Preparation method of bio-based low-temperature high-compressive-strength epoxy curing agent

Abstract

The invention relates to the technical field of material science and engineering, and discloses a preparation method of a bio-based low-temperature high-compressive-strength epoxy hardener, which comprises the following steps: weighing bisphenol A, cardanol, m-phenylenediamine, DMAPAPA, polyether amine D400 and a catalyst in parts by mass according to a formula, adding the materials into a four-neck flask, heating, stirring and dissolving, dropwise adding a 40% formaldehyde solution, and stirring for 20-30 minutes; controlling the temperature under the protection of nitrogen and carrying out precondensation reaction; starting a vacuum system to gradually heat, dehydrate and polycondense, heating to 180-185 DEG C, preserving heat, promoting molecular chain crosslinking, detecting compressive strength, glass transition temperature and gelation time indexes after the reaction is finished, adjusting if the indexes are not qualified, and cooling and discharging after the indexes are qualified to obtain the brown yellow viscous liquid curing agent, so that the solid content of the liquid curing agent is greater than or equal to 95%. Low-temperature promotion is realized by utilizing a tertiary amine structure of DMAPAPA, the toughness is improved by combining cardanol and polyether amine D400, the rigidity is enhanced by m-phenylenediamine, and the curing agent is endowed with excellent low-temperature curing performance and high compressive strength through cooperation of phenolic hydroxyl groups and tertiary amine.

Description

Technical Field

[0001] The present invention relates to the field of materials science and engineering technology, and in particular to a method for preparing a bio-based low-temperature and high-compressive strength epoxy curing agent. Background Art

[0002] In the field of materials science and engineering, the performance of epoxy curing agents directly affects the application scope and performance of epoxy resin composites. With the popularization of green environmental protection concepts and the growing demand for extreme environment engineering, the development of epoxy curing agents that combine bio-based properties, low-temperature curing capabilities, and high compressive strength has become a research hotspot. Traditional epoxy curing agents mostly rely on petrochemical raw materials and have low bio-based content, making it difficult to meet sustainable development requirements. In low-temperature environments, their slow curing speed and long gel time lead to low construction efficiency. At the same time, the insufficient compressive strength and thermal stability of the cured material limit its application in wind turbine tower bonding and polar engineering scenarios with strict requirements on mechanical properties and heat resistance. Although existing technologies have attempted to improve performance by introducing some bio-based raw materials or adjusting the formula, the problem of balancing bio-based content with mechanical properties and the inability to achieve both low-temperature curing efficiency and cured product strength remains. Therefore, a new preparation method is urgently needed to overcome the above technical bottlenecks and achieve a comprehensive improvement in the performance of epoxy curing agents. 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 a bio-based low-temperature, high-compressive strength epoxy curing agent, which has the advantages of high bio-based content, rapid low-temperature curing, high compressive strength and excellent thermal stability. It solves the problems of traditional epoxy curing agents such as the difficulty in balancing the bio-based components and mechanical properties, the inability to achieve both low-temperature curing efficiency and cured product strength, as well as low construction efficiency and limited application in extreme environments.

[0005] (2) Technical solution

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

[0007] S1. Prepare raw materials: weigh bisphenol A, cardanol, m-phenylenediamine, DMAPAPA, polyetheramine D400 and catalyst in the formula molar ratio;

[0008] S2. Mixing and dissolving raw materials: Add bisphenol A, cardanol, m-phenylenediamine, DMAPAPA, polyetheramine D400 and catalyst into a four-necked flask with a condenser, stir and heat to 60-90°C, and continue stirring until all solid raw materials are completely dissolved to form a uniform mixing system;

[0009] S3. Formaldehyde solution addition and pre-condensation reaction: Use a dropper to add 40% formaldehyde solution and control the drop rate. At the same time, introduce nitrogen protection to maintain the system temperature ≤ 95°C. After the addition is completed, keep the temperature at 90-95°C for 3.5-4 hours;

[0010] S4. Vacuum dehydration and polycondensation reaction: Start the vacuum system and gradually increase the temperature to 120-140°C at a heating rate of 1-2°C / min. Continue stirring and remove water from the system. When no distillate is produced, stop dehydration and continue heating.

[0011] S5. High temperature curing and cross-linking reaction: raise the temperature to 180-185°C and keep it for 1.5-2 hours to promote molecular chain cross-linking and network structure formation;

[0012] S6. Index testing and quality control: After the end of the insulation, take samples to test the compressive strength, glass transition temperature and gel time indicators. If they are unqualified, extend the insulation time or add catalyst;

[0013] S7. Cooling, discharging and post-processing: After the indicators are qualified, the temperature is lowered to below 100°C, the vacuum is broken, and the target product is discharged. The product is a brown-yellow viscous liquid curing agent with a solid content of ≥95%.

[0014] Preferably, the weight ratio of the raw materials is: 20-40 parts of bisphenol A; 30-50 parts of cardanol; 10-20 parts of m-phenylenediamine; 15-25 parts of DMAPAPA; 50-70 parts of polyetheramine D400; and 0.5-5 parts of catalyst.

[0015] Preferably, the amount of the catalyst used is 0.1% to 5% of the total raw material mass.

[0016] Preferably, the formaldehyde solution in S3 is added at a rate of 0.5-1 mL / min.

[0017] Preferably, the reaction formula of the formaldehyde solution dropwise addition and pre-condensation in S3 is:

[0018] Condensation of bisphenol A and formaldehyde:

[0019] HO-C6H4−C(CH3)2−C6H4−OH+HCHO→HO-C6H4−C(CH3)2−C6H4−O-CH2−OH

[0020] In the formula, HO-C6H4−C(CH3)2−C6H4−OH represents a bisphenol A molecule, and HCHO represents a formaldehyde molecule;

[0021] Condensation of cardanol and formaldehyde:

[0022] C 15 H 27−OH+HCHO→C 15 H 27 −O-CH2−OHC 15 H 27 −OH

[0023] Where C 15 H 27 −OH represents a cardanol molecule, and HCHO represents a formaldehyde molecule.

[0024] Preferably, the vacuum degree of the vacuum dehydration in S4 is ≥0.08 MPa.

[0025] Preferably, the vacuum dehydration and polycondensation reaction formula in S4 is:

[0026] HO-RO-CH2−OH+HO-R ， -O-CH2−OH→HO-RO-CH2−OR ， -OH+H2O

[0027] In the formula, HO-RO-CH2−OH represents a hydroxymethyl compound, HO-R ， -O-CH2 represents another hydroxymethyl compound.

[0028] Preferably, the high temperature curing and cross-linking reaction formula in S5 is:

[0029] DMAPAPA and epoxy ring-opening crosslinking:

[0030] DMAPAPA+epoxy→cross-linked network structure

[0031] In the formula, DMAPAPA molecules and epoxy groups form a cross-linked network structure through a ring-opening cross-linking reaction.

[0032] Preferably, the qualified indicators of the sampling test in S6 are: compressive strength ≥ 150 MPa, glass transition temperature Tg ≥ 80°C, and gel time ≤ 30 min.

[0033] Preferably, the overall molecular reaction formula of S1-S6 is:

[0034]

[0035] In the formula, under the action of a catalyst, bisphenol A, cardanol, formaldehyde, DMAPAPA, m-xylenediamine and polyetheramine D-400 undergo a condensation reaction to form an epoxy curing agent molecule with ultra-low temperature curing ability and high compressive strength.

[0036] Compared with the prior art, the present invention provides a method for preparing a bio-based low-temperature, high-compressive-strength epoxy curing agent, which has the following beneficial effects:

[0037] 1. The present invention achieves the beneficial effect of enhancing the bio-based properties and toughness of the curing agent by introducing the bio-based material cardanol and optimizing the raw material ratio. By using cardanol as the bio-based core component, not only can the bio-based content of the curing agent be increased, but also due to the presence of its long-chain hydrocarbon group, the toughness of the curing agent can be significantly enhanced. By precisely controlling the ratio of raw materials such as bisphenol A and cardanol, the rigidity and toughness of the curing agent are balanced, so that the curing agent has good flexibility while maintaining high strength.

[0038] 2. The present invention achieves the beneficial effects of shortening the gel time and improving the low-temperature curing ability by using DMAPAPA and precisely controlling the amount of catalyst. The tertiary amine structure in the molecular structure of DMAPAPA has a low-temperature promoting effect, which can effectively accelerate the epoxy ring-opening reaction and optimize the gel time and cross-linking density. At the same time, by precisely controlling the amount of catalyst, the reaction efficiency can be ensured, the gel time can be further shortened, and the low-temperature curing ability of the curing agent can be improved, so that the curing agent can be quickly cured even in a low-temperature environment.

[0039] 3. The present invention achieves the beneficial effect of improving the compressive strength and thermal stability of the curing agent through molecular structure design and process parameter control. By retaining the synergistic effect of multiple phenolic hydroxyl groups and tertiary amines, and through the temperature and time of high-temperature curing and cross-linking reactions, a bio-based epoxy curing agent with ultra-low temperature curing ability and the ability to impart high compressive strength to the cured product has been successfully developed. The curing agent of the present invention is superior to traditional curing agents in terms of compressive strength and glass transition temperature indicators, and shows excellent mechanical properties and thermal stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 A flow chart was prepared for the present invention. DETAILED DESCRIPTION

[0041] 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.

[0042] See also Figure 1 A method for preparing a bio-based low-temperature high-compressive strength epoxy curing agent comprises the following steps:

[0043] S1. Prepare raw materials: weigh bisphenol A (C 21 H 24 O2), cardanol (a long-chain unsaturated compound containing phenolic hydroxyl groups, the structural formula of which can be expressed as C 20 H32 O with a phenolic hydroxyl group −OH, where R is a long-chain hydrocarbon group), m-phenylenediamine (C6H8N2), DMAPAPA (an amine compound), polyetheramine D400 (H2N−(C2H 4O )n−C2H4−NH2, n makes the molecular weight about 400) and catalyst;

[0044] S2. Mixing and dissolving raw materials: Add bisphenol A (1 mol), cardanol (1 mol), m-phenylenediamine (1 mol), DMAPAPA (1 mol), polyetheramine D400 (1 mol) and catalyst into a four-necked flask with a condenser, stir and heat to 60-90°C, and continue stirring until all solid raw materials are completely dissolved to form a uniform mixing system;

[0045] S3. Formaldehyde solution addition and pre-condensation reaction: Use a dropper to add 4 mol of 40% formaldehyde solution, control the drop rate, and introduce nitrogen protection to maintain the system temperature ≤ 95°C. After the addition is completed, keep the temperature at 90-95°C for 3.5-4 hours;

[0046] S4. Vacuum dehydration and polycondensation reaction: Start the vacuum system and gradually increase the temperature to 120-140°C at a heating rate of 1-2°C / min. Continue stirring and remove water from the system. When no distillate is produced, stop dehydration and continue heating.

[0047] S5. High temperature curing and cross-linking reaction: raise the temperature to 180-185°C and keep it for 1.5-2 hours to promote molecular chain cross-linking and network structure formation;

[0048] S6. Index testing and quality control: After the end of the insulation, take samples to test the compressive strength, glass transition temperature and gel time. If they are unqualified, extend the insulation time or add catalyst (the formation of new group characteristic peaks or the weakening of the original group characteristic peaks through FTIR monitoring is used as the judgment standard);

[0049] S7. Cooling, discharging and post-processing: After the indicators are qualified, the temperature is lowered to below 100°C, the vacuum is broken, and the target product is discharged. The product is a brown-yellow viscous liquid curing agent with a solid content of ≥95%.

[0050] The advantages are: through molecular structure design and process parameter control, the beneficial effect of improving the compressive strength and thermal stability of the curing agent is achieved. Through ingenious molecular structure design, such as retaining the synergistic effect of multiple phenolic hydroxyl groups with tertiary amines, and through precise control of process parameters, such as the temperature and time of high-temperature curing and cross-linking reactions, a bio-based epoxy curing agent with ultra-low temperature curing ability and the ability to impart high compressive strength to the cured product has been successfully developed. The curing agent of the present invention is superior to traditional curing agents in terms of compressive strength and glass transition temperature indicators, and shows excellent mechanical properties and thermal stability.

[0051] Specifically, the mass ratio of the raw materials is as follows: 20-40 parts of bisphenol A, which serves as a rigid skeleton to provide mechanical strength. Too low a ratio will result in insufficient compressive strength, while too high a ratio will affect the low-temperature curing flexibility; 30-50 parts of cardanol, a bio-based core component, with long-chain hydrocarbon groups to enhance toughness, and the proportion must ensure that the bio-based content is greater than 30%; 10-20 parts of m-phenylenediamine, a highly active amine, promotes low-temperature cross-linking, and excessive amounts can easily lead to brittleness; 15-25 parts of DMAPAPA, a tertiary amine structure that accelerates epoxy ring opening and optimizes gel time and cross-linking density; 50-70 parts of polyetheramine D400, a flexible chain segment that adjusts the viscosity of the curing agent and enhances compatibility with epoxy resin; 0.5-5 parts of a catalyst, an organic metal compound (such as zinc acetylacetonate) that catalyzes the condensation reaction to ensure reaction efficiency.

[0052] Specifically, the amount of the catalyst used is 0.1% to 5% of the total raw material mass, and the concentration of the formaldehyde solution is between 39.95% and 40.05%.

[0053] Specifically, the formaldehyde solution in S3 is added at a rate of 0.5-1 mL / min.

[0054] Specifically, the reaction formula of the formaldehyde solution dropwise addition and pre-condensation in S3 is:

[0055] Condensation of bisphenol A and formaldehyde:

[0056] HO-C6H4−C(CH3)2−C6H4−OH+HCHO→HO-C6H4−C(CH3)2−C6H4−O-CH2−OH

[0057] In the formula, HO-C6H4−C(CH3)2−C6H4−OH represents a bisphenol A molecule, and HCHO represents a formaldehyde molecule;

[0058] Condensation of cardanol and formaldehyde:

[0059] C 15 H 27 −OH+HCHO→C 15 H 27 −O-CH2−OHC 15 H 27 −OH

[0060] Where C 15 H 27 −OH represents a cardanol molecule, and HCHO represents a formaldehyde molecule;

[0061] Formaldehyde (HCHO) undergoes a condensation reaction with compounds containing hydroxyl groups (-OH), such as bisphenol A and cardanol, to form new hydroxymethyl ether bonds (-O-CH2-O-).

[0062] The advantages are: by introducing the bio-based material cardanol and optimizing the raw material ratio, the beneficial effect of enhancing the bio-based characteristics and toughness of the curing agent is achieved. By using cardanol as the bio-based core component, not only the bio-based content of the curing agent can be increased, but also due to the presence of its long-chain hydrocarbon group, the toughness of the curing agent can be significantly enhanced. By precisely controlling the ratio of raw materials such as bisphenol A and cardanol, the rigidity and toughness of the curing agent are balanced, so that the curing agent has good flexibility while maintaining high strength.

[0063] Specifically, the vacuum degree of vacuum dehydration in S4 is ≥0.08 MPa.

[0064] Specifically, the vacuum dehydration and polycondensation reaction formula in S4 is: The reaction formula for the polycondensation of the hydroxymethyl compound to form an ether bond is:

[0065] HO-RO-CH2−OH+HO-R ， -O-CH2−OH→HO-RO-CH2−OR ， -OH+H2O

[0066] In the formula, HO-RO-CH2−OH represents a hydroxymethyl compound, HO-R ， -O-CH2 represents another hydroxymethyl compound, HO-RO-CH2−OR ， -OH represents the polymer formed by ether bond connection, H2O

[0067] Represents a water molecule.

[0068] Specifically, the high temperature curing and cross-linking reaction formula in S5 is:

[0069] DMAPAPA and epoxy ring-opening crosslinking:

[0070] DMAPAPA+epoxy→cross-linked network structure

[0071] In the formula, DMAPAPA represents a DMAPAPA molecule, epoxy represents an epoxy group, and cross-linked network structure represents a cross-linked network structure formed by a ring-opening cross-linking reaction;

[0072] In the above reaction formula, DMAPAPA (an amine compound) undergoes a ring-opening cross-linking reaction with the epoxy group to form a cross-linked network structure, which prompts the curing agent to form a high-strength network.

[0073] The advantages are: by using DMAPAPA and precisely controlling the amount of catalyst, the beneficial effects of shortening the gel time and improving the low-temperature curing ability are achieved. The tertiary amine structure in the molecular structure of DMAPAPA has a low-temperature promoting effect, which can effectively accelerate the epoxy ring-opening reaction and optimize the gel time and cross-linking density. At the same time, by precisely controlling the amount of catalyst, the reaction efficiency can be ensured, the gel time can be further shortened, and the low-temperature curing ability of the curing agent can be improved, so that the curing agent can be quickly cured even in a low-temperature environment.

[0074] Specifically, the qualified indicators of the sampling test in S6 are: compressive strength ≥ 150MPa, glass transition temperature Tg ≥ 80°C, and gel time ≤ 30min.

[0075] Specifically, the overall molecular reaction formula of S1-S6 is:

[0076]

[0077] In the formula, under the action of a catalyst, bisphenol A, cardanol, formaldehyde, DMAPAPA, m-xylenediamine and polyetheramine D-400 undergo a condensation reaction to form an epoxy curing agent molecule with ultra-low temperature curing ability and high compressive strength;

[0078] In this overall reaction formula, various raw materials undergo condensation reactions under the action of catalysts to form a complex polymer structure, namely an ultra-low temperature bio-based high compressive strength epoxy curing agent. This curing agent has excellent mechanical properties and low-temperature curing characteristics, and is suitable for the preparation of various high-performance materials.

[0079] The advantages are: the present invention uses bisphenol A as the main framework, and utilizes the tertiary amine structure with low-temperature promoting effect in the DMAPAPA molecular structure, which is grafted onto the bisphenol A molecule through a special chemical reaction and process. At the same time, the bio-based materials cardanol and D400 are introduced to improve the toughness of the cured product, and meta-xylylenediamine is introduced to provide the cured product with higher rigidity. In addition, multiple phenolic hydroxyl groups are retained in the new molecular structure, which synergistically act with the tertiary amine to jointly promote the low-temperature curing ability of the curing agent. Through clever material application and molecular structure design, a bio-based epoxy curing agent with ultra-low temperature curing ability and the ability to impart high compressive strength to the cured product has been successfully developed.

[0080] The parameters of the curing agent prepared by the present invention were compared with those of SBT competitors, and the data in Table 1 below were obtained:

[0081] Table 1

[0082]

[0083] From Table 1 we can get:

[0084] The curing agent of the present invention is a transparent orange-red liquid, while the SBT competitor is a colorless and transparent liquid. The difference in appearance may be related to the chemical composition of the curing agent, but does not affect the performance of the curing agent. The ammonia value of the curing agent of the present invention is 550, which is lower than the 896 of the SBT competitor. The ammonia value is an indicator of the free amine content in the curing agent. A lower ammonia value indicates that the curing agent has better stability. The active hydrogen equivalent (AHEW) of both is 65, indicating that the active hydrogen content of the two is comparable. The gel time of both at 0°C is 2 hours, indicating that the curing speed of the two is similar under low temperature conditions. Comparing typical performance parameters after curing, the glass transition temperature (Tg) of the curing agent of the present invention is 120°C, which is higher than the 85°C of the SBT competitor. The higher Tg value indicates that the curing agent has better thermal stability and heat resistance. The tensile strength of the curing agent of the present invention is 103 MPa, which is significantly higher than the 53 MPa of the SBT competitor, indicating that the curing agent of the present invention has better mechanical strength. The compressive strength of the curing agent of the present invention is 130 MPa, slightly higher than the 110 MPa of the SBT competitor, showing the advantage of the curing agent of the present invention in compressive performance.

[0085] In summary, the curing agent of the present invention outperforms SBT competitors in terms of thermal stability, mechanical strength, and compressive resistance, with a significant improvement in tensile strength in particular. These performance advantages make the curing agent of the present invention more suitable for the preparation of high-performance materials, especially in applications requiring high mechanical strength and heat resistance. In addition, the curing agent of the present invention also has ultra-low temperature curing capabilities, which makes it possible to use it in low-temperature environments.

[0086] The preparation steps of the present invention are presented in the Examples (curing agent of the present invention), and then compared with the Comparative Examples (traditional curing agent). The formula ratios (unit: part) of the Examples and Comparative Examples are shown in Table 2 below:

[0087] Table 2

[0088]

[0089] The examples and comparative examples were prepared into finished curing agents, and performance tests were performed. The test data are shown in Table 3 below:

[0090] Table 3

[0091]

[0092] From Table 2-3 we can get:

[0093] (1) Examples: The compressive strength of Examples 1-3 is greater than 150 MPa, which is better than that of the comparative example (the highest is 132 MPa); the low-temperature curing ability of the examples is higher than that of the comparative example, wherein the gel time is ≤30 min (Example 3 reaches 18 min), and the gel time of Comparative Example 2 is extended to 40 min due to the lack of DMAPAPA; the bio-based properties of the examples are better than those of the comparative example, wherein Example 2 has a 50% cardanol content and still maintains high strength (158 MPa), while Comparative Example 1 has high brittleness due to the lack of cardanol; the flexibility of the examples is better than that of the comparative example, wherein when the polyetheramine D400 in Examples 1-3 is sufficient, the curing agent has good flexibility, while Comparative Example 3 cracks due to insufficient D400.

[0094] (2) Comparative Example: Since Comparative Example 1 does not contain cardanol, its bio-based content is less than 30%, and its compressive strength and toughness are also significantly reduced. Since DMAPAPA is not added in Comparative Example 2, the tertiary amine structure is missing, the low-temperature curing ability of the curing agent is poor and the gel time is prolonged. Since the polyetheramine D400 in Comparative Example 3 is insufficient, the molecular chain flexibility of the formed curing agent is poor and it is easy to crack after curing.

[0095] Summary: The present invention achieves breakthroughs in ultra-low temperature curing (gel time ≤ 30 min), high compressive strength (≥150 MPa) and bio-based properties (cardanol content ≥30%) through the molecular design of bisphenol A-cardanol synergistic rigid skeleton, DMAPAPA low-temperature promotion, and polyetheramine D400 toughening, combined with precise control of process parameters. Its test performance is comprehensively superior to that of traditional comparative examples and can be applied to wind turbine tower bonding scenarios.

[0096] 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 a bio-based low-temperature high-compressive strength epoxy curing agent, characterized in that: The following steps are involved: S1. Prepare raw materials: weigh bisphenol A, cardanol, m-phenylenediamine, DMAPAPA, polyetheramine D400 and catalyst in the formula molar ratio; S2. Mixing and dissolving raw materials: Add bisphenol A, cardanol, m-phenylenediamine, DMAPAPA, polyetheramine D400 and catalyst into a four-necked flask with a condenser, stir and heat to 60-90°C, and continue stirring until all solid raw materials are completely dissolved to form a uniform mixing system; S3. Formaldehyde solution addition and pre-condensation reaction: Use a dropper to add 40% formaldehyde solution and control the drop rate. At the same time, introduce nitrogen protection to maintain the system temperature ≤ 95°C. After the addition is completed, keep the temperature at 90-95°C for 3.5-4 hours; S4. Vacuum dehydration and polycondensation reaction: Start the vacuum system and gradually increase the temperature to 120-140°C at a heating rate of 1-2°C / min. Continue stirring and remove water from the system. When no distillate is produced, stop dehydration and continue heating. S5. High temperature curing and cross-linking reaction: raise the temperature to 180-185°C and keep it for 1.5-2 hours to promote molecular chain cross-linking and network structure formation; S6. Index testing and quality control: After the end of the insulation, take samples to test the compressive strength, glass transition temperature and gel time indicators. If they are unqualified, extend the insulation time or add catalyst; S7. Cooling, discharging and post-processing: After the indicators are qualified, the temperature is lowered to below 100°C, the vacuum is broken, and the target product is discharged. The product is a brown-yellow viscous liquid curing agent with a solid content of ≥95%.

2. The method for preparing a bio-based low-temperature high-compressive strength epoxy curing agent according to claim 1, characterized in that: The raw materials are prepared in the following proportions by weight: 20-40 parts of bisphenol A; 30-50 parts of cardanol; 10-20 parts of m-phenylenediamine; 15-25 parts of DMAPAPA; 50-70 parts of polyetheramine D400; and 0.5-5 parts of a catalyst.

3. The method for preparing a bio-based low-temperature and high-compressive strength epoxy curing agent according to claim 1, characterized in that: The amount of the catalyst used is 0.1% to 5% of the total raw material mass.

4. The method for preparing a bio-based low-temperature and high-compressive strength epoxy curing agent according to claim 1, characterized in that: The formaldehyde solution in S3 has a dropping rate of 0.5-1 mL / min.

5. The method for preparing a bio-based low-temperature and high-compressive strength epoxy curing agent according to claim 1, characterized in that: The reaction formula of the formaldehyde solution dropwise addition and pre-condensation in S3 is: Condensation of bisphenol A and formaldehyde: HO-C6H4−C(CH3)2−C6H4−OH+HCHO→HO-C6H4−C(CH3)2−C6H4−O-CH2−OH In the formula, HO-C6H4−C(CH3)2−C6H4−OH represents a bisphenol A molecule, and HCHO represents a formaldehyde molecule; Condensation of cardanol and formaldehyde: C 15 H 27 −OH+HCHO→C 15 H 27 −O-CH2−OHC 15 H 27 −OH Where C 15 H 27 −OH represents a cardanol molecule, and HCHO represents a formaldehyde molecule.

6. The method for preparing a bio-based low-temperature and high-compressive strength epoxy curing agent according to claim 1, characterized in that: The vacuum degree of the vacuum dehydration in S4 is ≥0.08 MPa.

7. The method for preparing a bio-based low-temperature and high-compressive strength epoxy curing agent according to claim 1, characterized in that: The vacuum dehydration and polycondensation reaction formula in S4 is: HO-RO-CH2−OH+HO-R ， -O-CH2−OH→HO-RO-CH2−OR ， -OH+H2O In the formula, HO-RO-CH2−OH represents a hydroxymethyl compound, HO-R ， -O-CH2 represents another hydroxymethyl compound.

8. The method for preparing a bio-based low-temperature and high-compressive strength epoxy curing agent according to claim 1, characterized in that: The high temperature curing and cross-linking reaction formula in S5 is: DMAPAPA and epoxy ring-opening crosslinking: DMAPAPA+epoxy→cross-linked network structure In the formula, DMAPAPA molecules and epoxy groups form a cross-linked network structure through a ring-opening cross-linking reaction.

9. The method for preparing a bio-based low-temperature and high-compressive strength epoxy curing agent according to claim 1, characterized in that: The qualified indicators of the sampling test in S6 are: compressive strength ≥150MPa, glass transition temperature Tg ≥80°C, and gel time ≤30min.

10. The method for preparing a bio-based low-temperature and high-compressive strength epoxy curing agent according to claim 1, characterized in that: The overall molecular reaction formula of S1-S6 is: In the formula, under the action of a catalyst, bisphenol A, cardanol, formaldehyde, DMAPAPA, m-xylenediamine and polyetheramine D-400 undergo a condensation reaction to form an epoxy curing agent molecule with ultra-low temperature curing ability and high compressive strength.

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