High-strength bio-based epoxy resin with closed-loop recycling and preparation method, recycling method and application thereof

Abstract

This invention discloses a high-strength bio-based epoxy resin that can be recycled in a closed-loop manner, its preparation method, recycling method, and applications. The preparation method includes: Step 1, performing a ring-opening reaction on a lignin acid alcohol compound, epichlorohydrin, and a catalyst, followed by a cyclization reaction with an alkali metal hydroxide to obtain a lignin acid alcohol epoxy compound; Step 2, performing a curing reaction on the lignin acid alcohol epoxy compound obtained in Step 1 with an amine compound to obtain the high-strength bio-based epoxy resin that can be recycled in a closed-loop manner. The epoxy resin material prepared by this invention is a novel green, biodegradable, and reusable polymer material that can be applied in fields such as fiber modification, coatings, and adhesives.

Description

Technical Field

[0001] This invention relates to a high-strength bio-based epoxy resin that can be recycled in a closed loop, as well as its preparation method, recycling method and application, belonging to the field of bio-based polymer materials technology. Background Technology

[0002] Epoxy resins are widely used in the automotive industry, medical devices, construction and furniture, aerospace, and other fields due to their excellent thermal stability, mechanical stability, and morphological stability. Currently, most epoxy resins used in industry are prepared from bisphenol A (BPA). However, BPA is widely recognized as an unsafe chemical raw material due to its endocrine-disrupting properties and reproductive toxicity, threatening human health and environmental safety. Furthermore, the permanent cross-linked network of traditional epoxy resins makes them difficult to recycle and reuse, and the extensive landfilling and incineration methods cause environmental pollution and resource waste. Therefore, the development of closed-loop recyclable epoxy resins is urgently needed and is of great significance to human survival and sustainable development.

[0003] While there are existing reports on closed-loop recyclable epoxy resins, most are based on petrochemical raw materials. With the advocacy of green chemistry and the increasing depletion of petrochemical resources in recent years, these methods are still not conducive to sustainable development. Therefore, the development of closed-loop recyclable bio-based epoxy resins is of great research significance. Summary of the Invention

[0004] In view of this, the main objective of this invention is to provide a high-strength bio-based epoxy resin that can be recycled in a closed loop, as well as its preparation method, recycling method, and application. The technical problem to be solved is to use renewable bio-based epoxy compounds as raw materials and amine compounds as curing agents to prepare a high-strength bio-based epoxy resin that can be recycled in a closed loop under catalyst-free conditions. Through structural design, using specific functional groups of lignin acid alcohol compounds, an epoxy resin with an ester bond and tertiary amine self-catalytic network structure is constructed. While solving the problems of bisphenol A toxicity and unsustainable petrochemical raw materials in traditional epoxy resins, this invention also endows the material with recyclability.

[0005] The objective of this invention and the technical problem it solves are achieved through the following technical solution. This invention proposes a method for preparing a high-strength bio-based epoxy resin that can be recycled in a closed loop, comprising the following steps:

[0006] Step 1: The lignin acid alcohol compound, epichlorohydrin and catalyst are subjected to a ring-opening reaction, followed by the addition of alkali metal hydroxide to carry out a cyclization reaction to obtain the lignin acid alcohol epoxy compound.

[0007] Step 2: The lignin acid alcohol epoxy compound obtained in Step 1 is subjected to a curing reaction with an amine compound to obtain the high-strength bio-based epoxy resin that can be closed-loop recycled.

[0008] The objectives of this invention and the technical problems solved can be further achieved by the following technical measures.

[0009] Preferably, the aforementioned method for preparing the high-strength bio-based epoxy resin with closed-loop recyclability includes, in step one, the following steps: mixing the lignin acid alcohol compound, epichlorohydrin, and catalyst at 20-60°C until homogeneous, followed by a ring-opening reaction at 90-110°C for 1-4 hours; then cooling the resulting solution to 0-20°C, adding an aqueous solution of alkali metal hydroxide, and continuing the reaction at 0-20°C for 1-3 hours; after the reaction is complete, obtaining the lignin acid alcohol epoxy compound through extraction, washing with water, and distillation.

[0010] Preferably, in the aforementioned method for preparing high-strength bio-based epoxy resin that can be recycled in a closed loop, the molar ratio of the virgin acid alcohol compound, epichlorohydrin and catalyst in step one is 1:10:0.02-1:14:0.05.

[0011] Preferably, in the aforementioned method for preparing a closed-loop recyclable high-strength bio-based epoxy resin, in step one, the lignin acid alcohol compound includes at least one of ferulic acid, sinapic acid, and p-coumaric acid.

[0012] Preferably, in the aforementioned method for preparing a closed-loop recyclable high-strength bio-based epoxy resin, in step one, the catalyst includes at least one of tetrabutylammonium chloride, benzyltriethylammonium chloride, tetrabutylammonium iodide, and tetrabutylammonium sulfate.

[0013] Preferably, in the aforementioned method for preparing a closed-loop recyclable high-strength bio-based epoxy resin, in step one, the alkali metal hydroxide includes at least one of sodium hydroxide, lithium hydroxide, and potassium hydroxide.

[0014] Preferably, in the aforementioned method for preparing high-strength bio-based epoxy resin that is recyclable in a closed loop, the solute content of the alkali metal hydroxide aqueous solution in step one is 30-60%.

[0015] Preferably, in the aforementioned method for preparing a high-strength bio-based epoxy resin that can be closed-loop recycled, in step one, the amount of catalyst added is 1-5% of the total molar amount of hydroxyl and carboxyl groups in the lignin acid alcohol compound.

[0016] Preferably, in the aforementioned method for preparing the high-strength bio-based epoxy resin that can be closed-loop recycled, step two specifically includes: dissolving the lignin acid alcohol epoxy compound obtained in step one in a solvent at 40-60°C, adding an amine compound, and stirring the reaction for 0.5-1 h; subsequently, molding and curing at 60-180°C for 6-12 h to obtain the high-strength bio-based epoxy resin that can be closed-loop recycled.

[0017] Preferably, in the aforementioned method for preparing the high-strength bio-based epoxy resin that can be recycled in a closed loop, in step two, the curing reaction temperature is 60-180℃ and the curing reaction time is 6-12h.

[0018] Preferably, in the aforementioned method for preparing a closed-loop recyclable high-strength bio-based epoxy resin, the amine compound in step two includes one of hexamethylenediamine, decanediamine, p-phenylenediamine, and 4,4'-diaminodiphenylmethane.

[0019] Preferably, in the aforementioned method for preparing the high-strength bio-based epoxy resin that can be closed-loop recycled, in step two, the molar ratio of the epoxy group in the lignin acid alcohol epoxy compound to the amino functional group in the amino compound is 1:(0.5-1).

[0020] Preferably, in the aforementioned method for preparing a closed-loop recyclable high-strength bio-based epoxy resin, in step two, the solvent is selected from ethyl acetate, N,N-dimethylformamide, and dimethyl sulfoxide.

[0021] The objective of this invention and the technical problem it solves are achieved by the following technical solution. This invention proposes a high-strength bio-based epoxy resin that is recyclable in a closed loop, with a tensile stress of 121.8-154.1 MPa, an elongation at break of 9.4%-24.5%, and a glass transition temperature between 81.1-116.5°C; the high-strength bio-based epoxy resin is prepared by the above-described method.

[0022] The objective of this invention and the technical problem it solves are achieved through the following technical solution. This invention proposes an adhesive, wherein the adhesive is a high-strength bio-based epoxy resin that is recyclable in a closed loop; the high-strength bio-based epoxy resin has a tensile stress of 121.8-154.1 MPa, an elongation at break of 9.4%-24.5%, and a glass transition temperature between 81.1-116.5℃.

[0023] The objective of this invention and the technical problem it solves are achieved through the following technical solution: The application of the above-mentioned closed-loop recyclable high-strength bio-based epoxy resin method proposed in this invention in the modification of carbon fiber composite materials.

[0024] The objective of this invention and the technical problem it solves are achieved by the following technical solution. This invention proposes a closed-loop recyclable method for recovering high-strength bio-based epoxy resin, comprising the following steps: uniformly mixing the aforementioned closed-loop recyclable high-strength bio-based epoxy resin with ethanol; under the catalytic action of tertiary amine groups, the hydroxyl groups of the alcohol undergo a bond exchange reaction with the ester bonds to degrade the cross-linked network structure into small molecular segments; after removing excess solvent, drying the mixture; and then curing it again to obtain the bio-based epoxy resin.

[0025] The objectives of this invention and the technical problems solved can be further achieved by the following technical measures.

[0026] Preferably, in the aforementioned closed-loop recyclable high-strength bio-based epoxy resin recycling method, the degradation temperature is 160-200℃ and the degradation time is 8-12h.

[0027] Compared with existing technologies, the high-strength bio-based epoxy resin that can be recycled in a closed loop according to the present invention, its preparation method, recycling method, and application have the following beneficial effects:

[0028] This invention, starting from bio-based monomers, produces a high-strength bio-based epoxy resin that can be recycled in a closed-loop manner, effectively solving the problem of over-reliance on petrochemical raw materials. Through structural design, utilizing the specific functional groups of these bio-based monomers, an epoxy resin with ester bond and tertiary amine autocatalytic functions is constructed, achieving efficient material recycling and solving the problems of difficult recycling and poor performance of recycled products in traditional epoxy resins. Furthermore, the bio-based monomers used have advantages such as good biocompatibility, antibacterial properties, and antioxidant properties, solving the bisphenol A toxicity problem of traditional epoxy resins and conforming to the concept of sustainable development. Simultaneously, the preparation process of the high-strength bio-based epoxy resin that can be recycled in a closed-loop manner in this invention is simple and can be mass-produced; moreover, the lignin acid alcohol compounds used in this invention all contain rigid benzene ring structures, effectively improving the mechanical properties and thermal stability of the material.

[0029] The high-strength bio-based epoxy resin prepared by this invention, which is capable of closed-loop recycling, has a tensile stress of 121.8-154.1 MPa, an elongation at break of 9.4%-24.5%, and a glass transition temperature between 81.1-116.5℃. Furthermore, the material properties obtained through degradation and recycling can be restored to over 85%.

[0030] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, the preferred embodiments of the present invention are described in detail below. Attached Figure Description

[0031] Figure 1 This is a structural diagram of the high-strength bio-based epoxy resin that can be recycled in a closed loop according to the present invention.

[0032] Figure 2 The ferulic acid and ferulic acid diglycidyl ether in Example 1 of this invention 1 H NMR spectrum;

[0033] Figure 3 This is a stress-strain curve of the high-strength bio-based epoxy resin that can be recycled in a closed loop in Example 1 of the present invention.

[0034] Figure 4 Thermogravimetric curve of the high-strength bio-based epoxy resin that can be recycled in a closed loop in Example 1 of the present invention;

[0035] Figure 5 The DSC curve of the high-strength bio-based epoxy resin that can be recycled in a closed loop is shown in Example 1 of this invention.

[0036] Figure 6 The transmission spectrum of the high-strength bio-based epoxy resin that can be recycled in a closed loop in Example 1 of the present invention is shown in the wavelength range of 200-800 nm.

[0037] Figure 7 This is a stress-strain curve of the FDD-carbon fiber composite material in Application Example 1 of the present invention. Detailed Implementation

[0038] To further illustrate the technical means and effects adopted by the present invention to achieve its intended purpose, the following detailed description, in conjunction with preferred embodiments, provides a closed-loop recyclable high-strength bio-based epoxy resin, its preparation method, recycling method, and application, as well as its specific implementation methods, structures, features, and effects. In the following description, different "embodiments" or "embodiments" do not necessarily refer to the same embodiment. Furthermore, specific features, structures, or characteristics in one or more embodiments can be combined in any suitable manner.

[0039] Unless otherwise specified, all materials and reagents mentioned below are commercially available products well-known to those skilled in the art; unless otherwise specified, all methods described are methods known in the art. Unless otherwise defined, the technical or scientific terms used should have the ordinary meaning understood by those skilled in the art. Where specific experimental steps or conditions are not specified below, they can be performed according to the conventional experimental steps or conditions described in the literature in this field.

[0040] Some embodiments of the present invention provide a method for preparing a high-strength bio-based epoxy resin that is recyclable in a closed loop, comprising the following steps:

[0041] Step 1: After adding the lignin acid alcohol compound, epichlorohydrin, and catalyst in a molar ratio of 1:10:0.02-1:14:0.05 to the flask, if the molar ratio of the lignin acid alcohol compound, epichlorohydrin, and catalyst is less than 1:14:0.05, the lignin acid alcohol compound will react incompletely; if the molar ratio is greater than 1:10:0.02, the concentration of the lignin acid alcohol compound and catalyst in the reaction system will decrease, leading to a slower reaction rate. After stirring and mixing evenly at 20-60℃, if the temperature is below 20℃, the lignin acid alcohol compound will not completely dissolve in epichlorohydrin; if the temperature is above 60℃, the reaction system will start reacting prematurely. The ring-opening reaction will proceed at 90-110℃ for 1-4 hours; if the temperature is below 90℃, the lignin acid alcohol compound will react incompletely. Above 110℃, some ferulic acid raw materials will undergo decarboxylation; below 1 hour, the ferulic acid reaction will be incomplete; above 4 hours, more byproducts will be generated due to decarboxylation. Subsequently, the solution is cooled to 0-20℃; below 0℃, the subsequently added hydroxide aqueous solution will clump, resulting in incomplete ring-closing reaction; the addition of alkali metal hydroxide to the reaction system will release heat, causing the solution temperature to rise. Under high-temperature alkaline conditions, the ester bond in the ferulic acid diglycidyl ether intermediate is easily hydrolyzed and broken. Above 20℃, the reaction will be more vigorous, generating a large amount of heat, raising the solution temperature, and causing byproducts to be generated. The aqueous solution of alkali metal hydroxide is added, and the reaction continues at 0-20℃ for 1-3 hours; below 1 hour, the intermediate will not completely close the ring, and the yield of the target product will be low; within 1-3 hours, the intermediate will be basically completely closed, and the reaction will be completed; above 3 hours, it will lead to resource waste. After the reaction is completed, the lignin acid alcohol epoxy compound is obtained by extraction, water washing, and distillation.

[0042] Step 2: Dissolve the lignin-based epoxy compound obtained in Step 1 in a solvent at 40-60℃. Below 40℃, the lignin-based epoxy compound cannot be completely dissolved in the solvent; within 40-60℃, the raw material can be fully dissolved; above 60℃, it will lead to resource waste. After adding the amine compound, stir the reaction for 0.5-1 hour. Below 0.5 hours, the lignin-based epoxy compound and amine compound cannot be mixed evenly; within 1 hour, the raw material can be fully dissolved in the solvent; beyond 1 hour, it will lead to resource waste. Subsequently, pour it into a polytetrafluoroethylene mold and cure it in a vacuum oven at 60-180℃ for 6-12 hours. Below 60℃, the curing reaction of the material will be incomplete; within 60-180℃, the material can be fully cured; above 180℃, it will lead to resource waste. Below 6 hours, the material will be incompletely cured; 6-12 hours of curing will achieve the best performance; above 12 hours, the material performance will actually decrease. A high-strength bio-based epoxy resin that can be closed-loop recycled is obtained.

[0043] In some embodiments, optionally, in step one, the lignin acid alcohol compound includes at least one of ferulic acid, sinapic acid, and p-coumaric acid; using such an acid alcohol compound with a carboxyl group, a network structure with ester bonds can be constructed, which can endow the material with the function of closed-loop recycling.

[0044] In some embodiments, optionally, in step one, the catalyst includes at least one of tetrabutylammonium chloride, benzyltriethylammonium chloride, tetrabutylammonium iodide, and tetrabutylammonium sulfate; these four catalysts can catalyze the reaction of epichlorohydrin with the hydroxyl and carboxyl groups in the lignin alcohol compound.

[0045] In some embodiments, optionally, in step one, the alkali metal hydroxide includes at least one of sodium hydroxide, lithium hydroxide, and potassium hydroxide; the alkali metal hydroxide can catalyze the ring-closing reaction in the second step, ultimately forming an epoxy functional group.

[0046] In some embodiments, optionally, in step one, the solute content of the alkali metal hydroxide aqueous solution is 30-60 wt%. If the solute content is less than 30 wt%, the ring-closing reaction will be insufficient, resulting in a low yield of the target product. If the solute content is within 30-60%, complete ring closure can be achieved. If the solute content is higher than 60 wt%, it will lead to resource waste.

[0047] In some embodiments, optionally, in step one, the amount of catalyst added is 1-5% of the total molar amount of hydroxyl and carboxyl groups in the lignin acid alcohol compound; less than 1% will cause ferulic acid to react incompletely, 1-5% can make all ferulic acid react completely with epichlorohydrin; more than 5% will lead to waste of resources.

[0048] In some embodiments, optionally, in step two, the amine compound includes one of hexamethylenediamine, decanediamine, p-phenylenediamine, or 4,4'-diaminodiphenylmethane; these diamines can react with ferulic acid diglycidyl ether to obtain a polymeric material.

[0049] In some embodiments, optionally, in step two, the epoxy groups in the lignin-acid alcohol epoxy compound and the amino functional groups in the amino compound react in a molar ratio of 1:(0.5-1). Different molar ratios of epoxy groups to amino functional groups will cause the material to exhibit different properties; a ratio below the lower limit of 1:0.5 will result in poor mechanical properties of the material, while a ratio above 1:1 will result in an excess of amino functional groups, leading to poor mechanical properties of the material.

[0050] In some embodiments, optionally, in step two, the solvent is one of ethyl acetate, N,N-dimethylformamide, or dimethyl sulfoxide; these solvents can dissolve ferulic acid and amine compounds.

[0051] Some embodiments of the present invention also provide a high-strength bio-based epoxy resin that is recyclable in a closed loop (structural formula as shown in the original text). Figure 1 As shown), the tensile stress is 121.8-154.1 MPa, the elongation at break is 9.4%-24.5%, and the glass transition temperature is 81.1-116.5℃. The high-strength bio-based epoxy resin is prepared by the above method.

[0052] Some embodiments of the present invention also provide an adhesive, said adhesive being the above-mentioned closed-loop recyclable high-strength bio-based epoxy resin.

[0053] Some embodiments of the present invention also provide the application of the above-described method for closed-loop recyclable high-strength bio-based epoxy resin in the modification of carbon fiber composite materials.

[0054] Some embodiments of the present invention also provide a method for recycling a high-strength bio-based epoxy resin that can be recycled in a closed loop, comprising the following steps: adding the above-mentioned high-strength bio-based epoxy resin that can be recycled in a closed loop together with anhydrous ethanol into a high-pressure reactor and mixing them evenly; under the catalysis of tertiary amine groups, the hydroxyl groups of the alcohol undergo a bond exchange reaction with the ester bonds to degrade the cross-linked network structure into small molecular segments; after removing excess solvent, the resin is placed in an oven at 70-90°C for drying; the boiling point of anhydrous ethanol is 78.3°C; below 70°C, anhydrous ethanol cannot be completely removed; within the range of 70-90°C, anhydrous ethanol can be completely removed; above 90°C, it will lead to resource waste; after being cured again at 140-180°C; the temperature of the ester exchange of several materials is 140-180°C to obtain a bio-based epoxy resin; below 140°C, the curing will be incomplete, and the resulting material will have poor performance; between 140-180°C, the material can be completely cured; above 180°C, it will lead to resource waste.

[0055] In some embodiments, optionally, the degradation temperature is 160-200°C; below 160°C the material cannot be completely degraded, and above 200°C it will lead to resource waste; the degradation time is 8-12 hours; below 8 hours the material is not completely degraded, and above 12 hours the material can be completely degraded into small molecules.

[0056] The present invention will be further described below with reference to specific embodiments, but this should not be construed as a limitation on the scope of protection of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the above description of the present invention still fall within the scope of protection of the present invention.

[0057] Example 1

[0058] 20 g of ferulic acid and 132 g of epichlorohydrin were added to a three-necked flask equipped with a mechanical stirrer and mixed thoroughly at 50 °C. 0.68 g of tetrabutylammonium bromide was added, and the mixture was heated to 110 °C and reacted for 3 h. The mixture was then cooled to 0 °C using an ice-water bath, and 60 g of a 40% sodium hydroxide aqueous solution was added. The reaction was continued at 0 °C for 5 h. After the reaction was complete, 100 mL of ethyl acetate was added for extraction, followed by washing three times with deionized water. After separation, the mixture was dried over 10 g of anhydrous magnesium sulfate. Ethyl acetate and epichlorohydrin were removed by rotary evaporation (80 °C, -0.1 MPa) to obtain the crude product. The crude product was dissolved in 30 mL of ethyl acetate at 78 °C, and after cooling to room temperature, a white solid precipitated. The solution was removed by filtration, and the solid was dried to obtain the pure product, ferulic acid diglycidyl ether. Take 1g of ferulic acid diglycidyl ether obtained in the above steps and 0.19g of hexamethylenediamine and dissolve it in 1g of N,N-dimethylformamide. Stir at 60℃ for 30min. Then pour the resulting mixture into a polytetrafluoroethylene mold and place it in an oven at 60℃ to start curing. Curing is carried out at 60℃, 80℃, 100℃, 120℃, 140℃, 160℃ and 180℃ for 2h respectively. After cooling to room temperature, a complete and uniform yellow transparent film material (FDH) can be obtained, which is the high-strength bio-based epoxy resin that can be closed-loop recycled.

[0059] Figure 2 It is the ferulic acid and ferulic acid diglycidyl ether of Example 1 of this invention. 1 1H NMR spectrum, in ferulic acid diglycidyl ether 1 The presence of proton signals at 9.5 ppm and 12.0 ppm in the ¹H NMR spectrum, attributed to the disappearance of proton signals on the hydroxyl and carboxyl groups respectively, and the presence of proton signals on the methylene group near the epoxy group at 4.3–4.5 ppm, confirms the successful synthesis of ferulic acid diglycidyl ether. Figure 3 This is the stress-strain curve of the closed-loop recyclable high-strength bio-based epoxy resin (FDH). It can be seen that the tensile strength of this closed-loop recyclable high-strength bio-based epoxy resin is 133.6 MPa, and the elongation at break is 19.5%. Figure 4 As shown in the thermogravimetric curve, the temperature at which the closed-loop recyclable high-strength bio-based epoxy resin loses 5% of its weight is 268°C, indicating that the closed-loop recyclable high-strength bio-based epoxy resin has excellent thermal stability. Figure 5 This is the DSC curve of the high-strength bio-based epoxy resin that can be recycled in a closed loop in Example 1 of this invention. Figure 5 It can be seen that the glass transition temperature of this high-strength bio-based epoxy resin that can be recycled in a closed loop is 90.2℃. Figure 6 The transmission spectrum shows that the closed-loop recyclable high-strength bio-based epoxy resin can effectively shield ultraviolet radiation.

[0060] Example 2

[0061] 5g of sinapic acid and 29g of epichlorohydrin were added to a three-necked flask equipped with a mechanical stirrer and mixed thoroughly at 60°C. Then, 0.15g of tetrabutylammonium bromide was added, and the mixture was heated to 100°C and reacted for 1 hour. The mixture was then cooled to 0°C using an ice-water bath, and 15g of a 40% sodium hydroxide aqueous solution was added. The reaction was continued at 0°C for 3 hours. After the reaction was complete, 10ml of ethyl acetate was added for extraction, followed by washing three times with deionized water. After separation, the mixture was dried over 1g of anhydrous magnesium sulfate and evaporated using a rotary evaporator (80°C).

[0062] After removing ethyl acetate and epichlorohydrin at -0.1 MPa, a crude product was obtained. The crude product was dissolved in 10 ml of ethyl acetate at 78 °C, and after cooling to room temperature, a white solid precipitated. The solution was removed by filtration, and the product was dried to obtain pure sinapic acid diglycidyl ether. 1 g of the sinapic acid diglycidyl ether obtained in the above steps and 0.17 g of hexamethylenediamine were dissolved in 1 g of N,N-dimethylformamide and stirred at 60 °C for 30 min. The resulting mixture was then poured into a polytetrafluoroethylene mold and placed in an oven at 60 °C to begin curing. Curing was carried out at 60 °C, 80 °C, 100 °C, 120 °C, 140 °C, 160 °C, and 180 °C for 2 h respectively. After cooling to room temperature, a complete and uniform yellow transparent film material was obtained, which is the high-strength bio-based epoxy resin that can be closed-loop recycled.

[0063] The resulting high-strength bio-based epoxy resin, which can be recycled in a closed loop, has a tensile strength of 141.2 MPa, an elongation at break of 15.2%, a glass transition temperature of 95.2℃, and can effectively shield light in the wavelength range of 200-400 nm.

[0064] Example 3

[0065] 10 g of ferulic acid and 66 g of epichlorohydrin were added to a three-necked flask equipped with a mechanical stirrer and mixed thoroughly at 50 °C. Then, 0.34 g of tetrabutylammonium bromide was added, and the mixture was heated to 110 °C and reacted for 3 h. The mixture was then cooled to 0 °C using an ice-water bath, and 30 g of a 40% sodium hydroxide aqueous solution was added. The reaction was continued at 0 °C for 5 h. After the reaction was complete, 20 ml of ethyl acetate was added for extraction, followed by washing three times with deionized water. After separation, the mixture was dried over 2 g of anhydrous magnesium sulfate and evaporated using a rotary evaporator (80 °C).

[0066] After removing ethyl acetate and epichlorohydrin at -0.1 MPa, a crude product was obtained. The crude product was dissolved in 20 ml of ethyl acetate at 78 °C. After cooling to room temperature, a white solid precipitated. The solution was removed by filtration, and the product was dried to obtain the pure product, ferulic acid diglycidyl ether. 1 g of the ferulic acid diglycidyl ether obtained in the above steps and 0.28 g of decanediamine were dissolved in 1 g of N,N-dimethylformamide and stirred at 60 °C for 30 min. The resulting mixture was then poured into a polytetrafluoroethylene mold and placed in an oven at 60 °C to begin curing. Curing was carried out at 60 °C, 80 °C, 100 °C, 120 °C, 140 °C, 160 °C, and 180 °C for 2 h respectively. After cooling to room temperature, a complete and uniform yellow transparent film material was obtained, which is the high-strength bio-based epoxy resin that can be closed-loop recycled.

[0067] The resulting high-strength bio-based epoxy resin, which can be recycled in a closed loop, has a tensile strength of 121.8 MPa, an elongation at break of 22.8%, a glass transition temperature of 81.1℃, and can effectively shield light in the wavelength range of 200-400 nm.

[0068] Example 4

[0069] 10 g of ferulic acid and 66 g of epichlorohydrin were added to a three-necked flask equipped with a mechanical stirrer and mixed thoroughly at 50 °C. Then, 0.34 g of tetrabutylammonium bromide was added, and the mixture was heated to 110 °C and reacted for 3 h. The mixture was then cooled to 0 °C using an ice-water bath, and 30 g of a 40% sodium hydroxide aqueous solution was added. The reaction was continued at 0 °C for 5 h. After the reaction was complete, 20 mL of ethyl acetate was added for extraction, followed by washing three times with deionized water. After separation, the mixture was dried over 2 g of anhydrous magnesium sulfate. The ethyl acetate and epichlorohydrin were removed by rotary evaporation (80 °C, -0.1 MPa) to obtain the crude product. The crude product was dissolved in 20 mL of ethyl acetate at 78 °C, and after cooling to room temperature, a white solid precipitated. The solution was removed by filtration, and the solid was dried to obtain the pure product, ferulic acid diglycidyl ether. Take 1g of ferulic acid diglycidyl ether obtained in the above steps and 0.176g of p-phenylenediamine, dissolve them in 1g of N,N-dimethylformamide, stir at 60℃ for 30min, then pour the resulting mixture into a polytetrafluoroethylene mold, place it in an oven at 60℃ to begin curing, and cure at 60℃, 80℃, 100℃, 120℃, 140℃, 160℃ and 180℃ for 2h respectively. After cooling to room temperature, a complete and uniform black opaque film material can be obtained, which is the high-strength bio-based epoxy resin that can be closed-loop recycled.

[0070] The resulting high-strength bio-based epoxy resin, which can be recycled in a closed loop, has a tensile strength of 154.1 MPa, an elongation at break of 9.4%, a glass transition temperature of 116.5℃, and can effectively shield light in the wavelength range of 200-400 nm.

[0071] Example 5

[0072] 10 g of ferulic acid and 66 g of epichlorohydrin were added to a three-necked flask equipped with a mechanical stirrer and mixed thoroughly at 50 °C. Then, 0.34 g of tetrabutylammonium bromide was added, and the mixture was heated to 110 °C and reacted for 3 h. The mixture was then cooled to 0 °C using an ice-water bath, and 30 g of a 40% sodium hydroxide aqueous solution was added. The reaction was continued at 0 °C for 5 h. After the reaction was complete, 20 mL of ethyl acetate was added for extraction, followed by washing three times with deionized water. After separation, the mixture was dried over 2 g of anhydrous magnesium sulfate. The ethyl acetate and epichlorohydrin were removed by rotary evaporation (80 °C, -0.1 MPa) to obtain the crude product. The crude product was dissolved in 20 mL of ethyl acetate at 78 °C, and after cooling to room temperature, a white solid precipitated. The solution was removed by filtration, and the solid was dried to obtain the pure product, ferulic acid diglycidyl ether. Take 1g of ferulic acid diglycidyl ether obtained in the above steps and 0.31g of 4,4'-diaminodiphenylmethane and dissolve it in 1g of N,N-dimethylformamide. Stir at 60°C for 30min. Then pour the resulting mixture into a polytetrafluoroethylene mold and place it in an oven at 60°C to begin curing. Curing is carried out at 60°C, 80°C, 100°C, 120°C, 140°C, 160°C and 180°C for 2h respectively. After cooling to room temperature, a complete and uniform brownish-brown slightly transparent film material can be obtained, which is the high-strength bio-based epoxy resin that can be closed-loop recycled.

[0073] The resulting high-strength bio-based epoxy resin, which can be recycled in a closed loop, has a tensile strength of 140.8 MPa, an elongation at break of 11.2%, a glass transition temperature of 99.6℃, and can effectively shield light in the wavelength range of 200-400 nm.

[0074] Example 6

[0075] 5 g of p-coumaric acid and 39.45 g of epichlorohydrin were added to a three-necked flask equipped with a mechanical stirrer and mixed thoroughly at 40 °C. 0.196 g of tetrabutylammonium bromide was added, and the mixture was heated to 90 °C and reacted for 3 h. The mixture was then cooled to 0 °C using an ice-water bath, and 18.26 g of a 40% sodium hydroxide aqueous solution was added. The reaction was continued at 0 °C for 2 h. After the reaction was complete, 10 mL of ethyl acetate was added for extraction, followed by washing three times with deionized water. After separation, the mixture was dried over 1 g of anhydrous magnesium sulfate, and the ethyl acetate and epichlorohydrin were removed by rotary evaporation (80 °C, -0.1 MPa) to obtain a transparent, viscous liquid, p-coumaric acid diglycidyl ether. Take 1g of the p-coumaric acid diglycidyl ether obtained in the above steps and 0.21g of hexamethylenediamine, dissolve them in 1g of N,N-dimethylformamide, stir at 60℃ for 30min, then pour the resulting mixture into a polytetrafluoroethylene mold, place it in an oven at 60℃ to begin curing, and cure at 60℃, 80℃, 100℃, 120℃, 140℃, 160℃ and 180℃ for 2h respectively. After cooling to room temperature, a complete and uniform yellow transparent film material can be obtained, which is the high-strength bio-based epoxy resin that can be closed-loop recycled.

[0076] The resulting high-strength bio-based epoxy resin, which can be recycled in a closed loop, has a tensile strength of 125.6 MPa, an elongation at break of 24.5%, a glass transition temperature of 86.7℃, and can effectively shield light in the wavelength range of 200-400 nm.

[0077] The bio-based epoxy resins (1g) obtained in Examples 1-6 were added to a high-pressure reactor along with anhydrous ethanol (20ml). The reactor was stirred and degraded at 180°C for 10 hours, resulting in the degradation of the cross-linked network structure into small molecular segments. After removing the anhydrous ethanol, the resins were placed in an oven at 180°C and heated for 12 hours, allowing for re-curing to obtain bio-based epoxy resins. The properties of the bio-based epoxy resins in each example could be recovered to over 85%. Specifically, the tensile strength of the material recovered in Example 1 was 95%, the tensile strength of the bio-based epoxy resin recovered in Example 2 was 92%, the tensile strength of the bio-based epoxy resin recovered in Example 3 was 96%, the tensile strength of the bio-based epoxy resin recovered in Example 4 was 88%, the tensile strength of the bio-based epoxy resin recovered in Example 5 was 89%, and the tensile strength of the bio-based epoxy resin recovered in Example 6 was 95%.

[0078] Comparative Example 1

[0079] 5g of bisphenol A diglycidyl ether and 1.26g of decanediamine were dissolved in N,N-dimethylformamide and stirred at 60℃ for 30min. The resulting mixture was then poured into a polytetrafluoroethylene mold and placed in an oven at 60℃ for curing. Curing was carried out at 60℃, 80℃, 100℃, 120℃, 140℃, 160℃, and 180℃ for 2h, respectively. After cooling to room temperature, a complete and uniform yellow transparent film material was obtained. The tensile strength of the obtained material was 106.2MPa, and the elongation at break was 14.2%. When 1g of the obtained material was added to anhydrous ethanol (20ml) in a high-pressure reactor and stirred at 180℃ for 10h, the material could not depolymerize because its network structure was entirely connected by stable covalent bonds and lacked dynamic covalent bonds.

[0080] Application Example 1

[0081] The ferulic acid diglycidyl ether (0.437 g) and decanediamine (0.123 g) obtained in Example 3 were dissolved in 1 g of N,N-dimethylformamide and stirred at 60 °C for 30 min. This solution was then coated onto 1.44 g of carbon fiber. Three coated carbon fibers were then pressed together under a pressure of 0.1 MPa and cured at 60 °C, 80 °C, 100 °C, 120 °C, 140 °C, 160 °C, and 180 °C for 2 h each, respectively, to obtain the carbon fiber composite material. Figure 7 As shown, the tensile strength of the original carbon fiber material is 784.3 MPa, and the tensile strength of the modified carbon fiber composite material is increased to 1039.3 MPa.

[0082] Numerous specific details are set forth in this specification. However, it will be understood that embodiments of the invention may be practiced without these specific details. In some embodiments, well-known methods, structures, and techniques have not been shown in detail so as not to obscure the understanding of this specification.

[0083] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

[0084] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

[0085] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention shall still fall within the scope of the technical solution of the present invention.

Claims

1. A method for the preparation of a high-strength bio-based epoxy resin that is closed-loop recyclable, characterized in that, The method comprises the following steps: Step one, the lignin acid alcohol compound, epichlorohydrin and catalyst are subjected to ring-opening reaction, and then alkali metal hydroxide is added to perform ring-closing reaction to obtain a lignin acid alcohol epoxy compound; the molar ratio of the lignin acid alcohol compound, epichlorohydrin and catalyst is 1:10:0.02-1:14:0.05; the ring-opening reaction is performed at a temperature of 90-110℃; the ring-opening reaction is performed for 1-4h; the ring-closing reaction is performed at a temperature of 0-20℃; the ring-closing reaction is performed for 1-3h; the catalyst is added in an amount of 1-5% of the total molar amount of hydroxyl and carboxyl groups in the lignin acid alcohol compound; Step two, the lignin acid alcohol epoxy compound obtained in step one is subjected to curing reaction with an amine-based compound to obtain the high-strength bio-based epoxy resin capable of being recycled in a closed loop; the curing reaction is performed at 60℃, 80℃, 100℃, 120℃, 140℃, 160℃ and 180℃ for 2h respectively; the molar ratio of the epoxy groups in the lignin acid alcohol epoxy compound to the amine groups in the amine-based compound is 1:(0.5-1).

2. The production method according to claim 1, characterized by, Step one specifically comprises the following steps: the lignin acid alcohol compound, epichlorohydrin and catalyst are uniformly stirred and mixed at 20-60℃, and then subjected to ring-opening reaction at 90-110℃ for 1-4h; subsequently, the obtained solution is cooled to 0-20℃, and an aqueous solution of alkali metal hydroxide is added, and the reaction is continued at 0-20℃ for 1-3h; after the reaction is completed, the lignin acid alcohol epoxy compound is obtained through extraction, water washing and distillation.

3. The preparation method according to claim 1, characterized in that, In step one, the lignin acid alcohol compound comprises at least one of ferulic acid, sinapic acid and p-coumaric acid; and the catalyst comprises at least one of tetrabutylammonium chloride, benzyltriethylammonium chloride, tetrabutylammonium iodide and tetrabutylammonium sulfate.

4. The production method according to claim 2, characterized by, In step one, the alkali metal hydroxide comprises at least one of sodium hydroxide, lithium hydroxide and potassium hydroxide; and the solute content of the aqueous solution of alkali metal hydroxide is 30-60wt%.

5. The preparation method according to claim 1, characterized in that, Step two specifically comprises the following steps: the lignin acid alcohol epoxy compound obtained in step one is dissolved in a solvent at 40-60℃, and then an amine-based compound is added and stirred for 0.5-1h; subsequently, the curing reaction is performed at 60℃, 80℃, 100℃, 120℃, 140℃, 160℃ and 180℃ for 2h respectively to obtain the high-strength bio-based epoxy resin capable of being recycled in a closed loop.

6. The production method according to claim 5, wherein In step two, the amine-based compound comprises one of hexamethylenediamine, decanediamine, p-phenylenediamine and 4,4'-diaminodiphenylmethane; and the solvent is selected from one of ethyl acetate, N,N-dimethylformamide and dimethyl sulfoxide.

7. A high-strength bio-based epoxy resin that is closed loop recyclable, characterized in that, The high-strength bio-based epoxy resin has a tensile stress of 121.8-154.1 MPa, an elongation at break of 9.4%-24.5%, and a glass transition temperature of 81.1-116.5℃; and the high-strength bio-based epoxy resin is prepared by the method of any one of claims 1-6.

8. An adhesive characterized by, The adhesive is the high-strength bio-based epoxy resin capable of closed-loop recycling according to claim 7; the tensile stress of the high-strength bio-based epoxy resin is 121.8-154.1 MPa, the elongation at break is 9.4%-24.5%, and the glass transition temperature is 81.1-116.5 DEG C.

9. Use of the high-strength bio-based epoxy resin capable of closed-loop recycling according to any one of claims 1-6 in the modification of carbon fiber composites.

10. A recycling method of a high-strength bio-based epoxy resin that can be recycled in a closed loop, characterized by, The method comprises the following steps: mixing the high-strength bio-based epoxy resin capable of closed-loop recycling according to claim 7 with ethanol uniformly, under the catalysis of a tertiary amine group, the alcohol hydroxyl group and the ester bond are subjected to bond exchange reaction to degrade the crosslinked network structure into small molecular segments, after removing the excess solvent, drying is carried out, and the bio-based epoxy resin is obtained through secondary curing; the degradation temperature is 160-200 DEG C, and the degradation time is 8-12 h.

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