A cashew phenol curing agent at room temperature, and a preparation method and application thereof

Abstract

The application discloses a kind of ambient temperature fast-curing cardanol curing agent and its preparation method and application;The application is prepared by 2-bromoethylamine hydrobromide, potassium hydroxide and anhydrous ethanol after mixing reaction 2-bromoethylamine;Cardanol, diethylene triamine DETA, formaldehyde solution are mixed after reaction to obtain cardanol curing agent intermediate PK3;2-bromoethylamine, PK3, potassium carbonate and acetone are mixed after reaction to prepare ambient temperature fast-curing cardanol curing agent PK3-ENH2.The ambient temperature fast-curing cardanol curing agent production process of the application is simple, and the production equipment is not high in requirement.The ambient temperature fast-curing cardanol curing agent of the application has good chemical resistance, adhesion, physical and mechanical properties of solvent type epoxy coating, and has the characteristics of low pollution, simple construction, etc.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of organic synthesis, and particularly relates to a cashew phenol curing agent capable of being rapidly cured at room temperature, and a preparation method and application thereof. BACKGROUND

[0002] Cashew phenol is a renewable material extracted from natural cashew nut shell oil, has a unique chemical structure and excellent performance, and is increasingly concerned due to its abundant source. At present, the cashew phenol is mainly used in the fields of epoxy curing agent and phenolic resin. The paint film obtained after the epoxy curing agent prepared from the cashew phenol is cured with the epoxy resin has the advantages of corrosion resistance, high temperature resistance and convenient use at low temperature, and is mainly used in the aspect of coating.

[0003] At present, the preparation of the cashew phenol curing agent is mainly through the Mannich reaction of cashew phenol, aldehyde (such as formaldehyde, polyformaldehyde and trioxymethylene formaldehyde) and polyamine (which can also be mixed amine), and then removing the excess aldehyde and amine and water produced in the reaction. The polyamine includes ethylenediamine, diethylenetriamine, triethylenetetramine and pentaethylenehexamine, etc. The cashew phenol curing agent prepared by using these polyamines usually has a large viscosity, and a large amount of bubbles will be generated when mixed with the epoxy resin monomer, and these bubbles still exist after curing, which will have a great influence on the various performances of the cured resin material. At the same time, the molecular structure of the curing agent prepared by using these raw materials contains a phenolic hydroxyl group, and due to the hydrogen bond formed between the phenolic hydroxyl group and the hydrogen atom in the amine group, the interaction between the curing agents is increased, and the phenolic hydroxyl group is oxidized into quinone, which causes the change of the color of the curing agent and the decline of the performance. SUMMARY

[0004] In view of the deficiencies in the prior art, the purpose of the present application is to provide a cashew phenol curing agent capable of being rapidly cured at room temperature, and a preparation method and application thereof. The phenolic hydroxyl group in the molecular structure of the synthesized cashew phenol curing agent is introduced with an amine ethyl group to obtain the cashew phenol curing agent capable of being rapidly cured at room temperature.

[0005] The purpose of the present application is achieved by the following technical solutions.

[0006] The present application provides a cashew phenol curing agent capable of being rapidly cured at room temperature, and the structural formula is as follows:

[0007]

[0008] Among them,

[0009] The present application provides a preparation method of the above-mentioned cashew phenol curing agent capable of being rapidly cured 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) The cashew phenol, diethylene triamine DETA, and formaldehyde solution are mixed and reacted to obtain a cashew phenol curing agent intermediate PK3;

[0012] (3) 2-Bromoethylamine, PK3, potassium carbonate, and acetone are mixed and reacted to obtain a cashew phenol curing agent PK3-ENH2 that is rapidly cured at room temperature;

[0013] The reaction equation is as follows:

[0014]

[0015] wherein,

[0016] Preferably, the temperature of the reaction in step (1) is 60-70°C, and the 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 temperature of the reaction in step (2) is 65-80°C, and the time is 4-6h.

[0020] Preferably, the molar ratio of cashew phenol, diethylene triamine DETA, and formaldehyde in step (2) 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 performed below 60°C.

[0023] Preferably, the temperature of the reaction in step (3) is 40-60°C, and the 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 diethylene triamine DETA is greater than or equal to 99%.

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

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

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

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

[0031] Application of the above-mentioned room-temperature fast-curing cardanol curing agent in resin curing and bonding.

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

[0033] Preferably, the curing and bonding temperature is 20-70 DEG C; further preferably, room temperature.

[0034] In the present application, cardanol is a natural, non-toxic renewable material extracted from cashew nut shell liquid, which is subjected to Mannich reaction to generate intermediate substance Mannich base (PK3); then 2-bromoethylamine hydrobromide is reacted with alkali to generate 2-bromoethylamine; finally, 2-bromoethylamine is introduced with amine ethyl to obtain a room-temperature fast-curing curing agent, and the mechanism is as follows: cardanol is subjected to Mannich reaction to obtain Mannich base (PK3), 2-bromoethylamine hydrobromide is reacted with alkali to obtain 2-bromoethylamine, and 2-bromoethylamine attacks phenolic hydroxyl group and removes by-products to obtain the curing agent PK3-ENH2.

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

[0036] The prior art obtains a curing agent by reacting cardanol, polyamine and aldehyde and then performing vacuum distillation treatment, and the present application protects the phenolic hydroxyl group by subjecting the free phenolic hydroxyl group of the curing agent to Williamson etherification with 2-bromoethylamine, so that the phenolic hydroxyl group is prevented from being oxidized. Meanwhile, the active site is increased after the ether is generated, and the molecular structure does not contain a hydroxyl hydrogen atom, so that the intermolecular hydrogen bond is not generated, the viscosity is reduced, no bubbles are generated during use, no defoaming agent is needed, the performance of the cured resin is not affected, and the construction is facilitated.

[0037] The production process of the present application is simple, and the production equipment requirement is not high; the room-temperature fast-curing cardanol curing agent of the present application has good chemical resistance, adhesion, physical and mechanical properties of solvent-type epoxy coating, low pollution, simple construction and the like; and the room-temperature and high-temperature fast curing can be realized. BRIEF DESCRIPTION OF DRAWINGS

[0038] Figure 1 Stress-strain curves of samples after room-temperature curing of three kinds of curing agents and E51 epoxy resin.

[0039] Figure 2The 1H NMR spectrum of cashew phenol is shown.

[0040] Figure 3 The 1H NMR spectrum of the intermediate Mannich base PK3.

[0041] Figure 4 The 1H NMR spectrum of the room-temperature rapid curing agent PK3-ENH2 is shown.

[0042] Figure 5 The carbon NMR spectrum of cashew phenol is shown.

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

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

[0045] Figure 8 The infrared spectra of the raw material cashew phenol, the intermediate Mannich base PK3, and the curing agent PK3-ENH2 are shown. Detailed Implementation

[0046] The present invention will be specifically described below with reference to the embodiments, but the implementation and protection scope of the present invention are not limited to the following embodiments.

[0047] A method for preparing a room-temperature rapid-curing cashew phenol curing agent includes the following steps:

[0048] (1) KOH is slowly added to anhydrous ethanol at room temperature, and the temperature is controlled not to exceed 40℃. 2-bromoethylamine hydrobromide is added, and the temperature is raised to 60-65℃ and kept for 1.5-12h. The generated KBr solid is removed by filtration, and then the ethanol is removed by vacuum distillation to obtain a pale yellow 2-bromoethylamine oily liquid.

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

[0050] (3) Add acetone to dissolve the intermediate PK3 at room temperature, then add potassium carbonate, stir at room temperature for 0.5-1 h, then add 2-bromoethylamine dropwise, and then raise the temperature to 40-60 °C, and react for 6-12 h. After the reaction is completed, filter off the potassium carbonate solids, then remove the acetone and unreacted 2-bromoethylamine by distillation under reduced pressure, and then wash with water and dry to obtain a red-brown liquid PK3-ENH2.

[0051] The reaction equation is as follows:

[0052]

[0053] wherein,

[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 to be no more than 40 °C, add 2-bromoethylamine hydrobromide 61.5 g (0.3 mol), raise the temperature to 60 °C and keep for 12 h, filter off the generated KBr solids, and then remove the ethanol by distillation under reduced pressure to obtain a yellowish 2-bromoethylamine oily liquid.

[0056] (2) In a three-necked flask, add cardanol 60.4 g (0.2 mol), and then add diethylenetriamine (DETA) 41.3 g (0.4 mol) dropwise at room temperature, control the temperature to be no more than 50 °C during the dropwise addition, and then stir at room temperature for 1.5 h after the dropwise addition is completed, and then add 37 wt% aqueous formaldehyde solution 32.4 g (0.4 mol) dropwise at room temperature (the molar ratio of the three is 1:2:2), control the temperature to be no more than 60 °C, raise the temperature to 75 °C, keep for 5 h, and then separate the lower aqueous phase while hot after the reaction is completed, and then remove the residual water and unreacted polyamines and formaldehyde by distillation under reduced pressure to obtain the curing agent intermediate Mannich base (PK3).

[0057] (3) In a four-necked flask, dissolve the curing agent intermediate Mannich base (PK3) 21.0 g (0.05 mol) in 40 mL of acetone at room temperature, add 8.3 g (0.06 mol) of K2CO3 solids, stir at room temperature for 2 h, then add 6.8 g (0.055 mol) of 2-bromoethylamine, raise the temperature to 40 °C and keep for 12 h, filter off the unreacted K2CO3 solids and the generated KBr solids, wash and dry, and then remove the acetone by distillation under reduced pressure to obtain the room-temperature fast-curing cardanol curing agent PK3-ENH2.

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

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

[0060] The infrared spectra of the raw material cashew phenol, the intermediate Mannich base PK3, and the curing agent PK3-ENH2 are as follows: Figure 8 .

[0061] It can be seen that: Figure 2 , 3 As can be seen from the 1H NMR spectrum in section 4, the signals in the 0.5-3.0 ppm range represent alkyl methylene hydrogen, and the signals in the 4.9-5.9 ppm range represent hydrogen on the double bonds of the benzene ring side chain. Figures 1-5 The NMR spectrum of the intermediate PK3, formed by the reaction of cashew phenol with formaldehyde and diethylenetriamine, shows a characteristic peak of the methylene group linked to DETA at 3.0-4.5 ppm, and a characteristic peak of the -DETA portion at 2.0-3.0 ppm. The characteristic peak of the phenolic ether (ph-O-Pr) is at 0.5-1.5 ppm, indicating that the ethylamine group was successfully introduced into the curing agent molecule.

[0062] exist Figure 5 , 6 As can be seen from the carbon NMR spectrum in 7, Figure 5 A signal of 110-160 ppm represents aromatic ring carbon, while a signal of 0-50 ppm represents alkyl chains. Figure 6 The carbon spectrum of cashew phenol after the ortho-position of the phenolic hydroxyl group is replaced by DETA shows a characteristic peak of the methylene group linked to DETA in the 50-70 ppm range, indicating that the introduced DETA group has changed the chemical environment of the carbon. Figure 7 The carbon spectrum of the phenolic hydroxyl group after etherification was further shown, and the characteristic peak of phenolic ether (ph-O-Pr) appeared in the range of 60-90 ppm. This reflects the influence of the etherification reaction on the carbon environment, while the signal of the DETA part is still preserved.

[0063] exist Figure 8The infrared spectrum can be seen in the vicinity of 3000 cm"1-OH stretching vibration absorption peak. By reaction to generate PK3, its infrared spectrum shows obvious N-H absorption peak (about 3300 cm"1) and C-N absorption peak (about 1153 cm"1), indicating the introduction of amine group and amine compound. Further from PK3 to generate PK3-O-ENH2, the appearance of ph-O-C absorption peak (about 1075 cm"1and 1220 cm"1) shows that the intermediate PK3 phenolic hydroxyl -OH is successfully converted into ether bond.

[0064] The above analysis shows that the expected experimental design of the curing agent is 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, and the temperature was raised to 65 °C for 1.5 h, then the generated KBr solid was removed by filtration, and then the ethanol was removed by distillation under reduced pressure, to obtain 2-bromoethylamine.

[0067] (2) In a four-necked flask, cashew phenol 302 g (1.0 mol) was added at room temperature, and diethylene triamine (DETA) 309.5 g (3.0 mol) was added dropwise, the temperature was controlled not to exceed 50 °C during the dropwise addition, after the dropwise addition was completed, the mixture was stirred at room temperature for 1.5 h, then 37 wt% formaldehyde aqueous solution 243.2 g (3.0 mol) was added dropwise at room temperature (the molar ratio of the three was 1:3:3), the temperature was controlled below 60 °C, the temperature was raised to 75 °C, and the mixture was kept at this temperature for 5 h, after the reaction was completed, the mixture was separated while hot, the lower aqueous phase was removed, then the residual water and unreacted polyamine and formaldehyde were removed by distillation under reduced pressure, 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, after stirring at room temperature for 2 h, 68.2 g (0.55 mol) of 2-bromoethylamine was added, the temperature was raised to 40 °C for 12 h, then the unreacted K2CO3 solid and the generated KBr solid were removed by filtration, washed and dried, and then the acetone was removed by distillation under reduced pressure, to obtain the room temperature fast curing cashew phenol 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 below 40 °C, 153.6 g (0.75 mol) of 2-bromoethylamine hydrobromide was added, the temperature was raised to 65 °C and maintained for 3 h, the generated KBr solid was removed by filtration, then the ethanol was removed by distillation 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, 24.8 g (0.24 mol) of diethylenetriamine (DETA) was added dropwise, the temperature was controlled below 50 °C during the dropwise addition, after the dropwise addition was completed, the mixture was stirred at room temperature for 0.5 h, then 19.5 g (0.24 mol) of 37 wt% aqueous formaldehyde solution (molar ratio of 1:1.2:1.2) was added dropwise at room temperature, the temperature was controlled below 50 °C, the temperature was raised to 65 °C, and maintained for 5.5 h, after the reaction was completed, the mixture was separated while hot, the lower aqueous phase was removed, then the residual water, unreacted polyamine and formaldehyde were removed by distillation under reduced pressure 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, after stirring at room temperature for 2 h, 13.6 g (0.11 mol) of 2-bromoethylamine was added, the temperature was raised to 40 °C and maintained for 12 h, the unreacted K2CO3 solid and the generated KBr solid were removed by filtration, washed and dried, then the acetone was removed by distillation under reduced pressure to obtain the room temperature fast curing cardanol curing agent PK3-ENH2.

[0073] Determination of amine value of curing agent

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

[0075] Perchloric acid non-aqueous titration method: about 0.3 grams of curing agent sample was weighed to 0.0001 gram, placed in a 250 mL conical flask, about 25 mL of glacial acetic acid was added, shaken until completely dissolved, then 1-2 drops of methyl violet indicator was added, and titrated with perchloric acid standard solution.

[0076] Table 1 Amine values of three batches of different curing agents 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 there is no significant difference between batches. Moreover, the difference in amine value is within a reasonable range, which indicates that there is no major deviation in the preparation process.

[0079] Curing performance test

[0080] (1) Room temperature curing

[0081] Curing test Test procedure (indentation method): PK3-ENH2-1 curing agent synthesized in Comparative Example 1, cardanol-modified aliphatic amine PK3 with unreacted phenolic hydroxyl group (same preparation method as Example 1, except that step (3) was not performed), and PK3-Pr curing agent with propyl introduced into phenolic hydroxyl group as ether (same preparation method as Example 1, except that step (3) was performed using propyl bromide instead of 2-bromoethylamine) were mixed with E51 epoxy resin at a mass ratio of 1:1, and 20-30 wt% of ethyl acetate was added for stirring for 1-2 hours. After the solvent was volatilized, the mixture was cured at room temperature for 12 hours. The curing performance of the three curing agents was studied. The experimental results showed that this method can effectively mix the curing agent and the epoxy resin, and the ethyl acetate helps to reduce the viscosity and promote uniform distribution. The material cured by the PK3-ENH2 curing agent has good hardness and mechanical strength, and there is no obvious bubble, crack or delamination phenomenon, and the residual solvent is less, and the overall curing effect is good.

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

[0083]

[0084] (2) Heating curing

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

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

[0087]

[0088]

[0089] From the two groups of curing experiments of room temperature curing and 60°C heating curing, it can be seen that the PK3 curing agent with unreacted phenolic hydroxyl group will produce more bubbles during curing, which will have a significant impact on the performance of the cured material. If you want to reduce the bubbles produced, you need to add a defoaming agent. The PK3-Pr curing agent with propyl introduced into the phenolic hydroxyl group has a slow curing rate, and it needs more time to cure. The PK3-ENH2 curing agent has a shorter curing time than the other two curing agents under the same conditions, and almost no bubbles are produced during the curing process, and no defoaming agent is needed, avoiding the influence of the introduction of the defoaming agent on the performance of the epoxy resin material.

[0090] (3) Material pull-up performance test after room temperature curing

[0091] Figure 1are stress-strain curves of samples cured with three different curing agents and E51 epoxy resin at room temperature. Table 4 is the test data of tensile strength and elongation at break of samples cured with 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 PK3-ENH2 cured material is significantly improved. From the two aspects of elongation at break and tensile strength, the performance of the sample cured with PK3-ENH2 curing agent and E51 resin is the best.

[0092] Table 4 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 examples are the preferred embodiments of the present application, but the embodiments of the present application are not limited by the above examples, and any changes, modifications, substitutions, combinations, simplifications made without departing from the spirit and principles of the present application shall be equivalent replacement methods and shall be within the scope of protection of the present application.

Claims

1. A room temperature fast curing cardanol curing agent, characterized by, The structural formula is as follows: wherein 2. The method of claim 1, wherein the preparation of the room temperature fast curing cardanol curing agent is characterized by, The method comprises the following steps: (1) 2-bromoethylamine hydrobromide, potassium hydroxide and anhydrous ethanol are mixed to prepare 2-bromoethylamine; (2) cashew phenol, diethylene triamine DETA and formaldehyde solution are mixed to obtain a cashew phenol curing agent intermediate PK3; (3) 2-bromoethylamine, PK3, potassium carbonate and acetone are mixed to prepare a cashew phenol curing agent PK3-ENH2 which can be rapidly cured at room temperature; The reaction equation is as follows: wherein 3. The method of claim 2, wherein the preparation of the room temperature fast curing cardanol curing agent is characterized by, The temperature of the reaction in step (1) is 60-70 DEG C, and the time is 1-24 h.

4. The method of claim 2, wherein the preparation of the room temperature fast- curing cardanol curing agent is characterized by, 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 1-2 M.

5. The method of claim 2, wherein the preparation of the room temperature fast curing cardanol curing agent is characterized by, The temperature of the reaction in step (2) is 65-80 DEG C, and the time is 4-6 h.

6. The method of claim 2, wherein the preparation of the ambient fast-curing cardanol curing agent is characterized by, The molar ratio of cashew phenol, diethylene triamine DETA and formaldehyde in step (2) 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 below 60 DEG C.

7. The method of claim 2, wherein the preparation of the ambient fast-curing cardanol curing agent is characterized by, The temperature of the reaction in step (3) is 40-60 DEG C, and the time is 6-24 h.

8. The method of claim 2, wherein the preparation of the ambient fast-curing cardanol curing agent is characterized by, 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 1-2 M.

9. The application of the cashew phenol curing agent which can be rapidly cured at room temperature according to claim 1 in resin curing and bonding.

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

Images