Cardanol curing agent capable of being rapidly cured at normal temperature as well as preparation method and application of cardanol curing agent

Abstract

The invention discloses a normal-temperature fast curing cardanol curing agent as well as a preparation method and application thereof. The preparation method comprises the following steps: mixing 2-bromoethylamine hydrobromide, potassium hydroxide and absolute ethyl alcohol, and reacting to prepare 2-bromoethylamine; the preparation method comprises the following steps: mixing cardanol, diethylenetriamine DETA and a formaldehyde solution, and reacting to obtain a cardanol curing agent intermediate PK3; and mixing 2-bromoethylamine, PK3, potassium carbonate and acetone, and reacting to prepare the cardanol curing agent PK3-ENH2 capable of being rapidly cured at normal temperature. The normal-temperature rapidly-cured cardanol curing agent is simple and convenient in production process and low in requirement on production equipment, has good chemical resistance, adhesiveness and physical and mechanical properties of a solvent type epoxy coating, and also has the characteristics of low pollution, simplicity and convenience in construction and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of organic synthesis, and in particular relates to a cardanol curing agent that quickly solidifies at room temperature, and a preparation method and application thereof. Background Art

[0002] Cardanol is a renewable substance extracted from natural cashew nut shell oil. It has a unique chemical structure and excellent performance. At the same time, it has attracted more and more attention due to its abundant sources. At present, the use of cardanol is mainly in the fields of epoxy curing agent, phenolic resin, etc. The paint film obtained by curing the epoxy curing agent prepared by cardanol with epoxy resin has the advantages of corrosion resistance, high temperature resistance, and convenient use at low temperatures. It is mainly used in coatings.

[0003] At present, the preparation of cardanol curing agent mainly uses cardanol, aldehydes (such as formaldehyde, polyformaldehyde and trioxymethylene, etc.) and polyamines (also mixed amines) through Mannich reaction, and removes excess aldehydes and amines and water produced by the reaction after the reaction. Among them, polyamines include ethylenediamine, diethylenetriamine, triethylenetetramine and pentaethylenehexamine, etc. The cardanol curing agent prepared with these polyamines usually has a relatively large viscosity, and a large number of bubbles will be generated when mixed with epoxy resin monomers. These bubbles still exist after curing, which will have a huge impact on the various properties of the cured resin material. At the same time, the curing agent molecular structure prepared with these raw materials contains a phenolic hydroxyl group. Since the phenolic hydroxyl group easily forms hydrogen bonds with the hydrogen atoms in the amine group, the interaction between the curing agents increases, and the phenolic hydroxyl group is oxidized to quinone, resulting in a color change of the curing agent, and the performance will also decrease accordingly. Summary of the invention

[0004] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a cardanol curing agent that cures quickly at room temperature, and a preparation method and application thereof. The present invention introduces an aminoethyl group into the phenolic hydroxyl group in the molecular structure of the synthesized cardanol curing agent to obtain a cardanol curing agent that cures quickly at room temperature.

[0005] The purpose of the present invention is achieved through the following technical solutions:

[0006] The present invention provides a cardanol curing agent that cures quickly at room temperature, and the structural formula is as follows:

[0007]

[0008] in,

[0009] The present invention provides a method for preparing the above-mentioned cardanol curing agent that rapidly cures at room temperature, comprising the following steps:

[0010] (1) 2-bromoethylamine hydrobromide, potassium hydroxide and anhydrous ethanol are mixed and reacted to prepare 2-bromoethylamine;

[0011] (2) mixing cardanol, diethylenetriamine DETA, and formaldehyde solution and reacting to obtain cardanol curing agent intermediate PK3;

[0012] (3) 2-bromoethylamine, PK3, potassium carbonate and acetone were mixed and reacted to prepare the cardanol curing agent PK3-ENH2 which can be cured quickly at room temperature;

[0013] The reaction equation is as follows:

[0014]

[0015] in,

[0016] Preferably, the reaction temperature in step (1) is 60-70°C and the reaction time is 1-24h.

[0017] Preferably, the molar ratio of 2-bromoethylamine hydrobromide to potassium hydroxide in step (1) is 1:(1-2);

[0018] Preferably, the concentration of 2-bromoethylamine hydrobromide in anhydrous ethanol in step (1) is 1-2M.

[0019] Preferably, the reaction temperature in step (2) is 65-80°C and the reaction time is 4-6h.

[0020] Preferably, in step (2), the molar ratio of cardanol, diethylenetriamine DETA and formaldehyde is 1:2-3:2-3;

[0021] Preferably, the mass concentration of the formaldehyde solution in step (2) is 30-40%; further preferably, the mass concentration of the formaldehyde solution is 37wt%.

[0022] Preferably, the mixing in step (2) is carried out at a temperature below 60°C.

[0023] Preferably, the reaction temperature in step (3) is 40-60°C and the reaction time is 6-24h.

[0024] Preferably, the molar ratio of 2-bromoethylamine, PK3 and potassium carbonate in step (3) is 1-2:1:1-2;

[0025] Preferably, the concentration of PK3 in acetone in step (3) is 1-2M.

[0026] Preferably, the purity of the diethylenetriamine DETA is greater than or equal to 99%.

[0027] Preferably, the purity of the cardanol is greater than or equal to 90%.

[0028] Preferably, the purity of the 2-bromoethylamine hydrobromide is greater than or equal to 99%.

[0029] Preferably, the purity of the potassium hydroxide is greater than or equal to 85%.

[0030] Preferably, the concentration of anhydrous ethanol is greater than or equal to 99%.

[0031] The above-mentioned room temperature fast curing cardanol curing agent is used in resin curing and bonding.

[0032] Preferably, the resin is selected from epoxy resin or phenolic resin.

[0033] Preferably, the curing and bonding temperature is 20-70° C.; more preferably, it is room temperature.

[0034] In the present invention, cardanol is a natural, non-toxic and renewable substance extracted from cashew nut shell liquid, and undergoes a Mannich reaction to generate an intermediate substance Mannich base (PK3); then 2-bromoethylamine hydrobromide reacts with a base to generate 2-bromoethylamine; finally, 2-bromoethylamine is used to introduce an aminoethyl group to obtain a curing agent that cures rapidly at room temperature, and the mechanism is as follows: cardanol undergoes a Mannich reaction to obtain Mannich base (PK3), 2-bromoethylamine hydrobromide reacts with a base to obtain 2-bromoethylamine, and 2-bromoethylamine attacks a phenolic hydroxyl group, and then removes byproducts to obtain the curing agent PK3-ENH2.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] The prior art uses cardanol, polyamine and aldehyde to react and then undergo vacuum distillation to obtain a curing agent. Based on the prior art, the present invention uses Williamson etherification reaction between the free phenolic hydroxyl groups of the curing agent molecules and 2-bromoethylamine to protect the phenolic hydroxyl groups from being oxidized. At the same time, the generation of ether increases the active sites, and the molecular structure does not contain hydroxyl hydrogen atoms, so that hydrogen bonds between molecules are not generated, the viscosity is reduced, and bubbles are not generated during use. No defoamer is needed to avoid affecting the performance of the cured resin, and the construction is convenient.

[0037] The production process of the invention is simple and the requirements on production equipment are not high; the cardanol curing agent that cures quickly at room temperature has the good chemical resistance, adhesion and physical and mechanical properties of solvent-based epoxy coatings, and has the characteristics of low pollution and simple construction; and can be cured quickly at room temperature and high temperature. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 These are the stress-strain curves of the samples after curing with three curing agents and E51 epoxy resin at room temperature.

[0039] Figure 2This is the hydrogen nuclear magnetic resonance spectrum of the raw material cardanol.

[0040] Figure 3 This is the hydrogen nuclear magnetic resonance spectrum of the intermediate Mannich base PK3.

[0041] Figure 4 It is the nuclear magnetic resonance hydrogen spectrum of the room temperature fast curing agent PK3-ENH2.

[0042] Figure 5 This is the carbon NMR spectrum of the raw material cardanol.

[0043] Figure 6 This is the carbon NMR spectrum of the intermediate Mannich base PK3.

[0044] Figure 7 It is the carbon nuclear magnetic resonance spectrum of the room temperature fast curing agent PK3-ENH2.

[0045] Figure 8 This is the infrared spectra of the raw material cardanol, the intermediate Mannich base PK3 and the curing agent PK3-ENH2. DETAILED DESCRIPTION

[0046] The present invention is described in detail below in conjunction with examples, but the implementation manner and protection scope of the present invention are not limited to the following examples.

[0047] A method for preparing a cardanol curing agent that rapidly cures at room temperature comprises the following steps:

[0048] (1) Slowly add KOH to anhydrous ethanol at room temperature, control the temperature not to exceed 40°C, add 2-bromoethylamine hydrobromide, raise the temperature to 60-65°C and keep it for 1.5-12 hours, filter out the generated KBr solid, and then remove the ethanol by vacuum distillation to obtain a light yellow 2-bromoethylamine oily liquid.

[0049] (2) Add cardanol to a three-necked flask, add diethylenetriamine DETA dropwise at room temperature, control the temperature not to exceed 50° C. during the addition, stir at room temperature for 1 to 2 hours, then add 37 wt % formaldehyde aqueous solution dropwise at room temperature, control the temperature not to exceed 60° C. during the addition, then control the reaction temperature to about 75° C., react for 4 to 6 hours, separate the liquid while hot after the reaction, separate the lower aqueous phase, and then remove the residual water and unreacted polyamine and formaldehyde by reduced pressure distillation to obtain the curing agent intermediate PK3;

[0050] (3) Acetone was added at room temperature to dissolve the intermediate PK3, and then potassium carbonate was added. The mixture was stirred at room temperature for 0.5 to 1 h, and then 2-bromoethylamine was added dropwise. After the addition, the temperature was raised to 40-60° C. and the mixture was reacted for 6 to 12 h. After the reaction, the potassium carbonate solid was filtered out, and then the acetone and unreacted 2-bromoethylamine were removed by vacuum distillation. The mixture was washed with water and dried to obtain a reddish brown liquid PK3-ENH2.

[0051] The reaction equation is as follows:

[0052]

[0053] in,

[0054] Example 1

[0055] (1) In a three-necked flask, dissolve 25.2 g (0.45 mol) of KOH in 180 mL of anhydrous ethanol at room temperature. Control the temperature not to exceed 40°C, add 61.5 g (0.3 mol) of 2-bromoethylamine hydrobromide, raise the temperature to 60°C and keep it warm for 12 h. Filter out the generated KBr solid, and then distill off the ethanol under reduced pressure to obtain a light yellow 2-bromoethylamine oily liquid.

[0056] (2) In a three-necked flask, 60.4 g (0.2 mol) of cardanol was added, and 41.3 g (0.4 mol) of diethylenetriamine (DETA) was added dropwise at room temperature. The temperature was controlled not to exceed 50°C during the addition. After the addition was completed, the mixture was stirred at room temperature for 1.5 h. Then, 32.4 g (0.4 mol) of a 37 wt% formaldehyde aqueous solution (the molar ratio of the three was 1:2:2) was added dropwise at room temperature. The temperature was controlled below 60°C, and the temperature was raised to 75°C and kept warm for 5 hours. After the reaction was completed, the liquid was separated while hot, the lower aqueous phase was separated, and the residual water and unreacted polyamine and formaldehyde were removed by reduced pressure distillation to obtain the curing agent intermediate Mannich base (PK3).

[0057] (3) In a four-necked flask, 21.0 g (0.05 mol) of the chemical intermediate Mannich base (PK3) was dissolved in 40 mL of acetone at room temperature, 8.3 g (0.06 mol) of K2CO3 solid was added, and after stirring at room temperature for 2 h, 6.8 g (0.055 mol) of 2-bromoethylamine was added, and the temperature was raised to 40° C. and kept for 12 h. The unreacted K2CO3 solid and the generated KBr solid were filtered out, and the acetone was removed by vacuum distillation after washing and drying to obtain the room temperature fast curing cardanol curing agent PK3-ENH2.

[0058] The H NMR spectrum of raw material cardanol is as follows Figure 2 The H NMR spectrum of the intermediate Mannich base PK3 is as follows Figure 3The nuclear magnetic resonance hydrogen spectrum of the fast curing agent PK3-ENH2 is as follows Figure 4 .

[0059] The NMR carbon spectrum of raw material cardanol is as follows Figure 5 The C NMR spectrum of the intermediate Mannich base PK3 is as follows Figure 6 The carbon NMR spectrum of the fast curing agent PK3-ENH2 is as follows: Figure 7 .

[0060] The infrared spectra of raw material cardanol, intermediate Mannich base PK3 and curing agent PK3-ENH2 are shown in Figure 8 .

[0061] It can be seen that: Figure 2 , 3 From the H NMR spectra in 4, it can be seen that the signals at 0.5-3.0 ppm represent the alkyl methylene hydrogens. The signals at 4.9-5.9 ppm represent the hydrogens on the double bonds on the side chains of the benzene rings. Figure 1-5 This is the nuclear magnetic resonance hydrogen spectrum of the intermediate PK3 generated by the reaction of cardanol with formaldehyde and diethylenetriamine, in which the characteristic peak of the methylene connected to DETA is at 3.0-4.5ppm, and the characteristic peak of the -DETA part is at 2.0-3.0ppm. The characteristic peak of phenol ether (ph-O-Pr) is at 0.5-1.5ppm, indicating that the ethylamine group is successfully introduced into the curing agent molecule.

[0062] exist Figure 5 , 6 From the carbon NMR spectrum in 7, we can see that Figure 5 The signals at 110-160 ppm represent aromatic ring carbons, and the signals at 0-50 ppm are alkyl chains. Figure 6 This is the carbon spectrum after the ortho position of the phenolic hydroxyl group of cardanol is replaced by DETA. In the range of 50-70ppm, there is a characteristic peak of the methylene connected to DETA, which indicates that the introduced DETA group changes the chemical environment of the carbon. Figure 7 The carbon spectrum of the etherified phenolic hydroxyl group was further displayed, and the characteristic peaks of phenol ether (ph-O-Pr) appeared at 60-90 ppm, which reflected the effect of the etherification reaction on the carbon environment. At the same time, the signal of the DETA part was still retained.

[0063] exist Figure 8The infrared spectrum shows the -OH stretching vibration absorption peak near 3000cm-1. PK3 is generated by reaction, and its infrared spectrum shows obvious NH absorption peak (about 3300cm-1) and CN absorption peak (about 1153cm-1), indicating the introduction of amine groups and amine compounds. After PK3-O-ENH2 is further generated from PK3, the ph-OC absorption peaks (about 1075cm-1 and 1220cm-1) appear, indicating that the phenolic hydroxyl -OH of the intermediate PK3 is successfully converted into an ether bond.

[0064] The above analysis shows that the curing agent of the expected experimental design was successfully synthesized.

[0065] Example 2

[0066] (1) In a three-necked flask, 108.9 g (1.8 mol) of KOH was dissolved in 900 mL of anhydrous ethanol at room temperature. The temperature was controlled not to exceed 40°C. 307.3 g (1.5 mol) of 2-bromoethylamine hydrobromide was added. The temperature was raised to 65°C and kept for 1.5 h. The generated KBr solid was filtered out, and then the ethanol was removed by vacuum distillation to obtain 2-bromoethylamine.

[0067] (2) In a four-necked flask, 302 g (1.0 mol) of cardanol was added at room temperature, and 309.5 g (3.0 mol) of diethylenetriamine (DETA) was added dropwise. The temperature was controlled not to exceed 50°C during the addition. After the addition was completed, the mixture was stirred at room temperature for 1.5 h. Then, 243.2 g (3.0 mol) of a 37 wt% formaldehyde aqueous solution (the molar ratio of the three was 1:3:3) was added dropwise at room temperature. The temperature was controlled below 60°C, raised to 75°C, and kept warm for 5 hours. After the reaction was completed, the liquid was separated while hot, the lower aqueous phase was separated, and the residual water and unreacted polyamine and formaldehyde were removed by reduced pressure distillation to obtain PK3.

[0068] (3) In a four-necked flask, 210 g (0.5 mol) of PK3 was dissolved in 400 mL of acetone at room temperature, 83.0 g (0.6 mol) of K2CO3 solid was added, and after stirring at room temperature for 2 h, 68.2 g (0.55 mol) of 2-bromoethylamine was added, and the temperature was raised to 40° C. and kept for 12 h. The unreacted K2CO3 solid and the generated KBr solid were filtered out, and the acetone was removed by vacuum distillation after washing and drying to obtain the room temperature fast curing cardanol curing agent PK3-ENH2.

[0069] Example 3

[0070] (1) In a three-necked flask, 50.4 g (0.9 mol) of KOH was dissolved in 300 mL of anhydrous ethanol at room temperature. The temperature was controlled not to exceed 40°C. 153.6 g (0.75 mol) of 2-bromoethylamine hydrobromide was added. The temperature was raised to 65°C and kept for 3 h. The generated KBr solid was filtered out, and then the ethanol was distilled off under reduced pressure to obtain 2-bromoethylamine.

[0071] (2) In a four-necked flask, 60.4 g (0.2 mol) of cardanol was added at room temperature, and 24.8 g (0.24 mol) of diethylenetriamine (DETA) was added dropwise. The temperature was controlled not to exceed 50°C during the addition. After the addition was completed, the mixture was stirred at room temperature for 0.5 h. Then, 19.5 g (0.24 mol) of a 37 wt% formaldehyde aqueous solution (the molar ratio of the three was 1:1.2:1.2) was added dropwise at room temperature. The temperature was controlled below 50°C, and the temperature was raised to 65°C and kept warm for 5.5 hours. After the reaction was completed, the liquid was separated while hot, the lower aqueous phase was separated, and the residual water and unreacted polyamine and formaldehyde were removed by reduced pressure distillation to obtain PK3.

[0072] (3) In a four-necked flask, 42.0 g (0.1 mol) of PK3 was dissolved in 80 mL of acetone at room temperature, 16.6 g (0.12 mol) of K2CO3 solid was added, and after stirring at room temperature for 2 h, 13.6 g (0.11 mol) of 2-bromoethylamine was added, and the temperature was raised to 40° C. and kept for 12 h. The unreacted K2CO3 solid and the generated KBr solid were filtered out, and after washing and drying, the acetone was removed by vacuum distillation to obtain the room temperature fast curing cardanol curing agent PK3-ENH2.

[0073] Determination of amine value of curing agent

[0074] Amine value: Amine value refers to the number of milligrams of KOH required to neutralize every 1g of sample, and the unit is mgKOH / g.

[0075] Perchloric acid non-aqueous titration method: weigh about 0.3 g of curing agent sample, accurate to 0.0001 g, place it in a 250 ml conical flask, add about 25 ml of glacial acetic acid, shake until completely dissolved, add 1 to 2 drops of methyl violet indicator, and titrate with perchloric acid standard solution.

[0076] Table 1 Amine values ​​of three batches of different curing agent PK3-ENH2

[0077]

[0078] It can be seen that the amine values ​​of the three batches of curing agents are not much different, indicating the consistency of the amine values ​​and no significant differences between the batches. Moreover, the differences in amine values ​​are within a reasonable range, indicating that there are no major deviations in the preparation process.

[0079] Curing performance test

[0080] (1)Room temperature curing

[0081] Curing test test steps (indentation method): Comparative Example 1 synthesized PK3-ENH2-1 curing agent, cardanol modified fatty amine PK3 with unreacted phenolic hydroxyl group (same as the preparation method of Example 1, except that step (3) is not performed) and PK3-Pr curing agent with propyl group introduced into phenolic hydroxyl group to form ether (same as the preparation method of Example 1, except that bromopropane is used instead of 2-bromoethylamine in step (3)) are mixed with E51 epoxy resin in a mass ratio of 1:1, and 20-30wt% ethyl acetate is added for stirring for 1 to 2 hours, and cured at room temperature for 12 hours after the solvent evaporates. The curing properties of the three curing agents are studied. The experimental results show that this method can effectively mix the curing agent and epoxy resin, and ethyl acetate helps to reduce viscosity and promote uniform distribution. The material cured by PK3-ENH2 curing agent has good hardness and mechanical strength, no obvious bubbles, cracks or delamination, less residual solvent, and good overall curing effect.

[0082] Table 2 Comparison of room temperature curing performance of three different curing agents

[0083]

[0084] (2) Heating and curing

[0085] The curing test procedure (indentation method) is the same as room temperature curing, except that the curing is performed at 60°C for 10 h.

[0086] Table 3 Comparison of curing performance of three different curing agents at 60°C

[0087]

[0088]

[0089] From the two curing experiments of room temperature curing and 60℃ heating curing, it can be seen that the PK3 curing agent with unreacted phenolic hydroxyl groups will produce more bubbles during curing, which will have a significant impact on the performance of the cured material. To reduce the bubbles, a defoamer must be added. The PK3-Pr curing agent with phenolic hydroxyl groups introduced into the propyl group has a slow curing rate and requires more time to cure. When the PK3-ENH2 curing agent is cured under the same conditions as the other two curing agents, the curing time required is shorter, and almost no bubbles are generated during the curing process. No defoamer is required, which avoids the impact of the introduction of defoamers on the performance of epoxy resin materials.

[0090] (3) Material tensile performance test after room temperature curing

[0091] Figure 1Table 4 is the test data of tensile strength and elongation at break of samples cured by three different curing agents and E51 epoxy resin at room temperature. Compared with PK3 curing agent, the tensile strength of PK3-ENH2 is significantly increased. Compared with PK3-Pr, the elongation at break of materials cured by PK3-ENH2 is significantly improved. From the perspective of elongation at break and tensile strength, the sample cured by PK3-ENH2 curing agent and E51 resin has the best performance.

[0092] Table 4 Room temperature tensile strength and elongation at break of samples cured with three different curing agents and E51 epoxy resin at room temperature

[0093]

[0094]

[0095] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principle of the present invention shall be equivalent replacement modes and shall be included in the protection scope of the present invention.

Claims

1. A cardanol curing agent that cures quickly at room temperature, characterized in that: The structural formula is as follows: Among them 2. The method for preparing the cardanol curing agent that rapidly cures at room temperature according to claim 1, characterized in that: The following steps are involved: (1) 2-bromoethylamine hydrobromide, potassium hydroxide and anhydrous ethanol are mixed and reacted to prepare 2-bromoethylamine; (2) mixing cardanol, diethylenetriamine DETA, and formaldehyde solution and reacting to obtain cardanol curing agent intermediate PK3; (3) 2-bromoethylamine, PK3, potassium carbonate and acetone were mixed and reacted to prepare the cardanol curing agent PK3-ENH2 which can be cured quickly at room temperature; The reaction equation is as follows: in, 3. The method for preparing a cardanol curing agent that rapidly cures at room temperature according to claim 2, characterized in that: The reaction temperature of step (1) is 60-70°C and the reaction time is 1-24h.

4. The method for preparing a cardanol curing agent that rapidly cures at room temperature according to claim 2, characterized in that: The molar ratio of 2-bromoethylamine hydrobromide to potassium hydroxide in step (1) is 1:(1-2); The concentration of 2-bromoethylamine hydrobromide in anhydrous ethanol in step (1) is 1-2M.

5. The method for preparing a cardanol curing agent that rapidly cures at room temperature according to claim 2, characterized in that: The reaction temperature of step (2) is 65-80°C and the reaction time is 4-6h.

6. The method for preparing a cardanol curing agent that rapidly cures at room temperature according to claim 2, characterized in that: In step (2), the molar ratio of cardanol, diethylenetriamine DETA and formaldehyde is 1:2-3:2-3; The mass concentration of the formaldehyde solution in step (2) is 30-40%; The mixing in step (2) is carried out at a temperature below 60°C.

7. The method for preparing a cardanol curing agent that rapidly cures at room temperature according to claim 2, characterized in that: The reaction temperature of step (3) is 40-60°C and the reaction time is 6-24h.

8. The method for preparing a cardanol curing agent that rapidly cures at room temperature according to claim 2, characterized in that: The molar ratio of 2-bromoethylamine, PK3 and potassium carbonate in step (3) is 1-2:1:1-2; The concentration of PK3 in acetone in step (3) is 1-2M.

9. Use of the room temperature fast curing cardanol curing agent according to claim 1 in resin curing and bonding.

10. The use according to claim 9, characterized in that: The resin is selected from epoxy resin or phenolic resin.

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