwise (to inhibit side reactions);

[0084] Step 3: Add nano-silica after dehydration (to enhance rigidity);

[0085] Step 4: Use alternating heating method (85℃ / 2h→cooling to 70℃ / 2h);

[0086] Step 5: Introducing ultrasonic-assisted dispersion process;

[0087] Step 6: Segmented curing (180℃ / 0.5h→200℃ / 0.5h).

[0088] Comparative Example 1

[0089] Phenol was used to completely replace cardanol, and other raw materials and steps remained unchanged.

[0090] Comparative Example 2

[0091] The perchloric acid catalysis step was eliminated, and the other raw materials and steps remained unchanged.

[0092] Comparative Example 3

[0093] The molar ratio of m-phenylenediamine to formaldehyde was changed to 1:2, and the other raw materials and steps remained unchanged.

[0094] After the examples and comparative examples were made into finished curing agents, performance tests were conducted. The test data are shown in Table 2 below:

[0095] Table 2

[0096]

[0097] As shown in Table 2 above, through the IPN structure of the Mannich bridge (-CH2-NR-CH2-) and the phenolic network, the Tg of the embodiment exceeds 300°C, which is more than 20% higher than that of traditional phenolic curing agents (usually <250°C). The embodiments of the present invention surpass traditional phenolic curing agents in terms of heat resistance. The toughening effect of the long side chain of cardanol in the embodiments of the present invention enables the impact toughness to reach 30 kJ / m², overcoming the brittle defect of traditional amine curing agents (<15 kJ / m²) and achieving a toughness balance. The gradient addition of formaldehyde and staged dehydration in the embodiments of the present invention reduce side reactions by 13% (GC-MS detection of by-product content <0.8%), giving the curing agent of the present invention a process advantage. The biobased content in the embodiments of the present invention reaches up to 45%, meeting the EU REACH regulation requirement of ≥30% for biobased materials and meeting environmental requirements.

[0098] The finished curing agent of Example 3 of the present invention was applied to a practical scenario, and the following data in Table 3 were obtained:

[0099] Table 3

[0100]

[0101] Summary: By comparing and analyzing the data in Tables 2-3 above, the breakthrough progress of the curing agent of the present invention in high-temperature stability, environmental properties and comprehensive mechanical properties is fully presented. It can be applied to aircraft structural parts, engine components, power battery packaging, lightweight body parts, high-power electronic components and semiconductor device packaging, high-temperature reactors, heat exchangers, carbon fiber composites, high-temperature resistant structural adhesives and PCB substrate pressure measurement and curing scenarios.

[0102] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing an ultra-high temperature resistant bio-based epoxy curing agent, characterized in that: The following steps are involved: Step 1: Prepare raw materials: prepare cardanol, m-phenylenediamine, formaldehyde solution, phenol and perchloric acid solution; Step 2, primary condensation reaction: add cardanol and m-phenylenediamine into a reactor, stir and heat to 65-70°C for complete dissolution, add formaldehyde solution dropwise, keep warm for 3.5-4 hours after the addition is complete, heat to 115-120°C and dehydrate at normal pressure for 0.8-1 hour, continue to heat to 145-150°C and keep warm for 1.5-2 hours; Step 3: First dehydration and phenol addition: Cool to 75-80°C and perform vacuum dehydration, add phenol and stir evenly; Step 4: Acid-catalyzed reaction: add perchloric acid solution dropwise, and heat to 85-90°C and keep warm for 4-5 hours; Step 5, secondary condensation and heating: add the remaining m-phenylenediamine, cool to 68-70°C, then add the remaining formaldehyde solution dropwise, and perform heat preservation-heating-heating; Step 6: Final solidification and second dehydration: Continue to heat to 175-180°C and keep warm for 1-1.2 hours; cool down and vacuum dehydrate, then discharge the material to obtain the target product.

2. The method for preparing an ultra-high temperature resistant bio-based epoxy curing agent according to claim 1, wherein: The raw materials and their preparation weight parts in step 1 are: 220-240 weight parts of cardanol; 432-450 weight parts of m-phenylenediamine; 300-350 weight parts of formaldehyde solution; 94-100 weight parts of phenol; and 10-30 weight parts of perchloric acid solution.

3. The method for preparing an ultra-high temperature resistant bio-based epoxy curing agent according to claim 1, wherein: The raw material molar ratio of the cardanol, m-phenylenediamine, formaldehyde and phenol is 1:4:4:

1.

4. The method for preparing an ultra-high temperature resistant bio-based epoxy curing agent according to claim 1, wherein: The concentration of the formaldehyde solution is between 36.95% and 37.05%.

5. The method for preparing an ultra-high temperature resistant bio-based epoxy curing agent according to claim 1, wherein: When the formaldehyde solution is added dropwise in step 2, the solution temperature is controlled to be ≤95° C. The initial condensation reaction formula is: Cardanol+HCHO+m-PDA Mannich Bridge Structure + H20 In the formula, cardanol and m-phenylenediamine undergo a Mannich reaction under the action of formaldehyde to generate an intermediate containing a Mannich bridge.

6. The method for preparing an ultra-high temperature resistant bio-based epoxy curing agent according to claim 1, characterized in that: During the addition of phenol in step 3, the temperature is controlled between 55-60°C.

7. The method for preparing an ultra-high temperature resistant bio-based epoxy curing agent according to claim 1, characterized in that: When the perchloric acid solution is added dropwise in step 4, the temperature is controlled to be ≤70°C.

8. The method for preparing an ultra-high temperature resistant bio-based epoxy curing agent according to claim 1, wherein: After the remaining formaldehyde solution is added dropwise in step 5, the mixture is kept at 90-95° C. for 2-2.1 hours; and the mixture is heated to 145-150° C. and kept for 1.8-2 hours.

9. The method for preparing an ultra-high temperature resistant bio-based epoxy curing agent according to claim 1, characterized in that: The second dehydration temperature in step 6 is 85-90°C.

10. The method for preparing an ultra-high temperature resistant bio-based epoxy curing agent according to claim 1, characterized in that: The overall chemical molecular reaction formula of steps 1 to 6 is: In the formula, the phenolic hydroxyl group of cardanol and the amino group of m-phenylenediamine are connected through a hydroxymethylation reaction of formaldehyde to form a Mannich bridge. Phenol and formaldehyde condense under acidic conditions to form a phenolic resin skeleton. The Mannich bridge and the phenolic network are cured at high temperature to form an interpenetrating polymer network.

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