A polyamide epoxy resin curing agent and preparation method thereof and epoxy resin cured product

Abstract

The present invention provides a polyamide epoxy resin curing agent, a preparation method thereof and an epoxy resin cured product, and relates to the technical field of epoxy resin curing agents. The polyamide epoxy resin curing agent provided by the present invention has a structure shown in Formula I. The curing agent provided by the present invention has a relatively high molecular weight and more functional groups, and has the advantages of low volatility and high reactivity. Specifically, the amide group in the curing agent structure directly forms a conjugated structure with the benzene ring group, so that it itself has the characteristics of high tensile strength, low shrinkage at break and good impact resistance. It cures epoxy resin and can significantly enhance the mechanical properties of epoxy resin; and the presence of the benzene ring structure in the curing agent structure can also effectively improve the thermal stability of epoxy resin. Therefore, after the polyamide epoxy resin curing agent provided by the present invention is cured with epoxy resin, the obtained epoxy resin cured product has excellent mechanical properties and thermal stability.

Description

Technical Field

[0001] The invention relates to the technical field of epoxy resin curing agents, and in particular to a polyamide epoxy resin curing agent and a preparation method thereof and an epoxy resin cured product. Background Art

[0002] Epoxy resin is a basic chemical product widely used in many fields. It is a thermoplastic linear polymer. It cannot produce cross-linking and curing to exert its excellent properties under external conditions alone. Therefore, it is necessary to add a curing agent to perform a polyaddition reaction to form a three-dimensional network structure. Polyamine curing agents are the most commonly used type of epoxy resin curing agents, among which polyamide curing agents occupy an important position. Polyamide curing agents can be widely used in epoxy adhesives, epoxy mortars or floor primers, industrial anti-corrosion coatings, insulating materials, electronic potting, and equipment coatings for drinking water, medical equipment and food.

[0003] The polyamide used for epoxy resin curing is a modified polyamine, which is usually formed by the polycondensation reaction of linoleic acid dimer and fatty polyamine to form a polyamide curing agent. The patent with publication number CN112979924A provides a method for preparing a low molecular weight polyamide curing agent, which uses dimer acid and oligoether diamine to undergo polycondensation reaction under heating conditions to obtain a low molecular weight polyamide curing agent for concrete crack repair glue. In the document "Synthesis and Performance of Polyamide Curing Agent for Epoxy Resin" (Yin Hao et al., "China Adhesives", Vol. 25, No. 1, January 2016), DETA-MA, a Michael addition product of diethylenetriamine and methyl acrylate, is used as a self-condensation monomer, and polyetheramine is used as a capping agent to prepare a linear polyamide curing agent for epoxy resin. When these existing polyamide curing agents are used, there are generally problems of brittle epoxy resin cross-linking structure, low crack resistance and low fracture toughness, resulting in poor mechanical properties of epoxy resin, which limits its practical application in engineering and life fields. Summary of the invention

[0004] In view of this, the present invention aims to provide a polyamide epoxy resin curing agent and a preparation method thereof and epoxy resin cured product. After the polyamide epoxy resin curing agent provided by the present invention is cured with epoxy resin, the mechanical properties of the epoxy resin can be effectively improved.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] The present invention provides a polyamide epoxy resin curing agent having a structure shown in Formula I:

[0007]

[0008] The number average molecular weight of the polyamide epoxy resin curing agent is 10145-10161.

[0009] The present invention provides a method for preparing the polyamide epoxy resin curing agent described in the above technical solution, comprising the following steps:

[0010] Terephthaloyl chloride, an organic solvent, ethylenediamine and a NaOH aqueous solution are mixed for polycondensation reaction to obtain the polyamide epoxy resin curing agent.

[0011] Preferably, the molar ratio of terephthaloyl chloride, ethylenediamine and NaOH in the NaOH aqueous solution is 1:(1.2-1.8):(2-2.4); and the mass fraction of the NaOH aqueous solution is 30-50%.

[0012] Preferably, the organic solvent includes one or more of chloroform, dichloromethane and pyridine.

[0013] Preferably, the mixing method is:

[0014] Dissolving terephthaloyl chloride in an organic solvent to obtain a terephthaloyl chloride organic solution;

[0015] Dissolving ethylenediamine in a NaOH aqueous solution to obtain an ethylenediamine mixed solution;

[0016] The terephthaloyl chloride organic solution is placed in an ice water bath, and an ethylenediamine mixed solution is added dropwise thereto; the dropping rate of the ethylenediamine mixed solution is 1-3 mL / min.

[0017] Preferably, the polycondensation reaction is carried out at a temperature of 25 to 30° C. and for a time of 2.5 to 4 hours.

[0018] Preferably, after the polycondensation reaction, the obtained polycondensation reaction system is washed and dried in sequence; the washing includes washing with a saturated sodium bicarbonate aqueous solution, washing with saturated saline water and washing with distilled water in sequence; the pH value of the polycondensation reaction system after washing with saturated saline water is 6.5 to 7.2.

[0019] The present invention provides an epoxy resin cured product obtained by curing raw materials including epoxy resin and a curing agent, wherein the curing agent is the polyamide epoxy resin curing agent described in the above technical solution or the polyamide epoxy resin curing agent prepared by the preparation method of the above technical solution.

[0020] Preferably, the mass ratio of the epoxy resin to the curing agent is 1:(0.1-0.35).

[0021] Preferably, the curing includes a first curing and a second curing performed sequentially; the first curing is performed at a temperature of 78 to 83° C. for 3.5 to 4.5 hours; the second curing is performed at a temperature of 115 to 125° C. for 1 to 1.5 hours.

[0022] The present invention provides a polyamide epoxy resin curing agent having a structure shown in Formula I; the number average molecular weight of the polyamide epoxy resin curing agent is 10145 to 10161. The curing agent provided by the present invention has a relatively high molecular weight and more functional groups, and has the advantages of low volatility and high reactivity. Specifically, the amide group in the structure of the curing agent directly forms a conjugated structure with the benzene ring group, so that it itself has the characteristics of high tensile strength, low shrinkage at break and good impact resistance. It can significantly enhance the mechanical properties of epoxy resin by curing epoxy resin; and the presence of the benzene ring structure in the curing agent structure can also effectively improve the thermal stability of epoxy resin. Therefore, the macromolecular polyamide epoxy resin curing agent provided by the present invention, after being cured with epoxy resin, the obtained epoxy resin cured material has excellent mechanical properties and thermal stability. The results of the embodiments show that after the macromolecular polyamide epoxy resin curing agent provided by the present invention is cured with epoxy resin, the T of the obtained epoxy resin cured material is g The temperature is 95.7~104.3℃, the tensile strength is 76.54~85.35MPa, the elongation at break is 3.26~3.63%, and the impact strength is 2.78~3.52KJ / m 2 . DETAILED DESCRIPTION

[0023] The present invention provides a polyamide epoxy resin curing agent having a structure shown in Formula I:

[0024]

[0025] The number average molecular weight of the polyamide epoxy resin curing agent is 10145-10161.

[0026] In the present invention, the number average molecular weight of the polyamide epoxy resin curing agent is preferably 10152 to 10159. The curing agent provided by the present invention has a relatively high molecular weight and more functional groups, and has the advantages of low volatility and high reactivity; in the structure of the curing agent, the amide group directly forms a conjugated structure with the benzene ring group, so that it has the characteristics of high tensile strength, low break shrinkage and good impact resistance, and it can significantly enhance the mechanical properties of epoxy resin by curing epoxy resin; and the presence of the benzene ring structure in the curing agent structure can also effectively improve the thermal stability of epoxy resin.

[0027] The present invention provides a method for preparing the polyamide epoxy resin curing agent described in the above technical solution, comprising the following steps:

[0028] Terephthaloyl chloride, an organic solvent, ethylenediamine and a NaOH aqueous solution are mixed for polycondensation reaction to obtain the polyamide epoxy resin curing agent.

[0029] In the present invention, unless otherwise specified, the raw materials involved are commercially available products well known to those skilled in the art.

[0030] In the present invention, the molar ratio of terephthaloyl chloride, ethylenediamine and NaOH in the NaOH aqueous solution is preferably 1: (1.2-1.8): (2-2.4), more preferably 1: (1.5-1.8): (2-2.2); the mass fraction of the NaOH aqueous solution is preferably 30-50%, more preferably 32%. In the present invention, the organic solvent preferably includes one or more of chloroform, dichloromethane and pyridine, more preferably chloroform; the present invention has no special requirements for the amount of the organic solvent, as long as it can ensure the smooth progress of the reaction.

[0031] In the present invention, the mixing method is preferably:

[0032] Dissolving terephthaloyl chloride in an organic solvent to obtain a terephthaloyl chloride organic solution;

[0033] Dissolving ethylenediamine in a NaOH aqueous solution to obtain an ethylenediamine mixed solution;

[0034] The terephthaloyl chloride organic solution is placed in an ice-water bath, and the ethylenediamine mixed solution is added dropwise thereto.

[0035] In the present invention, the dropping rate of the ethylenediamine mixed solution is preferably 1-3 mL / min, specifically 1 mL / min, 2 mL / min, or 3 mL / min.

[0036] In the present invention, the temperature of the polycondensation reaction is preferably 25 to 30°C. In the embodiment of the present invention, the polycondensation reaction is carried out at room temperature (specifically 25°C); the time of the polycondensation reaction is preferably 2.5 to 4 hours, more preferably 2.5 to 3.5 hours, and further preferably 3 hours. The time of the polycondensation reaction is calculated from the completion of the dropwise addition of the ethylenediamine mixed solution; the polycondensation reaction is preferably carried out under stirring. In the present invention, the reaction formula of the polycondensation reaction is shown in formula a; the role of NaOH in the NaOH aqueous solution is to absorb the hydrochloric acid generated by the polycondensation reaction.

[0037]

[0038] After the polycondensation reaction is completed, the present invention also preferably washes and dries the obtained polycondensation reaction system in sequence. In the present invention, the washing preferably includes washing with a saturated sodium bicarbonate aqueous solution, washing with a saturated saline solution and washing with distilled water in sequence; the washing with a saturated sodium bicarbonate aqueous solution is used to remove residual hydrochloric acid in the polycondensation reaction system; the washing with a saturated saline solution is used to remove residual sodium carbonate in the polycondensation reaction system (organic phase), and the pH value of the polycondensation reaction system after washing with saturated saline solution is preferably 6.5 to 7.2, more preferably 6.8 to 7.1. In the present invention, the drying temperature is preferably 80°C, the drying time is based on drying to constant weight, and the drying is preferably vacuum drying. After drying, the polyamide epoxy resin curing agent is obtained.

[0039] The present invention provides an epoxy resin cured product, which is obtained by curing raw materials including epoxy resin and curing agent, wherein the curing agent is the polyamide epoxy resin curing agent described in the above technical solution or the polyamide epoxy resin curing agent prepared by the preparation method described in the above technical solution. In the present invention, the epoxy resin is preferably a bisphenol A type epoxy resin; the mass ratio of the epoxy resin to the curing agent is preferably 1: (0.1-0.35), more preferably 1: (0.1-0.25). In the present invention, the curing preferably includes a first curing and a second curing performed in sequence; the temperature of the first curing is preferably 78-83°C, more preferably 80°C, and the time is preferably 3.5-4.5h, more preferably 4h; the temperature of the second curing is preferably 115-125°C, more preferably 120°C, and the time is preferably 1-1.5h, more preferably 1h. In the present invention, the specific operation process of the curing is preferably: the curing agent and the epoxy resin are mixed evenly, the obtained mixed material is poured into a mold after ultrasonic degassing, and the curing is performed in the mold. The epoxy resin cured product provided by the invention has excellent mechanical properties and thermal stability.

[0040] The polyamide epoxy resin curing agent and its preparation method and epoxy resin cured product provided by the present invention are described in detail below in conjunction with the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0041] Example 1

[0042] The preparation method of polyamide epoxy resin curing agent is as follows:

[0043] Weigh 20g of terephthaloyl chloride in a round-bottom flask, add 100mL of chloroform, and place in an ice-water bath after the terephthaloyl chloride is completely dissolved; then dissolve 7.2g of ethylenediamine in 25g of 32wt% NaOH aqueous solution, and drip into the reaction system at a rate of 1mL / min; after the dripping is completed, stir at room temperature for 2.5h and then stop the reaction. Wash the reaction system with saturated sodium bicarbonate aqueous solution and saturated salt water in turn until the pH value of the system is 7.1, then wash with distilled water, and then dry at 80°C in vacuum to obtain a curing agent, namely the polyamide epoxy resin curing agent, and the number average molecular weight of the curing agent is 10149.

[0044] The preparation method of epoxy resin cured product is as follows:

[0045] 5 g of epoxy resin was evenly mixed with 0.5 g of the above curing agent, poured into a mold after ultrasonic degassing, cured at 80° C. for 4 h to form, and then cured at 120° C. for 1 h to obtain an epoxy resin cured product.

[0046] Example 2

[0047] The preparation method of polyamide epoxy resin curing agent is as follows:

[0048] Weigh 20g of terephthaloyl chloride in a round-bottom flask, add 100mL of chloroform, and place in an ice-water bath after the terephthaloyl chloride is completely dissolved; then dissolve 9g of ethylenediamine in 27.5g of 32wt% NaOH aqueous solution, and drip into the reaction system at a rate of 1mL / min; after the dripping is completed, stir at room temperature for 2.5h and stop the reaction. Wash the reaction system with saturated sodium bicarbonate aqueous solution and saturated salt water in turn until the pH value of the system is 6.8, then wash with distilled water, and then dry at 80°C in vacuum to obtain a curing agent, namely the polyamide epoxy resin curing agent, and the number average molecular weight of the curing agent is 10159.

[0049] The preparation method of epoxy resin cured product is as follows:

[0050] 5 g of epoxy resin and 1 g of the above curing agent were mixed evenly, poured into a mold after ultrasonic degassing, cured at 80° C. for 4 h to form, and then cured at 120° C. for 1 h to obtain an epoxy resin cured product.

[0051] Example 3

[0052] The preparation method of polyamide epoxy resin curing agent is as follows:

[0053] Weigh 20g of terephthaloyl chloride in a round-bottom flask, add 100mL of chloroform, and place in an ice-water bath after the terephthaloyl chloride is completely dissolved; then dissolve 9g of ethylenediamine in 25g of a 32wt% NaOH aqueous solution, and drip into the reaction system at a rate of 2mL / min; after the dripping is completed, stir at room temperature for 2.5h and then stop the reaction. Wash the reaction system with a saturated sodium bicarbonate aqueous solution and a saturated salt water solution in turn until the pH value of the system is 6.8, then wash with distilled water, and then dry at 80°C in vacuum to obtain a curing agent, namely the polyamide epoxy resin curing agent, and the number average molecular weight of the curing agent is 10152.

[0054] The preparation method of epoxy resin cured product is as follows:

[0055] 5 g of epoxy resin was evenly mixed with 1.25 g of the above curing agent, poured into a mold after ultrasonic degassing, cured at 80° C. for 4 h to form, and then cured at 120° C. for 1 h to obtain an epoxy resin cured product.

[0056] Example 4

[0057] The preparation method of polyamide epoxy resin curing agent is as follows:

[0058] Weigh 20g of terephthaloyl chloride in a round-bottom flask, add 100mL of chloroform, and place in an ice-water bath after the terephthaloyl chloride is completely dissolved; then dissolve 10.8g of ethylenediamine in 25g of 32wt% NaOH aqueous solution, and drip into the reaction system at a rate of 1mL / min; after the dripping is completed, stir at room temperature for 3.5h and then stop the reaction. Wash the reaction system with saturated sodium bicarbonate aqueous solution and saturated salt water in turn until the pH value of the system is 7.1, then wash with distilled water, and then dry at 80°C in vacuum to obtain a curing agent, namely the polyamide epoxy resin curing agent, and the number average molecular weight of the curing agent is 10156.

[0059] The preparation method of epoxy resin cured product is as follows:

[0060] 5 g of epoxy resin was evenly mixed with 1.75 g of the above curing agent, poured into a mold after ultrasonic degassing, cured at 80° C. for 4 h to form, and then cured at 120° C. for 1 h to obtain an epoxy resin cured product.

[0061] Example 5

[0062] The preparation method of polyamide epoxy resin curing agent is as follows:

[0063] Weigh 20g of terephthaloyl chloride in a round-bottom flask, add 100mL of chloroform, and place in an ice-water bath after the terephthaloyl chloride is completely dissolved; then dissolve 9g of ethylenediamine in 25g of 32wt% NaOH aqueous solution, and drip into the reaction system at a rate of 3mL / min; after the dripping is completed, stir at room temperature for 3h and then stop the reaction. Wash the reaction system with saturated sodium bicarbonate aqueous solution and saturated salt water in turn until the pH value of the system is 6.9, then wash with distilled water, and then dry at 80°C in vacuum to obtain a curing agent, namely the polyamide epoxy resin curing agent, and the number average molecular weight of the curing agent is 10161.

[0064] The preparation method of epoxy resin cured product is as follows:

[0065] 5 g of epoxy resin and 1 g of the above curing agent were mixed evenly, poured into a mold after ultrasonic degassing, cured at 80° C. for 4 h to form, and then cured at 120° C. for 1 h to obtain an epoxy resin cured product.

[0066] The performance tests of the epoxy resin cured products prepared in Examples 1 to 5 were carried out, wherein the tensile strength and elongation at break were tested according to the GB / T16421 method, and the impact strength was tested according to the GB / T2571 method. The performance test results of the epoxy resin cured products of each example are listed in Table 1:

[0067] Table 1 Performance test results of epoxy resin cured products prepared in Examples 1 to 5

[0068]

[0069]

[0070] It can be seen from the above technical solutions that after the polyamide epoxy resin curing agent provided by the present invention is cured with epoxy resin, the obtained epoxy resin cured product has excellent mechanical properties and thermal stability.

[0071] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A cured epoxy resin, characterized in that: The curing agent is obtained by curing raw materials including epoxy resin and curing agent, wherein the curing agent is a polyamide epoxy resin curing agent, and the polyamide epoxy resin curing agent has a structure shown in Formula I: Formula I; The number average molecular weight of the polyamide epoxy resin curing agent is 10145-10161; The preparation method of the polyamide epoxy resin curing agent comprises the following steps: The polyamide epoxy resin curing agent is obtained by mixing terephthaloyl chloride, an organic solvent, ethylenediamine and a NaOH aqueous solution for polycondensation reaction; The molar ratio of terephthaloyl chloride, ethylenediamine and NaOH in the NaOH aqueous solution is 1: (1.2-1.8): (2-2.4); the mass fraction of the NaOH aqueous solution is 30-50%; The mass ratio of the epoxy resin to the curing agent is 1: (0.1-0.35); The curing includes a first curing and a second curing performed sequentially; the temperature of the first curing is 78-83° C. and the time is 3.5-4.5 hours; the temperature of the second curing is 115-125° C. and the time is 1-1.5 hours.

2. The epoxy resin cured product according to claim 1, characterized in that The organic solvent includes one or more of chloroform, dichloromethane and pyridine.

3. The epoxy resin cured product according to claim 1 or 2, characterized in that: The mixing method is: Dissolving terephthaloyl chloride in an organic solvent to obtain a terephthaloyl chloride organic solution; Dissolving ethylenediamine in a NaOH aqueous solution to obtain an ethylenediamine mixed solution; The terephthaloyl chloride organic solution is placed in an ice water bath, and the ethylenediamine mixed solution is added dropwise thereto; the dropping rate of the ethylenediamine mixed solution is 1-3 mL / min.

4. The epoxy resin cured product according to claim 1, characterized in that: The temperature of the polycondensation reaction is 25-30° C. and the time is 2.5-4 hours.

5. The epoxy resin cured product according to claim 1 or 4, characterized in that: After the polycondensation reaction, the obtained polycondensation reaction system is washed and dried in sequence; the washing includes washing with a saturated sodium bicarbonate aqueous solution, washing with saturated saline water and washing with distilled water in sequence; the pH value of the polycondensation reaction system after washing with saturated saline water is 6.5-7.2.

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