A method for the preparation of a degradable vanillin-based epoxy resin for protective coatings

Abstract

The application belongs to the technical field of polymer materials, and relates to a preparation method of a degradable vanillin-based epoxy resin for a protective coating, comprising the following steps: S1, using tetrahydrofuran as a solvent, an intermediate di(4-formyl-2-methoxyphenyl) adipate is prepared by reacting vanillin, adipoyl chloride and 4-dimethylaminopyridine; S2, the intermediate di(4-formyl-2-methoxyphenyl) adipate prepared in step S1 is mixed with epoxy soybean oil or bisphenol A type epoxy resin and a curing agent, and a vanillin-based epoxy resin is obtained after curing. The epoxy resin prepared in the application simultaneously introduces ester groups and dynamic covalent bonds such as Schiff bases into the structure of the epoxy resin, so that the material is good in degradability and self-repairing capacity. In addition, the epoxy resin also has excellent mechanical properties, and the storage modulus is as high as 3066 MPa.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of high polymer materials, and relates to a preparation method of a degradable vanillin-based epoxy resin for a protective coating. BACKGROUND

[0002] Bisphenol A type epoxy resin (DGEBA) is widely used in modern industry in fields such as coatings, adhesives, electronic packaging and composites; however, traditional epoxy resin products have the problem of being difficult to naturally degrade after use, and the raw material bisphenol A (BPA) is mainly derived from non-renewable petroleum-based fossil resources and has certain biological toxicity, which can interfere with the endocrine system, and its large-scale use not only aggravates resource consumption and environmental pollution, but also brings a series of ecological and environmental problems in the synthesis, use and waste processes. Therefore, developing degradable and environmentally friendly epoxy resins based on renewable resources has become an urgent and important task in the field of materials.

[0003] Lignin is a natural renewable aromatic polymer with an extremely abundant reserve in nature, with an annual renewable amount of more than 500 billion tons, and is a resource-abundant, low-cost and environmentally friendly green raw material. Lignin is rich in aromatic rings and various active functional groups in its molecular structure, has natural non-toxicity, excellent antioxidant performance, good antibacterial properties and excellent ultraviolet absorption capacity, and is the most potential renewable resource for replacing petroleum-based aromatic chemicals. However, lignin itself has a high molecular weight, a complex structure, unevenly distributed functional groups and is difficult to accurately determine, and these characteristics seriously limit its direct application in high-performance polymer materials such as epoxy resins. In contrast, the product derived from depolymerization of lignin, such as vanillin, vanillic acid, eugenol and ferulic acid, can be used as a synthetic precursor to realize precise design and regulation of the structure of high polymer materials, which not only significantly improves the value-added utilization level of lignin, but also helps to reduce the dependence on traditional petroleum-based resources. Among these monomers, vanillin has realized industrialized large-scale production, the raw material is easy to obtain and the cost is relatively low, and vanillin has multi-functional reactivity and shows broad application prospects in the field of epoxy resins.

[0004] Therefore, in view of the problem of non-renewable petroleum-based raw materials required for the preparation of bisphenol A type epoxy resin, the present application prepares an epoxy resin with self-repairing performance, excellent mechanical properties and degradability by using vanillin as a raw material, effectively reduces the dependence on fossil raw materials, and provides a new technical scheme for the development of green and sustainable high polymer materials. SUMMARY

[0005] The application provides a preparation method of a degradable vanillin-based epoxy resin for protective coating. Vanillin is derived from renewable biomass resources and has multi-functional group reactivity, and is a good monomer for preparing thermosetting materials. The application constructs multiple dynamic covalent bonds by using vanillin as raw material, and endows the material with degradability and self-repairing function.

[0006] The specific technical solutions are as follows:

[0007] The application provides a preparation method of a degradable vanillin-based epoxy resin for protective coating, comprising the following steps:

[0008] S1, an intermediate di(4-formyl-2-methoxyphenyl) adipate is prepared by using vanillin, adipoyl chloride and 4-dimethylaminopyridine to react in tetrahydrofuran as a solvent;

[0009] S2, the intermediate di(4-formyl-2-methoxyphenyl) adipate prepared in step S1 is mixed with epoxy soybean oil or bisphenol A type epoxy resin and a curing agent, and a vanillin-based epoxy resin is obtained after curing.

[0010] Preferably, in step S1, the molar ratio of vanillin, adipoyl chloride and 4-dimethylaminopyridine is (1-4):(1-4):(1-4).

[0011] Preferably, in step S1, the purity of tetrahydrofuran is greater than or equal to 99.9%. Tetrahydrofuran is used to dissolve vanillin, adipoyl chloride and 4-dimethylaminopyridine, so that the reactants are in a single phase for reaction. Therefore, the amount of tetrahydrofuran used is adaptively adjusted according to the dissolution degree of the reactants. The more the amount of the reactants used, the more the amount of tetrahydrofuran used.

[0012] Preferably, in step S1, the reaction temperature is 0-50 DEG C, and the reaction time is 1-5 h.

[0013] Preferably, in step S2, the mixing mass ratio of the intermediate di(4-formyl-2-methoxyphenyl) adipate, the epoxy soybean oil and the curing agent is 1:(1-4):(0.8-1.7); and the mixing mass ratio of the intermediate di(4-formyl-2-methoxyphenyl) adipate, the bisphenol A type epoxy resin and the curing agent is 1:(0.2-0.6):(0.5-0.6).

[0014] Preferably, in step S2, the curing agent is 4,4'-diaminodiphenyl methane.

[0015] Preferably, in step S2, the curing is gradient curing, specifically: curing at 80-120 DEG C for 1-5 h, then curing at 130-160 DEG C for 1-5 h, and finally curing at 170-200 DEG C for 1-5 h.

[0016] Compared with the prior art, the present application has the following beneficial effects:

[0017] The present application takes vanillin, a phenolic monomer derived from lignin, as raw material, and converts it into a monomer, bis(4-formyl-2-methoxyphenyl) adipate (BA), which is suitable for preparing high-performance thermosetting materials, through chemical modification. Compared with existing synthesis technologies, the preparation process adopted by the present application has mild conditions and high efficiency, the raw materials are widely available and low in cost, the obtained monomer has multi-functional group reaction characteristics, and the yield is as high as 92.7%; the prepared epoxy resin structure simultaneously introduces ester groups and Schiff base dynamic covalent bonds: the ester group structure endows the material with good degradability, enabling it to gradually degrade in an alkaline environment; and the dynamic and reversible characteristics of the Schiff base enable the cured resin to have self-repairing ability, enabling it to realize self-repairing of micro-damage. In addition, the epoxy resin also exhibits excellent mechanical properties, with a storage modulus as high as 3066 MPa. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 Fourier transform infrared spectrograms of the epoxy resins obtained in Examples 1-4;

[0019] Figure 2 Fourier transform infrared spectrograms of the epoxy resins obtained in Examples 5-8;

[0020] Figure 3 Stress-strain diagrams of the epoxy resins obtained in Example 1, Example 8, and Comparative Example 1;

[0021] Figure 4 Storage modulus diagrams of the epoxy resins obtained in Examples 1-4;

[0022] Figure 5 Storage modulus diagrams of the epoxy resins obtained in Examples 5-8;

[0023] Figure 6 DSC diagram of the epoxy resin obtained in Example 1;

[0024] Figure 7 DSC diagram of the epoxy resin obtained in Example 8;

[0025] Figure 8 TGA diagrams of the epoxy resins obtained in Example 1, Example 8, and Comparative Example 1;

[0026] Figure 9 Solvent resistance test diagram of the epoxy resin obtained in Example 1;

[0027] Figure 10 Solvent resistance test diagram of the epoxy resin obtained in Example 8;

[0028] Figure 11Figure for biodegradability test of the epoxy resin obtained from Example 1, Example 8;

[0029] Figure 12 a-c are total ion current (TIC), vanillin chromatographic peak zoomed-in view and vanillin mass spectrum of the degradation product of the epoxy resin obtained from Example 1, respectively; Figure 12 d-f are total ion current (TIC), vanillin chromatographic peak zoomed-in view and vanillin mass spectrum of the degradation product of the epoxy resin obtained from Example 8, respectively;

[0030] Figure 13 Figure for self-repairing performance characterization of the epoxy resin obtained from Example 8;

[0031] Figure 14 Figure for thermal shape memory test of the epoxy resin obtained from Example 1;

[0032] Figure 15 Figure for thermal shape memory test of the epoxy resin obtained from Example 8;

[0033] Figure 16 Figure for lap shear strength of the epoxy resin obtained from Example 1;

[0034] Figure 17 Figure for lap shear strength of the epoxy resin obtained from Example 8. DETAILED DESCRIPTION

[0035] The embodiments of the present application will be further described in conjunction with the drawings and examples. The following examples are used to illustrate the present application but should not be used to limit the scope of the present application. The experimental methods used in the following examples are conventional methods unless otherwise specified. The materials, reagents, etc. used in the following examples can be obtained from commercial channels unless otherwise specified.

[0036] Example 1

[0037] A preparation method of a degradable vanillin-based epoxy resin for protective coating, comprising the following steps:

[0038] S1 5.0 g of vanillin, 3.0 g of adipoyl chloride, and 4.0 g of 4-dimethylaminopyridine were added to 30 mL of tetrahydrofuran in a molar ratio of 2:1:2, and stirred at 25°C for 2 hours. After the reaction was completed, the reaction mixture was filtered, washed with sodium carbonate solution, and freeze-dried to obtain intermediate bis(4-formyl-2-methoxyphenyl) adipate (BA) powder;

[0039] S2 Vanillin-based epoxy resin was prepared by mixing di(4-formyl-2-methoxyphenyl) adipate (BA) powder, epoxy soybean oil (ESO) and 4,4'-diaminodiphenyl methane (DDM) in a mass ratio of 1:1:0.8, first curing at 120°C for 4 hours, then at 150°C for 2 hours, and finally at 180°C for 1 hour, and recorded as BA / DDM-100wt%ESO.

[0040] Example 2

[0041] With reference to Example 1, the difference is that in step S2, the mixing mass ratio of di(4-formyl-2-methoxyphenyl) adipate (BA) powder, epoxy soybean oil (ESO) and 4,4'-diaminodiphenyl methane is 1:2:1, and recorded as BA / DDM-200wt%ESO.

[0042] Example 3

[0043] With reference to Example 1, the difference is that in step S2, the mixing mass ratio of di(4-formyl-2-methoxyphenyl) adipate (BA) powder, epoxy soybean oil (ESO) and 4,4'-diaminodiphenyl methane is 1:3:1.4, and recorded as BA / DDM-300wt%ESO.

[0044] Example 4

[0045] With reference to Example 1, the difference is that in step S2, the mixing mass ratio of di(4-formyl-2-methoxyphenyl) adipate (BA) powder, epoxy soybean oil (ESO) and 4,4'-diaminodiphenyl methane is 1:4:1.7, and recorded as BA / DDM-400wt%ESO.

[0046] Example 5

[0047] A method for preparing a degradable vanillin-based epoxy resin for protective coating, comprising the following steps:

[0048] S1 5.0g of vanillin, 3.0g of adipoyl chloride, and 4.0g of 4-dimethylaminopyridine were added to 30mL of tetrahydrofuran in a molar ratio of 2:1:2, and stirred at 25°C for 2 hours. After the reaction was completed, the intermediate di(4-formyl-2-methoxyphenyl) adipate (BA) powder was obtained by filtration, washing with sodium carbonate solution, and freeze-drying;

[0049] S2 Vanillin-based epoxy resin was prepared by mixing di(4-formyl-2-methoxyphenyl) adipate (BA) powder, bisphenol A type epoxy resin E51 and 4,4'-diaminodiphenyl methane (DDM) in a mass ratio of 1:0.2:0.5, first curing at 120℃ for 4 hours, then curing at 150℃ for 2 hours, and finally curing at 180℃ for 1 hour, and was recorded as BA / DDM-20wt%E51.

[0050] Example 6

[0051] Referring to Example 5, the difference is that in step S2, the mixing mass ratio of di(4-formyl-2-methoxyphenyl) adipate (BA) powder, bisphenol A type epoxy resin E51 and 4,4'-diaminodiphenyl methane is 1:0.4:0.6, and is recorded as BA / DDM-40wt%E51.

[0052] Example 7

[0053] Referring to Example 5, the difference is that in step S2, the mixing mass ratio of di(4-formyl-2-methoxyphenyl) adipate (BA) powder, bisphenol A type epoxy resin E51 and 4,4'-diaminodiphenyl methane is 1:0.5:0.6, and is recorded as BA / DDM-50wt%E51.

[0054] Example 8

[0055] Referring to Example 5, the difference is that in step S2, the mixing mass ratio of di(4-formyl-2-methoxyphenyl) adipate (BA) powder, bisphenol A type epoxy resin E51 and 4,4'-diaminodiphenyl methane is 1:0.6:0.6, and is recorded as BA / DDM-60wt%E51.

[0056] Comparative Example 1

[0057] Referring to Example 5, the difference is that the intermediate di(4-formyl-2-methoxyphenyl) adipate (BA) powder is not prepared; in step S2, only bisphenol A type epoxy resin E51 and 4,4'-diaminodiphenyl methane (DDM) are mixed and cured, and is recorded as DGEBA / DDM.

[0058] Performance test

[0059] The performances of the epoxy resins obtained in Examples 1-8 and Comparative Example 1 were systematically tested, including mechanical properties, thermal properties, solvent resistance, biodegradability, self-repairing property, and shape memory and bonding property, and the specific results are as follows:

[0060] (1) Chemical structure and curing behavior analysis

[0061] Figures 1-2 Fourier transform infrared spectra of the epoxy resins obtained in Examples 1-4 and Examples 5-8, respectively. As shown in the figure, the characteristic peak at 1697 cm -1 before curing disappeared after curing, while a new peak appeared at 1510 cm -1 , indicating that the aldehyde group had reacted completely and formed an imine bond, proving that the resin was completely cured.

[0062] (2) Mechanical properties

[0063] The tensile test was performed on the sample at a rate of 2 mm / min using a universal material testing machine (ETM504C, 50 kN), Figure 3 The stress-strain diagram of the epoxy resins obtained in Example 1, Example 8, and Comparative Example 1. As shown, the tensile strength of the epoxy resin obtained in Example 8 is higher than that of the epoxy resin obtained in Comparative Example 1, which is mainly due to the presence of more benzene ring structures in the molecule and the π-π conjugation between the benzene ring and the imine bond, which enhances the rigidity of the material. Further tested by dynamic mechanical analysis in single cantilever mode, Figure 3 The storage modulus diagram of the epoxy resins obtained in Examples 1-4 and Examples 5-8, respectively, the storage modulus of the epoxy resin obtained in Example 8 is as high as 3066 MPa, higher than that of the epoxy resin obtained in Comparative Example 1 (2480 MPa), which is due to the rigidity enhancement brought by more benzene ring structures in the BA molecule. Figures 4-5 The DSC diagram of the epoxy resins obtained in Example 1 and Example 8, respectively, as shown in the figure, the DSC test shows that the glass transition temperature of the two kinds of epoxy resins is low, which is speculated to be due to the high content of ester bond in the structure, the strong molecular chain movement ability, so as to overcome the intermolecular force at low temperature. Figures 6-7

[0064] (3) Thermal stability

[0065] The thermal gravimetric analyzer (Linseis TGA PT100, Germany) was used to test the sample at a rate of 10℃ / min from 30℃ to 800℃ under nitrogen atmosphere. Figure 8 The TGA diagram of the epoxy resins obtained in Example 1, Example 8, and Comparative Example 1, the results show that the carbon residue of the epoxy resins obtained in Example 1 and Example 8 is 33.26% and 23.81% respectively, which is 2.85 times and 2.04 times of the epoxy resin obtained in Comparative Example 1 (11.65%), showing good thermal stability.

[0066] (4) Solvent resistance

[0067] ​The epoxy resins obtained from Example 1 and Example 8 were cut into test blocks with similar mass, and were respectively immersed in 1 mol / L hydrochloric acid, 20 wt% sodium chloride solution, acetonitrile, ethanol, ethyl acetate and petroleum ether, and were taken out after 14 days, dried and weighed, and the results are shown in Table 1 and Table 2. It can be found that the mass of each test block did not change significantly. Figures 9-10 The solvent resistance test diagrams of the epoxy resins obtained from Example 1 and Example 8 respectively prove that they have good solvent resistance.

[0068] Table 1 Mass change of the epoxy resin obtained from Example 1 in different solvents

[0069]

[0070] Table 2 Mass change of the epoxy resin obtained from Example 8 in different solvents

[0071]

[0072] (5) Degradable performance

[0073] The epoxy resin samples obtained from Example 1 and Example 8 were placed in a mixed solution prepared by mixing 1 mol / L NaOH solution and ethanol at a volume ratio of 1:1, and their degradation behaviors were observed at room temperature, 40°C oven and 80°C high-temperature reaction kettle respectively. Figure 11 The degradation test diagrams of the epoxy resins obtained from Example 1 and Example 8 are shown on the left and right respectively. The results show that the epoxy resin obtained from Example 1 is basically completely degraded within 9h at room temperature, and the solution changes from transparent to brown; it is basically completely degraded within 6h at 40°C; and it can be basically degraded only within 1h at 80°C. Correspondingly, the epoxy resin obtained from Example 8 only shows partial degradation under the corresponding conditions. The degradation products of the epoxy resins obtained from Example 1 and Example 8 were analyzed by GC-MS, in which 12a-c are the total ion current diagram (TIC), the enlarged chromatogram of vanillin peak and the mass spectrum of vanillin of the degradation products of the epoxy resin obtained from Example 1 respectively; Figure 12 d-f are the total ion current diagram (TIC), the enlarged chromatogram of vanillin peak and the mass spectrum of vanillin of the degradation products of the epoxy resin obtained from Example 8 respectively, and the results show that in the total ion current diagram (TIC) Figure 12 a、 Figure 12 d), a main peak at 14.55 minutes is shown, which is enlarged (b, Figure 12 b、 Figure 12e) The peak at 14.55 min is observed to be sharp and the peak shape is sharp, and the characteristic ions 151.0 (molecular ion peak), 123.0, 109.0, 81.0, 53.0, etc. are observed in the mass spectrum, which is consistent with the standard mass spectrum of vanillin, proving that the epoxy resins obtained in Example 1 and Example 8 have been degraded, and vanillin is obtained by degradation. The above results prove that the vanillin-based epoxy resin of the present application has excellent degradation ability, which is mainly due to the presence of multiple ester bonds in its structure, which can be hydrolyzed under alkaline conditions.

[0074] (6) Self-repairing performance

[0075] Figure 13 The self-repairing performance of the epoxy resin obtained in Example 8 is characterized. After the epoxy resin obtained in Example 8 is broken, it is placed in an environment of 150°C, and after 1h, it is observed that the fracture surface is completely healed, indicating that the resin has good thermal-induced self-repairing function, which is mainly due to the presence of multiple Schiff base structures in its structure.

[0076] (7) Shape memory and bonding performance

[0077] The epoxy resins obtained in Example 1 and Example 8 are subjected to thermal shape memory test, and the tensile strength test is carried out before and after deformation, Figures 14-15 respectively, are the thermal shape memory test diagrams of the epoxy resins obtained in Example 1 and Example 8, and the results show that both resins have good shape memory stability. In addition, the lap shear strength test selects four substrates of aluminum, steel, iron and wood, Figures 16-17 respectively, are the lap shear strength diagrams of the epoxy resins obtained in Example 1 and Example 8. The results show that the lap shear strength of the epoxy resin containing the epoxy resin obtained in Example 8 to steel reaches 9MPa; in the test of wood, the fracture occurs in the wood body rather than the adhesive layer, indicating that its bonding strength is higher than the strength of wood itself.

[0078] The above only describes the preferred embodiments of the present application and does not limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing a biodegradable vanillin-based epoxy resin for protective coatings, characterized in that, Includes the following steps: S1 uses tetrahydrofuran as a solvent to prepare intermediate bis(4-formyl-2-methoxyphenyl) hexamethylene ester by reacting vanillin, adipicoyl chloride and 4-dimethylaminopyridine; S2 The intermediate bis(4-formyl-2-methoxyphenyl) adipate obtained in step S1 is mixed with epoxidized soybean oil or bisphenol A type epoxy resin and a curing agent, and after curing, vanillin-based epoxy resin is obtained.

2. The preparation method according to claim 1, characterized in that, In step S1, the molar ratio of vanillin, adipicoyl chloride, and 4-dimethylaminopyridine is (1~4):(1~4):(1~4).

3. The preparation method according to claim 1, characterized in that, In step S1, the reaction temperature is 0~50℃ and the reaction time is 1~5h.

4. The preparation method according to claim 1, characterized in that, In step S2, the mass ratio of intermediate di(4-formyl-2-methoxyphenyl) adipate to epoxidized soybean oil and curing agent is 1:(1~4):(0.8~1.7); the mass ratio of intermediate di(4-formyl-2-methoxyphenyl) adipate to bisphenol A epoxy resin and curing agent is 1:(0.2~0.6):(0.5~0.6).

5. The preparation method according to claim 1, characterized in that, In step S2, the curing agent is 4,4′-diaminodiphenylmethane.

6. The preparation method according to claim 1, characterized in that, In step S2, the curing is a gradient curing process, specifically: curing at 80~120℃ for 1~5 hours, followed by curing at 130~160℃ for 1~5 hours, and finally curing at 170~200℃ for 1~5 hours.

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