Preparation method of bio-based high-performance epoxy resin

Abstract

The invention provides a preparation method of bio-based high-performance epoxy resin. The preparation method comprises the following steps: firstly, taking bio-based aldehydes and p-aminophenol as raw materials, and reacting at 50 DEG C for 3 hours to obtain a bio-based aldehyde Schiff base-containing compound; secondly, reacting the bio-based aldehyde compound containing the Schiff base with epoxy chloropropane at 80 DEG C for 6 hours to obtain a bio-based aldehyde epoxy monomer containing the Schiff base; methyl tetrahydrophthalic anhydride is used as a curing agent, and the bio-based aldehyde Schiff base-containing epoxy monomer and bisphenol A epoxy resin are mixed according to a certain proportion to obtain the bio-based high-performance epoxy resin. The bio-based aldehyde epoxy resin researched and developed by the invention not only has innovativeness in technology, but also has wide application potential in practical application. In the field of traditional electrical insulation, the method is expected to become a powerful competitor in the market, and provides beneficial reference for sustainable development and green chemistry.

Description

Technical Field

[0001] This invention belongs to the field of green electrical materials, specifically relating to a method for preparing bio-based high-performance epoxy resin. Background Technology

[0002] Epoxy resin, a cross-linked polymer material with a three-dimensional network structure, plays a crucial role in many fields of electrical engineering due to its excellent adhesion, thermal stability, mechanical strength, weather resistance, and electrical insulation properties. However, once epoxy resin materials are damaged or discarded, they will burden the environment and cause a serious waste of valuable resources. Especially in the electronics and electrical industries, the post-use disposal of epoxy resins remains widespread, and these materials are difficult to effectively recycle and reuse due to their properties after curing.

[0003] Recent studies have reported on various raw materials for epoxy resin preparation derived from renewable resources, including vegetable oils, cashew nut shells, vanillin, rosin, lignin, and furan compounds. The exploration of these raw materials offers new possibilities for the sustainable production of epoxy resins. Biogenic aldehydes, as low-molecular-weight aldehyde monomers, have been widely synthesized worldwide, and the raw materials are inexpensive and readily available. Summary of the Invention

[0004] To address the aforementioned problems in the existing technology, the applicant of this invention provides a method for preparing a bio-based high-performance epoxy resin.

[0005] This invention is achieved through the following technical solution: a method for preparing a bio-based high-performance epoxy resin. The bio-based high-performance epoxy resin is composed of the following raw materials in molar proportions:

[0006] Bio-based aldehydes containing Schiff base epoxy monomers

[0007] E-51 type bisphenol A epoxy resin (DGEBA)

[0008] Curing agent: Methyltetrahydrophthalic anhydride (MTHPA)

[0009] Catalyst 2-methylimidazole

[0010] This invention involves an addition reaction of low molecular weight bio-based aldehydes with p-aminophenol to prepare a Schiff base structure with reversible covalent bonds. Epichlorohydrin is gradually added in subsequent reactions to ultimately obtain a bio-based aldehyde-containing Schiff base epoxy monomer. This monomer is then mixed uniformly with DGEBA commercial epoxy resin in a certain proportion to prepare a high-performance bio-aldehyde-based epoxy resin. The chemical reaction includes the following steps:

[0011] (1) A certain amount of anhydrous ethanol was placed in a round-bottom flask equipped with a condenser. Bio-based aldehydes and p-aminophenol were added to the flask sequentially. After stirring evenly, the mixture was heated to 50°C and refluxed for 3 hours. The product was filtered using a vacuum filter and washed several times with anhydrous ethanol. The vacuum oven was heated to 50°C and dried for 24 hours to obtain a pale yellow or yellow powder, which is the bio-based aldehyde containing Schiff bases.

[0012] (2) Heat an oil bath equipped with a magnetic stirrer to 80°C, and place a round-bottom flask equipped with a reflux condenser into the bath. The molar ratio of bio-based aldehyde containing Schiff base compound and epichlorohydrin is 1:20. Add them separately to the flask, stir to dissolve, and add 10% tetrabutylammonium bromide (by mass of bio-based aldehyde containing Schiff base compound). React for 3 hours. Add 20% sodium hydroxide solution dropwise to the flask over 30 minutes, maintaining the reaction temperature at 80°C and continuing the reaction for 4 hours. Extract the obtained product into an organic phase, then dilute it with a certain amount of petroleum ether, wash with distilled water, shake and let stand. Extract three times, remove excess epichlorohydrin and petroleum ether using a rotary evaporator, and finally dry the product overnight in a vacuum oven at 50°C to obtain the bio-based aldehyde containing Schiff base epoxy monomer.

[0013] (3) Mix DGEBA and bio-based aldehyde epoxy monomers containing Schiff bases in a certain proportion. Use methyltetrahydrophthalic anhydride as curing agent to mix the two with an epoxy resin to curing agent molar ratio of 1:1. After melting and mixing evenly, add catalyst, remove bubbles in vacuum oven, and cure in a stepped curing method of 90℃ / 2h and 140℃ / 5h.

[0014] The present invention adopts the above technical solution, and compared with the prior art, the present invention has the following technical effects:

[0015] (1) The present invention provides a high-performance bio-aldehyde-based epoxy resin, which uses inexpensive and readily available raw materials and is simple to prepare by reaction.

[0016] (2) The present invention provides a high-performance bio-aldehyde-based epoxy resin with mild curing conditions, easy curing, high degree of curing; good heat resistance, excellent electrical insulation and mechanical properties. Attached Figure Description

[0017] Figure 1 The synthesis process of the epoxy resin of this invention

[0018] Figure 2 The epoxy resin curing temperature curve obtained in this invention

[0019] Figure 3 The DMA curve of epoxy resin obtained in this invention

[0020] Figure 4 Mechanical property curves of the epoxy resin obtained in this invention.

[0021] Figure 5 TGA curves of epoxy resin obtained in this invention

[0022] Figure 6 The electrical property curves of epoxy resin obtained in this invention Detailed Implementation

[0023] The raw materials and equipment used in this invention are all commercially available.

[0024] Example 1: Synthesis of Syringaldehyde-based Epoxy Resins

[0025] (1) p-Aminophenol (10.9 g, 0.1 mol) and eugenol (18.2 g, 0.1 mol) were dissolved in 1000 mL of anhydrous ethanol, refluxed and stirred at 50 °C for 2 h, filtered at room temperature, and then washed three times with ethanol. The solution was then dried in a vacuum drying oven at 50 °C for 24 h to obtain a yellow powder, DV. The yield was 80%.

[0026] (2) The oil bath equipped with a magnetic stirrer was heated to 80°C. 27.3 g of DV (0.1 mol) and 180 g (2 mol) of epichlorohydrin were added to a 1000 ml round-bottom flask. Then, 2.43 g of tetrabutylammonium bromide (10% of the mass of DV) was added, stirred to dissolve, and refluxed for 3 hours. Over 30 minutes, 40 g of 20% sodium hydroxide solution was added dropwise to the mixture, maintaining the reaction temperature at 80°C. The resulting product was subjected to organic phase extraction, diluted with a certain amount of petroleum ether, washed with distilled water, shaken, and allowed to stand. The extraction was repeated three times. Excess epichlorohydrin and petroleum ether were removed using a rotary evaporator. Finally, the product was dried overnight in a vacuum oven at 50°C to obtain syringaldehyde-containing Schiff base epoxy monomers. The yield was 70%.

[0027] Example 2: Preparation of Cured Syringaldehyde Epoxy Resin (Van-1)

[0028] Mix 10g of eugenol-based Schiff base epoxy monomer, 4.5g of MTHPA, and 0.1g of 2-methylimidazole evenly, pour the mixture into a polytetrafluoroethylene mold, and cure at 90℃ for 2h followed by 140℃ for 5h. After curing, place the mixture in an oven to cool naturally to obtain the cured epoxy resin Van-1 of eugenol-based epoxy resin.

[0029] Example 3: Preparation of Cured Epoxy Resin Based on Eugenol (Van-0.75)

[0030] 9g of eugenol-based Schiff base epoxy monomer, 2.8g of DGEBA, 5.4g of MTHPA, and 0.1g of 2-methylimidazole were mixed and stirred evenly, then poured into a polytetrafluoroethylene mold and cured at 90℃ for 2h followed by 140℃ for 5h. After curing, the mixture was placed in an oven to cool naturally, resulting in the cured epoxy resin Van-0.75 of eugenol-based epoxy resin.

[0031] Example 4: Preparation of Cured Epoxy Resin Based on Eugenol (Van-0.5)

[0032] 7g of eugenol-based Schiff base epoxy monomer, 6.6g of DGEBA, 6.3g of MTHPA, and 0.2g of 2-methylimidazole were mixed and stirred evenly, then poured into a polytetrafluoroethylene mold and cured at 90℃ for 2h followed by 140℃ for 5h. After curing, the mixture was placed in an oven to cool naturally, resulting in cured eugenol-based epoxy resin Van-0.5.

[0033] Example 5: Preparation of Cured Epoxy Resin Based on Eugenol (Van-0.25)

[0034] Mix 3g of eugenol-based Schiff base epoxy monomer, 8.5g of DGEBA, 5.4g of MTHPA, and 0.1g of 2-methylimidazole until homogeneous, pour into a polytetrafluoroethylene mold, and cure at 90℃ for 2h followed by 140℃ for 5h. After curing, place in an oven to cool naturally to obtain eugenol-based epoxy resin Van-0.5.

[0035] Example 5: Preparation of cured eugenol-based epoxy resin Van-0.25.

[0036] Comparative Example 1: Preparation of Commercial Epoxy Resin (Van-0.)

[0037] Mix 10g DGEBA, 4.7g MTHPA, and 0.3g 2,4,6-tris(dimethylaminomethyl)phenol evenly, pour the mixture into a polytetrafluoroethylene mold, and cure at 90℃ for 2h + 140℃ for 5h. After curing, place the mixture in an oven to cool naturally to obtain commercially available bisphenol A type epoxy resin Van-0.

[0038] The following experimental examples demonstrate the beneficial effects of the present invention.

[0039] 1. Experimental Methods

[0040] Differential Scanning Calorimetry (DSC): The kinetic characteristics of the curing reaction were analyzed using a DSC3500 instrument. In the experiment, 5 to 10 mg of sample were weighed and placed in an aluminum crucible, and the test was conducted under a nitrogen flow rate of 20 mL / min. The initial temperature was set at 25 °C, and the final temperature was set at 250 °C. To investigate the optimal curing conditions for different mixtures, the heating rates were set to 5 K / min, 10 K / min, 15 K / min, and 20 K / min, and the curing curves for different resin mixing ratios were recorded.

[0041] Thermogravimetric analysis (TGA): The thermal stability of the samples was evaluated using a TGA4000 instrument. In the experiment, the disc-shaped samples were placed in an aluminum crucible and heated at a rate of 10 K / min under nitrogen atmosphere, with the test temperature covering the range from 30 °C to 800 °C.

[0042] Dynamic Mechanical Analysis (DMA): Tests were conducted using a TAQ800 Dynamic Thermomechanical Analyzer (Made in the USA) in single cantilever beam mode. The heating rate was set to 5°C / min, the test temperature range was from 30°C to 250°C, and the test frequency was fixed at 10Hz. In addition, tensile and bending tests were performed using a universal tensile testing machine at rates of 5 mm / min and 2 mm / min.

[0043] Electrical performance evaluation: Power frequency breakdown voltage was measured using spherical electrodes in dimethyl silicone oil, with a voltage ramp rate maintained at 2kV / s. Leakage current was measured using an MS2621VS tester, with a cylindrical sample size of 50mm in diameter and 30mm in height, a test voltage of 12kV, a ramp rate of 2kV / s, and a withstand voltage duration of 1 minute. Dielectric loss tangent (tanδ) was measured using a YG9100 fully automatic anti-interference precision dielectric loss tester, with the test voltage set within the range of 1.5-3kV.

[0044] 2. Experimental Results

[0045] Figure 2 By comparing the curing temperature curves of the epoxy resin prepared in this invention with those of commercial epoxy resin, it was observed that the epoxy resin in this study began to cure at temperatures below 100°C, showing high reactivity. Figure 3 The images show the DMA curves of the epoxy resin prepared in this invention and commercial epoxy resin. The glass transition temperature of the epoxy resin prepared in this invention is basically similar to that of commercial epoxy resin, and in some systems even exceeds that of commercial epoxy resin. Figure 4 The mechanical property curves of the epoxy resin prepared by this invention and commercial epoxy resin are shown. The epoxy resin prepared by this invention is comparable to commercial epoxy resin in terms of mechanical properties and exhibits a certain strength. Figure 5The TGA curves show the epoxy resin prepared in this invention and commercial epoxy resin. The epoxy resin prepared in this invention is slightly inferior to commercial epoxy resin in terms of heat resistance, but in terms of flame retardancy, the epoxy resin prepared in this invention has a carbon residue rate three times higher than that of commercial epoxy resin, and has good flame retardancy. Figure 6 The electrical performance curves of the epoxy resin prepared in this invention and commercial epoxy resin are shown. The electrical performance is similar to that of commercial epoxy resin to a certain extent, and some systems are even superior to commercial epoxy resin, indicating excellent electrical performance.

[0046] Invention Effects

[0047] This study employs an innovative approach, starting with renewable bio-based raw materials, and develops a bio-based epoxy resin containing dynamic imine bonds through a carefully designed synthetic route. This structure endows the resin with reactivity during chemical crosslinking. Through co-curing with commercially available bisphenol A type epoxy resin, the epoxy resin prepared in this invention exhibits a series of superior properties, which are crucial for many industrial applications and show excellent application prospects.

Claims

1. A method for preparing a bio-based high-performance epoxy resin, characterized in that, Includes the following steps: (1) Bio-based aldehydes containing Schiff bases were prepared by reacting bio-based aldehydes and p-aminophenol as raw materials. (2) Bio-based aldehydes containing Schiff bases are reacted with epichlorohydrin to obtain bio-based aldehydes containing Schiff bases epoxy monomers. (3) Bio-based aldehyde-containing Schiff base epoxy monomers and bisphenol A type epoxy resins are mixed in proportion, and then cured with methyltetrahydrophthalic anhydride as a curing agent to obtain bio-based high-performance epoxy resins.

2. The method for preparing bio-based aldehyde compounds containing Schiff bases according to claim 1, characterized in that, In step (1), the molar ratio of bio-based aldehydes to p-aminophenol is 1:1, the reaction temperature is 40-60℃, preferably 50℃, the reaction time is 3-5 hours, preferably 4 hours, and the solvent is anhydrous ethanol.

3. The method for preparing bio-based aldehyde compounds containing Schiff bases according to claim 2, characterized in that, In step (1), the concentration of vanillin in the solution is 0.1-0.2 mol / L, preferably 0.15 mol / L.

4. The method for preparing bio-based aldehyde containing Schiff base epoxy monomers according to claim 1, in step (2), the ratio of bio-based aldehyde containing Schiff base compound to epichlorohydrin is 1:(20-25), preferably 1:20; the reaction temperature is 70-85℃, preferably 80℃; and the reaction time is 7-8 hours, preferably 7 hours.

5. The method for preparing a bio-based high-performance epoxy resin according to claim 1, characterized in that, In step (3), the total molar ratio of bio-based aldehyde containing Schiff base epoxy monomer and bisphenol A type epoxy resin, and the molar ratio of curing agent methyltetrahydrophthalic anhydride are 1:

2. The curing reaction temperature is 90℃-140℃, the time is 7-8 hours, and the curing reaction adopts step temperature increase.

6. The method for preparing a bio-based high-performance epoxy resin according to claim 1, characterized in that, In step (1), bio-based aldehydes include, but are not limited to, aromatic aldehyde compounds such as vanillin, eugenol, and p-hydroxycinnamaldehyde.

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