Low viscosity epoxy curing agent based on renewable raw materials and process for its preparation

Abstract

The application relates to the field of epoxy curing agents, and particularly discloses a low-viscosity epoxy curing agent based on renewable raw materials and a preparation method thereof. The raw materials used in the epoxy curing agent include cashew phenol maleic acid amine, furfural, amine and a chain extender, wherein the molar ratio of the cashew phenol maleic acid amine, the furfural and the amine is (0.8-1.2):(1.0-1.5):(1.5-2.5), and the amount of the chain extender is 6-7% of the total mass of the raw materials. The epoxy curing agent has low viscosity, does not need to add an organic solvent when used in combination with an epoxy resin, significantly reduces the VOC volatilization of the entire protective coating system, uses renewable resources as much as possible to replace petroleum resources as raw materials, reduces chemical pollution and harm to the environment, and meets the requirements of social sustainable development.

Description

Technical Field

[0001] This application relates to the field of epoxy curing agents, and more specifically, to a low-viscosity epoxy curing agent based on renewable raw materials and a method for preparing the same. Background Technology

[0002] Two-component systems composed of epoxy resin and epoxy curing agent have wide applications in the industrial field. With the continuous development of industry, the requirements for material performance are also increasing. This two-component system, with its low curing shrinkage, excellent adhesion, heat resistance, chemical resistance, mechanical properties, and electrical properties, plays a vital role in many fields such as floor coatings, anti-corrosion coatings, adhesives, and composite materials, greatly promoting the development of related industries and improving product quality and performance. Among these, the epoxy curing agent, as an important component of the epoxy resin system, plays a crucial role in the performance of the epoxy system through its selection.

[0003] Currently, amine-based epoxy curing agents are the most common type available in the market. The typical preparation method involves synthesizing phenol or its derivatives with aldehydes and amines via a Mannich condensation reaction. This method has been used in the industry for many years and is a relatively mature technology. It utilizes raw materials extracted from resources such as petroleum and obtains the desired epoxy curing agent through specific chemical reactions, thus meeting market demand for epoxy curing agents to a certain extent.

[0004] However, this preparation method has significant drawbacks: the raw materials used in these methods are mostly derived from non-renewable resources such as petroleum, which are not only expensive but also harmful to the environment. Furthermore, when used in conjunction with epoxy resins, organic solvents are required, which causes serious chemical pollution and does not meet the requirements of current sustainable development. Summary of the Invention

[0005] To address the aforementioned technical problems, this application provides a low-viscosity epoxy curing agent based on renewable raw materials and its preparation method.

[0006] This application provides a low-viscosity epoxy curing agent based on renewable raw materials, employing the following technical solution:

[0007] A low-viscosity epoxy curing agent based on renewable raw materials, wherein the raw materials include cashew phenol maleic acid amine, furfural, amines and chain extenders, wherein the molar ratio of cashew phenol maleic acid amine, furfural and amines is (0.8-1.2):(1.0-1.5):(1.5-2.5), and the amount of chain extender is 6-7% of the total mass of raw materials.

[0008] By adopting the above technical solution, this application optimizes the material ratio between phenol, aldehyde, and amine, resulting in a significant excess of amines in the reaction system. The resulting epoxy curing agent has low viscosity, and when used in conjunction with epoxy resin, no organic solvents need to be added, significantly reducing VOC emissions from the entire protective coating system, minimizing chemical pollution and environmental damage, and meeting the requirements of sustainable development. Furthermore, the epoxy curing agent obtained in this application enables the cured epoxy resin to have high density, thus exhibiting excellent properties and providing good protection for the substrate.

[0009] Meanwhile, this application uses renewable resources to replace petroleum-based materials as raw materials as much as possible, which is in line with the concept of green environmental protection. Among the three types of raw materials, phenol, aldehyde, and amine, the phenol used is cashew phenol, which is a biomass material extracted from cashew shell liquid; the aldehyde used is furfural, which can be extracted from agricultural waste rich in pentoses, such as rice husks, sugarcane bagasse, oat husks, corn cobs, etc., as well as wood and wood products. It is a bio-based material with great economic benefits and environmental friendliness.

[0010] Preferably, the cashew phenol maleic acid amine is prepared by the following method:

[0011] Cashew nut phenol and maleic anhydride in a molar ratio of 1:(0.8-1.0) were reacted at 180-190℃ for 3-5 hours under the catalysis of Lewis acid to obtain cashew nut phenol maleic acid. Then, under the protection of an inert gas, cashew nut phenol maleic acid and ethyleneamine in a molar ratio of 1:(1.0-1.5) were subjected to a dehydration condensation reaction at 200-210℃ until no water was removed. After extraction and vacuum distillation, cashew nut phenol maleic acid amine was obtained.

[0012] While using cashew phenol as a raw material offers numerous advantages, practical applications have revealed that epoxy curing agents derived from it result in coatings with poor toughness and brittleness, thus affecting their lifespan. Furthermore, the rapid curing speed of this curing agent shortens the pot life of the coating at room temperature, hindering application. Additionally, the coating is prone to yellowing, impacting its appearance and rendering it unsuitable for use as a topcoat.

[0013] Therefore, by adopting the above technical solution, this application adds cashew phenol maleic acid amine as a reaction raw material to the curing agent, which enables the curing agent to give full play to the advantages of phenolic amine structural unit and polyamide structural unit at the same time. It has the characteristics of low viscosity and light color, and the resulting paint film has good flexibility, recoatability and yellowing resistance.

[0014] Preferably, the amines are composed of aliphatic amines and alicyclic amines in a weight ratio of (1.00-1.67):1.

[0015] By adopting the above technical solution, this application uses aliphatic amines and alicyclic amines in a certain ratio to combine their advantages. Aliphatic amines have the characteristics of high reactivity and fast curing speed, while alicyclic amines have good heat resistance and chemical resistance. The combination of the two can make the epoxy curing agent have both rapid curing and good heat resistance and chemical resistance, while also helping to adjust the viscosity of the curing agent to achieve a low viscosity effect.

[0016] Preferably, the fatty amine includes modified ethyleneamine and / or 1,5-pentanediamine.

[0017] Preferably, the modified ethyleneamine is prepared by the following method:

[0018] Under the protection of an inert gas, methyl cottonseed oil and ethyleneamine in a molar ratio of 1:(1.5-2.5) were mixed and stirred and heated to 95-105℃ for reflux reaction for 3.5-4.5 h. After the reaction was completed, the modified ethyleneamine was obtained by vacuum distillation.

[0019] By adopting the above technical solution, this application uses renewable resource methyl oleate to prepare a long-chain and environmentally friendly fatty amine through the addition of the unsaturated double bond of unsaturated fatty acid methyl ester to amine. It has good flexibility and can reduce the internal stress of epoxy resin cured products, thereby improving the comprehensive performance of epoxy resin cured products.

[0020] Preferably, the 1,5-pentanediamine is 1,5-pentanediamine made from renewable raw materials.

[0021] By adopting the above technical solution, this application uses 1,5-pentanediamine made from renewable raw materials instead of 1,5-pentanediamine made from fossil raw materials, which makes the epoxy resin curing agent more environmentally friendly, economically feasible, and promising in application. The 1,5-pentanediamine of this application is produced by a biological method using glucose as raw material, which generates oxaloacetic acid through the tricarboxylic acid cycle. Oxaloacetic acid is then converted to L-aspartic acid by aspartate aminotransferase catalysis. L-aspartic acid is then synthesized into L-lysine through the diaminopimelic acid pathway. L-lysine is then decarboxylated by lysine decarboxylase to generate 1,5-pentanediamine.

[0022] Preferably, the alicyclic amine includes one or more of isophorone diamine, m-phenylenediamine, cyclohexanediamine, and N-aminoethylpiperazine.

[0023] Preferably, the chain extender is furan methyl glycidyl ether.

[0024] Preferably, the furan methyl glycidyl ether is prepared by the following method:

[0025] 55-65 parts by volume of epichlorohydrin, 45-55 parts by volume of 50% sodium hydroxide solution, 1-2 parts by weight of tetrabutylammonium hydrogen sulfate, and 37-38 parts by weight of furfuryl alcohol are reacted at a temperature not exceeding 10°C for 3-5 hours to obtain a crude product. The crude product is then washed until neutral and dried under vacuum with anhydrous magnesium sulfate at a temperature of 65-75°C. After distillation, the fraction at 95-100°C is collected to obtain furan methyl glycidyl ether.

[0026] Since furfuryl alcohol is industrially prepared from furfural, and furfural can be extracted from pentose-rich agricultural wastes such as rice husks, sugarcane bagasse, oat husks, and corn cobs, as well as wood and wood products, it is a bio-based material with significant economic benefits and environmental friendliness. Therefore, by adopting the above-mentioned technical solution, this application uses furan methyl glycidyl ether prepared from furfuryl alcohol as a raw material to replace the commonly used benzyl glycidyl ether in industry, which can significantly reduce the negative environmental impact of epoxy curing agents. Furthermore, since the furan ring is a polar group containing oxygen atoms, it can greatly improve the adhesion and impact resistance of epoxy resin cured products, resulting in higher mechanical properties of the paint film and enhancing its usability.

[0027] Secondly, this application provides a method for preparing a low-viscosity epoxy curing agent based on renewable raw materials, which adopts the following technical solution:

[0028] A method for preparing a low-viscosity epoxy curing agent based on renewable raw materials includes the following steps:

[0029] Cashew phenol maleic acid amine, amines and furfural are mixed at 55-65℃, and then heated to 80-90℃ under inert gas protection and kept at this temperature for 1.0-1.5h. After the reaction is completed, a chain extender is added and the reaction is continued for 1-4h. Then, the product is obtained by vacuum distillation and excess amines are recovered.

[0030] By adopting the above technical solution, the epoxy curing agent prepared in this application has a low viscosity. When used in conjunction with epoxy resin, no organic solvents need to be added, significantly reducing the VOC emissions of the entire protective coating system. Furthermore, the preparation method of this application uses renewable resources as raw materials as much as possible, significantly reducing the negative environmental impact of the epoxy curing agent and improving its environmental and economic value. Moreover, compared with existing processes, after the production process is completed, excess amine is recovered and reused through vacuum distillation, further reducing the production cost of the epoxy curing agent, improving its economic value, and demonstrating extremely broad application prospects.

[0031] In summary, this application has the following beneficial technical effects:

[0032] 1. This application uses raw materials obtained from renewable resources to replace some raw materials obtained from non-renewable resources such as petroleum, which not only reduces production costs but also significantly reduces environmental pollution, thus having high environmental and economic value. Furthermore, the epoxy curing agent obtained enables epoxy resin cured products to have excellent comprehensive properties.

[0033] 2. The epoxy curing agent of this application has a low viscosity and can be used in conjunction with epoxy resin without the addition of organic solvents, which greatly reduces the volatilization of VOCs in the entire protective coating system and further reduces the chemical pollution to the environment, which meets the requirements of current social sustainable development.

[0034] 3. Compared with existing processes, the preparation method of epoxy curing agent of this application allows for the recovery and reuse of excess amine through vacuum distillation after the production process is completed, which further reduces the production cost of epoxy curing agent, improves its economic value, and has a very broad application prospect. Detailed Implementation

[0035] The present application will be further described in detail below with reference to the embodiments.

[0036] Unless otherwise specified, the raw materials used in this application can be purchased through regular commercial channels.

[0037] <Preparation Example 1.1>

[0038] Cashew phenol maleic acid amine is prepared by the following method:

[0039] High-purity cashew phenol (purity ≥95%) and maleic anhydride were reacted at 180°C for 5 hours under the catalysis of Lewis acid (aluminum trichloride) in a molar ratio of 1:0.8 to obtain cashew phenol maleic acid. Then, under nitrogen protection, cashew phenol maleic acid and ethyleneamine (diethylenetriamine) in a molar ratio of 1:1 were subjected to a dehydration condensation reaction at 200°C until no water was removed. After extraction and vacuum distillation, cashew phenol maleic acid amine was obtained.

[0040] <Preparation Example 1.2>

[0041] Cashew phenol maleic acid amine is prepared by the following method:

[0042] High-purity cashew phenol (purity ≥95%) and maleic anhydride were reacted at 185°C for 4 hours under the catalysis of Lewis acid (aluminum trichloride) in a molar ratio of 1:0.9 to obtain cashew phenol maleic acid. Then, under nitrogen protection, cashew phenol maleic acid and ethyleneamine (triethylenetetramine) in a molar ratio of 1:1.2 were subjected to a dehydration condensation reaction at 205°C until no water was removed. After extraction and vacuum distillation, cashew phenol maleic acid amine was obtained.

[0043] <Preparation Example 1.3>

[0044] Cashew phenol maleic acid amine is prepared by the following method:

[0045] High-purity cashew phenol (purity ≥95%) and maleic anhydride were reacted at 190°C for 3 hours under the catalysis of Lewis acid (aluminum trichloride) in a molar ratio of 1:1 to obtain cashew phenol maleic acid. Then, under nitrogen protection, cashew phenol maleic acid and ethyleneamine (diethylenetriamine) in a molar ratio of 1:1.5 were subjected to a dehydration condensation reaction at 210°C until no water was removed. After extraction and vacuum distillation, cashew phenol maleic acid amine was obtained.

[0046] <Preparation Example 2.1>

[0047] Modified ethyleneamine is prepared by the following method:

[0048] Under nitrogen protection, methyl cottonseed oil and ethyleneamine (diethylenetriamine) in a molar ratio of 1:1.5 were mixed and stirred and heated to 95°C for reflux reaction for 4.5 h. After the reaction was completed, the modified ethyleneamine was obtained by vacuum distillation.

[0049] <Preparation Example 2.2>

[0050] Modified ethyleneamine is prepared by the following method:

[0051] Under nitrogen protection, methyl cottonseed oil and ethyleneamine (triethylenetetramine) in a molar ratio of 1:2 were mixed and stirred and heated to 100°C for reflux reaction for 4 hours. After the reaction was completed, the mixture was distilled under reduced pressure to obtain modified ethyleneamine.

[0052] <Preparation Example 2.3>

[0053] Modified ethyleneamine is prepared by the following method:

[0054] Under nitrogen protection, methyl cottonseed oil and ethyleneamine (diethylenetriamine) in a molar ratio of 1:2.5 were mixed and stirred and heated to 105°C for reflux reaction for 3.5 h. After the reaction was completed, the modified ethyleneamine was obtained by vacuum distillation.

[0055] <Preparation Example 3.1>

[0056] Furan methyl glycidyl ether is prepared by the following method:

[0057] 55 L of epichlorohydrin, 45 L of 50% sodium hydroxide solution, and 1 kg of tetrabutylammonium hydrogen sulfate were mixed and stirred until homogeneous. Then, 37 kg of distilled and purified furfuryl alcohol was slowly added to the system. The mixture was reacted for 3 h at a temperature not exceeding 10 °C to obtain a crude product. The crude product was then washed with distilled water until neutral and dried under vacuum with anhydrous magnesium sulfate at 65 °C. The product was then distilled and the fraction at 95-100 °C was collected to obtain furan methyl glycidyl ether.

[0058] <Preparation Example 3.2>

[0059] Furan methyl glycidyl ether is prepared by the following method:

[0060] 60 L of epichlorohydrin, 50 L of 50% sodium hydroxide solution, and 1.5 kg of tetrabutylammonium hydrogen sulfate were mixed and stirred until homogeneous. Then, 37.5 kg of distilled and purified furfuryl alcohol was slowly added to the system. The mixture was reacted for 4 h at a temperature not exceeding 10 °C to obtain a crude product. The crude product was then washed with distilled water until neutral and dried under vacuum with anhydrous magnesium sulfate at 70 °C. The product was then distilled and the fraction at 95-100 °C was collected to obtain furan methyl glycidyl ether.

[0061] <Preparation Example 3.3>

[0062] Furan methyl glycidyl ether is prepared by the following method:

[0063] 65 L of epichlorohydrin, 55 L of 50% sodium hydroxide solution, and 2 kg of tetrabutylammonium hydrogen sulfate were mixed and stirred evenly. Then, 38 kg of distilled and purified furfuryl alcohol was slowly added to the system. The mixture was reacted for 5 h at a temperature not exceeding 10 °C to obtain a crude product. The crude product was then washed with distilled water until neutral, and then dried under vacuum with anhydrous magnesium sulfate at 75 °C. The fraction obtained at 95-100 °C was then distilled and collected to obtain furan methyl glycidyl ether.

[0064] <Example 1>

[0065] A method for preparing a low-viscosity epoxy curing agent based on renewable raw materials includes the following steps:

[0066] First, the cashew phenol maleic acid amine prepared in Preparation Example 1.1 was mixed and stirred evenly with amines. Then, furfural was added dropwise to the system at 55°C, and the temperature was raised to 80°C for 1.5 h under nitrogen protection. After the reaction was completed, a chain extender was added and the reaction was continued for 1 h. Then, the epoxy curing agent was obtained by vacuum distillation and the excess amines were recovered.

[0067] The molar ratio of cashew phenol maleic acid amine, furfural, and amines is 0.8:1.0:1.5.

[0068] The amount of chain extender added is 6% of the total mass of the raw materials;

[0069] The amines are composed of aliphatic amines and alicyclic amines in a weight ratio of 1:1. The aliphatic amine is the modified ethylene amine prepared in Preparation Example 2.1, and the alicyclic amine is isophorone diamine.

[0070] The chain extender used was furan methyl glycidyl ether prepared in Preparation Example 3.1.

[0071] <Example 2>

[0072] A method for preparing a low-viscosity epoxy curing agent based on renewable raw materials includes the following steps:

[0073] First, the cashew phenol maleic acid amine obtained in Preparation Example 1.2 was mixed and stirred evenly with amines. Then, furfural was added dropwise to the system at 60°C, and the temperature was raised to 85°C for 1.3 h under nitrogen protection. After the reaction was completed, a chain extender was added and the reaction was continued for 2.5 h. Then, the epoxy curing agent was obtained by vacuum distillation and the excess amines were recovered.

[0074] The molar ratio of cashew phenol maleic acid amine, furfural and amines is 1:1.2:2;

[0075] The amount of chain extender added is 6.5% of the total mass of the raw materials;

[0076] The amines are composed of aliphatic amines and alicyclic amines in a weight ratio of 1.3:1. The aliphatic amine is the modified ethylene amine prepared in Preparation Example 2.2, and the alicyclic amine is m-phenylenediamine.

[0077] The chain extender used was furan methyl glycidyl ether prepared in Preparation Example 3.2.

[0078] <Example 3>

[0079] A method for preparing a low-viscosity epoxy curing agent based on renewable raw materials includes the following steps:

[0080] First, the cashew phenol maleic acid amine and amines prepared in Preparation Example 1.3 were mixed and stirred evenly. Then, furfural was added dropwise to the system at 65°C and the temperature was raised to 90°C for 1 hour under nitrogen protection. After the reaction was completed, a chain extender was added and the reaction was continued for 4 hours. Then, the epoxy curing agent was obtained by vacuum distillation and the excess amines were recovered.

[0081] The molar ratio of cashew phenol maleic acid amine, furfural, and amines is 1.2:1.5:2.5.

[0082] The amount of chain extender added is 7% of the total mass of the raw materials;

[0083] The amines were composed of aliphatic amines and alicyclic amines in a weight ratio of 1.67:1. The aliphatic amine used was the modified ethylene amine prepared in Preparation Example 2.3, and the alicyclic amine used was cyclohexanediamine.

[0084] The chain extender used was furan methyl glycidyl ether prepared in Preparation Example 3.3.

[0085] <Example 4>

[0086] A method for preparing a low-viscosity epoxy curing agent based on renewable raw materials includes the following steps:

[0087] First, the cashew phenol maleic acid amine obtained in Preparation Example 1.2 was mixed and stirred evenly with amines. Then, furfural was added dropwise to the system at 58°C, and the temperature was raised to 83°C for 1.2 h under nitrogen protection. After the reaction was completed, a chain extender was added and the reaction was continued for 2 h. Then, the epoxy curing agent was obtained by vacuum distillation and the excess amines were recovered.

[0088] The molar ratio of cashew phenol maleic acid amine, furfural, and amines is 0.9:1.1:1.8.

[0089] The amount of chain extender added is 6% of the total mass of the raw materials;

[0090] The amines are composed of aliphatic amines and alicyclic amines in a weight ratio of 1.1:1. The aliphatic amine is 1,5-pentanediamine made from renewable raw materials, and the alicyclic amine is N-aminoethylpiperazine.

[0091] The chain extender used was furan methyl glycidyl ether prepared in Preparation Example 3.2.

[0092] <Example 5>

[0093] A method for preparing a low-viscosity epoxy curing agent based on renewable raw materials includes the following steps:

[0094] First, the cashew phenol maleic acid amine obtained in Preparation Example 1.2 was mixed and stirred evenly with amines. Then, furfural was added dropwise to the system at 63°C, and the temperature was raised to 88°C for 1.4 h under nitrogen protection. After the reaction was completed, a chain extender was added and the reaction was continued for 3 h. Then, the epoxy curing agent was obtained by vacuum distillation and the excess amines were recovered.

[0095] The molar ratio of cashew phenol maleic acid amine, furfural, and amines is 1.1:1.4:2.3.

[0096] The amount of chain extender added is 7% of the total mass of the raw materials;

[0097] The amines are composed of aliphatic amines and alicyclic amines in a weight ratio of 1.5:1. The aliphatic amine is 1,5-pentanediamine made from renewable raw materials, and the alicyclic amine is isophorone diamine.

[0098] The chain extender used was furan methyl glycidyl ether prepared in Preparation Example 3.2.

[0099] <Comparative Example 1>

[0100] The difference from Example 2 is that cashew phenol maleate is replaced with cashew phenol in equal amounts, while the rest is the same as in Example 2.

[0101] <Comparative Example 2>

[0102] The difference from Example 2 is that all amines used are aliphatic amines, and no alicyclic amines are added; otherwise, they are the same as in Example 2.

[0103] <Comparative Example 3>

[0104] The difference from Example 2 is that all amines used are alicyclic amines, and no fatty amines are added; otherwise, they are the same as in Example 2.

[0105] <Comparative Example 4>

[0106] The difference from Example 2 is that the modified ethyleneamine obtained in Preparation Example 2.2 was replaced with triethylenetetramine in equal amounts, and the rest was the same as in Example 2.

[0107] <Comparative Example 5>

[0108] The difference from Example 2 is that the furan methyl glycidyl ether obtained in Preparation Example 3.2 was replaced with an equal amount of benzyl glycidyl ether, and the rest was the same as in Example 2.

[0109] <Performance Detection>

[0110] The epoxy curing agent prepared in the above examples and comparative examples was mixed with bisphenol A epoxy resin (model E44) in a certain ratio to ensure that the hydrogen atoms on the amino group of the epoxy curing agent and the epoxy groups on the bisphenol A epoxy resin were of equal molar amount. The mixture was then poured into a mold and pre-cured at 25°C for 3 hours. After that, it was placed in an oven and cured at 80°C for 8 hours. After cooling, the epoxy resin cured test material was obtained. The tensile properties, impact resistance, and heat resistance of the prepared epoxy resin cured products were tested. Tensile property testing was conducted on a universal testing machine according to GB / T 1040.1-2006 standard, with a tensile rate of 50 mm / min and a material width of 10 ± 0.5 mm and a thickness of 4 ± 0.5 mm. Impact resistance was tested according to the simply supported beam impact toughness test in GB / T 1043.1-2008 standard, with a pendulum energy of 2.75 J and a material size of 80 mm × 10 mm × 4 mm. Heat resistance was tested using a PERKIN ELMER DIAMOND TG / DTA analyzer to measure the material's thermal weight loss, and the temperature at which the material lost 5% of its weight was recorded. All results are recorded in Table 1.

[0111] Table 1 Performance Test Results

[0112]

[0113] As can be seen from Table 1, the epoxy curing agent prepared in the embodiments of this application can enable the epoxy resin cured product to achieve a tensile strength of 71.69-75.82 MPa and an impact strength of 31.27-33.45 KJ / m. 2 The temperature at which the mass loss is 5% is 295-305℃, exhibiting significantly higher strength, toughness, and heat resistance. Furthermore, testing showed that the epoxy curing agent prepared in this application has a viscosity of 7000-9000 mPa·s at 25℃. It withstood immersion in 10% sulfuric acid for over 30 days without cracking, and withstood over 120 wiping cycles with methyl ethyl ketone without cracking. Experimental data demonstrate that this application uses renewable resources to replace some non-renewable resources such as petroleum, not only reducing production costs but also significantly reducing environmental pollution, thus possessing high environmental and economic value. Moreover, the resulting epoxy curing agent enables the cured epoxy resin to exhibit excellent comprehensive properties.

[0114] The tensile strength, impact strength, and thermogravimetric temperature of Comparative Example 1 were all inferior to those of Example 2. This indicates that by using cashew phenol maleic acid amine instead of cashew phenol as a reactant, the curing agent prepared in this application can simultaneously exert the advantages of phenolic amine structural units and polyamide structural units, thereby further improving the overall performance of epoxy resin cured products.

[0115] The tensile strength and thermal decomposition temperature of Comparative Example 2 are lower than those of Example 2, but the impact strength is higher than that of Example 2. The tensile strength and thermal decomposition temperature of Comparative Example 3 are higher than those of Example 2, but the impact strength is lower than that of Example 2. This shows that the present application uses a mixture of alicyclic amines and fatty amines, which can give full play to the advantages of both, thereby further improving the overall performance of epoxy resin cured products.

[0116] The tensile strength, impact strength, and thermogravimetric temperature of Comparative Example 4 were all lower than those of Example 2. This indicates that the present application uses renewable resource methyl oleate to prepare a long-chain and environmentally friendly fatty amine through the addition of the unsaturated double bond of unsaturated fatty acid methyl ester to amine. It has good flexibility and can reduce the internal stress of epoxy resin cured products, thereby improving the comprehensive performance of epoxy resin cured products.

[0117] The tensile strength, impact strength, and thermal decomposition temperature of Comparative Example 5 were all lower than those of Example 2. This indicates that the use of furan methyl glycidyl ether prepared from furfuryl alcohol as a raw material in this application to replace the commonly used benzyl glycidyl ether in industry can significantly reduce the negative environmental impact of epoxy curing agents and greatly improve the adhesion and impact resistance of epoxy resin cured products, resulting in higher mechanical properties of the paint film and enhanced usability of the paint film.

[0118] The embodiments described in this specific implementation are preferred embodiments of this application and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. A low-viscosity epoxy curing agent based on renewable raw materials, characterized in that, The raw materials used include cashew phenol maleate amine, furfural, amines and chain extenders, wherein the molar ratio of cashew phenol maleate amine, furfural and amines is (0.8-1.2):(1.0-1.5):(1.5-2.5), and the amount of chain extender is 6-7% of the total mass of raw materials; The cashew phenol maleic acid amine is prepared by the following method: Cashew nut phenol and maleic anhydride in a molar ratio of 1:(0.8-1.0) were reacted at 180-190℃ for 3-5 hours under the catalysis of Lewis acid to obtain cashew nut phenol maleic acid. Then, under the protection of inert gas, cashew nut phenol maleic acid and ethyleneamine in a molar ratio of 1:(1.0-1.5) were subjected to a dehydration condensation reaction at 200-210℃ until no water was removed. After extraction and vacuum distillation, cashew nut phenol maleic acid amine was obtained. The amines are composed of aliphatic amines and alicyclic amines in a weight ratio of (1.00-1.67):1; The chain extender is furan methyl glycidyl ether; The furan methyl glycidyl ether is prepared by the following method: 55-65 parts by volume of epichlorohydrin, 45-55 parts by volume of 50% sodium hydroxide solution, 1-2 parts by weight of tetrabutylammonium hydrogen sulfate and 37-38 parts by weight of furfuryl alcohol are reacted at a temperature not exceeding 10°C for 3-5 hours to obtain a crude product. The crude product is then washed until neutral and dried under vacuum with anhydrous magnesium sulfate at a temperature of 65-75°C. After distillation, the fraction at 95-100°C is collected to obtain furan methyl glycidyl ether. The fatty amines include modified ethyleneamine and / or 1,5-pentanediamine; The modified ethyleneamine was prepared by the following method: Under the protection of an inert gas, methyl cottonseed oil and ethyleneamine in a molar ratio of 1:(1.5-2.5) were mixed and stirred and heated to 95-105℃ for reflux reaction for 3.5-4.5 h. After the reaction was completed, the modified ethyleneamine was obtained by vacuum distillation.

2. The low-viscosity epoxy curing agent based on renewable raw materials according to claim 1, characterized in that, The 1,5-pentanediamine is 1,5-pentanediamine made from renewable raw materials.

3. The low-viscosity epoxy curing agent based on renewable raw materials according to claim 1, characterized in that, The alicyclic amines include one or more of isophorone diamine, cyclohexanediamine, and N-aminoethylpiperazine.

4. A method for preparing a low-viscosity epoxy curing agent based on renewable raw materials according to any one of claims 1-3, characterized in that, Includes the following steps: Cashew phenol maleic acid amine, amines and furfural are mixed at 55-65℃, and then heated to 80-90℃ under inert gas protection and kept at this temperature for 1.0-1.5h. After the reaction is completed, a chain extender is added and the reaction is continued for 1-4h. Then, the product is obtained by vacuum distillation and excess amines are recovered.

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