A carbon dot curing agent and its application

Abstract

The present invention discloses a carbon dot curing agent and its application. The carbon dot curing agent is obtained by heating a precursor to its pyrolysis temperature, keeping the temperature to pyrolyze, cooling to room temperature and dispersing it in water or ethanol, and finally centrifuging and filtering. The precursor is a carboxylic acid precursor, a phosphoric acid precursor, or a boric acid precursor. The present invention utilizes the abundant carboxylic acid, phosphoric acid, and boric acid groups on the surface of the carbon dot curing agent to react with epoxy to open the ring, achieving epoxy curing while constructing an ester exchange epoxy vitrimer system containing carboxylic acid esters, phosphate esters, boric acid esters, etc., and the high residual carbon rate of the carbon dots is expected to improve the flame retardancy of the epoxy vitrimer.

Description

Technical Field

[0001] The invention belongs to the field of epoxy resin curing agents, and particularly relates to a carbon dot curing agent and applications thereof. Background Art

[0002] After curing, epoxy resin exhibits excellent electrical insulation, high adhesion, dimensional stability, and corrosion resistance, making it widely used in coatings, chemical engineering, construction, and automotive applications. However, the inherent flammability of epoxy resins severely limits their practical application in production and life, and improving the flammability of epoxy resins has been a major research topic. Compared to traditional halogen flame retardants, which produce a large number of toxic pollutants, carbon dot flame-retardant epoxy materials are generally more environmentally friendly because carbon dots are carbon-based and do not contain harmful halogens or heavy metals. Fluorescent carbon dots (CDs) are expected to become a new generation of flame retardants due to their simple synthesis, good dispersibility in water and organic solvents, ease of doping with NP elements, low toxicity, and good biocompatibility.

[0003] Epoxy resins, as an important class of thermosetting materials, face challenges such as being unable to reprocess and recycle after molding due to their inherent insoluble and infusible properties. Epoxy vitrimers, due to the presence of exchangeable bonds in their cross-linked networks, not only exhibit properties similar to those of traditional thermosetting epoxy resins at low temperatures, but can also be reprocessed at high temperatures, such as reshaping and recycling. Ester exchange is an important type of dynamic bond in vitrimer systems. Epoxy resin ester exchange dynamic bond systems generally include phosphate esters, borate esters, and carboxylate esters. Specifically, substances containing carboxylic acid, boric acid, and phosphoric acid groups are used as curing agents. The curing of the epoxy resin is achieved through the ring-opening of the curing groups with the epoxy groups, and dynamic bonds are constructed within the system, thereby achieving properties such as the epoxy resin's reprocessability.

[0004] In the prior art, Lee et al. synthesized amino carbon dots, which were used for image anti-counterfeiting after curing epoxy resin. However, no carbon dots have yet been able to achieve epoxy curing and construct a Vitrimer system. Summary of the Invention

[0005] The purpose of the present invention is to overcome the defects of the prior art and provide a carbon dot curing agent.

[0006] Another object of the present invention is to provide applications of the carbon dot curing agent.

[0007] The technical solutions of the present invention are as follows:

[0008] A carbon dot curing agent is obtained by heating a precursor to its pyrolysis temperature, preserving the temperature for pyrolysis, cooling to room temperature and dispersing it in water or ethanol, and finally centrifuging and filtering, wherein:

[0009] The precursor is a carboxylic acid precursor, a phosphoric acid precursor or a boric acid precursor,

[0010] The carboxylic acid precursor is selected from malic acid, glutamic acid, itaconic acid, citric acid, succinic acid, gluconic acid and nitrilotriacetic acid,

[0011] The phosphoric acid precursor is selected from phytic acid, nitrilotrimethylenephosphonic acid, pyrophosphoric acid, iminobis(methylphosphonic acid), diethylenetriamine penta(methylphosphonic acid) solution and etidronic acid,

[0012] The boronic acid precursor is selected from 2-chlorophenylboronic acid, 4-hydroxyphenylboronic acid, phenylboronic acid, 3-aminophenylboronic acid and 2-aminopyrimidine-5-boronic acid.

[0013] In a preferred embodiment of the present invention, the carboxylic acid precursor is glutamic acid.

[0014] In a preferred embodiment of the present invention, the phosphoric acid precursor is nitrilotrimethylene phosphoric acid.

[0015] In a preferred embodiment of the present invention, the boronic acid precursor is 4-hydroxyphenylboronic acid.

[0016] Application of the above carbon dot curing agent in the preparation of epoxy Vitrimer system.

[0017] In a preferred embodiment of the present invention, the epoxy resin in the epoxy Vitrimer system is bisphenol A epoxy resin.

[0018] Further preferably, the molar ratio of the curing groups in the carbon dot curing agent to the epoxy groups in the epoxy resin is 0.5-1.5:1.

[0019] More preferably, the precursor is a carboxylic acid precursor, and the raw materials of the epoxy Vitrimer system further include a catalyst, which is selected from zinc acetylacetonate, zinc acetate, 1-methylimidazole, 2-methylimidazole and TBD.

[0020] Still further preferably, the molar ratio of the catalyst to the epoxy groups in the epoxy resin is 1-10:100.

[0021] An epoxy Vitrimer system, the raw materials of which include epoxy resin and the above-mentioned carbon dot curing agent.

[0022] In a preferred embodiment of the present invention, the epoxy resin is E-51 epoxy resin.

[0023] Further preferably, the molar ratio of the curing groups in the carbon dot curing agent to the epoxy groups in the epoxy resin is 0.5-1.5:1.

[0024] More preferably, the precursor is a carboxylic acid precursor, and the raw materials of the epoxy Vitrimer system further include a catalyst, which is selected from zinc acetylacetonate, zinc acetate, 1-methylimidazole, 2-methylimidazole and TBD.

[0025] Still further preferably, the molar ratio of the catalyst to the epoxy groups in the epoxy resin is 1-10:100.

[0026] The beneficial effects of the present invention are:

[0027] 1. The present invention combines carbon dots and epoxy resin, achieves epoxy curing through carbon dot surface groups, achieves good compatibility between the two, and constructs dynamic bonds in the system, which is expected to realize the reprocessing and recycling of epoxy resin.

[0028] 2. The present invention introduces a carbon dot curing agent into the epoxy resin. Due to the high carbonization rate and fluorescence of the carbon dots, the flame retardant properties of the epoxy resin can be improved and the epoxy resin can be given fluorescent properties.

[0029] 3. The carbon dot flame-retardant epoxy resin prepared by the present invention is a potential polymer composite material. It combines the excellent properties of carbon dots with the excellent performance of epoxy resin, bringing new solutions to the field of flame-retardant materials. At the same time, the photoelectric properties of carbon dots make carbon dot flame-retardant epoxy materials also applicable to the field of optoelectronics. It has broad application prospects and is expected to improve the flame-retardant properties of materials while reducing environmental and health risks, thereby promoting scientific and technological progress and sustainable development.

[0030] 4. The present invention utilizes the abundant carboxylic acid, phosphoric acid and boric acid groups on the surface of the carbon dot curing agent to react with epoxy to open the ring, thereby achieving epoxy curing and constructing an epoxy vitrimer system containing ester exchange of carboxylic acid ester, phosphate ester, borate ester, etc., which has good compatibility with epoxy resin. In addition, due to the high residual carbon rate of the carbon dots, the flame retardancy of the epoxy vitrimer can be improved.

[0031] 5. The carbon dot curing agent of the present invention is simple to synthesize, has abundant sources, is cheap and easy to obtain, and has high yield. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 Schematic diagram of carbon dot synthesis and composite material preparation of the present invention.

[0033] Figure 2 Graphs showing the fluorescence spectra of the carbon dot curing agents synthesized in Examples 1 to 3 of the present invention.

[0034] Figure 3 TEM and particle size distribution diagram of the carbon dot curing agent synthesized in Example 1 of the present invention.

[0035] Figure 4 FT-IR images of the carbon dot curing agent and carbon dot cured epoxy resin synthesized in Example 1 of the present invention.

[0036] Figure 5 These are the DSC graphs of the carbon dot-cured epoxies synthesized in Examples 1 to 3 of the present invention, with a heating rate of 10°C / min, including: (a) DSC graphs of different carbon dot-cured epoxies; (b) an enlarged DSC graph of the carbon dot-cured epoxy resin of Example 2.

[0037] Figure 6 The DSC graphs of the carbon dot-cured epoxy resins of Example 1 and Comparative Example 1 of the present invention are shown, with a heating rate of 10°C / min.

[0038] Figure 7 This is a fluorescence spectrum diagram of Example 1 of the present invention and the raw material cured epoxy resin.

[0039] Figure 8 This is a micro combustion calorimetry (MCC) diagram of Example 1 of the present invention and the raw material cured epoxy resin.

[0040] Figure 9 This is a diagram of the remodelability of the composite material prepared by carbon dot-cured epoxy resin in Example 1 of the present invention.

[0041] Figure 10 This is the stress relaxation diagram of the vitrimer material prepared by carbon dot-cured epoxy resin at 180°C in Example 1 of the present invention. DETAILED DESCRIPTION

[0042] The technical solution of the present invention is further illustrated and described below through specific implementation methods in conjunction with the accompanying drawings.

[0043] The preparation principles of the following examples are as follows Figure 1 shown.

[0044] Example 1

[0045] (1) Synthesis of carboxylic acid carbon dot curing agent by thermal decomposition (taking glutamic acid as an example): Weigh 2g of carbon dot precursor glutamic acid, place it in a 50mL single-necked flask, and heat it to 210℃. Glutamic acid gradually melts during the heating process. After reaching 210℃, glutamic acid completely melts into a colorless and transparent solution. Keep it at 210℃ for 20min. The solution changes from colorless and transparent to yellow and transparent, indicating the synthesis of carbon dots. After cooling to room temperature, add 20mL of water to disperse the synthesized glutamic acid carbon dots. After centrifugation at 11000rpm for 20min, filter through a filter membrane (0.22μm) to obtain the desired carbon dot curing agent (C-CDs), which is stored in the refrigerator for use.

[0046] (2) Prepare 0.02 mol / L sodium hydroxide solution: weigh 0.4 g of sodium hydroxide solid and place it in a beaker. Dissolve the sodium hydroxide with a small amount of distilled water and drain it into a 500 mL volumetric flask with a glass rod. Rinse the beaker and glass rod with distilled water several times and transfer the rinse solution to the 500 mL volumetric flask. Add water to the volumetric flask until it is almost below the scale line. Use a rubber-tipped dropper to add distilled water until the liquid level reaches the scale line. Cover the flask with a stopper and shake it upside down to mix well.

[0047] (3) Titration of functional groups on the surface of carbon dots: The prepared carbon dot solution was diluted 10 times, 10 mL was taken and placed in a conical flask, 2 drops of phenolphthalein indicator were added, and the carbon dot solution was titrated three times in parallel with the prepared 0.02 mol / L sodium hydroxide solution. The average value was taken to obtain the functional group concentration of the prepared carbon dots.

[0048] (4) Curing study of epoxy resin: The molar ratio of the curing group of the carbon dot curing agent to the epoxy group of the epoxy resin is 1:1. The mass of the required carbon dot solution is weighed in a flask, and the corresponding mass of epoxy resin is added after spin drying. The mixture is mixed evenly at 60°C, and 5 mg is taken for DSC testing.

[0049] like Figure 3 As shown, the transmission image shows that the particle size distribution of the carbon dot curing agent synthesized in this embodiment is uniform and has a lattice structure.

[0050] like Figure 4 As shown in the figure, comparing the infrared spectra of uncured epoxy resin and epoxy resin after carbon dot curing, it can be seen that the epoxy resin has an infrared spectroscopy at 910 cm -1 -930cm -1 The epoxy groups at the positions disappear, which preliminarily indicates that the carbon dot curing agent prepared in this example can successfully and completely cure the epoxy resin.

[0051] Example 2

[0052] (1) Synthesis of Boric Acid-Based Carbon Dot Curing Agents (4-hydroxyphenylboronic acid as an example) by Pyrolysis: Weigh 2 g of the carbon dot precursor 4-hydroxyphenylboronic acid into a 50 mL single-necked flask, heat to a melting point of 240°C, and maintain the pyrolysis temperature for 90 min. After cooling to room temperature, add 20 mL of water to disperse the synthesized 4-hydroxyphenylboronic acid carbon dots. Centrifuge at 11,000 rpm for 20 min and filter through a 0.22 μm filter membrane to obtain the desired carbon dot curing agent (B-CDs). Store in a refrigerator for use.

[0053] (2) Prepare 0.02 mol / L sodium hydroxide solution: weigh 0.4 g of sodium hydroxide solid and place it in a beaker. Dissolve the sodium hydroxide with a small amount of distilled water and drain it into a 500 mL volumetric flask with a glass rod. Rinse the beaker and glass rod with distilled water several times and transfer the rinse solution to the 500 mL volumetric flask. Add water to the volumetric flask until it is almost below the scale line. Use a rubber-tipped dropper to add distilled water until the liquid level reaches the scale line. Cover the flask with a stopper and shake it upside down to mix well.

[0054] (3) Titration of functional groups on the surface of carbon dots: The prepared carbon dot solution was diluted 10 times, 10 mL was taken and placed in a conical flask, 2 drops of phenolphthalein indicator were added, and the carbon dot solution was titrated three times in parallel with the prepared 0.02 mol / L sodium hydroxide solution. The average value was taken to obtain the functional group concentration of the prepared carbon dots.

[0055] (4) Investigation of epoxy resin curing: The molar ratio of the curing group of the carbon dot curing agent prepared in this example to the epoxy group of the epoxy resin is 1. The mass of the required carbon dot solution is weighed in a flask, and the corresponding mass of epoxy resin is added after spin drying. The mixture is mixed evenly at 60°C, and 5 mg is taken for DSC testing.

[0056] Example 3

[0057] (1) Synthesis of phosphoric acid-based carbon dot curing agent (using nitrilotrimethylene phosphoric acid as an example) by thermal decomposition: Weigh 2 g of carbon dot precursor nitrilotrimethylene phosphoric acid, place it in a 50 mL single-necked flask, and heat it to 210 ° C. During the heating process, nitrilotrimethylene phosphoric acid gradually becomes viscous. After reaching 210 ° C, keep it at 210 ° C for 90 min. After cooling to room temperature, add 20 mL of water to disperse the synthesized glutamic acid carbon dots. After centrifugation at 11000 rpm for 20 min, filter through a filter membrane (0.22 μm) to obtain the desired carbon dot curing agent (P-CDs), which is stored in the refrigerator for use.

[0058] (4) Prepare 0.02 mol / L sodium hydroxide solution: weigh 0.4 g of sodium hydroxide solid and place it in a beaker. Dissolve the sodium hydroxide with a small amount of distilled water and drain it into a 500 mL volumetric flask with a glass rod. Rinse the beaker and glass rod with distilled water several times and transfer the rinse solution to the 500 mL volumetric flask. Add water to the volumetric flask until it is almost below the scale line. Use a rubber-tipped dropper to add distilled water until the liquid level reaches the scale line. Cover the flask with a stopper and shake it upside down to mix well.

[0059] (5) Titration of carbon dot surface functional groups: The prepared carbon dot solution was diluted 10 times, 10 mL was taken and placed in a conical flask, 2 drops of phenolphthalein indicator were added, and the carbon dot solution was titrated three times in parallel with the prepared 0.02 mol / L sodium hydroxide solution. The average value was taken to obtain the functional group concentration of the prepared carbon dots.

[0060] (6) Investigation of epoxy resin curing: The molar ratio of the curing group of the carbon dot curing agent prepared in this example to the epoxy group of the epoxy resin is 1. The mass of the required carbon dot solution is weighed in a flask, and the corresponding mass of epoxy resin is added after spin drying. The mixture is mixed evenly at 60°C, and 5 mg is taken for DSC testing.

[0061] Comparative Example 1

[0062] The carbon dot curing agent was prepared according to the method of Example 1, and the surface functional groups of the carbon dots were titrated, except that a catalyst 2-methylimidazole with a molar ratio of 5% of epoxy groups was added in step (4).

[0063] Figure 1 Schematic diagrams showing the synthesis of carbon dots and the preparation of composite materials in Examples 1 to 3 of the present invention.

[0064] like Figures 2 to 3 As shown, it is shown that the carbon dot curing agents synthesized in Examples 1 to 3 of the present invention have good fluorescence properties and are dependent on the excitation wavelength; all of these indicate the successful synthesis of the carbon dot curing agent.

[0065] like Figure 5 As shown, the three carbon dot DSCs all showed curing peaks, indicating that the three carbon dot curing agents synthesized in Examples 1 to 3 of the present invention all achieved the curing of epoxy resin.

[0066] like Figure 6 As shown, during the curing process of the carbon dot curing agent prepared in Example 3, after adding 2-methylimidazole catalyst, the epoxy resin showed a curing peak at 115°C, indicating that the use of the catalyst effectively reduced the curing temperature and curing activation energy of the epoxy resin.

[0067] Figures 7 to 10 The relevant properties of the prepared composite materials are shown, which shows that the composite materials prepared by carbon dot-cured epoxy resin combine the advantages of both. Figure 7 Solid powder fluorescence testing showed that the epoxy resin cured with the raw material had no fluorescence, while the epoxy resin cured with carbon dots had a certain degree of fluorescence, indicating that the carbon dot curing agent prepared in Example 1 of the present invention imparted fluorescence properties to the epoxy resin. Figure 8 Microcalorimetry tests showed that the addition of the carbon dot curing agent prepared in Example 1 of the present invention improved its flame retardancy, reducing the epoxy resin's PHR from 447 w / g to 196 w / g and the total heat release THR from 28 kJ / g to 18 kJ / g, a decrease of 64.2% of the original values. Figure 9 This indicates that the transesterification system constructed by the system of Example 1 of the present invention realizes the reprocessability of epoxy as an insoluble and infusible thermosetting material. Figure 10 It shows that the vitrimer material prepared by carbon dot-cured epoxy resin in Example 1 has good relaxation behavior.

[0068] The above description is merely a preferred embodiment of the present invention and therefore cannot be used to limit the scope of the present invention. In other words, equivalent changes and modifications made within the scope of the present invention and the contents of the specification should still fall within the scope of the present invention.

Claims

1. Application of a carbon dot curing agent in the preparation of an epoxy Vitrimer system, characterized in that: The carbon dot curing agent is obtained by heating the precursor to its pyrolysis temperature, preserving the temperature for pyrolysis, cooling to room temperature and dispersing it in water or ethanol, and finally centrifuging and filtering. The precursor is a carboxylic acid precursor, a phosphoric acid precursor or a boric acid precursor, The carboxylic acid precursor is selected from malic acid, glutamic acid, itaconic acid, citric acid, succinic acid, gluconic acid and nitrilotriacetic acid; the phosphoric acid precursor is selected from phytic acid, nitrilotrimethylenephosphonic acid, pyrophosphoric acid, iminobis(methylphosphonic acid), diethylenetriamine penta(methylphosphonic acid) solution and etidronic acid. The boronic acid precursor is selected from 2-chlorophenylboronic acid, 4-hydroxyphenylboronic acid, phenylboronic acid, 3-aminophenylboronic acid and 2-aminopyrimidine-5-boronic acid.

2. The use according to claim 1, characterized in that: The carboxylic acid precursor is glutamic acid.

3. The use according to claim 1, characterized in that: The phosphoric acid precursor is nitrilotrimethylenephosphonic acid.

4. The use according to claim 1, wherein: The boric acid precursor is 4-hydroxyphenylboric acid.

5. The use according to claim 1, characterized in that: The epoxy resin in the epoxy Vitrimer system is bisphenol A epoxy resin.

6. The use according to claim 5, characterized in that: The molar ratio of the curing groups in the carbon dot curing agent to the epoxy groups in the epoxy resin is 0.5-1.5:1.

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